GEOCHEMICAL CHARACTERISTICS AND GEOLOGICAL IMPLICATION OF THE JILING DIABASE IN GANSU PROVINCE

As one of the important factors for uranium metallogenesis in southern China, diabase occurs around the Jiling sodium-metasomatic uranium deposit. With study on petrology, petrography, geochemistry and isotopic chronology, it is confirmed that the diabase surrounding the Jiling uranium deposit is the product of upwelling alkali basaltic magma, which is characterized by rich-aluminum (15.97%-19.21%), high-alkali (4.36%-6.89%), med-titanium (1.18%-2.02%) and weak negative Eu anomaly. The chondrite-normalized REE patterns show strong LREE and weak HREE fractionations, with relatively enriched LILEs (Rb and Ba) and incompatible elements (Th and U), and depleted HFSE (Nb, Ta, Hf and Ti). The LA-ICP-MS zircon U-Pb age of the diabase is 485 Ma, indicating it was formed in Early Ordovician. Both the MgO contents (3.79%-8.22%) and Mg^# values (42.4-66.5) vary greatly. The basic magma underwent the fractional crystallization of olivine, pyroxene and plagioclase before its emplacement into the crust. The Jiling diabase in the Longshoushan metallogenic belt marks the beginning of post-collisional extension setting, in which the upwelling mantle with heat brought the formation and evolution of acidic magma and alkaline rock, as well as the sodium-metasomatic uranium mineralization.