The Jiudinggou molybdenum deposit is situated along the southern margin of the North China Block and belongs to the East Qinling molybdenum belt. Molybdenum mineralization in the deposit is primarily takes place in a skarn zone where the Yanshanian granitoid pluton (Daping pluton) is in contact with older carbonate strata. We obtained an isochron Re-Os age of 141.1 ± 2.5 Ma for molybdenite from the Jiudinggou molybdenum deposit, which correlates well with the zircon U-Pb age of the Daping pluton of 141.2 ± 0.5 Ma, the host rock of the molybdenum deposit. The Daping pluton is a high-K, Si-rich, calc-alkaline granite with metaluminous to weakly peraluminous characteristics. Its chondrite-normalized REE patterns show moderately negative Eu anomalies and no Ce anomaly. Its primitive mantle-normalized elemental patterns indicate enrichment in LREEs (Light Rare Earth Elements) and LILEs (Large Ion Lithophile Elements), and depletion in HFSEs (High Field Strength Elements). These geochemical features are similar to those of highly fractionated I-type granites. Its zircon εHf(t) values and two-stage model ages (TDM2) range from –28.0 to –10.5 and 1857 to 2949 Ma, respectively, which indicate that the source material for the Daping granitoid pluton was derived from the remelting of subducted continental crust of the Yangtze Block. The geochronologic and geochemical analyses of the Jiudinggou molybdenum deposit and the molybdenum-related granite (Daping pluton) indicate that the observed molybdenum mineralization is closely related to a magmatic evolution under a transition in the tectonic regime from compression to extension during the Late Jurassic to Early Cretaceous.
The uptake of Au(III) complexes (initial [Au] = 25 μmol·dm–3) by Al-Si-bearing precipitates formed by the hydrolysis of aluminum ions (initial [Al] = 0.04 mol·dm–3) in the presence of either solid silica or aqueous silicic acid was investigated at pH 6.0, [Cl–] = 0.24 mol·dm–3, and ambient temperature. A maximum of 40% of the total quantity of Au(III) complexes present in solution was sorbed onto the precipitate after 24 h in the absence of silica. Both solid silica and silicic acid inhibited the gold uptake, and silicic acid was a more effective inhibitor. Analyses of the solids showed that the fraction of octahedrally coordinated aluminum decreased as the bulk atomic Si/Al ratio in the solid increased. This decrease was more rapid in the presence of silicic acid than solid silica owing to the more efficient incorporation of aluminum into the silica structure. The zeta potential of the precipitates decreased as the fraction of octahedrally coordinated aluminum decreased and the atomic Si/Al ratio increased. The gold uptake decreased as the zeta potential of the precipitates decreased, suggesting that negatively charged Au(III) complexes were sorbed on the precipitates via electrostatic interactions. Our findings suggest that the octahedrally coordinated aluminum determined the quantity of the gold uptake by governing the positive charge on the precipitate surface. In addition, desorption was promoted by the presence of solid silica after 5 h, suggesting that silica may promote the release of Au(III) chloro-hydroxy complexes as well as other negatively charged metal complexes from aluminum oxides or iron oxides in soil or sediment.
We measured 10 major (SiO2, TiO2, Al2O3, total Fe2O3, MnO, MgO, CaO, Na2O, K2O, and P2O5) and 34 trace (Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Sn, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th, and U) elements in 34 Geological Survey of Japan (GSJ) geochemical reference samples (JB-1, JB-1a, JB-1b, JB-2, JB-2a, JB-3, JB-3a, JA-1, JA-1a, JA-2, JA-3, JR-1, JR-2, JR-3, JGb-1, JGb-2, JG-1, JG-1a, JG-2, JG-3, JH-1, JSl-1, JSl-2, JSd-1, JSd-2, JSd-3, JSd-4, JSd-5, JLk-1, JMS-1, JMS-2, JMS-3, JSO-1, and JCFA-1) using inductively coupled plasma-mass spectrometry coupled with the femtosecond laser ablation sample introduction technique (fsLA-ICP-MS). Before the elemental analysis, glass beads were prepared by mixing each sample with a high-purity alkali flux with a 1:10 mixing ratio. The abundances of the major and trace elements were externally calibrated by using glass beads containing the major and trace elements prepared from six geochemical reference materials (AGV-1, AGV-2, BCR-1, BCR-2, BHVO-2, and DTS-1) distributed by the United States Geological Survey (USGS). Abundances of most major elements in the 34 GSJ geochemical reference samples were consistent with previously reported values. We rigorously tested the reliability of the trace-element abundance data against the data obtained from JB-1, JB-1a, JA-1, and JA-2, because the trace-element abundances of these reference samples were recently re-compiled. All trace-element compositions of these reference samples were consistent with the reference values, suggesting high reliability of the fsLA-ICP-MS analytical technique. Typical analysis repeatabilities for the GSJ geochemical reference samples were better than 3% for SiO2, Al2O3, Na2O, and K2O; <5% for TiO2, total Fe2O3, MnO, MgO, CaO, P2O5, V, Cr, Co, Ni, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu, Hf, Ta, Th, and U; and <9% for Sc, Cu, Zn, Sn, Yb, and Pb. These data clearly demonstrate that high analytical repeatability can be achieved by the fsLA-ICP-MS technique with glass beads made from 0.5 g or larger samples.
Carbonaceous matter from the matrix of the Murchison (CM2) meteorite and Northwest Africa (NWA) 801 (CR2) meteorite that were extremely rich in deuterium (D) and 15N was studied using in situ isotope imaging. The association of carbon, hydrogen, and nitrogen suggests that the carbonaceous matter was organic in nature, and the maximum magnitudes of D- and 15N-enrichment in the organic matter were δD = 2,880‰ and δ15N = 2,590‰ in Murchison, and δD = 7,500‰ and δ15N = 2,200‰ in NWA 801. The organic matter did not display a simple correlation between the magnitudes of D- and 15N-enrichment, and the isotopically anomalous organic matter was classified into three types based on the H and N isotopic characteristics: extremely 15N-rich without large D-enrichment (15N-rich), extremely D-rich without large 15N-enrichment (D-rich), and highly D- and 15N-rich (D-15N-rich). The occurrence of isotopically anomalous organic matter was attributed to their origin in the molecular clouds and outer solar nebula, ion-molecule reactions at low temperatures, grain surface reactions at low temperatures, and self-shielding effects in gas phase molecules. However, the observed D- and 15N-enrichment of the organic matter is much smaller than predicted by ion-molecule and grain surface reactions. This suggests a secondary modification of the H and N isotopic compositions of the organic matter in the solar nebula and in the parent body. In Murchison, the proportion of D-rich organic matter among the isotopically anomalous organic matter is smaller than in NWA 801, which presumably indicates that the D-enrichments are easily modified by aqueous alteration processes on the parent body. Scanning electron microscopy revealed the morphology of the D- and 15N-rich organic matter as aggregates of globules/particles or non-aggregated globules, where the size of each globule was <1 μm. Although there is no obvious correlation between the morphology of the organic matter and the H and N isotopic compositions, the result that Murchison contains more abundant globule/particle aggregates might suggests formation of aggregated nature due to aqueous activity.
Monte Carlo simulation of large replications of 100,000 was used to evaluate the final total propagated error represented by standard deviation or percentage of relative standard deviation (%RSD) in conventional ternary diagrams, as well as in bivariate diagrams based on statistically coherent additive, centered, and isometric log-ratio transformations of three compositional variables. The error distortion, amplification and reduction, evidenced in a ternary diagram, were not observed in any of the bivariate diagrams based on log-ratio transformations, in which equal %RSD errors in the initial compositional variables showed equal standard deviation values in the transformed space. As an example of these findings, the three types of log-ratio transformations were evaluated from a geochemical database of basaltic rocks from arc (IAB), within-plate (WPB), and mid-ocean ridge (MORB) tectonic settings, as better, statistically coherent alternatives to the highly used Zr-3Y-Ti/100 ternary diagram. This diagram showed relatively low (<25%), acceptable (86%), and non-existent (0%) correct discrimination for the arc, within-plate, and mid-ocean ridge settings, respectively. The exact same bivariate diagram, with correct discrimination of 46.2%, 89.0%, and 60.6%, respectively, for IAB, WPB, and MORB was obtained from linear discriminant analysis performed on the additive, centered, and isometric log-ratio transformations of the same database. Nevertheless, the fulfillment of the basic assumption of statistical samples drawn from binormal distributions before linear discriminant analysis increased the correct discrimination in the new bivariate diagrams by about 0.5% to 1.5% for IAB, 1.1% to 7.3% for WPB, and –7.7% to +0.9% for MORB. The performance of the new bivariate diagrams was significantly better than that of the ternary discrimination diagram. Thus, this work highlights the successful replacement of ternary diagrams by bivariate diagrams based on log-ratio transformations. Therefore, the bivariate diagram based on normally distributed isometric log-ratio data can be recommended to replace the widely used Zr-3Y-Ti/100 ternary diagram.
A total of eleven fault gouge samples were collected from the Daliushu Dam area in the Zhongwei-Tongxin Fault Zone (ZTFZ) and analyzed for the absorbed gas geochemistry. The concentration of absorbed gas was between 0.04 and 1.65 cm3STP/g, and the chemicals were determined as mainly CO2, N2, H2, Ar, and a few hydrocarbon gases. The ratios of N2 and Ar suggest the presence of water in the fault zone, leading to water-rock interaction and lower N2/Ar ratios. CO2 and H2 showed some signatures implying abiogenic origin, with relatively high δ13CCO2 (–1.7‰ to 0.95‰) and H2 being positively correlated to CO2 (r = 0.83). We speculate that the CO2 and H2 are correlated to lithic origins in the fault zone, carbonate and silicate, respectively. On the other hand, CH4 did show a biogenic signature, with low δ13CCO2 (–44.2‰ to –45.6‰). The variation trends among the absorbed gases in the fault profile show that the gas concentration is mainly related to the fault zone structure, petrology of the fault material, and porosity. The total amounts of absorbed gases including H2, CO2, and Ar observed were higher at site F201 than those at site F3, and since the F201 site is known to be much more active than F3, we propose that CO2, H2, and Ar could be useful indicators of fault activity.
A gem garnet, GA1, from Sri Lanka obtained through a gem market was characterized for major and trace element compositions using LA-ICP-MS with a laser spot of 35 μm. Analytical results show that a negative correlation on a logarithmic scale exists between the relative standard deviation and the concentration for elements ≤1500 ppm, suggesting that the difference in the scatter of apparent element concentrations is not due to chemical heterogeneity but due to analytical uncertainty. The GA1 is homogeneous, except for V. We concluded that the elemental abundances obtained for the GA1 can be considered as reference values during in situ microanalysis of garnet. Fragments of GA1 are distributed to interested laboratories under the distribution policy in this paper.
The Kuluketage block is the best area for Precambrian geology in north western China, because it contains the most complete Precambrian lithology units. Thus, the study of this ancient basement can improve the understanding of the Precambrian evolution of the Tarim Craton. In this study, we report LA-ICPMS zircon U-Pb ages and Hf isotopes of detrital zircons from a magnetite quartzite from the Shayiti Formation of the Xingditage Group. The 65 zircon ages and Hf isotopes obtained are used not only to constrain the maximum depositional ages of the Shayiti Formation but also to obtain the information about the evolution of regional tectonic-magmatic activities in the Paleoproterozoic of the Kuluketage block. According to the youngest concord 207Pb/206Pb zircon age of 1851 ± 36 Ma in magnetite quartzites and the 1.47 Ga of the diabase sills which intrude into the Shayiti Formation, the most probable depositional age of the Shayiti Formation is between 1.47 Ga and 1.85 Ga. The detrital zircon dates are mainly clustered at 1806 Ma to 1889 Ma, 1898 Ma to 1981 Ma, and 1988 Ma to 2054 Ma, with the most prominent age peak appearing at around 1900 Ma and the subordinate peak age at around 1960 Ma. The magmatic features of Cathodoluminescence (CL) images indicate that two large magmatic tectonic-magmatic activities occurred in this district. The metamorphic rims of magmatic zircons and some baddeleyites also show regional metamorphism in the Paleoproterozoic, which may be related to the amalgamation of the Columbia supercontinent. We obtained two sets of concordant U-Pb ages older than 2.5 Ga, and several sets of two-stage Hf model ages older than 3.0 Ga. Combined with previous data in the literature, we suggest that Meso- to Neo-Archean basement rocks existed in the Kuluketage block, but were strongly reformed by tectonics, magmatism, and metamorphism in the Paleoproterozoic.
Black slate in the Okcheon Metamorphic Belt (OMB) has been considered the perspective uranium ore in South Korea. In this study, three representative areas were selected for better understanding on the uranium-mineralogy and geochemistry of black slate in the OMB. It is found that the OMB black slate is highly enriched with metals such as U (~0.03%), V (~0.3%), Ba (~1.4%) and Mo (~0.04%). It is also notable that an average content of total organic carbon (TOC) is as high as 21.2%. Upon relationships between metals and TOC, Ba shows a weak correlation with TOC whereas the correlation is not clear for U, Mo, Cu, P, and V. In the comparison of the study areas, the average concentrations of metals such as Ba, U, and Mo and organic carbon decrease in the order of Goesan > Geumsan > Miwon. Four uranium-bearing minerals in the OMB black slate are identified. Tetravalent uranium (U4+) minerals such as uraninite and brannerite are found, whereas francevillite and Ba-bearing torbernite containing hexavalent-uranium (U6+) are observed. It is shown that uraninite and brannerite are less than 100 μm in dimension. In contrast, the size of francevillite or torbernite is larger, and the scaly texture with cracks is shown in their morphology. We note that uraninite is the most common uranium mineral throughout the black slate bed in OMB. It is demonstrated that the formation of U-bearing minerals in the bed is greatly affected by diversity of geochemical environments in the OMB, Korea.
The concentration of total metal sulfide throughout a water column over a submarine hydrothermal vent in Kikai Caldera south of Kyushu Island, Japan, at ~350 pmol/kg, was higher than that reported in previous studies, at <50 pmol/kg below the halocline. Seawater filtered at 0.2 μm pore size and unfiltered seawater exhibited almost identical metal sulfide concentrations throughout the water column, indicating that most metal sulfide existed in dissolved and particulate forms with diameters <0.2 μm. By using a mass balance calculation with the observed sulfide species of free and metal sulfides and carbonyl sulfide, we showed that ~70% of the metal sulfide supplied from hydrothermal vents were contained in the water column beyond the halocline without undergoing oxidative loss even after mixing into overlying oxic seawater. Our findings clearly indicate that sulfide and trace metals emitted from hydrothermal vents form a stable metal-sulfide complex with diameters <0.2 μm. These results also strongly support the recently proposed theory such that metal-sulfide complexation/nanoparticles play an important role in the long-distance transportation of trace metals in the ocean.
Uranium concentrations in the rivers of Okinawa Island, Japan were determined in this study. Most rivers in the southwestern area of the island showed high U concentrations, the highest of which was 87 and 11 times the average U levels in Japanese rivers and worldwide, respectively. The U concentration in two rivers exceeded the Japanese guideline for public waters. Thermodynamic calculations revealed that the predominant U species in the rivers was Ca2UO2(CO3)30 (aq) because of high concentrations of calcium and carbonate ions. However, the U concentrations were not explained by either the congruent dissolution of limestone or the input of seawater and/or sea salt aerosols. Therefore, selective dissolution of U from limestone as well as from other rocks and soils via the formation of calcium-uranyl-carbonate complexes may be a possible mechanism for the high riverine U concentrations.