Isabel Cecilia Contreras Acosta, 2017
“Mapping Epithermal alteration mineralogy with high spatial resolution hyperspectral imaging of rock
samples”. ITC Faculty, University of Twente. Enschede, The Netherlands.
Abstract:
Classifications of alterations zones have been done qualitatively, based on the minerals that exist or not in the alteration system. This results in a problem since minerals such as alunite can be formed by either hypogene or supergene processes. For mineral exploration purposes, these two groups should be mapped separately from each other to recognize which accumulations are prospective for important ore accumulations. This research uses the high-sulfidation epithermal system in the Rodalquilar Caldera Complex where hypogene alteration is associated with gold accumulations, and also supergene overprinting patterns occur. A total of 22 images were acquired with the high spatial resolution hyperspectral SWIR SPECIM camera, allowing not only to quantify mineral concentrations in a more representative way but also to evaluate the spatial distribution of the minerals in the samples. After the images were pre-processed for calibration issues, spectral and chemical differences of alunites were studied. As a validation of the alunite study, Inductively Coupled Plasma/Optical Emission Spectrometry and Thermogravimetric analyses were carried out. The Iterative Spectral Mixture Analysis (ISMA) algorithm was used and led to a more realistic quantification of the concentration of the minerals. The quantification of the aggregated partial fractions of the minerals per pixel was done to classify the rock samples. Spectral differences were found in alunites from the Rodalquilar. For the hypogene and supergene alunite, chemical differences were encountered in the composition and structure of the two minerals. K rich alunite is confirmed to have the 1480 feature at short wavelengths.
