207 research outputs found
ÂżEsfĂ©rulas de hierro y vĂtreas subducidas en el manto superior?
Spherules are documented in ophiolitic
mantle rocks such as peridotites
and associated chromitites. They
consist of: (1) native iron having
variable amounts of Ni with/without
inclusions of silicate glass or oxides
(wĂĽstite), (2) dendritic intergrowth of
oxides (magnetite, wĂĽstite and hematite)
with/without silicate glass and,
(3) silicate glass. Consensually, they
are interpreted as indigenous to chromitites
and related with high-temperature
processes operating in the
Earth’s upper mantle. However, their
similarity with terrestrial and extraterrestrial
spherules found in other
settings of the geological record is
remarkable. We raise the question on
such indigenous origin, relating them
to volcanic and cosmic material recycled
back to the mantle wedge where
chromitites form during subduction.Rocas del manto superior ofiolitico tales
como peridotitas y cromititas contienen esferas.
Estas consisten de: (1) hierro native con
cantidades variables de Ni con y sin inclusiones
de vidrio silicatdo y Ăłxidos (wĂĽstite),
(2) intercrecimientos dendrĂticos de Ăłxidos
(magnetita, wĂĽstita y hematites) con o sin
vidrio silicatado y, (2) vidrio silicatado.
UnĂsonamente, estas esferulas se interpretan
como indĂgenas a las cromititas y relacionadas
con procesos de alta temperatura que
tienen lugar en el manto superior terrestre.
Sin embargo, su parecido con aquellas esferas
de origen terrestre y extraterrestre descritas en
otros contextos geológicos es reseñable. En
este trabajo cuestionamos el origen autĂłctono
de las esferas en las rocas mantélicas,
interpretándolas como material de origen
volcánico y cósmico que ha sido reciclado
atraves de la cuña de manto superior donde
ser forman las cromititas durante los procesos
de subducciĂłn.Junta de Andaluci
Isotopic constraints on the age and source of ore-forming fluids of the Bou Azzer arsenide ores (Morocco)
The authors greatly acknowledge the geological survey of CTT-Bou Azzer mine for facilitating our geological field campaigns and specially to Clemente Recio (University of Salamanca) for his invaluable help to IS during the development of the analytical procedure to mea-sure S isotope compositions from the minor amounts of S extracted from arsenides and sulfarsenides. Authors would like to acknowledge the use of Servicio General de Apoyo a la Investigacion-SAI, Universidad de Zaragoza. This research was financially supported by the Spanish project RTI2018-099157-A-I00 granted by the "Ministerio de Ciencia, Innovacion y Universidades". The Swedish Research Council (infra-structure grant: Dnr. 2017-00671) is thanked for financial support to the Vegacenter national laboratory. This is Vegacenter publication number 124The Bou Azzer district in Morocco has a long mining history since the beginning of the XXst century during which
it has become the only world producer of Co from primary, hydrothermal Co arsenide ores. Orebodies are
structurally controlled, and mainly distributed along fault contacts between Cryogenian ophiolite-related serpentinite
bodies and intrusive quartz diorite or, locally, ophiolitic gabbros or Ediacaran volcanic rocks. Ore
formation took place through a multi-stage mineralizing process that included an early stage composed by gold,
quartz, chlorite, muscovite and calcite, followed by the main arsenide and sulfarsenide stage (subdivided into
three substages, IIa: Ni-rich, Co ores, IIb: Co-Fe ores and IIc: Fe-Co ores), and ending with an epithermal stage
characterized by the precipitation of sulfides along with quartz and calcite. Field relations and most previous
geochronologic dating pointed to a post Pan-African age of ore formation, mainly coincident with the Hercynian
orogeny.
The isotopic study presented in this paper includes S, Pb, Rb/Sr and Sm/Nd data of a set of ore mineral samples
from three deposits (Aghbar, Tamdrost and AĂŻt Ahmane), as well as of regional samples representative of the
different lithologies occurring in the Bou Azzer area. The isotope data set was completed with S isotope analyses
of arsenide and sulfarsenide minerals from five ore deposits (Filon 7/5, Aghbar, Tamdrost, Ightem and AĂŻt-
Ahmane) and of some whole-rock regional samples. Results show that ores formed during multi-episodic hydrothermal
events connected with hercynian reactivation of Devonian-Carboniferous faults, supporting previous
geochronologic dating. The obtained Pb, Sr, Nd and S isotopic signatures of ore minerals and regional rocks
further show that ophiolite-related lithologies became isotopically modified by interaction with crustal material
and afterwards acted as the main source of ore-forming elements. Nevertheless, isotopic data do not fully concur
with such a simple scenario but are quite consistent with a rather complex interpretation based on multi-source
origin of some elements and isotopes scavenged from a number of isotopically different lithologies both from the
inferred basement and the volcanic and sedimentary cover.Spanish Government RTI2018-099157-A-I00Swedish Research Council
European Commission Dnr. 2017-0067
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
Reflectancia multiespectral (visible e inferarrojo cercano) y composiciĂłn de las cromitas. Datos preliminares
Se aborda por primera vez la relación entre el espectro VNIR de reflectancia especular y los parámetros composicionales del grupo de las espinelas, particularmente cromit
The role of arsenide melts as collectros of platinum-group elements in Ni-Cu magmatic sulfide deposits
The Unconventional Peridotite-Related Mg-Fe-B Skarn of the El Robledal, SE Spain
The El Robledal deposit is a Mg-Fe-B skarn hosted in a dismembered block from the
footwall contact of the Ronda orogenic peridotites in the westernmost part of the Betic Cordillera.
The skarn is subdivided into two different zones according to the dominant ore mineral assemblage:
(1) the ludwigite–magnetite zone, hosted in a completely mineralized body along with
metasomatic forsterite, and (2) the magnetite–szaibelyite zone hosted in dolomitic marbles. In the
ludwigite–magnetite zone, the massive mineralization comprises ludwigite (Mg2Fe3+(BO3)O2), Mgrich
magnetite, and magnetite, with minor amounts of kotoite (Mg3(BO3)2), szaibelyite (MgBO2(OH)),
accessory schoenfliesite (MgSn4+(OH)6), and pentlandite. The ratio of ludwigite–magnetite decreases
downwards in the stratigraphy of this zone. In contrast, the mineralization in the magnetite–
szaibelyite zone is mainly composed of irregular and folded magnetite pods and bands with pull-apart
fractures, locally associated with a brucite-, szaibelyite-, and serpentine-rich groundmass. The set of
inclusions identified within these ore minerals, using a combination of a focused ion beam (FIB) and
high-resolution transmission electron microscope (HRTEM), supports the proposed evolution of the
system and reactions of the mineral formation of the skarn. The analysis of the microstructures of the
ores by means of electron backscatter diffraction (EBSD) allowed for the determination that the ores
experienced ductile deformation followed by variable degrees of recrystallization and annealing. We
propose a new classification of the deposit as well as a plausible genetic model in a deposit where the
heat source and the ore-fluid source are decoupled.PRE2019-088262 “Ayudas para contratos predoctorales
para la formación de doctores”, defrayed by the “Ministerio de Ciencia, Innovación y Universidades”the MECRAS Project A-RNM-356-UGR20 “Proyectos de I+D+i en el marco del Programa
Operativo FEDER AndalucĂa 2014-2020” defrayed by the “Junta de AndalucĂa
Metal Mobility in Embryonic-to-Proto-Ni-Laterite Profiles from Non-Tropical Climates
We evaluated the mobility of a wide suite of economic metals (Ni, Co, REE, Sc, PGE)
in Ni-laterites with different maturities, developed in the unconventional humid/hyper-humid
Mediterranean climate. An embryonic Ni-laterite was identified at Los Reales in southern Spain,
where a saprolite profile of ~1.5mthick was formed at the expense of peridotites of the subcontinental
lithospheric mantle. In contrast, a more mature laterite was reported from Camán in south-central
Chile, where the thicker (~7 m) weathering profile contains well-developed lower and upper oxide
horizons. This comparative study reveals that both embryonic and mature laterites can form outside
the typical (sub)-tropical climate conditions expected for lateritic soils, while demonstrating a similar
chemical evolution in terms of major (MgO, Fe2O3, and Al2O3), minor (Ni, Mn, Co, Ti, Cr), and
trace (REE, Y, Sc, PGE, Au) element concentrations. We show that, even in the earliest stages of
laterization, the metal remobilization from primary minerals can already result in uneconomic
concentration values.MECRAS Project A-RNM-356-UGR20 “Proyectos
de I+D+i en el marco del Programa Operativo FEDER AndalucĂa 2014-2020” of the ConsejerĂa de
EconomĂa, Conocimiento, Empresa
Metallogenic fingerprint of a metasomatized lithospheric mantle feeding gold endowment in the western Mediterranean basin
We thank the Associate Editor W.U. Reimold, and the referees T. Jalowitzki and M.L. Fioren-tini for their constructive reviews of the submitted version of the manuscript. This research was sup-ported by the BES-2017-079949 Ph.D. fellowship to ES. The Spanish projects PID2019-111715GB-I00/AEI/10.13039/501100011033 and RTI2018-099157-A-I00 provided funding for field emission gun-environmental scanning electron microscopy (FEG-ESEM) and electron microprobe microanaly-ses (EMPA) /laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses of sulfides, respectively, while the Junta de Andalucia project FUMESA B-RNM-189-UGR18 financed LA-ICP-MS analyses of silicates. Research grants, infrastructures, and human resources leading to this research have benefited from funding by the European Social Fund and the European Regional Development Fund. We thank Jesus Montes Rueda (Universidad de Granada) , Isabel Sanchez Almazo (Centro de Instru-mentacion Cientifica [CIC] , Universidad de Granada) , Xavier Llovet (Centres Cientifics i Tecnolgics, Uni-versitat de Barcelona) , Miguel Angel Hidalgo La-guna (CIC, Universidad de Granada) , and Manuel Jesus Roman Alpiste (Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Cientificas-Universidad de Granada) for their careful technical assistance during sample preparation, FEG-ESEM, electron microprobe analyzes, and LA-ICP-MS analyses, respectively.Spinel peridotite xenoliths (one plagioclase-
bearing) hosted in alkaline basalts
from Tallante (southeast Spain) record the
mineralogical and geochemical fingerprint
of the subcontinental lithospheric mantle
(SCLM) evolution beneath the southern Iberian
margin. Mantle metasomatism in fertile
lherzolites caused the crystallization of clinopyroxene
+ orthopyroxene + spinel clusters
through the percolation of Miocene subalkaline
melts during the westward migration of
the subduction front in the western Mediterranean.
In the Pliocene, heat and volatiles
provided by alkaline host-magmas triggered
very low melting degrees of metasomatic
pyroxene-spinel assemblages, producing
melt quenched to silicate glass and reactive
spongy coronae around clinopyroxene and
spinel. Refertilization of the Tallante peridotites
induced the precipitation of base-metal
sulfides (BMS) included in metasomatic
clino- and orthopyroxene. These sulfides
consist of pentlandite ± chalcopyrite ± bornite
aggregates with homogeneous composition
in terms of major elements (Ni, Fe, Cu)
and semi-metals (Se, As, Te, Sb, Bi), but with
wide variability of platinum-group elements
(PGE) fractionation (0.14 < PdN/IrN < 30.74).
Heterogeneous PGE signatures, as well
as the presence of euhedral Pt-Pd-Sn-rich
platinum-group minerals (PGM) and/or Auparticles
within BMS, cannot be explained by
conventional models of chalcophile partitioning
from sulfide melt. Alternatively, we suggest
that they reflect the incorporation of distinct
populations of BMS, PGM, and metal
nanoparticles (especially of Pt, Pd, and Au)
during mantle melting and/or melt percolation.
Therefore, we conclude that Miocene
subalkaline melts released by asthenosphere
upwelling upon slab tearing of the Iberian
continental margin effectively stored metals
in metasomatized domains of this sector
of the SCLM. Remarkably high Au concentrations
in Tallante BMS (median 1.78 ppm)
support that these metasomatized domains
provided a fertile source of metals, especially
gold, for the ore-productive Miocene magmatism
of the westernmost Mediterranean.Junta de Andalucia B-RNM-189-UGR18European Social Fund (ESF)European Commission
BES-2017-079949
PID2019-111715GB-I00/AEI/10.13039/501100011033
RTI2018-099157-A-I0
Mantle-to-crust metal transfer by nanomelts
The transfer of chalcophile metals across the continental lithosphere has been traditionally
modeled based on their chemical equilibrium partitioning in sulfide liquids and silicate magmas.
Here, we report a suite of Ni-Fe-Cu sulfide droplets across a trans-lithospheric magmatic
network linking the subcontinental lithospheric mantle to the overlying continental crust.
Petrographic characteristics and numerical calculations both support that the sulfide droplets
were mechanically scavenged from the mantle source during partial melting and transported
upwards by alkalinemagmas rising through the continental lithosphere. Nanoscale investigation
by high-resolution transmission electron microscopy (HR-TEM) documents the presence of
galena (PbS) nanoinclusions within the sulfide droplets that are involved in the mantle-to-crust
magma route. The galena nanoinclusions show a range of microstructural features that are
inconsistent with a derivation of PbS by exsolution from the solid products of the Ni-Fe-Cu
sulfide liquid. It is argued that galena nanoinclusions crystallized from a precursor Pb(-Cu)-rich
nanomelt, which was originally immiscible within the sulfide liquid even at Pb concentrations
largely below those required for attaining galena saturation. We suggest that evidence of
immiscibility between metal-rich nanomelts and sulfide liquids during magma transport would
disrupt the classical way by which metal flux and ore genesis are interpreted, hinting for
mechanical transfer of nanophases as a key mechanism for sourcing the amounts of mantlederived
metals that can be concentrated in the crust.BES-2017-079949The Spanish
projects PID2019-111715GB-I00/AEI/10.13039/501100011033NANOMET PID2022-
138768OB-I00MECOBE ProyExcel_00705(FEG-ESEM), focused-ion beam (FIB)High-resolution transmission electron microscopy (HR-TEM)Australian Research Council through ARC Linkage Project
LP190100785European Social FundEuropean Regional Development Fun
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