Characteristics Of Zongshan Granite And Middle Basic Velocity And Its Relationship With Uranium Mineralization

Xiangshan orefield is the largest volcanic type uranium orefield. Granite porphyry and intermediate-basic dyke rocks in the orefield are closely related to uranium mineralization temporally and spatially. However, researches on geological characteristics, formation mechanism and their relationship with uranium ore- forming process are still relatively weak. Based on previous research data and achievements,petrology, mineralogy, geochemistry, geochronology and Sr-Nd isotopic composition of intermediate-basic dyke rocks are systemically discussed, and combined with geological and geochemical characteristics of the deposits, the relationship between granite porphyry, intermediate-basic dyke rocks and uranium mineralization in space, time and genesis is studied. The main achievements are listed as follow:(1) According to the occurrence, forming ages and diagenesis, the magmatic evolution is divided into rhyodacite- porphyroclastic rhyolite- annular granitic porphyry series and veined granite porphyry- diabase- lamprophyre series, respectively, and granite porphyry is divided into the early-stage annular granite porphyry mainly controlled by volcanic structure and the late-stage veined granite porphyry mainly controlled by faults, respectively.(2) The study on isotopic geochronology indicates that granite porphyry is formed in 134~132Ma, and lamprophyre in Julong`an deposit yields the age of 87 Ma. According to forming ages of intermediate-basic dyke rocks, these dyke rocks are initially divided into three stages, namely 127~125Ma,109 Ma and 87~85Ma, and 87~85Ma may represents the main instrusive period of intermediate-basic dyke rocks.(3) Petrogeochemistry and Sr-Nd isotopic compositions indicate that granite porphyry belongs to shoshonitic S-type granite series, and mainly derived from partial melting of the upper crust material, and mantle material is involved in the formation process; basic dyke rocks are derived from different degree of partial melting of the same mantle source.(4) Research on trace elements of ores and C-O-S-Pb isotopic compositions show that ore- forming materials and fluids of Xiangshan orefield originated from the crust- mantle interaction system, and mantle-derived fluids play an important role in the uranium ore- forming process.(5) Study on the relationship between granite porphyry, intermediate-basic dyke rocks and uranium mineralization shows that granite porphyry, intermediate-basic dyke rocks in the basin are closely related to uranium ores spatially and can be used as an important identification of uranium prospecting. The intrusive ages of veined granite porphyry and intermediate-basic dyke rocks are similar and close to two period of mineralization ages, which are consistent with time of deep fault activity caused by crustal regional extension after large-scale volcanic intrusive activities in south China. In late Cretaceous, deep fluids carrying part of ore- forming minerals extracted uranium-rich crust and migrated to the shallow, and uranium- rich fluids were located in the structural fractures accompanied with granite porphyry and intermediate-basic dyke rocks, and finally deposited and became uranium ores in the appropriate physico-chemical conditions.