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EL-SAYED (1983) used the trace metals as a possible tool to descriminate amongst thedifferent reefal depositional environments in the area north of Jeddah. Strontium and magnesium inaragonite also were used by FRIEDMAN (1968) as a tool in the identification of the constituents inskeletal sands from Aqaba.Mineralogy of Reefs and Reefal Sediments:The framework builders of the reefs in the northern Red Sea utilize skeletons of aragonite andhigh Mg-calcite (FRIEDMAN, 1968 ; EL-WAKEEL et al., 1984). Aragonite is basically producedfrom cords, fragments of ffalimeda, and inorganic carbonate precipitates in local areas (e.g., RasMatarma lagoon). On the other hand, Mg-calcite is mostly produced from coralline algae andforaminifera. The relative abundance of the major carbonate minerals depends on the proportionalmixture of various organisms in the reefal sediments. The relation between the major carbonateminerals in the reefal sediments from different areas of the Red Sea is shown in Figure 6.HYDROTHERMAL, DEPOSITS IN THE NORTHERN RED SEAMetalliferous sediments associated with hot brines in the axial trough deeps were reportedtwo decades ago. Ever since their discovery, the geothermal system of the Red Sea rift zone has beeninvestigated nearly continuously. These investigations have revealed the presence of several deepscharacterized by the metalliferous sediments. BACKER and SCHOELL (1972) located 17 brinepools in the Red Sea floored by sediments of hydrothermal origin. Further investigations of the RedSea rift zone resulted in the discovery of new deeps in the northern part, increasing the number ofdeeps along the axial trough of the Red Sea to 20 (Fig. 7). Most of the deeps are filled with brines ofdifferent salt concentrations. However, the sediments underlying the brines in some deeps appear tobe normal deep-Red Sea sediments with a significant content of nannofossils and pelagicmicrofossils. In other deeps, where the hydrothermal influence is strong, the bottom is covered withmulticoloured, metal-rich sediments. The process of formation of these metalliferous sediments isclearly represented in the Atlantis I1 Deep, where metal-rich hydrothermal solutions are beingdischarged at the present time.The first major scientific results indicating the potential economic value of sediments and ofthe overlying brines in Atlantis II Deep were published by DEGENS and ROSS (1969). Subsequentstudies by BACKER and SCHOELL (1972) and BACKER and RICHTER (1973) focussed onvarious aspects of the brine sediments and helped to draw the attention of several ore-prospectingcompanies and scientific organizations to the Red Sea dee s. Intensive investigations were carriedout on the Atlantis I1 Deep, which covers an area of 60 km f . However, less attention was paid to theother deeps, particularly in the northern Red Sea, and therefore little is known about the compositionand the commercial values of the metalliferous sediments in these areas.Recently, however, BEHAIRY et al. (1985) studied some five sediment cores from the RedSea deeps, three of which came from the northern Red Sea (Fig. 7). The study of these cores revealthat a biostratigraphic division of sediments can be made by using the distribution of some planktonicforams which are sensitive to temperature and salinity. Most of the sediments in the cores representHolocene normal marine conditions and Upper Wiirm pleneglacial hypersaline conditions.Mineralogical and chemical data show that the sediments of Kebrit, New and Shaban deeps (Fig. 7)are similar to the normal deep-Red Sea sediments, which contain a mixture of organo-detritalcomponents. However, at various levels, there are intercalations of volcanic and/or hydrothermalmatedal sṪhe Holocene sedimentation rates in the deeps are highly variable (9-31 cm lo00 y-I), with ageneral increase northward. Slumping associated with tectonic activity in the north seems to havecontributed large quantities of sediments to the northern deeps.345