4.7 Article

Geology, fluid inclusion and H-O-S-Pb isotope constraint on the genesis of the Changxing gold deposit, Fujian, South China

Journal

ORE GEOLOGY REVIEWS
Volume 129, Issue -, Pages -

Publisher

ELSEVIER
DOI: 10.1016/j.oregeorev.2020.103887

Keywords

Fluid inclusion; Fluid immiscibility; H-O-S-Pb isotope; Magmatic hydrothermal gold deposit; Changxing gold deposit; South China

Funding

  1. Ministry of Nature Resources of the People's Republic of China [DD20160050, DD20190159]

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The Changxing gold deposit is located in the Wuyi metallogenic belt of South China, characterized by ore bodies hosted in K-feldspar migmatitic granite with various types of fluid inclusions in quartz veins. The fluid inclusion studies suggest that the deposit is a magmatic hydrothermal gold deposit.
The Changxing gold deposit is located in the Wuyi metallogenic belt of South China. Orebodies are primarily hosted in K-feldspar migmatitic granite along the NE- and NNE-striking ductile-brittle fracture structures. The ore minerals mainly include native gold, pyrite, chalcopyrite, whereas the main gangue minerals are quartz, sericite and chlorite. Fluid inclusion studies were conducted on the pre-ore stage quartz veins and main-ore stage quartz veins. Three types of fluid inclusions, namely, CO2-bearing inclusion with smaller carbonic proportion (<40%) (type I), CO2-rich inclusion with higher carbonic proportion (>60%) (type II), and aqueous fluid inclusions (type III) can be observed in the quartz. Primary type I inclusions in pre-ore quartz veins show consistent CO2 phase volumetric proportions with homogenization temperatures of 362-396 degrees C and salinities of 5.0-6.4 wt % NaCl equivalent. The primary coexisting type II and type III inclusions are observed in ore stage quartz vein, sharing similar homogenization temperatures in the range of 292-353 degrees C and 279-335 degrees C, but contrasting salinity values at 1.4- 5.3 and 5.3-10.5 wt% NaCl equivalent, respectively. Petrographic observations and microthermometric results collectively show that fluid immiscibility occurred concurrently with gold mineralization during the main-ore stage. The delta D (-88.9 parts per thousand to -71.8 parts per thousand) and delta O-18 (5.9 parts per thousand to 8.5 parts per thousand) of ore-forming fluids imply that the ore-forming fluids were mainly of magmatic origin. The delta S-34 values (2.1 parts per thousand to 4.9 parts per thousand, with average value of 3.1 parts per thousand) of the main-ore stage pyrite suggest that sulfur was derived from a homogeneous magmatic source. The lead isotopic compositions suggest that the migmatitization of the K-feldspar granitization granite (Pb-206/Pb-204 = 17.953 to 18.147, Pb-207/Pb-204 = 15.636 to 15.688, Pb-208/Pb-204 = 37.727 to 38.851) in the Caledonian had no genetic relationship with gold mineralization of Changxing gold deposit (Pb-206/Pb-204 = 17.466 to 18.157, Pb-207/Pb-204 = 15.551 to 15.619, Pb-208/Pb-204 = 37.727 to 38.508), and the Mesozoic magmatic activity likely provided ore materials of Changxing gold deposit. In summary, we propose that the Changxing deposit is a magmatic hydrothermal gold deposit.

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