Chlorite cement and its effect on the reservoir quality of sandstones from the Panyu low-uplift,Pearl River Mouth Basin

Based on porosity and permeability measurements, mercury porosimetry measurements, thin section analyses, SEM observations, X-ray diffraction （XRD） analysis and granulometric analyses, diagenetic features of reservoir sandstones taken from the Zhuhai formation in the Panyu low-uplift of the Pear River Mouth Basin were examined. This study shows that chlorite cements are one of the most important diagenetic features of reservoir sandstones. The precipitation of chlorite was controlled by multiple factors and its development occurred early in eo-diagenesis and continued till Stage A of middle diagenesis. The precipitation of chlorite at the early stage was mainly affected by the sedimentary environment and provenance. Abundant Fe- and Mg-rich materials were supplied during the deposition of distributary channel sediments in the deltaic front setting and mainly in alkaline conditions. With the burial depth increasing, smectite and kaolinite tended to be transformed into chlorite. Smectite cements were completely transformed into chlorite in sandstones of the studied area. Volcanic lithics rich in Fe and Mg materials were dissolved and released Fe2＋ and Mg 2＋ into the pore water. These cations precipitated as chlorite cements in middle diagenesis in an alkaline diagenetic environment. Chlorite coatings acted as porosity and permeability, thus helping preserve cements in the chlorite cemented sandstones. The reservoir quality of chlorite cemented sandstones is much better than sandstones without chlorite cements. Chlorite cements play an important role in the reservoir evolution that was mainly characterized by preserving intergranular porosity and forming better pore-throat structures of sandstones.

Origin and controlling factors of chlorite coatings—an example from the reservoir of T_3x Group of the Baojie area,Sichuan Basin,China

The study of the chlorite coatings always attracts scholars in China and other countries because the chlorite coatings play an important role in the preservation of residual primary pores in sandstone reservoirs.At present,the study of the origin and the controlling factors is relatively few.The occurrence,time of formation,genesis,controlling factors,and the mechanism of chlorite coatings inhibiting quartz overgrowths were studied in detail with thin section and SEM analysis.Samples were from the sandstone reservoirs of the T3x Group in the Baojie area,the transitional zone from the middle to the south of Sichuan Basin.The results indicate that the chlorite coatings on the walls of the pore spaces are oriented perpendicular to grain surfaces in the form of isopachous(even-thickness) grain-coating,while the chlorite coatings at the contacts between adjacent detrital grains are arranged with a preferred orientation tangential to the surface of detrital grains.The chlorite coatings were formed in the eogenetic stage.They were formed by recrystallization of Fe-rich clay films during the syndepositional period,and chlorite cements would be recrystallized after the coatings’ formation.The formation of chlorite coatings was mainly controlled by the depositional environment,provenance conditions,and diagenetic environment.The presence of chlorite coatings could result in the preservation of primary pores in deeply buried sandstone reservoirs by effectively inhibiting quartz overgrowths and the development of compaction and pressure solution.

Investigation of methane adsorption on chlorite by grand canonical Monte Carlo simulations

In this paper, the methane adsorption behaviours in slit-like chlorite nanopores were investigated using the grand canonical Monte Carlo simulation method, and the influences of the pore sizes, temperatures, water, and compositions on methane adsorption on chlorite were discussed. Our investigation revealed that the isosteric heat of adsorption of methane in slit-like chlorite nanopores decreased with an increase in pore size and was less than 42 kJ/mol, suggesting that methane adsorbed on chlorite through physical adsorption. The methane excess adsorp- tion capacity increased with the increase in the pore size in micropores and decreased with the increase in the pore size in mesopores. The methane excess adsorption capacity in chlorite pores increased with an increase in pressure or decrease in pore size. With an increase in temperature, the isosteric heats of adsorption of methane decreased and the methane adsorption sites on chlorite changed from lower- energy adsorption sites to higher-energy sites, leading to the reduction in the methane excess adsorption capacity. Water molecules in chlorite pores occupied the pore wall in a directional manner, which may be related to the van der Waals and Coulomb force interactions and the hydrogen bonding interaction. It was also found that water molecules existed as aggregates. With increasing water content, the water molecules occupied the adsorption sites and adsorption space of the methane, leading to a reduction in the methane excess adsorption capacity. The excess adsorption capacity of gas on chlorite decreased in the following order： carbon dioxide 〉 methane 〉 nitrogen. If the mole fraction of nitrogen or carbon dioxide in the binary gas mixture increased, the mole fraction of methane decreased, methane adsorption sites changed, and methane adsorption space was reduced, resulting in the decrease in the methane excess adsorption capacity.

Formation mechanisms and sequence response of authigenic grain-coating chlorite: evidence from the Upper Triassic Xujiahe Formation in the southern Sichuan Basin, China

Authigenic grain-coating chlorite is widely distributed in the clastic rocks of many sedimentary basins around the world. These iron minerals were mainly derived from flocculent precipitates formed when rivers flow into the ocean, especially in deltaic environments with high hydrodynamic conditions. At the same time, sandstone sequences with grain-coating chlorites also tend to have relatively high glauconite and pyrite content. EPMA composition analysis shows that glauconites with ‘‘high Al and low Fe’’ content indicate slightly to semi-saline marine environments with weak alkaline and weakly reducing conditions. By analyzing the chlorite-containing sandstone bodies of the southern Sichuan Xujiahe Formation, this study found that chlorite was mainly distributed in sedimentary microfacies, including underwater distributary channels, distributary channels, shallow lake sandstone dams, and mouth bars. Chlorite had a tendency to form in the upper parts of sandstone bodies with signs of increased base level, representing the influence of marine（lacustrine）transgression. This is believed to be influenced by megamonsoons in the Middle and Upper Yangtze Region during the Late Triassic Epoch. During periods of abundant precipitation, river discharges increased and more Fe particulates flowed into the ocean（lake）. In the meantime,increases or decreases in lake level were only affected byprecipitation for short periods of time. The sedimentary environment shifted from weakly oxidizing to weak alkaline, weakly reducing conditions as sea level increased, and Fe-rich minerals as authigenic chlorite and glauconite began to form and deposit.

Selective depression action of taurine in flotation separation of specularite and chlorite

Chlorite,as the most representative gangue mineral associated with specularite,of which the separation of these two minerals is difficult.This paper investigated the depression effect of taurine on specularite/chlorite separation via flotation experiments,adsorption tests,contact angle measurements,Zeta potential detection,FT-IR measurements,and XPS analyses.The results of single mineral flotation indicated that chlorite could be depressed selectively by taurine with the recovery of less than 30%,but the floatability of specularite remains high with recovery rate of 81.77%at pH 10.The artificial mixed mineral flotation results confirmed the effectiveness of taurine as a depressant.Surface adsorption,contact angle,and Zeta potential detection revealed taurine primarily adsorbs on the chlorite surface,which hampered the DDA’s subsequent adsorption and results in the chlorite’s poor floatability.The FT-IR spectra and XPS analyses provided further proof that taurine adsorbed on chlorite surface as an electron donor,and part of the electrons transferred from the sulfonic acid group of taurine to metal ions during the adsorption process.In addition,the hydrogen bond between amino-group of taurine and O ions in chlorite surface was also formed in the adsorption process.Finally,optimized adsorption configurations of taurine on chlorite surfaces were proposed.

A novel, simple and sensitive resonance scattering spectral method for the determination of chlorite in water by means of rhodamine B

A new resonance scattering method was proposed for the determination of chlorite, basing on the resonance scattering effect of rhodamine dye. In HCl-sodium acetate buffer solution, chlorite oxidizes 1- into 12 and the reaction of 12 and excess 1- results in If. It is respectively combined with rhodaminc dyes, including rhodamine B （RhB）, butyl rhodamine B （b-RhB）, rhodamine G （RhG） and rhodamine S （RhS）, to form association complex particles, which exhibit stronger resonance scattering （RS） effect at 400 nm. The chlorite concentration of ClO2 in the range of 0.00726-0.218 μg/ml, 0.0102-0.292 μg/ml, 0.00726-0.145 μg/ml and 0.0290- 0.174 μg/ml is respectively linear to the RS intensity of association complex particle systems at 400 nm for the RhB, b-RhB, RhG and RhS. The detection limits of the four systems were respectively 0.00436, 0.00652, 0.00580 and 0.01450μg/ml ClO2^-. In the four systems, the RhB system possesses good stability and high sensitivity. It has been applied to the analysis of chlorite in wastewater with satisfactory results.

Geochemistry and Tectonic Significance of Chlorite Amphibolite in Nanfen BIF, Benxi Area, Northeastern China

Benxi area, Northeastern China, is the main distribution area of Archean BIF-hosted iron deposits in China. In this area, Nanfen iron deposit is well known as the largest open-pit iron deposit not only in China but also in Asia. So far, the tectonic nature during Archean BIF formation period in Benxi area has been long disputed and the tectonic setting of Nanfen BIF had not been found. In this study, the geochemical characters of chlorite amphibolites closely associated with BIF have been investigated for the tectonic environment of Nanfen BIF. Chlortie amphibolites show the geochemical affinity to the back-arc basin basalt (BABB), indicating that the tectonic environment of Nanfen BIF is the back-arc basin. In conjunction with geological evidence of other BIFs at Benxi area, it is identified that BIF in Benxi area might be formed in the subduction-related back-arc basin, which provides a favorable sedimentary environment of Algoma-type BIF.

Mineralogical Characteristics and Short-wave Infrared Spectra of Chlorite as Indicators of Hydrothermal Centers: A Case Study of the Giant Porphyry Copper-Molybdenum Deposit at Qulong, Tibet

The Qulong deposit in Tibet is one of the largest porphyry copper-molybdenum deposits in China. We used short-wave infrared(SWIR) spectroscopy to examine the spectral characteristics of the extensively developed chlorite in this deposit. X-ray diffraction and electron microprobe analyses were used for phase identification and to obtain the chemical composition, ion substitution relationships, and formation environment of the chlorite. SWIR spectral parameters were applied to detect the hydrothermal centers. The results indicate that the wavelength of the absorption feature for Qulong chlorite Fe-OH(Pos2250) range from 2240 to 2268.4 nm;the chlorite substitution relationships are dominated by Mg-Fe substitution at the octahedral sites together with Al;-Si substitution at the tetrahedral sites;the chlorite formation temperatures range within the medium-low temperature hydrothermal alteration range from 164 to 281°C, with an average value of 264℃;the wavelength of the chlorite peak position for Fe-OH(2250 nm) absorption and its chemical composition are positively correlated with Al^(Ⅵ), Fe + Al^(Ⅵ), Fe/(Fe + Mg), Fe, and Fe + Al^(Ⅳ)but negatively correlated with Mg and Mg/(Fe + Mg);and the wavelength associated with the chlorite Fe-OH(2250 nm) absorption feature is positively correlated with the temperature at which the chlorite formed. These correlations indicate that more Fe and Al^(Ⅵ) ions and fewer Mg ions at the octahedral sites of chlorite lead to a longer the wavelength of the chlorite Fe-OH(2250 nm) absorption feature and a higher chlorite formation temperature. The wavelength of the Qulong chlorite Fe-OH(2250 nm) absorption feature(>2252 nm) can thus serve as an exploration indicator to guide the detection of hydrothermal centers in porphyry copper deposits. The results of the study indicate that the mineralogical and SWIR spectral characteristics of chlorite are significant indicators for locating hydrothermal centers within porphyry deposits.

Antimicrobial Activity of Acidified Sodium Chlorite and Cell Free Culture Supernatent of Lactic Acid Bacteria against <i>Salmonella</i>Typhimurium

Most methods used by food industries to decontaminate eggs involve washing of egg surface with various chemicals. In this study, the effectiveness of two organic decontaminants viz., acidified sodium chlorite (ASC) and cell free culture supernatant (CFCS) of two lactic acid bacteria (Lactobacillus plantarum and Pediococcus cerevisiae) was evaluated for the decontamination of spiked Salmonella Typhimurium on chicken egg shell surface. Acidified sodium chlorite at 100 μl/L concentration with the contact time of 20 min completely inhibited S. Typhimurium on egg shell surface while at 50 μl/L concentration 1 - 2 log10 units reduction was observed in counts of S. Typhimurium as compared to control group. Likewise, CFCS of P. cerevisiae completely inhibited the growth of S. Typhimurium on 30 min contact, whereas L. plantarum and combination of both were revealed significant reduction in the counts of S. Typhimurium counts.

Magnesium isotopes of chlorite-rich hydrothermal sediments in the Okinawa Trough and indications for Mg cycle

Seafloor hydrothermal systems play a significant role in the oceanic Mg cycle due to ubiquitous deposits of secondary Mg-rich clays during the strong fluid-rock reactions.However,the magnitude of net Mg enrichment and Mg isotopic fractionation,particularly within the medium-high temperature hydrothermal systems in felsic-hosted settings,are not well studied yet.Here we report elemental and isotopic compositions of Mg in hydrothermal chlorite-rich sediments,volcanic materials,and terrigenous sediments collected during the IODP Expedition 331 drilled to the thick sediment-covered and felsic-hosted middle Okinawa Trough(Iheya North Knoll) in the West Pacific.We investigate the sources of Mg in chlorite and Mg isotopic behavior at medium-high temperature hydrothermal alteration.After 1 mol/L HCl leaching,Mg isotopic compositions of chlorite-rich sediments present overall similar values in the residual fractions and bulk samples albeit with slightly higher values in the leachates.Mineralogical differentiation primarily determines the Mg isotopic compositions,showing that siliciclastic residues have slightly higher δ^(26) Mg values than the leachates dominated by carbonates and oxides/hydroxides.Significant Mg isotopic fractionation happened in the medium-high temperature(~150°C to 260°C) felsic-hosted hydrothermal system,with Δ^(26)MgChl-SW ranging from 0.15‰ to 0.71‰ and yielding a negative correlation with temperature.This observation suggests the preferential incorporation of heavy Mg isotopes by the secondary chlorite precipitation.We infer that the medium-high temperature hydrothermal systems can take up about 8–14% of riverine input of Mg in the arc and back-arc regions.Incomplete removal of aqueous Mg in porewater and vent fluids by the medium-high temperature hydrothermal alterations in the arc and back-arc basins provides constraints on the Mg budget and isotopic composition of seawater.

Iron species activating chlorite:Neglected selective oxidation for water treatment

Chlorite(ClO_(2)-)is the by-product of the water treatment process carried out using chlorine dioxide(ClO_(2))as an effective disinfectant and oxidant;however,the reactivation of ClO_(2)
has commonly been overlooked.Herein,it was unprecedentedly found that ClO_(2)
could be activated by iron species(Feb:Fe0,FeII,or FeIII),which contributed to the synchronous removal of ClO_(2)
and selective oxidative treatment of organic contaminants.However,the above-mentioned activation process presented intensive Ht-dependent reactivity.The introduction of Feb significantly shortened the autocatalysis process via the accumulation of Cl
or ClO
during the protonation of ClO_(2)
driven by ultrasonic field.Furthermore,it was found that the interdependent high-valent-Fe-oxo and ClO_(2),after identification,were the dominant active species for accelerating the oxidation process.Accordingly,the unified mechanisms based on coordination catalysis([FeN(H_(2)O)a(ClOxm)b]nt-P)were putative,and this process was thus used to account for the pollutant removal by the Feb-activated protonated ClO_(2).This study pioneers the activation of ClO_(2)
for water treatment and provides a novel strategy for“waste treating waste”.Derivatively,this activation process further provides the preparation methods for sulfones and ClO_(2),including the oriented oxidation of sulfoxides to sulfones and the production of ClO_(2) for on-site use.

Evolution of chlorite composition in the Paleogene prototype basin of Jiyang Depression, Shandong, China, and its implication for paleogeothermal gradient

The Dongying Basin, Huimin Basin, and Zhanhua Basin constitute the Jiyang Depression in Shandong Province. They are major oil and gas exploring districts within the depression. Through reconstruc-tions of the paleotemperature of the three basins facilitated with the chlorite geothermometry, the thermal history of the Paleogene prototype basin in Jiyang Depression and its geologic significance were explored. This study reveals that the Si4+ component in chlorites reduces gradually as its buried depth increases, while the AlIV component increases accordingly. The chlorite type changes from sili-con-rich diabantite to silicon-poor ferroamesite and prochlorite. The prochlorite in this district only appears in the deep buried depth, high temperature, and relatively old stratigraphies; while the diaban-tite appears in the shallower buried, low temperature, and newly formed strata; the ferroamesite exists in the conditions between prochlorite and diabantite formation. The diagenetic temperatures of the chlorites in these Paleogene basins are 171―238℃ for the Dongying Basin, 160―202℃ for the Huimin Basin, and 135―180℃ for the Zhanhua Basin. The differences of the chlorite diagenetic temperatures in the three basins were controlled by the duration time of the structural depressing processes. Higher temperature indicates longer depression time. The relationship between the chlorite diagenetic temperature and its buried depth indicates that the average paleogeothermal gradient is about 38.3℃ /km in the Paleogene prototype basin of Jiyang Depression. It was higher than the present geothermal gradient (29―30℃/km). This phenomenon was attributed to the evolution of the structural dynamics in the depression basin.

Effects of reductive inorganics and NOM on the formation of chlorite in the chlorine dioxide disinfection of drinking water

Chlorine dioxide(ClO_(2))disinfection usually does not produce halogenated disinfection byproducts,but the formation of the inorganic by-product chlorite(ClO^(–)_(2))is a serious consideration.In this study,the ClO^(–)_(2)formation rule in the ClO_(2)disinfection of drinking water was investigated in the presence of three representative reductive inorganics and four natural organic matters(NOMs),respectively.Fe^(2+)and S^(2–)mainly reduced ClO_(2)to ClO^(–)_(2)at low concentrations.When ClO_(2)was consumed,the ClO^(–)_(2)would be further reduced by Fe^(2+)and S^(2–),leading to the decrease of ClO^(–)_(2).The reaction efficiency of Mn^(2+)with ClO_(2)was lower than that of Fe^(2+)and S^(2–).It might be the case that Mn O 2 generated by the reaction between Mn^(2+)and ClO_(2)had adsorption and catalytic oxidation on Mn^(2+).However,Mn^(2+)would not reduce ClO^(–)_(2).Among the four NOMs,humic acid and fulvic acid reacted with ClO_(2)actively,followed by bovine serum albumin,while sodium alginate had almost no reaction with ClO_(2).The maximum ClO^(–)_(2)yields of reductive inorganics(70%)was higher than that of NOM(around 60%).The lower the concentration of reductive substances,the more ClO^(–)_(2)could be produced by per unit concentration of reductive substances.The results of the actual water samples showed that both reductive inorganics and NOM played an important role in the formation of ClO^(–)_(2)in disinfection.

Impact of chlorites on the wettability of tight oil sandstone reservoirs in the Upper Triassic Yanchang Formation,Ordos Basin,China

Wettability is an essential property of reservoirs that is of great importance for enhancing oil recovery(EOR)and oil migration.The wettability of reservoirs is generally believed to be strongly affected by mineral compositions but it is not always the case.An integrated study of petrography and wettability was carried out to determine the impact of chlorite minerals on the wettability of the sandstone reservoirs in the Upper Triassic Yanchang Formation.Chlorites are found to be commonly present in the reservoir sandstones as detrital grains,rim-shaped cements,and biotite-chloritized forms with the pore peripheries being largely coated by chlorite,which is the main mineral in direct contact with pores.At pore scale,the wetting state of chlorites can either be oil-wet or water-wet in the tight sandstone reservoirs depending on wettability alteration by oil charge.Chlorites in contact with pores occupy a large of proportions of oil-wet pore walls and are crucial for the formation of oil-wetting state of reservoir sandstones.At core scale,the contents of chlorites in direct contact with pores do not correlate well with the AmottHarvey index due to other factors such as heterogeneity,oil-bearing degrees of samples.

THE ELECTRON MICROSCOPY STUDY ON THE MIXED LAYER OF ILLITE AND CHLORITE

Clay minerals having the same type of octahedral layer commonly occur as mixed layers. With the application of electron microscopy in day mineralogy, it is recognized that clay minerals which have different octahedral sheets can also form mixed layers, such as the mixed layer of illite and chlorite which has been well studied. However, there are different opinions on its origin. Based on the study of transmission electron microscopy (TEM)

A novel co-catalyzed system between persulfate and chlorite by sonolysis for removing triphenylmethane derivative

Triphenylmethane(tpm) derivatives(e.g. tpm CV) have threatened the safety of the aquatic environment due to the potential toxicity and carcinogenicity. In this study, the novel ultrasonic/persulfate/chlorite(US/S_(2)O_(8)^(2-)/ClO_(2)^(-)) oxidation process was developed for the effective removal of tpm CV in wastewater. The apparent non-integer kinetics( n around 1.20) of tpm CV degradation under different factors( R^(2)_(Adj) > 0.990) were investigated, respectively. Inhibiting effects of anions were greater than those of cations(except Fe(Ⅱ/Ⅲ)). The adding of micromolecule organic acids could regulate degradation towards positive direction. The double response surface methodology(RSM) was designed to optimize tpm CV removal process, and the acoustic-piezoelectric interaction was simulated to determine the propagation process of acoustic wave in the reactor. The possible degradation pathway was explored to mainly include carbonylation, carboxylation, and demethylation. The estimated effectivemean temperature at the bubble-water interface was calculated from 721 to 566 K after introducing the ClO_(2)^(-), however, the adsorption or partitioning capacity of tpm CV in the reactive zone was widened from 0.0218 to 0.0982. The proposed co-catalysis of US/S_(2)O_(8)^(2-)/ClO_(2)^(-)was based on the determined active species mainly including ClO_(2), SO_(4)·^(-), and ·OH. Compared with other US-based processes, the operating cost(3.97 $/m^(3)) of US/S_(2)O_(8)^(2-)/ClO_(2)^(-)with the EE/O value(16.8 k Wh/m^(3)) was relatively reduced.

Study on the removal of NO_x from simulated flue gas using acidic NaClO_2 solution

The study on the removal of NOx from simulated flue gas has been carded out in a lab-scale bubbling reactor using acidic solutions of sodium chlorite. Experiments were performed at various pH values and inlet NO concentrations in the absence or presence of SO2 gas at 45℃. The effect of SO2 on NO oxidation and NO2 absorption was critically examined. The oxidative ability of sodium chlorite was investigated at different pH values and it was found to be a better oxidant at a pH less than 4. In acidic medium, sodium chlorite decomposed into C102 gas, which is believed to participate in NO oxidation as well as in NO2 absorption. A plausible NOx removal mechanism using acidic sodium chlorite solution has been postulated. A maximum NOx removal efficiency of about 81% has been achieved.

Authigenic clay minerals and calcite dissolution influence reservoir quality in tight sandstones:Insights from the central Junggar Basin,NW China

Authigenic clays and calcite cements are important in the development of reservoir tightness and the formation of hydrocarbon sweet spots.We investigated Jurassic low-permeability sandstone reservoirs in the central Junggar Basin,NW China,using petrography,mineralogy,porosity,and permeability assessment,and stable C and O isotope analysis to ascertain the influence of authigenic clays and calcites on reservoir quality.Here,we establish the properties and diagenetic processes of the reservoir sandstones,and construct a generalizable model of reservoir quality.The results show that the sandstones are mainly litharenite and feldspathic litharenite and can be classified into ductile-lithic-rich sandstones and ductile-lithic-poor sandstones according to rock composition.The ductile-lithic-rich sandstones are tight(mean porosity?7.31%;mean permeability?0.08 mD)as a result of intense compaction.In contrast,the ductile-lithic-poor sandstones can be classified into five types according to diagenetic process.The formation of favorable hydrocarbon reservoir properties is closely related to the presence of authigenic clays and dissolution of calcite.In particular,kaolinite fills intergranular pores,thereby blocking pore space and reducing reservoir quality.Chlorite coating resists compaction and limits the formation of quartz overgrowths,thereby preserving pore space and enhancing reservoir quality.Calcite controls reservoir quality through both precipitation and dissolution.Calcite precipitation results in reduced reservoir quality,whereby early calcites that were precipitated in formation water resist compaction and provide the basis for subsequent dissolution and late precipitation,whereas dissolution of calcite in mesodiagenesis improves reservoir quality.A generalized model is formulated by relating diagenetic facies types to depth and porosity,providing a reference for other similar reservoirs.Our data suggest that deeply buried tight sandstones can be exploration prospects under favorable conditions involving the presence of authigenic clays and dissolution of calcite,as in the central Junggar Basin of this study.

Experimental Study of Dissolution-Alteration of Amphibole in a Hydrothermal Environment

Amphibole is a rock-forming mineral widely existing on the earth.It is easily dissolved and altered during the later stage of diagenesis and mineralization,and often forms chloritization,which is an important indicator for prospecting.To explore amphibole's dissolution process and alteration mechanism,dissolution experiments were carried out under acidic conditions using pargasite-rich amphibole as raw material,and the effects of temperature,p H,and experiment duration on amphibole alteration were investigated.Experimental samples and products were analyzed using X-ray diffractometer,field emission scanning electron microscope,electron probe micro analyzer,and transmission electron microscopy.It was found that many pores and erosion edges are produced after amphibole dissolution,and there is a clear interface between the dissolved residual portion and the parent.The dissolved residual portion remains in the amphibole phase,but as the temperature and time increase,the intensity of the diffraction peak of the phase in the product decreases,and the peak position shifts to a small angle.Many clay minerals such as chlorite and griffithite formed on the amphibole surface.In an environment with strong acidity(p H=3),the amount of chamosite increases with temperature(180℃→210℃→240℃),whereas clinochlore is only increased in a 150–210℃environment.Griffithite growth was observed in the acidic(p H=6)and low temperature(<180℃)environments.Based on this analysis,large radius Cl–enters the amphibole lattice or cracks to promote dissolution.The Al-poor and Ca-and Fe-rich regions between the edge and core of the amphibole are caused by dynamic equilibrium in amphibole dissolution and alteration process,which is an essential indicator for the beginning of amphibole dissolution-alteration.Diffusion and the coupled dissolution-reprecipitation mechanism accomplishes the process of dissolution and alteration to form clay minerals.The energy of the system determined by temperature and p H is the key to controlling the rate of growth and nucleation of clay minerals.High temperature and strong acidity will dissolve more iron from amphibole,which is conducive to chlorite growth.Compared to chlorite,griffithite is more sensitive to temperature.Griffithite attaches on the amphibole surface with a star-like in a weak acid and low-temperature environment.The results of this study can provide a mineralogical basis for the analysis of hydrothermal alteration processes and the division of alteration zones.

Diagenesis and Very Low-Grade Metamorphism of the Upper Permian Yangjiagou Formation in Eastern Changchun, China:Evidence from Clay Mineral Geothermobarometers

The metamorphic conditions of the Upper Permian Yangjiagou Formation in eastern Changchun, China, were evaluated based on the mineral assemblage, illite crystallinity, illite polytypism,the b dimension of illite, and the chemical composition of chlorite. The pelitic rocks in the Yangjiagou Formation are characterized by illite + kaolinite + chlorite ± mixed-layer chlorite/smectite and detrital quartz + plagioclase. Illite in the formation has a crystallinity of 0.38-0.55 and comprises mixed 2 Mand1 Mpolytypes, indicating a metamorphic temperature of >200℃. Based on the chemical composition of chlorite and the chlorite geothermometer, we estimated diagenetic to very low-grade metamorphic conditions with temperatures of 185℃～204℃. The b dimension of illite varies from 8.992 A to 9.005 A.We used a mathematical algorithm to extend Guidotti and Sassi’s(1986) diagram relating illite b dimension with temperature and pressure, and used this diagram, together with illite crystallinity and chlorite chemical composition, to semi-quantitatively estimate the formation pressure at<1.2 kbar. These reveal that the Yangjiagou Formation has experienced very low-grade metamorphism.