This article addresses the relationship between science and propaganda using the Climate Change c... more This article addresses the relationship between science and propaganda using the Climate Change controversy as a study model. The United Nations International Panel on Climate Change (IPCC) is the recognized leader on this model issuing multiple Assessment Reports. This review begins with a discussion of the basics—what is propaganda and how does it work, followed by whether the IPCC adopted or rejected it. Next explored is how propaganda can be seamlessly fused into “report writing” in a way that arouses and makes interesting humdrum details. Some unexpected results emerged from current and historical observation data involving the Greenhouse theory, CO2 sources, ocean pH, sea levels, and ice balances. The final section confronts whether “a point of view” constrains objectivity in favor of outcome. The overall conclusion is that the earth is boringly healthy.
Based primarily on geologic field observations as recorded by numerous geoscientists over the las... more Based primarily on geologic field observations as recorded by numerous geoscientists over the last three decades, backed by more recent geochemical, seismic, gravity, magnetic, tomographic, and satellite-based techniques, an integrated synthesis and interpretation of the tectonic assembly of the entire Northern Andean Block (the Andes of Ecuador, Colombia, and Venezuela) is presented in this paper.
Phreatic and phreatomagmatic breccias are the two end-member styles of hydromagmatic breccias. A ... more Phreatic and phreatomagmatic breccias are the two end-member styles of hydromagmatic breccias. A previous contribution deals with phreatomagmatic breccias with an emphasis on their general features and those genetic criteria that allow an accurate and rapid recognition. Phreatic breccias are presented here. Their general features, i.e. environment/ depth of formation, general form/geometry, dimensions, contacts with the host rocks, fragments, matrix, alteration, mineralization, surface connection, fluidization and facies changes were examined. Furthermore, genetic criteria, very useful in phreatic breccia recognition are summarized
Breccias are among the most widely distributed rock textures found in hydrothermal vein-type depo... more Breccias are among the most widely distributed rock textures found in hydrothermal vein-type deposits. Previous studies have mainly been interested in developing qualitative descriptive approaches, leading to a confusing profusion of terms. Brecciation originates in numerous ways, resulting in highly complex classification systems and frequent misinterpretations of facies. Field observations are difficult to reconcile with physical theories of fragmentation, partly due to the fact that few satisfactory quantitative tools have been developed. A review of the main brecciation processes occurring in hydrothermal vein-type deposits allows for the discrimination between chemical and physical mechanisms, including tectonic comminu- tion, wear abrasion, two types of fluid-assisted brecciation hydraulic and critical., volume expansion or reduction, impact and collapse. Each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry, including fragment morphology, size distribution of the fragments, fabric, and dilation ratio. The first two parameters are especially important because: 1. the morphology of the fragments allows chemical and physical mechanical. breccias to be distinguished, and 2. the particle size distribution PSD. is a function of the energy input during breccia formation. The slope of the cumulative PSD fractal dimension. ranges from high values for high-energy brecciation processes, to low values for low energy processes indicated by an isometric distribution. The evolution of a vein system can be divided into three stages: propagation, wear and dilation. These stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity. These two thresholds also mark the transition between different types of brecciation. Mineralization occurs during all three stages and may display different textures due to pressure variations. The use of quantitative parameters in fault-related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment, including structural setting and crustal level, as well as fluid–rock interactions. Recognition of the different breccia types could also be important during the early stages of mineral exploration. q1997 Elsevier Science B.V.
Despite showing an important association with numerous types of gold deposits,
epigenetic breccia... more Despite showing an important association with numerous types of gold deposits, epigenetic breccias remain an enigmatic topic for many geologists. This classification of breccias is genetic and based on the inferred role of magmas, magmatic volatiles and their interaction with groundwaters. It is taken from a classification by Sillitoe (1985) and a modified and expanded classification in Lawless et al (1998).
Detailed geologic mapping has been used to show that Agua Rica is a porphyry-style Cu-Mo-Au depos... more Detailed geologic mapping has been used to show that Agua Rica is a porphyry-style Cu-Mo-Au deposit that was first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren surface-venting phreatomagmatic diatreme, prior to a final stage of supergene enrichment. It was emplaced in the Miocene (~8–5 Ma) as an outlier of the Farallón Negro Volcanic Complex in northwestern Argentina. The Agua Rica deposit lies next to the contact between Precambrian or lower Paleozoic metasedimentary rocks and coarse-grained Ordovician granites. In a first pulse of Miocene magmatism, equigranular to porphyritic intrusions were emplaced, with minor potassic alteration and weak Cu-Mo mineralization. Subsequent intrusion of feldspar porphyries was associated with intense porphyry-style stockwork veining, potassic and propylitic alteration, and disseminated Cu-Mo-Au mineralization (molybdenite, chalcopyrite ± bornite ± pyrite). The present alteration and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal assemblages (phyllic and advanced argillic alteration and Cu-Au-Ag-As-Pb-Zn mineralization) in breccia cements and as void fillings. Covellite is the dominant copper mineral in the ore and seems to have partly or completely replaced chalcopyrite and bornite of the earlier porphyry events. The high sulfidation epithermal assemblages are closely related to the emplacement of a largely clast-supported hydrothermal breccia. Three major bodies of this breccia have been mapped on the basis of clast lithology, clast shape and size, degree of alteration, and composition of breccia matrix. Igneous breccia with a fine-grained porphyritic matrix is intimately associated and interfingers with the base of the hydrothermal breccia columns. A final phase of magmatic hydrothermal activity formed a matrix-supported and commonly bedded crater infill breccia. It formed by a surface-venting phreatomagmatic eruption, as shown by a continuous downward transition from bedded breccias to clast-supported breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine-grained porphyritic matrix in the lower core of the conical crater infill breccia body. Graded, matrix-rich epiclastic sediments subsequently filled the crater. Magmatic activity was terminated by a dike of unmineralized biotite porphyry, which intruded the crater infill breccia. Talus breccia was shed into the crater from the rim. Supergene leaching and enrichment, which replaced covellite, pyrite, chalcopyrite, and bornite by chalcocite and secondary covellite, formed an enrichment blanket that was dissected by the present-day, steeply incised topography. The distinctive feature of the Agua Rica hydrothermal system is the occurrence of early, weakly mineralized intrusions, later feldspar porphyries with stockwork-hosted chalcopyrite-bornite-molybdenite mineralization, hydrothermal breccias with an epithermal pyrite-covellite overprint, and barren surface-venting breccias—all exposed at one location within 1,000 m of vertical exposure. Reconstruction of the time sequence of these geologic elements indicates that Agua Rica is the result of a protracted history of magmatic hydrothermal activity with superposition of several intrusion events that probably extended over several million years during progressive regional uplift, erosion, and explosive unroofing.
La minería es considerada por muchos una actividad que produce gran impacto ambiental negativo, y... more La minería es considerada por muchos una actividad que produce gran impacto ambiental negativo, y ha sufrido ataques muy duros desde diferentes frentes ambientalistas. No obstante son muchos los esfuerzos realizados, en tiempos recientes, para conseguir minimizar los impactos e incluso aportar activos ambientales, en tanto en cuanto es posible. En este marco se presentan ejemplos de actuaciones mineras ejemplares ambientalmente, que pueden servir de referencia de las posibilidades que ofrece la ingeniería ambiental en la rehabilitación de espacios mineros.
Si-undersaturated high-Mg basalts with early fractionated ultramafic cumulates (Viravira complex)... more Si-undersaturated high-Mg basalts with early fractionated ultramafic cumulates (Viravira complex) and a zoned ultramafic Alaskan-type intrusion (Condoto complex) are located in the upper Condoto River within the Western Cordillera of Colombia. These complexes are related in space and time and originated from a common parental magma.
The Alto Condoto Complex, dated at 20 Ma, is a zoned ultramafic intrusion with a magmatic rock se... more The Alto Condoto Complex, dated at 20 Ma, is a zoned ultramafic intrusion with a magmatic rock sequence ranging from dunitc to hornblendite. The different petrographic units are cumulates formed by fractional crystallization processes.
Magmatic deposits containing exploitable quantities of nickel, copper, and platinum group element... more Magmatic deposits containing exploitable quantities of nickel, copper, and platinum group elements (PGE) are associated with variable quantities of localized sulphide concentrations in mafi c and ultramafi c rocks. Ni-Cu deposits, nickel being the main economic commodity, are associated with high concentrations of sulphides, and the host bodies are classifi ed based on the nature of the confi ning magmatic environment: (1) meteorite-impact, (2) rift and continental fl ood basalt, (3) komatiitic, and (4) other related mafi c/ultramafi c bodies. Platinum group element deposits are also confi ned to mafi c/ultramafi c bodies, but are associated with low quantities of sulphides. Reef-type or stratiform PGE deposits form in large, well-layered mafi c/ultramafi c intrusions, whereas magmatic breccia-type deposits occurs in stock-like or layered bodies.
En el Segmento Norte de La Cordillera Occidental de Colombia, al norte del Cinturón plegado de It... more En el Segmento Norte de La Cordillera Occidental de Colombia, al norte del Cinturón plegado de Itsmina y la Falla del río San Juan que se localiza entre el Cerró Tatamá y los Farallones del Citará, afloran una serie de plutones que intruyen el Complejo Santa Cecilia -La Equis -Batolito de Mandé (Arco de Chocó -Panamá), el Complejo Cañasgordas y los Basaltos de El Botón (Arco de El Botón), cuerpos intrusivos que afloran desde Pueblo Rico (Risaralda) hasta Dabeiba (Antioquia).
This article addresses the relationship between science and propaganda using the Climate Change c... more This article addresses the relationship between science and propaganda using the Climate Change controversy as a study model. The United Nations International Panel on Climate Change (IPCC) is the recognized leader on this model issuing multiple Assessment Reports. This review begins with a discussion of the basics—what is propaganda and how does it work, followed by whether the IPCC adopted or rejected it. Next explored is how propaganda can be seamlessly fused into “report writing” in a way that arouses and makes interesting humdrum details. Some unexpected results emerged from current and historical observation data involving the Greenhouse theory, CO2 sources, ocean pH, sea levels, and ice balances. The final section confronts whether “a point of view” constrains objectivity in favor of outcome. The overall conclusion is that the earth is boringly healthy.
Based primarily on geologic field observations as recorded by numerous geoscientists over the las... more Based primarily on geologic field observations as recorded by numerous geoscientists over the last three decades, backed by more recent geochemical, seismic, gravity, magnetic, tomographic, and satellite-based techniques, an integrated synthesis and interpretation of the tectonic assembly of the entire Northern Andean Block (the Andes of Ecuador, Colombia, and Venezuela) is presented in this paper.
Phreatic and phreatomagmatic breccias are the two end-member styles of hydromagmatic breccias. A ... more Phreatic and phreatomagmatic breccias are the two end-member styles of hydromagmatic breccias. A previous contribution deals with phreatomagmatic breccias with an emphasis on their general features and those genetic criteria that allow an accurate and rapid recognition. Phreatic breccias are presented here. Their general features, i.e. environment/ depth of formation, general form/geometry, dimensions, contacts with the host rocks, fragments, matrix, alteration, mineralization, surface connection, fluidization and facies changes were examined. Furthermore, genetic criteria, very useful in phreatic breccia recognition are summarized
Breccias are among the most widely distributed rock textures found in hydrothermal vein-type depo... more Breccias are among the most widely distributed rock textures found in hydrothermal vein-type deposits. Previous studies have mainly been interested in developing qualitative descriptive approaches, leading to a confusing profusion of terms. Brecciation originates in numerous ways, resulting in highly complex classification systems and frequent misinterpretations of facies. Field observations are difficult to reconcile with physical theories of fragmentation, partly due to the fact that few satisfactory quantitative tools have been developed. A review of the main brecciation processes occurring in hydrothermal vein-type deposits allows for the discrimination between chemical and physical mechanisms, including tectonic comminu- tion, wear abrasion, two types of fluid-assisted brecciation hydraulic and critical., volume expansion or reduction, impact and collapse. Each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry, including fragment morphology, size distribution of the fragments, fabric, and dilation ratio. The first two parameters are especially important because: 1. the morphology of the fragments allows chemical and physical mechanical. breccias to be distinguished, and 2. the particle size distribution PSD. is a function of the energy input during breccia formation. The slope of the cumulative PSD fractal dimension. ranges from high values for high-energy brecciation processes, to low values for low energy processes indicated by an isometric distribution. The evolution of a vein system can be divided into three stages: propagation, wear and dilation. These stages are separated by one threshold of mechanical discontinuity and one of hydraulic continuity. These two thresholds also mark the transition between different types of brecciation. Mineralization occurs during all three stages and may display different textures due to pressure variations. The use of quantitative parameters in fault-related hydrothermal breccias allows a better understanding of the physical parameters related to a vein environment, including structural setting and crustal level, as well as fluid–rock interactions. Recognition of the different breccia types could also be important during the early stages of mineral exploration. q1997 Elsevier Science B.V.
Despite showing an important association with numerous types of gold deposits,
epigenetic breccia... more Despite showing an important association with numerous types of gold deposits, epigenetic breccias remain an enigmatic topic for many geologists. This classification of breccias is genetic and based on the inferred role of magmas, magmatic volatiles and their interaction with groundwaters. It is taken from a classification by Sillitoe (1985) and a modified and expanded classification in Lawless et al (1998).
Detailed geologic mapping has been used to show that Agua Rica is a porphyry-style Cu-Mo-Au depos... more Detailed geologic mapping has been used to show that Agua Rica is a porphyry-style Cu-Mo-Au deposit that was first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren surface-venting phreatomagmatic diatreme, prior to a final stage of supergene enrichment. It was emplaced in the Miocene (~8–5 Ma) as an outlier of the Farallón Negro Volcanic Complex in northwestern Argentina. The Agua Rica deposit lies next to the contact between Precambrian or lower Paleozoic metasedimentary rocks and coarse-grained Ordovician granites. In a first pulse of Miocene magmatism, equigranular to porphyritic intrusions were emplaced, with minor potassic alteration and weak Cu-Mo mineralization. Subsequent intrusion of feldspar porphyries was associated with intense porphyry-style stockwork veining, potassic and propylitic alteration, and disseminated Cu-Mo-Au mineralization (molybdenite, chalcopyrite ± bornite ± pyrite). The present alteration and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal assemblages (phyllic and advanced argillic alteration and Cu-Au-Ag-As-Pb-Zn mineralization) in breccia cements and as void fillings. Covellite is the dominant copper mineral in the ore and seems to have partly or completely replaced chalcopyrite and bornite of the earlier porphyry events. The high sulfidation epithermal assemblages are closely related to the emplacement of a largely clast-supported hydrothermal breccia. Three major bodies of this breccia have been mapped on the basis of clast lithology, clast shape and size, degree of alteration, and composition of breccia matrix. Igneous breccia with a fine-grained porphyritic matrix is intimately associated and interfingers with the base of the hydrothermal breccia columns. A final phase of magmatic hydrothermal activity formed a matrix-supported and commonly bedded crater infill breccia. It formed by a surface-venting phreatomagmatic eruption, as shown by a continuous downward transition from bedded breccias to clast-supported breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine-grained porphyritic matrix in the lower core of the conical crater infill breccia body. Graded, matrix-rich epiclastic sediments subsequently filled the crater. Magmatic activity was terminated by a dike of unmineralized biotite porphyry, which intruded the crater infill breccia. Talus breccia was shed into the crater from the rim. Supergene leaching and enrichment, which replaced covellite, pyrite, chalcopyrite, and bornite by chalcocite and secondary covellite, formed an enrichment blanket that was dissected by the present-day, steeply incised topography. The distinctive feature of the Agua Rica hydrothermal system is the occurrence of early, weakly mineralized intrusions, later feldspar porphyries with stockwork-hosted chalcopyrite-bornite-molybdenite mineralization, hydrothermal breccias with an epithermal pyrite-covellite overprint, and barren surface-venting breccias—all exposed at one location within 1,000 m of vertical exposure. Reconstruction of the time sequence of these geologic elements indicates that Agua Rica is the result of a protracted history of magmatic hydrothermal activity with superposition of several intrusion events that probably extended over several million years during progressive regional uplift, erosion, and explosive unroofing.
La minería es considerada por muchos una actividad que produce gran impacto ambiental negativo, y... more La minería es considerada por muchos una actividad que produce gran impacto ambiental negativo, y ha sufrido ataques muy duros desde diferentes frentes ambientalistas. No obstante son muchos los esfuerzos realizados, en tiempos recientes, para conseguir minimizar los impactos e incluso aportar activos ambientales, en tanto en cuanto es posible. En este marco se presentan ejemplos de actuaciones mineras ejemplares ambientalmente, que pueden servir de referencia de las posibilidades que ofrece la ingeniería ambiental en la rehabilitación de espacios mineros.
Si-undersaturated high-Mg basalts with early fractionated ultramafic cumulates (Viravira complex)... more Si-undersaturated high-Mg basalts with early fractionated ultramafic cumulates (Viravira complex) and a zoned ultramafic Alaskan-type intrusion (Condoto complex) are located in the upper Condoto River within the Western Cordillera of Colombia. These complexes are related in space and time and originated from a common parental magma.
The Alto Condoto Complex, dated at 20 Ma, is a zoned ultramafic intrusion with a magmatic rock se... more The Alto Condoto Complex, dated at 20 Ma, is a zoned ultramafic intrusion with a magmatic rock sequence ranging from dunitc to hornblendite. The different petrographic units are cumulates formed by fractional crystallization processes.
Magmatic deposits containing exploitable quantities of nickel, copper, and platinum group element... more Magmatic deposits containing exploitable quantities of nickel, copper, and platinum group elements (PGE) are associated with variable quantities of localized sulphide concentrations in mafi c and ultramafi c rocks. Ni-Cu deposits, nickel being the main economic commodity, are associated with high concentrations of sulphides, and the host bodies are classifi ed based on the nature of the confi ning magmatic environment: (1) meteorite-impact, (2) rift and continental fl ood basalt, (3) komatiitic, and (4) other related mafi c/ultramafi c bodies. Platinum group element deposits are also confi ned to mafi c/ultramafi c bodies, but are associated with low quantities of sulphides. Reef-type or stratiform PGE deposits form in large, well-layered mafi c/ultramafi c intrusions, whereas magmatic breccia-type deposits occurs in stock-like or layered bodies.
En el Segmento Norte de La Cordillera Occidental de Colombia, al norte del Cinturón plegado de It... more En el Segmento Norte de La Cordillera Occidental de Colombia, al norte del Cinturón plegado de Itsmina y la Falla del río San Juan que se localiza entre el Cerró Tatamá y los Farallones del Citará, afloran una serie de plutones que intruyen el Complejo Santa Cecilia -La Equis -Batolito de Mandé (Arco de Chocó -Panamá), el Complejo Cañasgordas y los Basaltos de El Botón (Arco de El Botón), cuerpos intrusivos que afloran desde Pueblo Rico (Risaralda) hasta Dabeiba (Antioquia).
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Papers by Lucas Vásquez
the entire Northern Andean Block (the Andes of Ecuador, Colombia, and Venezuela) is presented in this paper.
Phreatic breccias are presented here. Their general features, i.e. environment/ depth of formation, general form/geometry, dimensions, contacts with the host rocks, fragments, matrix, alteration, mineralization, surface connection, fluidization and facies changes were examined. Furthermore, genetic criteria, very useful in phreatic breccia recognition are summarized
have mainly been interested in developing qualitative descriptive approaches, leading to a confusing profusion of terms.
Brecciation originates in numerous ways, resulting in highly complex classification systems and frequent misinterpretations
of facies. Field observations are difficult to reconcile with physical theories of fragmentation, partly due to the fact that few
satisfactory quantitative tools have been developed. A review of the main brecciation processes occurring in hydrothermal
vein-type deposits allows for the discrimination between chemical and physical mechanisms, including tectonic comminu-
tion, wear abrasion, two types of fluid-assisted brecciation hydraulic and critical., volume expansion or reduction, impact
and collapse. Each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry,
including fragment morphology, size distribution of the fragments, fabric, and dilation ratio. The first two parameters are
especially important because: 1. the morphology of the fragments allows chemical and physical mechanical. breccias to be
distinguished, and 2. the particle size distribution PSD. is a function of the energy input during breccia formation. The
slope of the cumulative PSD fractal dimension. ranges from high values for high-energy brecciation processes, to low
values for low energy processes indicated by an isometric distribution. The evolution of a vein system can be divided into
three stages: propagation, wear and dilation. These stages are separated by one threshold of mechanical discontinuity and
one of hydraulic continuity. These two thresholds also mark the transition between different types of brecciation.
Mineralization occurs during all three stages and may display different textures due to pressure variations. The use of
quantitative parameters in fault-related hydrothermal breccias allows a better understanding of the physical parameters
related to a vein environment, including structural setting and crustal level, as well as fluid–rock interactions. Recognition of
the different breccia types could also be important during the early stages of mineral exploration. q1997 Elsevier Science
B.V.
epigenetic breccias remain an enigmatic topic for many geologists. This
classification of breccias is genetic and based on the inferred role of magmas,
magmatic volatiles and their interaction with groundwaters. It is taken from a
classification by Sillitoe (1985) and a modified and expanded classification in
Lawless et al (1998).
first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren
surface-venting phreatomagmatic diatreme, prior to a final stage of supergene enrichment. It was emplaced in the
Miocene (~8–5 Ma) as an outlier of the Farallón Negro Volcanic Complex in northwestern Argentina.
The Agua Rica deposit lies next to the contact between Precambrian or lower Paleozoic metasedimentary rocks
and coarse-grained Ordovician granites. In a first pulse of Miocene magmatism, equigranular to porphyritic intrusions
were emplaced, with minor potassic alteration and weak Cu-Mo mineralization. Subsequent intrusion of
feldspar porphyries was associated with intense porphyry-style stockwork veining, potassic and propylitic alteration,
and disseminated Cu-Mo-Au mineralization (molybdenite, chalcopyrite ± bornite ± pyrite). The present alteration
and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal
assemblages (phyllic and advanced argillic alteration and Cu-Au-Ag-As-Pb-Zn mineralization) in breccia cements
and as void fillings. Covellite is the dominant copper mineral in the ore and seems to have partly or completely
replaced chalcopyrite and bornite of the earlier porphyry events. The high sulfidation epithermal assemblages are
closely related to the emplacement of a largely clast-supported hydrothermal breccia. Three major bodies of this
breccia have been mapped on the basis of clast lithology, clast shape and size, degree of alteration, and composition
of breccia matrix. Igneous breccia with a fine-grained porphyritic matrix is intimately associated and interfingers
with the base of the hydrothermal breccia columns. A final phase of magmatic hydrothermal activity
formed a matrix-supported and commonly bedded crater infill breccia. It formed by a surface-venting
phreatomagmatic eruption, as shown by a continuous downward transition from bedded breccias to clast-supported
breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine-grained porphyritic matrix
in the lower core of the conical crater infill breccia body. Graded, matrix-rich epiclastic sediments subsequently
filled the crater. Magmatic activity was terminated by a dike of unmineralized biotite porphyry, which intruded
the crater infill breccia. Talus breccia was shed into the crater from the rim. Supergene leaching and enrichment,
which replaced covellite, pyrite, chalcopyrite, and bornite by chalcocite and secondary covellite, formed an enrichment
blanket that was dissected by the present-day, steeply incised topography.
The distinctive feature of the Agua Rica hydrothermal system is the occurrence of early, weakly mineralized
intrusions, later feldspar porphyries with stockwork-hosted chalcopyrite-bornite-molybdenite mineralization,
hydrothermal breccias with an epithermal pyrite-covellite overprint, and barren surface-venting breccias—all
exposed at one location within 1,000 m of vertical exposure. Reconstruction of the time sequence of these geologic
elements indicates that Agua Rica is the result of a protracted history of magmatic hydrothermal activity
with superposition of several intrusion events that probably extended over several million years during progressive
regional uplift, erosion, and explosive unroofing.
the entire Northern Andean Block (the Andes of Ecuador, Colombia, and Venezuela) is presented in this paper.
Phreatic breccias are presented here. Their general features, i.e. environment/ depth of formation, general form/geometry, dimensions, contacts with the host rocks, fragments, matrix, alteration, mineralization, surface connection, fluidization and facies changes were examined. Furthermore, genetic criteria, very useful in phreatic breccia recognition are summarized
have mainly been interested in developing qualitative descriptive approaches, leading to a confusing profusion of terms.
Brecciation originates in numerous ways, resulting in highly complex classification systems and frequent misinterpretations
of facies. Field observations are difficult to reconcile with physical theories of fragmentation, partly due to the fact that few
satisfactory quantitative tools have been developed. A review of the main brecciation processes occurring in hydrothermal
vein-type deposits allows for the discrimination between chemical and physical mechanisms, including tectonic comminu-
tion, wear abrasion, two types of fluid-assisted brecciation hydraulic and critical., volume expansion or reduction, impact
and collapse. Each of these mechanisms can be distinguished using nonscalar parameters that describe breccia geometry,
including fragment morphology, size distribution of the fragments, fabric, and dilation ratio. The first two parameters are
especially important because: 1. the morphology of the fragments allows chemical and physical mechanical. breccias to be
distinguished, and 2. the particle size distribution PSD. is a function of the energy input during breccia formation. The
slope of the cumulative PSD fractal dimension. ranges from high values for high-energy brecciation processes, to low
values for low energy processes indicated by an isometric distribution. The evolution of a vein system can be divided into
three stages: propagation, wear and dilation. These stages are separated by one threshold of mechanical discontinuity and
one of hydraulic continuity. These two thresholds also mark the transition between different types of brecciation.
Mineralization occurs during all three stages and may display different textures due to pressure variations. The use of
quantitative parameters in fault-related hydrothermal breccias allows a better understanding of the physical parameters
related to a vein environment, including structural setting and crustal level, as well as fluid–rock interactions. Recognition of
the different breccia types could also be important during the early stages of mineral exploration. q1997 Elsevier Science
B.V.
epigenetic breccias remain an enigmatic topic for many geologists. This
classification of breccias is genetic and based on the inferred role of magmas,
magmatic volatiles and their interaction with groundwaters. It is taken from a
classification by Sillitoe (1985) and a modified and expanded classification in
Lawless et al (1998).
first overprinted by polystage brecciation associated with a high sulfidation epithermal event and then by a barren
surface-venting phreatomagmatic diatreme, prior to a final stage of supergene enrichment. It was emplaced in the
Miocene (~8–5 Ma) as an outlier of the Farallón Negro Volcanic Complex in northwestern Argentina.
The Agua Rica deposit lies next to the contact between Precambrian or lower Paleozoic metasedimentary rocks
and coarse-grained Ordovician granites. In a first pulse of Miocene magmatism, equigranular to porphyritic intrusions
were emplaced, with minor potassic alteration and weak Cu-Mo mineralization. Subsequent intrusion of
feldspar porphyries was associated with intense porphyry-style stockwork veining, potassic and propylitic alteration,
and disseminated Cu-Mo-Au mineralization (molybdenite, chalcopyrite ± bornite ± pyrite). The present alteration
and mineralization pattern is dominated by an almost pervasive overprint of high sulfidation epithermal
assemblages (phyllic and advanced argillic alteration and Cu-Au-Ag-As-Pb-Zn mineralization) in breccia cements
and as void fillings. Covellite is the dominant copper mineral in the ore and seems to have partly or completely
replaced chalcopyrite and bornite of the earlier porphyry events. The high sulfidation epithermal assemblages are
closely related to the emplacement of a largely clast-supported hydrothermal breccia. Three major bodies of this
breccia have been mapped on the basis of clast lithology, clast shape and size, degree of alteration, and composition
of breccia matrix. Igneous breccia with a fine-grained porphyritic matrix is intimately associated and interfingers
with the base of the hydrothermal breccia columns. A final phase of magmatic hydrothermal activity
formed a matrix-supported and commonly bedded crater infill breccia. It formed by a surface-venting
phreatomagmatic eruption, as shown by a continuous downward transition from bedded breccias to clast-supported
breccias with sandy or pumiceous matrix to a solid igneous breccia with a fine-grained porphyritic matrix
in the lower core of the conical crater infill breccia body. Graded, matrix-rich epiclastic sediments subsequently
filled the crater. Magmatic activity was terminated by a dike of unmineralized biotite porphyry, which intruded
the crater infill breccia. Talus breccia was shed into the crater from the rim. Supergene leaching and enrichment,
which replaced covellite, pyrite, chalcopyrite, and bornite by chalcocite and secondary covellite, formed an enrichment
blanket that was dissected by the present-day, steeply incised topography.
The distinctive feature of the Agua Rica hydrothermal system is the occurrence of early, weakly mineralized
intrusions, later feldspar porphyries with stockwork-hosted chalcopyrite-bornite-molybdenite mineralization,
hydrothermal breccias with an epithermal pyrite-covellite overprint, and barren surface-venting breccias—all
exposed at one location within 1,000 m of vertical exposure. Reconstruction of the time sequence of these geologic
elements indicates that Agua Rica is the result of a protracted history of magmatic hydrothermal activity
with superposition of several intrusion events that probably extended over several million years during progressive
regional uplift, erosion, and explosive unroofing.