Among the rich REE-Nb ores of the upper ore horizon of the Tomtor deposit, under the Jurassic deposits (borehole 324, interval 47-62 m), ultrapotassic rocks (feldspar porphyrite), consisting of more than 90% potassium feldspar (K-feldspar), are found. The rocks contain titanium-niobium oxide and rare grains of fersmite, Ce-bastnaesite, Ce-monazite, calcite, barite, and strontianite. K-feldspar is unevenly replaced by muscovite. By the type of REE and element distribution on the multidiagrams, the rock correlates well with the rich REE-Nb ores from the Burannyi site at the lower levels of contents. The Ar-Ar age of K-feldspar corresponds to 323.4 Ma and is correlated with the geological time of the formation of the rich REE-Nb ores from the Tomtor deposit, as well as the time of occurrence of magmatic and hydrothermal activity in this part of the region during this period.