Insightful observations from the Hamama polymetallic gold prospect, Arabian–Nubian Shield, Egypt

The Arabian Nubian Shield is the largest Neoproterozoic juvenile crust on Earth, formed by the closure of the Mozambique ocean during the Pan-African Orogeny which gave rise to the formation of the supercontinent Gondwana. There is a broad consensus that the tectonic processes related to the assembly of Gondwana led to the formation of the numerous gold deposits distributed in the shield. Later in Cenozoic, the shield was dissected by the Oligo-Miocene Red Sea rift into two parts, which are the Nubian Shield which extends through Egypt, Sudan, Eritrea, and Ethiopia and on the other side the Arabian Shield covering large parts of Jordan, Saudi Arabia, and Yemen. The gold deposits include Au-bearing volcanogenic massive sulfide (VMS), orogenic gold, intrusion related gold and rare, but significant deposits described as epithermal gold deposits .

Hamama polymetallic gold prospect in Egypt has been intermittently investigated since 1970s and is traditionally known as Au-bearing VMS. Recent field mapping and extensive drilling by Aton Resources Inc. revealed that the metals are hosted in a horizon termed silica-carbonate-barite (SCB), which is surrounded by 695 Ma submarine metavolcanics. This horizon extends for about 3.2 km in NE-ENE direction, has a thickness of 15 to 40 meters and is intersected in drillholes at an average depth of about 120m. They estimated the inferred gold and silver resources from the Hamama West prospect at about 230 and 7,836 koz., respectively. Previously, and until recently, the SCB was believed to be a part of the Neoproterozoic submarine environment. The main debate has mainly revolved around its nature, whether it is an exhalative sedimentary rock or a felsic volcanic that suffered carbonatization.

We conducted two field trips and obtained representative borehole specimens to apply a more detailed work. We discovered that the SCB is a previously unreported sedimentary formation of Late Cretaceous entrapped between the Neoproterozoic metavolcanic piles. The conspicuous time gap was affirmed by field relations, first-time observed fossils and petrographic characters that aligns with the newly proposed model. The presentend findings argue against the deposition of Au in the shield merley in Precambrian.