Not to be confused with the neighbouring Democratic Republic of the Congo (DRC), the Republic of the Congo (ROC) has a surface area of 342.000 km2 with 170 km of coasts and a population of 4,5 million inhabitants in 2013. The country benefits from a stable political environment and a large diversity of resources, including potash.
Potash was first discovered in the region during the 1950’s during exploration for oil. The potash seams are hosted by the 300-900 m thick Lower Cretaceous aged (Aptian) Loeme Evaporite formation.
These sedimentary evaporite rocks belong to the Congo (Coastal) Basin which extends from the Cabinda enclave of Angola to southern from approximately 50 km and extending some 200-300 km offshore (Fig. 1).
The Republic of Congo (RoC), also known as Congo-Brazaville, is situated on the western edge of the African Continent and borders the countries of Angola (Cabinda Province), The Democratic Republic of the Congo, The Central African Republic and Gabon. It has a total land area of 342,000 km2 and a population of approximately 4.0 million people of which 45.9% are less than 14 years of age and an estimated 83% are literate (CIA World Fact Book).
The RoC was a former French colony which was granted independence in 1960. From 1960 to 1990 the country was effectively Marxist led however a democratically elected government took office in 1992. Although some political strife did occur in the mid 1990's, a peace accord was signed in 2003 between opposing parties and the country has been peaceful ever since.
The RoC is a mature oil producer with proven oil reserves estimated at about 2 billion barrels (IMF Country Report, September 2013). In 2012, oil production reached 100 million barrels, the fourth largest in Sub-Saharan Africa, and generated nearly US$4.5 billion in government oil revenues. The economy is heavily dependent on its oil production as it accounted for almost 87% of the country's export revenues and almost 80% of the government's total revenue in 2011, according to the International Monetary Fund (IMF).
Potash was first discovered in the region during the 1950’s during exploration for oil. The potash seams are hosted by the 300-900 m thick Lower Cretaceous aged (Aptian) Loeme Evaporite formation. These sedimentary evaporite rocks belong to the Congo (Coastal) Basin which extends from the Cabinda enclave of Angola in the south to Gabon in the north from approximately 50 km and extending some 200-300 km offshore (Fig. 1).
The evaporites were deposited between 125 and 112 million years ago, ‘proto Atlantic’ sub-sea level basin (Fig. 2) following the break-up of Gondwana into the Africa and South America continents. The evaporites formed by the seepage of brines unusually rich in potassium and magnesium chlorides into the basin and evaporation resulting in precipitation of evaporite minerals, principally halite (NaCl), carnallite (KMgCl3·6H2O) and bischofite (MgCl2·6H2O), which account for over 95% of the evaporite rocks (Fig. 3). This evaporation, year after year for 10’s of 1000’s of years formed a horizontally layered accumulation of ‘salt rocks’ between -900 m thick. The mineral sylvite (KCl), which is important at Kola, occurs in certain geological settings within the basin, as described below.
The ‘salt rocks’ are comprised of a number of ‘cycles’ and the many potash layers within them (Fig. 3). Potash layers are continuous for many 10’s of kilometres; they can be correlated from one end of the basin to the other. They are generally only absent if ‘removed’ by erosion along the ‘unconformity’ that occurs at the top of the salt rocks.
The evaporite is covered by a thick ‘cover equence’ of carbonate rocks and clastic sediments of Cretaceous age (Albian) to recent, which is over 500 m thick close to the coast and approximately 200 m thick close to the eastern limit of the basin. At the top of the evaporite formation, above the ‘salt rocks’, is a 10 to 20 m thick impermeable layer of anhydrite and clay (Fig. 3).
Potash is the common name given to a group of potassium-bearing minerals such as potassium chlorite and various mined and manufactured salts containing the element potassium. The term potash arose from the traditional practice of producing potassium carbonate, needed for making soap, by the leaching of wood ashes in large iron pots. The ash-like crystalline residue remaining in the large iron pots was called ‘‘pot ash’’. While there are a number of such minerals, only those that are water-soluble are of significant commercial interest. The most common commercial product is potassium chloride (‘‘KCl’’), also known as muriate of potash (‘‘MoP’’) or sylvite, a naturally occurring pink mineral.
According to the IFA, in 2010, approximately 90% of the world’s potash production was used as agricultural fertilizer. Plants deficient in potassium are less resistant to pests and disease, and have poor size, shape, colour, taste and shelf life. Most virgin soils contain adequate potassium to allow farmers to produce average crops. The agricultural cycle of growing and harvesting crops depletes the soil of potassium, nitrogen and phosphate, which need to be replenished in consistent ratios if the soil is to remain fertile.
This explains the historical agricultural practice of leaving land fallow for a number of years in order to replenish itself, however, this practise is becoming less practical in today’s world of scarce agricultural land.
Fertilizers replace the nutrients that crops remove from the soil, thereby sustaining or enhancing the yield of crops. Farmers determine the types, quantities and proportions of fertilizer to apply depending on the crop, soil quality, weather conditions, regional farming practices and fertilizer and crop prices. The functions potassium performs cannot be carried out by other nutrients and potash has no commercially viable substitute as a potassium fertilizer source. Besides agriculture, the remainder of potash consumption consists of the manufacture of potassium bearing chemicals, detergents, ceramics, pharmaceuticals, water conditioner and de-icing salt.
Since the amount of potassium contained in potash ores varies, the industry has established a common standard of measurement by defining a product’s potassium content in terms of equivalent percentages of potassium oxide (K2O) or potassium chloride (KCl). For example, sylvite contains approximately 63% K2O (100% KCl) equivalent and carnallite typically contains approximately 17% K2O (27% KCl) equivalent. A factor of 1.5837 can be used to convert between KCl and K2O grades.