Antarctic ice cores and ocean-sediment records preserve evidence for an increase in the amplitude of glacial-interglacial cycles at around 430 ka, known as the Mid-Brunhes Transition (MBT). However, similar evidence from non-polar terrestrial environments is rare, casting some doubt on the global extent of this transition. Here we present a multi-proxy speleothem record from Corchia Cave (Alpi Apuane, Italy) that spans the MBT. It comprises a stacked d18O and d13C time series from multiple stalagmites anchored in time by U-Th and U-Pb ages; and trace element, 87Sr/86Sr, and d18O and d13C profiles from a subaqueous calcite deposit (CD3) that has grown continuously from 970 ka to the present. We anchored the CD3 record to the chronology of a stalagmite stack by synchronisation of their respective d18O and d13C profiles. CD3 is well suited to this study because it yields a suite of proxies from just a single specimen that covers multiple glacial-interglacial cycles either side of the MBT. In particular, its d13C profile provides a reference for comparing the amplitude of glacial-interglacial temperature changes at Corchia to globally integrated ice-volume (LR04 benthic 18O/16O stack) and greenhouse gas (ice-core CO2 and CH4)time series. The CD3 temperature record builds on a previous trace element study, which revealed that the Mg/Ca in this speleothem is strongly influenced by mineralisation temperature (a proxy for external air temperature at the cave site). This is supported by subsequent clumped-isotope palaeothermometry. We thus developed a continuous palaeotemperature time series for CD3 extending to ~650 ka via a Mg-D47 transfer function. The temperature profile reveals compelling evidence for a shift in glacial-interglacial amplitude across the MBT. Temperatures during the interglacials of MIS15e, 15a and 13a are lower in Corchia compared to those of MIS11c, 9e, 5e and the Holocene; temperatures during MIS7e and 7c are the exception, only reaching the levels of the pre-MBT interglacials. Minimum glacial temperatures for MIS16 and 14 are warmer in Corchia than those of the subsequent glacial maxima, and the MIS12 and 6 glacials are the coldest of the last 650 kyr. All of these patterns are consistent with existing global ice-volume and greenhouse gas records but provide a rare and important terrestrial perspective. This finding confirms previous assessments that the MBT was global in extent.

This paper explores the rainfall variability across the western Mediterranean area from ca. 12 to 9 ka, and its climate teleconnection within the northern Hemisphere realm. A high-resolution stable isotope (delta 18O, delta 13C) and growth rate record from a Corchia Cave stalagmite (Apuan Alps, Central Italy) shows evidence of: 1) increased rainfall during the transition from the late Younger Dryas (YD) to the Holocene; and 2) two Early Holocene episodes of reduced rainfall during the so-called Preboreal and Boreal Oscillations (PBO and BO respectively). The YD to Holocene transition occurs at Corchia from 11.91+0.10/-0.11 to 11.33+0.07/-0.07 ka, in agreement with other Mediterranean records. The expression of PBO is constrained in Central Italy between 11.19+0.09/-0.08 and 11.04+0.09/-0.09 ka, while the BO from 10.42+0.13/-0.27 to 10.19+0.27/-0.24 ka, contemporaneous with a significant reduction of the Lago dell' Accesa lake levels (Central Italy). The new record suggests that the increase of rainfall at Corchia during the deglaciation is connected to the enhanced evaporation from a warming north Atlantic and the higher moisture amount across the Mediterranean delivered by the westerlies. Reduced rainfall is instead attested during PBO/BOs. The latter are often associated with fluxes of ice-sheet meltwaters into the Atlantic, which trigger a deficit in moisture availability resulting in lower humidity reaching the Mediterranean area. This work confirms that the PBO/BO relative aridity is restricted to the Mediterranean area, while mid-European records point to moister conditions within the same events. Thus, our results imply that future - even subtle- polar ice sheet instabilities, boosted by the ongoing climate crisis, might amplify the change of rainfall dynamics across the western Mediterranean, a hot-spot area for climatic change that is already experiencing an increasing number of drought years.

A popular conceptual tectonic model envisages the Great Glen Fault to be part of a sinistral strike-slip system active during the mid-Silurian to early Devonian with c. 700 km of displacement. Here we use sedimentological, geochemical and detrital zircon age data to show that restoring 250-300 km of displacement suffices to fulfil key geological constraints and reveal three new pre-strike-slip relationships: (1) Paleoproterozoic Makkovik-Ketilidian crust becomes placed proximal to numerous immature sandstone units in the Grampian and Northern Highlands of Scotland and County Mayo, Ireland, that are marked by single-mode peaks of 1.8-1.6 Ga detrital zircons sourced from that crust; (2) the two most concentrated occurrences of appinite and metadolerite/gabbro in the Scottish-Irish Caledonides become matched; (3) the Donegal and Argyll granite suites can be paired. That amount of displacement provides, at least in part, the separation required between the Northern and Grampian Highlands to account for Scandian-age (Silurian) deformation in the former and its absence in the latter.

A multiproxy record from a stalagmite collected from Torgashinskaya Cave (Southern Siberia, Russia) and growing between ca. 6 and 3.8 ka shows evidence for regional climatic changes occurring at ca. 5 ka. Interpretation of stable isotope ratios (δ18O and δ13C) and fluorescence data (intensity and wavelength of the emitted fluorescence) suggests that the interval between ca. 5 and 4.2 ka was generally warmer and drier than the interval between ca. 6 and 5 ka. The observed bipartitioning of the climate, attributable to the so-called ‘middle-late Holocene transition’, has a striking similarity to changes in K+ and Na+ concentration of Greenland ice cores (taken as indicators of the strength of the Siberian High and Icelandic Low, respectively), in the abundance of hematite-stained grains in subpolar North Atlantic sediments and, to lesser extent, in the summer Asian monsoon intensity deduced by δ18O from Chinese speleothems. In particular, the δ18O record at Torgashinskaya Cave can be interpreted as mostly driven by temperature changes. Besides several episodes of drift towards higher temperatures, it also strongly suggests the presence of short cooling events centered at 4.1+0.08/-0.07, 4.85+0.05/-0.06, 5.1+0.09/-0.09, 5.3+0.08/-0.07 and 5.8+0.12/-0.13 ka. Notably, the last three such events are in very good correspondence with spikes in the K+ and Na+ concentration of Greenland ice cores. Instead, the cooling around 4.1 ka could be the local response to the 4.2 event, a cold/dry episode identified in several records in the Northern Hemisphere. This suggests that δ18O of speleothem calcite from this area could be a useful proxy for defining the evolution of the Siberian High and its effect on the wider regional climate.

The Scottish Alliance of Geoscience, Environment and Society (SAGES) was launched in May 2007 and thrives to this day (https://www.sages.ac.uk). It is a major research partnership between ten institutions in Scotland squarely focused on the prime problem of our time, namely understanding how the natural world works and how it interacts with human society. The inspiration driving SAGES is that we can all contribute more if we collaborate. Paul Bishop was a staunch believer in collaboration and played a pivotal role in the building of SAGES. The early history of SAGES and Paul's contribution is little known and it seems fitting to address this in a special issue in his name.

The Tonian–Cambrian Dalradian Supergroup in Scotland is a siliciclastic–carbonate succession that can be up to 10 km thick. The consensus view is that its lower part, the mid- to late Tonian Grampian and Appin groups, formed in rift basins: the deep marine turbidites of the Grampian Group infilled rift depocentres, whereas the shallow marine strata of the Appin Group mark basin-bounding palaeohighs. This scenario is used as a key line of evidence to infer the onset of the break-up of Rodinia between Laurentia and Baltica. However, deformation during the mid-Ordovician Caledonian Orogeny obscured the original depositional frameworks. Reconstructing these frameworks (and hypothesized rift basins) has relied on the trace and major element log-ratio geochemistry of minor carbonate rocks to assign the units to either the Grampian or Appin group – that is, to rift depocentres or basin-bounding palaeohighs, respectively. We report new carbon and oxygen isotope and geochemical data and use these to create a revised stratigraphic framework for the Grampian and Appin groups. Our findings show that the previous geochemical-based correlations are unreliable and that there is no evidence for palaeohighs or rift basins. Instead, the Grampian–Appin groups are a deeper marine flysch to a shallower marine molasse succession formed in response to the mid-Tonian Knoydartian Orogeny. From a Scottish perspective, evidence for the break-up of Rodinia is recorded higher in the Dalradian succession during the deposition of the early Cryogenian Argyll Group. Supplementary material: Geochemical analysis of samples is available at https://doi.org/10.6084/m9.figshare.c.6317830 Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/topic/collections/the-caledonian-wilson-cycle

The Paleoproterozoic Lomagundi-Jatuli Event (LJE) is generally considered the largest, in both amplitude and duration, positive carbonate C-isotope (delta C-13(carb)) excursion in Earth history. Conventional thinking is that it represents a global perturbation of the carbon cycle between 2.3-2.1 Ga linked directly with, and in part causing, the postulated rise in atmospheric oxygen during the Great Oxidation Event. In addition to new high-resolution delta C-13(carb) measurements from LJE-bearing successions of NW Russia, we compiled 14 943 delta C-13(carb) values obtained from marine carbonate rocks 3.0-1.0 Ga in age and from selected Phanerozoic time intervals as a comparator of the LJE. Those data integrated with sedimentology show that, contra to consensus, the delta C-13(carb) trend of the LJE is facies (i.e. palaeoenvironment) dependent. Throughout the LJE interval, the C-isotope composition of open and deeper marine settings maintained a mean delta C-13(carb) value of +1.5 +/- 2.4 parts per thousand, comparable to those settings for most of Earth history. In contrast, the C-13-rich values that are the hallmark of the LJE are limited largely to nearshore-marine and coastal-evaporitic settings with mean delta C-13(carb) values of +6.2 +/- 2.0 parts per thousand and +8.1 +/- 3.8 parts per thousand, respectively. Our findings confirm that changes in delta C-13(carb) are linked directly to facies changes and archive contemporaneous dissolved inorganic carbon pools having variable C-isotopic compositions in laterally adjacent depositional settings. The implications are that the LJE cannot be construed a priori as representative of the global carbon cycle or a planetary-scale disturbance to that cycle, nor as direct evidence for oxygenation of the ocean-atmosphere system. This requires rethinking models relying on those concepts and framing new ideas in the search for understanding the genesis of the grandest of all positive C-isotope excursions, its timing and its hypothesized linkage to oxygenation of the atmosphere.

Tracing interactions during burial-induced organic maturation and associated clay-material alteration is of prime importance for understanding both the individual and combined mineral and organic processes. In the present study the light elements B, Li, O, and H of a sample from oil-prone Eocene Kreyenhagen Shale from San Joaquin Basin (California) were examined. The natural burial-induced temperature increase was simulated by pyrolysis experiments at progressively increasing temperatures (270–365°C) and for varied durations (72–216 h) applied to the whole rock and its <2 μm fraction. The illite structure as well as the K-rich interlayers of the illite-smectite mixed layers were not affected by the pyrolysis experiments and the smectite-rich interlayers did not collapse, while the soluble minerals and the organic matter were altered. The distribution pattern of the rare-earth elements (REEs) from untreated whole rock and of its pyrolyzed equivalents are within analytical uncertainty, which confirms that the changes induced by pyrolysis experiments were minimal in the bulk sample. Conversely, the REEs from the <2 μm fractions were modified significantly, suggesting that the whole rocks and the <2 μm fractions may contain different types of organic materials. Also, only the carbonates, oxides, chlorides, and organic matter were affected together with the smectite-rich interlayers of the illite-smectite structure. Bitumen coating of the smectite interlayers probably increased the amount of B of organic origin in their sites. The δ11B and δ7Li of the successively expelled hydrocarbon phases changed with increasing pyrolysis temperatures, together with the B and Li contents of the hydrocarbon-related fluids. On the basis of the δ11B and δ7Li from pyrolyzed clay fractions, the B released successively was not isotopically homogeneous, probably depending on how the type of organic matter decomposed during the successive pyrolysis steps, and on which components were released. The δ11B of organic-B increased progressively from –2‰ at low experimental temperature up to +9‰ at the highest temperature. The calculated δ7Li that was released also increased relative to the value of the outcropping sample used as a reference, but it remained almost constant from –7‰ at 310°C for 72 h to –8‰ at 365°C for 216 h. The δ18O values of the <2 μm size fractions decreased significantly during pyrolysis above 300°C, but the δD changes were rather modest. The total organic carbon (TOC) remained statistically constant after pyrolysis to 300°C, as did the δ7Li values. The pyrolysis experiments in the present study suggest the presence of bitumen-coated smectite interlayers that could have been misidentified as dehydrated smectite in the literature. Together with abnormal illite K-Ar ages, the occurrence of such bitumen-coated illite-smectite interlayers occurring in source and reservoir rocks could indicate the timing of hydrocarbon maturation relative to illitization.

The Khenchela massif, northeast Algeria, belongs to the eastern Saharan Atlas that extends northeasterly from the Aurès Chain, through the Mellegue mountains, to the Tunisian Atlas. This massif is characterized by sandstone and marl outcrops of the Lower Cretaceous that are overlain by limestone and marl of the Upper Cretaceous. The anticline structure was subjected to several NW–SE to WNW-ESE-directed major normal faults that split the massif into a number of mega-blocs. Triassic evaporitic lithologies crop out as diapirs at the northeastern and southwestern parts of the anticline. The Ain Mimoun region, located on the northern flank of the Khenchela anticline, is composed of Albian-Aptian sediments that host the barite veins of the so-called ‘Mizab barite deposit’. This deposit, which is currently exploited, consists of a dozen main veins composed mainly of barite with quartz, calcite, ankerite and rare base-metal sulphide mineralisation (galena, sphalerite, tennantite and chalcopyrite). The host sedimentary rocks were subjected to severe silicification and dolomitisation processes. Barite shows a number of aspects: banded, massive and stockwork; in all cases, barite shows tabular crystals of several millimeters in size. Microthermometric measurements carried out on primary two-phase fluid inclusions in barite crystals (barite I and barite II) and gangue quartz gave homogenization temperatures between 155 and 225 °C and salinities of 17.6 to 25.9% NaCl eq. The data show at least three types of mixing fluids that deposited the sulphate-sulphide mineralisation. δ34S values of barite are between + 17.9 and + 27.6‰ and the δ34S values of the associated sulphides vary between − 9.2 and + 3.0‰. These data indicate that the most likely source of sulphur is the sulphates (gypsum) of the Triassic evaporitic formation (δ34S ranging between + 11.5 and + 13.4‰). Thermochemical sulphate reduction is the most probable process by which H2S was produced, although relatively large negative δ34S values point to a possible minor contribution from the biogenic sulphate reduction process. Carbon and oxygen isotopic compositions of gangue carbonates (calcite and ankerite) and oxygen of gangue quartz indicate a common source of the mineralising fluid. Calculated δ18Ofluid from quartz oxygen isotope data varies between + 6 and + 12‰, indicating deep-seated brines with minor contribution from a surface water component. The relatively hot and saline fluids have most likely migrated upward in several pulses during the Triassic halokinesis and compressive/distensive Atlassic (Eocene) and Alpine (Miocene) tectonic phases. The Mizab barite deposit exhibits geological, fluid inclusion and isotopic features similar to those of the peridiapiric mineralisation of northeastern Algeria and Tunisia.

The geological timescale before 720 Ma uses rounded absolute ages rather than specific events recorded in rocks to subdivide time. This has led increasingly to mismatches between subdivisions and the features for which they were named. Here we review the formal processes that led to the current timescale, outline rock-based concepts that could be used to subdivide pre-Cryogenian time and propose revisions. An appraisal of the Precambrian rock record confirms that purely chronostratigraphic subdivision would require only modest deviation from current chronometric boundaries, removal of which could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions. Our review leads to the following conclusions: (1) the current informal four-fold Archean subdivision should be simplified to a tripartite scheme, pending more detailed analysis, and (2) an improved rock-based Proterozoic Eon might comprise a Paleoproterozoic Era with three periods (early Paleoproterozoic or Skourian, Rhyacian, Orosirian), Mesoproterozoic Era with four periods (Statherian, Calymmian, Ectasian, Stenian) and a Neoproterozoic Era with four periods (pre-Tonian or Kleisian, Tonian, Cryogenian and Ediacaran). These proposals stem from a wide community and could be used to guide future development of the pre-Cryogenian timescale by international bodies.

Four first-order (Hadean, Archean, Proterozoic and Phanerozoic eon) and nine second-order (Paleoarchean, Mesoarchean, Neoarchean, Paleoproterozoic, Mesoproterozoic, Neoproterozoic, Paleozoic, Mesozoic and Cenozoic era) units continue to provide intuitive subdivision of geological time. Major transitions in Earth’s tectonic, biological and environmental history occurred at approximately 2.5-2.3, 1.8-1.6, 1.0-0.8 and 0.7-0.5 Ga, and so future rock-based subdivision of pre-Cryogenian time, eventually by use of global stratotypes (GSSPs), will likely require only modest deviation from current chronometric boundaries (GSSAs) at 2.5, 1.6 and 1.0 Ga, respectively. Here we argue that removal of GSSAs could be expedited by establishing event-based concepts and provisional, approximate ages for eon-, era- and period-level subdivisions as soon as practicable, in line with ratification of an Ediacaran GSSP in 2004 and chronostratigraphic definition of the Cryogenian Period at c. 720 Ma in 2012. We also outline the geological basis behind current chronometric divisions, explore how they might differ in any future rock-based scheme, identify where major issues might arise during the transition, and outline where some immediate changes to the present scheme could be easily updated/formalised, as a framework for future GSSP development. In line with these aims, we note that the currently recommended four-fold Archean subdivision has not been formally ratified and agree with previous workers that it could be simplified to an informal three-fold subdivision, pending more detailed analysis. Although the ages of period boundaries would inevitably change in a more closely rock-based or chronostratigraphic scheme, we support retention of all currently ratified period names. Existing period names, borrowed from the Greek, were chosen to delimit natural phenomena of global reach. Any new global nomenclature ought to follow this lead for consistency, and so we discourage the use of supercontinent names (e.g. Rodinian, Columbian) and regional phenomena, however exceptional. In this regard, we tentatively suggest that a new period (e.g. the ‘Kratian’), could precede the Tonian as the first period of the Neoproterozoic Era and we concur with previous authors that the existing Siderian Period (named for banded iron formations) would fit better as a chronostratigraphically defined period of the terminal Archean. Indeed, all pre-Cryogenian subdivisions will need more conceptual grounding in any future chronostratigraphic scheme. We conclude that improved rock-based division of the Proterozoic Eon would likely comprise a three-fold, period-level subdivision of the Paleoproterozoic Era (Oxygenian Rhyacian, Orosirian), a four-fold subdivision of the Mesoproterozoic Era (Statherian, Calymmian, Ectasian, Stenian) and potentially four-fold subdivision of the Neoproterozoic Era (pre-Tonian ‘Kratian’, Tonian, Cryogenian and Ediacaran). Future refinements towards an improved rock-based pre-Cryogenian geological time scale could be propoosed by new international bodies to cover the 1) pre-Ediacaran Neoproterozoic, 2) Mesoproterozoic, 3) Paleoproterozoic and 4) Archean (and Hadean) as few experts and disciplines can speak to the entire pre-Cryogenian rock record.

The original article has been corrected. During proof correction of the article, mistakes in the author affiliations of Petra Bajo, John C. Hellstrom, Robert Wiśniewski, Anthony E. Fallick, Stefano Natali, and Marco Luppichini were introduced. Please find the correct affiliations here as well.

Radiometric dating of glacial terminations over the past 640,000 years suggests pacing by Earth's climatic precession, with each glacial-interglacial period spanning four or five cycles of ~20,000 years. However, the lack of firm age estimates for older Pleistocene terminations confounds attempts to test the persistence of precession forcing. We combine an Italian speleothem record anchored by a uranium-lead chronology with North Atlantic ocean data to show that the first two deglaciations of the so-called 100,000-year world are separated by two obliquity cycles, with each termination starting at the same high phase of obliquity, but at opposing phases of precession. An assessment of 11 radiometrically dated terminations spanning the past million years suggests that obliquity exerted a persistent influence on not only their initiation but also their duration.

Classification systems for corundum deposits have evolved over time and are based on different mineralogical and geological features. An enhanced classification for ruby deposits based on the geological environment, degree of metamorphism, styles of mineralization and the pressure-temperature conditions of formation is proposed : Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) Tectonic magmatic-related, and (Type II) Tectonic metamorphic-related. Type I is characterized by two sub-types: Type IA where xenocrysts or xenoliths of gem ruby of metamorphic origin are hosted by alkali basalts (Madagascar and others); and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo). Type II has two sub-types hosted either in metamorphic deposits sensu stricto (Type IIA) formed in the amphibolite to granulite facies, or metamorphic-metasomatic deposits (Type IIB) formed via high fluid-rock interaction and metasomatism: - Sub-Type IIA1 includes ruby in metamorphosed mafic and ultramafic rocks (M-UMR) as found at Montepuez (Mozambique) and Aappaluttoq (Greenland); - Sub-Type IIA2 concerns rubies in marble such those from the Mogok Stone Track (Myanmar), and from central and eastern Asia; - Sub-Type IIB1 corresponds to desilicated pegmatites i.e., plumasite in M-UMR as in the Rockland mine (Kenya) or Polar Urals (Russia); - Sub-Type IIB2 is characterized by ruby in shear zone-related or fold hinge-controlled deposits in different substrata, mainly ruby-bearing Mg-Cr-biotite schist (metamorphosed M-UMR) and marble. It includes the ruby occurrences of Zazafotsy (Madagascar), Kerala (southern India), Mahenge (Tanzania), and the Hokitika deposit (New-Zealand). Secondary ruby deposits i.e., placers, are termed Tectonic sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, silt) that formed due to erosion, gravity, mechanical transport and sedimentation along slopes or basins related to neotectonic movements. These are divided in two main sub-types: - Sub-Type IIIA i.e., gem placers in alkali basalt or kimberlite environments as in eastern Australia, central Madagascar, and the Democratic Republic of Congo; - Sub-Type IIIB i.e., gem placers in metamorphic environments such as at Montepuez in Mozambique or the Mogok Stone Track in Myanmar. - Sub-Type IIIC i.e., gem placers with ruby originating from multiple and unknown sources such as at Ilakaka (Madagascar), Tunduru and Songea (Tanzania).

The evolution of the Bacaba and Castanha iron oxide-copper-gold deposits, located in the Carajas Mineral Province, Brazil, is discussed based on petrography, scanning electron microscopy, stable isotopes, and fluid inclusion analyses. The Castanha deposit is mainly hosted by ca. 2.75 Ga subvolcanic and volcanic rhyodacitic rocks, and gabbros. Early sodic (albite, scapolite) alteration was followed by high-temperature calcic-iron (ac-tinolite-magnetite), potassic (biotite), and minor chlorite and sericite alteration. Calcite, REE carbonate, and epidote represent a late and proximal alteration to ore bodies. Ore breccias with Durchbewegung structure comprise chalcopyrite + pyrrhotite + pyrite +/- cobaltpentlandite +/- sphalerite +/- marcasite and are notable due to their nickel-(zinc) enrichment. The Bacaba Deposit is hosted by the ca. 3.00 Ga Bacaba Tonalite, 2.85 Ga Serra Dourada Granite, and gabbro bodies. Early (ca. 2.70 Ga) alteration at Bacaba includes sodic (albite, scapolite), iron (magnetite), and potassic-iron (K feldspar-magnetite, biotite) associations. Well-developed late chlorite, albite, sericite, calcite-hematite-(musketovite) alteration formed during a Paleoproterozoic overprinting (ca. 2.06 Ga). The Bacaba ore is composed of (I) chalcopyrite +/- magnetite +/- bornite, and (II) chalcopyrite +/- pyrite +/- hematite/musketovite, related to early potassic-iron and late alteration, respectively. The Castanha deposit was formed from magmatic fluid (delta O-18(H2O) = 9.5 +/- 0.5%o to 5.2 +/- 1.0 parts per thousand, at 500 to 400 degrees C) and sulfur (delta S-34 = 0.1-3%o) sources, with a limited contribution of externally-derived fluids during its evolution. Ore precipitation progressed under considerably low fS(2) and fO(2) conditions, at relatively high temperatures (> 370 +/- 50 degrees C). Fluid inclusion analyses indicate greater proximity of the Castanha deposit to the source of a hot overpressured magmatic fluid, suggesting its formation in a high-temperature hydrothermal center. Fluid rock interaction coupled with increasing pH might have been the critical factors in destabilizing the metal chloride complex in the Castanha deposit. The Bacaba deposit evolved from a fluid-mixing between hot (> 450 degrees C) hypersaline CaCl2-NaCl-bearing magmatic brine (> 30 mass % equivalent) and a less saline, colder, and O-18-depleted and D-enriched fluid (e.g., seawater or low-latitude meteoric water). Mixing resulted in an oxidizing environment, dilution (salinities between 35 and 4 mass % equivalent), and temperature drop (160-190 degrees C), triggering the ore precipitation. At Bacaba, the slightly higher delta S-34 values (1.3-5.4 parts per thousand) may reflect an additional contribution of externally-derived sulfur through the thermochemical reduction of oxidized sulfur species. In the Southern Copper Belt, the regional spatial distribution of the sulfur isotope compositions shows the highest delta S-34(sulfide) values close to the Paleoproterozoic Sossego Orebody and the Alvo 118 deposit. This might suggest significant involvement of externally-derived components (e.g., diluted fluids and sulfur) during late stages of a protracted hydrothermal evolution in the Carajas IOCG deposits.

To model the formation of orogenic gold deposits, in a global perspective, it is important to understand the ore-forming conditions not only for deposits hosted in greenschist facies rocks but also in amphibolite facies. The Paleoproterozoic Fäboliden deposit in northern Sweden belongs to the globally rare hypozonal group of orogenic gold deposits and, as such, constitutes a key addition to the understanding of amphibolite facies orogenic gold deposits. The Fäboliden deposit is characterized by auriferous arsenopyrite-rich quartz veins, hosted by amphibolite facies supracrustal rocks and controlled by a roughly N-striking shear zone. Gold is closely associated with arsenopyrite-löllingite and stibnite, and commonly found in fractures and as inclusions in the arsenopyrite-löllingite grains. The timing of mineralization is estimated from geothermometric data and field relations at c. 1.8 Ga. In order to constrain the origin of gold-bearing fluids in the Fäboliden deposit, oxygen, hydrogen, and sulfur isotope studies were undertaken. δ 18 O from quartz in veins shows a narrow range of + 10.6 to + 13.1‰. δD from biotite ranges between − 120 and − 67‰, with most data between − 95 and − 67‰. δ 34 S in arsenopyrite and pyrrhotite ranges from − 0.9 and + 3.6‰ and from − 1.5 and + 1.9‰, respectively. These stable isotope data, interpreted in the context of the regional and local geology and the estimated timing of mineralization, suggest that the sulfur- and gold-bearing fluid was generated from deep-crustal sedimentary rocks during decompressional uplift, late in the orogenic evolution of the area. At the site of gold ore formation, an 18 O-enriched magmatic fluid possibly interacted with the auriferous fluid, causing precipitation of Au and the formation of the Fäboliden hypozonal orogenic gold deposit.

In ancient basement regions such as the Lewisian Complex, NW Scotland, the ages of brittle deformation events are commonly poorly constrained owing to a lack of datable fills. An array of NW–SE sinistral and antithetic east–west dextral faults related to a regionally recognized episode of brittle shearing cut Neoarchean gneisses and c. 2.25 Ga quartz–pyrite veins close to the trace of an unexposed, regional-scale NW–SE fault. Copper–iron mineralization occurs at an intersection between an antithetic dextral fault and an older c. 2.25 Ga quartz vein. Optical microscopy, SEM and XRD analyses reveal an array of intergrown, co-genetic copper–iron sulfides, hematite and barite. Complex millimetre-thick zoned alteration rims rich in epidote occur at contacts between the sulfides and gneisses. Rhenium–osmium copper–iron sulfide geochronology yields an age of c . 1.55 Ga for the hydrothermal mineralization event associated with faulting. Fault movements demonstrably overlap with mineralization based on the asymmetric fibrous growth forms of these minerals within local dextral shears, which acted as local channelways for mineralizing fluids during and after faulting. We tentatively propose that this regionally recognized strike-slip faulting, previously termed the ‘Late Laxfordian’, should be referred to as the ‘Assyntian’ to distinguish it from kinematically distinct Laxfordian events.

Corundum is not uncommon on Earth but the gem varieties of ruby and sapphire are relatively rare. Gem corundum deposits are classified as primary and secondary deposits. Primary deposits contain corundum either in the rocks where it crystallized or as xenocrysts and xenoliths carried by magmas to the Earth’s surface. Classification systems for corundum deposits are based on different mineralogical and geological features. An up-to-date classification scheme for ruby deposits is described in the present paper. Ruby forms in mafic or felsic geological environments, or in metamorphosed carbonate platforms but it is always associated with rocks depleted in silica and enriched in alumina. Two major geological environments are favorable for the presence of ruby: (1) amphibolite to medium pressure granulite facies metamorphic belts and (2) alkaline basaltic volcanism in continental rifting environments. Primary ruby deposits formed from the Archean (2.71 Ga) in Greenland to the Pliocene (5 Ma) in Nepal. Secondary ruby deposits have formed at various times from the erosion of metamorphic belts (since the Precambrian) and alkali basalts (from the Cenozoic to the Quaternary). Primary ruby deposits are subdivided into two types based on their geological environment of formation: (Type I) magmatic-related and (Type II) metamorphic-related. Type I is characterized by two sub-types, specifically Type IA where xenocrysts or xenoliths of gem ruby of metamorphic (sometimes magmatic) origin are hosted by alkali basalts (Madagascar and others), and Type IB corresponding to xenocrysts of ruby in kimberlite (Democratic Republic of Congo). Type II also has two sub-types; metamorphic deposits sensu stricto (Type IIA) that formed in amphibolite to granulite facies environments, and metamorphic-metasomatic deposits (Type IIB) formed via high fluid–rock interaction and metasomatism. Secondary ruby deposits, i.e., placers are termed sedimentary-related (Type III). These placers are hosted in sedimentary rocks (soil, rudite, arenite, and silt) that formed via erosion, gravity effect, mechanical transport, and sedimentation along slopes or basins related to neotectonic motions and deformation.

This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (δ34S, 87Sr/86Sr, δ18O, and δ13C). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200–250°C and up to 430°C at the early hydrothermal stage in the veins. Low calculated ∑REE concentration for bulk vein (15 ppm) compared to greisen (75 ppm), country rocks (173–224 ppm), and the intruding granite (320 ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials. Taken together, these features confirm efficient REE retention in the early stages of the system and minor control of the REE uptake by mineral-specific partitioning. REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.