Petrology of the Yubileynaya kimberlite pipe: application to the variation of kimberlites composition with the depth

In this paper are summarized investigation results on the chemistry, petrography and mineralogy of kimberlitic rocks of the upper and deep levels of the Yubileynaya pipe. There are given original data on mineral phases contents in kimberlite ground mass,distribution of indicator minerals and olivine and its pseudomorphoses as well as autoliths (pyroclasts) in kimberlite drill cores of different levels (-)280 – (-)680m.

Petrologic evidence suggest that for the kimberlites of the Yubileynaya pipe is characteristic the prevalence garnet association of indicator minerals with the relatively low their whole content, predominance oflherzolitic pyropes, low content of titanium garnets, two types of ilmenites and chromespinelides.The particularity of this pipe is the presence, both eclogite and garnet websterite xenoliths as well as their diamondiferous varieties. This evidence is confirmed also by the composition of the paragenic associations of indicator minerals that is indicative of essential difference of lithospheric mantle under this given pipe in contrast with nearby kimberlitic pipes. It is possible to speculate that these peculiarities are specific for the kimberlite pipes of the middle diamond productivity.

Results of the garnets chemistry and the data of the distribution of eclogitic and ultramafic garnets in kimberlite concentrate of this pipe with the taking in account quantity of garnet variety potentially associated with diamonds suggest anincreased prevalence of eclogitic garnets among indicator minerals. This allowed making a statement about essential input of eclogitic paragenesis diamonds in the whole diamond production of this pipe. In our opinion these peculiarities also determine the increased content of large diamond crystals in kimberlites of the Yubileynaya pipe.