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LITHOSTRATIGRAPHIC ASSEMBLY AND STRUCTURAL SETTING OF GOLD MINERALIZATION IN THE EASTERN RICE LAKE GREENSTONE BELT K.H. Poulsen (GSC), W. Weber (Man. Energy and Mines),
R.
Brommecker (WMC
International) and D.N.Seneshen (Queen's University).
ABSTRACT
This field trip will examine the main lithostratigraphic assemblages and structural
settings of gold deposits in the Rice Lake greenstone belt in Uchi Subprovince. A circa
2.93 Ga quartzite-bearing continental platform assemblage and a circa 2.87 Ga
komatiite-bearing mafic plain assemblage will be examined near Wallace and Garner
Lakes respectively. An arc assemblage of circa 2.73 Ga mafic flows, intermediate
volcanic rocks and synvolcanic intrusions of the Rice Lake Group, host to most gold
deposits in the district, will be viewed in the Wadhope and Bissett areas. A slightly
younger and more felsic, shallow-water volcanic assemblage composed of ignimbrites,
tuffs and mafic flows will be visited near the Manigotagan River where it is overlain by
turbidites of the Edmunds Lake Formation, possibly representing a fore-arc
assemblage. The youngest rocks in the belt, cross-bedded arenites of the San Antonio
Formation, will be examined in the Bissett area where they unconformably overlie the
Rice Lake Group. The settings of San Antonio, Central Manitoba and Gunnar gold
deposits will receive particular attention during the trip.
INTRODUCTION
The Archean Rice Lake greenstone belt (Fig. 1) is Manitoba's most important
lode gold district, accounting for nearly two million ounces (approximately 60 tonnes) of
past gold production. The largest deposit is at the San Antonio Mine, located in the
northwestern part of the belt, which yielded almost 42 t of gold (Whiting and Sinclair, 1990):
this mine has undergone considerable re-evaluation recently and, at the time of writing, is
about to re-open with a reserve of approximately 32 t (Northern Miner, Aug. 28, 1995). A
concentration of smaller mines, with a combined production of approximately 10 t
(Stephenson, 1971) occurs in the southeastern part of the belt and numerous occurrences
are known throughout.
Prospecting in the Rice Lake greenstone belt dates back to 1911 after a gold
discovery near the San Antonio mine. Numerous geological studies
of
the region
accompanied the early stages of mining and exploration (e.g. Moore, 1912; Davies, 1963) and, in particular, the reports of Stockwell (1935) and Stockwell and Lord (1939) contain valuable accounts of the geology in the vicinity of the past gold producers, since they were able to examine the underground workings, many of which have now been closed for over forty years. They also had opportunities to examine excellent exposures that resulted from
1
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Gold Deposits
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Mesoarchean Volcanics Regional Faults Figure 1: Setting of the Rice Lake Greenstone Belt in the western part of Uchi Subprovince.
2
frequent forest fires in this region. Since then, however, the multidisciplinary study by the
Manitoba Mines Branch called "Geology and Geophysics of the Rice Lake Region, Southeastern
Manitoba (Project Pioneer), 1971" represents the most comprehensive work
available that addresses geological problems in and around the area.
With the revitalization of gold exploration and the implementation of the CanadaManitoba
Mineral Development Agreements from 1984-89 and 1989-93, new initiatives
were undertaken by the Geological Survey of Canada and Manitoba Energy and Mines
to further improve the level of geoscience documentation in this area, particularly as it
pertains to the occurrence of gold. Designed to complement a concurrent mineral
inventory by Manitoba Energy and Mines (Theyer and Yamada, 1989; Theyer and
Ferreira, 1990; Theyer, 1991, 1994a,b) , recent geological studies have focused on
regional and local features that are directly related to known gold deposits in the
Bissett and Beresford Lake areas. The relationships between gold-bearing structures
and regional generations of deformation, the recurring stratigraphic affiliations as a
guide to ore, and the role of hydrothermal alteration, principally carbonatization, in the
ore-forming process are all important topics relevant to this region. D.W. Davis
(Poulsen et aI., 1994; unpublished data) and
A.
Turek (Turek et aI., 1989; Turek and
Weber, 1991) have provided valuable geochronological data in support to the geological studies.
REGIONAL GEOLOGY
The Rice Lake greenstone belt is located about 170km northeast of Winnipeg,
Manitoba, in the Uchi Subprovince of the Superior Province (Fig. 1). It is composed mainly
of Archean mafic to felsic volcanic rocks flanked on the north by the Wanipigow River
Plutonic Complex and to the south by the Manigotagan Gneissic Belt, which is part of the
English River Subprovince (Fig. 2). The centre of the volcanic terrane is intruded by the
Ross River tonalitic pluton. The felsic to intermediate volcanic rocks and syn-volcanic
intrusive rocks of the Rice Lake belt are unconformably overlain by arenite and
conglomerate of the San Antonio Formation. The greenstone belt is bounded by two major
faults, the Wanipigow fault on the north and the Manigotagan fault on the south, both of
which show large apparent dextral offsets. Most of the rocks in the southeastern Rice Lake
greenstone belt have been metamorphosed to greenschist facies, although some
amphibolite facies assemblages occur around the plutons. Primary textures are usually
preserved so the prefix "meta" has been omitted from rock names for simplicity, and rocks
are classified principally by their primary textures.
3
GEM LAKE AREA
..,:
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RICE LAKE BELT
~;~~~~~I
Figure 2: Main geological elements of Rice Lake Belt and locations of specific areas
discussed in text.
4
REGIONAL GEOPHYSICS
A further appreciation of the overall setting and structure of the area is given by
available geophysical data. In addition to regional one-mile to one-inch aeromagnetic
coverage, there are in excess of 150 non-confidential 'files that contain ground and
airborne geophysical data on the region (Hosain et aI., 1993). The Geological Survey of
Canada has also completed airborne gradiometer of the Bissett area (GSC, 1988), as well
as recent aeromagnetic and airborne radiometric surveys that cover the entire eastern part
of the belt (Hetu and Holman, 1995).
A synthesis of the aeromagnetic data (Fig. 3) reveals several important features:
1. The most striking feature on the aeromagnetic maps ( McRitchie, 1971 c; Hetu and
Holman, 1995; GSC, 1988, for the Bissett area only) are discontinuous strings of linear,
very strong positive anomalies along the northern and eastern margin of the Rice Lake
belt, northwest of Bissett along the Wanipigow River, in the Wallace Lake-Siderock
Lake area and between Moore Lake and Garner Lake. They are caused by oxide facies
banded iron-formation. The absence of similar anomalies elsewhere in the supracrustal
belt sets these sedimentary and the associated rocks apart from the remainder of the
belt. As described below these iron-formations and the associated rocks are part of a
pre-2.8 Ga platformal assemblage, predating and largely in fault contact with the
younger dominantly volcanogenic assemblages of the Rice Lake Group.
2. A second order of regional, but lower amplitude, positive anomalies marks the
larger younger (
<
2.73 Ga) granitic intrusions in the greenstone belt and the
metasedimentary gneiss belt to the south. Particularly their margins are magnetically defined, e. g. the belt-central Ross River pluton, because of contrasts with adjacent volcanic rocks. 3. Strings of distinctly oval positive anomalies along the northern margin of the belt between Lake Winnipeg and Bissett are caused by serpentinites. These are spatially associated with the Wanipigow Fault. The textures of these bodies do not definitively indicate their origin but it is possible that they represent komatiites which have been tectonically re-intruded along late fault structures. 4. A large strong magnetic anomaly in the Garner Lake area is caused by the Garner Lake layered mafic/ultramafic intrusion. 5. A feature that is particularly noticeable on the
1:20,000 map (GSC, 1988)
is the
weakening, or disappearance, of positive magnetic anomalies in a northerly trending strip, extending from approximately 5 km west of Bissett to the eastern shore of Rice Lake. This termination appears to be in part related to the disappearance (or discontinuity) of iron formation, but the regional feature may be an expression of the breakdown of magnetite during impregnation with reducing fluids. There is some
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evidence for this in the Bissett area where similar gabbros lose much of their magnetic
signature in the vicinity of the San Antonio Mine, where intense carbonate alteration
has been documented (Ames et aI., 1990).
LOCAL GEOLOGY
Stockwell (1941) and other early workers coined the term Rice Lake Group to
identify all of the supracrustal rocks in Rice Lake belt. A more detailed lithostratigraphic
stratigraphic nomenclature was subsequently developed for the Rice Lake greenstone belt
in Project Pioneer (Weber, 1971; McRitchie, 1971 a; Campbell, 1971). In particular, the
volcanic rocks of the Rice Lake Group were divided into the Bidou Lake and Gem Lake
Subgroups and these in tum into formations: sedimentary rocks were also subdivided into
formations. In addition, many
of the important subdivisions of
the plutonic rocks of the
region were established by McRitchie (1971b) and Scoates (1971). Much of this early nomenclature is still useful in describing the local geology in specific areas within the Rice Lake belt (Fig. 2) even though some of the earlier correlations can no longer be sustained in the face of new structural and geochronological data. Table 1 combines the historically accepted stratigraphic nomenclature for the region with new data by introducing only one new term, "Gamer Lake Subgroup", for a volcanic sequence east of the Beresford River which was formerly portrayed partly as Gem Lake Subgroup and partly as Edmunds Lake Formation. In addition, there is new evidence (see below) that the Conley Formation (McRitchie, 1971) is both right-way-up and the oldest supracrustal unit in the belt, contrary to the views
of
earlier workers. Table 1 also illustrates that some units are present only in
certain areas and that de'finitive correlation from area to area is hampered by intervening faults. Bissett Area As demonstrated by previous workers, the stratigraphic succession in the Bissett area (Fig. 4) dips and faces northward with the exception of the arenite of the San Antonio Formation that OCCUffion the overturned limb of a major syncline southwest of Rice Lake. North and east of the contact with the arenite, volcanic and epiclastic rocks of the Bidou Lake Subgroup, principally of dacitic composition, are intruded by sills of fine to medium grained gabbro. The epiclastic rocks that underlie much of Rice Lake are primarily volcanic conglomerates and sandstones, interpreted to be braided fluvial deposits derived from unconsolidated pyroclastic debris on the slopes of a stratovolcano (Tirschmann,
1987).
The stratigraphically younger porphyritic dacite that occurs north of Rice Lake is
composed of euhedral to broken plagiocalse crystals, lithic fragments, pumice-like
fragments, amygdaloidal spherulitic fragments and irregular to rounded quartz crystals
in a fine grained matrix. The presence of brecciated zones, intercalated tuffs and relict
clastic textures favour a subaqueous pyroclastic origin for this unit (Tirschmann,1987).
7
Table 1 - Regional Stratigraphic Nomenclature of Rice Lake Group
Bissett Area Long Lake-stormy
Gem
Lake Area Gamer Lake Area Wallace Lake Area Wanipigow - LillIe
····saii...
L··a··k··e···A··r··e··a····&mid... Beaver Lake Area
.
Ross River Pluton
and
related
SynvoIcanic: gabbro to tonalite Bidou Lake Subgroup - Round Lake
fm.
• Townsite
fm.
- Hare's Island
fm.
Granodiorite
Intrusions
Edmunds
Lake
Fm.
Dove Lake Dyke??
Ross River Pluton
and
related
Synvolcanic: gabbro to
tonalite
Bidou Lake SUbgroup
- Manigolagan River
Fm.
- The
Narrtl'NS
Fm.
- stormy
Lake
Fm.
-GunnarFm.
- Dove Lake
Fm.
- Tinney Lake
Fm.
-Stove!
Fm.
- Unnamed
Basalt
Granodiorite Intrusions
Edmunds
Lake
Fm.
SynvoIcanic Porphyry
Gem
Lake SUbgroup
- Rathall Lake
Fm.
- Banksian Lake
Fm.
Synvolcanic tonalite?
Bidou Lake SUbgroup
- The
Narrows Fm.
8
tonalite
Layered
Intrusions:
- peridotite
pyroxenite
- gabbro, quartz diorite Serpentinite Gamer Lake Subgroup Tonalite
and
Granodiorite
of
Wanipigow Plutonic: Complex Serpentinite
Jeep
Granodiorite
and
Gabbro
Unnamed Volcanics
(possible
equivaJenls
of Gamer Lake
or
Bidou Lake
SUbgroups ?)
malic
to felsic: dykes
ConleyFm.
massive
tonarlte trondhjemite
Unnamed
me4asediments
and
lron-formalion
at Silver Falls
Tonalite
and
Granodiorite of
Wanipigow
Plutonic Complex
Serpentinite
Unnamed
VoIcanic:s
(possible
equivaJenlsof
Gamer Lake
SUbgroup?)
WANIPIGOW PLUTONIC COMPLEX
~
Granitoid rocks
(undivided) Bidou Lake Subgroup
I;;;
J
Tonalitic intrusion
I~;~;~;j
Mafic intrusions
I:: :
j
Intermediate volcanics
o
I
•
2.5km
I
Supracrustal rocks
(undivided)
1 - San Antonio Mine
2 -
Sannorm Deposit
3 • Vanson Mine
~-_-_-~
Metasedimentary rocks
(uncertain stratigraphic position San Antonio Fm. Way - up
8····&mi... ~ ~ ~ .......
Mafic volcanics
Figure 4: Geological sketch map of the Bissett area (adapted from Poulsen et aI.,
1986).
9
The gabbroic sills that intrude the epiclastic sequence are all compositionally
layered. Ames (1988) used petrographic and geochemical data to show that the sill
which hosts the San Antonio deposit is composed of three different types of gabbro:
fine grained gabbro of normal basaltic composition occupies the upper and lower
margins of the sill; melagabbro, enriched in MgO, FeO and Ni, comprises
approximately the lower one-third of the sill; and, leucogabbro that is relatively enriched
in AI203 and Ti02 occupies the upper two-thirds. Similar patterns of magmatic
differentiation were noted in a sill south of the Mine and in a large body of gabbro east
of Rice Lake (Fig. 4).
Long Lake- Stonny Lake Area
The volcanic and sedimentary rocks of the Rice Lake Group in this area were
divided into the Bidou Lake subgroup and the younger Gem Lake subgroup (Weber,
1971 a). The Bidou Lake subgroup is characterized by a bimodal basalt-dacite and
sedimentary rock assemblage whereas the Gem Lake subgroup to the southeast is
characterized by a basalt-andesite-rhyolite and sedimentary rock assemblage.
The dominant structure in the Long Lake-Stormy Lake area is a major northwest
trending anticlinorium (Fig. 5) which consists of the Beresford anticline and the
Beresford syncline (Campell, 1971 a). The oldest rocks in the core of the anticlinorium
are mafic volcanic flows and intercalated tuffaceous and sedimentary rocks of the
Bidou Lake subgroup that are extensively intruded by voluminous gabbro sills. Campell
(1971a) divided the Bidou Lake subgroup in this area into (from oldest to youngest):
Unnamed Basalt, StoveI Lake, Tinney Lake, Dove Lake, Gunnar, Stormy Lake, The
Narrows and Edmunds Lake Formations (Table 1). A U-Pb age of 2730.7±12.6 Ma for a
quartz-feldspar porphyry dyke is a minimum age for the host Gunnar Formation and a
U-Pb age of 2731 ±3.2 Ma for a Narrows Formation dacite dates the upper part of the
Bidou Lake subgroup volcanism (Turek et aI., 1989).
Seneshen and Owens (1985) recognized a distinct supracrustal sequence, the
Manigotagan River Formation, between The Narrows and Edmunds Lake Formations. It
consists of epiclastic rocks, mafic flows and mafic to felsic tuffs and Seneshen (1990)
interpreted it to have formed in nearshore environment. The Manigotagan River
Formation may actually be part of the Gem Lake Subgroup because it contains felsic
tuffs which contain fragments likely derived from Gem Lake Subgroup rhyolites
(Seneshen, 1990). The overlying Edmunds Lake Formation is either in transgressive or
in structural contact with both the Gem Lake and Bidou Lake Subgroups.
Abundant intrusions occur in the Long Lake - Stormy Lake area, including (from
oldest to youngest): mafic sills, in part differentiated; anorthositic gabbro or gabbro
with distinct glomeroporphyritic phases; tonalite-granodiorite, such as the Ross River
pluton; numerous felsic to intermediate dykes, particularly near the Ross River pluton;
and a unique differentiated ultramafic intrusion, the Dove Lake Dyke (Scoates, 1971).
10
LONG LAKE - STORMY LAKE AREA
INTRUSIONS
YoungIng direction
D
volcanic and
Epiclastic rocks Sedimentary rocks, minor tuff
I
~ ~ ~ ~ ~ I
Granodiorite (WPC)
m
,-,m-,-!,-il
Gabbro
W··
.••.••.••.• Tonalit
e
Shear Zone
Fault
o
--
-'-
21C1o
Figure 5: Geological sketch map of the Long Lake - Stormy Lake area. (adapted from
Brommecker, 1991).
11
This body intruded along a fault, the South Carbonate Shear, which formed after
intrusion of the intermediate-felsic dykes in the same area. It is likely that intermediatefelsic
intrusive rocks and the volcanic rocks of the Bidou and possibly also of the Gem
Lake subgroup are part of a essentially single volcano-plutonic event at about 2730±10
Ma (Turek et aI., 1989).
Gem Lake Area
The Gem Lake Subgroup occurs mainly in the Gem Lake area southeast of the
Long Lake - Stormy Lake area and its relationship to the rocks of the Bidou Lake
Subgroup is only weakly established. Originally postulated to be younger than the
Bidou Lake subgroup based on structural grounds (Weber, 1971b), a U-Pb age of
2721.7±2 Ma for the proximal vent facies rhyolite (Davis, unpublished) supports this
interpretation. However, it does not rule out that the two subgroups are essentially comagmatic
and only spatially separated, because the youngest units in the Long LakeStormy
Lake area may have been eroded. The rocks of the Gem Lake Subgroup
consist of a lower mafic Banksian Lake Formation and a upper felsic Rathall Lake
Formation. Like the Bidou Lake Subgroup, the Gem Lake Subgroup is overlain in
apparent conformity by the metaturbidites of the Edmunds Lake Formation.
Gamer Lake Area
This is one of the most geologically complex parts of the Rice Lake belt. One of
the contributing factors is likely the fact that the area is transected by numerous
northerly-striking shear zones that, along with north-northwest D2 cleavage and folds,
results in large-scale transposition of east-west striking primary units. The Beresford
Lake Shear Zone separates a western package of eastward facing rocks belonging to
the Bidou Lake Subgroup and Edmunds Lake Formation from an eastern package of
westerly facing supracrustal rocks east of Beresford Lake and northerly facing rocks
around Garner Lake. The Garner Lake Shear Zone further divides the second package
into geologically eastern and western parts ( Fig. 6) which themselves possess some
differences.
The eastern part of the Garner Lake area contains a relatively coherent eastwest
stratigraphic package of supracrustal and intrusive rocks that is at least 5 km thick
as measured in a north-south direction whereas the western part is more deformed.
The entire sequence, for which we propose the term "Garner Lake Subgroup" has been
metamorphosed to amphibolite facies assemblages and includes:
12
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1) a lowermost unit of banded intercalated felsic and mafic metamorphic rocks of
uncertain origin that occur south of Garner Lake: fine-grained felsic biotite-bearing
rocks dominate; these have either rhyolite or arenite protoliths but a strong foliation
precludes a convincing interpretation even though the felsites locally contain clasts.
The mafic component of this rock unit is strongly foliated homogenous amphibolite
which is consistent with a gabbroic protolith.
2) The Garner Lake ultramafic intrusion consists of alternating layers of serpentinite
and pyroxenite (Scoates, 1971) which, by their disposition/suggests their fractionation
within a sill (or series of sills) that have tops to the north. The pyroxenite locally
contains metre-wide gabbroic dykes that yielded circa 2870 Ma zircons ( Poulsen et aI.,
1993).
3) Gabbro, approximately 200 m thick, with minor pyroxenite layers occurs directly
north of the ultramafic rocks and, west of the Garner Lake Shear Zone, equivalent
rocks include quartz diorite. It is not known whether the gabbro and quartz diorite are
more fractionated phases of the Garner Lake layered intrusion or parts of a separate
body.
4) Overlying the gabbro are units of felsic tuff and volcanic breccia that were
hydrothermally altered prior to regional metamorphism. Mineral assemblages are
typified by biotite, anthophyllite (and possibly cordierite). Previously these rocks were
mapped as sediments, probably based on their biotite content. An exhalite unit
containing pyrite and traces of chalcopyrite occurs locally near the top of this unit.
5) The felsic volcanic rocks are overlain to the north by a north-facing sequence of
intercalated pillowed basalt and komatiitic basalt, and spinifex-textured komatiite. This
sequence locally contains interflow banded magnetite iron formation and a thin cap of
iron-formation.
6) The komatiitic section of the Garner Lake Subgroup is overlain by intercalated Mgtholeiitic
and calc-alkalic basalt which, near the Beresford Lake Shear Zone, contains
units of banded oxide and sulphide iron-formation and related metasedimentary rocks.
Wallace Lake area
McRitchie (1971) produced the most detailed stratigraphic framework of the
area. Re-examination of the area after recent forest fires and in view of new
geochronological data (Turek and Weber, 1991, Turek et aI., 1989; D.W. Davis,
unpublished) revealed that the metasedimentary rocks of the Wallace Lake area,
shown as relatively young on the previous maps are among the oldest, if not the oldest,
of the Rice Lake belt. A well-exposed section of the Conley formation in the vicinity of
the Conley shaft (Fig.7) demonstrates that quartz arenite was successively intruded by
14
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x x x x x x x x ;<x'
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+ +
x x x x x x x
+ + +
X \82
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D"
. "
Mafic volcanic Rocks
" "
1-- -- --
-~ Wacke
o
I
Conglomerate (local)
Limestone/marble
2.5 km
I
Figure 7: Geological sketch map of the Wallace Lake area (adapted from Weber and
McRitchie, 1971).
15
gabbro, diorite, feldspar porphyry and finally by 2.92 Ga quartz-feldspar porphyry prior
to regional deformation. Similar age relationships have been observed near the Jeep
Mine where 2880 Ma pre-deformational granodiorite intruded the Wallace Lake
assemblage.
This old gabbro-granitoid magmatism both predates and postdates the Conley
Formation and has been traditionally included in the Wanipigow Plutonic Suite (Marr,
1971). The term Wanipigow Plutonic Complex is more appropriate however because
the term "suite" implies co-magmatic plutons whereas available geochronology data
indicate that the granitoid belt north of the Rice Lake belt is a complex of intrusions of
variable composition and ranging in age from 3.0 Ga to 2.73 Ga (Ermanovics and
Wanless, 1983; Turek et aI., 1989; Turek and Weber, 1994).
Ultramafic rocks also are present at Wallace Lake of which there are two distinct
varieties: serpentinite and actinolite schist. Serpentinite had been recorded at one
locality on the north shore of Garner Lake (Scoates, 1971) but Theyer (1983) noted
that this was but part of a more extensive body. It is likely, based on chemical
composition and on field characteristics, that this serpentinite is of the same type as
found along the Hay Creek Belt and north of Garner Lake. The actinolite schists
(McRitchie, 1971) also occur in association with the Conley Formation as thin
concordant lenses. They have been regarded as either unusual clay-rich magnesian
metasedimentary rocks or as varieties of ultramafic rocks but this is not easy to resolve.
Wanipigow River - Little Beaver Lake Area
A belt containing ultramafic rocks has also been recently identified within the
Wanipigow Plutonic Complex northeast of Wanipigow Lake (Poulsen et aI., 1994).
Coincident with a well defined airborne gradiometer anomaly (GSC,1988), this belt is
the northernmost of two branches which split from the Hay Creek Serpentinite Belt (Fig.
8). Massive serpentinite is exposed in several outcrops (Garson Hill) but cannot be
traced any farther eastward suggesting a fault contact between the east-west ultramafic
belt and a prominent northeast-southwest belt of mafic-felsic volcanic rocks though
Little Beaver Lake. The contact between these supracrustal rocks of the Little Beaver
belt and the tonalite to the west is intrusive but pre-tectonic as evidenced by the local
tectonic transposition of rocks in the contact zone. Although the supracrustal rocks of
the Little Beaver belt are portrayed on some existing maps as metagreywacke, at least
some of them are actually intermediate to felsic volcanic rocks that have been
metamorphosed to the amphibolite facies, resulting in their high biotite content. Patchy
gossan zones within some felsic volcanic units are suggestive of synvolcanic sulphidic
stockworks and the local presence of garnets may reflect a precursor synvolcanic
hydrothermal alteration such as is known to occur in the vicinity of volcanogenic
massive sulphide deposits.
16
+ + +
x x x
x
+ + +
x x
x x
+
x
+
++ + +
x
x
Arenite/ argillite
Volcanic rocks
(Bidou Lake Subgroup)
~
~
I::·:·:·::!&mid...
San Antonio Fm.
[S]
Iron - formation
Conglomerate
0
2.5km
I
1+ + +1
Tonalitic intrusion
Q
Granitoid rocks
(WPC)
Gabbro
-
Serpent in it e
Volcanics rocks
LBL
Little Beaver Lake
Figure 8: Geological sketch map of the Wanipigow River - Little Beaver Lake area.
17
All of the granitoid rocks observed to the west of the Little Beaver Belt are
tonalitic. The Clinton-Poundmaker tonalite is massive and relatively undeformed
whereas its equivalent to the south between the Hay Creek Serpentinite Belt and the
Wanipigow Fault is foliated.
Iron-formation is indicated on several existing maps near the trace of the
Wanipigow River Fault to the east of Wanipigow Lake (Fig. 8). These occurrences
also coincide with positive airborne gradiometer anomalies (GSC, 1988). The iron
formation appears to be discontinuously developed but appears to occupy two spatially
and lithologically distinctive positions. The first is as narrow bands of lean iron
formation that occur intercalated with strongly foliated pillowed basalt directly north of
the Wanipigow Fault. The second, although not observed in outcrop has been drilled
and is well-located by magnetic anomalies to occur within a poorly exposed band of
sedimentary rocks that lies directly south of the Wanipigow Fault. These sedimentary
rocks are exposed at Silver Falls on the Wanipigow River where a southward-fining
clastic sequence includes coarse polymictic conglomerate, well bedded to massive
quartz arenite, siltstone and argillite to which the magnetic iron formation appears to be
associated. There are many uncertainties associated with correlating this sedimentary
package on a regional scale. It may either be a facies-equivalent of the San Antonio
Formation, which extends nearby from the Bissett area, or of the Edmunds Lake
Formation which also includes sections of mixed conglomerate, sandstone, argillite and
iron-formation.
STRUCTURE
Large-scale folds and faults are evident on geological maps from various parts of
Rice Lake belt. The structure of this region is the result of at least three phases of
deformation but correlation of deformation events from area to area has not been firmly
established.
Structural studies in the southeastern part of belt (McRitchie and Weber, 1971;
Weber, 1971a; Zwanzig) 1971; Brommecker et aI., Brommecker, 1991) all indicate that the
main generations of structures are as follows (Fig. 9):
01: isoclinal folding with variable cleavage development
02: tight folding with the development of the main penetrative foliation
03: open folding and kink folding with development of a crenulation cleavage. The
structural trends associated with each episode (Fig. 10) indicate the existence of
early northerly structures overprinted by NW-SE folds and cleavage, all of which are
overprinted by late ENE cleavage.
18
Oldest ------------------------------------ Youngest
DO D1 D2 D3
Time
Deformation
event
Possible tectonic
significance
Cleavage type
Minor folds
Major folds
Minor faults
and shear zones
Major faults
and shear
zones
Gold mineralization
Syn-volcanic and
syn-sedimentary
extension
None
Chaotic
Briltfe sbuctures,
fau~s
with felsic dykes
emplaced along them Thrusting Out
of
sequence Dextral strike-slip
thrusting Sl-penetrative, 52-penetrative, S3-crenulation, kink flattening, spaced flattening, spaced fracture fracture, crenulation Rare isoclines Closed to tight, lobate-
Open,ch~n,~
cuspate,
ch~n
kink
Early fold responsible
Beresford
Anticlinorium Major bend in the
for synclinal facing
Beresford Anticline axial trace of
the
across the Beresford Beresford Syncline
Beresford
Anticlinorium
Lake Main Shear Layer parallel shear Limb thrusts on F2 Dextral strike-slip zones, and shear folds, axial planar faults and shear zones, zones to accomodate shear zones, flexural conjugate sinistral the local extension and slip shear zones, shear strike-slip shear zones, compression of layers zones to accomodate Riedel pattem local extension and development compression
of
layers
Moore Lake Shear Main dextral D3
faun
North Carbonate Shear and shear zone
Beresford Lake Main Shear
----- south of
the Gunnar
South
Carbonate Shear
Mine
Igneous
history
Metamorphism
Dove
Lake Dyke
. -Homblende-biotit diorite Intermediate d ke with associated eccia
Figure 9: Summary of the structural history of the eastern part of the Rice Lake
Greenstone Belt (after Brommecker, 1991).
19
D1
STRUCTURAL
TRENDS
--- so:
BEDDING
- S1: PENETRATIVE FOLiATIO
-I-
F1: EARLY FOLDS
D1
I
D2: SHEAR ZONES
D2
STRUCTURAL
TRENDS
---52: CLEAVAGEICRENULATIO
+
F2:FOLDS
D11D2:
SHEAR ZONES
D3
STRUCTURAL
TRENDS
--- so:
BEDDING
---53: CRENULATION CEAVAGE
+
D3:FOLDS
D11D2:
SHEAR ZONES
D3:FAULTS
Figure 10: Structural trend maps of the three major deformation events in eastern Rice
Lake Belt (after Brommecker, 1991).
20
Down Plunge Section
Looking S.E.
NE
1km
L
1km
---. Younging Direction
Shear Zone
/ Fold Axial Planes
Hatch patterns as in Fig. 5
sw
Figure 11: Down plunge section of the Beresford Anticlinorium
21
Deformation has also involved movement along major shear zones and faults (Fig.
9). Large layer-parallel shear zones with unknown magnitudes of displacement are
common in the area. Examples are the North Carbonate Shear at the Central Manitoba
Mine (Stockwell and Lord, 1939) and the Beresford Lake Main Shear east of the Gunnar
Mine(Brommecker, 1991). Similar shear zones which cross-cut stratigraphy in some areas
have large offsets, as is the case with the South Carbonate Shear at Central Manitoba
(Stockwell and Lord, 1939). The Moore Lake Shear (Fig. 6; also known as the Beresford
Lake Deformation Zone) truncates stratigraphy at a high angle on its west side near the
Gunnar Mine and at a low angle on its east side. Some of these shear zones are of
different generations (Fig. 9,10).
A down-plunge view of the structure in the Stormy Lake area shows that the
southwest limb of the anticlinorium is overturned (Fig. 11). The Beresford anticline is
shown to be tight to closed whereas the Beresford syncline is open. The mafic rocks of the
Gamer Lake Subgroup east of the Beresford Lake Main Shear face opposite to structurally
underlying sediments of the Edmunds Lake Formation. Of particular significance are the
extreme variations in the thickness of units across the anticlinorium. The dramatic thinning
of all units on the north-eastern limb of the structure suggests that the limb may be
tectonically thinned. The down-plunge projection also shows that the South Carbonate
Shear is a reverse fault on a limb of the Beresford syncline. Other shear zones appear to
be folded about the Beresford anticlinorium.
Rocks in the Bissett area also show evidence of three penetrative deformations.
The most prominent evidence of ductile deformation is a penetrative schistosity that, on
average, strikes west-northwest and dips steeply northward. This foliation (regionally
S2 or S3) is axial planar to a large reclined syncline in San Antonio Formation and
locally overprints an earlier foliation (S1?) that is sub-concordant with bedding in the
Rice Lake Group volcanic and epiclastic rocks. A prominent mineral lineation is
coincident with the intersection of the two foliations. This lineation trends northward at
the south shore of Rice Lake but, north of Rice Lake, it deviates increasingly to the east
(Fig.12), a condition that is thought to result from D3 deformation along the Wanipigow
Fault (Poulsen et aI., 1986).
The most intense effects of deformation are found in ductile shear zones that are
common throughout the area. These zones are typically heavily carbonatized and
include two types: those, such as the Normandy Creek and footwall shears (Fig. 12)
that are concordant with lithological layering and those, such as the Rice Lake shear,
that are discordant. Although definitive evidence is lacking, the presence of "down-dip"
lineation and the fact that the Rice Lake shear places Rice Lake Group volcanic rocks
over younger arenites, indicate that at least some of these structures are dominantly
reverse faults (Fig. 12).
22
No Foliation
or
Lineation
Strike of foliation
Trend of lineation
N
t
"
" °L..I.............................. ....J
"
Plunge value of lineation
~
<30
~
30-45
1:::::::::::::::1
45 -60
D
>60
• San Antonio mine
m
Figure
12:
Structural trend map of foliation and lineation in the Bissett area (after
Poulsen et
aI.,
1986).
23
a)
FeO+Fe203+Ti02
BIDOU LAKE SUBGROUP
x
Gunnar Fm.
o
Stormy L.
Fm.
t:c.
Narrows Fm.
o
Manigotagan R.
Fm.
AI203
MgO
+
Magnesian Ba&alts
- Ba&alts - Gamer Lake Intrusion • Kometiites
2
......;. -
$-!
I>
1
4
FeO+Fe203+Ti02
GARNER LAKE SUBGROUP
b)
1 ultramafic komatiite
2 basaltic komatiite
3 Mg-tholeiitic basalt
4 Fe-tholeiitic basalt
5 tholeiitic andesite
6 tholeiitic dacite
7 tholeiitic rhyolite
8 calc-alkalic basalt
9 calc-alkalic andesite 5 \
10 calc-alkalic dacite
11 calc-alkalic rhyolite 6 \ II>
\j\l!-
+ 7\\ ~
.+r,
10 9 AI203
MgO
Figure 13: a) Jensen diagram showing the chemical compositions of volcanic and volcaniclastic rocks of the Bidou Lake Subgroup (after Brommecker, 1991). b) Jensen diagram showing the chemical compositions of volcanic rocks of the Garner Lake Subgroup and of the cumulate rocks in the Garner Lake layered intrusion (after Brommecker et al., 1993).
24
LITHOGEOCHEMISTRY
Church and Wilson (1971) made the first attempt to classify the volcanic rocks of
the Rice Lake Belt according to their bulk chemical compositions and to make
comparison with younger volcanic products. They noted that the volcanic sequences in
the Rice Lake belt are essentially bimodal and consist of mafic (mainly basalt, basaltic
andesite) and intermediate ( mainly dacite and dacitic andesite) rocks. They noted
further that the abundance of dacite compared to rhyolite is unusual by comparison
with other greenstone belts in Superior Province but could not decide if this bimodality
was an artifact of two separate magmas or rather of incomplete sampling of a more
continuous range of compositions. Recent additional analyses from the Bidou Lake
SIJbgrolJp (Brommecker, 1991) suggest that the second is most plausible (Fig. 13a).
We also now recognize the extensive occurrence of komatiites in the eastern
and northern parts of the Rice Lake belt, particularly in the Garner Lake area. Although
these rocks are not voluminous and most were recognized to be ultramafic in the past,
they were thought to be late-tectonic intrusions owing to their common preservation as
slices within the many faults and shear zones in the belt. Definitive textures (spinifex,
polysuturing) and distinctive chemical compositions (Fig. 13b) indicate, however, that
both komatiitic flows and subvolcanic intrusions are present in addition to Mg-tholeiitic
and calc-alkaline basalt.
GEOCHRONOLOGY
The earliest geochronological information for the Rice Lake greenstone belt was
provided by K-Ar determinations by the GSC and Rb-Sr studies by Turek (1971): both
confirmed the Archean age (circa 2700 Ma) of the rocks in the area and also indicated
younger metamorphic or alteration events at approximately 2500 Ma and 2300 Ma.
The first zircon studies, by T. Krogh (Krogh et aI., 1974) in the western part of the belt,
indicated, however, that much older crust (circa 3000 Ma) exists in the region. This
and several modern U-Pb zircon studies (Turek et aI., 1989; Turek and Weber, 1991,
1994; Davis unpublished) have shown that the rocks oJ Rice Lake greenstone belt span
the same wide range of ages as are found elsewhere in Uchi Subprovince. In
particular, there is considerable overlap and correlation of ages (Table 2) with similar
rocks in the Red Lake area (Corfu and Wallace, 1986; Corfu and Andrews, 1987; Corfu
and Davis, 1992).
25
Table 2 - Geochronology Data for Rice Lake and Red Lake
...
!~.l?'} ~.~ ~.~ ':!~ ~~~ ~
.
" Red Lake data
Wallace Lake
English Brook
west
Hole River
Wallace
Lake
"Hayles Bay
"Campbell Mine
"Trout Bay
*Trout Bay
Wallace Lake
LakeWpg.
Rice River
"Balmer
east
"Cochenour
Jeep
Mine
Gamer
Lake
Gamer
Lake
"Dickenson
"Trout
Lake
"Trout
Lake
"RahUlZone
"Madsen
"Austin! Madsen
"Balmer
Lake
"Heyson
Obukowin L. (n. of Wallace)
Beresford Lake
"Graves
Black Island
Wallace Lake
Manigolagan
R.
"LillIe
Vermilion L.
Beresford L. Hare's I. Rice L.
"Redcrest
Ross River
Gem
Lake
"McKenzie
Is.
"AbinoMine
"Dome
"HammellL.
Deer
Island East
3km
E. Black lsi.
"Dickenson
"Killala-Baird
*Wilmar Mine
*Walsh
Lake
s.
Manlgolagan
Black Lake
tonalite boulder
meta-tonalite
meta-tonalite
quartz
arenite
rhyolitic ash-fIaN bx. rhyolite Rhyolitic Iapilli
tuff
rhyolite
qtz.
porphyry dyke
quartzofelclspathic.
gneiss
quartzofelclspathic.
gneiss
tuff
rhyolite
tuff
foliated granodiorite
peg.
gabbro
tonalite
qtz.
gabbro
foliated tonalite foliated tonalite
felsic
dyke
spherulitic fIaN
Tuff
qtz-fsp
porphyry
rhyolite crystal
tuff
tonalite
qtz-fsp
porphyry dyke
rhyodacite rhyodacite tonalite
Narrows
dacite
granodiorite Gunnar Porphyry rhyolite
quartz
diorite
quartz
diorite
rhyolite granodiorite granodiorite dyke granodiorite granodiorite granodiorite gneiss granodiorite
qtz-fsp
porphyry
granodiorite granodiorite granodiorite paragneiss
&
orthogneiss
~-tect.
granite
3010
3003
2999
2998.7
2992
2989
2940.1
2925.4
2920.6
2900
2900
2894
2893.5
2880
2871
2871
2870
2838
2806
2757
2746
2744
2742
2739
2737
2732.8
2732.8
2732
2731
2731
2731
2730.7
2729
2729
2727.6
2721.7
2720
2720
2718.2
2717
2715
2715
2714
2704
2701
2699
2690
2663
26
13
3
10
1.3
209
3
2.41.7
3.42.9
3
10
10
2
1.4 1.2
9
1
1.5
15
43
122
94
36 17
1
32
3
10
6.2
1.4 1.2
10
10
3.2
3
12.6
3.2
1.5
8.4
2
2
75
1.1
2
10
10
4
1.5
1.5
1
10
7.3
Turek
Turek
Krogh
Davis
Corfu
Corfu
Corfu
Corfu
Davis
Krogh
Krogh
Corfu
Corfu
Turek
Davis
Davis
Corfu
Noble
Noble
Corfu
Corfu
Corfu
Corfu
Corfu
Krogh
Turek
Corfu
Wanless
Turek
Turek
Corfu
Turek
Turek
Corfu
Turek
Davis
Corfu
Corfu
Corfu
McMaster
Krogh
Krogh
Corfu
Corfu
Corfu
Noble
Krogh
Turek
1991
1994
1974
1994
1986
1986
1986
1986
1994
1974
1974
1987
1986
1989
1994
1994
1987
1989
1989
1986
1987
1987
1987
1986
1974
1991
1986
1983
1989
1989
1987
1989
1989
1987
1989
1994
1987
1987
1986
1974
1974
1987
1987
1987
1989
1974
1989
TECTONIC INTERPRETATION
Several attempts have been made to come up with a coherent tectonic
interpretation of the Rice Lake belt, in most cases supported by the results of extensive
geological mapping. For example, Stockwell (1940) was of the opinion that the overall
structure of the belt was anticlinorial so the oldest rocks occur in the centre (Fig. 14, a
modification of his Figure 2) and that rock units at the edges, for example the
sedimentary sequence at Wallace Lake and the volcanic rocks at Garner Lake, are the
youngest. Although advancing many local improvements, the regional stratigraphic
scheme of McRitchie (1971a,b) and Weber (1971a,b) led to similar conclusions
concerning the relative ages of major units. Recent structural mapping and
geochronological results (Table 2) contradict some aspects of this interpretation,
however, and support an interpretation that is more in accord that of the geology of the
adjacent Red Lake district in Ontario. Volcanic rocks at Red Lake that formed at
approximately 2730 Ma are similar to those in the centre of the Rice Lake belt and are
subordinate to, and in sharp contact with, a pre-2800 Ma sequence composed mainly
of basalts and komatiites, as well as both clastic and chemical sedimentary rocks and
minor felsic volcanics. The latest stratigraphic, structural, and geochronological
evidence suggests that the Rice Lake belt also is composed of two or more
fundamentally dissimilar volcanic sequences. In particular, komatiites occur with
magnesian and tholeiitic basalts, oxide facies iron formation, quartzites and carbonates
(Wallace Lake) and felsic pyroclastic rocks (Garner Lake): this association of rock
types is identical in most respects to that in the pre-2800 Ma Balmer, Ball and Bruce
Channel assemblages at Red Lake. These units are distintive from, but in uncertain
contact with, the more voluminous circa 2730 Ma volcanics of the Bidou Lake and Gem
Lake Subgroups.
Given the inferred similarity with Red Lake geology and considerable new data,
it is possible to view the supracrustal rocks of the Rice Lake also to be composed of
several distinctive "tectonic assemblages" in the same way that Stott and Corfu (1991)
have divided the Uchi Subprovince in Ontario. This is done, not so much as an
endorsement of the assemblage concept, but rather as an effective means of making
geological comparisons across the Ontario-Manitoba border. Using such an approach
we are able to identify several tectonic assemblages, using nomenclature that is as
consistent as possible with past lithostratigraphic nomenclature. The main
characteristics of the assemblages, their age constraints and their mutual contact
relationships are outlined in Table 3 and their distribution is shown in their present
configuration (Fig. 15).
27
o
Q~:!
~
0
E-<Z
~
~~~~~~~~~~~~~~~J!~~~~ ::~ .+ + + ............ ~ r.;: ~ + + + + + + + + + + ~+
+
~
+++++++++++++
-:~
+++++++++++
++++++++ +++
16 km
II
San Antonio Fm.
ITTI
Granitoid Rocks
RICE LAKE "SERIES"
~
E::J
Sediments
Upper
f'A4'A4'A)
Basic lava
[
~
Acid lava
Middle
~
t,.f,.f,)
Basic lava
Lower
t::::::::J Basic lava &
Pyroclastic sediments
Figure 14: An early example of regional stratigraphic interpretation of the Rice Lake
Belt by C. H. Stockwell (after his figure 2,1941).
28
6'l
"JSLnOUe suo 0l sd!4sUO!leISJ
u!elJs~un
JO pue s6e lUSJS,U1P JO (sdnoJ6qns) ss6elqwssse
SA!l~U!lS!P JO pssodwo~
6U!sq se
lisa SUOlSUSSJE) s>tel
S~!~ s4l JO '(6010s6 leuo!6sJ s4l JO UO!lelSJdJSlU!-SJ V :g ~
sJn6!.::1
UDlOL
sa6elQwassv
e~ 008Z-aJd
~
sa6elQwassv :l!ue:llo/\
e~ OC-olLZ
~
~
Table 3: Main Supracrustal Elements of Rice Lake Belt
Assemblage Age Lithological Characteristics Structural Characteristics Uchi Equivalents· Tectonic
Name Constraints Interpretation·
Wallace <3000 Ma quartzite, iron-formation, inferred to overlie Ball Assemblage shallow
Lake >2920 Ma komatiites (?); equigranular 3000 Ga submarine to
granitoid basement; overlain subaerial
by basalts of unknown age sedimentation
and volcanism
Gamer Lake >2870 Ma komatiites, mg- and Fe- basement unknown but Balmer oceanic mafic
basalt, iron-formation possibly metasedimentary; Assemblage plain
mainly fault- bounded
Bidou Lake >2729 Ma basalt-andesite-dacite; basement unknown Confederation arc volcanism
minor ss and congl. Assemblage
Gem Lake 2720 - 2730 basalt-rhyolite- ignimbrite conformably overlies Bidou St. Joseph arc volcanism -
Ma Lake? - in fault contact with Assemblage proximal and vent
Gamer Lake? facies
Edmunds <2720 Ma graded metagreywacke; possible conformable contact Billett Assemblage; late-orogenlc
Lake >2650 Ma argillite; minor congl., Fe fm (faulted?) with underlying English River turbidite basin;
Gem Lake Assemblage fore-arc wedge
San Antonio < 2730 Ma trough cross-bedded intact unconformable contact none alluvial-fluvial
quartz- and lithic-arenite; with underlying Bidou Lake molasse basin
minorcongl.
*
after Stott and Corfu, 1991
Although there is still much to be learned about the origin of these assemblages and their interrelationships, there are some clear alternatives of interpretation. The distribution of the assemblages suggests an original age and lithological progression from northeast to southwest: older Mesoarchean quartz arenite- bearing Conley Formation (Wallace Lake) and komatiite-bearing successions (Garner Lake) are both cut by ultramafic intrusions and give way southward to Neoarchean tholeiitic and calcalkaline volcanic rocks and subvolcanic intrusions formed mainly between 2730 and 2720 Ma in a submarine to locally subaerial arc (Bidou Lake, Gem Lake). Flyschoid rocks (Edmunds Lake) were deposited southward of this arc, possibly in a forearc accretionary wedge and molassic rocks (San Antonio) were deposited in more restricted basins, presumably in response to rapid uplift of the arc volcanics during faulting under transpressional conditions. Although the above interpretation is feasible in light of available data, there are uncertainties and unresolved issues surrounding it. First, it is not clear whether the inferred Neoarchean volcanic arc was formed directly on Mesoarchean sialic basement or whether it was essentially ensimatic and subsequently placed there along (thrust?) faults. This uncertainty stems from the difficulty of accurately identifying and interpreting the nature of the contacts between older and younger volcanic rocks which all display similar field characteristics. A possible clue, which suggests the direct deposition of the Bidou and Gem Lake volcanic rocks on the older basement, is the fact that the Wanipigow Plutonic Complex contains large volumes of equigranular and locally porphyritic tonalite that is identical in composition and, in one case,in age to the
30
subvolcanic Ross River intrusion (Turek et aI., 1989), in the greenstone belt. This
might be interpreted to indicate that the volcanic rocks of the Rice Lake belt are but one
higher level manifestation of a much wider circa 2730 Ma magmatic arc that extended
well into the Wanipigow Complex where subsequent uplift has resulted in the
preservation of only the deeper roots of the arc. A second point of uncertainty involves
the relationship of the Edmunds Lake Formation to the other supracrustal assemblages
of the region. Local field relationships suggest a near conformable transition from arc
volcanic rocks of the Bidou Lake Subgroup into volcanic-derived turbidites (see below).
On the other hand, similar relationships are observable where the turbidites are in
contact with the Garner Lake and Gem Lake Subgroups. Furthermore, D. W. Davis
(pers. comm., 1994) has identified zircons in the turbidites that suggest a circa 3000
Ma provenance for some of the detritus in these sediments and therefore not an
entirely local derivation. These inconsistencies either indicate that the Edmunds Lake
turbidites are, in most places, in fault contact (unexposed) with adjacent volcanic rocks
or that, despite local appearances of conformity, they were deposited above a profound
unconformity at a regional scale.
ECONOMIC GEOLOGY
There are more than 200 gold occurrence in the Rice Lake Greenstone belt (Fig.
16). They occur mainly in the circa 2730 Ma volcanic rocks and associated synvolcanic
intrusions. With the exception of the Ogama-Rockland deposit which is hosted by
tonalite of the Ross River pluton and the Jeep Mine which occurs in older gabbro of the
Wanipigow Plutonic Complex, most of the significant gold deposits in Rice Lake belt
are hosted by rocks of a restricted stratigraphic interval that is dominated byepiclastic
volcanic rocks, basalt flows and layered gabbroic sills of the Bidou Lake Subgroup (Fig.
17). Judging by the detailed mapping of layers and bulk chemical trends, the sequence
of layering in gabbros is similar across the belt, from a melagabbroic base to a
commonly quartz-bearing, leucogabbroic top. Quartz veins at the Central Manitoba,
Mirage, and Oro Grande deposits are hosted directly by leucogabbro but the epiclastic
and basaltic rocks in the Beresford Lake area also host significant veins.
Although there are a multitude of gold occurrences in Rice Lake District, each
with its unique attributes of structure, host rocks and alteration, there are several first
order generalizations which pertain to the most significant deposits (Fig. 17). Points of
consideration as the basis of an exploration model in this district include:
i) At a regional scale, most significant deposits occur in a restricted stratigraphic
interval that marks the transition from volcanic units that are predominantly composed
of basalt to those composed of porphyritic dacite. The interval of transition is marked by
the presence of epiclastic rocks, extensive gabbroic sills and locally, banded iron
formation. Although the full significance of this lithological association is not obvious,
31
1.
Luleo (Poundmaker)
2. San Antonio 3. Sannorm 4. Packsack 5. Gold Lake 6. Gold Pan 16 km 7. Moose
8.
Jeep
9.
Gatlan
10. Cryderman 11. Eldorado 12. Ogama-Rockland
x
x
x
x
x
x
x
x
x
x x
x
x x
x
13. Central Manitoba
14. Gunnar
15. Mirage
16. Eva
+ +
x
x
x
x
+
+
+ +
+
+
+
o
C:;.
Deposits
• Prospects
1+ +1
Tonalite
W
Granodiorite
Figure 16: Distribution of known gold deposits and occurrences in Rice Lake Belt
(adapted from Stockwell, 1941).
32
porphyritic Long
L. • Stormy
L.
/ breccia/tuff ............... /'). /'). /').
*
Gunnar
~~~~~*
Central Manitoba
~~~?l.Z~
* Oro Grande
a)
BISSET
200
m I
(approx.)
San Antonio
*
/'). /').
/'). /').
/').
/'). Numerous /'). -::. /').
/').
/').
/').
oc~~r.r~~~~~· ...•..., DACITE
/').
/'). /'). /').
" ••• '!Il/!'').•• _ •• _ ••••••
/').
)QQQQQQQQQQQQQQQQQQQ QQQQQQQQQQQQQQQ
) Q Q Q Q Q Q Q Q Q Q Q Q Q Q
Q~:: :::: •• _. ''':':'':. '-'-=0
Q Q Q Q Q Q Q Q
) Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q Q
Gunnan Q 9lASAL-F
Q Q
)QQQQQQQQQQQQQQQQQQQQQ
QQQQ~~~~QQQ
) Q Q Q Q Q Q Q Q Q Q Q Q Q
lPORPHYRITIC Q Q Q Q Q Q Q Q Q Q Q Q Q
"" - - - - ,.,. ,.,. ,.,. ,.,. ,.,. ,.,. ,.,. ........
I FELSIC -. .-. .-. 0 0 101 101 101 0 0 0
Q Q
DYKE
b)
Figure 17: a) Stratigraphic setting of some of the major gold deposits in the Rice Lake
Belt.
b) Schematic diagram illustrating the interrelationships of stratigraphic
position, structure and distribution of alteration for some of the major gold deposits in
the Rice Lake Belt (after Poulsen,
1989).
33
the structural anisotropy afforded by the intercalation of these rock types is one factor
that locally controls the location of veins.
ii) Two dominant types of structures host productive veins: veins that are longitudinal
with respect to lithological contacts are a product of layer-parallel shear whereas those
that are transverse are likely the result of local layer-parallel elongation and shortening
of the stiffest members of the stratigraphic sequence. Not all such structures formed
simultaneously, nor are they all prospective hosts for auriferous veins. Early formed
reverse faults are most favourable, but these are not easily distinguishable from
younger structures on the basis of orientation alone because successive generations of
structures resulted in probable reorientation, overprinting and reactivation of the
earliest structures. The interpretation consistent with deposit-scale observations is that
most formed dlJring or prior to D2 deformation and are overprinted by at least D3
structures (Lau, 1988; Brommecker, 1991).
iii) C02-bearing fluids of similar composition were present during the development of
virtually all veins and shear zones (Diamond, 1989; Diamond et aI., 1989), regardless
of their relative age and gold content. The intensity of carbonatization adjacent to
structures is not directly related to gold deposition nor to progressive changes in fluid
composition. However there is a direct relationship between carbonatization and
fracturing and, in that sense, the recognition of such alteration is a useful guide to
potential auriferous structures, if not to gold itself.
FIELD TRIP STOPS
The field trip is organized into a series of stops that are to be made over a
period of three days (Fig. 18). Some of the stops are optional owing to more difficult
logistics but their descriptions are included for completeness.
34
Folds
(anticline;
syncline)
Field trip
stop
x x x x x x x x
-1
x x x
x x x x x x x x x x x x x x x x x x x x x x x x
... ...
x
... ...
... ...
...
...
... ... ... ... ... ...
... ...
... ...
... ... ... ...
Kilometres
D
San Antonio Fonnation
~
Edmunds Lake Fonnation
[±]
Tonalite
I§il
Gabbro sills -1'- o Basalt; dacite
-r
r;;-, Wanipigow River
L..2!..I
Plutonic Complex
.4
D
Manigotagan gneisses
o
1
5 10
Figure 18: Simplified geological map to the Rice Lake Belt showing the locations of Field Trip Stops. 35 Day 1: The Long Lake - Stormy Lake - Manigotagan River Area This part of the field-trip will mainly examine the characteristic lithologies that constitute the Bidou Lake Assemblage which is part of the 2730-2720 Ma arc-like assemblage and, volumetrically, the most abundant supracrustal package in the belt. Typical examples of gold mineralization as well as structural features will also be examined. Drive east from the town of Bissett on Highway 304 for 34.2 km until you pass a large area of rusty tailings on both sides of the road. Continue past the tailings for 200 m and turn right on to a side road leading to the abandoned waste dump of the Central Manitoba Mine. Stop
1-1:
The Central Manitoba Mine
The Central Manitoba Mine milled approximately 395,000 Tonnes of ore grading
12.6g/t
gold between 1927 and 1937. The mine produced gold from a series of veins
in shear zones located within or along the margin of a differentiated, east-southeast striking, south dipping, gabbro sill (Fig. 19). The shear zones also strike eastsoutheast as well and dip steeply to shallowly to the south. The northward dipping South Carbonate Shear and southward dipping North Carbonate Shear form a wedgeshaped domain that bounds the zone of mineralization (Fig. 19). An excellent description of the underground development and the geology of the deposit as a whole can be found in Stockwell and Lord (1939).
Stop Descriptions:
Locality a: The Kitchener Vein and Central Manitoba Gabbro
From the parking area walk approximately 300 mwest across the remains of the
mine waste pile and through the bush to a series of low outcrops near the abandoned
Growler shaft.
Here, the Kitchener Vein, which produced over 90% of the gold from the Central
Manitoba Mine and the differentiated gabbro sill, which hosts mineralization
elsewhere, will be examined (Fig. 20). The vein is located in a shear zone at the
contact between the gabbro sill and a thin band of tuffaceous, cherty sedimentary
rocks. Ore shoots in the vein plunge shallowly to the east and are localized in s-shaped
folds in the shear zone (Stockwell and Lord, 1939). A stereographic projection (Fig.
19) summarizes the structural features associated with the Kitchener Vein. The quartz
vein is enveloped in a narrow zone of quartz-carbonate-chlorite-pyrite alteration. Ore
mineralogy consists of pyrite, chalcopyrite, minor pyrrhotite and gold.
36
KITCHENER VEIN
CENTRAL MANITOBA MINE
HOPE SHEAR ZONE
N
~
Epiclastic Rocks
~
Mafic Volcanic
G
Dove Lake Dyke
~
Gabbro
k
Kitchener V. Tene V. Hope V.
k'
'~~-2-50-m----'-~----:::Ci'::-l/~ Figure 19: Geological sketch map of the area around the Central Manitoba Mine (after Stockwell and Lord, 1939; Brommecker, 1991) 37 25
m
Gabbro
[£I]
Felsic dyke
g
Qtz-bearing pegmatitic ~ Mafic dyke
000
leucogabbro
xxx
g
Porphyri tic and layered I~I Kithener vein a a a gabbro
ITIIJ
Leucogabbro \qv Minor quartz veins
B
Tuff, epiclas tic sediments "'""'""'"~"'" Shear zone
Figure 20: Geological sketch of the outcrops in the vicinity of the Kitchener Vein,
Central Manitoba Mine (mapping by
R.
Brommecker, S. B. Green, K.A. Baker, Lin
Baoqin, Shang Ling, Shen Ershu, and Zhang Lidong).
38
The southern, uppermost third of the gabbro sill at this locality is distinctly more
leucocratic and texturally varied than the lower, northern two thirds of the sill. The top
third is also characterized by zones with pegmatoid patches and visible quartz
whereas the lower part is more equigranular and has no quartz visible to the naked
eye. Most sills in the Rice Lake belt display this differentiation and the more
fractionated portions can be important hosts to gold minralization. In fact, the eastern
end of the Kitchener Vein extends into this part of the Central Manitoba Sill and the
Tene Vein is entirely hosted by it (Fig. 19).
Return to the highway and drive south 1.6 km and park at the side of the road. Outcrop
is on left side of road.
Locality b: The South Carbonate Shear and Dove Lake Dyke
The regionally important South Carbonate Shear (Fig. 19) is intruded by the
Dove Lake Dyke in this location. The Dove Lake Dyke is compositionally zoned, from
cortlandite at its northwest end to quartz diorite at its southeast end. At this stop the
dyke is a "cortlandite" (Scoates, 1971) which is an ultramafic intnJsion with many relict
strongly pleochroic (red-brown to greenish-brown) igneous hornblende crystals
poikilitically enclosing polygonal pseudomorphs of olivine
andlor
pyroxene.
Continue south on Highway 304 for 1.4 km and turn right toward Long Lake at the Tintersection with Provincial Road 314. From this T-intersection drive 5.2 km until you reach a park plaque indicating you have arrived at the Ogama-Rockland Mine. Stop 1-2: The Ogama-Rockland Mine The Ogama-Rockland Mine produced approximately 134,000 Tonnes of ore at a grade of 12.3
glt
during sporadic operation from 1942 to 1951. Production was from
narrow veins within the tonalitic rocks of the Ross River Pluton. The shear zones hosting the gold-bearing veins dip steeply to the northeast (Fig. 21). The largest ore shoot plunges steeply in the Ogama Shear and, according to Troop (1949), the "major ore shoots appear to be connected with warpings in the shear plane". The ore shoot is broadly coincident with a right step (a bend to the right viewed along the strike of the shear zone) and a slight change in the attitude of the shear zone to a more northernly orientation to the south of the ore shoot. Striations and mineral lineations plunge shallowly to the northwest in the Ogama Shear where it outcrops just northwest of the shaft (Fig. 21). Foliation in the shear
zone is oblique to its boundaries in such a way as to indicate dextral movement.
Furthermore, a steeply dipping quartz-feldspar porphyry dyke displays dextral offset by
the Ogama Shear (Fig. 21). The Ogama Shear is therefore a dominantly dextral strikeslip
structure. This interpretation is consistent with Troop's (1949) statement that "the
relative movement of the hanging wall was to the SE". The ore shoot in the Ogama
Shear is therefore in the dilational zone of a fault jog.
39
OGAMA-ROCKLAND MINE
N
w
Ogarna Shaft NW
SE ,_,
1m
If
1m
If
1m
1m
Ig
Tonalite
Sb Wacke, Siltstone, Tuff
If
Felsic Porphyry Sa Epiclaslic Rocks
1m
Gabbro Vm Mafic Volcanic
Figure 21: Geological sketch of the geology in the vicinity of the Rockland, Ogama and
Onondaga veins, Long Lake area.
40
Stop Description:
At this stop we will examine the Ogama Shear zone at locality 1 (Fig. 21) and the
Rockland Shear at locality 2 (Fig. 21).
Locality a: The Ogama shear
The shear is exposed about 100m NW of the Ogama Shaft and contains little
significant veining. Dextral shear sense indicators can be seen along with shallow
lineations. The tonalite to quartz-diorite host rock is strongly foliated and altered to
assemblages containing abundant sericite, carbonate, and pyrite.
Locality b: the Rockland vein
The vein is exposed here and typical ore material can be found on the waste
pile. Again alteration of wall rocks is narrow and consists of sericite-carbonate-pyrite
with ore-veins consisting mainly of quartz-carbonate-pyrite-chalcopyrite and traces of
galena, sphalerite, and arsenopyrite.
Return to Long Lake and continue east to the T-intersection with Provincial Road 314.
From the intersection continue straight (southeastward) along Road 314 for 1.0 km.
Park near a bush trail on the right. Walk south and west along the bush trail 1.5 km.
Stop 1-3: "rhe Mirage Mine
The Mirage mine has no significant recorded gold production. It was, however.
the object of extensive exploration by Esso Minerals in the 1980's and is an excellent
example of the type of metagabbro-hosted mineralization that is so common in the Rice
Lake belt. Coarse gold occurs in quartz-ankerite veins in and around, a complex
network of shear zones (Fig. 22). Iron- carbonate, sericite, and chlorite are the main
alteration minerals. Sulfides, mainly pyrite, are minor. Mineralization is within a very
thick layered gabbro sill and is generally confined to an anorthositic-gabbro unit of the
sill. The geology of the occurrence has been described in detail by Keith (1988).
Stop Description:
Here we examine exposures in the Mirage Shaft Area (locality a, Fig. 22) and at
the Art Showing (locality b, Fig. 22) which typify the complex vein and shear zone
networks that can occur in the competent gabbro host rocks.
41
Figure 22b
o
20m
L-' ,
........................ h •••)
.............................1
(/
(-. .~.....~..,. c::'I..:::.~::.. ..•.•::l::=•=.•~.
----,
r··..··
""""1 : MIRAGE•.~.~.~F!
_,. ••.•.
···t \.
!:-::.~"'''''''.//n---- -:-~.;:~::::;::~::~:::: ~~~ .
-.. -'. '" i:..,,-\
~
•...
\~ ~..:::.::::-
.
i. .
\
\
.
a
o
10m
!
!
l
l
................
c::s:J
Quartz - carbonate - gold veins
CD
Diabase dykes
1:::::::\::::::\:::1 Carbonate alteration
b
Figure 22: a) Geological sketch of the Mirage deposit (from Brommecker, 1991).
b) Sketch of veins and alteration near the Mirage Shaft.
42
~"""""
'.
. ......::::
........
.....
..... ",... ...
...
;;-._---_.~
....." ... ..,··
.,
.
..
,, ,
10m
I
c::.:sl
Quartz-carbonate-gold veins
. o=J
Diabase dykes
~,.::::~:~~~~::::::::::::::::::t::::...
ate alteration
.
.,.~'"...: ----.~illo.o~
.'
o
I
•••• 7r:T'
'.
".
".
"
.
........... "' ......... 1 .. "' •
........-..........
'"
'"
...................... "...
..
.......
'
'.
(a
MIRAGE MINE
N
N
(b
Great circle
distribution of
poles to flal
veins due to
F2 folding
w
W-striking
shear zone
WNW-striking
shear zone
s
• Plunge of mineral
lineations in shear zonas EQUAL AREA LOWER HEMISPHERE PROJECTION
c Plunge of striations and tourmaline linealions
on fial veins
Figure 23: a) Sketch of veins and alteration at the Art Showing (after Brommecker,
1991)
b) Stereographic projections illustrating the orientations of structures at the
Mirage deposit.
43
Two types of gold-bearing veins are present at both localities: 1) steeply dipping
veins in shear zones and 2) shallowly dipping ''flat'' veins. The steeply dipping veins
occur as lenses, pods, and short tabular bodies along linear zones of highly strained
and altered rocks. The flat veins are 1-5cm wide continuous veins that occur near, and
often extend away from, the zones of high strain (Fig. 22). The flat veins commonly
display the morphology of an extensional vein. However, they also commonly contain
what appear to be slickensided planes parallel to their walls that contain a pronounced
down-dip lineation formed by the alignment of tourmaline crystals. The tourmaline
crystals are parallel to striations observed on some vein surfaces. Both the flat veins
and shear zone-hosted veins contain visible gold, but according to Keith (1988) and
Grant (1987) gold is most abundant in the flat veins. Preliminary drilling by Esso
Minerals in 1987 indicated that the zone of mineralized flat veins near the Mirage shaft
(Fig. 22) plunges shallowly to the west (Grant, 1987). Fig. 23 summarizes the
orientations of the structures that can be observed in this area.
Return to Provincial Road 314 and continue eastward for 4.0 km until you reach
the intersection with the road to Beresford Lake Campground. Turn left and continue
along this road for 1.5 km. Turn left onto a dirt road into the abandoned Gunnar Mine
site.
Stop 1-4: The Gunnar Mine and Gunnar Formation of the Bidou Assemblage
The Gunnar Mine produced 259,681 tonnes of ore at a grade of 11.9
glt
from
1936 to 1942. Most of the ore came from narrow quartz veins and lenses in the No. 1 Shear where it intersects a quartz-feldspar porphyry dyke. Sulfides associated with the mineralization within the quartz vein consist mainly of pyrite and minor sphalerite, pyrrhotite, and galena. Narrow (1-30cm) zones of alteration around the veins include ankerite, sericite, chlorite and pyrite. The Gunnar Mine is located near the axis of the Beresford anticline (Fig. 24). The deposit is within the pillowed and massive mafic volcanic flows of the Gunnar Formation. The Gunnar Formation in the area is intruded by a number of felsic to intermediate porphyry dykes which are parallel and strike north-northwest and dip eastnortheast. Thin beds of interflow sediment or pillow breccia mark the boundaries of flows. The flows in the mine area generally strike southeast and dip steeply to the southwest (Fig. 24). Some sedimentary beds were loci of strain and are highly sheared. The shear zones hosting gold-bearing veins strike and dip parallel to flow contacts (Le. strike southeast to east-southeast and dip steeply southwest).
44
D
MaficSfloTwsOP 1- 4: Gunnar Mine ! v yVV 01b or 02 WI Shaft
Shear Zones
D
~ Moore Lake Shear N ...
-
Sediments
Malor 01 high =:======= Road
strain zone
~
Intermediate Volcanics 1tl 51,52,53 e
Field Trip
Locality
G
Felsic to intermediate
porphyry and tonalite
~
Bedding trace
bodies
[SJ
0 100 200m
Porphyry dykes Figure 24: Geological sketch of the Gunnar Mine area (after Stockwell and Lord, 1939; Brommecker, 1991).
45
N
GUNNAR MINE
L2
No. 1 shaft SE
L_1_~~~'-'-\d+~,,:--line7
L4
w
E
L5
L6
L7
20m
s
La
L
20m
NW
surface
Figure
25: Structure of the Gunnar Mine. a) Longitudinal section, b)
stereographic
projection.
46
The geology and development of the Gunnar Mine has been described in detail
by Stockwell and Lord (1939), Shepherd (1939), and Lord (1942). Important aspects of
the underground development as described by the above authors is summarized below.
There were two main ore shoots in the mine, both within the Gunnar No.1 Shear (Fig.
25) and separated by a gently dipping fault. The upper ore shoot coincided with the
intersection of the shear and a quartz-feldspar porphyry dyke and the lower ore shoot
coincided with the intersection of the shear and a biotite lamprophyre (probably the
hornblende-biotite diorite mapped in this study and shown as "mafic dyke" on Fig. 25).
The lamprophyre is mostly undeformed, although locally it is cut by stringers of
auriferous quartz. Lord (1942) concludes that the lamprophyre dyke was intruded near
the end of the shearing and that the vein quartz was introduced shortly after intrusion of
the dyke.
Figure 25 summarizes the main structures that are observations in the Gunnar
Mine area. The interpreted movement direction on the No.1 Shear is perpendicular to
the plunge of the ore shoots in it. The geometric relationship of the lineations, ore
shoots and attitude of the shear zone indicate that the ore shoots are located on a
compressional fault bend.
Stop Description:
Numerous features will be examined at various localities in the Gunnar Mine
area (Fig. 24):
Locality a: East end of the Gunnar No.1 Shear Zone
The shear zone has no significant veining or mineralization at this location but
early fractures can be observed to bend into it in a sinistral sense. The quartz-feldspar
porphyry dyke that marks the eastern extent of the mineralization can also be examined
here.
Locality b: Mineralized section of Gunnar No.1 Shear Zone
A massive to brecciated quartz vein containing pyrite and minor pyrrhotite,
galena, and sphalerite is central to the shear zone. A thin alteration zone composed of
ankerite, sericite, chlorite and pyrite envelopes the vein. Directly south of the vein, a
set of porphyritic mafic dykes both cut and are cut by minor subsidiary shear zones.
Good examples of pillowed basalt typical of the Gunnar Formation are also present in
the adjacent outcrops.
Locality c: Gunnar No.3 Shear Zone cutting a body of tonalite
Porphyritic mafic (Iamprophyre) dykes cut the tonalite and both are cut by the
shear zone. The tonalite has been dated by Turek et al. (1989) at 2731 +/-13 Ma and
provides a minimum age for the Gunnar Formation and a maximum age for the
shearing.
47
Locality d: Breccia dykes
Intrusion breccias near the edge of the tonalite body cut mafic volcanics of the
Gunnar Formation at this locality.
Localitye: Moore Lake Shear Zone
The amount of deformation increases markedly and abruptly directly east of the
Gunnar Mine. At this location, intense foliation and extreme transposition of layering
defines the Moore Lake Shear zone which is one of the features which marks the
attenuated eastern limb of the Beresford Anticline. Multiple foliations, minor folds and
imbricated rock units are common in this outcrop.
Return to Provincial Road 314 and park at the Beresford Lake turn-off.
Stop 1-5: The Stormy Lake Formation of the Bidou Lake Subgroup
At this stop we will make a short traverse across a typical section of the Stormy
Lake Formation of the Bidou Lake Subgroup. A weakly differentiated sill will be
examined where it intrudes iron formation and volcanic wackes and volcanic breccias
which are part of a southward-facing sequence.
Stop Description
Sites to be examined (Fig. 26) include:
Locality a: N-S trending shear zone in gabbro with D3-kinks
Locality b: Coarse grained gabbro which is locally glomeroporphyritic
Locality c: Quartz-bearing leucogabbro.
Locality d: Medium grained gabbro showing intrusive contact with iron formation
Note typical F2-folds with axial-planar S2 cleavage at this location.
Locality e: Volcanic wackes, breccias, and tuffs of the Stormy Lake Formation
Note that the younging direction is to the south.
Continue south along Provincial Road 314 for approximately 5.2 km to a point
0.5 km north of the bridge across the Manigotagan River.
48
To
Bissett
87..
"}-:
o
!
~
t:....:....:...
~
~
~
~
Volcanic conglomerate
Tuff, lapilli tuff
Iron Formation
Areni te/argilli te
Granophyric gabbro
III
To
Beresford L.
Leucogabbro
Gabbro
Melagabbro
Quatrz-feldspar
porphyry
Figure
26:
Sketch map of the geology of the Stormy Lake Formation as exposed in
outcrops along Provincial Road 314 near the turnoff to Beresford Lake. (mapping by 49 Stop 1-6: The Narrows Formation Dacite and Glomeroporphyritic Gabbro The Narrows Formation, defined after bedrock exposures at The Narrows on Long Lake (Campbell, 1971), comprises mainly intermediate to felsic volcanic rocks which were deposited near or at the stratigraphic top of the Bidou Lake subgroup (Weber, 1971). The Narrows Formation overlies the Stormy Lake Formation of mixed intermediate and mafic volcanics and sediments and several older mainly mafic volcanic and sedimentary formations (Gunnar, Dove-Lake, Tinney Lake, Stovel Lake and Unnamed basalt formations; Campbell, 1971;
ct.
Table 1). Seneshen and Owens
(1985), who conducted the most detailed work in the Stormy Lake area, described three main lithologic units: (a) Lapilli tuff and crystal tuff; (b) heterolithic tuff breccia and (c) generally monolithic breccia. Both fragments and matrix are intermediate to felsic in composition. The formation has been interpreted as a succession of largely subaqueous origin, in part pyroclastic and in part laharic flows (Weber, 1971 b). A U-Pb zircon age of 2731±3 Ma (Turek et aI., 1989) was obtained from the rhyodacite of The Narrows Formation to be examined at this stop (Fig 27). All the intermediate to felsic extrusive and intrusive rocks dated in the Rice Lake belt have given the same age of ca. 2730 Ma, with the exception of the Gem Lake Subgroup rhyolite dome, which is slightly younger (2722±2 Ma; Table 2). This includes the Hare's Island Formation intermediate to felsic volcanics (2731±3 Ma), rhyodacite breccia of the Black Island succession at the western end of the Rice lake greenstone belt (2732±10 Ma), dykes in the Beresford Lake area (2731 ±13 Ma), the Ross River quartz diorite, the largest intrusion in the belt, and tonalite in the Wanipigow plutonic complex (2731±13, 2731 ±1 0 Ma; Turek et aI., 1989, Turek and Weber, 1991; Ermanovics and Wanless, 1983;
ct.
Table 2), suggesting that 2730 Ma intermediate to felsic magmatism in the
Rice Lake greenstone belt is widespread and probably the most voluminous in the belt. In contrast to the Bidou Lake subgroup which ranges from basalts to rhyodacites (4665% Si02), the Gem Lake subgroup ranges from basalts to rhyolites (up to 70-75% Si02). Although interpreted to being younger than the Bidou Lake subgroup (Weber, 1971b), and Gem Lake felsic volcanics indeed yield a slightly younger age than the Bidou Lake intermediate to felsic volcanic rocks, the two subgroups may be more spatially than temporally separated and are essentially co-magmatic. The Bidou Lake Subgroup contains 10-30% gabbroic sills. Some of the largest ones are differentiated into gabbro and anorthositic phases, such as the Stormy Lake gabbro, others are spectacularly glomeroporphyritic, with up to football size plagioclase aggregates, particularly along contacts of the gabbro with the host rocks. Phinney et al. (1988) have done extensive petrogenetic studies on these megacrystic mafic rocks in Manitoba and elsewhere. They found that the megacrysts have higher anorthite contents (An 80-85) than the matrix plagioclase laths (An 60-70) suggesting that the megacrysts were not in equilibrium with their host melts at the time of dyke emplacement. Based on experimental and geochemical data they conclude that high pressure fractionation from a primitive mafic melt led to ascension of a fractionated less dense melt to a low pressure magma chamber (at 1-2 kb) where plagioclase
50
1\
1\
1\
1\
1\ 1\
1\
1\ 1\
1\
1\ 1\
1\ 1\
1\ 1\
1\ 1\
1\ 1\
1\ 1\
1\ 1\
1\
1\
1\
1\
1\ 1\ 1\
1\
1\
1\ 1\
1\
1\
1\
1\ 1\ 1\
1\ 1\
1\
1\
1\
1\ 1\
1\
---
-----------------------------------
-
------------------
o
I
~
~ ~
~
~
~
0.5 km
I
Anorthositic gabbro
Gabbro
Edmunds Lake Fm.:
mainly turbidities
Manigotagan River Fm.: felsic to
mafic volcanics and sandstones
The Narrows Fm.: intermediate
to felsic volcanics
Stormy Lake Fm.: mafic to
intermediate vocanics and ss.
Figure
27:
Sketch map of the geology of the Narrows and Manigotagan River
Formations near Provincial Road 314 south of Stormy Lake. 51 megacrysts crystallized in anorthosite complexes and portions of these were flushed to the subsurface along with new melts flowing into the chamber. Stop description The outcrop to be examined is situated on the east side of Provincial Road 314, ca. 0.5 km north of the bridge over the Manigotagan River. The bedrock consists of massive dacite (to rhyodacite) with a joint-like fracture pattern along which greenish alteration is visible. If this fracture pattern is indeed a joint pattern it would imply a subaerial flow, although such flows have not been identified elsewhere in the Narrows Formation. Walk farther east and examine the football gabbro with glomeroporphryritic phases, which are particularly well developed along the footwall (northern) contact of the gabbro with the volcanic rocks. Continue along Provincial Road 314 to a point approximately 2.3 km south of the bridge across the Manigotagan River. Stop 1-7: Manigotagan River and Edmunds Lake Formations The southwest facing Manigotagan River Formation represents the uppermost part of the Bidou Lake subgroup and marks a transition between the volcanic rocks of the Narrows Formation and the overlying sedimentary rocks of the Edmunds Lake Formation (Fig. 27). It consists of seven lithologically distinct members (Table 4) which include primary and reworked felsic to mafic volcanic rocks and minor mafic lava flows. The members range from 5 to 103m thick and, although somewhat variable in thickness, all members are continuous across the map area for 1.2 km. Two chronologically and compositionally different mafic sills occur in the sequence, one at the base of the formation, and the other separating members 3 and 4; discontinuous gabbro intrusions also occur in members 2 and 3. There is an upward transition within the Manigotagan River Formation from felsic and mafic pyroclastic rocks in the lower part, through felsic, reworked pyroclastic rocks and mafic lava flows in the central part, to mafic lava flows and felsic pyroclastic rocks in the upper part (Fig. 28, Table 4). Felsic pyroclastic flow deposits at the base and top of the Formation (Members 1 and 7) were deposited subaqueously but were probably derived from subaerial eruptions. The subaqueous tephra-fall deposits (member 2) were probably derived from flank fissure-type phreatomagmatic eruptions. Member 3 represents a marked change in conditions; it is an upward coarsening, progradational, subaqueous fan succession. The lower thin-bedded turbidites (Fig. 28) represent an outer fan to basin plain environment. These grade upward to interchannel sandstones and siltstones and upward fining channel-fill conglomerate and sandstone sequences diagnostic of a mid-fan environment. The provenance was probably a subaerial, felsic to intermediate volcano; this is indicated by the compositions of clasts in the 52 100 200 Metres Symbols a Interbedded volcanic sandstone, siltstone and mudstonewith minor volcanic conglomerate and oxide-facies iron formation t
Field Trip Section
.Pc'
Bedding (overturned)
'"'J '"'J
Shear
Manigotagan River Formation
Irl~l~l ~~l~~; :;;N;~~;~~~~:)d
tuff
~
Turbidites (6)
~
Interbedded volcanic
sandstone and siltstone
I::I
Mafic Lava Flows (5)
Massive, pillowed and brecciated [[]]] Peperites (4) Volcanic sandstone, vesicular diabase lava pods and minor volcanic siltstone
D.
Progradational Subaqueous
Fan Succession (3) Interbedded volcanic sandstone and volcanic siltstone with local mafic, massive and pillowed lava flows
I;;;; l
Tephra-fall Deposits (2)
Mafic to in termediate lapilli-tuff and tuff
Ix xxl
Lower Ignimbrite
(l)
Felsic Lapilli-tuff and Tuff
Narrows Formation
Felsic to in termediate tuffbreccia,
lapilli-tuff and tuff
Mafic Intrusions
o
Gabbro (9)
1':%::1
Vesicular Diabase (8)
Edmunds Lake Formation
Figure
28:
Sketch map of the stratigraphy of the Manigotagan River Formation at Stop
1-7a (mapping by D. Seneshen). 53 Table 4: Summary of Members in the Manigotagan River Formation Member Thickness Composition Components Structural Features Genesis (m) Ignimbrite
(7)
15-50 felsic lapilli-tuff and tuff consist of thin to very thick bedded; subaerial eruptions
vitric ash, vitric felsic normal or, less commonly, generated pyroclastic fragments, pumice, dacite doubly graded flows which entered water fragments; plagioclase, quartz and microcline crystals Turbidite (6) 11-24 felsic sandstone consists of thin to very thick bedded; local slumps from the vesicular to non-vesicular normally graded Bouma higher parts of a mafic volcanic clasts; divisions; possible ripples sUbaqueous fan plagioclase and quartz and load structures generated by tUrbidity crystal grains and a siltstone flows matrix Lava Flows (5)
6-29
mafic amygdaloidal and massive lava flows have subaqueous flank fissure
plagioclase-phyric; brecciated upper and eruption fed by undet1ying recrystallized to locally felty lower zones; lateral diabase sill (unit 8) groundmass transition from massive to pillowed flows; concentric zoning of vesicles In some pillows; vesicularity increases upward in the sequence Peperite (4) 5-22 intermediate sandstone consists of felsic thin to very thick bedded; upper part of subaqueous volcanic clasts, plagioclase normal graded; local low- fan succession was and quartz crystal grains, angle cross laminations Intruded by a shallow mudstone matrix; lava pods diabase sill causing are amygdaloidal and mixing of magma and wet plagioclase-phyric with a sediment recrystallized groundmass Mass Flows; 32-103 felsic to conglomerate consists of thin to very thick bedded; renewed explosive minor Lava intermediate felsic, intermediate and normal graded; scours volcanic activity provided Flows (3) mafic volcanic clasts, and load structures felsic to Intermediate volcanic sandstone clasts, common; local trough and debris for progradation of plagioclase and quartz festoon cross bedded a subaqueous fan; mafic crystal grains and siltstone interpillow sandstone; lava flows erupted by matrix; sandstone consists some pillows show central or flank fissure of felsic volcanic lithic concentric zoning of eruptions concomitant grains, plagioclase and vesicles; vesicularity with fan progradation quartz crystal grains and a increases upward in lava siltstone matrix flows Tephra-fall 17-91 mafic to lapilli-tuff and tuff consist of thin to very thick bedded; tephra-fall from shallow Deposits; intermediate felsic to mafic, vesicular to lapilli-tuff and tuff beds water or subaerial, flank minor Volcanic non-vesicular volcanic non-graded and have fissure phreatomagmstic Conglomerate clasts, plagioclase and abrupt contacts; minor eruptlon(s); volcanic and Sandstone quartz crystal grains, volcanic conglomerate and conglomerate and (2) actinolite porphyroblasts sandstone beds are sandstone sequences are after clinopyroxene crystals normal graded; volcanic either channel-fill deposits and a mafic ash matrix; conglomerate beds have within tephra-fall deposits volcanic conglomerate and erosive basal contacts or erosional remnants sandstone consist of felsic to mafic, vesicular to nonvesicular volcanic clasts, plagioclase and quartz crystal grains in a siltstone matrix Ignimbrite (1) 6-39 felsic lapilli-tuff and tuff consist of medium to thick bedded; same as upper ignimbrite vitric ash, dacite fragments, normal to less common but fewer pyroclastic flows vitric felsic fragments, doubly graded in the examined section pumice and plagioclase and
9
uartz crystals
54
conglomerate, most of which are volcanic, and by the euhedral to subhedral shapes of
plagioclase and embayed quartz grains which resemble pyrogenic crystals in
underlying members. Mafic flows intercalated with the lower part of the fan succession
attest to contemporaneous volcanism and sedimentation. Peperite that comprises
Member 4 formed by the mixing of magma and wet sediment. Mixing occurred where a
shallow diabase sill (unit 8, Fig. 28) intruded volcanic sandstone and siltstone of the
upper part of the fan succession; irregular lava pods and dykes extended several
metres into the sediment and locally broke through the seafloor to feed massive,
pillowed, and brecciated lava flows of Member 5. Volcanic sandstone and siltstone
(Member 6) that overly the lava flows were probably deposited by turbidity flows
generated by local slumps from the higher parts of the subaqueous fan (Members 3
and 4).
The Manigotagan River Formation records multiple variations in magma
compositions, and in volcanic and sedimentary processes over time. The lower felsic
ignimbrite (member 1) and the mafic to intermediate tephra-fall deposits (member 2)
were apparently erupted in succession and represent the later eruptive phases of the
stratovolcano from which dacitic tephra of the underlying Narrows Formation was
erupted. The progradational fan succession, which largely consists of resedimented,
felsic to mafic pyroclastic debris, probably reflects a renewed, explosive eruptive event.
Mafic lava flows in the lower (member 3) and upper (member 5) parts of the fan
succession were probably erupted through fissures and were fed from the same
magma chamber. Following the eruption of the upper mafic lava flows, there was a
hiatus in volcanism, and the turbidites of member 6 were deposited. Subsequently,
another explosive eruption occurred and the felsic ignimbrites of member 7 were
deposited. After this final eruptive event, the stratovolcano apparently underwent
erosional destruction, subsidence and burial by the flysch sequence of the Edmunds
Lake Formation. Although the contact between the Edmunds Lake Formation and the
Manigotagan River Formation is not exposed, erosional destruction of the stratovolcano
is suggested by the petrographic similarity between sedimentary units in the former and
underlying felsic pyroclastic units in the latter (Seneshen and Owens, 1985).
On a regional scale, the Edmunds Lake Formation overlies both the Bidou Lake
and Gem Lake Subgroups of volcanic rocks without recognizable unconformity. The
formation is characterized by greywacke/mudstone turbidity current deposits. With the
exception of local gabbroic sills there are no volcanogenic magmatic rocks within the
formation. The formation grades towards the south into paragneisses and migmatites of
the Manigotagan gneiss belt of the English River Subprovince. Due to this transition the
thickness of the formation is unknown, but could be considerable. A granitoid intrusion
from Black Lake dated 2663±7 Ga (Turek et aI., 1989) is a minimum age for the
formation and dates the peak of the (Kenoran) metamorphism in the gneiss belt and
structural data suggests that the formation is older than the San Antonio Formation.
The latter has not been affected by the D1 deformation (Weber 1971b).
55
Campbell (1971) summarized the characteristics of the Edmunds Lake Formation as:
- thin-bedded units
- well-sorted sediments, markedly different in lithology from the underlying
sediments
- uniform grain size
-laterally continuous beds
- absence of cross-lamination
- abundant graded bedding
- conglomerate with increase in abundance and thickness upward in the
formation
( The latter only applies to the low grade metamorphic portion; in the higher
grade belts conglomerates are absent)
The lower stratigraphic portion is typified by cherty units locally with magnetite,
quartzose greywacke, and arkosic sandstone with pebble conglomerate.
Stratigraphically upwards the detritus influx increases and chemical sediments
disappear. Weber (1971b) compared the upper conglomeratic facies with a flyschoid
facies, with granitoid boulders in the conglomerates being derived from an older
basement to the north and northeast. U-Pb data from detrital zircons also indicate 3.0
and 3.1 Ga sources in the greywacke (D.W.Davis, pers. comm., 1994).
Stop Descriptions:
At this stop we examine outcrops representative of the Manigotagan River
Formation (locality a, Fig. 27, 28) and of the Edmunds Lake Formation (locality b, Fig.
27)
Locality a: Manigotagan River Formation
At this locality (Fig. 28), the upper part of the Formation (members 3-7) is
exposed. Vesicular diabase and layered gabbro with irregular distributed plagioclaserich
patches which are locally quartz-bearing is also present.
The upper ignimbrite consists of up to twelve flow units, 0.7 to 17 m thick
containing variable proportions of dacite fragments, vitric felsic fragments, pumice, rare
mafic scoria and microcline-phyric felsic fragments. Plagioclase and lesser quartz
crystals enclosed in a granoblastic quartzo-feldspathic matrix interpreted to be
recrystallized vitric ash. The ignimbrite consists of composite sheets of multiple flow
units most of which consist of a lower lapilli tuff and an upper non-bedded or planar
bedded tuff division. Individual flow units (Iapilli tuff or tuff divisions) show reverse
grading of pumice, normal grading of vitric and/or dacitic fragments and pumice-rich
and pumice-poor sequences indicate subaqueous pyroclastic flow deposits. Dark felsic
clasts, generally rounded with recrystallized (devitrified) ("Iisgang") rims are common.
56
The lower pillow basalt (member 5) shows an eroded top filled in with crossbedded
sand. The flow is vesicular at base.
Sediments beneath the basalt consist of thin-bedded siliceous siltstones/argillite
and thicker beds of higher energy mass flows with scattered clasts of underlying
sediments. Slab stacking indicates slope or flow to the east.
return to the parking area on Provincial Road 314.
locality b: Edmunds Lake Formation
The field trip stop is at the parking area for departure to stop
1-8-A.
At the
bottom of outcrop are exposures of mainly thin-bedded chert, mudstone argillite, and fine grained sandstone (10-20 cm thick). There is some evidence of density currents here in the form of unsorted conglomerate. A pair of flags mark a location where climbing ripples in finely laminated argillite indicate decreasing flow above density flow with graded beds. Nearby and further up section, decreasing numbers of ripples may indicate increasing flow. This probably indicates shallow water environments with periodic influx of density currents. - END OF DAY 1 -
57
Day 2 - The Gamer Lake-Wallace Lake-Wanipigow River Area
Drive east from Bissett on Highway 304 for approximately 37.5 km to the Tintersection
near Long Lake. Turn left (east) on Provincial Road 314 and continue
driving southward, passing the turnoff to Beresford Lake campground at a point
approximately 5 km from the T-intersection. Stay on Provincial Road 314 and travel an
addtional 1.4km south of the turnoff to a poorly maintained turnoff to the left (This road
is occasionally gated). Turn left onto the road and drive (or walk) approximately 1.7 km
east to the bridge across the Beresford River. The rocks to the west of the bridge
belong to the Manigotagan River and Edmunds Lake Formations and are on-strike
equivalents of those at Stop 1-8, locality b. Note that, here, graded bedding indicates
that the metasedimentary rocks face eastward. Walk across the bridge to examine a
series of outcrops to the east and south of this point.
Stop 11-1: Supracrustal rocks of the Gamer Lake Subgroup
The rocks south and east of Beresford Lake contrast strongly with those of the
Bidou Lake and Gem Lake Subgroups in that the sequence contains much more basalt
and recently recognized komatiite. Some of the rocks in this area had previously
correlated with the mafic Banksian Lake Formation of the Gem Lake Subgroup but, as
described above, are better viewed as part of a newly defined and distinctive Garner
Lake Subgroup. Note that, although supracrustal rocks in this area occupy a relatively
narrow north-south strip, the strata within the strip actually tend to strike east-west, only
bending into north-south strikes near the Beresford Lake Shear Zone (Fig. 29). The
series of localities visited at this stop therefore progress down the stratigraphic section
toward Garner Lake where even lower stratigraphic units can be examined in less
accessible exposures.
Stop Descriptions
Proceed eastward from the bridge (Fig. 29) for approximately 500 m to a series of low
outcrops on both sides of the fire road.
Locality a: Iron-formation and basalt
At this location folded banded iron-formation is interlayered with pale grey-green
Mg-basalt. The iron-formation is mainly magnetite facies although there are local
sulphide pods which may have resulted from epigenetic sulphidation. The basaltic
rocks are locally carbonatized to chlorite-ankerite schists.
Continue another 100 m eastward on the fire road to a small clearing on the right hand
side (there is a small outcrop of folded iron-formation at roadside). This marks the
beginning of a (generally very wet) trail that leads southward toward Garner Lake.
Follow the trail southward approximately 1 km to a point where the trail rises to a
58
I . I .
OJ
:~I ~
I
ni I
0'
c.
a
3
r
s:::::
D)
;::]
c.
en
r
D)
'
C"
D
"'T1
3
I
I
/
/
~
I
I
Way
up
-L
graded beds
---- pillow tops
STOP 11-1
~:::::::::I
Komatiite Section
- Iron-Formation
---
---shear zones
500m
Figure 29: Sketch map of the geology of the Garner Lake Subgroup between
Beresford and Garner Lakes (Stop 2-1).
59
relatively narrow passage between large outcrops on either side. Climb eastward
along the outcrop ridge to the left.
Locality b: Basaltic komatiite
At this location the rocks consist of interlayered northward-facing pillowed
basaltic komatiite flows and narrow buff-weathering massive komatiite units. Although
the massive units here are not convincingly flows they are basaltic komatiites in
composition (approximately 16% MgO anhydrous, Fig. 13b) and locally possess
excellent polysuture structure that is typical of ultramafic flows elsewhere in Superior
Province.
Continue southward for approximately 200 m along the ridge to a cluster of low
outcrops at its southern end.
Locality c: Komatiite and basaltic komatiite
The rocks here are similar to those at locality b but with greater evidence for the
origin of the buff-weathering komatiites. A 10-cm thick unit of spinifex texture and a
well-exposed rubbly flow-top both support an extrusive origin. Samples of this flow and
a spinifex-textured clast in the breccia contain 20 to 22% MgO (anhydrous). Note also
that some of the pillowed flows here are composed of basaltic komatiite (13 to 16%
MgO) containing common drainage cavities.
Return to the trail via locality c and continue southward approximately 600 m to a large
outcrop on the right side.
locality d: Spinifex-textured basaltic komatiite.
The spinifex in this large outcrop is mainly of the coarse "stringbeef
II
variety and
its morphology and arrangement within the outcrop further supports the observation that this is a northward-facing sequence of flows. Return along the trail to the fire road and return westward to Provincial Road 314. Head north to Highway 304 and continue northward to the turnoff to the Wallace Lake Campground. Turn right (north) and proceed approximately 1 km to and turn left into the garbage pit clearing (this turn is before the cottages appear). Follow the dirt road on the west of the garbage pits to the shore of Wallace Lake. Park by the large garage and follow the shoreline eastward for approximately 400 m to a series of exposures overlooking Wallace Lake (Fig. 30).
60
300m
I
o
I
·(+6,7) .
. (+6,7)·
v .......... vv , . v
·
.Yvvvvvvvvv.~v.vvJVVVVVVVVV~..
~VVVVVVVVVVVV
v v v v v v v v v v
v ,·V v v v v v v v v v W v v v W v v v v v v v V."aI'·V V V V V V V V V V V V V V .v... V v v v v v V Y40~V"'v V
v v:..... v v v v v v v.':; v v v v v v v v v v v v v v v
v~u·~~~~·~~vvvvvv~vvvv... VVVVVVVVVVVVVVVV~V~~VVVVVVVVVVVVVVVVVVV ·(~6·,7·) ,
,
,
... ...
"..."..."
...
~ ~ ~ ~ ~ ~
... ... ... ... ... ... ...
...
~ ~ ~ ~ ~ ~ ~ ~ ~
...
... ... ... ... ... ... ... ... ... ... ...
~---,;".~~-.._-,,~'I--,..
" t ,,'k'" " " " " "
~~~~~~~~~,
~ ~ ~ ~ ~~;~~~~,~~~ ~"'4~~"'~"'~~L"'~"'~"'~"'~'"
...~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ... ... \.,.... ', ...., ,.~(~
...
~ ~ ~ ~ ~ ~ ~ !'~ ~ ~ ~ ~
...~ ~ ~ ~ ~ ~ ~ ~ ~~~~ ... ~(~i~ ~ ~ ~ ~ ~ ~ ...~ ...~ ...~~~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
...
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~k~~ ~
I ~.~ ~ ~ ~ ~ ~ ~ ~ ~ ~ A~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ..................~ ...~ ......~'~ ~ ...;~<~ ...A'~ ...~ ...~ ...~ ...~ ...~ ...~ ...~ ... ~ ...~ ...~~~ ...~ ... ~ ...~ ...~ ...~ ... ~ ...~ ...~ ...~ ...
......
rn
•
Quartz - feldsparporphyry
dykes (2.92Ga)
Feldspar - porphyry dykes
STOP II -2
WALLACE LAKE ASSEMBLAGE
r...;...;i
Gabbro
Mafic volcanics Oxide facies BI F Marble, quartzite,argillite Quartz arenite (2.999 Ga)
Figure 30: Sketch map of the geology on the south shore of Wallace Lake (Stop 2-2).
61
Stop 11-2: The Conley Formation of the Wallace Assemblage
The Wallace Lake assemblage (WLA) is largely equivalent to the Conley
Formation (McRitchie,
1971
a) although additional work is required to establish its full
extent. Weber
(1988),
mainly on lithological grounds, postulated that these rocks are
part of the
2.8-3.4
Ga Mesoarchean continental platform assemblage as mapped and
defined in Northwestern Ontario (Thurston et aI.,
1987; Williams et aI., 1992).
Subsequent U-Pb zircon data from the Wallace Lake area have confirmed this
interpretation (Turek et aI.,
1989; Turek and Weber, 1991, 1994).
The WLA is exposed in a segment of the Rice greenstone belt that is separated
from the main Rice Lake greenstone belt by the Wanipigow Fault (Fig. 30). An
apparent dextral displacement of ca.
20
km is indicated along the Wanipigow fault,
based on the relative displacements of the contact between greenstones and granitoid rocks of the Wanipigow Plutonic Complex. However, lithologies can not be correlated across the fault. Gravity data collected and interpreted by Brisbin
(1971)
indicate a
relatively thick section of rocks
(5.5
km) at Wallace Lake north of the Wanipigow Fault
compared to Rice Lake
(3.3 km) and Beresford Lake (5.2
km) suggesting that different
crustal levels or possibly even different stratigraphic packages could be juxtaposed at the fault. The WLA comprises the lithologies listed in stratigraphic order in Table 1, Table 5. The lower half of the section will be encountered during the field trip (Fig. 30). This stratigraphic succession is a preliminary interpretation. A modern stratigraphic/structural study of the Wallace Lake area is still outstanding and desperately required, particularly because it probably has one of the best developed and exposed sections of the Mesoarchean platform assemblage in the Superior Province. Table 5: Units Comprising the Wallace Lake Assemblage
....
~~~!?!~j~L~D.~~
..
Intermediate to felsic volcanic rocks of uncertain age relationship and possibly representing more than one age.
ultramafic rocks (serpentinite), in part komatiitic f1ows(7)
gabbroic dykes2
mafic volcanic flows
oxide facies banded iron formation
greywacke/argillite
argillite
marble
interlayered marble and quartzite
quar2ite
guar2 arenite with conslomerate beds1
1Conglomerate clasts include 3.0 Ga tonalite clasts and intermediate-felsic
volcanic/subvolcanic rocks of unknown age.
2Gabbroic dykes have been intruded by feldspar porphyry dykes and subsequently by
2.92
Ga quartz feldspar porphyry dykes.
62
\
b
·:~
.
. fjI: .
~::
:1
Quartz (-feldspar) porphyry
~
Feldspar porphyry
IZJ
Diorite
D
Gabbro
D
Quartz sandstone
o
10m
I
I
~..
Pebble bed
~
Way - up
'\'
"
\ Foliated zone in gabbro
STOP II - 2, locality c
Figure 31: Geology of the quartzite section of the Conley Formation at Wallace Lake
(mapping by W. Weber and P. Adamo, 1994).
63
Quartz arenite with conglomerate beds forms a succession with an apparent
thickness of 1000 m in the Wallace Lake area. This formation is composed of immature
detritus shed from a largely granitoid hinterland and deposited in subaerial fluvial
environment. U-Pb data indicate that the formation was deposited, intruded by mafic
and felsic dykes, and deformed prior to 2.92 Ga (the U-Pb age of a 2.92 Ga quartzfeldspar
porphyry dyke). Tonalite clasts from conglomerate at the north shore of
Wallace lake have yielded a U-Pb zircon age of 301 0±13 Ma (Turek and Weber, 1991)
and detrital zircons have yielded similar ages (Poulsen et aI., 1994). This hinterland is
likely the Wanipigow Plutonic Complex (WPC). Although field relationships indicate
intrusive relationships between the quartz arenites and WPC in the Wallace Lake area
(McRitchie, 1971a), U-Pb zircon geochronology confirms the existence (or
preservation) of -3 Ga crust along the northern margin of the Rice Lake greenstone
belt between Lake Winnipeg and Wanipigow Lake (Ermanovics and Wanless, 1983;
Turek and Weber, 1994). At the western end of the Rice Lake greenstone belt near
Seymourville (Hole River settlement) a potentially very significant erosional
unconformity has been described (Ermanovics, 1981) where quartz arenite overlies 3.0
Ga tonalite. Ermanovics equated these quartz arenites with the San Antonio Formation,
but it is equally possible that these arenites are part of the Mesoarchean platform
assemblage.
The quartz arenite is commonly well bedded (Fig. 31). The grain size is highly
variable; conglomeratic beds with pebble sized clasts are commonly interlayered with
coarse grained quartz rich arenites. The clasts are: quartz, rounded and angular
(broken up quartz vein), light green mudstone rip ups, feldspar porphyry, quartz
feldspar porphyry, light green rhyolite. Coarser conglomerates with boulder sized
tonalite clasts occur locally. Green and dark grey thin, laminated siltstone interbeds are
scattered throughout the section.
The quartz arenite grades stratigraphically upward into protoquartzite and then
into fine grained quartzite
«
1m). Further up in the section these quartzites become
laminated (metachert?) and are interlayered with brown weathered carbonate (- 10m thick sequence). These carbonates show in places a distinct layering, possibly representing stromatolite structures. The carbonates higher up lack the quartzite beds and become more massive (-40 m). At Limestone Hill, west of the field trip section, the carbonates contain oxide facies banded iron-formation. Farther up in the section the carbonates are overlain by euxinic pyrite bearing slate and argillite, followed by interlayered argillite and greywacke. Throughout the Wallace Lake area, this section commonly contains oxide facies banded iron-formation up to 10m thick. This is the cause for the string of strongly positive magnetic anomalies in the region. This iron formation, the quartz arenites and the carbonates are the most distinctive stratigraphic units of the Wallace Lake assemblage. The iron formation appears again in the Moore Lake area, 10 km southeast of Wallace Lake, and continues into the Garner Lake area. This and the presence of ultramafic flows in
64
both areas suggest that the platform assemblage extends into the Garner Lake region,
an interpretation confirmed by U-Pb geochronology. However, this geochronology also
indicates that at least some of the rocks in the Garner Lake region are younger, i.e. 2.8
Ga.
Mafic volcanic rocks are locally associated with quartz arenites (Gaba and
Theyer, 1984) . However, the major basalts units shown on the maps
(ct.
McRitchie,
1971 b) may be part of the Rice Lake Group in a strict sense and are in tectonic contact with the Wallace Lake assemblage. Gabbroic dykes intrude the quartz arenites in many places. Some of them contain zones of distinctly layered more leucocratic quartzmagnetite layers. Quartz-feldspar phyric intermediate to felsic tuffs and intrusions occur at the north shore of Wallace Lake (Gaba and Theyer, 1984) and elsewhere. These rocks are difficult to distinguish from the quartz arenites in poorly exposed outcrops, but as the outcrop on the field trip demonstrate, intrusive phases are locally abundant(Fig. 31). There are two areas of outcrops of ultramafic rocks in the Wallace Lake. One is a serpentinite (antigorite with minor clinochlore, carbonate and magnetite; Scoates, 1971) in contact with 2730 Ma younger (?) tonalite, and is similar to the strings of serpentinites along the Wanipigow fault between Lake Winnipeg and Saxton Lake. The second occurrence has been described as a spinifex-textured ultramafic unit (Theyer, 1983), possibly a flow.
Stop Descriptions
Walk from garage over gabbro (part of Wallace Lake assemblage?). At pair of
flags, note local interlayers of quartz-magnetite bearing, slightly more leucocratic
gabbro. These phases are also typical of the Jeep gabbro which may be part of the
same gabbro intrusion. Walk along cleared trail through low bush and then onto slightly
higher area.
Locality a: At first pair of flags turn left towards shore;
a1) North of gabbro are brown relatively featureless carbonate ca. 40 m; towards
north: ca 10m of interlayered carbonate and chert, with fuchsite schist at bottom of one
outcrop. Walk inland to the next pair of flags: laminated chert interlayered with
carbonate which is in part also thinly layered (stromatolite structures?).
a2) Conley shaft; sulphide mineralization (malachite staining) in 3m of black euxinic
slate interlayered with "silicified limestone". Stephenson (1971) identified chalcopyrite,
sphalerite and galena, besides pyrite. Recently analyzed grab samples yielded
~0.02%
Cu or Pb.
Geochemical data published in Theyer (1991) from a property appraisal report, dated
1936 (Conley Jr., pers. comm.1990) list: "erratic, in cases very high gold and silver
65
concentrations in grab and drill core samples that range from nil to 2440
g/t
Au and
22g/t
Ag to a spectacular 20,228 kg/t
Ag. Recent analyses from Assessment Files
diamond drill core yielded 33 ppm Au over 0.5 m in hole No.1, 21 ppm over 0.5 m in hole NO.3 and 19 ppm Au over 0.3 m in hole NO.7 out of 7 holes drilled to a maximum depth of 21 m on the Conley property. Between location a2 and b1 there is approximately 50 m of dolomitic carbonate, locally with slate. Locality b: b1: At the bottom of the large outcrop (Fig. 30), fine grained quartzite, then coarse grained quartz-rich sandstone (protoquartzite) with granule and pebble sized clasts and local matrix supported pebble conglomerate beds. Green colour is the result of altered plagioclase. Clasts are:, quartz, rounded and angular (broken up quartz vein), light green mudstone rip ups, feldspar porphyry, quartz feldspar porphyry (subvolcanic or volcanic), light green rhyolite b2: At first pair of flags: good layering, graded bedding tops to east-southeast. Fine grained sediments (mudstone and layered argillite) probably represent the main period of deposition with little sediment influx. Earthquake induced and/or rising hinterland produce flash floods of detritus of weathered granitoid and felsic to intermediate volcanics source. Up the hill (down section) more rip-ups, less fine grained sediments, no layered argillite and thicker sandstone layers indicates higher energy sedimentation. locality c: Gabbro intruding east facing quartz arenites. Gabbro is intruded by felsite dyke (feldspar porphyry) which is folded and boudinaged and then in turn intruded by northwesterly trending quartz feldspar porphyry (Fig. 31). This latter has been dated at 2920.6±3 3a Ma (U/Pb zircon)(D.W.Davis, unpubl. report, 1994). Quartz arenites have yielded detrital zircons of 2999 Ma. which is in agreement with a 3.01 Ga age for tonalite boulder in conglomerate from the north shore of Wallace Lake (Turek and Weber, 1991), supporting the evidence that these rocks are Mesoarchean. Stop 3b. Just below 3a: Contact between quartz arenite and carbonate exposes 2-3m fine grained orthoquartzite, a relationship similar to Stop b2. Return to Highway 304 and turn right (west) continuing for approximately
1.9
km to the
Bissett airstrip located in the sand-covered area north of the highway. Turn right on a dirt road which loops around the east end of the airstrip and proceed to a quarry on its northeast side (Fig.32). Park here and walk to the quarry.
66
+
+
+
+
+
+
+
+
+
+
+
+
+
o
I
+ + + + + +
+
+ +
+ +
+
+ + +
~
+ +
+ +
+ +
fZ[Zl
~
•
Fault
I
mylonite zone (various
lithologic protoliths)
Tonalite, granodiorite
STOP II - 3
WALLACE LAKE ASSEMBLAGE
Meta gabbro /diorite
Meta volcanic rocks
Oxide facies BIF
Marble
Quartz arenite, arkosic wacke,
mudstone
Figure 32: Geology of the Wanipigow Fault in the vicinity of the Bissett airstrip near
Wallace Lake (after Gaboury and Weber, 1984).
67
Stop 11-3: The Wanipigow Fault Zone
The sigmoidal shape of the Rice Lake greenstone belt is the result of a
transpressional regime during which shortening took place in an approximate northsouth
direction. Major movements occurred along a dextral strike slip and high angle
reverse fault, the Wanipigow fault (WF) at the belts northern margin and a dextral slip
fault, the Manigotagan fault (MF) at its southern margin.
The WF is the more prominent and significant of the two. It coincides in most
places with a sharp boundary between supracrustal rocks of the greenstone belt and
granitoid rocks of the Wanipigow Plutonic Complex whereas the MF is a series of faults
developed along the transition zone between low metamorphic grade metasediments of
the Uchi Subprovince and high metamorphic grade gneisses of the English River
Subprovince. Offset of geological contacts suggests a dextral displacement of ca. 20
km in the Wallace Lake area along the WF and a similar displacement along the MF.
However, the fact that units can not be traced across the WF and retrogressed
granulites of the English Lake complex juxtapose greenschist facies rocks of the Rice
Lake belt west of Bissett (Weber, 1991) suggest also significant vertical displacements
along the WF, an interpretation confirmed by detailed structural data in the Bissett area
(Poulsen et aI., 1988).
The WF is less pronounced between the Ontario border and Red Lake and has
not been documented farther west than the east shore of lake Winnipeg. A distinct
feature of the WF is the string of associated irregularly spaced serpentinite lenses,
e.g. between Lake Winnipeg and Bissett. These serpentinites have been interpreted
(Scoates, 1971) to be related to ultramafic rocks, sills and flows occurring farther east
along the northern and eastern contact between the greenstone belt and the WPC, but
probably tectonically re-emplaced along the WF. This interpretation implies that
Mesoarchean platform assemblages initially were spread along the entire southern
margin of the WPC.
The fact that the Wallace Lake Mesoarchean platform assemblage is restricted
to the north of the WF and the Garner Lake platform assemblage is separated from the
Rice Lake Group by the Beresford Lake deformation zone (in the absence of WF in the
southeastern part of the belt) suggests that the WF was possibly superimposed onto an
earlier high angle reverse fault. Refraction seismic data (Haijnal, 1971) has indicated a
discontinuity at ca 20 km depth located ca.15 km north of the WF and the termination of
5 km deep "greenstone" related refractions 5 km north of the WF, suggesting that the
WF is possibly the surface expression of a shallow northerly dipping major crustal
reverse fault.
In the field the WF is defined by straight mylonites forming cliffs where granitoid
rocks juxtapose less resistant supracrustal or ultramafic rocks, such as along the south
shores of Wallace and Siderock lakes and in the Wanipigow Lake and English Brook
areas. Elsewhere the fault forms topographically low gullies without distinct cliffs, such
68
as between Bissett and Wallace Lake. South of the Jeep mine, granitoid rocks of the
WPC have been deformed to highly fissile in part porphyroclastic mylonite, resembling
laminated or thin-bedded arenite.
Stop Description:
Mylonite derived from granitoid rocks is exposed in the quarry (Fig. 32, locality
a). The protoliths are tonalite and granodiorite thought to be part of the Wanipigow
Plutonic Complex. Five hundred metres north of the quarry is a ridge of mylonite
(locality b) probably derived from epiclastic and fragmental volcanic rocks.
Return to Highway 304, turn right and continue 6 km west to a poorly marked sideroad (
note that beaver dams across a stream commonly result in the first 100 metres of this
road to be water covered. Walk northwards towards the abandoned Jeep Mine. A low
outcrop 200 m from highway 304 exposes strongly deformed schist (volcanic rocks)
within the Wanipigow Fault Zone displaying at least three generations of minor
structures (cleavage and asymmetric folds). Continue approximately 500 metres
farther along the road to a series of high ridges which expose granodiorite and gabbrodiorite
of the Wanipigow Plutonic Complex.
Stop 11-4: "rhe Wanipigow Plutonic Complex near the Jeep Mine
The Wanipigow Plutonic Complex (WPC) is defined as the approximately 10 km
wide "belt" of granitoid rocks along the northern margin of the Rice Lake greenstone
belt, generally north of the Wanipigow fault. The granitoid complex between Wallace
Lake and Garner Lake along the northeastern margin of the greenstone belt is also
considered part of the WPC. Minor supracrustal rocks, mafic and ultramafic rocks
occur at several locations within this granitoid terrain, such as northwest of Bissett. As
well as forming the northern margin of the Rice Lake greenstone belt the WPC also
forms the southern margin of the Berens Subprovince.
The term "Wanipigow Plutonic Complex" replaces the term" Wanipigow River
suite" introduced by Marr (1971) for the granitoid rocks north of the greenstone belt
between Bissett and the Ontario border, because more recent geochronology has
demonstrated that this granitic suite is a complex of intrusions of various ages, rather
than a differentiated synkinematic comagmatic suite as interpreted earlier by Marr
(1971 ).
Marr (1971) identified a range in composition from hornblende diorite to quartz
diorite and quartz monzonite
(=
granodiorite) based on a number of traverses through
the complex. Recent observations by the authors through access along new logging roads appear to indicate that most rocks are of quartz diorite or tonalite composition and are in fact very similar to the Ross River pluton. An exception is the presence of
69
+
Outcrop boundary
Mafic volcanics
STOP II - 4
Quartzite
Sample location
for U - Pb geochronology
Jeep Gabbro
Granodiorite
(2.88Ga)
.
.....•~ '..
.. - ..........#
I
v
I
[::"::·:::"::·:::"::S-...
*
Wanipigow Plutonic
Complex
1+ +I
Tonalite
I
x x xl
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
O.5km
I
o
I
Figure 33: Geology of the Jeep Mine area (after Gaboury and Weber, 1984)
70
more abundant pegmatitic phases in the WPC. Granodioritic compositions have been
observed near the Jeep Mine along the southern contact with the greenstone belt. .
U-Pb zircon geochronology indicates that rocks of the WPC range in age from 3.0 Ga
to 2.73 Ga. In two locations between 5eymourville (Hole River settlement) and
Wanipigow Lake, in the western part of the WPC, tonalites have yielded approximately
3 Ga ages (3003±3 Ma, Turek and Weber, 1994; 2999±10 Ma, Ermanovics and
Wanless, 1983). In two locations in the western part of the WPC, quartzo-feldspathic
gneisses have yielded 2900±10 Ma (Ermanovics and Wanless, 1983) and further east
near the Jeep mine a granodiorite has given an age of 2880±9 Ma (Turek et aI., 1989).
"5ynvolcanic" ages of 2737±10 Ma (Ermanovics and Wanless, 1983) and 2731±9 Ma
(Turek et aI., 1989) have been obtained from tonalites north of Wallace Lake and two
granodiorite from the WPC at the east shore of Lake Winnipeg have yielded even
younger U-Pb zircon ages of 2715±1 0 Ma (Ermanovics and Wanless, 1983). There
appears to be no distinct petrographic difference between the 3 Ga and 2.73 Ga
tonalites and the proportions of these rock units within the WPC could only be
determined by detailed mapping and geochronology.
Stop Description:
The ridges traversed by the Jeep Mine road (Fig. 33) contain outcrops of mainly
plutonic rocks.
locality a: 5top at a point along the road 600 m north of Highway 304. Here several
large outcrops expose 2.88 Ga granodiorite of the Wanipigow Plutonic Complex (Turek
et aI., 1989). This is consistent with the fact that the granodiorite elsewhere contains
inclusions of rocks belonging to the circa 2.93 Ga Wallace Lake Assemblage. The
single strong steep foliation in these rocks is relatively late (regional 52 or 53?).
Continue northward for an additional 250 m.
locality b: Outcrops in this area expose the southern part of the Jeep gabbro. At this
locality, the body is mainly dioritic and locally contains zones of intrusion breccia.
Xenolith types include tonalite, metapyroxenite and lamprophyre.
Return to Highway 304 and continue west to Bissett.
Return to Highway 304 and continue west to Bissett. Proceed west through the centre
of Bissett for approximately 1.5 km passing the Vanson Road (old road leading to
Vanson Mine) on your right. Continue west past this sideroad for .25 km and turn right
on the newer Abitibi bush road continuing for approximately 3.5 km ENE to a bridge
across the Wanipigow River. Cross the bridge and park opposite a trail leading into
the bush on the west side of the road. Follow the trail to abandoned Vanson Mine site
(Fig. 34).
71
PIT NEAR SHAFT
o
/3
SOm
STOP 11-5
Figure 34: Geology of the Vanson Mine area (based on mapping by
R.
Brommecker
and I. Derome, 1987).
72
Stop 11-5: The Vanson Mine
The development here took place mainly in the early 1930's but ultimately
proved unsuccessful (see below). The shaft was sunk on a wide quartz vein which is
still exposed at surface. The deposit is hosted felsic
I
mafic rocks (Fig 34) that are
strongly transposed in the vicinity of the Wanipigow Fault Zone in a part of the belt that is characterized by high strain. The vein is also transposed and deformed, locally forming a quartz mylonite, and demonstrates that considerable ductile deformation (02, D3?) took place after the vein formed. This is a general problem associated with deducing the timing of gold-quartz veins with respect to regional deformation: whether one interprets veins to be "early" or "late" can depend as much on where one observes them rather than when they formed.. The strong deformation at this deposit also makes it unclear as to which subgroup the rocks belong: intermediate to felsic lithologies are reminiscent of Bidou Lake Subgroup whereas local lenses of ultramafic rocks of komatiitic composition suggest affinities to the Garner Lake Subgroup. Given the high strain, the tectonic intercalation of the two is possible.
Stop Description:
The rocks at the Vanson Mine can be examined at two localities, at the shaft (a, Fig.
34) and at a point 200 m to the west (b, Fig. 34).
Locality a: Vanson vein
The main rock types in the area of the shaft are foliated, locally porphyritic,
dacite and rhyolitic sericite schist. Foliation strikes west-northwest and dips steeply
north. Minor folds are common and plunge steeply eastward. The local setting of the
quartz vein is best examined in a trench 15m northwest of the shaft. The main host
rock to the mylonitized 60 cm-wide quartz vein is massive to weakly foliated mafic rock
that may represent a dyke or sill. A silicified, "cherty" band along the northern contact
may represent a relict felsic volcanic rock.
Locality b: Transposed host rocks
This outcrop the shows the strongly banded nature of the rocks in this area.
Metre-wide intercalations ( in part tectonic?) of felsic, locally pyritic, sericite schist,
intermediate schistose feldspar porphyry and mafic dykes (?) are common throughout.
Note again the association of the quartz vein at the south end of the outcrop with a
narrow mafic body ( 21 %MgO anhydrous) and the local development of a green mica
as an alteration product.
-END OF DAY 2-
73
Day 3 - The Bissett Area
The Town of Bissett owes its existence to the San Antonio Gold Mine which is
the site of an initial gold discovery in 1911. The field trip will examine exposures near
the mine to illustrate the setting of gold in this area: an equivalent section of
hangingwall rocks is exposed east of the mine and representative examples of the
footwall rocks are well exposed on Hare's Island. Depending on availability,
exposures of the host "San Antonio Mine (SAM) Unit" (Theyer, 1983) as well as
representative mineralization and alteration may be examined underground or in
scattered surface outcrops. The unconformably overlying sandstone and conglomerate
of the San Antonio Formation is well exposed west of Bissett and its relationship to
underlying Rice Lake Group volcanic and plutonic rocks can be illustrated southwest of
Rice Lake near Red Rice Lake.
Proceed eastward along highway 304 from Bissett (Hotel San Antonio) for
approximately 1.3 km to a large open area created as a fire break in the late 1980's
(Fig. 35). Proceed southward along a bush road (drivable in dry weather) for
approximately one kilometre to a large outcrop overlooking Rice Lake (the headframe
of the San Antonio Mine should be visible to the west).
Stop 11I-1: Hangingwall Stratigraphy, San Antonio Mine area
Here rocks of the Rice Lake Group (Stockwell, 1938), were included into the
Bidou Lake subgroup by Weber (1971 a) and this correlation with the eastern part of the
belt was subsequently confirmed by geochronology (Turek et aI., 1989). Detailed
mapping by Stockwell (1938), Davies (1963), Poulsen et al. (1986), Tirschmann (1986)
and Ames (1988) in this 7.6 km thick section indicates that supracrustal rocks form a
north-dipping, north-facing homoclinal panel (Fig. 35). The stratigraphic section, which
is punctuated by two mafic sills, Unit A and the "SAM" Unit (Fig. 36) has been studied
in detail by Tirschmann (1986) and informal names have been attached to key units for
easy reference. The one km thick section that contains the SAM Unit and Unit A
consists of volcanic conglomerates and sandstones and is informally termed the Hare's
Island formation. Below the Sam Unit this formation consists mainly of volcanic
conglomerate and minor volcanic sandstone whereas volcanic sandstone is dominant
above the Sam Unit. Clasts in these mixed rocks range from dacite to rhyodacite
(Ames, 1988) and are dominantly feldspar-phyric and contain only rare millimetric
quartz eyes. Rocks of this formation have been interpreted to represent deposits of a
braided river proximal to an active volcanic source, perhaps on the slopes of a
stratovolcano (Tirschmann, 1986).
A unit of mafic volcanic rocks, informally termed the Shoreline volcanics, extends
along the north shore of Rice Lake and overlies the Hare's Island formation. This is
approximately 100 m thick and is composed mainly of basaltic andesite which
74
d
(projected)
AI
........
'~
...........
o .......
~
t::J
-_.....-_.....
....-
• ., 0
---
---
-----
--
------
Round Lake Volcanics
\
\
\
\
\
\
\
\
\
\
\
'-.
\
-
....
........
....
....
"
' ..................
:-:-A---:-:-:-:-:-:-:-:-:-
\.\..\...\......... ....~.... ..~..............-.. U..... ..m... ...·...t....A....- -:-> .. :-:-:-:-:-:-:-:-:-:....
\ -...... - ....
[IJ
San Antonio Fm. Gabbroic Units
Shoreline Basalt ~
IZI
shaft (active, abandoned)
Projection of Workings 200m 75 HE A' TOWNSITE VOLCANICS Bshefl 16 Level Ashefl 10 Level HARE'S ISlAND FORMATION .....
-...............-.......... . . . . . . . . . . . . . . .. . . .... .
. . . .
....................................... ....................................... . . ....................................... . .
..:-.:.-.:.-.:.-.:.-...-.:..:.-.:.-.:.-.:.-.:.-.:......:.-.:..-.:..-.:.-..:.-..:.-..:.-..:.:.:.:..:.:.:..:.:.:.:..:.:..:..:..:.:.:..:.............
..............
.......................................
;:;:;:;:;:;:;: SAN ANTONIO FORMATION
..........................
-
.................... . .
.
............................................
....
.
...........................................
..........................
SAN ANTONIO MINE
- 1- 1 - 1
1 - 1 - 1 - 1
-1-1-1
Gabbroic RocksGabbroic Rocks
Gabbroic Rocks
\Veins
Figure 36: Geological cross-section through the San Antonio Mine. 76 demonstrates good pillow and breccia structures that are diagnostic of an extrusive origin. The composition of the Shoreline basalt is similar to that of the leucogabbro of the SAM Unit suggesting an extrusive
I
subvolcanic intrusive relationship between
them. The Shoreline volcanics are overlain by massive to brecciated porphyritic dacite of the Townsite volcanics. This unit is commonly uniform in composition except at its base which is composed of heterolithic breccia. The main mass of the porphyritic dacite contains distinctive 5-10 mm phenocrysts, local zones of breccia and metre-thick intervals of thin bedded tuff. Although these rocks have been variously interpreted as an intrusion, lava flow or crystal tuff, the weight of evidence favours a subaqueous pyroclastic origin (Tirschmann, 1986). The uppermost stratigraphic unit in the Bissett area is termed the Round Lake volcanics. These rocks are more felsic than the Townsite volcanics and are composed mainly of coarse, heterolithic volcanic breccias, some of which are feldspar-phyric. Although the evidence is not abundant, the stratigraphic facing is thought to be consistent with the structural order of the units because: i) Scour channels in the Hare's Island formation were observed underground and convincingly show northward facing; ii) Moderately convincing northward facing pillow tops have been observed in the Shoreline volcanics; iii) The SAM unit is compositionally layered with a melagabbro base on the south side and a more leucocratic gabbroic top on the north side; iv) The SAM unit is cut by feldspar porphyry dykes which are identical in composition to the overlying Townsite volcanics for which the dykes are likely feeders.
Stop Descriptions:
Outcrops representative of the rocks above the SAM Unit can be examined at
this stop (Fig. 35).
Locality a: Townsite volcanics
The large outcrop north of the bush road exposes a good example of porphyritic
dacite of the Townsite volcanics. Look for subtle signs of breccia development and
local moderate NE plunge of deformed feldspar phenocrysts.
Locality b: Base of Townsite volcanics
The low outcrops south of the bush road reveal much more heterolithic breccia
containing clasts of porphyritic dacite. This is the basal part of the Townsite volcanics.
77
Locality c: Shoreline volcanics
The low outcrops along the shore of Rice Lake expose the Shoreline volcanics.
Look for repeating sequences of massive, pillowed and brecciated mafic flows. These
tend to support a northward facing direction for this unit.
Locality d: Hare's Island formation
These large outcrops of Hare's Island formation on the east side of a bay in Rice
Lake can be reached by a short traverse south from the bush road (locality b). The
outcrops illustrate the finer grained volcanic sandstone facies that is typical of the
upper part of the formation.
Stop 111-2: The lower part of Hare's Island Formation on Hare's Island (optional
Stop)
Hare's Island is accessible by boat from the Bissett town beach at Stop 111-3,
locality b.
The section on Hare's Island (Fig. 35) comprises volcanic conglomerate and
minor interbedded lithic arenites in the stratigraphically lower part of the formation. The
exposed 40m section beginning on the southeastern shore of the island entirely
underlies the SAM unit.
Conglomerate is clast supported (65-85% clasts, 15-35% matrix), crudely
bedded, nongraded to normally graded and poorly sorted. About 75% of the clasts are
felsic to mafic volcanic rocks. Clasts range in diameter from .4 to 10 em. The crude
bedding is indicated by variations in the proportions of clasts to matrix, as well as by
the localized presence of distinctive wispy orange fragments, particularly in the lower
part of the Hare's Island section. Individual beds range from 3.5-10.0 m in thickness.
Clasts in the conglomerate include (1) subrounded feldspar-quartz-phyric felsic
volcanics, (2) subangular to subround intermediate volcanic clasts ±feldspar
phenocrysts (3) flattened to deformed mafic clasts with plagioclase phenocrysts, (4)
subangular to subrounded aphyric felsic clasts and (5) angular to rounded milky quartz
clasts. In addition wispy, elongate orange fragments (.5-10 em), somewhat vesicular,
occur locally and are concentrated in a few zones where they comprise 5-20% of the
conglomerate. They have been interpreted as pumice.
A type 1 clast yielded a U-Pb zircon age of 2729±3.2 Ma (Turek et aI., 1989).
This age is identical to the age of the Narrows Formation in the Beresford Lake area.
78
Stop
111-3:
San Antonio Mine
A tholeiitic mafic body, less than 100m thick, within epiclastic rocks of the Hare's Island Formation of the Bidou Lake Subgroup hosts the San Antonio gold deposit (Fig. 35,36). This body, locally known as the San Antonio Mine or SAM unit has been variously interpreted as a sill (Stockwell, 1935; Poulsen et aI., 1986) or as a mafic flow (Theyer, 1983). The SAM Unit has a melanocratic base and a leucrocratic upper part which hosts most of the ore in the mine (Ames, 1988; Ames et aI., 1991). The gold orebodies are quartz veins and stockworks oblique to the plane of the Sam Unit (Fig. 37). (Lau, 1988) analyzed the relationship between these veins in a competent gabbroic host and the fabric of adjacent, relatively less competent, volcanic rocks of the Rice Lake Group. Five different fracture sets of successively decreasing relative age were identified within the northeasterly dipping gabbroic sill that hosts the deposit: i) The oldest set is transverse to the sill and is filled by dykes of mafic and intermediate bulk composition (Fig. 37). They are interpreted to be brittle extensional fractures of synvolcanic origin that have been subsequently rotated into their present position. ii) Complex, elongate lens shaped zones of intensely fractured and mineralized host rock, termed "stockworks" are confined to the sill in
en echelon
fashion.
Thirty steeply dipping stockworks have been identified to date and several of these attain thicknesses of ten metres: important examples include the No. 26, 36, 38 and 97 Veins (Fig. 36, 37). The stockworks typically comprise three structural elements: an inner central quartz vein; a central breccia zone composed of angular, altered wall rock 'fragments cemented by vein quartz; and a peripheral zone containing arrays of extensional, sigmoidally shaped "ladder veins" that are oriented at a mean angle of 45
0
to the stockwork zones. The stockworks, a major
source of ore in the mine, are interpreted to be brittle shear zones that have formed in two stages, an initial sinistral reverse movement to account for the orientation and sigmoidal shape of the ladder veins, followed by a dextral reverse movement to account for the observed dextral displacement of dykes cut by the central quartz veins. iii) Arrays of northeasterly striking and northwesterly dipping quartz veins are also important sources of ore in the mine: the most significant of these is the No. 16 vein (Fig. 37). These veins occupy central fractures in sinistral reverse ductile shear zones that comprise intensely foliated and lineated schists derived from the host rock. The shear veins, although of similar composition and gold grade as those of the stockworks, rarely exceed a width of one metre and tend to pinch and swell along strike and down dip.
79
N
7 th LEVEL, SAN ANTONIO MINE
HARE'S ISLAND FM.
FOOlWALL
SERICITE SCHIST
(Hare's Island Fm)
o
20m
---
1-1-1- Figure 37: Geological plan of the 7th Level, San Antonio Mine (adapted from Lau, 1988). 80 iv) The most prominent fracture set that post-dates ore-bearing veins consists of northeasterly striking and southeasterly dipping quartz carbonate veins, less than 50 centimetres wide, that occupy narrow ductile shear zones of dextral reverse sense (Fig. 37). These structures offset dykes, stockworks and mineralized shear veins thereby having a disruptive effect on the continuity of ore. v) The youngest set comprises northeasterly striking and southerly dipping postore brittle faults (Fig. 37). They have a dextral reverse sense of offset and contain vein breccias, typically 10 centimetres wide, that are composed of quartz, calcite and chlorite. The five fracture sets interact to produce a complex three-dimensional network (Lau, 1988) with a pronounced northeast plunge for the deposit as a whole (Fig. 35). This axial direction corresponds to a mineral elongation that is observed in adjacent volcanic rocks of the Rice Lake Group. Several different types of wallrock alteration were recognized by mine staff at San Antonio in the 1940's and were mapped routinely as a gUide to locating ore. D.E. Ames (Ames, 1988; Ames et aI., 1989) conducted an in depth study of the origin of this alteration and investigated its zonation with respect to ore-bearing veins. Carbonatization produced alteration mineral assemblages which pseudomorphically replace metamorphic minerals and which define alteration isograds that record changes in mineral assemblages. In the leucogabbro, these isograds correspond to the following changes (Ames et aI., 1989): i) actinolite + epidote + C02
=
chlorite + calcite + quartz
ii) titanite + C02
=
rutile + calcite + quartz
iii) chlorite + calcite + albite + C02
=
paragonite + quartz
+ ankerite + H20 iv) quartz + paragonite + K+
=
albite + muscovite + H+
These isograds are distributed in zones about the gold-bearing structures such that isograd (iv) is innermost and isograd (i) is outermost. The alteration assemblages and their zonation are similar in the vicinity of stockworks, shear veins and veins in southeast dipping fractures, indicating that the composition of the hydrothermal fluids remained relatively constant over the time span during which these different vein generations were formed. The alteration zonation about veins hosted by melagabbro is only recorded by isograds
(i) and (ii)
and, with increasing alteration, ankerite was
formed from tremolite and calcite, a reflection of the more mafic bulk composition of this host rock. Mass balance calculations (Ames, 1988) show that C02, Sand K were added to the gabbroic rocks from the hydrothermal fluid with a change in the oxidation state of iron towards reducing conditions. Boron and sodium were also added at the contacts of veins in the form of metasomatic tourmaline and albite. Pyrite is most directly related to the occurrence of gold and formed after muscovite and ankerite. Quartz-calcite-chlorite veins crosscut and replace earlier formed alteration minerals.
81
Surface Stop Descriptions:
The San Antonio Mine Unit is exposed at several localities along the north shore
of Rice Lake near the mine plant.
locality a: San Antonio Mine Site (ask permission of owners)
A large outcrop of the SAM Unit is exposed at the headframe of the Mine. The
rock here is relatively uniform in composition and fine grained. Local zones containing
white-weathering 2 to 5 mm spheroids are observable near the southeastern corner of
the headframe. These are granophyric quartz-albite intergrowths that are diagnostic of
the leucogabbro in the upper part of the unit. The preservation of epidote and actinolite
in these rocks indicates that they are not strongly carbonatized even though they are
located up-plunge from major orebodies.
locality b: SAM Unit at town beach
A knoll-like outcrop of the SAM Unit occurs at the Bissett town beach. Although
the metagabbro here is relatively featureless, a northeasterly striking feldspar porphyry
dyke is exposed in the western part of the outcrop. Such dykes are relatively common
in the mine and cut across the SAM Unit in an east-northeast direction. They are
carbonatized in the vicinity of ore.
locality c: Gabrielle Shaft southeast of the town curling rink along the lakeshore
A stamp mill and historic plaque marks the site of the original Gabrielle
discovery shaft (since backfilled). This was the first gold mill in Manitoba and was
brought into the area in 1912 after the 1911 discovery. This locality is of historical
interest because the veins and carbonate alteration present here are representative of
the "stockwork" style of mineralization. Although this was apparently the first style of
mineralization discovered at Rice Lake, its economic importance (larger, wider
orebodies) was not realized at the San Antonio Mine until the mid-1930's when the 26
and 36 veins were discovered.
locality d: Mineralization in outcrop 150 m west of c at shoreline (ask permission of
owners)
The small low outcrop along the shoreline illustrates small scale examples of
the main types of mineralization within the San Antonio Mine Unit. In the western part
of the outcrop is an east-northeast striking and moderate northerly dipping shear zone
which is representative of the 16-type vein structures. Note the local strong foliation. In
the eastern part of the outcrop is a small-scale example of a quartz-albite stockwork
zone. Note the local strong bleaching of the host (albite-ankerite-sericite alteration).
82
Underground Stop Descriptions:
Access to the San Antonio Mine is only by permission of the current owners, Rea
Gold Ltd. Although much of the current development at San Antonio is dedicated to
deeper levels, good representative exposures of the host rocks, structure, ore styles
and alteration remain on upper levels such as No. 7 (Fig. 37).
On the 7th level, as on many others in the mine, one approaches the SAM Unit
from the footwall side. The footwall rocks belong to the Hare's Island formation and are
commonly strongly carbonatized and foliated for a 50 to 100 m interval adjacent to the
sill. As a result they form the beige to salmon pink "footwall sericite schist" (note that
this rock also occurs locally in the hangingwall of the sill but is much thinner). The
southern, footwall contact of the SAM Unit is commonly a sharp and distinct colour
boundary from pink to dark green rocks. Note that the melagabbro of the SAM Unit is
also strongly carbonatized as well but this is not as visible owing to the larger amount
of carbonate that can be formed in it prior to "saturation" (Le. complete destruction of
Fe, Mg, Ca silicates) compared to the more felsic rocks of the Hare's Island formation.
To the north of the footwall contact the 701 crosscut branches into three parts. The left
branch leads to the 738 Stockwork zone which is now an open stope. The branch
straight ahead (716 Drift) follows the famous No. 16 vein which is well exposed in a
raise a few metres to the left of here. The right branch (710 cross-cut) leads to several
other shear veins similar in style and orientation to No. 16 (706, 708), to weak
stockwork type mineralization (704 and 729) and to examples of both late SE- and
SW-dipping faults. Carbonate-albite alteration is strong in the vicinity of veins and
mafic to intermediate dykes can be observed to cut the SAM Unit at several locations.
Return to Highway 304 and proceed west from the centre of Bissett for approximately
1.5 km passing the Vanson Road on your right. Continue west past this sideroad for to
an open area which marks the western firebreak. Turn left (south) onto a poorly
marked bush road (drivable in dry weather) and proceed approximately 200 m
southward to the first outcrop ridge ( Fig. 38)
Stop 111-4: Overturned Limb of San Antonio Formation
These outcrops occur along strike from similar ones on the southwest shore
of
Rice Lake (Fig. 35) and represent overturned strata of the San Antonio Formation
which unconformably overlies the host sequence at the San Antonio Mine (Fig. 36).
This contact of the San Antonio Formation is not exposed but has been observed in
drill core to be moderately sheared (see Stops 111-5, 6).
Stop Description:
The cross-bedded coarse quartzose arenite at these outcrops is typical of the
Formation elsewhere. Here the beds generally strike northwest and dip 60 degrees
83
BIDOU LAKE SUBGROUP
SAN ANTONIO FORMATlON . . - . . . - . . . . • . . .
~C¥~g06:/
.................. 7:'\.\. .
...
-_._--- .. _._-----_ .. - .. _---.- .. _-~_._-..
_._._-_._.-".-.".".".-.-.-.",-.-.
o
c
200m
Figure 38: Geology of an overturned panel of rocks of the San Antonio Formation at
the west end of Rice Lake.
84
northeast but face downward to the southwest on the basis of morphology of crossbeds.
A prominent east-west cleavage cuts the beds at several localities and locally
can be observed to cut an older weaker cleavage that is closer to the bedding
orientation. One Interpretation of the structure here is that these exposures occur on
the overturned northern limb of a northwest plunging reclined syncline.
Return to highway and proceed west to intersection with Quesnel (Caribou) Lake Road.
Turn left on the Quesnel Lake Road and proceed southward. At a distance of
approximately 5.5 km a sideroad takes off to the right to the Packsack gold deposit but
continue on the Caribou Lake Road for an additional 1.8 km to a series of exposures at
a bend in the road near the southwest corner of Red Rice Lake.
Stop 111-5: Nonconformity at base of San Antonio Formation in contact with
tonalite (Optional)
At this locality (Fig. 39), the conglomeratic base of the San Antonio Formation
overlaying tonalite (belonging to the pluton southwest of Bissett) is exposed. These
exposures are similar to the classical erosional unconformity on the tonalite pluton
exposed 10 km west of Bissett (Stockwell, 1938, 1945; Davies, 1963).
Stop Description:
From northeast to southwest the following lithologies are encountered:
1. Polymictic conglomerate with boulders of tonalite and layered quartz arenites (redeposited
tonalite regolith found elsewhere at the base of the SAF).
2. Conglomerate with round and subangular tonalite boulders, locally (at one of the
peeled locations) conglomerate layers with basaltic clasts.
3. Similar to 2 but essentially monomictic tonalite boulder conglomerate; clasts are
subangular to rounded; some clasts are brecciated. Local pink granitic and quartz
clasts are evidence that this is a conglomerate; otherwise this location could be
interpreted as brecciated tonalite.
4. A large outcrop extending to the south shore of Red Rice Lake exposes highly
brecciated and quartz veined tonalite. The contact between units 3 and 4 (above) is
exposed(?)in a bleached section.
Return northward along the Quesnel Lake Road for approximately 500 metres and
park in a clearing on the east side at the intersection with a bush road leading to the
east. Follow the bush road eastward for approximately 500 metres, turn to the northnorthwest
and proceed approximately 500 m through the bush to a low outcrop (among
the trees.
85
SOOm
RICE
o
100
Bush road
I
.,
. . .
\ -
\
--:-:-~\
.
- . - . - . - - - - - .
\
. .
- - - - -, - - - -, - - - . . - - - - - - .. - - .
.,
Figure 35: Geology of the San Antonio Mine area.
SAN ANTONIO MINE AREA
-_.....R.
Brommecker)
..............~- .- .- -.. .. - ...,'
~
..:.. ~..~~..:~ -. - - -
;,'
~
- -.. _ t.i[ 1"''' +1 " _._~!...:
+-
TONALITE
RED RICE LAKE
STOP 111-5
.-
.. _ ... _---------.-.---_._---------.-.- ..
_------~-----.-.-
,
,
'"
'"
"'"
·
. . . . - - - - . . . . - - - - . . . - - - - - - . .
,
-
:- :-:. :-:- :-:- :- :. :. :. :. :- :- :- :. :- :. :. :. :. :- :-:-:- :. :. :. ~.
"""
: : : : : : J
SAN ANTONIO FORMATION
I::::::::::::::::::::::::::::::.. \
. . . . - - - - . . . . - - - - . " LAKE
~
- ~ . ~ - ~ - ~ - ~ - ~ - ~ - ~ - ~ . ~ - ~ - :- ~ - ~ - ~ - ~ . ~ . ~ - ~ - ~ - ~ - ~ - ~ - ~ -~ . ~ . ~ . ~ .... - . "....
,,,,,
"'
....
\
....
-
- "'.. . - - .
,,
--~~- ----------_._~.; --~
: : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : :\:
~
:\,···"·...
· .
- - - - - - - -'\
-\
.~:~~R"<v:
:•.: :.· \\
:::::::::::::::: _::::::::::::::::::::::::::
:N~~\o----
STOP 111-0
· . . .
- - - - - - - . - . - - - - - - - - . . , ... - ... ---_._-~-_...
-.-.-----.-.-_._._._._.-\
.
- - - - - . . . - . . . , - - . . . . - - - - - - - -. .. - - - - - -
-,
-_
... _ .... -.-.-.-.--------~._..
-.-.----------,
::::::::::::::::::::::::::::::::::::...
..
- - ..... - - - - - ... - - - . -
....
Figure 39: Sketch of the geology between Rice Lake and Red Rice Lake showing the
distribution of rocks of the San Antonio Formation.
86
Pebble Conglomerate
NORTH
.~'
.':
"
Bual Conglomerate
Cross-bedded
Interval
o
5m
I
Figure
40:
Geological sketch of an outcrop showing the unconformable contact
between intermediate volcanic rocks of the Bidou Lake Subgroup and the overlying conglomerate and sandstone of the San Antonio Formation. 87 Stop 111-6: Unconformity at base of San Antonio Formation Stockwell (1938) interpreted an unconformable to nonconformable lower contact between the San Antonio Formation and Rice Lake Group volcanic rocks and coeval intrusions respectively (Fig. 39). At many localities the lower contact is sheared where exposed but an intact contact exists in this outcrop 600 m southeast of Rice Lake and 650 m northeast of Red Rice Lake. Stop Description: The outcrop is approximately 40 x 20 metres and is elongate in an east-west direction (Fig. 40). At the east end foliated, feldspar-phyric tuff breccia composed of one- to 20-cm clasts is exposed. Two northwesterly striking foliations intersect in a moderate plunging northerly trending lineation. The base of the overlying San Antonio Formation is marked by a one- to two-metre thick conglomerate bed containing mainly local debris but rare ovoid two- to five- mm quartz granules as well as elongate sericitic clasts and sericitic quartz sandstone. The basal conglomerate (regolith?) is separated from an overlying 15 em-thick pebble conglomerate bed by approximately one metre of quartz sandstone. Overlying this thin conglomerate is quartz sandstone with local thin siltstone layers containing possible ripple marks. At one location near the southern edge of the outcrop the silty beds are warped into a gentle NW trending open fold which is transected by an east-west (53?) cleavage. The western part of the outcrop is composed of coarse- to fine-grained cross-bedded quartzose arenite that is typical of the San Antonio formation elsewhere in the region. One- to two-mm pyrite cubes are widely distributed in the first three metres of this sandstone unit. - END OF FIELD TRIP - 88 MINING HISTORY The following summary has been compiled mainly from information contained in Tuba and Ostry (1994), Minton (1982), Cole (1938) as well as from press articles. It is included here for the general interest of users of the field guide. Manigotagan Area 1881: Gold was discovered on Black Island (Minton, 1982), shaft was sunk. 1885-86: Gold was discovered on the south side of Hole River close to its mouth (Minton). A tunnel was driven 50 feet into the rock, some test pits. Lotus 1924: Lotus (33 km NW of Bissett) 1924-35 trenching, pitting drilling. 1946-54 trenching. 1978-81 drilling. 1982 short production. Production (1982) 8287 tonnes at 4.56
gft
(0.13 ozlton) Au.
Reserves (1981) 18 140 t grading 10.29
gft(0.30
ozlton) Au.
Bissett Area
San Antonio Mine
1910-11: Discovery of gold at Rice Lake in 1911 (Gabrielle property) (Cole, 1938); or "a
few days after Christmas 1910" (Minton). (Background: In Febr. 1911 Duncan
Twohearts sent some samples to Arthur Quesnel at Manigotagan who gave them to
E.A. Pelletier an RCMP inspector and prospector. He panned them and one had gold.
In March he went to Twohearts' camp at Turtle Lake and then both went to Rice Lake.
Twoheart led Pelletier to a projection on the Lake on March 6, where the sample had
come from. The pair made a big fire. The heat chipped the rocks along the shore and
disclosed quartz veins and mineralization. Pelletier chipped on the quartz and finally
freed gold about the size of a small pea. He staked a claim, the first in the Rice lake
area, and named it in honor of a lady friend (after Minton)).
1911: the San Antonio claim was staked by A. Desautels and assigned to E.A. Pelletier.
1912: E.S. Moore (GSC) surveyed Rice Lake area and his report generated much
prospecting (Minton).
1912 (August): Pelletier erected a stamp mill on the northwest shore of Rice Lake, at a
location presently in front of the Newshams' house. The mill had been brought up Lake
Winnipeg to Manigotagan, across 28 portages to Rice Lake. A small amount of ore was
89
taken from the original shaft and crushed by hand before entering the mill. This was the
first gold milled in Manitoba.
1927: San Antonio Mines sink No 1 and No 2 shafts (Cole, 1938).
1928: No. 1 completed down to 50m with 305 m of lateral work on the 46 m level. No. 2
had reached 187 m with over 1220 m of drifting and cross cutting on 4 levels.
1929-30: Winze 1, inclined 60° was sunk from the 183 m level at a point 139 m
northeast of No. 2 shaft with stations at the 260 and 290 m levels.
1933: San Antonio started milling May 1st, 150 tons per day in August. NO.3 shaft
(main production, 3 compartments) was started.
1934: San Antonio paid first dividend, 5 cents a share, milling increased to 170
tons/day. In 1934 Gabrielle Mine also sinks shaft to 400 foot level and in1935 sells its
property to San Antonio Gold Mines Ltd.
1935-36: Milling at San Antonio increased to 275 tons/day. 1936 milling increased to
325 tons/day. In 1936 a 547 m cross cut to the Gabrielle workings was completed.
1938-40: No. 3 shaft was completed to 498 m in 1938. It is connected on the 366, 412,
and 458 m levels to winze 2 sunk in 1937 from the 320 to the 473 m level. In 1939,
NO.3 winze ( a 3 compartment internal shaft) was begun at a point 275 m northeast of
the NO.3 shaft on the 456 m level, completed in 1940 to 763 m, opening up 6 new
levels at 46 m intervals.
1947: NO.4 winze, located 275 m east of NO.3 winze was sunk from the 16th level
732 m to 1256 m below surface with 10 levels, the deepest (26th) at 1179 m.
In 1960 a 5th winze was completed, located on the adjoining leased property of FortyFour
Mines Ltd.. It extends from the 26th level for 372 m, to 1546 m below surface.
1968: Production ceased due to fire in main hoist and low gold prices. Company was
placed in receivership and its assets purchased by 3 of the former directors. Ore
reserves estimated at 186490 tonnes grading over 8.23g/tonne (0.24 ozlton) gold.
Independent consultant estimates that deep drilling would show 1 800000 tonnes
grading 10.63 g/tonne (0.31 oz).
1972: Chemalloy Minerals Ltd. took out a 60-day option to do work. Option not
exercised.
1980-84: Brinco and Forty-Four Mines conducted a 7 month feasibility study. It
confirmed mineable reserves of 725680 tonnes with average grade of 6.51 g/tonne
(0.19 ozlton) gold. Work was done to access levels down to 1586 m. In 1981 a $13
million program was started. A 408 tonne/day concentrator was build to replace the one
90
destroyed by fire in 1968. The mine re-opened in January 1982 designed to produce
684 kg gold from the upper levels only. Production reached 49.76 kg by July 1982.
Grades of ore only reached 4.8 g/tonne, so operations were terminated in May, 1983.
In 1983 Lathwell Resources Ltd. negotiated an option agreement with Brinco.
Exploration drilling during 1983 intersected the 97 stockwork with 9 holes. Average
thickness below 33 level was 3.45 m averaging 9.26 g/tonne (200000 tonnes of ore). In
1984 a D shaft ore reserve between the 26 and 36 levels was estimated as 1 203161
tonnes averaging 7.89g/tonne. Drill holes confirmed the presence of several new
stockworks (parallel 97 veins) on the 33 level. However Lathwell dropped the option
after phase I exploration work late in 1984.
1985 (November) to 1987: The San Antonio property was optioned by San Antonio
Resources, jointly owned by Inco Ltd., Quest Resources and private investors. A 6640
m underground drilling program was carried out that defined a "mineral resource" of
420 000 oz or 13 063 kg gold. In 1987 Kilborn-Cassiar confirms mineable reserves of
1,469,690 tons grading 0.2080zlton with operating costs of US $322/oz
1989: Early in the year Cassiar (Kilborn) estimates 1.23 million tons at an average
grade of 0.223 ozlton mineable reserves. Cost US $230/oz for the first 3 years, capital
cost $11.2 million for extending the A shaft 900ft to the 16th level and deepening the D
shaft to access the ore below the 26th level. Later in 1989 Rea Gold acquires San
Antonio from Cassiar Mining. Estimated mineable ore below the 26th level was 1.2
million tons grading 0.22 ozlton and 301,400 tons grading 0.192 oz above the 26th
level. Capital cost was estimated at $18.8 million, operating cost at $78.53/ton.
1993-present: In 1993 Rea Gold begins a pre-feasibility study involving underground
drilling in 1994. In 1994 Rea Gold begins engineering study to complete feasibility
study. Projected production 60 000-70 000 ozlyear, cost US$250/oz. Capital cost to
mine 1000 tons/day is $30 million. Mineable reserves >400000 oz.
In 1995 after an underground exploration drilling program in 1994 estimated 1.95
million tons grading 0.197 o.p.t., subsequent recalculations arrive at nearly 3 million
tons grading 0.275 o.p.t. Capital cost for bringing the mine back into production is
estimated at $30.3 million. Operating costs $61.22 per ton or $US 242 per ounce of
gold. Milling 1000t.p.d. upgraded within 2 years. During this period operating revenue
of $5.6 million from processing of development ore.
Gold production at San Antonio:
1932-68 41,519 kg (1,334,892 oz.)
1982 estimate 344 kg 11,050 oz.
1983 estimate 137 kg 4,393 oz.
Siver production:
1932-68 5,978.2 kg
91
Sannorm Mine (Hunter Group or Normandy)
1934: The Hunter Group was staked by several people. In 1934 it was assigned to
Normandy Mines Ltd. Two deposits were opned up in 1934. Property inactive until 1944
when claims were a 21 leases were assigned to the Hunter Group and Sannorm Mines
Ltd took over, magnetic surveys and diamond drilling started.
1947: Sangold Mines Ltd. to the north was purchased. A 2 level shaft (at 125
fft
intervals) was sunk but work was suspended in 1948.
1952: Consolidated Sannorm Mines Ltd. took over. Geophysical surveys between
1961 and 1971, drilling 1974,1978,1986-1989.
No production.
Reserves (1989) 177460 t grading 4.18gft (0.12 ozlton) Au including 106000 t grading
5.42 gft gold to a depth of 150 m.
Gold Field, Wingold
1913-15: 5 shallow shafts are sunk, 12-31 m deep; a small stamp mill operated for a
brief time on Wingold shaft/mine, produced one brick from Chicamon claim near Gold
lake. 100ff shaft was sunk on Big Four in 1914, 50 feet of drifting; Gold Cup (60 ft.
shaft, possibly 2 shafts), part of Wingold Group.
1934-36 underground work, Gold Fields shaft deepened to 91 m with 3 levels.
Reserves (1935) 6535 t grading 13.95 gft (0.41 ozlton) gold, 6349 t grading 7.20 gft
Au in a surface dump.
Emperor-Gold Standard
1912-17: 40 ft shaft on Emperor claim; 100 ft. shaft on Gold Standard (formerly
Independence)- some drifting,
properties sold to Forty-Four Mines.
Gold Pan, Gold Seal
1915: A 300 m shaft as sunk and short levels run from it; a mill was built. Mine closed
1916.
1917: Gold Pan Mine Ltd. produced $1400 from two shafts. Arthur Quesnel described
that were the vein crossed a diabase dyke, spectacular free gold was extracted and
samples were exhibited all over the country. Work continued until 1946-47 (Minton).
1980: drilling
1982: installation of small mill and flotation circuit.
Production (1919-1924) 7.49 kg of Au.
Reserves unknown.
Vanson Mine
1926: (Syndicate No.9,1 0 staked by Aronowitch and Bubis; shaft sunk in 1926 or 27. In
1932 Vanson Gold Mines Ltd. was formed and a 25 ton mill was installed in 1933 and
started working. This mill proved unsatisfactory and was replaced by a 2-stamo mill
with capacity of 18 tons per day. In 1935 a four-level shaft was completed, but only the
92
225 and 475 level-foot levels were developed. Equipment was converted from steam to
electric and a company town was built. Operations ceased in 1935. Geophysical
surveys in 1968, 1970 and 1971. ESL Resources Canada sampled in 1981.
No information on past production or reserves.
Eva
1921: 18 m shaft was sunk.
1950 drilling, 1970,71 geophysical surveys, 1979-81 feasibility study, 1981-82 drilling.
Reserves (1981) 15 964 t grading 6.17
glt
(0.18 ozlton) Au.
Packsack Mine
1917: staked as Moncalm claim, 4 km SW of Bissett.
1935: Packsack Mines Ltd. bought property and in 1936 sank a shaft down to 525 ft.
Lack of financing terminated project in 1937.
1940: Gods Lake Gold Mines gained control, but after much drilling and underground
development the mine was closed down again in 1940. Open End Mines was
processing stockpiled ore afterwards.
1985: small crusher installed and open cut and shaft sinking.
Production(1936-37) development ore stockpiled (1985) small (unknown) amount of
gold obtained.
Reserves (1937) 21 800 t at 12.36
glt (0.36 ozlton) and 4 536 t at 5.83 glt
(0.17 ozlton)
gold. (1979) 272 155 t grading 10.3
glt
(0.30 ozlton)
Wolf Prospect
(Fox-Prime)
1920: pitting. 1949-59: 47 drill holes 1981: drilling. Reserves (1981) Fox vein: probable reserves 1 807 t grading 6.86
glt
(0.20 ozlton),
possible reserves 12 228 t grading 6.86
g/t;
West Fox vein prob. reserves 910 t grading
16.8 glt
(0.49 ozlton) Au possible reserves are 5 080 t grading 16.8 glt:
prime vein
possible reserves 2993 t grading 25.71
glt
(0.75 ozlton) Au.
Rita No.
1 (Independence)
1934-37: pitting, trenching, 9 m shaft was sunk. 1964: drilling 1970-71: geophysical surveys, 1973 drilling 1983: geophysical surveys, soil geochem. Reserves (1938) 2585 t grading 25.4
glt
(0.74 ozlton) Au.
Moose
1914-16: pitting, trenching; 2 shafts sunk (7.6 and 30.5 m deep),
1936-43: drilling, 1961-62 drilling, 1980 drilling.
Reserves (1986) mine muck samples range 4.9
glt to 21.6 glt.
(1914-16) 16780 t
grading 34.29
glt
(1.0 ozlton) Au.
93
Gold Lake
1920: 2 shafts sunk, 6 and 15 m; pitting, trenching.
1935-36: drilling, 1 shaft deepened to 107 m, drifting and crosscutting;
1953 underground exploration, drilling,
1984 drilling.
Production :none
Reserves (1934) 79x1.7 m grading 14.4 g/t (0.42 ozlton) Au
Ranger
1914: 59 ft shaft sunk
1934: drilling
1981: prospecting.
Reserve (1981) 1787 t at 13.7g/t
Long Lake - Stormy Lake Area
Central Manitoba Mine
1925-26: Surface and underground development on the Kitchener group (later Central
Manitoba Mines) (Cole, 1938)
1927: Mill of 150 ton/day was erected and started operation at Central Manitoba
Mines (Cole, 1938).
Kitchener Mine producing from 1927 to 1937. Others to follow were Tene, Growler and
Hope (and Rogers shaft?) mines next to Kichener, operated by Central Manitoba from
1932 to 1937. 1977 trenching; 1981 geophysical surveys; 1982 surface material is
milled in Bissett; 1984 drilling.
Production (1927-37) 4 287 kg (or 160000 oz JS)of Au was produced. (1982) 437 t
were processed, but recovery unknown.
Reserves unknown.
Ogama-Rockland
1924-25: trenching;
1941: 36 m deep Ogama shaft sunk, deepened to 239 m in 1946-47.
1948: 2 shafts sunk on Rockland vein.
1948-51: Ogama shaft deepened to 314 m and Rockland to 83 m. Production
interrupted from 1942-48 , ceased in 1951.
1968, 1973: drilling
1981-82: geophysical surveys, 1984,87 drilling.
Production(1942-43 and 48-51) 50,000 oz (1 555 kg) Au.
Reserves (1950) No.4 vein - 30,137 t grading 11.66
gft
(0.34 ozlton) gold
Onondaga
1923-24: Onondaga claim staked, 31 m shaft sunk and five-stamp mill installed (Cole,
1938).
1949-50: shaft dewatering and drilling.
94
1981 geophysical surveys.
1984: drilling.
Production (1933-34) 0.933 kg (30 oz) of gold.
Reserves unknown.
Elora
1922: Two-stamp mill installed at Elora Fractional claim, Long Lake, 26 km SE of
Bissett (Cole, 1938).
1928 : drilling.
1981 geophysical surveys. 1984 drilling.
Production (1922) 113 t were milled which produced 3.21 kg (104.1 oz) of Au.
Macketta
1934: sampling on Halfway Lake, 25 km SE of Bissett;
1938-39: drilling, shaft sunk, drifting;
1963: geophysical surveys;
1978-81, 1986: trenching
1987-88: drilling. No production.
Reserves (1987) 68 000 t grading 4.46
gft
(0.13 ozlton) Au.
Contact between Rice Lake volcanics and Ross River tonalite.
Valley Vein,
1920-23: 2 shafts sunk (7.6 and 10 m);
1934: drilling,
1945: 10 m shaft deepened to 82 m;
1963 drilling;
1981 geophysical surveys, 1984 drilling.
No production, reserves unknown.
Eldorado
1927: Development work (Cole, 1938)
Gunnar Mine
1933-36: Diamond drilling at Gunnar Property, 35 km SE of Bissett. 1934 development
work: 2 shafts sunk to 305 and 380 m. 1935 mill construction, in operation in 1936.
1937-41: pays its first dividend. Main shaft sunk to 625 m. Operated until 1941.
Processing of mine tailings.
1980 geophysical surveys. 1984 geophysical surveys.
Production (1934-41) 3101.4 kg of Au was produced. (1979) 0.1 kg of Au.
Oro Grande-Solo Mines
1924-26: Development work at Oro Grande-Solo claims, Central Manitoba area (Cole,
1938),34 km SE of Bissett. 43 m (Solo) shaft sunk, 15 m (Oro Grande) shaft sunk.1928
both shafts deepened.
95
1932-34 milling commenced in 1932; in 1933 Oro Grande shaft deepened to 78 m and
connected to Solo shaft on the 38 m level; new mill installed.
1936-40 operations renewed.
1962 drilling and geophysical surveys.
1984 geophysical surveys.
Production (1932-34) 8.85 kg gold, (1938-40) 156.15 kg of gold.
Reserves (1985) 29290 t grading
19.29gft
(0.30 ozlton) between the 150 m level and
surface.
Mirage
1924: staked
1928-29: 9 m shaft was sunk, trenching and pitting;
1978-81: trenching
1986-87: 2 km2 overburden removal by Esso Resources Canada.
Mandalay
1919: staked by O.J. Quesnel.
1934-36: trenching and pitting; 15 m deep shaft,1936 drilling.
1980: sampling; 1984 geophysical and geochemical surveys.
Tut
trenching and pitting;
1994 geophysical surveys
Gem Lake Area
Diana Mine
1925-26: Gold discoveries near Gem Lake and Slate Lake (Cole, 1938)
1928-38: Gem Lake mine (Bon), 51 km SE of Bissett, 236 m shaft sunk with 6 levels.
1932: Gem Lake mine milling ore.
1933: Gem Lake Mines bankrupt, Diana Gold Mines takes over.
1967-68: trenching.
1974-77 geophysical surveys, sampling of tailings.
Production (1928-32) 16.95 kg of Au. (1934-36) 199.79 kg of Au. (1937-38) 15.83 kg of
Au, (1940-41) 3.02 kg of Au.
Reserves (1976) tailings 27 000 to 45 000 t grading 4,25
gft.
(0.124 ozlton)
Wallace Lake Area
Jeep
1934: staked
1946: transferred to Jeep Gold Mines Ltd. a subsidiary of San Antonio Mines Ltd.
96
1947-50: shaft sunk, underground exploration, crosscutting and drifting. Ore grade in
1947 26.5g/t
to 64.07 glt. In 1948 it averaged 27.29 glt.
in 1950 shaft deepened to 180
m with levels at 135 and 175 m. 1958-59 surface exploration. 1973: geophysical surveys, drilling; intention to develop an open pit. 1980 geophysical survey, feasibility study for a 180 tonneslday mill. Production (1947-50) 16319 tonnes were milled producing 432 kg (13889 oz) of Au. Reserves unknown Conley 1932: staked 1933-36: 10 pits (to shallow shafts) were dug, drilling. 1958 exploration activity. 1965 drilling for Ag, Au, Cu, Zn, Pb in graphitic slatelargillite, interlayered with silicified limestone. Gatlan 1932: staked; trenching, shaft sinking 1934: drilling 1950: drilling Cryderman Mine (Little Pal claim) 1925: staked 1926: Victoria Syndicate option and work on Cryderman property (Cole, 1938). In 1926 Mining Corporation of Canada sank a 260 ft shaft and 656 ft and 232 ft of drifting on the 125 ft and 250 ft level. 1928: Cryderman Mines Ltd. took over. No work until 1932, when shaft was dewatered, a 40 ton mill and a 100 ton mill were erected, but work stopped again at the end of 1932. 1936: drilling 1958: surface sampling Production (1931-32) 11.60 kg of gold. Reserves (1931) 67 m by 7.6 m that grades 17.83
glt.
(1959) 79.9 m by 1.0 m that
grades 19.2
glt
(0.56 Ozlton) Au
Moore Lake 1988: geophysical surveys, drilling Wanipigow River - Little Beaver Lake Area Luleo 1915: staked 1915-19: shaft sunk 3 500 ft NW of Little Beaver Lake, stamp mill, shut down in 1919. 1921-25: Selkirk Gold Mining Co. took over; its subsidiary, American Development Co.
97
replaced the mill, extended the shaft to over 525 ft. and did extensive development
work on 5 levels. Mine shut down in 1925.
1927-28: Selkirk Mines Ltd. did electromagnetic surveys and drilling in 1927 and 1928.
Average grade too low.
1934: Poundmaker Gold Mines Ltd. acquired the claims. Drilling;
1938: a new, hydroelectric mill capable of handling 100 tons per day was constructed,
but lack of financing finished the venture in 1942. Several new owners tried to make a
going: Jacknife Gold Mines Ltd. Jacobus Mining Co. Ltd. H. Barry, P.
E.
Beament
(1956)(Minton). 1968, 70, 71 :Magnetic surveys 1980-83: Production from muck pile in 1980 and 1982-83. Production 1923-24: 12.4 kg; 1980: 0.9 kg; 1982-83: 6.7 kg (2093 t) Reserves unknown.
Grand Central
1928: Grand Central (Gold) Mine (Lakeshore claim) on the north shore of Wanipigow
Lake. Staked by
E.
Bonus. Some pits and trenches in 1929.
1933: the Walsh brothers hand-sank a shaft to 107 feet and moved a 5-stamp mill to the property. Operation ceased in 1933 with 300 tons of ore milled which produced 0.93 kg (30 oz.) of Au. 1964, 68, 70, 71: Geophysical surveys 1982: muck pile sampled. 1986 assessment. Production 300 tons yielded 0.93 kg of Au. (Reserves unknown)
98
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I
Mineralogical Association of Canada, Program with Abstracts, Saskatoon,
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McRitchie, W.O.
1971 a: Geology of the Wallace Lake-Siderock Lake area; in Geology and Geophysics
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1971 b: Petrology and Environment of the acidic plutonic rocks of the WanipigowWinnipeg
Rivers region, southeastren Manitoba; in Geology and Geophysics of the
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106
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