Geochemistry and genesis of the Hongguleleng Manto-type Cu deposit, West Junggar, Xinjiang, China

Abstract

The Hongguleleng Cu deposit is a Manto-type deposit in the Central Asian Orogenic Belt, located in the east section of West Junggar, Xinjiang, China. It is hosted by Middle Ordovician volcano-sedimentary sequence, especially for porous units. Specifically, the orebodies of this Manto-type deposit are hosted in basalt, andesite, and andesitic breccia host rocks (the particular volcano-sedimentary sequence). The occurrence of these orebodies is controlled by normal faults. Chalcopyrite, pyrite, calcite, chlorite, and epidote are most common minerals of the Hongguleleng deposit. Three alternation belts and six ore related stages have been recognised. The epidote-chalcopyrite stage, quartz-calcite-chalcopyrite stage, and chlorite stage are ore forming stage. The δ34S of chalcopyrite in ore depositing stages varies from 0.94‰ to 2.59‰, indicating that the origin of sulfur is either magma or host volcanic rock. Further, the 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of the chlorite-chalcopyrite and quartz-calcite-chalcopyrite stages exist in the range of 17.443–17.847 and 17.855–17.973; 15.472–15.495 and 15.493–15.620; and 37.616–37.666 and 37.689–38.114, respectively, indicating that the metal originates from the Middle Ocean Ridge Basalt (MORB). The δ13CPDB value of calcite for the epidote-chalcopyrite stage ores, quartz-calcite-chalcopyrite ores with veinlet characteristics, quartz-calcite-chalcopyrite ores with brecciated characteristics, and chlorite-chalcopyrite ores range from −1.40 to −1.50‰, −2.01 to 0.41‰, −1.15 to 0.75‰, and −0.80 to 1.58‰, respectively, while the 18OSMOW ranges from 8.94–10.42‰, 11.83–13.17‰, 13.59–14.04‰, and 12.34–14.18‰, respectively. The CO isotope of calcite of the Hongguleleng deposit indicates that seawater is an essential fluid for ore formation and that modified seawater interacts with the host rock extensively. The hydrothermal magnetite in the quartz-magnetite stage and chlorite in the ore forming stages indicate that temperature decreases from its early to late stages. High Zn and Pb concentrations over four stages of pyrite, with a relatively stable contents, indicate that the content of Zn and Pb in fluid is also high. The concentration of Cu in these four stages of pyrite of the Hongguleleng deposit follow a decreasing trend, indicating that the concentration of Cu in the ore forming fluid decreases from the early to late stage. Based on information mentioned above, we argue that this deposit is a Manto-type deposit with modified seawater driving forces.

Keywords

• West Junggar
• The Hongguleleng Manto-type Cu deposit
• CO isotope
• S-Pb isotope
• Magnetite, chlorite, and pyrite electron microprobe analysis
• Ore genesis