| The Beishan lead-zinc deposit,located in the western margin of Nanling metallogenic belt,is one of the typical large-scale lead-zinc deposits in northern Guangxi.Its geotectonic location belongs to the southwestern margin of Jiangnan old land.This paper collects previous research data and consults relevant literature in northern Guangxi,and makes a thorough field investigation on the deposit.Based on the metallogenic geological background,geological characteristics,ore body morphology and ore isotope characteristics,the ore-controlling factors and ore-forming material sources of the deposit are studied,and the genesis of the deposit is further discussed.The main achievements obtained are as follows:1.The ore-forming structure types of ore bodies are divided into two types:one is karst type,the other is structural type,in which the No.I and II ore bodies belong to karst type,and the No.III ore bodies belong to structural type.The ore bodies are mostly layered,tubular,cystic and vein-like.The ore body morphology was evaluated accordingly.2.By observing the characteristics of hand specimens and the microscopic characteristics of ores,the Beishan lead-zinc deposit is divided into three metallogenic episodes and six stages of mineralization,namely,sedimentary-diagenetic episode?sedimentary-diagenetic stage?;Hydrothermal mineralization episode?pyrite stage,sphalerite stage,galena stage and pyrite stage?;and supergene oxidation episode?oxidation stage?.3 Isotope studies show that the sulfide value of the deposit varies from-3.84?+4.56,with an average value of-1.30,and concentrates near the zero value.It is believed that the sulfur element mainly comes from the sedimentary strata.The206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb ratio values of ores are 18.006?18.084,15.651?15.731 and 38.258?38.525 respectively,with an average value of18.043,15.688 and 38.437 respectively.Through the comparison of Pb isotopes,the points all fall near the average Pb evolution curve of the upper crust,indicating that the ore-forming metals have the characteristics of crustal origin and probably come from the basement.4.The Beishan lead-zinc deposit is controlled by three ore-controlling factors:strata,lithology and structure.The strata are mainly the Middle Devonian Donggangling Formation,and the lithology is mainly dolomite.Controlled by the structure of the study area,the ore bodies are mainly hosted by the structures beside the F4 fault,which are the interlayer fracture zone,interlayer fracture,paleokarst and small fissures.5.Under the background of regional tectonic evolution,the ore body morphology,metallogenic structure,isotope tracing and ore body evolution of the Beishan lead-zinc deposit are studied.It is inferred that the genesis of the deposit belongs to MVT type deposit,and the metallogenic age is from late Hercynian to early Indosinian epoch. |
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