Strata-bound copper-iron sulfide mineralization in a Proterozoic front arc setting at Boksputs,Northwest Cape,South Africa — a possible Besshi-type deposit

A low-grade, copper-iron sulfide deposit is present at Boksputs in the Northwest Cape, South Africa. It occurs in the Proterozoic amphibolite belt, the Areachap Group, along the eastern margin of the Namaqua mobile belt.The mineralization, which is dominated by pyrite, chalcocopyrite, sphalerite, and magnetite, occurs as disseminated ore and thin layers of massive-type ore in the lower massive amphibiolite and associated amphibole gneisses of the Kraalkop antiform and synform.Chemically, the host-rock amphibolite resembles low-K arc tholeiite and calc-alkaline volcanics, whereas the upper amphibolite is calc-alkaline.The sulfide mineralization and the host-rock composition is explained in terms of modern plate tectonic principles. It is concluded that the Boksputs mineralization is a syngenetic, strata-bound, copper-iron deposit which to some extend resembles Besshi-type deposits. It is associated with low-K arc tholeiite which is tectonically related to a front arc environment or a rifted arc system along the eastern margin of the Namaqua mobile belt.     

On the definition of the flux of sensible heat

The definition of the sensible heat flux is examined in the light of a paper published by Brook (1978). We show that the convergence of the flux defined in this paper and that of the standard definition are related to different quantities and that care must be taken to ensure that compatible definitions are used.     

Concentration,vertical flux,and remineralization of particulate uranium in seawater

Concentrations and fluxes of particulate U were measured throughout the water column at several locations in the Atlantic and Pacific Oceans with in situ filtration systems and sediment traps. The results indicate that dissolved U is fixed to particles in surface seawater. Organic matter appears to be the carrier phase. Formation of particulate authigenic U below the surface waters could not be detected. Authigenic U is remineralized within the bathypelagic layers at the open ocean sites studied. In the Panama Basin, an upwelling area with high biological productivity, remineralization of authigenic U in the deep water column was not observed. The rate of remineralization of authigenic U in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans. Formation of authigenic U in the water column in areas such as the Panama Basin is not a significant sink for U on an ocean wide basis.     

Sources of the Slowly-Varying Component of Solar Microwave Emission and their Relationship with their Host Active Regions

Daily surveys of the solar disc made at 2.8 cm wavelength over the period 1–13 November 1981, complemented by magnetograms and H filtergrams, are used to examine the relationship between sources of the slowly varying component of solar radio emission and properties of their host regions. Two classes of source are noted: diffuse and compact. Sources are designated compact when smaller than 40. The diffuse sources may be explained in terms of free–free thermal emission from trapped plasma in loops overlying the active region. The great majority of compact sources can be accounted for in terms of gyroresonance from thermal electrons in the strong magnetic fields overlying sunspots. A small minority are less amenable to this explanation. They are associated with magnetic complexity and dynamism, lie close to magnetic polarity reversals, and could be non-thermal. Microwave sources are an evolutionary feature common to all but the smallest active regions.