Geology, geochronology and isotopic geochemistry of the Xiaoliugou W-Mo ore field in the Qilian Orogen, NW China : case study of a skarn system formed during continental collision

This study is financially supported by the National Natural Science Foundation of China (41502068).The Xiaoliugou W-Mo ore field lies within the mid-Paleozoic North Qilian Orogen, NW China, and hosts a W resource of 48.8 Mt @ 0.4% and 412.6 Mt of Mo @ 0.075%. It contains five deposits, including Xiaoliugou, Qiqing, Guishan, Qibao and Shiji. The main mineralization styles at Xiaoliugou are skarn and veins in which the mineral sequence is scheelite > molybdenite > chalcopyrite and occurs in the endo- and exo-contact zones of granite intrusions. The scheelite-dominated orebodies are overprinted by molybdenite-dominated quartz veins. Two molybdenite samples yielded Silurian Re-Os model ages of 427.4 ± 6.0 Ma and 428.2 ± 6.0 Ma. Three muscovite samples coexisting with molybdenite yielded Middle Devonian Ar-Ar ages of 392.0 ± 2.7 Ma, 391.1 ± 2.7 Ma and 391.4 ± 2.8 Ma. The Re-Os and Ar-Ar ages indicate that the W-Mo mineralization and alteration occurred at ca. 428–391 Ma, which corresponds with regional continental collision within the Qilian Orogen. δ34S for the sulfides molybdenite and pyrite are 7.70–11.67 ‰ and 4.98–13.17 ‰, respectively. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb of the sulfides are 17.98–21.73, 15.34–18.81, and 37.18–38.63, respectively. The granites yield similar corrected (206Pb/204Pb)i, (207Pb/204Pb)i and (208Pb/204Pb)i, ranging 16.14–19.35, 15.44–15.63, and 37.41–38.31, respectively. Calculated δ18O of the fluid inclusions in quartz range from -3.38–2.34 ‰, whereas the δD of the hydrothermal fluids ranges from -94 to -47 ‰. The S-, Pb-, O- and D-isotopic data imply that the metals originated from the granite intrusion with a minor component sourced from the host sediments, and that the ore-forming fluids were dominated by magmatic-hydrothermal fluids mixed with minor meteoric water.PostprintPeer reviewe

Internal Activation of Peptidyl Prolyl Thioesters in Native Chemical Ligation

Prolyl thioesters have shown significantly lower reactivities in native chemical ligation (NCL) in comparison to that of the alanyl thioester. This report describes a mild and efficient internal activation protocol of peptidyl prolyl thioesters in NCL without using any thiol-based additives, where the introduction of a 4-mercaptan substituent on the C-terminal proline significantly improves the reactivity of prolyl thioesters via the formation of a bicyclic thiolactone intermediate. The kinetic data indicate that the reaction rate is comparable to that of the reported data of alanyl thioesters, and the mechanistic studies suggest that the ligation of two peptide segments proceeds through an NCL-like pathway instead of a direct aminolysis, which ensures the chemoselectivity and compatibility of various amino acid side chains. This 4-mercaptoprolyl thioester-based protocol also allows an efficient one-pot ligation–desulfurization procedure. The utility of this method has been further demonstrated in the synthesis of a proline-rich region of Wilms tumor protein 1

Isotope and trace element studies of the Xingdi II mafic–ultramafic complex in the northern rim of the Tarim Craton: Evidence for emplacement in a Neoproterozoic subduction zone

The Xingdi II mafic–ultramafic complex is located in the northern rim of the Tarim Craton, Northern Xinjiang, NW China. This complex is mainly composed of gabbro, gabbronorite, websterite and lherzolite, plusminor granodiorites and granites. The geodynamic setting of this complex and other Neoproterozoicmafic–ultramafic complexes in the region is debated, with opinions varying from mantle plume to a continental arc. A new zircon U–Pb age from this study reveals >7-myr difference for two gabbroic intrusive phases in the Xingdi II mafic–ultramafic complex andup to a 21-myr difference between this complex and the nearby mafic–ultramafic complexes that occur <12 km from this complex. The age changes for the Neoproterozoic (730–820 Ma)mafic–ultramafic complexes in the area occur in different directions and hence a mantle plume origin for the complexes is unlikely. The Xingdi II mafic–ultramafic intrusive rocks are characterized by moderate light-REE enrichments and pronounced negative Nb anomaly, which are common formafic–ultramafic rocks in convergent tectonic settings, and negative εNd(t) values (−9.2 to−5.1) and elevated initial ⁸⁷Sr/⁸⁶Sr ratios (0.7061 to 0.7086), which indicate enriched source mantle plus crustal contamination. The εHf(t) values of zircon crystals from the Xingdi II mafic–ultramafic complex are between −2.8 and −7.0. The trace element and isotope data together indicate that this complex formed from multiple pulses of contaminated subduction-related basaltic magma that were emplaced separately with a time gap of at least 7 myr. The results from this study support the viewpoint that in the Neoproterozoic the northern rim of the Tarim Craton was an active continental margin that belongs to the Circum-Rodinia Subduction System.This study was financially supported by the China Geological Survey Bureau (1212011140056)