Meter-wide veins and a kilometer-wide anomaly; wall-rock alteration at the Campbell Red Lake and Dickenson gold mines, Red Lake District, Ontario

CIM Bulletin, Vol. 75, No. 841, 1982

RJ. MacGEEHAN, T. SANDERS and C. JAY HODGSON, Department of Geological Sciences, Queen's University, Kingston, Ontario

The orebodies of the Campbell and Dickenson mines are localized within an anomalously fissile and deformed zone that transects the eastern margin of a dominantly mafic volcanic complex, close to its contact with a synchronously formed sedimentary basin containing clastic and chemical sedimentary rocks. The ore zones are mainly quartz-carbonate fissure veins and siliceous replacement zones formed during deformation and metamorphism, although there are some syn-volcanic ex-halative ore zones in the mines. On a regional scale, the volcanic rocks have been affected by syn-volcanic spilitic alteration which has involved the leaching of Fe, Mg, Au and As from, and the addition of Na and variable amounts of Si to bleached zones enveloping primary permeable structures in the rocks. The leached constituents were deposited on the contemporaneous sea floor as iron-rich chemical sedimentary rocks. Although this alteration is not closely related, spatially, to the ore zones, it is characteristic of the general environment, and may serve to distinguish gold-prospective from gold-barren areas on a mining-camp scale.Closely associated spatially with gold deposits is a zone of feldspar-destructive alteration within which the volcanic rocks are characteristically feldspar-free, enriched in As, Au and to a variable degree in Si, and depleted in Na, Ca and to a variable degree in Mg, Fe andK. The alteration zone is also characterized by abundant, variably transposed, small quartz-dolomite to ferrodolomite veinlets formed during deformation and meta-morphism, and includes, but extends outside of, the anomalously fissile zone hosting the orebodies. The alteration zone is interpreted to have formed syn-volcanicalfy within the upper part of a major submarine hydrothermal discharge zone.A km-wide, 2-km-long anomaly which envelopes the Camp-bell-Dickenson mines, and which is due to feldspar-destructive alteration can be defined by five independent parameters: values of peraluminosity index (mole % Al2O3/CaO + Na2O + K2O) > 2; Au content > 10 ppb; As content > 50ppm; the presence of abundant (> 20%) carbonate-quartz veinlets; and the fact that the carbonate in the veinlets and rocks is dolomite-ferrodolomite, rather than calcite, which is present outside of the alteration zone. This anomalous zone could have been detected in a regional exploration program by outcrop sampling at a density of only 1 sample per km2, and fully defined by sampling at a density of 5-10 samples per km2. Thus, lithogeochemistry may provide a major tool in exploration for Campbell-Dickenson-type gold deposits.

Keywords: Mineral exploration, Mine geology, Alteration, Wall-rock alteration, Campbell Red Lake mine, Dickenson mine, Red Lake district, Gold mines, Hydrothermal alteration, Spilitic alteration, Feldspar-destructive alteration, Lithogeochemistry, Geochemical anomalies, Peraluminosity index.