Carbon dioxide capture and storage by mineralization has been proposed as a possible technology to contribute to the reduction of global CO 2 levels. A main candidate as a feed material, to supply Mg cations for combination with CO 2 to form carbonate, is the family of ultramafic rocks, Mg‐rich silicate rocks with a range of naturally occurring mineralogical compositions. A classification scheme is described and a diagram is proposed to display the full range of both fresh and altered ultramafic rock compositions. This is particularly for the benefit 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 ultramafic 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 efficiency and development.

Abstract Carbon capture and storage by mineralization is a potential method for storing anthropogenic CO 2 emissions, and is based on the reaction between Mg silicate and CO 2 to form Mg carbonate. The conglomerates of the Barzaman Formation exposed in the eastern United Arab Emirates represent an excellent natural analogue of this process. These conglomerates were deposited as a series of alluvial fans along the western margin of the Hajar Mountains, part of the Oman-UAE Ophiolite, and are composed largely of ultramafic and lesser-mafic clasts. The clasts and matrix have been extensively altered to dolomite during diagenetic processes. Analysis and interpretation of rock textures provide evidence for the various factors that influenced the diagenetic processes and shed light on the silicate–carbonate transformation process. All the reactions have taken place in the near-surface environment; the silicate–carbonate conversion reaction is exothermic and occurs spontaneously at near-ambient pressure and temperature, probably no greater than 50 °C. Estimates of the amount of CO 2 stored in this way can be obtained from considerations of outcrop area, formation thickness and percentage of dolomite replacement, and show that c. 150 billion tonnes (equivalent to about 4 years of worldwide CO 2 emissions at current rates) are stored.

Mineral carbonation is a process whereby CO2 reacts with ultramafic rocks to form carbonate minerals such as calcite (CaCO3) and magnesite (MgCO3). This process can be induced artificially at high pressures and temperatures and therefore has potential to be adapted as a carbon capture and storage (CCS) technology.Large-scale surface and subsurface carbonate deposits of probable Quatemaiy age are associated with major faulting across the Oman-UAL ophiolite. Here, fractured rock forms a natural fluid pathway and increases the surface area available for carbonation. Modem springs along these faults typically discharge hyperalkaline (pH similar to 11), Ca(OH)(2)-rich waters that precipitate carbonates on reaction with atmospheric CO2.Carbonates formed by absorption of atmospheric CO2 into Ca(OH)(2) waters tend to display low delta C-13 (<<-20%0 PDB) as a result of kinetic fractionation. However, ancient travertines show a large range in delta C-13 of -10.5 to -21.896. PDB, produced by the mixing of the low delta C-13 end member with other carbon sources such as limestones or organic-derived soil bicarbonate.Strontium isotope ratios of samples indicate fluids that formed calcite and ma2nesite veins may have interacted with limestones around and beneath the ophiolite. These are a carbon source which can easily be reworked and incorporated into carbonate deposits elsewhere. Carbonate deposits may not be created solely from atmospheric CO2, but instead represent a mixture of carbon sources.Failure to account for multiple carbon sources or recycled carbon may result in poor estimates of the rates and volumes of carbon that natural systems sequester. Further investigation is therefore necessary to detemfine how much of the carbon held within carbonate deposits has been incorporated from reworked sources. (C) 2013 The Author- Published by Elsevier Ltd. Open access under CC BY-NC-ND license Selection and/or peer-review under responsibility of GMT

The ~500km-long mid-Cretaceous Semail nappe of the Sultanate of Oman and UAE (henceforth referred to as the Oman ophiolite) is the largest and best-preserved ophiolite complex known. It is of particular importance because it is generally believed to have an internal structure and composition closely comparable to that of crust formed at the present-day East Pacific Rise (EPR), making it our only known on-land analogue for ocean lithosphere formed at a fast spreading rate. On the basis of this assumption Oman has long played a pivotal role in guiding our conceptual understanding of fast-spreading ridge processes, as modern fast-spread ocean crust is largely inaccessible.

This project was undertaken in order to document all information concerning the distribution, physical properties and current uses of all the non-limestone ‘hard-rock’ (mainly ophiolite) resources of the UAE. It involved visiting all active and disused aggregate quarries to verify the rock-types used, in what form (i.e. particle size) and for what purpose. With this information a GIS was constructed, in conjunction with the geological maps produced from the previous BGS geological mapping project, in which it was made possible to identify areas of future quarry expansion and new quarry establishment, with various constraints such as environmental concerns. A ‘hard-rock’ usage map was published at 1:100 000 scale, along with this report. Possible future uses of the various rock-types available were considered.

Our recent geological survey of the basement of central and northern Madagascar allowed us to re-evaluate the evolution of this part of the East Africa-Antarctica Orogen (EAAO). Five crustal domains are recognized, characterized by distinctive lithologies and histories of sedimentation, magmatism, deformation and metamorphism, and separated by tectonic and/or unconformable contacts. Four consist largely of Archaean metamorphic rocks (Antongil, Masora and Antananarivo Cratons, Tsaratanana Complex). The fifth (Bemarivo Belt) comprises Proterozoic meta-igneous rocks. The older rocks were intruded by plutonic suites at c. 1000 Ma, 820-760 Ma, 630-595 Ma and 560-520 Ma. The evolution of the four Archaean domains and their boundaries remains contentious, with two end-member interpretations evaluated: (1) all five crustal domains are separate tectonic elements, juxtaposed along Neoproterozoic sutures and (2) the four Archaean domains are segments of an older Archaean craton, which was sutured against the Bemarivo Belt in the Neoproterozoic. Rodinia fragmented during the early Neoproterozoic with intracratonic rifts that sometimes developed into oceanic basins. Subsequent Mid-Neoproterozoic collision of smaller cratonic blocks was followed by renewed extension and magmatism. The global 'Terminal Pan-African' event (560-490 Ma) finally stitched together the Mid-Neoproterozoic cratons to form Gondwana.

Mercury is used in small-scale mining to amalgamate gold particles, facilitating their separation from heavy sands. The negative environmental/health-related effects of mercury in mining communities in Ghana and other countries have generated research interest into development of safer alternatives. This study tested direct smelting as an alternative to amalgamation. In laboratory investigations, direct smelting yielded 99.8% recovery against 97% for amalgamation. A locally-fabricated furnace, sika bukyia, was used in field tests, yielding an average recovery of 98.3% compared to 88% for amalgamation. Direct smelting has the potential to replace amalgamation and retorting because it is effective, easy, quick and transparent.

A study of the ASM sector of Ghana established the practices and attitudes of gold miners and proposed an alternative to mercury amalgamation. The study showed that miners were aware of health hazards associated with mercury but continued to use it because they knew of no credible alternative. It was realised that any process to replace amalgamation must be very efficient to capture gold around 50-100 μm. To be acceptable to the miners the method must be: easy, quick, cheap, transparent and suitable for processing small batches of concentrate. Direct smelting was selected as the technique of choice.

The Oman–United Arab Emirates ophiolite is the world’s largest ophiolite. It is divided into 12 separate fault-bounded blocks, of which the northern three lie wholly or partly in the United Arab Emirates. Extensive mapping has shown that the United Arab Emirates blocks contain mantle and crustal sections which correspond to the classic ‘Penrose conference’ ophiolite definition but which are cut by a voluminous later magmatic sequence including ultramafic, mafic and felsic components. Samples from the later magmatic sequence are dated at 96.4 ± 0.3, 95.74 ± 0.3 and 95.2 ± 0.3 Ma; the early crustal section, which has not been dated directly, is thus constrained to be older than c. 96.4 Ma. Petrological evidence shows that the early crustal section formed at a spreading ridge, but the later magmatic sequence was formed from hydrous magmas that produced different mineral crystallisation sequences to normal mid-ocean ridge basalt (MORB). Mineral and whole-rock geochemical analyses show that the early crustal rocks are chemically similar to MORB, but the later magmatic sequence has chemical features typically found in supra-subduction zone (SSZ) settings. The ophiolite in the United Arab Emirates thus preserves clear evidence for two stages of magmatism, an early episode formed at a spreading centre and a later episode associated with the onset of subduction. Similar two-stage magmatism has been recognised in the Oman sector, but the United Arab Emirates contains the most voluminous SSZ magmatism yet described from this ophiolite.

The Barzaman Formation in the UAE comprises a series of matrix supported to locally clasts supported, polymict alluvial conglomerates. The Formation is widely exposed on the western edge of the Hajar Mountains that are a part of the large and well known Oman-UAE ophiolite. The Formation was deposited as an ophiolite-derived conglomerate with a serpentinite and harzburgite matrix of sand, silt and clay grade constituents. It formed during a heavy, possibly seasonal rainfall that resulted in viscous, slurry-like, rapid mass movement, of diverse grain size that are called debris flows. The Formation is now typically strongly dolomite cemented and therefore stands proud as resistant outcrops of the alluvial fans that overlie a sequence of intensively altered ophiolite mantle rocks. There is a very distinctive lithological sequence below the contact, which comprises from the top downwards: silicified and carbonated serpentinite, carbonate-veined serpentinite and carbonate-veined partially serpentinised peridotite that passes downwards into the normal partially serpentinised peridotite. These units are the main source of the clasts for the Barzaman Formation. The most common lithology of the Barzaman Formation is poorly sorted, cobble to boulder conglomerate with clasts largely of harzburgite, serpentinite, silicified serpentinite, gabbro and a minor amount of metamorphic rocks, which are other components of the ophiolite thrust stack. They are cemented by dense, hard, weathering-resistant dolomite, which has precipitated from phreatic and locally vadose groundwater. A petrographical study using optical and scanning electron microscopy revealed that the cementation was preferential and it involved, firstly the complete replacement of the serpentinite and harzburgite sand and silt matrix and simultaneously or subsequently it strongly affected clasts. Both, physical erosion of clasts during transportation and exposure to various weathering conditions as well as extensive groundwater-rock interaction during diagenesis contributed to the presence of highly altered ophiolitic clasts. The mechanical erosion has created fractures and areas of enhanced weaknesses that were subsequently penetrated by groundwater leading to zonal and concentric dolomitization of clasts. The partial dissolution of silicate minerals locally resulted in simultaneous precipitation of clay minerals and/or Fe oxides/hydroxides, leaving a ghost texture as evidence of the presence of former clasts. Clasts with diverse original composition show distinctively different alteration patterns. The susceptibility to dissolution and subsequent dolomitization of ultramafic and mafic clasts is suggested as follows: harzburgite and serpentinite are the most susceptible followed by gabbro with intermediate susceptibility, and silicified serpentinite as the least prone to alteration.

The Logar Ophiolite Complex (LOC) is located 30 km south of Kabul, Afghanistan, and extends over approximately 2000 km(2). It comprises a lower lherzolitic-dunitic-harzburgitic-gabbro ultramafic-mafic unit that passes upwards into a dolerite dyke complex, basaltic pillow lavas and an uppermost sequence of volcaniclastic-and terrigenous-dominated sedimentary units. The ophiolite represents an obducted remnant of intra-Tethyan basin oceanic crust, thrust onto a platform-style cover component of the Kabul Terrane during the Himalayan orogeny. Platinumgroup minerals have been detected for the first time in chromitites and ultramafic units from the LOC. Two distinct types of chromitites and ultramafic lithologies with different origins have also been identified in this study. The first type is a low Cr, PGE-poor chromitite interpreted to have been produced in a mid ocean ridge (MOR) environment. The second type is a high Cr, relatively PGE-rich dunite and peridotite from a boninitic magma produced in a supra-subduction zone (SSZ) setting. Platinum group element (PGE) abundances in these chromitites average 12 ppb and 26 ppb for PtzPdzRh for the dunite and peridotite. Chondrite-normalised PGE patterns have two distinct trends: (a) the MOR rocks have a positive Ru anomaly with a negative Pt anomaly and a generally negative slope; and (b) the SSZ rocks show weak positive Ru and Pt anomalies and a positive slope. It is concluded that the negative sloping pattern is typical of PGE in most ophiolites elsewhere. In contrast, the positively sloping pattern is more unusual and may indicate PGE remobilisation and enrichment.

This report is a description of the 1:25 000 scale Hatta geological map sheet. It forms part of the published outputs from a contract between the United Arab Emirates Federal Government (Ministry of Energy) and the British Geological Survey (BGS) to produce geological maps, at various scales, of the solid and drift geology of the eastern part of the United Arab Emirates. These maps, which have accompanying Sheet Explanations, are listed below. Geological surveying of the Hatta Sheet was completed in three winter field campaigns carried out between October to December and January to March of 2002-2005. Field data were recorded on transparent overlays on 1:25 000 scale colour aerial photographs, used in conjunction with LANDSAT imagery and 1:50 000 topographic maps. The field data were transferred onto gridded transparent overlays on geo-rectified LANDSAT images at 1:25 000 scale. Geological mapping of the Hatta district was carried out by M T Styles (ophiolite), R J Thomas (ophiolite, Hatta Zone west, metamorphic rocks), E R Phillips (Hatta Zone east and west, metamorphic rocks), D I Schofield, K M Goodenough (ophiolite), and, A R Farrant contributing to mapping of the Quaternary deposits. Petrographical analyses were completed by E R Phillips, R J Thomas, M T Styles and K M Goodenough on samples collected by the mapping team. The Sheet Explanation was compiled by E R Phillips and R J Thomas. The word ‘district’ is used here to refer to the area represented by the geological map 1:25 000 series sheet Hatta. The grid references in the text are UTM Zone 40 using the Nahrawan datum, given in the form [0419633 2826172]. Symbols in brackets after lithostratigraphic names refer to symbols used on the 1:25 000 series geological map. Refrences to other Sheet Explanations in these series are given by Sheet name and number (e.g. Fujairah Sheet, 50-4).

The Fujairah 1:50 000 geological map sheet covers a segment of the Hajar Mountains extending from the Gulf of Oman around the city of Fujairah in the east, to the desert plains of the Rub’ Al Khali in the west. The solid geology predominantly comprises rocks of the Oman-UAE ophiolite complex, with a small area in the centre-north underlain by medium- to high-grade metamorphic rocks (Bani Hamid Group). The ophiolitic rocks comprise an earlier magmatic suite of mantle harzburgite and dunite, overlain by a classic spreading-ridge crustal section of layered gabbro, through “high-level” gabbro (mainly isotropic to varitextured gabbro), to a Sheeted Dyke Complex and topmost pillow basalt. These were intruded by a later magmatic suite comprising some dunite, a predominantly ultramafic “Mixed Unit” (including peridotites and pyroxenites), voluminous wehrlite bodies, and a suite of younger gabbroic rocks and associated minor intrusions (various mafic dykes, tonalites and bodies of magmatic breccia). The metamorphic rocks occur as thin tectonic slices within a major north-west-trending fault zone. They fall within the P4 unit of the Bani Hamid Group of rocks and comprise quartz schists and quartzites, with minor amphibolites and calc-silicate rocks, metamorphosed under amphibolite facies conditions. The solid geology is partially covered by Miocene-Pliocene and Quaternary deposits. These are most extensive in the west, where the Hajar Mountains descend onto the desert plains and comprise palaeo-alluvial fan sands and gravels deposited on variably silicified serpentinite and mantle peridotites. These have been incised by Quaternary fluvial systems and are patchily overlain by Recent alluvial fan deposits. Elsewhere, the Quaternary deposits consist of alluvium and dissected river terraces, with scree and alluvial cones developed on the mountain slopes. Coastal zone deposits of the eastern seaboard include raised beaches and sabkhas, locally overlain by broad, low-angled alluvial fans issuing from the main wadis.

This report is a description of the 1:50 000 scale Hatta geological map sheet. It forms part of the published outputs from a contract between the United Arab Emirates (UAE) Federal Government (Ministry of Energy) and the British Geological Survey (BGS) to produce geological maps, at various scales, of the solid and drift geology of the eastern part of the United Arab Emirates. These maps, which have accompanying Sheet Explanations, are listed below. Geological surveying of the Hatta Sheet was completed in three winter field seasons, carried out between October to December and January to March of 2002-2005. Field data was recorded on transparent overlays on 1:25 000 scale colour aerial photographs, used in conjunction with LANDSAT imagery and 1:50 000 topographical base maps. The field data were transferred onto gridded transparent overlays on georectified LANDSAT images at 1:25 000 scale. The mapping team for the Hatta district consisted of M T Styles, R J Thomas, D I Schofield, K M Goodenough, and E R Phillips, with A R Farrant contributing to mapping of the Quaternary deposits. Petrographic analyses were completed by M T Styles, R J Thomas, E R Phillips and K M Goodenough on samples collected by the mapping team. The Sheet Explanation was compiled by M T Styles. The word ‘district’ is used here to refer to the area represented by the geological map 1:50 000 series sheet Hatta. The grid references in the text are UTM Zone 40 using the Nahrawan datum, given in the form [0419633 2826172]. Symbols in brackets after lithostratigraphic names refer to symbols used on the 1:50 000 series geological map. References to other Sheet Explanations in these series are given by Sheet name and number e.g. (Fujairah Sheet, 50-4).

This volume forms part of the product of a multidisciplinary study by the British Geological Survey (BGS), commissioned by the UAE Federal Government, Ministry of Energy, to produce 1:50 000 scale geological maps of the bedrock and superficial geology of the northern part of the UAE. This volume contains information about the findings of the geological mapping and associated specialist research. The only large areas of exposed rocks in the UAE occur in the Hajar mountains in the northern Emirates. Previous geological maps were made more than 20 years ago and were based largely on air photo interpretation with limited ground-truthing. The rapid economic development in the intervening period has seen a tremendous expansion of the national infrastructure; this has greatly increased the demand for high quality, field-based geological maps. The mountain area was mapped at a scale of 1:25 000 and a series of maps at a scale of 1:50 000 have been produced, along with maps of areas of special interest at 1:25 000. The desert area to the west of the mountains, covered largely by Quaternary deposits, was mapped at a scale of 1:50 000 and maps produced at 1:100,000. All these maps are accompanied by a Sheet Explanation that describes the rock sequences in the area covered by that particular map. This report describes the broader features of the main rock groups on a regional basis and includes the results of the specialist laboratory studies that were used to define and interpret the geology of the project area. The field mapping was undertaken in the winter months between October 2002 and January 2006. The mapping was carried out by S L B Arkley, J N Carney, R A Ellison, A R Farrant, K M Goodenough, E R Phillips, E A Pickett, D I Schofield, D Stephenson, M T Styles, R J Thomas, D G Tragheim and M Warrak. The laboratory studies were mostly carried out at the BGS. The petrographic study of the ophiolite, metamorphic and Dibba and Hatta zone rocks was carried out by members of the mapping team, and the limestones of the Platform Carbonates were studied by G K Lott. J A McKervey made electron probe microanalysis of minerals, M A Woods made macropalaeontological studies and assisted with the field mapping, and I P Wilkinson made micropalaeontologial determinations. Q W Crowley carried out the geochronological studies. The Earth Science Department at Cardiff University carried out the whole rock geochemical analysis and was also involved in a collaborative geochemical research project. P Lappage drew the majority of the illustrations. This volume was complied and edited K M Goodenough.