Trace element signatures in rutile: characterization of standards and applications to accessory mineral behavior in metamorphic rocks

This study focuses on the trace element composition of rutile, a frequent accessory mineral in various rock types (mafic, pelitic and felsic protoliths; common at blueschist-, eclogite- and granulite-facies conditions) and one of the most stable minerals in sedimentary environments. Rutile is an important carrier of highly charged elements, such as Ti, V, Cr, Zr, Nb, Sn, Sb, Hf, Ta and W. Due to these characteristics rutile has attracted significant interest in various fields of geology, e.g., as a likely controller of Nb and Ta budgets in subduction zones. Furthermore, it is useful as a geothermometer (Zr incorporation is strongly temperature dependent in quartz- and zircon-bearing systems), and as a geochronological tool (U-Pb and (U-Th)/He dating), and to assess the nature of an initial source rock in sediment provenance studies (Nb and Cr contents can de used to distinguish between mafic and felsic sources). An increasing number of today’s geochemical studies, which include the investigations presented here, are based on microanalysis of trace elements, several of which are carried out in-situ. All of these techniques depend on calibration using a homogeneous material with well documented chemical concentration. In this sense, having a rutile standard is a key issue. A set of rutile crystals were investigated in order to find rutiles suitable for use as mineral standards. Trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Pb and Hf isotope data are presented for four large (centimeter size) and relatively homogeneous rutile grains. Analytical techniques used are SIMS, EMP, LA–ICP–MS, ID–MC–ICP–MS and TIMS. For most elements, homogeneity is usually within ±10% and variations are occasionally less than (±5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the element and agreement between techniques, are presented for Zr, Nb, Sn, Sb, Hf, Ta, W and U. One of the studied grains has a relatively high U concentration (ca. 30 ppm) and rather constant U–Pb ages (1085.1 to 1096.2 Ma, 207Pb/235U ages and 1086.3 to 1096.6 Ma, 206Pb/238U ages), favoring its application as an age standard for U-Pb rutile dating. The studied rutiles are useful as mineral standards in for in-situ rutile measurements, particularly for Zr–in–rutile thermometry, quantitative provenance studies (Nb and Cr concentrations as an index of source rock type) and U–Pb dating. The efforts in characterizing a set of rutile standards are not only relevant for the scientific community. It also provides the analytical background for the results presented here. Following the characterization of standards, textural observations and in-situ analyses were used to investigate trace element behavior during prograde and retrograde metamorphic reactions involving rutiles. The investigated samples derive from two well studied localities: the Ivrea-Verbano Zone (Italy) and the Erzgebirge (Germany). The Ivrea-Verbano Zone is a classic granulite area and rocks from the Strona and d’Ossola Valleys are an example of the amphibolite to granulite facies transition, where rutile growth is associated with the breakdown of high-Ti biotite. Rutile bearing rocks show a rich inventory of textures that allow for the investigation of trace element behavior in response to prograde rutile growth, and the effect of postpeak processes on rutile chemistry. Nb concentrations in rutile from lower grade samples show a larger spread (from 500 to 5000 ppm within one sample) when compared to those from higher grades. This pattern can be modeled using prograde rutile growth formed from biotite breakdown. Zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution. Maximum Zr concentrations increase according to the general metamorphic gradient known for this area. Temperatures (from Zr-in-rutile thermometry), although feasible, are considerably higher than previous calculations (increasing from ca. 850 to 930°). A second cluster of Zr concentrations in rutile occurs at rather constant concentrations (ca. 1000 ppm) for all localities and is interpreted to be related to intense fluid influx at high temperature and/or to post-peak diffusional resetting favored by slow cooling rates. Alteration textures, characterized by a complex network of microveins, are evidence for the late fluid influx. The fluid strongly affected the rutiles, which is evidenced by corrosion of older rutile grains and the formation of rutile veinlets. In the Ezgebirge, metamorphic texture support prograde rutile growth from ilmenite in low- to medium-grade (430-630C° metasedimentary rocks. Newly crystallized rutiles occur as polycrystalline aggregates that mimic the shape of the ilmenites. In-situ trace element data show that rutiles from the lowest grade samples (ca 480C° mirror the Nb/Ti ratio of ilmenite. Under these conditions, rutile did not equilibrate its chemistry with the remaining ilmenites. In higher grade samples, rutiles show a larger scatter in Nb and have Nb/Ti ratios higher than relict ilmenite. In these rocks, the Nb pattern can be modeled using prograde rutile growth from ilmenite, in a model similar to the one applied to granulites from the the Ivrea- Verbano Zone. Results indicate that rutiles from these rocks were able to reequilibrate its chemistry with the remaining ilmenites. Newly formed rutiles yield temperatures (from 500 to 630C° that are in agreement with the metamorphic conditions published for the studied rocks. Detrital rutile grains, identified by their distinct chemical composition (high Zr and Nb contents) and textures (single grains surrounded by fine grained ilmenites), occur in quartzites from the medium-grade rocks (ca 530C°. This confirms models in which detrital rutiles survive in quartzites to higher metamorphic grade compared to rutiles in metapelites. Preliminary calculations based on the grain size distribution of rutiles in the studied rocks show that quartzites are probably the main source of rutiles in sediments derived from low-grade metamorphic sequences, even if the occurrence of quartzite is minor. Part of the data obtained during the development of this thesis contributed to other publications related, directly or indirectly, to its topic. For example, to evaluate how well the Zr-in-rutile thermometer can be applied to eclogites; to evaluate the applicability of rutile trace element geochemistry to provenance studies; and to characterize the occurrence and stability of coesite-bearing tourmaline in ultra-high pressure metamorphic rocks

Discrimination of TiO2 polymorphs in sedimentary and metamorphic rocks

Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase, whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase trace element characteristics and re-equilibration of relict rutiles. Evaluation of trace element contents obtained by electron microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand. For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace elements proves to be a valuable tool besides Raman spectroscopy.Postprint (published version

IMAGENS LANDSAT-7/ETM+ E SRTM COMO FERRAMENTAS AUXILIARES NA IDENTIFICAÇÃO DE PERFIS LATERÍTICOS – EXEMPLO EM BOM JESUS DA PENHA (MG).

Os perfis lateríticos cobrem vasta área do território brasileiro e seus estudos são motivados por fins diversos. Internamente se estruturam na forma de horizontes com variação vertical de suas composições químicas e mineralógicas. O desenvolvimento e preservação dos perfis lateríticos são indissociáveis das características do modelado. Assim, as exposições dos horizontes de um evento de intemperismo se associam a determinadas feições e posições do relevo. Tomando por base variações químico-mineralógicas e posição no relevo, é possível aplicar técnicas de sensoriamento remoto para delimitar respostas desses horizontes quando aflorantes. Nesse trabalho, uma área na região de Bom Jesus da Penha (MG) foi previamente visitada para descrição de campo de um perfil laterítico desenvolvido a partir de gnaisses, clorita-anfibólio xisto e quartzitos, seguido de caracterizações mineralógicas dos horizontes de intemperismo do xisto ultramáfico (difração de raio X). Na sequência, foram aplicadas composições de bandas espectrais de imagens de satélite Landsat-7/ETM+ e modelos digitais de elevação e declividade do relevo, gerados de imagem de radar SRTM 1Arc-sec. Buscou-se, assim, identificar respostas espectrais para os horizontes de intemperismo descritos em campo. A aplicação do sensoriamento remoto permitiu a delimitação de áreas com características relacionáveis aos horizontes superiores do perfil laterítico identificado em campo

Trace elements, rare earth elements and scandium concentration in a weathering profile of metaultramafic rock (Bom Jesus da Penha, Minas Gerais, Brazil)

O processo de formação dos horizontes lateríticos é responsável pela reorganização química e mineralógica dos litotipos preexistentes. Esse arranjo é controlado pela mineralogia primária da rocha e pelas características de desenvolvimento do processo intempérico. Este artigo apresenta um estudo em um clorita-anfibólio xisto, a partir do qual se desenvolveram dois horizontes de intemperismo. No topo se observou solo caulinítico vermelho argiloso, enquanto abaixo se desenvolve um horizonte saprolítico verde com plintitas de cor ocre, o qual contém montmorillonita neoformada. Os elementos químicos analisados tiveram variações nos teores ao longo desse perfil, sendo que todos os metais tiveram, em determinadas amostras, picos de acúmulos superiores a 100% em relação à rocha. Al2O3, U, Th, Zr e TiO2 mostram concentração residual no topo do horizonte de solos, junto a caulinita e óxidos e hidróxidos de ferro; Fe2O3, V e Co tiveram maior acúmulo na base do horizonte de solos, próximo à transição para o saprolito; Mn, Cr2O3, Ni, Zn, Cu e elementos terras raras (ETR) apresentaram máximos de enriquecimento no horizonte plintificado, junto a montmorillonita; CaO, MgO e SiO2 tiveram redução dos teores ao longo de todo o perfil estudado. Tomando o litotipo metaultramáfico, destacam-se os enriquecimentos dos elementos terras raras e ítrio (ETRY) e escândio (Sc) no perfil de intemperismo, os quais são compatíveis com modelos de mineralização laterítica.The development of lateritic horizons is responsible for chemical and mineralogical reorganization in the parent rock. The final arrangement is controlled by the primary composition of the parent material, climate conditions, the presence of living organisms, topography, and time. This work presents chemical data on two weathering horizons developed from chlorite-amphibole schist. The upper horizon is composed of a red clayey kaolinitic soil. A green saprolitic horizon with ocher plinthite and neoformed montmorillonite occurs below it. Concentrations of analyzed elements vary along the soil profile and all of the metals have peak concentrations that are 100% higher than the parent rock. The upper part of the soil profile is enriched with Al2O3, U, Th, Zr and TiO2 as well as with kaolinite and iron oxide-hydroxides. The highest concentrations of Fe2O3, V and Co occur in the transition zone between the soil and saprolite horizons. On the other hand, the highest values of Mn, Cr2O3, Ni, Zn, Cu and Rare Earth Elements occur in the montmorillonite-bearing saprolite horizon. CaO, MgO and SiO2 are depleted along the profile. Considering the metaultramafic composition of the parent rock, we highlight the notable enrichment of rare earth elements, yttrium and scandium in the weathering profile, which can be compared to the lateritic mineralization models of these elements

EVIDÊNCIAS DE ENRIQUECIMENTO DE ETR DO TIPO ION-ADSORPTION CLAY NO PERFIL DE INTEMPERISMO DO GRANITO SÃO FRANCISCO (SÃO PAULO, BRASIL): Evidences of ion-adsorption clay-type REY enrichment in a weathered crust of the São Francisco Granite (São Paulo, Brazil)

The rare earth elements and yttrium (REY) ion-adsorption clay deposits (IAC) are important in the global supply chain of these metals, and originated by the weathering of biotite and/or muscovite syenogranite carrying REY weatherable minerals, with enrichment of REY occurring by adsorpotion in neoformed clay minerals, mainly kaolinite and halloysite. Evidences of REY IAC enrichment is reported, for the first time, in the 6,1 to 7,8-m-thick weathering profile on the São Francisco Granite (SFG - shoutheastern Brazil), a late-tectonic metaluminous to peraluminous greisenized syenogranite. Petrography and SEM/EDS analysis indicates that the parent rock, a peraluminous synogranite, hosts REY-(fluor)carbonate minerals originated by alteration process. X-ray diffraction of the weathering profile, with soil and saprolite horizons, indicates the presence of neoformed kaolinite and halloysite. Chemical analysis of the weathered profile indicates REY content modification along the weathering horizons. The enrichment factor presents REY loss in horizons with positive cerium anomalies and a high chemical index of alteration (CIA>90). Meanwhile, REY gain was observed in saprolite horizon with negative cerium anomalies and lower chemical alteration index (CIA<90 and >70). Mass balance calculation demonstrates the REY mobility and mass gain in the weathering profile in similar conditions to the Asian REY-IAC deposits.Os depósitos de elementos terras raras e ítrio (ETR) do tipo ion-adsorption clay (IAC) apresentam grande importância para o suprimento global desses metais e se originam pelo intemperismo de biotita e/ou muscovita sienogranitos portadores de minerais de ETR susceptíveis ao intemperismo, cujos ETR são enriquecidos por adsorção em caulinita e halloysita neoformadas. Evidências desse tipo de enriquecimento de ETR foram reconhecidas em perfil de intemperismo, com espessuras de 6,1 a 7,8 metros, no Granito São Francisco (GSF – sudeste do Brasil), corpo tardi-tectônico metaluminoso a peraluminoso submetido a greisenização. Petrografia e MEV/EDS indicaram a presença de minerais (fluor)carbonáticos de ETR, susceptíveis ao intemperismo, originados por processo de alteração no sienogranito. Difrações de raios X demostraram neoformação de caulinita no horizonte saprolítico, enquanto análises químicas revelaram modificações de conteúdo de ETR ao longo do perfil de intemperismo. O fator de enriquecimento indicou perda de ETR nos horizontes com Ce/Ce*>1 e valores de CIA>90, enquanto se identificou enriquecimento de ETR no saprolito com Ce/Ce*<1 e valores de 70<CIA<90. O balanço de massa demonstrou a mobilidade dos ETR e ganho de massa desses metais no perfil de intemperismo, condição essa similar aos depósitos de ETR do tipo IAC identificados no sudeste asiático

GEOLOGIA DO GRANITO CAPOTE, SEGMENTO MERIDIONAL DO BATOLITO TRÊS CORREGOS, SUL DO ESTADO DE SÃO PAULO: Geology of the Capote Granite, Southern segment of Três Córregos Batholith, South os São Paulo State

The Capote Granite constitutes an elongated intrusive body of 600 km2, located near the Capão Bonito, Guapiara and Ribeirão Branco and in the extreme northeast of Araçaíba region. It is associated with the Mantiqueira Central Province and correlated with the Apiaí Terra neoproterozoic evolution. The batholith rocks were divided into four facies: Paiol da Telha, Serra Velha, Capote Association and Apiaí-Mirim. Petrographically, these rocks constitute hornblende-biotite granodiorite to quartz monzonite (Paiol da Telha and Serra Velha facies), biotite monzogranite to syenogranite with hornblende (Capote Association and Apiaí Mirim facies), leukocratic, predominantly inequigranular, porphyritic, white to pink microcline phenocrystals with dimensions of less than 3 to 4 cm, fine to medium granulation, gray or pink and isotropic to sub-oriented with slight milonitic and/or cataclastic foliation. The Apiaí-Mirim facies is considered one indiscriminated facies, due to the high deformation rate, which generates milonites and cataclasites. Analyzes of mineral chemistry determine as main mineralogy microcline, oligoclase, amphibole (edenite to ferroedenite) and biotite (phlogopite and annita), with ferroedenite and annita more common in the most evolved facies. These granitoid rocks have a calc-alkaline character, peraluminous, I cordilleran type, sin collisional of a magmatic arc environment and generated by the fusion of rocks from the lower crust.O Granito Capote constitui um corpo intrusivo de forma alongada, de 600 Km2, localizado nas proximades das cidades de Capão Bonito, Guapiara e Ribeirão Branco e no extremo nordeste de Araçaíba. Está associado a Província Mantiqueira Central e correlacionado a evolução neoproterozoica do Terreno Apiaí. As rochas do batólito foram divididas em quatro fácies, denominadas de Paiol da Telha, Serra Velha, Associação Capote e Apiaí-Mirim. Petrograficamente suas rochas constituem hornblenda-biotita granodiorito a quartzo monzonito (Fácies Paiol da Telha e Serra Velha) a biotita monzogranito a sienogranito com hornblenda (Associação de Fácies Capote e Apiaí Mirim), leucocrática, predominantemente inequigranular, porfirítica, com fenocristais de microclínio branco a rosa de dimensões inferiores a 3 a 4 cm, granulação fina a média, coloração cinza ou rósea e isotrópica a sub-orientada com discreta foliação milonítica e ou cataclástica. A fácies Apiaí-Mirim é considerada uma fácies indiscriminada, devido à alta taxa de deformação, o que gera milonitos e cataclasitos. Análises de química mineral determinam como mineralogia principal microclínio, oligoclásio, anfibólio (edenita a ferroedenita) e biotita (flogopita e annita), com ferroedenita e annita mais comum nas fácies mais evoluídas. As rochas granitoides apresentam caráter cálcio alcalino, peraluminoso, do tipo I cordilheirano, sin colisional de ambiente de arco magmático e geradas pela fusão de rochas da crosta inferior

PETROGRAFIA, QUÍMICA MINERAL E GEOTERMOBAROMETRIA DE METAPELITO DO GRUPO CARRANCAS NA NAPPE DE LUMINÁRIAS (MG)

A Nappe Luminárias corresponde a estrutura alongada de orientação NNE-SSW, situada na porção sul do Orógeno Brasília e de idade neoproterozoica, na borda sul do Cráton do São Francisco. Tal estrutura é composta por metapelitos e quartzitos do Grupo Carrancas. O presente trabalho foca na caracterização metamórfica das suas rochas da, utilizando petrografia, química mineral e termobarometria. A paragênese observada na porção norte é Cld+Chl+Ky+Rt+Qtz+Ms; na porção centro norte é St+Grt+Rt+Qtz+Ms e na porção sul é Grt+Ky+St+Rt+Qtz+Ms. Biotita, clorita e ilmenita retrometamórficas são obervadas no centro-norte e sul. A granada apresenta aumento de almandina e piropo em direção às bordas. As condições obtidas pelo método average PT do THERMOCALC na porção centro-norte são de 591±59 ˚C e 8,3±1,8 kbar para o pico metamórfico e 571±20 ˚C e 10,1±4,8 kbar) para o retrometamorfismo. Na porção sul foi obtido 608±47 ˚C e 11,8±2,8 kbar para o pico metamórfico. Os resultados indicam a presença de gradiente metamórfico com condições variando de fácies xisto-verde na porção norte e centro-norte a fácies anfibolito/eclogito na porção sul

Influencia de la emulsión inhibida TCG en la reactividad de terrenos sulfurosos en la operación de voladura, Minera Yanacocha 2018

RESUMEN La presente tesis tiene como objetivo ayudar en el uso seguro de los explosivos en situaciones en las que puede existir un peligro específico adicional debido a la posible reacción no deseada entre un explosivo y la roca que se desea fragmentar. Bajo ciertas situaciones las reacciones no deseadas puedan dar lugar a detonaciones prematuras con resultados fatales, estas reacciones pueden ser por la química de la roca, la temperatura o combinación de ambos. Asimismo, describir sus características de la tecnología Inhibida y determinar que las voladuras realizadas con emulsión inhibida nos den resultados satisfactorios, una buena velocidad de detonación, buena fragmentación y la eliminación de gases nitrosos. La investigación desarrollada es experimental aplicada de tipo correlacional con diseño transversal. En nuestra hipótesis nuestra variable independiente es Influencia de la Emulsión Inhibida y la dependiente es Reactividad en Terrenos Sulfurosos, aplicando la Emulsión Inhibida en una malla mayor a los 150 taladros se presentaron gases nitrosos en 1% de color anaranjado. Con la Emulsión Inhibida realizamos una mezcla explosiva 80/20 es decir 80% de emulsión y 20% de nitrato de amonio la longitud de carga es de 6m obteniendo un factor de potencia de 1332 y su factor de carga es de 0.236 esto es en una malla con un burden de 8m por un espaciamiento de 9m con una altura de banco de 10m, con una densidad de roca de 1.85. PALABRAS CLAVE: Terrenos sulfurosos, temperatura, mezcla, emulsión inhibida.ABSTRACT The objetive of this thesis has as porpuse help in the safe use of explosives In situations where they may exist an additional specific danger due to possible un wanted Reaction bet ween an explosive and the rock that you want to fragment under certain situations the un wanted reactions can lead to premature detonations with fatal result these reactions can be by the chemistry of the rock, the temperature or combinations of both like wise describ its characteristics of inhibited technology and determinations that the voladure made with inhibited emulsion gives us results satisfactory a good detonation speed good fragmentation and elimination of nitrous gases the research the veloped is experimental aplicac correlation type with transversal design in out this thesis our independent variable is influence of the inhibited emulsion and the dependent is reactive in land Sulphur‟s by applying the inhibited emulsion in a larger mesh a hundred and fifty drills‟ nitrous gases were present in one percent orange . With the inhibited emulsion we perform an explosive mixture eighty twenty is the eighty percent emulsion and twenty percent of ammonium nitrate the loading length is six meters obtaining a power factor zero point to hundred thirty-six this is in a mesh with a burden of eight meters by a spacing of mine meters with a height bank of then meters with bank of then meters with a density of rock one point eighty-five. KEYWORDS: Sulfurous lands, temperature, mixture, emulsion inhibited

GEOLOGIA E GEOQUÍMICA DAS ROCHAS METABÁSICAS DO SUPERGRUPO AÇUNGUI, À NORTE DA ZONA DE CISALHAMENTO QUARENTA OITAVA, SUL DO ESTADO DE SÃO PAULO: Geology and geochemistry of metabasic rocks from Açungui Supergroup, North of Quarenta Oitava Shear Zone, South of São Paulo State

The basic and ultrabasic ortho-derived rocks are composed of amphibolites, metabasites and metaultrabasites of meso to neoproterozoic age, which are located in the southwest of tSão Paulo, in Ribeira Belt southern portion and north of Apiaí Terrain. These are inserted in Supergroup Açungui metavolcanicsedimentary rocks sequence, specifically in Água Clara Formation and Itaiacoca Group. The main mineral paragenesis consists of ferrotschermakite- ferrohornblende- magnesiohornblende ± oligoclase / andesine, representing the progressive regional metamorphism M1 climax, from 611 °C to 621 °C in temperature and 6.5 kbar to 7.3 kbar (± 0, 6) (Mid amphibolite facies); and a mineral paragenesis of actinolite / tremolite ± albite, from M3 regional retrometamorphism (low to mid greenschist facies). Compositional geochemical data classify the rocks as gabbro, basanite and picrite, low potassium sub alkaline to alkaline, Fe-tholeitic to Mg-tholeitic, with a slight tendency to komatiitic basalts. Geotectonic data, corroborated by the behavior of trace elements and REEs, indicate three main signatures for amphibolytic groups: basic tholeitic and komatiitic rocks associated with mid-ocean ridge (MORB), with possible crust interaction in subduction phase; ultrabasic alkaline ocean island rocks (OIA); and island arch tholeiitic basalts. Therefore, magmatisms are correlated to the initial stage of opening of the basin or to the beginning of closure, to the initial phase of tholeitic ocean floor nature, associated with ocean island alkaline basalts.As rochas ortoderivadas de composição básicas e ultrabásicas são constituídas por anfibolitos, metabasitos e metaultrabásitos de idade meso- a neoproterozoica, que se localizam no sudoeste do estado de São Paulo, na porção sul do Cinturão Ribeira e norte do Terreno Apiaí. Encontram-se inseridas em rochas da sequência metavulcanossedimentares do Supergrupo Açungui, especificamente na Formação Água Clara e no Grupo Itaiacoca. A paragênese mineral principal é constituída de ferrotschermakita- ferrohornblenda- magnesiohornblenda ± oligoclásio/andesina, representando o ápice do metamorfismo regional progressivo M1, de 611°C a 621°C de temperatura e 6,5 kbar a 7,3 kbar (±0,6) (Fácies anfibolito médio); e uma paragênese mineral de actinolita/tremolita ± albita, do retrometamorfismo regional M3 (fácies xisto verde baixo a médio). Dados geoquímicos composicionais classificam as rochas como gabro, basanito e picrito, sub alcalinos de baixo potássio a alcalinos, Fe-toleíticos a Mg-toleíticos, com leve tendência à basaltos komatiíticos. Já os dados geotectônicos, corroborados pelo comportamento dos elementos traços e dos ETRs, indicam três assinaturas principais para os grupos anfibolíticos: rochas básicas toleíticas a komatiíticas associadas a cadeia mesoceânicas (MORB), com possível interação da crosta na fase de subducção; rochas ultrabásicas alcalinas de ilha oceânica (OIA); e basaltos toleíticos de arco de ilha. Portanto, os magmatismos estão correlacionados ao estágio inicial de abertura de bacia ou ao início de fechamento à fase inicial de natureza toleítica de fundo oceânico, associado a basaltos alcalinos de ilha oceânica

LITOGEOQUIMICA E QUÍMICA MINERAL DAS ROCHAS DO MACIÇO CORREAS: Litogeochemistry and mineral chemistry from Correas Massif rocks

The Correas Massif is located in the southern region of São Paulo state, related to the neoproterozoic granitogenesis evolution in the northern part of Apiaí Terrain and intrusive in the surrounding rocks of the Água Clara Formation metavolcanicsedimentary sequence, from Açungui Supergroup and in Três Córregos Granitic Complex rocks. It constitutes an elongated granite stock of 5 km2 in the ENE-WSW direction and presents associated mineralizations of cassiterite and wolframite. It is characterized by the biotite porphyritic monzogranite, biotite-muscovite porphyritic syenogranite, muscovite-zinnwaldite-albite porphyritic granite with topaz and pegmatite facies. Mineral chemistry analyzes reveal the presence of biotite and muscovite in the oldest granite facies and prove the sodium character of plagioclases (albite) and variation in micas composition, from muscovite to predominantly zinnwaldite in the muscovite-zinnwaldite-albite porphyritic granite with topaz facies. These are peraluminous rocks belonging to monzogranitic calcium-alkaline series of high potassium to shoshonitic to sodium alkaline. Magmatism is compatible with A type granite, rapakivi, post-collisional to anorogenic associated with an intraplate environment to a post-collisional magmatic arc environment, with placement in tension structures correlated to the Itapirapuã Shear Zone, in an extensional environment at the end of Ribeira Orogenesis collisional event.O Maciço Correas está localizado na região sul do estado de São Paulo, relacionado à evolução da granitogênese neoproterozoica na parte norte do Terreno Apiaí e encontra-se intrusivo nas rochas encaixantes da sequência metavulcanossedimentar da Formação Água Clara, do Supergrupo Açungui e em rochas do Complexo Granítico Três Córregos. Constitui um stock granítico alongado de 5 km2 na direção ENE-WSW e apresenta mineralizações associadas de cassiterita e a volframita. É caracterizado pelas fácies biotita monzogranito porfirítico, biotita-muscovita sienogranito porfirítico, muscovita-zinnwaldita-albita granito porfirítico com topázio e pegmatito. Análises de química mineral revelam a presença de biotita e muscovita nas fácies graníticas mais antigas e comprovam o caráter sódico dos plagioclásios (albita) e variação na composição das micas, de muscovita a predominantemente na zinnwaldita na fácies muscovita-zinnwaldita-albita granito porfirítico com topázio. São rochas peraluminosas pertencentes às séries cálcio-alcalina monzogranítica de alto potássio a shoshonítica a alcalina sódica. O magmatismo é compatível com granito do tipo A, rapakivi, pós-colisional a anorogênico associado a um ambiente intraplaca a um ambiente sin- a pós-colisional de arco magmático, com colocação em estruturas transtensivas correlacionadas à Zona de Cisalhamento Itapirapuã, em ambiente extensional no final do evento colisional da Orogênese Ribeira