Geological and geochemical constraints on the genesis of the Bengge gold deposit in the Yidun Terrane, SE Tibet. (15th June 2020)

• Record Type: Journal Article
• Authors: Jiang, Lili; Xue, Chuandong; Li, Wenchang; Xiang, Kun; Wang, Baodi
• Is Part Of: Journal of Asian earth sciences. Volume 195(2020)
• Publication Date: 2020-06-15
• Subjects: 40Ar/39Ar dating -- Fluid inclusions -- Oxygen isotopes -- Intrusion-related gold -- Bengge gold deposit -- Southeastern Tethys; Earth sciences -- Asia -- Periodicals; Sciences de la terre -- Asie -- Périodiques; Earth sciences; Asia; Periodicals; 555.05
• DOI: 10.1016/j.jseaes.2020.104338
• Languages: English
• ISSNs: 1367-9120

Abstract

Graphical abstract: Highlights: The mineralization event at the Bengge gold deposit occurred during the Cretaceous. The ore bodies are closely related to phyllic alteration and the Bengge deposit is an intrusion-related gold deposit. Ore fluids with significant portion of magmatic waters were derived from deep unexposed intrusions during the Cretaceous. A Cretaceous gold mineralization event occurred in the Zhongdian–Muli region. Abstract: The Bengge gold deposit is one of a small number of deposits in the Zhongdian-Muli region, which is part of the southern segment of the Yidun Terrane in the eastern Tibetan Plateau. The deposit is hosted in a Late Triassic alkaline igneous complex comprising mainly biotite–pyroxene syenite and quartz syenite, emplaced into Triassic slate. These syenites show phyllic alteration with mineral association of quartz–sericite–pyrite–carbonate. The main gold mineralization occurs in fault zones as gold–sulfide–quartz veins, in altered syenite as telluride in veinlets, and as fissure-filling gold in disseminated pyrite. Four stages of veins are recognized: sheeted K-feldspar–quartz–magnetite veins (dikes) (stage I), quartz–carbonate–K-feldspar veins with sericite–quartz–pyrite alteration haloes (stage II), polymetallic sulfide–telluride–sericite–quartz veins with pervasive phyllic alteration (stage III), and quartz–carbonate–stibnite veins (stage Ⅳ). The stage II and III veins are closely related to gold mineralization. 40 Ar/ 39 Ar dating of hydrothermal sericites from the phyllic alteration zone, which are intergrown with gold-bearing pyrite and telluride, yielded an age of ~126 Ma, indicating the mineralization event occurred in the Cretaceous extensional setting. Raman spectroscopy and microthermometry study for fluid inclusions in quartz from stage II revealed heterogeneous trapping of low-salinity (0.14–6.63 wt% NaCl equivalent) and mesothermal (270–300 °C) CO2 –H2 O–NaCl ore-forming hydrothermal fluids. The calculated fluid-trapping pressures range mainly from 750 to 850 bar. δ 18 O values of quartz from the gold mineralization stage (stage II) vary between 15.21‰ and 19.35‰. The δ 18 O values for waters in equilibrium with quartz vary from 6.96‰ to 10.73‰, which are consistent with values for magmatic waters. We propose that the auriferous fluids were derived from an underlying intrusion during the Cretaceous. The geological characteristics, low salinity, and mesothermal CO2 –H2 O–NaCl fluids, and the magmatic source of the ore-forming fluids, all support the hypothesis that the Bengge deposit is an intrusion-related gold deposit.