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Ankerite

About: Ankerite is a research topic. Over the lifetime, 859 publications have been published within this topic receiving 23960 citations.


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Book ChapterDOI
01 Jan 2016
TL;DR: The Yuanjiacun banded iron formation (BIF) is a Superior-type BIF in the North China Craton (NCC) as mentioned in this paper, which is within a metasedimentary rock succession of the YuanjiACun Formation in the lower Luliang Group.
Abstract: The Paleoproterozoic (~2.38–2.21 Ga) Yuanjiacun banded iron formation (BIF), located in Shanxi Province, is a Superior-type BIF in the North China Craton (NCC). This BIF is within a metasedimentary rock succession of the Yuanjiacun Formation in the lower Luliang Group. The clastic metasediments associated with the BIF are mainly represented by well-bedded meta-pelites (chlorite schists and sericite-chlorite phyllites) and meta-arenites (sericite schists), which have undergone greenschist-facies metamorphism. The Yuanjiacun Formation had been originally deposited in a passive margin setting, most probably on a stable continental shelf. Iron oxide (magnetite and hematite), carbonate, and silicate facies are all present within the iron-rich layers. Integration of petrographic and isotopic evidence indicates that the most likely precursor materials were comprised predominantly of probably hydrous, Fe-silicate gels of stilpnomelane-type composition, amorphous silica gels, and ferrihydrite. The \({\text{P}}_{{{\text{O}}_{2} }}{-} {\text{P}}_{{{\text{CO}}_{2} }}\) and pH-Eh fields of the mineral assemblages (and/or their precursors) in the Yuanjiacun BIF indicate anoxic and near-neutral to slightly alkaline conditions for the original depositional environment except for the hematite precursor field (that of Fe(OH)3), which is very small and exists only at relatively high \({\text{P}}_{{{\text{O}}_{2} }}\) values. The eastward transition from carbonate- into oxide-facies iron formations is accompanied by a change in mineralogical composition from siderite in the west through magnetite-ankerite and magnetite-stilpnomelane assemblages in the transition zone to magnetite and then hematite in the east. These distinct lateral facies are also observed vertically within the BIF, i.e., the iron mineral assemblage changes up section from siderite through magnetite into hematite-rich iron formation. The oxide-facies BIF formed near shore, whereas carbonate (siderite)- and silicate-facies assemblages formed in deeper waters. Based on detailed analyses of these variations on a basinal scale, the BIF precipitated during a transgressive event within an environment that ranged from deep waters below storm-wave base to relatively shallow waters. The BIF samples display distinctively seawater-like REE + Y profiles that are characterized by positive La and Y anomalies and HREEs enrichment relative to LREEs in Post-Archean Australian shale-normalized diagrams. Consistently positive Eu anomalies are also observed, which are typical of reduced, high-temperature hydrothermal fluids. In addition, slightly negative to positive Ce anomalies, and a large range in ratios of light to heavy REEs and Y/Ho, are present in the oxide-facies BIF. These characteristics, in combination with consistently positive δ56Fe values, suggest that deposition of the BIF took place along the chemocline where upwelling of deep, anoxic, iron- and silica-rich hydrothermal fluids mixed with shallower and slightly oxygenated seawater. The ankerite displays highly depleted δ13C values and the carbonate-rich BIF has a high content of organic carbon, suggesting dissimilatory Fe(III) reduction of a ferric oxyhydroxide precursor during burial of biomass deposited from the water column; that same biomass was likely tied to the original oxidation of dissolved Fe(II). The fact that the more ferric BIF facies formed in shallower waters suggests that river-sourced nutrients would have been minimal, thus limiting primary productivity in the shallow waters and minimizing the organic carbon source necessary for reducing the hematite via dissimilatory Fe(III) reduction. By contrast, in deeper waters more proximal to the hydrothermal vents, nutrients were abundant, and high biomass productivity was coupled to increased carbon burial, leading to the deposition of iron-rich carbonates. The deposition of the Yuanjiacun BIF during the onset of the Great Oxidation Event (GOE; ca. 2.4–2.2 Ga) confirms that deep marine waters during this time period were still episodically ferruginous, but that shallow waters were sufficiently oxygenated that Fe(II) oxidation no longer needed to be tied directly to proximal cyanobacterial activity.

1 citations

Journal ArticleDOI
24 Aug 2022-Energies
TL;DR: In this paper , the influence of laminar structure on reservoir quality is examined using a combination of geochemistry, mineralogy, and pore structures in the Qingshankou Formation.
Abstract: This paper investigates high-maturity organic matter-rich shales with high clay mineral contents in the Qingshankou Formation, in the Gulong Depression of the Songliao Basin, at a sub-millimeter scale, using a new laminar division method based on XRF data. The influence of laminar structure on reservoir quality is examined using a combination of geochemistry, mineralogy, and pore structures. Explanatory models are established. Three types of laminar units are distinguished in the study area based on differences in pore structure. These are clay mineral laminae (UA), clay mineral-Ostracod laminae (UB), and clay mineral-felsic laminae (UC). UA has illite intergranular pores, micro-fractures, and organic pores, with diameters of 0.5~2 μm. UB primarily contains Ostracod shell margin fractures, pyrite intergranular pores, and chlorite intragranular pores. UC contains albite and illite intergranular pores. Nitrogen adsorption tests show that UA has the highest clay content and the best specific pore volume and specific surface area, indicating that clay minerals are the main contributors to the pores in this type of unit. 2D–3D models of different laminae reveal that carbonate cement is widely developed in UB and UC, but dissolution pores are less developed, with the result that the porosity of UA is two to three times greater than that of UB or UC. It appears that intergranular pores and fractures, formed during the transformation of clay minerals during the advanced thermal evolution stage, are the main contributors to storage space and flow channels. Thermal evolution, clay mineral transformation, and carbonate cementation are the key factors causing differences between laminar units. In addition, clay mineral laminae (UA) are the most important laminar units for shale oil enrichment in the study area. This finding is of great significance for accurately predicting the distribution of shale “sweet spots” and guiding shale oil and gas exploration.

1 citations

09 Dec 1985
TL;DR: In this paper, a rapid, automated procedure was employed to differentiate and quantify siderite, calcite and dolomite in geologic strata, based on the different rates of dissolution of the three carbonate species when reacted with excess 5 mol/litre HCl.
Abstract: A rapid, automated procedure was employed to differentiate and quantify siderite, calcite and dolomite in geologic strata. The technique is based on the different rates of dissolution of the three carbonate species when reacted with excess 5 mol/litre HCl. It has been shown that the pseudo-first order rate constants for the three minerals are 27.64, 6.75 and 0.23 (hr)/sup -1/ respectively. The above data point out that the effectiveness of calcite and dolomite in neutralizing acid drainages, considering that kinetic factors are involved, are vastly different. Furthermore, siderite is virtually indestructible in even very strong acid. Data from geologic samples revealed that the rates of dissolution of residual carbonates by a strong acid vary from that of calcite to siderite, even though x-ray diffraction revealed that the carbonates are mainly calcite and ankerite. This has some very important implications in evaluating effectiveness of these carbonates in neutralizing acid drainages. It appears that armoring and weak crystallinity of the carbonate particles play a very important role in controlling their reactivity. The technique presented effectively demonstrates carbonate reactivity. Furthermore, the technique was use to other minerals and colloidal phases. The technique can be used as means of quantifying the reactivity of residualmore » spoil carbonates and therefore allow one to predict the effectiveness of such carbonates in neutralizing and/or controlling acid mine drainage. 14 references, 6 figures, 1 table.« less

1 citations

01 Jan 1987
TL;DR: In this article, the results of an ongoing study indicate that the sandstones were deposited in fluvial and marginal lacustrine environments, and the percentages of clays and cements vary considerably from sample to sample, particularly between bitumen-bearing sandstones and adjacent lithologies.
Abstract: Sandstones that crop out along the Roan Cliffs near Sunnyside, Utah, are estimated to contain approximately 6 billion barrels of bitumen, making it one of the largest deposits in the United States. Little is known of the geologic aspects, particularly sedimentology, mineralogy (especially clays), and diagenesis, of these sandstones. These aspects of tar sands must be characterized before the feasibility of bitumen recovery can be assessed. Preliminary results of this ongoing study indicate that the sandstones were deposited in fluvial and marginal lacustrine environments. Sandstone geometry is dependent on depositional environment: Fluvial sandstones tend to be more extensive basinward but are less laterally extensive than the marginal lacustrine sandstones. The sandstones are mainly feldspathic arenites, containing both plagioclase and K-feldspar. Authigenic cements include calcite, dolomite, ankerite, siderite, and analcime. Authigenic clay minerals include kaolinite, illite, and smectite. The percentages of clays and cements vary considerably from sample to sample, particularly between bitumen-bearing sandstones and adjacent lithologies. Some of these authigenic minerals have replaced framework grains. Dissolution ha produced secondary porosity, and the bitumen appears to occupy secondary porosity, preferentially in the coarser grained sandstones.

1 citations

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.

1 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202332
202270
202140
202027
201946
201842