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Home , Lustre (mineralogy), Pegmatite, Silicic

Geology of the Creek District Gunnison County Colorado

GEOLOGICAL SURVEY PROFESSIONAL PAPER 265 GEOLOGY OF THE QUARTZ GREEK PEGMATITE DISTRICT, GUNNISON COUNTY, COLORADO

Bv MORTIMER H. STAATZ and ALBERT F. TRITES

ABSTRACT No correlation could be found between the of The Quartz Creek pegmatite district includes an area of about in the and the type of country , or 29 square miles in the vicinity of Quartz Creek in Gunnison the presence of various accessory . County, Colo. This area contains 1,803 pegmatites that are Median index of refraction determinations on 95 specimens intruded into pre-Cambrian rocks. of showed no constant variation from wall zone to core The rocks exposed in the district range in age from pre-Cambrian. or from layer to layer. Optical properties of curved muscovite to Recent. The oldest pre-Cambrian rocks are chiefly quartzites are identical with those of the flat variety. interbedded with a few arkoses and conglomerates. These The higher index of refraction was determined for 183 rocks are surrounded by more abundant specimens. Beryl in pegmatites containing only a wall zone and and tonalite. A small body of hornblende- tonalite a core showed no difference between zones; but in pegmatites and two thin layers of dacitic pillow lava are present. The that have intermediate zones, the indices of refraction of the hornblende gneiss and tonalite have the same composition and beryl indicated an increase in the alkali content inward from the differ only in texture. The older material (hornblende gneiss) contact. Beryl occurs with almost all the pegmatite minerals has a well-marked lineation, whereas the younger (tonalite) is and is not restricted in its associations. equigranular. Subsequently, a large body of quartz monzonite , with the exception of the black variety, is as­ was intruded along the northern boundary of the mapped area. sociated with . Dark-green and blue tourmaline is Later, coarse-grained was intruded in the southern part found in the outer zones of pegmatites containing lepidolite, and of the area. Dikes of fine-grained granite cut the coarse-grained the pink and light-green varieties are found in direct contact variety. The last stage of igneous activity in the pre-Cambrian with lepidolite. is marked by a large number of pegmatitic intrusions. Lepidolite occurs as aggregates of small flakes, as flat plates, and as curved plates; the three varieties are optically identical. The pre-Cambrian rocks were tilted and eroded, and the flat- The lighter colored varieties have higher indices of refraction lying Morrison formation of Jurassic age deposited on the irregular surface. This formation is conformably overlain by the and contain less lithia than the darker varieties. The following minerals are described in detail: perthite, quartz, Dakota sandstone of Cretaceous age. Faulting produced a martite, biotite, , -, , , vertical offset of 410 feet in the Mesozoic sediments along the , , , and an unidentified mineral. only large fault in the area. At the end of the Mesozoic era Lack of alteration in the wall rocks adjacent to the pegmatites there was another interval of erosion. Tertiary (?) tuff is exposed is interpreted as indicating that the original pegmatitic fluid in three small, scattered areas in the southern part of the dis­ did not have an excess of materials such as B, OH~, and P needed trict. It overlies both the Dakota sandstone and pre-Cambrian to form alteration minerals. Because of their low concentration, formations. Glacial till occurs along the edges of Quartz Creek the above materials were available only in the pegmatitic fluid and Wood Gulch. Quaternary alluvium fills valley bottoms. during its . Pegmatites that contain the rare Although the composition of the country rock has little effect on minerals, such as beryl, tourmaline, curved muscovite, biotite, the shape of the pegmatites, the foliation imposed on this rock , monazite, columbite-tantalite, cleavelandite, topaz, has a localizing effect and generally controls the ultimate shape of lepidolite, and microlite, show a grouping in clusters within the pegmatites. Zoned and related internal structures are not well district. developed in the pegmatites of this region. Many of the peg- Beryl-bearing pegmatites occur most abundantly in horn­ matities are homogeneous and those that are zoned usually blende gneiss and are only rarely found in either granite or contain a large wall zone and small discontinuous cores. In quartz monzonite. addition to the more common homogeneous and zoned pegma­ The types of minerals that form in a pegmatite appear to be tites, 7 percent of the pegmatites show a layered structure of determined by the character of the fluid segregated from the textual and mineralogical units not repeated on the opposite original and by the spacing and length of the period side of the pegmatite. Other internal structural units include during which it segregated. The distribution of the rarer pegmatites which vary in composition along strike, multiple or pegmatite minerals in different groups is related to their origin, "line-rock pegmatites," and fillings. and they are found in pegmatites derived by later segregation. The of the pegmatites is described in detail. The pegmatites formed from the earlier stages of the segregation Specific attention was given to most of the 27 observed minerals. contain minerals commonly found in . A study of indices of refraction of 439 specimens of plagioclase Inferred reserves of the district are estimated for beryl, scrap showed that the variation from zone to zone and layer to layer , to be expected from both hand-cobbing and is minor and that there is no systematic variation in the district. milling, lepidolite, columbite-tantalite, topaz, monazite, and QUARTZ CREEK PEGMATITE DISTRICT, COLORADO microlite. No sheet mica was found. As reserves are small and 3 E., New Mexico principal meridian, Gunnison County, transportation costs are high, substantial production of low- Colo. (fig. 1). It covers about 29 square miles in the priced feldspar and scrap mica will depend on the adoption of vicinity of Quartz Creek. State Highway 162 follows economical milling techniques for recovering the large quantities of feldspar available. Beryl is irregularly distributed, and its Quartz Creek through the district and joins United recovery as a byproduct will depend 011 the establishment of a States Highway 50, 2 miles south of the southern stable market for feldspar and scrap mica. Lepidolite reserves boundary of the mapped area. A road branching are small and of low grade. from State Highway 162 crosses the southeastern corner of the area and connects with United States INTRODUCTION Highway 50, 1 mile west of Doyleville. Unimproved Prior to World War II the Quartz Creek pegmatite roads follow several of the valleys, and a mine-access district was well known for its fine specimens of colored road, made during World War II, connects State High­ tourmaline, topaz, microlite, and books of lepidolite. way 162 with the Brown Derby mine. The nearest During and after World War II small quantities of railroad shipping point, Parlin, is on a narrow-gage line beryl, lepidolite, and minerals were produced of the Denver and Rio Grande Western Railroad, from the district. which connects with standard-gage lines of that rail­ road at Salida to the east and Montrose to the west. LOCATION AND SURFACE FEATURES The slopes are moderately steep, and the surface The Quartz Creek pegmatite district is on the western has a maximum relief of 2,200 feet. The highest point slope of the Sawatch Range in Tps. 49 and 50 N., R. in the district is near the northern boundary and has

109° 108° 107 106 105° 104° 103 102°

Quartz Creek Pegmatite District Gunnison

109° 108° 107° 106° 105° 104° 103° 102° FIGURE 1.—Index map of the Quartz Creek pegmatite district. Colo INTRODUCTION an altitude of 10,238 feet. Quartz Creek, the principal area mapped. No pegmatites are shown on their map, drainage of the area, flows through a flat cultivated and the area now known to contain them is designated valley that ranges from a quarter to half a mile in "granite." The area around Tomichi Dome, several width. The hills rising from Quartz Creek generally miles to the east of the Quartz Creek district, has been are sage covered, and the north-facing slopes of the described by Stark and Behre (1936, p. 101-110). higher hills are covered with aspen or spruce and pine. Between September 1942 and December 1944 the Quartz and Alder Creeks are the only permanent U. S. Geological Survey had several field parties map­ streams in the district, but water flows in Willow Creek ping in Colorado, under E. W. Heinrich in 1942, and un­ and through Wood Gulch during the spring and early der John B. Hanley in 1942-44 (Hanley, Heinrich, and summer. Page, 1950, p. 63-80). In the Quartz Creek district PRODUCTION these parties mapped in detail—on scales ranging from The recorded" production of pegmatite minerals from 1:240 to 1:600—the Opportunity No. 1 claim, the the Quartz Creek district is 51 tons of beryl, 283 tons Brown Derby No. 1 claim, the Brown Derby Ridge of lepidolite, 140 tons of scrap mica, 5,000 pounds of pegmatites, the Brown Derby No. 5, the White Spar tantalum and columbium minerals, and 15 pounds of No. 1, the White Spar No. 2, and the Bazooka pegma­ monazite. tites. In all, 25 pegmatites were mapped with plane From September 1943 to the spring of 1945 the table and telescopic alidade. Several other pegmatites Brown Derby property was leased by the Hayden were visited and described. Mining Co. Prior to Februaiy 1945, 3,155.67 pounds FIELD WORK AND ACKNOWLEDGMENTS of beryl (J. B. Hanley, oral communication) were sold to the Metals Reserve Company and 283 tons of The investigations carried out by the U. S. Geological lepidolite to the Corning Glass Co. In addition, 4,000 Survey in the Quartz Creek pegmatite district during pounds of microlite concentrate containing 52 percent World War II were concerned primarily with pegma­ microlite was stockpiled at the mill and later sold. tites from which feldspar, muscovite, and minerals Though the final production figures are not available, containing , tantalum, , and the rare they are not greatly in excess of these figures as mining earths were produced. Such pegmatites are in the was stopped in the spring of 1945. minority, and time did not permit detailed study of The White Spar No. 1 and No. 2 pegmatites, which the associated, more numerous, unproductive pegma­ are 0.8 mile north of the Brown Derby mine, for a tites, or of the broader relations of pegmatites to the short time during World War II were mined by the regional geology. This study, started in 1948, was Colorado Feldspar Co. The production of lepidolite made not only to provide an economic appraisal of and feldspar is not known but was small. individual deposits but also to determine the regional There was no mining in the district from 1945 to 1947. relationships of pegmatites and country rock. Mr. Rod Fields located the Bucky claim on the east The field work for this report was started on July 10, side of Willow Creek and started to mine beryl in the 1948. M. H. Staatz and P. T. Flawn began mapping spring of 1948. Mr. Fields produced 17 tons of beryl on the east side of Quartz Creek and A. F. Trites and and in November 1948 sold the property to Beryllium F. L. Klinger on the west side. Field work was re­ Mining Co., Inc., which has produced, to May 1950, cessed September 7, 1948. It was resumed on June 12, 32.0 tons of beryl, 139.6 tons of scrap mica, 1,020 1949. and completed December 10, 1949. The writers pounds of columbite-tantalite, 15 pounds of monazite, were assisted for 3 months during 1949 by F. L. Klinger and 13 pounds of a mineral resembling samarskite. and for 2 months by J. D. Vogel. Mapping was done The last two minerals were sold to Ward's Natural by pace and by Brunton compass; the Pitkin quad­ Science Establishment, Inc. rangle topographic map enlarged to a scale of 1:12,000 was used as a base (pi. 1). Individual pace and com­ PREVIOUS WORK pass maps also were made of each pegmatite on scales Early papers on the pegmatites of the Quartz Creek ranging from 1:480 to 1:2,400, depending upon the size district have been concerned chiefly with the miner­ of the pegmatite. Petrographic work was done during alogy of the Brown Derby pegmatites (Eckel, 1933, p. the spring of 1950. 239-245; Landes, 1935, p. 333; Eckel and Levering, The percentage of all minerals except beryl was 1935, p. 77-79). A map showing the regional geology visually estimated for each unit and is presented in of the Gold Brick district, on a scale of 1.5 inches equal table 20. Where a significant amount of beryl was 1 mile, was published by Crawford and Worcester (1916). present in a pegmatite unit, its percentage was deter­ The southwestern corner of their map, an area roughly mined by a modified large-scale Rosiwal method, by 3.3 by 2 miles, overlaps the northern part of the present which a measured area of the unit, at least 1,000 times QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

larger than its average grain size, was compared with intruded by many fine-grained pink granite dikes and the total measured area of beryl exposed in the unit. by a large number of pegmatites. Index determinations were made in white light, using An angular unconformity separates the pre-Cambrian carefully checked oils, and were corrected for variance rocks from the flat-lying Jurassic Morrison formation in temperature. In some cases, results were repeatedly and the Cretaceous Dakota sandstone which crop out checked, and it is believed that the index determina­ along the east and west sides of the area. tions for all minerals with indices below 1.700 have an Flat-lying Tertiary(?) tuff is exposed in three scat­ accuracy of ±0.001. Indices above 1.700 have an tered patches overlying unconformably both the Dakota accuracy of ±0.005. Specific gravities of monazite sandstone and pre-Cambrian rocks. Small areas of and columbite-tantalite were determined by Jolly bal­ glacial till border Quartz Creek and Wood Gulch, and ance. All specific gravity readings were made at least Quaternary alluvium fills many of the valley bottoms. twice, and it is probable that the accuracy of the re­ In general, the pre-Cambrian rocks dip steeply sults is about ±0.3. and have a northwesterly trend, which is shown by L. R. Page, of the Geological Survey, was the im­ the bedding of the metasedimentary rocks and the mediate supervisor of this project. McClelland Dings trend of the dacitic pillow lava. The pegmatites and Charles Robinson, also of the Survey, spent a day have a general northeast trend across all the earlier in the field helping in the stratigraphic study of the structures. Dakota and the Morrison formations. Two days were Only three faults with displacements of more than 20 spent with N. L. Bowen, J. F. Schairer, O. F. Tuttle, feet were found in the area. The largest of these and M. L. Keith, of the Geophysical Laboratory, in trends northwest and separates the Dakota and Mor­ reviewing some of the geochemical problems of peg­ rison. formations from the pre-Cambrian in the south­ matites. C. H. Behre, Jr., of Columbia University western corner of the district. Two other faults, cut spent 3 days in the field with the authors, and gave bj^ this large fault, separate a block of Dakota sandstone many valuable suggestions. Laboratory work was from the pre-Cambrian and Morrison formations. aided by helpful advice from John W. Adams. PRE-CAMBRIAN ROCKS The writers are glad to acknowledge the whole­ QUARTZITE hearted cooperation and hospitality of the people of the district. Particular thanks are due to Mr. Charles Pre-Cambrian quartzite, interbedded partly with Wemlinger, of the Beryllium Mining Co.; Mr. Rod arkosic quartzite and conglomerate (pi. 1), is best Fields, of the Bucky mine; and Mr. Jesse Fields, of the exposed on the slopes of Wood Gulch in four areas. Beryl and Rare Minerals lode. Two parallel bodies of arkosic quartzite, each about half a mile long, crop out along the headwaters of This investigation was made in part on behalf of the Division of Raw Materials of the United States Atomic Tollgate Gulch, a tributary of Quartz Creek, which is Energy Commission. northwest of Wood Gulch. Narrow outcrops, a few tens or hundreds of feet long, are found at widely GENERAL GEOLOGY scattered localities on the northern side of Quartz Creek. These rocks have been highly metamorphosed The rock units mapped in the Quartz Creek pegmatite and are part of a much larger area of sedimentary district range in age from pre-Cambrian to Recent rocks, separated by intrusive tonalite and hornblende (pi. 1). The age of the Brown Derby No. 1 pegmatite, gneiss. as determined from -bearing microlite collected The pre-Cambrian quartzites generally are dark by Eckel and Lovering (1935, p. 79), is 760 million years. gray but in places are white and brown. The original The oldest pre-Cambrian rocks consist of metasedi- sediments ranged in size from silt to gravel, but most mentary rocks, predominantly quartzites, surrounded were fine grained. Some of the quartzites are now by younger and more abundant hornblende tonalite slightly schistose. The northernmost unit of the meta­ and hornblende gneiss (a metatonalite). Included in sedimentary rocks in Wood Gulch is a conglomerate con­ this series are two small bands of dacitic pillow lava and taining pebbles that range in diameter from 0.1 to 2 one of hornblende-biotite tonalite. A coarse-grained inches. Some of the pebbles are elongated; the ratio porphyritic granite, similar in appearance to the Pikes of width to length ranging from 1:4 to 1:5. Feldspar Peak granite (Eckel, 1933, p. 240) intrudes the earlier (, , and plagioclase) is present pre-Cambrian rocks in the south-central part of the throughout the unit, but the proportion varies widely. district and a large quartz monzonite intrusive body The rocks along Wood Gulch are commonly quart­ occurs in the extreme northern part. The hornblende zites with only a few percent of feldspar, but those on gneiss, granite, and quartz monzonite are in turn the north side of Quartz Creek contained 20 percent or GENERAL GEOLOGY more of feldspar. The amount of the dominant dark Wood Gulch. It is approximately 900 feet long and mineral, biotite, ranges from a trace to about 15 percent. 110 feet wide and is bounded on the north by pre- Muscovite is common in amounts of one percent or less. Cambrian quartzite and on the south by hornblende In rocks rich in feldspar, is prominent and may gneiss. It is approximately 80 feet southwest of a band comprise more than 50 percent of the rock. One of pillow lava; the long axes of the outcrops of the specimen contains hornblende and as well hornblende-biotite tonalite and of the pillow lava are as biotite. , , and magnetite are common parallel. accessories. The biotite tonalite is dark gray with prominent Quartz-mica , composed chiefly of quartz, black hornblende , 0.05 inch in diameter, in a biotite, feldspar, and muscovite, are found in a few scattered outcrops in the northern part of the area. Locally, these schists contain well-developed porphyro- blasts of quartz and magnetite. At different exposures the formation ranges in thick­ ness from a few feet to a maximum of about 600 feet. The quartzites are the oldest rocks in the district and are surrounded by younger hornblende gneiss, tonalite, and granite. One xenolith of conglomerate was found in the granite.

DACITE Dacitic pillow lava crops out in two northwesterly- trending bands south of Quartz Creek; one on the north­ western slope of-Wood Gulch in sec. 11, T. 50 N., E 3 E. and the other about 900 feet northwest of the Brown Derby mine- The pillow lava is yellow green to dark green, de­ pending on the proportion of epidote. It is a fine­ grained, dense, vesicular rock. Some vesicles contain well-developed crystals of epidote and quartz; a few are completely filled with fine-grained quartz. Large ellipsoids or pillows (fig. 2), several feet long and about one foot wide, are common. LTnder the microscope the unaltered rock is seen to consist of green prismatic hornblende (50 percent), quartz (30 percent), and (20 percent). Epidote may be present almost to the exclusion of other minerals and is veined by . FIGUKE 2.—Pillow lava showing ellipsoidal pillows on northwest side of Wood Gulch. The band of pillow lava on the northwestern slope of black, speckled, fine-grained matrix. Plagioclase phe- Wood Gulch is 140 feet thick and is conformable with the enclosing pre-Cambrian quartzite and conglomerate. nocrysts, the same size as the hornblende crystals, This pillow lava, was extruded under water over a sand contain small included grains of biotite, epidote, and and was covered by later sediments. A second band of hornblende. Dark minerals make up about 50 percent pillow lava, 6,450 feet to the northwest, is enclosed in of the rock. Hornblende, the chief dark mineral, hornblende gneiss. The two areas of pillow lava (pi. 1) constitutes 25 percent of the rock and commonly forms are almost alined on strike and are probably remnants ragged prismatic grains; but locally it occurs as small of the same layer. Both bands of pillow lava are included grains in the plagioclase and quartz. Biotite younger than the pre-Cambrian quartzites to the constitutes 22 percent of the rock and occurs with northeast and older than the quartzites to the hornblende as aggregates and in the plagioclase as a southwest. myriad of randomly oriented fine grains. Epidote HORNBLENDE-BIOTITE TONALITE (3 percent) and magnetite «1 percent) are the other One small body of hornblende-biotite tonalite is dark minerals. Andesine (40 percent) forms large exposed in section 11 on the northwestern slope of crystals clouded with many fine crystals of biotite,

207133—55- 6 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO hornblende, and epidote. Quartz (10 percent) is host rocks for a very large number of pegmatites, and interstitial to the andesine. many fine-grained granite dikes. The hornblende-biotite tonalite occurs near the The hornblende gneiss and tonalite range in texture southwest edge of the pre-Cambrian quartzite and has from fine to coarse grained; the maximum grain size a trend parallel to the strike of the bedding in the is about 0.20 inch. Textures or structures commonly quartzite. It is similar in composition to the pillow found are: (1) Prominent, well-banded gneissic struc­ lava, but it is not vesicular and contains much less ture, (2) intersertal texture, (3) porphyritic texture, epidote and no calcite. It is also much coarser grained. and (4) equigranular texture. Exposures of this rock The similarity in trend and composition suggests that are, in general, poor, and even where well exposed the the hornblende-biotite tonalite and the pillow lava textural changes are so great that in most places separa­ were derived from the same magma. tion into mappable units was not feasible. Both rocks are dark gray to greenish black where fresh, and weather to colors whose extremes are greenish gray and The hornblende gneiss and the tonalite grade to­ reddish brown. The hornblende content ranges from 20 gether—sometimes in the same outcrop—and because to 80 percent, but most of the rock contains from 50 to the difference in the two rocks is one of structure, the 75 percent hornblende. Some facies are unusually rich hornblende gneiss and the tonalite were mapped sepa­ in hornblende, and the rock may then grade into a rately only along the northwestern slope of Wood hornblendite or perknite. Gulch, where fine-grained hornblende gneiss is very The minerals in the hornblende gneiss and tonalite schistose and is cut by the coarser, equigranular horn­ are essentially the same, but the proportions of each blende tonalite (fig. 3). These two rocks are evi- vary widely. Hornblende, biotite, and feldspar are the only minerals that can be identified megascopically. In places much of the hornblende has altered to biotite. Andesine is the dominant light-colored constituent, but quartz and microcline are present locally. The accessory minerals are apatite, zircon, sphene, mag­ netite, epidote, chlorite, and sericite. Much of the hornblende is present as distinct, dark- green euhedral crystals, but part is present as frayed, ragged, pale-green grains. In one place it is altered to chlorite. Biotite is not found in some areas, but in others it is abundant. It forms as much as 60 percent of the rock, commonly is unaltered, and occurs in brown prismatic crystals. Andesine (An30—An44) is poorly twinned and commonly is clouded with fine kaolin and FIGURE 3.—Tonalite outcrop on northwest side of Wood Gulch. sericite. The andesine crystallized after the hornblende dently of different ages, the tonalite having been in most places and fills the spaces between the horn­ intruded after the older rock had been metamorphosed blende crystals; in a few places the opposite is true. considerably. The intrusive hornblende tonalite bod­ In most specimens quartz is present, constituting a ies in Wood Gulch have a northwesterly trend, parallel maximum of 7 percent of the rock and occurs as small to that of the pre-Cambrian quartzitcs. clear grains with sutured borders. The grains are The foliation of the hornblende gneiss south of interstitial to the andesine; rarely they are micro- Quartz Creek has a north to northwesterly strike and graphically intergrown. Because of the presence of dips steeply in either direction. North of Quartz Creek a small amount of quartz, the rock is called a tonalite the strike ranges between north-northwest and north- rather than a (Crawford, 1916, p. 27-28). northeast, except adjacent to the quartz monzonite Microcline is present in a few places, but in most of the where the foliation parallels the contact. rock examined it is absent. A trace to several percent The hornblende gneiss and tonalite have the widest of apatite and zircon are almost universally present as distribution of any rock type and occupy the central euhedral crystals associated with biotite. Epidote and part of the Quartz Creek district. These rocks sphene are found locally, usually where the hornblende extend beyond the area mapped for a considerable is pale green and has been considerably altered. Mag­ distance to the northeast, where they have been de­ scribed by Crawford (1916, p. 27-28). They are the netite occurs in irregular grains and is not common. was noted in one specimen. GENERAL GEOLOGY

QUARTZ MONZONITE cuts across foliation in many places; and (3) the peg­ Quartz monzonite crops out along the northern bound­ matites that cut the granite and quartz monzonite ary of the Quartz Creek district. Pegmatites, similar have a composition more similar to the granite and in size and shape to those in hornblende gneiss, are appear to have been derived from it rather than from relatively large and regular near the outer edge of the the quartz monzonite. intrusive. Farther within the mass the pegmatites are only a few inches thick and are very irregular in COARSE-GRAINED GRANITE shape. A large band of coarse-grained granite (pi. 1) trends The quartz monzonite is a light- to dark-gray por- north-northwest across the district from the north­ phyritic rock that ranges in composition from quartz eastern corner of section 22 to the northern border of monzonite to . Poor exposures make it section 33. This granite forms the prominent moun­ difficult to map the variations of this rock in the field. tains on the southeast side of Quartz Creek. Another Mafic minerals (12 to 22 percent) form clots and band of massive granite crops out a mile to the west streaks composed of biotite, hornblende, zircon, sphene, and extends about a mile north of the southern bound­ magnetite, and apatite. Hornblende (trace to 15 ary of the area mapped. These two granite masses percent), the dominant dark mineral, generally has converge several miles south of the Quartz Creek been frayed and altered to biotite. Biotite (7 to 14 pegmatite district to form a large V-shaped intrusion. percent) occurs in small brown unaltered flakes and In addition to the two large granite plutons, many in clots or aggregates that appear megascopic-ally to be large crystals. Apatite and magnetite (1 to 2 percent) commonly occur with biotite. Zircon, in trace quan­ tities, is universally present as small crystals. Wedge- shaped crystals of brown sphene locally make up as much as 5 percent of the rock. The leucocratic min­ erals are quartz, andesine, and microclme. Both andesine and microcline are in large and in smaller grains in the groundmass. The feldspar content ranges from about 12 to 45 percent microcline and from about 30 to 65 percent andesine. The plagio- clase has a composition of An 31-An35 . Microcline shows crosshatch twinning in most places. No quartz is observed megascopically, but in thin section small clear grains, interstitial to the , make up 4 to PIQUEE 4.—Coarse-grained granite along the divide between "Wood Gulch and 15 percent of the ruck. The quartz exhibits strain Quartz Creek. shadows and in many places has sutured borders. The quartz monzonite was intruded into the horn­ small bodies that range in area of exposure from a few blende gneiss and, in turn, was cut by pegmatites. feet square to areas measuring 2,000 by 800 feet, are It is thus intermediate in age between pegmatite and scattered throughout the hornblende gneiss and tonalite hornblende gneiss. The age of the quartz monzonite terrain. The area of most abundant small scattered in relation to the coarse- to fine-grained granite is not granite intrusives is west of the main granite mass and definitely known, because the two rocks are not in con­ trends north-northwest. tact. The following evidence, however, suggests that The granite is a pink porphyritic rock (figs. 4, 5) that the quartz monzonite is older: (1) In many regions the forms well-rounded outcrops. The phenocrysts are differentiation of a results in the early forma­ crystals of pink microcline, 0.50 to 0.75 inch long, and tion of more mafic rocks; and subsequently, rocks of of grains of clear quartz, 0.25 to 0.50 inch long. In intermediate and granitic composition are formed; in thin section the microcline phenocrysts show many the Quartz Creek district the quartz monzonite is small included crystals of diversely oriented microcline, intermediate in composition between the granite and quartz, biotite, and . The quartz phenocrysts the earlier hornblende tonalite and might, therefore, are composed of several grains, commonly with sutured be interpreted as intermediate in age as well; (2) the borders. The coarse-grained groundmass consists of gneissic texture in the hornblende gneiss is parallel to microclme, quartz, biotite, albite, magnetite, apatite, the contact with the quartz monzonite (pi. 1); this and zircon. Some specimens also contain sericite, implies that the quartz monzonite was intruded during epidote, and chlorite. The average composition of this , whereas the coarse-grained granite rock is estimated to be microcline (71 percent), quartz QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

(20 percent), biotite (8 percent), albite (] percent), and and the coarse-grained granite. The fine-grained gran­ less than 1 percent of magnetite, apatite, and zircon, ite dikes are cut hy the pegmatites wherever found in and trace quantities of epidote, sericite, and chlorite. contact. The pegmatites are found throughout the Apatite and zircon are most abundant as small included district, except in the central parts of the two main crystals in larger crystals of biotite. Epidote com­ granite masses. The fine-grained granite is much more monly occurs near biotite, and chlorite is derived from restricted in distribution and occurs in dikes in a north- biotite. north westerly trending zone west of the largest granite There are two less common varieties of the coarse­ intrusion. The same zone contains manj- small intru­ grained granite. Granite gneiss occurs in a few isolated sive bodies of coarse-grained granite. A few fine­ masses near the western edge of the district and is grained granite dikes are found in hornblende gneiss characterized by the parallel arrangement of elongate 200 feet from the northeast edge of the largest granite quartz and biotite crystals, granulation, slickensiding, body. and recrystallization of quartz. Much of the biotite The structure in the earlier pre-Cambrian rocks is has been altered, and only small wisps and discolored followed in part by the granite dikes on the north side areas remain. The gneiss is believed to be a normal of Quartz Creek, which have a general trend of from granite that has been metamorphosed by shearing. N. 0°-20° W. (pi. 1). South of Quartz Creek the dikes

FIGURE 5.—Coarse-grained granite with two sets of joints at right angles. A red granite occurs in small patches within the two generally have a northeasterly trend but range from main granite masses. It has no large phenocrj^sts, has N. 20° W. to N. 50° E. man3- small vugs, contains only a few percent of quartz The pegmatites form both long narrow dikelike bodies and a trace of biotite, and has a high proportion of and irregular masses. Except in sec. 33, the dikes albite. trend from N. 15° to 60° E., and cut across the earlier The granite is younger than the hornblende gneiss, structure. In the vicinity of the southeast corner of tonalite, and pre-Cambrian quartzites because it cuts sec. 33, T. 50 N., R. 3 E., the pegmatites have an these rocks or contains partly assimilated inclusions of average trend of N. 35° W. The pegmatites are them. On Indian Head, a large granite mass jutting described in detail in a succeeding part of this report. out into the valley of Quartz Creek (pi. 1, sec. 4) The fine-grained granite is pink and has a grain size contains numerous partly assimilated fragments having of about 0.015 inch. The dikes range in width from a large microcline porphyroblasts. The granite is in few inches to 180 feet and in length from a few feet turn cut b}^ dikes of fine-grained granite and by pegma­ to 2,700 feet. The contacts with the surrounding rock tite. Its relation to the quartz monzonite is not clear, are sharp, and the granite forms prominent outcrops. but the quartz monzonite is probably older than the The rock is made up almost entirely of leucocratic granite. microcline, quartz, and plagioclase. Microcline (20 to 60 percent) has crosshatch twinning. Clear quartz (15 FINE-GRAINED GRANITE DIKES AND PEGMATITES to 40 percent) forms irregular grains, manj^ with sutured Pegmatite and fine-grained granite (pi. 1) are found borders, and is interstitial to plagioclase and microcline. together in manj^ places and cut both hornblende gneiss The plagioclase (20 to 40 percent) is albite (An4) and GENERAL GEOLOGY 9

occurs as crystals coated with kaolin and as inclusions Dings (oral communication, 1949) in the southwestern in microcline crystals. Bio tit e is the dominant dark corner of the adjacent Garfield quadrangle. His mineral, ranging from a trace to about 5 percent; the measurements, made under equally difficult conditions, average is less than 1 percent. Ragged grains of mus- with the exact position of the upper and lower limits covite, commonly included in large feldspar grains, inferred, indicate the thickness of the Morrison to be make up as much as a few percent of the rock in places. between 315 and 375 feet. A few euhedral crystals of apatite and irregular-shaped No fossils were found, and the identification of tho grains of magnetite are present in some specimens. Morrison formation in the Quartz Creek district is This rock, because of its granitic texture, is designated based on its lithologic similarity to this formation in a granite rather than an . nearby areas. The fine-grained granite is related in age to the coarse-grained granite and probably was derived from CRETACEOUS ROCKS, DAKOTA SANDSTONE the same magma, but at a later date. This age rela­ The Dakota sandstone is well exposed in a series of tionship is indicated by their areal distribution. The cliffs thai border Alder Creek (pi. 1). In figure 6, it is small coarse-grained granite bodies and the fine-grained granite dikes crop out in the same north-northwesterly trending band west of the main granite mass, and the fine-grained granite dikes also occur in a narrow zone along the northern contact of the largest granite mass. Both rocks are of the same mineral composition, but the fine-grained granite is commonly richer in plagio- clase and poorer in microcline and may represent a more sodic fraction of the magma.

JURASSIC BOCKS, MOBBISON FORMATION The Morrison formation unconformably overlies the pre-Cambrian rocks and is conformably overlain by the Dakota sandstone along the western and eastern edges of the Quartz Creek district. The Morrison

formation is covered in more than 90 percent of the FIGUEE 6.—Cliff of Dakota sandstone. area, and the outcrops are commonly of the more resistant sandstone lenses. shown capping the Morrison formation along the This formation is composed of a basal and an upper western border of the district; it also crops out east of sandstone that are separated by varicolored shale. the mapped area. The basal sandstone rests on the pre-Cambrian and The Dakota is made up of a basal pebble congloni- closely resembles the Dakota sandstone in appearance. merate and an overlying sandstone. The conglomerate It is white to tan and weathers buff to yellowish is composed of subrounded to rounded pebbles aver­ brown. The quartz grains are subrounded, and a few aging 0.25 inch in diameter. The pebbles are for the beds are quartzitic. The middle unit of the formation most part quartz, with subordinate amounts of black rarely is exposed. It is composed of green, brown, and chert and red . In part, the conglomerate is reddish shales with a few thin limestone and sandstone arkosic though much of the feldspar has altered to beds. Above the shales is a white fine-grained sand­ clay. The upper part of this unit is quite friable and stone flecked with iron oxide. This rock is prominently commonly crossbedded, whereas the lower part locally crossbedded and usually is friable; the individual quartz is cemented with and is very resistant. grains are well rounded. This sandstone is conformable The upper unit of the formation is composed almost with the basal pebble conglomerate of the Dakota entirely of sandstone, but the uppermost part contains sandstone. thin beds of fine-grained black to gray fissile shale a At no place in the area is a complete section of the few inches to 1.5 feet thick. This sandstone is com­ Morrison formation exposed, but a thickness of 355 posed dominantly of subrounded grains of quartz, and feet was measured along the west side of Alder Creek, subordinately, of orthoclase. The rock ranges from a in sec. 36, T. 50 N., R. 2 E., from the top of the under­ true arkose with about 25 percent feldspar to an almost lying pre-Cambrian (as determined by float) to the pure quartz sandstone. The cliff-forming units are base of the Dakota formation. The thickness of the well-cemented sandstones, but much of the formation is Morrison formation was also measured by McClelland soft and friable. Locally it has been indurated to 10 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO quartzite. The sandstone is white to gray and weathers minerals in approximate order of abundance are: buff or yellowish brown. One bed in the upper part is hornblende, quartz, scapolite, sphene, apatite, and marked by radiating 1-inch spheroids of zircon. pseudomorphous after . The tuff outcrops are erosional remnants, a few The Dakota sandstone is not completely exposed in tens of feet thick, of a thicker and more extensive tuff the area mapped, and the upper surface has been eroded. bed. The tuff that overlies the Dakota sandstone The maximum thickness obtained from the six sections along the east side of Quartz Creek has a minimum measured is 183 feet; the basal conglomerate is 33 feet thickness of 83 feet. The tuff is shown to be ^younger thick. than the faulting which brought pre-Cambrian rocks The only fossils that were found in this formation are against the Dakota sandstone, because the tuff crosses a poorly preserved gastropod of unidentifiable genus the fault line with no apparent displacement. It is and a few fragmentary casts of plant stems. overlain along Wood Gulch by glacial till, presumably of Pleistocene age. The tuff, therefore, has been TERTIARY(P) ROCKS, TUFF tentatively designated as Tertiary(?). A white tuff is well exposed on the south side of Quartz Creek, in the southeast corner of the Quartz QUATERNARY DEPOSITS Creek district (sec. 8), where it forms a small cliff GLACIAL TILL above the Dakota sandstone. At two smaller areas Pleistocene (?) glacial till overlies the other formations of outcrop, in sec. 16 on the south side of Wood Gulch along both sides of Quartz Creek and Wood Gulch and in sec. 5 on the north side of Quartz Creek, the and fills the broad valley of Quartz Creek, where it is tuff overlies pre-Cambrian rocks. covered by a foot or less of soil. On the south side of The tuff is a porous, white flaggy rock occurring in Quartz Creek the till is quite thin, and pegmatite out­ la\Ters 1 to 2 inches thick. The layering dips from 4 to crops protrude through it. The till was deposited 23 degrees northeast. A few subrounded fragments over areas having considerable differences in alti­ of darker (fig. 7) are enclosed in an apha- tude. The highest position is on the north side of Quartz Creek at 8,700 feet; on the south side the al­ titude is 8,250 feet. The till deposits on the north side are part of the lateral moraine, whereas those on the south side are till ridges in the valley moraine. The till near the mouth of Wood Gulch appears as thin irregular patches, which seem to be remnants of a broad valley moraine. The till is composed of clay, fine sand, pebbles, and boulders as much as 3 feet in diameter. The boulders are a heterogeneous mixture of several rock types and differ from place to place. On the south side of Quartz Creek and along Wood Gulch, hornblende gneiss and tonalite are the dominant rock types in the till and in FIGURE 7.—Tuff with large volcanic fragment. places form more than 80 percent of it. Near the mouth of Alder Creek on the north side of Quartz Creek, the nitic matrix containing phenocrysts, about one thirty- boulders in the till consist of sandstones of the Dakota second of an inch long, of plagioclase and biotite. The and the Morrison formations (30 percent), pegmatite orientation of the biotite, in general, is parallel to the (30 percent), fine-grained granite (20 percent), ryholite layering. (10 percent), and hornblende gneiss (10 In thin section, the tuff has a clastic texture and shows percent). Other identifiable boulders include chert, many scattered phenocrysts in a brown cryptocrystalline pre-Cambrian quartzite, Sawatch quartzite, epidote groundmass. The phenocrysts comprise about 35 per­ rock, quartz monzonite, , massive quartz, and cent of the rock. Andesine- (more than . 30 percent), commonly occurring as angular fragments or rarely as euhedral crystals, is the most common ALLUVIUM . Some of the plagioclase crystals show Recent alluvium forms a narrow strip in the bottom zoning. Biotite (3 percent) is the chief dark mineral of most of the valleys in the Quartz Creek district. and occurs in long prismatic crystals. Next in abund­ Along Quartz Creek this strip is % to % mile wide and ance is black anhedral magnetite (1 percent). Other extends northeastward across the entire district. The PEGMATITES 11 alluvium is dominantly fine silt, 4 to 8 inches thick, and the foliation also may have been the result of unrecog­ overlies glacial deposits along most of Quartz Creek. nized faulting. Two sheared and mineralized fractures were mapped STRUCTURAL GEOLOGY in the hornblende gneiss. The larger of these is south The structure of the older pre-Cambrian rocks of of Quartz Creek, 250 feet east of the Buckhorn pegma­ the Quartz Creek district has a general northwest tite (no. 659). The second is in the north­ trend, which is cut by stocks and of younger western part of the area mapped, where the southern pre-Cambrian granite and quartz monzonite. Meso- part of pegmatite 1199 has been displaced about zoic and later rocks are flat lying and are cut by several 3 feet to the west. faults in the southern part of the district. In the Mesozoic sedimentary rocks, faults are more The general trend of the pre-Cambrian metasedi- readily recognized. A major fault separates Dakota mentary rocks is northwest, with a steep dip southwest. sandstone from hornblende gneiss in the southwestern The foliation of the pre-Cambrian hornblende gneiss part of the district (pi. 1) and trends JST. 20°-42° W. strikes northwest, north, or northeast and dips steeply. A vertical displacement of 410 feet was measured on On the southeast side of Quartz Creek and along the the west side of Alder Creek, the southern block hav­ western edge of the district the foliation trends north­ ing moved downward with respect to the northern east and dips from 70° SE. through vertical to 59° NW. block. On the west side of Alder Creek the Dakota Around the edge of the quartz monzonite intrusion, sandstone has been sharply upturned by drag of the the foliation parallels the contact and dips steeply beds at the fault, in the southwestern part of the from it. In the northern part of the district, the district, along State Highway 162, a small segment of foliation strikes northeast and dips from steeply Dakota sandstone has been downfaulted between the southwest to vertical. large fault and two smaller ones to the level of the The large granite mass dips steeply to the northeast highway and folded into a gentle anticline (fig. 9). along its northeastern side. On the west, however, the contact was not exposed, but the innumerable small stocks along this side (pi. 1) suggest that the granite underlies the at shallow depth. The contact of the quartz monzonite was not exposed, but the strike of the foliation of the hornblende gneiss is parallel to that of the contact, and it is probable that the dip is also parallel. Most of the pegmatites trend northeast along joints and cut across the foliation of the older rocks. Groups of parallel lenticular pegmatites with this trend are common (fig. 8). Faults are difficult to recognize in the pre-Cambrian rocks except where pegmatites have been cut and offset. The displacement observed ranges from a few 1 inches to 4 feet. Drag folds and local disruptions in FIGURE 9.—Anticline in center of picture is a downfaulted block of Dakota sandstone.

PEGMATITES SIZE AND SHAPE OF PEGMATITES The pegmatites of the Quartz Creek district range in size from bodies a few inches wide and a few feet long to bodies such as the Black Wonder pegmatite, 12,600 feet in length and 6,700 feet in maximum width. Most of the pegmatites range from 100 to 400 feet in length, but 37 bodies are more than 1,000 feet long. The two largest pegmatites are the Bucky, 4,000 feet in length by 2,600 feet in maximum width, and the Black Won­ FIGUEE 8.—Outcrops of pegmatites showing regional trend. der; both are very irregular and have many small 12 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO branches. The small pegmatites are more common in of less than 60 degrees. The irregularity of the peg­ the granite and quartz monzonite. matites and their many changes in direction point to On the basis of shape, the pegmatites in the Quartz the emplacement of the pegmatites along irregular Creek district can be classified as: (1) Lenticular, (2) fractures and joints. The hornblende gneiss and tona­ lenticular-branching, (3) oval, and (4) irregular. lite are too poorly exposed to allow measurement of Examples of each are shown in figures 10 to 17, includ­ any over-all joint systems. The largest body of coarse­ ing both the extreme variations and the average shape grained granite is well exposed, and 638 joints were in each type. Each of these examples represents many measured in it (fig. 19). In local areas of several more pegmatites of similar shape. The lenticular pegmatites are 2.3 times more common than the ir­ regular pegmatites—the second most abundant type. The general order of frequency is 1 oval pegmatite to 2.3 lenticular-branching pegmatites, 2.8 irregular peg­ matites, and 6.6 lenticular pegmatites. Comparison of pegmatite shapes in this district with shapes in the (Page and others, 1953) and in other pegmatite districts has shown that shape of a granitic pegmatite is controlled primaruV by the type and competency of country rock, although the amount of intruded material also influences the shape of the pegmatite if that amount is large. FIGUBE 11.—Large branching pegmatite (no. 250) cutting hornblende gneiss.

hundred square feet, such as A, B, and C on plate 1 T where from 50 to 60 joints are exposed, these are related to 2 or 3 well-developed sets of joints. Over the entire granite body, however, 638 joints show a random orientation. The main granite body is cut by pegma­ tites only in its northwestern end, where the lenticular and lenticular-branching pegmatites trend JX". 45° W. In the hornblende gneiss and tonalite the pegmatites trend from N. 0°-45° E. (pi. 1). The trend of the lenticular pegmatites in the mafic rocks is very uniform over the whole district. This points to a districtwide joint system in the hornblende gneiss and tonalite, FIGUBE 10.—Small branching pegmatite cutting fine-ginmeu granite. whereas the joint systems in the granite vary from one The pegmatites in the Quartz Creek district for the locality to the next. A probable explanation of this most part are intruded into granite, quartz monzonite, peculiar feature is that the joint system in the more hornblende gneiss, and tonalite. The hornblende gneiss mafic rocks antedates the intrusion of the granite and and tonalite have similar compositions, but the horn­ that the jointing in the granite was caused by local blende gneiss is foliated, and the tonalite is more mas­ stresses at the time of the intrusion. sive. Both rocks are competent, and the pegmatites In comparing the various types of country rock with tend to follow fractures and joints that cut the poorly the shapes of pegmatites, it was found that in compe­ to well-developed foliation in the hornblende gneiss. tent rocks, lenticular-branching pegmatites and, to a Though the pegmatites intruded into hornblende gneiss lesser extent, irregular pegmatites are more common are usually well exposed, the adjacent gneiss is rarely than in competent rocks. The type of country rock seen. Wherever the foliation of the hornblende gneiss has little to do with the shape of the pegmatite, pro­ was exposed adjacent to the pegmatite, the angle be­ vided the rocks being compared are of equal compe­ tween the foliation plane and the side of the pegmatite tency. Table 1 shows the frequency of occurrence was measured; the results are plotted in figure 18 on a of each shape compared to the oval shape in each of bar graph. This graph indicates that there is no con­ the three most common types of country rock, horn­ stant angle at which the pegmatites cut the foliation of blende gneiss and tonalite, coarse-grained granite, and the country rock, though it is most commonly an angle quartz monzonite. SIZE AND SHAPE OF PEGMATITES 13

FIGURE 12.—Types of lenticular pegmatites, Quartz Creek pegmatite district 14 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

FIGURE 13.—Types of lenticular and branching pegmatites, Quartz Creek pegmatite district. SIZE AND SHAPE OF PEGMATITES 15

Q Quortz P Perthite P77 Mineral, percent j£s Strike and dip of pegmatite contact

400 Feet

FIGURE 14.—Shape of pegmatite 1294, Quartz Creek pegmatite district.

All pegmatites that cut more than one rock type are ferent shapes as a ratio related to the oval shape in omitted (fig. 17). Except for the larger number of hornblende gneiss and tonalite. irregular pegmatites in the quartz monzonite the ratios are remarkably similar. The higher ratio of irregular TABLE 2.—Ratio of pegmatite shapes to the oval-type shape in hornblende gneiss and tonalite, Quartz Creek pegmatite district. pegmatites in the quartz monzonite probably can be i correlated there with the greater number of large Pegmatite shapes pegmatites in this area. This is discussed in more Rock type 1 Lenticular- detail in a succeeding paragraph. The country rocks Lenticular branching Irregular Oval differ greatly in their mineralogy, texture, and chemical composition, and yet the shapes of the pegmatites 8.7 2. 0 2. 8 1. 0 show little variation. The rocks of this district have Hornblende tonalite 12. 0 9. 2 2. 2 1. 0 one important characteristic in common: they are all 1 Qradational rock types, such as those rocks which showed a slight foliation, are tight, brittle, and of equal competence. However, not included in this table. the effect on the shape of the pegmatites where the host rock possesses even minor foliation is very striking. Foliation has a profound effect in simplifying tlie Table 2 shows the frequency of occurrence of the dif- shapes of the pegmatites by decreasing the number of branching types; the lenticular-branching type is 4.6 TABLE 1.— Ratio of pegmatite, shapes to the oval-type shape in different kinds of country rock, Quartz Creek pegmatite district. times more common in the hornblende tonalite than in the hornblende gneiss. Pegmatite shapes Pegmatites in incompetent rocks, such as mica Rock type Lenticular- schist, are, in general, concordant with the foliation Lenticular branching Irregular Oval and were emplaced by shouldering apart the country Hornblende gneiss and rock. Pegmatites of this type are most commonly tonalite 5. 8 2. 6 2. 4 1. 0 lenticular, but other common forms are troughlike, Coarse-grained granite- __ 6. 2 2. 6 3. 8 1. 0 Quartz monzonite_ 6. 4 2. 0 6.0 1. 0 arcuate, and teardrop. Lenticular-branching pegma­ tites are extremely rare. The schistosity of the wall 16 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

No. 690 No. 528 Ab 60 /—) Ab 65 P 23 / -/-P 25 Q I 5 C—J Q 10 M 2

FIGURE 15.—Types of oval pegmatites, Quartz Creek pegmatite district. SIZE AND SHAPE OF PEGMATITES 17

Ab Albite P Perth! te Ab67 Minerol. percent

FIGURE 16.—Types of irregular pegmatites, Quartz Creek pegmatite district. 18 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

FIGURE 18.—Bar graph showing angle between pegmatite contacts and foliation of country rock.

and is found only in the small stringers that extend outward from the main mass. The competence of the country rock makes a great difference when predicting pegmatite shapes and at­ titudes underground for ore reserve calculations. Shapes in incompetent rocks may be projected with some confidence, whereas pegmatite shapes in com­ petent rocks, such as those in the Quartz Creek district, can be predicted only if the attitudes of the controlling fractures are known.

INTERNAL STRUCTURE Core: 43 percent quartz, 43 percent perthite, and 14 percent albite The recognition of distinct lithologic and structural units within pegmatites dates back many years. Hunt

Wall zone; 74 percent albite, 20 percent quartz, (1871, p. 182-186), who noted a remarkable banded 5 percent pethite, and 1 percent muscovite arrangement "formed by successive deposits of mineral Strike and dip of pegmatite contact matter" at Brunswick, Topsham, and Newry, Maine,

160 Feet appears to have been the first American geologist to recognize a regular internal structure in pegmatites. Many early authors of 25 to 40 years ago referred to

FIOUKE 17.—Pegmatite 297, Quartz Creek pegmatite district. segregations, veins, layers, bands, and streaks. An excellent historical review of these early writings is rock is commonly conformable around the entire given by Cameron, Jahns, McNair, and Page (1949, pegmatite. p. 10-13). Until about 1940 most of the work on The second factor influencing the shape of pegmatites pegmatites was carried out by mineralogists and geolo­ is in the quantity of material introduced. With the gists who emphasized the mineralogy and theories of intrusion of large quantities of pegmatitic material, genesis of pegmatites and put little emphasis on their the control of the country rock structures on the structure. See, for example: Fraser (1930, p. 349-364); shape is usually obscured; and the body becomes Hess (1925, p. 289-298; 1933, p. 447-462); Landes an irregular stocklike mass. Indications of initial (1923, p. 519-530, 537-558; 1925, p. 355-411; 1932, directional control that fractures had on large peg­ p. 211; 1933, p. 33-56, 95-103; 1935, p. 319-333); matites, such as the Black Wonder, Bucky, or Buck- and Schaller (1925, p. 269-279; 1927, p. 59-63; 1933, horn, were obliterated by the large quantity of material p. 144-151). INTERNAL STRUCTURE 19

E W

S S CONTOUR DIAGRAM OF 54 JOINTS AT LOCALITY A CONTOUR DIAGRAM OF 59 JOINTS AT LOCALITY B

E W

CONTOUR DIAGRAM OF 48 JOINTS AT LOCALITY C CONTOUR DIAGRAM OF 638 JOINTS FROM ENTIRE GRANITE AREA ON THE EAST SIDE OF QUARTZ CREEK EXPLANATION Percentage of joints measured

Less than 2 2-4 11-13

FIGURE 19.—Contour diagram of attitude of joints in granite; localities A, B and C are shown on plate 1. 20

After 1940, because of the wartime need for pegma­ If the core is not exposed at any one level, the inner­ tite minerals, the U. S. Geological Survey made many most exposed zone may be identified erroneously as a studies of the internal mineralogic and structural units core. in pegmatites. As the economical concentrations of BANDING valuable minerals in pegmatites tend to be concen­ Banding is the name given to the layered structures trated in rock units distinct from the adjacent barren forming pegmatite units that differ in mineralogy, units, detailed mapping and interpretation of various texture, or both and tend to have a nonconcentric pegmatite units have proved to be of much aid in arrangement within pegmatite bodies. Banding in a exploration, development work, and mining (Smith pegmatite may divide the body either across or along and Page, 1941, p. 295-630; Olson, 1942, p. 363-403; the strike. Several distinct types of banding are Bannerman, 1943, p. 1-22; Cameron, Larrabee, McNair, recognized in the Quartz Creek district. Page, and Shainin, 1945, p. 369-393; Johnston, 1945, p. 1015-1070; Jahns, 1946, 293 p.; Cameron, Jahn^, Banding parallel to strike.—Pegmatites in which band­ McNair, and Page, 1949, 115 p.; Hanley, Heinrich, ing is parallel to the strike and dip of the body are and Page, 1950, 124 p.). Drilling on the basis of struc­ called layered pegmatites (fig. 21). The distinct bands tural interpretation of the internal units has given or layers are mappable units of definite mineralogy or excellent results (Page, 1950, p. 12-34). texture and are not repeated. The layered pegmatites The internal units of pegmatites have been classi­ commonly consist of several tabular units whose fied as (1) zones, (2) fracture fillings, and (3) replace­ contacts are approximately parallel to the hanging- ment bodies (Cameron, Larrabee, McNair, and Stew- wall and footwall sides of the pegmatite. These art, 1944, p. 89; Jahns, 1946, p. 39-51; Heinrich, 1948, layers differ from zones in that there is no repetition of p. 436-442; Cameron, Jahns, McNair, and Page, 1949, units on the other side of the pegmatite. Pegmatites p. 13-97). Many of the pegmatites of the Quartz composed of two layers are by far the most common Creek district differ from those in other pegmatite type in this district. These units commonly extend areas in that, in addition to these three units, they may the entire length of the pegmatite and are from 1 to contain an internal structure designated as banding in 30 feet thick. This type of banding is confined to this paper. narrow lenticular and lenticular-branching pegmatites ZONES or to a narrow lenticular part of irregular pegmatites. The zones of a pegmatite in ideal development are It is not found in thick parts of irregular pegmatites concentric shells about an innermost zone or core or oval pegmatites. The distinct upper and lower (fig. 20); in many places they are incomplete, however, units in many of these layered pegmatites can be forming only along one end or in one part of the pegma­ distinguished in only certain parts of the body and tite. Zonal structure is formed during the primary merge along strike into a single unit. Where two layers consolidation of the pegmatitic magma and may be cut merge, or telescope, the unit formed has the bulk com­ by fracture fillings and replacement bodies. Zones position of the two combined layers and a texture have been classified (Jahns, 1946, p. 42; Cameron, intermediate between that of the upper and lower layers. Jahns, McNair, and Page, 1949, p. 20) as: (1) border In pegmatite 548, for example, an upper layer, consist­ zones, (2) wall zones, (3) intermediate zones, and ing of perthite (50 percent), quartz (33 percent), (4) cores. albite (15 percent), and muscovite (2 percent), and Border zones are fine-grained selvages that in most a lower layer, consisting of albite (74 percent), quartz pegmatites are a few inches or less in thickness. Most (20 percent), perthite (3 percent), and muscovite (3 are of little significance in the mining or quarrying of percent), become progressively less distinct to the south pegmatites and hence in the industry are not dis­ and finally merge into a single unit, consisting of tinguished from the adjoining wall zones that are more albite (63 percent), quartz (20 percent), perthite (15 coarsely granular and much thicker. Although wall percent), and muscovite (2 percent). zones actually are the second zones from the margins Banding across strike.—Some pegmatites are banded of pegmatite bodies, they are designated as such in across the strike into two or more mappable units recognition of terminology firmly established in the differing in mineralogy, texture, or both (fig. 22). pegmatite mining industry. The innermost zone or These are designated as pegmatites showing variation core occurs at or near the center of the pegmatite either in composition along strike. Banding across strike as an elongate lens or a series of disconnected segments. results in two or more pegmatite units that have their Any zone between the core and the wall zone is an contact at an angle to, rather than parallel to, the strike intermediate zone. Any number of intermediate zones of the pegmatite. Units in such pegmatites occupy the can exist, but few pegmatites contain more than three. full width of the body and are from 20 to several him- INTERNAL STRUCTURE 21

Cl G Cleovelondite Ab 45 Garnet Mineral, percent

Strike and dip of pegmatite contacts //:& Open cut and dump

FIOURE 20.—Zoned pegmatites, Quartz Creek pegmatite district. 22 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

Footwall layer Ab Albite P Perthite

Strike and dip of pegmatite contact

FIOURE 21.—Layered pegmatites, Quartz Creek pegmatite district. INTERNAL STRUCTURE 23

Strike and dip of pegmatite contact

FIGURE 22.—Pegmatites showing variation in composition along strike, Quartz Creek pegmatite district. dred feet across parallel to the strike of the pegmatite commonly as patches in a small part of the pegmatite. body. The units have the shape of whatever part of No pegmatite, with the exception of pegmatite 670, the pegmatite they occupy; thus, one unit may occupy contains more than 15 percent of line rock, and most of the short, thin, lenticular part and another the long, them contain less than 1 percent. Line-rock-bearing irregular, bulbous part of a pegmatite. Banding pegmatites, therefore, are not classified separately. across strike has been found only in lenticular and Line rock is most common in albite-rich pegmatites lenticular-branching pegmatites and all such bodies where obvious banding is caused by layers of garnet contain either 2 or 3 bands (fig. 22). and muscovite as much as a quarter of an inch thick Multiple banding.—Some pegmatites in the Quartz (Figs. 23, 24). Laj^ers of fine-grained albite-quartz Creek district are composed of innumerable very thin pegmatite are interspersed with coarser layers of bands that differ in texture, mineralogy, or both. The perthite-quartz-albite pegmatite (}{ to about 4 inches bands are rarely mappable on ordinary scales. This thick). The layers of perthite-quartz-albite pegmatite type of banded rock has been described as "line rock" are lenticular and usually pinch out within short dis­ in the Pala district, Calif. (Schaller, 1925. p. 273). tances. Other layers may occur above or below to Line rock in the Quartz Creek district is characterized form an echelon pattern. Rarely the albite-quartz by the repetition of bands of minerals from 0.01 inch pegmatite forms the lenticular units in line rock. The to 0.4 foot thick; the average thickness is less than banding may end abruptly against large crystals or an 0.5 inch. The banding in most places, as in pegmatite aggregate of minerals (fig. 25). Line rock is most 670, is parallel to the strike of the body, but in a few common adjacent to the walls of the pegmatite, espe­ places it cuts across the strike. Line rock is found cially on the footwall side. In several places thin 24 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

layers of garnet and albite were noted terminating abruptly against euhedral perthite crystals. The perthite is veined by albite along fractures and was either entirely crystallized or, at least, partly crystallized before all the albite formed. Thus, the perthite is not a later mineral which cut the layering but rather a buttress against which the layering stopped. The arrangement of and in bands suggests at least local movement of the pegmatite magma with rapid minor changes in composition so that first one mineral would be crystallizing and then another. Thus, a row of garnets might be formed in an area of movement up to a projecting perthite , which would either deflect the current or cause deposition of a row up to its side and another along its top. This FIGURE 23. — "Line rock" in the lower part of pegmatite 670. Fine dark layers are small garnets. row on top might be swept from its more exposed posi­ tion where narrowing of the channel caused the current to be swifter, or it might be incorporated into the perthite upon further growth. In this case the evidence is against replacement, because the banding is regular, the early perthite shows no corrosion by the later garnet and albite, and the incorporation of garnet in some perthite crystals points to simultaneous growth. The alternating lenses of perthite-quartz-albite peg­ matite in fine-grained albite-quartz pegmatite suggests zoned multiple pegmatites such as might be formed by crystallization from lenses of trapped liquid. Line rock is common in many pegmatites in other areas: the Crystal Mountain district, Colo. (W. R. Thurston, oral communication), the Middletown dis­ FIGURE 24.—"Line rock" from pegmatite 461. Black layers are garnet and musco- vite; white layers are mainly albite with a little quartz. trict, Conn., the Pala district, Calif. (Schaller, 1925, p. 272-273), the Eight Mile Park district, Colo. (Hein- rich, 1948, p. 448), and the Bridger Mountains district, Wyo. (McLaughlin, 1940, p. 62-63).

FRACTURE FILLINGS Fracture fillings are tabular bodies that extend from inner units into outer units of the pegmatite. In places they connect directly with the core. Fracture-filling units are common in pegmatites of the Quartz Creek district, but are usually small; many are only a few feet in length. Most of these units are only a minor part of a pegmatite, though there may be several in a single pegmatite. Discontinuous core segments and fracture fillings are difficult to distinguish in some irregular pegmatites. Most of the fracture fillings are coarse grained and consist predominantly of perthite-quartz pegmatite or of quartz pegmatite. In pegmatite 1096 a fracture filling of massive quartz extends from the core across the wall zone. REPLACEMENT UNITS Xo mappable replacement units were found in the FIGURE 25.—Relation of banding to crystals or to nonbanded mineral aggregates, pegmatite 70. pegmatities of the Quartz Creek area, although there INTERNAL STRUCTURE 25 are several places where small areas were replaced along: TYPES OF PEGMATITES fractures. Replacement units form by the replace­ Pegmatites may be divided into homogeneous and ment of preexisting consolidated pegmatite with later heterogeneous pegmatites. The homogeneous pegma­ material. The interaction of two minerals or of a tites are simple aggregates of feldspar, quartz, and mineral with the rest-solution during the process of accessory minerals that cannot be divided into con­ crystallization is not considered as replacement in this trasting units on the basis of mineralogy and texture. paper. The embayment of one mineral by another These pegmatites form the great bulk of pegmatites in and the filling of small fractures have been given as many regions, such as the Quartz Creek district, Colo., criteria of replacement, but these textures also can be Black Hills region, S. Dak., Spruce Pine district, N. C., formed if an early-formed mineral is corroded by the (D. A. Brobst, oral communication) and the Crys­ rest-solution and subsequently coated by a later mineral. tal Mountain district, Colo. (W. R. Thurston, oral The criteria used to distinguish a replacement body communication). Homogeneous pegmatites commonly are, therefore, the presence of relict textures or struc­ form relatively small dikes and rarely contain minable tures of the preexisting rock that indicate essentially concentrations of economic minerals. Because they complete consolidation prior to replacement. Where a lack the economic and rarer minerals, they have re­ pegmatite is not zoned or where no preexisting textures ceived little attention in the past by mineralogists and geologists. Most of the pegmatite literature is devoted to descriptions of pegmatites containing the rarer minerals. Recently, however, the U. S. Geological Survey has undertaken regional mapping of pegmatite districts in other parts of Colorado and in South Dakota, North Carolina, and Connecticut. These districts are all similar, and these studies should result in obtaining a broad knowledge of the character and distribution of all types of pegmatites. This work may yield the much-needed data required to understand the relationships of homogeneous and heterogeneous pegmatites. Heterogeneous pegmatites are those that can be divided into different rock units on the basis of either FIOTJKE 26.—Replacement of perthite by fine-grained muscovite (black). Note the unreplaced albite lamellae (white) of the perthitic structure in muscovite. mineralogy or texture or both.

HOMOGENEOUS PEGMATITES or structures remain, it may be very difficult to recog­ Homogeneous or one-unit pegmatites form the great nize a replacement body. bulk of the pegmatites in the Quartz Creek district. The interaction of one mineral on another during Of more than 1,800 pegmatites, 78 percent are homo­ the crystallization process is more pronounced in peg­ geneous or "unzoned." Homogeneous pegmatites occur matites than in other igneous rocks because of the large as lenticular, lenticular-branching, oval, and irregular grain size of the crystals which magnifies the embaying bodies. Only a few of the larger irregular pegmatites of one mineral by another. Thus, a crystal of one are zoned; they contain one or more discontinuous mineral may be partly or completely grown before the cores. Examples of homogeneous pegmatites are equilibrium in the solution will permit a second min­ shown in figures 12 to 16. The dominant minerals eral to start crystallizing. The new crystal may form are plagioclase, quartz, and perthite. Most of the around the first crystal or grow out from it or, in the pegmatites contain as much as 2 percent of one or more new equilibrium, the first mineral may be soluble and of the following minerals: Muscovite, garnet, biotite, may be replaced by the second. Evidence of this sort and magnetite. Beryl and tourmaline are present in does not prove or disprove the presence of a replacement some pegmatites but constitute only a small fraction unit. An excellent example of muscovite selectively of 1 percent.

replacing perthite and leaving narrow albite stringers HETEROGENEOUS PEGMATITES of the perthite intergrowth unreplaced is illustrated Zoned pegmatites.—Zoned pegmatites form roughly in figure 26. The pegmatite was essentially homo­ 14 percent of the pegmatites in the area (figs. 17 and geneous and shows no evidence of a separate replace­ 20); most have only a core, a wall zone, and a narrow ment body. border zone. Most of the border zones in the Quartz 26 QUARTZ CREEK PEGMATITE DISTRICT. COLORADO

Creek district are only a fraction of an inch thick and Judging from the sizes and distribution of the core are cooling selvages. Because of their thinness they segments, only a small proportion of pegmatitic liquid were mapped with the wall zones. remained after consolidation of the wall zone. This The mineralogy and texture of the wall zone usually crystallized in scattered areas as core segments. resembles the homogeneous pegmatites in the immediate Layered pegmatites.—Layered pegmatites make up vicinity. The core, except where the wall zone is approximately 7 percent of all pegmatites in the Quartz predominantly graphic granite, is commonly coarser Creek district. Layering is most common in the thin grained and contains more perthite or quartz, or dikelike lenticular and lenticular-branching types of both, than the surrounding wall zone. Cores consisting pegmatites. Layering is not common in large irregular only of massive quartz are very common (fig. 27) in pegmatites, although a few of the thinner irregular bodies are layered. Most of the layered pegmatites contain a perthite- rich hanging-wall unit and an albite-rich footwali unit (fig. 21). As an example, pegmatite 685 (pi. 1), on the north side of Wood Gulch, has a hanging-wall unit visu­ ally estimated to contain albite (30 percent), quartz (20 percent), perthite (48 percent), and muscovite (2 percent) and a footwali unit of albite (65 percent), quartz (15 percent), perthite (19 percent), and musco­ vite (1 percent). In a few pegmatites the hanging-wall unit has more albite than perthite, but the hanging-wall unit always contains more perthite than the footwali unit. Pegmatite 1363 (fig. 21 and pi. 1) is the only body that contains a higher proportion of perthite in what is believed to be the footwali unit; this pegmatite, FIGURE 27.—A thin zoned pegmatite with an albit.e-quartz wall zone and a quartz core. however, is nearly vertical (81°). The texture of the hanging-wall unit is coarser than that of the footwali the northwestern part of the district. Cores of perthite- unit, because perthite tends to form larger crystals quartz pegmatite also are common. Fourteen peg­ than albite. Perthite forms in crystals from 0.5 to 3 matites have cores of eleavelandite-quartz or cleave- inches in diameter, and albite forms in crystals from landite-lepidolite-quartz pegmatite. They include the 0.06 to 0.25 inch in diameter. In the albite-rich units the Bazooka, White Spar No. 2, and the Brown Derby quartz crystals are about the same size as those of albite, No. 2 and No. 3 pegmatites, which have been described but in the perthite-rich units they are nearly as large as previously by Hanley, Heinrich, and Page (1950, p. the perthite crystals. The above relationship would 66-68, 71-74, 77-80). Not all the lepidolite-bearing seem to suggest an immiscibility between - and cleavelandite-bearing pegmatites are zoned pegma­ rich and sodium-rich fluids, but the contact between tites; these minerals are also found in small homogeneous two immiscible layers would be horizontal and that of pegmatites, layered pegmatites, and pegmatites that these dikes is between 25° and 81°. vary in composition along their length. The cores in Layered pegmatites with a perthite-rich hanging-wall small pegmatites may form a large proportion of the layer and an albite-rich footwali layer have been de­ pegmatite (no. 267, fig. 20), but in large pegmatites scribed by Schaller (1925, p. 271-274) in the Pala they usually make up 1 percent or less of the total district, Calif. rock (fig. 17). Pegmatites having an intermediate The concentration of perthite as hoods in the upper zone as well as a core and a wall zone are rare. Only part of zoned pegmatites is common in pegmatites in 7 pegmatites in the Quartz Creek district contain inter­ many districts. Examples are the Ke3Ts No. 1 pegma­ mediate zones. In 5 pegmatites this zone consists of tite, Orange, N. H.; the W. T. Foster No. 1 pegmatite, muscovite-albite pegmatite surrounding one or more Shelby, N. C.; the Palermo No. 1, Grafton County, small discontinuous cores. N. H.; the Strickland-Cramer pegmatite, Portland, The Quartz Creek district has few well-zoned Conn.; and the Beecher Lode, Dyke Lode, Etta, Dan pegmatites. Those which are zoned commonly consist Patch, Hugo, and Bob Ingersoll Nos. 1 and 2 of of only a wall zone and a core. The core units are usu­ the Black Hills, S. Dak. (Cameron, Jahns, McNair, ally irregularly distributed, discontinuous segments, and Page, 1950, p. 44-45, 48). The perthite-rich hang­ and constitute only a small part of the pegmatite. ing-wall layers in pegmatites of the Quartz Creek dis- TYPES OF PEGMATITES 27 trict appear to be the extreme development of perthite- that the layers may telescope gradually into a homo­ rich hoods in thin lenticular bodies. Two of the lepi- geneous unit do not seem to fit the picture of irregular clolite-bearing pegmatites, pegmatite 306 (Opportunity replacement. No. 4 claim) and pegmatite 452 (the Brown Derby No. Pegmatites showing variation in composition along 1) are layered. Pegmatite 306 consists of an upper strike.—About 1 percent of the pegmatites have more albite-quartz-perthite unit and a lower cleavelandite- than one unit, where the mineral composition of the quartz-lepidolite unit. The Brown Derby No. 1 peg­ unit changes along the length rather than across the matite contains at least eight different units. Not pegmatite (fig. 22). In some lenticular-branching all these are present throughout the pegmatite: some pegmatites, each branch has a different mineral as­ form lenticular pods. The Brown Derby is described semblage. In lenticular pegmatites one end may be of by Hanley (Hanley, Heinrich, and Page, 1950, p. one mineral composition and the opposite end of 69-71) as having a border zone, a wall zone, a possible another, or the center of the pegmatite may be of one intermediate zone, and a compound core made up of mineral composition and the ends of a different mineral three different units. The Brown Derby has more composition. In a few pegmatites one part may con­ mappable units than any other pegmatite in the region. tain a core in addition to the layers across the pegmatite. Many of these layers are found in only certain parts of The dominant variation is the change from a unit the dike and merge along strike with other units. The rich in perthite to one in which perthite is less abundant central part of the unit has an albite-quariz wall zone or even absent; however, parts of some of the branching on both hanging-wall and footwall sides, but to the cleavelandite- and lepidolite-bearing pegmatites on the north the wall zone on the hanging-wall side disappears, Opportunity No. 1 claim (nos. 209, 213, 214, 215, and and the pegmatite becomes a layered pegmatite. 216) have similar units. Other layered pegmatites probably are incompletely Pegmatites showing variation in composition along developed zoned pegmatites. strike are lenticular and lenticular-branching pegmatites The layered pegmatites are most abundant (1) along and, in part, may represent multiple injections of the ridge just south of Quartz Creek in the southwestern pegmatite fluid. corner of the district, (2) in the vicinity of the Brown Multiple pegmatites.—Multiple pegmatites are formed Derby mine, and (3) along the western side of Big by multiple intrusions so that the walls of the peg­ Gulch. Layered pegmatites are sparsely distributed matite formed by the second injection are tangent to among other types of pegmatites in the first two areas that of the first. Thus, the various units have strikes but are the dominant type in the third area. The which trend within a few degrees of one another. layered type is almost absent in other areas. Branching and irregular pegmatite bodies may be the The distribution of the layered pegmatites suggests result of multiple intrusion of two or more pegmatite that their development is controlled by a particular set fluids into the same spot. In general, many adjacent of conditions. The country rock in these areas is pegmatites are often of similar composition and texture. hornblende gneiss, as in many areas that are void of It may be difficult, therefore, to distinguish between a layered pegmatites. The conditions under which these branching and a multiple pegmatite. There are in the bodies cooled and crystallized probably controlled their Quartz Creek district two pegmatites that have been formation. The original composition of the pegmatite formed by two separate injections of pegmatitic fluids. liquid, especially concentration of the fugitive con­ Pegmatite 251 is a lenticular-branching body with a stituents, may have been important but probably was wall zone and a thin core in each branch (fig. 28). The not the controlling factor, because there are different two branches join near the north end, and instead of mineral assemblages in layered pegmatites, and because the cores joining, as cores do in a normal branching- many unlay ered pegmatites are identical to layered pegmatite, there are two parallel cores at the junction, ones in mineralogy. The possibility of the layers being showing that it is a multiple pegmatite formed at formed b}^ replacement of preexisting pegmatite rather slightly different times by two separate injections. than by difference in crystallization history has been Pegmatite 216 on the Opportunity No. 1 claim is a considered, but most of the perthite is in well-formed north-trending albite-quartz-perthite pegmatite, which crystals, surrounded by later albite and quartz. The is cut by a northeasterly-trending body of perthite- crystals are only slightly embayed and are not cut by quartz and cleavelanclite-quartz pegmatite (fig. 28). vemlets of other minerals. The facts that the perthite Though this pegmatite resembles a multiple pegmatite layer, with only one possible exception, is on top, that in that it is formed of two separate injections, walls of the contact between the two layers is gradational, and the two pegmatites are crosscuttiug rather than tangent. 28 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

N A

No.216 No. 251

Ab 70 Q 20. P 10

EXPLANATION

Ab M Albite Muscovite P Q Perthite Quartz Ab 69 Cl Mineral, percent Cleavelandite 80 80 Feet I Strike and dip of pegmatite contact

FIGURE 28.—Multiple pegmatites, Quartz Creek pegmatite district.

MINERALOGY changes in their alkali content, and similarly the re­ A total of 27 minerals has been found in the pegma­ fractive index of muscovite can be related to its ferric tites of the Quartz Creek district. Perthite, plagio- iron content. Determinations of the refractive indices clase, and quartz are the essential minerals and form of these three minerals from various layers of layered om fr95 to more than 99 percent of most pegmatites. Only a very few pegmatites have units rich in muscovite; TABLE 3.—Occurrence of accessory minerals in 1,803 pegmatites of Quartz Creek district this mineral cannot be considered an essential mineral of the pegmatites of this district. The common acces­ Number of Percent of pegmatites in pegmatites in sory minerals are considered to be those found in more Mineral which mineral which mineral than 10 percent of the pegmatites. These minerals, was observed was observed in order of their frequency, are: muscovite, garnet, Muscovite.. _ _ 1,058 57. 9 biotite, magnetite, and beryl. The quantity of these 965 52. 9 minerals in any particular pegmatite is small; musco­ 422 23. 1 Biotite.. ______357 19. 6 vite commonly ranges from 0.5 to 3 percent; garnet, BeryL__ __.______232 12. 7 from 0.5 to 1 percent; biotite and magnetite, less than Tourmaline 48 2. 6 Columbite-tantalite 29 1. 6 1 percent; and beryl, a few small crystals. 23 1.3 The other 19 minerals are found in less than 3 per­ 17 . 9 Microlite _ _ _ _ _ 13 .7 cent of the pegmatites of the district and are consid­ 9 . 5 ered rare accessory minerals. They also commonly 8 . 4 Gahnite _ _ _ 8 . 4 amount to only a small fraction of 1 percent of any Samarskite__ 7 . 4 pegmatite. Table 3 lists all accessory minerals, the Epidote.. _ 3 . 2 3 . 2 number of pegmatites which contain these minerals 2 . 1 and the percent of the total pegmatites in which they 1 .06 1 . 06 are found. 1 . 06 The pegmatite minerals are described in detail with 1 . 06 . _ _ __ _ ----- _ _ _ _ 1 . 06 special attention to variations in composition as deter­ 1 .06 mined by differences in refractive index. Plagioclase Unknown __ 1 . 06 and beryl show variations in indices corresponding to MINEKALOGY 29 pegmatites and from poorly zoned pegmatites showed white and semitransparent. The surface of the crystal no appreciable variations. is wavy, and twin lamellae can be seen along the edges. Slight differences in the composition of beryl and The lower index (Na) of the (010) flakes was albite from the well-zoned pegmatites were indicated determined in white light on 17 specimens of cleave­ by differences in refractive index. The variations landite and on 439 specimens of other types of plagio­ showed that the alkali content of beryl and the albite clase from the Quartz Creek district. The cleaveland­ content of plagioclase increase inwardly from the wall ite is a sodic albite, its lower index ranging in value zone of the pegmatites. from 1.528 (Ab97An3) to 1.530 (AbggAns), with an The indices of plagioclase, muscovite, and beryl in average of 1.529 (Ab96An4). The other plagioclase pegmatites from different types of country rock were specimens vary in composition from sodic albite to found. If these pegmatites were formed from the calcic oligoclase; the lower index ranging in value country rock with the help of some submagmatic from 1.527 (AbggAn^ to 1.541 (Ab74An26), with an metamorphic metasomatic processes, as suggested by average of 1.532 (Ab93An7). Table 4 gives the results Ramberg (1949, p. 50-51), then the differences in the of these determinations, the type of country rock, and country rock should be reflected in the alkali content the type of pegmatite or pegmatite unit from which of the plagioclase and beryl and the ferric iron content each specimen was taken. of the muscovite. No relationship between the indices The lower refractive index of plagioclase was deter­ and type of country rock is apparent. mined for all internal units in each beryl-bearing peg­ Detailed results of the work on indices is given under matite and for a selected number of pegmatites in each each mineral. type of country rock. The refractive indices of the pla­ PLAGIOCLASE gioclase in pegmatites with the hornblende gneiss and Plagioclase occurs in all pegmatites of the Quartz tonalite wall rocks average 1.530, and those in the Creek district and is the dominant mineral in most. quartz monzonite average 1.538. Refractive index of It may form as much as 90 percent of all types of struc­ plagioclase in pegmatites from the hornblende gneiss tural or mineralogic units. The plagioclase occurs in near quartz monzonite is in the same range as those in fine-grained sugary aggregates of equigranular grains the quartz monzonite. The lower refractive index of and in coarse platy crystals (cleavelandite). Cleave- plagioclase in pegmatites in the hornblende gneiss de­ landite has been found in 28 pegmatites in this district. creases from the quartz monzonite area southward; the Where used in this report, the term "plagioclase" refers difference appears to be controlled by the regional only to the typical granular form, and the term distribution rather than composition of the country "cleavelandite" refers to the platy form. Plagioclase rock. commonly is abundant in (1) homogeneous pegmatites, In zoned pegmatites of the Black Hills (Page, and (2) wall zones of zoned pegmatites, and (3) footwall others, 1953) and other districts (Cameron, and others, layers of layered pegmatites. These units may contain 1949, p. 99), a systematic variation in the plagioclase more than 98 percent plagioclase and quartz. Cleave­ has been noted from zone to zone, the content landite, on the other hand, is restricted for the most decreasing toward the core. Most pegmatites in the part to central parts of the pegmatites. Quartz Creek district do not have well-developed zones The plagioclase ranges in size from less than 0.003 but, when zoned, show a rather large wall zone with to about 1.5 inches across; the average size is about 0.12 scattered core segments. Table 5 shows that, of the 19 inch. Crystal shape usually is not discernible, but the pegmatites considered, there is not much change in the cleavage surfaces commonly are curved or warped. indices in 17 pegmatites that are composed of only wall Twinning is visible only in the large crystals. Plagio­ zone and core; 8 showed no change of index, 5 decreased clase is found in graphic intergrowth with quartz in a slightly in index (0.001 to 0.002) from wall zone to core, few places. Most of the plagioclase is white, but cream, while 4 increased in index (0.001 to 0.006). In 2 well- brownish, and pinkish shades are common. The plagio­ segregated pegmatites with intermediate zones there clase locally resembles perthite in color but can usually is a decrease in refractive index of 0.005 towards the be distinguished by its warped surfaces, twinning la­ core, indicating a decrease in anorthite content, which mellae, lack of perthitic structure, and occurrence in is in accord with previous work. In a well-segregated fine aggregates. pegmatite the plagioclase probably will tend to show a Cleavelandite is found in thin plates 0.03 to 0.06 systematic decrease of the anorthite content toward the inch thick and 0.5 to 4 inches in maximum dimension. center; but when the zoning is poor, the plagioclase The average plate is approximately 2 inches long, 1.5 will either have the same composition or have errati­ inches wide, and 0.04 inch thick. The crystals are cally distributed values. 30 QUAKTZ CREEK PEGMATITE DISTRICT, COLORADO

TABLE 4.— The range in values of the lower refractive index (Not) of cleavelandite and other types of plagioclase in all pegmatite units in the Quartz Creek district and its relation to different types of country rock

Number of determinations of the lower refractive index (Na) in the indicated values for— Country rock and type of pegmatite or pegmatite unit Cleavelandite Other plagioclase

1.528 1.529 1.530 1.527 1.528 1.529 1.530 1.531 1.532 1.533 1.534 1.535 1.536 1.537 1.538 1.539 1.540 1.541

Hornblende gneiss and tonalite: Homogeneous pegmatite.. _____ . _ _ ... 16 41 39 11 11 8 6 8 4 10 5 2 1 Zoned pegmatites: Wall zone ______2 25 11 9 2 2 Intermediate zone(s) ...... 1 1 1 1 Core _ — ___ — ...... 6 2 2 5 5 1 1 Layered pegmatites: Lower layer ______6 3 1 1 Median layer. ______1 1 1 7 5 Pegmatites which change in composition along strike. ______-.—....— — ... ___ — . 1 1 2 1 1 1 1 1 1 Granite and hornblende gneiss or tonalite: 1 2 3 10 9 6 1 1 Zoned pegmatites: Wall zone ______- __ .- .... 1 2 2 2 1 i 1 1 1 2 3 Layered pegmatites: Lower layer.- ______2 1 2 1 1 Upper layer ______.... 2 2 1 1 1 1 Pegmatites which change in composition along 1 2 1 1 3 1 Fine- and coarse-grained granite: 6 9 9 5 10 1 1 Zoned pegmatites: Wall zone ...... 1 1 Core. ______... — ... . 1 1 1 Quartz monzonite: 1 4 7 19 12 5 Zoned pegmatites: 3 2 1 2 1 Layered pegmatite: Lower layer.. ______1 1 Country rock unknown: 1 1

A comparison was also made between the lower re­ in perthite and the footwall layer relatively poor, it fractive index of plagioclase from the hanging-wall was thought that this change in the alkali content layer and the footwall layer of layered pegmatites might be reflected in the ratio of sodium to calcium in (table 6). As the hanging-wall layer is relatively rich the plagioclase. Of the 11 pegmatites investigated, 6 TABLE 5.—Lower refractive index (Na) of plagioclase in zoned showed no variation in index, and 5 showed an increase pegmatites of Quartz Creek pegmatite district. of 0.001 to 0.002 in index from the hanging-wall layer to the footwall layer. As the limit of accuracy of the Ntt of plagi­ Na of plagi­ Pegmatite (pi. 2) oclase in wall oclase in inter­ Na of plagi­ index determinations, which were made by oil immer­ zone oclase in core mediate zone sion, is approximately O.OOldr, the results show a 174———— ————— ————— 1. 529 1. 528 negligible change. The concentration of perthite, and 279———— ———— ————— 1. 531 1. 529 thus, the potassium content in the upper layer, seems to 289-_------1. 529 1. 530 451__ _- _ _ -_ _ ___ 1.529 1. 529 have little effect on the ratio of sodium to calcium in 453 ______--- _ - 1. 529 1. 529 plagioclase. 454______-_ _ - 1. 529 1. 529 455_-__------_------1. 529 1. 529 A comparison of the refractive indices of plagioclase 456_-__------1.529 1. 529 in beryl-bearing and non-beryl-bearing pegmatites 535 _ _ _ - _ __ - -- 1. 535 1. 529 536———— ———— ————— 1. 528 1. 528 (table 11) shows that both have a wide range and that 674.. ------1. 531 1. 530 the non-beryl-bearing pegmatites have more calcic 847———— ————— ————— 1.533 1. 539 989------1. 530 1.529 plagioclase. 1002. ____--_-__---_---_-_ 1.531 1.530 1028.------1.529 1.531 Cleavelandite occurs in crystals generally many 1044______-_-_-_-_-_ 1.529 1.530 times larger than the more common form of plagioclase, 1202. ____-_____-_-_-__-_- 1. 530 1. 530 1402. __-__-_-_--_-_-_-_-_ 1.537 1. 532 has a flat platy , as compared with the 1666————— ———— ———— 1. 529 1. 529 more equant plagioclase crystals, and is invariably white or bluish white, whereas plagioclase is white, MINERALOGY 31 yellow, green or pink. These two varieties probably containing lepidolite. Among the possibilities sug­ did not form under identical chemical and physical gested are those that some of the elements common to conditions. Cleavelandite occurs in 20 pegmatites in lepidolite and its associated minerals may be respon­ the Quartz Creek district and has been noted in homo­ sible for the formation of platy cleavelandite, or temper­ geneous, zoned, and layered pegmatites and pegmatites ature and pressure conditions during which its asso­ which vary in composition along the strike. In zoned ciated minerals are deposited are the same as those for pegmatites it is found in the intermediate zone in 3 cleavelandite. The elements that might promote the places and in the core in 16. The tendency for cleave- growth of cleavelandite are lithium (in lepidolite, landite to form in the central part of pegmatites has , , and ), been noted in other parts of Colorado (Hanley and or cesium (in lepidolite, muscovite, tourmaline, beryl, others, 1950, p. 7) and in other districts in the United and ), and fluorine (in lepidolite, , and States (Cameron and others, 1949, p. 58). topaz). The role of fluorine is difficult to evaluate because it may be present as an essential constituent, TABLE 6.—Lower refractive index (Na) of plagioclase in layered pegmatites, Quartz Creek pegmatite district. as in fluorite, topaz, or lepidolite, or it may occur undetected as a minor constituent in other minerals Na of plagioclase such as muscovite by substituting for the OH~ radical. Pegmatite (pi. 2) in hanging-wall Na of plagioelase layer in footwall layer Spectrographic analyses should be made of both cleavelandite and other albite from a number of peg­ 270.____-___ — .___ — _____. — _ 1.528 1. 530 matites to determine whether small quantities of 432... ______1. 529 1.530 433— — - — — _ — — - — — — — 1.530 1. 530 lithium, fluorine, or other elements are present in one 435-__--_--_- ______1.529 1. 529 type of plagioclase and not in another. 462,____-___-__-__-_-______1.529 1.529 548-.— ______1. 529 1.529 778____ 1. 535 1.535 PERTHITE 1004______1.529 1.529 1043.______1.530 1. 531 All the potassium feldspar examined in pegmatites 1105——— - — -- — _ — _____ — — 1.530 1. 531 of the Quartz Creek district was white, cream, or pink 1172___._. ______1. 529 1.531 microcline-perthite; no orthoclase or microcline free of veinlike laminations of albite was noted. The albite Cleavelandite has distinctive mineral associations. laminae are thin, roughly parallel, and white. In the Quartz Creek district it is associated with Several types of perthite were noted in the few thin quartz, lepidolite, microlite, beryl, topaz, columbite- sections that were studied. In the most common tantalite, perthite, muscovite, garnet, and tourmaline. form, albite occurred in veinlets cutting the microcline Many of these minerals are normally found with at various angles. This type of perthite was called Cleavelandite though the reverse is not always true. perthite by Andersen (1928, p. 116-207). Cleavelandite is associated with lepidolite in 14 of the A second type showed thin films of albite, generally 17 lepidolite-bearing pegmatites, with topaz in all perpendicular to the (010) plane of the microcline. 8 topaz-bearing pegmatites and with microlite in 12 of This type of perthite Andersen called film perthite. the 13 microlite-bearing pegmatites. The association Andersen regards vein perthite as formed by the of Cleavelandite with lithium minerals and some of opening of contraction cracks, recrystallization of the rare accessory minerals has been noted in other microcline, and replacement. It should be noted that districts. In the Mountain pegmatite, Custer Andersen states that the circulating solutions that did County, S. Dak., cleavelandite occurs in the core the replacing were derived from the same pegmatitic associated with spodumene, lithium mica, beryl, ambly- magma from which the initial crystallization of the gonite, , columbite-tantalite, apatite, micro­ feldspar took place. Thus, he implies that the replace­ lite, and pollucite. In the Harding mine near Dixon, ment was a part of a reaction between the already N. Mex. (J. W. Adams, oral communication), crystallized material and the rest-solutions, rather cleavelandite in fracture fillings is associated with purple than a replacement by outside solutions. Film perth­ muscovite, microlite, and spodumene. In the Ruther­ ite is regarded by Andersen to be a product of ex- ford and Morefield pegmatites near Amelia, Va. (Glass, solution. 1935, p. 761-763), cleavelandite is associated with Perthite occurs in most pegmatites, and in some it is cassiterite, manganotantalite, microlite, and zircon. the predominant mineral. It is absent from some sodic- The regional distribution of cleavelandite-bearing rich units, but forms as much as 93 percent of perthite pegmatites (pi. 6) shows that, with the exception of cores. Sodic-rich pegmatites commonly contain less two bodies, all the deposits containing cleavelandite than 15 percent perthite; other pegmatites are in a also contain lepidolite or are adjacent to pegmatites large part graphic granite. Generally the perthite-rich 32 pegmatites are most abundant in the northwest part of quartz content is nearly everywhere 15 to 20 percent. the district. Many cores and fracture fillings are made up solely of All pegmatite units contain perthite, but it is most milky quartz, whereas other cores and fracture fillings abundant as graphic granite in homogeneous pegma­ are mixtures of blocky perthite and quartz. The quartz tites or in wall zones of zoned pegmatites and as blocky in fracture fillings, intermediate zones, and cores is 10 perthite in cores of quartz-perthite pegmatite. The to 100 percent of the unit. hanging-wall unit of layered pegmatites is commonly The quartz is generally white to gray, although smoky rich in perthite. varieties are found in a few pegmatites, commonly as The perthite is in crystals }{ inch to 8 feet in maxi­ small ellipsoids ranging from 1 to 10 millimeters in mum dimension. The crystals are largest in the cores, length.o The smokv«- varieties are usually*- associated where they average 1.5 feet. Perthite crystals in the with radioactive minerals—for example, with micro- wall zone or in layered and homogeneous pegmatites lite in pegmatites 215, 216, and 452 and with allanite are from 2 to 3 inches in size. In fine-grained plagio- in pegmatite 847. Small patches of have clase-rich pegmatites, the perthite crystals are smaller been found without visible radioactive minerals. than in pegmatites where perthite is the dominant Quartz in most places fills interstices and forms veins mineral. Graphic granite crystals are from 6 inches to in perthite crystals, indicating that it crystallized after 4 feet in length and average about 80 percent perthite the perthite. Rarely, however, the reverse is true. and 20 percent quartz. About a ton of graphic granite The quartz associated with blocky perthite is in crystals was crushed, quartered, and analyzed. 1 This analysis 2 to 18 inches in size and is commonly slightly finer (table 7) indicates that the soda is almost entirely in grained than perthite. In graphic granite, the quartz the albite laminae of the perthite. The list of norma­ forms crude cuniform rods 0.03- to 0.25-inch thick and tive minerals (Washington, 1917, p. 1162-1165), cal­ as much as 1.5 feet long. culated from this analysis, verifies the fact that there Albite is interstitial to quartz and in places appears to is little present other than quartz and feldspar and vein it. This relationship indicates that albite crystal­ that the microcline molecule is 4.5 times as abundant lized last, but in many places the mutual intergrowths as that of plagioclase. suggest a contemporaneous age. Where quartz occurs Perthite forms blocky equiclimensional crystals that solely with albite, it forms crystals 0.03 to 0.5 inch in are surrounded and veined by an aggregate of quartz, diameter; as the proportion of perthite increases in the albite, and muscovite. In most places perthite is the unit, the size generally increases. Muscovite and first essential mineral to crystallize, but rarely it ap­ quartz in many places are intergrown and appear to pears to be later than some or all the associated minerals. have crystallized almost simultaneously. TABLE 7.—Chemical analysis of graphic granite from the Bucky mine, Quartz Creek district, Colo. MUSCOVITE [G. A. Parker, analyst] Muscovite is found in about 60 percent of the pegma­ Oxide Percent tites in the Quartz Creek district. On the east side of Quartz Creek it occurs in 85 percent of the pegma­ SiO2— ___-______.__-__- 71. 56 tites. On the west side the iron content of the pegma­ A12O8— ------14. 82 K2O—— ------10.97 tites is higher; considerable magnetite is present; and Na2O______._.__^___ 1. 69 biotite occurs in place of part of the muscovite. Mus­ CaO—- — — — — — - — — _ 0. 08 FeaOs------0. 01 covite is found in all types of internal units in the pegma­ MgO— - ———— — — — -_ Tr. tites and generally forms 0.5 to 3 percent of the rock; Cr2O3—- — ---- — - — None rare small pegmatites contain as much as 10 percent. 99. 13 The muscovite is clear and colorless to green, and individual sheets show black mineral staining. The QUARTZ larger pieces have reeves and "A" structure. Most of the muscovite, however, is about 0.25 inch in diameter Quartz is estimated to comprise 15 to 30 percent of and commonly is intergrown with quartz. In only all pegmatites in the district; the average amount is two pegmatites, the Buckhorn (no. 659) and the Bucky about 20 percent in homogeneous pegmatites, non- (no. 1574), are muscovite books more than 3 inches in lepidolite-bearing layered pegmatites, and wall zones of size; books 1 foot in size occur in the Bucky pegmatite. zoned pegmatites. Although the ratio of perthite to plagioclase varies widely in these types of rock, the The muscovite occurs in both flat and curved forms. The flat variety is common in most rocks; the curved 1 Analysis obtained through the courtesy of C. A. Wemlinger, vice-president in charge of operations, Beryllium Mining Co., Inc. variety is found in 23 pegmatites, all on the northwestern MINEEA.LOGY 33 slope of Wood Gulch, where it occurs in a series of position of from the different zones of the concentric shells 0.12 to 0.5 inch thick. pegmatites, nor in those from different layers, nor in The composition of muscovite is expressed in three those that are found in pegmatites in different kinds constituent molecules (Winchell, 1947, p. 268; Volk, of country rock. 1939, p. 255-266), the end members of a triangular composition diagram, and the composition of any TABLE 8.—Number and distribution of median refractive indices -, f ., , , . „ , (AV) found in flat and curved muscovite sample ot muscovite can be expressed in terms of these ______three end members. The end members are pot as- Number of specimens sium muscovite, K2Al2 (Al2Si3Oi0) 2 (OH)4 ; phengite, Median index wo —————————— K2H2 (Fe,Mg) 2 (Al2Si3010) 2 (OH)4 ; and ferric iron m2gvite nSSSe muscovite, K2Fe 2 (Al2Si3O]0) 2 (OH)4. The refractive ———————————————————————— —————————— indices of muscovite increase with the proportion of 1.585—— ___ — —_ — _-_ — — — — ______1 1 the ferric iron muscovite in the mineral. The total 1-586—— — — ____ — — — — _ —— — ___ 1 0 amount of iron can not be ascertained from the indices 1.588______0 0 alone, however, as the iron may also be in the ferrous 1-589—- — — — _ — - — - — — — — — — —_ 0 2 form in the phengite member. Specimens containing 1.591______0 0 phengite and the potassium muscovite member have l-592______4 2 the same indices for equal amounts of the ferric iron 1.594______| 7 0 muscovite. Information obtainable from refractive isgellllll'IIIIII ~I I IIIIIIIIII IIIII 4 0 index determinations on the chemical composition of 1.597—__ — ______12 l muscovite is, therefore, less useful than similar data on J--598—— _ — — — — — - — - — - — _— 7 0 plagioclase and beryl. Volk (1939, p. 257-259) made L600—IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII 7 ; 0 22 chemical analyses and obtained the optical data on i'go2" ------8 1 muscovite from various pegmatites scattered throughout 1.603______6 1 the world. These analyses are in an area on the dia- l-604______1 0 gram midway between potassium muscovite, phengite, 1.606______l 0 and up to 38 percent ferric iron muscovite. The ——————————————————————————————'———— median refractive index (Np) was determined on 95 TABLE 9._MwWan refradive index (Nf} of muscovite from zoned specimens of muscovite from the Quartz Creek district -pegmatites and ranged from Np=l .585 to 1.606 (table 8), indicating ——————————————————————————————————— up to 28 percent of the ferric iron muscovite molecule. Pegmatite ^ovftfif N<5>$tf™' It was thought originally that a variation in the re- ______waiuone^ ^core_ fractive indices, and thus in ferric iron content, might be found between units or layers. Table 9 shows the 208IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII ~"L~599~ : l! 578 median refractive indices (Np) of muscovite from the 213______1. 592 1. 599 wall zone and core of seven zoned pegmatites. There 266IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII l! 597 l! 595 is a small variation in the refractive indices but the 288-______-_--______-_-_-_------__-_-_ 1-595 1.597 variation is not constant, either in direction or amount. ------' The median refractive indices of muscovite in layered i zinnwaidite. pegmatites (table 10) show a small but unsystematic variation between the hanging-wall and the footwall It was thought that the curved muscovite in the layers. A comparison of median refractive indices of Quartz Creek district might also be a lithium mica, muscovite from pegmatites in several types of country but median indices (Np) determined for 16 specimens rock was also made. The lack of sufficient samples of curved muscovite show the same range of index and from pegmatites in the granite and quartz monzonite approximately the same distribution as the flat musco- made this work inconclusive, but the variations are in vite (table 8). Furthermore, the angle 2V of the the same range as those from pegmatites in the horn- curved mica (40 degrees) is much too high for a lithium blende gneiss or tonalite. Comparison was also made mica. In making refractive index determinations on between the muscovite in various beryl-bearing and non- muscovite, however, several lithium micas were found, beryl-bearing units. The refractive indices of the These micas are colorless, flat, and associated with muscovite in the beryl-bearing units were in the same cleavelandite. Their median index ranges in value range as those in the nonberyl-bearing units. In short, from 1.560 to 1.578, which is below that of the musco- no markedly regular change can be recognized, insofar as vite series. These specimens are in the zinnwaldito refractive index may be used as a criterion, in the com- range of the lepidolite series. There is no definite QUARTZ CREEK PEGMATITE DISTRICT, COLORADO method to distinguish white lithium mica from musco- garnet in many pegmatites is clear reddish brown vite in the hand specimen, but the lithium micas are with no manganese staining. One of the larger crystals more brittle, and the presence of cleavelandite should is an intergrowth of garnet and quartz. lead one to consider the possibility that lithium micas The garnet group may be divided into six members: may be present. A simple test to distinguish the two almandite (Fe3Al2Si3Oi2), spessartite (Mn3Al2Si3O12), involves the use of a blowpipe: lithium mica can, but (Mg3Al2Si3Oi2), grossularite (Ca3Al2Si3Oi2), muscovite can not be fused. (Ca3Fe2Si3Oi2), anduvarovite (Ca3Cr2Si3O12). Ford (1915, p. 33-49), Fleischer (1937, p. 751-759), TABLE 10.—Median refractive index (Np) of muscovite in layered and Wright (1938, p. 436-449) have shown that garnet pegmatites specimens do not correspond usually to any simple Np of mus­ chemical type but contain two or more end members covite in Np of mus­ Pegmatite hanging covite in in solution. wall footwall It was shown first by Ford (1915, p. 33-49) that the index of refraction and the specific gravity of a garnet 913. ______-__-______--___-_____--_. 1.597 927.. ______1.604 1. 600 depend in a simple and direct way on the chemical 937. __--___-_-----_____---_-_-____--___ 1.597 composition. He calculated the index of refraction 944______1. 601 1. 601 953.. ______1.599 1. 602 and the specific gravity of 23 garnets from their chem­ 954 1.605 1.603 ical composition. These values agreed within less than 958. ______1.606 1. 598 959. ______1.605 1. 605 2 percent with those determined by direct measure­ 963. _ _ _ _ 1. 605 1. 603 ment. The reverse process is not so simple, as a single 969.. ______1. 605 1.602 975. ______1.598 1. 601 determination of refractive index or specific gravity 997. ______1. 603 1.598 may correspond to several combinations of end mem­ 1132_ _..._..______.______. __ ._ _ . 1. 601 1. 601 1172... ______1.595 1.594 bers. It would be possible from a series composed of three different molecules to have a number of different combinations with the same index of refraction. The GARNET problem is somewhat simplified because all garnets are Approximately 55 percent of the pegmatites of the in one of two groups: the aluminum-bearing garnets Quartz Creek district contain minor quantities of (almandite, spessartite, and pyrope) and the calcium- garnet. It is commonly in crystals less than 0.03 inch bearing garnets (grossularite, andradite, and ). in diameter and may easily be overlooked. Garnet These two groups, as shown diagrammatically by ranges in size from less than 0.01 inch to 1 inch in Winchell (1947, p. 175), are miscible with each other diameter, but crystals of more than 0.15 inch are rare. in only limited amounts. Wright (1938, p. 439, 446) This mineral occurs in all the pegmatite units but has a compiled 35 analyses of garnets from pegmatites and decided preference for the fine-grained plagioclase-rich 18 from granites which he converted into weight per­ parts, such as those found in the footwall units of cent of the 5 common members of the garnet group, layered pegmatites, the wall zones of zoned pegmatites, namely: almandite, spessartite, pyrope, grossularite, and homogeneous pegmatites. It is found in crystals and andradite. His conclusions from studies of garnet 0.20 inch and larger in the coarser-grained cores, but from pegmatites and other types of rock are: (1) There in most cores it is absent. Though garnet is widely is a remarkable constancy of one variety of garnet in distributed throughout the district, it constitutes only each rock type, and (2) spessartite and almandite a trace to less than 1 percent of most pegmatites; in constitute 85 to 90 percent of the garnet molecules in a few of the smaller ones it makes up as much as 1 pegmatites and granites. Thus, if one of the major percent of the rock. Garnet is erratically distributed, constituents is known, the other can be estimated and some parts of a pegmatite may contain several within a limit of error of 5 to 15 percent. Winchell percent while others contain none. In the Bucky (1947, p. 179-181) has compiled data by Ford and pegmatite, (no. 1574) rock exposed in two pits con­ others into several diagrams from which, if the garnet tains several percent of garnet, whereas in the same group is known, and the specific gravity and index of unit in other pits the mineral is absent. Brown garnet refraction have been determined, a general composition is conspicuous in "line rock," forming long thin bands in terms of the garnet molecules can be derived. which contrast with the white plagioclase-rich bands. Indices of refraction were determined on garnet from The garnet occurs singly or in clusters as light-brown, 15 widely scattered pegmatites in the Quartz Creek reddish-brown, and black euhedral crystals. Some district. Specific gravity was not determined, but all crystals are black because of manganese staining on specimens were qualitatively tested and found to con­ their surfaces; others are black throughout. The tain manganese. All the indices of refraction are MINERALOGY 35

between 1.810 and 1.820, many specimens having re­ free of iron would contain muscovite in place of biotite. fractive indices about 1.815. The indices of refraction BIOTITE show small variations, but, in general, the garnet of this region is remarkably constant in index and composition. Biotite is found in almost 20 percent of the pegmatites The proportion of almandite and spessartite can be on the west side of Quartz Creek but is found in only roughly evaluated by neglecting the small percent 6 percent of the pegmatites on the east side. In most pointed out by Wright to be taken up by the other pegmatites biotite forms considerably less than 1 per­ garnet molecules and assuming that the mineral to be cent of the rock; in a few of the smaller pegmatites it made up only of spessartite and almandite. In this forms several percent. case the garnet would range in composition from 67 Biotite is dark to greenish black and occurs in blades percent spessartite, 33 percent almandite (A7=1.810) from a fraction of an inch to 8 inches in maximum to 33 percent spessartite, 67 percent almandite diameter; in most pegmatites the flakes are 0.25 to (A7"=1.820). Most of the proportions would be 0.5 inch. The larger books usually occur in small nearer to 50 percent spessartite and 50 percent alman­ areas and may be either restricted to core segments or dite (7V=1.815). to small patches in the otherwise uniform homogeneous In this district garnet is associated with all the com­ pegmatite or the wall zone of a zoned pegmatite. mon and almost all the rare pegmatite minerals; how­ The median refractive index (Np) of seven specimens ever, it has a tendency to occur more abundantly with ranges from 1.636 to 1.671. Not only do the refractive fine-grained plagioclase. indices vary from specimen to specimen but also in different parts of the same book. Much of the biotite MAGNETITE AND MABTITE is partly altered to chlorite and the variation in re­ Magnetite, commonly altered to martite, is wide­ fractive index depends on the extent to which the bio­ spread in minor quantities and is found in approximately tite has been altered. These median refractive indices 20 percent of the pegmatites. Most pegmatites con­ indicate that the biotite approximates tain only a few scattered crystals, but several of the (Winchell, 1947, p. 273) in composition and is high-iron smaller pegmatites have about 1 percent. rather than high magnesium biotite. Magnetite and martite are dull to steely black and Biotite was found in part of the lepidolite-bearing rarely form well-developed octahedra. Almost all pegmatites, but it is not in the same units as lepidolite. specimens, however, have the good octahedral (111) It is common in both perthite- and albite-rich pegmatite parting that easily distinguishes this mineral from and is one of the few accessory minerals in graphic columbite-tantalite. The mineral ranges in size from granite. Biotite is commonly associated with magne­ grains of less than 0.10 inch to round masses as much tite or martite; muscovite is found only in the magnetite- as 3 inches in diameter. free part of these pegmatites. Magnetite and martite are found as accessory min­ BERYL erals in the feldspathic pegmatites but are not found in any of the lepidolite-bearing units. Magnetite Beryl is found in 232 pegmatites in the Quartz Creek occurs in both the perthite-rich and the albite-rich district and is widely distributed; yet in most pegma­ pegmatites and is one of the few accessory minerals tites there are only a few small crystals. Beryl is associated with graphic granite. The distribution of found in all types of pegmatites and pegmatite units: magnetite and martite is usually erratic; a few small homogeneous pegmatites; core, intermediate, and wall areas in the pegmatite may contain 1 or 2 percent and zones of zoned pegmatites; various layers of layered the rest of the pegmatite only a trace. These two pegmatites; and units of pegmatites that differ in com­ minerals are associated commonly with perthite, albite, position along the strike. quartz, and biotite, and in a few places with garnet. Beryl may be brown, white, gray, greenish white, Few beryl-bearing pegmatites contain either magnetite pale green, greenish gray, or pale blue green. White, or martite; the two minerals are nowhere adjacent to brown, and greenish white are the most common colors. each other. Muscovite is nowhere associated closely Beryl of such colors is difficult to distinguish from feld­ with the magnetite although they may both be in the spar in many exposures. The beryl crystals range same pegmatite, whereas biotite is closely associated from 0.006 inch to 2 feet in diameter. In fine-grained with magnetite or martite. albite-rich pegmatites beryl crystals are 0.10 to 0.25 The association of magnetite with biotite but not inch in diameter, but larger crystals occur in the more with muscovite is easily explained. Those parts of coarsely grained intermediate zones and cores. Al­ the pegmatite with sufficient iron to form magnetite though a higher percent of beryl was found in the albite- also had sufficient iron to form biotite; those parts rich units than in the units rich in perthite, only the 36 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

latter contained beryl in grains large enough to be Adams (1953, p. 117), and Schaller 4 have shown that hand cobbed. The average beryl crystal is approxi­ the decrease in BeO content is accompanied by an mately twice the size of the common form of albite and increase in the refractive indices and have compiled about half the size of the associated perthite grains. charts showing the alkali and BeO content for any Beryl occurs as subhedral to euhedral hexagonal particular refractive index. According to Schaller's crystals; tapered crystals are rare except at the Bucky chart, the refractive index of the slow ray (Nw) of pegmatite 2 (no. 1574). Intergrowths of beryl with beryl containing 14 percent BeO is 1.566, whereas the feldspar, quartz, tourmaline, or other minerals are refractive index of beryl containing 10 percent BeO is common in some regions, such as northeastern Brazil 1.600. (Johnston, 1945, p. 1032-1034), New Hampshire, The refractive index of the slow ray (Nu), deter­ Connecticut (Shaub, 1937, p. 1045-1051), and the mined for 183 beryl specimens from various units, Eight-Mile Park district, Colo. (Heinrich, 1948, p. ranges from 1.573 to 1.585 and averages 1.578. These 557-558), but in the Quartz Creek district only one determinations are compiled in table 11 together with mixed crystal was found. It was intergrown with the determinations of the minimum refractive index garnet and quartz near the center of the crystal and on cleavage plates of the associated plagioclase. The with albite near the outer edges. table is divided according to country rock types and Beryl may contain as much as the theoretical maxi­ subdivided according to the type of pegmatite and mum of 14.0 percent BeO. In most beryl, however, internal structure. This table shows that the refractive substitutions involving Cs2O, Li2O, Na2O and A12O3 index of beryl, and therefore the composition, varies decrease the BeO content so that it commonly ranges irregularly in the different types of pegmatites and from 11 to 13 percent.3 Winchell (1947, p. 213), internal units. There appears to be no correlation be­

2 The names of the pegmatites are purely economic terms and are not to be confused tween type of country rock and the refractive index of in any way with formal stratigraphic nomenclature. 3 Schaller, W. T., Unpublished chart. « Schaller, W. T., op. cit.

TABLE 11.— The number of refractive-index determinations of plagioclase and beryl, their relation to different types of country rock and types of pegmatites or units.

Number of determinations for indices riven

Lower refractive index on cleavage plates Higher refractive index on cleavage plates of beryl Country rock and type of unit of plagioclase

Other Other 1.581 1.528 1.529 1.530 1.531 values 1.575 1.576 1.577 1.578 1.579 1.580 values

Hornblende gneiss and tonnlite: f 1.573(1) f 1.532(5) 1 1.582(?> 13 16 21 C \ 1.533(3) 7 10 17 13 2 3 1 1. .5*3(1) 1 1. 534(1) } ' [ 1.585(1) Zoned pegmatites: 1 18 6 2 1. 534(1) 3 3 1 1 1 1 1 1 1 1 1 Core—. ______1 7 3 1 3 2 4 " 4 2 1. 582(2) Layered pegmatites: Lower layer . 5 3 1 1 1 Median layer(s) __ . 1 1 1 6 5 1 1 2 3 2 1 Pegmatites which change composition along strike _ ___ 2 1 3 1 1.527(1) *) Fracture filling. ______..... 1 1.534(1) 9 Granite and hornblende gneiss and tonalite: f 1.574(1) f 1.527(2) 3 8 9 6 2 4 6 3 4 2 i 1.584(1) \ 1. 532(1) } 2 1 1.585 a) Zoned pegmatites: Wall zone 2 2 1 Intermediate zone(s) ..... 1 1. 533(1) 1 1 1 Core...... — — .. . . 1 2 2 3 1. 539(1) 1 2 3 3 2 Layered pegmatite: Lower layer 2 1. .535(1) 1 1 Upper layer. .__.__.____ _ 3 1 1 1.535(1) 1 1 Pegmatites which change composition along strike 2 3 2 1 2 2 1 1.574(1)

Fine- and coarse-grained granite: homogeneous f 1. 58T(2) pegmatite 3 1 1 1 1 1 I 1.584(1) Quartz monzonite: Zoned pegmatites: Wall zone 1.537(1) 1 Core_._. f 1.532(1) 1 \ 1.535(1) }--- Country rock unknown: homogeneous pegmatites 1 1.532(1) 1 1 MINERALOGY 37 beryl. Only 2 specimens of beryl were obtained from Beryl is associated with plagioclase, quartz, pert/hite, pegmatites in the quartz monzonite and 6 from pegma­ muscovite, garnet, lepidolite, tourmaline, topaz, micro- tites in fine- and coarse-grained granite. lite, tantalite, monazite, gahnite, and biotite. Beryl is It has been noted in pegmatites of the Black Hills not associated with any particular pegmatite mineral (Page, and others, 1953) and other districts (Cameron, to the exclusion of others. It has not, however, been and others, 1949, p. 99) that there is a systematic in­ found in graphic granite pegmatite. Beryl usually crease in the alkali content of beryl from the wall zone occurs in clusters or groups of crystals. In pegmatite inward toward the core. Similar data on beryl from 279, 35 crystals of beryl were found in an area about 2 zoned pegmatites from the Quartz Creek district is feet square. This was the only beryl noted, although rather meager becauss a large part of the beryl found this branching pegmatite exceeds 720 feet in length. was from a single zone of a zoned pegmatite. The re­ Many other pegmatites have a similarly sporadic dis­ fractive indices of beryl from different units of zoned tribution of beryl. pegmatites are compiled in table 12 together with the TABLE 13.—Refractive indices of plagioclase and beryl from beryl- minimum refractive index of adjacent plagioclase for bearing layered pegmatites comparison. Most pegmatites have only small cores, and zoning is poorly developed. A difference of 0.001 Lower layer Upper layer Pegmatit e in indices is all that is noted from wall zone to core of Na of IVoOf Na ot No, Of the more simply zoned pegmatites. The refractive plagioclase beryl plagioclase beryl indices of the slow ray (Woo) of beryl from three peg­ 270._____-___-_--__-_-_ 1. 530 1. 528 matites that contain beryl in an intermediate zone as 417— ______1. 529 1. 577 1. 530 1. 577 well as in either a core or a wall zone differ as much as 432______1. 530 1. 529 1. 576 433 1. 530 1. 530 1. 577 0.003 between the intermediate zone and either the 435 1. 529 1. 529 1. 575 462______1. 529 1. 529 1. 578 core or wall zone. This increase inward in alkali con­ 548— --_-___-_------. 1. 529 1. 529 1. 576 tent is in accord with the findings of previous workers. 778 1. 535 1. 535 985— __--_-__-----__-- 1. 530 1. 578 1. 530 1. 577 1004______1. 529 1. 529 TABLE 12.—Refractive indices of plagioclase and beryl from beryl- 1105—— _ — _ — — — — - 1. 530 1. 579 1. 531 bearing units of zoned pegmatites 1172 1. 531 1. 529

Wall zone Intermediate zone Core TOURMALINE Pegmatite NaOt 7Vu of .ZV«of Na ot ATaOf Ar»of Tourmaline is relatively rare in the Quartz Creek plagioclase beryl plagioclase beryl plagioclase beryl district and has been found in only 48 of the 1,803 174______1. 529 1. 528 1. 580 pegmatites studied. It is common in most pegmatites, 250______1. 530 1. 580 1. 579 in many pegmatites areas, but the Quartz Creek district 279__.____ 1. 531 1. 576 1. 529 289______1. 529 1. 530 1. 578 is notable because of its paucity of tourmaline and the 436______1. 529 1. 578 1. 577 low content of its pegmatites. Except in the 454. 1. 529 1. 529 455______1. 529 1. 529 1. 578 lithium-bearing pegmatites, only a few tourmaline 535______1. 534 1. 577 1. 529 1. 580 crystals occur in each pegmatite. Some units in the 847______1. 533 1. 576 1. 539 1. 579 989 1. 530 1. 529 1. 580 lithium-bearing pegmatites contain as much as 3 per­ 1002 1. 531 1. 530 1. 578 cent tourmaline. 1025 1. 529 1. 531 1. 578 1044 _____ 1. 529 1. 530 1. 575 The colors are black, dark green, blue, light green, 1202 _ __ 1. 530 1. 530 1. 578 and pink. The green, blue, and pink varieties are 1402._____ (1)1.5321 { 1. 537 (2)1.535J 1.578 found only in the lepidolite-bearing pegmatites; the /_ 1574_ ____ {.:__.:. """ (1) 1.5281 1. 579 1. 528 1. 582 black variety occurs in both lepidolite- and non- (2)1.530] lepidolite-bearing pegmatites. Of the 48 tourmaline- bearing pegmatites, 38 contain only the black variety. Refractive indices of beryl and plagioclase from It occurs in subhedral to anhedral crystals; commonly layered pegmatites have not been published. Table the m(lOlb) and a (1120) prism faces are the only 13 gives the refractive indices of these two minerals in faces developed. In many places it is in small pods of 12 two-layered pegmatites, which contain an upper coarse-grained quartz or quartz-perthite pegmatite in perthite-rich layer and a lower albite-rich layer. Most an otherwise homogeneous body. Black tourmaline of the beryl is found in the coarser grained upper layer. has been found associated with quartz, perthite, albite, In two pegmatites beryl occurs in both layers but there cleavelandite, muscovite, beryl, garnet, biotite, mona­ is no important difference in value of the refractive zite, columbite-tantalite, and gahnite but not with index between units. lepidolite and topaz. 55———4 38 QUAKTZ CREEK PEGMATITE DISTRICT, COLORADO

The black tourmaline was found only in zones com­ Not only the color, but also the indices of refraction pletely free of lepidolite; in many zones it is restricted differ. Table 14 gives the higher refractive index to the extreme hanging wall or footwall part. Dark- (No) of 19 tourmaline specimens; 11 are of black tour­ green tourmaline was found either in zones containing maline and range in value from 1.652 to 1.664. The 2 lepidolite or in adjacent zones. It is common in the specimens with the smallest refractive indices are from outer part of lepidolite-bearing units and the inner part the outer edges of lithium-bearing pegmatites. The of the adjacent unit. It is nowhere in contact with 3 dark-green tourmaline specimens have refractive lepidolite but occurs in the cleavelandite-quartz part of indices of 1.646 or 1.647—all lower values than the the zones. Pink and pale-green varieties of tourmaline indices of black tourmaline. The black variety grades occur adjacent to lepidolite in lepidolite-bearing units. into the dark-green variety, and is to be expected that, These two varieties of tourmaline commonly occur if enough determinations of indices were made, a together; the pink variety is more abundant. In the gradational series would be found in which the green Brown Derby No. 1 pegmatite (no. 452) these varieties varieties would have the lower refractive indices. Two sometimes occur in single crystals which have a pink pink tourmaline specimens from different pegmatites core and a light-green rim and are known as "water­ have refractive indices (No) of 1.643 and 1.637. Both melon" tourmaline. The dark-blue variety of tour­ a pale-green tourmaline and a pink tourmaline from maline is not present as individual crystals but forms adjacent areas in pegmatite 452 have a refractive index massive wavy bands in lepidolite-bearing pegmatites, of 1.637 for the slow ray (Na); the pink core and the where it occurs in part with the black tourmaline and pale-green rim of a "watermelon" tourmaline have a in part with the dark-green tourmaline. There is refractive index of 1.634 for the slow ray Nu. The commonly a thin band of small garnets in the center of pale-green and pink varieties appear to vary in composi­ the blue bands. Figure 29, a sketch of part of pegma­ tion, but variation can not be correlated with color. tite 453, shows the relation of various colored tourma­ The different colors may be caused by the presence of lines to the pegmatite units. a minor element that does not affect the refractive

Upper contpct index, by oxidation or reduction of an element in dif­ of pegmatite ferent states of oxidation, or by a slight rearrangement of the molecular structure of tourmaline. The se­ quence from black tourmaline in the outer parts of lepidolite-bearing pegmatites to pale-green and pink tourmaline in the inner can be correlated with a progressive change in refractive indices, but the pale- green and pink crystals which grew together in the same environment without detectable differences in index can not be thus correlated.

TABLE 14.—Higher refractive index (Na~) of tourmaline, Quartz Creek pegmatite district

Pegmatite Name Color Na

205--. — -—-— 1.657 91 * 1.652 Black ______. — 1.657 251-- ———— ——— Black..——— ...... _. 1.657 TUaflr 1.655 311- ———— —— — Black ______1.663 1238-- ———— — -- Black.. ——————— 1.657 Black———— ——— 1.659 1278---- — —— — Black ...... 1.655 1322-- ——— ...— Black.. ——— ...... 1.665 1607 -- —— . ——— - Black—————— ——— 1.664 215 __ — — — — 1.646 qnft 1.647 Albite-quartz pegmatite; 63 percent albite. 1.646 306..... ———— — ... ..do— ———— ... ——— Pink...... —— ...... 1.643 30 percent quartz, 4 percent muscovite, 4KO Pink— ——— —— —— —— 1.637 2 percent tourmaline, and <1 percent garnet 1.637 452. ——— — ..— —— do— .—— —— — —— /(Pale-green rim) __ _ ... } 1.634

Cleavelandite-quartz-lepidolite pegmatite; 54 percent cleavelandite, 25 percent quartz, Early work has shown that change in color in tour­ 20 percent lepidolite, and

Hanley specimen. Because the niobium-tantalum Alonazite occurs as euhedral dark-red to clove-brown ratio commonly varies from zone to zone, as seems crystals that range in size from 0.25 inch long, 0.15 evident from specimens collected by Eckel and by inch wide, and 0.03 inch thick to 2 inches long, 1.2 Hanley, there is a discrepancy between the composition inches wide, and 0.5 inch thick. Most of the larger obtained from the specific gravity and that given by specimens come from the Brown Derby No. 1. Crystal Eckel. forms identified include the a(100), m(110), n(120), Kill), KH1), *(I01), c(001), and ^(305) faces. The TABLE 16.—Specific gravity measurements of columbite-tantalite samples crystals are usually flattened parallel to the a(100) face, and some of them are also twinned parallel to this face. Specific Pegmatite Internal unit gravity The specific gravity of the monazite ranges in value from 5.0 to 5.6, as determined by the Jolly balance. 205_ — _-- — _-_--__--_ Core 6. 1 Optically, the monazite is colorless to yellow, with 205 ______do^____^______^____. 6. 3 high birefringence. The lower index of refraction, (Na), 245 __ _.do______5. 7 452 5. 8 ranges from 1.78 to 1.80, in value, averaging about 1.79. 1234— ____...__._____ Wall zone. _^ 5. 0 Table 17 shows that the specific gravity and lower index 1234— _ — ____ ———— ______do.______5. 1 1557—— — — — -- — — 6. 7 (No) do not vary with a consistent relationship. 1574-. ______Intermediate zone 6. 0 In the Quartz Creek district monazite is associated with quartz, albite, perthite, muscovite, columbite- Columbite-tantalite is found in direct contact with tantalite, gahnite, biotite, and garnet; however, it is the following minerals in one or more pegmatites: found usually in a feldspar-rich part of the pegmatite. Quartz, albite, perthite, beryl, muscovite, monazite, Of the 24 pegmatites containing monazite, 9 also con­ biotite, tourmaline, and gahnite. It also has been tain columbite-tantalite. found in the same zones, but not in direct contact with TABLE 17.—Lower index of refraction (Na) and the specific garnet, topaz, microlite, martite, and lepidolite. Though gravity of monazite columbite-tantalite is associated with almost all the pegmatite minerals, there are three associations which Inde-c of Specific Pegmatite Internal unit refraction are most common in the Quartz Creek district: (1) With gravity massive quartz, (2) with cleavelandite or cleavelandite 452— ——— — — Pod__ 1.80 5.3 and quartz, and (3) with feldspar (either perthite or 290- — — — - — do 1. 79 5. 1 plagioclase) and monazite. Its association with mona­ 847.- — ------do ^______. 1. 78 5. 1 847---. — ------Interi 1. 78 5. 6 zite is not pure chance as it can be seen that 9 of the 997 Footv 1. 79 5.3 24 monazite-bearing pegmatites, or 37 percent, contain rolumbite-tantalite (pi. 5). LEPIDOLITE MONAZITE Lepidolite is found in 17 pegmatites; it occurs in Monazite (Ce, La, Nd, Pr) PO4 is found in 24, or homogeneous pegmatites, in core and intermediate approximately 1.5 percent, of the pegmatites. It zones of zoned pegmatites, in interior layers of layered occurs in homogeneous pegmatites; in the cores, pods, pegmatites, and in parts of pegmatites which show and intermediate zones of zoned pegmatites; and in variation in composition along strike. Thus, no par­ layered pegmatites. In 3 pegmatites, namely the ticular type of pegmatite seems to be favored. In the Brown Derby No. 1 (no. 452), the Black Wonder (no. very small number of zoned pegmatites, it appears to 847), and the Bucky (no. 1574), monazite is found in be most common in the central parts. more than a half-dozen crystals. A unit 20 feet long The lepidolite is white, lilac, or various shades of and 1 foot wide at the Brown Derby No. 1, pegmatite purple; lilac to purple varieties are most common. It 452, contains approximately 2.2 percent monazite. Of has three forms: (1) Fine-grained aggregates with two localities in the Black Wonder pegmatite (no. 847), individual sheets less than 0.25 inch in diameter, one is worthy of special attention in that it contains (2) large platy books 2 to 10 inches in diameter, and 0.05 percent monazite in an intermediate zone of (3) curved concentric books, 0.5 to 2 inches across plagioclase-muscovite-quartz pegmatite surrounding a (Fig. 30). The large platy lepidolite is found in only quartz pod. This intermediate zone is about 4 feet 5 of the 17 pegmatites that form a group between thick, and the quartz pod is approximately 15 feet long the Brown Derby No. 1 dike (no. 452) and the Brown and 6 feet wide. In the Bucky pegmatite (no. 1574) Derby No. 5 dike (no. 535), a maximum distance of the monazite is found sporadically in the mica zone 2,200 feet. Only 3 pegmatites on the Brown Derby around the quartz core. No. 1 claim (nos. 452, 454, and 457) have curved MINERALOGY 41

tive test for iron, and fall in the range of zinnwaldite rather than true lepidolite. The other four lepido ite specimens with high refractive indices are probably between lepidolite and zinnwaldite in composition. Three specimens of book lepidolite have median indices of 1.557, 1.559, and 1.562, and one specimen of curved lepidolite had a median index of 1.560. These values average only a little higher than the purple lepidolite occurring in fine-grained aggregates and show that the chemical composition of the different forms varies only to a minor extent. The shape and size of lepidolite give no clue as to its chemical composition or optical

FIGURE 30.—Lcpidolite, from left to right: fine-grained aggregate, curved plates, properties. The best guide noted is color, the paler and and large plates. the whiter forms having higher refractive indices and containing less lithia. lepidolite. Both plate and curved lepidolite are either purple or lilac. An analysis is reported by Stevens TABLE 18.—Median refractive index (Np) and description of lepid­ (1938. p. 615) on large plates of pale-purple lepidolite olite from Quartz Creek pegmatite district from Ohio City. The sample probably came from Peg­ Description either dikes 452, 453, or 454 (Brown Derby No. 1 matite Name N0 claim), as these dikes were the only ones containing 208-—. 1.578 White (}4- to W-inch sheets). lepidolite in large plates that had been developed at 215-- — Opportunity No. 1__ 1.565 White with lilac tinges, elongate 04-inch) blades in a radial aggregate. the time. The analysis follows: 308- —— Opportunity No. 4__ 1.557 Lilac (}4- to ^2-inch sheets). 306 — __ do . . _ _- - 1.55S Purple, fine-grained aggregates Gib-inch Li2O______5.05 MnO. 2.78 sheets). 306-.. _. ._ __do__ ———— ... _. 1. 564 White with lilac tinge (}4-inch sheets). SiOs—— - — — —— — — — 49.58 TiO2 .06 452_____ Brown Derby No. 1- 1.557 Purple, fine-grained aggregates (M'i-inch Al2Os——— — — — — —— ——— 23. 87 H20-. . 51 sheets) . K2O____-.-______- ______10.14 1.22 452 ... —— do 1.555 7.49 14-inch sheets). Na2O————— — —— ———— — .57 452_ .. do 1.559 CaO__-_.______None 452 ___ —— do______—— __ 1.560 Purple, curved lepidolite (1- to 'Mnch Rb2O-_ —— —— ————— 1.62 Total....—.. — . ______103. 19 curved books) . Less 0=F______.____.._ 3.15 461 _____ 1.562 Purple, book lepidolite (2-inch sheets). Cs2O———————— — — .09 535- __ Brown Derby No. 5- 1.560 Silvery-white blades (J4- to ^-inch sheets). FeO.._——————————— ! .21 do 1.564 MgO_____--____. ___- ____ None Ditference______.______100.04 sheets) . 535 __ - —— do__— —— — _ 1 557 1 Total iron reported as FeO. 637- ... 1.575 sheets) . The formula for this lepidolite as determined from the analysis is K4Li7Al5 - Al2Si15O4o(F,OH) 8. Hanley (1950, p. 72) reports that the physical and optical Lepidolite is found in amounts that range from a properties of all the lepidolite from the Brown Derby trace to 95 percent by volume of a pegmatite unit. claim (pegmatites 452, 453, and 454) are similar, and Only the Brown Derby No. 1 (no. 452) has units that the only chemical difference is that the manganese contain lepidolite in excess of 10 percent of the rock; content of the large plates is slightly higher. Winchell in the White Spar No. 2 (no. 602) lepidolite makes up (1947, p. 370) in a triangular diagram shows that the 6 to 10 percent of the rock, and all others contain median index of the lepidolite group of mica increased smaller proportions. The units that contain lepidolite from the polylithionite, K2Li4Si2(AlSi3O1c)2(OH,F)4, are commonly lens-shaped and small; several are less and lepidolite, K2Li3Al3(AlSi3Oio)2(OH,F)4, end mem­ than 15 feet long. The Brown Derby No. 1 pegmatite bers to the protolithionite end member, K2LiFe4Al- (no. 452) contains by far the largest lepidolite body. (AlSi3Oi0) 2(OH, F)4. This increase of refractive index This unit is 319 feet long. is, in general, parallel to an increase of iron and a de­ Lepidolite is associated with the following minerals: crease of lithium and can be used to determine the Cleavelandite, other albite, quartz, muscovite, perth- approximate Li2O content. The median index (Np) of ite, topaz, beryl, microlite, pink and green tourmaline, 14 lepidolite specimens from six different pegmatites columbite-tantalite, and apatite. Cleavelandite, the ranges in value from 1.555 to 1.578 (table 18). Six form of albite usually found with lepidolite, is its most specimens are white, or white with just a tinge of lilac, common associate. In two small pods the lithia mica and these specimens have the highest indices (Np= is white and probably is zinnwaldite. Topaz, micro­ 1.560, 1.564, 1.564, 1.565, 1.575, and 1.578). The lite, and colored tourmaline characterize the lepidolite two specimens with Np 1.575 and 1.578 give a qualita­ units and are rarely found outside of them. 42 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

Lepidolite in many places occurs in compact aggre­ TasOs— — — — — — --— 68.47 P205._ ...... NbsOs— — — — — — . — .. 4.45 CaO— ...... 9. 19 gates with cleavelandite or quartz; these minerals TiO2— — — — - — — -— .10 MgO— —„——_—— .04 appear to have crystallized simultaneously. In other SnOs ______— .. .95 PbO..—— ... —— —— .40 IT02— — ...... — ...... ___ 1.69 Na2O— „ ... — . ..-.— 2.94 places lepidolite veins cut cleavelandite, quartz, and ITOs— ... — ... — — — .— . 2.40 K2O.__.__...... 25 perthite. Topaz commonly is surrounded by a rim of F— .————————— 1.51 AlzOs— — — — —— — .— - .10 Cl...... — ...... lepidolite that may be in part a product of reaction — — 1.91 Insol.+SiOz __ _ .... .92 with the remaining liquid. Lepidolite appears to have MnO..._— — — — —— .11 HsO-..— - ...... 2.84 ZnO._.._— ...... been deposited late in the course of crystallization be­ CuO____ ...... — — .04 Total—————— 98.41 cause in zoned pegmatites it is confined to the core BizOs.— __ -______— .. .07 Less O=F ...... — .64 where it is in part contemporaneous with the quartz BeO— ...... __ None Difference ___ .. 97.77 and cleavelandite, and in part of later age. The specific gravity of this material is 5.604, and -MICROLITE its index of refraction, as determined by J. J. Glass of the Geological Survey, is close to 1.93. The analyses Pyiochlore-microlite is found in 14 pegmatites, all on indicate that the mineral is microlite having a high the east side of Quartz Creek. It is not found in ratio of tantalum to niobium. As would be sus­ homogeneous pegmatites, in wall zone of zoned peg­ pected from the uranium content, this mineral is highly matites, or in the hanging-wall layer of layered pegma­ radioactive and can be detected easily with a Geiger- tites; but it is found in the intermediate zone and cores Mueller counter. of zoned pegmatites, in the interior and the lower layer The material from the Brown Derby No. 1 pegmatite of layered pegmatites, and in units of pegmatites that (no. 452) is dark brown to light brown. An olive-green change in composition along strike. The most favor­ specimen from the Brown Derby No. 5 pegmatite able place is the core of zoned pegmatites. Pyrochlore- (no. 535) was analyzed spectrographically, and it was microlite commonly is found in a few scattered crystals found that the tantalum was more abundant than the only, except in pegmatite 217 (Opportunity No. 1 columbium. This specimen is thus also on the microlite claim) and pegmatite 452 (Brown Derby No. 1). In side of the series. It gave a positive test with the pegmatite 217 it occurs in concentrations of 10 or 12 Geiger-Mueller counter, but not as strong as that given crystals in cleavelandite and quartz, whereas pegma­ by the dark-brown variety. tite 452 contains 0.35 percent of microlite (Hanley, One light-greenish-yellow specimen from pegmatite and others, 1950, p. 73) in a central lepidolite unit. 461 gives no reaction to the Geiger-Mueller counter. Pyrochlore-microlite is light yellow, light greenish The dark color of the pyrochlore-microlite may be yellow, olive green, light brown, or dark brown. The caused by the radioactivity of the uranium, as are the crystals are from 0.01 to 0.4 inch in diameter. In brown halos surrounding the dark pyrochlore-microlite massive fine-grained lepidolite the crystals are anhedral, in the lepidolite. but in quartz and cleavelandite they are euhedral with Similar observations were made by J. W. Adams well-developed to distorted octahedra, o(lll), and mod­ (oral communication) at the Harding mine near ified dodecahedra, ^(110). Dixon, N. Mex., where he found that light microlite Pyrochlore is essentially NaCaCb2O6F, and microlite was not radioactive but dark microlite was. is essentially (Na, Ca)2Ta2O6(O, OH, F). The two Pyrochlore-microlite is associated in the Quartz species form an isomorphous series in which the colum- Creek district with cleavelandite, lepidolite, quartz, and bium-rich members are called pyrochlore and the muscovite. The two types of occurrence are: (1) With tantalum-rich members microlite. Besides the ele­ massive fine-grained lepidolite, and (2) with cleave­ ments given in the above formulas, oxides of some of landite and smoky quartz. In 8 pegmatites it is in the following elements may comprise several percent of lepidolite and in 6 in cleavelandite and quartz. In the mineral: K, Mg, Fe, Mn, Sb, Ce, La, Dy, Er, Y, Th, most places, if pyrochlore-microlite is with lepidolite, Zr, U, Ti, Sn, and W. cleavelandite is present in minor amounts; where Considerable work has been done on microlite from pyrochlore-microlite occurs in cleavelandite, lepidolite the Brown Derb\ No. 1 (pegmatite 452), especially is a minor constituent. Lepidolite is present in 12 of during World War II, when it was mined together the 14 pyrochlore-microlite-bearing units, and cleave­ with lepidolite. An analysis of microlite from this landite in 13. The association of pyrochlore-microlite pegmatite by J. G. Fairchild, as previously reported with either lepidolite, cleavelandite, or both is common (Eckel and Levering, 1935, p. 78-79), follows: in pegmatites in other areas. It is found with lepidolite MINERALOGY 43 and cleavelandite at the Bob Ingersoll mine, Pennington is part of the chemical composition of both minerals. County, S. Dak.; with cleavelandite and lepidolite at Stevens (1938, p. 615) analyzed 17 different lepidolite the Tin Mountain mine, Custer County, S. Dak.; with specimens and found that the fluorine content ranges cleavelandite and lithium mica in the Harding mine, from 4.09 to 9.19 percent, the average being 7.03 per­ near Dixon, N. Mex. (J. W. Adams, oral com­ cent. On the Opportunity No. 1 claim, pegmatite 215, munication) ; with cleavelandite at the Rutherford and some of the topaz has a pale-green thin micaceous Morefield mines, near Amelia, Va. (Glass, 1935, p. coating of polylithionite. This specimen of poly- 753); and with lepidolite and albite (type not defined) lithionite is biaxial negative and has Np= 1.558 and from a pegmatite at Topsham, Maine (Palache and JV7 = 1.565. Both polylithionite and lepidolite seem Gonyer, 1940, p. 412). to form as a product of reaction between the early- TOPAZ formed topaz crystals and the residual fluid; they Topaz is relatively rare in pegmatites and is entirely corrode the surface of the topaz crystals in some places. lacking in many districts. The Quartz Creek district Though less than 0.5 percent of the pegmatites of the contains eight topaz-bearing pegmatites, less than one- Quartz Creek district contain topaz, almost 50 percent half of 1 percent of all pegmatites mapped. of the lepidolite-bearing pegmatites have topaz. The topaz is milky white, though the exteriors of GAHNITE some crystals have a greenish stain. The crystals are subhedral to euhedral, and most are long and tapering. Gahnite, the zinc > is a rare mineral found in They are usually 4 to 8 inches in diameter and a foot only eight pegmatites. It occurs in homogeneous or two in length, but specimens have been found which pegmatites, in intermediate zones and cores of zoned are 12 inches in diameter and 4 feet in length. The pegmatites, and in layered pegmatites. prism faces m(110) and the pyramid faces -i(223) are Gahnite is greenish black to dark green and occurs in the best developed. The basal pinacoid c(001) was anhedral masses. The crystals are from 0.03 to 0.75 noted on a few specimens, and probably with con­ inch in diameter. The mineral is green, iso tropic, and tinued study other faces could be found. Basal cleav­ has an index of refraction of 1.81 ±0.005. age is well developed on most specimens. The lower Gahnite does not appear to have any favored mineral index of refraction (Na) was determined to range from association. In pegmatite 1540 it is found with massive 1.616 to 1.618 (table 19) on 4 topaz specimens from 3 quartz and muscovite; in pegmatite 1574, with albite, different pegmatites. Winchell (1947, p. 199) and quartz, muscovite, and beryl; and in pegmatite 452, Pardee, Glass, and Stevens (1937, p. 1063-1064) have with albite, columbite-tantalite, monazite, tourmaline, shown that the indices of topaz increase with the garnet, biotite, and quartz. The pegmatites containing increase of water content and decrease of the fluorine this mineral are widely distributed, and its presence content. The topaz in the Quartz Creek district has a depends upon the availability of zinc in the pegmatitic uniform water and fluorine content; and by interpola­ fluid. tion from a table given by Winchell (1947, p. 199), it Gahnite is rare or absent in most pegmatite districts was calculated that the topaz contains between 17.0 but has been reported from the Tims Hill deposit and 18.5 percent fluorine and 0.9 to 1.5 percent water. in Connecticut (Faye, 1922, p. 9).

TABLE 19.—Lower refractive index (Na~) of topaz from the Quartz Creek district Allanite is rare in the Quartz Creek district. In the Pegmatite Name Na Black Wonder (no. 847) it occurs in several pods, each a few feet thick and about 10 feet long. This 215 1. 616 pegmatite is over 6,700 feet wide and 12,600 feet long, 452 Brown Derby No. 1 _ .__ 1. 617 452 _ _ do______1.618 and the pods represent only a minute part of the total 1574 Bucky ______1. 616 volume of the pegmatite. The pods consist of quartz (about 90 percent) and albite. A few scattered crystals In the Quartz Creek district topaz is found only in of allanite occur in smoky quartz. lepidolite-bearing pegmatites and is directly associated The allanite is present as prismatic crystals up to 2 with the following minerals in one or more pegmatites: inches long, with a square cross section as much as 0,5 Lepidolite, cleavelandite, quartz, muscovite, beryl, inch across. The mineral is black, has a shiny lustre, perthite, and tourmaline. It is always found with the and is ringed by an unidentified reddish-brown de­ first three minerals. Purple lepidolite commonly composition product. At least three different sub­ forms a coating around topaz. The association of stances are observed under the microscope. One is topaz with lepidolite would be expected, as fluorine isotropic, reddish brown, and has a refractive index a 44 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

pegmatites and is in part an alteration product of Little less than 1.62; the second is anistropic and biotite. colorless; and the third is isotropic and grayish green. Samarskite, or a similar mineral such as , is These observations are in agreement with those of present in 7 pegmatites. It has refractive indices Bitchens who describes the allamte from Fitchburg, above 1.83; when in feldspar, it is surrounded by a Mass. (Kitchens, 1935, p. 18). reddish halo. This mineral is commonly associated with smoky quartz and is strongly radioactive. Only UNIDENTIFIED MINERAL 1 or 2 crystals of it, 0.03 to 0.5 inch long, have been An unidentified, shiny, greenish-black mineral, be­ found in each pegmatite. lieved to be a new species, was found at the Bucky Epidote is noted in 3 pegmatites as fine-green vein- pegmatite (no. 1574). This mineral occurs in scat­ lets and was introduced into the pegmatite after its tered pockets in the mica zone. A total of 17 pounds solidification. was collected during the mining operation. This Light-blue apatite, as crystals 0.25 to 0.5 inch across, mineral is associated with muscovite, altered feldspars, was found in 3 pegmatites. In most pegmatite districts quartz, monazite, and columbite-tantalite. It appears apatite is common, but in the Quartz Creek district to be most closely associated with and in places inter- it is rare. grown with columbite-tantalite. Light purple fluorite is found in 2 pegmatites as The mineral has a conchoidal fracture and super­ grains about 0.06 inch in size. It is extremely rare. ficially resembles samarskite, , or euxenite. Spodumene and amblygonite occur only in the A powder X-ray pattern was compared with the stand­ Bazooka pegmatite (no. 424) in a circular core unit ard patterns of known minerals in the files of the Geo­ 20 feet in diameter. White lathlike crystals of spodu- logical Survey and Columbia University with negative mene are found on the small dump. No amblygonite results. A spectrographic analysis by A. T. Meyers, was found by the writers, but it was observed by of the Geological Survey indicates with the order of Hanley (1950, p. 66-68). magnitude of concentration, the following components: Phosphates of the lithiophillite- series and

Cowcew- C07!C«W- their alteration products are found in the Bucky peg­ Component iraiiow Component tration matite (no. 1574). Two crystals were noted in the __ xo.o Y203 ---_------.X mica zone and one crystal in perthite-quartz pegmatite TaoO5 X.O SnO9_-__. -_____- .X TJsOs X.O La2O3 _ _ _ Traces adjacent to a subsidiary core segment, approximately ThO2 .X Ti02—— -_- — ___ .X 2,500 feet to the southeast. MnO-_- — — __ — . .X PbO-_ — — _ — -__ .X Betafite is reported by Hanley (1950, p. 71) asso­ .X .OX ciated with monazite, gahnite, and columbite-tantalite CaO______.X MgO_. ______in the Brown Derby No. 1 pegmatite (no. 452). It was ZrO,______. .X not observed by the writers and is probably very rare.

Looked for but not found: Na, Bi, W, and P. ALTERATION OF WALL BOCKS A determination of equivalent uranium made by The alteration of wall rock by the introduction of measuring the radiation from uranium and , pegmatitic materials is common in many districts. gave a value of 11 to 12 percent which would show that Jahns (1946, p. 52-54) describes impregnation of quart - the X.O given for U3O8 would be nearly 10 percent. zite and mica schists in the Petaca district by pegma­ Like many other radioactive columbo-tantalates the tite fluids that formed muscovite, microcline, and pla- unknown is metamict.6 gioclase~ to such an extent that the contact between In thin section, this mineral is pale yellow, isotropic, some of the pegmatites and the country rock is grada- and has an index of refraction of 1.80±0.05. tional. The formation of muscovite and tourmaline in It has a specific gravity of 3.8, and some of it contains the country rock adjacent to the pegmatites in New small cavities lined with a fine-grained yellow material. England has been briefly mentioned (Cameron, and

OTHER MINERALS others, 1953). Numerous pegmatites in the Black Hills of South Dakota show abundant alteration at the Chlorite occurs in 9 small pegmatites in the Quartz wall rock-pegmatite contact (Page, and others, 1953). Creek district. It comprises several percent of these Thus, along the margins of the Helen Beryl pegmatite pegmatites. The grains range in size from 0.03 to in Custer County are patches of granulite a few inches 0.06 inch. Chlorite is found in fine-grained albite-rich to 6 feet thick. The granulite differs in composition 6 Metamict n., An originally crystalline substance that has become amorphous. from place to place and consists of quartz (30 to 70 The energy for this change of state is generally agreed to arise from alpha particle bombardment. percent), muscovite (5 to 30 percent), biotite (2 to 15 ALTERATION OF WALL ROCKS 45 percent), and minor quantities of tourmaline and apa­ DISTRIBUTION OF MINERALS tite. The Elkhorn pegmatite, also in Custer County, Some pegmatite districts are important as sources of has intensely tourmalinized the quartz-mica schist on lepidolite, sheet mica, columbite-tantalite, beryl, or the hanging-wall side of the pegmatite. other pegmatite minerals. The granitic pegmatites of In the Quartz Creek district, however, there has been most districts consist essentially of perthite, plagioclase, practically no alteration of the country rock adjacent quartz, and muscovite, but not all pegmatite districts to the pegmatite. The only noticeable alteration is of have the same assemblage of minor minerals. It is hornblende gneiss, which appears slightly more friable this assemblage of minor minerals and variants of adjacent to the contact. The three main types of common minerals, such as curved muscovite and country rock, hornblende gneiss and tonalite, granite, colored tourmaline, that indicate the differences in the and quartz monzonite, are equally free of alteration. overall composition in the original source , as Alteration of country rock might not be expected in well as the original pressure-temperature relationship, the granite and quartz monzonite, as both rocks con­ of each district. tain essentially the same minerals as the pegmatites. Not only do the less common minerals vary from On the other hand, the hornblende gneiss and tonalite district to district, but from pegmatite to pegmatite. are markedly different in chemical composition from During World War II the United States Geological the pegmatites. Similar hornblende rocks in other Survey studied pegmatites from which critically needed districts have been intensely altered. In describing the materials were produced, and these pegmatites were Petaca district, Jahns (1946, p. 54) states, "Where simply classified according to minerals of economic schist lies against pegmatite, as in the Green interest. It was recognized by many investigators Peak deposit, it has been converted to a dense aggre­ that a certain type of mineral occurred in certain groups gate of biotite flakes." McLaughlin (1940, p. 53), of pegmatites; for example, the lithium-bearing peg­ discussing the pegmatites of the Bridger Mountains, matites were not distributed haphazardly throughout a Wyo., says that all the older pegmatite dikes are accom­ given district but appeared in clusters or groups. This panied by alteration on the hanging-wall side of the distribution of miiieralogically similar pegmatites is dike, where the percentage of hornblende in the original illustrated in the Black Hills of South Dakota, where hornblende schist was greatly reduced and quartz became such well-known lithium producing pegmatites as the the predominant mineral. Etta, Peerless, Hugo, and Edison occur in one small The type of country rock may affect the kind or region, and the Helen Beryl, Helen Beryl No. 2, and amount of alteration, but it does not seem to be the Tin Mountain in another. only controlling factor. Apparently composition of the The areal mapping 011 which this report is based original pegmatite fluid caused the difference between afforded an excellent opportunity to study the dis­ the pegmatites of the Quartz Creek district and those tribution of minerals in a medium-sized pegmatite of many other districts that have widespread altera­ district. A series of maps (pis. 2 to 6) shows the dis­ tion along pegmatite contacts. In all parts of the world tribution throughout the Quartz Creek district of beryl, tourmaline, apatite, and muscovite are among the most tourmaline, curved muscovite, biotite, magnetite, widespread minerals in the zone of alteration. In fact, monazite, columbite-tantalite, cleavelandite, topaz, both tourmaline and apatite are among the commoner lepidolite, and microlite. Some minerals—such as flat minerals in most pegmatite districts and may occur in muscovite and garnet—are too widely distributed to almost every pegmatite; yet in the Quartz Creek dis­ be significant, whereas others—such as chlorite, ambly­ trict tourmaline is a constituent (and a comparatively gonite, and spodumene—are too rare to be of use minor one) of only 48 of 1,803 pegmatites, while apa­ statistically. Two facts are emphasized by these tite is found in but 3. Tourmaline is the only boron maps: (1) The relation of distribution of certain mineral found; phosphorus occurs in 3 pegmatites as minerals to all the pegmatites in the district, and (2) apatite, in 1 pegmatite as lithiophillite-triphylite, in the constant association of two or more minerals. The another as amblygonite, and in 23 pegmatites as mona- associated minerals are grouped on the same figure. zite. These facts indicate that the original pegmatite Each pegmatite that contains at least one crystal of a magma contained little B, P, and OH~, and possibly particular mineral is indicated on the map as a bearer other . of that mineral. This scheme of representation has a Insufficient concentration of the elements needed to serious defect, because large pegmatites erroneously form alteration minerals seems responsible for the lack appear to have a greater quantity of the mineral than of alteration in the Quartz Creek district though such do the smaller pegmatites. For example, the Black elements were available in the pegmatite fluids in suffi­ Wonder pegmatite (12,600 feet long by 6,700 feet cient amounts to form rare minerals. wide), contains only a few crystals of beryl in two small 46 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO pockets, yet it appears on the map to be a large beryl- matites were derived from the original magma of either bearing area. of these two rock types. Plate 2 shows 232 beryl-bearing pegmatites in 5 main groups and a few scattered pegmatites in the north- RELATIONSHIP OF BERYL-BEARING PEGMATITES central part of the area. Beryl-bearing pegmatites are much more common in Plate 3 shows the location of the groups of pegmatites certain types of country rock than in others. The ratios bearing tourmaline and curved muscovite. It is sig­ of beryl-bearing pegmatites to non-beryl-bearing peg­ nificant that these relatively rare minerals are con­ matites in various types of country rock are: 1:6.4 in centrated in their distribution in relation to the hun­ hornblende gneiss and tonalite, 1:20 in granite, and dreds of pegmatites mapped. 1:189 in quartz monzonite. These figures show a wide Magnetite and biotite are found in 422 and 357 range and suggest that the concentration of beryl in pegmatites, respectively. These two minerals are pegmatites is influenced by the country rock, horn­ present in almost every pegmatite in the northern part blende gneiss being more favorable than granite and of the area (pi. 4), yet known in the southern part only quartz monzonite. in*a few small clusters of pegmatites. An attempt is made to explain the differences between Plate 5 shows the distribution of columbite-tantalite- the ratio in granite and that in hornblende gneiss of bearing and monazite-bearing pegmatites. Only 1 or beryl-bearing pegmatites to non-beryl-bearing pegma­ 2 crystals of this group of minerals were formed in tites. It was thought that the granite might have each pegmatite. absorbed BeO from the pegmatite fluid, thus raising Plate 6 shows the grouping of lepidolite-, cleave- the BeO concentration in the granite and lowering it landite-, topaz-, and microlite-bearing pegmatites. in the pegmatite. Bulk samples were taken from a graphic granite-rich pegmatite (no. 512) and the adjoin­ The intimate association of the 4 minerals is evident. These minerals are abundant in 4 main groups of ing coarse-grained granite. The pegmatite sample con­ pegmatites. sisted of perthite (62 percent), quartz (20 percent), albite (15 percent), and muscovite (3 percent). A little RELATIONSHIP OP THE PEGMATITES TO THE more than half of this rock was graphic granite. The COUNTRY ROCK granite was visually estimated to contain microcline REGIONAL RELATIONSHIP (67 percent), albite (20 percent), quartz (8 percent), The two acid plutons in the Quartz Creek district and biotite (5 percent). The pegmatite contained a and the pegmatites might have had a common parent trace of BeO, and the granite contained an amount less magma. A study of the areal distribution of the peg­ than was detectable spectrographically (under 0.0001 matites related to these igneous bodies did not establish percent). The granite shows no enrichment of the conclusively the genetic relationships between the peg­ BeO where adjacent to the pegmatite. On the other matites and the plutons. hand, the pegmatite contains very little BeO, and thus any enrichment of the granite would be small. If the pegmatites and the plutons were derived from a common magma, the regional pattern would be ex­ For comparative purposes, bulk samples were taken pected to show a concentration of the pegmatites along also of the footwall layer of the Brown Derby No. 1 the outer edges of the plutons and in the adjacent pegmatite (no. 452) and of the hornblende gneiss within country rock. In the Quartz Creek district the peg­ 8 inches of the contact. The pegmatite was estimated matites are found on the margins of both granite and to consist of albite (89 percent), quartz (10 percent), quartz monzonite bodies, as well as in the adjacent tourmaline (1 to 2 percent), muscovite (less than 1 country rock. percent), and garnet (trace). The analyses showed that this pegmatite contains 0.030 percent BeO, and A logical explanation for the concentration of pegma­ the hornblende gneiss a trace. Though the hornblende tites along the outer margins of the intrusions is that gneiss contains only a trace of BeO, this is more than the granite and quartz monzonite are more dense and is present in the granite. The results are inconclusive less fractured and thus should have afforded less easy owing to the small amounts of BeO in the samples, but passage to the pegmatite solutions than did the adjacent it is probable that some explanation other than absorp­ hornblende gneiss. Thus the only zones of weakness tion of BeO by the country rock accounts for the beryl- in the plutons available to pegmatite intrusions were the fractures formed during cooling that are common bearing pegmatites favoring certain rock types. along the edges of these intrusive bodies. The observed The possibility that the BeO in the pegmatite was pattern of pegmatite distribution in relation to the derived from the country rock was not investigated. plutons does not preclude the possibility that the peg­ Samples of hornblende gneiss and granite at a greater RELATIONSHIP OF THE PEGMATITES TO THE COUNTRY ROCK 47 distance from the pegmatite are needed to check the Quartz Creek district have an average grain size of average BeO content of each country rock type. less than 1 inch and in texture may even resemble fine- to coarse-grained granite. In the northern part of ORIGIN the area many of the pegmatites in texture resemble The problem of the origin of granitic pegmatites is typical granitic rocks; they have even been mapped by complex and involves not only the origin and separation Crawford and Worcester (1916, pi. 2) as granite. The of their constituents from the original magma but also lepidolite-bearing Brown Derby pegmatites, on the their crystallization. Granitic pegmatites in many other hand, are much coarser textured and contain areas appear to be related areally to large bodies of many minerals distinctive of pegmatites that have . Most of these intrusive rocks crys­ been described by Landes (1935, p. 333) as showing tallized from magmas of composition, and, thus, "abundant evidence of hydrothermal replacement." granitic pegmatites are commonly associated with the The outer parts of these pegmatites, however, are more silicic igneous rocks, such as granites. Goranson similar in composition and texture to the great majority (1931, p. 481) has shown that certain natural rhyolitic of the simple pegmatites in the district. glasses may contain 8 to 10 percent water. The The pegmatites of every district have some dis­ amount of water released in the later stages by slow tinctive characteristics, and these usually are caused crystallization of such a magma would be very large. by the presence of certain minerals. For example, the In addition, volatile elements such as F, Cl, B, and P, pegmatites of the Black Hills are, in general, rich in would be concentrated. The alkalies, Na, K, Li, Cs, tourmaline, muscovite, and apatite and other phos­ and Kb, also tend to be concentrated during the later phate minerals. Very little topaz and lepidolite are stages of crystallization. found in this large district. These minerals show that Granitic pegmatites have some of the properties the original magma was comparatively rich in P, B, of granites and some, of various types of veins. They OH~, and poor in F. The pegmatites of the Quartz appear to be an intermediate type and have been com­ Creek district, on the other hand, differ from those in the pared with both igneous rocks and veins by various South Dakota district and many others in that they are writers. Beryl, a typical pegmatite mineral, is found relatively lean in muscovite, biotite, tourmaline, and also in granites and quartz veins—a fact which suggests phosphate minerals and are relatively rich in topaz, a continuous gradation between these rock types. lepidolite, and columbite-tantalite. These minerals in­ Beryl, for example, is found in the granites on Mount dicate that the original magma of the Quartz Creek Antero, Colo. (Adams, J. W., 1953), and in the Sheep- district pegmatites was lean in OH~, B, and P and com­ rock Mountains, Utah; and beryl-quartz veins are paratively rich in F, Ta, and Cb. In the entire Quartz found in the Victorio Mountains (Holser, 1953); on Creek district, only three pegmatites contain enough Mount Antero—California vein (Adams, 1953); in muscovite to be considered sources of scrap mica; the Arizona—Boreana vein (Hobbs, 1944, p. 254); and at content is commonly 0.5 to 3 percent. Biotite content Kazakhstan, U. S. S. R. (Sinegub, 1943, p. 129-157). is less than 1 percent. The lack of these two minerals Most of the pegmatites in the Quartz Creek district in most pegmatites indicates that the pegmatites of are simple pegmatites composed of minerals typical of this area contain relatively little OH". Tourmaline is granites—perthite, quartz, plagioclase, muscovite, and found in only 48 pegmatites, and the content is only a garnet. The unusual "distinctive" minerals of peg­ fraction of 1 percent. The dominant phosphorus matites rarely are found. Such minerals as cleave- mineral is monazite, which is present only as a few landite, lepidolite, topaz, microlite, gahnite, and small crystals in 24 pegmatites. Other phosphate columbite-tantalite occur in less than 2 percent of the minerals, apatite, amblygonite, and lithiophillite- pegmatites in the district. The predominant miner- triphylite, found in only 1 to 3 pegmatites, are exceed­ alogical difference between pegmatites in many districts ingly rare. Fluorine is a constituent of topaz in 8 and their associated granites is that the pegmatites are pegmatites, lepidolite in 17 pegmatites, microlite in 14 somewhat higher in muscovite content, indicating a pegmatites, and fluorite in 2 pegmatites. Niobium higher water content of the original fluid. In the and tantalum are present in columbite-tantalite in 29 Quartz Creek district, however, muscovite is a rela­ pegmatites; in microlite in 14 pegmatites, and in tively minor mineral, a fact suggesting that the original samarskite(?) in 7 pegmatites, and in an unidentified magma was deficient in water. The few pegmatites that have minerals containing other volatile elements mineral in 1 pegmatite. are probably the result of a later stage of segregation Within a particular district considerable variation is and crystallization. shown in the areal distribution of pegmatite minerals. More than 90 percent of the pegmatites in the As previously indicated, pegmatites with certain of 48 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO the rare elements occur in definitely circumscribed same composition as the magma from which it formed. areas or groups. Perhaps pegmatite fluids escaped This explanation has been favored by Brogger (1880, p. from a particular part of the chamber of the parent 215-235), Kemp (1924, p. 708), Shaub (1940, p. 673- granitic magma and moved in a certain restricted 688), Johnston (1945, p. 1015-1070), and Cameron, direction, dividing into separate units before final Jahns, McNair, and Page (1949, p. 97-106). emplacement; this could account for the strikingly A second explanation is that such internal structure localized distribution of certain pegmatite minerals in is formed in an open system by successive deposition one area. The distribution of these minerals in dif­ of material along the walls by r^drothermal solutions. ferent groups is related to their origin. As the parent The composition of the solutions changes progressively granite magma cooled, it may be assumed the pegmatite so that successive layers of contrasting composition are fluids were segregated in different parts of the magma formed. Various modifications of this explanation have and escaped from various parts at different times. been given by Hunt (1871, p. 82-89, 182-191), and The pegmatite fluid that is driven from the parent Quirke and Kremers (1943, p. 571-580). chamber earliest contains less volatile material, prob­ A third explanation is that the development is in ably is under less vapor pressure, and forms the greater two stages: a magmatic stage in which the pegmatitic number of all pegmatites—those that most closely fluid is injected and crystallizes to form massive pegma­ resemble other granitic rocks. The minerals found in tite that has essentially the composition of a potash- any pegmatite depend on the original composition of rich granite and a hydrothermal stage during which the material segregated in a pocket and on the stage solutions passing through the pegmatite cause it to be of crystallization at which it was segregated. The partly or completely replaced. This hypothesis is an more highly volatile constituents are in the pegma­ adaptation of some of the theories of Hess (1925, p. tite fluids formed at a later stage and form a few rare 289-298), Schaller (1925, p. 269-279), Landes (1933, p. pegmatites. Many minerals are almost always found 33-56, 95-103), Gevers (1937, p. 331-377), and Derry in close association with certain other minerals because (1931, p. 454-475). they contain either common ions that make their as­ Any hypothesis advanced to explain the origin of sociation imperative or elements that are concentrated the internal structure must be in accord with all the at the same stage in crystallization. Such minerals with known features of heterogeneous pegmatites. Many common ions include: lepidolite, topaz, and micro- of the characteristics of heterogeneous pegmatites, lite—all of which contain F~; and lepidolite and lighter such as gradational or abrupt contacts between suc­ colored tourmaline both of which contain Li+. Min­ cessive layers or zones of contrasting composition, erals which owe their association to elements segregated could be formed by each of the above mentioned modes at approximately the same stage are columbite- of origin. Furthermore, it is not clear from the textural tantalite and monazite. In places where these two relations alone whether the first magmatic part of the minerals are not associated, it probably is due to a pegmatite has been replaced by later hydrothermal lack of elements to form one or the other mineral. solutions or whether the earlier crystallized minerals The more common minerals are segregated con­ were corroded by residual magmatic solutions as the tinuously or recurrently during the differentiation of chemical environment, pressure, and temperature the parent granite. In pegmatites containing the rarer changed. Therefore, the evidence in support of the elements, minerals such as plagioclase, perthite, quartz, origin of the internal structure of pegmatites must be and muscovite are still the predominant minerals. a composite of the mineralogical, structural, and tex­ The rarer elements, such as Li, Cs, Kb, F, Cl, Nb, and tural features. Ta, probably are in the more soluble part of the peg­ The Quartz Creek district has few well-zoned peg­ matite material and certainly are among the last to matites and does not present the wealth of structural, crystallize. textural, and mineralogical data that are available in The heterogeneous pegmatites show various types of many regions. Some of the outstanding features noted internal structure. Three principal explanations of the in heterogeneous pegmatites of the Quartz Creek dis­ origin of this structure have been advanced. trict that must be considered in determining origin of One explanation is that this type of structure is structural units are: formed by fractional crystallization of the pegmatitic 1. Poorly zoned pegmatites made up of a large wall fluid in place. Reaction between crystals and rest- zone and one or more core segments show, between the solution is incomplete, and succe sive layers of con­ wall zone and core, no consistent change in the anorthite trasting composition are deposited. Formation of in­ content of the plagioclase, alkali content of the beryl, ternal structures by this method requires that nothing or the ferric iron content of the muscovite. be added and that the pegmatite be essentially o" the 2. Pegmatites containing an intermediate zone in ORIGIN 49

addition to a wall zone and core show, from wall zone be explained either by fractional crystallization or by inward, a decrease in the anorthite content of plagio- deposition of material along open channels provided clase and an increase in the alkali content of beryl— that the channelway was through the center of the variations comparable to similar changes reported from pegmatite. other districts. Most of the minerals in granitic pegmatites are the 3. Tourmaline in zoned, lepidolite-bearing pegma­ same as those found in granites. A similar origin tites becomes gradually lighter colored from the outer might be expected for such similar rocks. edge of the wall zone toward the core. The color The age relations between the layers are not apparent change is paralleled by a decrease in index of refraction in layered pegmatites, especially for the more common which may be correlated with chemical composition. type, which has a perthite-rich hanging-wall grading 4. Most of the layered pegmatites are composed of into an albite-rich footwall. The presence of the a pert bite-rich hanging-wall and an albite-rich footwall perthite-rich layer always on the hanging-wall side of layer. the pegmatite is difficult to explain if one assumes 5. A few heterogeneous pegmatites contain lepidolite, that this unit formed by deposition of material along topaz, colimibite-tatitalite, and microlite in structural throughgoing channels or by successive replacement units adjacent to other units that do not contain these of massive pegmatite. rare minerals. The problem of origin of the internal structure of 6. The textures of the pegmatite units range from the Quartz Creek pegmatites is far from being solved, fine- to extremely coarse-grained, and adjacent units but the evidence presented suggests an origin by commonly have markedly different textures. fractional crystallization in place. 7. The fracture-filling units found in some pegma­ tites extend from the quartz core across, or cut, the RESERVES surrounding wall zone. Reserves of pegmatite minerals are difficult to esti­ Some of these features can be explained by several mate, because normal sampling procedures can not be hypotheses, but the writers believe that they are most used. Grade can be obtained by relating the areas of readily explained by a hypothesis involving fractional industrial minerals exposed on a pegmatite surface to crystallization of a magma in an essentially closed the total exposed area. The percent of mineral ex­ system. The relationship of fracture-filling units to posed may be converted to a weight percent of mineral wall zones indicates that wall zones formed before the by making proper corrections for specific gravity. cores. This age sequence, in conjunction with the The tonnage of rock containing an industrial mineral structural relations of the core and wall zones, is par­ can be calculated from a detailed map of the internal ticularly difficult to explain by the other hypotheses. structure of the pegmatite. If these zones were formed by successive replacement Reserve calculations have been made for all the of preexisting massive pegmatite, they would show industrial minerals in pegmatites of the Quartz Creek the reverse of this age sequence, because the contact district. Mining operations in the past were based of pegmatite and wall rock is a more likely place for on production of lepidolite, scrap muscovite, and beryl. penetration by replacing solutions than the gradational Reserves of potash feldspar might sustain mining oper­ contact between the internal structural units. ations, if transportation were less expensive. Assuming that pegmatite development proceeds The total reserves of clean, hand-cobbable feldspar with falling temperature, plagioclase of relatively high are estimated to be 795,600 tons of potash feldspar anorthite content should form first and become more and 9,740 tons of soda feldspar. These feldspar sodic later. Beryl with a low alkali content should reserves are all in pegmatite units containing more form early. This sequence was noted in the few than 25 percent feldspar, in grains greater than 12 better zoned pegmatites having an appreciable change inches in length. The minimum size of a unit in­ in mineral composition that indicated a decrease in cluded in these calculations was 200 feet long and temperature as deposition proceded toward the center 40 feet wide. of the pegmatite. Layered and poorly zoned pegma­ In addition, considerable feldspar is recoverable by tites show little change. milling. Most of this feldspar is in the form of graphic The gradual increase in some zoned lepidolite-bearing granite. A number of these pegmatites would pose pegmatites of the lithium content of tourmalines considerable transportation difficulties because they toward the center, as well as an increase in lepidolite, are several miles over mountainous terrain from the denotes a gradual increase of lithium content and nearest road. A total of 251,300,000 tons of milling- certain other elements, such as cesium, rubidium, and grade feldspar is calculated for 40 pegmatives. This fluorine. This gradual change of pegmatitic fluid can is an average of 6,028,000 tons per pegmatite. The 50 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO largest reserves are in the Black Wonder pegmatite beryl; none of the exposures contained as much as 2 (no. 847). square inches of beryl. Only one pegmatite in quartz No sheet mica and very little scrap mica are found monzonite contained beryl. All pegmatites in the in the Quartz Creek district. Scrap muscovite reserves Quartz Creek district that contained as much as 2 are estimated to be 13,500 tons, of which 1,400 tons square inches of beryl had hornblende gneiss wall rocks. are recoverable by hand cobbing. The scrap mica The hornblende gneiss is exposed in a large area favor­ obtained is a byproduct of the mining of beryl-bearing able for detailed prospecting. pegmatites. Only three pegmatites (the Bucky, the Although detailed studies indicate that beryl is most Buckhorn, and the Beryl and Kare Minerals Lode) common in albite-rich pegmatites, no beryl has been contain either enough muscovite or muscovite in large recovered commercially from those pegmatites because enough pieces to be considered recoverable as a by­ they are almost invariably too fine grained. The product of beryl mining. The muscovite reserves of beryl in them ranges in grain size from 0.06 to 0.5 these three pegmatites are calculated to be 1,400 tons. inch. In perthite-rich pegmatites, beryl is less com­ The total beryl reserve estimated for the Quartz mon, but most grains of beryl present are large enough Creek district is about 350 tons. One pegmatite was to be hand cobbed. The small grain size of the beryl- estimated to contain 160 tons of beryl; another, 75 tons; bearing, albite-rich pegmatites precludes economic and a third, 40 tons. Thirty-eight of the pegmatites recovery of beryl under present technological conditions; contain less than 10 tons of beryl. Of the total 350 deposits of this type, therefore, cannot be expected to tons of beryl, probably 325 tons are hand cobbable. be of immediate concern to the prospector. Ultimately, Some of the pegmatites that have beryl reserves also however, they may be treated by flotation and, if contain lepidolite, microlite, topaz, columbite-tantalite, found in sufficient quantities, may become economically and monazite. The lepidolite reserves of the entire important enough to warrant the erection of a mill. area amount to 3,560 tons. One pegmatite was esti­ Some pegmatites have both albite-rich and perthite- mated to contain 1,600 tons of lepidolite. Only four rich parts. The perthite-rich parts may be a source of lepidolite deposits have individual reserves exceeding beryl at the present time, but the albite-rich parts, 100 tons. For the district as a whole, reserves are 900 though equally rich in beryl, are at present too fine tons of topaz, 900 pounds of microlite, 4,000 pounds of grained to mine. The beryl in pegmatites containing columbite-tantalite, and 400 pounds of monazite. The cleavelandite is coarse grained and may be recovered reserves of the last three minerals, because they occur by hand methods; consequently cleavelandite-bearing in such small widely distributed quantities, are very pegmatites should be prospected carefully. difficult to calculate Graphic-granite pegmatites, one of the most com­ mon types of perthite-rich pegmatites in the district, PROSPECTING FOB BERYL do not contain beryl and should be avoided in searching Of the 1,803 pegmatites found in the Quartz Creek for beryl deposits. Beryl favors massive perthite- district, 232 contain some beryl. In most of these quartz pegmatite units or perthite-muscovite-rich pegmatites only 1 or 2 crystals of beryl 0.10 to 0.25 units, though the very irregular distribution of beryl inch in diameter, were noted. Of the 232 pegmatites, may cause one part of a unit to be completely barren 42 have more than 2 square inches of beryl exposed, of beryl although in other parts it may be abundant. and of these, only a very few could be considered as Lepidolite is considered one of the more favorable possible sources of appreciable beryl production. indicators of beryl in prospecting, because much beryl It is very difficult to find pegmatites that contain is found in lepidolite-bearing pegmatites. beryl in sufficient quantities to be of commercial value. In general, the Quartz Creek district is not a favorable The beryl in this district is commonly white and district in which to prospect for beryl, because the good resembles feldspar or quartz. It is usually overlooked mica and feldspar deposits are of small size and produc­ by prospectors. Favorable beryl-bearing zones are tion of beryl in the past has been a by-product of covered by overburden in many places, and diligent mining of one or the other of these minerals. There prospectors in these favorable areas might find worth­ are no sheet mica deposits in the district; the scrap while deposits. mica deposits are not large; feldspar in large quantities Several broad statements can be made concerning must be recovered by milling of graphic granite; and the favorable and unfavorable areas in which to look deposits of feldspar that can be hand cobbed are small. for beryl in pegmatites of the Quartz Creek district. The small size of the deposits of these minerals, in Granite and quartz monzonite are, apparently, def­ conjunction with the high cost of transportation, initely unfavorable as host rock for beryl pegmatites. almost precludes profitable mining operations in this Only three pegmatites in granite were found to contain district at 1951 prices. Only a small amount of feldspar DESCRIPTIONS OF INDIVIDUAL DEPOSITS 51 has been sold by local producers, and the high cost of size of 1.5 inches and is estimated to consist of white transportation and the small size of the perthite units cleavelandite (69 percent), quartz (20 percent), perthite in this district do not encourage the production of (8 percent), muscovite (2 percent), black and dark- feldspar. green tourmaline (1 percent), lepidolite (less than 1 percent), topaz (less than 0.5 percent), beryl (0.1 per­ DESCRIPTIONS OF INDIVIDUAL DEPOSITS cent), garnet (trace), microlite (trace), cohimbite- A detailed description is given below of some of the tantalite (trace), and monazite (trace). Concentra­ economically more interesting pegmatites. Only peg­ tions of lepidolite are present locally. In one 3-foot matites which have been producers in the past or may area lepidolite constitutes as much as 5 percent of the be potential producers in the future will be described. rock. It occurs as fine-grained aggregates and in larger plates 0.25 to 1 inch in diameter. The topaz isjnilky OPPORTUNITY NO. 1 CLAIM (PEGMATITE 215) The Opportunity No. I claim is in the NE% sec. 17, T. 49 N., E. 3 E. This prospect is claimed by Earl A. Serry and is south of the Doyleville road on the eastern slope of a north-trending ridge. The claim includes more than 10 pegmatites, but the main workings are on the largest one, no. 215. This pegmatite is exposed by 5 small cuts, the largest of which is 37 feet long, 10 feet wide, and 10 feet deep; the other 4 are each about 8 feet long, 4 feet wide, and 5 feet deep. No minerals have been produced from this prospect. The pegmatite is a lenticular-branching pegmatite 730 feet in maximum length and 40 feet in maximum width Much of the pegmatite, however, has a thick­ ness of less than 5 feet. It dips 45° to 80° SE. and cuts both fine-grained granite and hornblende gneiss. The pegmatite is divided into four units along the strike of the body (fig. 31). Albite-quartz-perthite peg­ matite forms a unit m the stringers extending from the northeast, the southwest, and the central part of the pegmatite. This unit has an average grain size of 0.25 inch and is estimated to consist of albite (65 percent), quartz (20 percent), perthite (15 percent), muscovite (less than 1 percent); it contained one small, 0.25 inch, pale-green beryl crystal. Near the south end of the pegmatite, the body widens considerably at the junction of a small northward-trending branch with the main body of the pegmatite. This wide area is made up of several units. The western side is a unit of quartz- albite pegmatite that has an average grain size of 3 to 4 inches and is estimated to contain quartz (75 percent), albite (20 percent), muscovite (3 percent), perthite (2 percent), and tourmaline (less than 1 percent). The eastern side of this bulge area is dominantly perthite- cleavelaDdite-quartz pegmatite, has an average grain size of about 2 to 3 inches, and is estimated to consist of pink perthite (60 percent), white cleavelandite (20 percent), quartz (20 percent), muscovite (less than 1 0 150 Feet percent), black tourmaline (less than 1 percent), and $(1 -' ' , , 1 1 garnet (trace). The perthite occurs in crystals as much as 12 inches long. The central part of this bulge, and Outline of pegmatite b the rest of the pegmatite to the north, is cleavelandite- Internal structure by quartz pegmatite. This pegmatite has an average grain FIGURE 31.—Geologic map, Opportunity No. 1 (no. 215) pegmatite. 52 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO white, has a good cleavage, and commonly occurs with landite core has been completely mined out (fig. 32). white beryl. Beryl and topaz have an irregular distri­ Furthermore, in the lepidolite-quartz-cleavelandite core bution. In the southern part of this unit microlite, in tunnel 2, the working face has been extended 30 associated with smoky quartz and platy cleavelandite, feet to the east for a width of 20 feet. This additional is found as clusters of distorted octahedra, as much as work was completed by the Hayden Mining Com­ 0.25 inch in diameter, modified by dodecahedra. Prob­ pany before it ceased mining in 1945. ably the microlite content of this small part of the In May and June 1950, the [Tnited States Bureau of pegmatite is a few pounds per ton. Columbite-tanta- Mines drilled two core holes. -drill hole 1 lite is less common than the microlite; and only a few (pi. 7) is inclined 60 degrees, has a bearing of N. 77° small crystals, the largest an inch across, were found. W., and was drilled from the dump of dike 1. The Four crystals of monazite associated with columbite- tantalite were noted.

PEGMATITE 417 Pegmatite 417 (pi. 1) is on the western side of the western branch of Wood Gulch, near the western limit of sec. 2, T. 49 N., K. 3 E. It is a few feet above the canyon bottom and can be reached by the secondary road running up Wood Gulch. It is opened by one small pit 18 feet long, 4 feet wide, and 4 feet deep at its western face. The pegmatite is irregular and is approximately 370 feet long and 105 feet in maximum width. Part of the irregularity is the result of its exposure on a dip slope. The pit, which is near the center of the pegmatite, FIGURE 32.—Mouth of stope of the Brown Derby No. 1 pegmatite (no. 452) showing cuts completely through the body, and at this point the contact of pegmatite with hornblende gneiss. pegmatite is 6 feet thick. The pegmatite intrudes hornblende gneiss and has a wall zone and a core. hole has a length of 208.5 feet and cuts dikes 2 and 3. The wall zone is the greater part of the body and has an Diamond-drill hole 2 was drilled from the hillside average grain size of 0.12 inch. It consists of albite above tunnel 3 and cut dikes 1, 2, and 3. The bearing (55 percent), quartz (35 percent), perthite (5 percent), of the hole is N. 88° W., and the inclination is a minus and muscovite (5 percent); one 0.75-inch crystal of 65 degrees. beryl was noted. The core has an average grain size The Brown Derby No. 1 dike is a lenticular and of 3 inches; it consists of perthite (45 percent), albite branching pegmatite, with two branches at its southern (42 percent), quartz (8 percent), muscovite (5 percent), end. It is exposed for a total length of 913 feet. and beryl (0.2 percent); one small piece of samarskite The west branch is exposed in a series of six prospect was noted. The beryl forms pale-green euhedral pits. It is made up of a wall zone of albite-quartz crystals that range in size from 0.25 inch by 0.25 inch pegmatite and a core of albite-quartz-biotite pegmatite. to 2 inches by 4 inches. A grain count of 101 square The albite-quartz pegmatite forms nearly all the feet of the core contained 0.2 percent beryl in 33 west branch of the dike. It has a grain size of 4 to 6 crystals. inches and is estimated to contain quartz (52 percent), cleavelandite (45 percent), muscovite (3 percent), and BROWN DERBY DIKE NO. i (PEGMATITE 452) less than 1 percent of garnet, tourmaline, and lepidolite. The Brown Derby Dike No. 1 is the easternmost of The albite-quartz-biotite pegmatite of the core is the Brown Derby group of dikes, in sec. 3, T. 49 N., exposed in pit 11 and is 20 feet long by 1.5 feet wide. E. 3 E. This dike is a few hundred feet below the The grain size of the core ranges from 0.12 to 0.25 inch. crest of a long ridge at 9,300 feet on the east side of The unit contains albite (86 percent); quartz (5 per­ Quartz Creek. An access road, built by the Federal cent); biotite (4 percent); monazite (2.2 percent); Government from Colorado State Highway 162 to the columbite-tantalite (1.4 percent); gahnite, the zinc workings, is approximately 2 miles long. spinel (1 percent); less than 1 percent of garnet and The pegmatite has been described by J. B. Hanley tourmaline; and trace quantites of fiuorite and betafite. (1950, p. 68-71). Since this mapping was finished Monazite forms well-developed euhedral crystals, 0.25 (December 1944), the high-grade pod-shaped con­ to 1.5 inches in diameter, and the columbite-tantalite centration of lepidolite in the lepidolite-quartz-cleave- forms tabular crystals, 0.25 to 1 inch across. DESCRIPTIONS OF INDIVIDUAL DEPOSITS 53

The main part of the pegmatite is composed of six crystals range from less than 0.01 inch to 0.25 inch in different units, identified from hanging wall to footwall diameter and are in shoots within the pods. This unit as follows: Perthite-albite-quartz pegmatite (hanging- in tunnel 2 is extremely low in microlite and has also a wall layer), hanging-wall quartz pod, curved-lepidolite low lepidolite content. The pod has been nearly mined layer, lepidolite-microlite pod, quartz-cleavelandite- out in the incline; the remainder shown in the bottom lepidolite-topaz layer, and albite pegmatite (footwall is pinching to the southeast. layer). The quartz-cleavelandite-lepidolite-topaz layer is the The perthite-albite-quartz pegmatite makes up the footwall part of the lepidolite-bearing units of the peg­ entire width of the northern part of the dike and the matite. It is exposed on the surface for a distance of eastern branch of the southern part of the dike. Else­ 319 feet and has an average thickness of 2 feet. The where in the lepidolite-bearing part of the dike, it unit has an average grain size of 4 to 6 inches and con­ occurs as the hanging-wall layer, with the exception of sists of quartz (55 percent), cleavelandite (25 percent), the vicinity of the inclined shaft where it is missing. lepidolite (10 percent), topaz (10 percent), less than 1 At this point the quartz pod takes the place of the percent muscovite, and less than 0.1 percent beryl. perthite-albite-quartz pegmatite. This pegmatite has Lepidolite is in flat books ranging from 1 to 7 inches an average thickness of about 8 feet. In the lepidolite- across and topaz crystals are as much as 42 inches bearing part of the pegmatite it does not exceed 4 feet. long. Beryl is in crystals ranging from 1 to 4 inches in The grain size of the unit is about 12 inches, and the diameter. composition is estimated to be perthite (40 percent), The albite pegmatite (footwall layer) has an average albite (30 percent), quartz (20 percent), muscovite (10 thickness of 1.5 feet. It occurs discontinuously along percent), beryl (0.1 percent), and trace of tourmaline. the lepidolite-bearing part of the pegmatite. It has a Beryl crystals range from 0.25 to 2 inches in diameter. grain size of 0.25 inch and composition estimated to be The hanging-wall quartz pod is approximately 84 feet albite (90 percent), quartz (8 percent), tourmaline (2 long and 2 feet thick. Its grain size is 24 inches, and percent), less than 1 percent garnet, and a trace of the constituents are estimated as quartz (70 percent), biotite. cleavelandite (25 percent), and lepidolite (5 percent). The lepidolite occurs in sheets from 3 to 4 inches across. BROWN DERBY NO. 5 (PEGMATITE 535) The curved-lepidolite layer is 190 feet long and aver­ The Brown Derby No. 5 (pegmatite 535) (pi. 1) is ages 2 feet in thickness. This unit forms the back of the in a small gulch on the west side of the Brown Derby extension of tunnel 2 and much of the back of the stoped ridge at an elevation of 8,900 feet. It is in the south- area in the inclined shaft. The grain size of the curved central part of sec. 34, T. 50 N., R. 3 E. lepidolite layer is 4 to 5 inches, and the composition is This claim is reached by a short spur road from the cleavelandite (44 percent), quartz (40 percent), curved main Brown Derby road and is owned by Mrs. Marie lepidolite (15 percent), topaz (1 percent), less than one Disberger. The workings consist of two small open- percent muscovite and tourmaline, and a trace of apa­ cuts and an adit. The larger cut has a main part, 32 tite. The curved lepidolite ranges from 0.25 to 2 inches feet long, 15 feet wide, and 18 feet deep at the eastern across, and the topaz ranges from 4 to 8 inches across. face. The southern branch of this cut is 12 feet long, Two principal lepidolite-microlite pods are known. 6 feet wide, and 6 feet deep at the northeast face. An In addition, smaller pods have been exposed in pits adit, approximately 10 feet long, was driven from the and trenches. The largest pod was mined in the in­ eastern end of this cut. A second shallow cut, 10 feet clined shaft, and the other was discovered underground long and 8 feet wide, is northeast of the main cut. and mined by tunnel 2. The pod at the inclined shaft This pegmatite was originally mapped by J. B. was approximately 60 feet long with a maximum width Hanley and Roswell Miller III, on September 3, 1943, of 8 feet. It was mined from the inclined shaft for a with plane table and telescopic alidade. The descrip­ total length of about 170 feet down the dip. The pod tion of the internal structure of the pegmatite was exposed in tunnel 2 is approximately 30 feet wide by revised by the writers in September 1949 (fig. 33). 6)2 feet thick and is present in the face of the tunnel. The Brown Derby No. 5 pegmatite intrudes greenish- The mined length is approximately 40 feet. The aver­ black hornblende tonalite. The pegmatite is irregular age grain size of the unit is 1 inch, and the average in shape, being 210 feet long and 50 feet wide (maxi­ composition is cleavelandite (43 percent), lepidolite mum). It consists of three zones—wall zone, inter­ (40 percent), quartz (15 percent), topaz (2 percent), mediate zone, and core. The wall zone is 2.5 feet thick microlite (0.35 percent), and a trace of beryl. The where exposed in the large opencut, has a range in lepidolite is in crystals 0.03 to 0.12 inch across and is grain size of from 0.12 to 0.25 inch, and consists of albite irregularly distributed within the pods. Microlite (61 percent), quartz (25 percent), perthite (10 percent), 54 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

microlite (trace), and columbite-tantalite (trace). Lepidolite occurs both as fine-grained aggregates and as large flat sheets up to 6 inches in diameter. The workings are on this zone, and mining was directed toward the recovery of the fine-grained lepidolite; most of the large sheets were thrown out on the dump. The beryl is in blue-green euhedral crystals from 0.5 to 3.5 inches in diameter The beryl content increases in the northern part of the zone and appears richest in the small northern pit. In this upper pit beryl count made on an area 4 feet by 5 feet indicated 0.43 percent beryl by volume. About 15 pounds of beryl was also found lying on the dump from this pit. The topaz is milky white and forms euhedral crystals, 4 to 6 inches long, adjacent to the lepidolite. The garnet forms crystals as much as 1.5 inches in diameter, and commonly is surrounded by coronas of muscovite. It is most common near the contact with the underlying wall zone. The apatite is in widely scattered, light-blue crystals Contact, showing dip; dashed 0.5 inch in diameter. Microlite was not seen in place Perthite-quartz-albite pegmatite where approximately located but was found on the dump in distorted octahedra, 0.12 to 0.25 inch in diameter. The olive-green microlite Contact between pegmatite units is faintly radioactive and is found between plates of cleavelandite. One crystal of columbite-tantalite, 0.06 by 0.75 inch, was found between plates of cleavelandite. The core at its southeastern end has a gradational Rim of excavation contact with the intermediate zone. The grains of the core average 6 inches in diameter. The core consists of

Tonalite white massive quartz (40 percent), white perthite Dump (39 percent), albite (20 percent), muscovite (1 percent), lepidolite (trace), blue-green beryl (only 1 crystal, 4 by 60 60 Feet I 6 inches), and columbite-tantalite (2 thin pieces, 0.5 by 0.06 inch). Geology by J. B. Hanley and R. Miller III, Sept. 1943 PEGMATITE 537 Revised by M. H. Staatz, Sept. 1949 Pegmatite 537 (pi. 1) is on a small ridge in the SE% FIGURE 33.—Geologic map, Brown Derby No. 5 (no. 635) pegmatite. sec. 34, T. 50 N., R. 3 E. It is penetrated by one small adit approximately 4 feet wide and 6 feet long. This muscovite (4 percent), black to greenish-black tour­ working is several hundred feet above and 600 feet to maline (less than 1 percent), lepidolite (trace), garnet the northeast of the Brown Derby mine road. (trace), and beryl (less than 0.1 percent). One exposed Pegmatite 537 is an irregular dumbbell-shaped body area of the wall zone, about 3 feet square, contains 17 (fig. 34), 530 feet long and 84 feet in maximum width. beryl crystals ranging in size from 0.5 by 0.5 inch to 1 The pegmatite intrudes hornblende gneiss. It has a by 1.3 inches. This unusually rich area averaged 1.13 fine-grained wall zone and three small discontinuous percent beryl in blue-green euhedral crystals, but con­ core segments. The wall zone makes up more than 90 tained only three crystals that could be hand cobbed. percent of the pegmatite, with an average grain size In the southeastern part of the pegmatite, within of 0.25 inch. It consists of albite (60 percent), quartz the wall zone is a small intermediate zone, approxi­ (25 percent), perthite (10 percent), muscovite (5 mately 50 feet long and 14 feet wide. It has an average percent), and garnet (less than 1 percent). grain size of 4 inches and consists of quartz (55 per­ The northern and southern core segments of this cent), white cleavelandite (35 percent), lepidolite (5 pegmatite have an average grain size of 6 inches and percent), white massive perthite (4 percent), muscovite consist of perthite (66 percent), quartz (20 percent), (1 percent), beryl (0.1 percent), topaz (less than 1 albite (10 percent), and muscovite (4 percent). Grains percent), garnet (less than 1 percent), greenish-black of perfchite range in diameter from 3 to 12 inches. tourmaline (less than 1 percent), apatite (trace), Beryl is found only in the northern core segment. A DESCRIPTIONS OF INDIVIDUAL DEPOSITS 55

of this pegmatite. This cut is approximately 650 feet northeast of the Brown Derby road and several hundred feet above it. Pegmatite 538 is an elongate lenticular-branching pegmatite, approximately 550 feet long and 60 feet in maximum width (fig. 34). The pegmatite intrudes hornblende gneiss and consists of wall zone and three small discontinuous cor^s segments located in the thicker parts of the pegmatite. The wall zone comprises more than 60 percent of the peg­ matite, has an average grain size of 0.25 inch, and consists of albite (57 percent), quartz (25 percent), perthite (10 percent), and muscovite (8 percent). The core segments have an average grain size of 4 inches and consist of quartz (50 percent), perthite (32 per­ cent), albite (15 percent), and muscovite (3 percent). Perthite occurs in crystals of 6 to 8 inches in diameter. Pale-green beryl was noted only in the southernmost core segment, where it was estimated from several beryl counts, to make up 0.95 percent of the rock. The beryl crystals range in size from 0.12 by 0.12 inch to 6 by 6 inches. The southern pod is 128 feet long and has a maximum width of 35 feet. PEGMATITE 560 Pegmatite 560 (pi. 1), on which no claim had been located, is at the foot of the mountains on the east side of Quartz Creek in the west-central part of sec. 34, T. 50 N., R. 3 E. This pegmatite is 1,500 feet south of State Highway 162 and lies directly beyond a meadow. It is extremely irregular (fig. 35) and has Contact between a length of 430 feet and a maximum width of 200 feet. XXXI I/- • \J pegmatite units Quartz pegmatite Albite-quartz pegmatite It cuts across the contact of the granite and the horn­ blende gneiss. This pegmatite consists of a narrow

Perthite-quartz pegmatite Hornblende gneiss wall zone, a large core, and a small pod near the south end. The grams of the wall zone average 0.12 inch in diameter. This zone consists of albite (60 percent), Quartz-perthite-albite pegmatite Contact, showing dip quartz (36 percent), perthite (4 percent), muscovite Geology by M. H. Staatz and P. T. Flawn, Aug. 1948 (less than 1 percent), and garnet (trace). The core FIGURE 34.—Geologic map of pegmatites 537 and 538. comprises the greater part of the pegmatite and has an average grain size of 4 inches. It consists of perthite grain count on the sides of the small adit in this core (50 percent), quartz (30 percent), albite (20 percent), showed 0.31 percent beryl. The beryl observed con­ and muscovite (trace). A lenticular pod, 78 by 18 sisted of 22 pale-green euhedral crystals ranging in feet, is found on the south end of the pegmatite. This size from 0.25 by 0.12 inch to 2.5 by 4 inches. The pod has an average grain size of 1 to 2 feet and contains core segment containing beryl is 52 feet long and 10 perthite (75 percent), quartz (20 percent), albite (5 feet wide. The central core segment is 3 to 5 feet wide, percent), and beryl (0.45 percent). The beryl is pale has an average grain diameter of 6 inches, and contains green and ranges in size from 1 by 2 inches to 4 by 8 quartz (85 percent), perthite (10 percent), albite (5 inches. This pod contains the only beryl noted in the percent), and muscovite (less than 1 percent). No pegmatite. beryl was noted in this pod. BERYL AND BABE MINERALS LODE (PEGMATITE PEGMATITE 538 590) Pegmatite 538 (pi. 1) caps the top of a small ridge in The Beryl and Rare Minerals Lode (no. 590, pi. 1) the SEK sec. 34, T. 50 N., R. 3 E. One small cut, 6 is a small lenticular pegmatite on the north-facing slope feet square and 1 foot deep, exposes the southern end of Tollgate Gulch, in the SEtf sec. 34, T. 50 N., R. 3 E. 56 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

Fields on November 27, 1949. Mr. Fields has opened at least six small pits; the smallest is a few feet square No. 560 and 1 foot deep and the largest 22 feet long, 10 feet wide, and 2 feet deep. These pits are on local concen­ trations of beryl and thus expose the richest parts of the beryl-bearing pegmatite. To 1950 Mr. Fields has recovered approximately 480 pounds of beryl, 2 pounds N of columbite-tantalite, and approximately 800 pounds A of muscovite. The Beryl and Rare Minerals pegmatite intrudes hornblende gneiss and may be divided into three zones: wall zone, intermediate zone, and core. The top of the pegmatite has been eroded, exposing the flatlying central units. The wall zone is thin and irreg­ ular and is exposed in only a few places along the edge of the pegmatite. It has an average grain size of 0.25 inch and consists of albite (55 percent), perthite (20 percent), quartz (25 percent), and muscovite (less than 1 percent). The intermediate zone is well exposed by the work­ ings. It has an average grain size of approximately 3 feet and is estimated to consist of perthite (50 percent), 0 150 Feet I I i I I I muscovite (30 percent), quartz (20 percent), albite (less than 1 percent), beryl (0.1 percent), columbite-tantalite No. 590 (less than 0.05 percent), traces of gahnite and an uni­ dentified mineral resembling the samarskite-fergusonite- euxenite group of minerals. The perthite occurs in crystals from 1 to 5 feet in diameter. Muscovite is abundant in the outer part of this zone and occurs in books as much as 8 inches across. It is reeved, soft, 100 Feet _J and heavily stained and is all scrap mica. It closely resembles the mica at the Bucky and Buckhorn prop­ EXPLANATION erties. Beryl ranges from 0.5 to 8 inches in diameter and is white. From the amount of beryl recovered and the size of the workings, the percentage of beryl ob­ tained in the pits is estimated to be 0.4 percent. Because the pits were in the beryl-rich parts of the pegmatite and because many parts of this zone are Hornblende gneiss completely barren of beryl, the overall content in this zone is approximately 0.1 percent. Columbite-tanta­ Contact, showing dip; dashed lite was found intergrown with perthite in one pit. Perthite-muscovite-quartz pegmatite where approximately located Contact between pegmatite units These crystals are from 0.01 to 0.12 inch thick and as Q== much as 2 inches across, but no columbite-tantalite is

Albite-quartz-perthite pegmatite Pit and dump exposed in the rest of the pegmatite. Gahnite is inter- Geology by M. H. Staatz, and P. T. Flawn, Aug. 1948 grown with fine muscovite in one small area. This mineral crystallizes as dark-green octahedra 0.01 inch FIGURE 35.—Geologic maps of pegmatites 560 and Beryl and Rare Minerals lode (no. 590). in diameter. Within the intermediate zone is a core made up entirely of quartz that extends the length of This lenticular pegmatite is 154 feet long and 55 feet the pegmatite. wide and dips gently to the south at an angle of from 5 to 10 degrees (fig. 35). WHITE SPAR NO. 2 (PEGMATITE 604) The property is about a quarter of a mile south of a The White Spar No. 2 pegmatite is in sec. 35, T. 50 small private road in the bottom of Tollgate Gulch and N., R. 3 E. It is on the north side of Tollgate Gulch, is reached by a narrow path winding up the hillside. 0.9 mile from State Highway 162, and is reached by a The claim on this pegmatite was located by Jesse mine road that follows the gulch. The pegmatite is DESCRIPTIONS OF INDIVIDUAL DEPOSITS 57 now being mined for lepidolite by the Consolidated The mine workings consist of five prospect pits, the Feldspar Co. It was located in August 1942 and is largest of which is 50 feet long and has a maximum owned by the Colorado Feldspar Co. width of 25 feet, The pegmatite was examined and mapped with plane The pegmatite crops out on the summit and on the table and telescopic alidade by E. W. Heinrich and south-facing slope of a narrow ridge paralleling and Koswell Miller III, on July 28, 1943 (Hanley, Hein­ separating Tollgate Gulch from a gulch to the north. rich, and Page, 1950, p. 77-80). The pegmatite is intruded into hornblende gneiss, but Two prospect pits have been made in the pegmatite, none of the contacts are exposed. one, about 40 feet long and 10 feet wide, at the north The pegmatite trends N. 20° E. and dips from 30° to end of the dike and one, approximately 60 feet long and 35° SE. It has a length of 200 feet and a maximum 25 feet wide, at the south end. width of 85 feet. The pegmatite is about 260 feet long and ranges in Four zones are well developed within the pegmatite. width from 6 feet near the center to nearly 50 feet at A wall zone of fine-grained albite-perthite-quartz- the north end. The trend is north, but the southern muscovite pegmatite completely surrounds an inter­ contact of the pegmatite strikes N. 15° W. and dips mediate zone of fine-grained cleavelandite-quartz- 70° NE. The pegmatite cuts hornblende gneiss, in perthite-lepidolite pegmatite and cores of lepidolite- which the foliation strikes N. 25° W. and dips from 70° quartz pegmatite and quartz pegmatite. The wall to 80° NE. The pegmatite consists of a core of fine­ zone is 9 feet thick on the hanging-wall side and 33 feet grained albite-quartz-perthite-lepidolite pegmatite sur­ on the footwall side (Hanley, Heinrich, and Page, rounded by a discontinuous wall zone of albite-perthite- 1950, p. 77) and has an average grain size of 2 inches. quartz-muscovite pegmatite. The wall zone is discon­ The composition is estimated to be 45 percent albite, tinuous along the pegmatite and has a maximum width 32 percent perthite, 20 percent quartz, and 3 percent of 5 feet. Its grain size averages 0.25 inch, and the muscovite. Perthite is in crystals as much as 24 inches composition is estimated to be 45 percent albite, 30 long and 15 inches wide, and muscovite in books that percent perthite, 20 percent quartz, 5 percent musco- average 1.5 inches across and 1 inch thick. vite, and less than 1 percent lepidolite. The lepidolite The cleavelandite-quartz-perthite-lepidolite interme­ has an average grain size of 0.12 inch but occurs in diate zone, on the western and southern edges of the books as much as 1 inch across. The core ranges from quartz core, is 90 feet long and ranges in width from 1 6 to 32 feet in width. It has a finer texture than the to 18 feet. The grain size is 1 inch, and the zone is wall zone, with grains averaging 0.02 inch in size. It estimated to contain 55 percent cleavelandite, 25 per­ contains 45 percent plagioclase, 35 percent quartz, cent quartz, 15 percent perthite, 5 percent lepidolite, 10 percent perthite, 10 percent lepidolite, less than 0.01 percent beryl, 0.003 percent topaz, and 0.0003 1 percent garnet, and traces of beryl, microlite, fluorite, percent columbite-tantalite, and a trace of microlite. and . The lepidolite has an average grain Perthite crystals average 12 inches in length and 8 size of 0.03 inch and occurs in lenses and stringers up inches in width. The lepidolite occurs in books 3 inches to 4 inches wide. The lepidolite exposed in the north­ across and 0.5 inch thick. The beryl is yellow to pale ern pit is banded with coarser grained albite and quartz. blue green and occurs in crystals from 0.5 to 1.75 inches A grab sample of the core taken by Heinrich (Hanley, in diameter. Topaz crystals are small, ranging in size Heinrich, and Page, 1950, p. 80) from the southern pit from 0.06 to 1 inch. The columbite-tantalite crystals and analyzed spectrographically by the Geological are as much as 0.4 inch long and 0.25 inch wide. Survey contained 0.7 percent Li2O, or about 17 percent The pegmatite cores are of two types: white, mas­ lepidolite, 0.05 percent BeO, and no Cb or Ta. sive, quartz pegmatite and lepidolite-quartz-microlite WHITE SPAR NO. 1 (PEGMATITE 636) pegmatite. The quartz pegmatite occurs as 1 large irregular mass, 80 feet long and 3 to 13 feet wide, and The White Spar No. 1 pegmatite is in sec. 35, T. as 7 smaller lenses. 50 N., R. 3 E. It is on the north side of Tollgate Gulch and is connected to State Highway 162 by a mine road The core of the lepidolite-quartz pegmatite is on 0.7 mile long. A claim was located on this pegmatite the west side of the quartz pegmatite, between the in 1942 by the Colorado Feldspar Co. E. W. Hein­ core and the intermediate zone of cleavelandite- rich and Roswell Miller III of the Survey examined quartz-perthite-lepidolite pegmatite. This core is 20 and mapped this property with plane table and tele­ feet long and from 1 to 8 feet wide, has a grain size of scopic alidade on July 29, 1942 (Hanley, Heinrich, and 0.03 inch, and contains approximately 90 percent lepid­ Page, 1950, p. 77-80). olite, 10 percent quartz, and 0.1 percent microlite. 58 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO BUCKHORN (PEGMATITE 659) the smallest 4 feet long, 3 feet wide, and 2 feet deep. The Buckhorn (pegmatite 659, pi. 1) caps the top of The Feldspar claim has a trench 15 feet long, 3 feet a ridge on the north side of Tollgate Gulch in the SE% wide, and 2 feet deep. Several hundred feet to the east sec. 27, T. 50 N., R. 3 E. It is irregular (fig. 36), of the Feldspar claim is an unnamed claim which has having a maximum length of 1,750 feet and a maximum a small shaft, 4 feet square and 8 feet deep, and several width of 1,360 feet. It is exposed at altitudes between hundred feet farther east a trench 15 feet long and 3 8,900 and 9,400 feet above sea level and 350 to 850 feet feet wide. No mining has been done on these claims. above Tollgate Gulch. The nearest road is State High­ The Buckhorn pegmatite (fig. 36) intrudes hornblende way 162, 0.4 mile to the west. gneiss and tonalite. The greater part of this pegmatite At least 3 claims have been located on this pegmatite. has only one zone, but it contains several small dis­ Claim notices show 2 of these to be: the Buckhorn, on connected core segments in its upper part along the the northwestern part of the pegmatite, and the Feld­ ridge. Around one of these cores is a small inter­ spar claim, in the northeastern part of the pegmatite, mediate zone. The small cuts in the Buckhorn claim both located by Bert and Florence Tucker. On the are made on this intermediate zone. The wall zone, Buckhorn claim there are several small trenches, the which forms more than 90 percent of the pegmatite, largest 30 feet long, 5 feet wide, and 8 feet deep, and has an average grain size of 0.25 to 0.5 inch. It is esti-

EXPLANATION

Strike and dip of pegmatite contact

Geology by M. H. Staatz and P. T. Flawn, Aug. 1948

FIGUKE 36.—Geologic map, Buckhorn (no. 659) pegmatite. DESCRIPTIONS OF INDIVIDUAL DEPOSITS 59 mated to contain albite (59 percent), quartz (20 per­ 28, 29, 32, and 33, T. 50 N., K. 3 E. It is 12,600 feet cent), white to pink perthite (20 percent), fine-grained long and has a maximum width of 6,700 feet. The gray-green muscovite (1 percent), garnet (trace), and northeast end is less than 200 feet from Willow Creek, biotite (trace). Though most of these minerals are and the southwest end is at Big Gulch. A road from fine grained, the perthite occurs in crystals 1 to 3 inches Big Gulch to the State Highway 162 traverses the in diameter. pegmatite for 1.5 miles. Much of the eastern edge is The intermediate zone is 1.5 to 2 feet thick. It has within a quarter of a mile of the highway. The an average grain diameter of approximately 1 foot and western part of the pegmatite forms the southern ex­ consists of perthite (50 percent), muscovite (40 per­ tension of a prominent north-trending ridge. This cent), and quartz (10 percent). A few greenish crystals ridge rises to the north, and the highest point on the of beryl, approximately 1 inch in diameter, were noted. pegmatite is over 9,700 feet. The southern and eastern Three or four crystals of columbite-tantalite and mona- edges of the pegmatite are at an altitude of slightly zite, about 0.5 inch long, were found adjacent to the above 8,500 feet. core in a feldspar-rich part of this zone. The muscovite The Black Wonder is extremely irregular, as it con­ in the intermediate zone occurs in books as large as sists of a large number of intersecting dikes of uneven 10 by 18 inches. It is greenish gray and has a strongly spacing and size. developed "A" structure. It closely resembles the Most of the pegmatite intrudes hornblende gneiss, but scrap mica from the Bucky mine, which is prized as a part of it cuts coarse-grained granite at the southeast grinding mica. The intermediate zone is about 150 feet and pre-Cambrian sedimentary rocks in a small area long and diminishes in mica content to the south. The at the northeast. amount of scrap mica available, therefore, is small. The pegmatite has aroused little mining interest. The core segment within the intermediate zone is Two claims, the Black Wonder and the Beryl, have south of the other core segments and differs consider­ been filed on different parts of the pegmatite. The ably from them in composition and texture. This core Black Wonder prospect, in the eastern part of sec. 29, has an average grain diameter of 2 feet and consists of was located in May 1948 on a magnetite-rich area in the perthite (91 percent), quartz (7 percent), muscovite (1 pegmatite and consists of one small pit. The Beryl percent), and beryl (0.7 percent). The beryl is pale claim, located in June 1948 by Bert Tucker, is in sec. 27 green and ranges in size from 0.2 by 0.7 inch to 3.2 by and the workings consist of three pits on a beryl- 5.5 inches. bearing unit and a fourth on a monazite-bearing The other cores are exposed along the top of an east- unit. west trending ridge and are only 10 to 20 feet thick. The pegmatite consists of a thick wall zone enclosing They may be the eroded remnants of a once much small widely scattered cores and cut by occasional larger and continuous core. The average grain size of fracture fillings. Only a few of the cores have an the minerals in these core segments is 8 to 12 inches; intermediate zone between them and the wall zone. and though they vary in the percentage of minerals, The wall zone, constituting over 95 percent of the they are estimated to contain perthite (53 percent), pegmatite, varies in texture and composition. In quartz (45 percent), albite (1 percent), and muscovite the southern and western parts of the pegmatite, it is a (1 percent). graphic granite unit, grading to the north and northeast The small shaft to the east of the Feldspar claim was into a unit with only a few crystals of graphic granite in sunk in a quartz-rich part of this pegmatite. It yielded a matrix of albite and quartz. The wall zone at the approximately 75 pounds of beryl. These beryl crys­ south and west end has an average grain size of 3 tals are 1 to 2 inches across, white, and closely re­ inches and is estimated to contain 60 percent perthite, semble quartz. This appears to be a beryl-rich pocket, 24 percent albite, 15 percent quartz, 1 percent martite, and others might be found on further exploration. The less than 1 percent biotite, and a trace of garnet. amount of beryl is not likely to be large, as the core Graphic granite crystals, as much as 5 feet across, segments are extremely thin. A limited amount of constitute 50 percent of this part of the wall zone. feldspar could be obtained from these core segments, Small local concentrations of martite are common, such but the low price of feldspar and high transportation as the one upon which the Black Wonder claim was costs make the economic feasibility of working it made. Martite comprises 10 percent of the wall zone questionable. at the prospect pit and to the northeast for 50 feet, in crystals as much as 4 inches across. The wall zone to BLACK WONDER (PEGMATITE 847) the north and east has an average grain size of 1.5 The Black Wonder pegmatite is the largest pegmatite inches and is estimated to contain 55 percent albite, 30 in the district, covering parts of sees. 20, 21, 22, 27, percent perthite, 15 percent quartz, less than 1 percent 60 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

garnet, and a trace of martite. Graphic granite con­ TRIO NO. 1 (PEGMATITE 1402) stitutes less than 10 percent of this part of the wall The Trio No. 1 pegmatite is on the ridge west of zone in crystals less than 6 inches across. Willow Creek at an altitude of 10,000 feet, in sees. 16 At the Beryl claim, two different types of inter­ and 21, T. 50 N., R. 3 E. The nearest road is along mediate zone surround quartz cores. One intermediate Willow Creek, 1 mile northeast of the claim. This zone contains monazite and columbite-tantalite; and road joins State Highway 162, 2.5 miles to the south­ the other, beryl crystals. The beryl-containing inter­ east. The claim was located on May 2, 1949 by Bert mediate zone occupies the space between two small Tucker, George Tucker, and A. T. Pearson. Discovery quartz pegmatite cores, 7 feet apart; the larger core is 25 workings consist of four small prospect pits, the largest feet long and 10 feet wide. Two prospect pits— of which is 13 feet long, 10 feet wide, and 4 feet deep. the larger 9 feet long by 6 feet wide—are on the east The pegmatite is 644 feet long and has a maximum side of the larger quartz pegmatite core. Another pit, width of 152 feet. It is irregular in shape and is in­ 15 feet long and 4 feet wide, is on the east side of the truded into quartz monzonite. The pegmatite is made smaller quartz pegmatite core. The intermediate up of 4 zones: a thick wall zone constituting over 90 zone is not exposed completely around the larger core percent of the pegmatite, 2 small intermediate zones, but lies east of it, surrounding the smaller one. This and several small discontinuous cores. The wall zone zone has a maximum size of 30 feet long and 15 feet has an average grain size of 0.75 inch and is made up wide. The grain size averages 2 inches, and the zone is of albite (45 percent), perthite (40 percent), quartz (15 estimated to contain 79 percent albite, 10 percent percent), biotite (less than 1 percent), and martite (less quartz, 5 percent perthite, 5 percent muscovite, 1 than 1 percent). The intermediate zones are of two percent garnet, and 0.2 percent beryl. The mus­ types: a quartz-albite-perthite pegmatite and a quartz- covite occurs in books from 0.25 to 5 inches across. albite-muscovite pegmatite, both found around one Garnet crystals range in size from 0.25 to 2 inches. core. The quartz-albite-perthite pegmatite interme­ Beryl, in semitransparent yellowish-green crystals diate zone, 20 feet long by 15 feet wide, is east of the from 0.5 to 1.25 inches in diameter, is concentrated along quartz-albite-muscovite pegmatite intermediate zone the eastern edge of the larger quartz pegmatite core. and separates it from the wall zone. This quartz- The monazite-bearing intermediate zone is ap­ albite-perthite pegmatite has an average grain size of proximately 400 feet northeast from the beryl-bearing 6 inches and is estimated to contain quartz (35 percent), zone and is exposed by a prospect pit 4 feet long and 3 albite (34 percent), perthite (30 percent), garnet (0.5 feet wide, on the east side of a quartz pegmatite core. percent), and biotite (0.5 percent). Six beryl crystals The core is 15 feet long, 6 feet wide and is 2 feet thick at from this zone were found on the stockpile, ranging its edge in the pit. This intermediate zone is estimated from 1 to 8 inches in diameter and from 1 to 6 inches to be 15 feet long and 4 feet wide. Its grain size is 6 in length. The quartz-albite-muscovite pegmatite is inches, and the composition is estimated to be 55 per­ 3.5 feet thick and surrounds the core of quartz pegma­ cent albite, 30 percent muscovite, 15 percent quartz, tite. This zone has an average grain size of 1 inch and and traces of monazite and columbite-tantalite. Books is made up of quartz (60 percent), albite (25 percent), of muscovite are as much as 8 inches across, and muscovite (15 percent), and garnet (less than 1 per­ crystals of monazite average 0.75 inch long by 0.12 cent). Muscovite crystals average 1 inch across and inch wide. The columbite-tantalite crystals average 1.5 inches thick. 0.12 by 0.06 inch. Cores of quartz pegmatite occur in several places and The cores are nearly all small, can be measured in are as much as 15 feet long by 12 feet wide. The core tens of feet in length, and are less than 10 feet wide. on which the workings are located is 20 feet long by They range in composition from 100 percent quartz to 5 feet wide and consists entirely of quartz. 10 percent quartz and 90 percent perthite. In the northeast part of the pegmatite, books of muscovite BUCKY (PEGMATITE 1574) form as much as 30 percent of the cores in crystals as GENERAL FEATURES much as 5 inches across. In some of the cores the The Bucky pegmatite is an irregular pegmatite on quartz is smoky, suggesting the presence of radioactive the ridge between Willow and Illinois Creeks. Numer­ minerals. Several small crystals of allanite were found ous claims are located on this pegmatite in the E}£ sec. in one core. 22, T. 50 N., R. 3 E. The Bucky claim, on which In various places the wall zone is cut by fracture the main workings are found, is on the northern end of fillings of white quartz. These fracture fillings range the pegmatite and covers a quartz pod 100 feet long and from a fraction of an inch to 6 inches in width. 60 feet wide. This claim was originally owned by Mr. DESCRIPTIONS OF INDIVIDUAL DEPOSITS 61

Rod Fields, who has driven several small adits along the (60 percent), perthite (20 percent), quartz (16 percent), southern side of the pod and from it has produced muscovite (4 percent), and a trace of garnet. approximately 17 tons of beryl, 100 pounds of colum- Inside the wall zone is a thick intermediate zone. bite-tantalite, 25 pounds of an unidentified mineral This is made up chiefly of graphic granite aggregates resembling samarskite, and 15 pounds of monazite. that range in diameter from 2 inches to 1 foot and The scrap mica was at first discarded, but approx­ average about 5 inches. Besides graphic granite, this imately 20 tons were stockpiled in September 1948. pegmatite unit contains 3 to 4 percent of cream-colored In the fall of 1948, Mr. Fields sold the property to the perthite, 1 percent of white quartz crystals, 3 percent Beryllium Mining Co., Inc., which has produced from of fine-grained cream-colored albite, and less than 1 open pits excavated by blasting and bulldozing. A percent of biotite. The biotite occurs in thin, 6-inch road was constructed to the mine workings, approx­ blades, localized in small areas in this rock. The albite imately 400 feet above the valley bottom, by the is difficult to distinguish from the perthite but is most Beryllium Mining Co., Inc. In May 1950 a small mill abundant along the contacts of the quartz-albite perth­ for separating the scrap mica was built beside the mine ite pegmatite; it has a low index of refraction (No) of road. Prior to May 15, 1950, the Beryllium Mining 1.530 ±0.002. The estimated bulk composition of this Co., Inc., had produced 32 tons of beryl, 139.6 tons of rock is perthite (77 percent), quartz (20 percent), albite scrap mica, 1,020 pounds of columbite-tantalite, 15 (3 percent), and biotite (1 percent). pounds of monazite, and 13 pounds of a mineral re­ The most common type of pegmatite adjacent to sembling samarskite. and surrounding the quartz pods is a quartz-albite The beryl was sold to several buyers in Colorado, and pegmatite. Some of these pods have no other inter­ part was trucked to Longmont, and part was sold on mediate zones separatirig them from the graphic gran­ the property. In 1950 the scrap mica was being ite pegmatite, while others, as previously stated, have shipped to Western Nonmetallics in Pueblo, Colo. as many as three. The quartz-albite intermediate zone No columbite-tantalite had been sold, and the small has an average grain size of 0.5 inch and usually con­ production of monazite and the mineral resembling tains equidimensional quartz grains surrounded by samarskite had been purchased by Ward's Natural albite. The estimated composition of this rock is Science Establishment for resale as mineral specimens. quartz (55 percent), albite (40 percent), perthite (3 The Bucky mine workings were mapped in September percent), muscovite (1 percent), and garnet (1 percent). 1948, with plane table and telescopic alidade. This The albite is cream colored and commonly is inter­ map (pi. 8) covered an area extending from the northern stitial to the quartz crystals. It has a lower index of re­ contact of the pegmatite with the schist to a point 180 fraction (Na) of 1.532 ±0.002. The perthite is most feet south of the main quartz pod. A beryl count was common near the perthite-quartz pegmatite zone where made in the mine workings. In November 1949, this it occurs as graphic granite; it also occurs near the map was revised to show the new workings. The muscovite-feldspar-quartz-beryl zone as cream-colored outline of the whole pegmatite was mapped (pi. 1) in crystals about 4 inches across. The muscovite is in September 1949. light-colored irregular books 0.25 to 0.75 inch long. GEOLOGY It occurs in local aggregates, comprising as much as 10 percent of the rock. Adjacent to the core of the Bucky The Bucky pegmatite has been intruded chiefly into mine, the feldspar is considerably kaolinized. hornblende gneiss, but it also cuts several small Muscovite-feldspar-quartz-beryl pegmatite predom­ bands of quartzite. The pegmatite is extremely ir­ inates around the large Bucky core segment (pi. 8) but regular and contains many small inclusions or pendants is also well developed around at least two other core of country rock. The main bulk of the pegmatite is segments and may be present to a minor extent around made up of a fine-grained discontinuous wall zone and several more. The zone weathers easily and is usually an intermediate zone of coarse-grained graphic granite. concealed by quartz float. It is well exposed along the Within this are scattered 36 cores of quartz pegmatite, southern and eastern side of the Bucky claim, where in several segments, each at least 10 feet long. Some mine faces are more than 20 feet high. This zone ex­ of the core segments are surrounded by as many as tends around three-fourths of the Bucky core segment three intermediate zones. The "core segments" have but pinches out in the northwest quarter and is from a peripheral arrangement (insert map, pi. 8), and some 1 to 10 feet thick. The muscovite-feldspar-quartz- may be fracture fillings rather than true core segments. beryl pegmatite zone has a grain size which ranges The discontinuous wall zone may be absent in some in diameter from 3 inches to over 8 feet and averages parts and several hundred feet thick in others. It has about 2 feet. It has an estimated composition of mus­ an average grain size of 0.25 inch and consists of albite covite (40 percent), feldspar (31 percent), quartz (20 297133—55———5 62 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO percent), beryl (8.9 percent), columbite-tantalite (0.11 crystals as much as 6 inches across. Monazite occurs percent), an unidentified mineral resembling samarskite in reddish-brown euhedral crystals 0.25 to 1 inch long, (0.003 percent), monazite (0.003 percent), topaz (less and the adjacent feldspar is frequently stained red. than 1 percent), gahnite (less than 1 percent), phos­ The unidentified mineral resembling samarskite has phates (trace), and lepidolite (trace). Muscovite been found in masses as much as 5 inches across. It is makes up from 10 to 80 percent of the rock and is found dark greenish black, has conchoidal fracture, a greasy in books as much as 1 foot across; the average is 6 luster, and no apparent crystal form. This mineral is inches. The books are heavily lined, have irregular metamict and its X-ray pattern does not agree with surfaces, contain minute crooked fractures, and have that of samarskite, fergusonite, euxenite, allanite, or a prominent "A" structure. Both red and black min­ . A more complete discussion of this mineral eral staining is common. This is scrap mica and is is given in the section on mineralogy. quite soft, a property that makes it an excellent grind­ Topaz has been reported from the Bucky core seg­ ing mica. The feldspar occurs chiefly as cream-colored ment, but it occurs in greater abundance around a massive perthite and as cream-colored fine-grained small pod on the southwestern part of the pegmatite. albite. The albite is commonest in heavy muscovite Topaz in crystals 1 to 4 inches across may constitute as concentrations and has a minimum index of refraction much as 1 percent of this zone. Lepidolite in very (Na) of 1.531 ±0.002. Because of the heavy kaoliniza- fine-grained aggregates has been found adjacent to the tion of both feldspars, the relative proportions of perth­ topaz but is quite rare. ite to albite could not be readily determined. Quartz Lithiophillite-triphylite occurs in a few crystals occurs as large white crystals several feet in diameter. adjacent to the Bucky core segment and in another Beryl is found in large white to pale-green euhedral small pod in the extreme northeastern end of the crystals. A total of 64 beryl crystals was noted in pegmatite. 344.5 square feet of muscovite-feldspar-quartz-beryl In addition to the muscovite-feldspar-beryl peg­ pegmatite measured along the mine walls. The basal matite, a coarse-grained perthite pegmatite envelopes area of the crystals ranged in size from 0.007 to 5.0 the Bucky core segment. This rock has an average square feet and averaged 0.70 square feet. Beryl is grain diameter of 6 feet and is estimated to consist of more common and occurs in larger crystals in the 93 percent of cream-colored perthite, 7 percent of perthite-quartz-rich part than in the muscovite-rich quartz, and less than 1 percent of albite and mus­ part. A beryl count, made in Mr. Fields' early work­ covite. The perthite is slightly kaolinized. About 30 ings, which follow a beryl-rich concentration, gave an tons of cream-colored perthite has been stockpiled at average of 13 percent beryl. Most of the zone worked the mine, but no sale had been made as of June 1950. since that time contained much less beryl. A second Quartz-core segments are found scattered throughout pocket, opened in April 1950, yielded approximately 9 the pegmatite and range in dimensions from a few feet tons of beryl, before June of the same year. The beryl long and less than 1 foot wide to 100 feet long and 80 in this, as in all zones, is again concentrated in pockets feet wide (the core on which the Bucky claim is located). separated by almost barren rock. The beryl has a The quartz pegmatite is made up entirely of pure white maximum index of refraction (Nui) of 1.578 ±0.002, massive quartz. As this rock is resistant to erosion, it which corresponds to approximately 13.2 percent BeO. forms prominent knobs, and joint blocks commonly A small part of the beryl has been kaolinized. The cover the adjoining pegmatite. columbite-tantalite, monazite, and an unidentified A unit believed to be a fracture filling is found in mineral resembling samarskite usually occur together two places along the outer edge of the pegmatite. This in erratically distributed pockets. They were found in has an average grain diameter of 3 feet and is es­ some of the early workings adjacent to the core seg­ timated to consist of 50 percent quartz and 50 percent ment. Columbite-tantalite occurs in black tabular perthite. LITERATURE CITED Adams, J. W., 1953, Beryllium deposits of the Mount Antero Glass, J. J., 1935, The pegmatite minerals from near Amelia, region, Chaffee County, Colorado: U. S. Geol. Survey Va.: Am. Mineralogist, v. 20, p. 741-768. Bull. 982-D. Goranson, R. W., 1931, The of water in granitic Andersen, Olaf, 1928, The genesis of some types of feldspar from magmas: Am. Jour. Sci., 5th ser., v. 22, p. 481-502. granite pegmatites: Norsk geol. tidsskr., v. 10, p. 116-207. Hanley, J. B., Heinrich, E. W., and Page, L. R., 1950, Pegmatite Bannerman, H. M., 1943, Structural and economic features of investigations in Colorado, Wyoming, and Utah, 1942-1944: some New Hampshire pegmatites: N. H. State Plan. U. S. Geol. Survey Prof. Paper 227, 124 p. Devel. Comm., Min. Res. Survey, Concord, p. 1-22. Heinrich, E. W., 1948, Pegmatites of Eight Mile Park, Fremont Brogger, W. C., 1880, Die Mineralien der Syenit pegmatit gauge County, Colorado: Am. Mineralogist, v. 33, p. 420-448, Sudnorwegischen Augit-und Nephelin : Zeitschr. 550-587. Krystallographie u. Mineralogie, Band 16, p. 215-235. Hess, F. L., 1925, The natural history of pegmatites: Eng. and Cameron, E. N., Jahns, R. H., McNair, A. H., and Page, L. R., Min. Jour.-Press, v. 120, p. 289-298. 1949, Internal structure of granitic pegmatites: Econ. ———— 1933, Pegmatites: Econ. Geology, v. 28, p. 447-462. Geology Mon. 2, 115 p. Kitchens, C. S., 1935, The pegmatites of Fitchburg, Mass.: Cameron, E. N., Larabee, D. M., McNair, A. H., Page, J. J., and Am. Mineralogist, v. 20, p. 1-24. Shainin, V. E., 1945, Structure and economic characteristics Hobbs, S. W., 1944, deposits in the Boreana district of New England mica deposits: Econ. Geology, v. 40, p. and the Aquarius Range, Mohave County, Ariz.: U. S. 369-393. Geol. Survey Bull. 940-1, p. 247-264. Cameron, E. N., Larabee, D. M., McNair, A. H., and Stewart, Holser, W. T., 1953, Beryllium minerals in the Victorio Moun­ G. W., 1944, Characteristics of some New England mica- tains, Luna County, N. Mex., Am. Mineralogist, v. 38, p. bearing pegmatites [abs.]: Econ. Geology, v. 39, p. 89. 599-611. Cameron, E. N., Larabee, D. M., Page, J. J., Stewart, G. W., and Hunt, T. S., 1871, Notes on granitic rocks: Am. Jour. Sci., 3d Shainin, V. E., 1953, Pegmatite investigations in Maine, ser., v. 1, p. 82-89, 182-191. New Hampshire, and Connecticut, 1942-1945: U. S. Geol. Jahns, R. H., 1946, Mica deposits of the Petaca district, Rio Survey Prof. Paper 255. [1954] Arriba County, N. Mex.: N. Mex. Bur. Mines Bull. 25, 294p. Crawford, R. D., and Worcester, P. G., 1916, Geology and ore Johnston, W. D., Jr., 1945, Beryl-tantalite pegmatites of north­ deposits of the Gold Brick district, Colorado: Colo. Geol. eastern Brazil: Geol. Soc. America Bull., v. 56, p. 1015-1070. Survey Bull. 10, 116 p. Kemp, J. F., 1924, The pegmatites: Econ. Geology, v. 19, p. D'Achiardi, A., 1872, Mineralogia della Toscana, Pisa. 697-723. D'Achiardi, G., 1896, Le tourmaline del graniteo elbano: Atti Landes, K. K., 1923, Sequence of mineralization in Keystone, della soc. Toscana di Sci. Nat. Mem. 15. S. Dak. pegmatites: Am. Mineralogist, v. 13, p. 519-530, De Almeida, S. C., Johnston, W. D., Leonardos, O. H., and 537-558. Scorza, E. P., 1944, The beryl-tantalite-cassiterite pegma­ ————— 1925, Paragenesis of the granitic pegmatites of central tites of Paraiba and Rio Grande do Norte, Northeastern Maine: Am. Mineralogist, v. 10, p. 355-411. Brazil: Econ. Geology, v. 39, p. 206-223. ———— 1932, Criteria of age relations of minerals: Econ. Geology, Derry, D. R., 1931, The genetic relationships of pegmatites, v. 27, p. 211. , and tin veins: Geol. Mag., v. 68, p. 454—475. Eckel, E. B., 1933, A new lepidolite deposit in Colorado: Am. ———— 1933, Origin and classification of pegmatites: Am. Ceramic Soc. Jour., v. 16, p. 239-245. Mineralogist, v. 18, p. 33-56, 95-103. Eckel, E. B., and Levering, T. S., 1935, Work of Eckel, Levering, ———— 1935, Colorado pegmatites: Am. Mineralogist, v. 20, p. and Fairchild—Microlite from Ohio City, Colo.: Report of 319-333. the Committee on the Measurement of Geologic Time, McLaughlin, T. G., 1940, Pegmatite dikes of the Bridger Moun­ Nat'1. Research Council, p. 77-79. tains, Wyo.: Am. Mineralogist, v. 25, p. 46-68. Fleischer, Michael, 1937, The relation between chemical com­ Olson, J. C., 1942, Mica-bearing pegmatites of New Hampshire: position and physical properties in the garnet group: Am. U. S. Geol. Survey Bull. 931-P, p. 363-403. Mineralogist, v. 22, p. 751-759. Page, L. R., 1950, Uranium in pegmatites: Econ. Geology, v. 45, Ford, W. E., 1915, A study of relationships existing between p. 12-34. the chemical, optical and other physical properties of the Page, L. R., and others, 1953, Pegmatite investigations 1942- members of the garnet group: Am. Jour. Sci., 4th ser., p. 33-49. 1945, Black Hills, S. Dak.: U. S. Geol. Survey Prof. Paper Faye, W. G., 1922, Mineral localities in the vicinity of Middle- 247, 228 p. town, Conn.: Am. Mineralogist, v. 7, p. 4-12. Palache, Charles, and Gonyer, F. A., 1940, Microlite and stibio- Fraser, H. J., 1930, Paragenesis of the Newry pegmatite, tantalite from Topsham, Maine: Am. Mineralogist, v. 25, Maine: Am. Mineralogist, v. 15, p. 349-364. p. 411-417. Gevers, T. W., 1937, Phases of mineralization in Namaqualand Pardee, J. T., 1937, Glass, J. J., and Stevens, R. E., 1937, pegmatites [1936]: Geol. Soc. South Africa Trans. and Proc., Massive low-fluorine topaz from the Brewer mine, South p. 331-377. Carolina: Am. Mineralogist, v. 22, p. 1058-1064. 63 64 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

Quirke, T. T., and Kremers, H. E., 1943, Pegmatite crystalliza­ Smith, W. C., and Page, L. R., 1941, Tin-bearing pegmatites of tion: Am. Mineralogist, v. 28, p. 571-580. the Tinton district, Lawrence County, S. Dak.: U. S. Geol. Ramberg, Hans, 1949, The facies classification of rocks: A clue Survey Bull. 922-T, p. 595-630. to the origin of quartzo-feldspathic massifs and veins: Jour. Stark, J. T., and Behre, C. H., Jr., 1936, Tomichi dome flow: Geology, v. 57, p. 18-54. Geol. Soc. America Bull., v. 47, p. 101-110. Schaller, W. T., 1925, The genesis of lithium pegmatities: Am. Stevens, R. E., 1938, New analyses of lepidolite and their inter­ Jour. Sci., 5th ser., v. 10, p. 269-279. pretation: Am. Mineralogist, v. 23, p. 607-628. ———— 1927, Mineral replacement in pegmatites: Am. Mineral­ Volk, G. W., 1939, Optical and chemical studies of muscovite: ogist, v. 12, p. 59-63. Am. Mineralogist, v. 24, p. 255-266. ———— 1933, Pegmatites: Ore deposits of the Western States, Warren, T. W., 1935, Spectrographic analysis of tourmalines Am. Inst. Min. Met. Eng., p. 144-151, New York. with correlation of color and composition: Am. Mineralo­ Shaub, B. M., 1937, Contemporaneous crystallization of beryl gist, v. 20, p. 531-536. and albite vs. replacement: Am. Mineralogist, v. 22, p. Washington, H. S., 1917, Chemical analyses of igneous rocks: 1045-1051. U. S. Geol. Survey Prof. Paper 99, 1201 p. ———— 1940, The origin of some pegmatites in the town of Winchell, A. N., 1947, Elements of optical mineralogy: pt. 2, Newry, Maine: Am. Mineralogist, v. 25, p. 673-688. 459 p., John Wiley and Sons, New York. Sinegub, E. S., 1943, Berill: Nemetallicheskoye iskopayeme Wright, W. I., 1938, The composition and occurrence of garnets: SSSR, Moscow-Leningrad, v. 2, p. 129-157. Am. Mineralogist, v. 23, p. 436-449. CHARACTERISTICS OF THE PEGMATITES (TABLE 20) TABLE 20.—Mineralogy of pegmatites O5 05 [Relation to wall rock: Ne, not exposed; C, cross-cutting; Of, conformable; Shape: L, lenticular; LB, lenticular-branching; Ir, irregular; Ov, oval; Percent: a check mark (K) indicates that mineral is present but was not measured in percent] Wall rock Pegmatite Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

1 -__——__. Tonalite...... Ne L lunit- —— ... ?4 45 35 <1 2...... _--.do —... — .... Ne L -...do— —— — _ 2-3 15 49 35 3——- —— — — -...do————.... Ne Ov —— do.... —— .. J.-4-b 47 25 25 3 <1 Trace... _ _ —— Y*2 4 .....do -- — -..... Ne L -——do———.— ?4-l 53 Me 15 30 12 1 1 n —— .do... —— „„ iBeryl...... „ H-3 5...... - — -.- Tonalite and None-. 0 Lb -...do—...... H 54 20 05 <1 £> coarse-grained granite. d 6_..---.- — -.. Granite. ... __ — — do— L —— do— ... — . 16_li 65 15 20 <1 Tr. 7—— ——— ._ — . Tonalite and Ne Lb —— do...... Js-M 58 20 20 2 <1 granite. Its 8— — — —— - Biotite gneiss and Of Lb —— .do— —— H 60 20 20 <1 Tr. granite. 9__...... Tonalite and -.do- 0 L -—_do___ _ — M-J-2 62 20 <1 <1 granite. 10— —— — —— Unknown.. . _ — __ L ——do— ——— He 69 10 20 Tr. <1 11— —— ———— Tonalite None c Lb ..—do— .. . H 20 20 <1 <1 12...... Tonalite, coarse­ —do- 0 Lb --.-do-__-— . \i-\*> <1 <1. grained granite, fine-grained granite. 13——— ———— Coarse-grained L — ..do————— x& n 65 20 <1 Tr. granite. 14 i. f{K 14--.- ———— .. Tonalite . c L —— do.—— — — 20 <1 <-!.<1 15...... Fine-grained gran­ L --— do—— _--- l 30 35 35 2 ite. 1,4-34 16—- — —— - Tonalite. Ne L --— do— ..— 15 35 <1 <1<-!. 17 Ne Lb -——do—————— fc-94 55 H 25 4-6 20 te <1 18——— ...... Tonalite and 0 Lb -....do— .— .... 3-4 15 Vs 59 8-10 25 8-10 1 3-4 <1 coarse-grained granite. 19..------.-... Ne L ——do——- . 4 25 25 Tr. 20-. ______-~- do—— None,. 0 Ir —— _do———— ^8 72 20 <1

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Mineralogy Number and name of Rela­ Tex­ pegmatite Alter- tion Graphic Garnet Other minerals (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite ation wall structure (in.) rock Per­ Per­ Per­ Per­ Per­ Per­ Size Size Size Size Size Size Mineral Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) percent (in.)

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Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

344———.——— Tonalite and gran­ Ne L V* \i 55 25 20 Tr. Tr. ite. 345------.--...... do-.. —— ——— C Lb —— do.... — „. H~H 65 15 20 <^-j Tr. 346——— ———— — -do-..- —— _—— .-do- L —— do...—— — 65 15 20 Tr. f2 crystals— . __ Me 347—— — - —— . Ne Lb —— do— ———— y* 60 20 20 Tr. Tr. Beryl..—— .___ H 348—. — ——— —— .do— ————— Ne Lb —— do— — — . 50 25 25 Tr. 349.-. — .-______. _do— ______Ne L —— do— —— _. 40 25 35 Tr. 350———————— Tonalite and gran­ Ne L —— do— — —— 65 15 20 Tr. Tr. ^j ite. fBiotite-———— Trace..-- ...... 351——————__ Granite ...... L — ..do— — —— 65 15 20 Tr. Tr. .._-do—------352————— ——— Tonalite and gran­ None Lb 55 30 15 Tr. Tr. ite. 353———— ——— —— do— —— —— ...... do— C L .....do— —— — 55 25 20 Tr. Trace.... — _ .. 354—— ———— ——do— ...... —— . ... do— C Lb .--do— -- — .. 70 15 15 Tr. Tr. ——do——— —— - ——do— ------_ 355—— — ——— —— do— — — — —do- C Lb __.-_do— ...... 58 25 2 Tr. fBiotite——— — Trace.. ———— - 356———— ——— . ——do.— —— —— Ne Lb _--do-— —— . 65 15 20 Tr. Tr. -.-do— ----- w (.Beryl-- — — — #-H /Wall zone--...-. 85 15 357_-______Tonalite--.. —— -. Ne Ir \Core—— —— — 100 358—————— . Hornblende gneiss, Ne L limit—————. 60 20 ...... 20 ...... Tr. Tr. — — - Beryl.. ————. 7l (Beryl- ———— . 359———- ——— -...do— —— ...... Ne L -...do— —— — 60 20 20 Tr.

385——— ...... ——do—— ...... Ne L -.._do—— ...... 6-8 7 53 33 40 Tr. ^Columbite-tan- Y2 ( talite. 386———. ——— . Ne L — .do—— —— 72 8 20 Tr. 387... — .--.__. Coarse-grained None _ L .....do-———— 60 OK 1 ^ granite. 388... ————.. —— do—— ...... — do— L — -do— -- — _- 75 10 15 ^ 389— ______. Tonalite--.- — — - ... do— C Lb — -do— —— _„ 73 20 Tr. 390——— ———— . Tonalite and gran­ — do— L —— do—— ——— 70 10 20 ^^ H ite. -..do- Lb /Wall zone...... 75 25 Tr. C \Core_ — __ 4-8 15 85 Tourmaline ..... 392——— ———— Ne Lb 1 unit— ______1-2 40 40 ^j Tr. 393——— —— — ..—do.— ...... Ne Ov — ..do— ... —— . 1 40 35 25 <1 394 ...... do—— —— —— Ne Ir —— do—————— H 63 7 25 5 Tr. 395— — — — - —— do..— ...... - Ne L ——do————— y%-y± 57 15 25 3 396——— — —— —— .do——————. Ne Lb ..... do— ... — - 1-2 49 40 10 1 397 do Ne L ——do...———— i£-j4 70 5 25 Tr. Tr. 398———— ——— — ..do... ——— —— Ne L do 1-2 38 45 20 15 2 QQQ — -do— ...... - Ne Ir —— .do— —— — 1-2 50 30 20 <1 Tr. <1— ... —— ... inn .—— do... _——— —— Ne L —— do—— ——— H 50 30 20 <1 Tr. X-H JBiotite-...... Trace..— 401 ..... do.,— ———— Ne Ir. —— .do... ——— . 70 10 20 -——do——... . Afvy — -do—— ...... —— Ne L —— do_.._ ——— 3A 40 45 15 Tr. Tr. do Ne L ..... do...... % 50 35 15 <1 Tr. 404...... ———— .—— do,.-- —— ... Ne L .——do.————— % 45 30 25 <1 Tr. 405 Tonalite— —— — Ne Lb ..... do——— —— % 55 15 30 406— — — —— —— do... ———— — Ne L l/2 47 30 6 20 3 407 Hornblende gneiss.. Ne L —— do———— — H 50 20 4 30 <1 408 .--do...—-. .... Ne Lb do K 60 10 30 <1 409——— —— —— — -do— —— ..— Ne L _ —— _dO—— ...... H 70 30 <1 H 85 15 do Ne L \Core...... --.-- 4-5 15 4 85 <1 411—— — — — L M 85 15 <1 Ne (.Core—— ——— 6 30 39 4-10 30 1 412——— ———— Ne L 3 53 H 35 10 10 2 Ne L ^ 72 5 15 8 BeryL...... 0.3-.- 413 .—— do——— ...... 6 15 44 40 <1 Beryl..————— <0.05_ — .-__do— ...... - Ne L T unit Vi. 44 20 35 1 415———— ——— —— do——— ...... _ Ne L ——— do.— ___ —— 1 57 8 3 35 <1 416 ——do... Ne L ——— do—— ———— % 55 35 10 <1 Tr. Beryl— ———— 4 crystals. . H Ir H 55 5 35 5 .——do..—— — . % 417——— —— — —— do— ——— —— Ne 3 42 45 4-6 8 5 .._-do— ...... 0.2.-..-. tt-2 418...———— —— —— do— ———— — Ne L y* 61 15 20 4 . — .do——— —— 1A 419———— ——— do Ne Lb —— do—— —— — % 75 15 10 <1 Tr. 420 ---do— Ne L . — _do_._— ..... % 75 10 15 Tr. Beryl..————— 2 crystals...... X —— do— Ne L ..—do—————— w 44 20 35 I No. 4). Hanging-wall 3 22 35 35 8 layer. Tonalite - . , , . Ne Lb ILepidolite—— ... 2—.- — Central unit—. _ ^ 281 2 0.01. — ... No. 1.) M Footwall layer. . H 50 40 8 423— ———— — Ne L X 49 35 15 1 X 2 82 10 Lepidolite _ .. 8——— ... . 1-2 215 85 424 (Bazooka).. Tonalite. Ne L [Microlite- ... 1 Lepidolite.-- .. 2 do 2 20 60 4 A^ ___-._ (.Amblygonite-— 6—— . 425.——— .—— Ne L \/. 60 15 25 BeryL -_. --__- 3 crystals. _ .. H 426 _ — ...... __ do. — . — - _ Ne L -....do...... % 54 H 10 4 35 1 427.. ——— — -. — -do... . —— . Ne L —— do— ——— 1 30 30 428 --.-do————— ... Ne L ---do...... 1 30 40 30 <1 Beryl... —— —— 2 crystals. y-2 429._———_ —— ——.do-.. ——— .. Ne L —— do.— ——— % 70 15 8 15 <1 430. —— —— —— -....do—— ...... Ne Ov ——do.————— % 55

Wall rock Pegmatite

Mineralogy Number and name of Rela­ Tex­ Graphic pegmatite Alter­ tion Internal Plagioclase Perthite Quartz Muscovite Garnet Other minerals (PI. 1) Type to Shape ture granite ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

451—— ——— ... Ne L 1 40 40 4 5-10 20 West branch wall zone, (Tourmaline...— quartz-cleave- 4-6 245 52

Hang ing- wall] layer, perth- (10) it e-albit e-1- 12 30 40 20 10 /Tourmaline. — Trace -.... quartz peg­ IBeryl-. —— — - 2 by 2. matite. J Hang ing- wall] 24 2 25 70 3-4 452 (Brown ——do...... None C Lb quartz pod. J Derby No. H-2 1). Curved lepido- 15.— ------Curved - lepido-1 4-5 244 40 olite lite layer. / 1— ------4-8 H 40—— — — — <32- Lepidolite-mi-] <8 crolite pegma-[ 1 243 15 0.35.. —— —— — tite layer. ) 2———. —— ----- 4-6 Quartz-cleave-] Beryl. — — — — 1 crystal _ __. .. H landite-lepido- 1 4-6 2 25 5-4-3 55 1-10 1 10.—————— 1-7 lit e-topaz[ 10. ———— —— - layer. J CO1-4 Footwall layer,] albite pegma-J- 90 Tr. /Biotite————- Trace...... tite. ) \Tourmaline_ — . /Wall zone...... * f 62 30 7 ^ I.—. __ — __.— 453 (Brown ....-do-——— —— . ...do... C L \Core__ ...... 2 53 40 <^1 Derby No.2). 1.1.---- — —— — 4-8 Microlite— — 1 crystal __ — — 12-24 10 74 12-24 75 15 1 Lepidolite _ ..-. 1 2—— — — — — 1/2-54 1-2 1-3 Beryl...... 2 crystals. . H 454 (Brown — ..do...... -do._ C Lb South end, 37 2 55 4 <' <1 —— .. ...—— Derby) No. wall zone. 3). Microlite.- __.. .. Trace.—- — _ ...... Columbite-tan- South end core... 5-6 247 1 38 4 talite.

3— . ——— ——— Southern and 82 10 8 northern ends. 455 (Brown Hornblende gneiss ... do... c L Southern part 24-36 10 80 10 Tr. Beryl ..-. 3 crystals.. ..---- 3-12 Derby Dike and biotite schist. core. No. 4). Central section.. 24-36 5 95 /Wall zone. .. .— H 65 20 15 ^j ^j 456 (Brown Ne L 2 56 H Derby Dike (.Core... __ . ... 8 45 1 No. 5). CHARACTERISTICS OF THE PEGMATITES (TABLE 20) 77

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Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex Graphic Other minerals (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

503 Coarse-grained Lb limit—— ——— 6 7 65 25 3 « granite. /Main unit...... 2 30 40 (') 25 5 504 Ov \Fracture filling.- 100 .. —— do— ————— Ir /Main unit ...... 2 30 45 4 40 25 .. — do— — —— ... Lb 4 15 55 85 30 Tr. Tr. /Main unit..— 2 20 55 80 25 507 ... do— Ov /Main unit- ...... 1-2 20 60 20 Tr. ... .do—— . .. — do— Ir 100 /Main unit..---. 40 30 V 30 509———————— -— do—— -.- — - —do— Ir ' Tr. /Main unit .. H 70 5 25 510- — ————— .——do.—,.. --. Ne L 100 /Main unit.-.. ... 1.2-1 30 40 V 30 511 do N"on6 L 6 10 90 512...... do ,-,do— Ir lunit—— . — ... 30 39 50 30 1 513 _ . do,. . Ne Ir .. do— . il 33 35 50 Yz 30 2 514———— ——— Hornblende gneiss Ne L ..—do—. ... 4 15 50 85 35 and granite. 515 Ne Ir -——do——. —— . 4 15 50 85 35 516-.. — ———— Hornblende gneiss Ne L —— do—— .... - 2 34 35 V 30 1 and granite. /Main unit, __ . 2-3 45 25 30 517 Hornblende gneiss, Ne Ir 518 . do . Ne Ir limit... 1-2 20 50 40 30 519 --—do.——- —— -. Ne L ..— do— ...... 1A 55 15 30 Biotite, Trace /Wall zone ...... A1 50 20 V 30 Tr. Tr. 520. ——— ——— — .-do....--...... Ne Ir \Core..— ...... 6 10 90 Ne L 65 5 30 W9 — -do— ..-..-. ... Ne L ..... do——— .... H 80 20 COQ do Ne Lb -——do—————— 2 50 30 (15) V 20 /Wall zone . . . 10 65 25 524—— ————— .... do—— Ne L V 1 Core——— — ... V V —— do-— — . — . Ne L h 57 25 18 ^••^ None.. L do Yi 55 20 (15) 25 527.-———.——— ---do-— — ..... - — do— L ..... do————— 1-1 1/2 20 50 30 ^-^ coo Hornblende gneiss . Ne Ov ... do— 1A 65 25 3A 10 529 Ne L — -do— ———— 4 V 85 V 530- — ——— . — . Hornblende gneissl Ne - /Main unit. _ .. 1-2 20 45 35 and granite. j Lb I Fracture filling 100 531—— ——— — Coarse-grained Ne Ir 1 25 40 35 granite. /Main unit- ...... 1A 50 25 (15) 25 Tr. — -do—— —— ...... Ne L \Fracture filling . 25 (19) 533—— ——— —— Dacite...... —— /Wall zone...... 53 20 2 H L J.UU ?& l i 58 15 2 534 Hornblende gneiss. Ir {Core- ————— . 4-12 7 62 30 1 Beryl , 1 crystal __ .. 4 [Fracture filling, . 6 7 62 30 1 [Tourmaline <^ H-H 61 10 25 4 Tr. J Lepidolite Trace . [Beryl,,.

Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

H 75 7 15 3 Tr. Hornblende gneiss Ne Ir 100 tori —— do- — ———— - Ne Ov H 80 15 <1 Tr. 581.- —— — — —— -do-. — - ——— Ne Ir —— _do.-.. — — ^-h 63 8 27 2 Tr. /Wall zone-..-- _ W 70 10 20 Tr. <1 582. ——— — — — —— .do— —— — —— Ne Ov 8 10 90 —— do.... —— --- Ne L >/2 40 H 30 4-6 30 <1 Tr. 584 __ -. __-. _do__. ------Ne Ir - — do..... — - H 37 25 35 3 Tr. —— do——— —— — Ne L —— _do— —— —— \i 30 39 (19) Ofl -—— do...... -- — Ne L --— do-. —— — % 25 45 30 <1 § 587. —— ------..do..-.. — —— . Ne Ir --— do-.. — — 1 49 tt 20 2-6 30 2-6 1 Tr. .— .do... . ------Ne L —— -do—— —— . H 53 20 (17) 2 589—— — - ——— — ..do... . —— — - Ne L -----do. ------U 32 35 1-2 30 3 Several crystals . H-3/i 1A 55 20 25 <1 Beryl. ..--_-__-. 0.2...--. — ... __ Ms-8 Columbite-tan- <0.05. .-_.._-. H-2 590 (Beryl and —— do..—— ——— Ne L Intermediate 30 <1 50 12-60 30 (i.) <1 talite. Rare Miner­ zone. Trace. __ - _

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Core pod— 1 220 35 8-12 40 5 ^Columbite-tan- 1 crystal—- — — —— do— ------— do— L l talite. Beryl-. —— ...... ---do-— ----- 2 M 2 50 5 4-10 30 15 .01------____. Trace. — — — — M 30 5 50 15 J layer. 628—— ————— -..-do ——-.-..... Ne L 70 30 64 Oft 1 3-4 639. ——— —— - —— do—— ———— Ne L /Wall zone.---.— M 59 20 20 0.5 H \Oorepod-- — — 10 20 8-15 67 3 ""y, 640— — — —— do—— —— —— Ne L 50 30 4-7 19 1 641— —— ——— Ne Ir — -do-— ---- Me 65 14 3-6 20 1 1-6 642-.-- . ——do —— — ..-. Ir .--.-do— ------Me 55 Tr. 14 72 7 20 1 Tr. 643...... --do- O Ir 20 55 15 4 1 Beryl i/ M 19 60 20 1 644....--- — — Ne L 1'4 43 40 10-12 15 2 i/ Tr. S/ia 94 1-1 H 20 1 0.5 645--...._...... --—do— ------None Ir Ir ^Core--- —— - — 3 19 40 2-3 40 1 2 1 18 2-3 80 2 3-4 1-2 646 --..-do—— ...---- L /Wall zone------H 49 20 30 1 Ne \Oore pod... — — 8 50 (.0) 40 4-7 647--. — .. .-..do- — ------/Wall zone. ...-.- 75 13 10 2 Tourmaline- - — Trace...... Ne L \Core pod.-- _ . 3 80 10 648-— — — .....do— ...... Ne Ir 8 5-7 M Tr. 54 10 35 1 Tr. Ne L 6-8 y>-% mica schist, and 1 30 47 20 3 quartzite. 650. —— —— Ne Ir 69 10 4-6 20 1 H 651.. — ...... Ne Ir -----do ------14 69 10 2^-3 20 1 V& 20 12-14 40 652——— ...... — ._do- ——— -_--. Ne L M . 70 9 2-3 20 1 16 Tr. 653—. ——— —— ..—do..— .. ——— . Lb w« 60 20 5-9 20 0.5 (21) Tr. .-.-do— ... ----- Ne Ov ...._do—— ---- Me 60 10 3-5}4 29 1 Me Tr. 8-12 (15) --— do— ------/Wall zone...- — . M 45 35 19 1 Ir \Core------2 10 52 35 3 0.5 C3) 656 - —— do-— ———— L Me 60 18 2-4 20 2 i& 4-10 657.. — ...... Ir /Wall zone- -.... Me 31 --__-- 40 25 4 % .....do— -—--. — . 65 15 20 658——— ————— -...do—— ------— do- L Me 50 19 3-4 30 1 H-h 59 20 1-3 20 1 Tr. Biotite— - ___ - i ' 12 50 10 40 4-12 —— do— —— — zone. 1 talite. 659 (Buckhorn — do- C Ir — -do———--.. .4 24 91 7 1 1 0.7- ——— — —— lodes) . claim. 8-12 1 53 45 1 —— do.— ——— 0.5-——————— H-2 ridge. 00 2 Cleavelandite. 3 Up to 3. Up to 6. Up to 2. 17 Up to 5. is Up to 8. 19 Up to 4. 1 Up to 10. a UptoH. 82 QUARTZ CREEK PEGMATITE DISTRICT, COLORADO

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CDt- 00 OS O i—I C 5 !>• !>• t-1- r- 5 CD CO CDCO O 5 CD CD CO CD CD CD O 699— — —— — —— do.. —— — —— Ne Ir — ..do--.-—— X 50 30 30 8 20 Tr. Tr. Me Biotite- —— ----- 700————— ——— -— do.... — .__ 30 50 15 /Magnetite--.. — Trace— — — — Me -—— do.. ------Ne Ir X 55 5 —— do... — — . Me 701—— ————— -—do.. ______Ne Ir - — do-.. — — - 1 20 50 10 30 Tr. Me Biotite————— Trace X 702- — ——— — — -do.- ———— - Ne L —— -do.... — — 2 35 50 40 10 15 Tr. -do....- —— —— Me 703— ———— — ____.do. --.. ______Ne Ov — -do.-...—— - M 50 30 20 Tr. Trace 704————.——— -—do. _-.,______Ne Ir —— do.- ———— H 50 35 30 15 705— — ———— — -do-.- ————— Ne L —— do-.- —— — 65 15 20 Biotite— ------Trace — — - 706- ————— —— __— do-. ______Ne L . — .do-.-- — - 40 30 707—— — ——— ——do.... ______Ne Ov --— do.... —— - Me 70 5 25 708————— — —— do.. ———— — Ne L — -do-... — — 2 10 65 80 25 709——— ———— — -do... ------Ne L --— do...... — - 2 10 65 80 25 710—————— — Ne L ——do. ..______1 30 40 711 —— — ——— —— do... ------Ne L —— .do...- — — 3 10 70 80 20 --— do.....-- — _-- Ne Ov — -do-.. —— . 3 10 60 (V) on 713_-_--______—..do--. . — -.____ Ne Ir —— do- ——— - 3 10 60 —— do———— —— Ne L — -do-..——— 3 10 60 80 30 Wall zone-..- .. 2 10 60 on Intermediate 50 50 ?i 715——— ———— .—— do... — ______Ne Ir zone. Core- — ------100 716- — - —— — Ne L I 3 10 70 20 Tr. 717— ——— ——— — -do. ______Ne L —— do..- ——— 2 10 70 20 718——— — — — -- — do————— _ Ne L —— do.... — — 3 70 80 20 719———— ——— --—do-....--- __. Ne Ov 70 10 8 30 Tr. 720—— ——— —— _-_-_do_-______Ne L — -do.. ______M 70 10 20 — -do.. ———— — Ne Ov ---do..... _ l 10 60 30 Tr. 722- — —— — — ..—do-... — ——— Ne L ---do..- ——— H 70 10 723—— ——— — Hornblende gneiss ------__ Ne L --_-_do----_____ X 50 30 20 Tr. Trace. — - _ -__. and coarse- grained granite. Hornblende gneiss__ Ne L -- — do-.-- —— X 60 10 30 725— — ——— — --— do.... —— --- Ne L X 50 20 30 726— ———— — -— do... — -- — Ne L ---do...... — X 50 30 727-- — ------__._do. ___.___._.._ Ne L -- — do-..--. X 60 10 30 1 10 65 75 25 llntermediate X 2 67 30 3 2 Beryl.- — — — 1 crystal _ __._ H — -do.... — —— - Ne Lb 1 zone. 80 20 X 70 10 20 llntermediate 2 40 60 —— .do———--.. . Ne L | zone. 4 20 80 730———— ——— .——do.. ..._____.._ Ne L Me 60 10 on Trace 731 ——— ______do..... _ ._ Ne L 30 50 (V) 20 732— — ——— — ——do — — — .— Ne Ov --—do...... — u. 80 15 733- — ------— -do... .._____.._ Ne L .- — do---.. — . 2 20 60 60 20 734— — ———— ____ do- — ——— ._. Ne L ---do...... Me 60 10 30 735— ——— —— —— do-- —— —— — Ne Lb 2 10 70 en 20 736. — — ——— - ..—do. ..._____.___ Ne Lb ----do. .-______X 70 10 20 737— ———— — -—do....--- _-_ Ne L ---do..- —— - 1 10 70 50 738——— ————— --— do-... — -..-- Ne L 2 10 70 60 20 739———— ——— . /Wall zone_-_- _. X 60 20 20 -—do--...— ._ Ne Lb 80 20 X 30 50 20 Tr. Intermediate 4 70 on 740.--- — — --. —— .do- ———— —— Ne Lb \ zone. Core—— — —— _ ISouthwest dike_ X 80 ______741——— ———— Hornblende gneiss L Ha 70 30 Trace and granite. 742— ——— ——— Hornblende gneiss . Ne Ov —— -do.. . ,___.__ 1 10 60 on Tr. 743——- —— — ----do.-.. — ----- Ne L ——do. ---_____. 2 10 70 60 20 M« 70 10 20 Intermediate Me 35 60 5 2 -——do-... — — ... Ne Lb zone. Core----.—... X 30 50 20 745———————— Ne Ov lunit— __-____. 2 10 70 70 20 746----- —— -. Ne L 2 10 70 70 on 30 50 20 747—————— (intermediate 20 70 10 IX Hornblende gneiss. No L | zone. (Core- ——— —— 100 70 10 llntermediate $ 50 45 5 IX — ..do..— —— .... Ne L 1 zone. 1 Core-.- — — . 100 749——— ———— — -do— — —— — Ne L lunit--- ——— -. 2 10 70 60 20 70 2 5 28 llntermediate 50 45 5 1J4 --...do— ------Ne L 1 zone. ICore—— — ..„. 100 751—— — —— ..--- do__ Ne L lunit— —— - — H' 30 SO an 2 Cleavelandite. 3 Up to 3. ' Up to 6 » Up to 2. i8 Up to 8. » Up to 4. 00 CO TABLE 20.—Mineralogy of pegmatites—Continued 00

Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

2 10 70 70 20 Intermediate % 10 75 15 1 752..-.------Hornblende gneiss Ne L zone. 100 7 eo -...-do— ------Ne L H 60 10 30 Tr. 7K4 — __do— —— — — Ne L -_--_do— -- — -. % 40 20 30 Tr. — __do—— —— —— Ne L -.-do— ------Me 50 10 40 756 ------...-do— - — ——— Ne L __--do— ------Me 65 15 -__5 20 £> 757 ____------___-do -. — -. — - Ne L .——do— —— — % 60 15 25 c| 7 eg —— do—— ------Ne L .--do—— ----- 3,^ 10 60 30 759—- — — — _-_._do— ------Ne L ----.do— ------Mt2 60 10 30 Tr. 760 ——do.— ------Ne L —— do —— —— Mi2 60 25 15 Tr. 761— — —— -- .-.. do— — ---„ ... Ne L —— do— ———— V* 70 10 20 ...-do... — — - — Ne L — ..do— —— — Ms 60 10 30 763-. — —— —— - — .do— — ------Ne L —— do-— —— - M 70 10 20 Tr. 764 -....do— — ------Ne L .....do———— — M>2 70 5 25 Tr. 765-. ------.-do— ------Ne L —— _do— — - lAi 70 5 25 Tr. 766 —— do—— — --- Ne Ov __ — do— - — — V* 70 10 20 767———— — — ——do... — ------Ne L —— do— ———— H 20 50 60 30 768------— --...... do——— - —— - Ne Ov ... ..do——— —— n 10 70 20 7AQ -..-.do—. ...------Ne Ov ___-do—— -- — - w 35 35 30 Biotite-. ..__---- 770———— ——— -_-do— ----- —— Ne L —— do—— - — w 30 40 50 30 __--do--— ---__ <1——— — —— Q 771————— ——— — ..do—— ------Ne L -.-..do— ------H 30 50 50 20 772.. ------—— do-— ------Ne Ov ..... do— - — — M 40 20 10 20 77S -___. do— ------Ne L .-.-do -__-.-___ H 50 20 15 30 Biotite- ——— — 3 25 60 50 8 15 /Magnetite. -....do— ----- 774---- —— -.. Coarse-grained Lb __---do-— ------H granite. 4 49.5 12 50 0.5———— —— 4 /Biotite------Trace. ------w -_-do.— ------... do— L 1 50 30 3 10 5 20 Tr. Me \Martite- — — . — ..do—————— 1A 776— — ———— --..do—— ------— do__. L .....do— ———— 1 10 69.5 V 20 Tr. 0.5——— ———— Mi2 ..—do. — ------/Biotite----— Trace - ..— — 777----- — -. ... do— L -...do ------1 50 30 40 20 Tr. \Magnetite-- — __—do ——— — . Hanging-wall 18 10 70 70 24 29 1. - ——— ..—.- layer. 77ft Coarse-grained -.do- Ir Foot wall layer. - 2 70 H 10 1 5 17 Tr. W Tr. 2 ----do—— — -. 3 2 granite and horn­ IMartite-— ----- 2 blende gneiss. 12 60 40 .--.-do— _--.-- 3 — ..do——— —— 770 Hornblende gneiss - Ne L limit———— — 5 50 15 35 8 35 1 (Hanging-wall /Biotite---- — Trace- — —— .— 780—.— ——— ._.._do— ------Ne L < layer. 5 10 60 3 70 8 30 >1— ————— __ iFootwall layer. . 1 70 5 10 3 25 /Wall zone— - 1H 5 65 3 75 5 30 Tr. Martite. ------>1— — —— _.. 781———- ——— ..... do..— - —— — Ne L 10 10 oy 1 2 782—— — .- — ..... do--_ — ----- /Wall zone.--. -- %. 4.5 60 3 75 5 35 Tr. Martite- — — — 0.5——— ————— Ne Ir 19 80 1 1 30 50 60 20 Tr. /Biotite—- — — Trace ------/ OO .. - ^ .. Co arse-grained None. C Ir — ..do— — — . granite and horn­ 3 65 30 2H blende gneiss. 784. — ----- Ne L 1 25 55 70 Tr. 785——— ———— --.-do.— ------Ne L ___.-do.— ...... Ma 40 35 3 40 25 Tr. 786—— ————— — ..do —.———..- Ne Lb _--._do— ------1 10 70 60 787———————— ___-.do — ——— —— Ne L ....-do—— ----- 2 10 65 80 25 Tr. 788—-- — — .-...do-.. — ------Ne L .---do.— ----- 3 10 75 15 789— — ———— —— do.———— —— Ne L .....do— —— —— 3 10 75 15 790——— ———— ___-do ——...... Ne Lb _---do— ------3 10 65 80 25 Tr. Tr. 791——— — —— ____-do — ------Ne Ov _-._do ..-...—— 2 10 65 .80 792—- — .——— L — -do——— — . 1A 60 20 20 6 20 793— —————— _-___do—— ------L __-_do—— ----- 1 10 65 80 25 794—— ------..do- — ------L —— do— ------H 50 on 40 6 20 795-. ———— .. —— .do——— ——— L -_...do— —— — Mi 35 45 20 796. ------——do——————— L --..do—— ----- 1 20 55 60 25 797———— ——— .-.. .do-— ------Lb .-. __do-— ------1 10 60 6 20 798—— ————— .--do—— ------L do 2 10 70 60 20 799--- ———— ..--do— ------L --.-.do——---. 2 10 60 50 30 CHARACTERISTICS OF THE PEGMATITES (.TABLE 20, 85

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u- -fe ci­ c > f e> p" •^ C£ t» OC i- ir CC i~ •j e< •*i IP r- 3SC f T 5 >p If "C 1C U3 CC te 2 .11 0(3 CD30<3 OC 013CK. a a a 00 00 00 00 00 CJO 00 0. oc 0( oc oc 0( oc oc ac oc 1 5 a§ S at OC ac 00 JOOC 01 oc oc OC oo at 00 ooa oc oc a0 OC oc > oc ac 00 00 «3 OC 0(>oc 0( TABLE 2 .—Mineralogy of pegmatites—Continued

Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

867- — - — - — Ne L U 60 20 20 868—— ______—— do— —— —— — Ne L --.-do—— ------H 60 10 30 Tr. 869— — — —— ——do———- — Ne L ..--do— — ----- Me 70 oe Tr. ——do- — --- — _ Ne Ov -- — do-——— — He 60 871———— — — -.—do— ------Ne Ov -— do— ----- H 65 15 10 20 Tr. - —— do-——— ----- Ne Lb ---do—. --_- He 70 10 V 873—— ——— — -— do— — — - — Ne L -— do— ----- H 55 20 10 25 874—— -_-- — —— do— —— — — Ne L —— do— ——— - i 30 50 40 20 Tr. 875— ——— ——— ---do— ------Ne L —— -do— —— — 50 30 20 Tr. 876- — ------do— -- — —— Ne L —— do— ——— r 40 40 30 20 Tr. 877— ------_____ do— ——— — Ne L ..—do-— — — il 60 20 20 Tr. 878————— — -— do— ----- Ne L -.-do— ----- X 50 30 20 Tr. 879... — ------Hornblende gneiss None- Ne L —— do— -- — -- H 50 30 20 20 Tr. and granite. 880- — — -- — Ne L ... -do— —— — H 40 40 30 20 SJ 881 — — —— — - — .do— —— —— — Ne L —— do— ------H 60 10 qn 882-- — ------.-do— ------Ne L —— do— — —— % 40 30 30 883— —— —— - -- — do— ------Ne Ov —— do— — —— K 50 20 10 30 884— ——— - — -___do-— ------Ne L --._do-— ----- H 60 10 30 Trace 885— — — — - ---__do— ------Ne L .—— do— --- — H 50 20 10 30 Tr. 886-—— — — —— do— --— — - Ne L - — do— — - — % 50 30 Tr. 887————— —— ---do— — — -- — Ne L —— _do— ----- % 60 20 10 888— ------— do—- - —— —— Ne L ... -do— —— — % 50 20 10 30 Tr. 889—— ———— _-_do-—-- --- Ne L — -do— --_- X 30 50 40 20 890— —— — — — ._do— ------Ne L -— do— —— — % 50 30 891——— —— — — -do— ------Ne L — ..do— ----- W 50 20 10 qn 892..-. ------_--_do-— ------Ne L —— do— — —~ te 30 50 40 20 893- ——— —— — __— do— ------Ne Ov --..do- ——— 1A 50 20 10 30 894_------_-__-do — —— —— - Ne L ---do—— ----- % 40 28 30 Hanging-wall H 50 17 30 3 one ___-do— — ------Ne L layer. {Foot wall layer - y& 60 20 19 1 Hanging-wall H 55 25 20 Tr. SQfi _.--do— ------Ne L • layer. Y32 75 5 20 Tr. Hanging-wall H 40 30 28 2 ftQ7 ... — do— — - — . Ne L • layer. Footwall layer _ ^2 60 20 19 1 898—— ------__ — do.... — ______Ne L lunit— — _ .... Vz 35 45 3 20 <1 899--- __-_-do— ------O L —— do———— — 1 30 50 3 20 Tr. V4 [Hanging-wall H 40 40 2 0.5 H 900—-———— -—— do- ———— —— Ne L < layer. iFootwall layer,. H 70 10 H 19.5 0.5 H {Hanging-wall 1 20 64.5 2 15 0.5 901— ------_do---- — ----- Ne L layer Footwall layer.. H- 50 40 ^ 10 <1 902— — ——— - —— do—- ——— — Ne L lunit— — —— H 48 30 3 2 H Tr. 903— ______Hornblende gneiss Ne L —— -do.-.-- — ._ % 35 50 3 ,<54 60 10 30 Tr. M ott 40 Qfl Biotite ______!---_. ..---.__„ 917--.- — _ -—do.. ..-.__„___ Ne layer. 14 2 50 20 30 Tr. H 50 Of) 10 1 918. — — .-_-- — -do.--.. _ No <. layer. ^ 10 Of) Tr. Biotite_---_____. 919__ —— __- --..do... ______Ne 14 28 40 2 1 14,1 70 10 20 Tr. H 30 1 920_-______...-do.------— - Ne zone. 5 59 34 1 M 8 70 0 V 20 2 921.. — --- _---do_. ______Ne < layer. 14o 60 20 Tr. 14 50 40 10 ^ Tr. 922.... — ...... ---.do....- —— ... Ne < layer. i<;2 70 on 10 H 48 20 20 2 1 923.-.. — ______.--do. ______— — Ne layer. H 55 14 30 1 V6 60 3 30 2 924_.______-____do______Ne < layer. Uo 19 40 1 14 30 50 20 1 layer. 15 60 25 H 925___---__ -.-do------Ne zone. 80 5 20 1^2 60 Of) 20 926--___-_- _-___do______.__._-. Ne L 16 65 10 24 1 H Tr. Monazite.- _____ 1 crystal.. __ _. 1& (Hornblende, gneiss ^ 10 15 <1 Tr. 927 ... Ne Ir •{ layer. I ed granite. 14 80 5 15 <1 Biotite______Trace-__-______. 928--.. — — — Ne L H 40 on 2 38 2 !/2 M 15 4 30 5 I/ 929_. ______— -.do...... —— Ne L \ layer. I4iA 60 1 H Qf\ 10 10 1 930.-. — ..- — --...do..—— . Ne L \ layer. Uo 75 25 Tr. H 30 40 20 10 1 Monazite___ ..._ 1 crystal _ ___... M 931- —— .. -__._do___.___ „ Ne Lb •^ layer. 60 10 29.5 0.5 Tr. H 30 50 17 3 y> Tr. 932____.__. —— do... —————— Ne L i layer. H 60 15 24 1 i* 10 fin 1 933-.-. — — ... —-do——.. —— __ Ne L { layer. M* 60 Af\ Tr. }4 Of) 4.f» 2 i 934... , . —— do. . . . Ne L < layer. ii. 60 10 28 2 14 30 40 5 1W 935- — .-. — ..do.—————... Ne L \ layer. ^4 60 4fl Tr. 936— —— ...... Lb H 63 15 2 » Tr. Me Beryl______1 crystal— ----- M ite and horn­ blende gneiss. 1» 20 Ho 65 15 0.1 H 937——— ———— - ... do— L { layer. 1- 65 JM 15 1 20 Tr. 938. —— — — - Ne L h OK 65 10 <1 ?4 40 38 20 2 w Tr. 939-....- — ... --..do-.. — ——— Ne L layer. fc 67 Tr. 14 2 3 940——— ——— . ..— do.— - ———— Ne L H 25 60 2J/2 14 1 941-... — ...... L —— do— ———— 1 15 55 5 5 30 Tr. Tr. blende gneiss. 942——— ———— ...do— L ——do————— 3/4 10 65 3 25 ,. 943——— —— — Gneissic granite...... _do___ C L . ....do— ...... 16 30 Hz 50 2 18 2 M 00 TABLE 20.—Mineralogy of pegmatites—Continued 00 00

Wall rock Pegmatite

Mineralogy Number and name of Rela­ Tex­ pegmatite Alter­ tion Internal Plagioclase Perthitc Graphic Quartz Muscovite Garnet Other minerals (PI. 1) Type to Shape ture granite ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.) 3A Granite and horn­ (Hanging-wall 20 15 4 15 15 H Tr. 944- — ...... blende gneiss. Ne L layer. Footwall layer .. U 50 i,i2 10 2 20 H 20 H 0.1 Hanging-wall 1W 15 J-32 60 3 15 10 H -do— ._- L layer. Pootwall layer, _ H 50 10 20 Hanging-wall ?4 30 20 2^2 50 Tr. 946. — — ——— Hornblende gneiss Ne Lb layer. Footwall layer.. H 50 40 <1 Hanging- wall 3A 30 50 2 20 Tr. 947——- — — . None— L layer. Footwall layer __ l/2 60 Ha 20 1 20 Hanging-wall 1A 55 15 28 2 948- — -_-.__-_ Hornblende gneiss Ne L layer. Footwall layer __ Me 60 10 30 Tr. Hanging-wall He 35 35 28 2 949— ...... — ... -do— — - Ne L layer. IFootwall layer _ Ha 60 9 30 1 (Hanging-wall 1A 40 30 28 2 950----..----... — -do— ——— Ne L i layer. IFootwall layer.. 1A2 60 9 30 1 Tr. [Hanging-wall % 40 40 17 3 961-.. — ...... — do-.-.-._...... Ne L layer. Footwall layer. . 1/64 70 9 20 1 Tr. Hanging-wall % 40 39 20 1 962...... - do---. . Ne L layer. Footwall layer. Ha 60 19 20 1 Hanging-wall % 45 25 28 2 953— —— ...... Hornblende gneiss Ne L layer. Footwall layer. 144 60 5 34 1 Tr. [Hanging-wall H 40 40 17 3 954————.—— -..-do...... — _.... Ne L layer. Footwall layer. 5/64 70 9 20 1 Tr. Hanging -wall He 63 20 15 965—.. — — . -——do— _-_..___- Ne L layer. Footwall layer . Ha 70 10 1 Hanging -wall H 58 20 20 2 _——do. — --.--. Ne L layer. Footwall layer- Ha 74 9 15 I Hanging -wall H 50 30 19 1 957------——do.— —— —— Ne L layer. Footwall layer ^2 70 Ne L Hanging -wall H 20 65 2H 15 and granite. layer. Footwall layer. !/i 45 40 1 Tr. Biotite— - —— | Hanging- wall 1 30 H 50 4 20 <1 i/l 959--. ------Hornblende gneiss Ne L i layer. IFootwall layer. 1A 70 Hi2 10 1 Tr. 960--. — .-.-- -.-.do - .--_._.__ Ne L 3A 45 40 2 15 <1 961------_ .. .-..do — — ... .. Ne L ----do——— ____. H; 55 He 25 3 0.5 H 962--.------. __-do _ --.—— . None.. C L --— do—— ---. 1 30 50 4 19 1 H (Hanging -wall h 48 H 963— — ---__ -...do ___--______. Ne L i layer. IFootwall layer. ite 70 4 964——— —— - — ___.do — ----_ Ne L limit————— He 50 20 30 965- — —— — . Coarse-grained None.. Lb -.—do———. H 50 V on granite and horn­ blende gneiss. 966— ------Ne L - — .do— .---_. H 20 967------.-----...... do— —— — „-- Ne L ..... do— —— — 1A 30 50 40 968—— — - — . ——do-... --.--.. Ne Ov . — -do— - —— ._ Mi 60 1 (Hanging -wall H 10 969- ——— — — ——do——.——— Ne L layer. [Footwall layer.. H 40 27 ' 30 ...... 3 970————- —— --..do-— ...... __ Ne L 1 unit...... i-64 80 20 ------i CHARACTERISTICS OF THE PEGMATITES (TABLE 20) 89

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u- CSI CO ^f tOt~ TABLE 20.—Mineralogy of pegmatites—Continued

Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

1008— — — ... Hornblende gneiss Ne Lb J-6-J4 55 15 30 <•( Tr. and fine-grained granite. 1009——— — —— L ---- do_—_ —— -. U-te 47 33 20 Tr. Tr. H-H 1010.-.------.-...... do— — ...... Ne Lb - — .do— — --- ?ie 55 30 2 15 Tr. He _____do______He-H 1011—————— Hornblende gneiss, Lb — ._ do______V* 45 35 20 <1 Tr. ____.do_,______H fine-grained gran­ ite, and coarse­ grained granite. Hornblende gneiss Ne L -——do——— —— V* 50 30 <1 Tr. ._ — do— ----- J4 and fine-grained granite. Hornblende gneiss Lb _---.do—— ______H 50 29 20 1 Tr. and coarse­ grained granite. <•( Hornblende gneiss, ___do___ Ne L ——_do————— H-U 55 25 20 Tr. % fine-grained gran­ ite, and coarse­ grained granite. 1015--. ------....-do— _ ... __ —do- Ne L ——do..——— — J4-J4 60 20 <1 Tr. — -do- — ----- U-H Ne L —— -do— — —— ?le 53 25 3 20 2 J-s Tr. H'28 _____do__—— ____ H 1017—— ————— _-.. do— ———— — Ne Lb ——do——— —— M 57.5 20 2 20 2 H 0.5 Ml —— .do——— ——— Ne L — ..do..—..— . % 45 30 3 20 5 H 0.1 Vie 1018-- — -- — - Hornblende gneiss Ne Lb ——do.—— —— % 42 30 2 20 3 15 8 h Tr. MU 1019 and fine-grained granite. 1020— — -- — . Ne L --. do— .__.— y* 30 40 3 30 3 20 10 1021... — -.--...... do— .. — ...— Ne L ——do—.. ----- H 50 25 3 10 20 5 H Tr. VZ2 L /Wall zone.-.. . He 50 Wa 20 28 2 Biotite Trace. ______Hornblende gneiss- Ne \Core- — — .—_ 2 10 49 3 30 1 /Wall zone. — — . H 60 19 20 1 — -.do———-.... Ne L \Core.-——— lH-3 50 3 50 —— -do—— _- — — /Wall zone_ __ __ y> 40 28 30 2 Ne L 3A-2tf 20 55 2^- Ne L /Wall zone _ _ _ H 55 10 30 5 ——do——— —— -- \Core— — — — H 30 37 30 3 1026------Fine-grained gran­ ite and horn­ None.. L /Wall zone _ __. . % 45 25 5 15 20 10 H Tr. Ha blende gneiss. 2 i/, 1027- — . — — — _.do—— —— — - — do... L /Wall zone.. __ He 60 20 3 15 5 Tr. He 4 10 35 10 H 2 crystals...... _. W-?i Hornblende gneiss, fine-grained granite and — do— Lb /Wall zone _ _ . M 63 10 1 15 5 H 2 Wi coarse-grained \Care~——— — 2 15 30 4 5 l 1 crystal H granite. 1029— — — — Hornblende gneiss — do... Lb J4 40 30 4 20 10 K> Tr. Ha and fine-grained granite. 1030———— ——— — -do——— ———— .-do- Lb — -do... — —— % 35 35 5 20 10 i,.. Tr. He 1031— — — — —— do———— ——— Ne L _--.do..-— --_ % 49 30 3 Tr. He 1 J-64 916 1032— — — — .—.do—--. — .. Ne L ——do————— 54 53 25 4 20 2 J-2 Tr. He —— -do————. —— .do-— — — He 1033——————— Ne L — ..do...— — .. % 49 25 4 5 J4 1 W4 _-_._do______He-H 1034— — — — Ne Lb —— .do...——-. Yl6 39.5 30 3 20 10 M 0.5 1-64 —— do—— ——— . Me 1035------. Hornblende gneiss Ne L — ..do——— —— He 61 20 3 15 2 J'S 2 J-04 Columbite-tan- -— do— —— — H and fine-grained talite. granite. 1 % 1036------. .-..do— _____ ...... Ne L — -do— —— — H 43.5 25 20 10 tt 0.5 H28 •^Columbite-tan- % talite. (.Beryl.-.-...... 2 crystals.- _ ... He-J-i 1037————— —— — -do— ...... Ne L — -do————— % 34.5 35 20 10 54 0.5 H28 CHARACTERISTICS OF THE PEGMATITES (TABLE 20) 91

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c* ^ C5 CN CO -^i »O T 10 10 10 10 IT coco t^. IN. I>- IS O O O O c o o o o c oo O O O O TABLE 20.—Mineralogy of pegmatites—Continued «D to

Wall rock Pegmatite

Mineralogy Number and name of Rela­ Tex­ pegmatite Alter­ tion Internal Plagioclase Perthite Graphic Quartz Muscovite Garnet Other minerals (PI. 1) Type to Shape ture granite ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

/Biotite--.______- Trace 1076. —— — —— Hornblende gneiss te 30 50 20 Tr. Tr. \Martite______and fine-grained Ne L Me-H granite. lOore— ...... — 1 10 50 40 /Beryl_-___-.__-- 2 crystals.- — .— U-tt 45 35 20 <1 Tr. 1077--. — — _. Hornblende gneiss . Ne Lb 5 <1 7 93 1078— ——— — . —— do—— ——— — Ne Lb !4-M 50 30 20 <1 Tr. 1079— ————— ..... do.— —— —— Ne L - do__. .... M 45 30 25 <1 Tr. 1080--— —— . Hornblende gneiss None Lb .... do——— -- V6-U 55 25 20 <1 Tr. and fine-grained granite. fBeryl_-______1 crystal ______H 1081——— ——— ...... do—— —— . —— — do... L — -do— —— —— H 54 25 20 1 <1 IMartite- ______1082—— —— —— —— do—————— — do— L —— do—-. —— . H-H 49 30 20 1 <1 Trace 1083— ——— — —— . do———— ... . — do— L —— do—— —— y* 60 20 20 <1 <1 BeryL------J-8-?8 10S4_ — ______do ...do- L — . do— ——— j-s- y* 59 20 20 1 <1 do 14 1 . 1085—— ————— Hornblende gneiss Ne L . — do——._ __ y2-H 43 30 25 2 Tr. -_.__do______?ie-?4 1086— —— ——— do Ne Lb -—do—. — - _ H-H 49 30 20 1 Tr. -__. do ?ie 1087- —— — -. ——do______.. —— . Ne L — . do______te-y* 60 20 20 <1 Tr. 1088——— ——— Hornblende gneiss] /Biotite------Trace______and fine-grained> None L —— do————— H 44 20 <1 3/16 granite. | \Beryl__-______3 crystals _ ____ o 1089- —— ——— Hornblende gneiss_ Ne L do J-S-H 49 30 20 1 <1 1090— — - ——— . _ .do-.... _ Ne L —— do—— —— J4 55 25 20 <1 <1 1091----...... ——do———— —— Ne L —— do_ M 39 40 20 1 Tr. Beryl_____ ... .. _ H /Wall zone, ______M-W 55 25 20 <1 <1 — ..do..... _ —— do y* Ne L \Core- — — —— 4-5 1 25 74 <1 1093— —— —— - —— do... -..-- — Ne L 4}.5 40 35 <1 Tr. H 1094— ———— __ do Ne L __.. do______M-^ 35 40 25 <1 Tr. H-te 1095——— — — do Ne L —— do... ______H 45 30 25 <1 Tr. -.. do______te 1096— — — — (Wall zone__.__ _ Js 35 45 20 <1 Tr. . do Ne L \Oore--- — ----- 4 1 25 74 Tr. 1097——— ——— —— do——— ———— Ne L X 15 20 <1 Tr. 1098______„ — - do .. . . Ne L .... do______H 44 35 20 Tr. 1099- — . —— . .. do Ne L ——do———— J-2-94 40 39 20 I Tr. 1100- — ———— do Ne Lb _.—do. ______M 44 Tr. Bervl M 1101-. — --. _--_ do Ne L ___..do______. U 45 30 <1 Tr. Trace 1102——— ———— .——do-— — . ... Ne L —— do———— . M 49 30 20 1 Tr. ?16 1103---- — — do Ne Lb —— do__ _._ M 44 35 20 1 1104______... — ..do—— —— .... Ne L —— do———— tt 46.5 30 on 3 0.5 Hanging -wall % 30 45 4 15 10 H Tr. M4 1105——— ———— --..do—— .. Ne L layer. { Me 67.5 15 2 15 2 H 0.5 M28 Beryl______M6 1106————— —— _____ do———— Ne L J4 49 35 3 15 1 H Tr. tt4 1107— ——— — Fine-grained gran-1 [Hang ing -wall H 50 30 3 15 5 M Tr. Me ite and horn-> L \ layer. blende gneiss ) .Footwall layer. _ tt2 72 10 H 15 1 M6 2 544 1108— — - — ... do .... — do... Lb X 44.5 30 2 20 5 H 0.5 M28 1109——— ——— ——do——— ... do... Lb -—— do——— Me 73 10 1 2 H 1110.———— ... .——do————— - —do... L ——do——— _____ Me 68 15 1111 ——————— ——do- .__do. . Lb ._ do_____ H 45 30 2 20 5 % 1112..— Hornblende gneiss- Ne Lb —— do—— — H 50 25 1 15 4 15 2 H 1113— — -_... Hornblende gneiss L ____.do____. ______% 39 45 3 15 1 H Tr. VM and fine-grained granite. 1114.. — —— -. — ..do.... .__do___ Lb — ..do— „__ Hz 74 10 % 15 1 Me <1 ^64 1115——— ——— .——do——... . __ — do... L —— do——— .._ Me 72 10 3 n Hanging-wall H 20 60 % 15 5 H 1116—.. . — .do- —do- L layer. Footwall layer__ H* 84 15 1 ^64 Hanging -wall y-2 15 40 Ite 40 5 H 1117———- — . Ne L layer Footwall layer__ n* 85 15 Tr. u* <1 H* 1118— — . . - Hornblende gneiss.. None.. Lb 1 unit, __ — .... Me 78 5 15 2 H Tr. ^64 and fine-grained granite. CHARACTERISTICS OF THE PEGMATITES (TABLE 20) 93

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Amount01- ; crystals8,_._ crystals22——___ percent r/ a "c- "3 "a Otherminerals -*- crystal.1 ra rs

Biotite—------Mineral

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-" 1""" Mineralogy «% rJ- rt.,rf.W. «x sec- -., rJX«N Vr^r- r-NiHN ^ r-tX Muscovite |5 j

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111 1 !MS- i ca ccnoo 2 If- 0*0 Pegmatite S g 88382 S S i i-^ C< Tj C^ ~ C^ CO CN i CrH TJHCO ? a S 8 a - a 8!gs S g Si co i S Sr^S c^ cc il | 88

Graphic ] 10 i granite .S_d 1! i 3 o 1 — < 1C ; | 0 IS O1 CO rH rH -^ CO CC 1C .c N j«uo CO CO C» W GO M *O o»c o o o o C 1C OrH L C •* - r-H C^ If. C^ •O NCO'tfr3388 'O -^ 5 S( a:^ s CO Tf 1C - 98S S i CO M "» M -^ C^l 1C

| • Plagioclase 13 i

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V2 7^ M ^J ' t« Hornblendegneiss. Hornblendegneiss horn­iteand Hornblendegiieiss- Homblendegneiss Hornblendegneiss. Hornblendegneiss Hornblendegneiss Hornblendegneiss. ite,andcoarse­ Hornblendegneiss Wallrock Fine-grainedgran­ andfine-grained --.do-——--- ,____do—„-___-_-_ ..-.do——------andfine-grained Hornblendegneiss. fine-grainedand fine-grainedgran­ grainedgranite. -...-do—------..---do---_._-. fine-grainedand .--.do—------blendegneiss. a andgranite. e granite. granite. granite. granite. c C C C D C Hn c •e T? 'c T: n; ^ ^ o 3 at c c &tS c W W u M t -a d ^

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(Intermediate 1unit.-- /Wallzone...- 1 O ^ O; a |zone. ; pi a PI S § fl a S i O " _• O o o 0 '3"° •dc ^j N S] C C I jj C O C 0 C § -4- C _O C O c c ^ c c g -4- Tore d *n '— i ^ s o (— i o •d -d i 4. a •a'd'd'd •c •c —i a Core1 ^ +j O s- p! 72 t- "-3 t "3 ^ P C3 M N O j3 w O ^ C 3£p03 o C c3 ^ c § § c O E ^M O PO i- _C ,- _0 r- | 1!'—— V— y ! 1—— v

ndegneiss ne-grained

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31 SI TABLE 20.—Mineralogy of pegmatites—Continued

Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type to Shape Internal ture Plagioelase Perthite granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

Vi 60 20 3 20 Tr. Ht M Hornblende gneiss. Ne Lb Ut 84 15 J6i ICore— ------V/2 60 40 1 94^ .. ... do——.. ------Ne L J64 84 15 }fe 1246- — ——— - „... do— ------Ne L -.-do.— ----- H 70 15 5 3 15 <1 M4 1247 —— do— — ----- Ne Ir ——do——— —— Me 80 5 1 15 <1_ —— — — — »i Me 65 20 10 8 15 <1 1248------—— do— ------Ne Ir /Wall zone ----- % Me Biotite.---- _ __ —— do— - — --. n Tr. ^4 .... .do— ——— — - Ne L U 70 15 6 15 Tr. M Tr. M* 1250- — — ——— .... .do— -- — — Ne L -____do— ------Me 75 15 5 5 10 Tr. Me <1 ^64 -—do—— --- — Ne L — ..do— ------Me 80 5 ¥2 15 <1 H4 <1 Ha ——do... — -- —— . Ne L — -do————— ^2 75 10 3 15 <1 VM Me 75 10 5 3 15 Tr. Me (intermediate 1 30 50 3 20 Tr. % Biotitc— —— — Trace-. ------l/2 —— do— — — — Ne L 1 zone. [Core—— ------25 75 --..do-— ----- —— .do— —— — 2 1254-- — -. — -. Coarse-grained L Me 75 10 2 15 ---do— —— — <1—— _-- —— l/Z2 granite and horn­ H-2 blende gneiss 1255 Hornblende gneiss - Ne L -....do— ———— H 55 30 3 15 Tr. Me Tr. ^64 1256- ——— ——— —— . do...... ----- Ne L ---..do——— — - M 55 30 20 5 15 <1 J64 <1—— - — ._.-- Hi Coarse-grained None Ov ..... do— .. — — H 65 20 10 5 15 Tr. Me MB granite and horn­ blende gneiss 1258- — — -- .....do—— ... —— .. — do— Ir —— .do——— —— Me 70 15 1 15 Tr. Me <1 5-64 — -.do— ------— do— Ir _--__do— ------% 55 30 20 5 15 1 % Tr. !/64 . — _ do—— ----- — do— Lb — __do—— — — Me 70 15 3 15 <1 V32 1261— — ——— -—do— ------— do— Ir — ..do— — --- y* 65 20 10 5 15 Tr. H Tr. Y32 V* 70 15 1 15 Tr. Y32 <1 }/64 Hornblende gneiss _ Ne L \Core. . ------11/2 75 5 2 20 Tr. Me Tr. Ma 1263.---______---do— . ------Ne L H 70 10 l}.^3~ 20 <1 5-64 1264— ————— — ..do—— ------Ne Lb _---do—— ------% 50 30 20 <1 Me 1265— —— — — .....do— —— — —— Ne L — _.do——— - — J-s 50 30 5 5 20 <1 ^4 ^ 1266. —— ———— Fine-grained gran­ L — -do-__ ——— % 62 20 2 15 3 M Tr. Mas ite and horn­ blende gneiss. 3 33 ------50 30 3 15 2 u Coarse-grained llntermediate \Vi 30 20 8 30 20 3 Tr. MB 1267...... ___. granite and horn- ...do- L ) zone. blente gneiss. (Core— —— — - 3 15 85 fBiotite ______<1 M 1268— Hornblende gneiss _ Ne Ir M 45 40 30 5 15 \Magnetite._ __ _ Ys 1269 - Hornblende gneiss None— C Ir —— do—- ——— X 60 15 3 25 <1 %z <1 Ys and granite. <•( 1270— ...... Hornblende gneiss. Ne L —— do— .... — M 35 50 15

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297133—55———8 TABLE 20.—Mineralogy of pegmatites—Continued CO 00 Wall rock Pegmatite

Mineralogy Number and name of Rela­ Tex­ pegmatite Alter­ tion Perthite Graphic (PI. 1) Type to Shape Internal ture Plagioclase granite Quartz Muscovite Garnet Other minerals ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

Hornblende gneiss. Ne L 6 43 35 25 10 20 Tr. H 2————— ————— ^ 1330- Ne Ir —— _do— ——— - 1 64.5 20 10 12 15 0.5 % U 1331— — —— do— — ———— Ne Ir ——do———.— 1 59.5 20 5 2 15 5 H .5————— ...... l/i 1332.______... —— do-__. —— ------Ne Ir ——do.... - — -- 3 60 25 15 [Hanging- wall 5 40 45 15 1333—_ —— _ ——do————. .. Ne Ir < layer. [Foot wall layer. _ M 79 5 15 Biotite--- — — !--_-_-_. __--_--. M 1334...... — .do.. ——— ..... Ne L lunit —— —— -- 4 60 25 15 15 Tr. 1335.__...... -.-.do__— — ______Ne Ov —— .do... ———— 2 44 40 30 15 Tr. % __ do 1 W 1336- — — - ... -do...... —— .. Ne L .... _do—— ——— 2 53 30 15 15 Tr. He —— do-... — — 2——— __ — _.___. H 1337...... —— do——— ——— Ne Lb —— do——— —— 1 60 25 15 15 —— do——— —— 1338- — .-..do— ——— —— Ne L —— do——— —— 2 50 20 30

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Mineralogy Number and Rela­ name of Alter­ tion Tex­ Graphic pegmatite Type to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals (PI. 1) ation wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

Ne Ir 1 unit----.--.. 2 37 46 15 2 Tr. 1510—— ——— . ..-do..—— —— — Ne L ——do——— — % 58 _____ 25 15 2 ... .do... — —— — Ne L ... .do—— —— 2 45 35 25 20 <1 H Tr. 1.32 i cl o ... do— — — — ~ Ne L ....do——— —— 1 65 20 15 10 15 <1 2 i Kiq —— do——— —— — Ne L ....do—. ----- m 55 25 20 5 20 <1 M Tr. Biotite— —— — Trace — ——— — l/2 ....do— —— —— .. Ne L —— do... ———— 3 40 45 10 35 24 15 Tr. Me ---_-do______1 ... do———. — —— Ne L —— do— — - — 1 35 40 30 12 25 Tr. H <1 -...do-— ------.do— ______%2 Wall zone ?4 55 30 5 20 8 15 Tr. —— .do— —— — -___ do— —— —— 1516——— — — - —— do——— —— ... Ne Ov i\j\j .0 1517—— — ——— ....do——— -__-- Ne L lunit-— --— - 4 10 90 1 crystal. _ ____ H d ....do— ...... Ne Ir f Wall zone _ _ - _ — H 55 30 15 1S18-- ————— JLUU __ do_— -- — _ 3£ -\ K1Q —— do.... —— —— Ne L lunit— ------2 60 20 20 <1 Tr. ....do—— — ... .. Ne L — -do-— ----- n 55 25 15 3 20 <1 i Biotite- ______

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crystal1______Amountor percent

O C C c o Otherminerals G a c -co -d a •C a C.> 8 -c -§ g 8-S S -i t' c, ^ c y OS <5 K i- t 2 E g i? T—— ^ _ •^ E- vl \ rn1 V V E^ E-1 E- E-1 vvVE- V VV Magnetite____ /Biotite_-__.__-_ Biotite.-.------Biotite------Mineral Q fl a a "3 C ai o^ a "Riot.it.p. c c 08 1 i 1 |l | c "c c c 11 08 I ci 03 c .2 1 ^ 3 S5 ^1 pq S EH£ w;§pq 5 | pq s ,———•>——— N ' ——V , —' '— .11 S,- — • j ' ——V- 11 .— •• — .,— •— •".S ssixs^ Garnet e |

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Wall rock Pegmatite

Mineralogy Number and name of Rela­ pegmatite Alter­ tion Tex­ Graphic (PI. 1) Type ation to Shape Internal ture Plagioclase Perthite granite Quartz Muscovite Garnet Other minerals wall structure (in.) rock Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Per­ Size Amount or Size cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) cent (in.) Mineral percent (in.)

Hornblende gneiss . ----- Ne Lb 2 15 65 70 (18) 20 ——do———— —— Ne L —— do-.—— — 2 20 55 50 (20) 25 1705----- — — _ — do—— —— ----- Ne L —.do...... —— . 45 35 25 20 1 7ftA Hornblende gneiss Ne L 30 50 60 20 Trace and quartz mon­ zonite Hornblende gneiss . Ne Lb ____do— ------60 _.-_. 25 (15) 1 15 fBiotite- — _ - - do M Magnetite— — — V2 1708— — — — ..._do—— ------Ne Ir H-tt 45 30 5 25 Trace. _____ /Biotite ___ -.. --do— — —— H 1709——— ———— .-.do— — —— —— Ne L ---do-— ----- 50 —— _ 30 10 ..... 20 Magnetite.------Vi 1710— —— ——— ....do.— ————— Ne L ——do——— — H V- 60 20 10 20 ------Tr. Trace. ____ — 1711 — .do—— ----- Ne L _— do— -_--- l 35 45 40 25 —— do———— - .—do—— -- — fBiotite- — ------1 719 Ne Ir ——do... - — — 40 40 20 20 Magnetite--. ... --do-— — --. /Biotite.— __ ... .„ .do——— — . 1713- — —— — - do Ne Lb -..do— —— — U 50 ----- 30 20 Tr. Tr. -.._do—— — ... 1714—— ———— --do-— ------Ne Lb -_-do—— —— - 45 35 5 6-10 20 Tr. ——do— ———— _--dO —— -.-.--.__ Ne L -..do...— — -- H 60 /16-J4 20 J-4-2 20 Tr. 1716---- — --- —do— — — - — . Ne L —— do— — —— 60 20 20 Tr. U M-J4 1717———— —— _— do— — --_- Ne Lb __-do——— — - l 35 45 20 20 ^-i^j U 1718- ———— - — _--dO—— ------Ne Lb -—do—— ----- l 50 30 5-.-S 30 20 ---do—— —— _ 1719 — .do—— -- — .-- Ne Ir --do— ----- M 60 20 J-2-1J/2 20 H-l 'Northeast and l 1 ;;;!! 79 10 20 Tr. ^j X 1720-- ————— - Hornblende gneiss Ir southwest and quartz mon­ ends. zonite. .Central part... - 35 45 20 &-1 J.-3 /Magnetite. ------M-H ... do— L 20 **.* 60 30 1-3 20 H V Tr. H Tr. H l 1 799 Hornblende gneiss —do- Lb -._do—— ----- 2 30 50 20 20 Tr. /Biotite— .„ —— —— .do— — —— and quartz mon­ [Magnetite— — — - * zonite. /Biotite- —— __--- Trace .. _ _ .. 1 793 --— do—— ... -„- Lb _——do— ----- 2 5 40 20 \Martite_ __ — — 1 794. Hornblende gneiss - Ne L — -do—— --- 3 30 50 30 20 Tr. }te iH 1725———— — - Ne L 60 25 10 6 15 --.do— .--__ _——do— — ..— .....do— ------Ne L -—do—— -- — H 30 3 20 He .——do..— — — 1 797 Ne L — ..do— — — . 35 10 5 20 Tr. He CA fBiotite— — _ — Trace- — ——— 1728— ——— — ---dO——— .... ----- Ne Ir -— do—— ----- 4 30 60 10 20 (.Magnetite. __ — — — ..do.— — .... 1729——— — — Hornblende gneiss Ne L ---do —— --_- H 45 35 3 20 ------Magnetite — _ ...... do— — —— and quartz mon­ zonite. 1730—- — - — --.-do— --- — . /Biotite-—---—- ---do--- — —. J6 Ne L 3 30 55 40 6 15 (Magnetite. — — .....do———— — /Biotite--- — - — — -do— — —— Hornblende gneiss . Ne L ...-do— ----- H 49.5 30 3 0.5 He \Magnetite-- _ .. —— _do- — — — 1732- —— ——— Hornblende gneiss Ne L ... ..do— ——— 65 20 20 4 15 ... ..do—— —— — and quartz mon­ % zonite. 1733— — ——— —— do—— .—— ... Ne Lb -----do—— --- H 45 oc 20 4 20 —— .do— —— — He ^•j 1734————— — ——do————_-.. Ne Lb ——do———— 6 10 70 85 20 Tr. •^Martite— —— -. lSamarskite(?) _ 3 crystals __ — """He 1735- —— — - Hornblende gneiss Ne Lb 55 %, 30 4 15 1736——— ——— Hornblende gneiss Ne L -—do... -- — - 2 30 50 4 30 6 20 — -do-. — .. - and quartz mon­ zonite. 1737— — ——— .....do— ... — .... Ne L -—— do— —— - 1 50 ---.. 30 3 15 4 20 * — ,.do— —— _ ..- —— -do.... ——— 1738- — — — „. ..do— —— —— Ne Lb —— do..— —— 2 40 34.5 40 8 25 0.5 Magnetite----,-. ....-do...——— 1^2-2 J Magnetite------_ ..-do...... _ ^4 L ---do— —— ... 30 50 50 20 1739 H LBiotite - ——do... ____..__ H fBiotite— — —— —— do...... —— Me-H 1740 Ne L --.-do—— — --. 35 50 8 15 [Magnetite _ — ---do.— ------and hornblende H« gneiss. L -__- do— — —— 3 30 50 65 8 20 ..-.do--- — ... .. X* 1742———— ——— —— do... ——— „. .. L ——do———— — 1W 35 50 35 5 15 1743 ——do——— ...... None Ir -—do. — - .... 2 40 45 30 5 15 Trace. .—..... H — ..do. .-______-- — do— ——— . 2 40 50 40 4 10 /Magnetite __ ___ te ——do.———.- L — _-do...... % - —— do.. - ______L _ — _do— — —— tt 60 25 20 5 15 -..-do..-.-- — Ha-l 1746 — -do— ————— - L - — .do— ——— H 50 30 30 5 20 —— do— —— —— —— do. ——— ___ Ma 1747— ——— — - — .do— ------L — ..do————— 5 25 65 70 8 15 ... ..do— ———— — L ——do——— ----- 1 55 35 4 15 5 20 <1 Ht Trace—-— ... Ma 1749 —— do— — ... —— L —— do— — —— 2 30 55 40 8 15 _-_.. do.... ______—do_ .___-. .. Ma 1 7^n -—— do— —— „ — . 1 35 45 20 8 20 Tr. [Magnetite— — — ---..do....- — .. Ha L —— do———- — .--.do. — --.... ^3 1751 ———— ——— — ..do— ... —— . ... L -—do—— ----- 4 20 60 60 8 20 ——do. ..______Ma 1 7^O ——do—— — ——— Lb — ..do—— — — M 55 30 2 15 -_--do.. ---.____ H 1 7^Q ——do——— — _..-- L ----do—. ------4 25 50 50 10 25 _ — _do——— ____ —— .do. ——— — ^3 1 7*^4. — -do—. —— ----- L - — .do—. ----- 1 55 35 4 15 5 20 <1 YM — ..do.— ______—— .do.. — —— Ma 1 7^ ___ ..do— ——— —— L — ..do— — —— 2 30 50 50 5 20 _____do——— ____ — -do—— ______u J/i —— .do— —— — — 25 60 15 fBiotite-- — - — -- — do..-— __ L _____do___ .--._-. 4 60 6 (Magnetite— — -- —— do..———— 9ie —— do.. ——— .. Vi2 1 7*V7 5 30 50 15 Tr. /Biotite— —--- _ -—do—— —— — - Lb .--.do— — —— 55 8 H* (Magnetite—— — ____. do.. - — ... Ha 1 7^8 —— .do.—— — ----- L _— _do——— — __ 4 30 55 50 10 15 Tr. M* <1—— ______t^ 2 1 7^Q ——do—————— Ir — ..do————— . 3 20 65 70 8 15 __.. -do— ______Trace--.- ______H 1760——— ——— Ne L _____do____— -___ 1V'2 20 65 60 15 ——do— — ---- _ —do.—. ----- }4 and hornblende gneiss. 1761—— ------Lb —— .do—— — — 3 45 40 40 8 15 —— do... —— — Trace _ ------Me 20 15 Tr. /Magnetite. — — .--.do— — —— Me 1762------. _.... do_———— .... L — ..do—— — — 2 45 40 6 Ha —— .do—... --- Ha 1763----- — -. -—do.— — .... - L .-..do— — — - 2 25 60 20 15 Tr. ..--.do..—.--. Ma 17fi4 -—do———— —— - L — ..do—— — — 3 30 55 50 8 15 -——do.—...... H 1765— — ——— ——do——— ------L --..do— ———— 2 30 55 40 15 —— -do——— — . . — .do—.. ---. Hi*-M 1766——— —— — —— do... —— —— — L -— do—— — ... 1 45 40 10 5 15 —— .do— —— ... _-_. -do— ______Me 1767— ——— — -...do.— ——— .. L .....do———— .. 3 20 65 60 12 15 .. — do... —— ... .——do — — .... Ma-1 1768—— ——— - - —— do————— — Lb ..--do— ———— 3 15 65 60 8 20 -.---do.— ______—— do.—. —— .- Me 1769. —— — --. ——do——— ——— L —— .do—— — — 2 30 55 50 8 15 — ..do— — —— —— do— ———— Me — ..do.— — . — - Lb . — .do__— ——— 2 30 55 50 5 15 — ..do— —— ...... -do— —— ... Hz 1771 — — — — ——do—————— Ir _____do____-_____- M 40 35 5 25 <1...... -do— .—— -... - Ir —— .do—.. — — 3 35 50 60 8 15 Trace.-...... J/32 1 77Q ____-do______.___. Lb — ..do— —— ... H 40 40 10 20 <1...... —— do.—. _-_-.-- L --.do—.. ----- 3 10 75 70 15 Trace- —— ..... H 7' 4 1775 . —— — .. 55 30 3 10 15 /Biotite _ ----- _. -__do— ______Me - —— do——— —— L — ..do— ------H \Magnetite______do____ H o 25 30 /Magnetite.. — __ —— do.—. — .„ Jle 1776----. —— ...... do—.. — —— - L -- — do—.. ---. 55 6 20 — ..do.——— —— H 1777— ————— - -...do——— -.-... L __—do_— — ___ 4 35 50 40 15 —— do— ——— . % 1778______. —— -do—— ______L .--.-do— --- — 1 50 30 20 20 —— do... ——— . .——do— ----- Hz ——do... — ...... -- L —— do—— — „. 20 65 70 15 —— .do— —— — __-_. do______M 1780———— ——— ——do——— ——— Lb -.—do——— —— 1 30 55 20 15 --...do— ______<1— ——— —— M- 1781— — ——— — ..do— - —— — - L -— do—— . — .. U 25 60 3 15 ----do— .---- H 1782————— —— ..—do. ______..___. L .._-_do____--_____ 2 25 50 10 25 - — -do-— ----- —— .do— ——— M 1783— — ——— . —— do. —--„ ——— L ---do—— —— ... 3 40 40 40 8 20 --— do... — —— . ----do... —— ... H 1784——. ——— ...... do—— —— —— L --— do— - —— . X 70 15 3 15 ---do— .. — ... --—do— — ----- Me-M --.-do—— __..__ 1785————— — . —— do———— —— L ---..do— --- — 3 30 50 40 8 20 /Biotite—- — — % (.Magnetite. — .— -——do—— .---_. ?16 1786——————— —— do——————— L —— do... —— — . 5 30 40 30 30

Up to 3. is Up to 2. is Up to 8. 2° Up to 10.

INDEX

A Page Page A structure,______32,59,62 Competent rocks, relation to shape of pegmatites.______12,18 Abstract-.—______1-2 Composition of layers______-__------___-_--_____-______20 Accessory minerals______5, 28 Conglomerate. _--___-______._--_--.-_-----__-_--______4,7 Acknowledgments for aid...______.___-__.-.-.-_...... 4 Cores..______20,26,29,32,52,54,56,57,60,61,62 Age of Brown Derby No. lpegmatite______-_---__-____-______- 4 Country rock.______.__.._._-.-_-_-_---__-_--__-----______27-29 Age relationships, pre-Cambrianrocks______4,6,7,8,9 control on pegmatite shape_---___-______12 quartz andalbite______32 Country rocks, common characteristic.------15 Tertiary tuff-.-_------_--_---_-_-_---__-__---.-----__------_--_-_-_-____ 10 Crawford, K. D., and Worcester, P. G., meiitioned______3 Albite— — — — —— ——— ——— — — ——— ——— — 7,8,24,25,26,27,31,32,43,50,61,62 Cretaceous rocks______.___.______. 9-10 Albite laminae.______31,32 Criteria of replacement. ______---_-_--_--_-__--____.______25 Albite-quartzpegmatite-_-______-___-______.______23, 24, 27, 52 Curved muscovite..-_._-_----_____-__------_-_--_-__-___-___---_-______33 Alkali-content increase, beryl__— — — — _____ — — — — — — —__ —__.... 37,49 Allanite-._-___-__--___--__--_____-___-______----__.------_--______-_- 43-44,60 D Alluvium—— — — — — — — .— — — .——— — ———— — — — . 10-11 Dacite__ —______.---.______5 Alteration, of biotite.------___-___-______-_---__-_-______8,35 Differences, between zoning and banding-___-___-_-______20 of wall rock. ______.-...... -.______._.______44-45 in indices, related to composition,__..__-_-______29,33, 41 Amblygonite.-.-______44 of pegmatites of Quartz Creek from those of other areas______20 Analysis, chemical, of graphic granite______-_-__-__.-.______32 Dikes, granite. See Granite, fine-grained. chemical of lepidolite______41 Dip, pre-Cambrian rocks.___.-______--__--_-_-_----_-__-___-_____ 4,11 chemical, of microlite.-----______43 Distribution, beryl,______------_-______37 partial spectrographic, of tourmaline.. ______38 biotite...______--„_.______35 qualitative spectrographic of unknown mineral. ______44 cleavelandite-bearing pegmatites. .-.._. —- — „_-- — _.. — .______31 Andesine______5,6,10 columbite-tantalite ______.- — — — ——— — — — ——— ——— — —— — —— ——— 39 Anorthite content of plagioclase______. __.-_-______29,48-49 garnet.-.- ______..._._._.______34 Apatite-———— — ———— — — ——— — — —— -. — ——— — - — —— 5,7,8,9,44,53,54 pyrochlore-microlite------— -----—- — -_ 42 Augite....—-_------—- — -— —— — —————— —— — ———— — — 0 layered pegmatites_------__ — ______27 minerals, general-.—______45-46 pegmatites_____.______---_-_--_-_____---____.__.__-_ 8 B Drainage. Banding, across strike______20-23 defined..______...______20 E multiple______——_ ————______._ 23-24 Epidote______--_---_--__--_---_-_-_--______5,7,8,44 Bazooka pegmatite. ______26,44 Essential minerals.___-_---_-___------___-_--_--_-___.______28 Beryl—-----__-_-_--_-_--__-_-__--______-._ 25,28,29,35-37,47,49,50,54,56,62 Extent of district-______— 2 Beryl and Bare Minerals Lode______...... ______. 50,55-56 Beryl-bearing pegmatites. _--______----_---_-_-___.___ _ 30,45-46,50 F Betafite..--______44,52 Fairchild, J. G., analysis by- ____------_---_--_--______..______42 Bibliography.______93-94 Faults.. ___-_-______4,11 Biotite._.. ———— ———— — — —— —— ————— - 5,6,7,8,9,10,25,28,35,46,47,61 Feldspar—.._---_-_--_- — ------—-- — ---_-- 4,49-50,62 Black Wonder pegmatite.___.______40,45,50,59-60 Field work.______-_---_-_-_--_----_-_----.______3 Boron content-----______....______--_-_-_-__------______37 Film perthite______31 Border zones_-_--______20 Fluorine__— — — ___—— —______— _-_-___-___-_.______31 Branching pegmatites__.-_-_.______14 Fluorite.------______44,52,57 Brown Derby No. lpegmatite__ _-______-_-_-_-. 27,39,40,41,42,44,46,52-53 Foliation-....-. —--_----.------— ---__ —------6,11,12 No. 2 pegmatite,. ______26 angle between plane of and pegmatite———— — — — — — — — __ — ___ __. 12,18 No. 3 pegmatite. ______.______26 Footwalllayers.-.-_-_---.-_.._-___-_-__---_-_-----__------_---_-______26,29,46,53 No. 5pegmatite__...______53-54 Fossils .______---______.....____ 10 Buckhornpegmatite,.______32,50,58-59 Fractional crystallization....______—— ______— ______48, 49 Buckypegmatite._.______3,40,44,50,60-62 Fracture fillings—------24, 32, 49, 59, 60, 62 Fractures, emplacement of pegmatites along.___- — —— — — - — _ —______12 sheared and mineralized--._ — _-_ ——— — - — ______— ------______.- 11 Calculations of percentages for table 20 ______3 Frequency of occurrence, minerals------_____-______„_____ 28 Chlorite______6,7,8,44 shapes __-————----_------_ — — — -_----_---_------_---_-___.______11,15 Chrysocolla ______...______57 Classification of internal units.______20 G Cleavelandite———_ —————— — —— —— ————— ———— ______29-31,40,52 Gahnite--- —------__ 43, 52, 56, 62 Cleavelandite-bearing pegmatites_-___-_--______....______27,50 Garnet———————-———. —— . —— — — — —— —— — 23, 24, 25, 28, 34-35 Clinozoisite______5 Geologic work in Quartz Creek district, other___— — ______.______— — ._ 3 Color, lepidolite.______40,41 Geology, general statements—____— — _-_- — ______— ______4, 11 quartz....______32 Glacial deposits. See Till. pyrochlore-microlite______42 Gneiss, hornblende.------__-__———_--—--—- — -_-__--_--__------_. 6 tourmaline.--..______..______._____„.--..-..-______37-39 Granite, coarse-grained—______—-____--__—__.__-.- 7,12,15, 37, 50 Columbite-tantalite____....______.__ 39-40,52 fine-grained. ______.__._-______-______8-9,37 109 110 INDEX

Page Granite gneiss.— ————— — — — — — — — — — —_--—__ — —— _ — ___— — — — 8 Mineral associations, pyrochlore-microlite—-- —--__-_-____— — — — — — — — 42-43 Qraphicgranite---... —.--.---.------. — --.-.----- 32, 37, 46, 50, 61 tourmaline_—__—_ — _———— — — „ —-—— — — _ — — -- — — ——------37 Mineralogy of pegmatites, general features— — ———— — — — — — ——— — —— — 28-29 individual units. — -._-_-.------_---_-___--___--- — _— — — — — — - — — 66-107 Hanging-wall layers__— — — — — — — —_—— — — ——— — — — — — — 26, 29, 49 Mining activities.——— — ——— — — — — — — — — — — — ———— — — — — — — 3 Heterogeneous pegmatites------.-.------_--_____.——— — — ——— — — — 25 Monazite.--.------—„- — -- — — -- — ---. — --. — --- —— - — -- 40,45,47,50,52 features of------_----_---_------_-----__----___.______48 Morrison formation_———————————————————————————— 9 Higher refractive index, beryL-.--_-____.-..__-__.______—— 36 Multiple pegmatites.-______------—— 23,27 tourmaline.-.------_------_------_-__---_------_-__ 38 Muscovite—------5,23,25,28,32-34,47,56,61,62 Homogeneous pegmatite.------— ------__--_--_--_--____._-__-____ 25, 29 Muscovite-albite pegmatite..___- — _-_ — -—— — — — — — -_ — — — —__-_____- 26 Hoods, concentration of perthite in.,------_-_-_--_-_..---._-___ 26-27 Hornblende.------_------___--__-__------. 5, 7 N Hornblende-biotite tonalite,. —------5-6 Niobium and tantalum....-_____.-.._..---__--_-_---_-_------39-40,42,47,48 Hornblend gneiss-______----„..„.. --______.__.___ 6, 12,15, 29 Host rock of the pegmatites_._ ____-_--_--___-__-_-_------______.-.-.-.. 12 Occurrence, beryl_._.-____.-______-_------_--_----___-___--_--_------36 biotite__..__--__--_-----______------_-_- — -.__---.------— --.- 35 cleavelandite--————- —— - — — — — - — — — —— —— — — - 29,30,31 Incompetent rocks and pegmatite shapes------15,18 columbite-tantalite------_------_------39 Increase of refractive indices, lepidolite-----— ------_-__-__._---____ 41 garnet-__-.--_-___.__-__-______------_--_.-._ — — — — — ——— 34 muscovite______-_-._--.__.___-____-__--_-__-___._-___... 33, 34 lepidolite------41,42 Index determinations.-.------_--__------.-----.------_-_---..__ 4 muscovite------— ----- —— — — 32 Indices, variations in---__--_-___-__------_---_-__-_____.___....--_... 28 quartz-..-._------_ — -_-- — — ___---___-_ ------— ------— - 32 Interaction of minerals-_.------______------__-_----._---. 25 perthite-- —— — ——— — - — -—————— — — ——— - — -———— 31,32 Intermediate zones. ——— —— ————— —— ————— 20, 26, 32,40,54, 57, 59, 60,61 pyrochlore-microlite.------— ______— _ — — ------42 Internal structure, heterogeneous pegmatites, origin. ___-_-__-__--______-.____ 48-49 tourmaline---- — — - — —— — —— —— —— —— ——— — — — — ——- 37,38 Intrusive rocks, granite.__.______-__.--__-„------.-...... -.. 5-9, 46 Opportunity No. 1 claim..______-___-_.___.______- 43,51-52 Iron content, lepidolite-_-----_-----__----- — - — —-_ — — _-___-_--——_ ——_- 41 No. 4 claim— — ——— ————— — — ——— —— ———— — ——— 27 muscovite.----_----_--__-_--.--.--. ——-— ———_-______.....____._.. 33 Optical angle, mascovite__----_-----.-_-______-_____------33 Irregular pegmatites__—— — __ — ____—__-_-—--————_—______— — 12,15, 17, 20 Origin, granitic pegmatites_____ —_-_—_ ——- — — _—— — - — _----_-_---_--- 46,47-49 lenticular and lenticular-branching pegmatites_-_-_-__-._-----_------27 line rock.—.—-__—_—- ——— — — _---_ — __-__ — — — _—- ———---——— — — 24 Joints...._-..---.._.— _— — _—_—— — — — -—— — — — Orthoclase, lack of-.____-.__._-__-______---___——.—-— 31 attitudes,.--.---_.-----.....-....------. Oval type shape..------12,15,16,20 Joint systems, contrasted in mafic rocks and granite- Jurassic rocks_------_---._—_------_.

K Pegmatite 216- Kaolinization. 62 251- ———— ————— — ———— ——— ——— . 252. See Opportunity No. 1 claim. Layered pegmatites __ ----_--__-______---_------__---_-___--_-______20,22,26 279- __ ———————— ————— ——— —— . 37 distribution,...... --______— __ 27 306. See Opportunity No. 4 claim. Layered structure. See banding. 417-———— —————— ——— ——— ——— — . Lenticular pegmatites...- ______------_ ___ .______12-15,20,23,27,56 452. See Brown Derby No. 1 pegmatite. Lenticular-branching pegmatites.. „ ______--..„...... 15,20,23,27,51 453. —— —— — — — —— — — — —-. Lepidolite-.-- — ---- — — ------.------.-._.------38,40-42,50,51,54 54-55 associated with cleavelandite...... ______.--...__-...... _ . 31 538------55 associated with topaz. — —— — — — -- — - ——— — .------______43 548------20 Lepidolite-bearing pegmatites. ---.-----_------_---_------..- 27,41,50 590--. —— ——— — —— — —— — — - 55 Limonite.— __ —————————————— _ ._.- ______-_---..--__ 10 656. See Buckhorn pegmatite. Line rock ______.._ __ , ______, ______. 23-24,34 847. See Black Wonder pegmatite. Lithiophillite-triphillite— ------.------_------— - 44,62 10%------—— —------—— — — — —— - — - — - — — — — — — ------24 Lithium-bearing pegmatites..- ______— ---- ______.______. 37 1234-- — — — —— — - — — — ——— - ——— ——— — — — —— - — — — 39 Location of area. ----__---__-_-__--_---_------._-----__ _ — — — 2 1363------__-___-----___.._____.______--____ 26 Localization of minerals, probable origin— -----_-__——---______--——___ 48 1402. See Trio No. 1. Lower refractive index, beryl— — — — — ——— — — — — — — — — ______36 Pegmatites, in general—_--______-_____._-_-_ ———————.— 25,45,47 cleavelandite. ---.______29,30 of Quartz Creek district, general statements.. — ______._-_._-—————— 11-12, monazite.-. ______-___-_-__--____-_-___-______. 40 15-18, 25, 29,37,45, 46, 47, 48, 50 plagioclase ______..-_-.--_.-.-.--_---._ _ ---____-_---_-_-----__-__ 29 low boron content------37 lack of tantalum____.___._.______— ___ — .—-—————— 39 M lack of tourmaline------— ------37 Mafic minerals- ---__-__--__-_------_ -—_—______-- ——___ 7 Pegmatites showing variation along strike.------——- 20,23, 27, 51-52 Magnetite-----. — --.. ._.__- ______----.---_------. 5,6,7,9,25,28,35,46 Perthite------24,25,26,27,28,29,31,32,51,62 Manganese. ______-_-__.-______-___-_____-______...._.____ 39 Perthitelayers- ——— - — — -- — — - — - — ———— —— — —— 27,37,49,50 Mapping. ----_-_ _ --___-___ _ —————— _ _ — — — _— __ _.-..____ 3,61 Perthite-quartz pegmatite, — _------— —. ———— — — — — — 24 Martite. See Magnetite. Perthite-quartz-albite pegmatite- — --- — .— _-_— — — - — — _._____-_-— 23,24,26 Median refractive index, biotite_--_-_- — ------_ — — — — — — 35 Pillow lavas...- — -_------__-______-_-_-_------5 Median refractive index, muscovite ______33 Plagioclase------5,8,9,25,28,29-31 Mergingoflayers-- — — ——_ — ______— _-_-_ — -_--_--_-__--_-- — - — — ____-_- 20 Plutons——— —— ——— ——————— —— —— ———— — —————————— 7,46 Mica, scrap- ______-__---- ______- _ ____ 50,56,61,62 Pods.-.-.----.__...._--.---..--.---.--.--_----.--.__------_--- 53,55 Mierocline— ______-_-______, ___ _-_-_-_ _ __ —— —— — — — — 4,6,7,9 Polylithionite-.------43 lack of ______„--._-_- ____ . ______31 Pre-Cambrian rocks — ______---__ — — — ———— — ——— ——— — — — ——— 4-9 Microlite— ——— — — — — — — — — — — ———— ———— — — __ — — 41,42,52 Prism faces.----- — ----.---.------37,39,40,43 Mineral associations, beryl. _-____-.-___—---_--__—— — — __—______— 37 Production. _---.---.---___-__--___---_------3,61 cleavelandite __ — _ — — — _ — — ___-- — — - _ _------__----_----_-----__ 31 Purpose of investigation —___ — ------3 columbite-tantalite- ______---______. __ - _ - _ 40, 48 Pyrochlore-microlite------42-43 due to (Xjmmonions- — .- ———— — _ — — ——— — — — — — — — — — — — — _. 48 garnet— _ _ -.-.-...-. __ -._._-___------___---___-______._.__.- 35 lepidolite.. _ . __ ...... __ ___ .. ______-.. _ — ... — . — . _ 41 Quartz...-._.--_-_--._---_--_--__-_--____-__----_--_---___----- 5,6,7,8,26,27,28,40 monazite __ _.-_-_-_ _ ...... -----.._.....--_. _-___-.--_--_-_._._ 40 Quartz monzonite------.------—------7,15,29,37,46,50 INDEX 111

Page Quartz pegmatite______24 Systematic variation, in beryl--.------.------— 37,49 Quartzite______4,5 in plagioclase------— ------29,49 Quaternary rocks.... ______.______10-11 in tourmaline ._____._------_- — _-.______--_---_. 38

R T Radioaeti vit y. .--___ — — — — — — — _ — —__ — — — — — — — — — — — — — —. 42,44 Reeves...__...... ______— — — — — —— — — — ____ — — — __ 82 Tantalum. See Niobium and tantalum. Refractive index related to specific gravity_ - ______34 Tertiary rocks.______— -_-. — --—. Relict structures_— _— — __— — — — — —____—_ —— _ — __ —— -_ — _____ — ._ — 25 Texture _ — _ — — — ——--— — — — — - — — — Replacement units...... _...__.....______24-25 Thickness, Dakota sandstone. — ——- — Rest solutions, reaction withcrystals— — — — ——— — __— — _ ——__——-__-__ 25,43,48 Morrisonformation.. _____----______. Reserves...______..______.___— —_____ 49-50 t iff-..... —_„_. ——- — — -- — _ — . 10 TiU-...— — ..--—— — — — — — -- — --- — — -- — — ------— 10 S Tonalite- — — — . — — .- — --- — -- — - — --- — --- — ----- 5-6,12,15,29 Samarskite. 44,52 Topography. _ ———————————————————————————————— 2-3 Sandstone.. 9 Topaz.. ______— - — - 41,42,43,50 Scapolite_ — 10 Tourmaline-— ------25,37-39,41,45,49 Schist...... 5 Trio No. 1 pegmatite------— ______— _.-. 60 Sericite.__ 6,7 Tuff..-.....------— ------10 Shale...... 9 Shanin, V., cited...__._.____.______39 U Shape of pegmatites_.______.__..___._.____.____ 7,12-15 Size, average, of mineral grains in pegmatites. ______47 Unzoiied pegmatites. See Homogeneous pegmatites. beryL._---._..______35-36 biotite_—_ _ ——_ — — _ — _ — — _—_ — — — - — — — — — ——— — — — —_____ 35 V cleavelandite--—— — — — — —— — — — — —— — _-__ — — ___—— — — _ ——— — — 29 Vein perthite_ ...-______-_------31 garnet---______.___._._...______...__.______..____..______..____. _ 34 Vesicles— .... _- — — . ———_ — — --- —— - — ——— —— -- — ----- 5 magnetite...... _._...______35 Volatile materials—_...______-----_.---- —..--______-_.--_____-______45,47,48 perthite_-___ — ______32 pyrochlore-microlite. -______-.-_—______— __ — — __ — __ — ___ ——___ 42 of pegmatites.______11 W Specific gravity, monazite.. — —- — — — --— — — _ — — — — — _— — — — —— ——- 40 Wall zones—— -____. —------20,26,29,48,52,53,57,58,59,60,61 related to columbium-tantalum ratio___--____-___--____-_.__-_-____.... 39 Watermelon tourmaline-.___.----_____-_-_------_-___--_-—---_------38 related to refractive index in garnet.______34 Well-zoned pegmatites, plagioclase in_ — _. — — ____.__.._____----. — --..-_-___ 29 Specific gravity determinations.______4,39,40 White Spar No. 1 pegmatite------3,57 Spectrographic analyses ______38 White Spar No. 2 pegmatite------3,26,56-57 Sphene.-..___....______.______.. 6 Spodumene.———_____--_--.__..---..-_-...______. 44 Stevens, R. E., cited.______..._...... _-_.. 41 Zircon....---.--..--___-----.------.------.------5,6,7,8 Structures, of pegmatites..____..____.______-__..___.-._... 20 Zonedpegmatites—------21,25-26,29,37 of rocks——-.--._-___-..__.____.-.---.----.--.__----.---_---..... 6,11 lepidoliteandpyrochlore-microliteincores—------— --- — — - — - — ---_- 42

U. S. GOVERNMENT PRINTING OFFICE: 1955