Drill Core Samples Research Articles

Characteristics and Formation Stages of Natural Fractures in the Fengcheng Formation of the Mahu Sag, China: Insights from Stable Carbon and Oxygen Isotope and Fluid Inclusion Analysis

The Fengcheng Formation of the Mahu Sag is an unconventional reservoir that is of paramount importance for exploration and development of hydrocarbon resource. However, current research on natural fractures in the Fengcheng Formation remains limited, posing challenges for exploration of hydrocarbon resource in the region. This study is based on core observations, thin section identification, geochemical testing and the evolution of regional tectonic movements to investigate the characteristics and periods of formation of natural fractures to address this gap. According to the characteristics of natural fractures in the drilling core samples and microsections, the natural fractures in the Fengcheng Formation can be grouped into structural fractures and atectonic fractures. Structural fractures can be further divided into three subtypes: high-angle interlayer shear fractures, along-layer shear fractures, and tensile fractures. Additionally, non-tectonic fractures in this studied area are primarily bedding fractures, hydraulic fractures, and hydrocarbon-generating overpressure fractures. Vertically, fracture development is more prominent at the bottom of Feng #2 Formation and at the top of Feng #3 Formation. Results also indicate that natural fractures primarily formed during three distinct tectonic movement periods. The initial stage of fracture evolution pertains to the Late Permian period (243–266 Ma), filled with fibrous calcite, and exhibiting a uniform temperature of 70–100 °C. The second stage of fracture evolution occurred during the Late Indosinian to Early Yanshanian period (181–208 Ma), mostly filled or semi-filled with calcite, with a uniform temperature of 110–130 °C. The third stage of fracture development happened during the late Yanshanian to early Himalaya period (50–87 Ma), predominantly filled with calcite, and presenting a uniform temperature of 130–150 °C. Among the various types of structural fractures, the density of high-angle interlayer shear fractures demonstrates a positive correlation with daily gas production, indicating their vital role in promoting hydrocarbon resource production and transportation. Furthermore, microfractures generated by hydrocarbon-generating overpressure fractures exhibit small pore sizes and strong connectivity. These microfractures can create an effective permeability system by connecting previously isolated micropores in shale reservoirs, thus establishing interconnected pore spaces in the shale formation.

Characteristics of the shortwave-thermal infrared spectra of the Zhuxi superlarge tungsten deposit in Jiangxi Province and their exploration significance

Infrared spectroscopy, as an innovative exploration tool, enables rapid identification of alteration minerals, thus can facilitate an improved understanding of mineralization and enhance prospecting efficiency. This paper specifically applies this methodology to drill core samples from the Zhuxi Deposit, Jiangxi Province, the world's largest tungsten deposit. Using shortwave and thermal infrared spectroscopy, this study aims to identify spectral characteristics of typical altered minerals within the deposit, establish the mineral identification methods and preferred spectrum bands, and discern spectral characteristics of varied altered mineral combinations. The variations observed in the characteristic bands of these isomorphic minerals serve as indicators of changes in the ore-forming environment. Specifically, absorption features around 2190 nm are indicative of paragonite formation in low-temperature environments, while features around 2210–2225 nm signify the presence of phengite in high-pressure, high-temperature conditions. Absorption at 2260 nm is characteristic of Fe-rich chlorite, suggesting a low-temperature, reducing environment, whereas Mg-rich chlorite exhibits absorption at 2250 nm, indicative of a higher-temperature environment. Based on depth, the deposit can be classified into three types of alteration mineralization: greisen, garnet skarn, and diopside skarn. Shortwave infrared spectroscopy proves effective for identifying muscovite in greisen and altered minerals such as serpentine and chlorite in diopside skarn. Thermal infrared spectroscopy, on the other hand, is ideal for quartz identification in greisen and garnet in garnet skarn. Intriguingly, the study finds that the absorption characteristics of garnet can reflect the metal mineralization type of the deposit. The absorption valley wavelength of garnet varies from around 11290–11380 nm in non-mineralized or poorly mineralized samples, to 11230–11290 nm when scheelite mineralization dominates, and to 11180–11230 nm when both scheelite and chalcopyrite are present. These findings contribute significantly to our understanding of the mineralogical characteristics and genetic environment of the Zhuxi deposit. Moreover, they provide valuable insights into the potential application of infrared spectroscopy for skarn zonation and mineral exploration.

Ambient Noise Tomography for Coral Islands

As valuable land in the ocean, coral islands are not only important bases for making use of marine resources and protecting marine rights and interests, but also important for breakthrough research in many fields of earth science. Hence, the economical and efficient determination of the underground structure of coral islands has become significant in coral island engineering geology, but remains challenging for traditional marine geophysical prospecting and drilling methods. While ambient noise tomography with dense arrays has been widely used in continental regions, its applicability to coral islands remains undetermined. In this study, based on the data recorded by a dense array on an isolated coral island in the South China Sea, we analyzed the ambient noise characteristics and obtained a 3D subsurface structure of the coral island using ambient noise tomography. We made the following findings: ① The ambient noise frequencies can be roughly categorized into three levels: < 1, 1–5, and > 5 Hz. The spectral characteristics of the noise below 5 Hz were consistent at different stations, but there were significant differences in the characteristics of the noise above 5 Hz. ② For ambient noise frequencies below 5 Hz, cross-correlation functions with high quality could be obtained with only 24 h of waveform data. However, it was difficult to extract meaningful cross-correlation functions for ambient noise frequencies above 5 Hz. ③ The S-wave velocity in the coral island was higher toward the sea and lower toward the lagoon, which was consistent with the high degree of cementation of the outer reef flat stratum on the seaward side. ④ There were two low-velocity horizons at 25–75 and 200–300 m, which were in good agreement with the high-porosity horizons that were revealed by drilling core samples, reflecting the weathering history of the reef. Our research demonstrates that ambient noise tomography is a potentially economical, efficient, and environmentally friendly method for the geological prospecting of coral reefs.

Enrichment of rare methanogenic Archaea shows their important ecological role in natural high-CO2 terrestrial subsurface environments.

Long-term stability of underground CO2 storage is partially affected by microbial activity but our knowledge of these effects is limited, mainly due to a lack of sites. A consistently high flux of mantle-derived CO2 makes the Eger Rift in the Czech Republic a natural analogue to underground CO2 storage. The Eger Rift is a seismically active region and H2 is produced abiotically during earthquakes, providing energy to indigenous microbial communities. To investigate the response of a microbial ecosystem to high levels of CO2 and H2, we enriched microorganisms from samples from a 239.5 m long drill core from the Eger Rift. Microbial abundance, diversity and community structure were assessed using qPCR and 16S rRNA gene sequencing. Enrichment cultures were set up with minimal mineral media and H2/CO2 headspace to simulate a seismically active period with elevated H2. Methane headspace concentrations in the enrichments indicated that active methanogens were almost exclusively restricted to enrichment cultures from Miocene lacustrine deposits (50-60 m), for which we observed the most significant growth. Taxonomic assessment showed microbial communities in these enrichments to be less diverse than those with little or no growth. Active enrichments were especially abundant in methanogens of the taxa Methanobacterium and Methanosphaerula. Concurrent to the emergence of methanogenic archaea, we also observed sulfate reducers with the metabolic ability to utilize H2 and CO2, specifically the genus Desulfosporosinus, which were able to outcompete methanogens in several enrichments. Low microbial abundance and a diverse non-CO2 driven microbial community, similar to that in drill core samples, also reflect the inactivity in these cultures. Significant growth of sulfate reducing and methanogenic microbial taxa, which make up only a small fraction of the total microbial community, emphasize the need to account for rare biosphere taxa when assessing the metabolic potential of microbial subsurface populations. The observation that CO2 and H2-utilizing microorganisms could only be enriched from a narrow depth interval suggests that factors such as sediment heterogeneity may also be important. This study provides new insight on subsurface microbes under the influence of high CO2 concentrations, similar to those found in CCS sites.

Comparative Laboratory Study of the Geochemical Reactivity of the Marcellus Shale: Rock–Fluid Interaction of Drilled Core Samples vs. Outcrop Specimens

The Marcellus shale is an unconventional reservoir of significant economic potential with Total Organic Carbon (TOC) ranging from 1 to 20%. Hydraulic fracturing is used to extract the shale’s resources, which requires large amounts of water and can result in mineral-rich flowback waters containing hazardous contaminants. This study focuses on a geochemical analysis of the flowback waters and an evaluation of the potential environmental impacts on water and soil quality. Drilled core samples from different depths were treated with lab-prepared hydraulic fracturing fluids. Rock samples were analyzed using Energy Dispersive Spectroscopy (EDS), while effluents’ chemical compositions were obtained using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). A comparison of results from drilled core samples treated with additives for hydraulic fracturing to those treated with deionized (DI) water confirms that, as expected, the major elements present in the effluent were Ca, Ba, and Cl in concentrations greater than 100 µg/L. The most concerning elements in the effluent samples include As, Ca, Cd, Pb, Se, S, K, Na, B, Mo, and Mn, with Cd and Cr values averaging 380 and 320 µg/L, respectively, which are above safe limits. Se concentrations and high levels of Ca pose major safety and scaling concerns, respectively. We also compared Marcellus shale drilled core samples’ geochemical reactivity to samples collected from an outcrop.

Rapid Analysis of Muscovites on a Lithium Pegmatite Prospect by Handheld LIBS

Laser-induced breakdown spectroscopy (LIBS) is a technology for compositional analysis that is particularly effective for light elements, particularly Li, which is a critical commodity for emerging green technologies. This study undertook analysis by handheld LIBS of muscovite from the drill core, outcrop, and soil on the Carolina Lithium Prospect (CLP) in Gaston County, North Carolina (USA), which lies within the Carolina Tin-Spodumene Belt (CTSB). Abundances of the alkali elements Li, K, and Rb were determined for more than 130 muscovites from the Li-rich pegmatites to track the degree of pegmatite fractionation as a pathfinder for spodumene mineralization. Across the CTSB and including the CLP, muscovite Li contents vary over an order of magnitude, ranging from 0.04 to 0.74 wt. %, with their K/Rb ratios varying between 63 and 8, features that together document the highly evolved character of pegmatites within the CTSB district. On average, muscovite Li contents are greater in spodumene-bearing pegmatites at 0.21 ± 0.12 wt. % than for common quartz-feldspar pegmatites at 0.14 ± 0.08 wt. %. Although overlapping substantially in the middle portions of their distributions, muscovite K/Rb ratios are biased toward low values for spodumene-bearing pegmatites (X- = 21 ± 6) compared to those for quartz-feldspar pegmatites (X- = 33 ± 9). This study provides a framework for the use of LIBS analysis of muscovite in outcrop, drill core, and soil samples as an analytical tool for in-field and on-site geochemical analysis during Li pegmatite exploration and prospect evaluation.

Improving spatially-resolved lithium quantification in drill core samples of spodumene pegmatite by using laser-induced breakdown spectroscopy and pixel-matched reference areas

Laser ablation-inductively coupled plasma-time of flight mass spectrometry (LA-ICP-TOFMS) concentrations were used to develop accurate calibration models for laser-induced breakdown spectroscopy (LIBS) mappings of pegmatitic drill cores samples. Both methods were applied on the same area of drill core samples, providing two spatially-resolved datasets for this area. The datasets were aligned pixel by pixel to create a pixel-matched reference area that covered the heterogeneity of the complete drill core. This way, different matrix effects affecting LIBS intensities could be taken into account and accurate spatial quantification of Li2O, SiO2, Al2O3, Na2O, and K2O from LIBS measurements was enabled.In particular, LIBS intensities and LA-ICP-TOFMS concentrations of individual pixels of the reference area were used as the input for a linear Partial Least Square Regression (PLSR) and a non-linear Least Square Support Vector Machines (LS-SVM) calibration model. Varying numbers between 100 and 2000 pixels were used for model creation, and root mean square error (RMSE) and R2 of each model were compared. Better values were achieved for the LS-SVM calibration model. Based on these results, the PLSR model was discarded and only the LS-SVM model with 1000 train pixels was further validated.For two different validation areas, LA-ICP-TOFMS concentrations were compared to LIBS-based concentrations obtained from the LS-SVM calibration model. The spatially-resolved quantification results of the LIBS data agree very well with the independently analysed LA-ICP-TOFMS concentrations, which is e.g. reflected in R2 values between 0.83 and 0.96 (mean 0.89) for Li2O, SiO2, Al2O3, Na2O, and K2O. In general, it was shown that the combination of LA-ICP-TOFMS and LIBS yields a comprehensive dataset for robust multivariate calibration. This enables spatially-resolved LIBS-based quantification of pegmatite samples that are subject to significant physical and chemical matrix effects.

Frontier of Understanding Earth's Dynamics

Frontier of Understanding Earth's Dynamics

Sources, transport, and deposition of metal(loid)s recorded by sulfide and rock geochemistry: constraints from a vertical profile through the epithermal Profitis Ilias Au prospect, Milos Island, Greece

Drill core samples from the Profitis Ilias Pb-Zn-Cu-Ag-Au vein mineralization on Milos Island, Greece provide new insights into (i) the metal sources, (ii) the primary vertical metal(loid) distribution, and (iii) the supergene enrichment processes in a transitional shallow-marine to subaerial hydrothermal environment. Metal contents of unaltered and altered host rocks combined with Pb isotope analyses of hydrothermal sulfides suggest that most metal(loid)s were derived by leaching of basement rocks, whereas the distinct enrichment of Te is related to the addition of Te by a magmatic fluid. The trace element contents of base metal sulfides record decreasing Au, Te, Se, and Co, but increasing Ag, Sb, and Tl concentrations with increasing elevation that can be related to progressive cooling and fluid boiling during the hypogene stage. The formation of base metal veins with porous pyrite hosting hessite inclusions at ~ 400 m below the surface was triggered by vigorous fluid boiling. By contrast, the enrichment of native Au associated with oxidized Fe and Cu phases in the shallower part of the hydrothermal system resulted from supergene remobilization of trace Au by oxidizing meteoric water after tectonic exhumation to subaerial levels. Disseminated pyrite with higher Tl/Pb ratios and locally elevated Hg concentrations relative to vein pyrite reflects infiltration of the host rocks by boiled liquids and condensed vapor fluids. The vertical and temporal evolution of the Profitis Ilias mineralization, therefore, provides unique insights into the transport and precipitation of Au, Ag, Te, and related metal(loid)s by multiple fluid processes.

Cd isotope constraints on metal sources of the Zhugongtang Zn–Pb deposit, NW Guizhou, China

The Sichuan–Yunnan–Guizhou metallogenic province (SYGMP) includes > 400 Zn − Pb deposits and prospects, eight of which are large-scale deposits with large reserves of critical metals such as Cd and Ge, including the Huize Zn − Pb − Cd − Ge and Daliangzi Zn–Pb–Ge–Cd deposits. The newly discovered Zhugongtang Zn − Pb deposit is a super-large deposit with Zn–Pb reserves of > 3 Mt. Its geochemical features are similar to those of the Huize deposit, with similar sulfide δ34S values and concentrations of critical elements in sphalerite (e.g., Cd and Ge). However, the two deposits have different host strata, and it remains unclear as to whether they have similar oregenesis. In this study, δ114/110Cd values and major- and trace-element compositions of sphalerites collected from a drill-core and tunnels of the Zhugongtang deposit were determined in an investigation of metal sources. Drill-core samples were impure and exhibited strong correlation (R2 = 0.89) between Zn and Cd contents. For samples from mining tunnels, the Cd and Fe contents of selected sphalerites were positively correlated, especially yellow sphalerites (R2 = 0.76). Cadmium is likely hosted in sphalerite by the substitution mechanism of (Fe2+, Cd2+) ↔ Zn2+. The δ114/110Cd values of all samples ranged from − 0.43 ‰ to 0.06 ‰. Based on Zn/Cd ratios, and excluding geochemical processes that may have caused the variable Cd isotopic compositions, we suggest that the metal sources of the deposit were derived from the mixing of sedimentary and basement rocks. This model is supported by the strong relationship between the δ114/110Cd and 1/Cd values of sphalerites from 11 typical Zn–Pb deposits in the SYGMP (R2 = 0.81). The quantification of metal contributions of source rocks indicates that deposits derived mainly from sedimentary rocks generally have relatively low sphalerite Ge contents and small Ge reserves, whereas those derived mainly from basement rocks have higher Ge contents and larger Ge reserves. This study provides a new model for explaining the enrichment of critical metals in Zn–Pb deposits of the SYGMP, thus extending the applications of Cd isotopes in hydrothermal systems.

Genesis of the Questa Mo Porphyry Deposit and Nearby Polymetallic Mineralization, New Mexico, USA

Abstract The Oligocene Latir magmatic center in northern New Mexico is an exceptionally well exposed volcano-plutonic complex that hosts a variety of magmatic-hydrothermal deposits, ranging from relatively deep, F-rich porphyry Mo mineralization to shallower epithermal deposits. We present new whole-rock chemical and isotopic data for plutonic rocks from the Latir magmatic center, including extensive sampling of drill core samples of intrusive rocks from the Questa porphyry Mo deposit. These data document temporal chemical trends of porphyry-related mineralization that occurred after caldera-forming magmatism and during postcaldera batholith assembly. Silicic magmas were generated multiple times throughout the history of the Latir magmatic center, but few are associated with the formation of a mineral deposit. Whole-rock trace element ratios and Sr, Nd, and Pb isotope compositions vary throughout the protracted history of silicic magmatism. The caldera-forming ignimbrite and early phase of postcaldera intrusions are unmineralized, more enriched in high field strength elements, and generally contain less radiogenic Sr and Pb and more radiogenic Nd than later intrusions. The Questa porphyry Mo deposit formed immediately after the most isotopically primitive phase of the batholith was assembled, ruling out simple reworking of juvenile mantle-derived crust as the source for mineralizing magmas. Rhyolite dikes associated with polymetallic sulfide deposits intruded ~800 k.y. after Mo mineralization, and Nd isotope data indicate that these dikes are associated with different batches of magma and are unrelated to the Mo-mineralizing intrusions at the Questa mine. Together, these data indicate that the source of magmas changed significantly throughout the 10-m.y. history of the magmatic center. We assess multiple genetic models for porphyry-related magmatism against this data set, favoring models with discrete periods of magma genesis from a deep hybridized zone in the lower crust giving rise to the punctuated periods of mineralization. These observations suggest that the formation of mineral deposits within a central magmatic locus is likely the result of the piecemeal assembly of individual hydrothermal-magmatic systems, and that distal and younger polymetallic mineralization commonly observed near known porphyry deposits represents decoupled processes.

Heat flow variations in 2 km deep borehole Litoměřice, Czechia

Temperature in 2 km deep borehole Litoměřice, drilled in 2007, was repeatedly logged down to 1700 m in the period 2007 – 2020. We were able to monitor a return of the temperature to the equilibrium temperature-depth profile undisturbed by drilling. The uppermost part of the profile contains signal of the recent warming manifested by a negative temperature gradient close to the surface and a temperature minimum at a depth of about 40 m. The minimum has been migrating downward at a rate of 1.5 – 2 m per year in the period 2015 – 2020.A detailed knowledge of temperature gradient together with thermal conductivity, diffusivity and heat production measurements on the drill-core samples of mica-schist that occurs below 900 m depth enabled us to analyze the heat flow vertical variations in the lithologically homogeneous depth section 900 – 1700 m. We came to the conclusion that temperature-depth profile in this section contains a robust climate signal of the last glacial cycle. The reconstructed ground surface temperature history indicates the magnitude of the last glacial – Holocene warming 13 -15 K and existence of a minimum 15 – 20 ka. The long-term mean ground surface temperature +1 - +2 °C suggests that the borehole site was permafrost free for most of the glacial cycle. Existence of about 100 m deep permafrost is possible in the coldest part of the last glacial.The steady-state surface heat flow has been estimated at 88 mW/m2. The reconstructed ground surface temperature history used as a surface forcing function in a numerical solution of the transient heat conduction equation provided an estimate of the present-day heat flow in the well. The estimate is practically independent from the poorly constrained conductivity of the 900 m thick sedimentary cover. According to it the present-day heat flow is lower than the steady-state one by 20 - 30 mW/m2 in the first hundreds of meters below the surface and still by about 10 mW/m2 at a depth of 1 km.

Scale Effect on Hydraulic Properties of Pore-Fissure Deep Rock Formations and Its Importance for the Mining Shaft-Sinking Process

The problem of hydraulic parameters estimation lies in the depth: the deeper the rock formation, the more expensive and difficult the field tests and samples acquisition, and the more challenging the technical issues. The article assesses the Triassic sandstone’s drainage potential at the stage of shaft sinking. It focuses on parameter analysis in varied scales, from drill-core sample laboratory testing, through a single well drawing test, to long-term pumping and recovery tests in the well with observation piezometers. The obtained results are compared to the values estimated in the past using different methods. Finally, the paper states whether it is reliable to forecast pore-fissure sandstone drainage potential based only on core samples’ laboratory tests. This research proved that lab tests underestimate pore-fissure rocks’ hydraulic parameters (mean hydraulic conductivity k = 9.79 × 10−8 m/s) tenfold more than long-term pumping tests (mean k = 4.45 × 10−7 m/s). However, it can be concluded that the group of so-called “witness samples”, 10% of all core samples with a top value of the hydraulic conductivity tested in the laboratory, can be representative of the aquifer and comparable to the values obtained in pumping tests. With this in mind, we recommend using the highest values of hydrogeological parameters from laboratory tests based on the worst-case scenario. Therefore, it is possible to forecast inflows to the shafts reliably. This methodology is recommended only for rocks of porous and pore-fissure character.

Nanopore Characteristics of the Cambrian Niutitang Formation Organic-Rich Shales in the Middle Yangtze Region and Its Formation Controlling Factors

The shale of Cambrian Niutitang Formation is one of the most important shale gas reservoirs in the Middle Yangtze region, South China. Nanopores are important reservoir spaces for shale gas. The study of pore characteristics and its formation controlling factors is of great significance for the exploration and development of shale gas in the Niutitang Formation. In this study, two drilling core samples and two profile samples were investigated. The laser Raman, X-ray diffraction analysis, FE-SEM, and low-pressure N2 and CO2 adsorption methods are used to study the geochemical and mineral compositions of the shales, and the nanopore characteristics and its formation controlling factors of the shales are discussed. Results show that the shales have the following features: (1) rich in organic matter (OM) and the total organic carbon (TOC) contents ranging from 2.65 to 11.33%, with an average value of 6.81%. (2) The main mineral components of these shales are quartz, feldspar, clay minerals, calcite, and a small amount of pyrite. (3) The samples from the center of the Middle Yangtze region (EY1 well and BGP profile) have a higher maturity value ( Rmc R 0 % = 4.0 %) relatively to the samples from the south of the Middle Yangtze region (XD1 well and JF profile), where the Rmc R 0 % is 2.8%. (4) The maximum N2 adsorption capacity of the four groups of shale samples ranges from 5.090 to 27.333 cm3/g, with an average value of 15.571 cm3/g, while the maximum CO2 adsorption capacity ranges from 2.686 to 5.567 cm3/g, with an average value of 3.776 cm3/g. The higher maturity leads to the EY1 well having the lowest average maximum N2 adsorption capacity, while most of the OM pores in the EY1 well and BGP profile samples are smaller than 10 nm in diameter. The tectonic uplift leads to the profile samples having more meso-macropores than the core samples. The dissolution pores and granular mineral support are the key factors for the better pore structure of the high-evolution stage Niutitang Formation shale.

Integrated subsurface investigation for magmatic sulfide mineralization in Betul Fold Belt, central India

Magnetotelluric (MT), Electrical Resistivity Tomography (ERT), Time-Domain Induced Polarization (TDIP), Geochemical and Geological studies followed by drilling and down-hole logging were undertaken with in the Betul Fold Belt (BFB) in Central India, to demarcate zones of magmatic Ni-Cu-PGE sulfide mineralization. The BFB is predominantly composed of circular to elongate gabbro bodies of the Padhar Mafic-Ultramafic Complex, intruded into a sequence of bimodal volcanic rocks and quartzites. Near-surface samples of ultramafic rocks were subjected to precise geochemical analysis and scanned by an electron microscopy with an energy dispersive spectrometer (SEM-EDS). This work indicated the presence of pyrite, pyrrhotite, chalcopyrite, pentlandite, and minor amounts of W-Cd bearing boweiite and palladenite assemblage. These minerals are regarded as favorable to the occurrence of Ni-Cu-PGE sulfide mineralization. MT data derived from two profiles were analyzed and modeled using 2D and 3D inversion algorithms. The robust conductivity anomalies obtained from the MT model have been interpreted coupled with electrical tomography, geology, and geochemistry data. The near-surface shallow depth conductors observed in the ERT sections are interpreted as the sulfide mineralized zones. They corroborate the MT results. These conductive zones reflect the occurrence of the magmatic Ni-Cu-PGE bearing sulfide mineralization associated with rocks of the mantle-derived Padhar Mafic Ultramafic Complex. This geophysical data, in conjunction with petrological and geochemical analysis of drill core samples have allowed the identification of the origin and paragenesis of sulphide mineralization in the study area. Geochemical studies suggest that the parental magma was generated from a subduction modified, metasomatized and an enriched mantle source that was subsequently emplaced in a magmatic continental arc setting. The interpreted conductors, observed at shallow depths (∼200-300 m), have been generated by secondary hydrothermal fluid circulation leading to vein formation in the host Padhar Mafic-Ultramafic Complex. The MT and electrical tomography models delineate the geological boundaries of the sulfide-bearing mineralized deposits in the BFB.

Stratiform Host-Rock Replacement via Self-Sustaining Reactions in a Clastic-Dominated (CD-type) Zn Deposit

Abstract Stratiform to stratabound replacement of a mixed siliciclastic-carbonate host rock is a defining characteristic of many sediment-hosted base metal deposits. Mineralized rocks in clastic-dominated (CD-type) Zn-Pb ore deposits, which represent our highest value base metal resources, are generally thin (101 m), laterally extensive (103 m), and stratiform to stratabound in fine-grained siltstone and mudstone facies. At the recently discovered Teena CD-type Zn-Pb deposit (Proterozoic Carpentaria province, Australia), the host rock was undergoing burial diagenesis when altered and mineralized by hydrothermal fluids that moved up to 2 km lateral to the fluid input conduit (growth fault) through intraformational intervals. In much of the deposit, carbonate dissolution was an important reaction permeability control, although significant amounts of mineralization also occur in carbonate-free siliciclastic beds. In this study, transmission electron microscopy (TEM) data has been generated on a drill core sample that preserves a sharp reaction front between mineralized and unmineralized domains of the fine-grained siliciclastic compositional end member (carbonate free). Petrographic and mineralogical data provide evidence that oxidized hydrothermal fluids moved through the protolith via reaction permeability that developed from feldspar dissolution. The nature of reactive fluid flow was determined by reactions that took place at the fluid-mineral interface. Pyrite formation during the earliest stage of the hydrothermal paragenesis increased the mineral reactive surface area in the protolith. Acidity was then generated in situ via self-sustaining reactions involving pyrite oxidation, transient Fe sulfate formation, and sphalerite precipitation, which provided positive feedbacks to enhance porosity creation and further fluid infiltration and mineralization. In the absence of carbonate, however, ore fluid pH was buffered by K-feldspar dissolution (~4.5), thereby ensuring sphalerite precipitation was not inhibited under more acidic conditions. All CD-type deposits in the Carpentaria province are hosted by a protolith comprising carbonate, K-feldspar, pyrite, and organic matter; these phases set the boundary conditions for the development of self-sustaining reactions during ore formation. Importantly, these self-sustaining reactions represent a Goldilocks zone for ore formation that is applicable to other sediment-hosted deposits that formed via replacement of mixed siliciclastic-carbonate host rocks (e.g., stratiform Cu).

The International Congress–Festival‐CIRIR 2022 (ICF‐CIRIR 2022), Rochechouart, France

AbstractCombining science, education, outreach, art, culture, and sustainable development, the International Congress–Festival‐CIRIR 2022 (ICF‐CIRIR 2022) was held from June 28 to July 2, 2022, in the Rochechouart impact structure. A total of 59 persons registered for the Congress–Festival, with 48 of these participating in person, from 18 countries on four continents, and with 46 abstract submissions. A field trip and a drill core sample screening party followed the event from July 4 to 6. Owing to the success of the event, it will be renewed every 3–4 years to help developing the interest of young scientists and the public at large, in impact processes and their role in the evolution of planets and life.

Heavy rare earth element and crustal-derived silicon enrichment in Huayangchuan carbonatites, Qinling orogenic belt

The Huayangchuan carbonatite is found in the North Qinling orogenic belt. It is distinguished from most carbonatites worldwide by its abundance of quartz and high heavy rare earth element (HREE) content. The origin of Si supersaturation and HREE enrichment in carbonatite is still unknown. Here, we conducted a detailed mineralogical investigation and in situ geochemical analyses on a suite of drill-core samples obtained from Huayangchuan carbonatite. In situ titanite and monazite UPb dating yielded ages of 212.3 ± 6.4 Ma and 211.8 ± 5.0 Ma, respectively, corresponding to the post-collision stage of the Qinling orogeny. Clinopyroxene and amphibole in the carbonatite are commonly intergrowth with quartz grains and trapped by quartz as mineral inclusions. The mineralogical textures and compositions indicate that quartz crystallized simultaneously with the mafic minerals from a Si supersaturation magma. The high Si activity during clinopyroxene formation may be related to Si assimilation from the wall-rocks. In situ Nd isotopic compositions of apatite and titanite show consistent εNd(t) ranging from −4.8 to −9.0, similar to the values of the whole-rocks and calcites. This indicates that the REE were derived from carbonatite magma without an external source. Two types of calcites were identified based on their cathodoluminescence characteristics, and they have variable chondrite-normalized REE patterns (La/Yb(CN) ranging from <0.01 to 19) but similar HREE contents. This implies that the carbonatite underwent strong crystal fractionation of early LREE-rich minerals, which may be essential for HREE enrichment. Therefore, we proposed that Si supersaturation in the carbonatite was probably caused by wall-rock assimilation, and fractional crystallization yielded primary HREE enrichment in the residual melts. Moreover, HREE enrichment in highly evolved carbonatites is further aided by high Si and alkaline activities.

Mineral Mapping on Hyperspectral Imageries Using Cohesion-based Self Merging Algorithm

Recently, hybrid clustering algorithms gained much research attention due to better clustering results and are computationally efficient. Hyperspectral image classification studies should be no exception, including mineral mapping. This study aims to tackle the biggest challenge of mapping the mineralogy of drill core samples, which consumes a lot of time. In this paper, we present the investigation using a hybrid clustering algorithm, cohesion-based self-merging (CSM), for mineral mapping to determine the number and location of minerals that formed the rock. The CSM clustering performance was then compared to its classical counterpart, K-means plus-plus (K-means++). We conducted experiments using hyperspectral images from multiple rock samples to understand how well the clustering algorithm segmented minerals that exist in the rock. The samples in this study contain minerals with identical absorption features in certain locations that increase the complexity. The elbow method and silhouette analysis did not perform well in deciding the optimum cluster size due to slight variance and high dimensionality of the datasets. Thus, iterations to the various numbers of k-clusters and m-subclusters of each rock were performed to get the mineral cluster. Both algorithms were able to distinguish slight variations of absorption features of any mineral. The spectral variation within a single mineral found by our algorithm might be studied further to understand any possible unidentified group of clusters. The spatial consideration of the CSM algorithm induced several misclassified pixels. Hence, the mineral maps produced in this study are not expected to be precisely similar to ground truths.

Calculation of hole spacing and surrounding rock damage analysis under the action of in situ stress and joints

In situ stress and joints have a significant impact on the propagation and attenuation pattern of blast stress waves, and they are two important factors that must be considered for tunnel blasting hole network deployment. This paper proposes a blast stress wave attenuation equation and a peripheral hole distance calculation method under the combined action of in situ stress and joints. First, the static and dynamic parameters of the jointed slate are obtained by drilling core samples in the field and conducting indoor tests. Next, considering the geometric and physical attenuation of the blast stress wave, the attenuation formula of the blast stress wave under the combined action of in situ stress and joints is derived. Based on the theory of the combined action of stress waves and explosive gas, a formula for calculating the peripheral hole distance that integrates the effects of in situ stress, joints, and tensile strength of the rock body is proposed. Finally, LS-PREPOST software is used to analyze the damage to the surrounding rock, verified by an on-site blasting test. The results show that the blast stress wave attenuation formula proposed in this paper can accurately predict the stress wave peak value under the combined action of in situ stress and joints. Combining the geological conditions and blasting parameters of the Bayueshan Tunnel study section, the optimal peripheral hole spacing is calculated to be 45 cm. The average over-excavation value of the grade IV surrounding rock is controlled within 22 cm and the over-consumption of concrete per linear meter is controlled within 100% using the peripheral hole layout method and the hole network layout parameters proposed in this paper. The research results provide a reference for the control of over-excavation and under-excavation in large-section tunnel blasting.