Use of immobile elements to determine mass changes and origin of hydrothermally altered rocks : Key Tuffite, Matagami, and New Insco mine, Noranda

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...

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Bibliographic Details
Main Author: Liaghat, Sassan
Format: Thesis
Language:English
Published: McGill University 1990
Subjects:
Online Access:http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22392
Description
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.