An andesite from Delarof Harbor, near which the Apollo mine is situated, forms in some respects a transition between the lava of St. Augustine and the more usual type of pyroxene-andesites. It is a greenish-black, somewhat vesicular porphyry, in which the microscope shows phenocrysts of augite, a rhombic pyroxene, which in this case seems to be enstatite rather than bronzite, and labradorite. The groundmass consists of "felted" feldspar microlites, a little augite, a little magnetite, and a considerable amount of glass. The feldspathic microlites are mainly alkaline labradorite, while the phenocrystic crystals are more calcareous, approaching Ab3 An4; but some of the microlites have angles of extinction appropriate to oligoclase. The slide shows decomposition products, especially chlorite, but not in important quantities.
Reconnaissance of the gold fields of southern Alaska with some notes on general geology