Multistage genesis of the late Cretaceous manganese karst-hosted Tasdremt deposit (High Atlas, Morocco)

Abstract

The eastern part of the Souss Basin (Morocco) contains several Mn deposits in the Tasdremt district. Three Mn orebodies occur within the Cenomanian-Turonian dolostones and the Senonian (Coniacian to Maastrichtian) detrital series, the main orebody being located at the boundary between them. The Mn ores consist of coronadite group minerals, mostly coronadite and hollandite, in a karstified dolostone. New field observations, petrographic analyses, and geochemical data define the Tasdremt deposits as a karst-hosted accumulation (11-60 wt.% Mn), particularly enriched in Ba (1.5-8.2 wt.%) and Pb (1.0-5.0 wt.%) with poor contaminations in Al, Fe, and P. This study shows that the ore-forming process is similar to that occurring in the Imini C3 level, located~100 km to the northeast. Such similarities with the high-grade pyrolusite-bearing ore suggest that the Tasdremt deposit is a lateral equivalent of the Imini deposits. However, the scarcity of pyrolusite in Tasdremt results in lower Mn grades, the Tasdremt ores being considered an aborted/ incomplete system in comparison with the Imini deposits. 40 Ar/ 39 Ar geochronology of K-bearing Mn oxides yields late Cretaceous ages, defining three phases at~91.5 Ma,~77.5-82 Ma, and~65-67 Ma. Although the source of metals remains hypothetical, mineralizing fluids were carried by O 2-free groundwater that mixed with O 2-rich shallow meteoric waters at the Tasdremt depositional site. The dissolution of the host dolostones and the karst environment have provided suitable conditions for the precipitation of Mn oxides, causing the coeval increase of pH and Eh, respectively. The Early Atlasic deformation during the Late Cretaceous is associated with mineralization events and was responsible for creation of low stand reliefs from Tasdremt to Imini. This period enabled karstification and mineralization. Connecting the Tasdremt deposits to other African Mn deposits is difficult since the latter consist of laterite resting above Paleoproterozoic Mn protores, and consequently formed under different conditions from karst-hosted deposits. It is likely that other Mn occurrences formed along the Atlas belt in similar settings.

(U-Th)/He Dating of Supergene Iron (Oxyhydr-)Oxides of the Nefza-Sejnane District (Tunisia): New Insights into Mineralization and Mammalian Biostratigraphy

“…In the same way, our results may be interpreted in relation with the regional Mediterranean geodynamics. In Morocco, weathering episodes are most likely associated with some of the four main Atlasic geodynamic events, as attested in recent geodynamic and ore deposits studies [48][49][50]. In Tunisia, both periods of weathering highlighted by our new (U-Th)/He data correspond to two distinct Alpine tectonic pulses that produced the exhumation of sulfides ores [35].…”

Origin of the Moroccan Touissit-Bou Beker and Jbel Bou Dahar Supergene Non-Sulfide Biomineralization and Its Relevance to Microbiological Activity, Late Miocene Uplift and Climate Changes

“…In this respect, it should be emphasized that large-scale, vertical, positive movements were able to produce uncapping and weathering of the primary hypogene sulfides by creating a gradient for the percolation of meteoric fluids. In Morocco, weathering episodes have been related to four main Atlasic geodynamic events referred to as D 0 (Late Cretaceous), D 1 (Late Eocene), D 2 (Early Miocene), and Late Miocene to Recent, consistent with the conclusions of [30,42,73,[110][111][112].…”

Petrogenesis and 40Ar/39Ar dating of hydrothermal romanechite from the sub-aerial fault-related Romanèche Mn deposit (France)

“…As such, romanechite precipitated in an open system (Figs. 3a, b, c and f), directly from the mineralizing fluid and not by replacement of lower valence Mn-bearing minerals as observed in other subsurface Mn oxide ores (Dekoninck et al, 2016(Dekoninck et al, , 2019(Dekoninck et al, , 2021Lafforgue et al, 2021). In this context, it is unlikely that the romanechite-bearing ore derived from in situ supergene weathering such as in gossan.…”

“…When datable minerals are present, it is of great importance to identify the process by which they have precipitated in order to better constrain the ore genesis. Mn oxides have long been used to date supergene deposits due to the extensive occurrence of K-bearing Mn oxides (e.g., Ruffet et al, 1996;Li et al, 2007;Beauvais and Chardon, 2013;Vasconcelos et al, 2013;Deng et al, 2016;Vasconcelos and Carmo, 2018;Jean et al, 2019;Dekoninck et al, 2019Dekoninck et al, , 2021De Putter and Ruffet, 2020). The most common species belong to the coronadite group [(Ba 2+ ,Pb 2+ ,Sr 2+ ,Na + ,K + ,)(Mn 4+ Mn 3+ or 2+ ) 8 O 16 ] (Lippolt and Hautmann, 1995;Ruffet et al, 1996;Vasconcelos et al, 1992Vasconcelos et al, , 1994Vasconcelos et al, , 1995 forming a typical tunnel.…”