Ankerite

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

Mineralogy of Iron-Rich Sediments of Benavi Area in Kurdistan Region—Northern Iraq

Abstract: Benavi iron-rich sediments (BIRS) is located about 20 km N–NW of Amadia district in Duhok Governorate – Northern Iraq. It occurs as an elongated E–W body within the Jurassic–Cretaceous sequences and extends about 2 km. The true thickness of BIRS outcrop ranges from 2.5 m to 12.8 m enclosed within highly fractured carbonate beds. Forty-eight samples collected from 10 sections represent the whole BIRS body. The sampling was systematic according to variations in color, hardness, texture, and iron content. Mineralogical study using instrumentations such as XRD, SEM, EDS, and TGA besides petrography showed that BIRS is composed of mineral assemblages: carbonates (calcite, siderite, ankerite), iron oxides/hydroxides (hematite, magnetite, goethite), sulphides (pyrite and arsenopyrite), silicates (kaolinite, chamosite, glauconite, quartz), and phosphates (collophane and apatite). Calcite is the predominant mineral in the whole BIRS, whereas siderite and ankerite are minor, and dolomite is trace. Shifts of the main real peaks values of calcite about the theoretical value in its d-space in all BIRS samples gave the indication that there is no pure calcite in most studied samples, but in a few samples it appears to be pure. Impure calcite presence is most likely due to Mg2+ and Fe2+ substitutions in the space lattice of the calcite crystals; this is supported by the EDS analysis which showed the presence of these elements in the calcite spectra. XRD results also showed that there is a negative relationship between calcite and iron oxides/hydroxides in BIRS. This is attributed to the loss of carbonate that took place during the oxidation of Fe2+ to Fe3+ and release of H1+ where the initial calcite had been dissolved and replacement of iron oxides/hydroxides occurred, frequently, yielding interpretation for partial and complete replacements of calcareous constituents by iron minerals. The main iron minerals are hematite and goethite. The former is higher at the upper part of BIRS; contrarily, the latter is higher at the middle part. This study proved that different goethites coexist. They differ in crystallization and Al3+ content; these are Al-poor and Al-rich goethites, supported via the wide range of decomposition temperature by TGA (263oC–350oC); besides the peaks shifts to higher 2O angles indicating Al3+ substitution for Fe3+. Most of the primary Al-poor goethite altered to Al-poor hematite (by dehydration), hence the prevailing of the latter at the upper part, whereas Al-rich goethite which dominated at the middle of BIRS is a secondary and it is produced by goethitization of pyrite, siderite, and chamosite under surface weathering circumstances. High specific surface area of iron oxides/hydroxides probably acted as important sorbents to dissolve species: particularly heavy metals, phosphates, and arsenate, then under reduction conditions most of the adsorbed species released from iron oxides/hydroxides surfaces. This may give a clue about the presence of phosphate minerals, as well as the presence of arsenopyrite in the lower part of BIRS. Clay minerals of BIRS were represented by kaolinite and chamosite as well as a trace of glauconite noted in some samples. Paragenetically, kaolinite may have recrystallized or transformed to chamosite under reducing conditions in the availability of Mg2+ and iron oxides. Arsenopyrite, which has not been mentioned before, was confirmed by EDS and it is found restricted at the base of BIRS. The presence of arsenopyrite mineral in BIRS may give vital evidence to hydrothermal activations in this area. Frequently, finding other ores in the study area is promising.

ToF‐SIMS as a tool for mapping reaction products of coupled dissolution–precipitation processes at mineral grain surfaces

Abstract: In this paper, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was investigated as a tool for analyzing changes on mineral grains (siderite and ankerite) caused by dissolution and precipitation processes. Carbon dioxide capture and sequestration is a technique investigated for its possible employment in the reduction of the amount of anthropogenic CO2 gas emitted into the atmosphere. Deep saline aquifers are one option for storing CO2 gas streams produced, e.g. by the combustion of fossil fuels at power plants. These gas streams contain different impurities depending on their origin, among them O2, NOx, SOx in addition to CO2. Geochemical experiments under in-situ pressure and temperature conditions of possible geological storage sites were performed, and preparation techniques for the solid products were developed for 3D analysis. The results show that it is possible to analyze the alterations that occur on the surface of siderite grains during CO2 or CO2/O2 exposures under CO2 storage site conditions. Copyright © 2014 John Wiley & Sons, Ltd.

Geochemical study of the microbial and inorganic precipitation of magnetite and siderite at low temperatures

Abstract: The origin, mechanism, and fate of fine-grained ironoxides (magnetite, hematite) and Fe-rich carbonates (siderite, ankerite) in nature are crucial to our understanding of numerous biogeochemical processes and remanent magnetization in the upper crust of the Earth. In recent years, we became increasingly aware of the importance of iron biomineralization in nature, including implications for the atmospheric evolution of the Earth and possible life on Mars. In order to better understand natural processes of iron-oxide and carbonate formation, we have been studying details of the mechanisms and processes of the microbial and inorganic precipitation of magnetite and siderite under well-controlled laboratory conditions (physical chemistry, microbiology, mineralogy, and isotopic fractionation). A particular interest in our study is how to distinguish microbial and inorganic origins of finegrained magnetite and siderite in nature, if possible. This article is a progress report of our activities to date.

Evidence of Biogenic Activity in Quartz-Hematite Rocks of the Urals VMS Deposits

Abstract: The textural, mineralogical, and geochemical features of quartz-hematite rocks associated with Urals VMS deposits indicate that the tube microfossils are responsible for immobilization and accumulation of chemical elements during precipitation of authigenic minerals. The crystallization of authigenic minerals is a result of submarine transformation of mixed hyaloclastitic, sulfide, and carbonate sediments and diagenetic processes, which modify the mineralogy and geochemistry of sediments. The tube microfossils about 100 μm across and up to 1 mm long consist of the external rim made up of fine-disperse hematite or hematite-quartz aggregates and of the internal channel filled with hematite and/or transparent quartz, fine-disperse hematite-quartz aggregates, leucoxene, rare sulfides, apatite, Fe-chlorite, and Mn-calcite. The carbon isotopic composition of calcite from quartz-hematite rocks with tube microfossils (up to −26.2 ‰) indicates its biogenic origin. The habitat conditions of the tube microfossils favored the mineral precipitation. The newly formed apatite, rutile, illite, monazite, dolomite, ankerite, siderite, monheimite, REE carbonates, anatase, leucoxene, Mn-oxides, titanomagnetite, and hematitized framboidal pyrite are observed in quartz-hematite matrix with abundant tube organisms in contrast to quartz-hematite rocks free of tube microfossils. Biomorphic hematite contains high contents of Mn (up to 9393 ppm), As (up to 1872 ppm), V (up to 779 ppm), W (up to 1091 ppm), Mo (up to 40 ppm), and U (up to 8.68 ppm), which are indicative of biological mechanisms of accumulation and conservation of these metals in the system.

Importance of olistostrome member for metallogeny of ljubija iron ore deposits

Abstract: Ljubija mining area is built of more formations that belong to the Carboniferous, Permian, Triassic and Cenozoic. From all of these, only two are metalliferous to iron: Javorik formation with olistostrome member and Neogene-Quaternary of Prijedor basin. The first includes primary siderite and ankerite partially limonitised ore and in the second only redeposited limonite (limonite pieces and dust, known under the commercial name "brand"). Appearance of iron is also in other members of Javorik formation and other formations, but these are just thin veins. They have no significance for the economic exploitation but are an important element in the interpretation of metallogeny in the region. These findings came from many years of fieldwork and synthesis of all published and unpublished data related to iron ore in this area. Therefore, this work gives special importance to olistostrome member, its stratigraphic position and metallogenic characteristics.