2006 年 40 巻 3 号 p. 265-275
The Meng'entaolegai Ag-Pb-Zn-In polymetallic deposit is located in the eastern part of Inner Mongolia. It consists of a hydrothermal quartz-sulfide vein deposit hosted within a Hercynian granite massif which is about 400 km2 in size. More than 40 orebodies are found in the orefield which is 6 km in length from east to west and 200 to 1,000 m in width from south to north. All orebodies are controlled by E-W trending faults. Economic resources are dominated by Pb and Zn (reserves of Pb and Zn are 0.17 Mt and 0.37 Mt, and their grades are 1% and 2.3%, respectively), with Ag, Sn, In and Cd (1,800 t Ag, >2,000 t Sn, >500 t In and 1800 t Cd) as by-products. The δ34SCDT values of sulfides range from -1.7‰ to +4.6‰, averaging 1.4‰, indicating that sulfur is magmatic in origin. The H-O isotopic compositions (δD values from -52.8‰ to -66.9‰ and δ18OH2O values from 4.8‰ to 7.9‰) of the fluid inclusion water in quartz show that the ore-forming fluid has a mainly magmatic source. The lead isotopic compositions of ore are relatively homogeneous and are significantly lower than those of feldspars and whole rock of the Hercynian Meng'entaolegai granite and the Yanshanian Duerji granite. Neither these granites nor the regional basement Precambrian metamorphic rocks provided ore with lead. By comparison, ore lead isotopic composition is the same as that of E-W trend diorite dykes which intruded the granites and this indicates that the ore lead is probably derived from magamatism which is related to these dykes. We considered therefore that although orebodies occurred within the Hercynian Meng'entaolegai granite, the deposit origin is not related to this stage of magmatism.
