Abstract

The geology, general mineralogy, and chemistry of a massive, mixed-sulfide deposit on Vanua Levu, Fiji, are described. The deposit is located in a sequence of Miocene-Pliocene rhyodacites, andesites, and basalts, with associated volcaniclastic sediments. It is believed that it was formed during a period of waning volcanism by fumarolic activity near the sea bed, and it shows resemblances to the kuroko ores of Japan.The common primary sulfides are pyrite, chalcopyrite, sphalerite, and galena with lesser amounts of enargite, tennantite, bornite, and idaite. Lead-zinc sulfides are concentrated toward the top of the deposit and copper sulfides toward the bottom. Covellite occurs in a zone of supergene enrichment below a well-developed gossan. Ore minerals were deposited by a mixture of open-space precipitation and replacement, and colloform textures are common. There is some evidence that Cu, Pb, and Zn have a direct magmatic origin. Ore deposition was accompanied by silicification, argillization (kaolinite and montmorillonite), introduction of gypsum, and barite.

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