In-situ sulfur isotope and trace element compositions of pyrite from the Neoproterozoic Haweit gold deposit, NE Sudan: Implications for the origin and source of the sulfur

Abstract

The Haweit gold deposit is located in the Neoproterozoic Hamisana Shear Zone in the Red Sea Hills of NE Sudan. In this study, we use major and trace element chemistry of pyrite, SEM studies, as well as the sulfur isotope composition of pyrite from the deposit to characterize the mineralization, origin of the ore-forming fluids and to constrain the ore-forming processes. Mineralization was controlled by NE- and NW-trending faults, which host many gold-bearing quartz veins in the Neoproterozoic andesitic and granitic country rocks. Fluids and melts associated with the quartz veins produced extensive zones of wall-rock alteration a few centimeters to several meters in thickness. The associated hydrothermal alteration is characterized by sericitization, carbonatization, silicification and pyritization. The Au mineralization is closely associated with the alteration zones, in which two generations of hydrothermal pyrite were identified on the basis of morphology; Py1 consisting of anhedral, elongate or spongy grains and Py2 consisting of medium- to coarse-grained, anhedral to subhedral crystals. Py1 is characterized by slighty lower concentrations of Au, whereas Py2 has slightly higher amounts of Au, As, and Zn. Arsenic, Co, Ni and Cu vary in concentration between the two types of pyrite as shown by their Co/Ni ratios ranging from 0.02 to 57 (average 13.5 ppm) in Py1 and from 0.04 to 165 (average 23.4 ppm) in Py2, indicating growth from magmatic-hydrothermal fluids. The δ34S values of the two types of pyrite are similar, ranging from −3.3 to 3.4‰, with an average value of −0.7%, suggesting a common, magmatic source for the sulfur. All available data point to a hydrothermal-magmatic source for the Haweit gold deposit.