Mineral Exploration of the Jabal Umm Mattirah Gold Prospect, Kingdom of Saudi Arabia

SGS-TR-2001-1 James E. Elliott, Saeed A. Al Yazidi, Eyad H. Jannadi, Alim A. Siddiqui, Mahmoud Al Shanti, Ahmed M. Zamzami, and Mambrouk H. Basahel
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Mineral exploration was conducted at the Jabal Umm Mattirah gold prospect (MODS 1172) during 1995, 1996, and 1997.
This prospect, located in the east-central Arabian Shield at latitude 21º23'N. and longitude of 43º29'E., covers an area of about 1 km2 and includes scattered old workings and the remains of an old mining village that are evidence of ancient mining.
The main or A zone, which was extensively worked, is marked by a line of sand-filled pits and dumps of broken quartz and altered volcanic rock.
New exploration at the prospect included geologic mapping and sampling, geophysical surveys, trenching, and drilling.
Gold occurs in mineralized zones, consisting of multiple quartz veins and veinlets bordered by altered wall rock, that strike N. 15º E. and dip about 40º to the west.
A sequence of mostly volcanic rocks, including andesite, volcanic breccia, and probable tuff, hosts the gold mineralization. This relatively undeformed volcanic sequence, which includes minor interbedded sandstone and conglomerate, strikes northwesterly and dips to the northeast and has been assigned to the Arfan formation of Neoproterozoic age.
Within the area, the Arfan rocks were intruded by gabbro-microgabbro, dacite porphyry, and andesite porphyry.
The majority of the mineralized vein zones are located within an area of about 500 m by 400 m and have been drilled to a depth of about 200 m vertically.
The results of drilling and assays of samples indicate that the vein zones are up to about 13 m thick and have grades in the range of 3 to 10 g/t gold.
Petrographic studies indicate that most of the gold occurs as tiny inclusions, usually less than 10 microns in diameter, in pyrite and, to a lesser extent, in arsenopyrite.
The sulfide minerals are concentrated in altered wall rock adjacent to quartz veins.
Arsenic, which occurs in concentrations of up to 2 percent, shows a strong positive correlation with gold contents.
The alteration assemblage includes quartz, sericite, calcite, chlorite, and epidote.
All rocks in the area are moderately propylitized and immediately adjacent to thicker vein zones; the wall rock alteration is sericitic.
Two classes of gold resources are estimated; one is based on a minimum true thickness of 2 m and a cutoff grade of 5.0 g/t gold and a second uses a minimum thickness of 1 m and 3.0 g/t gold cutoff.
For high-grade resources (5.0 g/t gold and 2 m thick) the total tonnage is estimated to be about 1,054,000 t with an average grade of 6.2 g/t gold, or about 6.5 t of gold total.
The total for low-grade resources (3.0 g/t gold and 1 m thick) is estimated at about 2,450,000 t with an average grade of 4.3 g/t gold, or about 10.5 t of gold.
The prospect probably cannot be mined as an open pit and is judged to be subeconomic at the present time.
However, additional gold-bearing vein zones may be found downward beyond the depth of drilling, and the prospect might be mineable as one of two or more deposits sufficiently close enough to supply a common milling facility.

Elliott, J.E., Al Yazidi, S.A., Jannadi, E.H., Siddiqui, A., Al Shanti, M., Zamzami, A.M., Basahel, M.H., 2001, Mineral exploration of the Jabal Umm Mattirah gold prospect, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2001-1, 41 p., 21 figs., 8 tables, 5 apps, 4 pls.