The Luanchuan Mo–W–Pb–Zn–Ag magmatic–hydrothermal system in the East Qinling metallogenic belt, China: Constrains on metallogenesis from C–H–O–S–Pb isotope compositions and Rb–Sr isochron ages

Abstract

The Luanchuan Mo–W–Pb–Zn–Ag polymetallic ore district is located in the East Qinling metallogenic belt on the southern margin of the North China Craton. Two ore fields (Nannihu and Yuku) are recognized in the district, and three types of deposits are identified from the two ore fields as follows: (1) the 6 proximal porphyry–skarn type Mo–W deposits occurring at the inner contact zone of the granite porphyries, (2) the 3 middle skarn–hydrothermal type Zn deposits, and (3) the 8 distal hydrothermal type Pb–Zn–Ag deposits at the periphery of the porphyry. We present C–H–O isotope compositions of hydrothermal quartz and calcite, S–Pb isotope compositions of sulfide minerals, and sphalerite Rb–Sr isochron ages from the 17 deposits. The geochemical and geochronological data from the two ore fields all show systematic temporal and spatial variation, and primarily lead to the following inferences. (1) The temperatures and salinities of the ore-forming fluids decreased during mineralization. The ore-forming fluids gradually evolved from magmatic water to mixed magmatic–meteoric water. (2) The metallogenic components were primarily derived from igneous rocks, with increasing proportions of the materials from the ore-bearing rocks. (3) The mineralization ages of these deposits are close (147–136Ma), which correspond to the emplacement of the granite intrusions. (4) The three types of deposits and the ore-related late Mesozoic intrusives constitute a unified magmatic–hydrothermal–mineralization system. Finally, we also suggest exploration strategies for the Luanchuan ore district.