Geoelectrical prospecting of glauberite deposits in the Ebro basin (Spain)
- Guinea, Ander, Playà, Elisabet, Rivero, Lluís, Salvany, Josep
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Salvany, Josep
- Date: 2014
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 174, no. (2014), p. 73-86
- Full Text:
- Reviewed:
- Description: Glauberite (Na2Ca[SO4]2) is an evaporitic mineral which is used in the industries of detergents, paper, glass, pharmacy, etc. Glauberite rocks are seldom found cropping out because they are very sensitive to weathering processes; for this reason their prospection is conducted by means of boreholes. Nowadays, geophysical techniques are not used to support the characterization of glauberite deposits due to the lack of knowledge of their physical properties.In this study geoelectrical methods are proposed as alternative techniques in the early stages of glauberite prospecting. Several glauberite units have been studied in different parts of the Ebro basin (Spain) by means of electrical resistivity tomography sections. The electrical resistivity range showed by glauberite deposits has been found to be low (10–100Ω·m) when the matrix component (clay and microcrystalline carbonates) is above 45% of the bulk composition of the rock. This type of rocks has been studied in Montes de Torrero (Zaragoza) and is the most common glauberite deposit case. Besides matrix-rich glauberite rocks, an exceptional case of a pure glauberite layer has been studied in Alcanadre (La Rioja). From this site, it has been estimated that deposits with glauberite crystal fraction close to 100% show a resistivity range of at least 3×103Ω·m.Using this extreme value as reference, the Hashin–Shtrikman bounds have been calculated for glauberite rocks considering that they are constituted of four phases (glauberite, gypsum, anhydrite and matrix). When the matrix fraction represents 45% or more of the bulk rock, the resistivity range will be that of the lower Hashin–Shtrikman bound, which is similar for any combination of sulfate (glauberite, gypsum and/or anhydrite) composition; hence, it can be considered as a two-phase system (matrix and sulfate). For rocks with less than 30% of matrix fraction, the upper Hashin–Shtrikman bound trend must be considered; however, the resistivity values overlap, making it impossible to establish a classification. Between 30 and 45% of matrix fraction, there is a transitional domain.Additionally, some theoretical models representing the most common structures in sulfate rocks have been elaborated in order to help in the interpretation of the inverted resistivity images obtained from the field data. Some artifacts generated by the complexity of the resistivity distribution of the terrain have been identified in both data sets. •Glauberite deposits are studied by means of electrical resistivity tomography.•The results of electrical imaging are compared with borehole cores.•Models representing typical structures in sulfates are compared with field results.•The electrical response of glauberite rocks for different compositions is defined.
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Salvany, Josep
- Date: 2014
- Type: Text , Journal article
- Relation: Engineering Geology Vol. 174, no. (2014), p. 73-86
- Full Text:
- Reviewed:
- Description: Glauberite (Na2Ca[SO4]2) is an evaporitic mineral which is used in the industries of detergents, paper, glass, pharmacy, etc. Glauberite rocks are seldom found cropping out because they are very sensitive to weathering processes; for this reason their prospection is conducted by means of boreholes. Nowadays, geophysical techniques are not used to support the characterization of glauberite deposits due to the lack of knowledge of their physical properties.In this study geoelectrical methods are proposed as alternative techniques in the early stages of glauberite prospecting. Several glauberite units have been studied in different parts of the Ebro basin (Spain) by means of electrical resistivity tomography sections. The electrical resistivity range showed by glauberite deposits has been found to be low (10–100Ω·m) when the matrix component (clay and microcrystalline carbonates) is above 45% of the bulk composition of the rock. This type of rocks has been studied in Montes de Torrero (Zaragoza) and is the most common glauberite deposit case. Besides matrix-rich glauberite rocks, an exceptional case of a pure glauberite layer has been studied in Alcanadre (La Rioja). From this site, it has been estimated that deposits with glauberite crystal fraction close to 100% show a resistivity range of at least 3×103Ω·m.Using this extreme value as reference, the Hashin–Shtrikman bounds have been calculated for glauberite rocks considering that they are constituted of four phases (glauberite, gypsum, anhydrite and matrix). When the matrix fraction represents 45% or more of the bulk rock, the resistivity range will be that of the lower Hashin–Shtrikman bound, which is similar for any combination of sulfate (glauberite, gypsum and/or anhydrite) composition; hence, it can be considered as a two-phase system (matrix and sulfate). For rocks with less than 30% of matrix fraction, the upper Hashin–Shtrikman bound trend must be considered; however, the resistivity values overlap, making it impossible to establish a classification. Between 30 and 45% of matrix fraction, there is a transitional domain.Additionally, some theoretical models representing the most common structures in sulfate rocks have been elaborated in order to help in the interpretation of the inverted resistivity images obtained from the field data. Some artifacts generated by the complexity of the resistivity distribution of the terrain have been identified in both data sets. •Glauberite deposits are studied by means of electrical resistivity tomography.•The results of electrical imaging are compared with borehole cores.•Models representing typical structures in sulfates are compared with field results.•The electrical response of glauberite rocks for different compositions is defined.
Electrical resistivity tomography applied at different stages of gypsum exploitation
- Guinea, Ander, Martínez, N., Playà, Elisabet, Rivero, Lluís, Casas, Albert
- Authors: Guinea, Ander , Martínez, N. , Playà, Elisabet , Rivero, Lluís , Casas, Albert
- Date: 2012
- Type: Text , Conference paper
- Relation: 18th European Meeting of Environmental and Engineering Geophysics of the Near Surface Geoscience Division of EAGE, Near Surface Geoscience 2012
- Full Text: false
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- Description: During the extraction of the rock in gypsum quarries, one of the most important parameter is the compositional changes in the deposit. Sudden changes in the purity makes the processing of the raw material less profitable. A resistivity survey has been carried out in an active gypsum quarry in the Gelsa Gypsum unit (Zaragoza, N Spain). The performed electrical resistivity tomography profiles have shown different gypsum layers from which the purest layers have been identified. These variations are displayed as changes in the conductivity of the rocks due to the presence of matrix. Additionally to the quarry front profiles, the quality of the gypsum deposits of a nearby area has been studied by parallel lines in order to evaluate the possibility of future exploitation. Additionally to the geophysical survey, the different gypsum levels of the quarry have been sampled in order to characterize them mineralogycally. With all this information, the planning of the present and future works can be improved.
The electrical properties of calcium sulfate rocks from decametric to micrometric scale
- Guinea, Ander, Playà, Elisabet, Rivero, Lluís, Ledo, Juan José, Queralt, Pilar
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Ledo, Juan José , Queralt, Pilar
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Applied Geophysics Vol. 85, no. (2012), p. 80-91
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- Description: Sulfate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulfate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulfate) is frequently found in gypsum quarries and in non-outcropping sulfates. 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 sulfates have been studied by means of geoelectrical methods.A direct relationship between the electrical conductivity values of the calcium sulfate 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 sulfate 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–Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulfate 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 104Ω·m and geoelectrical classification for calcium sulfate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulfate 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 sulfate 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.
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Ledo, Juan José , Queralt, Pilar
- Date: 2012
- Type: Text , Journal article
- Relation: Journal of Applied Geophysics Vol. 85, no. (2012), p. 80-91
- Full Text:
- Reviewed:
- Description: Sulfate rocks have a sedimentary evaporitic origin and are present in many deposits worldwide. Among them, gypsum (dihydrated calcium sulfate) is the most common and is exploited for industrial purposes. Anhydrite (calcium sulfate) is frequently found in gypsum quarries and in non-outcropping sulfates. 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 sulfates have been studied by means of geoelectrical methods.A direct relationship between the electrical conductivity values of the calcium sulfate 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 sulfate 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–Shtrikman lower bound for multiphase systems (considering gypsum, anhydrite and matrix as the components). On the other hand, when the rock is calcium sulfate 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 104Ω·m and geoelectrical classification for calcium sulfate rocks has been elaborated. With this classification it is possible to differentiate between calcium sulfate 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 sulfate 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.
Geoelectrical properties of calcium sulphate rocks
- Guinea, Ander, Playà, Elisabet, Rivero, Lluís, Himi, Mahjoub
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Himi, Mahjoub
- Date: 2011
- Type: Text , Conference paper
- Relation: 17th European Meeting of Environmental and Engineering Geophysics, Near Surface 2011
- Full Text: false
- Reviewed:
- Description: Sulphates are one of the principal groups of evaporitic rocks, Gypsum tends to become into anhydrite when buried because of dehydration and the opposite process also takes place when anhydrite is affected by weathering and superficial waters. One of the most important problems found while quarrying gypsum rock is the presence of anhydrite; the drilling machines can be damaged because of this hardness and when an anhydrite body appears, the exploitation must be stopped at the moment. A geoelectrical classification of calcium sulphate rocks has been elaborated comparing the resistivity values obtained from theoretical models, laboratory tests, and field examples. A Gypsum-Anhydrite-Lutite system has been elaborated using Hashin-Shtrikman bounds. The lower bound fits with the data obtained experimentally for a matrix presence below 60% and the upper bound for the rest. With this ternary system it is possible to interpret the composition of calcium sulphate rocks from ERT profiles. The electrical value of pure gypsum and anhydrite rocks has been defined (1000 and 5000 ohm.m respectively). The most important component in determining the electrical resistivity of the bulk rock is the quantity of lutitic matrix while the significance of gypsum and anhydrite presence only is important in the purest rocks.
Geoelectrical classification of gypsum rocks
- Guinea, Ander, Playà, Elisabet, Rivero, Lluís, Himi, Mahjoub, Bosch, Ricard
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Himi, Mahjoub , Bosch, Ricard
- Date: 2010
- Type: Text , Journal article
- Relation: Surveys in Geophysics Vol. 31, no. 6 (2010), p. 557-580
- Full Text:
- Reviewed:
- Description: Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations, laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field examples. A geoelectrical classification of gypsum rocks defining three types of gypsum rocks has been elaborated: (a) Pure Gypsum Rocks (>75% of gypsum content), (b) Transitional Gypsum Rocks (75–55%), and (c) Lutites and Gypsum-rich Lutites (<55%). From the economic point of view, the Pure Gypsum Rocks, displaying a resistivity value of >800 ohm.m, can be exploited as industrial rocks. The methodology used could be applied in other geoelectrical rock studies, given that this relationship between the resistive particles embedded within a conductive matrix depends on the connectivity of the matrix particles.
- Authors: Guinea, Ander , Playà, Elisabet , Rivero, Lluís , Himi, Mahjoub , Bosch, Ricard
- Date: 2010
- Type: Text , Journal article
- Relation: Surveys in Geophysics Vol. 31, no. 6 (2010), p. 557-580
- Full Text:
- Reviewed:
- Description: Gypsum rocks are widely exploited in the world as industrial minerals. The purity of the gypsum rocks (percentage in gypsum mineral in the whole rock) is a critical factor to evaluate the potential exploitability of a gypsum deposit. It is considered than purities higher than 80% in gypsum are required to be economically profitable. Gypsum deposits have been studied with geoelectrical methods; a direct relationship between the electrical resistivity values of the gypsum rocks and its lithological composition has been established, with the presence of lutites being the main controlling factor in the geoelectrical response of the deposit. This phenomenon has been quantified in the present study, by means of a combination of theoretical calculations, laboratory measurements and field data acquisition. Direct modelling has been performed; the data have been inverted to obtain the mean electrical resistivity of the models. The laboratory measurements have been obtained from artificial gypsum-clay mixture pills, and the electrical resistivity has been measured using a simple electrical circuit with direct current power supply. Finally, electrical resistivity tomography data have been acquired in different evaporite Tertiary basins located in North East Spain; the selected gypsum deposits have different gypsum compositions. The geoelectrical response of gypsum rocks has been determined by comparing the resistivity values obtained from theoretical models, laboratory tests and field examples. A geoelectrical classification of gypsum rocks defining three types of gypsum rocks has been elaborated: (a) Pure Gypsum Rocks (>75% of gypsum content), (b) Transitional Gypsum Rocks (75–55%), and (c) Lutites and Gypsum-rich Lutites (<55%). From the economic point of view, the Pure Gypsum Rocks, displaying a resistivity value of >800 ohm.m, can be exploited as industrial rocks. The methodology used could be applied in other geoelectrical rock studies, given that this relationship between the resistive particles embedded within a conductive matrix depends on the connectivity of the matrix particles.
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