Metallogenesis Of Precious-nonferrous Metal Deposits In Gerizhuotuo Area,Dulan Qinghai Province

The East Kunlun orogenic belt is located in the southern margin of the Qaidam Basin,which belongs to the western part of the Central Orogenic Belt of china.It has important geological content and information in the front of the modern geological science,such as:its complex geodynamic evolution,tectonic magmatic activity,multistage marginal orogeny,continent-continent collision orogeny,the potential of the rich mineral resources.It has aroused the attention of many geologists in China,and has carried out a number of related research work.Gerizhuotuo area is located in the A'nyemaqen ophiolitic mélange of the East Kunlun orogenic belt.There are still many problems such as geology,mineral through further research work to solve urgently,because of the natural geographical area,poor economic conditions,in addition to traffic conditions,most of the work carried out lots of work less,overall level is low.This paper studied the mineralization and metallogenic regularity of Gerizhuotuo area of precious metal and nonferrous metal deposit by based on the modern testing technology and combined with modern metallogenic theory,using advanced zircon U-Pb geochronology,petrology,mineralogy,geochemistry and(C-H-O-S-Pb)isotope geology and other methods.The main research results of this study are summarized as follows:(1)The Manite gneissic granodiorite is exposed to the southeastern part of Manit gold mine.The LA-ICP-MS zircon U-Pb dating of Manit Gneiss granite is 495.6 ± 1.1Ma,which is for the Late Cambrian,rather than the predecessors of the Triassic.Considering its relationship with the geological age of surrounding rock,fault contact,it is the tectonic slices in A'nyemaqen tectonic belt.The rock is located south of the South Kunlun fault,has a close spatial relationship with the Naij Tal volcano rock and volcano rock Wanbaogou group.It is believed that the gneissic granodiorite in the Manite area was formed in the environment of Proto-Tethys Ocean crust subduction.It is supposed tobelong to the southward subduction of oceanic crust.The crust between the Qaidam massif and Wanbaogou oceanic plateau occurred bidirectional subduction to the south and the north.(2)The paper makes systematic chronology,geochemistry and tectonic setting studies on the intrusive rocks which developed in Gerizhuotuo ore district.The results of SHRIMP U-Pb dating of the granodiorite zircons related to mineralization in the Gerizhuotuo gold-copper deposit are 223±2Ma,the results of SHRIMP U-Pb dating of the diorite porphyry zircons related to mineralization in the Manite Gold copper deposit are 217±2Ma.The geochemical analysis shows that both the formation of Old Tethys ocean closed after the collision environment,and signs the transformation from the compressional orogenic system to the post orogenic extensional system.The precise dating studies show that late Indosinian epoch is the main metallogenic period Gerizhuotuo area.(3)We are approaching a new understanding on the genesis types of the deposits in studying area by the field work and laboratory study: The Gerizhuotuo gold-copper deposit is a hydrothermal vein deposit not the skarn type deposit,Manit and Buqingshan gold deposit are orogenic gold deposits.Based on the background of metallogenic dynamics,it is believed that the three deposits,which were produced in the late Indosinian epoch,were the product of crust mantle interaction during the late Indosinian lithospheric delamination and underplating of mantle derived magmas.(4)The Gerizhuotuo area is widely distributed in ultrabasic rocks,and we analysis of the Chaganregegou ultrabasic rocks.The study shows that the ultrabasic rocks are mafic ultramafic rocks.and the main mineralization is Cu,Ni,etc.The variation range of SiO2 in rock samples is 39.26% ~ 40.82%,the content of Na2 O,K2O and CaO is very low,and the content of TFe2O3 and MgO was higher.The value of Mg# is 85 ~ 88,which is close to the mean value of Coleman(1977)of mantle peridotite(Mg#=85).The ?REE value of the total amount of rare earth is very low,and the ?Eu value has a strong positive anomaly.The value of m/f(4.56 ~ 6.05)is located between 2 and 6.5,which is related to copper nickel sulfide deposit.(5)The study of fluid inclusions in the deposit shows that the fluid inclusions in the Gerizhuotuo gold-copper deposit are mainly composed of gas liquid two-phase and three-phase inclusions containing CO2.The ore-forming fluid is NaCl-H2 O system,showing the characteristics of low,low salinity and low density.The C-H-O isotope characteristics indicate the mineralizing fluid is mainly magmatic water,atmospheric precipitation in different degree of mineralization process.The sulfur source of metal sulfide is single,which is mainly from the deep magma sulfur and has the characteristics of mantle derived sulfur.The lead isotope studies show that Pb is mainly a mixture of upper crust and mantle.The main types of fluid inclusions of the Manite gold deposit and Buqingshan gold deposit are the gas liquid two phase and the CO2 containing three phase inclusions.The ore-forming fluid of the Manite gold deposit and Buqingshan gold deposit are NaCl-H2 O system,showing the characteristics of low,low salinity and low density.The ore-forming fluids indicate the formation of late Indosinian Gerizhuotuo region of ore-forming materials with crust mantle mixing characteristics.(6)The paper proposes the existence of upper mantle gold in the A'nyemaqen ophiolitic mélange of the East Kunlun orogenic belt.According to the evolution of regional dynamics,the East Kunlun area has experienced several magmatic activities,especially in the late Indosinian period,which is an important turning point in the transition from compressional tectonic system to extensional tectonic system.In the late Indosinian period,the crust mantle interaction occurs in the region,the mantle derived magma is widely distributed in the region,the mantle derived C-H-O fluids bring a large amount of Au minerals.The formation of sulfide phase in the upper mantle of the A'nyemaqen ophiolitic mélange is caused by the melting of the unsaturated sulfide melt.Most of the gold deposits are trapped in the upper mantle,forming the upper mantle source region.Based on the above research,this paper summed up the metallogenic pattern,metallogenic conditions and metallogenic regularity of Gerizhuotuo region of typical ore deposits.The main metallogenic period is the late Indosinian period,A'nyemaqenBayanka La tectonic belt is the Indosinian fold belt.Its formation time is the shortest,andthe degree of denudation is the least.There are good metallogenic conditions in the area.The main types of ore deposits in this area are hydrothermal vein type gold polymetallic deposit,orogenic gold deposit,copper nickel sulfide deposit.