Geology of the Stall Lake copper deposit Snow Lake, Manitoba

CIM Bulletin, Vol. 75, No. 837, 1982

R.D. STUDER Mine Geologist, Hudson Bay Mining and Smelting Co., Ltd. Snow Lake, Manitoba

The Snow Lake massive sulphide deposits are hosted by Aphe-bian volcanic rocks of the Flin Flon - Snow Lake greenstone belt, which in this area were deformed and metamorphosed to the amphibolite fades during the Hudsonian orogeny. All the known deposits occur infelsic rocks a short distance below the contact with an overlying mafic rock unit.The Stall Lake copper deposit occurs close to the top of an explosive felsic volcanic sequence. Rocks stratigraphically underlying the deposit have been hydrothermally altered by the mineralizing fluids. The sulphides were probably deposited from submarine volcanic vent(s) on the flanks of a felsic dome. The ore has been tightly folded, flattened and elongated parallel to the northerly trending lineation of the surrounding rocks during the several periods of deformation. Strike lengths of the lenses range from 60 to 300 feet and plunge-to-strike ratios are as much as 15:1.Ore lenses 1 to 4 typically consist of massive coarse-grained pyrrhotite, chalcopyrite and pyrite. A stratigraphically higher lens differs in that it contains fine-grained pyrite and chalcopyrite, with an increase in sphalerite toward its hanging wall. The No. 4 orebody has a distinct footwall alteration zone characterized by brecciation and abundant chlorite-staurolite-garnet schist, with minor kyanite, anthophyllite, cordierite and anhydrite, as well as sulphide minerals. Chemically, the alteration zone is distinguished from the unaltered felsic rocks by Na2O depletion and Mg-Fe enrichment.
Keywords: Economic geology, Stall Lake deposit, Copper deposits, Snow Lake, Massive sulphide deposits, Alteration, Geochemistry.