Study On Metallogenesis Of Endogenetic Metal Deposits In The Qimantag Aera,East Kunlun,Qinghai Province

The Qimantage area of East Kunlun has great prospecting potential,which has been regarded as an important producing area of iron,copper,lead and zinc polymetallic minerals and one of the resource replacement bases in China.The unique geotectonic position makes the frequent and intense tectonic-magmatic activities frequent and intense in Qimantage area and provides a good place for the migration and precipitation of ore-forming materials.Geologists have discovered iron,copper,lead,zinc,tungsten,tin,gold and other metal minerals in Qimantage area after a large survey of land and resources at the beginning of this century.he overall level of basic geological work in Qimantage area is increasing year by year,but there are many types of deposits in the area,the mineralization is complex,and the metallogenic age and tectonic background are lack of systematic research.These factors restrict the further development of prospecting work to varying degrees.This paper is based on on the evolution of geodynamics and the comprehensive study of typical deposits,and we use modern metallogenic theory and combined field research and laboratory analysis.The regional metallogenic geological conditions are analyzed,the metallogenic model of typical deposits is established,and the regional metallogenic regularity and metallogenic potential are summarized,in order to provide help for further prospecting work.From the perspective of tectonics,the Qimantage area,as an important part of the East Kunlun orogenic belt,is equivalent to today`s Northeast Kunlun belt,which has experienced multiple complex tectonic-magmatic evolution.This study suggests that the Qimantage area does not have obvious oceanic evolution and subduction zone characteristics,and does not belong to the independent evolutionary orogenic belt.It should belong to the post-arc rift trough area of Northern Kunlun under the geodynamic background of the Proto-Tethys Ocean evolution,and is one of the important tectonic units of the East Kunlun orogenic belt.In the early Caledonian,the southern margin of the Qaidam Block,which was previously a passive continental margin,transformed into an active continental margin,and an active continental margin arc appeared in the Central Kunlun zone between the current NKF),Middle Kunlun fault and the the North Kunlun fault.The present North Kunlun area(Qimantage area from the west,may extend eastward to Dulan area in the east),formed a back-arc extensional environment on the Precambrian metamorphic crystalline basement during the Ordovician-Silurian period,forming a back-arc rift trough and developing a back-arc rift zone.Affected by the collage of Wanbaogou oceanic basalts plateau in the late Caledonian,the back-arc rift zone in northern Kunming closed quickly,during which volcanic and clastic deposits of the Tanjianshan Group(Qimantage Group)were accepted.This paper selected five typical deposits distributed in Qimantage area:1.Weibao lead-zinc deposit is skarn type deposit,later superimposed hydrothermal mineralization.There are two magmatic events in the mining area-Silurian-Devonian(ca.417.3 Ma diorite porphyry and ca.337.4 Ma diorite)and Late Triassic(ca.233.7 Ma porphyritic granodiorite and ca.228.3 Ma granite porphyry).The formation of the deposit is related to Late Triassic magmatic activity(ca.228.3 Ma).The sulfur isotope test results of 20 ore mineral samples in Weibao lead-zinc mine show that the?³⁴S values are ranging from-2.6‰to 3.4‰,with an mean value of 1.8‰,which shows the typical magmatic S characteristics.The Pb isotope test results of 18 ore mineral samples show that ²⁰⁶Pb/²⁰⁴Pb values are 18.234?18.342,²⁰⁷Pb/²⁰⁴Pb values are 15.570?15.663,²⁰⁸Pb/²⁰⁴Pb values are 37.973?38.252,and the lead source is the homogeneous mixing of mantle and upper crust.The types of fluid inclusions in the quartz-sulfide period include gas-rich inclusions,liquid-rich inclusions and CO₂-containing three-phase inclusions.The quartz veins in the hydrothermal period developed gas-liquid two-phase inclusions.The microscopic temperature measurement results showed that the ore-forming fluid in the early quartz-sulfide period was characterized by high temperature(peak value interval 340?360°C)and medium salinity(peak value interval 10?11 wt.%Na Cl eqv.).The ore-forming fluid in the late quartz-sulfide period showed the characteristics of low temperature(peak value interval 260?280°C)and low salinity(peak value interval 4?6wt.%Na Cl eqv.).The ore-forming fluid in the gray-white quartz veins in the hydrothermal period was characterized by low temperature(peak value interval 230?260°C),low salinity(peak value interval 6%?8%wt.%Na Cl eqv.)and low density(peak value interval0.84?0.88g/cm³).The ore-forming fluids of gray-white quartz veins in hydrothermal mineralization period are characterized by low temperature(peak value interval160?180°C),medium salinity(peak value interval 9?12 wt.%Na Cl eqv.)and high density(peak value interval 0.96?1.02 g/cm³).The H-O isotope test results of quartz vein in quartz-sulfide stage show that the ore-forming hydrothermal fluid comes from magmatic water and has the circulation of atmospheric water.The hydrothermal calcite?¹³C_V-PDB(‰)of gangue minerals in the ore is-7.3?-0.1,with mean value of-2.7.The?¹³O_V-SMOW(‰)values range from 13.9 to 22.7 with a mean value of 17.8.The C in the ore-forming fluid may be derived from the dissolution of marine carbonate,and its precipitation should be mainly caused by the coupling of water-rock reaction and temperature reduction.During the metallogenic process of Weibao Pb-Zn deposit,an immiscibility widely existed in ore-forming fluid.The solubility of CO₂ and other volatile components in the ore-forming solution decreased,and the volatile components such as CO₂ in the fluid escaped(separated),resulting in the separation of the phase of the fluid,resulting in the immiscibility of the fluid,which also led to the change of parameters such as p H value in the ore-forming fluid,leading to the loss of stability of metal complexes,and the precipitation and mineralization of Pb-Zn-Cu sulfides.Therefore,the immiscibility of the fluid is the most important mechanism for the metal precipitation of Weibao Pb-Zn deposit.The ore-forming rock mass of the deposit should be concealed in the south of the mining area,and the contact mode of the large angle oblique intersection between the deep rock mass and he strata in the mining area is the most important condition for it to become a large-scale skarn deposit;2.The Hutouya Fe-Cu-Pb-Zn polymetallic deposit is skarn type deposit.The zircon U-Pb dating of granodiorite and molybdenite Re-Os isotopic dating results are consistent within the error range,limiting its metallogenic age to ca.227 Ma.The?³⁴S_V-CDT values of six chalcopyrite samples range from+1.5‰to+5‰(mean value=4.1‰),the?³⁴S_V-CDT values of five pyrite samples range from+1.1‰to+1.8‰(mean value=1.3‰),the?³⁴S_V-CDT values of two galena samples range from+1.0‰to+1.3‰(mean value=1.7%),the?³⁴S_V-CDT values of two sphalerite samples range from+2.0‰to+2.4‰(mean value=2.2‰),showing the characteristics of typical magmatic S.The lead isotope test results of ore minerals show that ²⁰⁶Pb/²⁰⁴Pb ratios are 18.12?18.68,²⁰⁷Pb/²⁰⁴Pb ratios are 15.59?15.81,²⁰⁸Pb/²⁰⁴Pb ratios are 38.19?39.02,and the lead source is the uniform mixing of the upper crust and orogenic belt.The genetic type of the deposit should be skarn type,and the mining area can be divided into three zones from north to south.The mineralization in the central zone is the best.The preservation conditions in the northern zone are the best,and the metallogenic potential is the largest.The formation fragmentation in the southern zone is not conducive to the accumulation of metallogenic hydrothermal solution;3.Kendekeke Co-Bi-Au polymetallic deposit is a hydrothermal exhalative sedimentary superimposed hydrothermal transformation deposit.Early Paleozoic back-arc rift trough area in the North Kunlun deposited a large number of Au,Bi,Co,Cu,Pb,Zn and other metallogenic elements in siliceous rocks,forming the'mineral source strata'of the Kendekeke Co-Bi-Au polymetallic deposit.Extensive magmatic activities in the Middle-Late Triassic East Kunlun area provided heat sources and magmatic hydrothermal solutions for mineralization.This period is the main metallogenic period of the deposit.The interlayer contact zone formed skarn or skarnization affected by deep magmatic hydrothermal fluid.At the same time,hydrothermal solution reacts with rock by water-rock reaction,and extracts ore-forming elements in rock,so that Co,Bi,Au and other metal elements are migrated,enriched and formed in broken skarn with weak structure;4.Wulanwuzhuer 4041 highland tungsten-tin-copper polymetallic deposit is a high temperature hydrothermal vein type tungsten-tin-copper deposit,which is metasomatic mineralization.The ore body is obviously controlled by the main faults in the area.The metallogenic age of the deposit is limited to 457.5?436.9 Ma,which should be formed in the syncollisional tectonic background after the closure of the original Tethys Ocean in East Kunlun.;5.The iron-copper-lead-zinc polymetallic deposit in the south of Yazigou is a porphyry deposit.At present,three altered phases have been delineated through the mapping of altered phases in a large area of Qingpan rock belt on the surface,which determines the existence of the heat source center and preliminarily limits the approximate range of the heat source center(metallogenic porphyry).Potassium Granite Porphyry Rock Mass Closely related to the Cu-Pb-Zn Mineralization in the Fractured Alteration Zone of Late Metallogenic Period in the Surface of Mining Area shows the U-Pb age 226.6±1.1Ma,indicating that the deposit should be formed in Late Triassic.Qimantage area has superior regional metallogenic conditions such as strata,structures and magmatic rocks.The regional mineralization has obvious temporal and spatial regularity.Caledonian and Indosinian periods are the main mineralization periods in the study area,and the regional metallogenic model is:1.The early Caledonian period:starting from ca.473 Ma(the data are the zircon U-Pb age of Luotuogou quartz porphyry obtained by the project group),and the southern margin of the Qaidam block is transformed from passive continental margin to active continental margin,forming a complete trench-arc-basin system.At this time,the Qimantage area is characterized by the post-arc rift zone of The East Kunlun Orogenic Belt,and the submarine volcanic eruption is strong.At the same time,a large number of terrestrial materials are added,and a large number of siliceous rocks and clastic rocks are deposited in the rift trough.The siliceous rocks are rich in Au,Bi,Co,Cu,Pb,Zn and other metallogenic elements,completing the initial accumulation of metallogenic elements,and forming the‘ore source layer'of the Kendekeke polymetallic deposit.In late Caledonian,with the collage of Wanbaogou oceanic basalt plateau and Qaidam block,the Early Paleozoic back-arc rift zone in North Kunlun was closed,and W-Sn deposits such as Wulanwuzhuer 4041 highland were formed under the syn-collision tectonic setting.2.Late Caledonian period:With the closure of the Proto-Tethys Ocean in East Kunlun in the late Caledonian,the thick oceanic basalt plateau(?30km)hindered the further large angle subduction of the oceanic crust,and the subduction of the deep oceanic crust had not stopped,which eventually led to the formation of the'slab window'by the tearing and breaking of the subduction plate.With the upwelling of mantle-derived materials,the extensional stress environment emerged.At this point,the tectonic system of the whole East Kunlun area transformed from syn-collision collage to extension.The lithospheric mantle has also undergone decompression melting under the extensional environment by the heating of mantle-derived magma,thus forming a complex mantle-crust source magmatic activity.Finally,numerous mafic-ultramafic rocks and related Cu-Ni sulfide deposits formed,such as Xiarihamu(according to the research results of the project group,this paper does not elaborate).After the Caledonian period,the whole East Kunlun area was uplifted and eroded,and the shallow deposits were not easy to be preserved,but the W-Sn-Cu deposits with high temperature and deep formation in the Wulanwuzhuer 4041 highland were preserved.3.Early Indosinian period:During the Early Triassic,the subduction of the Paleo-Tethys oceanic crust in the eastern Kunlun induces partial melting of the lower crust heated by mantle-derived materials upwelling.The intermediate-acid intrusive rocks were widely distributed in the Central and Northern Kunlun belts,especially in the eastern part of the Central Kunlun belt.A large number of large-scale complex rock bases were developed.At this time,iron polymetallic deposits such as the Lalingzaohuo skarn-type Cu-Mo deposit and the Haxiyatu deposit were formed in the Qimantage area.4.Late Indosinian period:Late Indosinian is the most important metallogenic period in Qimantage area.During the Middle Triassic,the Paleo-Tethys Ocean in East Kunlun Orogenic Belt was closed.The Qimantage area began to transform from the compressional structure system to the extensional structure system in the late Triassic.The crust-mantle interaction was strong,and a large number of mantle-derived materials participated in magmatic activities and mineralization in the area,forming a series of hydrothermal deposits,such as the Weibao Pb-Zn deposit,the Hutouya Fe-Cu-Pb-Zn polymetallic deposit,Kendekeke Fe-Co-Bi-Au polymetallic deposit and the Yazigounan Cu-Pb-Zn polymetallic deposit in this paper.