Abstract
The Xinqiao and Baoshantao deposits in the Tongling ore-cluster region, Middle-Lower Yangtze River Metallogenic Belt (MLYRMB) are typical stratabound and skarn Cu-Au deposits, respectively. The genetic model of skarn deposits has been fully studied and well established, while the genesis of stratabound deposits remains ambiguous. Two principal viewpoints include a late Carboniferous seafloor exhalative formation and Yanshanian magmatic-hydrothermal origin. In this study, three types of pyrite samples are recognized and collected, they are defined as Py A, Py B and Py C, characterized by fine-grained and anhedral, medium-grained and subhedral, and coarse-grained and euhedral, respectively. EPMA, LA-ICP-MS, and LA-MC-ICP-MS were used to detect major elements, trace elements, and S isotopes of these different pyrites. Ratios of Fe/S (0.99 ∼ 1.05, in mol %), Co/Ni (mostly greater than 1) suggest that both the Xinqiao and Baoshantao deposits were formed in the Yanshanian magmatic-hydrothermal system. The Xinqiao stratabound deposit was formed in a more oxidizing environment and have relatively lower δ34SCDT value (2.57 ∼ 5.95‰) than the Baoshantao skarn deposit (4.97 ∼ 9.57‰), indicating that the ore-forming contribution of strata in Xinqiao deposit is dominated. Combined with regional geological background, it is believed that the ore-hosting strata as well as migrations of magmatic-hydrothermal fluids are two important factors, affecting differences of formation and mineralization between the two types of deposits. Our results directly provide important enlightenments for understanding regional metallogenic mechanism and application of pyrite geochemical exploration.
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