Portuguese granites associated with Sn-W and Au mineralizations

In northern and central Portugal, there are different tin-bearing granites. Most of them are of S-type, others have mixed characteristics of I-type and S-type granites and a few are of I-type. Tin-tungsten deposits are commonly associated with Hercynian tin-bearing S-type granites. Some quartz veins with wolframite are associated with an I-type granite, which has a low Sn content. In suites of tin-bearing S-type granitic rocks, Sn content increases as a function of the degree of fractional crystallization. Greisenizations of two-mica S-type granites associated with tin-tungsten mineralizations are accompanied by an increase in SiO2, H2O+, Sn, W, Nb, Ta, Rb, Zn, and Pb and decrease in MgO, Na2O, V, Sc,Zr, and Sr. The granite associated with the Jales gold deposit is of S-type and strongly differentiated like the tin-bearing S-type granites, but it has a very low Sn content. During fractional crystallization, Si, Rb, Sn, Pb, Au, As, Sb, and S increase. During increasing degree of hydrothermal alteration of this granite at the gold-quartz vein walls, there are progressive increases in K2O, H2O+, Sn, Cs, Cu, Pb, Au, Sb, As, and S

Syntectonic Variscan magmatism in the Aguiar da Beira region (Iberian Massif, Portugal)

The Aguiar da Beira region (Portugal) is located in the core of the Iberian Massif, more precisely in the Central-Iberian Zone, which is dominantly composed by abundant volumes of plutonic rocks, emplaced into Late Proterozoic – Early Cambrian and Palaeozoic metasediments, mainly during or slightly after the third deformation phase of the Variscan Orogeny (D3). A considerable amount of these granitoids are syntectonic, intruded during the peak of this deformation event (D3). In particular, at the Aguiar da Beira region, there are two syntectonic granitoids that represent two distinct magmatic series: a medium- to coarse-grained porphyritic biotite granodiorite-granite (322 Ma), which belongs to the early granodiorite series, and a medium-grained muscovite-biotite granite (317 Ma) that is part of the two-mica peraluminous leucogranites suite. The petrographical, geochemical (whole-rock and mineral compositions) and isotopical (Sr-Nd, 18O-wr and 18O-zr) study of the two intrusions revealed their remarkably different character, and allowed to conclude that they correspond to two independent magma pulses, derived from distinct sources and petrogenetic processes. The biotite granodiorite-granite is a weakly peraluminous intrusion, characterized by intermediate to felsic SiO2 contents (66 – 68%), high Ba, Sr and REE, and high Al and Mg biotite contents, typical of the calc-alkaline associations. The Sr-Nd initial ratios are homogeneous and overlap the lower crustal felsic metaigneous granulites signatures (Villaseca et al. 1999) which might suggest an origin by the anatexis of lower felsic metaigneous rocks, and is further supported by 18O-wr and 18O-zr data. However, the data, allied to the presence of microgranular enclaves present in this intrusion also raises the hypothesis of an origin by mixing of lower crustal derived magmas and mantle melts. Based on the available data these seem to be the two genetic scenarios that can best explain the geochemical signature of the biotite granodiorite-granite, not being possible to opt for any of the options. By contrast, the muscovite-biotite granite has an entirely distinct geochemical signature, typical of S-type granites: a highly evolved and strongly peraluminous character (SiO2 = 72 - 74%; CaO = 0.3-0.6%; A/CNK = 1.18 - 1.36, low Mg, Ti, Ba, Sr, REE, HFSE contents, and high Al2O3/TiO2 e Rb/Sr ratios), high (87Sr/86Sr)317 (0.71037 - 0.71459), low Ndi (-7.7 to -8.7), and high 18O (18O-wr = 11.33 ‰; 18O-zr = 9.5 ± 0.2‰). The data suggest that this magma was derived from the partial melting of metasedimentary middle crustal protoliths, which has been successfully modeled. The observed major and trace element composition variation suggests an evolution controlled by fractionation crystallization of a mineral association composed by plagioclase + biotite + apatite + zircon ± monazite ± ilmenite

Plagioclase and biotite compositions tracing granite genesis and evolution: insights from two syntectonic granitoids from Aguiar da Beira (N Portugal)

The Aguiar da Beira area (N Portugal) is located within the Central-Iberian Zone (CIZ) of the Iberian Variscan Belt. It is mainly composed by granitoids emplaced during (syntectonic) or slightly after (late- to post-tectonic) the last ductile deformation event of the Variscan orogeny (D3). From the petrological and geochemical point of view, the syntectonic granitoids from the CIZ can be included into two genetically distinct suites: (a) calc-alkaline granodiorites and biotite granites, and (b) strongly peraluminous leucogranites and two-mica granites. In the Aguiar da Beira area, the first group is represented by a small intrusion of a medium- to coarse-grained porphyritc biotite granodiorite-granite, emplaced 322 Ma ago, characterized by a slightly peraluminous and moderately evolved composition. The second group comprises a NW-SE elongated pluton of a strongly peraluminous and highly evolved medium- to fine-grained muscovite-biotite granite (317 Ma), showing occasionally a gneissic foliation concordant with the D3 variscan structures. Based on geochemical and Sr-Nd and 18O isotopic data, the biotite granodiorite-granite melt is interpreted either as the result of partial melting of heterogeneous lower crustal materials, or as the product of mixing of mantle derived magmas and lower crustal felsic anatectic melts. In contrast, the muscovite-biotite gneissic granite magma appears to have been exclusively generated by partial melting of upper crustal metasediments and suffered a subsequent evolution dominantly controlled by fractional crystallization processes. Plagioclase and biotite major and trace element compositions can be used to constrain the origin and evolution of the two granitoids and provide strong evidence in support of the proposed petrogenetic models. In the biotite granodiorite-granite, the plagioclase is characterized by a wide compositional range (An20-33), high Sr (749 – 869 ppm) and Ba (32 – 351 ppm) contents and a Sr discontinuous zonation pattern, whilst the biotite shows high TiO2 (2.92 – 3.30 wt%), Ba (407 – 589 ppm), V (214 – 234 ppm), and low Al2O3 (16.83 – 18.03 wt%), Li (335 – 367 ppm), Zn (262 – 279 ppm) and Fet/(Fet + Mg) (0.54 – 0.55) contents. These data confirm the typical calc-alkaline affinity of this intrusion and reveal that these phase minerals crystallized under disequilibrium conditions. In contrast, the plagioclase from the muscovite-biotite granite displays a narrower compositional range (An1-7), unzoned or normally zoned compositional patterns and lower Sr (19 – 33 ppm) and Ba (1.1 – 2.0 ppm) contents, reflecting the highly evolved character of this intrusion and near equilibrium crystallization conditions. The biotite crystals from the muscovite-biotite granite plot in the field of the alumino-potassic series in the AlVI versus Mg diagram (Nachit et al., 1983), supporting a major contribution of metasedimentary rocks for the genesis of this magma. Their AlVI contents increase with decreasing Mg suggesting an important role for fractional crystallization processes during magmatic evolution. The range of AlVI and Fet/(Fet + Mg) values (AlVI: 0.482 – 0.487; Fet/(Fet + Mg): 0.72 – 0.83) displayed by the biotites show that the muscovite-biotite granite crystallized from a reduced magma (low O2), which is consistent with its inferred sedimentary provenance

New insights from U–Pb zircon dating of Early Ordovician magmatism on

The Central Iberian–Ossa-Morena transition zone (SW Iberian Massif) represents a segment of the northern Gondwana margin with a long geodynamic evolution, characterized by the superposition of Cadomian and Variscan events. The Early Ordovician is mainly represented by porphyritic felsic volcaniclastic rocks (the Urra Formation) that pass up into a siliciclastic sediments typical of the Central Iberian Zone (Lower Ordovician Armorican Quartzite Formation). The Urra Formation unconformably overlies the previously deformed and metamorphosed Ediacaran sediments of the Série Negra (with Ossa-Morena Zone paleogeographic affinity). New SHRIMP zircon data obtained from the Urra Formation volcaniclastic rocks indicate an Early Ordovician age (206Pb/238U ages ranging from 494.6±6.8 Ma to 488.3±5.2 Ma) for this magmatic event. The inherited zircon cores indicate the presence of multicycle protoliths with different Precambrian ages: Neoproterozoic (698–577 Ma), Paleoproterozoic (2.33 Ga) and Paleoarchean (3.2–3.3 Ga). There is a noticeable lack of Meso- to Neoarchean and Mesoproterozoic ages. The data support the hypothesis that the volcaniclastic rocks were derived by partial melting of Cadomian basement (linked to a West African Craton provenance). The Urra Formation volcaniclastic rocks have rhyolitic to dacitic compositions, are peraluminous and similar to calc-alkaline high-K series suites elsewhere. Isotopic signatures present a wide range of values (87Sr/86Sr)t=0.7085–0.7190, more restricted εNdt (−2.65 to −0.35) and δ18O=9.63–10.34‰, compatible with magmas derived from crustal rocks, including portions of the lower crust. Some samples show disturbance of the Rb–Sr system as shown by unrealistic values for (87Sr/86Sr)tb0.703, probably due to Variscan deformation and metamorphism. The volcaniclastic rocks with a significant sedimentary contribution (upper unit) are distinguished from the others by the lowest values of εNdt (−5.53 to −4.85). The geochemical data are compatible with an orogenic geodynamic environment. However, the “orogenic” signature can be considered to represent, in part, an inherited feature caused by melting of the Cadomian basement which also has calc-alkaline affinities. The Early Ordovician crustal growth and associated magmatism, represented by the Urra felsic volcaniclastic rocks and associated calc-alkaline granitoids, diorites and gabbros, can be interpreted in terms of the underplating and temporal storage of mantle-derived magmas as the potential source for the “orogenic melts” that were intruded during Early Paleozoic extension. This record of Early Ordovician magmatism has striking similarities with other correlatives from the Iberian, Bohemian and Armorican massifs that are discussed in this paper. This comparison reinforces the probable existence of a large-scale crustal melting process linked to a significant episode of extension on the northern Gondwana margin that probably resulted in the birth of the Rheic Ocean

Turmalinas en la pegmatita granítica de Li-Cs-Ta del Grupo Namacotche, Mozambique: cristalquímica y origen

The field work, backscattered electron images and detailed microanalyses of three generations of tourmaline from the Namacotche LCT pegmatites allows de distinction between the compositional magmatic and hydrothermal tourmalines. The generation 1 occurs in the outer intermediate zone of the pegmatite. It consists of zoned crystals with an oscillatory inner core of foitite and schorl, an outer core of schorl and an Fe-rich fluor-elbaite rim. Unzoned Fe-rich fluor-elbaite crystals occur in the inner intermediate zone of the pegmatite. All the crystals are derived by fractionation of a (Al, Li, B)-rich pegmatite melt. However, the rim of zoned crystals and some compositions of unzoned crystals show evidence of hydrothermal fluids, as they plot outside the fractionation trends. The zoned fluor-elbaite crystals of the generation 2 are from the inner intermediate zone of the pegmatite. They have a pink core and a green rim. The rim has higher YFe2+, Na, F contents YFe2+/(YFe2++Licalc.) value and lower Si, YAl, Licalc. and X-site vacancy contents, X-vacancy/(Na+X-vacancy) value than the core. Both zones are hydrothermal. The rim is an overgrowth. The fluor-elbaite gemmy crystals of the generation 3 occur in sheared breccia blasts and clasts with a cookeite matrix. They depend mainly on the fluid-rich hydrothermal environment of low temperatures (280-150ºC). Some from the cycle a may result from the dissolution of magmatic tourmaline crystals of the generation 1 from the sheared outer and inner intermediate zones of the pegmatite due to reaction with late fluids in chemical disequilibrium, followed by growth of tourmaline with low temperature hydrothermal fluids. The evolution from the cycle a to the cycle b and to the cycle c of the generation 3 implies that the hydrothermal reacting fluids were undergoing fractionation and becoming richer in Li and poorer in Fe2+ during the late hydrothermal crystallization of the pegmatites.El trabajo de campo, las imágenes de electrones retrodispersados y microanálisis detallados de tres generaciones de turmalina de las pegmatitas LCT de Namacotche permiten distinguir entre las turmalinas magmáticas y las hidrotermales. La generación 1 aparece en la zona intermedia exterior de la pegmatita. Consiste en cristales zonados con un núcleo interno oscilante de foitita y esquisto, un núcleo externo de esquisto y un borde de fluor-elbaita rico en Fe. En la zona intermedia interior de la pegmatita aparecen cristales no zonados de fluor-elbaita ricos en Fe. Todos los cristales derivan del fraccionamiento de un fundido pegmatítico rico en Al, Li y B. Sin embargo, el borde de los cristales zonados y algunas composiciones de cristales no zonados muestran evidencias de fluidos hidrotermales, ya que trazan fuera de las tendencias de fraccionamiento. Los cristales zonados de fluor-elbaita de la generación 2 proceden de la zona intermedia interna de la pegmatita. Tienen un núcleo rosa y un borde verde. El borde tiene mayor contenido en YFe2+, Na, F (YFe2+/(YFe2++Licalc.)) y menor contenido en Si, YAl, Licalc. y vacantes X, vacantes X/(Na+X-vacantes) que el núcleo. Ambas zonas son hidrotermales. El borde es un sobrecrecimiento. Los cristales geminados de fluor-elbaita de la generación 3 aparecen en clastos de brechas cizalladas y en clastos con matriz de cookeita. Dependen principalmente del ambiente hidrotermal rico en fluidos de bajas temperaturas (280-150ºC). Algunos del ciclo a pueden ser el resultado de la disolución de cristales magmáticos de turmalina de la generación 1 de las zonas cizalladas externa e interna intermedia de la pegmatita debido a la reacción con fluidos tardíos en desequilibrio químico, seguida del crecimiento de la turmalina con fluidos hidrotermales de baja temperatura. La evolución del ciclo a al ciclo b y al ciclo c de la generación 3 implica que los fluidos hidrotermales reaccionantes estaban sufriendo fraccionamiento y haciéndose más ricos en Li y más pobres en Fe2+ durante la cristalización hidrotermal tardía de las pegmatitas

Non-invasive genetic sampling for molecular sexing and microsatellite genotyping of hyacinth macaw (Anodorhynchus hyacinthinus)

Molted feather sampling is a useful tool for genetic analyses of endangered species, but it is often very laborious due to the low quality and quantity of the DNA obtained. In the present study we show the parts of feathers that resulted in better yield of DNA. In descending order these were: blood clot outside the umbilicus, umbilicus (without blood clot), tip, inner membrane, and small calamus. Compared to DNA extracted from blood samples, DNA extracted from feathers produced microsatellite alleles of poorer quality and had to be processed immediately after extraction. As expected due to the level of DNA degradation, molecular sexing protocols that result in shorter PCR products were more efficient