Detection of asbestos minerals using a field portable spectrometer

Exploration drilling and mining in the Hamersley region of Western Australia can intercept lithologies (Banded Iron-Formations: BIF, shale, dolomitic BIF, dolerite and soil) containing fibrous minerals such as crocidolite. These fibrous minerals have been linked to human health problems and so improved identification and mapping of these materials would help in managing safe exploration drilling and mining practices. Field spectrometers, such as the PIMA-II, are now available for geologists to map a range of minerals including carbonates, sulfates, clays, phyllosilicates and inosilicates. In particular, the fibrous inosilicate riebeckite (also called crocidolite or blue asbestos) has diagnostic features at wavelength regions that can be discerned with the PIMA-II. The main objective of this study is to evaluate the use of PIMA-II for the detection of fibrous minerals in drill chips and powders (< 75 mu m) To achieve this goal, laboratory mixtures of known amounts of crocidolite were mixed with fresh BIF (both cherty and dolomitic), shale, dolerite and soil. The results of the crocidolite mixtures, the observed detection limit is 40% for cherty BIF, 9% for dolomitic BIF, 9% for dolerite, 5% for shale and 9% for soil. A simple pre-treatment was developed to concentrate the crocidolite in powdered samples. This method will be referred as WAS (Water Asbestos). The pretreatment is based on particular properties of asbestiform crocidolite namely, lower density of the crocidolite and "hydrophobic" properties (high surface area). By simply adding water to the powders, the asbestiform crocidolite "floats" at the surface which is then been dried and measured. This significantly increased the detection limits of the crocidolite mixed with cherty BIF to less than 0.5% (by weight).