Skaergaardite, PdCu, a new platinum-group intermetallic mineral from the Skaergaard intrusion, Greenland

N.S. Rudashevsky, A.M. McDonald, L.J. Cabri, T.F.D. Nielsen, C.J. Stanley, Yu L. Kretzer, V.N. Rudashevsky

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42 Citations (Scopus)

Abstract

Skaergaardite, PdCu, is a new mineral discovered in the Skaergaard intrusion, Kangerdlugssuaq area, East Greenland. It occurs in a tholeitiic gabbro associated with plagioclase, clinopyroxene, orthopyroxene, ilmenite, titanian magnetite, fayalite and accessory chlorite-group minerals, ferrosaponite, a member of the annite-phlogopite series, hornblende, actinolite, epidote, calcite, ankerite, apatite and baddeleyite. The mineral is found in composite microglobules composed of bornite, chalcocite, digenite, chalcopyrite, with rare cobalt pentlandite, cobaltoan pentlandite, sphalerite, keithconnite, vasilite, zvyagintsevite, (Cu,Pd,Au) and Pt-Fe-Cu-Pd alloys, unnamed PdCU 3, (Pd,Cu,Sn), AU 3Cu and PdAuCu. Skaergaardite occurs as droplets, equant grains with rounded outlines, subhedral to euhedral crystals and as irregular grains that vary in size from 2 to 75 μm, averaging 22 μm. It is steel grey with a bronze tint, has a black streak, a metallic lustre and is sectile. Neither cleavage nor fracture was observed. The mineral has a micro-indentation hardness of VHN 25 = 257. It is isotropic, non-pleochroic and exhibits neither discernible internal reflections nor evidence of twinning. Skaergaardite varies from bright creamy white (associated with bornite and chalcopyrite) to bright white (associated with digenite and chalcocite). Reflectance values in air (and in oil) are: 58.65 (47.4) at 470 nm, 62.6 (51.1) at 546 mn, 64.1 (52.8) at 589 mn and 65.25 (53.95) at 650 nm. The average of 311 electron-microprobe analyses gives: Pd 58.94, Pt 1.12, Au 2.23, Cu 29.84, Fe 3.85, Zn 1.46, Sn 1.08, Te 0.28 and Ph 0.39, total 99.19 wt.%, corresponding to (Pd 0.967Au 0.020Pt 0. 0100.997(Cu 0 . 820Fe 0.120 Zn 0.039Sn 0.16Te 0.004Pb 0.0031 . 002. The mineral is cubic, space group Pm3m, a = 3.0014(2) Å, V = 27.0378 Å 3, Z = 1. D calc is 10.64 g/cm 3 . The six strongest lines in the X-ray powder-diffraction pattern (d in Å(I)(hkl)] are: 2.122(100)(110), 1.5000(20)(200), 1.2254(50)(211), 0.9491(20)(310), 0.8666(10)(222), 0.8021(70)(321). The mineral has the CsCl-type structure. It is believed to be isostructural with wairauite (CoFe), synthetic CuZn (β-brass) and is structurally related to hongshiite (PtCu). Skaergaardite developed from a disordered Pd-Cu-rich metal alloy melt that bad exsolved from an earlier Cu-(Fe) sulphide melt. Ordering of Pd and Cu (beginning at T ≈ 600°C) results in development of the CsCl structure from a disordered face-centred cubic structure.

Original languageEnglish
Pages (from-to)615-632
Number of pages18
JournalMineralogical Magazine
Volume68
Issue number4
DOIs
Publication statusPublished - Aug 2004

Keywords

  • CsC1-type structure
  • Duluth intrusion
  • Greenland
  • Hydroseparation
  • Minnesota
  • New Mineral species
  • Pd-Cu intermetallic
  • Platinum-group elements
  • Skaergaard intrusion
  • Skaergaardite

Programme Area

  • Programme Area 4: Mineral Resources

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