MENSHIKOVITE, Pd3Ni2As3, A NEW PLATINUM-GROUP MINERAL SPECIES FROM TWO LAYERED COMPLEXES, RUSSIA

Abstract

Menshikovite, ideally Pd 3 Ni 2 As 3 , is a new mineral species found in two localities in Russia. It occurs in a pod of coarsegrained, entirely altered gabbronorite rich in sulfides (up to 30 vol.%), hosted by a microgabbronorite, in the Vostok deposit, Lukkulaisvaara intrusion, in Karelia. There, menshikovite (up to 0.2 mm) is associated with chalcopyrite, pentlandite, calcic amphibole (mostly actinolite), clinochlore, merenskyite, kotulskite, sobolevskite, michenerite, hollingworthite, hessite, and a Re-rich sulfide. Menshikovite (up to 0.1 mm) also occurs in mineralized quartz-feldspar sandstones, which are metasomatically altered and recrystallized. They are located at the lower (exo)-contact of the Chiney intrusion in Siberia, and contain amphibole(s), mica(s), chlorite, disseminated or massive sulfides (mostly chalcopyrite), Pd-rich maucherite, nickeline, sperrylite, mertieite-II or stibiopalladinite (or both), isomertieite, majakite, and michenerite. We also report a third occurrence of menshikovite from the Oktyabr' deposit, Noril'sk complex, in Siberia. In reflected light, menshikovite is pink and opaque. A cleavage is not observed. There is no evidence of bireflectance. The anisotropy is weak, from light gray to brownish gray. Reflectance percentages in air (and in oil) are, for R 1 and R 2 , at 470 nm 48.4, 50.2 (38.45, 39.3 (10)(112), 2.477(10)(202), 2.429(8)(300), 2.283(7)(301), 2.150(6)(103), 1.978(7)(113), 1.818(7)(400) and 1.757 (6)(401). Menshikovite formed in volatile-rich environments relatively late in the crystallization history of the layered complexes. The name honors Yurii P. Men'shikov, of the Kola Science Center, Apatity, Russia.Keywords: menshikovite, new mineral species, Pd-Ni-As system, arsenide, platinum-group mineral, platinum-group elements, layered intrusion, mafic-ultramafic rocks, Lukkulaisvaara, Chiney, Noril'sk, Russia. SOMMAIRELa menshikovite, dont la formule idéale est Pd 3 Ni 2 As 3 , est une nouvelle espèce minérale découverte en deux endroits en Russie. Elle se présente dans une lentille de gabbronorite à gros grains, entièrement altérée, riche en sulfures (jusqu'à 30% en volume), et encaissée par une microgabbronorite dans le gisement de Vostok, complexe de Lukkulaisvaara, en Karélie. La menshikovite, qui atteint une taille de 0.2 mm, y est associée à chalcopyrite, pentlandite, amphibole calcique (surtout actinolite), clinochlore, merenskyite, kotulskite, sobolevskite, michenerite, hollingworthite, hessite, et un sulfure riche en Re. La menshikovite (jusqu'à 0.1 mm de taille) se présente aussi dans des grès à quartz-feldspath minéralisés, modifiés par métasomatose et recristallisés. Ces roches sont situées près du contact externe inférieur du massif intrusif de Chiney, en Sibérie, et contiennent §

Nipalarsite, Ni8Pd3As4, a new platinum-group mineral from the Monchetundra Intrusion, Kola Peninsula, Russia

“…Nipalarsite does not have a structural analogue in the mineralogical system. From a chemical point of view, the most related minerals are majakite, PdNiAs, (Evstigneeva et al , 2000) and menshikovite, Pd 3 Ni 2 As 3 (Barkov et al , 2002). The majakite structure is based on [PdAs 5 ] square pyramids and [NiAs 4 ] distorted tetrahedra, the nipalarsite structure is typical for intermetallic compounds with high coordination numbers and hence is very different from that of majakite.…”