Regarlarities Of Mineralization-Alteration Lithofacies Zoning And Prospecting Direction In The Baixiangchang Pb-Zn-Ag-(Cu-Au)Polymetallic Deposit In Western Yunnan

The Pb-Zn-Ag-(Cu-Au)polymetallic deposit in Baixiangchang is one of the Himalayan porphyry-type Au polymetallic deposits in the Jinshajiang-Ailaoshan alkali-rich porphyry belt in the Sanjiang Tethys metallogenic area.This deposit is adjacent to the Beiya super-large Au polymetallic deposit,the Machangqing Cu-Mo-Au deposit.By fine analysis of typical mineralization-alteration types and their zoning characteristics,combined with the analysis of rock(ore)main-trace(rare earth)elements,fluid inclusions and LA-ICPMS,to invert the physical and chemical conditions of the process from migration of ore-forming fluid to precipitation and enrichment.The mineralization alteration zoning rule and its forming mechanism are revealed,the mineralization-alteration zoning model of porphyry polymetallic metallogenic system is established comprehensively,and the prospecting direction in this area is put forward,which provides an important basis for the prospecting and exploration in the depth and periphery of the deposit.Main research achievements and understandings are as follows:1.Through carrying out detailed geological survey,systematic rock ore identification and rock geochemical analysis of alkaloid-rich porphyry in the mining area,the result of the test indicates,the metallogenic rock mass of the deposit is a quartz monarchic porphyry intruded by rock branch and dike.It has the characteristics of high potassium(K₂O/Na₂O=1.06?2.28),alkali-rich(K₂O+Na₂O=8.08?10.98)and peraluminous.The analysis of trace and rare earth elements shows that the rocks are relatively enriched with large ionic lithophile elements(LILE)such as Rb,Ba,Sr and K,while the high field strength elements(HFSE)such as Ta,Nb,Ce,P and Ti are relatively deficient,?REE is higher,LREE enrichment and HREE loss obviously,has the high?LREE/?HREE and(La/Yb)_N ratio,has the characteristics such as weak Eu negative anomaly,there are both from the composition of the earth's crust and its source from the composition of the mantle,as the crust-mantle mixed source.2.The skarn Fe-Cu-(Au)mineralized bodies were first discovered in mine tunnel PD7-3 and PD2-3 by using large scale altered lithofacies mapping method,and the zoning of skarn mineral assemblages was relatively complete:From the inner contact band to the outer contact band,the sequence of mineral symbiotic associations is as follows:Diopside-garnet?Epidote-actinolite-hornblende-magnetite?Chalcopyrite-bornite-(molybdenite-gold)-pyrite-quartz-fluorspar-calcite,of which garnet is mainly calcium aluminum garnet,followed by calcium iron garnet.3.According to the vein puncture relations,ore fabric,alteration mineral assemblage characteristics,the diagenetic mineralization process of ore deposits including magmatic hydrothermal period(?)and oxidation leaching period(?).The former can be divided into six stages:(1)Diopside-garnet skarn stage;(2)Actinolite-magnetite stage;(3)Pyrite-chalcopyrite stage;(4)Quartz-chalcopyrite-pyrite stage;(5)Galena-sphalerite stage;(6)Calcite stage.The quartz and calcite produced in(2)Actinolite-Magnetite stage?(5)Galena-sphalerite stage stages were selected to carry out a systematic study of fluid inclusion lithography,development of gas liquid two phase(?-type),pure liquid(?-type),containing CO₂ three-phase(?-type),jing(?-type),pure gas phase(?-type)and melt inclusions(?-type),and extensively?and?inclusions.The result of the temperature measurement indicates,from porphyry type Cu-(Mo)-Au mineralization to skarn type Fe-Cu-Au ore body to hydrothermal vein type Pb-Zn-Ag(Au)ore body,there is an evolution process of high temperature,medium-low salinity?medium-high temperature,medium-low salinity?medium-low salinity.4.Aiming at the zoning rule and zoning mechanism of mineralization-alteration,the typical PD2-2,PD7-3and 2000m middle sections of the tunnel are selected to carry out the key analysis of altered mineral assemblage,altered rock fabric and mineralization-alteration zoning.It is found that the mineralization-alteration zoning of the deposit is clear and complete.From the metallogenic rock mass to the surrounding rock of the outer zone,the alteration(mineralization)type combination is as follows:Biotitization-potassic feldspathization(molybdenite mineralizatio)?Silicification-sericitization-pyritization(molybdenite(a little)-gold-chalcopyrite mineralizatio)?Propylitization?Skarnization-silicification(magnetite-chalcopyrite-gold-pyrrhotite mineralizatio)?Marbleized-silicification-pyritization-calcitization(galena(silver)-sphalerite)?Kaolinization(gold).The combination of alteration types corresponds to the combination of mineralization types in turn,indicating that hydrothermal alteration is closely related to mineralization.Based on this,the mineralization-alteration zoning model of the deposit is established:K-silicate zone(?)?Quartz-sericite-pyritization zone(?)?Propylitic zone(?)?Skarnization zone(?)?Marbleization zone(?)?Argillization zone(?).The mineral symbiotic association is as follows:Kf+Bit+Mol(?)?Ser+Qz+Py+Cp+Ng+Mol(a little)(?)?Ep+Chl+Py(?)?Di+Grt+Hbl+Ep+Act+Cal+Qz+Fl+Py+Mt+Ng+Mol+Cp+Bn+Pyr(?)?Cal+Qz+Py+Gn+Sph+Ng+Nsl(?)?K l+Ng+Cal+Py(?).5.From altered porphyry?porphyry type copper-gold ore?diopside-garnet skarn?skarn type magnetite ore?skarn type copper-(molybdenum-gold)-pyrrhotite?hydrothermal vein type lead zinc silver(gold)ore?marble,the Eu and Ce features are in order:weak Eu negative anomaly and no Ce anomaly?weak Eu negative anomaly and Ce positive anomaly?weak Eu positive anomaly and weak Ce negative anomaly?strong Eu positive anomaly and weak Ce negative anomaly?weak Eu positive anomaly and Ce negative anomaly?weak Eu positive anomaly and Ce negative anomaly?weak Eu negative anomaly and Ce negative anomaly?weak Eu negative anomaly and Ce negative anomaly?weak Eu negative anomaly and Ce negative anomaly?weak Eu negative anomaly and Ce negative anomaly?weak Eu negative anomaly and Ce negative anomaly It indicates that the metallogenic environment has undergone an evolution from a closed reduction environment to a relatively closed strong oxidation environment to an oxidation environment.At the same time,Quartz monzonite porphyry,porphyry type copper and gold ore and diopside-garnet skarn Y/Ho ratio are similar,there are similar ore-forming material sources.Skarn type magnetite has similar Y/Ho ratio with copper-(molybdenum-gold)-pyrrhotite,and its mineral source is consistent.The Y/Ho ratio of hydrothermal vein type lead zinc silver(gold)deposits is similar to that of marble,and there are similar sources of ore-forming(rock)materials,suggesting that the deposit has ore-forming materials from different sources,which provides important evidence for the study of mineralization.6.Based on a comprehensive study of mineralization-alteration zoning rules,fluid inclusions,the physical and chemical environment of each mineralization-alteration phase and the variation rules of mineralization-alteration elements were identified,and the comprehensive evaluation index and mineralization-alteration lithofacies zoning model were established.Based on the mineralization-altered lithofacies zoning model,ore prospecting markers were screened,and the ore prospecting target area was comprehensively delineated by combining with the research results of physicochemical exploration.The model plays an important role in guiding the prospecting direction of the deep and peripheral ore deposits,and is of great significance in the exploration of the same type of ore deposits in the"sanjiang"tethys metallogenic region.