Features of magnetite from kimberlite rocks

Abstract

Introduction: the main method of prospecting for diamond deposits is schlich-mineralogical (SMM) using the indicator minerals kimberlites (KIM) of diamond,pyrope,picroilmenite,chromium spinel,chromium diopside et. The effectiveness of this method is determined by the direct Signs of the diamond content of the territories by the discovety of diamond and other kimberlite minerals that have clearly defined typomorphic features.However when using CMM in some cases there are difficulties in identifying some minerals, especially thoseoccuring egually in both kimberlites and other rocks common in diamondiferous regions. These minerals inelude ore formations (primarily magnetite), whick are especially difficult to diagnose when individuals are small and mainly when thay are small disseminafed in rocks. Magnetite in these rocks usmally bears traces of serperimposed changes and therefore often diagnostics, as well as fine methods of pysiocochemical studies.

Оbjects, research methodology and discussion of the results: results of complex research of magnetite from kimberlites are provided, formation of which in certain cases took place in magmatic conditions, and in others (prevailing in pipes) – in the process of postmagmatic and hypergene alteration of rocks. Primary hypogene nonstoichiometric magnetite originates at temperature above 1200ºС. Since kinetic factor prevails in the process of magnetite transformation, then in the first turn intensive oxidation of fine-grained releases occurs, in comparison with coarse-grained differences. It is recommended to use crystal-chemical features of magnetite in practice, with consideration of staging of its alteration, when mapping kimberlite diatremes, quantitative determination of mineral in them by various methods of investigation, as well as for prospecting of secondary collectors and related with them diamond deposits of placer type. Comparative study of phase composition and structural features of magnetites from kimberlites, hosting diatremes of dolerites and sedimentary thick layers overlapping pipes, showed connection of these parameters with the type of rocks containing this mineral, geological conditions of bedding and specific features of their alteration.

Сonclussion: the conducted studies have shown that the absence of isomorphic replacement and the ubiauitous nonsfoichioiichiometrig nature of magnetite in kimberlites indicate the formation of its predominant fraction of relatively low thermobaric parameters of the media the postmagmatic stage of rock alteration. The stability of the phases is determined not only by the partial pressure of oxygen, the temperature of the medium, but also by the rate of the corresponding reactions. In the process of fransformation of magnetite, compared with coares-grocined difference. Information about the presence of vacancies in the structure of magnetite mast be faken into account in the case of determining the guantitative content of the mineral in the rock by the chemical method. The typomorpic features of magnetites, taking info account the stagesof their dange, con be used in the search for primary diamond deposits and associated secondary reservoirs.