Ni-sepiolite-falcondoite in garnierite mineralization from the Falcondo Ni-laterite deposit, Dominican Republic

Abstract

AB ST R ACT : 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) Å to 13.340(3), 27.001(6), 5.267(1) Å (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 (Fal 3 and Fal 77 ). Individual samples show a considerable range in composition with the widest range determined in one sample from 4.63 to 22.40 wt.% NiO.

Ni Enrichment and Stability of Al-Free Garnierite Solid-Solutions: A Thermodynamic Approach

“…The same samples were studied by Proenza et al (2008), Tauler et al (2009), Soler et al (2010, and Villanova- de-Benavent et al (2011ade-Benavent et al ( , 2011b. In addition, a list of garnierite minerals from Ni laterites worldwide was compiled in which accurate quantitative electron microprobe data are available (see Figure 1).…”

“…from Ni-serpentine to Ni-kerolite). Thin veinlets of quartz cross the garnierite structures (Tauler et al, 2009;Villanova-deBenavent et al, 2011b). As both the Lippmann and the activity diagrams were built on the basis of partially theoretically derived equilibrium constants (log K values for Ni end-members), having some experimental control over the reliability of the equilibrium constants used in the graphical representations was considered to be necessary.…”

“…However, the most frequent observation is the existence of equilibrium between two solids (two solid solutions or one solid solution and quartz), or simply a single solid Figure 1. Projection of Caribbean garnierite ore compositions (Proenza et al, 2008;Tauler et al, 2009;Soler et al, 2010;Villanovade-Benavent et al, 2011a, 2011b and published data (Brindley and Hang, 1973;Brindley, and Wan, 1975;Springer, 1974Springer, , 1976 for garnierites from different Ni-laterite deposits, in a Si-Ni-Mg ternary diagram (at.%). The positions of the solid-solution series between Ni-sepiolite (Sep)-falcondoite (Fal), kerolite (Ker)-pimelite (Pim), and lizardite (Srp)-népouite (Nep) are also indicated.…”

“…Gleeson et al, 2003). When only small amounts of Al are present in the protolith, garnierites can be formed by different combinations of the three main Mg-Ni solid solutions with serpentine, talc, and sepiolite-like structures; clays (chlorites and smectites) being absent (Wells et al, 2009;Tauler et al, 2009;Villanova-de-Benavent et al, 2011a).…”

“…The Mg-Ni-phyllosilicates are members of three solid-solution series extending from Mg and Ni endmembers (e.g. Springer, 1974Springer, , 1976Brindley et al, 1979;Gleeson et al, 2003;Tauler et al, 2009;Wells et al, 2009;Reddy et al, 2009;Villanova-de-Benavent et al, 2011b). The electron microprobe (EMP) analyses plotted in Figure 1 confirm (Brindley and Hang, 1973;Brindley and Maksimovic, 1974;Springer, 1974;Brindley and Wan, 1975;Brindley et al, 1979).…”