W-rich zircons from the granite in the Hukeng tungsten deposit, South China: Genesis and exploration significance

Abstract

South China is endowed with copious hydrothermal tungsten ore deposits, which are generally suggested to be associated with highly fractionated granites. However, the mechanism of tungsten enrichment and mineralization during magmatic-hydrothermal processes is not clear. Here, we clearly identified W-rich zircons (up to several thousand ppm) from the granite in the Hukeng tungsten deposit in South China. W-rich zircons are generally dark in cathodoluminescence images with irregular cracks, cavities and blurry oscillatory zones. They also show high contents of U, Nb, REEs, and high W/Gd ratios, which are not possible to be produced only by magma differentiation. Raman spectra of zircons indicate that these W-rich zircons have experienced different degrees of metamictization. Thus, these W-rich zircons should be crystallized from the late magma and subsequently altered by W-rich magmatic-hydrothermal fluids. W-rich zircons record the activity of W-rich ore-forming fluids which were exsolved from the granitic magma. We suggested that the W/Gd ratios of > 0.2 of zircons can be used as an indicator to estimate the W mineralization potential of a granite. This study provides a new pathway for using zircon to record tungsten mineralization processes and to guide tungsten ore prospecting.