The role of sulfur cycling in carbonate weathering: Isotope geochemistry of sulfur in the Wujiang River catchment, Southwest China

Water samples from the Wujiang River, a typical karst river system, were analyzed for major ion concentrations and δ34S values of dissolved sulfate in order to identify the sources of sulfate, quantify the sulfate export flux and understand the role of s…     

Anthropogenic influence on sedimentation during the last 100 years inferred from magnetic properties in the Changjiang Estuary, China

A 100-year sedimentary record in the Changjiang Estuary was examined to elucidate natural and anthropogenic influences on the morphodynamic evolution of the estuary. Two gravity cores were acquired and their magnetic properties, sediment size, chemical elements and ²¹⁰Pb geochronology were analyzed to infer the sedimentation. The results indicate that these sedimentological indexes, especially magnetic properties and trace elements, changed significantly during the last 100 years, with an abrupt change occurring at around 1960. This abrupt change is likely the result of a reduction in hydrodynamic energy caused by the narrowing of an upstream estuary reach due to reclamation. An increase of terrigenous input, due to soil erosion in the upper and middle reaches of the Changjiang, and increases in steel production may have also had a significant influence, as indicated by studies of other locations in the Changjiang drainage basin.     

Formation and geodynamic implication of the Early Yanshanian granites associated with W–Sn mineralization in the Nanling range,South China: an overview

ABSTRACT

The Nanling range (Nanling) is characterized by intense and widespread Mesozoic magmatism related large-scale W–Sn mineralization. A summary of geochemistry, geochronology, and petrogenesis for the W–Sn-bearing granites has been carried out in this study. A series of rock- and ore-forming ages in Nanling indicate that the W–Sn mineralization is closely related to the Early Yanshanian granitic magmatism both in temporal and spatial dimensions (165–150 Ma). Geochemical features show that both of the W- and Sn-bearing granites, which mainly belong to highly fractionated I-type granites with a few A-type granites, are characterized by high contents of SiO₂, Al₂O₃, Na₂O, and K₂O; enrichment in Rb, Th, U, Zr, Hf, and REE; depletion in Sr, Ba, P, and Ti; and high ratios of A/CNK. Furthermore, the different Sr–Nd–Hf isotopic compositions indicate that they are mainly originated from the partial melting of the Precambrian basement rocks of the Cathaysia Block at low oxygen fugacity, and the estimated temperatures for the tungsten-bearing and tin-bearing granites are ca. 700°C and ca. 800°C, respectively. The model of the mantle–crust interaction exhibits that different percentages of mantle-derived magma were likely involved in the generation of the tin-bearing granites and tungsten-bearing granites. In combination with previous studies, we propose that these granites in Nanling were emplaced in an extensional setting, as a response to the break-off and roll-back of the subducted Palaeo-Pacific Plate during 175–150 Ma.     

Geochronology and geochemistry of the Shilu Cu–Mo deposit in the Yunkai area,Guangdong Province,South China and its implication

Shilu is a large porphyry–skarn deposit in the Yunkai district in Guangdong Province, South China. The Shilu granitic intrusion in the mine area is a granodiorite which is genetically related to Cu mineralization. Plagioclase in the granodiorite has a zoned texture and is mainly andesine with minor amounts of labradorite, whereas the K-feldspars exhibit Carlsbad twins and some are also characterized by a zonal texture. K-feldspars from the granodiorite show high contents of Or (87–92 wt.%) with minor Ab (8–13 wt.%) and negligible An value of 0–0.3 wt.%. Biotite can be classified as magnesio-biotite, and is characterized by Mg-rich [Mg/(Mg + Fe) = 0.54–0.60] and Al^VI-low (average values = 0.11). Hornblende is chiefly magnesiohornblende and tschermakite. LA-ICP-MS zircon U–Pb age of the Shilu granodiorite is 107 ± 0.7 Ma, which is consistent with molybdenites Re–Os age of 104.1 ± 1.3 Ma. Geochemical data indicate that the Shilu granodiorite is silica-rich (SiO₂ = 63.43–65.03 wt.%) and alkali-rich (K₂O + Na₂O = 5.45–6.05 wt.%), as well as calcium-rich (CaO = 4.76–5.1 wt.%). Trace element geochemistry results show enrichments in large ion lithophile elements (e.g., Rb, K, and Ba) and depletions in some high field strength elements (e.g., Nb, P, Ta, and Ti). The total rare earth element (REE) content of the granodioritic rocks is low (∑ REE < 200 ppm), and is characterized by light REE enrichment [(La/Yb)_N > 9] and moderately negative Eu anomalies (Eu/Eu* = 0.83–0.90). These mineralogical, geochronological, and geochemical results suggest that the Shilu granodiorite has a mixed crust–mantle source with a geochemical affinity to I-type granitoids. Hornblende thermobarometry yielded magmatic crystallization temperatures of 686–785 °C and crystallization pressures between 1.0 and 2.34 kbar, which is converted to depths in a range of 3.31 to 7.71 km. Biotite thermobarometry yielded similar temperatures and lower pressures of 680–780 °C and 0.8–2 kbar (depth 2.64–6.6 km), respectively. The parent magma had a high oxygen fugacity. The Shilu granodiorite has a relatively low ε_Nd/t–t value and high (⁸⁷Sr/⁸⁶Sr)_i value, and Nd isotopes yield two-stage depleted mantle Nd model ages of 969–1590 Ma. Our new data, combined with previous studies, imply that the granodiorite and the associated Shilu Cu–Mo deposit was formed in an extensional environment, closely related to remelting of residual subducted slab fragments in the Jurassic.     

REE geochemistry of lamprophyres in Baimazhai nickel deposit, Yunnan Province, China： implication for the mantle source region

Lamprophyresarewidespreadinthe“Sanjiang”(tri river)alkali richintrusiverockbelt(Ailaoshan Jinshajiangalkali richintrusiverockbelt)insouth westernChinaandhaveaclosetemporalandspatialre lationwithAu,Cumineralization(HuYunzhonget al.,1995;HuangZhilongetal.,1999).Therefore,thereiscrucialsignificanceinsuchaspectsastectonic environment,mantlemetasomatism,crust mantlein teraction,magmaticevolutionandassociatedminerali zation.TheBaimazhainickeldepositislocatedinthe southernsegmentofthe“Sanjiang…     

Avalanche cycles in Austria: an analysis of the major events in the last 50 years

During the last 50 years, an average of 30 persons per year was killed by avalanches in Austria. About one-third of all avalanche fatalities occurred as a result of so-called ‘catastrophic avalanches’. ‘Catastrophic avalanches’ are spontaneously released avalanches that affect villages and cause damage to property (buildings, roads and other infrastructure). The biggest avalanche events in Austria were in 1950/1951 (135 fatalities), in 1953/1954 (143 fatalities) and in February 1999, when 38 persons were killed in Galtür and Valzur. This article deals with an analysis of nine major avalanche cycles in the last 55 years. An avalanche cycle in this article is defined as 50 recorded avalanches of at least size 3 in two days and/or 5 persons killed in villages within two days. The basis of this study are the well-documented records from Fliri (1998), who analysed natural disasters in the western part of Austria and the Trentino, including floods, mudflows, earthquakes and avalanches. The meteorological data were taken from two relevant observation sites in the northern part of the Austrian Alps, from two sites in an intermediate and continental region, respectively and from one site in the southern part of the Austrian Alps. Atmospheric patterns were analysed by using weather charts for the relevant periods. Both the meteorological data and the weather charts were provided by the Central Institute for Meteorology and Geodynamics (ZAMG). It was found that there was a major cycle every 6 years (on average). Two-thirds of all investigated cycles were characterised by a continuous increase of snow depth over a period of at least three days. In only three periods (1975, 1986, 1988), daily extreme values could be observed. More than 40% of all the cycles occurred in January. In two-thirds, a north-westerly oriented frontal zone was responsible for the formation of a major cycle. The remaining cycles were released by low-pressure areas over Central Europe and the Mediterranean Sea, respectively.     

Study on rainfall variations in the middle part of Inner Mongolia,China during the past 43 years

The study area, the middle part of Inner Mongolia including Hohhot city, Baotou city, Wulanchabu city, Ordos city, Bayannaoer city and Wuhai city, is one of typical eco-geographical transition zones in China. Using monthly precipitation data (1961–2003) from 45 meteorological stations in the study area, this paper analyzes characteristics and tendencies of annual and seasonal rainfall variations, and reveals multi-time scales structures of these time series through wavelet analyses; also, the periods of annual and seasonal precipitation series are identified, and the periodical oscillations and points of abrupt change at the principal period scale are discovered. The results show that annual precipitation varies in a large range, and has an ascending tendency at an increasing rate of 1.482 mm/10a; the multi-time scales periodical oscillations are clear; differences in tendencies, ranges and decadal precipitation anomalies exist within each decade during 1961–2000. The seasonal allocation of overall annual precipitation is extremely uneven; in terms of tendencies of seasonal precipitation, winter and spring have upward trends while summer and autumn have downward tendencies; distinctions in tendencies, ranges and decadal precipitation anomalies among each seasons are in existence within each decade during 1961–2000. The periodical oscillations of each seasonal precipitation time series are also evident. The research results not only provide convincing evidence for global climate change research, but also facilitate the understanding of specific natural process and pattern to make steps to rehabilitate and reconstruct vegetation, and contribute to fulfill the sustainability of water management.     

Redox State of the Granitic Rocks and Formation of the Scheelite Skarn in the Xintianling Deposit, Nanling Range, South China

Please?refer?to?the?attachment(s)?for?more?details.     

Carbonate weathering rates in the Jura Mountains, France-The influence of vegetation

In order to better understand what controls carbonate weathering rates, we report results from the Jura Mountains （East France）, an area exclusively composed of carbonate rocks. This region presents an altitude gradient increasing from 250 m to 1300 m. Over the basin, this gradient generates climatic contrasts of 5℃ and a runoff three times higher in altitude. This place offers a good opportunity for understanding the controlling factors of carbonate weathering. Contrary to thermodynamic calculations that predict the highest concentrations at low temperature, we observe that carbonate dissolution is two times higher at low elevation than in the mountains. This observation can only be explained by a variation in soil pCO2. In order to better constrain the observed variation in cation contents （principally Ca and Mg） of rivers, we used the ASPECTS ecological model （Rasse et al., 2001）. Based on both hourly climatic data, vegetation type and soil type, ASPECTS may reconstruct pCO2 in soil.     

Environment change of Sihu Lake in the past 450 years, southern China

In recent years, climate and environment changes since the Little Ice Age have become a focus in modern research. The paper selected the sediment (77 cm) of Sihu Lake, which was located in Guilin, southern China, as the research object and analyzed the karst wetland environmental changes within nearly 450 years. According to the vertical profile of indicators and geochemical elements in sediment core, the regional environmental evolution was divided into four stages. The former two stages were mainly influenced by Little Ice Age (1562–1895). The third stage climate has changed slowly. The fourth stage was mainly affected by human activities and global warming. The factor analysis of geochemical elements indicated that karst wetland regional environmental change was affected by four major factors. In the 53–77 cm stage (1562–1703), F1 (erosion factor), F2 (watershed runoff and diagenesis factor) and F3 (regional background factor) were reduced, indicating that it was in cold and dry stage of Little Ice Age. In the 20–53 cm stage (1703–1895), F1 and F2 increased, indicating that it was in cold and wet stage of Little Ice Age. In the 4–20 cm stage (1895–1987), F1, F2 and F4 (human activity factor) increased slowly, indicating that the climate was affected by global warming and more precipitation. In the 0–4 cm stage (1987–2007), F1 and F2 reduced and F4 increased, indicating the reduced precipitation, rising temperature and more impact of human activities. In addition, it was proposed that the Little Ice Age in Guilin District in southern China started in the 1560s and lasted until the 1895s or so.     

Carbonate weathering rates in the Jura Mountains, France—The influence of vegetation

In order to better understand what controls carbonate weathering rates, we report results from the Jura Mountains (East France), an area exclusively composed of carbonate rocks. This region presents an altitude gradient increasing from 250 m to 1300 m. Ov…     

Mineralogy of the Dahu Au-Mo Deposit, Xiaoqinling Region, Central China:Evidence for a Magmatic-hydrothermal Origin

Please refer to the attachment(s) for more details     

Multi-Stage Mineralization of the Early Yanshanian Granites from the Central Nanling Region, South China: Implications from REE Geochemistry

Please refer to the attachment(s) for more details.     

Geochronology of granite and associated Sn mineralization in the Shuangyuanchong Sn deposit and its implication for Sn-W prospecting potential in the Shizhuyuan-Hehuaping area,the Nanling region,South ChinaSCIEI北大核心CSCD

南岭成矿带是全球最重要的钨锡成矿带之一,区内钨锡成矿条件优渥,是开展钨锡找矿勘查的重要目标区。然而如何开展钨锡找矿工作,尤其是在已有矿床周缘圈定成矿远景区,是钨锡成矿作用研究以及找矿勘查工作关注的重要科学问题。双园冲矿床位于南岭成矿带中西段,处于荷花坪与柿竹园两个大型锡钨多金属矿田中间,并与两个矿田处于同一构造体系,但目前对该矿床的研究程度较低,由此也制约了其矿床成因研究及该区的找矿部署。本次研究获得双园冲云英岩化花岗岩的锆石和独居石原位LA-ICP-MS U-Pb年龄分别为161.2±2.5Ma和157.1±1.8Ma,与云英岩型矿石中锡石原位LA-ICP-MS U-Pb年龄(158.9±2.9Ma)一致,二者均形成于晚侏罗世,表明其具有密切的成因关系,这一年龄也与南岭成矿带钨锡成矿大爆发时代(150-160Ma)一致。综合对比双园冲锡矿及与其空间相邻的柿竹园和荷花坪锡多金属矿田特征显示,三者成岩成矿时代一致,岩体侵位和矿体分布均受NE向断裂控制,矿体也均赋存于中-上泥盆统碳酸盐岩地层中,并且成矿花岗岩具有相似的岩石学特征和岩浆源区。综合以上信息,本文提出三个矿床可能形成于同一次岩浆热液活动,成矿岩体可能来自地壳深部同一个大岩浆房,柿竹园和荷花坪之间的区域具有发育晚侏罗世花岗岩体及相关钨锡矿的较大潜力。根据双园冲锡矿及其周缘大型锡钨矿床浅部脉状Pb-Zn-Fe-Mn矿化和深部矽卡岩-云英岩型Sn-W矿化的特征,提出研究区乃至整个南岭地区浅部脉状Pb-Zn-Fe-Mn矿化是深部Sn-W找矿勘查的有利部位。     

Evolution Sequences of Granitic Magma and Uranium Mineralization in the Nanling Region,China

Granites are widespread in the Nanling region of Chian ,which were emplaced in different tectonic environments as a result of frequent and intense magmatic activity.Two evolution sequences have been distinguished:the extrusive-hypabyssal and plut onic-hypabyssal sequences.Different mecha-nisms governing the evolution,especially the differentiation, of the two sequences may account for the different mechanisms of uranium mineralization leading to the formation of various types ura-nium deposits in the Nanling region.     

In-situ LA–ICP-MS trace elemental analyses of magnetite: The Mesozoic Tengtie skarn Fe deposit in the Nanling Range,South China

The Nanling Range in South China hosts numerous world-class W–Sn deposits and some Fe deposits. The Mesozoic Tengtie Fe skarn deposit in the southern Nanling Range is contemporaneous with the regional Sn mineralization. The deposit is composed of numerous ore bodies along the contacts between the late Paleozoic or Mesozoic carbonate rocks and the Yanshanian Lianyang granitic complex. Interaction of the magma with hosting dolomitic limestone and limestone formed calcic (Ca-rich) and magnesian (Mg-rich) skarns, respectively. The Tengtie deposit has a paragenetic sequence of the prograde stage of anhydrous skarn minerals, followed by the retrograde stage of hydrous skarn minerals, and the final sulfide stage. Magnetite in the prograde and retrograde skarn stages is associated with diopside, garnet, chlorite, epidote, and phlogopite, whereas magnetite of the final stage is associated with chalcopyrite and pyrite. Massive magnetite ores crosscut by quartz and calcite veins are present mainly in the retrograde skarn stage. Laser ablation ICP-MS was used to determine trace elements of magnetite from different stages. Some magnetite grains have unusually high Ca, Na, K, and Si, possibly due to the presence of silicate mineral inclusions. Magnetite of the prograde stage has the highest Co contents, but that of the sulfide stage is extremely poor in Co which partitions in sulfides. Magnetite of magnesian skarns contains more Mg, Mn, and Al than that of calcic skarns, attributed to the interaction of the magma with compositionally different host rocks. Magnetite from calcic and magnesian skarns contains 6–185 ppm Sn and 61–1246 ppm Sn, respectively. The high Sn contents are not due to the presence of cassiterite inclusions which are not identified in magnetite. Instead, we believe that Sn resides in the magnetite structure. Regionally, intensive Mesozoic Sn mineralization in South China indicates that concurrent magmatic–hydrothermal fluids may be rich in Sn and contribute to the formation of high-Sn magnetite. Our study demonstrates that trace elements of magnetite can be a sensitive indicator for the skarn stages and wall-rock compositions, and as such, trace elemental chemistry of magnetite can be a potentially powerful fingerprint for sediment provenance and regional mineralization.     

Geochronology and geochemistry of Grenville-aged (1063 ± 16 Ma) metabasalts in the Shennongjia district,Yangtze block: implications for tectonic evolution of the South China Craton

To better understand the evolution of the South China Craton (SCC), we have determined the geochronological and geochemical compositions of newly recognized Grenville-aged metabasalts in the Shennongjia region of the northern Yangtze block. LA-ICP-MS U-Pb dating of zircons indicates that the metabasalts formed at 1063 ± 16 Ma. The rocks are calc-alkaline, are characterized by SiO₂ contents (50.50 to 55.62 wt.%), and have moderate-to-high MgO contents (7.25–9.60 wt.%). They display light rare earth element enrichment ((La/Yb)_N = 7.0–9.8) with slightly negative Eu anomalies (Eu/Eu* = 0.82–0.90) and have pronounced depletion in high-field strength elements as well as positive Pb anomalies in the primitive mantle-normalized trace element pattern. They possess high initial Sr isotopic ratios of 0.7092–0.7107, large negative ε_Nd(t) values of ?12.1 to ?11.0, and a relatively narrow range of initial Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb = 16.503–17.019, ²⁰⁷Pb/²⁰⁴Pb = 15.259–15.452, and ²⁰⁸Pb/²⁰⁴Pb = 36.169–36.994). These isotopic characteristics are typical of basalts derived from an EM2 source region and suggest a subcontinental lithospheric mantle source that was metasomatized by subducted components (fluids and melts). Integrating our new data with documented igneous and metamorphic events during late Mesoproterozoic to early Neoproterozoic time in the region and western segments of the Yangtze block, we suggest that the Shennongjia area might be a microcontinent that was independent of the continental nucleus of the Yangtze block and was accreted to the Yangtze block at the end of Mesoproterozoic time. This study thus argues against the traditional view that the SCC was formed simply by Yangtze–Cathaysia collision and supports a hypothesis in which the Yangtze block was a collage of microcontinents accreted during the Grenvillian period accompanying the assembly of the Rodinia supercontinent.     

Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China

The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores.     

Climate and environmental changes over the past 150 years inferred from the sediments of Chaiwopu Lake, central Tianshan Mountains, northwest China

We used a 55-cm sediment core from shallow Chaiwopu Lake in the central Tianshan Mountains of Xinjiang, northwest China, to investigate climate and environmental changes in this arid region over the past ~150 years. The core was dated using ¹³⁷Cs. We compared temporal changes in several sediment variables with recent meteorological and tree-ring records. Organic matter had a positive correlation with the Palmer Drought Severity Index in the central Tianshan Mountains, and the δ¹³C of organic matter had a positive correlation with regional temperature. We applied constrained incremental sum-of-squares cluster analysis to element concentrations in the core and identified three distinct zones: (1) 55–46 cm, ~1860–1910, (2) 46–26 cm, ~1910–1952, and (3) 26–0 cm, 1952–present. Between 1880 and 1910 AD, following the Little Ice Age (LIA), the sediment environment was relatively stable, climate was cold and dry, and the lake water displayed high salinity, in contrast to conditions during the LIA. During the LIA, westerlies carried more water vapor into Central Asia when the North Atlantic Oscillation was in a negative phase, and encountered the enhanced Siberia High, which probably led to increased precipitation. In the period 1910–1950 AD, the lake was shallow and the regional climate was unstable, with high temperatures and humidity. In the last ~15–20 years, human activities caused an increase in sediment magnetic susceptibility, and heavy metal and total phosphorus concentrations in the sediment were substantially enriched. Mean annual temperature displays a warming trend over the past 50 years, and the lowest temperature was observed in the 1950s. There has been an increase in annual total precipitation since the 1990s. The combined influences of climate and human activity on the lake environment during this period were faithfully recorded in sediments of Chaiwopu Lake. This study provides a scientific basis for environmental management and protection.     

Isotopic Geochronological Evidence for the Caledonian Xiongdian Eclogite in the Northwestern Dabie Mountains,China

A typical HP/MT (high pressure/medium temperature) eclogite from Xiongdian, northwestern Dabie Mountains, has been geochronologically studied using the single-zircon U-Pb, 40Ar-39Ar and Sm-Nd methods. Prismatic zircons occurring as inclusions within garnets define a minimum crystallization age of 399.5±1.6 Ma. 40Ar-39Ar dating on amphibole gives a plateau age.of 399.2 ± 4 Ma, which is interpreted as a retrogression age of amphibolite facies. This integrated study enables us to conclude that the age of high-pressure metamorphism is older than 399.5 ± 1.6 Ma, suggesting Caledonian collision between the North China and Yangtze plates. Round zircon within the aggregate of quartz and muscovite gives a concordant age of 301± 2 Ma, reflecting a later retrogression event. An age profile of post-eclogite metamorphism is documented, including amphibolite facies metamorphism at 399.2 Ma shortly after eclogitization and later retrogressive metamorphism at 301 Ma. Sm-Nd mineral isochron of garnet+omphacite gives