Ankerite

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

Diagenesis of Miocene pelitic sedimentary rocks in the Sava Depression (Croatia) Presented at the MECC'08 Conference

Abstract: AB ST R ACT : Miocene pelitic sedimentary rocks from six wells in the Sava Depression (sub-basin in the south-western part of the Pannonian Basin System) were investigated in order to determine the degrees of diagenetic alteration.Qualitative and semiquantitative mineral compositions of samples and the content of smectite in illite-smectite (I-S) were determined by X-ray powder diffraction (XRD).Vitrinite reflectance and thermal alteration index (TAI) were measured in order to estimate the palaeotemperatures.Carbonate minerals, clay minerals and quartz are the main constituents of the pelitic sediments.Feldspars (albite), pyrite, opal-CT and hematite are present as minor constituents in some rocks.The mineral composition of the rocks, apart from previously known differences caused by various depositional environments and clastic material provenance, is dependent on the degree of diagenetic processes.At elevated temperatures and large burial depths the minerals formed by alteration processes or precipitated at the surface; smectite, kaolinite and calcite were gradually replaced by minerals formed by diagenetic processes, i.e. by illite-smectite, illite, chlorite, Ca-excess dolomite/ankerite and albite.Based on XRD data for smectite, I-S and illite, three stages of diagenetic development have been established.The early stage was characteristic of samples at depths 1.8 km and temperature above 80oC.At depths >4. 6 km with corresponding temperatures >190oC, the late stage began, characterized by the presence of R>1 I-S with <10% smectite.

Tectono-magmatic events and genesis of Fe-Pb-Zn resources in Nefza area, NW Tunisia

Abstract: Fe-ore and Pb-Zn (Ag) resources of Nefza region occur within hydrothermally altered sericite-schists and breccias, with Neogene molasse and lacustrine sediments and with a sequence of tertiary granodiorite-rhyodacite and basalts. Intrusions of intermediate igneous rocks, whose correlate with the successive Alpine tectonic events, started at 15 Ma and continued to near 5 Ma. Four main stages of mineralization are identified: (1) the first stage started during or soon after the maximum alpine compression (Langhian-Lower Serravallian) and magmatism. Silicification and carbonatization prevailed and sericite-bearing sediments formed by K-sericite alteration. (2) During the second stage, a mixture of marine and meteoric ore-forming fluids (H2O, H2CO3, F and Cl; temperature range, 315–500 °C) has deposited mineralizations. The sericite schist assemblages and breccias were extremely altered and four types of minerals were formed: (i) silica, feldspar, Mg-micas, chlorite-vermiculite, Mg-clays, and kaolinite-halloysite; (ii) fluorite and sorbed U; (iii) Fe-(Mn) oxyhydroxides; (iv) Zn, Pb, Mn, and Fe, deposited in the carbonates, in coronadite and in minor sulfides. (3) The third stage was related to the extensional tectonic phase (Upper Serravallian-Lower Tortonian) and leads to the subsidence of Miocene grabens and deposition of molasse with interbeded pyroclastites. The strata-bound iron ores were reworked from pre-existing Fe-mineralization hosted in folded structures. (4) During the fourth stage (8 to 5 Ma), magmatic activity changed from calc-alkaline granitoid to alkaline basalt. This correlates with a moderate Atlasic compression, thrust faulting, and Miocene graben folding. During this stage, Pb (Ag)-Zn sulfides were deposited in veins that cut across the predating iron deposits, with neoformed Mg-rich clays and carbonates (calcite, siderite, ankerite) with noticeable Zn and Mn enrichments.

Temperatures of aqueous alteration on carbonaceous chondrite parent bodies

Abstract: Aqueous alteration of primitive meteorites is among the earliest and the most widespread geological processes in the solar system. A better understanding of these processes would help us constrain the early evolution condition of the solar system and test models of thermal and chemical evolution of planetesimals. In this study, we extended our previous work on CM chondrites by further applying carbonate clumped isotope thermometry to other types of carbonaceous chondrites (GRO 95577, CR1; Orgueil, CI; and Tagish Lake, ungrouped type 2) to determine the conditions of their aqueous alteration. Carbonate in GRO 95577 is almost exclusively calcite; both Orgueil and Tagish Lake contain complex mixtures of several carbonates, which necessitated stepped phosphoric acid digestion to separately analyze calcite, dolomite/ankerite and breunnerite. CO_2 gases derived from these acid digestions are exceptionally rich in sulfur and organic contaminants. While so far no consistent evidence suggests their influences on Δ_(47) after extensive purification, we are continuing working on this issue.