An evaluation of the applicability of the telluric-electric and audio-magnetotelluric methods to mineral assessment on the Arabian Shield, Kingdom of Saudi Arabia

Abstract

Feasibility studies of two electromagnetic methods were made in selected areas of the Jabal Hibshi (1:250,000) quadrangle, 26F, in the Kingdom of Saudi Arabia in March of 1983. The methods tested were the natural source-field telluricelectric and audio-magnetotelluric methods developed and extensively used in recent years by the U.S. Geological Survey in some of its domestic programs related to geothermal and mineral resource assessment. Results from limited studies in the Meshaheed district, the Jabal as Silsilah ring complex, and across a portion of the Raha fault zone clearly demonstrate the appropriateness of these sub-regional scale, reconnaissance-type studies to mineral resource assessment. The favorable results obtained are largely attributed to distinctive and large contrasts in the electrical resistivity of the major rock types encountered. It appears that the predominant controlling factor governing the rock resistivities is the amount of contained clay minerals. Accordingly, unaltered (specifically, non-argillic) igneous and metamorphic rocks have very high resistivities; metasedimentary rocks of the Murdama group that contain several percent clay minerals have intermediate values of resistivity; and highly altered rocks, containing abundant clay minerals, have very low values of resistivity. Water-filled fracture porosity may be a secondary, but important, factor in some settings. However, influences from variations in interstitial or intercrystalline, water-filled porosity are probably small because these types of porosity are generally low. It is reasonable to expect similar results in other areas within the Arabian Shield.

Geology of the Silsilah ring complex and associated tin mineralization, Kingdom of Saudi Arabia

“…Reconnaissance audiomagnetotelluric profiles across the Silsilah ring complex indicate that the thickness of the Murdama group rocks at the center of the ring complex does not exceed several hundred meters (Flanigan and Zablocki, 1983). The presence of the two cupolalike bodies of Fawwarah alkalifeldspar granite inside the ring, of aplite dikes that penetrate the graywacke sandstone near these granitic massifs, and of hydrothermally altered rock throughout the southwestern quadrant of the ring complex also suggest that igneous rock is present at a shallow depth.…”

Geology of the Ar Rahail ancient gold mine, Kingdom of Saudi Arabia

“…Telluric-electric (TE) profiles were made on four east-west traverses 500-750 m long and one north-south traverse 1250 m long across the crest of the hill at Ar Rahail by C. Zablocki (personal commun., 2/19/85) according to the method outlined by Flanigan and Zablocki (1984). These measurements, confirmed by Audio-magnetotelluric (AMT) soundings, define a northeast-trending anomaly 380 m long and 150 m wide that is believed to outline the subsurface configuration of the main mass of the Rahail stock, the top of which is about 50 m deep (pi.…”

Geology of the Precambrian rocks of the Jabal Habashi Quadrangle, sheet 26F, Kingdom of Saudi Arabia

“…Here the veins appear to be lenticular and average less than 1 m thick; a lessdistinct vein system, consisting of quartz-stibnite-pyrite stockwork, occurs in the intrusive basalt, and trenches occur locally along veins in the diorite. Both the gold-stibnitequartz mineralization, and the molybdenite-quartz-vein system in the vicinity of Meshaheed, described below, result from hydrothermal alteration, the effects of which are clearly evident in alteration of the country rocks and are coincident with resistivity anomalies caused by the increased clay content of the altered rocks (Flanigan and Zablocki, 1984). The alteration includes moderate to intense silicification, kaolinization, carbonatization, and the introduction of pyrite and pyrrhotite.…”