Exploration

Kulumaziba River (Kulu)

Geology

The Kulu copper resource was formed from the tailings from a washing plant that were ejected into the Kulu River over a period of about thirty years. The purpose of the plant, which was set up in the late 1950's and operated until the mine closed in 1987, was to remove the "fines" from "breche ore" mined at Mutoshi, before it was shipped to a concentrator in Kolwezi. It is estimated that the grade of the discharged tails was initially less than 1% Cu, but, with the winnowing action of the discharge waters and the natural flow of the river during the wet season, the resource has gradually been upgraded. The effects of this upgrading have been most profound in the upper reaches of the river, close to the original discharge point, where grades of more than 6% Cu are quite common. The deposit can rightly be classified as a placer copper deposit which formed over the last fifty years, and on both counts it is probably unique in the world.

The Kulu River deposit is 14km long, from the discharge point, located 3km east of the Mutoshi Mine, to the delta at Lake N'zilo, on the Lualaba River. In its upper section, the river is no more than 50m wide, but towards the delta, at Lake Nziga, it broadens up to 800m across.

The deposit is composed of a "sandy gravel" of weathered sedimentary material that contains nodules of malachite (and minor heterogenite) from less than 0.1mm up to 4cm across. In fact, two generations of tails were generated as a result of a change in the set-up of the washing plant in the early 1970's: the earlier material was finer grained and laid directly on the stream bed, while the later generation was coarser-grained and has cut anastomosing channels through the former; in some parts of the river, the two generations have mixed. Classic sedimentary textures and structures are well preserved in the deposit along the entire stream section.

Exploration History

In 2005, Anvil completed an evaluation of the top 12.5km of the Kulu River deposit (the delta at Lake N'zilo has not yet been sampled), as follows:

• The volume of sediment was calculated from measurements taken by augering on lines 50-100m apart - the average thickness of the top 10km was 2.15m (maximum 6.8m).
  

• Grades were estimated by systematic sampling of the deposit. The top 10km of the deposit was sampled from pits (spaced at 50 x 25m), while from 10-12.5km samples were collected by aircore drilling (on a 50 x 50m or 100 x 25m grid). The average depth of hole drilled was 7.6m (maximum 12.5m).