The Implications of HClO4 for Dissolving Large Masses of Low Level Os in Metal Sulfides and Factors that Influence Re-Os Dating

In general, no more than 1 g of metal sulfide can be completely digested in 20 mL of inverse aqua regia using the Carius tube technique. In this study, the sample weight increased after adding HClO4 to inverse aqua regia while the volume of acid concurrently decreased significantly. Three grams of metal sulfide were digested in 12 mL of acid (3 mL of HClO4 and 9 mL of inverse aqua regia) via the HClO4-inverse aqua regia method. The results using molybdenite reference materials JDC and HLP mixed with 3 g of pyrite were consistent with certified values. Compared to the traditional method, the HClO4-inverse aqua regia method could dissolve a larger sample mass (3 g) with a smaller volume of acids (12 mL). We simultaneously found that the oxidation of digestion acids greatly affected the Os signal but had no influence on the equilibrium of isotope exchange between 185Re and 190Os spikes in Re and Os samples. Remarkably, the heating temperature was the most significant factor influencing the equilibrium of isotope exchange, and the Os in a sample was not equilibrated with the spike until the heating temperature reached 190 °C

Depositional environment and origin of the Lilaozhuang Neoarchean BIF-hosted iron-magnesite deposit on the southern margin of the North China Craton

International audienceThe Neoarchean Lilaozhuang iron-magnesite deposit is located in the middle of the Huoqiu banded iron formation (BIF) ore belt in Anhui Province on the southern margin of the North China Craton. The Huoqiu BIF is the unique one that simultaneously develops quartz-type, silicate-type, and carbonate-type magnetite in the region. The Lilaozhuang deposit is characterized by magnesium-rich carbonate (magnesite) in magnetite ores. The BIF-hosted iron ores include mainly of silicate type and carbonate type, with a small amount of quartz type, which chiefly exhibit banded and massive structure, with minor disseminated structure. The magnesite ores occur as crystal-like bright white and exhibits massive structure. The Y/Ho ratio and REY pattern of both iron and magnesite ores are similar to that of seawater, while Eu shows positive anomaly, which is the sign of seafloor hydrothermal mixture. These features suggest that ore-forming materials of iron and magnesium in the Lilaozhuang deposit are mainly from the mixture of seafloor hydrothermal and seawater. Both ores do not exhibit negative Ce anomaly, which indicates that the deposit was formed in an environment showing a lack of oxygen. C-O isotopic compositions indicate that magnesite ore has been reformed by metamorphism of low amphibolite facies and later hydrothermal alteration. Based on the comprehensive analysis, authors suggest that iron and magnesite ores in the Lilaozhuang deposits formed in a confined sea basin on continental margin and was influenced by later complex geological processes

Zircon U-Pb-Hf-O and molybdenite Re-Os isotopic constraints on porphyry gold mineralization in the Bilihe deposit, NE China

The Bilihe gold deposit in Inner Mongolia is situated in the Central Asian Metallogenic Domain. Its major ore body II is a porphyry-type body, spatially and temporally associated with granodiorite porphyry and granite aplite. In this study, the timing of gold mineralization is precisely constrained by using the zircon U-Pb dating for pre-mineralization intrusions and the molybdenite Re-Os dating for later molybdenite veins. Furthermore, zircon lif-O isotope analyses have also been carried out to decipher the nature of primary magma. Zircon U-Pb dating shows that the granodiorite porphyry and the granite aplite were emplaced at 269 +/- 2 Ma and 270 +/- 2 Ma, respectively, indicating the gold mineralization occurring no earlier than 269 Ma. Meanwhile, molybdenite veins are developed within the fractures and commonly cut across the auriferous veins. Thus, combined with a molybdenite Re-Os isochron age of 268 +/- 1 Ma, the gold mineralization in the Bilihe deposit can be precisely restricted to ca. 269 Ma. Zircon epsilon(Hf) (t) values are mostly positive (1.6-11.3), along with high 5180 values of 6.20-7.63%o, suggesting a mixed source between mantle materials and ancient continental crust (such as the Bainaimiao Group) for the Bilihe magma. It is also supported by the presence of the captured detrital zircons in these intrusions. Given a universally metallogenic environment for porphyry gold deposits, a thicken crustal setting related to the collisional intermission of the Paleo-Asian Ocean is favored to interpret the formation setting of the Bilihe deposit

Distribution, Microfabric, and Geochemical Characteristics of Siliceous Rocks in Central Orogenic Belt, China: Implications for a Hydrothermal Sedimentation Model

Marine siliceous rocks are widely distributed in the central orogenic belt (COB) of China and have a close connection to the geological evolution and metallogenesis. They display periodic distributions from Mesoproterozoic to Jurassic with positive peaks in the Mesoproterozoic, Cambrian—Ordovician, and Carboniferous—Permian and their deposition is enhanced by the tensional geological settings. The compressional regimes during the Jinning, Caledonian, Hercynian, Indosinian, and Yanshanian orogenies resulted in sudden descent in their distribution. The siliceous rocks of the Bafangshan-Erlihe ore deposit include authigenic quartz, syn-depositional metal sulphides, and scattered carbonate minerals. Their SiO2 content (71.08–95.30%), Ba (42.45–503.0 ppm), and ΣREE (3.28–19.75 ppm) suggest a hydrothermal sedimentation origin. As evidenced by the Al/(Al + Fe + Mn), Sc/Th, (La/Yb)N, and (La/Ce)N ratios and δCe values, the studied siliceous rocks were deposited in a marginal sea basin of a limited ocean. We suggest that the Bafangshan-Erlihe area experienced high- and low-temperature stages of hydrothermal activities. The hydrothermal sediments of the former stage include metal sulphides and silica, while the latter was mainly composed of silica. Despite the hydrothermal sedimentation of the siliceous rocks, minor terrigenous input, magmatism, and biological activity partly contributed to geochemical features deviating from the typical hydrothermal characteristics

Distribution, Microfabric, and Geochemical Characteristics of Siliceous Rocks in Central Orogenic Belt, China: Implications for a Hydrothermal Sedimentation Model

Marine siliceous rocks are widely distributed in the central orogenic belt (COB) of China and have a close connection to the geological evolution and metallogenesis. They display periodic distributions from Mesoproterozoic to Jurassic with positive peaks in the Mesoproterozoic, Cambrian-Ordovician, and Carboniferous-Permian and their deposition is enhanced by the tensional geological settings. The compressional regimes during the Jinning, Caledonian, Hercynian, Indosinian, and Yanshanian orogenies resulted in sudden descent in their distribution. The siliceous rocks of the Bafangshan-Erlihe ore deposit include authigenic quartz, syn-depositional metal sulphides, and scattered carbonate minerals. Their SiO2 content (71.08-95.30%), Ba (42.45-503.0 ppm), and Sigma REE (3.28-19.75 ppm) suggest a hydrothermal sedimentation origin. As evidenced by theAl/(Al + Fe + Mn), Sc/Th, (La/Yb)(N), and (La/Ce)(N) ratios and delta Ce values, the studied siliceous rocks were deposited in a marginal sea basin of a limited ocean. We suggest that the Bafangshan-Erlihe area experienced high-and low-temperature stages of hydrothermal activities. The hydrothermal sediments of the former stage include metal sulphides and silica, while the latter was mainly composed of silica. Despite the hydrothermal sedimentation of the siliceous rocks, minor terrigenous input, magmatism, and biological activity partly contributed to geochemical features deviating from the typical hydrothermal characteristics

Multilevel Resistive Switching in Planar Graphene/SiO₂ Nanogap Structures

We report a planar graphene/SiO₂ nanogap structure for multilevel resistive switching. Nanosized gaps created on a SiO₂ substrate by electrical breakdown of nanographene electrodes were used as channels for resistive switching. Two-terminal devices exhibited excellent memory characteristics with good endurance up to 10⁴ cycles, long retention time more than 10⁵ s, and fast switching speed down to 500 ns. At least five conduction states with reliability and reproducibility were demonstrated in these memory devices. The mechanism of the resistance switching effect was attributed to a reversible thermal-assisted reduction and oxidation process that occurred at the breakdown region of the SiO₂ substrate. In addition, the uniform and wafer-size nanographene films with controlled layer thickness and electrical resistivity were grown directly on SiO₂ substrates for scalable device fabrications, making it attractive for developing high-density and low-cost nonvolatile memories