The Study On Pyrite And Fluid Inclusions Of Herzhedegai Gold Deposit In Gansu Province

The Herzhedegai gold deposit is a super-large independent gold deposit occurring in the Heiyingshan Arc of the eastern Tianshan-Beishan orogenic belt on the southern margin of the Central Asian orogenic belt.On the basis of field work,the types of pyrite,the characteristics of mineralized and non-mineralized quartz fluid inclusions were classified by microscopic petrographic observation,LA-ICP-MS,pyroelectricity,quartz fluid inclusions and other research methods.The in-situ test data,pyroelectric parameters of pyrite,quartz fluid inclusion temperature data and laser Raman data were analyzed,the occurrence of trace elements in pyrite,the origin of pyrite,fluid source and evolution,and the genesis and prospecting potential of the deposit are discussed,the following major progresses have been made:The ore bodies occur as veinlet in the fracture and fissure of the tonalite,have clear boundaries with the wall rock.The emergence stratums of mining area are Calc alka-line felsic volcanic sedimentary rocks and clastic rocks of the Carboniferous Baishan formation,the structure is dominated by NW-trending faults,and the magmatic rocks are mainly tonalite,in batholiths,stock output.The pyrites in the deposit are divided into four types,including pyrite?Py0?in andesitic tuff,pyrite?Py1?in magnetite quartzite,pyrite?Py2?in coarse quartz-pyrite vein,and light gray quartz-polymetallic sulfide vein?gold?stage pyrite?Py3?,LA-ICP-MS in situ analytical results show:The contents of Al,Ti,V,Cr,Mn,Co,Ni,Cu,Zn,Y,Zr and Pb in Py0 are relatively highest;Py1 is relatively enrich in Ti,Co,Ni,Cu,As,Se,Pb and Bi,except the contents of As and Se is higher than Py0,the others are lower than Py0;the contents of Ti,Co,Ni,Cu,Zn,As,Se in Py2 are relatively the lowest;the contents of Co and Ni in Py3 is lower than Py0,but higher than Py1 and Py2,The ore-forming elements such as Cu,Au,Ag,Pb and Bi are significantly higher than Py2.Co,Ni,As and Se enter the crystal lattice of pyrite in the form of isomorphism;Au exists in pyrite mainly in the form of Au⁺¹ solid solution,which may exist in the form of electrum inclusions,There are only some Au⁰ nanoparticles in Py3,and Ag may also be partially exist in the mineral inclu-sions of Bi-containing mineral.Cu and Pb in the form of mineral inclusions of chalco-pyrite and galena exist in Py0,Py1 and Py3.The conductivity types of the three pyrite samples of D348 were N-type,and the thermoelectric coefficient ranged from-280 to-120 uV/°C.The pyrite formation tem-perature was 212.71³48.25°C,the average value was 280°C.The denudation rate was84.25%⁸7%,indicating that the pyrite formation temperature is low and the ore body is denuded.The type of quartz fluid inclusions is mainly liquid-rich NaCl-H₂O type inclusions,with only a few inclusions include daughter mineral,which are mainly oval,rounded and irregular,the inclusion size is between 4 and 7?m,the homogenization temperature and salinity of mineralized and non-mineralized inclusions are 118.2²75.6°C,119.3²16.9°C,0.35¹1.93%NaCl.eqv,0.18¹1.93%NaCl.eqv,the temperature of mineralized quartz to non-mineralized quartz veins gradually decreases,but the fluid exhibits low temperature and low salinity characteristics.According to the analysis of pyrite and quartz fluid inclusions of the Herzhedegai gold deposit,it is an Epithermal gold deposit,Py0 and Py1 are granular pyrite formed in the Early Carboniferous during sedimentary and sediment reworking;Py2 and Py3are formed slightly later than Py0 and Py1,with the mixing of magmatic hydrothermal fluid and atmospheric precipitation,the mixing of fluids leads to the significant enrich-ment of ore-forming elements such as Au,Ag and Bi in Py3.The ore-forming materials are mainly derived from magmatic hydrothermal fluid and mixed with atmospheric pre-cipitation,with the increasing precipitation of the atmosphere,a large number of non-mineral quartz veins are formed in the formation.