The geological distribution of gold with respect to the time of their origin in geological periods involves to a certain extent the consideration of their distribution and occurrence according to the various periods. For example, the Pacific Coast ranges upon the west carry tin. The next belt is that of the Sierra Nevada and Oregon Cascades, which upon their west slope bear two zones, one of copper and a middle line of gold deposits. These gold veins and the resultant placer mines extend far into Alaska, characterized by the occurrence of gold in quartz,, by a small amount of that metal which entangled in iron sulphides, and by occupying splits in the upturned metamorphic strata of the Jurassic age.
Lying to the east of this zone, along the east base of the Sierras, and stretching southward into Mexico, there is a chain of silver deposits, containing comparatively little base metal and frequently included in volcanic rocks. Through Arizona, Nevada and Central Idaho is another potential zone of silver deposits, mineralized with complicated association of the base metals and more often occurring in older rocks. Through New Mexico, Utah and Western Montana were noted some zones of argentiferous galena. To the east, again, the New Mexico, Colorado, Wyoming and Montana, was identified the presence of a gold belt.
Although numerous rich locations occur in igneous formations of the Tertiary period, no many gold fields of the present day are identified with sedimentary rocks later than the cretaceous. Nevertheless, it can be stated that a conglomerate of undoubted Tertiary age, covering an extensive area in southeastern Colorado contains gold veins, which were mined at a profit. If eruptive rocks be included, the gold veins of the old Monte Cristo, in the state of Washington, occurred in andesite and tonalite of Pleistocene or Quaternary age, and at Steamboat Springs, Nevada, gold was detected in cracks traversing the sinter around a thermal vent. The granitoid gneiss of western Ontario is traversed by important gold-bearing veins. Therefore the record of the rocks, in regard to their association with the occurrence of gold is possible throughout the main divisions of geological time.
Deposits of gold are occurred in rocks of every age, and in rock of every kind. The precious metals was deposited later than the encasing rock and it is likely that since it was so deposited it has been subject to constant solution and precipitation, by which has been redistributed and concentrated. The first deposition, the time when it was brought from below the zone of fracture to the place of precipitation was associated with thermal activity following upon regional movements and volcanic eruptions, the time of first formation may have been late or early, in the Cambrian or the Cretaceous of geological history. But once so deposited, it became at once the sport of the chemical waters that find a passage from the surface and from the deep. These may have effected a redistribution of the gold along the fractures where the ore lies.