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The Angolan alkaline&ndash, carbonatite complex of Monte Verde has a semi-circular shape and is comprised of a central intrusion of foidolite rocks surrounded by concentrically arranged minor bodies of other alkaline rocks and carbonatite magmatic breccias. This rock association is hosted by fenitized Eburnean granites. Concentric swarms of alkaline dykes of late formation, mostly of nepheline trachyte composition, crosscut the previous units. Most high-field strength elements (HFSE) and rare earth elements (REE) are concentrated in pyrochlore crystals in the carbonatite and alkaline breccias. Magmatic fluornatropyrochlore is replaced and overgrown by five secondary generations of pyrochlore formed during subsolidus stages and have higher Th, REE, Si, U, Sr, Ba, Zr, and Ti contents. The second, third, and fourth pyrochlore generations are associated with late fluids also producing quartz and REE rich minerals, whereas fifth and sixth pyrochlore generations are linked to the fenitization process. On the other hand, minerals of the rinkite, rosenbuschite, w&ouml, hlerite, eudialyte groups, as well as loparite-(Ce), occur in accessory amounts in nepheline trachyte, recording low to moderate agpaicity. In addition, minor REE-bearing carbonates, silicates, and phosphates crystallize as late minor secondary minerals into carbonatite breccia and alkaline dykes. In conclusion, the scarcity of HFSE and REE minerals at the Monte Verde carbonatite-alkaline-agpaitic complex suggests low metallogenetic interest and economic potential for the outcrops analysed in this study. However, the potential for buried resources should not be neglected.

© The Author(s)., The Bonga complex is composed of a central carbonatite plug (with a ferrocarbonatite core) surrounded by carbonatite cone sheets and igneous breccias of carbonatitic, fenitic, phoscoritic and lamprophyric xenoliths set in a carbonatitic, lamprophyric or mingled mesostase. To reconstruct the dynamics of the complex, the pyrochlore composition and distribution have been used as a proxy of magmatic-hydrothermal evolution of the complex. An early Na-, F-rich pyrochlore is disseminated throughout the carbonatite plug and in some concentric dykes. Crystal accumulation led to enrichment of pyrochlore crystals in the plug margins, phoscoritic units producing high-grade concentric dykes. Degassing of the carbonatite magma and fenitization reduced F and Na activity, leading to the crystallization of magmatic Na-, F- poor pyrochlore but progressively enriched in LILE and HFSE. Mingling of lamprophyric and carbonatite magmas produced explosive processes and the formation of carbonatite breccia. Pyrochlore is the main Nb carrier in mingled carbonatites and phoscorites, whereas Nb is concentrated in perovskite within mingled lamprophyres. During subsolidus processes, hydrothermal fluids produced dolomitization, ankeritization and silicification. At least three pyrochlore generations are associated with late processes, progressively enriched in HFSE, LILE and REE. In the lamprophyric units, perovskite is replaced by secondary Nb-rich perovskite and Nb-rich rutile. REE-bearing carbonates and phosphates formed only in subsolidus stages, along with late quartz; they may have been deposited due to the release of the REE from magmatic carbonates during the hydrothermal processes, This research was funded by Ministerio de Ciencia e Innovación (Spain), grants number CGL2006-12973 and CGL2009-13758, the 2017 SGR 0707 of the AGAUR-Generalitat de Catalunya and a Ph.D. grant to S. Amores-Casals sponsored by the Generalitat de Catalunya; the Hugh. E. McKinstry fund grant from the Society of Economic Geologist to carry out field work in Angola. Logistic assistance for the field trips was provided by the Departmento de Geologia da Universidade Agostinho Neto (Luanda, Angola). The Ph.D. studies of A. Bambi in Barcelona were supported by an AECI grant. A. Costanzo acknowledges financial support provided by the SYNTHESIS (Project GB-TAF-3835).

The tin-rich polymetallic epithermal deposit of Poop&oacute, of plausible Late Miocene age, is part of the Bolivian Tin Belt. As an epithermal low sulfidation mineralisation, it represents a typological end-member within the &ldquo, family&rdquo, of Bolivian tin deposits. The emplacement of the mineralisation was controlled by the regional fault zone that constitutes the geological border between the Bolivian Altiplano and the Eastern Andes Cordillera. In addition to Sn and Ag, its economic interest resides in its potential in critical elements as In, Ga and Ge. This paper provides the first systematic characterisation of the complex mineralogy and mineral chemistry of the Poop&oacute, deposit with the twofold aim of identifying the mineral carriers of critical elements and endeavouring to ascertain plausible metallogenic processes for the formation of this deposit, by means of a multi-methodological approach. The poor development of hydrothermal alteration assemblage, the abundance of sulphosalts and the replacement of l&ouml, llingite and pyrrhotite by arsenopyrite and pyrite, respectively, indicate that this deposit is ascribed to the low-sulphidation subtype of epithermal deposits, with excursions into higher states of sulphidation. Additionally, the occurrence of pyrophyllite and topaz has been interpreted as the result of discrete pulses of high-sulphidation magmatic fluids. The &delta, 34SVCDT range in sulphides (&minus, 5.9 to &minus, 2.8&permil, ) is compatible either with: i. hybrid sulphur sources (i.e., magmatic and sedimentary or metasedimentary), or ii. a sole magmatic source involving magmas that derived from partial melting of sedimentary rocks or underwent crustal assimilation. In their overall contents in critical elements (In, Ga and Ge), the key minerals in the Poop&oacute, deposit, based on their abundance in the deposit and compositions, are rhodostannite, franckeite, cassiterite, stannite and, less importantly, teallite, sphalerite and jamesonite.

The polymetallic Huanuni deposit, a world-class tin deposit, is part of the Bolivian tin belt. As a likely case for a &ldquo, mesothermal&rdquo, or transitional deposit between epithermal and porphyry Sn types (or shallow porphyry Sn), it represents a case that contributes significantly to the systematic study of the distribution of critical elements within the &ldquo, family&rdquo, of Bolivian tin deposits. In addition to Sn, Zn and Ag, further economic interest in the area resides in its potential in critical elements such as In, Ga and Ge. This paper provides the first systematic characterisation of the complex mineralogy and mineral chemistry of the Huanuni deposit with the twofold aim of identifying the mineral carriers of critical elements and endeavouring plausible metallogenic processes for the formation of this deposit, by means of a multi-methodological approach. With In concentrations consistently over 2000 ppm, the highest potential for relevant concentrations in this metal resides in widespread tin minerals (cassiterite and stannite) and sphalerite. Hypogene alteration assemblages are hardly developed due to the metasedimentary nature of host rocks, but the occurrence of potassium feldspar, schorl, pyrophyllite and dickite as vein material stand for potassic to phyllic or advanced argillic alteration assemblages and relatively high-temperature (and low pH) mineralising fluids. District-scale mineralogical zonation suggests a thermal zonation with decreasing temperatures from the central to the peripheral areas. A district-scale zonation has been also determined for &delta, 34SVCDT values, which range &minus, 7.2&permil, to 0.2&permil, (mostly &minus, 7&permil, to &minus, 5&permil, ) in the central area and &minus, 4.2&permil, to 1.0&permil, (mainly constrained between &minus, 2&permil, and 1&permil, ) in peripheral areas. Such values stand for magmatic and metasedimentary sources for sulfur, and their spatial zoning may be related to differential reactivity between mineralising fluids and host rocks, outwardly decreasing from the central to the peripheral areas.

article i nfo Several chromitite bodies of variable sizes are hosted in dunite-harzburgite of the small (b3 km) mining district of Sagua de Tanamo, in the Mayari-Cristal ophiolitic massif, eastern of Cuba. The chromian spinel in these bodies displays a large range in Cr# (Cr/Cr + Al) atomic ratio from 0.74 to 0.45. In high-Cr chromitites, Cr# and Ti contents increase from harzburgite to dunite, to chromitite. A roughly opposite trend of variation in Cr# is observed in high-Al chromitites, although in this case Ti distributes randomly. The differences in the type of chromian spinel (i.e., high-Cr or high-Al) in the chromitite coincide with a different behavior of the platinum-group elements (PGE). Whereas high-Cr chromitites are rich in PGE and contain abundant grains of platinum-group minerals (PGM), high-Al chromitites are systematically poor in PGE and in PGM. The calculated melts in equilibrium with chromian spinel of high-Cr chromitite are island arc thoeliites (IAT) with boninitic affinity whereas those in equilibrium with chromian spinel of high-Al chromitites are back-arc basin basalts (BABB). The formation of high-Cr chromitites is interpreted as a result of the extensive reaction of harzburgite with migrating island arc tholeiite melts of boninitic affinity. Melt-rock reaction produces boninitic melts with variable composition and porous dunitic channels in which the mixing/mingling of melts promotes crystallization of mononomineralic high-Cr chromian spinel. In contrast, high-Al chromitites formed by the mixing/mingling of BABB melts within conduits not in equilibrium with dunite. Percolation of primitive BABB melts through pre-existing dunite dissolved olivine, producing melt conduits in which BABB melts mixed and formed high-Al chromian spinel. The higher PGE and PGM in high-Cr chromitites is not only a function of the degree of partial melting but is linked to interaction between the migrating melt and mantle harzburgite during the formation of the chromitite. The coexistence of both types of chromitites in one small mining district reflects the temporal and/or spatial variations of separate melt intrusions emplaced in different subarc mantle domains during the opening of a back-arc basin in a supra-subduction zone environment.

The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ΔNNO calculated value is from −3.82 to −0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ΔNNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f(CO2) and f(H2O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %-26.3 wt % TiO2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence.

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 lollingite. 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 V–Cr oxides. The occurrence of V oxides in apparent equilibrium with V-rich 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 V-,Cr-rich sedimentary rocks produced V- and Cr-rich silicates, such as goldmanite, V-rich amphiboles, V-rich titanite and V-rich allanite.

In the Cap de Creus peninsula (NE Spain), four granite pegmatite types are distinguished: microcline-rich; beryl- columbite;beryl- columbite-phosphate; and albite. Beryl -columbite-phosphate pegmatites are zoned, with border, wall, intermediate zones and a quartz core. In addition, albitic and quartz-muscovite replacement bodies occur. The intermediate zones are mainly constituted by quartz, microcline, albite, beryl, Nb Ta minerals and phosphates. In early stages, crystallization takes place from a volatile-saturated magma and a hypersaline (39–46 wt.% NaCl eq.), CO 2 -rich fluid exsolved from the magma. In the last stages of the crystallization of the intermediate zones, this fluid produced unmixing in two fluids: one CO 2 -rich, salts-poor (3–5 wt.% NaCl eq.) and the other saline (up to 34 wt.% NaCl eq.) and CO 2 -poor. The first fluid formed a quartz core at 430 °C and 2.7 kbar. The second fluid circulated through all the pegmatite due to the development of a fracture network produced by a hydraulic fracturation. This fluid replaced the previous zones. In addition, crystallization of fine-grained albitites (Ta P-rich) and late quartz-muscovite veins takes place in the fractures. The fluids that formed these veins are more saline than those from the albitites, with 36–38 wt.% NaCl eq. and with CO 2 and minor N 2 .

Coastal hydrothermal submarine vents occur near Punta Mita (Mexico) through a seafloor fissure hosted by basaltic rocks and partially covered by recent sediments. Hydrothermal venting produces calcareous tufa mounds, with minor sulfides, barite and apatite. Pyrite is the most abundant sulfide mineral that precipitates around the submarine hot springs. It occurs as framboids, euhedral crystals, thin botryoidal coatings interbedded with calcite, and as replacement of detrital magnetite grains. Vent fluids have temperature below 100 °C, and methane is abundant. Sulfur isotopic composition of pyrite predominantly has δ 34 S values from − 10.7 to +4.9 suggesting that the source of sulfur is microbially reduced sulfate seawater.

The El Cobre deposit, east of Cuba, lies in the intermediate volcanosedimentary sequence of the Sierra Maestra intraoceanic island arc. The structure of the deposit corresponds to that of a volcanogenic-hosted massive sulfide (VHMS) model. It comprises (a) thick stratiform bodies (baryte and anhydrite), (b) three stratabound bodies (formed by silicification and sulfidation of limestones or sulfate strata), (c) stockwork zones, an older anhydrite stockwork and a younger quartz-pyrite stockwork grading downwards to (d) simple veins (quartz with sulfide ores). Pyrite, chalcopyrite and sphalerite are the most abundant sulfides. Fluid inclusions from this deposit have a salinity between 2.3 and 5.7 wt.% NaCl eq., homogenization temperatures range between 177 and 300 °C. Sulfur exhibits a range of δ 14 S values from − 1.4 to +7.3 for sulfides and from + 16 to +21 for sulfates. Fluid inclusions and sulfur isotope data at El Cobre deposit indicate that the hydrothermal fluid from which the sulfide precipitated was seawater, modified by reaction with volcanic host rocks during hydrothermal circulation.

The Potosi Mine is located in the Moa-Baracoa massif in the easternmost part of the Cuban Ophiolitic Belt. Chromite mineralization occurs within the mantle–crust transition zone. Two events of magma intrusion overprint the chromitite bodies: one gave rise to the crystallization of pegmatitic olivine–norite dikes, and the other produced pegmatitic gabbro dikes. Sulfide-poor chromite ores, brecciated chromite ores, and sulfide-rich chromite ores can be distinguished in the different chromitite bodies. Sulfide-poor ores represent more than 80 vol% of the chromitites. This type occurs far from the zones intruded by pegmatitic gabbro dikes and shows petrographic and chemical features similar to other chromitite bodies described in the Moa-Baracoa massif. Brecciated chromite ores occur within pegmatitic gabbro dikes. In this type, chromite crystals occur included within chromian diopside and plagioclase. These silicates often contain droplet-like sulfide aggregates. Sulfide-rich ores are spatially associated to the contacts between sulfide-poor chromite and pegmatitic olivine–norite dikes. These ores mainly consist of recrystallized (coarse) chromite with interstitial pyrrhotite, pentlandite, cubanite, and chalcopyrite. Chromite from sulfide-rich ores exhibits TiO2, FeO, V2O3, MnO, and especially, Fe2O3 contents, higher than those of chromite from brecciated ores and much higher than those of chromite from sulfide-poor ores. The sulfide-rich ores are PGE-rich (up to 1,113 ppb of total PGE), and show nearly flat chondrite-normalized PGE patterns, slightly above 0.1 times chondritic values. Mineralogical and chemical data indicate that the chromite ores of the Potosi Mine were modified by the intrusions of olivine–norite and gabbro dikes. The interaction between pre-existing sulfide-poor chromite ores and the intruding volatile-rich silicate melts produced strong brecciation, partial dissolution, and recrystallization (coarsening) of chromite. The sulfide assemblage formed by fractionation of the immiscible sulfide melt segregated from the volatile-rich silicate melt that generated the pegmatitic olivine–norite. The segregation of the sulfide melt can be interpreted as the consequence of chemical interaction between intruding melts and the host chromite. The variable extent of this interaction produced chromite ores with variable sulfide ratios. The magmatic nature of the sulfide mineralization is supported by sulfur isotope data, which range from –0.4 to +0.9‰. Sulfide melt collected incompatible PGE (Rh, Pt, Pd) to produce the typical flat chondrite-normalized pattern of sulfide-rich chromite ores.

The Palaeozoic rocks outcropping around Valls are divided into two stratigraphic units. The boundary between both is an unconformity. The lower unit is composed by nearshore platform sediments and a Lower Cambrian age is indicated according to ichnotaxa content. The upper unit consists of pink nodular limestones and dark limestones, and it is followed by siliciclastic Culm Facies rocks. These limestones contain conodonts of the uppermost Tournaisian at its base (anchoralis-latus Zone) and lower Bashkirian (Namurian B) in the upper part. This condensed carbonate sequence was coeval with the thick siliciclastic Culm sedimentation in the surrounding areas. Consejo Interinstitucional de Ciencia y Tecnología; AMB94-0953-CO2-01 Consejo Interinstitucional de Ciencia y Tecnología; DGE-PB95-1047 Consejo Interinstitucional de Ciencia y Tecnología; PB98-1558

"The Pb-Zn-Cu deposit of Ulldemolins occurs within the Carboniferous sedimentary series of the southernmostCatalonian Coastal Ranges. It consists of sulphide-bearing calc-silicate assemblages, with epidote, Ca-amphiboles and Ca-garnet, which develop selectively along a dolomicrite bed near the contact with a granite porphyry. Two mineralisation styles can be differentiated: a) banded and b) irregular. Fluid inclusions and stable isotope compositions of sulphur in sulphides (sphalerite, galena and chalcopyrite) and carbon and oxygen in carbonates (calcite and dolomite) were studied in order to constrain the genesis and the source of mineralizing fluids. Fluid inclusions in sphalerite and calcite are aqueous, liquid+vapour and have a salinity between 1.2 and 7.2 wt% NaCl eq. and homogenization temperatures in the range of 273º to 368ºC. The 34S(V-CDT) values in the banded mineralisation are mostly between -1.5 and +2.1‰, and those from the irregular mineralisation are between -1.1 and +20.5‰. These 34S values of the banded mineralisation are in agreement with a magmatic origin of sulphur. In addition, the 18O(SMOW) values of hydrothermal calcite, from +6.9 to +12.5‰, are consistent with a magmatic origin of the fluids that formed the banded ore deposit. Later, a new input of fluids interacted with the previously formed mineral assemblages and modified part of the deposit, leading locally to an irregular skarn mineralisation."

The Atrevida vein is located at the south-western edge of the Catalonian Coastal Ranges, Spain. This vein extends for more than 3 km and is hosted by Silurian and Carboniferous metasediments, late Hercynian granites and continental conglomerates of Lower Triassic age. The Silurian metasediments contain massive sulphide layers with disseminations of platinum-group element (PGE)-bearing, Fe-Ni arsenides. Vein filling largely consists of banded and brecciated baryte rimmed by a complex polymetallic assemblage of Co-Ni-As-Bi-Ag(-U) ores. The Ni arsenide and sulpharsenide assemblage occurs only where the vein cuts the sulphide-bearing Silurian metasediments, and consists of nickeline, maucherite, rammelsbergite, gersdorffite and Ni-skutterudite. These Ni arsenides and sulpharsenides display rosettes, spherules, colloform and botryoidal textures, as well as subhedral crystals. The chemical compositions of these arsenide-sulpharsenide minerals exhibit limited cation substitution but substantial anion substitution of As by S and Sb, exceeding the expected theoretical values at low temperatures. This suggests that most of them formed under disequilibrium conditions. Ni arsenides and sulpharsenides also contain trace PGE. Palladium (up to 157 ppm) is the most abundant PGE, and occurs in solid-solution in all the phases studied, but shows the highest values in rammelsbergite and Niskutterudite. Pt only occurs in massive nickeline (54-1338 ppm Pt) and in zoned gersdorffite (29-360 ppm Pt) formed at the end of the depositional sequence of arsenides. The Ni arsenide and sulpharsenide ores at the Atrevida mine formed by reduction of PGE-bearing, oxidizing fluids at temperatures close to, or slightly above 100°C. These oxidizing fluids most probably collected their PGE budget from the nearby mineralized black shales. During the crystallization of the veined, Ni arsenide and sulpharsenide ores, Pd partly concentrated in the early nickeline and maucherite, but mainly fractionated to the late solutions from which rammelsbergite and Ni-skutterudite precipitated. Pt concentrated only in the latest nickeline and gersdorffite.

6 pages, 2 figures., The Mayarí — Baracoa Ophiolitic Belt (MBOB, eastern Cuba) is composed of two large, chromite-rich massifs: Mayarí —Cristaland Moa-Baracoa. The chromitites and hosting dunites were firstly affected by a regional serpentinization event, a subsequent episode of hydrothennal alteration (chloritization mainly) and, finally, these already altered bodies were crosscut by thin calcite-dominated veins. Analysed serpentines from serpentinized chromitites and dunites present very similar isotopic compositions (δ18O=+4.7 to +6.3 and δD= −67 to −60 , suggesting that the serpentinization process took place at moderate temperatures, in an oceanic environment. Serpentine formation by interaction with ocean water is also supported by the isotopic composition of chlorite and calcite. These results suggest that the serpentinization, chloritization and fracture filling processes of the Mayarí — Baracoa Ophiolite Belt took place in a subocean floor scenario and, thus, that the Mayarí — Baracoa serpentines represent a good example of serpentine formed during interaction with seawater. The oceanic origin of the serpentines from serpentinized chromitites and dunites from the MBOB indicate that the serpentinization of the mantle sequence occurred pre-thrusting (pre-emplacement in age)., This research was partially supported by a posdoctoral grant of Spanish Ministerio de Educaci6n y Cultura to EA. These results are contributions to the Spanish DGES project, BTE2001-3308, an AECI grant (Programa de Cooperaci6n Cientifica con Iberoam&ica 2000). SUERC is funded by NERC and a consortium of Scottish Universities. We thank R.A.J. Swennen and an anonymous referee for their constructive comments that helped to improve the manuscript.

The Mayarí-Baracoa ophiolitic belt in eastern Cuba hosts abundant chromite deposits of historical economic importance. Among these deposits, the chemistry of chromite ore is very variable, ranging from high Al (Cr#=0.43–0.55) to high Cr (Cr#=0.60–0.83) compositions. Platinum-group element (PGE) contents are also variable (from 33 ppb to 1.88 ppm) and correlate positively with the Cr# of the ore. Bulk PGE abundances correlate negatively with the Pd/Ir ratio showing that chromite concentrates mainly Os, Ir and Ru which gives rise to the characteristic negatively sloped, chrondrite-normalized PGE patterns in many chromitites. This is consistent with the mineralogy of PGEs, which is dominated by members of the laurite–erlichmanite solid solution series (RuS2–OsS2), with minor amounts of irarsite (IrAsS), Os–Ir alloys, Ru–Os–Ir–Fe–Ni alloys, Ni–Rh–As, and sulfides of Ir, Os, Rh, Cu, Ni, and/or Pd. Measured 187Os/188Os ratios (from 0.1304 to 0.1230) are among the lower values reported for podiform chromitites. The 187Os/188Os ratios decrease with increasing whole-rock PGE contents and Cr# of chromite. Furthermore, γOs values of all but one of the chromitite samples are negative indicating a subchondiritc mantle source. γOs decrease with increasing bulk Os content and decreasing 187Re/188Os ratios. These mineralogical and geochemical features are interpreted in terms of chromite crystallization from melts varying in composition from back-arc basalts (Al-rich chromite) to boninites (Cr-rich chromite) in a suprasubduction zone setting. Chromite crystallization occurs as a consequence of magma mixing and assimilation of preexisting gabbro sills at the mantle–crust transition zone. Cr#, PGE abundances, and bulk Os isotopic composition of chromitites are determined by the combined effects of mantle source heterogeneity, the degree of partial melting, the extent of melt-rock interactions, and the local sulfur fugacity. Small-scale (μm to cm) chemical and isotopic heterogeneities in the platinum-group minerals are controlled by the mechanism(s) of chromite crystallization in a heterogeneous environment created by the turbulent regime generated by successive inputs of different batches of melt.

The Lower Llandoverian metasedimentary series of the Prades Mountains, in southwestern Catalonia, Spain, consists of interbedded massive feldspar beds, composed of almost pure anorthite, with chert, phosphate beds, sulfide-rich black shale, massive sulfides and minor calc-silicate beds. The sulfides mainly consist of pyrrhotite with minor chalcopyrite. The metasedimentary rocks are anomalously V- and Cr-rich and contain disseminated minerals bearing precious metals, e.g. , sperrylite and palladian lollingite. On the basis of the geological setting of ore formation and the textural relationships among the minerals, a sedex model is proposed for the primary origin of these deposits and occurrences. However, textural patterns and mineral compositions were modified during several episodes. Firstly, Hercynian deformation and associated regional low-grade metamorphism produced cleavage and small-scale veining in the primary associations. Later, contact metamorphism related to Late Hercynian intrusions annealed the mineral associations. A sulfidation stage of mineralization caused replacement of Pd-bearing lollingite by arsenopyrite. During this process, the arsenopyrite structure was unable to accommodate such high Pd contents and, consequently, Pd was precipitated as PdAs 2 and scarce small grains of native Pd, disseminated along the lollingite – arsenopyrite contact, in association with argentian gold, and tellurides and selenides of Au, Ag, Bi and Pb.