Clay Alteration Research Articles

Inversion of downhole resistivity properties through infrared spectroscopy and whole‐rock geochemistry using machine‐learning

AbstractThe electrical properties of rocks are widely used in the geophysical exploration of natural resources, such as minerals, hydrocarbons and groundwater. In mining exploration, the primary goal is to map electrically anomalous geological features associated with different mineralization styles, such as clay alteration haloes, metal oxides and sulphides, weathered crystalline rocks or fractured zones. As such, the reconciliation of geophysical data with geological information (geochemistry, mineralogy, texture and lithology) is a critical step and can be performed based on petrophysical properties collected either on core samples or as downhole measurements. Based on data from 189 diamond drill cores collected for uranium exploration in the Athabasca Basin (Saskatchewan, Canada), this paper presents a case study of reconciliation of downhole resistivity probing with core sample geochemistry and short‐wave infrared spectroscopy (350–2500 nm) through three successive steps: (i) multivariate analysis of resistivity and other petrophysical properties (porosity, density) against geochemical and infrared spectroscopy information to characterize electrical properties of rocks with respect to other physical parameters, (ii) a machine‐learning workflow integrating geochemistry and spectral signatures in order to infer synthetic resistivity logs along with uncertainties. The best model in the basin was Light Gradient‐Boosting Machine with pairwise log‐ratio, which yielded a coefficient of determination R2 = 0.80 (root mean square error = 0.16), and in the basement, support vector regression with data fusion of infrared spectroscopy and pairwise log‐ratios on geochemistry yielded R2 = 0.82 (root mean square error = 0.35); (iii) the best model was then fitted on an area that was excluded from the original dataset (Getty Russell property) in order to infer synthetic resistivity logs for that zone. Software code is publicly available. This workflow can be re‐used for the valorization of legacy datasets.

Three-dimensional interpretation of magnetotelluric data at Fogo Volcano, Azores Islands

The resistivity structure of Fogo volcano and the seismically active Congro region of São Miguel Island has been determined by 3-D inversion from 44 magnetotelluric soundings to yield new insights into the internal architecture of this volcanic island. Following comprehensive testing of processing codes to yield optimum magnetotelluric responses from the collected time-series, a robust electrical resistivity model was obtained. Sensitivity analysis of various features from the inversion process was used to determine their reliability, and aid geological interpretation. The magnetotelluric data imaged, and provided new structural insights into the Ribeira Grande geothermal system on the northern flank of Fogo volcano, where a shallow low resistivity (1 - 5Ωm) region has strong correlation with borehole data, and is shown to be an excellent proxy for mapping temperature and clay alteration mineralogy. Beneath the central edifice of Fogo volcano and also throughout the Congro region, the geology is very resistive, however the new magnetotelluric observations do not yield any further constraints on the origin of the seismicity that poses threats to the local populations residing on this hazardous island.

Analysis of geological data of oil and gas survey and exploration combined with modern electronic technology

Abstract Modern electronic remote sensing technology is an advanced and effective high-tech means of obtaining information on earth’s resources and environment at low cost, which provides a practical and effective method for oil and gas exploration. Based on the hyperspectral remote sensing technology in modern electronic technology, the article analyzes the specific process of applying it to oil and gas exploration and combs through the spectral characteristics of hydrocarbon microleakage based on oil and gas microleakage. To prevent the “dimensionality disaster” of Hyperion remote sensing data, principal component analysis is introduced to downsize the remote sensing data, and the PCA-CWT algorithm is combined with the continuous wavelet transform to extract hydrocarbon features. Based on Hyperion remote sensing data, hydrocarbon microseepage deciphering was carried out, and strange information from hyperspectral remote sensing geological data was also analyzed. The clay alteration anomaly information has obvious absorption bands between [220nm and 2450nm], the spectral absorption ranges of iron oxide and ferrous oxide minerals are mainly around 750nm and 1250nm, and the absorption bands of carbonate minerals are concentrated in the intervals of 2350nm and 2500~2750nm. Based on modern electronic remote sensing technology can realize the precise positioning of oil and gas reservoir areas, and different spectral features express the alteration of oil and gas minerals, which provides reliable support for recognizing the accurate development and utilization of oil and gas reservoir areas.

Helium - Relationships to other reservoir gases and some implications for exploration: The New Mexico Example

Helium (He) is the second most abundant element in the universe after hydrogen but is relatively rare on earth. He occurs as two stable isotopes, 3He and 4He. 4He is the dominant isotope in crustal gases and is a radiogenic decay product of uranium and thorium mainly in granitic basement rocks. 3He is dominantly primordial and primarily originates from the earth’s mantle. 3He may also be formed by radiogenic decay of 6Li (Lithium) which may be found in argillaceous sediments deposited in evaporitic settings. Although He occurs in most natural gases, it almost always occurs in extremely low, subeconomic concentrations, less than 0.1%. It is rare in concentrations more than 1%. A very few small reservoirs have gases with more than 7% He. Other gases that constitute the dominant components of helium-bearing natural gases are nitrogen (N2), carbon dioxide (CO2), and methane (CH4). The highest He concentrations occur where the dominant gas is N2 but most He has historically been produced as a byproduct of gases that are hydrocarbons. Hydrocarbons are generated from petroleum source rocks. Their presence in a reservoir is dependent upon the presence of a mature source rock in the basin and a migration path between the source rock and the reservoir. Large accumulations of CO2 in the southwestern U.S. resulted from the degassing of rising Tertiary magmas and subsequent migration of the gases into crustal reservoirs. N2 appears to originate mostly from degassing of the mantle but may also be formed in some strata by the thermal maturation of kerogens or by diagenetic alteration of clays or organic compounds in red bed sequences. The presence of economic concentrations of He in reservoir gases is dependent not only on an adequate source of 4He generated from granitic basement rocks but also on accommodating flux rates of N2, CO2, and CH4. These gases differ in their origins, places of generation and rates of generation, migration and emplacement. While basement-derived 4He and N2 enter reservoirs at slow rates over long periods of geologic time, hydrocarbons and CO2 enter the reservoir over much shorter time periods and dilute the 4He and N2. Basement-derived gases may be characterized by differing N2:He ratios which may indicate greater rates of He production within the crust in some areas. Exploratory drilling for He on Chupadera Mesa in the late 1990’s and early 2000’s encountered He-rich gases in Lower Permian strata. Isotopic analyses suggest that 93% of Chupadera Mesa He originated from radiogenic decay in crustal rocks while 7% is derived from the mantle or with a possible contribution by evaporitic Permian shales. Marked differences in the CO2 concentrations in different strata indicate that some strata acted as carrier beds for magmatically-derived CO2 while strata with N2-rich and CO2-poor gases were isolated from CO2 sources.

Jurassic heritance of the geomorphology in Mid Norway

The age and formation of the Scandinavian mountains and the Norwegian strandflat have long been the subject of dispute. Some researchers argue that the present-day mountains are remains of the Caledonian orogen while others claim that the Caledonian nappes after erosion were buried by Mesozoic sediments and subsequently exhumed. In order to clarify these issues, we have studied remains of chemically weathered rocks (saprolites) from the coast to the interior of central Norway. The multidisciplinary study includes digital topography, electrical resistivity tomography (ERT), XRD, XRF, palynological analyses and K–Ar dating of samples from outcrops, trenches and core drilling. The coastal areas are dominated by an outer strandflat and an inner joint-valley landscape, while the interior is characterised by smoother landscapes referred to as palaeo-surfaces. Remnants of pre–Tertiary weathering occur in the joint valley landscape as well as on the palaeo-surfaces. The saprolites are found within fault- and fracture-zones and at depths exceeding 50 m in drillholes. It is suggested that the old saprolites were strongly eroded along the coast and in the fjords and valleys such as in Orkdalen and Sunndalen. K–Ar dating of mainland clay alteration most frequently yielded Jurassic ages along a profile extending from the coast to the Dovrefjell mountains (c. 1400 m a.s.l.). The formation age of the smectite- and kaolinite-containing saprolites seems to be almost contemporaneous along this profile implying that the entire area was subject to weathering in a warm and humid climate, such as prevailed during the Late Triassic and Jurassic. Palynological residues containing thermally altered Triassic and Jurassic pollen and spores in the clay-infected bedrock lend support to the saprolite interpretation. The Mesozoic landscape in central Norway was consequently shaped by uplift and deep weathering in the Jurassic. The entire Trøndelag county was most likely covered by Mesozoic sedimentary rocks until Cenozoic exhumation. The landscape was modified by Cenozoic tectonic uplift and erosion, and finally reworked by Pleistocene glacial erosion. We therefore conclude that both the observed saprolites and the shape of the present-day landscape in central Norway give a strong impression of the original Jurassic weathering surface.

Interpretasi Struktur Bawah Permukaan Menggunakan Data Anomali Medan Magnet Daerah Manifestasi Panas Bumi Sampuraga Kabupaten Mandailing Natal

This research was conducted to identify the distribution of magnetic field anomalies to determine the subsurface structure of the area around Sampuraga hot springs. Magnetic field data was measured using a magnetometer in an area with dimensions of 1400 m x 1100 m with 154 points. The measurement data is a total magnetic field, and to obtain magnetic field anomaly values, corrections are made for diurnal variation and IGRF correction. Magnetic field anomaly values range from 353,1 nT to 7622,0 nT. Magnetic field anomaly data were processed using the Oasis Montaj software by reducing to the poles, upward continuation, and 2D modeling. The 2D modeling results show three layers of soil in the study area. The upper part (first and second layers) is interpreted as a caprock. This layer consists of sedimentary rock types of sandstone and clay and igneous rock in the form of granite at a depth of up to 1700 m. The lower part (third layer) is interpreted as a reservoir. This layer consists of metasedimentary volcanic rock, clay alteration, andesitic lava, and dacitic lava with a depth of up to 2030 m from the ground surface. The results of this model also interpret the fault zone as an outflow zone so that it forms manifestations on the surface. These three geothermal system components show that the Sampuraga area can be further developed and explored.

3D inversion of multifrequency controlled-source electromagnetic data and its application to geothermal exploration in the Tianzhen region of the northern Datong Basin, China

Owing to its sensitivity to hydrothermal alteration and geothermal fluids, the distribution of subsurface electrical conductivity provides critical information for characterizing geothermal systems. For geothermal exploration, the controlled-source electromagnetic (CSEM) technique provides a crucial tool to image the subsurface resistivity structures, especially in areas with strong cultural noise. Usually, land-based CSEM surveys are carried out with dozens of operating frequencies to enhance spatial resolution. However, the 3D inversion of multifrequency CSEM data using the commonly used direct solver is challenging with limited computational resources. In this study, we implement a practical inversion strategy for interpreting 3D multifrequency CSEM data. By combining a hybrid direct-iterative solver with the inexact Gauss-Newton optimization, 3D inversion of CSEM data involving multiple frequencies can be performed effectively on typical workstations. First, we test the effectiveness of the developed approach using synthetic multifrequency 3D CSEM data generated for a simplified geothermal model. The inversion strategy is then applied to the multifrequency CSEM field data collected for the geothermal exploration at Tianzhen region in Shanxi Province, China. The comparison between the inversion results using the sparse data set (six frequencies) and the dense data set (12 frequencies) highlights the necessity of using data from more frequencies in the inversion to improve the resolution. The resulting 3D resistivity model clearly delineates the clay alteration layers and shallow thermal reservoirs of the potential high-temperature geothermal system within the study area, while its deep heat source is not revealed owing to the limited investigation depth of the survey.

Hydrogen's organic genesis

Natural hydrogen exploration has been restricted in scope due to the predominance in thinking that various rock interactions with water in cratonic settings offer the best natural hydrogen sources. The limited exploration findings in these areas in conjunction with advances in the understanding of hydrogen generation via anthropogenic methods suggest that other source alternatives such as organic hydrogen generation need to be revisited. The ideas on the maturation of organic matter may need to be reassessed with respect to hydrogen. It is suggested that an overlapping thermo-catalytic set of processes occurs to produce hydrocarbons and hydrogen. Initially clay reacts with kerogen producing hydrocarbons, hydrogen and amorphous carbon, the alteration of clays releasing hydronium. During the late catagenic phase thermo-catalysis of hydrocarbons by amorphous carbon create shorter chained hydrocarbons and hydrogen whilst amorphous carbon degrades to carbon black. During expulsion of hydrocarbons and hydrogen the permeability of the source rock becomes more heterogeneous, isolating some reactants creating pyrobitumens and other carbonaceous materials. At higher temperatures during metagenesis isolated pyrobitumens and other carbonaceous materials in shales are turned to graphite releasing gaseous hydrocarbons and eventually diatomic hydrogen in a second phase by thermo-catalytic reaction with carbon black. This matches the temperatures and results at which laboratory experiments and petrochemical processes used to generate hydrogen are observed. The current conclusion of the hydrocarbon generation story at the methane preservation limit should be recognized as the start of hydrogen generation and graphitization as the end of the process. Instead of basin exploration focused solely on hydrocarbons and stopping due to concerns of over maturity of source and reservoir, exploration may continue deeper in search of organic hydrogen. This should be noted as a primary hydrogen generation mechanism globally and provide a suitable model to aid hydrogen exploration and lead the energy transition into a hydrogen economy.

Mapping hydrothermal alterations and lineaments associated with epithermal and massive sulphides deposits of Tifraouine (northwest Algerian coast): Use of Landsat 8 OLI data and remote sensing

Within the context of studying mineralizations related to the Miocene volcanic rocks from the northern part of Algeria, Landsat 8 OLI data and remote sensing techniques are carried out to characterize and map hydrothermal alteration outcrops in the Miocene volcanic rocks of Tifraouine on the northwestern Algerian coast, where several indications of mineralization are known. Short-wave infrared (SWIR) bands allowed for the identification of clay alterations, while the visible and near-infrared bands help in the detection of iron alterations. Red-green-blue color combination images of 6/7, 4/2 and 5/6 ratios were produced. Principal component analysis (PCA) was computed to characterise altered zones and extract lineaments. Matched filtering technique (MF) allows direct detection after applying minimum noise fraction (MNF) transformation and pixel purity index to the spectra in order to obtain a distribution map of the target mineral species in studied area. The remote sensing results combined with the structural geological data determine a relationship between mineralization and structural features and show that hydrothermal alterations are clearly controlled by tectonic. They are highly concentrated in the calderas zone and extend towards the Bouzedjar area which allowed checking the map performed according to the field studies. This will contribute to preliminary studies related to mineral exploration and enhance the mining potential of Tifraouine. The acquisition of supplementary data would allow us to extend this study in coming works.

Integration of remote sensing and geophysical methods for structural and lithological mapping in a part of Precambrian Basement Rocks, northern Nigeria

Landsat 8 OLI data, Aeromagnetic data, and Radial Vertical Electrical Sounding (RVES) survey data were integrated to map lithology, delineate structures and their trends, and delineate possible mineralized zones in the area. Landsat 8 OLI data yielded a color composite image, and surface lineaments map of the area. The aeromagnetic maps were utilized to map lithology, and subsurface structures. A radial survey confirmed the fractures derived from the structural maps. Results classified the area into three geological units viz: migmatite, banded gneiss, and quartzite. The banded gneiss is the most deformed and contains series of structures that are significant for mineral and groundwater explorations. Clay alteration is the most dominant in the area, followed by iron oxide alterations. Lineament alignments are N-S, NNW-SSE, NNE-SSW, NE-SW, and E-W directions.

A GIS-based modified frequency ratio model for gold potential mapping in Kelantan Malaysia

Mineral system factors control the distributions of orogenic gold deposits in our immediate geological environment. The spatial knowledge of the relationship between the mineral factors and the gold deposits are crucial to locating these deposits in the environment. However, there is a current challenge in understanding the spatial correlation between ore genesis factors and orogenic deposits. Our paper analysed the spatial relationship between ore controlling factors and orogenic gold deposits in the Gua Musang area Kelantan, Malaysia. The procedure applied a modified frequency ratio model (MFR) to generate the gold potential map of the study area. The model relied on the spatial distribution of known gold deposits to predict new ones. Eight (8) known gold deposits and five (5) selected factors were used in the analysis. These factors include NE-SW lineaments, NW-SE lineament, host rock, heat source, alteration of iron and clay. The new findings show the factor with the highest predicting rate (Lineaments NE-SW) as the major gold deposits distribution factors within the study area. The created map highlight both known and new deposit locations. The area under curved (AUC) statistical graphs were used for the accuracy test. The results show 92.50% accuracy; thus, the approach is adaptable for gold mapping in Malaysia.

Comparing intrarift and border fault structure in the Malawi Rift: Implications for normal fault growth

Early stages of normal fault growth are seldom described using field observations of active normal faults. Here we first estimate the displacements of active border and intrarift faults in the Zomba Graben in the low extension (< 10 %) Malawi Rift, and then quantify micro-to macroscale fault damage and mineralisation associated with their surface exposures. The 22 km long Mlunguzi and 39 km long Chingale Step intrarift faults have fault zones 4–52 m wide. In contrast, we estimate the fault zone of the 51 km long Zomba border fault is 32–118 m wide. Calcite and clay alteration is limited to the fault damage zones and fault cores, and the extent and intensity of fault damage and mineral alteration is greater on the Zomba border fault compared to the intrarift faults. Relative to global compilations, normal faults in the Zomba Graben have lengthened quickly while developing narrow fault zones, given their displacement. The minor damage on these long, low-displacement normal faults may reflect the influence of lithology, negligible fault healing, and/or activation of pre-existing weaknesses.

Mineralogy and K–Ar geochronology of clay alteration associated with uranium mineralization in the Patterson Lake Corridor, Saskatchewan

The Patterson Lake Corridor (PLC) along the southwestern margin of the Athabasca Basin contains high-grade uranium deposits entirely within crystalline basement rocks. Visible–near infrared–shortwave infrared (VNIR–SWIR) spectroscopy measurements were collected on drill core samples from several locations in the PLC. The Triple R and Arrow deposits exhibit downhole spectral trends related to the crystallinity and thermal maturity of clays (illite and kaolinite) and mineralization. The K–Ar dates of silt-and-clay size fractions (10–6 μ m; 6–2 μ m; 2–0.6 μ m; 0.6–0.2 μ m; &lt;0.2 μ m) from five clay-altered samples decrease with grain size, and span 1608 ± 17 Ma to 1060 ± 14 Ma for the Spitfire discovery ( n = 14) and 1342 ± 17 Ma to 289 ± 4.3 Ma for the Arrow deposit ( n = 4). Alteration assemblages are broadly similar to Athabasca Basin basement-hosted deposits, and K–Ar dates indicate that high-grade uranium mineralization in the PLC reflects remobilization and concentration of primary ores. Integration of geochronology, clay mineralogy and VNIR–SWIR spectral parameters identify fertile fluid conduits when expanded to property or corridor scales, and provide additional evidence that ore grades of the Athabasca Basin deposits reflect several stages of hydrothermal mineralization spanning c. 1000 Ma. Supplementary material: Supporting information document and datasets are available at https://doi.org/10.6084/m9.figshare.c.6033890 Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

The Kupol Epithermal Au-Ag Vein District, Chukotka, Far Eastern Russia

Abstract The Kupol epithermal Au-Ag vein district is located in the northern part of the Okhotsk-Chukotka volcanic belt, a Late Cretaceous subduction-related continental volcanic arc exposed for &amp;gt;3,000 km along the eastern coast of Russia. High-grade veins are hosted in the Kupol andesite sequence, a 300- to 1,000-m-thick, subhorizontal, layered sequence of andesite flows, sills, and ash tuffs, dated at 97 to 96 Ma (Cenomanian). The Kupol andesite sequence is underlain by mixed mafic-felsic volcanic units plus sedimentary rocks (“older volcanics”) and overlain by a &amp;gt;1-km-thick “upper felsic” sequence of dacitic-rhyolitic tuffs and associated dikes and flow domes, dated at 95 to 85 Ma, with local sequences of fluvio-lacustrine sedimentary rocks. The epithermal veins occupy N-striking, steeply dipping normal faults that cut thick coherent andesite flows and sills in the central-upper part of the Kupol andesite sequence. The district is dominated by the large Kupol vein (180.7 tonnes (t) Au and 1,986 t Ag produced to 2020), hosted by the 5.5-km-long Kupol fault, which accommodates normal, east-side-down displacement of up to 190 m. The Moroshka and Providence veins, 5 km east-southeast of Kupol, occupy shorter faults (1- to 2-km strike) with smaller vertical displacements (to 70 m). The Moroshka vein is dated at 93.5 ± 1.5 Ma (Turonian; 40Ar/39Ar method on adularia), and the timing of vein mineralization here and at Kupol overlaps with the early stage of upper felsic sequence magmatism. Veins contain subhorizontal ore shoots, controlled by the intersection of the steep faults with flat-lying Kupol andesite sequence stratigraphy and by steepening of the faults to a more dilational orientation as the inferred paleosurface is approached. Local structural controls are also evident, reflecting a component of oblique slip on the Kupol fault, with the thickest vein segments at steeply pitching jogs and relays. Main-stage veins grew via repeated encrustation by quartz-chalcedony ± amethyst ± lattice bladed calcite (replaced by quartz), with Au-Ag–bearing crustiform adularia ± clays ± sulfides/sulfosalts/electrum ± chlorite ± hematite bands. The main controls on Au grade are inferred to have been boiling, resulting in sharp vertical limits to high metal grades typical of epithermal veins, coupled with optimal dilation of the vein system where the hosting normal fault steepens near surface with decreasing differential stress. Although much of the displacement on the controlling faults is pre-mineralization in timing, lithified cataclastic breccia, coeval with some vein stages, and vein geometry patterns indicate that some vein development occurred contemporaneously during late normal displacement along the fault system. Waning of the hydrothermal system is marked by late carbonate fill, initially Fe dolomite, then coarse calcite as veins, matrix to vein breccia, and central vein cavity fill. The Kupol district veins have proximal adularia-quartz alteration (haloes meters wide), within an extensive (hundreds of meters in scale) clay alteration halo. Clays are zoned both vertically and laterally with respect to veins, with inner illite-chlorite that was magnetite-destructive (at highest paleotemperature; &amp;gt;220°C), grading outward and upward to illite/interlayered illite-smectite with kaolinite, then to an outer zone (or upper blanket) of smectite, at lowest paleo-temperature (&amp;lt;150°C). The boundary between the illite and smectite zones is interpreted to mark the interaction limit of paleo-hydrothermal systems with cooler groundwater. District-scale pathfinder element zonation correlates with clays, with S-Te-Bi-As in the illite-chlorite core and Sb-Cs-Tl(-As-Li) in the smectite blanket. Pathfinder zonation patterns at Kupol point to a magmatic source at depth or, more likely given the scale of the anomalies, multiple magmatic sources, with the surface clay zonation indicating the extent of coalesced paleo-hydrothermal systems associated with upflow plumes. This is the best-defined alteration record with geochemical signature for a complete district hosting a large, high-grade vein deposit. Early definition of clay and pathfinder element patterns across an entire epithermal district can be carried out at low cost to provide useful constraints on vein targeting.

Three-dimensional magnetotelluric inversion reveals the typical geothermal structure of Yanggao geothermal field in Datong Basin, northern China

The Yanggao geothermal field, located in the north of the Datong Basin, and close to the Datong Volcanic Group, the geothermal field is affected by deep faults and vigorous tectonic activity. Yanggao has abundant geothermal resources, and contains a large number of hot springs. To explore the geothermal system and characterize the formation mechanism of the Yanggao geothermal field, we deployed 168 magnetotelluric (MT) sitesin the study area. MT phase tensor analysis is used to estimate the dimensionality of the subsurface. Furthermore, we conducted an inversion of the MT data to establish a 3D resistivity model of the study area. The results suggest that the Yanggao geothermal system can be divided into three layers. A low-resistivity layer (C1) exists at a depth of 2 km, which can be interpreted as the clay alteration layer (clay cap) and the reservoir of the geothermal system. Under the reservoir, the model indicates an additional low-resistivity zone (C3) at a depth of 8 km, which is presumed to be a heat source related to the Datong Volcanic Group. Moreover, a vertical low-resistivity zone (C2) between the reservoir and the heat source is related to the Yunmenshan Fault acting as a heat conduction path in the Yanggao geothermal field, controlling the infiltration and recharge of the hot springs.

3D deep geoelectrical exploration in the Larderello geothermal sites (Italy)

The paper describes a new experimental deep electrical resistivity acquisition (down to 1600 m) for exploring deep and shallow geothermal systems. The test site is located in the Larderello geothermal area, the oldest geothermal field in the world under exploitation for power production. In this area, many data have been acquired in the frame of previous exploration projects but nowadays several critical issues are still matter of debate: permeability distribution, depth and volume of the magmatic heat source, supercritical fluid condition at depth, and the occurrence of low resistivity anomalies in a dry-steam crystalline and carbonate reservoir. In order to develop new methods for contributing to the hydrothermal reservoir issues, an experimental high resolution 3D Surface-Hole Deep Electrical Resistivity Tomography (SH-DERT) was designed and the Venelle2 well in the Larderello geothermal site, hosted in the crystalline units, was used for the experiment. The design of the in-hole experiment and the results of the deep geoelectrical survey are hereby presented. SH-DERT was properly designed to face extreme conditions at depth characterizing the geothermal well. It provided a 3D resistivity distribution. Transmitting and receiving electrodes were distributed on a large surface (6 km2) and in the Venelle2 well (down to 1600 m). The in-hole electrical cable was equipped to be able to operate in very high temperature conditions. The experiment represents a challenge and an opportunity for the applied geophysics in geothermal areas, where a lowest resistivity is highlighted in a zone above the reservoir and the resistivity of the reservoir is higher. Moreover, the relationship between temperature, clay alteration and resistivity can define a challenger to enable better prediction of reservoir temperature distribution from resistivity measurements. It is a potential improvement of the reservoir knowledge and a useful success for exploration drilling.

Clay sediments derived from fluvial activity in and around Ladon basin, Mars

The morphology and mineralogy of light-toned layered sedimentary deposits were investigated using multiple orbital datasets across the Ladon basin region, including within northern Ladon Valles, southern Ladon basin, and the southwestern highlands of Ladon basin. Light-toned layered deposits are particularly widespread in Ladon Valles and Ladon basin, ranging laterally for distances over 200 km, with the thickest exposure (54 m) located at the mouth of Ladon Valles. The restriction of layered sediments below a common elevation (−1850 m) in Ladon Valles and Ladon basin and their broad conformable distribution with bedding dips between 1 and 4° favor a lacustrine environment within this region during the Late Noachian to Early Hesperian. The Ladon layered deposits have spectral signatures consistent with Mg-smectites, even when the morphology of the layering varies considerably in color and brightness. These phyllosilicates were most likely eroded from the highlands upstream to the south, but the lacustrine environment may have also been favorable for in situ alteration and formation of clays. The southwestern highlands also display light-toned layered deposits within valleys and small basins. These sediments predominantly have signatures of Mg-smectites, although we also identified Fe/Mg-smectites and additional hydrated phases in some deposits. One of these altered deposits was found within a younger Holden crater secondary chain, possessing a Late Hesperian to Early Amazonian age for valleys and sediments that postdate the deposits within Ladon Valles and Ladon basin. Phyllosilicate signatures were also detected in the ejecta from two fresh craters that exposed highland materials upstream of Arda Valles, revealing that the highlands are clay-bearing and may be the most plausible source of the clay-bearing fluvial-derived sediments found within the valleys and basins downstream. Some of the highland deposits are likely coeval to similar clay-bearing sediments found to the south within Holden and Eberswalde craters, indicating late, widespread fluvial activity and deposition of allochthonous clays within the broader Margaritifer Terra region when Mars was thought to be colder and drier.

Alteration Characteristics and Precious Metal Availability in Gunung Gembes &amp; Surroundings, Jeruk Village, Pacitan Regency, East Java Province

The research area is located in the area of Mount Gembes, Jeruk Village in Pacitan (East Java). This study aims to determine the characteristic and temperature in the formation of alteration which refers to petrography with the help of samples taken in the study area. The petrographic observations carried out were thin section observations which were then analyzed for the mineral content contained in the sample rock. After knowing the minerals contained in the sample rock, it is then entered into the mineral formation temperature diagram (White &amp; Hedenquist, 1995). The method used in this study includes primary data in the form of geological observations such as lithology, geological structure geomorphology, environmental geology and alteration observations and combined with secondary data. Alteration observations in this study were carried out descriptively (megascopic) and subjective (microscopic). The geomorphic unit that works is of volcanic origin, with high hilly sub-units of porphyry dacite intrusion (volcanic neck). Geological structures that develop in the study area are faults, namely the left horizontal fault of Jeruk 1, the left horizontal fault of Jeruk 2 and the interpretation of the oranges right horizontal fault. Geological resources or sources found in the research area are mineral potential resources that are economical, and negative sources are in the form of mass movement of debris flow type. The Zonation and the type of alteration that developed in the research area are the clay alteration zone and silicification. The clay zone is formed at a temperature &gt;100⁰C-220⁰C with a pH of 3-5 and a silicification zone is formed at a temperature&gt;100⁰C-300⁰C with a pH &lt;2 which is directly controlled by the faults found in the study site.

Magnetotelluric study on a vapor-dominated geothermal reservoir in the Matsukawa area, Japan

Vapor-dominated geothermal areas produce only vapor from geothermal reservoirs and have been reported worldwide (e.g., Larderello, Italy; The Geysers, United States; and Kamojang, Indonesia) and studied from several perspectives. White et al. (1971) proposed a typical vapor-dominated reservoir model, which has been applied to numerous vapor-dominated fields. The Matsukawa area, located in Iwate prefecture, is one of the few vapor-dominated geothermal areas in Japan that contains an operational power plant; therefore, it has been the site of many geological and drilling studies. For example, Ozeki et al. (2001) proposed a geological conceptual model of this area. In this study, we investigated the characteristic resistivity structure in a vapor-dominated geothermal reservoir in the Matsukawa geothermal area. We performed a three-dimensional (3D) inversion with ModEM (Egbert and Kelbert, 2012) for magnetotelluric data obtained from 68 stations. We determined an optimized solution according to the results with the smallest root mean square value by considering various calculation conditions, including the smoothing parameter and Lagrange multiplier. The 3D inversion results were used to confirm clay alteration zones, faulting, basement rocks, and low-permeability lateral shielding, which characterizes the vapor-dominated geothermal system in this area. The 3D resistivity structure is considered valid because it is consistent with logging data. In addition, we estimated the 3D temperature structure using the neural kriging method (e.g., Ishitsuka et al., 2018) based on the obtained resistivity structure, temperature logging data, and electrical logging data.

Influence of silane functionalized nanoclay on the barrier, mechanical and hydrophobic properties by clay nanocomposite films in an aggressive chloride medium

The surface alteration of silica clay by a silane coupling agent was done to improve the compatibility with epoxy polymer matrix. It can be attained with ethoxy based silanes namely (3-mercaptopropyl) triethoxysilane (MPTES), propyltriethoxysilane (PTES) and 3-aminopropyl(diethoxy)methylsilane (APDES) in order to enhance the anticorrosion potential of epoxy coatings on mild steel. The structural and thermal properties of the functionalized clay nanoparticles are studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphological features of the functional nanoclay were also described by employing field emission scanning electron microscopy with energy dispersive x-ray analysis (FE-SEM/ EDX) and TEM (Transmission electron microscopy) analysis. These analyses showed the well functionalization of nanoclay by silanes. The well dispersion of functionalized nanoclay in the epoxy resin produces better nanocomposites which are coated on the mild steel. The coated steel samples were analyzed in terms of microstructure and corrosion resistant properties in 3.5% NaCl solution. Electrochemical impedance spectroscopy (EIS), scanning electrochemical microscopy (SECM), salt spray analysis, and analysis of oxygen and water permeability were applied to assess the barrier properties against water permeation, oxygen penetration and protectiveness of silane-modified epoxy coatings. It was found that all the modified coatings showed higher barrier resistance and superior corrosion resistance than pure epoxy coating, which were described by higher charge transfer resistance (Rct) 6815.36 kΩcm2 and lower double-layer capacitance (Cdl) 405.51 µF at the electrolyte/metal interface. The tensile strength was found to be 113 MPa for EP-MPTES/clay nanocomposite while the value of pure epoxy coated specimen was 41 MPa. Therefore, the silane grafted clay nanoparticles results in slower diffusion processes, which specifically slow down the anodic reaction, thus blocking the overall corrosion path. Modified clay-epoxy nanocomposite displays good thermostability, better dispersion, outstanding mechanical property and superior water resistance property. Among the examined silanes, MPTES shows an effective functionalization of nanoclay, followed by the APDES and PTES. A possible mechanism has also been proposed.