R. 1. 4121 NOVEMBER 1947

UNITED STATES

DEPARTMENT OF THE INTERIOR

J. A. KRUG, SECRETARY

BUREAU OF MINES

JAMES BOYD, DIRECTOR

REPORT OF INVESTIGATIONS

INVESTIGATION OF THE MOUNT EIELSON ZINC-LEAD DEPOSITS

MOUNT MCKINLEY NATIONAL PARK, ALASKA

BY

NEAL M. MUIR, BRUCE I. THOMAS, AND ROBERT S. SANFORD
R. I. 4121,

November 1947..

WEPORT OF INVMSTIGATIONS

- 7 s ' " . . . ^ ' : , '.!~~~~~~~~~~~~~~~~~~~~

UNITEMD STATES DPAMEENT OF TIE -NtE IN IR - EtJIU . O}¢ S

: INV;TIGATION OF -MO3UNT EIELSON ZINC POSITS,

MOUNT McKINLEY NATIONAL PARBK..AA

By Neal M. Muir,../ Bruce I. Thomas and. Robert. S..Sanford.

CONTENTS

Page

Introduction ....... , , , -1 ,, ,,

Acknowledgents , ............. - '.. . . ... 

Loqatilon and accessibility' -i'^', ..., ^ +-,

c~sal, £eatures and cl ima e -''',,.. ,2'

History i A. i .* ...o9 . ..... '' ** '" 3-,

Ore deposits ' , 'a ' . 4,:,'

General geology - ,' * * 4

Structure . * 

Mineralization ' ..'.' ' ;, .. ,5"

InvestigatAln by the Bureau ofMines ... ** .,.t.

t Beneficiation tests ... .. '*'.*** ***.*,* a° ... a

INTROVUCTION

The presence of the zinc-lead-copper deposits an the north slope Qf.

Mount Iaelson, Mount McKinley National Park, Alaska, has been knov -or..

many years. The deposits were examined by J. C. Reed, '&geologist of the

United States Geological Survey during the summer of 1931. In the summer

of 1943 the authors and Clyde.Wahrhaftig, a geologist'of the Geological

Survey, examined the deposits.

. .. .ACIOWLEDGMENTS 0 ,, , ,,A , , *,

''In its program of investigation of mineral depbsits, the Bureau of.

Mines has as its primapry objective the more effective utilization of our

mineral resources to the end that they make the greatest possibl9 Gcqtribution to national security and economy. iEts the polOicyof the.Bur;eau t

publish the I'acts developed 4y each proJect assoon ,s p .racticabLe ater 

its con'cJusion. The Mining Branch, Lowell B. Moon, 'cief conduct0 preliminary exainstions, performs the. actual vestiat'$ewoqrk, at and, preprs

/ The Bure6;ui. oMines - will welcome reprintingo'f thib papet,,provid~e4dthofollowingfootnote aoknowled ent ie;-use&- ''tRp±ihted frcu Bureau oi

Mines Aeport of Investigations 4121."

2/ Mining engineer, Bureau of Mines, Juneau, Alaska.

E/ Mining engineer, Bureau of Mines, Juneau, Alaska.

J Acting chief, Alaska Division, Bureau of.Mines, Juneau, Alaska.,

1748
R. I. 4121

the final report. The Metallurgical Braach, Oliver C. Ralston, chief., analyzes samples and performs beneficiation tests.

Particular acknowledgment is dcue to Hpine Kenworthy, who conducted the

bPeeficiation tea-ta-under the supervision ofC. Travis Anderson; to Clyde

Wahrahaftig of the Geological Survey, wh1O completed the geologic and topographic maps8, to Graftt Pearson of' the NAtional. Park Service; and to 0. M.

Grant and Mrs. Frank MdGarvey for their assistance during the examination.

LOCATION AND ACCESSIBILITY

Mount Eielson is in south-central Alaska (fig. 1) and lies within the

boundaries of Mount McKinley National Park. The zinc-lead deposits are located at-approximately 630 251 mp"oVth. latitude and 1500 20? 00" west

longitude (fig. 2);'', ...

McKinley Pat f'ailr'6ad i st'ation is 548 miles north of Seward on the

Alaska Railroad; A two-lane gravel* 1ighway.conneets the station with Camp

Eielson and contiddsd'o'nr ~6 K antis4 *,,.This .road, although well-constructed,

was built prfrma2ly 'for scenic purpqs.Qs -with occasional steep grades and unnecessary length. T&e deposits are, .2, 1ja -south of a point on the highway

that is 70 miil'Os", fromi Mcinley ParAk*iIroad station.

No road. -conweecteThe zinc-leadi*eposits with the hig way. A tractor

road could be conStkUcte'& -at' nominal cost. To obtain favorable grades, the

road would start from a point approxiately 4 miles northedst of Camp Eielson and would be about 5 or 6 miles long. Thorofaro River can be crossed

by tractor and trailer on the- icoin-wizfter and by fording in summer. During the wanmest-weather of the slnmoeri haulage would be impeded by high

water caused by rapid glacier melting,. A tractor road would be sufficient

for small mining and mflling operajtion, but a large operation would require

a permanent truck road. -'

PHYSICAL FEATURES AUND CLIMATE

Mount Eielson rises just south of the east-ward-trending depression

that separates the Alaska, ange proper from its northern foothill belt.

Although it-s Va)art of the rng, A-t seems eomewhat isolated being set off

by Muldrow Glacier to the weastand stream valleys to the north, east and

south. '.

TIhe north 'alcb e of the mountainrises steeply" from Copper Mountain bar,

an old river beench with an average altitude of 3`5jOObfeet (fig. 2). The

mountain is composed of three heavily glac.iated. peeaks (altitudes 5,720;

-5,861, and 5,602 feoet)Y, which are canneote6- ban n east-west trending knifelike ridge. To the north of this ridge two deeply ineiSed cirques flanked

by sharp, nQxthward trending ridges are major- 'topographical features.

Grant Creek rises in, one of these and Granlte Cite6k -in the other.

1748 -2-
0JoD;~~~~b

'>/H At

C-MT.Fiur El -Not-eta lsa
0 N

COMPILED FROM MAPS BY

U.S. GEOLOGICAL SURVEY, BULL.849

I I 0_-O Mi.I

K~~PR

McKIN EY

'*-T O K A NTISIN AS'

Figure 2. -Mount Eielson and vicinity.
IH~GLAND

U ~~~~~~~~~LEARYO.

NO T E: SCA L(NORD

ah / 13,SOWNI PRNT OD 

t+'> > / ~~~~~~~CLAIMS, BOTH PRIOR TO AND

SINCE 1931, ARE SHOWN IN PAR-

'/ SINCE JAENTHESES. 1931 THE MA47

RELOCATIONS HAVE PROBABLY ALTERED POSITIONS AS SHOWN.

Figure 3. - Claim map, Mount Eielson.
R. I. 4121

The mineralized zone trends eo.st-west and. extends. al.^ot 1Lmiles along

the north flank of the mountain itedi4tely above and south of.gentle morrainal slopes leading down to the flats of.the ThorofareaRiver. The claims

lie between altitudes 3,300 and 4,250 feet.

The deposits are above timber line, which is at about 2,000 feet in

this region. Only a few shrublike willow and cottonwood trees border Thorofare River and a few of the creeks. All mine timber would have to be brought

from low country 20 miles to the north or west. This could be. accomplished

with tractor-drawn sleds in winter.

Water for milling is available. Grant Creek has flow enough to.furnish part of the power for milling during the summer months.

Winters are long and -cold and nsumers are moderate. Precipitation is

light, falling mostly as rain during the summer months. McKinley. Park station has a comparable geographic positionwith respect to the Alaska Range,

and weather statistic1 assembled over a:-period of 7 years are as follows:

Maximum temperature, degrees Fahrenheit ............. 89

Minimum temperature, degrees Fahrenheit ....... minus 54

Average number of days per year with temperature.

over 70 degrees Fahrenheit .................... 41

Average number of days per year with temperature-b's-:

low 32 degrees'Fahrenheit ... d ........... ' 133

Average number of days per year with temperature below 0 degrees FahrenheitV........ ... ...... .... ::-32

Average annual mean -temp4tature, degrepe F.. 28 2:

Average annual snowfall, inches ; 59.5 *....... 

Average annual preceipitatioh, inches .' ....... ! 14.38

The climate, while rigorous, would prove no serious hindxrnce to maintaining year-round underground operations Mining by open-cut-methods

would be limited to 8 months a year. Snow is not removed from the park

highway at present. Because of the low texaperatures, snow is dry and

drifts easily so that it is easy to remove, but it would be very difficult

to keep the highway open.

HISTORY

- The following historical outline was'obtained from 0. M. Grant, of

Fairbanks, Ala.aka, who has been familiar with the Mount Eiels on'district

since its discovery. The first four mining claims were staked by J B.B

and Fannie Quigley in 1920; later that year, two claims were staked by Biglow and Perry.;'-In 1921, 0. M. t andsF. -G.-.Jile' located several-claims.

Durixng subsequent years mpny claims revdrted to the public domain,

same have been.restaked with d.itf rnt 'boundaries .-d different names. The

claim map (fig. 3) show both The preseznt and' former names. Ad nearly as is

known, 0. M. Grant, John Anderson, and Mrs. Frank McGurvey, all of Fairbanks, are the present owners.

1748 -3-
.~. B.. I.. 4121

..Veryclittle' de*61opnent work has. been done'.Thiqe .are~three short

on tthe 3iled .- elim, two of which are caved , an a large number of

.0all pro e'ct-pitb'and open cuts. de~1opriont work ~.a bee doe r he hr.hr 

There has been no production from the district..

OR DEPO'ITS

General Geology .

The general geology of the Mount Eielson .istrict has been spmmarized

by John C. Reed ;a5 foljows:

The most widely distributed rocks of 'the district inclufi

a thick serid o~f~ *thin-bedid' limeatone, baJilcareous shale, and.

graywacke of Pbl6eozoic, prsba'hly De~orian, *,The.e sedi-

; :ments are cut by a mass of graxodiorite,'wh1.o.'orms most.of

-.. *:Mount Bielson and'which was intudedprobabdyi n late Mesozoico

time. The intrusive has sent a multitude Qf dikes and sills

into the. ussociated sediments.

Materil.. given off'by thc o.icŽ?ite ,as'permeated the

enclosing se~imenta and seloctiv&1l i F~lceoi them wi~th minerals

of the epidoted group and to a'soma~whit lesser extpnt. with sphalerite, gaaehaloopyrtej .d pyrit'

An- oreabearing zone c=n be-ded'fiitely traced.for a'bout 4

miles alcng .theriorth -side oftthe' granodiorite taps.. Ita widthl.

on the.surfaoe ies no', -uniform; buttpits 'thicknes5 8i 'aboit 2,000

*eet. Sphalerite is -the mobt tbunddnt sulphide and is several

times as abundant as galena. Chalcopyrite is present in.minor

quantities. Thedibll 'dmount iS? silver in the6'or6appars to

be irregularly distrlbuteod.'

According to Glyde W: hrhitig, S the'-o.Idqstt'rboc1 the.,vicinty of

,tha. ore deposits ar lpee"toneS, -piiyl!ites, aid'qiiatrt.it',E :f4. have been

recrystallized, and so@ of them have been inteniaey boared. n places,

the original material has been replaced in part or wholly by hydrothermally

introduced material.

A large' stock of granodiorite underlies most df Mount Aieison, an&

dikes from this stock'have intr66di the s mdhzlits, in the y i of t he

ore deposits. ,

'' le'ed, J. C., The Mount Eielson District, Alaska: Geol. Survey Bull.

. 8J49 (d.), 19533i, p. 231. .

;,.,/ Wahrhattig, Clyde, Zinc Deppooit of_,the MoUnt .EelsoD Vistribt', Alaska:

'3, S. Geol. Survey I forma4tign.Senvice Release, June 15, 1944 7'pp.,

1748 4-
N

S~~

SCALE IN FEET .0 7~I

t 18,E-!~~~~-2

=] TALUS L ALLVIU

BASALT DIKE

GRANODIORITE PORPH.

Mi LIMESTONE\ \\ <

EPIDOTIZED LIMESTONE

SULPHIDE-BEARING -EPIDOTIZED LIMESTONE\\\\\ \ Ei -- SHEAR ZONE

S:

COMPILED FROM SKETCH MAP BY GEOLOGICAL SURVEY4 1943

Fiqure i4. - Virginia and Denver claims.
50 0

LZ TALUS AND DRIFT 0 o k , * e.

* * * \ * eSCALE IN FEETe Lg3 SULPHIDE-BEARING TALUS i/ . , . S.

BLACKSMITH SHOP' B 0, * X I1 ALLUVIUM 0 *4

i BASALT DIKE

RHYCOLITE DIKE

~:PORPHYRY DIKE E\1

E2 PHYLLITE

JAN.gSCOMILE FO SKTC MAPe BYd GEOOgCA SURVEY, 1943

Figure and 5. Georgia - Jiles claims, Mount Elelson.~~
R. I. 4121

Structure -

! On the north a2lpe of Mount Eielson, in the vicinity of the ore deposits, the sediments generally dip toward the north;, locally they have been

contorted..'

The general strike of the dikes in the caniyon of Grant Creak is. east

and the dip is steep or vertical.

S~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mineralization

Shear zones have been noted in the vid.zity of th. zinc-lead deposits.

They appear td be earlier than or contemporafteoias with the intruwsions of

granodiorite porphyry and quartz-diorite porphyry.' Locally, the shear

zones )iave afforded channze8s for the orewformiBg fluids- Other channels

were afforded by the contacts of the dikes with. thesediments.

During and after' the intrusion of the porphyry Aljies, quantities of

quartz, epidote, and calcite were introduced into the sediments by hydro

thermal solutions. Limestone was replaced along contacts and shear zonee

by homnfels.

Sphalerite, galena, chalcopyrite, and pyrite replaced sote of the

hornfels and were deposited along fractures and grain boundaries of the rock.

A small amount of supergene alteration has taken place and resulted in

the formation of thin crusta and stains of secondary zinc, lad, iron, and

copper minerals.

INVESTIGATION BY THE BUREAU OF MINES

The Mount Eielson zinc-lead deposite were examined by the Bureau'from

July 30,, 1943, at24 1943. Camp was establiseed at the Forest Service shelter cabin 1 mile west of the deposit. 2*e program consisted in cleaning out a large number of trenches, test pits, and open cuts.

Twenty-three channel samples were cut in surface trenchesan pits. three

grab samples were taken from the surface of talus slopes below the outcrops.

(See figs. 4 -and 5.) These samples were slightly oxidized, and oxidation

interfered with the flotaticn-tests that are discussed in the following

chapter. An examination of the, one adit that is now openaAndicates that

the oxidation is only superficial.

The samples were, sent to a.private firm for analysis; results are

shown in the f6llowing table.

1748
R. I. 4121

IABLE 1. - List of channel-samples, Grant property, Mt. Bielson District, Alaska, taken by N. M. Muir,

mining engineer, Bureau of Mines, August 194)

Width 1

vein . Analysis,. ..

stampled, Percent 'Ounces a ton..

.Sample feet LeadlZincI C2222 Goldl Silver Name of working! Location Comments

E-l 3-0 3et85j5.° 1 0.15 0.0 1.70 Jiles claim- East face out from Fractured,..ueathered epi-

. . "Big Cut" north wall in south- dote with spphalerite and

. .. f 'erly extension of galena.

. .. |~~~~~~~~main out..

E-2 2,4. 2,o8 6.o,0 .- 1.82 do.. |Southerly from E-l IEpidote with some sphalerto south wall of |ite and galena.

.of cut.

>o '. o o do. featel wxtens o

E-3 4.5 2.60 ,46 0o2A 14 feet west from tHard and tough limestone

:-face of easterly Mx- and epidote with sphaler-

-;: ' , ,|' . I Itensioneof cut on iite and galena,

4.7' . *-':1 .. 2 j ;-iloping side of cut.l

E-4 3.0 4.504 . 0.25 0.0 2.00 do.- 113 feet west from jHar'd and tough epidote

: : | - --l - - - ! face of'easterly ex- with considerable galena

. -t- | -- " - .. ttension; northerly and sphalerite.

!from E-l to I foot

'; S -I| above . floor of cut.

E-5 5.8 1.46 4.'O t 0.10 !Io. O;1.54 do.- 16 feet west from Epidote and altered broken

. .. : .-. -| face .... on .... limestone .easterly with scme galena

- 1-i - I - ] twall of- cut 2 feet and sphalerite.

*t. @ 1 I iabove floor, 0 o.4~~o 0. do2.1thr

E-6 2.0 4.68 0.40 2.14 do, Southerly from E-5, !Weathered, altered lime-

;5 feet above floor Istone and epidote with

I ' ' :[' "t 1 |cut. aphalerite and galena.

E-7 12.5 1.97 3.64 - - 1.80| do. From 2.0 feet south 5 feet of sample carries

of south wall of 1most of the sulfides 7.5

easterly extension feet of sample with scatto south end of E-5, tered sulfides.,

taken 1.5 feet above

- ! I* - Ifloor -____________ _ of cut.

Continued --

1748 -6-
R. I. 4121

TABLE 1. - List of channel samples, Grant property, Mt. Eielson Districtx Alaska, taken by N. M. Muir,

mining engineer, Bureau of Mines, August 1943 (oont"'d.)

Width -

vein Analysis -

sampled, _ ercent lOunces a ton I -

aml feet Lead Zinc Copper Gold Silver Name of working| Location CommentsE-8 1.5 37 .24 -4l 1.42 Dee clalm, Lake1 5 fbet-east of ds-. Chip OmMple along outcrop.

-: : - .70 view Cut. covery monument.:

E_9 1.5 5.82 .5 40 1.70 Jiles claim in |Cut NoO. is or line kiieied m4teral with g+le-

; i Blackbmith Shop- o ridge sample from n& aria phaVerJte.

-- Gilch, * l No. --2 tthe face. - I l , -

l e~-ut. -

E-10 4,0 2.81 2 .94 0.25 0.0 1.50 Bladckmith Shop lo0 feet bielow sur- Limehtone with sphalerite,

( Oflch, Laige Iface. -ialtea, and dhal opy~Ze.

* .- .. ,; . .I.. : | No * il cut is - I -

near top of

I,. - ridge,- east -

E-ll 6.0 1.1 5.76 - - C.64 West side B. S. Badly broken f Idoto 'lieft one,,anoe'

Gulch Top cut. 1tion, sample across galepa, and. sphop rite.

apparent width.

E-12 4.5 3.20 5.30.1 0.20 0.0 1.3 East side B. S. Morth side of cut 'Hard and altered-_epidoote

Gulch No. 4 or from epidote band jand limestone with, limo-.

Bottom Cut 80 nnierly. ite, sph4erite, and, galefeet southeast | 1na.

2.421'' . . : \ . of forge.

E-13 2.7 1.25 2.42 0.15 0.0 0.22 East side B. S. Northerly from E-l2. Very hard epidote6a&d lime-

-W Gulch No. 4 or B stote.

Bottom Cut 80

lrei.t southeast

- . of ; forgi;.'

E-14 8 5.0 4.10 5.00 0.25 O.Q 1.62 East si6de B. 8. 'lorthoasterly from Hard, blocky, epidotized

l --- 1- -I Gulch No. 4 or -13 in bottom of limestone, considerable

I sc - -1 5Bottom Cut 80 cut. galena and sphalerite-.

- 1__ - l -|^feet j 8otthe at

1748I -oztgeu. - -f 7 1 of~torge;, l - -- ; f;~~~~~~~~~~~~~~~~~~~~~1n~ - - ,, .i.'- i::

1748 -7
R.-I. 4121

TABLE 1. - List of channel aapls, 'Grant property Mt. Eielon District Alaska, taken by N.-M. Muir,

mining engineer, Bureau of Mines, August 19 5cont'd.

Width I'

vein - Analysis, I

sampled, Percent lOunces a ton

Sample feet Lead Zinc Copper Gold Silver Name of working Location Comments

E-15 2.0 2. 2. 3 - - 0,22 Venora Dis'covery Face cut. i Chipped sample, limestone

Cutt and ep'odite, with sphalerE-16 0.55 4.0 10.0 13.22 I 6.90 2.62Venor. o. 2 C Lor ofite'id galena.-

E-16 4.0 3.22.6.90 _o.35 ! owo 2.62 Venora No, 2 Cut Lower face of cut. 'Hard and altered limestone

lend epidote with consider2.0 I 2.20 1468 'Grant 1.15 re, E of north |0.0 Iabla'oralena and sphalerite,'

E-17 2.0 4.68 6.36 1.15 0.0 2.20 !Grant Creeki t Va Face of north-or jLimestcne with epidote and

.Ii ! 3 ICut No. 1-a. (a) out, 8 feet in cherite,'codntaining considend l foot above |erable galena, sphalerite,

15*O0 0.90 |.~ Ifloor. - -andc'halcopyrite.

E-18 5.3.1 5. 4099, 0.90 0.015i 9.80 |Grant CreekEva Face between (a) Ifard, siliifie lmestone

;Cut:No. l-b. 'and (b 3 cuts. ;and epidote with considerI ! ' lable galena and sphalerite.

E-19 3.8 7.00 6.60 0.35 10.0 1.30 lGrant Creek, Eval Face, north sectiont Limestone with some epidote

jCut-No. .l-b. Iof cut. |and appreciable amounts of

| i g -galena -"'and s'phale'ite'.;g 

E-20 9.0 2. 300 Creek Cut pGrant FroZc south end. of Lizestcne and-epidotized.:

ii*o.5; i.e. out northerly for limestone with sparse galeIthird cut below 9.0 Seet: na aphalerite.

jgrassy bench.

E-21 7.8- 7.18 7.20 - - 1.66 Grant Creek, E From rLimestone 8-feet north and epddte with

Cut No. 3. of E-20, northerly some good galena and sphal-

. . | ~~~~~~~~~~~~~for 7,8f feet. -eri-te. -- --

B-22 25 8. - 0.62 Grant Creek, Xv Saple cut along Soft and hard'limestone

' | g 'I ' ' '':]'Out C No. 2 !bedding for 8 feet, with epidote and considerI J X I e able good galena and sphalI____________ i_____ ierite. _________________________________________ Continued --

1748 . 0' .... . ...-.

1748~~~~ '''''"-' '-'
-R..7I. 4121

TABIEf 1. - Lis-t "of channel samples, Grant property, Mt. Bielson Distript, Alaska, taken by N. l$. Muir,

mining engineer, Bure'aug of Mines,.' u 4 3 (cort±dj)

'; : 1 .": - q .:

Width : .. :

vein Analysi, . _ : ____-_'___ , :__._._-

sampledi Percent [Ounces a t .

Sample feet Lead ZjhcjCopper Gold Silver Name of working Location .Ccment

E-23 Grab - 54 40 .50 0.45 0.0 1..2 Lillian,:'claim, Grab of- 'chipped and Xepresentative-,of 8ix

Big Cliff on picked ore on north, stringers ranging from 2

west side Grant sid" of cliff. inches to 10 inches in

Creek.. - with.

E-24 Grab 6.80 8.70| 1.40 0.0 2,00 Liilian. Claim, Grab of. chipped and'. Repres ents about 2 feet of

Big Cliff on picked. ore on 8outh mineralization.

.west side.-Grant side of'cliff along

..C'reek, : ' "fault'I ravine.

E-25 3.7 4.16 5.86 - _0;.42 Wolf Cla Cut Face of cut'near Hardy blocky limestone . :. ,H - t No. 1, near bottom. with some goodi.alena and

mouth Grat .phalerite.

,I .- Creek Canyon.

E-26 Grab ~5.09 5.20 0.35 'O0: 1l50 us 6 E-26 Grab . 5g°9 5.20 oo35 ;,o~o l 1 T4, s sLope ITaken from an area Grab of picked and ,chipped

east BJlanlkamith 250: f eet aloing the sabiples weighing 6~_-pounds.-

. . 1 - Shop Guich, slope across a width

Ifrom 10 tO: P0 feet. ,_._;_;

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R. I. 4121

BEWICIAMION TESTS

During the Bureau's examination 26 samples were taken. Eighteen Aamples, containing over 7 percent of combined lead andzinc,. were composited

for the metallurgical work. The tests described in the following paragraphs

were conducted in the Bureau's laboratories in Rolia"' Mo.

Physical Character

The ore consisted of galena and sphalerite associated with the gsngue

minerals epidote, calcite, and quartz l; smaJ4er amounts. Cerussite, iron,

oxide; smithsonite, siderite, and chalcopyrite 1Jso were present in small

quantities. The calcite appeared to be an alteration.product of the epidote.

Water-soluble salts giving an affirmative test-for sulfate and calcium ions

were present.

Trhe sulfides were closely associated and disseminated throughout the

sample. The epidote was often cut by veinlets of galena approximately 80

microns in width. Microscopic examination of washed screen fractions showed

that about 75 percent of the sulfides were free in the 65- to 100-mesh range,

about 90 percent in the 100- to 150-mesh range, and about 95 percent 'i the

150- to 200-mesh range.

Chemical Character

The chemical analysis :of., the composite of samples E-1} E-2 B-3, E-4,

E-6, E-8, E-12, E-14, E-16,; E-17> E-18, E-19, and E-21 through E-26 was as

follows:

Analysis, percent

Pb-. i 0 Zn

Total Nonsulfide Total I Nonaulfido Cu Fe, Insol.

4.22 1.27 35.27 0.37 . 7, 69.5

Treatment Procedure

1. Selective flotation.

2. Bulk flotation.

Selective Flotation

Flotation tests were made 'to concentrate the lead and, then the zJino by

differential flotation. No treatment method was found that would givie satisfactory results. Apparently, the film of oxidation produoits'prepent: on nearly all of the galena particles prevented them from floating kith'the, lhaxacteristic ease of clean galena, these tests were made on mn',l00-me4h pulpe.

1148 10- "
Ft i. I4121

Bulk Flotation

Several flotation tests were made at 65-mesh, in which the suLfides

were floated and cleaned in bulk. Varied treatments were then. tried'to separate the lead and zinc minerals. The use of zinc depressants was not successful. Regrinding the bulk concentrate to minus 325-mesh before adding

zinc depressants gave only slightly better results. Tests to depress the

lead and float the zinc from the bulk concentrate gave somewhat bettbr results, but grades and recoveries were lower than-in commercial practice.

The lead was easier to depress at coarse sizes, as separation depended on

the presence or formation of an oxide film on the galena surfaced. A coarse

grind, however, was disadvantageous because of lcke& lead and zinc mineral

particles. Potassium dichromate was used as. the leadr depressant, and American Cyanamid reagent A33 added to the effectiveness of the dichromate. A

typical batch flotation test is shown in detail below.

A charge of the composite sample of the ore crushed through 20-mesh was

ground wet in stages to minus 65-mesh in a pebble mill. The thickened pulp

was conditioned in a subaerated mechanical-type flotation cell diluted to a

density of 25 percent solids with grind water, and the sulfides 'were floated.

The sulfide rougher concentrate was cleaned three times and then subjected

to a series of three lead-depressing treatments. The rougher bailing was

sulfidized in an attempt to float the cerussite remaining after.removal of

the sulfides from the pulp. Zoolite-softened water was used for grinding

and flotation. The results are as follows:

I Analysis, percent i Pbrcent of total

Pb b

Weight, Non- i -l oProduct percent Total sulfidej Zn Cu Totallsulfide Zn 'Cu

Sulfide lead 8 2 1 25.2

ConCentrate . 5.200 41.9 |2.45 12.5 l.73 51.00 l 8.2 -T2.4: 23.2

Oxide lead con- I 1 1.73

centrate .... 1.82 20.2 17.4 2.60 0.82 8.61 20.5 3 9 .8

Zinc concentrate ...... 8.08 5.90 1.15 49.5 1.78 11.2 6.o ° 76.5 37.0

Sulfide middling ....... 11.02 5.76 4.02 2.25 .'88 14.8 287 4.8 25.0

Oxide lead mid- i

dling ...... 3.64' 3.23 3.20 .97 .40t 2.7! 7.5 . 7 3.8

Tailing ....... 70.24 71 .64 .35 .34 11.7, 29.1 4. 7.2

Calculated head 100.o001 4.271 1.55 5.251 0.39 1100 100.0 jloo.0 100.0

1748 .
R. i. 4121

Operaing d4aia-

___________ ______POWABs pe], ton of ore

Bulk fl6tat on -- L66 dzinc separtion' Oxide flotation

Reaents Con.c Co.JR. 1 Cl . 2~~X 5 Oi. 3.1 )40ntC.5 Con.. Cl. 6, CinT Coxi. I Cl. 1

Cdopper sulfate .... 05 "7T

Aerofloat 25 ..... 0.121

.AniYl xanthate ... 0.05 0.15

Methyl amyl alcohol o .06 0 .0 o6..;Oj 0.04

Potassium dlchrcrmate. ,2 ~d00

Reagent 63 .~.:.... -0.~03 0. 025 0.025 - __

Sodium sulfide .. 2..00 _______

Con. -Conditioner*' -l Ceaner M R.-::Rouge J

1748 -2- 1 .
R. I. 4121

The tailing contained 0.30 percent of nonsulfide zinc. Sulfidization

recovered only a small emount of lead in a low-grade concentrate. The

grade could bo raised by more cleanings, but increased recovery was not obtained by the use of more sodium sulfide. The sulfide middling contained

much true middling and should be reground in a continuous circuit. Ccambining the oxide and sulfide lead concentrates would result in a product recovering 59.6 percent of the lead and containing 36.3 percent lead) 9.9 percent zinc, 1.49 percent copper, and 6.33 percent nonsulfide lead.

Summary

Due principally to locking and oxidation, this ore did not respond satisfactorily to concentration. The load concentrate contained 36.3 percent lead and 9.9 percent zinc with a recovery of 59.6 percent of the lead., The

zinc concentrate contained 49.5 percent zinc and 5.9 percent lead with recovery of 76.5 percent of the zinc.

1748 -13-