Ca-bearing Minerals Research Articles

The role of hydrothermal processes in the granite-hosted Zr, Y, REE deposit at Strange Lake, Quebec/Labrador: Evidence from fluid inclusions

The Strange Lake Zr, Y, REE, Nb, and Be deposit is hosted by a small, high-level, Late-Proterozoic peralkaline granite stock that intruded into high-grade metamorphic gneisses on the Quebec-Labrador border. The stock is extensively altered. Early alteration is manifested by the replacement of arfvedsonite with aegirine. Later alteration involved Ca-Na exchange. Zr, Ti, Y, REEs, Nb, and Be are concentrated in Ca-bearing minerals that, together with quartz, commonly pseudomorph Na-bearing minerals. Fluid inclusions in pseudomorphs comprise several distinct types: high-salinity (13 to 24 wt% NaCl eq.), Ca-rich aqueous inclusions that homogenize to liquid between 135 and 195°C; mixed aqueousmethane inclusions; methane inclusions; and solid-bearing inclusions. Aqueous-methane inclusions represent heterogeneous entrapment of immiscible high-salinity aqueous liquid and methane. Bastnäsite (tentatively identified by SEM analysis) occurs as a daughter mineral. Other daughter or trapped minerals include a Y, HREE-bearing mineral, possibly gagarinite, and hematite, galena, sphalerite, fluorite, pyrochlore, kutnahorite (?), and griceite (?). The first three inclusion types also occur in quartz in pegmatites and veins together with lower-temperature, lower-salinity, Na-dominated aqueous inclusions. The entrapment temperature inferred for the aqueous inclusions from microthermometry and the Na-K-Ca geothermometer range from 155 to 195°C for the higher-salinity inclusions and 100 to 165°C for the low-salinity inclusions. A model is proposed in which the intrusion of a peralkaline granite to high crustal levels initiated a ground/formational water-dominated hydrothermal system in adjacent gabbroic, calc-silicate, and graphitic gneisses. Reaction of the high-salinity, Ca-rich liquid with the graphitic gneisses led to the production of an immiscible methane gas. Subsequent interaction of this liquid with the granite led to extensive replacement of sodic minerals by calcium analogues at temperatures of less than 200°C. Some time after the onset of Ca metasomatism the high-salinity liquid mixed with a Ca-poor, low-salinity, low-temperature liquid that had leached F and rare metals from the granite. Yttrium and REE mineral deposition occurred as a result of the decreased ligand concentration that accompanied fluorite deposition during mixing of the Ca-rich and Ca-poor aqueous liquids.

The laser microprobe mass analyser for determining partitioning of minor and trace elements among intimately associated macerals: an example from the Swallow Wood coal bed, Yorkshire, UK

A study of the elemental composition of intimately associated coal macerals in the English Swallow Wood coal bed was conducted using a laser microprobe mass analyser, and indicated a similar trace and minor elemental chemistry in the vitrinite and cutinite and a different elemental signature in the fusinite. Three to six sites were analysed within each maceral during the study by laser micro mass spectrometry (LAMMS). Al, Ba, Ca, Cl, Cr, Dy, F, Fe, Ga, K, Li, Mg, Na, S, Si, Sr, Ti, V, and Y were detected by LAMMS in all three macerals but not necessarily at each site analysed. The signal intensities of major isotopic peaks were normalized to the signal intensity of the m z 85 peak (C 7H) to determine the relative minor- and trace-element concentrations among the three dominant macerals. The vitrinite and the cutinite were depleted in Ba, Ca, Dy, Li, Mg, Sr, and Y relative to their concentrations observed in the fusinite. The cutinite was distinguished over vitrinite by less Ti, V, Cr and Ca, and K Ca $ ̆ 1 (relative signal intensities). The fusinite, relative to the cutinite and vitrinite, was relatively depleted in Cr, Sc, Ti, and V. The fusinite, as compared with both the cutinite and vitrinite, was relatively enriched in Ba, Ca, Dy, Li, Mg, Sr, and Y, and also showed the most intense m z 64, 65, 66 signals (possibly S 2 +, HS 2 +, H 2S 2 +, respectively). The LAMMS data indicate a common source for most elements and selective loss from the maceral precursors in the peat or entrapment of certain elements as mineral matter, most likely during the peat stage or during early diagenesis. The relatively high amounts of Ba, Ca, Dy, Li, Mg, Sr, and Y in the fusinite are consistent with micron and submicron mineral-matter inclusions such as carbonates and Ca-Al phosphates (probably crandallite group minerals). Mineralogical data on the whole coal, the LAMMS chemistry of the vitrinite and cutinite, and scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDAX) of the elements in the macerals are consistent with the presence of micron and submicron inclusions of clays such as kaolinite, illite, and Ca-rich or Ca-bearing minerals (e.g. calcite, Ca-Al phosphates, and illite) which are different in kind and proportions in the three macerals. The variance as measured by the F-statistic for all three macerals indicates generally a nonuniform distribution of minor and trace elements in all three macerals, thus supporting a mineral-matter (inorganic) origin of the elements analysed. Exceptions are Al, K, Fe, Ga, and Sr in the vitrinite and cutinite, which is consistent with organic complexing or a uniform distribution of micron or submicron mineral matter such as illite and phosphate(s).

Variation of Elements in Self-Burning Coal Seam from Coalspur, Alberta, Canada

Abstract The elemental and mineralogical variation in a self-burning coal seam from Coalspur, Alberta, is determined using instrumental neutron activation analysis (INAA) and x-ray diffraction (XRD). The elemental variation in the coal seam is related to temperatures in the various alteration zones, i.e., oxidation, combustion, or carbonization and nature of elements. Mobilization of elements is greatest for As, Br, Cl, Mo, N, S, and Sb. Some of these elements are released to the atmosphere, as evident by the presence of orthorombic sulfur crystals on the surface or in vents at the top of the burning seam or saturation of oxidation char by volatile matter (tar). V/he-wellite (Ca C2O4, H2O) is the only Ca-bearing mineral found in the cooler area of the coal seam. Decomposition of this mineral, coupled with the presence of SO2 formed by reaction of organic sulfur with O2 in combustion, resulted information of a relatively high gypsum content in the combustion zone. Elements typically associated with carbonates, i.e., Ca, Ba, Fe, Mg, and Mn, follow similar trends and have their highest concentration in the combustion zone due to devolatilization of organic matter in coal and increase in ash content.

Geochemical characteristics of mid-ocean ridge basalts

Major and trace element (Rb, Sr, Y, Zr, Nb, Ba, Sc, Ni, Co, Cr, V) data are presented on ten mid-ocean ridge basalts (MORB), together with a basalt sample from the offshore slope of the Yap Trench and a basalt from the Tertiary ophiolite complex of eastern Taiwan. Rare earth element (REE) and Sr isotope data are presented on eight of the samples, together with REE data on U.S.G.S. standard rock, BHVO-1. A strong correlation exists between percent TiO 2 (proportional to amount of melting) and Al 2 O 3 /TiO 2 , CaO/TiO 2 ratios of these close to primary MORB. These ratios increase up to a maximum (about 20 and 17 respectively) as TiO 2 decreases, indicating a progressive release of Al and Ca from the mantle source. The limiting values of the ratios are close to chondritic and are reached at about 0.8% TiO 2 . At this high degree of melting, the major Al- and Ca-bearing mineral phases are eliminated from the mantle residue. Model calculations on the major element data indicate that MORB with 0.7% and 1.5% TiO 2 could represent about 25 and 15% melting (respectively). This modelling is consistent with the abundances of the first transition series metals (Sc to Ni), which are also interpretable in terms of degree of partial melting and residual mineralogy. Based on the REE data, the samples can be divided into depleted types (typical of “normal” MORB), and enriched types (the so-called “plume” and “transitional” types). Despite the range of (La/Sm) N in these samples (0.38–1.97) the Ti/Zr ratios remain close to chondritic (about 110) indicating that these two elements have a similar degree of incompatibility at this level of melting. Chondritic normalized patterns for typical “normal” (N)- and “plume” (P)-type MORB are presented for the REE and K, Nb, U, Th, Ba, Rb and Cs and it is suggested that this represents an increasing order of element incompatibility in MORB. The behaviour of Y, Ti, Zr, P and Sr relative to the REE is also discussed and it is shown that for most primitive MORB, Y = Ho, Ti = Eu, Zr = Sm, P = Nd and Sr is between Ce and Nd. In addition the Zr/Nb ratio correlates with the La/Sm ratio. This element correlation can be used to predict the general shape of REE patterns. The Sr isotope data are discussed in terms of already published data from the three oceans. It is suggested that P-type MORB originate from depleted mantle sources which only recently (say ≤300 m.y.) were added to by an incompatible-element-rich phase. Various models proposed to explain both the depletion in N-type, enrichment in the P-type MORB sources and the proposed mantle heterogeneity are discussed. It is concluded that mantle depletion is due to a continuing process rather than an episodic event in the early Archaean or 1.6 b.y. ago.

General relationships among sound speeds: II. Theory and discussion

The dependence of bulk sound speed V φ upon mean atomic weight m and density ρ can be expressed in a single equation: V φ=Bρ λ( m 0 m [ 1 2 +λ(1−c)] ( km/sec) Here B is an empirically determined “universal” parameter equal to 1.42, m 0 = 20.2 , a reference mean atomic weight for which well-determined elastic properties exist, and λ = 1.25 is a semi empirical parameter equal to γ − 1 3 where γ is a Grüneisen parameter. The constant c = ( ∂ ln V M/ ∂ ln m) X , where V M is molar volume, is in general different for different crystal structure series and different cation substitutions. However, it is possible to use c Fe = 0.14 for Fe 2+Mg 2+ and GeSi substitutions and c Ca ≅ 1.3 for CaMg substitutional series. With these values it is pos to deduce from the above equation Birch's law, its modifications introduced by Simmons to account for Ca-bearing minerals, variations in the seismic equation of state observed by D.L. Anderson, and the apparent proportionality of bulk modulus K to V M −4.

Petrologic properties of the upper 670 km of the earth's mantle; geophysical implications

The relative distribution of Fe 2+ and Mg 2+ between mantle minerals is calculated for various mantle thermal models and is used to estimate compressional and shear velocity and density profiles to depths of 670 km using ultrasonic, equation of state, and thermodynamic data for olivines, pyroxenes, garnets, and spinels. Except for uncertainties, arising from the lack of a quantitative description of the low-velocity zone, and inadequate elasticity data for Ca-bearing minerals, especially the clinopyroxenes, the calculated seismic profiles for pyrolite and lherzolite upper mantles are virtually identical. Varying the total iron content ratio, Fe t = Fe/(Fe + Mg) from 0.1 to 0.2, brackets the seismic observation Important constraints to the composition and thermal profile of the mantle underlying continental regions are obtainable by fitting theoretical models to the detailed V p -profile of Helmberger and Wiggins. This profile, although possibly inaccurate in the vicinity of the low-velocity zone, is well determined below 350 km. Values of Fe t = 0.15 − 0.5 with a pyroxene-garnet (pyrope-almandine, majorite, solid-solution) content of 25 ± 10% and a relatively cool geotherm (1630–1650°C, 570–670 km) are implied from the position of the α (olivine) to α + β to β (modified spinel) transition, at a depth centered at ∼420 km, the position of the β to β + γ to γ (spinel) transition, centered at ∼500 km as well as the absolute value of the P-wave velocity. Because of the low resolution of the V S - and ρ-profiles, presently offered by seismic techniques, the concomitant V S - and ρ-profiles are useful as predictive, rather than comparitive, tools. If, as has been suggested by Anderson and co-workers, substantial enrichment of iron occurs with increasing depth in the mantle, this study demonstrates that for at least the continental regions, such an increase, if it occurs, would take place at, or below the 670-km discontinuity in the mantle. Distribution coefficients, based on thermochemical data, predict that within the upper 100 km of the mantle, successively greater relative iron contents will be present in the order: orthopyroxene, clinopyroxene, olivine, and garnet. The distribution of Fe 2+ between orthopyroxene and the coexisting mantle phases is calculated (using the Mössbauer data of Virgo and Hafner for the M 1, M 2 intersite energy in the formulation of Grover and Orville). The relative enrichment of iron in orthopyroxene (relative to clinopyroxene) in the upper 100 km decreases rapidly with depth. Below 100 km, orthopyroxene composition becomes insensitive to the assumed intersite energy. In the upper 100 km Fe 2+ is markedly concentrated in the garnet phase. For a total mantle value of Fe t of 0.15 the garnet will have a composition corresponding to Fe/(Fe + Mg) = 0.30. At a depth of about 100–150 km the Fe 2+ content of the garnet decreases and approaches that of the bulk mantle. Below this depth range, the relative content of iron in the garnet again increases.