Abstract
In this study, the mineralogical and chemical compositions of bauxite from San Giovanni Rotondo (SGR) on the Gargano Promontory (northern Apulia, Italy) are presented and discussed with the aim of assessing the nature of its source material. Bauxite from the SGR, which is known as the “Montecatini mine”, was exploited intensively until the 1970s to recover alumina. As with most of the autochthonous peri-Mediterranean bauxites, the studied deposit is a karst bauxite with a massive, matrix-supported texture and an oolitic structure. Boehmite and hematite are the main mineral phases, and anatase, rutile, and kaolinite are present in lesser amounts along with detrital zircons and monazite grains. Calcite is abundant only in the deposit’s lower portion, triggering a significant dilution effect on trace element concentrations. However, with respect to the average crust and chondrite compositions, strong enrichments of trace metals (up to 10X Upper Continental Crust’s (UCC)) and rare earth elements (REEs, up to 800X chondrite) exist throughout the studied deposit. The distribution of REEs, the (La/Yb)N and Eu/Eu* ratios, and an Eu/Eu* versus Sm/Nd diagram have been used for determining the bauxite’s provenance. These geochemical proxies point to a parental material consisting of a mixture of distant magmatic and siliciclastic components.
Highlights
Bauxites are residual deposits that are formed as the result of intense weathering of alumosilicate-rich parent rocks, mainly in humid tropical to sub-tropical climates [1]
According to the geological features of bedrock, bauxite deposits can be grouped into two categories: karst bauxite and lateritic bauxite
Karst bauxite deposits have been the subject of numerous geological, petrographical, mineralogical, and geochemical investigations aimed at tracing their possible source rocks and revealing the ore-forming process [5,6,7,8,9,10,11,12]
Summary
Bauxites are residual deposits that are formed as the result of intense weathering of alumosilicate-rich parent rocks, mainly in humid tropical to sub-tropical climates [1]. Karst bauxites include deposits developed on and hosted by carbonate rocks; lateritic bauxites consist of deposits formed on alumosilicate rocks. Regardless of their parent rock, bauxites have great economic significance mainly because of the high concentrations of Al-bearing mineral phases. Karst bauxite deposits have been the subject of numerous geological, petrographical, mineralogical, and geochemical investigations aimed at tracing their possible source rocks and revealing the ore-forming process [5,6,7,8,9,10,11,12]. The lack of sediment and/or rock representing a bauxite deposit’s parental material makes the achievement of these goals more difficult, and commonly different findings are suggested for the same deposit
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