First insights into the mineralogy of the tailings dump of the Lojane Sb-As(-Cr) deposit, FYR of Macedonia

The abandoned Sb-As(-Cr) deposit Lojane in north-east Macedonia was mined for realgar, stibnite, and chromite until 1979. The mine site and associated waste and tailings dumps, located close to a school and some small villages, are a substantial source of antimony, arsenic, and chromium pollution and represent one of the major environmental problems for the country. More than one million tons of tailings containing As, Sb, and other hazardous substances are located in an open dumpsite for flotation waste. The tailings dam is completely unprotected and its orange colour (clearly visible from satellite images) suggests a high concentration of arsenic sulphides (Alderton et al., 2014). We have performed some preliminary characterization of waste samples from the tailings dump near Vaksince village using single-crystal and powder X-ray diffraction techniques which showed that the porous samples are comprised mostly of well crystallized realgar (70 vol.%), quartz (16 %), gypsum (11 %), and minor amounts of chromite, calcite, and sulphur. Additional SEM-EDS and Raman spectroscopic studies of selected polished sections confirmed that the majority of the dump material consists of realgar fragments about 50-150 μm in size, which are invariably coated by thin crusts of an As–Sb–Fe-oxide/hydroxide (with traces of S, Ca, Na, K, and Al) in which the As:Sb ratio varies from ca. 2:1 to 1:2.2, Fe contents being variable. This generally inhomogeneous oxide appears to be microcrystalline but may in part be amorphous; crystalline forms probably belong, at least in part, to the roméite group. Besides forming < 10 μm crusts (mostly As-dominant) around realgar and stibnite grains, Sb-dominant variants of this oxide also form larger homogeneous grains up to 500 μm, characterised by broad dehydration cracks and suggesting original formation as a gel. Very rare relic chromite and, less commonly, magnesiochromite are always Al-bearing and occur as anhedral, unaltered fragments (up to ~50 μm) which are chemically homogeneous but show minor variations of the Cr:Al and Fe:Mg ratios among different grains. Also confirmed were, in approximate order of decreasing abundance, gypsum, quartz, stibnite (superficially corroded grains between 1 and 100 μm in size, partly embedded in either quartz or realgar), pyrite (tiny euhedral crystals in quartz; always As-bearing, with up to ~5 at.% pfu), gersdorffite, scorodite, limonite, kaˇnkite(?), vaesite, magnetite, As-bearing sulphur, muscovite to illite, kaolinite-group representatives, fluorapatite, albite, rutile, and annabergite

Arsenic in roméite-group minerals formed by weathering of realgar-rich tailings (Lojane mine, North Macedonia)

Realgar and stibnite are the primary sources of arsenic and antimony contamination of the soils and water at the Sb–As–Cr Lojane mine (abandoned since 1979) in North Macedonia. The waste material comprises various waste dumps, an unprotected flotation tailings dump, and waste from a smelter. We have studied the association of As and Sb in realgar and stibnite weathering products from material sampled at the subsurface of the realgar-rich (up to 60 wt% realgar), fine-grained (20 to 100 μm) and porous tailings which contain significant amounts of stibnite (up to 13.5 wt%) [1]

Fluor-schorl, a new member of the tourmaline supergroup, and new data on schorl from the cotype localities

Fluor-schorl, NaFe^(2+) _3Al_6Si_6O_(18)(BO_3)_3(OH)_3F, is a new mineral species of the tourmaline supergroup from alluvial tin deposits near Steinberg, Zschorlau, Erzgebirge (Saxonian Ore Mountains), Saxony, Germany, and from pegmatites near Grasstein (area from Mittewald to Sachsenklemme), Trentino, South Tyrol, Italy. Fluor-schorl was formed as a pneumatolytic phase and in high-temperature hydrothermal veins in granitic pegmatites. Crystals are black (pale brownish to pale greyish-bluish, if distance (r^2 = 0.93). This correlation indicates that Fe^(2+)-rich tourmalines from the investigated localities clearly tend to have a F-rich or F-dominant composition. A further strong positive correlation (r^2 = 0.82) exists between the refined F content and the Y–W (F,OH) distance, and the latter may be used to quickly estimate the F content

Limitations of Fe^(2+) and Mn^(2+) site occupancy in tourmaline: Evidence from Fe^(2+)- and Mn^(2+)-rich tourmaline

Fe^(2+)- and Mn^(2+)-rich tourmalines were used to test whether Fe^(2+) and Mn^(2+) substitute on the Z site of tourmaline to a detectable degree. Fe-rich tourmaline from a pegmatite from Lower Austria was characterized by crystal-structure refinement, chemical analyses, and Mössbauer and optical spectroscopy. The sample has large amounts of Fe^(2+) (~2.3 apfu), and substantial amounts of Fe^(3+) (~1.0 apfu). On basis of the collected data, the structural refinement and the spectroscopic data, an initial formula was determined by assigning the entire amount of Fe^(3+) (no delocalized electrons) and Ti^(4+) to the Z site and the amount of Fe^(2+) and Fe^(3+) from delocalized electrons to the Y-Z ED doublet (delocalized electrons between Y-Z and Y-Y): X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(2.0)Al_(0.4)Mn^(2+)_(0.3)Fe^(3+)_(0.2)) ^Z(Al_(4.8)Fe^(3+)_(0.8)Fe^(2+)_(0.2)Ti^(4+)_(0.1)) ^T(Si_(5.9)Al_(0.1))O_(18) (BO_3)_3^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)] with α = 16.039(1) and c = 7.254(1) Å. This formula is consistent with lack of Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of a hopping electron. The formula was further modified by considering two ED doublets to yield: ^X(Na_(0.9)Ca_(0.1)) ^Y(Fe^(2+)_(1.8)Al_(0.5)Mn^(2+)_(0.3)Fe^(3+)_(0.3)) ^Z(Al_(4.8)Fe^(3+)_(0.7)Fe^(2+)_(0.4)Ti^(4+)_(0.1)) ^T(Si_(5.9_Al_(0.1))O_(18) (BO_3)_3 ^V(OH)_3 ^W[O_(0.5)F_(0.3)(OH)_(0.2)]. This formula requires some Fe^(2+) (~0.3 apfu) at the Z site, apart from that connected with delocalization of a hopping electron. Optical spectra were recorded from this sample as well as from two other Fe^(2+)-rich tourmalines to determine if there is any evidence for Fe^(2+) at Y and Z sites. If Fe^(2+) were to occupy two different 6-coordinated sites in significant amounts and if these polyhedra have different geometries or metal-oxygen distances, bands from each site should be observed. However, even in high-quality spectra we see no evidence for such a doubling of the bands. We conclude that there is no ultimate proof for Fe^(2+) at the Z site, apart from that occupancy connected with delocalization of hopping electrons involving Fe cations at the Y and Z sites. A very Mn-rich tourmaline from a pegmatite on Elba Island, Italy, was characterized by crystal-structure determination, chemical analyses, and optical spectroscopy. The optimized structural formula is ^X(Na_(0.6)□_(0.4)) ^Y(Mn^(2+)_(1.3)Al_(1.2)Li_(0.5)) ^ZAl_6 ^TSi_6O_(18) (BO_3)_3 ^V(OH)_3 ^W[F_(0.5)O_(0.5)], with α = 15.951(2) and c = 7.138(1) Å. Within a 3σ error there is no evidence for Mn occupancy at the Z site by refinement of Al ↔ Mn, and, thus, no final proof for Mn^(2+) at the Z site, either. Oxidation of these tourmalines at 700–750 °C and 1 bar for 10–72 h converted Fe^(2+) to Fe^(3+) and Mn^(2+) to Mn^(3+) with concomitant exchange with Al of the Z site. The refined ^ZFe content in the Fe-rich tourmaline increased by ~40% relative to its initial occupancy. The refined YFe content was smaller and the distance was significantly reduced relative to the unoxidized sample. A similar effect was observed for the oxidized Mn^(2+)-rich tourmaline. Simultaneously, H and F were expelled from both samples as indicated by structural refinements, and H expulsion was indicated by infrared spectroscopy. The final species after oxidizing the Fe^(2+)-rich tourmaline is buergerite. Its color had changed from blackish to brown-red. After oxidizing the Mn^(2+)-rich tourmaline, the previously dark yellow sample was very dark brown-red, as expected for the oxidation of Mn^(2+) to Mn^(3+). The unit-cell parameter α decreased during oxidation whereas the c parameter showed a slight increase

CsGa(HAsO4)2, the first Ga representative of the RbAl(HAsO4)2 structure type

The crystal structure of hydrothermally synthesized (T = 493 K, 7 d) caesium gallium bis[hydrogen arsenate(V)], CsGa(HAsO4)2, was solved by single-crystal X-ray diffraction. The compound crystallizes in the common RbAl(HAsO4)2 structure type (R32) and consists of a basic tetrahedral–octahedral framework topology that houses Cs+ cations in its channels. The AsO4 tetrahedron is disordered over two positions with site occupancy factors of 0.946 (1) and 0.054 (1). Strong hydrogen bonds strengthen the network. The structure was refined as inversion twin

KInAs2O7, a new diarsenate with the TlInAs2O7 structure type

Potassium indium diarsenate(V) was grown under mild hydrothermal conditions (T = 493 K, 7 d) at a pH value of about 1. It adopts the TlInAs2O7 structure type (P-1, Z = 4) and is closely related to the KAlP2O7 (P21/c) and RbAlAs2O7 (P-1) structure types. The framework topology of KInAs2O7 is built of two symmetrically non-equivalent As2O7 groups which share corners with InO6 octahedra. The K atoms are located in channels extending along [010]

The Crystal Chemistry of Rathite Based on New Electron-Microprobe Data and Single-Crystal Structure Refinements: The Role of Thallium

Crystal-structure refinements in space group P21/c were performed on five grains of rathite with different types and degrees of thallium, silver, and antimony substitutions, as well as quantitative electron-microprobe analyses of more than 800 different rathite samples. The results of these studies both enlarged and clarified the complex spectrum of cation substitutions and the crystal chemistry of rathite. The [Tl+ + As3+] &harr; 2Pb2+ scheme of substitution acts at the structural sites Pb1, Pb2, and Me6, the [Ag+ + As3+] &harr; 2Pb2+ substitution at Me5, and the Sb-for-As substitution at the Me3 site only. The homogeneity range of rathite was determined to be unusually large, ranging from very Tl-poor compositions (0.16 wt%; refined single-crystal unit-cell parameters: a = 8.471(2), b = 7.926(2), c = 25.186(5) &Aring;, &beta; = 100.58(3)&deg;, V = 1662.4(6) &Aring;3) to very Tl-rich compositions (11.78 wt%; a = 8.521(2), b = 8.005(2), c = 25.031(5) &Aring;, &beta; = 100.56(3)&deg;, V = 1678.4(6) &Aring;3). The Ag content is only slightly variable (3.1 wt%&ndash;4.1 wt%) with a mean value of 3.6 wt%. The Sb content is strongly variable (0.20 wt%&ndash;7.71 wt%) and not correlated with the Tl content. With increasing Tl content (0.16 wt%&ndash;11.78 wt%), a clear increase of the unit-cell parameters a, b, and V, and a slight decrease of c is observed, although this is somewhat masked by the randomly variable Sb content. The revised general formula of rathite may be written as AgxTlyPb16&minus;2(x+y)As16+x+y&minus;zSbzS40 (with 1.6 &lt; x &lt; 2, 0 &lt; y &lt; 3, 0 &lt; z &lt; 3.5). Based on Pb&ndash;S bond lengths, polyhedral characteristics and Pb-site bond-valence sums, we conclude that the Pb1 site is more affected by Tl substitution than the Pb2 site. When Tl substitution reaches values above 13 wt% (or 3 apfu), a new phase (&ldquo;SR&rdquo;), belonging to the rahite group, appears as lamellar exsolution intergrowths with Tl-rich rathite (11.78 wt%). Rathite is found only in the Lengenbach and Reckibach deposits, Binntal, Canton Wallis, Switzerland

M+M3+2As(HAsO4)6 (M+M3+ = TlGa, CsGa, CsAl): three new metal arsenates containing AsO6 octahedra

The crystal structures of hydrothermally synthesized (T = 493 K, 7 d) thallium(I) digallium arsenic(V) hexakis[hydrogenarsenate(V)], TlGa2As(HAsO4)6, caesium digallium arsenic(V) hexakis[hydrogenarsenate(V)], CsGa2As(HAsO4)6, and caesium dialuminium arsenic(V) hexakis[hydrogenarsenate(V)], CsAl2As(HAsO4)6, were solved by single-crystal X-ray diffraction. The three compounds are isotypic and adopt the structure type of RbAl2As(HAsO4)6 (R\overline{3}c), which itself represents a modification of the RbFe(HPO4)2 structure type and consists of a tetrahedral–octahedral framework in which the slightly disordered M+ cations are located in channels. The three new compounds contain AsO6 octahedra assuming the topological role of M3+O6 octahedra. The As—O bond lengths are among the shortest As—O bond lengths known so far in AsO6 octahedra