Ankerite

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

The microbial controls on the deposition of Pb‐Zn minerals in carbonate‐hosted Tunisian ore deposits

Abstract: The Ain Allega, Mjar Hannech and Sidi Driss Pb‐Zn‐Ba‐Sr‐As‐(Hg) deposits in northern Tunisia are hosted in a post‐nappe anticline with a core of a Triassic evaporite diapir affected by the NE–SW‐trending Ghardimaou‐Cap Serrat and E‐W lineament. The ore minerals show different styles; particularly, impregnation in dolomite, cement of breccias, replacement ore and open space filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite, pyrite and cinnabar. Principal gangue minerals are composed of barite, celestine, calcite, dolomite and quartz. The orebodies are hosted by Triassic carbonate rocks (Ain Allega ore deposits), Cretaceous carbonate rocks (Mjar Hannech ore deposits) and by the volcanoclastic layers (Sidi Driss ore deposits). These host rocks show hydrothermal alteration, dissolution and brecciation. Sphalerite in the carbonate‐hosted Zn‐Pb deposits in Tunisia occurs as nano‐size microglobular blebs and peloids and forms finely‐laminated bands with wavy and even ripped up features. Peloids are present in collapse breccias of karst cavities. Peloids (5–100 μm) and bacterial filaments (1 μm long) locally form the common micro‐texture of the sulfide mineralization. The core and the shell of peloids are composed of different minerals; there are 1–3 shells and each shell is 1–1.5 μm thick, commonly with coarse crystals. These textures probably represent fossil microbial mats as in‐situ sulfate‐reducing bacteria products and are similar to nano‐textures observed in bacterial biofilms. Electron microscopy, combined with major element changes (Zn, Pb, As, Fe, and Cd) and sulfur isotope values suggest that sphalerite nano‐textures and nano‐spheres are associated with fossilized bacterial‐mat. The δ34S values of sphalerite (−43.9 to +22.38‰) show that the microbial production of H2S controlled sphalerite precipitation. The biogenic nano‐ to macro‐textured sphalerite and sulfur isotope data suggest that microbes had an important role in the genesis of carbonate‐hosted Zn‐Pb deposits in Tunisia during the Miocene.

Diagenesis in Upper Miocene Sandstones, Louisiana Gulf Coast: ABSTRACT

Abstract: Study of diagenesis in upper Miocene sandstones of coastal Louisiana documents depth-related cementation and geochemical changes of primary detrital mineralogy. Samples were collected from depths of 8,000-20,000 ft (2,600-6,500 m) in an area roughly corresponding to the upper Miocene depocenter in the Terrebonne trough of southeast Louisiana. Sandstones are primarily subarkoses and sublitharenites with minor amounts of feldspathic litharenites and lithic arkoses. Plagioclase feldspar (oligoclase/andesine composition) composes approximately 60% of the detrital feldspar. Dominant rock fragments are siltstone or mudstone, silicified volcanic rock, and chert. Authigenic minerals and cements occur in the following order: dolomite, chlorite grain coats, albite overgrowths on plagioclase and K-feldspar, quartz, calcite, kaolinite, and ankerite. Calcite composition remains nearly constant with depth, but ankerite composition differs both with depth and within individual samples. In general, the mineralogy and order of cements resemble that of the lower Tertiary sandstones of the Texas Gulf Coast; however, in the upper Miocene, the volume of each cement is much less and the depth of first occurrence is greater. Feldspars have reacted substantially with pore fluids. With increasing depth, feldspar becomes more sodic because of albitization and dissolution of calcic plagioclase. At approximately 20,000 ft, 75% of the plagioclase is nearly pure albite. Alteration of K-feldspar is not common above 17,000 ft; below 17,000 ft occurrences are rare because of dissolution. End_of_Article - Last_Page 257------------

Study of opaque phases in carbonatites of the Grønnedal-Íka alkaline complex, Southwest Greenland

Abstract: Opaque phases from carbonatites of the Gronnedal-Ika alkaline complex (1299±17 Ma) of Southwest Greenland were analyzed in terms of their mineralogy and microstructure. The analysis demonstrates that a later intrusion by a 55 m wide dolerite dyke of unknown age has prompted the mineralization of magnetite by activating hydrothermal fluid convection. The fluid has interacted with the carbonatite, replacing siderite and ankerite by magnetite, which at places constitutes over half of the rock volume. Magnetite is shown to have become partly replaced by hematite at a later stage. A paragenetic sequence is suggested for the opaque phases that com- prise major magnetite and hematite, accessory pyrite and trace amounts of sphalerite, chalcopyrite and galena.

Simulation of long-term geochemical behavior and mineral trapping of CO 2 in saline aquifer

Abstract: Geochemistry plays a significant role in CO 2 storage, especially when considering on long term behavior of injected CO 2 . In this work, reactive transport modeling of supercritical CO 2 in a multilayered saline aquifer was performed. After injection for 30 years, the long-term behavior of the CO 2 by considering its geochemical reaction for 5,000 years was investigated. Result shows that mineral trapping occurs mainly within the shale layers. Mineralization becomes the dominant trapping mechanism after 1,000 years. Significant amounts of ankerite precipitate due to the mineralization of the injected CO 2 . Calcite dissolved rather than precipitated because of the decrease in pH. Because of the compensation effect among mineral species, precipitation/dissolution around the injection region does not play a significant role to change in porosity and permeability under the geologic conditions employed in this work. The results of this study will be applied to the CCS project that is underway in South Korea.