Composición del granate de la pegmatita LCT Reflejos de Mar, distrito Ancasti, Argentina, y su implicancia en la exploración de depósitos primarios de litio

La pegmatita Reflejos de Mar, ubicada en el distrito Ancasti de la Provincia Pegmatítica Pampeana (PPP), en el noroeste de Argentina, pertenece a la familia LCT (Li-Cs-Ta). Mediante microsonda electrónica, se determinaron los contenidos de elementos mayores y minoritarios (SiO2 , TiO2 , Al2 O3 , Cr2 O3 , MgO, CaO, MnO, FeO) del centro y borde de cuatro cristales de granates provenientes de una muestra extraída de la zona más externa de la pegmatita. De acuerdo con sus contenidos de Mn y Fe, los granates son asignados a la serie espesartina-almandino. Los centros y los bordes de los cristales analizados tienen similares valores de SiO2 y Al2 O3 , ~36 y ~21%, respectivamente, mientras que los contenidos de Cr2 O3 y TiO2 son muy bajos (˂0,17%). El mayor contraste entre el borde y centro de los cristales lo presentan los componentes divalentes en coordinación VIII, especialmente Mn y Fe. Los contenidos promedio de MnO y FeO en los centros de los granos son de 34,6 y 8,29% peso, respectivamente, mientras que en los bordes son 29,31 y 12,95% peso, respectivamente. La relación Fe/Mn en el centro de los granos es 0,24, mientras que en los bordes es de 0,44. La fórmula química del centro de los granates analizados puede ser expresada como [(Mn2,40 Fe0,57 Ca0,02 Mg0,02) 3,01 (Al1,99 Cr0,002) 2,00 (Si2,99 Ti0,01) 3,00 O12] y la fórmula molecular como {Sps79,8 Alm18,9 Grs0,7 Prp0,5}. A su vez, la fórmula química de los bordes es [(Mn2,04 Fe0,89 Ca0,05 Mg0,04)3,02 (Al2,00 Cr0,002)2,00 (Si2,98 Ti0,005)3,00 O12] y la fórmula molecular es {Sps67,6 Alm29,5 Grs1,6 Prp1,3}. La composición química obtenida para el granate de la pegmatita Reflejos de Mar es similar a la de otros ejemplos en el mundo en rocas similares, especialmente de pegmatitas LCT altamente evolucionadas asociadas con mineralización de litio. Esto nos permite sugerir que la composición del granate en las pegmatitas puede ser utilizado como una herramienta adicional, en la exploración de pegmatitas mineralizadas con Li en la PPP. Las diferencias composicionales de Mn y Fe entre el centro y el borde de los cristales podrían estar vinculadas a variaciones en la composición del magma pegmatítico y, adicionalmente, por la cristalización simultánea de otras fases minerales, tales como chorlita y fosfatos portadores de Mn y Fe.The Reflejos de Mar Li-pegmatite, located in northwestern Argentina, is part of the Villismán pegmatite group, Ancasti District, Pampean Pegmatite Province. Four garnet crystals from the outermost part of the pegmatite were analyzed by major and minor elements (SiO2, TiO2, Al2 O3, Cr2 O3, MgO, CaO, MnO, FeO) using electron microprobe. The pegmatite belongs to the rare-element class, spodumene type, LCT (Li-Cs-Ta) petrogenetic family. Based on their Mn and Fe contents, the analyzed garnet can be assigned to the spessartine-almandine serie. The cores and rims of the analyzed garnets show significant differences for the divalent components in VIII-coordination, especially, Mn and Fe. The average MnO and FeO contents in the cores of the grains is 34.6 and 8.29 wt%, respectively, while in the rims is 29.31 and 12.95 wt%, respectively. The Fe/Mn ratio at the core of the grains is 0.24 while at the rims it is 0.44. Cr2 O3 and TiO2 contents are very low (˂0.17 wt%) and the values of SiO2 and Al2 O3 are ~36 and ~21 wt%, respectively. The mean chemical and molecular formulas of the core can be expressed: [(Mn2.40 Fe0.57 Ca0.02 Mg0.02)3.01 (Al1.99 Cr0.002)2.00 (Si2.99 Ti0.01)3.00 O12 ]; {Sps79.8 Alm18.9 Grs0.7 Prp0.5 }; and the rim as: [(Mn2.04 Fe0.89 Ca0.05 Mg0.04)3.02 (Al2.00 Cr0.002)2.00 (Si2.98 Ti0.005)3.00 O12 ]; {Sps67.6 Alm29.5 Grs1.6 Prp1.3 }. The chemical composition of garnet from the Reflejos de Mar pegmatite is similar to other worldwide examples in similar rocks, especially LCT pegmatites, which are highly evolved and associated with Li mineralization. Therefore, its composition could be used as an additional tool in the exploration of Li-bearing pegmatites in the Pampean Pegmatite Province. The differences in Fe-Mn contents between core and rim of the crystals would be controlled by variations in composition of the pegmatitic melt and, in addition, by the simultaneous precipitation of other mineral phases, for example, schorl and Mn-Fe-bearing phosphates.Fil: Sardi, Fernando Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; ArgentinaFil: Boscato Gomes, Márcia Elisa. Universidade Federal do Rio Grande do Sul; BrasilFil: Marangone, Silvana Elizabeth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Instituto Superior de Correlación Geológica. Universidad Nacional de Tucumán. Facultad de Ciencias Naturales e Instituto Miguel Lillo. Departamento de Geología. Cátedra Geología Estructural. Instituto Superior de Correlación Geológica; Argentin

ARQUITETURA INTERNA E PETROGRAFIA DO DERRAME SALTO DO LONTRA, SUDOESTE DO ESTADO DO PARANÁ

O derrame Salto do Lontra está inserido na Província Magmática do Paraná e localiza-se no sudoeste do Estado do Paraná. O derrame possui 50 m de espessura e apresenta distribuição, arranjo de suas estruturas internas e padrões de fraturas bem definidos. Estas características permitem a divisão do derrame em: nível vesicular de topo, nível maciço central e nível vesicular de base. Estas características definem a arquitetura interna e sugerem que o derrame foi formado por processos de inflamento e se resfriou como um único corpo de lava, das bordas para o centro. Ocorrem corpos de pegmatito básico, com formas alongadas, alojados no terço superior do derrame. Estes corpos têm assembleia mineral semelhante aos basaltos encaixantes e são diferenciados principalmente pela granulação e presença de amígdalas. Os basaltos e pegmatitos possuem assembleia mineral primária constituída principalmente por andesina, augita, magnetita, ilmenita e apatita, e secundária por clorita e hematita

Paleoenvironmental implications of authigenic magnesian clay formation sequences in the Barra Velha formation (Santos Basin, Brazil)

The characterization of Mg-clays in rock samples (well P1) from the Barra Velha Formation (Early Cretaceous) allowed the establishment of mineral assemblages on the basis of their kerolite and Mg-smectite (stevensite and saponite) content. Kerolite-rich assemblages (A and B) rarely con-tain saponite. Assemblage B is composed of kerolite-stevensite mixed layers, while assemblage A consists of more than 95% kerolite. Mg-smectite-rich assemblages (C and CB) are made up of both Mg-smectites. The predominance of stevensite in the lower interval of the stratigraphic succession suggests evaporative conditions, higher salinity and pH, which would favor its authigenesis by neoformation. In the upper portion, the occurrence of thick kerolite-rich intervals suggests regular water inputs, contributing with a decreasing in salinity and pH, favoring the neoformation of kero-lite and later kerolite-stevensite mixed layering. The saponite would be the result of the transfor-mation from Al-smectite into Mg-smectite in a Mg2+ rich medium. The results indicate that lake hydrochemical processes would have allowed the establishment of a basic depositional sequence, from base to top, as follows: (i) initial lake expansion stage marked by the occurrence of saponite, (ii) later kerolite neoformation, (iii) formation of kerolite-stevensite mixed layer with increasing sa-linity, and (iv) neoformation of stevensite, marking a final stage of maximum salinity (evaporation) and alkalinity of the lak

MORPHOLOGICAL AND PETROGRAPHIC CHARACTERIZATION OF SALTO SEGREDO FLOW – SERRA GERAL FORMATION, PARANÁ STATE, BRAZIL

O derrame Salto Segredo localiza-se na localidade homônima, entre os municípios de Mangueirinha e Reserva do Iguaçu – PR, nos arredores da Usina Hidrelétrica Salto Segredo (Gov. Ney Braga). A área onde o derrame foi estudado é delimitada pelas coordenadas geográficas 52º5’ e 52º8’ W e 25º45’ e 25º’48 S. O escopo do trabalho é caracterizar as feições internas de uma parte do derrame Salto Segredo, com base no padrão de fraturas gerado pela contração da rocha durante o resfriamento, e variações estruturais, texturais e mineralógicas. O derrame possui aproximadamente 40 m de espessura e é composto majoritariamente por labradorita, augita, óxidos de Fe e Ti e mesóstase. De acordo com sua estruturação interna foi dividido em três níveis: (1) nível vesicular de base, caracterizado pela textura ofítica e padrão irregular de fraturas; (2) nível maciço central, o mais espesso do derrame, pode ainda ser subdividido em porção mediana-inferior, com fraturas irregulares e descontínuas subverticais; e porção mediana-superior, que apresenta fraturas regulares e contínuas subverticais com traçados retilíneos ou sigmoidais; (3) nível vesicular de topo, com abundante presença de vesículas, amígdalas e geodos e ausência de fraturas marcantes. Um segundo objetivo do trabalho é o reconhecimento de estruturas indicativas de segregação e inflação, como cilindros de vesículas, zonas vesiculares horizontais, lençóis de vesículas e amígdalas e geodos achatados.The Salto Segredo Flow is located in the homonymous locality, between Mangueirinha and Reserva do Iguaçu cities, Paraná State, Brazil, nearby Salto Segredo (Gov. Ney Braga) Hydropower Plant. The area where Salto Segredo flow was studied is delimited by geographic coordinates 52º5’ e 52º8’ W e 25º45’ e 25º’48 S. The work purpose is to characterize the internal structures of a part of the Salto Segredo flow, according to fractures patterns resulting from rock contraction during cooling, structural, textural and mineralogical variations. The flow is approximately 40 m thick and is majorly compound by labradorite, augite, Fe and Ti oxides and mesostasis. According to its internal structures the flow can be divided into three levels: (1) base vesicular level, characterized by the ophitic texture and irregular pattern o fractures; (2) center massive level, the thicker in the flow, can be divided into lower-median portion, with subvertical, irregular and discontinuous fractures; and upper-median portion, which presents subvertical, continuous and regular fractures, with rectilineal or curve tracks; (3) top vesicular level, abundant in vesicle, amygdules and geodes without distinguished fractures. A second aim of the present work is to recognize indicative structures of segregation and inflation process, such as vesicle cylinders, horizontal vesicular zones, vesicle sheets and flat amygdules and geodes

New Insights into the Evolution and Footprints of the Paraíba Au-Cu-Mo Deposit, Alta Floresta Mineral Province (Brazil), through Integration of Spectral and Conventional Methods

The Paraíba is an Au-Cu-Mo deposit located in the southern part of the Amazon Craton, in the Alta Floresta Mineral Province, Mato Grosso State, Brazil. It is composed of Au-Cu-bearing quartz veins and Cu-Mo-rich hydrothermal breccias and stockworks, both associated with several hydrothermal alteration zones. The integration of spectral (reflectance and imaging spectroscopy) and conventional techniques (core logging, petrography, mineral chemistry, and scanning electron microscopy) was applied to map alteration zones, identify mineral parageneses, and determine the evolution of the deposit to generate a solid proxy for mineralized zones. This study shows an overlapping of two different mineralization systems in the AFMP, referenced hereafter as alteration Groups 1 and 2. Group 1 is an Orogenic Gold system related to Au-Cu-rich quartz veins in phyllonites and mylonites. Group 2 is a Cu-Mo Porphyry system related to a syenogranite intrusion and the subsequent generation of several hydrothermal alteration zones, Cu and Mo hydrothermal breccias, and stockwork mineralization. This study reveals several alteration footprints, guides, and vectors for the mineral exploration of these deposits in the Alta Floresta Mineral Province

New Insights into the Evolution and Footprints of the Paraíba Au-Cu-Mo Deposit, Alta Floresta Mineral Province (Brazil), through Integration of Spectral and Conventional Methods

The Paraíba is an Au-Cu-Mo deposit located in the southern part of the Amazon Craton, in the Alta Floresta Mineral Province, Mato Grosso State, Brazil. It is composed of Au-Cu-bearing quartz veins and Cu-Mo-rich hydrothermal breccias and stockworks, both associated with several hydrothermal alteration zones. The integration of spectral (reflectance and imaging spectroscopy) and conventional techniques (core logging, petrography, mineral chemistry, and scanning electron microscopy) was applied to map alteration zones, identify mineral parageneses, and determine the evolution of the deposit to generate a solid proxy for mineralized zones. This study shows an overlapping of two different mineralization systems in the AFMP, referenced hereafter as alteration Groups 1 and 2. Group 1 is an Orogenic Gold system related to Au-Cu-rich quartz veins in phyllonites and mylonites. Group 2 is a Cu-Mo Porphyry system related to a syenogranite intrusion and the subsequent generation of several hydrothermal alteration zones, Cu and Mo hydrothermal breccias, and stockwork mineralization. This study reveals several alteration footprints, guides, and vectors for the mineral exploration of these deposits in the Alta Floresta Mineral Province

PETROGRAPHY AND MINERAL CHEMISTRY OF THE SÃO GERALDO GRANITE: EVIDENCE OF PERALUMINOUS MAGMATISM IN THE PORTO ALEGRE REGION.

Este trabalho descreve a primeira ocorrência de um granito peraluminoso na região de Porto Alegre, denominado Granito São Geraldo. Neste estudo foram realizadas análises petrográficas (microscopia óptica e eletrônica) e de química mineral (microssonda eletrônica) em lâminas delgadas oriundas de testemunhos de sondagem. O granito apresenta textura equigranular hipidiomórfica média e composição que varia de sieno a monzogranítica. Sua mineralogia é constituída por K-feldspato (37-48 %), quartzo (17-33 %), plagioclásio (23-28 %), muscovita + biotita (7-11 %) e, subordinadamente (< 1 %), granada, zircão, monazita, apatita, ilmenita e magnetita. A biotita, de origem primária, apresenta teores de elementos maiores (e.g. Al, Fe e Mg) compatível com as de granitos peraluminosos. A muscovita em geral é magmática, com composição similar a dos granitos fortemente peraluminosos (e.g. teores de Al, Fe, Mg e Ti). Os teores de Or do K-feldspato (ortoclásio) variam entre 86-97 %. O plagioclásio é  predominantemente oligoclásico, subordinadamente apresentando composição albítica. Teores elevados de espessartina da granada (26-32 %) sugerem uma origem magmática. A apatita (fluorapatita) apresenta teores de F entre 3,0-4,5 %. O caráter peraluminoso deste granito o difere de todos os granitos descritos na região de Porto Alegre. Sua composição é similar a dos granitos com duas micas que compõem a Suíte Cordilheira (Batólito Pelotas), a qual engloba a maioria dos granitos peraluminosos tipo-S, sintranscorrentes a zonas de cisalhamento transcorrentes dúcteis encontradas no domínio oriental do Cinturão Dom Feliciano.The present work describes the first occurrence of a peraluminous leucogranite in the Porto Alegre city region, named São Geraldo Granite. Thin sections from drill cores were studied through petrography (optical and electron microscopy) and mineral chemistry (electron probe microanalysis). The granite shows a medium to fine grained, equigranular hypidiomorphic texture, and a composition ranging from sieno- to monzogranitic. Its mineralogy comprises K-feldspar (37-48 %), quartz (17-33 %), plagioclase (23-28 %), muscovite + biotite (7 to 11%), and subordinate amounts (< 1%) of garnet, zircon, monazite, apatite, ilmenite, and magnetite. The biotite, interpreted as magmatic in origin, shows major element concentrations (e.g. Al, Fe, and Mg) compatible with those generated in peraluminous granites. The muscovite is predominantly magmatic, with a composition compatible with those of the strongly peraluminous granites. The Or contents of the K-feldspar (orthoclase) range from 86 to 97 %. The plagioclase is mostly oligoclase, showing secondary albitic composition. The spessartine contents of the garnet (26-32 %) suggest a magmatic origin. The apatite (fluorapatite) shows F concentration between 3.0-4.5 %. The peraluminous character of the studied granite differs from all granites described in the Porto Alegre region. Its composition is similar to those of the Cordilheira Suite (Pelotas Batholith), which encompasses most of the peraluminous S-type granites syncinematic emplaced in ductile shear zones found in the eastern domain of the Dom Feliciano Belt

Mineralogical Study of Levels with Magnesian Clay Minerals in the Santos Basin, Aptian Pre-Salt Brazil

The object of this study is magnesian clay minerals present in carbonate rocks of the post-rift phase of the pre-salt in the Santos Basin. These rocks developed in an Aptian-age alkaline lacustrine environment. This study summarizes the formation of clay minerals associated with different lithotypes in a range of 19 m and a depth of more than 5100 m. They were characterized from petrographic analysis by optical microscopy, X-ray diffraction (total sample and clay fraction), and modeling by Newmod®; and examined and analyzed by scanning electron microscopy. An approach based on identifying lithotypes and characterization of microsites allowed us to understand the occurrence of different clay minerals. Kerolite was the most abundant mineral in the sampled range. It occurs in lamellar aggregates under greater preservation of the original rock lamination and in association with spherulites and shrubs. The Stv/Ker mixed layers occurs in the same association, and formed finer unlaminated aggregates associated with the more intense dolomitization and silicification processes. Saponite occurs associated with detrital minerals forming clayey levels intercalated with microcrystalline carbonates. Fluids with a high Mg/Si and pH &lt; 9 favor the precipitation of kerolite. The increase in pH during diagenesis may be responsible for the formation of Stv/Ker mixed layers