Occurrence of SiC and Diamond Polytypes, Chromite and Uranophane in Breccia from Nickel Laterites (New Caledonia): Combined Analyses

Abstract

Different techniques have been combined to identify the structure and the chemical composition of siliceous breccia from a drill core of nickel laterites in New Caledonia (Tiebaghi mine). XRD analyses show quartz as a major phase. Micro-Raman spectroscopy confirmed the presence of reddish microcrystalline quartz as a major phase with inclusion of microparticles of iron oxides and oxyhydroxide. Lithoclasts present in breccia are composed of lizardite, chrysotile, forsterite, hedenbergite and saponite. The veins cutting through the breccia are filled with Ni-bearing talc. Furthermore, for the first time, we discovered the presence of diamond microcrystals accompanied by moissanite polytypes (SiC), chromite (FeCr2O4) and uranophane crystals (Ca(UO2)2(SiO3OH)2.5(H2O)) and lonsdaleite (2H-[C-C]) in the porosities of the breccia. The origin of SiC and diamond polytypes are attributed to ultrahigh-pressure crystallization in the lower mantle. The SiC and diamond polytypes are inherited from serpentinized peridotites having experienced interaction with a boninitic melt. Serpentinization, then weathering of the peridotites into saprolite, did not affect the resistant SiC polytypes, diamond and lonsdaleite. During karstification and brecciation, silica rich aqueous solutions partly digested the saprolite. Again, the SiC polymorph represent stable relicts from this dissolution process being deposited in breccia pores. Uranophane is a neoformed phase having crystallized from the silica rich aqueous solutions. Our study highlights the need of combining chemical and mineralogical analytical technologies to acquire the most comprehensive information on samples, as well as the value of Raman spectroscopy in characterizing structural properties of porous materials.

Ultrahigh-Pressure Mineral Inclusions in a Crustal Granite: Evidence for a Novel Transcrustal Transport Mechanism

“…In contrast to diamond polishing powder (D1 and D0.25 µm), Raman spectra of natural diamonds exhibit sharp lines. The Raman spectra of several diamond grains correspond to those of natural lonsdaleite (Figures 5 and 6) [17]. Raman spectrum of moissanite (bands at 755.5, 778.9, and 956.7 cm -1 ) containing two-phase particle of diamond-lonsdaleite (bands at 1310.7, 1322.3, and 1329.0 cm -1 ).…”

“…A diamond crystal (~20 × 15) µm in sample II yields a value of 1320.9 ± 0.4 cm -1 with an FWHM of 7.3 ± 0.4 cm -1 (n = 10), corresponding to the hexagonal diamond polytype lonsdaleite [17,20]. This type of diamond is not used for sample preparation.…”

Ultrahigh-Pressure Mineral Inclusions in a Crustal Granite: Evidence for a Novel Transcrustal Transport Mechanism

“…In contrast to diamond polishing powder (D1 and D0.25 µm), Raman spectra of natural diamonds exhibit sharp lines. The Raman spectra of several diamond grains correspond to those of natural lonsdaleite (Figure 6 and Figure 7) [17]. ).…”

Raman investigations and ab initio calculations of natural diamond-lonsdaleite originating from New Caledonia

“…They have survived hydrothermal (serpentinization) and weathering (atmospheric) conditions. Diamond microcrystals were inherited from the upper earth mantle [22].…”

“…The nickel laterite soils have been formed on serpentinized peridotite, a Mg-Fe-Si rich rock which presents the upper earth mantle. The diamonds were investigated by El Mendili et al [21,22]. The authors suggest that these diamonds were inherited from the saprolitized (weathered) serpentinized-peridotites.…”