Quantitative Mineralogical Characterization of Karst Bauxite Deposits in the Southern Apennines, Italy

Abstract

QEMSCAN® analysis can be applied to bauxite ores, allowing a rapid quantification of mineralogy (including trace detrital phases) and assessment of the individual textural characteristics of the bauxite lithotypes, showing a detailed image of the distribution of economic and non-economic minerals and their intergrowths. The published data on this subject are currently relatively scarce, and are unhelpful for understanding the basic principles and advantages of applying QEMSCAN® analysis to this kind of ore. In this study the QEMSCAN® development work has been applied to the South Italian karst bauxites, which consist of small deposits that are currently uneconomic, but that can be considered as a model analogue for truly economic karst bauxite ores. The representative samples considered for this study come from two different localities: the Matese Mountains and the Caserta district. The mineralogical composition of bauxite has been quantified by combined QEMSCAN® and XRD Rietveld Quantitative Phase Analysis (QPA), as well as with SEM-EDS techniques. Our results show that the QEMSCAN® data allow a detailed textural characterization and add significant information on the major and trace mineral distribution. This methodology can augment or replace other time-consuming quantitative phase analyses for mineralogical studies of bauxites, provided that the SIP (species identification protocol) database has been carefully validated by preliminary use of XRD and SEM-EDS. However, the XRD (QPA) and QEMSCAN® analytical techniques can be complementary for bauxite ore evaluation, and a very powerful tool for exploitation and mineral processing, as shown in several examples. The results obtained with each technique are compared, and the advantages extensively discussed

Genesis of autochthonous and allochthonous Apulian karst bauxites (Southern Italy): Climate constraints

“…It is thus not surprising that the wide and recent literature on bauxite deposits has focused on the genetic mechanisms promoting the formation of this type of sedimentary rock (e.g., Mongelli, 2002;Laskou and Economou-Eliopoulos, 2007;Mameli et al, 2007;Zarasvandi et al, 2008;Hoefs, 2009;Karadağ et al, 2009;Wang et al, 2010;Boni et al, 2013;Hanilçi, 2013;Zarasvandi et al, 2013;Abedini and Calagari, 2014;Mongelli et al, 2014;Peh and Kovačević Galović, 2014;Yu et al, 2014).…”

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

“…Gibbsite can transform to boehmite in surface environments and boehmite can transform to diaspore in a near-surface environment [18,[64][65][66][67]. Kaolinite and other clays such as nacrite can also be present in bauxite deposits [53]. The pisolitic texture results from aggregation of discolored pisolites showing evidence of deferrification process.…”

“…High content of trace elements such as Cr (132-1088 ppm), Zr (132-557 ppm) and Nb (28-77 ppm) is a significant and common feature of the Dopolan bauxite (Table 2). Trace elements such as Cr, Ni, V, Co, Zr are considered bauxitophilic [53] and they are used in geochemical calculations such as mass change and identification of parent rocks. Trace elements such as Zr, V, and Ga are enriched in all parts of the bauxite; these trace elements are low in the Khaneh-Kat Formation.…”

Geochemical Characterization of Bauxite Deposits from the Abruzzi Mining District (Italy)

“…The various mid-upper Cretaceous stratigraphic gaps are comprised in a wide time-span, thus supporting the presence of a complex, tectonically controlled paleotopography and the long-lived exposure of some sectors of the ACP [9,18,23]. The sub-aerial exposures resulted in an intense karstification, followed by bauxite deposition [8,10,24,25]. In the Abruzzi district, two main discontinuous bauxite horizons can be recognized: a first (bx1), which is the most prominent, locally reaching 10 m of thickness, corresponds to a Late Albian-Early Cenomanian stratigraphic gap, and a second (bx2), with a maximum thickness of 1 m, bounded by Late Cenomanian-Early Turonian limestones [12,26,27].…”

“…The chemical composition of the bauxites in the Abruzzi district has been compared with other bauxites from the major districts of the circum-Mediterranean area: Spinazzola (Apulia) [42], Salento and Gargano (Apulia) [11,57], Nurra (Sardinia) [44], Matese Mts. and Caserta districts (Campania) [8,10], Bolkardagi (Turkey) [58], Mortas (Turkey) [59] and the Parnassos-Ghiona district (Greece) [60].…”