Pyrite Content Research Articles

Organic petrographic and mineralogical composition of the No. 6 coal seam of the Soutpansberg Coalfield, South Africa: Insights into paleovegetation and depositional environment

This study investigates the paleodepositional conditions of the No. 6 Seam of the Madzaringwe Formation in Makhado and Voorburg south area of the Soutpansberg Coalfield (Limpopo Province, South Africa) utilizing organic petrography and inorganic geochemical proxies. The coals are predominantly high-volatile bituminous B-A rank with high ash yields (avg. 36.1 wt%), characterized by high-vitrinite (~ 41.5 vol%), moderate-to-high inertinite (9.8 vol%–33.7 vol%) and low liptinite (~ 2.3 vol%). The distribution of inertinite varies among different coal horizons (from bottom-lower to middle-upper), suggesting differential oxidation conditions and/or paleofire occurrence. Vitrinite-to-inertinite (V/I) ratio, tissue preservation–gelification index (TPI–GI), and groundwater–vegetation index (GWI–VI) plots, indicate that the peat-forming forest-swamp vegetation accumulated under mesotrophic-to-rheotrophic hydrological conditions. The presence of structured macerals (i.e., telinite, collotelinite, fusinite, and semifusinite) suggests well-preserved plant tissues, whereas framboidal pyrite and sulphur content (0.24 wt%–2.16 wt%) point to brackish-water influence at the peat stage. The coals contain quartz, kaolinite, siderite, muscovite, dolomite, calcite, and pyrite minerals, most of which were likely sourced from felsic igneous rocks. The Al/(Al+Fe+Mn) and (Fe+Mn)/Ti ratios for the studied samples range between 0.24–0.97 and 0.57–70.10, respectively. The ratios, Al–Fe–Mn plot, and presence of massive botryoidal-type pyrite imply some influence of meteoric waters or fluids from hydrothermal activity post-deposition. Moreover, the chemical index of alteration (CIA: 98.25–99.67), chemical index of weathering (CIW: 92.04–97.66), and A–CN–K ternary diagram suggest inorganic matter suffered strong chemical weathering, indicating warm paleoclimatic conditions during the coal formation.

Geochemical and mineralogical features as indicators of sulfate-methane transition zones in shallow gas-bearing offshore sediments from Zhoushan

Subsurface shallow gas, primarily composed of biogenic methane (>95%), is highly-enriched in global offshore sediments. The redox conditions of methane-rich pore fluid play a crucial role in shaping the geochemical signatures associated with the anaerobic oxidation of methane (AOM) and vertical displacement of sulfate-methane transition zones (SMTZs) within deep sedimentary records. However, long-period, and continuous records of AOM and SMTZs in shallow gas-bearing offshore sediments are sparse. Here, we employed a comprehensive analyses of iron sulfide, elemental, and stable isotopies on a 63-m drilled sediment core (JC-1) from offshore Zhoushan. Four different layers U1–U4 were identified in 11.5–24 mbsf, 24−42 mbsf, 42−51 mbsf, and 51−63 mbsf, respectively, as revealed by the lithofacies and sedimentary structures. By comparing the pyrite contents, total sulfur to total organic carbon ratios, and δ34S-chromium-reducible sulfur values, the commonly seen organoclastic sulfate reduction occurred in U1 and U2, whereas significant AOM activities were found in U1 and U4. Further, the peaks of total sulfur to total organic carbon ratios, sulfur contents, and multiple positive δ34S-chromium-reducible sulfur values indicated the presence of AOM in SMTZs at 18.3, 52, and 59 mbsf. These intervals were featured by a sub-oxic or anoxic condition with strong methane seepages, evident from the scarcity of metals and the enrichment of Mo/Al and U/Al ratios. The presence of multiple SMTZs was consistent with the pore-water data of the adjacent YS4 and YS7 cores. In light of these findings, it is prudent to exercise caution when utilizing geochemical indicators, such as trace element proxies and the δ34S values of sulfide minerals, to comprehend the progression of fluctuating depositional settings in reaction to sea-level fluctuations and shallow gas reservoirs. This study provides a new perspective to better understand the evolution of unsteady depositional environments in response to sea-level changes and shallow gas reservoirs.

Induced polarization of clay-rich materials — Part 3: Partially saturated mixtures of clay and pyrite

Source rocks for oil and gas are often associated with shales that are rich in pyrite and kerogen. Induced polarization is a suitable tool to characterize these formations. We develop a new experimental database of 43 laboratory experiments using mixtures of clay and pyrite under fully or partially water-saturated conditions. The liquid water saturation is in the range of 20%–100%, whereas the pyrite content is in the range of 0%–17%. Spectral-induced polarization measurements are performed in the frequency range of 0.1 Hz to 45 kHz at room temperature (approximately 25°C ± 1°C). The complex conductivity spectra are fitted with a Cole-Cole model, and the Cole-Cole parameters are determined using a stochastic procedure based on a Markov chain Monte Carlo sampler. The Cole-Cole parameters associated with low-frequency dispersion are then plotted as a function of the (water) saturation and pyrite content (volume fractions). Four predictions of the model are tested against the experimental data. We find that the model is able to explain the results, including (1) the chargeability depends on the pyrite content in a predictable way, (2) the (instantaneous) conductivity depends on the saturation according to Archie’s law, (3) the Cole-Cole exponent does not depend on the saturation and pyrite content (except at very small pyrite content of <1 vol%), and (4) the relaxation time is inversely proportional to the instantaneous conductivity. We also develop a more advanced petrophysical model using a double Cole-Cole distribution, in which one distribution is associated with the clay minerals and the other is associated with the pyrite.

Local depositional and diagenetic conditions control the positive δ34S excursion during the Ordovician-Silurian transition: Evidence from the Wufeng-Longmaxi formations in Sichuan Basin

The Ordovician-Silurian (OS) transition was characterized by significant changes in global climate, marine redox conditions, and biological evolution, which include global seawater euxinia, the onset of the Hirnantian glaciation, and large-scale extinctions. During this time, the marine sulfur cycle was disrupted, and the pyrite sulfur isotope (δ34Spy) showed a large positive excursion. This excursion is closely tied to the Hirnantian glaciation, with δ34Spy increasing at the start of and decreasing at the end of the glaciation. Although it is thought that variations in marine sulfate concentration and primary productivity are responsible for the positive excursion in δ34Spy, contemporary marine sediment δ34Spy data suggest that sedimentary processes can also lead to significant fluctuations in δ34Spy. To assess the impact of local changes in sedimentary conditions on this positive δ34Spy excursion event, we conducted detailed depositional and geochemical analyses of sedimentary pyrite found in black shales from the Wufeng-Longmaxi formations in the Weiyuan area of the Sichuan Basin, China. These sedimentary pyrites include three types: framboidal, euhedral, and laminated pyrite. Bulk sample sulfur isotope analyses revealed that δ34Spy values vary from −16.2‰ to 15.8‰ (mean = −3.8‰, n = 22). In situ analyses of δ34Spy show that different pyrite crystals exhibit a range of intragranular δ34Spy values that are likely indicators of diagenesis. Variations in bulk sample δ34Spy are strongly and negatively correlated with the proportion of framboidal pyrite, i.e., lower levels of framboidal pyrite content resulted in a higher bulk sample δ34Spy value, suggesting diagenetic alteration controls on δ34Spy. In addition, the δ34Spy excursion in the Wufeng-Longmaxi formations also appears to be compatible with lithological changes related to sedimentation rate. The δ34Spy values from the Guanyinqiao Bed, which consists of calcareous shales, are higher than those from black shales with a relatively low sedimentation rate. Our results suggest that the positive δ34Spy excursion during the OS transition during the Hirnantian glaciation is controlled not only by diagenetic alterations but also by local sedimentation rate.

Biological and paleoceanographic controls on the postglacial sulfur isotope records in Arctic shelf sediments

The Arctic Ocean has experienced environmental fluctuations during the Pleistocene glacial-interglacial cycles. Since the last deglaciation, the reinundation of the Bering Strait and regional transgression have led to dramatic changes in the western Arctic Ocean, affecting coastal landscapes, depositional processes, marine ecosystem, and, inherently, biogeochemical element cycles. Here, we investigate the records of sulfur, carbon, and iron cycles in the Chukchi Sea of the western Arctic, with a primary focus on microbial sulfate reduction and subsequent pyrite formation. Variations in the pyrite abundance and sulfur isotopic composition, derived from a 10-m sediment core, demonstrate that dynamic changes in the factors governing pyrite formation – organic electron donor, reactive iron, and sulfate – are closely linked to the regional environmental conditions. In the early Holocene sediment, pyrite precipitation was impeded by the lack of organic matter, even in the presence of abundant sulfate and reactive iron. In the overlying sediment, pyrite contents increased due to vigorous microbial sulfate reduction fueled by enhanced availability of organic substrate and additional methane from the sulfate-methane transition zone. In general, the increased supply of organic matter to the Chukchi Shelf sediments can be attributed to the resumed inflow of nutrient-rich Pacific Water through the flooded Bering Strait. The increase in pyrite content, however, does not correlate exactly with either the increase in TOC or the opening of the Bering Strait, both of which precede the increased pyrite formation. These lags reflect the balance between marine primary production and terrestrial carbon sources, as well as the balance between the Pacific Inflow and the Beaufort Gyre. While a comparable increase in pyrite and TOC contents during the Holocene deglaciation has also been reported in the Black and Baltic Sea sediments, their distinct sulfur isotope records, contingent upon the availability of sulfate and reactive iron, highlight that pyrite can serve as a valuable proxy for tracking past climate and environmental change, especially in barren sedimentary records such as those found in the Arctic Ocean.

Research on the Shale Reservoir Sensitivity by Using the Mineral Analysis Method.

Shale reservoirs have diverse mineral types, and analyzing the sensitivity of the mineral composition to shale pores is of great scientific and engineering significance. In this paper, first, X-ray diffraction (XRD) experiments on shale mineral compositions are carried out, and the characteristics of pore structure changes after shale mineral compositions interacted with external fluids (slick water and backflow fluid) are elucidated. Then, the effects of quartz, kaolinite, and pyrite on the pore structure and permeability of shale on the susceptibility to slick water are studied. The results show that (a) quartz and clay minerals are the dominant constituents of each core, with some cores containing minor amounts of plagioclase feldspar and rhodochrosite. (b) The composition of the shale changed significantly following the action of external fluids. The average quartz content of pure shale decreased from 31.62% to 29.1%. The average content of quartz in siliceous shale decreased from 36.53% to 33.5%. The average content of quartz in carbonaceous shale decreased from 9.15% to 8.05%. (c) Factors affecting the sensitivity of shale pore structure and permeability to slick water are mainly quartz, kaolinite, and pyrite. The contents of quartz, kaolinite, and pyrite decreased by an average of 5.1%, 4.6%, and 0.9%, respectively, after slick water action.

Measurement and modeling of moisture equilibrium and methane adsorption in shales from the southern Sichuan Basin

The adsorption characteristic of methane in water-bearing shale is essential for the accurate estimation of shale gas reserves. The sorption mechanisms of moisture and methane in shale remain poorly understood. In this work, moisture equilibrium measurements in shales were conducted to study moisture absorption characteristics. The governing factors for moisture absorption were determined, and the suitability of moisture absorption models was evaluated. An innovative water saturation apparatus and an improved methane adsorption system were built to measure methane adsorption in high water-bearing shales. The suitability of the Langmuir model in describing methane adsorption in water-bearing shale was studied. A predictive model for methane adsorption in water-bearing shale was developed based on improved BP neural network algorithm, which was further utilized to determine the primary governing factors for methane adsorption. The results revealed that the equilibrated moisture content in shale presents a three-stage and S-type ascending trend with increasing relative humidity. The methane adsorption amount shows a slide-type downward trend with the increase of water content. The Peleg model demonstrates the superior performance in describing the hygroscopic isotherms, and the Langmuir model performs poorly in characterizing methane adsorption in shales with high water contents. The controlling factors for the ultimate moisture content mainly include specific surface area, average pore diameter, carbonate and pyrite content. The methane adsorption in water-bearing shale is mainly governed by water content and specific surface area. The results of this work enrich the understanding of the adsorption mechanisms of shale gas and provide a solid basis for the assessment of shale gas reserves.

Prediction of HGI of South African coalfields: a comparative application of ANN, SVR and LSTM models

ABSTRACT Hardgrove grindability index (HGI) is a significant index used to determine a mill’s capability and overall efficiency in the grinding of coal. There are several factors that affect HGI due to the complex nature of coal. The influence of proximate analysis, calorific value, total sulfur, and pyrite content on the HGI values of 292 coal samples from South African coalfields were examined. Predictive models of HGI are developed by using soft computing techniques such as Long Short-Term Memory (LSTM), support vector regression (SVR), and Artificial Neural Network (ANN). This study shows that ANN is the most effective predictive model for all the three coalfields, with SVR models being second and LSTM models being the least effective. The correlation between the predicted value and the input data is established by using the cosine amplitude method (CAM). It was found that HGI is most influenced by the fixed carbon content, calorific value, ash content and volatile matter content while pyrite has the least influence.

Sulfur isotope and trace element geochemistry of sulfides from the unique Yaojialing Zn-Au-Cu deposit, Lower Yangtze River Metallogenic Belt, China: Implications for ore-forming process and exploration

The Yaojialing Zn-Au‑Cu deposit is a porphyry-skarn-epithermal vein-type compound deposit that consists of epithermal vein-type lead‑zinc‑silver orebodies, skarn Zn-Cu-Au orebodies, and porphyry CuAu orebodies from shallow level to depth. We decipher the source and metallogenic mechanism by studying the trace element and S isotopic compositions of sulfides (pyrite, sphalerite, chalcopyrite, and galena) from three types of orebodies. The collected pyrite can be divided into two types. PyI coexists with chalcopyrite, and PyII coexists with sphalerite or galena. In addition, PyI was further divided into PyIa (collected from porphyry copper bodies) and PyIb (collected from skarn copper bodies). PyII can be further divided into PyIIa (collected from skarn-type lead‑zinc ore body) and PyIIb (collected from vein lead‑zinc ore body in strata). Sphalerite and galena from skarn-type PbZn ore bodies and shallow vein-type PbZn ore bodies are named SpI and GnI, and SpII and GnII, respectively.Pyrite and sphalerite trace element thermometers revealed that the temperature of the ore-forming fluids decreased from 500 to 600 °C in the porphyry ore body to 300– 360 °C in the skarn ore body and then to 240– 280 °C in the shallow vein ore body. The decrease in the Co and Ni contents of pyrite collected from deep to shallow depths may indicate that meteoric water precipitated in the late ore-forming hydrothermal system. Rapid crystallization and variations in the physicochemical states (such as temperature, pH, fO2, and geochemical composition) of the fluids resulted in an obvious oscillating zone of euhedral PyI pyrite particles. It also affects the solubility of trace metal elements and leads to the selective entry of these elements into pyrite. PyII also shows obvious zonation characteristics rather than oscillating zonation, indicating that the growth rate of pyrite is relatively slow. Moreover, the relationships between the Au and As contents in the two types of pyrite are different. PyI is coupled, while PyII shows decoupling. We believe that this phenomenon is due to the high content of As in ore-forming fluid systems, which may inhibit the absorption of Au on the surface of pyrite rather than the decoupling of Au and As caused by rapid crystallization, based on the rapid increase in As content and non-oscillating zonation in PyII. According to the analysis of the sulfur isotopes of various sulfides, the solid evidences suggest that the ore-forming materials of each type of orebody in the Yaojialing deposit were mainly derived from magmatic-hydrothermal processes and that the fractionation of sulfur isotopes was the result of variations in physicochemical conditions caused by magma-hydrothermal evolution rather than the addition of foreign sulfur sources.

Study on Electrical Characteristics and Formation Mechanism of Micro-Ion Capacitor in Shale Pore and Fracture Structure

Due to the micro/nanoscale and intricate pore structure, poor connectivity, complex pathways, the presence of microfractures, and the coexistence of organic and inorganic pores, shale and other tight reservoirs exhibit increasingly complex conductive characteristics. This paper mainly studied the electrical properties of shale based on experimental test data, including scanning electron microscope (SEM) thin-section and microtomography CT (μ-CT) images, and analyzed the shale pore type, pore structure characteristics, and development of fracture. Then, the distribution of pyrite, content, and graphitization of organics and their influence on the electrical properties are discussed. Furthermore, the double electrical layer and zeta potential in the shale zone were discussed in depth. The results revealed that, within the content of pyrite, organics, and its graphitization, the vitrinite maturity are inversely proportional to shale resistivity. It was also found that in the presence of an external electromagnetic field, the fluid in shale pores is subjected to the combined strength of pore pressure and external field potential difference. Thus, its response equation should be an improved Navier-Stokes equation, which considers pore pressure, zeta potential, and Coulomb force. When shale is subjected to an external electromagnetic field, due to the complex pores structure and organic and inorganic minerals, it will represent more of a dielectric-like property than electricity. So, it will form special microscopic ionic capacitors, which are different from common plate capacitors. There are three special kinds of microscopic ionic capacitors, they are (I) the intergranular pore microscopic ionic capacitor model, (II) the particle with isolated pore microscopic ionic capacitor model, and (III) the pyrite or graphite or other organics microscopic ionic capacitor model. Finally, the characteristics of microscopic ion capacitors are summarized: irregular polar area and varying distance between poles, varying charges with time, and salinity of the formation water.

Modified approach to calculate brittleness index in shale reservoirs

The successful production of unconventional reservoirs through hydraulic fracturing is heavily dependent on the brittleness of the shale's. To precisely evaluate rock brittleness the mineral-based brittleness indices are considered reliable. Initially, only the weight fraction of quartz accounted for mineralogical brittleness, later dolomite was included in the group, further, it was divided into the silicate and carbonate groups. Due to its heterogeneous nature, shales contain some other minerals, however, the impact of these minerals on rock brittleness has yet to be analyzed. The mineral pyrite is commonly found in shales but its impact on rock brittleness is still undefined. In this research, we proposed a modified mineral-based brittleness index including mineral pyrite, and investigated its impact on rock brittleness. The modified index was evaluated using the data from three different shale reservoirs in China. In the next step, the Fracability Index (FI) model of rocks including pyrite mineral is calculated, and finally, the rock physics modeling is performed to evaluate the elastic response of the rock to this mineral. The modified brittleness index was found to be more accurate in predicting rock brittleness than other mineral-based brittleness indices. The correlation between the modified brittleness index and the FI model was higher than the correlation with other mineral-based brittleness indices. Further, rock physics modeling also proved that the rock with high pyrite content has low Poisson's ratio and high Young's modulus.. These properties are associated with brittle rocks, which further supports the inclusion of pyrite as a brittle mineral in the modified brittleness index. Hence, the findings of this research indicate that the modified brittleness index based on minerals is a reliable approach for predicting rock brittleness in shale reservoirs that contain pyrite. This study has an important application for the development and management of shale reservoirs. The modified brittleness index can be used to identify rocks that are more likely to be successfully fractured during hydraulic fracking process. Keywords: shale reservoirs; hydraulic fracturing; mineral brittleness; fracability index.

Gold source and deposition in the Sanakham gold deposit, SW Laos: Constrains from textures, trace element geochemistry and in-situ sulfur isotopes of pyrite

The Luang Prabang (Laos) – Loei (Thailand) metallogenetic belt is endowed with major porphyry-skarn, and epithermal gold deposits. The Sanakham gold deposit is a newly discovered hydrothermal vein-type orogenic gold deposits (10.6 t Au @ 3.05 g/t) in the belt, and consist of a series of quartz-sulfide veins that are controlled by secondary structures of the regional NNE-trending brittle-ductile shear zone. Its mineralization can be divided into four stages: (I) quartz–pyrite–arsenopyrite, (II) quartz–pyrite–pyrrhotite–chalcopyrite, (III) quartz–pyrite–base-metal sulfide, and (IV) quartz–carbonate. Three pyrite generations were identified: py1 (stage I) as disseminated euhedral to subhedral coarse grains; py2 (stage II) as subhedral to anhedral fine grains occur around the cataclastic and corrosion textures in py1; py3 (stage III) as subhedral to anhedral fine grains occurred in sulfide veins or veinlets that overprint the existing quartz-sulfides. All three generations of pyrite have low trace-element contents including very low lattice-bound gold (py1: 0.040 ppm; py2: 0.098 ppm; py3: 0.028 ppm) and arsenic (py1: 227 ppm; py2: 133 ppm; py3: 13.3 ppm) contents. Visible gold grains are sited in textures of pyrite grains that relate to brittle cataclastic deformation. Considering the relatively low contents of pyrite in the ores of Sanakham, it is impossible to derive the high-gold grade orebodies through local remobilization of originally lattice-bound gold in pyrite. The py2 might be formed during hydrothermal overprinting and dissolution of py1 led by continuous supply of ore fluids with relatively higher contents of Au, Ag, Cu, Sb, Te, Pb, and Bi. A reduction reaction related to reduced carbon species in wallrock is an assignable cause for gold deposition, even though the fluid-rock interaction and fluid immiscibility processes might be important. The Au- and As-poor pyrites have similar δ34S values (py1: –2.58 to –0.83 ‰; py2: –2.17 ‰ to + 0.25 ‰; py3: –1.24 to –0.60 ‰ ppm) that close to 0 ‰, indicating the sulfur may have been originated from magmatic or mantle sources. Therefore, we propose that the Sankham gold deposit is a member of the orogenic deposit class, but notably characterized by the low concentrations of invisible gold in the relatively As-poor pyrite lattice.

Pyrite Characteristics in Lacustrine Shale and Implications for Organic Matter Enrichment and Shale Oil: A Case Study from the Triassic Yanchang Formation in the Ordos Basin, NW China.

Pyrite is widely distributed in lacustrine shales and has become a research focus in unconventional oil and gas exploration. Pyrite morphology is useful for identifying different types of organic matter and assessing shale oil enrichment in organic-rich shale. Abundant pyrite is developed in the source rocks from the Chang 7 Member of the Yanchang Formation in the Ordos Basin, NW China. However, the relationship between different pyrite types and the differential enrichment of shale oil still needs to be clarified. The organic geochemistry, petrology, and isotopic composition of the Chang 7 Member samples were analyzed. The significance of pyrite types and sulfur isotopic compositions as indicators of depositional environments and shale oil enrichment was emphasized. The Chang 7 shales contain three pyrite morphologies, framboidal pyrite (type A), spherulitic pyrite (type B), and euhedral and anhedral pyrite (type C), and their aggregates. The sulfur isotopic compositions of pyrite (δ34Spy) in Chang 7 shales with different pyrite types exhibited regular patterns. The δ34S values of types A, B, and C pyrites were sequentially positive overall (average values are -2.739, 2.201, and 7.487‰ in sequence), indicating that type A pyrite was formed during the syn-sedimentary to early diagenetic stage and types B and C pyrites were formed during the early to middle diagenetic stage. Types A, B, and C pyrites showed sequentially increasing kerogen type index values and kerogen carbon isotope values (mean values of -31.59, -28.70, and -26.45‰, successively), indicating that the horizons where types A, B, and C pyrites developed correspond to types I, II, and III organic matter, respectively. Strong correlations between the pyrite content and oil components reveal that pyrite indicates shale oil enrichment. Moreover, variations in pyrite type significantly influenced the enrichment behavior of shale oil. Types A and B pyrites contributing to reservoir space showed shale oil enrichment. They promoted saturated hydrocarbon enrichment at >15% pyrite content, whereas type C pyrite did not indicate shale oil enrichment. These findings provide new insights into the differential enrichment of organic matter and shale oil and valuable guidance for the large-scale exploration and development of shale oil resources.

Impacts of solid rock components on resistivity-based reserves evaluation in organic-rich mudrocks

The effective electrical conductivity of organic-rich mudrocks can be influenced by the presence of clay, pyrite, and thermally mature organic matter. In this paper, we investigate the impacts of conductivity, volumetric concentrations, and spatial distribution/connectivity of clay, pyrite, and kerogen networks on the effective conductivity of the rock and how this affects the assessment of water/hydrocarbon saturation. This quantification enables an understanding of when such components need to be considered in interpreting resistivity measurements in organic-rich mudrocks. We perform sensitivity analysis on the impacts of (a) thermal-maturity-dependent kerogen conductivity, (b) volumetric concentration/spatial distribution of kerogen, (c) conductivity and volumetric concentration/spatial distribution of pyrite, and (d) cation exchange capacities of various clay minerals and their concentration/spatial distribution on the effective conductivity of the rock. The sensitivity analysis showed that with increasing pyrite concentration, the effective conductivity of the rock increased. This increment became significant when the concentration of pyrite was above 2%. Lastly, we observed that thermally mature kerogen increased the conductivity of the rock, with a significant increment occurring when the kerogen conductivity was above 0.01 S m −1 . Results confirmed that the incorporation of conductive rock components such as clay, pyrite, and kerogen into the electrical rock physics model improved the estimates of hydrocarbon reserves.

Relationship of lithological data with the sedimentation environment of the Upper Batian deposits of the Kogalym region

Research subject. Upper Batian deposits (formation U2) of the Eastern part of the Kogalym region, within the North Nizhnevartovsk monocline. Aim. Reconstruction of the sedimentation environment of the U2 formation in the Kogalym region. Materials and methods. The reconstruction of sedimentation environments was conducted based on a macroscopic description of core samples with identification of structural and textural features of rocks from 35 wells. The clarification of sedimentation settings was carried out based on the description of 41 thin sections and a granulometric analysis of the clastic part of the studied rocks. Results. According to the macroscopic study, the U2 layer is composed of an uneven alternation of silty-argillaceous and silty-sandy rocks with coal interlayers. The rocks are of a polyfacial nature, represented by deposits of continental, transitional, and marine genesis. The thickness of the deposits varies markedly depending on the paleorelief of the area. The optical petrographic study revealed the polymictic composition of the studied rocks, which, according to the classification by V.D. Shutova, correspond to the arkose (graywacke arkose), less often graywacke (feldspar-quartz, quartz-feldspar greywackes) group. Cement most often exhibits a carbonate-clay composition. Rocks of marine genesis are characterized by a decrease in the proportion of rock fragments and an increase in the proportion of mechanically stable accessory minerals (zircon, garnet, tourmaline). The rocks of continental genesis are characterized by the maximum content of micas and plant detritus. An increase in the content of pyrite is noted in the sediments transitional from the continent to the sea. The grain-size analysis data of reservoir rocks of the U2 formation showed that both coastal-marine and channel deposits were formed in environments with active hydrodynamics of the medium, when the dynamic processing of clastic material exceeded the intensity of its supply. Conclusions. The performed lithofacies studies made it possible to reconstruct the sedimentation environment, as well as to reveal specific features in the distribution of the silty-sandy rock components of the U2 formation.

Characterization of deep ore-forming fluid in the Zhaoxian gold deposit within the Jiaodong gold province: insights from quartz vein fluid inclusion, in-situ trace element analysis, and S isotopic composition in pyrite

The Jiaodong gold province, situated in the southeastern margin of the North China Craton, is globally renowned for its substantial gold reserves exceeding 5,000 tonnes. The Zhaoxian gold deposit is part of the significant Jiaojia gold belt within the Jiaodong gold province. Fieldwork has identified four distinct stages of ore formation in this study: an early barren quartz vein stage (Stage 1) containing fine-grained pyrite; a gold-bearing stage (Stage 2) consisting of quartz, pyrite, and native gold; a polymetallic sulfide-rich stage (Stage 3) comprising quartz, polymetallic sulfides, and native gold; and a late-stage (Stage 4) primarily composed of quartz and calcite with minimal pyrite content. We conducted fluid inclusion analysis using microthermometry and Raman spectroscopy techniques to examine the fluid characteristics. In-situ analysis of trace elements in pyrite was performed to investigate the fluid composition and evolution. Additionally, we determined the sulfur isotope composition in pyrite to analyze the source of sulfur. Our findings indicate that the ore-forming fluid in the Zhaoxian gold deposit belongs to a medium-to-low-salinity H₂O-NaCl-CO₂-CH₄ system. Fluctuations in Au and As concentrations observed along with oscillating zones and sulfide inclusions during Stage 2 suggest potential fluid boiling processes occurring during mineralization. High concentrations of Ag, Cu, Zn, Cd, In, Pb, and Bi without oscillating zones during Stage 3 imply precipitation of polymetallic sulfides under stable fluid conditions. The δ34S values observed in the Zhaoxian gold deposit are slightly higher than those found in granitoids from other areas within Jiaodong but similar to those seen in other deposits within the Jiaojia gold belt region. In conclusion, magmatic-hydrothermal ore-forming fluids were involved along with significant fluid-rock interaction during metallogenic processes of the Zhaoxian gold deposit.

REMAINS OF THE ALIMENTARY TRACT IN THE LATE ORDOVICIAN TRILOBITE <em>DALMANITINA</em> (PRAGUE BASIN, BARRANDIAN AREA, CZECH REPUBLIC)

Preservation of digestive structures in trilobites is generally rare; remains of the alimentary tract have been documented in about eighty of more than twenty thousand described species. Several tens of specimens belonging to five Cambrian and nine Ordovician species from the Barrandian area, Czech Republic, have markedly contributed to the knowledge of the trilobite digestive system. Here, we describe seven exceptionally preserved late holaspid trilobite specimens of species of the genus Dalmanitina collected from Upper Ordovician strata of the Barrandian area. All studied specimens are preserved as internal moulds and exhibit a narrow strip-like structure that runs sagitally or sub-sagitally under the axial lobe of the thoracopygon. These strip-like structures are markedly different from scavenger burrows and are interpreted as remains of the alimentary canal. A slightly expanded anterior-most part of the digestive system is preserved in the cephalic shield of six specimens and is interpreted as a remainder of the anterior midgut. A dark area is seen in the glabellar lobes of three specimens. These dark areas do not represent pyrite concentrations in the hypostome–glabellar cavity, because they contain only small amounts of Fe and S. These areas are interpreted as the remainder of cephalic digestive midgut diverticula, or the “perigastric organ”. Quantitative chemical analyses show that in species of Dalmanitina the digestive system is preserved as dark matter containing partly digested food particles and most probably also a higher amount of clay minerals. The described specimens constitute the first well-documented example of digestive structures in the subfamily Dalmanitininae.

Redox conditions of Datangpo-type manganese ores constrained by statistical analysis of pyrite framboids and iron isotopes

Datangpo-type manganese ores which originated in the Cryogenian Datangpo Formation, are overlaid and underlaid by Nantuo diamicite and Tiesi'ao silistones, respectively. A thorough understanding of the manganese mineralization process is currently limited by the continued uncertainty regarding the metallogenic redox condition of the Mn-bearing rock series. This study employed statistical analysis of pyrite framboid sizes and iron isotope (δ56Fe) to determine the redox conditions and constrain the mineralization process of Datangpo-type manganese ores in South China, considering the Gaolou in Chongqing, Yanglizhang in Guizhou, and Minle and Zhenxing in Hunan as examples. The results showed that Tiesi'ao siltstones mainly developed relatively larger diameter (7.29–7.68 μm) framboidal pyrites, whereas mudstones in the Datangpo Formation developed relatively smaller diameter (2.63–5.56 μm) framboidal pyrites. Furthermore, manganese ores produce non-framboidal pyrites. In three profiles, framboidal pyrite concentrations were found to be negatively correlated with Mn contents. These characteristics suggested that siltstones, mudstones, and manganese ores were deposited in oxic-anoxic, dysoxic-euxinic, and oxic-dysoxic conditions, respectively. The δ56Fe of whole rocks (δ56FeWR) exhibited a range from −0.73 ‰ to +0.48 ‰ (average of −0.32 ‰), whereas pyrite (δ56FePy) varied from +0.03 ‰ to +0.83 ‰ (average of +0.36 ‰). Furthermore, δ56FePy in manganese ore (average = +0.27 ‰) were lighter than those in mudstone (average = +0.49 ‰). The results of this study demonstrated that oxidation deposition played a role in pyrite formation, with manganese ores exhibiting more oxic conditions compared to mudstones. The findings of this study suggested that idiomorphic pyrite formation was similar to that of manganese ore, in which Mn precipitated in the form of manganese (hydro)oxides under oxic seawater, and then converted into rhodochrosite under anoxic sulfidic diagenetic conditions, with the involvement of microbes. This research has the potential to enhance comprehension regarding redox conditions and the regulation of sedimentary manganese ores via redox transformation.

Textures and trace element geochemistry of pyrite in Gaoloushan ore section of the Yangshan gold belt, West Qinling: Implications for ore genesis

The Devonian Sanhekou Group phyllite in the Yangshan gold belt includes multiple stages of pyrite development, and Au is mainly distributed within the pyrite. Bodies within the Gaoloushan ore section of the gold belt are located in the broken and altered carbonaceous phyllite and granitic rock dykes, where quartz vein-type gold ores are more common as compared to other ore sections (Anba, Getiaowan). Studying the trace element distribution characteristics of gold-bearing and non-gold-bearing pyrite can constrain the evolution of ore-forming fluids and the types of ore deposit genesis. Based on detailed fieldwork and microscopic identification, 48 pyrite samples from the 69th exploration line of the Gaoloushan ore section were analyzed in situ by LA-ICP-MS. The following conclusions were drawn: (1) The gold-bearing pyrite formed during the ore-forming stage while the non-gold-bearing pyrite formed during the sedimentary and metamorphic period. The morphology of the pyrites differs, with gold-bearing pyrite mainly characterized by medium-fine grains, impregnation, fine veins, and reticulate structure, with crystal morphology mainly pentagonal dodecahedra or pentagonal octahedra, whereas non-gold-bearing pyrite is mainly characterized by a medium or medium-coarse grains, with stellate, strawberry, or cluster structures, and crystal morphology mainly in the form of cubes or pentagonal octahedra; (2) The As and Te content of the sedimentary pyrite is low, locally below the detection limit, and the Co and Ni contents and ratios vary greatly, with a distribution of 117–945 ppm and ratio distribution of 0.11–1.92. Pyrite from the ore-forming stage is primarily characterized by high As, Pb, Co, Ni, Cu, Sb, Zn, and Se concentrations, with Bi, Au, and trace amounts of Tl, Te, and Sn observed in later formations; (3) Au and As are positively correlated. The average Au content of 60.53 ppm in pyrite from granite dykes is higher than the average Au 15.97 ppm in carbonaceous phyllite. Pyrite particles with Au contents below the detection limit are sourced in carbonaceous phyllite. In addition, the higher As enrichment is observed in pyrite from granite dykes, averaging 35 770.60 ppm with a maximum value of 72 930.19 ppm. In comparison, the average As content in carbonaceous phyllite is 8974.66 ppm, with a maximum of 69 800.50 ppm, and the Au-As diagram indicates that gold in the Gaoloushan ore section is mainly in the form of solid solution gold within the pyrite lattice; (4) Statistical analysis of the Co/Ni ratio variation in the different lithologies and pyrite stages reveals an initial increase followed by a decrease. The median Co/Ni ratio variations during the mineralization stages of Py1s (0.51–0.7), Py1m (1.35–2.25), Py2 (1.43–1.87), Py1-2 m (1.53), Py2a (1.59), Py2b (1.4), Py2s (1.2), Py2m (1.63), and Py3 (0.19–1.40) suggest that magmatic-hydrothermal fluids dominated during the early stage of mineralization in the gold belt and metamorphic fluids during the main mineralization stage, with deep-seated metamorphic fluids playing a significant role in the late mineralization stage. The varying proportions of ore-forming fluids are likely to have been crucial in controlling gold mineralization in the Yangshan gold belt.

Biooxidation of refractory sulfide-bearing ore using feroplasma acidophilum: Efficiency assessment and machine learning based prediction

The adhesive properties of microorganisms on the surface of minerals play an important role in the biooxidation efficiency of sulfidic refractory gold ores. In this research, the simultaneous effects of monosaccharides, ore content, pyrite content, and time on the activity and growth rate of Ferroplasma acidiphilum-from native Acid Mine Drainage (AMD)- was investigated during biooxidization alongside finding the best machine learning approach for the prediction of process efficiency using the independent variables. The results revealed that the optimum condition for reaching the highest pyrite dissolution (∼75 %) is 15 days of operating time, pyrite content of 7.2 wt%, and ore content of 5 wt%, pH of 1.47, and D-+-sucrose, D-+-galactose, and D-+-fructose concentrations of 0.52, 0.09, and 0.12 wt%, respectively. The results of the model comparison indicated that the Artificial Neural Network (ANN) model was able to predict the experimental results of this study with acceptable accuracy and better than Genetic Programming (GP) and Polynomial Regression informed by Response Surface Methodology (PR-RSM) from experimental data. Finally, the results showed that the change in D-+-fructose and D-+-galactose concentration has no significant effect on ferric ions concentration and pyrite dissolution content, while the influence of alteration in D-+-sucrose concentration is significantly high.