Sven Karup-Møller

Experimental studies on the phase systems Fe-Ni-Pd-S and Fe-Pt-Pd-As-S applied to PGE deposits

SummaryIn the present paper current results of experimental investigation of the phase system Pd-Fe-Ni-S at 900°C, 725°C, 550°C and 400°C as well as of the phase system Pt-Fe-As-S at 850°C and 470°C are summarized. A preliminary note on the system Pt-Pd-As-S is added. Individual phase assemblages are presented, data on solubility of PGE in base metal sulphides/arsenides or alloys are given and solid solution ranges of important minerals are described as a function of temperature and phase assemblage. The extent and role of sulphide/arsenide melts in these systems are presented together with hints for, and examples of the application of the current experimental results for the explanation of ore-geological processes.ZusammenfassungIn der vorliegenden Arbeit werden bisherige Ergebnisse experimenteller Untersuchungen in den Phasensystemen Pd-Fe-Ni-S bei 900°C, 725°C, 550°C sowie 400°C, bzw. Pt-Fe-As-S bei 850°C und 470°C zusammengefasst. Vorläufige Anmerkungen zum System Pt-Pd-As-S werden gegeben. Die Phasenbeziehungen und die Löslichkeitsdaten von PGEs in Buntmetall-Sulfiden/Arseniden sowie deren Verbindungen werden präsentiert. Die Mischungsbereiche der wichtigsten Minerale werden als Funktion von Temperatur und Phasenvergesellschaftung diskutiert. Die Rolle von Sulfid/Arsenid Schmelzen in diesen Systemen und Beispiele für die Anwendung dieser experimentellen Ergebnisse zur Erklärung lagerstättenkundlicher Prozesse werden beschrieben.

Spheroidal structures in arfvedsonite lujavrite, Ilı́maussaq alkaline complex, South Greenland—an example of macro-scale liquid immiscibility

Abstract Lujavrites are meso- to melanocratic agpaitic nepheline syenites and are the most highly evolved rocks of the Ilimaussaq complex, South Greenland. Spheroidal bodies measuring up to 20 cm in diameter occur locally in arfvedsonite lujavrite. They consist of a core rich in analcime and arfvedsonite and a rim rich in analcime, aegirine and a low temperature potassium feldspar. The host lujavrite is dominated by albite and arfvedsonite. The igneous lamination of the host continues undisturbed through rim and core of spheroids and the arfvedsonite crystals in host, rim and core have identical chemical compositions. There are sharp contacts between host and rim and rim and core. Host, rim and core contain the same accessory minerals and have almost identical chemical compositions, the main differences are high H 2 O and Na 2 O but low SiO 2 in the core and high Fe 2 O 3 in the rim. The spheroids are proposed to have been formed by separation of immiscible interstitial H 2 O-rich globules of magma from the host lujavrite magma at a late stage in the crystallization of the lujavritic melt.

Phase relations in the metal-rich portions of the phase system Pt-Ir-Fe-S at 1000°C and 1100°C

Abstract Phase relations in the S-poor portions of the dry condensed Pt-Ir-Fe-S system were determined at 1000° and 1100°C with a particular emphasis on delineation of the solid solubility fields of the Pt-Ir-Fe alloys. At both temperatures, a broad field of γ(Ir,Fe,Pt) alloy coexists with γ-(Pt,Fe), Pt3Fe and PtFe which dissolve respectively at least 5.1, 29.3 and 24.0 at.% Ir at 1100°C (2.2, 23.6 and ≤17.2 at.% Ir at 1000°C). Gaps between the nearly Ir-free Pt-Fe alloys γ(Pt,Fe), Pt3Fe s.s., PtFe s.s. and γ(Fe,Pt) were estimated as 20-23 at.%, 40-42 at.% and 54.2-~57 at.% Fe at 1100°C (18-23, 39.5-42.5 and 59-62 at.% Fe at 1000°C). The first gap agrees with data from natural phases by Cabri et al. (1996). The Fe-rich sulphide melt dissolves only traces of Pt and Ir; Fe1-xS dissolves up to 5.8 at.% Ir at 1100°C and 3.4 at.% Ir at 1000°C. These solubilities and the compositions of coexisting alloys (before low-temperature exsolution) may serve as geothermometers. The S-rich melt dissolves up to 8.2 at.% Pt and 2.5 at.% Ir (measured on a solidified melt) at 1100°C. The Fe-Ir thiospinel dissolves up to 2.2 at.% Pt (for the composition Fe21.6Ir18.9Pt2.2S57.3 at 1100°C). The 25-28 at.% Fe portions of Pt3Fe with <10 at.% Ir partake in all important sulphide (± melt)-alloy assemblages (with PtS, Ir2S3, pyrrhotite, S-rich melt and thiospinel). Therefore, their use in recognizing distinct natural assemblages of genetic importance is of limited value.

Exploratory studies on substitutions in the tetrahedrite-tennantite solid solution series Part III. The solubility of bismuth in tetrahedrite-tennantite containing iron and zinc

Bismuth-bearing tetrahedrite and tennanite were synthesized from dry runs in evacuated silica glass tubes at 350 °C, 450 °C and 520 °C, and studied by means of microprobe analyses on polished sections and X-ray powder diffraction. Charges were prepared with two Zn or Fe atoms p.f.u., with pure As, resp. Sb, or with As: Sb = 1:1 They were prepared with one and two atoms of Bi p.f.u., respectively, at all three temperatures. Separate sets of non-stoichiometric compositions were prepared in order to examine the influence of high- and low sulfur fugacity, respectively, on the solubility of Bi in tetrahedrite/tennantite. Our studies suggest that the solubility of Bi in tetrahedrite-tennanite is 0.8 atom p.f.u. at 350 °C and 1 atom p.f.u. at 450 °C and 520 °C, independent of the Sb/As ratio. It increases with the increase in S fugacity and vice versa. The average increment of the cubic lattice parameter a is 0.011A/1 Bi atom p.f.u. for tetrahedrite, that for tennantite is 0.036 A/ 1 Bi atom p.f.u. in the range investigated. The most prominent associated phases studied were Bi-bearing bornite, cuprobismutite, Phase Z, and wittichenite.

The metal-rich portions of the phase system Cu-Fe-Pd-S at 1000°C, 900°C and 725°C : implications for mineralization in the Skaergaard intrusion

Abstract The sulphur-poor portions of the dry condensed Cu-Fe-Pd-S systemwere studied at 1000°C, 900°C and 725°C by synthesis in evacuated silicate glass tubes, along with textural observations and electron microprobe analyses of equilibrated reaction products. Sulphide melt coexists with Cu-Fe-Pd alloys, bornite, Fe1−xS and iss (intermediate solid solution, Cabri, 1973) and Pd4S. Compositional data were obtained for the associations bornite-alloy-melt, pyrrhotite-alloy-melt and for immiscible Cu-rich sulphide melts. Partition coefficients for all three metals were derived for the association alloy-melt. Formation of the two new Cu-Pd alloy minerals, skaergaardite and nielsenite, is discussed in terms of the present findings.

The crystal structure of Cu4Bi4Se9

Abstract The crystal structure of Cu4Bi4Se9, synthesized at 400 °C, was determined from single crystal X-ray diffraction data and refined to the R1 value of 0.05. The compound is orthorhombic, with a = 32.692 Å, b = 4.120 Å, and c = 12.202 Å, space group Pnma. The structure contains three square pyramidal Bi sites, an octahedrally coordinated Bi site as well as two tetrahedrally and two irregularly coordinated Cu sites. The structure is an intergrowth of PbS-like slabs with irregularly configured slabs of Bi pyramids and Cu tetrahedra. It contains covalently bonded Se2 groups. Isotypy with Cu4Bi4S9 is connected with substantial changes in coordination details for two out of five distinct Cu sites. Modular relationships to the structures of the cuprobismutite series of Cu—Bi sulfosalts can be expressed as different ways of recombination of the same large structural fragment in the structures of Cu4Bi4Se9 and of the first cuprobismutite homologue, Cu4Bi5S10.

The system Pd-Fe-Ni-S at 900 and 725 degrees C

Abstract The system Pd-Fe-Ni-S was studied at 900 and 725°C by means of dry condensed charges. At both temperatures it is dominated by the phase relationships involving sulphide melt. Pd-Fe-Ni alloys with broad miscibility primarily coexist with the melt; they are relatively enriched in Pd, whereas the associated melt is enriched in Ni. With decreasing temperature the melt recedes from Fe-rich regions. The incompatibility of PdS (extensive solid solution with Ni) and mss at 900°C is replaced by their co-crystallization (± disulphide(s) of Ni,Fe or ± sulphide melt) at 725°C The Ni/Fe ratio in the melt changes regularly against that in mss with increasing S fugacity and Pd contents in these two phases. (Ni,Fe)3±xS2 and Pd4S play important roles at 725°C The data offer an array of distribution coefficients and solubility values suitable for geological interpretations.

The crystal structure of Cu1.78Bi4.73Se8, an N = 3 pavonite homologue with a Cu-for-Bi substitution

Summary Cu1.78Bi4.73Se8, synthesized in a dry phase system Cu—Bi—Se at 450 °C, is monoclinic, a = 13.759 Å, b = 4.168 Å, c = 14.683 Å, γ = 115.61°, space group C2/m. It is an N = 3 member of the pavonite homologous series, with the composition limits Cu1.96Bi4.67Se8—Cu1.77Bi4.60S8—Cu1.25Bi4.91Se8. The crystal structure is composed of two types of alternating slabs, with configurations typical for the above series. The first kind of slabs contains paired square pyramidal columns of Bi3, interconnected by octahedral columns with three distinct statistical copper sites (flattened tetrahedral sites in the octahedral interior and a tetrahedral site between adjacent octahedra). They add up to nearly 1.5 Cu. The second kind of slabs contains central octahedra of Bi1, flanked by marginal distorted octahedra of Bi2. These Bi sites are partly replaced by statistically occupied Cu1-3 sites, in flat-tetrahedral and irregular trigonal-planar coordinations. Details of the Cu-for-Bi substitutions are discussed and comparisons with other N = 3 homologues of pavonite are made in the paper.

Exploratory studies on substitutions in tetrahedrite–tennantite solid solution. Part IV. Substitution of germanium and tin

Forty-four charges with model compositions of Sn- and Ge-substituded tetrahedrite/tennantite were weighed out in the systems Cu-Sb (resp. As) - Fe (resp. Zn) - Sn (resp. Ge) - S. They alternatively modelled substitutions Cu 9 (Zn,Fe) 3 (Sn,Ge) 2 + (Sb,As) 3 + 3S 1 3 , Cu(Zn,Fe) 4 (Sn,Ge) 2 + 2(Sb,As) 3 + 2S 1 3 , Cu 1 0 Fe 3 + 2(Sn,Ge) 2 + 2 (Sb,As) 3 + 2S 1 3 , Cu 1 1 (Zn,Fe) 2 + 0.5(Sn,Ge) 4 + 0.5(Sb,As) 4 S 1 3 , Cu 1 0 (Sn,Ge) 4 + □(Sb,As) 4 S 1 3 ,Cu 6 (Sn,Ge) 4 + 2□ 4 (Sb,As) 4 S 1 3 , and Cu 1 1 (Sn,Ge) 2 + (Sn,Ge) 4 + (Sb,As) 3 S 1 3 . The resulting phases were investigated by microprobe analyses and X-ray powder diffraction. In no case the substitutions reached the planned end-members, producing a number of Sn- or Ge-containing phases that were detected and analysed in detail. For Sn & Ge substituting for semimetals, the substitution scheme (Sn,Ge) 2 + + (Fe,Zn) 2 + ⇄ (As,Sb) 3 + + Cu + is broadly followed; an alternative (Sn,Ge) 2 + + Fe 3 ⇄ (As,Sb) 3 + + Fe 2 + . The highest solubility observed is about 1.6 (Sn,Ge) 2 + p.f.u. In the case of tetravalent Sn and Ge, the trends Cu 0 . 5 + (Sn,Ge) 4 + 0.5 ⇄ Fe 3 + and, less developed, (Sn,Ge) 4 + + vacancy ⇄ Cut + Fe 3 + are observed. In Zn,Fe-free charges a double role of Sn, Ge was observed as well. The Ge-substituted tetrahedrite Cu 1 1 . 6 Ge 4 + 0.6Sb 3 . 9 S 1 2 . 9 has a equal to 10.345 A; tennantite with 0.5-0.6 Ge 4 + p.f.u. has 10.186 A. The Sn-substituted tetrahedrite Cu 1 1 . 4 Sn 4 + 0.8Sb 3 . 8 S 1 3 has a equal to 10.383 A and such tennantite Cu 1 1 . 7 Sn 4 + 0.5 As 3 . 9 S 1 2 . 9 has a = 10.22 A. Both in these substitutions and in those involving additional Fe and Zn, the interconversions between Cu + and Cu 2 + have decisive influence on the resulting a value.

Exploratory studies of element substitutions in synthetic tetrahedrite. Part V. Mercurian tetrahedrite

Thirty-one tetrahedrite charges were weighed out in the system Cu 1 2 Sb 4 S 1 3 -Cu 1 4 Sb 4 S 1 3 -Cu 1 0 Hg 2 Sb 4 S 1 3 , analysed by means of microprobe and the a parameter determined in a Guinier Haag camera. For Cu-poor tetrahedrites a = 0.096 Hg (p.f.u.) + 10.325 A and for Cu-rich tetrahedrites a = 0.032 Hg (p.f.u.) + 10.448 A. Up to ∼0.5 Hg p.f.u., low temperature exsolution into Cu-poor and a Cu-rich tetrahedrite takes place, above this value the field of Hg-tetrahedrite remains homogeneous. The resulting a value for Cu 1 0 Hg 2 Sb 4 S 1 3 is 10.515(2) A.