Geology, geochemistry and genesis of the world-class Shizhushan wollastonite deposit, Mengshan area, South China

Abstract

The recently discovered Shizhushan wollastonite deposit in the Mengshan district contains about 54 Mt of wollastonite, making it the world’s largest wollastonite deposit. Zircon U–Pb geochronological results indicate that the Mengshan composite pluton evolved during a prolonged magmatic history (ca. 230–218 Ma). The pluton and the surrounding carbonate units of the Maokou Formation have distinct initial 87Sr/86Sr ratios, with values of 0.7107–0.7162 and 0.7070–0.7075, respectively. Pure wollastonite crystals in the Maokou Formation are characterized by uniform 87Sr/86Sr values of 0.7070 that are indistinguishable from the carbonates, suggesting that the wollastonite was formed during contact metamorphism. Limestones of the Maokou Formation are characterized by variable δ13CV-PDB (−5.2 to 4.0‰) and δ18OSMOW (10.3 to 22.6‰) values. Carbonates with the lowest δ13CV-PDB and δ18OSMOW values (and elevated 87Sr/86Sr ratios) occur in the vicinity of a regional structure, suggesting that magmatic–hydrothermal fluids and CO2 were channeled along this fault.Based on new geological, geochronological and geochemical data, we propose that the world‐class wollastonite deposit formed as a result of several factors related to a relatively stable depositional environment during the Late Paleozoic as well as structural deformation and magmatic events during the Early Mesozoic. These features include: 1) juxtaposition of abundant sediment-hosted chert (SiO2) and limestone (CaCO3) units, 2) a prolonged heat source provided by multiple magmatic events, 3) CO2 degassing along the regional structure promoted wollastonite-forming reactions, and 4) the proximity of the Si- and Ca-rich sedimentary layers subparallel to the intrusion contact. Our study documents the important roles of Early Mesozoic deformation and magmatism in the genesis of non-metallic mineral deposits in south China.