Geochemical And Metallogenic Fluid Characteristics Of Jiguanzui Cu-Au Deposit,Southeast Of Hubei Province

The Jiguanzui Cu-Au deposit is located in the southwest of Daye City,Hubei Province,which is the the typical skarn deposit in southeastern Hubei district Metallogenic belt,it is in the core of ore concentration area and the condition of mineralization is good.This paper is based on the detailed field geology survey and the study of indoor mineralization,Using the modern geochemical analysis technology,fluid inclusions microscopic measuring temperature,and through the electronic probe?EMPA?,laser ablation inductively coupled plasma mass spectrometry?LA-ICP-MS?technology,for its metallogenic source rock and the output characteristics of evolution,garnet and ore-forming fluid properties and evolution system studied.The main conclusions are as follows:1.The Jiguanzui Cu-Au deposit is related with Tonglvshan intrusive stock which located in the northwestern of Yangxin complex massif,its lithology are mainly quartz monzonite diorite porphyrite and quartz diorite porphyrite,its ore body exists in Triassic Daye formation in the contact zone and magmatite rock and carbonate rock xenoliths,ore bodies mainly cystic,lenticular,saddle,layered,between cryptoexplosive breccia type,depth gradually appear porphyry orebody.The ore mainly consists of metasomatism and crystalline structure,and the decomposition and crushing structure of solid solution are also developed.The main structure of ore is block,dip,strip and breccia.The alteration of the surrounding rock of the deposit is widely developed,which is closely related to skarn,gold mica,carbonation,green mud,petrifaction and mineralization.2.The REE distribution pattern of Jiguanzui deposit three of the granite are consistent,showing LREE enrichment,hree and LREE,part difference,part of the heavy rare earth flat,indicating the consistency of three magma sources,and are derived from the upper mantle or lower crust,and the uniform distribution pattern the world of similar rock.Jiguanzui skarn rock REE chondrite normalized patterns and similar rock,with LREE enrichment,hree characteristics,showed that the inheritance of origin,but showed great heterogeneity in REE and the change trend,show that the skarn metasomatic reaction after more complex.The distribution patterns of ore rare earth are diverse,and in general,there are obvious Eu anomalies and Tm anomalies,indicating that the formation of ore has more complex hydrothermal participation.3.Jiguanzui deposit skarn period is divided into early and late stage of skarn skarn stage.the typical transparent mineral rock of early skarn stage is garnet,diopside,late skarn stage is mainly composed of chlorite and epidote,The transparent minerals in the phase of the sulphide are mainly composed of quartz and calcite,Petrographic studies show that quartz sulfide phase inclusion density than skarn period is significantly larger,fluid inclusion types,mainly by the rich liquid gas-liquid two-phase fluid inclusions,gas rich gas-liquid two-phase fluid inclusions containing Daughter Minerals and form multiphase fluid inclusions,in addition to pure gas inclusions and a small amount of pure liquid fluid phase fluid inclusions.4.The metallogenic fluids of Jiguanzui Cu-Au deposit are mainly magmatic fluids,which are characterized by high temperature,high salinity and strong oxidization.The precipitation of magnetite in the skarn late stage leads to a significant reduction in the oxidation of the metallogenic fluids,and the main metal minerals such as copper and gold enter the fluid phase and are transported in the form of complex complexes.In the early phase of the quartz sulfide,the temperature dropped to a certain degree?about 350³75??precipitated in the form of sulfide,forming a large number of chalcopyrite,pyrite,porphyry,silver gold and so on.At the end of this stage,calcite and sphalerite gradually formed,and the fluid had medium to high temperature,high salinity and weak oxidation.It is gradually converted to reducibility.At the stage of late sulfides,it mainly formed low temperature minerals such as sphalerite and calcite.The temperature and salinity of the ore-forming fluid decreased significantly at this stage,and the phase continued to fall below the average temperature of the fluid to below 300.The hydrothermal ore forming process tends to end and enters the supergene period,mainly due to the uplift and denudation of the deposits and the destruction of ore bodies by tectonic activities.5.Jiguanzui deposit garnet is divided into three phases:the first phase of the light pink,fine and compact features,garnet content of more than 80%,annulus not development;the second stage is brown red,medium and coarse grain structure,euhedral degree is good,and with the production of microscopic geode,often producing a ring.The width of the homogeneous and non homogeneous complex;third garnet pink vein deposit produced in the fault zone,found in calcite veinlets with veins.The second phase ring of garnet was studied by electron probe and laser ablation plasma mass spectrometry?LA-ICP-MS?,the result shows that the Jiguanzui copper gold deposit for Calcium Aluminum Garnet Ring-andradite series,Grossular and andradite ratio had little difference,the contents of FeO and Al₂O₃ fluctuated from the inside to the outside,meanwhile,the content of the main component SiO₂ of the garnet is positively correlated with the content of CaO,which reflects the nature of its contact metasomatism.The distribution pattern of chondrite normalized REE garnet is relatively complex,generally show LREE enrichment,hree and LREE,in part of the left and right part of the heavy rare earth invasion of the inverted"V"type distribution pattern,but the distribution pattern of each point of garnet is obviously different,especially the homogeneity and heterogeneity of the more obvious changes rapidly in garnet,which reflects the dramatic changes in the external environment change of garnet,garnet is mainly reflected off for metasomatism.It shows that the formation of the deposit has undergone the process of oxidation-reduction-oxidation,which is consistent with the results of previous field observation.6.Two processes are responsible for the Cu-Au mineralization in the Jiguanzui deposit,including the magmastic process and the hydrothermal process.Generally,the ore-related granite is believed to be produced by gradual crystallization and differentiation of upwelling basic magmas derived from the enriched mantle.When the resedual magmas reached to shallower levels about 2 km depth from the earth's surface,the hydrothermal fluid were exsolved as a abrupt decrease in temperature and pressure.The exsolving fluids during water saturation can carry significant amounts of metallic elements like Cu and Au,and this stage is generally documented as the magmatic-hydrothermal trasition which represents the end of magmatic process and beginning of hydrothermal process.Three paragenetic sequence has been recognized in this deposit,including the prograde and retrograde skarn stages,followed by a sulfide stage.In the prograde skarn stage,the high temperature,high salinity,oxidized and weak alkaline magmatic-hydrothermal fluids interacted with the surrounding wall rock and generated anhydrosilicate alteration assemblages such as garnet and diopside.In the retrograde skarn stage,the early-precipitated garnet was usually overprinted by hydrosilicate alteration assemblages,with the formation of epidote and magnetite,and are cut by quarta-sulfide veins.This stage is characterized by a decrease of oxidation stage and ph in fluids,which lay the foundations for the precipitation of the main sulfide minerals.In the quartz-sulfide stage,with the progressive precipitation of chalcopyrite and pyrite,the fluids varied from weak oxidizing stage to the neutral stage.Lastly,calcite and sphalerite crystallized at low temperature,low salinity,and low density fluids and the ore-forming processes tend to be over.