PRACTICAL USES OF PIMA IN EXPLORATION
Chris Horsfall and David Cohen
Mapping of alteration mineralogy is an important tool in mineral exploration. Differentiating transported from residual overburden is critical in the design of geochemical exploration surveys and in the interpretation of trace element geochemical data, especially selective extraction trace element signatures in regolith. Identifying the mineral products of alteration and weathering in the field has, in the past, been difficult for geologists, let alone determining the crystallinity and composition of such minerals.
The PIMA is a field portable infrared spectrometer that measures the reflectance spectra of rocks, minerals, drill core, cuttings and pulps in the 1300 nm to 2500 nm range of the electromagnetic spectrum. Measurements can be taken the field in less than 40 seconds and generally no sample preparation is required. Minerals that contain hydroxyl radicals (such as clays, amphiboles, some sulphates) and carbonate radicals, absorb incident radiation at specific wavelengths in this wavelength region and in relative amounts that are diagnostic of such mineral species. The PIMA provides a fast means of identifying these minerals, their crystallinity and compositional variations and plotting these variations down drillhole or along traverse. Mapping these characteristics of alteration mineralogy facilitates the determination of vectors to mineralisation.
The PIMA case studies presented include:
1. Distinguishing transported overburden, weathered rock and altered rock in a geochemical sampling program near Cobar NSW.
2. Discrimination of crater fill from host rock in a diamond exploration program in Northern Australia.
3. AGSO work in the definition of high temperature alteration zones in the Panorama VHMS district, Central Pilbara Craton
4. Identification of parent rocks from weathered equivalents in drill cuttings, Eastern Goldfields, WA.
Other applications of the PIMA will be discussed.
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After work as an engineering geophysicist with BMR (AGSO) and as a geologist in regional geological mapping for the Northern Territory Geological Survey, Chris Horsfall joined the CSIRO Division of Exploration and Mining in 1983 and conducted research in the spectral properties of Australian terrain for eight years. After a period of consulting and further study he joined Geoterrex and later Integrated Spectronics.
David Cohen completed graduate studies in exploration geochemistry at Queen's University (Canada) and at UNSW where he is presently director of undergraduate studies in geology. His research interests in exploration and environmental geochemistry include projects in Cyprus, Pakistan, Indonesia and eastern Australia. He is an associate of CRC LEME and on the council of the Association of Exploration Geochemists.