TY - THES

T1 - Underwater dredge mining

AU - Pöhl, Anja

N1 - embargoed until null

PY - 2009

Y1 - 2009

N2 - The uranium deposits from Bakouma in the Central African Republic are in a tropical rain forest in a very humid zone. The rainy season can last up to 9 months per year; the ground water table is at a maximum depth of 10 m and the future mining sites are regularly flooded during the rainy season. Pumping the water is a major difficulty for a traditional mining site in an open pit and it also represents an important cost factor. To be certain from a conceptual point of view Areva wanted to study an alternative mining technique: underwater dredging. The installation of such a technique needs a radical different mining organization and planning compared to a classical open pit mining. First, the dredging boats are limited in their dredging depth, which demands a progressive adaption of the water level in the pit; the mining has to be done in successive horizontal levels. Further, the ore is produced in a slurry form with solid content of approximately 20 to 30 %; this is no storable product; the mouth-to-mouth function of the mining and treatment is a very important point. The waste material of the overburden is also under water. Important volumes of overburden in slurry form must be treated and stored in accordance with environmental exigencies and conditions of Areva. For the belongings to handle the waste slurry decantation and sedimentation, tests were performed in the laboratory with samples coming from different depths of the deposits in Bakouma. The study showed that underwater dredging is a technically possible solution. It presents advantages for the climatic and hydrological conditions (quasi-continuous work). On the other side it presents also a worst case mining which does not allow stabilizing the ore production over the lifetime of the mine, due to the heterogeneity of ore in the horizontal layers that have to be mined successive. Further the handling of the slurry and water is an essential challenge for the success of the operation. Economically is underwater dredge mining compared to a traditional open pit mining for the conditions in Bakouma no favourable solution because higher capital and operating costs of the total scenario.

AB - The uranium deposits from Bakouma in the Central African Republic are in a tropical rain forest in a very humid zone. The rainy season can last up to 9 months per year; the ground water table is at a maximum depth of 10 m and the future mining sites are regularly flooded during the rainy season. Pumping the water is a major difficulty for a traditional mining site in an open pit and it also represents an important cost factor. To be certain from a conceptual point of view Areva wanted to study an alternative mining technique: underwater dredging. The installation of such a technique needs a radical different mining organization and planning compared to a classical open pit mining. First, the dredging boats are limited in their dredging depth, which demands a progressive adaption of the water level in the pit; the mining has to be done in successive horizontal levels. Further, the ore is produced in a slurry form with solid content of approximately 20 to 30 %; this is no storable product; the mouth-to-mouth function of the mining and treatment is a very important point. The waste material of the overburden is also under water. Important volumes of overburden in slurry form must be treated and stored in accordance with environmental exigencies and conditions of Areva. For the belongings to handle the waste slurry decantation and sedimentation, tests were performed in the laboratory with samples coming from different depths of the deposits in Bakouma. The study showed that underwater dredging is a technically possible solution. It presents advantages for the climatic and hydrological conditions (quasi-continuous work). On the other side it presents also a worst case mining which does not allow stabilizing the ore production over the lifetime of the mine, due to the heterogeneity of ore in the horizontal layers that have to be mined successive. Further the handling of the slurry and water is an essential challenge for the success of the operation. Economically is underwater dredge mining compared to a traditional open pit mining for the conditions in Bakouma no favourable solution because higher capital and operating costs of the total scenario.

KW - underwater dredge-mining Bakouma Central African Republic uranium Areva

KW - unterwasser Bagger-Abbau Bakouma Zentralafrikanische Republik Uran/Areva

M3 - Master's Thesis

ER -