Geology and beryllium deposits of the Lake George (or Badger Flats) beryllium area, Park and Jefferson Counties, Colorado

Abstract

The Lal\:e George (or Badger Flats) beryllium area is a terrane of Precambrian rocks on tlie southwest side of the Front Range in Colorado. Its southeastern and southwestern parts are underlain mainly IJy the metasedimentary Idaho Springs Formation, the metaigneous Boulder Creek ( ?) Granodiorite, and the Silver Plume( •n Granite. The northern and central parts of the area are underlain principally by the Pikes Peak and Redsldn Granites. Locally the Precambrian rocks are masked by thin tuffs and boulder deposits of Tertiary ( ? ) age and by colluvium and alluvium of Quaternary age.The oldest rocks-Idaho Springs Formation, amphi•bolite and hornblendite, and Boulder Creek ( ?) Granodiorite-were in-• volved in a period of plastic deformation during which a major north-northeast-trending fold, the Round Mountain syncline, formed. Subsequently they were strongly deformed and regressively metamorphosed by the intrusion of the Silver Plume(?) Granite. The emplacement of the youngest Precambrian igneous rocks-the gabbro and monzonite, Pikes Peak Granite, and Redskin Granite-had little structural effect on the older rocks. Locally the rocks were cataclastically deformed sometime after the plastic deformation but before emplacement of the youngest igneous rocks. They were faulted in several episodes. Movement along the Badger Flats fault, a major structure of the area, possibly occurred before emplacement of the Silver Plume ( ?) . Movement -along most of the other faults first occurred in Precambrian time.The principal ore deposits are nonpegmatitic beryllium deposits that occur in veins, pipes, and other forms generally encased in greisenized wallrocks. The greisens contain quartz, muscovite, topaz, and fluorite, and trace elements, such as lithium and tin, that are typical of greisens. The principal deposits are concentrated in four parts of the area that are in or very near the Redskin Granite. Small concentrations of beryllium minerals and greisen bodies that contain only trace amounts of beryllium are more widely distributed.Most of the beryllium occurs in beryl, which forms hexagonal crystals and massive poikiloblastic grains. Some of the beryllium occurs in bertrandite, which may be the dominant beryllium mineral in some ore bodies or parts of ore bodies. Very small amounts of the beryllium occurs in euclase. The beryllium deposits locally contain arsenopyrite, wolframite, molybdenite, galena, and dark sphalerite, and these minerals and other sulfides and oxides are locally concentrated in small ore shoots near beryllium deposits or in greisenized rocks nearly free of beryllium. The gangue of most deposits is formed by the typical greisen minerals.Though the deposition of ore minerals and the formation of greisens were nearly contemporaneous, the ore minerals are somewhat younger than the greisens. Quartz, muscovite, and fluorite, which form the bulk of the greisens, also occur with the ore minerals and were deposited during a long period of time .. The beryllium deposits and associated greisen are closely related ...

Non-pegmatitic Deposits of Beryllium: Mineralogy, Geology, Phase Equilibria and Origin

“…Petrological studies of several systems in Nigeria, Karelia and Mongolia show that mineralizing fluids are of magmatic origin and saline (10 to >40 wt % NaCl eq ), can have moderate CO 2 contents, commonly show evidence of phase separation, and were trapped at temperatures from 200 to 500°C (Haapala 1977a;Imeokparia 1992; Akande and Kinnaird 1993;Graupner et al 1999). (Hawley 1969). The Redskin granite is late, highly evolved phase of the 1 Ga Pikes Peak batholith (Desborough et al 1980).…”

A review of the Pikes Peak batholith, Front Range, central Colorado: A "type example" of A-type granitic magmatism

“…Hutchinson mapped flow structures and primary fracture systems that defined inwarddipping, funnel shaped patterns within each center, indicating that magma was fed into the centers at an angle of 65' -80" along S 40" -50' E direction. Other studies were conducted by Hawley and his colleagues (Hawley et al, 1966;Hawley, 1969;Hawley and Wobus, 1977), who worked in the Wrryall Mountains and Redskin stock, and by Gross andHeinrich (1965, 1966), who focused on the Mount Rosa intrusive center. Sage (1966) and Stewart (1964) completed master's theses on the Cripple Creek and Lake George intrusive centers, respectively.…”

Uranium concentrations in natural waters, South Park, Colorado. [Part of National Uranium Resource Evaluation program]

“…'ire, in adjacent Jefferson County, produces uranium from Tertiary ores rr--2;-ir,g sitchblende, torbernite, and autunite in the metasediments of the --=c="iri3n Idaho Springs formation. 18 Uraninite in small amounts (mostly of -"5 sc-OTy pitchblende variety, all in ore deposits of Precambrian age), is rezzr-rez' fron the Boomer, Redskin, and Black Prince Mines, 16 of the Boomer Mine, where anomalous radioactivity was noted on the mine dump in the early 1950's, are in the Idaho Springs formation and the Salver Plune (?) granits.…”

“…The group of springs located in the Badger Fiats District, where uranium has been reported, 16 all have waters with relatively high uranium concentrations (Sites 94-99 and Site 108). All of these springs emanate from the Precambrian granites known to contain radioactive minerals in greisen pipes, stocks, and fault zones, as described in Section !V.…”

“…However, the Lady Stith uraniferous fluoritebearing veins are in the general vicinity, 19 and similar rocks in the Badger Flats area, some 25 to 30 km to the northwest, are known to possess some uranium mineralization in fault zones and greisen pipes. 16…”