Evolution of ore-forming fluids associated with late Hercynian antimony deposits in Central/Western Spain: case study of Mari Rosa and El Juncalón

Located in Central-Western Spain, the late Hercynian Mari Rosa and El Juncalon vein-type antimony deposits are hosted by Late Precambrian metasedimentary rocks and are spatially related to Late Carboniferous/Early Permian granitoids. At Mari Rosa, the following hydrothermal stages are recognized: 1) arsenopyrite-(pyrite), 2) stibnite-gold and 3) pyrite-(pyrrhotite-galena-sphalerite-chalcopyrite-tetrahedrite-boulangerite-berthierite-stibniteullmannite- cobaltite). Only the second stage is of economic importance, containing massive stibnite. El Juncalon is characterized by a simple mineral paragenesis composed of stibnite with very minor pyrite. Gold is associated with stibnite, which contains up to 30 ppm Au at Mari Rosa and up to 0.4 ppm Au at El Juncalon. Fluids associated with ore deposition lie in the H2O-NaCl-CO2-CH4-N2 system, but CO2 is absent in the El Juncalon mineralized rocks. The fluids cooled progressively, from initial circulation temperatures close to 400°C in the early stages to temperatures of approximately 150°C in the late episodes. The fluid composition evolution is also characterized by a progressive increase in the overall water content of the fluids and by an increase in the relative proportions of N2 with respect to CH4 and CO2 in the volatile fraction. At Mari Rosa, massive stibnite deposition resulted from a boiling process at 300°C and 0.9-1 kbar. Unmixing of the fluid was induced by sudden pressure drops associated with dilational jogs during low-angle fault movements. Cooling of the fluid is recognized as the driving mechanism for stibnite deposition at 250°-270°C and 50-300 bars at El Juncalon

El origen del azufre en mineralizaciones filonianas en el centro de la Península Ibérica

Sufphur isotope data from severa/ base metals-Ba-(F)-(Ag) and Ag-base metals vein-type deposits in the Central Jberian Zone of the Hesperian Massif suggest a magmatic and/or metasedimentary origin of this ore-forming component. Deposits exclusive/y hosted in metasediments (p.e. Alcudia Va/ley, type IV) display a magmatic signature. Even those /odes and stratabound deposits hosted by Permian-Triassic terrigenous and andesites (Las Torrecillas-Linares y Atienza) are formed by "igneous" sulphur

a model based on fluid inclusion and geologic evidence

Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

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

La actividad metalogénica durante el Tardihercínico en el centro de España: una visión desde cinco localidades tipo

The most outstanding metallogenic period in central Spain took place during the so-cal/ed lateHercynian episode. This episode was characterized by widespread extensional conditions resulting from the collapse of an overthickened and overheated Hercynian orogen. A combination of magmatic activity and favorable structures induced hydrothermal activity leading to Sn-W, Pb-Zn, Ag-base metals, base metals-Ba-(F) and Sb-(Au) deposition. Five ore deposits/districts: El Trasquilón (Sn), Linares-La CarolinaTorrecillas (Pb-Zn-Ba-[Ag]), Sierra de Guadarrama (Ba-(F)-[base metals]), El Juncalón (Sb-[Au]), and Hiendelaencina (Ag-base metals) allow characterization of the main geologic features of this metallogenic episode.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Cu, Mn, and Ag mineralization in the Quebrada Marquesa Quadrangle, Chile: the Talcuna and Arqueros districts

The Quebrada Marquesa Quadrangle in Chile exhibits a series of mineralizations comprising manto-type manganese and copper deposits of Lower Creta-ceous age, and copper and silver veins of Tertiary age. The deposits are hosted by volcanic and volcaniclastic units of the Arqueros (Hauterivian-Barremian) and Quebrada Marquesa (Barremian-Albian) Formations. Three episodes of manganese mineralization (Mn1-3) are recognized within the study area. Hydrothermal activity leading to episodes 1 and 3 was of minor importance, while the second one (Mn2) gave rise to major manto-type deposits of both manganese and copper in the Talcuna mining district. Extensional faulting during Tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments (Arqueros Formation). This episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the Arqueros (Ag) and Talcuna (Cu) districts. The latter veins cross-cut the previous manto-type copper deposits. Ore mineralogy is similar in both styles of mineralization (manto- and vein-type) and consists mainly of chalcopyrite and bor-nite, with variable amounts of galena, tetrahedrite (vein-related), chalcocite, sphalerite, pyrite, hematite, digenite and covellite. Alteration processes at Talcuna can be divided into two categories, those related to the Lower Cretaceous manto-type episode (LK alteration: chlorite-epidote-calcite-albite, prehnite, zeolite), and those associated with the locally mineralized normal faults of Tertiary age (Tt alteration: chlorite-calcite, sericite). The Arqueros silver veins display an ore mineralogy consisting of arquerite, argentite, native silver, polybasite, cerargyrite and pyrargyrite-proustite; associated altera-tion includes strong chloritization of the country rock. The manto-type deposits formed from fluids of salinity between 11 and 19 wt.% NaCl equivalent and temperatures between 120 and 205 °C. Mineralizing fluids during the vein-type stage circulated at lower temperatures, between 70 and 170 °C, with salinity values in a wide range from 3 to 27 wt.% NaCl equivalent. This distribution of salinities is interpreted as the result of the complex interplay of two diferent processes: boiling and fluid mixing; the former is considered to control the major mineralogical, textural and fluid inclusion features of the vein-type deposits. We suggest that the Lower Cretaceous mineralization (manto-type stage) developed in response to widespread hydrothermal activity (geothermal field-type) involving basinal brines