Helicopter EM (ZTEM-VTEM) Survey Results over the Nuqrah Cu-Pb-Zn-Au Sedex massive sulphide deposit in the Western Arabian Shield

Abstract

Mineral exploration in the Precambrian Arabian Shield region of the Kingdom of Saudi Arabia has identified thousands of mineral occurrences in the last 40 years and has included airborne geophysics, primarily regional magnetics and radiometrics but, more recently, electromagnetics. As part of a larger survey campaign in the western Arabian Shield, helicopter EM survey tests were flown for comparison purposes over the 1.4Mt Nuqrah sedex (sedimentary exhalative) copper-lead-zinc-gold massive sulphide deposit, using the VTEM and ZTEM systems. The Nuqrah deposit comprises mineralized bodies, Nuqrah North and Nuqrah South that are 4km apart, each marked by a gossan, and hosted between beds of dolomitic marble and either volcanic tuffs or diabase intrusives. The active source VTEM survey was able to characterize the regional geology and localized high conductivity signatures associated with known Nuqrah North and Nuqrah South sedex deposits. As well, new targets of low to moderate conductance have been identified that potentially represent massive to semi-massive sulphides. The passive source ZTEM survey also structurally mapped the Nuqrah survey area but penetrated more deeply. Both survey data indicate that the major controlling structures that host Nuqrah North and South also remain open to the northeast and south of the survey area. The active and passive EM anomalies generally coincide well with the North and South Nuqrah deposits, with the VTEM able to define the smaller, shorter strike-length and more massive sulphide mineralized vent portions of the sedex orebodies; whereas the ZTEM defined the larger, less mineralized but more clay-altered and less conductive distal portions of the sedex system. Interestingly, the passive EM survey appears to also have detected a deeper conductive feature lying further west of the South Nuqrah that potentially represents a down-dip extension of sedex deposit below 750m depths.