Alteration mapping with short wavelength infrared (SWIR) spectroscopy on Xiaokelehe porphyry Cu-Mo deposit in the Great Xing’an Range, NE China: Metallogenic and exploration implications
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Keywords:
Sericite
Muscovite
Illite
Hypogene
Molybdenite
The Talnikovoye ore field where previous academic research and exploration work revealed porphyry copper mineralization is described. Our data show that mineralization is confined to the intrusions of Turonian granodiorite and quartz diorite (91 Ma, U-Pb metohod), as well as the accompanying hydrothermal-explosive breccias. Biotite-epidote-chlorite propylites are widespread within the ore field; in the southern part, phyllic alteration is superimposed on the halo of K-feldspar alteration. The ore occurs in zones of intense quartz, chlorite-epidote-quartz (with chalcopyrite and molybdenite), sulfide-potassium feldspar-quartz (with chalcopyrite and bornite), and sulfide-quartz-sericite (with chalcopyrite) stockwork veining with copper-molybdenum mineralization. They are characterized by moderate concentrations of Cu (0.1–0.3 %, reaching 1.1 %) and Mo (up to 0.1 %), low concentrations of Au (up to 0.1 g/t) and Ag (up to 2.6 g/t) and have a Cu-Mo-(Au, Ag, Pb, Zn, Sb, As) geochemical signature. Fluid inclusion data suggest the formation of mineralized veinlet quartz during the magmatic-hydrothermal transition (430–150 °С) with solutions at high (50 wt % NaCl equiv.), medium and low concentration (5–18.9 wt % NaCl equiv.) involved under the cooling-dilution scenario. Values of the main geochemical indicators, such as Cu/Mo (30–60) and Cu/Au (> 1 × 105) ratios allowed us to assign the Tal’nikovoye ore field to the porphyry copper-molybdenum type characteristic of continental-margin volcano-plutonic belts formed at the mafic island-arc basement. The geochemical parameters of porphyry granitoids indicate their formation in a setting of subduction-to-transform plate boundary transition.
Molybdenite
Sericite
Hypogene
Stockwork
Bornite
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Sericite
Argillic alteration
Hypogene
Alunite
Bornite
VNIR
Illite
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Alteration minerals are important prospecting indicators, and multispectral and hyperspectral remote sensing technologies are important prospecting tools. Multispectral remote sensing data such as ASTER have been widely used for extracting alteration mineral information. The dataset is easy to access, cost-effective to use, and rich in rock and ore spectrum information. Recently, the use of alteration mineral identification technology and hyperspectral satellite data for fine prospecting has become feasible in China, considering the development of hyperspectral remote sensing technology, especially the launch of the ZY1-02D satellite in China. Pulang porphyry copper deposit, Southwest China, is a largescale, explored deposit with unclear peripheral prospecting. Therefore, principal component analysis (PCA) and mixed tuned matched filtering (MTMF) methods were used in this study to extract the mineralized alteration minerals of the Pulang porphyry copper deposit area from the ASTER multispectral data and ZY1-02D hyperspectral data. Then, Al-OH and Fe-Mg-OH alteration information was obtained from the ASTER data using the PCA method. Meanwhile, sericite, chlorite, and epidote alteration information was extracted using the MTMF method and ASTER data. With the ZY1-02D data, the alterations of sericite, chlorite, and epidote were extracted by the PCA and MTMF methods. A field verification showed that the overall accuracy of the ASTER-based alteration extraction was up to 0.57, and the overall accuracy of the ZY1-02D-based alteration extraction was up to 0.88. And circled six favorable areas of copper deposit based on alteration mapping. Therefore, the ZY1-02D data can be regarded as a reliable and promising tool for delineating potential prospecting areas according to the mapping of hydrothermal alteration information, which can be explored further in the prospecting field in the future. The eastern and northern parts of the first mining area should be further explored for potential prospecting.
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