Ankerite

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

The Importance of Mineral Surface Areas Exposed to Open Pores in Rotliegend Sandstones for Modelling CO2 Water-rock Interactions

Abstract: Rotliegend reservoir rocks from the northern Netherlands were analysed in terms of mineralogical features, diagenetic mineral types and mineral surface areas which are exposed to open pores (effective mineralogy). The consideration of the effective mineralogy in comparison to the volumetric bulk rock composition of sandstones and the integration into CO2-water-rock simulation has shown that the mineral reactions are sensitive according to the initial data set. For the test scenario the results show that during CO2 storage especially long-term carbonate and silica reactions are affected. For the effective mineralogy data Mg-smectite stays in equilibrium with the solution which is caused by a higher initial amount of hematite and the release of iron for siderite precipitation. This reaction lowers the bicarbonate content in the solution and forces dolomite and ankerite to dissolve consequently. On the other hand Mg-smectite is unstable and carbonate minerals stay in equilibrium at the end of the simulation according to the volumetric mineralogy data.

THE TIMING OF MINERALIZATION AT THE JACLYN ZONE GOLD DEPOSIT, CENTRAL NEWFOUNDLAND: CONSTRAINTS FROM 40 Ar/ 39 Ar STUDIES OF WHITE MICA ALTERATION ADJACENT TO AURIFEROUS QUARTZ VEINS

Abstract: The Jaclyn Zone gold deposit (the Golden Promise deposit), is located in the western Exploits Subzone of the central mobile belt of the Newfoundland Appalachian Orogen. The gold resource at the deposit is based upon a ~1-m-wide, northeast-trending and steeply southeast-dipping quartz-vein network termed the Jaclyn Main vein; this is only one of several such veins exposed in the deposit area. Vein textures are varied, including laminated- and comb-textured material and these are hosted by interlayered, mafic volcaniclastic arenite, siltstone and wacke of the Noel Paul’s Brook Group of the Middle–Late Ordovician Victoria Lake supergroup. Regional metamorphic grade is low (sub-greenschist facies). The veins are developed in the uppermost strata of the supergroup, directly below the conformable transition to Sandbian (Caradocian) black shale. Native gold occurs as blebs in the comb-textured quartz and in the margins of laminated veins. Alteration in the footwall of the veins is dominated by illite+ankerite+Fe-chlorite+albite, whereas alteration in the immediate hanging wall is dominated by ankerite+albite+Fe-chlorite+illite+barian-potassium feldspar (adularia). The 40 Ar/ 39 Ar thermochronology on 2 samples from the immediate structural footwall of 2 major veins (Jaclyn Main and Christopher) indicate that the illite-dominated assemblage formed at ca. 428 Ma. The ankerite+Fe-chlorite+albite+illite+adularia-bearing assemblage in the hanging wall yielded a less robust age of ca. 400 Ma. Because the latter sample contains two distinct potassium-bearing phases, its younger age may be derived from a mixture of argon from sparse, ca. 428 Ma illite and from fine-grained and disseminated, younger (ca. 400–380 Ma?) adularia. Presently, the ca. 428 Ma age is interpreted to be the best estimate for the time of gold mineralization.

Geochemistry of storing CO2 and NOx in the deep Precipice Sandstone

Abstract: The Precipice Sandstone in the Surat Basin is being appraised for CO2 geological storage owing to its high porosity and permeability and expected high injectivity. Generally it is quartz rich with variable kaolinite, however detailed characterisation of core shows that it contains minor to trace amounts of potentially reactive minerals including carbonates, plagioclase, chlorite, and muscovite, increasing towards the overlying Evergreen Formation top seal. The Evergreen Formation is more variable, with interbedded low porosity and permeability mudstones, fine-grained sandstones, and calcite cemented zones. Injected CO2 dissolves into formation water forming carbonic acid. The geochemical reactivity of drill core samples affects the predicted pH and the dissolution or precipitation of minerals which could permanently trap CO2 as carbonates such as siderite, or dynamically change porosity and permeability altering CO2 migration. Comparative kinetic geochemical modelling of the CO2 reactivity of four representative mineralogies from drill core samples from deeper parts of the central basin indicates that the Evergreen Formation is potentially more reactive to CO2 than the Precipice Sandstone, especially for calcite or siderite containing zones. In the Precipice Sandstone small amounts of albite and siderite dissolved with traces of siderite and kaolinite precipitated. Dissolution of calcite and siderite in the Evergreen Formation favourably buffered acidity, with predicted precipitated minerals including siderite, kaolinite, ankerite, and smectites. The geochemical models indicate overall changes to porosity are however minor. Recent data from capture technologies has reported that CO2 from coal combustion may retain NOx impurities in the form of NO. Simulations with the addition of 30-100 ppm NO in the CO2 stream indicated the generated pH in the quartz rich Precipice Sandstone is similar to that on injection of pure CO2 after 30 years. The precipitation of Fe-rich smectite clays was additionally predicted.