The Geochemical Feature And Genesis Of Nuri Skarndeposit In Tibet

Nuri Skarn deposit,located in the South secondary delt of the east Gangdese Cu-Mo metallogenic belt,is an importantdeposit with several mental rich in.It is equipped with special mineralization,and aslo it is the largest tungsten deposit in the Gangdesemetallogenic belt.The discovery of this deposit is of great significance for explorationand study on the Gangdesemetallogenic belt.This passage choose the Nuri Skarn deposit as aresearch object,and with a focus on stratum, magmatite, mineral, structure of the deposit.The following results are achieved through research:(1) The strata are main Cretaceous and the upper Cretaceous-Paleogene in ore district.The depositexposedintermediate-acidic magamtic rocks which from the late Cretaceous-Oligocene,and aslo there are NE trending detachment fault which between the layers,the inheritedfault,nearly E-W trending,NW trending normal fault,and many derived fault.Ore mainly occurs in the skarn ore bodies in K1b4with the form of stratiform or stratoid.The deposit is controlled byNE trending detachment fault which between the layers and it’sinheritedfault.(2) The mineralization process of Nuri deposit can be divided into3times: the skarn stage, quartz-polymetallic sulfidestage, supergene oxidation stage. The skarn stageis further divided into3stages: early skarn stage, retrograde stage, oxide stage.The quartz-polymetallic sulfidestageis further divided into2stages: quartz-polymetallic sulfide stage, quartz-carbonate stage.The oxide stage of the skarn stageis the major period for tungsten mineralization.The main mineralized types is the skarn,aslo include some quartz vein type and a little veinlet disseminated mineralization. In horizontal and vertical direction, the type of skarn has a significance zoning.In horizontaldirection,the Cu mineralization become obviously attenuated from the south ore belt to north.but W and Mo mineralization become enhanced.In vertical direction,it is skarn mineralization of W and Cu t hat distributed in the earth’s surface.The skarn and quartz veinmineralization of Cu-Moand Cu-Mo-W are rich in deepside.In deeper side, The skarnmineralization of W become attenuated, The mineralization of Cu-Mo get much more enhanced,so is it in deepest side,and Vein or net vein quartz and feldspar-sulfide and quartz vein body-sulfide vein bodies can be found there.(3) The data of the lead isotope of the surrounding rock,magmatic rocks and metal sulfides in Nuri Skarn deposit shows that different age of magmatic rocks are contaminated by crustal material when they intruding. The data of metal sulfide suggest thatmetallogenic material mainly comes from intermediate-acid magma.Those data indicate that the lead come from orogenic belt, crustal material maybe come from crystalline basement of Lhasa block.(4) The data of major elements from thesurrounding rock and stratum show that theskarn in the deposit are rich in silicateminerals with aluminum, calcium and ironcontain in,and poor in Minerals about manganese and magnesium.It can be know from thosedata that andradite, bredbergite, diopside are the composition of the skarn.And the middle of the ore domain rich in diopside-garnet skarn,the north ore domain rich in garnetskarn.Whenskarn forming, limestone accepteda large number of SiO2in hydrothermalbrought from the outside world, and send a large number of Ca, Ti, Al, Mg, Mn, Feand other elements into hydrothermal.At the contact parts of the fluid and limestone replacement reaction,the garnet,diopside skarn minerals,etc was formed. The data of major elements from the magmatic rock show that quartz diorite, quartz diorite porphyry,granodiorite,quartz porphyry are belong to high-K calc-alkaline series which sames to magmatite in Gangdise90-95Ma ago.Tuff belongs to shoshonite series which sames to magmatite in Gangdise30-35Ma ago.Andesite and parts of quartzite, alterated in later period,belongs to calc-alkali series and the alkali basalt magma series.All magmatic rock belong toperaluminous sames.(5) The trace elements show that skarn and limestone get high Sr/Y. The spider diagram of quartz vein and quartz diorite porphyrite are common with each other.Thoseindicate that quartz diorite porphyrite has a direct effect on mineralization.The low Content of Zr and with Nb negative anomaly of magmatic rock in the deposit indicate thatin the process of magma rising with the earth’s crustjoin in.Beside,same to the Chengba deposit with the character ofadakite, the acidic magmatic rocks get high Sr/Y.(6) The data of REE show that the REE of the skarn is the same as ntrusive roc k.The formation of skarn in K1b has a direct relationship about carbonate formation-clastic rock and intrusive rock.K1b is closely related to mineralization，and E-K1d have acertain relationship with orebody，this is to be further proved.