The Late Cretaceous Mata da Corda Formation, located in the eastern part of the Alto Paranaíba Igneous Province (APIP), Central Brazil, is one of the few places on Earth where kamafugite melts ...reached the surface generating large volumes of lava, pyroclastic rocks and shallow intrusions over an area of 4,500 km
2
. The western part of the APIP, however, is dominated by hundreds of diatreme-like kamafugites and shallow kimberlite intrusions and by the occurrence of multi-stage alkaline-carbonatite complexes. These complexes feature silica-undersaturated K-rich alkaline rocks, such as aillikite, that closely resemble the mineralogy and geochemistry of kamafugite, albeit lacking feldspathoids. The spatial and temporal distribution of kamafugite and aillikite within the APIP suggests a connection between them. In addition, on a regional scale, airborne magnetic data show three highly magnetic dipole-like structures to the south of the Mata da Corda Formation of an undisclosed nature, which bear geophysical similar responses to the neighbouring alkaline-carbonatite complexes. Links between kamafugite and aillikite are evaluated by the following chemical and isotopic evidence: (1) kamafugite and aillikite compositions plot in the kamafugite field of Foley's ultrapotassic rock classification; (2) similar CI chondrite-normalized REE distribution, with aillikite enriched up to 2 times in REE compared to kamafugite; (3) both lithologies share almost the same rock-forming minerals; and (4) similar
143
Nd/
144
Nd
(i)
and
87
Sr/
86
Sr
(i)
ratios for all the APIP alkaline-carbonatite rocks, indicating a common source from an enriched lithospheric mantle. Therefore, silica-undersaturated rocks from alkaline-carbonatite complexes display an evolved ultrapotassic affinity indicative of a genetic link.
Alkaline‑carbonatite complexes are the main source of critical raw materials such as niobium (Nb) and rare earth elements (REE), which concentrate through a combination of magmatic and ...carbohydrothermal processes. These systems typically occur in close spatial connection with altered country rocks resulting from metasomatic alteration by exsolved K-Na-rich fluids, a process known as fenitization. Thus, the association between Nb-REE-rich carbonatites and fenites provides a unique opportunity for the investigation of carbohydrothermal alteration processes leading to critical metal enrichment. In this study, we focused on K-rich fenites associated with a shallow dike swarm system in the Boa Vista niobium deposit, the second-largest global producer of Nb, which is hosted within the Catalão II alkaline‑carbonatite complex in Central Brazil. We used a combination of micro-analytical techniques including EBSD, EMPA, and μ-EDXRF to unravel the complex micro-textural features of the fenites. Our data suggest that alkaline fluids exsolved vigorously from the carbonatite melts upon dike emplacement and pervasively metasomatized the country rocks, forming a melanocratic proximal fenite (phlogopitite), and distal fine-grained orthoclase-phlogopite-calcite fenites. Fluid alteration mobilized soluble cations (K, Fe, Mg, Ba, and Sr) plus S, CO2 and OH−, whereas Nb and REE were retained in the carbonatite dikes. The consistent dike-orthogonal orientation of metasomatic phlogopite and orthoclase grains in the proximal fenite, determined by EBSD, suggests that newly formed metasomatic minerals precipitated from the fenitizing fluids along the flow path. These orientations differ from the isotropic textures defined by primary (magmatic) minerals like pyrochlore, tetraferriphlogopite, dolomite, and calcite. However, and despite the microstructural differences between magmatic and carbohydrothermal phlogopite, their mineral chemistry is similar, suggesting that fenites are almost synchronous to the emplacement of carbonatites. These data indicate that fenites provide a rich archive of alkali-rich fluid infiltration around Nb-REE-rich carbonatite intrusions.
•The Catalão II carbonatite complex produced a pervasive potassium-rich fenitization.•K-rich fenites include phlogopitite and phlogopite-orthoclase-calcite fenite.•Mineral chemistry of metasomatic phlogopite is similar to magmatic phlogopite cores.•Oriented basal plane of metasomatic phlogopite crystallized orthogonal to the dikes.•The metasomatic event was probably simultaneous with the carbonatite intrusion.
After the German geologist Emil Jakob Grosse concluded his work as head of the General Geological Commission of Colombia in April 1931, he lived and worked between Germany and Brazil, where his ...record has been largely unknown to the present date. In this contribution, we document some historical aspects of his life and briefly review Emil Grosse’s trajectory from Germany to Brazil. The oldest record of Emil Grosse in Brazil dates from August 20, 1936, when he worked at the “Fábrica mine” until 1939. The Fábrica mine contains an iron deposit located southeast of the São Francisco Craton in what is now known as Quadrilátero Ferrífero, within the municipality of Ouro Preto. Grosse worked in a hematite ore site located in a banded iron formation (BIF), but there is no record of him having worked in the coal deposits. Years after, in 1946, the Fábrica mine changed owners and name to Ferteco, a subsidiary of the German corporation Industriegewerkschaft Bergbau, with headquarters in Bochum, Germany, where Grosse possibly worked to validate the deposit. In the 1940s, Grosse lived between the steelworks town of Peine, Germany, and Belo Horizonte, Brazil. There is a record of his trip in the middle of the Second World War on October 26, 1942. In 1946, his work on the Fábrica mine was finally published in Volume XI (No. 62) of the Brazilian journal Mineração e Metalurgia. Later, on August 18, 1949, Grosse obtained his permanent visa through the mediation of the Brazilian Military Mission and the German control council. Finally, he settled in Würzburg, Germany, where in 1971, he died at the age of 91.
•The São Tomé intrusion, crystallized at ∼ 3.5 Ga, is the earliest record of continental crust generation in South America.•An intense fractional crystallization triggered immiscibility which was ...responsible for formation of Fe-Ti-V oxide ores.•Metasomatic imprint revealed Ar-Ar plateau ages of 597 ± 5 Ma and 517 ± 6 Ma that are coherent to the emplacement of local granites.
The São Tomé mafic-ultramafic intrusion, located in the Borborema Province, NE Brazil, consists of a group of metamorphosed dismembered intrusive rocks, composed of ol-websterite and clinopyroxenite, which host stratiform meter-sized massive ilmenite-magnetite lenses with up to 1.98 wt% V2O3 in magnetite. The ol-websterite rocks display dark discontinuous olivine bands intercalated with cumulate augite, whereas the clinopyroxenite rocks are composed mainly of anhedral augite. The mineral chemistry analysis of the mafic phases resulted in contents up to Fo87.28 and 4605 ppm of Ni in the olivine crystals and high-MgO augite (22.59 wt% MgO), suggesting that these rocks formed from the differentiation of a primitive, fertile peridotite melt. The retention of high nickel contents in the olivine crystals, despite the crustal contaminated signature revealed by Sm-Nd isotopes, suggests that there was no early sulfur saturation in the magma; additionally, the magnetite crystallization did not trigger sulfur saturation, inhibiting Ni-Cu sulfide precipitation or even the formation of individual platinum group metals (PGM) grains. Metamorphism at amphibolite-facies conditions resulted in the development of penetrative foliation and mineral assemblages, wherein tschermakite is dominant. Ultimately, the metasomatic imprint included the following stages: (1) a K-P-H2O stage, represented by newly formed phlogopite, apatite, chlorite and hornblende; (2) a calcic stage, with epidote-group minerals, calcite and minor pyrite, and (3) the least potassic alteration forming diablastic phlogopite and microcline. LA-ICP-MS U-Pb zircon data reveal a concordant age of 3506 ± 29 Ma for the São Tomé intrusion, interpreted as the igneous crystallization age, and thus, it represents the oldest record of continental crust generation in South America. 40Ar/39Ar phlogopite dating, on the other hand, revealed plateau ages of 597 ± 5 Ma and 517 ± 6 Ma. These Ediacaran-to-Cambrian ages represent the emplacement of local granites, which bear heavily on the source of magmatic fluids.
The Cauca metallogenic belt is an inter-Andean area located along the Cauca-Romeral fault zone, which is made up of a group of twelve Miocene magmatic-hydrothermal Au-Ag-Cu mineral deposits ...positioned between the Western and Central Cordillera of Colombia. In addition to being a widely developed region in exploration and exploitation with known Au endowments of over 1,700 tons, this area represents an exceptional metallogenetic laboratory for modeling a typical Andean-type mineralization from a calc-alkaline source with high Sr/Y ratios. Efficiency processes such as ion and halogen transport, oxygen fugacity and sulfur content have been extensively studied with a geochemical approach; however, the quantification and modeling of these efficiency processes currently debated. Through multiple iterations using Monte Carlo simulations (N > 2 million), the modeled reservoirs corresponding to the upper crust, using a high flux of dacitic magma of 0.007 km3/year and efficiencies of 1 – 2 %, showed that gold endowments bear heavily with magmatic and hydrothermal Au deposits in the Cauca Metallogenic Belt. Outcomes including Au endowments up to 1,000 tons can be obtained for reservoirs below 400 km3 of hydrous melt in brief mineralization intervals between 40 to 120 ka and for volumes of 400 to 800 km3 in a 120 to 200 ka window. In contrast, the hypothetical reservoirs for the lower and middle crust, through a basaltic calc-alkaline magma flux between 0.0007 and 0.0011 km3/year, an efficiency of ~0.7%, and pressures below 5 kbar, showed sufficient available content of exsolvable H2O and gold to feed the reservoirs in the upper crust or to generate gold deposits from them, but in longer time intervals (>1 Ma).
ABSTRACT The Cauca Metallogenic Belt (CMB) is an inter-Andean area located along the Cauca-Romeral fault zone of Colombia. The CMB comprises a group of twelve Late Miocene magmatic-hydrothermal ...Au-Ag-Cu mineral deposits positioned between the Western and Central Cordillera of Colombia. In addition to being a widely developed region in exploration and exploitation with known Au endowments of over 1,700 tons, this area represents an exceptional metallogenetic laboratory for modeling an archetype Andean mineralization from a calc-alkaline source with high Sr/Y ratios. Efficiency processes such as ion and halogen transport, oxygen fugacity, and sulfur content have been extensively studied in magmatic-hydrothermal deposits with a geochemical approach. However, the quantification and modeling of these efficiency processes are currently debated. Through multiple iterations using Monte Carlo simulations (N > 2 million), the authors modeled those reservoirs corresponding to the CMB's upper crust. In this way, a high flux of dacitic magma of 0.007 km3/year and efficiencies of 1-2% showed that gold endowments bear heavily with magmatic and hydrothermal Au deposits of the CMB. Outcomes including Au endowments up to 1,000 tons can be obtained for reservoirs below 400 km3 of hydrous melt in brief mineralization intervals between 40 to 120 ka, whereas volumes of400 to 800 km3 are obtained in a 120 to 200 ka range. In contrast, the hypothetical reservoirs for the lower and middle crust of the CMB, through a basaltic calc-alkaline magma flux between 0.0007 and 0.0011 km3/year, the efficiency of ~0.7%, and pressures below 5 kbar, showed sufficient available content of exsolvable H2O and gold to feed the reservoirs in the upper crust of the CMB or to generate gold deposits from them, but in longer time intervals (>1 Ma).
The Carboniferous Tertiary of Antioquia (TCA), published by Dr. Jakob Emil Grosse in 1926, is one of the most influential scientific results of the Ordinance 16 of 1918 of the Honorable Departmental ...Assembly of Antioquia. The work began with the main objective of quantifying the coal reserves of Antioquia, and showing their surface extension on a scale of 1:50 000, in a region that includes the Arma river to the Puente de Occidente and from the western side of the Cauca River to the Romeral lineament and the plains of Ovejas. As a result, extensive work comprising petrological, structural, and economic geology studies was published in a manuscript published in Spanish and German, plus four attached maps, including coal, gold, silver, kaolin, and carbonate mines, among others. In the present work, the four TCA maps were digitized at a scale of 1:50 000 with Bessel 1841 datum and created a unified file in .kml format, which can be used directly in field trips, via Google Earth on cell phones, tablets, or computers. The metadata associates the information in the TCA with the Servicio Geológico Colombiano for the year 2015. In addition, 480 thin sections were scanned, which were donated by Dr. Grosse to the Escuela Nacional de Minas and today are in the Museum of Geosciences of the Faculty of Mines of the Universidad Nacional de Colombia. The geospatial information contained in each thin section was interpreted and georeferenced, obtaining, as a result, a list with north and west geographic coordinates, in degrees, minutes, and seconds. This unpublished information is available in the supplementary material of this article. Finally, nine field trips were made to the places referenced in 23 photographs of the TCA between 1920 and 1923 to take their current equivalent and thus carry out a multi-temporal analysis of the TCA.
The Cauca Metallogenic Belt (CMB) is an inter-Andean area located along the Cauca-Romeral fault zone of Colombia. The CMB comprises a group of twelve Late Miocene magmatic-hydrothermal Au-Ag-Cu ...mineral deposits positioned between the Western and Central Cordillera of Colombia. In addition to being a widely developed region in exploration and exploitation with known Au endowments of over 1,700 tons, this area represents an exceptional metallogenetic laboratory for modeling an archetype Andean mineralization from a calc-alkaline source with high Sr/Y ratios. Efficiency processes such as ion and halogen transport, oxygen fugacity and sulfur content have been extensively studied in magmatic-hydrothermal deposits with a geochemical approach. However, the quantification and modeling of these efficiency processes are currently debated. Through multiple iterations using Monte Carlo simulations (N > 2 million), the authors modeled those reservoirs corresponding to the CMB's upper crust. In this way, a high flux of dacitic magma of 0.007 kirrVyear and efficiencies of 1-2% showed that gold endowments bear heavily with magmatic and hydrothermal Au deposits of the CMB. Outcomes including Au endowments up to 1,000 tons can be obtained for reservoirs below 400 km.sup.3 of hydrous melt in brief mineralization intervals between 40 to 120 ka, whereas volumes of 400 to 800 km.sup.3 are obtained in a 120 to 200 ka range. In contrast, the hypothetical reservoirs for the lower and middle crust of the CMB, through a basaltic calc-alkaline magma flux between 0.0007 and 0.0011 kirrVyear, the efficiency of ~0.7%, and pressures below 5 kbar, showed sufficient available content of exsolvable H.sub.2O and gold to feed the reservoirs in the upper crust of the CMB or to generate gold deposits from them, but in longer time intervals (>1 Ma). Keywords: Modeling; Monte Carlo simulations; Northern Andes; Miocene magmatism; CaucaMetallogenic Belt El Cinturon Metalogenico del Cauca (CMC) es un area interandina ubicada a lo largo de la zona de falla Cauca-Romeral de Colombia. El CMC esta compuesto por un grupo de doce depositos magmatico-hidrotermal de Au-Ag-Cu del Mioceno Tardio, ubicados entre la Cordillera Occidental y Central de Colombia. Ademas de ser una region ampliamente desarrollada en exploration y explotacion mineral, con dotaciones de Au conocidas de mas de 1700 toneladas, el CMC representa un laboratorio metalogenetico excepcional para modelar mineralizaciones de tipo andino a partir de una fuente calco-alcalina con altas razones de Sr/Y. A pesar que los procesos de eficiencia en depositos magmatico-hidrotermal han sido ampliamente estudiados con un enfoque geoquimico, como el transporte de iones y halogenos, la fugacidad de oxigeno y el contenido de azufre, entre otros, la cuantificacion y modelado de estos procesos de eficiencia han sido debatidos actualmente. A traves de multiples iteraciones usando simulaciones de Monte Carlo (N>2 millones), modelamos reservorios que corresponden a la corteza superior del CMC. Nuestros resultados aplicando un alto flujo de magma dacitico de 0.007 km.sup.3/ano y eficiencias entre 1-2%, mostraron que las dotaciones modeladas de oro corresponden fuertemente a las cantidades de Au reportadas de los depositos magmatico-hidrotermal del CMC. Con dicho modelado se pueden obtener dotaciones de Au de hasta 1000 toneladas para reservorios inferiores de 400 km.sup.3 de magma hidratado en breves intervalos de mineralizacion entre 40 y 120 ka, mientras que se obtienen volumenes de 400 a 800 km.sup.3 con un periodo de mineralizacion entre 120 a 200 ka. Por el contrario, los reservorios modelados para la corteza inferior y media del CMC, a traves de un flujo de magma basaltico calco-alcalino entre 0,0007 y 0,0011 km.sup.3/ano, una eficiencia de ~0,7% y presiones menores a 5 kbar, mostraron suficiente contenido de H.sub.2O soluble y oro disponible para alimentar los reservorios en la corteza superior del CMC, o para generar depositos de oro a partir de ellos, pero en intervalos de tiempo mas largos (> 1 Ma). Palabras clave; Modelado; Simulaciones de Monte Carlo; Andes del norte; Magmatismo Mioceno; Cinturon Metalogenico del Cauca
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