Cassiterite and zircon U-Pb ages and compositions from ore-bearing and barren granites in Thailand: Constraints on the formation of tin deposits in Southeast Asia
Liang Liu, Ruizhong Hu, Yazhou Fu, Jie‐Hua Yang, Mei‐Fu Zhou, Wei Mao, Yanwen Tang, Alongkot Fanka, Zhen Li
Abstract
• Two-stage Sn deposits in Thailand deviate from the distribution of granite belts. • The Sn-rich sources were vital for the formation of Sn deposits in Thailand. • Two-stage Sn-enriched melts were induced by entirely different tectonic settings. The Southeast Asian Tin Province comprises western, central, and eastern belts and hosts significant granite-related Sn deposits. The genetic links between granites and Sn mineralization are still unclear. Most Sn deposits are in Thailand’s western and central belts, but their origin remains poorly elucidated due to the absence of direct dating of mineralization. Herein in-situ U-Pb age data of wolframite and cassiterite grains from nine representative Sn deposits in Thailand are obtained, which fall into two stages. Triassic deposits (224–210 Ma) are found in the Central belt, with Cretaceous deposits (78–67 Ma) in the Central belt being younger than those in the Western belt (84–74 Ma). However, ore-bearing granites, spanning two periods (227 − 205 Ma and 85 − 69 Ma), occur in central and western belts. Some Triassic ore-bearing granites exhibit significantly older ages than ore-forming ages. Newly identified ore-forming granites contain zircon grains with relatively low ε Hf ( t ) values (−29.5 to + 4.1; average = − 11.8), indicative of an origin from supracrustal sediments from the Sibumasu block. In contrast, barren granites have ages from 303 − 224 Ma and higher zircon ε Hf ( t ) values (−9.9 to + 13.2; average = +1.2), which suggests that they were derived from the juvenile mafic crust. Even after experiencing hydrothermal fluids exsolution, some low-fractionated ore-forming granites (D.I. < 90) still maintain remarkably high tin contents. Both ore-forming and barren granites crystallized under reducing conditions. Our study highlights the importance of Sn-rich sources of parental magmas in forming Sn deposits. The metasediment-rich basement of the Sibumasu block distributing along the continental margin is likely the Sn-rich source. These sources played a crucial role in forming two stages of tin deposits in distinct tectonic settings, that are syn -collisional crustal thickening in Paleo-Tethys and post-collisional extension-related settings in Neo-Tethys.