Origin and deposition of a graphitic schist-hosted metamorphogenic Au-W deposit,Macraes, East Otago,New Zealand

The Macraes gold-tungsten deposit occurs in a low-angle thrust system in biotite grade Otago Schist. Native gold, scheelite, pyrite and arsenopyrite are found in and adjacent to quartz veins and silicified schist of lenticular reef zones, where the thrust system cuts through graphitic pelitic schist. Mineralization is confined to a shear zone, up to 80 m thick, which is closely sub-parallel to the regional schistosity. Chemical alteration is dominated by silicification, with some addition of Cr and depletion of Sr and Ba. Alteration extends only about 5 m from major veins. Oxygen becomes isotopically heavier away from veins due to temperature decrease as hot fluids penetrated into cooler (250°C?) rock. Graphite within the shear zone rocks has reflectance of 6–7% (in oil), similar to graphite in medium-high grade Otago Schist, and is presumed to be metamorphic in origin. This graphite has acted as a reducing agent to cause precipitation of gold where the thrust system, acting as a conduit for metamorphic fluids, intersects the graphitic schist. The metals were derived from the underlying schist pile which may include an over-thrust oceanic assemblage containing metal-enriched horizons.     

Limitations and feasibility of the land disposal of organic solvent-contaminated wastes

The limitations and feasibility of the land disposal of solid wastes containing organic solvents and refrigerants (chlorinated fluorocarbons) were investigated by evaluating the attenuation capacity of a hypothetical waste-disposal site by numerical modeling. The basic theorem of this approach was that the land disposal of wastes would be environmentally acceptable if subsurface attenuation reduced groundwater concentrations of organic compounds to concentrations that were less than health-based, water-quality criteria. Computer simulations indicated that the predicted concentrations of 13 of 33 organic compounds in groundwater would be less than their health-based criteria. Hence, solid wastes containing these compounds could be safely disposed at the site. The attenuation capacity of the site was insufficient to reduce concentrations of four compounds to safe levels without limiting the amount of mass available to leach into groundwater. Threshold masses based on time-dependent migration simulations were estimated for these compounds. The remaining 16 compounds, which consisted mainly of chlorinated hydrocarbons and fluorocarbons could not be safely landfilled without severe restrictions on the amounts disposed. These organic compounds were candidates to ban from land disposal.     

Pressure-induced incipient amorphization of α-quartz and transition to coesite in an eclogite from Antarctica: a first record and some consequences

Monocrystalline quartz inclusions in garnet and omphacite from various eclogite samples from the Lanterman Range (Northern Victoria Land, Antarctica) have been investigated by cathodoluminescence (CL), Raman spectroscopy and imaging, and in situ X‐ray (XR) microdiffraction using the synchrotron. A few inclusions, with a clear‐to‐opalescent lustre, show ‘anomalous’ Raman spectra characterized by weak α‐quartz modes, the broadening of the main α‐quartz peak at 465 cm^?1, and additional vibrations at 480–485, 520–523 and 608 cm^?1. CL and Raman imaging indicate that this ‘anomalous’α‐quartz occurs as relicts within ordinary α‐quartz, and that it was preserved in the internal parts of small quartz inclusions. XR diffraction circular patterns display irregular and broad α‐quartz spots, some of which show an anomalous d‐spacing tightening of ～2%. They also show some very weak, hazy clouds that have d‐spacing compatible with coesite but not with α‐quartz. Raman spectrometry and XR microdiffraction characterize the anomalies with respect to α‐quartz as (i) a pressure‐induced disordering and incipient amorphization, mainly revealed by the 480–485 and 608‐cm^?1 Raman bands, together with (ii) a lattice densification, evidenced by d‐spacing tightening; (iii) the cryptic development of coesite, 520–523 cm^?1 being the main Raman peak of coesite and (iv) Brazil micro‐twinning. This ‘anomalous’α‐quartz represents the first example of pressure‐induced incipient amorphization of a metastable phase in a crustal rock. This issue is really surprising because pressure‐induced amorphization of metastable α‐quartz, observed in impactites and known to occur between 15 and 32 GPa during ultrahigh‐pressure (UHP) experiments at room temperature, is in principle irrelevant under normal geological P–T conditions. A shock (due to a seism?) or a local overpressure at the inclusion scale (due to expansion mismatch between quartz and its host mineral) seem the only geological mechanisms that can produce such incipient amorphization in crustal rocks. This discovery throws new light on the modality of the quartz‐coesite transition and on the pressure regimes (non‐lithostatic v. lithostatic) during high‐pressure/UHP metamorphism. In particular, incipient amorphization of quartz could favour the quartz‐coesite transition, or allow the growth of metastable coesite, as already experimentally observed.     

The ionosphere: effects,GPS modeling and the benefits for space geodetic techniques

The main goal of this paper is to provide a summary of our current knowledge of the ionosphere as it relates to space geodetic techniques, especially the most informative technology, global navigation satellite systems (GNSS), specifically the fully deployed and operational global positioning system (GPS). As such, the main relevant modeling points are discussed, and the corresponding results of ionospheric monitoring are related, which were mostly computed using GPS data and based on the direct experience of the authors. We address various phenomena such as horizontal and vertical ionospheric morphology in quiet conditions, traveling ionospheric disturbances, solar flares, ionospheric storms and scintillation. Finally, we also tackle the question of how improved knowledge of ionospheric conditions, especially in terms of an accurate understanding of the distribution of free electrons, can improve space geodetic techniques at different levels, such as higher-order ionospheric effects, precise GNSS navigation, single-antenna GNSS orientation and real-time GNSS meteorology.     

L'apport métallifère «direct» du volcanisme continental

Recent geochemical investigation of ash-flow revealed important quantity of base metals in form of soluble salts coating ash particles. Metallogenic speculation is made for the formation of several and different kinds of ore deposits in sediments and volcanics, marine or continental, by direct concentration of these metals transported in solution. Soil process is not always required to “filter‘ metalliferous continental volcanics and concentrate the ore.     

Anomalously high uplift rates along the Ventura—Santa Barbara Coast, California—tectonic implications

The NW—SE trending segments of the California coastline from Point Arena to Point Conception (500 km) and from Los Angeles to San Diego (200 km) generally parallel major right-lateral strike-slip fault systems. Minor vertical crustal movements associated with the dominant horizontal displacements along these fault systems are recorded in local sedimentary basins and slightly deformed marine terraces. Typical maximum uplift rates during Late Quaternary time are about 0.3 m/ka, based on U-series ages of corals and amino-acid age estimates of fossil mollusks from the lowest emergent terraces.In contrast, the E–W-trending segments of the California coastline between Point Conception and Los Angeles (200 km) parallel predominantly northward-dipping thrust and high-angle reverse faults of the western Transverse Ranges. Along this coast, marine terraces display significantly greater vertical deformation. Amino-acid age estimates of mollusks from elevated marine terraces along the Ventura—Santa Barbara coast imply anomalously high uplift rates of between 1 and 6 m/ka over the past 40 to 100 ka. The deduced rate of terrace uplift decreases from Ventura to Los Angeles, conforming with a similar trend observed by others in contemporary geodetic data.The more rapid rates of terrace uplift in the western Transverse Ranges reflect N—S crustal shortening that is probably a local accommodation of the dominant right-lateral shear strain along coastal California.     

Dimensions of drought: South African case studies

The recent drought in southern Africa has underscored the need for detailed analysis of the phenomenon. While geographers have researched the causes and impacts of drought in many African contexts, South Africa and in particular its Bantustans have not received sufficient similar attention. This paper outlines firstly the dimensions of drought in South Africa, including the biophysical and socio-economic factors. Issues such as land-use management, drought planning and relief are interrogated in the South African context. The final section of the paper highlights these debates with specific reference to case studies of past and present drought initiatives in South Africa.     

Reconstruction of palaeosalinity using carbon isotopes and benthic associations: a comparison

Carbon and oxygen isotopes were determined on 40 recrystallized shells of Late Jurassic bivalves from the Lusitanian Basin of Portugal. In contrast with the oxygen isotopes, which exhibited considerable diagenetic distortion, the carbon isotopes are thought to preserve a record of the salinity of the Jurassic marginal marine seas in which these bivalves lived. The reconstructed palaeosalinities range from 35%o (euhaline) to 5% (oligohaline). Comparing these values with the palaeosalinity reconstructed from a palaeoecological analysis of 17 stratigraphic levels within the basin, the independently derived values agree in most cases. Strongly differing values are explained as being due to biotic factors and to diagenetic distortion of the isotopic signal; they are less likely to be due to smallscale time-averaging or insufficient microstratigraphic sampling. On the whole, the carbon isotope analyses are thought to produce reasonable palaeosalinity values, although data from infaunal, originally aragonitic bivalves appear to be less reliable than those from epifaunal bivalves with a predominantly or exclusively calcitic shell. As diagenetic alteration of the carbon isotope signal is, however, unpredictable and biotic effects on the isotopic composition are insufficiently known, palaeosalinity reconstructions based on stable isotope data should be supported by palaeoecological data.     

Tectonically driven fluid flow and associated low-grade metamorphism during the Alpine compression in the eastern Iberian Chain (Spain)

Fluid inclusions and clay mineralogy of the Permo-Triassic rocks from the Espina and Espadà Ranges (SE Iberian Chain, Spain) have been investigated to establish their relationship with hydrothermal fluid circulation during the Alpine Orogeny. Primary fluid inclusions in quartz-filled tension gashes in Permo-Triassic sandstones reveal maximum temperatures around 230 °C and very constant salinities of 8.5% wt. eq. NaCl. Secondary fluid inclusions found in quartz from the Santonian Ba–Cu–Hg deposits show similar compositional and thermodynamic characteristics, denoting an Alpine recrystallization. Clay mineral composition of Permo-Triassic mudrocks is characterized by pyrophyillite, indicating low-grade metamorphic conditions. Field observations and experimental data suggest that the crystallization of quartz in tension gashes, the formation of secondary fluid inclusions and the development of the metamorphism are contemporaneous and related to fluid circulation during the Alpine compression. Fluid flow took place along the Hercynian fault system that was reactivated during the Mesozoic rift stage and inverted during the Alpine deformation.