Detrital zircon geochemistry and U–Pb geochronology as an indicator of provenance of the Namakwa Sands heavy mineral deposit, west coast of South Africa

Abstract

A representative suite of detrital zircons from the Cenozoic Namakwa Sands heavy mineral placer deposit, which is hosted by mainly unconsolidated clastic sediments of the West Coast Group, has been studied from a provenance perspective. The deposit is located along the west coast of South Africa and is underlain by a metamorphosed Meso- and Neoproterozoic basement. Mineral geochemistry of individual zircon grains indicated that the entire population is continentally derived and is dominated by zircons from a felsic magmatic source, some highly evolved, with minor contributions from a metamorphic and mafic provenance.The U–Pb zircon age distribution is diverse, but is dominated by three distinct age populations. The 1100–1020Ma interval can be equated with the felsic meta-intrusives of the Namaquan Orogeny of the Namaqualand Metamorphic Province, and the 650–500Ma period with the meta-volcanosedimentary Pan-African Gariep and Saldania Belts. A particularly dominant group with a narrow time interval (145–130Ma) is correlated with the proximal intrusives of the anorogenic Koegel Fontein Complex. Equivalent source rocks of the above time intervals occur proximal to the Namakwa Sands deposit. As a result, it was demonstrated that the Namakwa Sands zircon population has mainly a proximal, primary provenance, whereas contributions attributed to secondary, reworked or distal sources proved minor.The high concentration and quality of zircons in this deposit compared to similar placers globally is attributed to the proximity of a primary, zircon-rich provenance to a geomorphologically controlled depositional trap. The results of the study suggest that the contribution of Pan-African (750–500Ma) sources is a key prerequisite in the successful exploration for similar high-quality zircon placer deposits along the west coast of South Africa.