Parental Magma and Emplacement of the Stratiform Uitkomst Complex, South Africa

Abstract

The Uitkomst Complex, a Ni-Cu-PGE-Cr-mineralized layered basic intrusion situated approximately 200 km due east of Pretoria, South Africa, hosts commercially viable magmatic base-metal sulfide deposits. The Complex has a concordant 207 Pb/ 206 Pb zircon age of 2044 ± 8 Ma, suggesting that it is coeval with the Rustenburg Layered Suite (RLS) of the Bushveld Complex. Chemical modeling, using summation and least-squares optimization techniques, provides evidence that the boninitic Bushveld B1 magma is parental to both the lower ultrabasic and upper basic layered series of the Uitkomst Complex. The layered series crystallized in two stages, i.e., a lower conduit and an upper closed-system stage. The tubular shape of the Uitkomst Complex is the result of the intersection of a near-horizontal bedding plane fault with an existing vertical fracture zone under tensional conditions. During the conduit stage, a combination of magma mixing, contamination and flow dynamics may have facilitated sulfide formation and segregation. The identification of Bushveld B1 magma as the major parental magma of the Uitkomst Complex has significance in the exploration for similarly mineralized sub-RLS intrusive bodies. Mots-clés: massif intrusif basique stratiforme, complexe de Uitkomst, minéralisation en Ni-Cu-PGE-Cr, mélange de magmas, ségrégation de sulfures, Afrique du Sud. §

The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology

“…The new U-Pb zircon age for the Uitkomst diorite of 2057.64 ± 0.69 Ma overlaps within uncertainty with a 207 Pb/ 206 Pb baddeleyite age of 2054.5 ± 6.9 Ma from a coarse-grained gabbro, taken from tailings, that likely represents the Main Gabbronorite (Wabo et al 2015) and it is significantly older than the previous U-Pb zircon SHRIMP age of 2044 ± 8 Ma from a diorite also from the Main Gabbronorite (De Waal et al 2001; Fig. 12).…”

“…However, until recently, this model lacked clear geochronological support. De Waal et al (2001) determined an age of 2044 ± 8 Ma, not overlapping with recent ages for the Bushveld (2055-2056 ± ∼1 Ma, Zeh et al 2015;2056.88 ± 0.41-2057.04 ± 0.55 Ma, Scoates and Wall 2015). The multi-grain baddeleyite age for Uitkomst of Wabo et al (2015, 2054 shows better overlap with the Bushveld event, but still lacks sufficient precision.…”

“…De Waal et al (2001) proposed that "the tubular morphology of the Uitkomst Complex resulted when a near-horizontal bedding plane fault intersected and was offset by an existing northwest-trending vertical fracture zone". A different interpretation was advanced by Hornsey (1999) who suggested, based on underground mapping, that the elongated and horizontally disposed dolomite xenoliths are side wall pendants.…”

The Trompsburg Complex, South Africa: A preliminary three dimensional model

“…Anhaeusser (2004) reflects that although the Trompsburg intrusion could represent a significant exploration target for platinum group metals, the great depth of the intrusion will probably preclude any mineral occurrences being exploited in the foreseeable future. Economic or sub economic Cu-Ni-PGE sulphide ores are also found in some satellite intrusions of Bushveld lineage, notably the Uitkomst Complex (De Waal et al, 2001). Satellite intrusions of the Bushveld Complex (e.g.…”

“…Molopo Farms, Uitkomst, Roodekraal, Lindequesdrift, Rietfontein etc., Fig. 1) occur up to several hundred km in the periphery of the Bushveld (Anhaeusser, 2004;De Waal et al, 2001;Tankard et al, 1982 andVon Gruenewaldt et al, 1988) which previously led to the thinking that the Trompsburg intrusion constitutes part of the Bushveld igneous Complex (Maier et al, 2003). However, results of a SHRIMP U/Pb isotope study on zircons from two gabbroic samples of the Trompsburg intrusion (Maier et al, 2003) indicated a crystallisation age of 1915 ± 6 Ma.…”