Gold deposition and resource potential of the Linglong gold deposit, Jiaodong Peninsula: Geochemical comparison of ore fluids

• Published in: Ore geology reviews Vol. 120; p. 103434
• Main Authors: Guo, Lin-Nan, Deng, Jun, Yang, Li-Qiang, Wang, Zhong-Liang, Wang, Si-Rui, Wei, Yu-Ji, Chen, Bing-Han
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.05.2020
• Subjects: Fluid inclusions; H-O-S isotope; Jiaodong Peninsula, China; Linglong gold deposit; Orefluids comparison; Linglong gold deposit; Orefluids comparison; H-O-S isotope; Fluid inclusions; Jiaodong Peninsula, China
• ISSN: 0169-1368; 1872-7360
• DOI: 10.1016/j.oregeorev.2020.103434

[Display omitted] •Medium temperatures, low salinity, and CO2-rich H2O–CO2–NaCl ± CH4 orefluids.•Gold deposition mainly led by fluid immiscibility at 242–54 MPa and 348–269 °C.•Stage 2 ores have higher CO2 and CH4 contents, and more intense fluid immiscibility than stage 3 ores.•Gold mineralization likely occurred at a depth of 5.4–9.0 km, deep gold exploration is expectable in Linglong. The Linglong gold deposit is a super large deposit in the Linglong goldfield, northern Jiaodong Peninsula. The orebodies consist of hundreds of auriferous quartz veins that surrounded by relatively narrow K-feldspar alteration halos. Four mineralization stages have been identified on the basis of cross-cutting relationships, and mineralogical and textural characteristics: milky quartz–pyrite (stage 1), grey-white quartz–pyrite (stage 2), quartz–pyrite–base-metal sulfide (stage 3), and quartz–carbonate (stage 4). Native gold was mainly deposited in stages 2 and 3. Petrographical and microthermometric studies on quartz from stages 2 and 3 ores reveal three types of fluid inclusions associated with gold mineralization: Type 1 H2O–CO2–NaCl ± CH4 inclusion that consisting FIA 1 and represent a homogeneous fluid trapped at the same pressure and temperature; coexisting Type 2a H2O-rich H2O–CO2–NaCl ± CH4 and Type 2b CO2-rich H2O–CO2–NaCl ± CH4 inclusions that constitute FIA 2 and are interpreted to be products of a heterogeneously trapped fluid. The ore-forming fluids belong to a H2O–NaCl–CO2 ± CH4 system with medium temperatures (~290–340 °C), low salinity (~4–7 wt% NaCl eq.), and are CO2-rich (~15% mol) with minor CH4 (~2–5% mol). The δD–δ18O values of ore-forming fluids vary from −63 to −57‰ and 6.0‰ to 9.3‰, respectively, overlap both the magmatic and metamorphic fluid fields. The δ34S values of hydrothermal pyrite have a narrow range from 5.6‰ to 7.9‰, and are within the ranges of Neoarchean Jiaodong Group, and Mesozoic Linglong granite, Guojialing granitoid and intermediate–basic dikes. Combined with H–O–S isotope data, fluid inclusions compositions, and regional geological events, the ore-forming fluids may have a metamorphic-dominate origin, but a mantle or crustal contribution cannot be excluded. Fluid immiscibility played a major role, and fluid-wallrock interaction may be a subordinate reason for gold deposition in Linglong. The stage 2 quartz grains contain more FIAs 2 and volatiles than those in stage 3 quartz, indicating a more extensive fluid-immiscibility process which has a positive-correlated higher gold grade. Based on the data of FIAs 2, the P–T conditions of gold depositions generally range from 242 to 54 MPa and 348 to 269 °C, with a depth of metallogenesis of 5.4–9.0 km. Considering the depth of regional post-ore exhumation has been calculated as about 5–7 km, the space with deep gold exploration is expectable at Linglong.