Ankerite

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

Trace elements in recent groundwater of an artesian flow system and comparison with snow: enrichments, depletions, and chemical evolution of the water.

Abstract: Snow samples collected from hand-dug pits at two sites in Simcoe County, Ontario, Canada were analysed for major and trace elements using the clean lab methods established for polar ice. Potentially toxic, chalcophile elements are highly enriched in snow, relative to their natural abundance in crustal rocks, with enrichment factor (EF) values (calculated using Sc) in the range 107 to 1081 for Ag, As, Bi, Cd, Cu, Mo, Pb, Sb, Te, and Zn. Relative to M/Sc ratios in snow, water samples collected at two artesian flows in this area are significantly depleted in Ag, Al, Be, Bi, Cd, Cr, Cu, Ni, Pb, Sb, Tl, V, and Zn at both sites, and in Co, Th and Tl at one of the sites. The removal from the waters of these elements is presumably due to such processes as physical retention (filtration) of metal-bearing atmospheric aerosols by organic and mineral soil components as well as adsorption and surface complexation of ionic species onto organic, metal oxyhydroxide and clay mineral surfaces. In the case of Pb, the removal processes are so effective that apparently “natural” ratios of Pb to Sc are found in the groundwaters. Tritium measurements show that the groundwater at one of the sites is modern (ie not more than 30 years old) meaning that the inputs of Pb and other trace elements to the groundwaters may originally have been much higher than they are today; the M/Sc ratios measured in the groundwaters today, therefore, represent a conservative estimate of the extent of metal removal along the flow path. Lithogenic elements significantly enriched in the groundwaters at both sites include Ba, Ca, Li, Mg, Mn, Na, Rb, S, Si, Sr, and Ti. The abundance of these elements can largely be explained in terms of weathering of the dominant silicate (plagioclase, potassium feldspar, amphibole and biotite) and carbonate minerals (calcite, dolomite and ankerite) in the soils and sediments of the watershed. Arsenic, Mo, Te, and especially U are also highly enriched in the groundwaters, due to chemical weathering: these could easily be explained if there are small amounts of sulfides (As, Mo, Te) and apatite (U) in the soils of the source area. Elements neither significantly enriched nor depleted at both sites include Fe, Ga, Ge, and P.

Diagenesis and reservoir quality of the Aldebaran Sandstone, Denison Trough, east‐central Queensland, Australia

Abstract: The Lower Permian Aldebaran Sandstone is the principal hydrocarbon reservoir in the Denison Trough (Bowen Basin), east‐central Queensland, Australia. It accumulated in a wide range of fluvio‐deltaic and nearshore marine environments. Detailed petrological study of the unit by thin section, X‐ray diffraction, scanning electron microscopy, electron microprobe and isotopic analysis reveals a complex diagenetic history which can be directly related to depositional environment, initial composition and burial‐temperature history. Early diagenetic effects included the precipitation of pyrite, siderite and illite‐smectite rims (δO (SMOW) =+8.9 to + 11.3‰). Deep burial effects included physico‐chemical compaction and the formation of quartz overgrowths, siderite (δC(PDB) =−34.0 to + 11.5‰, δO =−0.7 to +22.7‰), illite/illite‐smectite and ankerite (δC=−9.3 to −4.9‰) δO=+ 7.6 to + 14.4‰). Involved fluids were in part ‘connate meteoric’ water derived from compaction of the underlying freshwater Reids Dome beds. Important post‐maximum burial effects, controlled by deep meteoric influx from the surface, were ankerite and labile grain dissolution and formation of kaolinite (δO=+7.8 to +8.9‰, δD=−115 to −99‰), calcite (δC=−9.5 to +0.9‰, δO=+9.0 to +20.0‰) and dawsonite (δC=−4.0 to +2.3‰, δO=+9.8 to +19.8‰), the formation of dawsonite reflecting eventual stagnation of the aquifer. Entrapment of contained hydrocarbons was a relatively recent event which may be continuing today. Reservoir quality varies from marginal to good in the west to poor in the east, with predictable trends being directly linked to depositional environment and diagenesis.

The origin of authigenic ankerite from the Ninian Field, UK North Sea

Abstract: The carbonate minerals ankerite and ferroan dolomite are widely reported in studies of concretions1,2 and of sandstone hydrocarbon reservoirs3–8. These minerals are often thought to have formed relatively late in the sandstones' diagenetic history and in the Gulf Coast their occurrence has been linked to clay mineral diagenesis in the surrounding shales9. I describe here authigenic ankerite from the Ninian Field10. Ankerite formation was probably synchronous with hydrocarbon emplacement and is related to clay mineral diagenesis in the hydrocarbon source rocks of the Viking Graben. It occurs throughout the reservoir sandstones but is particularly abundant below the oil–water contact. This distribution reflects hydrocarbon emplacement arresting diagenesis at progressively deeper levels of the reservoir. The resulting preferential cementation may adversely affect transmissibility between the aquifer and the oil column and consequently could reduce hydrocarbon recovery.

Mineralogy and Geochemistry of the Carbonatites of the Sevathur and Samalpatti Complexes, Tamil Nadu

Abstract: The Proterozoic carbonatites and associated pyroxenites and syenites of Tamil Nadu are emplaced in the Precambrian gneissic rocks. The carbonatite complexes are located along a major NE trending lineament. In Sevathur, dolomitic carbonatite is predominant over sovite and ankeritic carbonatite whereas in Samalpatti, sovite and silico-sovite form the major bulk of carbonatite mass with small dykes of dolomitic and ankeritic carbonatites. In different types of carbonatites, in addition to calcite, dolomite and ankerite, phlogopite, amphibole, magnetite, and apatite are found in varying amounts between 2% and 10% with accessory amounts of pyrochlore, perovskite, monazite, NbiImenorutile, zircon, baddeIeyite, pyrite, ilmenite, galena and thorite. Both mica and amphibole show change in composition from Fe-rich in syenite and sovite to Mg-rich in the dolomitic carbonatite. The carbonatites are enriched in Ba, Sr, Nb, REE's, Th and U in comparison to the primitive mantle values. Pyroxenites are characterized by high abundances of Mg, Cr and Ni and, low abundances of Nb and Zr. The petrographic evidence, with globules silicate rocks surrounded by carbonatitic matrix is sufficiently clear to suggest a genetic link between syenite and carbonatite by liquid immiscibility.