Iron isotope fractionation during hydrothermal ore deposition and alteration   总被引：4，自引：0，他引：4  

Gregor Markl  Friedhelm von Blanckenburg 《Geochimica et cosmochimica acta》2006,70(12):3011-3030

Iron isotopes fractionate during hydrothermal processes. Therefore, the Fe isotope composition of ore-forming minerals characterizes either iron sources or fluid histories. The former potentially serves to distinguish between sedimentary, magmatic or metamorphic iron sources, and the latter allows the reconstruction of precipitation and redox processes. These processes take place during ore formation or alteration. The aim of this contribution is to investigate the suitability of this new isotope method as a probe of ore-related processes. For this purpose 51 samples of iron ores and iron mineral separates from the Schwarzwald region, southwest Germany, were analyzed for their iron isotope composition using multicollector ICP-MS. Further, the ore-forming and ore-altering processes were quantitatively modeled using reaction path calculations. The Schwarzwald mining district hosts mineralizations that formed discontinuously over almost 300 Ma of hydrothermal activity. Primary hematite, siderite and sulfides formed from mixing of meteoric fluids with deeper crustal brines. Later, these minerals were partly dissolved and oxidized, and secondary hematite, goethite and iron arsenates were precipitated. Two types of alteration products formed: (1) primary and high-temperature secondary Fe minerals formed between 120 and 300 °C, and (2) low-temperature secondary Fe minerals formed under supergene conditions (<100 °C). Measured iron isotope compositions are variable and cover a range in δ⁵⁶Fe between −2.3‰ and +1.3‰. Primary hematite (δ⁵⁶Fe: −0.5‰ to +0.5‰) precipitated by mixing oxidizing surface waters with a hydrothermal fluid that contained moderately light Fe (δ⁵⁶Fe: −0.5‰) leached from the crystalline basement. Occasional input of CO₂-rich waters resulted in precipitation of isotopically light siderite (δ⁵⁶Fe: −1.4 to −0.7‰). The difference between hematite and siderite is compatible with published Fe isotope fractionation factors. The observed range in isotopic compositions can be accounted for by variable fractions of Fe precipitating from the fluid. Therefore, both fluid processes and mass balance can be inferred from Fe isotopes. Supergene weathering of siderite by oxidizing surface waters led to replacement of isotopically light primary siderite by similarly light secondary hematite and goethite, respectively. Because this replacement entails quantitative transfer of iron from precursor mineral to product, no significant isotope fractionation is produced. Hence, Fe isotopes potentially serve to identify precursors in ore alteration products. Goethites from oolitic sedimentary iron ores were also analyzed. Their compositional range appears to indicate oxidative precipitation from relatively uniform Fe dissolved in coastal water. This comprehensive iron isotope study illustrates the potential of the new technique in deciphering ore formation and alteration processes. Isotope ratios are strongly dependent on and highly characteristic of fluid and precipitation histories. Therefore, they are less suitable to provide information on Fe sources. However, it will be possible to unravel the physico-chemical processes leading to the formation, dissolution and redeposition of ores in great detail.  相似文献   

Probabilities in climate policy advice: a critical comment     

Gregor Betz 《Climatic change》2007,85(1-2):1-9

This essay explores as to whether probabilistic climate forecasting is consistent with the prerequisites of democratic scientific policy advice. It argues that, given the boundaries of our current knowledge, it is highly problematic to assign exact, unconditional probabilities to possible values of climate sensitivity. The range of possible–instead of probable–future climate scenarios is what climate policy should be based on.  相似文献   

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

Reza Ghasemi  Behzad Tokhmechi  Gregor Borg 《Arabian Journal of Geosciences》2018,11(19):588

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.  相似文献   

Centrifuge modelling of rainfall-induced slope failure in variably saturated soil     

Wang  Shun  Idinger  Gregor  Wu  Wei 《Acta Geotechnica》2021,16(9):2899-2916

Acta Geotechnica - This paper presents the results of centrifuge tests on rainfall-induced instabilities in variably saturated slopes. The roles of rainfall intensity and initial conditions, such...  相似文献   

Developing Africa’s energy mix     

Gregor Schwerhoff  Mouhamadou Sy 《Climate Policy》2019,19(1):108-124

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.

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P-T-X-controlled element transport through granulite-facies ternary feldspar from Lofoten,Norway   总被引：1，自引：1，他引：0  

Katharina Hartmann  Richard Wirth  Gregor Markl 《Contributions to Mineralogy and Petrology》2008,156(3):359-375

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.  相似文献   

Precipitation intercomparison of a set of satellite- and raingauge-derived datasets,ERA Interim reanalysis,and a single WRF regional climate simulation over Europe and the North Atlantic   总被引：1，自引：0，他引：1  

Gregor Skok  Nedjeljka Žagar  Luka Honzak  Rahela Žabkar  Jože Rakovec  Andrej Ceglar 《Theoretical and Applied Climatology》2016,123(1-2):217-232

  相似文献   

Indicative mean transit time estimation from δ<Superscript>18</Superscript>O values as groundwater vulnerability indicator in karst-fissure aquifers     

P. Malík  J. Švasta  J. Michalko  M. Gregor 《Environmental Earth Sciences》2016,75(12):988

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Measurements and Models of the Mass Balance of Hintereisferner   总被引：1，自引：0，他引：1  

M. Kuhn  E. Dreiseitl  S. Hofinger  G. Markl  N. Span  & G. Kaser 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):659-670

This paper summarizes the methods applied to determine the mass balance of Hintereisferner and several other glaciers in the Tyrolean Alps since 1952. On an annual basis the direct glaciological method was applied with fixed date measurements on 10–15 accumulation pits and 30–90 ablation stakes on 9 km².
Indirect mass balance determination from equilibrium line altitude, accumulation area ratios or representative stakes, yield fair results and some exceptions could be related to anomalous meteorological conditions.
Monthly or more frequent stake readings supplied time series of ablation at various altitudes and slope aspects that served as basis for the calibration of energy and mass balance models. Of various models developed, two are presented in this paper. Both are based on degree days, one using daily values from a valley station to predict the mean annual balance of the entire glacier, while the other calculates day-to-day changes at 50-m grid points on the glacier.
The geodetic method has been applied for longer periods and yields results consistent with those of the glaciological method. The balance velocity calculated from recent ice thickness soundings and accumulation measurements is significantly less than observed velocity.  相似文献   

Projections of global warming-induced impacts on winter storm losses in the German private household sector     

Hermann Held  Friedrich-Wilhelm Gerstengarbe  Tobias Pardowitz  Joaquim G. Pinto  Uwe Ulbrich  Kai Born  Markus G. Donat  Melanie K. Karremann  Gregor C. Leckebusch  Patrick Ludwig  Katrin M. Nissen  Hermann Österle  Boris F. Prahl  Peter C. Werner  Daniel J. Befort  Olaf Burghoff 《Climatic change》2013,121(2):195-207

We present projections of winter storm-induced insured losses in the German residential building sector for the 21st century. With this aim, two structurally most independent downscaling methods and one hybrid downscaling method are applied to a 3-member ensemble of ECHAM5/MPI-OM1 A1B scenario simulations. One method uses dynamical downscaling of intense winter storm events in the global model, and a transfer function to relate regional wind speeds to losses. The second method is based on a reshuffling of present day weather situations and sequences taking into account the change of their frequencies according to the linear temperature trends of the global runs. The third method uses statistical-dynamical downscaling, considering frequency changes of the occurrence of storm-prone weather patterns, and translation into loss by using empirical statistical distributions. The A1B scenario ensemble was downscaled by all three methods until 2070, and by the (statistical-) dynamical methods until 2100. Furthermore, all methods assume a constant statistical relationship between meteorology and insured losses and no developments other than climate change, such as in constructions or claims management. The study utilizes data provided by the German Insurance Association encompassing 24 years and with district-scale resolution. Compared to 1971–2000, the downscaling methods indicate an increase of 10-year return values (i.e. loss ratios per return period) of 6–35 % for 2011–2040, of 20–30 % for 2041–2070, and of 40–55 % for 2071–2100, respectively. Convolving various sources of uncertainty in one confidence statement (data-, loss model-, storm realization-, and Pareto fit-uncertainty), the return-level confidence interval for a return period of 15 years expands by more than a factor of two. Finally, we suggest how practitioners can deal with alternative scenarios or possible natural excursions of observed losses.  相似文献