Dating quartz veins
Volcanic rocks, because they are able to cool and crystalize rapidly, have a very fine-grained texture; the individual mineral grains are too small to see easily with the naked eye.
Plutonic rocks on the other hand cool very slowly, on the order of a million years or more for some deeply buried and insulated magmas.
These veins are probably similar to others that are widespread in the southern Valdez quadrangle.
Data summarized by Goldfarb and others (1997) show that gold-bearing quartz veins in the Valdez Group commonly contain pyrite, arsenopyrite, carbonate minerals, chlorite, and white mica and formed from water-rich fluids with 5 to 15 mole percent CO2 and significant amounts of CH4, N2, and H2S.
Nine lode claims were staked near Tertiary felsic dikes on narrow, gold-bearing quartz veins in metaflysch of the Valdez Group (Moffit, 1918; Winkler and others, 1981 [OFR 80-892-B]).
The quartz veins contain arsenopyrite, gold, galena, chalcopyrite, and sphalerite. D., 1981, Map and summary table describing mineral deposits in the Valdez quadrangle, southern Alaska: U. Geological Survey Open-File Report 80-892-B, 2 sheets, scale l:250,000.
One such individual is Robert Gentry, who holds a Master's degree in Physics (and an honorary doctorate from the fundamentalist Columbia Union College).
This prospect is on the east side of a souht tributary to Hurtle Creek; it is 1.7 miles southwest of elevation about 5,640 at an elevation of 4,000 feet in the NE1/4 section 8, T. It is locality 48 of Cobb and Matson (1972) and included in locality 40 of Winkler and others (1981 [OFR 80-892-B]).
This prospect is probably located to within 1 mile. M., Jr., 1981, Geologic map and summary geochronology of the Valdez quadrangle, southern Alaska: U. Geological Survey Open-File Report 80-892-A, 2 sheets, scale 0,000.
The mineral grains in these rocks can grow very large and are readily distinguished in hand samples.
Granite is a well-known type of plutonic igneous rock, but there are many others as well.