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This paper presents the first petro-structural data as well as morphological characterization of alluvial gold nuggets and related heavy minerals, from the Guiwa-Yangamo area within the Batouri goldfield (Cameroon). This area comprises metamorphic rocks including various gneisses and amphibolite, intruded by granite and granodiorite. Structural analysis reveals four main tectonic phases: the early (D1) and D2 deformations show ductile behavior, while D3 and D4 are ductile-brittle and late brittle respectively. Two main shear zones comprising the NW–SE- to NNW–SSE-trending ductile shear and ENE–WSW-trending ductile-brittle shear zone related respectively to D2 and D3 deformations are distinguished. These shear zones are well known in the Batouri goldfield as hosting gold-bearing quartz veins. Evidences for hydrothermal alteration such as chloritization, sericitization, and silification were identified in gold-bearing granitoids of the Batouri goldfield. Morphological characterization of alluvial gold grains and analysis of related heavy minerals indicate both long transport (> 1000m) and relatively short transport (0–300m), suggesting that they come from either the neighboring Lom group rocks or a local source (probably from the surrounding magmatic and metamorphic rocks). A shear zone–related origin is also proposed.

As rock textures reflect the physical conditions and the mechanisms of formation of the rocks, new approaches are used for improving texture analyses, both qualitatively and quantitatively. Pioneer work has recently boosted interest in fractal analysis for quantifying and correlating patterns. Fractal-like patterns relate to a degree of multiscale organization, and fractal dimensions (FD) and their potential variations can be used to infer the physical conditions of rock formation at various scales of observation. Here, we characterize quantitatively the shape and distribution of orthopyroxene grains in ultramafic xenoliths in terms of FD and their relation with temperature of equilibration. Fractal analysis has been applied to several populations of mantle xenoliths: 7 xenoliths collected in the vicinity of Pico Santa Isabel on Bioko Island, an alkaline basaltic volcano in oceanic domain (Gulf of Guinea, Equatorial Atlantic), 9 samples from Sangilen, in the Agardag alkaline lamprophyre dyke (Russia), and 11 samples form Śnieznik (Lutynia, Poland), in the continental domain. Fractal analysis has been conducted to characterize the degree of complexity of the petrographic textures: it is indeed known that large values of FD are associated to more complex textures. The correlation here observed between the orthopyroxene fractal dimension and the temperature of equilibration suggests that FD captures a significant textural feature directly related to the temperature (i.e. generated by a temperature-controlled process). The significant difference in the FD–T correlation observed for the continental and oceanic mantle domains suggests that the mechanical and rheological behaviour is distinct in the oceanic and continental lithospheres. These first promising results should be confirmed by analysing other mantle suites of rocks in different geodynamic settings. Copyright © 2015 John Wiley & Sons, Ltd.