The Neoproterozoic Katangan rocks in the Copperbelt of Shaba (Democratic
Republic of the Congo) and Zambia contain the world's largest concentration
of stratiform copper-cobalt ores. We propose that during the Lufilian
orogeny, the Katangan basin was radically transformed first by extrusion
of allochthonous evaporites then by orogenic shortening. Salt tectonics
plausibly explains spectacular breccias underlying 25,000 km2 and
containing gigaclasts up to 10 km long. The brecciated Shaban Roan
Supergroup-the lowermost Katangan unit-forms regional detachments
and diapirs. The former existence of Roan evaporites is indicated
by sabkha facies, crystals and pseudomorphs of gypsum and anhydrite,
stratigraphic gaps underlain by collapse breccias, chloride inclusions
in ores, hydrothermally propylitized ore hosts, and saline springs.
Salt tectonics began during deposition of the Roan Supergroup between
1050 and 950 Ma. In mid-Roan time, small walls and extrusions of evaporite-gigabreccia
began to be emplaced. In early Kundelungu time (940-850 Ma), evaporitic
diapirs enlarged. Lufilian deformation began between 850 and 650 Ma
by laterally squeezing diapirs to form salt welds. Then, a large sheet
of commingled Roan evaporite and carbonate-dominated sediments and
ores was extruded northward by ~65 km. Extrusion was fast enough to
blanket a uniform preorogenic footwall unit without overriding any
synorogenic deposits. Continued shortening then emplaced large thrust
sheets, lubricated by the pre-existing salt-sediment extrusive sheet.
Restoration suggests that the Lufilian foreland in this area shortened
from 193 km to 85 km.
northern edge of the evaporite basin controlled the shape of the
Outer Lufilian Arc. We infer three original salt provinces. The
large-scale salt tectonics inferred here has implications for ore
genesis and may yet be recognized in other Precambrian basins.
O. N. Warin,
Consultant, 910 Butterfield Rd, San Anselmo, CA 94960 (formerly
BHP Minerals, Senior Vice-President for Exploration)
G. M. Woad, BHP Billiton, Suite 1400, 1111 W. Georgia St., Vancouver
BC, V6E M43, Canada