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<br /> ter),which resembles the South Platte district pegmatites with
<br /> its crude zonation and its enrichment in yttrium and rare earth
<br /> elements(Glass and Rose,1958).
<br /> As described by Foord and Martin(1979),the most charac-
<br /> teristic Lake George pegmatites are of the simple (unzoned) y
<br /> type, containing crystal-lined pockets that are mushroom-
<br /> shaped in cross-section and with a flat floor that is typically
<br /> above the median line of a pegmatite dike.Circular or elliptical a
<br /> in plan view and up to several meters in diameter and height,
<br /> these pockets may be completely filled with crystalline phases or 1
<br /> may have open space remaining.Most pockets with original void
<br /> space have collapsed,however,due to weathering and frost ac-
<br /> tion near the ground surface, and many are partly or entirely
<br /> filled with clay. Figure 3.Crystal-lined ceiling plate from Key-Hole vug,show-
<br /> ing well formed amazonite crystals interspersed with clevelan-
<br /> dite (albite)rosettes.Coin is 2.3 cm in diameter.
<br /> HISTORY AND PRODUCTIVITY OF they had originally grown in one of the ceiling or floor plates and
<br /> THE TEN PERCENTER CLAIM were broken off at the time of collapse of the pocket.
<br /> One of the largest specimens from the Key-Hole vug may now
<br /> The Ten Percenter claim has been owned and operated by be viewed in the Mineral Hall at the Smithsonian Institution in
<br /> Don L Smith of Florissant since 1973, although its history can Washington, D.C. Other large specimens have been sold to
<br /> be traced back to the early 1900's when it was prospected by natural history museums in Los Angeles,Houston,and Munich
<br /> Morgan James.James was more interested in locating gold than and to the University of Delaware and the New Mexico Institute
<br /> amazonite,however,and he threw what amazonite he found at of Mining and Technology. Private dealers and collectors have
<br /> the original excavation(next to the"upper pit")into the dump. purchased the rest.
<br /> The mine today consists of three open cuts, referred to as the
<br /> upper,central,and lower pits(figure 2).The area of the claim
<br /> is underlain primarily by coarse-grained Pikes Peak Granite GENESIS OF THE KEY-HOLE VUG
<br /> which is cut by an arcuate dike of quartz syenite at the eastern
<br /> edge of the claim. Large xenoliths of diorite porphyry and The sequence of events that produced the remarkable
<br /> granodiorite are enclosed by the granite and are exposed in both specimens of the Key-Hole vug appears to fit the model
<br /> the upper and lower workings. proposed by Foord and Martin(1979)for other amazonite-bear-
<br /> Minerals that have been extracted from pegmatites on the ing pegmatites of the Pikes Peak batholith. According to this
<br /> Ten Percenter claim include,in alphabetical order:amazonite, model, adapted from the classic Jahns and Burnham study of
<br /> apatite, clevelandite (albite), columbite-tantalite, fluorite, pegmatite genesis (1969), pegmatite dikes form from residual
<br /> galena,phenakite,smoky quartz,and topaz.The most important hydrous fluids during the late stages of consolidation of a granite
<br /> production to date occurred in June,1986,with the discovery of magma. A pocket such as the Key-Hole vug is most likely to
<br /> the Key-Hole vug in the lower pit of the Ten Percenter claim. develop above the median line of such a dike,particularly at an
<br /> (For a detailed account of this discovery, see Smith and inflection point where the dip of the dike suddenly changes.
<br /> Rosemeyer, 1986).This vug,with the characteristic mushroom As elaborated by Foord (pers. communication, 1986), the
<br /> shape and flat floor,is nearly 23 in high and 2 m in diamter.It silica- enriched volatiles from which the crystals of the cavity
<br /> is located at an upward bend in a gently dipping pegmatite dike. formed might,under more typical conditions,have continued to
<br /> A vein of milky quartz 15 cm wide that cuts all other rock types precipitate quartz to fill the cavity completely with a massive
<br /> is exposed in the roof above the cavity. quartz core,thus freezing in many of the earlier formed crystals
<br /> The vug yielded sixteen large crystal-lined ceiling and floor in a quartz matrix from which they might not have been extrac-
<br /> plates,some weighing more than 100 kg and measuring up to 80 table. Alternatively, had the vapor phase remained in contact
<br /> cm across. The plates consist mostly of deep blue-green am- with the earlier formed amazonite and albite crystals for a longer
<br /> zonite crystals up to 10 cm long interspersed with fine-quality time under changing conditions of pressure and/or temperature,
<br /> white clevelandite rosettes several cm in diameter (figure 3)_ some of the feldspars might have been redissolved in or at least
<br /> Only a few small smoky quartz crystals protrude from any of the severely etched by the vapor, thereby either detracting from
<br /> specimens;the rest of the more than 1000 larger smoky quartz their quality or destroying them entirely.Clearly neither of these
<br /> crystals recovered were imbedded in a jackstraw fashion in iron- alternatives was realized during formation of the Key-Hole vug,
<br /> stained clays on the floor of the vug.Several of these crystals ex- most likely due to a relatively rare situation involving rupture of
<br /> ceed 30 cm in length, 80 percent are doubly terminated, and the pocket and the bleeding off of its volatiles at a critical time
<br /> some have broken bases with albite attached, suggesting that aL=formation of the feldspar crystals but pLiar IQ the time when
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