Feldspar Sandstone Research Articles

Petrological Characteristics Research of Denglouku Formation Reservoir in Changling Fault Depression, Southern Part of Songliao Basin

We analyzed the petrology characteristics of Denglouku formation reservoir in Changling fault depression, by 47 ordinary thin sections, 42 thin casting sections, 30 scanning electron microscopy samples and 19 cathodoluminescent samples. The results show that: the main rock types are feldspar debris sandstone and debris feldspar sandstone. The reservoir consists of low compositional maturity, relatively poor psephicity, well graded, high rock debris content. It suggests that the sedimentary environment has strong energy, the moving distance is short, the study area is near the mother rock zone. From north to south, granularity gets coarse. The main cement types are carbonate and argillaceous.

Pore system changes during experimental CO2 injection into detritic rocks: Studies of potential storage rocks from some sedimentary basins of Spain

The effects of experimental injection of CO2 into potential deep sedimentary formations are investigated, focusing on detrital rocks with interconnected pore networks. This approach consisted in the qualitative and quantitative determination of mineralogical and textural changes in selected sedimentary rock samples after injection of supercritical CO2 (P≈75bar, T≈35°C, 12–970h exposure time and dry conditions). The mineralogy and texture were studied before and after the injection by optical and scanning electron microscopy, and quantification was done with digital image analysis. The studied rocks were sampled from different sedimentary basins in Spain and consist of feldspar sandstones with similar mineralogy but different textures (homogeneous vs. heterogeneous).The results obtained in the CO2-treated samples indicate a porosity increase (Δn=3.75%) and a qualitative permeability rise. Intergranular clay matrix detachment and partial removal from the rock sample (due to CO2 input/release drag and electrical-polarity forces) are the main processes that explain the porosity increase. In contrast, carbonate cements were stable and no substantial changes were observed. Additional textural changes were minor and consisted on variations in the roughness of grain-pore contacts, pore shape and aspect ratio. Primary texture of the rock subjected to CO2 injection is an important factor and seems to enhance textural/mineralogical changes in heterogeneous systems.These results simulate the CO2 injection nearest to the injection well and indicate that, in this environment, where CO2 push out the brine fluids and interacts with rocks in dry conditions, several mineralogy/texture re-adjustments take place. Consequences derived from these changes are variable. Possible porosity and permeability increases could facilitate further CO2 injection but textural re-adjustment could also affect the rock physical properties.

Albitization of feldspars in sandstones of the accretionary complexes in the North Kitakami Belt, NE Japan

Albitization of feldspars in sandstones of the accretionary complexes in the North Kitakami Belt, NE Japan

Diagenetic albitization in the Tera Group, Cameros Basin (NE Spain) recorded by trace elements and spectral cathodoluminescence

This paper deals with the diagenetic albitization of both plagioclases and K-feldspars in the Tithonian fluvial sandstones of a rift basin (Cameros Basin). The sandstones in the lower part of the rift record have not suffered this albitization process. A clear relationship is observed between sodium contents, as the main element of some feldspars and their cathodoluminescence (CL) color (the higher the sodium content, the lower is their CL intensity). In conclusion, albitization processes are detectable by decreased CL intensities and changes in the CL spectra.In addition, very different trace element compositions are obtained by laser ablation when comparing trace elements of non-albitized feldspars in sandstones of the lower part of the rift record with those of albitized feldspars in sandstones of the infill top. Non-albitized K-feldspars show Rb, Sr, Ba and Pb contents of up to 1000ppm. In contrast, very flat profiles of trace element contents (<250ppm) are recorded in albitized feldspars (both K-feldspars and plagioclases). Thus, albitization implies feldspars impoverished in trace elements, including REE, which suggests that albitization is a dissolution and reprecipitation process. Further, albitized plagioclases show higher REE contents than albitized K-feldspars. We report here that REE patterns partly depend on the initial composition of the feldspar (K-feldspar or plagioclase) as a useful geochemical criterion for distinguishing albitized detrital plagioclases from albitized detrital K-feldspars.CL spectra from non-albitized and albitized K-feldspars and plagioclases revealed marked differences. Non-albitized K-feldspars present blue (main emission band at 460nm) and brownish CL colors (590nm), sometimes in the same grain. Brownish colors are related to weathering processes. The primary blue emission is related to Al–O−–Al centers, enhanced probably by Al incorporation due to the coupled substitution of Ba2++Al3+↔M++Si4+. Weathered K-feldspars present 4.8 times lower Ba content than fresh blue luminescent ones. The brownish colors are related to the external border or fractured grain zones, altered by weathering processes. Therefore, the observed 590nm emission is assumed to be caused by structural defects resulting from weathering and alteration.Albitized K-feldspars are usually weak luminescent with a typical CL emission band at 620nm. Sometimes, relicts of the original blue luminescence (460nm band) are still present. The leaching of probably both Al and Ba can be responsible for the decrease in the blue band. The characteristic 620nm band is also dominant in albitized weak luminescent plagioclases. Two additional emission bands at 440nm (Al–O−–Al center) and 565nm (Mn2+) occur, when albitized plagioclases preserved their original CL characteristics (green CL color). Another spectral peak at ca. 720nm can be explained by Fe3+ activation due to Fe3+–Al3+ substitution. The spectral CL measurements indicate that changes in luminescence due to albitization (620nm emission) seem to be more related to structural defects than to trace element activation or quenching.

Changes of deformational and reservoir properties of arenaceous-argillaceous rocks due to operation of underground gas storage facilities

This paper discusses issues of the decline of the reservoir properties of arenaceous-argillaceous rocks as a result of declining porosity due to long-term operation of underground gas storage facilities. An analysis of the many-year operation of storage facilities, as well as calculation, has revealed that the active capacity of a storage reservoir gradually decreases under certain conditions of underground storage operations. We performed a series of experiments with model specimens in order to support the hypothesis of decreasing reservoir (capacity-filtration) properties because of changes in the value and structure of the pore space. These experiments showed that the cyclic loading and unloading of arenaceous-silty rocks during long-term operation of underground gas storage facilities can significantly decrease the reservoir parameters of reservoirs created within worked out gas-and-gas condensate fields. Laboratory studies of model specimens corresponding to feldspar sandstone in their composition, porosity, and strength proved that porosity considerably decreases in such reservoirs at actually existing values of formation pressure. Tests of sand performed under conditions close to those existing during the development of hydrocarbon fields also showed that their permeability gradually decreases in the process of cyclic changes of effective pressure.

Elemental and Sm-Nd isotopic geochemistry on detrital sedimentary rocks in the Ganzi-Songpan block and Longmen Mountains

Systematic results of major and trace element geochemistry and Sm-Nd isotopic geochemistry on detrital sedimentary rocks of Precambrian to Triassic in the Ganzi-Songpan block and Longmen Mountains are presented. The rocks are classified into greywackes or feldspar sandstones, grains of which are the mixtures of mafic rocks, felsic rocks, and quartz+calcite. Total rare earth elements (REE) contents of the rocks increase gradually and negative Eu anomalies become more obvious from Precambrian to Triassic, which may indicate intensifying crustal anatexis. Tectonic setting was stable during the Late Paleozoic, therefore there are obvious negative Ce anomalies. Nd model ages are between 1.6 Ga and 2.4 Ga, which are very similar to those of the Yangtze craton, South Qinling and North Qinling belts and quite different from those of the North China craton. Therefore, provenance of the sedimentary rocks in the Ganzi-Songpan block and Longmen Mountains was the Yangtze craton and/or the Qinling orogen, which evolved on the basis of the Yangtze craton. The correlation between provenances and tectonostratigraphic strata of the western Yangtze craton shows that the source materials should be primarily from Neoproterozoic. Secondary sources were Archean and Paleoproterozoic strata. Triassic clastic sedimentary rocks contain Late Paleozoic mantle-derived materials, represented by the Emeishan Permian flood basalts. Spatial distribution of initial Nd isotopic compositions indicates that denudating areas were in the east and the north and depositing areas of deep water were in the west and the south for the Ganzi-Songpan basin during Triassic.

MENSHIKOVITE, Pd3Ni2As3, A NEW PLATINUM-GROUP MINERAL SPECIES FROM TWO LAYERED COMPLEXES, RUSSIA

Menshikovite, ideally Pd3Ni2As3, is a new mineral species found in two localities in Russia. It occurs in a pod of coarsegrained, entirely altered gabbronorite rich in sulfides (up to 30 vol.%), hosted by a microgabbronorite, in the Vostok deposit, Lukkulaisvaara intrusion, in Karelia. There, menshikovite (up to 0.2 mm) is associated with chalcopyrite, pentlandite, calcic amphibole (mostly actinolite), clinochlore, merenskyite, kotulskite, sobolevskite, michenerite, hollingworthite, hessite, and a Re-rich sulfide. Menshikovite (up to 0.1 mm) also occurs in mineralized quartz–feldspar sandstones, which are metasomatically altered and recrystallized. They are located at the lower (exo)-contact of the Chiney intrusion in Siberia, and contain amphibo le(s), mica(s), chlorite, disseminated or massive sulfides (mostly chalcopyrite), Pd-rich maucherite, nickeline, sperrylite, mertieite -II or stibiopalladinite (or both), isomertieite, majakite, and michenerite. We also report a third occurrence of menshikovite from th e Oktyabr’ deposit, Noril’sk complex, in Siberia. In reflected light, menshikovite is pink and opaque. A cleavage is not observed. There is no evidence of bireflectance. The anisotropy is weak, from light gray to brownish gray. Reflectance percentages in air (and in oil) are, for R 1 and R2, at 470 nm 48.4, 50.2 (38.45, 39.3), at 546 nm 51.2, 53.2 (41.0, 41.8), at 589 nm 53.2, 55.3 (42.3, 43.3), and at 650 nm 56.6, 58.7 (46.6, 47.8). Fine twins are present. The average value of microhardness VHN 40, 50, 65 is 517.1 kg/ mm 2 ; it has Mohs hardness of ~5 and is brittle. The average of two sets of multiple wavelength-dispersion electron-microprobe analyses of menshikovite from Lukkulaisvaara gave Pd 48.18, Pt 0.07, Ni 17.77, Fe 0.07, As 33.91, the total is 100.0 wt.% (not normalized), corresponding to Pd2.99(Ni2.00Fe0.01)2.01As2.99 (basis: atoms = 8). Compositions of menshikovite from Chiney vary from Pd3.00(Ni1.98Co0.01)1.99As2.99 to Pd3.15(Ni1.97Co0.01)1.98As2.86. A solid-solution series probably exists between menshikovite and majakite [i.e., (Pd,Ni)2As of the -Pd2As type]. The powder pattern of menshikovite from Lukkulaisvaara was indexed on a hexagonal cell with a 8.406(4), c 6.740(4) A, and V 412.4(6) A 3 . The strongest eight lines in this pattern [ d in A (I)(hkl)] are 2.626(10)(112), 2.477(10)(202), 2.429(8)(300), 2.283(7)(301), 2.150(6)(103), 1.978(7)(113), 1.818(7)(400) and 1.757(6)(401). Menshikovite formed in volatile-rich environments relatively late in the crystallization history of the layered complexes. The name honors Yurii P. Men’shikov, of the Kola Science Center, Apatity, Russia.

韓国の奉化 (Bongwha) 地域の卯谷 (Myogog) 層砂岩の長石アルバイト化

韓国の奉化 (Bongwha) 地域の卯谷 (Myogog) 層砂岩の長石アルバイト化

Albitization of feldspars in sandstones from the Gohan (Permian) and Donggo (Permo-Triassic) formations, Gohan area, Kangwondo, Korea

Sandstones in the Gohan and Donggo formations in the Gohan area, Korea, contain considerable amounts of feldspars. Electron probe microanalysis (EPMA), backscattered electron microscopy (BSE), cathodoluminescence (CL), and microscopic petrography show that many of these feldspars consist of albite. Most of these albites are characterized by moderately high chemical purity (Ab 97–100) and do not display cathodoluminescence. These characteristics suggest that the albite is probably authigenic, formed during burial diagenesis by alteration of plagioclase and K-feldspar. The presence of abundant albite suggests that the sediments were buried to depths corresponding to the burial temperature that probably exceeds 90°C.

Reverse Weathering, the Carbonate-Feldspar System, and Porosity Evolution during Burial of Sandstones

Acid generated by reverse weathering in mudrocks drives linked reactions involving carbonates and feldspars that in turn have a profound impact on the evolution of porosity during burial diagenesis of sandstones. In the Oligocene Frio Formation along the Texas Gulf Coast, petrographic evidence at various scales in both sandstones and shales, and modern pore fluid compositions are all consistent with this idea. Acid released during illitization of smectite dissolves marine skeletal and detrital carbonate in shales. Shales export excess H+, dissolved CA++, and CO{sub 2} to the sandstones. Resultant interaction of sandstones with these shale-derived fluids is primarily controlled by the feldspar content of the sandstones. If the sandstones contain reactive feldspar content of the sandstones. If the sandstones contain reactive feldspar, acid from the shales is effectively buffered, thus allowing precipitation of calcite as cements and grain replacements in the sandstones and maintenance of fluids with low pCO{sub 2}. Once the supply of reactive detrital feldspar is exhausted through dissolution and albitization, shale-derived H+ remobilizes carbonate in sandstones, generating secondary porosity and fluids with high pCO{sub 2}. Acid generated through thermal maturation of organic matter plays only a trivial role in this system of reactions because the quantity ofmore » acid required for dissolution of carbonate and feldspar far exceeds the amount of kerogen in the system. The balance between the local acid generation capacity of shales, the local buffering capacity of feldspars in sandstones, and the availability of externally derived acids and ions is the primary control on the sequence of reactions occurring during burial metamorphism of sandstones.« less

A SEM study of diagenetic kaolinization and illitization of detrital feldspars in sandstones

A SEM study of diagenetic kaolinization and illitization of detrital feldspars in sandstones

Diagenetic chloritization of feldspars in sandstones

Detrital microcline and albite are commonly replaced diagenetically by chlorite in sandstones of the Visingsö Group (Upper Proterozoic, southern Sweden). Authigenic quartz and, in some cases, albite and illite are associated with the chlorite. The SEM examinations suggest that chloritization of feldspar has usually been preceded by dissolution of the replaced feldspar grain. Fe 2+ and Mg 2+, which are needed for the chloritization, have partly been derived from the detrital Fe-Mg silicates (mainly biotite) Fe-oxide pigment and Fe-Ti oxide grains, whereas Si 4+ and Al 3+ are supplied mostly by the altered feldspars. The K + released from microcline and Na − from albite were mostly incorporated in authigenic illite and albite, respectively.

Provenance Studies and Mudrocks

ABSTRACT Provenance studies based on the mineralogy of sandstones seem to be falling rapidly into disrepute as a result of the increasing emphasis on the effects of diagenesis on the original detrital mineral composition. Feldspars in sandstones commonly are dissolved, altered to clay minerals, and albitized by widely occurring diagenetic processes. Accessory minerals all too frequently are confined in ancient sandstones to ZTR. Mudrocks, in contrast, have the potential of greater preservation of feldspars and accessory minerals because of their lesser permeabilities. Few studies have attempted to use the nonclay mineralogy of mudrocks for provenance work, and these few have had promising but mixed results. Mudrocks deserve more attention in provenance studies than they have received.

Authigenic Feldspar in Sandstones of Southeastern Minnesota

ABSTRACT Feldspar grains of sandstones of southeastern Minnesota are characterized by secondary enlargements. Detailed study of the feldspar of the New Richmond sandstone shows rounded detrital grains of microcline have been enlarged by growth of orthoclase. The feldspar enlargements may possibly represent a sedimentary product, but an alternate hypothesis of hydrothermal origin is also considered.