Economic geology of the Georgetown quadrangle (together with the Empire district), Colorado

Abstract

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Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

“…The name Silver Plume Granite was first applied to granitic rocks in the Georgetown quadrangle by Ball in Spurr and Garrey (1908). The rock of the type locality is aquigranular to porphyritic and has a hypidiomorphic-granular texture in thin section.…”

Journal of Research of the U. S. Geological Survey, 1974, volume 2, issue 5

“…The geology of the area has been described by S. H. Ball (in Spurr and Garrey, 1908) and Levering and Goddard (1950) Boulder Creek Granite in the west. Small dikes of bostonite and alaskite porphyry of Tertiary age intrude the older rocks.…”

Economic geology of the Idaho Springs district, Clear Creek and Gilpin Counties, Colorado

“…This age is close to approximate absolute age of 60 million years determined on uraninite from metalliferous veins of the region (Faul, 1954, p. 263), for the veins formed during the waning stage of igneous activity. Spurr and Garrey (1908), Ball (1908), and Bastin and Hill (1917) made the first comprehensive studies of the porphyries in the parts of the Idaho Springs district dealt with in their respective reports. Lovering and Goddard (1950) utilized these previous reports to aid their investigation of the whole Front Range mineral belt.…”

“…Spurr and Garrey (1908) and Ball (1908), during study of the Georgetown quadrangle, mapped the southern part of the district on a scale of 1: 62,500 and studied many of the most productive mines. Bastin and Hill (1917) mapped the north half of the Idaho Springs district (scale 1:12,000) during their study of the Central City quadrangle.…”