STATE OF CALIFORNIA

EARL WARREN, Governor

DEPARTMENT OF NATURAL RESOURCES

WARREN T. HANNUM. Director

DIVISION OF MINES

FERRY BUILDING, SAN FRANCISCO 11
OLAF P. JENKINS. Chief

SAN FRANCISCO SPECIAL REPORT 16 DECEMBER 1951

GEOLOGY OF
THE SHASTA KING MINE

SHASTA COUNTY, CALIFORNIA

By A. R. KINKEL. JR.. and WAYNE E. HALL

Prepared in cooperation with the

U. S. Geological Survey

Digitized by the Internet Archive

in 2012 with funding from

University of California, Davis Libraries

http://archive.org/details/geologyofshastak16kink

GEOLOGY OF THE SHASTA KING MINE
SHASTA COUNTY, CALIFORNIA

By A. R. Kinkel, Jr.,* and Wayne E. Hall •

OUTLINE OF REPORT

Tage

Vbstract 3

Introduction 3

jliegional geology 3

)re body . 7

General character and occurrence 7

Minerals of the primary ore 7

i (Jangue minerals S

Faults 8

Ore controls 8

Oxidation and enrichment 10

References 11

Illustrations

Figure 1. Index map showing location of West Shasta copper-
zinc district 4

2. Photo of Shasta King mine ~>

3. Photo and sketch of Shasta King mine (i

4. Geologic details of ore contacts

Plate 1. Geologic map of Shasta King mine In pocket

2. Geologic map of underground workings In pocket

3. Cross-sections and longitudinal sections, Shasta

King mine In pocket

ABSTRACT

The Shasta King mine of the West Shasta copper-zinc district
is at an elevation of 1800 feet in the foothills of the Klamath Moun-
tains, 12 miles northwest of Redding in northern California. The
ore body is a flat-lying lens of massive pyrite that contains chalcopy-
rite and sphalerite, and minor amounts of gold and silver.

The ore body is in the Ralaklala rhyolite. This formation is
a volcanic complex composed of silicic flows and pyroclastic rocks
of Middle Devonian age. The formation contains a few shaly tuffs
and amygdaloidal mafic flows. The ore body occurs in a porphyritic
variety of the rhyolite. It is overlain in part by a thin bed of shaly
tuff and volcanic breccia and underlain in part by nonporphyritic
rhyolite; its outlines parallel the layering in the volcanic rocks. The
saucerlike shape of the ore body is due to the replacement of a
porphyritic layer in the volcanic rocks. Roth premineral and post-
mineral faults have been recognized; some of the premineral faults
are mineralized locally. The mineralized faults were not necessarily
feeder-channels, as evidence of mineralization extends only a short
distance away from ore bodies.

The Shasta King mine was operated from 1002 to 1000 and
again in 1018 and 1910. During these periods 83,880 tons of ore
was mined.

INTRODUCTION

The Shasta King mine is in Shasta County, Califor-
nia, sec. 12, T. 33 N., R. 6 W„ in the central part of the
West Shasta copper-zinc district. The mine is in the bottom
of the narrow canyon of Squaw Creek in the northwest
corner of the Redding quadrangle (tip:. 1) about 19 miles
by road from Redding, the county seat of Shasta County.
Access to the mine by automobile was not possible, how-
ever, during 1949 because of washouts near the mine. By
rebuilding about H miles of road it would be possible to
drive from the Shasta Dam to the mine. A hard-surfaced
road extends from Redding to the dam.

The topography in the vicinity of the mine is rugged.
In the canyon of Squaw Creek few slopes are less than
35° and slopes of 50° are common (figs. 2 and 3).

Most of the area has large, bold outcrops, but some
parts are mantled with slopewash. The flat-lying ore body

* Geologist, V. S. Geological Survey. Manuscript submitted for
publication July 1951. Published by permission of the Director, U. S.
Geological Survey.

of the Shasta King mine crops out about 150 feet above
Squaw Creek and is exploited by adits in the canyon wall.

The Shasta King mine was studied by the writers as
a part of a survey of the West Shasta copper-zinc district
made for the IT. S. Geological Survey in 1949, in coopera-
tion with the California State Division of Mines.

The writers' thanks are due to W. .J. Walker for
assistance in mapping the underground workings, and
R. T. Walker and W. J. Walker, the owners of the mine,
for maps of the mine, for information on the history and
production, and for permission to publish the data in this
report.

The Shasta King mine was operated from 1902 to
1909 by the Trinity Copper Corporation, and the ore was
shipped to the Ralaklala smelter at Coram, California.
The property was idle from 1909 to 1917, when it was
leased to the United States Smelting, Refining and Mining
Company, who operated the mine during 1918 and 1919.
The ore mined during this period was smelted in blast
furnaces at the smelter of the United States Smelting
Refining and Mining Company, at Kennett, California.
Operations were stopped at the mine in March 1919, and a
fire destroyed the mine camp, Boralma, in 1924, but most
of the mine workings were open and accessible in 1949.
The mine was purchased by the present owners, Walker
and Walker, of Leadville, Colorado, in 1944.

Data are incomplete on the amount of copper pro-
duced from the Shasta King mine. The production figures
given in table 1 were furnished bv R. T. AValker and
W. J. Walker.

I'd hie 1. Production from the Shasta King mine,
Shasta County, California

Au Ag

Tons o

of ore
Trinity Copper Corp., 1008-1000
United States Smelting, Refining
and Mining Co., 1918-1919.__

83,880

The ore contains substantial amounts of zinc, but as
zinc was not recovered in the smelters, no estimate of the
zinc content of the mined ore can be made. A probable
copper-zinc ratio of 1 : 3 is suggested by assays furnished
by AValker and Walker of samples taken in 1948. These
assays averaged 2.") percent copper and 7.61 percent zinc.

REGIONAL GEOLOGY

The following description of the general features of
the regional geology is taken from Kinkel and Albers. 1

The rocks in the West Shasta copper-zinc district con-
sist of a thick series of lava flows and pyroclastic rocks that
are overlain by sedimentary formations. The Copley green-
stone, consisting of mafic Hows and pyroclastics of probable
Lower or Middle Devonian age, is the oldest formation
exposed in the district. It is here called the Copley green-

< Kinkel, A. R., Jr., and Albers, J. P., Geology of the massive
sulfide deposits at Iron Mountain, Shasta County, California: Cali-
fornia Div. .Minis Special Rept. 14, 1!> pp., 1951.

Operator

Tons
of ore
15,000

oz. per oz. per

ton ton

Unknown

percent

68,889

0.034 1.01

2.92

(3 )

Special Report 16

MASSIVE SULFIDE MINES

SUTRG
,STAUFFER
.GOLINSKY
.MAMMOTH

EARLY BIRD

SHASTA KING
.BALAKLALA
.KEYSTONE
.SPREAD EAGLE
-STOWELL
.SUGARLOAF

LONE STAR

IRON MOUNTAIN

EXPLANATION

B'otite quartz diortte

Albite granite

Paleozoic sedimentary rocks

Bataklola rhyolite

a I v.

5 Miles

Copley greenstone

Geology by AR Kinkel, Jr ond JPAIbers

Figure 1. Map showing location of the West Shasta copper-zinc district and its generalized geologic setting.

Shasta King Mink, Shasta County

SHASTA KING MINE

Figure 2. Shasta King mine as seen from west along Squaw Creek.

stone because it is a greenish metamorphosed rock in which
the primary ferromagnesian minerals have been altered
to chlorite and epidote. Some units show andesitic tex-
tures, but other units contain basalt and mafic pyroclastic
rocks. The Copley is overlain by silicic flows and pyro-
clastics of the Baiaklala rhyolite of Middle Devonian age.
The name "Baiaklala rhyolite" of Diller 2 had been aban-
doned by Graton, 3 but the authors are reintroducing the
name because new evidence indicates that the formation
is composed principally of extrusive rhyolite and pyro-
clastics.

A subsidence in Middle Devonian time resulted in
Baiaklala rhyolite being overlain conformably by the
Kennett formation of Middle Devonian age which con-
sists of tuff, shale, and limestone. Uplift followed by
erosion removed the Kennett formation from part of the
area, but renewed subsidence initiated the deposition of
a great thickness of sedimentary material, beginning with
the shales, sandstones, and conglomerates of the Bragdon
formation of Mississippian age. No sedimentary forma-
tions younger than the Bra<rdon are found in the imme-
diate ' vicinity of the copper district, but younger
sedimentarv rocks overlie the Bragdon east of the district.

a Diller, J. S., U. S. Geol. Survey Geol. Atlas, Redding folio (No.

138) '3 P ('Jaton L C, The copper deposits of Shasta County, California:
U. S. Geol. Survey Bull. 430, pp. Sl-85, 1909.

The volcanic rocks of the Copley greenstone and
Baiaklala rhyolite are cut by two masses of intrusive rock,
which according to Diller ' intrude the Mississippian
sedimentary rocks and according to Hinds 5 are overlain
by Lower Cretaceous strata. The volcanic rocks and the
Mississippian sedimentary rocks are folded and locally
sheared. The major folds are broad, with moderate dips
and low angles of plunge, but in places the folds are tight.

Baiaklala Rhyolite. The Baiaklala rhyolite, which
has a thickness of more than 2000 feet in the central part
of the West Shasta mining district, consists principally
of light-colored porphyritic and nonporphyritic flows
interlayered with coarse and fine rhyolitic pyroclastics;
about one-fourth of the Baiaklala is pyroclastic. 6 Dikes
and plugs, which were feeders for the extrusive material,
are included with the Baiaklala rhyolite. The flows and
pyroclastics are abnormally rich in soda and silica and
commonly contain phenocrysts of quartz and albite that
range in diameter from less than 1 millimeter to 1 centi-
meter. Megascopically the quartz phenocrysts are more
conspicuous than the feldspar phenocrysts because the
feldspar is altered to sericite and clay minerals and blends
with the groundmass. Some of the rhyolite is amygda-
loidal, and locally it is flow banded. Amygdaloidal ande-
site forms thin flows in the lower part of the Baiaklala.

The Baiaklala rhyolite contains the ore body of the
Shasta King mine; no other formations are exposed in
the vicinity of the mine. The rocks adjoining the ore are
porphyritic and nonporphyritic varieties of the Baiaklala
rhyolite and well-bedded rhyolitic tuff and volcanic
breccia (pi. 1). The nonporphyritic rhyolite is locally
flow-banded. Although the nonporphyritic rhyolite con-
tains a few quartz and feldspar phenocrysts under 1 milli-
meter in diameter, it is mainly nonporphyritic, which
distinguishes it from other flows.

The porphyritic units of the Baiaklala rhyolite are
subdivided into two principal rock types: (1) rhyolite
with quartz phenocrysts 1 millimeter to 4 millimeters in
diameter; (2) rhyolite with quartz phenocrysts larger
than 4 millimeters. Type one comprises several individual
flows, including flow-banded porphyritic rhyolite, rhyo-
lite with abundant small feldspar phenocrysts, and a dark
purple porphyritic rhyolite; but it was not possible to
map these varieties separately because of their inadequate
underground exposures. Type two— the porphyritic rhyo-
lite Avith large quartz phenocrysts— appears to be intru-
sive into the rhyolitic flows in the mine area, but in other
parts of the district similar rhyolite containing coarse
phenocrvsts is present as flows and crystal tuft.

A bed of tuff and volcanic breccia that lies imme-
diately above the gossan at the surface is found in the back
of the stopes in the southwestern part of the mine. The
bed is composed of shaly rhyolitic tuff that is interlayered
with fine and coarse volcanic breccia. The tuff is variable
in texture along the strike of the bed where it is exposed
at the surface. The southwestern part of the bed is com-
posed principally of layered tuff; the central part con-
tains mixed shaly tuff and volcanic breccia ; and the north-

'K^N.^.T, Jurassic age £ the , as f granitoid intrusivesin
the Klamath Mountains, California: Am. Jour. Sci., 5th ser., vol. -.,

""' 18 «The 2 'nam e 4 ' Baiaklala rhyolite of Diller is used to denote the
formation that contains rhyolite flews and pyroclastic rocks : the
Ss ,»..ri,hvrifK- and nonporphyritic rhyolite and rhyolitic pyroclas-
tics are used for lithologic units.

Special Report 16

Figure 3. Shasta King mine as seen from south. Diagram in lower half of figure is sketch drawn f

rom photograph above.

Shasta King Mine, Shasta Count?

eastern part of the bed consists almost entirely of coarse
volcanic breccia that is underlain by a thin layer of tuff.
Columnar sections of the bed at the surface are shown in
figure 4, A.

ORE BODY

General Character and Occurrence

The Shasta King ore body is a lenticular body of mas-
sive pyrite that contains copper and zinc minerals and
minor amounts of gold and silver. The ore body crops out
along the steep north slope of the canyon of Squaw Creek
(fig.^3) and has been partly removed by erosion. The
remnant of the ore body has the shape of a shallow basin
elongated in a northeasterly direction. The outcrop of the
ore bodv has a length of 590 feet in a northeasterly direc-
tion and a maximum thickness of 42 feet. Underground
work has shown its width to be at least 500 feet. Gossan
erops out on the opposite side of the canyon southwest of
the mapped area, suggesting that the ore body was much
larger before erosion. The ore is thickest where it is ex-
posed at the present erosion surface. In places it thins to a
few feet toward the northwest, but exploration has not
delimited the northerly extent of the ore body.

The ore body is developed by adits, and most of the
mine workings are now (1949) open and accessible. The
location and geology of the underground workings are
shown on plate 2.

The Shasta King ore body is continuous throughout
the mine (pi. 3). The ore is uniform and structureless in
appearance, and is composed principally of massive pyrite
with lesser amounts of chalcopyrite and sphalerite. The
pyrite is anhedral and commonly fine grained, the grains
averaging 1 millimeter in diameter. Megascopic chalco-
pvrite and sphalerite in small irregular patches can be
seen in the massive sulfide ore, but no megascopic veinlets
of chalcopyrite or sphalerite were found. The ore contains
very little gangue except near the margins of the ore body.
A few nodules of porphyritic rhyolite, which are un-
replaced remnants of the host rock, occur in the central
part of the massive sulfide ore. Such nodules are common
at the upper contact of the ore body at several places in
the mine (fig. 4, C). The nodules range from less than an
inch to several feet across. Some are rounded and have
sharp contacts with sulfide ore; others are irregular in
shape and the boundaries are gradational from barren
rock to pvritized rock to massive sulfides. The nodules are
composed of porphyritic rhyolite with phenocrysts about
2 millimeters in diameter.

The contact between massive sulfide ore and the wall
rock is sharp at some places and gradational at others.
Where the contacts are sharp, the massive sulfide ore ends
abruptly against an unmineralized white clay and sericite
schist that constitutes a strong gouge. This type of con-
tact is exposed in the backs of some of the stopes on the
830-foot level, where the ore ends against No. 1 fault, and
on the 910-foot level along No. 10 and No. 11 faults. The
gouge and sericite schist are rarely over a foot thick;
they contain no crushed sulfides, and the porphyritic
rhyolite outside of the gouge zone is unsheared at most
localities. Other contacts between ore and wall rock show
a gradation from massive sulfide ore to unmineralized
rock, and bodies of partly replaced porphyritic rhyolite
remain in the ore. Soft, sandy- or sugary-looking sulfides
occur around some edges of the ore body. At these places

the ore ranges from DO percent pyrite to 30 or 40 percent
pyrite in schistose sericitic rock, and minable ore is deter-
mined by assays. Relict quartz phenocrysts that average
about 2 millimeters in diameter remain in the partly re-
placed rock.

The rock near the ore contacts is in many places
hydrothermally altered and schistose. Consequently it is
difficult to differentiate the porphyritic and nonpor-
phyritic types of rhyolite, but the porphyritic types fre-
quently can be distinguished by the presence of relict
quartz phenocrysts. Relict phenocrysts are present in the
less altered facies of the rock above the ore, in nodules of
waste in the ore, and at a few localities below the ore.
Information on the types of rock surrounding the ore body
is obtainable only from a few development workings, and
a few exposures in stopes at the edges of the ore body, or
from pieces of rock that have fallen from the backs of
stopes. The base of the ore is not exposed in most of
the stopes. Although the ore is generally underlain by
nonporphyritic rhyolite, it is underlain in a few places by
porphvrit'ic rhyolite that was not completely replaced
by the ore to the rhyolite contact. The ore at the west end
of the No. 6 adit is underlain by chloritic rock. This rock is
a chloritized facies of the nonporphyritic rhyolite and not
a mafic flow interlayered with the Balaklala rhyolite, be-
cause it contains a' few 1-millimeter quartz phenocrysts
and resembles chloritized rhyolite found at a few other
places in the district.

Minerals of the Primary Ore

The principal ore minerals are pyrite, chalcopyrite,
sphalerite, galena, and tetrahedrite. Small amounts of
gold and silver were recovered from the ore, although no
free gold has been seen. Tetrahedrite probably accounts
for the silver content of the ore.

Sulfide minerals constitute 85 to 90 percent of the ore
body. The gangue consists of unreplaced nodules of
porphvritic rhvolite, unreplaced quartz phenocrysts, sen-
cite, and introduced quartz. The nodules of porphyritic
rhyolite are concentrated near the borders of the ore body
as' shown in figure 4, C. Quartz and sericite are present
throughout the ore body.

Pyrite.— Pyrite is the principal sulfide mineral and
constitutes about 65 percent of the ore body. It is very
fine grained, ranging from 0.1 to 1 millimeter and some
2-millimeter pyrite cubes disseminated through the finer-
grained sulfides. Only the larger pyrite grains have a
euhedral cubic form ; the fine-grained pyrite has a massive,
metallic appearance.

Deposition of pyrite ceased before the other sulfide
minerals were introduced. Pyrite was corroded by quartz
and all later sulfide minerals and appears as isolated
relicts in them. Therefore, a large massive pyrite body was
formed before the other sulfides were introduced, and this
body was irregularly replaced by eopper-lead-zinc min-
erals.

Chalcopyrite.— Chalcopyrite is rather uniformly dis-
tributed throughout the massive pyrite and constitutes
about 10 percent of the ore mined. It has three distinct
modes of occurrence: as a network of chalcopyrite sur-
rounding and filling in between pyrite -rains ; with quartz
in veinlets that cut and replace pyrite; and as minute,
irregular blebs in sphalerite.

Special Report 16

Where massive chalcopyrite is present, it lias had
little corrosive effect upon the pyrite and mainly fills in
around and in fractures through pyrite. Quartz is closely
associated in time and space with chalcopyrite, and the two
minerals occur together in tiny anastomosing veinlets cut-
ting and replacing the pyrite body.

Evidently chalcopyrite was deposited over a long
period. Where it is associated with quartz, it is later than
pyrite, but it is earlier than the main sphalerite period of
deposition. This is shown by abundant corroded inclusions
of quartz and chalcopyrite in sphalerite. Although chalco-
pyrite started to deposit before sphalerite, it continued
to deposit throughout the sphalerite period of mineraliza-
tion, and chalcopyrite is always present with sphalerite.
It occurs commonly as small, irregular, worm-shaped in-
clusions in sphalerite forming a pseudoeutectic texture. 7
In addition, chalcopyrite occurs unevenly distributed
through sphalerite as minute "lobules that were deposited
perhaps simultaneously with sphalerite.

Sphalerite. — Sphalerite is present in considerable
quantities in the ore body but has an uneven distribution.
It is a massive reddish-black variety that contains a con-
siderable amount of iron. It is closely associated in space
with chalcopyrite, galena, and tetrahedrite. Pyrite has
been extremely corroded by the sphalerite so that only
tiny pyrite relicts are present in massive sphalerite. There-
fore much less pyrite is present in the zinc-rich parts of
the ore body than in those parts where only chalcopyrite
and pyrite are present.

Tetrahedrite. — Tetrahedrite occurs in very small
quantities in the zinc-rich parts of the ore body. It is
present as small irregular grains in sphalerite. The rela-
tive age of the tetrahedrite could not be determined defi-
nitely, but its association only with sphalerite as isolated
pains in sphalerite supp-ests that the two minerals were
lormed simultaneously.

Galena.— Galena is present in small quantities in the
zinc-rich shoots in the ore body. Galena is concentrated
along borders between quartz and sphalerite and also as
tiny veinlets and inclusions in sphalerite. Galena is later
than sphalerite, as it contains corroded relicts of sphal-
erite, it veins sphalerite, and it was introduced alone
borders of sphalerite. The relative age of tetrahedrite and
galena was not evident in the polished sections studied.

Gold and silver.— No gold or silver minerals have
been observed but gold and silver have been recovered
fromthe ,„,, Tetrahedrite is present in small quantities
and it is probably argentiferous, as the ore bodies in the
district that contain larger quantities of tetrahedrite are
richer in silver content.

Gangue Minerals

About 15 pereent of the ore body is gangue The
gangue consists of relict nodules of porphyritic rhyolite
near the margins of the ore body, unreplaced quartz
phenocrysts, sencite, and introduced quartz. Quartz is the
predominant gangue mineral. I, occurs partly as isolated
relict quartz phenocrysts derived from porphyritic rhyo-
lite but mostly as tiny veinlets in pyrite or as thin films
PP. l-l^lffo 6 "' W ' Pseud0 -^tectic textures: Econ. Geol., vol. 25,
Geol., A vof29? n pp A S7V:58 S 9? r i93r eUd0 " eUteCtlC " r< ' stru <*™*: Econ.

surrounding pyrite grains. The vein quartz was intro
duced with chalcopyrite. A little quartz is postsulfide
ape and fills vugs or fractures in the sulfide body.

FAULTS
Faults, which are both premineral and postminer
in ape, are conspicuous in both surface and undergroun
exposures. ( >nly the most important faults have been give:
numbers on the geologic maps and sections, but many oth
faults undoubtedly exist outside the developed area.

The premineral faults are No. 3, No. 5, and No. 1
(pi. 1 ). The evidence for a premineral age for these fault*
is the presence of iron oxides along the faults away from
the ore bodies, and the presence of hydrothermal clay
minerals along the faults. The minerals formed alonp th
faults are primary and are not due to deposition of iroi
oxides in the fractured zone by supergene solutions, be
cause pyrite casts are present. Pyrite occurs as much as,
75 feet vertically above the gossan on the No. 3 fault. In
addition, a small fault in the No. 6 adit (870-foot level),
2340 feet east on the coordinate system, contains small
lenses of massive sulfide ore that appear to have formed in
place along the fault. Hydrothermal alteration was ob-
served along No. 6 fault ; the fault may be premineral in
age but may have moved apain after mineralization. No. 3
and No. 5 faults also moved both before and after the
sulfides were deposited.

All the faults except No. 12 have some postmineral
movement. The direction of displacement on No. 1 fault
was determined from the position of mafic flows that crop
out to the west of the fault (pi. 1). From geologic work
outside of the mine area, these mafic flows are known to
be lower in the stratigraphic sequence than rocks exposed
east of the fault. The vertical offset on the fault is several
hundred feet or more. The direction of offset on No. 8 fault
is not known with certainty, but the northeast side is
probably upthrown relative to the southwest side. The
direction and amount of postmineral dip-slip movement on
Nos. 2, 5, 6, and 7 faults are shown by the offset of the
gossan at the surface. No. 2, No. 5 and' No. 7 faults must
have moved horizontally as well as vertically, as the offset
of the gossan at the surface, where the dip is steeper, is
preater than the offset of the ore underground, where the
dips are at low anples. In addition, the thicknesses of the
gossan are not the same on opposite sides of these faults
at the surface. The ore body thins toward the northwest,
and horizontal movement along northwesterly faults
would result in differences in thickness of the ore on oppo-
site sides of the faults.

ORE CONTROLS
The Shasta King ore body formed bv the partial to
complete replacement of a thin flow of porphyritic rhyolite
that lies between a bed of pyroclastic rock above and a
flow of nonporphyritic rhyolite below. The ore bodv is con-
formable with the contacts of the flow, but it does not
everywhere completely replace the flow of porphyritic
rhyolite. The porphyritic rhyolite that is the host rock of
the ore body contains 2- to 3-millimeter quartz pheno-
crysts that are distributed through a very fine grained
siliceous matrix. Smaller feldspar phenocrysts are present
but not prominent. The unreplaced remnants of the por-
phyritic rhyolite in the ore are generally massive and
unsheared. Many fragments of the porphyritic rhyolite

Shasta King Mine, Shasta County

|g==3=i|. Rhyohtic luff

7 ^S

Porphyntic rhyolite

Thin-bedded shoiy^
rhyohti_c tuff

Thick- bedded rhyohtic tuff
and fine volconic breccio

Thin- bedded
rhyohtic tuff

v' Gosson

Porphyntic rhyolite
locally tuffaceous

6"-l2" porphyrTtic rhyolite
fragments in coarsV volcanic
breccia with minor tuff^ — C""

Interlayered thin-bedded tuff
and volcanic breccia

Thin- bedded '"
rhyohtic tuff

£_♦_! * *

Porphyntic rhyolite

Fairly well-bedded
volconic breccio

| Thin-bedded
rhyohtic tuff

AT SECTION A-A' AT SECTION B-B' AT SECTION C-C'

COLUMNAR SECTIONS OF TUFF AND VOLCANIC BRECCIA OVER THE GOSSAN

Back of stope

2±

6*±

JJnshoared porphyntic rhyolite

Sheared porphy n lie rhyolite

7fjT.-^p..Vf?.*.v' Replacement of volcanic
breccia by sulfide ore

Massive sulfide ore
(Base of ore not exposed)

SMI of stope

UPPER ORE CONTACT IN THE STOPE ON THE
870-FOOT LEVEL NEAR CROSS SECTION F-F'

Gossan

; gosson

Dotum is mean sea level

Adit IMo 9
900 fool level

SECTION LOOKING NORTHEAST
ALONG NO 12 FAULT

Figure 4. Geologic details of ore contacts.

Special Report 16

remain as unreplaced or partly replaced remnants in the
massive sulfide ore, and all gradations exisl between un-
replaced porphyritic rhyolite and massive sulfide ore. Al-
though assays are not available, visual inspection shows
that the evidence of mineralization in the transition zones
between ore and waste consists entirely of pyrite, and that
copper and zinc minerals are limited to massive sulfide ore.
The ore contacts are sharp against clay and sericite
gouge at some places, hut a gradation exists between mas-
sive sulfide ore and hydrothermally altered wall rock at
many contacts. Where a transition zone is present between
ore and waste, pyrite can he seen to replace preferentially
the schistose portion of the rock. Within the transition
zones, anastomosing hands of foliated sericite cut the
massive porphyritic rhyolite, hut lenticular bodies of
unsheared rock a few inches to a few feet in length remain.
During the period of ore formation pyrite completely re-
placed the foliated (sheared) parts of the porphyritic
rhyolite before it replaced the massive nodules. The por-
phyritic rhyolite above the ore in the central part of the
ore body is unsheared, and the evidence seems good at the
Shasta Kin- mine that the scattered residual nodules of
waste in the ore, and the unreplaced part of the flow of
porphyritic rhyolite that contains the ore were not re-
placed because they were not sheared. The isolated un-
replaced remnants of rock in the main body of the massive
sulfide ore differ in origin and appearance from the partly
replaced volcanic breccia in the back of the stopes at the
northeast end of the mine in the stope on the 870-foot level.
Many contacts between the ore and the porphyritic
rhyolite are sharp. These contacts are marked by a white
Hay gouge that ranges in thickness from a fraction of an
inch to a foot. The wall rock is locally schistose behind the
gouge, but there are no sulfide minerals in the gouge or in
the foliated wall rock at these localities. The fact that the
sericite bands at ore contacts are foliated parallel to the
contact indicates that this zone is not due to hydrothermal
alteration alone. Ore solutions were apparently stopped
bypremmeral foliated bands of gouge and sericite at these
points. There is no evidence of postmineral movement
such as crushed or slickensided sulfides, that would be
sufficient to orient the sericite parallel to the sulfide con-
tact. A lew bands of gouge, ranging from a thin film to
a foot in thickness, are found in the massive sulfide ore
Ihese are composed of soft, sticky clav and have sharp
contacts with the massive sulfide ore. They appear to be
unreplaced prcmincral bands of gouge.

The ore along the No. (J fault on the 870-foot level
( pi. - ! is in sharp contact with unmineralized fault gouge
up to a foot thick, except in the vicinity of No. 6 adit At
this locality the contact is sharp but irregular and does
not lie against the fault, and the massive sulfide ore has
smooth, curved contacts with porphyritic rhyolite There
is no gouge at the contact and no evidence of movement
although a claylike alteration of the porphyry a few milli-
meters thick occurs at a few contacts.

A bed of tuff and volcanic breccia overlies the gossan
;,( the outcrop of the ore body, but it is found in the stopes
only in the southwestern and (less definitely) in the
northeastern parts of the mine. Well-bedded shaly tuff
occurs in the back of the stop,, on the' 830-foot level and
materia] closely resembling the volcanic breccia occurs in
the back of the stope on the 870-foot level. En the latter
stope the fragments of porphyritic rhyolite in the ore at

its upper contact closely resemble the volcanic breccia
exposed at the surface (fig. 4, A). In addition, the massive
sulfide ore. now represented by gossan, replaced tuff am
volcanic breccia in the vicinity of cross section C-C a
the surface. The fragments of porphyritic rhvolite in the
ore (fig. 4, B) have been interpreted by some observers as
a breccia formed by replacement along fractures but the
fragments are not of uniform rock type, nor do they have
the same type of alteration. Some fragments are silicified
contain no sulfide minerals, and have sharp, smooth boun-
daries. Other fragments are soft and are replaced by
pyrite, sericite, and clay minerals. The soft fragments
commonly have gradational boundaries against massive
sulfide ore. The fragments of porphyritic rhyolite in the
ore in the lower part of the breccia are alined parallel
to the ore contact.

It seems probable that the breccia fragments in the
ore represent unreplaced fragments in the volcanic brec-
cia-tuff bed and that this bed caps the ore in both the
northeastern and southwestern stopes. The tuff bed can
thus be expected to lie a short distance above the ore in
the central part of the mine unless it pinches out between
the outcrop and the stopes.

The openings that served as channels for the ore- i
forming solutions have not been located. No. 3, No. 5, and
No. 12 faults are mineralized, but only near the gossan
No. 12 fault contained up to 4 feet of massive sulfide ore
which is now oxidized to gossan, along the fault below
the bottom of the main ore body (fig. 4, C) , but the massive
sulfide changes to slightly mineralized rock less than 50
feet below the ore body. One or all of these faults may
have been feeders to the ore body, but it is equally prob-
able, as suggested by R. T. Walker and W. J. Walker 8
that ore solutions traveling horizontally would tend to
work out along premineral faults of this type, which would
then simulate feeder-channels in appearance.

OXIDATION AND ENRICHMENT

The gossan that formed from oxidation of the massive
sulfide ore extends from the outcrop of the ore body into
the wall of the canyon a distance of 30 to 50 feet. Steep
topography and a shaly tuff cover have prevented exten-
sive oxidation of the ore, and relict nodules of massive
sulfide ore occur in the gossan less than 10 feet from the
surface. The gossan is solid and resistant to erosion. It
is composed of dense to slightly porous limonite that con-
tains minor septa of secondary silica forming a coarse
silica sponge m the limonite. No collapsed breccia was seen
in the gossan, and there is little transported limonite. The
rhyolite below the gossan is iron-stained along fractures,
but it is not extensively replaced by limonite.

No assays are available on the gold content of the
gossan. On the basis of experience at other mines in the
district, it can be assumed that the gossan contains about
twice as much gold as the primary ore because of residual
enrichment of gold. The weight of the gossan is roughly
half that of the massive sulfide ore, and little or no leach-
ing of gold occurs in gossans of this type elsewhere in the
district/'

Secondary copper minerals are rare, but a little chal-
cocite occurs in the sulfide ore just below the gossan in
the No. 8 adit.

"Personal communication.

"Kmkel, A. R., Jr., and Albers, J. P.,

op. cit.

Shasta King Mine, Shasta County

REFERENCES

piderson, A. L., Some pseudo-euteetic ore structures : Econ. Geol.,

vol. 2!>, pp. 577-58!), 1934.
>iller. J. S., U. S. Geol. Survey Geol. Atlas. Redding folio (no. 138),

1'MHi.
■ raton, I/. ("., The copper deposits of Shasta County, California:

l\ S. Geol. Survey Bull. 4:t<>, pp. 71-111, 1909.

Hinds, X. K. A., Jurassic age of the last granitoid intrusive* in the
Klamath Mountains, California : Am. .lour. Sci., 5th scr. vol. 27,
pp. 183-192, 1934.

Kinkel, A. R., Jr., and Alhcrs, J. 1'., Geology of the massive sul-
fide deposits at Iron Mountain, Shasta County, California: Cali-
fornia l)iv. Mines Special Kept. 14, 1951.

Lindgren, W., 1'seudo-eutectic textures : Kcon. Geol., vol. 25, pp. 1-13,
1930.

43982 9-51 2M

DIVISION OF MINES
OLAF P. JENKINS, CHIEF

GEOLOGIC MAP OF THE SHASTA KING MINE, SHASTA COUNTY, CALIFORNIA

25 feet
;ea level

Geology by A R Kinkel, Jr , ond W E Hon, 1950

UNITED STATES DEPARTMENT OF THE INTERIOR
GEOLOGICAL SURVEY

LOWER LEVELS

GEOLOGIC MAPS OF UNDERGROUND WORKINGS, SHASTA KING MINE, SHASTA COUNTY, CALIFORNIA

CROSS SECTION A-A

CROSS SECTION E-E

EXPLANATION

Tuff ond volcanic brecci
Chlonlizod rhyolite

Nonporphynlic rhyolite
observed projected

CROSS SECTION B-B

CROSS SECTION F-F

Massive sulfide <

CROSS SECTION C-C'

Idoshed where approximately locored)

Probable fault

a a

Underground worhing

(doshed where promoted)

(dotted where coved)

LONGITUDINAL SECTION G-G

CROSS SECTION D-D'

LONGITUDINAL SECTION H-H 1

SECTIONS OF THE SHASTA KING MINE, SHASTA COUNTY, CALIFORNIA