Mineralogical and geochemical spatial analyses of a waste-rock dump at the Libiola Fe–Cu sulphide mine (Eastern Liguria, Italy)

Abstract

In this work, we investigated a 3 ha sulphidebearing waste-rock dump (Libiola Mine, Italy) using mineralogical, geochemical, and geostatistical analyses. The dumped materials were highly heterogeneous in grain size and lithology and varied both laterally and vertically. Other than the host rock of the ore, basalts and serpentinites, the dumped materials contained high amounts of low-grade chalcopyriteand pyrite-rich mineralisations. Due to these characteristics and to the absence of minerals able to neutralise acidity, this waste-rock dump can be classified as an acid mine drainage (AMD) producer. The study confirms that AMD is still active and, in the best scenario, can persist for up to 6.17 9 10 3 years. The consequences of this process are of serious environmental concern as it involves strong acidification of the circulating waters, the release of potentially toxic metals into the soil, streams and rivers and the precipitation of huge quantities of secondary Fe-oxides and Fe-oxyhydroxides.

Biodiversity in Metal-Contaminated Sites – Problem and Perspective – A Case Study

“…Sulphide mineralization occurs within the Jurassic ophiolites of the Northern Apennines (Vara supergroup; [66]) and is geologically characterized primarily by pillow basalts with minor serpentinites, gabbros and ophiolitic breccias. During exploitation, five major waste-rock dumps were built up through the progressive accumulation of heterogeneous sterile rocks (derived from galleries and open-pit excavations) and nonvaluable ore-fragments, with metal concentrations below the economic cut-off produced during beneficiation processes [67]. The soils of the dumps are characterized by severe edaphic conditions due to their peculiar physical (steep slopes, low moisture retainability, impermeabilization due to cementification and hardpan formation; [68]) and chemical (high Cr-, Cu-, Co-, Ni-and Zn-concentrations, low pH values and the low availability of essential macronutrients) properties.…”

“…Most of the dumps evidence strong superficial cementation induced by Fe-oxides precipitating from acid sulphate water seepage, which determines the formation of centimetre-thick impermeable hardpans on several parts of the exposed surface of the dumps [67,68].…”

“…The studied samples are mainly composed of polycrystalline rock fragments, which can be grouped into the following lithological classes [65,67,68]: 1) serpentinites 20%-50%; 2) basalts 5%-10%; 3) sulphide mineralizations (2%-10%); 4) massive Fe-oxyhydroxides and -oxides clasts (35%-65%). Other subordinate components (3%-6%) are represented by garnet-and epidote-rich rodingites, polygenic ophiolitic breccias and brecciated basalts.…”

“…The mineral species occurring within the waste-rock dump [65,67,68] can be divided into three major groups on the basis of their origin and/or origin: 1) host rocks and gangue minerals; 2) ore minerals with different degrees of alteration; 3) authigenic secondary minerals. Serpentine minerals (60%-70% of the recognized mineral species) and Fe-oxyhydroxides (mainly goethite) are by far the most abundant species, respectively representing the main rockforming minerals of the lithotypes of the surrounding area and the main authigenic minerals forming as a result of the ongoing AMD processes.…”

Influence of freeze–thaw dynamics on internal geochemical evolution of low sulfide waste rock

“…The release and transport of oxidation products, progression of acid neutralization and pH, and the appearance and evolution of major cation and trace metal concentrations are well documented in mine tailings Blowes and Jambor, 1990;Lindsay et al, 2009;Moncur et al, 2005) rock (Marescotti et al, 2010;Smith et al, 2013a;Sracek et al, 2004;Stockwell et al, 2006). A conceptual model of the common sequence of acid-neutralization reactions taking place within mine tailings impoundments was described by Jurjovec et al (2002).…”