Mineralogical Characteristic of Dashan Stone from Shoushan and Its Genesis

Mineralogical characteristics have significant indicative importance in the study of the genesis of ore deposits. To investigate the mineralogical characteristics and genesis of Dashan stone from Shoushan, this study utilized polarizing microscopy, X-ray powder diffraction, Raman spectroscopy, and electron microprobe analysis to conduct an in-depth investigation of the mineralogical features. Based on these characteristics, the fluid properties, formation environment, and temperature were discussed. The main minerals of Dashan stone from Shoushan are kaolinite and dickite, with some pyrophyllite; the secondary minerals include quartz, pyrite, hematite, anatase, rutile, and ilmenite, among others. Some minerals, such as pyrite, show signs of surface dissolution. The Raman spectra and electron microprobe results indicate that the presence of anatase, rutile, and pyrite in Dashan stone from Shoushan is related to magmatic hydrothermal fluids. The negative correlation between As and S and Fe in pyrite, along with the dissolution phenomena on its surface, suggest that the ore-forming fluids experienced a reduction environment followed by an oxidation environment. Based on the main mineral assemblage of Dashan stone from Shoushan and the phase change temperature-pressure conditions of the Al₂O₃-SiO₂-H₂O system, it is concluded that the stable temperature for the mineral assemblage of Dashan Stone is approximately 250-270 ℃.