Malayaite as an effective geochronometer and geochemical tracer for tin deposits: Constraining ore-forming processes of Jianfengpo tin deposit (Jiangxi, South China)

Malayaite, a Sn-bearing silicate mineral, holds great promise for constraining the timing of tin mineralization, yet its reliability and practical utility as a direct geochronometer for tin deposits remains unvalidated by systematic in situ analyses and cross-comparison with coexisting ore minerals. This study focuses on the Jianfengpo stratabound tin deposit in the middle Jiangnan Metallogenic Belt, Jiangxi Province, South China, with the main objective of rigorously establishing malayaite as an effective, reliable geochronometer for tin deposits; and secondarily deciphering the deposit’s ore-forming processes and genetic model via integrated in situ geochronological and geochemical analytical techniques. The deposit, hosted in Neoproterozoic Liantuo Group sandstone and conglomerate, contains two genetically distinct types of malayaite (Mly-I, Mly-II) and three types of cassiterite (Cst-I, Cst-II, Cst-III) in its hydrothermal assemblages. In situ laser ablation–inductively coupled plasma–mass spectrometry U-Pb dating yields a precise age of 128.5 ± 4.4 Ma for Mly-I, which forms in the early high-temperature ore-forming stage. This age is consistent, within analytical uncertainty, with the ages of coexisting cassiterite (Cst-I: 124.9 ± 2.1 Ma; Cst-III: 124.0 ± 2.5 Ma) and the zircon U-Pb ages (129–128 Ma) of the nearby Pengshan Yanshanian granite, the causative magmatic body for mineralization. This age consistency provides definitive, direct validation that malayaite functions as an effective geochronometer for tin deposits, addressing the limitation of cassiterite, which may only crystallize in narrow hydrothermal windows and thus fails to record the full initiation and evolution of Sn-bearing fluid activity, while malayaite forms in the early high-temperature stage and preserves the initial timing of the tin ore-forming system. Complementary in situ geochemical analyses further constrain the ore-forming mechanism and fluid evolution: (1) Cathodoluminescence and trace element data of malayaite reveal a gradual weakening of Sn4+-Ti4+ substitution from Mly-I to Mly-II, a clear indicator of a continuous temperature decrease in ore-forming fluid from high-temperature Stage A to moderate-temperature Stage B. (2) Garnet major element variations (increasing andradite content from Grt-I to Grt-II) and cassiterite trace element signatures (enhanced Sb-W correlation, decreased U/Zr-Hf ratio) collectively document a persistent rise in fluid oxygen fugacity. (3) Sulfur isotopic compositions of sulfides from ores (δ34S: 6‰–12‰) match those of pyrite in Pengshan muscovite granite, confirming a magmatic fluid source with minor modification by country rock interaction. Integrated results confirm that the Jianfengpo deposit is a magmatic-hydrothermal alteration deposit and elucidate the key controls on Sn mineral partitioning: High-temperature Sn-bearing magmatic fluids from the Pengshan granite migrated via faults to the Liantuo Group strata; in closed, high-temperature systems, Sn preferentially incorporated into malayaite (non-economic); and subsequent evolution to open systems (e.g., meteoric water mixing) triggered rapid cooling and a sharp elevation in oxygen fugacity, which drove Sn to crystallize as cassiterite and form economic orebodies. This study establishes a foundational framework for the use of malayaite as a dual geochronological and geochemical tracer for tin deposits. Beyond resolving the genetic controversy of the Jianfengpo deposit, this work provides a new genetic model for stratabound tin deposits in the Jiangnan Metallogenic Belt and introduces a transformative new tool for global tin deposit geochronology and metallogenic process research.