Studies On The Ore-forming Material Sources Of The Nanmushu Lead-zine Despoit In Mayuan Area,Shaanxi Province

Nanmushu deposit is located in southern of the Qinling orogenic belt,northern of the Yangtze plate,eastern margin of the Micangshan uplift.The ore-bearing strata is Sinian Dengying Formation brecciated dolomite and ore body is obviously controlled by strata,fracture zone.The mineral compositions are relatively simple.The main metallic minerals are sphalerite,galena,pyrite.The nonmetallic minerals are dolomite,quartz,barite,bitumen..And asphalt has close relationship with the lead/zinc in space.It takes the Nanmushu lead-zine deposit in shaanxi Ma Yuan area as the research object,mineralogy,petrology and geochemistry are used to analyze the geological characteristics,mineral characteristics,elemental geochemical characteristics and isotopic geochemical characteristics of the deposit.To analysis the sources of this lead-zine deposit ore-forming material,and to discuss the relationship between source rocks and hydrocarbon source rocks.The trace elements of sphalerite are characterized by high content of Zn and low content of Fe,and the content of Mn and In is low,which is consistent with that of MVT lead-zine deposit.Sphalerite,asphalt carbon isotope has a large negative value,showing a significant source of organic carbon.Natural asphalt kerogen carbon isotope indicates that the carbonaceous slate in the Cambrian Guojiaba Formation is related to the natural asphalt in the dolomite dolomite.And the S/Ni ratios to the asphalt indicate that most of them may transport from the Cambrian system.Layer in the surrounding rocks around the Pb,Zn and other ore-forming elements analysis results show that the Pb and Zn elements in the lower strata of the Guojiaba Formation are the highest.The ability of the Zn and Pb mineralization is most abundant in the strata of the GuoJiaba Formation,and the mineralization elements in the metallogenic elements are obviously depleted,suggesting that the ore-forming elements may have been migrated and may provide mineralization.The C-O isotopic results of dolomite and calcite show that the ore-forming fluids have a much lower?¹³C value than that of the ore-bearing rocks,suggesting that the carbon dioxide in the ore-forming fluids is the cause of the dissolution of the Sinian carbonate rocks and the origin of the ore-forming fluidsor through organic-rich strata.H-O isotopic composition implies that the ore-forming fluid may come from the bottom of the secretion of metamorphic hydrothermal fluid,in the process of upward migration with reaction of surrounding rock,substance and isotope exchange occurring the fluid in their process of migration may flow through the organic stratum which leads to its lower.The?³⁴S value of the sphalerite and galena suggests that the reduced sulfur cause the metal precipitation and mineralization may come from thermal degradation of organic matter and thermal reduction of the marine sulphate.The lead isotopic characteristics of sphalerite and galena show that there may be a certain relationship between the lead source in sphalerite and crystalline basement,the Dengying Formation and the Upper Cambrian strata.Results show the formation time of the ore is about 486.7±3.1Ma.The initial strontium isotopes at the time of ore formation indicate that the ore-forming material originates from the source region relatively rich in radioactive genes.Ore-forming fluids have flowed through the radiation-rich strontium,suggest that basal rocks-basement metamorphic rocks rich in radioactive strontium must be one of the ore source for the formation of deposits.But it is impossible to be a mixture of the Cambrian and Dengying Formation,more likely for the clastic rocks of lower Dengying Formation and the basement rock.In summary,this paper argues that the carbonaceous slate in the Cambrian group Guojiaba group is not only the main source of ore-forming material in the lead-zinc deposit,but also the natural bitumen of the dolomite.The dating of rubidium strontium isotopes in sphalerite is t=?486.7±3.1?Ma,and the mineralization time is close to that of the first stage oil reservoir.The metal mineralization shows a strong coupling with the reservoir."Nanzheng uplifted"makes the ancient reservoirs destroyed and makes ancient gas reservoirs and organic matter such as asphalt formed;at the same time makes Dengying Formation forming interglacial crushing to provides space for the migration and precipitation.Pyrolysis of CH₄ acts as a reducing agent to reduce the sulfate to provide reduced sulfur and lead mineral deposit.When the later tectonic movement produces migration channels,the Ore-forming fluids migrate along the channel up to the breccia zone in Dengying Formation and mixed with low temperatures water or sea water in shallow,lower the fluid temperature,higher the pH to cause the metal precipitation filling open space...