The perspectives of finding of giant CLIPPIR-type diamonds in weakly diamondiferous kimberlites of the north of Yakutia (Western Anabar region) using method of 5E Mitchells’s diagrams and cluster analyses

Finding of the giant diamond in Ebelyakh of CLIPPIR type of IIa type (Moor, 2014) suggest that similar diamonds should be found in the source kimberlites in Anabar basing and nearest Northern fields located within collision Khapchan terrain. To predict the finding authors are using the method of 5E diagrams based on the principle of analogy of the compositions Fe/(Fe+Mg) – Cr/(Cr+Al) – (Mn,Na) (Mitchell, 1986) for satellite minerals (Gar, Cpx, Chr and Ilmenites) of diamond (DSM) comparing with the etalon diagram for Karowe pipe (reference) and any other pipe. The forecast is quantified by the probability of convergence of these compositions using the division to the cluster groups. It was shown that the convergence of the DSM compositions of the Karowe and Grib pipes is 74%, which can be regarded as an indicator of the possible presence of diamonds in the predicted CLIPPIR pipe (Zinchenko et al., 2021).

 The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

 

A.

 

B.

Fig.1.  Mitchels’s diagram for minerals from Leningrad  and Malokuhamskay (B) pipes in comporisond with the Karowe pipe (contur lines) Cr- pyropes, Cr-diopsides, Ilmenites, Cr -spinels together. B. Triangle Na-Mn-Ti and C. Triangle Na-Al-Cr for Cr-diopsides and pyropes. D. distributions of the cluster groups for different minerals. E. Correltions of diamond grade with TiO₂ in garnest, Cr-diopsides and Cr-spinels and Fe₂O₃ in ilmenites

The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

 

C.

Fig.2. PTXFO₂ diagram for all xenocrysts from Leningrad (A), Malokuonamskaya (B) and Karowe AK-6 pipes. Symboles see legend

Russian Science Foundation grant 23-17-00030