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

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 parts per thousand to 12.5 parts per thousand and from -1.3 parts per thousand to 24.5 parts per thousand, 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.