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Titanium and zirconium. Ilmenite, rutile and zirconium are developed in Quaternary beach placers and dunes on the Atlantic coast. The biggest placers are located to the south of Dakar, between the capital and Cape Sangomar, in Goudlou, M'Bour, Ngasobal, Ngalu-Sessen and Niodor sectors. Useful component recovery is quite high in the placers. In the mouth of Salun river, in the old delta black sands make up small dunes with average 57% of ilmenite and 23% of zirconium.
In the coastal lands between Saint-Louis and Dakar many beach placers are known. They are located in a sector of 100 km length and 10 km width. Black sand reserves in this sector used to be assessed at 10 mln tons of heavy fraction minerals. In the southern sector, between Joal and Nyaning, black sands were totaling circa 2 mln tons with 35% of ilmenite, rutile and zirconium. In the mouth of Casamans river, in the Bukote-Uolof coastal sands ilmenite resources amounted to 375,000 tons.
Senegalese black sand placers were under development in 1923-1964. Maximum titanium-zirconium production and export was reached in 1960-1962 when ilmenite extraction totaled 2,241 tons (1962), rutile extraction - 736 tons (1962) and zirconium 10,349 tons (1960). In 1960 ilmenite and zirconium export came to 32,616 and 10,772 tons respectively. After this, in 1963-1964 black sands extraction and export declined dramatically and in 1965 stopped. The main reason was sudden prospection and development of fabulously rich Australian black sand placers, and due to this fact Australia quite soon took hold of the zirconium and titanium world market. Senegalese deposits became non-competitive and their development, for lack of foreign demand, was closed.
Tin, tantalum, niobium. A series of small pegmatite and quartz-greisen bodies containing cassiterite, lepidolite, monazite, columbite and tantalite is related to alkaline granite of the south-east of Senegal. Supposed reserves equal 3 to 5 thousand tons.
Besides the above-mentioned occurrences, in the Gambia river valley, on the south of Galaman, 10 or so alluvial placers of tantalo-niobate, cassiterite and gold are known. They are located along Gambia valley, from the town of Kedougou to Sukuta village. The placers aren't big, but at times some of them were developed by prospectors. There were years when cassiterite export would reach 156 tons (1971). In most cases, however, it would vary between 14 and 95 tons.
Phosphorites. Total phosphorites reserves in Senegal make 500 mln tons of ore, including 150 mln tons of proved reserves, with 23-32% of phosphoric anhydride content. Phosphorite deposits are developed throughout the country. They exist on the left bank of Senegal river - Ussourogi, Canel, Potel-Olab between the town of Kadre-Pavy on the north-west and the town of Semme on the south east, in Louga, Kebemer, Kaolack, Thaiba, Thies regions. The two last regions include all the explored deposits that are presently being developed. Almost all the industrial phosphorites of Senegal are located on the ore-bearing fields of Thaiba and Thies.
First Senegalese phosphorites were discovered in the valley of the Senegal river in 1936. In early 1950s were detected and by 1957-1960 fully explored phosphorite deposits in Thaiba and Thies regions, located on the west of the Senegalese phosphorite-bearing field that occupies the major part of the country's territory.
Thaiba formations lie 80 km to the north-east of Dakar within a north-east-ward synclinal. In the basement of the columnar section you can see layers of clay, marl and limestone with interlayers of sandstone and conglomerates up to 1,000 meters thick. This mass dates back to Maastricht - Lower Eocene. Its upper part consists of attapulgite clays of Ypresian stage (6-7 meters), saturated with nodular flints and biogenic-granular phosphate material. Above it with washout lies phosphorite-bearing horizon of Lutetian stage (5-15 meters), composed of granular calcium phosphates intercrossed with lenses and beds of flinty sand-clay and clay-carbonate formations strongly saturated with nummulitic, globigerina and algal residues. The thickness of the producing layers of granular phosphorites, sometimes affected by severe lateritic weathering, varies from 3 to 6.5 meters with 23-32% of phosphoric anhydride content. Having them enriched by way of washing and screening you get phosphorite concentrate with 37.5% P2O5 content.
Phosphorite-bearing horizon is overlapped by clays (4 meters) containing flinty-ferrous concretions of lateritic nature. Clays lie in the upper part of Middle Eocene stratum. Over the clays are deposited "lateritoid phosphates" (3 meters), mainly in form of crandallite-type alumophosphate. On the top of the columnar section we see terrigenous and sand-clay ferruginous formations and the shell of Neogenic hematite-goethite plate.
In the row of phosphorites mineral subgroups can be distinguished: carbonate-fluorapatite and fluorapatite. Accompanying clay minerals have an increased admixture content (Ba, V, Ni, Co, B, Ca). Unlike others, Ba, Sr and P can be found mostly in montmorillonites. Here are the components contained in phosphorites (%%):
27,61 |
15,2 |
2,85 |
0,46 |
42,32 |
1,71 |
0,05 |
0,15 |
0,11 |
0,15 |
2,75 |
7,05 |
Total phosphorite reserves in Thaiba deposits make up 200 mln tons, including 130 mln tons of positive and possible reserves. KSFT corporation carries out the extraction and exportation of Senegalese calcium phosphorites since 1957. In the recent years, the statistics has been the following (in thousand tons):
Recovery |
2100 |
1689 |
1587 |
1503 |
1470 |
1590 |
1503 |
The major part of the recovered phosphorites KSFT exports to England, Finland, Greece, France and other countries of the EU. Besides that, every year KSFT burns and exports from 70,000 to 110,000 tons of clinker produced from aluminophosphates. Annual supply of carbonate phosphorites on the domestic market count 50-75 thousand tons.
Thies formations (including Pollo and others) are represented by calcareous (calcium phosphate) and alumina (aluminophosphate) types of phosphorites. Calcareous phosphates are primary-sedimentary granular phosphorites formed in shallow shelf zones of phosphate accumulation. Alumina phosphates, or "lateritoid aluminophosphates", substitute fully or partly the horizons of the primary granular phosphorites which have suffered a dramatic change after intense lateritic weathering. Lateritoid aluminophosphates are characterized by the following components (%%):
25,0-31,1 |
23,6-27,4 |
4,8-12,7 |
8,7-10 |
1,9-2,4 |
2,8-10,7 |
The thickness of the aluminophosphate horizons ranges from 9 to 12 meters. The rocks lie in the section of Eocene sediments, with circa 6 meters' overburden. Total reserves of aluminophosphates make up 50 mln tons including 20 mln tons of proved reserves. When enriched, aluminophosphate concentrates acquire a different structure (all in %%):
34,6 |
35,9 |
10,9 |
9,1 |
2,9 |
1,9 |
0,3 |
4,4 |
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