National Mineral-Resource Assessment · contain all five metals (gold, silver, LS05 copper, lead,...
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Introduction Mining has occurred in the United States from pre-Revolutionary times. How much of our Nation’s total mineral wealth has already been discovered? How much is left? For conventional-type deposits that contain gold, silver, copper, lead, or zinc, about as much is left to be discovered in the conterminous 48 States as has already been discovered. Why a Mineral-Resource Assessment Is Needed As the Nation’s economy matures, progressively greater attention is paid to land use and environmental quality, as well as sustainability of mineral supplies to provide for the needs of future generations. National mineral-resource assessments provide a framework for addressing these issues by monitoring the Nation’s mineral wealth and by contributing to the debate over resource extraction versus environmental security. For responsible stewardship of our Nation’s lands, we need to know in which areas future mineral resources may be located, how much metal such resources might contain, and what environmental impacts might result from extraction of such resources. The U.S. Geological Survey (USGS) conducted a scientific study to estimate, for the first time, the amount of undiscovered gold, silver, coper, lead, and zinc that could be present in yet-to- be-discovered mineral deposits 1 kilometer or less below the surface of the ground of the conterminous United States. This estimate is based on the best information and theory available to the USGS and is the most thorough, well- documented assessment of undiscovered deposits of gold, silver, copper, lead, and zinc ever assesmbled at this scale. Table 1 summarizes data on U.S. and world resources of gold, silver, copper, lead, and zinc. In Table 1, the estimated undiscovered U.S. resources can be described as the estimated amount of metal expected or most likely to occur in the undiscovered deposits. Statisticians define the values as “the mean of a probability distribution.” To estimate undiscovered mineral resources, earth scientists actually begin by analyzing their data and then estimating the number of undiscovered mineral deposits of a specific geologic type that they believe occur in an area. They make this estimate at several levels of certainty. For example, they may estimate from the geologic data that there is a 90-percent chance that the area has at least 1 or more undiscovered deposits of a specific type; a 50-percent chance of 3 or more deposits; and a 10-percent chance of 5 or more. They also know the amounts of metal contained in both large and small deposits of this type previously discovered in the area, nearby, and often around the world. With statistical methods and with the aid of a computer, scientists can combine their estimates with the information on the metal contents of discovered deposits to predict the probable amounts of metal expected to occur in undiscovered deposits in the study area. How the Assessment Was Done The assessment was based on mineral- deposit models. These models are sets of data that describe a group of deposits that have similar geologic characteristics, form in similar geologic settings, and have distinctive sizes and distinctive amounts of metal. Earth scientists begin an assessment by outlining large regions having geologic characteristics and settings broadly similar to those of one or more mineral-deposit models. Sub- sequently, scientists examine the geology of the region in detail in order to outline much smaller tracts of land having geologic features that more closely match those of the models. These tracts are considered to be permissive for the occurrence of a specific type of mineral deposit. A total of 46 mineral-deposit models were used to delineate 12 regions (fig. 1, table 2) and 281 permissive tracts (fig. 2) in the conterminous United Figure 1. Map of the conterminous United States showing the 12 National mineral-resource assessment regions. National Mineral-Resource Assessment: The 1996 Estimate of Undiscovered Gold, Silver, Copper, Lead, and Zinc Remaining in the United States Map projection in Albers Equal Area 0 200 400 miles Pacific Coast Northern Rocky Mountains Great Basin Colorado Plateau Southern Basin and Range Central and Southern Rocky Mountains Lake Superior Great Plains Southern Appalachian Mountains East-central United States Adirondack Mountains Northern Appala- chian Mountains Table 1. U.S. and world resources of gold, silver, copper, lead, and zinc. Gold Silver Copper Lead Zinc (tons) (tons) (kilotons) (kilotons) (kilotons) Estimated undiscovered U.S. resources 14,000 430,000 280,000 55,000 150,000 Discovered U.S. resources 1 22,000 400,000 320,000 75,000 140,000 Total U.S. resources 36,000 830,000 600,000 130,000 290,000 Minable world resources, excluding the United States 2 61,000 390,000 570,000 110,000 310,000 1 Estimates of discovered resources based on Singer, D.A., 1995, World class base and precious metal deposits—A quantitative analysis: Economic Geology, v. 90, p. 88-104. 2 Same as the estimates of the Total, Reserve base, World total (excluding the United States) based on U.S. Geological Survey, 1996, Mineral Commodity Summaries 1996, 195 p.
Transcript of National Mineral-Resource Assessment · contain all five metals (gold, silver, LS05 copper, lead,...
Introduction
Mining has occurred in the UnitedStates from pre-Revolutionary times.How much of our Nation’s total mineralwealth has already been discovered?How much is left? For conventional-typedeposits that contain gold, silver, copper,lead, or zinc, about as much is left to bediscovered in the conterminous 48 Statesas has already been discovered.
Why a Mineral-ResourceAssessment Is Needed
As the Nation’s economy matures,progressively greater attention is paid toland use and environmental quality, aswell as sustainability of mineral suppliesto provide for the needs of futuregenerations. National mineral-resourceassessments provide a framework foraddressing these issues by monitoring theNation’s mineral wealth and bycontributing to the debate over resourceextraction versus environmental security.For responsible stewardship of ourNation’s lands, we need to know inwhich areas future mineral resources maybe located, how much metal suchresources might contain, and whatenvironmental impacts might result fromextraction of such resources.
The U.S. Geological Survey (USGS)conducted a scientific study to estimate,for the first time, the amount ofundiscovered gold, silver, coper, lead,and zinc that could be present in yet-to-be-discovered mineral deposits 1kilometer or less below the surface of theground of the conterminous UnitedStates. This estimate is based on the bestinformation and theory available to the
USGS and is the most thorough, well-documented assessment of undiscovereddeposits of gold, silver, copper, lead, andzinc ever assesmbled at this scale. Table1 summarizes data on U.S. and worldresources of gold, silver, copper, lead,and zinc. In Table 1, the estimatedundiscovered U.S. resources can bedescribed as the estimated amount ofmetal expected or most likely to occur inthe undiscovered deposits. Statisticiansdefine the values as “the mean of aprobability distribution.” To estimateundiscovered mineral resources, earthscientists actually begin by analyzingtheir data and then estimating the numberof undiscovered mineral deposits of aspecific geologic type that they believeoccur in an area. They make this estimateat several levels of certainty. Forexample, they may estimate from thegeologic data that there is a 90-percent
chance that the area has at least 1 or moreundiscovered deposits of a specific type;a 50-percent chance of 3 or moredeposits; and a 10-percent chance of 5 ormore. They also know the amounts ofmetal contained in both large and smalldeposits of this type previouslydiscovered in the area, nearby, and oftenaround the world. With statisticalmethods and with the aid of a computer,scientists can combine their estimateswith the information on the metalcontents of discovered deposits to predictthe probable amounts of metal expectedto occur in undiscovered deposits in thestudy area.
How the Assessment Was Done
The assessment was based on mineral-deposit models. These models are sets ofdata that describe a group of deposits thathave similar geologic characteristics,form in similar geologic settings, andhave distinctive sizes and distinctiveamounts of metal. Earth scientists beginan assessment by outlining large regionshaving geologic characteristics andsettings broadly similar to those of one ormore mineral-deposit models. Sub-sequently, scientists examine the geologyof the region in detail in order to outlinemuch smaller tracts of land havinggeologic features that more closely matchthose of the models. These tracts areconsidered to be permissive for theoccurrence of a specific type of mineraldeposit. A total of 46 mineral-depositmodels were used to delineate 12 regions(fig. 1, table 2) and 281 permissive tracts(fig. 2) in the conterminous United
Figure 1.
Map of the conterminous United States showing the 12 Nationalmineral-resource assessment regions.
National Mineral-Resource Assessment:The 1996 Estimate of Undiscovered Gold, Silver, Copper, Lead, and Zinc Remaining in the United States
Map projection in Albers Equal Area0 200 400 miles
Pacific
Coast
Northern
Rocky
Mountains
Great Basin
Colorado
Plateau
Southern
Basin and
Range
Central and Southern Rocky Mountains
Lake Superior
Great Plains
Southern
Appalachian
Mountains
East-central
United States
Adirondack Mountains
Northern
Appala-
chian
Mountains
Table 1. U.S. and world resources of gold, silver, copper, lead, and zinc.
Gold Silver Copper Lead Zinc (tons) (tons) (kilotons) (kilotons) (kilotons)
Estimated undiscovered U.S. resources 14,000 430,000 280,000 55,000 150,000
Discovered U.S. resources 1 22,000 400,000 320,000 75,000 140,000
Total U.S. resources 36,000 830,000 600,000 130,000 290,000Minable world resources,
excluding the United States 2 61,000 390,000 570,000 110,000 310,000
1Estimates of discovered resources based on Singer, D.A., 1995, World class base and precious metaldeposits—A quantitative analysis: Economic Geology, v. 90, p. 88-104.2Same as the estimates of the Total, Reserve base, World total (excluding the United States) based on U.S.Geological Survey, 1996, Mineral Commodity Summaries 1996, 195 p.
States. These models fall into fivegeneral types of mineral deposits calledvein, porphyry, replacement, stratiform-massive, and stratiform-disseminateddeposits. Some of the deposit typescontain all five metals (gold, silver,copper, lead, and zinc), some containonly one or two, and some of thesemetals are present in only small amounts(table 3).
At today?s prices, the gross value ofgold, silver, copper, lead, and zinc inundiscovered deposits is estimated to be$1.2 trillion. Included in this gross valueare the value of the metals, the cost ofsalaries paid for labor to find the metalsand to build and operate the facilities toextract and refine them, and the returns(profits) to investors in metalsexploration and development. The grossvalue of the five metals in undiscovereddeposits can be compared with the grossvalue of the discovered (past productionplus remaining reserves) gold, silver,copper, lead, and zinc, which iscalculated to be $1.4 trillion. Thus, forconventional-type deposits in theconterminous 48 States, about as much isleft to be discovered as has already beendiscovered. The gross value of the fivemetals in undiscovered deposits bygeneral mineral-deposit type is shown infigure 3. This assessment marks thebeginning of an ongoing assessment bythe USGS of all mineral resources in theUnited States. Detailed results of theNational assessment are available inUSGS Open-File Report 96Ï96, DataBase for a National Mineral-ResourceAssessment of Undiscovered Deposits ofGold, Silver, Copper, Lead, and Zinc inthe Conterminous United States. Thisreport is available on CD-ROM from theUSGS Information Services, Box 25286,Denver Federal Center, Denver CO80225-0046, Tel: 303-202-4700; Fax303-202-4188. The data base consists ofa series of computer files in MicrosoftExcel, Microsoft Word, and AdobeIllustrator formats. These can be used togenerate tables, text files, maps, andgraphs, along with an executable AdobeAcrobat file that can be used with thefollowing operating systems: MacintoshOS , MS-DOS , Windows 3.1 Windows 95 , Windows 98 , Windows NT , and UNIX.1
1Any use of trade, firm, or product names is fordescriptive purposes only and does not implyendorsement by the U.S. Government.
For more information, please contact:Table 3. Results of the National assessment by mineral deposit types.
Undiscovered Gold Silver Copper Lead Zinc
General mineral deposit type (tons) (tons) (kilotons) (kilotons) (kilotons)
Vein Porphyry Replacement Stratiform-massive Stratiform-disseminated
Total, undiscovered resources
Table 2. Results of the National assessment by region.
UndiscoveredGold Silver Copper Lead Zinc
Region (tons) (tons) (kilotons) (kilotons) (kilotons)
Adirondack Mountains Central and Southern Rocky Mountains
Colorado Plateau East Central Great Basin Great Plains Lake Superior Northern Appalachians Northern Rocky Mountains Pacific Coast Southern Appalachians Southern Basin and Range
Total, undiscovered deposits
0
1,20000
4,1000
1,100200
2,1002,1001,2002,000
14,000
00
97,00053,000
0
150,000
00
36,00019,000
0
55,000
9,000190,000
4,00019,00058,000
280,000
120,00042,00075,00053,000
140,000
430,000
7,8002,800
400900
2,100
14,000
700
3,0000
57,00010,00017,00015,00017,00012,000
2,0008,3008,000
150,000
0
8,000100
044,00020,00039,000
9,90026,00011,00011,000
111,000
280,000
0
19,0000
7,000100,000
22,00067,00019,00073,00036,00019,00068,000
430,000
0
2,8000
8,3008,5008,3001,1008,7007,200
7002,6006,800
55,000
U.S. Department of the InteriorU.S. Geological Survey
November 1997 (rev. August, 1999)USGS Information Handout
Vein12%
$138 billion
Porphyry45%
$545 billionReplacement14%
$163 billion
Stratiform-massive
12%$148 billion
Stratiform-disseminated
17%$206 billion
CR24
Tracts
CR25GB21LS02LS03LS04LS05NA11NA12NA13NA14NA15NA16NR18NR19NR20PC12PC13PC14PC15PC16PC17PC18SA04SA05SA06SA07SA08SA09SB25SB26
12
1
1 234 5
67
1
2
1
1
2
1
1
2
1
1-3
1
2
31
23
1
12 34
5-67
0 200 400 milesMap projection in Albers equal area
Figure 2. Example permissive tract map - Kuroko-type massive sulfide deposit.
Figure 3. Gross value, in U.S. dollars, of the five general deposit types.
TM TM
TM TMTM
TM
Joseph A. Briskey, Jr.U.S. Geological SurveyNational Center, MS 954Reston, Va 20192Telephone: (703) 648-6112E-Mail: [email protected] G. SchrubenU.S. Geological SurveyNational Center, MS 954Reston, Va 20192Telephone: (703) 648-6142E-Mail: [email protected]
