The Metallogenic Model And Prospecting Of The Shangmanggang Gold Deposit, Luxi Area, Yunnan

The Shangmanggang gold deposit is located in Gaoli-Gongshan tectonic-magmatic metallogenic belt,western Nujiang river within the "Three-River region".It was the first Carlin-type gold deposit found in the neighboring area between Yunnan and Burma.The Gaoli-Gongshan metallogenic belt located in the "Three Rivers" tectonic-magmatic belt of western Yunnan and strikes north-south,and iron,copper,lead,tungsten,tin,gold,silver and polymetals mineralization occurs.Therefore,it should become one of the key mineral resource development areas.However,duing to the poor work on the basic geology and mineral exploration in this belt during the past years and recently,the proven mineral resource is far less than the predicted mineral potential.Now,it is still unclear for the prospecting target in this belt as well as beyond this region and not sure how much mineral resources and resource bases in this region.The previous geological work indicated that the deposit in this belt is mesothermal type deposit strictly controlled by the unconformity.And or laterite type gold deposit is the key target in this belt that confined the further exploration.Therefore,it is significant valuable for applying the new prospecting theory,new method and new technique to the mineral exploration in the most complex area of this "Three-River" belt.Through the systematic and detailed study on the Carlin-type Shangmanggang gold deposit and the reddish clay-typegold deposit,it will help to identify the ore-controlling conditions and the polymetals mineralization enriching rules,analyze and summarize the relationship between various of ore-controlling factors and the mineralization process,re-observe and analyze the temporal and spacial deposition process of gold deposits(orebodies),integrity and build the gold deposit model.Further more,it will guide outlining of the prospecting potential in the deposit area and the surrounding areas.This not only deepens the newly geological cognition for this type of gold deposit,but also provide a typical example for discovering and studying this kind of Carlin type gold deposit in "Three Rivers" belt,and widen prospecting routes and exploration plan.As a result,it will increase the potential resources in the deposit area and the surrounding areas in this belt.The geological characteristics,mineralogy,trace elements,rare earth elements,stable isotope geochemistry and fluid inclusions of different types of gold deposits in the Shangmanggang gold deposit area was studied respectivly on the basis of recognizing regional metallogenic background in this paper.Based on the summarization of ore-controlling rules,the metallogenic process was analyzed systematically also,and the metallogenic model of gold deposits was built.After applying multi-prospecting techniques for the studied area,such as X-fluorescence measurement,γ-energy spectrometry measurement,radon gas measurement,geo-electrochemical and geochemical survey,the author conducted the metallogenic prognosis in the Shangmanggang gold deposit area as well as its surrounding areas.Furthermore,the author proposed potential prospecting areas and preferred prospecting target areas.The research achievement and conclusions are as follows:1.The Shangmanggang gold deposit is located in the secondary extensional tectonic unit within active tectonic conversion area,eastern edge of the collision and conjunction between Gondwana continent and Euro-Asia continent,which is part of the Luxi gold mineralization zone,middle part of Longling-Ruili fault zone,that is located in the southern part of Gaoli-Gongshan gold-silver polymetals mineralization zone,northweast edge of the Chanbang terrain.Since Mesozoic and Cenozoic times,this area was formed to the Mesozoic-Cenozoic fold zone or overriding zone or active structural zone along edge of the continent due to the continuous intensive pushing,colliding,subducting and orogenesis of the India continent to the Euro-Asian continent,locally it was evolved into the intra-continent meta-terrain.2.The formation and evolution of this intra-continent orogenesis belt not only depends on the collision and continuous squeezing of Cenozoic India plate into Euro-Asian plate,but also is closely associated with main tectonic control of Late-Paleozoic Tethys ocean basin evolution.Therefore,the unique dynamic process in Late-Paleozoic and Cenozoic times results in the formation of significant tectonic setting which controls Gaoli-Gongshan gold-silver multi-metals mineralization zone,and thus forms preferred ore-forming conditions for the Carlin-type,Reddish Clay-type,ductile-shear zone type and modern hot spring type gold deposits in this belt.3.Main gold deposit types are Calin-type and Reddish Clay-type in this deposit area. From characteristics of trace elements and REE geochemistry of gold deposits,it showed that the reddish clay-type gold deposit is derived from the Carlin-type gold deposit,i.e.,the representation of Carlin-type gold orebody in the oxidized zone,both are closely associated. Based on the systematic study on this reddish clay-type deposit,it was found that this type of gold deposit has lots of similarity with the worldwide so-called "Laterite-type" gold deposit,but there is still big difference between these two kinds of gold deposits.Therefore, in this paper,the author names this kind of gold deposit after the reddish clay-type gold deposit in order to reflect its specific characters.4.On the basis of summarizing systematically general characteristics of Carlin-type gold deposits in the western USA and Yunnan-Guizhou-Guangxi gold triangle areas and Sichuan-Gansu-Shanxi gold triangle areas,the author conducted the comparison between the above-mentioned Carlin-type gold deposits and the Shangmanggang gold deposits in aspects of ore deposit characters,ore-controlling structures,mineralization and alteration etc.,it was found there are great similarities between among them in geology and geochemistry.Therefore,it is concluded that the Shangmanggang gold deposit is a Carlin-type gold deposit indeed.Previously it was believed that the Shangmanggang gold orebody was mainly located in the unconformity plane between Middle-Jurassic Mengga Fm.elastic rock and Lower-Permian Shazipo Fm.carbonate rocks.Through the systematical research on deposit geology,ore mineralogy,trace elements of ore and wall rocks,rare earth elments stable isotope geochemistry and fluid inclusion,the author proposed a new prospecting clue,i.e.,the Carlin-type gold orebody in the Shangmanggang deposit area,also located in the NW-dipping Mengga Fm.and Shazipo Fm.carbonate and clastic rocks in the depth along the Shangmanggang fault zone,which widened the previous gold mineralization controlled by the unconformity in the Shangmanggang gold deposit area.5.Except the reddish clay-type gold deposit which occurred in the sub-surface,the Carlin-type gold deposit in this area can be classified into the following four types from the upper to the lower level based on the spatial distribution of gold orebodies,that is,(a) Mabozi-type bed-like gold orebody that occurred in the unconformity between Upper -Middle Jurassic and Permian strata,(b)Shangmanggang vein-type gold orebody that controlled by the NE-trending fault,(c)Yingpan-type veinlets gold orebody that is located in the Middle-lower part of Permian strata,upper of the Gongyanghe Group hangingwall,and (d)Nongqiuba-type curved gold orebody that is located in the contact zone of the deep concealed porphyry.The above-mentioned four types of gold orebodies form five types of spatial association,i.e.,clustered,wedged,stromatolited,irregular and branched or anthus-like.6.The metallogenic models of the "Reddish clay-type" and the "Carlin-type" gold deposits in the Shangmanggang gold mineralization zone was built,i.e.,during a period of Late Jurassic to early Late Cretaceous,the deep mantle-source materials melt and upwelled due to plate press,collision and subduction.Then,the assimilation and mixture process took place between the crystallized and differentiated mantle-source materials and crust materials, and this resulted in the formation of deep mantle-source ore-forming fluids.This kind of ore-forming fluid transported along regional Longli-Ruili ductile-brittle fault zone and deposited in the secondary faults-Shangmanggang fault and Mabozi fault and some others which are parallel to Longlin-Ruili fault,and thus formed the Carlin-type gold deposit in Late Yanshanian period.The gold mineralization is enriched in the transitional part of structural deformation and extensional part of the slipping fault.Theoretically,the dynamitic process of tectonic collision between Indian plate and Asian Plate should have apparently influence in this area during Himalayan period,the mineralization associated with that tectonic movement needs to do further research.The above-mentioned Carlin-type gold deposit provided the source for the formation of the reddish clay-type gold deposit.During the period from Late Tertiary to Quaternary,on the basis of Shazipo formation carbonate karst,the ore-forming matter was transported short distances and re-deposited due to the karst slumping(cave collapse).After weathering and leaching,the "reddish clay-type" gold deposit was formed,which is closely associated with the original Carlin-type gold deposit,climate,tectonic uplift speed and terrain.This kind of "laterite" process is not completely one,i.e.,not fully de-silica process and weak oxidization. Therefore,it only reaches the clay-forming stage,i.e.,early and middle stage of "laterite" process.7.The author further pointed out that the deep and large-sized Longling-Ruili fault zone is a channel for the deep mantle-source ore-forming fluid transportation,and the secondary faults that parallel to Longling-Ruili fault are not only channels for ore-forming fluid transportation,but also favorable space for the Carlin-type gold orebodies.Thus,the main prospecting target area for the Carlin-type gold deposit is located in the deep part along Shangmanggang fault zone,and for the reddish clay-type gold deposit is located in the small-size basin nearby the Carlin-type gold deposit.8.Based on the built metallogenic models,physical model of gold deposits and the summarized ore-forming rules,in combination with geochemical exploration achievement and integration of the productive data in the studied area,the outlining of five metallogenic and prospecting areas,such as the deep part of Shangmanggang gold deposit area, Mengmo-Laibashan,Huilongcun-Xiangqiu,Hebianzhai and Mabozi were carried out.In more details,the author further proposed that the Guanglingpo ore section,Maiwoba ore section,Mengmo and Hongqiuhe are preferred targeting areas.In the Guanglingpo and Maiwoba sections,the prospecting target is the Carlin-type gold orebody at depth,and nearby the surface,there is still potential prospects for enlarging the reddish clay-type gold deposit.In the Mengmo area,the main prospecting target is the reddish clay-type gold deposit.And in the Hongqiuhe area,the prospecting targets are the Carlin-type gold deposit as well as the reddish clay-type gold deposit.Moreover,there is a potential for prospecting the ductile-brittle type gold deposit.