Summary The Layo epithermal deposit, cutting Miocene-Pliocene calc-alkaline volcanites of the Tacaza group, includes a well-developed eastern zone (Vetas 7 and 8) in which brecciated and banded textures are associated with a large, intensely argillized zone containing diaspore and alunite. The vetas contain a typical Cu-As mineralogy of the acid-sulfate type (pyrite, enargite, Cu-excess tennantite, chalcopyrite, covellite) with an associated original stanniferous paragenesis including vinciennite and mawsonite. The vinciennite is close to the ideal end-member (Cu10Fe4SnAsS16) and the Cu-excess tennantite (Cu11FeAs4S13) shows a total absence of Zn and Ag; its very specific chemical composition suggests that all the iron is Fe3+, equilibrated by Cu+ and probably minor Cu2+.This particular mineralogical association implies deposition at relatively low temperature (sim" align="MIDDLE" BORDER="0">300°C) and high aS2 (10–6.5 decreasing to 10–8.5), from a Cu-S-rich and Fe-Zn-poor fluid. The acid-sulfate epithermal mineralization of the eastern vetas of Layo appears to have preceded an adularia-sericite epithermal mineralization expressed in the western vetas of Layo and also in the nearby large epithermal veins at Orcopampa and Shila. It also supports the genetic relationship that is commonly evoked between porphyry copper and epithermal deposits.
Le minéralogie originale à vinciente et tennantite riche du gisement épithermal (Cu, Sn, As, Au) de Layo (Sud Péru)
Résumé Le gîte épithermal de Layo est encaissé dans les volcanites calco-alcalines Miocène-Pliocène du groupe de Tacaza. Sa zone orientale renferme des corps minéralisés (Vetas 7 et 8) bien développés, à textures bréchiques et rubanées associées à une large zone intensément argilisée contenant diaspore et alunite.Les vetas présentent une association minéralogique à As-Cu typique des gisements acide-sulfate (pyrite, énargite, tennantite riche en cuivre, chalcopyrite, covellite) et une paragenèse stannifère originale renfermant vinciennite et mawsonite. La vinciennite est proche du pôle théorique (Cu10Fe4SnAsS16) et la tennantite riche en Cu (Cu11FeAs4S13) est dépourvue de Zn et de Ag; sa composition chimique suggère que tout le fer se présente sous la forme Fe3+, en équilibre avec Cu+, avec probablement une participation mineure de Cu2+.Cette association minéralogique particulière implique une mise en place sous forte fugacité en soufre (aS2 = 10–6.5 décroissant jusqu'à 10–8.5) à une température relativement basse de l'ordre de 300°C à partir d'un fluide riche en Cu et S et pauvre en Fe et Zn. La minéralisation de type acide-sulfate des vetas orientales de Layo précéderait celles de type adulaire-sericite des vetas occidentales de Layo et des gisements voisins de Orcopampa et Shila. Elle contribue à renforcer le lien fréquemment évoqué entre les porphyres cuprifères et les gisements épithermaux.
The Mercury Laser Altimeter on the NASA MESSENGER mission has ranged to several ridges and lobate scarps during two equatorial flybys of the planet Mercury. The tectonic features sampled, like others documented by spacecraft imaging and Earth-based radar, are spatially isolated and have vertical relief in excess of 1 km. The profiles also indicate that the faulting associated with their formation penetrated to tens of kilometers depth into the lithosphere and accommodated substantial shortening. To gain insight into the mechanism(s) of strain accommodation across these structures, we perform analytical and numerical modeling of representative dynamic localization mechanisms. We find that ductile localization due to shear heating is not favored, given our current understanding of thermal gradients and shallow thermal structure of Mercury at the time of ridge and scarp formation, and is likely to be of secondary importance at best. Brittle localization, associated with loss of resistance during fault development or with velocity weakening during sliding on mature faults, is weakly localizing but permits slip to accumulate over geological time scales. The range of shallow thermal gradients that produce isolated faults rather than distributed fault sets under the assumption of modest fault weakening is consistent with previous models for Mercury’s early global thermal history. To be consistent with strain rates predicted from thermal history models and the amount of shortening required to account for the underlying large-offset faults, ridges and scarps on Mercury likely developed over geologically substantial time spans. 相似文献
This paper highlights the problem of step-length selection for the one-step-ahead prediction of ozone called the data time interval. This is done using a case study-based comparison of two approaches for predicting the maximum daily values of tropospheric ozone. The first approach is the 1-day-ahead prediction and the second is the prediction of the maximum values based on a multi-step-ahead iteration of 1-h predictions. Gaussian process modelling is utilised for this comparison. In particular, evolving Gaussian-process models are used that update on-line with the incoming measurement data. These sorts of models have been successfully used in the past for the prediction of ozone pollution. This paper contributes an assessment of the way that the maximum ozone values are predicted. A comparison of the daily maximum ozone values forecasted by a model based on 1-day-ahead predictions with those obtained by iterated 1-h-ahead predictions of the ozone with predictions at predetermined hours of the day is given. The forecast results are in favour of the on-line model based on hourly predictions when approaching closer to the real maximum values of ozone, and in favour of the daily predictions when they are made on a daily basis. 相似文献
One of the most important challenges for the South East Europe region will be replacing more than 30% of its presently installed fossil fuel generation capacity by the end of 2030, and more than 95% by 2050 if its age structure is considered. This requires a strong policy framework to incentivise new investments in a region currently lacking investors, but also presents an opportunity to shape the electricity sector over the long term according to the broader energy transition strategy of the EU and the Energy Community. The aim of this paper is to assess what type of long-term pathways exist for electricity sector development in the region if they follow the energy transition process of the EU. In this model-based scenario assessment, long term electricity sector futures are explored using a set of interlinked electricity models evaluating the level of renewable energy investment required in the region to reach a deep decarbonization target, assuming emission reduction above 94% by 2050 compared to 1990 in line with the long term market integration and climate policy goals of the EU. It also explores what are the most important system wide impacts of the high deployment of renewable energy concerning generation adequacy and security of supply.
Energy policies in the South East Europe (SEE) region, both at the national and regional level, should focus on enabling renewable energy integration, as this will be a key component of the future energy mix.
EU and Energy Community policies should be incorporated into national energy planning to ensure that SEE countries embark on the energy transition process at an early stage.
Stranded costs should be carefully considered in decision-making on new fossil-fuel generation and gas network investment in order to avoid lock-in to carbon intensive technologies.
If consistent decarbonization policy prevails, with a significant and persistent CO2 price signal, the role of natural gas remains transitory in the region.
The SEE region offers relatively cheap decarbonization options: the power sector can reduce GHG emissions above 94% by 2050 in the modelled scenarios.
Among the numerous factors that trigger landslide events, the anthropogenic impact caused by inadequate planning and faulty land use in urban areas is increasing. The Zemun settlement on the northern outskirts of Belgrade has experienced a number of landslides in the last three decades, endangering buildings and roads, and claiming human lives, particularly in the case of the 2010/2011 landslides. Selected meteorological parameters were used to calculate rainfall erosivity indices such as Precipitation Concentration Index and Modified Fournier Index over the period 1991–2015. Drought indices, Lang aridity index and Palfai Drought Index were calculated as well. Mann–Kendall trend test was applied to identify potential rising and/or declining trends both in meteorological parameters and calculated indices. Trend analysis of the annual and seasonal scales yielded a statistically significant trend in the spring time series. Stable arid and pronounced drought conditions were recorded. The modified Fournier index based on monthly mean values yields moderate aggressiveness, with several extreme values indicating very high erosivity classes, especially for 2010/2011. The geological substrate is predominantly loess and hence highly susceptible to erosion and slope failure when climatological conditions are suitable. Accelerated urbanization at the end of the last century reduced vegetation cover, intensified pressure on the vertical loess slope, and lacked suitable rain drainage systems so that surface-water runoff was directed into the porous loess, thereby endangering slope stability. We proposed a geomorphic model to describe the nature of the erosional processes on the loess cliffs of the Zemun loess plateau. Results from this study have implications for mitigation strategies. 相似文献
The traditional concept of the Early Proterozoic gold deposits in Ghana — i.e. gold-bearing shear zones overlain by Tarkwaian paleoplacers containing reworked gold derived from the shear-zones — needs to be reconsidered in the light of recent research in Ghana, the Ivory Coast and French Guiana. This research has revealed a consistent pattern of geostructural and metallogenic evolution in which both the Birimian and the Tarkwaian rocks were deformed by a major Eburnean compression (D2). It has shown that the NE-SW faults controlling the Gold Coast Range shear-zone mineralization (Ashanti-Prestea) were formed during the Eburnean D2 episode of thrusting that was followed by hydrothermal activity with the emplacement of auriferous arsenopyrite and then by the development of quartz veinlets and native gold; thus the shear-zone mineralization could only have appeared during the D2 late-orogenic stage. It has also shown evidence of post-depositional D2 deformation in the gold sites examined in the Tarkwa gold-bearing conglomerate, although the effects are limited and primary lithological controls have been preserved that reveal these deposits to be modified paleo-placers. Thus, the Tarkwaian gold could not be derived from the gold-bearing shear-zones. 相似文献