The geochemistry of selenium associated with coal waste in the Elk River Valley,Canada

Selenium (Se) concentrations more than 12 times greater than the provincial freshwater quality guideline (2 µg/L) were detected in the Elk River downstream from the five open-pit coal mines in southeastern British Columbia's Elk River Valley. To identify possible sources of Se to the Elk River, samples from the coal-bearing Mist Mountain Formation were studied using X-ray diffraction, elemental and oxide analyses, sequential extractions and heavy liquid separation. Between 2.5 and 21.3% of the total Se in the five types of materials studied is water-soluble and 1.0 to 10.6% is associated with hydrous ferric and manganese oxides. Se associated with sulphides and organic material varies between 60 and 84% of the total Se and Se in the silicate structure varies from 5.9 to 24.7%. The ratio of sulphides to the total of organic carbon is well-correlated with the amount of Se in materials closely associated with coal seams containing less than 6 mg/kg of Se (r=0.916). This may suggest that the amount of organic matter present during deposition affects the amount of Se incorporated into sulphides.     

Sulphur isotope constraints on formation conditions of the Luiswishi ore deposit, Democratic Republic of Congo (DRC)

Luiswishi is a Congo-type Neoproterozoic sediment-hosted stratiform Cu–Co ore deposit of the Central Africa Copperbelt, located northwest of Lubumbashi (DRC). The ores form two main Cu–Co orebodies hosted by the Mines Subgroup, one in the lower part of the Kamoto Formation and the other at the base of the Dolomitic Shales Formation. Sulphides occur essentially as early parallel layers of chalcopyrite and carrolite, and secondarily as late stockwork sulphides cross-cutting the bedding and the early sulphide generation. Both types of stratiform and stockwork chalcopyrite and carrolite were systematically analyzed for sulphur isotopes, along the lithostratigraphic succession of the Mine Series. The quite similar δ³⁴S values of stratiform sulphides and late stockwork sulphides suggest an in situ recrystallization or a slight remobilization of stockwork sulphides without attainment of isotopic equilibrium between different sulphide phases (chalcopyrite and carrolite). The distribution of δ³⁴S values (−14.4‰ to +17.5‰) combined with the lithology indicates a strong stratigraphic control of the sulphur isotope signature, supporting bacterial sulphate reduction during early diagenesis of the host sediments, in a shallow marine to lacustrine environment. Petrological features combined with sulphur isotopic data of sulphides at Luiswishi and previous results on nodules of anhydrite in the Mine Series indicate a dominant seawater/lacustrine origin for sulphates, precluding a possible hydrothermal participation. The high positive δ³⁴S values of sulphides in the lower orebody at Luiswishi, hosted in massive chloritic–dolomitic siltite (known as Grey R.A.T.), fine-grained stratified dolostone (D.Strat.) and silicified-stromatolitic dolomites alternating with chloritic–dolomitic silty beds (R.S.F.), suggest that they were probably deposited during a period of regression in a basin cut off from seawater. The variations of δ³⁴S values (i.e. the decrease of δ³⁴S values from the Kamoto Formation to the overlying Dolomitic Shales and then the slight increase from S.D.2d to S.D.3a and S.D.3b members) are in perfect agreement with the inferred lithological and transgressive–regressive evolution of the ore-hosting sedimentary rocks [Cailteux, J., 1994. Lithostratigraphy of the Neoproterozoic Shaba-type (Zaire) Roan Supergroup and metallogenesis of associated stratiform mineralization. In: Kampunzu A.B., Lubala, R.T. (Eds.), Neoproterozoic Belts of Zambia, Zaire and Namibia. Journal of African Earth Sciences 19, 279–301].     

Textural and mineralogical evidence for a Cadomian tectonothermal event in the eastern Mediterranean (Sandıklı-Afyon area, western Taurides, Turkey)

In the Sandıklı-Afyon area, the very low-grade metamorphic Sandıklı Basement Complex with clastic sediments and Late Neoproterozoic felsic igneous rocks are unconformably overlain by a cover succession with red continental clastic rocks, tholeiitic basalts and siliciclastic rocks with Early Cambrian trace fossils. Illite crystallinity studies reveal that both the basement and cover units were metamorphosed at high anchizonal to epizonal conditions ( 300 °C). Textural data together with the detailed evaluation of the P–T–b₀ grid, however, indicate that this thermal event has multiple phases. The first tectonothermal event was realized at pressures of  4.2 kb on the basis of b₀-data and resulted in development of blastomylonites. This is supported by the presence of dynamo-metamorphosed pebbles within the basal conglomerates of the Lower Paleozoic cover series. The second event is post-Ordovician–pre-Jurassic in age, occurred at lower pressures  3.2 kb and produced a weakly developed cleavage in the siliciclastic rocks of the cover. The mineralogical/textural data across the basement-cover boundary therefore indicate the removal of an entire metamorphic zone and thus a metamorphic hiatus.

These data suggest that the Taurides were affected by a Late Neoproterozoic event as part of the peri-Gondwana during the Cadomian orogeny.     

Dissolution rates of metals in Fe oxides: implications for sampling ferruginous materials with significant relict Fe oxides

A study of the pattern of dissolution of synthetic and natural Fe oxides in 6 M HCl indicates that the rate of element release from synthetic Fe oxides is strongly influenced by mineralogy and the level of element incorporation. Synthetic maghemite (γ-Fe₂O₃) samples are subject to much more rapid dissolution than goethite (FeOOH) and hematite (α-Fe₂O₃). In samples dominated by hematite and maghemite, Cu, Zn and particularly Pb, in comparison to Fe, are preferentially released during the early stages of dissolution. Similar patterns are apparent from the dissolution of hematite- and maghemite-dominated samples derived from natural gossan. Comparison of XRD scans with data from the dissolution of natural gossan samples transformed by incremental heating to hematite- and maghemite-dominated assemblages suggests that the degree of crystallinity may also be a significant factor in the release of elements incorporated in the Fe oxides. Ferruginous materials made up of varying proportions of goethite, hematite, maghemite, kaolinite and quartz are important sampling materials in a range of regolith environments. These are products of complex chemical and mechanical mobilization over long periods of geological time. If the patterns of Fe oxide dissolution in 6 M HCl and the release of incorporated metals reflect stability in such weathering regimes, knowledge of the retention characteristics of incorporated metals in different Fe oxide phases, as indicated by this study, will be useful in the planning and interpretation of geochemical surveys in such regions.     

新疆阿尔泰钾长石矿物学特征及开发利用

阿尔泰钾长石是新疆优势非金属矿产资源之一，主要赋存在花岗伟晶岩矿脉、钾长花岗岩和碱性花岗岩中，钾长石资源储量大、品位高，易采易选，但尚未很好开发利用。通过阿尔泰钾长石矿物的物理特征、光学性质、化学成分以及工艺矿物学特征的研究，阐述了钾长石资源在工农业中的应用状况和应用范围，经与国内同类型矿种对比，指出新疆阿尔泰钾长石开发利用有着广阔的前景。     

Exsolution intergrowths of titanian ferrocolumbite and niobian rutile from the Weinebene Spodumene Pegmatites,Carinthia, Austria

Summary Titanian ferrocolumbite is a rare accessory mineral in the spodumene-bearing pegmatites at Weinebene, Carinthia, Austria. It contains abundant exsolved niobian rutile and scarce inclusions of cassiterite that may be primary. The titanian ferrocolumbite is relatively homogeneous with Mn/(Mn + Fe) 0.24–0.33, Ta/(Ta + Nb) 0.09–0.13 (atomic ratios) and 0.47–0.88 Ti per 12 cations (2.7–5.0 wt.% TiO₂). Natural specimens are considerably disordered but become more ordered on heating. Niobian rutile has Mn/(Mn + Fe) 0.00–0.04 and Ta/(Ta + Nb) 0.26–0.38; it concentrates Fe, Ta, Ti and Sn relative to the Mn- and Nb-enriched ferrocolumbite. The overall scarcity of Nb, Ta-oxide minerals in the spodumene-bearing pegmatites of southern Ostalpen conforms to their general features ranking them with the albite-spodumene type of rare-element pegmatites.With 4 Figures     

Slake durability and mineralogical properties of some pyroclastic and sedimentary rocks

Slake durability of rocks is an important property of rock-mass and rock-materials in geotechnical practice. The slake durability of rocks is closely related to their mineralogical composition. In this paper, mineralogical examinations and slake durability tests for argillaceous clastic rocks, especially pyroclastic rocks, sandstones and mudstones of Neogene Tertiary age from Japan, were performed in order to assess the slake durability and rock alteration process of these rocks as well as to understand the relationship between mineralogy and durability.The mineral composition and textural features of the rocks were studied by means of optical microscopy (OM), X-ray diffractometry (XRD), electron microprobe analysis (EPMA), and scanning electron microscopy (SEM). In addition, the slake durability test was carried out by using the standard testing method of ISRM [Int. J. Rock Mech. Min. Sci. 16 (1979) 148] in distilled water and in the aqueous solutions with dissolved electrolytes of NaCl and CaCl₂.The pyroclastic rocks and tuffaceous sandstone, rich in di-octahedral and tri-octahedral Fe smectite, respectively, show distinctively different slaking behaviors. The pyroclastic rocks show relatively high slaking (Id₂=55.5% and Id₁₀=10.5%) than the tuffaceous sandstone (Id₂=94.1% and Id₁₀=87.8%, refer to text for Id₂ and Id₁₀). This difference in the slake durability observed in these rocks is due to the microscopic occurrences of smectite present in the interspaces between the particles (pyroclastic rocks) and zeolite cementing the interspaces (tuffaceous sandstone) as alteration minerals. In addition, the durability results of tuffaceous sandstone show that the slake durability decreases as the degree of weathering increases (weathered material Id₂=88.7% and Id₁₀=65.3%). Furthermore, two mudstones of Miocene and Pliocene ages, having different clay mineral compositions (smectite vs. illite+chlorite), show the lowest and the highest slake durability among the tested clastic rocks. Hard mudstone shows the highest (Id₂=98.1% and Id₁₀=95.5%) while the soft mudstone shows the lowest (Id₂=33.9% and Id₆=0.4%.) slake durability. Thus, the slake durability of pyroclastic and sedimentary rocks is greatly affected by their mineral composition and texture, and is closely related to their alteration history. Slake durability is also affected by the kind of dissolved electrolyte and its concentration in the aqueous solution, providing some useful information for geotechnical practice.     

Mineralogical constraints on the determination of neutralization potential and prediction of acid mine drainage

 Acid-base accounting tests, commonly used as a screening tool in acid mine drainage (AMD) predictions, have limitations in (1) measuring with confidence the amount of neutralizers present in samples and (2) affording an interpretation of what the test results mean in terms of predicting the occurrence of acid mine drainage. Aside from the analytical difficulties inherent to the conventional methods, a potential source of error in neutralization potential (NP) measurements is the contribution from the dissolution of non-carbonate minerals. Non-carbonate alkalinity measured during static tests may or may not be available to neutralize acidity produced in the field. In order to assess the value-added of extending the NP with the knowledge of mineralogical composition and evaluate potential sources of errors in NP measurements, a suite of samples were examined and characterized in terms of their mineralogical and chemical compositions. The results indicate that although the acid-base accounting tests work well for simple compositions, the tests may result in overestimation or underestimation of NP values for field samples. Mineralogical constraint diagrams relating NP determinations to Ca, Mg and CO₂ concentrations were developed with the purpose to serve as supplementary guides to conventional static tests in identifying possible NP contributions from non-carbonate minerals and checking the quality of the chemical testing results. Mineralogical NP makes it possible to interpret the meaning of NP results and to assess the behaviour of samples over time by predicting the onset of AMD and calculating NP values for individual size fractions. Received: 1 June 1998 · Accepted: 6 October 1998     

Comparison of color, chemical and mineralogical compositions of mine drainage sediments to pigment

 Forty-three untreated and actively and passively (wetland) treated coal mine drainage sediments and five yellow-red pigments were characterized using X-ray fluorescence, fusion-inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and tristimulus colorimeter. Primary crystalline iron-bearing phases were goethite and lepidocrocite, and iron phases converted to hematite upon heating. Quartz was nearly ubiquitous except for synthetic pigments. Gypsum, bassinite, calcite, and ettringite were found in active treatment sediments. Iron concentrations from highest to lowest were synthetic pigment>wetland sediment>natural pigment>active treatment (untreated sediments varied more widely), and manganese was highest in actively treated sediments. Loss on ignition was highest for passively treated sediments. No clear trends were observed between quantified color parameters (L*, a*, b*, and Redness Index) and chemical compositions. Because sediments from passive treatment are similar in chemistry, mineralogy, and color to natural pigments, the mine drainage sediments may be an untapped resource for pigment. Received: 29 December 1997 · Accepted: 11 May 1998     

滇西北羊拉铜矿区路农岩体矿物学、地球化学特征及其地质意义

路农岩体位于滇西北羊拉铜矿区南部,岩体与围岩接触带上广泛发育层状矽卡岩型矿体,而斑岩型矿化较弱。其斑岩型铜矿化的潜力如何是羊拉铜矿床研究与勘查工作的难点之一,路农岩体岩石成因及源区认识存在不足。为此,本文选取路农岩体中新发现的暗色包体和寄主岩石花岗闪长岩进行了岩石地球化学及矿物学研究。结果表明:路农岩体暗色包体显示高镁闪长岩特征(Si O2=53. 83%～63. 91%、Mg O=2. 30%～4. 46%),寄主岩石属于I型花岗岩,属于准铝质-高钾钙碱性系列。二者具经典弧岩浆岩特征,富集Rb、K、Pb、Th、U等大离子亲石元素,亏损Nb、Ta、Ti、P等高场强元素,与里农岩体具有相似的稀土元素配分模式,均为右倾型,但二者稀土元素总量差异较大(∑REE=114. 8×10-6～261. 6×10-6),寄主岩石轻重稀土分馏更为明显(LREE/HREE=3. 81～13. 96),而暗色包体显示更强的负Eu异常(δEu=0. 31～0. 47)特征。结合岩体侵位时间(238～230Ma,锆石U-Pb年龄),认为路农岩体可能形成于后碰撞或碰撞晚期的背景下,板片断离造成软流圈物质上涌,携带少量幔源熔浆底侵于下地壳,诱发部分熔融形成长英质熔浆,二者在深部岩浆房混合形成混合熔浆,向上侵位至浅部地壳,经过结晶分异形成路农花岗闪长岩,包裹的幔源镁铁质岩浆残余体低度分异形成暗色包体。角闪石和黑云母的矿物化学特征指示路农岩体侵位较深(4. 35～7. 24km)、压力较大(121～178MPa)、岩浆温度(777～836℃)较高,氧逸度(logf_(O2)=-13. 84～-12. 77)相对较低,不利于形成大规模斑岩型铜矿化,因此路农矿段斑岩型矿化不发育。