FE OXIDE-CU-AU SYTEMS IN THE LUFILIAN OROGEN OF SOUTHERN AFRICA

The Lufilan fold belt of southern Africa, which contains the major copperbelts of Zambia and Congo, consists of an intracratonic rift basin which underwent orogenic collapse during Pan-African orogenesis. Significant magmatic activity appears to be restricted to the southern or inner portions of the arc where intermediate to felsic magmas (Hook granite suite) were intruded during late orogenesis. Iron oxide-Cu-Au systems occur around the Hook granite. These are characterized by vertically oriented, structurally-controlled hematite-rich breccia zones up to several kilometers in length with late pyrite and chalcopyrite. Intrusive and volcanic rocks within these systems have undergone pre-mineralization potassic alteration characterized by the formation of potassium feldspar. Potassically altered rocks are then cut by magnetite which is in turn replaced by hematite during a hydrolytic (sericite-chlorite) alteration event. Sulfidation is the final event resulting in the precipitation of pyrite and then chalcopyrite. A number of minor magnetite deposits are present in central and northern Zambia associated with sodic and sodic-calcic alteration. These massive magnetite bodies are associated with to mafic intrusive ("diorites") stocks or sills which have undergone extreme sodic alteration which has resulted in the formation of albite-actinolite-scapolite assemblages. Copper-(U-Au) deposits associated with intense sodic alteration (e.g. Kansanshi) are also present in the inner portion of the Lufilian arc. Although these deposits lack significant iron oxides, the intense sodic alteration at both deposits is somewhat similar to that observed in many magnetite-apatite systems.