Northwest Africa 5790. Top Sequence of the Nakhlite Pile

NWA 5790 is a recently discovered nakhlite. Its mineralogy, petrology and geochemistry suggest that it is the topmost sequence of the nakhlite lava pile

Copper porphyry exploration: Combination of X-ray investigations with other methods

International audienceCopper porphyries represent complex alteration zones, hosting variable grades of Cu-(Au-Mo), but also Pb, Zn, Te, Bi and Ag. Processing of these ores becomes more difficult and more expensive as metal grades are lower and highly variable. Reducing the operational costs while increasing the resource efficiency at constant production is the challenge for the mining industries. Samples from specific alteration zones of the Niaz porphyry copper (Mo)-deposit in NW Iran were analyzed by different methods (e.g. scanning electron microscopy (SEM), dual energy (DE) and multi energy (ME) X-ray transmission (XRT) as well as X-ray computed tomography (CT)). The alteration zones are potassic-phyllic, propylitic, phyllic-argillic and peripheral skarn. The propylitic alteration zone is characterized by a coarse-grained diorite composed of feldspars, amphiboles, epidotes, biotite, chlorite, and minor calcite. Ore phases are pyrite, molybdenite, galena Te-Bi phases and sphalerite. The phyllic-argillic mineralized zone is represented by a microgranular quartz-diorite composed of quartz, feldspars, amphibole, biotite, kaolinite and rare siderite. Ore phases are various Cu-sulfides. The peripheral part of the porphyry is a coarse-grained skarn composed of chlorite, amphibole, garnet, epidote, rare diopside, quartz calcite and apatite in the matrix and veins. Ore phases are chalcopyrite, pyrite, Ag-sulfides and Te-Bi clusters attached to galena. Analysis of reconstructed three-dimensional CT volume data revealed structural information as well as two or three different groups of elements (low, medium and high effective atomic number). With these data, in combination with other methods, mine-geologists can assign grey values to minerals based on densities. Thus, it is possible to locate rapidly mineralization in the alteration zones for unknown samples. With XRT, fractions of heavy and light materials can be revealed in two-dimensional radiographs. While CT is useful for a small selection of samples as it is time consuming, XRT can be used in real-time on conveyor belts

Street Dust: Source and Sink of Heavy Metals To Urban Environment

Air-transferred solid material accumulated for 40 years in different places in an urban area, Grenoble city, France. An appropriate fractionation procedure allowed to separate: 1) a coarse inorganic fraction, 2) a coarse organic fraction, 3) a slowly depositing organo-clay fraction and 4) very fine particles. The composition of each fraction was determined for 20 elements and for isotopic lead signature. The organo-clay fraction was especially rich in Ag, Cd, Co, Cr, Ni and Ti. The sand fraction showed very high concentrations specifically in Cu, Pb and Fe. In contrast, Cd and Zn were mainly accumulated in the coarse organic fraction. The SEM-EDX study of the coarse inorganic fraction showed the presence of red particles associating Pb and Fe, black particles rich in Cu and typical fly ashes originating mostly from iron industry. This sand fraction is suspected to contribute to the contamination of the organo-clay fraction through adsorption. The Pb-Fe contamination likely originates from the neighbouring road surface contaminated by car traffic for several decades. The 206Pb/207Pb ratio showed that these street dust samples may contain up to 50% of lead originated from leaded gasoline additives, twelve years after their prohibition. All these features clearly differ from the composition found for the deposit on tree bark in the same place. These results demonstrate that the deposition over several decades is a very complex phenomenon which requires multi-techniques investigations to be understood thoroughly. They also show that large dense particles which can only be transported on a limited distance by high magnitude events may play a major role in the long-term contamination of urban soils

TAMDAKHT METEORITE (MOROCCO): AN IMPORTANT FALL WITH A RARE FUSION CRUST

80th Annual Meeting of the Meteoritical-Society, Santa Fe, NM, JUL 23-28, 2017International audienc

Late Neoproterozoic Takab iron formation, NW Iran: Implication for BIF depositional setting

International audienceThe Takab banded iron formation occurred in one of the most important part of the Iranian plateau containing Precambrian crustal segments, now embedded in the Alpine-Himalayan orogenic system. The Takab BIF is hosted in low to medium grade metamorphic rocks including schist, quartzite and marble as well meta-basalt and meta-rhyolite interlayers. The structures of the iron formation are dominated by bands or streaks. The ore body is composed of alternating iron-and silica-rich laminates predominately composed of quartz and mainly magnetite that may be partly transformed into hematite, and goethite. The iron layers and lenses have followed the foliation and deformation of host rocks. All the Fe deposits display similar geological features, with variable trending and dipping, because of folding. The studied iron ore deposits occurred in forms of banded, disseminated and nodular ores. The ore laminas vary in thickness from a few mm to 4 cm. U–Pb dating results on detrital zircons of the associated schist rocks from lower and upper layers of the orebody bracket the age of 550 Ma for the iron deposition. Major, trace and rare earth elements support the contribution of seawater and hydrothermal fluids through iron precipitation and up to ca. 20% incorporation of terrigenous materials into the chemical precipitate of the original BIF. The geochemical as well as Nd isotopic data, suggest the Neoproterozoic felsic to intermediate crystalline basement in the Takab area as the precursor of sedimentary input. The Ce anomaly suggest suboxic condition for seawater mass during Ediacaran. Based on geochronological and geochemical data from the Takab iron formation together with those reported from other Neoproterozoic formations and crystalline rocks in the Iranian plateau, as well evidence from glacial sediments and the bimodal volcanism in study area, we propose that the Takab BIF formed in a back-arc basin environment, and can be classified as Rapitan-type. The occurrences of late Ediacaran BIFs and metasedimentary formations with glaciogenic records suggest the presence of active-magmatic marine anoxic basins at ca. ∼555 Ma, equivalent to the Ediacaran Sinian glaciation time interval (600-550 Ma)

Petrology and geochemistry of the unbrecciated achondrite Northwest Africa 1240 (NWA 1240): An HED parent body impact melt

NWA 1240 is an unusual eucrite recently recovered in Morocco as a single stone of 98 g. It is an unbrecciated greenish-brown rock nearly devoid of fusion crust. It displays porphyritic texture consisting of skeletal hollow low-Ca pyroxene phenocrysts set in a variolitic (fan-spherulitic) mesostasis of fine elongate pyroxene and plagioclase crystals. Minor phases are skeletal chromite, iron, silica, troilite, ilmenite and minute amounts of phosphate and fayalite. Pyroxenes are unequilibrated and show one of the widest ranges of composition so far described for a eucrite, from En(76.0)Wo(1.9)FS(22.1) to compositions nearly devoid of Mg (unusual ferrosilite and Fe-augite symplectites and possibly pyroxferroite). Plagioclase crystals contain significant amounts of Fe and Mg, which are possibly controlled by the Ca(Mg,Fe2+)Si3O8 plagioclase component

Tissint martian meteorite: a fresh look at the interior, surface, and atmosphere of Mars

Tissint (Morocco) is the fifth martian meteorite collected after it was witnessed falling to Earth. Our integrated mineralogical, petrological, and geochemical study shows that it is a depleted picritic shergottite similar to EETA79001A. Highly magnesian olivine and abundant glass containing martian atmosphere are present in Tissint. Refractory trace element, sulfur, and fluorine data for the matrix and glass veins in the meteorite indicate the presence of a martian surface component. Thus, the influence of in situ martian weathering can be unambiguously distinguished from terrestrial contamination in this meteorite. Martian weathering features in Tissint are compatible with the results of spacecraft observations of Mars. Tissint has a cosmic-ray exposure age of 0.7 ± 0.3 million years, consistent with those of many other shergottites, notably EETA79001, suggesting that they were ejected from Mars during the same event

Selective zircon accumulation in a new benthic foraminifer, Psammophaga zirconia, sp. nov.

Benthic foraminifera are single-celled eukaryotes that make a protective organic, agglutinated or calcareous test. Some agglutinated, single-chambered taxa, including Psammophaga Arnold, 1982, retain mineral particles in their cytoplasm, but the selective mechanism of accumulation is not clear. Here, we report the ability of a foraminiferal species to select and accumulate zircons and other heavy minerals in their cytoplasm. In particular, the use of Scanning Electron Microscope coupled with an Energy Dispersive X-ray microanalysis system (SEM–EDS) enabled a representative overview of the mineral diversity and showed that the analysed Psammophaga zirconia sp. nov. individuals contained dominantly crystals of zircon (51%), titanium oxides (27%), and ilmenite (11%) along with minor magnetite and other minerals. The studied specimens occur in the shallow central Adriatic Sea where the sediment has a content of zircon below 1% and of other heavy minerals below 4%. For that reason, we suggest that: (i) P. zirconia may be able to chemically select minerals, specifically zircon and rutile; (ii) the chemical mechanism allowing the selection is based on electrostatic interaction, and it could work also for agglutinated foraminifera. In particular, this aptitude for high preferential uptake and differential ingestion or retention of zircon is reported here for the first time, together with the selection of other heavy minerals already described in members of the genus Psammophaga. They are generally counted among early foraminifera, constructing a morphologically simple test with a single chamber. Our molecular phylogenetic study confirms that P. zirconia is a new species, genetically distinctive from other Psammophaga, and occurs in the Adriatic as well as in the Black Sea. Finally, the presence of eukaryotic soft-walled monothalamous microfossils, capable of building a fine aluminosilicate case, in the Precambrian geological record, makes them useful as a valuable record of the early evolution of foraminifera, suggesting that biological agglutination was already present in this group. P. zirconia is a new documented example among foraminifera capable of highly intriguing preferential mineral uptake, showing that this behavior could have emerged very early in their evolution

Selective zircon accumulation in a new benthic foraminifer, Psammophaga zirconia, sp. nov.

Benthic foraminifera are single-celled eukaryotes that make a protective organic, agglutinated or calcareous test. Some agglutinated, single-chambered taxa, including Psammophaga Arnold, 1982, retain mineral particles in their cytoplasm, but the selective mechanism of accumulation is not clear. Here, we report the ability of a foraminiferal species to select and accumulate zircons and other heavy minerals in their cytoplasm. In particular, the use of Scanning Electron Microscope coupled with an Energy Dispersive X-ray microanalysis system (SEM–EDS) enabled a representative overview of the mineral diversity and showed that the analysed Psammophaga zirconia sp. nov. individuals contained dominantly crystals of zircon (51%), titanium oxides (27%), and ilmenite (11%) along with minor magnetite and other minerals. The studied specimens occur in the shallow central Adriatic Sea where the sediment has a content of zircon below 1% and of other heavy minerals below 4%. For that reason, we suggest that: (i) P. zirconia may be able to chemically select minerals, specifically zircon and rutile; (ii) the chemical mechanism allowing the selection is based on electrostatic interaction, and it could work also for agglutinated foraminifera. In particular, this aptitude for high preferential uptake and differential ingestion or retention of zircon is reported here for the first time, together with the selection of other heavy minerals already described in members of the genus Psammophaga. They are generally counted among early foraminifera, constructing a morphologically simple test with a single chamber. Our molecular phylogenetic study confirms that P. zirconia is a new species, genetically distinctive from other Psammophaga, and occurs in the Adriatic as well as in the Black Sea. Finally, the presence of eukaryotic soft-walled monothalamous microfossils, capable of building a fine aluminosilicate case, in the Precambrian geological record, makes them useful as a valuable record of the early evolution of foraminifera, suggesting that biological agglutination was already present in this group. P. zirconia is a new documented example among foraminifera capable of highly intriguing preferential mineral uptake, showing that this behavior could have emerged very early in their evolution