Geological, geochemical and mineralogical features of some bauxite deposits from Nurra (Western Sardinia, Italy): insights on conditions of formation and parental affinity

Abstract

Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al 2 O 3 and residual 'immobile' elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO 2 and Fe 2 O 3 . Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnä site group. Conservative indices, including TiO 2 /Al 2 O 3 and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous.

Rare earth element geochemistry of the Upper Permian limestone: the Kanigorgeh mining district, NW Iran

“…In addition, Eu anomaly can be used as a conservative elemental index in weathered environments for determination of parental affinity for bauxite ores (Mongelli, 1997;Mameli et al, 2007;Mongelli et al, 2014). By noting these explanations, in this study the distribution patterns of REEs along with Eu anomaly in the bauxitic ores and the host limestone were compared to determine the potential role of the latter in supplying REEs for the former.…”

Mineralogy, Geochemistry and Stable Isotope Studies of the Dopolan Bauxite Deposit, Zagros Mountain, Iran

“…Zr, Hf, Nb and Ta are immobile elements and show positive correlations (R 2 = 0.64 to 0.87) with TiO2 ( Figure 8). The high SiO2 content of the bauxite facies is a result of weak lateritization [8] and the presence of kaolinite [11]. Based on the Al2O3-Fe2O3-SiO2 ternary diagram [50], organic-rich and clay-rich bauxite horizons show weak and moderate lateritization, respectively, whereas oolitic, pisolitic and iron-rich bauxites plot in the strong lateritization field ( Figure 6).…”

“…Whole rock major, trace and rare earth element (REE) analyses of bauxite horizons are provided in The high SiO 2 content of the bauxite facies is a result of weak lateritization [8] and the presence of kaolinite [11]. Based on the Al 2 O 3 -Fe 2 O 3 -SiO 2 ternary diagram [50], organic-rich and clay-rich bauxite horizons show weak and moderate lateritization, respectively, whereas oolitic, pisolitic and iron-rich suggesting tropical paleo-geographic conditions which favored bauxitization and the formation of bauxite horizons [9,51].…”

“…The mobility and behavior of elements during bauxitization have also been discussed by a number of researchers [8,11,14,[17][18][19][20][21][22]. To investigate mobility of elements in weathered systems, various methods have been discussed by some researchers [10,14,[23][24][25].…”

“…Residual bauxite deposits are classified as karst bauxite and laterite type bauxite [1]. Karst bauxite deposits from the Mediterranean region and other worldwide bauxite formations have been investigated by a number of authors [2][3][4][5][6][7][8][9][10][11]. Karst bauxite genesis is related to paleo-weathering products derived from different rocks types including carbonate rocks, marl, volcanic and magmatic rocks [12][13][14][15][16][17].…”