1. A PROPER APPROACH TO PROSPECTING OF PEGMATITES FOR
GEMSTONE: A GUIDE TO SMALL SCALE MINERS IN MALAWI.
Grain W.P. Malunga MIMM
ABSTRACT
Gemstones are precious and semi precious stones which are suitable for cutting as gems. Common gemstones in
Malawi belong to tourmaline, garnet, quartz, beryl and corundum. Most of these gemstones are found in proterozoic
pegmatites of northern Malawi
Gemstone mining in Malawi is a recent activity and mainly involves mining of aquamarine. Most mines emerged after
discovery of the stones in top soil as float. Most prospectors have spent a lot of money due to lack of proper
prospecting, evaluation and grading of these stones before taking them for marketing.
1.0 INTRODUCTION
Pegmatite is a term applied to graphic granite which is an extremely coarse
grained rock containing the worlds largest crystals which can be choicest
mineral specimens as well. The dominant mineral constituent is alkali
feldspar associated with quartz and white mica. Accessory minerals include
lanthanides and gemstones. The northern region of Malawi has the largest
dyke swarm of granitic pegmatites extending into Zambia and
Tanzania/Mozambique (trending NE)
Of specific interest in the pegmatites, for Malawi prospectors are gemstones
stones which are suitable for cutting as gems. Well-known gemstones, here,
include tourmaline, garnet, quartz, beryl and corundum, although some topaz
may be found. Below are the constituents of the minerals mentioned above:
TOURMALINE
Its gem varieties are
• verdelite, a light green variety owing its colour to ferrous iron,
• pink rubellite whose colour comes from the presence of
manganese,
• dravite, rich in magnesium giving it a brown colour
• And indicolite which is blue probably due to the presence of iron
and manganese.
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2. GARNET
The famous gem variety of garnet is
- rhodolite bearing a rose like colour corresponding with the presence
of 2 pyrope and 1 almandite,
- and almandite which is sometimes called almond stone.
QUARTZ
Known almost to every prospector or small scale miner (SSM) in this
category is amethyst although other varieties listed below exist.
- smoky quartz having a brownish colour due to the presence of
aluminium and the effect of radio activity bombardment.
- rose quartz, having rosy colour due to the presence of manganese
and /or lithium, sodium and titanium.
- amethyst, a purple or bluish-violet quartz having its colour from the
presence of iron.
- blue quartz, this is blue due to the inclusion of tiny needles of
tourmaline,
- citrine which is yellow quartz
- and clear or colourless quartz known as rock crystal.
BERYL
- aquamarine, this is clear transparent bearing pale green yellowish
green or bluish green colours. The most common gem stone in the
region.
- emerald is grass green in colour. Although mostly restricted to
metamorphic paragenesis, it has been observed in Mzimba pegmatites
(Chatupa J.; 1977).
- heliodor; this is amber or golden yellow.
- morganite, a pink variety.
The last three gem stones are rare in the region. Emeralds have been found
in Mzimba while a few heliodors have been found in Chitipa-Karonga area.
CORUNDUM
Although it is restricted to syenitic pegmatites, its occurrence has been noted
in granitic pegmatites.
- ruby is dark red and rich in chromium.
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3. - sapphire is common and has a clear blue colour although white, pink,
yellow and green varieties exist. The blue sapphire owes its colour to
the presence of iron and titanium while the yellow and green varieties
are a result of varying amounts of ferric and ferrous iron in them.
- topaz is used as a gem especially when it is yellow in colour.
1.2 HISTORICAL BACKGROUND OF GEMSTONE MINING IN
MALAWI
Most SSMs have gone straight into mining without carrying out systematic
prospecting but have discovered the stones in their gardens or farms as float.
This is mainly true for Euthini, Mpherembe, Kafukule and Mtantha areas in
Mzimba District. Some people with the knowledge of the Mines and
Minerals act have applied for Non Exclusive Prospecting Licences (NEPL)
and eventually applied for Mining Claims (MC) to start mining. Others
have used the NEPLS to sell their stones and sometimes to start mining.
The rest have picked the stones and kept them in pots in their houses not
knowing where to sell them.
A majority of the miners and prospectors have had their knowledge of
gemstones from Zambia but have lacked an economical approach to
prospecting. This has cost them a lot of money. Those who have nearly
exhausted their money before finding any gemstone have managed to pull
through by buying stones from the people with NEPL or the local farmers
who have kept their stones in pots.
This paper tries to advise on the proper approach to prospecting for
gemstones so that maximum economy is exercised to save money and time;
and indeed to educate people on the proper way of mining.
2.0 PROSPECTING PROCEDURES
2.1 AREA SELECTION
After being issued an NEPL by the Commissioner for Mines and
Minerals, Area selection should be affected and this involves desk
studies using geological bulletins and unpublished technical reports
produced by the Department of Geological Survey (GSD). Maps are
studied to locate pegmatite occurrences.
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4. Since NEPLs are issued for the whole district, area selection aims at
selecting target area for prospecting within the district. These areas
are usually metamorphic regions intruded by pegmatites of granitic
affinities in which the gemstones are found.
It is recommended that satellite photos (landsat image) and aerial
photos be used n tracing lineaments or ridges. These are usually
associated with pegmatites. The only problem here is that most SSMs
are not qualified enough to do remote sensing, not to mention that
these photos are expensive.
In conclusion, area selection enables people to select areas where they
are going to do field investigations. The tools to be used during area
selection are geological reports and maps, landsat imagery and aerial
photos and their accessories such as stereoscopes, tracing papers, pens
and pencils and mathematical sets.
2.2 FIELD INVESTIGATIONS
The equipment associated with field investigation/work comprises of,
camping gear, a geological hammer, a compass, a camper’s axe,
panga knives, a field note book, aerial photos, hand lens
(Magnification x6) and a hardness testing hard steel knife or pencil.
The existence of pegmatites can be known through observation of
float material, shrubs and trees, colour contrasts, topography and
sampling of scree:
o float material exists in form of gemstones themselves as for the
Euthini and Mtantha cases for aquamarine. Look for quartz,
tourmaline and mica floats.
o Most buried pegmatites are over lain with grass or shrubs.
Close examination may reveal outcrops of quartz or mica.
o Look out for colour contrasts. Different rock types weather to
form topsoil with different colours. Hornblende biotite gneisses
may weather to form reddish sandy clays while pegmatites
(quartz feldspar + mica and tourmaline) may weather to form
whitish to brownish sandy clays. For pegmatites the colour
contrasts may spread in form of irregular segregations and
linear shapes mixed with quartz.
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5. o Topography: generally pegmatites are more resistant than their
host rocks. This results into formation of pegmatites ridges
occurring in form of irregular segregations.
o Sampling of scree covering stones of a hill may lead to
knowledge of whether a hill or cliff is a pegmatitic body or not.
o Stream sediments if panned may contain some gemstones or
pegmatitic mineral assemblage
This may help identify pegmatites within the vicinity.
In conclusion, field investigation should involve identification of float
material, vegetation type, soil colour contrasts, topography, scree and
panned concentrates from stream sediments.
The field team should consist of at least a prospector and two chain
men.
2.3 EVALUATION AND ASSESSMENT
Once the pegmatites have been identified, trenching and pitting
commences in order to see if they bear gemstones.
o trenching should always be across pegmatites to save time and
money. The trenches should be spaced at a distance of about 10
metres. Pitting should usually be done where soil colour
contrasts exists just to reach weathered debris or bed rock.
The depth of the trenches and pits will be determined by the nature of
material found. If trenches and pits are dug up to 1.5m and no
gemstone is found, it may be worthy abandoning them. If weathered
or “rotten” gemstones are found, dig until you find no more as it is
possible that at greater depths good gemstones may be recovered-even
if water table is reached. After gemstones have been found and
sampled, the samples must be examined to see if they are valuable.
o examination of samples concerns mainly an establishment of
grade of material. This is through establishment of colour,
cloudiness, size, hardness and refraction.
o Gemstone colour (chroma or hue) range from colourless to
black. The more brown and grey colour is the less desirable.
This is worthy observing.
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6. o Cloudiness of gemstones is an effect of the existences of
inclusions and pits. This can be observed by exposing the stone
to light. The way a gemstone grew can best be done through
testing with ultra violet or infra Red rays. Infra Red rays works
better. Inclusions are usually made of minerals such as rutile
and tourmaline; and liquids. Remember inclusions and pits
should be as few as possible. Clarity is very important.
o The bigger the size of a gemstone the more valuable it is. It
should be born in mind that if a stone is faceted, it usually has
20% of its original weight (recovery = 20%)
o Hardness can help identify mineral. For example Beryl has a
hardness ranging from 7.8 corundum 9, quartz 7, garnet 6 – 7 .5
and Topaz 8.
o Refraction is a more advanced way of testing samples. This is
through the use of a refractometer. With the instrument you
can also determine their optical character (uni axial or bi axial)
and their refractive index:
Corundum :RI = 1.76 – 1.77
Beryl :RI = 1.57 – 1.58
Quartz :RI = 1.54 – 1.55
Tourmaline :RI = 1.62 – 1.64
Topaz :RI = 1.61 – 1.64
After testing, the gemstones must be graded. Here is a simple chart for
grading:
GRADING
C
O
L
O
U
R
1
2
3
4
FI LI MI HI EI
INCLUSIONS
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FI Fairly Included
LI Lightly Included
MI Moderately
Included
HI Highly Included
EI Exclusively
Included

7. Remember: Graded stones will fetch more money than ungraded stones.
The following is a list of equipment which will be needed during evaluation
and assessment of pegmatite deposits.
Trenching and Pitting : 2 Crow bars
: 4 14lb hammers
: 4 Mortar pans
: 2 Muttock picks / Hole picks
: 2 Hoes
: 2 Chisels
: 4 Shovels
: 1 Campers axe
: 2 Panga knives
: 4 Safety goggles
Testing of samples : “Human eyes” and colour chart
ultraviolet/infra red view cabinet
Hardness pencils
Refractometer/Sodium lamp
Hand lens/Gemolite
3.0 REVIEW OF PROJECT COST
Before beginning prospecting operations a financial assessment of the
project must be given in form of estimates. Main items of considerable
importance are the cost for prospecting equipment, salaries and wages,
transport (to and from field) administrative overheads such as stationery and
telecommunications and subsistence allowances.
These costs must be reviewed to find the actual expenditures so that future
prospecting should have viable expenditures to avoid running out of money
or over expenditures.
4.0 PEGGING CLAIMS
Once one has discovered a deposit of the gemstones specified in his NEPL,
he is entitled to peg a claim and apply to the Commissioner for Mines and
Minerals for his or her claim to be registered. If the deposit is to large for
SSM a mining licence should be applied for.
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8. Registration of claims has the advantage that one has the right to mine
minerals in the claim without external interference or has legal protection for
the ownership of the minerals he is mining.
It is recommended to seek services of experts to peg one’s claim. Much of
the pegging is carried out by qualified personnel from the Department of
Mines (D.M). Other experts/surveyors can be obtained from the Geological
Survey Department (G.S.D.), Agricultural Development Divisions (ADD)
and the Surveys Department (SD).
REFERENCES
DEER W., HOWIE R. and ZUSSMAN J. (1978): An Introduction to the
Rock-Forming Minerals. Longman, London.
MALUNGA G.W.P (1989): Njira yofufuzira ma gem stones. Paper
presented to Small Scale Miners Seminar; November 1, 1989, Mzuzu.
Author’s Address
Grain W.P. Malunga
Department of mines
P.O. Box 251
Lilongwe
Malawi
E-mail: gwpm@sdnp.org.mw
mines@malawi.net
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