Mineral and inorganic chemical composition of the Pernik coal, Bulgaria

The mineral and inorganic chemical composition of five types of samples from the Pernik subbituminous coals and their products generated from the Pernik preparation plant were studied. They include feed coal, low-grade coal, high-grade coal, coal slime, and host rock. The mineral matter of the coals contains 44 species that belong mainly to silicates, carbonates, sulphates, sulphides, and oxides/hydroxides, and to a lesser extent, chlorides, biogenic minerals, and organic minerals. The detrital minerals are quartz, kaolinite, micas, feldspars, magnetite, cristobalite, spessartine, and amphibole. The authigenic minerals include various sulphides, silicates, oxihydroxides, sulphates, and carbonates. Several stages and substages of formation were identified during the syngenetic and epigenetic mineral precipitations of these coals. The authigenic minerals show the greatest diversity of mineral species as the epigenetic mineralization (mostly sulphides, carbonates, and sulphates) dominates qualitatively and quantitatively. The epigenetic mineralization was a result of complex processes occurring mostly during the late development of the Pernik basin. These processes indicate intensive tectonic, hydrothermal and volcanic activities accompanied by a change from fresh to marine sedimentation environment. Thermally altered organic matter due to some of the above processes was also identified in the basin. Most of the trace elements in the Pernik coals (Mo, Be, S, Zr, Y, Cl, Ba, Sc, Ga, Ag, V, P, Br, Ni, Co, Pb, Ca, and Ti) show an affinity to OM and phases intimately associated with OM. Some of the trace elements (Sr, Ti, Mn, Ba, Pb, Cu, Zn, Co, Cr, Ni, As, Ag, Yb, Sn, Ga, Ge, etc.) are impurities in authigenic and accessory minerals, while other trace elements (La, Ba, Cu, Ce, Sb, Bi, Zn, Pb, Cd, Nd, etc.) occur as discrete phases. Elements such as Sc, Be, Y, Ba, V, Zr, S, Mo, Ti, and Ga exceed Clarke concentrations in all of the coal types studied. It was also found that a number of elements in the Pernik coals (F, V, As, Pb, Mo, Li, Sr, Ti, Ga, Ni, Ge, Cr, Mn, etc.) reveal mobility in water and could have some environmental concerns.     

Modal mineralogy and chemical composition of the Uralide lower crust determined from physical properties data

Modeling of rock physical properties of the Uralide lower crust is carried out using the Physprops Excel worksheet, which calculates its P-wave (Vp), S-wave (Vs), Poisson's ratio (σ), and density (ρ). The mineral modal abundance and composition of mafic granulite, mafic garnet granulite, amphibolite, and gabbronorite is modeled, and the composition of each is determined by converting the aggregate mineralogy into wt.% oxides. The modeled wt.% oxide composition of mafic (+ garnet) granulite fit well with those estimated for post-Archean terrains, and all are within 1σ of the average of all lower crustal xenoliths. The modeled gabbronorite also shows a reasonable fit with these estimates. The modeled amphibolite compositions show variations in the wt.% SiO₂, FeO and MgO with respect to the estimates of mafic granulite and amphibolite. The differences in the composition across the Uralide lower crust are largely due to the presence or absence of garnet in the mafic granulite, which may be a result of higher temperatures having been reached in the interior part of the orogen.     

长江水中悬浮物含量与矿物和化学组成及其地质环境意义

在2003～2007年间,在长江干流的25个水文站及主要支流的13个水文站系统采样,对悬浮物的含量及其矿物与化学组成系统地进行了测定。根据这些数据,对长江悬浮物的矿物和化学组成的时空变化及其地质与环境意义进行了系统研究。 本次所采样品中悬浮物含量平均值为256.5mg/L,在世界各大河中居于中等水平。悬浮物含量呈现大幅度的时空变化,与水流速度、径流量及泥沙供给情况的变化相对应,受河床坡度、降雨量、风化强度、侵蚀情况及人工活动等多种因素的影响。近年来,长江悬浮物含量逐渐下降,与上游的退耕还林和水库建设密切相关。特别是三峡水库工程引起泥沙在库区大量沉积,显著降低河水的悬浮物含量,导致其下游河段堤岸冲刷加剧,洞庭湖、鄱阳湖和长江口的沉积减少。这种变化带来的环境效应巨大,需要慎重评估和应对。 长江水中悬浮物主要由粘土矿物、碎屑硅酸盐矿物和碎屑碳硅酸盐矿物组成,并含有少量重矿物、氢氧化物和有机物。与黄河悬浮物矿物组成的对比研究表明长江流域的化学风化作用明显强于黄河流域,而物理侵蚀作用明显弱于黄河流域。由上游到下游,长江悬浮物中粘土和碎屑硅酸盐矿物逐渐增高,而碎屑碳硅酸盐逐步降低,与中下游地区气候变得湿热,化学风化变强的情况相对应。 与上地壳岩石平均值相比,长江悬浮物的SiO2、CaO、K2O 、Na2O含量较低,而TFe2O3含量较高,反映硅酸盐矿物化学风化过程中部分硅、钾、钠、钙的流失和铁的富集。与全球河流悬浮物和黄河悬浮物相比,长江悬浮物的SiO2、Na2O含量较低,反映长江流域的化学风化作用较强。与长江水系沉积物相比,长江悬浮物的SiO2、Na2O含量较低,而Al2O3、K2O 、MgO、TFe2O3较高,反映悬浮物比较富含粒度较小的粘土与铁质成分。从上游往下游,长江悬浮物中CaO、MgO含量逐渐降低,SiO2 含量逐步升高,与粘土矿物含量增高和碳酸盐含量降低的趋势相对应。 长江悬浮物中Co、Ni、Cu、Zn、Pb、Cd含量均高于上地壳岩石的平均含量,可能由这些元素在风化过程优先为粘土所吸附所引起。在攀枝花、宜宾、九江、大通、南京等站悬浮物中发现的铜、铅、锌的高含量,可能均与相关地段采矿活动有关。2005年7月在富顺和长沙发现Cd的高异常值引人注目。悬浮物中Cu、Pb、Zn、Cd的含量较长江水系沉积物的平均含量高出数倍、乃至数十倍,可能反映近年来流域采矿活动加剧,其对流域环境的长远影响值得关注。 长江悬浮物的稀土总量与全球页岩的平均值相比略显偏高。长江悬浮物的REE分布形式于上地壳基本一致,表明长江流域出露的岩石的化学组成与上地壳岩石平均组成没有明显差别,而且岩石风化过程中稀土元素未出现明显分馏。     

Calculated phase equilibria for a morb composition in a P–T range, 450–650 °C and 18–28 kbar: the stability of eclogite

Lower temperature eclogite (with T = 600 °C) represents a significant part of the occurrences of eclogite in orogenic belts. ‘True’ eclogite, with, for example, garnet + omphacite >70%, is well represented in such an occurrence. Calculated phase equilibria in Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–O (NCKFMASHTO), for just one rock composition – that of a representative mid‐ocean ridge basalt, morb – are used to see under what circumstances ‘true’ eclogite is predicted to occur. The variables considered are not only pressure (P) and temperature (T) but also water content and oxidation state. The latter two variables are known to exert a significant control on mineral assemblage but are difficult to establish retrospectively from the observed rocks themselves. It is found that whereas oxidation state does have a strong effect on mineral assemblage, the key control on developing ‘true’ eclogite is shown to be temperature and water content. If temperature is established to be <600 °C, water content has to be low (less or much less than that for H₂O saturation) in order for ‘true’ eclogite to form. Moreover, unless pressure is at the high end in the range considered, lawsonite eclogite and ‘true’ eclogite will tend to be mutually exclusive, with the former requiring high water content at the lower temperature where it occurs, but the latter requiring low water content.