Abstract
As part of a larger survey campaign in the western Arabian Shield, helicopter electromagnetic survey tests were performed using the ZTEM (z-axis tipper electromagnetic) passive airborne EM (AFMAG) system over the 30.6Mt Ad Duwayhi gold porphyry deposit, in order to determine its airborne geophysical signatures. Ad Duwayhi is a Precambrian, shear-zone/vein-hosted, gold porphyry deposit that is located approximately 450 km SW of Riyadh and 450 km E/NE of Jeddah, KSA. The deposit is hosted within a late- to post-orogenic, Neoproterozoic age, northwest oriented granite body and a comagmatic, square quartz-porphyry that is possibly a younger phase of the granite. The Ad Duwayhi gold mineralization is characterized by low sulphide and base-metal content that typifies gold porphyries. The survey appears to have been able to characterize the regional geologic and localized resistivity signatures associated with the Ad Duwayhi gold porphyry deposit. It defined the larger, low porosity felsic-rich/quartz-altered intrusive host as a resistivity high, whereas the more fractured/porous vein systems that host the mineralization are defined as more localized, weak, linear resistivity lows. The resistivity high signature appears to lack a well-defined, surrounding resistivity low halo, due to phyllic-propyllitic alteration, that normally characterizes other copper-porphyries surveyed. More importantly, a flanking resistivity and magnetic high feature was mapped 1.5km further west, below a thin layer of conductive overburden, and might also represent another target of interest. The survey results suggest that Ad Duwayhi remains open to the southwest. The combined aeromagnetic and passive AEM signatures (high resistivity and low magnetic susceptibility) for Ad Duwayhi might be distinguishing characteristics for similar porphyry gold deposits regionally. Although 2D inversion modeling supports the interpretation of the ZTEM data in plan, more advanced 3D inversion and ground follow-up are required to further validate these targets of interest.
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