Al Lugatah Gold Deposit, Asir Region, Kingdom of Saudi Arabia

SGS-TR-2009-5 Yasin T. Saleh, Raul A. Escarrachi, Mohammed Al Shanti, Ahmed H. Sarhen, and Alim A. Siddiqui
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ABSTRACT


The Al Lugatah prospect (MODS 0628) is located in the Asir Administrative Region, 15 km northwest of Tathlith town, at about lat. 19°39’N. and long. 43°27´E. The Al Lugatah prospect was rediscovered in 1956 as a result of regional reconnaissance and exploration programs for ancient mines by USGS - BRGM missions and Riofinex. Schaffner (1956) indicated the presence of gold (7 to 8.15 g/t) from 11 surface dump samples. Later Worl (1979) did some reconnaissance of the area and vicinity for the USGS as part of the Saudi Arabia Mission tasks. He did mapping and took some economic surface samples from vein systems and dump areas, which gave high and low results. He determined geological reserves of 19 million tonnes with an average grade of 2.5 g/t gold and recommended follow up work including drilling.  Based on the previous results, SGS proceeded with further exploration work in order to re-evaluate the economic potential of this prospect, and to find more reserves near Al Lugatah. We also wished to understand the genesis of this gold deposit in relation to the major (regional) Nabitah fault, in order to obtain a pattern or geochemical fingerprint that can be extrapolated to find other deposits with similar characteristics in the region.  Hence from 2001 to 2004 a work program was executed including detailed mapping, surveying, trenching, and drilling.   The prospect covers an area of 600 m by 60 m, and is part a band of shear zone hosting mineralized quartz vein systems. Host rocks mainly comprise chlorite schists affected by a strong mylonitization of metasedimentary and metavolcanic rocks of the Hulayfah (Halaban Group). The Nabitah regional fault separates schist units from the granitic rocks in this area.  The mineral assemblage found at the Al Lugatah prospect consists mainly of gold, chalcopyrite, arsenopyrite, sphalerite, tetrahedrite, galena, and pyrite. Mineralization occurs as aggregates and streaks in both quartz vein fractures and adjacent alteration zones.  However, there is a tendency for high gold values to occur at the selvage zones and/or alteration bands composed of chlorite, sericite, quartz and minor carbonates. Gold values vary from 0.02 g/t Au (lower detection limit) to 84.73-152.2 g/t Au at DDH-C007 (38.5 m) and DDH-C007 (23.50 m) respectively. The northern part tends to have higher values as well as tonnage, due to the large number of vein occurrences. Due to the sulfide content and mineral association this deposit is defined as a low sulfidation hydrothermal system and the mineral association is Py – Au – Cpy – Zn – Ag – Pb – Cc.  The orebody at Al Lugatah is an elongated package of semi-parallel quartz veins running north-south. It has approximately 100 m of real thickness, is 650 m long along strike and dips on a 45° angle to the west south-west for about 280 m. The northern portion has a greater abundance of quartz veins and is of higher grade than the south due to the association of the shearing zone band, which is greater and up to a 100 m wide in the north. The shear zone is approximately 50 to 60 m in width in the south, and the shearing band and mylonitic structure have affected both volcanic and granitic rocks.  The study concludes that work to date on the property has outlined an indicated resource of 414,126 tonnes grading 5.10 g/t Au at a cut off of 0.3 g/t.  The estimated inferred resource is 6,667,941 tonnes grading 4.5 g/t Au at a cut off of 0.3 g/t. The grand total of estimated and inferred resources is 7.08 MT containing 1.03 million ounces Au. Metallurgical recoveries and net smelter returns are assumed to be 80 percent.

 

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Saleh, Y.T., Escarrachi, R.A., Al Shanti, M., Sarhen, A.H., and Siddiqui, A.A., 2011, Al Lugatah gold deposit, Asir region, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2009-5, 30 p., 19 figs., 5 tables, 2 apps.