Apatite as an Indicator for the Formation of PGE Mineralization as Exemplified by Anorthosites of the Kievey Deposit, Fedorova-Pana Layered Complex, Kola Peninsula, Russia

Abstract

This paper presents petrography, X-ray electron probe energy-dispersive (EDS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and Raman spectroscopy data to characterize the mineral associations and composition of apatite group minerals from anorthosites of the Kievey deposit, North platinum group-element (PGE) Reef, Fedorova-Pana Complex, Kola Peninsula, Russia. The mineralized coarse-grained anorthosite belongs to the most common rock type of the main ore body, and hosts irregular interstitial sulfide disseminations of 5–7 vol.%. Apatite in the anorthosite occurs as (a) euhedral grains included in the marginal parts of cumulus plagioclase laths, and (b) xenomorphic grains associated with intercumulus minerals. The composition of apatite evolves along a narrow trend from fluorapatite to hydroxylapatite. The F content of apatite reaches 2.21 wt.%; the maximum Sr and rare earth element (REE) concentrations are 257 and 5623 ppm, respectively, while the average ratio of La/YbN = 11.78, Sr/Sr* = 0.01, and Eu/Eu* = 0.06. Compared to classic PGE reefs in layered intrusions, such as Bushveld in South Africa and Stillwater in the United States, the mineralized anorthosite is distinguished by apatite with an unusually low chlorine concentration of only 0.46 wt.%. A suggested reason for this difference is the percolating nature of sulfide liquid, which has not been enriched in PGE in situ.