X-ray Computed Tomography of PGE-Rich Anorthosite from the Main Reef of the Yoko–Dovyren Layered Massif

Abstract

For the first time, we present results of a detailed X-ray computed tomography of mineralized anorthosite from the main low-sulfide PGE-rich horizon of the Yoko–Dovyren intrusion in Southern Siberia. These studies were carried out in three stages with the acquisition of information on different scales. At the first stage, a 5 × 6 cm size sample was scanned with a resolution as high as 200 µm; at the second stage, two 10 mm cores were drilled out of its most sulfide-rich zones, in which probable platinum group minerals (PGM) were found; the third stage included drilling out 3 mm cores in the areas potentially enriched in PGMs. Such a systematic study made it possible to visualize the distribution of sulfide in the volume of the plagioclase matrix, as well as to establish the spatial relationships of sulfides and PGMs. The mineralized layers of the anorthosite are characterized by a heterogeneous distribution of sulfides within 1 cm, while their contents do not exceed 10 vol.%. Most PGMs look like sub-isometric ones, as they are confined to the edges of sulfide segregations, less often occurring inside them; their size does not exceed 135 µm. Based on the results of stereological reconstructions, two small polished mounts were prepared that exposed the two largest grains of the probable PGMs. According to the results of SEM studies, one grain 35 µm in diameter in association with chalcopyrite and epidote at the margin of a sulfide segregation was identified as moncheite, and an elongated 135 µm long grain in the intergrowth with cubanite was identified as electrum.