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The Wondong Fe-Pb-Zn polymetallic skarn deposit is located in the Taebaeksan Basin, South Korea. This deposit is associated with the Paleocene quartz porphyry and characterized by abundant exoskarn and subordinate endoskarn. A general zonation pattern is developed comprising a proximal reddish-brown garnet-rich zone, a distal greenish garnet ± pyroxene zone, and a wollastonite-rich zone at the marble front. The mineralization is characterized by Fe in the proximal garnet-rich zone and Pb-Zn within and beyond the garnet ± pyroxene zone. In general, skarn deposits show complex geophysical signatures in their rock properties in relation to metasomatism. Garnet-rich and garnet ± pyroxene skarns accompanying Fe-oxides and sulfides are significantly denser (3.3–3.4 g/cm 3 ) than the other rocks (2.5–3.0 g/cm 3 ) such as quartz porphyry, wollastonite-rich skarn, and silicic hornfels. Reactions related to creating garnet may increase porosity, which promotes further infiltration and reaction to produce garnet growth. The porosity of skarn rocks (1.8–8.4%) has a broad range and is generally higher than the other rocks (0.8–3.3%). In contrast, most skarn rocks show a remarkably low electrical resistivity (mostly 211–848 Ωm) than the other rocks (1,815–8,601 Ωm). Magnetic susceptibilities of skarn rocks (15–140 × 10 –5 SI) are higher than quartz porphyry and siliceous hornfels (<25 × 10 –5 SI). P wave velocities in the garnet ± pyroxene zone at the skarn front show lower values (1,487–3,674 m/s) than the other rocks (2,902–5,590 m/s), which is likely related to the porosity of the rocks. Thus, in general, the physical properties of rocks as exampled above from the skarn environment reflect their mineral assemblages and can be used for mineral exploration of skarn deposits.

Monitoring the leakage of leachate from a landfill is critical in preventing possible contamination in the surrounding area. Time-lapse (TL) electrical resistivity tomography (ERT) has been performed along eleven survey lines at four different time points in a landfill in Korea. The TL data sets were interpreted using an in-house 4D inversion algorithm. Changes in 4D inversion results were analyzed in order to interpret a leachate-contaminant region. Since the rainy season started during obtaining TL ERT data sets, the effects of precipitation on TL ERT data are also analyzed. Changes in electrical resistivity (ER) showed that precipitation increases ER of contaminant zones. As hydrogeochemical data offer contamination information in some areas where boreholes are located, these are helpful to interpret and compare with ERT inversion results to evaluate the extent of the contaminated plume. We also classified soil textures from particle size analysis on soil samples and analyzed electrical conductivity (EC) and dissolved oxygen (DO) using groundwater samples obtained from observation wells in the survey site. The information on soil structure as well as the results of 4D inversion provided insight into the location of a preferential flow path.

The main goal of active fault investigation is obtaining evidence of the Quaternary fault activity through trenching. To accomplish this, electrical resistivity surveys are widely utilized to accurately detect faults buried beneath alluvium. In this study, 2D and 3D electrical resistivity surveys were conducted at the Miho site of the southern Yangsan Fault, the Quaternary active fault area already well-studied via trench investigations. The efficacy of electrical resistivity surveys for fault detection was examined by comparing the resistivity distributions against data in the trench logs. At the Miho site, three lines were installed for the 2D electrical resistivity survey and 22 lines were set within a 27 × 27 m square area for the 3D electrical resistivity survey. The length of each survey line was 27 m with an electrode spacing of 1 m. A dipole-dipole array was used to measure the potential difference between each measurement electrode using the same transmitted current and voltage. To derive the 2D and 3D resistivity distributions from the data acquired in the field, the inversion programs DC_2DPRO and DC_3DPRO were employed. Comparison of the 2D resistivity distribution with trench log data shows that the zone of dacitic welded tuff west of the Quaternary fault plane has relatively high resistivity, while the zone of foliate gouge and breccia derived from sedimentary rocks east of the Quaternary fault plane has a low resistivity of less than 40 Ω·m. From these results, it is evident that the method is effective, particularly when different rock types are distributed on either side of the fault boundary or when highly conductive materials, such as clay-rich fault gouges, are present within the fault zone. The resistivity distribution in the 3D survey area can be depicted using both block diagrams and depth-specific slices, facilitating a spatial understanding of the continuity of fault (or fracture) zones. Consequently, this study demonstrates that 3D surveys offer numerous advantages over 2D surveys by accurately capturing planar structures and enabling spatial interpretation based on 3D resistivity distribution.

The highway of Yongweol-ri, Muan-gun, south-western part of the South Korean Peninsula, is underlain by the abandoned of subsurface cavities, which were discovered in 2005. These cavities lie at shallow depths with the range of 5∼15 meters below the ground surface. Numerous subsidence events have repeatedly occurred in the past few years, damaging infrastructure and highway. As a result of continuing subsidence issues, the Korean Institute of Geosciences and Mineral Resources (KIGAM) was requested by local administration to resolve the issue. The KIGAM used geophysical methods to delineate subsurface cavities and improve more refined understanding of the cavities network in the study area. Cement based grouting has been widely employed in the construction industry to reinforce subsurface ground. In this research work, time-lapse electrical resistivity surveys were accomplished to monitor the grouting injection in the subsurface cavities beneath the highway, which have provided a quasi-real-time monitoring for modifying the subsurface cavities related to ground reinforcement, which would be difficult with direct methods. The results obtained from time-lapse electrical resistivity technique have satisfactory imaged the grouting injection experiment in the subsurface cavities beneath the highway. Furthermore, the borehole camera confirmed the presence of grouting material in the subsurface cavities, and hence this procedure increases the mechanical resistance of subsurface cavities below the highway.

Karst voids were encountered during road construction in Yongweol-ri, South Korea Attempts to determine the extent of the karst voids through drilling was expensive, time-consuming and too dangerous An electrical resistivity survey was thus carried out to investigate current subsurface geology beneath the proposed road network. This investigation was aimed at imaging karstic voids and detecting areas prone to ground subsidence through the collapse of cavities beneath a road segment overlying such features A numerical modelling study preceded the field survey to determine whether the electrical resistivity method could identify such features. The field data set consisted of eleven electric profiles acquired using dipole-dipole array; electrical resistivity profiles (100 m and 300 m length) were measured using a dipole-dipole electrode configuration and electrode spacing was kept at 5 m to ensure good coverage of the study area. The resistivity data was inverted using 2D and 3D algorithms based on the least squares smoothness constraint technique. The inverted resistivity images provide a clear view of weathered soils, the distribution of weak areas or karst voids and bed rock. Several low resistivity areas were identified and the subsequent drilling of such anomalous areas led to the discovery of several weak zones or clayfilled underground cavities; the drilling results had excellent correlation with the resistivity images. The electrical resistivity imaging result proved precise and extremely efficient in delineating the karstic void investigation and should be taken into account when choosing an investigation technique to be used at complex geological sites A remedial action plan involving consolidation grouting work has been suggested prior to road construction

Recently, the electrical resistivity tomography (ERT) technique has been increasingly applied to underground cavity detection filled with groundwater and/or clay. In this study, an ERT survey was conducted to examine the spatial distribution and shape of underground cavities in a karst area in Korea. Numerical ERT modeling and inversion were carried out to select appropriate field survey parameters. Two geological structures, similar to those that exist in the field survey area, were modeled: a sinkhole model and a vein-type structure. Electrode configurations using pole–pole, pole–dipole, dipole–pole, and dipole–dipole arrays were tested with the two geologic models and compared. The numerical modeling showed that the resistivity distribution of the ERT tomogram using the pole–dipole array produced the best representation of the two models. The pole–dipole and pole–pole array configurations were applied in an ERT field survey using six boreholes. The field ERT results show that cavity areas filled with clay or groundwater appeared as low-resistivity anomalies in the limestone formation. This was particularly evident in the inclined vein-type structures attributed to fracture zones, where the field data were similar to the modeling results. Therefore, the ERT technique could be effectively used for detecting underground limestone cavities under similar geological conditions as those at our study area.

Spectral-induced polarization (SIP) using the electrochemical reaction at the interface between mineral particle and groundwater is a powerful tool for the exploration of minerals. However, SIP responses of rocks have not been fully characterized because it is influenced by various petrological properties. In this study, the relationship between SIP responses and the petrological features of representative rocks from skarn deposits was analyzed. For the evaluation of the SIP responses, chargeability and relaxation time of time domain induced polarization (IP) were calculated by an equivalent circuit analysis. Among various circuit models used for the analysis, an existing circuit model was utilized for this study because it sufficiently describes the electrochemical reaction of water-saturated rocks and is more suitable for the analysis of heterogeneous rocks than the other models. The circuit model was found to be appropriate because the normalized root mean square error between the observed values and ones obtained through the model fittings reasonably low, ranging from 4.18 to 0.05 %. The chargeability values of the mineralized rocks were higher than those of the non-mineralized rocks (igneous and carbonates), and the relaxation time was related to the grain size of the magnetite. It was found that the SIP characteristics of the mineralized rocks are dependent on features of the ore minerals. In the non-mineralized rocks, there was little difference in the chargeability, whereas the variation in their relaxation time values was influenced by the feldspar content (sericitization) and the grain size of the calcite (recrystallization). The SIP characteristics of the non-mineralized rocks are considered to be dependent on the grade of the hydrothermal alteration.

Purpose – Turbulent air flows within a channel with 45° angled rib turbulators on the top and bottom walls are numerically predicted using the numerical code. For the predictions, a v2-f turbulence model (velocity variance scale and elliptic relaxation factor model) is utilized. The paper aims to discuss these issues. Design/methodology/approach – Three different rib arrangements with or without gap are investigated to present information on the effects of gap size on flow structure and heat transfer characteristics. Three-dimensional turbulent transport, and detailed flow structural characteristics are considered to provide new insight into the mechanisms which result in surface heat transfer augmentations. Findings – Compared to the baseline rib arrangement, the numerically predicted results show that the parallel ribs with gap (where the width of the gap is two times of rib height) shows the highest local Nusselt number ratios. This is a result of locally increased vorticity distributions, as well as augmented local magnitudes of mixing, secondary flows, and turbulent transport. Local transport changes are less pronounced when the gap width of gap is 0.5 times of rib height. As a result, associated local and spatially averaged Nusselt number ratios are also lower for this arrangement. Practical implications – Results will give improved heat transfer augmentation technologies. Originality/value – The present investigation provides new information and insight into flow structural characteristics in a channel with rib turbulators, both with and without gaps, especially the mechanisms which result in surface heat transfer augmentations, which are not available in any other existing numerical or experimental investigation.

We develop a two-stage method to invert induced polarization (IP) data. First, DC resistivity data are inverted to recover a background resistivity that is used to generate a sensitivity matrix for the IP inversion. The second stage accepts the background resistivity as the true resistivity of the medium and attempts to find a polarizability that satisfies the IP data. This is done by linearizing the equations for the background resistivity to produce a linear inverse problem that can be solved for the distribution of the subsurface polarizability. Smoothness and base-model constraints are used to stabilize the IP inversion process. These regularization methods are validated by inverting both synthetic and field data obtained in the Haenam epithermal mineralized area, Korea. As a result, the IP anomaly recovered from the base-model constraint indicates that fine-grained pyrite is disseminated in a shallow zone beneath the ridge of this site, which is confirmed by core samples.

Turbulent air flows within a channel with angled rib turbulators (45 degrees) on one wall are numerically predicted using the numerical code ANSYS CFX with a Shear-stress transport (SST) κ-ω turbulence model, and a hexahedral grid with 7115346 cells and no wall function. Three-dimensional turbulent transport, and detailed flow structural characteristics are considered to provide new insight into the mechanisms which result in surface heat transfer augmentations. Time-averaged turbulent flow characteristics and surface Nusselt number distributions are presented for an inlet turbulence intensity level of 1.0 percent, and for Reynolds numbers based upon channel height of 18300 and 48000. Overall, the numerically-predicted results show that large-scale, secondary flow induces a collection of small-scale vortical flows in the channel, as a result of local interactions with individual rib turbulators. These are often associated with different sized and highly skewed vortex pairs, which also induce secondary advection and increased turbulent mixing near ribbed channel surfaces. Within the flow separation regions, just downstream of each rib, surface Nusselt number ratios which are locally lower than for other surface locations, and local secondary flows are generally and partially characterized as upwash flows, with large positive magnitudes of spanwise vorticity, large static pressure deficits, and large static pressure augmentation regions. As the shear layers (initially located above the recirculation zones) impinge onto the test surface, increased mixing develops, as well as local thinning of the reattaching boundary layers, which lead to local Nusselt numbers which are generally higher than for other locations along the test surface.