Sedimentology of the lower Hofuf Formation, Eastern Province of Saudi Arabia, and the chances for gold prospection

摘要

Fine-grained to pebbly coarse-grained fluvial sandstones of the Late Miocene to Pliocene Hofuf Formation crop out in the Eastern Province of Saudi Arabia. The sandstones comprise three distinct fades: clast-supported gravel and conglomerate, coarse-grained sandstone and fine-grained sandstone. The gravels and conglomerates are rich in pebbles of various igneous and metamorphic rocks derived from the gold-bearing Arabian Shield as well as limestone, dolomite and marl derived from the Phanerozoic. The sandstone shows a uniform framework composition dominated by monocrystalline quartz and feldspar with less abundant polycrystalline quartz, calcite, and micas and igneous, metamorphic and sedimentary rock fragments. A geochemical signature of gold (placer) deposits was detected in the lower unit of the Hofuf Formation in the Hofuf and Harad areas. The very fine-grained fraction (O < 125 μm) of the Hofuf area contains the highest amounts of gold (0.16-1.87 ppm), the gold dispersion anomaly in the Haradh area is of a high extent (24.22-4.83 ppm). The primary gold source is probably related to weathering of paleo-placers, and/or to weathering and transport of gold-bearing igneous rocks from the Arabian Shield.