The Ashele VMS-type Cu-Zn Deposit in Xinjiang, NW China Formed in a Rifted Arc Setting

Abstract

The Ashele Cu-Zn deposit is a typical VMS deposit in Chinese Altay located in the southern margin of the Altaid orogen. The deposit occurred in the polyphase fold system, and the main orebody is located at the hinge of the syncline. All orebodies show lenticular form, and are stratabound by a suite of early to middle Devonian bimodal volcanic rocks. The hosting basalt is low K tholeiite and characterized with high Mg, Fe, Ca and low K, Ti. These basalts show flat REE pattern with Ce negative anomaly (Ce/Ce* 0.73-0.76). Niobium, Ta, Zr, Hf are depleted and Rb, Ba, Th, U, Sr, Pb are enriched with respect to the N-MORB. Both the Sr and Nd isotopes show depleted properties, while the ( 87 Sr/ 86 Sr)i and the eNd(t) range from 0.70469 to 0.70488 and 4.6 to 5.3, respectively. All geochemical and isotopic data from the hosting basalt show that it originates from an island arc source. We also report the S isotope data from the massive orebody, and d 34 S‰ change from 1.8‰ to 5.6‰. The S isotope data provide evidence that the sulfur originates from a mixing source between magma and seawater sulfate. We propose that the mafic magma provides the ore-forming metal and some percentage of sulfur, while it also acts as a heat engine which makes the fluids leach the metal from the underlying volcanic rocks. Combining the geological characteristics of the Ashele and geochemical data, and comparing with other Cu-Zn VMS deposits in the world, we propose that Ashele formed in a rifted arc setting.

Metamorphosed Pb–Zn–(Ag) ores of the Keketale VMS deposit, NW China: Evidence from ore textures, fluid inclusions, geochronology and pyrite compositions

“…6). Stage A ores are interpreted to be the result of primary depositional sea-floor volcanichydrothermal activity (Wan et al, 2010a). However, the primary layered pyrite of stage A is commonly replaced by later polymetallic sulfides, i.e., pyrite with skeleton texture enveloped by later sphalerite, galena, chalcopyrite ( Fig …”

“…The Devonian strata in the Altay Orogen host the giant Ashele Cu-Zn, Keketale Pb-Zn and Mengku iron deposits (Wan et al, 2010a(Wan et al, ,b, 2012Wang et al, 1998), and the Abagong polymetallic belt Zheng et al, 2012). The Devonian rocks comprise a sequence of low-grade metamorphic rocks interpreted as continentally-derived turbidites (e.g., the Habahe Group), volcanic rocks (e.g., the Altay Formation) and volcanic-sedimentary rocks (e.g., the Kangbutiebao Formation) that formed in a volcanic arc or rift basin (Chai et al, 2009).…”

“…The deposit was discovered in 1986 and has been mined since 1999, with a published resource of Pb (0.89 Mt @ 1.51 wt.%), Zn (1.94 Mt @ 3.16 wt.%) and Ag (650 t @ 40 g/t; Wang et al, 1998). The deposit has been variously classified as a VMS (Wan et al, 2010a), or a VMS-SEDEX transition and SEDEX (Jiang, 2003). Zircon U-Pb geochronology and sulfide Pb-Pb geochronology confirm that the possible syn-VMS process occurred at ca.…”

Mid-Late Paleozoic metallogenesis and evolution of the Chinese Altai and East Junggar Orogenic Belt, NW China, Central Asia

“…The VMS Cu-Zn and Pb-Zn deposits (e.g. Ashele and Keketale) formed in the forearc setting (Wan et al 2010), whereas the orogenic gold deposits (e.g., Saidu and Duodalasayi) developed in association with collision tectonics (Yakubchuk et al 2003). This terrane is probably equivalent to the Rudnyi Altai Block in Russian Altai (Buslov et al 2001(Buslov et al , 2004D'yachkov et al 2009;Kruk et al 2011), and the Turgen Block in eastern Mongolia (Badarch et al 2002;Goldfarb et al 2003).…”

“…The presence of high-Mg andesites and high-Mg adakites in the Ashele Fm. indicates that they formed in a forearc setting (Niu et al 1999;Zhang ZC et al 2005;Wan et al 2010). Metasediments from four locations in the Qiongkuer-Abagong Terrane gave U-Thtotal Pb isochron ages (CHIME) on monazite of 377 ± 30 Ma and 268 ± 10 to 261 ± 20 Ma, reflecting the times of regional metamorphism (Zheng et al 2007).…”