Reconnaissance geology of the Uqlat as Suqur Quadrangle, sheet 25/42 A, Kingdom of Saudi Arabia

Abstract

The geology of the Uqlat as Suqur quadrangle provides a detailed record of the late Proterozoic layered and intrusive rock units,-their interrelationships, and the structural evolution of a large portion of the northeastern Shield of Saudi Arabia. Four major unconformities and three well-defined intrusive episodes identified in the quadrangle provide a rational basis for describing and defining lithostratigraphic units, and for interpreting the deformational history within the region. The oldest rocks consist chiefly of low-potassium mafic and felsic metavolcanic rocks (Dhiran meta-andesite) that were intruded 690 Ma to at least 680 Ma ago by the (possibly cogenetic) Suwaj suite, represented in this quadrangle by low-potassium microdiorite and granodiorite granophyre. The Dhiran-Suwaj terrane was deformed and metamorphosed during a regional erogenic event and became the principal source of clastic material for the Murdama group, which was deposited in subsiding marine basins marginal to emergent highlands. Coarse conglomerate and shallow-water limestone were characteristically deposited near these margins, whereas thick, monotonous sandstone accumulated in the deep-water basin centers. The unlithified Murdama deposits were .gently deformed but regionally folded along north-south trends between rigid blocks-of the Dhiran-Suwaj terrane after about 650 Ma. Regional extension and volcanic activity began at about 640 Ma and produced voluminous calc-alkaline andesite, volcaniclastic sandstone, and volcaniclastic conglomerate of the Jurdhawiyah group. Primary volcanic materials and their rapidly eroded detritus were deposited in linear (probably fault-bounded) basins that were partly shallow-water marine and partly terrestrial. The largest Jurdhawiyah basin began to warp and close during the waning stages of volcanic activity in response to northward-directed compression. High-angle reverse faults displaced the southern basin margin, and a fault-bounded structural arch rose along the northern margin and shed coarse debris into the basin. This intense deformation was closely followed by intrusion of voluminous calc-alkaline granodiorite, diorite, and granite (Idah suite), 620 Ma to 615 Ma ago, that may have been cogenetic with the Jurdhawiyah volcanic rocks. Mineralization is widely associated with this intrusive episode, in the form of gold-bearing quartz veins within and marginal to these plutons. Uplift, erosion, and probable planation characterized the subsequent interval of about 30 Ma, during which no rocks are known to have formed. Beginning at about 585 Ma during a period of regional cratonic extension, high-silica peraluminous granite magma was emplaced in the Qitan complex, and peralkaline magmas were intruded as dikes and extruded as rhyolite and tuff (Humaliyah formation). The Qitan complex and its environs may have potential for tin, tungsten, and(or) base metals.

Lithofacies and depositional environment of the Maraghan Formation, and speculation on the origin of gold in ancient mines, An Najady area, Kingdom of Saudi Arabia

“…Exposures of marble were correlated with the Faridah marble known from the central part of the basin (Delfour, 1977;Greene, 1983). Later mapping by Johnson and Williams (1984), Pallister, (1984), and Cole (1985, suggested that the Hibshi formation may not be part of the Murdama group and is possibly younger; the name Maraghan formation was proposed to replace the name Hadiyah formation.…”

“…Williams (1983) showed the distribution of rocks of the Murdama group in the Samirah quadrangle, sheet 26/42C, (scale 1:100,000), which encompasses the northern part of the study area of this report. The Uglat as Suqur quadrangle, sheet 25/42A (scale 1:100,000) mapped by Cole (1985) shows the distribution of conglomerate, and overlying carbonate and coarse-grained sandstone in the southern part of the study area. Quick and DoebrichCjj/l*} and Williams and Simonds, (1985) showed the distribution of the upper Murdama group in the southeastern part of the Wadi Ash Shi'bah quadrangle, sheet 26E, (scale 1:250,000), which encompasses the western part of this study area.…”

“…Seven days of field work in March, 1985, were devoted to regional mapping of lithofacies and to sampling rarely exposed shale beds in the Maraghan formation. The general geology of the .region was adapted from Williams (1983), Cole (1985), and Quick and DoebrichCtf«*J*:/}« Analytical data on gold concentrations were provided by laboratories of the Deputy Ministry for Mineral Resources in Jiddah under the direction of K. J. Curry, USGS. The graphite furnace and atomic absorption method was used to determine gold concentrations to 4 ppb.…”

“…In general, the amount of calcite and dolomite interbeds decreases upward through the five lithofacies. Coarse-clastic lithofacies appear to thicken from west to east and the lower fine-grained lithofacies appears to become coarser grained and thinner toward the east The composition and texture of clastic rocks of the Maraghan formation have been summarized by Williams (1983), Johnson and Williams (1984), Cole (1985), and Greene (in prep.). Generally, sandstone beds are classified as lithic graywacke, which have varying percentages of quartz, volcanic rock fragments, feldspar, and matrix.…”

“…) and 20 percent (Williams, 1983). Sandstones characteristically contain a matrix of fine-grained chlorite, clay minerals, silt-sized grains, and carbonate minerals; the relative percentages of these components vary considerably (Williams, 1983;Johnson and Williams, 1984;Cole, 1985). The composition of siltstone and shale has not been studied.…”