Environmental mineralogy in the mining area of Montevecchio Ponente (SW Sardinia)

Sedda L.

;Podda F.;Naitza S.

2022-01-01

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Abstract

The Montevecchio mining area (Arbus – Guspini, Sardinia SW) has been exploited for centuries, for the extraction of lead and zinc minerals. The following work focuses on the study and characterization of the sources and contaminants present in the “Cantieri Sanna” from the area of Montevecchio Ponente. There is a large amount of mining residues in the area downstream of the washing plants, affected by important erosion phenomena, which involve a solid transport of contaminants in solution. These mineral residues were characterized by diffractometric (XRD) and chemical analysis (ICP-MS), after their solubilization. The whitish biomineral patinas present along the Rio Roia Cani were also analyzed by means of diffractometric analysis and a scanning electron microscope (SEM). From the analysis carried out, the presence of secondary phases emerged, such as: epsomite, glaucocerinite, goethite, hydroxyapatite, minium, nantokite, plumbojarosite and zincite, indicating a remarkable reactivity of the tailings with atmospheric agents; these results made it possible to identify tailings as a source of contamination. Furthermore, the presence of sub-economic contents of rare earths elements (REE), more particularly of light rare earths elements (LREE), and of Al, Fe, Pb and Zn emerged. Biomineralization occurs in the area was found in the streambed of rio Roja Cani; it appears like that which forms in the bed of the rio Naracauli, described in detail in Medas et al. (2014). SEM-EDS analysis confirm that biomineralization is mediated by bacterial activity, due to the filamentous and tubular structures present in biofilms; furthermore, the presence of zinc and oxygen emerges from the compositional maps, confirming that the biomineralization is composed of hydrozincite, as revealed by the XRD analysis. We argued that this biomineralization rules natural attenuation of zinc as already found in rio Naracauli (Wanty et al., 2013; De Giudici et al., 2014).