Abstract:There is a suite of acid rocks consisting of rhyolitic breccia, rhyolite and perlite in Shuidong area, Xuancheng City, in the middle-lower reaches of the Yangtze River. In this paper, the authors reported detailed studies of the LA-ICP-MS zircon U-Pb dating, major elements, trace elements, whole-rock Nd isotopic compositions and zircon Hf isotopic compositions of the acid rocks. The results of zircon LA-ICPMS U-Pb dating are 133.2±0.8 Ma (rhyolitic breccia), 133.4±0.8 Ma (rhyolite) and 131.5±0.9 Ma (perlite), respectively. Geochemical researches indicate that the acid volcanic rocks are rich in silica (SiO₂=72.51%~81.79%), K (K₂O/Na₂O=2.04~14.93, 6.72 on average) and poor in calcium (CaO=0.19%~1.57%) and magnesium (MgO=0.06%~0.29%), implying a typical high-K calc-alkaline to shoshonitic series with weakly peraluminous features (A/CNK=1.02~1.24). The rocks are enriched in LREE, LILEs (Rb, Ba, Th and K) but depleted in HFSE, especially Nb, Sr, P and Ti. The Eu/Eu^* ratios vary from 0.44 to 0.60, with most rocks having prominent negative Eu anomalies. Based on integration of the geological characteristics of the study area, the authors proposed that the acid rocks were formed by anatexis of the Neoproterozoic middle and upper crust. The petrogenetic event probably occurred in an intraplate extensional environment after the subdutiion of the Pacific Plate at~135 Ma.

Abstract:In this paper, the authors report new zircon U-Pb ages, whole-rock major and trace elements composition and Sr-Nd isotopic data for the Baiyunshan alkalic rocks in the northern part of the western area of the Gejiu tin-polymetallic ore district. The Late Cretaceous age (80.0±0.6 Ma) using the zircon LA ICP-MS U-Pb dating for the alkalic syenites indicates that they occurred with the contemporaneous gabbrodiorites and granites. This suggests that these rocks were all formed during the same magmatic-tectonic event. The geochemical characteristics and Sr-Nd isotopic compositions indicate that the alkaline syenite and the nepheline syenite were derived from an enriched mantle, and subsequently underwent different evolution processes. Combined with the previous studies, the authors hold that the alkali rocks, intermediate-mafic rocks and ore-related granites were derived from the enriched lithospheric mantle, the normal lithospheric mantle and the crust source, respectively. In the Late Cretaceous, the parental melts of the alkali rocks and gabbrodiorite magmas were formed by partial melting of the heterogeneity of the lithosphere mantle triggered by an extensional tectonic setting. Uprising of the above mantle melts promoted the partial melting of middle-lower crust and formed the granitic melts. These Late Cretaceous magmatism caused the activity and enrichment of the ore-forming material within a mutual tectonic belt, and then formed the superlarge tin-polymetallic deposit in the Gejiu ore district. It can be said that the enriched mantle-derived alkaline magmatism not only offered energy during the formation and mineralization of the ore-bearing granitic magma but also played some other roles.

Abstract:This paper reports the characteristics of the Beizhan phlogopite pyroxene peridotite pluton and diorite veins from West Tianshan, Xinjiang. Laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS) U-Pb zircon dating of the Beizhan phlogopite pyroxene peridotite yielded an age of 302.5±1.3 Ma, and phlogopites from phlogopite pyroxene peridotite yielded a well-defined ⁴⁰Ar/³⁹Ar plateau age of 298.1±1.9 Ma, which show excellent agreement with the mineralization age of the Beizhan iron deposit. Beizhan phlogolite pyroxene peridotite exhibits relatively lower SiO₂ (42.51%~50.82%),Al₂O₃ (4.87%~7.38%),TiO₂ (0.25%~0.77%), Na₂O+K₂O (0.87%~1.87%),and higher MgO (26.36%~30.17%), TFeO (12.33%~15.99%) content. The high Cr (523×10^-6~7 026×10^-6), Ni (906×10^-6~1 088×10^-6), Co (109×10^-6~132×10^-6) and Mg^#(0.76~0.79)values of the Beizhan phlogolite pyroxene peridotite suggest that olivine accumulation occurred in the magma. The calculation based on the highest Fo of olivine from phlogolite pyroxene peridotite and the TFeO content of the whole rocks suggest that its parent magma is basaltic affinity. All the rocks display LREE-enriched and flat HREE patterns,and show the enrichment of large ion lithophile elements (Rb, Ba, U, K) and the depletion of high field-strength elements (Nb, Ta, Zr, Hf, Ti), as well as the positive Pb anomaly. Phlogopite proxene peridotite has low initial ⁸⁷Sr/⁸⁶Sr ratios of 0.704 4~0.704 7 and high εNd(t) values of 2.23~3.90,and diorite has initial ⁸⁷Sr/⁸⁶Sr ratios of 0.704 4 and εNd(t) values of 3.79~4.07. These homogeneous Sr, Nd isotope compositions suggest that they were derived from the same source region. Furthermore, the trace element signature suggests that phlogolite pyroxene peridotite was derived from a spinel-facies asthenosphere mantle source, which had been modified by subduction-related melts/fluids. Combined with regional tectonic setting, the authors infer that the Beizhan phlogopite pyroxene peridotite was derived from the upwelling of asthenosphere mantle caused by the detachment of the West Tianshan orogenic root zone in Neopaleozoic. It is also suggested that the Beizhan iron deposit was formed under the same geodynamic setting.

Abstract:Large quantities of Early Carboniferous-Early Permian magmatic rocks are exposed on the western side of the Langshan Mountain, Inner Mongolia. The Early Carboniferous rocks mainly consist of hornblende gabbro and granodiorite outcropped on the west side of Chaogewenduer Town. The hornblende gabbros assume the form of individual guttate bodies and were cut by the granodiorite. LA-ICP-MS U-Pb dating of hornblende gabbro yielded weighted mean ²⁰⁶Pb/²³⁸U age of 329.0±2.3 Ma, while dating of two granodiorite samples yielded 331.1±0.9 Ma and 330.0±4.2 Ma respectively. The mafic mineral in granodiortie is dominated by hornblende. Whole rock geochemical data reveal that the granodiorite is calc-alkaline nature characterized by enrichment of Na₂O (3.48%~4.46%), high Na₂O/K₂O ratios (1.03~2.39) and shows good negative correlation between P₂O₅ and SiO₂. The similar Hf isotopic signature between the hornblende gabbro and the granodiorite and their behavior in elemen-tal geochemical characteristics together indicate their co-magmatic origin derived from depleted mantle which suffered from crustal contamination. The two types of rocks show similar patterns on the chondrite-normalized REE patterns, and display relatively high concentration of light rare earth elements but low content of heavy rare earth elements with minor negative Eu anomalies. The overall chemical similarities of these rocks on the primitive mantle-normalized variation diagrams suggest affinity to arc signature. In combination with the authors'work and the large scale regional exposure of hornblende gabbro+quartz diorite+ granodiorite rock assemblage, the authors hold that the Langshan area was under the tectonic setting of continental margin arc during Early Carboniferous.

Abstract:Two ductile deformations were identified in Beidashan area, which lies in the western Alxa Block. Early ductile deformation is characterized by top-to-the-north (northwest) ductile thrust structure, and a late Silurian metamorphic age of 422±1 Ma was yielded by the paragneiss which was related to the thrust deformation. Later ductile deformation was characterized by EW-trending sinistral shear, and two zircon U-Pb crystallization ages of 326.2±1.2 Ma and 323.8±2.6 Ma were yielded for two monzonitic granites which experienced the shear deformation. Combined with previous research on Alxa Block, a comprehensive comparison of the late Ordovician-Carboniferous magmatic-metamorphic-deformation events between the western and the eastern Alxa Block was made in this study. On the one hand, the characteristics and ages of two ductile deformations in Beidashan are similar to those of Bayanwulashan-Langshan which lies in the eastern Alxa Block. On the other hand, late Ordovician-Carboniferous magmatic rocks in the western and eastern Alxa Block also have similar rock types, ages as well as geochemical and Nd isotopic characteristics. All these characteristics indicate that the western and eastern Alxa Block went through the same tectonic evolution, and these authors also hold that a late Ordovician-Carboniferous tectonic-magmatic belt was developed in the early Precambrian metamorphic basement of the Alxa Block. This tectonic-magmatic belt extends from the Taohualashan in the west, through Beidashan, Nuoergong, Bayanwulashan, to the Langshan in the east and its origin was related to the continuous southward subduction of the Paleo Asian Ocean.

Abstract:This paper reports the geochemical characteristics of platinum-group elements (PGEs) in nephelinite lavas from Wajilitag complexes of Bachu County in Xinjiang. The magma source and the magma evolution of nephelinite are discussed. The values of such platinum-group elements as Os, Ir, Ru, Rh, Pt and Pd in nephelinite were determined by ICP-MS. They display a positive slope in the mantle-normalized pattern. The fact that Pd/Ir values are higher than those of the primitive mantle suggests the fractionation of PGE in nephelinite. And positive correlations for PGE versus MgO, negative correlations for Pd/Ir and Cu/Pd versus MgO suggest that the PGE differentiation was probably controlled by crystallization differentiation of olivine. It is also one of the factors that cause the high Cu/Pd ratio and magma S saturation. The Cu/Pd ratio indicates that the magma is sulfur saturated magma, but there is no factor that leads to the S-oversaturation of magma and sulfide liquation. Sulfur capacity calculation shows that, compared with other rocks of large igneous province, Wajilitag nephelinite is extremely depleted in PGE due to the S-oversaturation of parent magma, with the main reason being the low degree partial melting of the mantle. It is considered that the partial melting degree of mantle source played an important role in the formation of Cu-Ni sulfide PGE deposits in the Tarim Large Igneous Province.

Abstract:Mafic granulites as veins or lens are commonly identified within Milan Rock Group and TTG gneiss in Annanba area of Aksay County, Gansu Province. The granulite is composed of plagioclase (Pl), orthopyroxene (Opx), clinopyroxene (Cpx), amphibole (Amp) and magnetite (Mt), which is characteristic of typical medium-low pressure granulite facies rocks. Ti, P, Nb, Ta, Th, Hf, Sr and REE are well related to Zr of mafic granulites from Annan area, which shows that these elements remained basically unchanged and kept stable during the metamorphic process. Geochemical analysis shows that the mafic granulites belong to tholeiite series rocks, depleted in SiO₂, TiO₂, Al₂O₃ and P₂O₅, and enriched in CaO, MgO, Mg^# (41.52~43.09). The values of Fe₂O₃^T, MgO and CaO are negatively correlated with SiO₂, suggesting separation crystallization of pyroxene and amphibole during the evolution of the magma. The chondrite-normalized REE patterns show right-inclined feature with no obvious Eu(Eu/Eu^*=0.91~1.01) anomalies, whereas the primitive mantle normalized trace element spidergrams are characterized by enriched LILE (such as Rb, Ba and S) and depleted HFSE (such as Nb, Ta, Zr and Ti), similar to the typical feature of Phanerozoic arc basalt. Sr, Nd, Pb isotopic compositions suggest that the protolith of mafic granulites was derived from enriched mantle, and underwent crustal contamination. Combined with the tectonic evolution of southeastern Tarim, the authors hold that the protolith of mafic granulites was formed in island arc, and related to a subduction environment. The formation process of mafic magma may be as follows:the mantle wedge was metasomatized by the fluid and simultaneously formed enriched mantle; back-arc extension took place under the mechanism of subduction, which triggered partial melting of enriched mantle, and then the mafic magma moved upward to the upper crust along the fissures to form gabbro or diabase veins; later, they were metamorphized into mafic granulite under the granulite facies metamorphism.

Abstract:According to the modes of occurrence, nephrite can be divided into dolomite-related nephrite and serpentinite-related nephrite. In previous studies and exploration, serpentinite-related nephrite was hardly found in Hetian dolomite-related nephrite belt in Western Kunlun Mountains. During 2014~2015, lots of geological examination and collection of information concerning the location of serpentinite-related nephrite were carried out, and then some information about the occurrence of serpentinite-related nephrite orebody near the Altun fault zone was found in Qiemo County. Based on EMPA (electron microprobe analysis), XRF (X-ray fluorescence), ICP-MS (inductively coupled plasma mass spectrometry) and oxygen isotopic analysis, δ¹⁸O (15.2‰~15.4‰), Mg/(Mg+Fe²⁺)=0.83~0.89, Cr₂O₃=0.08%~1.65%, NiO=0.14%~0.22% and other geochemical data were acquired, which suggest a serpentinite-related nephrite origin. Wall rock of diorite also indicates that they formed at 267±14 Ma and 272±14 Ma, as shown by the SHRIMP U-Pb dating on zircons, which suggests the upper limit of the formation time of the serpentinite-related nephrite. Inverse isochronal age of Ar-Ar dating on biotite associated with serpentinite-related nephrite is 260.6±1.5 Ma. Both ages imply that they have relationship in genesis. Possibly due to the similar hydrothermal alteration of diorite, dolomite marble and tremolite, they have the close oxygen isotopic values (δ¹⁸O=14.3‰~14.7‰, δ¹⁸O=15.2‰~15.9‰ and δ¹⁸O=15.3‰). According to the chemical composition from bulk analysis of diorite (Cr=107×10^-6~155×10^-6, Ni=53.5×10^-6~85.8×10^-6), marble (Cr=2 036×10^-6~2 415×10^-6, Ni=1 403×10^-6~1 933×10^-6) and nephrite (Cr=867×10^-6~2 418×10^-6, Ni=960×10^-6~1 662×10^-6), together with the occurrence of chromite in nephrite, it is concluded that granodiorite and marble provided the ore materials for the formation of nephrite, and hydrothermal fluids were probably derived from both magmatic water and meteoric water in serpentine rock.

Abstract:The Jiaodong (eastern Shandong) hydrothermal gold deposits consisting of several world-class gold deposits have been producing a great majority of gold in China. The main types of mineralization are characterized by the distribution of gold within quartz veins and altered rocks, with the latter being more important. There are still many controversies about the evolution of metallogenic indicators and tracer elements in Jiaodong gold deposits. As rutile has great stability in the petrogenesis and metamorphism, the authors investigated detailed typomorphic characteristics and the chemical composition of rutiles from the fresh granites, sericitolites and beresites in Shangzhuang and Xiadian gold deposits and made dating by electron microprobe analysis. The genetic type of rutile and its change of Fe-Si-Ti-W content were discussed. Detailed studies reveal that rutiles in Shangzhuang and Xiadian gold deposits are mainly of metamorphic origin and were mainly formed by the alteration of biotite with the release of Ti. Moreover, this kind of rutile is mainly distributed at the edge of biotite. Ti values of rutiles exhibit a decreasing trend from sericite to beresite, forming a Ti halo that can be used as a sign of gold enrichment. In addition, W content in rutile has another enrichment trend from fresh granite through sericitolite to beresit, indicating that W can be used as an indicator to trace gold migration. These signatures can be regarded as evaluation indices for delineating the gold target and can provide new models for the study of gold deposits.

Abstract:Jordanite is a rare sulfosalt mineral. This paper reports the first discovery of jordanite in the Panlong lead-zinc deposit, Wuxuan County, Guangxi. The jordanite is associated with pyrite, galena, sphalerite and barite appearing as irregular granular grains in pyrite. The optical characteristics in reflective microscope of jordanite are as follows:double reflection is clear, two reflectivities under white light of jordanite are equal to 38.6% and 41.8% respectively; the reflection color is pure white with a little blue tint; reflection pleochroism is weak; heterogeneity is strong. The empirical formula which is determined by the method of EPMA of jordanite is Pb_14.05(As_2.66,Sb_3.23)_5.89S_22.99. The cell parameters are inferred by X-ray diffraction techniques. The results are listed as follows:a=8.91(2) Å, b=31.96(6) Å,c=8.47(2) Å, β=117.77°, V=2 135.49 ų, Z=2, and the space group is P2₁/m. With the use of XRD and EPMA in combination with previous research on the metallogenic epoch of the Panlong lead-zinc deposit, the authors also investigated the origin of the jordanite.

Abstract:Due to their many novel physicochemical properties different from the bulk counterparts, zerovalent iron nanoparticles are of great potential in contaminants removal from waste water. Montmorillonite-supported zerovalent iron nanoparticles were prepared using borohydride solution reduction method. As revealed by combined spectroscopic and microscopic techniques, the resultant iron particles were nearly spherical core-shell entities (about 55 nm mean diameter) well dispersed on the montmorillonite surface, in which the shell (iron oxide) preserved the core (metallic iron) from complete oxidation in air atmosphere. Batch tests were carried out to investigate the adsorption of Cr(Ⅵ) by thus obtained composite. At the optimized solution pH of 1.0, the Cr(Ⅵ) uptake was mainly governed by the reduction of Cr(Ⅵ) to Cr(Ⅲ) at the interface of metallic iron, which could be accessed by Cr(Ⅵ) owing to the dissolved oxide shell in acidic media. The kinetics of the adsorption followed the pseudo-second-order model, the adsorption data fitted well with the Langmuir equation, and the adsorption was spontaneous and exothermic in nature. These results are important for developing advanced nanomaterials based on zerovalent iron and for their use in remediation of Cr(Ⅵ)-contaminated water.