Deep Gold Exploration with SQUID TEM in the Qingchengzi Orefield, Eastern Liaoning, Northeast China

The Qingchengzi orefield is an important polymetallic ore concentration zone in the northern margin of the North China Craton (NCC). The region has significant metallogenic potential for deep mining. Many areas with gold mineralization have been found in the shallow area of Taoyuan–Xiaotongjiapuzi–Linjiasandaogou in the east of the Qingchengzi orefield. To assess the distribution of mineralization levels, we carried out deep exploration using the transient electromagnetic method (TEM). A superconductive quantum interference device (SQUID) magnetometer and a conventional induction coil were used for field data acquisition. The SQUID data inversion results reflect the bottom interface of the high-conductivity area, the fold state of the underlying dolomite marble stratum, and the deep structural characteristics of the syncline. Secondary crumples appear in the inversion results of the southern segment of TEM, which is inferred as a favorable area for deep gold mineralization. Negative values appear in the SQUID data of some stations, to varying degrees. This induced polarization phenomenon may be related to deep gold mineralization.

Laplace Transform for Finite Element Analysis of Electromagnetic Interferences in Underground Metallic Structures

A numerical methodology is proposed for the calculation of transient electromagnetic interference induced by overhead high-voltage power lines in metallic structures buried in soil—pipelines for oil or gas transportation. A series of 2D finite element simulations was employed to sample the harmonic response of a given geometry section. The numerical inverse Laplace transform of the results allowed obtaining the time domain evolution of the induced voltages and currents in the buried conductors, for any given condition of the power line.

Recharge mechanism and salinization processes in coastal aquifers in Nam Dinh province, Vietnam

In Nam Dinh province, in the Red River delta plain in Northern Vietnam, groundwater in the shallow Holocene aquifer shows elevated total dissolved solids up to 35 km from the coastline, indicating a saltwater intrusion from the Gulf of Tonkin. High groundwater salinities have been encountered below and adjacent to the Red River in the deep Pleistocene aquifer. Since 1996, large-scale groundwater abstraction was initiated from the deep aquifer, and the observed elevated salinities now raise concerns about whether the groundwater abstraction is undertaken sustainably. We have conducted a study to obtain a fundamental understanding of the recharge mechanisms and salinization processes in the Nam Dinh province. A holistic approach with multiple methods including transient electromagnetic sounding and borehole logging, exploratory drilling, sampling and analyzing primary ion and stable isotope compositions of water and pore water, groundwater head monitoring, hydraulic experiments laboratory of clay layers, and groundwater modeling by using the SEAWAT code. Results reveal that saline river water is leached from the Red River and its distributaries into the shallow aquifers. The distribution and occurrence of salty pore water in the Holocene aquitard clay shows that meteoric water has not been flowing through these low permeable clay layers. Marine pore water has, however, been leached out of the Pleistocene clay. When this layer is present, it offers protection of the lower aquifer against high salinity water from above. Salinity as high as 80 % of oceanic water is observed in interstitial pore water of the transgressive Holocene clay. Saltwater is transported into the Pleistocene aquifer, where the Holocene clay is directly overlying the aquifer.

Sizing by optimization of line-start synchronous motor

Purpose The purpose of this paper is to develop an algorithm and software for determining the size of a line-start permanent magnet synchronous motor (LSPMSMs) based on its optimization. Design/methodology/approach The software consists of an optimization procedure that cooperates with a FEM model to provide the desired behavior of the motor under consideration. The proposed improved version of the genetic algorithm has modifications enabling efficient optimization of LSPMSMs. The objective function consists of three important functional parameters describing the designed machine. The 2-D field-circuit mathematical model of the dynamics operation of the LSPMSMs consists of transient electromagnetic field equations, equations describing electric windings and mechanical motion equations. The model has been developed in the ANSYS Maxwell environment. Findings In this proposed approach, the set of design variables contains the variables describing the stator and rotor structure. The improved procedure of the optimization algorithm makes it possible to find an optimal motor structure with correct synchronization properties. The proposed modifications make the optimization procedure faster and more Originality/value This proposed approach can be successfully applied to solve the design problems of LSPMSMs.

Investigation of Multiple Hole Grouting for Reducing Water Inrush Risk in Underground Engineering

Reinforcement with grout as an environmentally friendly technology has played a key role in underground coal mining. The risk of the water inrush into coal mines can all be reduced by grouting. A model that integrates a geographic information system (GIS), distribution of quantity of grouting injected, and water inflow correlation method is proposed here to evaluate the effects of grouted reinforcement in coal mining. The temporal and spatial characteristics of the volume of grout injected and water yield of aquifers are analyzed by using the GIS, and the rate of filling of cement slurry and its distribution characteristics are determined. The effects of grouting on the aquifers which has been carried out to reduce their permeability are determined by comparing the spatial temporal variations in the volume of the grout injected, water yield, and rate of filling of the cement slurry. The method was applied in a case study in a coalmine in Henan province, China, in which the risk of the water inrush from karst aquifers has been reduced by grouting. There are three limestone aquifers, namely, L8, L10, and L11 which underlie an exploitable coal seam. The result indicates that most of the cement slurry is consumed when the water yield is 20 to 30 m3/h; and that there are minimal changes of the electrical properties of the rock stratum under coal seam when the water yield of L11 is low within the range of 40 m. The resistivity of the aquifers before and after grouting and their spatial characteristics are tested by using the transient electromagnetic method (TEM), and this shows that there are no areas with low resistivity. The electrical properties of the strata at a depth that ranges from 40–80 m with transverse homogeneity show that Aquifers L10 and L11 have been transformed into aquicludes. The reinforcement effect of aquifers with grout is good.

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

Mapping Saltwater Intrusion using Transient ElectroMagnetic Data in Maopa, Central Province, Papua New Guinea

<p>Saltwater intrusion studies in coastal Papua New Guinea (PNG) are a rarity despite recognized vulnerabilities to salination of coastal groundwater resources. For many seaside communities such as Maopa the threat of salination is exacerbated by high extraction rates by a growing population and the likelihood of the effects of climate change. Saltwater intrusion can be addressed using various methods, including direct water sampling from wells and electrical resistivity measurements. This study advances knowledge of a previous assessment of saltwater intrusion and groundwater in this region that used DC Schlumberger resistivity soundings, through an extensive and cost-effective Transient ElectroMagnetic (TEM) survey. The study aims to map the lateral and vertical extent of salination and the characterization of groundwater in the landward direction over seven lines of TEM soundings along Keakalo Bay. The TEM method proved successful in identifying four main geoelectric layers. The top layer has a highly variable resistivity (range of 5 to 355 Ωm) inferred as the vadose zone. Beneath this layer is a layer of intermediate resistivity (100 Ωm > p ≥ 20 Ωm) characterizing a perched freshwater aquifer with a thickness range of 3.2 to 15 m. An intermediate layer of low resistivity (20 Ωm > p ≥ 3 Ωm) was detected at the boundary separating the freshwater aquifer from the inferred saltwater intrusion. This layer is typically thicker than the freshwater aquifer and is referred to as the mixing zone. The deepest layer constituting the salination zone has a very low resistivity (3 Ωm > p ≥ 0.4 Ωm), occurring at depths of up to 42 m. The depth to the salination zone varied from deep in the middle of the survey area to shallow in the fringes of the survey. This pattern is reflective of surface seawater infiltration marked by mangrove forest in the interior and subsurface infiltration from the coast. Similar depth trends but at shallower depths were also observed for the mixing zone, and the freshwater region. In some cases the mixing area overwhelms the freshwater regions. Layering confirmed groundwater resource and salination patterns as those of basic models reflective of small island hydrology, except that salination and the freshwater boundary were less distinctive due to the relatively high thickness of the dispersion zone. The use of different sounding parameters in line 7 provided useful information about the nature of the deep basement unit and thickness of the overlying unconsolidated quaternary sediment.</p>

Technical note: Efficient imaging of hydrological units below lakes and fjords with a floating, transient electromagnetic system (FloaTEM)

Imagining geological layers beneath lakes, rivers, and shallow seawater provides detailed information critical for hydrological modelling, geologic studies, contaminant mapping, and more. However, significant engineering and interpretation challenges have limited the applications, preventing widespread adoption in aquatic environments. We have developed a towed transient electromagnetic (tTEM) system to a new, easily configurable floating, transient electromagnetic instrument (FloaTEM) capable of imaging the subsurface beneath both fresh and saltwater water bodies. Based on the terrestrial tTEM instrument, the FloaTEM system utilizes a similar philosophy of a lightweight towed transmitter with a trailing, offset receiver, pulled by a small boat. The FloaTEM system is tailored to the specific fresh or saltwater application as necessary, allowing investigations down to 100 m in freshwater environments, and up to 20 m on saline waters. Through synthetic analysis we show how the depth of investigation of the FloaTEM system greatly depends on the resistivity and thickness of the water column. The system has been successfully deployed in Denmark for a variety of hydrologic investigations, improving the ability to understand and model processes beneath water bodies. We present two freshwater applications and a saltwater application. Imaging results reveal significant heterogeneities in the sediment types below the freshwater lakes. The saline water example demonstrates that the system is capable to identify and distinguish clay and sand layers below the saline water column.