Abstract The determination of alteration mineralogy with field portable short wavelength infrared (SWIR) spectrometers is common in numerous exploration and mining programs, but frequently the application is simply one of mineral identification. In fact, such spectrometers and the recently developed core scanners can be used to map both mineral assemblages and changes in mineral composition, as well as provide data to aid lithological characterization and the development of alteration maps and three-dimensional deposit models. This paper utilizes data sets from three volcanogenic massive sulfide (VMS) deposits (Kristineberg, Sweden; Hellyer, Tasmania; and Teutonic Bore, Western Australia) to assess relative amounts of chlorite and white mica, determine subtle variations in the phyllosilicate compositions, and integrate voluminous data collected with a drill core scanning system (the HyLogger™). The data sets illustrate the variety of approaches to collection and analysis of field spectral data that are reasonable in the context of mineral exploration. These techniques may be applied in a wide variety of ore-deposit environments.

Abstract Plagioclase feldspar composition is a potentially useful geobarometer and indicator for metasomatism in many styles of gold and base metal deposits. However, routine measurement of feldspar composition for exploration purposes is challenging using conventional laboratory methods such as X-ray diffraction, because of the time and cost to conduct these analyses. The thermal infrared (TIR) wavelength region between 7 and 14 μm provides diagnostic spectral information about silicates, including the composition of feldspars. To capture this information for routine logging of diamond drill core, CSIRO developed a line-profiling, bidirectional reflectance TIR scientific prototype called the TIRLogger. This paper examines the efficacy of the TIRLogger’s bidirectional reflectance measurements and the derived mineral information products through comparison with laboratory MicroFTIR™ emissivity measurements, X-ray diffraction, X-ray fluorescence, and electron microprobe data of the same samples. The results show that the plagioclase XRD 111 and 131 hkl peaks are significantly correlated with the normalized height of the background-corrected TIR reflectance peaks at 9.6 and 9.9 μm, with increasing Ca content in plagioclase associated with a relatively lower 9.6 μm peak. TIRLogger analysis of two diamond drill holes intersecting Archean greenstones from the St. Ives area in Western Australia show that Ca plagioclase, together with dolomite and quartz, are developed in areas of anomalously high Au content, whereas albite and calcite were detected in unaltered rocks, except for ultramafic rocks, which also shows that dolomite is developed.