The Barroso–Alvão Pegmatite Field (Galicia-Trás-os-Montes Zone of the Iberian Massif) has been a target of abundant geological and mineral resource exploration studies in the last decades. Since lithium demand is increasing significantly at global scale as critical raw material for green technologies, the region has acquired a special relevance in terms of Li exploration. Within the distinguished aplite-pegmatite types in the area, the dyke of Alijó (currently in exploitation) corresponds to the spodumene-bearing type. The estimation of the P-T-t conditions for its intrusion provides useful information to constrain petrogenetic processes related to the origin of the cited pegmatite field.

The presence of albite and K-feldspar coexisting in the studied dyke point to a high H₂O activity in the pegmatitic melt, which would decrease the temperature (T) of the solidus. Additionally, the lattice twin observed in microcline indicates that the crystallization of orthoclase took place followed by a rapid decrease of T, leading to the conversion of orthoclase to microcline. Thus, the presence of the lattice twin shows that the crystallization T must have been above 450–500°C (Ribbe, 1983). Considering the abovementioned minimum crystallization temperatures, the paragenesis of both primary and secondary spodumene (the later as a result of primary petalite replacement) restricts the primary pressure conditions to 2–3 kbar (e.g. London, 1984). Besides this paragenesis, the occurrence of eucryptite supports a sufficiently rapid decrease of T (and P) to allow the coexistence of these phases in the studied aplite-pegmatite. In agreement with the mentioned, the frequently observed ‘comb-like’ Unidirectional Solidification Textures (UST) in the margins of the dyke imply a strong and rapid undercooling of the system, probably caused by the exsolution of a H₂O-rich fluid phase from the pegmatitic melt, once intruded into the open fracture where it occurs, combined with the high contrast of T between the pegmatitic melt and the relatively cooled host metasedimentary rocks.

London, D., 1984. Experimental phase equilibria in the system LiAlSiO₄–SiO₂–H₂O: a petrogenetic grid for lithium-rich pegmatites. American Mineralogist, 69: 995-1004

Ribbe, P. H., 1983. Feldspar mineralogy 2nd edition. De Gruyter, Berlin, 362pp

Financial support: European Commission’s Horizon 2020 Innovation Programme [grant agreement No 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources]

How to cite: Santos-Loyola, N., Roda-Robles, E., Garate-Olave, I., Errandonea-Martin, J., and Lima, A.: Pressure–temperature–time assessment for the intrusion of the spodumene-bearing dyke from Alijó (northern Portugal), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3480, https://doi.org/10.5194/egusphere-egu22-3480, 2022.

Granitic pegmatites represent an important source of numerous critical raw materials, and subsequently, the exploration of new deposits has become a crucial objective in the energy transition towards green technologies. Systematic studies of geochemical aureoles related to late-Variscan Lithium-Cesium-Tantalum (LCT) pegmatites at the Fregeneda–Almendra Pegmatite Field (Central Iberian Zone; Iberian Massif), have provided valuable information to consider in mineral exploration. Due to the relative homogeneity of host psammitic and pelitic metasediments (SiO₂/Al₂O₃ of 2.57–5.59 wt.%, and Fe₂O₃^t/K₂O values of 0.24 to 4.19 wt.%), it has been possible to establish an ideal composition for the country rocks to assess the chemical behavior of some key elements associated to the studied LCT pegmatites.

The performed geochemical modelling (based on Gresens’ (1967) equation) shows that the intrusion of evolved aplite-pegmatites (Li-mica- and spodumene-bearing) produced an enrichment in the host rocks of several elements defined as highly mobile (F, B, Li, Rb, Cs, Sn, Be and Tl) in comparison with the determined immobile elements (Si, Al and Ti). Calculated gains and losses of such highly mobile elements display exponential decreasing trends according to the distance from the pegmatitic dyke, with Li and Cs reaching furthest from the dykes (first evidence of anomalous contents starting at distances of 4–5 times the thickness of the dyke). In terms of mineral exploration, the extent of such aureoles associated with potentially economically interesting dykes may be traceable by different small-footprint exploration tools as remote sensing, X-Ray Fluorescence, or Laser-Induced Breakdown Spectroscopy (LIBS).

Gresens, R. L. (1967). Composition–volume relationships of metasomatism. Chemical Geology 2, 47–55.

Financial support: European Commission’s Horizon 2020 Innovation Programme [grant agreement No 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources]

How to cite: Errandonea-Martin, J., Garate-Olave, I., Roda-Robles, E., Cardoso-Fernandes, J., Lima, A., Ribeiro, M. D. A., and Teodoro, A. C.: Metasomatic aureoles of highly mobile elements related to evolved granitic aplite-pegmatites from Fregeneda–Almendra (Spain–Portugal), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2508, https://doi.org/10.5194/egusphere-egu22-2508, 2022.

Solubility and complexation data are necessary for understanding conditions for the formation of magmatic and hydrothermal ore deposits. The magmatic HFSE deposits imply high solubility of these elements in alkaline silicate melts, with the most important parameters being alkalinity, halogen and water contents, temperature of the magma, and silica activity. We have conducted a series of experiments on the solubility of Nb in alkaline silica-undersaturated melts. Experiments were carried out with using two synthetic silicate glasses with different Na/Al values: NAS4 (Na₂O 26.0 %(m/m), Al₂O₃ 12.5 %(m/m), SiO₂ 61.5 %(m/m)) with molar Na/Al = 3.36, and NAS2 (Na₂O 20.9 %(m/m), Al₂O₃ 17.8 % (m/m), SiO₂ 61.3 %(m/m)) with  Na/Al = 1.93.  The glasses were prepared from finely ground mixtures of quartz, aluminium oxide, and sodium carbonate. The mixtures were heated in a Pt crucible at 900 °C and subsequently at 1100 °C, and then crushed and remelted three times. Various amounts of Nb₂O₅ + glass (NAS4/NAS2) were placed in 1 cm long and 3mm wide Pt capsules and arc-welded shut. Then the capsules were placed in a cold-seal autoclave and run at 200 MPa and 750 ^°C for about 2 weeks. Rapid quench pressure vessels were used for experiments at 850 °C, 100 MPa, and run durations of 48 – 72 hours. In some runs, distilled water and/or CaF₂, NaCl were added to the reactant mixtures. Experimental products were analyzed by EMPA.

Liquids in all experiments quenched to transparent glass with small (5-10 μm) euhedral crystals of NaNbO₃ composition. These NaNbO₃ crystals are the only solid phase at the liquidus. In low-temperature experiments (750 °C) using the highly peralkaline glass NAS4, the Nb solubility increases substantially with addition of water from 2.54 %(m/m) Nb₂O₅ at dry conditions up to 2.91 %(m/m) Nb₂O₅ at 5 %(m/m) H₂O. The Nb solubility at dry conditions at 850 ^°C is higher in NAS4 in comparison with less alkaline NAS2 melt (3.72 %(m/m) Nb₂O₅ and 2.04 %(m/m) Nb₂O₅, respectively). Our data at 850 °C show that the solubility of Nb in the liquid increases significantly with the addition of water and NaCl for NAS4 (4.16 %(m/m) Nb₂O₅ and 4.35 %(m/m) Nb₂O₅, respectively) and for NAS2 (2.77 %(m/m) Nb₂O₅ and 2.17 %(m/m) Nb₂O₅). The effect of CaF₂ addition on the Nb solubility was insignificant.

In conclusion, the Nb solubility in silica-undersaturated melts is already high at 750 °C, and increases substantially with temperature. It also increases strongly with Na/Al ratio in the melt, with the addition of water and NaCl, but not in the presence of CaF₂. This suggests that chlorine, unlike fluorine, is a ligand strongly enhancing Nb solubility in alkaline silicate melts.

This work was supported by the Deutsche Forschungsgemeinschaft via SPP2238 grants SCHM2415/7-1 and VE 619/7-1.

How to cite: Nikolenko, A., Schmidt, C., and Veksler, I.: Solubility of niobium in peralkaline silica-undersaturated melts at 750–850 °C, 100–200 MPa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7751, https://doi.org/10.5194/egusphere-egu22-7751, 2022.

Bastnäsite [REE(CO₃)F] is the main mineral of REE ore deposits in carbonatites. Synthetic bastnäsite-like compounds have been precipitated from aqueous solutions by many different methods but previous attempts to model magmatic crystallization of bastnäsite from hydrous calciocarbonatite melts were unsuccessful. Here we present the first experimental evidence that bastnäsite and two other REE carbonates, burbankite and lukechangite, can crystallize from carbonatite melt in the synthetic system La(CO₃)F – CaCO₃ – Na₂CO₃ at temperatures between 580 and 850 °C and pressure 100 MPa. The experiments on starting mixtures of reagent-grade CaCO₃, Na₂CO₃, La₂(CO₃)₃ and LaF₃ were carried out in cold-seal rapid-quench pressure vessels. The studied system is an isobaric pseudoternary join of a quinary system where CO₂ and fluorides act as independent components.  Liquidus phases in the run products are calcite, nyerereite, Na carbonate, bastnäsite, burbankite solid solution (Na,Ca)₃(Ca,La)₃(CO₃)₅ and lukechangite Na₃La₂(CO₃)₄F. Calcite and bastnäsite form a eutectic in the boundary join La(CO₃)F – CaCO₃ at 780 ± 20 °C and 58 wt% La(CO₃)F. Phase equilibria in the boundary join La(CO₃)F – Na₂CO₃ are complicated by peritectic reaction between Ca-free endmember of burbankite solid solution petersenite (Pet) and lukechangite (Luk) with liquid (L):

Na₄La₂(CO₃)₅ (Pet) + NaF (L) = Na₃La₂(CO₃)₄F (Luk) + Na₂CO₃ (Nc)

The righthand-side assemblage becomes stable below 600 ± 20 °C. In ternary mixtures, bastnäsite (Bst), burbankite (Bur) and calcite (Cc) are involved in another peritectic reaction:

2 La(CO₃)F (Bst) + CaCO₃ (Cc) + 2 Na₂CO₃ (L) = Na₂CaLa₂(CO₃)₅ (Bur) + 2 NaF (L)

Burbankite in equilibrium with calcite replaces bastnäsite below 730 ± 20 °C. Stable solidus assemblages in the pseudoternary system are: basnäsite-burbankite-fluorite-calcite, basnäsite-burbankite-fluorite-lukechangite, bastnäsite-burbankite-lukechagite, burbankite-lukechangite-nyerereite-calcite and burbankite-lukechangite-nyerereite-natrite. Addition of 10 wt% Ca₃(PO₄)₂ to ternary mixtures resulted in massive crystallization of La-bearing apatite and monazite, and complete disappearance of bastnäsite and burbankite. Our results confirm that REE-bearing phosphates are much more stable than carbonates and fluorocarbonates. Therefore, primary crystallization of the latter from common carbonatite magmas is unlikely. Possible exceptions are carbonatites at Mountain Pass that are characterized by very low P₂O₅ concentrations (usually at or below 0.5 wt%) and extremely high REE contents in the order of a few weight percent or more. In other carbonatites, bastnäsite and burbankite probably crystallized from highly concentrated alkaline carbonate-chloride brines that have been found in melt inclusions and are thought to be responsible for widespread fenitization around carbonatite bodies.

This study was supported by RSF grant № 19-17-00013.

How to cite: Veksler, I., Nikolenko, A., and Stepanov, K.: Experimental study of phase equilibria between bastnäsite, burbankite and La phosphates in the system La(CO3)F – CaCO3 – Na2CO3 - Ca3(PO4)2 at 100 MPa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6360, https://doi.org/10.5194/egusphere-egu22-6360, 2022.

In porphyry copper deposits, where ore grades are low, the volume of the ore body determines its economic potential. However, the factors that control their size are still an open question and understanding them is crucial for finding new and large porphyry copper deposits (PCDs); especially in a society with an ever-increasing Cu demand. One of the most important, but highly debated size-modulating factors, time, could make the difference for a magmatic system to form small or large PCDs. The limited access to the plutonic roots of PCDs hinders our ability to study the plutonic and the porphyritic systems as a whole. However, Cenozoic tilting of the Yerington district (Nevada, USA) make it the perfect place for a key study as the Yerington batholith and associated volcanic sequences, porphyritic dikes and Cu mineralized centers are exposed. The complex upper-crustal batholith is comprised of three consecutive plutons that with time increase in silica content, granulometry and depth of emplacement while decreasing in volume: the McLeod quartz monzodiorite, the Bear quartz monzonite and the Luhr Hill granite with associated porphyritic dikes that formed Cu mineralization. Field observations show sharp intrusive contacts between the three plutons, until now have been interpreted as periods of magmatic quiescence that separate the emplacement of the three intrusions, overall accounting for 1 Ma of magmatic activity (Dilles & Wright, 1988; Schöpa et al., 2017). However, our new high-precision zircon U-Pb ID-TIMS dates spread over 2 Ma and show a continuum in zircon crystallization from the McLeod quartz monzodiorite and coeval volcanics to the Luhr Hill granite and porphyritic dikes with no hiatuses. In-situ trace element LA-ICPMS analyses on zircon further indicate a continuous geochemical evolution from intermediate compositions and higher Ti-in-zircon temperatures in the oldest zircons towards colder and evolved ones in the youngest ones, following normal fractional crystallization trends with the onset of titanite crystallization during evolution. These data argue for a sustained crystallization of the three main plutonic bodies. Our new lifetime of the magmatic system in view of zircon crystallization ages changes the previously defined thermal models for the Yerington district and affects how we assess its mineralizing potential. This questions the thermal budget of these upper crustal magma chambers, which should remain partially molten for about a million years to produce the observed zircon age spectra in each pluton. Such considerations open the discussion of zircon crystallization in the deep crust, reconciling these new high-precision data and the well-stablished field crosscutting relationships, and impacting the current understanding and application of zircon petrochronology in porphyry copper systems.  

John H. Dilles, James E. Wright; The chronology of early Mesozoic arc magmatism in the Yerington district of western Nevada and its regional implications. GSA Bulletin 1988; 100 (5): 644–652. 

Anne Schöpa, Catherine Annen, John H. Dilles, R. Stephen J. Sparks, Jon D. Blundy; Magma Emplacement Rates and Porphyry Copper Deposits: Thermal Modeling of the Yerington Batholith, Nevada. Economic Geology 2017; 112 (7): 1653–1672. 

How to cite: Castellanos Melendez, M. P. and Chelle-Michou, C.: Emplacement of the Yerington batholith and associated porphyry dikes, Nevada, USA: a conciliation challenge between field observations and high precision zircon petrochronology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12753, https://doi.org/10.5194/egusphere-egu22-12753, 2022.

The Santa Helena Breccia (SHB) is a unique case of a collapse breccia with a late injection breccia in the Iberian Peninsula. The SHB is located in the NE Portugal in the contact between the Central Iberian Zone and the Galiza Trás os Montes Zone. This type of W deposit is a very uncommon example in the European Variscan Belt with only another similar deposit known, the Puy le Vignes in French Central Massif. The SHB is a sub-vertical structure, with an ellipsoidal shape with N-S major axis revealing at least 575 m in length, over 150 m in width, and at least 200 m in depth. This structural body occurs in the contact between synorogenic Variscan granites and metasedimentary rocks (Silurian in age). The lithological composition of the fragments is identical to the surrounding rocks cemented by quartz and lately cute by an injection breccia cemented by a leucocratic matrix. In the 60s of last century, a small exploitation of the SHB was performed in outcrops near two N-S subvertical quartz veins that limit SHB at east and west. The main goal of this study was to characterize and understand the behaviour of the mineralizing fluids in the breccia body.

The study of fluid inclusions in different types of quartz revealed the presence of four distinct types of fluids. The fluid 1 occurs in two phase aqueous fluid inclusions (FI) with an average salinity of 3.91 wt% Eq. NaCl, an average bulk density of 1.03 g/cc and an homogenization temperature (Th) between 250 to 300º C. Fluid 2 occurs in in three phase aqueous-carbonic FI with an average salinity of 5.93 wt% Eq. NaCl and an average bulk density of 1.07 g/cc. The lower entrapment temperature for fluid 2 was 250º C. Later in the SBH occur a fluid 3 which characterized by a lowest average salinity. The fluid 3 show an average salinity of 3.03 wt% Eq. NaCl and an average bulk density of 1.02 g/cc. The lowest Th of this fluid is 190ºC. A last fluid 4 shows an average salinity of 4.00 wt% Eq. NaCl and an average bulk density of 1.03 g/cc. This fluid was entrapped at the lowest temperatures (Th between 90º and 190ºC).

The FI results together with ore petrography showed that although the presence of four distinct fluids, two main ore stages occurred at SHB genetic model. The first one is characterized by the presence of the oxide minerals associated with fluids 1 and 2) and characterize the collapsing and the injection of the leucocratic rock into the SHB at higher temperature and pressure that were responsible for the W mineralization. After, a late stage where fluids 3 and 4 were responsible by a scarce sulfidic mineralization at lower pressure and temperature.  

Acknowledgements: The work was supported by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 - ICT (Institute of Earth Sciences). Lima, L is financed by FCT trough the PhD. scholarship SFRH/BD/144894/2019.

How to cite: Lima, L., Guedes, A., Bobos, I., and Noronha, F.: The mineralizing fluids of the Santa Helena Breccia- a unique W deposit in the Iberian Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8165, https://doi.org/10.5194/egusphere-egu22-8165, 2022.

The Zinnwald/Cinovec Sn-W-Li deposit on the border between Germany and Czech Republic in the eastern part of Krušné Hory/Erzgebirge represents a fluorine-rich hydrothermal alteration of a granite-rhyolite association. The host rock can be divided into two parts: 1) zinnwaldite granite (upper part) with massive greisen body and various hydrothermal veins and 2) homogeneous protolithionite granite (lower part). The basement is the Krušné Hory/Erzgebirge crystalline complex with different metamorphic grades, overlain by the Teplice rhyolite, which also contains greisen veins and is the focus of this study.

In this study, we focus on the effects of fluid-rock interaction on distal rhyolites of the deposit. We combine whole rock chemistry with petrological data to constrain mass gain or loss of economically interesting elements. The samples were selected from the upper contact zone between granite and rhyolite. Three distinct zones of high- and low-degree greisenization (HG and LG) and albitization (A) developed with different textures, mineral assemblages and mineral compositions. Beyond the albitization zone, a continuous transition to the least altered rhyolite was observed. In the greisen part, the predominant minerals are quartz (~80 vol%) and topaz (~10 vol%) with minor biotite (~5 vol%). The albitization zone contains mostly albite (~40 vol%), quartz (~25 vol%), orthoclase (~25 vol%), and biotite (~10 vol%). In comparison to the composition of the rhyolite wall rock, mass balance calculations show that the greisen has 50%-100% loss of LILEs, 15%-20% loss of HREEs, and 7%-11% gain of LREEs.  The Th/U, Zr/Hf, Y/Ho, and La/Yb ratios are similar between the rhyolite and the greisen zone but very different for the albitization zone. This suggests a dynamic dissolution/precipitation process in the albitization zone caused by the particularly high F- and Na-activity in this zone compared to the unaltered rhyolite but also the greisen (where F is precipitated as topaz and fluorite whereas Na is lost to the fluid). The chemical changes show that the F-rich fluid carried LILEs and LREES to the greisen, and also resulted in the loss of HREEs and alkaline elements.

How to cite: Qiao, S., John, T., and Loges, A.: Element redistribution by greisenization in rhyolite, Zinnwald/Cinovec, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11806, https://doi.org/10.5194/egusphere-egu22-11806, 2022.

The skarns at Gryll’s Bunny are dominated by garnet and magnetite with small amounts of hornblende, epidote, apatite and tourmaline. They formed discordantly within a succession of metabasalts and metapelites (the Mylor Slate formation) within the metamorphic aureole of the Land’s End granite. The skarns subdivide into discrete mineralogical types that include garnet-skarn with medium-coarse grained garnet, epidote, tourmaline, amphibole and biotite; hornblende-skarn with coarse-grained tabular hornblende, medium grained garnet, epidote, titanite, apatite and tourmaline; the foliated metapelite contains fine-grained hornblende and garnet with alkali feldspar, sericite, muscovite, titanite, quartz, epidote, apatite and tourmaline; cassiterite-rich “tin floors” are overlain by (variably metasomatized) metabasite that include horizontal bodies of tourmalinite with cassiterite, titanite, chlorite and apatite.

The lithologies contain variable amounts of magnetite that can be classified into 5 types. Magnetite in the metapelite (type 1) is very fine grained. Magnetite in hornblende-skarn associated with the metapelite (type 2) is fine grained with ilmenite lamellae and is associated with maghemite. Magnetite in the hornblende skarn adjacent to garnet skarn (type 3) contains abundant ulvöspinel lamellae. Magnetite in the garnet skarn is medium to coarse-grained with a granular recrystallized texture and spinel exsolutions (type 4). All of these types have been partially replaced by hematite along edges and cracks. Magnetite related with the tourmaline zone (type 5) is generally euhedral and free of exsolution lamellae. In addition, the tourmaline-cassiterite zone has abundant titanite with ilmenite laths.

Fluid inclusions in garnet, amphibole and epidote of the metasomatized rocks, garnet related with type-3 magnetite has higher homogenization temperature (291- >600 ^oC) and almost similar low-moderate salinity (2.4-13.7 wt. % NaCl equiv.) than that of type-2 magnetite (222-428 ^oC and 3.9-14.8 wt. % NaCl equiv).

EPMA and LA-ICP-MS analysis demonstrate that garnets are of grossular (60-76)-andradite (13-32) composition and rich in TiO₂; amphiboles are sadanagaite-pargasite, tourmalines are shorl-feruvite and apatites are fluor- and hydroxyl-apatite composition. V/Ti and Ga/Ti in magnetite decrease progressively from type 1 to 5, indicating that type 1 and 2 retain characteristics of their mafic host rock as well as metamorphic process, development towards type 5 is interpreted by the increasing significance of granitic fluids. All of the magnetite types have elevated Sn and Zn whilst Zr, Mg and Al are low. The homogeneity of type 5 magnetite supports a purely metasomatic origin at the final stage of skarn development.

Key words: SW England, Gryll’s Bunny skarns, Botallack, Magnetite, Mineralogy, Geochemistry, Fluid inclusions

How to cite: Kirat, E., Andersen, J. C. Ø., and Williamson, B. J.: Characteristics of Magnetite and Calc-Silicate Minerals in the Gryll’s Bunny Skarn in the Land's End Aureole, SW England, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4200, https://doi.org/10.5194/egusphere-egu22-4200, 2022.

Several studies on polymetallic hydrothermal veins of western Europe recently highlighted the role of physicochemical controls in determining and enhancing mineralizing processes in structurally defined, spatially limited environments (vein “ore shoots”). Host rocks have critical roles: a) the development and geometry of the structures and veins depend on their rheological features; b) they may act as sources of elements and c) regulate the type and kinetics of chemical reactions after fluid-rock interaction. An excellent example is provided in SW Sardinia by the five-elements (Ni-Co-As-Ag-Bi) veins of the Arburèse District. These late- to post-Variscan low-temperature veins are hosted in Ordovician-Silurian very low-grade metamorphic siliciclastic rocks outcropping between the Arbus granitoid (304±1 Ma) and the Mt. Linas granite (289±1 Ma). Ordovician host rocks mostly include sandstones and siltstones, while Silurian rocks are dominated by carbonaceous argillites (black shales). The distinct competence of these host rocks resulted in different geometries of spaces opened to fluid circulation, leading to the formation of orebodies with different shapes: large veins mainly occur in Ordovician sandstones and siltstones (e.g., Pira Inferida mine), while thinner, often anastomosed veins occur in Silurian black shales (e.g. Acqua Is Prunas mine). Vein formation is triggered by seismic cycles in faults at shallow crustal levels, as testified by widespread breccia and cockade textures. The ore shoots display complex mineral assemblages: native Bi; Ni-Co-Fe arsenides and antimonides (nickeline, breithauptite, rammelsbergite, safflorite, skutterudite, loellingite); Ni-Co-Fe sulfarsenides-sulfantimonides (gersdorffite, cobaltite, ullmannite, arsenopyrite); and Pb-Zn-Cu-Fe sulfides (galena, sphalerite, chalcopyrite, pyrite); Ag-Sb-As and Se sulfosalts. Carbonates (mainly siderite, minor ankerite, dolomite-calcite) and quartz are the main gangue minerals. Field, textural and analytical data support an overall rapid formation of ore minerals under multiple and distinct mineralizing pulses, starting with native elements and arsenides, followed by sulfarsenides and sulfides. Ore shoots must have formed in relatively restricted environments chemically marked by the abundant redox agents (carbonaceous matter, pyrite and, possibly, hydrocarbons) provided by Silurian black shales, which may have supplied sulfur and other elements (e.g., Se) for mineralization. Thus, differences in host rock geochemistry may explain local differences in ore shoots composition and paragenetic sequences. A further control at the district scale is represented by the repeated intersections of the five-elements vein system with earlier Mt. Linas granite-related Sn-As and W-Bi-Te-Au veins, documented in several ore shoots of the district (Pira Inferida, Acqua is Prunas and Sa Menga mines). Such intersections formed preferred pathways for fluid circulation and wider spaces for mineral precipitation during ore-forming processes; moreover, main components of five-elements ores (e.g., As, Bi) appear to be inherited by remobilization from granite-related veins. In summary, ore shoot mineralization in the studied vein system may have been controlled by multiple factors (host structures; host rock rheology and composition; intersections with other vein systems) that may be assumed as key prospection guidelines for further mineral exploration in the area; until now this vein system has only been explored in its shallower parts, and it is possible that much of the ore shoots has yet to be discovered.

How to cite: Scano, I., Deidda, M. L., Fancello, D., Moroni, M., and Naitza, S.: Geological and chemical controls in ore shoot mineralization of polymetallic veins: insights from the five-elements Ni-Co-As-Ag-Bi hydrothermal veins of SW Sardinia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1110, https://doi.org/10.5194/egusphere-egu22-1110, 2022.

Bismuth is recognized as a Critical Raw Material by the EU Commission and it is found in many ore deposits across the world. In Southwestern (SWS) and Southeastern (SES) Sardinia, Bi-minerals are commonly found in two main groups of ore deposit: 1) late Variscan granite-related orebodies including greisens, W-Mo(-Sn) HT hydrothermal veins, skarns and  hornfelses; and 2) late- to post-Variscan five-element (Ni-Co-As-Bi-Ag) LT hydrothermal veins.

In the first group, greisens (Flumini Binu prospect, SWS) and HT hydrothermal W-Mo(-Sn) veins (Perd’e Pibera mine and Togoro prospect, SWS; Perda Majori-Bruncu Spangas prospects, SES) tipically host native Bi, bismuthinite and, subordinately, Pb-Ag-Bi-sulfosalts interstitial to molybdenite and/or scattered in the quartz-feldspar(-fluorite-topaz) gangue. Locally, maldonite (Au₂Bi), Bi-tellurides (hedleyite Bi₇Te₃, and Bi₂Te) and probable russellite (Bi₂WO₆) are abundant in wolframite-rich veins (Togoro prospect), associated with native Au. Small grains of native Bi have also been found in some poorly mineralized garnet-vesuvianite-epidote calc-silicate hornfelses (Domus De Maria, SWS). Besides native Bi and bismuthinite, skarn orebodies frequently host wider assemblages consisting of Bi-Pb-Ag-Cu-sulfosalts intergrowths, once again associated with wolframates (scheelite at Monte Tamara prospect and Sa Marchesa mine, SWS) and molybdenite (Monte Tamara, Sa Marchesa and Morettu prospect, SWS). As a reference, the Monte Tamara assemblage includes “phase 88.6” (Cu_0.33Pb_0.33Bi_7.67S₁₂), pekoite (PbCuBi₁₁S₁₆Se₂), salzburgite-paarite (Cu_1.58-1.67Fe²⁺_0.03-0.01Pb_1.65-1.72Bi_6.38-6.3S_12-12.06), gustavite (PbAgBi₃S₆) xilingolite-lillianite (Pb₃Bi₂S₆), cosalite (Pb₂Bi₂S₆), berryite (Cu₃Ag₂Pb₃Bi₇S₁₆), ourayite (Pb₄Ag₃Bi₅S₁₃) and cupropavonite (Cu_0.9Ag_0.5Pb_0.6Bi_2.5S₅), identified by means of EPMA analyses. Moreover, since high Bi(-Ag-Te) contents have been detected in sulfides (sphalerite, galena, arsenopyrite), micro-inclusions of -sulfosalts and/or -tellurides may also occur. In the same area, wittichenite ((Bi,Cu)₂S₃) and hammariite (Pb₂Cu₂Bi₄S₉) have been previously identified, while schapbachite (AgBiS₂) has been reported at the Sa Marchesa mine.
The second group of Bi-bearing orebodies includes the five-element veins of the Arburèse district (Pira Inferìda, Acqua Is Prunas and Sa Menga mines, SWS), where native Bi and bismuthinite tipically occur at the core of Ni-Co arsenides-sulfarsenides (e.g. nickeline and gersdorffite-cobaltite) concentric growths.

Therefore, the strong affinity of bismuth for granite-related W-Mo(-Sn) deposits of Southern Sardinia indicates that the late-Variscan (Early Permian) granites represent its main metallogenic source. However, the formation of such diverse Bi-minerals assemblages is seemingly controlled by local-scale conditions. In skarn ores, the Bi-Pb-Ag-Cu-sulfosalts intergrowths formed during the sulfide stages, apparently after the interaction between primary Bi-phases and Pb-Ag-Cu-bearing hydrothermal fluids and under oscillatory variations of metals availability and stability. Conversely, in W-Mo(-Sn) hydrothermal veins and greisens, where sulfides are apparently more scarce, the array of Bi-phases is usually more limited. Furthermore, field and analytical data point towards a selective remobilization of bismuth from the primary native and -tellurides assemblage of HT wolframite-quartz veins (Togoro, SWS) by late cross-cutting LT five-element veins, suggesting that multiple, spaced over time hydrothermal-veining events occurred in the same area.
In conclusion, bismuth and related mineral phases could serve as important markers, providing useful qualitative indications regarding the source of metals, the ore-forming processes and the relationships between different ore deposits at the district-scale.

How to cite: Deidda, M. L., Fancello, D., Stefano, N., Moroni, M., and Scano, I.: Bi-minerals occurrence in various ore deposits of Southern Sardinia: a short review., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1018, https://doi.org/10.5194/egusphere-egu22-1018, 2022.

The B prospect is located at the southeast of the Chatree gold-silver deposit. The mineralization is hosted in the Late Permian-Early Triassic Chatree volcanic sequence consisting of volcaniclastic and volcanogenic-sedimentary rocks ranging in composition from basaltic andesite to rhyolite. At the study area, the total thickness of volcanic succession is about 300 meters, and the succession can be divided into three main stratigraphic units from bottom to top, namely, 1) porphyritic andesite unit (Unit 3), 2) polymictic intermediate breccia unit (Unit 2), and 3) volcanogenic sedimentary unit (Unit 1). The ore zones are mainly confined to polymictic intermediate breccia and volcanogenic sedimentary units (Units 1 and 2). At least three stages of mineralization have been identified, namely 1) quartz -pyrite (Stage 1), 2) quartz-chlorite-calcite-sulfides-electrum (Stage 2) and 3) quartz-calcite (stage 3) veins/veinlets. Gold occurs chiefly in Stage 2 mineralization which is characterized by typical vein textures of low sulfidation epithermal deposit (e.g., crustiform, colloform banding, comb textures). Pyrite is a primary sulfide mineral with minor sphalerite, chalcopyrite, and galena. Gold occurs as electrum with fineness ranging from 506 to 632 ppm. The hydrothermal alteration at B prospect is composed of two main types: 1) quartz-adularia (silicic alteration) assemblage close to ore zone, and 2) adularia-quartz-illite-calcite-chlorite (phyllic alteration) assemblage distal to ore zone. Based on characteristics of mineral assemblages, textures, and alterations the mineralization at B prospect can be classified as a low sulfidation epithermal gold-silver style deposit. 

How to cite: Kaewpaluk, S., Salam, A., Assawincharoenkij, T., Manaka, T., Poompuang, S., and Munsamai, S.: Geology, mineralization, and alteration of B prospect of the epithermal Au-Ag deposit in central Thailand: A study on Chatree’s peripheral deposit for further gold exploration., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2962, https://doi.org/10.5194/egusphere-egu22-2962, 2022.

The Iberian Pyrite Belt (IPB) in Portugal and Spain is a world-class metallogenic province that contains more than 1800 Mt of massive sulfide ore in over 100 deposits. The orebodies are hosted by submarine lithologies comprising felsic and mafic volcanic rocks and sedimentary units from the Volcanic-Sedimentary Complex (VSC) of Devonian-Carboniferous age. This study reports preliminary geological, mineralogical, and geochemical results from the Sesmarias prospect.

The Sesmarias VMS prospect is a blind discovery (~100 m of Tertiary cover) with the first lens intersected by drilling in 2014 (10.85 meters @ 1.81% Cu, 2.57% Pb, 4.38% Zn, 0.13% Sn, and 75.27 g/t Ag). Recent drilling has encountered 39.2 meters @ 0.44% Cu, 0.71 g/t Au, 27.1 g/t Ag, 2.07% Zn, and 0.79% Pb and 36.45 meters @ 0.72% Cu, 0.36 g/t Au, 0.82% Pb, and 21 g/t Ag in separate holes, and has extended the mineralization further to the SE. Through all phases of drilling, the company intersected copper-zinc massive sulfide mineralization in various lenses over a strike length of about 1.7 km; however, this value may easily increase with the continuation of the drilling program.

The Sesmarias massive sulfide system is heavily folded and strongly modified by several post-mineralization deformation events. The VSC at Sesmarias comprises black shales and felsic volcanics that are the primary hosts of the massive and semi-massive sulfide mineralization and a younger thick sequence of mafic volcanics (including intrusives) which overlap grey/green shales. Macroscopic observations complemented by petrographic studies and bulk rock chemistry of the volcanic rocks allowed to distinguish two main groups of volcanics rocks. The-mafic rocks are composed of plagioclase, relics of amphibole and pyroxene (±quartz), and are dominated by an alteration assemblage that includes chlorite, calcite, dolomite, epidote, (±quartz), and iron (hydro-)oxides. The felsic rocks include lavas and associated volcaniclastic rocks that are composed of quartz, plagioclase and are altered to muscovite ± chlorite. Compositionally, all major elements except for Na₂O, K₂O, and Al₂O₃, show roughly negative correlations with SiO₂ and allow the discrimination of mafic from felsic rocks; however, the trends of magmatic differentiation are compromised due to secondary alteration. The results show that the VSC at Sesmarias is dominated by mafic rocks of basaltic composition (alkaline basalts) which are strongly spilitized. In contrast, the felsic rocks that host the mineralization are manly rhyodacites and dacites. Overall the magmatism at Sesmarias is more mafic in comparison with other mineralized areas such as Aljustrel and Neves Corvo, where the volcanism is predominantly rhyolitic.

How to cite: Codeço, M., Gleeson, S., Rosa, C., Kuhn, P., Trumbull, R., Weis, P., Schleicher, A., Stammeier, J., and Wilke, F.: The Sesmarias massive sulfide discovery in Portugal (Iberian Pyrite Belt): preliminary geochemical and petrological studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6130, https://doi.org/10.5194/egusphere-egu22-6130, 2022.

The metamorphosed, stratiform, c. 1.9 Ga Zinkgruvan Zn-Pb-Ag deposit is one of Europe’s largest producers of Zn. Since 2010, disseminated Cu mineralization is also mined from dolomite marble in a hydrothermal vent-proximal position in the stratigraphic footwall. Local enrichments of Co and REE exist in the vent-proximal mineralization types, albeit their distribution is poorly known. This contribution provides new data on the distribution of Co and REE within the Zinkgruvan deposit.

LA-ICP-MS analysis suggest that lattice-bound cobalt in sphalerite range between 44 ppm and 1372 ppm, with the lowest and highest values occurring in distal and proximal mineralization, respectively. Proximal Co-rich sphalerite is always Fe-rich. Lattice-bound Co also occur in pyrrhotite; ranging from 52 ppm in distal ore to 1608 ppm in proximal ore. There is a concurrent increase in lattice-bound Ni from 3 ppm to 529 ppm. In proximal ore, Co is also hosted by cobalt minerals such as costibite (27.37 wt.% Co), safflorite (16.21 wt.% Co), nickeline (7.54 wt.% Co), cobaltite (32.74 wt.% Co) and cobaltpentlandite (25.49 wt.% Co). Automated quantitative mineralogy suggest that these minerals are highly subordinate to sphalerite (<70.11%) and pyrrhotite (<14.69%), amounting to <2.88% cobalt minerals with safflorite being most common (up to 2.67%). Cobalt deportment calculations suggest that the proportion of whole-rock Co that is lattice-bound to sphalerite and pyrrhotite ranges from 7.80% to 100%, with sphalerite being the main host. Whole-rock As and Ni contents pose a strong control on whether Co occurs lattice-bound or as Co minerals.

LA-ICP-MS analysis show that accessory apatite in proximal, marble-hosted Cu mineralization carries a few thousand ppm ∑REE, but locally up to c. 1.6 wt.% ∑REE. The apatite can be subdivided into two types. Type 1 apatite is characterized by dumbbell-shaped chondrite-normalized REE profiles with relative enrichment of in particular Sm-Tb, depletion of Yb-Lu relative to La-Pr, local positive Gd anomalies, and weak positive to negative Eu anomalies. Type 2 apatite is characterized by flat to negatively sloping REE profiles from La to Gd and relative HREE depletion. Additional REE is hosted by monazite. Type 1 apatite was only found as a gangue to Cu mineralization. The Type 1 apatite REE signature is characteristic of hydrothermal apatite, and a direct genetic association with vent-proximal Cu mineralization can be inferred.

Comparison with published REE contents in apatite suggest that vent-proximal Zinkgruvan apatite is locally as REE-rich as apatite from Kiruna-type apatite iron oxide deposits, and more REE-rich than apatite in other metamorphosed sediment-hosted sulphide deposits in the world, such as the Gamsberg deposit (RSA).

How to cite: Jansson, N., Hjorth, I., Ivarsson, F., Aiglsperger, T., M. Azim Zadeh, A., Kooijman, E., Kielman-Schmitt, M., Drakou, F., and Kozub-Budzyń, G.: Cobalt and REE distribution at the Zinkgruvan Zn-Pb-Ag and Cu deposit, Bergslagen, Sweden, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1067, https://doi.org/10.5194/egusphere-egu22-1067, 2022.

The Kayad Zn-Pb deposit in Ajmer, Rajasthan is a Proterozoic SEDEX deposit located in the Aravalli-Delhi fold belt of western India. The ore mineralization comprising predominantly of sphalerite and galena and subordinate chalcopyrite and pyrrhotite occurs in quartz mica schist (QMS), calc-silicate, quartzite and pegmatite, of which QMS hosts the majority of it. Other minerals such as arsenopyrite, lollingite and sulfosalts such as pyrargyrite, gudmundite and breithauptite are commonly associated with the massive ores in QMS.

The mineralization occurs as dissemination in calcsilicate and quartzite, in veins intruding pegmatite or on the wall rock of pegmatite, and occurs as lamination and massive ores in QMS. The laminated ores conform to the schistosity whereas the coarse, massive ores disrupt and overprint the metamorphic fabric. The massive sphalerite and galena (± chalcopyrite and pyrrhotite) ores are commonly associated with one or more of the hydrothermal minerals such as prehnite, Al-pumpellyite, albite and allanite replacing K-feldspar and plagioclase which indicates episode of Ca-Na metasomatism. On the other hand, pyrrhotite and chalcopyrite are mostly associated with chamosite, albite and potash-feldspar replacing other minerals in the host rock suggesting  -Fe-Na-K metasomatism. Sphalerite, galena, and arsenopyrite have been analysed by the SHRIMP SI ion microprobe for δ³⁴S while multiple sulfur isotope (³²S, ³³S, ³⁴S, and ³⁶S) study has been attempted on pyrrhotite and chalcopyrite. δ³⁴S of chalcopyrite (+6.4 to +8.8‰), pyrrhotite (+6.1 to +11.3‰) and arsenopyrite (+7.1 to +9.4‰) are relatively compact and consistent while sphalerite shows a larger variation from +2.7‰ to +8.9‰ across host rocks. Galena, however, shows the highest δ³⁴S values ranging from +7.8 to +24.3‰. Such high variations for both sphalerite and galena can result partly from crystal orientation effect during analysis. Average ∆³³S and ∆³⁶S of pyrrhotite are -0.01±0.06‰ (2 S.D.) and 0.03±0.02‰ (2 S.D.) respectively that show no MIF-S signatures. However, in the case of chalcopyrite, a few ∆³³S values deviate up to 0.33‰ from the mean of 0.11±0.15 (2 S.D.)‰.

Various microscale and mesoscale textures in massive sulfides, like attenuation of fold limbs of QMS and accumulation of sulfides at fold hinges, discrete blebs of galena and chalcopyrite in a matrix of sphalerite and extremely low dihedral angles among them, and prominent durchbewegung textures indicate the ores have been mobilized. Mineralogy (presence of sulfosalts) and geochemical analysis of the massive sulfides show enriched concentrations of low chalcophile elements like Ag, Sb, As, Bi, Se, Tl which indicate metamorphism-induced sulfide melting might have been an important process in migration of pre-existing ore. However, presence of hydrothermal alterations in close proximity with the mobilized massive ores suggests that fluid-mediated chemical mobilization also played a crucial role in such remobilization. Consistently high positive values of δ³⁴S hint at a thermochemical reduction of seawater sulfate during SEDEX mineralization and recycling of the sulfur during remobilization that formed massive ores.

How to cite: Das, E., Pal, D. C., and Fu, B.: Hydrothermal alteration and multiple sulfur isotope chemistry of Kayad Zn-Pb deposit, Ajmer, Rajasthan, western India: Implications for ore genesis, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9098, https://doi.org/10.5194/egusphere-egu22-9098, 2022.

Shallow seawater-hydrothermal circulation plays a crucial role in the subseafloor mineralization of the hydrothermal system. However, its key fluid processes and impacts on the metal mobilization and sulfur cycles in the stockwork mineralization are still poorly understood. We first present the systemic variations in micro-scale trace element and sulfur isotope compositions of pyrite varieties in a stockwork-like sulfide from the Longqi hydrothermal field to constrain the metal transport and deposition and sulfur origins and cycles in the shallow seawater-hydrothermal circulation. Pyrites considered as the dominant sulfides can be clarified into disseminated fine-grained (Py-I), euhedral (Py-II), and subhedral-euhedral (Py-III) varieties based on texture. The wall-rock-derived elements Ti, Cu, Ni, Mg, and Mn and seawater-derived elements Mo, V, and U are concentrated in Py-I within the breccias and related to the fluid-rock reaction and fluid-seawater mixing in the shallow seawater-hydrothermal circulation system. Short-lived shallow circulation results in fluid fluctuation and oscillatory-zoned Py-II with depletion of Co, Ni, Cu, As, and Se in the mantles relative to those in the rims and cores. As the later hydrothermal activity was active, Py-III that was overgrown from Py-II is rich in hydrothermally inherited metals Se, Te, and Co, possibly implying the hydrothermal field is coming into the main mineralization. The sulfur isotope compositions of pyrites range from 4.30 to 9.98‰ (n=37), with distinct δ³⁴S variations in the individual Py-I crystal (> 1.5 ‰ within a 20 × 20 µm² region). This variation is attributed to changes in the relative proportion of sulfur sourced from (i) the shallow-origin reduced seawater via reduction by ferrous iron released from basalt (ii) the reduction of pre-existing anhydrite by later hydrothermal overprinting in the shallow subseafloor. These findings provide evidence for a model to better understand the effect of shallow seawater-hydrothermal circulation on the subseafloor stockwork mineralization of hydrothermal fields.

How to cite: Meng, X., Li, X., Jin, X., Chu, F., Zhu, J., and Wang, Y.: Subseafloor mineralization related to shallow seawater-hydrothermal circulation in the Longqi hydrothermal field, Southwest Indian Ridge (49.6°E): Evidence from in situ trace element and sulfur isotope compositions of pyrite varieties, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-907, https://doi.org/10.5194/egusphere-egu22-907, 2022.

Abstract

Iran is one of the most significant producers of copper in the world and hosts varieties of copper deposits, including porphyry Cu-Mo, vein-type, volcanogenic massive sulfide (VMS), sediment-hosted stratabound copper (SSC), Manto-type, and skarn.

Manto-type deposits are the second producer of copper in Iran, mostly hosted in basalt, basalt-andesite to andesite volcanic rocks. There are more than 40 Manto-type copper deposits and occurrences in Iran, such as Mari, Abbas-Abad, Vorezg, Robat, Simakan, and Sorkho, and most of them are economically deposits. Most of these deposits occur in Eocene volcanic rocks, and a small amount of them (such as KeshtMahki, Hassanabad, Khorjan, and Simakan) are hosted in the Early Cretaceous volcanic rocks that mainly concentrated in the Saveh-Yazd (in the Urumieh-Dokhtar magmatic belt), Qazvin-Zanjan, Sabzevar-Neishabour, Semnan-Shahroud volcanic zones, and eastern Iran.

The stratabound sulfide ores in these Manto-type copper deposits include chalcocite, chalcopyrite, and bornite, associated with covellite, malachite, atacamite, chrysocolla, and minor azurite in the oxidized and supergene ore zones. Sulfide mineralization usually occurs as a replacement in pyrites and feldspars, vein and veinless, and breccia, which is accompanied by carbonatization, propylitic, and minor sericite alterations. Geological and geochemical data indicate that most of these deposits formed within plate failed continental rift and back-arc extensional environments related to the subduction of the oceanic crust of neo-Tethys beneath the Iranian Plateau.

Furthermore, the temporal and spatial distribution of these deposits in terms of time shows a close relationship with evaporitic basins. This phenomenon suggests a genetic relationship between the formation of Manto-type deposits and the circulation of brines from adjacent evaporitic basins in shallow extensional tectonic environments.

How to cite: Momenipour, S., Rajabi, A., and Rezaei, S.: Metallogeny of Manto-type Copper Deposits of Iran: A Possible Link to the Evaporitic basins, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1555, https://doi.org/10.5194/egusphere-egu22-1555, 2022.

The Tomtor carbonatite complex with the area of 250 km² is confined to the Eastern framing of the Anabar Anteclise. It is located in the Udja province of ultrabasic alkaline rocks and carbonatites (Northeast of Siberian Platform). The Tomtor apatite-magnetite deposit is located on the Northeastern border of the carbonatite core. Apatite-magnetite ores (camaforites, phoscorites, nelsonites) form a series of ore steeply dipping (75-80^o) lenticular bodies of the Northwestern strike. The resources of the apatite-magnetite ores of the Tomtor massif are about 1 billion tons of iron (Tolstov, 1994).

The subject of research is magnetite with ilmenite decomposition structures, which composes up to 70% of phoscorite. The microprobe analysis established the compositions of 34 grains of magnetite isolated from the core of well No. 801; and ilmenite, which forms decomposition structures in these grains. Based on the compositions, the temperatures of their formation and oxygen fugacity were calculated.

Magnetite forms massive accumulations with hypidiomorphic crystals up to a few centimeters in size. Magnetite contains (in wt%): TiO₂ (1,21-4,72), MnO (0,48-1,9), MgO (0,08-0,41); Cr₂O₃ (до 0,14); BaO (до 0,32); ZnO (0,06-0,53); V₂O₃ (0,25-0,52).

Ilmenite varies within a wide range in the content of hematite minal (2.15 - 62.19%), corresponding to the ilmenite-hematite trend on the diagram in the coordinates TiO₂-Fe₂O₃-FeO. Ilmenite has a significant range of Mn contents (1.34-14); it may contain MgO (up to 1.57), Cr₂O₃ (up to 0.21), BaO (up to 1.09), ZnO (up to 0.2), V₂O₃ (up to 0.2).

It was established that the temperatures of magnetite formation create a continuous series from 459 to 914 ° C; oxygen fugacity (fO₂) varies respectively in the range from -10 to -24. These data confirm the magmatic nature of magnetite.

Magnetite is the main and one of the highest-temperature minerals of the Tomtor phoscorites. Accordingly, the upper limit of the obtained temperatures is the minimum for fractionation of the P-Fe melt and characterizes the onset of crystallization of phoscorites.

The obtained results confirm the magmatic nature of the phoscorites of the Tomtor massif from the initial P-Fe melt with the participation of the crystallization differentiation mechanism and reaffirm the conclusions of previous studies based on the results of studies of the mineralogical-geochemical (thermo-barometric) and structural and textural features of apatite-magnetite ores (Baranov, 2018; Baranov, 2020).

References

• Baranov L.N., Tolstov A.V. Typomorphic features of magnetite from tomtor massif camaphorites. Proceedings of higher educational establishments. Geology and Exploration. 2020;63(5):96—106. https://doi.org/10.32454/0016-7762-2020-63-5-96-106 (in Russian).
• Baranov, L.N., Tolstov, A.V., Okrugin, A.V., & Sleptsov, A.P. (2018). New in mineralogy and geochemistry of apatite-magnetite ores of the Tomtor massif, northeast of the Siberian platform. Ores and metals, (2) (in Russian).
• Tolstov, A.V., 1994. Mineralogy and geochemistry of apatite-magnetite ores of the Tomtor Massif (NorthwesternYakutia). Russ.Geol. Geophys.35,76–84.

How to cite: Baranov, L. and Tolstov, A.: Formation conditions for magnetite of phoscorites of the Tomtor massif (NE, Russia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6717, https://doi.org/10.5194/egusphere-egu22-6717, 2022.

Lateritic Ni-Co deposits are supergene deposits that develop due to intense weathering of the underlying ultramafic parent rocks and/or their serpentinized equivalents under tropical to sub-tropical climatic conditions. These deposits are important sources of valuable products such as iron, aluminium, nickel and cobalt. On the other hand, they directly point out typical climatic conditions. In this regard, geochronological studies on these deposits are very valuable to determine the timing of these paleo-climatic conditions that is not only important for better understanding of the paleoclimate of a region but also implying the favourable weathering period that can be targeted in exploration of undiscovered lateritic deposits in a region. Although there are limited studies about absolute dating of lateritic Ni-Co deposits by Ar/Ar dating of Mn oxides, there is no study on application of (U+Th)/⁴He hematite geochronology to these deposits.

The main aim of this study is to apply hematite (U+Th)/⁴He dating to the well-preserved Çaldağ lateritic Ni-Co deposit in Western Turkey. In this regard, we sampled the different parts of the lateritic profile from the different laterite zones at the Çaldağ deposit. In addition, we determined the different phases of iron oxides in order to identify the primary hematite, formed during primary lateritization with the help of polished thin section analyses. Then, we applied Scanning Electron Microscopy (SEM) analysis and TESCAN Integrated Mineral Analyser (TIMA) mineral mapping to identify the suitable areas on primary hematites for (U+Th)/⁴He dating. Finally, we obtained credible (U+Th)/⁴He ages from the four selected hematites.

We detected primary hematites at the base of the lateritic profiles (transition between the limonite zone and altered serpentinite) that are only in-situ parts of the laterites exposed in two different pits in the deposit. The ages we obtained from the hematites indicate 501.5 ky, 205.8 ky, 175.4 ky and 63.4 ky that are getting younger at the direction of weathering and corresponding to the interglacial periods recorded for the surrounded region. The ages propose that although the main intensive lateralization period is suggested as Middle Eocene or Miocene, the weathering processes should have lasted until Quaternary by some interruptions (?) during interglacial periods. Permeability of the overlying limestone should have been enhanced by the active tectonics of the region that in turn caused progressive deeper weathering during humid (and warm?) climates at interglacial periods. Briefly, our results suggest that in contrast to the short-living lateritization model for lateritic Ni-Co deposits, they may have multi-stage weathering history throughout their long-lasting development.

 This study presents the first hematite (U+Th)/⁴He dating of lateritic Ni-Co deposits and demonstrates the reliable use of this method on these deposits after a careful selection of hematite samples. In addition, the study has implications on potential contribution of dating lateritic weathering on understanding the paleoclimate of a region. Finally, knowledge of the favourable paleoclimatic periods of weathering of a region may help in determining the potential areas on ultramafic exposures for discovering new lateritic deposits.

This study was supported by the Scientific and Technological Research Council of Turkey (Grant No: 120Y275)

How to cite: Gülyüz, N., Kuşcu, İ., and Danisik, M.: Application of (U+Th)/4He hematite geochronology to the Caldag lateritic Ni-Co deposit, Western Turkey: implications for multi-stage weathering events during interglacial periods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11734, https://doi.org/10.5194/egusphere-egu22-11734, 2022.

A range of geochemical data has been used to navigate the complexity of systems that build critical energy resources.  Society’s need for hydrocarbons and metals are among these resources.  However, petroleum and ore deposits are traditionally studied as two completely different disciplines in geoscience.  We argue that they share a common heritage, or at a minimum an intersection in that the source rocks for oil also present source rocks for metals in sedimentary basins. 

In this presentation, we demonstrate the value of merging the study and teaching of these two disciplines: petroleum geology and ore deposit geology associated with sedimentary basins.  We present several possibilities, for example, (1) the hydrothermal fluid may be the hydrocarbon-carrying fluid, and (2) mixing of a hydrocarbon-bearing fluid with a metalliferous brine may precipitate sulfide intermingled with oil.  The end locations for the two resulting resources, however, may be spatially displaced from one another. 

Using a petroleum discovery from the Barents Sea as an example, we will illustrate the intimacy between metal and hydrocarbon deposition, and we will show petrographically the episodic, locally catastrophic events that formed the two resources in the same space.  We will show critical relationships between replacement textures and explosive overpressure textures, the latter leading to capture of chalcedony-oil and barite-oil emulsions.  We will show sulfide veins with visible oil inclusions.  Sphalerite-galena-fluorite are all critical players.  Our results highlight poorly understood infusions of sphalerite, co-mingled with oil, residing in biogenic carbonate rocks. 

Further, from the perspective of ore geology, our interpretations challenge classic replacement textures in some ore-forming environments.  Seemingly abrupt changes in sulfide mineralogy, or the switch to oxide minerals, may be violent rupture of earlier sulfides by catastrophic fluid ingress and infilling with a new mineralogy – rather than passive replacement as is the common interpretation. 

Designing strategic sampling in these complex environments often requires many analyses to build a forest of persuasive evidence to inform exploration models.  Reliance on small or isolated data sets may lead to highly erroneous interpretations.  Application of Re-Os geochronology and trace element geochemistry places fluid compositions in a time context, useful in both petroleum and sulfide settings.  At the same time, this information distinguishes slow continuous deposition from small catastrophic events during construction of petroleum and ore systems.  Long-term investment of industry in resource-related research rewards all parties, with the common goal of meeting the needs of society and expanding the technologies that will give humanity a more sustainable future.  Cross-disciplinary approaches, marrying metals and hydrocarbons, will be essential for efficient exploration and advancement of resource knowledge. 

Funding – Partial funding for this project was provided by Lundin Energy Norway.  Colorado State University-Geosciences provides no funding for the personnel and operation of the AIRIE Program and its Re-Os laboratories. 

How to cite: Stein, H., Hannah, J., Rameil, N., and Pedersen, J. H.: Slow and Steady or Episodically Catastrophic?  Timescales and Processes for Hydrocarbon and Metallic Resource Development, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5712, https://doi.org/10.5194/egusphere-egu22-5712, 2022.

Ore geology research conventionally relies on macroscopic and microscopic two dimensional (2D) observations of hand specimens and thin or polished sections. Although 2D techniques such as optical microscopy and scanning electron microscopy (SEM) are well-known and, therefore, commonly used for the characterization of ore samples, they are not capable of reproducing the real three-dimensional (3D) interior (Wang & Miller, 2020). A rising number of new developments in innovative characterization methods and data analysis methods in the field of ore geology research (e.g. Pearce et al., 2018; Warlo et al., 2021 & Guntoro et al., 2019) indicates the current necessity for adequate 3D ore characterization.

By combining X-ray micro-computed tomography (µCT) and SEM within a comprehensive workflow, we investigated a case study of the pegmatite-hosted Sn-Nb-Ta mineralization of the Gatumba area (Rwanda) (Dewaele et al., 2011). In this research, we present the possibilities to both visualize and quantify mineralogical data in 3D.

Automated mineralogy software within a SEM equipped with a field emission gun (Hrstka et al. 2018) served as an ideal tool to provide us the ground truth to interpret 3D µCT data. A new depth of information was obtained by describing the shape and orientation of individual minerals and the 3D inter-relationships between different mineral phases, by respectively using the Pearson correlation coefficient and the coefficient of variation. Additionally, relative elemental concentrations of niobium and tantalum for the solid-solution series columbite-tantalite and the concentration of economic interesting low atomic number elements (e.g. lithium) were deduced from µCT images.

The combination of SEM and µCT, within a lab-based workflow, enables the description of ore samples into 3D, which is especially important to provide representative mineral inter-relationships and quantitative estimations of economically interesting elements. Extending the potential of this technique to economic geology studies (e.g. core logging for exploration studies or to improve extraction procedures) will improve the sustainable management of ore deposits.

Acknowledgement
This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 101005611.

References
Dewaele et al., 2011. Late Neoproterozoic overprinting of the cassiterite and columbite-tantalite bearing pegmatites of the Gatumba area, Rwanda (Central Africa). Journal of African Earth Sciences 61(1): 10-26.

Guntoro et al., 2019. X-ray Microcomputed Tomography (μCT) for Mineral Characterization: A Review of Data Analysis Methods. Minerals 9(3): 183.

Hrstka et al., 2018. Automated mineralogy and petrology – applications of TESCAN Integrated Mineral Analyzer (TIMA). Journal of Geosciences 63(1): 47-63.

Pearce et al., 2018. Microscale data to macroscale processes: a review of microcharacterization applied to mineral systems. In Gessner, K., Blenkinsop, T. G. & Sorjonen-Ward, P. (eds), Geological Society, London, Special Publications 453(1): 7-39.

Wang & Miller, 2020. Current developments and applications of micro-CT for the 3D analysis of multiphase mineral systems in geometallurgy. Earth-Science Reviews 211: 103406.

Warlo et al., 2021. Multi-scale X-ray computed tomography analysis to aid automated mineralogy in ore geology research. Frontiers in Earth Science 9: 789372.

How to cite: Buyse, F., Dewaele, S., Boone, M., and Cnudde, V.: Application of a comprehensive workflow to characterize the petrology and mineralogy of ore samples in 3D., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7854, https://doi.org/10.5194/egusphere-egu22-7854, 2022.