Key factors controlling Neoproterozoic tin metallogenic events in southwestern China: Multidisciplinary approach using geology, geochemistry, and geochronology

Abstract

The scarcity of Precambrian tin deposits in China has drawn significant interest to their formation. The Chahe tin deposit (26 Mt @ 0.38 % Sn), one of the oldest in China, provides a valuable opportunity to investigate the key factors controlling the development of such deposits. Situated along the western margin of the Yangtze craton in southwestern China, this deposit exhibits diverse mineralization types, including greisen cassiterite mineralizations located on top of the granitic cupola, skarn-cassiterite-axinite-quartz veins, and cassiterite-sulfide veins at the granite-limestone contact, and structurally controlled occurrences within siliciclastic metasedimentary rocks along secondary faults. Extensive U-Pb dating reveals that both barren and tin-bearing granites associated with the deposit share similar ages, ranging from 851 ± 4 Ma to 848 ± 4 Ma. These ages closely match, within error, the cassiterite U-Pb age of 843–853 Ma and the rutile U-Pb age of 859 ± 27 Ma for greisen veins/veinlets hosted in granite. Additionally, a cassiterite U-Pb age of 844 ± 9 Ma has been identified in the cassiterite–axinite–quartz veins hosted in the skarn. These findings provide direct evidence for the spatial, temporal, and genetic association of tin mineralization with Neoproterozoic Mosuoying granites. The granites in the region are categorized as peraluminous calc-alkali granites, characterized by high FeO, Ga/Al ratios, and zircon saturation temperatures, indicative of A-type granite features. In comparison to regional contemporaneous granites, the barren and tin-bearing granites exhibit high Rb/Ba and Rb/Sr ratios, variable ε_Hf(t) values (–17.8 to + 3.1), and two-stage Hf model ages (T_DM2) spanning from 2.6 to 1.5 Ga. These characteristics indicate a common source and origin through the reworking of Paleo- to Mesoproterozoic metasedimentary crust in response to the breakup of the Rodinia supercontinent. Simultaneously, they display low whole-rock Fe₂O₃/FeO and zircon Ce⁴⁺/Ce³⁺ ratios, consistent with those observed in typical Sn-bearing ilmenite-series granites globally. Notably, the tin-bearing granites manifest a highly fractionated nature, evident in their REE distribution patterns with a pronounced tetrad effect, as well as lower Nb/Ta and Zr/Hf ratios for twin elements. In summary, this study emphasizes the significance of a metasediment-derived source and the presence of highly evolved, reduced, or ilmenite-series granitic magma in the development of highly fractionated A-type granites associated with Neoproterozoic tin mineralization. These findings provide insights into the crucial factors controlling Neoproterozoic tin metallogenic events, shedding light on metallogenic processes and systematic exploration strategies for tin in Precambrian terranes.