Abstract
The Kengdenongshe Au–Ag–Pb–Zn polymetallic deposit, a newly discovered large-scale polymetallic deposit in the southeastern section of the East Kunlun Orogen (EKO), contains an Au resource of 40 t, Ag resource of 690 t and Pb–Zn resource of 10.5 × 105 t. The ore-bearing rocks are mainly composed of laminar barite and rhyolitic tuff. In this study, LA-ICP-MS zircon U–Pb dating and whole rock major and trace elements analyses have been conducted on the ore-bearing rhyolitic tuff. LA-ICP-MS zircon U–Pb dating data show that these rhyolitic tuffs were emplaced at ca. 243.3 ± 1.6 Ma. The samples show similar features to those of S-type granites, including high contents of SiO2 (76.4–82.6 wt. %) and Al2O3 (11.0–12.7 wt. %) and relatively low concentrations of Na2O (0.35–2.43 wt. %) and CaO (0.095–0.124 wt. %), with high A/CNK (molar [Al2O3/(CaO + Na2O + K2O)]) (1.72–2.03) and K2O/Na2O ratios (1.41–17.1). Further, they exhibit depletion in HFSEs (High Field Strength Elements) and enrichment in LREEs (Light Rare Earth Element) with negative Eu anomalies (Eu/Eu* = 0.51–0.64). These geochemical characteristics indicate that the Kengdenongcuo rhyolitic tuff originated from the fluid-absent melting of a plagioclase-poor, clay-rich metapelitic source and experienced minor fractional crystallization. In combination with arc-type magmatism and contemporaneous syn-collision granitoids in the region, the Kengdenongcuo tuff formed in a continental collision setting, implying that the Bayan Har–Songpan Ganzi Terrane collided with the East Kunlun Terrane and the Paleo-Tethys Ocean was closed at the period of ~243 Ma. The Kengdenongcuo polymetallic deposit formed at about the same time.
Highlights
The East Kunlun Orogen (EKO) has been recognized to have been formed via the collision between the Qaidam Block and the Qiangtang or Bayanhar Terrane resulting from the closure of the Paleo-Tethyan Ocean [1,2,3,4,5]
Minerals 2019, 9, 589 ore deposits, most of which are associated with Early Paleozoic and Late Paleozoic-Early Mesozoic composite orogenic processes [6,7,8,9,10,11]
Previous research in this area has mostly focused on single aspects such as tectonic evolution, magmatism, mineralization and resource potential evaluation, as well as specific studies of individual ore deposits [12,13,14,15,16,17]
Summary
The East Kunlun Orogen (EKO) has been recognized to have been formed via the collision between the Qaidam Block and the Qiangtang or Bayanhar Terrane resulting from the closure of the Paleo-Tethyan Ocean [1,2,3,4,5]. Minerals 2019, 9, 589 ore deposits, most of which are associated with Early Paleozoic and Late Paleozoic-Early Mesozoic composite orogenic processes [6,7,8,9,10,11] Previous research in this area has mostly focused on single aspects such as tectonic evolution, magmatism, mineralization and resource potential evaluation, as well as specific studies of individual ore deposits [12,13,14,15,16,17]. The Paleo-Tethys Ocean subducted northward beneath the EKO, producing subduction-related granitoids (261–248 Ma of zircon U–Pb age [72,73,74]). The timing of Paleo-Tethys Ocean closure remains debated [75,76,77]
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