Study Of Panlong Lead-Zinc Deposit Organic Mineralization In Guangxi

The combination of the west side of the Dayao Mountain and the Guizhong hollow is an important lead and zinc producing area in Guangxi,and the extensively developed Devonian carbonate layers generally contain organic matter.The regional secondary syngenetic fault is a ore-conducting structure,and the inter-layer fracture zone in the middle and lower strata of the Devonian is a ore-bearing structure.Minerals originate from the deep crust and have little to do with the middle and lower strata of the Devonian.On the basis of extensive collection of predecessor data and sampling surveys,the organic matter of ore and surrounding rock in the Panlong lead-zinc mining area are studied.The main-trace element geochemical analysis is auxiliary method.The following findings are obtained.The analysis shows that the sample saturated hydrocarbon chromatogram has a bimodal type,the ?C_21-/?C₂₂₊ratio is larger,(nC₂₁+nC₂₂)/(nC₂₈+nC₂₉)range from0.453 to 2.847,and the ratio of regular sterane/17??H?-hopane is 1.0 and lower,which indicate that the organic matrix of the mining area is a mixed source of terrestrial and aquatic,and land-based plants are the main source.The values of OEP and CPI range from 0.764 to 1.253,indicating that the organic matter after diagenesis comes from carbonate and mudstone.The two parameters Pr/C₁₇ and Ph/C₁₈ are about 0.6 and the Ts/Tm ratio is greater than 1.The hopane C₃₂ 22S/?22S+22R?is between 0.553 and0.604,and the??-moretane/??-hopane ranges from 0.151 to 0.215,the average ratios of C₂₉ sterane 20S/?20R+20S?and??/???+???are 0.442 and 0.460 respectively.The rearrangement of regular sterane is not obvious.These characteristics indicate that the organic matter in the mining area has reached Mature stage,but has not yet entered the mature stage.The analysis also shows that the main rocks in the Panlong lead-zinc mining area are obviously enriched in elements such as As,Ba,Sb,Sr,Tl et al,and relatively depleted in elements such as Be,Cu,Ga,Hf,Nd,Rb,Sc,Ta,Tb et al,the ratios of U/Th ranges from 1.98 to 13.69.The Zn/?Pb+Zn?ratio of the ore sample is close to 1.These characteristics suggest that the Panlong deposit occurred exhalative activity.The REE content of the main rock in the mining area is low,and the average value is only18.174?g/g.LREE is more concentrated than HREE and has a stronger differentiation.Mineralized hydrothermal water has the characteristics of mixing hot water with seawater.The chromatographic peaks of saturated hydrocarbons in the test samples are uplifted,and the decane had the distribution characteristics of C₂₉>C₂₇>C₂₈.The peak shape curve of the ascending hopane C₃₁^C₃₅ is smooth on the mass chromatogram.The gamma wax index of organic matter in the sample ranges from 0.151 to 0.215.The homohopane index C₃₅/?(C₃₁-C₃₅)ranges from 0.040 to 0.090.Two types of geochemical parameters suggest that the ore-forming environment is a reduced-weak oxidizing,low-salt and shallow water environment in Panlong Lead-Zinc Deposit.In addition to,organic matter is degraded by microorganisms to some extent.According to comprehensive analysis,this paper concludes that organic matter can promote the transition from an early relatively open ore-forming environment to a reducing state under the influence of jet hydrothermal fluid.During this period,organic matter can also be complexed with metal cations such as lead and zinc to migrate minerals to favorable metallogenic sites.During the jet deposition period,the thermochemical reduction of native organic matter and sulfate or the thermal decomposition of sulfur-containing organic matter produces H₂S which causes most minerals to precipitate as metal sulfides.During the transformation period after consolidation and diagenesis,the organic hot fluid rich in reduced sulfur meets with the ore-bearing fluid,causing precipitation of some metal sulfides.