José Carlos Gaspar

Phlogopite and tetra-ferriphlogopite from Brazilian carbonatite complexes: petrogenetic constraints and implications for mineral-chemistry systematics ☆

Abstract The results of a mineral-chemistry study of phlogopite and tetra-ferriphlogopite in carbonatites and associated alkaline silicate rocks from the Brazilian carbonatite complexes of Jacupiranga, Tapira and Catalao are presented. A wide textural variety of mica is found, ranging from primary magmatic crystals to late-stage metasomatic phases. Primary micas from the carbonatites and from the associated plutonic silicate rocks follow distinct evolution paths with magma differentiation. In all three complexes, micas from the silicate rocks evolve from phlogopite towards annite, although in Jacupiranga they are more Al-rich. Among the micas crystallising from carbonatite liquids, those from Jacupiranga are typically Al- and Mg-rich, while in Tapira and Catalao they are extremely Al-poor. Metasomatic micas bridge the gap between primary micas from silicate-rocks and from carbonatites. The complete phlogopite–tetra-ferriphlogopite series is reported from the Catalao and Tapira complexes. This study shows that micas from carbonatite complexes may span a wide compositional range, largely overlapping the fields of micas from several types of alkaline ultrapotassic rocks, especially regarding Ti and Al contents. The use of phlogopite composition and evolution to discriminate between different types of alkaline rocks should be undertaken with caution.

Geochemistry of Santo Antônio da Barra Kamafugites, Goiás, Brazil

Abstract This work focuses on the kamafugites from Santo Antonio da Barra, Minas–Goias Alkaline Province. These rocks contain olivine, clinopyroxene, titanomagnetite, perovskite, leucite (pseudomorphs), kalsilite, nepheline, and phlogopite. The rocks investigated are ultrabasic, with high contents of CaO, FeO, and TiO 2 , high to moderate contents of Al 2 O 3 , alkalis, and P 2 O 5 , and low contents of MgO. The alkaline characteristic of the rocks is reflected in TiO 2 , K 2 O, and Na 2 O contents and in the frequent presence of normative nepheline and leucite. K 2 O contents are not primary since most of the leucite was replaced by analcime. The negative K anomaly verified in the extended incompatible element distribution diagram for kamafugites seems to be mainly related to alteration. Kamafugites are characterized by a marked enrichment in incompatible and large ion lithophile elements together with other typical compatible elements. The Santo Antonio da Barra kamafugites are less enriched in titanium, niobium, zirconium, and REE than the Mata da Corda and most of the Toro-Ankole ones. San Venanzo–Cupaello rocks have much lower titanium contents.

Oxygen isotope thermometry of Brazilian potassic volcanic rocks of kamafugitic affinities

Abstract Oxygen isotope analyses have been obtained for magnetite and diopside from mafic alkaline volcanic rocks of kamafugitic affinities from Brazil. These rocks are part of the Alto do Paranaiba and Santo Antonio volcanic provinces of Cretaceous age. Based on the clinopyroxene–magnetite pair, the isotopic temperatures obtained for the rocks of the two provinces are: mafitites −1140–920°C; leucitites −920–830°C; kalsilitites −820°C; analcimites (originally leucitites) −1060–1050°C; cumulate pyroxenites 750–690°C. The Mata da Corda (Alto Paranaiba Province) and Santo Antonio da Barra range in δ 18 O coincides with typical values for mantle-derived magmas.

Composition of priderite in phlogopites from the Catalao I carbonatite complex, Brazil

Magnetite grains with exsolved ilmenite lamellae may be replaced by pyrite or carbonate in phlogopitites of the Catal~o I carbonatite complex, Goi~is State, Brazil. The ilmenite is transformed in part to priderite and sometimes to rutile. Priderite occurs as small anhedral grains (< 0.2mm) or composite crystals associated with ilmenite and rutile. Chalcopyrite, magnetite, monazite, and pyrochlore also occur inside the area of original magnetite grains. The priderite belongs to the K2FeTiTOI6-BaFeTi7016 series with K/(K+ Ba) ranging from 1.0 to 0.53. The highest contents for other elements are: V203 2.65, Cr203 4.1, and Nb205 1.98 wt.%. Priderites associated with magnetite have the highest V, Cr, and Nb contents whereas others have the highest Ba content. Zoning characterized by K-Ba substitution is patchy but always present. V- and Cr-poor priderites are similar in composition to priderites from lamproites, and the V- and Cr-rich ones are compositionally similar to hollandite-group minerals found in kimberlites.

Concentração por flotação da apatita proveniente de rochas de filiação carbonatítica

The current processing study seeks to improve operations for the direct and reverse flotation of apatite originating from carbonatically-affiliated rocks to obtain an apatite concentrate in accordance with the phosphoric acid industry specifications. The direct flotation of apatite was carried out in two flotation phases, rougher and cleaner. The aim of direct flotation was to generate a product to feed the reverse flotation circuit of apatite. Reverse flotation was performed in three stages (rougher, cleaner and recleaner) and at pH 5.0, using phosphoric acid (H3PO4) as an apatite depressor. Summing up, the results of reverse flotation tests pointed out apatite recovery, which shows that the specific reagents used favored system selectivity. It was possible to obtain an apatite concentrate with 38.11% of P2O5, 50.98% of CaO, 1.07% of Fe2O3, 0.67% of MgO and ratio CaO/ P2O5 of 1.34.

Radiação gama e resistividade elétrica em solo com aplicação de carbonatito e fertilizantes agrícolas no Distrito Federal

EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria) and Brasilia University developed a research project about the viability of carbonatite rock as agricultural fertilizer. As an initial experiment, several mixtures of carbonatite, limestone, phosphorous and potassium compounds were added as fertilizers in an oxisol area (red-latosol, according with Brazilian System of Soil Classification), in Distrito Federal, central Brazil. The experiment area was divided in 56 plots (4 × 7m) and each plot received a fertilizer mixture. The purpose of this work was to verify if the addition of fertilizer mixture to the soil modified its radiometric and resistivity properties and if it is possible to identify this change. Gamma-ray and electrical resistivity measurements were obtained in an experimental area and in a natural savannah type vegetation area. The results showed that the fertilizer addition modified soil natural properties causing a small increase in K, U, Th levels and decreasing ten times electrical resistivity. A low contrast of radiation was observed between plots, and then it was not possible to differentiate the several treatments in base of gamma-ray measurements. Electrical resistivity was efficient to identify three groups of plots related to mixtures characteristics, respectively with phosphorous, potassium and limestone / carbonatite predominance.

EVOLUÇÃO ATUAL DA COBERTURA LATERÍTICO-BAUXÍTICA DA SERRA DE TRUCARÁ, BAIXO RIO TOCANTINS, PARÁ

O manto intemperico que capeia a Serra de Trucara e atualmente palco de dois processos distintos e antagonicos : na sua base, ocorre a ferralitizacao dos basaltos com intercalacoes peliticas da Formacao Caraipe e o consequente espessamento da zona saprolitica, enquanto no topo observa-se a degradacao quimica e fisica da couraca lateritico-bauxitica e dos depositos coluviais resultantes do desmantelamento desta. Atraves do estudo, por um lado, dos produtos solidos de degradacao superficial da couraca, e por outro, das aguas subterrâneas coletadas em nascentes e pocos em quatro epocas diferentes do ano, foi possivel evidenciar : 1) na base do perfil intemperico, a lixiviacao de parte da silica e dos elementos alcalinos e alcalino-terrosos, a preservacao do quartzo e a neoformacao de caolinita mal cristalizada e goethita, que periodicamente sofrem dissolucao e reprecipitacao; 2) no topo do saprolito, a dissolucao incongruente da caolinita que resulta em formacao de gibbsita, a lenta degradacao do quartzo e a periodica dissolucao/reprecipitacao dos oxi-hidroxidos de ferro; 3) no topo do perfil, a degradacao quimica e fisica da couraca lateritico-bauxitica, em particular a lixiviacao sazonal do aluminio e do ferro, a qual contribui provavelmente a materia orgânica. A remocao do aluminio do topo da cobertura de alteracao resultaria em enriquecimento absoluto neste elemento da base da couraca e do topo do saprolito, e em cimentacao por gibbsita de coluvios recentes.