Ore-forming Fluid and Metallogenic Mechanism of Wolframite-Quartz Vein-type Tungsten Deposits in South China

South China is endowed with copious wolframite-quartz vein-type W deposits that provide a significant contribution to the world‘s tungsten production.Mineralization is spatially associated with highly evolved granites,which have been interpreted as products of ancient crustal anatexis.Ore veins are mainly hosted in low-grade metamorphosed quartz sandstone,slate and granitic rocks.The ore minerals mainly comprise wolframite,cassiterite,scheelite and pyrite,with minor molybdenite,arsenopyrite and chalcopyrite.Typical steeply dipping veins can be divided into five zones from top to the bottom,namely:(Ⅰ)thread,(Ⅱ)veinlet,(Ⅲ)moderate vein,(Ⅳ)thick vein,and(Ⅴ)thin out zones.In general,three types of fluid inclusions at room temperature are commonly recognized in wolframite and/or quartz from these veins:two-phase liquid-rich(type L),two-phase CO2-bearing(type CB),and CO2-rich(type C).Comparative microthermometry performed on fluid inclusions hosted in wolframite and associated quartz indicates that most wolframite was not coprecipitated with the coexisting quartz.Detailed petrographic observation and cathodoluminescence(CL)imaging on coexisting wolframite and quartz of the Yaogangxian deposit,show repeated precipitation of quartz,wolframite,and muscovite,suggesting a more complex fluid process forming these veins.Previous studies of H-O isotopes and fluid inclusions suggested that the main ore-forming fluids forming the wolframite-quartz vein-type deposits had a magmatic source,whereas an unresolved debate is centered on whether mantle material supplemented the ore-forming fluids.The variable CO2 contents in the ore-forming fluids also implies that CO2 might have had a positive effect on ore formation.Fluid inclusion studies indicate that wolframite was most likely deposited during cooling from an initial H2 O+Na Cl±CO2 magmatic fluid.In addition,fluid-phase separation and/or mixing with sedimentary fluid might also have played an important role in promoting wolframite deposition.We speculate that these processes determine the precipitation of W to varying degrees whereas the leading mechanistic cause remains an open question.Comprehensive studies on spatial variation of fluid inclusions show that both the steeply and gently dipping veins are consistent with the"five floors"model that may have broader applications to exploration of wolframite-quartz vein-type deposits.Recent quantitative analysis of wolframite-and quartz-hosted fluid inclusions by laser ablation inductively-coupled plasma mass spectrometry shows enhanced advantages in revealing fluid evolution,tracing the fluid source and dissecting the ore precipitation process.Further studies on wolframite-quartz vein-type W deposits to bring a deeper understanding on ore-forming fluids and the metallogenic mechanism involved.

The effect of Fe-Mn minerals and seawater interface and enrich-ment mechanism of ore-forming elements of polymetallic crusts and nodules from the South China Sea

Ferromanganese crusts and nodules are important submarine mineral resources that contain various metal elements with significant economic value. In this study, polymetallic crusts and nodules obtained from the South China Sea （SCS） were determined by using X-ray power diffraction （XRD）, Raman spectroscopy （RS）, Fourier transform infrared spectroscopy （FTIR）, and X-ray photoelectron spectroscopy （XPS） to systematically investigate and analyze the mineralogical and spectral characteristics of the Fe-Mn minerals. XRD measurements revealed that the SCS polymetallic crusts and nodules were composed of vernadite, quartz, and plagioclase. The nodules also contained todorokite. The Fe-phase minerals of the SCS crusts and nodules were composed of amorphous Fe oxide/hydroxide, and the Mn- and Fe-phases minerals exhibited relatively poor degrees of crystallization. FTIR results showed that the Fe-Mn minerals in the crusts and nodules included a large number of surface hydroxyl groups. These surface hydroxyl groups contained protons that could provide reactive sites for complexation of ore-forming elements in seawater. XPS results indicated that the surfaces of the Fe-Mn minerals mainly contained Fe, Mn, and O. Fe was present in the trivalent oxidation state, while Mn, which may contain several bivalent oxidation state, was present in the tetravalent and trivalent oxidation states. The SCS polymetallic crusts and nodules were compared with Pacific seamount crusts, and results showed that the surface hydroxyl （-OH） groups of the SCS crusts and nodules numbered more than the lattice oxygen （O^2-）. But the lattice oxygen of Pacific seamount crusts numbered more than the surface hydroxyl groups. This characteristic indicated that the degree of crystallization of Fe-Mn minerals from the Pacific Ocean was higher than that of minerals from the South China Sea. Comprehensive studies showed that ore-forming elements in the interface between seawater and the Fe-Mn minerals in the submarine ferromanganese crusts and nodules employed the following enrichment mechanisms： （1） the metal ion complexed with the surface hydroxyl of Fe-Mn minerals to form hydroxyl complexes, which were connected by coordination bonds or stable inner-sphere complexes that exchanged protons on the mineral surfaces; （2） the charged surfaces of the minerals and metal cations formed outer-sphere complexes, which made up the electrostatic double layer, through electrostatic adsorption; and （3） the metal cations isomorphously exchanged the Mn and Fe ions of the mineral lattice structure.

Melt-Fluid and Fluid-Fluid Immiscibility in a Na_(2)SO_(4)-SiO_(2)-H_(2)O System and Implications for the Formation of Rare Earth Deposits

Liquid-liquid immiscibility has crucial influences on geological processes,such as magma degassing and formation of ore deposits.Sulfate,as an important component,associates with many kinds of deposits.Two types of immiscibility,including(i)fluid-melt immiscibility between an aqueous solution and a sulfate melt,and(ii)fluid-fluid immiscibility between two aqueous fluids with different sulfate concentrations,have been identified for sulfate-water systems.In this study,we investigated the immiscibility behaviors of a sulfate-and quartz-saturated Na_(2)SO_(4)-SiO_(2)-H_(2)O system at elevated temperature,to explore the phase relationships involving both types of immiscibility.The fluid-melt immiscibility appeared first when the Na_(2)SO_(4)-SiO_(2)-H_(2)O sample was heated to~270℃,and then fluid-fluid immiscibility emerged while the sample was further heated to~450℃.At this stage,the coexistence of one water-saturated sulfate melt and two aqueous fluids with distinct sulfate concentrations was observed.The three immiscible phases remain stable over a wide pressure-temperature range,and the appearance temperature of the fluid-fluid immiscibility increases with the increased pressure.Considering that sulfate components occur extensively in carbonatite-related deposits,the fluid-fluid immiscibility can result in significant sulfate fractionation and provides implications for understanding the formation of carbonatite-related rare earth deposits.

Himalayas as a global hot spot of springtime stratospheric intrusions:Insight from isotopic signatures in sulfate aerosols

Downward transport of stratospheric air into the troposphere(identified as stratospheric intrusions)could potentially modify the radiation budget and chemical of the Earth's surface atmosphere.As the highest and largest plateau on earth,the Tibetan Plateau including the Himalayas couples to global climate,and has attracted widespread attention due to rapid warming and cryospheric shrinking.Previous studies recognized strong stratospheric intrusions in the Himalayas but are poorly understood due to limited direct evidences and the complexity of the meteorological dynamics of the third pole.Cosmogenic^(35)S is a radioactive isotope predominately produced in the lower stratosphere and has been demonstrated as a sensitive chemical tracer to detect stratospherically sourced air mass in the planetary boundary layer.Here,we report 6-month(April–September 2018)observation of^(35)S in atmospheric sulfate aerosols(^(35)SO_(4)^(2-))collected from a remote site in the Himalayas to reveal the stratospheric intrusion phenomenon as well as its potential impacts in this region.Throughout the sampling campaign,the^(35)SO_(4)^(2-)concentrations show an average of 1,070±980 atoms/m^(3).In springtime,the average is 1,620±730 atoms/m^(3),significantly higher than the global existing data measured so far.The significant enrichments of^(35)SO_(4)^(2-)measured in this study verified the hypothesis that the Himalayas is a global hot spot of stratospheric intrusions,especially during the springtime as a consequence of its unique geology and atmospheric couplings.In combined with the ancillary evidences,e.g.,oxygen-17 anomaly in sulfate and modeling results,we found that the stratospheric intrusions have a profound impact on the surface ozone concentrations over the study region,and potentially have the ability to constrain how the mechanisms of sulfate oxidation are affected by a change in plateau atmospheric properties and conditions.This study provides new observational constraints on stratospheric intrusions in the Himalayas,which would further provide additional information for a deeper understanding on the environment and climatic changes over the Tibetan Plateau.

Crustal stress field in Yunnan: implication for crust-mantle coupling

We applied the g CAP algorithm to determine 239 focal mechanism solutions 3：0≤MW≤ 6：0） with records of dense Chin Array stations deployed in Yunnan,and then inverted 686 focal mechanisms（including 447 previous results） for the regional crustal stress field with a damped linear inversion. The results indicate dominantly strike-slip environment in Yunnan as both the maximum（r1） and minimum（r3） principal stress axes are sub-horizontal. We further calculated the horizontal stress orientations（i.e., maximum and minimum horizontal compressive stress axes： S H and S h, respectively） accordingly and found an abrupt change near ＊26°N. To the north, S H aligns NW-SE to nearly E-W while S h aligns nearly N-S. In contrast, to the south, both S H and S h rotate laterally and show dominantly fan-shaped patterns. The minimum horizontal stress（i.e., maximum strain axis） S h rotates from NW-SE to the west of Tengchong volcano gradually to nearly E-W in west Yunnan, and further toNE-SW in the South China block in the east. The crustal strain field is consistent with the upper mantle strain field indicated by shear-wave splitting observations in Yunnan but not in other regions. Therefore, the crust and upper mantle in Yunnan are coupled and suffering vertically coherent pure-shear deformation in the lithosphere.

The Genesis Mechanism of the Mantle Fluid Action and Evolution in the Ore-Forming Process: A Case Study of the Laowangzhai Gold Deposit in Yunnan, China

Based on petrological studies of the wall rocks, mineralizing rocks, ores and veins from the Laowangzhai gold deposit, it is discovered that along with the development of silication, carbonation and sulfidation, a kind of black opaque ultra-microlite material runs through the spaces between grains, fissures and cleavages. Under observations of the electron microprobe, scanning electronic microscopy and energy spectrum, this kind of ultra-microlite material is confirmed to consist of ultra microcrystalline quartz, silicate, sulfides and carbonates, as well as rutile, scheelite and specularite （magnetite）, showing characters of liquation by the analyses of SEM and energy spectrum. The coexistence of immiscibility and precipitating co-crystallization strongly suggests that the mineralizing fluid changed from the melt to the hydrothermal fluid. Combined with the element geochemical researches, it is realized that the ultra-microlite aggregate is the direct relics of the mantle fluid behaving like a melt and supercritical fluid, which goes along with the mantle-derived magma and will escape from the magma body at a proper time. During the alteration process, the nature of the mantle fluid changed and it is mixed with the crustal fluid, which are favorable for mineralization in the Loawangzhai gold deposit.

Apatite fission track thermochronology in the Kuluketage and Aksu areas,NW China:Implication for tectonic evolution of the northern Tarim

Tarim Precambrian bedrocks are well exposed in the Kuluketage and Aksu areas, where twenty four samples were taken to reveal the denudation history of the northern Tarim Craton. Apatite fission track dating and thermal history modeling suggest that the northern Tarim experienced multi-stage cooling events which were assumed to be associated with the distant effects of the Cimmerian orogeny and India-Eurasia collision in the past. But the first episode of exhumation in the northern Tarim, occurring in the mid-Permian to Triassic, is here suggested to be induced by docking of the Tarim Craton and final amalgamation of the Central Asian Orogenic Belt. The cooling event at ca. 170 Ma may be triggered by the Qiangtang-Eurasia collision. Widespread Cretaceous exhumation could be linked with docking of the Lhasa terrane in the late Jurassic. Cenozoic reheating and recooling likely occurred because of the northpropagating stress, however, this has not affected the northern Tarim much because the Tarim is characterized by rigid block-like motion.

Neoproterozoic–Early Paleozoic Tectonic Evolution of the South China Craton： New Insights from the Polyphase Deformation in the Southwestern Jiangnan Orogen

A 〉1500–km–long northeast–southwest trending Neoproterozoic metamorphic belt in the South China Craton（SCC） consists of subduction mélange and extensional basin deposits. This belt is present under an unconformity of Devonian–Carboniferous sediments. Tectonic evolution of the Neoproterozoic rocks is crucial to determining the geology of the SCC and further influences the reconstruction of the Rodinia supercontinent. A subduction mélange unit enclosed ca.1000–850–Ma mafic blocks, which defined a Neoproterozoic ocean that existed within the SCC, is exposed at the bottom of the Jiangnan Orogen（JO） and experienced at least two phases deformation. Combined with new（detrital） zircon U–Pb ages from metasandstones, as well as igneous rocks within the metamorphic belt, we restrict the strongly deformed subduction mélange as younger than the minimum detrital age ca. 835 Ma and older than the ca. 815 Ma intruded granite. Unconformably overlying the subduction mélange and the intruded granite, an intra–continental rift basin developed 〈800 Ma that involved abundant mantle inputs, such as mafic dikes. This stratum only experienced one main phase deformation. According to our white mica ^40Ar/^（30）Ar data and previously documented thermochronology, both the Neoproterozoic mélange and younger strata were exhumed by a 490–400–Ma crustal–scale positive flower structure. This orogenic event probably induced the thick–skinned structures and was accompanied by crustal thickening, metamorphism and magmatism and led to the closure of the pre–existing rift basin. Integrating previously published data and our new results, we agree that the SCC was located on the periphery of the Rodinia supercontinent from the Neoproterozic until the Ordovician. Furthermore, we prefer that the convergence and dispersal of the SCC were primarily controlled by oceanic subduction forces that occurred within or periphery of the SCC.

Discovery of shale oil in alkaline lacustrine basins:The Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China

A new type of shale oil in alkaline lacustrine sediments has been discovered in the Late Paleozoic Fengcheng Formation,Mahu Sag,Junggar Basin,China.The fine-grained sedimentary rocks deposited in this alkaline lacustrine environment can be divided into four types and eight sub-types:mudstone(with no alkali minerals),including massive dolomitic mudstone,and massive and laminated calcareous mudstone;dolomite,including massive argillaceous dolomite(with alkali minerals),and massive and laminated argillaceous dolomite(with no alkali minerals);evaporites;and pyroclastic rocks.The massive argillaceous dolomite(with alkali minerals)and pyroclastic rocks have the highest shale oil potential,with average oil saturation index(OSI)values of 344.67 and 124.65 mg HC/g TOC,respectively.Shale oil exploration in the representative well MY1 indicates that the Fengcheng Formation is thick and contains abundant natural fractures,brittle minerals,and mobile oil.The entire Fengcheng Formation is oilbearing and contains three concentrated stratigraphic intervals of shale oil(i.e.,sweet spots).Well MY1 indicates that,compared with source rocks developed in marine and sulfate-type saline basins,the fine-grained sedimentary rocks deposited in alkaline lacustrine environments can also have high shale oil potential.The co-existence and regular distribution of conventional and unconventional reservoirs in the Fengcheng Formation indicate that it is an ideal exploration target for multiple resource types.

Enrichment of Mantle-derived Fluids in the Formation Process of Granitoids: Evidence from the Himalayan Granitoids around Kunjirap in the Western Qinghai-Tibet Plateau

Taking the Himalayan granitoids around Kunjirap in the western Qinghai-Tibetplateau as an example, the authors present in this paper the characteristics of the granitoids richin mantle-derived fluid components and discuss their rock-forming mechanism. The research resultsindicate that the rock assemblage of the studied granitoids involves diopside syenite-diopsidegranite-biotite (monzonitic) granite, consisting mainly of K-feldspar, oligoclase, quartz,iron-phlogolite, diopside and edenite. The rocks are rich in mantle-derived fluid components ofvolatiles including F, alkali metal elements such as K, Na, Rb, Sr and Ha, and radiogenicheat-producing elements such as U and Th. They were generated by the influx of mantle-derived fluidsinto the lower crest to give rise to partial melting during the lithosphere thinning in theQinghai-Tibet plateau.

Early Cambrian carbon isotope stratigraphy in the Tarim Basin and a correlation with the Yangtze Platform

Carbon isotope chemostratigraphy has been used worldwide for stratigraphic correlation.In this study,δ13Ccarb values are estimated for the Early Cambrian Sugaitebulake section in the Tarim Basin,Xinjiang Autonomous Region,China.As a result,one positive and two negative carbon isotope excursions in the studied section were iden-tified.The δ13Ccarb values reached the maximum negative excursion(N1:-12.39‰) at the basal of the Yuertusi For-mation,and then increased to P1.After P1,δ13Ccarb values sharply decreased to about-7.06‰(N2) in the studied section.The pattern of δ13Ccarb in the Early Cambrian is comparable to the synchronous records of other sections,such as the Laolin section,the Xiaotan section and the Anjiahe section of the Yangtze Platform.It is concluded that the Early Cambrian Yuertusi Formation from the Tarim Basin is within the Nemakit-Daldynian stage,and the lower strata of the Yuertusi Formation may belong to the Zhujiaqing Formation(Meishucun Formation) of the Yangtze Platform.The Ediacaran/Cambrian boundary of the Tarim Block should be located in cherts and phosphorites suc-cessions at the basal of the Yuertusi Formation.The δ13Ccarb negative excursion N1 is just across the PC/C boundary,and may be related to certain biomass extinction due to anoxic sedimentary environment,transgression and/or the oceanic overturn.The second δ13Ccarb negative excursion N2 may account for the sea-level falling in the Early Cam-brian.

Study on the origin and rock-forming simulation experiments of aquamarine-bearing pegmatites of Ailaoshan,Yunnan,China

The Ailaoshan aquamarine-bearing pegmatites are associated with Proterozoic metamorphic rocks in the southern portion of the Ailaoshan fault-folded complex.The gem-bearing pegmatite mineralization zones of the region occur in areas generally consistent with the regional tectonic trend.The pegmatites are found in metamorphic rocks,migmatites and in the inner/outer contact zones of gneissoid granites. The Rb-Sr isochron drawn for the pegmatites is 26～31 Ma,(i.e.in Himalayan).The homogenization temperatures of melt and liquid inclusions in minerals vary from 185 to 920℃,which are comparable to the inclusions observed in banded migmatites and ptygmatic quartz veins in the surrounding metamorphic rocks. The mineralization fluids of the pegmatite were rich in HCO_3 and CO_2,and their compositional assemblages are comparable to metamorphic fluids.Results of H,O,C,Si etc.isotopic analyses and REE,and Be analyses indicates that the sources of mineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphic rocks. A pegmatite structure simulation experiment was conducted at high temperature and pressure(840℃and 1,500×105Pa.),with various metamorphic rock samples in a water-rich and volatile-rich environment.When the liquidus was reached,the temperature was gradually decreased at the rate of 5～10℃/day over a time period of three months.SEM energy-dispersive spectrum analyses were performed on the experimental products.A series of pegmatoid textures were observed including zonal texture,megacryst texture,drusy cavities,crystal druses,and vesicular texture along with more than ten types of minerals including plagioclase,microcline,quartz and biotite.Different metamorphic rock melts generated different mineral assemblages.Experiment results revealed that the partial melting of metamorphic rocks could form melts similar to pegmatite magmas. Based upon the geological characteristics,geochemistry,and pegmatite texture simulation experimental results,it is concluded that the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks.The petrogenetic model for the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis.

Geochemistry and Petrogenesis of Late Cretaceous–Paleocene Granites from the Tengchong Block, Western Yunnan: Implications for Angle-switching of Subducting Slab

The Cenozoic geological hallmark of Western Yunnan is the characteristic voluminous Late Cretaceous-Eocene granites;however, their geological background and petrogenesis have not been well constrained and elucidated. In this study, we present new zircon U-Pb dating, along with geochemical and Sr-Nd-Hf isotopic data for granites from the Tengchong–Lianghe granitoid belt(as abbreviated to Tengliang belt) and West Yingjiang batholiths from the Tengchong block. The mineralogical and geochemical features of the Tengliang granites and the West Yingjiang batholiths are ascribed to aluminous S-type granites and weak peraluminous I-type, respectively. Zircon U-Pb analyses yielded consistent ages ranging from 67.5 Ma, 68.4 Ma and 66.2 Ma from the Tengliang granitoid belt and 50.4 Ma to 60.8 Ma for three samples from the west Yingjiang batholiths. The Tengliang granites were emplaced during the Late Cretaceous(68-66 Ma) and demonstrate negative ε_(Hf)(t) values(-24 to-4) and initial ~(87)Sr/~(86)Sr ratios of 0.7101–0.7139 and significant negative ε_(Nd)(t) values from-8.91 to-13.2, indicating a Proterozoic sedimentary source or enriched components. The hornblende-bearing I-type granites from West Yingjiang are characterized by lower initial ~(87)Sr/~(86)Sr ratios of 0.7076–0.7106, compared to Tengliang granite and negative whole-rock ε_(Nd)(t) values from-4.0 to-11.9. The early Eocene west Yingjiang gneissic granites show wide ranges of ε_(Hf)(t) values from +7.4 to-8.5 and T_(2DM) of 1.30–0.65 Ga, indicating partial melting of ancient crust with contributions of depleted mantle materials. In combination with the regional background and previous studies, we propose that such a spatio-temporal distribution of the Tengchong granitoid belt might be related to the rollback or angleswitching of the Neo-Tethyan subducting slab. This study sheds new light on the evolutionary history of the Tengchong block.

Neoproterozoic Banded Iron Formation in the Central Tianshan, NW China: The Shalong Example

Objective Banded Iron Formations （BIFs） are ferruginous chemical sedimentary rocks that precipitated throughout the Precambrain, which constitute the most important iron resources in the world. The majority of BIFs were developed in the Neoarchean and early Paleoproterozoic periods （3.2-1.8 Ga）, which are well known and have been mined for centuries. Another type of the BIFs which was formed in the Neoproterozoic period （0.85-0.7 Ga） is much smaller in scale but widespread on the Earth and record important information of the evolution of the Earth. The Neoarchean and Paleoproterozoic BIFs have been well studied and understood, while few detailed studies on Neoproterozoic BIFs have been made, and only a few modem geochronology studies were carried out on Neoproterozoic BIFs.

Carbon Isotope Features of the Sugetbrak Section in the Aksu-Wushi Area, Northwest China: Implications for the Precambrian/Cambrian Stratigraphic Correlations

The upper Qigeblaq Formation （Fm） dolostones and the Yurtus Fm phosphatic cherts, black shales, limestones, and dolostones are widely distributed in the Precambrian/Cambrian transitional succession of the Aksu-Wushi area. Negative δ13C excursion above the Yurtus Fm/ Qigeblaq Fm boundary was determined in this study. The pronounced negative carbon isotope excursion occurs in the phosphatic chert layers at the bottom of the Cambrian Yurtus Fm, below which the first appearance of the Asteridium- Heh＇osphaeridium-Comasphaeridium （AHC） acritarch assemblage zone. The δ13C curve of the lower part of the Yurtus Fm in the Aksu-Wushi area was found to be correlated with the early Cambrian δ13C curves of the Zhujiaqing Fm （Daibu Member）, the lower part of the Yanjiahe Fm on the Yangtze Platform in China, the lower Tal Fm in India, the Sukharikha Fm in Siberia, and the upper part of the Tsagaan Oloom Fm in Mongolia through biostigraphy. The lower part of the Yurtus Fm in the Tarim Basin is at the Nemakit-Daldynian stage, and the Precambrian/Cambrian boundary of the Aksu-Wushi area may be located in the phosphatic chert unit which just below the first appearance AHC acritarch assemblage zone. The negative δ13C excursion （N1） across the Precambrian/Cambrian boundary in the studied section may have resulted from oceanic overturning and sea level rise.

A New Potential Caledonian–Indosinian Ore Concentration Area:Evidence from Diagenesis and Mineralization Ages of the Miao'ershan–Yuechengling Region

Objective The Miao＇ershan-Yuechengling composite granite, located in northern Guangxi at the western section of the Nanling Range, is a multi-period and multi-stage composite pluton with an exposed area of more than 3000 km2 （Fig. 1）. Paleozoic and Proterozoic strata are exposed around it, and magmatic activities mainly occurred during the Caledonian and Indosinian periods. Till now, more than one hundred W-Sn-Mo-Pb-Zn-Cu （U） deposits and ore occurrences have been discovered along the inner and outer contact zones of this granite. Through recent years＇ research, we infer that this area is not only a preferred area for studying granite and mineralization in Caledonian and lndosinian periods, but also a potential Caledonian- lndosinian ore-concentrated area.

Trace and Rare Earth Element Geochemistry of Micrite Mound Carbonates and Other Related REE Mineralized Carbonates from Bayan Obo Area in Inner Mongolia

Geochemical study on trace and rare earth element geochemistry was carried out for different carbonates including the very REE-rich ones in the main ore bodies, a carbonatite dyke and two micrite mounds from Heilaobao far away from the Bayan Obo ore deposit, and Xishan in west Beijing. The results show that both carbonatite dyke and REE mineralized carbonates (dolomite and marble) in the main ore bodies and outside ore bodies have similarities to each other, with very extreme positive anomaly of Ba, Th, Nb, La, Ce, Nd, Sm, Pb, medium positive anomaly of Y, Ho, Tb, Er, Yb and negative anomaly of Sc, Ti and Cu. The REE concentration in the mineralized carbonates changes greatly, the total REE content changes from 262×10^(-6) in both east and west ore deposits to 104562 ×10^(-6) (10.46%), which is relatively lower than those samples of carbonatite dyke, whose REE contents vary greatly, from 1% up to 20 % of mass fraction. Light REE in the carbonatites are enriched and highly fractionated relative to heavy REE and there is no Eu anomaly. The REE distribution patterns of both mineralized carbonate and carbonatite dyke are of some similarities. However, the sedimentary carbonate micrite of Salinhudong Group in Heilaobao far outside the ore bodies and the pure carbonates from Xishan in Beijing, central part of North China plate, have the similarities in REE distributions with much lower REE contents, which are significantly different from those of carbonatite dyke and REE mineralized carbonate. In Bayan Obo district, both carbonates in the ore deposit and micrite mound outside the ore deposit underwent widespread metasomatism by fluids that resulted in formation of the superlager Fe-Nb-REE mineralization. It appears that the carbonates represent the evolution products of different geological stages.

Sedimentary Facies, Provenance and Geochronology of the Heshangzhen Group: Implications for the Tectonic Evolution of the Eastern Jiangnan Orogen, South China

The Neoproterozoic Jiangnan orogen plays an important role in the study of the Precambrian tectonic evolution of South China. The tectonic nature of the Neoproterozoic sedimentary basins is still controversial, due to poor understanding of the sedimentary sequences and the lack of geochronological data. Here, we present sedimentological, provenance and geochronological data from the Heshangzhen Group in the eastern Jiangnan orogen. Sedimentological analysis shows that the Luojiamen Formation was deposited in a submarine fan, and the overlying Hongchicun Formation was deposited in front of a fan delta. The youngest detrital zircons constrain the lower Luojiamen and Hongchicun formations with ages of 827.3 ± 8.4 Ma and 825 ± 12 Ma, respectively. The sandstones of the Luojiamen Formation are characterized by a large number of intermediate to felsic volcanic grains, suggesting a volcanic arc source. In contrast, quartz and sedimentary lithic grains increase in the Hongchicun Formation, showing a new input from a collisional orogenic source. Detrital zircon from six sandstone samples in the Luojiamen and Hongchicun formations yield similar age spectra of 930–820 Ma with a peak at ca. 845–860 Ma, with one main cluster at 930–820 Ma. Detrital zircons of 930–845 Ma show a positive value of εHf(t)(+2.4 to +11, mean +7.6), which is similar to the volcanic arc of the nearby Shuangxiwu Group. There are a minor group of zircons with U-Pb ages ranging from 820 Ma to 845 Ma from the middle part of the Luojiamen Formation and Hongchicun Formation, with εHf(t) values between-20 to +2.4, which are consistent with the characteristics of the Shuangqiaoshan Group. within light of the bidirectional paleocurrents in the Luojiamen Formation, it is speculated that the zircons of 820–845 Ma were recycled from the Shuangqiaoshan Group, which is derived from a continental arc to the northwest. Our data suggests that the Luojiamen Formation was formed in an inter-arc basin, while the Hongchicun Formation was formed in an accretionary wedge-top basin. When juxtaposed with the conglomeratic characteristics at the bottom of the Luojiamen Formation, it is believed that the unconformity represented by the ‘Shen Gong Movement' reflects the rapid erosion and accumulation process of island arc volcanic material. The disconformity between the Luojiamen and Hongchicun formations is the imprint of transition from inter-arc basin to accretionary wedge-top basin,which represents the collision between the Shuangxiwu arc and the Yangtze Plate.

Material Properties of Marine Hydrogenous Ferromanganese Crust and Its Performance in Desulfurization

Marine hydrogenous ferromanganese crust, an important metal resource in the future, has significant potential in various applications as a type of natural nano-structured material. By employing scanning electronic microscopy, nitrogen adsorption-desorption isotherm measurement, Xray fluorescence spectrometer and X-ray diffraction methods, the micro-structure, surface properties and chemical composition of several plate-like ferromanganese crusts sampled from the northwestern Pacific were investigated comprehensively. Although obvious differences were observed from different layers, the crust is a typical porous material with high specific surface area, unique pore structure and abundant transition elements. Furthermore, the performance of natural crust in desulfurization process was preliminarily tested in laboratory experiments. The suffur capacities of the crust are 13.1% and 18.1% at room temperature and 350 ℃, respectively. The crust can be used not only as a metal resource, but also as an environmental material.