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JONASSONITE, Au(Bi,Pb)₅S₄, A NEW MINERAL SPECIES FROM NAGYBÖRZSÖNY, HUNGARY

Werner H. Paar^1,, Hubert Putz¹, Dan Topa¹, Andrew C. Roberts², Chris J. Stanley³ and Franz J. Culetto⁴

¹ Department of Material Science, Division of Applied Mineralogy, University of Salzburg, Hellbrunnerstr. 34, A-5020 Salzburg, Austria
² Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario KlA OE8, Canada
³ Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, U.K.
⁴ KELAG - Kärntner Elektrizitäts-Aktiengesellschaft, Arnulfpl. 2, A-9020 Klagenfurt, Austria

E-mail address: werner.paar{at}sbg.ac.at

Jonassonite, ideally Au(Bi,Pb)₅S₄, was detected in old mining dumps of the abandoned Nagybörzsöny deposit at Alsó–Rózsa, on the western margin of the Börzsöny Mountains, northern Hungary. The mineralization is hosted by Miocene calc-alkaline volcanic rocks and occurs as a stockwork in a propylitized dacite breccia pipe. The assemblage of metallic minerals with which jonassonite is associated consists of arsenopyrite, pyrite, marcasite, pyrrhotite, sphalerite, chalcopyrite, native gold, native bismuth, bismuthinite, ikunolite, cosalite, lillianite and possibly cannizzarite. Jonassonite occurs as anhedral grains of up to 500 x 150 µm, and contains inclusions of native bismuth, ikunolite and bismuthinite. It is megascopically tin-white with a metallic luster and a black streak. The mineral is brittle, with no obvious cleavage. Twinning is present. VHN₅ ranges between 125 and 153 (mean 134.5) kg/mm² (Mohs hardness of about 2 to 3). In plane-polarized reflected light, jonassonite is opaque, pale grey with a bluish tint, has weak bireflectance and pleochroism, and is distinctly anisotropic. Internal reflections are absent. The reflectances in air and oil, respectively, are 48.6–50.1, 35.0–36.7 (470 nm), 46.6–49.4, 32.7–35.7 (546 nm), 46.6–48.9, 32.9–35.2 (589 nm) and 48.0–48.8, 34.2–35.0 (650 nm). The chemical composition based on four analyses is: Au 14.95, Ag 0.09, Bi 69.06, Pb 6.12, Cd 0.06, Sb 0.08 S 9.76, Se 0.41, total 100.53 wt.%. This leads to the empirical formula (Au_1.02Ag_0.01)_1.03(Bi_4.42 Pb_0.39Cd_0.01Sb_0.01)_4.83(S_4.07Se_0.07)_4.14. The ideal formula, AuBi₅S₄, requires Au 14.38, Bi 76.26, S 9.36, total 100 wt.%. Jonassonite is monoclinic with unit-cell parameters, refined from powder data: a 18.329(29), b 4.108(4), c 13.974(16) Å, ß 100.90(10)°, V 1033(2) ų, space-group choices F2/m, F2 or Fm, and Z = 4. The density could not be measured because suitable material was not available. It was calculated using the empirical formula: 8.64 g/cm³. The strongest seven lines of the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 9.002(40)(200), 6.876(30)(002), 3.460(30)(402,04), 3.382(40)(11), 2.959(100)(02,113), 2.101(50)(711) and 2.086(50)(15). The relationship to other species is unknown, and the mineral appears to have a unique prototype structure. The mineral name honors Dr. Ian Roy Jonasson, an economic geologist at the Geological Survey of Canada, Ottawa, for his outstanding contributions to global ore-deposit research. Both the mineral and the name have been approved by the Commission on New Minerals and Mineral Names, IMA (2004–031).

Keywords: jonassonite, new mineral species, gold bismuth sulfide, electron-microprobe analyses, X-ray data, reflectance data, Nagybörzsöny, Hungary.

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