ABSTRACT
Materials of potential economic value in Taiwan’s shelf sediments include iron, titanium, thorium and zirconium-bearing minerals, and calcareous shells. The average overall or total heavy mineral content of sand samples from Taiwan Strait is only about 0.6%, although one sample collected a few kilometers southwest of the Penghu Islands contains 3.8% heavy minerals. However, sands along the southwestern offshore bars contain relatively high heavy mineral concentrations. It has been suggested that there are 500,000 tons of heavy sand existing in the offshore bars of southwestern Taiwan, among which 10% is black monazite containing about 1.3% thorium dioxide. The commercial value of the black monazite is estimated to be about US$500 million. Calcareous shells are particularly abundant in three areas of the shelf They make up 30% to 80% of the surface sediment over a large portion of the shelf north of Taiwan, 30% to 60% of the surface materials in an area of Taiwan Strait southwest of the Penghu Islands, and 40% to 70% of the surface sediment on the shelf off the southern end of Taiwan. The manganese nodules dredged from the Kyushu Palau Ridge and near the central basin fault consist mainly of todorokite, birnessite, and akaganeite.
