Geology and genesis of the world-class wollastonite deposit at Shizhushan in South China and implications for exploration

ABSTRACT Wollastonite is an important calc-silicate mineral that has been widely used in industrial manufacturing. However, massive accumulations of wollastonite are not common in nature. In this study, we investigated the geology and genesis of the world’s largest wollastonite deposit (69.55 million tonnes [Mt] of wollastonite) at Shizhushan in the Mengshan district, South China. The wollastonite orebodies in the Shizhushan deposit are hosted by chert-bearing limestones within the Permian Makou Formation formed during the contact metamorphic stage, which is largely dependent on the distance between the Late Triassic magma and strata. Garnet and calcite veinlets, which crosscut the wollastonite orebodies, yielded well-constrained U-Pb ages of 225.3 ± 2.4 Ma (mean square weighted deviation [MSWD] = 0.9; n = 51) and 224.9 ± 2.6 Ma (MSWD = 1.1; n = 45), respectively. These determined ages are coeval with previously published ages of the medium-grained porphyritic biotite granite and fine-grained porphyritic granite (ca. 226 Ma), implying that the emplacement of Late Triassic granites into the chert-bearing limestone led to the formation of the Shizhushan wollastonite deposit. We compiled geological features of wollastonite deposits worldwide and used thermodynamic and thermal diffusion modeling to constrain the key factors controlling the formation of giant wollastonite deposits. These compiled geological features, as well as our thermodynamic and thermal diffusion modeling results collectively unveil that (1) chert-bearing limestone or interbedding of limestone and siliceous rocks (i.e., with minimal dolomite content), (2) enough fluid infiltration, and (3) a sufficient supply of thermal energy from deep-seated plutons (2–4 kbar), are three critical factors controlling the formation of giant wollastonite deposits.