Argentian Pentlandite from the Falconbridge Mine in the Sudbury Area of Ontario, Canada

Abstract

Argentian pentlandite has been found in the nickel-copper sulphide ores from the Falconbridge Mine in the Sudbury Area of Ontario, Canada. The present argentian pentlandite occurs as a micro-volume mineral up to 200μ across in chalcopyrite, closely associated with normal pentlandite, mackinawite and the unidentified sulphide(s). In reflected light, it has a reddish-brown colour and is isotropic between crossed polars. The development of cleavage traces is not discernible in it. The Vickers microhardness number (VHN) ranges from 146 to 153 kg/mm² at a 25 g load. Its average chemical composition as determined by electron microprobe method is, Ag 13.0, Ni 20.1, Fe 36.1, Cu 0.3, Co 0.0, S 31.3, Total 100.8 (in weight per cent). The corresponding structural formula on the basis of S=8 is, (Ag_0.99 Ni_2.81 Fe_5.30 Cu_0.04)_9.14 S₈, Z=4. From this, atom numbers per unit-cell may be approximated by Ag₄ Ni₁₂, Fe₂₀ S₃₂. The reflections with strong and moderate intensities appearing on the X-ray diffraction pattern are, 3.18 Å (10) (113), 2.03 Å (4) (115, 333) and 1.861 Å (10) (044). It has a face-centered cubic structure with a=10.53 Å, and the powder data are in harmony with the space group Fm3m as normal pentlandite. Its density is calculated as 4.70 g/cm³.
In so far as the present Falconbridge material is concerned, the chemical composition seems to be consistent with the observation by HALL & STEWART (1973) that Ag replaces Ni and Fe only in the octahedrally coordinated 4b sites of pentlandite-type structure.