PHOSPHATE
Introduction.
Two major types of phosphate mineralization
are known in Tanzania; that associated with carbonatites, described above (p
82-84); and sedimentary phosphates as exemplified by the Minjingu deposit.
Minjingu Mine.
This is a guano accumulation, re-worked and
re-deposited by ancestral Lake Manyara during Pleistocene period of high
water level. The phosphate horizon is near to surface, sub horizontal and
only weakly consolidated. The deposit was mined from 1981 until early 1991,
when the sole consumer, the Tanga Fertilizer Plant, closed due to problems
with acidulation equipment. The average P2O5 content of 22% for run-of-mine
material was upgraded on site to 30% by dry grinding and screening. Reserves
are slightly less than 10Mt.