Economic geology of Gilpin County and adjacent parts of Clear Creek and Boulder Counties, Colorado

Geology and ore deposits of the Chicago Creek area, Clear Creek County, Colorado

“…ORIGIN The gradation between biotite-quartz-plagioclase gneiss, sillimanitic biotite-quartz gneiss, lime-silicate gneiss, and amphibolite and the interlayering and interlensing of the units suggest to the writers that these rocks are metamorphosed sedimentary rocks. The broad regional distribution of rocks of similar character has been pointed out by Ball (Spurr, Garrey, and Ball, 1908), Bastin (Bastin and Hill, 1917), Lovering and Goddard (1950), andLovering andTweto (1954). These rocks now contain mineral assemblages characteristic of the upper part of the amphibolite facies as defined by Turner (1948, p. 76-88).…”

Ages of selected intrusive rocks and associated ore deposits in the Colorado mineral belt

“…In the La Plata Mountains, it is associated with Laramide syenites that are among the latest intrusions. Tellurides formed during the latest of the four stages of mineralization at Central City (Bastin and Hill, 1917;Sims and others, 1963); the gold-telluride mineralization has been related genetically to an alkalic rhyolitic stock and may be younger than 53 Ma . At Jamestown, the telluride mineralization was probably related to the sodic granite stock dated at 45 Ma.…”

Paragenesis and structure of pitchblende-bearing veins, Central City District, Gilpin County, Colorado

“…In both the Quartz Hill and the Eureka Gulch areas, which contain the largest number and the most important deposits, the uranium occurrences ar«j along two or more fracture sets, some of which intersect0 At Quartz Hill, deposits in the German-Belcher, Kirk, and Wood veins have been mined (Bastin and Hill, 1917) 0 At Nigger Hill, in the Eureka Gulch area (Sims, Osteywald, and Tooker, 1955, p!0 1), deposits occur in three different fracture sets; the deposits in each of the sets are proved or are of probable economic importance,…”

“…Several papers describing certain aspects of the pitchblende deposits of the Central City district have been published,, The most important of these are Pearce (1895), Rickard (1913), Moore and Kithil (1913), Alsdorf (1916),, Bastin (1915Bastin ( , 1916, Bastin and Hill (1917), Lwering and Goddard (1950), and Phair and Levine (1953) Aside from the biotite-muscovite granite and the post-granite pegmatite, the rocks are metamorphosed and folded,, The major fold axes trend northeasterly and plunge gently to the northeast or southwest0 The folds are predominantly open and, except locally, the limbs dip less than 60°8 Lovering and Goddard (1950).…”