The Role of Organic Matter in Peralkaline Pegmatites: Comparison of Minerogenetic and Technological Processes

Abstract

Solid bituminous substances (SBS) are known as usual components of late hydrothermal parageneses in peralkaline pegmatites of the Khibiny and Lovozero agpaitic massifs at Kola peninsula, Russia (Antonov et al., 1933; Labuntsov, 1937; Petersil’e, 1959, 1960, 1964; Linde, 1961; Sokolova, 1965; Zezin and Sokolova, 1967; Florovskaya et al., 1968; Loskutov and Polezhaeva, 1968; Pekov, 1998, 2001; Chukanov et al., 2005, 2006; Kartashov et al., 2006). The following occurrences of SBS are the most common: 1. Macroscopic (from 0.1mm to 1–2 cm) spheroidal or drop-like segregations of black or dark-brown bituminous substance overgrowing (or included in) aggregates of different minerals of late hydrothermal assemblages. Very often microporous hetero-framework zeolite-like silicates (MHFZ) with Ti, Nb or Zr (elpidite, labuntsovite- and hilairite-group minerals, umbite, paraumbite etc.) are substrates for SBS. Association of bitumen-like substances with aluminosilicate zeolites and alkaline heterophyllosilicates (murmanite, lomonosovite, astrophyllite- and lamprophyllite-group minerals) is also typical. Sometimes abundant organic substances are present in cavities with MHFZ whereas in neighbouting cavities without MHFZ, bituminous substances are absent. 2. SBS are habitual microscopic inclusions in thorium minerals formed in peralkaline pegmatites of the Khibiny and Lovozero massifs on hydrothermal stage: thorite, steacyite, Na,Th- and Na,Ti,Th-silicates, Th-phosphate, Th-bearing karnasurtite-(Ce). 3. In hydrothermal bodies of the Lovozero massif, abundant SBS have been detected in micro-heterogeneous aggregates forming rims around grains of Th- and REE-minerals (karnasurtite-(Ce), Na,Th-silicate, belovite-(Ce), etc.). 4. High concentrations of microscopic inclusions of SBS are typical for polymineral pseudomorphs after steenstrupine-(Ce) formed on hydrothermal stage (Shkatulka pegmatite, Lovozero). 5. Often films of SBS cover surfaces of mineral aggregates in cavities. Close association of SBS with MHFZ is very typical.