Papers by Fernando Tornos
Magnetite-apatite deposits are important sources of iron and other metals. A prominent exam- ple ... more Magnetite-apatite deposits are important sources of iron and other metals. A prominent exam- ple are the magnetite lavas at the El Laco volcano, Northern Chile. Their formation processes remain debated. Here, we test the genetic hypothesis that an Fe-rich melt separated from silicate magma and ascended along collapse-related fractures. We complement recent analy- ses with thermodynamic modelling to corroborate Fe-Si liquid immiscibility evident in melt inclusions at El Laco and present viscometry of Fe- and Si-rich melts to assess the time and length scales of immiscible liquid separation. Using a rock deformation model, we demonstrate that volcano collapse can form failure zones extending towards the edifice flanks along which the ore liquid ascends towards extrusion driven by vapour exsolution despite its high density. Our results support the proposed magmatic genesis for the El Laco deposits. Geochemical and textural similarities indicate magnetite-apatite deposits elsewhere form...
Remote Sensing
Soil instability is a major hazard facing the mining industry in its role of supplying the indisp... more Soil instability is a major hazard facing the mining industry in its role of supplying the indispensable mineral resources that our societal challenges require. Aiming to demonstrate the monitoring potential of radar satellites in the mining sector, we analyze the deformation field in the Riotinto mine, Spain. We propose a new method for combining ascending and descending results into a common dataset that provides better resolution. We project the LOS measurements resulting from both geometries to a common reference system without applying any type of geometric restriction. As a projection system, we use the vertical direction in flat areas and the slope in steep topographies. We then identify and remove outliers and artifacts from the joint dataset to finally obtain a deformation map that combines the two acquisition perspectives. The results in the Atalaya pit are consistent with GNSS measurements. The movements observed in the rock dumps were unknown before this study. We demons...
Dolomitization played a very important role in producing porosity within the Late Aptian shallow ... more Dolomitization played a very important role in producing porosity within the Late Aptian shallow marine carbonates hosting the El Soplao Cave and La Forida mine deposit. A detailed petrographic study of samples from a stratigraphic section across these limestones and dolostones has revealed three diagenetic stages from shallow to late burial and finally uplift. During these stages, at least four phases of calcite cementation (C1 to C4) and five phases of dolomite formation and recrystallization (D1 to D5) took place. The timing of dolomitization is still uncertain, but the first phase (D1) occurred shortly after limestone deposition (shallow burial diagenesis) as cement filling primary and early secondary (mouldic) porosity. Calcite cements C1 and C2 occurred also in this diagenetic stage. Later, pervasive replacement dolomitization (D2, idiotopic) and dolomite recrystallization (D3, xenotopic) took place in the burial realm. Saddle dolomite (D4) occurred in continuity with xenotopi...
Geoconvention 2020. 11-13 May 2020, celebrated in Calgary (Canada)Iron oxide-copper-gold (IOCG) d... more Geoconvention 2020. 11-13 May 2020, celebrated in Calgary (Canada)Iron oxide-copper-gold (IOCG) deposits are a controversial group of ore deposits that share common characteristics, such as the abundance of iron oxides, and the associated sodic or sodic-calcic alteration. The IOCG (sensu stricto) deposits contain Cu and Au minerals and iron oxides. The mineralogy consists of low-Ti magnetite or/and hematite, actinolite and/or pyroxene, and chalcopyrite, with subordinate bornite, pyrite, and pyrrhotite, and they are known from the Archean (Carajàs, Brazil) to the Mesozoic (Peru and Chilean iron belts). The other type of deposit in this group, magnetite-apatite (MtAp) or Kiruna-type deposits, contain low-Ti magnetite with apatite and actinolite and/or pyroxene. They are principally associated with calc-alkaline to alkaline volcanic or plutonic rocks, and are present from theProterozoic (e.g. Kiruna, Sweden) to the Pliocene (El Laco, Chile; Abovian, Armenia). Despite ahistory of variable genetic interpretationsof MtAp and IOCG deposits, their shared characteristics and temporal and spatial relationshipshave led several authors to propose that they are end-members on a continuous spectrum, with both typesof deposits being formed from the same melt/fluid source, and recording mineralization from evolving fluids. To clarify the possible relationship between these two types of deposits, and to understand the behaviour of the actinolite in these deposits, several analyses have been made in deposits from Chile and Perú that comprise a MtAp mineralization event overprinted by an IOCG event: Marcona MtAp deposit, and Mina Justa and Monterrosas IOCG deposits in Peru, and Montecristo IOCG deposit, and Los Colorados and Pleito-Melón MtAp deposits in Chile, among others. The study principally focuses on the characterization of the actinolite from MtAp and IOCG deposits, using the EPMA for chemical analyses and x-ray maps, the LA-ICPMS for trace elements analyses, and 40Ar-39Ar geochronology for age determinations in actinolite associated with the alteration halo in the deposits. The characterizationof the actinolite in these types of deposits is a novel study that will lead to a better understanding of the deposit formation and the possible relationshipbetween both deposits, along with the magnetite and apatite. Other analyses in this research include Re-Os dating in molybdenite, d34S isotopes in sulphides, and U-Pb dating in zircons from the host rock in the Montecristo deposit for a clearer knowledge about thetiming of the mineralization events andthe formation conditions
Journal of Iberian Geology, 2021
The Monchi Mine (Ossa Morena Zone, SW Iberia) is a rather unique ore deposit characterized by unu... more The Monchi Mine (Ossa Morena Zone, SW Iberia) is a rather unique ore deposit characterized by unusually high Fe grades and an ore assemblage that includes dominant magnetite but with abundant B (vonsenite), U (uraninite), Co (cobaltite), As (löllingite, safflorite) and rare earth elements (allanite). The mineralization occurs at the western edge of a Variscan concentrically zoned gabbro to granodiorite pluton, the Burguillos del Cerro Plutonic Complex. Moreover the western side of the complex is within a large N–S trending dextral strike-slip shear zone in which Ediacaran to early Cambrian metapelitic and calc-silicate hornfels and marble constitute a vertical screen between an outer syn-tectonic sheet of foliated biotite monzogranite and an inner post-tectonic amphibole-biotite diorite unit. The magnetite-vonsenite mineralization is adjacent to the screen and forms large lens-shaped bodies with sharp contacts with the intrusive rocks and is directly related with a granoblastic U-REE-bearing Fe-pyroxene-rich hornfels which is locally brecciated and cemented by pegmatite dominated by albite, K feldspar, quartz, clinoamphibole/biotite and axinite. Within the enclave there is a large post-tectonic exoskarn, including calcic and magnesian types which predates the diorite that mainly replaced the calc-silicate hornfels and the marble. The calcic exoskarn is dominated by grandite and hedenbergite and was retrogressed to actinolite, epidote, calcite and magnetite with variable amounts of pyrite and chalcopyrite. U–Pb TIMS dating of allanite from the U-REE-rich hornfels yielded 337.13 ± 0.99 Ma, i.e., within the range of ages of the Burguillos Plutonic Complex (335–340 Ma). Sr–Nd isotope geochemistry shows that the mineralization (including skarn and massive ore) has isotope signatures (εNd338 between -0.8 and -4.1; 87Sr/86Sr338 = 0.7071–0.7112) mostly intermediate between those of the igneous (− 6.8 to − 2.3; 0.7047–0.7097, respectively) and the sedimentary (− 11.7 to − 8.3; 0.7090–0.7164, respectively) rocks. The massive high grade mineralization could be the result of a syn-magmatic interaction of an unknown protolith with deep sourced fluids that were focused along early thrusts and shear zones probably rooted at a magma chamber in the middle crust. Alternatively it could also be the product of crystallization of a boron-bearing iron melt. This melt would be somewhat similar to the magnetite-(apatite) deposits elsewhere but in which the fluxing agent is boron. Fluids exsolved from these rocks produced a high-temperature magmatic-hydrothermal system that formed the post-tectonic exoskarn. The ultimate origin of these immiscible Fe-B melts could hypothetically be the assimilation at depth of former shallow marine metasediments.
Ore Geology Reviews, 2021
Solid Earth Discussions, 2021
Abstract. Volcanogenic Massive Sulphide (VMS) deposits represent a major source of base, precious... more Abstract. Volcanogenic Massive Sulphide (VMS) deposits represent a major source of base, precious and other metals of economic and industrial importance. As in other mineral systems, progressive exhaustion of the shallowest and most easily accessible deposits is leading to increasingly complex exploration. In this context vectors to ore play a vital role. The Iberian Pyrite Belt (IPB) is an outstanding VMS district located in the SW Iberian Peninsula, which represents the main mining area in Spain and one of the main zones of base metal production in Europe. But the work on vectors to ore in the IPB is far from systematic or complete. In this work we have performed a detailed study of the main vectors to ore related to mineral zoning and whole rock geochemistry that are currently used in the exploration of VMS systems to a representative volcanic rock hosted replacive VMS deposit located in the northern IPB, the Aguas Tenidas deposit. Results have been compared to other deposits in ...
Geological Society of America Abstracts with Programs, 2021
Geological Society of America Abstracts with Programs, 2021
Goldschmidt Abstracts, 2020
Ore Geology Reviews, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Mineralium Deposita, 2015
El Domo is a Cu-Au-Zn-Ag volcanogenic massive sulfide deposit (VMS) within the Paleocene-Eocene s... more El Domo is a Cu-Au-Zn-Ag volcanogenic massive sulfide deposit (VMS) within the Paleocene-Eocene submarine arc rocks of the Macuchi Formation in central Ecuador. The mineralization includes massive and semi-massive sulfides located at the interface between a submarine rhyodacite dome complex and overlying mafic volcanic and volcaniclastic rocks, including chaotic and unsorted debris flow deposits. Whole rock geochemical analyses show that the felsic rocks belong to a calc-alkaline sequence, whereas the mafic assemblages have a tholeiitic affinity, reflecting a magmatic association typically found in many VMS districts. This geochemical change temporally coincides with the formation of the massive sulfides. New zircon Hf isotopic data collected from a hanging wall rhyodacite suggest that the presence of an over-thickened crust of oceanic plateau affinity may have influenced the composition of the magmatic rocks. The timing of massive sulfide formation is constrained by an 40 Ar/ 39 Ar age of 41.49±0.37 Ma (2σ) from the volcaniclastic sequence which hosts the massive sulfides and a U/Pb zircon age date of 42.13±0.54 Ma (2σ) from the footwall rhyodacite; both ages are interpreted to provide minimum and maximum ages for mineralization. The massive sulfides are zoned and contain variable proportions of pyrite, sphalerite, and chalcopyrite. Minor accumulations of galena, bornite, tennantite, stromeyerite, and proustite are also present; the latter two minerals are the major carriers of silver whereas gold typically occurs as minute-free grains or in solid solution with silver. Ore minerals are intergrown with variable proportions of chlorite, barite, quartz, anhydrite, and smectite. The footwall rhyodacite hosts an irregular stringer zone which is rich in pyrite and gypsum and is characterized by intense quartzsericite-pyrite alteration. The hanging wall volcaniclastic lithologies exhibit pervasive but vertically limited (8-10 m) silicification, chloritization, and argillization. Both felsic and mafic glass-rich rocks located near the contact between rhyodacites and mafic volcaniclastic rocks are replaced by
Mineral Resource Reviews, 2015
The 250 × 20-70 km Iberian Pyrite Belt (IPB) is a Variscan metallogenic province in SW Portugal a... more The 250 × 20-70 km Iberian Pyrite Belt (IPB) is a Variscan metallogenic province in SW Portugal and Spain hosting the largest concentration of massive sulphide deposits worldwide. The lowermost stratigraphic unit is the early Givetian to late Famennian-Strunian (base unknown) Phyllite-Quartzite Group (PQG), with shales, quartz-sandstones, quartzwacke siltstones, minor conglomerate and limestones at the top. The PQG is overlain by the Volcanic Sedimentary Complex (VSC), of late Famennian to mid-late Visean age, with a lower part of mafic volcanic rocks, rhyolites, dacites and dark shales, hosting VHMS deposits on top (many times capped by a jasper/chert layer), and an upper part, with dark, purple and other shales and volcanogenic/volcaniclastic rocks, carrying Mn oxide deposits. The VSC is covered by the thousands of meters thick Baixo Alentejo Flysch Group of late Visean to Moscovian age. The VSC
Mineral Resource Reviews, 2015
Mineral Resource Reviews, 2015
Mineralogical Magazine, 1991
Fluid inclusion data and geochemical evidence lead to a genesis of Ba-F (Pb-Zn) lodes of the Span... more Fluid inclusion data and geochemical evidence lead to a genesis of Ba-F (Pb-Zn) lodes of the Spanish Central System as related to fluid mixing of hot (>300 °C), low saline (<0.6 molal), Na-K deep fluids and cool (<100 °C), oxidized, more saline (>2.8 molal), Na-K-Ca-Mg brines of phraeatic origin. Ore formation took place at relative low depth and temperatures (from 270 to 120 °C) in a regime of increasing fO2, (Ca + Mg)/Na ratio and pH of the fluids towards the surface. Such evolution destabilizes the chloride metal complexes, allowing for the precipitation of Zn and Pb carried by the deep solution.Vertical fluorite-baryte zonation is explained in terms of mineral solubilities. Fluorite deposition in the deeper mineralized zone is related to a slight increase of mCa2+ of the fluid in the lower part of the fluid mixing zone; further increase of mCa2+ and mMg2+ towards the surface promotes fluorite dissolution. Increase of fO2 in the shallow part of the hydrothermal system...
Geogaceta, 2006
... Oficina de Proyectos de Salamanca. C/ Azafranal 48. 37001 Salamanca. (2) Dirección actual: IN... more ... Oficina de Proyectos de Salamanca. C/ Azafranal 48. 37001 Salamanca. (2) Dirección actual: INETI, Departamento de Geologia, Ap. 7586, 2720-866, Amadora, Portugal. d.mellado@igme. es; [email protected]; [email protected]; [email protected]. ABSTRACT: ...
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Papers by Fernando Tornos