Cristina Carbone

Genetic evolution of nanocrystalline Fe oxide and oxyhydroxide assemblages from the Libiola mine (eastern Liguria, Italy) structural and microstructural investigations

The Libiola Fe-Cu-sulphide mine, near Sestri Levante (eastern Liguria), represents one of the most extensively exploited sulphide deposits in Italy. In this area, active Acid Rock Drainage (ARD) processes are evident. The major resulting mineral phases are Fe oxides and oxyhydroxides, occurring in varicoloured crusts on the surface of waste rocks and in unconsolidated muds. In this study, the Fe assemblages of the waste rock were investigated by microchemical (SEM), structural (XRD), microstructural (TEM) and spectroscopic (DRS, IR, μ-Raman) techniques, in order to determine the phase composition, the textural relations among the minerals and their genetic evolution. They are characterized by intimate intergrowths of hematite and goethite with minor quartz and lepidocrocite; in some samples, the presence of very minor schwertmannite was detected. TEM and HR-TEM observations revealed that hematite is present within pseudo-elliptical bodies as pseudo-hexagonal to subrounded nanocrystalline lamellae (from 18.9 to 26.5 nm in diameter), whereas goethite occurs either as parallel intergrowths of acicular crystals (from 10 to 16.3 μm in length) or as sheaf-like assemblages. On the basis of the present data, the studied Fe oxide and oxyhydroxide assemblages are found to represent distinct spatial and temporal stages of a nano-scale evolution process.

Weissite from Gambatesa mine, Val Graveglia, Liguria, Italy: occurrence, composition and determination of the crystal structure

Abstract Weissite, Cu2−xTe (x ≈ 0.21), a very rare copper telluride, occurs in a sample from the Gambatesa mine, Val Graveglia, Liguria, Italy, where it occurs as purplish black anhedral grains up to 0.1 mm in length and shows a black streak. No cleavage is observed and the Vickers hardness (VHN100) is 142 kg/mm2. Weissite is dark bluish black, weakly pleochroic, and moderately anisotropic in bluish tints. Reflectance percentages in air for Rmin and Rmax are 37.0, 38.4 (471.1 nm), 33.2, 34.2 (548.3 nm), 31.2, 32.1 (586.6 nm), and 28.6, 31.0 (652.3 nm), respectively. Weissite is trigonal and belongs to the space group P3m1 with the following unit-cell parameters: a = 8.3124(7) Å c = 21.546(1) Å , V = 1289.3(2)Å3, and Z = 24. Electron microprobe analyses gave the chemical formula (Cu1.62Ag0.04Au0.04Fe0.04Sb0.04)∑=1.78(Te0.96S0.02Se0.02). The crystal structure has been solved and refined to R = 1.95%. It consists of Cu and Te polyhedra forming complex crystal-chemical environments as is typical of many intermetallic compounds. The exceedingly short bond distances observed among the metals are discussed in relation to other copper tellurides and pure metals.

Marine sediment contamination and dynamics at the mouth of a contaminated torrent: The case of the Gromolo Torrent (Sestri Levante, north-western Italy)

In this study we have examined the currents and hydrological characteristics of the water column off the mouth of the Gromolo Torrent (north-western Italy) in relation to the grain-size, mineralogical characteristics and metal distribution in the marine sediment sampled. Our purpose was to quantify and map the contamination that was carried out to sea from the abandoned Libiola Fe-Cu sulphide mine that has heavily impacted the torrent. Our results show high concentrations of Cu and Zn, and relatively high concentrations of Cd and Ni inside the bay into which the Gromolo Torrent flows. However, high concentrations of As, Cr, Hg, Mn, Pb, and V found in the northern and/or eastern parts of the study area originated from other sources. The subdivision of study stations in terms of metal and mineral contents in the bottom sediments highlighted the clear influence of the currents on their dispersion and distribution in the area.

Cerchiaraite-(Fe) and cerchiaraite-(Al), two new barium cyclosilicate chlorides from Italy and California, USA

Abstract The ideal formula for members of the cerchiaraite group is Ba4M4(Si4O12)O2(OH)4Cl2[Si2O3(OH)4], where M represents Mn3+, Fe3+ or Al in the octahedral site. A suffix-based naming scheme is used in which the original cerchiaraite is renamed cerchiaraite-(Mn) and two new minerals are named cerchiaraite-(Fe) and cerchiaraite-(Al). The type localities for cerchiaraite-(Fe) are the Cerchiara mine, Liguria, Italy and the Esquire No. 7 and No. 8 claims, Big Creek, Fresno County, California, USA. The type localities for cerchiaraite-(Al) are the Esquire No. 1 claim, Rush Creek, Fresno County, California, USA and the Esquire No. 7 and No. 8 claims noted above. At the Cerchiara mine, cerchiaraite-(Fe) occurs in small fractures and veinlets in a Jurassic ophiolitic sequence. It is of secondary hydrothermal origin and occurs as tan to brown thin prisms and matted fibres. Cerchiaraite- (Fe) and cerchiaraite-(Al) from the Esquire No. 1, No. 7 and No. 8 claims occur in parallel-bedded quartz-sanbornite vein assemblages which formed as a result of fluid interaction along the margin of the vein. At the Esquire No. 1, No. 7 and No. 8 claims, both cerchiaraite-(Fe) and cerchiaraite-(Al) occur as subparallel aggregates of blue to bluish green irregular prisms. Both minerals are transparent with a vitreous lustre, Mohs hardness ~4½, brittle tenacity, irregular fracture and no cleavage. The calculated density of cerchiaraite-(Fe) is 3.710 g cm-3; the measured density of cerchiaraite-(Al) is 3.69(3) g cm-3 and the calculated density is 3.643 g cm-3. Cerchiaraite-(Fe) is uniaxial (+), with ω = 1.741(2) and Ɛ = 1.768(2); it is weakly pleochroic and O is colourless and E is yellow. Cerchiaraite- (Al) is uniaxial (-), with ω = 1.695(2) and Ɛ = 1.677(2); it is strongly pleochroic and O is colourless and E is blue. Electron-microprobe analyses yielded empirical formulae ranging from (Ba3.82Na0.02Ca0.04)Σ3.88(Fe3.423+Ti0.274+Al0.253+Mn0.043+Mg0.02)Σ4.00Si5.62O15.47(OH)9.31Cl2.22 (Cerchiara mine) to Ba4.00(Al2.403+Fe1.123+Mg0.15Fe0.122+Mn0.062+)Σ3.85Si5.78O15.34(OH)8.75Cl2.91 (Esquire No. 1 claim). Cerchiaraite is tetragonal with Z = 2 and crystallizes in space group I4/mmm. The cell parameters for cerchiaraite-(Fe) are a = 14.3554(12), c = 6.0065(5) Å and V = 1237.80(5) Å3; those for cerchiaraite- (Al) are a = 14.317(4), c = 6.0037(18) Å and V = 1230.6(6) Å3. In the cerchiaraite-(Fe) structure, SiO4 tetrahedra share corners forming a four-membered Si4O12 ring. The ring is corner-linked to an edgesharing chain of Fe3+O6 octahedra running parallel to c. A Cl site alternates along c with the Si4O12 ring. A large channel in the framework contains Ba atoms around its periphery and statistically distributed Si2O7 silicate dimers and Cl atoms. The strong blue pleochroic colour is attributed to Fe2+-Fe3+ intervalence charge transfer along the octahedral chain.

Application of synchrotron radiation-based techniques (μ-XRD, μ-XRF, and μ-XANES) to study Fe-rich hardpans within waste-rock dump

Recently, several techniques based on synchrotron radiation have been applied to environmental sciences giving the possibility for non-destructive investigations with micrometer spatial resolution. In particular, a combination of synchrotron methods (μ-XRF, μ-XRD, and μ-XAS) have been undertaken to investigate the metals speciation in mine wastes and soils. With this work, after a review on the mineralogical aspects of sulphide-rich waste-rock deposits and the application of synchrotron- based techniques for their characterization, we present a combined synchrotron-based μ-XRD, μ-XRF, and μ-XANES study to determine the mineralogy and the elemental distribution of metals in partially altered sulphide-mineralization fragments deposited within an open-air waste-rock dump (Libiola mine, eastern Liguria, Italy). The selected samples are composed of heterogeneous assemblages of Fe-bearing precipitates formed as a consequence of Fe-Cu sulphide alteration processes that occur within the main waste rock dump of the mining area. The results evidenced that the authigenic iron-rich phases generally contain signifi cant amounts of hazardous elements such as Cu, Zn, Mo, As, and Se. Moreover, a signifi cant mineralogical control on the mobility of these elements have been observed; in particular, the goethite-rich assemblages show high affi nity for Cu and Zn, whereas hematite-rich assemblages selectively concentrate As, Se, Mo, Cu and Zn.

Mineralogical and chemical variations of ochreous precipitates from acid sulphate waters (asw) at the Roşia Montană gold mine (Romania)

The mineralogical and chemical variations of ochreous precipitates forming from acid sulphate waters discharged from the lowest mine adit (“Sf. Cruci din Orlea”) of the Roşia Montană Gold Mine (Romania) were investigated by a multianalytical approach (XRPD, IR, TEM, ICP) applied to surface precipitates and associated waters. The mineralogy of the precipitates changed significantly as a consequence of the variations in the chemical parameters of the circulating solutions (mainly pH, Eh, and sulphate concentrations) which were mainly controlled by mixing with unpolluted waters of Roşia River. Ochreous precipitates are characterized by high concentrations of potentially toxic elements (PTEs; in particular Cr, Co, Ni, Cu, Zn, As, Cd, and Pb) and consist of a mixture, in variable proportion, of jarosite and schwertmannite, which represent the stable secondary minerals along the investigated transect of Roşia River. Particular regard is given to the ability of authigenic phases to selectively scavenge selected PTEs from contaminated solutions during their genesis and minerogenetic evolution. Furthermore, laboratory kinetic batch experiments on natural heterogeneous samples of ochreous precipitates were carried out to investigate the release processes involving PTEs and to verify the type and the amount of elements that can be temporarily/permanently trapped by the solid phase from the contaminated solutions. The comparative analysis of the precipitates and waters of the Roşia Montană mining area indicated that the role of secondary minerals as “mitigating agents” can be limited because even minor pH–Eh oscillations would cause mineralogical transformations that could lead to trace elements mobilization in the environment.

Mcalpineite from the Gambatesa mine, Italy, and redefinition of the species

Abstract Mcalpineite has been found in the Gambatesa mine (eastern Liguria, Italy). It occurs in a quartz vein mainly as yellowish green earthy crusts consisting of poorly crystallized mcalpineite intergrown with an unidentified Cu-Te phase, as well as quite pure aggregates of well euhedral emerald green crystals (individually reaching up to 50 μm), associated with black fragments of paratellurite (TeO2) and weissite (Cu2-xTe). The chemical formula of this rare mineral, found at the McAlpine mine (typelocality; California, U.S.A.) and at the Centennial Eureka mine (Utah, U.S.A., co-type locality), was originally given Cu3TeO6·H2O. X‑ray powder diffraction and selected-area electron diffraction data of mcalpineite are in good agreement with those of synthetic Cu3TeO6. In addition no evidence for structural OH group was detected by micro-Raman analysis carried out on samples from Gambatesa, Centennial Eureka, and McAlpine (co-type sample) mines. Taking into account structural, topological, and experimental evidence, the crystal structure and chemical composition of mcalpineite must be revised: the mineral crystallizes in the Ia3̄ space group and the correct chemical formula is Cu3TeO6.

Bassoite, SrV3O7·4H2O, a new mineral from Molinello mine, Val Graveglia, eastern Liguria, Italy

Abstract Bassoite, ideally SrV3O7·4H2O, is a new mineral from the Molinello manganese mine, Val Graveglia, eastern Liguria, northern Apennines, Italy. It occurs as black euhedral to subhedral grains up to 400 μm across, closely associated with rhodonite, quartz and braunite. Bassoite is opaque with a sub-metallic lustre and a black streak. It is brittle and neither fracture nor cleavage was observed; the Vickers micro-hardness (VHN100) is 150 kg/mm2 (range 142-165; corresponding to a Mohs hardness of 4-4½). The calculated density is 2.940 g/cm3 (on the basis of the empirical formula and X-ray single-crystal data). Bassoite is weakly bireflectant and very weakly pleochroic from grey to a dark green. Internal reflections are absent. The mineral is anisotropic, without characteristic rotation tints. Reflectance percentages (Rmin and Rmax) for the four standard COM wavelengths are 18.5%, 19.0% (471.1 nm); 17.2%, 17.8% (548.3 nm); 16.8%, 17.5% (586.6 nm) and 16.2%, 16.8% (652.3 nm), respectively. Bassoite is monoclinic, space group P21/m, with unit-cell parameters: a = 5.313(3) Å, b = 10.495(3) Å, c = 8.568(4) Å, β = 91.14(5)º, V = 477.7(4) Å3, a:b:c = 0.506:1:0.816, and Z = 2. The crystal structure was refined to R1 = 0.0209 for 1148 reflections with Fo > 4σ(Fo) and it consists of layers of VO5 pyramids (with vanadium in the tetravalent state) pointing up and down alternately with Sr between the layers (in nine-fold coordination). The nine most intense X-ray powder-diffraction lines [d in Å (I/I0) (hkl)] are: 8.5663 (100) (001); 6.6363 (14) (011); 3.4399 (14) (1̄21); 3.4049 (17) (121); 2.8339 (15) (1̄22); 2.7949 (11) (122); 2.6550 (15) (200); 2.6237 (11) (040) and 1.8666 (15) (240). Electron microprobe analyses produce a chemical formula (Sr0.97Ca0.02Na0.01)V3.00O7·4H2O, on the basis of ∑(Sr+Ca+Na) = 1, taking the results of the structure refinement into account. The presence of water molecules was confirmed by micro-Raman spectroscopy. The name honours Riccardo Basso (b. 1947), full professor of Mineralogy and Crystallography at the University of Genova. The new mineral and mineral name have been approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2011-028).

Plant Colonization on a Contaminated Serpentine Site

Abstract This study evaluated relationships between the serpentine soil from a waste-rock dump of the abandoned Libiola sulphide mine (NW Italy) and its pioneer vegetation. We identified the tolerance of various species to environmental conditions and evaluated physical or chemical factors that influenced the first plants to colonize this stressful environment. Thirteen sampling sites were identified in the rock dump from characterization of surface or near-surface oxidation zone and vegetation type. Sampling sites were analyzed for slope, pH, mineralogy, soil chemistry, floristic composition, and the percent coverage of each species. In all the plots, species richness and vegetation cover were extremely low. The flora showed an acidophilous character.

Cassagnaite, a new, V-bearing silicate mineral from the Cassagna mine, northern Apennines, Italy

Cassagnaite occurs at the Cassagna manganese mine (Eastern Liguria, Italy), filling fractures in braunite +quartz layered mineralizations together with piemontite. It occurs as very rare isolated prismatic to tabular {001} crystals, usually elongated along [100], and as entangled aggregates of a few crystals. Few aggregates consist of very small cassagnaite crystals (maximum size up to 0.05 mm) closely associated with much larger piemontite, quartz, and braunite crystals. The crystals are generally very small, with a maximum size up to 0.1 mm, golden brown in colour, transparent with vitreous lustre. The crystal structure, refined in the space group Cmcm with cell parameters a = 6.066(1) A, b = 8.908(1) A, c = 18.995(2) A and Z = 2, may be described as a layer stacking along [001] of a fundamental building block of composition [M1 2 (OH) 2 (SiO 4 ) 2 ] 4− that alternates with intersheets, randomly occurring in a ratio ideally 1:1, of type 1 [(Ca, Mn 2+ ) 2 SiO 2 ] 4+ and of type 2 (Ca, Mn 2+ ) 2 M2 2 (OH) 2 O 2 ] 4+ , where Fe 3+ and Mn 3+ populate 3/4 of the M1 site and Al the remaining 1/4, while V 3+ , Mg and Al occupy in nearly equal proportions the M2 site. The simplified formula, inferred from chemical analyses, structure refinement and crystal-chemical considerations, may be written as (Ca, Mn 2+ ) 4 (Fe 3+ , Mn 3+ , Al) 4 (OH) 4 (V 3+ , Mg, Al) 2 (O, OH) 4 (SiO 4 ) 2 (Si 3 O 10 ). From the composition of the “dominant” end-member of the complex solid-solution the end-member formula Ca 4 Fe 4 3+ (OH) 4 V 2 3+ O 2 (OH) 2 (SiO 4 ) 2 (Si 3 O 10 ) may be proposed for cassagnaite. So, cassagnaite may be classified as sorosilicate with insular and triple tetrahedral groups and belongs to the ardennite group in Dana’s classification.