Gold-quartz veins, widely spaced over an area of 6 by 8 km, are thin and lenticular, and contain moderate to high amounts of gold. The veins, possibly cogenetic with granites of the nearby Jabal Silsilah ring complex, are in a structurally and geologically complex area where the Raha fault zone probably dips south beneath the area, and where Najd faults cross the mineral zone. Felsic dikes from the ring complex cross the Shiaila area, and in many places, structurally controlled gold-quartz deposition. Granitic cupolas and related gold-quartz deposition may exist at depth. Rock chip sampling in the area denotes a higher than average content of arsenic and antimony in listwaenite of the Raha fault, as well as chromium and nickel in felsic dikes and gold-quartz veins. Present investigations, begun by Smith during the field season 1401/1402, included reconnaissance dump sampling at ancient mine sites and rock chip sampling along the Raha fault. Samater, assisted by Waiss Issa Assumali and Ali Dualeh, sampled dumps and located ancient workings on enlarged aerial photographs of the area during the field season 1402/03. In 1404 Smith sampled dumps of ancient workings in greater detail, mapped the geology of the area at a scale of 1:20,000, collected numerous rock chip samples, and directed trenching across several ancient workings. Waiss Issa Assumali operated the backhoe in performing the trenching operations. 42°00' 42-30' 43-00' 2«-00'-2S*SO' SHIAILA AREA (MODS 1383) MESHAHEED AREA (MODS 1266) AN NAJADI AREA (MODS 1272

Quartz dumps of the Al Khaymah ancient workings display an unusual amount of free gold, as do some quartz veins in the surrounding 36 square km. The veins, however, are thin, of short strike length, and thinly scattered in the area. Repeated assays gave widely dissimilar results that preclude an estimate of the average gold grade.The Al Khaymah region is within a fault-bounded block called the Ata-Shara block that is defined by the Ata fault on the north and the Shara fault on the south. Both faults have been active throughout much of the late Proterozoic history. Within the block, gold-quartz veins cut andesitic volcanic rocks of the Jurdhawiyah group and the older Dhiran meta-andesite. All structures within the region are cut by Idah-suite diorite-granodiorite plutons. Diorite dikes are associated with gold-quartz veins and aeromagnetic data indicate the probability of near surface plutonic rocks in the vicinity of the ancient mines.A large chalcopyrite-bearing quartz stockwork in a granodiorite pluton extends about 3 km and is 250 m wide, and two small workings on copper-stained gossans on the south side of Wadi ar Rumah are on the same trend.Regional rock-chip sampling along the Ata fault system found notable values in arsenic, antimony, lead, zinc, copper, and tin.

Wadi-sediment samples were collected from 450 sites in a 580-km2 area (sample density 1.5 per km2) as part of an exploration program designed to assess the mineral potential of the Farah Garan -Kutam mineral belt and to evaluate mineralization at the Farah Garan ancient working (DGMR Project 3.03.10). Demagnetized panned-concentrate and sieved minus-80-mesh fractions were prepared from each bulk sample of approximately 5 kg. The fractions were analyzed for silver, arsenic, copper, lead, and zinc by atomic-absorption methods and for gold by an atomic-absorption graphite-furnace method.The analytical results for the panned-concentrate samples delineate 21 anomalies, and the results for the minus-80-mesh samples delineate 24. Of the latter, 14 are coincident with panned-concentrate anomaly areas, whereas 10 are uniquely defined. The analytical results of the panned-concentrate samples uniquely define two areas. Overall, the panned-concentrate samples yielded threshold values higher than the threshold values for the minus-80-mesh samples (for gold, 10 times higher), and delineate anomalous areas larger than those for the minus-80-mesh samples. This observation is consistent with the results of similar surveys elsewhere in the Arabian Shield, which indicate that panned-concentrate samples more effectively outline geochemical anomalies than sieved fine-grained samples.In the present survey, geochemical anomalies locate all the sites of mineralization known from previous work. The survey is therefore technically a success. However, a large number of these anomalies probably result from contamination of the wadi systems by metal dispersed from ancient mine workings, and this particular survey, overall, may be of limited value as a guide to the discovery of hitherto unknown mineralization. Nevertheless, the survey outlines two areas that may mark extensions to known mineralization, and a number of other areas in which no mineralization is known. Based on a consideration of the character of the bedrock geology, the value of each reported analytical result in relation to the respective element thresholds, and the number of anomalous samples that cluster in any given area, four areas are recommended for high-priority follow-up sampling.

A great number of ancient workings on quartz veins in metasediments are in an area 4 km long and as much as 700 m wide at An Najadi. The mining activity was apparently in quest of gold, since the quartz is nearly barren of other metals. Further evidence of ancient activity in gold recovery from quartz is a large area covered by mill tailings and numerous stone crushers. Few exposures of quartz veins in place are available for examination, but quartz on dumps is milky white and moderately iron stained and contains only sparse pyrite. Detailed sampling of quartz and hydrothermally altered wall rock from mine dumps resulted in gold analyses much lower than those reported in similar studies of other ancient mines in the area, and no information was gained as to the reason for the apparent discrepancy between these low values and the evidence of a great amount of mining activity over a large area. The ancient mines at nearby Agob are a single line of workings extending 800 m. Quartz on dumps is similar to that of An Najadi, but dump sampling gave higher assay results for gold, similar to past sampling efforts. Agob North is also a single line of workings about 300 m long, located 4 km north of Agob. The quartz veins are associated with diorite dikes, and preliminary dump sampling resulted in moderate gold values.

A reconnaissance wadi-sediment geochemical survey was conducted in the Al Jurdhawiyah (sheet 25/42 D) and Wadi al Jarir (sheet 25/42 C) quadrangles in order to identify anomalies potentially related to mineralized rock. Sieved bulk-sediment fractions and pan concentrates were created from the original samples collected from wadis in the two quadrangles. A semiquantitative 30-element spectrographic analysis was completed on both the sieved bulk-sediment fraction and the pan concentrate of each sample. The results were statistically analyzed in an attempt to identify anomalous regions. Anomaly threshold values were calculated for most elements; the threshold value of an element in a data set is defined as the geometric mean value plus two standard deviations. I/ U.S.. Geological Survey Saudi Arabian Mission * Lower limit of detection taken as threshold for elements with no uncensored (unqualified) values (see text).