Letters Pinchi Lake

In addition to this style of gold deposit, an abundance of other types of auriferous and non-auriferous metal concentrations collectively form an array representative of deep (high- temperature) through to shallow (low-temperature) depositional environments These are: porphyry copper-molybdenum, mesothermal gold veins, auriferous polymetallic veins (as at the Minto mine), auriferous stibnite veins (as at the Congress mine and Howard and Lou prospects), scheelite-stibnite veins, and cinnabar (plus or minus stibnite) veinlets and disseminations Within the Congress mine, a change in the nature and abundance of metallic minerals is apparent with depth: cinnabar locally accompanies stibnite in upper levels, whereas with depth the abundance of pyrite, arsenopyrite and gold increases relative to stibnite (Cairnes 1937, G S C Memoir 213)

Regional mapping between Taseko Lakes and Carpenter Lake, funded through the Canada-British Columbia Mineral Development Agreement (1985-1990), has enabled us to trace several fault strands of a regionally extensive northwest-trending dextral strike-slip fault system into the Bridge River mining camp and evaluate their relation to metal distribution Metal concentrations, such as mesothermal, polymetallic and stibnite veins, seem spatially (and in many cases, genetically) related to Late Cretaceous to Early Tertiary dykes within structurally complex zones, whereas scheelite- stibnite veins and cinnabar veinlets and disseminations occur within or adjacent to major faults Furthermore, differential uplift across some faults (during Late Cretaceous to Early Tertiary time) may be responsible for the close juxtaposition of metal concentrations deposited at different crustal levels For example: the Apex mercury prospect within the Yalakom fault is adjacent to the Poison Mountain porphyry copper-molybdenum deposit; and the Wayside mesothermal gold deposit is closely juxtaposed to the area of the Howard-Congress- Reliance stibnite vein systems which, in turn, are adjacent to the area of the Minto mine/Olympic polymetallic vein systems

These observations and interpretations are in accordance with ideas conveyed by George Albino of the University of Western Ontario (see “Research,” September, 1988): the nature of the metal assemblage of a metallic mineral prospect or deposit, particularly within a structurally complex area, provides important and valuable information in deciphering the crustal level at which the concentration probably formed and, hence, where (or in what direction) the greatest gold concentration should be in relation to the known metal concentration In this light, concentrations of cinnabar (plus or minus stibnite) within the Yalakom and Marshall Creek faults, particularly those adjacent to extensively carbonate-altered rocks (some of which contain scheelite-stibnite veins with up to 133 parts per million arsenic and 480 parts per billion gold), are intriguing when one compares their setting with the Pinchi area and the possibilities that may exist for additional metal concentrations at depth Is this the near-surface expression of a mother lode-type gold deposit? R G Gaba, P Schiarizza, Ministry of Energy, Mines and Petroleum Resources, Geological Survey Branch, Victoria, B C , and J I Garver, Depart of Geological Sciences, University of Washington, Seattle, Wash

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