Geochemistry of Platinum Group and Rare Earth Elements of the Polymetallic Layer in the Lower Cambrian,Weng'an,Guizhou Province

The black shales of the Lower Cambrian Niutitang Formation in Weng＇an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements （PGE） has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum （Mo）, nickel （Ni）, vanadium （V）, lead （Pb）, strontium （Sr）, barium （Ba）, uranium （U）, arsenic （As）, and rare earth elements （REE） in abundance. High uranium/ thorium （U/Th） ratios （U/Th〉I） indicated that mineralization was mainly influenced by the hydrothermal process. The 8U value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements （LREE） （heavy rare earth elements （HREE） （LREE/HREE=5-17）, slightly negative europium （Eu） and cerium （Ce） anomalies （δEu=0.81- 0.93）, and positive Ce anomalies （δCe=0.76-1.12）. PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum （Pt）, palladium （Pd）, ruthenium （Ru） and osmium （Os）. The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent.

Re-Os Dating of Molybdenite from the Yaogangxian Tungsten Deposit,South China,and Its Geological Significance

The Yaogangxian tungsten deposit is located in the central part of the Nanling polymetailic metallogenic province. The orebodies occur as veins. Wolframite and molybdenite are the dominant ore minerals. Two samples were selected for molybdenite Re-Os dating in order to elucidate the timing of mineralization. Re-Os datings of molybdenite from quartz-woiframite veins and disseminated in granite yield ages of 153±7 Ma and 163.2±4.2 Ma respectively. The results indicate that the Yaogangxian tungsten deposit is the product of large-scale metallogenesis in the middle Yanshanian period in South China, and that the evolution from late magmatic to postmagmatic hypothermal mineralization occurred at about 10 Ma. The rhenium content of molybdenite in the Yaogangxian tungsten deposit suggests that the ore materials originated from the crust.

Sedimentary Characteristics and Paleoenvironmental Records of Zabuye Salt Lake,Tibetan Plateau,since 128 ka BP

This paper for the first time reveals high-resolution core records of Zabuye Salt Lake in the interior of the Qinghai-Tibet Plateau. According to 1346 samples taken continuously, relatively accurate 14^C, U-series disequilibrium and ESR ages have been obtained, thus revealing that the lake core ages from 0 to 83.63 m of hole SZK02 are -800 to over 128 ka. In the paper, the lake core sedimentary characteristics （including the lithologies and mineral assemblages） are analyzed in detail and correlated with ostracod assemblages I to XX and sporopollen zones A to I, and on the basis of an integrated analysis of the δ^18O values of authigenic calcium-magnesium carbonate and environmental proxies of minerals, sporopollen and microfossils in the lake core, a correlation has been made of oxygen isotope change between this lake core and the Greenland GISP2 and GRIP and Guliya ice cores, and the climate of Zabuye Salt Lake since 128 ka BP is divided into the last interglacial stage （including substages e, d, c, b and a） of oxygen isotope stage （OIS） 5, early glacial stadial of the last glacial stage of OIS 4, interglacial stadial of the last glacial stage of OIS 3, late glacial stadial of the last glacial stage or Last Glacial Maximum of OIS 2 and postglacial state of OIS 1; in addition, 6 Heinrich （H6-H1） events, Younger Dryas event and 8.2 ka BP cold event have been recognized.

Experimental Study on Formation Conditions of Ammoniojarosite and Its Environmental Significance

Formation conditions of ammoniojarosite in system Fe2（SO4）3-（NH4）2SO4-H2O are investigated in this paper. The results show that ammoniojarosite can be formed rapidly under normal temperature and pressure by controlling suitable pH value and Fe2（SO4）3 and （NH4）2SO4 concentrations. The pH value, temperature and concentration of Fe2（SO4）3 medium are key factors influencing the formation of ammoniojarosite. Under normal temperature, precipitation of ammoniojarosite can be seen within 24 hours at pH values between 2.6-3.1, and a great quantity of ammoniojarosite is formed within 48 hours. At about 90℃, the pH value range forming ammoniojarosite extends to 1.2-3.1, and within this range the rise of pH value is advantageous to the formation of ammoniojarosite and high Fe2（SO4）3 concentration is also advantageous. Relative pure ammoniojarosite is synthesized under high Fe2（SO4）3 concentration （≥0.05 M） and ammoniojarosite containing melanterite and colloid amorphous hydroxide vitriol iron is formed at low Fe2（SO4）3 concentration. The deposition process of ammoniojarosite can be used to harness wastewater from mines and other industries and remove S, Fe and other toxic and harmful elements, such as As, Cr, Hg, Pb in water. Rapid formation of ammoniojarosite and other jarosite analogs under normal temperature and pressure has a good potential prospect for harnessing acid wastewater by means of precipitation of jarosite and its analogs.

Experimental Study on Treatment of High-concentrated Sulfur Wastewater by Process of Depositing Natrojarosite and Its Environmental Significance

High-concentrated sulfur wastewater with sodium and COD （chemical oxygen demand） up to 26000 mg/L from a chemical plant, Jiangsu Province of China has been treated by deposition of natrojarosite in lab. The results indicated that the COD of the wastewater was decreased sharply from 26000 mg/L to 1001 mg/L, with removal rate of COD up to 96% by twice precipitations of natrojarosite and twice oxidation of H202. The treated sulfur wastewater reached the requirement of subsequent biochemical treatment to water quality. The optimal operational parameters should be controlled on pH value between 2.50 and 3.20 and 50 g FeCly6H2O solid added in per liter wastewater. The study provided an experimental basis for pretreatment of high-concentrated sulfur wastewater and proposed a new mineralogical method on treatment of other wastewaters. Depositing process of jarosite and its analogs should be able to be used to treat wastewater from mine and other industries to remove S, Fe and other toxic and harmful elements, such as As, Cr, Hg, Pb, etc. in the water.

The Impact of Climatic and Environmental Factors on n-Alkanes Indices in Southwestern Tibetan Plateau

n-Alkanes are widely used in paleoenvironmental reconstructions.However,our understanding of changes in the distribution of n-alkanes with climatic and environmental factors remains unclear in arid/semi-arid regions.We sampled 26 surface sediments from three climatic zones across the southwestern Tibetan Plateau to evaluate the sensitivity of chain length distributions of n-alkanes to climatic and environmental parameters.Our observations demonstrate that average chain length(ACL),proportion of aquatic macrophyte(Paq),carbon preference index(CPI)and ratio of the contents of nC_(27)and nC_(31)(nC_(27)/nC_(31))are all sensitive to hydroclimatic conditions.In contrast to commonly-adopted assumptions,the correlations between these indices and hydrological parameters are not always good,which indicates that the interpretation of n-alkane indices is special on the southwestern Tibetan Plateau.These might be related to the vegetation characteristics and seasonality of biological activity,and need to be considered in paleoclimatic reconstruction.The impact of seasonal precipitation on n-alkanes indices was also evaluated.

Discovery of Cosmic Spherules from the Mesoproterozoic Strata and its Significance——in Case of the Ming Tombs Area, Beijing

This study covers cosmic spherules derived from the Mesoproterozoic Dahongyu Formation in the Ming Tombs area, Beijing. The cosmic spherules include iron oxide cosmic spherules, carbonaceous chondrites, and atomic iron "steely bead"-shaped cosmic spherules. The mineral assemblage of silicon carbide, forsterite, zircon, and glass spherules and fragments were picked from melt-silicified carbonate of the Mesoproterozoic Dahongyu Formation(ca. 1625 Ma). Cosmic spherule assemblages are solely discovered from sedimentary rocks in China. Platinum group elements(PGE) were determined for the first time in cosmic spherules and associated minerals. PGE comparative observation between meteorite and cosmic spherules is presented in this study. It is recognized that an extraterrestrial meteorite impact event might have occurred in the Dahongyu Stage. The main evidence is a large number of iron cosmic spherules in silicified oncolitic limestone, and associated cosmic silicon carbide, glass spherules, and fragments, as well as the presence of forsterite. The impact-volcanic crater is characteristic of a big black shale block dropped into the bended silicified limestone.

Microbial Gas in the Mohe Permafrost, Northeast China and its Significance to Gas Hydrate Accumulation in Permafrost across China

The Mohe permafrost in northeast China possesses favorable subsurface ambient temperature, salinity, Eh values and pH levels of groundwater for the formation of microbial gas, and the Mohe Basin contains rich organic matter in the Middle Jurassic dark mudstones. This work conducted gas chromatography and isotope mass spectrometry analyses of nearly 90 core gas samples from the Mk-2 well in the Mohe Basin. The results show that the dryness coefficient(C1/C1–5) of core hydrocarbon gas from approximately 900 m intervals below the surface is larger than 98%, over 70% of the δ13 C values of methane are smaller than-55‰, and almost all δD values of methane are smaller than-250‰, indicative of a microbial origin of the gas from almost 900 m of the upper intervals in the Mohe permafrost. Moreover, the biomarker analyses of 72 mudstone samples from the Mohe area indicate that all of them contain 25-norhopane series compounds, thereby suggesting widely distributed microbial activities in the permafrost. This work has confirmed the prevailing existence of microbial gas in the Mohe area, which may be a potential gas source of gas hydrate formation in the Mohe permafrost. This result is of great significance to gas hydrate accumulation in the permafrost across China.

Re-Os dating of auriferous pyrite from the Zhenyuan super-large gold deposit in Ailaoshan gold belt,Yunnan Province,Southwestern China

Zhenyuan gold deposit is the largest super large gold deposit in the Ailaoshan gold belt,but its precise mineralization age is still lack.Re-Os isotopic age of the auriferous pyrite from the Zhenyuan gold deposit was determined by using a high-resolution inductively coupled plasma mass spectrometry(HR-ICP-MS).The pyrite samples were decomposed in carius tubes,Os was separated by distillation and Re was extracted by acetone,respectively.The results show that the Re-Os isochron age is 229±38 Ma(MSWD=2.0,confidence level is 95%),with an initial 187 Os/188 Os value of 0.68±0.24 and a corresponding Os value of 442±91.The Re/Os ratios of the pyrite vary from 40.8 to 100.5.The data suggest that at least one important ore-forming event was occurred during Indosinian epoch,and the ore-forming materials probably derived from mixed sources of crustal and mantle,while the later dominated.The Ailaoshan composite orogen experienced complicated evolutional processes,including formation of Precambrian-Early Paleozoic basement,subduction and orogenesis of Late Paleozoic era,collisional orogenesis of Late Hercynian-Indosinain epoch,and extensional or striking orogenesis of Yanshainan-Cenozoic epoch.The polycycle tectonic evolution and magmatism in this area caused multi-stage and superposition metallization characteristics of the Zhenyuan gold deposit:the mineralization probably occur mainly during the Indosinian collisional orogeny,while the minor gold ores of altered granite-porphyry and altered lamprophyre may be formed in the late superposition metallization.

Re-Os dating of gold-bearing arsenopyrite of the Maoling gold deposit,Liaoning Province,Northeast China and its geological significance

The Maoling gold deposit, one of the large gold deposits in eastern Liaoning Province, NE China, is an ar- senopyrite-disseminated gold deposit with a resource of ap- proximately 25 t Au and an average Au grade of 3.2 g/t. Six arsenopyrites closely related to Au mineralization of the Maoling gold deposit are dated by Re-Os technique and de- fine a Re-Os isochron with an age of 2316±140 Ma, which suggests that the deposit was formed in the Paleoproterozoic era rather than in the Indosinian period as some early re- searchers suggested. High initial 187Os/188Os ratio of 1.32±0.48 indicates a crustal derivation of the ore-forming material of the deposit, which may be derived from rocks of the Gaixian formation of the Liaohe Group. Furthermore, the result also implies that the age of the Gaixian Formation in the Maoling district is older than 2316±140 Ma.

Geology, Geochronology, and Hf Isotopic Composition of the Pha Lek Fe Deposit, Northern Laos: Implications for Early Permian Subduction-Related Skarn Fe Mineralization in the Truong Son Belt

The Truong Son metallogenic belt in central Laos and Vietnam is an important Fe-Cu-Sn-Au polymetallic ore district. The Pha Lek Fe deposit is closely related to Late Carboniferous– Early Permian I-type granitic magmatism, and contains >50 Mt @ 45% to 50% of Fe ore. Ore minerals occur mainly as magnetite and hematite in the skarn alteration zone between a granitic pluton and metamorphosed Middle–Upper Devonian carbonates. The granitic pluton comprises granodiorite and granite, with zircon U-Pb dating indicating synchronous emplacement at 288.2±1.3 and 284.9±1.2 Ma, respectively. Zircons from these granitoids have ε_(Hf)(t) values of 2.9–11.2 and relatively young TDM2 ages(<1.0 Ga), indicating an origin by partial melting of depleted mafic crust or magma mixing. Previous studies have shown that these granitoids have high Y, Yb, and K_2O contents, and low Sr and Na_2O contents, which are interpreted as the melting of mafic continental crust. Pyrite of the main mineralization stage yields an ^(187)Re/^(188)Os-^(187)Os/^(188)Os isochron age of 287±17 Ma, indicating that mineralization is associated with Pha Lek granitic magmatism. A Late Carboniferous–Early Permian subduction-related skarn-type Fe mineralization model is proposed for the Pha Lek deposit. More evidence is needed to verify a hypothesis of volcanic overprinting during Late Triassic post-collisional extension.

Distribution of n-alkanes in Miocene loess in Qinan, western Chinese Loess Plateau, and its palaeoenvironmental implications

Neogene eolian successions are one of the most important terrestrial palaeoenvironmental archives in East Asia.However, they have received far less attention than Quaternary loess deposits, especially in the case of lipid biomarker analysis.In order to obtain a better insight into the early-middle Miocene palaeoenvironment, we conducted a study of n-alkane biomarkers from sediments of the QA-I section(Qinan) in the western Chinese Loess Plateau, and compared the results with those of previous n-alkane analyses of eolian and aquatic sediments of varying age. Our principal results are as follows:(1) All QA-I samples contain n-alkanes ranging from C_(14) to C_(35), among which the relative content of short-chain n-alkanes(C_(14)–C_(20)) from microorganisms is significantly greater than that of long-chain n-alkanes(C_(26)–C_(35)) from the waxes of terrestrial higher plants;the main peak is at C_(16)–C_(18). All samples have a relatively lower abundance of medium-chain n-alkanes(C_(21)–C_(25)) than that of long-and short-chain n-alkanes, similar to strongly weathered palaeosols in Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth; however, this distribution is significantly different from that in weakly-weathered loess of Quaternary loess and Late Miocene-Pliocene Hipparion Red-Earth, as well as from aquatic sediments.(2) Despite some odd-over-even carbon predominance of long-chain n-alkanes in the QA-I samples, the carbon preference index(CPI) values are significantly lower than those of most of the weakly-weathered sediments. Our results show that strong weathering and microbial processes have significantly altered the n-alkanes in the Miocene eolian deposits in Qinan, and led to a significant oxidation and degradation of long-chain n-alkanes and the predominance of short-chain n-alkanes from bacteria. Therefore, the contribution of microorganism to total organic carbon(TOC) and its resulting in carbon isotopic composition should be carefully assessed in future studies.