Provenance of detrital pyrite in Archean sedimentary rocks: Examples from the Witwatersrand Basin

Abstract

Detrital pyrite is an accessory mineral in clastic sedimentary rocks deposited prior to c. 2.4 Ga. It is a redox-sensitive mineral and an indicator of low oxygen levels prior to the rise of atmospheric oxygen in the early Paleoproterozoic. Resistance to mechanical abrasion, availability in Archean source rocks, and high density make it a common component of Archean quartz pebble conglomerates, some of which may be gold-bearing. The provenance of pyrite may include sediments and sedimentary rock successions, volcanogenic or sedimentary exhalative massive sulfide deposits, magmatic-hydrothermal deposits, and igneous rocks. The morphology and texture of pyrite grains, the nature of mineral inclusions, trace element geochemistry, and isotopic composition as well as age are the main variables that can be used to evaluate their source. In the Mesoarchean Witwatersrand Basin of South Africa, the world's largest gold deposit, detrital pyrite is mainly derived from sedimentary sources and synsedimentary precipitates.