Fractionation characteristics of magnesium isotope in the ancient weathering crust

Weathering has always been a concerned around the world,as the first and most important step in the global cycle of elements,which leads to the fractionation of isotopes on the scale of geological age.The Middle Ordovician Majiagou Formation in Daniudi area of the Ordos Basin had experienced weathering for>130 Myr.Through thin section observation,major and trace element analysis,carbon,oxygen,and magnesium isotopes composition analysis,the dolomitization modes and weathering of ancient dolo-mite in Daniudi area were analyzed in detail.The results showed that the Sabkha and brine-reflux dolomitization modes had developed,and the Mg isotopes in different layers of the karst crust were fractionated by various factors.The vertical vadose zone was affected by weathering,the Mg isotope of dolomite(δ^(26)Mgdol)showed a downward decreasing trend;the horizontal underflow zone was controlled by diagenesis and formation fluid,δ^(26)Mgdol showed a vertical invariance and negative;the main reason for Mg isotope fractionation in the deep slow-flow zone was the brine-reflux dolomitization mode during early burial period,which showed a vertical downward increase.Finally,the Mg isotope characteristic data of the ancient weathering crust were provided and the process of Mg isotope frac-tionationinthekarstcrust was explained.

Characteristics and identification of weathering crust of Pennsylvanian volcanic rocks in Shixi area,Junggar Basin

Based on drill core and thin section observation,major geochemical element analysis and con-ventional well log analysis,this study summarizes the characteristics and thickness of weathering crust of Pennsylvanian volcanic rocks(Carboniferous)in Shixi area,Junggar Basin.The weathering crust is identified and divided into three types according to the petrological characteristics and well log interpretations in Shixi area,and the isopach of weathering crust is mapped.The results show that:(1)With the increase of depth,the weathering weakens,and the rocks become less fractured with decreased porosity;(2)the weathering crust of the Upper Carboniferous volcanic rocks can be divided into strongly weathered and mildly weathered layers in Shixi area;(3)the weathering crust is relatively thicker in Dinan uplift and Shixi uplift.This study provides research basis for further evaluation of Upper Carboniferous volcanic reservoir,and will benefit for well location deployment and potential oilfield development in the Shixi area.

Effects of cementation on physical properties of clastic rock-originated weathering crust reservoirs in the Kexia region,Junggar Basin,NW China

Cements are widely developed in clastic rock-originated weathering crust(CWC)reservoirs in the Kexia region along the northwestern margin of the Junggar Basin and significantly affect reservoir physical properties and oil and gas distribution in this area.Focusing on the CWC reservoirs at the top of both the Permian Jiamuhe Formation and the Triassic Karamay Formation,this study analyzed the types and characteristics of cements in the reservoirs and explored their effects on reservoir physical properties based on thin sections,SEM images,XRD results,and tests of physical properties.The main results are as follows.The cements in the CWC reservoirs in Kexia region mainly consist of carbonate minerals(41.5%),clay minerals(27.8%)and zeolite minerals(30%),as well as small amount of siliceous minerals.Among them,the carbonate minerals are dominated by siderite and calcite,the clay minerals mainly include kaolinite,interstratified illite/smectite(I/S)and chlorite,and the zeolite minerals primarily comprise heulandite and laumontite.These different types of multiphase cements are generally paragenetic or associated and affect reservoir physical properties to different degrees.Specifically,the carbonate and clay cements of the early diagenetic stage reduced the reservoirs’average porosity from 21%to 15%.The dissolution of some carbonate and zeolite cements in the early A substage of the middle diagenetic stage restored the average porosity to 18%,and the cementation in the late A substage decreased the average porosity to 13%again,of which about 4%was reduced by carbonate cements.The average porosity of the CWC reservoirs gradually decreased to the current value of approximately 10%in the B substage of the middle diagenetic stage.The impact of cementation on the CWC reservoirs can reach as far as 70 m below the unconformity.Moreover,the types and contents of cements vary with their depth below the unconformity surface,leading to the development of multiple zones with high cement content and the differentiated oil and gas distribution.

A new type of rare earth elements deposit in weathering crust of Permian basalt in western Guizhou, NW China

A new type of rare earth elements （REEs） deposit was discovered from the gaolinite mudstone in the weathering crust of Permian basalt, Bijie region, western Guizhou, China. It contained ∑RE2O3 0.065%-1.086%. This type of REEs deposit was widely distributed with steady horizon and thickness of 3-4 m. The ore-bearing weathering crust （kaolinite） of the three discovered REEs deposits belonged to the third episode of the Emeishan basalt eruption. The new type of REEs deposit was suggested that basalt （tuff） weathering could lead to the enrichment of the rare earth elements. Therefore, it is of important economic significance to explore REEs deposits in the weathering crust of basalt （tuffs） in Yunnan, Guizhou, and Sichuan Provinces.

Fission Track Dating of Authigenic Quartz in Red Weathering Crusts of Carbonate Rocks in Guizhou Province

The Cenozoic evolution history of Guizhou Province, which is located on the southeastern flank of the Qinghai-Tibet Plateau, is unclear because of the lack of sedimentation records. The red weathering crusts widespread on the Yunnan-Guizhou Plateau may bear critical information about their evolution history. This work firstly determined the ages of four red weathering crusts in eastern, central and northern Guizhou. The material used in fission track dating is well-crystallized quartz occurring in many in-situ weathering crusts of carbonate rocks. The results showed that the fission track ages of quartz vary over a wide range from 1 to 25 Ma in the four profiles, significantly younger than the ages of the Triassic and Cambrian parent rocks. In combination with the evolution history of the regional geology during the period from 25 to 1 Ma, the ages of quartz can exclude the possibility that the origin of quartz has nothing to do with primary clastic minerals in parent rocks, authigenesis during diagenesis and hydrothermal precipitation or roplacement by volcanic activities. It is deduced that the well-crystallized quartz was precipitated from Si-rich weathering fluids during the weathering process of carbonate rocks. The recorded ages of quartz from the four profiles are consistent with the episodes of the planation surfaces on the Qinghai-Tibet Plateau, the forming stages of red soil in the tropics of South China, the tectonically stable periods in Guizhou, and the ages of weathering in other parts of the world during the Cenozoic era. That is to say, the ages of authigenic quartz dated by the fission track method are well feasible and credible.

The Identification and Modeling of the Volcanic Weathering Crust in the Yingcheng Formation of the Xujiaweizi Fault Depression, Songliao Basin

Through the analysis of core descriptions, well-logs, seismic data, geochemical data and structural settings of the volcanic rock of the Yingcheng Formation in the Xujiaweizi fault depression, Songliao Basin, and the geological section of the Yingcheng Formation in the southeast uplift area, this work determined the existence of volcanic weathering crust exists in the study area. The identification marks on the volcanic weathering crust can be recognized on the scale of core, logging, seismic, geochemistry, etc. In the study area, the structure of this crust is divided into clay layer, leached zone, fracture zone and host rocks, which are 5-118 m thick （averaging 27.5 m）. The lithology of the weathering crust includes basalt, andesite, rhyolite and volcanic breccia, and the lithofacies are igneous effusive and extrusive facies. The volcanic weathering crusts are clustered together in the Dashen zone and the middle of the Xuzhong zone, whereas in the Shengshen zone and other parts of the Xuzhong zone, they have a relatively scattered distribution. It is a major volcanic reservoir bed, which covers an area of 2104.16 km2. According to the geotectonic setting of the Songliao Basin, the formation process of the weathering crust is complete. Combining the macroscopic and microscopic features of the weathering crust of the Yingcheng Formation in Xujiaweizi with the logging and three-dimensional seismic sections, we established a developmental model of the paleo uplift and a developmental model of the slope belt that coexists with the sag on the Xujiaweizi volcanic weathering crust. In addition, the relationship between the volcanic weathering crust and the formation and distribution of the oil/gas reservoir is discussed.

Heterogeneity of Parent Rocks and Its Constraints on Geochemical Criteria in Weathering Crusts of Carbonate Rocks

Owing to the low contents of their acid-insoluble components, carbonate rocks tend to decrease sharply in volume in association with the formation of weathering crust. The formation of a 1 m-thick weathering crust would usually consume more than ten meters to several tens of meters of thickness of parent rocks. The knowledge of how to identify the homogeneity of parent rocks is essential to understand the formation mechanism of weathering crust in karst regions, especially that of thick-layered red weathering crust. In this work the grain-size analyses have demonstrated that the three profiles studied are the residual weathering crust of carbonate rocks and further showed that there objectively exists the heterogeneity of parent rocks in the three studied weathering crusts. The heterogeneity of parent rocks can also be reflected m geochemical parameters of major elements, just as the characteristics of frequency plot of grain-size distribution. Conservative trace element ratios Zr/Hf and Nb/Ta are proven to be unsuitable for tracing the heterogeneity of parent rocks of weathering crust, but its geochemical mechanism is unclear. The authors strongly suggest in this paper that the identification of the homogeneity of parent rocks of weathering crust in karst regions is of prime necessity.

Study on Microbes and Their Effects on Rare Earth Extraction in Weathering Crust of Granite

Microbes were cultured from the samples at various depths in a weathering profile of RE-bearing granite in Gonghe RE mine, Guangdong Province. The cultured microbes, existing at a depth of 0.2 similar to 12 in and being more plentiful within 3 in in the profile, include bacteria ( Bacillus, Enterobacter, Escherichia, Alkaligenes, Neisseria, Staphylococcus and anaerobic bacteria such as Clostridium), fungi ( Aspergillus niger, Aspergillus flavus, Penicillium, Mucor and Saccharomycete) and actinomyces. Experiments were made under room temperature by using solutions of the cultured microbes and their metabolites, compared with distilled water and the culture solution without microbes, to leach RE from the sample of the weathering crust. The results are shown by the experiments: (1) The mixed microbes cultured from the profile and their metabolites increase the quantity of RE leached from the sample and reduce the pH of the solutions. (2) The ability to leach RE from the sample varies with various microbes, decreasing in a sequence of fungi ( Mucor, saccharomycete, Aspegillus and Penicillium), zymotic bacilli (Enterobacter, Escherichia etc.), Staphylococcus, zymotic Bacillus, actinomyces and Alkaligenes. (3) The RE leached with bacteria is mainly related to the pH value of the solutions influenced by the metabolites of the bacteria; whereas that leached with fungi is mainly related to the adsorption and imbibition of RE by the fungi and the complexing of RE with their metabolites. (4) Compared with that leached with ammonium sulfate, the fractionation of the RE leached with microbes is characterized by higher delta (Ce), lower delta (Eu) and lower ratios of N-La/Sm and N-Gd/Yb . The result of the fractionation of RE accords with the distribution of RE in the various layers of a profile of weathering crust of granite in South China. The experimental results indicate that microbes and their metabolites should play a positive role in the mobilization, migration and fractionation of RE in the weathering crust in South China.

ON CHEMICAL WEATHERING OF WEATHERING CRUST AT THE GREAT WALL STATION REGION, ANTARCTICA

The chief aim of this study is to investigate the chemical weathering process of the weathering crust in Great Wall Station region of China (in Fildes Peninsula), Antarctica by the method of sedimentology.CW,SW,GW,TW,WE weathering crusts developed on volcanic clastic rock, gray aptitic basalt with tuff or basaltic bedrock. On change of minerals, geochemical behaviors of elements, migration and enrichment regularities of elements, Correlation between element geochemical behaviors, change of weathering potential of rocks in chemical weathering process are studied by us.We can see that the sequence fo weathering strengths of the abovementioned sections, from high to low, should reflected in TW, GW, CW and SWT and basical correspond with that calculated from the enrichment and differentiation indexes.

Hydrocarbon accumulation mechanism and structure of largescale volcanic weathering crust of the Carboniferous in northern Xinjiang,China

The Upper Carboniferous in northern Xinjiang, China was formed in a post-collisional depression and collapsed structural setting. Within the Upper Carboniferous, volcanic rocks and source rocks alternate over a wide region. At the end of the Carboniferous, these layers were uplifted by plate collisions and subsequently weathered and leached. Volcanic weathering and leaching led to the establishment of weathered crusts that can be divided into five layers. Corrosion and crumble zones in these layers form favorable reservoirs. Volcanic weathering crust formed in sub-aerially exposed paleogeomorphic areas; the five relatively continuous layers are generally preserved in paleogeomorphic lowland and slope regions, but the upper soil layer is usually absent in structurally higher parts of the rock record. The thickness of the weathered layer has a positive nonlinear ex- ponential relationship to the duration of weathering and leaching, and the dynamic equilibrium time of weathered crust is about 36.3 Ma. The thickest weathered layer （~450 m） is located in fracture zones. Weathered crusts are possible from a range of volcanic rocks with different lithologies, given sufficient time for weathering and leaching. The combination of volcanic weathered crust and source rocks results in three types of hydrocarbon accumulation models： （1） sequences of volcanic weathered crust interbedded with source rocks, （2） a quasi-layered weathered volcanic core located above source rocks, and （3） volcanic rocks associated with pectinate unconformities adjacent to source rocks. Each of these three types has the potential to form a giant stratigraphic reservoir of volcanic weathered crust. This knowledge has changed the traditional exploration model of searching for favorable lithologic and lithofacies zones in volcanic rocks, and has changed the viewpoint that the Carboniferous does not have the genetic potential to be the basement of the basin in northern Xinjiang. The concepts developed here are of great scientific significance and application for focusing oil and gas exploration on volcanic weathered crust. As such, the Paleozoic volcanic weathered crust in the midwestern part of China may possibly contain large-scale stratigraphic reservoirs and thus could be a new oil and gas exploration target in the future.

Paleogeomorphy evolution of the Ordovician weathering crust and its implication for reservoir development,eastern Ordos Basin

Gas reservoir development of the Ordovician weathering crust in the Ordos Basin is closely controlled by the pre-Carboniferous paleogeomorphy.Previous studies show that the paleogeomorphy is high in the west and low in the east,and the karst highland,karst slope and karst basin are developed from west to east.With further exploration in recent years,many karst breccia that represent strong karstification,are found in the east area which previously is considered to be the Ordovician karst basin.Thus,it is necessary to revaluate controlling factors of karst paleogeomorphy development from a viewpoint of the dynamic paleogeomorphy evolution,to investigate the paleogeomorphy evolution of the Ordovician weathering crust in geological history and guide further research and prediction of development law of reservoir spaces.In order to reconstruct the paleogeomorphy of the weathering crust in the top of Ordovician in the east Ordos Basin,paleogeography,thickness of residual strata and paleokarst characteristics are well studied.The result shows that a wide range of paleokarst highland occurred in the central to east part of Ordos Basin in the early period,and the karst reservoir spaces were formed;but in the late period,the east part of the basin gradually evolved into the paleokarst basin,the current pre-Carboniferous paleogeomorphy was thus formed,and the dissolution reservoir spaces formed in the early period were mostly filled,accordingly the reservoirs were tight.However fracture networks formed by cave collapse connect intercrystalline pores of dolomite,therefore,the reservoirs can still be well preserved locally and are worthy targets for hydrocarbon exploration.

Compounding Pattern of REE， Clay and Humic Acid in the Weathering Crust of Granites

An anomalous phase containing clays and humic acid was found while extraction humic acid from samples of weathering crust of REE-bearing granites by using 0.1 mol/L NaOH solution.Studied by chemical separation experiments,column chromatography,ion-exchange chromatography,infrared spectrum.fluorescence spectrum,polarimicroscopic testing and elemental determination by ultraviolet-visible spectrometer and atomic absorption spectrometer.it was proved to be a compound of humic acid and clays which are connected in the form of bridge by heteronuclearpolynuclear complexing ions formed by cations of RE￣(5+),Al￣(3+).Fe￣(3+) etc.The compounding pattern was further proved by the experiment for compounding humic acid,REE and kaolinite.

Organic Metallogeny of Weathering Crust RE Deposit

A series of experimental geochemical studies have been done to confirm the organic metallogenic mechanism of weathering crust RE deposits. It has been concluded that: (1) Rich REbearing weathering crusts contain abundant organisms such as monoacids, diacids and nonacid compounds. Varieties and quantities of the organisms decrease from the upper to the lower of the profile. Humic acids are mainly fulvic acids, which are characterized by containing conjugated π system, carboxylic group, hydroxyl group and only a few nitrogenous groups. No obvious benzene ring has been found. (2) The upper part of the weathering crust contains a great deal of microorganisms, of which the varieties and quantities decrease from the upper to the lower of the profile. No microorganism has been found in the deep part of the profile. The microorganisms and their metabolites such as aminoacids, shortchain acids and organic compounds with small molecular weights can form water soluble RE complexes, which accelerate the RE transportation from original rocks and precipitation states to watersoluble states and thus provide prerequisites for retransportation and reaccumulation of RE. (3) Medium and longchain acids can form REnAm(OH)x(H2O)y type mixedligand polynuclear RE complexes, which devoted to the RE accumulation, whereas shortchain acids and aminoacids can form not only mixedligand complexes with RE, but also water soluble complex ions, which also devoted to the transport and accumulation of RE. (4) The fulvic acids are very soluble in water. They are apt to be mobile in the weathering crust and are able to form soluble complex ions and insoluble mixedligand polynuclear complexes with RE at normal temperature and atmospheric pressure and pH4～6. The composition of these complexes varies with different conditions of the weathering crust. (5) All the organic acids, fulvic acids and microorgaisms have contributed to keeping constant pH condition of the weathering crust. (6) Complexes consisting of clays, RE(Al, Fe……) and fulvic acids have been found in the weathering crust and a bonding pattern has been preliminarily studied. As a conclusion, the dissolution, transport and accumulaiton of REE during weathering is a organic and inorganic interacted process.

Quantitative characterization of vertical zonation of Mesozoic granite weathering reservoirs in the coastal area of eastern Fujian Province,China

Weathering crust reservoirs have obvious vertical zonation,which is the focus of weathering crust reservoir research,but there is a lack of quantitative characterization indexes.To achieve the quantitative characterization of granite weathering crust reservoir and provide the basis for oil exploration of granite weathering crust buried hill reservoir,in this paper,the vertical zonation of granite weathering crust reservoir is quantitatively divided by testing and analyzing the uniaxial compressive strength(UCS),magnetic susceptibility(MS),permeability,and chemical index of alteration(CIA)of the Mesozoic granite weathering crust in the coastal area of eastern Fujian.The results show that the granite weathering crust reservoir can be divided into four zones vertically:a soil zone(SZ),weathered and dissolved zone(WDZ),fracture zone(FZ),and bedrock zone(BZ).A cataclastic area is developed in the FZ and BZ,in which structural fractures are well-developed,the fracture surface density is usually greater than 200 m/m^(2),and the contribution to the fractures in the rock mass is up to about 50%,making this the sweet spot of the reservoir.In the SZ,the rocks are loose,and the pores are well-developed.The UCS is less than 10 MPa,and the average rate of change of the UCS(Δ_(σ))is 0.90.The average permeability is 2823.00 mD,and the average rate of change of the permeability(Δ_(κ))is 5.13.The average CIA is 74.9%.The average clay mineral content is 7%.The rocks in the WDZ have been significantly weathered by physical and chemical processes,and the weathering fractures and dissolution pores are well-developed.The average UCS is 18.2 MPa,and the averageΔ_(σ)is 0.70.The average permeability is 143.80 mD,and averageΔ_(κ)is 4.17.The average CIA is 65.3%.The average clay mineral content is 4%.Under the influence of tectonic movement and physical weathering,the rocks in the FZ have developed structural fractures and a few weathered fractures.The average UCS is 57.9 MPa,and the averageΔ_(σ)is 0.18.The average permeability is 5.50 mD,and the averageΔ_(κ)is 2.55.The average CIA is 61.6%.The average clay mineral content is 2%.In the BZ,the rocks are intact and hard.The average UCS is 69.9 MPa,and the average Ds is 0.13.The average permeability is 1.46 mD,and the averageΔ_(κ)is 1.43.The average CIA is 57.8%.The average clay mineral content is less than 1%.The multi-parameter combination of the UCS,Δ_(σ),permeability,Δ_(κ),CIA,and clay mineral content achieved good results in the division of the zones of the weathering crust.The UCS increases gradually from top to bottom,while Ds,permeability,Δ_(κ),CIA,and clay mineral content all decrease gradually.In addition,based on the petrophysical parameters of the rocks,including the density,resistivity,and acoustic velocity,a good division effect was also achieved,which can provide a basis for the vertical zonation of the granite buried-hill weathering crust reservoir.

Effect of surfactant addition on leaching process of weathered crust elution-deposited rare earth ores with magnesium sulfate

Surfactants were proposed to be added into magnesium sulfate solution to improve the leaching process of weathered crust elution-deposited rare earth ores(WREOs).Effects of surfactants and their concentration on the seepage of leaching solutions and the leaching efficiency of rare earth(RE)and aluminum(Al)were investigated,and the leaching kinetics,the mass transfer process,the adhesion work and the adhesion work reduction factor were analyzed to reveal its strengthening leaching mechanism.The results show that cetyltrimethylammonium bromide(CTAB)has a better strengthening effect on the leaching process than dodecyl trimethyl ammonium bromide(DTAB),sodium dodecyl sulfate(SDS),sodium oleate and oleic acid.In the presence of 0.04%CTAB in 0.2 mol/L solution,the permeability coefficient of WREOs increases from 0.945×10^(-5)to 1.640×10^(-5)cm·s^(-1),and the leaching efficiency of RE increases from 80%to 90%,confirming the promotion of surfactants on the leaching process of WREOs.Kinetic analysis shows that the leaching process conforms to the inner diffusion control model,and the leaching kinetics equations of RE and Al related to CTAB content are obtained.Mass transfer discussion shows a smaller height equivalent to theoretical plate(HETP)of RE and Al at CTAB content of 0.04%,suggesting the higher mass transfer efficiency here.According to the interfacial properties of leaching solutions,the calculated adhesion work and the adhesion work reduction factor further demonstrate the strengthening leaching effect of CTAB on the leaching process of WREOs.

Salt-Lake Basin Bedrock Weathered Crust Gas Reservoir in the Altun Mountains Front of the Qaidam Basin,Western China

The bedrock weathered crust in front of the Altun Mountains in the Qaidam Basin,western China,is different from others because this is a salt-lake basin,where saline water fluid infiltrates and is deposited in the overlying strata.A large amount of gypsum infills the bedrock weathered crust,and this has changed the pore structure.Using core observation,polarized light microscopy,electron probe,physical property analysis and field emission scanning electron microscopy experiments,the characteristics of the weathered bedrock have been studied.There are cracks and a small number of dissolved pores in the interior of the weathered crust.Matrix micropores are widely developed,especially the various matrix cracks formed by tectonics and weathering,as well as the stress characteristics of small dissolved pores,and physical properties such as porosity and permeability.This‘dual structure’developed in the bedrock is important for guiding the exploration of the lake basin bedrock for natural gas.

Effect of particle gradation on pore structure and seepage law of solution in weathered crust elution-deposited rare earth ores

Both CT and Avizo software were used to explore the effect of particle gradation on the evolution characteristics of pore structure and seepage paths in weathered crust elution-deposited rare earth ores during leaching.The results showed that the pore areas in four kinds of ore samples before leaching were mainly concentrated in 10^(4)–10^(7)μm^(2),whose pore quantities accounted for 96.89%,94.94%,90.48%,and 89.45%,respectively,while the corresponding pore volume only accounted for 30.74%,14.55%,7.58%,and 2.84%of the total pore volume.With the decrease of fractal dimension,the average pore throat length increased,but pore throat quantities,the average pore throat radius and coordination number decreased.Compared with that before leaching,the change degree of pore structure during leaching increased with the fractal dimension decreasing.For example,the reduction rate of the average coordination number of ore samples was 14.36%,21.30%,28.00%,and 32.90%,respectively.Seepage simulation results indicated that seepage paths were uniformly distributed before leaching while the streamline density and seepage velocity increased with the fractal dimension decreasing.Besides,the phenomenon of the streamline interruption gradually reduced during leaching while preferential seepage got more obvious with the decrease of the fractal dimension.

Ordovician reservoirs in Fuxian area:Gas accumulation patterns and their implications for the exploration of lower Paleozoic carbonates in the southern Ordos Basin

In recent years,the Fuxian area in the southeastern Ordos Basin has undergone significant exploration,with industrial gas flow tested in wells drilled into the Ordovician marine carbonates.Despite this,the gas accumulation patterns of this area are not fully understood,posing challenges for further exploration.Our analysis of geological conditions indicates that the Ordovician Majiagou Formation in this area hosts two gas plays:one found in weathering crusts and the other found in interior of the formation.We investigated various typical gas reservoirs in the area,focusing on differentiating the geological conditions and factors controlling gas accumulation in the weathering-crust and interior gas reservoirs.The results suggest three primary gas accumulation patterns in the Majiagou Formation in the Fuxian area:(1)upper gas accumulation in weathering crusts,present in the high parts of landforms such as residual paleo-hills or buried paleo-platform(Pattern I);(2)the stereoscopic pattern with gas accumulation in both weathering crusts and strata interior,arising in high parts of landforms such as residual paleo-hills or buried paleo-platforms(Pattern II);(3)lower gas accumulation in strata interior,occurring in the upper reaches and on both sides of paleo-trenches(Pattern III).This study will serve as a geological basis for future exploration deployment in the Fuxian area.

Column leaching process of rare earth and aluminum from weathered crust elution-deposited rare earth ore with ammonium salts

In order to better understand the leaching process of rare earth （RE） and aluminum （Al） from the weathered crust elutiondepositedRE ore, the mass transfer of RE and Al in column leaching was investigated using the chromatographic plate theory. Theresults show that a higher initial ammonium concentration in a certain range can enhance the mass transfer process. pH of leachingagent in the range of 2 to 8 almost has no effect on the mass transfer efficiency of RE, but plays a positive role in the mass transferefficiency of Al under strong acidic condition （pH〈4）. There is an optimum flow rate that makes the highest mass transfer efficiency.The optimum leaching condition of RE is the leaching agent pH of 4？8, ammonium concentration of 0.4 mol/L and flow rate of0.5 mL/min. The mass transfer efficiencies of RE and Al both follow the order： （NH4）2SO4〈NH4Cl〈NH4NO3, implying thecomplexing ability of anion.

Particle Size Distribution of Kaolinite and Halloysite in Weathering Products of Granite and Its Implications for Pedogenesis

The kaolins collected from a profile of weathered granite at Yichun County, Jiangxi Province have been subjected to particle size fractionation by the conventional sedimentation method and examined by XRD,SEM and TEM. All of them exhibit a mixture phase of poorly crystallized kaolinites and halloysites (0.7 nm) occurring as the main clay minerals. Electron micrographs reveal that plate kaolinites are the principal constitution in the coarse fraction, and more tubular and curled halloysite (0.7 nm) in the fine fraction. Both of them show normal probability curves in particle size distributions. The ratios of kaolinite and halloysite (0.7 nm) in different size fractions are examined by X-ray diffraction with a series of X-ray patterns characterized by three main peaks at d(001), d(002) and d(020),varying in intensity. Therefore, an index Qhm, expressed as (Id(001) + Id(002))/(2×Id(020)), is designed to indicate relative ratios of the two clay minerals in a number of mixture phases. Because kaolinite and halloysite (0.7nm) commonly occurred, respectively, in low and medium leaching microenvironment, the index Qhm can be used to indicate weathering and pedogenic.conditions of a weathering crust.