The evaporite sequence of the Congolese coastal basin consists of essentially flat-lying, but locally undulating salt layers of interbedded halite (NaCl), and other higher salts such as sylvite (KCl), carnallite (KMgCl3·6H2O), bischofite (MgCl2·6(H2O)), and minor anhydrite (CaSO4) and dolomite (CaMg(CO3)2) beds that extend from the onshore Congo Basin north and south to sedimentary basins in adjacent West-African countries, as well as west into offshore regions.
The potash occurs within the Lower Cretaceous Loeme Evaporite Formation. At the Kola deposit, seven depositional cycles can be differentiated within the evaporite sections comprising alternations of the rock salt and carnallitite (carnallite and halite) converted locally to sylvinite (sylvite and halite). Evaluation of drill core, assays, down hole geophysical logs, and seismic data suggest that potentially economic potash mineralisation occurs within the upper portion (cycles VI and VII) of the evaporite sequence.
The interpreted extent and structure of the potash beds is based on examination of new drill-hole data, regional historic drilling conducted by the previous explorers, and review of seismic data. Based on this data approximately 7% of the area surveyed by high resolution 2D seismic surveys contains geological anomalies (structural lows or disturbance areas). The structurally anomalous areas may impact the thickness, grade and potential mineability of the potash mineralisation and therefore further site-specific studies are required to assess these areas. For this reason, the areas identified as disturbance areas have been excluded from estimates of Mineral Resources.
Sintoukola Potash Project - Cross Section View Looking NW
Four mineralised seams were interpreted and are named, starting with the uppermost, as the Hangingwall Seam (HWS), Upper Seam (US), Lower Seam (LS), and the Footwall Seam (FWS). The potash seams can be correlated across the deposit extent and are generally sub-horizontal with local undulations; modeled dips do not exceed 15 degrees.
The top of the salt sequence is marked by an unconformable contact. Depending on the position of the seams relative to this contact, they may be locally removed.
The mineralisation comprises sylvinite layers, carnallitite layers or less frequently both sylvinite and carnallitite. In the latter, the two mineralisation types are not inter-mixed; the sylvinite occurs above the carnallitite.
Sylvite is a considered to be a secondary mineral, forming by the leaching of magnesium chloride from primary carnallite. At the Kola deposit, it is envisaged that the replacement of carnallite by sylvite was controlled by the vertical and lateral movement of leaching brines originating from the top of the salt sequence.
The uppermost seam modelled to date is the HWS and is separated by approximately 60 m of halite from the top of US. The HWS is known to consist of high grade sylvinite with a thin layer of carnallitite towards the base of some intersections.
The US and LS are in close vertical proximity, separated by a barren halite interval with average thickness of 3.6 m. The US consists predominantly of sylvinite with an increasing proportion of halite towards the upper contact. The LS is either entirely of carnallitite or sylvinite, or comprised of sylvinite above carnallitite.
The FWS is the lowermost significant potash seam. It is separated by approximately 45 m of halite from the base of the LS. In places where the US and LS have been largely or entirely removed, it consists of sylvinite, elsewhere the FWS is known to consist of carnallitite and bischofite.
On the basis of potash mineralogy, sylvinite and carnallitite domains can be delineated within the US and LS. These are identified as Upper Seam Sylvinite (USS) and Upper Seam Carnallitite (USC) and the Lower Seam Sylvinite (LSS) and Lower Seam Carnallitite (LSC). Within the HWS and FWS, only domains of sylvinite mineralisation (HWSS and FWSS) were modelled for estimation of Mineral Resources. The FWS also has a carnallitic domain (often with significant bischofite) but as this mineralisation has not yet been systematically sampled, it has not been included in estimates of Mineral Resources. All mineralised domains have been constrained using "hard boundaries" from interpretation of geological logs, down hole geophysics, modelled seismic data and assay results.