Vectors to ore in replacive VMS deposits of the northern Iberian Pyrite Belt: the case study of Aguas Teñidas deposit

Volcanogenic Massive Sulphide (VMS) deposits represent a major source of base, precious and other metals of economic and industrial importance. The Iberian Pyrite Belt (IPB) is an outstanding VMS district located in the SW Iberian Peninsula. It is arguably the largest known accumulation of sulphides on the Earth's crust, and represents the main mining area in Spain and one of the main zones of base metal production in Europe. As in other mining areas, progressive exhaustion of the most shallow and easily accessible deposits is leading to increasingly complex exploration. In this context, the combined study of the mineral systems and the development of new exploration strategies and technologies based on geophysical methods and vectors to ore play a vital role

300 Million years of episodic hydrothermal activity: stable isotope evidence from hydrothermal rocks of the Eastern Iberian Central System

The Eastern Iberian Central System has abundant ore showings hosted by a wide variety of hydrothermal rocks; they include Sn-W, Fe and Zn-(W) calcic and magnesian skarns, shear zone- and episyenitehosted Cu-Zn-Sn-W orebodies, Cu-W-Sn greisens and W-(Sn), base metal and fluorite-barite veins. Systematic dating and fluid inclusion studies show that they can be grouped into several hydrothermal episodes related with the waning Variscan orogeny. The first event was at about 295 Ma followed by younger pulses associated with Early Alpine rifting and extension and dated near 277, 150 and 100 to 20 Ma, respectively (events n IV). The δ18O-δD and δ34S studies of hydrothermal rocks have elucidated the hydrological evolution of these systems. The event 1 fluids are of mixed origin. They are metamorphic fluids (H20-COrCH4-NaCl; δ18SO = 4.7 to 9.3‰; δD ab.-34‰) related to W-(Sn) veins and modified meteoric waters in the deep magnesian Sn-W skarns (H20-NaCl, 4.5 6.4 wt% NaCl eq.; δI8O = 7.3 7.8‰; δD = -77 to -74‰) and epizonal shallow calcic Zn-(W) and Fe skarns (H20-NaCl, < 8 wt% NaCl eq.; δ18O = -0.4 to 3.4‰; δD = -75 to -58‰). They were probably formed by local hydrothermal cells that were spatially and temporally related to the youngest. Variscan granites, the metals precipitating by fluid unmixing and fluid-rock reactions. The minor influence of magmatic fluids confirms that the intrusion of these granites was essentially water-undersaturated, as most of the hydrothermal fluids were external to the igneous rocks. The fluids involved in the younger hydrothermal systems (events n nI) are very similar. The waters involved in the formation of episyenites, chlorite-rich greisens, retrograde skarns and phyllic and chlorite-rich alterations in the shear zones show no major chemical or isotopic differences. Interaction of the hydrothermal fluids with the host rocks was the main mechanism of ore formation. The composition (H20-NaCl fluids with original salinities below 6.2 wt% NaCl eq.) and the δ18O (-4.6 to 6.3‰) and δD (-51 to -40‰) values are consistent with a meteoric origin, with a δ18O-shift caused by the interaction with the, mostly igneous, host rocks. These fluids circulated within regional-scale convective cells and were then channelled along major crustal discontinuities. In these shear zones the more easily altered minerals such as feldspars, actinolite and chlorite had their δ18O signatures overprinted by low temperature younger events while the quartz inherited the original signature. In the shallower portions of the hydrothermal systems, basement-cover fluorite-barite-base metal veins formed by mixing of these deep fluids with downwards percolating brines. These brines are also interpreted as of meteoric origin (δ18O< ≈ -4‰; δD = -65 to -36‰) that leached the solutes (salinity >14 wt% NaCl eq.) from evaporites hosted in the post -Variscan sequence. The δD values are very similar to most of those recorded by Kelly and Rye in Panasqueira and confirm that the Upper Paleozoic meteoric waters in central Iberia had very negative δD values (≤-52‰) whereas those of Early Mesozoic age ranged between -65 and -36‰

Vectors to ore in replacive volcanogenic massive sulfide (VMS) deposits of the northern Iberian Pyrite Belt: Mineral zoning, whole rock geochemistry, and application of portable X-ray fluorescence

In this work we have performed a detailed study of vectors to ore to a representative volcanic-rock-hosted replacive volcanogenic massive sulfide (VMS) deposit located in the northern Iberian Pyrite Belt (Spain), the Aguas Teñidas deposit. The investigated vectors include the following: (1) mineralogical zoning, (2) host sequence characterization and mineralized unit identification based on whole rock geochemistry discrimination diagrams, (3) study of the characteristics and behaviour of whole rock geochemical anomalies around the ore (e.g. alteration-related compositional changes, characteristics and extent of geochemical halos of indicative elements such as Cu, Zn, Pb, Sb, Tl, and Ba around the deposit), and (4) application of portable X-ray fluorescence (p-XRF) analysis to the detection of the previous vectors

Episodic palaeo-hydrothermal activity in the Sierra de Guadarrama (Spanish Central System): new K-Ar ages and tectonic correlation with the Iberian chain

Episodic hydrothermal alterations in the Sierra de Guadarrama took place between ca. 300 Ma and 10 Ma. New K-Ar ages for hydrothermal minerals have been obtained that along with previous data allow to better constrain the late- to post-Variscan history of tectono-hydrothermal activity. This activity can further be correlated with Alpine tectonic events in central Iberia recorded in Permian to Cainozoic sedimentary basins. Dating of hydrothermal events in the basement is thus a useful tool to better constrain the chronology of tectono-sedimentary events in the cove

The Aguablanca Cu-Ni(PGE) intraplutonic ore deposit (Extremadura, Spain). Isotope (Sr, Nd, S) consfraints on the source and evolution of magmas and sulfides

The Aguablanca Cu-Ni(PGE) ore is a case of an intraplutonic ore deposito It is hosted by mafic and ultramafic cumulates of the Aguablanca Stock, which is part of the larger calcalkaline Santa Olalla Plutonic Complex of 359±18Ma age (Rb-Sr whole rock determination). Primary mineralization consists of pyrrothite, pentlandite and chalcopyrite and resulted from the crystallization of an inmiscible sulfiderich liquid. Several stages of hydrothermal alteration are superimposed. Isotope work on the host igneous rocks (Sr, Nd) and the ore (S), suggests that contamination with a crustalsource took place at some depth before final emplacement of the plutons (ε Nd360= -5.8 to -7.2; Sr(360) = 0.7082 to 0.7103; (δ14S(sulfides) near + 7.4‰). Assimilation - fractional crystallization (AFC) processes are invoked to explain de chemical variability of magmas

Mechanisms for Pd-Au enrichment in porphyry-epithermal ores of the Elatsite deposit, Bulgaria

This research was supported by Spanish projects: RTI2018-099157-A-I00, CGL2015-65824-P and CGL2016-81085-R granted by the "Ministerio de Ciencia, Innovacion y Universidades" and "Ministerio de Economia y Competitividad" (MINECO), respectively. Additional funding for chemical analysis was provided by the Ramon y Cajal Fellowship RYC-2015-17596 to JMGJ. Maria del Mar Abad, Isabel Sancez Almazo and Rocio Marquez Crespo (CIC, University of Granada) are acknowledged for her assistance with HRTEM, and HR-SEM and FESEM analysis respectively. We are also indebted to Miguel Angel Hidalgo Laguna from CIC of University of Granada and Xavier Llovet from the Centres Cientifics i Tecnologics of the Universitat of Barcelona (CCiTUB) for their careful help with EMPA. This paper was written during the lockdown provoked by the pandemic COVID-19 and the authors would like to dedicate this manuscript to the memory of those who lost their lives.Porphyry Cu can contain significant concentrations of platinum-group elements (PGE: Os, Ir, Ru, Rh, Pt, Pd). In this study, we provide a comprehensive in situ analysis of noble metals (PGE, Au, Ag) for (Cusingle bondFe)-rich sulfides from the Elatsite, one of the world's PGE-richest porphyry Cu deposits. These data, acquired using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), indicate that Pd was concentrated in all the (Cusingle bondFe)-rich sulfides at ppm-levels, with higher values in pyrite (~6 ppm) formed at the latest epithermal stage (i.e., quartz–galena–sphalerite assemblage) than in bornite and chalcopyrite (<5 ppm) from the hypogene quartz–magnetite–bornite–chalcopyrite ores. Likewise, Au is significantly more concentrated in pyrite (~5 ppm) than in the (Cusingle bondFe)-rich sulfides (≤0.08 ppm). In contrast, Ag reaches hundreds of ppm in pyrite and bornite (~240 ppm) but is in much lesser amounts in chalcopyrite (<25 ppm). The inspection of the time-resolved spectra collected during LA-IPC-MS analyses indicates that noble metals are present in the sulfides in two forms: (1) structurally bound (i.e., solid solution) in the lattice of sulfides and, (2) as nano- to micron-sized inclusions (Pdsingle bondTe and Au). These observations are further confirmed by careful investigations of the PGE-rich (Cusingle bondFe)-rich sulfides by combining high-spatial resolution of field emission scanning electron microscope (FESEM) and focused ion beam and high-resolution transmission electron microscopy (FIB/HRTEM). A typical Pd-bearing mineral includes the composition PdTe2 close to the ideal merenskyite but with a distinct crystallographic structure, whereas Au is mainly found as native element. Our detailed mineralogical study coupled with previous knowledge on noble-metal inclusions in the studied ores reveals that noble metal enrichment in the Elatsite porphyry ores was mainly precipitated from droplets of Au-Pd-Ag telluride melt (s) entrained in the high-temperature hydrothermal fluid. These telluride melts could separate at the time of fluid unmixing from the silicate magma or already be present in the latter either derived from deep-seated crustal or mantle sources. Significant enrichment in Pd and Au (the latter correlated with As) in low-temperature pyrite is interpreted as remobilization of these noble metals from pre-existing hypogene ores during the epithermal overprinting.Spanish projects - "Ministerio de Ciencia, Innovacion y Universidades" RTI2018-099157-A-I00 CGL2015-65824-P CGL2016-81085-RSpanish projects - "Ministerio de Economia y Competitividad" (MINECO) RTI2018-099157-A-I00 CGL2015-65824-P CGL2016-81085-RSpanish Government RYC-2015-1759

Palaeostress and geotectonic interpretation of the Alpine Cycle onset in the Sierra del Guadarrama (eastern Iberian Central System), based on evidence from episyenites

Several episodes of hydrothermal activity related to periods of fracturing and/or reactivation of previous structures took place from 300 to - at least - 100 Ma, in the Sierra del Guadarrama, which is part of the crystalline axis of the Iberian Hercynian Fold Belt (Central-Iberian Zone). One of these episodes led to the formation of episyenites, which are de-quartzified and alkalinized granites. Episyenite formation took place on a regional scale and in a short period (approx. at 277 Ma). The episyenites were formed by the action of fluids at temperatures between 350°C and 650°C, at depths of about 6.5 km, and in microfractured dilatancy zones developed under a regional extensional regime. These zones are crosscut by normal faults, developed during the progressive deformation process accompanying the formation of the episyenites. The calculated regional palaeostress tensor has ~r I close to vertical and σ3 between NI0-20E and an average value of the stress ratio (Ф) of 0.19 [Ф = (σ2 - σ3)/(σ1 - σ3)]. Because σ1 is close to vertical the stress tensor is compatible with an extensional deformation field. The analysis also shows that most of the faults that slip under this stress field have an average coefficient of friction of 0.8. This extensional regime was probably accompanied by a regional thermal anomaly, as suggested by the high temperature of the fluids involved, which are amagmatic. This thermo-tectonic episode is interpreted as representative of the generalized extensional regime corresponding to the onset of the Alpine Cycle. The episode was preceded by a wrench-faulting event, equivalent to the Late Variscan event of Arthaud and Matte (1977), for which an age of - at least - 300-290 Ma is indicated by recent radiometric data. In its turn, this event was preceded by the regional extensional gravitative collapse of the Hercynian orogen. A correlation between evidence from the cover (stratigraphy and volcanism) and evidence from the basement (hydrothermal alterations, dyke injection episodes and granitic magmatism) is attempted on the basis of new available radiometric data