25 research outputs found
Syntectonic mobility of supergene nickel ores of New Caledonia (Southwest Pacific). Evidence from faulted regolith and garnierite veins.
International audienceSupergene nickel deposits of New Caledonia that have been formed in the Neogene by weathering of obducted ultramafic rocks are tightly controlled by fracture development. The relationship of tropical weathering and tectonic structures, faults and tension gashes, have been investigated in order to determine whether fractures have play a passive role only, as previously thought; or alternatively, if brittle tectonics was acting together with alteration. From the observation of time-relationship, textures, and mineralogy of various fracture fills and fault gouges, it may be unambiguously established that active faulting has play a prominent role not only in facilitating drainage and providing room for synkinematic crystallisation of supergene nickel silicate, but also in mobilising already formed sparse nickel ore, giving birth to the very high grade ore nicknamed "green gold"
Modalités des néogeneses dans des systèmes hétérogènes renfermant des phases peu solubles
Ni-sepiolite-falcondoite in garnierite mineralization from the Falcondo Ni-laterite deposit, Dominican Republic
New chemical and structural data on sepiolite-falcondoite in garnierite veins from
the Falcondo Ni-laterite deposits, central Dominican Republic, are reported. Samples of Ni-sepiolitefalcondoite
vary in colour from whitish green to green depending on the NiO content (wt.%) and the
amount of silica present. The texture is normally schistose and friable but samples with considerable
quartz and/or amorphous silica are compact and hard. Back-scattered electron images indicate that
the samples are composed of at least three generations of Ni-sepiolite-falcondoite. The extreme
refined cell parameters for Ni-sepiolite-falcondoite vary from 13.400(2), 27.006(4), 5.273(1) AËš to
13.340(3), 27.001(6), 5.267(1) AËš (space group Pncn). As the Ni content increases there is a small
reduction in the a parameter. Chemical compositions determined by electron probe microanalysis
cover a large interval of the Ni-sepiolite-falcondoite solid solution (Fal3 and Fal77). Individual
samples show a considerable range in composition with the widest range determined in one sample
from 4.63 to 22.40 wt.% NiO
Microanalyses geochimiques de mineraux argileux de sediments preleves et Atlantique Nord (Forages du DSDP)
Controlled rate thermal analysis of sepiolite
CRTA technology offers better resolution and a more detailed interpretation of the decomposition processes of a clay mineral such as sepiolite via approaching equilibrium conditions of decomposition through the elimination of the slow transfer of heat to the sample as a controlling parameter on the process of decomposition. Constant-rate decomposition processes of non-isothermal nature reveal changes in the sepiolite as the sepiolite is converted to an anhydride. In the dynamic experiment two dehydration steps are observed over the ~20-170 and 170-350°C temperature range. In the dynamic experiment three dehydroxylation steps are observed over the temperature ranges 201-337, 337-638 and 638-982°C. The CRTA technology enables the separation of the thermal decomposition steps