A geochemical model for evaluating theories on the genesis of Florida's sedimentary phosphate deposits

Present ionic concentrations of Ca ⁺⁺,HCO ₃ ^- ,and HPO ₄ ⁼ in surface and groundwater runoff in Florida indicate that phosphorus is being concentrated in rock through dissolution and reprecipitation, with calcium phosphate increasing at the expense of calcium carbonate. Analog computer simulation of a systems model of this process suggests that significant enrichment can occur in 20 million years. The degree of enrichment depends on the supply of new phosphorus to Florida through rain and oceanic exchange processes. If the calcium phosphate content of original rock is 0.5 to 1.0 percent (0.52 to 1.05 percent P ₂ O ₅),a formation with 10 to 20 percent calcium phosphate (CaPO ₄ or 10.5 to 21.0 percent P ₂ O ₅)as in the Hawthorn Formation (Miocene)may result. Nutrient upwelling along the continental slope coupled with transport to the estuaries by lateral eddy diffusion can supply an additional 400 mg P|m ² |yr which, if deposited, would result in a sediment with a 4.3 percent CaPO ₄ (4.5 percent P ₂ O ₅)content. If this is enriched later by resolution, 40 percent CaPO ₄ (42 percent P ₂ O ₅)results. Through geologic time, the ocean may be considered as a source of phosphorus to the land through rain or estuarine sediment.     

Mineralogical and geochemical investigation of clay-rich mine tailings from a closed phosphate mine, Bartow Florida, USA

Clay-rich mine tailings from phosphate mine operations in Florida are a major environmental and economic problem. Options for reclamation and restoration for these tailings are very limited and are fundamentally restricted by poor physical properties such as low mechanical strength, low hydraulic conductivity, and heavy metal content. The major control on these bulk physical properties is the mineralogy of the materials. Eight continuous push borings were obtained to investigate stratigraphy, mineralogy, aspects of geochemistry, and bulk properties of a deposit of clay-rich mine tailings from a phosphate mine near Bartow, Florida that ceased operations in the early 1970s. Stratigraphy is dominated by laminated clay-rich sediment with minor units of silt and sand. An intact kaolinite liner occurs near the impoundment walls and the impoundment floor has approximately 4 m of relief. Moisture content varies from 4.35 to 57.40 wt% and organic content varies from 0.41 to 9.53 wt%. Bulk XRF investigation indicates that the P₂O₅ concentrations vary from approximately 4 to 21 wt%. A very strong correlation (r ² = 0.92) between CaO and P₂O₅ indicates that apatite is a major control on the phosphate. The strong correlation (r ² = 0.77) of Al₂O₃ and TiO₂ suggests that the source materials for this deposit are comparatively uniform. A number of heavy metal elements and trace elements occur. Cr, V, Ni, Cu are interpreted to be in phosphate minerals, largely apatite. Sr and Pb are interpreted to be in both phyllosilicates and phosphate minerals. Two populations of apatite were observed in the clay-sized fraction, one that was Fe and Si- bearing and another that was only Si-bearing. Fe-bearing apatite had Fe₂O₃ contents that varied from 0.38 to 5.32 wt% and SiO₂ contents that varied from 0.90 to 3.32 wt%. The other apatite population had a wider range of SiO₂ contents that varied from 0.77 to 8.80 wt%. TEM imaging shows that apatite grains are dominantly single crystals with lesser amounts of aggregates. Wavellite commonly occurs as individual or clusters of lath-like crystals and the chemical composition differs from the pure aluminium phosphate end member with average concentrations of components being that of CaO (1.57 wt%), Fe₂O₃ (1.98 wt%), SiO₂ (5.94 wt%). In the clay-sized phosphate minerals investigated no fluorine was found above detection limit (approximately 0.15 wt%), nor was any uranium, radium, heavy metal, or REE element detected. The phyllosilicate mineralogy of the deposit is dominated by smectite (montmorillonite with lesser amounts of nontronite), palygorskite, illite and kaolinite. No systematic variation in the relative proportions of phyllosilicates was observed in the clay deposit. Energy dispersive spectroscopy EDS analysis indicates that chemical compositions of phyllosilicates are somewhat typical but overall are enriched with respect to Fe compared to theoretical end members. The relative enrichment of Fe is interpreted to be a primary sedimentary feature. Ca content in smectite minerals is high and may inhibit stabilization using lime or similar methods. The high percentages of montmorillonite and palygorskite explain the high bulk water contents observed. This investigation provides fundamentally new details regarding clay tailing deposits from closed phosphate mines in central Florida which can be used in restoration and reclamation efforts.     

The role of phosphorus in rhyolitic liquids as determined from the homogeneous iron redox equilibrium

The redox ratio of iron is used as an indicator of solution properties of silicate liquids in the system (SiO–Al₂O₃–K₂O–FeO–Fe₂O₃–P₂O₅). Glasses containing 80–85 mol% SiO₂ with 1 mol% Fe₂O₃ and compositions covering a range of K₂O/Al₂O₃ were synthesized at 1400°C in air (fixed fO₂). Variations in the ratio FeO/FeO_1.5 resulting from the addition of P₂O₅ are used to determine the solution behavior of phosphorus and its interactions with other cations in the silicate melt. In 80 mol% SiO₂ peralkaline melts the redox ratio, expressed as FeO/FeO_1.5, is unchanged relative to the reference curve with the addition of 3 mol% P₂O₅. Yet, the iron redox ratio in the 85 mol% SiO₂ potassium aluminosilicate melts is decreased relative to phosphorus-free liquids even for small amounts of P₂O₅ (0.5 mol%). The redox ratio in peraluminous melts is decreased relative to phosphorus- free liquids at P₂O₅ concentrations of 3 mol%. In peraluminous liquids, complexing of both Fe⁺³–O–P⁺⁵ and Al⁺³–O–P⁺⁵ occur. The activity coefficient of Fe⁺³ is decreased because more ferric iron can be accommodated than in phosphorus-free liquids. In peralkaline melts, there is no evidence that P⁺⁵ is removing K⁺ from either Al⁺³ or Fe⁺³ species. In chargebalanced melts with 3 mol% Fe₂O₃ and very high P₂O₅ concentrations, phosphorus removes K⁺ from K–O–Fe⁺³ complexes resulting in a redox increase. P₂O₅ should be accommodated easily in peraluminous rhyolitic liquids and phosphate saturation may be suppressed relative to metaluminous rhyolites. In peralkaline melts, phosphate solubility may increase as a result of phosphorus complexing with alkalis. The complexing stoichiometry may be variable, however, and the relative influence of peralkalinity versus temperature on phosphate solubility in rhyolitic melts deserves greater attention.     

A modern, guano-related occurrence of foggite, CaAl(PO4)(OH)2 · H2O and churchite-(Y), YPO4 · 2H2O in Cioclovina Cave, Romania

Summary This study reports foggite and churchite-(Y) from two spatially separate locations in the guano-related phosphate deposit from the Cioclovina Cave, Romania. Optical microscope observations, powder X-ray diffraction, electron microprobe analyses, and FTIR were used in the analysis of the two minerals. The chemical composition of foggite was determined to be Ca_0.925(Al_0.91Fe²⁺_0.016)_Σ0.926(P_0.991Si_0.043)_Σ1.034O_3.74(OH)_2.26 · H₂O and churchite-(Y) [(Y_0.830Dy_0.043Er_0.033Gd_0.029Yb_0.022)_Σ0.957Ca_0.009]P_1.023O_4.00 · 2H₂O. Chemical analyses of Cioclovina churchite-(Y) clearly revealed enrichment in lanthanides of even atomic number. The refined unit-cell parameters are for foggite (orthorhombic) a = 9.264(1) ?, b = 21.334(8) ?, c = 5.197(7) ?, and V = 1027.13(8) ?³ (Z = 8); for churchite-(Y) (monoclinic): a = 5.578(8) ?, b = 15.013(6) ?, c = 6.277(8) ?, β = 117.94(4)°, and V = 464.38(5) ?³ (Z = 4). FTIR spectrum of churchite-(Y) exhibits all the bands assigned to the vibrations of PO₄, OH, and water groups. Unlike other documented occurrences of foggite and churchite-(Y), in Cioclovina Cave, the occurrence of these minerals are related to a process that phosphatized subjacent limestone and various cave sediments (sand, clay, and limy mud) to form a complex phosphate assemblage. The minerals are presumably derived from phosphate-rich solutions that reacted with clay earth while moving downward through the sediments. Foggite was formed at the expense of the originally precipitated crandallite. Locally concentrated yttrium, REE, and dissolved phosphate are probably responsible for the precipitation of churchite-(Y). Present address: Department of Geology, University of South Florida, Tampa, FL, USA     

硅酸钙晶种法回收污水中磷的实验研究

实验研究了以钾长石水热分解的副产物沉淀硅酸钙为晶种,回收模拟污水中磷的效果。结果表明,晶种用量0.4 g/L、p H值为8、Ca/P(摩尔比)=2条件下反应2 h后,污水中剩余磷浓度为0.32 mg/L,低于我国污水综合排放一级A标准0.5 mg/L。沉淀硅酸钙重复使用60次后回收磷的效果仍然较好,回收率为79.5%以上。采用扫描电镜、红外光谱、粉晶X射线衍射等测试手段对回收产物进行的分析表明,回收磷产物以羟磷灰石形态存在,产物中P2O5含量在35%以上,达到了富磷矿的品位。沉淀硅酸钙有望成为回收磷的理想晶种材料。     

Tracing sources and cycling of phosphorus in Peru Margin sediments using oxygen isotopes in authigenic and detrital phosphates

Many (bio)geochemical processes that bring about changes in sediment chemistry normally begin at the sediment-water interface, continue at depth within the sediment column and may persist throughout the lifetime of sediments. Because of the differential reactivity of sedimentary phosphate phases in response to diagenesis, dissolution/precipitation and biological cycling, the oxygen isotope ratios of phosphate (δ¹⁸O_P) can carry a distinct signature of these processes, as well as inform on the origin of specific P phases. Here, we present results of sequential sediment extraction (SEDEX) analyses combined with δ¹⁸O_P measurements, aimed at characterizing authigenic and detrital phosphate phases in continental margin sediments from three sites (Sites 1227, 1228 and 1229) along the Peru Margin collected during ODP Leg 201. Our results show that the amount of P in different reservoirs varies significantly in the upper 50 m of the sediment column, but with a consistent pattern, for example, detrital P is highest in siliciclastic-rich layers. The δ¹⁸O_P values of authigenic phosphate vary between 20.2‰ and 24.8‰ and can be classified into at least two major groups: authigenic phosphate precipitated at/near the sediment-water interface in equilibrium with paleo-water oxygen isotope ratios (δ¹⁸O_w) and temperature, and phosphate derived from hydrolysis of organic matter (P_org) with subsequent incomplete to complete re-equlibration and precipitated deeper in the sediments column. The δ¹⁸O_P values of detrital phosphate, which vary from 7.7-15.4‰, suggest two possible terrigenous sources and their mixtures in different proportions: phosphate from igneous/metamorphic rocks and phosphate precipitated in source regions in equilibrium with δ¹⁸O_w of meteoric water. More importantly, original isotopic compositions of at least one phase of authigenic phosphates and all detrital phosphates are not altered by diagenesis and other biogeochemical changes within the sediment column. These findings help to understand the origin and provenance of P phases and paleoenvironmental conditions at/near the sediment-water interface, and to infer post-depositional activities within the sediment column.     

Raman spectroscopy and heat capacity measurement of calcium ferrite type MgAl2O4 and CaAl2O4

Raman spectroscopy of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ and heat capacity measurement of CaAl₂O₄ calcium ferrite were performed. The heat-capacity of CaAl₂O₄ calcium ferrite measured by a differential scanning calorimeter (DSC) was represented as C_P(T)=190.6–1.116 × 10⁷T^–2 + 1.491 × 10⁹T^–3 above 250 K (T in K). The obtained Raman spectra were applied to lattice dynamics calculation of heat capacity using the Kieffer model. The calculated heat capacity for CaAl₂O₄ calcium ferrite showed good agreement with that by the DSC measurement. A Kieffer model calculation for MgAl₂O₄ calcium ferrite similar to that for CaAl₂O₄ calcium ferrite was made to estimate the heat capacity of the former. The heat capacity of MgAl₂O₄ calcium ferrite was represented as C_P(T)=223.4–1352T ^–0.5 – 4.181 × 10⁶T ^–2 + 4.300 × 10⁸T ^–3 above 250 K. The calculation also gave approximated vibrational entropies at 298 K of calcium ferrite type MgAl₂O₄ and CaAl₂O₄ as 97.6 and 114.9 J mol^–1 K^–1, respectively.     

云南省镇雄县羊场磷矿地球化学特征及其沉积环境分析

羊场磷矿是近年来在云南评价确认的沉积大型磷矿床,磷矿体赋存于下寒武统梅树村组碳酸盐岩-泥质碎屑岩沉积中部的一套含磷岩系中,呈层状、似层状展布于羊场背斜两翼,其产状与地层产状基本一致,含矿岩性为含磷白云岩、磷质岩、磷块岩、硅质岩建造。通过分析该矿床矿体特征和梅树村组磷块岩的主微量元素组成,研究了羊场磷矿的地球化学特征及其沉积环境。结果表明,羊场磷矿磷块岩具有富钙（w（CaO）=42.07%~45.01%）、磷（w（P₂O₅）=27.66%~39.25%）和贫硅（w（SiO₂）=8.27%~15.40%）的特征;w（P₂O₅）与w（CaO）呈较好的正相关关系,与w（MgO）呈负相关关系,与w（Al₂O₃）呈较明显的负相关关系。矿石的w（Th）/w（U）值小于1、Pb （亲硫元素）和Sr富集（Pb平均富集系数16.66,Sr平均富集系数1.17）特征表明,羊场磷矿可能是热水沉积成矿与生物成矿双重作用的结果;微量元素特征值反映,羊场磷矿形成于深海到浅海的变化环境,为海相沉积型磷块岩,沉积时水体呈还原环境。     

The use of soil geochemistry in outlining phosphate deposits, northern and southern Venezuela

Phosphate deposits have been outlined in Falcón State (Northern Venezuela) and Táchira State (Southwestern Venezuela) using geochemical soil methods.The phosphate deposits located in Falcón State constitute lenses and masses interbedded with Tertiary limestone and shales. The area is covered by a thick soil with few outerops and the region is characterized by typical tropical rain forest. Soil samples taken every 1000 m across complete stratigraphic sequences were analyzed for P₂O₅ content. An anomalous area with a P₂O₅ content ranging from 3.19% to 9.04% was outlined accompanied by areas with less than 0.83% of P₂O₅. More than 11 million metric tons of commercial phosphatic rock were associated with this anomaly.In Táchira State several stratigraphic sequences of potentially phosphatic rocks with a thick cover of black soil were geochemically investigated. Soil samples taken each 10 m were analyzed for P₂O₅. A sequence of phosphatic rock was outlined showing a P₂O₅ content varying between 7.3% and 9.2%. Apparently the sequence is interbedded with phosphate-poor siliceous rocks showing a P₂O₅ content below 2%.As result of this preliminary investigation, expensive trenching, pitting and drilling works can be carefully planned.     

The effect of phosphorus on the iron redox ratio,viscosity, and density of an evolved ferro-basalt

Despite the abundant evidence for the enrichment of phosphorus during the petrogenesis of natural ferro-basalts, the effect of phosphorus on the physical properties of these melts is poorly understood. The effects of phosphorus on the viscosity, density and redox ratio of a ferro-basaltic melt have been determined experimentally. The viscosity measurements were obtained using the concentric cylinder method on a ferro-basaltic melt above its liquidus, at 1 atm, in equilibrium with air and with CO₂. The density measurements were performed using the double Pt-bob Archimedean method at superliquidus conditions under 1 atm of air. The redox ratio was obtained by wet chemical analysis of samples collected during physical property measurements. Phosphorus pentoxide reduces ferric iron in ferro-basaltic melt. The reduction due to P₂O₅ is much larger than that for most other oxide components in basaltic melts. A coefficient for the reduction of ferric iron has been generated for inclusion in calculation schemes. The effect of P₂O₅ on the viscosity is shown to be complex. The initial reduction of ferric iron with the addition of P₂O₅ results in a relatively small change in viscosity, while further addition of P₂O₅ results in a strong increase. The addition of phosphorus to a ferro-basaltic melt also reduces the density. A partial molar volume of 64.5±0.7 cm³/mol for P₂O₅ in this melt has been obtained at 1300° C, yielding a volume of 12.9 cm³/mol per oxygen, consistent with a tetrahedral coordination for this high field strength cation. The effects of P₂O₅ on redox state, density and viscosity provide constraints on the structural role of phosphorus in these melts. The results suggest a complex interaction of phosphorus with the aluminosilicate network, and tetrahedral ferric iron. In light of the significant effects of phosphorus on the physical and chemical properties of ferro-basaltic liquids, and the extreme enrichments possible in these liquids in nature, the role of phosphorus in these melts should, in future, be considered more carefully.     

Rapid analysis of Florida phosphates by energy-dispersive X-ray fluorescence

A rapid X-ray fluorescence technique has been developed to determine the BPL (Ca₃(PO₄)₂ or Bone Phosphate of Lime) content of various streams in Florida phosphate beneficiation and in supporting laboratory flotation experiments. The method, which requires simple sample preparation, a 100-sec counting, and has an accuracy of better than 2% BPL (0.4% P), employs an Fe⁵⁵ radioactive source and a room temperature detector to analyze for calcium. The BPL values, which can not be obtained readily and directly because of the weak fluorescence of phosphorus, are instead derived from a close correlation found to exist between the phosphorus and calcium concentrations.     

Phosphorus solubility mechanisms in haplogranitic aluminosilicate glass and melt: effect of temperature and aluminum content

The solubility behavior of phosphorus in glasses and melts in the system Na₂O-Al₂O₃-SiO₂-P₂O₅ has been examined as a function of temperature and Al₂O₃ content with microRaman spectroscopy. The Al₂O₃ was added (2, 4, 5, 6, and 8 mol% Al₂O₃) to melts with 80 mol% SiO₂ and ∼2 mol% P₂O₅. The compositions range from peralkaline, via meta-aluminous to peraluminous. Raman spectra were obtained of both the phosphorus-free and phosphorous-bearing glasses and melts between 25 and 1218 °C. The Raman spectrum of Al-free, P-bearing glass exhibits a characteristic strong band near 940 cm⁻¹ assigned to P=O stretching in orthophosphate complexes together with a weaker band near 1000 cm⁻¹ assigned P₂O₇ complexes. With increasing Al content, the proportion of P₂O₇ initially increases relative to PO₄ and is joined by AlPO₄ complexes which exhibit a characteristic P-O stretch mode slightly above 1100 cm⁻¹. The latter complex appears to dominate in meta-aluminosilicate glass and is the only phosphate complex in peraluminous glasses. When P-bearing peralkaline silicate and aluminosilicate glasses are transformed to supercooled melts, there is a rapid decrease in PO₄/P₂O₇ so that in the molten state, PO₄ units are barely discernible. The P₂O₇/AlPO₄ abundance ratio in peralkaline compositions increases with increasing temperature. This decrease in PO₄/P₂O₇ with increasing temperature results in depolymerization of the silicate melts. Dissolved P₂O₅ in peraluminous glass and melts forms AlPO₄ complexes only. This solution mechanism has no discernible influence on the aluminosilicate melt structure. There is no effect of temperature on this solution mechanism. Received: 7 October 1997 / Accepted: 11 May 1998     

Controls on the formation of authigenic minerals in association with decaying organic matter: an experimental approach

Carcasses of the shrimp Crangon crangon were incubated in a marine medium under oxic conditions at 15°C which was inoculated with a consortium of sulfate-reducing, sulfide-oxidizing, and fermentative bacteria. These standard conditions were varied by adding sediment, omitting sulfate, adding glucose, omitting the inoculum, adding phosphate, and enhancing the buffer capacity. The chemical gradients generated by decay were monitored over a period of 29 days with O₂, pH- and sulfide-microelectrodes. In most of the experiments oxygen was depleted, pH decreased and sulfide accumulated around the carcass within a week, creating steep chemical gradients, and decay was predominantly anaerobic. By 29 days maximum change in O₂ concentration was from around 200 to 0 μM, in pH from 7.5 to 6.2, and in sulphide concentration from 0 to 5.6 mM. Although weight loss and general decay were least when only indigenous bacteria were present, only CaCO₃ crystal bundles formed and there was no soft tissue preservation. In contrast, where decay and weight loss were more extensive anaerobic sulphate reduction was intense, pH decreased markedly, and some muscle tissue was replicated in CaPO₄. The pH close to the decaying carcass seemed to determine whether CaCO₃ or CaPO₄ formed. Paradoxically, the exceptional preservation of soft-tissues in fossils requires elevated rather than restricted microbial activity as this leads to anaerobically driven authigenic mineral formation.     

贵州瓮福磷矿含磷岩系层序特征及黔中古陆控矿意义

新元古代末期震旦系陡山沱阶和早古生代早期寒武系梅树村阶是全球两大成磷时期.贵州瓮福磷矿含磷岩系—早震旦世陡山沱组磷矿a矿层与b矿层,是震旦系陡山沱阶成磷事件的典型代表.瓮福磷矿含磷岩系为在浅水陆棚地区沉积的一套与磷矿有成因联系的岩石组合,属于浅海台地相型;含磷岩系具备早期准备阶段、磷质富集阶段及晚期磷质贫化消失阶段的沉...     

Geochemical and statistical characterization of the phosphate facies of the Farim‐Saliquinhé phosphate mineralization (Guinea‐Bissau)

The Eocene Farim‐Saliquinhé phosphate mineralization (FSPM) is a buried sedimentary deposit located in the northern part of Guinea‐Bissau, discovered and spatially constrained during the 1980s by the French Geological Survey (BRGM). In the present work some of the data collected at that time are reworked in the framework of the development of a 3D geological and geochemical model of this mineralization. We show the usefulness of two classical multivariate statistical methods – principal component analysis (PCA) and cluster analysis (CA) – applied to eight geochemical variables (P₂O₅, SiO₂, Al₂O₃, Fe₂O₃, CaO, MgO, F and CO₂) measured in 247 samples from phosphate facies, for differentiation of samples taken from the different phosphate facies recognized in the FSPM, namely the main ore FPA (30 to 35% high grade phosphate), the calcareous low grade phosphate FPB (10 to 20% P₂O₅) (both Lutetian), and a mineralized Upper Eocene to Lower Oligocene cover (mainly including the FPO level and a silico‐aluminous phosphate bed), overlying the FPA, which can also be considered a third set of phosphate facies associated with the FSPM.     

A comparative study of Pleistocene phosphorites from the continental slope off western India

Two types of phosphorite recovered from the continental slope off western India are described. The first type, phosphorite 1, comprises a hard, grey nodule composed of carbonate fluorapatite (CFA) and calcite as major minerals. The phosphorite consists of light‐brown microcrystalline apatite containing a few skeletal fragments and planktonic foraminifera. Scanning electron microscope (SEM) studies show evidence of dissolution of skeletal calcite and filling of the resulting cavities by phosphate composed of ovoid to rod‐shaped apatite microparticles. Apatite also occurs as coatings on these particles. The P₂O₅ content of the phosphorite is 29%, and the CO₂ content of the CFA is about 4·5%. The rare‐earth element (REE) abundance (ΣREE=2·02 μg g^–1) is lower than in other modern phosphorites. The ⁸⁷Sr/⁸⁶Sr ratio and ?Nd value of this sample are 0·70921 and –9·9 respectively. The ¹⁴C age found through accelerator mass spectrometry (AMS) dating (18 720 ± 120 years BP) is much younger than that determined by the U‐series method (100 ka). The second type, phosphorite 2, comprises a friable, light‐brown nodule consisting of CFA as the only major mineral, with a CO₂ content of the CFA of 4·5%. In thin section, the phosphate is light brown and homogeneous, and a few bone fragments are present. The P₂O₅ content is 33%, and REE contents (ΣREE = 0·18 μg g^–1) are lower than in phosphorite 1. The age of phosphorite 2 is >300 ka. Phosphorite 1 appears to have formed during the late Pleistocene through replacement of carbonate by phosphate; phosphorite 2 is also of Pleistocene age but is much older than phosphorite 1. The initial substrate for phosphorite 2 was a fish coprolite, which was subsequently phosphatized during slow sedimentation under low‐energy conditions. Microbial mediation is evident in both phosphorites. The colour, density and P₂O₅ content of the phosphorites are found to be dependent on the nature of the initial substrates and physico‐chemical conditions during phosphatization. The CO₂ content of the CFA is not related to the precursor carbonate phase. The nature of sediments, rates of sedimentation and the time spent undergoing phosphogenesis at the sediment–water interface may control REE concentrations in phosphorites.     

华南埃迪卡拉纪陡山沱组物源风化对全球性成磷事件的启示

华南埃迪卡拉纪陡山沱组沉积于原始地球-生命系统向现代地球-生命系统过渡的关键时期,该套地层记录了地质历史时期一次大规模成磷事件,但关于该次成磷事件中磷元素的来源仍存在诸多争议。浅海区磷元素主要来源于由河流搬运的陆表含磷矿物风化产物及上升流作用所带来的其他海域含磷水体,这两种来源可以通过全岩碎屑元素(Al、Fe、Th等)和稀土元素的含量及其分布特征进行区分。本文通过对上扬子地区乡党坪剖面和四斗坪剖面的陡山沱组主、微量元素特征的综合分析,恢复了该地区的物源体系及其风化作用过程。较高的P₂O₅-Al₂O₃、P₂O₅-Fe₂O₃相关性,表明该时期磷来源于陆地风化而非上升流;较低的Th/Co、La/Sc、Th/Cr等比值,TiO₂-Zr相关性以及Th-Hf-Co、La-Th-Sc三角图分布关系,表明研究区内陡山沱组的物源体系主要为玄武岩;较高的化学蚀变指数(CIA)和较低的Sr/Cu值,表明物源区当时...     

A chemical survey of the Mississippi estuary

A “snap shot” survey of the Mississippi estuary was made during a period of low river discharge, when the estuarine mixing zone was within the deltaic channels. Concentrations of H⁺, Ca²⁺, inorganic phosphorus and inorganic carbon suggest that the waters of the river and the low salinity (<5‰) portion of the estuary are near saturation with respect to calcite and sedimentary calcium phosphate. An input of oxidized nitrogen species and N₂O was observed in the estuary between 0 and 4‰ salinity. The concentrations of dissolved NH₄ ⁺ and O₂, over most of the estuary, appeared to be influenced by decomposition of terrestrial organic matter in bottom sediments. The estuarine bottom also appears to be a source of CH₄ which has been suggested to originate from petroleum shipping and refining operations. Estuarine mixing with offshore Gulf waters was the dominant influence on distributions of dissolved species over most of the estuary (i.e., from salinities >5‰). The phytoplankton abundance (measured as chlorophylla) increased as the depth of the mixed layer decreased in a manner consistent with that expected for a light-limited ecosystem. Fluxes of NO₃ ^?+NO₂ ^? and soluble inorganic phosphorus to the Gulf of Mexico were estimated to be 3.4±0.2×10³ g N s^?1 and 1.9±0.2 g P s^?1 respectively, at the time of this study.     

Chemical mass transfer in magmatic processes IV. A revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures

A revised regular solution-type thermodynamic model for twelve-component silicate liquids in the system SiO₂-TiO₂-Al₂O₃-Fe₂O₃-Cr₂O₃-FeO-MgO-CaO-Na₂O-K₂O-P₂O₅-H₂O is calibrated. The model is referenced to previously published standard state thermodynamic properties and is derived from a set of internally consistent thermodynamic models for solid solutions of the igneous rock forming minerals, including: (Mg,Fe²⁺,Ca)-olivines, (Na,Mg,Fe²⁺,Ca)^M2 (Mg,Fe²⁺, Ti, Fe³⁺, Al)^M1 (Fe³⁺, Al,Si)₂ ^TETO₆-pyroxenes, (Na,Ca,K)-feldspars, (Mg,Fe²⁺) (Fe³⁺, Al, Cr)₂O₄-(Mg,Fe²⁺)₂ TiO₄ spinels and (Fe²⁺, Mg, Mn²⁺)TiO₃-Fe₂O₃ rhombohedral oxides. The calibration utilizes over 2,500 experimentally determined compositions of silicate liquids coexisting at known temperatures, pressures and oxygen fugacities with apatite ±feldspar ±leucite ±olivine ±pyroxene ±quartz ±rhombohedral oxides ±spinel ±whitlockite ±water. The model is applicable to natural magmatic compositions (both hydrous and anhydrous), ranging from potash ankaratrites to rhyolites, over the temperature (T) range 900°–1700°C and pressures (P) up to 4 GPa. The model is implemented as a software package (MELTS) which may be used to simulate igneous processes such as (1) equilibrium or fractional crystallization, (2) isothermal, isenthalpic or isochoric assimilation, and (3) degassing of volatiles. Phase equilibria are predicted using the MELTS package by specifying bulk composition of the system and either (1) T and P, (2) enthalpy (H) and P, (3) entropy (S) and P, or (4) T and volume (V). Phase relations in systems open to oxygen are determined by directly specifying the f _{o 2} or the T-P-f _{o 2} (or equivalently H-P-f _{o 2}, S-P-f _{o 2}, T-V-f _{o 2}) evolution path. Calculations are performed by constrained minimization of the appropriate thermodynamic potential. Compositions and proportions of solids and liquids in the equilibrium assemblage are computed.     

The geochemistry of iodine in near-shore carbonate sediments

The total concentration of I is commonly higher in surface terrigenous sediments relative to more deeply buried material. Diagenetic release, loss of dissolved I during burial, and back-reaction of I with the solid phase under oxidizing conditions contribute to I enrichment near the sediment/water interface. In order to differentiate between scavenging of dissolved I by organic matter or metal oxides, the diagenetic behavior of I was examined in the Fe-poor carbonate sediments of Florida Bay, Florida. In this environment I is released by organic decomposition at I/C ratios similar to terrigenous environments (~0.5 mmole/mole), transported to the oxygenated sediment/water interface, and lost to the overlying water. The dissolved I flux from these deposits is roughly equivalent to the production rate within the deposit (~10 μmole/m²/day at 28°C). No significant enrichment is observed in the solid phase.Dissolved iodine transport within the sediment column may also be controlled by non-steady-state lateral diffusion into burrows. These observations, together with laboratory experiments which demonstrate IO^?₃ scavenging by Fe-oxyhydroxides at pH ≤ 8, imply that enrichment of I in terrigenous surface sediments results predominantly from the initial oxidation of I^? to IO^?₃ by microorganisms, followed by sorption on Fe oxides. Upon burial and reduction during anaerobic decomposition, this metal-associated I is released to solution, in a manner similar to phosphate.