Chemical and phase heterogeneity of Ti-Fe-Mn-silica microspherules in crushed ore samples

Abstract

A Fe-Ti-Mn-silicate microspherule from the heavy mineral fraction of crushed geological samples from an underground mine (Kellyam gold deposit, Yakutia) was examined by transmission electron microscopy. The 400-μm microspherule has a complex chemical composition and contains the following elements (in order of decreasing content): O, Ti, Si, Mn, Fe, Al, Mg, Ca, and K. The material of the micro-spherule shows a polyphase structure and chemical heterogeneity with separation into amorphous oxide-silicate (SiO2) and crystalline metallic (α-Ti + FeTi) constituents. The spherical shape and the character of internal heterogeneity suggest that the microspherule was formed owing to the rapid solidification of a melt droplet. The nanoscale heterogeneity of the microspherule is a consequence of a two-stage process. (1) Liquid immiscibility in the initial melt droplet before its solidification resulted in the incomplete spatial separation of Si + Al and Ti + Fe + Mn and appearance of SiO2 globules with admixtures of Al, Ca, K, Mg, Ti, Fe, and Mn approximately 100 nm in size. (2) Chemical heterogeneity developed subsequently both within the globules and within the matrix at the stage of melt solidification or after the solidification. The second-stage chemical heterogeneity was manifested in (a) the separation of heavy minor element oxides (Ti, Fe, and Mn) from the light elements Si, Al, K, Ca, and Mg(?) within the globules and (b) the separation of the matrix material into crystalline metallic (α-Ti + FeTi) and amorphous oxide-silicate [SiO2-MgO-Mn3O4(?)-Fe2O3(?)-TiO2(?)] parts. The obtained results do not rule out the possibility of formation of such microspherules during drilling operations.