Fluid evolution and ore genesis of the Lianhuashan lode gold deposit, northern North China Craton: evidence from fluid inclusions and H–O–C–S–Pb isotopes

Abstract

The Lianhuashan Au deposit, located in the northern margin of North China Craton, is hosted in the metamorphic rocks of Neoarchean Wulashanyan Group along NNW-to N-trending faults, with pyrite as the predominant ore mineral. The mineralization process can be divided into four stages, involving stage I quartz-pyrite, stage II quartz-magnetite-chalcopyrite, stage III quartz-marcasite-pyrite, and stage IV quartz-calcite. Three types of fluid inclusions (FIs) have been identified, namely, pure carbonic inclusions (PC-type), aqueous-carbonic inclusions (AC-type), and aqueous inclusions (A-type). Stage I auriferous quartz veins host all three types of FIs, inclusions from stage II quartz are AC-and A-type, and only A-type FIs are recognized in stage III quartz and stage IV calcite veins. The FIs of stages I to IV were homogenized at temperatures of 300-360 °C, 275-326 °C, 252-289 °C, and 220-264 °C, with salinities of 4.0-11.7 wt%, 3.4-9.3 wt%, 2.1-7.0 wt%, and 1.4-3.1 wt% NaCl eqv., respectively. The ore-forming fluids belong to a medium-temperature, low-salinity H 2 O-NaCl-CO 2 system. Gold deposition was likely caused by fluid immiscibility. The δD H2O and δ 18 O H2O values of ore fluids vary from −121.1 to −112.4‰ and from 2.8 to 6.2‰, respectively, within the range of enriched mantle-derived fluids in the North China Craton. The carbon isotope compositions of calcite (δ 13 C PDB = −2.87 to −2.38‰) show the features of mantle carbon. S-Pb isotope compositions of pyrite (δ 34 S = 2. 58-3.96, 206 Pb/ 204 Pb = 16. and 208 Pb/ 204 Pb = 37.305-37.338) reveal that the ore-forming materials may have originated from crustal rocks. Based on the geological and geochemical observations, we suggest that the Lianhuashan deposit can be classified as an orogenic gold deposit.