Simulation of mineral grades with hard and soft conditioning data: application to a porphyry copper deposit

This work deals with the geostatistical simulation of mineral grades whose distribution exhibits spatial trends within the ore deposit. It is suggested that these trends can be reproduced by using a stationary random field model and by conditioning the realizations to data that incorporate the available information on the local grade distribution. These can be hard data (e.g., assays on samples) or soft data (e.g., rock-type information) that account for expert geological knowledge and supply the lack of hard data in scarcely sampled areas. Two algorithms are proposed, depending on the kind of soft data under consideration: interval constraints or local moment constraints. An application to a porphyry copper deposit is presented, in which it is shown that the incorporation of soft conditioning data associated with the prevailing rock type improves the modeling of the uncertainty in the actual copper grades.     

Free allocation rules in the EU emissions trading system: what does the empirical literature show?

This paper analyses the rules for free allocation in the EU Emissions Trading System (EU ETS). The analysis draws on the empirical evidence emerging from two literature strands. One group of studies sheds light on the following questions: how efficient are free allocation rules in minimizing the risk of carbon leakage? Have they become more efficient over the trading periods? What are the technical limits to making them more efficient? Further: is firm behaviour affected by allowance allocation? Did specific provisions induce strategic behaviour with unintended effects? Studies from the second group estimate sectoral pass-through rates for the costs imposed by the EU ETS. Taking cost pass-through into account is necessary for properly targeting free allocation. The difficulty of accurately quantifying sectoral differences in cost pass-through ability, especially in manufacturing sectors (due to limited data availability and market heterogeneity), is the main hindrance to achieving further efficiency in allowance allocation. The new rules defined in the reform for Phase IV (2021–2030) nevertheless make some progress in this direction.

Key policy insights

• The difficulty of accurately quantifying sectoral differences in cost pass-through ability is the main hindrance to efficient free allocation in minimizing carbon leakage risk.

• In Phase IV (2021–2030), carbon leakage risk will be assessed more accurately thanks to: a) carbon intensity and trade intensity considered together through a combined indicator; b) possible use of more disaggregated data, and c) possible consideration of complementary qualitative assessments of abatement potential, market characteristics and profit margins.

• It is expected that benchmarked allocation introduced in Phase III (2013–2020) has induced additional emission abatement, but there is still a lack of empirical evidence.

     

New Insights in Shallow Gas Generation from Very High Resolution Seismic and Bathymetric Surveys in the Marennes-Oléron Bay, France

Very high resolution seismic profiles, ground-truthed by vibrocores, have revealed the occurrence of kilometre-scale acoustic turbidity in the Marennes-Oléron Bay, France. Such acoustic turbidity is commonly interpreted as gas-charged sediments. Comparison between accurate historical bathymetric data and the present day bathymetry has shown high sediment accretion zones in the study area (locally up to 8 m since 1824). The superimposition of seismic and bathymetric datasets displays a striking correlation between the high sedimentation rate area and the boundaries of the acoustic turbidity, i.e. gas-charged sediments. The key role of sedimentation rates in shallow gas generation in the study area is pointed out. It is also concluded that shallow gas is probably generated at short (decadal to secular) time scales.     

Simulating Large Gaussian Random Vectors Subject to Inequality Constraints by Gibbs Sampling

The Gibbs sampler is an iterative algorithm used to simulate Gaussian random vectors subject to inequality constraints. This algorithm relies on the fact that the distribution of a vector component conditioned by the other components is Gaussian, the mean and variance of which are obtained by solving a kriging system. If the number of components is large, kriging is usually applied with a moving search neighborhood, but this practice can make the simulated vector not reproduce the target correlation matrix. To avoid these problems, variations of the Gibbs sampler are presented. The conditioning to inequality constraints on the vector components can be achieved by simulated annealing or by restricting the transition matrix of the iterative algorithm. Numerical experiments indicate that both approaches provide realizations that reproduce the correlation matrix of the Gaussian random vector, but some conditioning constraints may not be satisfied when using simulated annealing. On the contrary, the restriction of the transition matrix manages to satisfy all the constraints, although at the cost of a large number of iterations.     

Looking beyond the fisheries crisis: Cumulative learning from small-scale fisheries through diagnostic approaches

The common scientific and media narrative in fisheries is one of failure: poor governance, collapsed stocks, and vanishing livelihoods. Yet, there are successful fisheries – instances where governments and/or communities have maintained or rebuilt stocks, where fishers have robust livelihoods, and where institutions are strong. Scientists and managers alike are becoming increasingly interested in moving beyond the doom-and-gloom stories of fisheries failures toward cumulative knowledge for making fisheries governance more successful. Recent literature has attempted to determine what separates the successes from the failures and better understand how lessons learned for effective fisheries governance can be cumulatively compiled. In this special issue, we present a range of fisheries studies from around the world – Latin America, The Pacific, and East Africa. The studies look at varying fisheries outcomes, including sustainability, cooperation, self-governance, and sustaining livelihoods. The contributions in this special issue all tackle the challenge of exploring, testing, and refining the Diagnostic Framework for Analyzing Social-Ecological Systems developed by Elinor Ostrom as a way to cumulate knowledge on the potential conditions that could be causing a problem or creating a benefit in the governance of small-scale marine fisheries. These articles successfully explore the applicability and contributions of the framework while providing important theoretical refinements for small-scale fisheries.     

Late Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40°40′ S)

A late Quaternary diatom stratigraphy of Lago Puyehue (40°40′ S, 72°28′ W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, ¹⁴C-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Niño events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP–present) might have marked subsequent increased frequency of El Niño occurrences, leading to drier summers and slightly moister winters in the area.     

Lateral variations of attenuation coefficients, group and phase velocities of rayleigh waves in Europe

Rayleigh wave group and phase velocities and attenuation coefficients are investigated in the 15–60-s period range for earthquakes occurring in the European area and registered at European stations. Observed group and phase velocities show clear differences in the period range 20–40 s, whereas attenuation coefficients are differentiated from 45 s to larger periods. From the shape of dispersion and attenuation curves, two broad zones have been isolated and designated as Western Europe and Southeastern Europe. Although some scatter is present, specially for attenuation, the data suggest that in general the shear velocity and Q_β values are higher for Southeastern Europe than for Western Europe. For Southeastern Europe there is a channel of low velocity and low Q_β, apparently correlated, located at the lower crust: in both regions there is a channel of low velocity and low Q_β values located at the uppermost mantle. In each case there also exists a channel of high Q_β values located at the lower crust but at slightly different depths.     

Micromechanics of saturated and unsaturated porous media

The homogenization method is used to determine the formulation of the behaviour of both saturated and unsaturated porous media. This approach makes it possible to assess the validity of the effective stress concept as a function of the properties of the porous media at the microscopic scale. Furthermore, the influence of the morphologies of the solid and fluid phases on the macroscopic behaviour is studied. The strain induced by drying is examined as a function of the morphological properties. Copyright © 2002 John Wiley & Sons, Ltd.     

The Piànico tephra: an early Middle Pleistocene record of intraplate volcanism in the Mediterranean

ABSTRACT Distal tephra are a valuable record of the volcano-tectonic evolution of an area under study. Here, we document the case of the Early Middle Pleistocene rhyolitic tephra of Piànico, discovered in the Southern Italian Alps. The geochemical characteristics of Piànico are unique among the distal tephra outcropping in Italy and indicate an intraplate volcanism at the source. The alkali composition and trace elements show a striking resemblance with the rhyolitic complex of the Euganean Hills, located 170 km from Piànico. However, these rhyolites are much older (Oligocene). Alternatively, the source of this intraplate volcanic episode could be located in the southern Tyrrhenian Sea.