Geochemistry of gold deposits in the Zhangbaling Tectonic Belt, Anhui province, China

摘要

The Zhangbaling Tectonic Belt (ZTB) is located in eastern Anhui province, adjacent to the Tan-Lu fault zone to the W and the Lower and Middle Yangtze River metallogenic zone to the E. Two types of gold deposits: (1) altered-tectonite gold and (2) quartz-vein gold are present in the ZTB. Three ranges of homogenization temperatures (T_h) were obtained by fluid inclusion investigations of the altered-tectonite gold deposits: 115– 165℃, 235–275℃, and 335–395℃; and of the quartz-vein gold deposits: 145–195℃, 205–255℃, and 255–335℃, respectively. δD values of the ore-forming fluids range from -52.2‰ to -75.3‰, and their isotopic compositions calculated from quartz analytical data show negative δ~(18)O values (-6.3–0.1‰) for the quartz-vein gold deposits. The calculated δ~(18)O values of water are evidently lower than magmatic water, and probably were derived from mixtures of magmatic and meteoric water. Although the total rare earth elements (REE) content of the quartz-vein gold ores are much lower than those of the spatially associated granites, their chondrite-normalized patterns are similar, indicating that ore-forming elements in the ZTB quartz-vein gold deposits probably were derived from the plutons. Ores from the altered-tectonite gold deposits show dEu values and chondrite-normalized REE patterns similar to those of the granites, indicating that ore-forming elements of the altered-tectonite gold deposits also were sourced in the Yanshanian plutons. The gold deposits in the ZTB are remarkably similar to those in the Jiaodong gold metallogenic province with regard to tectonic settings, mineralizationcontrolling factors, mineralization ages, and the ore-forming temperatures and the stable isotopic compositions.