The application of near-infrared spectroscopy to identify altered minerals and its implications for geologic prospecting: A case study of the Gangcha gold deposit in Gansu Province

Located on the northwestern side of Luqu-Chengxian thrust nappe zone in Qinling orogenic zone, the Gangcha gold deposit is a classical fractural alteration type gold deposit, in which the reserves of metal gold is up to medium scale. On the basis of geological mapping of the mining area, a BJKF-1 near-infrared mineral analyzer was used for drill hole ZK07-4 along No. 7 exploration line, drill hole ZK08-6 along No. 8 exploration line, and drill holes ZK27-1, ZK27-3, ZK27-4 along No. 27 exploration line to study the alteration characteristics. Some major alteration minerals were identified by the analyzer, which included illite, mica, dickite, kaolinite etc. According to the distribution and content changes of alteration minerals, phyllic alteration is related to mineralization, and the proven orebodies are mainly located in the phyllic alteration zone. Besides, a study of illite spectral reflectance parameters shows that illite crystallinity and Al-OH characteristic absorption peak patterns change regularly, that is to say that the ore part's illite crystallinity is large (5.5~5.7), the absorption peak of Al-OH is sharp, the surrounding rock's illite crystallinity is small (1.3~1.5), and the absorption peak of Al-OH is flat, suggesting that the ore-bearing part's illite was formed at high temperature. These results suggest that phyllic alteration, illite crystallinity and Al-OH profile can be taken as the indicator of mineralization during mineral exploration.