Stoichiometric substitution in natural quartz

Evidence is presented for the substitution of foreign elements in quartz in such a way as to preserve electrical neutrality. The nature of the substituting species is controlled by both the abundance of elements in the environment and by crystal chemical parameters.     

Luminescence properties of Pr3+ and Sm3+ ions in natural apatites

The luminescence spectra of Pr³⁺ and Sm³⁺ ions in apatite Ca₅[F∣(PO₄)₃] crystals from Spain and Russia have been compared with those for phosphate glasses doped with Pr³⁺, Sm³⁺ and Pr³⁺, Sm³⁺ ions. Time-resolved spectra measurements confirm that, in apatites, samarium ions occupy two non-equivalent crystal sites; the same is assumed for praseodymium ions. For the first time in minerals, the Stark splitting energy levels ΔE for ³H₆ and ¹D₂ of Pr³⁺ ion and ⁶H_7/2 of Sm³⁺ ion were determined. Some small differences in ΔE values for the Spanish and Russian apatite are discussed. The decay times of the excited levels of Pr³⁺, Sm³⁺ and Pr³⁺, Sm³⁺ doped in phosphate glass were measured at room temperature and at 77 K. The energy transfer process between samarium and praseodymium ions was observed and the energy transfer rate was calculated.     

Geochemistry of organic matter in natural apatites of phosphorites according to EPR spectra of free radicals

The following organic radicals were identified by EPR spectroscopy in apatite from marine phosphorites (granular, nodular, shelly, and microcrystalline), supergene phosphorites (from ocean islands only), and modern and fossil biological materials (human dental enamel, fossil shark teeth, and pathogenic cardioliths): ?H₃, ?H₂-R, HO?HR,(CH₃)₂-?R,₃?_org, PO ₃ ^2? , P(OR)₃, and perinaphteenyl. Each textural and petrographic type of apatite corresponds to a specific model of organic radicals, which correlates with the type of organic matter (sapropelic, humic, guano, or collagen). The latter is controlled by the conditions of mineral formation, including climatic ones, and postdiagenetic (catagenetic) processes. A relationship was established between the EPR spectra of observed organic radicals and the valence state and structural position of impurity ions: (1) vanadium: V⁴⁺ (VO²⁺) in the Ca²⁺ II site or V⁵⁺ (VO₄)^3? ?? (PO₄)^3? and (2) uranium: U⁴⁺(UO₂) in the Ca²⁺ II site or U⁶⁺ chemisorbed on the surface as UO ₂ ²⁺      

Emission of carbon-bearing gases and aerosols from natural fires on the territory of Russia based on space monitoring

The results of the space monitoring of natural fires during the period 2010–2014 to estimate the areas destroyed by fire, volumes of the emissions of greenhouse gases, and fine particulate aerosols over the entire territory of Russia and its individual regions are presented. The methods of research, the regularities of the seasonal recurrence of fires distinguished in different regions, as well as the peculiarities of emissions of small gas components and aerosols in different months are described.     

F-OH substitution in natural tremolite,talc, and phlogopite

The distribution of F between tremolite and talc has been determined in metamorphosed siliceous carbonates from the Grenville Province, Ontario. Wavelength dispersive electron microprobe analyses of contiguous, texturally compatible tremolite-talc pairs indicate that the substitution of F for OH is the most significant deviation from end-member stoichiometry in the samples studied. Mixing of F and OH components has been represented by an ideal solution model for F in tremolite and an asymmetric model for F in talc. Both linear and nonlinear regression techniques have been used to derive activity coefficients for the exchange of one equivalent of OH and F components in talc. The following expressions are the result of nonlinear regression of 32 analyses from coexisting mineral pairs: $$\begin{gathered} \ln \gamma _{TC(OH)} = X_{TC(F)}^2 [2.447 - 2.845X_{TC(OH)} ] \hfill \\ \ln \gamma _{TC(F)} = X_{TC(OH)}^2 [1.024 + 2.845X_{TC(F} ] \hfill \\ \end{gathered} $$ Isobaric \(T - X_{CO_2 } \) sections constructed using these equations show an enhanced stability for the assemblages talc+calcite and phlogopite+quartz+calcite with F substituting for OH. Projection of isothermal invariant points into P-T space predicts a shift in the stability of the assemblage talc-calcite from lower grade into the sillimanite field with increasing substitution of F for OH in talc.     

Crystal-chemical examination of natural diopsides: Some geometrical indications of Si-Ti tetrahedral substitution

Summary The crystal structures of 20 natural diopsides have been refined. For some samples, microprobe analyses show a Si deficiency in the tetrahedron with no A1 present; this suggests that some Ti⁴⁺ may enter the tetrahedral site. Geometrical variations in these samples with respect to the others are discussed in the light of this Si Ti⁴⁺ substitution. The volumes of their M1 sites are larger because of the absence of R³⁺ cations, the octahedron being very regular; in the same way, the volumes of M2 sites of these samples are greater not because of different site occupancies but because of significant charge modifications around the O3 and O1 oxygens, caused by the tetrahedral site. The low distortion of M1 site and the lengthening of (M2-O1) and M2-O3 bond lengths are a clue to the presence of small amounts of Ti at the tetrahedral site.

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Kristallchemische untersuchung natürlicher diopside: Geometrische hinweise für tetraedrische Si-Ti substitution

Zusammenfassung Die Kristallstrukturen von zwanzig natürlichen Diopsiden sind verfeinert worden. In einigen Proben zeigen Mikrosondenanalysen zu geringe Si-Werte im Tetraeder ohne daß A1 anwesend wäre. Dies weist darauf hin, daß Ti⁴⁺ Tetraederplätze einnehmen könnte. Geometrische Variationen in diesen Proben werden im Lichte der genannten Substitution diskutiert. Die Volumen von M1-Plätzen sind größer wegen der Abwesenheit von R³⁺ Kationen, wobei das Oktaeder sehr gleichmäßig ist. Die Volumina von M2-Plätzen sind noch größer nicht wegen verschiedener Besetzungen dieser Plätze sondern wegen signifikanter Ladungsmodifikationen im Bereich von O3 und O1 Sauerstoffen, die durch die tetraedrische Position bewirkt wird. Die geringe Distortion der M1-Plätze und die Verlängerung der (M2-O1) und (M2-O3) Abstände weisen auf die Anwesenheit von geringen Titangehalten auf Tetraederplätzen hin.

     

鲁西碳酸岩中磷灰石的原位激光探针分析及其成岩意义

以鲁西雪野和八陡碳酸岩中的磷灰石为对象,运用EMPA和LA-ICP-MS技术,分别测定了它们的主量与微量元素组成,并据此讨论了它们的成岩意义.研究结果表明,这些磷灰石富F(=1.07%～2.74%)贫Cl(＜0.04%),种属为羟氟磷灰石或氟羟磷灰石.微量元素组成上富Sr、Th、U、Pb和轻稀土,是全岩中上述元素的主要载体之一.磷灰石的Sr、F含量与∑REE及LREE/HREE比值均表现出较明显的正相关性,其富Sr、贫Y和富轻稀土等特点与世界典型碳酸岩中的磷灰石相似,但它们具有更高的Sr/Y和Th/U比值,Sr、Ce、Th、Y含量接近地幔中由交代作用形成的磷灰石,说明其寄主碳酸岩岩浆源区应为遭受过流体交代作用的富集地幔.这些磷灰石的(La/Nd)_N比值＞1,(La/Yb)_N比值多数在100以上,与世界其他地区典型碳酸岩中的磷灰石相比铕负异常相对更明显,表明其寄主碳酸岩浆经历一定程度的分异演化.雪野较八陡碳酸岩中磷灰石含更高的F、Sr和∑REE含量及(La/Yb)_N比值,说明其寄主岩浆的演化程度更高.     

基于Biot-Gassmann 方程的流体替换技术在番禺天然气区PY 气田的应用

珠江口盆地番禺天然气区PY 气田位于坡折带上,特殊的沉积环境导致该气田已钻探的各井 T50 储层泊松比关系异常,含油气性特征非常复杂。为更好的判断储层的含油气性,利用Biot-Gassmann 方程对坡折带储层的流体性质进行了替换,考查不同流体性质下储层的含油气响应特征。研究结果表明: Biot-Gassmann 方程能有效的用于坡折带储层的流体替换研究; 坡折带T50 储层含水和含气时的AVO 响应特征相近,但两者响应的幅值不同,含水砂岩的幅值更小。     

Diamond dissolution and the production of methane and other carbon-bearing species in hydrothermal diamond-anvil cells

Raman analysis of the vapor phase formed after heating pure water to near critical (355-374 °C) temperatures in a hydrothermal diamond-anvil cell (HDAC) reveals the synthesis of abiogenic methane. This unexpected result demonstrates the chemical reactivity of diamond at relatively low temperatures. The rate of methane production from the reaction between water and diamond increases with increasing temperature and is enhanced by the presence of a metal gasket (Re, Ir, or Inconel) which is compressed between the diamond anvils to seal the aqueous sample. The minimum detection limit for methane using Raman spectroscopy was determined to be ca. 0.047 MPa, indicating that more than 1.4 nanograms (or 8.6 × 10⁻¹¹ mol) of methane were produced in the HDAC at 355 °C and 30 MPa over a period of ten minutes. At temperatures of 650 °C and greater, hydrogen and carbon dioxide were detected in addition to methane. The production of abiogenic methane, observed in all HDAC experiments where a gasket was used, necessitates a reexamination of the assumed chemical systems and intensive parameters reported in previous hydrothermal investigations employing diamonds. The results also demonstrate the need to minimize or eliminate the production of methane and other carbonic species in experiments by containing the sample within a HDAC without using a metal gasket.     

Non-Henry’s Law behavior of REE partitioning between fluorapatite and CaF2-rich melts: Controls of intrinsic vacancies and implications for natural apatites

The partitioning of rare-earth elements (REEs: Gd and multiple REEs), Sr, and Mn between fluorapatite and CaF₂-rich melts was investigated over a wide range of REE concentrations (i.e., from 0.8 ± 0.1 to 25,000 ± 2600 ppm Gd in fluorapatite) in two different sample assemblies (i.e., tightly covered Pt crucibles and sealed Pt capsules) at 1220 °C and atmospheric pressure. Attainment of equilibrium is indicated by selected reversal experiments. The partition coefficient D(Gd) decreases from ∼2 to ∼0.5 with increasing Gd in fluorapatite, hence a marked non-Henry’s Law behavior, but becomes independent of composition at and above ∼5000 and ∼1000 ppm Gd for experiments in Pt crucibles and Pt capsules, respectively. Non-Henry’s Law behavior is also observed in experiments involving multiple REEs. All REE patterns are convex upward in shape with maxima between Nd and Gd, and D(La)/D(Nd) and D(Nd)/D(Yb) decrease systematically with increasing total REEs in fluorapatite, suggesting that REE fractionations are partly related to non-Henry’s Law behavior. These experimental results and local structural data from previous electron paramagnetic resonance spectroscopic studies suggest that the non-Henry’s Law behavior of REE partitioning between fluorapatite and melt is controlled by intrinsic Ca²⁺ vacancies in the c-axis channels. The D(Sr) and D(Mn) values are independent of composition and, therefore, do not deviate from the Henry’s Law in their respective compositional ranges investigated in this study.Nonstoichiometry, such as Ca²⁺ and F⁻ vacancies in the c-axis channels, is well known in natural apatites, particularly in biogenic apatites. Therefore, the observed non-Henry’s Law behavior of REE partitioning is expected to have important implications for REE geochemical modeling involving apatites and for the uptake of REEs by natural apatites. Particularly, the non-Henry’s Law behavior of REE partitioning is at least partly responsible for the commonly observed, bell-shaped REE patterns in fossil biogenic apatites.     

Analysis and application of carbon-bearing rate of reservoirs in the Puguang gas field, northeastern Sichuan Basin

With wells Puguang 2 and 6 in the Puguang gas field as the research objects by choosing organic carbon as characterization reservoir carbon(indirectly reflecting the bitumen contents),this paper discusses the relationship between bitumen contents and lithologic characteristics,reservoir characteristics,and calculates the volume of paleo-oil and oil cracked gas.The study shows that the organic carbon contents of the reservoirs are related to lithologic characteristics.Due to variations in the particle size or structure of rocks,the porosity of the reservoirs varies,furthermore,it will influence the contents of organic carbon.And the relationship between these two parameters is positive.Based on the analysis,the relationship between total organic carbon(TOC)and the contents of reservoir bitumen also appears to be positive.The volume of paleo-oil and cracked gas of the Changxing-Feixian’guan Formation are respectively 495 million tons and 360.4 billion m3 through the calculation of reservoir’s organic carbon.Therefore,the relationship between carbon-bearing rate and characteristics of the reservoirs can be used to indirectly evaluate reservoir types.Besides,the carbon-bearing rate of the reservoirs also reflects the contents of reservoir bitumen,paleo-oil as well as natural gas.It makes a new approach for the study of the types of reservoirs and the amounts of paleo-oil and oil cracked gas in northeastern Sichuan Basin.     

Trace‐element signatures of apatites in granitoids from the Mt Isa Inlier,northwestern Queensland

The concentrations of trace elements in apatite from granitoid rocks of the Mt Isa Inlier have been investigated using the laser‐ablation inductively coupled plasma‐mass spectrometry (ICP‐MS) microprobe. The results indicate that the distribution of trace elements (especially rare‐earth elements (REE), Sr, Y, Mn and Th) in apatite strongly reflects the chemical characteristics of the parental rock. The variations in the trace‐element concentrations of apatite are correlated with parameters such as the SiO₂ content, oxidation state of iron, total alkalis and the aluminium saturation index (ASI). The relative enrichment of Y, HREE and Mn and the relative depletion of Sr in the apatites studied reflect the degree of fractionation of the host granite. Apatites from strongly oxidised plutons tend to have higher concentrations of LREE relative to MREE. Manganese concentrations are higher in apatite from reduced granitoids because Mn²⁺substitutes directly for Ca²⁺. The La/Ce ratio of apatite is well‐correlated with the whole‐rock K²O and Na²O contents, as well as with the oxidation state and ASI. Because apatite trace‐element composition reflects the chemistry of the whole rock, it can be a useful indicator mineral for the recognition of mineralised granite suites, where particular mineralisation styles are associated with granitoids that have specific geochemical fingerprints.     

Study of the Mineralization Process of granular apatites in Weng’an Baidou Phosphate Deposit Using Microbeam Analyses

<正>1 Introduction Studies of marine sedimentary phosphate rock have lasted decades,scholars proposed some standpoints about mineralization,however,the genesis of mineral deposits remains to be a controversial question(She et al.,2013).There are many viewpoints of mineralization about the Doushantuo phosphorites,Central Guizhou,including biological mineralization(Mi et al.,2010;Shi et al.,2005),     

Mechanisms of isomorphic substitution in quartz

Mechanisms of the incorporation of isomorphic impurities of Al, Ti, and Ge into quartz were studied by EPR techniques. For this purpose, laboratory experiments were carried out on quartz annealing, which allowed us to model the processes of impurity atom introduction into the quartz lattice. The investigation of the kinetics of these processes showed that they are described by diffusion-controlled reactions. In many samples, a proportional relationship was observed between the concentrations of Al and Ti impurities incorporated into the quartz structure during laboratory annealing. A comparison of the experimental results with the character of the natural distribution of isomorphic impurities in quartz revealed their similarity. Based on the analysis of the results of our investigations, two main mechanisms were proposed for isomorphic substitutions in quartz. One of them is referred to as the capture mechanism and corresponds to the incorporation of isomorphic impurities during mineral formation. The second, diffusion mechanism operates after the crystallization of quartz. The isomorphic impurities incorporated into the quartz structure by this mechanism are either formed through the decomposition and transformation of composite complexes or as a result of diffusion from crystalline and gas-liquid inclusions. It was suggested that both mechanisms are responsible for the incorporation of Al and Ge impurities into the mineral lattice, whereas Ti is introduced mainly by the diffusion mechanism. The accounting for the mechanisms of isomorphic substitutions provides a means to significantly increase the reliability of the interpretation of genetic information recorded in the distribution of structural impurities in quartz. Original Russian Text ? L.T. Rakov, 2006, published in Geokhimiya, 2006, No. 10, pp. 1085–1096.     

青海玉树地区探槽和剖面揭露的全新世含炭地层及其气候环境意义

对青藏高原东南部青海玉树地区的39个泥炭和含炭砂土样品进行了AMS 14C年龄测试,这些样品来自于为研究玉树断裂开挖的2个探槽和2个剖面。通过分析泥炭层及其他含炭地层的宏观岩性及其中样品的AMS 14C年龄,将玉树地区的全新世含炭地层的沉积过程划分为4个阶段：阶段Ⅰ：早全新世,10100~6000a BP,非常适宜泥炭的形成;阶段Ⅱ：中—晚全新世,6000~3500a BP,较不适宜泥炭的稳定形成,沉积物中含炭量相对减少,碎屑增加,颜色变浅;阶段Ⅲ：晚全新世阶段,3500~1500a BP。该阶段的气候总体变的更加干旱和凉爽,基本上不能形成泥炭,碎屑沉积在持续增加;阶段Ⅳ：1500a BP以来：自1500~1100a BP,气候可能更加干冷,沉积物中主要为碎屑沉积;1100a BP以来,受中世纪暖期气候变化影响,在本区许多地貌单元近地表形成一层灰黑色的炭质层。这4个阶段与红原泥炭所反映的全新世气候变化波动趋势能较一致。气候、地貌和构造因素三者共同控制本区域内泥炭和炭质层的发育和形成。     

Evidence for manganese substitution in synthetic goethite

Goethite (α-FeOOH) synthesized in the presence of Mn incorporates up to ca. 15 mole% Mn into its structure. This conclusion is based on a shift towards the isostructural groutite (α-MnOOH) of the unit cell dimensions a, b and c, and of the OH-bending modes. These results and a chemical test indicate trivalency of the incorporated Mn. The dehydroxylation (DTA) and the crystallinity (XRD line broadening) are also modified by Mn incorporation. All modifications of the goethites are analogous to the Al-for-Fe substitution.     

Effects of Ca-Mg substitution in C2/c pyroxene structure on natural clinopyroxenes from spinel peridotite nodules (Pico Cabugi,Brazil)

X-ray crystal structure refinements and microprobe analyses of clinopyroxenes from two suites of spinel-peridotite nodules are compared for an understanding of the structural response to a decrease in Ca content. The kinking of the tetrahedral chain (O3-O3-O3 angle) of the C2/c structure associated with decreased Ca content shows behavior similar to that observed for the A-tetrahedral chain of the P2₁/c structure. Contemporaneously the occupancy of the M2′ split site increases. In addition, as a consequence of the low Ca content, the M2 polyhedron dominates the structural rearrangement of the clinopyroxenes considered here.