Discovery of new copper mineralized zone in Namosi area, Republic of Fiji Islands.
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概要
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The Namosi exploration licensed area is located 30km north west of Suva (the capital city) in the Republic of Fiji Islands. This area has been recognized as a copper prospecting area for more than 30 years. The Waivaka Corridor area is located in the centre of the Namosi exploration licensed area. Nittetsu Mining Co., Ltd and Mitsubishi Materials Corporation had conducted geological, geochemical, magnetic survey on the surface in the area in 2004 and also carried out three dimensional analysis for the data of TDIP survey (electrical exploration method) which was carried out in 2001 in the same area by Metal Mining Agency of Japan(present: Japan Oil, Gas and Metals National Corporation). In addition, on the basis of the surface survey data and analysis, drilling survey program(10 holes, total drill length 3, 401.75m) was carried out in the area in 2005. The comprehensive summary is shown as follows.<BR>(1) The geology of the Waivaka Corridor area is consisted of the Medrausucu group(middle Miocene to Pliocene) and dioritic and quartzdioritic porphyries. The Medrausucu group is mainly composed of andesitic lava, tuff and pyroclastics. The intrusive rocks of these porphyries had caused porphyry copper type mineralization in late Miocene to early Pliocene based on the data of K-Ar dating.<BR>(2) Six prospecting areas were extracted for drilling survey, on the basis of the data and interpretation of the results which were obtained by above mentioned surface survey, such as the existence of outcrop and float with Cu oxide, distribution of Cu and Au anomalies in the soil geochemical survey, the distribution of the positive anomaly of the reduced to the pole anomalies calculated from IGRF residuals in magnetic survey and low resistivity and middle chargeability of the TDIP survey (electrical exploration method).<BR>(3) On the basis of the drill core and microscopic observation, the copper mineralization can be characterized by the bornite-chalcopyrite mineral assemblage accompanied by strong silicification and/or quartz vein stockwork and magnetite. The copper mineralized zones mostly occurred in the dioritic porphyry intrusion and also it can be observed in the contact part between dioritic porphyry and andesitic pyroclastics. The shape of the ore body is seemed to be controlled by ENE-WSW and NE-SW trending fracture system as we had observed quartz vein stockwork on the surface of the Wainaoulo creek.<BR>(4)From the results of drilling survey program in 2005, some remarkable copper mineralized zones were newly discovered in Wainaoulo and Wainaoulo southeast of the Waivaka Corridor area and this discovery of the copper mineralized zones sug-gests possibility of upgrading copper development potential in the Waivaka Corridor area.
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