Ochreous laterite: a nickel ore from Punta Gorda, Cuba

The 'ochreous laterite' is the oxidised nickel ore from the Punta Gorda dep osit, Cuba. Mossbauer spectroscopy, X-ray diffraction (XRD), thermal method s and selective extraction techniques have been used to characterise the or e. The ore consists mainly of poorly crystalline Al-substituted goethite. T he poor crystallinity of goethite is demonstrated by broad lines in the dif fraction patterns and hence, low mean crystallite dimension (MCD) values, l ow dehydroxylation temperatures, high weight losses between 100 and 1000 de greesC, and the magnetic hyperfine field distribution. Also present in the ore are minor quantities of hematite, gibbsite, chromite, and manganese min erals. Most of the nickel is associated with goethite. Cobalt is mainly ass ociated with the manganese minerals. The Ni-rich ore, with contents of Fe2O 3 between 72.1 and 77.2% and contents of Ni between 1.6 and 2.1%, is probab ly derived from a peridotite bedrock containing, in addition to olivine, Ni -bearing orthopyroxenes. Peridotite containing Al-clinopyroxene might be, o n the other hand, the parent rock of the Ni-poor ore, with Fe2O3 contents b etween 42.6 and 62.6% and Ni contents between 0.24 and 0.96%. (C) 2001 Else vier Science Ltd. All rights reserved.