Potential deposits of the rare earth elements and associated critical metals in the circum-Mediterranean regions

The ‘critical metals’ are those metals for wh ich demand is increasing, typically due to their use in green and high-tech applicati ons, and for which there are concerns about supply risk. Several different methods have been used to estimate criticality (e.g. EC, 2014; Graedel et al., 2015). Virtually all studi es place the rare earth elements (REE) among the most critical of all raw materi als, due to the concentration of their production in China. Other crit ical metals that may be fo und in association with the REE include niobium (Nb) and tantalum (Ta)

Primary Rare Earth Resources in Europe: an Overview

The rare earth elements (REE) have been identified by the European Commission as among the most critical raw materials, due a combination of their economic importance and supply risks. The supply risk is not the result of a shortage of REE resources in the Earth’s crust, but is related to a concentration of production in China. A number of supply chain issues can be recognized, including: economic challenges that currently make it very difficult to open a REE mine outside China; complex ore mineralogy and textures, which mean that a specific beneficiation flowsheet must be developed for each REE deposit; the limited number of facilities for REE extraction and separation outside China; and potential environmental problems such as the common association of the REE with U and Th

Long-term memory of subduction processes in the lithospheric mantle: evidence from the geochemistry of basic dykes in the Gardar Province of South Greenland

The rift-related magmas of the Proterozoic Gardar Igneous Province were emplaced across the contact between the South Greenland Archaean craton and the Palaeoproterozoic Ketilidian mobile belt. It has been suggested that the geochemistry of Gardar intrusive rocks in the two areas varies across the craton margin and that this reflects a lithospheric control. However, comparison of the geochemical and isotopic signatures of basic and ultrabasic dykes from across the area shows that there is no systematic variation related to the age of the country rock. All the Gardar basic rocks are inferred to have been derived from the mantle, with relatively little crustal contamination. We suggest that the lithospheric mantle beneath the Gardar Province was enriched by slab-derived fluids during the Ketilidian orogeny (c. 1800 Ma). Subsequent melting of this mantle source was promoted during Gardar rifting when volatile-rich, small-degree melts from the asthenosphere were introduced into the lithospheric mantle, forming enriched metasomites. Ultrabasic lamprophyre dykes in the Gardar Province represent melts derived largely from these metasomites, whereas basaltic magmas were formed by larger-scale melting of the lithospheric mantle, inheriting a subductionrelated signature. There is no evidence that the Gardar magmas were derived from a highly enriched lithospheric keel that had existed since craton formation

The Caledonian minor intrusions of the Assynt region

This report provides a full description of new mapping, petrographical and geochemical studies of the minor intrusions of the Assynt area of the Northwest Highlands. These intrusions were studied in detail by Sabine (1953) but since then little has been published on them, although a PhD study was carried out by Young (1989). The minor intrusions are divided into six main groups, each of which is described in detail

European REE resources: alkaline magmatism and beyond

Europe has resources of many of the critical metals, pa rticularly the rare earth el ements (REE); yet economic, environmental and accessibility issues have combined to slow progress toward the explo itation of these resources. The EURARE project, funded by the EU’s Seventh Framework programme, brings together a number of partners from across Europe to assess Europe’s REE resources and to se t the basis for an European REE industry. This talk will describe new research on some of the wide range of potential REE resources within Europe and showcase the diversity of resources available

Structure and stratigraphy of the Morar Group in Knoydart, NW Highlands: implications for the history of the Moine Nappe and stratigraphic links between the Moine and Torridonian successions

The Caledonian Orogen in northern Scotland comprises two major thrust nappes: the Moine and the Sgurr Beag Nappe. The Moine Nappe contains early Neoproterozoic Morar Group rocks (Moine Supergroup) and basement inliers. This paper describes the structure and stratigraphy of the Knoydart peninsula, a key area within the southern Moine Nappe. The geology of Knoydart is dominated by a thick internally coherent sequence of Morar Group rocks. This sequence is shown to be deformed by large-scale, west-vergent and west-facing Caledonian (early Palaeozoic) folds that represent D2 within the southern Moine Nappe. Subsequent D3 deformation led to refolding or tightening of F2 folds, so that the major Morar Antiform is, in essence, a composite F2/F3 fold. F2 and F3 folds are broadly co-axial, but F3 folds have steeper axial planes. The F2/F3 folds refold a regional-scale, originally recumbent, isoclinal F1 fold nappe of probable Knoydartian (mid-Neoproterozoic) age. The F1 fold nappe is cored by a thin sliver of basement gneiss; the lower limb comprises migmatitic Morar Group rocks, exposed in the Morar Window. The upper limb of the F1 fold nappe occupies most of Knoydart and is stratigraphically coherent and right-way-up. Within this sequence, the upper unit of the Lower Morar Psammite is barely deformed, preserving trough-cross-bedding and large-scale channels in thick beds. This suggests braided river deposition, similar to the Torridon Group west of the Moine Thrust and the Morar Group in the northern part of the Moine Nappe. On the basis of lithological similarity and stratigraphic disposition, it is suggested that the lowermost part of the Morar Group in Knoydart correlates with the Neoproterozoic Sleat Group on Skye

Geological mapping of Sierra Leone : baseline assessment and next steps

Sierra Leone is a resource-rich country, with extensive known and potential mineral and petroleum resources. However, knowledge about the geology of the country is limited, with very little modern data in the public domain, and this hinders sustainable development of these resources for the national good. The lack of data is now being addressed by the Extractive Industries Technical Assistance Programme Phase 2 (EITAP 2) which is funded by the World Bank, and which aims to deliver a national airborne geophysical survey and subsequent geological mapping of the country (World Bank, 2017). Alongside EITAP 2, the UK government is funding the British Geological Survey (BGS) to work in partnership with relevant institutions in Sierra Leone, including the National Minerals Agency (NMA), the Petroleum Directorate (PD) and Fourah Bay College (FBC), to build their capacity to collect, manage and disseminate geological data. As part of that work, a field reconnaissance was carried out across Sierra Leone in January 2018 to assess the state of current geological mapping, visit mines and exploration projects, and to discuss how best to plan and carry out a mapping programme. The field trip was led by three British Geological Survey (BGS) staff members (Kathryn Goodenough, Jon Ford, and Darren Jones) together with 11 geologists from the NMA, two geologists from the PD, and two staff members from the Geology Department at Fourah Bay College. Pauline Scott and Avril Jamieson from the Department for International Development (DFID) joined the first two days of the trip. This report describes the conclusions arising from that field reconnaissance and associated literature review, including a baseline assessment of the current geological mapping of Sierra Leone, and suggestions for next steps. Some information is also derived from separate field visits to the AMR Gold licence area in the Loko Hills (April 2017) and coastal outcrops in the Lungi area (June 2017)

Post-collisional Pan-African granitoids and rare metal pegmatites in western Nigeria: age, petrogenesis, and the ‘pegmatite conundrum’

The Minna area of western Nigeria lies within a Pan-African orogenic belt that extends along the margin of the West African Craton, from Algeria southwards through Nigeria, Benin and Ghana, and into the Borborema Province of Brazil. This belt is characterised by voluminous post-collisional granitoid plutons that are well exposed around the city of Minna. In this paper we present new information about their age and petrogenesis. The Pan-African plutons around Minna can be divided into two main groups: a group of largely peraluminous biotite–muscovite granites that show varying levels of deformation in late Pan-African shear zones; and a younger group of relatively undeformed, predominantly metaluminous hornblende granitoids. Pegmatites, including both barren and rare-metal types, occur at the margins of some of the plutons. New U–Pb zircon dating presented here, in combination with published data, indicates an early phase of magmatism at c. 790–760 Ma in the Minna area. This magmatism could be related either to continental rifting, or to subduction around the margins of an existing continent. The peraluminous biotite–muscovite granites were intruded at c. 650–600 Ma during regional shearing in the orogenic belt, and are likely to have formed largely by crustal melting. Subsequent emplacement of metaluminous granitoids at c. 590 Ma indicates the onset of post-orogenic extension in this area, with a contribution from mantle-derived magmas. The rare-metal pegmatites represent the youngest intrusions in this area and thus are likely to have formed in a separate magmatic episode, post-dating granite intrusion

Revision of the solid geology shown on the 'Assynt District' special geological map : a report on the 2002 fieldwork

The report provides an overview of the main findings from the first field season in the Assynt District of the Moine Thrust Project. Detailed mapping in the eastern part of the Assynt halfwindow has resulted in a new interpretation of the geometry and behaviour of the Ben More Thrust. This reinterpretation of the thrust satisfactorily resolves the conflicts between the various previous models. The remapping confirmed that the Ben More Thrust can be traced, as shown on the published 1923 Assynt District geological map, along the western flank of Na Tuadhan to Bealach a’ Mhadhaidh. The Ben More Thrust is then traced to [NC 30026 24416] where it is displaced across a steep reverse fault to [NC 30514 23953]. It then continues NNW as a readily traceable feature placing gneisses of the Lewisian Gneiss Complex over quartzite along Leathaid Riabhach [NC 298 252]. Here the Ben More Thrust progressively steepens into a sub-vertical structure that has gneiss to the NE and quartzite to the SW. The thrust follows a prominent gully along Leathaid Riabhach to A’ Chailleach. From here the Ben More Thrust more or less follows the top of a monoclinally folded quartzite that forms the summit of Beinn Uidhe and is exposed in the valley floor NW of A’ Chailleach. It retains thrust geometry with hangingwall gneisses and footwall quartzites and becomes a steep feature that approximately follows ‘Glen Beag’ (the un-named glen south of the Stack of Glencoul). The Ben More Thrust meets, but does not displace the Glencoul Thrust at the head of Loch Glencoul. Therefore it is proposed that there is a branch line here where the two thrusts meet so that all the rocks NE of Loch Glencoul and east of Loch Beag are part of the Ben More Thrust Sheet. Figure 2.7 in the report provides a clear pictorial description of the geometry of the Ben More Thrust in the northern part of the Assynt half-window. A significant new ductile structure has been identified within the Ben More Thrust Sheet, termed the Coire a’ Mhadhaidh Detachment, that mostly follows the Lewisian gneisses/quartzite contact. It has been traced from the northern limits of the Loch Ailsh intrusion across Ben More Assynt, along the eastern slopes of Na Tuadhan, across Cailleach an t-Sniomha to the west of Gorm Loch Mòr and immediately west of the Stack of Glencoul into Glen Coul (Figure 2.1 in the report). The sense of shearing in the detachment is almost always top-to-west. Similar smaller shears have also been recognised within the Lewisian gneisses in the thrust sheet. However, no ductile shearing was noted at the gneiss/quartzite contact below the Ben More Thrust. Several of the complex imbricate structures mapped by previous workers were revisited. The imbricates in the Loch an Eircill–Loch nan Caorach area appear to be simpler than shown on the published Assynt District map. An alternative solution is provided for the southern termination of the Glencoul Thrust south of Inchnadamph although it is noted that more detailed work needs to be done, notably south of Conival. Brief descriptions are given of Moine rocks above the Moine Thrust in the north-eastern part of the Assynt District map. There appears to be a lateral facies change with semipelitic schists dominant in upper Glen Cassley and psammites becoming dominant to the north. Fabrics associated with several deformation phases have largely obliterated sedimentary structures although transposed bedding traces can be seen between a spaced foliation that controls the flaggy character of the psammites. Widely spaced traverses across the major Lewisian outcrop areas, within the Assynt half-window as well as in the western foreland to the thrust belt, largely confirmed the work of the primary surveyors. Thus all of the Lewisian comprises orthogneisses, mostly hornblende-gneisses but with more felsic pyroxene-bearing gneisses in the north, that all contain ultramafic and mafic pods and layers. The traces of the various Scourie dykes are correctly shown on the published Assynt District map. The Canisp Shear Zone has been traced eastwards, south of Canisp, eventually disappears under Cambrian quartzites. A second parallel shear has also been delineated north of Loch Assynt. The polyphase nature of ductile deformation in the Lewisian gneisses elucidated by previous workers is confirmed. However, the deformation state of the gneisses is extremely variable on all scales, with intense deformation confined to specific (shear) zones that vary in thickness from several centimetres up to hundreds of metres. Descriptions of the numerous minor intrusions and the Quaternary deposits studied during the fieldwork are given in separate reports