anoldmine
Newmethods
ofworking
NM
Casehistory0l theEberleGroup,Mogollon,
NM
Socorro,
Bureau
of Mines& MineralResources,
MiningEngineer,
NewMexico
W.Eveleth,
byRobert
presented
atand
subrished
8lJ[i.';:
iliT
w0rrd
conference'
cesscouldbe economicallyappliedto lowgradegold ore. Activatedcharcoalcould
be used to extract the gold from unclarified cyanidesolutions(Zadra,l950). Unfortunately, the method was only suited
to relatively silver-free ore becausethe
causticsodium sulphidesolution usedto
leach the gold from the loaded carbon
also fixed the silver. In 1952the process
was improved by using hot caustic cyanide solution to strip gold and silver
from the loaded charcoal (Zadra and
the processreothers,1952).Nevertheless
mained unattractiveto the small operator
becausestripping was time-consuming,
requiring a minimum of 50 hours. Continuedresearchby the NevadaBureauhas
developeda processwherebythe stripping
time has been markedly reduced(Heinen
This newmethod
and others,1976,19'77).
to processlowsmall
operator
the
allows
grade ores of the Mogollon district
economically.
additional$5 million of ore wasproduced
Introductionand history
"flx.,;::if,yfi::
The Cooney (Mogollon) mining district (Thompson,1962).
The closingof the Fanny Mill on June
is located in southwestCatron County,
western New Mexico. Access to this 18, 1942forced a shutdownof the entire
remotedistrict is via US-180and NM-78. districtbecausethe mill had beenprocessThe area, due to its isolation, has never ing ore for the local mines including the
had rail servicealthoughplansweremade Last Chance,Pacific, Fanny,Eberle,and
at various times to constructlines from others (Weatherly,1949).SeveralsubseSilver City, 80 mi south, or Magdalena, quent attemptswere made to revive min130mi northeast.During the earlydaysof ing in Mogollon district, but without a
the raw ore was mill, ore had to be shippeddirectly to a
the district (1880-1900),
shippedto a smelterby freight wagonat a smelter.Gradeswere not then, nor are
cost of $50 per ton (Thompson, 1962), they now, high enough to sustainsuch
virtually precludingany large-scalepro- operations.With the exceptionof a brief
duction until milling facilitieswere con- periodof activitybetween1943and1946,
structed locally around 1900 (Allen, most such efforts failed and the district
Eberlemine
has remained virtually dormant. New
1909).
Aker collected samples
David
1967
reln
would
be
the
ideas
modern
technology
and
A German itinerant discovered
district in 1870(Jones, 1904);however, quired for Mogollon to becomean eco- in the Eberlemine but found the ore was
Iittle developmentoccurreduntil the area nomic mining district once again. The too low grade to warrant shippingto a
was re-discoveredin 1875 by JamesC. technologywasto comein the 1970'sin a smelter.Nine yearslater, R' C. Manning
Cooney,an army sergeanton a scouting processknown as cyanideheap leaching. visited several successful, small heapmission from Fort Bayard, New Mexico A group named ChallengeMining Com- leaching operations in Nevada and
familiarized himself with the hydroTerritory. In 1876,after retirementfrom panywouldprovidethe newideas.
metallurgicalwork of the U.S. Bureauof
the military, Cooney, for whom the
Recoveryof preciousmetals
Minesat Reno,Nevada.Manningand his
districtis named,organizeda prospecting
by cyanidation
partner at the time, GeneCook, submitparty to developthe wide, rich veins he
Although the solubility of gold in ted a sampleof Eberle ore to the U'S.
had discoveredearlier. But the area was
the stronghold of a band of Apachesled cyanidehad beenknown for more than a Bureau of Mines for testing. Results
by Victorio; constantharassmentby the hundredyears,the mining world did not showedthat the ore wasamenableto heap
Indianswasto preventfull-scaledevelop- recognizethe processuntil J. H. Rae ob- leaching(Heinen,1977).Mr.Cook dropmentuntil the 1880's.Cooneyhimselfwas taineda patentin 1867for "an improved ped out of the partnershipand was rekilled during one encounter.The Indian methodfor treatingauriferousand argen- placedby Aker. ChallengeMining Comproblems were gradually resolved, en- tiferous ores." The processproved im- pany was subsequentlyformed and an
at Mogollon. Extenabling productionto increaserapidly. By practical until l89l when a plant con- assaylab established
that material
determined
used
has
testing
sive
Africa
successfully
produced
in
structed
South
of
a
total
1905,the district had
in the area'
dumps
in
the
mine
gold
of
process
from
some
dissolved
gold,
which
a
in
and
copper
million
in
silver,
$5
(Lindgren,l9l0).
cyanide was precipitated on zinc dust particularlythe Confidenceminedump, is
The introduction of the cyanidation (Allen,19ll). Todayhowever,the costof also economicallyamenableto the heapprocessto the districtby ErnestineMining a conventionalcyanide mill, which in- leachingprocess.Testinghasalso yielded
Companyin l9l0 (Allen, l9l l) alongwith cludes crushing and fine-grind circuits, additionaldata regardingpropergrinding
efficient large-scale mills enabled agitation of the fine ore in vats with size,reagentconsumption,and optimum
Mogollon'sminesto expandsteadilyuntil cyanide,de-aerationand clarification of leach-cycletime. A carbon desorptionl9l4 when annual production peakedat the leach solutions, and the ultimate electrowinningplant similar in designto
$1.5 million (Ferguson, 1927). When precipitationof the preciousmetalon zinc the Reno plant built by the U.S. Bureau
operationsceasedin 1926due to rising dust is prohibitive for a small operation of Mines has been constructed at
Mogollon. A descriptionof the recovery
low-gradeores.
costsand decreasingprofits, the Cooney that processes
processfollows.
a
concept
Cyanide heap leaching,
district had produced more than $15
with
along
1967
recently
as
developed
as
gold,
a
and copper at
million in silver,
carbon'adsorption,
Heap-leaching,
time whenthe priceof silveraveragedless new techniquesfor recoveringgold and
process
at Challenge
electrowinning
than $1.00 per oz. Operationsresumed silver,however,providesan economically
Mining
ComPanY
to
again in 1931.Becauseof new orebodies attractivemeansfor the smalloperator
The completeheap-leachingfacility and
(althoughlower grade),efficientmanage- processsuch ores. In 1950, the United
circuit is shownin fig. l. Ore is
Nevada,
crushing
Reno,
prices,
Mines
at
Bureau
of
States
in
metal
an
increase
and
ment,
these operations were successful for demonstrated that a cyanide-leach, crushedto minus % inchesand stackedup
another l1 years,during which period an carbon-adsorption,electrowinningpro- to 12 ft high on the leachpads.Pad con-
February l9?9
NewMexicoGeology
1
P lo s t i c k e y w o y
36'mil reinforced
s o l o r -r e s i s t o npf I o s t i c
D e t o i l so f s o l u t i o nl o n k
Slimes
6 w o s h e ds o n d 2 2 - m i l p l o s l i c 6 " f i n e s o n d
D eettooi il ss o ff p oo dd o nn dd p oo dd b oo ssee
Frcurr 2-DerAILs oF cyANlDE soLUTtoN TANKSAND
LEAcH pADs. Courtesy Challenge Mining Company.
FtcunE 3-Flow
DIAcRAM oF HEAp LEACHTNGcARBoNADsoRprroN-DEsoRprroN
sysrEM.Adapted
from Heap leach processing of sold ores by
Heinen,Peterson,and Lindstrom,U.S. Bureauof
Mines,Reno,NV, 1977.
fourth. The nearly barren solution flowing from the fourth columnis recycledto
the cyanide-solutionholding tank. A
completeflow diagramis shownin fig. 3.
In the electrowinningplant, the loaded
Only 85 percentof the dissolvedsilveris carbon is placedin the strippingcolumn
removedprior to carbonadsorption,thus (fie. a). A solution containingI percent
assuring that excessNarS will not be NaOH (sodium hydroxide), 0.1 percent
recycledback to the holding tank and the NaCN (sodium cyanide),and 20-volume
FrcunE l-Lnyour
oF TANKS,cRUsHER,
LEACHpADs. heapwhereit would preventthe leaching percentethanol is heatedto 90o C, and
AND cARBoN coLUMNs. Courtesy Challenge Minpumpedupward through the carbon,disof the silverminerals.
ing Company.
After eachday's operation,the loaded solvingthe gold and silver.The pregnant
carbonfrom the first columnis sentto an solutionis cooledand storedin an agitastructiondetailis shownin fig. 2. Cyanide electrowinningplant. The carbon in col- tion tank. The silver is precipitated as
solution(0.5lb per ton strength)sprinkled umn two is movedup to columnone, col- Ag,S (silver sulphide)by agitation with
over the heap percolatesdown through umn three to column two; and column NarS. Calcium oxide (0.5 lb per ton of
the crushedmaterial,dissolvingthe gold four receivesa fresh 150-lbchargeof car- solution) is usedas a flocculatingagent.
and silver. Leach-cycletime rangesfrom bon.
Precipitation of the silver is complete
z$0to 60 days. Testsindicate 50 percent
recoveryin 19 days; however,the company hopesto attain 70 percentminimum
recoveryand will allow up to 60 daysto
Recycle
achieveit. Washing the spent ore with
b or r en s
----->
waterrequiresan additional20days-for
a total maximum cycleof 80 days. Each
rll'
tiil
of the two padswill hold 3,500tons-for
t" l
an annualcapacityof 34,000tons.
Eleclrowinning cells
The pH is maintainedbetween10 and
C or b o n
I I by the addition of lime. The pregnant
column
leach solution flows by gravity into the
II l t
R e s evr o ir
pregnant-solutiontank. From there, the
ilY
solutionis pumpedfirst into a slimessetC
o
o
l
i
n
g
Rec
tling tank and then into an agitation tank
bor
whereenoughNa,S (sodium sulphide)is
added to precipitate85 percent of the
dissolvedsilver. The remainingsolution,
containing15percentof the silverand all
Precipiiote
of the gold is slowing pumped through
to filter press
Corbon
Aq ^S
four columns(eachcontainingl50lbs of
stripping
o g i l o l i o nt o n k
activatedcharcoal)to removethe remaining silverand gold. The overflowfrom the Frcunt 4-Flow
DTAcRAMoF cARBoN DESoRprroNELEcrRowrNNrNc ILANT. Adapted from Gold desorption
first column flows into the second,the sefrom activated carbon with alkaline alcohol solutions by Heinen, Peterson, and Lindstrom, U.S. Bureau
cond into the third. and the third into the
of Mines, Reno,NV, 1976.
setlling
tll
I
,11:
Februaryl9T9
NewMexicoGeology
anotherconceptwith potentialbenefitto
the smallmineoperator.
Frounp S-TnucK BAcKEDup ro uNrr ANDwtNcH cABLEATTAcHEDTo HousrNc Courtesy Challenge Mining
Company.
after approximatelyone hour. The Ag:S
3) relativelyfreeof acid-formingagents
whichconsume
slurryis removedin a filter press;the gold
lime
in the filtrate is removedby electrowinnfines which will
4) free from excessive
preventpercolationof cyanidesoluing on steel wool cathodes.The barren
cyanidesolution is recyledto the cyanide
tionsthroughthe heap.
holdingtank.
Ores that satisfy theseconditionsmay
The advantagesof the heap-leaching be treated by heap-leachingtechniques,
processthat make the method so attrac- but only extensivetestingcan determine
tive to the smallmineoperatorfollow:
the economics.
l) Plant costsare about 20 percentof
In addition to the economicsrealized
from the use of cyanideheap leaching,
conventionalcosts.
2) Operatingcostsareabout40 percent ChallengeMining Companyhasdesigned
of conventionalcosts.
and fabricated portable equipment3) High recoveriescan be obtained
with low-gradeores.
4) Environmental damage is minimized.
5) Silver is selectivelyrecoveredprior
to carbon adsorption, minimizing
(the amountof
carbonrequirements
carbon required to absorb Ag is
=30 times that requiredfor Au of
equalvalue).
6) A batchofcarbon canbe strippedin
6-8hoursinsteadof = 50 hours.
7) Carbon can be reused, thereby
eliminatingsmeltingto recoverpreciousmetals.
Unfortunately, not all ores are amenable to the heap-leachingprocess;only
those ores that meet the following basic
requirements
canbe first considered.Ores
mustbe:
l) relatively free from carbonaceous
materialsthat precipitategold and
silver
2) freefrom cyanide-consuming
agents Ftoune 6-UNtr ts DRAwN up oN BED JUsr BEyoND
such as sulfidesof copper,arsenic,
CENTERoF GRAvrry Courtesy Challenge Mining
Company.
and antimony
Portableequipmentat Challenge
MiningCompany
R. C. Manningoriginallyconceivedthe
idea of portablemilling equipmentwhen
he was in the trucking businesshauling
grain in seasonand buying, selling,and
haulingmilling machineryduring the offseason.He subsequentlyrebuilt a 1970
Mack truck and a 1974Fruehauf trailer
and equipped them with hydraulically
operatedbedsfitted with rollersand a 35ton winch. Steel containers,8 x A ft
weredesignedand built with underframes
and rollers to match the truck and trailer
beds.The containersare open at the top,
have double doors at the rear (which
operatesimilarto thoseof a semitrailer),
and have optional steelbows that can be
fitted to the top of the unit and covered
with a heavycanvastarpaulin.Thesecontainers are suitable for hauling many
materialsincluding grain, ore for small
mining operations,and machinery. An
emptycontaineris left on locationand the
full containeris hauledto a mill. In the
caseof a smallmining operation,this service eliminatesthe need of a permanent
ore storage facility. The operator is
chargedonly the freight and a nominal
rentalfeefor the container.
While buying and selling machinery
mills, Manning recogand disassembling
nized that once an operationfolded, the
mill, being too costly to tear down and
move, becameessentiallyworthlessscrap
Frcune 7-Bpp rs LowERED,UNIT RoLLEDFoRwARD
ANDLocKEDINTopLAcE.Courtesy Challenge Mining Company.
February1979
New MexicoGeology
9
iron. On the other hand, if the machinery
wasportable,it would retain somevalue.
He then designedwaysto mount various
piecesof milling machineryin the containershe had usedin his grain-andorehauling operations. A set of flotation
cells, for example,could be mounted in
one container;and a ball mill in another.
Larger pieces of equipment could be
designedto roll directly onto the bed of
the truck or trailer. Puttinga mill together
with equipmentof this sort is just a matter
of mechanicalingenuity.Theseideasand
designshave been refined to the point
where all the equipment in use at the
Eberleventuretoday, with the exception
of the leach pads and holding tanks, is
portable. The equipment includes rolls
and classifer, crusher, ore bin, bucket
elevator,and power plants. The carbondesorption and electrowinningplant is
built into a semitrailer.
The largestsinglepieceof machineryis
the rolls and classifierunit, weighingapproximately40,000lbs. The Mack truck
handlesthis load with relativeease.First,
the truck is backedup to the unit (fig. 5).
The rollers on the truck bed and the
classifierhousingallow the heavyunit to
roll easilyonto the bed. A winch cableis
connectedto the classifierhousing, and
the unit is drawnup on the raisedbed to a
point just beyond the unit's center of
gravity (fig. 6). The bed is then lowered
and the unit rolled forward into traveling
position and locked into place (fig. 7).
Unloading is the reverse of this procedure.The truck or trailer can be loaded
in this mannerin lessthan two minutes.
The use of portable equipment has
manyadvantages:
l) Concrete foundations are not
needed.
2) Mill setup and disassemblytime is
heldto a minimum.
3) Permanent structures are not
abandonedwhenoperationscease.
4) When a property ceases to be
economical,the machineryis loaded
up and movedto anotherlocationthe operator is no longer out of
business
whenthe ore is depleted.
Challenge Mining Company is conductingmining and milling operationson
landswithin the Gila NationalForest.The
U.S. Forest Service has approved the
company'splansmainly becausethe portableequipmenthaslittle impactupon the
environment.
Economics
Discussingprofitability of a company
not yet in productionis premature.Many
things can go wrong. The ore, however,
l0
February 1979
NewMexicoGeology
has been tested by the U.S. Bureau of
Mines and repeatedlytestedby Challenge
Mining Company.Testresultshaveyielded reagent,fuel, and electricitycostsfrom
whichper-toncostshavebeencalculated.
Easily mined surfaceore on the south
end of the Eberle vein and a srnall quantity of high grade ore underground
amounts to approximately28,000 tons
averaging.08oz gold per ton and 4.5 oz
silver per ton. Confidence dump ore
amounts to approximately30,000 tons
assaying.045 oz gold per ton and 2.5 oz
silverper ton. Other smallerdumpsunder
lease contain a few thousand tons of
similargradematerial.
The company'stwo-year plan calls for
processing34,000tons of vein and dump
materialper year. Gold recoveryis 82.5
percent; silver 69 percent. Profits and
costsareoutlinedbelow:
ANNuar pnooucrroN:34.000ToNs
Eberleore
14,000tonsperyr.
Gold perton
.08oz
Totalgold
ll20oz
Productionat82.5v/o
recovery
924o2
Silverperton
4.5 oz
Total silver
63,000o2
Productionat 6990recovery
43,472oz
Dump ore
20,000tons per year
Cold perton
.045oz
Total gold
9A0oz
Productionat 82.590recoverv
743oz
Sifverperton
2.5 oz
Total silver
50.000oz
Productionat 6990recovery
34,500oz
Total annualproductiongold:
1,667oz
77,972oz
silver:
The economicsof the Eberlegroupventure wereoriginallybasedupon $150-peroz gold and $4.50-per-ozsilver. These
priceswill be usedherefor the purposeof
cost/profit projection,for as the price of
preciousmetalsincreases,
operatingcosts
will increaseaccordingly.
OpgnenNccosts
Dollars
Per Ton
Mining: Supervision,
insurance,
labor,
fuel, explosives,
maintenance,
expendables
2.225
Milling: Supervision
.705
Labor (mill operation,ore hauling) .95
Power(fuel,electricity)
.70
Reagents(lime, cyanide,sodium
hydroxide)
.'15
Water
.10
Maintenance
.44
Royalties(leases)
.97
Ore handling(transportation,
Ioading)
.40
Carbonadsorption(carbon,lime,
sodiumsulphide)
.24
Gold recovery(alcohol,sodium
sulphide,steelwool)
.24
Supportfacilities(assays)
.12
Fixedpaymentson machinery
2.57
Total
$10.41
Pnorrr
Total gold value,1,667oz at $150
peroz
Total silver value,77,9'12oz at
$4.50per oz
Grossvalue
Operatingcosts,34,000tons at
perton
$10.41
Annual profit
$250,050.00
350,874.U
$600,924.00
$353,940.00
$246,984.00
ChallengeMining Companyis a partnershipownedby threepersons.Two are
operating partners who enteredthe venture with approximately$300,000worth
of machinery, supplies,and cash. The
third memberis a financial partner who
matched the operating partners' investment by putting up $300,000for expenses
incurred during constructionand startup. The total investment therefore is
A projectedannualprofit of
$600,000.00.
$247,000.00should amortize the investmentin lessthan threeyears.
Futureof ChallengeMining Company
Phaseone of ChallengeMining Company's plan of operationsprovides for
processing34,0N tonsofsurfaceveinand
dump material per year. Surfacematerial
will be depletedin two years.The operation, if it is to survivebeyondthat point,
will haveto beginfull-scaleunderground
mining. The future for processingunderground ores is bright. Production at the
time of shutdownin 1942wasminedfrom
a winze sunk from the third level of the
mine. Recordsof ore shippedto the Fanny Mill at this time (138tons)show0.17
oz gold per ton and'l .28 oz silverper ton
(Weatherby,1949).The ore left untouched, however,averages4 oz silverper ton
and .08 oz gold per ton. Material of this
gradewasuneconomicalto mine and processby conventionalmethodsand, therefore, was left. Today, a minimum of
300,000tons of this low-gradematerialis
availablefor mining.
Summary
Production from the Cooney mining
district has been minimal for more than
30 years.Known ore bodiesin the areaare
of insufficientgrade and tonnageto attract the interestof a large mining company. Challenge Mining Company, a
small operator, is taking advantageof
new,low-costtechnologyand a few novel
ideasof its own to treat theselow-grade
ores,
AcrxowLnocvpnrs-The author wishesto thank
David P. Aker and Richard C. Manning of
ChallengeMining Companywithout whosecooperation this paperwould havebeenimpossible.
References
cited
Allen, R. S., ed., 1909, The Mogollon Mines:
Mogollon,NewMexico,v. l, Novembert*n
-_