The Golden Bear Mine: Carlin-Type Sediment-Hosted, Disseminated Gold Deposits in Northwestern British Colombia

The Golden Bear deposits in northwestern British Columbia
were originally considered to be gold-silver mesothermal vein
deposits but detailed studies of geology and geochemistry
described in this paper suggest that they are Carlin-type gold
deposits. To date, the mine has produced 10,007 kg (321,730 oz) of
gold from three separate ore bodies: Bear Main, Kodiak A and the
Ursa. Three other gold deposits (Grizzly, Kodiak B, and Kodiak C)
have drill indicated reserves. The total resource of the six deposits
before mining was 2.58 MT, grading 7.95 g/T gold with 20 492 kg
(658,850 oz) of contained gold. The objective of this paper is to
describe the regional setting of the gold deposits, their characteristics,
compare them to NevadaÕs Carlin-type deposits, and suggest
potential exploration criteria.
These sediment-hosted, disseminated gold deposits are hosted
in the upper Paleozoic Stikine assemblage, predominantly in
Permian carbonates and lesser mafic volcanic rocks. They occur
along the Ophir Break, an important ore controlling, regional northtrending
series of anastomosing faults. The structurally inverted succession
in the mine area includes Late Devonian to lower
Carboniferous mafic volcanics, upper Carboniferous felsic volcaniclastics
and Lower Permian carbonate. The latter is the major host to
mineralization and includes silty and quartz-rich calcareous strata.
Only Mesozoic intrusions occur in the immediate mine area. They
have no known spatial association with gold mineralization. Northtrending
strike-slip faults, including the 25 km long Ophir Break,
succeeded folding events.
Gold mineralization is hosted mainly in variably silicified carbonate
breccias and fault zones, although some occurs in mafic
flows and tuffs. The most abundant alteration facies are silicification,
decalcification, argillization, pyritization and iron carbonatization.
Native gold occurs as micron-sized grains within arsenical rims
of pyrite (sulfide ore) in the Bear Main and Grizzly deposits, and as
micron-size native gold associated with iron-oxides (oxide ore) in
the Kodiak and Ursa deposits. The only visible sulfide is very finegrained,
dark grey pyrite. Minor to trace microscopic minerals
include arsenopyrite, native mercury, and mercury, silver, and goldsilver
tellurides, native gold, native silver, tetrahedrite, pyrrhotite,
chalcopyrite, sphalerite, galena and bravoite.
The Golden Bear deposits share similarities with the deep,
hypogene and shallow, oxide ores found in NevadaÕs Carlin-type
sediment-hosted, disseminated gold deposits:
¥ micron-sized native gold grains within arsenical pyrite;
¥ high grade, refractory sulfide and low grade, oxide ores;
¥ minor to trace sulfides other than pyrite;
¥ association of gold mineralization with silicification,
argillization and decalcification;
¥ variable silicification of carbonate rocks (local jasperoid
development);
¥ strong structural controls (faults, breccia zones);
¥ stratigraphically favourable calcareous units; and,
¥ geochemically anomalous in Ag, As, Sb, Hg, and Te.
Identification of sediment-hosted Carlin-type gold deposits at
the Golden Bear Mine clearly points to new opportunities for gold
exploration in this under explored region of British Columbia.
Regionally, Permian carbonates cut by faults are favourable targets
for deposits of this type.