U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2012–3128

November 2012

Prepared under the auspices of the U.S. Department of State

A Methodology for Conducting National-Scale Alluvial 

Diamond Resource Potential and Production Capacity 

Assessments, with a Focus on Artisanal Mining

Introduction

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

South Africa, by representatives of the diamond industry and 

leaders of African governments to develop a certification process intended to assure that export shipments of rough diamonds 

were free of conflict concerns. Outcomes of the meeting were 

formally supported later in December of 2000 by the United 

Nations in a resolution adopted by the General Assembly. By 

2002, the Kimberley Process Certification Scheme was ratified and signed by diamond-producing and diamond-importing 

countries. As of August 2012, the Kimberley Process (KP) had 

51 participants representing 77 countries.

It is often difficult to obtain independent verification of the 

diamond production statistics that are provided to the KP. However, some degree of independent verification can be obtained 

through an understanding of a country’s naturally occurring 

endowment of diamonds and the intensity of mining activities. Studies that integrate these two components can produce a 

range of estimated values for a country’s diamond production, 

and these estimates can then be compared to the production 

statistics released by that country.

This methodology is used to calculate (1) the diamond 

resource potential of a country, which refers to the total number 

of carats estimated to be remaining in the country, and (2) the 

diamond production capacity of a country, which is the current 

volume of diamonds that may realistically be produced per year 

utilizing current human and physical resources. The following 

sections outline the methodology used by the U.S. Geological 

Survey (USGS) to perform diamond assessments in Mali, the 

Central African Republic, Ghana, and Guinea (Chirico and 

others 2010a, b, c; in press).

Figure 1. A satellite image 

of a mining site in Guinea. 

The visible mining areas have 

been delineated in red and 

added to the digital database 

of diamond occurrences. The 

USGS GPS track route is from 

fieldwork done in March 2010. 

13°03'W 13°02'30"W

9°27'N

0 50 100 150 200 METERS

0 250 500 FEET

Background image from ALOS PRISM, March 4, 2010

Other base features from U.S. Geological Survey digital files

EXPLANATION

Current and

 (or) historical 

 mining activity

USGS track route

Village

Printed on recycled paper
Oda

Kade

Aduasa

Wenchi

Edubia

Akwatia

Ntronang

Akim

Swedru

1°10'W 1°0'W 0°50'W

6°10'N

6°0'N

5°50'N

0

0 1 2 3 4 5 MILES

5 10 KILOMETERS

EXPLANATION

Reserve type Watershed

Strahler stream 

 order

Diamond

 occurrence

Indicated

Proven

Diamond 

 workings

3

4

5

6

7

Base modified from Survey Department of Ghana, 1997

Figure 2. The hydrologic model produced for the Birim watershed, Ghana.

Methodology

Bibliographic and Historical Research 

The first step of the methodology includes the research, 

collection, and organization of all available data related to 

diamond resources and production in the country of interest. 

All available reports documenting occurrences of diamonds 

are collected, including reports by private mining companies, 

geophysical studies, geologic maps, and journal articles. A 

digital database of diamond occurrences is then developed from 

these sources. The digital database consists of a record for each 

known occurrence with attribute information on the size of the 

deposit, grade, and so on.

Field Assessment

Field mapping is conducted at several sites within the 

study area in order to develop a database of information on the 

terrain, geomorphology, geology, mineral deposits, and current 

mining activities of the area. To ensure the accurate and consistent collection of data, a comprehensive questionnaire was 

developed and is used in gathering information in the field. The 

data gathered during the field assessment are then incorporated 

into the digital database of diamond occurrences.

Remote Sensing

Satellite imagery of the study sites is acquired and analyzed to map the extent of all visible diamond mining areas 

(fig. 1). Satellite images can also be used to document whether a 

site is active or inactive or to map changes over time at the site. 

This technique involves using imagery to estimate the volume 

of material worked at a site, and this information helps to determine the productivity of miners at a deposit.
Oda

Kade

Aduasa

Wenchi

Edubia

Akwatia

Ntronang

Akim

Swedru

1°10'W 1°0'W 0°50'W

6°10'N

6°0'N

5°50'N

0

0 1 2 3 4 5 MILES

5 10 KILOMETERS

EXPLANATION

Reserve type Geomorphology Strahler 

 stream 

 order

Diamond

 occurrence

Indicated

Proven

Diamond 

 workings

Alluvial flat

Low terrace

High terrace

Upland 

3

4

5

6

7

Base modified from Survey Department of Ghana, 1997

Figure 3. The geomorphic model produced for the Birim watershed, Ghana.

Geographic Information Systems

Occurrences in the diamond database are attributed with 

geographic coordinates so that the occurrences can be mapped 

and the spatial distribution of the deposits can be examined in a 

geographic information system (GIS). The locations of occurrences are then used in further hydrologic and geomorphic 

modeling of the diamond mining areas.

Hydrologic Analysis

A GIS model of diamond-bearing river basins is created 

from a digital elevation model (DEM) using the Strahler (1964) 

stream order system (fig. 2). The analysis is performed only 

on subbasins containing a diamond occurrence, as it is often 

unlikely that the entire watershed is diamondiferous. The logic 

behind the Strahler system is that the stream order number is 

directly proportional to the size of the contributing watershed, 

to channel dimensions, and to stream-discharge measurements 

for each stream segment. Typically, the hydrologic model 

develops subbasins for Strahler order 2 and higher stream 

segments, although order 1 segments may also be delineated 

for site-specific analysis.

Geomorphic Modeling

Closely related to the hydrologic analysis, the geomorphic model uses a DEM to calculate the geographic extent of 

the alluvial flat, low terrace, and high terrace landforms within 

each of the diamondiferous subbasins (fig. 3). Mapping the 

geomorphology is critical, as previous research has established 

that diamond deposit grades are correlated with their location in 

either alluvial flat or terrace formations. Using the geomorphic 

model, the volume and grade of deposits in the selected subbasins are calculated on the basis of surface area of the flats and 

terraces, available grade data, and geomorphic measurements 

of the diamondiferous gravel layer thickness determined from 

field measurements. 
Diamond Resource Potential Formula

Diamond resource potential is calculated using the volume 

and grade methodological approach. This mathematical analysis relies on volume and grade data. The volume of alluvium is 

determined by estimating the width of the alluvial flat deposit 

and multiplying it by the thickness of the gravel layer being 

mined. Different gravel deposits may have higher concentrations of diamonds, so to account for these variations two gravel 

grades are typically used in the formula. The first is the “basic” 

grade and is applied to a large percentage of the alluvial gravels, 

while the second is the “concentration” grade and is applied to 

the remaining percentage of the alluvial gravels. The ratio of 

“basic” to “concentration” grade gravels is determined on the 

basis of the characteristics of the specific study area.

Diamond Production Capacity Formula

A mathematical formula is also used to calculate diamond 

production capacity. This formula relies on the following variables: the volume of material worked per digger per day, the 

average gravel grade, the total number of days a digger works 

per year, estimated industrial production, and the total number 

of diggers estimated to be actively mining diamonds.

Conclusion

This methodology provides a quantitative analytical 

technique that may be used to assess alluvial diamond 

resources. The results of the methodology are limited by the 

availability of input data, yet the results provide a basic level 

of information on reserves and capacity. As more data are 

collected, these estimates may be recalculated to produce results 

with greater accuracy.

References Cited

Chirico, P.G., Barthélémy, Francis, and Koné, Fatiaga, 2010a, 

Alluvial diamond resource potential and production capacity 

assessment of Mali: U.S. Geological Survey Scientific Investigations Report 2010–5044, 23 p.

Chirico, P.G., Barthélémy, Francis, and Ngbokoto, F.A., 2010b, 

Alluvial diamond resource potential and production capacity 

assessment of the Central African Republic: U.S. Geological 

Survey Scientific Investigations Report 2010–5043, 22 p.

Chirico, P.G., Malpeli, K.C., Anum, Solomon, and Phillips, 

E.C., 2010c, Alluvial diamond resource potential and production capacity assessment of Ghana: U.S. Geological Survey 

Scientific Investigations Report 2010–5045, 25 p. 

Chirico, P.G., Malpeli, K.C., Van Bockstael, Mark, Diaby, 

Mamadou, Cissé, Kabinet, Diallo, T.A., and Sano, Mahmoud, 

in press, Alluvial diamond resource potential and production capacity assessment of Guinea: U.S. Geological Survey 

Scientific Investigations Report.

Strahler, A.N., 1964, Quantitative geomorphology of drainage 

basins and channel networks, in Chow, V.T., ed., Handbook 

of applied hydrology: McGraw-Hill, p. 4 – 40.

Additional Information

Peter G. Chirico

12201 Sunrise Valley Drive

National Center, MS 926A

Reston, VA 20192

pchirico@usgs.gov

Katherine C. Malpeli

12201 Sunrise Valley Drive

National Center, MS 926A

Reston, VA 20192

kmalpeli@usgs.gov

An artisanal mine site visited during fieldwork in Forécariah, Guinea.