Metallogenesis Of The Jiawula-Chaganbulagen Pb-Zn-Ag Orefield, Inner Mongolia, China

The Jiawula-Chaganbulagen(Jia-Cha for short) orefield is located in the southwest part of the Derbugan metallogenic belt, including the Jiawula and Chaganbulagen large Pb-Zn-Ag deposit. This paper systematically studies the fluid inclusion, geochronology and geochemistry of the Jia-Cha orefield. The fluid inclusions of porphyry Mo-mineralization in the Jia-Cha orefield include liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions and have homogenization temperatures, densities, and salinities of 225°C to 438 °C, 0.35 g/cm3 to 1.37 g/cm3, and 0.8 wt% NaCl eqv. to 44.6 wt% NaCl eqv., respectively. The gas phase components are mainly H2 O, CO2 and CH4. The fluid inclusions of the main stage in the Jiawula deposit are liquid-rich, gas-rich and H2O–CO2 inclusions with homogenization temperature, densities, and salinities of 190°C to 332°C, 0.65 g/cm3 to 0.88 g/cm3, and 0.2 wt% NaCl eqv. to 4.2 wt%NaCl eqv., respectively. The gas phase components are mainly H2 O, CO2 and a small amount of CH4. The fluid inclusions of the main stage in the Chaganbulagen deposit have only liquid inclusions with omogenization temperatures, densities, and salinities of 209°C to 265 °C, 0.75 g/cm3 to 0.86 g/cm3, and 0.5 wt% NaCl eqv. to 5.7 wt% NaCl eqv., respectively. The gas phase components are mainly H2 O, CO2 and a small amount of CH4. The studies of fluid inclusions indicated the fluid boiling and temperature decrease are the dominant mechanism for the deposition of ore-forming materials in the Jiawula and Chaganbulagen deposit, respectively. The δDV-SMOW and δ18Owater values vary from-166‰ to-133‰ and-13.4‰ to-9.1‰ in the Jiawula deposit, and from-166‰ to-127‰ and-17.9‰ to-10.8‰ in the Chaganbulagen deposit, suggesting that the ore-forming fluids mainly consist of meteoric water with a small amount of magmatic water in the Jiawula deposit and meteoric water in the Chaganbulagen deposit. The δ34SV-CDT values range from 1.2‰ to 8.4‰. The 206Pb/204 Pb, 207Pb/204 Pb, and 208Pb/204 Pb values of the ore minerals are in the ranges of 18.302-19.037, 15.473-15.596, and 38.094-38.945, respectively. The δ34S∑ and μ values of the Jia-Cha orefield respectively is 2.8 ~ 7.1‰ and 9.2 ~ 9.5, indicating the ore-forming materials came from Mesozoic magma. The sulfide Rb–Sr isochron age of the Jiawula deposit is ca. 143–142 Ma,the sericite sample yielded a 40Ar–39Ar plateau age of 138 ± 1 Ma and an isochron age of 137 ± 3 Ma, and the zircon LA-ICP-MS U–Pb age of monzogranite porphyry was 143 ± 2 Ma, indicating the age of mineralization and monzogranite porphyry in the Jia-Cha orefield should be the Early Cretaceous. The data of zircon U-Pb dating show that the Tamulagou Formation formed in 173 ~ 172 Ma, the Manketouebo Formation formed in 154 Ma, the Late Hercynian granite formed in 258 ~ 252 Ma. The geological characteristics, fluid inclusions and geochemistry suggested the Jiawula and Chaganbulagen vein-type Pb-Zn-Ag deposits are the low-sulfidation epithermal deposits. The vein-type Pb-Zn-Ag deposits and porphyry Mo mineralization belong to the same porphyry-epithermal mineralization system. The important mineralization in the Manzhouli area occurred in three periods:(1) Late Triassic porphyry Cu–Mo mineralization;(2) Early Jurassic porphyry Cu–Mo mineralization; and(3) Early Cretaceous epithermal Pb–Zn–Ag, Ag, and Au–Cu mineralization.. The deposit types are mainly porphyry, epithermal and skarn.