Sediment Dispersal Patterns as Clues to Placer Like Platinum Accumulation in and near Chagvan Bay, Alaska

Abstract

The modern sediments of Chagvan Bay, Alaska contain zones of platinum enrichment which suggest an external source of platinum-host sediments. Two mathematical sediment tracing techniques, based on vector and multiple regression analyses of geochemical data, are used to determine the provenance and dispersal patterns of the bay deposits. Criteria for the selection of natural sediment tracers are presented, and the application of tracing techniques to the exploration for high latitude marine placers is discussed.

Textural and mineralogical variations in the surficial sediments of Chagvan Bay, Alaska: Some stratigraphic implications of a subarctic bay

“…The mining history and general and economic geology of this region have been extensively reported by Mertie (1940;1969;. Small zones of platinum enrichment (0.03--0.5 ppm) above baseline levels (<0.01 ppm) also occur in the modern sediments of Chagvan Bay (Owen and Moore, 1976) and in the nearshore surflcial sediments of the Bering Sea adjacent to the bay (Moore and Welkie, 1976). The spatial extent and value of platinum in these modern deposits has yet to be determined.…”

“…Lithic fragments are predominant in the principal gravel mode (--3 to --2 4) and quartz and feldspar grains are predominant in the fine sand mode (2--3 4). Comparison studies of the trace-element geochemistry of the principal gravel and fine sand modes with detrital material from apparent source areas around Chagvan Bay have shown that these two modes are derived from the coastal bluffs and Bering Sea shelf, respectively (Owen, 1975;Owen and Moore, 1976). Identifiable grains in the coarse silt mode (4--5 4) from the Kinegnak River are composed primarily of quartz.…”

“…Fine sands (2--3 ¢) in Chagvan Bay (Fig.9) are derived from the adjacent nearshore shelf sediments in the Bering Sea and from beach deposits along the Bering Sea coast north of the bay, such as those which have produced the spit which forms the western boundary (Owen, 1975). Previously, an attempt was made to determine if the shelf and beach sediments do, in fact, represent a single or separate source areas by analyzing samples from both locations for a variety of physical and geochemical properties (Owen, 1975(Owen, , 1976Owen and Moore, 1976). These studies showed that there is no basis for considering these locations as separate source areas.…”

“…The several Holocene bays which indent this coastline, such as Chagvan Bay, are essentially virgin territories for scientific investigation. Moreover, Chagvan Bay and other bays along this coastline contain either known or suspected placer-like accumulations of noble metals in the surficial sediments {Moore, 1972; Moore and Welkie, 1976;Owen and Moore, 1976). The objectives of this study were to determine the textural and mineralogical characteristics of the surficial sediments of Chagvan Bay, to relate this information to the depositional processes and to consider the stratigraphic implications of these deposits.…”