The first identification of cronstedtite in Cu–Ni–PGE ores of the Talnakh intrusion

Abstract

Abstract We present new mineralogical data of cronstedtite from the Southern-2 orebody, located in the South-Western branch of the Talnakh intrusion (Noril'sk camp) composed of massive sulfides in which the total amount of oxides and silicates does not exceed 1–3 vol. %. The petrographic and mineralogical features of these ores indicated occurrence of fine-grained, fibrous needle like clusters <50-µm-sized grains of cronstedtite (7,09 Å along its c-axis). This mineral confirmed by a number of analytical techniques (powder X-ray diffraction of balk samples, transmission electron microscopy, scanning electron microscopy, Raman and Infrared spectroscopy). Cronstedtite contains impurities of Al, Ni, Ca and filling the cracks between sulfides of copper (chalcopyrite) and iron (pyrrhotite, pentlandite, troilite). In some cases, cronstedtite contains micron-sized PGE, and associates with magnetite, kaolinite, gypsum, calcite, quartz, and cristobalite. The findings of cronstedtite in Noril'sk camp have never been mentioned publicly before. Its occurrence is the northernmost known locality in the world. Our results imply that the formation of cronstedtite in the Talnakh intrusion could be possible by the active participation low-temperatures fluids within the relatively near-surface (<2 km of paleosurface) conditions of intrusion emplacement, in contrast to other deep-seated supergiant Cu-Ni-PGE deposits in the world.