Ankerite

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

A Note on the Trace Element Contents of Carbonatites of a MBA Dongar and Surrounding Areas, Chhota Udaipur

Abstract: The note incorporates trace element analyses of carbonatites from Amba Dongar and surrounding areas. Mineralogical study indicates that pyrochlore is the only diagnostic mineral present in some of these rocks. Though the rare earth minerals proper are absent, the analyses reveal a fair concentration of the rare earth elements. It is therefore concluded that these elements are mainly contained in calcite and ankerite. Also, some calcareous rocks of dyke-like nature from Bakhatgarh and Dehi, suspected to be carbonatites, have been analysed. However, their trace element contents do not conclusively prove them to be so.

Геохимическая и Sr–Nd–Pb изотопная характеристики щелочных пород и карбонатитов Белозиминского массива (Восточный Саян)

Abstract: Belaya Zima alkaline carbonatite complex (East Sayan, Russia) is a multiphase intrusion of the central type. The carbonatite stock is exposed in the central part of the complex, which is composed of different mineralized carbonatite. Alkaline silicate rocks form ring-shaped bodies surrounding the central carbonatite and are represented by melteigites and ijolites, dyke-shaped bodies of alkaline syenites. The article presents the results of Pb/Pb dating, petrological and geochemical studies, including radiogenic (Nd, Pb and Sr) isotopic data. The age value of 631 ± 11 Ma, obtained from the Pb/Pb isochron line for all rocks of intrusion, is consistent with the previous age determinations [643 ± 3 Ma, Yarmolyuk et al. 2005 and 645 ± 6 Ma, Doroshkevich et al., 2016; 645 ± 6 Ma, Salnikova et al., 2019]. The age is in the range of 700-600 Ma, the interval of the formation of alkaline carbonatite complexes located along the edge of the Siberian craton (Aldan-Stanovoy shield, Yenisei Ridge, East Sayan). Emplacement of the complexes is associated with the final stage of the break-up of the Rodinia supercontinent [Yarmolyuk et al., 2005]. Melteigites are more magnesium (Mg # = 28–35) in comparison with ijolites (Mg # = 24–30) and alkaline syenites (Mg # = 15–29), which proves the lowest degree of differentiation of the former. The low total Mg # of the Belaya Zima alkaline silicate rocks, their low nickel and chromium concentrations confirm the fact that olivine crystallization has completed. Early crystallization of perovskite in melteigites led to depletion of the residual melt in REEs and Nb and formation of REE-depleted ijolites and nepheline syenites. There are the evolution trend of HFSE and REEs from early calcite carbonatite to calcite-dolomite and ankerite carbonatites. The calcite and calcite-dolomite carbonatites have the highest contents of Nb-Ta and Zr-Hf and reflect the early crystallization of pyrochlore and zirconolite. Late ankerite carbonatites are enriched in REEs in comparison with calcite and calcite-dolomite carbonatites, are REEs are concentrated in rare earth carbonates and monazite (Ce). Isotopic data (87Sr/86Sr = 0.702672–0.703125 and eNd (Т) = 3.14–4.97) for rocks of the Belaya Zima complex indicate that primary melts were formed from a heterogeneous, moderately depleted mantle source. The high concentration of incompatible elements in the rocks (Sr and Nb, La/Sm ratio), the presence of carbonatites in the complex indicate that the possible mantle metasomatic agent had a carbonate initial composition. This conclusion is confirmed by the results of melt inclusions study in minerals from the Belaya Zima ijolites [Andreeva et al., 2007]. A high Gd/Yb ratio (up to 7) in the rocks indicates that they were derivatives of primary melts formed by low degree of partial melting of a garnet-bearing source.

A Zincian Chrome-Spinel from the Cr-Ba-Fe-Cu-Zn Deposit near Busovaca (Bosnia and Herzegovina)

Abstract: The metamorphic complex of the Busovaca area is mostly composed of Upper Silurian-Lower Devonian metapelites, metapsammites and metarhyolites formed under low grade metamorphism at 350° to 450°C and 3 to 5 kbars. The ore minerals of the Busovaca deposit are: magnetite (with relics of zincian chrome-spinel), rimmed by ferrichromite, and pyrite, chalcopyrite, enargite, bornite and siegenite. The gangue minerals are: siderite, quartz, albite, hyalophane, muscovite, chromian-chlorite and manganoan ankerite. Proton microprobe analyses (PIXE) were made of samples A (core Ac of the slightly altered chrome-spinel), B (strongly altered chrome-spinel with Bc-core, Bfc-ferrichromite zones, Br-magnetite rim) and C (cryptically zoned magnetite with Cc-core and Cr-magnetite rim). The results are recalculated in formulae, and presented on separate diagrams. The optical investigations, microprobe analyses, beam-scan photographs, diffusion rates of Mg, Al, Zn, Cr, and Mn, and diagrams, allow the following conclusions to be made: (1) magmatic origin of the primary chrome-spinel, (2) the emplacement of the Zn was prior to the alteration under very low f02, most probably synchronous with the sulphide mineralization; (3) the alteration process took place in two phases: (a) the early stage volume-for-volume replacement and formation of the ferrichromite and magnetite zones, (b) the late stage characterized by decolourization and/or resorption, and/or dissolution of the core (patches, specks, “atoll structure”); (4) released Al, Cr, Mn, and Zn have been taken up by silicate, carbonate and oxide minerals forming chromian-chlorite, manganoan ankerite or contaminated siderite and pyrite; (5) the diffusion rates among Al, Zn, Cr, and Mn during different stages of the alteration have the following sequence: Al - Zn - Cr - Mn; (6) the optically unzoned magnetite crystals or aggregates originated in chrome-spinel; (7) the mineral assemblage of the Busovaca deposit co-exists with the surrounding metamorphic complex belonging to the greenschist facies.

Discussion on the Genesis of Baixintu Uranium Deposit in Sonliao Basin

Abstract: Baixintu uranium deposit is with the following major features:(1) well developed low temperature hydrothermal alteration of kaolinization,carbonation,pyritization,hydromicazation,sericitization,hematization et al,and uranium mineral coexisted with hydrothermal pyrite and ankerite and hematite in colloid,mass,strawberry;(2) vein orebody with coffinite as main mineral and a little pitchblende and titanium;(3) complicated isotopes feature of Carbon(δ13C is-268‰～-1049‰),oxygen(δ18O is-1074‰～-171‰),sulfur(δ34S is 1224‰～1433‰ and-3306‰) which are related to atmosphere water,magma,biological transformation and the dissolution of carbonate and sulfateThe above feature shew obvious oxidization and hydrothermal action,and the synthesyzed results of shallow-oxidization and deep fluid actionIn other word,the deposit has "double-open metallogenic system" characteristics of infiltration-type and exudation-type

Caracterização e evolução geoquímica das águas subterrâneas da mina de Candiota (RS), Brasil

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