Topsoils near active and abandoned mining and smelting sites are highly polluted by metal(loid) contaminants, which are often bound to particulates emitted from ore processing facilities and/or windblown from waste disposal sites. To quantitatively determine the contaminant partitioning in the soil particulates, we tested an automated mineralogy approach on the heavy mineral fraction extracted from the mining- and smelting-polluted topsoils exhibiting up to 1920 mg/kg As, 5840 mg/kg Cu, 4880 mg/kg Pb and 3310 mg/kg Zn. A new generation of automated scanning electron microscopy (autoSEM) was combined and optimized with conventional mineralogical techniques (XRD, SEM/EDS, EPMA). Parallel digestions and bulk chemical analyses were used as an independent control of the autoSEM-calculated concentrations of the key elements. This method provides faster data acquisition, the full integration of the quantitative EDS data and better detection limits for the elements of interest. We found that As was mainly bound to the apatite group minerals, slag glass and metal arsenates. Copper was predominantly hosted by the sulfides/sulfosalts and the Cu-bearing secondary carbonates. The deportment of Pb is relatively complex: slag glass, Fe and Mn (oxyhydr)oxides, metal arsenates/vanadates and cerussite were the most important carriers for Pb. Zinc is mainly bound to the slag glass, Fe (oxyhydr)oxides, smithsonite and sphalerite. Limitations exist for the less abundant contaminants, which cannot be fully quantified by autoSEM due to spectral overlaps with some major elements (e.g., Sb vs. Ca, Cd vs. K and Ca in the studied soils). AutoSEM was found to be a useful tool for the determination of the modal phase distribution and element partitioning in the metal(loid)-bearing soil particulates and will definitely find more applications in environmental soil sciences in the future.

The Gaching high-sulfidation epithermal deposit in the Maletoyvayam ore field features a wide range of Se-containing minerals and selenides, as well as complex gold oxides, Au tellurides (calaverite, krennerite) and native gold typical for epithermal deposits. Pyrite included in quartzites and quartz-alunite rocks was probably formed during an early stage of the ore-forming process. During the following Au-rich stage, the $f_{{\rm S}{\rm e}_{\rm 2}}$ / $f_{{\rm S}_{\rm 2}}$ increased with $f_{{\rm O}_{\rm 2}}$ being relatively high, resulting in the formation of very rare compounds that have not been previously described in nature. These include Au₂Te₄(Se,S)₃, Se₃Te₂, AuSe and Au(Te,Se,S) phases. The Au₂Te₄(Se,S)₃compounds have some variations in composition: the complete isomorphic series between Au₂Te₄Se₃and Au₂Te₄S₃was observed. The gold and Au-minerals at the main ore stage can be stable within a range of log $f_{{\rm O}_{\rm 2}}$ of −27.3 and atmospheric oxygen (?); log $f_{{\rm S}{\rm e}_{\rm 2}}$ between −12.4 and −5.7; log $f_{{\rm T}{\rm e}_{\rm 2}}$ between −10.5 and −7.8; and log $f_{{\rm S}_{\rm 2}}$ between −12.8 and −6.8 (at 250°C). The increasing oxygen fugacity during the final stage of mineralization resulted in the formation of complex Sb,As,Te,S-bearing Au oxides. Gold-oxide formation occurs due to oxidation of Au-tellurides. The final products of this process are newly-formed secondary mustard gold and Te–Se solid solutions.

Maletoyvayamite, Au₃Se₄Te₆, is a new mineral discovered in a heavy-mineral concentrate from the Gaching occurrence of the Maletoyvayam deposit, Kamchatka, Russia (60°19′51.87″N, 164°46′25.65″E). It forms anhedral grains (10 to 50 μm in size) and is found in intergrowths with native gold (Au–Ag), Au tellurides (calaverite), unnamed phases (AuSe, Au₂TeSe and Au oxide), native tellurium, sulfosalts (tennantite, tetrahedrite, goldfieldite and watanabeite) and supergene tripuhyite. Maletoyvayamite has a good cleavage on {010} and {001}. In plane-polarised light, maletoyvayamite is grey, has strong bireflectance (grey to bluish grey), and strong anisotropy; it exhibits no internal reflections. Reflectance values for maletoyvayamite in air (R_min,R_maxin %) are: 38.9, 39.1 at 470 nm; 39.3, 39.5 at 546 nm; 39.3, 39.6 at 589 nm; and 39.4, 39.7 at 650 nm. Sixteen electron-microprobe analyses of maletoyvayamite gave an average composition: Au 34.46, Se 16.76, Te 47.23 and S 0.84, total 99.29 wt.%, corresponding to the formula Au_2.90(Se_3.52S_0.44)_Σ3.96Te_6.14based on 13 atoms; the average of eleven analyses on synthetic analogue is: Au 34.20, Se 19.68 and Te 45.42, total 99.30 wt.%, corresponding to Au_2.90Se_4.16Te_5.94. The calculated density is 7.98 g/cm³. The mineral is triclinic, space groupP1, witha= 8.901(2),b= 9.0451(14),c= 9.265(4) Å, α = 97.66(3), β = 106.70(2), γ = 101.399(14)°,V= 685.9(4) ųandZ= 2. The crystal structure of maletoyvayamite represents a unique structure type resembling a molecular structure. There are cube-like [Au₆Se₈Te₁₂] clusters linkedviavan der Waals interactions. The structural identity of maletoyvayamite with the synthetic Au₃Se₄Te₆was confirmed by powder X-ray diffraction and Raman spectroscopy.

Gachingite, Au(Te_1–xSe_x), 0.2 ≈ x ≤ 0.5, is a new mineral discovered in the Gaching ore occurrence of the Maletoyvayam epithermal deposit, Kamchatka, Russia. Gachingite forms individual droplet-like grains of sizes from 2 to 10 μm included in native gold (Au–Ag), associated with calaverite, maletoyvayamite, watanabeite and Au–Sb oxides. The aggregates do not exceed 100 μm in diameter. In plane-polarised light, gachingite is grey with a bluish tint, has bireflectance (bluish-grey to deep grey), and strong anisotropy with rotation tints blue to dark blue to brown. Reflectance values for gachingite in air (R_min, R_max in %) are: 39.9, 40.3 at 470 nm; 41.6, 43.3 at 546 nm; 42.0, 43.7 at 589 nm; and 43.0, 44.0 at 650 nm. Eighteen electron-microprobe analyses of gachingite gave an average composition: Au 62.40, Ag 0.57, Se 9.78, Te 27.33 and S 0.01, total 100.09 wt.%, corresponding to the formula (Au_0.96Ag_0.02)_Σ0.98(Te_0.65Se_0.37)_Σ1.02 based on 2 apfu, the simplified formula is Au(Te_0.65Se_0.35); the average analyses of its synthetic analogue is Au 65.7, Se 13.1 and Te 21.1, total 99.9 wt.%, corresponding to Au_1.00(Te_0.50Se_0.50). The calculated density is 10.47 g/cm³. The mineral is orthorhombic, space group Cmce (#64) with a = 7.5379 Å, b = 5.7415 Å, c = 8.8985 Å, V = 385.12 ų and Z = 8. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic Au_1.00(Te_0.50Se_0.50). The crystal structure of gachingite represents a unique structure type, containing linear [Au–Au–Au] chains running along the b-axis indicating strong metallic interaction in one direction. The structural identity of gachingite and its synthetic analogue Au_1.00(Te_0.50Se_0.50) was confirmed by electron back-scatter diffraction and Raman spectroscopy. The formation of gachingite requires an abundant source of Au and Se and a high oxidising environment. Gachingite is related to the gold-bearing productive stage of ore mineralisation, which is stable at 250°C in log $f_{{\rm S}{\rm e}_ 2}$ range of −12.4 and −5.7. The mineral is named after its type locality.