Paleomagnetic constraints on ages of mineralization in the Kalahari manganese field, South Africa

We report paleomagnetic data from samples spanning several grades of enrich ment in the Kalahari manganese field, South Africa, in order to assess mine ralogical aspects of the ore-forming stages, and also to date these stages through comparison to previously existing, well dated paleomagnetic results from the Kaapvaal-galahari craton. Our paleomagnetic study confirms a mult istage evolution for the orebodies, with three distinct, ancient remanent d irections preserved.,An early diagenetic remanence direction (MAM-1), assoc iated with "dusty" hematite inclusions (1-10 mum) that are omnipresent in t he microcrystalline matrix of low-grade, Mamatwan-type ore, yields a tilt-c orrected paleomagnetic pole (-08.2 degrees N, 111.1 degrees E, dp = 5.6 deg rees, dm = 11.1 degrees: n = 6 specimens) that is similar to previous resul ts from the immediately underlying Ongeluk lavas. A late diagenetic or weak metamorphic overprint (MAM-2), carried by recrystallized hematite (20-250 mum), within both Mamatwan- and Wessels-type ore: generates a paleomagnetic pole (present coordinates 12.1 degrees N, 321.8 degrees E, dp = 3.4 degree s, dm = 6.0 degrees; tilt-corrected 16.1 degrees N, 317.8 degrees E, dp = 3 .4 degrees, dm = 6.4 degrees; n = 14 specimens) that resembles those from t he ca. 1900 Ma Hartley lavas and Mashonaland sills. The MAM-2 overprint may be related to Kheis thrusting at 1750 to 1800 Ma as previously proposed or to magma-driven fluid migration during rifting as the Hartley-Mashonaland igneous event perforated the Kalahari craton. The third magnetic component observed in our sample suite (WESS) is restricted to high-grade Wessels-typ e ore, rich in high Fe hausmannite and coarser hematite (0.1-1.0 mm, in the immediate vicinity of north-trending normal faults. It yields a pole (54.4 degrees N, 033.7 degreesE, dp = 4.7 degrees, dm = 9.1 degrees; n. = 7 spec imens) that is similar to both the ca. 1250 and 1100 Ma portions of the Kal ahari craton's apparent polar wander path. Either of these ages would be in accordance with previous multigenetic models for the Wessels event and its regional crosscutting relationships, Our WESS paleomagnetic pole, combined with previous paleomagnetic results from the Sishen-Postmasburg region, te mporary links Kalahari manganese field hydrothermal upgrading with east ver gent thrusting ill the Griqualand West foreland, during the early or medial stages of the late h Mesoproterozoic Namaqua orogeny.