Mineralization And Alteration Geological Characteristics Study In Erentaolegai Silver Deposit,Inner Mongolia

The Erentaolegai silver deposit is located in New Barag Right Banner, southwest of Erguna plot which is a large epithermal silver deposit in Inner Mongolia.According to the studies on isotopic geochronology, the zircon U-Pb ages of quartz porphyry, quartz monzonite, biotite syenogranite and fine-grained granite are 285.4±1.9Ma,294.3±0.6Ma,287.0±1.2Ma and243.9±1.6Ma separately which shows that intrusions in mineral field are formed in Late Hercynian and Indosinian. The wall rock of the mineral field is Tamulangou volcanic rocks formation in the Middle Jurassic, and its K-Ar isochron age is about 160 Ma, which shows that there is no genetic relationship between the intrusion samples and the deposit.Geochemical features of intrusions in Late Hercynian and Indosinian show a loss of large ion incompatible elements such as Ba, Nb, Sr, Zr and Ti, a remarkable enrichment of K and a loss of Ta, a weak negative Eu anomalies, and both displayed as arc granite in tectonic environment discrimination diagrams and show peraluminous S type granite and Under the regional tectonic evolution, which show that the formation of the former three intrusive rock affected by Gu Ya Zhou ocean closed and the last intrusive rock affected by the intracontinental subduction of the Mongol-Okhotian ocean. Geochemical features of volcanic rocks of Tamulangou and Mketouebo group show a high content of Si O2and(K2O+Na2O), high degree of fractionation between heavy and light rare earth elements, an enrichment of light rare earth elements, an enrichment of Rb, Ba,Th, U, and a loss of Nb, Ta, Ti and HREE and a weak negative Eu anomaly, and this two group show features of bimodal volcanic rock which are two end member component. Under the regional tectonic evolution, Tamulangou and Mketouebo group are products of magmatic differentiation evolution with the same magma origin,and their formationinfluenced by lithospheric stretching after the closing of Mongol-Okhotian ocean which are product of stretch tectonic environment.Petrography and electron probe analysis show the ore minerals are mainly galena, sphalerite,chalcopyrite, the gangue minerals are mainly quartz, chlorite, epidote, sericite, biotite, calcite, dolomite, dolomite, manganese calcite. Ag mainly form as independent silver minerals, Silver minerals are mainly argentite and silver halide and manganese oxide has the most closely relationship with silver mineral which has the highest silver content of all minerals.Fluid inclusion studies indicate that the inclusions in mian mineralization stage are all gas-liquid two-phase aqueous inclusions. With the the decrease of the ore-forming temperature, fluid salinity variation is not obvious. The temperature range of sulfide mineralization stage is 285~352℃, with a peak of 320~340℃, the salinity varies is12.62%~2.07%Na Cleqv, with a peak of 2.24%~5.86%Na Cleqv; The temperature range of silver mineralization stage is 171~243℃, with a peak of 220~240 ℃, the salinity varies is 14.97%~1.91%Na Cleqv, with a peak of 2.07%~4.80%Na Cleqv. All these above studies show that this ore deposit has a characteristics of low temperature and low salinity and it is a large epithermal silver deposit.The H-O and C-O isotopic features shows that the ore fluids are mainly derived from the magmatic water, and is a mixture of magmatic water and meteoric fluids; S isotopic features shows that the ore-forming materials may also originate from the magma.The Erentaolegai silver deposit hasmagmatic hydrothermalorigin. Volcanic-subvolcanic magma in the late Mesozoic may offer metallogenic hydrothermal and part of ore-forming materials for the deposit. Halogen such as Cl, Br, I in meteoric fluids are easy to combine with Ag ions to form silver halide, sulfide and sulfosalt of silver which lead to the enrichment of silver and mineralization. Manganese oxide has a strong adsorption capacity to silver, and the supergene weathering leaching process lead to a secondary enrichment of silver.