Petrogenesis of Late Jurassic granitoids and relationship to polymetallic deposits in southern China: The Huangshaping example

摘要

Southern Hunan Province, located in the Cathaysia Block where the Shi-Hang zone and Nanling belt meet, is characterized by extensive Mesozoic magmatism and coeval polymetallic mineralization. The Huangshaping W-Mo-Pb-Zn-(Cu) deposit is representative in this area. However, the petrogenesis of the granitoids associated with the Huangshaping deposit, and their relationships with mineralization, remain undetermined. In this paper we focus on zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd-Pb-Hf isotopic compositions in order to further our understanding of these issues, as well as their regional implications. The Huangshaping granitoids are characterized by two pulses of intrusive activity: a first-stage quartz porphyry and a second-stage felsite and granite porphyry, our new data show that the quartz porphyry and felsite formed at 160.5 +/- 1.3 and 156.6 +/- 1.4 Ma, respectively, representing a period of Late Jurassic magmatism. Granitic enclaves within the quartz porphyry crystallized at 160.2 +/- 1.6 Ma, and zircons and apatites from the enclaves exhibit Hf isotopic and geochemical compositions that suggest a Palaeoproterozoic lower crustal melt as one end-member of the magma that formed the quartz porphyry, whereas another likely end-member was coeval mantle-derived magma, as indicated by the geochemistry and Sr-Nd-Pb-Hf isotopes. However, both the felsite and granite porphyry were probably derived from the melting of metamorphic basement rocks in the upper crust. The felsite clearly formed as a result of the rapid ascent and cooling of magma, whereas the granite porphyry underwent fractional crystallization. The magma sources and evolution of the granitoids, as well as their association with the Huangshaping mineralization, suggest that melting of upper crustal components controlled the W-Mo and Pb-Zn mineralization, whereas dehydration of a subducted slab provided the Cu mineralization in southern Hunan Province.