Mineral CuFe₂S₄ from sulfide Copper–Nickel ores of the Lovnoozero deposit, Kola Peninsula

Abstract

The unnamed mineral CuFe₂S₄ has been found from sulfide Cu–Ni ores of the Lovnoozero deposit in the Kola Peninsula, Russia. It occurs in norite composed of orthopyroxene (bronzite), Ca-rich plagioclase (66% An), pargasite, and phlogopite. The last two minerals are replaced by talc, chlorite and carbonates. Monoclinic pyrrhotite, pentlandite, chalcopyrite, and pyrite are associated ore minerals. Phase CuFe₂S₄ is enclosed predominantly in chalcopyrite, probably replacing it, and occurs in later carbonate veinlets together with redeposited sulfides. It is light yellow with a brownish tint and metallic luster. The Mohs hardness is 5–5.5; VHN 654 ± 86 kgs/mm². Density (calc.) = 4.524 g/cm³. The mineral is anisotropic, internal reflections are absent. Reflectance values (λ, nm R′ _g and R′ _p %) are: 440 30.3 29.5, 500 43.7 42.8, 560 50.9 49.6, 620 52.4 51.2, 640 52.6 51.4, 680 52.8 51.6, 700 52.7 51.4. CuFe₂S₄ is monoclinic, a = 6.260(4), b = 5.39(1), c = 13.19(1) Å, β = 94.88(7)°, V = 443(1) ų, Z = 4. The strongest reflections in the powder diffraction pattern are [d, Å (I) (hkl)]: 4.150 (10) (012), 3.559 (4) ($11\bar 2$ ), 3.020 (4) ($10\bar 4$ ), 2.560 (3) ($21\bar 2$), 2.500 (3) ($10\bar 5$), 2.340 (3) ($12\bar 2$), 1.817 (3) (215), 1.489 (3) (402). The chemical composition is as follows, wt %: 20.44 Cu, 35.85 Fe, 0.65 Ni, 0.14 Co, 43.15 S, total is 100.23. The empirical formula calculated on the basis of 7 atoms is Cu_0.969(Fe_1.934Ni_0.034Co_0.007)_1.975S_4.056. According to its mode of occurrence, the mineral was formed as a result of low temperature processes involving metamorphic hydrothermal solutions.