Sphalerite Chemistry and Carbonate (C, O) Isotope Zonation in the Nayongzhi Mississippi Valley-Type Deposit, Southwest China

Abstract Metal zonation patterns are common in Mississippi Valley-type (MVT) deposits but have received comparatively little attention. The recognition of such patterns can help to fingerprint fluid flow paths and provide valuable vectors for near-mine exploration. The Nayongzhi deposit (30.1 million tonnes [Mt] at 6.57% Zn and 0.91% Pb) exhibits clear lateral and vertical zonation patterns in ore types and metal ratios, making it an ideal case study to explore the behavior of other geochemical zonation markers. In this contribution, we report zonation patterns observed in both carbonate C-O isotope compositions and the trace element chemistry of sphalerite. Ore-related dolomite shows systematically higher δ13CV-PDB (Vienna-Pee Dee Belemnite) and δ18OV-SMOW (Vienna-standard mean ocean water) values with increasing distance to the feeder structure, probably reflecting a decrease in the fluid-rock ratios. In addition, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis of sphalerite revealed systematic spatial and temporal variations in trace element contents. The contents of Mn, Fe, Cu, Ga, Ge, and In decrease with distance from the feeder fault, whereas the contents of Cd increase. Manganese, Fe, Ge, and Tl are also concentrated in early sphalerite, whereas Ga and Cd are more abundant in later sphalerite. Such variations appear to be predominantly governed by changes in physicochemical parameters, such as temperature, fS2, and fluid composition. Finally, multivariate regression analysis identified three footprint elements in sphalerite—Mn, Ga, and In—whose combined compositional variations are particularly informative concerning the relative distances of samples to the feeder fault. The application of the resultant sphalerite proximitor to another structurally controlled MVT deposit effectively traced fluid flow paths and identified the relative distances of samples to the fluid influx center. Consequently, our study highlights the potential of sphalerite trace element chemistry, together with C-O isotopes, to serve as a novel exploration tool in MVT deposits. However, our results also demonstrate that the accurate petrologic identification of paragenetic mineral generations will generally be essential for reliably vectoring toward fluid influx centers.