challis precious metals report

8/3/2019 Challis Precious Metals Report

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Quantitative Mineral Resource AsseSelected Mineral Deposits in theChallis National Forest, Idaho

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Quantitative Mineral Resource AssessmSelected Mineral Deposits in theChallis National Forest, IdahoBy MARK W. BULTMAN


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U.S. DEPARTMENT OF THE INTERIORMANUEL LUJAN, JR., Secretary

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CONTENTSSummary 1History of mineral production in Challis National Forest 1Methodology of the quantitative assessm ent 2Quantitative mineral resource assessment in Challis National Forest 3Quantitative assessm ent of selected mineral deposit models 4Polymetallic vein deposits 6Precious-metal vein deposits 6Stockwork molybdenum deposits (Cretaceous) 7Polymetallic skam deposits (tungsten skarns an d copper skarns) 9Irregular replacement deposits of base and precious metals 9Sediment-hosted, jasperoid-associated, precious-metal deposits 1 0Stratabound syngenetic deposits of precious an d base metals 1 0Gold placer deposits 1 1Summary of quantitative assessment of Challis National Forest 11Selected references 11FIGURES

1 . Map showing location of Challis National Forest an d principal miningdistricts 162. Graph showing discoveries of mineral deposits in Challis National Forest3. Graph showing tonnages of ore in poly metallic vein deposits 1 74. Map showing tracts permissive fo r occurrence of polymetallic vein deposits5. Graph show ing tonnages of ore in precious-metal vein deposits 186. Graph showing gold grades of ore in precious-metal vein deposits 197. Graph showing silver grades of ore in precious-metal vein deposits 198. Map showing tracts permissive fo r occurrence of precious-metal veindeposits 209. Map showing tracts permissive fo r occurrence of Cretaceous stockworkmolybdenum deposits 2010. Map showing tracts permissive for occurrence of tungsten skarns an d coppeskarns 2111-15. Graphs showing:

11. Tonnages of ore in irregular replacement deposits of base and precmetals 2112. Lead grades of or e in irregular replacem ent deposits of base an dprecious metals 2213. Silver grades of or e in irregular replacement deposits of base an dprecious metals 22

14. Copper grades of or e in irregular replacement deposits of base and


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TABLES1 . Mineral deposit models an d grade an d tonnage models used in this report2. Probabilistic estimate of number of undiscovered deposits of selected min

deposit models in Chalk's National Forest 73. Probabilistic estimates of tonnages of metals and ore in undiscovered deposelected mineral deposit models in Challis National Forest 84. Summation of probabilistic estimates of tonnages of metals and ore in unddeposits in Challis National Forest 11


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Quantitative Mineral Resource Assessment of SMineral Deposits in the Challis National ForesByMark W. BultmanSummary

This quantitative assessment of selected mineraldeposits in the Challis National Forest, Idaho, is providedto assist the U.S. Forest Service in complying with Title 36,Chapter 2, part 219.22, Code of Federal Regulations,which requires the Forest Service to provide informationand interpretations so that mineral resources can beconsidered with other kinds of resources in land useplanning.

This report is a companion publication to MineralResource Potential and Geology of the Challis NationalForest, Idaho, U.S. Geological Survey Bulletin 1873, byWorl and others (1989). Geologic, geophysical,geochemical, mineral resource, an d mineral deposit datain Bulletin 1873 were used in this study to producequantitative estimates of the potential resources availablefrom selected mineral deposits in the Challis NationalForest.

The quantitative assessment involves three steps(W.D. Menzie, written commun., 1988) that are followedby a computer simulation. Known and possible mineraloccurrences ar e identified an d classified into appropriatemineral deposit models in the first step. The second step isthe production of a mineral resource assessment map,which delineates tracts that are permissive for theoccurrence of deposits described by the models defined instep one. The third step is the estimation of the number ofundiscovered mineral deposits in each mineral depositmodel. The computer simulation is carried out by aprogram informally referred to as MARK3. The output fromthe MARK3 program is a probabilistic estimate of the oreand metal contained in deposits of each mineral depositmodel.

Using available information and the MARK3

HISTORY OF MINERAL PROCHALLIS NATIONAL FORES

T he Challis National ForForest") contains 4,338 m i 2 ofthree separate areas (fig. 1); eleproximately 6,000 ft on the marPlain to 12,662 ft on th e summitest includes the following physiotral Idaho: th e Lost River Range,tains, the Boulder Mountains, thethe Stanley and Copper basins, Range, the Pioneer Mountains, ththe Salmon River Mountains.The Forest and the surrouhistory of mineral exploration aplayed a major role in the ecoMetals produced from mines in thest include gold, silver, lead, zindenum. Small amounts of fluorsearth-element minerals have anumber of other mineral commoed to be present in the Forest, buduced. These include iron, baritfur, antimony, manganese, and arThe discovery of mineral dbeen quite sporadic since 1860discoveries are mostly a reflectiothe minerals industry. Gold attracto the area of the present-day CFrom the early 1860 's to 1869 mplacer deposits an d a considerab


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copper, and zinc from multimetal veins, but tungstenproduction was also important during this time. Therewas considerable exploration fo r uranium in th e 1950 'san d 1960's, resulting in some production of uranium in1959 an d 1960. A number of porphyry molybdenum de posits were discovered in th e 1960's, including th eThom pson Creek deposit, which is still producing ore to day. Another exploration program in th e 1960 's an d1970's delineated a number of large stratabound depositsin th e Bayhorse region, bu t no mineral production ha syet (1989) resulted from the discovery of these deposits.

M ETH O D O L O G Y OF TH E QUANTITATIVEASSESSMENT

The quantitative assessment presented in this reportis based on the concept of a mineral deposit model. Amineral deposit model can be defined as the systematically arranged information that describes the essential attributes of a particular group or class of mineral deposits(Cox and Singer, 1986). For the most part, these at tributes are geologic, but they may also include characteristics affected by th e utilization of a deposit, such asthe grade of ore produced from it . For a deposit modelto be of an y use in a quantitative assessment, it must becombined with tonnage and grade models based on alarge proportion of the deposits known to belong to thegiven deposit model. Such models are produced by plotting tonnage and grade against percentage of deposits.The resulting frequency distributions, which are most of ten approximated by the log normal distribution, showth e percentage of deposits of a given model that have aparticular tonnage or grade.The quantitative assessment involves three steps(W.D. Menzie, written com mun., 1988) that are followedby a computer simulation. The first step is to identifyknown and possible mineral deposits in the region and toclassify each into a mineral deposit model. This stepm ay include an extensive literature search, a search ofcomputerized data bases, and possibly field verification.The second step is to produce a mineral resourceassessment map. This m ap delineates al l of the geologicterranes (based on rock type) that ar e permissive for the

deposits in the tracts delinmineral deposit model. Thisstep in assessing undiscoverdefinitive statements ca n bemake such estimates (W.D1988). In general, the estimand are based on geologic question an d knowledge ofsidered. Often the estimateered mineral deposits is madty distribution, an d estimatean d 90-percent levels of con

The estimates of the neral deposits in this report on the information availableassessment was made. All ogeological analogy. Such estion of al l of th e available gphysical, an d mineral-occurth e postulation that areas wimay contain similar densitieEstimation of the numwas done in two parts. Firstknown mineral districts an dattributes favorable for the eIn the latter group, depositsimilar to those in the minelatter group are areas of higed by Worl an d others (1 989

known mineral districts. Thhigh resource potential requthat indicate a high degree ocumulation and evidence ofat least part of the area (WorSecond, estimates werside known mineral districtsattributes. These areas havegy fo r deposits describedmodel, but they lack a knowattributes that make it highlare present. The two typesbined in a final estimate ofdeposits of a given mineralFinally, th e probabilit


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amining the results. For each deposit model, MARK3randomly selects a number of deposits from the probability distribution of deposit occurrence provided by theassessor. It then selects a tonnage an d grade fo r each deposit from tonnage and grade models that ar e providedby the assessor or are already in the MARK3 program asa result of previous studies (most of the tonnage andgrade models used in this study fall into the latter category). The simulator calculates the types an d amounts ofmetals in each of the deposits. The process is repeatedmany times and produces frequency distributions of metal s contained in deposits of th e given deposit model.MARKS assumes that the frequency distribution ofth e logs of tonnages and grades for a given deposit model can be modelled as individually normal and jointly bi-variate normal. The parameters of the distributions arechosen in such a way that the median and mean of th eindividual normal distributions ar e equal to the medianan d mean of the tonnage and grade data. For the bivari-ate normal distribution, the correlation is chosen so thatthe mean of th e product of the tonnage and grade distributions for a given deposit model is equal to the meanmetal content of deposits in the model (Root and Scott,1988).Different deposits in the same deposit model maycontain different suites of metals. In such a case, theMARKS program divides th e deposit model into subtypes such that the deposits of each subtype all containthe same suite of metals. Distributions of tonnage an dgrade ar e calculated separately fo r each subtype. For ex ample, if MARKS is working with deposit model A,which ha s some deposits containing Cu and Au (subtypeAI) and some deposits containing only Cu (subtype A 2 ),it will calculate distributions of tonnage, Cu grade, an dAu grade for subtype A ls an d distributions of tonnagean d Cu grade for subtype A 2 . When MARKS is asked tosimulate the tonnage and grade of a metal in depositmodel A, it will select a subtype at random. Then it willrandomly select tonnage an d grade values from the tonnage and grade distributions it ha s constructed fo r thatsubtype. The likelihood that MARKS will select a certain subtype is set equal to the fraction of deposits in thegiven deposit model that belong to that subtype. Aftermany random selections, MARKS will have combined

deposits can be estimated as if athe region and then conditionedprospects are for that on e occuprobability for the existence of adeposit of a given deposit modmined by the assessor.Steps one and two of the thsessment method described abovWorl and others (1989) and willthe purposes of this report. Worsented mineral deposit models"deposit types") for the mineralin the Forest, and they delineatehigh resource potential for eachModifications have been made tmodels in order to use existing els. Also, in place of their areamineral resource potential, this rare simply permissive for the occgiven mineral deposit model. Asource potential, discussed abothan permissive tracts. Areasmoderate mineral resource potenamong other things, "geologic,physical characteristics indicatefavorable for resource occurrencof data indicate a reasonable likemulation, and (or) where an apposit models indicates favorable type(s) of deposits" (Worl and ohave the possibility of being mmissive tracts.This study focuses on the tative assessment method descrtion of the number of undiscovsents th e results of a simulaMARKS.

QUANTITATIVE MINERAL RASSESSMENT IN CHALLIS N

The Challis National Foresic an d metallogenic history. A


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of mineral deposits within a terrane depends on manyfactors including regional an d local structures, facieschanges within units, an d juxtaposition of terranes.A quantitative assessment of th e mineral resourcesin a region is based on th e availability of tonnage andgrade models for each of the mineral deposit modelsconsidered. Worl and others (1989) presented a numberof mineral deposit models that describe th e depositspresent, or suspected to be present, in the Challis National Forest. Many of these deposit models are based onlocal deposits with little or no record of production, an dtherefore they have no associated grade or tonnage model . Others ar e identical to or directly related to depositmodels in th e report by Cox and Singer (1986). Many ofthe deposit models of Cox and Singer (1986) are accompanied by tonnage and grade models and ca n be immediately incorporated into th e quantitative assessment.Where the tonnage and grade models of Cox and Singer(1986) are used, the name of the mineral deposit modelin this report is th e same as that of Worl and others(1989; see table 1).

Two strategies have been used in this report todeal with models presented by Worl an d others (1989)fo r which no tonnage and grade information exists. First,an extensive literature search was done in an attempt tocreate tonnage and grade models for an y local depositswith adequate data. Because most mining ha s long sinceceased in this area, records with both grades and tonnages of an y deposits were extremely hard to find. Only twodeposit models had enough data to allow the creation oftonnage an d grade models . These models, to be discussed later, are the precious-metal veins model and theirregular replacement deposits of base an d precious metals model.The second strategy used to deal with mineral de posit models of Worl an d others (1989) that lack gradean d tonnage information was to aggregate or disaggregate those models until they matched one of the modelsof Cox and Singer (1986). The four polymetallic veindeposit models presented by Worl and others (1989) areclassified on the basis of the terranes in which they oc cur, one each fo r th e black-shale terrane, the carbonateterrane, the quartzite terrane, and th e Tertiary extrusiveterrane. The polymetallic vein deposit model of Bliss

grade data were available. Tposits, which include at leasrane, were combined an d plotion of tonnage (fig. 3 5 ) wtonnage distribution (fig. 3Atallic vein model of Bliss an dfour polymetallic vein depscribed by a single deposit mWorl and others (198skarn deposit model that consten skarns. Their model difsten skarns as subtypes of areport by Cox and Singer (posit models for copper andport, copper and tungsten skin order to take advantageSinger (1986).Worl and others (1989)their stockwork molybdenuCretaceous and Tertiary stoits. In this study these ar e treCretaceous model after Hamodel after Kiilsgaard and ceous model corresponds toodore (1986) in the reportThere is no analog to the Tnu m deposit model in th e(1986). Thus, grade and toonly fo r the Cretaceous stocmodel, and only the Cretacethis report.

QUANTITATIVE ASSESSMINERAL DEPOSIT MOD

A complete list compaby Worl an d others (1989)and grade models used in thThe report by Cox an d Singemineral deposit models and amodels produced by manythors of this volume will beD ue to the lack of ton


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Table 1. Mineral deposit models and grade and tonnage models used in this reportMineral deposit models ofWorl and others (1989) Corresponding mineral deposit models(first citation) and grade and tonnage models

(second citation) of Cox and Singer (1986)A. Fluorspar veins No n eB. Polymetallic veins in black-shale terrane.C. Polymetallic veins in quartziteterrane.D . Polymetall ic veins in carbonate

terrane.E. Polymetallic veins in Tertiaryextrusive terrane.F . Precious-metal veins

Polymetallic veins (Cox, 1986a; Bliss an dCox, 1986).

None

G. Base-metal veins No n eH. Vein uranium deposits NoneI. Tungsten stockwork an d vein deposits oneJ. Stockwork molybdenum deposits:Cretaceous

Tertiary

Porphyry Mo, low-F (Theodore, 1986;Menzie and Theodore, 1986).Noneprecious-metal deposits.

L. Polymetallic skarn deposits

M. Irregular replacements of base andprecious metals.

W skarn deposits (Cox, 1986b;Menzie and Jones, 1986).Cu skarn deposits (Cox and Theodore,

1986; Jones an d Menzie, 1986).No n e

None.

Polymetal

Precious-m(GradepresenNone.None.None.

Stockwor(CretacNone.

Polymetalskarns

Irregular rand prnage m

N . Fluorspar breccia manto deposits one None.O. Sediment-hosted, jasperoid-associated,precious-metal deposits. Carbonate-hosted Au-Ag (Berger, 1986;Bagby and others, 1986).

Sediment-preciou


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Polymetallic Vein DepositsAs explained earlier, the polymetallic vein modelswere aggregated into on e polymetallic vein model (Cox,

1986) in order to use the tonnage and grade models presented by Bliss and Cox (1986).The polymetallic vein deposits of the Forest produced mainly silver and lead and lesser amounts of zinc,gold, and copper. Some production of tin, antimony, andbromine has been reported. The deposits are found nearhigh-angle faults and flat to steeply dipping shear zonesbeneath major thrust faults or near regional unconformities, an d they are associated with nearby plutonic or hyp-abyssal rocks (Worl and others, 1989). The host rocksan d the alteration associated with the ore bodies are different in each of the terranes and will be discussed on aterrane-by-terrane basis.Within the black-shale terrane the host rocks aregenerally black argillite or carbonaceous micritic limestone, but may also include siltite, siltstone, shale, finegrained quartzite, and gray limestone. Veins are foundmainly in contact metamorphic zones close to felsic intrusive bodies where the country rocks have been alteredto hornfels, tremolite-bearing limestone, calc-hornfels,an d locally skarn. Known polymetallic vein depositswithin this terrane al l lie within 3.5 mi of a felsic intrusive body (Worl and others, 1989).Polymetallic vein deposits found within the quartzite terrane are generally hosted by quartzite or dolomiticquartzite. Sandy dolomite, shaly limestone, and blackshale are often found near the deposits. Where dolomiteis the host, it commonly ha s been altered to jasperoid.The quartzite host rocks display carbonate replacementan d a halo of manganese and iron oxides. The alteredan d mineralized zones are concentrated in north- tonorthwest-striking high-angle faults an d near north-trending folds and associated thrust faults. The majormineralized zones are found in the dolomitic members ofthe quartzite, in carbonatized quartzite, or along highlyfractured zones in the quartzite (Worl an d others, 1989).Polymetallic veins found within the carbonate terrane are hosted by white to blue, massive to thick-bedde d limestone. The deposits occur as replacements oflimestone along both fractures and bedding planes. The

Johnson, 1987) and include and hypabyssal intrusions. bleached light gray and disprite; they are silicified, serivicinity of the ore bodies. Stensive form of alteration, Ihe lodes, and wall-rock textnear the lodes (Worl and othveins in the Tertiary extrusivth e intersections of northwstriking high-angle faults, anminor fissures and zones otions (Worl and olhers, 1989Tracts delineated as peof polymetallic vein depositportions of the black-shaleTertiary extrusive lerranes (fresource potential were ide(1989) on Ihe basis of Ihe pevidence of alteration zonehypabyssal bodies, an d anomand zinc; these areas were cthe number of undiscovered On the basis of availabed at a 50-percent confidencvein deposits remain to be dculations made using MARKcovered deposits contain 10tonnes of silver, and 71,00mean tonnage of or e from undeposits is estimated at 1,40of the number of undiscovereamount of contained metalForest is presented in tables

Precious-Metal Vein DepoThe precious-metal veies t ar e hosted by Cretaceoustrusive rocks that include diof these deposits are in theseries of northeast-striking hother northeast- or northwest


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Table 2. Probabilistic estimate of number of undiscovered deposits of selected mineral deposit models[A 100-percent probability that on e or more deposits are present (see third column) indicates that a t least on e deposit of thediscovered in the Forest]

Probability that on eor more depositsare present __(percent) 90 perce

Mineral deposit model (names modifiedfrom Worl and others, 1989; see table 1) Tonnage and grade model Estimadepo

Polymetall ic vein deposits

Precious-metal vein deposits

Stockwork molybdenum deposits(Cretaceous).Polymetallic skarn deposits:Tungsten skarns -

Copper skarns

Irregular replacemen t depositsof base an d precious m etals.

Sediment-hosted, jasperoid-associated,precious-metal deposits.

Stratabound syngenetic deposits ofprecious and base m etals.Gold placer deposits -

Polymetall ic veins (Bliss an dCox, 1986).Precious-metal vein deposits

(this report).Porphyry Mo, low-F (Menzie

an d Theodore, 1986).

W skarn deposits(Menzie and Jones, 1986).Cu skarn deposits

(Jones and Menzie, 1986).Irregular replacement deposits

of base an d precious metals(this report).

Carbonate-hosted Au-Ag(Bagby and others,1986).

Sedimentary exhalative Zn-Pb(Menzie and Mosier, 1986).Placer Au-PGE (Orris andBliss, 1986).

1 00

1 00

1 00

1 00

1 00

1 00

20

1 001 00

An extensive literature search was conducted in anattempt to create tonnage an d grade estimates fo r thesedeposits, which have no real analog in the report by Coxan d Singer (1986). Although data on contained metal areabundant, only eight deposits have enough tonnage an dgrade data to allow an accurate estimate. The resultingtonnage an d grade models fo r the precious-metal veindeposits ar e presented in figures 5, 6, an d 7.

levels of copper, lead, and zisamples.On the basis of available ined at a 50-percent confidence lmetal vein deposits remain to be(table 2). Calculations made usinthese undiscovered deposits conor e containing 5.7 tonnes of gold


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Table 3 . Probabilistic estimates of tonnages of metals and ore in undiscovered deposits odeposit models in Challis National Forest

Mineral deposit model

Stockwork m olybdenumdeposits (Cretaceous).Polymetall ic skarn deposits:

Copper skams

Irregular replacement deposits ofbase and precious metals.

Sediment-hosted, jasperoid-associated, precious-metaldeposits.Stratabound syngenetic deposits

of precious and base metals.

Metal

CopperGoldZincSilverLeadO reGoldSilverOreMolybdenumOre

TungstenO reCopperGoldSilverOreCopperGoldSilverLeadOreGoldSilverO reZincSilverLeadOreGoldOre

Estimated tonnages ( in tonne90 percent1 .3X10 24 .0X10 ' 23 .3X10 37 .2X10 19 .5X10 31 .3X10 57.0X1 0' 13 .8X109 .9X1041 .8X10 42 .0X10 7

4 .7X1 0 28 .4X1042 .5X10 30 .0X100 .0X101 .6 X10 53.6X10 10 .0X109 .0X103 .2X10 32 .8X1040 .0X100 .0X100 .0X102 .6X10 54 . 1 X 1 0 11 .2 X10 55 .7X10 62 .7X10 ' 13.6X10 5

50 perc1 .5X13 .4X17 . 1 X 11 .2 X11 .0X11 .4X15 .7X16.7X16.4X12 .2X12 .8X15 .3X17 . 1 X 11 .1X11 .7X11 .7X18.5X16.5X14.0X11 .4X14.9X17.4X12.3X13.9X19.0X17.8X16.2X14.6X11 .1X11.2X11.7X1

compositionally zoned bodies with high strontium-rubidium ratios and low niobium concentrations com tonnage and grade model (1986) is presented in the sa


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Cretaceous plutons or hypab yssal bodies. Several areasof high resource potential were identified by Worl andothers (1989) on the basis of alteration and geochemistry. These areas w ere considered in making the estimatesof the number of undiscovered deposits.On the basis of available information, it is estimated at a 50-percent confidence level that on e Cretaceousstockwork molybdenum deposit remains to be discoveredin the Forest (table 2). Calculations made using MARKSindicate that undiscovered deposits contain 28 5 milliontonnes of ore and 221,000 tonnes of molybdenum. Abreakdown of the estimated number of undiscovereddeposits and the predicted contained metal in Cretaceousstockwork molybdenum deposits in the Forest is presented in tables 2 an d 3, respectively.

Polymetallic Skarn Deposits (Tungsten Skarns an dCopper Skarns)The host rocks for the polymetallic skarn deposits

are carbonate or carbonate-bearing rocks mainly cleanto impure limestone, carbonaceous micritic limestone,and limy sandstone that are in contact with felsic intrusive rocks. The carbonate rocks within the contact zonehave been altered to Fe-Mg-Mn-silicate mineral assemblages. Skarns occur where conditions were right fo rcarbonate minerals to be replaced by silicate and oreminerals. This location is controlled by the ability ofore-forming solutions to penetrate the rocks, which isitself controlled by the relationship between beddingplanes, faults, an d breccia zones at the contact betweenthe intrusive body and the carbonate host rock (Worl an dothers, 1989; Cookro and others, 1987). The commodities produced from these deposits vary according to thetype of skarn. Tungsten skarns produce mainly tungsten,whereas copper skarns produce copper, silver, and gold.Several tracts in the Forest have been delineated aspermissive for the occurrence of polymetallic skarns (fig.10). The tracts are divided into those that are permissivefor tungsten skarns, those that are permissive fo r copperskarns, and those that are permissive fo r both. In general, the tungsten skarn tracts include roof pendants in theIdaho batholith, the eastern margin of the Idaho batho-

Menzie and Jones (1986) for tgrade and tonnage model of Jofor copper skarns. These models skarn model) are for the most pthan deposit based. This means thindividual deposits have been codistrict, and only the district toconstruction of grade and tonnagof undiscovered deposits were cundiscovered districts to make thgrade and tonnage models. The dividing the estimate of undiscnumber of deposits generally fousulting estimates of undiscoverbined with the district-based grain the MARKS program to prodan d tungsten contained in undisForest.It is estimated at a 50-percthere is on e tungsten skarn remaithe Forest. Also, it is estimateddence level that there are two copbe discovered in the Forest. CMARKS indicate that undiscovetain 53,000 tonnes of tungsten atungsten ore. Undiscovered coppto contain 109,000 tonnes of tonnes of copper ore. A breaknumber of undiscovered depositstained metal in tungsten and copis presented in tables 2 an d 3, res

Irregular Replacement DeposPrecious MetalsThe irregular replacement dcious metals in the Forest are ho

or dolomitic rocks with varyingThe movement of ore-forming sby high-angle faults an d shearThese solutions were trapped inimpervious shale an d siltstone splaced by thrusting. Anticlines


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nage and grade models. Enough data were available toallow the creation of tonnage an d grade models from deposits within the Forest. Data from 22 deposits wereused, including data from the Pittsburgh-Idaho, Rams-horn, Clayton, and Latest Out mines, and the models areshown in figures 1 1 through 1 5 . The deposits in the Fores t may be similar to those described in the polymetallicreplacement deposit model of Morris (1986); however,that model 's associated grade an d tonnage model isbased not on deposits but on districts with over 100,000tonnes of production (Mosier and others, 1986), and it isquite different from the deposit-based model used here.The tracts delineated as permissive for the occurrence of irregular replacement deposits in the Forest areshown in figure 16. The tracts outline the rocks of theblack-shale terrane and part of the flysch terrane. Areasof high resource potential, identified by Worl and others(1989), are defined by north-striking high-angle faults,nearby intrusive rocks, the presence of gossans, and evidence of base- and precious-metal mineralization. Theseareas were considered in making estimates of the numbe r of undiscovered deposits.The tonnage and grade model presented here wasused for the quantitative assessment of irregular replacement deposits. On the basis of available information, itis estimated at a 50-percent confidence level that eightirregular replacement deposits of base and precious metals remain to be discovered in the Forest. Calculationsmade using MARKS indicate that these undiscovered deposits contain 49,000 tonnes of lead, 650 tonnes of copper, an d 140 tonnes of silver in 740,000 tonnes of ore. Abreakdown of the estimated number of undiscovered deposits and the predicted contained metal in these deposits is presented in tables 2 an d 3, respectively.

Sediment-Hosted, Jasperoid-Associated, Precious-Metal DepositsThe sediment-hosted, jasperoid-associated, precious-metal deposits are found in carbonaceous limestone and dolomite, calcareous carbonaceous shale andsiltstone, and bioclastic limestone. This deposit model ishere considered identical to the carbonate-hosted Au-Ag

modities are gold and silver;and mercury are present in traCurrently, no sedimented , precious-metal deposits hChallis National Forest or thare, however, several areas wfo r the occurrence of these dareas, shown as tracts in figthe basis of carbonaceous seserve as host rocks for theseblack-shale terrane and partsSince no sediment-hoprecious-metal deposits existof undiscovered deposits wasthat there is a 20-percent chdeposit exists in the Forest. Oformation, it is estimated at ael that there are three undiscoperoid-associated, precious-mNational Forest. Calculationscate that these undiscovered of gold, 39 tonnes of silver, aA breakdown of the numberdeposits and the predicted coposits is presented in tables 2

Stratabound Syngenetic DBase MetalsThe host rocks of the posits of precious and base mmarine sedimentary rocks. Thfacies carbonaceous argilligrained gray limestone or mstone. The deposits are stratifin sphalerite and galena; alsotite, barite, arsenopyrite, qua

and tremolite. The deposits ft ional environments wherebrines were localized (Wor1987b). The commodities proinclude zinc, lead, silver, anlybdenum are present in tra


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Table 4 . Summation of probabilistic estimates of tonnagesof metals an d ore in undiscovered deposits in ChallisNational Forest

Metal Estimated tonnages (in tonnes)at given probabilities

GoldSilver - ----CopperLeadZincTungstenMolybdenum

90 percent1 . 1 X 1 0 1 .2 X10 22 .7X10 31 .3X10 52 .6X10 54 .7X10 21 .8X10 4

50 percent3 .5X10 17 .7X10 31 .3X10 44 .8X10 67 .9X10 65 .3X10 42 .2X10 5

1 0 percent1 .0X10 22 .1X10 43 .1X10 51 .3X10 72 .0X10 71 .5 X10 56.0X10 5

centrations of zinc an d (or) lead, and these areas wereconsidered in the estimate of the number of undiscovered deposits.The tonnage an d grade model used fo r thesedeposits is by Menzie and Mosier (1986). On the basisof available information, it is estimated at a 50-percentconfidence level that there are two undiscovered strata-bound syngenetic deposits of base and precious metals inthe Forest. Calculations made using MARKS indicatethat these undiscovered deposits contain 7,800,000tonnes of zinc, 6,200 tonnes of silver, 4,600,000 tonnesof lead, and 10,700,000 tonnes of ore. A breakdown ofthe number of undiscovered deposits an d the containedmetal in these deposits is presented in tables 2 an d 3,respectively.

Gold Placer DepositsThe gold placer deposits in the Forest are fluvialaccumulations of elemental gold with sand, gravel, an dboulders. Gold, silver, and other heavy minerals wereconcentrated by streams where turbulent and irregularflow patterns separated the light and heavy mineral frac

tracts include mapped fluvial acfluvial accumulations. Worl and areas of high resource potentialrence of precious metals in stretions within 5 mi (downstream)deposit. These areas were consmates of the number of undiscovThe tonnage and grade mposits is by Orris and Bliss (1950-percent confidence level thacovered gold placer deposits in test. Calculations made using MAundiscovered deposits contain1,730,000 tonnes of ore. A breaestimated undiscovered depositstained metal in these depositsand 3, respectively.

SUMMARY OF QUANTITATOF CHALLIS NATIONAL FOThe summary of the quansented in tables 2, 3, and 4. Theport an d the probability distributposits (used as input to thepresented in table 2. The distribment for each deposit (the resultdure) are given in table 3. Thesummed for each metal and show

presents a distribution of the todeposits of the mineral deposit port) in the Challis National ForeNote that although this infa quantitative, probabilistic formon subjective estimates of the mineral deposits fo r each specificonsidered. These estimates areauthor's knowledge at the time oand are not probabilistic in a stat

SELECTED REFERENCES


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Anderson, R.A., 1948 , Reconnaissance survey of th e geologyan d ore deposits of the southwestern portion of the LemhiRange, Idaho: Idaho Bureau of Mines an d Geology Pamphlet P-80, 18 p.Bagby, W.C., Menzie, W.D. , Mosier , D.L. an d Singer, D.A.,1986, Grade an d tonnage model of carbonate-hosted A u-A g, in Cox, D.P. , an d Singer, D.A., eds., Mineral depositmodels: U.S. Geological Survey Bulletin 1693 , p. ITS-IT?.Bennett , E.H., 19 80 , Granitic rocks of Tertiary age in the Idahobatholith an d their relation to mineral izat ion: EconomicGeology, v. 75, no . 2, p. 278-288.Berger , B.R., 1986, Descriptive model of carbonate-hosted Au-Ag, in Cox, D.P. , an d Singer, D.A., eds., Mineral depositmodels: U.S. G eological Survey Bulletin 1693, p. 175.Bliss, J.D., and Cox, D.P., 1986, Grade an d tonnage model ofpolymetallic veins, in Cox, D.P. , an d Singer , D.A . , eds.,Mineral deposit models: U.S . Geological Survey Bulletin1693, p. 125-129 .Bond, J.C., 1978 , Geologic map of Idaho: Idaho Bureau ofMines and Geology Miscellaneous Map Series, scale1:500,000.

Briskey, J.A., 1986, Descriptive model of sedimentaryexhala t ive Zn-Pb, in Cox, D.P., and Singer, D.A., eds.,Mineral deposit models: U .S . Geological Survey Bulletin1693, p. 211-212.Callaghan, Eugene, an d Lemmon, D.M. , 1941 , Tungsten re sources of th e Blue Wing district, Lemhi County, Idaho:U.S . Geological Survey Bulletin 931-A, 21 p.Cater, F.W., and others, 1973 , Mineral Resources of th e IdahoPrimitive Area an d vicinity, Idaho: U.S . Geological Surve y Bulletin 1304 , 431 p.Chambers , A.E., 1966, Geology and mineral resources of th eBayhorse Mining district, Custer County, Idaho: Tucson,University of Arizona, Ph.D. dissertation, 271 p .Cook, E.E. , 1956, Tungsten deposi ts of south-central Idaho:Idaho Bureau of Mines an d Geology Pamphlet P-108, 4 0P-Cookro, T .M., Hall, W.E . , an d Hobbs, S.W., 1987 , Polymetallic skarn deposits, in Fisher , F .S. , and Johnson, K.M.,eds., Preliminary manuscript fo r "Mineral-resource potential and geology of th e Challis Ix2 quadrangle, Idaho":U.S. Geological Survey Open File Report 87-480, p.172-175.Cox, D.P. , 1986a, Descriptive model of polymetallic veins, inCox, D.P., an d Singer, D.A., eds., Mineral deposit models:U .S . Geological Survey Bulletin 1693, p. 125.Cox, D.P. , 1986b , Descript ive model of W skarn deposi ts , in

Fisher, F.S. , Kiilsgaard, T.H.,E.H., 1987 , Precious-metaJohnson, K.M., eds., Prelimresource potential an d geolorangle, Idaho": U.S. Geolog87^80, p. 1 1 7 - 1 2 5 .Fisher, F.S., and May, G.D., 198of metall i ferous Salmon RU.S . Geological Survey OpeFisher, F.S., May, G.D., Mclnt1983 , Mineral resource potecal maps of part of th e WArea, Custer County, Idahocellaneous Field Studies Ma

Fisher, F.S. , Mclntyre, D.H., anlogic m ap of the Challis 1 Geological Survey Open-Fi1:250,000.Hall , W.E. , 1985 , Stratigraphymiddle and upper Paleozoiceral belt , central Idaho, ChSymposium on the geologyChallis Ix2 quadrangle , IBulletin 16 5 8 , p. 1 1 7 - 1 3 2 .1987a, Cretaceous molybF.S. , an d Johnson, K.M., ed"Mineral-resource potentiaIx2 quadrangle , Idaho":File Report 87-480, p. 152--1987b, Stratabound syngebase metals in argillic rocFisher, F.S., and Johnson, script for "Mineral-resourceChallis Ix2 quadrangle, IOpen File Report 87-480, pHobbs, S .W. , 1985 , Precambriterranes in th e Bayhorse aChap. D in Mclntyre , D.H.,gy and mineral deposits ofIdaho: U.S. Geological SurvHobbs, S.W., Fisher, F.S., and replacement deposits of bFisher, F .S. , an d Johnson, script for "Mineral-resourceChallis Ix2 quadrangle, IOpen File Report 87-480, pHustedde, G.S. , Copeland, J.A.,and Bennett, E.H., 1 9 8 1 ,


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Boulder Creek mining district, Custer County, Idaho:Idaho Bureau of Mines and Geology Pamphlet 89, 27 p.Kiilsgaard, T.H., an d Bennet t , E.H., 1985, Mineral deposits inth e southern part of th e Atlanta lobe of th e Idaho batholithan d their genetic relation to Tertiary intrusive rocks an dfaults, Chap. M in Mclntyre, D.H., ed., Symposium on th egeology and minera l deposits of th e Challis Ix2 quadrangle, Idaho: U.S . Geological Survey Bulletin 1658, p .1 5 3 - 1 6 5 .1987, Tert iary molybdenum stockworks, in Fisher, F.S.,and Johnson, K.M., eds., Preliminary manuscript for"Mineral-resource potential and geology of th e ChallisIx2 quadrangle , Idaho": U.S. Geological Survey OpenFile Report 87^80, p.158-162.

Kiilsgaard, T.H., and Lewis, R.S., 1985, Plutonic rocks of Cretaceous ag e an d faults in the Atlanta lobe of the Idahobatholith, Challis quadrangle , Chap. B in Mclntyre , D.H.,ed . , Symposium on the geology an d mineral deposits ofth e Challis Ix2 quadrangle, Idaho: U.S. Geological Surve y Bulletin 1658, p. 29-42.Kiilsgaard, T.H., and Van Noy, R.M., 1984 , Eastern part of th eSawtooth N at ional R ecreation Area, Idaho, in Marsh, S.P.,Kropschot , S.T., and Dickerson, R.G., eds., Wildernessmineral potential Assessment of mineral resource potential in U.S . Forest Service lands studied 1 9 6 4 - 1 9 8 4 : U.S.Geological Survey Professional Paper 1300, p . 573-576.Mabey, D.R., and Webring, M.W., 1985, Regional geophysicalstudies in the Challis quadrangle, Chap. E in Mclntyre ,D.H., ed . , Symposium on th e geology an d mineral deposits of the Challis Ix2 quadrangle, Idaho: U.S . Geologica l Survey Bulletin 1658, p. 69-79.Menzie , W . D . , an d Jones , G.M., 1986 , Grade an d tonnagemodel of W skam deposits, in Cox, D.P. , an d Singer ,D.A., eds., Mineral deposit models: U.S . Geological Surve y Bulletin 1693, p. 55-57.Menzie, W.D., an d Mosier , D.L . , 1986, Grade an d tonnagemodel of sedimentary exhalat ive Zn-Pb, in Cox, D.P., andSinger, D.A., eds., Mineral deposit models: U.S . Geologica l Survey Bulletin 1693, p. 212-215.Menzie, W.D., an d Theodore, T.G., 1986, Grade an d tonnagemodel of porphyry Mo, low-F, in Cox, D.P. , an d Singer,D.A., eds., Mineral deposit models : U .S . Geological Surve y Bulletin 1693, p. 120-122 .Mitchell, V.E., St roud, W.B., Hustedde, G.S. , an d Bennett,E.H., 198la, Mines and prospects of the Challis quadrangle, Idaho: Idaho Bureau of Mines an d Geology, Minesan d Prospects Map Series, 47 p., scale 1:250,000.198b, Mines an d prospects of th e Dubois quadrangle,

Mines an d Prospects Map SeriMorris, H.T., 1986, Descriptive moment deposi ts , in Cox, D.P. , aeral deposit models: U . S . G1693, p. 99-100.

Mosier, D.L., Morris, H.T., and Sintonnage model of polymeta llCox, D.P., an d Singer, D.A., eU .S . Geological Survey BulletiOrris, G.J., an d Bliss, J.D., 1986, Gplacer Au-PGE, in Cox, D.P. ,eral deposit models : U.S . G1693, p. 261-264.Root , D.H., an d Scot t , W.A., 198simulation program: U.S. GeReport 88-15, 64 p.

Ross, C.P. , 1 9 3 0 , The Thunder Custer and C a m a s CountiesMines an d Geology Pamphlet1937, Geology an d ore depoCuster County, Idaho: U.S.877 , 171 p.-1963, Mining history of soureau of Mines and Geology PaStroud, W . B . , Mitchell, V.E., HuE.H., 1981 , Mines an d prosperangle, Idaho: Idaho Bureau ofan d Prospects Map Series, 1 0 pTheodore, T.G., 1986, Descript ive mF, in Cox, D.P . , and Singer,models: U.S. Geological SurveTreves, S.B., an d Melear, J.D., 195posits of th e Seafoam mininIdaho: Idaho Bureau of Mines1 9 p.Umpleby, J .B. , 1912 , T he lead-sdistrict, Idaho: U.S . Geologic212-222 .U.S. Geological Survey, 1988 , Mi(MRDS) (ac t ive computer fillogical Survey. [Avai lable froBranch of Resource Analys22092.]Wells, M.W., 1983, Gold campsIdaho Bureau of Mines an d GeWorl , R.G., Wilson, A.B., Smith, 1 9 8 9 , Mineral resource potChallis National Forest, Idah


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FIGURES 1-19


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11530'45 11500' 11400'

4400

Figure 1. Location of Challis National Forest and principal mining districts within oboundaries (Worl and others, 1989). Mining districts: 1, Yellow Pine; 2, Thunder MRange; 4, Sea Foam; 5, Sheep Mountain; 6, Loon Creek; 7, Parker Mountain; 8, Stan10 , Robinson Bar; 11, Bayhorse; 12 , Boulder Creek; 13 , East Fork; 14, Warm SpCopper Basin; 17, Alder Creek; 18 , Little Wood River; 19, Lava Creek; 20, McDevitt;Junction; 23 , Texas; 24 , Spring Mountain; 25 , Hamilton; 26 , Dome.


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0 . 00.00002 0 . 0 0 0 1 0.0004 0 . 0 0 1 6 0 . 0 0 6 3 0 . 0 2 5 0 . 1 0 . 4

ORE, IN MILLION TONNES6.3


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1 1 5 0 0 ' 1 1 4 0 0 '

4 4 0 0

Figure 4. Tracts (shaded) permissive for occurrence of polymetallic vein deposits.


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