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Geologic framework for late Cretaceous magmatic-hydrothermal mineralization in the Taseko Lakes region, Southwestern BC Blevings, Scott Kenneth

Abstract

The Taseko Lakes region is located in Southwestern British Columbia along the contact between the Coast Plutonic Complex (CPC) and the Southeast Coast Belt (SECB). Three separate generations of faults occur in the region: sub-vertical sinistral-reverse faults (Dl), moderate- to high-angle south- and north-vergent contractional faults (D2) and large-scale dextral faults (D3). Several mineral deposits are located in the southern Taseko Lakes region. Three of these deposits were examined during this study: the Empress (porphyry Cu), Pellaire (gold-telluride) and Taylor-Windfall (high-suiphidation epithermal Au-Ag) deposits. The deposits were examined in order to characterize the known mineralization in the Taseko Lakes region and better understand the conditions and times at which mineralization took place. The Empress deposit formed at approximately 88 to 87 Ma at depths of roughly 5 km when large volumes of high-temperature, oxidized magmatic-hydrothermal fluids from an unidentified source intrusion migrated laterally along a trough-shaped topographic low along the upper margin of an underlying intrusion — the Empress pluton. This horizontal flow produced subhorizontal-layered alteration and mineralization within the overlying Falls River succession. The Taylor-Windfall deposit formed at about 89 to 87 Ma when magmatic-dominated, moderate- to low-temperature hydothermal fluids ascended along faults and fractures. An initial high-temperature vapour phase produced a central core of vuggy-silica and corundum-andalusite alteration. A second phase of cooler, re-condensed vapours overprinted early high-temperature assemblages with lower temperature intermediate and advanced argillic alteration assemblages. The Pellaire deposit formed at 85 Ma when mineralizing fluids migrated distally from a magmatic source along (D2) south-vergent contractional faults. Mineralization occurred when fluids crossed from the Falls River succession into the Mount McLeod granodiorite and were cooled and disturbed from chemical equilibrium, which resulted in the emplacement of quartzveins in the south-vergent faults and deposition of ore minerals. All three deposits formed from magmatic-dominated fluids (with variable meteoric input) between approximately 89 and 85 Ma. The similarities in ages, fluid compositions and sources between the deposits indicate they formed from similar magmatic-hydrothermal systems. The varying mineralization styles exhibited by the deposits in this study illustrate the variability of mineralizing styles that can occur in magmatic-hydrothemal systems. This variability arises largely due to differing characteristics of pre-existing geology and the location of the deposits with respect to the overall system.

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