Ussuri

In the upper reaches of the Ussuri River more than 30 isolated outcrops of alkaline basaltoids are known. They traverse and overlie ancient crystalline Archaean and Proterozoic rocks and some outcrops cut through gravels of Pliocene age. The basaltic rocks form pyroclastics and lavas, dykes and breccia pipes up to 2 km2 in area. Limburgite, leucite ankaratrite, nepheline basanite, nepheline basalt and essexite-dolerite are represented. The limburgites form small isolated outcrops overlying Archaean schists. They are black, dense rocks with brecciated structures and are often porous. They consist of volcanic glass in which are set microlites of titanaugite and olivine as well as xenocrysts and aggregates of olivine and clino- and ortho-pyroxene and spinel. The leucite ankaratrites have been found in one outcrop only, where they comprise part of the eruptive, fragmentary agglomerate of a breccia pipe. They have a fine-grained texture and consist of microlites of titanaugite, leucite, opaque minerals and plagioclase with interstitial volcanic glass. Xenocrysts of amphibole, biotite, olivine, pyroxene and spinel are also present. Ankaratrite-picrites are the most widespread rock type of this locality. They are fine-grained polycrystalline rocks consisting of microlites of titanaugite and small crystals of nepheline, olivine and ore minerals; apatite and analcime are present in accessory amounts. Larger xenocrysts of olivine, clino- and ortho-pyroxene and spinel surrounded by reaction borders of opaque minerals are also present.