Аннотация:Organic substances are typical components of hydrothermal associations of agpaitic pegmatites. Bituminous substances (BS) from Khibiny and Lovozero pegmatites have been widely studied since 1960s. Most researchers support the conception of abiogenic origin of BS. A close connection of BS with a number of rare elements (mainly Th and REE) has been established. However, organic substance and pegmatite minerals have mainly been studied separately. Besides there is still a number of unanswered questions related to formation, reduction and polymerization of low-molecular organic compounds and mechanisms of rare elements concentration.
In order to answer these questions, we are continuing to study the subject with the use of current analytic methods. The data for this research has been collected and published in the period from 2002 to 2010. This abstract represents the summary of these results.
Organic substances formation is only possible in reduction environment. The main oxidation-reduction pairs in alkaline fluid are given on the slide. Taking into account that the formation of significant amounts of BS in pegmatites is as a rule preceded by mass crystallization of aegirine NaFe3+Si2O6, the main scheme of carbon reduction is as follows.
The catalytic role of microporous heteropolyhedral framework minerals of Ti, Nb and Zr is a pre-condition of further organic substance evolution. This fact is supported by multiple examples of BS overgrowth on these minerals aggregates’ surface as well as by previously frequently observed catalytic activity of similar synthetic materials in organic reactions.
The certain group of elements found in hydrothermal parageneses of Khibiny-Lovozero complex (mainly Th but also U, REE, Ti, Nb, Zr) is frequently closely connected with organic substance, often in the form of microscopic intergrowths. Such microscopic intergrowths of BS with rare element minerals are commonly found in hydrothermal zones of agpaitic pegmatites. The close association with BS is most typical for Th. Intensive mineral formation that includes Th, REE, Ti, Nb, Zr under hydrothermal conditions is only possible in the presence of complex-forming compounds that provide high mobility of these elements.
The obvious close association of minerals of these elements with BS in alkaline hyrothermalites shows that oxygen-containing aromatic organic substances are the complex-forming compounds in this case. BS form inclusions in Th minerals, as well as macroscopic segregations with inclusions of Th and REE minerals at hydrothermal (but not early-pegmatite) stage. As a rule, inclusions of organic substances are not found in associated hydrothermal minerals that do not contain Th and REE. It is interesting that a similar set of rare elements (namely U, Th, REE, Y, Be, Ti, Nb, Zr, Ge) is usually found in over-clarke concentrations in deposits of caustobioliths.
BS associations typically have unique mineral diversity and a high degree of separation of Th, U and different REE. In these associations we didn’t only observe new mineral species for Khibiny (steacyite) and Lovozero (remondite-(Ce), belovite-(La)) massifs (Chukanov et al., 2005) but also a number of phases, containing Ti, Nb, Zr, Th, U, Ce, La, Nd and other rare elements, that have not been known as mineral species.
