Showing papers on "Ankerite published in 2008"
TL;DR: The Middle-Upper Palaeocene sandstones (subarkoses to arkoses) from the Shetland-Faroes Basin, British continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates, quartz and clay minerals.
170 citations
TL;DR: The Shanggong Au deposit in the Xiong’er Terrane, East Qinling, China, has resources of about 30 ton Au, making it one of the largest orogenic-mesothermal Au deposits hosted in volcanic rocks of the Mesoproterozoic Zou et al. as mentioned in this paper.
139 citations
TL;DR: Xenotime-(Y) is a common accessory mineral in many igneous and high-grade metamorphic rocks, but it is very rare in carbonatite as discussed by the authors.
Abstract: Xenotime-(Y) is a common accessory mineral in many igneous and high-grade metamorphic rocks, but it is very rare in carbonatite. Uniquely, at Lofdal, Namibia, xenotime-(Y) occurs in many carbonatite dykes. It mantles and replaces zircon in calcite carbonatite and also occurs as aggregates in ankerite carbonatite, aggregates associated with hematite, and crystals associated with monazite-(Ce) and synchysite-(Ce) in highly oxidized iron-rich calcite carbonatites. The paragenetic sequence places the xenotime-(Y) at the end of magmatic activity and certainly into the hydrothermal stage. A U-Pb date of 765 +/- 16 Ma (2 sigma) for xenotime-(Y) overgrowths on zircon obtained by LA-ICP-MS, the first dating of fine overgrowths of xenotime on zircon by this technique, confirms that the formation of xenotime-( Y) is directly related to the crystallization of the carbonatite and provides a date consistent with published dates for Lofdal and Oas syenites. The xenotime-(Y) is heavy-REE-enriched (chondrite-normalized graphs peak at Lu) but can be distinguished from xenotime-(Y) in granitic rocks by the lack of Eu anomaly, higher Gd (reaching > 6 wt%) and lower Yb (below 4 wt%). A monazite-(Ce) - xenotime-(Y) geothermometer developed for metamorphic rocks gives possible but relatively high temperatures of > 450 degrees C for the formation of xenotime-(Y). Overall, the whole-rock compositions are light-REE-enriched, in common with most carbonatites, but the degree of light REE enrichment is less than almost all published datasets (La/Yb-n at Lofdal ranges from 1 to 70), and at 0.5-0.8 wt%, the total REE content at Lofdal is also higher than in many carbonatites. These features are most important in controlling the production of xenotime-( Y) at Lofdal. Exploration for Y in carbonatites should therefore concentrate on rocks that have REE concentrations above 2000 ppm and La/Yb values lower than 70, similar to Lofdal, as well as weathered carbonatite regoliths and carbonatites subjected to extreme hydrothermal conditions, where Y can be concentrated.
72 citations
TL;DR: In this article, a textural, geochemical and mineralogical evolution is proposed to explain the coexistence of different morphologies in the multiframboidal texture: (a) growth and aggregation of microcrystals as typical framboidal-type mineralogical associations; (b) development of euhedral habits; (c) coalescence and homogenization of the microcrystal into large size (euhedral to anhedral) crystals, and (d) formation of polycrystalline masses, with complete loss of framboid texture.
62 citations
TL;DR: In this paper, the effect of carbonisation on coal mineral matter has been investigated by a detailed quantitative mineralogical examination of nine cokes and their parent coals, using SIROQUANT ™.
50 citations
TL;DR: In this paper, it is shown that the COX porewater is in equilibrium with the following carbonate minerals, calcite, dolomite and ankerite/sideroplesite, but not with strontianite.
43 citations
TL;DR: In this paper, the authors used the flux distribution method to calculate the long-term average weathering rates of REE-rich epidote, garnet, and ankerite within the Brubaker Run watershed.
35 citations
Journal Article•
TL;DR: Xu et al. as mentioned in this paper developed numerical models that simulate the co-injection of H 2 S or SO 2 with CO 2 into an arkose formation at a depth of about 2 km and 75 ° C.
Abstract: Numerical Modeling of Injection and Mineral Trapping of CO 2 with H 2 S and SO 2 in a Sandstone Formation Tianfu Xu 1 , John A. Apps 1 , Karsten Pruess 1 , and Hajime Yamamoto 2 Earth Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720, USA Civil Engineering Research Institute, Taisei Corporation, 344-1, Nase-cho, Totsuka-ku, Yokohama 245-0051, Japan Abstract. Carbon dioxide (CO 2 ) injection into deep geologic formations could decrease the atmospheric accumulation of this gas from anthropogenic sources. Furthermore, by co-injecting H 2 S or SO 2 , the products respectively of coal gasification or combustion, with captured CO 2 , problems associated with surface disposal would be mitigated. We developed models that simulate the co-injection of H 2 S or SO 2 with CO 2 into an arkose formation at a depth of about 2 km and 75 ° C. The hydrogeology and mineralogy of the injected formation are typical of those encountered in Gulf Coast aquifers of the United States. Six numerical simulations of a simplified 1-D radial region surrounding the injection well were performed. The injection of CO 2 alone or co-injection with SO 2 or H 2 S results in a concentrically zoned distribution of secondary minerals surrounding a leached and acidified region adjacent to the injection well. Co-injection of SO 2 with CO 2 results in a larger and more strongly acidified zone, and alteration differs substantially from that caused by the co-injection of H 2 S or injection of CO 2 alone. Precipitation of carbonates occurs within a higher pH (pH > 5) peripheral zone. Significant quantities of CO 2 are sequestered by ankerite, dawsonite, and lesser siderite. The CO 2 mineral-trapping capacity of the formation can attain 40-50 kg/m 3 medium for the selected arkose. In contrast, secondary sulfates precipitate at lower pH (pH < 5) within the acidified zone. Most of the injected SO 2 is transformed and immobilized through alunite precipitation with lesser amounts of anhydrite and minor quantities of pyrite. The dissolved CO 2 increases with time (enhanced solubility trapping). The mineral alteration induced by injection of CO 2 with either SO 2 or H 2 S leads to corresponding changes in porosity.
31 citations
TL;DR: The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile).
Abstract: The El Dorado Au-Cu deposit is located in an extensive intra-caldera zone of hydrothermal alteration affecting Upper Cretaceous andesites of the Los Elquinos Formation at La Serena (≈ 29°47′S Lat., 70°43′W Long., Chile). Quartz-sulfide veins of economic potential are hosted by N25W and N20E fault structures associated with quartz-illite alteration (+supergene kaolinite). The main ore minerals in the deposit are pyrite, chalcopyrite ± fahlore (As/(As + Sb): 0.06−0.98), with electrum, sphalerite, galena, bournonite-seligmanite (As/(As + Sb): 0.21−0.31), marcasite, pyrrhotite being accessory phases. Electrum, with an Ag content between 32 and 37 at.%, occurs interstitial to pyrite aggregates or along pyrite fractures. Pyrite commonly exhibits chemical zonation with some zones up to 1.96 at.% As. Electron probe microanalyses of pyrite indicate that As-rich zones do not exhibit detectable Au values. Fluid inclusion microthermometry shows homogenization temperatures between 130 and 352 °C and salinities between 1.6 and 6.9 wt.% NaCl eq. Isotope data for quartz, ankerite and phyllosilicates and estimated temperatures show that δ18O and δD for the hydrothermal fluids were between 3 and 10‰ and between −95 and −75‰, respectively. These results suggest the mineralizing fluids were a mixture of meteoric and magmatic waters. An epithermal intermediate-sulfidation model is proposed for the formation of the El Dorado deposit.
12 citations
TL;DR: The mine of Via Tirapelle in Verona is a paleokarst cave filled with insoluble material coming from the dissolution of the carbonatic formation; the size distribution generally belongs to the class of lime and clay as discussed by the authors.
Abstract: The mine of Via Tirapelle in Verona is a paleokarst cave filled with insoluble material coming from the dissolution of the carbonatic formation; the size distribution generally belongs to the class of lime and clay.
No more information is available on these natural earths.
The analysis carried out in the past on these materials refer that the pigment was limonite.
X-ray diffraction powder (XRD) analysis allows to refer that the yellow ocher is only the orthorhombic goethite. Goethite is locally associated with calcite, quartz and dolomite. Ankerite was found as a constituent of two samples deriving from the replacement of Fe inside the dolomite. X-ray fluorescence (XRF) analysis of major elements shows that the contents of Fe are related to goethite and ankerite, and to the poorly crystalline phases.
Inductively coupled plasma emission spectrometry (ICP-ES) analysis of trace elements Cd, Co, Cr, Cu, Ni, Pb, Zn shows a linear correlation between Fe2O3 and Cd, Cu, Ni, Zn. Copyright © 2008 John Wiley & Sons, Ltd.
7 citations
TL;DR: Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ18O values range from −0.3
Abstract: Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ18O values range from −0.3‰–−0.1‰) and lighter oxygen isotope (their δ18O values range from −22.1‰–−19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later dissolution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ13C values ranging from −8.02‰ to −3.23‰, and lighter oxygen isotope with δ18O values ranging from −22.9‰ to −19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous calcites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ13C values ranging from −1.92‰ to −0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ18O values ranging from −20.5‰ to −12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process.
Journal Article•
TL;DR: In this paper, the authors analyzed thin section, cathodoluminescence, and elemental composition and carbon isotope of carbonate cements in the reservoir sandstone of the Pinghu Formation in Xihu Sag, East China Sea Basin.
Abstract: Carbonate cements are the most abundant authigenic minerals in the reservoir sandstone of Pinghu Formation in Xihu Sag,East China Sea Basin.The analyses on thin section,cathodoluminescence,and elemental composition and carbon isotope show that siderite,ankerite and calcite are the main minerals of the carbonate cements in Pinghu Formation.The siderite cement is mainly generated from syngenesis to early diagenesis,with highest δ13C (0.75‰) and δ18O(-10.22‰).The δ13C of ankerite varies from -2.45‰ to -2.98‰,which is concordant with the coeval sea water,and the δ18O of ankerite is low,with least of -12.39‰,and occurs during the early diagenetic stage.Granular and poikilitic cementations are the main occurrences of calcite cement.Granular calcite has many origins;however,the origin of the poikilitic calcite cement is closely related to the aluminosilicate minerals and the transformation of clay minerals.The siderite and ankerite precipitated in the early diagenetic stage enhanced the mechanical strength of rock and resistance to compaction,which is favorable for the reservoir quality,while the intergrowth calcite cementation generated in the late period is disadvantageous for the reservoir quality.
01 Jan 2008
TL;DR: In this article, the results of studies on Upper Rotliegend sandstones from 23 boreholes of Western Pomerania, acquired by applying different analytical methods (digital image analysis of thin sections, CL, SEM, EDS ISIS, XRD, stable isotope determinations, K/Ar age determination of crystallization of fibrous illite, organic matter studies).
Abstract: DIAGENESIS AND DEVELOPMENT OF THE PORE SPACE IN THE UPPER ROTLIEGEND SANDSTONES OF POMERANIA Abstract The paper presents the results of studies on Upper Rotliegend sandstones from 23 boreholes of Western Pomerania, acquired by applying different analytical methods (digital image analysis of thin sections, CL, SEM, EDS ISIS, XRD, stable isotope determinations, K/Ar age determination of crystallization of fibrous illite, organic matter studies) and the results of petrophysical analyses These sandstones are represented mainly by sublithic and lithic arenites Apart from detrital grains (quartz, feldspars, lithoclasts), authigenic minerals were identified in the sandstones’ cements They correspond to iron oxides and hydroxides, clay minerals (kaolinite, chlorite, illite), carbonates (calcite, dolomite, ankerite), sulphates and quartz The sandstones underwent a number of diagenetic processes These are mechanical and chemical compaction, cementation and replacement, and dissolution and alteration of unstable components The effects of these processes proceeded within the sediment with a different intensity being dependent on its mineral composition, degree of burial and temperature In reference to that, two stages have been distinguished in the history of diagenesis: eo- and mesodiagenesis The presumed maximum temperatures that affected the sediment could reach 160oC It is suggested that the cementation, compaction and diagenetic dissolution had the main influence on the formation of the pore space in the sandstones The closure of the pore space in the Permian sediments, preventing flow of formation fluids, occurred in the Early and Middle Jurassic
TL;DR: In this paper, geochemical studies were carried out on water and paralic sandstones of the Rio Bonito Formation, which constitutes a granular aquifers system, to evaluate the mining activities influences of Candiota Mine, the largest Brazilian coal reserve over the groundwater quality.
Abstract: In order to evaluate the mining activities influences of Candiota Mine, the largest Brazilian coal reserve, over the groundwater quality, geochemical studies were carried out on water and paralic sandstones of the Rio Bonito Formation, which constitutes a granular aquifers system. Geochemical modeling indicates that for most cases, groundwater is subsatured in relation to the balance water-carbonates and supersatured in relation to the balance water-goethite and -kaolinite. The phisico-chemical results of the water samples showed little evidence of significant acidification or sulphatisation of groundwater by acid mine drainage of mining activities. A natural but limited pyrite oxidation by the restricted entrance of oxygen in the aquifer system seems to be responsible for the positive correlations between sulphate and iron. However, the iron contents is lower than the expected value from pyrite dissolution which can be explained by the precipitation of Fe-oxi-hydroxides (e.g. goethite). The dissolution of carbonates (calcite, siderite and ankerite) is an important process of the neutralization of acidity, controlling the chemical composition of the groundwater by consuming protons and releasing Ca2+ and Mg2+. Relatively to the superficial waters, calcium and magnesium are more significantly depleted than sodium and potassium in the groundwater, probably related to the selective adsorption. For the calcium-bicarbonate correlation, atmospheric and soil CO2 as well as organic matter oxidation are considered to contribute to the increase in the total content of bicarbonate
01 Jan 2008
TL;DR: In this paper, a diagenetic history of the Pennsylvanian sandstones from Western Pomerania includes eo- and mesodiagenesis, and the estimated maximum temperature that affected the rocks during diagenesis could exceed 140°C.
Abstract: DIAGENESIS AND PORE SPACE EVOLUTION IN PENNSYLVANIAN SANDSTONES FROM WESTERN POMERANIA Abstract. The Pennsylvanian sandstones of Western Pomerania are represented chiefly by quartz arenites and wackes. The main cement components are authigenic quartz, authigenic clay minerals (kaolinite, dickite and illite), carbonates (Mn-calcite, dolomite, ankerite, siderite), hematite and Fe oxides. Sulphates (anhydrite and barite) are common, but occur in small amounts. Locally, organic matter is observed. Diagenetic history of the Pennsylvanian sandstones from Western Pomerania includes eo- and mesodiagenesis. The estimated maximum temperature that affected the rocks during diagenesis could exceed 140°C. Porosity of the sandstones varies from 0 to about 20%. Primary porosity is predominant, whereas secondary porosity accounts for a small percentage. The major diagenetic processes, affecting petrophysical properties of the rocks, were compaction and cementation. Compaction resulted in primary porosity reduction by 37%, cementation by approximately 52% on average. Among the Pennsylvanian deposits, the best reservoir properties are observed in sandstones from the Dźwirzyno 3, Gorzyslaw 10 and Sarbinowo 1 boreholes.
01 Jan 2008
TL;DR: The Voring Basin forms an integrated part of the passive margin off central Norway as mentioned in this paper, and Cretaceous sandstones are among the most important hydrocarbon exploration targets in the basin.
Abstract: The Voring Basin forms an integrated part of the passive margin off central Norway. Cretaceous sandstones are among the most important hydrocarbon exploration targets in the basin. One of the most significant features of the sandstone reservoirs is the excellent reservoir quality. The lack of early pervasive diagenetic cements and the high compositional maturity have contributed to the preservation of primary porosity. Reservoir quality evolution of the sandstones was equally controlled by cementation and compaction. Primary porosity was subjected to overall successive deterioration with increase in burial depth until the precipitation of post-compaction (mesogenetic) cements (quartz overgrowths, rhombic dolomite/ankerite, saddle dolomite and calcite). However, reservoir quality was improved through the partial to total dissolution of framework grains (mainly feldspars). The sources of acidic fluid to accomplish this dissolution are uncertain, but could be organic acids derived form thermal maturation of organic matter.
01 Jan 2008
TL;DR: In this article, the results of investigations of sandstones observed between the Carboniferous Rega Formation and the Lower Permian Wielkopolska Volcanigenic Formation in West Pomerania are presented.
Abstract: THE SANDSTONES FROM THE PENNSYLVANIAN/LOWER PERMIAN TRANSITION IN WESTERN POMERANIA: DIAGENESIS AND ITS ROLE IN RESERVOIR QUALITY Abstract. The paper presents the results of investigations of sandstones observed between the Carboniferous Rega Formation and the Lower Permian Wielkopolska Volcanigenic Formation in West Pomerania. The results have been acquired using various analytical methods (polarizing microscope, CL, SEM, EDS ISIS, XRD, light element stable isotope, infrared analysis). The sandstones are represented mostly by quartz arenites. Apart from detrital grains (quartz, feldspars, lithoclasts), authigenic minerals are observed in the sandstones. They correspond to iron oxides and hydroxides, clay minerals (kaolinite/dickite, chlorite, illite), carbonate minerals (calcite, dolomite, ankerite), sulphate minerals and quartz.Anumber of processes have been identified, which affected the sandstones. These are mechanical and chemical compaction, cementation, replacement, dissolution and alteration of unstable components. The effects of the processes have been variously marked within the deposits, depending on the mineral composition, burial depth and temperature. As a result, two diagenetic stages can be identified: eo- and mesodiagenesis. The deposits may have been heated to the maximum temperatures of approximately 130C.
01 Jan 2008
TL;DR: The Voring Basin forms an integrated part of the passive margin off central Norway as mentioned in this paper, and Cretaceous sandstones are among the most important hydrocarbon exploration targets in the basin.
Abstract: The Voring Basin forms an integrated part of the passive margin off central Norway. Cretaceous sandstones are among the most important hydrocarbon exploration targets in the basin. One of the most significant features of the sandstone reservoirs is the excellent reservoir quality. The lack of early pervasive diagenetic cements and the high compositional maturity have contributed to the preservation of primary porosity. Reservoir quality evolution of the sandstones was equally controlled by cementation and compaction. Primary porosity was subjected to overall successive deterioration with increase in burial depth until the precipitation of post-compaction (mesogenetic) cements (quartz overgrowths, rhombic dolomite/ankerite, saddle dolomite and calcite). However, reservoir quality was improved through the partial to total dissolution of framework grains (mainly feldspars). The sources of acidic fluid to accomplish this dissolution are uncertain, but could be organic acids derived form thermal maturation of organic matter.
01 Jan 2008
TL;DR: In this paper, the authors developed a data table of measurements made on core and outcrop samples comprising quantitative mineral abundances, chemical concentrations, and computed properties from nuclear forward modeling.
Abstract: Determination of those parameters which are suitable for converting Green River well log data into useful variables is a challenging task because the formation components are very different from those encountered in conventional oil reservoirs. Among the differences are the solid nature of the hydrocarbon and the presence in significant abundance of unusual minerals such as dawsonite and nahcolite. We have found that a useful approach in such a case is to develop a data table of measurements made on core and outcrop samples comprising quantitative mineral abundances, chemical concentrations, and computed properties from nuclear forward modeling. As a prelude to mineral analysis of Green River samples, we have upgraded our analysis system. In 1993 and 1997, we showed that assemblages of common sedimentary minerals could be quantitatively analyzed using Dual Range (combined mid- and far-IR) Fourier Transform Infrared (DRFT-IR) spectroscopy. The technique relied on rigorous sample preparation procedures which produced spectra that honored the linear portion of Beer-Lambert law. We analyzed known artificial mixtures as a function of the spectra of standard minerals and in each case, the standard errors on minerals identified by our technique were 1- 2 weight percent. Mineral standards now include quartz, feldspars, calcite, dolomite, ankerite, siderite, illite, smectite, kaolinite, chlorite, glauconite, muscovite, biotite, pyrite, dawsonite, nahcolite, trona, buddingtonite, and halite. We have collected over 110 outcrop samples and 160 core samples from the Green River formation. Analysis of chemistry and mineralogy of these samples is underway and preliminary results will be presented.
DOI•
06 Aug 2008
TL;DR: A Pb-Zn-Ag deposit located at Tanjung Balit, Limapuluh Kota Regency, West Sumatra, is hosted within the meta sedimentary rocks of the Tapanuli Group as mentioned in this paper.
Abstract: A Pb-Zn-Ag deposit located at Tanjung Balit, Limapuluh Kota Regency, West Sumatra, is hosted within the meta sedimentary rocks of the Tapanuli Group. The lithology consists of interbedded shale, meta sandstone, slate and phyllite (Kuantan Formation). The deposit is in the form of veins, veinlets and disseminated. The thickness of veins ranges from few centimeters up to 5 meters. In places, some ore bodies are conformable with the host rocks. The main ores are lead, sphalerite, chalcopyrite, pyrite and silver with minor marcasite, magnetite, chalcosite and gold. Hydrothermal mineral assemblages consist of silica, illite, monmorillonite, pyrophyllite, muscovite, siderite, diaspore, dickite, magnesite, chlorite, carbonate, rhodochrosite, analcime, alunite, smectite, ankerite, calcite, dolomite, sericite and zeolite. Fluid inclusion measurements of secondary inclusions within quartz veins indicate that the homogenization temperature (Th) ranges from 185 - 350oC. The presence of alunite, higher content of base metals as well as higher temperature range of the secondary fluids suggests that the deposit may characterize a high suphidation epithermal type. Keywords : Tanjung Balit, Tapanuli Group, fluid inclusion, high sulphidation epithermal