Fracture survey at Waisoi copper deposits in Namosi area in the Republic of Fiji Islands
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概要
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In the Namosi district located 30km of Suva, the capital city of Fiji, there are more than fifteen porphyry Cu-Au prospects. The Waisoi is one of the largest prospecting area among them and is composed of two major deposits (Waisoi West ore deposit and Waisoi East ore deposit) which were surveyed by several major exploration companies through in 1970's to 1990's.<BR>We conducted geological survey and geo-structural survey (fracture survey) at the Waisoi area for the exploration of middle to high grade copper ore deposit which can be developed in a current economic circumstance. Summaries are as follows:<BR>(1) Late Oligocene to Middle Miocene Wainimala formation and Middle Miocene to Pliocene Madurausucu formation are distributed in the area and some intrusive rocks (diorite porphyry, quartz diorite porphyry, quartz porphyry) are observed in the area.<BR>(2) Two remarkable silicified and argillized zones with ENE-WSW direction which are recognized from the results of the distribution of strong silicification and argillization zones and direction of fracturing and quartz vein system. The alteration mineral assemblage is mainly sericite-chlorite in these two altered zone.<BR>(3) In the Waisoi West deposit, the directions of quartz veins are mainly NW-SE and ENE-WSW and the shape of ore body is structurally controlled with the same direction as quartz veins. On the other hand, in the Waisoi East deposit, the direction of quartz veins are mainly NE-SW and ENE-WSW, middle to high grade copper mineralization is structurally controlled by the fracture and quartz vein with NE-SW and ENE-WSW direction.<BR>(4) In the Waisoi West deposit, the middle to high grade copper mineralization was thought to be caused by hornblende diorite porphyry intrusion in the early mineralization stage and after this stage, the silicification and quartz veining occurred with the open fracturing of NNW-SSE-NW-SE direction and copper re-enrichment in the Waisoi West ore deposit was thought to be caused by the hydrothermal system in this later stage.<BR>(5) The promising areas of middle to high grade copper mineralization should be qualified by the existence of intrusion of hornblende diorite porphyry and quartz veining with silicification and argillization in the mineralized area which is identified in this survey, and these three promising areas, upper part of Wainitotoyeuyeu, the area from upper part of Wainisovasovatabua to upper part of Wainimasiadamu, upper part of Wainividrausa are extracted on the basis of these qualifications.
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