The Jbel Saghro is interpreted as part of a long-lived silicic large igneous province. The area comprises two lithostructural complexes. The Lower Complex consists of folded metagreywackes and N070–090°E dextral shear zones, which roughly results from a NW–SE to NNW–SSE shortening direction related to a D₁ transpressive tectonic stage. D₁ is also combined with syntectonic plutons emplaced between ca. 615 and 575 Ma. The Upper Complex is defined by ash-flow caldera emplacements, thick and widespread ignimbrites, lavas and volcaniclastic sedimentary rocks with related intrusives that were emplaced in three main magmatic flare ups at ca. 575, 565 and 555 Ma. It lies unconformably on the Lower Complex units and was affected by a D₂ trantensive tectonic stage. Between 550 and 540 Ma, the magmatic activity became slightly alkaline and of lower extent. Ore deposits show specific features, but remain controlled by the same structural setting: a NNW–SSE shortening direction related to both D₁ and D₂ stages. Porphyry Au(–Cu–Mo) and intrusion-related gold deposits were emplaced in an earlier stage between 580 and 565 Ma. Intermediate sulfidation epithermal deposits may have been emplaced during lull periods after the second and (or) the third flare-ups (560–550 Ma). Low sulfidation epithermal deposits were emplaced late during the felsic alkaline magmatic stage (550–520 Ma). The D₂ stage, therefore, provided extensional structures that enabled fluid circulations and magmatic-hydrothermal ore forming processes.

Rhyolitic pyroclastic deposits, mostly ignimbrites (ash-and-pumice flow deposits) from plinian eruptions belonging to the early activity (> 2.5 Ma) of the Plio-Quaternary Monts Dore volcanic field (Massif central, France) are documented in order to provide lithofacies and compositional data that could serve as a rational basis for ignimbrite discrimination and tephrostratigraphic correlations. We define or redefine six major pyroclastic units (five ignimbrites and one pumice fallout deposit), based mainly on pumice texture and mineral assemblage. Pumices and quartz-hosted glass inclusions are rather uniform compositionally, being high-silica rhyolites with very low CaO, MgO and FeO contents. Juvenile mineral assemblages are K-feldspar ± quartz ± plagioclase, with rare biotite ± amphibole + accessory phases (mostly sphene, zircon, oxides, apatite). The feldspars, biotite and amphibole compositions of all units strongly overlap and poorly constrain ignimbrite discrimination. These data provide clues to some volcanological issues under debate in the Monts Dore volcanic field. The major rhyolitic pyroclastics found on the Monts Dore margins, e.g. the conspicuous « Grande Nappe » unit of previous authors, are here interpreted as stratigraphical units beneath those exposed in proximal areas, and concealed in the central structural depression (caldera) suggested by previous gravimetric studies. The poorly constrained caldera geometry should be envisioned as a compound, polygenic structure related to several ignimbrite eruptions spanning at least 350 ky, whose vent locations may have shifted with time. The very scarce Fe-Mg silicate phases, biotite and amphibole found in the pumices and ignimbrite matrices show complex compositional populations which can be explained only partly by xenocrystic contamination and require further petrological investigations.