Origin and tectonic setting of Pingqiao fluorite-lithium deposit in the Guizhou, southwest Yangtze Block, China

Abstract

Fluorite and lithium have become extremely important minerals globally. The newly discovered medium-to-large-scale Pingqiao fluorite-lithium deposit in the southwest Yangtze Block contains a rare mineral system with fluorite and lithium associations. This unique deposit provides an excellent example for the study of the origin and formation processes of the fluorite-lithium mineral system. The fluorite ore bodies in the Pingqiao mining area are hosted in the silicified limestone of the late Carboniferous Nandan Formation, and the lithium-bearing ore bodies occur in the claystone and micrite of the early Permian Longyin Formation. Fluorite and lithium clay show different REE patterns, but both have negative Eu and Ce anomalies. The isochron age yielded by the fluorite Sm-Nd isotope data was 152.0 ± 3.7 Ma. The δDV-SMOW values ranged between −63.1‰ and −56.8‰, and the δ18OV-SMOW values ranged from −5.7‰ to −4.9‰. The δ13CV-PDB values were between 1.3 and 2.7‰ for calcite. The 87Sr/86Sr ratios ranged between 0.708489 and 0.708810 for Li-clay and 0.708584 to 0.709180 for fluorite. The field geological, petrological, and geochemical data reported in this study indicate the following salient findings: (1) the ore-forming fluid was formed by mixing basinal water and meteoric water; (2) the ore-forming materials originated from the Cambrian, Ordovician, and Devonian carbonate rocks, and Carboniferous limestone; and (3) the deposit was formed in an extensional setting within the Yangtze Block and is closely associated with the late Jurassic to early Cretaceous polymetallic events and is related to the flat-slab subduction and delamination of the Paleo-Pacific plate. We propose a model of fluorite-lithium mineralisation that explains the fluid composition, transport, and precipitation mechanisms involved in the mineral system.