Structure analysis on synthetic emerald crystals

Single crystals of emerald synthesized by means of the flux method were adopted for crystallographic analyses. Emerald crystals with a wide range of Cr³⁺-doping content up to 3.16 wt% Cr₂O₃ were examined by X-ray single crystal diffraction refinement method. The crystal structures of the emerald crystals were refined to R ₁ (all data) of 0.019–0.024 and wR ₂ (all data) of 0.061–0.073. When Cr³⁺ substitutes for Al³⁺, the main adjustment takes place in the Al-octahedron and Be-tetrahedron. The effect of substitution of Cr³⁺ for Al³⁺ in the beryl structure results in progressively lengthening of the Al–O distance, while the length of the other bonds remains nearly unchanged. The substitution of Cr³⁺ for Al³⁺ may have caused the expansion of a axis, while keeping the c axis unchanged in the emerald lattice. As a consequence, the Al–O–Si and Al–O–Be bonding angles are found to decrease, while the angle of Si–O–Be increases as the Al–O distance increases during the Cr replacement.     

Pedogenically degenerated illite and chlorite lattices aid to palaeoclimatic reconstruction for chronologically constrained(8-130 ka) loess-palaeosols of Dilpur Formation,Kashmir,India

Chronologically well-constrained loess-palaeosols(recorded glacial and inter-glacial climate) revealed pedogenesis induced ionic substitutions,caused end-member compositional deviations in illite and chlorite,linked to widespread climatic changes occurred during Late Pleistocene.Further,micro-level climatic resolution is yet to be resolved.Thus,layer-wise X-ray diffraction analyses of clay separates,followed by Rietveld refinement revealed varied cell parameters and interatomic distances.Obtained values for detrital and pedogenic illite and chlorite when plotted against stratigraphic succession show notable changes in the crystallographic axes.The illite lattices associated with inadequately pedogenized palaeosols have been altered into illite/smectite mixed layers,but,the chlorite lattices represent expansion of a-,b-and contraction of c-axes with much greater amount of distortions,suggestive of warm-humid and acidic environment.The detrital 48,44 and 83,74 bonded illite and chlorite with2 sub-types each,when pedogenized retained 48,44 and 34;and 83 and 74 bonds(in their neo-formed 3 and 2 sub-types),respectively.The Al-O bond shows expansion,but,unchanged Si-O and decreased Si-K and K-O bonds show loss of Al and retention of Si and K ions in the illite lattices.The illite with 32 atoms and 48 bonds represent contraction of K-O,Si-K,Al-O and Si-O bonds caused bond reinforcement;however,loss of Al~(3+)reflects all-out illite alteration.Owing to Al-O and K-O bond expansion,major K~+ and Al~(3+) ionic loss occurred during the LGM,however,further ionic loss depends upon the magnitude of the loess-palaeosol weathering that they have suffered.The clilate sensitive Fe,Mg and Al ionic losses for Fe-O,Mg-O and Al_(11)-O_9 bond length expansions were recognized in the chlorite lattices.Such ionic losses are common,but,complete distortion is attributed to Al,Si,Fe and Mg ionic losses,followed by weakening of Al-O,Si-O,Fe-O and Mg-O bonds.Though,Si-O_4 and Fe_1-O_4 bonds,and Si and Fe_(1 st) ions remain intact.Thus,three major glacial episodes of ～5 ka each occurred under alkaline environment,but,intervened by two successive cycles of 55 ka each,encompassing three alternate warm and cold climatic sub-cycles of 12-15 ka.But,the coldness increases with each warm-cold sub-cycle that attained the glacial maxima.Further,these events correlate well with the deep-sea records of the North Atlantic(MIS-1 to MIS-5 e) and CLP loess-palaeosols(～127 ka).     

The Loewenstein rule: the increase in electron kinetic energy as the reason for instability of Al–O–Al linkage in aluminosilicate zeolites

Problem of Al–O–Al linkage in aluminosilicate materials or Al-avoidance is discussed for two zeolite structures (phillipsite and brewsterite) exchanged with Mg²⁺ cations. All models are fully optimized at periodic Hartree–Fock and hybrid density functional theory levels (the CRYSTAL code). Their properties are then calculated at the periodic level with the same basis sets. The reasons for the instability of the zeolite structures including the Al–O–Al moieties are interpreted on the basis of cell energy decomposition. This destabilization comes from an increase in kinetic energy if the Al–O(Mg)–Al moieties are present in zeolites. This effect is discussed in parallel with already known variational evidences in favor of dominating role of kinetic energy for stability of molecular systems.     

新疆达坂城西南一带奇尔古斯套组硅质岩地球化学特征及成因讨论

奇尔古斯套组硅质岩SiO2含量较高,Al2O3、TiO2含量变化较大,反映出较多的外来物质的加入;Si/ (Al+Fe+Mn)、Al/ (Al+ Fe+ Mn)、MnO/TiO2、Al2 O3/(Al2 O3+ Fe3 O2)值较高,反映其为生物化学成因,形成于大陆边缘环境;Fe2O3/TiO2对Al2O3/(Al2 O3+ Fe2O3)图解同样说明其形成于大陆边缘环境.REE较高,HREE富集不明显,北美页岩标准化后的稀土配分模式曲线较为平坦,向左倾斜不明显,(La/Ce)shale值较低,δCeshale值较高,无明显Ce负异常,反映奇尔古斯套组硅质岩属生物化学成因硅质岩,形成于大陆边缘环境; (La/Ce)shale对Al2 O3/(Al2 O3+Fe2 O3)图解亦说明其形成于大陆边缘环境.微量元素中Hf含量高,而Be、Li、Nb、Rb、Sr、Ta、Th、U、V、Zr含量低;Ba元素含量低;Co、Ni贫富相当,Co/Ni值较高,U/Th值低,说明奇尔古斯套组硅质岩属于正常的生物化学成因的硅质岩.     

Geothermobarometry on anatectic melts – a high-pressure Variscan migmatite from northeast Sardinia

We studied a high-pressure amphibole-bearing migmatite cropping out along the northeastern coast of Sardinia, a few kilometres northeast of Olbia, in order to improve our knowledge about its evolution using pressure–temperature (P–T) pseudosections. Thermodynamic calculations with PERPLE_X were undertaken in the system Na₂O–K₂O–CaO–FeO–MnO–MgO–Al₂O₃–TiO₂–SiO₂–H₂O using a haplogranitic melt model. Calculations were conducted for average compositions of the protolith and the tonalitic leucosome with different contents of H₂O to construct various pseudosections in the P–T range 2–20 kbar and 550–900°C. We demonstrate that the molar ratios Na/K and Si/Al of the anatectic melt are of high geothermobarometric value. Particularly the melt field in the P–T pseudosection for the protolith, contoured by Si/Al isolines, shows a significant decrease in this ratio with rising pressure. This ratio is only weakly dependent on variable H₂O contents of the amphibole-bearing migmatite as demonstrated by contoured T–H₂O pseudosections. The application of the Na/K and Si/Al ratios in melt yielded P–T conditions close to 13 kbar and 700°C, assigned as the conditions of partial melting. Evaluation of contoured P–T pseudosections for the leucosome composition resulted in conditions of about 10.5 kbar and 700°C for the crystallization of amphibole in the leucosome melt, and 9 kbar and 680°C for complete crystallization of this melt.     

Mechanisms and geochemical significance of Si–Al substitution in zeolite solid solutions

Rock-forming zeolites often exhibit complex solid solutions reflecting isomorphous substitutions between Si and Al in tetrahedral framework sites, between charge-balancing extraframework cations, and between water molecules and vacancies. Although the number of moles of charge on extraframework cations in a zeolite must equal the moles of Al in order to maintain charge balance, the relationships between Si–Al and extraframework substitutions vary considerably across this mineral group. Review of available compositional data suggests that there are three main modes of Si–Al substitution in zeolites: 1) coupled CaAl–NaSi substitution; 2) coupled substitution of a single extraframework cation plus Al for Si; and 3) completely uncoupled substitution among extraframework cations and Si and Al on tetrahedral sites. Among zeolites that exhibit the latter two modes of solid solution, Si–Al substitution can be described by an SiO₂ (± H₂O) compositional exchange vector from a hypothetical, pure-silica endmember composition. Recent calorimetric, structural, and theoretical investigations suggest that Si–Al substitution follows a non-ideal, athermal solution model characterized by no excess enthalpies of mixing and negative excess entropies of mixing. Because Si–Al exchange in these minerals can be explicitly or implicitly described by exchange of an SiO₂ component, the Si/Al ratio in their framework can be predicted solely as a function of temperature, pressure, and the chemical potential of SiO₂. Application of this model leads to calculated Si/Al ratios in stilbite (coexisting with albite), analcime, and chabazite consistent with observed mineral compositions and parageneses in very low-grade metamorphic environments. Coexistence of silica polymorphs with zeolites containing SiO₂·nH₂O exchange vectors potentially provides a means of performing thermobarometric calculations in very low-grade metamorphic and diagenetic environments.     

添加氧化铝对微生物修复裂缝影响的分析

微生物修复裂缝技术由于环保经济的特点被广泛关注,但修复效率因混凝土内碱性环境受到很大影响;开展提高该技术的修复效率与效果的研究具有重要意义。探究高碱性环境下Al2O3对微生物钙化的促进作用,然后添加Al2O3对不同裂缝宽度的混凝土试件进行修复,修复中检测浸出液pH值与尿素含量,修复后通过声时值、碳酸钙生成效率、无侧限抗压强度等指标评价修复效果。结果表明：Al2O3能够降低碱性环境对细菌活性的抑制,提升其脲酶活性与碳酸钙转化效率。添加Al2O3使试件浸出液pH值从12降为9,pH值为9时更适合菌种的繁殖,尿素利用率显著提升到81%,提高了碳酸钙的产出率,明显缩短修复时间。添加Al2O3修复试件的声时值接近无裂缝试件,明显优于无添加试件。添加Al2O3后2 mm裂缝试件的碳酸钙生成率为77.32%,远高过无添加试件的20.98%。添加Al2O3修复试件强度恢复远高于无添加Al2O3修复试件,且强度恢复随裂缝宽度减小而增加。因此,混凝土修复过程中添加Al2O3能有效提高修复效率,减少修复时间,为后续实际工程中微生物快速高效修复裂缝提供重要参考。     

广西钦州板城晚泥盆世硅质岩地球化学特征及沉积环境探讨

广西钦州小董——板城地区发育较好的晚泥盆世至晚二叠世含放射虫硅质岩,剖面连续。本文对板城地区石梯水库晚泥盆世含放射虫硅质岩进行了主量元素、微量元素和稀土元素的分析,指示这些硅质岩形成于大陆边缘与深海盆地之间的过渡地带,说明在晚泥盆世钦州地区不存在大洋,与当时在华南板块与扬子板块之间发育古特提斯洋不符。     

Transition from I‐type to A‐type magmatism in the Sanandaj–Sirjan Zone,NW Iran: an extensional intra‐continental arc

The South Dehgolan pluton, in NW Iran was emplaced into the Sanandaj–Sirjan magmatic–metamorphic zone. This composite intrusion comprises three main groups: (1) monzogabbro–monzodiorite rocks, (2) quartz monzonite–syenite rocks, and (3) a granite suite which crops out in most of the area. The granites generally show high SiO₂ content from 72.1%–77.6 wt.% with diagnostic mineralogy consisting of biotite and amphibole along the boundaries of feldspar–quartz crystals which implies anhydrous primary magma compositions. The granite suite is metaluminous and distinguished by high FeOt/MgO ratios (av. 9.6 wt.%), typical of ferroan compositions with a pronounced A‐type affinity with high Na₂O + K₂O contents, high Ga/Al ratios, enrichment in Zr, Nb, REE, and depletion in Eu. The quartz monzonite–syenites show intermediate SiO₂ levels (59.8%–64.5 wt.%) with metaluminous, magnesian to ferroan characteristics, intermediate Na₂O + K₂O contents, enrichment in Zr, Nb, REE, Ga/Al, and depletion in Eu. The monzogabbro–monzodiorites show overall lower SiO₂ content (48.5%–55.9 wt.%) with metaluminous and calc‐alkaline compositions, relatively lower Na₂O + K₂O contents, low Ga/Al ratios, and FeOt/MgO (av. 1.6 wt.%) ratios, low abundances of Zr, Nb, and lower REE element concentrations relative to the granites and quartz monzonite–syenites. These geochemical differences among the three different rocks suites are likely to indicate different melt origins. We suggest that the South Dehgolan pluton resulted from a change in the geodynamic regime, from compression to extension in the Sanandaj–Sirjan zone during Mesozoic subduction of the Neo‐Tethys oceanic crust beneath the Central Iranian microcontinent. Copyright © 2015 John Wiley & Sons, Ltd.     

Pro- and retrograde P–T evolution of granulites of the Beit Bridge Complex (Limpopo Belt, South Africa): constraints from quantitative phase diagrams and geotectonic implications

Interpretations based on quantitative phase diagrams in the system CaO–Na₂O–K₂O–TiO₂–MnO–FeO–MgO–Al₂O₃–SiO₂–H₂O indicate that mineral assemblages, zonations and microstructures observed in migmatitic rocks from the Beit Bridge Complex (Messina area, Limpopo Belt) formed along a clockwise P–T path. That path displays a prograde P–T increase from 600 °C/7.0 kbar to 780 °C/9–10 kbar (pressure peak) and 820 °C/8 kbar (thermal peak), followed by a P–T decrease to 600 °C/4 kbar. The data used to construct the P–T path were derived from three samples of migmatitic gneiss from a restricted area, each of which has a distinct bulk composition: (1) a K, Al‐rich garnet–biotite–cordierite–sillimanite–K‐feldspar–plagioclase–quartz–graphite gneiss (2) a K‐poor, Al‐rich garnet–biotite–staurolite–cordierite–kyanite–sillimanite–plagioclase–quartz–rutile gneiss, and (3) a K, Al‐poor, Fe‐rich garnet–orthopyroxene–biotite–chlorite–plagioclase–quartz–rutile–ilmenite gneiss. Preservation of continuous prograde garnet growth zonation demonstrates that the pro‐ and retrograde P–T evolution of the gneisses must have been rapid, occurring during a single orogenic cycle. These petrological findings in combination with existing geochronological and structural data show that granulite facies metamorphism of the Beit Bridge metasedimentary rocks resulted from an orogenic event during the Palaeoproterozoic (c. 2.0 Ga), caused by oblique collision between the Kaapvaal and Zimbabwe Cratons. Abbreviations follow Kretz (1983 ).     

氟盐取代-EDTA滴定法测定铝土矿中铝量

采用EDTA滴定法(氟盐取代)对高铁质铝土矿石中三氧化二铝的含量进行测定。重点探讨了氟化钾的加入量及煮沸时间对三氧化二铝测定结果的影响。方法用于实际样品中三氧化二铝的测定,结果符合质量管理规范。     

滇西上芒岗红色粘土型金矿常量元素地球化学

滇西上芒岗红色粘土剖面中常量元素的垂向分布研究表明，K2O、Fe2O3、Al2O3在剖面中的变化一致，呈双峰曲线变化，即在坡积带稍有富集、在残积带明显富集；而SiO2与铁、铝等在剖面中的变化相反。红色粘土与矿区地层和矿化蚀变岩的常量元素对比分析表明了红色粘土可能来源于地层和矿化蚀变岩。常量元素之间的相关性以及常量元素与金的相关性分析表明K2O、Fe2O3、Al2O3在红色粘土中为共生元素；金的富集主要受红色粘土中褐铁矿和伊利石的吸附影响。红土化参数分析说明了红色粘土剖面经历两次红土化作用，残积带相对于其它带经受过较强的红土化作用，但整个红色粘土剖面遭受的红土化作用不强，红土化程度低，仅处于粘土化阶段。     

The compositional variation of synthetic sodic amphiboles at high and ultra-high pressures

Sodic amphiboles in high pressure and ultra-high pressure (UHP) metamorphic rocks are complex solid solutions in the system Na₂O–MgO–Al₂O₃–SiO₂–H₂O (NMASH) whose compositions vary with pressure and temperature. We conducted piston-cylinder experiments at 20–30?kbar and 700–800?°C to investigate the stability and compositional variations of sodic amphiboles, based on the reaction glaucophane=2jadeite+talc, by using the starting assemblage of natural glaucophane, talc and quartz, with synthetic jadeite. A close approach to equilibrium was achieved by performing compositional reversals, by evaluating compositional changes with time, and by suppressing the formation of Na-phyllosilicates. STEM observations show that the abundance of wide-chain structures in the synthetic amphiboles is low. An important feature of sodic amphibole in the NMASH system is that the assemblage jadeite–talc?±?quartz does not fix its composition at glaucophane. This is because other amphibole species such as cummingtonite (Cm), nyböite (Nyb), Al–Na-cummingtonite (Al–Na-Cm) and sodium anthophyllite (Na-Anth) are also buffered via the model reactions: 3cummingtonite?+?4quartz?+?4H₂O=7talc, nyböite?+?3quartz=3jadeite?+?talc, 3Al–Na-cummingtonite + 11quartz + 2H₂O=6jadeite + 5talc, and 3 sodium anthophyllite?+?13quartz?+?4H₂O=3 jadeite + 7talc. We observed that at all pressures and temperatures investigated, the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of Al^IV for Si, Mg on the M(4) site, and Na on the A-site. The deviation can be described chiefly by two compositional vectors: [Na^AAl^IV]<=>[□^ASi] (edenite) toward nyböite, and [Na^(M4)Al^VI]<=>[Mg^(M4)Mg^VI] toward cummingtonite. The extent of nyböite and cummingtonite substitution increases with temperature and decreases with pressure in the experiments. Similar compositional variations occur in sodic amphiboles from UHP rocks. The experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications.     

中国东部中-新生代玄武质火山岩的主量元素地球化学特征

用MgO=8％标准化后,中国东部中-新生代玄武质火山岩表现为高Al2O3／TiO2、SiO2,低CaO／Al2O3的特征;新生代玄武质火山岩表现为低SiO2和低Al2O3／TiO2;高Fe8.0、Na8.0、CaO／Al2O3的特征。与区域软流圈地慢上涌和岩石圈伸展构造环境下形成的桂东南钾玄质岩石的高Fe8.0、低Na8.0和CaO／Al2O3值有明显的差异。中国东部中一新生代玄武质火山岩主量元素的特征,可能反映了与桂东南钾玄质岩石不同的形成环境。而中、新生代玄武质火山岩主量元素特征上的差异反映了岩浆来源区的变化。     

Thermal stability of extended clusters in dravite: a combined EMP,SREF and FTIR study

A dravite from Yemen of near end-member composition was treated in air and hydrogen atmospheres at 600–900 °C to reveal changes in Mg and Al order over the octahedrally coordinated Y and Z sites, and to explore related changes in the characteristic vibrational bands in the principal (OH)-stretching frequency. Relevant information was obtained using electron microprobe analysis (EMPA), structural refinement (SREF) and polarized infrared (IR) single-crystal spectroscopy. Overall, the EMPA, SREF and IR data show that only minor changes occur during thermal treatment up to at least 800 °C, including variations in structural parameters, Mg–Al order–disorder and (OH)-stretching bands, indicating limited hydrogen loss. Untreated and treated dravite samples have very similar long-range and short-range atomic structures, which may be related to the occurrence of stable Al–Mg extended clusters around the O1 (=W) and O3 (=V) sites: ^W(F)–^Y(MgMgMg)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]; ^W(OH)–^Y(MgMgAl)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]; ^W(O^2–)–^Y(AlAlAl)–^V(OH)₃–^Z[AlAlAlAlAl(Al,Mg)]. These extended clusters remain stable to temperatures close to the observed start of decomposition (~900 °C).     

Composition,Structure, and Conditions of Formation of Fluorine-Bearing Sodalite: Experimental Evidence

Fluoro-sodalite was synthesized for the first time at temperatures of 400–800°C and H₂O pressures of 1–2 kbar in the Si–Al–Na–H–O–F system. X-ray diffraction and infrared spectroscopic investigations showed that fluorine is incorporated in the sodalite structure as anionic octahedral groups, [AlF₆]^3–, the number of which can vary from 0 to 1. Correspondingly, the end-members of the F-sodalite series are Na₇(H₂O)₈[Si₅Al₇O₂₄] and Na₈(AlF₆)(H₂O)₄[Si₇Al₅O₂₄]. Depending on the composition of the system, F-sodalite associates at 500–650°C with nepheline, albite, cryolite, and villiaumite, which are joined by analcime below 500°C and aluminosilicate melt above 650°C. Fluorine-bearing sulfate–chlorine-sodalite was found for the first time in a pegmatite sample from the Lovozero massif. The highest fraction of the fluorine end-member in natural sodalite is 0.2. The incorporation of F into the sodalite structure requires much more energy compared with Cl^– and SO ₄ ^2- , because it is accompanied by a structural rearrangement and a transition from tetrahedral Al to octahedral Al.     

Geochemical characterization of Cretaceous sandstones from the Southern Benue Trough,Nigeria

Geochemical studies of sandstones from the three lithostratigraphic successions in the southern Benue Trough of Nigeria were undertaken for a geochemical characterization of the sandstones, and to assess their strati-graphic and source evolution.Major and trace elements data were obtained from outcrop sandstone samples. The SIO2/Al2O2, Fe2O3/K2O ra-tios and CaO contents have been used to characterize the Cretaceous sandstones into Al-rich and high and low Fe2O3/K2O ratio sandstones. Results indicate that there are geochemical features that display stratigraphic trends across the succession from the Asu River Group, Eze-Aku Group to the proto-Niger Delta succession which may imply a discontinuous evolution from different source terrains of Precambrian and Mesozoic ages that supplied the sediments. The Asu River Group sandstones have lower SiO2, Al2O3, Fe2O3 and higher MgO; the Eze-Aku sand-stones have higher TiO2, CaO, alkalis and lower MgO while the proto-Niger Delta sandstones have higher SiO2, Al2O3, Fe2O3 and lower alkalis and CaO. These discontinuities signify the influence of tectonic impulses that af-fected the southern Benue Trough during the Cretaceous time. Changes in ratios of TiO2/Al2O3, Fe2O3, Cr and Zr suggest an increasingly mafic contribution to the depositional basin with time. The chemical index of alteration in-creases with time, possibly suggesting that a more intense weathering regime in the hinterland developed with time.     

柱撑蒙脱石吸附水中硫酸根离子的实验研究

在实验条件下，制备了两种柱撑蒙脱石，用X射线衍射分析和BET N2比表面积分析对其进行了表征，并对水中的硫酸根离子进行了吸附试验，通过正交实验研究了柱撑蒙脱石对水中硫酸根离子的吸附率、吸附容量及其与硫酸根离子初始浓度、PH值、吸附时间等因素间的关系，确定了它们吸附硫酸根离子的适宜条件，并与钠蒙脱石对水中硫酸根离子的吸附情况进行了对比。在此基础上初步探讨了吸附的机理，认为A13及Al2O3柱撑蒙脱石具有很强的吸附硫酸根离子的能力，在pH分别为4和5时硫酸根离子去除效果最好。     

胜利油田火山岩辉石中岩浆包裹体成分及有关成因问题

对胜利油田火山岩中辉石及其中岩浆包裹体成分的研究表明：ＣＯ２气藏区和非ＣＯ２气藏区新生代火山岩辉石及其中岩浆包裹体成分有明显区别,前者中辉石为普通辉石,成分相对富ＳｉＯ２,而贫Ａｌ２Ｏ３、ＴｉＯ２、ＭｇＯ和挥发成分;而后者中辉石为透辉石,成分相对贫ＳｉＯ２和挥发份,而富Ａｌ２Ｏ３、ＴｉＯ２和ＭｇＯ。前者岩浆包裹体玻相中富含ＣＯ２,包裹体中的金属子矿物多为黄铁矿;而后者岩浆包裹体玻相中贫ＣＯ２;包裹     

浙西石炭纪层状硅质岩地球化学特征及其意义

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