Application and Significance of Geological, Geochemical, and Geophysical Methods in the Nanpo Gold Field in Laos

As the main part of the Indosinian metallogenic province in the eastern part of the Tethys metallogenic domain, Southeast Asia has experienced multiple stages of tectonic magnetic activities accompanied by the formation of rich mineral resources. However, due to the undeveloped economy, low degree of geological work, dense vegetation cover, and lack of obvious prospecting marks, traditional geological prospecting work in the area is not optimal. Consequently, the combination of high-precision geophysics and geochemistry has become an important method of looking for ore bodies deep underground in this area. The Nanpo gold deposit is a hydrothermal gold deposit that occurs in the Indosinian felsic volcanic rock body, and its mineralization is closely related to felsic magmatism. This study carried out comprehensive geophysical and geochemical exploration methods of soil geochemical survey, induced polarization (IP) survey, and audio-frequency magnetotelluric (AMT) survey. Based on the characteristics of geophysical and geochemical anomalies, geological inference, and interpretation, the integrated geophysical and geochemical prospecting criteria of the ore area have been determined: The large-scale and overlapping Au-Ag-Cu anomaly area in the host felsic magmatic rocks (mainly diorite, monzodiorite and granodiorite) is a favorable metallogenic area. Two anomalies, P1–H1 and P3–H6, with the best metallogenetic conditions and the deepest extensions of the known ore bodies, were further selected as engineering verification targets. After the study of the drill core, gold (mineralized) bodies consistent with the anomalies were found, indicating that the combined method is suitable for the exploration of mineral resources in this area, and the prospecting effect is good. At the same time, the metallogenic prediction shows that the deep part of the mining area still has great metallogenic prospects and prospecting potential. The characteristics of geophysical and geochemical anomalies and prospecting experience in the study area can provide references for the prospecting of hydrothermal gold deposits in the Luang Prabang–Loei structural belt.

Faulting of rocks as a critical energy process

Faulting of rocks is a dominant earth process that governs small-scale fracturing, formation of tectonic plate boundaries, and earthquakes occurrence1–4. Since the 18th century, the mechanical settings for rock faulting were commonly analyzed with the Coulomb criterion5 that offers empirical, useful tools for scientific and engineering applications1,6–12. Here we revisit the processes of rock faulting by an alternative approach that incorporates elastic energy, strain-state, and three-dimensional deformation; these mechanical fundamentals are missing in Coulomb criterion. We propose that a stressed rock-body fails as two conditions are met: (1) The elastic energy generated by the loading system equals or exceeds a critical energy intensity that is required for the faulting process; (2) The internal strain of the stressed rock-body due to slip and dilation along the developing faults equals the strain-state created by the loading system to maintain physical continuity13,14. Our simulations reveal that meeting these energy and strain conditions requires an orthorhombic, polymodal fault geometry that is similar to natural and experimental fault systems15–20. The application of our formulation to hundreds of rock-mechanics experiments11,21–28 provides a new, comprehensive benchmark for rock-faulting.

PETROGRAPHIC FEATURES AND MODELLING OF SOME WATERFALL ROCKS IN KENYIR LAKE, TERENGGANU: A MICROSCOPIC PERSPECTIVE APPROACH IN SUSTAINABLE GEOTOURISM

Waterfalls around Kenyir Lake, Terengganu naturally serve as an iconic symbol of amazing rock bounded formation amidst the wilderness, which stores a hidden story for millions of years. The waterfalls feeding the Kenyir Lake have become tourists’ main attractions since they are located separately on a different island. There are three naturally picturesque waterfalls worth seeing in the study area, namely Sungai Buweh Waterfall, Lasir Waterfall, and Saok Waterfall, which are made up of granitic rock body that emerged in the Eastern Belt during the Late Triassic (~251.2 Ma). To date, the waterfall landscape in any area concerned with geotourism focusses more on outcrop architecture and geomorphological features, but has only limited accessibility to rock records. This study was carried out to evaluate the geo heritage features, of the waterfall landscape as well as its rock-forming minerals. Three rock samples were carefully collected from the waterfalls and subsequently prepared for optical thin section petrography analysis using a polarised light microscope. The optical thin section petrography further revealed precise mineral compositions, fabrics, and microstructures. A photomicrograph of the thin sections was also taken at low and high magnification levels in plane polarised light (PPL) and cross polarised light (XPL). Additionally, petrographic modelling was constructed using optical microscopic data to help identify a microscopic mineral (a hidden material in rock) in detail so that the mineral becomes clear to both geologists and the public at large. Generally, this modelling will enlighten the public on the material embedded in the rocks and illustrate the importance of learning about rock-forming minerals as well as to embed the idea of making the waterfall a Sustainable Development Goal (SDG). Besides making geology an interesting field to embark on, this mineral find affirms the beauty of the waterfalls for tourism purposes, thereby connecting geotourism and nature. The minerals from various constituents are also useful for scientific heritage purposes and may benefit the economy by serving as sustainable tourism while being part of a geopark.

Instability Mode and Movement Characteristics of Dangerous Rock Body in Steep Rock Slope

The cutting relationship and development degree of structural plane control the instability mode and scale of rock slope. The trajectory of rock mass after instability is an important basis for the design of dangerous rock prevention. The back slope of a residential area was investigated in this paper. Based on the survey data of the field structure surfaces, the possible instability mode of the slope rock mass was analyzed by using the stereographic projection method. The shear strength parameters of the rock mass were inverted through the investigation of dangerous rock mass. Finally, ANSYS/LS-DYNA was used to simulate the dangerous rock mass motion trajectory. This study provides a reference for the analysis of the instability process of single rock.

Numerical Analysis of Thermal Environment in Deep Mining

To analyze heat effect in deep metal mines, it is crucial to understand the temperature field distribution around the mine tunnel. In this paper, a numerical model of the random mineral composition of the rock body is established based on finite element software to analyze the influence of the internal composition of the surrounding rock on the temperature field, and a numerical simulation model based on COMSOL finite element software is established based on the two heat exchange modes of heat conduction and heat convection in the surrounding rock. The results show that the numerical simulation results of a typical numerical simulation model using a single material are lower than the real situation; increasing the tunnel length does not increase the heat exchange efficiency between the rock wall and the air; increasing the wind velocity has a limited impact on the temperature field; the wind temperature more directly affects the mining surface; and the effect of wet air on the temperature field of the surrounding rock has a more substantial variation.

Quantifying the Porosity of Crystalline Rocks by In Situ and Laboratory Injection Methods

The porosity and pore geometry of rock samples from a coherent granodioritic rock body at the Grimsel Test Site in Switzerland was characterised by different methods using injection techniques. Results from in situ and laboratory techniques are compared by applying innovative in situ resin impregnation techniques as well as rock impregnation and mercury injection under laboratory conditions. In situ resin impregnation of the rock matrix shows an interconnected pore network throughout the rock body, consisting mainly of grain-boundary pores and solution pores in magmatic feldspar, providing an important reservoir for pore water and solutes, accessible by diffusion. Porosity and pore connectivity do not vary as a function of distance to brittle shear zones. In situ porosity was found to be about 0.3 vol.%, which is about half the porosity value that was determined based on rock samples in the laboratory. Samples that were dried and impregnated in the laboratory were affected by artefacts created since core recovery, and thus showed higher porosity values than samples impregnated under in situ conditions. The extrapolation of laboratory measurements to in situ conditions requires great care and may not be feasible in all cases.

Study on the Key Technology of Controlling the Instability of Deep High-Stress Coal and Rock Mass and Relieving the Danger

In order to solve the problem of stress concentration and gas overrun in the process of uncovering high gas and thick coal seam, combined with the occurrence characteristics of coal seams in Wuyang Coal Mine, the measures of “hydraulic and mechanical cavity making + steel screen pipe + surrounding rock grouting” are adopted to establish a method for mutual verification of multiple effect test indexes of residual stress, residual gas content, coal seam moisture content, and microseismic signal characteristics, and the three-dimensional accurate analysis of the influence range of hydraulic cavitation is effectively realized. By comparing and analyzing the gas extraction amount, the surrounding borehole stress change and the microseismic monitoring signals before and after the application of hydraulic cavitation technology are studied. The results show the following. (1) The pressure relief effect of the hydraulic cavity on surrounding coal decreases with the increase of distance, and the pressure relief effect is most obvious at 1.0∼2.5 m, in the range of 2.5–3.5 m around the hydraulic drilling hole, the duration, rate, and amplitude of pressure relief are reduced compared with those in the range of less than 2.5 m, while in the range of more than 3.5 m, the effect of pressure relief is very weak. (2) During the period of hydraulic cavitation release hole, the radius of water supply to coal seam is within 1.5 m, which accounts for 79% of coal wall area. (3) It is also a process where the stress distribution in the coal and rock body needs to be rebalanced before and after hydraulic caverning, which is often accompanied by microfracture of coal and rock mass. The analysis shows that, before hydraulic caverning, the waveform of coal and rock fracture signal has a short duration, large amplitude, and obvious signal mutation, and the dominant frequency of the signal is about 250 Hz, with large total energy. After hydraulic caverning, the intensity of coal and rock fracture events is greatly reduced. The research results can effectively identify the influence range of hydraulic cavitation, improve the detection accuracy and efficiency of hydraulic cavitation range, effectively predict and warn the hidden danger of mine safety, and provide a reference for the work of similar mines.

Multifield Coupling Mechanism of Unloading Deformation and Fracture of Composite Coal-Rock

The deformation and fracture evolution of coal and rock under unloading are prone to sudden instability or dynamic damage. To solve the problem, this paper combines interdisciplinary theories such as damage mechanics and electromagnetic field theory. The mathematical model of multiphysics coupling during loading and unloading of composite coal-rock is deduced. In addition, numerical simulations along with experimental verification are carried out to study multi-physical field variation and coupling mechanisms. The composite coal-rock deforms and ruptures under unloading, and the brittle failure of the rock body becomes more sudden when the confining pressure is unloaded. Macroscopically, many microcracks are generated and expanded during the loading and unloading of composite coal-rock. Microscopically, the internal old molecular chains are broken to form new molecular chains by the force. Simulation results show that, during the loading and unloading process, the three physical fields of the composite coal-rock all change regularly. During the unloading of coal and rock, there is a transition period in which the temperature increases sharply and reaches the maximum. Then, the temperature decreases due to the gradual decrease of its bearing capacity. Besides, the electromagnetic field is strongest on the surface of the coal body, and its propagation in the air decays exponentially. There are small fluctuations that appear at the junction of the coal body and the air. The experimental results show that the internal infrared radiation temperature of the composite coal-rock decreases during the initial stage of loading and unloading due to the discharge of internal gas. In the first stage of “loading and unloading,” it increases with the increase in stress, and the temperature suddenly increases in a short time after unloading. The electromagnetic radiation fluctuates in small amplitudes at the initial stage. When the stress is about to reach the peak, the electromagnetic radiation intensity increases and reaches the peak suddenly. Then, the coal-rock ruptures, the stress decreases, and the electromagnetic radiation weakens. The experiment and simulation results are consistent. The multiphysics coupling model is used to study the characteristics of coal and rock unloading under complex conditions, providing a theoretical basis and new method for the prediction and forecast of coal and rock mining dynamic disasters.

Contrasting metamorphic and post-metamorphic evolutions within the Algyő basement high (Tisza Mega-unit, SE Hungary). Consequences for structural history

The Algyő High (AH) is an elevated crystalline block in southeastern Hungary covered by thick Neogene sediments. Although productive hydrocarbon reservoirs are found in these Neogene sequences, numerous fractured reservoirs also occur in the pre-Neogene basement of the Pannonian Basin. Based on these analogies, the rock body of the AH might also play a key role in fluid storage and migration; however, its structure and therefore the reservoir potential is little known. Based on a comprehensive petrologic study in conjunction with analysis of the spatial position of the major lithologies, the AH is considered to have been assembled from blocks with different petrographic features and metamorphic history. The most common lithologies of garnet-kyanite gneiss and mica schist associated with garnetiferous amphibolite are dominant in the northwestern and southeastern parts of the AH. The first regional amphibolite facies metamorphism of the gneiss and mica schist was overprinted by a contact metamorphic (metasomatic) event during decompression in the stability field of kyanite. Garnet-bearing amphibolite experienced amphibolite facies peak conditions comparable with the host gneiss. Regarding the similarities in petrologic features, the northwestern and southeastern parts of the area represent disaggregated blocks of the same rock body. The central part of the AH area is characterized by an epidote gneiss-dominated block metamorphosed along with a greenschist-facies retrograde pathway as well as a chlorite schist-dominated block formed by greenschist-facies progressive metamorphism. The independent evolution of these two blocks is further confirmed by the presence of a propylitic overprint in the chlorite schists. The different metamorphic blocks of the northwestern, southeastern and central parts of the AH probably became juxtaposed along post-metamorphic normal faults developed due to extensional processes. The supposed brittle structural boundaries between the blocks could have provided hydrocarbon migration pathways from the adjacent over-pressured sub-basins, or could even represent suitable reservoirs.

Flow-induced microfracturing of granite in superhot geothermal environments

<p>Superhot geothermal environments with temperatures of approximately 400-500<sup>︒</sup>C at depth of approximately 2-4 km are expected as a new geothermal energy frontier. In order to efficiently exploit the superhot geothermal resources, fracture systems are necessary as flow path of working fluid. Hydraulic fracturing is a promising technique because it is able to create a new fracture system or enhance the permeability of preexisting fracture system. Laboratory-scale hydraulic fracturing experiments of granite have demonstrated the formation of densely distributed network of permeable fractures throughout the entire rock body at or near the supercritical temperature for water. Though the process has been presumed to involve continuous infiltration of low-viscosity water into preexisting microfractures followed by creation and merger of the subsequent fractures, plausible criterion for the fracturing is yet to be clarified. The possibility that the Griffith failure criterion is available to predict the occurrence of fracturing was shown by hydraulic fracturing experiments with acoustic emission measurements of granite at 400<sup>︒</sup>C under true triaxial stress. The present study provides a theoretical basis required to establish the procedure for hydraulic fracturing in superhot geothermal environment.</p>