To meet targets set in the Paris Agreement, we must stop emissions and actively strip carbon diox... more To meet targets set in the Paris Agreement, we must stop emissions and actively strip carbon dioxide from the atmosphere. Rachael James and colleagues discuss two geological techniques – enhanced rock weathering and carbon mineralisation – that show promise for CO2 removal.
There is growing urgency for CO2 removal strategies to slow the increase of, and potentially lowe... more There is growing urgency for CO2 removal strategies to slow the increase of, and potentially lower, atmospheric CO2 concentrations. Enhanced weathering, whereby the natural reactions between CO2 and silicate minerals that produce dissolved bicarbonate ions are accelerated, has the potential to remove substantial CO2 on decadal to centennial timescales. The global mining industry produces huge volumes of fine wastes that could be utilised as feedstock for enhanced weathering. We have compiled a global database of the enhanced weathering potential of mined metal and diamond commodity tailings from silicate-hosted deposits. Our data indicate that all deposit types, notably mafic and ultramafic rock-hosted operations and high tonnage Cu-hosting deposits, have the potential to capture ∼1.1–4.5 Gt CO2 annually, between 31 and 125% of the industry’s primary emissions. However, current knowledge suggests that dissolution rates of many minerals are relatively slow, such that only a fraction (∼3–21%) of this potential may be realised on timescales of <50 years. Field trials in mine settings are urgently needed and, if this prediction is confirmed, then methodologies for accelerating weathering reactions will need to be developed.
Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have be... more Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (-platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals.
Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in t... more Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in the UK has been recognized as a major environmental issue. Acid mine drainage and hydrous ferric oxide deposition are environmental hazards resulting from centuries of extensive coal mining activities across the UK. Oxidative weathering of pyrite in coal from spoil heaps and exposed bedrock can liberate trace elements, releasing them into local water systems. In addition to posing an environmental threat through water and ground contamination, ochres can also act as a remediation material, trapping elements such as selenium. Trace elements with a close association to iron oxides, such as selenium, may fix to the fine-grained ochre materials, resulting in hyper-enriched ochres. Selenium in coals has been known to cause an environmental issue in areas of North America but is also an important commodity for solar cells and nanotechnologies. Coal-bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal-derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal-mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.
A compilation of new and previously published vitrinite reflectance (R 0) data from Carboniferous... more A compilation of new and previously published vitrinite reflectance (R 0) data from Carboniferous coals constitutes the most comprehensive map of reflectance across Great Britain. Values of R 0 range from 0.38 to 3.29%, recording an ambient thermal maturity in the early oil window (standard reference point for reflectance studies), modified by elevated heat flow in northern England and along the Variscan orogenic front. The map provides a context for other geological datasets.
A method for ultra-trace determination of Se and Te in coal by inductively coupled plasma mass sp... more A method for ultra-trace determination of Se and Te in coal by inductively coupled plasma mass spectrometry (ICP-MS) was developed. Samples (up to 500 mg) were prepared by microwave-induced combustion (MIC) in a closed system pressurized with 20 bar of oxygen. Inorganic acids or their mixtures were evaluated as absorbing solution. Using HNO3 + HCl (1 + 1), results obtained for Se and Te after sample preparation by MIC agreed with those obtained by reference methods, microwave-assisted wet digestion (MAWD) using concentrated HNO3 and HF, and solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (SS-ETV-ICP-MS), and also with a certified reference material of coal (NIST 1632c) for Se. Very low limits of quantification (LOQ) were obtained: 0.002 and 0.007 mg kg1 for Se and Te, respectively. Major elements were determined in final solutions obtained by MAWD and MIC, and their concentration in solutions of MIC was negligible (<10 mg L1), minimizing the risk of interference in ICP-MS analysis. The proposed method was applied to samples of coal from the United Kingdom, with a wide range of inorganic composition (from 3 to 41% ash content), showing its robustness and feasibility for routine analysis. Se concentration ranged from 0.291 to 11.5 mg kg1, and Te was mainly found at ultra-trace levels (<0.007 to 0.11 mg kg1 ). The proposed method presents several advantages over the reference methods, such as the use of a higher sample mass, low LOQs and, an important aspect, no need of using HF.
Journal of Volcanology and Geothermal Research, 2019
Textural evidence from occurrences of mingled magmas in lava flows often yields insights into che... more Textural evidence from occurrences of mingled magmas in lava flows often yields insights into chemical and thermal disequilibrium between multiple magma batches at depth. An understanding of these interactions is key as they can occur on short timescales and may act as eruption triggers, particularly important in very active volcanic settings. This paper focuses on the Pietre Cotte lava flow(Vulcano, Aeolian Islands, Italy), a short (b1 km in length), texturally-heterogeneous rhyolitic extrusion on the northern slope of the active Fossa Cone. The occurrence of (i)multiple magma compositions, (ii) distinct magmatic cumulates (as glomerocrysts) and (iii)mineral resorption textures within glomerocrysts and isolated feldspar phenocrysts in the Pietre Cotte lava flow highlight a complex pre-eruptive magmatic history, including crystal mush remobilisation. Petrographic observations and mineral, bulk rock and glass geochemistry suggest that multiple mingling events occurred during the evolution of the Pietre Cotte magmatic system, evidenced by the recognition of the following components: (1) a remobilised predominantly mafic crystal mush, evident as macrocrysts (crystals N500 μm), which form glomerocrysts within enclaves, (2) a microlitic (b100 μm) trachytic enclave groundmass with microcrysts (100–500 μm), and (3) a rhyolitic glass, which hosts both the enclaves and the glomerocrysts. The macrocrystic mafic assemblage includes clinopyroxene (En38-47Wo45–50; Mg# 0.72–0.89), olivine (Fo49–66) an magnetite (Usp7–26), with plagioclase (An40–63Ab5–50) and rare alkali feldspar (Or41–57) also present. Enclaves are comprised of a groundmass of plagioclase (An43–47) and alkali feldspar (Or33–57) microlites, with clinopyroxene microcrysts (En39-42Wo47–51; Mg# 0.75–0.81) and trachyte groundmass glass. The rhyolitic host is characterised by glass, spherulites, microlites and enclave-derived macrocrysts. Compositionally and texturally distinct magmas are attributed to storage and interactions of distinct magma batches and their cumulates at various temperatures and depths beneath the Fossa Cone. Compositions vary frombasaltic-shoshonitic, through latitic-trachytic and rhyoliticmagmas. Themacrocrystic glomerocryst assemblage shows resorbed, chemically-zoned and cumulate textures; the glomerocrysts are attributed to a shoshonitic parent and remobilisation from a crystal mush. Macrocrysts formed at a pressure of 825 ± 80 MPa and temperatures of 789–1117 °C at around the Moho (~23–28 km). Pressure and temperature calculations of the shoshonitic mineral assemblage give average crystallisation conditions of 710 ± 80 MPa (above the Moho) and 1128± 25 °C, respectively. The trachytic magma crystallised at ~640 ± 75 MPa and 1000–1130 °C. The average liquidus of the rhyolitic magma has been calculated at 970±7 °C, at depths of b5 km(b60 MPa). New textural observations and intensive variable calculations permit the development of a new pressure and temperature-constrained model of the magmatic evolution of the Pietre Cotte system prior to eruption,with useful insights into the interactions of different magmatic components prior to and during the rapid onset of eruptions linked to magma mingling/mixing.
The Bowland Shale Formation is anomalously rich in selenium (Se) at levels an order of magnitude ... more The Bowland Shale Formation is anomalously rich in selenium (Se) at levels an order of magnitude greater than other black shales. The Mam Tor landslide, Derbyshire, England, offers an opportunity to measure whether the Se anomaly is conferred to the alteration products formed by oxidative water flow through the shale. Selenium in the shale is concentrated in diagenetic pyrite. Alteration of the shale causes decomposition of the pyrite to iron oxyhydroxide, which is carried in colloidal form (ochre) by springs draining the landslide. The iron oxyhydroxide contains anomalously high Se, and anomalously high Se was measured in water ponded where the ochre precipitated, although not in flowing groundwater. Other trace elements including cadmium and thallium also occur at concentrations higher than in other ochres. Given the widespread nature of the Se anomaly in the Bowland Shale Formation and equivalents across Britain and Ireland, any alteration products derived from workings through the shale should be disposed of with care.
The former mining site at Kisgruva near Kongsberg, Norway, is primarily composed of worked sulphi... more The former mining site at Kisgruva near Kongsberg, Norway, is primarily composed of worked sulphide ore deposits, of hydrothermal origin, which occur within Precambrian metamorphic basement. Though the original targets at the Kisgruva mine site were extraction of copper (Cu), sulphur (S) and iron (Fe), the sulphide ore also contains exceptionally high concentrations of selenium (Se) and tellurium (Te), hosted within selenides (clausthalite and minor naumannite) and tellurides (hessite and minor altaite and tellurobismuthite). Both Se and Te are also present within the sulphide ore in pyrite and chalcopyrite, which contain exceptionally high concentrations of up to 688 ppm Se and 81 ppm Te. Additionally, oxidative weathering of the exposed bedrock has resulted in the accumulation of hyper-enriched, unconsolidated weathered crust deposits at surface (Se up to 1590 ppm; Te up to 63 ppm), containing selenite (SeO32−) and tellurite (TeO32−) ions. Concentrations of Se and Te are subsequently higher in the weathering products than in the sulphide ore, due to fixation on to organic matter (∼0.4% in weathered ore crusts), jarosite (formed from oxidation of sulphides from the primary ore), ferric oxide and hydroxide phases (goethite and haematite). Increasing demand for Se and Te to use in green technologies has led to the reassessment of these orebodies and their associated weathered ore crust deposits. Though these elements are currently considered mining contaminants, this and similar sites may be of future economic importance, particularly as demand for Se and Te continues to rise.
Standard mode and collision/reaction cell mass spectroscopy methods have been utilized in order t... more Standard mode and collision/reaction cell mass spectroscopy methods have been utilized in order to overcome spectral interferences and provide ultra‐low quantification of selenium (Se) and tellurium (Te) in British Carboniferous coals for the first time. The accurate detection of Se and Te in coals is becoming increasingly important, as coals and pyrite have been identified as potentially significant trace element sources. The mean Se concentration of British coals bear comparison to that of world coals, with anomalous Se content (concentrations above 4 mg/kg) across westerly exposures, often coinciding with high sulphur (S) content and visible pyrite. New Te data for British coals gives a mean concentration of 0.02 mg/kg, with anomalous Te in Ayrshire. There is a positive correlation in the Te/Se ratio across the sample set. The close relationship between Se and Te, as well as Se–Te with both early syngenetic and later cleat‐filling pyrite, confirms an important role for sulphides in Se and Te sequestration in British coals. The high Se‐Bowland Shale and/or Ordovician volcanics may have provided the trace element source for British coals of similar or younger age. Regional intrusive activity (shallow tabular intrusions or more extensive plutons) and episodes of intense deformation can alter the thermal maturity of coals and may have driven the movement of trace element‐rich fluids through strata, locally enriching coals in Se and Te.
The Carboniferous Lower and Middle Coal Measures coals of the Northumberland Coalfield are anomal... more The Carboniferous Lower and Middle Coal Measures coals of the Northumberland Coalfield are anomalously rich in selenium (Se) content (up to 62 ppm) compared to the averages for the common UK and worldwide coals. As well as posing an environmental toxicity threat, Se is now regarded as an important resource for alloys, photovoltaic products and nanotechnologies, and high Se coals in North East England offer an opportunity to assess the Se means of occurrence, origins, transport mechanisms and enrichment in coals. At least two generations of pyrite host high Se in the sampled coal seams: microbial-formed disseminated pyrite (both cubic and framboidal in habit) and later cleat-filling pyrite, identified by petrographic observations, laser ablation methods and sulphur isotope compositions. There is a notable Se enrichment of up to 250 ppm in later formed cleat-filling pyrite. Trace element enrichment may have been sourced and influenced by seawater distribution during diagenesis, and localised dykes and deformation may have acted as an enrichment mechanism for sampled seams in the region. The high Se coals in Northumberland may provide a potential E tech element source and should be considered and carefully managed as coal mining and production are reduced in the area. The study also highlights the nature of Se enrichment in pyritic coals affected by cleat formation and multiple episodes of mineralisation, important as critical element demand continues to increase worldwide.
The Neoproterozoic Dalradian Supergroup contains widespread diagenetic sulphides present as pyrit... more The Neoproterozoic Dalradian Supergroup contains widespread diagenetic sulphides present as pyrite. The sulphides occur in both carbonaceous shales and glacial diamictites, that were deposited in relatively reducing and oxidising conditions respectively. The trace element compositions of the pyrite, and consequently the whole rock compositions, contrast between the two lithologies. The highest concentrations of selenium, tellurium and gold are all found in diamictite-hosted pyrite. The data suggest that increased mobility of these elements in oxidising conditions led to greater uptake when pyrite was precipitated. As one model for the formation of orogenic gold ore deposits assumes a sulphide-rich protolith, pyrite ultimately formed during relatively oxidising conditions could make a contribution, including the widespread pyrite precipitated during the Neoproterozoic 'Snowball Earth' glaciations.
The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), an... more The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), and preserves evidence for a multi-stage emplacement history. Due to the viscous nature of the advancing lava (10^8 to 10^10 Pa s), indicators of complex emplacement processes are preserved in the final flow. This study focuses on structural mapping of the flow to highlight the interplay of cooling, crust formation and underlying slope in the development of rhyolitic lavas. The flow is made up of two prominent lobes, small (< 0.2 m) to large (> 0.2 m) scale folding and a channelled geometry. Foliations dip at 2–4° over the flatter topography close to the vent, and up to 30–50° over steeper mid-flow topography. Brittle faults, tension gashes and conjugate fractures are also evident across flow. Heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
A method is proposed for the determination of selenium at low concentration in coal by collision/... more A method is proposed for the determination of selenium at low concentration in coal by collision/reaction cell technology inductively coupled plasma mass spectrometry (CRC-ICP-MS). Samples were decomposed by high pressure microwave-assisted wet digestion (MAWD) using 250 mg of coal, a mixture of 5 mL of 14.4 mol L−1 HNO3 and 1 mL of 40% HF and 70 min of heating program (200 °C and 40 bar). Hydrogen gas used in the collision/reaction cell was investigated to minimize the argon-based interferences at m/z 77, 78 and 80. The rejection parameter (RPq) and the H2 gas flow rate were set to 0.45 and 4.8 mL min−1, respectively. The use of H2 in the cell resulted in other polyatomic interferences, such as 76Ge1H+, 79Br1H+ and 81Br1H+, which impaired Se determination using 77Se, 80Se and 82Se isotopes, thus Se determination was carried out by monitoring only 78Se isotope. Selenium determination was performed in certified reference materials of coal (NIST 1635 and SARM 20) and an agreement better than 95% was observed between the results obtained by CRC-ICP-MS and the certified values. Under optimized conditions, the instrumental limit of detection was 0.01 μg L−1 and the method limit of detection was 0.01 μg g−1, which was suitable for Se determination at very low concentration in coal.
Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellu... more Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O2 concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record, important to understand, and suggests that new resources may be sought based on black shale protoliths from this period.
Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancie... more Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancient Egyptian empire and possibly even King Solomon's Mines and the Queen of Sheba. Today, gold occurs in the Pan-African age schist belt and Tertiary basaltic lavas of the Asosa region of Benishangul-Gumuz, western Ethiopia. There is widespread artisanal gold production in the Asosa region, with moderate activity by small numbers of local workers producing relatively large amounts of gold. There is a strong relationship between predominantly shear zone-hosted gold deposits and the Kuluck shear zone, suggesting a structural control on gold accumulation. Gold is also commonly associated with secondary sulphide mineralization and magnetite alteration in Asosa rocks. The source of the gold is thought to be the sub-volcanic intrusions generated during the subduction of the oceanic crust at the trench island-arc system, akin to what we see today in epithermal and porphyry type gold systems. Historical workings and anomalous gold concentrations in rock, soil and stream sediments point to a potentially significant untapped gold resource in the Asosa region of western Ethiopia.
Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average U... more Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average UK and world compositions, substituting for sulphur in pyrite. Greenburn surface mine coals are characterized by syngenetic concretionary pyrite (c. 15% total area), occurring as bedding-parallel banding, and later-formed (epigenetic) cross-cutting pyrite in cleats (c. 9% total area). In these, sulphur isotope compositions for both syngenetic and epigenetic pyrite include isotopically light and heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se (up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm). Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. T... more The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. The host succession includes carbonaceous, pyritic shales (pelites) which were a source of trace elements, including gold and tellurium. LA-ICP-MS mapping of pyrite crystals shows that late stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits.
Mid-Jurassic pyritic coals exposed at the village of Brora, northern Scotland, UK, contain a mark... more Mid-Jurassic pyritic coals exposed at the village of Brora, northern Scotland, UK, contain a marked enrichment of tellurium (Te) relative to crustal mean, average world coal compositions and British Isles Carboniferous coals. The Te content of Brora coal pyrite is more than one order of magnitude higher than in sampled pyrite of Carboniferous coals. The Te enrichment coincides with selenium (Se) and mercury (Hg) enrichment in the rims of pyrite, and Se/Te is much lower than in pyrites of Carboniferous coals. Initial pyrite formation is attributed to early burial (syn-diagenesis), with incorporation of Te, Se, Hg and lead (Pb) during later pyrite formation. The source of Te may have been a local hydrothermal system which was responsible for alluvial gold (Au) in the region, with some Au in Brora headwaters occurring as tellurides. Anomalous Te is not ubiquitous in coal, but may occur locally, and is detectable by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS).
To meet targets set in the Paris Agreement, we must stop emissions and actively strip carbon diox... more To meet targets set in the Paris Agreement, we must stop emissions and actively strip carbon dioxide from the atmosphere. Rachael James and colleagues discuss two geological techniques – enhanced rock weathering and carbon mineralisation – that show promise for CO2 removal.
There is growing urgency for CO2 removal strategies to slow the increase of, and potentially lowe... more There is growing urgency for CO2 removal strategies to slow the increase of, and potentially lower, atmospheric CO2 concentrations. Enhanced weathering, whereby the natural reactions between CO2 and silicate minerals that produce dissolved bicarbonate ions are accelerated, has the potential to remove substantial CO2 on decadal to centennial timescales. The global mining industry produces huge volumes of fine wastes that could be utilised as feedstock for enhanced weathering. We have compiled a global database of the enhanced weathering potential of mined metal and diamond commodity tailings from silicate-hosted deposits. Our data indicate that all deposit types, notably mafic and ultramafic rock-hosted operations and high tonnage Cu-hosting deposits, have the potential to capture ∼1.1–4.5 Gt CO2 annually, between 31 and 125% of the industry’s primary emissions. However, current knowledge suggests that dissolution rates of many minerals are relatively slow, such that only a fraction (∼3–21%) of this potential may be realised on timescales of <50 years. Field trials in mine settings are urgently needed and, if this prediction is confirmed, then methodologies for accelerating weathering reactions will need to be developed.
Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have be... more Gold grains, up to 40 μm in size and containing variable percentages of admixed platinum, have been identified in coals from the Leinster Coalfield, Castlecomer, SE Ireland, for the first time. Gold mineralisation occurs in sideritic nodules in coals and in association with pyrite and anomalous selenium content. Mineralisation here may have reflected very high heat flow in foreland basins north of the emerging Variscan orogenic front, responsible for gold occurrence in the South Wales Coalfield. At Castlecomer, gold (-platinum) is attributed to precipitation with replacive pyrite and selenium from groundwaters at redox interfaces, such as siderite nodules. Pyrite in the cores of the nodules indicates fluid ingress. The underlying Caledonian basement bedrock is mineralised by gold, and thus likely provided a source for gold. The combination of the gold occurrences in coal in Castlecomer and in South Wales, proximal to the Variscan orogenic front, suggests that these coals along the front could comprise an exploration target for low-temperature concentrations of precious metals.
Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in t... more Thanks to the pioneering research of Paul Younger over the past 20 years, acid mine drainage in the UK has been recognized as a major environmental issue. Acid mine drainage and hydrous ferric oxide deposition are environmental hazards resulting from centuries of extensive coal mining activities across the UK. Oxidative weathering of pyrite in coal from spoil heaps and exposed bedrock can liberate trace elements, releasing them into local water systems. In addition to posing an environmental threat through water and ground contamination, ochres can also act as a remediation material, trapping elements such as selenium. Trace elements with a close association to iron oxides, such as selenium, may fix to the fine-grained ochre materials, resulting in hyper-enriched ochres. Selenium in coals has been known to cause an environmental issue in areas of North America but is also an important commodity for solar cells and nanotechnologies. Coal-bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal-derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal-mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.
A compilation of new and previously published vitrinite reflectance (R 0) data from Carboniferous... more A compilation of new and previously published vitrinite reflectance (R 0) data from Carboniferous coals constitutes the most comprehensive map of reflectance across Great Britain. Values of R 0 range from 0.38 to 3.29%, recording an ambient thermal maturity in the early oil window (standard reference point for reflectance studies), modified by elevated heat flow in northern England and along the Variscan orogenic front. The map provides a context for other geological datasets.
A method for ultra-trace determination of Se and Te in coal by inductively coupled plasma mass sp... more A method for ultra-trace determination of Se and Te in coal by inductively coupled plasma mass spectrometry (ICP-MS) was developed. Samples (up to 500 mg) were prepared by microwave-induced combustion (MIC) in a closed system pressurized with 20 bar of oxygen. Inorganic acids or their mixtures were evaluated as absorbing solution. Using HNO3 + HCl (1 + 1), results obtained for Se and Te after sample preparation by MIC agreed with those obtained by reference methods, microwave-assisted wet digestion (MAWD) using concentrated HNO3 and HF, and solid sampling electrothermal vaporization inductively coupled plasma mass spectrometry (SS-ETV-ICP-MS), and also with a certified reference material of coal (NIST 1632c) for Se. Very low limits of quantification (LOQ) were obtained: 0.002 and 0.007 mg kg1 for Se and Te, respectively. Major elements were determined in final solutions obtained by MAWD and MIC, and their concentration in solutions of MIC was negligible (<10 mg L1), minimizing the risk of interference in ICP-MS analysis. The proposed method was applied to samples of coal from the United Kingdom, with a wide range of inorganic composition (from 3 to 41% ash content), showing its robustness and feasibility for routine analysis. Se concentration ranged from 0.291 to 11.5 mg kg1, and Te was mainly found at ultra-trace levels (<0.007 to 0.11 mg kg1 ). The proposed method presents several advantages over the reference methods, such as the use of a higher sample mass, low LOQs and, an important aspect, no need of using HF.
Journal of Volcanology and Geothermal Research, 2019
Textural evidence from occurrences of mingled magmas in lava flows often yields insights into che... more Textural evidence from occurrences of mingled magmas in lava flows often yields insights into chemical and thermal disequilibrium between multiple magma batches at depth. An understanding of these interactions is key as they can occur on short timescales and may act as eruption triggers, particularly important in very active volcanic settings. This paper focuses on the Pietre Cotte lava flow(Vulcano, Aeolian Islands, Italy), a short (b1 km in length), texturally-heterogeneous rhyolitic extrusion on the northern slope of the active Fossa Cone. The occurrence of (i)multiple magma compositions, (ii) distinct magmatic cumulates (as glomerocrysts) and (iii)mineral resorption textures within glomerocrysts and isolated feldspar phenocrysts in the Pietre Cotte lava flow highlight a complex pre-eruptive magmatic history, including crystal mush remobilisation. Petrographic observations and mineral, bulk rock and glass geochemistry suggest that multiple mingling events occurred during the evolution of the Pietre Cotte magmatic system, evidenced by the recognition of the following components: (1) a remobilised predominantly mafic crystal mush, evident as macrocrysts (crystals N500 μm), which form glomerocrysts within enclaves, (2) a microlitic (b100 μm) trachytic enclave groundmass with microcrysts (100–500 μm), and (3) a rhyolitic glass, which hosts both the enclaves and the glomerocrysts. The macrocrystic mafic assemblage includes clinopyroxene (En38-47Wo45–50; Mg# 0.72–0.89), olivine (Fo49–66) an magnetite (Usp7–26), with plagioclase (An40–63Ab5–50) and rare alkali feldspar (Or41–57) also present. Enclaves are comprised of a groundmass of plagioclase (An43–47) and alkali feldspar (Or33–57) microlites, with clinopyroxene microcrysts (En39-42Wo47–51; Mg# 0.75–0.81) and trachyte groundmass glass. The rhyolitic host is characterised by glass, spherulites, microlites and enclave-derived macrocrysts. Compositionally and texturally distinct magmas are attributed to storage and interactions of distinct magma batches and their cumulates at various temperatures and depths beneath the Fossa Cone. Compositions vary frombasaltic-shoshonitic, through latitic-trachytic and rhyoliticmagmas. Themacrocrystic glomerocryst assemblage shows resorbed, chemically-zoned and cumulate textures; the glomerocrysts are attributed to a shoshonitic parent and remobilisation from a crystal mush. Macrocrysts formed at a pressure of 825 ± 80 MPa and temperatures of 789–1117 °C at around the Moho (~23–28 km). Pressure and temperature calculations of the shoshonitic mineral assemblage give average crystallisation conditions of 710 ± 80 MPa (above the Moho) and 1128± 25 °C, respectively. The trachytic magma crystallised at ~640 ± 75 MPa and 1000–1130 °C. The average liquidus of the rhyolitic magma has been calculated at 970±7 °C, at depths of b5 km(b60 MPa). New textural observations and intensive variable calculations permit the development of a new pressure and temperature-constrained model of the magmatic evolution of the Pietre Cotte system prior to eruption,with useful insights into the interactions of different magmatic components prior to and during the rapid onset of eruptions linked to magma mingling/mixing.
The Bowland Shale Formation is anomalously rich in selenium (Se) at levels an order of magnitude ... more The Bowland Shale Formation is anomalously rich in selenium (Se) at levels an order of magnitude greater than other black shales. The Mam Tor landslide, Derbyshire, England, offers an opportunity to measure whether the Se anomaly is conferred to the alteration products formed by oxidative water flow through the shale. Selenium in the shale is concentrated in diagenetic pyrite. Alteration of the shale causes decomposition of the pyrite to iron oxyhydroxide, which is carried in colloidal form (ochre) by springs draining the landslide. The iron oxyhydroxide contains anomalously high Se, and anomalously high Se was measured in water ponded where the ochre precipitated, although not in flowing groundwater. Other trace elements including cadmium and thallium also occur at concentrations higher than in other ochres. Given the widespread nature of the Se anomaly in the Bowland Shale Formation and equivalents across Britain and Ireland, any alteration products derived from workings through the shale should be disposed of with care.
The former mining site at Kisgruva near Kongsberg, Norway, is primarily composed of worked sulphi... more The former mining site at Kisgruva near Kongsberg, Norway, is primarily composed of worked sulphide ore deposits, of hydrothermal origin, which occur within Precambrian metamorphic basement. Though the original targets at the Kisgruva mine site were extraction of copper (Cu), sulphur (S) and iron (Fe), the sulphide ore also contains exceptionally high concentrations of selenium (Se) and tellurium (Te), hosted within selenides (clausthalite and minor naumannite) and tellurides (hessite and minor altaite and tellurobismuthite). Both Se and Te are also present within the sulphide ore in pyrite and chalcopyrite, which contain exceptionally high concentrations of up to 688 ppm Se and 81 ppm Te. Additionally, oxidative weathering of the exposed bedrock has resulted in the accumulation of hyper-enriched, unconsolidated weathered crust deposits at surface (Se up to 1590 ppm; Te up to 63 ppm), containing selenite (SeO32−) and tellurite (TeO32−) ions. Concentrations of Se and Te are subsequently higher in the weathering products than in the sulphide ore, due to fixation on to organic matter (∼0.4% in weathered ore crusts), jarosite (formed from oxidation of sulphides from the primary ore), ferric oxide and hydroxide phases (goethite and haematite). Increasing demand for Se and Te to use in green technologies has led to the reassessment of these orebodies and their associated weathered ore crust deposits. Though these elements are currently considered mining contaminants, this and similar sites may be of future economic importance, particularly as demand for Se and Te continues to rise.
Standard mode and collision/reaction cell mass spectroscopy methods have been utilized in order t... more Standard mode and collision/reaction cell mass spectroscopy methods have been utilized in order to overcome spectral interferences and provide ultra‐low quantification of selenium (Se) and tellurium (Te) in British Carboniferous coals for the first time. The accurate detection of Se and Te in coals is becoming increasingly important, as coals and pyrite have been identified as potentially significant trace element sources. The mean Se concentration of British coals bear comparison to that of world coals, with anomalous Se content (concentrations above 4 mg/kg) across westerly exposures, often coinciding with high sulphur (S) content and visible pyrite. New Te data for British coals gives a mean concentration of 0.02 mg/kg, with anomalous Te in Ayrshire. There is a positive correlation in the Te/Se ratio across the sample set. The close relationship between Se and Te, as well as Se–Te with both early syngenetic and later cleat‐filling pyrite, confirms an important role for sulphides in Se and Te sequestration in British coals. The high Se‐Bowland Shale and/or Ordovician volcanics may have provided the trace element source for British coals of similar or younger age. Regional intrusive activity (shallow tabular intrusions or more extensive plutons) and episodes of intense deformation can alter the thermal maturity of coals and may have driven the movement of trace element‐rich fluids through strata, locally enriching coals in Se and Te.
The Carboniferous Lower and Middle Coal Measures coals of the Northumberland Coalfield are anomal... more The Carboniferous Lower and Middle Coal Measures coals of the Northumberland Coalfield are anomalously rich in selenium (Se) content (up to 62 ppm) compared to the averages for the common UK and worldwide coals. As well as posing an environmental toxicity threat, Se is now regarded as an important resource for alloys, photovoltaic products and nanotechnologies, and high Se coals in North East England offer an opportunity to assess the Se means of occurrence, origins, transport mechanisms and enrichment in coals. At least two generations of pyrite host high Se in the sampled coal seams: microbial-formed disseminated pyrite (both cubic and framboidal in habit) and later cleat-filling pyrite, identified by petrographic observations, laser ablation methods and sulphur isotope compositions. There is a notable Se enrichment of up to 250 ppm in later formed cleat-filling pyrite. Trace element enrichment may have been sourced and influenced by seawater distribution during diagenesis, and localised dykes and deformation may have acted as an enrichment mechanism for sampled seams in the region. The high Se coals in Northumberland may provide a potential E tech element source and should be considered and carefully managed as coal mining and production are reduced in the area. The study also highlights the nature of Se enrichment in pyritic coals affected by cleat formation and multiple episodes of mineralisation, important as critical element demand continues to increase worldwide.
The Neoproterozoic Dalradian Supergroup contains widespread diagenetic sulphides present as pyrit... more The Neoproterozoic Dalradian Supergroup contains widespread diagenetic sulphides present as pyrite. The sulphides occur in both carbonaceous shales and glacial diamictites, that were deposited in relatively reducing and oxidising conditions respectively. The trace element compositions of the pyrite, and consequently the whole rock compositions, contrast between the two lithologies. The highest concentrations of selenium, tellurium and gold are all found in diamictite-hosted pyrite. The data suggest that increased mobility of these elements in oxidising conditions led to greater uptake when pyrite was precipitated. As one model for the formation of orogenic gold ore deposits assumes a sulphide-rich protolith, pyrite ultimately formed during relatively oxidising conditions could make a contribution, including the widespread pyrite precipitated during the Neoproterozoic 'Snowball Earth' glaciations.
The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), an... more The Rocche Rosse lava flow marks the most recent rhyolitic extrusion on Lipari island (Italy), and preserves evidence for a multi-stage emplacement history. Due to the viscous nature of the advancing lava (10^8 to 10^10 Pa s), indicators of complex emplacement processes are preserved in the final flow. This study focuses on structural mapping of the flow to highlight the interplay of cooling, crust formation and underlying slope in the development of rhyolitic lavas. The flow is made up of two prominent lobes, small (< 0.2 m) to large (> 0.2 m) scale folding and a channelled geometry. Foliations dip at 2–4° over the flatter topography close to the vent, and up to 30–50° over steeper mid-flow topography. Brittle faults, tension gashes and conjugate fractures are also evident across flow. Heterogeneous deformation is evident through increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
A method is proposed for the determination of selenium at low concentration in coal by collision/... more A method is proposed for the determination of selenium at low concentration in coal by collision/reaction cell technology inductively coupled plasma mass spectrometry (CRC-ICP-MS). Samples were decomposed by high pressure microwave-assisted wet digestion (MAWD) using 250 mg of coal, a mixture of 5 mL of 14.4 mol L−1 HNO3 and 1 mL of 40% HF and 70 min of heating program (200 °C and 40 bar). Hydrogen gas used in the collision/reaction cell was investigated to minimize the argon-based interferences at m/z 77, 78 and 80. The rejection parameter (RPq) and the H2 gas flow rate were set to 0.45 and 4.8 mL min−1, respectively. The use of H2 in the cell resulted in other polyatomic interferences, such as 76Ge1H+, 79Br1H+ and 81Br1H+, which impaired Se determination using 77Se, 80Se and 82Se isotopes, thus Se determination was carried out by monitoring only 78Se isotope. Selenium determination was performed in certified reference materials of coal (NIST 1635 and SARM 20) and an agreement better than 95% was observed between the results obtained by CRC-ICP-MS and the certified values. Under optimized conditions, the instrumental limit of detection was 0.01 μg L−1 and the method limit of detection was 0.01 μg g−1, which was suitable for Se determination at very low concentration in coal.
Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellu... more Black shales of the late Neoproterozoic Gwna Group (570–580 Ma), UK, contain enrichments of tellurium (Te), selenium (Se) and cobalt (Co) relative to average shale compositions. The Te and Co enrichments bear comparison with those of ferromanganese crusts in the modern deep ocean. Gwna Group deposition coincides with the Second Great Oxidation Event, which had a significant effect on trace element fixation globally. Selenium and Te concentrations within these black shales indicate increased continental weathering rates, high biological productivity and corresponding increases in atmospheric O2 concentrations. Cobalt, nickel (Ni) and arsenic (As) enrichments in this succession are secondary mineralisation phases. Demand for many of the trace elements found enriched in the Gwna Group black shales make their mechanisms of accumulation, and variations through the geological record, important to understand, and suggests that new resources may be sought based on black shale protoliths from this period.
Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancie... more Gold mining has a legendary history in Ethiopia, with Ethiopian mines providing gold to the ancient Egyptian empire and possibly even King Solomon's Mines and the Queen of Sheba. Today, gold occurs in the Pan-African age schist belt and Tertiary basaltic lavas of the Asosa region of Benishangul-Gumuz, western Ethiopia. There is widespread artisanal gold production in the Asosa region, with moderate activity by small numbers of local workers producing relatively large amounts of gold. There is a strong relationship between predominantly shear zone-hosted gold deposits and the Kuluck shear zone, suggesting a structural control on gold accumulation. Gold is also commonly associated with secondary sulphide mineralization and magnetite alteration in Asosa rocks. The source of the gold is thought to be the sub-volcanic intrusions generated during the subduction of the oceanic crust at the trench island-arc system, akin to what we see today in epithermal and porphyry type gold systems. Historical workings and anomalous gold concentrations in rock, soil and stream sediments point to a potentially significant untapped gold resource in the Asosa region of western Ethiopia.
Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average U... more Carboniferous coals of the Ayrshire Coalfield are enriched in selenium (Se) relative to average UK and world compositions, substituting for sulphur in pyrite. Greenburn surface mine coals are characterized by syngenetic concretionary pyrite (c. 15% total area), occurring as bedding-parallel banding, and later-formed (epigenetic) cross-cutting pyrite in cleats (c. 9% total area). In these, sulphur isotope compositions for both syngenetic and epigenetic pyrite include isotopically light and heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se (up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm). Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. T... more The Dalradian Supergroup of Britain and Ireland is mineralised by gold-tellurium vein deposits. The host succession includes carbonaceous, pyritic shales (pelites) which were a source of trace elements, including gold and tellurium. LA-ICP-MS mapping of pyrite crystals shows that late stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits.
Mid-Jurassic pyritic coals exposed at the village of Brora, northern Scotland, UK, contain a mark... more Mid-Jurassic pyritic coals exposed at the village of Brora, northern Scotland, UK, contain a marked enrichment of tellurium (Te) relative to crustal mean, average world coal compositions and British Isles Carboniferous coals. The Te content of Brora coal pyrite is more than one order of magnitude higher than in sampled pyrite of Carboniferous coals. The Te enrichment coincides with selenium (Se) and mercury (Hg) enrichment in the rims of pyrite, and Se/Te is much lower than in pyrites of Carboniferous coals. Initial pyrite formation is attributed to early burial (syn-diagenesis), with incorporation of Te, Se, Hg and lead (Pb) during later pyrite formation. The source of Te may have been a local hydrothermal system which was responsible for alluvial gold (Au) in the region, with some Au in Brora headwaters occurring as tellurides. Anomalous Te is not ubiquitous in coal, but may occur locally, and is detectable by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS).
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centennial timescales. The global mining industry produces huge volumes of fine wastes that could be utilised as feedstock for enhanced weathering. We have compiled a global database of the enhanced weathering potential of mined metal and diamond commodity
tailings from silicate-hosted deposits. Our data indicate that all deposit types, notably mafic and ultramafic rock-hosted operations and high tonnage Cu-hosting deposits, have the potential to capture ∼1.1–4.5 Gt CO2 annually, between 31 and 125% of the industry’s primary emissions. However, current knowledge suggests that dissolution rates of many minerals are relatively slow, such that only a fraction (∼3–21%) of this
potential may be realised on timescales of <50 years. Field trials in mine settings are urgently needed and, if this prediction is confirmed, then methodologies for accelerating weathering reactions will need to be developed.
in hyper-enriched ochres. Selenium in coals has been known to cause an
environmental issue in areas of North America but is also an important
commodity for solar cells and nanotechnologies. Coal-bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal-derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal-mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.
material of coal (NIST 1632c) for Se. Very low limits of quantification (LOQ) were obtained: 0.002 and 0.007 mg kg1 for Se and Te, respectively. Major elements were determined in final solutions obtained
by MAWD and MIC, and their concentration in solutions of MIC was negligible (<10 mg L1), minimizing the risk of interference in ICP-MS analysis. The proposed method was applied to samples of coal from
the United Kingdom, with a wide range of inorganic composition (from 3 to 41% ash content), showing its robustness and feasibility for routine analysis. Se concentration ranged from 0.291 to 11.5 mg kg1,
and Te was mainly found at ultra-trace levels (<0.007 to 0.11 mg kg1
). The proposed method presents several advantages over the reference methods, such as the use of a higher sample mass, low LOQs and,
an important aspect, no need of using HF.
Petrographic observations and mineral, bulk rock and glass geochemistry suggest that multiple mingling events
occurred during the evolution of the Pietre Cotte magmatic system, evidenced by the recognition of the following components: (1) a remobilised predominantly mafic crystal mush, evident as macrocrysts (crystals N500 μm), which form glomerocrysts within enclaves, (2) a microlitic (b100 μm) trachytic enclave groundmass with microcrysts (100–500 μm), and (3) a rhyolitic glass, which hosts both the enclaves and the glomerocrysts. The macrocrystic mafic assemblage includes clinopyroxene (En38-47Wo45–50; Mg# 0.72–0.89), olivine (Fo49–66) an
magnetite (Usp7–26), with plagioclase (An40–63Ab5–50) and rare alkali feldspar (Or41–57) also present. Enclaves are comprised of a groundmass of plagioclase (An43–47) and alkali feldspar (Or33–57) microlites, with clinopyroxene microcrysts (En39-42Wo47–51; Mg# 0.75–0.81) and trachyte groundmass glass. The rhyolitic host
is characterised by glass, spherulites, microlites and enclave-derived macrocrysts.
Compositionally and texturally distinct magmas are attributed to storage and interactions of distinct magma batches and their cumulates at various temperatures and depths beneath the Fossa Cone. Compositions vary frombasaltic-shoshonitic, through latitic-trachytic and rhyoliticmagmas. Themacrocrystic glomerocryst assemblage
shows resorbed, chemically-zoned and cumulate textures; the glomerocrysts are attributed to a shoshonitic parent and remobilisation from a crystal mush. Macrocrysts formed at a pressure of 825 ± 80 MPa
and temperatures of 789–1117 °C at around the Moho (~23–28 km). Pressure and temperature calculations of the shoshonitic mineral assemblage give average crystallisation conditions of 710 ± 80 MPa (above the Moho) and 1128± 25 °C, respectively. The trachytic magma crystallised at ~640 ± 75 MPa and 1000–1130 °C. The average
liquidus of the rhyolitic magma has been calculated at 970±7 °C, at depths of b5 km(b60 MPa). New textural observations and intensive variable calculations permit the development of a new pressure and
temperature-constrained model of the magmatic evolution of the Pietre Cotte system prior to eruption,with useful insights into the interactions of different magmatic components prior to and during the rapid onset of eruptions linked to magma mingling/mixing.
increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe
development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at
the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se
(up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm).
Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of
the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during
metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits.
centennial timescales. The global mining industry produces huge volumes of fine wastes that could be utilised as feedstock for enhanced weathering. We have compiled a global database of the enhanced weathering potential of mined metal and diamond commodity
tailings from silicate-hosted deposits. Our data indicate that all deposit types, notably mafic and ultramafic rock-hosted operations and high tonnage Cu-hosting deposits, have the potential to capture ∼1.1–4.5 Gt CO2 annually, between 31 and 125% of the industry’s primary emissions. However, current knowledge suggests that dissolution rates of many minerals are relatively slow, such that only a fraction (∼3–21%) of this
potential may be realised on timescales of <50 years. Field trials in mine settings are urgently needed and, if this prediction is confirmed, then methodologies for accelerating weathering reactions will need to be developed.
in hyper-enriched ochres. Selenium in coals has been known to cause an
environmental issue in areas of North America but is also an important
commodity for solar cells and nanotechnologies. Coal-bearing areas of the UK, such as Northumberland, are known to contain a high selenium content, and coal-derived ochres in these regions also contain significant selenium. The widespread occurrence of ochres in UK coal-mining regions may therefore present a unique ‘E tech’ trace element source and prevent a toxicity problem for which they were once thought to be responsible.
material of coal (NIST 1632c) for Se. Very low limits of quantification (LOQ) were obtained: 0.002 and 0.007 mg kg1 for Se and Te, respectively. Major elements were determined in final solutions obtained
by MAWD and MIC, and their concentration in solutions of MIC was negligible (<10 mg L1), minimizing the risk of interference in ICP-MS analysis. The proposed method was applied to samples of coal from
the United Kingdom, with a wide range of inorganic composition (from 3 to 41% ash content), showing its robustness and feasibility for routine analysis. Se concentration ranged from 0.291 to 11.5 mg kg1,
and Te was mainly found at ultra-trace levels (<0.007 to 0.11 mg kg1
). The proposed method presents several advantages over the reference methods, such as the use of a higher sample mass, low LOQs and,
an important aspect, no need of using HF.
Petrographic observations and mineral, bulk rock and glass geochemistry suggest that multiple mingling events
occurred during the evolution of the Pietre Cotte magmatic system, evidenced by the recognition of the following components: (1) a remobilised predominantly mafic crystal mush, evident as macrocrysts (crystals N500 μm), which form glomerocrysts within enclaves, (2) a microlitic (b100 μm) trachytic enclave groundmass with microcrysts (100–500 μm), and (3) a rhyolitic glass, which hosts both the enclaves and the glomerocrysts. The macrocrystic mafic assemblage includes clinopyroxene (En38-47Wo45–50; Mg# 0.72–0.89), olivine (Fo49–66) an
magnetite (Usp7–26), with plagioclase (An40–63Ab5–50) and rare alkali feldspar (Or41–57) also present. Enclaves are comprised of a groundmass of plagioclase (An43–47) and alkali feldspar (Or33–57) microlites, with clinopyroxene microcrysts (En39-42Wo47–51; Mg# 0.75–0.81) and trachyte groundmass glass. The rhyolitic host
is characterised by glass, spherulites, microlites and enclave-derived macrocrysts.
Compositionally and texturally distinct magmas are attributed to storage and interactions of distinct magma batches and their cumulates at various temperatures and depths beneath the Fossa Cone. Compositions vary frombasaltic-shoshonitic, through latitic-trachytic and rhyoliticmagmas. Themacrocrystic glomerocryst assemblage
shows resorbed, chemically-zoned and cumulate textures; the glomerocrysts are attributed to a shoshonitic parent and remobilisation from a crystal mush. Macrocrysts formed at a pressure of 825 ± 80 MPa
and temperatures of 789–1117 °C at around the Moho (~23–28 km). Pressure and temperature calculations of the shoshonitic mineral assemblage give average crystallisation conditions of 710 ± 80 MPa (above the Moho) and 1128± 25 °C, respectively. The trachytic magma crystallised at ~640 ± 75 MPa and 1000–1130 °C. The average
liquidus of the rhyolitic magma has been calculated at 970±7 °C, at depths of b5 km(b60 MPa). New textural observations and intensive variable calculations permit the development of a new pressure and
temperature-constrained model of the magmatic evolution of the Pietre Cotte system prior to eruption,with useful insights into the interactions of different magmatic components prior to and during the rapid onset of eruptions linked to magma mingling/mixing.
increasing fold asymmetry from the vent due to downflow cooling and stagnation. A steeper underlying topography mid-flow led to development of a channelled morphology, and compression at topographic breaks resulted in fold superimposition in the channel. We propose an emplacement history that involved the evolution through five stages, each associated with the following flow regimes: (1) initial extrusion, crustal development and small scale folding; (2) extensional strain, stretching lineations and channel development over steeper topography; (3) compression at topographic break, autobrecciation, lobe
development and medium scale folding; (4) progressive deformation with stagnation, large-scale folding and refolding; and (5) brittle deformation following flow termination. The complex array of structural elements observed within the Rocche Rosse lava flow facilitates comparisons to be made with actively deforming rhyolitic lava flows at
the Chilean volcanoes of Chaitén and Cordón Caulle, offering a fluid dynamic and structural framework within which to evaluate our data.
heavy variants, suggesting diagenetic and hydrothermal fluid formation. Late/post-Visean cleat-filling pyrite is enriched in Se
(up to 266 ppm) compared to the earlier-formed material (Se up to 181 ppm).
Anomalous Se may have been sourced from near-by sulphidic Dalradian metamorphic rocks. Initial Se sequestration is associated with syngenetic pyrite mineralization, absorbed from seawater and pore waters, with additional Se introduced from fluids mobilized during epigenetic pyrite formation. Cleats from local brittle fracturing provided channels for fluid flow and a locus for precipitation of comparatively high-Se pyrite. Permian dolerite intrusions may have provided an enrichment source and/or fluid distribution mechanism. The Se concentrations of the Greenburn coals relate to multi-stage mineralization, with cleat-filling pyrite showing the highest Se content, and highlight the potential for high Se in similarly altered and fractured coal deposits worldwide.
stages are enriched in gold, tellurium and lead, representing concentration of these elements during metamorphism and related hydrothermal activity. The sulphur isotope composition of
the pyrite varies with stratigraphic position, reflecting an origin for the pyrite in the depositional environment through microbial sulphate reduction. Where pyrite was converted to pyrrhotite, trace element contents are much lower, indicating element liberation during
metamorphism. These observations are consistent with a model of black shale protoliths for orogenic gold deposits.