Ore genesis and tectonic setting of the Bieluwutu Cu-Pb-Zn volcanogenic massive sulfide deposit in Xing'an-Mongolia orogenic belt, China

The Bieluwutu Cu-Pb-Zn deposit is located in the Ondor Sum region of the western Xing'an-Mongolia orogenic belt, North China. The host rocks of the deposit consist of metasandstone, tuffaceous slate, andesitic tuff and fragmented felsic volcanic rocks, which have previously been regarded as the Early Carboniferous Amushan Group. Zircon U-Pb ages for two tuffaceous units are 435 ± 2 Ma and 430 ± 2 Ma, showing that volcanism occurred in the Early Silurian. The tuffaceous rocks are enriched in large ion lithophile elements (LILE; e.g., Rb, Ba, K) and light REE, and depleted in high field strength elements (HFSE; e.g., Nb, Ta and Ti) with depleted isotopic components (ε_Nd(t) = 0.14–0.84), indicating that they were derived from partial melting of lower continental crust with the involvement of mafic magma.

Bieluwutu is intended to be a Kuroko-type VHMS deposit formed in an interarc rift basin in the Early Silurian. Three types of ores have been identified at Bieluwutu, including massive Pb-Zn, brecciated Cu-Zn and disseminated Cu ores. Results of sulfide laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Se and Sn are enriched in chalcopyrite from the disseminated and brecciated ores with high Se/Te ratios. Tellurium, Co, Pb and Bi are enriched in chalcopyrite, sphalerite and pyrite from the brecciated ores, whereas Mn, Ni and Tl concentrations are higher in pyrite from the massive ores. These differences suggest a decreasing temperature and increasing %fnof;(O₂) trend from the disseminated to brecciated and massive ores. High contents of Mn, Tl, Ni in massive ores are typical for metals derived from surrounding felsic volcanic rocks. Strong enrichment of trace elements, such as Bi, Te, Se and Sn, is consistent with a magmatic contribution to the ore-forming fluids. The underlying subvolcanic intrusion not only served as a heat engine but also supplied volatiles and metals.