在吐温—40存在下矿石中的硫氰酸盐光度法测定

本文研究了铁(Ⅰ)与硫氰酸盐-吐温-40的显色反应。在pH1.7—3.3的盐酸-乙酸钠介质中显色。络合物的最大吸收峰位于484 nm,摩尔吸收系数为2.13×10~4L·mol~(-1)·cm~(-1),铁量在0—200μg/25ml服从比尔定律。方法适用于矿石中铁的测定。     

在曲通x—100存在下金试剂与金显色反应的研究——全差示分光光度法在分析中的应用

金试剂(4.4′—双(二乙氨基)二苯基甲硫酮)是金的灵敏显色剂。本文研究了在曲通X—100存在下金试剂与金的显色反应的性质和显色条件。研究表明,金一金试剂一曲通X—100体系显色的最佳酸度为3.5～5.2,络合物的组成,金:金试剂=1:4,络合物表观摩尔吸光系数为1.65×10~5升/克分子·厘米(560纳米处),络合物的不稳定常数为4.79×10~(-22)。在25毫升体积中,金量在0—20微克范围内符合比尔定律。     

锰—二氯苯基荧光酮—混合表面活性剂体系测定痕量锰

本文研究了在CTMAB-OP存在下,Mn(Ⅱ)与2′,4′-二氯苯基荧光酮、水杨基荧光酮(SAF)及邻硝基苯基荧光酮的显色反应。结果表明,以2′,4′-二氯苯基荧光酮体系的灵敏度为最高。其ε=1.64×10~5L·mol~(-1)·cm~(-1),线性范围在0—5μg/25ml Mn(Ⅱ)。采用MIBK萃取分离可消除Fe(Ⅲ)等的干扰,而避免使用KCN。方法已用于测定白云石、磁铁矿、高硼玻璃及铝合金中的Mn,所得结果与标准值基本符合。     

PAN—S光度法测定水,河泥和土壤中微量铜

本文研究了PAN-S与铜的显色反应条件。配合物的最大吸收峰位于550nm波长处,表观摩尔吸光系数ε为2.3×10~4L·mol~(-1)·cm~~(-1),于25ml溶液中铜(Ⅱ)量在0—1.6μg/ml范围内服从比尔定律,方法用于水、河泥和土壤中微量铜的测定,结果良好。     

溴代十六烷基吡啶存在下金与硫代米蚩酮显色反应的研究及其应用

作者研究了在阳离子表面活性剂溴代十六烷基吡啶(CPB)存在下,金与硫代米蚩酮的显色反应。最佳显色酸度为pH3.0—4.3。表观摩尔吸光系数为1.32×10~5L·mol~(-1)·cm~(-1)。金的含量在0—17μg·(25ml)~(-1)范围内符合比尔定律。外来离子的干扰用活性炭吸附来消除。这个方法用于测定矿石中的微量金取得满意的效果。     

水和土壤中微量镍测定的研究

本文研究了PAN-S与镍的显色反应条件。镍与PAN-S反应的最佳pH范围为3.8—9.0。配合物的最大吸收峰位于560nm波长处,表观摩尔吸光系数为3.30×10~4L·mol~(-1)·cm~(-1),25ml试液中镍量在0—1μg/ml范围内服从比尔定律,方法用于水和土壤样品中微量镍的测定,结果良好。     

罗丹明6G光度法测定矿石中微量汞

本文试验了在阿拉伯树胶存在下,汞(Ⅱ)—碘化钾—罗丹明6G在水溶液中的显色反应,在本法拟定的条件下灵敏度高(ε=1.70×10~5L·mol~(-1)·cm~(-1)),酸度范围宽容易控制,稳定性和重现性都好,显色迅速,操作简便,可用于矿石中微量汞的测定。     

罗丹明6G光度法测定矿石中微量汞

本文试验了在阿拉伯树胶存在下,汞(Ⅱ)—碘化钾—罗丹明6G在水溶液中的显色反应,在本法拟定的条件下灵敏度高(ε=1.70×10~5L·mol~(-1)·cm~(-1)),酸度范围宽容易控制,稳定性和重现性都好,显色迅速,操作简便,可用于矿石中微量汞的测定。     

新显色剂—苯重氮氨基偶氮苯测定岩矿中的痕量镉

本文研究了新显色剂苯重氮氨基偶氮苯与镉(Ⅱ)在TritonX-100存在下的显色反应。实验表明,在pH10的硼砂—氢氧化钠缓冲溶液中显色剂同镉生成红色配合物,λ_(max)为525nm,ε=1.77×10~5L·mol~(-1)·cm~(-1),镉(Ⅱ)在0—10μg/25ml范围内服从比尔定律。采用D235大孔阴离子交换树脂分离富集,能够测定岩矿试样中的痕     

TMK萃取比色测定金

本文研究了以TMK为显色剂,萃取比色测定痕量的金。试验表明,金与TMK在pH2.5—4.5的HAc-NH_4Ac介质中显色,定量的萃取于CHCl_3:MIBK:CH_3COOC_4Hg(2:1:1),吸收曲线的吸收峰是545nm。金量在0—4微克的范围内遵守比尔定律。摩尔吸光系数是1.68×10~5升·厘米~(-1)·摩尔~(-1)。本法具有较高的灵敏度和选择性,可测定n×10~(-3)g/t以上岩、矿中的金。     

Phase equilibria of bastnaesite,allanite, and monazite: Bastnaesite-out isograde in metapelites of the Vorontsovskaya group,Voronezh crystalline massif

Paleoproterozoic metapelites of the Vorontsovskaya structure contain accessory REE phosphates (monazite, xenotime, and REE-apatite), fluorine-carbonates (bastnaesite and synchysite), and silicate (allanite). Analysis of phase equilibria involving REE-bearing minerals indicates that bastnaesite is stable only in the greenschist facies and decomposes with the synthesis of monazite at temperatures below the staurolite isograde (490–500°C) at a pressure of 3 kbar. Monazite first appears in the greenschist facies, and its stability expands with increasing temperature, including the granulite facies. A diversity of reaction textures suggests that the mineral is formed in the garnet zone by a reaction of bastnaesite with apatite and by the partial decomposition of REE-bearing chlorite. Monazite is produced in the garnet and staurolite zones by a reaction of allanite with apatite and by a decomposition reaction of REE-bearing apatite.     

Chemographic relationships of biotite and cordierite in the McGerrigle thermal aureole, Gaspé, Quebec

Abstract Biotite and cordierite occur in a 1-km wide zone of pelitic hornfelses around the McGerrigle pluton. These phases display systematic changes in X _Fe that can be attributed to continuous reactions involving chlorite or andalusite in the system KFMASH. Through much of the zone biotite and cordierite were products of the 'breakdown'of chlorite. Close to the pluton this continuous reaction was terminated by a discontinuous reaction that introduced andalusite. Pelites which interdigitate with apophyses of the intrusive at the pluton margin contain assemblages that record a continuous reaction between biotite, cordierite, andalusite, muscovite, and quartz or, alternatively, the discontinuous breakdown of muscovite and quartz to K-feldspar and andalusite.
The mole fraction of Fe in biotite and cordierite increased significantly with the progress of the first continuous reaction and apparently decreased during the second continuous reaction. The K _D of Fe-Mg between the minerals decreased and apparently increased, respectively, during the two reactions.
Biotite-cordierite-chlorite assemblages are interpreted to have been stable at temperatures between 525° C and 615° C and biotite-cordierite-andalusite assemblages stable at temperatures between 615° C and 635° C. The confining pressure was estimated to have been < 2 kbar.
The results of this study suggest that the K _D of Fe-Mg between biotite and cordierite is a function of temperature, the Fe-Mg exchange characteristics of the controlling continuous reaction and non-ideal mixing of Fe and Mg.     

Mechanisms of myrmekite formation: case study from the Weinsberg granite,Moldanubian zone,Upper Austria

Myrmekites have attracted the attention of petrographers over more than a century, and several genetic models have been proposed. We report on myrmekites from the Weinsberg granite of the Moldanubian zone of Upper Austria. Based on petrographic evidence, fluid-mediated replacement of alkali feldspar by myrmekite during the sub-solidus evolution of the granite is inferred. The replacement was metasomatic on the scale of the myrmekite domains requiring addition of sodium and calcium and removal of potassium from the reaction site. In contrast, silica and aluminum were conserved across the reaction front. Myrmekite formation appears to have been synchronous with and related to the hydration of orthopyroxene and concomitant replacement of primary magmatic plagioclase by biotite at around 500 °C. The evolution of the myrmekite microstructure and a peculiar composition zoning of the plagioclase constituting the myrmekite matrix is qualitatively explained by a model for discontinuous precipitation, which accounts for chemical segregation by diffusion within the reaction front and the propagation of the reaction front with finite mobility as potentially rate limiting processes. Constraints on the underlying reaction rates are derived from the preserved microstructure and chemical pattern. Crystal orientation imaging by electron backscatter diffraction reveals grain-internal deformation, which is primarily concentrated in the quartz and less pronounced in the plagioclase matrix of the myrmekite. This is interpreted as a growth feature related to different transformation strain at the segments of the myrmekite reaction front, where quartz and plagioclase are formed.     

Garnet reaction rims from the breakdown of Staurolite in polymetamorphic micashists from the Rappold complex, Austroalpine basement, Eastern Alps

In polymetamorphic pelites of the Rappold complex in the Wölz crystalline basement (Eastern Alps) reaction rim garnets at staurolite-quartz interfaces (type I) and single grain garnets along previous staurolite-white mica interfaces (type II) were formed. The garnet reaction rims were formed during the Cretaceous amphibolite facies metamorphic overprint of the pre-existing mineral assemblages comprising garnet, staurolite, and kyanite from an amphibolite facies metamorphic event probably of Variscian age. The newly formed garnet may take the form of reaction rims along the margins of large pre-existing staurolite blasts. The initial growth increments of garnet have low grossular content, and reaction rim growth was controlled by the transfer of Fe, Mg and Mn components from the staurolite-garnet interface to the quartz-garnet interface. Later garnet growth increments have relatively high grossular content due to consumption of matrix plagioclase, which was destabilized by successive pressure increase. The grossular content of newly formed garnet shows systematic increase towards sites where plagioclase breaks down indicating that transport of calcium through the matrix was sluggish. On the basis of reaction microstructures it is demonstrated that the mineral assemblage garnet?+?kyanite?+?biotite?+?paragonite was formed at the conditions of eo-alpine amphibolite facies overprint while staurolite and plagioclase broke down successively with increasing pressure.     

The nature and significance of the mechanism of sillimanite growth in the Connemara schists,Ireland

During prograde metamorphism of the Connemara pelites, sillimanite first develops in biotite immediately adjacent to, or replacing, garnet. In some rocks, breakdown of garnet+muscovite and staurolite +muscovite+quartz leads to the development of fibrolite pseudomorphs after garnet. The textures indicate a constant volume replacement of garnet with movement of Al from staurolite and muscovite in the matrix towards the few, widely scattered, garnet sites. The complex ionic reaction patterns are the result of the strong preference of sillimanite to grow on biotite that is replacing garnet, and this pattern of preferred nucleations is taken to indicate that the equilibrium conditions for the reaction were only overstepped by the minimum required for initial sillimanite nucleation. Chemical movements were controlled by the heterogeneous nucleation pattern, not by intrinsic properties of the moving species. In order for extensive reaction to occur under near-equilibrium conditions, the rate at which the total thermal reaction proceeded must have been controlled by the supply of heat to the rocks rather than by diffusion or local reaction steps.     

Controls on the first appearance of jadeitic pyroxene, northern Diablo Range, California

A reaction producing jadeitic pyroxene in metagreywackes of the northern Diablo Range has been identified on the basis of mineral distribution, isograd patterns and composition of coexisting minerals. The appearance of jadeitic pyroxene (∼Jd₈₀) is closely followed by the disappearance of pumpellyite, which indicates that pumpellyite plays a major role in the pyroxene-producing reaction. A new projection from hematite, lawsonite, chlorite, quartz and H₂O on to the NaAlO₂-FeO-MgO ternary confirms the role of pumpellyite in pyroxene production and suggests a reaction of the form: 1.00 pumpellyite + 0.31 chlorite + 8.71 albite + 0.70 hematite + 2.00 H₂O = 8.54 jadeite + 0.57 glaucophane + 3.09 lawsonite + 5.26 quartz. Metagreywackes of the northern Diablo Range were metamorphosed under conditions of P _H2O= P _total at 200-300 °C and 7.5-10.0 kbar. Despite the low temperatures attained during metamorphism, the assumption of equilibrium yields results consistent with field observations and phase relations.     

The origin of olivine-plagioclase coronas in metagabbros from the Adirondack Mountains, New York

Olivine-plagioclase coronas in metagabbros from the Adirondack Mountains, New York (USA) are spatially well-organized reaction textures consisting most commonly of sequential layers of orthopyroxene, clinopyroxene, plagioclase, and garnet; the textures are characteristic of diffusion-controlled reaction kinetics. Although similar coronas have been interpreted by previous workers in terms of an isochemical steady-state diffusion model, petrographical relations and material-balance calculations establish that coronas in the Adirondack metagabbros cannot be treated as isochemical and do not form in a single-stage steady-state process; instead they evolve through time in a complex open-system reaction. In this study, the isochemical diffusion model is modified to account for elemental fluxes across the outer boundaries of the coronal reaction band, thereby approximating the open-system behaviour of the coronas. The sequence and relative proportions of product minerals calculated by the open-system steady-state model correspond closely to those observed in coronas of the Adirondacks, over a wide range of values for the relative diffusivities of chemical components involved in the reaction, regardless of the particular method used to determine material balance in the reaction texture. Despite this correspondence, petrographical evidence for successive replacement of coronal product layers reveals that the Adirondack coronas evolved through one or more transient states, rather than forming in a single-stage steady-state process. There is no evidence that the successive replacement of coronal product layers resulted from changes in pressure or temperature, but there is petrographical evidence that these changes resulted from modification of the composition of reactant plagioclase as the corona-forming reaction proceeded. This is confirmed by the fact that the evolution of the coronas over time can be replicated with the open-system diffusion model by simulating the effect of the gradual exhaustion of plagioclase as a source of the Ca and Si components required for reaction. These simulations suggest that successive stages in the evolution of the coronas are characterized by these product sequences: (i) orthopyroxene-clinopyroxene-plagioclase-garnet; (ii) orthopyroxene-clinopyroxene-garnet; and (iii) orthopyroxene-garnet. All of these stages, and the transitions between them, are observed petrographically. Coronas in Adirondack metagabbros appear, therefore, to have originated in a complex, open-system, diffusion-controlled reaction in which the product assemblages changed as the reaction progressed.     

Groundwater in fractured crystalline rocks, the Clara mine, Black Forest (Germany)

The chemical composition of water sampled in a 700 m deep underground barite-fluorite mine in the crystalline basement of the Black Forest area (SW Germany) varies systematically with depth and the length of flow paths trough, the fracture porosity of the gneiss matrix. Calcium and sulfate increase as a result of a combined sulfide oxidation and plagioclase alteration reaction. The gneiss contains andesine–plagioclase (An₂₀–An₄₀) and is rich in primary sulfide. As an effect of Ca and SO₄ release by the prime water–rock reaction, dissolved oxygen decreases and the waters become more reduced. The waters have Cl/Br mass ratios of about 50, which is very close to that of experimentally leached gneiss powders indicating that the rock matrix is the source of the halogens. The waters are undersaturated with respect to calcite in the upper parts of the mine. With increasing reaction progress, calcite saturation is reached and carbonate forms as a reaction product of the prime reaction that also controls the partial pressure of CO₂ to progressively lower values. The chemical evolution of groundwater in fractured basement of the Clara mine suggests that the partial pressure of CO₂ is an internally buffered parameter rather than a controlling external variable.     

Hercynite as the product of staurolite decomposition in the contact aureole of Vedrette di Ries,eastern Alps,Italy

Metapelitic hornfelses in the contact aureole of the Vedrette di Ries pluton exhibit the terminal decomposition of Zn-poor Fe-staurolite in a muscovite-quartz-free domain. The reaction takes place only within coarsegrained sillimanite that has replaced andalusite porphyroblasts during prograde metamorphism. The product is a gahnite-poor hercynitic spinel, which occurs as very small grains closely associated in space with resorbed staurolite. Microstructural observations indicate that bereynite growth postdates the pseudomorphs of sillimanite after andalusite. The textural evidence for a genetic relationship between hercynite and staurolite is confirmed by the identical Fe/Mg/Zn ratios of the two minerals, which causes the collinearity of hercynite, staurolite and Al₂SiO₅ in FeO–MgO–ZnO–Al₂O₃–SiO₂–H₂O composition space (FMZASH), and indicates hercynite formed by the reaction: Fe-staurolite = 3.85hercynite + 5.1sillimanite + 2.55quartz + 2H₂O Staurolite inclusions within andalusite did not break down to form hercynite, indicating a kinetic control, as well as little overstepping of the equilibrium conditions, of the reaction forming hercynite. Assuming overstepping did not occur, modelling of the reaction with existing thermodynamic data in the simplified FASH system suggests that the terminal breakdown of staurolite to form hercynite occurred at 2.5–3.75kbar and 585–655°C.     

Aggregation of colloidal iron during estuarine mixing: Kinetics,mechanism, and seasonality

The colloid chemistry of iron and humic aggregation was studied in a series of laboratory experiments, which were related to seasonal aggregation extent data collected in a temperate estuary. Kinetically, the aggregation of iron occurs with a rapid initial reaction, finished within a few minutes, followed by an extensive, slow second reaction, which lasts for several hours. Organic carbon aggregation, however, occurs primarily in the first reaction. The first reaction is perikinetic while the second reaction is observed to be either perikinetic or orthokinetic, depending on the pore size of the filter used to clarify the suspension. The second reaction involves aggregation of small filtrable colloids (<0.5 μm) with larger aggregates formed in the first reaction, and follows pseudo-second order kinetics with respect to the filtrable iron concentration when finer filters (<0.5 μm) are used for clarification. Little or no temperature dependence is evident for the first reaction extent, while increasing temperature strongly enhances the second reaction. An activation energy of 9–11 kcal·mole^?1 for the second reaction is due to a combination of transport and charge repulsion terms. Field data show a correspondingly greater aggregation extent of iron with salinity in warmer months relative to colder months.