Rb-Sr dating of pyrite, Zircon U-Pb geochronology, and Sr-Nd-Hf isotopic geochemistry of the Baiyun Au deposit in the Qingchengzi Orefield, Liaodong Peninsula, Northeast China

Abstract

The Baiyun Au deposit (>20 t/5.86 g/t) is situated in the eastern Liaodong Peninsula.

(LP). More than 68 orebodies are found in the Precambrian metamorphic rocks and include altered rock type (ART) and quartz vein type (QVT). Pyrite Rb-Sr and zircon U-Pb dating, the elements and Sr-Nd-Hf isotopic geochemical data, and trace element contents of pyrite are adopted to control the ore genesis, petrogenesis, and the tectonic dynamics background of the Baiyun Au deposit. Isotopic chronology reveals that the magmatism can be divided into the Late Triassic (226–216 Ma), the Middle Jurassic (164.4 ± 0.4 Ma), and the Early Cretaceous (129.0–95.0 Ma). The 218.6 ± 0.4 Ma, which is obtained by pyrite Rb-Sr dating, represents the ore-forming age of the Baiyun Au deposit. Geochemically, the granite porphyry is enriched in K, Rb, and light rare earth elements (LREEs), and depleted in Nb, Ti, Ta, P, and heavy rare earth elements (HREEs), which belong to metaluminous adakite rocks. In addition, the initial ⁸⁷Sr/⁸⁶Sr ratios of the granite porphyry are between 0.71053 and 0.71141, the εNd(t) values and two-stage model ages (TDM₂) of granite porphyry range from −17.9 to −17.1 and 2.458 to 2.387 Ga, respectively. Its εHf(t) values and TDM₂ range from −14.46 to −12.48 and 2.159 to 2.054 Ga, respectively. Therefore, we proposed that the granite porphyry may be derived from ancient crustal sources. The quartz porphyry is enriched in Pb, K, Sr, and LREEs, and depleted in Ti, Nb, P, Ta, and HREEs, which belongs to the high-K Cal-alkaline and metaluminous to weakly peraluminous series. The initial ⁸⁷Sr/⁸⁶Sr ratios of quartz porphyry are between 0.71537 and 0.71690, εNd(t) values are between −17.1 and − 15.6, TDM₂ values are between 2.405 Ga and 2.295 Ga, and its εHf(t) values range from −17.58 to −14.07, TDM₂ ages range from 2.262 to 2.159 Ga, suggesting that the quartz porphyry mainly derived from ancient crustal sources. Three generations of pyrite (PyI, PyII, and PyIII) are identified. PyI and PyII occur in the first and second stages, respectively, and Py III occurs in schist (host strata). Py II has higher Au concentrations than Py I and Py III, indicating that gold is mainly deposited in the second stage. The pyrite has a medium-high proportion of Co and Ni, indicating a mixed fluid of magmatic water and other fluid origins. Combined with regional tectonic evolution, we classified the Baiyun Au deposit as a Late Triassic intrusion-related gold deposit. The Baiyun gold deposit and Late Triassic intrusions were formed during the Yangtze Craton (YC) subducted beneath the North China Craton (NCC). The rocks that formed during the Middle Jurassic and the Early-Late Cretaceous may be related to the subduction of the Paleo-Pacific Plate.