内蒙古长山壕金矿矿床地球化学特征与成因研究

Geological-Geochemical Characteristics and Genesis of Changshanhao Gold Deposit in Inner Mongolia,China

长山壕金矿是近年来在内蒙古中部发现的一个大型浅变质碎屑岩型金矿,产于中—新元古代白云鄂博群比鲁特组碳质板岩和千枚岩中,矿体与围岩呈渐变关系。矿石呈硫化物细脉和石英硫化物细脉状,产于地层层理、节理和破碎带中,与地层同步褶皱变形。矿石的微量元素特征与围岩一致,矿石铅同位素为208Pb/204Pb为37.430 8～38.9792,207Pb/204Pb为15.452 2～15.674 1,206Pb/204Pb为17.109～18.921 7,与地层铅同位素接近。流体包裹体以液相包裹体为主,均一温度230～370℃,平均286.8℃;盐度w(NaCl)为6.01%～20.52%,平均10.84%;包裹体水的δD为-108‰～-112‰,δ18O为6.4‰～9.4‰。地质地球化学特征表明成矿物质来自地层,成矿热液主要来自地层水。研究认为长山壕金矿为沉积-变质型金矿,后期的岩浆活动对成矿作用影响较小。

Changshanhao gold deposit is a large metamorphic microclastic rock type gold deposit hosted in carbonaceous slates and phyllites of the Meso-Neoproterozoic Bilute Formation of Bayan Obo Group in central Inner Mongolia.The gold ore bodies are tabular and lenticular and no clear boundary to wall rocks;the ores occur as sulfur veinlets or quartz-sulfide veinlets deformed with strata in beddings,joints and fractures,which consist of simple minerals with weak alterations.The ore and wall rocks have the similar trace element geochemical feature.The ranges of ore 208Pb/204Pb,207Pb/204Pb and 206Pb/204Pb,close to those of strata,are 37.430 8 to 38.979 2,15.452 2 to 15.674 1 and 17.109 to 18.921 7,respectively.Gold-bearing quartz veins mainly contain liquid fluid inclusion with homogenization temperature of 230 to 370 ℃ and salinity of 6.01% to 20.52% NaCl eqv.δD and δ18O of the fluid are-108‰ to-112‰ and 6.4‰ to 9.4‰.These geological-geochemical characteristics indicate that ore-forming material and fluid come from strata.The authors infer that Changshanhao gold deposit is a sediment-metamorphism mesotherm deposit,and the later magmatic activity had a little effect on the metallogenesis.