In situ U-Pb dating of calcite indicates a Miocene Sb-Pb mineralization event in the Sanjiang base metal metallogenic belt, SW China

Abstract

The Sanjiang base metal metallogenic belt (SMB) in southwestern China is characteristic of composite mineralization during the India-Asia continental collision. However, the geodynamic settings of the composite processes of this belt are poorly understood. The Lanuoma deposit, located in the Changdu Basin in the central segment of the SMB, is a Zn-Pb-Sb polymetallic deposit. The cross-cutting relationships and paragenetic mineral associations suggest the superimposition of a late Sb-Pb mineralization event over an early Zn-dominant mineralization event. Calcite is the main gangue mineral, intergrown with late Sb-Pb minerals (e.g., boulangerite, zinkenite, sorbyite and plagionite). In situ U-Pb dating by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) was successfully carried out on calcite from this deposit, and restricts the Sb-Pb mineralization to 19.7 ± 1.6 Ma, with a mean square weighted deviation (MSWD) of 1.2. This age is approximately synchronous with that of strike-slip shearing-related leucogranites in the marginal orogens; together with previous data, this result suggests that the contemporaneous magmatism significantly contributed to the ore-forming fluids associated with the Sb-Pb mineralization. Overprinting of the Miocene Sb-Pb event in a transtensional regime on the Oligocene transpression-driven Zn mineralization resulted in the characteristic Zn-Pb-Sb assemblage at Lanuoma. Moreover, this study indicates that the SMB holds great exploration potential for Sb(-Pb) resources.