Essaïd Bilal

Géochronologie U–Pb et géochimie isotopique Sr–Nd des granitoïdes néoprotérozoïques des suites Galiléia et Urucum, vallée du Rio Doce, Sud-Est du Brésil

Kesnact S Tb geocinonology and St-Nd isotopes of Ganicia and Grachnn Ncoproterozoic granitoids suites in south-eastern Brazil. U-Pb zircon and monazite dating and whole-rock Sr-Nd isotopes have been applied on Neoproterozoic granitoids from the Atlantic shear belt, south-eastern Brazil. U-Pb zircon results on the Galileia metaluminous and Urucum peraluminous suites indicate crystallisation ages of 594 ± 6 Ma and 582 ± 2 Ma respectively. Whole-rock Rb-Sr and Sm-Nd analyses on representative samples from both suites demonstrate that they mainly derive from melting of older crustal rocks. The occurrence of an old isotopic memory in the zircons from the Urucum granitoids around 2.2 Ga, in agreement with Nd model ages, suggests a Palaeoproterozoic age for the crustal protolith of these two suites, probably associated with the Transamazonico event. Owing to these new dating results and previous regional geochronological data, it can lie proposed that the metaluminous magmatism ended around 590 Ma and that the collisional peraluminous magmatism associated with the Brasiliano progeny occurred between 584 and 570 Ma.

Differentiated hydrothermal and meteoric alterations of the Lueshe carbonatite complex (Democratic Republic of Congo) identified by a REE study combined with a sequential acid-leaching experiment

The behavior of rare-earth elements (REE) during hydrothermal alteration and progressive weathering has been studied by acid-leaching experiments on minerals and whole-rock samples of the Lueshe carbonatite complex (NE of Democratic Republic of Congo). The fresh and hydrothermally altered samples were successively leached with acetic acid (HAc, 1 N) and hydrochloric acid (HCl, 1 N). An additional leaching step with nitric acid (HNO3, 1 N) was applied on meteoric weathered material. After this sequential extraction procedure, the residues were dissolved in a fluorhydric-nitric solution (HF+HNO3). The Lueshe carbonatite complex contains a suite of REE-carriers identified as Ca-bearing minerals including carbonates, apatite and pyrochlore as primary minerals that are accompanied by hydrothermal ancylite-(Ce), parisite-(Ce), synchysite-(Ce) and monazite-(Ce). The hydrothermal alteration induces an enrichment in the light REE, but the authigenic minerals (except monazite) do not, in fact, play an important part in the pre-lateritic REE stock, because of their low amounts. During the early stage of weathering, the residual minerals retain the bulk of the REE, the distribution being only slightly modified. During intense weathering, the leaching experiments indicate that the REE are redistributed among secondary REE-phosphate minerals and bonded to Fe-hydroxides, in the lateritic profile.

Évolution géochimique du pyrochlore au cours de l'altération météorique du gisement de Catalão II (Goiás, Brésil)

The crystallochemical evolution of pyrochlores in the course of the meteoric alteration has been followed, with classical techniques of mineralogical investigation (optical microscopy, SEM, electron microprobe SX50 CAMECA), on drilling and trenches tallying the thick ferrallitic alteration cover in the Catalao II ore deposit (the Goias state, Brazil). An abrupt transformation of the primary pyrochlores (pyrochlore s.s.) into secondary species of the type bario or cerio-pyrochlore has thus been observable to the pedogenetic silcrete level of depth (30–40 m). This transformation shows the characteristics of a pseudomorphose and results from the preferential washing of some cations (Na, Ca) and anions (F), partially replaced by Ba or REE and (OH).

Les tholeiites a affinité alcaline du secteur ouest du Siroua (Anti-Atlas central, Maroc): temoins d'une distension au Néoproterozoïque

Resume Les granitoides du Proterozoique superieur du secteur ouest du massif du Siroua (Anti-Atlas central, Maroc) sont recoupes par des filons de dolerites injectes selon des directions submeridiennes et subequatoriales. Ces filons sont mis en place anterieurement au depot de la serie volcano-detritique du Neoproterozoique terminal (PIII). Its se repartissent selon leurs teneurs en Cr et les rapports entre incompatibles inertes en deux groupes chimiques distincts, independamment de leur epaisseur et de leur orientation. Les deux groupes presentent un enrichissement important en elements lithophiles a large rayon ionique, Zr, Th et terres rares legeres et sapparentent a des tholeiites continentales daffinite alcaline. Laffinite alcaline est egalement confirmee par la chimie du clinopyroxene et de Iamphibole. La mise en place des dolerites dans le secteur ouest du massif du Siroua est conforme a la distension qua connu la chaine Anti-Atlasique au Proterozoique superieur.

PEGMATITES IN SOUTHEASTERN BRAZIL

Two pegmatite groups are represented in southeastern Brazil. The first group, resulting from fractional crystallization, is linked to syn-tectonic granites (580 Ma – deformation event D1) and the second one is associated with another partial melting event of the crust which simultaneously produced porphyritic leucogranites [(520-500 Ma)- later deformation event D2 ] and pegmatites themselves. The Fe/Mn ratios of tourmalines, micas and columbite-tantalites decrease continuously from simple pegmatites to gem quality elbaite-rich ones. The Fe/Mn ratio has been used as a qualitative fractionation index which seems to reflect the regional zoning of the first pegmatites group around a hidden granite body. The Fe/Mn ratio values correlate negatively with Na and Li contents in tourmalines and mica. The REE, Nb, Co and Zn contents in tourmalines, micas, and columbite-tantalites are controlled by their mineral assemblages.

Altération hydrothermale des monazites-(Ce) des pegmatites du district de Santa Maria de Itabira (Minas Gerais, Brésil)*

Monazite-(Ce) is found in granitic pegmatites in the Santa Maria de Itabira pegmatite district (Minas Gerais, Brazil). During the magmatic stage, monazite-(Ce) seems to have had higher contents of cheralite and huttonite in the solid solution. The Th content in primary monazite-(Ce) is high and characteristic for each pegmatite body. During the late stage (albitization), the mean LREE content in the altered zone is slightly higher and Th content is very low. The accessory mineral assemblages changed; huttonite and cheralite crystallize together with Th-poor and La-rich monazite-(Ce) at the border of altered crystals. Nd/Sm and U/Pb ratios are also changed during the hydrothermal stage.

Petrogenesis and tectonic of the Urucum granitic suite, Rio Doce Valley (Minas Gerais – Brazil): an example of syn to late collisional peraluminous magmatism associated with high-angle transcurrent shear zone

The Urucum suite (582 ± 2 Ma, zircon U-Pb age), situated in the Mid-Rio Doce Valley, eastern part of Minas Gerais State, is characterized by elongated, NW-SE and N-S trending granitic massifs associated with the Conselho Pena-Resplendor high-angle shear zone. It corresponds to a syn to late collisional magmatism that presents dominant solid-state foliation. Four facies are distinguished within the Urucum suite: (i) a porphyritic (Urucum); (ii) a medium- to coarse nequigranular (Palmital); (iii) a tourmaline-bearing; and (iv) a pegmatitic facies. These facies are peraluminous, with alumina saturation index varying from 0.98 to 1.38. SiO2 contents vary from 70.7 to 73.7 wt%, with K2O values ranging from 3.5 to 5.7 wt%, Na2O from 1.9 to 4.4 wt%, MgO from 0.6 to 1.2 wt%, and CaO from 0.3 to 0.9%. Harker-type diagrams show rather continuous trends from the less-evolved Urucum facies to the more evolved tourmaline-bearing and pegmatitic facies. The behavior of several major oxides and trace elements (Fe2O3, MgO, MnO, CaO, TiO2, Al2O3, K2O, Rb and Ba) reflects the role played by fractionation of ferromagnesian minerals, feldspars and accessory minerals. Initial Sr87/Sr86 ratios vary from 0.711 to 0.716, with eNd (580 Ma) values between -7.4 to -8.2, and Sm-Nd TDM model ages ranging from 2290 to 1840 Ma.

Transfert heavy metal sewage sludge as fertilizer from soil to ray grass

The land application of sewage sludge reveals a significant increase in dray matter production of Ray Grass ( Lolium perenne L. ). In equivalent dose of liquid sludge, we registered a lower production of dry material. Besides, neither the dose nor type of sludge seems to have an effect on heavy metals contents in the air part plant. On the other hand, contribution of sludge under dry or liquid forms increases significantly heavy metals contents in roots with regard to witness without sludge. The comparison between the beginning and end of culture, revealed a decrease heavy metals contents in soil in particular at horizon 0-40 cm deep. Besides, this decrease Cd, Zn, Pb and Cu contents in soil is not linking to transfer from soil to air part of plant, but rather is the accumulation in roots, which play the role of a barrier.

Typology of the granitic stones of the cathedral of Évora (Portugal): a combined contribution of geochemistry and 57Fe Mössbauer spectroscopy

Abstract A geochemical study, including a detailed investigation of Fe by Mossbauer spectroscopy, was undertaken to characterise the different varieties of the stones in the cathedral of Evora (Portugal). Ten representative stone samples were collected. Bulk analytical techniques, including ICPES, INAA and XRF, were performed, as well as Mossbauer spectroscopy. The stones have consistent linear geochemical variations, well constrained by a limited number of inter-element ratios involving Ti, Mg, Fe and Al. Taking into account the REE distribution, the Mg, Fe and Ti contents and the Fe 3+ /Fe 2+ ratio, two types of stones were distinguished. The type-1 stones show REE normalised patterns with negative Eu anomaly, and are relatively Al rich. The type-2 stones without Eu anomaly, more REE fractionated, are relatively LREE, TiO 2 , MgO and Fe 2 O 3 rich. In agreement with the geochemical results, the Mossbauer data have shown that the Fe 3+ /Fe 2+ ratio was correlated with the magmatic differentiation and further suggested that the presence of Fe (Ti) oxides is related to a higher magmatic evolution. Both stone types have a MgO/TiO 2 ratio close to 2, which is characteristic of calco-alcaline granite. The chemical inter-element variation along the same constant ratio, as well as the REE pattern and the Fe oxidation state, seems to indicate a magmatic filiation from type-2 to type-1 stones. The combination of REE patterns and Fe/Mg, Ti/Mg and Fe 3+ /Fe 2+ geochemical indexes could be used as efficient discrimination tools for other stones of monuments built of granite.

THE ALUMINIUM SATURATION INDEX AND THE MgO/Ti02 RATIO: TWO PARAMETERS INFLUENCED BY PH20 AND THEIR USE TO DISCRIMINATE MAGMA SERIES

The Aluminum Saturation Index is related to the MgO/TiO 2 xa0ratio and both may be added to other typological parameters commonly used in the granitic series discrimination. Some well-known examples are listed and they lead to propose new geochemical limits characterizing different geodynamic settings. Four main groups may be recognized, 1: calc-alkaline granitoids (high Ca and low K) together with the island arc tholeiitic granitoids (ASI=1 for MgO=1.8% and MgO/TiO 2 xa0=2); 2: crustal peraluminous granitoids (ASI>1 and MgO/TiO 2 xa0= 3) produced in the collision zones; 3: tardi- and post-collision (K calc-alkaline) granitoids (ASI=1 for MgO=3.7% and MgO/TiO 2 xa0=4) and 4: the alkaline and peralkaline granitoids and the mid-ocean ridge tholeiitic granitoids emplaced in rifting or doming zones (ASI=1 for MgO=0.8% and MgO/TiO 2 =l).