| Summary: | Immobile elements are used to determine rock affinities, precursors, and mass changes that occur during hydrothermal alteration. Altered rocks at the New Insco mine are calc-alkaline andesites (SiO$ sb2 / sim$ 60 wt%, Zr/Y = 6.5, La$ sb{ rm N}$/Yb$ sb{ rm N}$ = 5.3). A tholeiitic rhyolite (SiO$ sb2 / sim$ 77 wt%, Zr/Y = 3.4, La$ sb{ rm N}$/Yb$ sb{ rm N}$ = 2) is located 0.5 km south of the orebody. Net mass change of +11% resulted from additions of Fe$ sb2$O$ sb3$ (16%) and MgO (3%), and losses of Na$ sb2$O (3%) and CaO (3%). Three major alteration assemblages with up to 80% chlorite, 57% sericite and 50% quartz are identified. Mineral and cation plots outline chloritization, sericitization and silicification trends. The Key Tuffite is at the contact of Watson Lake tholeiitic rhyolite and Wabassee mixed calc-alkaline and tholeiitic andesites. Pyroclastic components of the Tuffite are from both rock groups: a tholeiitic rhyolite component--Zr/Y = 2.8 and La$ sb{ rm N}$/Yb$ sb{ rm N}$ = 2.1, and a calc-alkaline andesitic component--Zr/Y = 8.9, La$ sb{ rm N}$/Yb$ sb{ rm N}$ = 6.4. During formation Fe$ sb2$O$ sb3$ (27%, total iron), SiO$ sb2$ (14%), CaO (8%), S and K$ sb2$O were added to the pyroclastic components. The Key Tuffite is composed of 33% quartz, 28% sulfide, 16% sericite, 8% carbonate, 6% chlorite and 9% others. Geochemical and mineralogical trends in altered rocks and tuffites increase toward orebodies and can be used as mineral exploration guides.
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