The structure and petrology of the Cnoc nan Cuilean Intrusion, Loch Loyal Syenite Complex, NW Scotland

In NW Scotland, several alkaline intrusive complexes of Silurian age intrude the Caledonian orogenic front. The most northerly is the Loch Loyal Syenite Complex, which is divided into three separate intrusions (Ben Loyal, Beinn Stumanadh and Cnoc nan Cuilean). Mapping of the Cnoc nan Cuilean intrusion shows two main zones: a Mixed Syenite Zone (MZ) and a Massive Leucosyenite Zone (LZ), with a gradational contact. The MZ forms a lopolith, with multiple syenitic lithologies, including early basic melasyenites and later felsic leucosyenites. Leucosyenite melts mixed and mingled with melasyenites, resulting in extreme heterogeneity within the MZ. Continued felsic magmatism resulted in formation of the relatively homogeneous LZ, invading western parts of the MZ and now forming the topographically highest terrane. The identification of pegmatites, microgranitic veins and unusual biotite-magnetite veins demonstrates the intrusion's complex petrogenesis. Cross-sections have been used to create a novel 3D GoCad™ model contributing to our understanding of the intrusion. The Loch Loyal Syenite Complex is known to have relatively high concentrations of rare earth elements (REEs), and thus the area has potential economic and strategic value. At Cnoc nan Cuilean, abundant REE-bearing allanite is present within melasyenites of the MZ. Extensive hydrothermal alteration of melasyenites here formed steeply dipping biotite-magnetite veins, most enriched in allanite and other REE-bearing accessories. This study has thus identified the area of greatest importance for further study of REE enrichment processes in the Cnoc nan Cuilean intrusion

The variation in composition of ultramafic rocks and the effect on their suitability for carbon dioxide sequestration by mineralization following acid leaching

Carbon dioxide capture and storage by mineralization has been proposed as a possible technology to contribute to the reduction of global CO2 levels. A main candidate as a feed material, to supply Mg cations for combination with CO2 to form carbonate, is the family of ultramafi c rocks, Mgrich silicate rocks with a range of naturally occurring mineralogical compositions. A classifi cation scheme is described and a diagram is proposed to display the full range of both fresh and altered ultramafi c rock compositions. This is particularly for the benefi t of technologists to raise the awareness of the variation in possible feedstock materials. A systematic set of acid leaching experiments, in the presence of recyclable ammonium bisulphate, has been carried out covering the range of ultramafi c rock compositions. The results show that lizardite serpentinite releases the most Mg with 78% removed after 1 h, while an olivine rock (dunite) gave 55% and serpentinized peridotites intermediate values. Antigorite serpentinite only released 40% and pyroxene- and amphibole-rich rocks only 25%, showing they are unsuitable for the acid leaching method used. This wide variation in rock compositions highlights the necessity for accurate mineralogical characterization of potential resources and for technologists to be aware of the impact of feed material variations on process effi ciency and development

Microbiological influences on fracture surfaces of intact mudstone and the implications for geological disposal of radioactive waste

The significance of the potential impacts of microbial activity on the transport properties of host rocks for geological repositories is an area of active research. Most recent work has focused on granitic environments. This paper describes pilot studies investigating changes in transport properties that are produced by microbial activity in sedimentary rock environments in northern Japan. For the first time, these short experiments (39 days maximum) have shown that the denitrifying bacteria, Pseudomonas denitrificans, can survive and thrive when injected into flow-through column experiments containing fractured diatomaceous mudstone and synthetic groundwater under pressurized conditions. Although there were few significant changes in the fluid chemistry, changes in the permeability of the biotic column, which can be explained by the observed biofilm formation, were quantitatively monitored. These same methodologies could also be adapted to obtain information from cores originating from a variety of geological environments including oil reservoirs, aquifers and toxic waste disposal sites to provide an understanding of the impact of microbial activity on the transport of a range of solutes, such as groundwater contaminants and gases (e.g. injected carbon dioxide)

The Effect of X-ray Energy Overlaps on the Microanalysis of Chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22 Using SEM EDS-WDS

A light REE (LREE)-bearing mineral called chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22, originating from a heavy metal placer deposit Aksu Diamas in Turkey, previously assessed for potential REE extraction as a by-product of magnetite production, was studied using scanning electron microscopy with energy and wavelength-dispersive spectrometers (SEM EDS-WDS). This mineral exhibits analytical challenges associated with severe X-ray energy overlaps between the REE, titanium, and barium. Here, we present an iterative process, showing that SEM EDS-WDS is a viable technique for obtaining good quality quantitative data. SEM EDS-WDS is an in situ, non-destructive, and relatively non-expensive technique, but operator’s experience is essential to obtain good quality data. In cases where the peak fitting remains challenging, in particular, and where the constituents have large differences in abundance, an assessment of the X-ray spectrum to qualitatively assign all peaks is essential prior to quantitative analysi

Volcanic-derived placers as a potential resource of Rare Earth Elements: the Aksu Diamas Case Study, Turkey

Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important to determine what alternative sources exist. REE placers have been known for many years, and require less energy than mining of hard rock, but the REE ore minerals are typically derived from eroded granitic rocks and are commonly radioactive. Other types of REE placers, such as those derived from volcanic activity, are rare. The Aksu Diamas heavy mineral placer in Turkey has been assessed for potential REE extraction as a by-product of magnetite production, but its genesis was not previously well understood. REE at Aksu Diamas are hosted in an array of mineral phases, including apatite, chevkinite group minerals (CGM), monazite, allanite and britholite, which are concentrated in lenses and channels in unconsolidated Quaternary sands. Fingerprinting of pyroxene, CGM, magnetite and zircon have identified the source of the placer as the nearby Gölcük alkaline volcanic complex, which has a history of eruption throughout the Plio-Quaternary. Heavy minerals were eroded from tephra and reworked into basinal sediments. This type of deposit may represent a potential resource of REE in other areas of alkaline volcanis

Influence of biofilms on transport of fluids in subsurface granitic environments : some mineralogical and petrographical observations of materials from column experiments

Landfill and radioactive waste disposal risk assessments focus on contaminant transport and are principally concerned with understanding the movement of gas, water and solutes through engineered barriers and natural groundwater systems. However, microbiological activity can impact on transport processes changing the chemical and physical characteristics of the subsurface environment. Such effects are generally caused by biofilms attached to rock surfaces. This paper will present some mineralogical and petrographical observations of materials extracted at the completion of an experimental column study which examined the influences of biofilm growth on groundwater flow through crushed diorite from the Äspö Hard Rock Underground Research Laboratory, Sweden

The impact of hydrothermal alteration on the physiochemical characteristics of reservoir rocks: the case of the Los Humeros geothermal field (Mexico)

Hydrothermal alteration is a common process in active geothermal systems and can significantly change the physiochemical properties of rocks. To improve reservoir assessment and modeling of high-temperature geothermal resources linked to active volcanic settings, a detailed understanding of the reservoir is needed. The Los Humeros Volcanic Complex, hosting the third largest exploited geothermal field in Mexico, represents a natural laboratory to investigate the impact of hydrothermal processes on the rock properties through andesitic reservoir cores and outcropping analogs. Complementary petrographic and chemical analyses were used to characterize the intensities and facies of hydrothermal alteration. The alteration varies from argillic and propylitic facies characterized by no significant changes of the REE budget indicating an inert behavior to silicic facies and skarn instead showing highly variable REE contents. Unaltered outcrop samples predominantly feature low matrix permeabilities ( 1.67 W m−1 K−1; > 0.91 10–6 m2 s−1), but a significant loss of magnetic susceptibility (10–3–10–6 SI). In particular, this latter characteristic appears to be a suitable indicator during geophysical survey for the identification of hydrothermalized domains and possible pathways for fluids. The lack of clear trends between alteration facies, alteration intensity, and chemical indices in the studied samples is interpreted as the response to multiple and/or repeated hydrothermal events. Finally, the proposed integrated field-based approach shows the capability to unravel the complexity of geothermal reservoir rocks in active volcanic settings

Potential for critical raw material prospectivity in the UK

The UK Critical Minerals Strategy (BEIS, 2022) includes a commitment to “begin a nationalscale assessment of the critical minerals within the UK. By March 2023, we will collate geoscientific data and identify target areas of potential”. This report provides that national-scale assessment of the geological potential for critical raw materials in the UK. It represents the published output of a study, jointly funded by the British Geological Survey and the Department for Business and Trade, which reviewed available geoscientific data in order to identify areas of potential geological prospectivity for critical raw materials in the UK. Critical raw materials (CRMs) are those mineral commodities that are both economically important and at risk of supply disruption. The commodities addressed in this report are those identified as critical to the UK by the Critical Minerals Intelligence Centre (CMIC) (Lusty et al., 2021). These CRMs are currently obtained from mining across the world, but at the time of writing none are produced in the UK, although tungsten has been mined in recent years. Some CRMs such as lithium, tin and graphite are typically the primary products of mines, whereas others are produced as co- or by-products of major commodities such as gold, copper or zinc. Current understanding of the UK’s mineral resource endowment rests largely on evidence from historic mining and exploration, together with targeted academic research. The UK has an extensive history of mining that dates to prehistoric times. Gold, barite, fluorite, gypsum, potash and polyhalite are among the commodities that are currently mined, and exploration for many raw materials is occurring across the whole of the UK. The work presented in this report follows a methodology known as a mineral systems approach, which relies on the concept that all mineral deposits of a certain type were formed by a combination of particular geological processes (McCuaig et al., 2010). The processes that must operate for a mineral deposit to form are identified and translated into mappable target criteria derived from available datasets. Key datasets to be used would typically include geological maps, geochemical soil and stream sediment maps, geophysical maps, and mineral occurrence databases. The UK has full geological map coverage, but other datasets are incomplete, with high-resolution geophysical data only being available for limited areas. New stream sediment geochemistry maps were created as part of this work and are available on the CMIC interactive map portal1 , but the whole country is not covered for all elements. These data limitations mean that this report only provides a knowledge-driven assessment of geological potential for CRM prospectivity across the UK. It provides maps for CRMs (grouped or singly as geologically appropriate) indicating the areas where the geological criteria have been met and thus there is potential for deposits of these CRMs to occur. It is important to note that the maps represent areas of potential prospectivity, not where deposits of critical minerals are guaranteed to be found, and also that mineral deposits could be found beyond the identified prospective areas, where localised geological conditions are suitable. The areas identified in the maps can be considered as targets for more detailed research and exploration. This report focuses solely on the geological potential and does not consider other aspects such as environmental designations and planning considerations that may affect the development of a mineral deposit. Combining all the individual maps highlights areas that are prospective for several CRMs and are thus priority for further geological investigations. From north to south, these areas include: areas of prospective geology around Loch Maree near Gairloch; parts of the central Highlands and Aberdeenshire; areas of prospective geology in mid-County Tyrone in Northern Ireland; parts of Cumbria; parts of the North Pennine Orefield; areas in north-west Wales and Pembrokeshire; and south-west England. These areas should now be the focus for collection of new geological, geochemical and geophysical data, in order to identify new CRM prospects for detailed investigation

A natural analogue study of CO2-cement interaction : carbonate alteration of calcium silicate hydrate-bearing rocks from Northern Ireland

The underground sequestration of anthropogenic carbon dioxide (CO2) is one potential methodology for reducing our emissions of this greenhouse gas into the atmosphere, and hence reducing a driver for climate change. For this technique to be effective, the CO2 must remain underground for timescales measurable in thousands of years or more. A key factor in such long-term containment is the efficacy of the seals overlying the stored CO2. Boreholes penetrating potential CO2 storage aquifer/reservoir formations provide potential pathways for CO2 leakage that may cross formations and breach overlying seals strata. In this respect, understanding the long-term stability of cement and steel casing used in borehole completion and sealing, and their interaction with CO2 are of paramount importance. The focus of this report is to provide an insight into the long-term stability of borehole cement and its potential interactions with CO2 from studying the alteration, through carbonation, of naturally-occurring cementitious calcium silicate and calcium silicate hydrate (CSH) materials in natural systems (i.e. “natural analogues”). These natural analogues observations may provide information on processes and reactions that may affect the long-term stability of borehole cements over greater timescales than can be studied in laboratory experiments (which are limited by reaction kinetics and may be influenced by the formation of metastable phases)