|Preliminary Map 25 describes the geology and mineral deposits of the Goldstream area (82M), which includes about 400 square kilometres of mountainous terrain in the northern Selkirk Mountains of southeastern British Columbia. The geology map is at 1:50 000 scale and cross-sections, structural domain plots, and lists of mineral occurrences.
The geology of the area consists of intensely deformed Late Proterozoic/Early Paleozoic metasedimentary and metavolcanic rocks, which have been intruded by a number of granitic plutons. The metasedimentary and metavolcanic rocks comprise a heterogeneous package of quartzites, schists, phyllites, calc-schists, and carbonates, interlayered with greenstone and chloritic phyllite.
The greenstones and chloritic phyllites are metamorphosed equivalents of tholeiitic flows and basic tuffs. Derivatives of more acid volcanic rocks may now be preserved as quartz-sericite phyllite, quartz-augen phyllite, quartz-feldspar-sericite-chlorite phyllite, and perhaps some of the 'grit' unit.
Horsethief Creek Group rocks are separated into three units. The lower unit consists of pelitic schists, marbles and amphibolites and are the oldest strata exposed. The middle unit comprises marbles and calcareous pelitic schists, and the upper unit rocks are very similar to those of the overlying Lowe Paleozoic package. The Paleozoic package consists of quartzites, semi-pelites, psammites, grits, pelitic rocks including graphitic schists, marbles impure marbles, metavolcanic rocks and amphibolites.
The structure of the area is dominated by tight to isoclinal, north trending Phase 2 folds. These folds are interpreted to have developed in an initially inverted panel of rocks, which may be the underlimb of an earlier (Phase 1) nappe.
The most important mineral deposits of the area are stratabound copper-zinc deposits. They include Standard, in a basic volcanic pile, and Montgomery and Goldstream, contained in metasedimentary rocks.
Goldstream is a sheet of massive sulphides (dominated by pyrrhotite, sphalerite, and chalcopyrite) 3 to 4 metres thick, 500 metres wide, and at least 1 200 metres long. It occurs within a quartz-rich phyllite that is structurally overlain by a spessartine-chlorite phyllite and chert unit, which in turn is overlain by 220 metres of dark calcareous phyllite. The massive sulphide layer and quartz-rich phyllite are underlain by a grey limestone.
Massive sulphide deposits in the Goldstream area are similar to the 'bedded cupriferous iron sulphide' or 'Besshi' deposits. They are commonly bed-like in form, are composed primarily of iron sulphide/chalcopyrite ore, and occur in geosynclinal crystalline schists associated with basic submarine volcanism.
Placer and lode gold occurrences are also known.