Geochemistry Characteristics Of Neoproterozoic Igneous Rocks And Related Uranium Mineralizations In Datian, Panzhihua And Xujie, Mouding, Southwestern China

Neoproterozoic plutons (TTG combination) exposed widly in Kangdian axis are the oldest crystalline basements in the Yangtze Platform. In the margin of the plutons , there are migmatitic contact zones and a number of uranium mineralization occurences. The study of geochemistry of migmatitic complex at the region of Uranium mineralization is significant to study the role of uranium mineralization in the basement of Yangtze platform.The thesis disscused the elemental geochemistry and Lead isotope geochemistry of Neoproterozoic magmatic rocks, as well as the relationship between the magmatic rocks and the uranium mineralizations, in Datian district,Panzhihua and Xujie district,Mouding.The main conclusion are as following:The geochemistry researchs of the rocks demonstrated that the tectonic settings of the quartz diorite or granodiorites in Datian pluton, formed in Island-arc environment, while the oligoclase granitic pluton of Huatan and some of granite veins and felsic dykes which introsived into the pluton, like adakite.These causes are related to plate subduction-related partial melting.The geocheminstry composition of the granites of Heime pluton likes that of A-type granite. Lead isotope geochemistry shows that diorite, quartz diorite, basic veins and grey granitic veins are of the characteristics of magmatic belting and crust-mantle mixed source,but the quantity of the mantle-derived composition is small. The granite veins, granitic gneisses and augen granitic gneiss have the characteristics of upper crustal source. Some of granitic gneiss with K-feldspar porphyroblast, diorites and granites have abnormal radiogenic lead showing much more Th and U content.The geochemistry of the plagioclase amphibolitic schist at Mouding 1101 shows that they formed in an island-arc environment.The REE-chondrited patterns of some granule-granite and the ore-bearing plagioclase amphibolites schist like that of A-type granite rocks.The plagioclase amphibolitic schist was subjected to reform by fliud and hydrothermal of the granite.The forming environment of granite in Xujie is similar to rock mass of Heime in Datian.Those might be formed in the intracontinental extension environment.This thesis discussed the contolling factors of the uranium mineralization of Datian 505 and Mouding 1101. It revealed that : (1) the uranium mineralization of Datian 505 formed in two major stages. The host rocks were subjected to albitization, epidotization, chloritization and other alterations by metasomatism, uranium was activated and transferred, formed uraninite(pitchblende) and background enriched U , Th. At that stage ,many elements like Ta,Th,Zr,Hf,Cr were migrated with uranium. At late stage, silicate, haematization,and uraninite pitchblende formed. It demonstrates that the metallogeny of uranium is controlled by fractures and low-temperature hydrothermal alteration. The uranium came from the magma similar to A-type granite.In this period the elements associated with the uranium is simple. (2) uranium mineralization of Mouding 1101 located in a residual cap edge of the migmatitic contact zones, controlled by several stages of tectonic and low-temperature hydrothermal alteration. there are uranium mineralization of more than two stages. The alteration in the host rocks(plagioclase amphibolites schist) included oligoclase albitization,epidotization,rutilation and so on. During which uranium in the host rocks was reworked and transferred into microfructures, and iron was separated out, formed pyrite, chalcopyrite and ulrichite. During the period of late hydrothermal activity Ba,As,Ag,Pb,Zn and U and so on,were add, and formed massive boulangerite, heterolith and uraninite pitchbende.At Datian 505 and Mouding 1101, the uranium mineralization in the migmatitic contact zones and controlled by the tectonic and the hydrothermal activity, may be as a response to the transition of tectonic evolution of the Rodinia super continent.The host rock was subjected to the reform by the fliuds from the granite veins and felsic dykes and low-temperature hydrothermal alteration. Uranium may mainly from the activities of magma similar to A-type granite, some from ore-bearing rocks .