RECOGNITION OF PORPHYRY QUARTZ IN STREAM SEDIMENTS BY FLUID INCLUSION PETROGRAPHY AND CATHODOLUMINESCENCE MICROSCOPY: RESULTS OF SYSTEMATIC DISPERSION STUDIES AND POTENTIAL APPLICATIONS IN PORPHYRY EXPLORATION

Abstract

Regional stream sediment surveys are an important exploration tool used in the search for concealed or partially concealed porphyry deposits. It is shown here that quartz contained in the coarse fraction of stream sediments can be used as an indicator mineral to supplement geochemical analyses conducted on the fine fraction, such as the measurement of the bulk cyanide leach extractable gold content. A method is proposed that allows separation of quartz grains from the coarse rejects of stream sediment samples to prepare grain mounts for petrographic analysis. Based on optical cathodoluminescence microscopy and fluid inclusion petrography, the number of porphyry quartz grains in each grain mount is then identified. Case studies conducted at Vert de Gris in Haiti and Hides Creek in Papua New Guinea show that porphyry quartz grains could be confidently identified in sediments in the catchment areas of both porphyries. Because the cost of microscopic analysis of quartz is small compared to the expense of sampling and geochemical analysis, the developed technique could be routinely used in large greenfield exploration programs. It is envisaged here that petrographic analysis of quartz grains can contribute valuable information for prioritization of targets defined based on their geochemical signatures.