Showing papers on "Ankerite published in 2021"
TL;DR: In this paper, the kinetic geochemical CO2 reactivity of different rock facies from three regions were predicted over 30 and 1000-year time periods, and it was shown that from a geochemical perspective, the Precipice Sandstone is a suitable storage reservoir, whereas mineral trapping would occur in the overlying Evergreen Formation.
Abstract: Injected CO2 streams may have geochemical reactivity to different rock types in a CO2 storage complex depending on solubility and formation water chemistry. The Precipice Sandstone and Evergreen Formation are a low-salinity reservoir–seal pair in the Surat Basin, Australia, targeted for potential CO2 storage. The kinetic geochemical CO2 reactivity of different rock facies from three regions were predicted over 30 and 1000 year time periods. No material CO2 mineral trapping in the quartz-rich Precipice Sandstone reservoir was predicted, owing to the low rock reactivity. Predicted CO2 mineral trapping in the Evergreen Formation was more variable due to different amounts of more reactive feldspars, clays, calcite and siderite. Predicted mineral trapping as siderite and ankerite was between 0.03 and 8.4 kg m−3 CO2, and mainly depends on chlorite and plagioclase content. Predicted pH was between 5 and 7.5 after 1000 years. Pyrite precipitation was also predicted with SO2 present in the injectate. QEMSCAN and SEM-EDS (scanning electron microscopy and energy-dispersive spectroscopy) spot imaging of samples from the seal containing natural fractures filled by siderite, pyrite, clays, ankerite, calcite, barite and apatite represent a natural analogue for natural mineral trapping. These are in good agreement with our model predictions. This study suggests that, from a geochemical perspective, the Precipice Sandstone is a suitable storage reservoir, whereas mineral trapping would occur in the overlying Evergreen Formation. Supplementary material: Additional model inputs, characterization and model images, and an excel file of QEMSCAN mineral and porosity components, are available at https://doi.org/10.6084/m9.figshare.c.5395393 Thematic collection: This article is part of the Geoscience for CO2 storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage
15 citations
TL;DR: In this paper, the chemistry of dolomite-ankerite from the Bohai Bay Basin, China, changes in a cyclic way from core to rim, reflecting a dynamic system perturbated several times from thermodynamic steady-state.
15 citations
TL;DR: The second member of the Upper Triassic Xujiahe Formation is an important target for tight gas exploration in the western Sichuan Basin and the diagenetic history and reservoir evolution were investigated using integrated analyses of petrography, X-ray diffraction (XRD), scanning electron microscopy (SEM), cathodoluminescence (CL), fluid inclusion microthermometry and stable carbon and oxygen isotopes as discussed by the authors.
14 citations
TL;DR: In this article, an unsupervised ML approach, non-negative matrix factorization with custom k-means clustering (NMF k ) was applied to the data generated by reactive-transport simulations of GCS.
13 citations
TL;DR: In this paper, an exceptional example for evaluating effects of igneous intrusions on diagenesis and reservoir quality of sandstone has been found in the Qianjiadian area, Songliao Basin.
12 citations
TL;DR: In this article, chemical properties, the statistical variation in elements, paleo-environmental properties and accumulation, density maps, degree of weathering and the classification of the beach sand were investigated.
Abstract: This study investigates chemical properties, the statistical variation in elements, paleo-environmental properties and accumulation, density maps, degree of weathering and the classification of the beach sand. Forty-seven samples were collected along the sampled beach sand. Chemical analysis was done on fine grains of all 47 beach sand samples and coarse grains of 19 selected rock samples by X-ray fluorescence analysis. CaO, SiO2 and MgO were the most abundant major elements in the samples. CaO and MgO show high concentrations in the northern section of the study area, while SiO2 is more prevalent in the southern section of the study area. Relatively higher concentrations of CaO, Al2O3, Fe2O3, TiO2, K2O, P2O5 and SO3 were observed in the fine grains, due to their susceptibility to weathering, while relatively higher SiO2 and MgO were observed in the coarse grains due to their resistance to weathering. Calcite and dolomite are major sources for the high concentrations of Ca and Mg, especially in the northern sections of the study area, while augite, clinoenstatite, ankerite, clinopyroxene, cordierite, magnetite are likely sources of Si, Mg and Fe. The beach sand indicated a mixture of high-CaO source type and high-SiO2 source type, with the high-CaO type dominating. Investigations revealed the sand as marine carbonaceous to carbonaceous ferrites with magnesium association, deposited in an oxic environment where the marine skeleton could not be preserved due to high aerobic activity, and not far from their carbonate (neritic) parent source. The high-SiO2 resulted from the Tekirova ophiolite in the region.
11 citations
TL;DR: In this paper, the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the late Ediacaran Shuram Excursion, contains mineralogical and geochemical signatures related to igneous processes.
Abstract: The late Ediacaran Shuram Excursion (SE) records the most prominent negative δ13C excursions (δ13C = −12‰) during Earth’s history. It has been hypothesized to have resulted from oxidation of dissolved organic matter, diagenetic or authigenic precipitates. However, the origin of the SE remains enigmatic; current models face challenges regarding the significant amount of atmospheric oxygen needed to balance such extensive oxidation and sustained inputs of light carbon with extremely negative C isotope compositions. Here, we show that the Doushantuo Formation at the Jiulongwan section in South China, a key stratum recording the SE event, contains mineralogical and geochemical signatures related to igneous processes. Both the occurrence of ankerite, feldspar, moissanite and euhedral quartz in the SE samples and the relatively consistent Ce anomalies of carbonate and O isotopes of quartz indicate a contribution from an igneous source. In particular, the SE samples have trace element and C isotope compositions similar to those of recycled carbonatites formed by decarbonation and melting of sedimentary carbonate rocks. These observations suggest that the deep cycle of ancient carbonate rocks, which were subjected to decarbonation during subduction, melting and eruption related to the breakup of the Rodinia supercontinent, contributed to the SE. This igneous model for the SE may provide a connection between the deep and shallow carbon cycles of the Earth.
10 citations
TL;DR: In this paper, the structure of the naturally occurring, iron-rich mineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study.
Abstract: The structure of the naturally occurring, iron-rich mineral Ca1.08(6)Mg0.24(2)Fe0.64(4)Mn0.04(1)(CO3)2 ankerite was studied in a joint experimental and computational study. Synchrotron X-ray powder diffraction measurements up to 20 GPa were complemented by density functional theory calculations. The rhombohedral ankerite structure is stable under compression up to 12 GPa. A third-order Birch–Murnaghan equation of state yields V0 = 328.2(3) A3, bulk modulus B0 = 89(4) GPa, and its first-pressure derivative B’0 = 5.3(8)—values which are in good agreement with those obtained in our calculations for an ideal CaFe(CO3)2 ankerite composition. At 12 GPa, the iron-rich ankerite structure undergoes a reversible phase transition that could be a consequence of increasingly non-hydrostatic conditions above 10 GPa. The high-pressure phase could not be characterized. DFT calculations were used to explore the relative stability of several potential high-pressure phases (dolomite-II-, dolomite-III- and dolomite-V-type structures), and suggest that the dolomite-V phase is the thermodynamically stable phase above 5 GPa. A novel high-pressure polymorph more stable than the dolomite-III-type phase for ideal CaFe(CO3)2 ankerite was also proposed. This high-pressure phase consists of Fe and Ca atoms in sevenfold and ninefold coordination, respectively, while carbonate groups remain in a trigonal planar configuration. This phase could be a candidate structure for dense carbonates in other compositional systems.
9 citations
TL;DR: In this article, Fe and Mg isotope compositions of whole-rocks, Fe-bearing minerals (pyrite and ankerite) and mg-bearing mineral (ankerite) from the Shuangwang gold deposits are investigated to evaluate Fe and Magnesium isotope behaviors in a gold deposit hydrothermal system and provide new constraints on ore-forming processes.
9 citations
TL;DR: In this article, the main reservoir quality controls in Triassic Buntsandstein deposits in the Upper Rhine Graben and surrounding outcrops in Germany and France are discussed to be authigenic mineral precipitates and the vicinity to structural elements (faults and fractures).
8 citations
TL;DR: In this article, the authors compared the style, magnitude and timing of diagenesis in the northern Steep Slope and Sag Zone (SSSZ) and the southern Gentle Slope Zone (GSZ) by means of drill core observations, thin section petrography, high resolution scanning electron microscopy, fluid inclusion microthermometry, as well as cathodoluminescence and carbonate stable isotope analysis.
TL;DR: In this paper, the distribution of carbonate cements in Eocene turbidite-delta sandstones of the Dongying Depression has been investigated and shown to be mainly calcite with minor ankerite that precipitated in deep burial settings.
TL;DR: In this paper, the mineral paragenesis for coal, coke, and thermally-altered coal in an igneous intrusion zone was studied using SEM, XRD, and Raman spectroscopy.
Abstract: Mesozoic and Cenozoic magma activity in the Wolong Lake mining area of Huaibei is frequent, and the degree of magma intrusion into coal seams remarkable. On the one hand, magma intrusion affects the utilization of coal resources; on the other hand, the macro and trace elements in coal are redistributed to form new mineral types. This study uses the Wolong Lake magma intrusion coal seam as a research object. The mineral paragenesis for igneous rock, coke, and thermally-altered coal in an igneous intrusion zone is studied using SEM, XRD, and Raman spectroscopy. During igneous intrusion, the temperature and pressure of igneous rock metamorphose ambient low-rank coal to high-rank coal and coke. The response mechanism of minerals and trace elements to magmatic intrusion is discussed. The results are: ① SEM analysis shows that ankerite and pyrite are formed from magma intrusion. Both minerals are strongly developed in the magma-coal contact zone, and less well developed in thermally-altered coal. ② XRD analysis shows that igneous intrusion strongly influences the types and content of minerals in coke and thermally-altered coal. In addition to the increase amounts of ankerite and pyrite, chlorite, serpentine, and muscovite, and other secondary minerals, are generated following igneous intrusion. ③ Raman analysis suggests that thermally-altered coal possesses the characteristics of both pyrite and coke. Coke from the magma-coal boundary zone possesses the typical characteristics of pyrite. Igneous rock contains a mineral similar to pyrite, confirmed by both having similar Raman peaks. The scattering intensity of Ag indicates that the formation pressure of pyrite increases from thermally-altered coal via the boundary between the coke zone and the igneous rock.
TL;DR: In this paper, triple oxygen isotope analyses were carried out on carbonatites from sixteen localities worldwide in order to assess the behaviour of oxygen isotopes (mass-dependent fractionation) during their formation.
TL;DR: In this paper, a combination of optical microscopy and scanning electron imaging, electron microprobe and bulk geochemical analyses, and X-ray fluorescence mapping was used to evaluate glauconite carbonation reactions and improve our understanding of glau-convexite diagenesis.
TL;DR: In this article, petrography, mineralogy and carbonate geochemistry and stable isotopy of various types of ocelli (silicate-carbonate globules) observed in the lamprophyres from the Chadobets Uplift, southwestern Siberian craton were reported.
Abstract: The study reports petrography, mineralogy and carbonate geochemistry and stable isotopy of various types of ocelli (silicate-carbonate globules) observed in the lamprophyres from the Chadobets Uplift, southwestern Siberian craton. The Chadobets lamprophyres are related to the REE-bearing Chuktukon carbonatites. On the basis of their morphology, mineralogy and relation with the surrounding groundmass, we distinguish three types of ocelli: carbonate-silicate, containing carbonate, scapolite, sodalite, potassium feldspar, albite, apatite and minor quartz ocelli (K-Na-CSO); carbonate–silicate ocelli, containing natrolite and sodalite (Na-CSO); and silicate-carbonate, containing potassium feldspar and phlogopite (K-SCO). The K-Na-CSO present in the most evolved damtjernite with irregular and polygonal patches was distributed within the groundmass; the patches consist of minerals identical to minerals in ocelli. Carbonate in the K-Na-CSO are calcite, Fe-dolomite and ankerite with high Sr concentration and igneous-type REE patterns. The Na-CSO present in Na-rich damtjernite with geochemical signature indicates the loss of the carbonate component. Carbonate phases are calcite and Fe-dolomite, and they depleted in LREE. The K-SCO was present in the K-rich least-evolved damtjernite. Calcite in the K-SCO has the highest Ba and the lowest Sr concentration and U-shaped REE pattern. The textural, mineralogical and geochemical features of the ocelli and their host rock can be interpreted as follows: (i) the K-Na-CSO are droplets of an alkali–carbonate melt that separated from residual alkali and carbonate-rich melt in highly evolved damtjernite; (ii) the Na-CSO are droplets of late magmatic fluid that once exsolved from a melt and then began to dissolve; (iii) the K-SCO are bubbles of K-P-CO2 fluid liberated from an almost-crystallised magma during the magmatic–hydrothermal stage. The geochemical signature of the K-SCO carbonate shows that the late fluid could leach REE from the host lamprophyre and provide for REE mobility.
TL;DR: In this paper, in-situ analyses of vein-hosted hydrothermal minerals (such as: xenotime U-Pb dating, ankerite Rb-Sr isotopes and monazite Sm-Nd isotopes) and sulfur isotopic analyses of gold-bearing sulfides are used to constrain the timing of mineralization and to better understand the ore genesis.
TL;DR: In this article, a high resolution characterization of micro-textural features, mineral assemblage and distribution to gather evidence for two microbial ore forming systems: Fe- and Mn-oxidizing metabolic processes and cyanobacterial activity Optical-and cathodoluminescence rock microscopy, Fourier Transform Infrared (FTIR), and Raman spectroscopy allowed the identification of syngenetic and diagenetic minerals.
TL;DR: In this article, grain-size statistical parameters, cumulative curves, and bivariate analysis on twenty-five sediment samples were used to decipher depositional processes and paleoenvironments for an upper Paleocene to middle Eocene deep-water pelagic succession of the Pabdeh Formation in the Paryab section, Zagros Mountains, NW, Iran.
Abstract: Sedimentological and geochemical records are presented for an upper Paleocene to middle Eocene deep-water pelagic succession of the Pabdeh Formation in the Paryab section, Zagros Mountains, NW, Iran. In this study, grain-size statistical parameters, cumulative curves, and bivariate analysis on twenty-five sediment samples were used to decipher depositional processes and paleoenvironments. XRD analysis of the fine-grained silt to clay sediments indicates that quartz, calcite, ankerite/dolomite, and clay minerals such as illite, chlorite, and kaolinite constitute the main minerals within these sediments. Elemental and isotopic chemostratigraphies are used to infer depositional conditions and sea level trends through time. TOC-CaCO3 trends of the samples are used to interpret the type of deposition and sediment accumulation rates, rhythmic bedding, and identification of regressional and transgressional phases. In the studied section, the manganese contents exhibit a declining trend along the lowstand systems tract that terminates in a sea level lowstand and the subsequent start of a transgressive trend. Some geochemical parameters such as Mn values and δ13C contents of sediments along a sequence can be used as potential sea level proxies that are tested in this study. The Paleocene-Eocene Thermal Maximum (PETM) interval of the Pabdeh Formation coincides with increasing Mn contents and Mn/Al ratios. Ti/Al and Si/Al ratios show contrasting trends to Mn values and Mn/Al ratios. Generally, elemental and isotopic results of the Pabdeh Formation confirm the presence of a long-term three-stage sea level cycle in the studied interval that is related to the PETM event. Based on elemental analyses such as Co, Mo, Ni, V, and Cr contents, the Pabdeh Formation sediments were deposited in suboxic to slightly anoxic conditions.
TL;DR: In this paper, petrological, geochemical, and microfacies analysis of the Sylhet limestone was carried out by analyzing twenty-eight (28) samples from the two exposed sections and two underground (boreholes) in the Bengal Basin.
Abstract: The fossiliferous Sylhet limestone formation of the Eocene age in the Bengal Basin is important for scientific and geoheritage study. This formation is exposed in the two locations of Bengal Basin; however, it is least studied. In this study, petrological, geochemical, and microfacies analysis of the Sylhet limestone was carried out by analyzing twenty-eight (28) samples from the two exposed sections and two underground (boreholes) in the Bengal Basin. The microscopic and XRD analysis shows that the calcite is the most dominant mineral in the studied samples along with some amount of dolomite, siderite, ankerite, pyrite, and quartz. The presence of the crystal structure of calcite, dolomite, quartz, and pyrite was confirmed through SEM-EDX. Geochemical results show that the samples are composed of high CaO (14.296 to 53.326%) with a significant amount of Fe2O3 (0.095 to 18.482%), Al2O3 (0.664 to 7.357%), K20 (0.83 to 2.274%), MgO (0.157 to 8.109%), and SiO2 (0.08 to 0.451%). Beside the major oxides, some minor and trace elements including Sr, Mn, Zr, Zn, Sc, Co, V, Ba, Ni, and Cu were also measured. Among these, Sr, V, Mn, and Cu concentration within the Sylhet limestone directly indicates its depositional environment at a shallow continental shelf in open marine condition and its diagenetic change to convert as dolomitic limestone. Geochemical characteristics indicate that the Sylhet limestone is highly dolomitized with high Ca/Mg ratio and was deposited in a low-energy shallow continental shelf marine depositional environment. Higher values of the Ca/Mg ratio of the studied samples also confirm lower salinity during its deposition. The presence of silica in the limestone was observed with a positive/negative correlation with Ca which implies that the silica is derived either from a terrestrial source due to increases of sediment supply during the Middle Eocene for the consequences of the Indo-Asian plate Himalayan Collision or dissolution from the siliceous shells of fossils that replace the calcite. Eight (08) microfacies (MFT) types were identified based on abundance of foraminifera or calcareous algae (e.g., Nummulites sp., Discocyclina sp., Alveolina sp., Quinqueloculina sp., Cibicides sp., Lenticulina sp., Ovulites sp.) which are similar to grainstone/packstone carbonate of 18 standard microfacies types (SMF 18). The observed SMF was deposited under restricted to open marine carbonate platform of shallow water depth at different hydrodynamic conditions.
TL;DR: A kinetic leach column study was performed to evaluate the behaviour of these tailings in a northern context (i.e., freeze-thaw cycles) as discussed by the authors. But the results showed that the tailings were not acid generating but deemed leachable for Cd, Pb, Zn and Mn.
TL;DR: The mineralogical characterization of dark green cements of intraclasts and their host sandstones, developed using optical petrography, X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive Xray spectroscopy (EDX) and organic petrographery, provides new insights about the diagenetic evolution and depositional conditions of the late Oligocene-middle Miocene Amaga Formation, northwestern Colombia as mentioned in this paper.
TL;DR: In this paper, the authors used petrographic and mineralogical data from mudstones from the Serpukhovian Morridge Formation in the Widmerpool Gulf, UK to investigate the paragenetic succession and associated mineral precipitation during diagenesis of mudstones.
TL;DR: In this article, in situ C-O isotope analyses were conducted for zoned dolomite-ankerite/calcite cements from the Permian Lucaogou Formation in the Junggar Basin, China, using secondary ion mass spectrometry (SIMS) combined with mineralogical and elemental analyses.
TL;DR: In this article, the authors show that the primary sources of transition metals contamination in potable groundwater is a consequence of natural processes and propose that the nano particulate adsorption method that has been developed will provide for an economical method of purification treatment.
Abstract: Shallow groundwater resources in the lower Kelantan River Basin show anomalously high concentrations of iron and manganese. In some cases, other transition metals and metalloids such as arsenic are also present at elevated levels. Coupled mineral stability and aqueous geochemical models were used to determine the possible sources of iron and manganese in the groundwater. High concentrations of dissolved iron and manganese are related to Na-Cl groundwater types. Geochemical modeling of Fe2+/Fe3+ and S2−/SO42− redox pairs showed that there is a state of redox disequilibrium in the groundwater. Redox conditions control mineral precipitation and dissolution of iron oxy-hydroxides, acid volatile sulphides and subordinate influence from pH fluctuations governs the stability of iron bearing carbonates. Speciation modelling results show the presences of ferric iron complexes and aqueous sulphides, despite supersaturation with respect to hematite, goethite and pyrite. Dissolved manganese in the groundwater possibly originated from the dissolution of amorphous oxide-hydroxides and siderite, having substituted for iron as a minor impurity. The shallow sediments of the Kelantan Basin host high concentrations of iron and manganese bearing minerals that are subject to reductive dissolution during recharge events. Additionally, meteoric recharge is characteristically acidic, destabilizing iron-bearing carbonates phases such as siderite and ankerite. Naturally occurring metal contamination in potable groundwater supplies requires an economical method of remediation to avoid environmental and human health risks. Synthesized magnetic nano-particles created by a one-step method shows effective removal capacity of high iron and manganese concentrations in the groundwater samples at room temperature. The result of this work show that the primary sources of transition metals contamination in potable groundwater is a consequence of natural processes. It is proposed that the nano particulate adsorption method that has recently been developed will provide for an economical method of purification treatment.
TL;DR: In this article, an experimental modeling of ankerite-pyrite interaction was carried out on a multi-anvil high-pressure apparatus of a split sphere type (6.3 GPa, 1050-1550 °C, 20-60 h), and the formation of pyrrhotite, dolomite, magnesite, and metastable graphite was established.
Abstract: Experimental modeling of ankerite–pyrite interaction was carried out on a multi-anvil high-pressure apparatus of a “split sphere” type (6.3 GPa, 1050–1550 °C, 20–60 h). At T ≤ 1250 °C, the formation of pyrrhotite, dolomite, magnesite, and metastable graphite was established. At higher temperatures, the generation of two immiscible melts (carbonate and sulfide ones), as well as graphite crystallization and diamond growth on seeds, occurred. It was established that the decrease in iron concentration in ankerite occurs by extraction of iron by sulfide and leads to the formation of pyrrhotite or sulfide melt, with corresponding ankerite breakdown into dolomite and magnesite. Further redox interaction of Ca,Mg,Fe carbonates with pyrrhotite (or between carbonate and sulfide melts) results in the carbonate reduction to C0 and metastable graphite formation (±diamond growth on seeds). It was established that the ankerite–pyrite interaction, which can occur in a downgoing slab, involves ankerite sulfidation that triggers further graphite-forming redox reactions and can be one of the scenarios of the elemental carbon formation under subduction settings.
TL;DR: In this article, the authors identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene.
Abstract: The characterization of organic matter (OM) composition, physico-chemical, geochemical, and mineralogical studies of sedimentary core can help to better understand the paleoclimates and the depositional environments. The purpose of this work is to identify the factors monitoring the mineralogical composition and the sedimentation of sebkha Mhabeul sediments (southeastern Tunisia), during the Holocene. A 100.5 cm core (Mh 1) collected from this sebkha was analyzed for the determination of chemical composition by X-ray fluorescence (XRF), carbonate content by Bernard calcimetry, grain-sized sediments by AFNOR sieves, OM content by Rock-Eval 6 Pyrolysis, and mineralogical composition by X-ray diffraction (XRD), scanning electronic microscope (SEM), and infrared spectroscopy (IR). The sedimentary fillings of this sebkha, constituted by fine fractions, are characterized by the dominance of the detrital minerals (72–96 %) with high quartz percentages (42.2–91.5 %). The mineralogical composition of the studied sediments included detrital minerals (clay minerals, quartz, and feldspars), carbonate minerals (ankerite, dolomite, and calcite), and evaporitic minerals (halite, bassanite). The clay minerals (11–14%) are composed of a mixture of kaolinite, illite and palygorskite. Fourier transform infrared (FTIR) absorption spectra of all sediment samples confirm the mineralogical composition obtained by XRD and the existence of OM, by defining the band assignments for OM and different minerals as quartz, feldspar, clay, and carbonate minerals. The Rock Eval pyrolysis shows that the OM is immature and has a mixed origin (terrestrial and aquatic). The statistical analyses prove the results of geochemical and mineralogical studies. Indeed, the principal component analysis (PCA) of geochemical and mineralogical data and the depth help to prove the relationships between minerals and chemical elements. Moreover, the negative correlation between the Rock Eval Pyrolysis parameters and the depth shows a homogenous statistical group.
TL;DR: In this article, the authors deciphers the origin and distribution of multiphase carbonate cementations and assesses their implications for reservoir quality of the Eocene delta hydrocarbon sandstones in the Bohai Bay Basin.
TL;DR: In this article, the Mihalyi-Repcelak field (Pannonian Basin, Central Europe) is one of the largest natural CO2-bearing reservoirs in Europe (25 Mt).
TL;DR: In this paper, the state of the art on clastic sedimentary rocks from the Carboniferous complex in the SW part of the Polish Lowlands, studied to help determine their potential prospectivity for the occurrence of oil and/or gas deposits.
Abstract: The paper presents the latest state of knowledge on clastic sedimentary rocks from the Carboniferous complex in the SW part of the Polish Lowlands, studied to help determine their potential prospectivity for the occurrence of oil and/or gas deposits. Rocks were analyzed with respect to the petrographic-mineralogical characteristics of the Carboniferous deposits, their diagenesis, determinations of pressure-temperature conditions of mineral formation and the hydrocarbon occurrence. Analyses were carried out on samples from four selected boreholes in the Fore-Sudetic Monocline. After microscopic analysis of rocks and minerals in thin sections, the following techniques were used: luminescence analysis (UV, blue light), microthermometric analysis of fluid inclusions in double-sided polished wafers, cathodoluminescence analysis, electron scanning microscope studies, XRD analyses, stable isotopic analyses (carbon, oxygen) on calcite and dolomite-ankerite and Raman spectra of fluid inclusions. Orthochemical components, such as carbonates and authigenic quartz, that form cements or fill the veins cutting the sample material have been studied. Fluid inclusion data in quartz and carbonates result in homogenization temperatures of 74–233 °C. The Raman analysis gives temperature estimations for the organic matter of about 164 °C and 197 °C, depending on the borehole, which points to a low coalification degree. The post-sedimentary processes of compaction, cementation and diagenetic dissolution under eo- and meso-diagenetic conditions to temperatures of over 160 °C influenced the present character of the deposits. P-T conditions of brines and methane trapping have been estimated to be ~850–920 bars and 185–210 °C (vein calcite) and ~1140 bars and 220 °C (Fe-dolomite/ankerite). Therefore, locally, temperatures might have been higher (>200 °C), which may be a symptom of local regional metamorphism of a very low degree.