Genesis Of Silver Polymetallic Deposit In Hariza Area Qinghai Province

The silver polymetallic deposit in Hariza Area is located in the Reshui town,Dulan County,Qinghai Province.It belongs to the eastern part of Kunlun Mountains.By the end of 2017,a total of 318,100 tons of copper,lead,zinc,tin metal,999.82 tons of silver metal,and 2,995.58 kg of gold metal had been submitted.The silver resources in the Hariza area are concentrated in the V,VI ore belt.And the main rock in V,VI ore belt is Crystalline tuff lava,one continental volcanic rocks of the Elashan Formation.The relationship between continental volcanic rocks and silver polymetallic deposit,in this area,is not clear.So,this paper relies on the“Detailed investigation of polymetallic deposit in Hariza area”project and the“Mineralization and Target Selection of Devonian-Triassic Continental Volcanic Rocks around Qaidam,Qinghai Province”project to discuss the question.Zircon U-Pb dating of Crystalline tuff lava of Elashan Formation shows that its diagenetic age is 225 Ma,which limits the upper limit of metallogenic age,i.e.the metallogenic age is later than the Middle Triassic.The studies of fluid inclusions of ore-bearing quartz show that,the uniform temperature of gas-liquid two-phase inclusions was concentrated at 180°C²40°C,the salinity was concentrated in 6%to 10%,and the uniform temperature of three-phase inclusions,containing CO₂,was mainly distributed at 220°C.²80°C,there is also a dense distribution zone between 340°C and 360°C.The salinity is mainly distributed in10%-18%.The ore-forming fluid is generally a medium-temperature,low-salt,low-density H₂O-NaCl system.The ore-forming pressure of gas-liquid two-phase inclusions is calculated to be 15.3³2.2MPa,and the ore-forming pressure of three-phase inclusions is 20⁴0MPa.The calculated ore depth is 1.6⁴km,which means the silver polymetallic deposit is shallow depth.The sulfide isotope composition of the deposit is stable.The pyrite?34S is between-0.1‰and 0.6‰,the galena?³⁴S value is around-1.6‰,and the arsenopyrite?³⁴S is between-0.3‰⁰.5‰.Minerals are mainly derived from deep magma.The hydrogen and oxygen isotope composition of quartz samples in V and VI ore belts shows that the source of ore-forming fluids is mainly provided by magma,and a few atmospheric water is added later.According to the analysis of ore-forming elements in the volcanic rocks of the Elashan Formation,the content of ore-forming elements such as Ag,Cu and Pb is lower or slightly higher than the Clark value,indicating that the continental volcanic rocks of the Elashan Formation are not the source layer.The the volcanic rocks of the Elashan Formation is brittle,and the tectonic activity during and after the Indosinian period are so strong that a large number of ore-conducting and ore-bearing structures,which provides a good space for hydrothermal migration and enrichment of ore-forming elements,have been formed in the continental volcanic rocks of the Elashan Formation,.In summary,the silver polymetallic deposit in Hariza Area is a shallow,medium-low temperature hydrothermal vein deposit.The ore body is mainly controlled by structure.The fluid source is mainly magmatic water and a few atmospheric water.The source of ore-forming material is mainly magma.The metallogenic background is the post-collision extension environment of Late Triassic.The continental volcanic rocks of the Elashan Formation develops as the ore-bearing rocks of the silver polymetallic deposit,rather than the ore source layer.