Genesis of the Thien Ke tungsten deposit, Northeast Vietnam: Evidence from mineral composition, fluid inclusions, S-O isotope systematics and U-Pb zircon ages

Abstract

In the South Asia region, tungsten deposits are mostly distributed in the South China block, covering South China and North Vietnam. These deposits host the majority of the mineralization with over 10 million tons of WO3. Northeastern Vietnam contains the Nui Phao W-F-Cu-Au-Bi deposit, one of the largest tungsten mine in the world. It is characterized by both skarn and greisen features and is genetically linked to the Late Cretaceous Da Lien two-mica granite from the Pia Oac Complex. Furthermore, there is another two-mica granite of presumably Cretaceous age at this location, the Thien Ke intrusion, which is also a host to tungsten mineralization in the Tam Dao District. The Thien Ke quartz vein-type tungsten deposit is located in the southern part of the Lo Gam domain, 24 km west of the largest Nui Phao tungsten deposit in Vietnam. So far, whether the Tien Ke and Nui Phao deposits have formed within a single metallogenic process or are derivatives of unrelated events is unknown. Based on our observations, the Thien Ke deposit is distinguished by at least three evolutionary stages: greisenization, early W-Mo ore deposition, and late sulfide ore deposition. Fluid inclusion studies show that early mineral assemblage with the W-Mo mineralization formed by fluid with temperatures varying from 265 °C to 320 °C and moderate salinities, while late sulfide association was formed at temperatures of 250 °C-300 °C and salinities of 2.5–9 wt% NaCl-eq. Relatively homogeneous isotopic compositions of oxygen (δ18OH2O(SNOW) = +4‰ to + 7.4‰) and sulfur (δ34S(CDT) = −1.4‰ to −3.0‰) suggest that the ore fluid was generated from cooling granite pluton without meteoric water contribution. This work suggests that there are many similar features between the Thien Ke and Nui Phao deposits. The LA-ICP-MS U-Pb zircon age of the Thien Ke granite has been estimated to be ca. 87 Ma, confirming that the Thien Ke and Nui Phao deposits had the common deep-seated magma chamber in the Cretaceous and formed during a single metallogenic process.