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Instrumental methods applied in the investigations of carbonate minerals in the Middle Jurassic sideritic rocks with respect to diagenetic processes

Kozłowska Aleksandra

Biuletyn Państwowego Instytutu Geologicznego

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2019

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nr 474

31--42

EN

Carbonate minerals in the Middle Jurassic sideritic rocks from the Polish Lowlands, north-eastern margin of the Holy Cross Mountains and the Częstochowa region have been studied applying accessible instrumental methods. The following techniques were applied: polarization microscope, staining with the Evamy’s solution, cathodoluminescence, microprobe, fluid inclusions and isotopic analyses. Most of these methods were not available either in the 20ies of the past century when studies of sideritic iron ores in Poland had begun, or in 50ies and 60ies when they were in full progress. The sideritic rocks are mainly represented by clayey siderites (they contain also muddy and sandy varieties), sideritic sandstones and sideritic coquina, less frequently by sideritic conglomerates and mudstones. Sideroplesite is the main carbonate mineral that builds the sideritic rocks, while pistomesite and siderite are less frequent. Fe-calcite and Fe-dolomite, ankerite, and sporadic dolomite occur in lesser amounts. Syderoplesite and siderite have crystallized in the early diagenesis (eodiagenesis), in the zone of microbiologic methanogenesis, at temperatures of about 20°C, from the porous waters of marine origin, or from marine waters mixed with fresh waters. Sideroplesite enriched in magnesium, pistomesite, calcite and ankerite sequently have formed at the later diagenetic stage (mezodiagenesis). These minerals have crystallized at temperatures above 60°C, from the porous waters of marine origin, or from the fluid which interacted with the adjacent rocks. Fe-calcite was formed in the zone of microbiologic methanogenesis, while the ankerite – in the zone of thermal decarboxylation.

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Na podstawie dostępnych obecnie metod instrumentalnych zbadano minerały węglanowe skał syderytowych jury środkowej z Niżu Polskiego, północno-wschodniego obrzeżenia Gór Świętokrzyskich i rejonu Częstochowy. Zastosowano: mikroskop polaryzacyjny, barwienie roztworem Evamy’ego, katodoluminescencję, mikrosondę energetyczną, analizę inkluzji fluidalnych i izotopową. Większość z tych metod nie była dostępna w latach dwudziestych, kiedy rozpoczęto badania syderytowych rud żelaza w Polsce, ani w latach pięćdziesiątych i sześćdziesiątych, kiedy były kontynuowane. Skały syderytowe są reprezentowane głównie przez: syderyty ilaste (obejmują również odmiany mułkowe i piaszczyste), piaskowce syderytowe i muszlowce syderytowe, rzadziej przez zlepieńce syderytowe i mułowce syderytowe. Głównym minerałem węglanowym budującym skały syderytowe jest syderoplesyt, rzadziej pojawiają się pistomesyt i syderyt. W zmiennych ilościach występują Fe-kalcyt oraz Fe-dolomit i ankeryt, sporadycznie dolomit. Syderoplesyt i syderyt krystalizowały we wczesnej diagenezie (eodiagenezie) w strefie mikrobiologicznej metanogenezy w temperaturze ok. 20°C z wód porowych pochodzenia morskiego lub wód morskich zmieszanych z wodami słodkimi. W późniejszym etapie diagene¬zy (mezodiagenezie) tworzyły się w kolejności: syderoplesyt z większą zawartością magnezu, pistomesyt, kalcyt i ankeryt. Minerały te krystalizowały w temperaturze powyżej 60°C z wody porowej pochodzenia morskiego lub wody, która weszła w reakcję z otaczającymi skałami. Fe-kalcyt tworzył się w strefie mikrobiologicznej metanogenezy, natomiast ankeryt w strefie termalnej dekarboksylacji.

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Hydrochloric acid leaching for upgrading flotation concentrate from a low-grade bauxite ore

Guan C., Chen L., Zheng Y., Sun W., Zheng Y.

Physicochemical Problems of Mineral Processing

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2017

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Vol. 53, iss. 2

1038--1046

EN

Bauxite is the major raw material for alumina production, and its Al2O3 grade improvement or desilication is a necessary process for production of high-grade alumina concentrates from bauxite ores. In practice, flotation presents an effective method for the processing of such ores. However, it is not sufficient to produce a concentrate product with high Al2O3 grade from the ores with a single flotation process, especially from these containing abundant carbonate minerals. In this investigation, hydrochloric acid leaching was used to remove dolomite impurity from the flotation concentrate of a bauxite ore, to improve its Al2O3 grade and Al2O3/SiO2 (A/S) ratio. Effects of three dominant parameters on the leaching performance, that is leaching time, leaching temperature and hydrochloric acid concentration, were investigated in details. When these parameters were optimized, the aluminum concentrate assaying 67.41% Al2O3 with 66.84% recovery and 7.44 A/S ratio was obtained from the bauxite ore assaying 42.94% Al2O3 with 2.48 A/S ratio. It was concluded that hydrochloric acid leaching proved an effective method for upgrading of flotation concentrate from a low-grade bauxite ore containing carbonate minerals.

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Temperature and isotopic relations in carbonate minerals in the Middle Jurassic sideritic rocks of central and southern Poland

Jarmołowicz-Szulc K., Kozłowska A.

Geological Quarterly

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2016

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Vol. 60, No. 4

881-892

EN

The present study assesses the physico-chemical character of the fluids responsible for the genesis of carbonate minerals in the Middle Jurassic sideritic rocks at the northeastern margin of the Holy Cross Mts. and in the Częstochowa region. These rocks occur at present at depths between 30 and 600 m. Fluid inclusion and isotopic analyses have been performed in the carbonate minerals from sideritic sandstones, clayey siderites and sideritic coquinas. Siderite is the main carbonate mineral of the sideritic rocks. Calcite and ankerite are also present. The siderite is represented by two varieties, Mg-rich siderite (sideroplesite, less commonly – pistomesite) and siderite. Two generations of siderite have been distinguished – an early and a late one. The early siderite was formed at temperatures of about 20°C in the zone of microbiological methanogenesis from marine waters with some influence of meteoric waters (δ18O from –7.84 to –1.92‰ VSMOW). The late siderite crystallized at temperatures of about 62–110°C from pore waters enriched in 18O (δ18O >0‰ VSMOW) as compared with the isotopic composition of the waters responsible for the early siderite generation. The conducted fluid inclusion analyses point to formation of the cements from complex fluids of brine and carbon dioxide character, with densities slightly exceeding 1 g/cm3 and salinities varying from 10.5 to 16.9 wt.% NaCl eq. and from 6.4 to 14.0 wt.% NaCl eq. in the Holy Cross Mts. and in the Częstochowa region, respectively. The homogenization temperatures lie in the intervals of 62–110°C and 60–97°C, respectively and represent elevated values compared with data from the Polish Lowlands. Apart from burial, other heat sources must have been important for the lithogenesis of the Middle Jurassic deposits.