Genesis Of The Lamo Zn-Cu Deposit,Nandan,Guangxi

The LamoZn-Cu deposit is an important deposit of Dachang ore field located at the middle segment of Danchi metallogenic belt.Based on the summary and analysis of predecessor research results and field geological survey,using a variety of analytical testing methods,this paper makes a study of the deposit geological feature,trace elements and REE of rock and pyrite,chronology of molybdenite,comparing the feature of geochemistry,source of ore-forming materials,ore-forming fluid and the age of ore-forming.We explored the relationship of two types of ore bodies,and then give a reasonable explanation about its genesis.The main results and conclusions obtained were as follows:(1)By observing two types of ore bodies under the mine well,we kown metal mineral combination of stratiform and vein ore bodies are similar,including pyrite,sphalerite,chalcopyrite,pyrrhotite,arsenopyrite and a bit molybdenite.Vein ore has mainly brecciated structure and disseminated.Stratiform ore has mainly massive structure and banded structure.Based on the field geological survey,this thesis determines its wall rock alteration has mainly skarnization,silicification,marbleization,tourmalinization,limonitization.(2)The geochemical characteristics and composition of trace elements,REE of two types of ore bodies of pyrite are similar.The result shows their source and character of ore-forming fluids are similar.By combining previous research about fluid inclusions and H-O isotope characteristics in the Lamo Zn-Cu deposit show that the source of ore-forming fluid was mianly derived from magmatic water,but in late stage,it could be mixed with atmospheric precipitation.The fluid is high in chlorine in medium-high temperature at comparative reducing environment.Comparing the geochemical characteristics of trace element,REE of Longxianggai pluton,we can kown they have close relationship.The composition of two types of ore bodies of S,Pb isopote are similar.The result shows their source of ore-forming material is similar.The source of ore-forming material was mainly derived from mixture of crust-mantle materials.(3)The Re-Os dating of the molybdenite samples from quartz-vein type ore yields a Re-Os model age ranging from 91.36±1.47 to 93.27±1.53 Ma.The Re-Os dating of the molybdenite samples from skarn-type ore is 90.97±1.74 Ma.The ore-forming ages both quartz-vien and skarn type ores are identical within error,and they may belong to the same metallogenic period.The Re-Os isochron age of the smples is 91.55±0.67.The result is close to the Longxianggai biotite granite zircon LA-ICP-MS U-Pb age(91.63±0.28Ma).The above results show that the formation of Lamo Zn-Cu deposit was genetically associated to that of the Longxianggai pluton.(4)Lamo Zn-Cu deposit is formed in Devonian carbonate strata,and the Longxianggai pluton provides ore-forming materials and fluid,and is magmatichydrothermal skarn deposit.Based above,its metallogenic model is established,including deep contribution,vertical migration,lateral metasomatism.