Geological And Geochemical Characteristics Of Orebody And Deep Ore Exploration For Yangla Ore Deposit,Western Yunnan

The large copper deposit, Yangla deposit, which belongs to Jinsha River plate suture zone gripped by Zhongza landmass and Changdu-Simao landmass, lies in the middle piece of the three-rivers(Jinsha River, Lancang River and Nu River) Paleo Tethys tectonic zone. The Yangla copper orefield discussed by this article contains the Jiangbian ore block, the Linong ore block and the Lunong ore block from north to south, the Linong and Lunong ore blocks are the main mining section. Based on the thorough discussion on the geochemistry characteristics of the ore-related surrounding rocks, granite and skarn, this article takes the Yangla orefield, especially the typical skarn type ore body in the Linong ore block, as main object of study, mainly discusses the mineralogical, petrological and geochemical characteristics of the â…¡#and â…¤#ore body in the Linong ore block. Finally, the author summarizes the metallogenic diversity and the metallogenic model of the deposit, and makes a deep prospecting prediction evaluation. The main results obtained as follows:(1)Based on the element content analysis, the wall rocks are found to be rich in Cu,Pb, Zn,Bi,Zn,W,Mo, etc. Laminated siliceous rocks development and Ba enrichment in country rocks might represent that the stratum have experienced Hot water deposition, and the surrounding rocks might have provided some ore-forming materials.(2)Based on the mineralogy, major elements and trace elements analyses of the main granites in the Yangla orefield, the magma sources, the geological background and ore-bearing ability of the granites are discussed:the Yangla granite belongs to the calc-alkaline slightly peraluminous I type granite. The granites are commonly rich in large-ion lithophile elements such as Rb,Th,U,K and La, but in depletion of HFS elements such as Nb,Ta,Zr and Hf. The REE distribution patterns are characterized by LREE enrichment and slightly negative Eu anomalies, which represent that the granites have the same magma source. The granites in the Yangla orefield mainly formed in island arc environment which formed because of the subduction of the Jinsha River ocean basin under the Xichangdu-Lanping landmass. The granites have both volcanic arc type and S-COLG type. The magmatism plays a significant role in the activation of ore-forming materials and the formation of the Yangla deposit.(3)Some new progress has been made in the mineralogy and geochemistry of the skarn and its role in the ore-forming process. The skarn mainly consists of pyroxene and garnet. The pyroxene are mainly hedenbergite and malacolite, while the garnets are mainly andradite and essonite. The skarn has some kind of zoning in space. The rock near terrace contains more garnet, while others far away from the terrace contain more malacolite. Bands, which reflect changes in the physical chemical conditions and fluid composition, can be seen in the garnet of the deposit. The garnet has a high content of the element Sn, which occurs in the form of isomorphism as Sn4+. This article also discusses the REE distribution pattern of the skarn minerals and the reason why Eu content is abnormal. It has been proved by the geochemical analyzes of the typical section that there was material interchange between the granites and wall rocks during the skarn formation. The mineralization has been proved to be dimetasomatism.(4) Geological and geochemical study progress has been made for the â…¡#and â…¤#ore body. Quantitative analysis of mineralization grade and its space variation has been made. The mineralization grade has a character of two-peak type or multi-peak type. The mineralization has been divided into three phases, the quartz sulfide phase is the main metallogenic phase. The vertical primary halo pattern of the ore body has been made:As,Pb,Zn enrichment mainly occurs in upper part of the ore body, while Ag,W,Bi,Mn in the central section and Sn,Cu, Mo in the bottom, which represents the changes in the mineral formation from mesotherm-microthermal to highheat environment. The the quantitative evaluation model has been built, chosing the zoing index as the Pb*Zn*Ag*Bi/Cu*Sn*Mo as the indicator of the model.(5) Evidence of the source of ore-forming materials have been put forward by analysing the Pb, S, C, H, O isotope. The Pb isotope of the ore mainly lies between the evolution line of the upper crust and orogenic belt, while minority samples lies between the evolution line of the upper mantle and orogenic belt, which indicates that the Pb of the deposit mainly came from crust, but also with some mantle materials. Most of the Pb isotope of feldspar and ores lie in the district of island arc, which implies that this area is island arc while the mineralization took place. The S isotope data are concentrated close to0, which occurs as a tower distribution. It suggests that the ore-forming fluid had a single S source. The S of the deposit may came from mantle and has an intimate relationship with granites in this district. The H-O isotope suggests both magmatic water and atmospheric water are involved in the ore-forming fluid, and atmospheric water mainly occured during the late phase of the mineralization. The C-O isotope implies that the C and O element in the calcite vein, around the terrace, or the marble type ore may have relation with both the marble and the influence of the Linong rock mass.(6) The metallogenic diversity has been discussed, the regularity sequence and the time-space-genesis pedigree has been built. This article also compares the main copper deposit types in the Jinsha River tectonic zone, and summarizes the ore-controlling factors, the prospecting indicators, and metallogenic model of the Yangla deposit. Finally, the author put forward the ore-hunting prospect areas in this district by different evidences and specific method. The author pointed out that combining site of the Linong and Lunong district, the deep part of the Linong district and the north of the Lunong district may have great ore prospecting potential.