Silicate and carbonate mineral weathering in soil profiles developed on Pleistocene glacial drift (Michigan, USA): Mass balances based on soil water geochemistry

Geochemistry of soil, soil water, and soil gas was characterized in representative soil profiles of three Michigan watersheds. Because of differences in source regions, parent materials in the Upper Peninsula of Michigan (the Tahquamenon watershed) contain only silicates, while those in the Lower Peninsula (the Cheboygan and the Huron watersheds) have significant mixtures of silicate and carbonate minerals. These differences in soil mineralogy and climate conditions permit us to examine controls on carbonate and silicate mineral weathering rates and to better define the importance of silicate versus carbonate dissolution in the early stage of soil-water cation acquisition.Soil waters of the Tahquamenon watershed are the most dilute; solutes reflect amphibole and plagioclase dissolution along with significant contributions from atmospheric precipitation sources. Soil waters in the Cheboygan and the Huron watersheds begin their evolution as relatively dilute solutions dominated by silicate weathering in shallow carbonate-free soil horizons. Here, silicate dissolution is rapid and reaction rates dominantly are controlled by mineral abundances. In the deeper soil horizons, silicate dissolution slows down and soil-water chemistry is dominated by calcite and dolomite weathering, where solutions reach equilibrium with carbonate minerals within the soil profile. Thus, carbonate weathering intensities are dominantly controlled by annual precipitation, temperature and soil pCO₂. Results of a conceptual model support these field observations, implying that dolomite and calcite are dissolving at a similar rate, and further dissolution of more soluble dolomite after calcite equilibrium produces higher dissolved inorganic carbon concentrations and a Mg²⁺/Ca²⁺ ratio of 0.4.Mass balance calculations show that overall, silicate minerals and atmospheric inputs generally contribute <10% of Ca²⁺ and Mg²⁺ in natural waters. Dolomite dissolution appears to be a major process, rivaling calcite dissolution as a control on divalent cation and inorganic carbon contents of soil waters. Furthermore, the fraction of Mg²⁺ derived from silicate mineral weathering is much smaller than most of the values previously estimated from riverine chemistry.     

Water chemistry and control of weathering of Pichola Lake,Udaipur District,Rajasthan, India

The water chemistry of Pichola lake revealed that it is dominated by Na and HCO₃. The lake water chemistry strongly reflects the dominance of continental weathering aided by anthropogenic activity, such as tourist influx, developmental activities in the catchment area, and disposal of untreated municipal and domestic sewage into the lake basin. The supply of major ions is mainly through weathering of the silicate rock exposed in the drainage basin and the contribution from saline and alkaline soils/groundwater because of the semiarid conditions of the region. The increase in phosphate loading and consequent depletion of silica suggests biological consumption of the latter. The observed chemical data of Pichola lake was used to predict the mineral assemblages in the carbonate and aluminosilicate system. It demonstrates that calcite and dolomite are the possible minerals that are in equilibrium with the lake water system and that the lake water chemistry is in the range of stability of kaolinite.     

碳酸盐岩溶解-沉淀热力学模型及其在塔北地区的应用

 碳酸盐岩作为一种化学岩类其物性受成岩作用的影响十分明显,溶解作用是否发育直接关系到碳酸盐岩储层质量的好坏。碳酸盐矿物在埋藏环境中的溶解度与地层水的化学成分、环境的温度、pH等有着密切的关系。利用地层水化学资料,根据化学热力学的理论,通过方解石及白云石与地层水作用的平衡反应,计算吉布斯自由能变化ΔG,以此来判断方解石及白云石的溶解趋势,并建立了封闭系统中这两种矿物与水作用的热力学模型。根据这个理论模型,对塔北地区159口井奥陶系及6口井的寒武系地层水进行了ΔG的计算,结果显示,塔北地区碳酸盐岩与地层水反应的ΔG基本为负值,表明该地区总体处于碳酸盐岩溶解的环境,寒武系白云岩反应的自由能小于奥陶系灰岩,即在这种深埋条件下白云岩比灰岩更易溶解,这一点在实际岩芯资料上及前人的实验模拟中均有显示。塔北于奇地区自由能的计算结果也为负值,说明该地区强烈的充填作用并非发生在现今条件下,于奇地区现今的埋藏环境是有利于碳酸盐矿物溶解的,这一结论也在该地区奥陶系及寒武系岩芯上得到了验证。
      

Dissolution and Deformation Characteristics of Limestones Containing Different Calcite and Dolomite Content Induced by CO2-Water-Rock Interaction

To investigate the impacts of mineral composition on physical and mechanical properties of carbonate rocks, limestone specimens containing different contents in calcite and dolomite are selected to perform CO2-water-rock reaction experiments. The X-ray Diffraction (XRD) and Nuclear Magnetic Resonance (NMR) are carried out to examine the change characteristics of mineral dissolution and pore structure after reaction. The core flooding experiments with Fiber Bragg gratings are implemented to examine the stress sensitivity of carbonate rocks. The results show that the limestones containing pure calcite are more susceptible to acid dissolution compared to limestone containing impure dolomite. The calcite content in pure limestone decreases as the reaction undergoes. The dissolution of dolomite leads to the formation of calcite in impure limestone. Calcite dissolution leads to the formation of macropore and flow channels in pure limestone, while the effects of impure dolomite in impure limestone results in mesopore formation. When confining pressure is lower than 12 MPa, pure limestones demonstrate higher strain sensitivity coefficients compared to impure limestone containing dolomite after reaction. When confining pressure exceeds 12 MPa, the strain sensitivity coefficients of both pure and impure limestones become almost equal.     

Hydrologic controls on radiogenic Sr in meltwater from an alpine glacier system: Athabasca Glacier,Canada

Filtered subglacial meltwater samples were collected daily during the onset of melt (May) and peak melt (July) over the 2011 melt season at the Athabasca Glacier (Alberta, Canada) and analyzed for strontium-87/strontium-86 (⁸⁷Sr/⁸⁶Sr) isotopic composition to infer the evolution of subglacial weathering processes. Both the underlying bedrock composition and subglacial water–rock interaction time are the primary influences on meltwater ⁸⁷Sr/⁸⁶Sr. The Athabasca Glacier is situated atop Middle Cambrian carbonate bedrock that also contains silicate minerals. The length of time that subglacial meltwater interacts with the underlying bedrock and substrate is a predominant determining factor in solute concentration. Over the course of the melt season, increasing trends in Ca/K and Ca/Mg correspond to overall decreasing trends in ⁸⁷Sr/⁸⁶Sr, which indicate a shift in weathering processes from the presence of silicate weathering to primarily carbonate weathering.Early in the melt season, rates of carbonate dissolution slow as meltwater approaches saturation with respect to calcite and dolomite, corresponding to an increase in silicate weathering that includes Sr-rich silicate minerals, and an increase in meltwater ⁸⁷Sr/⁸⁶Sr. However, carbonate minerals are preferentially weathered in unsaturated waters. During the warmest part of a melt season the discharged meltwater is under saturated, causing an increase in carbonate weathering and a decrease in the radiogenic Sr signal. Likewise, larger fraction contributions of meltwater from glacial ice corresponds to lower ⁸⁷Sr/⁸⁶Sr values, as the meltwater has lower water–rock interaction times in the subglacial system. These results indicate that although weathering of Sr-containing silicate minerals occurs in carbonate dominated glaciated terrains, the continual contribution of new meltwater permits the carbonate weathering signal to dominate.     

Dolomite Versus Calcite Weathering in Hydrogeochemically Diverse Watersheds Established on Bedded Carbonates (Sava and So?a Rivers, Slovenia)

The relative contributions of dolomite to calcite weathering related to riverine fluxes are investigated on a highly resolved spatial scale in the diverse watersheds of Slovenia, which previous work has shown have some of the highest carbonate-weathering intensities in the world and suggests that dolomite weathering is favored over limestone weathering in mixed carbonate watersheds. The forested Sava and So?a River watersheds of Slovenia with their headwaters in the Julian Alps drain alpine regions with thin soils (<30 cm) and dinaric karst regions with thicker soils (0 to greater than 70 cm) all developed over bedded Mesozoic carbonates (limestone and dolomite), and siliclastic sediments is the ideal location for examining temperate zone carbonate weathering. This study extends previous work, presenting geochemical data on source springs and documenting downstream geochemical fluctuations within tributaries of the Sava and So?a Rivers. More refined sampling strategies of springs and discrete drainages permit directly linking the stream Mg²⁺/Ca²⁺ ratios to the local bedrock lithology and the HCO₃ ^? concentrations to the relative soil depths of the tributary drainages. Due to differences in carbonate source lithologies of springs and tributary streams, calcite and dolomite weathering end members can be identified. The Mg²⁺/Ca²⁺ ratio of the main channel of the Sava River indicates that the HCO₃ ^? concentration can be attributed to nearly equal proportions by mass of dolomite relative to calcite mineral weathering (e.g., Mg²⁺/Ca²⁺ mole ratio of 0.33). The HCO₃ ^? concentration and pCO₂ values increase as soil thickness and alluvium increase for discrete spring samples, which are near equilibrium with respect to calcite. Typically, this results in approximately 1.5 meq/l increase in HCO₃ ^? from the alpine to the dinaric karst regions. Streams in general do not change in HCO₃ ^?, Mg²⁺/Ca²⁺, or Mg²⁺/HCO₃ ^? concentrations down course, but warming and degassing of CO₂ produce high degrees of supersaturation with respect to calcite. Carbonate-weathering intensity (mmol/km²-s) is highest within the alpine regions where stream discharge values range widely to extreme values during spring snowmelt. Overall, the elemental fluxes of HCO₃ ^?, Ca²⁺, and Mg²⁺ from the tributary watersheds are proportional to the total water flux because carbonates dissolve rapidly to near equilibrium. Importantly, dolomite weathers preferentially over calcite except for pure limestone catchments.     

白云岩和石灰岩山区石漠化速度差异原因分析

石漠化主要形成在由白云岩和石灰岩组成的碳酸盐岩分布区。白云岩石漠化的发生率较石灰岩低。主要原因是白云岩与石灰岩相比,总体特征是风化颜色深、矿物颗粒粗且分布不均匀、硬度大容易破碎、孔隙并口裂隙发育、表面粗糙。白云岩的这些特征有利于物理风化成壤,有利于保存土壤和植被生活,石漠化的发生率就相对较低。     

Mineralogy of granulated wood ash from a heating plant in Kalmar, Sweden

The central heating plant of Kalmar, Sweden produces 200-300 tons wood ash every year. A stabilised material for nutrient recycling is produced by adding water and dolomite to the wood ash and granulating the mixture. Combined mineralogy and chemistry can be used to interpret the transformation processes that occur during hardening and weathering of the granules, thus leading to a possibility to refine the production process and final characteristics of the granules. Mineralogy was separately studied in the wood ash, dolomite, self-hardened wood ash and granules by X-ray diffraction. Magnesium- and calcium-containing minerals are most common in the ash materials in the present study. The amounts of portlandite and calcite present in self-hardened and granulated ash samples are clearly higher than those in the untreated ash, showing that these minerals are formed during the treatments. Additionally, one potassium-containing secondary mineral, syngenite, is formed during the self-hardening of wood ash. Quartz, dolomite and the Fe-K-Mg-silicate in the granules originate from dolomite. The secondary minerals gypsum and calcium silicate hydrate are present in the granules. Portlandite occurs only in control granules in the field study. This suggests that hardening of granules continues in the field and portlandite is transformed into calcite. After up to 3 years on forest soil, the crystalline compounds dolomite, calcite, quartz, ankerite, albite and alumohydrocalcite are present in granules, of which alumohydrocalcite is formed as a secondary mineral in the field. These results suggest that the dissolution of granulated wood ash is strongly delayed compared with untreated wood ash and self-hardened wood ash because of the formation of less soluble compounds during the granulation process.     

热带地区碳酸盐岩上覆红色风化壳的成因机理及元素演化

开展热带岩溶地区红色风化壳元素地球化学演化规律研究,有助于丰富碳酸盐岩风化成土理论的认识。在越南北部选取典型的碳酸盐岩风化剖面,分析热带气候条件下碳酸盐岩上覆红色风化壳中主量元素的物质来源和演化特征。结果表明:无论Ti/Zr的元素比值分析,Hf-Zr、Nb-Ta及Sm-Nd的元素对协变分析,还是上地壳元素平均值(UCC)标准化分析,两个剖面的上覆风化壳均显示原地残积的特征,即两个剖面是碳酸盐岩的原位风化产物。碳酸盐岩风化成土过程中,CaO、MgO淋失明显,Al_2O_3和Fe_2O_3发生富集,显示两个剖面均经历较强的风化过程,但是白云岩和灰岩剖面有一定的分异特征。越南北部白云岩风化剖面从基岩到上部土层显示出稳定的Ti-Fe元素共富集特征,而灰岩剖面中Fe的增长速率明显超过Ti。白云岩上覆风化壳经历了强烈的风化作用,其脱硅作用弱于灰岩风化剖面,而富集铝的作用强于灰岩。迁移系数的演化规律说明两个剖面中长石成分(钾长石、钠长石等)或次生矿物(伊利石等)在风化成土过程中逐渐分解,同时Al、Fe、Si等稳定元素的在风化剖面中不断富集。     

X射线粉晶衍射仪在大理岩鉴定与分类中的应用

大理岩主要有方解石大理岩、白云石大理岩和菱镁矿大理岩三种。以往大理岩是依据偏光显微镜下观察岩石结构构造及矿物成分进行分类定名,由于方解石、白云石、菱镁矿都属于三方晶系,具有闪突起、高级白干涉色、一轴晶负光性和菱形解理等相同晶体光学特征,偏光显微镜下区分十分困难。为了准确鉴定大理岩中碳酸盐矿物种类及其相对含量,本文利用岩石薄片偏光显微镜和X射线粉晶衍射技术对32件大理岩岩石样品进行分析测试。岩石薄片鉴定结果表明:大理岩造岩矿物主要有方解石、白云石、菱镁矿、石英、斜长石、白云母、黑云母、绿泥石、黏土和金属矿物。根据岩石结构构造及矿物组分特征,可把32件大理岩样品划分为方解石大理岩、长英质方解石大理岩、石英绿泥白云石大理岩、白云石大理岩、云英质白云石大理岩和菱镁矿大理岩等15个类型。X射线粉晶衍射分析表明:大理岩造岩矿物主要有方解石、白云石、菱镁矿、石英、斜长石、钾长石、云母、绿泥石、滑石和蒙脱石。综合分析认为:岩石薄片偏光显微镜鉴定技术很难区分方解石、白云石和菱镁矿等碳酸盐矿物,以及细小的石英、钾长石和斜长石、滑石和白云母等鳞片状硅酸盐矿物;X射线粉晶衍射分析技术不仅能准确检测出大理岩中方解石、白云石和菱镁矿等碳酸盐矿物种类及相对含量(方解石、白云石和菱镁矿的X射线衍射主峰有明显差异,d值分别为0.303 nm、0.288 nm和0.274 nm),而且能够有效鉴别岩石中粉砂级斜长石、钾长石与石英(三种矿物的X射线衍射主峰d值分别为0.319 nm、0.324 nm、0.334 nm);且能区分蒙脱石、绿泥石、云母和滑石等层状硅酸盐矿物(四种硅酸盐矿物的X射线衍射主峰d值分别为1.400 nm、0.705 nm、0.989 nm、0.938 nm)。综合岩石薄片偏光显微镜鉴定和X射线粉晶衍射分析结果,最终确定32件大理岩样品划分为22个岩石类型。研究认为:仅根据岩石薄片偏光显微镜鉴定或X射线粉晶衍射技术其中一种方法不能准确鉴定大理岩岩石,应将大理岩岩石野外观察、岩石薄片鉴定和X射线粉晶衍射技术结合起来,才能准确确定大理岩岩石类型。     

发育完整的灰岩风化壳及其矿物学和地球化学特征

对于碳酸盐岩土覆土壤成因、尽管碳酸盐岩风化残积成土说被多数学者认同,但由于碳酸盐岩中酸不溶物含量极低,在风化成土过程中会伴随着巨大的体积缩小变化,原岩结构和半风化带无法保留,从而缺失了探索上覆土壤物质来源的重要中间环节,使得这种观点缺乏野外宏观证据的支持。最近,我们在贵州、湖南等地发现了数个以泥质灰岩和泥质白云岩为基岩的碳酸盐岩风化壳剖面,尚保留有较好的原岩结构,具有明显的风化壳分带和过渡现象。这些风化壳剖面的发现为深入研究碳酸盐岩风化成土过程提供了良好的研究场所。本文选取了较为典型的吉首泥灰岩风化壳剖面,从矿物学地球化学的角度来探讨碳酸盐岩风化壳的形成过程和发育特征,结果表明该风化壳既遵循非碳酸盐岩（主要是结晶岩类）风化壳的发育特征,也具有自己独特的地球化学演化规律。风化壳总体特点受碳酸盐中的酸不溶物矿物组合及化学成分的影响甚至控制,风化非碳酸盐风壳相似的发育特征。吉首泥灰岩风化壳剖面的发育特征和作者早先提出 的碳酸盐岩风化成土的两阶段模式是一致的,即以碳酸盐矿物大量淋失、酸不溶物逐渐堆积或残积为特征的早期阶段和残积物进一步风化成土的阶段,后一阶段的演化类似非碳酸盐岩类的风化过程。     

Authigenic titanite in weathered basalts: Implications for paleoatmospheric reconstructions

The stability of titanite is sensitive to temperature and partial pressure of CO₂. The finding of authigenic titanite grains in weathering regolith formed on Paraná basalts, Brazil, under tropical climatic conditions, reveals the thermodynamically-driven conversion from calcite to titanite at elevated ambient temperatures. Being unusual nowadays, this phase transition provides important implications for the understanding of silicate weathering in earlier geological epochs.Two types of secondary titanites were identified in the weathering profile of the study area. The tiny grains of 10 ​μm are forming in the microscopic voids in the rock. Also, large fractures filled with Fe-rich clay minerals contain bigger specimens of up to 170 ​μm. The titanites of second type often coexist with chalcedony and barite. No carbonate minerals were found in the weathering profile. Weathering sphene can be discriminated from other titanite types by its strong positive Eu anomaly, increased Al₂O₃ content and low content of trace elements. Its specific chemical composition and reactive transport modeling link this secondary mineral with dissolution of plagioclase. The titanite precipitation is controlled by slow diffusion in poorly-aerated, highly-alkaline pore fluids.The subaerial weathering of basaltic rocks provides a significant reservoir for atmospheric CO₂. However, the deposition of carbonate minerals is thermodynamically avoided at the stability field of titanite. We demonstrate a complex feedback between CO₂ and soil carbonates. The rise in pCO₂ triggers the precipitation of calcite in the weathering regolith, but the greenhouse effect increasing the temperature can cease carbonate deposition. Secondary titanites were found in several paleosols and at least a part of them can be of weathering origin.     

Spatial variations in chemical compositions along Langtang–Narayani river system in central Nepal

Surface water samples were collected from Langtang Lirung glacier outlet point to the Narayani river system in central Nepal in order to investigate the role of elevation in the variation of chemistry along the drainage networks. The chemistry of Langtang–Narayani river system was dominated by sulfide oxidation coupled with carbonate dissolution and weathering of silicate minerals. Calcium and magnesium concentrations were relatively higher than other cations and the sum of both species strongly correlated with alkalinity, supporting the dissolution of carbonate and dolomite as the dominant source for these ions. Aluminosilicate minerals primarily as albite and anorthite appeared as dominant silicate minerals within the drainage basin. Bisiallitization was the dominant type of weathering within the entire drainage system. Hydrogen ion concentration was lower in the low elevation sites than in high elevation sites reflecting the more consumption of carbon dioxide in the low elevation sites due to enhanced chemical weathering rates. Furthermore, major solutes like sum of base cations, silicon as well as alkalinity increased in concentration in the lower elevation sites. All regulating factors appeared to be directly related to elevation and hence elevation appeared to be the prime factor for the variation in chemical species along the Langtang–Narayani river system. Toshiyuki Masuzawa: deceased.     

疏勒河源区水化学特征及其控制因素分析

以疏勒河源区为研究区,自2018年12月至2019年11月分别采集河水、泉水和雪样样品44个、4个和7个,综合运用Piper三线图、Gibbs图、离子比值法定性分析不同水体水化学特征及控制因素,利用质量平衡法（正向地球化学模型）量化不同来源对不同季节河水水化学成分的贡献率。结果表明：疏勒河源区不同水体水化学特征存在差异,TDS含量为泉水>河水>冰川融水>雪水,河水水化学类型冬季为HCO₃^--Mg²⁺?Ca²⁺型,春季为HCO₃^--Ca²⁺?Mg²⁺?Na⁺型,夏、秋季均为HCO₃^--Ca²⁺?Mg²⁺型,泉水和雪水分别为HCO₃^--Ca²⁺?Mg²⁺型、HCO₃^--Ca²⁺型;受多种因素共同影响,不同季节河水主离子时空变化均存在差异;河水和泉水水化学组成受岩石风化作用控制,主离子来源于以白云石为主的碳酸盐岩风化、硅酸盐岩风化和盐岩、石膏、硫酸盐矿物等蒸发岩溶解;正向地球化学模型计算结果表明冬春季河水阳离子主要来源于硅酸盐岩风化溶解,夏秋季碳酸盐岩对河水阳离子贡献率大于硅酸盐岩,总体河水阳离子主要来源于碳酸盐岩和硅酸盐岩风化。     

The weathering of norite at Black Hill,South Australia

Black Hill is a boulder‐strewn residual of norite standing 45 m above the Murray Plains about 80 km northeast of Adelaide. Between the boulders, the crystalline rock has weathered to a dark‐brown terra rossa‐rendzina soil with calcite, illite, kaolin, and hematite as the principal secondary minerals. At one site on the smooth lower slopes of the outcrop, the material above the norite consists of partially weathered granular fragments with considerable dolomite and some calcite in nodular form. Below the surface, the rock has been weathered along joints to produce the clay mineral nontronite, and between each corestone and this plastic clay there is a zone of laminated but essentially unaltered rock 10–25 cm thick. Pieces of amorphous silica occur sporadically in some joints and on the surface.

The dark‐brown soil appears to be related to the present environment but the nontronite in the joint weathering, the dolomite, and the amorphous silica are all consistent with the norite having been inundated, possibly during the Miocene marine transgression.

Calculations based on the retention of elements such as aluminium, potassium, titanium, and iron have been used to predict quantitatively the amount of certain minerals such as quartz, calcite, and dolomite introduced to the weathering profiles.     

Seasonality of bedrock weathering chemistry and CO2 consumption in a small watershed, the White River, Vermont

The draw down of CO₂ from the atmosphere during mineral weathering plays a major role in the global budget of this greenhouse gas. Silicate minerals remove twice the CO₂ of carbonate minerals per mole of calcium in runoff during weathering. Bedrock weathering chemistry was investigated in the White River watershed of northeastern USA to investigate whether there are seasonal differences in carbonate and silicate weathering chemistry. Geographic Information Systems analyses of bedrock geology were combined with major element concentrations in river waters to gain an understanding of the consistency of mineral weathering during three seasons. The percent of carbonate mineralogy comprising the bedrock in tributaries of the White River varied from less than 5% to 45% by area. A mass balance calculation using major element concentrations in waters was applied to estimate the seasonal relationships between bedrock geology and bicarbonate flux. In all tributaries and the main stem of the White River the highest calculated percent of bicarbonate from carbonate mineral weathering was measured in the late fall. The results suggest that carbonate and silicate bedrock weathering processes are seasonally controlled. Thus single season sampling could not accurately represent an entire year's geochemical budget. In the White River, water samples obtained solely during the summer would consistently underestimate the total yearly source of bicarbonate from carbonate bedrock weathering. The same sample set would also provide data that would lead to an underestimation of the yearly atmospheric CO₂ draw down by bedrock weathering in the watershed. For example at four of the seven locations studied there was an almost two-fold difference between summer and spring calculated atmospheric CO₂ consumption rates.     

青海省阿尔金黄石山地区近红外蚀变矿物填图

利用近红外光谱对羟基(OH-)等敏感的特性,可以区分多种蚀变矿物及其矿物的不同结晶度,如舍羟基之硅酸盐矿物(绿帘石、闪石等),碳酸盐矿物(方解石、白云石等),层状硅酸盐中单矿物(粘土矿物、绿泥石、蛇纹石等),硫酸盐矿物(明矾石、黄钾铁矾、石膏等)等;矿物的结晶度不同,其红外吸收峰形也不相同,而矿物的结晶度标志着矿化作用...     

Effect of mechanical treatment on the mineralogical constituents of Abu-Tartour phosphate ore,Egypt

This study deals with the effect of mechanical treatment, using vibrating mill, on the mineralogy and structure of apatite and associated gangue minerals (dolomite, calcite, quartz, pyrite and gypsum) in Abu-Tartour phosphate ore, Egypt. The evolution of mineralogy, crystallinity and deformation mechanism were evaluated with different techniques (XRD, DTA, TGA and FT-IR). Data obtained using these techniques give a good picture about the mechanochemical behavior of the different components in the ore. X-ray diffraction (XRD) indicated that the mineralogy has been changed quantitatively at short time grinding (30 min). After 45 min of grinding, the sample contained mainly carbonate apatite, quartz and pyrite. On the other hand, dolomite mineral disappeared, while calcite was partially transformed into aragonite. This transformation increased with increasing grinding time. Both Fourier Transform Infrared (FT-IR) and differential thermal analysis (DTA) analyses revealed that remarkable changes in the structural groups have occurred after 45 min of grinding. After 75 min of grinding, the carbonate in the apatite mineral partially decomposed and tricalcium phosphate formed instead. The formation of that simple form (tricalcium phosphate) may be another reason, besides surface area, for increasing the reactivity of phosphate ore by grinding. Scanning electron micrographs (SEM) revealed some idea about the grinding mechanisms of Abu-Tartour phosphate using vibrating mill. They indicate that the different minerals are ground differently. The apatite minerals are ground mostly by abrasion mechanism, while the carbonate minerals are ground mostly by compression. Also, these minerals are ground with different rates, where dolomite is ground faster than calcite, which are referred to the crystal lattice.     

碳酸酐酶对碳酸盐岩溶解的催化作用及其在大气CO2沉降中的意义

CO2向H^ 和HCO3^－的转换是一相对慢速过程。因此，其动力学可能决定碳酸盐岩的溶解速率。在灰岩和白云岩的溶解实验中，使用了自然界普遍存在的碳酸酐酶（CA）来催化这一CO2转换反应，结果发现，对灰岩而言，加入CA后，其溶解速率在高CO2分层时可增加10倍，而对白云岩，其溶解速率增加主要在低CO2分压时，可达3倍左右。这一发现表明，化学风化（包括碳酸盐岩溶解和硅酸盐风化）作用在大气CO2沉降和全球碳循环里的所谓丢失的汇中的重要性需要重新评价。毫无疑问，已往的研究由于未认识到CA在风化中的催化作用，因此低估了风化作用的速率，同时也低估了风化作用对大气CO2沉降的贡献。另一方面，也表明了研究自然界不同水体中CA分布及其活度和CA在自然界风化作用中的作用的必要性。     

鄂尔多斯盆地渭北地区上三叠统延长组长7油层组碳酸盐结核中自生碳酸盐矿物的特征

早期形成的碳酸盐结核在埋藏期间会经历多种碳酸盐矿物相沉淀的复杂胶结作用,岩石学研究是探究结核成因的关键。通过野外剖面观察、岩石学观察和阴极发光技术,分析了鄂尔多斯盆地渭北地区上三叠统延长组长7油层组泥页岩中各种形状的方解石和白云石结核中自生碳酸盐矿物的特征。这些结核为成岩早期的产物,构成结核的自生碳酸盐矿物特征显著:(1)球粒方解石结核中,方解石呈纤维状或刃片状,球粒间充填晶粒方解石或因压实呈贴面结合,纤维状方解石发桔红色和暗红色2种光,刃片状方解石发暗红色光;(2)粉晶方解石结核中,方解石呈他形粒状,含有机质包裹体或纤维状晶形残余,晶间含沥青和纤维状方解石残余,主要发暗红色光;(3)白云石结核有泥晶和粉晶2种晶体类型,粉晶白云石结核含较多泥质,泥质条带或有机质条带处常见纤柱状白云石;(4)沿裂缝充填的方解石和白云石常呈纤维状或纤柱状结构,发暗红色光或不发光。研究区长7油层组碳酸盐结核中的方解石和白云石具有不同的成因类型和复杂的胶结作用:球粒方解石和泥晶白云石代表了结核开始形成时的胶结作用,可以准确地反映结核的成因;粉晶方解石、粉晶白云石反映了交代成因;裂缝中纤维状、纤柱状方解石和白云石集合体则为结核经历了较强压实作用之后充填裂缝而成。