Lithologies
Intermediate and Mafic Volcanic Units
Rocks of andesitic composition have been divided into either flows, or
fragmentals/pyroclastics, based on rock textures:
• Porphyritic andesite flows: two laterally continuous, massive units. One,
which primarily crops out to the west of the Kupol vein, is feldspar-phyric
and may represent a thick flow unit or sub-volcanic sill. It has a high
percentage (40–60%) of 1–4 mm euhedral feldspar phenocrysts, the
presence of clinopyroxene and biotite, and weak magnetism. The second is
an andesitic flow that has a grey-green fine-grained to aphanitic matrix and
may be an altered trachyandesite.