Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from in... more Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from inactive and active recently discovered cold seep sites in central Guaymas Basin.. In this study, for first time, redox conditions and fluid sources involved in mineral precipitation were investigated by analyzing the mineralogy and textures of surface samples, along with skeletal contents, and C, O and S isotopes variations. The δ 13 C values of aragonitic bivalve shells and non-skeletal carbonate
In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentrati... more In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentration experiments was performed to investigate the scheelite liberation and distribution density calculation procedure. In this work, one sample from a Mittersill tungsten ore was studied. This work describes a method for determining the downstream milling energy requirements for rod mill products based on a Bond mill test performance. The grade distribution of particles at a given size fraction was calculated using a predictive liberation model. The concentration behavior of these particles in size fractions was evaluated using batch concentrate tests. The recovery of particles in size/grade classes, image analysis using mineral liberation analysis (MLA), and function calculations were implemented for the modeling of the liberation. By describing the size, grade, and recovery data of particles in size/grade classes, a technique for the measurement of distribution functions was developed th...
The Misky gold deposit is one of the several Intrusion Related gold deposits that occur in the oc... more The Misky gold deposit is one of the several Intrusion Related gold deposits that occur in the ocona river basin, southern Peru. They are hosted in magmatic rocks from the Nazca-Palpa-Ocona belt, from the Coastal Batholith. In this study, a petrologic and geochemical characterisation of the host rocks of the Misky deposit is presented to contribute to prove the deposit model. XRD, electron microscopy and electron microprobe analyses were used to characterize the ore and major and trace elements of host rocks were analysed by ICP-Ms. The Misky deposit, Cretaceous in age, consists mainly in quartz veins of lenticular morphology that can be more than 3 Km long and less than 1 m wide. At least two generations of magmatic host rocks are differentiated by the field relationships. The older generation is composed of plutonic rocks of the Incahuasi Unit constituted by diorites, quartz-monzonites, quartz-diorites and granodiorites in minor amounts. These rocks are crosscut by dykes of gabbro...
The Malayer-Esfahan Metallogenic belt (MEMB), in the southwestern Iran, contains numerous differe... more The Malayer-Esfahan Metallogenic belt (MEMB), in the southwestern Iran, contains numerous different types of the sediment-hosted Zn-Pb (±Ba±Ag), volcanicsediment hosted Zn-Pb±Ba, sideritic Fe-Mn-Pb (±Ba±Cu), and barite mineralizations. These deposits are hosted mostly in Jurassic shales and sandstones and in Early to Late Cretaceous carbonates and siltstones with minor volcanic rocks. In contrast to the orogenic-related Mississippi Valley type (MVT) deposits, the MEMB deposits formed in an extensional back-arc environment and are characterized by their stratabound and stratiform orebodies. In these deposits, silicification and dolomitization (± sericitization) are the main wall-rock alteration styles. The presence of primary laminated sulfides, fine-grained disseminated sphalerite and galena in association with framboidal pyrite, sedimentary structures in sulfide laminae and bands, and the association of some tuffaceous and volcanic rocks with sulfide mineralizations, along with replacement ore textures in the MEMB deposits are not compatible with orogenic-related MVT model for these mineralization. These characteristics in the Cretaceous MEMB deposits are more compatible with a submarine hydrothermal system with sub-seafloor replacement mineralization (e.g., Irish type). Some deposits also share characteristics between Irish type and volcanogenic massive sulfide (VMS) deposits, called VSHMS in this paper. The main argument against the MVT model of Karimpour and Sadeghi (2018) is that this model is not acceptable for the MEMB deposits and could not explain metallogenic aspects of the Zn-Pb (±Ba±Ag) and other mineralizations in this belt.
The Ab-Bagh clastic-and carbonate-hosted stratabound and stratiform Zn-Pb deposit in the Sanandaj... more The Ab-Bagh clastic-and carbonate-hosted stratabound and stratiform Zn-Pb deposit in the Sanandaj-Sirjan zone, in the southeastern corner of the Malayer-Esfahan metallogenic belt of Iran, is typical of several sedimentary-exhalative (SEDEX) deposits in this metallogenic belt. The deposit is hosted in a late Jurassic-early Cretaceous sedimentary sequence. Based on position, there are two Zn-Pb-bearing stratigraphic ore horizons. Ore horizon 1 is hosted by late Jurassic-early Cretaceous black shale and siltstone. The wedge-shaped ore body is located close to a synsedimentary normal fault. Petrographic studies indicates that mineralization comprises three sulfide ore facies: stockwork, bedded and massive ore facies. Ore horizon 2 occurs in early Cretaceous carbonates and comprises a massive-replacement ore facies that is concordant with host rock layering; it is also underlain by a stockwork facies. Textures include framboidal, laminated, breccia, replacement, massive and vein-veinlet. Hypogene sulfide minerals are predominantly sphalerite, galena, pyrite and chalcopyrite. Calcite and quartz are major gangue minerals. Silicification and carbonatization are the main wallrock alteration styles; alteration intensity increases towards the feeder zone. Based on relationships between ore minerals and rockforming minerals, sulfide mineralization in the Ab-Bagh deposit formed during two main stages: fine-grained sulfide bands (stage I) are intricately interlayered with organic matter-rich beds of black shale and siltstone. Sulfide bands exhibit classic sedimentary textures, such as laminations and bedding, indicative of a synsedimentary origin. Coarser-grained stage II base metal sulfides show breccia and vein-veinlet textures, and are considered to have formed by replacement during sub-seafloor fluid flow. Fluid inclusion microthermometry was carried out on calcite associated with sulfides of the stockwork ore facies. Homogenization temperatures are in the range of 180-301°C, and the average salinity is 17.93 wt% NaCl eq. The size distribution of pyrite framboids of the bedded ore, geochemistry of host rock and presence of organic matter, collectively suggest anoxic to locally suboxic ambient conditions for the host basin. The δ 34 S composition of pyrite, sphalerite, and galena ranges from −5.08 to +4.51‰. The highest δ 34 S values are from massive and stockwork ore facies (+2.66 to + 4.51‰) and the lowest from bedded ore (−5.08 to −4.72‰). In the bedded ore facies, the main sulfur source was bacterially reduced seawater sulfate. Whereas in massive and stockwork ore facies, thermochemically reduced seawater sulfate was the main source of sulfur. The 87 Sr/ 86 Sr ratios of calcite indicate that origin of ore forming fluids is Paleozoic radiogenic basement. Collectively, the isotopic, sedimentological, textural, mineralogical, fluid inclusion, and geochemical data for the Ab-Bagh deposit support a vent-proximal sub-seafloor replacement SEDEX ore deposit.
ABSTRACTThe Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola wh... more ABSTRACTThe Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola where Ta minerals occur mainly as disseminations in a leucogranite body intruded in Precambrian–Lower Cambrian gneisses and mica-schists. This leucogranite is a medium- to fine-grained inequigranular rock consisting mainly of quartz, albite, K-feldspar and muscovite. Accessory minerals are mainly of spessartine, zircon, cassiterite, Nb-Ta oxides, monazite, xenotime, native bismuth and pyrite. The alteration processes were mainly albitization, muscovitization and kaolinitization.This leucogranite is peraluminous and P-poor, with 0.03–0.07 wt.% P2O5, 900–1500 ppm Rb, 30–65 ppm Cs, 120–533 ppm Li, 80–140 ppm Ta, 51–81 ppm Nb and up to 569 ppm of Sn.Mineralogical characterization of Nb-Ta oxide minerals was determined by X-ray diffraction, scanning electron microscopy, electron microprobe analysis and mineral liberation analysis. Mn-rich members of the columbite-group minerals (CGM) are the mo...
Future engineers, in addition to technical knowledge, should incorporate in their academic curric... more Future engineers, in addition to technical knowledge, should incorporate in their academic curricula aspects that contribute to make mining a sustainable activity. This will contribute to changing the concept that society has about mining and to be a socially accepted activity. In the mining engineering studies at the Universitat Politècnica de Catalunya (UPC), students have the opportunity to develop cooperation projects together with professors and other staff members. They all collaborate with artisanal miners from different underdeveloped countries, mainly from Latin America, and contribute to making mining more environmentally friendly. Moreover, they have the opportunity to acquire a social sensitivity that can be of great importance during the development of their professional career. This study presents some experiences of undergraduate, master, and doctoral students in cooperation activities in mining. The projects were developed as a collaboration between UPC and universities or NOGs in Latin America. The activities have been carried out in underdeveloped areas where mining is practiced with a high environmental impact and poor use of resources. A survey among the participants in the projects shows the students' favourable perception of this activity.
For several years, engineering students from the Escola Politècnica Superior d'Enginyeria de Manr... more For several years, engineering students from the Escola Politècnica Superior d'Enginyeria de Manresa have been participating in development cooperation projects as activities of the non-governmental Organization Mining for Development, with the support of the Center for Development Cooperation of the UPC. Activities were carried out in several mining sites in South American countries, mainly in Bolivia and Peru. Although the motivation for the students may have been initially a desire for adventure and volunteering, the experience turned into meaningful learning, as intended by the faculty leading the project. This paper presents the findings of a study carried out to analyze how these experiences contributed to the learning of engineering students, within the framework of what is known as service learning. The study is based on the reports written by the students at the end of the experience and interviews conducted afterward when the experience had been fully internalized. The characteristic elements of service learning have been identified. In addition, the analysis revealed how the experiences had a significant impact on subsequent learning, even beyond the initially intended objectives.
Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from in... more Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from inactive and active recently discovered cold seep sites in central Guaymas Basin.. In this study, for first time, redox conditions and fluid sources involved in mineral precipitation were investigated by analyzing the mineralogy and textures of surface samples, along with skeletal contents, and C, O and S isotopes variations. The δ 13 C values of aragonitic bivalve shells and non-skeletal carbonate
In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentrati... more In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentration experiments was performed to investigate the scheelite liberation and distribution density calculation procedure. In this work, one sample from a Mittersill tungsten ore was studied. This work describes a method for determining the downstream milling energy requirements for rod mill products based on a Bond mill test performance. The grade distribution of particles at a given size fraction was calculated using a predictive liberation model. The concentration behavior of these particles in size fractions was evaluated using batch concentrate tests. The recovery of particles in size/grade classes, image analysis using mineral liberation analysis (MLA), and function calculations were implemented for the modeling of the liberation. By describing the size, grade, and recovery data of particles in size/grade classes, a technique for the measurement of distribution functions was developed that relates beta distribution, a model for the function based on the incomplete beta function, and a solution to produce liberation modeling. It was shown that the predicted results agreed well with the observed results. With a procedure for measuring the liberation, it was possible to carry out the first experimental measurement of the beta distribution. This liberation/concentrate model has wide potential applications for metallurgy and plant design, where the liberation modeling is to be determined with the distribution density solution to the predictive mineral liberation function equation, which includes the liberation of ore samples and their liberation characteristics.
Journal of Thermal Analysis and Calorimetry, Oct 15, 2021
The thermal properties and evolution of mineralogy and colour of kaolinitic clay from the Terra A... more The thermal properties and evolution of mineralogy and colour of kaolinitic clay from the Terra Alta region were studied. The mineralogy of these materials consists mainly of kaolinite (13-27 mass%) and quartz (48-86 mass%). Minor illite, hematite, K-feldspar and calcite also occur. The linear expansion and absorption curves were used to predict the optimal firing temperature of the raw clays. During firing, from 1100 °C the water absorption decreases steeply, due to an increase in liquid phase, which penetrates into the pores and close the porosity. At this temperature, the firing shrinkage increases progressively. The fired clays are mainly composed of quartz, cristobalite and mullite, with minor hematite and rutile. Mullite starts to appear at 1050-1100 °C. SEM observations show that porosity decreases with the firing temperature. The colour properties were measured in the raw clays and in the fired bricks at different temperatures. The lightness, L*, is lower in the fired test pieces respect to the natural clays. This colour varies according to the hematite content, being from white to reddish in the fired samples.
Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from in... more Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from inactive and active recently discovered cold seep sites in central Guaymas Basin.. In this study, for first time, redox conditions and fluid sources involved in mineral precipitation were investigated by analyzing the mineralogy and textures of surface samples, along with skeletal contents, and C, O and S isotopes variations. The δ 13 C values of aragonitic bivalve shells and non-skeletal carbonate
In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentrati... more In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentration experiments was performed to investigate the scheelite liberation and distribution density calculation procedure. In this work, one sample from a Mittersill tungsten ore was studied. This work describes a method for determining the downstream milling energy requirements for rod mill products based on a Bond mill test performance. The grade distribution of particles at a given size fraction was calculated using a predictive liberation model. The concentration behavior of these particles in size fractions was evaluated using batch concentrate tests. The recovery of particles in size/grade classes, image analysis using mineral liberation analysis (MLA), and function calculations were implemented for the modeling of the liberation. By describing the size, grade, and recovery data of particles in size/grade classes, a technique for the measurement of distribution functions was developed th...
The Misky gold deposit is one of the several Intrusion Related gold deposits that occur in the oc... more The Misky gold deposit is one of the several Intrusion Related gold deposits that occur in the ocona river basin, southern Peru. They are hosted in magmatic rocks from the Nazca-Palpa-Ocona belt, from the Coastal Batholith. In this study, a petrologic and geochemical characterisation of the host rocks of the Misky deposit is presented to contribute to prove the deposit model. XRD, electron microscopy and electron microprobe analyses were used to characterize the ore and major and trace elements of host rocks were analysed by ICP-Ms. The Misky deposit, Cretaceous in age, consists mainly in quartz veins of lenticular morphology that can be more than 3 Km long and less than 1 m wide. At least two generations of magmatic host rocks are differentiated by the field relationships. The older generation is composed of plutonic rocks of the Incahuasi Unit constituted by diorites, quartz-monzonites, quartz-diorites and granodiorites in minor amounts. These rocks are crosscut by dykes of gabbro...
The Malayer-Esfahan Metallogenic belt (MEMB), in the southwestern Iran, contains numerous differe... more The Malayer-Esfahan Metallogenic belt (MEMB), in the southwestern Iran, contains numerous different types of the sediment-hosted Zn-Pb (±Ba±Ag), volcanicsediment hosted Zn-Pb±Ba, sideritic Fe-Mn-Pb (±Ba±Cu), and barite mineralizations. These deposits are hosted mostly in Jurassic shales and sandstones and in Early to Late Cretaceous carbonates and siltstones with minor volcanic rocks. In contrast to the orogenic-related Mississippi Valley type (MVT) deposits, the MEMB deposits formed in an extensional back-arc environment and are characterized by their stratabound and stratiform orebodies. In these deposits, silicification and dolomitization (± sericitization) are the main wall-rock alteration styles. The presence of primary laminated sulfides, fine-grained disseminated sphalerite and galena in association with framboidal pyrite, sedimentary structures in sulfide laminae and bands, and the association of some tuffaceous and volcanic rocks with sulfide mineralizations, along with replacement ore textures in the MEMB deposits are not compatible with orogenic-related MVT model for these mineralization. These characteristics in the Cretaceous MEMB deposits are more compatible with a submarine hydrothermal system with sub-seafloor replacement mineralization (e.g., Irish type). Some deposits also share characteristics between Irish type and volcanogenic massive sulfide (VMS) deposits, called VSHMS in this paper. The main argument against the MVT model of Karimpour and Sadeghi (2018) is that this model is not acceptable for the MEMB deposits and could not explain metallogenic aspects of the Zn-Pb (±Ba±Ag) and other mineralizations in this belt.
The Ab-Bagh clastic-and carbonate-hosted stratabound and stratiform Zn-Pb deposit in the Sanandaj... more The Ab-Bagh clastic-and carbonate-hosted stratabound and stratiform Zn-Pb deposit in the Sanandaj-Sirjan zone, in the southeastern corner of the Malayer-Esfahan metallogenic belt of Iran, is typical of several sedimentary-exhalative (SEDEX) deposits in this metallogenic belt. The deposit is hosted in a late Jurassic-early Cretaceous sedimentary sequence. Based on position, there are two Zn-Pb-bearing stratigraphic ore horizons. Ore horizon 1 is hosted by late Jurassic-early Cretaceous black shale and siltstone. The wedge-shaped ore body is located close to a synsedimentary normal fault. Petrographic studies indicates that mineralization comprises three sulfide ore facies: stockwork, bedded and massive ore facies. Ore horizon 2 occurs in early Cretaceous carbonates and comprises a massive-replacement ore facies that is concordant with host rock layering; it is also underlain by a stockwork facies. Textures include framboidal, laminated, breccia, replacement, massive and vein-veinlet. Hypogene sulfide minerals are predominantly sphalerite, galena, pyrite and chalcopyrite. Calcite and quartz are major gangue minerals. Silicification and carbonatization are the main wallrock alteration styles; alteration intensity increases towards the feeder zone. Based on relationships between ore minerals and rockforming minerals, sulfide mineralization in the Ab-Bagh deposit formed during two main stages: fine-grained sulfide bands (stage I) are intricately interlayered with organic matter-rich beds of black shale and siltstone. Sulfide bands exhibit classic sedimentary textures, such as laminations and bedding, indicative of a synsedimentary origin. Coarser-grained stage II base metal sulfides show breccia and vein-veinlet textures, and are considered to have formed by replacement during sub-seafloor fluid flow. Fluid inclusion microthermometry was carried out on calcite associated with sulfides of the stockwork ore facies. Homogenization temperatures are in the range of 180-301°C, and the average salinity is 17.93 wt% NaCl eq. The size distribution of pyrite framboids of the bedded ore, geochemistry of host rock and presence of organic matter, collectively suggest anoxic to locally suboxic ambient conditions for the host basin. The δ 34 S composition of pyrite, sphalerite, and galena ranges from −5.08 to +4.51‰. The highest δ 34 S values are from massive and stockwork ore facies (+2.66 to + 4.51‰) and the lowest from bedded ore (−5.08 to −4.72‰). In the bedded ore facies, the main sulfur source was bacterially reduced seawater sulfate. Whereas in massive and stockwork ore facies, thermochemically reduced seawater sulfate was the main source of sulfur. The 87 Sr/ 86 Sr ratios of calcite indicate that origin of ore forming fluids is Paleozoic radiogenic basement. Collectively, the isotopic, sedimentological, textural, mineralogical, fluid inclusion, and geochemical data for the Ab-Bagh deposit support a vent-proximal sub-seafloor replacement SEDEX ore deposit.
ABSTRACTThe Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola wh... more ABSTRACTThe Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola where Ta minerals occur mainly as disseminations in a leucogranite body intruded in Precambrian–Lower Cambrian gneisses and mica-schists. This leucogranite is a medium- to fine-grained inequigranular rock consisting mainly of quartz, albite, K-feldspar and muscovite. Accessory minerals are mainly of spessartine, zircon, cassiterite, Nb-Ta oxides, monazite, xenotime, native bismuth and pyrite. The alteration processes were mainly albitization, muscovitization and kaolinitization.This leucogranite is peraluminous and P-poor, with 0.03–0.07 wt.% P2O5, 900–1500 ppm Rb, 30–65 ppm Cs, 120–533 ppm Li, 80–140 ppm Ta, 51–81 ppm Nb and up to 569 ppm of Sn.Mineralogical characterization of Nb-Ta oxide minerals was determined by X-ray diffraction, scanning electron microscopy, electron microprobe analysis and mineral liberation analysis. Mn-rich members of the columbite-group minerals (CGM) are the mo...
Future engineers, in addition to technical knowledge, should incorporate in their academic curric... more Future engineers, in addition to technical knowledge, should incorporate in their academic curricula aspects that contribute to make mining a sustainable activity. This will contribute to changing the concept that society has about mining and to be a socially accepted activity. In the mining engineering studies at the Universitat Politècnica de Catalunya (UPC), students have the opportunity to develop cooperation projects together with professors and other staff members. They all collaborate with artisanal miners from different underdeveloped countries, mainly from Latin America, and contribute to making mining more environmentally friendly. Moreover, they have the opportunity to acquire a social sensitivity that can be of great importance during the development of their professional career. This study presents some experiences of undergraduate, master, and doctoral students in cooperation activities in mining. The projects were developed as a collaboration between UPC and universities or NOGs in Latin America. The activities have been carried out in underdeveloped areas where mining is practiced with a high environmental impact and poor use of resources. A survey among the participants in the projects shows the students' favourable perception of this activity.
For several years, engineering students from the Escola Politècnica Superior d'Enginyeria de Manr... more For several years, engineering students from the Escola Politècnica Superior d'Enginyeria de Manresa have been participating in development cooperation projects as activities of the non-governmental Organization Mining for Development, with the support of the Center for Development Cooperation of the UPC. Activities were carried out in several mining sites in South American countries, mainly in Bolivia and Peru. Although the motivation for the students may have been initially a desire for adventure and volunteering, the experience turned into meaningful learning, as intended by the faculty leading the project. This paper presents the findings of a study carried out to analyze how these experiences contributed to the learning of engineering students, within the framework of what is known as service learning. The study is based on the reports written by the students at the end of the experience and interviews conducted afterward when the experience had been fully internalized. The characteristic elements of service learning have been identified. In addition, the analysis revealed how the experiences had a significant impact on subsequent learning, even beyond the initially intended objectives.
Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from in... more Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from inactive and active recently discovered cold seep sites in central Guaymas Basin.. In this study, for first time, redox conditions and fluid sources involved in mineral precipitation were investigated by analyzing the mineralogy and textures of surface samples, along with skeletal contents, and C, O and S isotopes variations. The δ 13 C values of aragonitic bivalve shells and non-skeletal carbonate
In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentrati... more In this paper, the modeling of the liberation of scheelite is presented. A pattern of concentration experiments was performed to investigate the scheelite liberation and distribution density calculation procedure. In this work, one sample from a Mittersill tungsten ore was studied. This work describes a method for determining the downstream milling energy requirements for rod mill products based on a Bond mill test performance. The grade distribution of particles at a given size fraction was calculated using a predictive liberation model. The concentration behavior of these particles in size fractions was evaluated using batch concentrate tests. The recovery of particles in size/grade classes, image analysis using mineral liberation analysis (MLA), and function calculations were implemented for the modeling of the liberation. By describing the size, grade, and recovery data of particles in size/grade classes, a technique for the measurement of distribution functions was developed that relates beta distribution, a model for the function based on the incomplete beta function, and a solution to produce liberation modeling. It was shown that the predicted results agreed well with the observed results. With a procedure for measuring the liberation, it was possible to carry out the first experimental measurement of the beta distribution. This liberation/concentrate model has wide potential applications for metallurgy and plant design, where the liberation modeling is to be determined with the distribution density solution to the predictive mineral liberation function equation, which includes the liberation of ore samples and their liberation characteristics.
Journal of Thermal Analysis and Calorimetry, Oct 15, 2021
The thermal properties and evolution of mineralogy and colour of kaolinitic clay from the Terra A... more The thermal properties and evolution of mineralogy and colour of kaolinitic clay from the Terra Alta region were studied. The mineralogy of these materials consists mainly of kaolinite (13-27 mass%) and quartz (48-86 mass%). Minor illite, hematite, K-feldspar and calcite also occur. The linear expansion and absorption curves were used to predict the optimal firing temperature of the raw clays. During firing, from 1100 °C the water absorption decreases steeply, due to an increase in liquid phase, which penetrates into the pores and close the porosity. At this temperature, the firing shrinkage increases progressively. The fired clays are mainly composed of quartz, cristobalite and mullite, with minor hematite and rutile. Mullite starts to appear at 1050-1100 °C. SEM observations show that porosity decreases with the firing temperature. The colour properties were measured in the raw clays and in the fired bricks at different temperatures. The lightness, L*, is lower in the fired test pieces respect to the natural clays. This colour varies according to the hematite content, being from white to reddish in the fired samples.
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