*Mg-Ilmenite from Kimberlites, Its Origin DOI: http://dx.doi.org/10.5772/intechopen.102676*

Fe2O3 and an increase in the content of MnO, the content of Cr2O3 remains unchanged (**Table 3**). MnO-containing Ilm (up to 4.6 wt% MnO) and vein-like Ilm ( 30 μm– **Figure 9a**–point 7; **Figure 9b**–point 5; see **Table 3**) are found in the intergranular space. it is possible that the granulation of Ilm macrocrysts is caused by deformation processes, during which deformed lherzolites were formed. It is important to bear in


### **Table 3.**

*Chemical composition of the zoned macrocryst of Ilm from Zarnitsa (see Figure 7) and Komsomol'skaya pipes (Figure 8) and polygranular macrocrysts of Ilm from Mir pipe (Figure 9).*

**Figure 10.** *A plot of the composition of Ilm in the coordinates of MgO-Cr2O3 at different points (see Figure 9) of polygrainular grains from the Mir pipe.*

mind that despite the change in the MgO content in the recrystallized macrocrysts Ilm, the Cr2O3 content remains constant within the entire grain (**Figure 10**).

## **4. Ilm-bearing sheared peridotites**

Compositional features of minerals from Ilm-bearing deformed peridotites provide important arguments for developing a model of Ilm genesis in kimberlites. The similarity of the compositions of olivine, garnet, and Mg-ilmenite from deformed peridotites and the corresponding megacrysts from kimberlite rocks [28–30] indicates a genetic relationship between them. We present a brief description of the petrographic and geochemical features of Ilm-bearing deformed lherzolite (sample 00–83) from the Udachnaya-Eastern kimberlite, described earlier in the article by Solov'eva et al. [31].

Sample 00–83 is an Ol-Phl-Ilm sheared peridotite xenolith with a fluidal porphyroclastic texture. This sample contains 30 vol% olivine (Ol), 40 vol% phlogopite (Phl), and 30 vol% Ilm. Ol predominantly occurs as small (0.05– 0.2 mm) euhedral neoblasts, but rare anhedral porphyroclasts (< 1 mm) are present. Laminar Phl porphyroclasts (< 2 mm) are deformed. Ilm occurs as thin lenses (≤0.5 cm wide and ≤ 4 cm long; **Figure 11**), which have polygranular textures (**Figure 9a**). In a similar manner to the polygranular Ilm macrocrysts, titaniferousmagnetite has precipitated in the interstitial space between Ilm granules and at the grain margins of Ilm lenses. Ilm from this xenolith is characterized by wide variations in MgO contents (8.6–12.5 wt%) with relatively constant Cr2O3 contents (i.e., 2.6–2.9 wt% –**Table 3**). Ar40/Ar39 dating of Phl from this sample yields an age of 367.1 1.4 Ma [32], which overlaps the age of host kimberlite (i.e., 367 Ma, [33]).

*Mg-Ilmenite from Kimberlites, Its Origin DOI: http://dx.doi.org/10.5772/intechopen.102676*

**Figure 11.**

*Sample 00–83. Xenolith of deformed peridotite Phl-Ilm-Ol composition from the pipe Udachnaya-Eastern. Ilm forms micro-veins and micro-lenses. Photo of the section with crossed Nicol. The size of the photo is 6* x *4 mm.*
