J. Rose-Hansen

Partitioning of nickel, copper, iridium, rhenium, platinum, and palladium between monosulfide solid solution and sulfide liquid: Effects of composition and temperature

Abstract Partitioning of Ni, Cu, and Pt-group elements (Ir, Rh, Pt, Pd) between monosulfide solid solution (Mss) and sulfide liquid has been investigated in the Fe-Ni-Cu-S system at 1000 and 1100°C and one atmosphere pressure. The Nernst partition coefficients (D = wt% in Mss/wt% in sulfide liquid) for Ni vary significantly from 0.19 to 1.17, while the values of DCu show a limited range of 0.17–0.27. The partition coefficients for Ir range from 1.06 to 13. Rhodium has a partition coefficient slightly lower than that of Ir under the same conditions, ranging from 0.37 to 8.23. The partition coefficients for Pt and Pd vary from 0.05 to 0.16, and from 0.08 to 0.27, respectively. The partition coefficients depend strongly on the bulk S contents of the system. They increase with increasing S contents in both Mss and liquid. Platinum, Pd, and Cu behave incompatibly during Mss crystallization, strongly partitioning into sulfide liquid. Nickel is incompatible in S-undersaturated systems and S-saturated systems. It becomes compatible when the system is S-oversaturated. Rhodium is compatible in S-saturated and S-oversaturated systems, but incompatible in S-undersaturated systems. Iridium changes from highly compatible through moderately compatible to slightly compatible when the system changes from S-oversaturated through S-saturated to S-undersaturated. The effect of temperature on metal partitioning is observed only in S-oversaturated systems, in which the partition coefficients for Ni and Rh increase with decrease of temperature. The compatible behavior of Ir and Rh, and incompatible behavior of Pt and Pd and Cu under S-saturated conditions appears to support the hypothesis that the observed metal zonation in many sulfide ore deposits such as Sudbury, Ontario and Norilsk, Siberia resulted from sulfide liquid fractionation.

Combined Raman microprobe spectrometry and microthermometry of fluid inclusions in minerals from igneous rocks of the Gardar province (south Greenland)

Abstract Raman microprobe spectrometry has been applied to analysis of the gaseous phase in individual fluid inclusions in minerals from alkalic igneous rock types and associated hydrothermal veins from the Gardar province, south Greenland. Quantitative analyses are given for CO2, CH4, C2H6, H2 and H2S. Traces of CO were observed in one CO2 inclusion. In conjunction with data from microthermometry, the results permit calculation of the bulk chemical composition of entrapped fluids and evaluation of the possible pressure, temperature, oxygen fugacity and sulphur fugacity during entrapment of the individual fluid inclusions. Calculated oxygen fugacity values correspond to those of the NNO and QFM buffer reactions at temperatures of 300–400°C and pressures of 0.5–1.0 kbar. Calculated sulphur fugacity values are within the range of normal ore forming solutions (log fS2: −6 to −10).

Volatiles associated with alkaline igneous rift activity: Fluid inclusions in the Ilímaussaq intrusion and the Gardar granitic complexes (south Greenland)☆☆☆

Abstract Fluid inclusions in minerals from Si-oversaturated and Si-undersaturated alkalic igneous complexes belonging to the Precambrian Gardar Rift Province in South Greenland contain distinctly different carbon-bearing gases: granites and quartz syenites are characterized by CO2 and only minor CH4 whereas agpaitic nepheline syenites are dominated by hydrocarbons (essentially CH4) and contain only insignificant amounts of CO2 and/or CO. In the alkaline Ilimaussaq Intrusion the hydrocarbon-rich gases may well reflect equilibration with graphite at magmatic temperatures and at oxygen fugacities approaching those defined by the synthetic MW buffer reaction. In general, formation of hydrocarbon gases in agpaitic nepheline syenites is considered to reflect the fulfillment of three basic conditions: (1) low oxygen fugacities; (2) a wide temperature range of crystallization and a low-temperature solidus; and (3) retention of volatiles during crystallization. The characteristic carbon-bearing vapour associated with continental alkaline igneous activity is, however, considered to be CO2.

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.

Experimental Evidence on the Formation and Mineralogy of Platinum and Palladium Ore Deposits

The dry, condensed phase systems Pt-Fe-S and Pd-Fe-S were studied by means of laboratory syntheses at 900°, 500° and by long annealing at 300 °C. Reconnaissance runs were made in these systems with either Cu or Ni added. High solid solubility of Pt and Pd in pyrrhotite was established at 900 °C; it drops considerably towards 500° and 300 °C. Pentlandite acts as a concentrator of Pd but not Pt at 500 °C. Sulphide melts in the systems Pd-Fe-S and Cu-Fe-Pt (or Pd)-S act as concentrators of these PGE. Numerous applications of these observations to natural phenomena in PGE deposits are given.

The application of radioelement studies in solving petrological problems of the Precambrian intrusive Homme granite in the Flekkefjord area, south Norway

Abstract A Th- and U-enriched granite has been found within a sequence of high-grade metamorphic gneisses and migmatites in the Flekkefjord area bordering the S Rogaland anorthosite province in SW Norway, where the country rocks and the other intrusions all have very low contents of these elements. The major-element distribution within the Homme granite suggests a certain magmatic differentiation, although a K- and Si-rich zone in connection with the discordant northern contact is supposed to be due to assimilation of felsic country rocks. This model was tested by studying the radioelements which exhibit the lowest values exactly in the northern K- and Si-rich zone, thus supporting the model of assimilation, while the alkali enrichment in the southernmost part is connected with high contents of radioelements, thus suggesting a rest magmatic stage.

Determination of [Fe2+]/[Fe3+]-ratios in Arfvedsonite by Mössbauer Spectroscopy

Abstract The Mossbauer absorption spectra of arfvedsonite are composed of three quadrupole doublets which are ascribed to Fe 2+ in M 1 and M 2 sites and to Fe 3+ in M 2 sites. The relative intensities of the resonances are a measure of the distribution of iron at the different sites, but it is necessary to correct for a difference between the recoil-free fractions. At room temperature [Fe 2+ ] seems detected with an efficiency of only about 85% of that of [Fe 3+ ]. Results of [Fe 2+ ]/[Fe 3+ ] determinations by Mossbauer spectroscopy and by wet chemical analysis of a series of arfvedsonite samples, separated from various rocks from the Ilimaussaq intrusion, south Greenland, are compared and agree reasonably well.

Astrophyllite-group minerals from the Ilímaussaq complex, South Greenland (contribution to the mineralogy of Ilímaussaq no. 123)

Abstract Electron microprobe analyses are presented for astrophyllite-group minerals from hydrothermal veins and pegmatites of the Ilímaussaq complex, South Greenland. The analyses fall mainly into two groups: (1) niobophyllites with the highest Nb/(Nb+Ti) ratios yet recorded (~0.9), occurring only in the veins, and (2) an essentially continuous sequence from astrophyllite to niobophyllite with Nb/(Nb+Ti) up to 0.6, found in veins and pegmatites. It is highly likely that there is complete solid solution between astrophyllite and niobophyllite. More limited substitution of Mn for Fe has resulted in the formation of kupletskite in some rocks. Altered zones in certain astrophyllites and niobophyllites have compositional features similar to the type ‘hydroastrophyllite’. The astrophyllite-group minerals in the hydrothermal veins crystallized at temperatures below 400°C at 1 kbar and under high pH and low oxygen fugacity, whereas those in the pegmatites were formed from water-rich melts which were hotter (≥450°C), less basicand more oxidized.