Gems TV

MINING GEMSTONES

In antiquity, most gemstones were discovered near the surface, generally by accident. While this has somewhat changed in modern times, prospecting for coloured gemstones is still a fairly primitive affair, relying more on observation and chance, than the intensive scientific methods employed by the large multinational corporations involved in Diamond exploration. Once work begins on a gemstone deposit, it is correctly called a “mine.”

One of the most intriguing aspects of gemstone mining is the diversity of techniques employed in their extraction. These range from low tech tools such as shovels and sieves, to the high tech methods used to extract Diamonds from pipes (a volcanic pathway that connects the earth’s deep mantle to the surface). Apart from the introduction of power tools and pumps, most coloured gem mining hasn’t changed dramatically in thousands of years and still relies on three key things - perseverance, hand tools and elbow grease.

With a radiocarbon age of 43,000 years, the oldest known mine is the “Lion Cave” in Swaziland. At this site, people mined the iron-containing mineral Hematite, which they presumably ground to produce the red pigment, ochre. Sites of a similar age were also found by archaeologists in the Netherlands and Hungary, which may have been worked for flint in weapons and tools. Another early mining operation was the Turquoise mine operated by the ancient Egyptians at Wady Maghareh on the Sinai Peninsula. Turquoise was also mined in pre-Columbian America in the Cerillos mining district in New Mexico, where a mass of rock 60 metres in depth and 90 metres in width was removed with stone tools. The resulting mine dump of unusable rock covers 8 hectares.

Gemstones are generally obtained by alluvial or host rock mining.

Alluvial mining

By far the most common method of mining gemstones, alluvial mining is the extraction of gems from sedimentary deposits, also known as placer or secondary deposits.

They are called secondary deposits because the gems are not found in the rock in which they formed or are hosted, but in deposits caused by the weathering and erosion of primary deposits. It includes the prospecting of riverbeds (i.e. the water flow is dammed so the less dense clay and sand is swept away - the remaining gem gravel is then agitated so the gems can be extracted and sorted) or the mining of gems from sedimentary deposits located beneath the earth’s surface (i.e. the digging of pits, vertical shafts and tunnels to reach gem gravels). A variation of alluvial mining is “marine mining”, which is the mining of sandy coastal strata by dredging (e.g. Amber from Kaliningrad, Russia). Examples of alluvial mining include river mining in Ratnapura, Sri Lanka and shaft mining in Ilakaka, Madagascar.

Typically, a miner will dig using either hand tools (on a small scale mine) or heavy industrial machinery. The earth is then taken to be washed either by hand or with the aid of machinery. This is exactly how it sounds - the loose earth is washed with water to get rid of the debris, leaving gemstones in the “wash”. This wash is then trawled through to find the rough gemstones. It is an incredibly laborious and time consuming process that can from day to day, yield very little. Typically, only a few little gems remain at the end of washing and sorting.

Alluvial deposits tend to include more than one gem type and this can be useful, as the presence of one gem type can often indicate the presence of another. Such gems are called “tracer” gems, as they allow prospectors to “trace down” other varieties. Other methods of prospecting include the mapping of ancient riverbeds and streams.

Although gem crystals from alluvial deposits tend to be rounded, scratched and cracked due to the weathering processes they have endured, this is actually beneficial as the culling of poorer specimens has already occurred. In fact, the percentage of gem quality crystals found in alluvial deposits is generally higher than those obtained from primary host rock deposits.

Host rock mining

Also known as primary deposits, host rock mining is the chipping of gems from the rock in which they formed or are hosted. Crystals from these deposits are extracted from their host rock by hand tools, pneumatic tools and even explosives. Performed for centuries, this mining is typically done by digging underground tunnels. In some cases, gemstones can be harvested directly from underground caves (e.g. the mining of Moonstone from limestone caves near the village of Kangayam in Tamil Nadu, southern India).

Depending on the hardness of the primary material, host rock mining can either be comparatively easy (e.g. mining of Kunzite from pegmatites at Betafo, Madagascar) or extremely difficult (e.g. mining of Tanzanite from metamorphic rocks at the Merelani Foothills in northern Tanzania).

While some gems are easily removed by picks or drills, sometimes the host material must be crushed before the gems can be extracted and sorted for quality. At the Cullinan mine in Pretoria, South Africa they use a “sticky table”, which is a table covered in grease that the Diamond-rich Kimberlite (the host rock in which most Diamonds are found) stick to because of their density (i.e. the Kimberlite that contains no Diamonds falls away).

Ethical mining

GemsTV strongly encourages mining methods that are environmentally sound, such as:

For example, in the Masuguru district of Songea in southern Tanzania, one mine owner, Brad Mitchell, suffers from freelance miners encroaching on his holding. They destroy trees and excavate dozens of holes every day in search of the coveted Songea Sapphire. As it is a condition of his mining license that he leaves the area exactly as he found it, Brad ensures every hole is filled, more trees are planted than are removed and that the landscape is left in a better condition than when he arrived. Many countries ensure conditions such as this are adhered to; sadly, some do not.

GemsTV also strongly encourages fair labour practices that conform to local labour laws where our gems are mined or cut. We sell gems that have been mined using legitimate labour that has been paid a fair wage (i.e. no child labour, slave labour or unfair labour practices). Also, we believe mining and cutting facilities should provide a clean, safe and well lit working environment. For example, in April, 2007 an average of only 0.53 milligrams of dust per cubic metre was recorded during the annual health and safety inspection of our workshops in Chanthaburi, Thailand - 15 milligrams per cubic metre is considered normal.