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43
<br /> Wobus, R. A., Finnemore, S., and Smith, D.; Geology of the Ten Percenter Pegmatite Mine, Lake
<br /> George District, Teller County, Colorado, in Holden, G. S., ed., Field Trip Guidebook, Geological
<br /> Society of America 1888-1988 Centennial Meeting, Denver, Colorado, Colorado School of Mines
<br /> Professional Contributions No. 12, p. 43-46
<br /> GEOLOGY OF THE TEN PERCENTER PEGMATITE MINE,
<br /> LAKE GEORGE DISTRICT, TELLER COUNTY, COLORADO
<br /> Reinhard A. Wobus 1, Sara Finnemore1, and Don L. Smith
<br /> iDepartment of Geology,Williams College, Williamstown,MA 01267
<br /> 2P.O. Box 55, Florissant,CO 80816
<br /> INTRODUCTION outer part of the Lake George intrusive center, and some are
<br /> also found in the coarse-grained granite nearby. The finer
<br /> The Ten Percenter pegmatite mine is on an active mining grained rocks have greater resistance to erosion than does the
<br /> claim in the Pike National Forest approximately 10 km north of typical coarse- grained Pikes Peak Granite, and most of the
<br /> Florissant, Colorado, and about 50 km northwest of Colorado higher elevations of the area,including Crystal Peak(2920 m),
<br /> Springs (Figure 1). It is located in the Lake George (Crystal are underlain by these finer textured granites.
<br /> Peak) pegmatite district, an area famous for museum-quality The amazonite-bearing pegmatites of the Lake George dis-
<br /> specimens of amazonite (blue-green microcline) and smoky tract are both mineralogically and structurally distinct from those
<br /> quartz for more than a century. (For the history of mineral col- of other well known pegmatite districts within the Pikes Peak
<br /> lecting in the area,see Odiorne, 1978,and for an explanation of batholith, such as the zinc-enriched pegmatites in the alkalic
<br /> the blue-green color of amazonite,see Foord, 1986.) Geologi- rocks of the St.Peters Dome Mount Rosa area southeast of Pikes
<br /> cally its location is near the western margin of the Late Peak(Gross and Heinrich, 1966)and the concentrically zoned
<br /> Proterozoic Pikes Peak batholith (ca. 1,010 Ma) (Hutchinson, pegmatites enriched in fluorine and rare-earth elements of the
<br /> 1986;Wobus,1986)and at the northern edge of the Lake George South Platte region in the northern part of the batholith(Sim-
<br /> intrusive center within the batholith (Wobus and Anderson, mons and Heinrich, 1980). They even differ from the nearby
<br /> 1978) Teller pegmatite(in Pikes Peak Granite only 10 km SW of the
<br /> The Lake George intrusive center consists of a late stock, Ten Percenter but lying outside the Lake George intrusive cen-
<br /> about 7 km in diameter,of finer grained textural variants of the Poe
<br /> Pikes Peak Granite which have been intruded by ring dikes and T. n—w a..•
<br /> a central stock of more sodie rocks such as syenomonzonite, °
<br /> quartz syenite,and fayalite granite.Large xenoliths of alkali gab- N
<br /> bro, some of them hundreds of meters long, occur in the
<br /> syenomonozonite stock and in the adjacent fine-grained Pikes -.••.# .
<br /> Peak Granite. Smaller xenoliths of diorite porphyry and
<br /> granodiorite are also found in Pikes Peak Granite in and near VXt cecnae
<br /> the intrusive center.As noted by Tweto(1987,P.A44),the com-
<br /> posite pluton at Lake George "...neatly records progressive ~ L SAM
<br /> change in magma composition"within the Pikes Peak batholith,
<br /> as it contains rock types representative of both the potassic and U.S.-2•
<br /> sodic differentiation trends observed in the batholith (Barker
<br /> and others, 1975). - a 1 2
<br /> Pegmatites and crystal-bearing miarolitic cavities are espe-
<br /> cially common in the fine- and medium-grained granite of the Figure 1.Index map showing location of Ten Percenter claim.
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