Geofluids (2013) 13, 528–541
doi: 10.1111/gfl.12065
Fluid inclusions at different depths in the Sanshandao gold deposit, Jiaodong Peninsula, China F. F. HU1, H. R. FAN1, X. H. JIANG1, X. C. LI1, K. F. YANG1 AND T. MERNAGH2 1 2
Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; Minerals and Natural Hazards Division, Geoscience Australia, Canberra, ACT, Australia
ABSTRACT The Sanshandao gold deposit, located at northwestern edge of the Jiaodong Peninsula, eastern North China Craton, is one of the largest gold deposits in the Jiaodong gold province. In the deposit, disseminated- and stockwork-style ores are hosted in Mesozoic granitoids. Mineralization and alteration are largely controlled by the regional Sanshandao–Cangshang fault. Sericite separated from alteration rocks in the mineralized zone yields an Rb–Sr isochron age of 117.6 3.0 Ma. The ore-forming fluids in the Sanshandao gold deposit contain CO2H2O-NaClCH4 with low to intermediate temperatures and low salinities. Microthermometric analysis shows that homogenization temperatures gradually decrease from the early mineralizing stage (258–416°C) to main mineralizing stage (180–321°C) and to late mineralizing stage (112–231°C). Homogenization temperatures from the same mineralizing stage are nearly same and do not show an increase with depth. The nature of the ore-forming fluids remains nearly the same over a 2000 m vertical depth interval. Key words: alteration wallrock type gold deposit, fluid inclusion, Jiaodong Peninsula, Sanshandao Received 30 November 2012; accepted 21 August 2013 Corresponding author: Hongrui Fan, Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China. Email:
[email protected]. Tel: 86 10 82998218. Fax: 86 10 62010846. Geofluids (2013) 13, 528–541
INTRODUCTION The Jiaodong Peninsula is currently the most important gold province in China, with a total gold ore reserve of 1300 tons (Li et al. 2007). It is located along the southeastern margin of the North China Craton (NCC, see Fig. 1), which is the largest and oldest (2.5–3.8 Ga) craton in China (Zhai & Santosh 2011). Mesozoic granitoids, occupying >50 percent of the northwestern part of the Jiaodong Peninsula, intrude into Precambrian basement rocks, which have undergone amphibolite to granulite metamorphism. The majority of gold resources (>95%) are hosted by these granitoids, making the Jiaodong gold province one of the largest granitoid-hosted gold provinces presently recognized in the world (Qiu et al. 2002). Gold deposits of this district have been classified as the Linglong type and the Jiaojia type, both of which are essentially fault controlled (Lu & Kong 1993). The Linglong-type mineralization is characterized by massive auriferous quartz veins hosted in subsidiary secondor third-order faults cutting Mesozoic granitoids, whereas the Jiaojia-type mineralization consists of disseminated-
and stockwork-style ores located in the regional faults, which are enveloped by broad alteration halos. Many papers, mostly in Chinese, have been published recently on the Jiaodong gold deposits and related igneous rocks (e.g. Luo & Wu 1987; Chen et al. 1989, 2005; Li & Yang 1993; Lu & Kong 1993; Yang & Lu 1996; Wang et al. 1998; Yang et al. 1998, 2012; Yang & Zhou 2001; Qiu et al. 2002; Fan et al. 2003, 2005; Lu et al. 2004; Li et al. 2006; Goldfarb et al. 2007; Mao et al. 2008), mainly focusing on the geological features, age, and geodynamic mechanism of the ore deposits. These investigations have shown that ore mineralogy, hydrothermal fluids, stable isotope compositions, and ore-forming P-T conditions of the Jiaodong gold deposits are similar to those of typical orogenic gold deposits (Goldfarb et al. 2001; Qiu et al. 2002). Previous studies on ore-forming fluids in the peninsula were mainly focused on the shallow depths, mostly
