Anna Vymazalová

The system Ag–Pd–Te: phase relations and mineral assemblages

Abstract The phase equilibria in the system Ag−Pd−Te were studied by the technique of using an evacuated silica glass tube at 350° and 450°C. Five ternary phases were synthesized: sopcheite (Pd3Ag4Te4), lukkulaisvaaraite (Pd14Ag2Te9), telargpalite (Pd2−xAg1+xTe) and the previously unknown phases Pd7.5−xAg0.5+xTe3 and Pd2+xAg2−xTe. The synthetic telargpalite has a compositional range from 26 to 29 wt.% Ag, with the formula Pd2−xAg1+xTe, where x varies from 0.09 to 0.22. The phase Pd2+xAg2−xTe has a compositional range from 34 to 35 wt.% Ag, where x varies from 0.18 to 0.24. The phase Pd7.5−xAg0.5+xTe3 forms a solid solution from 4 to 11 wt.% Ag, where x varies from 0.02 to 0.83. Phases Pd20Te7 and Pd13Te3 dissolve up to 3.5 and 2 wt.% Ag, respectively. Other binary palladium tellurides do not dissolve Ag. The phase Pd3Ag4Te4, an analogue of the mineral sopcheite, forms a stable association with hessite and kotulskite it also coexists with lukkulaisvaaraite. Sopcheite is stable up to 383°С. Natural occurrences of hessite, kotulskite and lukkulaisvaaraite together in equilibrium indicate formation above this temperature. Phase relations defined the mineral assemblages that can be expected to occur in nature. The phase Pd7.5−xAg0.5+xTe3 potentially represents a new mineral; it will probably be found in association with lukkulaisvaaraite and telargpalite or telluropalladinite, among other platinum-group minerals. The phase Pd2+xAg2−xTe can be found in association with telargpalite. Mineral assemblages defined in this study can be expected in Cu-Ni-PGE mineral deposits, associated with mafic and ultramafic igneous rocks, particularly in mineralized zones with known silver-palladium tellurides.

Poorly crystalline Pd–Hg–Au intermetallic compounds from Córrego Bom Sucesso, southern Serra do Espinhaço, Brazil

Potarite, ideally PdHg, is reported in the literature to have compositions varying from PdHg or Pd(Hg,Au) to Pd3Hg2. Such a Pd3Hg2 phase is unknown in the synthetic Pd–Hg binary system. For the first time, Pd–Hg grains recovered from the historical Bom Sucesso alluvium, regarded as the type locality of Pd, are shown to consist of arborescent and lamellar intergrowths of two intermetallic compounds, compositionally close to empirical Pd(Hg,Au), i.e. auriferous potarite, and (Pd,Au)3Hg2. The Pd–Hg–Au grains have a rim of palladiferous Pt. The otherwise sharp Pd–Hg–Au intergrowths become diffuse at the contact with the palladiferous Pt rim. Both the Pd–Hg–Au compounds and the palladiferous Pt rim did not diffract using the electron-backscattered diffraction (EBSD) and powder X-ray microdiffraction techniques, indicating that they are poorly crystalline. Their poor crystallinity and the diffuse zone between the Pd–Hg–Au core and the Pt-rich overgrowth are suggestive of electrochemical metal precipitation from dilute solutions within the alluvium.

Lukkulaisvaaraite, Pd14Ag2Te9, a new mineral from Lukkulaisvaara intrusion, northern Russian Karelia, Russia

Abstract Lukkulaisvaaraite, Pd14Ag2Te9, is a new platinum-group mineral discovered in the Lukkulaisvaara intrusion, northern Russian Karelia, Russia. In polished section crystals are ~40 μm across, rimmed by tulameenite and accompanied to varying degrees by telargpalite and Bi-rich kotulskite. Lukkulaisvaaraite is brittle, has a metallic lustre and a grey streak. Values of VHN20 fall between 339 and 371 kg mm-2, with a mean value of 355 kg mm-2, corresponding to a Mohs hardness of ~4. In plane-polarized light, lukkulaisvaaraite is light grey with a brownish tinge, has strong bireflectance, light brownish-grey to greyish-brown pleochroism and distinct to strong anisotropy; it exhibits no internal reflections. Reflectance values of lukkulaisvaaraite in air (R1, R2, in %) are: 40.9, 48.3 at 470 nm, 47.6, 56.4 at 546 nm, 52.1, 61.0 at 589 nm and 57.5, 65.2 at 650 nm. Five electron microprobe analyses of natural lukkulaisvaaraite gave the average composition Pd 52.17, Ag 7.03 and Te 40.36, total 99.61 wt.%, corresponding to the empirical formula Pd14.05Ag1.88Te9.06 based on 25 atoms; the average of nine analyses on synthetic lukkulaisvaaraite is Pd 52.13, Ag 7.31 and Te 40.58, total 100.02 wt.%, corresponding to Pd13.99Ag1.93Te9.08. The mineral is tetragonal, space group I4/m, with a = 8.9599(6), c = 11.822(1) Å , V = 949.1(1) Å3 and Z = 2. The crystal structure was solved and refined from the powder X-ray diffraction (XRD) data of synthetic Pd14Ag2Te9. Lukkulaisvaaraite has a unique structure type and shows similarities to that of sopcheite (Ag4Pd3Te4) and palladseite (Pd17Se15). The strongest lines in the powder XRD pattern of synthetic lukkulaisvaaraite [d(Å),I,hkl] are: 2.8323(58)(130,310), 2.8088(92),(213), 2.5542(66)(312), 2.4312(41)(321,231), 2.1367(57)(411,141), 2.1015(52)(233,323), 2.0449(100)(314), 2.0031(63)(420,240), 1.9700(30)(006), 1.4049(30)(246,426), 1.3187(36)(543,453). The mineral is named for the type locality, the Lukkulaisvaara intrusion in Russian Karelia.

Synthesis and crystal structure of tischendorfite, Pd 8 Hg 3 Se 9

The synthetic analogue of the mineral tischendorfite, Pd 8 Hg 3 Se 9 , was prepared using the silica glass tube technique and its crystal structure was solved and refined from powder X-ray diffraction data. The structure is orthorhombic, space group Pmmn , with a = 7.1886(2), b = 16.8083(5), c = 6.4762(2) A, V = 782.51(4) A 3 and Z = 2. There are three Pd, two Hg and four Se independent positions. Tischendorfite crystallizes in a framework structure, where Pd atoms show two types of coordination by Se atoms: [PdSe 4 ] squares and [PdSe 5 ] pyramids. The [PdSe 5 ] pyramid shares two opposite Se–Se edges with adjacent pyramids forming linear isolated chains running along the a -axis, whereas [PdSe 4 ] squares are paired via one common Se–Se edge. The paired squares and chains of pyramids form characteristic slabs parallel to (010). Both types of slabs alternate along the b -axis. The Hg atoms occupy the anti-cubooctahedral voids formed by Se atoms. The structure is stabilized by a system of Pd–Hg and Pd–Pd metallic bonds.

Kitagohaite, Pt7Cu, a new mineral from the Lubero region, North Kivu, Democratic Republic of the Congo

Abstract Kitagohaite, ideally Pt7Cu, is a new mineral from the Lubero region of North Kivu, Democratic Republic of the Congo. The mineral occurs as alluvial grains that were recovered together with other Pt-rich intermetallic compounds and Au. Kitagohaite is opaque, greyish white and malleable and has a metallic lustre and a grey streak. In reflected light, kitagohaite is white and isotropic. The crystal structure of kitagohaite is cubic, space group Fm3̄m, of the Ca7Ge type, with a = 7.7891(3) Å, V = 472.57(5) Å3 and Z = 4. The strongest diffraction lines [d in Å (I)(hkl)] are: 2.246 (100)(222), 1.948(8)(004), 1.377 (77)(044), 1.174(27)(622), 1.123 (31)(444) and 0.893 (13)(662). The Vickers hardness is 217 kg mm-2 (VHN100), which is equivalent to a Mohs hardness of 3 ½ and the calculated density is 19.958(2) g cm-3. Electron-microprobe analyses gave a mean value (n = 13) of 95.49 wt.% Pt and 4.78 wt.% Cu, which corresponds to Pt6.93Cu1.07 on the basis of eight atoms. The new mineral is named for the Kitagoha river, in the Lubero region.

Crystal structure and powder diffraction pattern of high-temperature modification of Pd73Sn14Te13

Crystal structure of high-temperature modification of Pd 73 Sn 14 Te 13 has been refined by the Rietveld method from laboratory X-ray powder diffraction data. Refined crystallographic data of Pd 73 Sn 14 Te 13 are a =7.6456(3) A, c =13.9575(9) A, V =706.75(6) A 3 , space group P 6 3 cm (No. 185), Z =6, and D x =10.71 g/cm 3 . The title compound is isostructural with Pd 5 Sb 2 and Ni 5 As 2 ; it can be considered as a stacking and filling variant of the Ni 2 In structure. An important structural feature in the high-temperature modification of Pd 73 Sn 14 Te 13 is the presence of various Pd-Pd bonds.

Powder X-ray diffraction study of synthetic PdSn

Improved X-ray powder diffraction data for synthetic PdSn are reported. Powder diffraction data were collected with a laboratory X-ray source (Cu K α ) for Rietveld refinement. Refined crystallographic data for PdSn (orthorhombic, P n m a ) are a =6.1388(4), b =3.89226(3), c =6.3377(4) A, V =151.43(2) A 3 , Z =4, and D x =9.87 g∕cm 3 .

Norilskite, (Pd,Ag)7Pb4, a new mineral from Noril'sk-Talnakh deposit, Russia

Abstract Norilskite, (Pd,Ag)7Pb4 is a new platinum-group mineral discovered in the Mayak mine of the Talnakh deposit, Russia. It forms anhedral grains in aggregates (up to ∼400 μm) with polarite, zvyagintsevite, Pd-rich tetra-auricupride, Pd-Pt bearing auricupride, Ag-Au alloys, (Pb,As,Sb) bearing atokite, mayakite, Bi-Pb-rich kotulskite and sperrylite in pentlandite, cubanite and talnakhite. Norilskite is brittle, has a metallic lustre and a grey streak. Values of VHN20 fall between 296 and 342 kg mm-2, with a mean value of 310 kg mm-2, corresponding to a Mohs hardness of ∼4. In plane-polarized light, norilskite is orangebrownish pink, has moderate to strong bireflectance, orange-pink to greyish-pink pleochroism, and strong anisotropy; it exhibits no internal reflections. Reflectance values of norilskite in air (Ro, Re′ in %) are: 51.1, 48.8 at 470 nm, 56.8, 52.2 at 546 nm, 59.9, 53.5 at 589 nm and 64.7, 55.5 at 650 nm. Sixteen electronmicroprobe analyses of natural norilskite gave an average composition: Pd 44.33, Ag 2.68, Bi 0.33 and Pb 52.34, total 99.68 wt.%, corresponding to the empirical formula (Pd6.56Ag0.39)Σ6.95(Pb3.97Bi0.03)Σ4.00 based on 4 Pb + Bi atoms; the average of eight analyses on synthetic norilskite is: Pd 42.95, Ag 3.87 and Pb 53.51, total 100.33 wt.%, corresponding to (Pd6.25Ag0.56)Σ6.81Pb4.00. The mineral is trigonal, space group P3121, with a = 8.9656(4), c = 17.2801(8) Å, V = 1202.92(9) Å3 and Z = 6. The crystal structure was solved and refined from the powder X-ray diffraction data of synthetic (Pd,Ag)7Pb4. Norilskite crystallizes in the Ni13Ga3Ge6 structure type, related to nickeline. The strongest lines in the powder X-ray diffraction pattern of synthetic norilskite [d in Å (I) (hkl) ] are: 3.2201(29)(023,203), 2.3130(91)(026,206), 2.2414(100)(220), 1.6098(28)(046,406), 1.3076(38)(246,462), 1.2942(18)(600), 1.2115(37)(22.12,12.13), 0.9626(44) (06.12,60.12). The mineral is named for the locality, the Noril’sk district in Russia.

Kojonenite, a new palladium tin telluride mineral from the Stillwater Layered Igneous Intrusion, Montana, U.S.A.

Abstract Kojonenite, Pd7-xSnTe2 (where 0.3 ≤ x ≤ 0.8), is a new mineral (IMA 2013-132) discovered in specimens from the Stillwater Layered Igneous Intrusion, Stillwater Valley, Montana, U.S.A. (45°23′11′′N and 109°53′03′′W). Synthetic kojonenite is tetragonal, space group I4/mmm, with a = 4.001(1) Å and c = 20.929(3) Å giving V = 335.0(1) Å3 with Z = 2. Strongest lines in the synthetic powder pattern [PDF 01-073-5652] are (d in Å, I, hkl) 10.465, 29, 002; 2.496, 52, 114; 2.1986, 100, 116; 2.0930, 18, 00 10; 2.0025, 48, 200. Identity between natural and synthetic kojonenite is illustrated by an electron backscattered diffraction (EBSD) study. Reflectance data for natural kojonenite for the four COM wavelengths are [λ (nm), Ro, Re′] 470, 55.0, 52.7; 546, 58.5, 56.5; 589, 61.0, 58.3; 650, 63.9, 60.1 and the mineral is uniaxial negative. Electron microprobe analysis of natural kojonenite yields a simplified formula of Pd6SnTe2 that extends the range reported for the synthetic of Pd7-xSnTe2 (where 0.3 ≤ x ≤ 0.8).

Experimental Aspects of Platinum-Group Minerals

Abstract This Chapter consolidates the experimental methods that can be applied for the synthesis of platinum-group compounds and minerals. Dry synthesis and the principal experimental methods used to obtain single crystals are summarized. Examples of crystal growth and synthesis conditions for selected platinum-group phases and minerals are shown and discussed. We present an updated list of platinum-group minerals (PGMs) since the revision of Cabri (2002); there are now 136 recognized PGM. PGMs with revised crystal structures are also listed. We provide an overview of 27 PGMs described since 2002 and discuss their experimental aspects. We summarize the ternary PGM and corresponding systems, and summarize the data available on phase diagrams in the literature. This chapter encourages the application of experimental studies for a better understanding of the PGM, their formation and occurrence under natural conditions.