The geology and geochemistry of the Lumwana Cu (± Co ± U) deposits, NW Zambia

The Lumwana Cu (± Co ± U) deposits of NW Zambia are large, tabular, disseminated ore bodies, hosted within the Mwombezhi Dome of the Lufilian Arc. The host rocks to the Lumwana deposits are two mineralogically similar but texturally distinct gneisses, a granitic to pegmatitic gneiss and a banded to augen gneiss which both comprise quartz–feldspar ± biotite ± muscovite ± haematite ± amphibole and intervening quartz–feldspar ± biotite schist. The sulphide ore horizons are typically developed within a biotite–muscovite–quartz–kyanite schist, although mineralization locally occurs within internal gneiss units. Contacts between the ore and host rocks are transitional and characterized by a loss of feldspar. Kinematic indicators, such as S-C fabrics and pressure shadows on porphyroblasts, suggest a top to the north shear sense. The sulphides are deformed by a strong shear fabric, enclosed within kyanite or concentrated into low strain zones and pressure shadows around kyanite porphyroblasts. This suggests that the copper mineralization was introduced either syn- or pre-peak metamorphism. In addition to Cu and Co, the ores are also characterized by enrichments in U, V, Ni, Ba and S and small, discrete zones of uranium mineralization, occur adjacent to the hanging wall and footwall of the copper ore bodies or in the immediate footwall to the copper mineralization. Unlike typical Copperbelt mineralization, unmineralized units show very low background copper values. Whole rock geochemical analyses of the interlayered schist and ore schist, compared to the gneiss, show depletions in Ca, Na and Sr and enrichments in Mg and K, consistent with replacement of feldspar by biotite. The mineral chemistry of muscovite, biotite and chlorite reflect changes in the bulk rock chemistry and show consistent increases in X _Mg as the schists develop. δ³⁴S for copper sulphides range from +2.3?‰ to +18.5?‰, with pyrite typically restricted to values between +3.9?‰ and +6.2?‰. These values are atypical of sulphides precipitated by bacteriogenic sulphate reduction. δ³⁴S data for Chimiwungo (Cu + Co) show a broader range and increased δ³⁴S values compared to the Malundwe (Cu) mineralization. The Lumwana deposits show many characteristics which distinguish them from classical Copperbelt mineralization and which suggests that they are formed by metasomatic alteration, mineralization and shearing of pre-Katangan basement. Although this style of mineralization is reported elsewhere in the Copperbelt, sometimes associated with the more widely reported stratiform ores of the Lower Roan, none of the previously reported occurrences have so far developed the tonnages of ore reported at Lumwana.     

Distribution of Palaeozoic reworking in the Western Arunta Region and northwestern Amadeus Basin from 40Ar/39Ar thermochronology: implications for the evolution of intracratonic basins

The Centralian Superbasin in central Australia is one of the most extensive intracratonic basins known from a stable continental setting, but the factors controlling its formation and subsequent structural dismemberment continue to be debated. Argon thermochronology of K-feldspar, sensitive to a broad range of temperatures (∼150 to 350 °C), provides evidence for the former extent and thickness of the superbasin and points toward thickening of the superbasin succession over the now exhumed Arunta Region basement. These data suggest that before Palaeozoic tectonism, there was around 5–6 km of sediment present over what is now the northern margin of the Amadeus Basin, and, if the Centralian superbasin was continuous, between 6 and 8 km over the now exhumed basement. ⁴⁰Ar/³⁹Ar data from neoformed fine-grained muscovite suggests that Palaeozoic deformation and new mineral growth occurred during the earliest compressional phase of the Alice Springs Orogeny (ASO) (440–375 Ma) and was restricted to shear zones. Significantly, several shear zones active during the late Mesoproterozoic Teapot Orogeny were not reactivated at this time, suggesting that the presence of pre-existing structures was not the only controlling factor in localizing Palaeozoic deformation. A range of Palaeozoic ages of 440–300 Ma from samples within and external to shear zones points to thermal disturbance from at least the early Silurian through until the late Carboniferous and suggests final cooling and exhumation of the terrane in this interval. The absence of evidence for active deformation and/or new mineral growth in the late stages of the ASO (350–300 Ma) is consistent with a change in orogenic dynamics from thick-skinned regionally extensive deformation to a more restricted localized high-geothermal gradient event.     

Migration - why doesn't it work for deep continental data?

Summary. Conventional migration of deep seismic reflection data often produces disappointingly poor results even when the original unmigrated data are of high quality and are relatively noise free. Surprisingly, deep data often subjectively appear to be best migrated at velocities which are up to 50% less than appropriate interval velocities derived from crustal refraction experiments or directly from stacking velocities. The explanation for this behaviour is that near surface features distort and attenuate the seismic wave field and produce apparent discontinuities in deep reflections. Since these discontinuities are spurious they are not associated with the appropriate large diffractions which real discontinuities at depth would produce. During the process of migration reflections are invented in order to cancel out the missing diffractions thereby producing a "smiley" section which appears overmigrated. Since the lateral extent of individual smiles increases with increasing migration velocity, increasing two-way-time, and increasing seismic wavelength, the effect" is almost unnoticeable on conventional shallow seismic data but is overwhelming for deep crustal data.     

Interstellar heliospheric probe/heliospheric boundary explorer mission—a mission to the outermost boundaries of the solar system

The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere.     

Application of a new river classification scheme to Australia's tropical rivers

A revised typology of Australian tropical rivers was applied to the complete channel network (named and major rivers) shown on 1:250 000 topographic maps for three large drainage basins in northern Australia (Daly River, NT; Fitzroy River, WA; Flinders River, Qld). Reach mapping and classification were conducted using the revised typology. The 12 major river types proposed were: (1) bedrock rivers; (2) bedrock‐confined and ‐constrained rivers; (3) low sinuosity (straight) rivers; (4) meandering rivers; (5) wandering rivers; (6) anabranching rivers; (7) chains of ponds; (8) gullies; (9) floodouts; (10) lakes, swamps, billabongs and wetlands; (11) non‐channelized valley floors; and (12) estuarine rivers. The 12 major river types were developed based on river reach mapping for more than 264 000 km² of tropical Australian catchments. At scales larger than 1:250 000, subdivision of each major river type is recommended. In the Daly and Fitzroy catchments, confined and constrained rivers dominate, whereas in the Flinders and Fitzroy catchments, anabranching rivers dominate. The dominant river types need benchmarking with adequate numbers of control reaches so that channel changes induced by human and natural impacts can be measured by reference to the stability of these controls. Wandering rivers, floodouts and non‐channelized valley floors were rare for the 1:250 000 channel network in northern Australia but need inclusion in national parks.     

Gully systems under undisturbed indigenous forest, East Coast Region, New Zealand

Gully erosion is commonly associated with agricultural landscapes where vegetation clearance and farming practices increase runoff, leading to fluvial incision. However, gully erosion can also occur in forests that have undergone some form of disturbance, either natural or resulting from human impacts. This paper reports on recent gully development within areas of undisturbed indigenous forest as a result of a high magnitude rainfall event on the East Coast of New Zealand's North Island. This region, through a combination of crushed and sheared rock types, steep topography, and tectonic and climatic setting, has high natural rates of erosion, exacerbated by European deforestation in the late 19th and early 20th centuries.Sequential air photographs, spanning a 58 year period between 1939 and 1997 were used to classify and document the growth and recovery of gully systems in the 14.1 km² headwaters of the Mangaoporo catchment. Following a severe cyclone in 1988, with a rainfall of 535 mm, there were 21 active gully systems within the indigenous forest. On photography prior to 1988 only four gully systems were present. During this period there were 8 major rainfall events (150–250 mm). Despite further 5 rainfall events of 150–250 mm between 1988 and 1997 all gully systems showed signs of recovery, with a combined reduction in active area of 37%. The nature and location of these features is strongly influenced by lithology (orientation of jointing and bedding), and to a topographic threshold defined by catchment slope and catchment area.     

The prelude of the end-Permian mass extinction predates a postulated bolide impact

The mass extinction at the Permian–Triassic Boundary (PTB) is said to have been abrupt and probably caused by an extraterrestrial impact. However, evidence from the Global Stratotype Section and Point (GSSP) of the base of the Induan at Meishan, China, shows that the biotic crisis began prior to the level, in beds 25 and 26 at which the postulated impact event occurred. Evidence of such an earlier biotic crisis occurs in other sections in South China, and in central and western Tethyan regions. This event is characterized by the extinction of a range of faunas, including corals, deep-water radiolarians, most fusulinids and pseudotirolitid ammonoids, and many Permian brachiopods. In all sections, this extinction level is usually a few decimeters to meters below that of the main mass extinction in the event beds (25 and 26) at Meishan, and their correlatives elsewhere. This earlier extinction event happened before the postulated bolide impact at the level of beds 25 and 26, and constrains interpretation of the mechanisms that brought about this greatest mass extinction. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.