APPLICATION OF LITHOGEOCHEMISTRY TO EXPLORATION FOR DEEP VMS DEPOSITSIN HIGH-GRADE METAMORPHIC ROCKS, SNOW LAKE, MANITOBA

Volcanic-associated massive sulphide deposits in the Snow Lake area of Manitoba are related to mineralogically and chemically distinct alter ation zones. It is generally accepted that these zones represent cross cutting, subconformable or conformable synvolcanic alteration zones, w hich were coeval with and have been metamorphosed with the massive sul phides. Metamorphism ranges from upper greenschist facies to middle am phibolite facies. Surface lithogeochemical anomalies led to the discov ery of small massive sulphide lenses at a vertical depth of 250 m in t he Raindrop Lake area, southwest of Snow Lake, Manitoba. Variations in mineral assemblages of middle amphibolite facies alteration zones and analysis of variations in major and trace element chemistry were used to guide deep drilling at Raindrop Lake. The massive sulphide lenses are stratigraphically underlain by a low angle cross-cutting ''pipe'' and a conformable footwall ''apron'' alteration. The alteration zones are composed of assemblages of garnet, staurolite and chlorite, and, l ess significantly, biotite, muscovite and kyanite. They are characteri zed by loss of Na and Ca, and addition of Fe, Mg, Cu and Zn. Mapping t he alteration is aided by the application of the metamorphic AFM phase diagram for the appropriate metamorphic facies. Increasing intensity of alteration can be identified by the first appearance of new mineral phases, which are represented on the AFM diagram. These mineral trend s coincide with loss of Na and Ca relative to Al, and increased Mg and Fe. Chemical alteration indices ACNK (molecular proportion Al2O3/(CaO + Na2O + K2O) and AI = 100 X [(MgO + K2O)/(MgO + K2O + CaO + Na2O)] c ombined with Cu and Zn variation helped to quantify the intensity of a lteration, despite being insensitive to Fe. The crosscutting pipe is d ominantly Fe enriched, with a Cu-enriched core, Zn enriched margins an d widespread Na and Ca depletion. Mineralogically it is identified by garnet, staurolite and chlorite and follows an iron and aluminum enric hment trend on the AFM diagram. The conformable alteration zone is cha racterized by local strong Mg enrichment, extensive Na and Ca depletio n and variable Cu and Zn. Mineralogically it is characterized by the p resence of chlorite and kyanite and follows a magnesium and aluminum e nrichment trend on the AFM diagram.