Identification of illite polytype zoning in disseminated gold deposits using reflectance spectroscopy and X-ray diffraction-potential for mapping with imaging spectrometers

X-ray diffraction studies of clay minerals from disseminated gold deposits in Nevada demonstrate that illite polytypes are often laterally and vertically zoned around ore bodies. Polytypes act as geothermometers indicating temperatures of ore deposition and thus proximity to the hydrothermal fluids during deposition. Visible/infrared reflectance spectroscopy for field identification and mapping of the illite polytypes is evaluated. The results demonstrate that reflectance spectroscopy can be used to assist gold exploration efforts by providing detailed mineralogical information in real time at the field location. As the new generation of imaging spectrometers is developed, it is likely that subtle spectral differences such as those between the illite polytypes will become useful for remote exploration for gold deposits