The Bilihe Big Porphyry Au Deposit In Inner Mongolia: Geological Character, Its Discovery And Singnificance

The north edge of North-China Plate is one of important gold-polymetal metallogenic belts. It undergone poly-periods plate subduction and continental-margin accretion of Paleozoic era, had strong structure-magmatic activity and ascendant metallogenic geological condition. The Bilihe gold deposit locates in the Paleozoic accretion zones of north edge of North-China Plate, is a state-operated mine at resource conjuncture and close to bankrupt. Based on analysis of regional metallogenic geological condition, evaluation of mine resource potential and research of field geological character, the deposit was a epithermal-porphyry type gold deposit that formed after paleo-Asia ocean subducting collision and accretion of north-margin of North-China in Early Paleozoic, superimposed continental-margin volcanic-magmatic setting of Later Paleozoic (Permian Period). This paper took pertinency geological research as guidance, porphyry type model as direction, general technique methods as means, and prospecting exploration as basic way, discovered a large concealed porphyry type gold deposit around Bilihe mine firstly. The Bilihe gold deposit had character of large scale(more than 20 t per orebody), high grade(top to 52.75×10-6), small change, shallow embedding, low content of metallic mineral(less than 3%), simple ore, and easy mine and dressing. The mineralization age of the Bilihe deposit was (271.3±1.7)Ma(MSWD=1.06). The deposit was controlled by combined part of NE and NW strike structure and granodioritic porphyry units. The zoning character of the deposit from depth to shallow, from center to border was kali-silicate alteralization zone→kali-silicate alteralization zone+quartz-sericitization congruence zone→quartz-sericitization + intermediate argilization→kaolinization and opalizztion. The homogenization temperatures of quartz had two zones of 550℃and 380℃. The salinity was 0.88%~8.68%. The character of H, O isotope indicated that the mineralizing fluid was the mixture of magmatic water and meteroric water. The describing model was established in this paper. The discovery of the Bilihe deposit had important significances as follows: 1)provided a typical example for triumphant actualizing conjuncture mine succeed resources item; 2) explained a science topic that this area as a typical arc-structure-magma setting but no typical porphyry deposit; 3)provided new clew for regional fundamental geological study; 4)offered scientific lead for porphyry deposit founding in similar setting; 5)supplied new model for forecasting prospect in this area.