GEOCHEMICAL BEHAVIOR OF AU IN TERRIGENOUS AND PELAGIC MARINE-SEDIMENTS

A total of 224 marine sediments of terrigenous and pelagic origin were collected from the Obama Bay, Suruga Bay, south of Kii Strait, off No rtheast Japan and the Japan Trench (terrigenous sediments), and the Ce ntral Pacific (pelagic sediments). These samples were analyzed for Au by atomic absorption spectrometry using a graphite furnace atomizer af ter solvent extraction separation. The average Au content of the terri genous (2.4 +/- 1.2 ppb, n = 85) and the pelagic (1.4 +/- 1.3 ppb, n = 139) sediments were similar to crustal abundance. A significant corre lation (r = 0.82) was found for Au and Cu in terrigenous sediments, wh ile no such trend was found in the pelagic sediments. Sediments collec ted around the Au mineralized regions are known to exhibit high Au/Cu ratios. Therefore, the Au/Cu ratio should serve as a useful indicator for the geochemical exploration of Au deposits. With respect to the co ntent of Au and organic carbon in the pelagic sediments, surface sampl es had higher values, whereas deeper sediments were depleted. There wa s no such vertical concentration trend for Au and organic carbon in th e terrigenous sediments. The vertical profile of Au in the pelagic sed iments is thought to be a result of upward migration of Au-organometal lic complexes during early diagenesis. Since the most probable form of Au in the terrigenous sediments is elemental, significant migration d uring diagenesis would not occur, explaining the lack of a vertical tr end for Au.