Abstract

The Tuvatu gold-silver telluride deposit with reserves of 13 t Au is the second largest gold deposit in Fiji after the large Emperor gold telluride deposit (production, and proven and probable reserves of 280 t Au). The deposits are 50 km apart and occur along the >250-km east-northeast–trending Viti Levu lineament. They are spatially associated with alkaline rocks of almost identical age (~5.4–4.6 Ma) and having a shoshonitic affinity. The gold mineralization in both deposits is spatially and genetically related to monzonite intrusions and to a low-grade porphyry copper-style system. The Emperor deposit occurs along the margins of the Tavua volcano whereas the Tuvatu deposit may occur adjacent to an eroded shoshonite volcano. At both locations, low-sulfidation, epithermal gold telluride mineralization occurs in flat-lying veins, steep faults, shatter zones, stock-works, and hydrothermal breccias. Mineralization in both deposits formed in multiple stages and is characterized by the presence of quartz-roscoelite telluride veins in which gold-rich tellurides were deposited prior to silver-rich tellurides. Gold tellurides and vanadium minerals were deposited at approximately 250°C from moderately saline fluids. Oxygen and hydrogen isotope compositions of ore fluids at Emperor and Tuvatu are similar to the composition of waters exsolved from arc magmas. Previously published values of δ34S of sulfides (–20.3 to +3.9‰) from Emperor are like those obtained from the Tuvatu deposit (−15.3 to −3.2‰) and indicate, along with mineral assemblages, that the ore fluids were oxidizing and near the hematite-pyrite buffer.

The similar igneous lithological units of almost identical age, transition from porphyry- to epithermal-style mineralization, paragenetic relationships, and comparable fluid inclusion and stable isotope data suggest a common origin for sulfide and gold telluride mineralization at the Tuvatu and Emperor deposits. Potential exists for additional epithermal gold telluride mineralization near volcanic centers in shoshonitic rocks (Ba and Koroimavua Volcanic groups) spatially related to the Viti Levu lineament in northern Viti Levu.

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