Textural development in sulfide-matrix ore breccias in the Aguablanca Ni-Cu deposit, Spain, revealed by X-ray fluorescence microscopy

The intrusion-hosted Ni-Cu sulfide deposit at Aguablanca in south-western Spain contains a high proportion of ores in the form of sulfide-matrix ore breccias. These are polymict, comprising autoliths and xenoliths in sulfide-rich and/or sulfide-poor matrices. Inclusion lithologies include calc-silicate skarn rocks from the adjacent marbles, ultramafic and mafic cumulates, and remelted and recrystallized mafic rocks containing spinifex-like textures. Breccia textures have been investigated at mm to cm scale using desk-top and synchrotron-based microbeam XRF mapping which reveal a number of distinctive common features: disaggregation of inclusions into adjacent sulfide along original silicate grain boundaries; complex reverse and oscillatory zoning in Cr content of clinopyroxene grains within sulfide and inside inclusions; narrow reaction rims between country rock clasts and enclosing silicates; and preferential disposition of pyroxene crystals within pyrrhotite-pentlandite aggregates (original MSS) relative to inclusion-poor chalcopyrite. The observed range of textures is explained by a model of percolation of molten sulfide through a pre-existing silicate-matrix intrusion breccia, preferentially displacing a cotectic or eutectic plagioclase-pyroxene melt. The process is analogous to that believed to have formed interspinifex ore in komatiite-hosted deposits, and also to that responsible for superficially similar sulfide matrix ore breccias at Voisey’s Bay. The preserved range of textures is interpreted as being due to late stage gravity-driven percolation of sulfide liquid from above into a pre-existing partially molten intrusion breccia. This intrusion breccia itself may have been emplaced into the neck of the Aguablanca stock, in the waning stages of magma flow

Geochemical Constraints on the Origin of the Ni–Cu Sulfide Ores in the Tejadillas Prospect (Cortegana Igneous Complex, SW Spain)

After the discovery of theAguablanca ore deposit (the unique Ni–Cu mine operating in SW Europe), a number of mafic-ultramafic intrusions bearing Ni–Cu magmatic sulfides have been found in the Ossa–Morena Zone of the Iberian Massif (SW Iberian Peninsula). The Tejadillas prospect is one of these intrusions, situated close to the border between the Ossa–Morena Zone and the South Portuguese Zone of the Iberian Massif. This prospect contains an average grade of 0.16 wt%Ni and 0.08 wt%Cu with peaks of 1.2 wt%Ni and 0.2 wt%Cu. It forms part of the Cortegana Igneous Complex, a group of small mafic-ultramafic igneous bodies located 65 km west of the Aguablanca deposit. In spite of good initial results, exploration work has revealed that sulfide mineralization is much less abundant than in Aguablanca. A comparative study using whole-rock geochemical data between Aguablanca aand Tejadillas shows that the Tejadillas igneous rocks present a lower degree of crustal contamination than those of Aguablanca. The low crustal contamination of the Tejadillas magmas inhibited the assimilation of significant amounts of crustal sulfur to the silicate magmas, resulting in the sparse formation of sulfides. In addition, Tejadillas sulfides are strongly depleted in PGE, with total PGE contents ranging from 14 to 81 ppb, the sum of Pd and Pt, since Os, Ir, Ru and Rh are usually below or close to the detection limit (2 ppb). High Cu/Pd ratios (9700–146,000) and depleted mantle-normalized PGE patterns suggest that the Tejadillas sulfides formed from PGE-depleted silicate magmas. Modeling has led us to establish that these sulfides segregated under R-factors between 1000 and 10,000 from a silicate melt that previously experienced 0.015% of sulfide extraction. All these results highlight the importance of contamination processes with S-rich crustal rocks and multiple episodes of sulfide segregations in the genesis of high-tenor Ni–Cu–PGE ore deposits in mafic-ultramafic intrusions of the region

Analysis of the correlation between deformation and temperature in a concrete dam

Deformational control of structures has its greatest exponent in large dams monitoring, which, depending on their structural typology, can be subjected to movements generally based on both the pressure that they upport and the temperature.The designer usually calculates the theoretical displacements that the dam will suffer onsidering the hydrostatic thrust and the temperature, but it is also true that these displacements are theoretical and they do not often fit to the real movements, due to the uncertainties that arise during the onstruction of any dam and make the final structure have changes which can be more or less significant with respect to the originally projected one. However, it is worth mentioning that they are usually lower than those theoretically calculated. The present research work focuses on a potential correlation and the subsequent determination of an mpirical model that allows calculating the deformation by means of a polynomial fit, working on the basis of temperature observations held over 14 years. This empirical model is contrasted and validated with the observations taken during the following year, and although it is only valid for the dam where the test has been made (“La Cohilla” Dam), the methodology is suitable for any other structure

Determination of an empirical model for calculating the strain of a dam in terms of hydrostatic thrust

The deformational control of structures has its greatest exponent in the control of large dams, which depending on structural typology, can be subjected to movement generally based on the pressure that it suffers. The designer usually calculates the theoretical displacements that the dam must suffer depending on the ydrostatic pressure, function of the thrust bearing, but it is also true that this calculation is theoretical and it is not usually adjusted to the real movements, due to the uncertainties that arise in the construction of any dam and make the original project have more or less significant changes in the final construction. In favour of the builder, it must be said that the actual displacements are usually lower than the theoretical ones. The present research focuses on the determination of an empirical model that allows calculating the deformation based on practical observations of a direct pendulum over 14 years, which determines the isplacement and the pressure experienced by the dam represented by the height of water contained, by means of a polynomial adjustment. This empirical model is tested and then validated with observations over the ollowing year and, although it is only valid for the dam where the trial (La Cohilla Dam) is made, the ethodology is applicable to any other structure

Caracterización químico-mineralógica de las cromitas ofiolíticas de Calzadilla de los Barros (Badajoz)

The Cerro Cabrera and Sierra Cabeza Gorda peridotite massifs (Calzadilla de los Barros, Badajoz) comprise serpentinites hosting podiform chromite mineralization and have been interpreted as part of an ophiolitic slab. The chromites are Al-rich and cristallized from a MORB-type melt. The subsolidus reequilibration with olivine depleted the chromite margins in Al and Mg. Later metamorphic alteration produced a enrichment in Fe3+, resulting in the formation of ferrichromite

Trazas de elementos del grupo del platino en los sulfuros de Aguablanca: Datos de LAICP- MS

España. Ministerio de Educación y CienciaDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Determination of an empirical model for the deformation of a dam on the basis of the hydrostatic thrust and temperature

The deformational control of structures has its main exponent in the geometric control of large dams. Considering the constructive typology, they can suffer deformation, which is function of the hydrostatic thrust and the temperature that supports the dam under usual circumstances. The project designer usually calculates the deformation that the dam will suffer on the basis of thrust and temperature, but this calculation is theoretical, and it must be contrasted with the real data about deformation that are periodically observed in the dam, in order to certificate the adequate evolution of the structure through time. This research work is focused on the determination of an empirical model that allows the calculation of the deformation on the basis of the simultaneous observations of a direct pendulum that have been recorded with the correspondent temperatures during 14 years. This empirical model is later contrasted and validated with the records taken during the subsequent year. Although it is only valid for the dam where the tests were held (La Cohilla Dam, Cantabria, Spain), the methodology is suitable for any other structure. The main contribution of this research is the methodology itself, which allows obtaining an empirical model that determines the expected deformation, whatever the conditions of hydrostatic thrust and temperature are. It complements the theoretical model that the project designer has established, which is done just for a certain set of conditions of these variables