Influences of Low-Temperature Hydrothermal Fluids on the Re-distributions and Occurrences of Associated Elements in Coal——A Case Study from the Late Permian Coals in the Zhijin Coalfield, Guizhou Province. Southern China

The occurrences of associated elements and their genetic factors in the No. 30 coal seam in the Zhijin Coalfield were studied using instrumental neutron activation analysis, inductively coupled plasma-atomic emission spectroscopy, and a scanning electron microscope equipped with an energy-dispersive X-ray analyzer. And, a microscope photometer system (Leitz MPV-Ⅲ) was used to observe the characteristics of coal petrology. According to the influence degree by the siliceous low-temperature hydrothermal fluids, the organic matter is divided into four types: A, B, C, and D of the hydrothermally-altered organic matter (HAOM). The study shows that the high content of Fe (2.31%) is not from pyrite, but mostly from the siliceous low-temperature hydrothermal fluids. The occurrences of the associated elements in the four organic matter types are different. The contents of Fe, Si, and Al are decreasing, but S and Cu are increasing in the order of the HAOM-A, HAOM-B, HAOM-C, and HAOM-D. The losing rate of sulfur in organic matter is 0.35% and the content of Fe taken from the low-temperature hydrothermal fluids into the organic matter is 0.794% during the siliceous low-temperature hydrothermal fluids invading the coal seam. The above facts indicate that the low-temperature hydrothermal fluids play a crucial role in the re-distributions and occurrences of associated elements in coal.

Activity of Silica-Rich Hydrothermal Fluid and Its Impact on Deep Dolomite Reservoirs in the Sichuan Basin, Southern China

Well-developed dissolution pores occur in the dolomites of the Sinian Dengying Formation, which is an important oil and gas reservoir layer in the Sichuan Basin and adjacent areas in southern China. The pores are often filled with quartz, and some dolomites have been metasomatically altered to siliceous chert. Few studies have documented the characteristics, source or origin of silica-rich fluids and their effects on the dolomite reservoir. The peak homogenisation temperatures （Th） of fluid inclusions in pore-filling quartz are between 150~C and 190~C, with an average of 173.7~C. Gases in the inclusions are mainly composed of CO2, CH4 and N2. Compared with host dolomite, pore-filling quartz and metasomatic chert contain higher amounts of Cr, Co, Mo, W and Fe, with average concentrations of 461.58, 3.99, 5.05, 31.43 and 6666.83 ppm in quartz and 308.98, 0.99, 1.04, 13.81 and 4703.50 ppm in chert, respectively. Strontium levels are lower than that in the host dolomite, with average concentrations in quartz and chert of 4.81 and 11.06 ppm, respectively. Rare earth element compositions in quartz and chert display positive Eu anomalies with a maximum δEu of 5.72. The δDsMow values of hydrogen isotopes in water from quartz inclusions vary from -85.1‰ to -53.1‰ with an average of-64.3‰, whereas the δ18OsMow values range from 7.2‰ to 8.5‰ with an average of 8.2‰. The average 87Sr/86Sr ratios in quartz and chert are 0.711586 and 0.709917, respectively, which are higher than that in the host dolomite. The fluid inclusions, elemental and isotopic compositions demonstrate that the formation of quartz and chert was related to silica-rich hydrothermal fluid and that the fluid was the deep circulation of meteoric water along basement faults. Interactions with silica-rich hydrothermal fluids resulted in densification of dolomite reservoirs in the Dengying Formation through quartz precipitation and siliceous metasomatism. However, it increased the resistance of the host dolomite to compaction, improving the ability to maintain reservoir spaces during deep burial. Evidence for silica-rich hydrothermal activity is common in the Yangtze Platform and Tarim Basin and its influence on deep dolomite reservoirs should be thoroughly considered.

Tectonic Dynamic Metallization of Silver-GoldHydrothermal Fluids in Proterozoic GneissTerrene Shear Zones, Suichang, Zhejiang, China

The Suichang mine is the largest silicified vein-type silver-gold mineralization system in Southeast China, whose ore bodies are controlled by shear zones developing in Lower Proterozoic gneiss terrene with initial migmatization, which is covered by Upper Jurassic and Lower Cretaceous volcanic rock system and cut by acidic igneous veins of Jurassic and Cretaceous. The conclusions are as follows: (1) The ore-forming fluid is defined as superhigh tectonic-metamorphic fluid on the base of : 1 (D)-(18O) values 2 fluid inclusions;3 trace elements of pyrite from ores. (2) The shear zone silicified orebod-ies occurred in proterozoic, Jurassic and Cretaceous, which have been transforms in part by ore-bearing comb quartz vein of volcanism.

A Method for Detection of Trace Concentrations of Underivatized Amino Acid in Hydrothermal Fluids by Ion-Pairing Reversed-Phase UPLC-ESI-QTOF-MS

Investigation of amino acids in hydrothermal systems is of prime importance for the understanding of geochemistry and microbiology of hydrothermal vents and plumes, for carbon and metals global cycles, for metabolism of some hydrothermal microorganisms and for the origin of life issue. Extensive theoretical and experimental work on amino acids behaviour in hydrothermal fluids has been done, conversely only few data exist on natural samples. Because each hydrothermal vent is unique, the more data we collect the better we will be able to address each of these questions. Usually amino acids in hydrothermal fluids have been measured by HPLC-FLD. The chromatographic separation was at least 26 min and up to 135 min and the required derivatization step may be time consuming, may use harmful chemicals and may be source of contamination. Alternatively, we describe here a method combining quickness (4.5 min), high resolution (10,000), very low LOD (sub-ppb) and without derivatization. Characterisation and separation of 10 relevant proteinogenic underivatized amino acids was achieved by ion-pairing reversed-phase Ultra-high Performance Liquid Chromatography-Electrospray Ionisation-Quadrupole Time of Flight-Mass Spectrometry (UPLC-ESI-QTOF-MS). Excellent linearity in the response was obtained for all amino acids with correlation coefficients > 0.9921. This method was successfully applied to natural hydrothermal fluid samples from ultramafic-hosted vents of the Mid-Atlantic Ridge region. Results are consistent with the only 2 other studies published on ultramafic-hosted vents and complete the few available data.

A molecular simulation study of Cs-Cl and Cs-F ion pairs in hydrothermal fluids

Magmatic-hydrothermal processes play an important role in the transport, enrichment, and mineralization of cesium. In this study, classical molecular dynamics simulations were performed to investigate the properties of Cs-Cl and Cs-F ion pairs in hydrothermal fluids. The association constants(log_(10)K_(A)(m)) under a wide range of temperature(i.e. 298–1273 K) and fluid density(i.e. 0.1–1.0 g/cm^(3)) were derived from the potential of mean force(PMF) curves. The results indicate that CsCl and Cs-F ion pairs have similar stabilities. This is different from other alkali metal cations(e.g., Li^(+), Na^(+), and K^(+)), which prefer binding with F over Cl. The stabilities of Cs-Cl and Cs-F ion pairs increase with increasing temperature(except for the fluid density ≤ 0.1 g/cm^(3)) or decreasing fluid density, which is similar to other alkali halide ion pairs. Comparisons among the stabilities of CsCl/F and other alkali halide ion pairs indicate that the Li–F ion pair has the highest stability in hydrothermal fluids.

Magmatic hydrothermal fluid genesis of zeolite in the Paleogene Kongdian Formation of Zaoyuan oilfield,Bohai Bay Basin,China

Electronic probe,fluid inclusion homogenization temperature,Raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry were utilized to identify the hydrothermal fluid-rock interactions in the second member of the Paleogene Kongdian Formation of Zaoyuan oilfield in Bohai Bay Basin(Kong 2 Member for short)of Well Z56 to find out the relationship between zeolite and hydrothermal fluid.The experimental results show that:(1)Pyrobitumen coexists with hydrothermal fluid characteristic minerals such as chlorite,barite,chalcopyrite,pyrite,natrolite and analcime in mudstone fractures.(2)The temperatures calculated from laser Raman spectrum of pyrobitumen,from the chlorite geothermometer and from measured homogenization temperature of natrolite inclusions are 324-354℃,124-166℃ and 89-196℃,respectively;although vary widely,all the temperatures are obviously higher than the normal geothermal temperature.(3)The positive Eu anomaly of chlorite and barite,and the similar distribution pattern in rare earth elements between natrolite and basalt indicate they are from magmatic hydrothermal fluid.Moreover,drilling data shows that the Kong 2 Member in Well Z56 has several sets of basalt interlayers,suggesting there was geologic base of magmatic hydrothermal fluid activity.The magmatic hydrothermal fluid-rock interaction may be one of the reasons for the abnormal enrichment of zeolite in Kong 2 Member of the Cangdong Sag.

Episodic hydrothermal alteration on Middle Permian carbonate reservoirs and its geological significance in southwestern Sichuan Basin,SW China

To analyze the episodic alteration of Middle Permian carbonate reservoirs by complex hydrothermal fluid in southwestern Sichuan Basin,petrology,geochemistry,fluid inclusion and U-Pb dating researches are conducted.The fractures and vugs of Middle Permian Qixia–Maokou formations are filled with multi-stage medium-coarse saddle dolomites and associated hydrothermal minerals,which indicates that the early limestone/dolomite episodic alteration was caused by the large-scale,high-temperature,deep magnesium-rich brine along flowing channels such as basement faults or associated fractures under the tectonic compression and napping during the Indosinian.The time of magnesium-rich hydrothermal activity was from the Middle Triassic to the Late Triassic.The siliceous and calcite fillings were triggered by hydrothermal alteration in the Middle and Late Yanshanian Movement and Himalayan Movement.Hydrothermal dolomitization is controlled by fault,hydrothermal property,flowing channel and surrounding rock lithology,which occur as equilibrium effect of porosity and permeability.The thick massive grainstone/dolomites were mainly altered by modification such as hydrothermal dolomitization/recrystallization,brecciation and fracture-vugs filling.Early thin-medium packstones were mainly altered by dissolution and infilling of fracturing,bedding dolomitization,dissolution and associated mineral fillings.The dissolved vugs and fractures are the main reservoir space under hydrothermal conditions,and the connection of dissolved vugs and network fractures is favorable for forming high-quality dolomite reservoir.Hydrothermal dolomite reservoirs are developed within a range of 1 km near faults,with a thickness of 30–60 m.Hydrothermal dolomite reservoirs with local connected pore/vugs and fractures have exploration potential.

Sources and Thermo-Chemical Sulfate Reduction for Reduced Sulfur in the Hydrothermal Fluids, Southeastern SYG Pb-Zn Metallogenic Province, SW China

Located on the western Yangtze Block, the Sichuan （四川）-Yunnan （云南）-Guizhou （贵州） （SYG） Pb-Zn metallogenic province has been a major source of base metals for China. In the south- eastern SYG province, structures are well developed and strictly control about 100 Pb-Zn deposits. Al- most all the deposits are hosted in Devonian to Permian carbonate rocks. Lead-zinc ores occur either as veinlets or disseminations in dolomitic rocks with massive and disseminated textures. Ore minerals are composed of pyrite, sphalerite and galena, and gangue minerals are calcite and dolomite. Sulfide min- erals from four typical Pb-Zn deposits are analyzed for sulfur isotope compositions to trace the origin and evolution of hydrothermal fluids. The results show that 034S values of sulfide minerals range from ＋3.50%0 to ＋20.26%0, with a broad peak in ＋10%0 to ＋16%0, unlike mantle-derived sulfur （0±3%0）. How- ever, the mean δ34Ssulflde and δ34S∑s-fluids values are similar to that of sulfate-bearing evaporites in the host rocks （gypsum： -＋15%0 and barite： ＋22%0 to ＋28%0） and Cambrian to Permian seawater sulfate （＋15%0 to ＋35%0）. This suggests that reduced sulfur in hydrothermal fluids was likely derived from evaporates in the host rocks by thermo-chemical sulfate reduction （TSR）. Calculated δ34S∑s-fluids values of the Shanshulin （杉树林）, Qingshan （青山）, Shaojiwan （筲箕湾） and Tianqiao （天桥） Pb-Zn deposits are ＋21.59‰, ＋18.33‰, ＋11.4‰ and ＋10.62‰, respectively, indicating sulfur-bearing hydrothermal fluids may be evolved from the Shanshulin to Qingshan and then the Shaojiwan to Tianqiao deposition sites along the Yadu （垭都）-Ziyun （紫云） lithospheric fracture in the southeastern SYG province.

Constrains of eruption environment and hydrothermal fluid on the Permian pyroclastic reservoirs in the Sichuan Basin,SW China

A breakthrough has been recently made in the hydrocarbon exploration of the Permian pyroclastic rocks in the Jianyang Area,western Sichuan Basin,China.With an aim to decipher the impacts of the eruption environment,the temperature of hydrothermal fluids,and the paleo-salinity on the formation of authigenic mineral assemblage and pores,this study implements comprehensive petrographic and geochemical studies through the integrated core and thin section analyses.The data presented demonstrate that the Permian volcanic intervals are intensively affected by an event of Emei taphrogeny.During basaltic magma upward migration,fractional crystallization of anorthose results in slightlyalkaline magma.The specific pyroclastic rocks are formed by the eruption of slightly-alkaline magma in the sea or a salt lake and subsequent hydrothermal alteration.During deposition and diagenesis,the authigenic mineral association is constrained jointly by the sodium-rich and high salinity water environment,and mid-high temperature,high-salinity hydrothermal fluid.Specifically,the sodium-rich hydrothermal fluid,which may sustain till the late diagenesis stage,caused pervasive albitization of pyroclastic rocks,then leading to mineral transformation and formation of a series of mineral associations.Therefore,zeolitization of volcanic glass and vesicle-infillings of zeolite is an essential condition for later mineral transformation and dissolution.Albitization of analcite,recrystallization induced by deep hydrothermal fluids,and both meteoric and deep burial dissolution expanding the micro-pore space ultimately formed porous pyroclastic reservoirs.

Geochronology,Geochemistry,Fluid Inclusion and C,O Isotope Compositions of Calcite Veins in the Paleogene of the Jiangling Basin,South China:Implications for Fluid Evolution and Brine Potash Mineralization

Deep-seated potassium-rich brines were identified in the Jiangling Basin,South China.Although magmatichydrothermal sources have been proposed,the relationship between brine-type potash mineralization and volcanism remains unclear.In this study,U-Pb geochronology,geochemistry,fluid inclusion and C-O isotopic compositions of hydrothermal vein minerals in the Jiangling Basin are examined.Laser ablation U-Pb dating of calcite veins indicates that the ages are slightly younger than the formation age of the Balingshan basalt.Fluid inclusions in hydrothermal minerals show medium–low homogenization temperatures(160–220℃)and low salinities(0.14 to 4.9 wt%NaCl eqv.)and densities(0.882–0.944 g/cm^(3)).The liquid compositions of fluid inclusions in calcite veins from sedimentary strata have higher contents of potassium,compared with those from basalt.The coupled negativeδ^(13)CPDB(-10.3‰to-8.0‰)and positiveδ^(18)OSMOW(17.4‰to 20.7‰)values imply that calcite precipitation resulted from CO_(2)degassing of the basaltic magmatic fluids,as indicated by the gas composition of these inclusions in hydrothermal minerals.Rare earth element patterns indicate that water-rock interaction between hydrothermal fluids and sedimentary wall rocks contributed to the calcite precipitation in sedimentary strata.It is proposed that high-temperature water-rock interaction between magmatic fluids and sedimentary strata resulted in the potassium enrichment in fluids,interpreted as one of the sources of potassium-rich brines in the Jiangling Basin.

Geochemistry of hydrothermal gold deposits:A review

Mineral assemblages formed during hydrothermal alteration reflect the geochemical composition of ore-forming fluids. Gold is mainly transported in solution as Au-CI and Au-S complexes. The change of physicochemical conditions such as temperature, pressure, oxygen fugacity, and sulfur fugacity are effective mechanisms for gold precipitation. Gold tends to be concentrated in the vapor phase of fluids at high temperatures and pressures. Au-As and Au-Sb associations are common in gold deposit. Native antimony and/or arsenic -- native gold assemblages may precipitate from hydrothermal fluids with low sulfur fugacity. Hydrothermal fluids forming epithermal gold deposits are Au-saturated in most cases, whereas fluids of Carlin-type are Au-undersaturated. Quasi-steady As-bearing pyrite extracts solid solution Au from hydrothermal fluids through absorption. The capability of As-bearing pyrite to absorb An from under-saturated fluid is the key to the formation of large-scale Carlin-type deposits. With increasing new data, studies on the geochemistry of gold deposits can be used to trace the origin of ore-forming fluids, the source of gold, and the transporting form of Au and other ore-forming elements, such as Si, S, F, Cl, As and Ag.

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.

Major Factors Controlling Calcite Dissolution in Hydrothermal Karst Systems

To find out major factors controlling the dissolution of calcite in hydrothermal systems, equations describing the relationship between Ca2+ concentration at equilibrium and partial pressure p (CO2) are deduced for different thermodynamic conditions. The calculation results show that the intensity of calcite dissolution increases with the increase of p(CO2), temperatures around 363 K are the most favorable ambient temperature for hydrothermal karst development, and that the volume ratio of CO2 gas over water and the mass fraction of foreign ions also have some efrects on calcite dissolution.

Metallogenetic Mechanism and Timing of Late Superimposing Fluid Mineralization in the Dongguashan Diplogenetic Stratified Copper Deposit,Anhui Province

An important diplogenetic mineralization event superimposed on pre-existing exhalation sediments in the Tongling area, Anhui province, was triggered by widespread granitic magmatism along the northeastern margin of the Yangtze Block during 140–135 Ma under extensional tectonic circumstances following the collision between the North China and Yangtze blocks. The main orebodies of the Dongguashan copper deposit, a typical diplogenetic stratified deposit among many polymetallic ore deposits in China, are hosted by strata between Upper Devonian sandstone and Carboniferous limestone, and its mineralization was genetically related to the Qingshanjiao intrusive. The Rb-Sr isotopic isochron of the Qingshanjiao intrusive yields an age of about 136.5±1.4 Ma. The ore-forming fluid reflected by the inclusion fluid in quartz veins is characterized by high temperature and high salinity, and its age was also determined by Rb -Sr isotope dating as 134±11 Ma. Oxygen and hydrogen isotope composition data suggest that the ore-forming fluid was derived mainly from magmatism. By integrating these isotopic dating data, characteristics of fluid inclusions and the geology of the deposit, the mineralization of the Dongguashan copper deposit is divided into two stages. First, a stratiform sedimentary deposit or protore layer formed in the Late Devonian to the Early Carboniferous, while in the second stage the pre-existing protore was superimposed by hydrothermal fluid that was derived from the Yanshanian magmatic activities occurring around 135 Ma ago. This two-stage mineralization formed the Dongguashan statiform copper deposit. Associated “porphyry” mineralization found in the bottom of and in surrounding intrusive rocks of the orebodies might have occurred in the same period as a second-stage mineralization of this deposit.

Major and trace element composition of surface sediments from the Southwest Indian Ridge:evidence for the incorporation of a hydrothermal component

Hydrothermal materials in deep-sea sediments provide a robust tracer to the localized hydrothermal activity at mid-ocean ridges. Major, trace and rare earth element（REE） data for surface sediments collected from the ultraslow spreading Southwest Indian Ridge are presented to examine the existence of hydrothermal component.Biogenic carbonate oozes dominate all the sediment samples, with CaO content varying from 85.5% to 89.9% on a volatile-free basis. The leaching residue of bulk sediments by ~5% HCl is compositionally comparable to the Upper Continental Crust（UCC） in SiO_2, Al_2O_3, CaO, MgO, alkali elements（Rb, Cs） and high field strength elements（Nb, Ta, Zr, Hf, Ti）. These detritus-hosted elements are inferred to be prominently derived from the Australian continent by means of eolian dust, while the contribution of local volcaniclastics is insignificant. In addition, the residual fraction shows a clear enrichment in Fe, Mn, and Ba compared with the UCC. Combining the positive Eu anomaly of residual fraction which is opposed to the UCC but the characteristic of hydrothermal fluids and associated precipitates occurred at mid-ocean ridges, the incorporation of localized hydrothermal component can be constrained. REE mixing calculations indicate that more than half REE within the residual fraction（~55%–60%） are derived from a hydrothermal component, which is inferred to be resulted from a diffuse fluid mineralization. The low-temperature diffuse flow may be widely distributed along the slow-ultraslow spreading ridges where crustal faults and fissures abound, and probably have a great mineralization potential.

Diagenetic evolution and effects on reservoir development of the Dengying and Longwangmiao formations,Central Sichuan Basin,Southwestern China

The deeply buried Lower Cambrian Longwangmiao Formation and Upper Ediacaran Dengying Formation from the Sichuan Basin,China,have a total natural gas reserve up to 3×10^(12)m^(3).The complex diagenetic evolution and their impacts on the present-day reservoir quality have not been systematically elucidated,hampering the current exploration.Crucially,the integration and comparation diagenetic study on these two formations,which may be able to shed new lights on reservoir formation mechanism,are yet to be systemically evaluated.By compiling geochemistry data,including carbonate U-Pb ages and petrophysics data,coupled with new petrology,trace elements,and strontium isotope data,of various types of diagenetic carbonates,this study aims to decipher the potential links between diagenesis and reservoir development of both formations.Intriguingly,similar diagenetic sequence,which contains five distinctive dolomite phases,is established in both formations.The matrix dolomite(D1)and early dolomite cement(D2)were likely formed by reflux dolomitization,as inferred by their nearly syn-depositional U-Pb ages and elevatedδ^(18)O caused by seawater evaporation.The subsequent moderate burial dolomite cement(D3)was most plausibly the product of burial compaction as indicated by its lighterδ^(18)O and slightly younger U-Pb ages compared with D1 and D2.Whereas deep burial dolomite cements(D4 and D5)yield markedly depletedδ^(18)O,elevated ^(87)Sr/^(86)Sr,along with much younger U-Pb ages and higher precipitation temperatures,suggesting that they were likely linked to hydrothermal fluids.Despite the wide occurrence of meteoric and organic acids leaching and thermochemical sulfate reduction,they may have only played a subsidiary role on these reservoirs development.Instead,superior reservoir quality is tightly linked to tectonics as inferred by higher reservoir quality closely related to the well-developed fractures and faults filled with abundant hydrothermal minerals.Notably,good reservoirs in both formations are mainly attributed to high permeability caused by tectonics.Hence,this new contribution emphasizes the crucial role of tectonics on spatially explicit reservoir prediction of deep to ultra-deep(up to>8000 m)carbonates in the Sichuan Basin,as well as other sedimentary basin analogues in China.

Genesis of Fibrous Calcite in the Chang 7 Member of the Yanchang Formation,Ordos Basin,China

To explore the genesis of the laminated calcite veins developed in the black shale of Chang 73 submember of the Ordos Basin,the petrology,microstructure and geochemistry of calcite veins are studied using thin sections,fluid inclusions,trace elements and isotopic geochemistry.The source,the time of formation,the mechanism of formation,and the dynamic background of the veins are discussed.The veins are mostly made up of calcite,mixed with lenticular or spindle-shape solid wall rock inclusions.Three structures are identified in the calcite minerals:fibrous,rhombic cleavage,and wedge-like structure.Trace elements and isotopes of carbon and oxygen confirm that the calcite veins were formed from a high density hydrothermal fluid.It is assumed that calcite veins formed prior to wall rock consolidation during the formation of the Qinling Orogenic Belt in the Middle and Late Triassic.The results show that the sedimentary sources of Chang 73 submember were influenced by hydrothermal materials besides terrigenous detritus.The fibrous calcite is different from the fibrous calcite reported in the morphology and mechanism of formation.In this way,the research complements and improves the morphology and the mechanism of formation of fibrous calcite.

3D Modeling and Determination of Factors Responsible for Zinc-Lead Mineralization in the Mehdiabad Deposit,Central Iran,based on Statistical Analysis of Geochemical Data

Although the Mehdiabad zinc-lead deposit is one of the most well-known deposits in the central Iran structural zone,the genesis of the deposit remains controversial.The host rock of the ore is a dolomitic limestone of the Lower Cretaceous Taft Formation.In the two main orebodies of the deposit,which includes the Black Hill and East Ridge ore zones,the oxide and sulfide ores are observed at the surface and at depth,respectively.The elements Zn,Fe,Mn and Mg are more abundant in the East Ridge ore zone(in both sulfide and oxide ores),with Ba,Pb,Ag and Cu being more abundant in the Black Hill oxide ore.Based on the distribution of elements and their correlation with each other in these ore zones,the elements are divided into three general groups,that of terrigenous elements,chemically-deposited elements and oreforming(hydrothermally deposited)elements,a division that is supported by the results of factor analyses.The spatial distribution of elements is jointly affected by contact with host rocks,the boundary of oxide-sulfide ores and fault zones.The main factors governing the distribution of elements are the mechanical transfer of detrital sediments,chemical sedimentation,transfer by hydrothermal fluids,oxidation and surface dissolution,all of which affected the spatial distribution of elements.The ore-forming elements are mostly affected by hydrothermal fluids and oxidation.This study not only provides additional information about the genesis of the Mehdiabad deposit,but also could assist in the exploitation of ore and further exploration purposes.The results of this study can aid in the exploration and exploitation of the Mehdiabad deposit and similar deposits in the region.

Geochemical Characteristics of a Carbonatite Dyke Rich in Rare Earths from Bayan Obo, China

The whole-rock geochemistry of a rare earths rich carbonatite dykes that locates at Dulahala and lies 3 km north-east to the East Ore body of the giant Bayan Obo RE-Nb-Fe deposit was analysed. The dyke cuts cross H1 coarse quartz sandstone and H2 fine quartzite of the Proterozoic Bayan Obo group. RE content in the dyke varies greatly up to 20% (mass fraction), which comprises rich RE ores. Light RE in carbonatites are extremely enriched and strongly fractionated relative to heavy RE, but no Eu anomaly. The carbonatite may be produced by mechanisms as follows: the carbonatite mana is directly formed by very low degree (F <1%) partial melting of enriched lithospheric mantle, leaving residual minerals characterized by abundant garnet; then the magma arises into a chamber within the crust where they will undergo fractional crystallization, which makes RE further concentrated in carbonatite. The RE patterns and spider diagrams of the carbonatite are identical to those fine-grained dolomite marble that is the ore-host rock for the Bayan Obo deposit. However, the carbonatite is calcic, which is different from the fine-grained dolomite marble in major element geochemistry. The difference is suggested to be resulted from that the carbonatite dyke is not affected by a large scale dolomitization, while the fine-grained dolomite marble might be the product of dolomitized carbonatite intrusive body that might set up a hydrothermal system in the region, which transported Mg from the Bayan Obo sediments, especially form the shales to the carbonatite intrusion.

Relationship between Thermal Metamorphism of Coal and the Periodic Variation Law of Geochemical Behavior of Elements:A Study on the C2 Coal Seam in the Fengfeng Mining Area of the Handan Coalfield in Hebei,China

This study highlights the response of the periodic variation of the geochemical behavior of elements to the thermal metamorphism of coal by considering the differentiation mode and differentiation degree of elements of the C2 coal seam in the Fengfeng mining area of the Handan Coalfield in Hebei,China.The periodic variation of the geochemical behavior of elements was observed to change towards a certain direction as the degree of metamorphism of a geological body increased.Based on the coincidence degree(or similarity degree)between the geochemical behavior of elements and periodic variation of elements,the 57 elements in this study were divided into two levels.The periodic variation of the geochemical behavior of first-level elements was largely synchronous with that of their first ionization energy,suggesting that only one differentiation mode exists and the elements are mainly inorganically associated.The differentiation mode of the second-level elements deviated to a certain extent from their first ionization energy;the larger the deviation,the more complicated and diverse was the differentiation mode.Among the second-level elements,the grade of coal metamorphism has evident and intuitive effects on the proportion of elements with particular structural features,such as the 4q+3 type of elements and the odd-odd elements.In addition,the distribution of elements in organic and inorganic matter within coal are subject to the structural features of the elements.The differentiation mode and differentiation intensity of elements could be characterized by the hierarchical parameter and differentiation intensity.The hierarchical parameter and differentiation intensity of certain elements showed a good positive or negative correlation with R_(max) in coal.The 57 elements in this study were quantitatively ordered according to the degree of magmatic hydrothermal fluid influence and thermal metamorphism of coal through graphs depicting the goodness of fit,correlation coefficient with R_(max),and differentiation intensity.The results of this study are consistent with the results of previous field research,illustrating the scientific significance and application value of this study on the periodic variation of the geochemical behavior of elements.