Ochreous laterite: a nickel ore from Punta Gorda, Cuba

The ‘ochreous laterite’ is the oxidised nickel ore from the Punta Gorda deposit, Cuba. Mössbauer spectroscopy, X-ray diffraction (XRD), thermal methods and selective extraction techniques have been used to characterise the ore. The ore consists mainly of poorly crystalline Al-substituted goethite. The poor crystallinity of goethite is demonstrated by broad lines in the diffraction patterns and hence, low mean crystallite dimension (MCD) values, low dehydroxylation temperatures, high weight losses between 100 and 1000°C, and the magnetic hyperfine field distribution. Also present in the ore are minor quantities of hematite, gibbsite, chromite, and manganese minerals. Most of the nickel is associated with goethite. Cobalt is mainly associated with the manganese minerals. The Ni-rich ore, with contents of Fe2O3 between 72.1 and 77.2% and contents of Ni between 1.6 and 2.1%, is probably derived from a peridotite bedrock containing, in addition to olivine, Ni-bearing orthopyroxenes. Peridotite containing Al-clinopyroxene might be, on the other hand, the parent rock of the Ni-poor ore, with Fe2O3 contents between 42.6 and 62.6% and Ni contents between 0.24 and 0.96%.