Case history of copper exploration in Namosi District, the Republic of Fiji Islands

Abstract

In 2001, Nittetsu Mining Co., Ltd. started copper exploration program in Namosi district, the Republic of Fiji Islands. In the exploration program, we conducted induced polarization (IP) survey and land magnetic surveys. The IP survey was conducted on 34 survey lines that were 63 km length totally. As we recognized that 2D analysis was not fully capable of adjusting effects by the very hilly topography in the district, we applied 3D analysis. Low resistivity zones by the 3D analysis corresponded very well to the distributions of outcrops disseminated with malachite. And the copper mineralization zones showed middle range chargeability (12 to 18mV/V) by the results of 3D analysis. The pyrite mineralization zones around the copper mineralization zones were indicated as the higher chargeability areas. Therefore, the distribution of low resistivity and middle chargeability was regarded as one of the exploration guidelines for prospective copper mineralization area. In 2004, we conducted a land magnetic survey because large amounts of magnetite had been observed around the copper mineralized zones in Namosi district. The total survey areas were 2.4 km. After reduction to the pole (RTP) based on data acquired in the survey, over 1,000nT positive magnetic anomalies were observed in copper mineral occurrences. Such magnetic anomalies were also regarded as one of the exploration guidelines. Following the exploration guidelines that had been examined based on the above data, we conducted the drilling program and acquired a new promising copper mineralized zone.