Dating of granite-related tin mineralisation at Quy Hop, Vietnam: Constraints from zircon and cassiterite U-Pb and muscovite 40Ar/39Ar geochronology

Quy Hop is an important tin mining district in the North Central Coast province of Vietnam. The exposed magmatic plutons include Late Oligocene - Early Miocene granitoid and Middle Triassic granitic gneiss. Tin mineralisation in the area is spatially associated with biotite granite of the Ban Chieng Complex. Quartz vein-type and greisen-type tin ores occur in quartz-sericite-graphite schist of the Ordovician-Silurian Song Ca Formation and the greisenised granite of the Late Oligocene Ban Chieng Complex, respectively. The lack of accurate geochronological dates for the tin deposits and spatially associated granitic rocks limits our understanding of the genetic relationship between tin mineralisation and granitoid intrusions. In this study, granitic zircon and cassiterite laser ablation and inductively coupled plasma mass spectrometry U-Pb and muscovite 40Ar/39Ar dating techniques were applied to address this lack of understanding. Granitic zircon U-Pb dating of two biotite granite samples obtained from Ban Chieng yielded intersection ages of 26.65 +/- 0.33 and 23.89 +/- 0.15 Ma, interpreted here as representative igneous emplacement ages. Cassiterite U-Pb analyses yielded Pb-207/Pb-206-U-238/Pb-206 intersection ages of 26.81 +/- 1.92 Ma for the quartz vein ore from Suoi Bac and 23.23 +/- 0.89 Ma for greisen ore from Ban Ngoc. Muscovite 40Ar/39Ar laser step heating of the greisen ore yielded a plateau age of 23.87 +/- 0.14 Ma and a corresponding inverse isochron age of 23.85 +/- 0.16 Ma. These geochronological results strongly suggest that tin mineralisation at Quy Hop occurred in the period between 26 and 23 Ma and, therefore, is closely genetically related to the Late Palaeogene granites of the Ban Chieng Complex. The exploration implication of the new age data is considerable, indicating that biotite granite intrusions may be favourable for tin mineralisation across the entire Phu Hoat Terrane.

Automated summary

The study shows that tin mineralisation in Quy Hop is closely related to Late Palaeogene granites of the Ban Chieng Complex and occurred between 26 and 23 Ma. This finding has important implications for tin exploration in the Quy Hop area.