The Geology of Star Basin and Star Mine Gunnison County, Colorado

64 Pages·032.176 MB·English

by  Garrett, Howard L

THE GEOLOGY* OF STAR SAS III AND STAR MINE
GUNNISON COUNTY, COLORADO
By
Howard L. Garrett
Colorado School of Mines
Golden, Colorado
March 1950
ProQuest Number: 10781402
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5 3 3 1 3
A th esis submitted to the Faculty and the
Board of Trustees of the Colorado School of Mines
in p artial fu lfillm en t of the requirements for the
degree of Master of Science.
Signed
Howard L. G arrett
Golden, Colorado
Approved
f." H." VârTTüy'T
ruman H . K
CONTENTS
Page
A b str a c t................................................................................................. 1
Introduction ................................................................................................. 2
Purpose and Scope of I n v e s t ig a t io n .......................... *2
F ield W o r k ................................... 2
Previous Geologic Work . . . .................................... 3
Acknowledgments .............................................. . . . . . . 4
Geography ....................................................................................................... 5
Location ............................................................................................ 5
A ccessib ility .................................................................................. 5
Climate and V e g e t a t io n ......................... 5
G eom orphology................................................................................. 8
G e o lo g y ..................................................................................................................11
General Statement .....................................................11
Sedimentary R o c k s..............................................................................12
Sawatch Quartzite ......................................................... 12
Manitou D o lo m ite....................................................................12
Chaffee Formation....................................................................15
L eadville L im e s to n e ..........................................................17
Hermosa Formation ......................................................... 19
Igneous Rocks ................................................................................... 21
Pre-Cambrian Rocks ......................................................... 21
North Ita lia n Mountain I n tr u s iv e ...........................21
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Structure . . . . ................................................................... 23
F a u lt s ....................................................................................... 23
F o l d s ......................'............................................................... 27
Summary of Mesozoic and Cenozoic
Geologic H istory .............................................................. 28
Ore D e p o s its .................................................................................................. 29
General S ta tem en t.................................................................. . 29
H istory and Production .......................................... 30
M in e r a lo g y ........................................................................................ 31
Secondary M inerals . ................................................... 31
Primary M etallic M inerals . .......................... 31
Gangue M in e r a ls ............................................................. 33
Controls for Ore D eposition . . . . . . . . . . 35
A lt e r a t io n ........................................................................................ 39
Tenor of the O r e ......................... 40
Genesis of the D e p o s i t ........................................................ 40
Conclusions and R ecom m endations................................... . . 42
B ib lio g ra p h y .................................................................................................. 44
Table 1 Production, Star Mine, 1927-1928 . . . . 32
Table 2 Abbreviations Used on M aps................................. 45
ILLUSTRATIONS
1 Index map of Colorado .................................................... 6
2 Panoramic photograph looking south across
Star basin, showing overturned sediments . . 9
3 Photograph taken from North Ita lia n
Mountain looking northeast ......................................... 10
4 Area northwest of Mount T ilton , looking
northwest .................................................................................. 13
5 Sawatch quartz it e , showing rounded
elongated g r a in s ........................................................* . . 14
6 Sawatch q u artzite, showing highly angular
s ilic lf le d fra g m en ts......................................... . . . 14
7 Chert stringers in Manitou dolomite . . . . 16
8 Contact of Chaffee formation and
Manitou dolomite ................................................................... 16
9 Dyer dolom ite, showing intercalated shales . 18
10 Parting quartzite-L eadville lim estone
contact ....................................................................................... 18
11 L eadville lim estone with lin ea tio n due to
elongated c a lc ite rhombohedrons . . . . . . 18
12 Hermosa formation as roof pendant in
intrusive .................................................................................. 20
13 Herm osa-intrusive contact ......................................... 20
14 Thin section of gran ite, showing highly
altered orthoclase and plagioclase
feldspars . . ................................................................... 22
15 Thin section of gran ite, showing altered
orthoclase phenocrysts with inclu sion of
b io tite , quartz, and orthoclase . . . . . . 22
16 Quartz monzonite, showing zoned plagio­
clase feldspar ........................................................................ 24
iv
FÏKUi-e Page
17 Quartz la tite dike rock, showing pheno-
crysts in a f e ls it ic grou n d m ass................................24
18 Ridge extending east of North Ita lia n
M ountain..............................................................................................26
19 Overturned a n ticlin a l r o ll in
L eadville formation ............................................................ 26
20 Galena embaying lim estone ............................................... 34
21 B arite in lim e s t o n e .................................................................34
22 Unconsolidated sand of solu tion c a v itie s,
showing angularity of grains ........................................ 36
23 M ineralized b r e c c i a .................................................................36
24 Stained b r e c c i a ............................................................................38
25 Matrix around breccia fragm en t........................................38
Plate
1 Drainage map showing geology ...................................... pocket
2 Stratigraphie section and t r a v e r s e ............................ ,f
3 Claim m a p ......................................................................................... ”
4 Workings of Star mine ..................................... 11
5 Geology of workings above f ir s t lev e l . . . w
6 Geology of fir s t le v e l .......................................................... ”
7 Geology of h a lf l e v e l .......................................................... ”
8 Geology of second lev e l ..................................................... n
9 Geology of third lev el .......................................... ”
10 G eneralized stratigraphie section .......................... 11A
11 Geologic cross section through ridge lin e . 27A
12 Geologic cross section through Star mine . . 39A
ABSTRACT
The Star b asin , a cirque at the base of North Ita lia n
Mountain on the western rim of Taylor Park, is 55 m iles
northeast of the city of Gunnison in Gunnison County,
Colorado.
North Ita lia n Mountain is developed upon a T ertiary,
monzonite stock that intrudes a Paleozoic sedimentary sec­
tio n , composed e sse n tia lly of carbonate rocks. This sec­
tion includes the Sawatch q u artzite. Manitou dolom ite,
Chaffee form ation, L eadville lim estone, and Hermosa forma­
tio n . At Star basin the formations are in reverse sequence
because of overthrusting1 from the east.
The oxidized ores of the Star, mined for th eir lead
and silv e r content, are found in a zone of lim estone brec­
cia in the L eadville form ation. D irectly over the lim e­
stone breccia is a zone containing sand pockets. Sulphide
m inerals are found in len ses or pods in unbroken L eadville
lim estone above the layer containing the sand pockets and
below the breccia zone.
arthub lakes library
COLORADO SCHOOL OF MINES
GOLDEN, CO 80401
INTRODUCTION
purpose and Scope of In vestigation
The general geology of Star basin was studied to
determine the controls for m ineralization. The work was
carried out underground as w ell as on the surface and in­
cluded the study of the stratigraphy, structure, petrogra­
phy, and mineral stu d ies, including polished sectio n s.
Id en tifica tio n and age c la ssific a tio n of the sediment­
ary form ations was made by lith o lo g ie and stratigraphie
relation sh ip s, based on published data of the surrounding
d is tr ic t s .
F ield Work
The fie ld work for th is study was commenced in July,
1949, and was completed by the end of August of the same
year. IT. S. Forest Service aerial photographs on a scale
of 4 Inches to a m ile served as a base for surface mapping;
C.D.L. 32-41 through 32-44 in clu sive are the numbers on the
photographs flown October 22, 1939.
The underground mine maps supplied by Mr. Lambertson,
mine operator, were prepared by means of a Brunton-and-tape
survey on a scale of 1 inch to 40 fe e t. They were supple­
mented by additional maps based on a survey by the author.
3
The elevation of Star mine is 11,600 fe e t, and alpine
willow s and Engelmann spruce grow abundantly at th is eleva­
tio n . This cover, combined with g la cia l m aterial, makes
surface mapping very d iffic u lt, esp ecially in topographic
lows ; thus, the surface mapping was based largely on out­
crops found on ridges and slop es. The areal d istrib u tion
of the form ations that outcrop in Star basin is represented
on the drainage map (p l. 1, in pocket).
Previous G eologic Work
The principal published a r tic le s on the geology of
Star basin examined in the preparation of th is th esis are
as follow s;
In 1931 and 1934 J. Harlan Johnson measured a s tr a ti­
graphie section near North Ita lia n Mountain, which was pub­
lish ed in the B u lletin of the G eological Society of America
for March 1944. The t i t le of th is a r tic le is "Paleozoic
Stratigraphy of the Sawatch Range, Colorado.11
Cross and Shannon studied the intrusive of North I t a l­
ian Mountain and published th eir report, "Geology of I ta l­
ian Mountain, Gunnison County, Colorado," in the Proceed­
ings of the United States National Museum (vol. 71, no.
2690, Sept. 26, 1927).
The Star mine and area was Included in the Tincup
mining d is tr ic t in Albert W olf's 1915 geologic reconnais­
sance report of the area. This report is In a f ile of min­
ing p rop erties, the C ollins f i l e s , of the Colorado School
of Mines lib rary.
ARTHUR LAKES LIBRARY
COLORADO SCHOOL OF MINES
GOLDEN, CO 80401