Review of the stable isotope geochemistry of Mesozoic igneous rocks and Cu–Au deposits along the middle–lower Yangtze Metallogenic Belt, China

Abstract

Ore deposition took place in the Yangtze Valley episodically during the Jurassic and Cretaceous periods, generating approximately 200 polymetallic Cu–Fe–Au, Mo, Zn, Pb, and Ag deposits. We analysed the stable isotopes of sulphur, oxygen, and hydrogen from the Cu–Au deposits and correlated our new data with published stable isotope for associated Yanshanian (Mesozoic) igneous rocks. The latter bears a close relationship to Cu–Au mineralization in the area. Cu–Au deposits in the middle–lower Yangtze Valley can be divided into three types: skarn, porphyry, and volcanic. The S–O–H isotopic values allow constraints to be placed on the conditions of origin of these famous Cu–Au ores and their related igneous rocks.

Sulphur from the sulphide ores mostly was derived from a magmatic source; however, a few deposits reflect a sedimentary source of sulphur. Oxygen isotope values in quartz from the Shaxi porphyry Cu–Au deposit and from the Tongling skarn Cu–Au deposits range from 2.6‰ to 12.5‰ and from −1.3‰ to 24.5‰, respectively; these values represent larger variations compared with those from other Cu–Au deposits in this metallogenic belt. Hydrogen versus oxygen isotope plots of the Cu–Au ore-forming fluids demonstrate that the fluids came from different sources: the most important involved the mixing of magmatic and meteoric water; the second most important was strictly magmatic water; and the third most important may have been a mixture of formation water or meteoric water that had reacted with carbonate wall rocks.

Keywords:

• porphyry Cu–Au deposits
• stable isotope geochemistry
• sulphur
• hydrogen
• oxygen isotopes
• middle–lower Yangtze metallogenic province

Acknowledgements

This study was supported by the Knowledge Innovation Project of the Chinese Academy of Sciences (Grant No. KZCX1-YW-15-3), the National Natural Science Foundation of China (Nos. 9014008 and 40921002), and the Opening Foundation of State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, CAS (No. 2008011). We thank Prof. Chang Yinfo for his kind guidance. We owe special thanks to the geological experts from the No. 326, 327, and 321 Geology Surveys of Anhui Province, China, for providing some samples and for giving generous permission to access the geological data.

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