| The Lala Copper Deposit in Huili County,Sichuan Province is an important large-scale copper polymetallic deposit in southwestern China.Its regional geodetic structure is located at the southwestern end of the Yangtze Plate and in the middle of the Kang-Dian platform.Lala Copper Mine,as the largest copper mine discovered in Sichuan Province,is also the largest copper mine mining and production mine in Sichuan Province.Because of excessive and unreasonable mining,the country has designated it as a crisis mine.Therefore,it is the primary task to increase the research level of the Lala copper deposit,search for alternative minerals,and deepen the exploration and definition of its metallogenic information.Therefore,this article conducts deposit research in this context.In this paper,the regional metallogenic geological conditions of the Lala copper deposit,the geological characteristics of the ore body,the characteristics of the fluid inclusions,the isotope geochemical characteristics,etc.were studied.The genesis model of the deposit was discussed and the following knowledge was obtained:1.The area to which the Lala Copper Mine belongs is strongly affected by the structure,and the tectonic movement also has complex and diverse characteristics,which is manifested as a composite superposition of east-west and north-south directions,with various faults and fold structures developed;And has the characteristics of multiple stages and multiple cycles,divided into Jinning cycle and Huali-Indosinian cycle;the Lala copper deposit was formed in a strong regional metamorphism.The Lala deposit is located in this volcanic-sedimentary metamorphic rock,the degree of metamorphism reaches high green schist facies.2.The main ore-bearing strata of the Lala Copper Mine are located in the middle and lower sedimentary metamorphic rocks of the Taihe Formation in the estuary community.The ore-bearing lithology is fine bicornitic porphyry.Gradual integration contact with surrounding rock,stratum control characteristics are obvious.The main mineral components are magnetite,chalcopyrite,pyrite,etc.3.The deposit has undergone complex tectonic activities and regional metamorphism in the process of mineralization.The ore structure is complex anddiverse,and the automorphic-semi-automorphic-other-shaped grain-like structure,metasomatic residual structure,inclusion structure and block Structure,breccia structure,vein-reticulate structure,etc.;strong alteration of surrounding rock occurs at the same time,mainly including biotization,silicification,carbonateization,etc.4.According to the inclusion test,it is found that there are liquid inclusions,pure liquid inclusions,gas inclusions and child-bearing mineral inclusions.Pure gas inclusions are rare.Experiments on the physical characteristics of typical gas-liquid inclusion samples were conducted to measure the homogeneity and freezing point temperature,and the salinity,density,and pressure were calculated,and the metallogenic depth was roughly estimated.Based on this,it is inferred that the salinity of the Lala copper deposit and the ore-forming fluid are relatively high.At the same time,new fluids may be introduced in the later period,resulting in a difference in salinity concentration,which is consistent with the characteristics of the deposit formation temperature and wide pressure range.5.The H-O isotope study found that the medium water in the ore-forming fluid in the metamorphic ore-forming period was mainly metamorphic water,and the ore-forming fluid in the hydrothermal ore-forming period evolved from magmatic hydrothermal fluid to atmospheric precipitation hydrothermal fluid.The S source of the La copper deposit is mainly mantle sulfur sulfide;the lead isotope composition implies that lead has mixed source characteristics;the Pb of the La La copper deposit originates from the upper crust environment and the contaminated environment between the upper mantle and the lower crust.6.Based on the above research,it is inferred that the genetic model of the Lala copper deposit is a deep source-multi-stage composite superposition model with multiple stages and multiple effects:Paleoproterozoic initial ore source formation period(?1.7Ga): due to plate extension,the Kang-Yun Platform produced continental rifts,and molten hydrothermal fluid from the mantle and crystalline basement upwelled to form fine bicornitic porphyry and albite;meanwhile Intrusive volcano-sedimentary rock forms diabase;three cycles in the next stage to form ore-forming strata of the Hekou Group.From the late Mesoproterozoic to the Neoproterozoic main ore-forming period(?1.0Ga),the oceanic crust was punched into the mantle to take out the basalt magma and separate out the ore-forming materials.After entering the estuary group,the surrounding rock broke into breccia due to the pressure difference.Rock-type ore,and due to the reduction of temperature and pressure,the ore-forming materials are quicklyunloaded and precipitated to form the estuary formations based on molybdenite,chalcopyrite,fluorite and calcite(carbonate minerals).Neoproterozoic metamorphic hydrothermal transformation in the ore-forming period(700?900Ma): The Kang-Dian rift was initially formed,and the squeezing caused the asthenospheric mantle to move upward while bringing out part of the molten basic magma into the rift to form The gabbro diabase veins,broken breccias form ore-bearing breccias;the mantle plume magma migrates and differentiates to form ore-rich hydrothermal fluids,and alternates with the surrounding rocks to form chalcopyrite and molybdenite-rich veins.7.In summary,the author believes that the Lala copper deposit has the characteristics of the typical IOCG type metallogenic age,metallogenic environment,magmatic activity,crust-mantle effect,so it is judged that the Lala copper deposit is an IOCG type deposit. |
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