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

Published online by Cambridge University Press:  05 July 2018

N. S. Rudashevsky ,
A. M. McDonald ,
L. J. Cabri ,
T. F. D. Nielsen ,
C. J. Stanley ,
Yu. L. Kretzer  and
V. N. Rudashevsky
N. S. Rudashevsky*
Affiliation:
Centre for New Technologies, Svetlanovsky ave., 75-41, St. Petersburg, 195427, Russia
A. M. McDonald
Affiliation:
Department of Earth Sciences, Laurentian University, Ramsy Lake Road, Sudbury, Ontario, Canada
L. J. Cabri
Affiliation:
Cabri Consulting Inc., 99, Fifth Avenue, Suite 122, Ottawa, Ontario, Canada K1S 5P5 CANMET/MMSL, Ottawa, Canada K1A 0G1
T. F. D. Nielsen
Affiliation:
Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark
C. J. Stanley
Affiliation:
The Natural History Museum, Cromwell Road, London SW7 5BD, UK
Yu. L. Kretzer
Affiliation:
Centre for New Technologies, Svetlanovsky ave., 75-41, St. Petersburg, 195427, Russia
V. N. Rudashevsky
Affiliation:
Centre for New Technologies, Svetlanovsky ave., 75-41, St. Petersburg, 195427, Russia
*
*E-mail: [email protected]
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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 PdCu3, (Pd,Cu,Sn), Au3Cu 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 VHN25 = 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 nm, 64.1 (52.8) at 589 nm 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 Pb 0.39, total 99.19 wt.%, corresponding to (Pd0.967Au0.020Pt0.010)Σ0.997(Cu0.820Fe0.120 Zn0.039Sn0.016Te0.004Pb0.003)Σ1.002. The mineral is cubic, space group Pm3m, a = 3.0014(2) Å, V = 27.0378 Å3, Z = 1. Dcalc is 10.64 g/cm3. 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 had 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.

Keywords

skaergaarditePd-Cu intermetallicnew mineral speciesCsCl-type structureplatinum-group elementshydroseparationSkaergaard intrusionGreenlandDuluth intrusionMinnesota.
Type
Research Article
Information
Mineralogical Magazine , Volume 68 , Issue 4 , August 2004 , pp. 615 - 632
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2004

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