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Nickel-Bearing Laterite Deposits in Accretionary Context

                         and the Case of New Caledonia: From the Large-Scale

                          Structure of Earth to Our Everyday Appliances






          Pierre Maurizot*, Brice Sevin, Marion Iseppi, Geological Survey of New Caledonia (SGNC/DIMENC), BP 465, 98845,
          Noumea, New Caledonia; Tanguy Giband, Mineral Authority (SMC/DIMENC), BP M2, 98849, Noumea, New Caledonia


          ABSTRACT                           control nickel deposits is therefore crucial   Ultramafic rocks are composed of silicate
            Nickel production is vital to modern   to industrial development.   minerals, notably olivine, which are,
          economic development. Of the different   If one excludes polymetallic nodules of   under wet and warm intertropical cli-
          ore types, supergene Ni-laterite produc-  the ocean floor, for which mining tech-  mates, unstable and rapidly weathered
          tion, as open-cast mining exploitation,    nology and jurisdictional issues are still   (Thorne et al., 2012; Wilson, 2004). Mg
          is on the rise and surpassing the more   not solved (Volkmann and Lehnen, 2017),   and Si are released, whereas Fe, Al, Ni,
          conventional hypogene sulfide type. This   two main types of nickel deposits are   and Co stay in situ. Consequently, a thick,
          trend will likely continue. Assessing the   known on land worldwide (Mudd and   soft, residual cover of typical red- to
          global resource of Ni laterite is therefore   Jowitt, 2014): (i) hypogene magmatic   yellow-colored Fe oxy-hydroxides accu-
          of crucial importance. Compilation of   nickel-sulfide deposits are found as lodes   mulates, at times capped with ferricrete
          scientific publications shows that the   or layered complexes in ancient cratons   (Fig. 2). Nickel is then concentrated up to
          main producers and occurrences are    and are mostly mined underground; and   a grade of 1%–2% or even more (Butt,
          concentrated in a few countries in South-  (ii) supergene Ni-laterite deposits, which   2007; Freyssinet et al., 2005; Gleeson et
          east Asia (New Caledonia, Indonesia,    are formed by weathering of exposed   al., 2003). This natural supergene process
          the Philippines) and the Caribbean region   ultramafic units, and as such are exploited   of enrichment is very efficient with a
          (Cuba and the Dominican Republic). In   in open pits.                 second-enrichment factor of 10 times
          these regions a common geological back-  Supergene mineral deposits are low-  compared to the initial ultramafic proto-
          ground appears, characterized by large   grade, large-tonnage resources, exploited   lith and 200 times the average Earth crust
          obducted ophiolites in tectonically active   in easy surface conditions (ICMM, 2012).   composition. Grades of Ni-laterite depos-
                                             In the last decade, global production of Ni
                                                                                its (0.8–15 wt% Ni) exceed that of mag-
          settings, subject to weathering during the   laterite has overtaken Ni sulfide (60% vs.   matic Ni-sulfide deposits (0.5–5 wt% Ni;
          Neogene. The neoformed mineralogy    40% according to Mudd and Jowitt, 2014),   Arndt and Ganino, 2012). Cobalt is, in
          of such surficial deposits is well docu-  and the laterite proportion is still growing.  some deposits, enriched in the same
          mented. A model is proposed, based on   Nickel-laterite deposits require ultra-  proportion, but its initial and final con-
          the knowledge gained on Ni-laterite   mafic protoliths, such as Precambrian   centrations are roughly 10 times lower.
          deposits in New Caledonia, that could    komatiites and layered complexes or   In addition, recent studies about scan-
          be applied to similar geological settings   Phanerozoic ophiolites. Ophiolites corre-  dium enrichment within Ni-Co laterites
          worldwide. This model states that in   spond to remnants of oceanic mantle and   of New Caledonia show that Sc-bearing
          accretionary terranes, vertical motions   crust emplaced on land in collision zones   goethites contain about 10 times the Sc
          during weathering control both ore    involving oceanic plates (Coleman, 1977).   content of the parent rock (up to 100 ppm;
          type and location.                 Mantle rocks are not commonly exposed   Teitler et al., 2018).
                                             at Earth’s surface and hence are restricted   Scientific research on Ni-Co laterites,
          INTRODUCTION                       to a few countries (Fig. 1).       which present in essence a strong hetero-
            Nickel-based alloys are used in many   Typical mantle rocks have been   geneity, is still low globally. New
          applications, from modern information   enriched, through repeated partial melt-  Caledonia, a small French overseas
          and communication technologies to large-  ing and extraction episodes, in nickel up   territory in the southwest Pacific, holds
          scale industrial infrastructures, including   to 0.18 wt%; i.e., 20 times the average   ~25% of the global Ni-laterite resource
          stainless-steel products used in our every-  Earth crust concentration (Palme and   (Berger et al., 2011; Mudd and Jowitt,
          day life, such as coins, beer kegs, coffee   O’Neill, 2014). However, economically,   2014). In terms of surface (18,500 km )
                                                                                                             2
          spoons, and much more. Improving   this is not significant, and a secondary   and population (~300,000), the archipel-
          knowledge about geological factors that   enrichment process has to take place.   ago is certainly the smallest among the




          GSA Today, v. 29, doi: 10.1130/GSATG364A.1. Copyright 2019, The Geological Society of America. CC-BY-NC.
          *Email: pierre.maurizot@gouv.nc

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