Scheelite bearing quartz veins from Poblet (Catalonian Coastal Ranges): Characterisation of fluid inclussions and genetic model

Scheelite-bearing quartz veins from Poblet, trending in a NE-SW direction, are hosted by calcic granitoids of Late Hercynian age in the southern part of the Catalonian Coast Range. Fluid inclusions from quartz and scheelite have been characterized using microthermometry, Raman microspectrometry and Scanning Electron Microscopy. Except for type I inclusions (not observed in scheelite), similar inclusions have been observed in both minerals. One recognizes, in order of formation : Type I inclusions containing brine, daughter phases (halite, sylvite and sometimes iron chloride) and incidentally trapped minerals (ankerite, siderite, muscovite, K-felspar and unidentified species). Type II(L) inclusions have a low salinity (1 to 6 % eq. NaCl) and homogenize in the liquid phase in the range of 300-400 °C or under critical conditions near 400 °C. Type II(V) are low density, CO2-poor aqueous inclusions, homogenizing in the gas phase in the range of 350-420 °C. Type II(V') have higher CO2 contents. Type II inclusions appear as samples of an initially hypercritical fluid, trapped at different stages of its evolutions towards two subcritical fluids. Type III inclusions indicate later circulation of a colder, low-salinity solution (Th : 150 to 300 °C ; salinity : 0 to 3.5 % NaCl wt %). Abundant iron contents in type I inclusions suggest some interaction at elevated temperature (400 to 600°C) with a biotite granite (Whitney et al., 1985). P-T conditions compatible with measurements performed on type II inclusions are about 400 °C and 0.8 kbar, in a range similar to that determined for the Djbel Aouam occurrence in Hercynian Morocco (Cheilletz, 1984). Equivalent conditions have been postulated for scheelite precipitation at Poblet

Styles of Alteration of Ti Oxides of the Kimberlite Groundmass: Implications on the Petrogenesis and Classification of Kimberlites and Similar Rocks

The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ΔNNO calculated value is from −3.82 to −0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ΔNNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f(CO2) and f(H2O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %-26.3 wt % TiO2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence

Palynological age constraint of Les Vilelles unit, Catalan Coastal Chain, Spain

The Les Vilelles unit is a detrital sequence exposes at the southwestern margin of the Catalonian Coastal Range, NE Spain, below the Carboniferous turbiditic series. Based on the palynological content, the age of this unit was initially assigned to the Middle-Late Devonian (Eifelian to Famennian). Additional radiolarian and connodont findings were considered to be Early-Middle Mississippian (Tournaisian to early Viséan). This age inconsistency and the broad time interval, especially of the first dating, produce some ambiguity in the regional interpretations of the Les Vilelles unit and the overlying Carboniferous sequence. A palynostratigraphic analysis conducted in a section representative of the Les Vilelles unit has provided an assemblage containing miospores, acritarchs, prasinophyta phycomata and chitinozoan that can be confidently assigned to a latest Frasnian interval, in contact with the Frasnian-Famennian boundary. This dating casts doubt on the radiolarian/connodont age assignment and considerably refines the Middle -Late Devonian age formerly established. This study also includes a systematic section with the description of three newly established miospore species:Dibolisporites coniugatum, Dibolisporites priorato and Rugospora spinosa

Estudi geològic i mineralògic de mines de l'època Neolítica a la Serra de les Ferreres (Mines de Gavà)

Aquest estudi s'ha efectuat en dues fases, seguint el desenvolupament de les obres que van donar lloc a les intervencions arqueològiques. El primer estudi va ser efectuat per Carme Cirera, sota la direcció de Joan Carles Melgarejo, i va tenir lloc durant els treballs d'excavació de la mina número 83. El segon estudi va ser efectuat posteriorment pel mateix Joan Carles Melgarejo i per Joaquín Proenza, i va tenir lloc durant els treballs d'excavació de les mines números 84 i següents

Uvarovite in podiform chromitite; the Moa-Baracoa ophiolitic massif, Cuba

The chromitite pods of the Moa-Baracoa massif, in the eastern ophiolitic belt of Cuba, contain pre-existing gabbro sills. This association is affected by two processes of hydrothermal alteration. The chromitites and the hosting dunites and harzburgites are affected first by regional serpentinization; a second alteration, represented by chloritization accompanied with formation of ferrian chromite, is mainly located in the pods and their immediate vicinity. The altered chromitite pods and enclosed gabbro sills iue cross cut by millimeter-wide veins. The vein filling consists of a sequence of clinochlore, uvarovite, chromian clinochlore, rutile, titanite and calcite. Uvarovite also occurs in the vicinity of veins Uvarovite is concentrically zoned, covering compositions in the uvarovite-grossular solid solution series between Uva17 and Uvae:; the andradite component is very low. These compositions suggest a complete miscibility along the grossular-uvarovite join at relatively low temperature. On the basis of the mineral sequence and mineral chemistry (major and trace elements), the uvarovite crystals, as well as the vein assemblage, formed by a low-temperature leaching, Ca probably from the gabbro sills, and Cr and Al from the chromite dunng the formation of ferrian chromite Cr and A1 would have been mobile only at the scale of a pod during this process

Sequence of crystallisation of pegmatites: the Angola case

The Precambrian basement of Angola contains several pegmatite fields, although most of them have not been studied yet. Some of them include pegmatites devoid of rare elements, as those found close to Caxito, about 100 km ENE Luanda. These pegmatites are exploited for the production of industrial minerals. Moreover, some rare element pegmatite fi elds occur close to Namibe, in the desertic part of the southwest of the country. These pegmatites were prospected for Be and Ta in the 1960's. The distribution of the pegmatite types, as well as the exceptional quality of the outcrops, due to lack of weathering or soil cover, allow a complete sampling in order to study the evolution of a pegmatite field, from parental granites to barren pegmatites, beryl-columbite-phosphate pegmatites and spodumene pegmatites. Furthermore, the internal evolution of each pegmatite type has been also studied

Nb and REE Distribution in the Monte Verde Carbonatite-Alkaline-Agpaitic Complex (Angola)

The Angolan alkaline-carbonatite complex of Monte Verde has a semi-circular shape and is comprised of a central intrusion of foidolite rocks surrounded by concentrically arranged minor bodies of other alkaline rocks and carbonatite magmatic breccias. This rock association is hosted by fenitized Eburnean granites. Concentric swarms of alkaline dykes of late formation, mostly of nepheline trachyte composition, crosscut the previous units. Most high-field strength elements (HFSE) and rare earth elements (REE) are concentrated in pyrochlore crystals in the carbonatite and alkaline breccias. Magmatic fluornatropyrochlore is replaced and overgrown by five secondary generations of pyrochlore formed during subsolidus stages and have higher Th, REE, Si, U, Sr, Ba, Zr, and Ti contents. The second, third, and fourth pyrochlore generations are associated with late fluids also producing quartz and REE rich minerals; whereas fifth and sixth pyrochlore generations are linked to the fenitization process. On the other hand, minerals of the rinkite, rosenbuschite, wöhlerite, eudialyte groups, as well as loparite-(Ce), occur in accessory amounts in nepheline trachyte, recording low to moderate agpaicity. In addition, minor REE-bearing carbonates, silicates, and phosphates crystallize as late minor secondary minerals into carbonatite breccia and alkaline dykes. In conclusion, the scarcity of HFSE and REE minerals at the Monte Verde carbonatite-alkaline-agpaitic complex suggests low metallogenetic interest and economic potential for the outcrops analysed in this study. However, the potential for buried resources should not be neglected

Los minerales de colección como recurso económico en países en vías de desarrollo

El coleccionismo de minerales es una actividad en expansión. El alto nivel de demanda de minerales y de sus derivados posibilita la creación de microempresas en países en vías de desarrollo que, con muy poca inversión de capital, pueden facilitar el desarrollo de áreas rurales sin producir apenas impacto en el medio natural. Un aspecto muy importante para la supervivencia de estas microempresas es que el material tenga la calidad adecuada para su óptima comercialización, cosa que no ocurre en la actualidad con la mayor parte del material que procede de los países en vías de desarrollo. En este trabajo se proporcionan, de forma ilustrada, los criterios que se deben usar para identificar el tipo de material que puede ser interesante para ser comercializado, así como los mecanismos de tratamiento de los minerales desde su lugar de extracción hasta el punto de venta. Mineral collecting is a growing activity. The high demand for minerals and their derivatives has resulted in the creation of micro- companies around the mineral trade in developing countries. This activity could facilitate the development of rural areas with no need of a large capital investment and with minimal environmental impact. The high quality of their products is the most important aspect for the survival of these micro-companies, but nowadays the material that comes from developing countries does not always arrive in the best condition. In this essay the basic criteria are provided for identifying the kind of minerals that are interesting enough to be commercialized, and also the procedures recommended for commercializing them from the place where they are extracted to their point of sale