U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5043

Prepared in cooperation with the Bureau de Recherches Géologiques et Minières and the 

Direction Générale des Mines under the auspices of the U.S. Department of State

Alluvial Diamond Resource Potential and Production 

Capacity Assessment of the Central African Republic
Cover. Artisanal diamond mining of upper terrace deposits along the Kotto River near Oro, Central African Republic, May 2007.
Alluvial Diamond Resource Potential and 

Production Capacity Assessment of the 

Central African Republic

By Peter G. Chirico, Francis Barthélémy, and François A. Ngbokoto

Prepared in cooperation with the Bureau de Recherches Géologiques et 

Minières and the Direction Générale des Mines under the auspices of the 

U.S. Department of State

Scientific Investigations Report 2010–5043

U.S. Department of the Interior

U.S. Geological Survey

Road from Dimbi to Sibut, May 2007
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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Suggested citation:

Chirico, P.G., Barthélémy, Francis, and Ngbokoto, F.A., 2010, Alluvial diamond resource potential and production 

capacity assessment of the Central African Republic: U.S. Geological Survey Scientific Investigations 

Report 2010–5043, 22 p.

(available only online at http://pubs.usgs.gov/sir/2010/5043/)
iii

Contents

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

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

Kimberley Process Certification Scheme.........................................................................................1

Kimberley Process Verification ..........................................................................................................2

Project Objectives.................................................................................................................................2

Work Plan and Timetable.....................................................................................................................2

Phase 1: Research.......................................................................................................................2

Phase 2: Field Evaluation............................................................................................................2

Phase 3: Report Preparation......................................................................................................3

Phase 4: Project Finalization......................................................................................................3

Team Organization ................................................................................................................................3

Geologic Description of the Central African Republic with a Focus on Diamond Areas ..................3

Introduction to the Geology of the Central African Republic ........................................................3

Carnot Sandstone .................................................................................................................................5

Mouka-Ouadda Sandstone .................................................................................................................5

Ferricrete Duricrust..............................................................................................................................5

Source of Diamond Occurrences ......................................................................................................6

Alluvial Diamond Deposits...................................................................................................................6

History of Diamond Mining and Production ..............................................................................................7

Methodology for Assessing the Central African Republic Diamond Resource Potential .................9

Field Data Collection and Basic Research .......................................................................................9

Volume and Grade Approach............................................................................................................12

Content per Kilometer Approach .....................................................................................................13

Methodology to Estimate the Capacity of the Central African Republic Diamond Production ......13

Results ...........................................................................................................................................................14

Volume and Grade Results ................................................................................................................14

Western Zone .............................................................................................................................14

Eastern Zone...............................................................................................................................14

Results of the Content per Kilometer Approach............................................................................14

Diamond-Production Capacity Results ...........................................................................................19

Conclusions...................................................................................................................................................19

References Cited..........................................................................................................................................21

Figures

1. Map showing the geology of the Central African Republic...................................................4

2. Map showing the Carnot and Mouka-Ouadda Sandstones, Central African Republic....7

3. Diagram depicting official diamond transactions, Central African Republic.....................8

4. Map showing diamondiferous contour zones in the western 

Central African Republic ...........................................................................................................10

5. Map showing diamondiferous contour zones in the eastern 

Central African Republic ...........................................................................................................11
iv

Tables

1. Strahler stream orders and corresponding alluvial flat widths ............................................9

2. Diamond yield per kilometer of stream length.......................................................................13

3. Results of the volume and grade approach for calculating total diamond 

endowment for the western Central African Republic.........................................................15

4. Results of the volume and grade approach for calculating total diamond 

endowment for the eastern Central African Republic.........................................................16

5. Results for the content per kilometer approach for calculating total diamond 

endowment for the western zone, Central African Republic..............................................17

6. Results for the content per kilometer approach for calculating total diamond 

endowment for the eastern zone, Central African Republic...............................................18

7. Inferred and speculative diamond resources of the eastern plateau, 

Central African Republic ...........................................................................................................20

8. Summary of estimated diamond-resource endowments 

of the Central African Republic ................................................................................................20

Conversion Factors

Multiply by To obtain

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

square meter (m2

) 0.0002471 acre

square kilometer (km2

) 247.1 acre

cubic meter (m3

) 35.31 cubic foot (ft3)
Abstract

In May of 2000, a meeting was convened in Kimberley, 

South Africa, and attended by representatives of the diamond 

industry and leaders of African governments to develop a 

certification process intended to assure that rough, exported 

diamonds were free of conflict concerns. This meeting was 

supported later in 2000 by the United Nations in a resolution 

adopted by the General Assembly. By 2002, the Kimberly 

Process Certification Scheme (KPCS) was ratified and signed 

by diamond-producing and diamond-importing countries. 

Over 70 countries were included as members of the KPCS at 

the end of 2007.

To prevent trade in “conflict diamonds” while protecting 

legitimate trade, the KPCS requires that each country set up 

an internal system of controls to prevent conflict diamonds 

from entering any imported or exported shipments of rough 

diamonds. Every diamond or diamond shipment must be 

accompanied by a Kimberley Process (KP) certificate and be 

contained in tamper-proof packaging.

The objective of this study was (1) to assess the naturally 

occurring endowment of diamonds in the Central African 

Republic (potential resources) based on geological evidence, 

previous studies, and recent field data and (2) to assess the 

diamond-production capacity and measure the intensity of 

mining activity. Several possible methods can be used to 

estimate the potential diamond resource. However, because 

there is generally a lack of sufficient and consistent data 

recording all diamond mining in the Central African Republic 

and because time to conduct fieldwork and accessibility to 

the diamond mining areas are limited, two different methodologies were used: the volume and grade approach and the 

content per kilometer approach.

Estimates are that approximately 39,000,000 carats of 

alluvial diamonds remain in the eastern and western zones of 

the CAR combined. This amount is roughly twice the total 

amount of diamonds reportedly exported from the Central 

African Republic since 1931. Production capacity is calculated 

to be 840,000 carats per year, a number that is nearly twice 

the 450,000 carats per year reported annually by the Central 

African Republic. The difference in the two numbers reflects 

the lack of sufficient data on diamond resource grades, 

worker productivity, and the number and locations of sites 

being worked. 

Introduction

Kimberley Process Certification Scheme

During the late 1990s the issue of “conflict diamonds,” 

or “blood diamonds,” became increasingly recognized by 

the global community, largely due to civil unrest and wars 

in Sierra Leone and in Angola. In 2001, the United Nations 

imposed sanctions against the Liberian diamond trade after 

it accused Liberian President Charles Taylor of supplying 

weapons and training in exchange for diamonds from the 

Revolutionary United Front (RUF), which was engaged 

in a civil war with the government of Sierra Leone. The 

Democratic Republic of the Congo (DRC) also experienced 

several civil uprisings during the 1990s, and diamonds were 

reportedly used to fund rebel forces (Le Billon, 2008). 

In May of 2000, a meeting was convened in Kimberley, 

South Africa, and attended by representatives of the diamond 

industry and leaders of African governments to develop a 

certification process intended to assure that rough, exported 

diamonds were free of conflictual concerns. This meeting was 

supported later in 2000 by the United Nations in a resolution 

adopted by the General Assembly. By 2002, the Kimberly 

Process Certification Scheme (KPCS) was ratified and signed 

by diamond-producing and diamond-importing countries. 

Over 70 countries were included as members of the KPCS at 

the end of 2007.

The KPCS is an international activity whose goal is to 

prevent trade in conflict diamonds while helping to protect 

legitimate trade through monitoring of the production, 

Alluvial Diamond Resource Potential and Production 

Capacity Assessment of the Central African Republic

By Peter G. Chirico,1 Francis Barthélémy,2 and François A. Ngbokoto3

1

 U.S. Geological Survey, Reston, Virginia.

2

 Bureau de Recherches Géologiques et Minières, France.

3

 Direction Générale des Mines, Central African Republic.
2 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

exportation, and importation of rough diamonds throughout 

the world. To accomplish this task, the KPCS requires that 

each country set up an internal system of controls to prevent 

conflict diamonds from entering any imported or exported 

shipments of rough diamonds. Every diamond or diamond 

shipment must be accompanied by a Kimberley Process (KP) 

certificate and be contained in tamper-proof packaging. The 

certificate includes an export origin section, an import verification section, and a security slip. The KP also requires that no 

diamonds be imported from or exported to a nonmember of 

the KPCS. Additionally, a recommendation of the KPCS is 

that all artisanal miners and buyers within a country should be 

licensed by the host government (Olsson, 2006).

Countries that are members of the scheme are required 

to report their official amount of diamond imports and 

exports, as well as the value of the diamonds each year to the 

KP. These data are then made public and provided to other 

organizations in order to monitor the official statistics reported 

by all KP members.

Kimberley Process Verification

It is often difficult to obtain independent verification of 

diamond-production statistics provided by KPCS member 

countries. However, some degree of independent verification 

can be obtained by combining an understanding of the 

naturally occurring endowment of diamond resources with 

the country’s diamond-production capacity or intensity of 

mining activity. Studies integrating these two components can 

produce an estimated range of production values for a country 

that can then be compared with the actual reported production 

statistics. Reported production statistics that fall far outside the 

estimated possible production values may be further investigated to ensure that infiltration of conflict diamonds from an 

outside source is not occurring.

Recently, the Bureau de Recherches Géologiques et 

Minières (BRGM) produced an assessment for the Republic 

of the Congo (Congo Brazzaville) (Barthélémy and others, 

2006). This assessment was acclaimed within the KPCS 

community as a method for independent verification of 

alluvial diamond resources. A similar assessment was also 

conducted by the U.S. Geological Survey (USGS) in Liberia 

(Wahl and others, 2007). The USGS assessment made substantial contributions to the assessment process of the diamond 

potential and contributed to a lifting of the sanctions on 

mining and selling of diamonds imposed on Liberia through 

the Kimberley Process.

The work of both the BRGM and the USGS in this field 

continues as the organizations have partnered to conduct 

independent evaluations of the diamond potential in Mali and 

the Central African Republic.

Project Objectives

There are six main objectives of this project:

1. Produce a synthesis of geological and alluvial (placer) 

diamond-production information for the Central African 

Republic (CAR) from historical documentation. 

2. Develop a model to estimate the endowment of undiscovered diamond resources in the CAR. 

3. Use the model to estimate the CAR’s production capacity 

for rough diamonds. 

4. Create a detailed geographic information system (GIS) of 

diamond mining. 

5. Transfer to the CAR information resources to monitor 

diamond mining areas. 

6. Develop and conduct a workshop to present the final 

report results in conjunction with the Central African 

Republic Direction Général des Mines (DGM). 

Work Plan and Timetable

The CAR evaluation was completed in four phases, 

from research to a field evaluation to initial report preparation 

to project finalization. The entire process occurred over a 

timeframe of approximately 1 year.

Phase 1: Research

Phase 1 of this study included research, collection, 

and organization of all available data related to diamond 

resources and production in the CAR. This endeavor required 

a significant bibliographic study and the collection of geologic 

maps, geophysical data, and remotely sensed satellite imagery. 

During this phase, basic evaluations of the incoming data were 

conducted to assess its relevance, quality, and importance. 

Reports were examined to find all documented occurrences of diamonds and, where possible, the grade recorded at 

these locations. A digital database of diamond occurrences and 

grades was compiled to include coordinate information. This 

database was then mapped to display the spatial distribution of 

diamond occurrences based on historical field surveys. Phase 1 

was completed over the course of 4 months.

Phase 2: Field Evaluation

The second phase of this project was the field evaluation 

phase. This phase incorporated all aspects of the planning 

and execution of on-the-ground field studies and field data 

collection in the diamond mining areas of the CAR. Also 

included was time spent developing contacts and working with 

the scientists and staff of the DGM in Bangui. 
Geologic Description of the Central African Republic with a Focus on Diamond Areas 3

Two field excursions were completed under the scope 

of this study. The first was composed of project members 

representing the USGS, the BRGM, and the DGM and 

occurred in May 2007. The second field excursion occurred in 

September 2007 and was composed of project members from 

the BRGM and the DGM.

The fieldwork component of the project identified and 

characterized the mining regions of the eastern and western 

parts of the CAR. Fieldwork was conducted in both regions. 

One team composed of two project scientists visited the 

western diamondiferous zone. Two teams composed of five 

project members visited the eastern diamondiferous zone. The 

main goal of these field excursions was the characterization 

of the mining areas, evaluation of current artisanal mines, and 

field data collection. 

The goal of the second field season was mainly data 

development and characterization of diamond-production 

capacity. Phase 2 was completed over the course of approximately 2 months.

Phase 3: Report Preparation

Phase 3 incorporated the preparation of the resource 

assessments and the production capacity estimates. All field 

data were compiled, organized digitally, and analyzed. The 

GIS database was developed using both the data gained 

from the historical research as well as the field surveys from 

phase 2. Once the compilation and analysis of the data and 

the GIS database were complete, this final report was written. 

Phase 3 was completed over the course of 5 months.

Phase 4: Project Finalization

The final phase of the project was the presentation and 

final discussions of the project report. An in-country workshop 

was organized to include both practical fieldwork-oriented 

training and discussions of the project report among the team 

members. After the workshop and training were completed, 

the reports were finalized to reflect the discussions and recommendations of the team members and delivered to all parties 

involved. Phase 4 was completed over the course of 2 months.

Team Organization

This project was supported by the Economic Support 

Fund (ESF) provided by the U.S. Department of State and was 

executed by a trilateral partnership of scientists and technical 

professionals from the USGS, the BRGM, and the DGM of 

the Central African Republic.

Peter G. Chirico, USGS, Project Chief, Geographer

Emily Phillips, USGS, Researcher

Michael Warner, USGS, GIS/Remote Sensing Analyst

François M.J. Lampietti, USGS, Consulting 

Economic Geologist

Francis Barthélémy, BRGM, Geologist

Yves Husson, BRGM, Geologist

Alain Lambert, BRGM, Geologist

Jean-Michele Eberlé, BRGM, Diamond Expert, Geologist

Jean Sylvain Feïgoudozouï, DGM, Directeur Générale 

des Mines

Richard Ricardo Bangoto, DGM, Charge de Mission 

des Mines

François Alain Ngbokoto, DGM, Mining Engineer

Fernand Nanibet, DGM, Geologist

In addition, the field staff was aided by the Gendarme 

Mining Police.

Eloi-Arthur Ouazounam, Maréchal des Logis

Isaac Nanbeam, Gendarme 1st Class 

Maioret Vicko, Gendarme 1st Class

Gabriel Koae, Gendarme 2nd Class

Michel Toute-Nzola, Gendarme 2nd Class

Leon Suge Simon, Gendarme

Geologic Description of the Central 

African Republic with a Focus on 

Diamond Areas

Introduction to the Geology of the Central 

African Republic

The underlying geology of the CAR consists mainly of 

basement rocks of Archean and Proterozoic age, which can 

be divided into two main geologic groups: a granitic-gneissic 

complex and a schist-quartzitic complex. The granitic-gneissic 

complex is probably of Neoarchean age and is composed of 

gneissic, granite, and amphibolitic rocks. Also included in this 

group of basement rocks is a series of sedimentary volcanic 

sequences that are typically referred to as “greenstones.” 

Overlying the Archean basement rocks is the schist-quartzitic 

complex, which is thought to be of Neoproterozoic age and 

is composed of quartzitic and schistose rocks that are only 

weakly metamorphosed and generally folded. Both of these 

complexes are intruded throughout the country by basic rocks 

of Neoproterozoic age (Schlüter, 2006).

Overlying these older rocks is a sequence of Paleozoic 

rocks. The two major Paleozoic formations are the Mambéré 

Formation located in the western CAR and the Kombélé 

Formation located in the eastern CAR (fig. 1). Both Paleozoic 

formations are of glacial origin. The Mambéré Formation 

is a tillite composed of both basal and flow tills as well as 

reworked glacial deposits derived from sandstone, conglomeratic sandstone, and siltstone that occur in continuous beds, 
4 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

lenses, and isolated blocks (Censier and Lang, 1992). Similarly, the Kombélé Formation is a conglomeratic sandstone tillite composed of glacial-outwash plain sediments (Censier and 

others, 1992). Both the Mambéré and the Kombélé Formations 

generally range in thickness from 30 to 50 meters (m) and are 

covered by Cretaceous sandstone units lying unconformably 

above them. The exact areal extent of the Paleozoic rocks 

is not known because the more recent Mesozoic geology 

conceals a great deal of them. The Paleozoic units crop out in 

selected locations at the margins and in selected river valleys 

where the Mesozoic units have been completely eroded 

(Censier, 1996).

The Mesozoic, probably Cretaceous, fluvial sequences of 

conglomeritic sandstones concealing the Paleozoic glacial tillites form two distinct plateaus, one in the east and one in the 

west. The western plateau is made up of the Carnot Sandstone, 

and the eastern plateau is composed of the Mouka-Ouadda 

Sandstone. At one time, these two sandstone units extended 

much farther south and somewhat farther north than they do 

today. Later erosion of these two formations developed the 

current plateau landforms, which characterize the eastern and 

western CAR landscape (Censier and Tourenq, 1986; Censier, 

1996). These two sandstone units are widely reported to be the 

secondary hosts of the diamonds in the CAR. 

Figure 1. The geology of the Central African Republic.

CHAD

SUDAN

DEMOCRATIC REPUBLIC

OF THE CONGO REPUBLIC OF

THE CONGO

CAMEROON

Kotto

Kotto

Lobaye

Lobaye

Mambéré

Mpoko

Sangha

Ouham

Chinko

Bahr Oulou

Bamingui

Oubangui

Koukourou Bria

Obo

Bangassou

Mobaye

Bambari

Batangafo

Bangui

Nola

Berberati

Carnot

Bouar

Bossangoa

Birao

K

K

K

C

Z

Z

Z

Z

Z

Z

Z

_

_

_

Q

Q

X

X

X

X

X X

X

X

X

X

:

:

:

:

Y

Y

Y

Y

V V

V

V

V

V

V

W

U

W

15° 20° 25°

10°

5°

CENTRAL AFRICAN REPUBLIC 

Shaded relief modifed from Shuttle Radar Topography Mission 0 150 225 300 KILOMETERS

Other base features modified from the U.S. Geological Survey 

 Global Geographic Information Systems database

Geology modified from

Lescuyer and Milési, 2004

75

0 50 100 150 MILES

EXPLANATION

Quaternary

Paleogene

Cretaceous

Carboniferous

Q

K

C

_

Z

Y

X

W

V

U

:

Cambrian

Neoproterozoic

Mesoproterozoic

Paleoproterozoic

Neoarchean

Mesoarchean

Paleoarchean

Figure 1. 

Bahr 

Kameur

W

AFRICA

Map

area
Geologic Description of the Central African Republic with a Focus on Diamond Areas 5

A series of Cenozoic rocks occurs in two distinct zones 

within the CAR. The first is a series Paleo-Tchadienne 

continental terminal sandstones extending north of Batangafo 

to the northern border of the CAR, forming smaller distinct 

plateaus. The second is the Bambio Sandstone, which is generally located between Nola and Boda just north of the Bangui 

River in the southwestern part of the country. The Bambio 

Sandstone lies atop the Carnot Sandstone but only covers an 

area of approximately 1,700 square kilometers (km2).

Recent Pleistocene deposits have filled in the northern 

basin and are generally divided into either Neo-Tchadienne 

alluvium or recent alluvial deposits. Quaternary alluvial 

deposits are also found in the many riverine floodplains 

throughout the country. Chemical weathering, which is 

typical in the humid tropical environment, has created lateritic 

duricrusts and ferricretes during the Quaternary. The weathering crusts may be as thick as 40 m in places and extend over 

large portions of the topography throughout the CAR (Petit, 

1985; Beauvais, 1989; Beauvais and Roquin, 1996).

Carnot Sandstone 

The Carnot Sandstone is of Mesozoic age and of fluviatile 

origin, which, in the most recent depositional environments, 

may have also included lacustrine and palustrine deposits. As 

a result, the formation is composed of several successional 

layers of conglomerates, sandstones and mudstones, and 

siltstones. It lies in the southwestern part of the CAR and 

covers an area of more than 40,000 km2. The thickness of the 

unit is highly variable but has been reported to be as thick as 

300 to 400 m in places (Censier, 1990). Heavy mineral and 

quartz exoscopic analysis (Censier, 1990) demonstrate that the 

detrital material of the Carnot came from a southerly origin, 

has similar mineralogical composition throughout the whole 

infilled basin, and was composed of reworked detrital formations. The Nola and Bolé River series was originally thought 

to be the source of the reworked material. Subsequent analysis 

supports the assigning of the glacial Devonian–Carboniferous 

Mambéré Formation and the Precambrian schist and quartzite 

rocks as the source of the detrital materials that have been 

reworked and cemented into the Carnot Sandstone. The 

underlying Precambrian granitic-gneissic complex of rocks 

formed the landscape for Carnot deposition (Censier and 

Lang, 1999). The paleogeography and paleotopography show 

that this landscape was a general peneplain with monadnocks. 

The monadnocks’ subsequent erosion causes the mineralogical 

heterogeneities in the current landscape and also results in 

the irregularities in the basal surface of the Carnot Sandstone. 

The surface of the original sedimentary basin was much larger 

than has been interpreted on the basis of current limits of the 

Carnot Sandstone. The western margin may have extended 

beyond the CAR and Cameroon border (Censier, 1990).

Deposition of the reworked material occurred from 

the Albian to the Maastrichtian in north-northwest- flowing 

riverine braided channels flowing into the Doba Trough 

(Chad) and into the Touboro Basin (Cameroon) (Censier 

and Lang, 1999). Subsequent uplift and faulting during the 

Cenozoic reversed the direction of flow and erosion of the 

Carnot from north-northwest to south-southeast and emplaced 

the current fluvial drainage system.

Mouka-Ouadda Sandstone 

The Mouka-Ouadda Sandstone is a Cretaceous fluviatile 

sandstone that lies in the eastern Central African Republic. It is 

thought to be the secondary host rock of the alluvial diamond 

deposits in the region. The Mouka-Ouadda Sandstone covers 

an area of approximately 40,000 km2, forming a plateau that 

is generally less than 500 m thick. It is composed of layers 

of sandstone and conglomerate. Similar to that of the Carnot 

Sandstone, the Mouka-Ouadda is thought to have been derived 

from detrital material from the fluvial-glacial Kombélé Formation and from the Precambrian schist and quartzite complex 

and was also deposited on a peneplained Precambrian graniticgneissic basement. Paleocurrent measurements indicate that 

the major source of sediment lies to the south-southwest, and 

the direction of deposition was to the north-northeast. As 

structural evolution of the landscape progressed, the orogenic 

uplift to the north reversed the riverine flow, thus developing 

the current drainage system (Malingbar and others, 2006). 

Ferricrete Duricrust

Duricrust is a general term for a surficial crust that is 

formed by the accumulation of soluble minerals deposited 

by mineral-bearing water that moves up the weathering soil 

profile during wet periods and evaporates down the profile 

in dry periods. Central Africa is home to large swaths of 

ferruginous duricrusts typically named ferricretes. The 

ferricretes in the CAR cover large portions of the country and 

are typically characterized by a crust that ranges in thickness 

from tens of centimeters to tens of meters and that in turn is 

lying upon a lateritic weathering soil profile. The ferricretes in 

central Africa are the result of paleoclimatic evolution over the 

past approximately 150 million years. Different geomorphic 

types of ferricretes have been characterized. Beauvais (1989) 

has described three ferricrete systems present in the CAR that 

relate to high plateaus, hillslopes, and low plateaus. Mineralogically, the high plateaus are the most evolved and thicker 

and rich in hematite and kaolinite. Ferricretes developing on 

hillslopes are softer crusts containing goethite and kaolininte, 

and the thinnest and least evolved ferricretes are present on 

the low plateaus. Ferricretes that mineralogically contain 

more hematite tend to correspond to less humid and generally 

warmer paleoclimates that have been present in the CAR 

throughout the past 70 million years (Tardy and others, 1991). 

Beauvais and Roquin (1996) suggest that the ferrricretes in 

the CAR reflect the processes of erosion and weathering more 

than they reflect the parent material of the underlying bedrock, 

although there tends to be more influence of the underlying 
6 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

bedrock in the hillslope and low plateau ferricretes than in the 

high plateau ferricretes. High plateau and hillslope ferricretes 

studied in the southeastern CAR are 10 to 12 m thick, with 

the top 3–4 m composed of the massive or protonodular facies 

(Beauvais, 1999).

Source of Diamond Occurrences 

No kimberlites, lamproites, or other primary geologic 

deposits of diamonds have been discovered in the CAR. The 

current understanding of the geologic origin of the diamonds 

in the region is that the original kimberlites from which CAR 

diamonds were eroded may lie undiscovered in the northern 

part of the Democratic Republic of the Congo. Again, no 

direct evidence for this exists, but Censier (1996) claims that 

tectonic, mineralogical, and crystallographic evidence strongly 

support this interpretation.

Kimberlitic intrusions occurred in the Central African 

region during the Mesoproterozoic (Kibarian) and more 

recently during the Early Cretaceous (Giresse, 2005). 

Because the diamonds are entrained in the Upper Cretaceous 

(from Albian to Maastrichtian) Carnot and Mouka-Ouadda 

Sandstones, Censier (1996) proposes that it is unlikely that the 

diamonds’ primary source would be from kimberlitic intrusions during the Early Cretaceous. If the primary kimberlitic 

source of the CAR diamonds is from the Precambrian, as 

is the case of the nearest kimberlite pipe located in Mitzic, 

Gabon, it is possible that the diamonds in the CAR may have 

been deposited and reworked two or three times (Demptser 

and Tutusaus, 1995). In any event, the likely location of the 

primary kimberlitic sources is assumed to be in the northern 

region of the DRC. It is interesting to note that much of the 

northern area of the DRC is covered by Quaternary sediments 

that may be covering geologic evidence of primary kimberlitic 

source rocks, if they exist.

Diamonds are believed to be hosted by Mouka-Ouadda 

and Carnot Sandstones as secondary source rocks. It is possible that the Paleozoic formations underlying the Mesozoic 

sandstone plateaus may also be secondary source rocks for 

diamonds, but that has not been proven by direct evidence. 

Despite sampling of the Carnot and Mouka-Ouadda Sandstones, no direct indications of diamonds in the sandstones 

have been discovered either. The diamonds are found in recent 

alluvial terraces and flood-plain deposits lying both on top of 

the sandstone plateaus and in detrital valleys eroding 

the plateaus.

The Central African Republic is also host to a type of 

diamond called a “carbonado.” Carbonados are defined as an 

“opaque aggregate composed of minute diamond particles 

forming a mass with a granular structure and superior 

toughness” (Bates and Jackson, 1984). This diamond type 

was first observed in Brazil and parts of Venezuela as early 

as the 1840s. The term carbonado is itself of Brazilian origin. 

The polycrystalline structure of the carbonado makes it 

extremely durable; therefore, it has been in great demand for 

use in industrial applications such as cutting tools and drilling 

equipment. It has been estimated that up to 30 percent of the 

diamonds in the western zone and 7 percent in the eastern 

zone of the CAR are of the carbonado variety (Erlich and 

Hausel, 2002).

Diamond occurrences outside the immediate areas of 

the two secondary plateaus do exist and may be from either 

the plateaus themselves or from other isolated occurrences. It 

is understood that the two Cretaceous sandstone formations 

covered a much larger area in the past than they do at present, 

and diamond occurrences that are far from the current extent 

of the Cretaceous formations may in fact originate from 

eroded remnants of the same formations. 

As the Cretaceous sandstone plateaus erode, diamonds 

are liberated from the secondary host rock. The liberated 

diamonds are washed downstream and deposited in recent 

Quaternary alluvium and terrace deposits along the river 

courses. Three alluvial placer deposit types have been 

observed: alluvial flat and channel deposits, low terrace 

deposits, and high terrace deposits.

Alluvial Diamond Deposits

The Central African Republic has been host to the geologic, tectonic, and climatic environment that has developed a 

geomorphology conducive to the formation of placer deposits. 

The first factor controlling development of the placer deposit 

is the presence of nearby, although undiscovered, primary 

diamond mineralization. Secondly, the tectonic setting in 

which the Cretaceous sandstones have been uplifted, reversing 

the flow direction of the river systems and subsequently 

eroding them, has created an environment where erosion of 

the secondary host rocks liberates the diamonds and redeposits 

them in alluvial deposits in the river valleys. 

Over the past 100 million years (Ma) the climatic 

conditions in the CAR have fluctuated between wetter periods 

and drier periods. From the Late Albian (~100 Ma) the 

Congo Basin experienced widespread humid conditions, but 

during the Late Cretaceous to Paleogene (~65 Ma) there was 

a marked drying trend throughout the basin which includes 

some areas being exposed to eolian mobilization of sediments 

(Giresse, 2005). Subsequently, during the Neogene (~23 Ma) 

wetter conditions re-emerged. This fluctuation allows for the 

liberation and erosion of diamonds during wetter periods and 

the concentration of diamonds in alluvial deposits during 

the drier periods. Burton and Fralick (2003) showed that 

long intervals of average flows interspersed with large-scale 

flooding events are the optimum conditions for the formation 

of longitudinal placer development. This scenario seems 

consistent with the depositional history of the CAR alluvial 

materials. Consequently, the alluvial geomorphology of the 

current-day landscape is an important factor in the location of 

diamond placer reserves (Sutherland, 1985).
History of Diamond Mining and Production 7

For the purposes of this report, the alluvial diamond 

deposits are divided into two main diamondiferous areas: one 

in the west, which is associated with the Carnot Sandstone and 

occurs in the Kadéi-Mambéré-Sangha region, and one that lies 

in the east and is associated with the Mouka-Ouadda Sandstone in the Haute-Kotto region (fig. 2). Censier (1996) asserts 

that both areas are entirely diamondiferous owing to the large 

number of rivers that local diggers have been exploiting with 

alluvial workings. Previous studies had postulated that only 

the lower members of the Cretaceous sandstone layers were 

diamondiferous. However, diamonds have been recovered 

only in the alluvial material despite many studies that have 

tested the sandstones and conglomerates directly for diamonds 

(Censier, 1996).

History of Diamond Mining 

and Production

Diamonds were discovered in the CAR in 1914 and 

again in 1929 when the widespread presence of alluvial 

diamond deposits was recognized (Dempster and Tutusaus, 

1995). Commercial mining and production began in 1931 

in the Bossangoa and Nola regions (western region) and 

rapidly expanded from 1935 to 1945. The alluvial exploitation 

of the eastern region expanded from 1943 to the present. 

Several mining companies exclusively exploited the diamond 

resources in the CAR from 1931 until 1960, and diamond 

production remained relatively low, averaging about 75,000 to 

Figure 2. The Carnot and Mouka-Ouadda Sandstones, Central African Republic.

CHAD SUDAN

DEMOCRATIC REPUBLIC

OF THE CONGO

REPUBLIC OF

THE CONGO

CAMEROON

Kotto

Kotto

Lobaye

Lobaye

Mpoko

Sangha

Ouham

Chinko

Bahr Oulou

Oubangui

Bahr 

Kameur

Bamingui

Mambéré

Koukourou Bria

Obo

Bangassou

Mobaye

Bambari

Bangui

Nola

Berberati

Carnot

Bouar

Bossangoa

Birao

Batangafo Mouka-Ouadda

Sandstone

Area of figure 5

Area of figure 4

 Carnot

Sandstone

15° 20° 25°

10°

5°

CENTRAL AFRICAN REPUBLIC

Shaded relief modifed from Shuttle Radar Topography Mission

Other base features modified from the U.S. Geological Survey 

 Global Geographic Information Systems database

Geology modified from

Lescuyer and Milési, 2004

Figure 2. 

0 75 150 225 300 KILOMETERS

0 50 100 150 MILES
8 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

100,000 carats per year. In 1960, the Central African Republic 

gained independence and shortly thereafter, in April 1961, 

authorized the Bureau d’Achat to act as an organization of 

diamond export companies. In addition, the government of 

the CAR began licensing artisanal miners who, in turn, hired 

diggers to exploit the alluvial deposits. From 1961 through 

the early 1970s, production of diamonds increased rapidly 

from approximately 100,000 carats a year to approximately 

450,000 carats a year. The increase was largely due to the 

authorization and introduction of artisanal miners working 

throughout the sector. Annual production of diamonds varies 

from year to year in relation to the seasonal environmental 

conditions, stability and security within the country, and the 

number of diggers employed in the sector.

As of 2006, there were 7 Bureaux d’Achat and 18 Centre 

d’Achat acting as buyers and diamond exporters. There are 

estimated to be approximately 300 collecteurs who purchase 

the diamonds locally from artisans close to the alluvial mining 

sites and resell them to the Bureau d’Achat for sale and export. 

There are 1,988 artisanal miners and 6,515 ouvrier miniers for 

a total of 8,503 artisanal miners. Ouvrier miniers are licensed 

artisans who work on smaller scales and pay less of a licensing 

fee than the other artisanal miners. Each artisanal miner hires a 

team of diggers, which may range in size from 6 to 15 persons. 

There are also a few small-scale mining companies that 

operate in the CAR either through hiring diggers to exploit the 

deposits or by acting as buyers, collecteurs, and exporters.

It is estimated that between 50,000 and 100,000 diggers 

are exploiting alluvial diamond deposits in the CAR. Dietrich 

(2003) has reported the total number of licensed artisanal 

diggers as being approximately 50,000, while Censier (1996) 

reported an estimated 70,000. According to a 2003 unpublished report by Koyatro (Direction Générale des Mines), it 

is estimated that the total number of diggers is around 70,000 

and that teams are typically constituted of approximately 

10 to 15 diggers. Each team is hired and organized by a 

licensed artisan. Licensed artisans may sell diamonds either 

to a collecteur or directly to one of the registered diamond 

buying offices composing the Bureau d’Achat. The collecteurs

may buy diamonds from many artisans and generally act as 

middlemen between the artisan and the bureau (fig. 3). 

In 1982, the Bureau d’Evaluation et de Contrôle de Diamant et d’Or (BECDOR) was established to officially value 

all diamond and gold exports. BECDOR assesses the value of 

all official diamond exports from the CAR and collects official 

statistics on diamond and gold production within the CAR. 

BECDOR also evaluates the receipts of sale from artisans and 

export companies operating in the CAR for all diamonds that 

they have purchased from artisans and mining societies. Each 

diamond sale is recorded through a series of receipts listed 

Figure 3. Official diamond transactions, Central African Republic.

COLLECTEURS (300)

BUREAUX D’ACHAT (7)

BECDOR

Bureau d’Evaluation et de Contrôle

de Diamant et d’Or

SOCIÉTÉ MINIER (12)

ARTISAN MINIERS (2,000)

OUVRIERS MINIERS (6,500)

COOPERATIVE

• under the direction of the artisan

• a group of at least 10 patented

artisanal miners

• can have a site that is

500 × 500 meters

• can sell directly to the

international market

• each is allocated a zone and supports

the artisanal miners in its zone

• buys the mining product from the zone

• direct production at the mine site

• site size of up to 100 × 100 meters

• patented

• non-mechanized methods

“middlemen”

• support artisans they finance 

and have the exclusive right 

to buy from

• diamond exporting companies

• oversees the international diamond

market from mine to export

• evaluates the diamonds

Figure 3. 
Methodology for Assessing the Central African Republic Diamond Resource Potential 9

with the buyer’s and seller’s names and license numbers, in 

addition to carat, value, and place of origin of the diamonds. 

Artisans and the teams of diggers that they employ utilize 

little if any mining technology beyond the occasional pumps. 

Most continue to use hand tools, sieves, jigs, and local timber 

and wood resources to perform the mining activities. Therefore, there are few barriers to entry for diamond diggers, as 

little or no training is required and basic tools are used. Often 

diggers move seasonally from site to site as new deposits are 

mined or as variations in the farming seasons occur. 

While there are teams of 6 to 15 diggers typically 

employed by the artisans, there are often a number of ancillary 

workers at mine sites. These ancillary workers are usually 

family members of the diggers and include their wives and 

children. Women and children perform tasks such as transporting, washing, and sorting the gravel ore. Consequently, at a 

site where an artisan has a team of 10 diggers, there may be as 

many as 50 individuals working throughout all phases of the 

extraction and production process.

In addition, at some larger mine sites, women were 

observed cooking and selling food to the mine workers, 

operating independently of any specific digger family group. 

Markets may also be located close to the mine sites on certain 

days, developing a small-scale informal economy that may 

consist of all types of food and material sales and services. 

Methodology for Assessing the 

Central African Republic Diamond 

Resource Potential

The objective of this study was twofold. The first goal 

was to assess the naturally occurring endowment of diamonds 

in the CAR, which can be termed the “potential diamond 

resources,” on the basis of geologic evidence, previous 

studies, and recent field data collection. The second goal was 

to assess diamond-production capacity through an understanding of current human and resource conditions in the CAR 

and to measure the intensity of mining activity. A degree of 

independent analysis is reached by assessing both the potential 

resources and the production capacity and comparing these 

data with the published diamond-production figures from 

the CAR.

Several possible methods can be used to estimate the 

potential diamond resource. However, because there is 

generally a lack of sufficient and consistent data recording 

all diamond mining in the CAR and because time to conduct 

fieldwork and accessibility to the diamond mining areas are 

limited, two different methodologies were used in this study to 

assess the diamond potential. The results of these two methods 

were cross-checked with one another to help provide clarification and redundancy in error checking.

Field Data Collection and Basic Research

An extensive search for literature on the geology and 

diamond mining of the CAR was performed under the scope 

of this study. The purpose behind completing a bibliographic 

research study was to determine the extent of data that have 

already been collected and that may prove useful in the 

development of diamond mining assessments and general 

geologic background. Information on diamond mining sites, 

techniques, grades of diamond workings, and the history of 

diamond mining was extracted from many different publications and developed into a database of all diamond showings. 

The database was then used to extract key parameters for 

both the eastern and western CAR diamond deposits. These 

parameters populate the tables presented in this study.

In addition, data collected during the field campaigns 

provided valuable information on the number of artisans and 

diamond diggers operating in the country. Also, information 

about the productivity of diamond workings and the amount of 

overburden at specific sites was measured and recorded. Site 

visits revealed the nature of the diamond deposit, the thickness 

of the gravel layers being mined, and the geomorphologic 

deposit type. To accurately gather the information from the 

field, a comprehensive questionnaire was developed and used. 

Each field team was provided a set of questionnaire 

booklets. The booklets contained blank forms which the 

field teams filled out at every site that was visited during the 

field study. It was important to record spatial location of the 

mine sites accurately (longitude and latitude) as well as mine 

conditions. Mine conditions may have included the size and 

depth of the mine, the distance from the closest river, town, 

and road, the depth of the overburden, or the thickness of the 

gravel. In addition, questions were asked regarding the flow 

of production, number of miners and teams, and additional 

Artisanal diamond miners washing gravels near Wango, CAR, May 2007
10 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

Figure 4. Diamondiferous contour zones in the western Central African Republic.

jobs noted in the surrounding areas. The standardized questionnaire ensured that a consistent set of data was gathered at 

each site, even though the teams were working separately at 

different sites throughout the country. The field data gathered 

through this method were incorporated into the database of 

diamond occurrences.

A map database of alluvial diamond diggings, workings, 

mine sites, and diamond recoveries was used to develop the 

current active mining diamondiferous deposit zones within the 

western and the eastern CAR (fig. 2). The zones were developed in a GIS by grouping diamond showings into contiguous 

groups spatially. These contoured zones are used in both 

methodological assessments to limit the calculations to the 

areas most actively being mined within the CAR. The contour 

zones for the western diamond deposits are shown in figure 4, 

and contour zones for the eastern zone diamond deposits are 

shown in figure 5. Rivers lying between contoured zones are 

also included in the assessments. These rivers are Strahler 

Lobaye

Lobaye

Mpoko

Mambéré

Sangha

Shaded relief modifed from Shuttle Radar Topography Mission

Other base features modified from the U.S. Geological Survey 

 Global Geographic Information Systems database

Geology modified from

Lescuyer and Milési, 2004

0 25 50 75 100 KILOMETERS

0 10 20 30 40 50 MILES

Nola

Bouar

Carnot

Berberati

REPUBLIC OF

THE CONGO

CAMEROON

Zone 6

Zone 5

Zone 4

Zone 8

Zone 11 Zone 10

Zone 2

Zone 3

Zone 9

Zone 1

Zone 7

16° 18°

6°

4°

CENTRAL AFRICAN REPUBLIC

EXPLANATION

Figure 5. 

Carnot Sandstone

Contour zone and number

Diamond showing

Gold showing

Major stream USGS/ BRGM study site

Minor stream
Methodology for Assessing the Central African Republic Diamond Resource Potential 11

Figure 5. Diamondiferous contour zones in the eastern Central African Republic.

Oubangui

Kotto

Kotto

Koukourou

Mobaye

Bangassou

Bria

Bambari

SUDAN

DEMOCRATIC REPUBLIC 

OF THE CONGO

EXPLANATION

Mouka-Ouadda Sandstone

Contour zone and number

Diamond showing

Gold showing

Major stream USGS/ BRGM study site

Minor stream

Shaded relief modifed from Shuttle Radar Topography Mission

Other base features modified from the U.S. Geological Survey 

 Global Geographic Information Systems database

Geology modified from

Lescuyer and Milési, 2004

 Zone 

 8

Zone 10

Zone 9

Zone 

11

Zone 12

Zone 7

Zone 1 Zone 6

Zone 2

Zone 3

Zone 4

Zone 5

0 50 75 100 KILOMETERS 25

0 10 20 30 40 50 MILES

Figure 4. 

20° 22° 24°

8°

6°

CENTRAL AFRICAN REPUBLIC
12 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

orders 6, 7, and 8 and represent large rivers with significant 

potential to have alluvial diamond deposits. The larger order 

rivers are included in the assessment calculations as complementary areas. The results from these areas are contained in 

the tables for the eastern and western zones, respectively, but 

are entered separately to distinguish between deposits in areas 

of active diamond showings and areas of significant potential 

that have no recorded active diamond diggings.

The first approach estimates a volume of alluvial material 

in the contoured diamondiferous deposit zones and assigns 

a diamond ore grade for each cubic meter of alluvium. The 

second method uses a cumulative river length for contoured 

diamondiferous deposit zones and assigns a diamond grade for 

the different lengths of stream based on how rich the alluvial 

material along those selected stream reaches may be. 

For each method, historical data were collected on the 

diamond grades, excavations, and yields for each of the 

diamondiferous zones. A digital elevation model (DEM) was 

used to derive the streams and rivers and overall database of 

the hydrologic drainage system of the country. The calculation 

of linear length values of the drainage network was measured 

using a GIS.

Volume and Grade Approach

The volume and grade methodological approach can be 

described mathematically as:

P V T1 V T2 = × + × ( ) (1 4 ),

where

P is the estimated diamond resource potential, 

and

V is the volume of alluvium.

The volume of alluvium is determined, in this method, by estimating the width of the alluvial flat deposit and multiplying it 

by the thickness of the gravel layer being mined. The product 

of this multiplication yields a number equal to the volume of 

diamondiferous gravel. Alluvial flat widths are determined by 

assigning a width based on the order of the river or stream. 

Stream ordering is a process whereby a river system 

channel-network map is analyzed quantitatively. The smallest 

tributaries in the uppermost portions of watershed are assigned 

an order of one. They are the smallest and shortest segments 

of the riverine network. When two first-order streams come 

together, a second-order stream is formed. Only when two 

second-order streams join is a third-order stream formed. This 

analysis continues until all streams and river channels in the 

network have been classified. The logic behind the stream 

ordering system developed by Strahler (1964) is that order 

number is directly proportional to the size of the contributing 

watershed, to channel dimensions, and to stream discharge 

measurements for each stream segment.

Following this logic, the widths of the alluvial flats along 

stream segments of the same order will be proportional. The 

flat widths have been determined by previous studies (Barthélémy and others, 2006) and secondarily verified and modified 

by field observations. Table 1 demonstrates how each stream is 

assigned an alluvial width based on its order.

For each alluvial flat width there is also a corresponding 

measurement of the thickness of the gravel layer within the 

alluvial deposit that is known to be diamondiferous. Again, 

the values of the gravel thickness are modeled from previous 

studies in central Africa and are based on recent field observations. The thickness of gravel layers corresponds to the order 

of the streams because larger higher order streams have a 

greater depositional history and have been verified in the field 

to have larger and thicker gravel deposits. 

The gravel layers are not all equally endowed with the 

same content of diamonds. Different gravel deposits within 

the alluvial flats may have higher concentrations on the 

basis of depositional history, the type of fluvial environment 

present, and the time period during which the alluvial gravels 

were originally deposited. To account for these variations 

in depositional history, two gravel grades are used in the 

formula. One grade is described as the “basic” grade and is 

applied to all of the alluvial gravels calculated for the volume. 

The second grade is the “concentration” grade. This value is 

applied only to one-fourth of the total calculated volume of 

alluvial gravel in the deposit.

T1 corresponds to the “basic” grade and is applied to 

the entire volume of the alluvial flat. The basic grades are 

determined from previous field observations listed in the 

tables according to the study area. They are either determined 

as an average of field sampling results or they are a 

weighted average.

T2 corresponds to the “concentration” grade of the 

alluvial gravels. This grade accounts for the fact that diamond 

occurrences are not uniformly consistent throughout the 

(1)

Table 1. Strahler (1964) stream orders and 

corresponding alluvial flat widths.

Strahler 

stream order

Width of alluvial flat 

(meters)

Thickness of 

diamondiferous 

gravel layer 

(meters)

1 5 0.15

2 10 0.20

3 20 0.30

4 30 0.40

5 40 0.50

6 50 0.60

7 70 0.80

8 100 1.00
Methodology to Estimate the Capacity of the Central African Republic Diamond Production 13

entire deposit. In addition, previous studies have determined 

that artisanal miners are unlikely to work gravels where the 

grade is less than 0.1 to 0.2 carats per cubic meter (kt/m3) 

(Barthélémy and others, 2006). There are exceptions to this, 

where artisanal diggers may dig in the hope of finding a rare 

but single large stone in an otherwise very low-grade deposit.

Certain areas that fall outside the contoured zones have 

been included in the volume and grade assessment approach as 

complementary areas that interconnect the contoured zones. In 

particular, rivers and streams of Strahler orders 6, 7, and 8 that 

connect diamondiferous contour zones or flow from them have 

been included.

Content per Kilometer Approach

Bardet (1974) proposed another possible approach to 

determining the potential diamond resources of the Central 

African Republic’s alluvial deposits. It involves assessing 

the grade of the diamond resources as a function of the carats 

recovered per kilometer of length of the stream or river along 

which they are recovered. His studies classified rivers and 

streams as being in one of three general categories: very rich, 

rich, or poor. Bardet assigned ranges of values of grades from 

400 carats per kilometer (kt/km) to 10,000 kt/km to each of the 

categories. The fieldwork conducted by the team determined 

the following categories of diamondiferous content per 

kilometer for rivers, presented in table 2.

Following this categorization, this study used a modified 

version of Bardet’s approach, which can be expressed by 

the formula:

R ( ) ( ) ( ), total = × + × + × L1 T1 L2 T2 L3 T3

concentrated and where R = × + × ( ) ( ). V2 T2 V3 T3

Each contoured zone was assigned an average diamond grade 

per kilometer of stream length. These grades correspond to T1

for very rich, T2 for rich, and T3 for poor. The total length of 

streams within each study area is calculated. The total length 

of streams that fall into each of the categories (very rich, rich, 

and poor) was then calculated from the total and assigned to 

each of the L1, L2, and L3 variables. These two parameters 

are used to develop the cumulative length of streams falling 

into each of the three categories of stream endowments. The 

cumulative length of streams within each category was then 

multiplied by the number of carats per kilometer for that type 

of stream. The result of the multiplication is a total estimated 

amount of carats for each stream endowment type for each 

study area. The total carats per kilometer was summed for 

each study area, and these values then provided a total estimated endowment for each study area. 

Certain areas that fall outside the contoured zones 

have been included in the content per kilometer assessment 

approach as complementary areas that interconnect or 

drain the contoured zones. In particular, rivers and streams 

of Strahler orders 6, 7, and 8 that connect diamondiferous 

contour zones or flow from them have been included and 

treated as separate complementary zones.

Methodology to Estimate the Capacity 

of the Central African Republic 

Diamond Production 

Diamond-production capacity is defined as the current 

volume of diamonds (calculated as total number of carats) 

that can be produced utilizing current human and physical 

resources. The estimate of diamond-production capacity 

does not reflect the possibility of future introduction of new 

financial capital investment or of improved exploration or 

mining techniques, nor does it model increases of human 

resources (labor capital) in the mining sector. Rather, it is a 

measure of the current state of the diamond mining sector 

based on recent field data collected and on previous research 

studies of diamond mining, gravel grades, and estimates of 

Table 2. Diamond yield per kilometer of stream length.

[kt/km, carat per kilometer]

Zone

T1 – 

Very rich streams 

(kt/km) 

T2 – 

Rich streams 

(kt/km)

T3 – 

Poor streams 

(kt/km)

Eastern 6,000 1,500 500

Western 7,500 2,500 850

(2)

(3)

53-carat rough diamond being evaluated at BECDOR 

in Bangui prior to export, July 2008
14 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic

the total number of alluvial diamond diggers and small 

mining cooperatives. To assess the diamond-production 

capacity, a formulaic model was developed. It can be stated 

mathematically as

( ) , P V j t j A i m = × × × i

where 

Pi is the total current production capacity, 

V j m is the volume of material worked for each 

digger per day, 

t is the average gravel grade, 

j is the total number of days that a digger works 

per year, and

Ai is the total number of diggers.

Results

Volume and Grade Results

Eleven contoured zones of diamond deposits were 

derived from the point location database showing the location 

of recorded diamond diggings, workings, and recoveries in the 

western CAR. For each of the diamondiferous deposit zones, 

the calculation for volume and grade was performed.

The results of the volume and grade methodological 

assessment are presented for each diamond deposit zone 

identified in the mapping. Results are presented separately for 

the western and eastern zones. 

Western Zone

Table 3 gives the computational results for the western 

zone. The results table identifies the number of the contour 

zone and lists the total volume of alluvium for that zone. The 

total volume of “basic” grade gravels is calculated from the 

total by dividing it by three-fourths. For the basic gravels of 

the western CAR, a grade of 0.05 kt/m3

 is applied, which then 

results in the estimated endowment of the basic grade gravels 

for that zone.

For each contoured zone, the volume of “concentration” 

grade gravels is calculated as one-fourth of the total alluvium 

of the zone. The concentration grade (T2) of the western 

zone gravels is 0.40 kt/m3. The estimated endowment of the 

concentration grade gravels is calculated by multiplying the 

concentration volume by the concentration grade, which yields 

the estimated endowment of concentration grade gravels.

For the western zone, three complementary areas are 

included in the assessment. These zones represent alluvial 

diamond deposits lying along rivers and streams corresponding to Strahler order streams 6, 7, and 8.

The total estimated endowments for each zone are then 

summed. The estimated endowment for “concentration” grade 

gravel deposits of the western zone is 21,256,539.60 carats. 

When combined with the “basic” grade gravel endowments, the total estimated resource for the western zone is 

29,227,741.95 carats.

Eastern Zone

Table 4 gives the computational results for the eastern 

zone. The results table identifies the number of the contour 

zone and lists the total volume of alluvium for that zone. The 

total volume of “basic” grade gravels is calculated from the 

total by dividing it by three-fourths. For the basic gravels of 

the eastern CAR, a grade of 0.05 kt/m3 is applied, which then 

results in the estimated endowment of the basic grade gravels 

for that zone.

For each contoured zone the volume of “concentration” 

grade gravels is calculated as one-fourth of the total alluvium 

of the zone. The concentration grade (T2) of eastern zone 

gravels is 0.30 kt/m3. The estimated endowment of the 

concentration grade gravels is calculated by multiplying the 

concentration volume by the concentration grade, which yields 

the estimated endowment of concentration grade gravels.

The total estimated endowments for each zone are then 

summed. The estimated endowment for “concentration” grade 

gravel deposits of the eastern zone is 18,157,072.20 carats. 

When combined with the “basic” grade gravel endowments, 

the total estimated resource is 27,235,608.30 carats.

Results of the Content per Kilometer Approach

Tables 5 and 6 give the results of the content per 

kilometer approach. The total stream lengths are derived from 

the GIS for the contoured zones known to be diamondiferous. 

From the total length, percentages are derived according to 

the classification of the lengths into “very rich,” “rich,” and 

“poor” streams. For the western zone 10 percent of the total 

stream length is classified as very rich, 20 percent is classified 

as rich, and the remaining 70 percent is classified as poor. 

Similarly for the eastern zone, 5 percent of the total stream 

length is classified as very rich, 20 percent is classified as rich, 

and the remaining 75 percent is classified as poor.

Each classified stream length per zone is multiplied by 

the estimated content per kilometer and finally summed by 

zone. In the western zone, very rich deposits are estimated 

at 7,500 kt/km, rich deposits are estimated at 2,500 kt/km, 

and poor deposits are estimated at 850 kt/km. The eastern 

zone deposits are estimated to be slightly less rich than the 

western deposits. Therefore, very rich deposits are estimated 

at 6,000 kt/km, rich deposits are estimated at 1,500 kt/km, and 

poor deposits are estimated at 500 kt/km.

The total estimated deposits of the western zone, 

according to the content per kilometer approach, are 

37,055,662.90 carats. The total estimated deposits of the 

eastern zone, according to the content per kilometer approach, 

are 26,966,767.01 carats. 

(4)
Results

15

Table 3. Results of the volume and grade approach for calculating total diamond endowment for the western Central African Republic.[m3, cubic meter; kt/m3, carat per cubic meter; kt, carat]

Contour zone

(fig. 4)

Total volume 

of alluvium 

(m3)

Volume of basic 

grade gravels 

(3/4 of total) 

(m3)

T1 

(Basic grade) 

(kt/m3)

Estimated 

endowment 

of basic grade 

gravels 

(kt)

Volume of 

concentration 

grade gravels 

(1/4 of total) 

(m3)

T2 

(Concentration 

grade) 

(kt/m3)

Estimated 

endowment of 

concentration 

grade gravels 

(kt)

Estimated 

total 

endowment 

(kt)

Contour zone 1 63,160,529.00 47,370,396.75 0.05 2,368,519.84 15,790,132.25 0.40 6,316,052.90 8,684,572.74

Contour zone 2 2,823,703.00 2,117,777.25 0.05 105,888.86 705,925.75 0.40 282,370.30 388,259.16

Contour zone 3 360,850.00 270,637.50 0.05 13,531.88 90,212.50 0.40 36,085.00 49,616.88

Contour zone 4 3,474,242.00 2,605,681.50 0.05 130,284.08 868,560.50 0.40 347,424.20 477,708.28

Contour zone 5 163,620.00 122,715.00 0.05 6,135.75 40,905.00 0.40 16,362.00 22,497.75

Contour zone 6 1,708,004.00 1,281,003.00 0.05 64,050.15 427,001.00 0.40 170,800.40 234,850.55

Contour zone 7 144,298.00 108,223.50 0.05 5,411.18 36,074.50 0.40 14,429.80 19,840.98

Contour zone 8 3,641,489.00 2,731,116.75 0.05 136,555.84 910,372.25 0.40 364,148.90 500,704.74

Contour zone 9 223,165.00 167,373.75 0.05 8,368.69 55,791.25 0.40 22,316.50 30,685.19

Contour zone 10 11,100,230.00 8,325,172.50 0.05 416,258.63 2,775,057.50 0.40 1,110,023.00 1,526,281.63

Contour zone 11 30,836,456.00 23,127,342.00 0.05 1,156,367.10 7,709,114.00 0.40 3,083,645.60 4,240,012.70

Total 117,636,586.00 88,227,439.50 4,411,371.98 29,409,146.50 11,763,658.60 16,175,030.58

Complementary areas (drainages outside of zones)

Strahler order 6 7,491,480.00 5,618,610.00 0.05 280,930.50 1,872,870.00 0.40 749,148.00 1,030,078.50

Strahler order 7 21,899,570.00 16,424,677.50 0.05 821,233.88 5,474,892.50 0.40 2,189,957.00 3,011,190.88

Strahler order 8 65,537,760.00 49,153,320.00 0.05 2,457,666.00 16,384,440.00 0.40 6,553,776.00 9,011,442.00

Total 94,928,810.00 71,196,607.50 3,559,830.38 23,732,202.50 9,492,881.00 13,052,711.38

Estimated endowment of concentration grade gravels 21,256,539.60Total estimated endowment 29,227,741.95
16 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic Table 4. Results of the volume and grade approach for calculating total diamond endowment for the eastern Central African Republic. [m3, cubic meter; kt/m3, carat per cubic meter; kt, carat] Contour zone (fig. 5) Total volume of alluvium (m3) Volume of basic grade gravels (3/4 of total) (m3) T1 (Basic grade) (kt/m3) Estimated endowment of basic grade gravels (kt) Volume of concentration grade gravels (1/4 of total) (m3) T2 (Concentration grade) (kt/m3) Estimated endowment of concentration grade gravels (kt) Estimated total endowment (kt) Contour zone 1 247,069.00 185,301.75 0.05 9,265.09 61,767.25 0.30 18,530.18 27,795.26 Contour zone 2 5,112,401.00 3,834,300.75 0.05 191,715.04 1,278,100.25 0.30 383,430.08 575,145.11 Contour zone 3 676,599.00 507,449.25 0.05 25,372.46 169,149.75 0.30 50,744.93 76,117.39 Contour zone 4 50,088,950.00 37,566,712.50 0.05 1,878,335.63 12,522,237.50 0.30 3,756,671.25 5,635,006.88 Contour zone 5 26,389,620.00 19,792,215.00 0.05 989,610.75 6,597,405.00 0.30 1,979,221.50 2,968,832.25 Contour zone 6 28,154,775.00 21,116,081.25 0.05 1,055,804.06 7,038,693.75 0.30 2,111,608.13 3,167,412.19 Contour zone 7 7,390,256.00 5,542,692.00 0.05 277,134.60 1,847,564.00 0.30 554,269.20 831,403.80 Contour zone 8 6,384,885.00 4,788,663.75 0.05 239,433.19 1,596,221.25 0.30 478,866.38 718,299.56 Contour zone 9 4,633,572.00 3,475,179.00 0.05 173,758.95 1,158,393.00 0.30 347,517.90 521,276.85 Contour zone 10 572,880.00 429,660.00 0.05 21,483.00 143,220.00 0.30 42,966.00 64,449.00 Contour zone 11 8,804,331.00 6,603,248.25 0.05 330,162.41 2,201,082.75 0.30 660,324.83 990,487.24 Contour zone 12 323,728.00 242,796.00 0.05 12,139.80 80,932.00 0.30 24,279.60 36,419.40 Total 138,779,066.00 104,084,299.50 5,204,214.98 34,694,766.50 10,408,429.95 15,612,644.93 Complementary areas (drainage outside of zones) Drainage 1 103,315,230.00 77,486,422.50 0.05 3,874,321.13 25,828,807.50 0.30 7,748,642.25 11,622,963.38 Total 103,315,230.00 77,486,422.50 3,874,321.13 25,828,807.50 7,748,642.25 11,622,963.38 Estimated endowment of concentration grade gravels 18,157,072.20 Total estimated endowment 27,235,608.30
Results

17

Table 5. Results for the content per kilometer approach for calculating total diamond endowment for the western zone, Central African Republic. [kt/km, carat per kilometer; kt, carat]

Contour zone

(fig. 4)

Total 

stream 

length

L1 – 

10% of total 

length 

classified 

as very rich

T1 – 

Very rich 

streams 

(kt/km) 

Very rich 

stream 

calculated 

content 

(kt)

L2 – 

20% of total 

length 

classified 

as rich

T2 – 

Rich 

streams 

(kt/km)

Rich stream 

calculated 

content 

(kt)

L3 – 

70% of total 

length 

classified 

as poor

T3 – 

Poor 

streams 

(kt/km)

Poor stream 

calculated 

content 

(kt)

Total 

(kt)

Contour zone 1 12,385.74 1,238.57 7,500.00 9,289,305.00 2,477.15 2,500.00 6,192,870.00 8,670.02 850.00 7,369,515.30 22,866,187.47

Contour zone 2 467.77 46.78 7,500.00 350,827.50 93.55 2,500.00 233,885.00 327.44 850.00 278,323.15 866,806.64

Contour zone 3 154.31 15.43 7,500.00 115,732.50 30.86 2,500.00 77,155.00 108.02 850.00 91,814.45 288,190.83

Contour zone 4 296.27 29.63 7,500.00 222,202.50 59.25 2,500.00 148,135.00 207.39 850.00 176,280.65 550,234.79

Contour zone 5 58.57 5.86 7,500.00 43,927.50 11.71 2,500.00 29,285.00 41.00 850.00 34,849.15 111,464.36

Contour zone 6 608.38 60.84 7,500.00 456,285.00 121.68 2,500.00 304,190.00 425.87 850.00 361,986.10 1,126,358.64

Contour zone 7 56.99 5.70 7,500.00 42,742.50 11.40 2,500.00 28,495.00 39.89 850.00 33,909.05 108,547.84

Contour zone 8 827.30 82.73 7,500.00 620,475.00 165.46 2,500.00 413,650.00 579.11 850.00 492,243.50 1,530,463.07

Contour zone 9 90.38 9.04 7,500.00 67,785.00 18.08 2,500.00 45,190.00 63.27 850.00 53,776.10 170,182.44

Contour zone 10 669.37 66.94 7,500.00 502,027.50 133.87 2,500.00 334,685.00 468.56 850.00 398,275.15 1,238,940.08

Contour zone 11 3,461.91 346.19 7,500.00 2,596,432.50 692.38 2,500.00 1,730,955.00 2,423.34 850.00 2,059,836.45 6,393,689.67

Total 19,076.99 14,307,742.50 9,538,495.00 11,350,809.05 35,251,065.84

Complementary areas (drainages outside of zones)

Strahler order 6 249.72 24.97 7,500.00 187,290.00 49.94 2,500.00 124,860.00 174.80 850.00 148,583.40 464,308.15

Strahler order 7 312.85 31.29 7,500.00 234,637.50 62.57 2,500.00 156,425.00 219.00 850.00 186,145.75 580,839.82

Strahler order 8 409.61 40.96 7,500.00 307,207.50 81.92 2,500.00 204,805.00 286.73 850.00 243,717.95 759,449.10

Total 972.18 729,135.00 486,090.00 578,447.10 1,804,597.06Estimated endowment of concentration zones (very rich stream calculated content + rich stream 

calculated content) 25,061,462.50

Total estimated endowment 37,055,662.90
18 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic Table 6. Results for the content per kilometer approach for calculating total diamond endowment for the eastern zone, Central African Republic. [kt/km, carat per kilometer; kt, carat] Contour zone (fig. 5) Total stream length L1 – 5% of total length classified as very rich T1 – Very rich streams (kt/km) Very rich stream calculated content (kt) L2 – 20% of total length classified as rich T2 – Rich streams (kt/km) Rich stream calculated content (kt) L3 – 75% of total length classified as poor T3 – Poor streams (kt/km) Poor stream calculated content (kt) Total (kt) Contour zone 1 83.20 4.16 6,000.00 24,960.00 16.64 1,500.00 24,960.00 62.40 500.00 31,200.00 83,199.04 Contour zone 2 1,382.44 69.12 6,000.00 414,732.00 276.49 1,500.00 414,732.00 1,036.83 500.00 518,415.00 1,351,192.32 Contour zone 3 268.44 13.42 6,000.00 80,532.00 53.69 1,500.00 80,532.00 201.33 500.00 100,665.00 263,984.02 Contour zone 4 12,125.33 606.27 6,000.00 3,637,599.00 2,425.07 1,500.00 3,637,599.00 9,094.00 500.00 4,546,998.75 11,835,715.81 Contour zone 5 3,831.47 191.57 6,000.00 1,149,441.00 766.29 1,500.00 1,149,441.00 2,873.60 500.00 1,436,801.25 3,741,323.15 Contour zone 6 3,773.84 188.69 6,000.00 1,132,152.00 754.77 1,500.00 1,132,152.00 2,830.38 500.00 1,415,190.00 3,685,079.15 Contour zone 7 1,095.37 54.77 6,000.00 328,611.00 219.07 1,500.00 328,611.00 821.53 500.00 410,763.75 1,071,026.35 Contour zone 8 1,795.03 89.75 6,000.00 538,509.00 359.01 1,500.00 538,509.00 1,346.27 500.00 673,136.25 1,753,859.53 Contour zone 9 1,223.54 61.18 6,000.00 367,062.00 244.71 1,500.00 367,062.00 917.66 500.00 458,827.50 1,196,113.86 Contour zone 10 171.43 8.57 6,000.00 51,429.00 34.29 1,500.00 51,429.00 128.57 500.00 64,286.25 169,307.11 Contour zone 11 1,150.44 57.52 6,000.00 345,132.00 230.09 1,500.00 345,132.00 862.83 500.00 431,415.00 1,124,771.92 Contour zone 12 118.17 5.91 6,000.00 35,451.00 23.63 1,500.00 35,451.00 88.63 500.00 44,313.75 117,328.01 Total 27,018.70 8,105,610.00 8,105,610.00 10,132,012.50 26,275,572.25 Complementary areas (drainage outside of zones) Drainage 1 930.69 46.53 4,000.00 186,138.00 186.14 1,200.00 223,365.60 698.02 400.00 279,207.00 691,194.76 Total 930.69 186,138.00 223,365.60 279,207.00 691,194.76 Estimated endowment of concentration zones (very rich stream calculated content + rich stream calculated content) 16,620,723.60 Total estimated endowment 26,966,767.01
Conclusions 19

Speculative calculations were performed for the diamond 

resources of the eastern plateau (table 7). This estimation is a 

result of the surface-area approach to estimating the diamond 

resources of the Mouka-Ouadda Plateau. The total surface 

area of the plateau is derived from the GIS for the current 

extent of the Cretaceous sandstone of the eastern zone. A 

“basic” grade of 0.01 kt/m3 is applied to 75 percent of the 

total surface area, and a “concentration” grade of 0.30 kt/m3 is 

applied to the remaining 25 percent. Concentration gravels are 

estimated to be 0.80 m thick, and basic gravels are estimated 

at 0.20 m thick. From these parameters, an inferred total of 

reserve diamond resources is calculated for the plateau of 

3,568,084.74 carats.

Table 8 gives the results of the estimated diamond 

resource endowment for the estimated remaining diamonds 

of both the western and eastern plateaus. This table lists the 

estimated endowments of both “basic” and “concentration” 

grades from both methods. Subtracted from these estimated 

total endowments are the total amounts of diamonds that have 

been documented to have been exported from the CAR since 

1931. The remaining amount is the estimated total endowment 

of the CAR diamond resources.

The mean total estimated diamond resources remaining 

in the CAR are calculated to be a total of 39,185,397.98 carats. 

The total remaining resources within concentration diamond 

zones are calculated to be 26,482,116.05 carats. The total 

remaining resources are calculated to be approximately twice 

the total historical production of diamonds exported from the 

CAR since 1931.

Diamond-Production Capacity Results

The diamond-production capacity model was used to 

calculate the estimated production capacity of the CAR. Based 

on observations made in the field during the two field excursions, the following parameters were developed. The grade 

(g) parameter used for the evaluation is the mean value of the 

eastern and western zones and is 0.35 kt/m3. Human mining 

activity (Vm/j) is calculated to be 0.2 m3 per miner per day 

and takes into account the highly variable situations across the 

country and also incorporates the overall stripping ratio range 

of approximately from 0 to 30:1 for the deposits. The total 

number of days (j) worked is estimated to be 200 days a year 

and takes into account seasonal variables and inaccessibility 

of many of the deposits during the rainy season. The total 

number of diggers estimated during reconnaissance fieldwork 

(Ai

), including artisans and registered workers, is 8,500, but 

the total number of artisans and workers is estimated to be 

60,000 including hired permanent workers. The total number 

of diggers ranges from 60,000 to 90,000. The production 

potential was calculated using about 60,000 workers based 

on BRGM documentation of licensed artisanal miners 

(~8,500) × 5–10 diggers for each team of hired diggers.

Given the parameters above, the calculation of production 

capacity from equation 4 is given as

840,000 (0.2 0.35) 200 60,000. = × × ×

The results of this estimated model are higher than the current 

annual production of approximately 450,000 carats per year. 

Part of the reason for this result is that many of the diamond 

areas are not currently mined because of their remote nature, 

unsecured status, and unproductive workings. Therefore, this 

estimation should be considered an ideal evaluation that could 

be attainable given the best possible conditions, not a realistic 

view that is based on actual conditions. 

Conclusions

The goal of this study was to estimate the alluvialdiamond resource endowment and to estimate the current 

production capacity of the alluvial-diamond mining sector 

of the Central African Republic. Two models were used to 

conduct the alluvial-diamond resource assessment. First, 

diamond resources were estimated by using a volume and 

grade approach. Second, the resource was estimated using the 

content per kilometer approach. The production capacity of 

the sector was estimated using a formulaic expression of the 

number of workers reported in the sector, their productivity, 

and the average grade of deposits mined. 

It remains challenging to acquire data at the level of 

detail required to accurately estimate the parameters for 

alluvial diamond resources. In this study, calculations were 

made on the basis of modeling of the parameters of alluvial 

deposits, grades of deposits, and human resources engaged in 

the artisanal mining sector. Alluvial flat widths and volume 

calculations, diamond-deposit grade data, and the number and 

location of active mining sites are some of the more significant 

components of this study that could be improved with more 

detailed data-gathering efforts.

Alluvial flat widths were modeled as a dependent variable 

to the stream order. While these flat widths were selectively 

measured in the field, it is understood that there is a great deal 

more variability in the width of alluvial flats than is modeled 

using the basic approach of this study. The stream ordering 

technique itself is also highly dependent on the digital elevation model and derived hydrologic network. 

The known grades of alluvial diamond deposits in the 

CAR have largely been taken from previously published 

studies and geologic investigations. These studies were 

conducted only for certain areas and were not conducted 

recently. Therefore, more information on the grades of 

deposits throughout the CAR would assist in developing a 

more detailed analysis of endowment and worker productivity. 

However, gathering data on the grades of diamond deposits 

requires extended periods of time in the field to conduct 

appropriate sampling methodologies.

This study estimates that there are approximately 

39,000,000 carats of alluvial diamonds remaining in both the 

western and eastern zones of the CAR. This figure is roughly 

twice the total amount of diamonds reported to have been 

exported from the CAR since 1931. Production capacity is (5)
20 Alluvial Diamond Resource Potential and Production Capacity Assessment of the Central African Republic Table 7. Inferred and speculative diamond resources of the eastern plateau, Central African Republic. [m2, square meter; m, meter; m3, cubic meter; kt/m3, carat per cubic meter; kt, carat] Total surface area of eastern plateau (m2

)

Surface area 

of plateau 

covered by 

basic grade 

gravels 

(75% of 

total area)

 Basic grade 

gravel 

thickness 

(m)

Estimated 

volume of 

basic grade 

diamondiferous 

gravels 

(m3

)

 Basic gravel 

grade 

(kt/m3)

Diamond 

resources 

of basic 

grade gravels 

on plateau 

(kt)

Surface area 

of plateau 

covered by 

concentration 

grade gravels 

(25% of 

total area)

Concentration 

grade gravel 

thickness 

(m)

Estimated 

volume of 

concentration 

grade 

diamondiferous 

gravels 

(m3)

Concentration 

gravel 

grade 

(kt/m3

)

Diamond 

resources of 

concentration 

grade gravels 

on plateau 

(kt)

58,017,638.00 43,513,228.50 0.20 8,702,645.70 0.01 87,026.46 14,504,409.50 0.80 11,603,527.60 0.30 3,481,058.28

Total 87,026.46 3,481,058.28

Speculative diamond endowment of the concentration grade gravels of the eastern plateau, CAR, surface area approach 3,481,058.28Total speculative diamond edowment of the eastern plateau, CAR, surface area approach 3,568,084.74

Table 8. Summary of estimated diamond-resource endowments of the Central African Republic.[kt, carat] 

Zone

Total estimated 

resources, 

volume 

and grade 

approach 

(kt)

Total estimated 

concentration 

zone resources, 

volume and grade 

approach 

(kt)

Total estimated 

resources, 

content per 

kilometer 

approach 

(kt)

Total estimated 

concentration 

zone resources, 

content per 

kilometer 

approach 

(kt)

Total 

estimated 

resources, 

surface area 

approach 

(kt)

Total estimated 

concentration 

zone resources, 

surface area 

approach 

(kt)

Mean total 

estimated 

resources 

(kt)

Mean total 

estimated 

concentration 

zone 

resources 

(kt)

Western zone 29,227,742.00 21,256,540.00 36,990,718.65 25,061,462.50 33,109,230.33 23,159,001.25

Eastern zone 27,235,608.30 18,157,072.00 26,916,727.00 16,620,723.60 27,076,167.65 17,388,897.80

Berm of the High Terrace (Eastern zone) 3,568,084.00 3,481,058.00Total resources 56,463,350.30 39,413,612.00 63,907,445.65 41,682,186.10 60,185,397.98 40,547,899.05

Historical past production from 1931 to 2006 21,000,000.00 14,065,783.00

Total resources remaining 39,185,397.98 26,482,116.05
References Cited 21

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resource grades, worker productivity, and the number and 

locations of sites currently being worked. Annual production 

is highly dependent on national security and stability, the 

numbers of seasonal workers actively mining in the sector, and 

environmental conditions that influence seasonal farming. 

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