(Excert from Nickel Field Trip, South of Timmins, Abitibi Greenstone Belt, Northeastern Ontario. Fieldtrip Guide Oct 2005 by B.T. Atkinson, M.G. Houle and G. Wm Seim pp 4-7)

HALLIDAY DOME

The Halliday Dome area is located ~ 80 km south of Timmins. It represents a major antiformal structure that trends eastward from Sothman Township across Halliday Township into Midlothian Township before disappearing beneath Proterozoic sedimentsThe dome is cored by massive or pillowed intermediate volcanic and fragmental felsic volcanic rocks overlain by an extensive komatiitic horizon hat can be traced over several kilometres. A few pods of ultramafic rock have been found in the core of the Halliday Dome, which may represent sills analogous to those in the Shaw Dome.

SOTHMAN NICKEL DEPOSIT, SOTHMAN TOWNSHIP

FOCUS

Basal Sulphide Mineralization within Komatiitic Sill, Halliday Dome,

Sothman Township

Access Located in the south part of Sothman Township, the Sothman nickel deposit is accessed by a trail leading eastward from Pine Street South to Looning Lake

The Sothman Ni-Cu-(PGE) deposit is hosted by a thick ultramafic body with a dunite core and peridotite margins that has been previously interpreted to be a sill intruded into intermediate volcanic rocks Figure 5), but is most likely a channelized sheet flow/sill.

An area along the basal contact of the body was stripped in 2000 by Hucamp Mines Ltd., providing near complete exposure of glacially-polished outcrops of the embayed contact between footwall massive andesite and the overlying cumulate komatiite unit. Field work done in this area did not reveal any evidence for an extrusive or intrusive origin for this ultramafic body, as the stripped area exposes only the basal part and not the upper part which might exhibit extrusive or intrusive features. Nevertheless, this environment clearly represents a channelized flow or channelized sill where magma flow was focussed within a topographic and/or thermomechanically-produced embayment similar to those observed at Alexo. The underlying andesites exhibit patchy alteration ansilica veining within 30 cm of the contact with overlying olivine pyroxenite, which are most pervasive at the base of the channel, suggesting that they represent a contact metamorphic feature. Thin (~10-50 cm) felsic dikes, which cross-cut the komatiitic unit at a high angle and terminate at the basal contact, may represent partial melts of the andesite produced during thermal erosion of the environment (P.C. Davis, pers. comm., 2001).

The mineralization occurs ~0.8 m above the basal contact within olivine pyroxenite and is composed of interlayered net-textured sulfides, disseminated sulfides, and barren olivine pyroxenite. However, disseminated mineralization always overlies net-textured mineralization, suggesting that the sequence youngs toward the south, consistent with the regional geology. The presence of barren komatiitic cumulate rocks within the main mineralized horizon and the apparent disruption of mineralized zones by olivine pyroxenites suggest that the environment was quite dynamic and was characterized by successive replenishment of magma and sulfides into the channel.

REFERENCES

Watkins, J.J., 1972. The Sothman sill nickel deposit; B.Sc. thesis, Queen’s University, Kingston, Canada,

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