Processes controlling volcanic and epiclastic reservoir formation in a buried polygenetic stratocone

Understanding the formation of volcanic and epiclastic reservoirs is pivotal for exploring geoenergy resources such as geothermal energy, hydrocarbons, and new CO2 sequestration and hydrogen storage opportunities. This paper examines the processes controlling the quality of pyroclastic and epiclastic reservoirs of the Kora volcano, an extinct stratocone presently buried in the offshore Taranaki Basin, New Zealand. We conduct detailed seismic reflection interpretation, drillcore lithofacies and wireline-log description, petrographic analysis, and analytical tests to generate a unified framework that explains the formation of volcaniclastic reservoirs from basin to pore-scale.Each stage of construction and degradation of the Kora volcano is associated with particular processes that increase or reduce reservoir quality. Primary processes include quench fragmentation, deuteric mineral dissolution, and epiclastic sedimentation. Secondary processes comprise mineral alteration (mainly meteoric; minor hydrothermal and diagenetic), mechanical stress fracturing (mainly tectonic; minor magmatic and burial deformation), and pervasive biogenic cementation. Epiclastic conglomerates present the highest reservoir quality (average 23% porosity and up to 997 mD permeability), followed by lapilli-tuffs and tuff-breccias. In contrast, bioclastic epiclastic sandstones are typically cemented by carbonates and pyrite. Our models and interpretations will increase understanding of the formation of volcaniclastic reservoirs and aid exploration of geoenergy resources in volcanic terrains.

A New Interpretation of Geodynamic Context and Typology of Moroccan Anti-Atlas Silver Deposits

The argentiferous deposits in the Anti-Atlasic chain in Morocco are encased in the meta-sedimentary, volcanic-sedimentary and volcanic terrains of the Neoproterozoic, structured and schistosed during the Pan-African orogenesis. These deposits are associated with terminal Neoproterozoic rhyolites and granitoids. The deposits of Zgounder, Imiter and Bou Madine have similarities; Structurally are controlled and associated with faults; The source of the mineralization is generally magmatic or crustal. Precipitation of the mineralization would result from the mixing of mineralized fluids with meteoric waters or brine pools. The silver deposits in the Anti-Atlas are characterized by a number of criteria, which confirm their orogenic character. These deposits are associated with orogenic accretion events in relation to Pan-African orogenesis during the Neoproterozoic. Mineralization is syn- to post-peak metamorphism, controlled and associated faults, with veins that can have significant vertical extensions. The pressure gradients, and temperature metamorphism, indicating an orogenic environment, with metamorphic facies greenschist in general. These deposits can all be linked to an argentiferous mega-event during the Upper Neoproterozoic and thus define an argentiferous metallogenic province.