Comparative study of stream sediments and heavy mineral concentrates using SEM-based Automated Mineralogy (QEMSCAN) from remote areas of Northern Pakistan

This study investigates the usefulness of QEMSCAN for mineralogical analysis of stream sediments and heavy mineral concentrates. This study was an orientation study of known and lesser understood gold-rich prospect areas in northern Pakistan. Mineralogical anomalies in this area are more obvious in heavy mineral concentrates than stream sediments from both known and lesser known areas, probably as a result of dilution by glacial material. The sampling strategy involved the collection of stream sediments (<180 μm) and panned concentrates (<180 μm) from known Shoghor and Bagrot prospects and lesser understood areas such as Asheriat, Teru and Pakora where the sources of the anomalies were unknown. Samples from all areas were analysed by conventional ICP-MS and XRF, as well as detailed physiochemical study of gold grains observed in panned concentrates. A selected number (16) of samples from stream sediments and heavy minerals were subjected to advance mineralogical analysis using QEMSCAN. Data were output on the modal mineralogy and mineral associations for both heavy mineral concentrates and stream sediments. The mineral proportions and associations in the heavy mineral concentrates (<180 μm) from the Shoghor and Bagrot catchments were characteristic of their known styles of mineralization, containing stibnite, galena, chalcopyrite and arsenopyrite, along with secondary minerals such as PbSbO (probably bindheimite) and SbO (possibly stibiconite). The modal abundances and associations of sulphide minerals and also secondary phases were better detected in the heavy mineral concentrates than stream sediments as concentrations of the latter were often below detection limits. The known Pb-Sb mineralization in Shoghor was well defined by modal mineralogy and mineral associations of rare minerals including stibnite, galena and also secondary phases such as SbO and PbSbO. Furthermore indication of similar types of mineralization have been found in heavy mineral concentrates from the lesser known Asheriat, Teru and Pakora areas. Results from both media indicated the mineralogy of sources and are useful to mineral exploration, either on their own or in combination with conventional geochemical methods. However the panned concentrates give more useful information than stream sediments and is recommended for detailed study of sulphide minerals, although costs are currently high (~£250 per sample). Detection limits for automated mineralogy are comparable to those of ICP-MS for transition metals.