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Jordan's maiden gold discovery.

An area of southern Jordan is believed to host economic quantifies of supergene gold mineralisation, the first discovery of its kind in the country. Geochemical exploration undertaken by the Jordanian Natural Resources Authority (NRA) and Bureau de Reserches et Geologique between 1992 and 1994 over the southern Jordanian basement identified enhanced gold concentrations over felsic volcanic rocks of the Aheimir Suite in Wadi Araba. Heavy mineral concentrates taken in the wadi system, some 90 km northeast of the port of Aqaba, returned values of up to 40 g/t Au and small gold nuggets were observed in a number of the concentrates. The area has since been investigated in detail by Harmony Gold Mining's ore reserve manager, in association with a team from the NRA, with attention focussing on the surface extent of the mineralisation, the limits and types of alteration, the presence of fracture zones and the relationship between lithology and gold mineralisation.

The basement of southern Jordan is comprised principally of felsic plutonic igneous rocks, with subordinate felsic and basic volcanics, and constitute the northernmost exposed portion of the Arabian-Nubian Shield (ANS). In southern Jordan, this structure has been subdivided into the lower Aqaba complex, comprised of a sequence of schistose and gneissic metamorphic remnants and plutonic rocks, and the overlying Araba complex, made up principally of alkaline, rhyolitic lavas and sub-volcanic intrusions. The two complexes are separated by an unconformity dated at around 560 Ma.

The Araba complex is dominated by the Aheimir volcanic suite, which hosts the Wadi Abu Kusheiba gold occurrence. The suite, dominated by alkaline effusive and extrusive quartz and quartz feldspar porphyries with subordinate andesite, trends north-northeast and crops out in a belt 2-4 km wide over some 70 km.

Geological mapping of the 1.4 [km.sup.2] prospect area has identified altered and unaltered, locally amygdaloidal, felsic porphyries, felsic volcanic breccias and a rhyolite dyke. Alteration of the porphyries is common, consisting principally of silicification and argillisation, with lesser potassic alteration. Areas of silicification are characterised by zones of intense fracturing up to 100 m in diameter and the presence of numerous quartz veinlets. The brecciated volcanic rocks, meanwhile, are located to the west of the study area and are considered proximal to a volcanic centre.

Small gold nuggets observed in two samples of loose gravels taken near fractured, silicified and altered felsic volcanic rocks identified these as the most likely sites of the gold mineralisation. Furthermore, the presence of these discrete nuggets in oxidised and highly weathered surface material is consistent with the supergene gold mineralisation found in similar deposits in other parts of the ANS.

Weathered rock and soft samples taken over a 50 x 100 m grid generally returned values of less than 10 ppb gold, with higher values obtained over zones of alteration. Fourteen such zones were mapped and sampled and whilst they appear as discreet areas, they define a general zone of alteration trending west-northwest through the prospect area. Gold grades vary from just over 10 ppb to 5 g/t.

Further work is still required in the Wadi Abu Kusheiba prospect area to ascertain the true surface extent of the gold anomalies and alteration zones, and the distribution of the gold in the weathering profile. In addition, volcanic rocks adjacent to the prospect area need to be assessed with a view to delineating known gold anomalies to the northwest and southeast. However, to become economic, gold grades would have to increase considerably with depth.

The NRA, with minimal expertise in the fields of gold exploration and mining, is currently looking for partners from outside Jordan to assist in the evaluation of the occurrence. Interested parties are invited to contact the geochemical division of the NRA directly at PO Box 70 or 2220, Amman, Jordan.
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Publication:Mining Magazine
Date:Dec 1, 1996
Words:629
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