Feldspar Albite Research Articles

Origin of Ca [sbnd]Cl brines in Devonian formations, western Canada sedimentary basin

The majority of waters in Devonian formations of the western Canada sedimentary basin are high salinity Ca Cl brines. This relatively rare type of brine is of economic interest because of its association with both oil and hydrothermal ore deposits. These brines are important sources of Ca 2+, Mg 2+ and ore metals in sedimentary basins. It is possible to generate the Ca Cl brines by modification of residual evaporite brines. The evaporation of Devonian sea water produced large quantities of gypsum and halite such as the Prairie Formation. Residual brines were not retained in the evaporating system. Quantities of dense, halite-saturated brine, sufficient to account for the high salinity formation waters in the basin, were lost syndepositionally. The Cl − and Br − content of waters within Devonian formations in the basin can be explained by dilution of the residual evaporite brines. Brine composition was modified as a result of density driven reflux to depths of several kilometers. This placed concentrated brines in contact with Precambrian basement rocks at elevated temperatures (100–300°C). The most important reactions between the brine and basement rocks appear to involve albitization of feldspars. Further modification of the brines occured as cements formed in Devonian carbonates. Volumetrically, the most important of these is dolomite, in addition some Devonian carbonates were dolomitized. During ascent along faults Mg 2+ was lost from hot brines as dolomite formed.

Oxygen-isotope studies of clastic diagenesis in the Lower Cretaceous Viking Formation, Alberta: implications for the role of meteoric water

Summary The oxygen-isotope compositions and paragenetic sequence of diagenetic minerals from the Lower Cretaceous Viking sandstone and conglomerate from south-central Alberta, Canada have been used to identify changes in porewater composition during diagenesis and to relate these changes to major geological events within the western Canada sedimentary basin. Large-scale influx of meteoric water has played an important role in diagenesis of this unit, especially following uplift of the basin in early Eocene time. Diagenetic phases include early kaolinite ( δ 18 O SMOW = + 24.9 to +28.2 ‰), siderite ( δ 18 O SMOW = + 22.0 to + 23.9 ‰; δ 13 C PDB = −6.3 to −1.3 ‰), calcite ( δ 18 O SMOW = + 26.0 ‰; δ 13 C PDB = −0.4 ‰) and chlorite ( δ 18 O SMOW = + 10.7 − + 13.4 ‰), followed in order by dolomite ( δ 18 O SMOW = + 19.3 − + 22.1 ‰; δ 13 C PDB = −5.9 to −2.6 ‰), calcite ( δ 18 O SMOW = + 13.9 − + 15.9 ‰; δ 13 C PDB = −8.4 to −6.1 ‰), ankerite ( δ 18 O SMOW = + 16.3 − + 17.9 ‰; δ 13 C PDB = −12.4 to −3.5 ‰), kaolin group minerals ( δ 18 O SMOW = + 12.0 − + 15.7 ‰), and illite ( δ 18 O SMOW = + 14.2 − + 15.7 ‰) and illite/smectite ( δ 18 O SMOW = + 13.8 − + 16.5 ‰). Quartz overgrowths ( δ 18 O SMOW = + 16.2 − + 27.4 ‰) began crystallizing relatively early during burial diagenesis and continued to form at least up to the onset of late diagenetic formation of clay minerals. The interpretation of these results is that shallow diagenesis, early in the burial history (glauconite, pyrite, calcite, chlorite), occurred largely in the presence of seawater-derived fluids, although a freshwater influence is indicated where siderite and(or) early kaolinite cements are abundant. As compaction and burial diagenesis proceeded (diagenetic chlorite, quartz overgrowths, dolomite), the porewaters became enriched in 18 O due to water/rock interaction. Burial diagenesis was terminated in the early Eocene by uplift related to the major Laramide Orogeny. Recharge of the basin by low 18 O meteoric water occurred at this time. The meteoric water then became involved in the formation of diagenetic quartz, calcite and ankerite (and the dissolution and albitization of feldspar) at or near maximum burial temperatures, and in the crystallization at lower temperatures of kaolin group minerals, illite and illite/smectite as the post-Eocene erosion progressed.

Reconsideration of ‘soda-minettes’

AbstractIt is shown here that dyke rocks of type localities for ‘soda-minettes’ are not minettes (= lamprophyres dominated by phlogopite and K-rich feldspar). It has long been suggested that ‘soda-minette’ also be applied to otherwise normal minettes from elsewhere that carry modally variable amounts of groundmass aegirine and/or, more commonly, arfvedsonitic to riebeckitic amphibole. Despite the presence of sodic pyriboles, these rocks are poorer in Na2O then minettes lacking these phases. ‘Soda-minette’ is thus misleading and self-contradictory to the many petrologists to whom ‘soda-’ legitimately connotes that the rock in question either has K/Na < 1 and/or is rich in albitic feldspar. To eliminate this ambiguity it is recommended, with the approval of twenty-six other petrologists, that ‘soda-minette’ no longer be used as a rock name. As minettes with Na-pyribole(s) are markedly K-rich and most are both ultrapotassic and peralkaline, independent of the modal abundance of the Na-pyrobile, it is suggested that one of these three chemical characteristics be utilized adjectivally in naming these minettes.

Relationship between cry and social support in preterm and term infants

We investigated a shock vein of the Yamato 791384 L6 chondrite to clarify the nature and sequence of the dynamic processes that resulted from the shock events. The chondritic host-rock of Y-791384 mainly consists of olivine (Fa24–25), low-Ca pyroxene (Fs18–22), albitic feldspar (An9–10Ab84–86Or5–7), troilite and metallic Fe–Ni. The shock vein contains majorite (or majorite-pyropess) and magnesiowüstite (+ minor jadeite) as high-pressure polymorphs. Two different dynamic events were recorded in the shock vein. The majorite grain contained vitrified (Mg,Fe)SiO3-perovskite inclusions. The (Mg,Fe)SiO3-perovskite was crystallized from a chondritic melt, and is a remnant of a first dynamic event. The majorite and magnesiowüstite were also crystallized directly from a chondritic melt but induced by a second dynamic event. The pressure condition for the first and second dynamic events would be >~24 GPa and <~22 GPa, respectively. Pervasive feather-shaped olivine (Fa16) nucleated on the magnesiowüstite and majorite. This feather-shaped olivine is evidence for rapidly grown olivine from the melt related to the shock event. Phase relations deduced from high-pressure melting experiments of the Allende meteorite and peridotite indicate that the magnesiowüstite and majorite + olivine pair cannot coexist at equilibrium condition. The disequilibrium assemblage reflects a decompression stage. These features demonstrate the complexity of events during a natural dynamic process.

Geologic, fluid inclusion, and geochemical studies of the mineralized breccias at Cumobabi, Sonora, Mexico

Cumobabi, a Cu-Mo-mineralized breccia-hosted deposit, is associated with 56-m.y.-old in- trusive rocks of the Mexican porphyry belt. About 35 breccias that crosscut volcanic flows and small intrusive bodies crop out in the Cumobabi area, but only five central breccias are mineralized significantly. These mineralized breccias occur as fingers of strong potassic alteration which crosscut surrounding zones ofpropylitic alteration. Distal, unmineralized breccias exhibit strong sericitization and tourmalinization. Stage I mineralization, consisting of abundant molybdenite-pyrite-quartz, occurred subsequent to both brecciation and the onset of potassic alteration. Later, stage II mineralization replaced pyrite with chalcopyrite and tetrahedrite in genetically related, but crosscutting, zones of strong sericitic alteration.Three types of well-developed primary inclusions (vapor, moderate-salinity liquid, and high-salinity liquid phases) are abundant in stage I quartz. The distribution of salinities of the inclusions suggest that episodic boiling of a probable magmatic fluid at 440 degrees to 350 degrees C accompanied and may have been responsible for mineral deposition. Episodic boiling is supported by (1) separation of inclusion salinities, (2) absence of intermediate salinity inclusions in quartz, (3) zoning of quartz crystals, with each zone representing a renewed boiling event, and (4) variation of pressure between hydrostatic and lithostatic load. A comparison of data from Cumobabi to experimental data on the NaCl-H 2 O system suggests that boiling of a 6 to 9 wt percent solution at depths of 1.0 to 1.5 km may have formed two residual phases: a lowsalinity vapor phase and a 30 to 50 wt percent salinity liquid rich in metal cations. The resulting concentration produced by boiling gave rise to a varied daughter mineral suite. Many of the daughter minerals from type III inclusions were identified under the SEM. Hematite, chalcopyrite, and delafossite, along with halite and sylvite, were common. Other unidentified daughter minerals were shown to contain Cu, Fe, Mn, and Zn, with anions presumed to be oxide, hydroxide, or carbonate. These results suggest that solutions are capable of carrying sufficient metals to form an ore deposit but may be deficient in reduced sulfur. In addition, the close association of molybdenite deposition with boiling suggests that such boiling is an important ore-forming process.Fluid inclusion-rich quartz samples from the mineralized breccia pipes were analyzed for gas and solute components. Gases were analyzed after vacuum line extraction by mass spectrometry, whereas solute components were extracted by leaching techniques and the washings analyzed by DC-plasma atomic emission spectrometry. Gas and fluid analyses along with appropriate thermodynamic data permitted computation of temperature dependent ionic equilibria, including pH and f (sub O 2 ) . These data provide requisite information to constrain fluid chemistry responsible for hydrothermal alteration and metallogenesis at Cumobabi.Computed reaction paths involving interaction of an NaCl brine with a hypothetical quartz monzonite rock illustrate the role of water/rock ratio on hydrothermal alteration at Cumobabi and the effect of temperature on metal mobility. Reaction path calculations demonstrate, for example, that high water/rock ratios stabilize sericite and propylitic assemblages at a constant temperature. Silicate reactions control pH, whereas f (sub O 2 ) controls sulfide deposition. Under the conditions modeled here Mo never exceeds concentrations of 3 ppm in solution, whereas Cu can be maintained in solution at 3,000 ppm. Temperature reduction results in albitization of feldspar and precipitation of sulfides, drastically reducing metal contents in solution.

Maturity Anomalies, Fluid Flow, and Permeability Preservation in Frio and Anahuac Formations, Upper Texas Gulf Coast: ABSTRACT

The Pleasant Bayou geopressured-geothermal test wells in Brazoria County, Texas, display a prominent thermal maturity anomaly in the Oligocene Anahuac and Frio Formations. Highly geopressured, more-mature shales are interbedded with hydropressured to moderately geopressured sandstones in the upper Frio and Anahuac. In contrast, shales and sandstones in the lower Frio, including the Andrau geopressure-geothermal production zone, are highly geopressured and exhibit lower thermal maturities. In the deeper lower maturity sandstones, porosity is dominantly secondary. These sandstones are more permeable by an order of magnitude than the more-mature shallower sandstones. The intense dissolution of grains in the highly geopressured lower Frio Formation is directly related to the increasing solubility of CO2 (released during the maturation of organic matter) with increasing pore pressure. Maturity data at Pleasant Bayou indicates that the upper Frio was subjected to an extended period of upwelling basinal-fluid flow that caused the thermal anomaly. Updip flow of hot basinal fluids was largely arrested in the lower Frio by the high geopressure. Consequently, the maturity of the lower Frio was not increased. Late-state porosity and permeability destruction by carbonate cementation seen elsewhere in the Gulf Coast was inhibited in the deeper Frio by the low influx of Ca2+ ions contained in the fluids. These Ca2+ ions were released from albitization of feldspars at more-mature, deeper levels. End_of_Article - Last_Page 279------------

Prospecção de Urânio no Estado de Goiás

Nuclam started in 1977 a reconnaissance project in central Goias based on previous work carried out by CNEN and Nuclebras. The main motivation has been the similarity in regional geology to areas of Canada and North Australia where some years ago important uranium deposits have been found. Systematic prospecting by means of various technics ranging from regional to detailed scale have been carried out from 1978 to 1980 with promising results. In the Northwestern part of the project area a pegmatite type Uranium mineralization has been localized, which is characterized by low grade and small tonnage. More favourable are the mineralizations encountered in the South and West of Campos Belos. They are related to faults and cataclastic schists, formed out of basement rocks by shear tectonics of the Uruacuan orogenetic cycle (structure controlled mineralization). Another promising mineralization has been encountered recently, further to the West, in migmatitic rocks of the basement. The host rock is characterized mainly by a high amount of albite feldspar and only traces of quartz which points to Na-metasomatic events as source of uranium. The metasomatism apparently started during the Uruacuan Cycle and has been still active post-tectonically. The lithologically and structurally controlled mineralization is spread out over an area of ca. 6 x 1,5 km. The field work is still in the preliminary phase, thus final results have not yet been obtained. The finding of the metasomatic mineralization type in Goias is the first located in central Brazil.

PROSPECÇÃO DE URÂNIO NO ESTADO DE GOIÁS

Nuclam started in 1977 a reconnaissance project in central Goiás based on previous work carried out by CNEN and Nuclebrás. The main motivation has been the similarity in regional geology to areas of Canada and North Australia where some years ago important uranium deposits have been found. Systematic prospecting by means of various technics ranging from regional to detailed scale have been carried out from 1978 to 1980 with promising results. In the Northwestern part of the project area a pegmatite type Uranium mineralization has been localized, which is characterized by low grade and small tonnage. More favourable are the mineralizations encountered in the South and West of Campos Belos. They are related to faults and cataclastic schists, formed out of basement rocks by shear tectonics of the Uruaçuan orogenetic cycle (structure controlled mineralization). Another promising mineralization has been encountered recently, further to the West, in migmatitic rocks of the basement. The host rock is characterized mainly by a high amount of albite feldspar and only traces of quartz which points to Na-metasomatic events as source of uranium. The metasomatism apparently started during the Uruaçuan Cycle and has been still active post-tectonically. The lithologically and structurally controlled mineralization is spread out over an area of ca. 6 x 1,5 km. The field work is still in the preliminary phase, thus final results have not yet been obtained. The finding of the metasomatic mineralization type in Goiás is the first located in central Brazil.

The superheating of an albite feldspar

The superheating of an albite feldspar

Variation in the composition of muscovite and albite in a pegmatite dike near Yellowknife

Regular and irregular variations were found in the concentration of elements in muscovite and albite in relation to the distance from margin to center of a pegmatite dike near Yellow knife. For example, the magnesium content of muscovite increases towards the center, iron decreases, and lithium varies irregularly.The distribution of sodium and potassium among muscovite, albite, and potassium feldspar is considered in relation to mineral reactions and phase equilibrium. Comparison with experimental data indicates that the pegmatite specimens attained near-equilibrium at approximately 450 °C.

The superheating of an albite feldspar

The superheating of an albite feldspar

The mineralogy and petrology of chondritic meteorites

Chondritic meteorites are naturally divided into five chemical groups according to their chemical compositions. Within each group a range of textures exists which is generally interpreted as representing progressive degrees of recrystallization, although there are also significant primary variations in each group. In most chondrites the major minerals are olivine, orthopyroxene, albitic feldspar, troilite, calcic pyroxene, and metallic nickel-iron; the compositions of the silicate minerals are usually uniform within recrystallized chondrites and very similar for individual chondrites belonging to a given group. In unrecrystallized chondrites the minerals are usually quite variable in composition and the primary structures of individual chondrules are well preserved. Most of the properties of chondrites can be interpreted in terms of metamorphic equilibration and recrystallization of primary chondritic matter, although alternative hypotheses exist.

The Evolution of the Granodioritic Rocks of the South-Eastern End of the Kopaonik Batholith, Yugoslavia

Summary and ConclusionsThe composite granodiorite batholith of the Kopaonik Mountains forms one of the more southerly members of the peri-Adriatic tonalitic intrusions. In the area discussed in this paper it intrudes a series of sedimentary rocks which range from dominantly calcareous to pelitic types. Metamorphism of these rocks has produced crystalline limestones, skarns, and calc-silicate hornfelses, which grade downwards into mica-, amphibole-, epidote-, and locally cordierite-bearing rocks. The pelitic and amphibole-bearing hornfelses are in immediate proximity to the batholith on the surface. The amphibole-bearing types are mainly confined to a relatively small area, well within the zone of high-grade metamorphism and overlying the southerly pitching nose of the intrusion. With them are associated hornfelses which carry porphyroblasts of albitic feldspar. It appears that the persistence of the amphibole and the development of these feldspar porphyroblasts may have been caused by hydrous and probably sodic emanations which permeated the sediments above and ahead of the advancing igneous mass.

Authigenic Feldspar in Limestone at Glens Falls, New York

Introduction Small quarries on both sides of the Hudson at Glens Falls, New York, are producing stone for lime-burning from beds of Trenton limestone that are 15 feet thick and that dip gently to the south. The lime enjoys an almost exclusive market for use in drawing steel wire because of its freedom from constituents that scratch the wire. A microscopic examination of the insoluble residue of a sample of the limestone showed that it contains many completely developed crystals of albitic feldspar of authigenic origin. Character of the Limestone The limestone is a dark gray to nearly black crystalline-looking rock, which in thin-section is seen to consist of clouded aggregates of very finely crystalline calcite in a matrix of more coarsely crystalline calcite. The clouded aggregates are more or less spherical and have a microcrystalline and cryptocrystalline texture. Their dark color is due to an abundance of minute inclusions . . .