The setting, age, alteration and mineralization at the MAX molybdenum Mine

Abstract

MAX is a porphyry Mo deposit at the northern end of the Kootenay Arc and located near Trout Lake village in southeastern British Columbia (5609565N, 457374E, NAD 83, Zone 11). Molybdenite is hosted by the Late Cretaceous Trout Lake stock (80.2 ± 1.0 Ma; see below) in a well developed quartz vein stockwork. Intrusive phases range in composition from granodiorite to tonalite and quartz diorite. They intruded multiply-deformed phyllite, schist, and marble of the Paleozoic Lardeau Group which are regionally and contact metamorphosed. Previous studies demonstrated that many giant porphyry deposits possess long-lived histories characterized by repeated pulses of magmatism and hydrothermal activity. MAX is a relatively small, but locally high-grade porphyry Mo deposit, which lacks multiple long-lived overprinting hydrothermal events. Consequently, the detailed relative history of small-scale intrusive (dike emplacement) and hydrothermal events (vein paragenesis) can be clearly established. In this study, we attempted to resolve the absolute timing of these intrusive and hydrothermal events by utilizing multiple geochronometers. Lithogeochemistry and fluid inclusion results were then interpreted within this temporal framework. This poster is a summary of Lawley (2009). MAX is typical of low grade, arc-related deposits associated with fluorinepoor and calc-alkaline magmas (Carten et al., 1997) typical of most porphyry Mo deposits in British Columbia Low salinity MAX fluids are also typical of porphyry Mo deposits globally. The results of the U-Pb (80.9 ± 1.6 Ma and 80.2 ± 1.0 Ma) and Re-Os dating (80.5 ± 0.4 Ma, 80.2 ± 0.4 Ma, and 80.1 ± 0.4 Ma; average = 80.3 ± 0.2 Ma) of early and late dikes and molybdenite all overlap within analytical error, showing that magmatism and Mo mineralization occurred on a time scale shorter than the resolution of these methods. 40Ar/39Ar plateau ages for igneous and hydrothermal biotite, and hydrothermal muscovite from Mo veins range from 80 - 76 Ma, and are consistent with cooling ages or minor 40Ar-loss following a short-lived magmatic - hydrothermal event at ~80 Ma