Aussie Sapphire is one aspect of a family owned business involved in farming and sapphire mining. While sapphires have been mined on our farm for many years, we became directly involved in running a commercial mine in 1998. This was a challenge as we had to learn about many other aspects of the sapphire mining business – being a successful sapphire miner today is not “just digging them up” and hoping someone will buy the rough. This article outlines the process of commercial mining up to the finished product of a faceted gemstone or piece of fine jewellery – we hope you will be as interested to read about it as we have been to learn how to do it.
Where to dig?
The first step of the process is deciding where to start digging! This usually requires a mixture of experience, use of test holes (we use an excavator but others use core test drills), prior knowledge on where the old ground is and inspired guesswork. I also like to add in a bit of divining using 2 bits of old fencing wire and a big chunk of corundum – sounds like moonshine but it works. (see short video clip of working excavator)
Following the wash
Once you have found a promising spot to dig, the first step is to strip off the overburden and start the open cut. To understand the process, let’s explain the soil layers. On top of course is the top soil, in our case around 200mm, then the subsoil which goes down to the depth of the wash which varies considerably from 1m to about 4m. Some wash layers in certain areas are deeper but we’re lucky with relatively shallow wash. Below the subsoil is the all important wash layer this is often only about 100mm thick although it varies greatly.
I am often asked what does wash look like – there is no simple explanation. Our wash changes considerably, it is unusual for us to dig more than a few metres of the same kind of wash; depth and thickness also changes constantly. Our wash layer is also usually very clayey with large lumps of mud mixed with the sapphire bearing gravels. This requires the excavator operator to keep on his toes as money can be lost with an operator who cannot recognise the wash layer properly. As the excavator works along the cut following the wash, it is progressively filled back in with processed gravel returning from the mining plant and subsoil which has been set aside. The final step is to replace the top soil which is spread over the layer of subsoil that has been levelled and rolled with the excavator.
The mining plant
Truckloads of wash are then transported to the plant in tip trucks. To explain the sapphire plant operation I will break the plant operations up.
1. Nozzle box: This consists of a large steel bin big enough to hold at least one truckload of wash – about 10 m3 in our case. At the front of this bin is a large water nozzle, usually in a shed, here a workman spends his day washing the dirt and feeding the plant. This sometimes requires breaking up lumps of mud with a shovel and getting wet with spray – not a pleasant job during cold Glen Innes winters.
2. Trommel: Consisting of a large rotating barrel with paddle structures inside to help break up the wash as it passes through. This also has a series of different size screens sizing the material with large going straight through and small being channelled to the next important part of the plant: the pulsators. (Click here for short video clip of trommel and jigs)
3. Pulsating jigs: These jigs move back and forth (us miners are inventive with names) causing the water to pulse up and down over a stainless steel mesh like base. The jigs are divided into individual sections which trap the heavier material at the bottom (black spinel and the sapphire are heavier than most of other gravel), the lighter material moves across the jigs with any heavier material settling in divided sections. The best sapphire is always in the first couple of bays as it is heavier. These bays are emptied or “robbed” at the end of each day. We look through each bay manually as we remove the concentrate picking out any larger sapphire that we see. This is the best part of the day but can sometimes bring disappointment.
This is a hard game with huge running costs and often poor returns. People who say we’re lucky to be a miner are often threatened with a hypothetical trip to the bottom of the cut but on good days the satisfaction of finding the best sapphire in Australia keeps us going. The concentrate is then sized through another small trommel and taken for further processing. Any solid material which passes through the plant is taken back to the cut. Water is recycled through the plant and slurry (liquid mud) is trapped in a series of settling trenches. These must be regularly pumped out. Everything is recycled and used or returned to the cut.
Separating the concentrate
At this stage of the process, the sapphires are still mixed in with a large amount of other rocks and stones. After drying on trays, the concentrate is sorted using magnetic separation which removes the magnetic ironstone and catches the sapphires and other non-magnetic stones. Usually the concentrate must be passed through the magnetic separator several times to reach the desired level of separation. Even then, much hand sorting and grading is necessary to produce a parcel ready for sale. (Click here for short video clip of magnetic separator)
Hand sorting and grading
Finally, many truckloads of gravel are reduced to just a small container of sapphires and other material. The final step is to manually sort out the other material which has made it through all the automatic separating processes (some ironstone, zircon, black spinel, etc). The final concentrate is washed by tumbling in water and detergent – this removes the reddish colouration on the surface caused by sapphires being mixed in with ironstone and makes it easier to grade up the parcel. If the parcel is being sold as mine run, it is separated into 3 sizes with corundum remaining with the gem grade sapphire. If the parcel is being sold as gem grade only or as individual stones, then further hand grading and sorting is required. This is extremely time consuming. Depending in where the stone is to be marketed, it will be sold as bulk mine run, catalogued and described for sale as individual rough, or sent to our cutters for production of gems and jewellery.
Traditionally, almost all our sapphire has been bought and further processed in Thailand. While it is certainly easier to sell mine run parcels to trade buyers, unfortunately this has resulted in our sapphire losing its true identity only to be marketed as whatever is flavour of the month. Unfortunately our better Aussie sapphire is hardly ever sold as such – after many decades of only the inferior grades of sapphire being labelled as Australian, it has been difficult to educate the gem-buying public that Australia can produce very fine blue sapphire.
To try and overcome this problem, many have tried in the past to cut and sell within Australia – unfortunately most have not succeeded. More recently, some like ourselves are successfully selling product to niche markets domestically and overseas (USA,UK, Japan). The growth of the internet is certainly the key to this success now when it hasn’t worked in the past – buyers are increasingly confident about buying online and see value in being able to buy direct from the miner with full information on gem provenance.
Tourism is also a small but important part of the industry although insurance issues and problems with council red tape in some areas limit growth in this area. Certainly we have looked at this issue in some detail but have not been able to come up with a viable plan – until some of these problems can be overcome, those interested in our mine will have to settle for the “virtual tour” on our website (photos and more video clips are available at this link)
Cheers for now from Aussie Sapphire