The Penouta Sn-Ta deposit, in the northwest of Spain, is a greisenized granitic cupola where Ta minerals occur mainly as disseminations in a leucogranite body intruded in Precambrian–Lower Cambrian gneisses and mica-schists. This leucogranite is a medium- to fine-grained inequigranular rock consisting mainly of quartz, albite, K-feldspar and muscovite. Accessory minerals are mainly of spessartine, zircon, cassiterite, Nb-Ta oxides, monazite, xenotime, native bismuth and pyrite. The alteration processes were mainly albitization, muscovitization and kaolinitization.This leucogranite is peraluminous and P-poor, with 0.03–0.07 wt.% P2O5, 900–1500 ppm Rb, 30–65 ppm Cs, 120–533 ppm Li, 80–140 ppm Ta, 51–81 ppm Nb and up to 569 ppm of Sn.Mineralogical characterization of Nb-Ta oxide minerals was determined by X-ray diffraction, scanning electron microscopy, electron microprobe analysis and mineral liberation analysis. Mn-rich members of the columbite-group minerals (CGM) are the most common Ta-bearing phases, but microlite, wodginite, tapiolite and Ta-rich cassiterite occur also. CGM crystals are commonly zoned concentrically, with a Nb-rich core surrounded by a Ta-rich rim, with a sharp boundary between them. Convoluted zoning occurs also. Dissolution textures resulting from the corrosion of columbite and tantalite rims, in particular, are common. The Mn/(Mn + Fe) ratio varies between 0.33 and 0.97 and the Ta/(Ta + Nb) ratio between 0.07 and 0.93. Wodginite and microlite formed as late replacements of CGM and occur associated with tantalite and cassiterite. Subhedral to anhedral cassiterite crystals, usually up to 200 μm across, occur in two generations: the earlier one is Nb,Ta-poor whereas in the later generation, the Ta content can reach >9 wt.% of Ta2O5 and 1.7 wt.% of Nb. The presence of a fluid phase in the apical zone of the granite, probably related to the separation of a fluid/vapour of the melt, could explain the sponge-like textures, the Ta enrichment associated with these textures, the occurrence of Ta-enriched mineral phases (microlite and wodginite) and their common interstitial character.

The Cap de Creus pegmatite field exhibits a well-defined regional zonation of four types of granitic pegmatite: barren Kfeldspar-rich pegmatites (type I), beryl-columbite-subtype pegmatites (type II), beryl-columbite-phosphate-subtype pegmatites (type III) and albite-type pegmatites (type IV). There is an increase in the albite content, relative to K-feldspar, with increasing pegmatite evolution. Type-I microcline-rich pegmatites have low contents of albite, whereas in type IV, albite is the only feldspar. The K/Rb value in K-feldspar decreases progressively from type-I to type-III pegmatites. In addition, there is a progressive enrichment in P, Rb, Cs, Y, Sr, Ga, Ce, W and Sn from type-I to type-IV pegmatites. Concentrations of Pb and Zr decrease in Kfeldspar from type-I to type-III pegmatites. K-feldspar from the Cap de Creus pegmatites exhibits higher contents in Ba, Rb, Cs, Nb, Y, Sn, V and Cr than albite. Albite is richer in Sr, Zr, Cu, As, Ce and Ga. Pb, Zn, W, Co and Ni have similar affinity for Kfeldspar and albite. Muscovite exhibits similar geochemical evolution to K-feldspar. These progressive trends suggest a common origin for all of the Cap de Creus pegmatites by fractionation of the same parental magma. The high P content of feldspars, up to 1.67 wt.% P 2 O 5 in K-feldspar and 1.75 wt.% in albite, indicates buildup in this element from the earliest stages of pegmatite crystallization. Trace-element variation in feldspars and muscovite reflects enrichments in the melt; a higher content correlates with characteristic minerals of these elements. In particular, the phosphorus content of albite is proposed as a useful mineralogical guide to niobium-tantalum-rich oxide mineralization. SOMMAIRE La suite de pegmatites granitiques du Cap de Creus démontre bien une zonation régionale dans la disbtribution de quatre types de pegmatite: pegmatites stériles enrichies en feldspath potassique (type I), pegmatites du sous-type à béryl-columbite (type II), pegmatites du sous-type à béryl -columbite -phosphate (type III), et pegmatites à albite (type IV). Il y a une augmentation progressive de la teneur en albite par rapport à celle du feldspath potassique, avec le degré de fractionnement. Les pegmatites du type I, riches en microcline, ont une faible teneur en albite, tandis que dans les pegmatites de type IV, l'albite est le seul feldspath. La valeur de K/Rb du feldspath potassique diminue progressivement des pegmatites du type I à celles du type III. De plus, il y a un enrichissement progressif en P, Rb, Cs, Y, Sr, Ga, Ce, W et Sn du type I au type IV. Les concentrations de Pb et Zr diminuent dans le feldspath potassique des pegmatites du type I à celles du type III. Le feldspath potassique des pegmatites du Cap de Creus fait preuve de teneurs plus élevées en Ba, Rb, Cs, Nb, Y, Sn, V et Cr que l'albite. En revanche, l'albite est plus riche en Sr, Zr, Cu, As, Ce et Ga. Le Pb, Zn, W, Co et Ni ont un degré d'enrichissement semblable dans le feldspath potassique et l'albite. La muscovite fait preuve d'enrichissements ...

The Lower Llandoverian metasedimentary rocks of the Prades Mountains, southwestern Catalonia, Spain, consist of interstratified anorthite-rich beds, chert beds, phosphate beds, sulfide-rich black shale (with mainly pyrrhotite and minor chalcopyrite), massive sulfide lenses and calc-silicate beds. These metasedimentary rocks are anomalously enriched in V and Cr, and have disseminated minerals of precious metals: mainly sperrylite and palladian löllingite. The V-and Cr-rich associations are the result of an isochemical metamorphism of V-and Cr-rich protoliths. The contact metamorphism of V-rich shale produced metapelitic hornfels with V-rich aluminosilicates and VCr oxides. The occurrence of V oxides in apparent equilibrium with Vrich silicates suggests a limit for the V and Cr contents in these aluminosilicates at the conditions of thermal metamorphism. On the other hand, metamorphism of anorthite-and VCr r-rich sedimentary rocks produced V-and Cr-rich silicates, such as goldmanite, V-rich amphiboles, V-rich titanite and V-rich allanite.

Authigenic carbonate crusts, surface muds and bivalve shell fragments have been recovered from inactive and active recently discovered cold seep sites in central Guaymas Basin.. In this study, for first time, redox conditions and fluid sources involved in mineral precipitation were investigated by analyzing the mineralogy and textures of surface samples, along with skeletal contents, and C, O and S isotopes variations. The δ 13 C values of aragonitic bivalve shells and non-skeletal carbonate

A volcanic dome complex of Miocene age hosts the In-bearing Ánimas–Chocaya–Siete Suyos district in SW Bolivia. Ore mineralization occurs as banded and massive infillings in sub-vertical, NE-SW striking veins. In this article, a detailed petrographic study is combined with in situ mineral geochemistry determinations in ore from the Arturo, Chorro and Diez veins in the Siete Suyos mine, the Ánimas, Burton, Colorada, and Rosario veins in the Ánimas mine and the Nueva vein in the Chocaya mine. A three-stage paragenetic sequence is roughly determined for all of them, and includes (1) an early low-sulfidation stage that is dominated by cassiterite, pyrrhotite, arsenopyrite, and high-Fe sphalerite (FeS > 21 mol. %); (2) a second intermediate-sulfidation stage dominated by pyrite + marcasite ± intermediate product, sphalerite (FeS < 21 mol. %), stannite, and local famatinite; and, (3) a late intermediate-sulfidation stage dominated by galena and Ag-Pb-Sn sulfosalts. Electron-probe microanalyses reveal high indium enrichment in stage-2 sphalerite (up to 9.66 wt.% In) and stannite (up to 4.11 wt.% In), and a moderate enrichment in rare wurtzite (up to 1.61 wt.% In), stage-1 sphalerite (0.35 wt.% In), cassiterite (up to 0.25 wt.% In2O3), and ramdohrite (up to 0.24 wt.% In). Therefore, the main indium mineralization in the district can be associated to the second, intermediate-sulfidation stage, chiefly in those veins in which sphalerite and stannite are more abundant. Atomic concentrations of In and Cu in sphalerite yield a positive correlation at Cu/In = 1 that agrees with a (Cu+ + In3+) 2Zn2+ coupled substitution. The availability of Cu in the mineralizing fluids during the crystallization of sphalerite is, in consequence, essential for the incorporation of indium in its crystal lattice and would control the distribution of indium enrichment at different scales. The highest concentrations of indium in sphalerite, which is found in the Diez vein in the Siete Suyos mine, occur in crustiform bands of sphalerite with local “chalcopyrite disease” texture, which has not been observed in the other studied veins. In stannite, the atomic concentrations of In are negatively correlated with those of Cu and Sn at Cu + In = 2 and Sn + In = 1. Thus, atomic proportions and correlations suggest the contextualization of the main indium mineralization in the sphalerite–stannite–roquesite pseudoternary system.