The temperature dependence of the magnetic properties was systemically studied by dc/ac magnetization and specific heat measurement for heavy rare earth HoCrO3 chromites.The results revealed the existence of complex p...The temperature dependence of the magnetic properties was systemically studied by dc/ac magnetization and specific heat measurement for heavy rare earth HoCrO3 chromites.The results revealed the existence of complex phase coexistence and competitive magnetic behavior in HoCrO3 chromites.It was found that,in the region of higher temperature above 141.0 K,HoCrO3 behaved as a typical Curie-Weiss paramagnetic（PM）.And in the region of low temperature,a novel magnetization behavior was observed with negative magnetization（diamagnetism-like） characteristics under an external field of 100 Oe and M-T curves exhibited two symmetrical branches for field cooling（FC） and zero field cooling（ZFC） modes.This behavior indicated the coexistence of canted antiferromagnetic（CAFM） and weak ferromagnetic（FM） phase.These also exhibited the existence of competition mechanism below characteristic temperature TN1=141.0 K and the magnetic order of Ho ion below 7.5 K.The current complex magnetization might be attributed to the interaction between paramagnetic Ho3＋ moments and canted Cr3＋ moments.展开更多
Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Mont...Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990）.Evidence for mafic/ultramafic target rocks was reinforced by discovery of chromites,some with shock planar deformation features（PDF）,in impact layer samples from sites in southern Colorado and eastern Wyoming（Bohor et al.,1990）.However,until now it was unclear whether the chromites originated with an impactor or with terrestrial target rocks.To this end,high-precision 54Cr/52Cr isotope ratios were measured on KT boundary chromites along with known terrestrial chromites.We find a terrestrial 54Cr/52Cr ratio in KT boundary chromites from impact layer samples collected at the above sites over the last several years（Fig.1）.Ejected terrestrial chromites suggest the impact sampled terrestrial mafic and/or ultramafic target rocks not known to exist in the Chicxulub target area.展开更多
Phase transition of LaCrO3 and doped-LaCrO3 was studied by DSC, TG and XRD, and thermal expansion during the transition was analyzed. It is found that phase transition of LaCrO3 begins at about 240℃ and ends at about...Phase transition of LaCrO3 and doped-LaCrO3 was studied by DSC, TG and XRD, and thermal expansion during the transition was analyzed. It is found that phase transition of LaCrO3 begins at about 240℃ and ends at about 265 ℃. Temperatures of phase transition rise obviously with increasing Ca^2＋ content. The transition of LaCrO3 and Ca-doped LaCrO3 from orthorhombic to rhombohedral is accompanied with endothermic reaction. No obvious change occurs in mass, but remarkable shrinkage occurs during phase transition.展开更多
The Kuda ophiolite belongs to the early Paleozoic ophiolite belt in Western Kunlun Mountains and is composed of metamorphic peridotites,cumulate peridotites,mafic volcanic rocks and quartzites(Li et al.,
The Polar Urals region of northern Russia is well known for large chromium （Cr）-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolit...The Polar Urals region of northern Russia is well known for large chromium （Cr）-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum （Pt）-group elements （PGE）, geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium （Ir） values. These values indicate the predominance of ruthenium--osmium--iridium （Ru--Os--Ir）-bearing phases among the platinum-group mineral （PGM） assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite （up to 15 μm）. Less common are cuproiridsite （up to 5 μm）, irarsite （up to 4--5 μm）, and laurite （up to 4 μm）. The predominant sulfide is heazlewoodite, in intergrowth with Ni--Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and esti- mated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE.展开更多
The chrome spinel(chromite)in mantle peridotites from ophiolites can shed light on the formation and evolution process of ophiolites.Podiform chromites were found in the Late Proterozoic Miaowan ophiolitic complex(MOC...The chrome spinel(chromite)in mantle peridotites from ophiolites can shed light on the formation and evolution process of ophiolites.Podiform chromites were found in the Late Proterozoic Miaowan ophiolitic complex(MOC),Yangtze Craton.Due to the metamorphism and intense deformation,most chromite grains in the MOC peridotites show typical chemical zoning(core-rim texture).The values of major and trace elements largely vary from core to rim within chromite grains,indicating that the chromites have undergone strong alteration and element mobility.Major and trace elements in the core parts of chromites are used to infer the tectonic origins and evolution of mantle peridotites in the MOC.The chromites from the MOC peridotites have higher Cr#values and lower Ni and Ga contents with respect to those from Phanero-zoic mantle peridotites,indicating a higher degree of depletion.In-situ major and trace elements(e.g.,Ga)characteristics of podiform chromites in the MOC show that chromites from both harzburgites and dunites have strong subduction-related signatures,indicating that the MOC has formed in a supra-subduction setting which is consistent with the geological and geochemical data presented in previous studies.展开更多
A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are...A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are identified on the basis of integrated petrographic,mineralogical and geochemical study.The first type,represented by Yinshanzhai serpentinite complex(Group 1)comprises heterogeneous lithology as a massive serpentinite matrix“intruded”by antigoriteenriched serpentinite lenses.They are both pseudomorphic textured with different mineral assemblages indicating an increasing temperature-pressure condition.Serpentinite matrix(Group 1a)is chemically characterized by high MgO/SiO_(2)and low Al_(2)O_(3)/SiO_(2),Ti and Ca contents,suggesting a depleted mantle wedge origin.The coexistence of compositionally-heterogeneous chromite with highCr^(#)(0.78-0.96)and intermediate-Cr^(#)(0.59-0.70)pristine cores indicates extensive mantle melting.Meanwhile,extremely high Fo olivine relicts(96-97)with considerably higher MnO and lower NiO contents than mantle olivine indicate that they are metamorphic products from serpentine decomposition.Accordingly,we propose that Yinshanzhai serpentinite complex experienced two distinct episodes of hydration.The serpentinite lenses(Group 1b)show higher SiO_(2)and lower MgO concentrations.Nevertheless,the trace elements of groups 1a and 1b are consistent:U-shaped REE patterns,positive Eu anomalies and enrichment of LILE(i.e.,Cs,U)are all identified as forearc properties.They are affected by reducing slab-derived fluids in forearc mantle,with f_(O2)of 1 to 2 logarithmic units below f_(O2)of fayalite-magnetite-quartz buffer(FMQ-2~FMQ-1).The second type is antigorite-serpentinites(Group2)represented by Ximaoshan and Wangchunwan blocks.They are non-pseudomorphic,with no primary framework silicate surviving.Fertile compositions(i.e.,higher Al_(2)O_(3)and Al_(2)O_(3)/SiO_(2),nearly flat REE patterns)and conjoint enrichment of LILE with HFSE suggest melt/rock interaction.Negative Ce,Eu anomalies,and enriched U relative to alkaline elements demonstrate interactions with more oxidized seawater or seafloor fluids(FMQ~FMQ-1).Remarkable Sr negative anomalies may be attributed to Sr release during lizardite/antigorite transition in subduction zone,indicating interaction with low-Sr slab fluids.We propose that Group 2 serpentinites originate either from mantle wedge or abyssal peridotites,refertilized by mantle melts,then hydrated in seafloor or shallow forearc and entrapped into subduction channel.Combined with geochronology and tectonic constraints of associated eclogites in Hong'an terrane,the two types of serpentinites may correlate with subduction of different oceanic basins during the late Paleozoic and/or Proterozoic eras.It raises possibility of defining an ophiolitic setting in Hong'an Orogen for which further evidence is required.展开更多
To elucidate the formation mechanisms of burn-on sand and metal penetration during sand casting,some laboratory experiments were carried out at different temperatures(1813,1833,1853,and 1873 K)and holding time(20,40,6...To elucidate the formation mechanisms of burn-on sand and metal penetration during sand casting,some laboratory experiments were carried out at different temperatures(1813,1833,1853,and 1873 K)and holding time(20,40,60,and 90 min)to simulate the interaction between ZG13Cr9Mo1VNbN stainless steel and chromite sand.The results demonstrate that the defects primarily consist of a mixture of the liquid phase,chromite,and metal.The main components of the liquid phase are SiO_(2),MnO,MgO,Cr_(2)O_(3),FeO,and Al_(2)O_(3),and the formation of Cr_(2)O_(3)through interfacial redox reactions has been discovered.The presence of a liquid phase plays a pivotal role in influencing burn-on sand and metal penetration.Interface reactions are prioritized,with burn-on sand maintaining a predominant influence.As the liquid phase quantity within the sand escalates,there is a corresponding incremental rise in the incidence of metal penetration.Even a minimal presence of the silicon element in steel can impact the liquid phase’s formation.Moreover,the decomposition or dissolution of chromite sand is a significant factor in the development of burn-on sand and metal penetration.Thus,a thorough investigation into the conditions and contributing factors of this phenomenon is essential for its effective management and mitigation.展开更多
The enrichment of chromium in the magnetic iron chromite(Fe(Cr_(x)Fe_(1-x))_(2)O_(4))phase is crucial for the recovery and recycling of chromium in stainless-steel pickling sludge.The kinetics and reaction mechanism o...The enrichment of chromium in the magnetic iron chromite(Fe(Cr_(x)Fe_(1-x))_(2)O_(4))phase is crucial for the recovery and recycling of chromium in stainless-steel pickling sludge.The kinetics and reaction mechanism of the solid-phase reaction between Fe_(3)O_(4)and Cr_(2)O_(3)were investigated using the diffusion couple method at 1473 K.Not only the diffusion behavior of Fe^(2+)ions and Cr^(3+)ions was elucidated,but also the solid solution behavior of Fe^(3+)ions was discussed clearly.The microscopic morphology of the diffusion couple and the change in the concentrations of Fe and Cr cations across the diffusion layers were analyzed using scanning electron microscopy and en-ergy dispersive spectroscopy.The self-diffusion coefficients of cations were calculated based on the concentration profiles of Fe and Cr,with the results indicating that the self-diffusion coefficient of the Fe ions was consistently higher than that of the Cr ions.Additionally,a mixture of Fe_(3)O_(4)and Cr_(2)O_(3)was annealed at 1373-1473 K for 1-5 h,and the kinetic parameters were calculated by studying the phase content of the product.The phase content of Fe(Cr_(x)Fe_(1-x))_(2)O_(4)in the product was determined by Rietveld refinement of X-ray diffraction data,revealing that an activation energy(E)of 177.20 kJ·mol^(-1) and a pre-exponential factor(B)of 610.78 min^(-1)of the solid-phase reac-tion that produced the Fe(Cr_(x)Fe_(1-x))_(2)O_(4)spinel.展开更多
Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This stud...Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This study investigated hydrogen plasma smelting reduction as a novel,sustainable,and efficient method for producing stainless steel directly from lateritic nickel and chromite ores.The research aimed to examine the effect of ore proportion on AISI 300 series stainless steel production and assess the reduction process over time through thermochemical calculations and experimental studies.Results showed that increasing the proportion of chromite ore in the feed raises Cr content and reduces Ni content in metals while increasing Cr_(2)O_(3) and Al_(2)O_(3) content in oxides.A briquette comprising 30wt%chromite ore and 70wt%calcined nickel ore yields better results for AISI 300 stainless steel,with Fe,Cr,Ni,and Si content of 62.95wt%,19.37wt%,11.83wt%,and 0.72wt%,respectively,after 180 s of hydrogen plasma exposure.Nearly all NiO compounds are converted into Ni after 60 s of smelting reduction,whereas FeO compounds are almost fully converted into Fe after 120 s of smelting reduction.AISI 300 series stainless steel is successfully produced after 120 s of reduction,achieving Fe,Cr,Ni,and Si content of 64.36wt%,21.92wt%,10.08wt%,and 0.61wt%,respectively.Process optimization remains promising because the Cr_(2)O_(3) content in the slag is still relatively high at 15.52wt%.This ultrafast and direct production method holds considerable potential to transform stainless steel production by reducing environmental impact and enhancing process efficiency.Specifically,the method eliminates the use of an argon oxygen decarburization converter and vacuum oxygen decarburization in stainless steelmaking.展开更多
Huang Shaoxian(1914-1989),born in Jimo County,Shandong Province in 1914.Huang Shaoxian graduated from the Department of Geology,Geography and Meteorology at the National Southwestern Associated University in 1940.He w...Huang Shaoxian(1914-1989),born in Jimo County,Shandong Province in 1914.Huang Shaoxian graduated from the Department of Geology,Geography and Meteorology at the National Southwestern Associated University in 1940.He was elected as an academician of the Chinese Academy of Science in 1980 and served as Deputy Director and Senior Engineer at the Third Research Institute of the Ministry of Nuclear Industry.He achieved the first domestic discovery of chromite deposits in China,filling a critical gap in the nation's mineral resources.Dedicated to uranium resource exploration and scientific research throughout his career,he led the working group to achieve breakthroughs in exploration technologies for granite-type and carbon-siliceous-pelitic rock-type uranium deposits.As a pioneer and foundational figure in China's uranium geology,he made significant contributions to the development of the country's nuclear industry and uranium geology.展开更多
The high-carbon ferrochrome is an essential raw material for producing stainless steel,and the demand of it increases with the increase of stainless steel.So increasing Cr recovery rate from chromite is essential for ...The high-carbon ferrochrome is an essential raw material for producing stainless steel,and the demand of it increases with the increase of stainless steel.So increasing Cr recovery rate from chromite is essential for lower costs and higher economic benefits in high-carbon ferrochrome production process.This study calculated the activity of CrO_(x)in slag and investigated the distribution behavior of Cr between slag and alloy.Theω(MgO)/ω(Al_(2)O_(3))was 1.0,and the w(CaO)/w(SiO_(2))was from 0.2 to 0.6 in this study.The calculation and experimental results showed that the main phases of the slag were chrome-containing spinel,magnesium-aluminum spinel,olivine and melilite.The content of spinel in slag decreased with the increasing w(CaO)/w(SiO_(2)),and the w(CrO_(x))in spinel also reduced,but the content of melilite increased.The distribution ratio of Cr between slag and alloy decreased with the increase of slag basicity at 1600℃,meansning that increasing the w(CaO)/w(SiO_(2))of slag can improve the recovery of Cr in chromite smelting process.展开更多
The podiform chromitites in the Luobusha ophiolite have been thought to experience a very deep formation,but the maximum depth is still an open issue.Here,we have investigated the structural stability of natural magne...The podiform chromitites in the Luobusha ophiolite have been thought to experience a very deep formation,but the maximum depth is still an open issue.Here,we have investigated the structural stability of natural magnesiochromite using the synchrotron-based powder X-ray diffraction and diamond anvil cells up to 48.6 GPa and 2450 K.The results have shown that spinel-type magnesiochromite first decomposes into corundum-type‘Cr_(2)O_(3)’+B1-type‘MgO’at 11–14 GPa and 1250–1450 K,then modified ludwigite(mLd)-type‘Mg_(2)Cr_(2)O_(5)’+corundum-type‘Cr_(2)O_(3)’at 14.3–20.5 GPa and 1300–2000 K,and finally CaTi_(2)O_(4)-type phase at 24.5 GPa.During the quenching procession from high-temperature-pressure conditions,the mLd-type phase appeared again and was kept at ambient conditions.We also obtained the isothermal equation states of spinel-type and CaTi_(2)O_(4)-type phases,revealing the composition effect on their elasticities.Based on the updated results,we propose chromitites could not experience pressure exceeding∼14.3 GPa(approximate maximum depth∼400 km)in the subduction-recycling genesis model.展开更多
Mineralogical characterization and liberation of valuable minerals are primary concerns in rnineml processing industries. The pre- sent investigation focuses on quantitative mineralogy, elemental deportment, and locki...Mineralogical characterization and liberation of valuable minerals are primary concerns in rnineml processing industries. The pre- sent investigation focuses on quantitative mineralogy, elemental deportment, and locking-liberation characteristics of the beneficiation of tailings from a chrome ore beneficiation plant in the Sukinda region, Odisha; methods used for the study of the beneficiated tailings are QEMSCAN~, X-ray diffraction （XRD）, and mineral chemistry by a scanning electron microscope equipped with an energy-dispersive spec- trometer （SEM-EDS）. The tailing sample was fine grained （69.48wt% below 45 μm size）, containing 20.25wt% Cr203 and 39.19wt% Fe203, with a Cr：Fe mass ratio of 0.51. Mineralogical investigations using QEMSCAN studies revealed that chromite, goethite, and gibbsite are the dominant mineral phases with minor amounts of hematite, kaolinite, and quartz. The sample contained 34.22wt% chromite, and chromite liberation is more than 80% for grains smaller than 250 ~tm in size. Based on these results, it was predicted that liberated chromite and high-grade middling chromite particles could be separated from the gangue by various concentration techniques. The tailing sample was beneficiated by hydrocyclone, tabling, wet high-intensity magnetic separation （WHIMS）, and flotation in order to recover the chromite. A chromite concentrate with 45.29wt% Cr203 and a Cr：Fe mass ratio of 1.85 can be produced from these low-grade chromite ore beneficiation plant rejects.展开更多
Understanding Archean crustal and mantle evolution hinges upon identification and characterization of oceanic lithosphere. We report and update here more than 10 years work on a complete, yet dismembered and metamorph...Understanding Archean crustal and mantle evolution hinges upon identification and characterization of oceanic lithosphere. We report and update here more than 10 years work on a complete, yet dismembered and metamorphosed Archcan ophiolite sequence in the North China craton, in the Dongwanzi （东湾子）-Zunhua （遵化） structural belt and correlatives in the Wutaishan （五台山） area. Banded iron formation structurally overlies several tens of meters of variably deformed pillow lavas, mafic flows, and picritic amphibolites. These are in structural contact with a 2 km thick mixed gabbro and dike complex with gabbro screens, exposed discontinuously along strike for more than 20 km. The dikes consist of metamorphosed diabase, basalt, Hb-Cpx-gabbro, and pyroxenite. The dike/gabbro complex is underlain by several kilometers of mixed isotropic and foliated gabbro, which preserve compositional layering approximately 2 km below the dike complex, and then over several hundred meters merge into strongly compositionally layered gabbro and olivine-gabbro. The layered gabbro becomes mixed with layered pyroxenite/gabbro marking a transition zone into emulate ultramaflc rocks including serpentinzed dunite, pyroxenite and wehrlite, and finally into strongly deformed and serpentinized olivine and orthopyroxene-bearing ultraInafic rocks interpreted as depleted mantle harzburgite tectoultes. A U/Pb zircon age of 2.505 Ga from gabbro of the Dongwanzi ophioUte makes it one of the world＇s oldest recognized, laterally. extensive complete ophiolite sequences, though older dismembered ophiolites are recognized in South Africa and Greenland, extending back to 3.8 Ga. This age is confirmed by a ca. 2.6 Ga Re-Os isochron from chromites from the belt, and a number of dated 2.5-2.4 Ga cross-cuttlng younger igneous units. The Dongwanzi ophiolite is one of the largest well-preserved greenstone belts in the central orogenic belt that divides the North China craton into eastern and western blocks. More than 1 000 other fragments of gabbro, pillow lava, sheeted dikes, harzburgite,and podiform-chromite bearing dunite occur as tectonic blocks （tens to hundreds of meters long） in a biotite-gneiss and BIF matrix, intruded by tonalite and granodiorite, in the Zunhua structural belt. Blocks in this metamorphosed Archcan ophiolitic melange preserve deeper levels of oceanic mantle than the Dongwanzi ophiolite. The ophiolite-related melange marks a suture zone across the North China craton, traced for more than 1 600 km along the central orogenic belt. Many of the chromitite bodies are localized in dunite envelopes within harzburgite tectonite, and have characteristic nodular and orbicular chromite textures, known elsewhere only from ophiolites. The chromites have variable but high chrome numbers （Cr/（Cr＋Al）=0.74-0.93） and elevated P, also characteristic of suprasubduction zone ophiolites. The high chrome numbers, coupled with TiO2〈0.2 wt.% and V2O5〈0.1 wt.% indicate high degrees of partial melting from a very depleted mantle source and primitive melt for the chromite. A Re-Os isochron from the chromites indicates an age of 2.6 Ga, showing that they are the same age as the Dongwanzi ophiolite. The range in initial Os isotopic compositions in the chromites in these ophiolitic blocks is small and well within the range seen in modern ophiolites. The ultramafic and ophiolitic blocks in the Zunhua melange are therefore interpreted as dismembered and strongly deformed parts of the Dongwanzi ophiolite. We suggest the name ＂Dongwanzi-Zunhua ophiolite belt＂ for these rocks. Geochemical and structural features of the Dongwanzi ophiolite suggest that it formed in a forearc environment and was incorporated in an accretionary prism soon after it formed. Neoarchean and Paleoproterozoic （2.50 and 1.90 Ga） high-pressure granulites form a belt more than 700 km long along the western side of the central orogenic belt. Several Neoarchean sedimentary basins consisting of conglomerate, greywacke, and shale are located along the eastern side of the central orogenic belt, and are interpreted as remnants of a foreland basin. The three belts record the Neoarchcan subduction and collision between an arc terrane and eastern blocks of the North China craton in the Neoarchean, and further deformation and metamorphism in the Paleoproterozoic related to collisions on the northern margin of the already amalgamated North China craton.展开更多
Listwanite from the Luobusa ophiolite, Tibet, forms a narrow, discontinuous band along the eastern part of the southern boundary fault. We undertook a detailed petrographic and geochemical study to understand the mine...Listwanite from the Luobusa ophiolite, Tibet, forms a narrow, discontinuous band along the eastern part of the southern boundary fault. We undertook a detailed petrographic and geochemical study to understand the mineral transformation processes and the behaviour of major and trace elements during listwanite formation. Three alteration zones characterized by distinct mineral components and texture are recognized and, in order of increasing degree of alteration, these are： zonem is rich in serpentine minerals; zonen is rich in talc and carbonates; and zone_Ⅰ is mainly composed of carbonates and quartz. Geochemical data for the three alteration zones show significant modification of some major and trace elements in the protolith, although some oxides show linear correlations with MgO. Gold mineralization is recognized in the Luobusa listwanite and may signify an important target for future mineral exploration. Gold enrichment occurs in both zone_Ⅰ and zone_Ⅱ and is up to 0.91 g/t in one sample from zonei. We show that CO_2-rich hydrothermal fluids can modify both the occurrence and composition of chromite grains, indicating some degree of chromite mobility. Low-Cr anhedral grains are more easily altered than high-Cr varieties. The compositions of chromite and olivine grains in the listwanite suggest a dunite protolith.展开更多
To explicate the thermodynamics of the chromite ore lime-free roasting process, the thermodynamics of reactions involved in this process was calculated and the phrases of sinter with different roasting times were stud...To explicate the thermodynamics of the chromite ore lime-free roasting process, the thermodynamics of reactions involved in this process was calculated and the phrases of sinter with different roasting times were studied. The thermodynamics calculation shows that all the standard Gibbs free energy changes of the reactions to form Na2CrO4, Na2O-Fe2O3, Na2O·Al2O3 and Na2O3 SiO2 via chromite ore and Na2CO3 are negative, and the standard Gibbs free energy changes of the reactions between MgO, Fe2O3 and SiO2 released from chromite spinel to form MgO-Fe2O3 and MgO·SiO2 are also negative at the oxidative roasting temperatures （1 173 1 473 K）. The phrase analysis of the sinter in lime-free roasting process shows that Na2O·Fe2O3, Na2O·Al2O3 and Na2O·SiO2 can be formed in the first 20 min, but they decrease in contents and finally disappear with the increase of roasting time. The final phase compositions of the sinter are Na2CrO4, MgO·Fe2O3, MgO·SiO2 and MgO. The results indicate that Na2CrO4 can be formed easily via the reaction ofNa2CO3 with chromite ore. Na2O·Fe2O3, Na2O-Al2O3 and Na2O·SiO2 can be formed as intermediate compounds in the roasting process and they can further react with chromite ore to form Na2CrO4. MgO released from chromite ore may react with iron oxides and silicon oxide to form stable compounds of MgO·Fe2O3 and MgO·SiO2, respectively.展开更多
A new mineral species, named naquite（FeSi）, is found in the podiform chromitites of the Luobusha ophiolite in Qusong County, Tibet, China. The detailed composition is Fe 65.65, Si 32.57 and Al 1.78 wt%. The mineral ...A new mineral species, named naquite（FeSi）, is found in the podiform chromitites of the Luobusha ophiolite in Qusong County, Tibet, China. The detailed composition is Fe 65.65, Si 32.57 and Al 1.78 wt%. The mineral is cubic, space group P213. The irregular crystals range from 15 to 50 μm in diameter and form an intergrowth with luobusaite. Naquite is steel grey in color, opaque, with a metallic lustre and gives a grayish-black streak. The mineral is brittle, has a conchoidal fracture and no apparent cleavage. The estimated Mohs hardness is 6.5, and the calculated density is 6.128 g/cm3. Unit-cell parameters are a 4.486 （4） A, V 90.28 （6）A^3, Z=4. The five strongest powder diffraction lines [d inA（hkl） （I/I0）] are： 3.1742 （110） （40）, 2.5917（111） （43）, 2.0076 （210） （100）, 1.8307 （211） （65）, and 1.1990 （321） （36）. Originally called ＇fersilicite＇, the species and new name have now been approved by the CNMNC （IMA 2010-010）.展开更多
Mechanical activation was used to improve the extraction of chromium in molten NaOH.It is observed that the extraction ratio reaches 97% after leaching for 200 min when chromite ore is mechanically activated for 10 mi...Mechanical activation was used to improve the extraction of chromium in molten NaOH.It is observed that the extraction ratio reaches 97% after leaching for 200 min when chromite ore is mechanically activated for 10 min,but only 34% if not activated.Mechanical activation can decrease the particle size,increase the surface area,and enhance the lattice distortion.Further,the mechanisms for mechanical activation were exposed.The results show that the mechanical activation mainly focuses on chromite ore particle size decrease and the lattice distortion.The formation of aggregation weakens the strengthening effect of mechanical activation for releasing high surface energy.展开更多
Voluminous platinum-group mineral （PGM） inclusions including erlichmanite （Os,Ru）S2, laurite （Ru,Os）S2, and irarsite （Ir, Os,Ru,Rh）AsS, as well as native osmium Os（Ir） and inclusions of base metal sulphides ...Voluminous platinum-group mineral （PGM） inclusions including erlichmanite （Os,Ru）S2, laurite （Ru,Os）S2, and irarsite （Ir, Os,Ru,Rh）AsS, as well as native osmium Os（Ir） and inclusions of base metal sulphides （BMS）, including millerite （NiS）, heazlewoodite （NiaS2）, covellite （CuS） and digenite （Cu3S2）, accompanied by native iron, have been identified in chromitites of the Zedang ophiolite, Tibet. The PGMs occur as both inclusions in magnesiochromite grains and as small interstitial granules between them; most are less than 10 ~m in size and vary in shape from euhedral to anhedral. They occur either as single or composite （biphase or polyphase） grains composed solely of PGM, or PGM associated with silicate grains. Os-, Ir-, and Ru-rich PGMs are the common species and Pt-, Pd-, and Rh-rich varieties have not been identified. Sulfur fugacity and temperature appear to be the main factors that controlled the PGE mineralogy during crystallization of the host chromitite in the upper mantle. If the activity of chalcogenides （such as S, and As） is low, PGE clusters will remain suspended in the silicate melt until they can coalesce to form alloys. Under appropriate conditions of fS2 and fO2, PGE alloys might react with the melt to form sulfides-sulfarsenides. Thus, we suggest that the Os, Ir and Ru metallic clusters and alloys in the Zedang chromitites crystallized first under high temperature and low fS2, followed by crystallization of sulphides of the laurite-erlichmanite, solid-solution series as the magma cooled and fS2 increased. The abundance of primary BMS in the chromitites suggests that fS2 reached relatively high values during the final stages of magnesiochromite crystallization. The diversity of the PGE minerals, in combination with differences in the petrological characteristics of the magnesiochromites, suggest different degrees of partial melting, perhaps at different depths in the mantle. The estimated parental magma composition suggests formation in a suprasubduction zone environment, perhaps in a forearc.展开更多
基金Project supported by the National Natural Science Foundation of China (10774097,10875107)the Science & Technology Committee of Shanghai Municipality (08dj1400202)+1 种基金the Natural Science Foundation of Henan Province (092300410138,102300410108)the Doctoral Innovation Fund of Zhengzhou University of Light Industry (2010BSJJ027)
文摘The temperature dependence of the magnetic properties was systemically studied by dc/ac magnetization and specific heat measurement for heavy rare earth HoCrO3 chromites.The results revealed the existence of complex phase coexistence and competitive magnetic behavior in HoCrO3 chromites.It was found that,in the region of higher temperature above 141.0 K,HoCrO3 behaved as a typical Curie-Weiss paramagnetic（PM）.And in the region of low temperature,a novel magnetization behavior was observed with negative magnetization（diamagnetism-like） characteristics under an external field of 100 Oe and M-T curves exhibited two symmetrical branches for field cooling（FC） and zero field cooling（ZFC） modes.This behavior indicated the coexistence of canted antiferromagnetic（CAFM） and weak ferromagnetic（FM） phase.These also exhibited the existence of competition mechanism below characteristic temperature TN1=141.0 K and the magnetic order of Ho ion below 7.5 K.The current complex magnetization might be attributed to the interaction between paramagnetic Ho3＋ moments and canted Cr3＋ moments.
文摘Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on;5km thick continental crust（De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990）.Evidence for mafic/ultramafic target rocks was reinforced by discovery of chromites,some with shock planar deformation features（PDF）,in impact layer samples from sites in southern Colorado and eastern Wyoming（Bohor et al.,1990）.However,until now it was unclear whether the chromites originated with an impactor or with terrestrial target rocks.To this end,high-precision 54Cr/52Cr isotope ratios were measured on KT boundary chromites along with known terrestrial chromites.We find a terrestrial 54Cr/52Cr ratio in KT boundary chromites from impact layer samples collected at the above sites over the last several years（Fig.1）.Ejected terrestrial chromites suggest the impact sampled terrestrial mafic and/or ultramafic target rocks not known to exist in the Chicxulub target area.
基金Project supported bythe National Natural Science Foundation of China (50362001)
文摘Phase transition of LaCrO3 and doped-LaCrO3 was studied by DSC, TG and XRD, and thermal expansion during the transition was analyzed. It is found that phase transition of LaCrO3 begins at about 240℃ and ends at about 265 ℃. Temperatures of phase transition rise obviously with increasing Ca^2＋ content. The transition of LaCrO3 and Ca-doped LaCrO3 from orthorhombic to rhombohedral is accompanied with endothermic reaction. No obvious change occurs in mass, but remarkable shrinkage occurs during phase transition.
基金supported by National Natural Science Foundation Project(grant number 41302051)Shaanxi Province Science Technology Research Development Plan Project(grant number 2014JM2-4037)National Sci-Tech Support Plan Project(grant number 2011BAB06B05-02)
文摘The Kuda ophiolite belongs to the early Paleozoic ophiolite belt in Western Kunlun Mountains and is composed of metamorphic peridotites,cumulate peridotites,mafic volcanic rocks and quartzites(Li et al.,
文摘The Polar Urals region of northern Russia is well known for large chromium （Cr）-bearing massifs with major chromite orebodies, including the Centralnoye I deposit in the Ray-Iz ultramafic massif of the Ural ophiolite belt. New data on platinum （Pt）-group elements （PGE）, geochemistry and mineralogy of the host dunite shows that the deposit has anomalous iridium （Ir） values. These values indicate the predominance of ruthenium--osmium--iridium （Ru--Os--Ir）-bearing phases among the platinum-group mineral （PGM） assemblage that is typical of mantle-hosted chromite ores. Low Pt values in chromites and increased Pt values in host dunites might reflect the presence of cumulus PGM grains. The most abundant PGM found in the chromite is erlichmanite （up to 15 μm）. Less common are cuproiridsite （up to 5 μm）, irarsite （up to 4--5 μm）, and laurite （up to 4 μm）. The predominant sulfide is heazlewoodite, in intergrowth with Ni--Fe alloys, sporadically with pentlandite, and rarely with pure nickel. Based on the average PGE values and esti- mated Cr-ore resources, the Centralnoye I deposit can be considered as an important resource of PGE.
基金This study was supported by the National Natural Science Foundation of China(Nos.41802240,41902036)the Fundamental Research Funds of the Central Universities granted by China University of Geosciences(Wuhan)(No.007-G1323541792)to Hao DengThis research was also supported by an opening fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Wuhan)(No.GRMR201607).
文摘The chrome spinel(chromite)in mantle peridotites from ophiolites can shed light on the formation and evolution process of ophiolites.Podiform chromites were found in the Late Proterozoic Miaowan ophiolitic complex(MOC),Yangtze Craton.Due to the metamorphism and intense deformation,most chromite grains in the MOC peridotites show typical chemical zoning(core-rim texture).The values of major and trace elements largely vary from core to rim within chromite grains,indicating that the chromites have undergone strong alteration and element mobility.Major and trace elements in the core parts of chromites are used to infer the tectonic origins and evolution of mantle peridotites in the MOC.The chromites from the MOC peridotites have higher Cr#values and lower Ni and Ga contents with respect to those from Phanero-zoic mantle peridotites,indicating a higher degree of depletion.In-situ major and trace elements(e.g.,Ga)characteristics of podiform chromites in the MOC show that chromites from both harzburgites and dunites have strong subduction-related signatures,indicating that the MOC has formed in a supra-subduction setting which is consistent with the geological and geochemical data presented in previous studies.
基金funded by the National Natural Science Foundation of China(No.42130309)China Geological Survey(Nos.DD20160030,DD20190050)。
文摘A cluster of serpentinite bodies has been recognized tectonically emplaced within the greenschist-amphibolite-facies metamorphic terrane in Hong'an,western Dabie orogen,central China.Two types of serpentinites are identified on the basis of integrated petrographic,mineralogical and geochemical study.The first type,represented by Yinshanzhai serpentinite complex(Group 1)comprises heterogeneous lithology as a massive serpentinite matrix“intruded”by antigoriteenriched serpentinite lenses.They are both pseudomorphic textured with different mineral assemblages indicating an increasing temperature-pressure condition.Serpentinite matrix(Group 1a)is chemically characterized by high MgO/SiO_(2)and low Al_(2)O_(3)/SiO_(2),Ti and Ca contents,suggesting a depleted mantle wedge origin.The coexistence of compositionally-heterogeneous chromite with highCr^(#)(0.78-0.96)and intermediate-Cr^(#)(0.59-0.70)pristine cores indicates extensive mantle melting.Meanwhile,extremely high Fo olivine relicts(96-97)with considerably higher MnO and lower NiO contents than mantle olivine indicate that they are metamorphic products from serpentine decomposition.Accordingly,we propose that Yinshanzhai serpentinite complex experienced two distinct episodes of hydration.The serpentinite lenses(Group 1b)show higher SiO_(2)and lower MgO concentrations.Nevertheless,the trace elements of groups 1a and 1b are consistent:U-shaped REE patterns,positive Eu anomalies and enrichment of LILE(i.e.,Cs,U)are all identified as forearc properties.They are affected by reducing slab-derived fluids in forearc mantle,with f_(O2)of 1 to 2 logarithmic units below f_(O2)of fayalite-magnetite-quartz buffer(FMQ-2~FMQ-1).The second type is antigorite-serpentinites(Group2)represented by Ximaoshan and Wangchunwan blocks.They are non-pseudomorphic,with no primary framework silicate surviving.Fertile compositions(i.e.,higher Al_(2)O_(3)and Al_(2)O_(3)/SiO_(2),nearly flat REE patterns)and conjoint enrichment of LILE with HFSE suggest melt/rock interaction.Negative Ce,Eu anomalies,and enriched U relative to alkaline elements demonstrate interactions with more oxidized seawater or seafloor fluids(FMQ~FMQ-1).Remarkable Sr negative anomalies may be attributed to Sr release during lizardite/antigorite transition in subduction zone,indicating interaction with low-Sr slab fluids.We propose that Group 2 serpentinites originate either from mantle wedge or abyssal peridotites,refertilized by mantle melts,then hydrated in seafloor or shallow forearc and entrapped into subduction channel.Combined with geochronology and tectonic constraints of associated eclogites in Hong'an terrane,the two types of serpentinites may correlate with subduction of different oceanic basins during the late Paleozoic and/or Proterozoic eras.It raises possibility of defining an ophiolitic setting in Hong'an Orogen for which further evidence is required.
基金appreciation to National Natural Science Foundation of China(Nos.52174317,52274337 and U1960203).
文摘To elucidate the formation mechanisms of burn-on sand and metal penetration during sand casting,some laboratory experiments were carried out at different temperatures(1813,1833,1853,and 1873 K)and holding time(20,40,60,and 90 min)to simulate the interaction between ZG13Cr9Mo1VNbN stainless steel and chromite sand.The results demonstrate that the defects primarily consist of a mixture of the liquid phase,chromite,and metal.The main components of the liquid phase are SiO_(2),MnO,MgO,Cr_(2)O_(3),FeO,and Al_(2)O_(3),and the formation of Cr_(2)O_(3)through interfacial redox reactions has been discovered.The presence of a liquid phase plays a pivotal role in influencing burn-on sand and metal penetration.Interface reactions are prioritized,with burn-on sand maintaining a predominant influence.As the liquid phase quantity within the sand escalates,there is a corresponding incremental rise in the incidence of metal penetration.Even a minimal presence of the silicon element in steel can impact the liquid phase’s formation.Moreover,the decomposition or dissolution of chromite sand is a significant factor in the development of burn-on sand and metal penetration.Thus,a thorough investigation into the conditions and contributing factors of this phenomenon is essential for its effective management and mitigation.
基金supported by the National Natural Science Foundation of China(No.52274306)Open Fund of State Key Laboratory of Silicate Materials for Architectures(Wuhan University of Technology),China(No.SYSJJ2020-03).
文摘The enrichment of chromium in the magnetic iron chromite(Fe(Cr_(x)Fe_(1-x))_(2)O_(4))phase is crucial for the recovery and recycling of chromium in stainless-steel pickling sludge.The kinetics and reaction mechanism of the solid-phase reaction between Fe_(3)O_(4)and Cr_(2)O_(3)were investigated using the diffusion couple method at 1473 K.Not only the diffusion behavior of Fe^(2+)ions and Cr^(3+)ions was elucidated,but also the solid solution behavior of Fe^(3+)ions was discussed clearly.The microscopic morphology of the diffusion couple and the change in the concentrations of Fe and Cr cations across the diffusion layers were analyzed using scanning electron microscopy and en-ergy dispersive spectroscopy.The self-diffusion coefficients of cations were calculated based on the concentration profiles of Fe and Cr,with the results indicating that the self-diffusion coefficient of the Fe ions was consistently higher than that of the Cr ions.Additionally,a mixture of Fe_(3)O_(4)and Cr_(2)O_(3)was annealed at 1373-1473 K for 1-5 h,and the kinetic parameters were calculated by studying the phase content of the product.The phase content of Fe(Cr_(x)Fe_(1-x))_(2)O_(4)in the product was determined by Rietveld refinement of X-ray diffraction data,revealing that an activation energy(E)of 177.20 kJ·mol^(-1) and a pre-exponential factor(B)of 610.78 min^(-1)of the solid-phase reac-tion that produced the Fe(Cr_(x)Fe_(1-x))_(2)O_(4)spinel.
文摘Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This study investigated hydrogen plasma smelting reduction as a novel,sustainable,and efficient method for producing stainless steel directly from lateritic nickel and chromite ores.The research aimed to examine the effect of ore proportion on AISI 300 series stainless steel production and assess the reduction process over time through thermochemical calculations and experimental studies.Results showed that increasing the proportion of chromite ore in the feed raises Cr content and reduces Ni content in metals while increasing Cr_(2)O_(3) and Al_(2)O_(3) content in oxides.A briquette comprising 30wt%chromite ore and 70wt%calcined nickel ore yields better results for AISI 300 stainless steel,with Fe,Cr,Ni,and Si content of 62.95wt%,19.37wt%,11.83wt%,and 0.72wt%,respectively,after 180 s of hydrogen plasma exposure.Nearly all NiO compounds are converted into Ni after 60 s of smelting reduction,whereas FeO compounds are almost fully converted into Fe after 120 s of smelting reduction.AISI 300 series stainless steel is successfully produced after 120 s of reduction,achieving Fe,Cr,Ni,and Si content of 64.36wt%,21.92wt%,10.08wt%,and 0.61wt%,respectively.Process optimization remains promising because the Cr_(2)O_(3) content in the slag is still relatively high at 15.52wt%.This ultrafast and direct production method holds considerable potential to transform stainless steel production by reducing environmental impact and enhancing process efficiency.Specifically,the method eliminates the use of an argon oxygen decarburization converter and vacuum oxygen decarburization in stainless steelmaking.
文摘Huang Shaoxian(1914-1989),born in Jimo County,Shandong Province in 1914.Huang Shaoxian graduated from the Department of Geology,Geography and Meteorology at the National Southwestern Associated University in 1940.He was elected as an academician of the Chinese Academy of Science in 1980 and served as Deputy Director and Senior Engineer at the Third Research Institute of the Ministry of Nuclear Industry.He achieved the first domestic discovery of chromite deposits in China,filling a critical gap in the nation's mineral resources.Dedicated to uranium resource exploration and scientific research throughout his career,he led the working group to achieve breakthroughs in exploration technologies for granite-type and carbon-siliceous-pelitic rock-type uranium deposits.As a pioneer and foundational figure in China's uranium geology,he made significant contributions to the development of the country's nuclear industry and uranium geology.
基金Project(2023XQLH055)supported by Central South University Graduate Research Innovation Project(University-Enterprise Joint Project),China。
文摘The high-carbon ferrochrome is an essential raw material for producing stainless steel,and the demand of it increases with the increase of stainless steel.So increasing Cr recovery rate from chromite is essential for lower costs and higher economic benefits in high-carbon ferrochrome production process.This study calculated the activity of CrO_(x)in slag and investigated the distribution behavior of Cr between slag and alloy.Theω(MgO)/ω(Al_(2)O_(3))was 1.0,and the w(CaO)/w(SiO_(2))was from 0.2 to 0.6 in this study.The calculation and experimental results showed that the main phases of the slag were chrome-containing spinel,magnesium-aluminum spinel,olivine and melilite.The content of spinel in slag decreased with the increasing w(CaO)/w(SiO_(2)),and the w(CrO_(x))in spinel also reduced,but the content of melilite increased.The distribution ratio of Cr between slag and alloy decreased with the increase of slag basicity at 1600℃,meansning that increasing the w(CaO)/w(SiO_(2))of slag can improve the recovery of Cr in chromite smelting process.
基金supported by the National Science Foundation of China(No.41827802)performed at GeoSoilEnviroCARS(Sector 13-ID-D)+3 种基金Advanced Photon Source(APS),Argonne National Laboratory(ANL)supported by the National Science Foundation-Earth Sciences(No.EAR-1634415)the Department of Energy,Geosciences(No.DE-FG02-94ER14466)APS is supported by DOE-BES(No.DE-AC02-06CH11357).
文摘The podiform chromitites in the Luobusha ophiolite have been thought to experience a very deep formation,but the maximum depth is still an open issue.Here,we have investigated the structural stability of natural magnesiochromite using the synchrotron-based powder X-ray diffraction and diamond anvil cells up to 48.6 GPa and 2450 K.The results have shown that spinel-type magnesiochromite first decomposes into corundum-type‘Cr_(2)O_(3)’+B1-type‘MgO’at 11–14 GPa and 1250–1450 K,then modified ludwigite(mLd)-type‘Mg_(2)Cr_(2)O_(5)’+corundum-type‘Cr_(2)O_(3)’at 14.3–20.5 GPa and 1300–2000 K,and finally CaTi_(2)O_(4)-type phase at 24.5 GPa.During the quenching procession from high-temperature-pressure conditions,the mLd-type phase appeared again and was kept at ambient conditions.We also obtained the isothermal equation states of spinel-type and CaTi_(2)O_(4)-type phases,revealing the composition effect on their elasticities.Based on the updated results,we propose chromitites could not experience pressure exceeding∼14.3 GPa(approximate maximum depth∼400 km)in the subduction-recycling genesis model.
文摘Mineralogical characterization and liberation of valuable minerals are primary concerns in rnineml processing industries. The pre- sent investigation focuses on quantitative mineralogy, elemental deportment, and locking-liberation characteristics of the beneficiation of tailings from a chrome ore beneficiation plant in the Sukinda region, Odisha; methods used for the study of the beneficiated tailings are QEMSCAN~, X-ray diffraction （XRD）, and mineral chemistry by a scanning electron microscope equipped with an energy-dispersive spec- trometer （SEM-EDS）. The tailing sample was fine grained （69.48wt% below 45 μm size）, containing 20.25wt% Cr203 and 39.19wt% Fe203, with a Cr：Fe mass ratio of 0.51. Mineralogical investigations using QEMSCAN studies revealed that chromite, goethite, and gibbsite are the dominant mineral phases with minor amounts of hematite, kaolinite, and quartz. The sample contained 34.22wt% chromite, and chromite liberation is more than 80% for grains smaller than 250 ~tm in size. Based on these results, it was predicted that liberated chromite and high-grade middling chromite particles could be separated from the gangue by various concentration techniques. The tailing sample was beneficiated by hydrocyclone, tabling, wet high-intensity magnetic separation （WHIMS）, and flotation in order to recover the chromite. A chromite concentrate with 45.29wt% Cr203 and a Cr：Fe mass ratio of 1.85 can be produced from these low-grade chromite ore beneficiation plant rejects.
基金supported by the US National Science Founda-tion (Nos. 02-07886, 01-25925)awarded to Timothy M Kusky, the National Natural Science Foundation of China (Nos. 49832030, 40821061)+1 种基金the Peking University Project (No. 985)the Ministry of Education of China (No. B07039) awarded to Li Jianghai
文摘Understanding Archean crustal and mantle evolution hinges upon identification and characterization of oceanic lithosphere. We report and update here more than 10 years work on a complete, yet dismembered and metamorphosed Archcan ophiolite sequence in the North China craton, in the Dongwanzi （东湾子）-Zunhua （遵化） structural belt and correlatives in the Wutaishan （五台山） area. Banded iron formation structurally overlies several tens of meters of variably deformed pillow lavas, mafic flows, and picritic amphibolites. These are in structural contact with a 2 km thick mixed gabbro and dike complex with gabbro screens, exposed discontinuously along strike for more than 20 km. The dikes consist of metamorphosed diabase, basalt, Hb-Cpx-gabbro, and pyroxenite. The dike/gabbro complex is underlain by several kilometers of mixed isotropic and foliated gabbro, which preserve compositional layering approximately 2 km below the dike complex, and then over several hundred meters merge into strongly compositionally layered gabbro and olivine-gabbro. The layered gabbro becomes mixed with layered pyroxenite/gabbro marking a transition zone into emulate ultramaflc rocks including serpentinzed dunite, pyroxenite and wehrlite, and finally into strongly deformed and serpentinized olivine and orthopyroxene-bearing ultraInafic rocks interpreted as depleted mantle harzburgite tectoultes. A U/Pb zircon age of 2.505 Ga from gabbro of the Dongwanzi ophioUte makes it one of the world＇s oldest recognized, laterally. extensive complete ophiolite sequences, though older dismembered ophiolites are recognized in South Africa and Greenland, extending back to 3.8 Ga. This age is confirmed by a ca. 2.6 Ga Re-Os isochron from chromites from the belt, and a number of dated 2.5-2.4 Ga cross-cuttlng younger igneous units. The Dongwanzi ophiolite is one of the largest well-preserved greenstone belts in the central orogenic belt that divides the North China craton into eastern and western blocks. More than 1 000 other fragments of gabbro, pillow lava, sheeted dikes, harzburgite,and podiform-chromite bearing dunite occur as tectonic blocks （tens to hundreds of meters long） in a biotite-gneiss and BIF matrix, intruded by tonalite and granodiorite, in the Zunhua structural belt. Blocks in this metamorphosed Archcan ophiolitic melange preserve deeper levels of oceanic mantle than the Dongwanzi ophiolite. The ophiolite-related melange marks a suture zone across the North China craton, traced for more than 1 600 km along the central orogenic belt. Many of the chromitite bodies are localized in dunite envelopes within harzburgite tectonite, and have characteristic nodular and orbicular chromite textures, known elsewhere only from ophiolites. The chromites have variable but high chrome numbers （Cr/（Cr＋Al）=0.74-0.93） and elevated P, also characteristic of suprasubduction zone ophiolites. The high chrome numbers, coupled with TiO2〈0.2 wt.% and V2O5〈0.1 wt.% indicate high degrees of partial melting from a very depleted mantle source and primitive melt for the chromite. A Re-Os isochron from the chromites indicates an age of 2.6 Ga, showing that they are the same age as the Dongwanzi ophiolite. The range in initial Os isotopic compositions in the chromites in these ophiolitic blocks is small and well within the range seen in modern ophiolites. The ultramafic and ophiolitic blocks in the Zunhua melange are therefore interpreted as dismembered and strongly deformed parts of the Dongwanzi ophiolite. We suggest the name ＂Dongwanzi-Zunhua ophiolite belt＂ for these rocks. Geochemical and structural features of the Dongwanzi ophiolite suggest that it formed in a forearc environment and was incorporated in an accretionary prism soon after it formed. Neoarchean and Paleoproterozoic （2.50 and 1.90 Ga） high-pressure granulites form a belt more than 700 km long along the western side of the central orogenic belt. Several Neoarchean sedimentary basins consisting of conglomerate, greywacke, and shale are located along the eastern side of the central orogenic belt, and are interpreted as remnants of a foreland basin. The three belts record the Neoarchcan subduction and collision between an arc terrane and eastern blocks of the North China craton in the Neoarchean, and further deformation and metamorphism in the Paleoproterozoic related to collisions on the northern margin of the already amalgamated North China craton.
基金funded by National Natural Science Foundation of China (Grant No.40930313)the China Geological Survey (Grants No.12120114061801+1 种基金 No.12120114057701 and No.12120114061501)
文摘Listwanite from the Luobusa ophiolite, Tibet, forms a narrow, discontinuous band along the eastern part of the southern boundary fault. We undertook a detailed petrographic and geochemical study to understand the mineral transformation processes and the behaviour of major and trace elements during listwanite formation. Three alteration zones characterized by distinct mineral components and texture are recognized and, in order of increasing degree of alteration, these are： zonem is rich in serpentine minerals; zonen is rich in talc and carbonates; and zone_Ⅰ is mainly composed of carbonates and quartz. Geochemical data for the three alteration zones show significant modification of some major and trace elements in the protolith, although some oxides show linear correlations with MgO. Gold mineralization is recognized in the Luobusa listwanite and may signify an important target for future mineral exploration. Gold enrichment occurs in both zone_Ⅰ and zone_Ⅱ and is up to 0.91 g/t in one sample from zonei. We show that CO_2-rich hydrothermal fluids can modify both the occurrence and composition of chromite grains, indicating some degree of chromite mobility. Low-Cr anhedral grains are more easily altered than high-Cr varieties. The compositions of chromite and olivine grains in the listwanite suggest a dunite protolith.
基金Project(2009FJ1009) supported by the Major Science and Technology Program of Hunan Province,China
文摘To explicate the thermodynamics of the chromite ore lime-free roasting process, the thermodynamics of reactions involved in this process was calculated and the phrases of sinter with different roasting times were studied. The thermodynamics calculation shows that all the standard Gibbs free energy changes of the reactions to form Na2CrO4, Na2O-Fe2O3, Na2O·Al2O3 and Na2O3 SiO2 via chromite ore and Na2CO3 are negative, and the standard Gibbs free energy changes of the reactions between MgO, Fe2O3 and SiO2 released from chromite spinel to form MgO-Fe2O3 and MgO·SiO2 are also negative at the oxidative roasting temperatures （1 173 1 473 K）. The phrase analysis of the sinter in lime-free roasting process shows that Na2O·Fe2O3, Na2O·Al2O3 and Na2O·SiO2 can be formed in the first 20 min, but they decrease in contents and finally disappear with the increase of roasting time. The final phase compositions of the sinter are Na2CrO4, MgO·Fe2O3, MgO·SiO2 and MgO. The results indicate that Na2CrO4 can be formed easily via the reaction ofNa2CO3 with chromite ore. Na2O·Fe2O3, Na2O-Al2O3 and Na2O·SiO2 can be formed as intermediate compounds in the roasting process and they can further react with chromite ore to form Na2CrO4. MgO released from chromite ore may react with iron oxides and silicon oxide to form stable compounds of MgO·Fe2O3 and MgO·SiO2, respectively.
基金supported financially by the National Natural Science Foundation of China (Grant No. 40472025, 40620120098,40872043)
文摘A new mineral species, named naquite（FeSi）, is found in the podiform chromitites of the Luobusha ophiolite in Qusong County, Tibet, China. The detailed composition is Fe 65.65, Si 32.57 and Al 1.78 wt%. The mineral is cubic, space group P213. The irregular crystals range from 15 to 50 μm in diameter and form an intergrowth with luobusaite. Naquite is steel grey in color, opaque, with a metallic lustre and gives a grayish-black streak. The mineral is brittle, has a conchoidal fracture and no apparent cleavage. The estimated Mohs hardness is 6.5, and the calculated density is 6.128 g/cm3. Unit-cell parameters are a 4.486 （4） A, V 90.28 （6）A^3, Z=4. The five strongest powder diffraction lines [d inA（hkl） （I/I0）] are： 3.1742 （110） （40）, 2.5917（111） （43）, 2.0076 （210） （100）, 1.8307 （211） （65）, and 1.1990 （321） （36）. Originally called ＇fersilicite＇, the species and new name have now been approved by the CNMNC （IMA 2010-010）.
基金Project(2009AA06XK1485430) supported by the National Hi-tech Research and Development Program of ChinaProject(2007CB613501) supported by the National Basic Research Program of China
文摘Mechanical activation was used to improve the extraction of chromium in molten NaOH.It is observed that the extraction ratio reaches 97% after leaching for 200 min when chromite ore is mechanically activated for 10 min,but only 34% if not activated.Mechanical activation can decrease the particle size,increase the surface area,and enhance the lattice distortion.Further,the mechanisms for mechanical activation were exposed.The results show that the mechanical activation mainly focuses on chromite ore particle size decrease and the lattice distortion.The formation of aggregation weakens the strengthening effect of mechanical activation for releasing high surface energy.
基金financially supported by the National Natural Science Foundation of China (Grant No.41262002,40930313,41302052,41502062)National Industry Special Projects (Sino Probe-05-02)+2 种基金China Bureau of Geological Survey Projects (DD20160023-01)IGCP-649Institute of Geology, Chinese Academy of Geological Science (J1526)
文摘Voluminous platinum-group mineral （PGM） inclusions including erlichmanite （Os,Ru）S2, laurite （Ru,Os）S2, and irarsite （Ir, Os,Ru,Rh）AsS, as well as native osmium Os（Ir） and inclusions of base metal sulphides （BMS）, including millerite （NiS）, heazlewoodite （NiaS2）, covellite （CuS） and digenite （Cu3S2）, accompanied by native iron, have been identified in chromitites of the Zedang ophiolite, Tibet. The PGMs occur as both inclusions in magnesiochromite grains and as small interstitial granules between them; most are less than 10 ~m in size and vary in shape from euhedral to anhedral. They occur either as single or composite （biphase or polyphase） grains composed solely of PGM, or PGM associated with silicate grains. Os-, Ir-, and Ru-rich PGMs are the common species and Pt-, Pd-, and Rh-rich varieties have not been identified. Sulfur fugacity and temperature appear to be the main factors that controlled the PGE mineralogy during crystallization of the host chromitite in the upper mantle. If the activity of chalcogenides （such as S, and As） is low, PGE clusters will remain suspended in the silicate melt until they can coalesce to form alloys. Under appropriate conditions of fS2 and fO2, PGE alloys might react with the melt to form sulfides-sulfarsenides. Thus, we suggest that the Os, Ir and Ru metallic clusters and alloys in the Zedang chromitites crystallized first under high temperature and low fS2, followed by crystallization of sulphides of the laurite-erlichmanite, solid-solution series as the magma cooled and fS2 increased. The abundance of primary BMS in the chromitites suggests that fS2 reached relatively high values during the final stages of magnesiochromite crystallization. The diversity of the PGE minerals, in combination with differences in the petrological characteristics of the magnesiochromites, suggest different degrees of partial melting, perhaps at different depths in the mantle. The estimated parental magma composition suggests formation in a suprasubduction zone environment, perhaps in a forearc.
