Dating quartz veins
Other plutonic rocks have less quartz and potassium, and different ratios of calcium and sodium feldspar minerals.True granites are relative latecomers on the geologic scene as they required a number of recycles of crustal material to differentiate and concentrate potassium.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. As igneous rocks cool, mineral crystals form following a specific sequence.The crystals develop an interlocking texture with some of the trace minerals becoming completely surrounded by later forming crystals.
Sedimentary rocks are secondary in formation, being the product of precursor rocks (of any type).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.Through the cycles of burial, folding, faulting, and subduction of crustal plates, rocks get pushed and dragged down to depths where - under heat and pressure - changes take place.In metamorphic rocks, new minerals form that are more stable at higher temperatures and pressures.
Geologists distinguish these types of rock based on their chemical and mineralogical composition.