Virtual Museum ID: 19-D26-05
Foliation parallel quartz sweats and stringers; isoclinal chert fold hinge
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Original Collection:Smithers Exploration Group (SEG)
Sub Collection:Pinchi Mercury
Virtual Museum ID:19-D26-05
Date Added to VM:2019-08-22
Sample Origin:Pinchi Lake, B.C.
Datum:09 (NAD 83)
Primary Features:Graphitic argillite
Primary Mineral Formula:C
Advanced Geological Information
The following section provides geological data relating to the specimen or the site it was collected from, when available. Information has been obtained from various sources including private and government datasets but may not be up to date. Any geological time periods or ages listed often relate to the primary geology of the area, and may not be the actual date of an event such as mineral formation.
Geological Formation:Cache Creek Complex (Group)/Takla Group
Geological Period:Carboniferous-Jurassic/Upper Triassic
Geological Terrane:Cache Creek
Minfile ID:093K 049
The Pinchi Lake mercury mine is located on a prominent limestone hill on the north shore of Pinchi Lake about 25 kilometres from Fort St. James.
The deposit was discovered in 1937 by J.G. Gray of the Geological Survey of Canada. The area was staked in 1938 by A.J. Ostrem and optioned to Cominco. Production first occurred in 1940 with peak production in 1943. Due to the falling price of mercury production ceased in 1944. The mine was reopened in 1968 and operated until 1975 when mercury prices declined.
The deposit is associated with the Pinchi fault which separates Carboniferous-Jurassic Cache Creek Complex (Group) rocks from Upper Triassic Takla Group rocks. Cache Creek Complex rocks which in the area consist of ribbon chert, quartzite, schist, limestone and minor greenstone, all of which have a general northwesterly strike and a steep northeasterly dip. Small bodies of serpentinite intrude the Cache Creek rocks. A number of faults, mostly with a northwesterly trend, occur in the Pinchi fault zone.
Cinnabar mineralization is concentrated in breccia zones along the faults as well as in strata cut by the faults. Known orebodies roughly parallel the bedding and occur mainly in dolomitized limestone beneath bands of impervious schist although some ore is also found in the quartz-carbonate-mica schists. Most of the cinnabar occurs as veinlets and blebs filling pre-existing openings such as fissures, solution cavities and interstices between grains and breccia fragments. The cinnabar is mainly a massive red variety but there is also some bright red earthy cinnabar as well as some crystallized cinnabar. A little stibnite and scattered grains of pyrite have been found.
The south fault, which hosts most of the mineralization, strikes about 320 degrees and dips about 60 degrees west. The faulting style changes from one distinct fault to a group of closely spaced faults 300 metres to the northwest.
Possible resources are 1.1 million tonnes grading 3.2 kilograms per tonne mercury (Cominco Ltd. Annual Report 1992).