The Mineragraphic Characteristics Of Xilang Cu-Pb-Zn Deposit And Its Metallogenetic Significance Of Jinggu County In Yunan Province

Xilang Cu-Pb-Zn deposit of Jinggu County in Yunan Province is a Cu poly-metal deposit which is newly found in Yunnan Sanjiang Mt.Wuliang area. Its geotectonic characteristic is a second class structural division of Changdu-Lanping under first grade structural division of Qiangtang-Sanjiang orogenic.Yunxian-Jinghong continental margin arc zone(P1-T3) is located in the east of the southern Lancang River joint zone and the west of Jiufang fault, and the extension of Qiangtang-Sanjiang Orogenic system in Kaixinling-Zaduo-Zuka continental margin arc zone, mainly distributed in the line of Lincang-Yun county of the eastern Langcang block-Jinghong, and basically distributed along the Lancang River Valley, it is tectonic activity region which is collide and joint gradually from late Paleozoic to Cenozoic. The oldest stratum exposed in the continental margin arc zone is upper-medium Devonian. This volcano-magma arc structure is deformated realtively strong, as a whole, its characteristic is the eastward thrust fault. In the vicinity of the Lancang River fault, stratum of Jurassic-Cretaceous has got part deformation and metamorphism and become slate, it is main relate to the tectonization of later fault stage. The stratum of late Paleozoic-Triassic has the characteristic of uneven metamorphism and deformation, further metamorphism when close to the Lancang River fault. In the wild, strong metamorphism, deformation belt and thrust-nappe structure is common and closely, produced a series of imbricate thrust-nappe structure and west reversed, east-dipping axial planes’ homocline overfold, it indicates that its kinematics characteristic of tectonic thrusting from east to west may relate to the superimposion-reformation NWW Hongjing left-lateral and strike-slip fault.From late Paleozoic to Paleocene-Eocene of Paleogene, the continental margin arc zone has experienced several tectonism, that is, Hercynian Indosinian and Himalayan, and accompanied with relatively magma intrusion and volcanic eruption, fault interveined, exposed stratum is from upper Paleozoic to Paleogene, its structure and sedimentary evolution could approximately be divided into 4 stages: late Paleozoic, stretching and subduction, produced the tectonic framework with the characteristic of arc and basin combination, deposited lots of clastic and carbonate rocks of Carboniferous, Permian and Triassic etc, and developed basic and acidic volcano rock; Late Triassic orogeny of Indosinian, the east margin’s arc-basin system of Yangtze block completely gathered and spliced into Qiangtang-Sanjiang orogenic. From Jurassic-Cretaceous, Changdu-Lanping-Simao block produced continental basin for intraeontinental extension, and then formed red thick terrigenous clastic sedimentary formation. Under the continent-continent collision mechanism, formed a series of open-closed fold, large thrust and thrust-nappe structure, and formed a series of intermountain fault basin and marginal depression basin, deposited red fluviolacustrine facies terrigenous clastic rocks. Along the Lancang River, Hercynian-Indochina early acid granite base of Lincang-Menghai, mafic ultrabasic-basic rock belt in Banpo of Jinggu and Mt.Nanlin of Jinghong.Around the world, the research about the origin of low-medium temperature hydrothermal copper is pretty mature, lots of research achievements about its geological structure, geochemical features, ore-controlling factors and its genetic model have been reached.The main tectonic line of Xilang Cu poly-metal deposit area is nearly north-south, its main fault is Puer fault belt, and ore’s distribution of this area is controlled by the fault. Stratum exposed in deposit area is from upper Paleozoic to Paleogene. The stratum which copper, lead and zinc ore existed is main middle Permian Najing Group(P2nq) of the east of Puer Fault zone and lower Cretaceous Nanxin Group(K1n).As a newly found Cu-Pb-Zn deposit in Sanjiang metallogenic belt, almost no study have been made about the deposit geology, deposit geochemistry, fluid inclusion, adjacent rock alteration and deposit’s origin of the Xilang Cu-Pb-Zn deposit. This paper aims at mineralographic studies of the Xilang Cu-Pb-Zn deposit, under the foundation of the data collection of geologic survey, preliminary exploration and prospecting, grasping the regional metallogenic geological condition of Xilang Cu-Pb-Zn deposit. By participating the preliminary exploration and studies, a comprehensive understanding to the amount, scale and occurrence of the ore body, and realizing the stratum which ore existed, adjacent rock alteration and the main ore-controlling factors. Under the foundation of collecting rocks and ore sample systematically and the observation and study of macro geological characteristics of ore, especially pay attention to the investigation about the relationship between massive veins in the wild, and basically realized its interpenetrative relationships.This paper tries to combine the study of macroscopic characteristics and microscopic characteristics about ore, and then getting a comprehensive understanding about the composition of mineral and ore structure, for the purpose of realizing ore type and the sequence of mineral formation, and establishing time hierarchy of this Cu poly-metal deposit’s formation, then compartmentalize the ore-forming stage and ore-forming period, providing basic data about mineragraphy for establishing deposit’s genetic model. At the same time, summarizing the main controlling factors and summing up prospecting marks, providing technical support of mineragraphy for deep and peripheral prospecting.In this paper, lots of thin sections polished sections have been manufactured, through the systemic observation and study by using microscope, it is founded that the main metallic minerals of Xilang Cu-Pb-Zn deposit are Tetrahedrite and tennantite, then chalcocite bornite, chalcopyrite, copper, bismuth sulfide, sulfur and copper and cobalt mining, galena, sphalerite, limonite, pyrite, covellite, azurite and malachite, occasionally native silver, argentite and kongsbergite.The wall rock alteration of Xilang Cu-Pb-Zn deposit include sulfuration, silicification and carbonatization, produced lots of pyrite, chalcopyrite, tetrahedrite, galena, sphalerite, quartz, calciteand dolomite; In diorite, epidotization and chloritization are developed. In surface oxidation stage, malachite, azurite, bornite and limonite is produced.The ore-forming sequence of Xilang poly-metal deposit are as follows: tetrahedrite + bornite + chalcopyrite(a few)â†'carrollite + witticheniteâ†'Limonite + Malachit + bornite +covellite. This deposit has experienced 2 primary metallogenic period, that is, hydrothermal quartz-sulfide phase and epigenenesis.According to the ore’s texture and structure, mineral zonage, typomorphic mineral, mineral symbiotic relationship, ore-forming sequence and wall rock alteration of Xilang Cu-Pb-Zn deposit, combined with the result of preliminary exploration, this paper suggests that Xilang Cu-Pb-Zn deposit is a low-medium temperature hydrothermal deposit(epigenetic deposit).