XU Yan-xiao1,2，WANG Chao-wen1*，LIU Ming-jun3，ZHOU Wu-bang1，CHEN Tao1，YANG Ming-xing1，HONG Han-lie2*
(1. Gemmological Institute, China University of Geosciences, Wuhan 430074, China;
2. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;
3. Natural Resources and Planning Bureau of Taishun County, Wenzhou 325500, China)
Abstract: The ‘Taishunshi’ is a kind of pyrophyllite-type carving stone occurred in the Guihu township, Taishun County, Wenzhou City, Zhejiang Province. It has occupied a certain market share. The pyrophyllite in the ‘Taishunshi’ can be classified into the hydrothermal metasomatic type and hydrothermal infilling type. At present, there is relatively lack of understandings on the process, environment, temperature and pressure conditions of the formation of ‘Taishunshi’. Especially, there is still a great controversy on the alteration and evolution process of the formation of ‘Taishunshi’. In this study, optical microscope, X-ray diffraction (XRD) spectrometer, laser Raman spectroscopy (LRM), and X-ray fluorescence spectrometer are used to study the mineralogical characteristics of the ‘Taishunshi’ and to analyze its formation environment and process. The results show that the ‘Taishunshi’, including dominant high-aluminum pyrophyllite type and high-silicon pyrophyllite type, are composed of major pyrophyllite and minor quartz, diaspore, kaolinite, illite, hematite, and corundum. Petrographic observation revealed that the hydrothermal metasomatic-type pyrophyllite is appeared to have reacted with feldspar and diaspore in the wall rock, with metasomatic relict texture and metasomatic pseudomorphic texture. The hydrothermal infilling-type pyrophyllite is appeared to have filled in cracks at the late-ore stage. Diaspore and corundum, as paragenetic minerals formed in the formation process of pyrophyllite, occurred as stone nails and blue nails in the ‘Taishunshi’, respectively. The different mineral assemblages of the ‘Taishunshi’ samples had directly or indirectly recorded the metasomatic alteration ofthe rhyolitic crystalline tuff by the hydrothermal fluid, such as pyrophyllitization, diasporization, etc. The existence of hematite in the red ‘Taishunshi’ likely indicate the transition toward oxidization environment in the late-ore stage. These mineral assemblages of the samples may indicate that the ‘Taishunshi’ could be mainly formed in an mesothermal environment with temperatures ranging from 300 to 410 (±10) ℃.
Keywords: ‘Taishunshi’; carving stone; pyrophyllite; diaspore
ACTA MINERALOGICA SINICA Vol. 41, No.2, 2021, page 213
