Abstract: The Shanghuofang area is located at the central crater of the Guangxing-Zhirui basin in the Guyuan-Hongshanzi uranium and polymetallic metallogenic belt. Many uranium-molybdenum industrial-grade drill holes and mineralization occurrences have been identified. The molybdenum resource potential has reached the level of a medium-sized deposit, and the metallogenic conditions are favorable. The main ore-hosting country rock for uranium-molybdenum mineralization is rhyolite porphyry. In order to further investigate the geochemical characteristics and the tectonic setting of the rhyolite porphyry, this paper employed zircon U-Pb dating and whole-rock major and trace element analyses. The results show that the zircon U-Pb age of the rhyolite porphyry is 157 Ma, indicating that it formed in the Late Jurassic. Geochemical studies show that it has high SiO2 (w(SiO2)＞70%), high total alkali content (w(K2O+Na2O) >8%), low MgO (w(MgO)<0.5%), and is characterized by enrichment in large-ion lithophile elements (Rb, K, Ba, Th) and Zr, relative depletion in high-field-strength elements (P, Ta, Ti). The trace element characteristics indicate that the rhyolite porphyry in the Shanghuofang area is a typical post-orogenic A-type granite. Based on the regional tectonic background, we suggest that its formation is related to the post-collision extensional tectonic action following the closure of the Mongolia-Okhotsk Ocean.

Key words: rhyolite porphyry, geochronology, geochemistry, Guangxing-Zhirui basin, uranium-molybdenum deposit