Gemstone Mining
Gemstone Deposits
A deposit is defined as a group of occurrences large enough
to be worked (also called a mine). A find is described as
a single occurrence.
Primary deposits refer to gems found in their original location.
The yield is generally low due to the fact that many tons
of non-gem bearing material have to be excavated.
Secondary deposits refer to gems which have been transported
by the actions of wind, rain and flowing water.
Fluvial deposits are created by rivers, marine deposits by
the sea and aeolian Deposits by the wind.
The distribution of gems around the world is irregular. Gem
deposits occupy only a tiny proportion of the earth's crust.
Some of the more favoured regions are:
The gem-rich metamorphosed limestones of Upper Mayanmar (including
the "Mogok Stone Tract") renowned for Rubies, Sapphires and
Spinels.
The alluvial deposits of Sri Lanka, Vietnam, Thailand and
Madagascar and the Minas Gerais and Minas Novas districts
of Brazil.
Mining Methods
Most gemstones are discovered by accident. There is no systematic
approach used for Coloured Gemstones due to the lack of capital.
Exceptions being Australia where the mining of Sapphires is
more mechanized and systematic.
Recovery is accomplished invariably by simple means without
the use of modern techniques or scientific basis. In many
cases, the methods are very primitive and have remained unchanged
virtually for 2,000 years.
They consist of:-
- Collecting gems from the surface, from dry river beds,
or rock fissures.
- Sinking shafts into the ground sometimes up to 30ft deep.
- Panning rivers.
- Driving short tunnels into the sides of hillsides (used
for mining Ruby, Sapphire in Mayanmar and Emerald in Colombia)
- Open-cast mining (i.e Ammolite)
- Using powerful jets of water, when available, to loosen
the gem material from the overburden.
- Digging pits into ancient river beds to reach the "Gem
Gravels", (i.e Sri Lanka, Mayanmar, Thailand).
- Terrace mining (i.e The Chivor Mine in Colombia).
- Underground mining which is expensive and can only be
justified if a significant vein is located.
|
