| Title | NEW IMPLICATION OF WALL ROCK ALTERATION MINERALOGY IN THE HISHIKARI EPITHERMAL GOLD DEPOSIT, JAPAN |
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| Authors | Y. Gonoi, A. Imai, K. Yonezu, T. Tindell, K. Watanabe |
| Year | 2019 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Hydrothermal alteration zoning, interstratified clay mineral, chlorite, epidote, Hishikari epithermal gold deposit |
| Abstract | This work seeks to establish a new alteration mineral zonation in the Hishikari mine for more efficient exploration. Detailed analysis of wall rock alteration was conducted by means of microscopic observation, X-ray diffraction and electron probe micro analysis. Samples used here were collected from four underground cross cuts and five drill cores to cover mainly the Honko and Sanjin deposits. As a result of analysis, dominant alteration minerals identified were chlorite-smectite interstratified mineral (C/S) and/or illite-smectite interstratified mineral (I/S). These are common in cross cuts and drill cores. However, some areas of the southern part of the deposit have dominated chlorite with minor illite. In the same region, epidote was remarkably recognized. Epidote is a mineral which occurs at higher temperatures than chlorite and illite in general and can be a potential as a new index mineral for the division of alteration zoning. Previous fluid inclusion studies in Hishikari mine reported that some higher homogenization temperatures were recorded in the Sanjin deposit than in the Honko and Yamada deposits. The presence of epidote is consistent with these study, suggesting that this mineral will be useful especially in the Sanjin deposit. Chlorite compositions were analyzed by EPMA. The comparison with the data of the previous study suggest chlorites of the Sanjin have higher formation temperature than the Honko and the Yamada. |