Díez Torres, J.A., Añorbe Urmeneta, M., Suárez Barrios, M., Navarrete López-Cozar, J. & Martín Pozas, J.M. (1990): Presencia y génesis de los minerales fibrosos de la arcilla en las proximidades de Villamuriel de Cerrato, Provincia de Palencia. Stvdia Geologica Salmanticensia, 26: 7-25.
ABSTRACT: Neogene Marly materials are studied near Villamuriel de Cerrato, in the province of Palencia (Duero Basin, Spain), The presence practically constant of sepiolite, palygorskite and illite, have been observed. Smectites and kaolinite are seldom found. Sepiolite predominates over the rest of clay minerals. Genetic conditions which are necesary for growing fibrous minerals are revised. In our case, we have observed a straight relation between dissolution of dolomite, silicated gel formation and development of sepiolite and palygorskite fibers from it.
Suárez, M., Armenteros, I., Martín Pozas, J.M. & Navarrete, J. (1990): El yacimiento de paligorskita de Bercimuel (Segovia): Génesis y propiedades tecnológicas. Stvdia Geologica Salmanticensia, 26: 27-46.
ABSTRACT: The palygorskite deposit of Bercimuel (Segovia) is studied. It is situated at the top of the Miocene filling of an cratonic SW-NE basin in the southeastern part of the Tertiary Duero Basin. The age of the bed is upper Miocene. A complementary study is also made for other sections and outcrops located in the neighbourhood of the Bercimuel deposit.
The palygorskite can be 80% of the total rock, and it appear with quartz, illite and kaolinite are inherited minerals. The palygorskite is associated with smectites and interstratified of the type smectite illite, these minerals are minerals of transformation.
The filling of this basin has been made hy two alluvial fans from the pre Neogene rocks in the elevated blocks flanking the depresion. The Bercimuel deposit lies approximately over the meeting of the two alluvial fans over an extensive level of caliche, which together with its lithological, structural, textural and mineralogical characteristics allows one to propose an origin for the palygorskite based on the following: 1) Alteration of the phillosilicates and quartz present in the profile; 2) the solutes dissolved in the runoff water originating from the weathering of the reliefs composed of pre Neogene rocks (gneiss, schist, dolornite, limestone...).
In viev of the features of hydromorphosis observed in the profile it may be inferred that there is a fluctuating ground water table that is affected by existence of underground caliche that would have acted as an impermeable layer. This circumstance may have been crucial for the development of the alteration of the minerals in the profile and to achieve the chemical (cation concentrations, pH), and physical (climatic drainage) conditions required for the genesis of the palygorskite. Regarding the fluctuating ground water table, it has been observed that alteration decreases from the base to the top of the profile; in the other words, it is better developed in the more permanently waterlogged levels of the lower part of the profile. By the excelents thecnological properties of the deposit, it present a economic interest.
Pérez del Villar, L. & Cruz Cantero, B. de la (1990): Caracterización mineralógica y geoquímica del granito sano y alterado del macizo de "El Berrocal" (Sierra de Gredos, Provincia de Toledo). Stvdia Geologica Salmanticensia, 26: 47-80.
ABSTRACT: In relation to the project on migration of U in a fissured granitic environment, carried out by C I.E.M.A.T., the granite of "E1 Berrocal" massif has been characterized from a mineralogical and geochemical point of view. This work is based on the study of fresh and altered samples from the mine of El Berrocal.
Based on the mineralogical composition, the fresh granite is classified as alkaline feldspar granite with muscovite as dominating mica, and is characterized by the following accesory mineral association: ilmenite (anatase), monazite, zircon, apatite, uraninite, pyrite and fluorite. The first three minerals are enclosed preferentially in biotite; apatite occurs in a paragenetic position similar to that of the leucocratic minerals of the rock; uraninite and pyrite, closely related between them are ubiquitous concerning their host minerals; and fluorite is interstitial.
From a geochemica] point Of view, the unaltered granite is rich ln SiO2, Al2O3, K2O, P2O5, Li, F, Rb, Zn and U; and poor in Cao, Ba and Sr. The value Of the relation K/Rb is low, while U/Th is high.
The unaltered granite belongs to the series of alkali feldspar granites, with an internal evolutive trend from a potassic to a more sodic pole. It is peraluminous, hypocalcic, highly evolved, U "fertile" and enriched in incompatible elements of the Sn group. These characteristics are proper of the S type granite.
The altered granite comes from the former due to a tectonization proces and a hydrothermal alteration, which originate an increase of quartz and sericite and a decrease of plagioclase, K feldspar and biotite. Carbonates and Mg rich chlorite were neoformed.
From a chemical point of view, these transformations are accounted for by an increase Of Fe2O3, MgO, K2O, H2O+, CO2T, Ba, Sr, CU, Zn, Y, ce, La, Th and U contents, and a decrease of FeO and Na2O The content of SiO2 Al2O3, P2O5, V and Zr are kept invariable. The loss of CaO, Rb and Li is related to the later weathering processes.
In the unaltered granite, around 50 60% of the total U of the rock occurs as uraninite, while in the altered one it appears as autunite, fundamentally.
Pérez del Villar, L. & Moro Benito, C. (1990): Características geológicas y mineralógicas de los indicios uraníferos del Complejo Esquisto-Grauváquico en el área Acehuche-Ceclavín (Provincia de Cáceres): El yacimiento de La Espigadera. Stvdia Geologica Salmanticensia, 26: 81-107.
ABSTRACT: Some of the metallogenic characteristics of the U mineralizations of the Acehuche Ceclavín area are summarized in this paper, being its principal representative the Espigadera deposits. These characteristics have been determined from electric and radiometric logs, and from samples taken from the boreholes carried out during the exploration of these deposits.
From a tectonic control point of view, as well as from the morphology, epithermal paragenesis, constituted by pyrite marcasite, pitchblende coffinite and carbonates, and their textural features, the studied mineralizations are very similar to the ones in the province of Salamanca.
Pérez del Villar, L. & Moro Benito, C. (1990): Estudio geoquímico comparativo entre las rocas encajantes y las mineralizaciones de uranio del Complejo Esquisto-Grauváquico en el área Acehuche-Ceclavín (Provincia de Cáceres). Stvdia Geologica Salmanticensia, 26: 109-134.
ABSTRACT: The geochemical characteristics of the host rocks and the uranium deposits of the Acehuche Ceclavín area are studied and compared in this paper. In the first ones, the possible geochemical evolution of the organic matter, uranium and other metallic elements, during metamorphism, is established, as well as the uranium "fertile" character of the "Complejo Esquisto Grauvaquico (C.E.G.)" level, to which the host rocks belong to.
In the same way, the geochemical modifications, originated by the mineralization processes in the host rocks, are studied, and it is deduced that the most probable source of the uranium concentrated in the studied mineralization is the C.E.G. level, where the deposits are located.
Pérez del Villar, L. & Moro, C. (1990): Los yacimientos peribatolíticos de uranio encajados en metasedimentos: Comparación con los del área Acehuche-Ceclavín (Provincia de Cáceres). Stvdia Geologica Salmanticensia, 26: 135-161.
ABSTRACT: The geological and metallogenic characteristics of the peribatholitic uranium deposits in metasediments of the European Hercynian belt and North America are summarized in this paper. They are compared with the mineralizations of the Acehuche Ceclavín area and their differences and similarities are established. The remarkable similarities existing among the studied mineralizations of the province of Caceres and the ones from Salamanca allow the establishment of their the correlation in time, as well as certain genetic aspects among them.
Pérez del Villar, L. (1990): Las mineralizaciones de uranio en el Complejo Esquisto-Grauváquico en el área Acehuche-Ceclavín (Provincia de Cáceres): Una hipótesis genética. Stvdia Geologica Salmanticensia, 26: 163-177.
ABSTRACT: A genetic hypothesis is proposed for the uraniferous peribatholitic mineralizations of the Acehuche Ceclavín area. This hypothesis is based on their metallogenic characteristics, on the correlations established between the former deposits and the ones from the province of Salamanca and on regional geological, paleographic and geothermal data.
It is assumed that the U comes from the host shales and/or from possibly older peribatolithic deposits, leached by descending meteoric, bicarbonated, slightlyacid and 12C-enriched waters. These wathers would come from edaphic profiles and/or continental sedimentation environments, corresponding to the Mesozoic Tertiary transition, enriched in humic organic matter and typical of subtropical climates.
The U mineralization is epithermal and was probably originated by ascending mineralized solutions, which were mobilized by thermal and hydraulic effects associated with the Pyrinnaic phase of the Alpine Orogeny.
The probable physico chemical processes present during the deposition of the U ore are pointed out, and it is suggested that the present hydrothermal manifestations in the province of Caceres, similar to the ones from Salamanca, would represent residual geothermal phenomena, responsible for the formation of the studied mineralizations.
The physico chemical characteristics of these thermal waters would be more or less like the ones from the mineralizing solutions, once they have deposited their metallic load, transported by solution.
Gil Acero, M., Hernández Sánchez, M.E. & Moro Benito, M.C. (1990): Relaciones genéticas entre las mineralizaciones de Sn, W y P de C.E.G. y las de complejo Villaseco-Pereruela (Zamora). Stvdia Geologica Salmanticensia, 26: 179-194.
ABSTRACT: The objective of this work, considering the geological data, is to stablish a genetic relation beetwen the W, Sn and P mineralizations asociated to the calcosilicate levels southern Villalcampo and the diseminated casiterite in intragranitic quarz veins in the Complejo de Villaseco Pereruela, so that the anatexi or the partial asimilation of the metamorphic mineralizated serie by a very diferenciated melt could explain the genesis of the intragranitic mineralizations.
Reguilón Bragado, R.M. & Arribas Moreno, A. (1990): Contenido y distribución de U y Th en el granito de Albalá (Cáceres, España). Stvdia Geologica Salmanticensia, 26: 195-214.
ABSTRACT: The Albala granite (Caceres) consist of three main facies. Facies I, made up of medium to coarse two mica granites with a predominance of muscovite. Facies II, is composed of fine grain two mica granites with a biotite predominance. Facies III, is made up of coarse grain granites biotitic, with little muscovite.
Geochemically, the granites are alkaline with a marked peralouminous nature.
The uranium concentrations are ranged between 3 and 26.3 ppm, with a mean of 6.97 ppm, whereas those of thorium are 3 and 22.4 ppm and the mean content is 7.97 ppm. The highest uranium contents are found in facies II, within the two mica granites with a predominance of biotite, whereas those of thorium contents are found in facies III, of biotitic granites.
In the case of uranium, the mean contens are higuer than those reported by Rogers and Adams (1969) for several worl granites considered to be standard (3.9 ppm). By contrast, those of thorium are considerably lower than those give by same autors for the same granites (20 ppm). The high mean conten of uranium in the Albalá granite have that it should be considered as fertil for uranium, with a great number of uranium vestige.
Encinas, L.H. & Bea, F. (1990): Técnicas geomatemáticas para la separación de diferentes series de rocas ígneas a partir de elementos mayores. Stvdia Geologica Salmanticensia, 26: 215-247.
ABSTRACT: Given an aleatory set of igneous rocks samples, we study how to recognize the different rock series represented, and how to assign each sample to the series to which it really belongs. Therefore, we have studied near to 1000 samples from the literature which belong to (1) tholeiitic (2) alkaline and (3) calc alkaline series. We conclude that a normalization step is necessary. We have studied two normalization techniques: (1) to 57 wt% SiO2 and (2) to zero value of the coordinate on the first principal component. Both of them give good results, but the normalization to 57 wt% SiO2 produces a lot of negative values, which involves a high percentage of that samples should be eliminated. Thus the normalization to zero value on the first principal component is preferred.
Pereira Gómez, Mª.D. (1990): Evolución petrológica y geoquímica de las granodioritas subautóctonas del complejo anatéctico de la Peña Negra (Sector Batolito de Ávila). Stvdia Geologica Salmanticensia, 26: 249-268.
ABSTRACT: In the Peña Negra Anatectic Complex there are several thick subhorizontal sheets of cordierite bearing megacrystic granodiorites concordantly interlayered inside of the regional migmatites. The migmatization and the formation of these granodioritic sheets are approximately contemporaneous (syn phase II). Such a spatial temporal relationships suggest a possible derivation of granodiorites from migmatites through anatexis. To check this possibility we made a mass balance study using the Anatexis Mixing Model. We conclude that an hybrid source between a regional migmatites and orthogneiss is needed to generate the granodiorites, leaving a residue made up of sillimanite and quarz with variable amounts of cordierite, depending of the composition of the involved mesocratic migmatite.
González Delgado, J.A. (1990): Estudio sistemático de los gasterópodos del Plioceno de Huelva (SW de España) IV: Neogastropoda (Muricaea, Buccinacea). Stvdia Geologica Salmanticensia, 26: 269-315.
ABSTRACT: The present work is a systematic study of 26 species of Neogastropoda from different pliocene outcrops (Zanclean) from Huelva (Guadalquivir Bassin). Also presented are their abundance, chronostratigraphic, bathymetric and geographic distribution together with the substrate type, nutrients and recent citations in the Spanish Pliocene.
Andrés, I. (1990): Estudio sistemático de los bivalvos Palaeotaxodonta y Pteriomorphia (Arcoida, Mytiloida) del Plioceno de Bonares (Huelva, España). Stvdia Geologica Salmanticensia, 26: 317-353.
ABSTRACT: In the present paper 15 species of Bivalvia -Palaeotaxodonta and Pteriomorphia (Arcoida, Mytiloida)-from Bonares (Guadalquivir Basin, Spain), in Pliocene (Zanclean) sediments are described and figured. Paleoecologic, chronostratigrafic and geographic distribution data have also been included.
Martín de Jesús, S., Jiménez Fuentes, E. & Mulas Alonso, E. (1990): Un pelomedúsido (Chelonia) con malformaciones patológicas, del Eoceno de Zamora. Stvdia Geologica Salmanticensia, 26: 355-364.
ABSTRACT: A pelomedusidae fossil from the Eocene in Zamora was studied. It has anomalies in one of its pelvics girdles and in a xiphiplastra. A case of compensatory exostosis was diagnosed. The specimen can be determined as Neochelys aff. salmanticensis (Jimenez).
Martín de Jesús, S. (1990): Triang: Soporte informático para la representación de diagramas triangulares. Stvdia Geologica Salmanticensia, 26: 365-378.
ABSTRACT: Introducing a program for triangular diagram design. Five groups of points may be represented on the same diagram. The diagram size may be increased or decreased, and a grill may be invoked if wanted. Data may be entered as percentages or as real numbers, later automaticaly converted in percentages. Data may be recorded or loaded to or from ASCII files.