IBERLID: A lead isotope database and tool for metal provenance and ore deposits research

[EN] Although sometimes controversial, the use of Pb isotope data in geological research of ore deposits and metal provenance studies in archaeology has proved a useful tool for investigation of the relations between ore sources and raw materials used by humans. Users of this kind of information have often asked for complete datasets that would include not only numerical values of isotope ratios but also mineralogical and geological information about the samples analysed so as to allow for conscientious data comparison. The IBERLID database here presented has been designed to include available information for nearly 3000 samples from the Iberian Peninsula and Balearic Islands in a unique, complete to the extent possible, upgradable dataset using standardized variables. This allows to compare data and establish groups based upon isotopic ratios, mineralogy and other geological characteristics of the samples. The database is available through an online interactive public tool (www.ehu.eus/ibercron/iberlid) that provides for data search, comparison and graphics design, and may be furthermore exported for enhanced statistical treatment. By direct use of the proposed standardized variables, the compiled results allow to discern among 3 main mineralization events within the Iberian realm, while interpolation of Pb isotope data allow to draw the first maps of model age, mu and kappa parameters. The problem of radiogenic lead in some compiled data requires additional analyses of elemental concentrations, which so far has been generally neglected.Financial support was provided by the Spanish Ministry of Economy, Industry and Competitiveness, and the European Regional Development Fund (MINECO/ERDF CGL2015-63530-P) , and by the UPV/EHU (GIU15/05) . The authors are grateful to Sabine Klein and two anony-mous reviewers for constructive comments which improved this manuscript, and to Huayong Chen for suggestions and editorial handling

The late-Variscan peraluminous Valdepeñas pluton (southern Central Iberian Zone)

The Valdepeñas pluton is the easternmost outcrop of the Cáceres-Valdepeñas magmatic alignment (southern Central Iberian Zone). This massif is constituted by a cordierite-bearing porphyritic monzogranite and may be grouped within the so-called "Serie Mixta" granitoids. The Valdepeñas monzogranite is of magnesian [FeOt /(FeOt +MgO)~0.76], alkali-calcic [(Na2O+K2O)-CaO=7.8-8.5] and peraluminous (A/CNK=1.14-1.20) composition. Multielemental- and REE-normalized patterns are comparable to those of similar rocks in the NisaAlburquerque-Los Pedroches magmatic alignment, and slightly differ from those of the Montes de Toledo batholith, both in the southern Central Iberian Zone. The U-Pb zircon age of 303±3Ma is consistent with the late-orogenic character of the intrusion and is in accordance with most of the granitic peraluminous intrusions in the southern Central Iberian Zone. 86Sr/87Sr300Ma ratios (0.707424-0.711253), εNd300Ma values (-5.53 to -6.68) and whole-rock major and trace element compositions of the studied rocks, suggest that the parental magma of the Valdepeñas monzogranite could derive from a crustal metaigneous source. The U-Pb ages (552-650Ma) of inherited zircon cores found in Valdepeñas monzogranite samples match those often found in Lower Paleozoic metavolcanics and granitic orthogneisses of Central Iberia and, furthermore, point to Upper Neoproterozoic metaigneous basement rocks as possible protoliths at the magma source. Based on the solubility of monazite in peraluminous melts, the estimated emplacement temperature of the studied monzogranite is 742-762ºC. The results obtained in this work would contribute to a better understanding of the origin of the "Serie Mixta" granitoids

ANALYTICA CHIMICA ACTA ELSEVIER Sequential separation of light rare-earth elements, thorium and uranium by miniaturized extraction chromatography: Application to isotopic analyses of silicate rocks

International audienceA new method for the concomitant separation of the light rare-earth elements (LREEs), thorium and uranium is described, and applied to the determination of '43Nd/'MNd ratios, and concentrations of Sm, Nd, Th and U in silicate rocks, using isotope dilution and thermal ionization mass spectrometry. The proposed scheme is based on two recently introduced extraction chromatographic materials, referred to as TRU.Spec (TRansUranic-element Specific) and Ln.Spec. For most geological samples, the TRU.Spec 'resin' affords a straightforward separation of LREE, U and Th with high yield, good purity and satisfactory blank levels, on a single small (0.25 ml) column. Only Fe3+ was found to have detrimental effects on the LREE yields. For iron-rich samples, this troublesome interference was overcome by pretreatment on a short cation exchange column. Besides, a tandem column arrangement with the Ln.Spec 'resin' enables the isolation of neodymium and samarium from bulk rock solutions be made in a single run. The validity of the method is illustrated by the measurement of Sm. Nd, Th and U concentrations along with '43Nd/144Nd ratios in 15 international standard reference materials

Ceochemieal characterization ofthe peridotítes from thc Sierra de Aguas massif (Malaga)

In order to constraint geochemical differences related to the petrogenesis ofthe Ronda peridotites, major and trace elements combined with chondrite normalized REE patterns of the Sierra de Aguas Massif peridotites, near Carratraca (Málaga), have been compared with the similar published data from Sierra Bermeja Massif. The results establish a well geochemical distinction between previously petrographically identificated granular and porphyroclastic domains. The analyses also confirm that granular peridotites represent a more depleted mantle source than the porphyroclastics, apparently related with a fractional equilibrium melting process. Nevertheless, "U-shape" REE patterns and some REE ratios point to a more complex formation proces

New petrological data, Rb-Sr geochronology and isotope geochemistry (Sr, Nd) of the Ventosilla pluton (Sierra de Guadarrama, Spanish Central System)

Whole rock Rb-Sr ¡sotopic analyses on granites from Ventosilla pluton yield an age of 346 ± 63 Ma, and intercept at 0.708688 ± 0.00094. This age increases the time-span of the Hercynian plutonism in the area up to 70 Ma. The presence of a complex residual mineralogy and their Sr and Nd isotopic signatures, overlapping the previous isotopic data on peraluminous granites from the Spanish Central.System, suggest melting of mainly crustal sources for the origin of this pluto

Aplicación de métodos de cromatografía de extracción específica al estudio isotópico de Rb-Sr, Sm-Nd en muestrasgeológicas: el granito de Hombreiro-Santa Eulalia (Lugo, NW de España)

The analytical application to geological samples of three new chromatographic resins, TRU-Spec ®, Sr-Spec ® and LN-Spec ®) has been investigated. Seven samples of the Hombreiro massif (Lugo, NW Spain) have been studied, that yield a Rb-Sr age of 298 ±5 Ma (SrQ = 0.7086, MSWD = 7.64) for the magma crystallization. Sm-Nd data results for the same massif give eNd values dose to -2 at 300 Ma. This suggests that the origin of the magma might be related to the partial melting of immature sediments, likely involving volcanoclastic sequencesSe han investigado las posibilidades analíticas, en muestras geológicas, de tres nuevos tipos de resinas cromatográficas, TRU-Spec®, Sr-Spec®y LN-Spec®. A partir de siete muestras estudiadas, pertenecientes al macizo de Hombreiro (Lugo, NW de España), se ha obtenido una una edad Rb-Sr, para la cristalización del magma, de 298 ± 5 Ma (Sr0 = 0.7086, MSWD = 1.64). Los resultados de Sm-Nd, indican un valor de sNd cercano a -2 para una edad de 300 Ma. Todo éllo sugiere que el origen de dicho magma se puede relacionar con la fusión pardal de sedimentos poco evolucionados, posiblemente asociados a secuencias volcanoclástica

Heterogeneidades isotópicas de Nd en plutones graníticos tardi-hercínicos de la Región Central Española

Some Hercynian granitic plutons from Central Spain show variation in initial Nd isotopic ratios defining different trends with increasing silica content. There is a decoupling between the Sr and Nd isotopic systems as these plutons present homogeneous initial Sr ratios. Magmatic processes could explain this Nd isotopic disequilibrium; it is suggested that Nd-bearing restitic or early precipitating accesory phases could control the Nd isotopic heterogeneity of the granite

Pb isotopic composition of galenas from the Azuaga Fault region. Contribution to the plumbotectonic model of the Ossa-Morena Zone

New Pb isotopic analyses have been obtained on twenty samples of galena from the Azuaga area. In spite of the overall homogeneity, the results for samples to the North of the Azuaga Fault are perceptible different from those to the South. The observed difference is tentatively related to the nature of the host rocks on both sides of the fault. The new data are consistent with previous values of Pb isotopic composition for galenas from the same region. Yet, these results reveal some incongruity in previous models as regards the origin of Pb in the Azuaga area. We favour a model involving the participation of lower crustal or equivalent rock units rather than a mantle-related source for the P

Geochronology of the Campanario-La Haba pluton (Badajoz) by means of Pb isotope data on zircons and U-Th-Pblglaj in monazites

The Campanario-La Haba pluton is located to the north of the Los Pedroches batholith in the southern part of the Central-lberian Zone. The age of the emplacement had been established between 304 and 314 Ma using K-Ar and Rb-Sr methods. In this study we have applied two different new techniques in an attempt to precise the age of the intrusion. The results obtained, are as follows: (1) the Pb isotopic composition of five zircon fractions have yielded a 206Pbl204Pb vs. 207Pb/204Pb isochron of 307 ± 16 Ma (MSWD = 0,33); (2) the U-Th-Pb content of monazites analysed by EM PA does not allow for reliable age results; althouth their ages are close to those obtained by other methods, there is distinct evidence of Pb-loss processes subsequent to the crystallization of this mineral, for which reason the ages obtained must be handled with care. The age of the postcrystalization events and their significance remain unknwo

Pb isotope composition variations in galenas from the Los Pedroches area: difference between the El Zumajo and Linares-La Carolina mineralizations

We report the results of Pb isotope analyses on representative galena samples from the El Zumajo quartz-rich dyke. This is a late intrusion within the Cardeha-Virgen de La Cabeza granite of the Los Pedroches Hercynian batholith. The batholith granodiorite-granite alignment accounts for the largest composite granitic intrusive in southern sectors of the Central Iberian Zone of southwestern Spain. Located in the south of this magmatic lineation there occurs the Cardena-Virgen de La Cabeza granite, the largest pluton of the granitic unit of the batholith. An important dyke complex, mainly composed of trachyandesite, dacite, rhyolite, aplite, pegmatite and quartz dykes (Carracedo et al., 1993, 1994), outcrops in central sectors, mostly within the granodioritic unit, of the batholith. The El Zumajo dyke is distinctive because of its composition (almost only quartz with an important amount of galena), direction (N 120°E, that is, similar to the dacite-rhyolite dykes and different from that of the other quartz dykes) and because it is found in the granite unit which bears scarce evidence of dyke intrusions. Isotopic compositions of analysed galena are: 206Pb/204Pb = 18.457, 207Pb/204Pb = 15.636 and 20SPb/204Pb = 38.611. These data were compared with published data from the same mineral of the Linares-La Carolina sector, a mining district also related to granites of the Los Pedroches batholith. The new results are markedly different from those published by Lillo (1992) and Arribas (1993) for Linares-La Carolina. The observed difference in Pb isotopic compositions with respect to the known data might be related to: a different age of the intrusion, a difference source for the metal enrichments, or to a combination of both factors. On the basis of field relationships, it appears evident that the dyke is younger than nearby intrusives, including other dyke types. Nevertheless, the possibility of a different source cannot be discarded. A more solid conclusion would require new Pb and other isotope data on the Linares-La Carolina sector and related granites, and further more precise structural constrains on the relationships between the granites and the mineralization