Strontium isotope stratigraphy of the platreef at Turfspruit, Northern Limb, Bushveld Igneous Complex

Abstract

The origin of the Platreef in the Northern Limb of the Bushveld Igneous Complex (BIC) and its correlation as the stratigraphic equivalent of the Merensky Reef in the Eastern and Western limbs has been long debated. Strontium isotope stratigraphy across the Platreef was completed on drillcore from the Turfspruit farm to test a possible correlation with the Merensky Reef. The results show a significant 87Sr/86Sri shift from ~0.7060 to 0.7090 through the mineralized section of the Upper Platreef, which decreases to 0.7074 and then increases again and stabilize at ~0.708 in the Main Zone. This matches the isotopic shift previously documented through the Merensky and Bastard Cyclic units in the Eastern and Western limbs of the BIC. This coincident shift in 87Sr/86Sri is substantive evidence to confirm that the mineralized intervals in the Upper Platreef are the stratigraphic equivalent to the Merensky and Bastard Cyclic units. This thesis also documents the presence of micro-cycles within magmatic units (up to 350 cycles identified through 215 meters). Working hypotheses linking the micro-cycles to thickness of mineralization are suggested. Testing those hypotheses are outside of the main scope of this study and are suggested for future work.