Abstract
The paper presents new insights to gold mineralization at the Jabal Umm Watirah (JUW) area in western Saudi Arabia using surface and sub-surface information from field, mineralogical, and geochemical studies. Host rocks are Neoproterozoic serpentinites and arcmeta-andesite. Gold in serpentinites is enriched in listwaenite that results from silica and CO2 metasomatism. In the meta-andesite, prominent NW-SE alteration zones follow the Najd fault system (NFS) along the Ruwah fault zone (RFZ). These alterations are sulfide-rich and show sericitization, chloritization, silicification, and hematitization. The auriferous pyrite-rich listwaenite contains relict of Cr-spinel of the ophiolitic serpentinite precursor. Anomalous gold up to 10 g/t in listwaenite is encountered in one borehole whereas the rest assay up to 0.27 g/t with the exception of silicified serpentinite and quartz–carbonate rocks with up to 0.59 and 0.57 g/t gold, respectively. Hydrothermally altered arc meta-andesite contains up to ~ 25% sulfides (mostly pyrite, arsenopyrite, and chalcopyrite) with up to 1.62 wt% As2O5 and up to ~ 21 g/t gold. The results indicate that arsenic is a pathfinder for the studied gold mineralization. On the other hand, fresh meta-andesite is very poor in gold, up to 0.05 g/t only. Remobilized visible gold ore can be seen in some quartz veins and stringers with 150–170 μm wide gold along fractures. Gold enrichment is confirmed in the meta-andesite from boreholes up to ~ 250 m deep that are dug beneath ancient workings and dumps at the two sectors in the JUW prospect. Gold mineralization in the JUW prospect is structurally controlled orogenic gold mineralization because of the following reasons: (1) proximity to the major first order structure, (2) host rocks are metamorphosed in the greenschist facies conditions, and (3) listwaenitization by carbonic and silicic metasomatism of the ophiolitic serpentinite.
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