PRELIMINARY GEOCHEMICAL AND MINERALOGICAL ASSESSMENT OF THE BEACH SAND, VIEQUES, PUERTO RICO

Representative beach sand samples were collected from Vieques (18.095901948142554, -65.49229758368986; Puerto Rico) and chemically analyzed for provenance interpretation. Puerto Rico is the eastern-most island of the Greater Antilles, which is a group of islands in the Caribbean Sea that includes the countries of Cuba, Hispaniola (Haiti and the Dominican Republic), Jamaica, and the U.S. territory – the Commonwealth of Puerto Rico. Puerto Rico (and its outlying islands of Culebra and Vieques), along with the U.S and British Virgin Islands are the subaerial form of a microplate that exists at a seismically active plate boundary between the North American plate and the northeast margin of the Caribbean plate (United States Geological Survey Bulletin #1042-1, 1957). The Black Sand Beach is a short drive from the town of La Esperanza and it’s about a quarter of a mile long. Samples were collected from low-and high tide dominated areas. The most abundant heavy mineral in the beach sands of Puerto Rico is magnetite. It occurs on all shores of the island. Ilmenite is present, associated with the magnetite. The beach sands also contain minor amounts of chromite. The west and southwest shores, from Punta Guanajiba to Ponce, are composed of weathered rocks, mangrove swamps, and beaches composed of shell fragments. Heavy minerals are a major constituent of the beach sand in many places on the south coast and magnetite often constitutes more than 15 percent of the sand. The east coast, from the Rio Grande de Patillas to Naguabo, consists of outcropping volcanic and intrusive rocks of Cretaceous and early Tertiary age and sandy beaches. Rich concentrations of heavy minerals occur locally. Both bulk oxide (silica, alumina, soda, potash, magnesia, both ferrous and ferric oxide, calcium oxide, etc.) and trace elements (Ti, Zr, Y, Cr, Sr, Rb, Ce, La, etc.) analyses were performed on collected sands by using both X-ray Fluorescence (XRF) and Inductively coupled plasma mass spectrometry (ICP-MS). Based on geochemical discriminating factor, there seemed to be an affinity of most of the black sands with volcanic-sourced derivation. Ceaseless shoreline processes ultimately fractionated heavy mineral concentrations in black sands due to hydraulic sorting.