Geology of the Malachite Mine Jefferson County, Colorado

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G E O L O G Y

OF

T H E

J E F F E R S O N

M A L A C H I T E

C O U N T Y ,

C O L O R A D O

library

COLORADO SCHOOL OF MINES GOLDEN,COLORADO

By George E. Morehouse

M I N E

ProQuest N um ber: 10781407

All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted. In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript and there are missing pages, these will be noted. Also, if m aterial had to be rem oved, a n o te will ind ica te the deletion.

uest ProQuest 10781407 Published by ProQuest LLC (2018). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106 - 1346

53663

A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science*

Signed: eorge

53663

Golden, Colorado Date:

Z_______ , 1950

Approved: ZF. M. Van Tuyl

CONTENTS

Z2SÎ Abstract

............

.

1

.

2

.

2

.

2

Introduction Location . . . . . . . . . . . Acknowledgments Previous Work

...............

. . . . . . . . . .

Field Procedure

.............................. . . . . .

2

.....................

5

. . . . . . . . . . . . .

5

P h y s i o g r a p h y....................................

5

Climate and Vegetation . . . . . . . . . . . . .

7

Geography

Geology

...............

.........

.

.

.

.

.

.

.

.

.

.

.

.

Regional » . . . ................... Idaho Springs Formation Local Geology

..

..

. .

10

.. .

10

............. 10 ..

..

17

Metamorphie R o c k s .........................

17

Igneous Rocks

• • • • • ..............

19

Ore D e p o s i t s ....................................

20

History and Production . . . . . . .

...........

D i s t r i b u t i o n .......... Structural Relations Folding

20 22

..........

. . . . . . . .

22

................

F a u l t i n g ............................. M i n e r a l o g y .......... Hypogene Ore Minerals

22 28 52

............. 52

il

P.gJBâ Ore Deposits - Continued Gangue M i n e r a l s .............................. 34 Supergene Ore M i n e r a l s ...................

.

34

P a r a g e n e s i s ...................................37 Wall-Rock A l t e r a t i o n ............ Classification

............

. . .

42 ........... 43

Age of D e p o s i t ..................................... 43 Tenor of O r e ....................................... 45 Description of P r o p e r t y .............................. 47 C o n c l u s i o n s .........

* ................... 51

B i b l i o g r a p h y ........................................... 54

Table 1

Paragenesis of Ore Minerals at Malachite Mine .......... .............

. .

41

. . #

46

Table 2

Outcrop Assays

Appendix "A”

Index of Property Ownership in Malachite Mine A r e a ............

53

Hi

ILLUSTRATIONS figure 1

2 3 4

Page Picture taken from road north of East Portal area, looking southeast across .......................... Bear Greek Canyon

6

Vegetation pattern running east-west over outcrop . . • • •

9

Differential weathering and intense fold­ ing of recrystallised limestone bed . • . .

16

Isoclinal and ptygmatic folding in Idaho Springs f o r m a t i o n ................... ..

24

♦ .

Intense folding and differential weathering in Idaho Springs formation, showing pegma­ tite stringer cutting folds . . . . . . .

25

Knife blade wedged on right flank of a sync line and on left flank of an anti­ clinal structure . . . . . . . . .

26

7

Curved and plunging f o l d ...........

27

8

Normal fault on west wall of Upper East tunnel 60 feet from P o r t a l ..........

29

Growth-sohing of pyrite with gangue Inclusions . . . . . . . . . .

30

Hand specimen of well-formed crystalline pyrite from Lower East Portal . . . . . . .

31

Photomicrograph of covellite velnlets re­ placing chalcopyrite with fissures ex­ tending through chalcopyrite into quartz gangue . . . . . . . . . . . ...............

35

6

6

9 10 11

12

Photomicrograph of ohalcoelte in chalcopyrite, with borolte in top c e n t e r ....................36

13

Miorophotograph of ex-solution particles of chalcopyrite in sphalerite . . . . . . .

39

Anticlinal structure filled with vuggy pyrite crystals ............... . . . . . .

40

14

It

Plgur* 15 16

P«g* Mlojrpphotograph ofpyrite fissure filling quartz ................. . . . . . .

44

Portion of stope

49

in

Lower Sast workings

. .

1

Index M a p ......................

la

2

Property m a p ...............................

lb

5

Map of vertical magnet le intensity

4

Aerial photograph of area

5

Regional map of lime-s 111 cate member

. . . ”

6

Surface geology m a p ................ ..

. . .

7

Underground geology m a p

* ...

. . . . . .

In pocket *

n tt



n

rt

rt

ABSTRACT

The geologic investigation of the Malachite mine Includes a brief review of the regional physiography and geology.

A reconnaissance survey was made of the llme-

silic&te member of the Idaho Springs formation, which occurs in the vicinity of the mine, to establish the

con­

tinuity of the member and the extent of tungsten minerali­ sation.

The ore body at the Malachite mine is in an east-

west shear zone in the Idaho Springs formation, with an outcrop length of about 3,@00 feet.

The mineralization

consists of chalcopyrite and sphalerite with minor amounts of gold and silver.

The mineral associations along with

their par agenetic relationships indicate a hypothermal type of deposit.

Although the mine has been operated

intermittently since its discovery in 1866, the total production has been small. tonnage of low-grade ore,

Because of the large probable the mine has possibilities

becoming a small producer of copper, zinc, gold, and ver.

of sil­

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