Geochemical Study On Multi-Level Tectonic Slippage Metallogenic System Of Nanpanjiang-Youjiang Carlin Type Gold Deposit

Nanpanjiang-Youjiang area is one of the most important concentrated producing area of Carlin type gold deposits in China.It is also recognized as the second largest low-temperature metallogenic domain in the world,and it is also an important part of a large-scale low-temperature metallogenic domain in South China.There are hundreds of gold deposits（spots）in this area,including two super large gold deposits（Shuiyidong and Lannigou）,more than a dozen giant gold deposits（including Jiadi,Nibao,etc.）and a large number of small and medium-sized gold deposits,which together constitute the famous“Golden Triangle”area in Southwest China.Predecessors have carried out a lot of research on the typical deposits in this area,mainly focusing on the regional geological background,deposit characteristics and ore control conditions,mineral composition and symbiotic sequence,mineral fabric characteristics and division of metallogenic stages,complete analysis of trace and rare earth elements of ores and the surrounding rocks,trace elements and sulfur isotopes of main ore minerals,occurrence state of main mineralized elements,in situ trace elements and isotopes of gold-bearing minerals and trace element,isotope,and geochronology of main gangue minerals（quartz,calcite,fluorite,apatite,etc.）,but the research focuses on individual gold deposits in Southwest Guizhou and Northwest Guangxi,there is a lack of overall research and comparative analysis of gold deposits in the whole region（Southwest Guizhou,Northwest Guangxi and Southeast Yunnan）.In particular,the research degree of gold deposits in Southeast Yunnan is very low,and only a small amount of descriptive research and ore trace element data have been reported,which is extremely unfavorable to understand the genetic mechanism of Carlin type gold deposits in Nanpanjiang-Youjiang.This study mainly selects the Tangshang,Laozhaiwan,Gedang,Gaolong and Maxiong gold deposits with low research degree in Southeast Yunnan and Northwest Guangxi as the object.Firstly,based on the detailed petrographic study of electron microscope（EM）,scanning electron microscope（SEM）and energy spectrum（EDS）.The advanced and relatively mature in-situ analysis methods（LA-ICP-MS,LA-MC-ICP-MS and EMPA,etc.）are used to carry out fine in-situ trace element and S-Sr isotope analysis of the main gold-bearing sulfides and calcite in each deposit.In addition,the micro-temperature measurement experiment is carried out for the fluid inclusions in the quartz vein related to gold mineralization in the ores of each deposit,and the single quartz mineral is selected to test the H-O isotopic composition of the inclusions.On this basis,the sources of mineralized elements（mainly the Au）and gold-bearing hydrothermal solution of the corresponding deposit and the possible genesis of the deposit are discussed,combined with the main and trace elements content of ores and surrounding rocks and in-situ trace element content characteristics of main gold-bearing minerals,explore the sources of elements such as W,Ti,Co,Ni and Ag,solve the source problem of so-called high-temperature elements with significant differences between Nanpanjiang-Youjiang Carlin type gold deposit and Nevada gold deposit,and analyze the uniqueness of metallogenic conditions in Nanpanjiang-Youjiang area.Based on the above research contents,combined with regional geological,geophysical,geochemical and geochronological data,this work discusses the genesis and metallogenic process of the deposit,as well as the control factors affecting gold precipitation and enrichment,and constructs a regional metallogenic model.The main conclusions of this study are as follows:（1）Through the field investigation and study of a large number of Carlin type gold deposits in Nanpanjiang-Youjiang area,it is found that in addition to the structural altered body（SBT）between Maokou Formation and Longtan Formation or Emeishan Basalt Formation in the Middle-to the Late-Permian in Southwest Guizhou,this special geological body formed by regional detachment tectonism and hydrothermal alteration is common in more older and newer strata.From the perspective of regional sedimentary sequence,on the unconformity interface and lithologic interface between D/∈,C/D,P/C,P₃/P₂,T₂/P₁₊₃and T₂/T₁strata,due to the significant difference of rock strength and permeability,under the background of regional tectonic evolution,the upper clastic rock system is violently deformed and crumpled,while the underlying carbonate rock stratum is often bent and deformed under the action of geological stress to form anticline structure due to its high strength.When the gold-bearing hydrothermal fluid enters the above interlayer fracture zone and fault system,under the favorable lithologic combination,multi-level SBT and its controlled gold orebodies are formed.The above structural types and the gold orebodies produced in SBT constitute a unique orebody occurrence and ore control characteristic framework in Nanpanjiang Youjiang area.（2）Various alteration types of Carlin type gold deposits are widely developed in the typical gold deposits of Nanpanjiang-Youjiang,and corresponding hydrothermal gold-carrying minerals and other gangue minerals are formed,and the mineral fabric characteristics are very similar.The division of metallogenic stages and mineral symbiotic sequence based on mineralogy are basically the same,indicating that they have similar metallogenic conditions and genetic characteristics.（3）The trace element of ore and surrounding rock show that the gold-bearing fluid of Nanpanjiang-Youjiang Carlin type gold deposit is rich in Au,As,Hg,Sb,Tl,Se,Cu,Ag,W,Rb and Li.The contents of Cr,Co,Ba,Zn,V,U,Ti,Rb,Ni and Mo show basically no change in the magmatic rocks（basalt and diabase）host area,while the above elements show different degrees of enrichment of Cr,Co,W,Ag,V,Ti,Rb and Li in the sedimentary rocks host area,indicating the enrichment of these elements in the gold-bearing fluid.In addition,the in-situ trace elements of pre-ore pyrite and ore-stage pyrite in gold deposits produced by different host rocks show that compared with pre-ore pyrite,the ore-stage pyrite is more enriched in V,Ti,Ni and Co,indicating that there are abundant above elements in gold-bearing fluid relative to surrounding rocks.Based on the in-situ trace elements of ores and gold-bearing pyrite,indicating that Au,As,Hg,Sb,Tl,Se,Cu,V,Ti,Ni,Co,Cr,W,Ag,Rb and Li are enriched in the gold-bearing fluid.At the same time,it is confirmed that they are not brought out by the water rock exchange reaction of gold-bearing fluid from magmatic rocks such as basalt and diabase,and which can be used as indicator elements of gold mineralization in prospecting and exploration.（4）Most of the in-situ sulfur isotope values of multi-sulfides tested in this study are positive（-0.49～16.92‰）,while the sulfur isotope values of chalcopyrite symbiotic with gold-bearing pyrite produced by Laozhaiwan gold deposit are close to zero（-2.49～1.54‰）.However,the data shows that the in-situ sulfur isotope value of the core of zonal pyrite and the pyrite in the surrounding rock of the corresponding deposit is often higher than that of pyrite formed in the mineralization period.Compared with the pre-ore stage pyrite,the mineralization process is accompanied by the reduction of sulfur isotope value of hydrothermal sulfide.We believe that the gold-bearing fluid with low sulfur isotope value forming this phenomenon may mainly come from the deep concealed granite,and the fluid from this source can also reasonably explain the composition characteristics that the in-situ strontium isotope of calcite vein in gold ores are relatively close to the value of magmatic rock.（5）The homogenization temperature of fluid inclusions in typical gold deposits is relatively concentrated（roughly concentrated at 130～380℃）,and the continuous distribution is not interrupted.They are all aqueous inclusions and CO₂containing inclusions,and the gas-liquid ratio is mainly concentrated at 20%～35%.Most of them are homogeneous to the liquid phase,and a few are homogeneous to the gas phase,indicating that the gold-bearing fluid has experienced immiscibility and/or fluids mixing.At the same time,the salinity distribution of fluid inclusions in quartz in these deposits is uneven,which can be roughly divided into three main sections:0～3 wt.%Na Cl equiv.,3.8～8 wt.%Na Cl equiv.and 11.33～11.47 wt.%Na Cl equiv.,and each section is completely separated,it is also confirmed that the mixing of two or more fluids with different temperatures and salinities occurred in the process of mineralization.At the same time,the cooling process of gold-bearing fluid caused by this mixing may be one of the important mechanisms of gold precipitation and mineralization.The H-O isotopic data of inclusions in quartz shows that they all fall within the range of magmatic water and meteoric water and near the water rock exchange curve below,which may indicate that there is a mixed fluid of magmatic water,metamorphic water and meteoric water involved in the metallogenic process of these gold deposits,but the gold background value of sedimentary strata in the distribution area of the above deposits is low,as well as no medium to high-grade metamorphic rocks are found in Nanpanjiang-Youjiang area,so we believe that the ore-forming fluid comes from the deep concealed granite,but it is mixed with metamorphic water and meteoric water in the process of upward migration.（6）Based on the detailed geochemical analysis of several gold deposits in different regions,combined with the previous studies and the main ore controlling structural framework of the region are formed in the Yanshanian,the geophysical exploration found concealed granite bodies in the deep of the main gold deposits,and a large number of relatively reliable chronological data were concentrated in the late Jurassic to early Cretaceous（150～120 Ma）,We put forward the metallogenic model of the multi-level tectonic detachment metallogenic system of Nanpanjiang-Youjiang Carlin type gold deposit,which is genetically related to the concealed granite and centered on the ore control of the multi-level tectonic detachment system.It shows that under the background of the westward subduction of the Pacific plate in the Yanshanian,more and more researchers believe that extensive Yanshanian gold mineralization occurred in the Nanpanjiang-Youjiang area.