Petrogenesis of layered Devonian granites in the Jinshuikou area of East Kunlun and its prospecting significance
The East Kunlun orogenic belt is a giant magmatic belt which is comparable to the Gangdese belt in the Qinghai-Tibet Plateau,however,it is still unclear whether it holds any potential for forming hard-rock rare-metal deposits.Recently,lithium-beryllium mineralized pegmatites have been discovered in the Jinshuikou area of East Kunlun,suggesting that it may become a potential rare-metal metallogenic area dominated by lithium-beryllium.This paper reports the geochemical characteristics and ages of layered granite intrusions in the Jinshuikou area that are spatially closely associated with the mineralized pegmatites and discusses their petrogenesis and prospecting significance.The lower part of the layered granite intrusions in the Jinshuikou area is composed of weakly peraluminous high-potassium calc-alkaline biotite monzogranites,while the upper part consists of highly fractionated and strongly peraluminous two-mica syenogranites,garnet alkali feldspar granites,and albite granites.LA-ICP-MS zircon and monazite U-Pb ages of the granites are 396～395 Ma and 396～391 Ma,respectively.Furthermore,these granites share similar Nd isotopic compositions with the eNd(t)values of-6.52～-4.48.Biotite monzogranites and two-mica syenogranites have similar whole-rock Pb isotopic compositions(208 Pb/204 Pb(t)=38.187～38.219,207 Pb/204 Pb(t)=15.627～15.652,206 Pb/204 Pb(t)=18.299～18.527)and zircon Hf isotopic compositions(εHf(t)=-6.25～+0.58).The lower and upper granites were both derived from a lower crustal source composed of Proterozoic rocks with minor juvenile crustal material.They are I-type granites formed in a postcollisional extensional tectonic environment.Li,Be,Nb,Ta and Sn were enriched during the magmatic evolution of the Jinshuikou layered granites.These granites,together with eastern Yuejinshan granites,constitute parent granites for potential rare-metal mineralized pegmatites.It is inferred that the southern and eastern parts of the Yuejinshan granite intrusion are potential areas for pegmatite-type Li-Be mineralization.The occurrence of Devonian Li-Be mineralization in the East Kunlun orogenic belt indicates that in addition to the Mesozoic era,the Paleozoic era also has significant mineralization potential for Li-Be ores along the northern Qinghai-Tibet Plateau.
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维普
