Characteristics Of The Ore-forming Fluids And Oreforming Mechanism Of Hadat Tolgoi Lead-zinc(silver) Deposit

The Hadat Tolgoi deposit is a medium-sized lead-zinc?silver?deposit discovered in the Abaqi Banner in Inner Mongolia in recent years.The deposit is located in the Erlianhot-Dongwuqi copper-molybdenum-silver-lead-polymetallic metallogenic belt in the northern section of the Greater Xing'an Mountains.The ore bodies are mainly vein-like and lenticular,mainly occurring in the Devonian and Permian tectonic alteration fracture zones and structural fractures.Field observation and petrographic studies show that the mineralization of the deposit can be divided into three stages:pyrite-quartz stage,galena-sphalerite-pyrite?silver?mineral-quartz and calcite-fluorite-quartz stage.The hand specimens were observed under the microscope and found that the metal minerals of the deposit were mainly galena,sphalerite,pyrite,chalcopyrite and pyrrhotite.Silver minerals are mainly distributed between sulfide mineral fractures and interstices or intermediate sulfides.Fluid inclusion studies indicate that the inclusions are mainly of liquid-rich and gas-rich inclusions,containing a small amount of CO₂ three-phase inclusions and single gas or liquid inclusions.Mineralization fluid salinity changes are not obvious,respectively 0.88¹1.22 wt.%NaCl equiv,1.57¹3.40 wt.%NaCl equiv,2.07¹3.18 wt.%NaCl equiv.The ore-forming fluids are characterized by medium to high temperatures,low salinities and low densities,belonging to the H₂O-NaCl±CO₂ fluid system.Carbon and oxygen isotope analyses show that?¹⁸O_V-_SMOW and?¹³C _V-_PDB were-2‰to+8.8‰,and-6.8‰to-4.4‰,respectively,indicating that the ore-forming fluid is derived from magmatic hydrothermal,with a subsequent involvement of meteoric water.The ore-forming fluid in the late stage is marked by the mixed fluid of magmatic water with meteoric water.The?³⁴S values of sulfides vary from+3.7 to+8.6‰,indicating that the sulfur of Hardat Tolgoi lead-zinc?-silver?deposit is mainly derived from magma and strata.The lead isotope data of sulfides indicate that the ore-forming metals are derived from deep magma,and there might be an involvement of wall rocks during the mineralization processes.Combined with fluid inclusions and isotopic data,the ore-forming fluids are mainly of magmatic signature,and ore-forming metals are characteristed by a mixture source.Fluid mixing is likely to be an important mechanism in leading to the precipitation of ore-forming elements such as lead,zinc,and silver.The Hardat Tolgoi lead-zinc?silver?deposit belongs to the medium-high temperature hydrothermal metasomatic deposit.