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Kalungaite, PdAsSe, a new platinum-group mineral from the Buraco do Ouro gold mine, Cavalcante, Goiás State, Brazil

¹ Instituto de Geociências, Universidade de Brasília, DF, 70910-900 Brazil
² Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada K7L 3N6
³ The Natural History Museum, Cromwell Road, London SW7 5BD, UK

^* E-mail: nilsonfb{at}unb.br

Kalungaite, PdAsSe, is a new mineral discovered in the Buraco do Ouro gold mine, Cavalcante town, Goiás State, Brazil. It occurs in a quartz-muscovite mylonite, related to a peraluminous granite, in platy anhedral aggregates along foliation planes. Associated ore minerals are gold, chalcopyrite, bohdanowiczite, an unnamed Pb-Bi-Se-S mineral, clausthalite, guanajuatite, stibiopalladinite, sperrylite and padmaite. Gangue minerals are muscovite, quartz and rare tourmaline and magnetite. Kalungaite is lead-grey, has a metallic lustre, a black streak and is brittle with uneven fracture. No cleavage was observed. The mineral has a micro-indentation hardness of VHN₂₅ = 438 (range of 429–455 kg/mm² from five indentations). Under reflected light, kalungaite is cream, or creamy grey adjacent to gold grains, has no internal reflections and is isotropic. Reflectance values in air (and in oil) are: 47.5 (33.3) at 470 nm, 46.9 (32.6) at 546 nm, 46.8 (32.6) at 589 nm and 48.0 (34.0) at 650 nm. The average of eight electron-microprobe analyses gives: Pd 41.32, As 27.49, Bi 0.35, Sb 1.59, Se 27.67 and S 1.22, total 99.64 wt. %, corresponding to Pd_1.006(As_0.950Sb_0.034Bi_0.004)_0.988(Se_0.908S_0.099)_1.007. Kalungaite is cubic, space group Pa, a = 6.089(4) Å, V = 225.78 Å ³, Z = 4. D_calc is 7.59 g/cm³. The strongest seven X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 3.027(75)(002), 1.838(100)(113), 1.172(95)(115, 333), 1.077(80)(044, 144, 334), 0.988(70)(116, 235, 253), 0.929(90)(335) and 0.918(70)(226). Kalungaite is interpreted as having formed from hydrothermal fluids of granitic origin, during synemplacement shearing and alteration, producing an unusual gold-platinum-group element deposit.

KEYWORDS: Kalungaite, PdAsSe, new mineral species, Brazil, Buraco do Ouro, gold deposit