The early Paleozoic Huangtupo VMS Cu—Zn deposit in Kalatag, Eastern Tianshan: Implications from geochemistry and zircon U—Pb geochronology of volcanic host rocks

Abstract

The Tianshan in China forms the southern part of the Central Asian Orogenic Belt (CAOB) and also hosts important polymetallic resources. Here we investigate the Huangtupo medium–size copper–zinc deposit, located in the central part of the Kalatag copper Polymetallic Belt with a view to evaluate the nature and genesis of the early Paleozoic volcanogenic massive sulfide (VMS) Cu—Zn deposits. This deposit is correlated to intermediate–felsic volcano–sedimentary sequences of the early Paleozoic Daliugou Formation which are mainly composed of andesite, dacite, and rhyolite with minor basalt, as well as their pyroclastic equivalents. The ore bodies are hosted in the contact zone between andesitic volcanic breccia and tuff representing an eruptive hiatus between the two volcanic cycles with massive sulphide lens at the top and stockwork zone at lower part of the Daliugou Formation. We report new zircon U—Pb data, major and trace element geochemistry and Sr—Nd isotopes from the andesite, dacite and andesitic tuff in the Huangtupo deposit. Zircon from the dacite and the andesite occurring above the ore bodies yield and age of 440.1 ± 1.2 Ma and 439.7 ± 0.95 Ma, and that from the andesitic tuff in footwall shows and age of 442.0 ± 1.1 Ma. All samples show typical geochemical signatures of subduction–related calc–alkaline magmas with slight enrichment in LILE and LREE but depletion in Nb and Ti content relative to primitive mantle. The andesites are characterized by high MgO (7.6–10.8 wt%) contents and Mg# values (64–72) with low Sr/Y and La/Yb ratios, belonging to sanukite. Both dacite and tuff have low MgO (<2.5 wt%) and Al2O3 content (15–16.4 and 11.3–15.3 wt%) with Eu negative anomalies (Eu/Eu* = 0.71–0.75 and 0.44–0.6), showing their low–MgO affinity. All the volcanic rocks display similar Nd and Sr isotopic signature, with εNd(t) of 6.5 to 7.3 and moderately high (87Sr/86Sr)i ratios of 0.705274 to 0.706977. The geochemical characteristics and regional geology indicate that these volcanic rocks were formed in an intra–oceanic arc during southward subduction of the oceanic lithosphere in the northern part of the Eastern Tianshan. They were most likely derived from the partial melting of the mantle wedge with input and interaction with subducted–related melts and/or fluids. We also propose that the Huangtupo VMS deposit is analogous to Kuroko type VMS deposits developed within intra–oceanic rift.