Triassic granitic magmatism in the Lancangjiang zone in southwestern China associated with Paleo-Tethys evolution and its control on tin mineralization

Abstract

Tin deposits are predominantly associated with granitic rocks, yet the factors controlling tin enrichment in granites remain controversial. Here, we investigated the Daguanshan pluton within the central part of the Lincang batholith in the Lancangjiang zone, southwestern China, representing a northern extension of the Southeast Asian tin belt (spanning Thailand, Malaysia, and Indonesia) as part of the Paleo-Tethyan tectonic realm. The Daguanshan pluton, linked to the Hongmaoling tin deposit, is composed of variably evolved granite units, including hornblende-biotite granite, biotite granite, two-mica granite, and muscovite granite. Zircon U-Pb ages of the Daguanshan granite units range from 235.2 ± 0.7 Ma to 230.3 ± 1.2 Ma, consistent with the cassiterite U-Pb age of 238.2 ± 4.5 Ma for Hongmaoling mineralization. The four granite units have similar zircon εHf(t) values (−11.1 to −5.1) and bulk-rock εNd(t) values (−10.1 to −9.5) and show a magmatic fractionation trend. The less evolved hornblende-biotite granite and biotite granite, characterized as I-type granites, were probably derived from the remelting of early Paleozoic metamorphic igneous rocks in a postcollisional setting. Subsequently, the more evolved two-mica and muscovite granites emerged from these magmas, enriching tin contents from ∼3.7 ppm to 25 ppm. Analysis of whole-rock Fe2O3/FeO ratios and zircon oxybarometry indicates that the oxygen fugacity of the less evolved granites was lower than the fayalite + magnetite + quartz (FMQ) buffer, and it decreased further with magma fractionation due to magnetite crystallization. Comparative assessments of the Daguanshan granites and the broader Lincang batholith, alongside Triassic tin granites in Southeast Asia, illuminate a cohesive tectonic origin linked to a collisional setting subsequent to the closure of the Paleo-Tethyan Ocean. These findings highlight the potential for significant tin mineralization within the highly evolved Triassic granites in the Lancangjiang zone.