Itrace chang analysis1/13/2024 ![]() Previous studies paid much attention to the metallogenic setting and ore geology (Ying et al., 2006, He et al., 2008, Chen et al., 2010, Yang et al., 2010, Yang et al., 2011, Zhang et al., 2010, Li et al., 2011b, Li et al., 2013b), but the ore genesis is still open. The Chang'an gold deposit was discovered at the southern segment of the Ailaoshan gold belt in 2001. It also hosts a number of other ore deposits, including the Hercynian Baimazhai magmatic Cu–Ni deposit, the Cenozoic Tongchang porphyry Cu deposit, and the Anding hydrothermal Ni deposit (Ying et al., 2006, Sun et al., 2009). To date, five large gold deposits, i.e., Laowangzhai (22 t at 5.29 g/t Au in metal), Donggualin (45 t at 5.10 g/t), Jinchang (32 t at 2.69 g/t), Chang'an (31 t at 5.84 g/t) and Daping (60 t at 14.30 g/t) areas (Yang et al., 2010), and eight medium and numerous small gold deposits have been discovered in the belt (Fig. 1). The belt is developed with complicated thrusts and nappes formed from the India–Asia continental collision since the Paleocene (Hou et al., 2007, Mo et al., 2007, Deng et al., 2010a, Deng et al., 2010b, Deng et al., 2013a, Fan et al., 2010). It strikes 120 km long, with width of 0.5–5 km, along the Jinshajiang suture. The Ailaoshan gold belt (Fig. 1) in Yunnan province is the most important in the Sanjiang Tethyan metallogenic domain. The Sanjiang Tethyan metallogenic domain in southwestern China is a significant part of the Tethyan metallogenic belt (Hou et al., 2007, Deng et al., 2013b, Lehmann et al., 2013, Wang et al., 2013a, Wang et al., 2013b, Tang et al., 2013), which tectonically connects the Yangtze Craton to the east and the Tibet plateau to the west. The Tethyan belt covers the southern half of mainland China, with the Qinling–Dabie–Sulu orogenic belt as its northernmost unit (Zhang et al., 2009, Li et al., 2013a), hosting numerous giant mineral systems, such as the Jinding Pb–Zn deposit in Yunnan (Hou et al., 2007, Deng et al., 2013b), Yangshan Au deposit in Gansu (Yang et al., 2006, Yang et al., 2009), and the Mo cluster in Henan (Chen et al., 2000, Li et al., 2007, Li et al., 2011a) and gold province in eastern Shandong (Chen et al., 2005, Guo et al., 2013). the Tethyan, Paleo-Asian and Circum-Pacific belts (Chen, 2002, Chen et al., 2009, Pirajno, 2013). In the world, China is a unique area accommodating three global metallogenic belts, i.e. Hence we consider that the deposit was formed during India–Asia collision, slightly postdate the 33–35 Ma tectono-magmatism. This interpretation is supported by the observation that the high-grade ores generally contain lots of Py2 and P圓. The P圓 grains and the growth rims of Py1 and Py2 show consistently high contents of Au, As, Pb and Co, suggesting that all of them were rapidly deposited from a mixing fluid system that was probably composed of fluids of metamorphic and magmatic origins. The cores of Py2 were formed by metamorphic fluids and have relatively high Au, Ag, Ni, Pb and Cu concentrations. The cores of Py1 were formed by magmatic fluids and have the lowest concentrations of Au, As, Cu and Zn. Their trace elements exhibit different concentrations, associations and rim–core zoning, implying different geneses and crystallization processes. Three types of hydrothermal pyrite were identified in the ores and wall rocks, i.e., the coarse euhedral crystals in syenite (Py1), the coarse grains disseminated in altered sandstones or sandstone ores (Py2), and the fine-grained euhedral pyrite in sandstone ores (P圓). Geochemical study of pyrite in the deposit was conducted using laser ablation inductively coupled plasma mass spectroscopy. The Chang'an gold deposit, Yunnan province is one of five large gold deposits in the Ailaoshan gold belt that is the most important ore belt of the Sanjiang Tethyan metallogenic domain.
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