/7

Geology of the High 

Climb Pegmatite 

Custer County 

South Dakota

GEOL.OGICAL SURVEY BULLETIN 1015-C

Geology of the High 

Climb Pegmatite 

Custer County 

South Dakota

By DOUGLAS M. SHERIDAN

A CONTRIBUTION TO ECONOMIC GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1015-C

This report concerns work done partly 

on behalf of the U. S. Atomic Energy 

Commission and is published with the 

permission of the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1955
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 65 cents (paper cover)
CONTENTS

Page

Abstract. _ ________________________________________________________ 59

Introduction ______________________________________________________ 60

Location and surface features______________________________ 60

Ownership and production-_____________________________________ 60

Mine workings________________________________________________ 62

Previous work_________________________________________________ 62

Present investigation____________________________________ 62

General geology. __________________________________________________ 63

Regional setting.___________________________________________ 63

Metamorphic rocks ____________________________________________ 63

Quartz-mica schist-________________________________________ 64

Micaceous quartzite_______________________________________ 64

Porphyroblastic quartz-mica schist___________________________ 64

Lime silicate-quartz lenses __________________________________ 65

Graphitic schist- __________________________________________ 66

Altered rocks adjacent to pegmatite__________________________ 66

Pegmatite ____________________________________________________ 67

Quartz veins._________________________________________________ 67

High Climb pegmatite _____________________________________________ 67

Size, shape, and structure_______________________________________ 67

Pegmatite units _______________________________________________ 71

Albite-quartz pegmatite.___________________________________ 73

Albite-quartz-muscovite pegmatite.-_________________________ 74

Perthite-quartz-albite pegmatite.____________________________ 78

Quartz-cleavelandite pegmatite._____________________________ 79

Quartz pegmatite._________________________________________ 84

Quartz-perthite-muscovite-albite pegmatite ___________________ 84

Muscovite pegmatite.______________________________________ 84

Origin, _______________________________________________________ 84

Mineral deposits.______________________________________________ 91

Amblygonite- _____________________________________________ 91

Beryl.___________________________________________________ 91

Columbite-tantalite__ _ _____________________________________ 92

Potash feldspar.-__________________________________________ 93

Mica___________________________________________________ 93

Reserves-____________________________________________________ 94

Amblygonite_ _ ____________________________________________ 94

Beryl and mica__________________________________________ 94

Potash feldspar___________.________________________________ 94

Literature cited.___-__-_-_-_--_-___-_-__________-______-__--_-___.. 95

Index______.____________________________________________________ 97

ill
IV CONTENTS

ILLUSTRATIONS

Page

PLATE 7. Geologic map and sections of the High Climb pegmatite, __ In pocket 

FIGURE 13. Map showing location of High Climb pegmatite. ___________ 61

14. Large outcrop of schist at east corner of main pit__ _________ 68

15. Roll in pegmatite contact, southern end of northern part of

High Climb pegmatite__________--_-___---_--_________ 69

16. Large roll in pegmatite contact, northeast side of High Climb

pegmatite. __________________________________________ 70

TABLES

TABLE 1. Average mineralogic compositions of zones in the High Climb

pegmatite, based on visual estimates of all exposures _____ 72

2. Variations in grain size and mineralogic composition of albitequartz pegmatite (wall zone), High Climb pegmatite______ 73

3. Mineralogy of albite-quartz pegmatite (wall zone), High Climb

pegmatite ___________________________________________ 75

4. Mineralogy of albite-quartz-muscovite pegmatite (first intermediate zone), High Climb pegmatite.__________________ 76

5. Mineralogy of perthite-quartz-albite pegmatite (second intermediate zone), High Climb pegmatite^ ______ ____________ 80

6. Mineralogy of quartz-cleavelandite pegmatite (third intermediate zone), High Climb pegmatite___________________ 82
A CONTRIBUTION TO ECONOMIC GEOLOGY

GEOLOGY OF THE HIGH CLIMB PEGMATITE, 

CUSTER COUNTY, S. DAK.

By DOUGLAS M. SHERIDAN

ABSTRACT

The High Climb pegmatite, Ouster County, S. Dak., belongs to the series of 

pegmatitic and granitic rocks that characterize the Harney Peak region of the 

southern Black Hills. It intrudes pre-Cambrian metamorphic rocks consisting 

chiefly of quartz-mica schist. Along part of the pegmatite contact the country 

rock has been altered to a tourmaline-rich schist.

The structure of the pegmatite, in general, is concordant with the westwarddipping schistose structure of the country rock, but locally the pegmatite cuts it. 

The main part of the pegmatite is an irregularly shaped pipe that plunges 45° N. 

40° W., parallel to the average plunge of rolls in the footwall. A small northern 

extension of the pegmatite has a lenticular shape, and cuts the schist at a low 

angle. Rolls in this part of the pegmatite have an average plunge of 28° N. 25° 

W. One large north-trending crestal roll divides the outcrop of the northern 

segment of the pegmatite into two parts.

The pegmatite has a well-defined internal structure and is made up of five zones. 

The outer units, a flue-grained wall zone consisting of albite-quartz pegmatite, and 

a medium-grained first intermediate zone consisting of albite-quartz-muscovite 

pegmatite, form incomplete concentric shells. The second intermediate zone, 

perthite-quartz-albite pegmatite, forms a hood-shaped unit between the outer 

units and the third intermediate zone along the crest and hanging-wall of the 

pegmatite. The third intermediate zone, a concentric shell of quartz-cleavelandite pegmatite, surrounds a lenticular core of quartz pegmatite containing 

altered spodumene. In addition to the five zones, a fracture-filling unit of quartzperthite-muscovite-albite pegmatite and a possible sixth zone (or replacement 

unit?) of very fine-grained muscovite pegmatite were recognized.

The essential minerals of the pegmatite include microcline-perthite, quartz, 

albite, and muscovite. Accessory minerals include tourmaline, beryl, arnblygonite 

(variety montebrasite), apatite, columbite-tantalite, loellingite, altered spodumene, many unidentified dark-colored phosphate minerals, a manganese-bearing carbonate, garnet, and chalcopyrite.

A satisfactory explanation of the origin of the pegmatite requires processes of 

fractional crystallization and incomplete reaction in a restricted system. The 

concentric zonal structure and the general increase in grain size from the wall

59
60 CONTRIBUTIONS TO ECONOMIC GEOLOGY

zone to the core suggest that the pegmatite units formed in successive order by 

crystallization from the walls inward. No true replacement stages occurred.

Beryl, amblygonite, potash feldspar, columbite-tantalite, scrap mica, and sheet 

mica have been produced as industrial minerals.

INTRODUCTION

The High Climb pegmatite is a zoned pegmatite that has been the 

source of amblygonite, beryl, mica, feldspar, and colnmbite-tantalite. 

Geologic interest has been stimulated not only by the economic possibilities of the pegmatite as a source of beryl and scrap mica, but also 

by its complex structure and its unusually well developed series of 

zones containing widely varied mineral assemblages.

LOCATION AND SURFACE FEATURES

The High Climb pegmatite in Custer County, S. Dak., is near the 

section line between the SE%, sec. 22 and the NEi/4, sec. 27, T. 2 S., 

R. 4 E., about 6 miles north of the town of Custer, and just south of 

the Pennington County line (fig. 13). A road log from Custer to the 

pegmatite is given below:

Miles 

0.0 At Custer County Bank, Custer, South Dakota. Travel north on State

Route 16A (fig. 13). Recently changed to U. S. Highway 16. 

6.3 Turn right to ungraded road. 

6.5 Travel across small intermittent stream in Tenderfoot Gulch, under

the Chicago, Burlington, and Quincy Railroad trestle, and across

small log-dirt bridge. Proceed north along Tenderfoot Gulch. 

6.8 Road crosses small stream and winds northeastward up the slope on

the east side of Tenderfoot Gulch. 

7.0 Road turns sharply to the right at crest of ridge and winds across

small valley. 

7.3 High Climb pegmatite.

The pegmatite crops out between altitudes of 5,680 feet and 5,750 

feet on the east side of Tenderfoot Gulch and 011 the west side of a 

northward-trending ridge approximately 300 feet above the floor of 

the gulch. The relief of the area is rugged, and the pine-covered 

slopes drop steeply to the valleys below.

OWNERSHIP AND PRODUCTION

The High Climb pegmatite is on an unpatented claim owned by Mrs. 

Gladys Wells and Mr. Fred Heidepriem, both of Custer, S. Dak. 

Mining operations on the claim began in 1932 and have been continued 

intermittently since then.

Minerals that have been produced from the High Climb pegmatite 

are amblygonite, beryl, columbite-tantalite, scrap mica, punch and
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 61

R. 4 E, R. 5 E.

FIGDEB 13. Map showing location of the High Climb pegmatite.

plate mica, and feldspar. W. C. Stoll a received the following data 

from Mrs. Wells on the approximate total production through 1940:

Amblygonite___________ Estimated 100-350 tons (no accurate figures available)

Beryl_______________. 60 tons

Scrap mica__________ 100 tons (including about 150 pounds of

punch and sheet mica)

Feldspar_____________. 150-180 tons

Columbite____________. 100 pounds

In 1944-^5 the mine was worked intermittently for feldspar, but no 

production figures are available. In 1948 the mine was operated for

1 Stoll. W. C., 1942, Map and brief accounts of the High Climb pegmatite, Custer, S. 

Dak. [Unpublished memorandum report in the flies of the U. S. Geological Survey.]
62 CONTRIBUTIONS TO ECONOMIC GEOLOGY

beryl and scrap mica. Mrs. Wells and C. K. Koch, the mine operator, 

have provided the following figures for 1948:

Beryl________________ 4,832 pounds shipped, and approximately

2,000 pounds mined but not cobbed 

Scrap mica _________. 25,270' pounds

According to Mrs. Wells (oral communication, 1951), production 

since 1948 has been negligible, and no production figures are available.

MINE WORKINGS

The High Climb pegmatite has been mined by two opencuts in the 

southern end of the body and three small opencuts to the north. The 

main pit extends 140 feet southeast across the southern or main part 

of the pegmatite (pi. 7) ; the pit is 50 feet wide and 42 feet deep. The 

main pit was originally operated from an opening in the southeast 

side of the pegmatite; a large dump made at that time extends 160 feet 

southeast from the pegmatite. More recently the lower part of the 

main pit has been mined through the narrow cut that opens to the 

northwest (pi. 7) at an altitude of 5,710 feet. A smaller opencut, 40 

feet long, 30 feet wide, and 20 feet deep, is 30 feet northeast from the 

lower entrance to the main pit. The large dump, extending 170 feet 

to the northwest, consists of rock derived from operations in the lower 

part of the main pit and in the smaller opencut.

Three small cuts are in the northern part of the pegmatite; the 

largest of these is only 10 feet deep. One small prospect trench 

to the northeast of the pegmatite was cut in schist.

PREVIOUS WORK

In 1941 Fisher (1942, p. 17-23) prepared a generalized map of the 

High Climb pegmatite and the mine workings; Fisher's report includes descriptions of the geology, mineralogy, and paragenetic relations, and also sections showing the mineralogic and textural relations on the walls of the main pit. Fisher (1945, p. 18-20, figs- 4 and 

5) later illustrated and described a process of so-called "albitization 

of microcline", using examples from the High Climb pegmatite. In 

1942, W. C. Stoll 2 used Fisher's map as a base for preparing an unpublished memorandum on strategic minerals for the files of the U. S. 

Geological Survey. The results of Stoll's examinations were revised 

by J. W. Adams (Adams and Stoll, 1953, p. 131).

PRESENT INVESTIGATION

The purpose of the present investigation was to make a study of 

the internal structure and the lithologic units in the High Climb 

pegmatite, as a contribution to the Geological Survey's investigations

2 See footnote 1, page 61.
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 63

of the pegmatites of the Black Hills. Although previous workers had 

prepared generalized maps and collected descriptive data, no detailed 

map or systematic study of the internal structure had been made.

The field work was carried out intermittently from July through 

December 1948. This work was done partly on behalf of the Division of Kaw Materials of the Atomic Energy Commission. A detailed 

map (pi. 7) and geologic sections (pi. 7) w^ere prepared, using planetable methods. K. E. lioadifer, V. K. Wilmarth, J. J. Norton, and 

L. R. Page assisted the writer during the mapping. A. J. Lang and 

D. B. Stewart measured beryl crystals on typical exposures.

Microscopic studies of grains and thin sections of pegmatite minerals were carried on at the University of Minnesota from January 

to June 1949.

The writer is indebted to Mrs. Gladys Wells, Mr. Fred Heidepriem, 

and Mr. C. K. Koch for providing production figures and information 

regarding the mineralogical character of mined-out parts of the main 

pit. The writer appreciates the advice of Professor S. S. Goldich and 

other staff members of the Department of Geology and Mineralogy 

of the University of Minnesota during the laboratory investigations.

GENERAL GEOLOGY

REGIONAL SETTING

The Black Hills of South Dakota is a mountainous area resulting 

from erosion of a domal uplift, the long axis of which strikes northnorthwest and is 125 miles long; the uplift is about 60 miles wide. 

The central part of the Black Hills consists predominantly of igneous 

and metamorphic rocks of pre-Cambrian age that crop out in an area 

60 miles long and 25 miles wide. Paleozoic and younger sedimentary 

rocks dip away on all sides from the pre-Cambrian area and form inward-facing scarps of hogback ridges.

The southern part of the pre-Cambrian core of the Black Hills contains many intrusives of pegmatitic rocks in a 250-square mile area 

surrounding Harney Peak. Many of the intrusives approach granite 

in texture and composition, whereas others are well-zoned pegmatites. 

The High Climb pegmatite is one of the well-zoned pegmatites. It 

lies about 5 miles west of Harney Peak (fig. 13).

METAMORPHIC ROCKS

The country rocks of the High Climb pegmatite consist of a series 

of metamorphosed pre-Cambrian sedimentary rocks, now mainly 

quartz-mica schists. The schistosity of these rocks, in general, strikes 

X. 20°-30° E. and dips from 40° to 85° NW. Bedding has approximately the same strike as the schistosity, but usually dips about 10 

degrees less than the schistosity.

309393 55 2
64 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The country rock has been shown on the map as consisting entirely 

of quartz-mica schist, with the exception of one outcrop of graphitic 

schist cut by quartz stringers in the northwest corner of the area 

(pi. 7). Interbedded with the quartz-mica schist, however, are less 

abundant beds of lime silicate-quartz rock, micaceous quartzite, and 

porphyroblastic quartz-mica schist.

QTJARTZ-MICA SCHIST

The brownish-gray to silvery quartz-mica schist crops out in wellfoliated beds that alternate with micaceous quartzite, lime silicatequartz rock, and porphyroblastic quartz-mica schist. The beds range 

in thickness from less than an inch to more than 12 inches. All gradations exist between schist and quartzite.

Study of thin-sections indicates that the quartz-mica schist is composed of quartz, 40 to 50 percent; biotite, 30 to 40 percent; muscovite, 

10 to 20 percent; zircon, less than 1 percent; and traces of magnetite, 

garnet, apatite, microcline, plagioclase, and tourmaline. Most of the 

individual grains in the schist are about 0.01 inch or less in size. Some 

of the muscovite occurs in relatively coarse plates that cut across 

quartz grains.

MICACEOUS QUARTZITE

All gradations exist between massive, blocky micaceous quartzite 

and schist. In thin sections the micaceous quartzite is seen to consist 

of quartz, 85 to 90 percent; biotite, 10 percent; muscovite, 1 percent; 

zircon, less than 1 percent; tourmaline, less than 1 percent; and traces 

of garnet, apatite, and magnetite (?). The quartz grains have a granoblastic texture, but the platy parallelism of the mica grains gives 

the rock a definite schistose appearance. Skeletal tourmaline crystals 

are present in amounts as much as 4 percent in quartzite near small 

pegmatite stringers. The tourmaline has quartz inclusions and 

cuts across biotite flakes.

PORPHYROBLASTIC QUARTZ-MICA SCHIST

Part of the quartz-mica schist contains 5 percent or more of porphyroblasts and augenlike lenses. These rocks include quartz-micagarnet schist, quartz-mica-garnet-chiorite schist, and quartz-micagarnet-si llimanite schist.

The quartz-mica-garnet schist contains 5 to 10 percent garnet, in 

reddish-brown to pink euhedral grains ranging from less than 0.05 

inch to 0.15 inch in diameter. With the exception of garnet, the proportion of other minerals is the same as in normal quartz-mica schist. 

The foliation ordinarily bends around the garnet grains, but in some 

places it is cut by the garnet. Most of the garnet crystals are euhedral 

and contain numerous poikilitic inclusions of quartz, but some very 

irregular crystals enclose both quartz and biotite. Zircon, apatite, and
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 65

magnetite (?) are minor accessory minerals. Some of the apatite is 

granulated. Minor amounts of tourmaline occur in parts of the 

quartz-mica-garnet schist.

Quartz-mica-garnet-chlorite schist is similar to the quartz-micagarnet schist, but characteristically is more crumpled and contains 

green-black metacrysts of chlorite, 0.2 inch to 0.5 inch in length. 

Some of the dark-colored metacrysts have the shape of a cross, and 

thin-section studies suggest that some of these metacrysts may be a 

result of retrogressive metamorphism of staurolite twins. Most of 

the garnet grains exhibit euhedral or skeletal forms and appear quite 

fresh, but one grain observed in thin-section has been altered 

to a fine-grained mass of chlorite. Pod-shaped aggregates of relatively coarse quartz and muscovite are irregularly distributed in the 

rock. The muscovite in these aggregates cuts across the elongated 

quartz grains.

Quartz-mica-garnet-sillimanite schist contains small grayish-white, 

augenlike lenses, 0.1 to 0.3 inch in length. Thin-section study of this 

schist indicates that the general composition is much like that of the 

quartz-mica-garnet schist, but the small lenses contain sericite and 

relicts of sillimanite. Sericite surrounds and apparently has replaced 

the sillimanite, and it cuts quartz grains around the margins of the 

lenses. The sericite is probably younger than the relatively coarse 

biotite and muscovite in the matrix of the schist.

LIMB SILICATE-QUARTZ LENSES

Iii the northeastern part of the mapped area (pi. 7) lime silicatequartz lenses, ranging from 1 foot to more than 20 feet in length and 

from 1 inch to 12 inches in thickness, are interbedded with quartz-mica 

schist and quartzite. The lenses have a pale reddish-white to greenishwhite central layer bordered on both sides by darker colored marginal 

layers that characteristically have greenish-black grains of amphibole 

oriented parallel to the surfaces of the lenses.

The light-colored central layer shows no orientation of the minerals 

and is composed of quartz, 50 percent; plagioclase, 25 percent; garnet, 

10 percent; pyroxene, 10 percent; zoisite and/or clinozoisite, 5 percent; 

and less than 1 percent sphene. The minimum index of refraction 

(N«') of cleavage fragments (001) of the plagioclase is 1.576 ± 0.001, 

indicating that the composition is about Ab10An90 , that is, bytowniteanorthite.3 Zoisite in irregular grains is intimately associated with 

the plagioclase. Some of the grains have the slightly greenish yellow 

interference color characteristic of clinozoisite rather than the anomalous blue color of zoisite. The pyroxene is mainly diopside, but several grains have extinction angles that indicate the variety pigeonite.

3 The plagioclase curves used for this report are those after Tsuboi, as diagrammed by 

Wmchell (1951, p. 280, fig. 173).
66 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The banded marginal layers of the lenses are composed of quartz, 45 

to 50 percent; amphibole, 20 to 25 percent; plagioclase, 15 to 20 percent; garnet, 5 to 10 percent; zoisite and/or clinozoisite, 5 percent; 

sphene, less than 1 percent; and a trace of rutile. The amphibole is 

probably hornblende, but was not identified specifically. The plagioclase is highly calcic, as in the central layer.

The occurrence of the lime silicate-quartz rock as conformable lenticular layers in the metamorphosed sedimentary series suggests that 

it was originally a calcareous sediment, probably a calcareous silt or a 

calcareous argillaceous sand. The presence of pyroxene in the central 

layer and amphibole but no pyroxene in the well-banded marginal 

layers is not so easily explained. Runner and Hamilton (1934, p. 

51-64) have studied similar rocks in the southern Black Hills, but their 

report deals mainly with metamorphosed concretions that have similar characteristics. They suggest that there were two periods of 

metamorphism: an early period in which the lime silicate minerals 

and quartz were formed, and a later period in which outer layers were 

altered under stress to a banded amphibole-bearing rock.

GRAPHITIC SCHIST

Dark-colored graphitic schist crops out along the northwestern margin of the mapped area (pi. 7). The schist is cut in an intricate manner by abundant, irregular quartz veins. In thin-sections the graphitic material obscures the other minerals, but there are abundant 

minute crystals of tourmaline, in addition to graphite, quartz, biotite, 

and muscovite. The tourmaline may have been introduced at the 

time of the formation of the quartz veins.

ALTERED ROCKS ADJACENT TO PEGMATITE

The country rock along the pegmatite contacts has been variously 

altered to tourmaline-rich schist, muscovite-rich schist, and a nonschistose rock consisting of tourmaline, quartz, and plagioclase. The 

altered rock does not form a complete shell surrounding the pegmatite ; along much of the contact no significant alteration was observed. 

The outcrops of altered rock have not been differentiated from 

"quartz-mica schist" on the map (pi. 7) because of their small size and 

irregular distribution. Thin stringers of pegmatite (less than 0.25 

inch thick) are common as lit-par-lit injections in the altered rock.

Tourmaline is the characteristic mineral of most of the altered rock; 

it forms as much as 75 percent of the rock near the pegmatite contact, 

but decreases in abundance outward from the pegmatite. The thickness of the tourmaline-rich schist rarely exceeds 4 feet. Tourmaline 

crystals are euhedral and have irregular color zoning from brown 

through grayish to light green. Quartz is included in the tourmaline. 

Quartz generally forms at least 25 percent of the tourmaline-rich 

schist, and muscovite is an esential constitutent of the outer part of
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 67

the altered zone. Accessory minerals are zircon, apatite, garnet, plagioclase, and microcline. In some places thin continuous layers of 

relatively coarse quartz are parallel to the schistosity.

A nonschistose rock, usually less than 6 inches thick and consisting 

mainly of tourmaline, quartz, and plagioclase, occurs along some of the 

discordant pegmatite contacts. Although the platy minerals are not 

parallel, this rock is very similar in character to the tourmaline-rich 

schist.

A less common type of altered rock, a schist, containing as much as 

SO percent muscovite, occurs as a 6-inch layer along part of the pegmatite contact. Clusters of tiny crystals of green apatite are abundant in this schist one-fourth to one-half inch from the pegmatite 

contact. The muscovite (average grain size, 0.05 inch) is generally 

coarser than in schist farther from the contact.

PEGMATITE

The High Climb pegmatite is a lenticular, well-zoned body containing quartz, albite, microcline-perthite, muscovite, tourmaline, beryl, 

amblygonite, apatite, columbite-tantalite, loellingite, spodumene, 

many dark-colored phosphate minerals, a manganese-bearing carbonate, garnet, and chalcopyrite. Fisher (1942, p. 22) also found a 

brown mineral resembling strueverite or tapiolite on the dump.

Many small pegmatite stringers intrude the metamorphic rocks 

in both lit-par-lit and crosscutting relationships. Most of the 

stringers are from less than one-half inch to 1% inches thick and 

commonly show "pinch-and-swell" structure. Some stringers are 

largely quartz with minor plagioclase; others contain differing proportions of microcline-perthite, quartz, plagioclase, muscovite, apatite, and tourmaline. The texture of the stringers is usually fine 

grained. The thicker stringers contain muscovite, quartz, and plagioclase in a fine-grained marginal zone, and potash feldspar in a coarser 

grained central zone.

QUARTZ VEINS

Milky to colorless quartz veins, ranging from less than 6 inches to 

3 feet in thickness, are abundant in the High Climb area. For the 

most part they are concordant, but some cut and distort the schistosity. 

No complete gradation could be traced from pegmatite to veins consisting solely of quartz, but some of the lit-par-lit pegmatite stringers 

consist mainly of quartz with only a small amount of plagioclase.

HIGH CLIMB PEGMATITE

SIZE, SHAPE, AND STRUCTURE

The outcrop of the High Climb pegmatite has a tadpole shape (pi. 

7), is 335 feet long, trends N. 10° E., and is as much as 180 feet wide
68 CONTRIBUTIONS TO ECONOMIC GEOLOGY

FIGURE 14. Large outcrop of schist at east corner of main pit, High Climb pegmatite. 

Schist inside the white and black lines is bounded on both sides by pegmatite. This structure constitutes a major flngerlike roll plunging 57° N. 40° W.

(in the vicinity of the main pit) ; the maximum thickness is about 

85 feet (pi. 7, section C-C'). The pegmatite dips to the west and, in 

general, is roughly concordant with the schistosity. The strike of 

the schistosity ranges from north to N". 55° E.; the dip is from 38° 

to 84° W. Locally the pegmatite contact crosscuts the schistosity. 

The main or southern part of the pegmatite has a pipelike structure 

with an elliptical to thickly lenticular cross section (pi. 7, sections 

C-C', D-D', E-E' ). The average plunge is about 45° N. 40° W. The 

shape of the pegmatite is complicated by large fingerlike rolls, most 

of which are exposed on the eastern or footwall side of the intrusive. 

Perhaps the most conspicuous of the irregularities is at the east corner of the main pit (fig. 14), where a large arcuate offshoot from the 

pegmatite extends around the eastern side of an outcrop of schist. 

The plunge of this structure is 57° N. 40° W., but the angle of plunge
FIGUEE 15. i ,- ,-,--..-- contact, southern end of northern part of High Climb 

pegmatite. Axis of roll (in line with handle of pick) plunges 46° S. 88° W.

apparently decreases at depth. Another prominent roll in the contact exposed in the southeast end of the main pit (pi. V) plunges 45° 

N. 40° W. Other rolls in the south wall of the main pit plunge 30° 

to 40° X. 32° W. The position of the hanging-wall contact is obscure, 

and consequently the shape of the pegmatite northwest of section 

C~C' (pi. 7) is not well known. Likewise, the structure of the extreme southern part of the body is imperfectly known; its shape in 

cross section has been determined by projecting the inferred contacts 

downplunge. Most of the foot wall of the southern half of the pegmatite is concordant with the foliation in the schist, but locally along some 

of the sharp rolls and in the extreme southern part of the body the 

footwall contact cuts the foliation.

A small northern extension of the pegmatite is separated at the 

surface from the larger southern part by a small area of overburden, 

schist, and a few small outcrops of pegmatite (pi. 7). Although there 

is no conclusive evidence that the two parts of the pegmatite are joined
70 CONTRIBUTIONS TO ECONOMIC GEOLOGY

FIGURE 16. Large roll in pegmatite contact, northeast side of High Climb pegmatite. 

Axis of the roll (white arrow) plunges 32° N. 20° W.

at the surface, as shown on the map (pi. 7), a roll in the contact 

(fig. 15) plunging 46° S. 88° W. at the southern end of the northern 

extension of the pegmatite suggests that they join, at least at depth. 

The northern part of the pegmatite is lenticular, but only the crest 

is exposed. The contacts are complicated by many rolls (pi. 7 and 

fig. 16). One crestal roll trends north across the central part of the 

northern extension of the pegmatite; this roll is nearly horizontal and 

may be a relatively shallow feature. Other rolls plunge 15° to 66° 

N. 12° W. to N. 60° W.; the average plunge is 28° X. 25° W. The 

footwall contact, on the northeast side of the outcrop, has an average 

dip of about 75° SW. Exposures of the hanging wall contact are 

fewer, but the dips range from 28° to 70° SW. The dike apparently 

widens slightly below the surface before pinching out in depth. Projections from the surface exposures suggest that the maximum thickness of the concealed part of the northern half of the pegmatite is 

probably not more than 55 feet.
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 71

The High Climb pegmatite is cut by many fractures, most of which 

are small, very irregular, branching, and discontinuous. None of the 

fractures, with the exception of a single prominent joint in the southern part of the body, are shown on the map (pi. 7). One poorly exposed fracture in the north wall of the main pit may be a fault with a 

displacement of about 1 foot. Some of the fractures near phosphaterich parts of the pegmatite are heavily stained by iron and manganese 

oxides.

PEGMATITE UNITS

In accordance with the classification of internal structural units in 

pegmatites as defined by Cameron, Jahns, McNair, and Page (1949, 

p. 1-1), 5 units have been mapped in the High Climb pegmatite: a wall 

zone, 3 intermediate zones, and a central zone or core. In addition to 

these units a possible sixth zone (or replacement unit ?) and a fracturefilling unit were recognized.

A wall zone of albite-quartz pegmatite forms an almost continuous 

shell around the pegmatite (pi. 7). In some outcrops a very thin 

discontinuous border zone rich in quartz and muscovite occurs along 

the pegmatite contact; because of the small volume of this zone, it 

has not been mapped and its description is included in that of the 

wall zone. Along some of the rolls the wall zone is locally absent and 

the first intermediate zone lies adjacent to the schist (for example, 

pi. 7, section D-D', footwall of the pegmatite). The first intermediate zone, composed of albite-quartz-muscovite pegmatite, is discontinuous along the crest of the pegmatite, but it is rarely, if ever, absent 

on the footwall side of the pegmatite. The second intermediate zone 

is an arcuate-shaped unit composed of perthite-quartz-albite pegmatite that is confined to the crest and hanging wall side of the pegmatite 

(pi. 7). This unit forms a hood above the quartz-cleavelandite pegmatite of the third intermediate zone. The core is quartz pegmatite.

The average mineralogic composition of each of the five zones in the 

High Climb pegmatite is given in table 1. The size classification for 

pegmatite textures in this report conforms to the system of Cameron, 

Jahns, McNair, and Page (1949, p. 16) as follows:

Term General grain xize 

Fine _ _ __ ___ . Less than 1 inch 

Medium____________________. 1 to 4 inches

Coarse- _ _______________- 4 to 12 inches

Very coarse__________________ Greater than 12 inches

Small fracture fillings of quartz-perthite-muscovite-albite pegmatite occur in the wall zone in the southern part of the pegmatite. Some 

of the waste rock on the dump southeast of the pegmatite suggests that 

a unit composed of very fine yellowish to grayish mica has been completely mined out. This may have been a discontinuous zone or a 

replacement body.

309393 55 3
72 CONTRIBUTIONS TO ECONOMIC GEOLOGY

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GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 73

ALBITE-QUARTZ PEGMATITE

The albite-quartz pegmatite or wall zone forms a shell around most 

of the High Climb pegmatite. Locally, however, the wall zone is 

absent, and the first intermediate zone is in contact with schist. The 

thickness of the wall zone is as much as 14 feet along the footwall of the 

pegmatite (pi. 7, section B-B'}. The average thickness along the 

f ootwall in the southern or main part of the pegmatite is about 4 feet, 

and in the northern part between 6 inches and 1 foot. The overall 

average grain size of the wall zone is about 0.1 inch.

Along the crest of the northern part of the pegmatite the wall 

zone is thin and discontinuous. Albite-quartz pegmatite forms about 

60 percent of the exposures mapped as wall zone in the northern area 

(pi. 7), and the rest is albite-quartz-muscovite pegmatite (first intermediate zone) in patches too small to map.

The mineralogic composition and grain size of the wall zone differ 

from place to place (table 2). Three main types of wall zone have 

been mapped as a single structural unit on the basis of texture, because all are fine-grained (average grain size less than one inch) in 

contrast to the medium-grained intermediate zones. All three types 

contain albite and quartz as the predominant essential minerals, but 

the proportions of tourmaline, muscovite, and perthite are variable. 

Lack of exposures in critical areas prevented the study of possible, 

"telescoping" (Cameron, Jahns, McNair, and Page, 1949, p. 19) of 

these types of wall zone.

TABLE 2. Variations in grain size and 'mineralogie composition of alMte-quartz 

pegmatite (icall zone), High Clim'b pegmatite

Locat on

In sugary-textured type,

along footwall in main pit

(southern part of pegmatite) and in several irregular outcrops in the northern part of the pegmatite. .

Wall zone in rest of southern

part of the pegmatite.

Most of the wall zone in

northern part of the pegmatite. ------ _ _. ._- _

Average 2 ..- ._ .- . -

Average 

grain 

size ' 

(inches)

0.03

.25

.15

0.1

Mineralogic composition (percent)

Albite

71

66

59

63

Quartz

19

20

34

26

Muscovite

1

5

5

4

Tourmaline

8

<1

<1

3

Perthite

0

8

0

3

Apatite

<1

<1

<1

<1

Garnet

0

<1

1

<1

Unidentified phosphate

minerals

<1

0

0

<1

Beryl

0

<1

<1

<1

1 Average grain size means the average maximum dimension of the grains.

2 Mineralogic composition compiled from visual estimates at many exposures of the zone; the percentages 

for each of the three types were weighted against the estimated volume of each type.
74 CONTRIBUTIONS TO ECONOMIC GEOLOGY

In addition to the three main types of the wall zone, another subdivision could be made on some of the dip slopes and along some of 

the contacts where the outer 0.5 to 2 inches is relatively rich in quartz 

and muscovite. Because the total volume of this "border zone" is 

negligible and because it is irregularly distributed, it was not mapped 

as a unit, and its mineralogic composition was not computed separately 

from the rest of the wall zone.

Mineralogical data for the albite-quartz pegmatite (wall zone) are 

given in table 3. Thin sections of the sugary-textured (0.03 inch 

grain size) type show that tourmaline crystals have inclusions of 

quartz and albite and show color zoning from blue at the edge to 

yellow-brown near the center. Microcliiie-perthite occurs as blocky 

grains in part of the wall zone in the southern part of the pegmatite. 

(All perthite in the High Climb pegmatite is microcline-perthite.) 

Iron and maganese oxides, resulting from the alteration of phosphate 

minerals, cause irregular straining of much of the sugary-textured 

f ootwall part of the albite-quartz pegmatite. Beryl occurs only along 

gradational contacts with the first intermediate zone. It is commonly 

much less than 0.5 percent of the wall zone, whereas it generally constitutes I percent of the first intermediate zone. Optical properties of 

the beryl are the same as those of beryl in the first intermediate zone.

ALBITE-QTJARTZ-MTJSCOVITE PEGMATITE

Albite-quartz-muscovite pegmatite forms the first intermediate 

zone in the High Climb pegmatite. On some of the rolls and in places 

along the footwall of the southern half of the pegmatite, where the 

wall zone is absent, the first intermediate zone is in direct contact with 

the schist. The first intermediate zone borders the third intermediate 

zone in the keelward and footwall parts of the pegmatite and borders 

the second intermediate zone along the hanging wall side and the 

crest (pi. 7). The first intermediate zone is as much as 5 feet thick; 

the average thickness is about 2.5 feet. The zone is thickest along the 

complex rolls 011 the footwall of the southern part of the pegmatite. 

The average size of individual grains is about 1 inch, but the grain size 

ranges widely.

The average mineralogic composition of the albite-quartz-muscovite 

pegmatite is shown in table 4. The relative proportions of albite and 

muscovite range widely. In most of the exposures of the zone, muscovite forms at least 20 percent and in a few it constitutes as much as 50 

percent of the zone. In the northern segment of the pegmatite, finegrained (average 0.5 inch) albite-rich areas are irregularly distributed 

in the zone. These contain albite (55 percent), quartz (25 to 30 percent) , muscovite (10 percent), tourmaline (3 percent), beryl (as much 

as 3 percent), amblygonite (variety, moiitebrasite) (1 percent), and 

accessory apatite and dark-colored phosphate minerals.
TABLE 3. Mineralogy of alMte-quarts pegmatite (wait motif

Mineral

Albite------ - 

T^uscovite

Unidentified phosphate minerals.

Beryl ..............

Average 

composition of 

zone 

(percent)

63

26

4 

3

3 

<1

<1 

<1

<1

Size of mineral (in.)

Range

0.01-0.5 _ _ 

0.01-0.6 _ _

0.01-0.75___

0.02-0.75 

0.01-0.2 

0.1-3.5_ ...

0.5-2.5_____

Average '

0.02 (in sugary-textured type); 0.1 

(in other types) . 

0.1 (sugary-textured 

type); 0.2 (in other 

types) . 

0.2

.2 ........ ....

1.75- 

<0.1_. ______________

.1

.n...... ...........

1.0

Occurrence

Irregular grains and masses 

intimately intergrowii 

with plagioclase.

Rounded grains irregularly 

distributed. 

Irregular grains irregularly 

distributed along inner 

edge of wall zone near 

phosphate-rich parts of 

first intermediate zone.

Color

White - 

Colorless to 

milky.

Black to bluish

Buff-white to f

Brownish to g

White 

1 The. "average" size is the average maximum dimension of the grains of each mineral. 

3 Na' is the minimum index of refraction, as determined on cleavage fragments (001).

The plagioclase cu

Winehell (1951, fig. 1
76 CONTRIBUTIONS TO ECONOMIC GEOLOGY

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2 Na' is the minimum index of refraction, as determined on cleavage fragments (001). 3 Trace. 
78 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Optical data and descriptions of the minerals of the albite-quartzmuscovite pegmatite (first intermediate zone) are included in table 

4. In most of the zone the albite is platy (variety, cleavelandite), 

but in the relatively fine-grained mica-poor parts of the zone, it is 

blocky to subplaty. The maximum index of refraction (N^) of the 

beryl ranges from 1.5794 to 1.5865 (± 0.0005). An unpublished curve 4 

compiled by W. T. Schaller of the U. S. Geological Survey shows 

that the BeO content of beryl having these indices ranges from 13.10 

percent for the grains of lowest index to 12.35 percent for grains of 

the highest index. Unidentified dark-colored phosphate minerals 

intimately intergrown with other minerals of the zone are commonly 

concentrated in irregular, heavily-stained pods, from 1 foot to 6 feet 

in length, along the inner edge of the zone; the pods contain as much 

as 10 percent phosphate minerals. Some of these minerals are probably members of the lithiophilite-triphylite group. Fisher (1942, 

p. 19) has reported heterosite and triplite in the phosphate-bearing 

rocks of the High Climb pegmatite. Amblygonite (variety, montebrasite) commonly occurs in the albite-rich parts of the zone. The 

maximum index of refraction (Ny') of the montebrasite ranges from 

1.634 to 1.638 (±0.002), which, according to Wmchell's curves (1951, 

p. 224, fig. 121), places the mineral at the extreme montebrasite end 

of the amblygonite-montebrasite series. A partial analysis of the 

montebrasite, made by C. M. Warshaw and W. W. Brannock of the 

U. S. Geological Survey, gave the following:

Oxide Percent 

A12O3 _______________________________________ 33.15 

Li3O" _______________________________________ 9. 51 

H2O"___________ _______________________________ 4. 88 

F__________________________________________ .59

a Determined with flame photometer by W. W. Brannock. 

b Averages of three determinations of total H2O.

In the phosphate-rich parts of the zone, the montebrasite is intimateh 

intergrown with anhedral blue-black tourmaline and commonly is 

veined by the dark-colored phosphate minerals.

PERTHITE-QTJARTZ-AXBITE PEGMATITE

Perthite-quartz-albite pegmatite forms the second intermediate 

zone in the High Climb pegmatite. In the southern half of the pegmatite this zone is arcuate in cross section (pi. 7, sections G-C'', D-D', 

and E~Ef ) and occurs as a hood above the inner zones. The maximum 

thickness of the unmmed parts of the zone is 26 feet (pi. 7, section 

A-A'}. The zone thins away from the crest of the pegmatite, and 

on the footwall side it pinches out completely. Only the upper parts

4 Schaller, W. T., Curves showing the relation of the maximum index of refraction 

(Nw) of beryl to the specific gravity and BeO content. (Unpublished manuscript in files 

of the U. S. Geological Survey.)
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 79

of the second intermediate zone are exposed in the northern half of 

the pegmatite, and its full extent is not known. The overall, average 

size of individual grains in the zone is about 8 inches, but the size of 

grains varies widely. Relatively large perthite crystals are enclosed 

in a matrix of relatively fine grained quartz and albite.

The average mineralogic composition of the perthite-quartz-albite 

pegmatite (second intermediate zone) is shown in table 5. Variations in the mineralogical composition of the zone are chiefly in the 

proportion of perthite. The upper parts, near the crest of the pegmatite, contain as much as 75 percent perthite; the percentage of perthite 

decreases downward and the lower parts of the zone contain as little 

as 25 percent perthite. In the northern part of the pegmatite, perthite grains averaging 1 foot in size constitute 60 percent of the visible 

exposures, and the quartz is probably more abundant in the matrix 

than in the southern part of the pegmatite.

Optical data and descriptions of the minerals of the perthite-quartzalbite pegmatite (second intermediate zone) are given in table 5. 

Unidentified dark-colored phosphate minerals are associated with 

amblygonite (variety, montebrasite), loellingite, manganese-bearing 

carbonate, and bluish-black anhedral tourmaline. These are distributed in heavily stained aggregates along the zonal contacts with the 

first and third intermediate zones.

QUARTZ-CLEAVHLANDITE PEGMATITE

Quartz-cleavelandite pegmatite of the third intermediate zone underlies the hood-shaped second intermediate zone. In the lower parts 

of the pegmatite the third intermediate zone is in contact with the 

first intermediate zone (pi. 7). Quartz-cleavelandite pegmatite forms 

a shell ranging in thickness from 2 feet to 30 feet average about 14 

feet around the quartz core. The average size of individual grains 

is about 1.25 inches, but the average size of aggregates of grains is 

about 3 inches.

The average mineralogic composition of the quartz-cleavelandite 

pegmatite (third intermediate zone) is shown in table 6. Several 

exposures of the innermost 1 to 2 feet of the zone, marginal to the 

quartz core, contain as much as 70 percent of cleavelandite and 10 percent montebrasite. In other exposures quartz forms 60 percent of the 

zone, cleavelandite only 35 percent, and montebrasite is absent.

Descriptive data for individual minerals of the third intermediate 

zone are listed in table 6. All the plagioclase in this zone is the platy 

variety of albite, cleavelandite. The phosphate-rich parts of the 

zone are generally in elongate heavily-stained pods, as much as 10 

feet in length, and are most common near the zonal contacts with the 

other intermediate zones.
80 CONTRIBUTIONS TO ECONOMIC GEOLOGY

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84 CONTRIBUTIONS TO ECONOMIC GEOLOGY

QTJARTZ PEGMATITE

The quartz core is entirely enclosed by the third intermediate zone. 

In cross section (pi. 7) the shape of the core is thinly to thickly lenticular. The texture is massive.

The core is composed of milky to colorless quartz (97 percent) and 

altered spodumene (3 percent). Kemnants of altered spodumene 

crystals, as much as 3 feet in length, are diversely oriented in a matrix 

of massive quartz in the north wall at the northwest end of the main 

pit (pi. 7). The alteration products of the spodumene are chiefly 

white to yellowish-white fine micaceous materials, some of which may 

be eucryptite. A thin section of part of one spodumene relict shows 

an aggregate of very fine-grained pale-yellowish micaceous material 

intergrown with small quantities of fine-grained quartz and albite.

QT7ARTZ-PERTHITE-MUSCOVITE-AL,BITE PEGMATITE

Fracture-filling units of quartz-perthite-muscovite-albite pegmatite 

cut the wall zone south of the main pit. The largest fracture fillings 

are only 2 feet long and 6 inches wide, and cannot be shown on the map. 

The average grain size is about 3 inches.

The fracture fillings are estimated to contain quartz (45 percent), 

perthite (35 percent), muscovite (10 percent), and albite (10 percent). 

Colorless to milky quartz and flesh-colored perthite grains are 2 to 8 

inches in maximum size. Subplaty to platy albite is intergrown with 

quartz. Yellowish-silvery muscovite books, averaging about 0.75 inch 

in size, commonly occur at the margins of the fracture fillings.

MUSCOVITE PEGMATITE

Blocks of very fine-grained muscovite pegmatite were found 011 the 

large dump southeast of the main pit, but similar rock was not found 

in place. The rock is composed almost entirely of yellowish to grayish 

muscovite flakes, less than 0.2 inch in size, intergrown with a little 

platy albite and quartz. Some of the muscovite-rich material is associated with coarse perthite blocks that are apparently corroded and 

embayed by the mica. This fine-grained muscovite pegmatite may 

have been derived from a discontinuous zone adjacent to the second 

intermediate zone or from a replacement unit of unknown shape and 

position. The color of the material suggests that it may be a lithiumbearing mica, but Fisher (1942, p. 22) reports that this mineral is not 

lepidolite but muscovite.

ORIGIN

The High Climb pegmatite has many of the characteristics that 

led Page and others (1953, p. 17-24) to conclude that zoned pegmatites of the Black Hills were intruded as a viscous liquid and that the 

internal units resulted from fractional crystallization in an essen-
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 85

tially closed system. Other authors, however, have not arrived at 

these conclusions, and for this reason a brief statement of the evidence 

from the High Climb pegmatite and a discussion of what the evidence 

means are presented herewith.

Geologists are in fairly general agreement that pegmatites are 

formed by fluids derived from a differentiating granite magma. The 

principal dissent from this opinion with regard to origin of Black 

Hills pegmatites has been presented by Higazy (1949, p. 555-581); he 

believes that the pegmatites were formed by metasomatism of schist. 

Many of Higazy's arguments rest on the assumption that the Black 

Hills pegmatites consist chiefly of perthite, whereas perthite actually 

is less abundant than quartz and plagioclase. The predominance of 

eoda feldspar over potash feldspar in the bulk composition of many of 

the well-zoned pegmatites in the Black Hills and the presence of notable quantities of lithium, beryllium, and phosphate minerals are 

not adequately explained by a granitization theory that relies heavily 

on the movement of potassium ions. Furthermore, Higazy failed to 

describe such features as island-mainland structure, gradational phases 

between schist and the different kinds of pegmatite, or the changes in 

pegmatite composition correlated with changes in composition of the 

country rock; these features should be present if his theory is correct. 

The High Climb pegmatite has sharp contacts with the country rock, 

and evidence for a gradational change from one to the other cannot 

be recognized.

The close areal proximity of the High Climb pegmatite to the granite of Harney Peak and the similarities in mineralogy and composition strongly suggest that the pegmatite and the granite are genetically related. Both have microcline-perthite, sodic plagioclase, 

quartz, tourmaline, and muscovite as the dominant constituents. It is 

not known whether the Harney Peak mass was the actual source of the 

material of the High Climb pegmatite and other pegmatites in the 

southern Black Hills or whether the granite and the pegmatites 

originated in a common deep-seated batholithic source.

The composition of the fluid or magma which formed the High 

Climb pegmatite is indicated in a general way by its mineralogy. 

Quartz, albite, perthite, and muscovite are the major minerals, indicating that the pegmatite fluid was rich in silicon, sodium, potassium, 

and water. Significant amounts of beryl, phosphate minerals, tourmaline, and amblygonite also indicate that the pegmatite fluid contained lithium, beryllium, boron, and phosphorous. This assemblage 

of elements together with significant amounts of water suggests that 

the pegmatite fluid was a late stage product resulting from the differentiation of a granitic magma.

The overall general concordance of the High Climb pegmatite with 

the schistosity in the country rock suggests that the emplacement of
86 CONTRIBUTIONS TO ECONOMIC GEOLOGY

the pegmatite was controlled mainly by the regional schistosity. 

Locally the pegmatite contact cuts the schistosity, indicating that the 

viscosity of the pegmatite fluid and the force of its movement were 

sufficient to breach the country rock. A noteworthy example of this 

breaching occurs along the f ootwall of the southern part of the pegmatite (pi. 7, section E-E'}, where a large fingerlike extension of the 

pegmatite cuts the schist and then extends parallel to the main contact.

Speculation about the history of crystallization of pegmatites after 

emplacement has brought forth the greatest diversity of opinion 

among geologists. Many geologists, including Schaller (1925, p. 269- 

279), Landes (1925, p. 355-411), and Hess (1925, p. 289-298), believed 

that complex pegmatites are formed in two or more phases: an initial 

intrusion and crystallization of a magma, simple in composition, followed by one or more hydrothermal phases, during which the original 

material was partly or completely replaced by hydrothermal minerals. 

Quirke and Kremers (1943, p. 571-580) supported the idea that pegmatites were formed by crystallization of solutions moving through 

open systems. Recently many writers (Cameron, Jahns, McNair, and 

Page, 1949, p. 104; Page and others, 1953, p. 20-24; Haiiley, Heinrich, 

and Page, 1950, p. 8; Jahns, Griffitts, and Heinrich, 1952, p. 45) have 

shown that the internal structure of pegmatites supports the concept 

that pegmatite zones developed by fractional crystallization and incomplete reaction in a restricted system. Stockwell (1933, p. 38-39) 

had earlier expressed essentially this same concept to explain the 

origin of Manitoba pegmatites, which, he believes, show a definite 

order of solidification progressing inward from the walls.

Fisher (1942, p. 23) has postulated a three-fold sequence for the 

genesis of the High Climb pegmatite: originally, the pegmatite was 

formed as a small mass consisting of the "soda aplite"; subsequently 

the "quartz-microcline-microperthite aggregate" was introduced; finally "most of the ]ater components were formed by replacement from 

solutions that continued to penetrate the already solidified pegmatite". 

Fisher's initial "soda aplite" is apparently the same rock described in 

the present report as a sugary-grained type of albite-quartz pegmatite 

(wall zone). In a later report Fisher (1945, p. 14-20, fig. 4, fig. 5) used 

textural studies showing "albitization" of microcline at the High Climb 

pegmatite as evidence for replacement to support a general genetic 

theory consisting of several stages. In Fisher's "igneous" stage, a 

light fluid portion of a deeply buried magma was forced up into the 

schist and yielded the bulk of the pegmatite material (mainly potash 

feldspar, quartz, and minor muscovite and black tourmaline). Fisher 

postulated that during later "hydrothermal" stages residual waterrich portions of increasingly fluid nature were forced out of the magma 

at depth, and they moved upward to replace some of the earlier formed
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 87

pegmatite. He further postulated that a final stage of alteration was 

effected in some pegmatites by meteoric waters, after a period of considerable erosion.

The textural phenomena cited by Fisher are of value in determining 

the detailed paragenetic sequence of minerals within an individual 

zone. In the present investigation, for example, detailed thin section 

studies of material from the second intermediate zone show that the albite of the matrix appears to replace microcline-perthite in some specimens, and in others the microline replaces and veins the albite of the 

matrix and poikilitically includes crystals of cleavelandite. Textural 

studies alone, however, do not determine which process caused the 

embaying, veining, and corroding; the overall structural and mineralogic relations in the pegmatite must also be considered. The so-called 

replacement textures can be caused by several processes, including 

hydrothermal replacement, pneumatolytic action, and the incomplete reaction between rest liquids and crystals during fractional 

crystallization.

The well-developed zonal structure, the general increase in grain 

size inward, the concentration of mineral assemblages in definite 

zonal positions, and the similarity of the zonal sequence with that 

of other pegmatites constitutes evidence in favor of fractional crystallization in situ. The internal structure of the High Climb pegmatite strongly indicates that the so-called replacement textures were 

actually formed by incomplete reaction between newly-formed crystals 

and a progressively crystallizing rest liquid, and that the process 

operated in an essentially closed system with no addition of hydrothermal fluids from outside the system after the original emplacement.

The concentric zonal arrangement could not have been formed 

in successive stages by deposition in an open system, as in the process 

suggested by Quirke and Kremers (1943, p. 571-580), because the 

combination of wall zone and first intermediate zone completely encloses the other zones in the High Climb pegmatite at all exposures 

except where mining or erosion has cut through the outer zones. The 

concentric zonal arrangement and the concentration of certain mineral assemblages in definite zonal positions suggest that processes of 

differentiation, fractional crystallization, and segregation were operating throughout the time of the solidification of the High Climb 

pegmatite.. The internal structure and zonal sequence in the High 

Climb pegmatite is compatible with the internal structure and zonal 

sequence in many other pegmatites in the United States (Cameron, 

Jahns, McNair, and Page, 1949, p. 59-70) and is best explained by 

fractional crystallization. It seems very improbable that either the 

open system of Quirke and Kremers (1943, p. 571-580) or the successive stages of hydrothermal replacement of preexisting pegmatite,
88 CONTRIBUTIONS TO ECONOMIC GEOLOGY

as proposed by Landes (1925, p. 355-411), could cause such a uniformity of sequence of the dominant mineral assemblages in concentric lithologic zones in so many districts. Consequently, it seems most 

probable that the solidification of the pegmatite magma was an orderly process involving differentiation and fractional crystallization 

in a restricted system. Crystallization started at the walls and 

progressed inward, forming concentric zones differing in mineralogic 

composition and texture. The entire process of fractional crystallization was accompanied by incomplete reaction between the rest liquid 

and the newly formed crystals.

An outer zone of fine-grained albite-quartz pegmatite formed at 

the contact and is separated from the schist only by a very thin, discontinuous chilled margin, or border zone, rich in quartz and muscovite. Along the foot wall of the southern part of the body, rapid loss 

of volatile material probably was the cause of the formation of the 

sugary-grained f acies of the wall zone. The escape of volatile material 

is indicated by alteration of the adjacent schist. Probably most of 

the volatile material, however, streamed inward and upward along 

the major structural rolls in the footwall and by retarding the rate 

of crystallization at these sites caused the crystallization of mediumgrained albite-quartz-muscovite pegmatite adjacent to schist. The 

crystallization of this medium-grained first intermediate zone occurred in part simultaneous with and in part subsequent to the formation of fine-grained albite-quartz pegmatite elsewhere along the contact (for example, pi. 7, section E-E'}.

It is possible that the sugary-grained f acies of the wall zone may 

actually be a replacement body formed by solutions rich in sodium 

aluminum silicate escaping from the rest liquid at the time the first 

intermediate zone was crystallizing. If so, these escaping solutions 

should have replaced a preexisting wall zone or schist to form the 

sugary-grained unit. However, because no consistent cross-cutting 

relations and no pseudomorphic textures either of schist or of a preexisting wall zone were recognized, the sugary-grained rock is best 

considered to be a f acies of the wall zone.

As crystallization proceeded, the distinctive mineral assemblages of 

the first, second, and third intermediate zones were deposited as 

quasi-concentric shells. The distribution of minerals in these units 

suggests a certain degree of segregation in the liquid prior to crystallization or during crystallization. The best development of the micaand beryl-rich first intermediate zone was in the lower part of the pegmatite and a fraction rich in potash and poor in water segregated near 

the crest to form the hood-shaped second intermediate zone. Fractures formed after crystallization of the wall zone in the southern part 

of the pegmatite were filled by liquid that crystallized and formed
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 89

some of the essential minerals of both the first and second intermediate 

zones. Phosphate-rich materials containing some lithium, arsenic, 

copper, and carbonate, were segregated along the inner edge of the 

first intermediate zone, where it is in contact with the second and third 

intermediate zones, and also along the contact between the second and 

third intermediate zones. Other fractions of fluid rich in water reacted elsewhere along the underside of the perthite-rich second intermediate zone to form a discontinuous unit of fine-grained muscovite 

rock. It is possible that some of these segregations may be replacement units, but no evidence of relict pegmatite was found.

When the process of crystallization was nearly completed, the residual material became sufficiently concentrated in lithium to form a 

mesh of spodumene crystals. The spodumene, however, subsequently 

was altered almost completely to fine micaceous material. The alteration was not the result of late weathering processes, because other 

silicate minerals in the pegmatite exhibit very little alteration. 

The alteration of the spodumene could not have been caused by 

the introduction of hydrothermal solutions after the crystallization of 

the pegmatite, because there is no evidence to indicate that such solutions passed through other units of the pegmatite. It seems very likely 

that the spodumene crystals altered simply by their reaction with the 

rest liquid. The cause of this reaction, however, is not entirely clear. 

It is not readily apparent why the rest liquid, so soon after crystallization of spodumene, should change in composition sufficiently to replace 

the spodumene pseudomorphically. A possible explanation is that 

the crystallization of the spodumene may have occurred before the 

completion of crystallization of the third intermediate zone. Then, 

reaction between the progressively crystallizing inner part of the third 

intermediate zone and the rest liquid may have changed the composition of the rest liquid enough to cause it, in turn, to react with and to 

alter the spodumene.

If the alteration of the spodumene was accomplished by simple reaction between the crystals and the rest liquid, as the field evidence 

seems to indicate, there still remains the problem of the disposal of the 

lithium. It is important to note that the actual exposure of the quartz 

core is rather small and that the altered spodumene crystals were observed only near the upper and outer edge of this exposure. Altered 

or "rotten" spodumene crystals have also been reported at the Edison 

and Etta pegmatites in Pennington County, S. Dak. (Page and others, 

1953, p. 112 and p. 118); in these pegmatites the altered crystals generally occur in the outer, spodumene-bearing units or in the outer 

parts of central units, whereas unaltered spodumene generally occurs 

in the inner parts of the pegmatites. According to Page (oral communication, 1953), the lithium from the altered crystals at the Edison
90 CONTRIBUTIONS TO ECONOMIC GEOLOGY

and Etta pegmatites probably was taken into the rest liquid and then 

formed the unaltered crystals of the relatively younger, inner parts 

of these pegmatites. If unaltered spodumene occurs in the unexposed 

inner part of the core of the High Climb pegmatite, Page's explanation would also apply in the genetic sequence there. If, however, all 

the spodumene in the core of the High Climb pegmatite is altered, a 

possible explanation may be that the lithium is now disseminated in 

the molecules of the micas and the quartz that make up the core. The 

altered spodumene forms only 3 percent of the exposure of the core. 

If this percentage applies to the entire core, then the total quantity of 

lithium present in the original crystals was rather small, and dissemination of this small quantity throughout the entire volume of the core 

does not seem unreasonable.

The final product of crystallization at the High Climb pegmatite 

was a silica-rich fluid that crystallized as a quartz core, enclosing the 

mesh of altered spodumene logs. There is no evidence that at any 

time during the entire process of crystallization, from the formation 

of the outermost zones through the crystallization of the core, was 

material added to the pegmatite by open system hydrothermal solutions. The pegmatite fluid crystallized in essentially a closed system, 

although a minor amount of violatile material escaped into and altered 

the adjacent schist.

In its late stages the pegmatite fluid may well have been more nearly 

hydrothermal than magmatic. The boundary between processes which 

have been termed "magmatic," or "igneous," and processes which have 

been termed "hydrothermal" has long been a controversial problem. 

It is true that many minerals, such as beryl and muscovite, occur not 

only in pegmatites but also in quartz veins. Adams (1953, p. 98-100), 

for example, has reported beryl both in pegmatites and in quartz veins 

of the Mount Antero region, Colorado. The fact that some minerals 

occur in hydrothermal quartz veins does not necessarily mean that the 

occurrence of these same minerals in pegmatites should demand a 

separate stage in the genetic sequence, as postulated by Landes (1925, 

p. 355-111) and Schaller (1933, p. 144-151). Landes (1933, p. 55) 

later recognized the possibility that the hydrothermal solutions may 

be "residua" of the crystallization of pegmatite magma in the larger 

pegmatites. The process of fractional crystallization of a pegmatite 

magma in an essentially closed system, as postulated by Cameron, 

Jahiis, McNair, and Page (1949, p. 97-106), is entirely compatible 

with the so-called hydrothermal character of some of the younger 

minerals in pegmatites. During the process of fractional crystallization the proportion of mineralizers in the rest liquid tends to increase, 

and the solution may change from a viscous liquid essentially magmatic in character to one that is essentially hydrothermal. The exact 

nature of the change from magmatic to hydrothermal conditions has
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 91

been difficult to study in the laboratory because extreme difficulties are 

encountered in working with concentrations of mineralizers under 

combined conditions of heat and pressure. However, the change in 

character of the solution during fractional crystallization is indicated 

in many pegmatites by the increase in grain size from the walls to the 

center of the pegmatite, by the increase in abundance of reaction 

replacement textures inwards in the pegmatite, and by the presence, 

in some pegmatites, of true replacement bodies that extend outward 

from inner zones and replace parts of older zones.

The High Climb pegmatite contains no evidence that there have 

been any significant changes since the original crystallization of the 

pegmatite, although there has been minor alteration of the phosphate 

minerals. Certainly there is no evidence of carbonate veins cutting 

the pegmatite. The carbon in the manganese-bearing carbonate in 

the phosphate-rich assemblage of minerals could easily have been a 

primary constituent of the source magma or could have been derived 

by partial assimilation of carbonaceous metasediments as the pegmatite fluid moved through the schists to its present site.

MINERAL DEPOSITS

The industrial minerals that have been produced at the High Climb 

pegmatite are amblybonite; beryl; columbite-tantalite; potash feldspar; scrap, punch, and sheet mica. The pegmatite still has significant quantities of all these minerals except columbite-tantalite.

AMBLYGONTTE

The amblygonite in the High Climb pegmatite is the high hyclroxyl 

and low fluorine variety, montebrasite. It is mainly in quartz-cleavelandite pegmatite (third intermediate zone), especially in a 2-foot 

thickness of cleavelandite-rich rock marginal to the core. It occurs 

as rounded nodules that average about 3.5 inches and range from 0.5 

inch to 8 inches in size.

The percentage of montebrasite in the third intermediate zone is 

estimated to be between 0.25 percent and 0.5 percent. The distribution, however, is very spotty. The montebrasite content of the other 

zones is negligible.

BERYL

Beryl is confined almost entirely to the first intermediate zone of 

albite-quartz-muscovite pegmatite; this zone is also the main mica 

deposit in the High Climb pegmatite. Minor quantities of beryl (less 

than 1 percent) occur in the innermost part of the wall zone and in 

the extreme outer part of the third intermediate zone, where these 

zones are adjacent to albite-quartz-muscovite pegmatite.

The beryl in the High Climb pegmatite is white to greenish white, 

but generally carries considerable reddish-brown iron stain. Beryl
92 CONTRIBUTIONS TO ECONOMIC GEOLOGY

from areas rich in phosphate minerals is stained brown to gray-black 

by alteration products of the phosphate minerals. The length of 

crystals ranges from 0.5 inch to 12 inches; the average crystal is about 

3.5 inches long and 1.5 inches in diameter. Most of the beryl is in 

euhedral crystals, but some is in subhedral intergrowths with albite 

and muscovite. Refractive indices indicate that the BeO content 

of the beryl ranges from 12.35 to 13.10 percent.

The average beryl content of the albite-quartz-muscovite pegmatite 

(first intermediate zone) is estimated to be about 1 percent. This estimate was obtained by measuring the area of beryl on three rich faces 

and estimating the beryl content of many other exposures of the zone. 

On the north wall of the main pit 17.5 square feet of albite-quartz-muscovite pegmatite was found to contain 31 crystals of beryl totaling 0.88 

square foot in area, for a grade of 5.03 percent beryl; the exposed area 

of individual crystals in this rich face ranges from 0.0025 square foot 

to 0.1 square foot. Measurements of beryl crystals were made by Lang 

and Stewart 5 on two exposures of the first intermediate zone in the 

northern extension of the pegmatite. An area of 21 square feet of this 

zone in the south wall of the northernmost pit (pi. 7) contained 2.3 percent beryl in 22 beryl crystals with a total area of 0.48 square foot. In 

the south wall of the southern cut (pi. 7) in the northern half of the 

pegmatite a grade of 0.8 percent beryl was indicated in an area of 40 

square feet that had 50 crystals of beryl having a total area of 0.31 

square foot. Visual estimates of several other exposures of the zone 

indicate beryl contents of less than 0.5 percent.

The beryl content of those parts of the wall zone and the third intermediate zone immediately adjacent to the main beryl deposit (first intermediate zone) is less than 1 percent, and beryl has not been found 

elsewhere in the pegmatite. The beryl from both the wall zone and 

the third intermediate zone can be mined at the same time as the beryl 

is mined from the main deposit.

The percentage of beryl that can be hand-cobbed from the albitequartz-muscovite pegmatite differs from place to place. Lang and 

Stewart estimated 96 percent and 41 percent in the 2 exposures they 

measured. Probably the average percentage of cobbable beryl in the 

entire zone is in the order of 40 to 50 percent. The rest of the beryl 

would have to be recovered by some other method.

COL.UMBITE-TANTALITE

Columbite-tantalite was not observed by the writer in the present 

workings, but according to descriptions by C. K. Koch, mine operator, 

the 100 pounds that were produced occurred mainly in the part of the

5 Lang, A. J , and Stewart, D. B., 1948, Estimated beryl reserves in the small pegmatite 

just north of the main pegmatite on the High Climb claim. [Unpublished report in the 

flies of the U. S. Geological Survey.]
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 93

quartz-cleavelandite pegmatite (third intermediate zone) that was 

mined from the northwestern end of the main pit. It was also reported by Fisher (1942).

POTASH FELDSPAR

The only minable deposit of potash feldspar in the High Climb 

pegmatite is the second intermediate zone of perthite-quartz-albite 

pegmatite. Only very small quantities of this mineral occur in other 

zones.

The potash feldspar is flesh white to buff creamy-white microclineperthite which for the most part is clean and free from excessive iron 

stain except near irregular fractures. The size of the individual crystals of the perthite in the second intermediate zone ranges from less 

than 1 foot to 5 feet, but the average size is probably about 1.5 feet in 

the southern part of the pegmatite and 1 foot in the northern part.

The average perthite content of the second intermediate zone in the 

southern part of the pegmatite is about 50 percent. The grade in the 

uppermost parts of the zone is as much as 75 percent, and in the lower 

parts of the zone, as little as 25 percent. In the northern part of the 

pegmatite the average grade of the exposures of the zone is about 60 

percent perthite.

MICA

Muscovite occurs in all the units of the High Climb pegmatite, but it 

is most abundant in albite-quartz-muscovite pegmatite (first intermediate zone), which is also the main beryl deposit in the High Climb 

pegmatite. The muscovite in this zone is silvery, yellowish-silvery, 

pale ruby, and pale greenish-brown in color. Books range in size from 

less than 0.25 inch to 10 inches; the average size is about 3 inches. 

Most of the mica contains varying amounts of "A" structure and 

herringbone structure, and some contains mineral-inclusions and hair 

cracks. In parts of the zone near phosphate-rich pods, the mica is 

badly stained. Muscovite from elsewhere in the zone is sold as white 

scrap mica.

The average muscovite content of the first intermediate zone is estimated to be about 22 percent. The amount of sheet mica in present 

exposures is negligible. Adams and Stoll (1953, p. 131) estimated 

that about 10 percent of the small quantity of sheet mica recovered 

was of No. 1 and 2 qualities.

Muscovite also occurs in the wall zone, in the second and third intermediate zones, and in fracture fillings of quartz-perthite-muscovitealbite pegmatite, but the grade in these units is too low for economic 

recovery of scrap mica by hand sorting. Furthermore, the small 

quantity of other economic minerals in these units decreases the possibility that the mica will be extracted even as a by-product.
94 CONTRIBUTIONS TO ECONOMIC GEOLOGY

BESEEVES 

AMBL.YGONITE

The main deposit is the third intermediate zone of quartz-cleavelaiidite pegmatite, which is estimated to contain between 0.25 and 0.5 

percent amblygonite (montebrasite). The average thickness of the 

third intermediate zone in the southern part of the pegmatite is about 

li feet, but most of the exposed montebrasite is in the inner 2 feet of 

the zone. The length of the third intermediate zone, measured normal 

to the plunge, is about 125 feet; the depth of the zone, measured down 

the plunge (pi. 7, sections A-A', B-B'), is at least 110 feet and may be 

as much as 250 feet. This zone is not exposed in the northern part of 

the High Climb pegmatite.

BERYL. AND MICA

The principal reserves of both beryl and mica are in albite-quartzmuscovite pegmatite (first intermediate zone), which is estimated 

to contain 1 percent beryl and 22 percent mica. Not more than about 

half of the beryl and less than half of the mica can be recovered by 

cobbing.

The average thickness of the first intermediate zone is about 2.5 

feet in the southern half of the High Climb pegmatite, but the zone 

is as much as 5 feet thick; the thickest exposures occur along the footwall. The depth of the deposit, inferred down the plunge along the 

footwall (pi. 7, sections A-Af and B-B'), is at least 105 feet but may 

be as much as 250 feet. The total length of exposures of the first intermediate zone in the southern half of the pegmatite is about 200 

feet, but the shape is very irregular, reflecting the many rolls in the 

pegmatite contact.

In the dikelike northern extension of the pegmatite the first intermediate zone is exposed for a total of 60 feet along the strike of the 

pegmatite and averages about 2 feet in thickness. The depth of this 

beryl deposit is not known but is probably at least 50 feet.

POTASH FELDSPAR

Reserves of potash feldspar are in the second intermediate zone, 

perthite-quartz-albite pegmatite. The grade ranges from 25 to 75 

percent; the average is about 50 percent.

In the southern part of the pegmatite, the maximum thickness of 

the perthite-quartz-albite pegmatite is about 26 feet. The zone pinches 

out on the footwall side and thins down-dip on the hanging-wall side. 

The maximum depth, measured down the plunge (pi. 7, section A-A'}* 

is 190 feet and the length, measured normal to the plunge, is about 

110 feet.
GEOLOGY OF THE HIGH CLIMB PEGMATITE, SOUTH DAKOTA 95

In the northern part of the pegmatite, the second intermediate zone 

is exposed for a total of 75 feet along the strike of the dike. Exposures 

are too poor to allow accurate determination of the thickness and 

depth in this part of the pegmatite.

The low grade, small size, and erratic distribution of perthite in 

the wall zone, in the first intermediate zone, and in the fracturefilling unit are unfavorable to mining of these units for potash feldspar.

LITERATURE CITED

Adams, J. W., 1953, Beryllium deposits of the Mount Antero region, Chaffee

County, Colo.: U. S. Geol. Survey Bull. 982-D, p. 95-118. 

Adams, J. W., and Stoll, W. C., High Climb mine, in Page, L. R., and others, 1953,

Pegmatite investigations, 1942-45, Black Hills, S. Dak.: U. S. Geol. Survey

Prof. Paper 247, p. 131. 

Cameron, E. N., Jahns, R. H., McNair, A. H., and Page, L. R., 1949, Internal

structure of granitic pegmatites: Econ. Geology Mon. 2. 

Fisher, D. J., 1942, Preliminary report on some pegmatites of the Custer district:

South Dakota Geol. Survey Rept. Inv. 44.

 1945, Preliminary report on the mineralogy of some pegmatites near

Custer: South Dakota Geol. Survey Rept. Inv. 50. 

Hanley, J. B., Heinrich, E. W., and Page, L. R., 1950, Pegmatite investigations in

Colorado, Wyoming, and Utah, 1942-1944: U. S. Geol. Survey Prof. Paper

227. 

Hess, F. L., 1925, The natural history of the pegmatites: Eng. and Min. Jour.-

Press, v. 120, p. 289-298. 

Higazy, R. A., 1949, Petrogenesis of perthite pegmatites in the Black Hills, S.

Dak.: Jour. Geology, v. 57, p. 555-581. 

Jahns, R. H., Griffitts, W. R., and Heinrich, E. W., 1952, Mica deposits of the

southeastern Piedmont, pt. 1, general features: U. S. Geol. Survey Prof.

Paper 248-A. 

Landes. K. K., 1925, The paragenesis of the granite pegmatites of Central Maine:

Am. Mineralogist, v. 10, p. 355-411.

 1933, Origin and classification of pegmatites: Am. Mineralogist, v. 18, 

p. 33-56, 95-103.

Page, L. R., and others, 1953, Pegmatite investigations, 1942-45, Black Hills, 

S. Dak.: U. S. Geol. Survey Prof. Paper 247.

Quirke, T. T., and Kremers, H. E., 1943, Pegmatite crystallization: Am. Mineralogist, v. 28, p. 571-580.

Runner, J. J., and Hamilton. R. G., 1934, Metamorphosed calcareous concretions 

and their genetic and structural significance: Am. Jour. Sci., 5th ser., v. 28, 

p. 51-64.

Schaller, W. T., 1925, The genesis of lithium pegmatites: Am. Jour. Sci., 5th ser., 

v. 10, p. 269-279.

 1933, Pegmatites, in Ore deposits of the western states (Lindgren

volume) : p. 144-151, Am. Inst. Min. Met. Eng. 

Stockwell, C. H., 1933, The genesis of pegmatites of southeast Manitoba: Royal

Soc. Canada Trans., 3d ser., v. 27, sec. 4, p. 37-51. 

Winchell, A. N., 1951, Elements of optical mineralogy: pt. 2, Descriptions of

minerals, 4th ed., John Wiley and Sons.

INDEX

Page

Abstract--.------- -.----------------- 59-60

Acknowledgments _ _ -_ 63

Adams, J. W., and Stoll, W. C., cited._______ 93

Albite- 67, 72, 73, 75, 76,80,82,84,85,87

Albite-quartz muscovite pegmatite. - 71, 72, 74,

76-78,88

Al bite-quartz pegmatite -... _ 71, 72, 73-74, 75, 88 

Alteration, spodumene_.__ _____ ____________ 89-90

Altered rocks adjacent to pegmatite __________ 66

Amblygonite-. 60, 61, 67,72,77, 78, 79,81, 82, 85, 91,94 

Amphibole- - ---- 65,66

Analysis, partial, of montebrasite_ _________ 78

Apatite, in metamorphic rocks ___________ 64, 65, 67

in pegmatite _______________ 07, 72, 73, 75,77, 80, 83

Bedding---------------------------------- 63

Beryl, composition______-__________________ 78,92

descriptive data____________________ 75,76,78,83

deposits._------_-----------_ 91,92

general statements - __ _____ ____ 60, 67, 85

percentages of pegmatite zones. _ _ _ _ _ _ 72, 73, 74

production ___ _ _________________________ 61-62

reserves 94

Biotite. -------------------------------- 64,66

Black Hills ---------------------------- 63,66

B order zone _---- _ 71, 74

Brannoek, W. W., and Warsliaw, C. M.,

partial analysis by______________ 78

By t ownite anorthite __ _-----___-__________ 65

Carbon, source-__-_--_--__-__________________ 91

Chalcopyrite ______________________ ______ 67, 72,83

Chlorite--.----_______________________________ 72,83

Cleavelandite.---_--_-------_____-________ 79,82,87

C olumbite-tantalite. _____________ 60, 61, 67, 72,83, 92

C ore of pegmatite ______________________ 71, 72,84, 90

Country rock. See Metamorphic rocks. 

Clinozoisite --- -- -- - _ _-__ _________ 65

Crystallization of pegmatites, theories__ _ _ 86

Dip of pegmatite _ 68

Field work..----..-.----..------ ------ 63

Feldspar, potash- .- ----- - - 61,93,94

See also Perthite. 

Fisher, D. J., eited___--_______-__ 62,67,78,

Fractional crystallization. ___________ 86,87,88,90, 91

Fracture flllings______--___-___---_---__--___ 71,88

Fractures __ - - _ 71,88

Garnet, in metamorphic rocks_____ __ 64, 65, 66, 67

in pegmatite-- _________ _______ 67,72,73,75

General geology ______ ______ ___ ____ 63-67

Grain size, pegmatite. _ ___---__ 71,72,73, 74, 79,84,87

schist-- -- - - 64

Granite, Harney Peak________ _____ 85

Graphitic schist______--__ -_____ __

Page

Hamilton, R. G., and Runner, J. J., cited_ _ 66 

Harney Peak area--_--_-__---_ _____________ 63

High Climb pegmatite- ___-__ _____ _ 67-94

average grain size and mineralogic composition of zones _______________ 72

composition of magma._ 85

general statement-_______________________ 60,67

geologic interest._-___-_--___________,__ 60

location-______________________________ 60,61,63

mineral deposits...-___ __-_____-_____ 91-93

mineralogic data.._________ 72, 73, 75, 76-77, 80-81

origin- .- -- ._ __ 84-91 

pegmatite units - _ ._ _ 71-84

reserves -- -- -- ---___ ____ _ _ 94

size, shape, and structure _________________ 67-71

textures of zones._________________________ 72

Hydrothermal processes. See Magmatie and 

hydrothermal processes.

Indices of refraction. See Optical data. 

Industrial minerals. See High Climb pegmatite, mineral deposits. 

Intermediate zone, first..____________________ 71, 72,

74, 76-77, 78,88, 91, 92, 93,94 

second. ___________ 71, 72, 78-79, 80-81,88, 93, 94

third-.- - 71,72,79,82-83,91,94 

Internal structure, units. See High Climb 

pegmatite, pegmatite units.

Koch, C. K., eited---_-__--_____. ________ 92-93

Koch, C. K., and Wells, Gladys, cited_______ 62

Lang, A. J., and Stewart, D. B., cited________ 92

Lenses, lime silicate-quartz,__________________ 65-60

Location, High Climb pegmatite _____________ 60, 61

Loellinginte_ _ ______'______________ 67, 72, 77, 79,81,83

Magmatie and hydrothermal processes. ______ 90

Magnetite-------------_--------___-______-__ 64,65

Manganese-bearing carbonate. 67, 72, 77, 79,81,83,91 

Metamorphic rocks..__ - _ _ _ 63-66 

Micaceous quartzite -___ _____- __ 64

Microcline, in quartz-mica schist _____________ 64

Microeline-perthite. See Perthite.

Mine workings. _____ _______________________ 62

Mineral deposits- _- - --___---________ 91-93

Mineralogic composition, pegmatite zones,___ 72 

Mineralogic data, metamorphie rocks... ______ 64-67

pegmatite. See High Climb pegmatite,

mineralogie data. 

Mining operations...____ __ _ ______ 60,61-62

Montebrasite. See amblygonite.

Muscovite, in metamorphic rocks _____ 64, 65, 66, 67

in pegmatite_67, 72, 73, 74,75,76, 80,82,84, 85,93, 94 

Muscovite deposits. See Scrap mica. 

Muscovite pegmatite. 84

Northern part of pegmatite _ _ _ 62, 69-70, 73, 79, 94, 95

97
98 INDEX

Page 

Opencuts_________________ _ _______________ 62

Optical data, pegmatite minerals _____________ 75,

76, 77, 78, 80, 81, 82

plagioclase in lime silicate-quart? lenses _ 65 

Origin, lime silicate-quartz lenses. ____________ 66

pegmatite. See High Climb pegmatite,

origin. 

Ownership. ____________________________ 60

Page, L. R., and others, cited_______ 84-85, 86,

Pegmatite, detailed description. See High

Climb pegmatite, 

general description _______________________

size classification of textures ______________

Perthite___ 07, 72, 73, 74, 75, 77, 78, 79, 80, 84, 85, 

Perthite-quartz-albite pegmatite. _ 71, 72, 78-79, 

Phosphate minerals, unidentifled-____________

73, 75, 77, 78, 79, 80,

67 

71

93, 94

80-81

72,

82,89 

65

Plagioelase in High Climb pegmatite. See

Albite: Cleavelandite.

in metamorphic rocks_ __ __ 64, 65, 66, 67 

in small pegmatite stringers ___________ _ 67

Plunge------ ----.----- ------- 68, 69, 70

Pods, phosphate-rich_______________________ 78, 79

Porphyroblastic quartz-mica schist ___________ 64-65

Pre-Cambriau core of Black Hills_________ 63

Production,__________________________________ 61-62

Purpose of present investigation._____________ 62-63

Pyroxene - - _- __ 65, 66

Quartz, in metamorphic rocks._______ 64, 65, 66, 67

in pegmatite. -_ - __ _________ 67,

72, 73, 74, 75, 76, 79, 80, 82, 84, 85, 90 

Quartz pegmatite (core)______________________ 84

Quartz veins. See Veins, quartz.

Quartz-mica schist____--_-___--_-___________ 64

Quartz-perthite-museovite-albite pegmatite. _ 84 

Quartzite. See Micaceous quartzite.

Reaction between crystals and rest liquid__ 87,

88,89 

Replacement _ ____ ____________ 86, 87

Replacement unit, hypothetical. 71, 84, 88, 89 

Road log._____________________________ 60

Rolls in pegmatite contact. .._______ 68-69, 70, 74

Page

Runner, J. J., and Hamilton, R. G., cited.,. _ 66

Schist. See Metamorphie rocks.

Schistosity.__----______________________ 63, 68, 85-86

Scrap mica_____________________________ 60,61, 62,93

Sericite -- -__----- - --_------ ____ 65

Shape, pegmatite. See High Climb pegmatite,

size, shape, and structure. 

Sillimanite----------_- ---- ---_____-- 65

Size, pegmatite. See High Climb pegmatite,

size, shape, and structure.

pegmatite minerals . 75, 76-77, 80-81, 82-83, 84 

Sphene------------.------------ ---------- 65, 66

Spodumne, altered._____________________ 72, 84, 89-90

Stewart, D. B., and Lang, A. J., cited........ 92

Stoll, W. C., cited._______.___________________ 61, 62

Stoll, W. C., and Adams, J. W.. eited_-.__._- 93 

Structure. See High Climb pegmatite, size,

shape, and structure. 

Strueverite ________________________________ 67

Tapiolite----------------------------------- 67

Tenderfoot Gulch__._________________________ 60

Texture, granoblastic..-_ -_ -_ -_-___ - 64

Tourmaline, in metamorphic rocks__.__ 64, 65, 66, 67

in pegmatite.__________--_-_-_-_______-_ 67,

72, 73, 74, 75, 76, 78, 79, 80, 82, 85

Units, pegmatite. See High Climb pegmatite, 

pegmatite units.

Veins, quartz_.____________-__-__________-___- 66, 67

Volatile material _____________________________ 88

Wall zone---------------- 71, 72, 73, 74, 75,91, 92, 93

Warshaw, C. M., and Brannock, W. W.,

partial analysis by_.______________ 78

Water, in pegmatite fluid.......______________ 85,89

Well-zoned pegmatites._._.-._______________ 63

Wells, Gladys, and Koch, C. K., cited_______ 62

Workings. See Mine workings.

Zircon__ _ - _ - ----_ - 64 

Zoisite- -- -- -- ~ 65 

Zones, pegmatite________ __ .______ 71,72, 73,84

o