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Contrasting geochemical expressions of copper mineralization at Namosi, Fiji

1977; Elsevier BV; Volume: 8; Issue: 1-2 Linguagem: Inglês

10.1016/0375-6742(77)90066-8

1879-1689

M.D. Leggo,

Geological and Geophysical Studies

Three areas of Cu mineralization have been extensively diamond drilled at Namosi on the island of Viti Levu, Fiji. Two of these areas, Waisoi and Waivaka, were initially located by stream sediment geochemistry whilst the third, Wainabama, provided very little stream sediment geochemical response because of dilution by externally derived material. One-kilometre sample spacing at the first two prospects would produce two or three locations anomalous in either total Cu or cold-extractable Cu. Despite similar topographic, climatic and geological settings, detailed soil and pit geochemistry was useful in siting drill holes at Waivaka, moderately useful at Wainabama, but of little value at the principal prospect of Waisoi. Two main factors are involved. Firstly, recent superficial cover of both alluvial and “mud avalanche” origin has obscured the surface geochemistry in places. Secondly, the geochemical expression varies as a function of pyrite content, its geometry relative to the Cu mineralization and the relationship of the sulphide mineralization to weathering and drainage. Cu, Pb, Zn, Mo, Au and pH determinations were used to reach these conclusions. Magnetics and induced polarization showed a good correlation with hydrothermal magnetite and sulphides respectively at Waivaka and, to a lesser extent, at Wainabama, and were used to define and seek extensions of mineralization. A combination of these two geophysical techniques at Waisoi was useful in understanding the generalized geology, but was not directly applicable in the detailed definition of drill targets. Quartz veining density was the other principal quantitative approach used at the three prospects and this proved to be of considerable value.