Apsara Gems - Kanchanaburi

The Sapphire Deposits of Bo Ploi, Kanchanaburi.

Bo Ploi is a sapphire mining town which lies 35 km north of Kanchanaburi and about 230 km north west of Bangkok. Blue Sapphires have been mined at Bo Ploi for over eighty years but large scale mining only really began in the mid 1980's with the arrival of modern mining techniques and improvements in heat treatment technology. At it's peak there were as much as 20 large-scale mining operations in Kanchanaburi. In 2005 only four of the larger mining companies remained. Today (2011) there is very little mining activity taking place due to rising fuel costs and the present economic climate.

The alluvial deposits are spread out over a huge valley surrounded by basaltic hills. In the past the sapphires were found fairly close to the ground surface but today the JCB’s have to dig down about 20 metres to recover the gems. The soil is transported by truck to very large jigs where powerful hoses wash the soil leaving behind the gem bearing gravel. The gravel is then processed through a sieving machine and graded for size. The different sizes are taken for sorting and the sapphires are picked out by hand. The rough sapphires are then graded into faceting or cabochon qualities and sent for heat-treatment. Finally the stones are cut and polished and ready for sale. The return yield from rough to cut is about a 30%.

The quality of the sapphires recovered is mostly of commercial quality but occasionally stones of similar appearance to fine Sri Lankan sapphires are found. Of the sapphires mined in the area approximately 95% are blue with the remaining 5% being lemon yellow-green or occasionally pink. Some very large stones have been found at Bo Ploi and the mines still produce commercial stones of 10 carats and over. The only other type of gemstone found in region is black spinel or nin, as it is known locally. These spinels are often faceted, made into inexpensive jewellery and sold locally. These spinels are also found salting the parcels of dark Australian or African sapphires.

The blue sapphires are characterised by strong colour zoning and tiny particles giving the stones a milky appearance. The colour of the stones ranges from mid-blue through to fairly dark blue but not as dark as some Australian sapphires. Paler coloured stones are also occasionally found. The distinctive sleepy appearance makes these stones relatively easy to identify as Kanchanaburi sapphires. Heat treatment of Kanchanaburi blue sapphires can improve them dramatically.

At its peak the Bo Ploi deposit had the world’s largest production of blue sapphires. However, with the high costs involved in mining, it remains to be seen how much longer this deposit will continue to be economically viable. There will only be the quantity of gems that nature has provided and eventually the mines will dry up. The Bo Ploi deposits have not suffered from ecological damage sometimes associated with opencast mining. As the mining areas become exhausted, trees are planted; the ground is landscaped and some areas have been replaced with fishing parks and golf courses.

Kanchanaburi Pics

Re-cycling the rocks

There are a lot of rocks dug up during the mining process which are graded for size and colour and sold on for various uses.

Water pumps

Huge pumps used to pump the water up to the high pressure hoses used to wash the gem bearing soil.

A jig

A very large jig used to wash the gem bearing soil. To give an idea of the size of this machine, if you look 1cm from the top and about 2 cm from the right into the picture, you will be able to make out a 10 wheeled truck arriving at the jig with a truck load of soil.

This is where the trucks tip the soil into the jig. The two high pressure hoses are mounted above to wash the soil down into the jig.

Ancient trees

These trees are dug up during the mining operation, collected and replanted in a specific area. There are hundreds of these ancient trees giving the area an apocalyptic look.

Lucky tree

The Thais are very superstitious and believe that the ancient trees will bring them good fortune. Another 'lucky tree' can be seen below.

Conveyor belt

The washed gravel passes by on a conveyor belt and the sapphires are picked out by hand. The workers are continually watched by security personnel and CCTV to ensure no sapphires are swallowed.

Combing through the gravel

Each time a sapphire is found it is placed in a locked and sealed pot which hangs over the belt. Some days no sapphires are found other days there could be kilos.

Sealed & locked pots

The sealed pots are used to collect the sapphires as they are found.

The sieving machine used to grade the smaller sized stones.

Minor blockage

Occasionally the gravel gets blocked up and needs a poke.

The black stones on the belt are black spinels or nin as they are known locally. Some pieces are picked out but only the perfectly formed octahedral crystals.

Sapphire crystal