Geology of Vatukoula The Fijian archipelago of over 300 islands lies along the edge of the Pacific Ring of Fire, a volatile zone of frequent volcanic and seismic activity partially encircling the basin of the Pacific Ocean. The Ring of Fire is known for its rich array of precious metal deposits. Vatukoula, literally meaning 'rock of gold,' is situated in the collapsed caldera of an extinct volcano, near the edge of the Nakauvadra mountain range, in northwest Viti Levu, the largest Fijian island. Gold deposits were formed at Vatukoula between 3 and 7 million years ago during a period of volcanic activity when hydrothermal forces caused boiling liquid to precipitate gold in thin veins. The rocks of the ancient Tavua Volcano originated as potassium-rich magma of the shoshonite association, which evolved from absarokite (olivine-basalt) parent magma to shoshonite, banakite and monzonite derivatives (Mineral Resources Department: Government of Fiji, 2008). Today, the gold at Vatukoula is mostly located within a two square kilometer fractured block, close to the surface (within 600 m). Gold primarily occurs in three types of structural settings:
Gold occurs primarily as gold-tellurides and sub-microscopic gold in pyrite. The specific type of gold deposit at Vatukoula is known as a Low-Sulfidation epithermal gold deposit. There are two main types of epithermal gold deposits, Low-Sulfidation (LS) and High-Sulfidation (HS), each forming from waters of differing chemical composition, and in a distinct volcanic environment. LS epithermal gold deposits are commonly associated with the presence of the following metals: Silver (Ag), Lead (Pb), Copper (Cu), Zinc (Zn), Arsenic (As), Mercury (Hg), Selenium (Se), Cadmium (Cd), and sometimes Antimony (Sb) (University of Otago Department of Geology, 2008). |
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