The document summarizes alluvial diamond mining in Angola. It discusses sampling methods used to evaluate placer deposits for diamonds, including grab samples, excavations, and drilling. Key challenges with placer sampling involve large rocks obscuring finer materials and ensuring samples are not unintentionally enriched. Accurate record keeping of sample data is also essential for reserve estimation. The document then outlines various methods used to estimate reserves and value placer diamond deposits. Careful consideration of geological conditions is important when selecting appropriate sampling and evaluation techniques.

1. ALLUVIAL
DIAMONDS
Retrospect & Prospect
By
S.G SURENDER

2. “All works of history are interim reports,
what people did in the past is not
preserved in amber……Each generation
looks back and drawing from its own
experience and presumes to find patterns
tat illustrate past and present”.
-- John Noble Wilfred

3. Introduction
“A mineral is defined as a naturally occurring
homogenous solid with a definite chemical
composition and highly ordered atomic structure”.
Minerals with their intricate properties, that marks
its presence in the industry.
Diamond the mineral form of element carbon, the
mere mention of its word fills the mind with
multitude of concepts and images. Peerless “King
of Gems” that glitters, dazzles that symbolizes
purity and strength.

4. Diamond is indomitable the hardest substance known;
with exceptional qualities that collectively makes it an
important social, industrial and scientific material.
Diamond is likely one of the oldest thing that a
man would posses; 3 million years in age;
(two thirds the age of

5. Classification
Bruton (1978), have classified diamonds into
three major groups
DIAMOND
GEM INDUSTRIAL DIAMOND
DIAMONDS STONES BORT*
Shaped Rough
Diamonds Stones
* bort- Minutely and randomly crystallized and shapeless diamond
extremely hard and has high abrasive value.

6. Properties and Uses
 Category Native Nonmetal,
 Mineral Chemical formula: Carbon, C
 Identification Color Most often colorless to yellow or brown.
Rarely pink, orange, green or blue.
 Crystal habit: Octahedral, spherical or massive;
 Crystal system: Isometric
 Cleavage: Octahedral; perfect and easy
 Fracture: Conchoidal
 Mohs Scale: hardness10
 Luster :Adamantine to greasy
 Refractive index: 2.417
 Pleochroism: None; Streak: None; Specific gravity: 3.516–3.525
 Fusibility: Burns above 800°C, melting point 3550 °C
 Solubility: Resistant to acids, but melts in hot steel Diaphaneity
Clear to not
 Major varieties Ballas Spherical, radial structure, cryptocrystalline,
opaque black Bort Poorly-formed, cryptocrystalline, shapeless,
translucent, Carbonado Massive, microcrystalline, opaque black.

7. Due to its exceptional properties diamond is used for a
variety of purposes, namely:
 Due to its hardness; diamond is either used as single
crystals or finely ground powder are used in cutting
abrading, polishing tools. (it is imbedded in another
material and used as a tool or abrasive).
 Industrial diamond are extensively used in drill bits
& cutting devices.
 Other applications include their use in mining,
electronic, optical, thermal, machining, dentistry
and medicinal industries.
 Scientific applications include radiation, photo
detection, etc.

8. MARKET
 Of the several billion dollars of annual transaction in
gems, 90% of the value are accounted for by diamonds.
 80% Eighty percent of the diamonds mined annually are
used in industry; 4 times that production is grown
synthetically for industry - that's a total of over 500
million carats or 100 metric tons.
 Compared to most other gem minerals the percentage of
gem quality crystals recovered is quite high in diamond.
20% of the diamond is of gem quality.

9. Brief Geology of Angola
THE GEOLOGY OF ANGOLA IS RELATIVELY
COMPLEX, IMPERFECTLY KNOWN IN SPITE OF A BIG
RECENT PROGRESS, THE FORMATIONS BEING
DISTRIBUTED PARALLEL TO THE COAST, NNW TO THE
NORTH, NNE TO THE SOUTH.
The CrysTalline BasemenT; a Big parT of The
CounTry is formed By The preCamBrian
BasemenT of The "Basis Complex", wiTh Twi
very Big BaTholiThs of graniTe To The n. and
To The s. of The Cuanza. The exTreme ne is a
parT of The very old Kasaï shield (2,500 my
or more); a zone TheoreTiCally favoraBle To
The KimBerliTiC inTrusions.

10. The Study Area

11. Alluvial Diamonds- Chitamba Area

12. Economic viability & Feasibility of the
Chitamba Area for alluvial diamonds.

13. FIELD
PHOTOGRAPHS

16. SAMPLING METHODS
The sampling methods vary from simple grab samples on
existing exposures to sophisticated drilling methods. The
disposition and density of sampling must be adapted to each
placer. The rule is: "A minimum of samples for a maximum
of information.
Existing Exposures
Hand-Dug Excavations ( Pits & Trenches)
Backhoe Trenches
Bulldozer Trenches
Churn Drills

17. Other Machine-Dug Excavations
 Machine-dug excavations are shafts or pits that
are dug using powered equipment such as large
augers, bucket drills, or clamshell-type
excavators. Digging shafts with the aid of
powered equipment requires experienced
operators and suitable machine access. Dry,
stable ground is also needed for successful
sampling operations when digging shafts and
pits.

19. Some of the Special Problems Associated
with Placer Sampling
Large Rocks and Boulders: In sampling alluvial, there is
a tendency to bypass areas containing many boulders or
to sample the easily collected finer material around the
boulders. In many cases, this is essentially salting the
sample since the valuable material in a placer deposit
usually occurs in the finer material.
Uncased Holes: The use of uncased drill holes should be
discouraged in placer sampling, especially in sampling
ground with a high unit value mineral. If uncased holes
are used, there is a tendency to unintentionally salt the
sample and get overvalued sample results.

20. Data Processing and Record Keeping
Accurate, systematic records must be kept for proper placer
evaluation. As an example, data that must be recorded on a
log sheet when churn drilling a placer gold deposit
includes:
1) Name of property
2) Location
3) Date
4) Pits – trench hole line number
5) Hole number
6) Hole collar elevation
7) Time (the time is given for each bailing. A summary of
time consumed in drilling, pulling, moving, repairs, etc. )
8) Depth of the drive shoe for each sample interval
9) Depth of pumping for each drive or sample interval

21. 10) Total hole depth
11) Core rise in the pipe for each drive
14) Volume bucket measurement
18) Depth and nature of overburden
19) Labour used
20) Depth of the pay gravel
21) Depth to bedrock
22) Nature of bedrock
23) Thickness of pay zone
24) Diameter of the drive shoe
30) Value in milligrams, grams or cents per cubic meter
(cubic yard)
31) Price of gold used in calculations if cents per volume are
used
32) Signature of the driller, panner, and helper

22. RENDERING POINTS
 The detailed records can be efficiently used to
determine the value of the deposit and its
mineablity.
 Information obtained from the drill logs can be
used in selecting its mining method.
 The value of the placer material is reported as
bank cubic yards.

24. Reserve Estimation and Valuation
After samples have been collected, washed, and assayed,
reserves for a deposit can be estimated. There are many
placer reserve estimation methods available. Some of these
are the block, triangle, polygonal, traverses, and diamond
methods.
Methods that can be used for reserve estimation and
placer valuation are:
(1) block method
(2) triangle method
(3) polygonal method
(4) cross-section method
(5) method of diamonds.

25. CONCLUSION
 It is important to remember to use care in sampling and to
select the method that best suits the type of occurrence
that is being sampled
 Placers formed in cold climates like Alaska or Yukon, are
very different from tropical placers formed under
laterization processes.
 Geological Province/Terrain characteristics must be kept
in consent.
 Prospection for one mineral may lead to the discovery of
many other essential minerals.

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