Geology and Resources of Basalt Quarry Site Kishb-12, Southern Harrat Kishb
Abdularaman A. Sabbahi
Quarry site Kishb-12 contains a single extinct and eroded scoria cone known as Jabal Hilayyat Miqarr Hilal, assigned to the Tertiary-Quaternary lower Nafrat basalt. It is located at the southern part of Harrat Kishb, nearly 220 km northeast of At Taif city. The site lies between lat 22°37’02” to 22°39’43”N., and long 41°05’51” to 41°07’21”E., and measures 5.1 km north-south by 2.6 km east-west and was mapped at 1:16,000 scale. The upper parts of the cone consist of red agglutinated spatter and the crater is preserved. Basaltic lava flows extend from the crater; extensive areas of Quaternary debris fan deposits eroded from the cone surrounding it. These layers of debris fans are thin and may overlie airfall ash deposits. There are two basalt resources. Most abundant is dense basalt lava flow of density range 2.62 to 2.83, suitable for crushing for dense aggregate. In contrast the lava from Jabal Hilayyat Miqarr Hilal is scoriaceous with a density of 2.08. Dense basalt outcrops over 5.32 km2 and extends outside the mapped area in unlimited quantities. There is also a minor resource of vesicular airfall scoria (ash and lapilli) suitable for lightweight aggregate, which is concentrated along the eastern side of the cone, extending to the north and south. Nine holes were auger-drilled to a total depth of 59.5 m, 23 pits were dug, which prove a minimum resource estimated at 0.84 million m3, or 0.59 million tons. A number of laboratory tests were carried out on the vesicular basaltic samples obtained from the ground surface, drill holes, and pits. Thirty-two samples were tested for density by measuring 100 clasts for each sample. The clast density ranges from 0.7 to 3.2, but the mean density for the clasts ranges from 1.2 to 2.5. In addition, 13 lava flow samples were tested for density by measuring 2 cm chips for each sample. Their density ranges from 2.6 to 2.8. Grain-size analyses were carried out on 32 samples of vesicular basaltic scoria from drill holes and pits. The grain size ranges from 64 mm to dust. Most samples have a mean grain size ranging from f intervals 32 to 2 mm. Thirty-two samples were subjected to 15-day tests for pozzolanic activity. All samples were 100 percent positive for pozzolanic activity. Whole-rock chemical analyses were made for 43 samples of vesicular basaltic scoria, drill holes, and pits with a silica range from 35.00 percent up to 47.86 percent. The low silica values were obtained on weathered scoria contaminated by clay and caliche.
Sabbahi, A.A., 2002, Geology and resources of basalt quarry site Kishb-12, southern Harrat Kishb, Kingdom of Saudi Arabia: Saudi Geological Survey SGS-OF-2002-1, 31 p., 18 figs., 9 tables, 3 apps., 1 pl.