Investigation of ferroelectric effects in two sulfide deposits

Journal of Applied Geophysics, 1994

Laboratory studies by different investigators using various techniques have expanded the number of known ferroelectric ore minerals to about twenty at present from the first discovery of makedonite (PbTiO 3) in 1950. These include such common ore minerals as bismuthinite (Bi 2S 3), cassiterite (SnO 2), chalcocite (Cu 2S), pyrrhotite (Fe 1- xS), and stibnite (Sb 2S 3). Two field investigations of sulfide ore bodies that contain known ferroelectric minerals were undertaken to investigate possible in-situ effects in these deposits. These deposits, at Mount Emmons (38°53'N, 107°03'W), Colorado, and Three R Canyon (31°28'N, 110°46'W) in the Patagonia Mountains, Arizona, demonstrate ferroelectric effects that include directional polarization and apparent resistivity, electrically-excited resonance, and lack of reciprocity. Other phenomena include history-dependent electrical behavior and inductive effects. Ferroelectrics polarize as a function of applied potential. It is much easier to generate a large potential than the high currents commonly used in IP surveys. Thus, in electrical surveys of deposits known, or suspected, to contain ferroelectric minerals it may be advantageous to maximize the applied potential. It may also be relatively easy to induce electrical resonance in these deposits that could provide an inexpensive reconnaissance technique. In IP and CR surveys, ferroelectric effects can mask the deposit since ϱa may approach zero in the polar direction, or chargeability may be undetectable. Phase relations will most likely be uninterpretable in CR surveys over such deposits. In CSAMT surveys, directional resonance effects may preclude depth interpretation. Frequency-dependent inductive and capacitive effects may be observed in CR and CSAMT surveys over deposits containing significant quantities of ferroelectric minerals. Ferroelectricity may also be useful in exploitation efforts for electrical beneficiation during ore processing.

1996

Significant electrical resistivity anisotropy, up to 1OO0:1, has been observed in rock samples containing sulphides and samples barren of sulphides. Anisotropy associated with sulphides generally has nsistivity in one direction within the typical ground EM detection limit (less than IO but in the perpendicular directions the resitivity can be well above this limit (100 to 19,000 Such examples have been observed in rocks from Snow Lake (Manitoba), the Bathurst Mining Camp (New Brunswick) and the Trans-Hudson orogen (Saskatchewan). The Snow Lake study was the first of these studies and was carried out to seek an explanation for the weaker than expected electromagnetic (EM) responses of several of tbe sulphide bodies in the region. This continuing study attempts to understand the electrical mechanisms involved in such anisotropic processes in order to provide information for development of improved EM interpretation and survey methods, and of improved EM instrumentation.

Open-File Report, 1996

Journal of Geophysical Research, 1986

Electrical impedance in a partially molten gabbro was measured with the two-electrode method in the frequency range of 0.032 Hz to 10 kHz. Samples of different thicknesses were used to separate the bulk polarization effect from the sample-electrode interface polarization effect. The measurements show that both real and imaginary impedances increase linearly with increasing sample thickness. When the impedance data are extrapolated to zero thickness, the real impedance is as small as the experimental error, whereas the imaginary impedance has a finite value. This result indicates that the real impedance is mainly controlled by the electrical properties of the partially molten gabbro itself and that only small amounts of electrode interface polarization contribute to the imaginary impedance. After correction for the interface polarization effect, the present data were analyzed by the theoretical expression that describes the electrical impedance of partially molten rocks. The results show that frequency dispersion of electrical impedance in partially molten gabbro is associated with the polarization effect of ions in the partial melt. Introduct ion Anomalously high electrical conductivity zones have been inferred in the earth's upper mantle from geomagnetic variation data [Porath and Gough, 1971; Honkura, 1974; Filloux, 1980; Oldenburg, 1981]. On the basis of laboratory conductivity data, these anomalous zones have been associated with partial melting in the upper mantle [Shankland and Waff, 1977; Oldenburg, 1981; Shankland et al., 1981]. However, the frequency range of geomagnetic variations ordinarily is much lower (<0.1 Hz) than that of laboratory conductivity measurements (>100 Hz). To cover this frequency gap, Sato and Ida [1984] developed a method to determine electrical impedance of rocks as a function of frequency in the range 10 -3~ 104 Hz. This method was used to show that the conductivity of partially molten gabbro depends on frequency even at very low frequencies (<1 Hz). Such frequency dependence was related to the electrical properties of partial melt. The present work is an extension of that performed by Sato and Ida [1984]. Two platinum

Periodico Di Mineralogia, 2016

The Earth&#39;s core, mantle and crust are composed of rocks and minerals, and exhibit electrical and magnetic phenomena. Electrical data in particular are extremely sparse for Earth materials; fewer than one hundred minerals have piezoelectric data associated with them, for example. More data would help to constrain Earth processes and structures, such as core and mantle composition, geomagnetic anomalies, seismic electric signals, and others. Herein, two hundred seventeen minerals exhibiting ferroelectricity, pyroelectricity or piezoelectricity are presented, with quantitative data where known. Fifty-three of these are centrosymmetric, and explanations are given for their apparent violations of crystal theory. Some thermoelectric and magnetic data are also presented for minerals, and an overview of rock electricity is included. Recommendations for further study are given, as well, such as determining the dielectric behavior of rocks and minerals at depth, and testing minerals for ...

Geophysical Research Letters, 1987

A structural phase transition, conductivity and dielectric permittivity anomalies, together with a polarization hysteresis loop which collapses above the Curie temperature (~105øC) provide converging lines of evidence for ferroelectricity in the single and polycrystalline natural samples of chalcocite, Cu2S, investigated. Chalcocite is an important ore of copper, and its electrical properties are a factor both in exploration for the mineral and processing the ore.

Pakistan Journal of Geology

This paper focuses on the review of electrical geophysical methods such as electrical resistivity and induced polarization as a technique for mineral exploration. It highlights the general fundamental principles of the electrical methods and result from other investigations. Most rock – forming minerals are insulators, and electrical current is carried through rocks mainly by the passage of ions in pore waters. In light of this, most rocks conduct electricity by electrolytic rather than electronic processes. Since metals and most metallic sulphides conduct electricity efficiently by the flow of electrons, electrical method is efficient and important in environmental investigation especially in areas where metallic objects are the targets and also in the search for sulphide ores. The results from various research showed the applicability of these geophysical ground methods, specially the Induce Polarization method, as a support tool in the identification and selection of exploration ...

Journal of Applied Geophysics, 2012

Sulphate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulphate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulphate) is frequently found in gypsum quarries and in non-outcropping sulphates. The greater hardness of anhydrite compared to gypsum causes a problem for gypsum extraction; quarry fronts have to be halted as soon as anhydrite is found. In this work the electrical properties of calcium sulphates have been studied by means of geoelectrical methods. A direct relationship between the electrical conductivity values of the calcium sulphate rocks and their lithological composition has been established with the lutitic matrix being the main controlling factor when it is well connected. When the matrix is under the percolation threshold the sulphate phases are dominant, and the electrical response of the rocks depends on the percentage of each phase. When the rock is matrix dominant, the electrical resistivity trend fits with the Hashin-2nd revision Click here to view linked References 2 Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulphate dominant the trend shows the one of the Hashin-Shtrikman upper bound. The reference electrical resistivity value of pure anhydrite rocks has been defined as 10 4 Ω.m and geoelectrical classification for calcium sulphate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulphate rocks with different composition from their electrical resistivity value. This classification has been checked with field examples and calculating the theoretical resistivity value of thin section photographs with the program ELECFEM2D. The electrical behavior of calcium sulphate rocks is a good reference for other type of rocks with electrically differentiated components, and similar methods can be used to define their geoelectrical responses.

2016

The Earth’s core, mantle and crust are composed of rocks and minerals, and exhibit electrical and magnetic phenomena. Electrical data in particular are extremely sparse for Earth materials; fewer than one hundred minerals have piezoelectric data associated with them, for example. This type of data helps to constrain Earth processes and structures, such as core and mantle composition, geomagnetic anomalies, seismic electric signals, and others. In this review, two hundred seventeen minerals exhibiting ferroelectricity, pyroelectricity or piezoelectricity are presented, with quantitative data where known. Fifty-three of these are centrosymmetric, and explanations are given for their apparent violations of crystal theory. Some thermoelectric and magnetic data are also presented for minerals, and an overview of rock electricity is included. Recommendations for further study are given, as well, such as determining the dielectric behavior of rocks and minerals at depth, and testing minerals for alternative energy applications.

Minerals

Disseminated ores in porous or fractured media can be polarized under the application of an external low-frequency electrical field. This polarization is characterized by a dimensionless property that is called the “chargeability”. Induced polarization is a nonintrusive geophysical sensing technique that be used in the field to image both the electrical conductivity and the chargeability of porous rocks together with a characteristic relaxation time. A petrophysical model of the induced polarization of metallic ores immersed in a porous conductive and polarizable material is reviewed, and its predictions are compared to a large dataset of experimental data. The model shows that the chargeability of the material is linearly dependent on the volume fraction of the ore and the chargeability of the background material, which can, in turn, be related to the conductivity of the pore water and the cation exchange capacity of the clay fraction. The relaxation time depends on the grain sizes...