Paleontological, mineralogical and chemical studies of syngenetic and epigenetic Pb–Zn–Ba–P mineralizations at the stratotype of the K/P boundary (El Kef area, Tunisia)

Abstract

The El Kef area, Tunisia, is host of the official stratotype of the K/P boundary and of a complex metallic and non-metallic mineralization at Djebel Sekarna, encompassing syn(dia)genetic shale-and carbonate-hosted Zn-P and epigenetic Pb-Zn-Ba ore mineralizations. Micropaleontological, geological, mineralogical, and chemical studies (major and minor elements, C-and O-isotopes) of Upper Santonian to Lower Eocene calcareoussiliciclastic sediments resulted in a subdivision of this mineralization into eight mineralizing stages. Stages 1 and 2 (late Cretaceous-early Paleogene) are representative of syn(diagenetic) shale-and carbonate-hosted sulfidic and siliceous (Fe)-Zn-P mineralization deposited in shallow marine to slightly brackish sediments. Stages 3-5 (early Eocene respectively-pre-and post-Nummulites involutusexilis zones) are representatives of epigenetic sulfidic and sulfatic (Fe)-Zn-Pb-Ba mineralizations at temperatures as high as 170/200°C and stages 6 and 7 (early Eocene respectively-post-Alveolina oblonga zone) cover the nonsulfidic Zn-(Pb) mineralization at temperatures as high as 60°C which is transitional from hypogene into supergene mineralization (''epithermal calamine deposits''). Stage 8 represents alteration of the pre-existing mineral assemblages in course of the Holocene weathering. The Cretaceous through Paleogene aquatic system is characterized by a poisoning of the sea with base metals, mainly Zn, and the atmosphere was chocked with clouds of fine-grained volcanic ejecta. Both processes contributed to the build-up of Zn-(Pb) deposits and vast, but uneconomic bentonitic clay deposits around the K/P boundary. Ore mineralization in the El Kef area is a multiple-phase process which reached its climax during the early Eocene as indicated by the large foram zones. These inorganic concentration processes resulting in the formation of mineral deposits had obviously also a negative effect on the long-term course of regional Earth's biological history during the late Cretaceous-early Eocene period with lethal consequences for some species. The joint studies of inorganic and organic data reveal that such extraordinary metallogenetic processes close to the K/P boundary in its stratotype area in Tunisia were ''strictly terrestrial''.

Geological, geochemical, and fluid inclusion evidences for the origin of the Ravanj Pb–Ba–Ag deposit, north of Delijan city, Markazi Province, Iran

“…Textural evidences of the Ravanj ore minerals are compatible with epigenetic mineralization. Simple mineralogy and low Ag, Sb, and Cu content are consistent with MVT deposits (Dill et al, 2011). It appears that deposition of ore at Ravanj is more compatible with carbonate-hosted MVT deposits than syngenetic SEDEX shale-hosted deposits (Leach et al, 2005) or magmatic Pb-Zn deposits that have complex mineralogy and high content of Ag, Sb, Cu, and/or Au (Sagiroglu and Sasmaz, 2004;Paiement et al, 2012).…”

“…Silver content of the Ravanj deposit is low (2-550 ppm, average 80 ppm). Ag content of <100 ppm is considered to be an indicator of low-temperature hydrothermal solutions at shallow depth (Dill et al, 2011). The low content of Ag in the Ravanj ore deposit correlates with low temperature mineralization by sedimentary source fluids.…”

Geochemical Assessment and Mobility of Undesired Elements in the Sludge of the Phosphate Industry of Gafsa-Metlaoui Basin, (Southern Tunisia)

“…In another respect, and compared to other sedimentary rocks, it is generally known that REEs are enriched in marine phosphorites [37,40,41,[45][46][47]. In our samples, and even though characterized by patterns similar in shape, the REEs show variable concentration rates (Table 3), all of which display a slight enrichment in light REEs (LREEs), compared to heavy REEs (HREEs), along with negative Ce and Tb anomalies and a positive Eu anomaly (Figure 3).…”