Modern and Ancient Sabkha Environments -Boron Isotopes as Discriminators of Facies and Uses in Base Metal Exploration

Abstract

Boron isotopic analyses were performed on samples of stromatolite representative of intertidal conditions within modem and Early Proterozoic sabkhas. The intertidal zone at Al-Khiran in southern Kuwait shows a range of 5^ values from 21.2-39.1 per mil. The stromatolites values are constrained between S^B 21.2-21.25 per mil and the brine medium in which they grow is characterized by values that range from 5'^ 25.6-39.1, or close to the seawater average. Both these data together with published ^0 data, indicate a southwesterly trend towards lighter values for all isotopic systems, indicating an increasingly continental influence and precipitation of isotopically light carbon within the tidal creek. Their Early Proterozoic analogues from southern Africa have very different signatures, with a range of 5^ from 6.2-6.8 and indicating a more pronounced continental influence in pore water chemistry. These results have important implications for reconstructing palaeoenvironments where discrimination of fades is difficult in rapidly accumulating regressive/transgressive cycles. The observations have implications in exploration for stratabound Cu and stratiform Zn deposits in an evaporitic-sabkha setting where prediction on the continental/marine interface (and hence the ore itself) is critical to successful exploratory drilling.