Valor patrimonial de las pegmatitas del Cap de Creus

Las pegmatitas graníticas del Cap de Creus constituyen un importante elemento de nuestro patrimonio geológico, con importantes aportaciones, tanto por su gran variedad mineralógica como por la información científica que aporta su estudio. El campo pegmatítico presenta extensos afloramientos que facilitan su estudio. Este campo pegmatítico, con unos 400 cuerpos, consta de cuatro tipos de pegmatitas, encajadas en rocas metapelíticas: microclínicas (I), de berilo-columbita (II), de berilo-columbita-fosfatos (III) y de tipo albítico (IV). El grado de evolución de estas pegmatitas aumenta hacia las situadas en zonas más internas, siendo éstas las que contienen una mayor variedad mineral: silicatos, fosfatos, óxidos e hidróxidos (minerales de Nb-Ta, casiterita, gahnita, nigerita, crisoberilo, corindón). Los fosfatos presentan una gran variedad, siendo de la asociación Ca-Fe-Mg-Mn en los tipos menos evolucionados y de Li-Al o Li-Fe-Mn en las más evolucionadas. Algunos fosfatos poco comunes presentes en estas pegmatitas son la herderiderita, berlinita y staneckita.Peer ReviewedPostprint (published version

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

Stratigraphy of lower Cambrian and unconformable lower Carboniferous beds from the Valls unit (Catalonian coastal ranges)

The Palaeozoic rocks outcropping around Valls are divided into two stratigraphic units. The boundary between both is an unconformity. The lower unit is composed by nearshore platform sediments and a Lower Cambrian age is indicated according to ichnotaxa content. The upper unit consists of pink nodular limestones and dark limestones, and it is followed by siliciclastic Culm Facies rocks. These limestones contain conodonts of the uppermost Tournaisian at its base (anchoralis-latus Zone) and lower Bashkirian (Namurian B) in the upper part. This condensed carbonate sequence was coeval with the thick siliciclastic Culm sedimentation in the surrounding areas.Consejo Interinstitucional de Ciencia y Tecnología; AMB94-0953-CO2-01Consejo Interinstitucional de Ciencia y Tecnología; DGE-PB95-1047Consejo Interinstitucional de Ciencia y Tecnología; PB98-155

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

Sequence of crystallisation of pegmatites: the Angola case

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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