U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007-5082

Volcanogenic Massive Sulfide Deposit Density

Volcanogenic Massive Sulfide Deposit Density

By Dan L. Mosier, Donald A. Singer, and Vladimir I. Berger

Scientific Investigations Report 2007–5082 

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

This report and any updates to it are available at: 

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Manuscript approved for publication, May 3, 2007

Text edited by Tracey Suzuki

Layout by David R. Jones

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

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Cataloging-in-publication data are on file with the Library of Congress (http://www.loc.gov/).

Cover—View of the United Verde mine (upper left), the Edith and Audrey shafts of the United Verde 

Extension mine (foreground), and the abandoned Little Daisy Hotel, which was a dormitory for the miners (upper right), Jerome, Arizona. (U.S. Geological Survey photograph taken by Dan Mosier in 2002)
iii

Contents

Abstract ..........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Methodology ..................................................................................................................................................2

Delineation of Control Areas........................................................................................................................6

Volcanogenic Massive Sulfide Deposit Densities..................................................................................10

Erosion and Densities ........................................................................................................................10

Map Scales and Densities................................................................................................................10

Area and Densities.............................................................................................................................11

Summary and Conclusions.........................................................................................................................12

Acknowledgments.......................................................................................................................................12

References Cited..........................................................................................................................................12

Figures

1. Histogram of volcanogenic massive sulfide deposit densities per 100,000 square kilometers ...10

2. Relationship of map scale and volcanogenic massive sulfide deposits 

per 100,000 square kilometers ...........................................................................................................11

3. Volcanogenic massive sulfide deposits control area exposed versus

density of deposits .............................................................................................................................11

4. Volcanogenic massive sulfide control area exposed versus number of deposits .......................11

Tables

1. Name and location of control areas with number of deposits, permissive area, 

deposit density, deposit age, and map scale used in this study ..................................................3

2. Name and location of control areas with permissive rock units and source 

of geologic maps used in this study..................................................................................................4

3. Names of control area and volcanogenic massive sulfide deposits, location, 

and tonnage...........................................................................................................................................7

Volcanogenic Massive Sulfide Deposit Density

By Dan L. Mosier, Donald A. Singer, and Vladimir I. Berger

Abstract 

A mineral-deposit density model for volcanogenic massive sulfide deposits was constructed from 38 well-explored 

control areas from around the world. Control areas contain at 

least one exposed volcanogenic massive sulfide deposit. The 

control areas used in this study contain 150 kuroko, 14 Urals, 

and 25 Cyprus massive sulfide subtypes of volcanogenic massive sulfide deposits. For each control area, extent of permissive rock, number of exposed volcanogenic massive sulfide 

deposits, map scale, deposit age, and deposit density were 

determined. The frequency distribution of deposit densities in 

these 38 control areas provides probabilistic estimates of the 

number of deposits for tracts that are permissive for volcanogenic massive sulfide deposits—90 percent of the control 

areas have densities of 100 or more deposits per 100,000 

square kilometers, 50 percent of the control areas have densities of 700 or more deposits per 100,000 square kilometers, 

and 10 percent of the control areas have densities of 3,700 or 

more deposits per 100,000 square kilometers. Both map scale 

and the size of the control area are shown to be predictors of 

deposit density. Probabilistic estimates of the number of volcanogenic massive sulfide deposits can be made by conditioning 

the estimates on sizes of permissive area. 

The model constructed for this study provides a powerful 

tool for estimating the number of undiscovered volcanogenic 

massive sulfide deposits when conducting resource assessments. The value of these deposit densities is due to the consistency of these models with the grade and tonnage and the 

descriptive models. Mineral-deposit density models combined 

with grade and tonnage models allow reasonable estimates of 

the number, size, and grades of volcanogenic massive sulfide 

deposits to be made.

Introduction 

Estimating the Earth’s undiscovered mineral resources is 

crucial in considering the future supply of minerals. Quantitative statistical methods can be applied to make unbiased 

estimates of undiscovered deposits where analogies to wellexplored areas are made (Singer and others, 2001). Estimates 

of the number of undiscovered deposits can rely on analogies 

to similar well-explored areas in the same way that grades and 

tonnages of well-explored deposits serve as analogs of the 

grades and tonnages of similar undiscovered deposits. These 

statistical estimates, or base-rates, are prepared from counts of 

known deposits per unit area in explored regions. 

In an early attempt at making quantitative estimates of 

undiscovered deposits, the number of ore deposits per square 

kilometer from several explored areas was used with the Poisson distribution to estimate the number of ore deposits existing 

in a relatively unexplored area (Allais, 1957). Bliss and others 

(1987) described a method of using mineral-deposit densities 

by deposit types as a useful tool for mineral resource assessments. These statistical estimates, or base-rates, used counts 

of known deposits per unit area in explored regions for some 

deposit types. These deposit types can be used as a guide for 

number-of-deposits estimates: low-sulfide gold-quartz veins 

(Bliss and others, 1987, Bliss and Menzie, 1993), four subtypes of volcanogenic manganese deposits (Mosier and Page, 

1988), bedded barite deposits (Orris and Bliss, 1989), diamond 

kimberlite pipes (Bliss, 1992), vein mercury (Root and others, 

1992), podiform chromite (Singer, 1994), placer gold, kuroko 

massive sulfide, porphyry copper, Climax porphyry molybdenum, and wolframite quartz vein deposits (Singer and others, 

2001), and three subtypes of porphyry copper deposits (Singer 

and others, 2005). 

Most of these studies provide point or single estimates 

of the number of deposits per unit area. In some studies, 

these single estimates of a deposit type might represent high 

estimates of the number of undiscovered deposits because 

the studies were restricted to well-documented places with 

large resources and high densities of deposits. Recent studies 

(Singer, 1994; Singer and others, 2005) document the variability in densities in porphyry copper and podiform chromite 

deposit types. Frequencies of deposit densities in well-studied 

geologically similar regions can be used to estimate frequencies of densities of deposits in assessed regions, just as 

frequencies of tonnages and grades of well-explored deposits 

can be used to estimate grades and tonnages of undiscovered 

deposits. This study presents 38 control areas of deposit densities for volcanogenic massive sulfide deposits from around the 

world. This large number of deposit densities for volcanogenic 

massive sulfide deposits allows the variability of depositdensity estimates and the examination of possible effects of 

deposit tonnage, deposit age, and map scale on these deposit 

densities to be studied.
 Volcanogenic Massive Sulfide Deposit Density

Methodology 

Volcanogenic massive sulfide deposits, also referred 

to as volcanic-hosted massive sulfide deposits, have been 

variously grouped into different classes based primarily on 

geologic setting. Classification of the subtypes is not generally agreed upon in the scientific literature, but this study recognizes two broad subtypes of volcanogenic massive sulfide 

deposits, designated as kuroko- and Cyprus-type as defined 

by Cox and Singer (1986). In known world resources, these 

deposits contain 5 percent of the world’s copper, 22 percent 

of the world’s zinc, 10 percent of the world’s lead, 2 percent of the world’s gold, and 9 percent of the world’s silver 

(Singer, 1995). 

In this study, 38 control areas from around the world 

that contain volcanogenic massive sulfide deposits, and that 

are considered to be well explored, were selected for mineral-deposit density modeling. There are 31 control areas 

containing 145 kuroko-type deposits, 1 control area containing a mixture of 5 kuroko-type and 14 Urals-type deposits, 

and 6 control areas containing 25 Cyprus-type massive sulfide 

deposits. The kuroko massive sulfide and Cyprus massive 

sulfide deposit types used in the density model are defined in 

the descriptive and tonnage-grade models for kuroko (Singer, 

1986b; Singer and Mosier, 1986b) and Cyprus (Singer, 1986a; 

Singer and Mosier, 1986a) massive sulfide deposits. The Urals 

massive sulfide deposits provisionally used in the density 

model are based on recent regional studies (Herrington and 

others, 2005; Prokin and Buslaev, 1999) of the Urals of Russia 

and Kazakhstan. Descriptive and tonnage-grade models of 

possible subtypes of massive sulfide deposits are under active 

study. Using consistent models helps to avoid introduction of 

biases in assessments. 

Kuroko-type massive sulfide deposits typically occur in 

marine felsic to mafic volcanic and associated sedimentary 

rocks that formed in or near continental margin arcs and back 

arcs (Singer, 1986b). The deposits usually are formed by 

submarine hydrothermal activity during the waning stages of 

volcanism, and many are associated with local, small rhyoliticto dacitic-intrusive bodies. These deposits commonly have 

massive lenses of sphalerite, pyrite, chalcopyrite, and locally, 

galena, gold- and silver-bearing minerals, and other minor 

sulfides. A footwall stockwork zone of stringers and disseminations of iron- and copper-bearing sulfides accompany some 

massive sulfide lenses. The median tonnage of 432 deposits in 

the kuroko massive sulfide model is 1.5 million metric tons, 

and median grades are 1.3 percent copper, 2.0 percent zinc, 

0.16 grams per metric ton gold, and 13 grams per metric ton 

silver (Singer and Mosier, 1986b).

Urals-type massive sulfide deposits occur in marine mafic 

and subordinate felsic volcanic rocks formed in spreading 

back-arc and front-arc rift basins. The deposits are formed by 

submarine hydrothermal activity during the waning stages of 

volcanism in local depressions and mostly near small rhyolitic to dacitic subvolcanic bodies. The deposits form massive 

lenses of pyrite, chalcopyrite, sphalerite, and other minor 

sulfides. According to preliminary estimates for this study, the 

median tonnage for 30 Urals-type massive sulfide deposits is 

18 million metric tons, and the median grades are 2.0 percent 

copper and 1.5 percent zinc (Herrington and others, 2005; 

Prokin and Buslaev, 1999). 

Cyprus-type massive sulfide deposits occur in marine 

mafic volcanic and associated sedimentary rocks that form 

along oceanic ridges or in spreading back-arc rift basins 

(Singer, 1986a). The pillow basalts and diabase dikes that 

host the deposits form the upper part of ophiolite sequences. 

The deposits form massive lenses of pyrite, chalcopyrite, 

sphalerite, gold- and silver-bearing minerals, and other minor 

sulfides. A footwall stockwork zone of stringers and disseminations of sulfides accompany some massive sulfide lenses. 

Median tonnage for 49 deposits in the Cyprus massive sulfide 

model is 1.6 million metric tons, and the median copper grade 

is 1.7 percent (Singer and Mosier, 1986a).

In this study, selection of density-control areas had to 

meet three criteria:

The area had to contain exposed volcanogenic massive 

sulfide deposits with tonnages and grades consistent 

with the grade-tonnage models for kuroko- or Cyprustype deposits. Each deposit needed to be separated 

from other deposits by at least 500 meters of barren 

rock. Exposure of the deposits had to include the 

weathered gossan zones, or part of the massive sulfide 

bodies themselves.

Permissive host rocks or hosting units needed to be 

shown as outcrops on geologic maps with scales no 

smaller than 1:2,500,000. 

Surficial areas of permissive host rocks must have been 

well explored, and all deposits exposed at the surface 

must be believed to have been found. Although it 

was not necessary that the control area be completely 

explored, it was important that the proportion of the 

number of exposed deposits and areas explored be 

estimated. 

To determine the size of the permissive control areas, the 

geologic maps were scanned and imported into MapInfoTM

v. 4.0. The geologic contacts were digitized as polygons and 

the areas were computed in square kilometers. 

Deposit densities were computed by dividing the number 

of exposed deposits by the permissive area for the occurrence 

of the deposit type. Densities were normalized to 100,000 

square kilometers in order to present the data as whole numbers of deposits, rather than as fractions of deposits, and to 

make the numbers compatible with densities recently published for other deposit types. The control-area data used in 

this study are presented in table 1. The permissive rocks in 

the control areas and source maps are listed in table 2. The 

volcanogenic massive sulfide deposits and their sizes are listed 

in table 3. 

1.

2.

3.
Methodology 

Table 1. Name and location of control areas with number of deposits, permissive area, deposit density, deposit age, and map scale 

used in this study.

[n, number; km2, square kilometers; USA, United States of America]

Control area name and location Type Deposits 

(n)

Permissive 

area

(km2)

Density 

(deposits/

km2)

Normalized 

density

(density x 105)

Age 

(Ma)

Map scale 

(1:n)

Ammonoosuc, Maine-Connecticutt, USA kuroko 3 1,136 0.0026 264 450 500,000

Ashland, Alabama, USA kuroko 1 81 0.0123 1235 1,000 500,000

Betts Cove, Newfoundland, Canada Cyprus 4 433 0.0092 924 500 250,000

Big Mike, Nevada, USA Cyprus 1 420 0.0024 238 295 250,000

Binghampton, Arizona, USA kuroko 1 26 0.0385 3,846 1,640 62,500

Buchans, New Brunswick, Canada kuroko 4 1,051 0.0038 381 430 250,000

Castine, Maine, USA kuroko 3 236 0.0127 1,271 400 500,000

Chestatee, Georgia, USA kuroko 1 27 0.0370 3,704 850 500,000

Copper Hill, California, USA kuroko 4 424 0.0094 943 154 250,000

Dominican Republic kuroko 3 338 0.0089 888 120 250,000

East Shasta, California, USA kuroko 2 73 0.0274 2,740 250 250,000

Flin Flon-Snow Lake, Manitoba-Saskatchewan, 

Canada

kuroko 15 2,656 0.0056 565 1,800 1,000,000

Gopher Ridge, California, USA kuroko 8 1,343 0.0060 596 154 250,000

Hawley-Bernard, Massachusetts-Vermont, USA kuroko 1 297 0.0034 337 450 250,000

Hillabee, Alabama-Georgia, USA kuroko 2 218 0.0092 917 390 500,000

Hokoruku, Japan kuroko 8 900 0.0089 889 15 200,000

Iberian Pyrite Belt, Spain-Portugal kuroko 48 1,300 0.0369 3,692 350 200,000

Jerome, Arizona, USA kuroko 1 24 0.0417 4,167 1,750 24,000

Kunitomi, Japan kuroko 5 416 0.0120 1,202 15 200,000

Kutcho Creek, British Columbia, Canada kuroko 1 243 0.0041 412 244 1,267,200

Lokken, Norway Cyprus 2 949 0.0021 211 450 1,000,000

Mount Read, Tasmania, Australia kuroko 4 825 0.0048 485 502 250,000

Myra Falls, British Columbia, Canada kuroko 2 1,117 0.0018 179 370 1,267,200

New Georgia Group, Georgia, USA kuroko 2 587 0.0034 341 850 500,000

North Haven, Maine, USA kuroko 1 36 0.0278 2,778 680 500,000

Orient, Cuba kuroko 2 3,390 0.0006 59 53 250,000

Pecos, New Mexico, USA kuroko 1 149 0.0067 671 1,500 500,000

Quoddy, Maine, USA kuroko 2 233 0.0086 858 430 500,000

Rudny-Altai, Russia-Kazakhstan-China kuroko 8 20,539 0.0004 39 390 2,500,000

Smartville, California, USA Cyprus 3 518 0.0058 579 170 250,000

Snake River, Oregon-Idaho, USA kuroko 2 1,071 0.0019 187 250 500,000

Standing Pond, Massachusetts-Vermont, USA kuroko 1 123 0.0081 813 390 250,000

Sunro, British Columbia, Canada Cyprus 1 480 0.0021 208 40 1,267,200

Troodos, Cyprus Cyprus 14 1,016 0.0138 1,378 85 250,000

Urals, Russia-Kazakhstan Urals, 

kuroko

19 81,615 0.0002 23 400 2,500,000

West Shasta, California, USA kuroko 8 117 0.0684 6,838 380 250,000

Winterville, Maine, USA kuroko 1 621 0.0016 161 450 500,000

Yavapai, Arizona, USA kuroko 1 89 0.0112 1,124 1,700 375,000
Table 2. Name and location of control areas with permissive rock units and source of geologic maps used in this study. [Fm, Formation; USA, United States of America] Control area name and location Permissive rock units Source Ammonoosuc, Maine- Connecticut, USA Ordovician Ammonoosuc Volcanics and Middleton Fm Osberg, Hussey, and Boone, 1985; Rodgers, 19

Zen and others, 1983; Lyons and others, 199

Ashland, Alabama, USA Precambrian (Algonkian) Ashland amphibolite Stone, 1926 Betts Cove, Newfoundland, Canada Ordovician Betts Cove and Lush Bight Group Kean, Dean, and Strong, 1981 Big Mike, Nevada, USA Pennsylvanian Pumpernickel Fm Johnson, 1977; Stewart, McKee, and Stager, 19

Willden and Speed, 1974; Willden, 1964 Binghampton, Arizona, USA Precambrian Spud Mountain Volcanics (andesite breccia unit) Anderson and Blacet, 1972a, 1972b Buchans, New Brunswick, Canada Ordovician Buchans and Roberts Arm Group Kean, Dean, and Strong, 1981 Castine, Maine, USA Silurian-Devonian Castine Fm and equivalent unnamed unit Osberg, Hussey, and Boone, 1985 Chestatee, Georgia, USA Upper Precambrian Amphibolite (mm1) Lawton and others, 1976

Copper Hill, California, USA Jurassic Copper Hill Volcanics Kemp, 1982; Strand and Koenig, 1965; Saucedo 

Bortugno, and McJunkin, 1990; Wagner and 

Dominican Republic Cretaceous Maimon Fm and Amina Schist Blesch, 1967East Shasta, California, USA Permian Bully Hill Rhyolite Albers and Robertson, 1961; Fraticelli and otheFlin Flon-Snow Lake, ManitobaSaskatchewan, Canada Precambrian Amisk Group Manitoba Mineral Resources Division, 1980; Whitaker and Pearson, 1972Gopher Ridge, California, USA Jurassic Gopher Ridge Volcanics and Western Volcanics Kemp, 1982; Strand and Koenig, 1965; Saucedo 

Bortugno, and McJunkin, 1990; Wagner and 

Hawley-Bernard, MassachusettsVermont, USA Ordovician Hawley Fm and Bernard Volcanics Zen and others, 1983; Doll and others, 1961Hillabee, Alabama-Georgia, USA Post-Carboniferous Hillabee Schist (Alabama), Mafic Schist-Amphibolite Schist-Amphibolite (ms2, Georgia) Lawton and others, 1976; Stone, 1926Hokoruku, Japan Middle Miocene felsic volcanic rocks Singer and others, 2001Iberian Pyrite Belt, Spain-Portugal Devonian-Carboniferous VolcanoSedimentary Complex Instituto Geológico y Minero de España, 1970a

and others, 1984; Oliveira and others, 1989

Jerome, Arizona, USA Proterozoic Ash Creek Group Anderson and Creasey, 1958Kunitomi, Japan Middle Miocene Kunitomi Fm and other volcanic units Ishida, Mimura, and Hiroshima, 1991Kutcho Creek, British Columbia, 

Canada

Lower-Middle Jurassic Maude Fm sedimentary and volcanic rocks 

(map unit 49c, now designated as Permian-Triassic Kutcho Assemblage)

Little, 1962; Childe and Thompson, 1997

Lokken, Norway Cambrian-Silurian basic effusive rocks, partly green schists Holtedahl and Dons, 1953
Table 2. Name and location of control areas with permissive rock units and source of geologic maps used in this study—Continued. 

Control area name and location Permissive rock units Source

Mount Read, Tasmania, Australia Cambrian Mount Read Volcanics Williams and Corbett, 1977; Williams and Turn

Brown, 1976

Myra Falls, British Columbia, 

Canada

Permian sedimentary and volcanic rocks (map unit 38, Sicker Group 

volcanic-sedimentary rocks)

Little, 1962

New Georgia Group, Georgia, 

USA

Upper Precambrian Hornblende Gneiss (mm3) Lawton and others, 1976

North Haven, Maine, USA Precambrian North Haven Fm Osberg, Hussey, and Boone, 1985Orient, Cuba Paleocene-Eocene Cobre Fm Instituto de Geológica y Paleontologia, 1988a, Pecos, New Mexico, USA Precambrian metavolcanic rocks Hunt, 1977Quoddy, Maine, USA Silurian Quoddy Fm Osberg, Hussey, and Boone, 1985Rudny-Altai, Russia-KazakhstanChina Devonian volcanic and volcanic-sedimentary rocks Han and others, 2006; Nalivkin and Sokolov, 1

1985; Shcherba, 1983

Smartville, California, USA Jurassic Smartville Complex (Lower Volcanic Unit) Saucedo and Wagner, 1992Snake River, Oregon-Idaho, USA Permian-Triassic Hunsaker Creek Fm (Oregon) and Seven Devils 

Volcanics (Idaho)

Vallier, 1974; Walker and McLeod, 1991; Gast

son and Raines, 1996; Bond and others, 197

Standing Pond, MassachusettsVermont, USA Devonian Standing Pond Volcanics Zen and others, 1983; Doll and others, 1961Sunro, British Columbia, Canada Paleocene to Oligocene sedimentary and volcanic rocks (map unit 58, 

now designated as Eocene Metchosin Volcanics

Little, 1962; Canada Department of Energy, M

Troodos, Cyprus Upper Cretaceous Troodos Upper Pillow Lava, Lower Pillow Lava, 

and Basal Group

Geological Survey Department, Cyprus, 1979

Urals, Russia-Kazakhstan Silurian to Middle Devonian volcanic and volcanic-sedimentary 

rocks

Nalivkin and Sokolov, 1983; Shatov, Seltmann

Herrington and others, 2005; Prokin and Bus

West Shasta, California, USA Devonian Balaklala Rhyolite Lydon, 1972Winterville, Maine, USA Ordovician Winterville Fm Osberg, Hussey, and Boone, 1985Yavapai, Arizona, USA Precambrian Schist (includes Bridle Fm) Arizona Bureau of Mines, 1953
 Volcanogenic Massive Sulfide Deposit Density

(Canada Department of Energy, Mines and Resources, 1980), 

and the age of the deposit is listed as Eocene in table 1.

In the Kunitomi district of Hokkaido, Japan, dacite of the 

Middle Miocene Kunitomi Formation hosts volcanogenic massive sulfide deposits (Ogura, 1974). However, on the geologic 

map by Ishida, Mimura, and Hiroshima (1991) that was used 

to delineate the control area, the permissive Kunitomi Formation could not be separated from the nonpermissive Ohiragawa, Shibaribetsugawa, and Furubira formations because 

all four units were combined as a single unit on the map. 

The Rudny-Altai volcanic arc, extending from Kazakhstan and southwestern Russia into northwestern China, is a 

Devonian bimodal suite of volcanic rocks that hosts many 

volcanogenic massive sulfide deposits. The control area 

delineated in the Rudny-Altai was based on Devonian units 

that included both volcanic and undifferentiated rocks on the 

geologic maps for Russia (Nalivkin and Sokolov, 1983) and 

China (Zhefu and others, 1985).

By using the geologic map of Nalivkin and Sokolov 

(1983) for the Russian Urals, the control area was delineated 

around Silurian and Lower to Middle Devonian volcanic 

and undifferentiated rocks that host important volcanogenic 

massive sulfide deposits. These deposits are classified in the 

Russian literature as Urals- and (or) Baimak-type (kuroko) 

deposits that are associated with bimodal volcanic arcs (Prokin 

and Buslaev, 1999). There were probably multiple volcanic 

arcs in the Urals that were active during the Silurian to Middle 

Devonian. These units were combined into a single control 

area for this study because of the uncertainty of the ages of 

some of the hosting rock units. The map of the Southern Urals 

by Shatov and others (2001) was used primarily to verify the 

locations of the deposits and their hosting units. 

In the Snake River area of Oregon and Idaho, the Permian Hunsaker Creek Formation of Vallier (1974), with some 

modifications to the geologic map of Oregon of Walker and 

McLeod (1991), was delineated as permissive for volcanogenic massive sulfide deposits. The equivalent formation in 

Idaho is the Permian-Triassic Seven Devils volcanic rocks 

(Gaston and Bennett, 1979; Bond and others, 1978). Walker 

and McLeod (1991) reduced the extent of the Hunsaker Creek 

Formation in the Wallowa Mountains, Oregon, where some 

rocks of the Hunsaker Creek Formation west of Homestead 

were reassigned to the Triassic-Jurassic Hurwal Formation. In 

the Oxbow along Indian Creek south of Homestead, Oregon, 

Walker and McLeod (1991) also reassigned the OxbowCuprum shear zone of Vallier (1974) to the Hunsaker Creek 

Formation. 

Deposit densities for the Sierra Nevada, California; 

Tasmania, Australia; Snow Lake, Canada; and the island of 

Cyprus are refined here from Singer and others (2001). The 

largest change is in the Snow Lake area, where the size of the 

permissive Amisk Group was increased by the addition of the 

Flin Flon area. This significantly decreased the deposit density 

for the Flin Flon-Snow Lake area, resulting in a more realistic 

density value for the Amisk Group (table 1).

Delineation of Control Areas

From data in the descriptive deposit models mentioned 

previously, kuroko massive sulfide deposits can be expected 

to be found in marine rhyolitic- to andesitic-volcanic rocks 

associated with island arcs, and Cyprus massive sulfide deposits can be expected to be found in pillow basalts associated 

with oceanic spreading ridges. In order to use these models 

for mineral resource assessments, geologic maps that show the 

permissive rocks for these deposits must be found. Permissive 

rocks for volcanogenic massive sulfide deposits are the volcanic or sedimentary rocks that host most ore bodies because 

the deposits are conformable with the host rocks. These rocks 

should be delineated as permissive. 

The immediate hosting rocks, however, are often lenses 

or thin layers within a thicker sequence of volcanic and sedimentary rocks and are not differentiated on most geologic map 

scales. Larger scale maps may show these rock units in greater 

detail, but larger scale maps are not always available for consistent delineation of control areas, or for delineating permissive tracts in assessments. Smaller scale maps frequently generalize the rock units of relevance into broader rock categories 

or ages. Grouping these generalized rock sequences results in 

including rocks that are not considered permissive, thereby 

increasing the size of the permissive area, which in turn lowers 

deposit densities. 

Other situations may include rock units that conceal 

permissive rocks, younger intrusive bodies, and water bodies 

that cover permissive rocks within the polygon of permissive 

units. Attention was taken to the extent possible to exclude any 

of these nonpermissive units shown on the map. 

The second column in table 2 lists the volcanic rock 

units or formations that were delineated for the control areas 

after the data were adjusted for cover or rocks that are not 

permissive. Special treatment and further explanation of some 

of the control areas are discussed in more detail below where 

some effects of assignment of rocks, ages, or affiliations are 

examined.

The 1962 geologic map of British Columbia, Canada 

(Little, 1962), that was used for three control areas, exemplifies a common problem encountered when using a small-scale 

map that contains out-of-date information. In the Kutcho 

Creek control area, Little’s map displays the permissive rocks 

for the Kutcho Creek massive sulfide deposit as the Lower to 

Middle Jurassic Maude Formation, consisting of sedimentary 

and volcanic rocks. Childe and Thompson (1997), however, 

have reassigned these rocks to the Kutcho Assemblage of 

Permian to Triassic age. The Maude Formation (table 2) was, 

therefore, delineated for the permissive area as it closely 

approximates the extent of the Kutcho Assemblage, but the 

age of the deposit has been assigned to Triassic rather than 

Jurassic age (table 1).

In the Sunro area of British Columbia, Little’s (1962) 

Paleocene to Oligocene sedimentary and volcanic rocks were 

delineated as permissive (table 2). These sedimentary and 

volcanic rocks have been renamed as the Metchosin Formation 
Delineation of Control Areas 

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

Ammonoosuc Croydon New Hamphire, 

USA

0.05 kuroko

Milan New Hamphire, 

USA

0.50 kuroko

Ore Hill New Hamphire, 

USA

0.10 kuroko

Ashland Stone Hill Alabama, USA 1.30 kuroko

Betts Cove Betts Cove Newfoundland, 

Canada

0.12 Cyprus

Little Bay Newfoundland, 

Canada

2.95 Cyprus

Tilt Cove Newfoundland, 

Canada

12.38 Cyprus

Whalesback Newfoundland, 

Canada

4.89 Cyprus

Big Mike Big Mike Nevada, USA 0.10 Cyprus

Binghampton Binghampton Arizona, USA 0.36 kuroko

Buchans Gullbridge New Brunswick, 

Canada

4.70 kuroko

Lucky StrikeRothermereNew Brunswick, 

Canada

9.07 kuroko

MacLean New Brunswick, 

Canada

3.77 kuroko

Old Buchans New Brunswick, 

Canada

2.59 kuroko

Castine Emerson Maine, USA 0.15 kuroko

Penobscot Maine, USA 0.80 kuroko

Tapley Maine, USA 0.05 kuroko

Chestatee Chestatee Georgia, USA 1.10 kuroko

Copper Hill Copper Hill California, USA 0.27 kuroko

KeystoneUnionCalifornia, USA 1.20 kuroko

Newton California, USA 0.15 kuroko

North KeystoneCalifornia, USA 0.21 kuroko

Dominican 

Republic 

Cerro de 

Maimon

Dominican 

Republic 

3.36 kuroko

El Anon Dominican 

Republic 

0.27 kuroko

Loma Pesada Dominican 

Republic 

1.11 kuroko

East Shasta Afterthought California, USA 0.15 kuroko

Bully HillRising StarCalifornia, USA 0.62 kuroko 

Flin FlonSnow LakeBomber Manitoba, 

Canada

0.68 kuroko

Callinan Manitoba, 

Canada

2.80 kuroko

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

Copper Man Manitoba, 

Canada

0.22 kuroko

Cuprus Manitoba, 

Canada

0.46 kuroko

Dickstone Manitoba, 

Canada

1.08 kuroko

Don Jon Manitoba, 

Canada

0.08 kuroko

Flin Flon Manitoba, 

Canada

62.40 kuroko

Fourmile 

Island

Manitoba, 

Canada

1.35 kuroko

Mandy Manitoba, 

Canada

0.15 kuroko

Pot Lake Manitoba, 

Canada

0.10 kuroko

Ramsay Saskatchewan, 

Canada

0.71 kuroko

Schist Lake Manitoba, 

Canada

1.88 kuroko

Stall Lake Manitoba, 

Canada

6.30 kuroko

Sun Manitoba, 

Canada

0.50 kuroko

Vamp Lake Manitoba, 

Canada

0.45 kuroko

Gopher Ridge Akoz California, USA 0.52 kuroko

Big Bend California, USA 0.05 kuroko

Blue Moon California, USA 0.11 kuroko

Diary Farm California, USA 2.00 kuroko

Oak Hill California, USA 0.06 kuroko

Penn California, USA 0.88 kuroko

Quail Hill California, USA 0.01 kuroko

Valley View California, USA 0.05 kuroko

Hawley-BernardDavis Massachusetts, 

USA

0.90 kuroko

Hillabee Pyriton Alabama, USA 2.75 kuroko

Tallapoosa Georgia, USA 0.09 kuroko

Hokuroku Ezuri Japan 3.00 kuroko

Fukazawa Japan 6.47 kuroko

Furutobe-AinaiJapan 14.24 kuroko

HanaokaDoyashikiJapan 22.88 kuroko

HanaokaMatsumineShakanaiJapan 54.20 kuroko

Table 3. Names of control area and volcanogenic massive sulfide deposits, location, and tonnage.

[USA, United States of America]
 Volcanogenic Massive Sulfide Deposit Density

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

KosakaUchinotaiJapan 19.86 kuroko

KosakaMotoyamaJapan 8.00 kuroko

Nurukawa Japan 0.05 kuroko

Iberian

Pyrite Belt

Aguas TenidasSpain 0.88 kuroko

AlmagreraLapillaSpain 15.50 kuroko

Angostura Spain 1.85 kuroko

Cabeza del 

Pasto

Spain 0.57 kuroko

Campanario Spain 0.91 kuroko

Caridad Spain 3.56 kuroko

Carpio Spain 3.35 kuroko

Castillo BuitronSpain 3.80 kuroko

Castillo de la 

Guardas

Spain 2.75 kuroko

Concepcion Spain 55.85 kuroko

Cueva de la 

Mora

Spain 4.20 kuroko

Esperanza Spain 1.70 kuroko

Filon SurEsperanzaSpain 110.00 kuroko

Gloria Spain 0.01 kuroko

Herrerias Spain 7.30 kuroko

La Chaparrita Spain 0.07 kuroko

La DescamisadaSpain 2.88 kuroko

La Joya Spain 0.01 kuroko

La Ratera Spain 0.93 kuroko

La Torerrera Spain 1.50 kuroko

La Zarza Spain 164.00 kuroko

Lagunazo Spain 6.00 kuroko

LomeroPoyatosSpain 4.33 kuroko

Lousal Portugal 0.60 kuroko

Monte 

Romero

Spain 8.60 kuroko

Paymogo Spain 0.82 kuroko

Pena de 

Hierro

Spain 5.00 kuroko

Perrunal Spain 12.00 kuroko

Poderosa Spain 0.61 kuroko

Prado Vicioso Spain 0.22 kuroko

Rio Tinto Spain 334.30 kuroko

Romanera Spain 34.00 kuroko

San AntonioPlanesSpain 27.00 kuroko

Table 3. Names of control area and volcanogenic massive sulfide deposits, location, and tonnage—Continued.

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

San Domingos Portugal 20.00 kuroko

San Eduardo Spain 0.07 kuroko

San GuillermoSierra BullonesFilon NorteFilon CentreSpain 127.50 kuroko

San Miguel Spain 1.29 kuroko

San Pedro Spain 0.23 kuroko

San Platon Spain 1.50 kuroko

San Telmo Spain 11.40 kuroko

Santa Rosa Spain 0.50 kuroko

Sierrecilla Spain 0.20 kuroko

Sorpresa Spain 0.01 kuroko

Sotiel Spain 41.00 kuroko

TintoSanta RosaSpain 1.66 kuroko

Valle Spain 0.19 kuroko

Vuelta Falsa Spain 1.00 kuroko

Vulcano Spain 0.06 kuroko

Jerome United Verde Arizona, USA 29.00 kuroko

Kunitomi Kunitomi 

1-5-1N

Japan 2.10 kuroko

Kunitomi 

3-4-6

Japan 0.70 kuroko

Kunitomi 7-8 Japan 0.40 kuroko

Meiji Japan 0.10 kuroko

Yoichi Japan 0.74 kuroko

Kutcho Creek Kutcho Creek British Columbia, 

Canada

22.60 kuroko

Lokken Hoydal Norway 0.10 Cyprus

Lokken Norway 25.00 Cyprus

Mount Read Hercules Tasmania, 

Australia

2.36 kuroko

Mount Lyell Tasmania, 

Australia

119.92 kuroko

Que River Tasmania, 

Australia

6.00 kuroko

RoseberyReadTasmania, 

Australia

28.29 kuroko

Myra Falls Lenora-Twin J British Columbia, 

Canada

0.27 kuroko

Myra FallsLynxBritish Columbia, Canada5.18 kuroko

New Georgia 

Group

Jenny Stone Georgia, USA 0.57 kuroko

Little Bob Georgia, USA 0.14 kuroko

North Haven Deer Isle Maine, USA 0.05 kuroko

Orient El Cobre Cuba 11.44 kuroko

La Cristina Cuba 0.50 kuroko
Delineation of Control Areas 

Table 3. Names of control area and volcanogenic massive sulfide deposits, location, and tonnage—Continued.

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

Pecos Pecos New Mexico, 

USA

2.09 kuroko

Quoddy Barrett Maine, USA 0.40 kuroko

Big Hill Maine, USA 0.75 kuroko

Rudny-Altai Belousovskoe Kazakhstan >0.01 kuroko

Berezovskoe Kazakhstan >0.01 kuroko

Keketale China 64.20 kuroko

Maiskoe Russia 1.00 kuroko

Orlovskoe Kazakhstan 29.00 kuroko

RidderSokol’noeKazakhstan 46.30 kuroko

ShemonaikhinskoeKazakhstan >0.01 kuroko

Zyryanovskoe Kazakhstan 65.90 kuroko

Smartville Boss California, USA 0.01 Cyprus

Spenceville California, USA 0.14 Cyprus

Western 

World

California, USA 1.36 Cyprus

Snake River Iron Dyke Oregon, USA 0.51 kuroko

Red Ledge Idaho, USA 39.00 kuroko

Standing 

Pond

Orange & 

Gove

Vermont, USA 0.05 kuroko

Sunro Sunro British Columbia, 

Canada

2.78 Cyprus

Troodos Agrokipia Cyprus 1.42 Cyprus

Ambelikou Cyprus 0.02 Cyprus

Apliki Cyprus 1.50 Cyprus

Kapedhes Cyprus 0.05 Cyprus

KokkinopezoulaCyprus 5.00 Cyprus

Kokkinoyia Cyprus 0.91 Cyprus

Limni Cyprus 4.22 Cyprus

Mathiati 

North

Cyprus 2.50 Cyprus

Mavrovouni Cyprus 15.00 Cyprus

MousoulosKalavososCyprus 6.92 Cyprus

Pervasa Cyprus 0.09 Cyprus

Control area

name

Deposit Deposit

location

Tonnage 

(millions 

metric tons)

Deposit 

type

Sha Cyprus 0.32 Cyprus

Skouriotissa Cyprus 5.40 Cyprus

Troulli Cyprus 0.27 Cyprus

Urals 50 Let 

Oktyabrya

Kazakhstan 46.00 Urals

AleksandrinskoeRussia 10.00 kuroko

Avangard Russia >0.01 Urals

Bakr-Usyak Russia 3.00 Urals

Blyavinskoe Russia 19.30 Urals

Buribaiskoe Russia 30.00 Urals?

Degtyarskoe Russia 130.00 Urals

Dzerzhinskoe Russia 8.60 Urals

KrasnogvardeiskoeRussia 14.10 Urals

Levikhinskoe Russia 8.40 Urals

NovoShaitanskoeRussia >0.01 Urals

Pervomaiskoe Russia 7.50 Urals

Sibaiskoe Russia 111.40 Urals

Tarnyerskoe Russia 9.10 Urals

Tubinskoe Russia 2.20 kuroko

Uchalinskoe Russia 226.00 Urals

Valentorskoe Russia 1.50 kuroko

Yulalinskoe Russia 0.70 kuroko

ZapadnoAshchebutakRussia 3.00 kuroko

West Shasta Early Bird California, USA 0.04 kuroko

Iron Mountain California, USA 7.88 kuroko

Keystone California, USA 0.11 kuroko

Mammoth California, USA 3.10 kuroko

Shasta King California, USA 0.20 kuroko

Stowell California, USA 0.15 kuroko

Sutro California, USA 0.03 kuroko

Winterville Bald Mountain Maine, USA 33.00 kuroko

Yavapai Bruce Arizona, USA 1.43 kuroko
10 Volcanogenic Massive Sulfide Deposit Density

Figure 1. Histogram of volcanogenic massive sulfide deposit 

densities per 100,000 square kilometers for 38 control areas used 

in this study.

Erosion and Densities

It is reasonable to assume that erosion would affect sizes 

and densities of volcanogenic massive sulfide deposits. If 

exposure to erosion over time removed deposits, there should 

be a lower density of deposits in older control areas. If parts 

of deposits were removed by erosion or tectonics over time, 

there also should be smaller deposits in older control areas. 

Deposit densities of volcanogenic massive sulfide deposits 

were compared to deposit ages to determine if they are related. 

Deposit densities, however, are not significantly correlated 

with deposit age (r = 0.17, n = 38). This lack of correlation is 

also supported by the observations in this study that indicate 

younger deposits are not larger in tonnage than older deposits 

(r = -0.006, n = 189). Thus, erosion over time has no measurable effect on the size or deposit densities of volcanogenic 

massive sulfide deposits. Similar observations were made with 

porphyry copper deposits (Singer and others, 2005). Thus, we 

reject the hypothesis that deposit densities decrease through 

time. Effects of erosion cannot be demonstrated by diminished 

sizes of volcanogenic massive sulfide deposits or by lower 

deposit densities through time.

Map Scales and Densities

The scale of a geologic map may affect the extent of the 

permissive rocks. As already mentioned, small-scale maps tend 

to generalize rock units by combining permissive rocks with 

nonpermissive rocks, that is, combining felsic volcanic rocks 

with mafic volcanic rocks. Some small-scale maps may display 

rocks by geologic age rather than by rock type. For example, the 

geologic map of the Urals of Russia used in this study (Nalivkin 

and Sokolov, 1983) combines the volcanic and sedimentary 

rocks into undifferentiated Silurian or Devonian units. Furthermore, because of the uncertainty of the rock ages around some 

of the volcanogenic massive sulfide deposits, it was sometimes 

necessary to combine two age units into a single permissive 

area. Thus the delineation of the Urals by using a map scale of 

1:2,500,000 probably results in overestimation of the permissive 

area, which is expected when using small-scale geologic maps 

and is likely to result in a smaller mineral-deposit density value. 

In resource assessments, small-scale maps are commonly the 

only geologic maps available, therefore, lower mineral-deposit 

density estimates can be expected. 

Deposit density is inversely correlated with map scale 

(significant at one percent level, r = – 0.63, n = 38; fig. 2). Map 

scales used in this study range from 1:24,000 to 1:2,500,000. 

Control areas based on small-scale maps typically contain 

rocks that are not permissive for volcanogenic massive sulfide 

deposits, which results in lower deposit densities. Larger scale, 

more detailed maps are more likely to have excluded areas 

of nonpermissive rocks resulting in higher deposit densities. 

Although it might be possible to develop mineral deposit densities from larger scale maps that have more detailed mapping, 

in applying densities in assessments, such detailed maps are 

frequently not available. This inverse relationship is inherent 

The Hokuroku district, Japan, was added to the data set 

for this study from data in a previous study by Singer and 

others (2001). The deposit density for the Hokuroko district 

is based on eight deposits in the 900-square kilometer basin 

underlain by Middle Miocene felsic volcanic rocks and overlain mostly by younger sediments. Because the basin has been 

extensively drilled, with little chance of finding new deposits 

near the drilling, it was included as part of the control area.

Volcanogenic Massive Sulfide Deposit 

Densities

The number of exposed volcanogenic massive sulfide 

deposits in each control area, adjusted for cover, provides the 

deposit densities per 100,000 square kilometers listed in table 1. 

A comparison of the deposit densities between the kuroko (plus 

Urals) and Cyprus massive sulfides using the t test demonstrates 

that there is not a significant difference in their densities, so all 

subtypes are combined in this study and are hereinafter referred 

to as volcanogenic massive sulfide deposits. 

A histogram of volcanogenic massive sulfide deposit 

densities (fig. 1) shows a skewed distribution similar to those 

documented for podiform chromite deposits (Singer, 1994) 

and porphyry copper deposits (Singer and others, 2005). In 

such skewed distributions, a few high densities affect the 

mean density. Although the mean is one measure of central 

tendency, the median is often a preferable measure in such 

skewed distributions because it is less affected by a few 

extreme sample values.

Probabilistic estimates of deposit densities can be made 

that are not affected by the few high values. A frequency distribution of log densities provides the probabilistic estimates. 

In table 1, 90 percent of the control areas have densities of 100 

or more volcanogenic massive sulfide deposits per 100,000 

square kilometers, 50 percent have densities of 700 or more 

deposits per 100,000 square kilometers, and 10 percent have 

densities of 3,700 or more deposits per 100,000 square kilometers. However, there may be factors that allow refinement of 

these estimates as discussed below.

15

10

5

0

COUNT

NUMBER OF DEPOSITS PER 100,000 SQUARE KILOMETERS

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000
Volcanogenic Massive Sulfide Deposit Densities 11

in the rules used to define control areas, which depend on map 

scale and information content.

Area and Densities

Control areas in this study range in size from 24 to 

82,000 square kilometers and contain at least one exposed 

volcanogenic massive sulfide deposit. Typically, control-area 

sizes represent the extent of exposed rocks permissive for volcanogenic massive sulfide deposits. As noted above, control 

areas with larger sizes may contain some nonpermissive rock 

units because of the way the units are generalized on the map, 

resulting in lower deposit-density values. Control areas with 

smaller sizes are more likely to contain only rock units permissive for volcanogenic massive sulfide deposits, thus resulting in higher deposit densities. Mineral deposit densities are 

inversely related to the size of the permissive control areas (fig. 

3; significant at the one percent level, r = –0.8, n = 38). This 

relationship suggests the size of the permissive area can be 

used directly to estimate the number of deposits similar to the 

way podiform chromite deposits (Singer, 1994) and porphyry 

copper deposits were evaluated (Singer and others, 2005). 

Estimates of the number of volcanogenic massive sulfide 

deposits can be made from figure 4 by using the permissive 

area on the X-axis projected to the 90-percent confidence limit 

for a lower estimate of the number of deposits, to the regression line for the 50-percent estimate, and to the 10-percent 

confidence limit for an upper estimate. The linear regression 

line and confidence limits to estimate the number of deposits 

for individual permissive areas are based on 38 control areas. 

For more precise estimates than can be shown in the log-log 

plot, the following two equations are provided:

R50 = –0.5846 + 0.3846 log10(area) (1)

L90 , U10 = (R50 ± t sy|x √ (1+(1/n) +

(log10(area) – 2.637)2/(n-1)sx

2

) (2)

Where, area is the area that is permissive in square kilometers, the mean area is 2.637, t (Student’s t at the 10-percent 

level with 36 degrees of freedom, t10,36df) is 1.688, sy|x (standard 

Figure 2. Relationship of map scale and volcanogenic massive 

sulfide deposits densities per 100,000 square kilometers (**significant at one-percent level of confidence). Dots represent control 

areas scattered about the regression line.

Figure 3. Volcanogenic massive sulfide deposits control area 

exposed versus density of deposits. Dots represent control areas 

scattered about the regression line.

Figure 4. Volcanogenic massive sulfide control area exposed versus 

number of deposits with 90-percent (lower line) and 10-percent 

(upper line) confidence limits for number of deposits. Dots represent control areas scattered about the regression line (middle line). 

Arrow at 22,900 square kilometers on the permissive-area axis 

refers to the sample given in the text where equation 1 is discussed. 

MAP SCALE

1:32,000 1:100,000 1:320,000 1:1,000,000 1:3,200,000

NUMBER OF DEPOSITS

PER 100,000 SQUARE KILOMETERS

32

100

320

1,000

3,200

10,000

r = –0.63**

NUMBER OF DEPOSITS

PER 100,000 SQUARE KILOMETERS

32

100

320

1,000

3,200

10,000

PERMISSIVE AREA EXPOSED PER 100,000 SQUARE KILOMETERS

10 32 100 320 1,000 3,200 10,000 32,000 100,000

Log AREA

1 1.5 2 2.5 3 3.5 4 4.5 5

Log NUMBER OF DEPOSITS

NUMBER OF DEPOSITS

1

1.8

3.2

5.6

10

18

32

56

0.56

100

1.75

2

1.5

1.25

1

0.75

0.5

0.25

0

–0.25

PERMISSIVE AREA PER 100 SQUARE KILOMETERS

0.1 0.18 0.32 0.56 1 1.8 3.2 5.6 10 18 32 56 100 180 320 560 1,000
12  Volcanogenic Massive Sulfide Deposit Density

deviation of number of deposits given area) is 0.3379, n = 38, 

sx

2

 (variance of area) is 0.5258, and the R50, L90, and U10 estimates are used as exponents to the power of 10. For example, 

if the permissive area were 22,900 square kilometers, then the 

50th percentile estimate would be 12 deposits (that is, 101.092 or 

10 (– 0.5846+0.3846 log10(22,900))). The 90th percentile estimate would 

be 3 deposits (that is, 10(1.092 – 1.688•0.3379 √ (1+(1/38) + (4.360 – 2.637)^2 

/37•0.5258)), and the 10th percentile estimate would be 48 deposits—these estimates can be approximated from figure 4. These 

estimates represent the total number of volcanogenic massive 

sulfide deposits in a permissive tract of 22,900 square kilometers, and any discovered deposits would need to be subtracted 

to estimate the number of undiscovered deposits. 

Summary and Conclusions

A mineral deposit-density model provides frequencies of 

deposits per square kilometer in well-explored permissive terranes. Frequencies of deposit densities for a deposit type allow 

reasonable probabilistic estimates of undiscovered deposits to 

be made in geologically similar, relatively unexplored terranes. 

Such models, developed for particular deposit types, can be 

used to estimate the number of undiscovered deposits of that 

type in resource assessments. 

Because this model is derived from well-explored volcanogenic massive sulfide deposits that occur at the surface, it 

should be applied to estimates of undiscovered deposits at the 

surface, not at depth, in similar geologic environments. The 

effect of this limitation is not known with certainty. In some 

locations there appear to be multiple horizons containing volcanogenic massive sulfide deposits, for example, Mount Read 

Volcanics, Tasmania (Large and others, 2001). Where multiple 

horizons are suspected in an assessment the best policy would 

seem to be to apply the density models to each horizon. 

The volcanogenic massive sulfide deposit-density model 

was constructed from 38 areas from around the world that are 

known to contain at least one deposit that is consistent with 

the descriptive models and the grade and tonnage models for 

kuroko or Cyprus massive sulfide deposits. Deposits selected in 

these control areas are exposed at the surface, and the areas of 

permissive rock exposed at the surface are well explored, such 

that there is little or no chance of finding additional deposits 

at the surface. The permissive area should represent only the 

hosting units, and all nonhosting units or cover material within 

the permissive areas should be excluded to the extent possible. 

The level of geologic mapping and map scale affect the final 

size of the permissive area resulting in lower deposit densities 

for areas mapped at smaller scales and for larger areas that may 

contain nonpermissive rocks that cannot be differentiated. Thus, 

it is important to use the most detailed geologic map available 

(large-scale map) when delineating permissive areas in order to 

improve the precision of number-of-deposit estimates. 

Deposit densities are computed by dividing the number of 

exposed deposits in the control area by the area of permissive 

rock per square kilometer. Density values multiplied by the 

arbitrary unit area, 100,000 square kilometers, present the densities as integers rather than as decimals. Kuroko and Cyprus 

massive sulfide deposit types show no difference in mineral 

deposit densities, so they have been combined in this study. 

The data for this study indicates that 90 percent of the 

control areas have densities of 100 or more deposits per 

100,000 square kilometers, 50 percent of the control areas 

have densities of 700 or more deposits per 100,000 square 

kilometers, and 10 percent of the control areas have densities 

of 3,700 or more deposits per 100,000 square kilometers. A 

plot of the log number of deposits and the log areas for the 38 

control areas produces a regression line and confidence bands 

that can be used to estimate the number of deposits at the 50th, 

10th, and 90th probability levels, given the area of permissive 

rock in a mineral resource assessment. 

This study provides a powerful tool for estimating the number of undiscovered volcanogenic massive sulfide deposits in 

resource assessments. The value of these densities derives in part 

from the consistency of these models with the grade and tonnage 

and the descriptive models. Combined with grade and tonnage 

models, reasonable estimates of the number, tonnage, and grades 

of volcanogenic massive sulfide deposits can be made.

Acknowledgments

We thank W. David Menzie, III, James Bliss, and Thomas 

Frost of the USGS for helpful comments on this manuscript. 

We thank Anna Tellez, Susie Bravos, Tammy Huang, Jon 

DeBord, Brenda Graff, and Jean Shea of the USGS library 

staff for helping us find geologic maps and reports from 

around the world. We thank Tracey Suzuki and James W. Hendley for editing the manuscript. 

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