Geoelectrical Classification of Gypsum Rocks |
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Authors: | Ander Guinea Elisabet Playà Lluís Rivero Mahjoub Himi Ricard Bosch |
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Institution: | 1.Departament de Geoquímica, Petrologia i Prospecció Geològica, Facultat de Geologia,Universitat de Barcelona (UB),Barcelona,Spain;2.Departament d’Enginyeria Elèctrica. ETSEIB,Universitat Politècnica de Catalunya (UPC),Barcelona,Spain |
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Abstract: | 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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