Elemental Geochemical Characteristics And Geological Significance Of The Jialu Formation In The Ore-bearing Strata Of The Copper-gold Polymetallic Deposit In Southeastern Guizhou

With the gathering and collision of Cathaysia Landmass and Yangtze landmass during the middle Neoproterozoic,wide and major Wuling orogeny occurred in the Jiangnan Orogenic Belt,forming South China plate.Afterwards,with the splitting of South China Plate,the east of Guizhou and its adjacent areas showed high north(west)and low south(east),with the paleogeographic pattern from the land to shallow sea gradually,developing deposition in different phase zone of the same rifted sedimentary basin,namely Banxi Group,Xiajiang Group and Danzhou Group divided in Hunan,Guizhou and Guangxi Province(district).At present,dating data are limited to deposition record between 820 and 760 Ma.Jialu Formation for Xiajiang Group in the southeast area of Guizhou during the Precambrian System was composed of Jialu Formulation I section and Jialu Formulation II section,with occurrence of various copper-gold-polymetallic deposits.On the basis of previous researches,the Paper provided field geological investigation and research on element geochemistry characteristic for Jialu Formulation to analyze geological significance such as its original rock type,original rock source,structural environment and oreforming instruction of intra-class occurred deposit.The following understandings are obtained:(1)After analyzing major elements,micro elements and rare earth elements for stratum in the Jialu Formation,the original rock of its schist,phyllite and metasandstone is argillaceous sedimentary rock.The original sedimentary rock sources are multisource,mainly from felsic source area of Detrital source in stable structure type.Combined with graphic analysis of Co/Th—La/Sc and La/Th—Hf,substance in the source area for sedimentary original rock of metamorphic rock in Jialu Formulation is felsic— acid arc volcanic rock of continental island,and tectonic setting is passive continental margin.As ore-bearing stratum of copper-goldpolymetallic deposits,the original rock of argillaceous sedimentary rock of Jialu Formulation is relatively dense,and can be taken as retaining layer and geochemical barriers.It may provide necessary retaining conditions for enrichment and deposition of metallogenic materials.(2)CIA distribution characteristics show that substances in the source area of the original rock of metamorphic rock in Jialy Formulation may be subject to strongchemical weathering under damp and hot conditions.ICV<1.0 shows that its original rock contains lots of clay minerals,and maturity of the original rock is higher.Combined with graphic ICV—CIA indicators,it is judged that the original rock should be the product under the strong chemical weathering under the first deposition process.(3)Structure in the bare land of Jialu Formulation is complex,and stronger metamorphism and tectonics destroy the original stratum.Decollement zone of detachment structure and secondary folding(anticline)shaft generated by it and faults,joints,fractures and fracture zones become the channel for the transfer of ore-forming hydrothermal water.Beneficial part of its structure become the ore-bearing place of ore-forming hydrothermal water.Through content test for main ore-forming elements of rock,it can be obtained that rock association in Jialu Formulation has higher background values of ore-forming elements such as Fe-Cu-Pb-Zn through,so Jialu Formulation may have the potential to provide a large number of metallogenic materials for corresponding deposits as the ore-bearing stratum.