The mineral deposits and metallogenesis of the Fiji Platform

Porphyry copper assessment of Southeast Asia and Melanesia: Chapter D in <i>Global mineral resource assessment</i>

“…6) by Eocene time (Schellart and Appendix V-Tract 009pCu7210 307 Table V2. Map units that define tract 009pCu7210, Outer Melanesian Arc II-Melanesia (Solomon Islands, Vanuatu, and Fiji Colley and Flint (1995), Colley and Greenbaum (1980), Leggo (1977), Lum and Calicutt (1989) Appendix V-Tract 009pCu7210 Geology of New Georgia Group, 1:250,000 Abraham and others (1987) New Georgia Geological Map Sheet NG 6 1:100,000 Dunkley and Philip (1986) New Georgia Geological Map Sheet NG 7…”

“…Regional stream-sediment and soil geochemistry is one of the primary mineral-exploration tools used in Southeast Asia to target areas for more detailed mapping, exploration geophysical surveys, exploration geochemical surveys using rock-chip sampling and trenching, and drilling. Greenbaum, 1980 andHindle, 1984 …”

“…The evolution of Fiji is characterized by 4 stages: (1) early arc stage (35-12 Ma) characterized by primitive, low-K thloeiites with pre-Miocene volcanism associated with subduction along the Vitiaz Trench; (2) mature arc stage (12-7 Ma) represented by the Colo Plutonic Suite, which is referred to as the Tholo Suite in some references; (3) early arc rifting stage (7-3 Ma) associated with tholeiitic to calc-alkalic rocks; and (4) late arc rifting stage (3 Ma to Holocene), associated with ocean-island basalts and on some islands, high-K andesites. Porphyry systems are associated with the mature arc and early extensional (rifting) stages (Colley and Greenbaum, 1980;Fiji Ministry of Lands and Mineral Resources, 2010). Epithermal gold-telluride systems, such as the Emperor deposit, are associated with calderas of the early rifting stage (Fiji Ministry of Lands and Mineral Resources, 2010).…”

“…The main plutons of the Colo (Tholo) Suite are tonalite and gabbro, with marginal facies, including trondhjemite, diorite, and hornblende andesite-microdiorite; coeval volcanic rocks are absent. Colley and Greenbaum (1980) noted 7 porphyry-type copper ±molyb-denum prospects associated with plutons of the Colo (Tholo) orogeny, as well as copper skarns; no economic deposits are associated with these rocks. The Yavuna stock in western Viti Levu, dated at 33 Ma, and the Mbotenaulu stock in central Viti Levu are mapped as first phase, pre-Miocene, synorogenic intrusions of the Colo (Tholo) plutonic suite, whereas the other plutons of the Colo (Tholo) suite are mapped as second-phase, late Miocene (7-11 Ma) synorogenic intrusions.…”

“…Permissive rocks on Vanuatu are confined to the western belt of the archipelago, where late Miocene diorite, microdiorite, and andesite stocks intrude Miocene volcanic rocks. In Fiji, porphyry-type prospects are associated with orogenic and post-orogenic magmatism on Viti Levu and with post-orogenic magmatism on Vanua Levu (Colley and Greenbaum, 1980). The 2,700-km-long southeast-trending archipelagos that comprise the fragmented, Paleogene-Neogene Outer Melanesian Arc system south of Papua New Guinea are delineated as a single permissive tract for several reasons: (1) both early and late stages of arc evolution are preserved in close spatial proximity on some islands, (2) insufficient age information is available to subdivide the tract by age, (3) dioritic intrusions and andesitic volcanic rocks permissive for porphyry copper deposits occur throughout the evolution of the arc, (4) the likelihood of occurrence of undiscovered porphyry copper deposits is uniform throughout the tract area, and (5) the availability and quality of geologic mapping and mineral occurrence data is consistent throughout the study area.…”