The Origin of Associated Basic and Acid Rocks in the Lebombo--Nuanetsi Igneous Province, Southern Africa, as implied by Strontium Isotopes

Whole rock Rb–Sr measurements were made on associatedbasic and acid intrusives and extrusives from the northern andsouthern ends of the Lebombo monocline with a view to determineif the acid rocks came from the mantle or from the crust. Inthe south, in Swaziland (now called Ngwame) and Zululand, rhyolitesand granophyres (age 202 14 m.y.) have an initial Si⁸⁷–Sr⁸⁶ratio of 0.7042 0.0005; in the north, in the Nuanetsi syncline,rhyolites (age 206 13 m.y.) and granites from ring complexes(age 177 7 m.y.) have initial ratios of 0.7081 0.0008 and0.7085 0.0007, respectively. The initial ratios of the basicrocks, basalts and gabbros, vary in both areas and have a rangefrom 0.7042 to 0.7125 which can be explained by crustal contamination.The low initial ratios and isotopic homogeneity of the acidmagmas over long distances (160 km) in Swaziland and Zululandare interpreted as implying that they were derived from themantle.     

Ionospheric conditions

A general analysis of ionospheric conditions has been made in the light of possible ionic reactions occurring in the upper atmosphere. Data obtained on various parameters, such as ionic production and recombination, show that precise knowledge of the spectral distribution of solar radiation is needed and that other experimental determinations on dissociative recombinations are required.

The ionic complexity of the ionosphere is underlined by describing how the atomic ions O⁺ and N⁺ react with N₂, O₂ and NO molecules. The behavior of the molecular ions N⁺₂, O⁺₂and NO⁺depends on a group of simultaneous processes involving charge transfers and ionatom interchanges which are more important than dissociative recombinations. The altitude distribution of ions is exemplified by discussing the relative importance of various loss coefficients in the D-, E- and F-regions. It is seen that molecular nitrogen ions are subject to important charge transfer processes, that nitric oxide ions are always final products destroyed only by dissociative recombination. Additionally, the entire production of atomic oxygen ions is related to the photoionization of molecular nitrogen. Some information is also given on possible anomalies in the ratio of O⁺₂ and NO⁺ densities in the lower ionosphere. From the lack of sufficient experimental information on ionic processes it is shown that a precise analysis of ionospheric behavior remains highly speculative.     

Carte Métallogénique de la Bulgarie

Résumé On peut, en résumé, caractériser ainsi les principales provinces de la Bulgarie: — les Rhodopes constituent une zone typiquement polymétallique avec une prépondérance soulignée de Pb, Zn; le F, Cr, Ni, y existent en quantité subordonnée; en traces viennent encore: le Ba, Mn, Cd, Sb, W, Mo, Bi, As, Au, Ag, V; — la Sredna Gora est caractérisée comme une zone de cuivre typique, avec la présence de Fe, Mn, et en quantitée subordonnée de Pb, Zn, Mo, Ti, V, Au. — les Balkans portent les particularités d'une zone polymétallique (Pb, Zn, Cu) avec fer. On y remarque souvent des gîtes individualisés de cuivre, polymétallique avec fer, argent, ainsi que des gîtes complexes. Le Mn, Ba, Au, Ag, Co, Mo, As, Hg, V, W viennent en quantité subordonnée; — la zone des Kraistides, analogue à la précédente, se caractérise par des gisements polymétalliques pauvres et des gîtes à or et scheelite. Les éléments principaux sont: Au, Ba et secondaires: Pb, Zn, Cu, V et en partie du Fe et Hg; — la plateforme mésique, outre le gaz, se caractérise par le manganèse de la dépression de Varna.

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The metallogenic map of Bulgaria displays the following four major and distinct provinces: The Rhodopes as a typically polymetallic zone, mainly with Pb and Zn, but also with F, Cr and Ni, and minor or trace amounts of Ba, Mn, Cd, Sb, Mo, Bi, As, Au, Ag, V. The Sredna-gora is a distinct copper zone, with Fe and Mn, and minor amounts of Pb, Zn, Mo, Ti, V, Au. The Balkan is again a polymetallic zone of Pb, Zn and Cu with Fe; but Cu-Fe-Ag-deposits also occur. The other elements are present in minor quantities only. The Kraiste-Zone resembles the previous one and contains low grade polymetallic and scheelite deposits. The main elements are Au, Ba, and minor quantities of Pb, Zn, Cu, V and in part Fe and Hg. The zone of the Mésie platform contains only the manganese deposits of the Varna depression, in addition to natural gas.