Chatkalita, nekrasovita y otros minerales del grupo de la estannita de veta María Eugenia, Cerro Atajo, Catamarca

Abstract

The association of tin minerals integrated by: chatkalite Cu₆Fe2+Sn₂S₈, nekrasovite Cu₂₆V₂(Sn,As,Sb)₆S₃₂, colusite Cu₂₆V₂(As,Sn,Sb)₆S₃₂, kësterite Cu₂(Zn,Fe)SnS₄ and stannoidite Cu₈(Fe,Zn)₃Sn₂S₁₂ was found at veta María Eugenia, Cerro Atajo, Catamarca. These minerals are included in watanabeite and accompanied by pyrite, sphalerite, chalcopyrite, tetrahedrite, bornite and galena as the main minerals, and aikinite, enargite, luzonite, marcasite, arsenopyrite and pyrrhotite as accessory minerals. Chatkalite is light pink with a delicate orange hue, birreflectant and anisotropic with brown polarization colours, occurs as irregular aggregates up to 40 µm, associated to kësterite and stannoidite; its chemical composition (wt.%) range is: S=29.76-30.37, Fe=4.53-7.92, Cu=39.13-43.21, Zn=0.75-5.53, As=0.19-2.42, Sn=15.27-20.50 and Sb=0.00-0.32. Nekrasovite is isotropic, brown with a violet-pink hue; it is associated with stannoidite, and its chemical composition range is: S=30.29-30.63, Fe=3.41-4.75, Cu=44.26- 45.70, Zn=0.56-1.00, As=4.18-4.71, Sn=12.53-13.64 and Sb=0.71-0.77. Colusite is yellowish-brown, isotropic, occurs as irregular patches and discontinue ribbons in tennantite and its chemical composition range is: S=30.59-30.74, Fe=2.18-3.58, Cu=47.22-48.13, Zn=0.21-0.64, As=6.38-6.61, Sn=9.04-9.33 and Sb=0.49-1.66. Kësterite is greyish-brown, with a weak birreflectance and brown polarization colours and sometimes is surrounded by chatkalite; its chemical composition range is: S=28.68-29.14, Fe=1.98-2.14, Cu=31.06-32.51, Zn=9.03-11.57 and Sn=26.39-27.03. Stannoidite is brown, pleochroic (pinkish-brown to greyish-brown), anisotropic, with brown and yellowish-brown polarization colours; it occurs as irregular patches or as bands bordering tennantite. Its chemical composition range is: S=29.11-29.83, Fe=8.45-10.30, Cu=38.05-41.01, Zn=3.18- 4.90, and Sn=15.84-18.94. The reflectivity and polishing hardness of all these minerals are similar to that of watanabeite; in none of them were observed cleavage, twinning or internal reflections.