Carbonatites of the World, 

Explored Deposits of Nb and 

REE—Database and Grade 

and Tonnage Models

By Vladimir I. Berger, Donald A. Singer, and Greta J. Orris

Open-File Report 2009-1139

U.S. Department of the Interior 

U.S. Geological Survey 
ii

U.S. Department of the Interior 

KEN SALAZAR, Secretary

U.S. Geological Survey 

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009 

 

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Suggested citation: 

Berger, V.I., Singer, D.A., and Orris, G.J., 2009, Carbonatites of the world, explored deposits of Nb and REE—

database and grade and tonnage models: U.S. Geological Survey Open-File Report 2009-1139, 17 p. and 

database [http://pubs.usgs.gov/of/2009/1139/]. 

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

endorsement by the U.S. Government. 
iii

Contents

Introduction 1 

Rules Used 2 

Data Fields 2 

Preliminary analysis: —Grade and Tonnage Models 13 

Acknowledgments 16 

References 16 

Figures 

Figure 1. Location of explored Nb– and REE–carbonatite deposits 

 included in the database and grade and tonnage models 4 

Figure 2. Cumulative frequency of ore tonnages of Nb– and 

 REE–carbonatite deposits 14 

Figure 3 Cumulative frequency of Nb2O5 grades of Nb– and 

 REE–carbonatite deposits 15 

Figure 4 Cumulative frequency of RE2O3 grades of Nb– and 

 REE–carbonatite deposits 15

Figure 4 Cumulative frequency of P2O5 grades of Nb– and 

 REE–carbonatite deposits 16

Tables

 

Table 1. Country names and country codes used in this report 3 

Table 2. Grouping of deposits by age intervals 5 

Table 3. Frequency of rocks associated with carbonatites 6 

Table 4. Frequency of country rocks of the carbonatite deposits 7 

Table 5. Range of tonnages and alteration areas by 

configuration of carbonatite deposits 8 

Table 6. Frequency of main ore minerals 10 

Table 7. Frequency of minor and rare ore minerals 11 

Table 8. Frequency of main gangue minerals 12 

Table 9. Frequency of minor and rare gangue minerals 12 

Table 10. Grade and tonnage models of carbonatite deposits 14 
1

Introduction

This report is based on published tonnage and grade data on 58 Nb– and rare-earthelement (REE)–bearing carbonatite deposits that are mostly well explored and are 

partially mined or contain resources of these elements. The deposits represent only a part 

of the known 527 carbonatites around the world (Woolley and Kjarsgaard, 2008), but 

they are characterized by reliable quantitative data on ore tonnages and grades of niobium 

and REE. 

Grade and tonnage models are an important component of mineral resource assessments. 

Carbonatites present one of the main natural sources of niobium and rare-earth elements, 

the economic importance of which grows consistently. A purpose of this report is to 

update earlier publications (Singer, 1986a, 1986b, 1998; Orris and Grauch, 2002). New 

information about known deposits, as well as data on new deposits published during the 

last decade, are incorporated in the present paper. The compiled database (appendix 1) 

contains 60 explored Nb– and REE–bearing carbonatite deposits—resources of 55 of 

these deposits are taken from publications. In the present updated grade-tonnage model 

we have added 24 deposits comparing with the previous model of Singer (1998). 

Resources of most deposits are residuum ores in the upper part of carbonatite bodies. 

Mineral-deposit models are important in exploration planning and quantitative resource 

assessments for two reasons: (1) grades and tonnages among deposit types vary 

significantly, and (2) deposits of different types are present in distinct geologic settings 

that can be identified from geologic maps. Mineral-deposit models combine the diverse 

geoscience information on geology, mineral occurrences, geophysics, and geochemistry 

used in resource assessments and mineral exploration. Globally based deposit models 

allow recognition of important features and demonstrate how common different features 

are. Well-designed deposit models allow geologists to deduce possible mineral-deposit 

types in a given geologic environment, and the grade and tonnage models allow 

economists to estimate the possible economic viability of these resources. Thus, mineraldeposit models play a central role in presenting geoscience information in a useful form 

to policy makers. The foundation of mineral-deposit models is information about known 

deposits. This publication presents the latest geologic information and newly developed 

grade and tonnage models for Nb– and REE –carbonatite deposits in digital form. The 

publication contains computer files with information on deposits from around the world. 

It also contains a text file allowing locations of all deposits to be plotted in geographic 

information system (GIS) programs. The data are presented in FileMaker Pro as well as 

in .xls and text files to make the information available to a broadly based audience. The 

value of this information and any derived analyses depends critically on the consistent 

manner of data gathering. For this reason, we first discuss the rules used in this 

compilation. Next, the fields of the database are explained. Finally, we provide new grade 

and tonnage models and analysis of the information in the file. 
2

Rules Used

A mineral deposit is a mineral occurrence of sufficient size and grade that might, under 

the most favorable circumstances, be considered to have economic potential (Cox and 

others, 1986). Deposits sharing a relatively wide variety and large number of attributes 

are characterized as a "type," and a model representing that type can be developed.

 

Nb– and REE–carbonatite deposits consist of plugs, oval intrusions, dikes, veins, and 

stockworks generally restricted to large alkaline intrusive complexes or to their locally 

highly metamorphosed country rocks. They commonly have parts containing altered 

fenitized rocks. Deposits that may be derived from, or affected by, hypogene and 

supergene processes are included in the models.

 

An important consideration at the data-gathering stage is the question of what the 

sampling unit should be. Grade and tonnage data are available to varying degrees for 

districts, deposits, and mines. For the deposits in this model, the following rule was used 

to determine which ore bodies were combined. All mineralized rock or altered rock 

within two (2) kilometers was combined into one deposit. Some examples illustrate the 

effects of the application of this rule: (1) Salitre I and II deposits in Brazil and (2) Upper 

Fir and Fir in Canada. Carbonatite deposits are remote from one another. 

Data Fields

The information on the explored Nb– and REE–carbonatite deposits included in the 

database and grade and tonnage models is contained in the files 

of2009-1139_carbonatite.fp7, of2009-1139_carbonatite.xls, and of2009-

1139_carbonatite.tab.txt, which are FileMaker Pro 7, Excel, and tab-delineated text files, 

respectively. The fields in all files are described below. The “n.d.” abbreviation in 

various fields indicates “no data,” “not detected,” or “not defined.” 

Deposit Name

The most recent deposit name is used in the “NameDeposit” field. There is another field, 

"OtherNames," which contains alternative names that have been used for the deposit. A 

third field, "Includes," provides the names of deposits that have been combined with the 

primary deposit as a result of the two-kilometer minimum separation rule.

Locations

A number of fields are provided to show the deposit's location. "Country" and 

"StateProvince" are used for general locations. "CountryCode" is an abbreviated version 

of the country information (table 1). Degrees, minutes, and seconds of longitude and 

latitude are provided in the separate fields. Decimal degrees of latitude 

("LatitudeDecimal") and longitude ("LongitudeDecimal") are calculated from the 

degrees, minutes, and seconds fields. Southern latitudes and western longitudes are 
3

negative values. Longitudes and latitudes of all localities were checked and corrected 

using the “Google Earth 5.” Deposits included in the database and tonnage and grade

models are located on the world map (fig. 1) and are plotted on the “Google Earth 5” 

image using the of2009-1139_carbonatite.kmz file. 

Table 1. Country names and country codes used in this report 

Country StateProvince CountryCode

Angola ANGL

Australia West Australia AUWA

Brazil BRZL

Burundi BRND

Canada British Columbia CNBC

Canada Ontario CNON

Canada Quebec CNQU

China CINA

Democratic Republic of Congo DRCO

Gabon GABN

India INDA

Kenya KNYA

Malawi MLWI

Mauritania MRTA

Mongolia MNGL

Namibia NAMB

Norway NRWY

Russia RUSA

South Africa SAFR

Tanzania TNZN

Turkey TRKY

Uganda UGND

United States Arkansas USAR

United States California USCA

United States Colorado USCO

Zambia ZMBA

Activity

Where the discovery date is known, it is recorded in the "DiscoveryDate" field. The 

startup date of mining is listed in the "StartUp" field. 

Grades and Tonnages

Data gathered for each deposit include the average grade of each metal or mineral 

commodity of possible economic interest and the associated tonnage on the basis of the 

total production, reserves, and resources at the lowest possible cutoff grade. All further 

references to tonnage follow this definition. All tonnages reported here ("Tonnage") are 

in millions of “metric tons” or “tonnes.” Niobium ("Nb2O5 grade"), rare earth ("RE2O3

grade"), and phosphorus ("P2O5 grade") grades are reported as percents of the stated 
4

oxides. Grades not available (always for byproducts) are treated as zero. The 

"Comments" field contains supplementary information about some grades, such as 

thallium, uranium, and thorium when available. Three significant digits are used for 

tonnage and grades. The special field indicates sources of tonnage-grade data. If required, 

more detailed information about reserves, resources, and production is placed in 

“Comments.” 

Figure 1. Location of explored Nb– and REE–carbonatite deposits included in the 

database and grade and tonnage models.

Age

In the field "DepositAge," ages are in standard divisions of geologic time or in millions 

of years when available. This field contains also common symbols of the dating method 

used (such as K-Ar, Ar-Ar, U-Pb) and whether the age was on the defined mineral or 

whole rock. Radiometric ages are reported in millions of years before the present 

("AgeMY" field) based on defined radiological ages or midpoints of geologic time scale 

units (Remane, 1998). Table 2 illustrates grouping of the deposits and their tonnages by 

age intervals. The two youngest Cenozoic and Mesozoic groups in the two upper rows of 

the table contain half of the considered deposits with 59 percent of the total tonnage. 

Such a time-distribution of Nb– and REE–carbonatite deposits might be caused by an 

evolution of mantle-crust rifting activity within platforms and (or) by erosion of older 

deposits. However, this impressive tonnage proportion might change dramatically, if the 

problematic Cretaceous age of the Seis Lagos deposit, Brazil, the largest niobium deposit 

with 2.9 Gt of ore, were to be changed to Precambrian as was proposed by Antonini and 

others (2003). 

Carbonatite Deposits

0 5,000 Km

0o

30o

60o

30o

60o

30o 60o 30o 60o 90o 0o 120o 150o 180o 90o 120o 150o 180o
5

Table 2. Grouping of deposits by age intervals 

[n.d., not dated.] 

Geologic Setting

Geologic setting of the deposits is characterized in several data fields: tectonic setting, 

spatially associated rocks, shape of carbonatite bodies, and area occupied by carbonatites. 

Tectonic setting

A majority of carbonatite deposits are localized within stable continental tectonic units, 

such as shields, cratons, and crystalline blocks, with well-developed old Earth crust. 

Inside these large regional structures, carbonatites are confined to alkaline magmatic 

provinces controlled by intracontinental rift and fault systems. There are few exceptions 

from such a predominant tectonic setting. The Carboniferous Aley deposit, British 

Columbia, Canada, is present in the Paleozoic foreland belt at the western margin of the 

North American continent (Pell and Höy, 1989). Two deposits, Cenozoic Dalucao and 

Maoniuping, Sichuan, China, are localized in the western margin of the Yangtze craton in 

the Cenozoic collision-related Himalayan Mianning-Dechang REE zone (Hou and others, 

in press). Meanwhile, this zone was superimposed on the Paleozoic longitudinal Panxi 

rift (Niu and others, 2003). 

Rocks Associated with Carbonatites 

Rocks in and around the carbonatite deposit are recorded here in the same terms used in 

the published maps and reports. We have used two fields in an attempt to provide some 

spatial information. The field "RocksInDeposit" is used for rocks that are only 

represented in the deposit itself and not observable on a regional map. This field includes 

listed magmatic and metasomatic rocks associated with carbonatites. Table 3 shows the 

frequency of these rocks in deposits. The rocks are divided into five groups: (1) 

Carbonatitic rocks that include, besides carbonatite itself, breccia in 30 percent of 

deposits and agglomerate in 12 percent of deposits; in many deposits the breccia is 

defined as “eruptive” and actually might be an analog of agglomerate; (2) Alkaline rocks

ranging from syenite (33 percent) to relatively rare alkaline granite (5 percent); (3) 

Alkaline nepheline-feldspathoid syenitic rocks are also widespread mainly as nepheline 

Age MY groups (Ma)

Number of 

deposits

Percent of 

dDeposits %

Summary 

tonnage

Percent of 

tonnage %

10.4–100 15 24 4381 37

101–265 16 26 2553 22

344–520 6 10 1295 11

558–680 11 19 1310 11

1010–1400 7 12 1038 9

1655–2047 3 5 978 9

n.d. 2 4 194 1

Total 60 100 11,749 100
6

syenite (35 percent) and ijolite (28 percent); (4) Alkaline ultramafic and mafic rocks are 

represented commonly by pyroxenite (28 percent), mainly bebedourite, combined with 

syenitic rocks of the two former groups; and (5) Metasomatic rocks contain mostly fenite 

(12 percent) and glimmerite (9 percent). 

Table 3. Frequency of rocks associated with carbonatites

[Count is number of deposits; % is percentage of deposits 

with associated rock type. Many deposits associated 

with more than one rock type.] 

Rock type Count %

Carbonatitic rocks

carbonatitic breccia 18 30 

carbonatitic agglomerate 7 12

Alkaline rocks

syenite 20 33

trachyte 9 15 

nordmarkite 4 7

alkaline granite, pegmatite 3 5

Alkaline nepheline-feldspathoid syenitic 

rocks

nepheline-syenite 21 35 

ijolite 16 27

melteigite 7 12

phonolite 5 8

foyaite 4 7 

nephelinite 3 5

urtite 3 5

malignite 2 3

shonkinite 2 3 

okaite 2 3

tephrite 1 2

melilitolite 1 2

Alkaline ultramafic and mafic rocks 

pyroxenite (incl. bebedourite) 17 28

lamprophyre, monchiquite, alnoite 9 15

phoscorite 7 12

jacupirangite 6 10 

gabbro, diabase 6 10

peridotite 5 9 

tuff 5 9

dunite 4 7 

basalt 1 2

Metasomatic rocks 

fenite 7 12

glimmerite 5 8

albitite 3 5

silexite 1 2
7

Rock alteration type is shown also in the special field “AlterType;” in 85 percent of the 

deposits, it is fenite surrounding carbonatite-alkaline intrusive complexes. The width of 

such fenite rings ranges from 0.15 to 2.5 km (see the “Alteration Width” field). 

With respect to associated rock types, the entire population of deposits can be roughly 

divided into two groups, 35 syenite-related deposits with total tonnage of 6.851 Mt and 

25 ultramafic (±syenite)-related deposits containing 4,905 Mt. Statistical test showed 

insignificant difference in tonnage and grades between these two groups.

Country Rocks

Country rocks that are recorded both in the deposits and on a regional map are placed in 

the field "RocksOnMapInDeposit," which also contains the geologic age of the rocks (in 

parentheses after rock definitions). In table 4, the country rocks are divided into two 

categories. Among Metamorphic rocks, gneiss, schist, and quartzite are dominant. Most 

are Archean (28 percent), Proterozoic (29 percent), and undivided Precambrian (31 

percent) complexes. Prevailing old ages of metamorphic rocks correspond to cratonrelated “Tectonic Setting” described above. Sedimentary and magmatic rocks of 

Paleozoic (13 percent) and Mesozoic (3 percent) ages are not typical for the country 

rocks of carbonatite deposits. A part of sedimentary country rocks pertains to 

Precambrian complexes.

Table 4. Frequency of country rocks of the carbonatite deposits 

[Count is number of deposits; % is percentage of deposits with associated 

rock type. Many deposits associated with more than one rock type.] 

Rock Count %

Metamorphic rocks 

gneiss, granite gneiss, granulite 40 67

schist 13 22

quartzite 13 22

shale, phyllite 10 17

metamorphic mafic and ultramafic rocks (amphibolite, 

serpentinite, etc.) 6 10

metavolcanic rocks 5 9

Sedimentary and magmatic rocks 

clastic rocks (sandstone, siltstone, conglomerate) 21 35

carbonate rocks (dolomite, limestone, marble) 11 18

felsic volcanics 4 7

mafic volcanics 5 9

granitoids 14 25

gabbro 1 2
8

Shape of Carbonatite Intrusions

The “CarbonatiteShape” field illustrates configuration of single carbonatite intrusions and 

alkali-carbonatite intrusive complexes. The generalized types of occurrences and 

proportions of their sizes (“CarbonatiteArea”) and ore tonnage limits are shown in table 

5. In order to consistently capture information about the size and shape of carbonatites as 

presented in two-dimensional projection to the surface, the shortest dimension (b axis) is 

measured as the distance between parallel lines that just touch the object. After the short 

dimension is determined, the long axis is measured perpendicular to the b axis using the 

same criteria. Many carbonatite intrusions can be well represented by an ellipse. Where 

published estimates of the projected area of the body are not available we estimated the 

area using the standard formula for area of an ellipse (area = 3.14159 a b / 4). 

Simple circular or oval carbonatite plugs with or without mapped alkaline intrusive rocks 

are dominant, composing 45 percent of deposits. Maximum tonnage of 2,898 Mt is 

indicated in the Seis Lagos niobium deposit, Brazil; minimum tonnage of 0.2 Mt is 

known in the Karonge deposit, Burundi. Alkali-carbonatite intrusive complexes are larger 

and, as a rule, contain carbonatite only as subordinate intrusions forming conic circular 

sheets, lenses, and small plugs among surrounding alkaline and ultramafic rocks. The 

third group consists of fissure-filling carbonatite dikes, veins, and stockworks partially of 

hydrothermal origin (Mitchell, 2005). Statistical tests do not show significant correlation 

between area and tonnage of deposits in these three groups. 

Table 5. Range of tonnages and alteration areas by configuration 

of carbonatite deposits [Mt, million tonnes; n.d., no data] 

Mineralogical Subtypes of Carbonatite Deposits

Carbonatites are divided into three main mineralogical subtypes ("MineralType") by 

dominant carbonate mineral compositions and textural features. These subtypes are 

determined from the original sources for each deposits with respect to general 

“Carbonatite nomenclature” by Kresten (1983). (1) Sövite and alvikite have been defined 

as calcitic carbonatites; this subtype is most widespread (26 deposits, 43 percent). (2) 

Configuration 

Number 

of 

deposits %

Carbonatite 

area,

sq. km

Tonnage 

limits, 

Mt

from to from to

Plug 27 45 12.6 0.3 2898 0.2

Alkali-carbonatite 

complex 18 30 1327 1.4 1255 11

Dike, vein 15 25 15.8 0.6 455 0.03

n.d. 1 2 n.d. 0.1
9

Beforsite and (or) rauhaugite indicate dolomite-ankeritic carbonatites; this subtype has 

been observed in 9 deposits (16 percent). Alvikite and beforsite are fine-grained 

“hypabyssic equivalents” of carbonatites mostly composing dikes, veins, and sheets. (3) 

A combination of sövite and beforsite (±rauhaugite) is recognized in 23 deposits (38 

percent). (Besides these main varieties, Fe-(ankerite, siderite)-carbonatite is noted as a 

considerable component in 5 sövite deposits and Si-(quartz)-carbonatite in 2 sövite 

deposits). Statistical tests of three main mineralogical subtypes—sövite, beforsite, and 

combined sövite-beforsite—did not reveal any significant differences in tonnages and 

grades.

Mineralogy

Information on the mineralogy of the deposits varies widely in quantity and quality. 

Depending on the purpose of a study and the researcher's interest, a report on a mineral 

deposit might contain a detailed list of alteration minerals and a mention of unnamed 

phosphate, rare earth, thorium, and uranium minerals; a detailed list of ore minerals and 

mention of alteration in broad terms; a complete list of all minerals; or a sparse list of 

minerals. In some studies, the author attempted to list the relative or absolute amounts of 

each mineral. Unfortunately, these attempts are not common and frequently not 

comparable among reports because of different standards. Thus, it was decided to use 

only the presence or absence of ore and gangue minerals ("Ore Minerals" and 

"GangueRock Minerals") in this file. General frequencies of minerals of both fields are 

presented in tables 6, 7, 8, and 9. Main ore minerals are listed in table 6, showing 

pyrochlore as a major source of Nb; Nb–rutile and Nb–ilmenite also are essential in some 

deposits. Monazite, bastnaesite, and synchysite are the most important source of REE 

elements. Predominance of calcite and dolomite among gangue minerals (tables 8, 9) 

corresponds to the main mineral subtypes of carbonatites. 
10

Table 6. Frequency of main ore minerals

[Count, number of deposits; %, percentage of deposits containing the mineral] 

Minerals Count %

apatite 57 95

pyrochlore, Ba-, Ce-, Sr-, U- 53 88

barite, Sr-barite 45 75

magnetite 44 73

pyrite 40 67

monazite, monazite-(Ce) 36 60

fluorite 28 47

rutile, Nb-rutile, ilmenorutile 27 45

bastnaesite, bastnaesite-(Ce) 25 42

zircon 25 42

ilmenite, Nb-ilmenite 24 40

hematite 23 38

perovskite, perovskite-(Ce) 21 35

galena 19 32

pyrrhotite 18 30

strontianite 18 30

goethite 16 27

synchysite, synchysite-(Ce) 16 27

titanite 16 27

chalcopyrite 15 25

anatase 14 23

parisite, -(Ce), -(Nd) 14 23

columbite 13 22

sphalerite 13 22

baddeleyite 11 18

florencite, florencite-(Ce) 10 17

ancyllite, ancyllite-(Ce) 9 15

goyazite 9 15

crandallite, Ce-crandallite 9 15

gorceixite 9 15

allanite 8 13

celestite, Ba-celestite 8 13

limonite 8 13

thorite 8 13

sphene, Nb-sphene 8 13

molybdenite 7 12

thorianite, U-thorianite 7 12
11

Table 7. Frequency of minor and rare ore minerals 

[Count, number of deposits; %, percentage of deposits containing each 

mineral of the group] 

Minerals

Count

(for each 

mineral) %

carbocernaite, -(Ce); pyrolusite; xenotime, -(Y), -(Ce) 6 10

aeschynite, Nb-aeschynite; alloy Cu-Zn, Sn-Cu, Sn-Zn; 

burbankite; cerianite, -(Ce); fergusonite, -(Nd), -(Ce), -(Y); 

fersmite; psilomelane, zirconolite 5 8

britholite, britholite-(Ce); brookite, chevkinite, chevkinite-

(Ce); rhabdophane, rhabdophane-(Ce); wulfenite 4 7

betafite; Nb-brookite; calzirtite; cebaite-(Ce), cebaite-(Nd); 

copper; cordylite, cordylite-(Ce); daqingshanite, -(Ce); 

eudialyte; gold, electrum; isokite; pentlandite, Ag-, Co-; 

uraninite; zirkelite 3 5

bornite; cerussite; chalcocite; cheralite; chromite; churchite; 

fluocerite; götzenite; huanghoite-(Ce); röntgenite-(Ce); 

samarskite, -(Y); tin 2 3

aenigmatite; azurite/malachite; bafertisite; baotite; 

betekhtinite; beudantite; bismuth; braunite; bravoite; 

cabriite; cassiterite; cerite; chondrodite; cubanite; 

dingdaohengite-(Ce); froodite; hessite; hibonite; iron; 

jalpaite; juonniite; kainosite-(Y); kimzeyite; kobeite-(Y); 

kukharenkoite-(Ce); küstelite; lanthanite; lead; leucoxene; 

loparite-(Ce); lusungite; mackelveyite-(Y); mackinawite; 

majakite; manganite; maoniupingite-(Ce); marcasite; 

marianoite; millerite; naummanite; niocalite; parkerite; 

perrierite-(Ce); pyromorphite; pyrophanite; REE-carbonate; 

REE-phosphate; sahamalite-(Ce); sellaite; shadlunite; 

siegenite; silver; sperrylite; Sr-Ba carbonate; Sr-REE 

carbonate; stromeyerite; talnakhite; tetrahedrite; thortveitite; 

tongxinite; valleriite; villiaumite; violarite; witherite; 

wittichenite; wöhlerite 1 2
12

Table 8. Frequency of main gangue minerals

[ount, number of deposits; %, percentage of deposits containing the mineral] 

Minerals Count %

calcite, Sr-, Mn- 56 93

dolomite 43 72

phlogopite, Ba-, Fe- 42 70

biotite 37 62

quartz 31 52

aegerine, aegerine-augite, augite 29 48

ankerite 20 33

K-feldspar 20 33

pyroxene, diopside 19 32

garnet, melanite 17 28

olivine 16 27

vermiculite 15 25

siderite, Mn-siderite 14 24

amphibole 13 22

riebeckite, Mg-riebeckite 12 20

chlorite 11 18

kaolinite, dickite 9 15

wollastonite 7 12

Table 9. Frequency of minor and rare gangue minerals 

[Count, number of deposits; %, percentage of deposits containing each 

mineral of the group] 

Minerals

Count

(for each 

mineral) %

albite 6 10

cancrinite; epidote; muscovite; nepheline; serpentine; 

spinel 5 8

arfvedsonite; barytocalcite; montichellite; norsethite; 

zeolite 4 7

crocidolite, Mg-crocidolite; gypsum; melilite; 

pectolite, Mn-pectolite; tremolite

 

3 5

actinolite; bömite; gibbsite; hematite; hornblende; 

rhodochrosite; strontianite; svanbergite; talc; 

vesuvianite; 2 3

alstonite; alunite; benstonite; breunnerite; brucite; 

clinohumite; corundum; dawsonite; eckermannite; 

edingtonite; hauyne; hercynite; hydromica; 

hyalophane; jacobsite; leucite; magnesite; 

montmorillonite; natrolite; pyrophyllite; richterite; 

sanidine, scapolite; staurolite; vivianite 1 2
13

Spatially related deposits

Here we record other deposits by type that are within 5 km (“Assoc Deposits less 5km”) 

and within 10 km (“Assoc Deposits less 10km”) of a carbonatite deposit. In many 

situations, these other spatially related deposits are merely occurrences and not economic 

mineral deposits. Nevertheless, many of these occurrences can be typed and their types 

might provide important information about the possible association with carbonatite 

deposits. Each deposit type is coded with the deposit type number and deposit type as 

listed in U.S. Geological Survey Bulletins 1693 (Cox and Singer, 1986) and 2004 (Bliss, 

1992). Within 5 km, 13 thorium-rare-earth veins closely associated with carbonatite 

(Model 11d, described by Staatz, 1992), 3 carbonatite (Model 10), 3 apatite-magnetite, 

and 1 titanium deposits are known. Within 10 km, 7 carbonatite and 1 apatite deposits are 

noted. These data accentuate the separate grouping of Nb– and REE–carbonatites that are 

generally located in large regional alkaline provinces and belts mainly far from other 

mineral deposits. 

Preliminary Analysis

Grade and Tonnage Models

Grade and tonnage models of mineral deposits are useful in quantitative resource 

assessments and exploration planning. Having some idea of the possible values of 

alternative kinds of deposits that might be sought is critical to good exploration planning. 

In quantitative resource assessments, these models play two roles: (1) grade and tonnage 

models can help classify the known well-explored deposits in a region into types and 

therefore aid in delineation of areas permissive for types and (2) the models provide 

information about the potential value of undiscovered deposits in the assessment area, a 

key to economic analyses of these resources. Construction of grade and tonnage models 

involves multiple steps. The first is the identification of a group of well-explored deposits 

that are believed to belong to the mineral deposit type being modeled. “Well-explored” 

here means completely drilled in three dimensions. After deposits are identified, data 

from each are compiled. These data consist of average grades of each metal or mineral 

commodity of possible economic interest and tonnages based on the total production, 

reserves, and resources at the lowest available cutoff grade. Here we use the deposits that 

have tonnages recorded in the “Tonnage” field. We exclude deposits with grades and 

tonnages only in the “Comments” field because of indications that more exploration is 

needed for these deposits. 

Relations among grade and tonnage variables are important for simulations of resources. 

These relations also affect our understanding of how deposits form and our assumptions 

about resource availability. Tonnage is correlated with REE grade (r = -0.48**, n = 35). 

(** means significant at the 1-percent level). 15 deposits of 55 deposits with tonnages 

have no Nb grades reported. 

Frequency distributions of the tonnages and niobium, REE, and phosphorus grades for 

the deposits of the well-explored carbonatite deposits reported in the file can be 
14

employed as models of the grades and tonnages of undiscovered deposits. Here these 

frequencies are plotted in figures 2–5 and are summarized in table 10. Grade and tonnage 

models are presented in a graphical format in order to easily compare deposit types and to 

display the data. The grade and tonnage plots show the cumulative proportion of deposits 

versus the tonnage or grade of the deposits. Individual symbols represent the deposits, 

and intercepts for the 90th, 50th, and 10th percentiles are plotted. Percentiles of grades that 

contain unreported values, such as Nb, REE, and P, were based on the observed 

distributions. Based on the Shapiro-Wilk W test, tonnage, Nb, and P grades are not 

significantly different from the lognormal distribution at the 1-percent level. Using the 

same test, the distribution of REE is significantly different from lognormal at the 1-

percent level because of a single low-grade deposit. 

Table 10. Grade and tonnage models of carbonatite deposits 

[Mt, million tones. See also figures 2-5.] 

 

Number

deposits 

10th percentile

of deposits 

50th percentile

of deposits

90th percentile

of deposits

Tonnage (Mt) 55 650 49.0 0.58

Nb2O5 grade (%) 55 2.0 0.23 0.0

RE2O3 grade (%) 55 4.6 0.61 0.0

P2O5 grade (%) 55 16.0 0.0 0.0

Figure 2. Cumulative frequency of ore tonnage of Nb– and REE–carbonatite deposits. 

Each circle represents an individual deposit. Intercepts for the 90th, 50th, and 10th

percentiles of the observed distribution are provided.

0.00063 0.0025 0.01 0.160.04 0.63 2.5

MILLION TONNES

4010 160 630 2,500

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

PROPORTION OF DEPOSITS

N = 55

0.58 49 650
15

Figure 3. Cumulative frequency of Nb2O5 grade of Nb– and REE–carbonatite deposits. 

Each circle represents an individual deposit. Intercepts for the 50th and 10th percentiles of 

the observed distribution are provided. 

0.0320 0.056 0.1 0.18

NIOBIUM GRADE IN PERCENT Nb2O5

0.018 0.32 0.56 1.0 1.8 3.2 5.6

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

PROPORTION OF DEPOSITS

N = 55

0.23 2

0.001 1.6 4 10

RARE-EARTH OXIDE GRADE IN PERCENT RE2

O5

0.0025 0.0063 0.630.250.10.040.016

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

PROPORTION OF DEPOSITS

N = 55

0.61 4.6
16

Figure 4. Cumulative frequency of RE2O3 elements grade of Nb– and REE–carbonatite 

deposits. Each circle represents an individual deposit. Intercepts for the 50th and 10th

percentiles of the observed distribution are provided.

Figure 5. Cumulative frequency of P2O5 grade of Nb– and REE–carbonatite deposits. 

Each circle represents an individual deposit. Intercept for 10th percentile of the observed 

distribution is provided.

Acknowledgments

We gratefully acknowledge Dan Mosier and Ted Theodore for their helpful reviews and 

valuable advise.

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0

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