Volcano-sedimentary Complex Research Articles

Updating Geological Information about the Metallogenesis of the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB) represents one of the largest districts of volcanogenic massive sulfide (VMS) deposits in the world, and is a critical source of base metals (Cu, Pb, and Zn) for Europe. Confirmed resources exceed 1700 Mt of massive sulfides with grades of around 1.2% Cu, 1% Pb, and 3% Zn as well as more than 300 Mt of stockwork-type copper mineralization. Significant resources of Sn, precious metals (Au and Ag), and critical metals (Co, Bi, Sb, In, and Se) have also been evaluated. The genesis of these deposits is related to a complex geological evolution during the late Devonian and Mississippian periods. The geological record of such evolution is represented by three main lithological units: Phyllite–Quartzite Group, the volcano–sedimentary Complex (VSC), and the so-called Culm Group. The sulfide deposits are located in the VSC, associated with felsic volcanic rocks or sedimentary rocks such as black shales. The massive sulfide deposits occur as tabular bodies and replacement masses associated with both volcanic and sedimentary rocks. Their mineralogical composition is relatively simple, dominated by pyrite, chalcopyrite, sphalerite, and galena. Their origin is related to three evolutionary stages at increasing temperatures, and a subsequent stage associated with the Variscan deformation. The present paper summarizes the latest developments in the IPB and revises research areas requiring further investigation.

New Data on the Neogene Volcano-sedimentary Complex of the Icha Depression: The Tyrkachyn Section (West Kamchatka)

New Data on the Neogene Volcano-sedimentary Complex of the Icha Depression: The Tyrkachyn Section (West Kamchatka)

The Charnwood Terrane revisited: an integrated petrogenetic and petrophysical model for crustal structure in southern Britain

We based an integrated petrological and petrophysical model for the Ediacaran crust of southern Britain on a review of the c. 570–550 Ma Charnian volcano-sedimentary complex. The latter was emplaced in a magmatic rift wedge within the juvenile continental crust of the c. 720–600 Ma Marches Terrane, a subduction magmatic domain formed at the margin of the Gondwana palaeocontinent. The Charnian magmatic arc is characterized by primitive island arc tholeiite to more evolved calc-alkaline compositions. The inversion of aeromagnetic potential field data and petrophysical modelling reveals details of the internal structure of the Charnian Domain, including a median rift, superimposed annular structures and partitioning lineaments. The modelling suggests that the arc foundation could incorporate magnetite-rich cumulates, which may explain the anomalous geophysical properties, including crustal thickness, rigidity and buoyancy. There is no evidence for significant tectonic displacement between the Charnian Domain and its Marches Terrane host. Instead, the domain likely occupies a wedge-shaped arc/marginal rift basin complex, propagated from a neighbouring ocean into the Gondwana margin. Contemporaneous volcanic rift successions in the Welsh Borderland and Wales of the 570–550 Ma Charnian magmatic phase developed in coeval ensialic rifts within less strongly extended Marches Terrane lithosphere. A comparable diversity of subduction-related magmatism is found in the Neogene–recent Hikurangi destructive margin of New Zealand, providing a plausible analogue for Charnian magmatism. Supplementary material: Supplementary Publication 1 (borehole geophysical log correlation; petrophysical data table; unannotated geophysical maps and sections) and Supplementary Publication 2 (geochemistry analytical conditions and data table) are available at https://doi.org/10.6084/m9.figshare.c.6805248

Growth faults and avalanches: Reconstructing Paleoarchean basins in the Pilbara and Kaapvaal cratons

Four new volcano-sedimentary complexes (VSC's), respectively c. 3510, 3460, 3430, and 3320 Ma old, are identified in the East Strelley, Coongan, and Kelly belts of the East Pilbara craton and compared with the extraordinarily complete c. 3450 Ma Buck Reef-VSC in the southern African Kaapvaal craton. The VSC’s reveal an intricate relationship between volcanic deposition, sedimentation, development of syndepositional fault arrays, both extensional and contractional, and magmatism. The geometry and kinematics of these fault systems were analyzed after restoring the tilt of the stratigraphic sequences back to the depositional horizontal. The growth fault arrays are interpreted to have been generated by lack of lateral support of depositional basin margin prisms as known from present-day deltas and passive margins. This ‘basin margin collapse’ scenario for deformation and kinematics of the topmost section of the crust relies on topographic relief combined with vertical crustal oscillation. The relationship between supracrustal collapse and coeval deformation on deeper-seated detachments within the basement of the Pilbara remains as yet unsolved.The restoration corroborates the (semi-)circular basin architecture we proposed in 2017, which preceded, and is unrelated to, the present-day configuration of granitoid complexes and greenstone belts. The new findings also assess an early, syndepositional presence of the east–west Warrawoona Lineament as a major dividing line of as yet unknown structural character between two areas of basin superposition.For the Coonterunah Subgroup a multistorey architecture is established: the Table Top/Coucal-VSC with its near-water level chert top is overlain by regularly bedded Double Bar Basalt. The ensemble is truncated by the newly introduced tectono-stratigraphic Bergamina Unit, interpreted as a mega-avalanche emplaced somewhere between 3496 and 3466 Ma, possibly time-equivalent to the Duffer Fm.The crustal depths of the detachments below the (water-level) tops of all VSC’s identified, in other words the thicknesses of the VSC’s, are used as proxy for determining minimum basin centre depths ranging from 1000 to 3800 m. The greatest depth was reached in the North and South Coongan Basins, where voluminous bimodal volcanism of the Duffer Fm, maximum subsidence and deposition rates resulted in maximum basin margin instability.

New investigations about three young volcano-sedimentary systems of Velay-Vivarais (France) and co-evolution humans-volcanoes in the background

After presenting the geographical framework of this region on the south-eastern edge of the Massif Central which saw the birth of volcanology and still fuels debates on the contemporaneity of man and extinct volcanoes, we recall the general context and chronology of recent volcanic activity in the Velay-Vivarais, known as the “Young Volcanoes of Ardèche”. We insist on the contra- dictory results provided by the different dating methods used in recent decades (14C, OSL, TL, K/Ar and 40Ar/39Ar) and provide new results about three localities: the Grand Suc de Breysse (Présailles, Haute-Loire), the Suc de Bauzon whose flow dammed the Palaeo-Loire at Rieutord (Usclades-et-Rieutord, Ardèche) and the Issarlès maar (Le Lac d’Issarlès, Ardèche) with lacustrine sedi- mentary archives preserved below a 108.5 m waterbody. The eruption of the Grand Suc de Breysse began with a phreatomagmatic phase during MIS 5 (OSL, TL, K/Ar). The filling of the Rieutord volcanic dam paleo-lake fossilises a basaltic flow dated at 85 ± 4 ka (K/Ar) and continues during MIS 3: in its central part, the upper part of the preserved deposit is dated between 41.7 and 18.2 ka (14C and OSL); in its upstream part, deltaic deposits of the paleo-Loire are dated between 52 ± 2 and 35 ± 3 ka (OSL). The eruption of the Issarlès maar is dated at 54 ± 8 ka (TL), confirming that it belongs to a recent phase of the volcanism of the “Young Volcanoes of Ardèche”. At the moment, no Palaeolithic vestiges are directly associated with these three volcano-sedimentary complexes.

Mineralogie sulfidických rud z Měděné štoly ve zlatohorském rudním revíru

Until 1993, sulfide ores of copper, lead and zinc, as well as native gold were mined in the Zlaté Hory ore district in the Jeseníky Mountains. These deposits occur in the Devonian volcano-sedimentary complex of the Vrbno Group, which consists of quartzites, phyllites, limestones and metamorphic igneous rocks of intrusive and extrusive nature. The main ore bodies are located in a quartzite horizon containing lenses of felsic metavolcanic rocks or in the underlying and overlying rocks (mainly phyllites). Sulfide mineralization of the Měděná Adit in the Zlaté Hory ore district concentrated in greenschists containing three mineral assembblages: i) chlorite + quartz + albite + barian feldspar + siderite + dolomite (ankerite) ± ilmenite, ii) chlorite + phlogopite + quartz + albite + siderite + dolomite (ankerite) ± magnetite ± ilmenite, iii) chlorite + muscovite + quartz + albite + ilmenite ± siderite ± magnetite. Micas have elevated barium contents (2.2 to 5.5 wt. % BaO in phlogopite, 2.6 to 4.6 wt. % BaO in muscovite) and represent the dominant carrier of this element in the rock. In the case that mica is absent in the rock, barium is bound in barian feldspar. When content of quartz in these greenschists is high, they pass into quartzite. Three types of sulfide ore were found in the Měděná Adit: A) banded copper ore in biotite-chlorite greenschist, which is formed dominantly by disseminated pyrite and pyrrhotite, accompanied by a small amount of chalcopyrite (the ore contains approx. 0.7 wt.% Cu), B) disseminated copper mineralization in quartz-rich bands or quartzite intercalations in chlorite greenschist, consisting mainly of pyrrhotite, less voluminous pyrite, and small amounts of chalcopyrite and galena (the ore contains approx. 0.3 wt.% Cu, the lead content is highly variable, up to 0.15 wt.% Pb), C) vein-like copper ore in greenschist with chalcopyrite dominating over pyrrhotite and pyrite (the ore has a very high copper content, 13.6 and 24.7 wt.% Cu in two analyzed samples). With its mineral composition, structural features and the character of the ore-bearing rocks, disseminated copper mineralization is similar to the Cyprus-type ores (so-called Cu-pyrite ores). The vein copper mineralization is probably a result of copper remobilization during regional metamorphism.

Kvartérní sedimenty a nálezy rostlinných fosilií v Salvadoru, Střední Amerika

Development cooperation projects implemented by the Czech Geological Survey in the area of Central America, focused on the evaluation of natural hazards, took place in the years 1997–2009. They started in Nicaragua (since 1997), continued in El Salvador (since 2003) and then also in Costa Rica (since 2006). The results of these projects were always handed over to local organizations (INETER, SNET and MINAE) in the form of final reports, and summarized last year in the book by Hradecký et al. 2021. As a supplement to this book, we present here some other findings of projects in El Salvador (from the years 2003–2005) that did not fit into its scope. They relate to the geology of Quaternary sediments and interesting findings of plant fossils preserved in the Neogene volcanosedimentary complexes. In the 2003 stage, work took place in the Gulf of Fonseca in south- -eastern part of El Salvador, with the dominant volcano Conchagua and the important port of La Unión. In addition to classic Quaternary sediments, the following phenomena were described: oyster hems (rims) around the islands of Periquito and Perico, volcaniclastic rocks (“tobas”) fallen into the lake environment near the Los Chorros lagoon (Břízová et al. 2004), and polygenetic sediments on the slopes of the formerly active volcano Conchagua, showing the existence of debris flows and lahars. Plant fossils have been found at one locality only, in fine-grained ash deposits of the maar sequence near El Naranjo (Figs 1 to 3). In the 2004 stage, work took place inland, in an area north of the capital city San Salvador, with the dominant volcano Guazapa. In addition to the classical Quaternary sediments, the following phenomena were described: polygenetic sediments of the depressions north of the town of Aguilares (Figs 4 to 9) and outcrops of lake sediments, exposed in the north of the studied territory on steep slopes near the Río Lempa dam (Fig. 10), south-east of the city of Colima (Havlíček – Vorel 2005). In the same area, on the bank of the dam near the town of San Cristobal, interesting consolidated (cemented) mudflows with the occurrence of fossil wood were also documented (Figs 11 and 12). In the year 2004, a paleontological expedition to the Río Sisimico canyon, about 40 km to the SE from the primarily studied area (Figs 13 to 16), was also carried out. The findings of plant remains from this locality are shown in Figs 17 to 22. Plant remains were further found at two localities in the primarily studied area: Suchitoto (Figs 23 to 29) and in the area south of El Molino (only indeterminable remains). Charred (and buried) tree trunks were also found in the white pumice tuffs called “Tierra Blanca” in several places of the studied area (Fig. 30). In the 2005 stage, the work took place in the north-western part of El Salvador, near the borders with Guatemala and Honduras, in the vicinity of the Metapán city. In addition to classic Quaternary sediments (Figs 31 and 32), the following phenomena were described: three generations of alluvial fans (alluvial gravels and sands) near the Metapán city, “kettle holes” created by water erosion in the river bottom (Fig. 33) and aeolian (wind-deposited) sediments from the Matalapa desert. The most interesting, however, were the secondarily tilted (and not yet fully consolidated) gravels and sands of the oldest generation of alluvial fans in the south-western surroundings of the city of Metapán (Figs 34 to 39). In the open cut along the CA12 road to Metapán (La Pedrera area, Fig. 40), small, although indeterminable remains of flora and possibly also fauna (fish scales?) in diatomite-like rocks were found. However, the locality is promising for future research. All the findings published in this paper were also mentioned in the final reports which were handed over in Spanish translation to the Salvadoran SNET institution (Hradecký et al. 2003, 2004 and 2005).

Geology, Geochemistry, and Geochronology of the Giant Rio Tinto VMS Deposit, Iberian Pyrite Belt, Spain

Abstract The Rio Tinto deposit is a giant volcanogenic massive sulfide deposit (VMS) that contains more than 500 Mt of pyrite-rich massive sulfides and more than 2 Gt of mineralized stockwork. Three broad lithostratigraphic groups occur in the regional stratigraphy: the phyllite-quartzite group, the volcano-sedimentary complex, and the Baixo Alentejo Flysch Group. These three major packages reflect the evolution of a depositional environment from a stable platform to deposition in pull-apart continental basins during oblique subduction and collision and coeval synorogenic flysch sequence. The volcano-sedimentary complex, which hosts massive sulfide mineralization at Rio Tinto, can be divided into four major units: (1) the Mafic Siliciclastic Unit, (2) the Lower Sedimentary Unit, (3) the Felsic Unit, and (4) the Upper Sedimentary Unit. The Felsic Unit is further subdivided based on new U-Pb zircon geochronology into three distinct subunits. Felsic Unit I (ca. 356 Ma) includes dome complexes dominated by rhyodacite and reflects the onset of felsic magmatism in the region. Felsic Unit II (ca. 352–348 Ma) represents the main interval of volcanic activity, also dominated by rhyodacite domes and related aprons, and is associated with widespread VMS mineralization. Felsic Unit III (ca. 340 Ma) reflects a late pulse of rhyolitic volcanism. Massive sulfides occur as two different styles of mineralization: (1) replacive ores as discordant pipes hosted by glass-rich felsic rocks and enclosed by a large zone of stockwork-like mineralization and (2) overlying shale-hosted exhalative mineralization in small anoxic basins, probably formed during the collapse of the volcanic domes of Felsic Unit II in the Middle-Late Tournaisian. New lithogeochemical data illustrate two types of mafic rocks in the Mafic Siliciclastic Unit: a basaltic andesite and a high–Ti-Zr basalt, both of tholeiitic affinity. Using immobile element ratios (heavy rare earth elements [HREEs], Al, Y, Zr, and Ti) of the Felsic Unit, fundamental differences have been recognized between the subunits. The unmineralized Felsic Unit I is characterized by high Zr content (225–300 ppm) and a pronounced Eu negative anomaly, and probably represents the most fractionated rocks. Felsic Unit II is characterized by Zr values between 50 and 200 ppm. The low Zr values of the mineralized unit contrast with the typically high Zr values of the felsic rocks related to volcanogenic massive sulfides elsewhere and, at a regional scale, can help to discriminate potentially fertile domes from barren volcanism.

Lithostratigraphy of the Bumbeni Complex and its associated subdivisions, South Africa

Abstract The Bumbeni Complex represents an Early Cretaceous volcanic complex that developed at the southern termination of the Lebombo mountain range in northern KwaZulu-Natal, South Africa. The volcano-sedimentary complex intrudes and disconformably overlies the Lebombo Group of the Karoo Large Igneous Province. The volcano-stratigraphy is defined by an assemblage of volcanic and volcaniclastic rocks as well as late stage quartz-syenite intrusions. Based on current geological and geophysical studies the complex is considered to represent the remnants of a collapsed cauldron structure. The stratigraphic succession is intricate and laterally discontinuous, comprising mafic and felsic lava flows, welded and non-welded tuffs, ignimbrites, lahar deposits, rhyolite domes and dykes and coarse-grained syenitic rocks. Rhyolite dome formation and collapse, and associated plinian eruptions and column collapse, were largely responsible for the variety of volcaniclastic rocks, including classic air-fall tuff deposits. The complex forms part of a northeast trending volcanic basement lineament known as the Bumbeni Ridge defined by aeromagnetic data.

Ordovician stratigraphy and benthic community replacements in the eastern Anti-Atlas, Morocco

Abstract The Anti-Atlas contains a thick, volcanic-free Ordovician succession that originally deposited in a passive-margin basin. Three main sedimentary packages are bounded by major unconformities: (i) the Tremadocian–Floian Lower Fezouata and Upper Fezouata formations, which unconformably overlie a palaeorelief of Cambrian rifting volcanosedimentary complexes, and are subsequently topped by a Dapingian paraconformable gap; (ii) the Darriwilian–Katian Tachilla Formation and First Bani and Ktaoua groups, the latter unconformably overlain by a Hirnantian glaciogenic succession; and (iii) the Second Bani Group, which subsequently infilled the former glaciogenic palaeorelief. Due to the scarcity of carbonate interbeds for etching analyses, leading to rare references of conodonts, the global Ordovician chart is interpolated on the basis of microphytoplancton (acritarchs and chitinozoans), regional graptolites and brachiopods. The Ordovician counter-clockwise rotation of Gondwana led its Moroccan margin from mid- to high-latitude positions, leading to the onset of a siliciclastic, wave- and storm-dominated platform. Flooding surfaces are marked by shelly silty carbonate interbeds that reflect the episodic development of echinoderm–bryozoan meadows during Katian times; in areas protected from siliciclastic input, they reached massive and bedded bioaccumulations (Khabt-el-Hajar Formation). The Hirnantian glaciation controlled the incision of numerous tunnel channels, infilled with both alluvial to fluvial sediments and glaciomarine diamictites. The Hirnantian palaeorelief was definitively sealed during Silurian times.

Mapping and Petro-Structural Study of Northern Komborodougou Formations, in Korhogo Gold District: A Substantial Contribution to the Discovery of a Potential Gold Mineralization in Birimian Greenstone Belts

The Gold District of Korhogo, in the northern region of C?te d’Ivoire, holds enormous potential for gold mineralizations, some of which are under exploration phase and others in exploitation phase (example of Tongon Gold Mine). Dormant since 1998, Mapping Services of most of the West African countries hardly provide geological maps at the scales of: 1/200,000, 1/50,000 and 1/25,000. This situation of unavailability of detailed geological maps does not help mining operators in the selection of prolific areas and also in the interpretation of in soil geochem anomies or gold mineralizations. Consequently, during the years 2020 and 2021, we have undertaken a campaign of geological mapping and petro-structural study of the northern sector of Komborodougou, located in the southern extension of Banfora Birimian Belt. This work, which allowed the realization of a geological map at 1/20,000 scale, reveals that: the mapped area includes three (3) major lithological units: 1) a volcano-sedimentary unit made up of metasediments (metaarenites, metasiltites and metaflyschs) and metavolcanites (metabasalts), which are metamorphosed and outcrop in the form of schists; 2) a metaplutonic and intrusive unit composed on the one hand of quartz-diorites and metagabbros, and on the other hand of granites and granodiorites; 3) and finally, a unit of dikes formed by microgranites, microgabbros, aplites and quartzites. The volcano-sedimentary complex is affected by a regional fold with an axis subparallel to the regional tectonic grain and an S1 schistosity oriented NE-SW to NNE-SSW with steep dips (>60o), except for those of the metaflyschs which are weak (o); a regional NW-SE compression would be at the origin of the setting of this schistosity. The volcano-sediment and metaplutonite complex is crossed in a NNE-SSW direction by a senetral shear-zone or main shear-zone and secondary shear-zones oriented sometimes NE-SW or N-S. These shear-zones are intersected by more or less dextral or senestral strike-slip faults of NW-SE and E-W trends. N-S to NNE-SSW (N0o - N20o) and NW-SE (N130o - N160o) vein systems associated with the various shear-zones are the hosts of the gold mineralization in the region. These veins have been mined by orpaillors for more than two decades. The northern sector of Komborodougou is in the NNE continuity of the gold mineralization highlighted by the mining company Mako Gold Sarl on its Gogbala and Tchaga prospects, Napie project.

Geochemistry, Formation Settings, and Ore Potential of the Volcano-Sedimentary Complexes of Pryangarya, Yenisei Ridge

Geochemistry, Formation Settings, and Ore Potential of the Volcano-Sedimentary Complexes of Pryangarya, Yenisei Ridge

The Ludicovian of the Raahe–Ladoga Zone of the Fennoscandian Shield (Isotope-Geochemical Composition and Geodynamic Nature)

Abstract —In the northern Ladoga area, the age of the Sortavala Group rocks in the southeast of the Raahe–Ladoga zone of junction of the epi-Archean Fenno-Karelian Craton and the Paleoproterozoic Svecofennian province, their relationship with dome granitoids, the age of the provenances, and the time of metamorphic processes were estimated. The study was focused on the Nd isotope composition of rocks, the geochemical and isotope-geochronological parameters of zircon from the granite-gneisses of the Kirjavalakhti dome, the basal graywackes of the lower unit and the trachytes of the middle unit of the Sortavala Group, and the plagio- and diorite-porphyry dikes cutting the volcanosedimentary units of this group. The new isotope-geochemical data show a Neoarchean age of the granitoids of the Kirjavalakhti dome (2695 ± 13 Ma) and their juvenile nature (εNd(T) = +1.5). The granitoids underwent tectonometamorphic transformations (rheomorphism) in the Paleoproterozoic (Sumian) (2.50–2.45 Ga), which are recorded in the U–Th–Pb isotope system of the rims of the ancient cores of zircon crystals. The volcanosedimentary complex of the Sortavala Group formed on the heterogeneous polychronous (3.10–2.46 Ga) continental crust of the epi-Archean Fenno-Karelian Craton. With regard to the errors in determination of the age of clastic zircon, the minimum concordant U–Th–Pb ages of 1940–1990 Ma of detrital zircon from volcanomictic graywackes of the Pitkyaranta Formation can be taken as the upper age bound of terrigenous rocks, which agrees with the maximum age of the Sortavala Group rocks estimated from the U–Th–Pb (SIMS) age of 1922 ± 11 Ma of the Tervaoya diorites (Matrenichev et al., 2006). According to the proposed new tectonic model, the accumulation of the volcanosedimentary complex of the Sortavala Group, its metamorphism, erosion, and overlapping by the Ladoga Group turbidites had already occurred in the pericratonic part of the epi-Archean Fenno-Karelian Craton by the time of the Svecofennian continent–island arc collision, subduction, and formation of bimodal volcanoplutonic complexes of the young Pyhäsalmi island arcs and felsic volcanics of the Savo schist belt (1920–1890 Ma).

Pb-Nd-Sr Isotope Geochemistry of Metapelites from the Iberian Pyrite Belt and Its Relevance to Provenance Analysis and Mineral Exploration Surveys

Abstract The Iberian Pyrite Belt is a world-class metallogenic district developed at the Devonian-Carboniferous boundary in the Iberian Variscides that currently has seven active mines: Neves Corvo (Cu-Zn-Sn) and Aljustrel (Cu-Zn) in Portugal, and Riotinto (Cu), Las Cruces (Cu), Aguas Teñidas (Cu-Zn-Pb), Sotiel-Coronada (Cu-Zn-Pb), and La Magdalena (Cu-Zn-Pb) in Spain. The Iberian Pyrite Belt massive sulfide ores are usually hosted in the lower sections of the volcano-sedimentary complex (late Famennian to late Visean), but they also occur in the uppermost levels of the phyllite-quartzite group at the Neves Corvo deposit, stratigraphically below the volcano-sedimentary complex. A Pb-Nd-Sr isotope dataset was obtained for 98 Iberian Pyrite Belt metapelite samples (from Givetian to upper Visean), representing several phyllite-quartzite group and volcano-sedimentary complex sections that include the footwall and hanging-wall domains of ore horizons at the Neves Corvo, Aljustrel, and Lousal mines. The combination of whole-rock Nd and Sr isotopes with Th/Sc ratios shows that the siliciclastic components of Iberian Pyrite Belt metapelites are derived from older quartz-feldspathic basement rocks (–11 ≤ εNdinitial ≤ –8 and (87Sr/86Sr)i up to 0.727). The younger volcano-sedimentary complex metapelites (upper Tournaisian) often comprise volcanic-derived constituents with a juvenile isotopic signature, shifting the εNdi up to +0.2. The Pb isotope data confirm that the phyllite-quartzite group and volcano-sedimentary complex successions are crustal reservoirs for metals found in the deposits. In Neves Corvo, where there is more significant Sn- and Cu-rich mineralization, the higher (206Pb/204Pb)i and (207Pb/204Pb)i values displayed by phyllite-quartzite group and lower volcano-sedimentary complex metapelites (up to 15.66 and 18.33, respectively) suggest additional contributions to the metal budget from a deeper and more radiogenic source. The proximity to Iberian Pyrite Belt massive sulfide ore systems hosted in metapelite successions is observed when (207Pb/204Pb)i >15.60 and Fe2O3/TiO2 or (Cu+Zn+Pb)/Sc >10. These are important criteria that should be considered in geochemical exploration surveys designed for the Iberian Pyrite Belt.

Crustal stabilization: Evidence from the geochemistry and U–Pb detrital zircon geochronology of quartzites from Simlipal Complex, Singhbhum Craton, India

Cratonic stabilization was a critical crustal process during the Hadean to Archean for the formation of cratons. The understanding of how and where this process took place is significant to evaluate the architecture of continents. The Singhbhum Craton of eastern India has well preserved Precambrian volcano-sedimentary sequences. The Simlipal volcano-sedimentary complex of Singhbhum Craton consists of circular bands of mafic volcanic rocks interlayered with quartzites/ shales/phyllites. In the present study, we report petrographic and geochemical characteristics of quartzites from Simlipal Complex coupled with U–Pb ages of detrital zircons and zircon geochemistry to understand the provenance and depositional conditions and its connection with the crustal stabilization in the Singhbhum Craton. The quartzites are texturally mature with sub-angular to sub-rounded quartz grains followed by feldspars embedded in a silty matrix. Based on modal compositions and major element ratios, these quartzites are categorized as quartz arenite and sub-lithic arenites. Trace element abundances normalized to Archean Upper Continental Crust (AUCC) display positive anomalies at U, Zr, Hf and negative anomalies at Nb. REE patterns are characterized by negative Eu anomalies (Eu/Eu* = 0.47–0.97) and flat HREE suggesting felsic provenance. These quartzites show depletion of LILE, enrichment of HFSE and transition metals relative to AUCC. High weathering indices such as CIA, PIA, and ICV are suggestive of moderate to intense chemical weathering. Low trace element ratios such as Th/Cr, Th/Sc, La/Sc, La/Co and Th/Co indicate a predominantly felsic source for these rocks. The overall geochemical signatures indicate passive margin deposition for these quartzites. Detrital zircons from the Simlipal quartzites yield U–Pb ages 3156 ± 31 Ma suggesting Mesoarchean crustal heritage. The trace element geochemistry of detrital zircons suggests that the zircons are magmatic in origin and possibly derived from the 3.1 Ga anorogenic granite/granitoid provenance of Singhbhum Craton. These observations collectively indicate the Mayurbhanj Granite and Singhbhum Granite (SBG-III) provenance for these quartzites, thereby tracking the stabilization of the eastern Indian Shield/Singhbhum Craton back to Mesoarchean.

Geology of the recently discovered massive and stockwork sulphide mineralization at Semblana, Rosa Magra and Monte Branco, Neves–Corvo mine region, Iberian Pyrite Belt, Portugal

AbstractThe recently discovered massive and stockwork sulphide mineralization of Semblana-Rosa Magra and Monte Branco, situated ESE of the Neves–Corvo volcanogenic massive sulphide (VMS) deposit in the Iberian Pyrite Belt (IPB) is presented. Geological setting and tectonic model is discussed based on proxies such as palynostratigraphy and U–Pb zircon geochronology. The mineralization is found within the IPB Volcano-Sedimentary Complex (VSC) Lower sequence, which includes felsic volcanic rocks (rhyolites) with U–Pb ages in zircons of 359.6 ± 1.6 Ma, and black shales of the Neves Formation of late Strunian age. Massive sulphides are enveloped by these shales, implying that felsic volcanism, mineralization and shale sedimentation are essentially coeval. This circumstance is considered highly prospective, as it represents an important exploration vector to target VMS mineralization across the IPB, in areas where the Lower VSC sequence is present. The Upper VSC sequence, with siliciclastic and volcanogenic sedimentary rocks of middle–late Visean age, shows no massive mineralization but a late Tournaisian (350.9 ± 2.3 Ma) volcanism with disseminated sulphides was also identified. Nevertheless, stratigraphic palynological gaps were found within the Strunian and in the Tournaisian sediments, between the Lower and Upper VSC sequences, reflecting probable erosion and uplift mechanisms linked with extensional tectonics. The Semblana and Monte Branco deposits and the Rosa Magra stockwork are enclosed by tectonic sheets that dismembered the VSC sequence in a fold-and-thrust tectonic complex, characteristic of the NE Neves–Corvo region. The methodologies used allow a geological comparison between Neves–Corvo and other IPB mine regions such as Lousal–Caveira, Herrerias, Tharsis and Aznalcollar.

Unravelling depositional setting, age and provenance of the Simlipal volcano-sedimentary complex, Singhbhum craton: Evidence for Hadean crust and Mesoarchean marginal marine sedimentation

The Singhbhum craton of eastern India preserves an extensive record of basin formation spanning the Paleoarchean to Neoarchean. Although spatially extensive and well exposed, the absolute age, depositional environment, and regional correlations of many of the purportedly Archean basins of this craton remain poorly resolved. We present a detailed lithostratigraphic analysis of siliciclastic strata in the (lower) Simlipal volcano-sedimentary succession and report the first detrital zircon U-Pb ages from this succession. The studied section is dominated by fine- to medium-grained, quartz-rich sandstones, which preserve herringbone stratification, tidal bundles, soft sediment deformation structures along with ubiquitous trough cross-stratification. Petrographic study confirms these sandstones as quartz arenites and reveal their high textural and mineralogical maturity. These features are consistent with deposition of the lower siliciclastic succession of the Simlipal volcano-sedimentary complex within a tidally-influenced marginal marine setting. The new detrital zircon data support a ~3.08 Ga maximum depositional age for the succession and reveal a provenance with age peaks at ca. 3.55–3.45 Ga, 3.38–3.24 Ga, and 3.10–3.08 Ga. These ages likely correspond to local basement sources including the Older Metamorphic Tonalite Gneisses, the Singhbhum Granitoid Complex, and the Mayurbhanj Granite Suite. Two detrital zircons from our dataset have concordant ages of ~4.02 Ga and ~4.03 Ga. They represent the first Hadean detrital zircons recovered from any Archean strata in the Singhbhum craton, documenting the involvement of Hadean crust in the early development of the craton. The detrital zircons show prominent Pb-loss at ~1.2–1.0 Ga that exemplifies the tectonothermal imprint of a late Mesoproterozoic to early Neoproterozoic orogeny (likely related to the assembly of Rodinia) on the Singhbhum craton. Our findings further support the interpretation that the lower siliciclastic strata in the Simlipal succession are the lateral facies equivalents of alluvial fan deposits at the base of the Dhanjori Formation, exposed to the north.

The Mineral Composition of Paleoproterozoic Metamorphosed Massive Sulfide Ores in the Kola Region (A Case Study of the Bragino Ore Occurrence, Southern Pechenga)

Many massive sulfide ore occurrences and deposits in the Kola region are located within the Paleoproterozoic Pechenga–Imandra–Varzuga rift belt (2.5–1.7 Ga). They are hosted by volcanosedimentary complexes of the South Pechenga (Bragino ore occurrence) and western Imandra–Varzuga structural zones (Pirrotinovoe Ushchel’e deposit, Tahtarvumchorr ore occurrence, etc.). The age of the massive sulfide ore was estimated at ca. 1.9 Ga. The ores and their host complexes underwent amphibolite-facies metamorphism, which accounts for their specific mineral composition. The types of ores in the Bragino ore occurrence are discussed, the mineral assemblages are listed, and the major ore minerals, that is, pyrrhotite, pyrite, sphalerite, marcasite, etc., are characterized.

Mineral Inventory of the Algares 30-Level Adit, Aljustrel Mine, Iberian Pyrite Belt, Portugal

Mining activity in Algares (Aljustrel Mine, Portuguese sector of the Iberian Pyrite Belt, IPB) stems prior to Roman times. As the orebody is vertical and relatively thin, mining was carried out mainly along underground adits (galleries). Nowadays, the deposit is considered exhausted and the area is being rehabilitated for a different use. The Algares +30 level adit intersects two volcanic units of the IPB Volcano-Sedimentary Complex. The massive sulphide and related stockwork zone are hosted by the Mine Tuff volcanic unit and are exposed in the walls of the gallery, showing intense hydrothermal alteration. Along the mine adit, the geological sequence is affected by strong oxidation and supergene alteration, giving rise to the formation of secondary minerals through the oxidation of the sulphides. The most common minerals found were melanterite (FeSO4·7H2O) and chalcanthite (CuSO4·5H2O), forming essentially massive or crystalline aggregates, ranging from greenish to bluish colours. Melanterite from the walls revealed to be Cu-rich by opposition to that from stalactites/stalagmites formed below the old ore storage silo revealing the low-copper-grade ores exploited underground. The mineralogy of the efflorescent salts was used to ascertain the processes involved in their formation, and moreover, the inventory of minerals is presented, as well as their principal characteristics.

New insights on the middle Givetian/middle Frasnian palynofloras from the Phyllite-Quartzite Formation in the Neves-Corvo mine region (Iberian Pyrite Belt, Portugal)

A detailed palynostratigraphic study of two Somincor/Lundin Mining exploration drill holes intercepting the Phyllite-Quartzite (PQ) Formation in the geological basement of the Neves-Corvo mine region (Portuguese sector of the Iberian Pyrite Belt – IPB) allowed to first recognise the oldest ages for this formation in this region, ranging from midGivetian/midFrasnian (base unknown) to late Famennian. The TA Miospore Biozone (Cristatisporites triangulatus-Ancyrospora ancyrea) of middle Givetian age (Middle Devonian) was identified in NK30B-1 drill hole (Lombador North mine sector), whereas the BM Miospore Biozone (Verrucosisporites bulliferus-Lophozonotriletes media) and IV Miospore Biozone (based in the first occurrence of Rugospora bricei and Diducites cf. poljessicus) of middle Frasnian (Late Devonian) age were both recognised in drill hole SJ32 (Corvo-Semblana mine sector). The common presence of Early-Middle Devonian reworked spores, as well as similar inherited zircon ages may suggest that the lower PQ Formation age is not yet known.At Neves-Corvo mine, the Volcano-Sedimentary Complex is deposited directly above the PQ basement, spanning different ages, pointing out two major unconformities, a VSC/upper and/or lower PQ sequences and an upper PQ/lower PQ sequences.A palynostratigraphic correlation of the lowermost Phyllite-Quartzite Formation across the IPB is established. Phyllite-Quartzite Formation palynoassemblage of Neves-Corvo region is compared with lowermost PQ assemblages recovered in the NW sector of IPB (S. Francisco da Serra and Lousal-Caveira mine structures, Portugal) and in E sectors of the IPB in Spain (Gerena-El Garrobo section). The similar palynological record (also including the same reworked taxa signature) and ages obtained, suggests identical sedimentary provenance, close paleogeographic domain and temporal affinity throughout the lowermost IPB Phyllite-Quartzite Formation.