Geochemistry and petrography of the Grywacke Wallrock hosting the Three Nations Gold-Quartz Vein system, Pamour #1 Mine, Timmins, Ontario

Abstract

This study investigates geochemical and mineralogical changes in altered Archean metagreywacke around the Three Nations Gold-Quartz Veins, Pamour 1 Mine, Timmins, Ontario. Variation in the clay contents of the unaltered greywacke-argillite host rock make interpretation of geochemical trends very difficult. These difficulties were overcome by using Si0₂/Al₂0₃ ratios as an estimate of clay content in these rocks. Oxide versus Si0₂/Al₂0₃ diagrams for selected oxides in the unaltered rocks illustrations compositional variations by the use of end member mixing curve from which pre-alteration element abundance may be estimated for any sample or Si0₂/Al₂0₃ value. The difference between the altered rock, element abundance and its corresponding calculated pre-alteration abundance represents the estimated per cent alteration which has occurred. Percent alteration profiles across the vein system show much less background scatter than unprocessed date profiles and more clearly represent the degree of alteration. Per cent alteration profile and petrographic data outline three alteration zones associated with the vein: Ⅰ. The outer sericite-chlorite zone which consists of chlorite, sericite, plagioclase, albite, dolomite and pyrite; Ⅱ. The sericite zone which consists of sericite, relic plagioclase, dolomite and pyrrhotite pseudomorphs after pyrite; Ⅲ. The innermost arsenopyrite zone which consists of sericite, dolomite, arsenipyrite and pyrrhotite with arsenopyrite and magnetite directly adjacent to the vein. The variations in the silicate and sulphide mineralogy and percent alteration around the vein are the result of changes in the aK⁺/aH⁺ and the S/0 fugacity ration in solutions as alteration progressed.