The Characteristics And Ore-bearing Property Evaluation Of Ordovician Granite In Lincang,Western Yunnan

In Lincang composite batholith which is widely distributed on the west side of the South Lancang River Belt,a orthoclase granite pluton was identified from the Cenozoic pluton which was divided by the predecessors,the zircon U-Pb isotopic dating results show that this pluton was emplaced in 464.2±3.6Ma?474.1±1.6Ma(Ordovician),which represents the early Paleozoic magmatic activities in this area,and reflects the magma evolution record of Proto-Tethys in Lincang composite batholith.The pluton has the characteristics of high silicon(73.38%?77.34%),rich Kalium(K₂O/Na₂O=0.92?1.66)and strong aluminum(A/CNK=1.52?2.1),by the CIPW standard mineral calculation,all the samples of corundum content are greater than 1%,the differentiation index DI=90.7?94.97.All samples show that Lincang Ordovician granite has high REE content(average 215.8×10^-6),obvious differentiation characteristics between Light and Heavy rare earths,LREE/HREE=3.92?9.45,La/Yb_N=3.96?12.07,?eu=0.09?0.29,all samples have similar distribution characteristics in the trace element spider diagram,enriched in LILEs and depleted in HFSEs,remarkably positive Pb anomalies,loss Ba compare to Rb and Th.The above characteristics show that Lincang Ordovician granite is high-K calc-alkaline and strongly peraluminous s-type granite.In this paper,author selected the Pinghe early Paleozoic granite pluton in Paoshan and the middle-late Triassic granite batholith in Lincang as comparison,the results show that the Pinghe early Paleozoic granite pluton and Lincang Ordovician granite pluton have distinct different magmatic source areas,Pinghe pluton mainly originates from the metamorphic sand cuttings rock,and the Lincang Ordovician granite mainly originates from the metamorphic argillaceous rocks.Compared with Lincang mid-late Triassic granite,Lincang Ordovician granite and Pinghe early Paleozoic granite were less contaminated by mantle-derived materials.Related other early Paleozoic magmatic activities and tectonic events whice have founded in this area,indicated Lincang Ordovician granite pluton is likely produced by the eastward subduction of Proto-Tethys ocean in the background of spreading,related to a partial extension(such as arc after stretching)caused by subduction,reflecting during 480?420Ma in this area,exists effection of Proto-Tethys ocean eastward subduction.At the same time,Lincang composite batholith can be reformulated,that is,Lincang composite batholith is formed by polyphasic intrusion,whose main body is middle-late Triassic granite,and Permian,Yanshanian period and Ordovician granite as supplements.In addition,through comparative study,this pluton has better mineralization conditions of kaolin and ion adsorption type rare earth ore.