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The nickel-silicate deposits and associated nickelcobalt-manganese-oxide deposits on the summit area of the Serra da Mantiqueira, north of Sao Jose do Tocantins, State of Goiaz, Brazil, rest on unserpentlnized pyroxenite, which is interlayered with serpentinized peridotite. The layers of intrusive igneous rock have a northerly trend and a steep westerly dip. All the known deposits are at high altitudes, from 950 meters to 1,130 meters, which is that of the summit, and are related to an ancient uplifted and dissected erosion surface. Serpentinized rocks have weathered to a yellow-brown ferruginous-siliceous clay and to residual blocks of jasperoidal chalcedony, which cap most of the high ridges. The nickel district has an area of 36 square kilometers (13.7 sq. miles), and the forty-five deposits that have been prospected and sampled have a total measured surface area of about 74,400 square meters. The measured ore reserve, calculated to a depth of 1 meter and with the cut-off grade placed at 2 percent, is at least 184,000 metric tons having an average tenor of 4 percent of nickel. With a 4-percent cut-off grade, the measured reserve would be about 85,000 metric tons averaging 5.5 percent of nickel, and with a cut-off of 6 percent it would be about 25,000 metric tons containing 6.5 percent of nickel. The indicated reserve would be much greater. With a 2percent cut-off grade it would be at least 4 million tons containing between 2 'and 4 percent of nickel; wi-th a 4-percent cut-off, about 1,220,000 metric tons having an average tenor of 4,5 percent of nickel; and with a 6-percent cut-off, 305,000 tons having a tenor of from 6 to 8 percent of nickel. Prospecting in other geologically and topographically favorable areas is expected to yield additional tonnage. The inferred maximum reserve in the district is estimated to be between 9 and 16 million tons averaging between 1 and 3 percent of nickel. Between 20,000 and 75,000 metric tons of black, concretionary "pebbles" embedded in the near-surface soil in two accessible deposits can be recovered mechanically by screening. The pebbles are expected to contain between 1 and 2 percent of cobalt, small but appreciable quantities of nickel, copper, and barium, and much larger quantities of manganese and iron. The central part of the deposits is 22 kilometers north of Sao Jose' do Tocantins, and 340 kilometers north of Anapolis, a 247 248 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS railhead 1,221 kilometers by rail north of the port of Santos on the Atlantic Ocean.

Nickel-silicate and associated nickel-cobalt-manganese-oxide deposits near Sao Jose do Tocantins, Goiaz, Brazil