A new linguistic quantifier knowledge-guided OWA approach for mineral prospectivity mapping: a case study of the Bavanat Region,Iran

The main purpose of this study is to introduce a geographic information system (GIS)-based, multi-criteria decision analysis method for selection of favourable environments for Besshi-type volcanic-hosted massive sulphide (VHMS) deposits. The approach integrates two multi-criteria decision methods (analytical hierarchy process and ordered weighted averaging) and theory of fuzzy sets, within a GIS environment, to solve the problem of big suggested areas and missing known ore deposits in favourable environment maps for time and cost reduction. We doubled the fuzzy linguistic variables’ significance as a method to apply the arrange weights that the analytical hierarchy process (AHP)-ordered weighted averaging (OWA) hybrid procedure depends on. Another aim of this work is to assist mineral deposit exploration by modelling existing uncertainty in decision-making. Both AHP and fuzzy logic methods are knowledge-based, and they are affected by decision maker judgments. We used data-driven OWA approach in a hybrid method for solving this problem. We applied a new knowledge-guided OWA approach on data with changing linguistic variables according to the mineral system for VHMS deposits. Additionally, we used a vector-based method combination, which increased the precision of results. Results of knowledge-guided OWA showed that all of the mines and discovered deposits have been predicted with 100% accuracy in half of the size of the suggested area. To summarize, results improved the selection of possible target sites and increased the accuracy of results as well as reducing the time and cost, which will be used for field exploration. Finally, the hybrid methods with a knowledge-guided OWA approach have delivered more reliable results compared to exclusively knowledge-driven or data-driven methods. The study proved that expert knowledge and processed data (information) are critical important keys to exploration, and both of them should be applied in hybrid methods for reaching reliable results in mineral prospectivity mapping.     

Developing Africa’s energy mix

Africa is growing rapidly both in terms of population size and economically. It is also becoming increasingly clear that fossil fuels impose a high price on society through local environmental pollution and Africa’s particular vulnerability to climate change. At the same time, Africa has an excellent renewable energy potential and prices for renewable energy are reaching the price range of fossil fuels. Comparing results from state-of-the-art Integrated Assessment Models we find different options for achieving a sustainable energy supply in Africa. They have in common, however, that strong economic development is considered compatible with the 2°C climate target. Taking both challenges and appropriate solutions into account, some models find that a complete switch to renewable energy in electricity production is possible in the medium term. The continental analysis identifies important synergy effects, in particular the exchange of electricity between neighbouring countries. The optimal energy mix varies considerably between African countries, but there is sufficient renewable energy for each country. The intermittency and higher capital intensity of renewable energy are important challenges, but proven solutions are available for them. In addition, we analyse the political economy of a sustainable energy transition in Africa.

Key policy insights

• An almost complete shift towards renewable energy (RE) is considered feasible and affordable in Africa.

• By 2050, electricity generation could be sourced largely from solar, wind and hydro power.

• Prices for RE in Africa are now within the price range of fossil fuels, partly due to the excellent RE potential.

• The optimal energy mix varies strongly between countries, but RE is sufficiently available everywhere.

• Addressing intermittency is possible, but requires investments and cooperation on the grid.

     

Factors contributing to the development of extreme North Atlantic cyclones and their relationship with the NAO

The occurrence of extreme cyclones is analysed in terms of their relationship to the NAO phase and the dominating environmental variables controlling their intensification. These are latent energy (equivalent potential temperature 850 hPa is used as an indicator), upper-air baroclinicity, horizontal divergence and jet stream strength. Cyclones over the North Atlantic are identified and tracked using a numerical algorithm, permitting a detailed analysis of their life cycles. Extreme cyclones are selected as the 10% most severe in terms of intensity. Investigations focus on the main strengthening phase of each cyclone. The environmental factors are related to the NAO, which affects the location and orientation of the cyclone tracks, thus explaining why extreme cyclones occur more (less) frequently during strong positive (negative) NAO phases. The enhanced number of extreme cyclones in positive NAO phases can be explained by the larger area with suitable growth conditions, which is better aligned with the cyclone tracks and is associated with increased cyclone life time and intensity. Moreover, strong intensification of cyclones is frequently linked to the occurrence of extreme values of growth factors in the immediate vicinity of the cyclone centre. Similar results are found for ECHAM5/OM1 for present day conditions, demonstrating that relationships between the environment factors and cyclones are also valid in the GCM. For future climate conditions (following the SRES A1B scenario), the results are similar, but a small increase of the frequency of extreme values is detected near the cyclone cores. On the other hand, total cyclone numbers decrease by 10% over the North Atlantic. An exception is the region near the British Isles, which features increased track density and intensity of extreme cyclones irrespective of the NAO phase. These changes are associated with an intensified jet stream close to Europe. Moreover, an enhanced frequency of explosive developments over the British Isles is found, leading to more frequent windstorms affecting Europe.

Long‐Term Sediment Export Estimates from Northern Jordan using Roman Cisterns as Sediment Traps

Roman cisterns served as rainwater storage devices for centuries and are densely distributed in parts of northern Jordan. A major earthquake hit the region ca. A.D. 750 and in a short time many settlements were abandoned. As a consequence, most cisterns were not maintained, and they filled with sediments that today provide a postabandonment depositional record. In two field surveys, we mapped the locations of more than 100 cisterns in the Wadi Al‐Arab basin and selected two for detailed stratigraphic analysis that included ¹⁴C and optically stimulated luminescence dating. Catchment basin area for each cistern was determined by differential GPS. Both cisterns filled with sediments after the great earthquake and consequent abandonment of the region. Calculated sediment volumes are translated to long‐term average sediment export rates of 2.6–6.6 t ha⁻¹a⁻¹, which are comparable to erosion and sediment yield rates from other studies within the Mediterranean region. Our pilot study suggests that this approach can be applied elsewhere to calculate long‐term sediment export rates on hill slopes containing relict cisterns.     

Seepage of methane at Jaco Scar,a slide caused by seamount subduction offshore Costa Rica

Methane (CH₄) concentrations and CH₄ stable carbon isotopic composition ( \( \delta^{13} {\text{C}}_{{{\text{CH}}_{4} }} \) ) were investigated in the water column within Jaco Scar. It is one of several scars formed by massive slides resulting from the subduction of seamounts offshore Costa Rica, a process that can open up structural and stratigraphical pathways for migrating CH₄. The release of large amounts of CH₄ into the adjacent water column was discovered at the outcropping lowermost sedimentary sequence of the hanging wall in the northwest corner of Jaco Scar, where concentrations reached up to 1,500 nmol L^?1. There CH₄-rich fluids seeping from the sedimentary sequence stimulate both growth and activity of a dense chemosynthetic community. Additional point sources supplying CH₄ at lower concentrations were identified in density layers above and below the main plume from light carbon isotope ratios. The injected CH₄ is most likely a mixture of microbial and thermogenic CH₄ as suggested by \( \delta^{13} {\text{C}}_{{{\text{CH}}_{4} }} \) values between ?50 and ?62 ‰ Vienna Pee Dee Belemnite. This CH₄ spreads along isopycnal surfaces throughout the whole area of the scar, and the concentrations decrease due to mixing with ocean water and microbial oxidation. The supply of CH₄ appears to be persistent as repeatedly high CH₄ concentrations were found within the scar over 6 years. The maximum CH₄ concentration and average excess CH₄ concentration at Jaco Scar indicate that CH₄ seepage from scars might be as significant as seepage from other tectonic structures in the marine realm. Hence, taking into account the global abundance of scars, such structures might constitute a substantial, hitherto unconsidered contribution to natural CH₄ sources at the seafloor.     

Electron Transfer Between Sulfide and Humic Acid: Electrochemical Evaluation of the Reactivity of Sigma-Aldrich Humic Acid Toward Sulfide

Little is known of potential reactivity and redox properties of reduced dissolved organic matter (DOM), although DOM in anoxic environments, e.g., groundwater, peat soils, or lake sediments, can be expected to differ from DOM of oxidized environments. We therefore investigated the impact of electrochemical and wet chemical [hydrogen (H₂)/Pd catalyst] reduction in Sigma-Aldrich humic acid (HA) as a model DOM for high salinity, high ionic strength, or iron-rich systems on its reactivity toward sulfide. Mediated electrochemical measurement showed that the reactivity of HA toward sulfide decreased in the order non-reduced HA > electrochemically reduced (?0.1 V) HA > H₂/Pd-reduced HA > electrochemically reduced (?0.4 V) HA. Results indicated that measured initial values of electron-accepting capacities of HA had a strongly positive correlation with the sulfide transformation, except for the H₂/Pd treatment of HA. This latter treatment obviously changed HA structures and lead to a different reactivity toward sulfide, limiting a direct comparison to electrochemically reduced organic matter. Our result confirmed that reduced HA was still reactive toward sulfide, although to a lower extent compared with oxidized HA. Compared to electrochemical reduction, H₂/Pd pre-treatment of HA alters redox properties and reactivity of organic matter and may therefore lead to results that cannot be transferred to natural systems.     

Microstructural evolution during experimental albitization of K-rich alkali feldspar

Crystals of K-feldspar (C2/m), in contact with highly concentrated aqueous NaCl solutions at 500°C and 200 MPa, are pseudomorphically replaced by high albite (C[`1]) (C\bar{1}) as a result of an interface-coupled dissolution/reprecipitation process. The reaction occurs at an extremely sharp reaction front (<10 nm) and involves the complete breakdown of the initial framework structure. This results in the release of tetrahedrally incorporated elements such as Fe³⁺ and Ti⁴⁺ and a significant increase in Si/Al disorder across the reaction interface. The evolving microstructure is controlled by crystallographic relations between the phases. This leads to highly anisotropic, sawtooth-shaped intergrowths of albite and initial K-feldspar, resulting in the least structural misfit between the two framework structures. As a result, the newly formed interfaces appear to be semicoherent, and cracks across the reaction fronts even indicate elastic strain. The reaction produces 2 distinctive albite types (albite-1 and albite-2). Both are polycrystalline, with albite-2 showing significantly larger subgrain sizes. This indicates a secondary coarsening step driven by the reduction in interfacial energy within the polycrystalline replacement product. The reaction also produces a highly porous rim. However, the porosity is not evenly distributed resulting in a porous albite-1 and a non-porous albite-2 that mostly surrounds large, euhedral pores. Despite the substantial volume fraction of porosity in albite-1, no significant 3D interconnectivity could be detected, making the presence of a pervasive porosity unlikely. However, the result of coarsening is the continuous modification of the 3D porosity distribution. This could potentially provide a mechanism for fluid transport through the replacement rim until textural and chemical equilibration is achieved.     

P-T-X-controlled element transport through granulite-facies ternary feldspar from Lofoten,Norway

Fluid transport on the grain-scale controls many rock properties and governs chemical exchange. Charnockites from Lofoten indicate fluid penetration into ternary alkali feldspars controlled by their microtextures. In a process of fluid infiltration at granulite-facies conditions (∼600°C and 8–11 kbar), tiny pyroxenes enclosed in alkali feldspar reacted to amphiboles, which are always spatially connected to perthitic albite. Investigation of these microtextures by TEM imaging of Focused Ion Beam (FIB) prepared foils revealed that pyroxenes in contact with albite lamellae show dissolution features. An amorphous Fe- and Cl-bearing material interpreted to be a residuum of the percolating fluid was found within albite lamellae. Textures and mineral compositions indicate that a Cl-rich aqueous fluid attacked the lamellae, which then provided pathways for further fluid flow. A correspondence was found between feldspar compositions, their microtexture and their degree of alteration as a result of their permeability for fluids at specific temperatures. Hence, in addition to pressure and temperature, small variations of feldspar composition can strongly influence the fluid permeability of feldspathic rocks under lower crustal conditions.     

Paleomagnetism of the Cu�CZn�CPb-bearing Kupferschiefer black shale (Upper Permian) at Sangerhausen, Germany

Syngenetic, diagenetic and epigenetic models have been proposed for the Cu?CZn?CPb Kupferschiefer mineralization at Sangerhausen, Germany. Paleomagnetic and rock magnetic measurements have been made on 205 specimens from mine workings on the margin of the Sangerhausen Syncline. The mineralization is richest in the ??0.5-m-thick Upper Permian (258?±?2?Ma) Kupferschiefer black marly shale (nine sites) and dies out over ??0.2?m in the underlying Weisliegend sandstones (three sites) and overlying Zechstein carbonates (two sites). Except for one site of fault zone gypsum, characteristic remanent magnetization directions were isolated for all 14 sites using alternating field and thermal step demagnetization. These directions provide a negative fold test, indicating that the remanence postdates Jurassic fault block tilting. Rock magnetic measurements show that the Kupferschiefer shale marks a redox front between the oxidized Weissliegend sandstones and non-oxidized Zechstein carbonates. The 14 site directions give a Late Jurassic paleopole at 149?±?3?Ma. It is significantly different from the paleopole reported by E.C. Jowett and others for primary or early diagenetic Rote F?ule alteration that gives an age of 254?±?6?Ma on the current apparent polar wander path and is associated with Kupferschiefer mineralization. We suggest that the Late Jurassic extensional tectonic event that formed the nearby North German Basin also reactivated Variscan basement faults and extended them up through the overlying strata, thereby allowing hydrothermal basement fluids to ascend and epigenetically mineralize the Kupferschiefer shale. The possibility of a 53?±?3?Ma mineralization age is also considered.