Geochemical characteristics of magnesiocarbonatites from Muostalaah apatite occurrence and Birikeen apatite deposit (Aldan-Stanovoy shield, South Yakutia, Russia)

Abstract

Apatite-bearing ore occurrence Muostalaah and phosphate deposit Birikeen are magnesiocarbonatite complexes of the Seligdar type, located within the Nimnyrskaya submeridional metallogenic domain in the Aldan-Stanovoy shield in South Yakutia, Russia. This study presents geochemical characteristics of carbonatites and adjacent apatite-bearing silicate rocks of the Birikeen apatite deposit and Muostalaah apatite occurrence. Comparison of these complexes with the Seligdar deposit and other magnesiocarbonatite complexes of the world was made. Based on the chemical analysis of the petrogenic components of the Muostalaah and Biriken carbonatites, it was concluded that these rocks belong to magnesiocarbonatites, similar to the magnesiocarbonatites of the Seligdar deposit. The chondrite-normalized REE spectra of magnesiocarbonatites and apatite rocks are characterized by LREE enrichment relative to HREE with average La/Yb(cn) ratios of 45 and 100 for the Muostalaah and Birikeen rocks, respectively. Most of the REE patterns are within the field of the world magnesiocarbonatites. The trace-elements abundances of carbonatites and apatite rocks record negative Nb, Pb, Sr, Zr, Hf and Ti anomalies and Th, U and REE enrichment. Сoncentrations of Th, U, Zr, and Hf are characterized by a wide spread of values. The trace-element patterns of the Birikeen and Muostalaah carbonatites are generally similar to the patterns of the world magnesiocarbonatites, including Seligdar rocks. Based on the results of isotopic studies of the Sm/Nd and Rb/ Sr systems, it was concluded that the primary melts for the Muostalah and Birikeen carbonatites were formed from a long-lived enriched mantle source that separated from the depleted mantle in the Late Archean.