PRECIOUS METAL TELLURIDE OCCURRENCES IN FIJI

Precious metal tellurides occur in various geological settings in Fiji including porphyry Cu mineralization (e.g., Namosi), low-sulfidation epithermal Au deposits associated with low-grade porphyry Cu mineralization (e.g., Emperor, Tuvatu, North Tuvatu, Banana Creek), high-sulfidation epithermal Au systems (e.g., Mt. Kasi), and gabbro intrusions (e.g., Wainadoi). Of these occurrences, Emperor (reserves of 280 t Au), Tuvatu (reserves of 12 t Au), and Mt. Kasi (resources of 9 t Au) are the three largest gold deposits in Fiji whereas Namosi is the largest porphyry Cu deposit (930 Mt of 0.43 % Cu and 0.14 g/t Au). On a regional scale, the Emperor, Tuvatu, Mt. Kasi, and Banana Creek deposits are spatially associated with the > 250 km ENE-trending Viti Levu lineament. The Tavua (Emperor) and Navilawa (Tuvatu, Banana Creek, North Tuvatu) calderas produce prominent bulls-eye gravity anomalies that are targets for gold exploration. Gold mineralization associated with the Tavua and Navilawa calderas are spatially related to monzonite intrusives with a shoshonitic affinity. Spider-diagrams of trace element data for igneous rocks from both locations are almost identical. Moreover, the age of these rocks (~5.2 to 4.6 Ma) is virtually the same. Seven different tellurides occur at Tuvatu (altaite and calaverite are most abundant) whereas at Emperor, thirteen different Te-bearing minerals were identified (krennerite and sylvanite are the most common). Fluid inclusion and stable isotope data (S, O, and H) from both locations overlap and suggest Te-bearing minerals were deposited at ~ 250^oC from ore fluids that were derived from arc magmas (or possibly from subduction-related volcanic vapors). Ore at Mt. Kasi also formed around 250^oC in veins and breccias in basaltic and andesitic flows, breccias, and tuffs. Tellurides and goldfieldite formed in the main gold-bearing stage. Sylvanite and petzite are present in epithermal gold veins in the Wainadoi prospect, which are hosted in gabbro of the Late Miocene Colo Plutonic Suite. Although uncommon, hessite is present in the Wainisavusavu prospect (Namosi district). Tellurides are located over a broad geographical area in Fiji and were derived from volcanic and intrusive rocks of Pliocene-Late Miocene age. These rocks formed during the break-up of the Vanuatu-Fiji-Tonga arc following intra-arc collision.