Genesis of Two Different Types of Gold Mineralization in the Linglong Gold Field, China: Constrains from Geology, Fluid Inclusio
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Ore Geology Reviews 65 (2015) 643–658 Contents lists available at ScienceDirect Ore Geology Reviews journal homepage: www.elsevier.com/locate/oregeorev Genesis of two different types of gold mineralization in the Linglong gold field, China: Constrains from geology, fluid inclusions and stable isotope Bo-Jie Wen a,Hong-RuiFana,⁎,M.Santoshb, Fang-Fang Hu a,FrancoPirajnoc, Kui-Feng Yang a a Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China b School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China c Centre for Exploration Targeting, University of Western Australia, Crawley, WA 6009, Australia article info abstract Article history: The Dongfeng and Linglong gold deposits are located in the northwest Jiaodong Peninsula, North China Craton. Received 21 December 2013 The deposits are mainly hosted in the Mesozoic granitoids and structurally controlled by the Zhaoyuan–Pingdu Received in revised form 26 March 2014 fault zone. Gold mineralization at Dongfeng occurs as disseminated ores and sulfide stockworks, typically Accepted 26 March 2014 enveloped by broad alteration selvages. In contrast, mineralization at Linglong is characterized by massive Available online 13 April 2014 auriferous quartz veins with narrow alteration halos. Three stages of mineralization were identified in both deposits, with the early stage represented by quartz ± pyrite, the middle stage by gold + quartz + pyrite or Keywords: fi Fluid inclusion gold + quartz + base metal sul des, and the late stage by quartz + carbonate ± pyrite, respectively. Four Water–rock interaction types of fluid inclusions were distinguished based on petrography, microthermometry, and laser Raman Phase separation spectroscopy, including (1) pure CO2 fluid inclusions (type I), (2) H2O–CO2–NaCl fluid inclusions (type II), Dongfeng gold deposit (3) H2O–NaCl fluid inclusions (type III), and (4) daughter mineral-bearing or multiphase fluid inclusions (type IV). Linglong gold deposit In the Dongfeng gold deposit, the early- and middle-stage quartz mainly contains primary type II fluid inclusions Northwest Jiaodong that completely homogenized at temperatures of 276–341 °C with salinities of 2.8–11.7 wt.% NaCl equivalent, Eastern China and temperatures of 248–310 °C with salinities of 3.3–10.8 wt.% NaCl equivalent, respectively. A few primary type I fluid inclusions could be observed in the early-stage quartz. In contrast, the late-stage quartz contains only the type III fluid inclusions with homogenization temperatures of 117–219 °C, and salinities of 0.5–8.5 wt.% NaCl equivalent. The estimated pressures for the middle-stage fluids are 226–338 MPa, suggesting that gold mineralization mainly occurred at paleodepths of deeper than 8.4–12.5 km. The mineralization resulted from extensive water–rock interaction between the H2O–CO2–NaCl fluids and wallrocks in the first-order fault. In the Linglong gold deposit, the early-stage quartz mainly contains primary type II fluid inclusions and a few type I fluid inclusions, of which type II fluid inclusions have salinities of 3.3–7.5 wt.% NaCl equivalent and homogeni- zation temperatures of 271–374 °C. The middle-stage quartz mainly contains all four types of fluid inclusions, among which the type II fluid inclusions yield homogenization temperatures of 251–287 °C and salinities of 5.5–10.3 wt.% NaCl equivalent, while the type III fluid inclusions have homogenization temperatures of 244–291 °C and salinities of 4.1–13.3 wt.% NaCl equivalent. Fluid inclusions in the late-stage quartz are type III fluid inclusions with low salinities of 0.3–8.2 wt.% NaCl equivalent and low homogenization temperatures of 103–215 °C. The trapping pressure estimated for the middle-stage fluids is 228–326 MPa, suggesting that the gold mineralization mainly occurred at paleodepths of about 8.4–12.1 km. Precipitation of gold is possibly a con- sequence of phase separation or boiling of the H2O–CO2–NaCl fluids in response to pressure and temperature fluctuations in the open space of the secondary faults. The δ34S values of pyrite are similar for the Dongfeng and Linglong deposits and show a range of 5.8 to 7.0‰ and 5.9 to 7.4‰, respectively. Oxygen and hydrogen stable isotopic analyses for quartz yielded the following results: δ18O=−3.8 to +6.4‰ and δD=−90.5 to −82.7‰ for the Dongfeng deposit, and δ18O = 0.0 to +8.9‰ and δD=−77.4 to −63.7‰ for the Linglong deposit. Stable isotope data show that the ore-forming fluids of the two gold deposits are of magmatic origin, with gradual incorporation of shallower meteoric water during/after mineralization. © 2014 Elsevier B.V. All rights reserved. 1. Introduction ⁎ Corresponding author. Tel.: +86 10 82998218; fax: +86 10 62010846. China is the largest gold-producer in the world. Its gold production is E-mail address: [email protected] (H.-R. Fan). increasing rapidly and had reached to 428.163 metric tons in 2013 http://dx.doi.org/10.1016/j.oregeorev.2014.03.018 0169-1368/© 2014 Elsevier B.V. All rights reserved. 644 B.-J. Wen et al. / Ore Geology Reviews 65 (2015) 643–658 (China Gold Association, http://www.cngold.org.cn/newsinfo.aspx? Gold Group Co., Ltd, unpublished data). The annual gold production in ID=996). The Jiaodong gold province located in the Jiaodong Peninsula the Dongfeng and Linglong deposits has climbed to ~3.6 metric tons in of eastern China (Fig. 1) is the most important gold-producing district 2013 (Shandong Gold Group Co., Ltd, personal communication). and is the host for several world-class gold deposits (N100 t gold) in The Jiaodong gold province hosts dozens of gold deposits. Genetic the country (Fan et al., 2003; Hu et al., 2013; Qiu et al., 2002; Zhou differences between the Linglong-type deposits and the Jiaojia-type and Lü, 2000). The region occupies less than 0.2% of China's land area, deposits have not been investigated, though most of them have been but yields about a quarter of the country's gold production. Gold extensively described. This paper attempts to evaluate the contrast be- deposits in the Peninsula are mainly distributed along three gold belts tween the Dongfeng and Linglong gold mineralization in the Linglong from west to east, i.e., the Zhaoyuan–Laizhou, Penglai–Qixia and gold field from field observations, ore geology, fluid inclusion and stable Muping–Rushan belts (Fan et al., 2003; Hu et al., 2006). These gold isotope analysis in order to reveal the nature and evolution of the ore- deposits are controlled by NE- or NNE-trending faults and hosted in forming fluid system, and to probe the ore genesis in both types of the Precambrian high-grade metamorphic basement rocks as well as deposits. the Mesozoic granitoids. They were divided into two types according to ore occurrence, referred to as “Linglong-type” and “Jiaojia-type” (Goldfarb and Santosh, 2014; Qiu et al., 1988). The Linglong-type lode 2. Regional geology gold mineralization is characterized by massive auriferous quartz veins with narrow alteration halos and usually occurs in subsidiary The Jiaodong gold province is located along the southeastern margin second- or third-order faults. The Jiaojia-type disseminated and of the North China Craton (NCC) and at the western margin of the Pacific stockwork gold mineralization is usually surrounded by broad alter- Plate. It is bounded by the NE- to NNE-trending Tan–Lu fault zone to the ation zones and generally develops along major first-order regional west and by the Su–Lu ultrahigh pressure metamorphic belt to the faults. The lode gold deposits usually have smaller reserves and higher south (Fig. 1). Exposed rocks in the area comprise metamorphosed grades, whereas the disseminated and stockwork gold deposits have Precambrian basement sequences and a series of Mesozoic intrusive larger reserves and lower grades. and volcanic rocks (Zhou and Lü, 2000). The Precambrian sequences in- The Zhaoyuan–Laizhou gold belt, located in the northwest Jiaodong, clude the Archean Jiaodong Group and the Proterozoic Jingshan and shows the highest concentration of gold deposits, with over 80% of the Fenzishan Groups (Guo et al., 2005; Yang et al., 2012). These groups Jiaodong gold concentrated within an area of ~3500 km2 (Zhou and consist of mafic to felsic volcanic and sedimentary rocks metamor- Lü, 2000). The Linglong gold field in this belt is the typical example of phosed to amphibolite and granulite facies. The Mesozoic volcanic “Linglong-type” lode gold mineralization, which together with some rocks, namely Qingshan Formation, are mainly distributed in the Jiaolai other deposits such as the Taishang gold deposit, account for an overall Basin, and were formed at 108–110 Ma (Qiu et al., 2001a). The Qingshan gold reserve of more than 1000 metric tons. Recently, a giant and new Formation comprises two units, with the lower assemblage composed “Jiaojia-type” gold mineralization (Dongfeng gold deposit) was discov- of trachybasalt, latite, and trachyte, overlain by an upper assemblage ered. It has been confirmed that the gold reserve at Dongfeng is dominated by rhyolite flows and pyroclastic rocks (Li et al., 2006; Qiu 158.475 metric tons, with average grade of 2.75 × 10−6 (Shandong et al., 2001a). Fig. 1. Simplified geological map of the Jiaodong Peninsula showing location of the major gold deposits (modified after Fan et al., 2003). The size of the symbols of the gold deposits indicates the gold reserves: large symbol means Au N 50 t, small symbol means Au b 50 t. The Dongfeng and Linglong deposits occur at the northwestern part of the gold province. B.-J. Wen et al. / Ore Geology Reviews 65 (2015) 643–658 645 Mesozoic granitoid rocks are widespread in the Jiaodong gold prov- trending faults, which cut through the Mesozoic granitoids.