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Paleoproterozoic (2.05 Ga) komatiites are widespread in the Central Lapland Greenstone Belt (CLGB), northern Finland. Close association with sulfur (S)-rich country rocks and spatiotemporal connection with the Cu-Ni(-PGE) deposits of Kevitsa and Sakatti make these komatiites interesting targets for sulfide deposit exploration. We provide whole-rock geochemical data from Sattasvaara komatiites and combine it with literature data to form a geochemical database for the CLGB komatiites. We construct a model for the komatiites from adiabatic melting of the mantle source to fractional crystallization at crustal conditions. Using MELTS, we calculate three parental melts (MgO = 20.6–25.7 wt%) in equilibrium with Fo92, Fo93, and Fo94 olivine for the CLGB komatiites. Based on REEBOX PRO simulations, these parental melts can form from a single mantle source by different pressures and degrees of melting when the potential temperature is 1575–1700 °C. We calculate ranges of S contents for the parental melts based on the different mantle melting conditions and degrees of melting. We use Magma Chamber Simulator to fractionally crystallize the parental melt at crustal conditions. These simulations reproduce the major element oxide, Ni, Cu, and S contents from our komatiite database. Simulated Ni contents in olivine are compatible with literature data from Kevitsa and Sakatti, hence providing a baseline to identify Ni-depleted olivine in CLGB komatiites and related intrusive rocks. We show that fractional crystallization of the komatiitic parental melt can form either Ni-rich or Cu-rich sulfide melt, depending on the initial Ni and S content of the parental melt. [ABSTRACT FROM AUTHOR]

New mapping of the Barberton Greenstone Belt in South Africa shows that the central part is a pseudo-stratigraphy made of shallow-water and deep-water siliciclastic and volcanic slide blocks, with individual blocks ranging in size from tens of meters to >10 km in length. The outcrop pattern and scale are remarkably similar to those of large-scale Miocene to recent submarine landslides in New Zealand along the active Hikurangi subduction zone that are periodically triggered by earthquakes on the subduction megathrust, providing evidence for megathrust earthquakes in the Paleoarchean. [ABSTRACT FROM AUTHOR]

The Laird Lake property, southwest Red Lake greenstone belt, straddles the contact between the Balmer (2.99–2.96 Ga) and the Confederation (2.74–2.73 Ga) assemblages. The property is 10 km along strike from the Madsen and Starrat–Olsen Au mines that are hosted near the contact. The Balmer assemblage consists of fine-grained, aphyric, locally pillowed mafic volcanic rocks, ultramafic intrusive and volcanic rocks with flow breccia textures hosting local spinifex-bearing clasts, and banded-iron formations. In contrast, the Confederation assemblage comprises porphyritic mafic volcanic rocks intercalated with intermediate to felsic volcanic rocks that include crystal lapilli tuffs, crystal tuffs, and tuffs. The Balmer assemblage is composed of tholeiitic mafic volcanic rocks with minor Al-undepleted komatiites, whereas the Confederation assemblage is calc–alkalic. Neodymium isotopes, in conjunction with trace element geochemistry, suggests that parts of the Balmer assemblage were weakly contaminated by an older intermediate basement. Both arc and back-arc volcanism occurs in the Confederation assemblage, with the arc rocks showing a stronger crustal component than the back-arc rocks. A maximum U–Pb age of 2741 ± 19 Ma for a crystal tuff and an age of 2737.68 ± 0.79 Ma for a diorite are consistent with a Confederation assemblage affinity for the intermediate calc–alkaline rocks south of the Au-bearing horizon. The Balmer assemblage represents an oceanic plateau formed by plume magmatism on the margins of the North Caribou Terrane, whereas the Confederation assemblage at Laird Lake formed in an oceanic arc setting where both arc and back-arc volcanism occurred simultaneously. [ABSTRACT FROM AUTHOR]

Despite countless advances in recent years, exploration for volcanogenic massive sulfide (VMS) deposits remains challenging. This is particularly the case in the Yilgarn Craton of Western Australia, where outcrop is limited, weathering is deep and extensive, and metamorphism is variable. At Erayinia in the southern Kurnalpi terrane, intercepts of VMS-style mineralization occur along ~35 km strike length of stratigraphy, and a small Zn (-Cu) deposit has been defined at King (2.15 Mt at 3.47% Zn). An extensive aircore and reverse circulation drilling campaign on the regional stratigraphy identified additional VMS targets, including the King North prospect. Through a combination of detailed rock chip logging, petrography (inc. SEM imaging), and lithogeochemistry, we have reconstructed the volcanic stratigraphy and alteration halos associated with the King North prospect. Hydrothermal alteration assemblages and geochemical characteristics at King North (Mg-Si-K enrichment, Na depletion, and high Sb, Tl, Eu/Eu*, alteration index, CCPI, and normative corundum abundance values) are consistent with an overturned VMS system. The overturned footwall stratigraphy at King North is dominated by metamorphosed volcanic rocks, namely the following: garnet amphibolite (tholeiitic, basaltic), biotite amphibolite (andesitic, calc-alkaline), chlorite–quartz schist (dacitic), and narrow horizons of muscovite–quartz schist (dacitic to rhyolitic, HFSE-enriched). The hanging-wall to the Zn-bearing sequence is characterized by quartz–albite schists (metasedimentary rocks) and thick sequences of amphibolite (calc-alkaline, basaltic andesite). An iron-rich unit (>25% Fe2O3) of chlorite–actinolite–quartz schist, interpreted as a meta-exhalite, is associated with significant Cu-Au mineralization, adjacent to a likely syn-volcanic fault. Extensive Mg metasomatism of the immediate felsic footwall is represented by muscovite–chlorite schist. Diamond drilling into the deep hanging-wall stratigraphy at both King North and King has also revealed the potential for additional, stacked VMS prospective horizons in the greenstone belt stratigraphy. The discovery of HFSE-enriched rhyolites, zones of muscovite–chlorite schist, presence of abundant sulfide-rich argillaceous metasedimentary rocks, and a second upper meta-exhalite horizon further expand the exploration potential of the King–King North region. Our combined petrographic and lithogeochemical approach demonstrates that complex volcanic lithologies and VMS alteration signatures can be established across variably metamorphosed greenstone belts. This has wider implications for more cost-effective exploration across the Yilgarn Craton, utilizing RC drilling to reconstruct the local geology and identify proximal halos, and limiting more costly diamond drilling to key areas of complex geology and deeper EM targets. [ABSTRACT FROM AUTHOR]

There are numerous Neoarchean metasedimentary rock packages in the Slave craton, and they serve as important archives of tectonic processes. Little is documented on the Neoarchean sedimentary packages of the Winter Lake greenstone belt of the central Slave craton, however, and their interpretation can aid in the understanding of the final stages of Slave craton amalgamation. This project investigates the depositional environments and tectonic settings of the Itchen Formation and Sherpa Formation of the Winter Lake greenstone belt. Our study provides constraints for reconstructing the Neoarchean evolution of the central Slave craton through bedrock mapping and facies analysis. The Itchen Formation consists of submature mudstone, siltstone, and sandstone, with preserved graded bedding, planar bedding, and flame structures. Unconformably overlying the Itchen Formation is the Sherpa Formation, which is dominated by polymictic conglomerates and coarse-grained sandstones with preserved cross-bedding, imbricated clasts, and scour surfaces. The Itchen Formation is interpreted to have been deposited in a convergent basin (i.e., retro-arc foreland basin), where two facies associations outline turbidite and suspension sedimentation consistent with submarine fan deposition on a continental slope and a basin floor environment. By contrast, the Sherpa Formation has three facies associations representing dominantly alluvial–fluvial environments in terrestrial–marine–lacustrine settings deposited in pull-apart basins resulting from transtensional forces associated with the Beniah fault zone. [ABSTRACT FROM AUTHOR]

The biological nitrogen (N) cycle on early Earth is enigmatic because of limited data from Archean (meta-)sediments and the potential alteration of primary biotic signatures. Here we further investigate unusual 15N enrichments reported in 2.7 Ga meta-sediments from the Abitibi greenstone belt, Canada, purportedly related to a 15N-enriched Archean atmosphere. Given that sediments from this region are contemporaneous with large-scale volcanogenic massive sulfide deposits, we utilize Cu and Zn contents to trace the effects of hydrothermal circulation on N isotope fractionation. We show that high δ15Nbulk values as high as +23‰ are associated with Cu-Zn mineralization, whereas unmineralized organic-rich shales exhibit much lower δ15Nbulk and δ15Nkerogen values. Moreover, we find a large offset between δ15Nbulk and δ15Nkerogen of as much as 17‰ and relate this to the addition of organic-bound N during the late-stage emplacement of organic-rich veins. We conclude that the previously reported high δ15N values are most parsimoniously explained by biotic and abiotic mechanisms rather than a 15N-enriched atmosphere. Crucially, both mechanisms require the presence of NH4 + in hydrothermal fluids, supporting the hypothesis that hydrothermal discharge was an important nutrient source for Neoarchean marine life. [ABSTRACT FROM AUTHOR]

The results of studies of carbonaceous matter (CM) and the S isotopic composition of associated sulfides in metapelites of the Neoarchean banded iron formation of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandinavian Shield) are presented. The petrographic observations show that the CM occurs inside and between silicates, in sulfides, or at the grain boundaries between the sulfide crystals and biotite or amphibole. The results of scanning electron and atomic force microscopy showed the presence of several CM types distinct in structure and C content. The analysis of Raman spectra of CM revealed the presence both of well-ordered graphite and weakly structured kerogene in samples. The isotopic composition of the total organic carbon is typical of biogenic processes. The δ13Corg values from –27.9 to –30.6‰ are consistent with the fixation of carbon by photo- or chemoautotrophs. The S isotopic composition of associated sulfides is characterized by a positive Δ33S anomaly (up to +0.94‰) and negative δ34S values (from –2.06 to –4.1‰). The positive Δ33S values indicate a genetic link with photochemical elemental sulfur (S8) from the atmosphere, whereas the negative δ34S values reflect the fractionation of isotopes during bacterial-related processes. Based on these observations, we suggest that the primary CM mostly has a biogenic origin. [ABSTRACT FROM AUTHOR]

Petrochronology of monazite in volcanic rocks of the Hutti deposit in the Eastern Dharwar Craton (India) has been studied to understand the magmatic and hydrothermal events that have affected the area. The volcanic rocks occurring in the Hutti greenstone belt are bimodal in nature and contain both felsic and metabasalt. The felsic volcanic rocks in the area preserve accessory minerals like monazite, allanite, and apatite, whereas the same is absent in metabasalts. Petrographic observation of felsic volcanic rock shows corona growth of allanite and apatite (in addition to huttonite) clustering around monazite grains. This corona texture, termed allanite cluster, occurs parallel to the shear planes (C‐plane) of the felsic volcanic rock and characterizes late‐stage hydrothermal activity in the area. Texturally, monazite in the felsic volcanic rock occurs included within arsenopyrite (<1 μm), and in association with apatite, allanite, and occasionally with huttonite/thorite (~10–40 μm), in which monazite grains preserve geochemical heterogeneity in both intra‐ and inter‐grains. The U–Th–PbTotal dating of monazite associated with the allanite cluster shows two age peaks (both from intra‐ and inter‐grains) at 2658 ± 17 Ma (older) and 2534 ± 38 Ma (younger), in which the older age represents the magmatic/crystallization age of the studied felsic volcanic rock overprinted by a later hydrothermal event in the study area. Based on monazite geochemistry‐geochronology, the present study deduces two texturally constrained events related to the primary crystallization of monazite (~2.65 Ga) and subsequent alteration of the same during a later hydrothermal event (ca. 2.53 Ga) that has affected the felsic volcanic rock in the Hutti gold deposit. [ABSTRACT FROM AUTHOR]

Rare-metal granite pegmatites of the lithium-cesium-tantalum (LCT) type are widely distributed in Early Precambrian Greenstone belts worldwide, including the Canadian and Australian shields. However, the Middle Dnipro Granite-Greenstone region, which includes a lot of greenstone belts such as Sura, Verkhivtseve, Konka, Sofiivka, Chortomlyk, etc., remains insufficiently studied in terms of these pegmatites. This article presents previously unpublished data on the pegmatites of the Sura and Verkhivtseve greenstone structures or belts, obtained through a meticulous study, analysis, and reinterpretation of repository and archive materials. It reveals their geological-structural setting, distribution limits, mineralogical and geochemical characteristics, and their connection with granite complexes and massifs. Furthermore, the article outlines the prospects for rare-metal mineralization in these pegmatites. Pegmatites within the Sura greenstone structures or belts were discovered on its northern flank within the Karnaukhivka synclinal branch, associated with the ultramafic massif of the same name. Over 60 pegmatite veins were encountered during the 1961 exploration for silicate nickel, with most veins intruding serpentinized ultrabasites. The extension of the veins aligns with the general extension of the Karnaukhivka ultramafic massif, and their average length ranges from 150 to 250 m. The majority of the pegmatite bodies likely dip subvertically and exhibit a zonal structure comprising aplite, multi-grained granite, pegmatoid, blocky quartz, and microcline. The northwestern part of the Sura greenstone structures or belts presents a promising Pravda-Karnaukhivka pegmatite field. The Verkhivtseve greenstone stroctures or belts displays a complex block structure, suggesting the presence of deeply eroded pegmatite-bearing blocks. Isolated bodies of pegmatites have been found on the southeastern flank of the structure, primarily within the Shmakove branch and its surrounding granitoids. A series of pegmatite and aplite veins with anomalous contents of rare metals and rare earth elements are localized in plagiogranites of Sura, granites of Demuryne, and plagiomigmatites of Dnipropetrovsk complexes. The highest niobium content of 0.048% and tantalum content of 0.005% were determined in drill-hole 0151. These pegmatite-bearing greenstone formations in the Shmakove branch and the associated granitoids are designated as the Hrushivka-Rudytsynske pegmatite field. Specialized prospecting for rare-metal mineralization associated with pegmatites within the Pravda-Karnaukhivka and Hrushivka-Rudytsynske pegmatite fields is recommended.

The greenstone belts of the Crixás-Goiás Domain are economically important due to significant epigenetic gold deposits and the potential for under-researched syngenetic deposits. The gold occurrences associated with the volcanogenic massive sulfide (VMS) deposits in the region are documented only in the volcanoclastic rocks of the Digo-Digo Formation, Serra de Santa Rita greenstone belt. The objective of this work is to discuss the efficiency of the induced polarization methods in the time and frequency domains for differentiating and identifying potentially mineralized zones in the exhalites associated with the VMS-type gold of the Digo-Digo Formation. Data were acquired using a multielectrode resistivity meter with the dipole–dipole array and 10 m spacing between electrodes, as well as different current injection times (250, 1000, and 2000 ms). After the electrical data processing and inversion, the sections were integrated into ternary red-green-blue and cyan-magenta-yellow models to highlight areas of high chargeability, low resistivity, and high metal factor (frequency domain) and, thus, map the higher potential zones to host polarizable metallic minerals. The geological–geophysical model elaborated from the correlation of electrical and surface geological data allowed us to identify four anomalous areas related to potential mineralized zones. The geological data confirm that two targets are associated with the geological contacts between metamafic and intermediate metavolcanic units and the exhalative horizon. One of the targets coincides with a sulfide-rich exhalative horizon (VMS), while the last target occurs in the occurrence area of metaultramafic rocks, where gold mineralization occurrences have not been previously described, being a promising target for future investigations. [ABSTRACT FROM AUTHOR]

Vast clay deposits of Chitradurga and Sandur greenstone belts of the Dharwar Craton, southern peninsular India, hosting pockets of high‐grade manganese (Mn) ore, provide remarkable clues related to the ore‐forming processes and palaeo‐environmental conditions. In this study these Fe–Mn‐rich clays were investigated through mineralogical and geochemical characteristics to comprehend their palaeo‐weathering and genetic constraints and their role in the supergene accumulation of Mn ore. Their mineralogy is characterized by predominant kaolinite, muscovite, birnessite, haematite, goethite, halloysite along with quartz and traces of ilmenite. Chemical indices of alteration and weathering indicate intense weathering conditions under high palaeo‐precipitation rates in a humid, tropical climate under shallow burial conditions and K‐metasomatism. The presence of authigenic kaolinite and absence of illite reflect on diagenesis up to mesodiagenetic stage. Positive to negative Ce anomalies (Ce/Ce* = 0.67–5.93) of these clays suggest varying oxic‐anoxic conditions during their genesis, whereas conspicuous negative Eu anomalies (Eu/Eu* = 0.61–0.99) are attributed to precursor sediment signatures and hydrothermal imprints of the Mn ore. These kaolinite‐rich clays are suggested to have been formed by in situ chemical alteration, whereas kaolinitization of the Fe–Mn‐rich arenaceous and argillaceous sediments was derived from predominant tonalite and felsic provenance in a shallow marine passive margin setting. Based on the morphologies of birnessite, haematite and goethite in the investigated clays, we propose that these clays have played a key role in the oxidation and deposition of Mn (II) from the migrating aqueous solutions and acted as organo‐polymerization templates for the proliferation of ancient microbial life on the planet Earth. [ABSTRACT FROM AUTHOR]

Due to the inherently fluid‐mobile nature of W, the 182W record of the early Earth may have been obscured by fluid‐induced mobilization of W. To investigate W mobilization in Archean greenstone sequences, we analyzed 182W isotope systematics and major and trace element concentrations in samples from the 3.53 Ga old Onverwacht Group of the Kaapvaal Craton (South Africa) and the >3.51 Ga old Badampahar Group of the Singhbhum Craton (India). Our results for mafic and ultramafic metavolcanic rocks show W/Th ratios significantly higher than primary magmatic values, which suggests fluid‐induced W enrichment. Samples least affected by secondary W enrichment (W/Th < 0.26) show no resolvable W isotope anomalies from modern mantle values in both cratons. Samples from the Kaapvaal Craton with elevated W/Th exhibit deficits in 182W as low as −8.1 ± 4.3 ppm compared to the modern mantle. Covariations of μ182W with W/Th, and Ce/Pb suggest that negative isotope signatures were introduced during secondary fluid‐mediated processes. The enrichment of W is most evident in altered ultramafic rocks comprising serpentine, resulting in additional covariations between MgO, LOI, and W/Th. The W isotope composition of serpentinized komatiites reflects the composition of younger intruding granitoids. We therefore infer the latter as a possible source of W‐rich fluids. The Badampahar Group samples exhibit little W isotope variability. A well‐resolved 182W deficit of −6.2 ± 2.9 ppm was determined in a single komatiite sample, which indicates an unknown fluid source, currently not represented in any other unit of the Singhbhum Craton. Plain Language Summary: The tungsten (W) isotope composition of ancient rocks can be used to trace processes that occurred during Earth's early evolution. However, interactions between rocks and fluids may alter the W concentration and therefore influence the interpretation of W isotope data. To identify the source of such fluids and the processes by which they affect the W isotope composition of rocks, we analyzed ancient rock samples from South Africa and India. The isotope composition of rocks with a low W concentration reflects that of the modern Earth. Therefore, they do not trace the processes that occurred during Earth's early evolution. Samples from South Africa with untypically high W concentrations show a different isotopic composition. The variation in the W isotope signature correlates with other chemical indices that are susceptible to modification by fluid‐related processes. This shows that the W within the rocks is derived from an external fluid source and not from their original magmatic source. Samples with the highest W enrichment have a similar isotope composition as spatially associated intrusive rocks. By inference, the latter likely represent the source of W‐rich fluids. The samples from India show similar enrichment in W, indicating similar fluid‐related processes and W sources at both localities. Key Points: The magmatic sources of metavolcanic rocks from the Onverwacht Group and the Badampahar Group do not exhibit W isotope anomaliesNegative W isotope signatures in the Onverwacht Group are likely derived from fluids sourced from younger intrusive granitoidsFelsic intrusive rocks are a major source of W‐rich fluids in Paleoarchean greenstone units [ABSTRACT FROM AUTHOR]

The paper presents the first SIMS SHRIMP U-Pb data for zircon from an olivine horizon within the Nyud intrusion of the ore-bearing layered Monchegorsk pluton (Monchepluton) in the Kola Region, Russia. A 100–150 m-thick olivine horizon occurs nearly horizontally between the melanocratic and mesocratic norite of the Nyud intrusion, which disturbs its normal cumulus stratigraphic sequence. In addition, the pyroxene-plagioclase hornfelses are present at the upper contact with the olivine horizon. Twenty-three zircon grains were extracted from the large-volume olivine plagio-orthopyroxenite sample and clustered into two populations. The first population of magmatic zircon (n = 8) has a concordant and weighted average 207Pb/206Pb age of 2484.3 ± 5.6 Ma, which characterizes the formation time of the olivine horizon rocks. This serves as evidence of the olivine horizon that forms as a result of additional magma injection, which does not contradict the geological data. The 207Pb/206Pb age of single-grain zircon is 2414 ± 25 Ma, which indicates the time of postmagmatic transformations. The second population of zircon (n = 16) has a concordant and weighted average U-Pb age of 2700.6 ± 4.6 Ma, which indicates zircon absorption by olivine horizon magma probably from the rocks of the Archean greenstone belt. [ABSTRACT FROM AUTHOR]

The north‐dipping Hout River Shear Zone (HRSZ), which marks the boundary between the high‐grade Limpopo Complex in its hanging wall and the low‐grade granite‐greenstone terrane of the Kaapvaal Craton in South Africa in its footwall, is a deep‐crustal shear zone that controlled emplacement of hot Limpopo Complex granulites over and against low‐grade granite‐greenstones during exhumation at ~2.72–2.62 Ga. This major shear zone controlled migration of large volumes of hydrous fluids released during devolatilization of underthrusted greenstones that infiltrated into hot overlying granulites, establishing a retrograde anthophyllite‐in isograd and associated zone of retrograde rehydrated granulite that bounds the Limpopo Complex in the south. Here, we report new petrological data based on mineral equilibrium modelling of amphibolites from the Rhenosterkoppies Greenstone Belt (RGB) located in the immediate footwall of the HRSZ and discuss evidence that these rocks also interacted with high‐temperature fluids that infiltrated along the HRSZ. This study provides an important perspective of the interaction of hot granulites with underthrusted relatively cold greenschist‐facies rocks along the steeply north‐dipping section of the HRSZ, and shows that evidence for such interaction is restricted to a relatively narrow zone in the footwall of the HRSZ termed a hot‐iron‐zone. The peak mineral assemblage of a garnet‐free amphibolite from the RGB (magnesio‐hornblende + plagioclase + quartz + clinopyroxene + titanite + ilmenite) yielded the peak P–T condition of 7–8 kbar and 640–680°C with H2O content of 3.5–3.8 mol%. Clinopyroxene is replaced by actinolite + quartz and epidote + quartz symplectites by a post‐peak hydration event at <5 kbar and <590°C caused by elevated H2O content in the rock (>4.0 mol%), possibly related to fluid infiltration along the HRSZ. Mineral equilibria in a garnet‐bearing amphibolite records a prograde path from 5 to 7 kbar and 540–630°C to the peak conditions at 7.6–8.7 kbar and 620–650°C. A clockwise P–T path suggesting rapid compression and decompression has been inferred for the amphibolites from the RGB, possibly because of pressure increase related to overthrusting of the high‐grade terrane (Southern Marginal Zone of the Limpopo Complex) onto the low‐grade granite‐greenstone terrane, followed by rapid exhumation. The quantity of H2O associated with the amphibolite‐facies metamorphism in the RGB was elevated from the peak stage (M(H2O) = 3.5–3.8 mol%) to the retrograde stage (M(H2O) = 4.0–4.5 mol%) of metamorphism in the RGB, possibly suggesting fluid infiltration not only from internal sources but also from external sources. The results of this study indicate that a H2O‐bearing fluid, which infiltrated along the HRSZ, affected both the footwall and the hanging wall sections of the shear zone, although the effect on the footwall section was limited. [ABSTRACT FROM AUTHOR]

The Wawa Gold Corridor, a series of Archean orogenic Au deposits in the Michipicoten greenstone belt, Canada, comprises two styles of Au mineralization: (1) syn-deformation gold associated with pyrite and arsenopyrite; and (2) late- to post-deformation gold associated with chalcopyrite and Bi-Te(-S) phases. Through petrographic and mineral–chemical analysis, it was determined that gold in the latter assemblages precipitated from Bi-rich polymetallic melts during hydrothermal overprinting of the earlier Au-As-S mineralization; this event was likely driven by the emplacement of Archean lamprophyres. The formation and evolution of these melts was governed by fluid–pyrite reaction interfaces, where the bulk composition of the melts was broadly controlled by the trace-element chemistry of the sulphide minerals in the local host rocks. This suggests that the melt-formation event involved mobilization of existing metal endowments related to early Au events, rather than addition of new Au, Bi, and Te. Thus, the deposition of high-grade Au by Bi-rich melts was dependent on pre-existing sulphide mineralization, both as a source of metals and as micro-environments that stabilized the melts. The paragenesis documented in the Wawa Gold Corridor (i.e., early hydrothermal Au-As-S mineralization and late melt-related Au-Bi-Te mineralization) has been previously recognized in numerous other orogenic and non-orogenic Au deposits. Herein, it is suggested that this apparent consistency in the timing of melt events across multiple systems probably reflects the physicochemical conditions (i.e., fO2-aH2S) of orogenic fluids being incompatible with molten Bi. Bi-rich polymetallic melts are hence unlikely to form primary Au mineralization in orogenic systems but can, however, have a significant impact on the ultimate deposit-scale distribution of Au via secondary mobilization and enrichment. [ABSTRACT FROM AUTHOR]

Rare-metal granite pegmatites of the lithium-cesium-tantalum (LCT) type are widely distributed in Early Precambrian Greenstone belts worldwide, including the Canadian and Australian shields. However, the Middle Dnipro Granite-Greenstone region, which includes a lot of greenstone belts such as Sura, Verkhivtseve, Konka, Sofiivka, Chortomlyk, etc., remains insufficiently studied in terms of these pegmatites. This article presents previously unpublished data on the pegmatites of the Sura and Verkhivtseve greenstone structures or belts, obtained through a meticulous study, analysis, and reinterpretation of repository and archive materials. It reveals their geological-structural setting, distribution limits, mineralogical and geochemical characteristics, and their connection with granite complexes and massifs. Furthermore, the article outlines the prospects for rare-metal mineralization in these pegmatites. Pegmatites within the Sura greenstone structures or belts were discovered on its northern flank within the Karnaukhivka synclinal branch, associated with the ultramafic massif of the same name. Over 60 pegmatite veins were encountered during the 1961 exploration for silicate nickel, with most veins intruding serpentinized ultrabasites. The extension of the veins aligns with the general extension of the Karnaukhivka ultramafic massif, and their average length ranges from 150 to 250 m. The majority of the pegmatite bodies likely dip subvertically and exhibit a zonal structure comprising aplite, multi-grained granite, pegmatoid, blocky quartz, and microcline. The northwestern part of the Sura greenstone structures or belts presents a promising Pravda-Karnaukhivka pegmatite field. The Verkhivtseve greenstone stroctures or belts displays a complex block structure, suggesting the presence of deeply eroded pegmatite-bearing blocks. Isolated bodies of pegmatites have been found on the southeastern flank of the structure, primarily within the Shmakove branch and its surrounding granitoids. A series of pegmatite and aplite veins with anomalous contents of rare metals and rare earth elements are localized in plagiogranites of Sura, granites of Demuryne, and plagiomigmatites of Dnipropetrovsk complexes. The highest niobium content of 0.048% and tantalum content of 0.005% were determined in drill-hole 0151. These pegmatite-bearing greenstone formations in the Shmakove branch and the associated granitoids are designated as the Hrushivka-Rudytsynske pegmatite field. Specialized prospecting for rare-metal mineralization associated with pegmatites within the Pravda-Karnaukhivka and Hrushivka-Rudytsynske pegmatite fields is recommended. [ABSTRACT FROM AUTHOR]

This study investigates the structural control of the numerous gold occurrences in the southern part of the Barberton Greenstone Belt in the Malolotja and Steynsdorp areas. The gold-bearing event distribution is studied using field structural geology associated with a petrological and microstructural analysis. Three major tectonic events have been identified in quartz veins and direct country rocks. The first event (De) created a regional schistosity (Se), probably associated with an early thrusting event. The second event (Df) is related to a large-scale folding, which formed the anticline at Steynsdorp and synform at Malolotja. It resulted from a main E–W direction of shortening and is responsible for the folding of the Se schistosity. It formed a N–S-striking axial planar cleavage (Sf), observed and associated with the emplacement of the main gold-bearing veins. The mineralised system exhibits a complex vein network, in which shallow dipping veins have developed coevally with steep west- and east-dipping veins. A third deformation event (Dl) produced by NE–SW shortening is related to the late barren hydrothermal quartz vein formation. Mineralogically, the veins are filled with abundant quartz, and scarce tourmaline and feldspars. Alteration halos composed of neoformed tourmaline and plagioclase within a talc and white mica matrix developed specifically during the late Dl event. A model of regional deformation giving rise to large-scale folds and quartz vein formation formed in response to E–W and NE–SW directions of shortening globally is proposed and discussed in this paper. [ABSTRACT FROM AUTHOR]

The first data on the multi-isotopic S composition of sulfides of the Neoarchean banded iron formations (BIFs) of the Kostomuksha greenstone belt of Karelia (Karelian Craton of the Fennoscandian Shield) formed 2760–2740 Ma ago are presented in this paper. Pyrite associated with fine-grained magnetite has negative δ34S (to –7.8‰) and positive Δ33S (to +0.7‰) values. Pyrrhotite from stringer-disseminated ores associated with schists exhibits negative values of both δ34S (to –6‰) and Δ33S (to –0.46‰). Our data provide grounds to suggest that the BIF sulfides sourced photolitic elementary sulfur from the atmosphere, sulfate from seawater, and sulfur from magma. The S isotope ratios of sulfides reflect the interaction between abiotic (atmospheric, hydrothermal) and biotic (microbial dissimilation reduction) processes during the formation of iron deposits of the Kostomuksha greenstone belt of Karelia. [ABSTRACT FROM AUTHOR]

The ca. 3.5 Ga Bon Accord Ni deposit was located in the Barberton Greenstone Belt of the Kaapvaal Craton, South Africa, and contained a unique assemblage of Ni-rich minerals including trevorite (NiFe2O4). It was initially interpreted as a metamorphosed extraterrestrial body, recently ruled out by Cr isotope data, and subsequently as a fragment of the Archean Earth's core. More recent suggestions have highlighted similarities between Bon Accord and Archean magmatic sulfide mineralization. We present a geochemical (rare earth element [REE], halogen, and highly siderophile element [HSE] abundance) and isotopic (noble gases, Zn, Cr, and Re-Os) study to elucidate the origin of this enigmatic body. Bon Accord is enriched in the REE relative to primitive mantle (PM), with a pattern resembling that of Aldepleted komatiites. The bulk material has >10 PM Os and Ir, >100 - PM Ru, Pt, Pd, and Re, and radiogenic 187Os/188Os. Trevorite, silicates, and two bulk-rock samples are consistent with chondritic to sub-chondritic initial 187Os/188Os at the time of formation. The new REE data implicate a komatiite precursor in the formation of Bon Accord, and the HSE data bear striking similarities to those of Ni-enriched Archean magmatic sulfide deposits. Enrichment in the heavier Zn isotopes supports desulfurization of a sulfide (isotopically light) deposit during serpentinization to produce the trevorite-dominated body. We conservatively estimate this process could have mobilized as much as -9.2 x 104 tonnes of H2S, offering an intriguing possibility for sourcing of the sulfur that fixes the historically important gold mineralization in the Barberton Greenstone Belt. [ABSTRACT FROM AUTHOR]

Petrographic, whole‐rock geochemical and geochronological analysis of polymictic conglomerate, associated siltstone and greywacke in the Neoarchean Gadag Greenstone Belt in the Western Dharwar Craton, India, provides new insights into sedimentary provenance and tectonic setting. The polymictic conglomerate contains granitic, gneissic, felsic and mafic volcanic, quartzite and banded ferruginous chert clasts within a quartzo‐feldspathic matrix. Framework grains in the siltstone and greywacke are quartz, feldspar with rock fragments, embedded in a chlorite‐dominant matrix. The chemical index of alteration values (~70) and A‐CN‐K plot for the rocks suggest a low‐to‐moderate degree of weathering. Rare earth element (REE) patterns show moderate fractionation (LaN/YbN ~ 12.31) with a weak negative europium anomaly (0.82). Enrichment in transition elements (Ni, Cr, Co, Sc) and depletion in high‐field‐strength elements, as well as relatively low La/Co (0.62), moderate to high Th/Yb (3.06), La/Th (5.16), La/Yb (17.5), and La/Sc (~2.37) ratios, suggest a mixed felsic‐mafic provenance. U–Pb dating of detrital zircon from the conglomerate and greywacke revealed major age peaks at ca. (3.2, 2.9, 2.8, 2.6, 2.5 Ga) and a maximum age of deposition of 2,508 ± 26 Ma, 2,493 ± 20 Ma, respectively. The above data suggest low to moderately weathered proximal sources for both conglomerate and greywacke, indicating that these two rock types were not deposited simultaneously, but rather separately. The association of these conglomerates and greywacke with continental arc‐related volcanics indicates the closing of an arc at the time of sedimentation. Complex provenance consisting of recycled and magmatic arc during basin closure confirm the notion of modern style plate tectonics operating during Neoarchaean. [ABSTRACT FROM AUTHOR]

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A magnetotelluric (MT) study across the Red Lake greenstone belt of the western Superior craton, Canada, images a 50-km-long north-dipping conductor (<20 Ω·m) at 20-25 km depth and subvertical conductors spatially correlated with crustal-scale shear zones and large orogenic gold deposits. The conductors are interpreted to be the conductivity signature of the deep crustal source of the auriferous fluids and pathways of the orogenic gold system. The geophysical results, supported by existing geochemical and fluid inclusion studies, suggest that the Au- and CO2-rich fluids responsible for gold mineralization were released by devolatilization of supracrustal rocks underthrust to mid- to lower-crustal levels during subduction. This MT study links shallow gold mineralization to a deep crustal source region, demonstrating the connection between a crustal suture zone and the formation of orogenic gold deposits in an Archean greenstone belt. [ABSTRACT FROM AUTHOR]

The carbonates of the Dodguni area of the Chitradurga greenstone belt, Dharwar Craton, India were studied to understand the Archean diagenetic and palaeo‐depositional conditions using carbon and oxygen isotopes along with whole‐rock geochemistry. These carbonates show significant variation in δ13C and δ18O (−1.73‰ Vienna Peedee Belemnite [VPDB] to −0.45‰ VPDB and δ18O vary from −13.51‰ VPDB to −8.46‰ VPDB, respectively). The rare earth element (REE) + Y (rare earth elements and yttrium) of the studied carbonate rocks exhibit flat and uniform patterns (PrSN/YbSN = 0.4–1), slight positive La, Eu and Gd anomalies (CeSN/CeSN* = 0.8–0.9; EuSN/EuSN* = 0.7–1.4 and GdSN/GdSN* = 2–2.3, respectively) with slight positive Ce anomalies (PrSN/PrSN* = 0.84–0.86) and superchondritic Y/Ho ratios (Y/Ho = 29–45; chondritic Y/Ho = 28). Their negative δ13C (−1.75‰ to −0.45‰) values are attributed to the influence of higher bio‐productivity during their deposition and oxidation of organic carbon. The geochemical and isotopic systematics suggest that the Dodguni limestones are not affected by the diagenetic and metamorphic processes and record the REE geochemistry of the ancient seawater in which they were precipitated. The comprehensive geochemical including the isotopic studies of the Archean carbonate rocks of the Dharwar Craton, indicate their deposition in shallow marine conditions, precipitation in high temperatures with significant hydrothermal input under the influence of high bio‐productivity, thereby providing valuable constraints on the palaeoceanography and geochemical evolution of the Archean sea. [ABSTRACT FROM AUTHOR]

Mass movements naturally occurring along slopes, especially after heavy rains, cause heavy losses of materials and life and affect highways, pipelines, and bridges, among other structures. Among the most common mass movements, landslides and subsequent mass flows especially stand out. Remote sensing and geoprocessing techniques are useful tools for geological and geotechnical analysis, here applied to characterization of mass movements from the analysis of the influence of slopes, lineaments or fractures, and geological-geotechnical at the junction of the Curral homocline and the Moeda syncline, Quadrilátero Ferrífero, Southeast Brazil. The area consists of Archean granitic-gneissic basement and the greenstone belt sequence of the Rio das Velhas Supergroup with Proterozoic metasedimentary rocks of the Minas Supergroup covering these two older successions. Based on satellite images, a preliminary map of lineaments was created, and fractures were grouped according to their direction before being rasterized. Each lineament group was associated with a previously known geological and/or structural feature. Geological units mapped in the area were numerically classified according to their mass movement susceptibility and related geotechnical units. Using a Shuttle Radar Topography Mission (SRTM) image, a terrain slope raster was generated. The objective was to obtain a raster indicating low and high probabilities of mass movements. Four sets of lineaments were identified: the first set associated with the northeast strike stratification of the rocks of the Moeda Formation; the second set related to eastward-trending warp axis lineations; the third set related to the southeast trend of stretch lineaments or mafic dykes directions; and the fourth set evidently associated with the watershed pattern of the Curral Range crest, perpendicular to the strike of the rocks in the area. Simulations with different combinations of parameters produced eight scenarios were generated were constructed to classify the area as to its susceptibility to rupture through changes in slope, lithotype, and lineament density; the first four (1 to 4) were classified by using the slope percentage raster without interval reclassification, so its values in the cartographic algebra were not grouped. The last for (5 to 8), consider the slope percentage classified. This methodology successfully combines mathematical models for predicting mass movements and determining areas in the urban landscape most susceptible to these phenomena. As such, it comprises a useful tool for government planning of preventative actions for areas of high risk. [ABSTRACT FROM AUTHOR]

New geochemical data demonstrate the similarity between Neoarchaean TTGs found in the middle crust of the Zimbabwe Craton and the lower crust of the Northern Marginal Zone of the Limpopo Belt. Hence the Neoarchaean segment of the Zimbabwe Craton provides a complete crustal section—from lower crustal granulites to the supracrustal rocks of the greenstone belts. Mantle activity recorded in the basalts of the greenstone belts is interpreted as plume volcanism, setting a context for the process of crustal generation. However, published isotopic data and new trace element data reported here show that magma genesis in Zimbabwe Craton in the Neoarchaean incorporated up to 20% of older crust, indicating that not all the granitoids are juvenile. This paper seeks to identify the trace element composition of the parental melts to the TTGs of the Zimbabwe Craton, define the petrological processes by which they were generated and set limits on possible petrological models for the process of crust generation. The least contaminated TTGs have low SiO2 and moderately fractionated trace element patterns. Calculations indicate that they were derived by the partial melting of a garnet amphibolite source at ca 10 kb depth. Rare intrusive diorites represent a low fraction melt of an enriched mantle source derived from refertilised depleted mantle. These observations lead to a model in which the source material of the TTGs was basaltic and the thermal energy to melt the basalts came from continued basaltic and komatiitic magmatism. Partial melts of old felsic crust were incorporated into the TTG magmas. The resulting 'enriched' TTGs provided a fertile lower crust from which an extensive suite of late tectonic granites could be generated. These data do not support a modern-style plate tectonic model for the growth of the Zimbabwe Craton in the Neoarchaean. [ABSTRACT FROM AUTHOR]

Studies of accreted oceanic plateau sections provide crucial information on their structures, compositions, and origins. We investigate the petrogenesis of ultramafic–mafic rocks in the Tangjia–Sumdo greenstone belt of southeast Tibet using petrography, whole-rock geochemistry, and U-Pb zircon geochronology. These rocks are divided into four groups based on geochemical characteristics that include depleted and tholeiitic mafic rocks, transitional mafic rocks, enriched and alkaline mafic rocks, and picritic ultramafic rocks. Depleted and tholeiitic mafic rocks have the oldest crystallization ages (∼272 Ma), followed by picritic ultramafic rocks (∼270 Ma), transitional mafic rocks (267–254 Ma), and enriched and alkaline mafic rocks (252–250 Ma). Hafnium and neodymium isotope ratios of depleted and tholeiitic mafic rocks (εHf(t) = +13.1–+16.9; εNd(t) = +6.9–+7.1), transitional mafic rocks (εHf(t) = +1.8–+16.9; εNd(t) = +0.8–+5.5), enriched and alkaline mafic rocks (εHf(t) = +0.5–+5.4; εNd(t) = −1.5 to +1.9) and picritic ultramafic rocks (εHf(t) = +14.9–+17.2; εNd(t) = +7.8–+9.0) are similar to those of N-MORB, E-MORB, OIB and depleted-type picritic mafic rocks in other oceanic plateaus, respectively. The geochemical characteristics of the depleted and tholeiitic mafic rocks suggest that they formed by partial melting of depleted spinel lherzolite in a mid-ocean ridge setting, whereas the picritic ultramafic rocks suggest a high degree of partial melting of depleted lherzolite in a hot mantle plume head. The transitional mafic rocks formed by partial melting of moderately enriched garnet lherzolite. The youngest rocks (enriched and alkaline mafic rocks) formed by partial melting of a more enriched garnet lherzolite (compared to transitional mafic rocks) at relatively low temperatures. We propose that the depleted and tholeiitic mafic rocks represent normal oceanic crust of the Sumdo Paleo-Tethys Ocean and the transitional mafic rocks, enriched and alkaline mafic rocks and picritic ultramafic rocks are the fragments of the oceanic plateau, which were related to middle–late Permian mantle plume activity in the Sumdo Paleo-Tethys Ocean. We further suggest that the majority of the Tangjia–Sumdo greenstone belt represents a middle–late Permian oceanic plateau that reflects a previously unrecognized middle–late Permian mantle plume.

The paper presents data on geology and composition of rocks from the Ustoyarvi region (the North-Western Arctic zone of Russian Federation). Their compositional analysis (including mathematical evaluation of the similarity/difference measure) provided much reliable conclusion that the rocks from this area, which are presumably attributed to the Ustoyarvi structure (Ustoyarvinsky Greenstone Belt) were similar to those from the Ura-Guba area in the Kolmozero-Voronya Belt and continued it. In addition, it has been shown that from west to east lithotectonic units in the adjacent (Suormussky) Block become gradually impregnated with tectonic wedges of rocks of the Ustoyarvi Greenstone Belt. It indicates increasing collisional interaction between rock associations with a varied genesis. P-T formation parameters have been specified for komatiites from greenstone belts, i. e. the Kolmozero-Voronya, Ura-Guba, Ustoyarvi and Western Litsa area. It has been defined that komatiites of the Ustoyarvi Greenstone Belt were formed under pressure of about 5 hPa, komatiites of the Ura-Guba area – about 4.5 hPa, komatiites of the Kolmozero-Voronya – about 2 hPa. Thus, komatiites of the Ustoyarvi Greenstone Belt are more high-pressure formations.

The nature of the early Archean ocean floor remains a topic of important debate. There are relatively few well-preserved occurrences worldwide where such terrains may be studied in detail because of structural dismemberment, metamorphic overprinting and pervasive early stage hydrothermal alteration to recent weathering. The 3.41-Ga dominantly mafic formations of the Nondweni Greenstone Belt (NGB) covering 270 km2 in the south-eastern Kaapvaal Craton comprise submarine volcanics that exhibit a wide range of textural features, including pillows, chill zones and brecciated flow tops, and various spinifex textures, including the rare platy pyroxene type, cumulate layers, and tuffs. Channelized subaqueous lava lakes that underwent fractionation are capped by thick spinifex-textured units and pillows. Early stage seafloor alteration is regionally variable, ranging from intense to minimal, with preservation of original mineralogy in many areas. Mafic volcanic rocks of the NGB contrast with those of the Barberton Greenstone Belt both in the style of volcanism and in the associated compositional range of komatiitic basalt to basalt with a complete absence of high-Mg komatiites. Olivine-phyric rocks, or derivatives thereof, are largely absent and pyroxene is the main controlling phase with orthopyroxene in the most primitive komatiitic basalts and clinopyroxene in the evolved lava lake sequences. The abundance of orthopyroxene typifies the long-standing silica-enriched character of the Kaapvaal Craton. Three exceptionally well-preserved and well-exposed sequences were studied utilizing hand-drilled samples and deep coring providing unprecedented stratigraphic and textural detail and field controls for more than 400 samples. A unifying feature of the mafic volcanics of the NGB is the range of compositions and ratios of incompatible elements most clearly illustrated by a series of high- and low-Ti compositional lineages reflecting differing sources or degrees of mantle partial melting. Sharp boundaries between high- and low-Ti flow successions indicate sudden changes in the melting regimes or the interaction of flow sequences from different volcanic centres. Th/Nb ranges from 0.1 to 0.2 and reveals crustal contamination of primitive lavas. The primary magma that gave rise to the most primitive komatiitic basalts with 19.5% MgO was derived from partial melting of a mantle plume source in the garnet stability field. Trace element modeling shows that the sequences studied in detail have been modified by fractionation and crustal contamination with the most likely contaminant being the Ancient Gneiss Complex (3.43–3.66 Ga), which is extensively exposed in Eswatini and probably underlies the Paleoarchean terrains in the southern Kaapvaal Craton. The geotectonic setting was likely that of a submerged felsic crustal platform as enclaves within an oceanic plateau. [ABSTRACT FROM AUTHOR]

Orogenic gold deposits are comprised of complex quartz vein arrays that form as a result of fluid flow along transcrustal fault zones in active orogenic belts. Mineral precipitation in these deposits occurs under variable pressure conditions, but a mechanism explaining how the pressure regimes evolve through time has not previously been proposed. Here we show that extensional quartz veins at the Garrcon deposit in the Abitibi greenstone belt of Canada preserve petrographic characteristics suggesting that the three recognized paragenetic stages formed within different pressure regimes. The first stage involved the growth of interlocking quartz grains competing for space in fractures held open by hydrothermal fluids at supralithostatic pressures. Subsequent fluid flow at fluctuating pressure conditions caused recrystallization of the vein quartz and the precipitation of sulfide minerals through wall-rock sulfidation, with some of the sulfide minerals containing microscopic gold. These pressure fluctuations between supralithostatic to near-hydrostatic conditions resulted in the post-entrapment modification of the fluid inclusion inventory of the quartz. Late fluid flow occurred at near-hydrostatic conditions and resulted in the formation of fluid inclusions that have not been affected by post-entrapment modification as pressure conditions never returned to supralithostatic conditions. This late fluid flow is interpreted to have formed the texturally late, coarse native gold that occurs along quartz grain boundaries and in open spaces. The systematic evolution of the pressure regimes in orogenic gold deposits such as Garrcon can be explained by relative movement of fault-fracture meshes across the base of the upper crustal brittle-ductile transition zone. We conclude that early vein quartz in orogenic deposits is precipitated at near-lithostatic conditions whereas the paragenetically late gold is introduced at distinctly lower pressure. [ABSTRACT FROM AUTHOR]

In Cameroon, most of the iron formation occurrences reported are found within the Nyong and Ntem Complexes. The Anyouzok iron deposit is located in the Nyong Complex greenstone belts, which represent the NW margin of this Congo craton. The main lithological units comprise the iron formations (IFs) unit, consisting of banded IFs (BIFs) and sheared BIFs (SBIFs), and the associated metavolcanic rocks unit consisting of mafic granulite, garnet amphibolite, and biotite gneiss. Within the Anyouzok area, BIFs are rare, while SBIFs are ubiquitous. This study reports the petrography, mineralogy, and whole rock geochemistry of IFs and interbedded metavolcanic rocks of the Anyouzok iron deposit. The abundance of cavities, higher Fe contents (49.60–55.20 wt%), and strong Eu anomalies (Eu/Eu* = 2.14–3.17) within the SBIFs compared to the BIFs suggest that SBIFs were upgraded through post-depositional hydrothermal alteration activities. REE signatures indicate the contribution of both seawater and hydrothermal fluids during BIFs precipitation. Mafic granulite and garnet amphibolite protoliths were derived from the partial melting of a metasomatized spinel lherzolite depleted mantle source. The overall compositional variations of the Anyouzok IFs and interbedded metavolcanic rocks endorse an Algoma-type formation deposited in the back-arc basin under suboxic to anoxic conditions. [ABSTRACT FROM AUTHOR]

In orogenic gold systems, the source of the fluids and the processes leading to mobilization, transport, and deposition of gold remain debated. Most studies focus on endowed rather than on gold-poor orogenic systems to unravel the "key" parameters of gold mineralizing processes. Here, we present stable isotope (O, H) data from the Moly-Desgagné–Guercheville fault system (gold-free to low gold endowment) in the Chibougamau area, Abitibi greenstone belt, Canada. The gold-free Moly-Desgagné showing and nearby poorly endowed Hazeur showing and Monster Lake deposit share similar features typical of orogenic systems. The stable isotope compositions of tourmaline and quartz from the Moly-Desgagné–Guercheville fault system also display similar characteristics, such as (1) temperature of vein formation of 345 ± 86 °C (1σ); (2) fluid mixing between an upper crustal reservoir (low T – high δD – low δ18O) and a metamorphic water reservoir (high T – low δD – high δ18O); and (3) positive δDfluid values consistent with multiple boiling-condensation cycles related to fault-valve processes. These characteristics are similar to those from the gold-endowed Val-d'Or vein field. The difference in gold endowment between the Moly-Desgagné–Guercheville and Val-d'Or vein fields may be related to the nature of the fault system (i.e., terrane-bounding or "intragreenstone belt") and the volume and (or) composition (i.e., gold, its ligands, CO2) of the fluid source rocks. [ABSTRACT FROM AUTHOR]

Earth's mineral deposits show a non-uniform spatial distribution from the craton-scale, to the scale of individual mineral districts. Although this pattern of differential metal endowment is underpinned by lithospheric-scale processes the geological features that cause clustering of deposits remains enigmatic. The integration of geological and geophysical (seismic, gravity, and magnetotelluric) features has produced the first whole-of-crust image through an iconic Neoarchean volcanic complex and mineral district in the Abitibi Greenstone Belt, Superior Province, Canada. Observations indicate an asymmetry in surface geology, structure, and crustal architecture that defines deep transcrustal magmatic-hydrothermal upflow zones and the limits of the Noranda District ore system. Here, extreme volcanogenic massive sulfide (VMS) endowment is confined to a smaller area adjacent to an ancestral transcrustal structure interpreted to have localized and optimized magmatic and ore forming processes. Although lithospheric-scale evolutionary processes might act as the fundamental control on metal endowment, the new crustal reconstruction explains the clustering of deposits on both belt and district scales. The results highlight a strong magmatic control on metal and in particular Au endowment in VMS systems. Overprinting by clusters of ca. 30 Ma younger orogenic Au deposits suggest the ore systems accessed an upper lithospheric mantle enriched in Au and metals. [ABSTRACT FROM AUTHOR]

Understanding the dominant crustal accretion model in any Archean craton is the key to understanding the dominant geodynamic process responsible for early crust formation during the Hadean (> 4.0 Ga) and Archaean (4.0–2.5 Ga). The continental crust has been proposed to have formed through either horizontal/vertical accretion related to subduction or mantle plume tectonic processes. Here, the Moho depths and average crustal Vp/Vs ratios are modelled at 16 broadband stations in the Eastern Indian Shield (EIS) through HK stacking of radial P-receiver functions (PRFs). These modelled parameters are used to test both plume and subduction models, which might have played a key role in the crustal accretion of the EIS throughout the Archean. We observe a correlation between crustal age and composition within the ellipsoidal Paleoarchean cratonic domain in the Singhbhum-Odisha-Craton (SOC), which reveals an increase in age from the younger granitoid core of the SOC (with thinning of felsic crust) to the surrounding older greenstone belts (with thickening of felsic crust). A thinner mafic crust resulting from multiple magmatic events characterizes the neighbouring Meso-Proterozoic Chotanagpur Granitic Gneissic terrain (CGGT). The Common Conversion Point (CCP) image of radial PRFs reveals northward subduction of the Paleoarchean SOC below the Meso-Proterozoic CGGT. [ABSTRACT FROM AUTHOR]

Palaeo‐Mesoarchean Banded Iron formations (BIFs) of central Bundelkhand greenstone belts occur from Babina (in the west) to Mahoba (in the east) via Mauranipur along with the E–W trending of the Bundelkhand Tectonic Zone (BTZ). In the present study, we report petrological, geochemical, and mineralogical data of BIFs from the Babina, Mauranipur, and Mahoba greenstone belts of central Bundelkhand Greenstone Complex to address their source characteristics and deposition environment. The lithological association of BIFs in the Babina and Mauranipur greenstone belts consists of pillowed basic–ultrabasic volcanics and metasediments, whereas in the Mahoba greenstone belt, BIFs and quartzite occur within basic volcanics. These lithological associations collectively suggest that the entire succession was deposited in a marine environment. Based on geological setting, they are classified as Algoma‐type. The main mineral assemblages of the Babina and Mauranipur BIFs are composed of magnetite, quartz, ±garnet, hornblende, chlorite, and apatite, whereas the Mahoba BIFs along with magnetite and quartz, poised of two distinct mineral assemblages; the first one is Opx–Cpx–Grt and the other one is Grt–Hbl. The preliminary P–T study of these BIFs implies that they had gone through amphibolite‐ to granulite‐facies metamorphism. The geochemical characteristics show that BIFs from the Babina and Mauranipur greenstone belts are dominated by higher quartz and magnetite (total content = 90.63–99.95 wt.%), whereas the Mahoba greenstone belt is characterized by lesser quartz and magnetite components (total content = 86.68–94.58 wt.%). The PAAS (Post Archean Average of Australian Sediments)‐normalized REE patterns display significant positive Eu anomaly (Eu/Eu* up to 2.50) with well‐represented negative Ce anomalies (Ce/Ce* = 0.27–1.20). The REE and trace element ratios of BIFs from the Babina and Mauranipur greenstone belts suggest that they were formed by high‐T hydrothermal fluid activity without or very less continental input. Moreover, the Mahoba greenstone belt BIFs are formed by low‐T hydrothermal fluid activity with substantial continental input. Their chemical variation suggests the shallowing of the proto‐basin from the Babina in the west to Mahoba in the east. Tectonic discrimination plots imply the BIFs of the Babina, Mauranipur, and Mahoba greenstone belts of the central Bundelkhand Greenstone Complex are formed in a back‐arc tectonic setting. [ABSTRACT FROM AUTHOR]

It is well established that the major and minor element contents of chromites are subject to change during greenschist to amphibolite facies metamorphism. During upper amphibolite facies metamorphism, chromite can be completely converted to chrome magnetite. However, not all elements are affected to the same degree, the concentrations of +2 ions (e.g. Zn, Co, Mn) being particularly vulnerable to modification. The degree to which trace elements, particularly the platinum-group elements (PGE), are affected has not been closely examined. The compositions and textures of chromites from komatiites of the Gorumahishani greenstone belt of the Singhbhum Craton (India) have experienced a range of metamorphic conditions from greenschist to amphibolite facies, providing the opportunity to study the changes of trace and platinum-group element composition with metamorphic grade. Five types of altered chromites are identified from the komatiitic suite of rocks in the ~120-km-long greenstone belt. The type-I chromites are non-porous and characterized by the least modified cores. These chromites are mostly present in the northern Maharajgunj-Tua Dungri section where rocks show metamorphism from greenschist to greenschist-amphibolite transition facies. The type-II and type-III chromites are porous and mostly found in the southern Kapili section of the greenstone belt where rocks show metamorphism up to the mid-amphibolite facies. Type-IV and type-V chromites are completely modified to ferritchromit and chrome magnetite, respectively, and are present in the komatiitic rocks from the entire greenstone belt. The central cores of the type-I and type-II grains have relatively higher concentrations of mobile trace elements (e.g. Zn, Co, and Mn) with higher Mg# [Mg/(Mg + Fe2+)], lower Cr# [Cr/(Cr + Al)], and lower Fe3+/R3+ (R3+ = Fe3+ + Cr3+ + Al3+) ratios than their respective rims. Significantly higher concentrations of the immobile trace elements (e.g. Ti and V) in the cores of the type-II grains relative to their chrome magnetite rims from the Kapili section and to the type-I varieties from other sections might be due to the metamorphism of the komatiitic rocks under higher-grade conditions (amphibolite facies). In situ LA-ICPMS analysis for PGE reveals a relatively higher concentration of Ru and Rh in the rims of the type-I chromites than in the cores which is due to the diffusion of these elements from the normal spinel structure of the cores towards the bivalent octahedral sites of the inverse spinel structure of the chrome magnetite rims during metamorphic processes. The lower concentrations of Os, Ir, Ru, and Rh in the cores of the type-II chromites from the Kapili section might be related to the metamorphism of the rocks under higher-grade conditions that facilitated the diffusion of these elements to associated sulphide or platinum-group mineral or alloy phases. The calculated partition coefficients of Sc, Ti, V, Mn, Ni, Ga, Os, Ir, Ru, and Rh from the least altered chromite cores assuming equilibrium with the parental komatiitic melt also suggest the variable effects of metamorphism when compared with global experimental and empirical values of the natural samples. [ABSTRACT FROM AUTHOR]

The Hole Narsipur Greenstone Belt (HGB), in the Western Dharwar Craton, South India, preserves evidence for three cycles of metamorphism spanning the Archaean–Proterozoic transition. Changes in metamorphic style across the transition are investigated using integrated petrographic, mineral chemical, metamorphic evolutionary history, conventional geothermobarometry, and phase equilibria modeling studies of rocks of diverse bulk rock composition from the belt. These rocks record signatures of three overprinting metamorphic cycles (M2 → M3 → M4 in sequence), postdating a Mesoarchaean, M1 event in the craton. The M2 cycle represents characteristic LP–HT metamorphism along a counterclockwise (CCW) metamorphic P–T path, peak metamorphism at 4–5 kbar, 515–595°C, and high thermobaric ratios (T/P ~1050–1525°C/GPa) at the M2 peak. The intermediate M3 metamorphic cycle records a prograde burial of partially cooled M2 rocks to middle-lower crustal depths, peak metamorphism at P ~7.5–10.2 kbar, T ~630–655°C, and corresponding intermediate T/P ratios (T/P ~620–875°C/GPa) and a retrograde stage, marked by combined exhumation and cooling to P ~5.3–6.4 kbar, T ~530–575°C. The resultant P–T paths of evolution show variability of clockwise (CW) paths from classical hairpin type to two-stage prograde heating segments. During the M4 metamorphism (T Max ~630–640°C at ~8.9–10.3 kbar and with lower T/P ratios at ~610–720°C/GPa), the partially exhumed M3 crust is re-buried to lower crustal depths along an intermediate thermal gradient as during the M3 metamorphic cycle. We interpret the thermal transition, tectonic thickening along a cooler thermal gradient, repeated burial-exhumation cycles in the orogenic wedge, and tectonic mixing of the three metamorphic cycles in terms of a three-stage tectonic evolution of the HGB. These in a sequence are (a) the development of a hot and thinned crust (cf. M2 cycle), (b) the transition to a thickened crustal zone tectonic domain (cf. M3 cycle), with both the domains being part of the lithospheric peel-back driven convergence setting and (c) finally continental collision tectonics (cf. M4 cycle). The pulsating nature of orogenesis at the Archaean–Proterozoic boundary deduced here distinguishes the Western Dharwar Craton from other cratonic blocks globally at the same time frame. [ABSTRACT FROM AUTHOR]

The collaborative federal–provincial Southern Indian Lake project in north-central Manitoba covered an area of more than 3500 km2 of the Trans-Hudson orogen. Regional-scale geological mapping, sampling, and lithogeochemical, isotopic, and geochronological studies resulted in the identification of distinct assemblages of supracrustal rocks and varied episodes of plutonism. A granodiorite gneiss dated at ca. 2520 Ma is interpreted to represent the basement of the Southern Indian domain and is considered a separate crustal domain, named the Partridge Breast block. The Churchill River assemblage is composed of juvenile pillow basalt with intervening clastic sedimentary rocks, possibly a reflection of plume magmatism related to initial rifting of the Hearne craton margin. The Pukatawakan Bay assemblage consists mainly of massive to pillowed, juvenile metabasaltic rocks and associated basinal metasedimentary rocks. The Partridge Breast Lake assemblage is dominated by continental-arc volcanic and volcaniclastic rocks associated with basinal metasedimentary rocks. The Strawberry Island assemblage, consisting of arenite and polymictic conglomerate, is interpreted to have been deposited in a foreland-basin basin or intra-orogen pull-apart basin environment. The Whyme Bay assemblage is characterized by fluvial-alluvial orogenic sediments and is temporally linked to the Sickle Group rocks in the Lynn Lake greenstone belt. Granitoid rocks, dominantly monzogranite and granodiorite, range in age from ca. 1890 to 1830 Ma and occur throughout the Southern Indian domain, and intermediate and mafic intrusions of similar ages are also present. In this paper, we integrate these new data into a tectonic framework for the Southern Indian domain of the Trans-Hudson orogen in Manitoba. [ABSTRACT FROM AUTHOR]

Radiogenic isotope systems are important geochemical tools to unravel geodynamic processes on Earth. Applied to ancient marine chemical sediments such as banded iron formations, the short-lived 182Hf-182W isotope system can serve as key instrument to decipher Earth's geodynamic evolution. Here we show high-precision 182W isotope data of the 2.7 Ga old banded iron formation from the Temagami Greenstone Belt, NE Canada, that reveal distinct 182W differences in alternating Si-rich (7.9 ppm enrichment) and Fe-rich (5.3 ppm enrichment) bands reflecting variable flux of W from continental and hydrothermal mantle sources into ambient seawater, respectively. Greater 182W excesses in Si-rich layers relative to associated shales (5.9 ppm enrichment), representing regional upper continental crust composition, suggest that the Si-rich bands record the global rather than the local seawater 182W signature. The distinct intra-band differences highlight the potential of 182W isotope signatures in banded iron formations to simultaneously track the evolution of crust and upper mantle through deep time. Banded iron formations, precipitates of Precambrian seawater, record global 182W isotope signatures derived from continental weathering and hydrothermal mantle fluxes into ancient oceans, tracking Earth's geodynamic evolution through deep time. [ABSTRACT FROM AUTHOR]

Two main stages of formation of gold deposits are identified in the north-eastern part of the Fennoscandian Shield—Neoarchean (2.7–2.6 Ga) and Paleoproterozoic (1.92–1.74 Ga). These were the stages of rapid growth of the continental crust of the Earth and the consolidation of the ancient supercontinents, Kenorland in the Neoarchean, and Fennoscandia (or Columbia) in the Paleoproterozoic. Gold deposits and occurrences, which formed in the Archean (Oleninskoe and Nyalm in the Kolmozero–Voron'ya belt, and the Olenegorsk group of BIF deposits) were later metamorphosed in the Paleoproterozoic, and isotope data for the rocks and minerals of these deposits detect both Archean and Paleoproterozoic events. The Paleoproterozoic stage was the most important for the formation of gold deposits in the region, as at this stage the deposits formed not only in the Proterozoic greenstone belts, but in those Archean belts as well, which were involved in the Svecofennian tectonic processes in the Paleoproterozoic. As it is shown in the example of the deposits in the Central Lapland Paleoproterozoic belt, gold mineralization formed with a series of impulses of hydrothermal activity, and these impulses correlate with the formation of different generations of minor granite intrusions and dykes. [ABSTRACT FROM AUTHOR]

Some of the world's largest orogenic gold deposits are hosted within granite-greenstone subprovinces of the Superior Province of Canada. The known gold endowment of the western Wabigoon subprovince is much less than that of the Abitibi subprovince, despite both Neoarchean subprovinces sharing similar structural and metallogenic histories. Further, the relationship between regional deformation and orogenic gold mineralizing events in the western Wabigoon subprovince is poorly constrained in comparison with other greenstone belts within the Superior Province. New structural mapping of the Dryden area of the western Wabigoon subprovince indicates that it experienced a N–S shortening event (D1), circa 2705–2695 Ma, which reactivated, or initiated the formation of, the E–W-trending Wabigoon and Mosher Bay – Washeibemaga deformation zones (Wdz and MBWdz, respectively). Following the D1 event, after 2695 Ma, a protracted period of NNW–SSE shortening (D2) localized transpression along the Manitou Dinorwic deformation zone (MDdz), which is spatially associated with orogenic gold systems, including the Goldlund deposit (∼1.7 Moz Au) and Kenwest prospect (∼0.3 Moz Au). During D2, the MDdz experienced NW-over-SE sinistral transpression, while the Wdz and MBWdz experienced N-over-S dextral-sense movement. U–Pb geochronology of vein-hosted xenotime from the Goldlund deposit and Kenwest prospect indicate that the main hydrothermal event, and likely gold mineralization, occurred syn- to late-D2 deformation around 2664 ± 8.3 Ma. A second population of xenotime, and overgrowths, recorded a younger hydrothermal overprint between ∼2590 and ∼2580 Ma. These ages are comparable with other absolute geochronology data on hydrothermal events in the gold-rich Abitibi subprovince. The structural evolution and timing of orogenic hydrothermal events in the western Wabigoon subprovince are broadly similar to the Abitibi subprovince. Therefore, we propose that the structural evolution and timing of individual greenstone belts is not the primary controlling factor on their bulk gold endowment. Nevertheless, orogenic gold deposits are spatially associated with major D2 deformation zones and linked to widespread hydrothermal event(s), spanning 2680–2660 Ma across the southern Superior Province. [ABSTRACT FROM AUTHOR]

The Kapuskasing Structural Zone transects the Wawa and Abitibi greenstone belts in the Superior province of the Canadian Shield. At the southern margin of the Kapuskasing Structural Zone (KSZ), the Borden Gold deposit hosts low-grade-gold mineralization within upper amphibolite- to granulite-facies sillimanite-garnet-biotite gneisses. Here, we present the geochemistry and Lu-Hf geochronological studies of a gold-hosting garnet-bearing gneiss to constrain the formation history of the deposit and regional geological history. The garnet is almandine-rich, and contains inclusions of quartz, biotite, pyrite, and zircon. The absence of chemical zoning in garnet is likely due to intracrystalline diffusion at peak metamorphic temperatures. The 176Lu-176Hf internal isochron of two garnet fractions and three corresponding whole-rock splits from a gneissic unit yield a precise internal isochron age at 2629.0 ± 4.3 Ma (MSWD = 0.66), with an initial 176Hf/177Hf = 0.281210 ± 0.000010 corresponding to an εHfi = +4.1. This signature suggests a mafic source, which was derived from a long-term depleted reservoir, for this metasediment. The Lu-Hf age is consistent with the youngest age population of zircons from the paragneisses, which were previously dated in the area. Our results thus provide upper constraints on the timing of retrograde upper-amphibolite metamorphism and gold mineralization at Borden. [ABSTRACT FROM AUTHOR]

The main aspects of perspectives and ways to create the gold mining industry of Ukraine as a source of replenishment of gold and foreign exchange reserves and an integral part of high-tech production have been considered. The latest EU trends in the mining industry, which have led to an increase of investment in geological exploration and, as a consequence, discovery and exploitation of new gold deposits, have been described. Brief information on the gold-bearing Archean-Proterozoic complexes of the world, which indicates a high concentration of deposits within the gold ore areas, has been given. The concentration of deposits is observed in zones of tectonic disturbance and metasomatic change of rock complexes, contrasting in composition. The geological characteristics of the most studied gold ore manifestations of the Ukrainian Shield (USh), where after additional studies it is possible to indicate industrial concentrations with significant increase of gold resources and start the production, have been presented. Similarities between USh manifestations and known Precambrian gold ore deposits of the world have been demonstrated. These are gold ore deposits of Precambrian green-stone belts and metamorphogenic-hydrothermal systems, so-called shear-zones of orogenic mesothermal type. Gold deposition is generally associated with sulfidization and associated quartzization and/or carbonation, the mineralization stage is preceded by albitization. Gold deposits were formed in several episodes over 2,1–1,8 billion years. Mostly native gold has a high proof quality, inherent associations with arsenic, tellurium and bismuth. The process of ore formation is multi-stage. The state of exploration and commercial attractiveness of USh gold ore objects for further works have been described by the example of the Maiske deposit. Methodological approaches to geological and economic assessment of gold ore objects have been considered. It has been demonstrated that determination of the gold content has been performed without taking into account the presence of gold particles of significant size and therefore its average content cannot be considered proven. Lack of information obtained during mining exploration leaves room for significant changes in the spatial and qualitative parameters of mineralization. Main unresolved problems, detected during researches, and ways to solve them have been outlined. Mining exploration of certain deposits will highlight the prospects of previously established gold ore areas.

The modern concepts of magmatic plumbing systems have evolved from simple models of melt-dominated crustal magma chambers to magmatic systems that span the continental crust. The geochemistry of these systems is challenging to model numerically because of a complex polybaric and multiphase evolution, which is not well described by mathematic end-member formulas. We propose that a recent modelling tool, the Magma Chamber Simulator (MCS), can reveal part of the petrological complexities of such systems. The MCS numerically models phase equilibria, mineral chemistry and major and trace elements in multicomponent–multiphase systems by finding the extremes of the appropriate state functions. This study presents new petrographical and geochemical data from the Palaeoproterozoic Gallujavri ultramafic intrusion in the Karasjok Greenstone Belt, Arctic Norway. Our data indicate that (1) the intrusion is affected by crustal assimilation, (2) phase equilibria require polybaric crystallisation and (3) spinel compositions are similar to sub-volcanic intrusions of continental flood basalt provinces. We utilise the MCS to simulate the petrogenesis of the intrusion and test the model by comparing it against our reported petrological and geochemical data. Our modelling shows that the parental magma of the intrusion is consistent with coeval Karasjok-type komatiites observed at various places throughout the greenstone belt. First, the komatiitic primary magma intruded Archaean lower crust (c. 700 MPa), where fractionation and assimilation resulted in a hybrid melt. Second, the hybrid melt migrated and accumulated in a mid-crustal magma chamber (c. 400 MPa), where it continued to fractionate and assimilate while remaining open to recharge of mantle-derived komatiitic melts, forming the Gallujavri intrusion. We interpret the Gallujavri intrusion as part of a Palaeoproterozoic trans-crustal magma plumbing system, with many similarities to other Fennoscandian ultramafic-mafic layered intrusions. [ABSTRACT FROM AUTHOR]

Clast morphometry and sedimentary facies analysis of polymictic conglomerate of the Hiriyur Formation in the Gadag greenstone Belt, Western Dharwar Craton, India, was conducted to constrain the palaeohydraulic condition, depositional environment, and type of sedimentary basin. The conglomerate grades from clast‐supported to matrix‐supported with siltstone‐sandstone intercalations. Eight lithofacies along with five major lithofacies associations are recognized in the Majjur and Attikatti Domains of the Gadag greenstone Belt. The lithofacies architecture suggests sedimentation commenced with rapid deposition of slope‐derived debris in a proximal high‐energy alluvial fan setting followed by a braided river environment. Clast morphometry and palaeohydraulic data indicate a low palaeoslope (0.000024 m/m), and stream discharge value (1.913 m3/s) calculated from the channel fill conglomerates. Greywacke overlying the conglomerate has been interpreted as turbidites from a continental slope. The accompanying 40‐m‐thick banded iron formation and carbonate rocks also support a marine context. The lack of transitional deposits between river and deep marine settings suggests that the greywacke turbidites sequence is separated from the conglomerate deposits by substantial unconformities. This change in depositional setting could be due to a change in basin subsidence rate, tectonic rejuvenation, or major sea‐level changes. [ABSTRACT FROM AUTHOR]

The deep upper mantle is the main source of high-temperature magmatism, but the only known naturally occurring samples of high-pressure mantle constituents are mineral inclusions in diamonds. Trace elements in olivine crystals from the 3.33 Ga Commondale Greenstone Belt in South Africa reveal that these crystals formed in the deep upper mantle as high-pressure phenocrysts, and some perhaps even formed in the mantle transition zone (410-600 km) where they began as wadsleyite. The crystals were entrained within ascending komatiite magma and conveyed to the surface. The olivine crystals have the highest contents of Al2O3 (0.3 wt%) recorded in any terrestrial olivine, which is indicative of formation at high pressure. The deep mantle gave rise to Archean komatiites, extraordinarily hot magmas (up to 1700 °C), which provide insight into Earth's early mantle evolution and the formation of most ancient continental and oceanic crust. In spite of extensive research since their discovery over 50 years ago, the origins of komatiites have remained contentious. Plumes--thermochemical instabilities originating at the core-mantle boundary--are the most likely source, but no direct evidence of a deep mantle origin of komatiite has yet been recognized. [ABSTRACT FROM AUTHOR]

Zircon provides essential information on the age and oxidation state of magmatic systems and can be used to characterize magmatic-hydrothermal Au mineralizing systems. Using the Douay intrusion-related gold system (IRGS) as a type example of Neoarchean syenite-associated mineralization (Abitibi greenstone belt), we demonstrate that zircon from altered quartz-monzonite rocks can also be used to infer the age of a magmatic-hydrothermal event. Here, zircon chemistry is used to identify the following sequence of events at the Douay exploration project: (1) the crystallization of zircon at ~2690 Ma in evolved residual melts with distinct U-contents (quartz-monzonite magma); (2) the extensive radiation damage for the U-rich grains over a period of ~10–15 My; and (3) the alteration of zircon grains at ~2676 Ma by interaction with magmatic-hydrothermal mineralizing fluids derived from syenite and carbonatite intrusive phases. This study also distinguishes extensively altered zircon grains from pristine to least-altered zircon formed in distinct magmatic environments using a Th/U vs. U discrimination diagram. [ABSTRACT FROM AUTHOR]

Trace element and isotopic data for basalts from the Isua greenstone belt, West Greenland, indicate that they were derived from a range of mantle reservoirs that included depleted lower mantle, the mantle transition zone, and a primitive mantle reservoir probably located in the shallow upper mantle. Modeling of trace element compositions indicates that the Isua basalts were formed through the mixing between and refertilization of these diverse sources and their resultant melts and that this took place in the shallow upper mantle. It is proposed that the melting and mixing were driven by the heat transferred from hot deep mantle sources. This geochemical interpretation leads to a geodynamic model in which deep mantle domains rise to melt in the shallow mantle where there is mixing between a range of sources and melts. There is no evidence for material descending from the shallow to deeper mantle and no necessity for the involvement of crustal materials. These processes imply the activity of a mantle plume and/or heat pipe. [ABSTRACT FROM AUTHOR]