Geochemistry and Nd isotopes of the François Lake plutonic suite, Endako batholith: host and progenitor to the Endako molybdenum camp, central British Columbia

Abstract

The Endako low-F granodiorite-type porphyry Mo deposit is hosted by the Triassic to Eocene Endako batholith, which comprises five temporally distinct plutonic suites, only one of which is mineralized. Pre-mineralization suites range in composition from diorite to granodiorite. The synmineralization Jurassic–Cretaceous François Lake suite includes two granodiorite- to monzogranite-bearing subsuites. Postmineralization phases include the Eocene Sam Ross Creek monzogranite. The batholith spans a silica range of 44–80 wt.% and consists of metaluminous to slightly peraluminous, low- to high-K, I-type granitoids; the Sam Ross Creek phase is an A-type granite. Positive ε Nd(T) values (+1.1 to +7.2) indicate derivation predominately from juvenile source materials, but with variable input from an older crustal component. Evidence suggests generation of older plutonic suites in a juvenile arc-type setting and younger K-rich felsic suites via recycling of juvenile arc crust without significant mantle-derived contributions. Three distinct Mo-deposition events in the Endako camp are linked to repeated generations of oxidized, highly evolved monzogranitic phases (pre-ore dykes, aplitic Nithi and Casey intrusions) belonging to both François Lake subsuites. Late pre-ore dykes with "Casey-like" geochemical signatures, along with massive unmineralized Casey intrusions near the Endako deposit, could reflect repeated injections from an underlying magma chamber that remained molten during the youngest Mo-deposition event. A genetic link may exist between the Sam Ross Creek phase, a pluton with Climax-type granite characteristics, and Eocene kaolinite alteration in the Endako deposit. Also, potential exists for Eocene-age Climax-type Mo mineralization within the Endako mining camp.