Tectonomagmatic setting and magmatic Cu-PGE metallogeny during the late Neoproterozoic in the Eastern Kunlun Orogen, NW China: Insights from the Hatu Cu-Pt-Pd-bearing mafic-ultramafic intrusion

Abstract

The Hatu Intrusion is the first late Neoproterozoic Cu-PGE-bearing mafic–ultramafic intrusion in the Eastern Kunlun Orogen. The No. I intrusion with the largest scale and best mineralization delineated six Cu-Pt-Pd ore/mineralized bodies with Cu and Pt + Pd grades of 0.44–1.10% and 0.30–1.00 g/t, respectively. Chalcopyrite-bornite-(pyrrholite) is a common sulfide assemblage that disseminates in ultramafic rocks (e.g., olivine websterite, liherzolite) enriched in chrysolyte (Fo = 76–81) and orthopyroxene (En = 68–69). Zircons from the gabbro show magmatic zircons with blurred oscillatory zoning and Th/U ratios of 0.31–0.71 and yield a weighted mean age of 556 ± 4 Ma, indicating mafic–ultramafic magmatism with Cu-PGE mineralization in the late Neoproterozoic. The Hatu Intrusion exhibits the properties of continental basalt (e.g., 87Sr/86Sr = 0.71317–0.72541, 143Nd/144Nd = 0.51202–0.51246, and Ta/Hf = 0.19–1.16), indicating the geodynamic setting of terminal continental rift-related extension in response to continuous magmatism under the Rodinia supercontinent break-up in the late Neoproterozoic. The primary magma originated from low-degree (∼15–20%) partial melting of slightly metasomatized depleted mantle without accumulating sufficiently radiogenic isotopes, resulting in zircon positive εHf(t) values (5.2–15.0) and some geochemical properties of arc magma. The mafic–ultramafic rocks have Sr-Nd-Pb isotope compositions between depleted mantle and II-type enriched mantle with negative εNd(t) values (-12.4 – −1.7), and their S/Se ratios are 1628–7189, among which most samples (S/Se = 4534–7189) are higher than that of mantle (S/Se = 2850–4350); the δ34S values of sulfide are 0.7–2.6 ‰ and slightly greater than that of depleted mantle (δ34S = -1.8‰). The above geochemical and isotopic signals reveal the contribution of crustal sulfur to the Hatu Intrusion, which is enough to trigger sulfide saturation of Cu-Pt-Pd.