The Li-Bearing Pegmatites from the Pampean Pegmatite Province, Argentina: Metallogenesis and Resources

The Li-bearing pegmatites of the Pampean Pegmatite Province (PPP) occur in a rare-element pegmatite belt developed mainly in the Lower Paleozoic age on the southwestern margin of Gondwana. The pegmatites show Li, Rb, Nb ≤ Ta, Be, P, B, Bi enrichment, and belong to the Li-Cs-Ta (LCT) petrogenetic family, Rare-Element-Li (REL-Li) subclass; most of them are of complex type and spodumene subtype, some are of albite-spodumene type, and a few of petalite subtype. The origin of the pegmatites is attributed predominantly to fractionation of fertile S-type granitic melts produced by either fluid-absent or fluid-assisted anatexis of a thick pile of Gondwana-derived turbiditic sediments. Most of the pegmatites are orogenic (530–440 Ma) and developed during two overlapped collisional orogenies (Pampean and Famatinian); a few are postorogenic (~370 Ma), related to crustal contaminated A-type granites. The pegmatites were likely intruded in the hinterland, preferably in medium-grade metamorphic rocks with PT conditions ~200–500 MPa and 400–650 °C, where they are concentrated in districts and groups. Known combined resources add up 200,000 t of spodumene, with variable grades between 5 and 8 wt.% Li2O. The potential for future findings and enlargement of the resources is high, since no systematic exploration program has yet been developed.This research was funded by CONICET grants during several periods and lastly by PIP 1489 from CONICET to M.F.M.-Z. The Spanish Ministry of Economy, Industry and Competitiveness (project no. RTI2018-094097-B-100, with ERDF funds), and the European Union’s Horizon 2020 Innovation Programme (grant agreement no. 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources) granted E.R.-R

U-Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Precise U-Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U-Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59 ± 0.29Ma followed by granodiorite porphyries at 90.47 ± 0.30 and 90.27 ± 0.60Ma and by crosscutting aplite dykes at 90.12 ± 0.36Ma. These units were overprinted by potassic alteration and host economic copper-(Mo-Au) mineralization. The main magmatic-hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26 ± 0.32Ma, only contains an uneconomic quartz-pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle-crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ɛ-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E-W extension associated with N-S compression, whereas the younger granodiorite dyke was emplaced during subsequent N-S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeabilit

Late Cretaceous porphyry Cu and epithermal Cu-Au association in the Southern Panagyurishte District, Bulgaria: the paired Vlaykov Vruh and Elshitsa deposits

Vlaykov Vruh-Elshitsa represents the best example of paired porphyry Cu and epithermal Cu-Au deposits within the Late Cretaceous Apuseni-Banat-Timok-Srednogorie magmatic and metallogenic belt of Eastern Europe. The two deposits are part of the NW trending Panagyurishte magmato-tectonic corridor of central Bulgaria. The deposits were formed along the SW flank of the Elshitsa volcano-intrusive complex and are spatially associated with N110-120-trending hypabyssal and subvolcanic bodies of granodioritic composition. At Elshitsa, more than ten lenticular to columnar massive ore bodies are discordant with respect to the host rock and are structurally controlled. A particular feature of the mineralization is the overprinting of an early stage high-sulfidation mineral assemblage (pyrite ± enargite ± covellite ± goldfieldite) by an intermediate-sulfidation paragenesis with a characteristic Cu-Bi-Te-Pb-Zn signature forming the main economic parts of the ore bodies. The two stages of mineralization produced two compositionally different types of ores—massive pyrite and copper-pyrite bodies. Vlaykov Vruh shares features with typical porphyry Cu systems. Their common geological and structural setting, ore-forming processes, and paragenesis, as well as the observed alteration and geochemical lateral and vertical zonation, allow us to interpret the Elshitsa and Vlaykov Vruh deposits as the deep part of a high-sulfidation epithermal system and its spatially and genetically related porphyry Cu counterpart, respectively. The magmatic-hydrothermal system at Vlaykov Vruh-Elshitsa produced much smaller deposits than similar complexes in the northern part of the Panagyurishte district (Chelopech, Elatsite, Assarel). Magma chemistry and isotopic signature are some of the main differences between the northern and southern parts of the district. Major and trace element geochemistry of the Elshitsa magmatic complex are indicative for the medium- to high-K calc-alkaline character of the magmas. 87Sr/86Sr(i) ratios of igneous rocks in the range of 0.70464 to 0.70612 and 143Nd/144Nd(i) ratios in the range of 0.51241 to 0.51255 indicate mixed crustal-mantle components of the magmas dominated by mantellic signatures. The epsilon Hf composition of magmatic zircons (+6.2 to +9.6) also suggests mixed mantellic-crustal sources of the magmas. However, Pb isotopic signatures of whole rocks (206Pb/204Pb = 18.13-18.64, 207Pb/204Pb = 15.58-15.64, and 208Pb/204Pb = 37.69-38.56) along with common inheritance component detected in magmatic zircons also imply assimilation processes of pre-Variscan and Variscan basement at various scales. U-Pb zircon and rutile dating allowed determination of the timing of porphyry ore formation at Vlaykov Vruh (85.6 ± 0.9Ma), which immediately followed the crystallization of the subvolcanic dacitic bodies at Elshitsa (86.11 ± 0.23Ma) and the Elshitsa granite (86.62 ± 0.02Ma). Strontium isotope analyses of hydrothermal sulfates and carbonates (87Sr/86Sr = 0.70581-0.70729) suggest large-scale interaction between mineralizing fluids and basement lithologies at Elshitsa-Vlaykov Vruh. Lead isotope compositions of hydrothermal sulfides (206Pb/204Pb = 18.432-18.534, 207Pb/204Pb = 15.608-15.647, and 208Pb/204Pb = 37.497-38.630) allow attribution of ore-formation in the porphyry and epithermal deposits in the Southern Panagyurishte district to a single metallogenic event with a common source of metal

Continuity in geochemistry and time of the Tertiary Bergell intrusion (Central Alps)

The calc-alkaline Bergell intrusion is classically mapped as a main tonalite and main granodiorite unit, whose ages have been determined at 32 and 30Ma, respectively. These units are separated by a mostly thin band interpreted as magmatic "transition zone”. High precision U-Pb dating of zircons and whole rock geochemistry of transition zone rocks are combined with a compilation of available geochemical analyses and ages to characterize the emplacement and magmatic evolution of the Bergell intrusion. Detailed field work shows that the transition zone is heterogeneous, characterized by multiple intrusions of tonalites to granodiorites to quartz-monzonites containing mafic enclaves and leucocratic dykes. Commonly, magmatic flow structures such as compositional banding, schlieren and accumulation of K-feldspar megacrystals are observed. The compositions of the transition zone intrusives as well as of the geochemically fairly heterogeneous tonalite and granodiorite units span a continuous range from 49-76wt% SiO2 for mafic enclaves to leucocratic dykes. Major and trace element trends are consistent with a predominant fractional crystallization. High precision U-Pb dating of single zircon grains separated from tonalites and granodiorites of the transition zone yields crystallization ages of 31.22±0.04 and 31.13±0.10Ma, respectively. Hence, the transition zone represents an own phase of intrusion during which a range of magma types were coeval. The available ages and compositional data suggest magmatic activity over the entire range from 28 to 33Ma across the Bergell intrusion, which should not be described by two main "tonalite” and "granodiorite” stages but by a model with several magmatic main phases during which most magma types developed multiply. Geobarometry of tonalite boulders in the Como molasse (yielding a zircon crystallization age of 32.06±0.13Ma) indicate average erosion rates for the Bergell intrusion of 1.9mm/a between 32-25Ma and of 0.5mm/a since then

Early to Mid-Miocene syn-extensional massive silicic volcanism in the Pannonian Basin (East-Central Europe): Eruption chronology, correlation potential and geodynamic implications

eruptions of compositionally diverse magmas during the Neogene to Quaternary. The long-lasting magmatic activity began with some of the most voluminous silicic eruptions in Europe for the last 20Myr. This paper describes the eruption chronology of this volcanic activity using new, high-quality zircon U-Pb dates, and provides the first estimates on the volume and areal distribution of the volcanic products, characterizes the magma composition and discusses the silicic magmatism in a region, where the continental lithosphere underwent significant extension. A thorough zircon geochronological study was conducted on samples collected from ignimbrites and pyroclastic fall deposits exposed in the Bükkalja Volcanic Field. In-situ LA-ICP-MS analysis on zircon grains provided a fast, cheap and accurate method for such detailed geochronological work, where the volcanic products occur in scattered outcrops that often have poor stratigraphic constraints. The interpreted eruption ages were determined from the youngest zircon age population within the samples and this methodology was validated by new single zircon CA-ID-TIMS dates and sanidine Ar-Ar ages. The volcanism covers about 4Myrs, from 18.2Ma to 14.4Ma and involved at least eight eruptive phases. Within this, four large eruption events were recognized at 14.358±0.015Ma (Harsány ignimbrite), 14.880±0.014Ma (Demjén ignimbrite), 16.816±0.059Ma (Bogács unit) and 17.055±0.024Ma (Mangó ignimbrite), which are found in areas across the Pannonian Basin and elsewhere in central Europe. Considering all the potential sources of silicic ash found in the Paratethys sub-basins around the Pannonian Basin and along the northern Alps and in central Italy, we suggest that they were probably derived almost exclusively from the Pannonian Basin as shown by zircon U-Pb dates presented in this paper and published comparable age data from several localities. The new eruption ages considerably refine the Early to Mid-Miocene chronostratigraphy of the Pannonian basin, where the extensive volcanoclastic horizons are used as important marker layers. The cumulative volume of the volcanic material formed during this 4Myr long silicic volcanism is estimated to be >4000km⁠3, consistent with a significant ignimbrite flare-up event. Zircon crystallization ages indicate magma intrusions and formations of magma reservoirs in the continental crust for prolonged period, likely >1Myr prior to the onset of the silicic volcanism accompanied with sporadic andesitic to dacitic volcanic activities. Mafic magmas were formed by melting of the thinned lithospheric mantle metasomatized previously by subduction-related fluids and emplaced at the crust-mantle boundary. They evolved further by assimilation and fractional crystallization to generate silicic magmas, which ascended into the pre-warmed upper crust and formed extended magma storage regions. Zircon Hf isotope and bulk rock Sr-Nd isotopic data indicate a sharp decrease of crustal and/or increase of asthenospheric mantle input after 16.2Ma, suggesting that by this time the crust, and the lithospheric mantle was considerably thinned. This magmatism appears to have had a structural relationship to tectonic movements characterized by strike-slip and normal faults within the Mid-Hungarian Shear Zone as well as vertical axis block rotations, when the two microplates were juxtaposed. Our new zircon ages helped to refine the age of two major block-rotation phases associated with faulting. This volcanism shows many similarities with other rift-related silicic volcanic activities such as the Taupo Volcanic Zone (New Zealand) and the Basin and Range Province (USA)

Geochemical and isotopic evidence for Carboniferous rifting : mafic dykes in the central Sanandaj-Sirjan zone (Dorud-Azna, West Iran)

In this paper, we present detailed field observations, chronological, geochemical and SrNd isotopic data and discuss the petrogenetic aspects of two types of mafic dykes, of alkaline to subalkaline nature. The alkaline mafic dykes exhibit a cumulate to foliated texture and strike NWSE, parallel to the main trend of the region. The 40Ar/39Ar amphibole age of 321.32 0.55 Ma from an alkaline mafic dyke is interpreted as an indication of Carboniferous cooling through ca. 550 C after intrusion of the dyke into the granitic Galeh-Doz orthogneiss and Amphibolite-Metagabbro units, the latter with Early Carboniferous amphibolite facies grade metamorphism and containing the Dare-Hedavand metagabbro with a similar Carboniferous age. The alkaline and subalkaline mafic dykes can be geochemically categorized into those with light REE-enriched patterns [(La/Yb)N = 8.329.28] and others with a rather flat REE pattern [(La/Yb)N = 1.16] and with a negative Nb anomaly. Together, the mafic dykes show oceanic island basalt to MORB geochemical signature, respectively. This is consistent, as well, with the (Tb/Yb)PM ratios. The alkaline mafic dykes were formed within an enriched mantle source at depths of 90 km, generating a suite of alkaline basalts. In comparison, the subalkaline mafic dykes were formed within more depleted mantle source at depths of 90 km. The subalkaline mafic dyke is characterized by 87Sr/86Sr ratio of 0.706 and positive Nd(t) value of + 0.77, whereas 87Sr/86Sr ratio of 0.708 and Nd(t) value of + 1.65 of the alkaline mafic dyke, consistent with the derivation from an enriched mantle source. There is no evidence that the mafic dykes were affected by significant crustal contamination during emplacement. Because of the similar age, the generation of magmas of alkaline mafic dykes and of the Dare-Hedavand metagabbro are assumed to reflect the same process of lithospheric or asthenospheric melting. Carboniferous back-arc rifting is the likely geodynamic setting of mafic dyke generation and emplacement. In contrast, the subalkaline mafic sill is likely related to the emplacement of the Jurassic Darijune gabbro.(VLID)223441

Sulfide trace element signatures and S- and Pb-isotope geochemistry of porphyry copper and epithermal gold-base metal mineralization in the Elatsite–Chelopech ore field (Bulgaria)

The Elatsite–Chelopech ore field in the northern part of the Panagyurishte district in Central Bulgaria comprises numerous spatially associated porphyry copper and epithermal gold deposits and prospects. In addition to the mineralization and alteration features, trace elements, lead and sulfur isotope signatures of sulfide minerals from porphyry copper, base metal and gold-base metal deposits/prospects have been studied. LA-ICP-MS analyses of pyrite, arsenopyrite and sulfosalt minerals validate them as major carriers for Au, Ag, Sb, Se and Co. Pyrite from the three types of mineralization has specific geochemical characteristics. Pyrite from the porphyry copper deposits/prospects has generally lower total trace element content compared to pyrite from the epithermal prospects, except for Se, Co and Ni. Pyrite from the base metal and gold-base metal veins is enriched in As, Au, Ag, Sb and Pb. In pyrite from the base metal deposits, Co and Ni have contents comparable to the pyrite from the porphyry copper deposits, while pyrite from the gold-base metal veins shows lower Co and Ni. Arsenopyrite from these deposits shows similar features. Similarly, sphalerite from the gold-base metal veins also has lower Co content compared to sphalerite from the base metal veins but higher In and Cu contents. In addition to the close spatial relationships between the Elatsite and Gorna Kamenitsa porphyry Cu deposits and Negarstitsa-West and Dolna Kamenitsa base metal prospects, as well as similarities in the mineralization and alteration styles, the lead isotopic (206Pb/204Pb = 18.61–18.68, 207Pb/204Pb = 15.64–15.65 for porphyry and 206Pb/204Pb = 18.55–18.67, 207Pb/204Pb = 15.64–15.68 for base metal) and sulfur isotopic (δ34S values of −3 to +1‰ for porphyry and δ34S values of −1.7 to +3.5‰ for base metal) signatures of sulfides support the idea of a genetic link between these two types of deposits. The porphyry and base-metal mineralization result from a common major ore-forming event during the Late Cretaceous, corresponding to deep/higher-temperature and shallower/distal/lower-temperature environments, respectively. In particular, more radiogenic lead (206Pb/204Pb = 18.41–18.47, 207Pb/204Pb = 15.67–15.76) and slightly different sulfur isotopic compositions (δ34S values of +3.5 to +10.6‰) of sulfides from the distal gold-base metal veins of Kordunsko Dere, Svishti Plaz and Shipkite might be a consequence of the interaction of the ore-forming fluids with an external older crustal and isotopically positive S source. Alternatively, a different fluid source/event for the formation of these gold-base metal veins may be suggested

Provenance of the Ciénaga de Oro Formation: unveiling the tectonic evolution of the Colombian Caribbean margin during the Oligocene - Early Miocene

Se realizó el estudio de una sección estratigráfica en el Cinturón Plegado y de Cabalgamiento de San Jacinto, localizado en el noroccidente de Colombia. En esta sección aflora parte de la Formación Ciénaga de Oro del Oligoceno-Mioceno temprano. Este trabajo analiza la procedencia de los sedimentos, utilizando un enfoque de múltiples herramientas que incluye: (I) conteo de clastos de areniscas y conglomerados con malla, (II) minerales pesados, y (III) paleocorrientes y (IV) edades U-Pb de circones detríticos. La secuencia sedimentaria fue depositada en un ambiente deltaico a transicional, con reducción del efecto del oleaje y la marea junto con el incremento de la dominancia de los procesos transicionales de río hacia el tope de la sección. Se identificó dos áreas fuentes de una provincia de arco disectado: principalmente un área fuente de composición granítica a pegmatítica y un área fuente secundaria de composición ígnea a básica, localizadas al este y suroeste de la posición actual de la secuencia. El análisis geocronológico de circones detríticos muestra cuatro poblaciones de edades: (I) Devónico-Pérmico, (II) Pérmico-Triásico, (III) Jurásico y (IV) Cretácico. Las edades máximas de depositación corresponden a 75,2±0,9 Ma en la parte más baja de la sección, 68,9±0,6 Ma en el medio y 74,5±0,7 Ma para la parte superior de la sección. Se propone que el material depositado en COF fue suministrado desde sistemas fluviales del sur hacia el norte, que erosionaron bloques de basamento expuesto y su cobertura sedimentaria (Cretácico tardío a Paleógena) durante el Oligoceno. Este sistema fluvial transportó sedimentos desde plutones tipo Batolito Antioqueño del Cretácico Tardío y rocas máficas/ultramáficas, como las encontradas en las Cordillera Central y Occidental.A stratigraphic section in the San Jacinto fold and thrust belt located at northwestern Colombia was studied. This section displays part of the Oligocene-Early Miocene Ciénaga de Oro Formation (COF). This work analyses the sediments provenance using a multi-tool approach which include: (I) conglomerate and sandstone counting clast with mesh, (II) heavy minerals assemblages, (III) paleocurrents and (IV) U/Pb detrital zircon ages. The sedimentary sequence was deposited in deltaic to transitional environment deposition, with reduction in the waves and tidal effect, and increase in the dominance of transitional river processes upward the section. Two main source areas have been identified from a dissected arc province: a main granitic to pegmatitic and a secondary basic igneous source rocks, located to the east and southwest of the current position. Detrital zircon U-Pb geochronology analysis display four age populations: (I) Devonian-Permian, (II) Permian-Triassic, (III) Jurassic and (IV) Cretaceous, with maximum deposition ages of 75.2±0.9 Ma in the lower part of the section, 68.9±0.6 Ma in the middle and 74.5±0.7 Ma for the upper part. It is proposed that COF was sediment-supplied by a south-to-north flvial system, which drained exposed basement blocks and their late Cretaceous to Paleogene sedimentary cover during the Oligocene. This fluvial system carried sediments from late Cretaceous plutons like the Antioqueño Batholith and mafi/ultramafi rocks, which make up the basement of the Western and Central Cordilleras