PROVENANCE OF A GARNET-RICH BEACH PLACER DEPOSIT, MONTAUK POINT, LONG ISLAND, NY

Garnet and magnetite rich sand, also enriched in monazite and zircon, has been observed and sampled near Montauk Point, Long Island. The sediment is derived from the glacial till and stratified drift of the Ronkonkoma Moraine by mechanical weathering and erosion due to wave action at Montauk Point, the headland on the eastern tip of Long Island. Sand sized sediment is moved westward along the southern shore of Long Island by longshore transport. The garnet and magnetite components of this sediment are significantly denser than the quartzo-feldspathic components. This allows for hydraulic segregation of these components, by wave action, producing a placer deposit of sand enriched in garnet and magnetite. Although the proximal source of the sediment is obviously the Ronkonkoma Moraine, the ultimate source remains to be determined. The chemical composition of selected minerals in the placer deposit is compared that of the same minerals in the rocks of the glacial till. Preliminary results indicate similar garnet compositions, for the most part, in the placer deposit and the rocks of the glacial till. However the possibility of a mixed provenance for some of the beach sand minerals exists. For example, stratified drift in the Montauk Point area may, in part, be derived from the Harbor Hill Moraine as well as from the Ronkonkoma Moraine. Rocks of the glcial till may come from different source areas as well.