Abstract: Yeshan iron deposit is a small-scale Carboniferous syn-sedimentary hydrothermally overprinted deposit in the Xinqiao ore field, Tongling mineralization cluster. In this paper, systematic mineralogical research has been carried out on sedimentary
rocks of the Late Devonian Wutong Formation in Yeshan iron deposit using powder X-ray diffraction (XRD), scanning electron microscopy (SEM). Our results indicate that the dominant minerals in the Wutong Formation are detrital quartz and feldspar, and clay minerals including pyrophyllite, illite, and kaolinite, with some hematite and goethite. Higher average concentration of pyrophyllite in the studied Wutong sedimentary profile with from 7.54% to 70% occurs in the middle of the profile. Pyrophyllite in the samples shows micrometer scale euhedral to semi-euhedral block forms and grew around quartz particles. Pseudomorphic hexagonal prisms quartz particles consisting of lamellar pyrophyllite are also identified in the sedimentary rocks. The pyrophllite bearing ore compositions based on the XRF data show that the SiO2 content ranges from 44.47% to 80.23%, and Al2O3 from 10.49% to 28.75%. According to mineral assemblages and chemical compositions of the Wutong Formation sedimentary rocks from the Yeshan deposit, pyrophyllite bearing sedimentary rocks are proposed to be pyrophyllite ore and the ore belongs to silicaalumina pyrophyllite ores, which is an important raw clay mineral resource applied in the fields of ceramic raw material, refractory material, and alkali-free glass. The microstr uctures of the ore and the geological background of the mining area indicate that the pyrophyllite in the Wutong Formation may be the products of the reactivation of detrial kaolinite and quartz under Mesozoism. The finding of this study is an important for pyrophyllite ore prospecting in the Tongling region and the Middle-Lower Yangtze River Mineralization Belt which has similar ore-forming geological settings including the Wutong formation and Mesozoic magma.

Key words: Tongling area, Wutong Foramtion, pyrophyllite ore, genesis type, nonmetallic resources