Geological and geochemical characteristics of Erentaolegai large-scale silver deposit,Inner Mongolia
The Erentaolegai silver deposit in Inner Mongolia is a large-scale silver deposit in the southwestern part of the Derbugan metallogenic belt,and is located between the Mongolia-Okhotsk orogenic belt and the Derbugan fault.This study shows that ore-forming process of the E'rentaolegai silver deposit can be divided into three stag-es,including quartz-pyrite stage(stage Ⅰ),quartz-sulfide stage(stage Ⅱ),and quartz-manganese carbonate stage(stage Ⅲ).Microthermometric data indicate homogenization temperatures of fluid inclusions ranging mainly from 200℃ to 365℃ in the first two stages with salinities of 13.82％～16.05％and 0.18％～8.14％NaCl equiva-lent,respecively and those of fluid inclusions ranging from 124℃ to 245℃ in the third stage,with salinities of 0.18％～15.42％NaCl equivalent.The temperature and salinity from early to late stage decrease gradually.The metallogenic depth of the main metallogenic stage is estimated to be about 0.48～1.4 1km,with an average of 0.76 km.The hydrogen(δ18OH2O=-11.6‰ to-3.3‰)and oxygen isotopic composition is located at the lower left of range of primary magmatic water but close to that of meteoric water,indicating that the ore-forming fluid was derived originally from a mixture of primary magmatic water and meteoric water,with dominant meteoric water in later stages.The δ34S values of sulfide minerals in the deposit range from-4.0‰ to 4.5‰,implying a mantle sulfur contribution.Lead isotope data of sulfide minerals indicate that the ore-forming materials derived mainly from the deep crust or upper mantle.Integrating geological and geochemical characteristics,the Erentaolegai sil-ver deposit can be interpreted as an epithermal silver deposit related to volcanic-subvolcanic activity.Further-more,we put forward a new genetic model for mineralization of the deposit,and discovered a number of gold,sil-ver and molybdenum polymetallic ore(mineralization)points in the periphery of the deposit.
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