Examining trace elements of cassiterite as fingerprints for tectonic settings of tin deposits: An example from the SE Asian tin province

Abstract

Southeast Asia is a major global tin province and consists of three metallogenic belts: the Eastern, Central, and Western belts, which formed in oceanic subduction, continental collision, and post-subduction extensional settings, respectively. This study applies machine learning (eXtreme Gradient Boosting and SHapley Additive exPlanations) to cassiterite trace element data from SE Asia to identify key fingerprint elements and/or element ratios that distinguish these settings. Significant differences in Ti/Hf, Zr/Hf, Sc/Hf, Ti/Fe, and W/U ratios were observed, aligning with machine learning results. Compiling geochemical data from ore-forming granites in the three belts indicates that the elemental composition of cassiterite is closely linked to the geochemical characteristics of the corresponding granites. In the Western belt, mantle degassing contributed to highly evolved, fluorine-rich granites, producing cassiterite with the lowest Ti/Hf, Zr/Hf, and Sc/Hf ratios. The Central belt granites, derived from a reduced crust in a collision setting, enriched fluids in divalent Fe, leading to cassiterite with the highest Ti/Fe ratio. The Eastern belt, associated with fewer W-bearing minerals, shows higher W/U ratios due to limited tungsten depletion in ore-forming fluids. Using these five fingerprints, linear discriminant functions distinguish the three belts with 87% accuracy. Our findings indicate that the volatile content, differentiation, and oxygen fugacity of magma vary with tectonic settings and significantly influence the trace element composition of cassiterite. Therefore, this evolutionary pattern, from tectonic settings to magma properties and ultimately to tin mineralization characteristics, suggests that cassiterite may serve as an effective indicator for determining the tectonic setting of tin deposits.