This paper deals with the geologic setting of the Yakokut lamproite rocks, their geochemistry and genesis. It is established that according to main petrogenetic characteristics they are identical to lamproite rocks of Aldan Shield and differ, to a degree, from the lamproites of Australia and USA. The rocks are Ti-poor and Mg-rich, contain 4.5-8.5 wt.% Al2O3 and 3-5 wt.% K2O, and belong to the miaskite series. Their phenocrysts are forsterites as well as low-alumina diopside and phlogopite. The fine-grained groundmass contains K-saturated feldspar and feldspar-substituted leucite; secondary minerals are tetraferriphlogopite and K-richterite. There are chromite crystallites in olivine phenocrysts, and fresh leucite crystallites in diopside. Study of phenocrysts in olivine and pyroxene has shown that the rocks were crystallized from melts heated to more than 1300 degrees-C. In their chemistry, the melts were rather similar to the rock composition, but in the process of crystallization the proportion of alkalis and Al in them changed considerably, and as a result the melts acquired alternatively either miaskitic or agpaitic character. The melts were Fe-rich (less than 50 mol.%), with SiO2 much predominant over Al2O3 (more than 5 molar quantities). During olivine crystallization the fluids contained 41 mol.% CO2 and 58.9 mol.% N2; during diopside crystallization they contained 100 mol.% nitrogen. The features, distinguishing the Yakokut rocks from typical lamproites, may be related either to melting of mantle substrate under low-pressure conditions, or to mixing of simple lamproite magmas with derivatives of high-alkaline K-basaltoid melts.
