Search

• These granitoids were emplaced between 132 Ma and 127 Ma. • These granitoids derived from mixing of Taihua Group, Xiong'er Group and mantle. • The ore-bearing granite porphyry possesses higher fO 2 than the ore-barren plutons. The petrogenesis and genetic relationship of molybdenum mineralization in the Late Mesozoic granitoids from the Xiong'ershan area remains controversial. This study presents integrated whole-rock geochemistry, zircon U-Pb geochronology and Hf-O isotopes for Late Mesozoic ore-bearing granite porphyry stock (Leimengou granite porphyry) and ore-barren plutons (Haoping and Jinshanmiao plutons) in the Xiong'ershan area of the East Qinling Orogen Belt (EQOB). The ore-barren granitoids are high-K subalkaline, metaluminous, and show negative correlations between Al 2 O 3 , MgO, TiO 2 , MnO, CaO, FeOT and P 2 O 5 with SiO 2. However, the Leimengou granite porphyry lacks distinctive linear correlation between major oxides with SiO 2 except Al 2 O 3 , K 2 O and Na 2 O. These granitoids are enriched in LREE over HREE with slightly negative europium anomalies. Most samples show enrichment of Rb, Ba, Th, U, K and Pb, and depletion of Nb, Ta, P and Ti, mostly overlapping the ranges of the Taihua Group. Zircon U-Pb ages from the Haoping pluton, Jinshanmiao pluton and Leimengou granite porphyry are 130.9 ± 0.4 Ma, 127.7 ± 0.7 Ma and 131.5 ± 0.9 Ma, respectively. The Hf-O isotopic features of zircon from the Leimengou granite porphyry (δ18O zircon = 5.03‰ − 5.86‰, εHf (t) = −24.3 to −14.4) are markedly similar with the Haoping pluton (δ18O zircon = 5.17‰ − 5.61‰ and εHf (t) = −26.6 to −21.4). Zircon grains from the Jinshanmiao pluton have unique δ18O zircon ranging from 6.01‰ to 8.90‰ and εHf (t) from −15.6 to −12.2. The co-variations of whole-rock geochemistry and Hf-O isotopic features in the samples suggest that Haoping pluton and Leimengou granite porphyry originated from mixture of partial melts of the Taihua Group with mantle-derived material, whereas the Jinshanmiao pluton originated from mixture of Xiong'er Group and mantle-derived material, with minor input of Taihua Group. The zircon grains from the Leimengou granite porphyry have significant higher Ce4+/Ce3+ (mean 547) and δEu (mean 0.65) ratios than those in the ore-barren Haoping pluton (mean 207 and 0.54, Ce4+/Ce3+ and δEu, respectively) and the Jinshanmiao pluton (mean 235 and 0.62, respectively). The main controlling factors for porphyry-type Mo mineralization are likely the oxygen fugacity (fO 2) of the magma and input of mantle-derived material in the Xiong'ershan area. The geochemical and isotopic data show that the emplacement of these intrusions in the EQOB occurred in the post-collision settings during 132–127 Ma. [ABSTRACT FROM AUTHOR]

Our understanding of crust – mantle evolution and geodynamics of the early Earth has been hampered by the scarcity of Hadean to Eoarchean rocks and by the almost ubiquitous isotopic disturbance of the oldest rocks. Here we present in-situ zircon U-Pb ages, O-OH and Lu-Hf isotopes, as well as whole-rock Sr-Nd-Hf-Pb isotopes for the recently identified Eoarchean Aktash gneisses in the Tarim Craton, NW China. The new age data confirm that the Aktash gneisses were formed at least by ∼3.72 Ga and were affected by two metamorphic events at ∼3.56 and ∼2.0 Ga, respectively. Whole-rock isotopic data show that the Sr-Nd-Hf-Pb isotopic systematics have all been variously disturbed by ∼2.0 Ga regional granulite facies metamorphism, resulting in decoupling of Nd-Hf isotopic systematics that is, in some samples, similar to that observed in SW Greenland. The least disturbed sample (16ALT67), however, yielded chondritic to slightly sub-chondritic whole-rock ε Nd (−0.3) and ε Hf (−0.9). This is consistent with the in-situ magmatic zircon ε Hf (weighted mean −0.2 to −1.8) for most samples of the Aktash gneisses, suggesting a mafic source derived from chondritic mantle with a short crustal residence time. Our data thus provide no evidence for the presence of an Eoarchean depleted mantle or a Hadean enriched crust, implying that early Earth crust – mantle differentiation was either limited or balanced by large-scale crustal recycling. In-situ zircon O–OH data show that metamorphism and later alteration tend to decrease the zircon δ 18 O of the Aktash gneisses, and the weighed mean δ 18 O of pristine magmatic zircons (6.2–6.3‰) from the least disturbed samples indicate that the mafic source was mildly altered at low temperature by the early hydrosphere, facilitating partial melting and formation of some of the earliest preserved continental crust known on Earth. • Zircon Hf-O and whole-rock Sr-Nd-Hf-Pb isotopic data for the 3.72 Ga Aktash gneisses. • Whole-rock Nd-Hf isotopic decoupling resulted from granulite-facies metamorphism. • Primary isotopic data indicate an altered mafic source derived from chondritic mantle. • Filtered zircon Hf-O isotopic data suggest similar sources for other Eoarchean rocks. [ABSTRACT FROM AUTHOR]

• Hydrothermal pyrites are classified into three types (Py1, Py2c and Py2r). • Two distinct stages of mineralization are revealed with diverse source materials. • The sources of the early and main stages show lower crust and mantle contributions. The Shanggong lode deposit represents one of the largest Mesozoic orogenic gold deposits in the East Qinling metallogenic belt of central China. Here we investigate the texture, trace element and sulfur isotopic composition of pyrite from this deposit to gain insights in the ore genesis. Three types of pyrite are recognized by its texture: Py1 is represented by coarse-grained cubic and pentagonal dodecahedron belonging to the stage I quartz-pyrite vein; Py2 comprises fine-grained disseminated pentagonal dodecahedron belonging to stage II quartz-sulfides vein; Py2 can be further divided into core and rim: porous cores (Py2c) carrying abundant, visible mineral inclusions and significantly higher arsenic concentration, and clean rims (Py2r) with low arsenic. Systematic LA-ICPMS trace elements and SIMS sulfur isotopic analyses reveal two distinct stages of mineralization with diverse source materials. 1) The early stage is represented by Py1 which contains 0.65–70 ppm Au (average 11.6 ppm), with relatively low and variable concentrations of Cu, Ag, Te, Pb, Zn, and Bi. The δ34S values of Py1 range from −2.7‰ to 7.2‰, suggesting that the sulfur source for the early stage fluid was mainly derived from the Taihua and Xiong'er Groups and that the depleted δ34S values reflect changes of pH, f O2 and fluid-rock interaction. 2) The main stage is represented by Py2 which contains Au in the range of 0.14–189 ppm (average 39.7 ppm). The Py2 carries significantly higher contents of compatible elements (Ni, Co, V, and Cr) and ore metals (e.g. Au, Ag, Pb, Zn, As, Te) than those in Py1, with the ore metals occurring as invisible lattice bound or nanosized particles and visible micron-sized inclusions. The δ34S values of Py2 show marked depletion with a range of −16.3‰ to −11.7‰, attributing to the fractionation between barite and sulfide minerals. Together with previous studies and trace element characters in Py2, we identify a contribution of Au from mantle source into the ore-forming fluid system during the main stage. We propose that the two stages of gold mineralization in the Shanggong deposit, in response to the collisional assembly of Qinling Orogenic Belt, preserve evidence for diverse metal sources with the early stage derived from partial melting of the lower crust (Taihua and Xiong'er Groups) in the compressional stage, and the main stage characterized by mantle contribution in a post-collisional extensional setting. Our findings may have important implications for the exploration of regional Triassic gold and molybdenum deposits. [ABSTRACT FROM AUTHOR]