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Localized zones of Roan Breccia with very large clasts, termed écaille, occur throughout the arcuate Lufilian Arc of Central Africa. The breccia zones consist of mineralized Mines Subgroup rocks with Roches Argilo-Talcqueuses (R.A.T.) at their base. Several of these areas, such as Mashitu/Tenke-Fungurume, Kamoya-Kambove and Shinkolobwe, contain significant Cu and Co resources. A new model, termed the Thrust Belt Boudinage model, ascribes their formation and mineralization to localized lateral extension of the fold-and-thrust belt as the arc flexed during its development. Roan Breccia-rich areas, termed Double Cuspate Zones (DCZs), initiated from early, major, strike-perpendicular fractures. These progressively dilating areas became sumps for detritus shed from — and pushed ahead of — advancing thrust units. Detritus entrained into the base of advancing thrust units, which adopted a pseudo-lamination, was incorporated into R.A.T. Over-riding thrust units were locally unsupported by these dilating Roan Breccia-filled DCZs, resulting in delamination of the highly fractured, pervasively veined and mineralized lower portions of the Mines Subgroup, which slumped into DCZs at various attitudes. These écaille preserve disharmonic folding, with respect to longer-wavelength Kundelungu Group folds that are evident on Lufilian Arc maps. DCZs bear a remarkable resemblance to zones of foliation boudinage, suggesting that they were low-pressure depositional sites for metal- and brine-rich fluids. The process is encapsulated in a physically-and geologically-accurate animation video. While the new model does not replace the role of halite-rich fluids transporting mineralization, it obviates the requirement for very large volumes of salt transporting écaille physically and en masse. [ABSTRACT FROM AUTHOR]

Abstract: The present comparative histological study of the pectoral, caudal and anal fins of the polypterid Polypterus senegalus reveals the presence of a layer of dentine identified between the superficial ganoine patches and the bony part of the lepidotrichia in the three fins. Its extent varies depending on the fins. Similarly, the ganoine layer present at the surface of the proximal lepidotrichia shows fin-dependent differences in extent and distribution. The dentine layer is crossed by a system of thin worm-like vascular canaliculi that reach the ganoine layer and even penetrate within it as in the scales. In the lepidotrichia, the dentine lays directly on bone, which differs from the scales where dentine lies on isopedine, a plywood-like structure. Another difference between scales and lepidotrichia is the presence of actinotrichia that are unmineralised, fusiform rods of elastoidine located at the tip of the fins. Ontogenesis with differentiation of actinotrichia has no equivalent in scale formation. Although structural features are shared by lepidotrichia and scales in P. senegalus, observations on the scales and lepidotrichia support the hypothesis of Schaeffer (1977) that “scales and lepidotrichia are somewhat differently shaped manifestations of the same morphogenetic system”. [Copyright &y& Elsevier]