The interpretation of geochemical data from a regional survey of the Aban al Ahmar quadrangle resulted in the selection of areas for follow-up studies. The results of detailed geochemical studies of these areas, combined with field observation, resulted in the selection of areas of moderate to high mineral resource potential. The most important areas are (1) the Jibal Minyah area, Aban al Asmar area, Jibal Suwaj area, and Nubayah area where tin and tungsten mineralization are associated with Abanat-suite rocks or possible buried Abanat-suite plutons; (2) several areas containing rocks of the Murdama group in the northern part of the quadrangle, the Buqaya al Luaah area, and the Jabal Akkash area where precious-and base-metal mineralization are generally associated with small Idah-suite plutons; and (3) the southern periphery of Jibal Qitan associated with skarn mineralization.. The Aban al Ahmar quadrangle (sheet 25F) lies in the northeastern part of the Proterozoic Arabian Shield. Plots showing the distribution of single elements and factor scores of the regional geochemical data for wadi concentrates were used to select favorable areas for follow-up work. Detailed follow-up studies consisted of the collection of samples of rocks, wadi concentrates, and wadi sediments. The most useful pathfinder elements for precious-and base-metal mineralization are Cu and Pb, and for tin and tungsten mineralization they are Sn, La, Nb, Y, and Be. R-mode factor analysis of the regional geochemical data resulted in two factors that reflect mineralization: precious-and base-metal mineralization; and Abanat-suite lithology and, therefore, tin and tungsten mineralization.A major problem in the interpretation of the regional geochemical data resulted from incomplete removal of magnetite from the samples prior to analysis. The presence of magnetite can cause anomalous values of Ni, Fe, V, Cu, and Co in samples because of it's ability to incorporate these elements into its structure during magmatic crystallization.

Detailed geological, geochemical, and geophysical investigations of the Rois Malk gold prospect on the Island of Babelthuap, Republic of Palau, resulted in the identification of more than mineralized veins, shear zones, and brecciated areas in a 1.5 by 1 km area. The Rois Malk study area is located in the southern part of Babelthuap Island, which is the largest of Palau's 200 islands. The study area is underlain by Eocene (?) and basaltic andesite flows and flow breccia which have undergone deep lateritic weathering. The veins and shear zones range in width from less than a centimeter to several meters and strike NE to NW with steep dips. The longest vein extends over 500 m along trend. Most of the veins contained anomalous amounts of gold up to as much as 13 ppm. It is likely that veins continue beyond the study area, but are obscured by dense jungle and intense weathering. The veins show typical comb quartz textures and open space fillings. Shear zones consist of multiple stages of brecciated rock cemented by quartz and iron and'manganese oxides. Sulfides associated with the mineralization are pyrite, sphalerite, chalcopyrite, and galena. Gold occurs as native gold, electrum, and Au-Ag telluride. Elements associated with gold include Mo, Te, Bi, Pb, Ag, Cu, Zn, and As. The most effective sample media for geochemical exploration is stream sediments. Au is the most diagnostic pathfinder element followed by Te, Zn, Pb, and Cu. Heavy-mineral concentrates from stream sediments are also useful particularly for determination of the mineralogy. Bottom sediment samples collected from mangrove swamps are effective in rapid detection of onshore mineralization adjacent to mangrove swamp and coast. The results of this study suggest that the Rois Malk system is similar to the top of other productive epithermal vein systems and may represent the lower levels of an enargite subtype epithermal system. Tonnages of known enargite type deposits elsewhere in the world range from 0.2 to 11 million tonnes and gold grades from 3 to 18 ppm. The vein system at Rois Malk warrants further surface exploration and subsurface drilling. The methods used in this study can be used to evaluate other parts of Palau as well as other areas with similar environments particularly in the western Pacific. The Palau trench is well developed offshore of the northern part of the arc where ocean depths consistently exceed 6,000 m (fig. 2). In the southern part of the arc-trench system, the trench is less well defined and less than 6,000 m in depth. The deepest trenches in the region occur offshore of the active Mariana arc where ocean depths generally exceed 8,000 m with local areas exceeding 9,000 m. Extending northward from the Palau arc is the Palau-Kyushu ridge. It transects the Philippine plate into two distinct basins: the west Philippine basin and the Parece Vela basin. Formation of the Palau-Kyushu ridge began in the early Tertiary, at about the same time of formation as the west Philippine basin (Karig, 1975). With the cessation of volcanic activi...

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Introduction 1 Acknowledgments 2 Regional geologic setting 2 Geology of the Rois Malk study area 4 Techniques for collection, preparation, and analysis 6 Rocks 6 Trenches and road cuts 6 Soils 6 Stream sediments and heavy-mineral concentrates 6 Mangrove sediments 7 Mineral system 8 Hydrothermal alteration 9 Veins and shear zones 10 VS-1 vein 10 VR-1 and 2 veins 12 VT veins 13 VA veins 14 Brecciated areas 16 VB-1, 2, and 3 brecciated areas 16 Geochemistry of the vein system 18 Generation of statistics and maps 18 Epithermal suite (Au, Ag, Te, Bi, As, and Hg) 18 Base-metal suite (Cu, Pb, Zn, Cd, and Mo) 21 Mafic suite (Mn, Co, Cr) 22 Conclusions about the vein system 23 Media for geochemical exploration 29 Stream sediments and heavy-mineral concentrates 29 Soils 32 East-west soil traverse 32 Detailed soil traverse 33 Mangrove sediments 36 Summary on the effectiveness of geochemical media 36 Interpretation and conclusions 39 References cited 43 Appendix A. Description of vein, rock, and channel samples, Rois Malk study area 48 Appendix B. Chemical data for vein, channel, soil, stream-sediment, and heavy-mineral concentrates, Rois Malk study area 53 Appendix C. Description of soil samples from the Rois Malk study area 85 Appendix D. Description of mangrove sediment samples from the eastern side of Babelthuap Island 85 Contents Ill Contents V