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Cobalt is a highly sought-after metal due to its economic importance in many hightech applications. It is mainly obtained from sedimentary-hosted Cu-Co deposits and magmatic Ni-Cu deposits as a by-product. We describe a recently discovered Co-enriched Cu-Ni deposit hosted by the Hietakero mafic intrusion in north-western Finnish Lapland. The intrusion contains gabbroic to pyroxenitic cumulates and was emplaced into a supracrustal strata composed mainly of mafic volcanic rocks, sulfurbearing graphite schists and felsic volcanic interlayers. Hybrid rocks provide clear evidence for interaction of mafic magma with its country rocks. All these rocks have undergone intensive post-magmatic hydrothermal alteration by influx of H2O-, CO2- and Cl-bearing saline fluids, forming strongly scapolitized (±albitized) rocks and resulting in re-mobilization of sulfides and their metals. The Hietakero deposit is associated with pyroxenitic cumulates and hybrid rocks, with the sulfides (pyrrhotite, cobaltian pentlandite, chalcopyrite and pyrite) occurring as patches, brecciated to net-textured and vein to veinlet forms. Sulfur content is 6.1 wt.% on average, reaching 20 wt.% in some cases. Nickel and Cu tenors are low, but Co is elevated, resulting in very low Ni/Co of 2.6 compared to ‘classic’ Ni-Cu sulfide deposit globally. The average metal tenors are: 0.55 wt.% Ni, 1.07 wt.% Cu, and 0.23 wt.% Co. In-situ sulfur isotope analyses of sulfides from mineralized rocks yielded δ34S values from -2.0 to +4.5‰. In spite of strong post-magmatic alteration, we can conclude that the Hietakero cumulates were formed from a low-MgO and PGE-depleted basaltic magma, which developed in a staging chamber at a deeper crustal level. The magma produced compositionally different gabbroic to pyroxenitic rocks (i.e., high-Ti and low- Ti groups). Model calculations indicate that the relatively high Co tenor and low Ni/Co cannot be explained by an earlier phase of fractional crystallization or sulfide segregation. Instead, an external source of cobalt is needed, which is also consistent with the high Zn, Pb and Mo contents of the mineralized rocks. Based on sulfur isotope compositions, the associated black shales were not the primary source of sulfur, but sulfur was rather derived from a so far unrecognized, potentially Co-bearing contaminant with close to mantle-like δ34S. Our study reveals a new Co-Cu-Ni deposit type related to the widespread Paleoproterozoic mafic magmatism in Lapland.

Atmospheric mineral dust is a poorly constrained yet extremely important component of the climate system. Provenance studies from geologic dust archives are crucial to understand the drivers of the dust cycle over long time scales. Our multi‐technique provenance analysis of a rare Paleogene (35–27 Ma) eolian dust sequence from Ulantatal, ∼400 km northwest of the Chinese Loess Plateau (CLP), shows that Paleogene dust transporting winds generally varied between northwesterly and westerly, the same as those in the late Neogene‐Quaternary bipolar icehouse. We propose that, as today, westerly wind circulation patterns would have been modulated by an Arctic Oscillation (AO)‐like situation, and that the warm Eocene favored a long‐term negative phase of AO, leading to meridional westerly circulation and the dominance of a northwesterly dust transport pathway. After the Eocene‐Oligocene transition (EOT), long‐term positive phase of AO‐like conditions initiated, leading to stronger and more zonal westerlies. The Siberian High (SH) also formed or strengthened at the EOT and started to control dust storm activity along the northwesterly transport pathway. We argue that increased Paleogene Northern Hemisphere (NH) ice volume was the ultimate driver of this modern‐type dust transport regime in the Ulantatal region, possibly also controlling initial Ulantatal dust sequence formation via the development of the SH and modern‐type eolian regime. The similarity between the Ulantatal and late Neogene northern CLP dust provenance signals suggests that the increased NH ice volume, via its control on the northwesterly dust transport, could have promoted increased loess formation also in the late Miocene. Plain Language Summary: Understanding the effects and responses of atmospheric mineral dust to climate changes in the geologic past is crucial for predicting future scenarios. Analysis of the source of dust deposited 35–27 million years ago in Ulantatal, Inner Mongolia, China reveals that the Central‐East Asian atmospheric circulation during this time interval was similar to that of today. Specifically, dust transport was dominated by northwesterly and westerly winds despite a significantly warmer global climate. We also propose that Arctic Oscillation (AO)‐type conditions, stemming from the temperature difference between the high and low latitudes, modulated planetary westerly winds during this period. Our results suggest that during warmer phases, a negative AO type dominated and resulted in wave‐like westerly wind patterns and a northwesterly dust transport pathway to Ulantatal. During cooler phases, the westerly circulation became stronger and more zonal. The Siberian High pressure system was possibly strengthened during increased Northern Hemisphere (NH) ice volume and further affected northwesterly dust transport. Our findings suggest that NH ice volume increase was possibly also responsible for the formation of the Ulantatal dust sequence itself. Our results imply that even under significantly warmer conditions than today, polar ice affects the long‐term dustiness in this highly populated region. Key Points: The provenance of a Paleogene (35–27 Ma) eolian dust sequence in Ulantatal, Inner Mongolia, China, reveals a modern‐type eolian regimeGlobal cooling and possibly expansion of Northern Hemisphere ice volume modulated the dust provenance by strengthening the Siberian HighLong‐term negative (positive) phase of Arctic Oscillation‐like conditions were favored in the warmhouse Eocene (coolhouse Oligocene) [ABSTRACT FROM AUTHOR]

The main arguments used to support the concept that komatiites form by melting of hydrous mantle are as follows: (1) Water reduces liquidus temperatures from extreme values to lower, more 'normal' temperatures. (2) Some komatiites are pyroclastic and some contain vesicles, features that have been attributed to magmatic volatiles. (3) It is claimed from experimental studies of peridotite melting that the chemical composition of komatiite requires the presence of water, as does their characteristic spinifex textures. Counterarguments are the following: (1) Loss of volatiles as hydrous komatiite approaches the surface should produce degassing textures and structures, which, though not unknown, are rare in komatiites. Degassing should produce a highly supercooled liquid that partially crystallizes to porphyritic magma; komatiites commonly erupt as phenocryst-poor, highly magnesian lavas. (2) Chemical and isotopic compositions of most komatiites indicate that their mantle source became depleted in incompatible elements soon before magma formation. Such depletion removes water, leaving a dry source. (3) The experimental data are at best ambiguous; neither the chemical composition of komatiites, nor the crystallization of spinifex, requires the presence of water. We conclude that although some rare komatiites may be hydrous, most are dry.

The earliest Svecofennian magmatism in southern Finland has been dated to 1.90-1.88Ga. As an example of this, the Orijärvi (ca. 1.89Ga) and Enklinge (ca. 1.88Ga) volcanic centres comprise bimodal plutonic batholiths surrounded by volcanic rocks of comparable ages and chemical compositions. The rock types range from gabbros to granites and indicate a subduction-related continental margin setting. The zircons from the Orijärvi granodiorite define an age of 1892±4Ma whereas the Enklinge granodiorite yields an age of 1882±6Ma. Several inherited ages of 2.25-1.95Ga as well as younger metamorphic ages of 1.86-1.80Ga were found in the Enklinge granodiorite. The initial eNd values of the mafic rocks from both locations fall in the range +1.1 to +2.9, whereas the felsic rocks exhibit initial eNd values of -0.4 to +1.2. The magmatic zircons from the Orijärvi and Enklinge granodiorites show average initial eHf values of -1.1 (at 1892Ma) and zero (at 1882Ma), respectively, both with a spread of about 7 e-units. The initial eHf values for the inherited zircons from Enklinge range from +3.5 to +7.6 with increasing age. The Sm-Nd data indicate that the mafic rocks were derived from a "mildly depleted" mantle source while the felsic rocks show some crustal contribution. Also, the variation in eHf values indicates minor mixing between mildly depleted mantle-derived magmas and crustal sources. U-Pb ages and Hf isotopes for inherited zircons from the Enklinge granodiorite suggest the presence of juvenile Svecofennian "proto-crust" at depth. [ABSTRACT FROM AUTHOR]

The Monts de Cristal Complex of Gabon consists of several igneous bodies interpreted to be remnants of a tectonically dismembered, >100 km long and 1-3 km wide, ultramafic-mafic intrusion emplaced at 2765-2775 Ma. It is the most significant mafic-ultramafic layered complex yet identified on the Congo Craton. The complex consists largely of orthopyroxenite cumulates, with less abundant olivine-orthopyroxenite and norite, and rare harzburgite and dunite. Mineral compositions (Fool 84, Mg#Opx 85, Anplag 60-68, Cr/Fe chromite 1-1·45) and whole-rock data suggest that the parent magma was a low-Ti basalt containing approximately 10% MgO and 0·5% TiO2. Trace element and Rb-Sr and Sm-Nd isotope data indicate the presence of an enriched component, possibly derived from crustal contamination of a magma generated in the sub-lithospheric mantle. Most rocks show a highly unusual pattern of strong Pt enrichment (10-150 ppb) at low concentrations of Pd (1-15 ppb), Au (1-2 ppb), Cu (1-20 ppm), and S (<500 ppm), suggesting that unlike in most other PGE-rich intrusions globally, platinum in the Monts de Cristal Complex is not hosted in magmatic sulfides. Synchrotron X-ray fluorescence mapping has revealed the location of buried small Pt particles, most of which are associated with As. We propose that this constitutes some of the strongest evidence yet in support of magmatic crystallization of a Pt-As phase from S-undersaturated magma. [ABSTRACT FROM AUTHOR]

The mid-Proterozoic, locus classicus Wiborg rapakivi granite batholith of southeastern Finland and adjacent Russia comprises a varying, bimodal (silicic-basic) sequence of plutonic, subvolcanic, and volcanic rocks. At the current level of erosion silicic rocks are dominant, the most prominent of which are wiborgites and dark wiborgites (that have been considered to mark the main build-up stage of the batholith) and pyterlites. New observations and optical microscopy data from the dark wiborgite-dominated Ristisaari Island in the southern, off-shore part of the Wiborg batholith show that dark plagioclase megacrysts in dark wiborgite are calcic xenoc-rysts. They were probably incorporated into wiborgite magma from consanguineous massif-type anorthosite magmas in the course of the evolution of the bimodal magmatic system. Our new ID-TIMS U-Pb zircon age of the Ristisaari Island dark wiborgite, 1627±3 Ma, is the youngest isotopic age so far determined for the plutonic rocks of the Wiborg batholith. This, combined with preexisting U-Pb zircon data, implies a minimum duration of 12 m.y. (1642-1630 Ma) for the emplacement of the plutonic rocks of the batholith. Combined with data on high-level dike rocks, a window of at least 20 m.y. (1642-1622 Ma) is implied. Furthermore, as the batholith grew, the overall locus of magmatism may have shifted southwards. New whole-rock Nd isotope data on the dark wiborgite of the Ristisaari Island and three further granites of the batholith, as well as Nd (whole-rock) and Sr (whole-rock, plagioclase) isotope data on a spect- rolite massif-type anorthosite from the east-central part of the batholith, are also presented. These data suggest that the lithosphere across the Wiborg batholith area in the southeastern part of the Svecofennian orogen may vary slightly in overall mantle separation age. [ABSTRACT FROM AUTHOR]

This project follows on from an initial study of Celtic gold coins from the Middle Rhine/Moselle region, which was based on material found at the Martberg, a Late Iron Age/Roman sanctuary and settlement (River Moselle, western Germany; Bendall 2003 ). The earlier work was expanded to encompass over 100 examples of various other regional Celtic gold coinages from the collection of the Römisch-Germanisches Zentralmuseum, Mainz. The alloy (Au–Ag–Cu) and trace element compositions (in particular Ni, Sb and Pt) were determined by EPMA and LA–ICP–MS, respectively, and their Pb isotope signatures were measured by LA–MC–ICP–MS. Of the 28 trace elements measured, only Ni, Sb and Pt were found to show meaningful variations and so only they are presented here. In particular, differences in the Pt/Au ratios between various groups of earlier coinage (imitations of Philippus and Alexander/Nike staters, Sch. 23 and some early Boian coins) on the one hand, and the majority of the Boian and the southern rainbow cup coinages on the other, indicate a significant difference in the gold sources exploited for these regional coinages. The Pb isotope data confirm previous conclusions that the contribution of gold to the total lead in the Au–Ag–Cu coin alloys can be detected, especially for coins with over 70% gold, and show that possible gold sources include both eastern Mediterranean and Alpine sources. Combining the Pb isotope data with the Pt/Au ratios allows the potential gold sources to be further differentiated. [ABSTRACT FROM AUTHOR]

Lead and copper isotopes of Roman Imperial copper coins (denominations as and quadrans) were analysed by MC–ICP–MS. We concentrated on well-dated coins minted at the official mint of Rome under the Emperors Augustus and Tiberius (between 16bcandad37). The lead isotope results were compared with published lead isotope data of ore bodies from the Aegaean, Cyprus, Italy and Spain, in order to fingerprint the sources of Roman copper. During the Augustan period the main copper supply, as judged from the copper coins, is from Sardinia and south-east Spain, with minor contributions from Tuscany. Except for Tuscany, this continued into the Tiberian period, when Cypriot copper also appears. Augustan quadrantes and late Tiberian asses came solely from the Rio Tinto area in south-west Spain. Copper isotopes were applied here for the first time to systematic archaeometric studies. They are supplementary to lead isotopes and allow further grouping and classification of the copper coins. [ABSTRACT FROM AUTHOR]

Pyrite-δ 34 S and -δ 56 Fe isotopes represent highly sensitive diagnostic paleoenvironmental proxies that express high variability at the bed (< 10 mm) scale that has so far defied explanation by a single formative process. This study reveals for the first time the paleoenvironmental context of exceptionally enriched pyrite-δ 34 S and -δ 56 Fe in bioturbated, storm-reworked mudstones of an early Ordovician storm-dominated delta (Tremadocian Beach Formation, Bell Island Group, Newfoundland). Very few studies provide insight into the low-temperature sulfur and iron cycling from bioturbated muddy settings for time periods prior to the evolution of deep soil horizons on land. Secondary ion mass spectroscopy (SIMS) analyses performed on Beach Formation muddy storm event beds reveal spatially distinct δ 34 S and δ 56 Fe values in: (a) tubular biogenic structures and trails (δ 34 S ~ +40‰; δ 56 Fe ~ -0.5‰), (b) silt-filled Planolites burrows (δ 34 S ~ +40‰; δ 56 Fe ~ +0.5 to + 2.1‰), and (c) non-bioturbated mudstone (δ 34 S ~ +35‰; δ 56 Fe ~ +0.5‰). δ 34 S values of well above + 40.0‰ indicate at least some pyrite precipitation in the presence of a 34 S-depleted pore water sulfide reservoir, via closed system (Raleigh-type) fractionation. The preferential enrichment of 56 Fe in Planolites burrows is best explained via microbially-driven liberation of Fe(II) from solid iron parent phases and precipitation from a depleted 54 Fe dissolved Fe(II) reservoir. Rigorous sedimentological analysis represents a gateway to critically test the paleoenvironmental models describing the formation of a wide range of mudstones and elucidates the origins of variability in the global stable S and Fe isotope record.

The Mawat ophiolite, NE Iraq, is one of the Neo-Tethyan ophiolites within the Iraqi Zagros orogen. It consists of many metre-to kilometre-sized tectonic slices of serpentinized dunite, peridotite, gabbro, basaltic rocks and associated oceanic metasediments. Felsic intrusions crosscut the ophiolite. We present U-Pb zircon and monazite ages and Hf zircon isotopes from two crosscutting felsic dykes and a gabbro from the mantle section of the ophiolite. Zircons from the felsic dykes contain spongy domains and xenotime and monazite inclusions. They give ages from 222 to 46 Ma. The age range is interpreted to be caused by secondary processes such as radiogenic Pb mobility and Pb loss. The monazite age of 94.6 ± 1.2 Ma is considered to give a crystallisation age of the felsic dykes. The gabbro zircons give ages between 81 to 38 Ma of which the two oldest grains give the weighted average age of 81.2 ± 2.5 Ma which we interpret to be the crystallisation age of the gabbro. The zircon initial ε Hf values in the felsic dykes are negative (averages -2.7 and -3.1) while they in the gabbro are positive (average + 3.5), indicating that the felsic magma comes from an older source while the mafic magma comes from a juvenile one. Two mafic units of different ages were identified: the older unit is cut by the 95 Ma felsic dykes and the younger one is represented by the 81 Ma gabbro located within a thrust zone. The youngest ages of 40 Ma are considered to be related to crustal extension., (© 2019 The Author(s).)