Elements Geochemistry Of Ore-bearing Porphyry In The Bolong Copper Mine District, Tibet

The Bolong Copper deposit is one of the typical large-scaled porphyry depositwhich located in the Bangongco metallogenetic belt in the Bangongco-Nujiang suturezone south of the Qiangtang terrane.In this paper, the auther mainly talked about the geological background of theformation of deposits, the ore body and ore characteristics, wall rock alteration,andafter constant elements,trace elements and REE characteristics of the ore-bearinggranodiorite porphyry,tectonic setting of the ore-bearing porphyry being analyzed andthe element geochemistry beingsummarized.The results show that:The ore body of the Bolong copper deposits is buried-half buried,which is occurin the granodiorite porphyry and metamorphic sandstone of wall rocks which belongto Quse Formation in Lower Jurassic（J1q）.Porphyry copper ore body is an irregularcylindrical body.The structure of ore are manly veinlets-disseminated,vein, disseminated et al.Themain texture are self-crystals to semi-crystals, xenotopic,inclusion and coterminaltexture et al.Metallic minerals are manly pyrite,chalcopyrite et al; gangue minerals arequartz, feldspar etc. Element of production-grade are Cu, while Au,Ag,Ga and S canbe comprehensive utilizationed.The mine district is characterized by the strong potassium and potassiumsilicide.Chalcopyrite are enriched in the phyllic zone.We divided the metallogenicprocess into three stage named magma-advanced atage,hydrotherm ore forming stageand supergene stage while the hydrotherm stage is the most important ore formingstage.The ore-bearing granodiorite porphyry are gray, porphyritic texture, massive structure. The composition of phenocrysts of plagioclase, quartz and dark minerals andgroundmass mainly is felsic minerals. Rock with pyrite and copper mineralization.Ore-bearing granitic diorite porphyry is has a higher SiO₂（62.24%⁶9.41%）,K₂O/Na₂O（6.04～17.57）; AR is vary from1.52to2.82; σ is0.64～2.35;DI is form67.28to77.81and SI is8.51～15.94; τ is35.35～53.54,which showorogenic characteritics; The A/CNK of rock are greater than1.1which shows stronglyperaluminous characteristics.Rocks are characterized with high-K quality which belongs to shoshonitic seriesor K calc-alkaline series and ore-bearing porphyry is the sub-alkaline series.Ore-bearing porphyry with low Na2O content, higher K₂O/Na₂Oratios and higher A/CNK values （greater than1.1）, which indicated that the porphyry is S-type granitoids.ΣREE of ore-bearing porphyry is30.22×10^-6～94.28×10^-6, LREE/HREE ratios is5.29to12.44and light REE is enriched. the differentiation of LREE is strong butHREE is not obvious; weak positive Eu anomalies or no Eu anomaly.Rocks arerelatively enriched in incompatible elements （LILE） but depleted high field strengthelements （HFSE） and rock is with weak positive of Ti, Nb Ta.The ore-bearing porphyry with the characteristics of island arc and continentalarc environment and mineral assemblage with the characteristics of orogeniccharacter;constant element indicate that the porphyry formed in a continental arcenvironment;trace element indicate that ore-bearing porphyry formation in maturecontinental margin arc environment; REE characteristics closely related to the islandarc environment.The character of constant,trace elements and REE show that the Bolongore-bearing granodiorite porphyry has the characteristics of the general ore （copper）porphyry but the degree of differentiation is relatively high.By a compare of typical porphyry copper deposit, the Bolong and EI Tenienteore-bearing porphyry are with similar internal control factors,which suggesting a goodexploration potential for Bolong copper deposits.