Hydrothermal Fluid Sources of the Fengjia Barite–fluorite Deposit in Southeast Sichuan, China: Evidence from Fluid Inclusions and Hydrogen and Oxygen Isotopes

Abstract

The Fengjia barite–fluorite deposit in southeast Sichuan is a stratabound ore deposit which occurs mainly in Lower Ordovician carbonate rocks. Here we present results from fluid inclusion and oxygen and hydrogen isotope studies to determine the nature and origin of the hydrothermal fluids that generated the deposit. The temperature of the ore‐forming fluid shows a range of 86 to 302 °C. Our detailed microthermometric data show that the temperature during mineralization of the fluorite and barite in the early ore‐forming stage was higher than that during the formation of the calcite in the late ore‐forming stage. The salinity varied substantially from 0.18% to 21.19% NaCl eqv., whereas the density was around 1.00 g/cm3. The fluid composition was mainly H2O (>91.33%), followed by CO2, CH4 and traces of C2H6, CO, Ar, and H2S. The dominant cation was Na+ and the dominant anion Cl‐, followed by Ca2+, SO42‐, K+, and Mg2+, indicating a mid–low‐temperature, mid‐low‐salinity, low‐density NaCl–H2O system. Our results demonstrate that the temperature decreased during the ore‐forming process and the fluid system changed from a closed reducing environment to an open oxidizing environment. The hydrogen and oxygen isotope data demonstrate that the hydrothermal fluids in the study area had multiple sources, primarily formation water, as well as meteoric water and metamorphic water. Combined with the geological setting and mineralization features we infer that the stratabound barite–fluorite deposits originated from mid–low‐temperature hydrothermal fluids and formed vein filling in the fault zone.

Nature and Genesis of the Xiaobeigou Fluorite Deposit, Inner Mongolia, Northeast China: Evidence from Fluid Inclusions and Stable Isotopes

“…The analytical method and procedure were similar to those previously described in detail by Burke () and Zou et al . ().…”

Formation timing and genesis of Madiu fluorite deposit in East Qinling, China: Constraints from fluid inclusion, geochemistry, and H–O–Sr–Nd isotopes

“…The precisions of the δD H2O and δ 18 O H2O analyses were ±2‰ and ±0.2‰, respectively. Detailed analytical procedures were described in Cao et al () and Zou et al ().…”

“…Fluid inclusions (Fls) and stable isotopes (e.g., hydrogen and oxygen) have been widely used to recognize the origin and evolution of ore-forming fluids (Constantopoulos, 1988;Guilhaumou, Ellouz, Jaswal, & Mougin, 2000;Palmer & Williams-Jones, 1996;Pei et al, 2017;Zou, Zhang, Chen, Fang, & Zeng, 2016), and rare earth element (REE) studies are helpful to reveal the genesis of fluorite deposits (Fawzy, 2018;Sánchez et al, 2010;Schwinn & Markl, 2005;Subías & Fernández-Nieto, 1995). Due to the similar elemental behaviours between Sr and Ca, Sr isotopes can be used to determine the source of Ca (Deng et al, 2015;Ruiz, Kesler, & Jones, 1985;Ruiz, Kesler, Jones, & Sutter, 1980;Sato et al, 2003).…”

New evidence from the Wuliji'Oboo fluorite deposit for the role of the paleo‐Pacific Plate and Mongol–Okhotsk suture in creating extensive fluorite mineralization in the Great Xing'an Range, NE China

“…Hydrogen isotopes in fluid inclusions were determined using the water burst method to extract the water and the zinc method to extract the hydrogen with an explosion temperature of 350°C. Hydrogen and oxygen isotope analysis accuracies were ± 2‰ and ± 0.2‰, respectively, based on the analysis of standard mean ocean water (SMOW) standards (Zou et al, 2016).…”