rock talk volume 6 number 2 _colorado department of natural resources

8/17/2019 Rock Talk Volume 6 Number 2 _Colorado Department of Natural Resources

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Colorado Geological Survey ROCKTALK Vol. 6, No. 21

Division of Minerals and GeologyColorado Geological SurveyVolume 6, Number 2 April 2003

GOLD

Just the mention of that

word whets the appetite forriches, adventure, and the

excitement of discovery. Menhave been giving up the com-forts of home to search for goldsince before recorded history.They have climbed over vastand imposing mountain ranges,suffered the biting blasts of thearctic, fought through diseaseinfested jungles, and wanderedacross parched and lonely deserts

all for gold, the most beautifuland most desired of all metals.

Gold has been treasuredsince prehistoric times. Goldartifacts are found in some of the earliest archeological sites.The earliest known geologicalmap is Egyptian, and it datesfrom about 3,300 years ago. Themap depicts “mountains of

gold” and shows areas wheregold was recovered and whereminers lived. No one is sure of the exact location of this ancientmine; however, it may be in the

Red Sea Hills near the presentday Suez Canal.

What is it about gold thatmakes it so attractive and souseful? Gold is not very hard; aknife can easily scratch puregold. Gold is very heavy ordense, having a specific gravityof 19.3+ (extremely heavy evenfor metallic minerals). Some of the other characteristics of goldare ductility, malleability and

sectility, meaning it can bestretched into a wire, poundedinto other shapes, and cut intoslices. Gold is the most ductileand malleable element on ourplanet. A single ounce of goldcan be drawn into a wire 35miles long and it can be ham-mered into sheets less than fivemillionths of an inch thick. Goldis a great metal for jewelry, as itnever tarnishes.

The color and luster of goldare what make this metal soattractive. Gold is almost inde-structible and has been used andreused for centuries, to theextent that all of the gold that iscurrently being used by mankindis almost equal to all the goldthat has ever been mined.

When we think of gold ourfirst thoughts go to jewelry and

INSIDE

Publications_________________13

The Rock Doctor Asks ________13

San Luis Valley Science Fair ___13

Geosciences Critical toColorado’s Future ___________14

CGS Celebrates a Decadeof Excellence________________14

Book Review________________16

Twenty-four carat gold leaf glimmers fromthe Capitol’s dome. It symbolizes the prideColorado’s citizens have always taken in thbuilding. But the dome was not always goldWhen built in the mid 1890s, it was

sheathed in copper, which quickly tarnishedto dull green. The dome was first gilded in1908. The job required 200 ounces of goldthen valued at $20 per ounce. A dome of gold, said the newspapers, belonged in agold state, but by the 1940s the gold leaf had worn off, leaving the dome again tar-nished. Further applications of gold weredone in 1950, 1980, and 1991. (FROM HTTP://ME-WWW.COLORADO.EDU/CENTERS/COMBUSTION/STATECAP.HTML)

D

E N V E R P U B L I C L I B R A R Y

C AMP BIRD GOLD MILL

Gold! Gold! Gold!


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2 Colorado Geological Survey ROCKTALK Vol. 6, No. 2

other ornamentations made fromgold. In today’s modern high techeconomy gold has found otheruses as well. Gold has superiorelectrical conductivity, resistanceto corrosion, and other desirablecombinations of physical andchemical properties that haveallowed it to become an essential

industrial metal. Gold performscritical functions in computers,communications equipment, space-craft, jet aircraft engines, airbags inautomobiles, and a host of otherproducts. Gold has been used formany years in dentistry, mainly because of its lack of reactivitywith other materials. Gold is alsoused in custom paints; the domeof the Colorado State Capitol building is painted with a special

gold paint. Gold is also perceivedto be the one commodity that is along-term store of value. Untilrecent times, it was consideredessentially a monetary metal, andmost of the bullion produced eachyear went into the vaults of gov-ernment treasuries or central banks.

There are very few true goldminerals besides native gold. Goldforms a major part of only a few

rare minerals; it is found as littlemore than a trace in a few others,or it is alloyed to a small extentwith other metals such as silverand copper. A few of the mineralsthat bear gold in their respectiveformulae are in a class of mineralscalled the tellurides. The elementgold seems to have an affinity fortellurium and is one of the onlyelements that gold can bond witheasily.

Gold-silver alloys usually havea whiter color than pure gold, andgold-copper alloys tend to have aslight reddish tint. The gold con-tent of a gold alloy is measured inkarats; 24 karat is 100 percent, 18karat is 75 percent gold and 25percent other metals, and 14 karatis 58 percent gold and 42 percentother metals.

T he first documented report of gold in Colorado was in 1803 by an explorer named James

Purcell who collected some goldnuggets along the South PlatteRiver. Through the 1830s and1840s there were sporadic andill-defined reports of gold inColorado from trappers and other adventurers.

The great California gold rush of 1849 opened up theopportunity for gold seekers to pass through the Rocky

Mountains. A party of prospectors from Auraria, Georgia(a settlement in the Dahlonega gold district in Georgia)passed through Colorado on their way to the California goldfields and noted that there was potential for gold deposits in thestreams flowing out of the Front Range. After finding only dis-appointment and little gold in California, the Georgians underthe direction of William Russell, John Beck, and Lewis Ral-ston returned to Colorado in 1858 and began prospecting forgold along the South Platte River, Cherry Creek, and ClearCreek near the present site of Denver. They settled on thesouth side of Cherry Creek near the confluence of the SouthPlatte River. In remembrance of their home in Georgia, they

named the settlement Auraria (today the home of the Aurariacampus of CU Denver, Metropolitan State College, and the Tivoli Brew-ery). Through 1858 and early 1859 these prospectors and others foundgold in these streams but never a rich amount-always just a tease. Thelocal prospectors and their financial backers in the east were beginning tothink that the Pikes Peak Gold Rush (as it was called, even though it wasnowhere near Pikes Peak) was a bust!!

In the late summer of 1859, George Jackson, another prospector fromGeorgia, began prospecting along Clear Creek near the present site of thecity of Golden (oddly Golden is not named for gold, but for a man named

S o u t h

Clea r C r

e e k

C h e r r y C r e e k

P l a t t

e

R i v

e r

Black Hawk

Golden

Auraria

DENVER

Parker

Franktown

Russelv

First godiscove

Significant goldplacer deposit

Idaho Springs

Gold in Colorado:

a Brief History

Gold in Colorado:

a Brief History


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Tom Golden, an early prospector). Jackson found significant amountsof gold as he continued up ClearCreek until he discovered andstarting mining the rich placer*deposits where Chicago Creek joinsClear Creek near Idaho Springs.

Later that same year, anotherGeorgia prospector, John Gregory,

prospected for gold along ClearCreek and then up the North Forkto the present site of Blackhawk.There he found an outcroppingquartz vein with gold, the first“lode”* gold discovery in Colorado,which led to the development of the Blackhawk–Central Citymining district. During that yearand in 1860, gold was discoveredin many locations throughout thestate including Boulder Creek,

Nederland, Breckenridge, Silver-ton, Telluride, Leadville, and otherfamous Colorado mining sites.

LeadvilleThe discovery of gold nearLeadville in the gravel deposits of California Gulch lead to a shortlived placer gold boom in thatarea. The discovery of veins withlarge masses of free gold at thePrinter Boy Mine in 1868 helped

extend the life of the camp, but didnot reverse the trend of decliningproduction. One of the problems

the placer miners encountered wasa strange brown material that keptclogging up the gold placer miningoperations. In 1874 the brownmaterial was recognized as a silver–lead ore and the great lead–zinc–silver-gold deposits of theLeadville district were quickly dis-covered and developed.

During the 1860s, most all of Colorado’s easily mined golddeposits, placer and oxidized goldlode deposits were exploited. Asthe 1870s and 1880s came to aclose, new processing techniquesallowed the development of under-ground lode gold mines through-out the state. During these yearssilver, especially in the Alma dis-trict, Leadville district, and San Juan Mountains, became the domi-

nant commodity mined in Colo-rado. Gold mining suffered and thehuge bonanza gold district eludeddetection, that is until 1891.

Cripple CreekEarly reports of gold in the areaaround Pikes Peak in 1874 and1884 never “panned out”(a com-mon expression related to goldprospecting). In 1891, a localrancher named Robert Womack

made a gold discovery in PovertyGulch, just east of the present daytown of Cripple Creek, and locatedthe El Paso claim. This claim waslater developed into the Gold King

Mine, the first of a series of golddiscoveries that led to the rapiddevelopment of the Cripple Creekdistrict. The rich undergroundmines in the early years of the dis-trict’s history had an average gradeof 1 to 2 ounces of gold per ton.

The Cripple Creek District hasproduced more than 23 million

ounces of gold, about half ofColorado’s total production of 45million ounces. In the peak year of production, 1900, 879,000 ounces ofgold were produced. By 1920 pro-duction from the district hadstarted to decline because of laborshortages, wage disputes, andwater problems.

In 1933, the price of goldincreased from $20.67 to $35.00 anounce, which fostered a small min-

ing boom in the state until the out- break of World War II and theclosure of all non-essential mines by the War Production Board. Goldmining in Colorado languished inthe years after World War II, pri-marily because of the low price of gold.

All restrictions on the price of gold were lifted during the mid-1970s and interest focused on lowgrade (0.03 to 0.2 ounces of gold

per ton) bulk-tonnage golddeposits. Gold production began tosteadily increase during the 1980sand 1990s from deposits locatednear Silverton at the Sunnyside* See Definitions on page 12

Gold Production Price, $/ounce

Gold Production in Colorado 1858—2001

P r o d u c t i o n i n 1 , 0

0 0 O u n c e s

P r i c eP er O un c ei nD ol l ar s

1,600

1,400

1,200

1,000

800

600

400

200

0

800

700

600

500

400

300

200

100

0

Discovery of Cripple Creek

district

Gold mineclosure for

World War II

Modernresurgence of gold mining


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how to order CGS publications

how to order CGS publications

Mail:Colorado Geological Survey,

1313 Sherman Street,Room 715, Denver, CO 80203

Phone: (303) 866-2611

Fax: (303) 866-2461

E-mail:[email protected]

VISA® and MasterCard®

accepted.

Prepayment required.

SHIPPING AND HANDLING

Please contact the CGS forshipping and handling costs.

Discounts

Available on bulk orders.

Call for a completepublication list

Mentioned in This IssueIS 33Gold Panning and Placering In Colorado:How and Where $12.00

IS 63Colorado Mineral and Mineral Fuel

Activity, 2001 $6.00

MS 28Location Map and Descriptions of MetalOccurrences in Colorado with Notes onEconomic Potential $10.00

RS 28Gold Occurrences of Colorado $14.00

RS 35 Alkalic Igneous Rocks of Colorado andTheir Associated Ore Deposits $12.00

RS 37Geology and Mineral Resources of Gunnison County, Colorado $18.00

RS 40Geology and Mineral Resources of Park County, Colorado $30.00

SP 53Ground Water Atlas of Colorado $40.00

New CGS Website address:http://geosurvey.state.co.us

T he Colorado Mineral Belt played an important role in the distribu-tion of the different types mineral deposits in Colorado. Most of Colorado’s gold deposits are within the Colorado Mineral Belt

with one rather important exception. The Colorado Mineral Belt (page 5)was recognized early in the development of Colorado’s mineral explo-ration history. Josiah Spurr, in his 1908 study of the Georgetown—SilverPlume area, was the first scientist to recognize and publish the observa-tion that mining districts in Colorado tended to line up in a northeasterlydirection.

Later workers came to realize that this northeasterly-trending zonewas, in fact, a zone of fracturing and igneous intrusion that formed duringthe Laramide Orogeny* (about 75 million years to 40 million years ago).These intrusions and fractures are thought to follow a much older, Pre-cambrian age zone of crustal weakness and shearing. Most of Colorado’svein, placer, and replacement ore bodies occur within the bounds of theColorado Mineral Belt. However, it should be noted that Colorado’sgreatest gold producing district, the Cripple Creek district, is well out-side of the Colorado Mineral Belt and is some 10 million years youngerthan the mineral deposits related to the Laramide Orogeny.

All of the lode* gold deposits described below commonly containmore than one type of gold deposit; for example, the massive sulfidereplacement deposits of the Leadville district also contain vein deposits.

Vein DepositsOre-bearing veins are open-space fillings along fractures or fault zones inthe country rock. Veins usually consist of some non-ore mineral material(gangue), like quartz or calcite, and ore minerals like gold, silver, and basemetal (lead, zinc, copper, and iron) sulfides.

Quartz-base metal-gold veins are the most common type of ore bodyin the mining districts of the Front Range of Colorado. Here, the veinsgenerally fill north-northeast to east-trending fractures and faults in Pre-cambrian igneous and metamorphic rocks and, locally, a type of Laramide Orogeny-age, igneous rock called porphyry*. Veins generally

Geology of Gold Deposits

in Colorado

Geology of Gold Deposits

in Colorado

Mine, near Ouray at the CampBird Mine, the Summitville Minein the San Juan Mountains, theGlobe Hill and Iron Clad mines inthe Cripple Creek district, and theSan Luis Gold Mine in the Sangrede Cristo Mountains.

Gold mining still continuestoday in the Cripple Creek District

with the 1995 development of theCresson surface mine by the

Cripple Creek & Victor Gold Min-ing Company (CC&V), which is a joint venture between AngloGold(Colorado) Corp. (67%) and Gold-en Cycle Gold Corporation (33%).The operation has produced 1.62million gold ounces since early1995. The project employs over300 people and is currently accel-

erating production to over 400,000gold ounces per year.


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are a few thousand feet in length; the longest vein inthe Central City district is the California-Mammothvein, which is over two miles in length. Veins in theCentral City district vary in width from a few inchesto about 40 feet (at right). The veins “pinch out”at depths of 1,000 to 2,000 feet below the surface.Ore from the Mammoth Vein is typical of thedistrict; gold contents ranged from 0.5 to 26ounces per ton; silver ranged from 1.5 tohundreds of ounces per ton. Most of the gold- bearing veins of the Front Range miningdistricts also produced considerable amounts of

lead, zinc, and copper.The spectacular San Juan Mountains of

southwestern Colorado also contain severalmining districts that have gold-base metal veins;however, in this area the veins are related to thedevelopment of a post-Laramide Orogeny-agevolcanic field. Most of the veins are related topost-eruption subsidence of volcanoes, calledcalderas (next page). Some of the better knownmining districts of the San Juan Mountains

include Silverton, Creede, Sum-mitville, Telluride, Lake City, andImogene Basin (near Ouray). Mostof the mining camps of the San Juan Mountains produced consid-erably more silver than gold;however, gold was the mostimportant mineral, economically.

Veins in the San Juan Moun-

tains have lengths up to about9,000 feet, with depths to over2,500 feet. Vein widths averagethree to six feet; the largest are upto 50 feet wide.

Gangue minerals in the veinsof the San Juans include quartz,calcite, barite, fluorite, and a richvariety of manganese mineralsincluding rhodochrosite (the newState Mineral), rhodonite, andothers.

Ore minerals include the basemetal sulfides: pyrite, sphalerite,galena, tennantite, and chalcopy-rite. Gold is generally associatedwith the pyrite and chalcopyriteand most of the silver is associatedwith tennantite.

ReplacementDeposits

Replacement deposits are, for themost part, hosted by Paleozoic-age

carbonate rocks, limestone and dolomites. Thereplacement ore bodies are composed of zones of almost entirely sulfide minerals (called massivesulfide deposits), usually galena, sphalerite, pyrite,

LAS

ANIMAS

HUERFANO

PUEBLO

EL

PASO

ARAPAHOE

ADAMS

TELLER

L A R I M E R

J E F F E R S

O NGILPIN

CLEAR

CREEK

P A R K

CUSTER

FREMONT

CHAFFEE

GU N N I S O N

LAKE

S U M M I T

G R A N D

COSTILLA

CONEJOS

ALAMOSARIO

GRANDE

MINERAL

HINSDALE

ARCHU LE TA

E A G L E

P I T K I N

MONTEZUMA

D O L O R E S

S A N M I G U E L

SAN

JUAN

OURAY

M O N T R O S E

D E L T A

M E S A

W E L D

LA PLATA

ROUTT

JACKSON

BOULDER

G A R F I E L D

S A G U A C H E

DOUGLAS

DEN

GILPI

CH

I S O N

LAKE

K I N

L

Gold Hill

Cent r alCit y Idaho

Spr ings

Mont e zumaBr eckenr idge

AlmaLeadv ille

CrippleCreek

Bonan za Silv er Clif f Rosita Hills

San Luis

Summit v ille

Cr eedeSilverton

La Plata

Rico

Sneffels

Telluride

GunnisonGold Belt

W hitepine

Car ibou

Important

Gold and silver

Occurrences

of

Colorado

Important gold occurrence

Other occurrence

3 f t

v e i n

Zones of pyrite-goldenrichment in quartz

M o s t l y

q u a r t z

Precambrianmetamorphic

rocks

Precambrianmetamorphic

rocks

Alteredmetamorphic

rocks

Vein

Typical gold vein


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and others. Gangue minerals are minor and consistmostly of quartz and calcite. Silver is commonly asso-ciated with galena and gold is commonly associatedwith pyrite. Most of the replacement deposits in Col-orado are associated with Laramide Orogeny-age por-phyry intrusions. They include the Leadville district,the Aspen district, the Gilman district, and the LaPlata district in the southwestern corner of Colorado.Only the Leadville district and the Gilman district pro-duced significant amounts of gold from replacementdeposits..

The Leadville district is noted for six types ofmineral deposits:

1) Zinc-lead-silver-gold replacement bodies havetypical grades of 0.05–0.2 ounces of gold perton, 2-6 ounces of silver per ton, 3–8 percentlead, 6–30 percent zinc, and 0.1–0.3 percentcopper;

2) Quartz-base metal veins have typical grades of 0.1–0.5 ounces of gold per ton, 2-13 ounces of silver per ton, 5–15 percent lead, and 4-10 per-cent zinc;

3) Magnetite-serpentine-gold replacement bodies

have average grades of 0.06–0.17 ounces of gold per ton, 2–4 ounces of silver per ton, andsome copper;

4) Quartz-pyrite-gold veins have average gradesof 0.5 ounces of gold per ton, 30–40 ounces of silver per ton;

5) Disseminated pyrite-gold in igneous intru-sions, mainly porphyritic rocks, have historicgrades of 0.15–0.9 ounces of gold per ton;

6) Placer gold.

Stratabound Gold-Sulfide Deposits

Disseminated gold and base metal mineral-ization occurs along structures or other zonesthat are parallel to foliation or original bed-ding in Precambrian age metamorphic rocksin several areas of the state, including thePearl district in Jackson County, the Salida

area of Chaffee County, and the “GunnisonGold Belt” in Gunnison County.

These types of deposits never producedmuch gold in Colorado; however, theyremain an intriguing target for gold prospec-tors, especially in other parts of the world.

Gold Depositsin Alkalic Volcanic Rocks

Alkalic igneous rocks form a unique suite of rocks that are depleted in silica and relativelyenriched in sodium and potassium comparedto other igneous rocks. The Cripple Creek

district is located within a small (approximately sixsquare miles) 32–28 million year old alkalic intrusive-diatreme complex emplaced at the junction of fourPrecambrian igneous and metamorphic units.Diatremes are neck-like volcanic features composed of breccia formed by the explosive activity that resultswhen molten rock interacts with abundant groundwa-ter near the surface. The complex consists primarily of a large mass of phonolite, an alkalic igneous rock, and


Magma-generatedhydrothermal

fluidsHot igneous rocks

Subvolcanicbasement

Linear veins

Hot springs

Basemetaland

Ag-rich

Au > AgPrecious

metalrich

H 2 O

c o n v ec t i o n

Cross section of a volcano showing collapsing caldera and relation-ship of precious metal vein deposits —ADAPTED FROM GUILBERT AND PARK, 1985, P. 537

Mineral Chemical ChemicalName Composition Name

Quartz SiO2 Silicon dioxide

Calcite CaCO3 Calcium carbonate

Fluorite CaF2 Calcium fluoride

Rhodonite MnSiO3 Manganese silicate

Rhodochrosite MnCO3 Manganese carbonate

Pyrite FeS2 Iron sulfide

Sphalerite ZnS Zinc sulfideGalena PbS Lead sulfide

Chalcopyrite CuFeS2 Copper-iron sulfide

Tennantite 3CuS2.As2S3 Copper sulfide–arsenicsulfide

Calaverite AuTe2 Gold telluride

Sylvanite (Au,Ag)Te2 Gold-silver telluride

Petzite (Ag,Au)Te2 Silver-gold telluride

Just a few of the many minerals associated with golddeposits in Colorado and elsewhere.


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phonolite breccia. There are also lake sediments, treetrunks, and coal layers within parts of the complex,which indicate that these igneous rocks formed asmall volcanic center at the surface.

Because of their unique composition, ore depositsassociated with alkalic igneous rocks have distinctiveset of gangue and ore minerals. The principal ore min-erals in the Cripple Creek district are gold tellurideminerals: calaverite, and rarely sylvanite and petzite.

Calaverite from district mines contains 39 percent to43 percent gold and minor amounts of silver.

The Cripple Creek district is in Teller County, wellsouth of the Colorado Mineral Belt. The district is themost important gold-producing camp in the state; ithas produced more than 23 million ounces of goldsince its discovery in 1891. In comparison, the entirestate of Colorado has produced about 45 million ounces.

Four main types of ore deposits are found withinthe Cripple Creek district: vein deposits, diatreme-hosted deposits, hydrothermal breccia-hosteddeposits, and bedded rock-hosted deposits.

Vein DepositsThe vein and fissure vein deposits of the Cripple Creekdistrict were the first discovered. The veins generallydip steeply and show a general radial pattern withinthe district. The veins of the district range from simplefissure fillings less than an inch thick to sheeted zonesthat are several feet, and as much as 100 feet, in width.The Ajax vein system is typical of the district; the Ajaxvein is exposed throughout a vertical range of greaterthan 3,000 feet with virtually no change in ore gradeor mineralogy. The Ajax Mine began production in

1895 and produced more than 700,000 ounces of goldat grades of 0.6 to 1.04 ounces per ton.

Diatreme-hosted DepositsThe most economically significant diatreme-hosteddeposit in the Cripple Creek district was the CressonMine. It yielded 28.3 million tons of ore at a grade of 0.55 ounces of gold per ton from 1904 to 1959. Themine’s production of over 15 million ounces of gold

was about 70 percent of the district’s total production.In 1914 a very rich part of the deposit known as theCresson Vug was discovered and during a period of four weeks it yielded approximately 58,000 ounces of gold from an open cavity 23 feet by 13 feet by 40 feethigh.

Hydrothermal Breccia DepositsThe northern part of the Cripple Creek district is dom-inated by hydrothermal breccia gold deposits. Thesedeposits consist of low grade, native gold ores withinstrongly altered and hydrothermal brecciated alkalic

porphyry. The hydrothermal breccias of the Globe Hilland Ironclad deposits were mined during the periodfrom 1992 to 1995 using modern surface mining tech-niques.

Sedimentary Rock-hosted DepositsLake and river sediments are common in the easternpart of the Cripple Creek intrusive-diatreme complex.Sedimentary rocks are found at the surface and in thedeepest mine workings, 3,200 feet below the surface,indicating a substantial amount of subsidence withinthe complex. The Cameron Mine contains disseminat-ed gold in sediments.

Placer DepositsA placer deposit is an accumulation of rock frag-

ments formed by processes of sedimentationor weathering in which gold or other

heavy minerals are concen-trated by mechanicalprocesses, such asgravity. Placerdeposits occur inalluvial deposits of sand and gravel inmodern day streams,

older bench or terracegravel deposits, alluvial fans,

and deposits left or modified byglaciers. Other placer deposits include

eluvial, which are formed in soils by theweathering of bedrock (lode) gold deposits.

Colluvial placer deposits occur by gold particlesmoving down slope solely by gravity, generally fromeluvial gold deposits (left). The largest gold lode


Z one of w eather ing

Bedrock gold

deposit

A l l u v i a l

p l a c e

r s

S o i l

a n d

m a

n t l e

p l a c e r s

S t r e a m G u l c h p l a c e r s

C o l l u v i a l p l a c e r s

A l l u v i a l

p l a c e r s

Different types ofplacer deposits


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deposits in the world, the Witswa-tersrand in South Africa, wereoriginally formed in alluvial beachplacers during the early Precam- brian (about 2,200 to 3,000 millionyears ago). These gravels weresubsequently turned into hard rock by heat and pressure.

In Colorado the most common

type of gold placer deposits arealluvial deposits formed in thesand and gravel of modern daystreams. In many cases olderstream deposits called benches orterraces, which formed during theQuaternary Period (the last twomillion years) are also good hostsfor placer gold deposits. The firstgold discoveries in Colorado wereplacer deposits in and around thepresent site of Denver. Other

notable placer mining areas inColorado include Clear Creekfrom Golden to Idaho Springs, theBlue River near Breckenridge, andthe South Platte River near Fairplay.

Gold from placer deposits has been recovered by a variety of methods including panning (below),sluice boxes, hydraulic mining,and dredging and drift mining.For a more complete description of these placer-mining methods

please refer to Parker (1992).

Prospector panning for gold —PHOTOFROM DENVER PUBLIC LIBRARY

Fairplay Dredge No. 1 —PHOTO COURTESY COLORADO H ISTORICAL SOCIET Y, ZELLARS COLLECTION

Economically significant placermining in Colorado ended in 1951with the shutdown of the “Fair-

play Dredge,” (above) a largedredging machine that recoveredgold from the South Platte Rivernear Fairplay.

Even today, small amounts of gold are recovered from sand andgravel quarries along the South

Platte River. Also, many peoplecome to Colorado to do recreation-al gold panning; these modern dayprospectors recover small amountsof gold. — Jim Cappa

Colorado’s only active

gold mine—

Cripple Creek & Victor Gold Mining Company

Colorado’s only active

gold mine—

Cripple Creek & Victor Gold Mining Company

T he Cripple Creek & VictorGold Mining Company ispresently the only active

large scale gold mining operationin Colorado. It is located 52 mileswest of Colorado Springs near thehistoric gold mining towns of Cripple Creek and Victor. Anglo-Gold (Colorado) Corp. operatesthis large surface mine, whichemploys about 300 people and isthe largest private employer inTeller County.

Whereas the old-time miners inthe area searched for and minedrich “high grade” gold ore fromnarrow veins, the modern minetakes advantage of new miningtechnology to extract gold remain-

ing in the “low grade” ore thatwas left untouched by the old-timers. Although the ore is notrich, there is a lot of it. At the beginning of 2002, geologists at themine estimated a reserve of 157million tons of gold-bearing orecontaining 5.0 million ounces of gold. The ore has an estimatedaverage grade of only about 0.032ounces of gold per ton. Modern-era surface mining began in theCripple Creek district in 1991.Underground mining ceased inCripple Creek in 1961, 70 yearsafter the discovery of gold in thedistrict. (left)

In 2002, the Cripple Creek &Victor Gold Mining Company


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produced 224,000 ounces of gold. In Octo- ber 2002, the company completed a majorexpansion of its production capabilitythat will permit the mine production toramp-up to 400,000 ounces of gold peryear. At the expanded rate of production,the ore reserve base will support miningthrough 2012.

Mining and ProcessingThe low-grade gold ore at Cripple Creek& Victor is mined at a rate of about 55,000tons per day. The ore is blasted fromactive mining “benches” within the openpit and loaded by enormous shovels intogiant trucks that can haul 310 tons of rockin a single load (below). The trucks deliv-er the raw ore to a crushing plant that

crushes the rock to a specified mesh size,about 5/8 inch in diameter. The crushedore is then placed on a heap leach pad(page 10). A slow-drip system applies asolution of water and sodium cyanide tothe ore. The cyanide solution soaks intothe pad and dissolves the microscopic

particles of gold within the ore. Thecyanide solution is then collected at the base of the pad by a system of pipes andheavy liners. Care is taken to avoid anyleaks of cyanide solution, not only toprotect the groundwater, but to protectprofits. Losing cyanide solution at thispoint means losing gold. After being col-lected, the gold-bearing cyanide solutionis treated with activated carbon, whichacts like a chemical sponge and reduces

The Cripple Creek & Victor gold mine. Note the drilling rigs forming a

blasthole pattern in the bottom of the mine. Massive new truck at the Cripple Creek &Victor with the capacity to haul 310 tons of ore per load.

Crushing and sorting facility, Cripple Creek & Victor Gold Mine


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Getting ready to pour gold at Cripple Creek & Victor Gold Mine

Heap leach pad with a drip system that gently applies a solution of water and sodium cyanide to crushed and screened gold ore at the Cripple Creek & Victor Gold Mine.

State of ColoradoBill Owens, Governor

Department of Natural ResourcesGreg E. Walcher, Executive Director

Division of Minerals and GeologyRonald W. Cattany, Director

Natural Resource Trustee

Colorado

Geological Survey

Ronald W. Cattany, Acting Directorand State Geologist

James A. Cappa, Mineral Resources

Vince Matthews,Senior Science Advisor

David C. Noe, Engineering Geology

Randal C. Phillips, GIS andTechnical Services

Patricia Young, Administrationand Outreach

Matt Sares, Environmental Geology

Knox Williams, Colorado AvalancheInformation Center

Administration and OutreachBetty Fox, Brenda Hannu,

Melissa Ingrisano, Dori Vigil

Avalanche Information CenterDale Atkins, Nick Logan, Scott Toepfer

Mapping, Outreach, and Earthquakes John Keller, Bob Kirkham,

Matt Morgan, Beth Widmann

Engineering Geology and Land UseKaren Berry, Jill Carlson, Sean Gaffney,

Celia Greenman, Jim Soule, T.C. Wait, Jon White

Environmental GeologyPeter Barkmann, David Bird, Ralf Topper,

Bob Wood

GIS and Technical ServicesCheryl Brchan, Karen Morgan, Larry Scott,

Jason Wilson

Mineral FuelsChris Carroll

Minerals John Keller, Beth Widmann

RockTalk is published by theColorado Geological Survey

1313 Sherman Street,Room 715, Denver, CO 80203

Back issues and subscriptions canbe obtained FREE by contacting CGSor download them from our Web site

Phone: (303) 866-2611Fax: (303) 866-2461

E-mail: [email protected] site: http://geosurvey.state.co.us

THIS ISSUEEditors: Jim Cappa, John Keller,

Cheryl BrchanProduction: Cheryl Brchan


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the gold out of the solution. The gold (along with alittle silver) is then smelted into doré bars of crudemetal, which is sent to a gold refinery in another statefor purification. — John Keller

References

and Further Reading

Boyle, R.W., 1987, Gold, history and genesis of deposits: NewYork, Van Nostrand Reinhold Co., 676 p.

Boyle, R.W., 1979, The geochemistry of gold and its deposits:Canada Geological Survey Bulletin 280, 584 p.

Cappa, J.A., 1998, Alkalic igneous rocks of Colorado and theirassociated ore deposits: Colorado Geological SurveyResource Series 35, 138 p.

Davis, M.W., and Streufert, R.K., 1990, Gold occurrences of Colorado: Colorado Geological Survey Resource Series 28,101 p.

Guilbert, J.M., and Park, C.F., Jr., 1985, The geology of oredeposits: New York, W.H. Freeman and Co., 985 p.

Parker, B.H., Jr., 1992, Gold panning and placering in Colorado:Colorado Geological Survey Information Series 33, 83 p.

Vanderwilt, J.W., 1947, Mineral resources of Colorado: Denver,

State of Colorado Mineral Resources Board, 547 p.Voynick, S.M., 1992, Colorado gold, from the Pikes Peak rush

to the present: Missoula, Mont., Mountain Press Publish-ing Co., 206 p.

Definitions (From Glossary of Geology,

American Geological Institute)

Ore deposit—Ore is defined as a naturally occurringmaterial from which a mineral, or minerals, of economic value can be extracted.

Grade—The relative quantity or percentage of oremineral content in a body of rock. For gold usual-ly expressed as ounces of gold per ton.

Lode deposit—A mineral deposit in consolidated rockas opposed to most placer deposits which are inunconsolidated materials.

Withthe worst drought onrecord in 2002, water is

a topic that gets a bit more attentionthroughout Colorado these days. Infor-

mation on this subject is more soughtafter than ever. Now, the ColoradoGeological Survey delivers a benchmarkpublication, compiling basic ground-waterinformation from an abundance of sources intoone volume, the Ground Water Atlas of Colorado.

The Ground Water Atlas ofColorado is a comprehensive, map-based look at ground water in ourstate, an important part of the

water resource picture. It summa-rizes the location, geography,geology, water quality, and hydro-logic characteristics of the promi-nent aquifers in each part of Col-orado. The large-format, full-coloratlas was produced in cooperationwith the Colorado Water Conserva-tion Board and the Division ofWater Resources.

The Ground Water Atlas of

Colorado presents ground waterinformation in a way that isapproachable by laypersons as well as those well-versed in the subject. A multitudeof maps, diagrams, pictures, tables, and graphs help make the technical aspects ofground water more understandable. With over 200 pages, the basic ground waterinformation you need is probably covered.

The Ground Water Atlas of Colorado (Special Publication 53) is now available at theColorado Geological Survey at a cost of $40.00. Call (303) 866-2611 and order yours today!


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Argo Gold Mine and Mill (tour)Idaho Springs, Colorado(303) 567 2421http://www.historicargotours.com/

Bachelor Syracuse Mine (tour)Ouray 970-325-0220http://www.ouraycolorado.com/activits.html

Clear Creek Mining and Milling Museum23rd Avenue and Riverside DriveIdaho Springs

Colo. School of Mines Geology MuseumCurrently in Berthoud Hall, CSM campus.Soon in new building!Phone: (303) 273-3823http://www.mines.edu/academic/geolo-gy/museum/

Country Boy Mine (tour)542 French Gulch Road, Breckenridge970-453-4405

http://www.summitnet.com/countryboymine/ Cripple Creek District Museum5th and Bennett Avenues, Cripple Creek (719) 689-2634http://www.cripple-creek.co.us/ccdm.html

Creede Underground Mining Museum(and tour)Creede719-658-0811http://www.museumtrail.org/CreedeUndergroundMiningMuseum.asp

Denver Museum of Nature and Science

2001 Colorado Blvd., Denver (303) 322-7009http://www.dmnh.org/

Edgar Mine (tour)Colorado Avenue & 8th Street Idaho Springs(303) 567 2911http://www.mines.edu/Academic/min-ing/edgar.html

Gilpin County Historical Society andMuseum228 High Street Central City, CO 80427(303) 582 5283http://www.coloradomuseums.org/gilpin.htm

Hard Tack Mine (tour)Lake City

970-944-2506http://www.lakecityco.com/lakecityRecreation.html

Hidee Gold Mine (tour, appointment only)County Rd. 6, Central City/Blackhawk 303-989-2861

Lafayette Miners’ Museum1087 E. Simpson Street Lafayette, CO 80026(303) 665 7030

Lowell Thomas Museum3rd and Victor Avenue, Victor

http://www.byways.org/image_library/ media_details.html?CX_MEDIA=26638

Lebanon Mine (tour) and GeorgetownLoop RailroadGeorgetown(303) 569 2403http://gtownloop.com/mine.html

Matchless Mine (tour)414 W. 7th Street, Leadville(719) 486-3900http://www.matchlessmine.com/

Mayflower Mill (tour)

2 miles north of Silverton, Hwy 110County Rd 2(970) 387 0294

Mollie Kathleen Gold Mine (tour)Cripple Creek (719) 689 2466http://www.goldminetours.com/

National Mining Hall of Fame & Museum120 W. 9th, Leadville(719) 486-1229http://www.leadville.com/miningmuseum/

Nederland Historical Society and Museum4th and Bridge Streets, Nederland,Boulder County (303) 285-3575

Ouray County Historical Society andMuseum420 Sixth Street, Ouray

http://www.ouraycountyhistoricalsoci-ety.org/

Old Hundred Gold Mine (tour)Silverton(970) 387-5444 or 1-800-872-3009http://www.minetour.com/

Phoenix Mine (tour)Idaho Springs(303) 567 0422http://www.phoenixgoldmine.com./

Smuggler Mine and Compromise Mine(tour, reservations required)

Aspen970-925-2049

Walsenburg Mining Museum101 E. 5th Street, Walsenburg719-738-1992http://www.hchstsoc.org/Walsenburg%20Mining%20Museum.html

Western Museum of Mining and Industry 1025 Northgate Road, Colorado Springs(719) 488-0880 or 1-800-752-6558http://www.wmmi.org/

C olorado Mining and Mineral Museums

and Mine T ours Orogeny—The process by whichstructures in mountain areasare formed including brittlefolding and faulting in theouter layers of the earth andplastic folding, metamorphism,and igneous intrusions in the

inner layers of the earth.Porphyry—An igneous rock in

which larger crystals (phe-nocrysts) are set in a finergroundmass, which may becrystalline or glassy, or both.

Placer deposit—An accumulationof rock fragments formed byprocesses of sedimentation orweathering in which gold orother heavy minerals areconcentrated by mechanicalprocesses such as gravity.

Colorado’s mining history has left a rich legacy. But, this legacy alsoincludes 23,000 inactive and abandoned mines that can be as dangerousas they are picturesque. Mine sites may look safe to explore, but theyoften contain unstable soil, unsafe roofs and ladders, deadly gasses,poisonous snakes and dangerous explosives. The Colorado Division of

Minerals and Geology asks you to “Stay Out and Stay Alive” and notexplore abandoned mines but encourages you to learn more about min-ing and Colorado’s historic mining past by visiting a mining museum ortourist mine in Colorado.

Definitions from p. 11


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13Colorado Geological Survey ROCKTALK Vol. 6, No. 2

The Rock

Doctor Asks

“Did You Know?”Did you know how importantColorado is to the Cretaceous/

Tertiary (K/T) boundary story?In the 1940s South Table Moun-tain (near Golden) was the firstplace in the world where theK/T boundary was described interrestrial rocks; with dinosaur bones below, only mammalsabove. This site is so significantthat the National Science Foun-dation held its 50th birthdayparty on the outcrop at SouthTable Mountain in 2000.

In 1980 scientists proposedthat the Cretaceous Period endedon Earth with the impact of anasteroid or comet traveling at100,000 miles per hour. Coloradosites and geologists played keyroles in proving the impacthypothesis, locating the crater atChicxulub on the Yucatan Penin-sula of Mexico, and proving thatChicxulub was the source of theimpact debris. The existence of

an iridium anomaly at the K/T boundary in coal-swampdeposits in Colorado proved

that the iridium anomaly wasnot just some phenomenon creat-ed by seawater, but was falloutfrom an extraterrestrial event.Indeed, Colorado has the highestiridium anomaly ever measuredin terrestrial rocks. Coloradosites also showed the presence of

shocked quartz grains that couldonly be caused by impact. Thesize of the shocked quartz frag-ments and the existence of twolayers of fallout debris inColorado sites also indi-cated to cratersearchers that theimpact must have beenlocated near NorthAmerica.

Once Chicxulub

was proposed as thesite of impact, Colo-rado once again pro-vided key evidenceconfirming it. The nailwas put in the coffin bycomparing the lead-lossof zircons from Chicxu-lub’s rocks with the lead-loss of zircons in the K/T boundarylayer from a number of sites.Most of these samples were fromColorado. Colorado also provid-ed the world with its firstknown, shocked zircon grains.

Southern Colorado’sdozen sites that preserve theK/T boundary layer are soimportant that the SmithsonianInstitution archived a 2.5-tonsample of the K/T boundaryfrom south of Trinidad and has iton display in Washington, D.C.

A good place to observe the K/Tlayer is in Trinidad Lake StatePark where a new informationsign was recently

erected onthe Long Canyon Trail. An excel-lent book about the developmentof the asteroid-impact theory isNight Comes to the Cretaceous by James Powell.

Elementary level: Shelly Moeller, “Break ThatRock,” Manassa Elementary School. Shelby col-lected samples of scoria, soaked them in water,and froze them. She measured the width of thecracks caused by freezing and compared themto physical properties of the samples.

Junior level: Beth Garc ia , “Rock-N-Roll,”Sargent Middle School (located between MonteVista and Center in Rio Grande County). Bethexamined several rock outcrops around SanLuis Valley. Assisted by published geologic

mapping, she identified the rocks exposed in

her study sites, which included tuff, rhyolite, breccia, basalt, and granite.

Senior level: Ricardo Devine , “Sangre deCristo Fault: Is It A Sleeping Giant?,” SierraGrande High School in Blanca. Ricardoresearched information of earthquakes and

faults in San Luis Valley, and concluded thatthe Sangre de Cristo Fault could cause a largeearthquake. Ricardo lost his mother in the 1987El Salvador earthquake.

Congratulations2003 CGS AWARDS FOR THE SAN LUIS VALLEY

REGIONAL SCIENCE FAIR


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Geosciences Critical to

Colorado’s future

By Greg E. Walcher, Executive Director Department of Natural Resources

T he present-day Colorado Geological Survey (CGS)and Department of Natural Resources (DNR) were

both formed in the late 1960s, and both continue to pro-vide outstanding service to the citizens of Colorado. Thelegislation establishing the Geological Survey listed nineobjectives, including:

1) Assist, consult with, and advise existing stateand local governmental agencies on geologicproblems;

2) promote economic development of mineralresource;

3) conduct studies to develop geologic information;4) inventory and analyze the state’s mineral

resources as to quantity, chemical composition,physical properties, location, and possible use;

5) collect and preserve geologic information;6) advise the state and act as liaison agency on

transactions dealing with natural resources between state agencies and with other states andthe federal government on common problemsand studies;

7) evaluate the physical features of Colorado withreference to present and potential human andanimal use;

8) prepare, publish, and distribute reports, mapsand bulletins when necessary to achieve thesepurposes; and

9) determine areas of natural geologic hazards thatcould affect the safety of, or economic loss to, thecitizens of Colorado.

CGS has done an outstanding job of meeting theseobjectives, and with the support of the ColoradoSeverance Tax and it is well-positioned to continue theirexcellent performance into the future.

The Geologic Mapping Program is providingdetailed geologic maps for use by local government, stateand federal agencies, scientists, consultants, and thepublic. The Minerals Program provides data, maps, stud-ies, and statistics on the mining and oil and gas indus-tries that contributed an estimated $14 billion to

Colorado’s economy in 2002. The Land-Use ReviewProgram conducts more than 500 reviews per year forlocal governments to ensure safe mitigation of geologichazards in the nation’s third-fastest-growing state. TheColorado Avalanche Information Center provides ava-lanche warnings and education programs that havehelped reduce the incidences of deaths from avalanches.The Environmental Program applies geology to under-standing environmental and water-resource issues includ-ing water quality, ground water, abandoned mine lands,

and wetlands. The Critical Hazards Program conductsstudies, issues reports, and responds to emergency inci-dents involving hazardous soils, landslides, mudslides,earthquakes, and rockfalls.

Governor Owens joins me in congratulating theSurvey on 35 years of excellence in providing sound sci-ence as the basis for many of the economic and socialissues facing the state.

Greg Walcher was appointed by ColoradoGovernor Bill Owens as Executive Director of theDepartment of Natural Resources in January1999. He brings to the position 20 years experi-ence in natural resource issues. From 1989–99Walcher served as president of CLUB 20. Duringhis tenure CLUB 20 membership and budgetnearly tripled, and he was credited with bringinga new level of activity, visibility and effectivenessto the Western Slope. Prior to that, Walcher spent10 years in Washington, D.C., on the staff of U.S.Sen. Bill Armstrong, including 5 years as execu-

tive director. He handled issues as diverse astransportation, agriculture, governmental affairs,and natural resources. He is currently the chair of the Natural Resource Leadership Council.

A fifth-generation native of Colorado,Walcher was born and raised in Grand Junctionand received hisdegree from MesaState College, wherehe served as stu-dent body presidentand became anational collegedebate champion.He and his wifeDiana operate a 15-acre peach orchardin Palisade.

Colorado Geological

Survey Celebrates a Decade

of Excellence

By Ronald W. CattanyDirector, Division of Minerals and Geology

In 1872 the Legislature empowered the TerritorialGovernor to appoint a Territorial Geologist. Seven

scientists occupied the position until 1907. The ColoradoGeological Survey (CGS) was established in 1907 with theChair of the Geology Department at the University ofColorado serving as State Geologist until 1927, when it wasdeactivated. The CGS was re-established in 1967 with John


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W. Rold serving as State Geologist until 1992, and VickiCowart until 2003. Under threir excellent leadership, theSurvey has gained an international reputation of scientificexcellence.

The survey was incorporated in the Department of Natural Resources (DNR) in 1968 and the Division ofMinerals and Geology (DMG) in 1992. Since then, it hasproduced over 170 publications, beginning with the verypopular Colorado’s Dinosaurs. In 1994, CGS began reporting

on the Mineral and Mineral Fuel Activity of Colorado, inresponse to the legislative mandae of the Mineral, Energy,and Geology Policy Advisory Board. The first 1:24,000geologic map—the 1995 Shoshone quadrangle in GarfieldCounty—was the first of what will be 50 new geologicquadrangle maps produced by CGS mappers by the end of the 2003 field season.

The Colorado Avalanche Information Center (CAIC)produced The Snowy Torrents. In 1996 because of height-ened avalanche awareness. The next year, CAIC beganpublishing The Beacon for the Friends of the Center.

The Survey has sold over 165,000 copies of the 1997publication, The Guide to Swelling Soils for Colorado Home-

buyers and Homeowners—making it the most widely distrib-uted book ever produced by a state geological survey. In January 1998 RockTalk began; with 20 editions in publica-tion and available for information and education purposes.

Today, CGS has five science sections—each one pro-ducing excellent information in a variety of media. The firstwater quality directory was produced in 1999, followed bythe digital publication of Colorado’s earthquake informa-tion, the Handbook of Colorado’s Meteorites, and the first of the county report series—Geology and Mineral Resources of Gunnison County, and a new oil and gas fields map as wellas the Colorado coal directory. A significant achievement

last year was the production of the Department of NaturalResources’ first Web site publication, the Colorado LateCenozoic Fault and Fold Database and Internet Map Server. Justrecently, the CAIC unveiled a set of avalanche advisorytools that are user-friendly and available on the web, theEngineering Geology Section produced significant studiesof collapsible soils in the Roaring Fork Valley and land-slides in Colorado Springs, and the Minerals and MineralFuels section published a CD-ROM compilation abouthistoric coal mines.

These are a small sampling of the reports, maps and books, many award-winning, that the Colorado GeologicalSurvey has produced in the last few years. All this while

answering citizen phone calls and questions, leadingpublic, educational, and professional field trips, andproducing a successful series of geologic hazards technolo-gy transfer conferences. Since June 1993, CGS has providedapproximately 6,000 land use reviews for local govern-ments, created inventories and reports on abandoned minesites of the state’s mineral areas, and given hundreds of geologic talks to schools, community groups and profes-sional societies.

The CGS has a host of exciting activities and publica-tions that are underway—a new digital atlas of the ParadoxBasin, nearest neighbor models for avalanche forecasting,important studies of recent faults, and two world-class books—the Ground-Water Atlas of Colorado and Natural AcidRock Drainage Associated with Hydrothermally Altered Terranein Colorado. Since 1993 the budget of the Survey has nearlydoubled and the professional staff has increased nearly athird—making 2002–2003 the fiscal year with the largest

number of grants and contracts from client agencies in thehistory of the Survey.

The mission of the CGS is to serve and inform the peo-ple of Colorado by providing sound geologic informationand evaluation, and to educate the public about the impor-tant role of earth science in everyday life in Colorado. Thework of the people of the Colorado Geological Survey andthe Colorado Avalanche Information Center is important toColorado’s economy and to Colorado’s citizens. I congratu-late the Survey in its commitment to excellence.

In August 2002, Governor Bill Owens andDNR Executive Director Greg Walcher appoint-ed Ronald W. Cattany director of the Divisionof Minerals and Geology. He also serves as oneof three Natural Resource Trustees appointed bythe Governor to oversee natural resource dam-age issues under CERCLA, and as a member of the Colorado Commission of Indian Affairs. Heis also currently serving as the interim Directorof the Colorado Geological Survey and StateGeologist. From 1991 to 2002 he served as theDeputy Director of the Colorado Department of Natural Resources. From 1981 to 1991 he served

as Assistant Director of the Department, focus-ing on activities related to natural hazard man-agement, economic impacts of energy develop-ment on local communities, Indian reservedwater rights, mineral and energy regulation andpromotion, and public land management. In1977 he co-founded the Colorado Office ofEnergy Conservation, serving as its director of policy and planning. He was an energy econo-mist for the Colorado Energy Research Institutefrom 1974 to 1977. He is the author of over 50publications. He holds a B.S. in Mineral Engi-

neering and an M.S.

in Mineral Econom-ics from the Col-orado School of Mines, and was aSenior Executive Fel-low at the KennedySchool at Harvard in1985.

Mr. Cattany is anative of Colorado.


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16Colorado Geological Survey ROCKTALK Vol. 6, No. 2

C O L

OR AD O

G E O

L O G I C A L S U R

V E Y

Colorado Geological SurveyDivision of Minerals and Geology1313 Sherman Street, Room 715Denver, CO 80203

PIA 341100040

PRESORTED STANDARDU.S. POSTAGE PAID

DENVER COPERMIT 738

BOOK REVIEW Information Series 33

Gold Panning and Placering in Colorado: How and WhereBy Ben H. Parker, Jr.

Gold Panning and Placering in Colorado: How and Where is a greatreference text for the recreational gold panner. Ben Parker’s book

provides insight on how to pan for gold, the history of placer recov-

ery in the state, techniques commonly used for gold recovery, andthe geology of placer deposits. This detailed history aids your understanding how thoroughly a stream may have been workedin the past and whether the techniques used may have left someareas overlooked. The book also describes the recharge of placer deposits and how they may be fruitful in the future.

I especially enjoyed the detail given to the variousregions depicted in this book. Specific warnings about millsites, erodible banks, and the responsibility of panning onprivate lands gives the reader fair warning about fieldrealities. The geologic explanation of gold-bearing land-forms can greatly increase your understanding and

identification of the best places to pan. Tips on panningthese areas are given for each section such as notusing magnetite in your pan as an indicator of gold

abundance. Consider it a place to start and gather additionalinformation prior to your gold panning trip.

Gold Panning and Placering in Colorado is an enjoyable book with color-ful characters making the story of Colorado’s gold rush more interesting. Ienjoyed the story of the great diamond hoax that snagged investors from acrossthe country and the depiction of elaborate hydraulic mining operations thatmoved incredible amounts of earth. Historical photographs throughout the textshow the amazing ingenuity of these miners who made their living recoveringgold from placers deposits. Personally, I would enjoy funding my next vacation

to the Rocky Mountains by panning for gold. —Reviewed by Melissa Ingrisano

rock talk volume 6 number 2 _colorado department of natural resources

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