The San Antonio mine is within the 5-20 km wide Rice Lake greenstone belt of the Archean

Uchi Subprovince. The belt is composed of 2728-2731 Ma felsic, intermediate and mafic

metavolcanic rocks, associated subvolcanic intrusions and volcanically derived clastic

sedimentary rocks (Turek et al., 1989). In the Bissett area, the sequence is approximately 7

km thick, and forms a north facing, steep north dipping, homoclinal sequence termed the

Bidou Lake subgroup (Stockwell, 1938; Tirschmann, 1986; Poulsen et al, 1996). In this

area, the sequence comprises, from stratigraphically lowest to highest (south to north;

Figure 1), the following units: (i) intermediate volcanic rocks to the south of Rice Lake, (ii)

a band of mafic metavolcanic rocks and gabbro (Unit A) underlying Rice Lake, (iii) felsic

metavolcanic and clastic rocks of the Hare’s Island Formation, host to the San Antonio mine

gabbro unit, (iv) mafic metavolcanic rocks (Shoreline basalt) on the northern margin of Rice

Lake, (v) plagioclase porphyritic flows, tuff, tuff breccia and possible subvolcanic intrusions

of intermediate composition (Townsite and Round Lake volcanics), and finally (vi) felsic

metavolcanic rocks and clastic sediments at the northern margin of the belt (Tirschmann,

1986; Poulsen et al, 1986, 1996). This sequence is unconformably and structurally overlain

by clastic sedimentary rocks of the San Antonio formation to the west (Figure 1). All

lithologies are affected by lower greenschist facies metamorphism defined by assemblages

of muscovite, chlorite, Fe-carbonate and albite in felsic metavolcanic rocks, and epidote,

carbonates, chlorite and albite assemblages in the mafic mine units. For brevity, the prefix

meta- is excluded from lithologic names throughout the text here.