Hydrothermal zircon geochronology: Age constraint on Nanling Range tungsten mineralization (Southeast China)

Abstract

The Nanling Range (Southeast China) is well known for its wolframite-bearing-quartz-vein (WQV) tungsten deposit. This study focuses on the geochemistry and geochronology of zircons from the WQV and challenges the current view of the tungsten mineralization in the Nanling Range. The features of the WQV zircons include: (1) pale brown, murky brown, or orange-red color and translucence under microscope; (2) {110}+{101} type crystal form; (3) weak cathodoluminescence; (4) enrichment of Hf (ranging from 1.97 to 7.83wt.% HfO2), U (ranging from 0.02 to 3.97wt.% UO2), Th (ranging from 0 to 0.65wt.% ThO2), and P (ranging from 0 to 1.82wt.% P2O5); and (5) presence of solid (hydrothermal and ore minerals) and fluid inclusions. These features indicate that the WQV zircons crystallized from hydrothermal fluids during tungsten mineralization. The in-situ LA-ICPMS U–Pb results of the WQV zircons from five different tungsten deposits in the Nanling Range yield similar ages, ranging from 134.4±1.9Ma to 132.9±1.5Ma, approximately 20millionyears younger than proposed tungsten ore ages (155±5Ma). Several mineralization characteristics and field observations also cast doubt on the current model — Nanling Range tungsten ore is the result of orthomagmatic processes. The zircon characterization method provided in this study could be applied to tungsten metallogenic research in other parts of the world.