The rare-metal mineralogical study on the Kuqu Li-Be-rich granitic pegmatite from the eastern Himalaya
A few leucogranitic plutons related to lithium and beryllium mineralization including Pusila,Rachu,Gyirong and Lhozhag in the Himalayan orogen have been found with the occurrence of large-scale spodumene pegmatite(aplite included).Recently the spodumene pegmatite was found in the field of the Kuqu pluton in the eastern Himalaya,with various types of rare-metal pegmatites all intruded into the main body muscovite granite.The petrographic characteristics,mineralogy,and geochronology of the Kuqu pegmatites were studied in this paper.Based on the mineral assemblage and the location,the Kuqu pegmatites are classified into four types,namely,the pervasive pegmatite Ⅰ(consisting of feldspar-quartz-muscovite),the pegmatite Ⅱ(consisting of albite-quartz-muscovite zone and fine-grained albite zone),the pegmatite Ⅲ(spodumene-albite-quartz zone)in the western Sangyu village and the aplite dike in the eastern Kuqu pluton.The pegmatites all contain various abundance of garnet and tourmaline,and minor rare-metal minerals such as beryl,columbite-group minerals(CGMs)and cassiterite.The U(-Th)-Pb isotopic results of monazite and CGMs indicate the pegmatite Ⅰ,Ⅱ and Ⅲ formed at～25Ma,the main magmatic activity in the Kuqu pluton,and a late magmatic activity of the aplite occurred at～14Ma.The contemporary pegmatite Ⅰ,Ⅱ,and Ⅲ have the decreased trends of the K2O/Na2O,Zr/Hf and Nb/Ta ratios,the total rare-earth elements(REEs)concentration and Eu/Eu*value,and the increased trends of the rare-metal(Li,Be,Nb,Ta,Rb,and Cs)contents.Moreover,the minerals show the more obvious evolved trends,such as the lowering K/Rb ratio and MgO content in the muscovite,the increasing Li concentration in the tourmaline,the increasing spessartine content in the garnet,the increasing mangancolumbite content in the CGMs(close to the Mn-rich end-member),and the increasing Li-Cs content in the beryl.The cassiterite is commonly intergrown with the spodumene in the pegmatite Ⅲ and its abundance is highest in all the samples.The mineralogical features of the younger aplite fall between those of pegmatite Ⅰand Ⅱ.Accordingly,the Kuqu pegmatites are the final product of the evolution of the magmatic evolution suggested by the effective mineral indicators.The related rare-metal mineralizations vary from the Be-,through Be-Nb-Ta(-Sn),to Li-Be-Nb-Ta-Sn mineralization.Spodumene is the primary Li-rich minerals in the Kuqu pegmatite,while the symplektitic spodumene and quartz are possibly secondary products of the Li-rich fluid and feldspar but not from the decomposition of the petalite during the Kuqu pegmatite intruded into the wall-rock.
Spodumene pegmatiteBerylEvolution degreeMineralogical indicatorsEnd-member mineral
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维普
