Preliminary Map No. 40: Geology of the Mount Richards Area, Vancouver Island(092E/13E)
View Map (PDF, 2.3 MB), (1:15 840)
Preliminary Map 40 describes the geology of the Mount Richards area near Crofton on southern Vancouver Island. The 1:15 840 scale geology map includes a legend and notes about the geology.
The Sicker Group is host to the Lenora-Tyee gold-silver-copper-lead-zinc-cadmium orebodies on Big Sicker Mountain and to the orebodies of Western Mines Limited near Buttle Lake. The latter orebodies appear to be controlled stratigraphically as well as structurally, therefore detailed mapping was begun to determine the stratigraphic sequence near the type area. On Big Sicker Mountain the nature and relationships of the rocks are obscured by intense shearing, but in the Richards group intense shearing is largely confined to the most northerly ridge.
In the north part of the Richards group there is a north-south progression of rock types in the Sicker Group, which appears, from comparison with the sequence in the Cowichan Lake area, to be in order of increasing age. Poor graded bedding in a few places is consistent with this interpretation. Along the crest and south face of Mount Richards ridge the Sicker rocks are more or less coarsely fragmental and include at least two bands characterized by medium to coarse hornblende grains in a fine-grained matrix. These grains may be phenocrysts but are more likely pyroclastic. It is uncertain whether the sequence is homoclinal or whether the hornblendic layer has been repeated by folding.
The Sicker rocks have been successively intruded by mainly small bodies of quartz-feldspar porphyry and medium to large bodies of shonkinite. The shonkinite resembles gabbro in texture and the abundance of dark minerals, but the feldspar is albite-oligoclase. The older rocks are overlapped on the north by poorly exposed clastic sedimentary rocks of the Nanaimo Group, and are probably in fault contact with them to the south. Post-Nanaimo faulting has produced a Sicker inlier along the Chemainus River.
Pyrite is common to abundant, particularly in the Sicker upper division, but contains only traces of gold and silver. Small amounts of chalcopyrite and malachite occur in several small shear zones and quartz veins.
The area is prospective for Noranda/Kuroko massive sulphide copper-lead-zinc-precious metal deposits.
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