Chemical characterization of heavy minerals and stream sediment of Betare-Oya gold district and implications for gold mineralization

Abstract

Stream sediment geochemical survey was carried out in Boyo, situated in Betare-Oya gold district. The study was aimed to determine the primary source of gold, mineralogy of heavy mineral concentrate, provenance, weathering conditions and tectonic setting. Samples were collected by panning and analyzed using inductively coupled plasma mass spectrometry. Heavy minerals present in concentrates include gold, zircon and magnetite and the grains count of gold is 15–37, the grains vary in size from 0.125–1 mm, suggesting nugget effect. They exhibit sub-angular and angular shapes, indicating they were proximal to the source. Sediments reveal enrichment in Au (8440- > 10000 ppb), Mn (250–350 ppm), Hg (40–560 ppm), Th (186- > 200 ppm), Y (67.5–117 ppm), large ion lithophile elements, rare earth element (REE: 1684.9–2382.6 ppm) and depletion in Fe 2 O 3 (1.08–2.25 wt.%), Nb (0.4–1.6 ppm), Mo (0.03–0.21 ppm), high field strength elements. REE patterns show LREE enrichment (La N /Sm N = 1.06–1.24) relative to HREE (Gd N /Yb N = 2.20–9.29), negative Eu anomaly (Eu/Eu* = 0.24–0.31) and positive Ce anomaly. Factors 1, 4 and 5 point to the presence of granitic rocks and indicate a lithologic control. Factor 2, 3 and 6 were inferred as the mineralization factors, while the elements Bi, Pb, Sb, Sn and Zn serve as pathfinders for Au. The paragenesis Bi-Pb-Sb-Sn-Zn represents a barren sulphidation event with respect to Au. Sediments were sourced from mafic igneous provenance. Sediments were immature, had undergone intense weathering, were transported a short distance, and were deposited in a passive margin under oxidizing conditions.