On The Mineral Composition And Gold Occurrence State Of The Shuanghuwan Gold Deposit At Nalan,Simao County,Western Yunnan

In the"Sanjiang"tectonic region of western Yunnan,SW China,there are multiple periods of large-scale orogeny and metallogenesis.Dapingzhang and Dazhonghe volcanic and intrusive systems represent typical arc-related igneous events records the Proto-Tethys Ocean subduction.Among them,the famous Dapingzhang VHMS Cu deposit is produced in the Dapingzhang volcanic and intrusive system,and is the"Dazhonghe volcanic and intrusive system",which also represents the Proto-Tethys subduction-collision tectonic magma event,accompanied by the similar mineralization?Obviously,there is an urgence to anatomy and answer.From 2011 to 2013,Simao District Shanshui Copper Co.,Ltd.carried out systematic geological exploration of"Dazhonghe Volcanic Rocks"and achieved major discoveries and breakthroughs in gold ore prospecting.A concealed independent Au ore body,Shuanghuwan Au polymetallic deposit,was found in the deep,with a medium scale.However,at present,the basic geology and geological research of the deposit are still in the initial stage,especially the understanding of the mineral composition of the deposit and the occurrence state of gold is relatively weak,which limits the understanding of the genesis of the deposit and the summary of the ore-forming rules,and makes it more difficult to establish the genetic connection with Dapingzhang Cu deposit.Therefore,on the basis of field geological profile measurement,surface structure-alteration-lithologic mapping and borehole geological logging,the geological characteristics of the deposit are comprehensively identified,and the ore mineral composition,the chemical characteristics of main minerals,occurrence state of gold minerals and other aspects are emphatically analyzed to discuss the genetic types of the deposit.The main achievements and understandings of this research are as follows:1.The two known ore body groups of Shuanghuwan Au deposit can be divided into three types of mineralization and two major metallogenic series.The three mineralization types are:1)large vein and large lenticular independent Au ore bodies;(2)small vein and small lenticular Au polymetallic ore bodies,including Au polymetallic ore bodies,main Cu ore bodies and main Zn ore bodies;3)massive sulfide Cu-Fe ore body shows the characteristics of being reformed by later tectonic action.The above three types of mineralization can be classified into two major metallogenic series,namely:1)ore bodies related to volcanic exhalation-sedimentation mineralization,including massive sulfide Cu-Fe ore bodies and small vein and small lenticular ore bodies(mineralization elements are different Au-Cu-Zn-Ag combinations),both of which show the output characteristics of layer+vein mineralization combinations;2)Orebodies related to epithermal mineralization are mainly large vein and large lenticular independent Au orebodies.2.The mineral composition of the ore deposit is complex and diverse,including Calaverite(Cav),oblique Calaverite(Krt),tellurium bismuth ore(Teb),tellurium nickel ore(Mel),Altaite(Alt),tellurium mercury ore(Mgn)in telluride,and natural tellurium(Te),natural gold(Au),natural silver(Ag),Native copper(Cu)in natural mineral elements.Sulfides include pyrite(Py),chalcopyrite(Ccp),galena(Gn),sphalerite(Sp),tetrahedrite(THr),arsenopyrite(Apy),oxides include Shi Ying(Qtz),limonite(Lm),rutile(Rt),silicate minerals include sericite(Ser),kaolinite(Kln),pyrophyllite(Prl),chlorite(Chl),plagioclase(Pl),potash feldspar(Kfs).Phosphate minerals has apatite(Ap),monazite(Mnz),carbonate minerals calcite(Cal),sulfate minerals barite(Brt),halides fluorite(Fl),potassium salt(Kcl)etc.3.The gold mineralization can be divided into five stages:sericitization stage(?),quartz-pyrite stage(?),quartz-polymetallic sulphide stage(?),pyrite-telluride stage(IV)and quartz-carbonate stage(V).Among them,gold mineralization is mainly developed in pyrite-telluride stage(IV).4.Au in the ore mainly occurs in the independent mineral—Calaverite(its theoretical chemical formula is Au Te₂),a small number exists in the form of natural gold,and a very small number occurs in sulfide,oxide,silicate,carbonate,sulfate and halide.The first two are single,conjoined visible wrapped gold and fissure gold,while the other are lattice gold or isomorphism gold or enclosed wrapped particle gold.5.According to the comprehensive analysis of mineral composition of ore,occurrence state of Au and genetic information traced by trace elements of pyrite minerals,and by comparing typical epithermal deposits and typical Te-Au deposits,it is determined that Nalan Shuanghuwan Au deposit is a low-sulfur epithermal Te-Au deposit,which may represent a brand-new mineralization type in the south-central section of"Sanjiang"in southwest China.6.The deposit is located in the geodynamic background related to the subduction of Proto-Tethys Ocean.The ore-forming materials come from deep magma melt.Its mineralization is a response to the subduction,accretion and orogeny of Proto-Tethys Ocean.Together with Lancang Huimin Fe deposit and Dapingzhang Cu polymetallic deposit,it forms a complete original Tethys accretion orogenic metallogenic series,namely,Huimin Fe deposit in pre-arc Accretionary wedge,Nalan Shuanghuwan Te-Au polymetallic deposit in volcanic magma arc and Dapingzhang Cu polymetallic deposit related to back-arc basin.7.This metallogenic knowledge can provide important basis for regional resource potential evaluation and prospecting.