Geochemical and paleoenvironmental characteristics of upper Neoproterozoic ore-hosting black shales in the Bafq metallogenic zone, Central Iran

Abstract

The black shales of the Koushk series in the Bafq metallogenic zone, which are part of the upper Neoproterozoic shales of Central Iran, are typically comparable with the Proterozoic Shale signature but comprehensive information about formational conditions and geochemical characteristics is scarce. In this study, the chemical composition, provenance, tectonic setting, climatic conditions during the weathering of source rocks and paleoredox depositional environments for Koushk shales are investigated. Compared with ‘Post Archean Average Shale’, the samples are depleted in Fe2O3, MgO, TiO2, K2O, Na2O, Sc, Co, Th, V and Cr, owing to the chemical composition and degree of weathering of the source rocks. The provenance study implies that the sediments originated from felsic igneous rocks with a moderate degree of weathering in a semiarid to arid climate. The ratios of redox-sensitive elements [e.g. V/Cr, V/(V + Ni)] revealed that the studied black shales were deposited under moderately anoxic conditions. Furthermore, trace-element ratios (e.g. La–Th–Sc) suggest a continental arc setting for the provenance, which is consistent with the tectonic evolutionary history of Central Iran throughout the late Neoproterozoic. KEY POINTS Neoproterozoic black shales of the Koushk series in the Bafq metallogenic zone host a Zn–Pb SEDEX deposit with 13 Mt, averaging 7 wt% Zn and 3 wt%. The provenance discrimination diagram of the black shales suggests their derivation from felsic source rocks. The black shales were deposited under a moderately anoxic environment. Trace-element ratios reveal a continental arc setting for the source rocks.