The ore COLTAN which encompasses the elements Nb and Ta plays a significant role for the economy of the DR Congo but it is not easy to provide a full blown picture because of the lack of a reliable dataset. The most important mining sites are in the provinces N- and S Kivu. There are large-scale producers such as the Lueshe mine which is operated for pyrochlore and many artisanal mining operations which are difficult to monitor. There are also mining sites in the Manono-Kitolo District where pegmatite COLTAN is exploited. Official figures for columbite-tantalite concentrate show rather fluctuating numbers between 20 and 120 metric tons of Nb and Ta at the same magnitude. The mining techniques in the various provinces are different from each other and in some cases very labor intensive; on the other hand there were also forced shut-downs due to armed conflicts. More than an "atmospheric picture" is difficult to be given here. I hope this will be of assistance to you.