ON THE ORIGIN OF LAMPROITES OF THE MOLBO RIVER (WESTERN ALDAN)

In mineralogical studies of diopside and phlogopite phenocrysts of oli vine-leucitic rocks of Molbo river the crystallites of fresh leucite w ith 3.5 wt% FeO were ascribed. The latter are associated with unaltere d olivine crystals of Fo(82-84) composition. It was round that pseudo- leucitic phenocrysts consist of high potassium felspar enriched in FeO (up to 1.5-2.5 wt%). In the zonal phlogopite phenocrysts the Ti conte nt: increases fi om the central to peripheric zones whereas the Al con tent dicreases. Thermobaromateric studies of melt inclusions in minera ls showed that the pyroxene crystallisation is corresponding to 1210 /- 30 degrees C whereas the apatite within 1150 degrees-1030 degrees C temperature range. It was-found that the initial melts were low alumi na bearing (6-8 wt% Al2O3), high magnesial (4-8 wt% MgO), enriched in Ba and Sr. Melts were regarded Lo agpaitic rock family as SiO2/Al2O3 r atio is not higher than. The melts studied are greatly enriched in SO3 anti Cl correspondingly Hp to 0.37 and 0.47 wt.% resulted in the bari te-celestine crystallisation at the megmatic stage of rock formation. The study shows than the olivine-leucitic rocks of Molbo rivet should be related to the low titanium species of lamproite rock family. These rocks are mostly similar to diopside-leicitic lamproites of Nunkabach (Western Australia) as well as wyomingites and orendites of Leicite-H ills in USA.