File:Cripple Creek Leucogranite (Mesoproterozoic, 1.43 Ga; Squaw Gulch roadcut, Cripple Creek Mining District, Colorado, USA) 1.jpg

English: Weathered granite in the Precambrian of Colorado, USA.

This roadcut is at the western boundary of the Cripple Creek Diatreme, the root zone of an ancient, eroded volcanic center of Oligocene age. The diatreme is variably mineralized with a suite of gold-bearing minerals.

Although mostly obscured by weathering stains, the rocks seen here represent the host rocks through which the diatreme intruded. This is part of the Cripple Creek Leucogranite. The rocks themselves are granitoids variously described as granite or quartz monzonite, but are best referred to as leucogranites (see discussion in Jensen, 2003, p. 561).

Cripple Creek Leucogranite consists of quartz, potassium feldspar (orthoclase & microcline), and plagioclase feldspar, plus minor dark minerals such as biotite mica, magnetite, and hornblende amphibole (Jensen, 2003).

This locality no longer exists. Since 2007, the road has been diverted, the adjacent valley of Squaw Gulch has been filled in, and the area is now part of the mining operation.

Geologic unit: Cripple Creek Leucogranite, Mesoproterozoic, 1.43 Ga

Locality: former Route 67 roadcut along the northern side of Squaw Gulch, Cripple Creek Mining District, southern Teller County, central Colorado, USA

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Reference cited:

Jensen (2003) - Magmatic and Hydrothermal Evolution of the Cripple Creek Gold Deposit, Colorado, and Comparisons with Regional and Global Magmatic-Hydrothermal Systems Associated with Alkaline Magmatism. Ph.D. dissertation. University of Arizona. 846 pp. 5 pls.