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sapphire information
Sources
Originally,
the best sapphires and rubies came from Burma, where they are believed to have
been mined possibly from prehistoric times. Certainly they appear to have been
worked during the times of Marco Polo.
Kashmir is another source of very fine sapphires, famous for its cornflower
blue stones.
Thailand, previously called Siam, is an important source of attractive sapphire.
The term Ceylon sapphire is frequently used to denote pale to medium sapphires.
Unless the stone is known to originate from Sri Lanka, as it is now called,
such sapphire should accurately be called "Ceylon-type" sapphire.
Currently most dark sapphires come from Australia, and the term "Australian
sapphire" is often used to denote dark colored sapphires, in a similar
way to the term "Ceylon sapphire" for lighter stones.
Sapphires are also found in Montana and Colorado in the USA, India, with small
quantities being found in numerous other countries.
Sapphires from Australia
Sapphire and ruby, the gem varieties of the mineral corundum is found in many
east coast locations of Australia. Sapphire is found from north Queensland
to north-east Tasmania and in NSW is concentrated in the highland regions along
the Great Dividing Range. Ruby is less common in Australia but may be found
at various sites in NSW – notably the Gloucester area but also near Tumbarumba
as well as the Macquarie and Cudgegong Rivers.
Sapphires were first discovered in Australia as early as 1851 when they were found at the Cudgegong and Macquarie Rivers during the Gold Rush period. Sapphire was found alongside gold and tin in many highland regions during prospecting and mining activity.
The largest and most economic sapphire deposits are in the New England region
of New South Wales (NSW) around Inverell and Glen Innes, and central Queensland
around Anakie and Rubyvale. The New England gemfield is said to produce Australia’s
finest blue sapphire with Queensland sapphire renowned for their range of color
(including yellow, green and parti sapphire).
Sapphire was not mined commercially in NSW until 1919 when a rich area on Frazers Creek near Inverell was worked by CL Smith. This encouraged more mining in much of the sapphire bearing area of Glen Innes and Inverell which continued for 10 years until the Great Depression. Large scale commercial mining did not resume until 1959 when prices for rough increased due to a shortage from the traditional sources in South East Asia.
At the height of the sapphire boom in the 1970’s, there were well over 100 mining plants operating in the New England region (Mumme, 1988). There was some consolidation of the industry during the 1980’s in response to lower prices and exhaustion of some of the very rich alluvial sources in the area. Market conditions have continued to be difficult resulting in a decline in mining activity within the region – there are now only a very small number of commercial miners still operating.
Within the New England gemfield, sapphires typically occur in Quaternary and Tertiary alluvial deposits in both present day watercourses and fossil drainage systems. The sapphire-bearing gravel layer (or “wash”) varies in thickness and depth but may be up to a few metres thick in some palaeo-alluvial channel systems. It is thought that most of the sapphire was derived from the weathering and erosion of volcanic ash deposits (volcaniclastic rocks) that were erupted onto the earth’s surface during early explosive phases of volcanic activity (Facer & Stewart, 1995). These deposits were then distributed and concentrated along drainage channels.
Within the New England region, these processes have combined to create major sapphire deposits along Reddestone Creek, Wellingrove Creek, Kings Plains Creek, Horse Gully, Frasers Creek and Swanbrook (see map). In these areas, sapphire is commonly found in association with pleonaste (Black Spinel MgAl2O4) and zircon.
Australian sapphires are typical of corundum formed in iron-rich alkali basalt terrains and they have similar gemmological properties to those from other such deposits found in Thailand, China and Cambodia. The color is quite saturated compared to sapphires found in some other resources – for example the Geuda sapphire of Sri Lanka which is extremely pale before heat treatment to intensify color. Colour zoning is also common in Australian sapphire and may appear as hexagonal crystal growth patterns or parallel to the prism (Mumme, 1988; Sutherland and Webb, 2000).
The sapphire is also often strongly dichroic with a strong blue color on the main axis and lighter blue or green from the other direction being common. Sapphire from the Reddestone Creek in the New England is known for producing a higher proportion of sapphire that shows blue on both axes or blue with a greyish cross– these sapphires that possess a blue “cross table” are locally referred to as “blue on blue” and command higher prices than those with a green cross or less desirable color. Yellow sapphire is relatively rare in the New England resource compared to Queensland although Wellingrove Creek in particular was noted for producing some very fine yellows.
Gem quality corundum makes up only a very small proportion of all mine production with most corundum found being opaque, translucent or heavily included. Due to the volcaniclastic nature of these minerals, size tends to be relatively small compared to some very large corundum specimens found in other locations. Corundum specimens larger than 200 carats are rarely found in the New England gem field and gem quality sapphire above 30 carats in weight may still be found but are now considered somewhat rare.
Sapphires often occur as tapering hexagonal pyramids and are known as dog tooth crystals. These often show distinct color zoning as striping along the crystal or lighter zones at the tip. Crystals may be round and smooth or may have distinct faces in a hexagonal shape. Occasionally crystals may be found that are fused together or barrel shaped with double terminations. The following photographs show some typical examples – all found within the Reddestone Creek within the past decade.
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Ruby
Ruby is less common in Australia but may be found at various sites in New
South Wales, including the Macquarie and Cudgegong Rivers and the Tumbarumba
area. The major source of gem quality ruby is in the Gloucester-Barrington
area, in the drainage of the ancient Barrington volcano. In this area, rubies
are found in association with sapphires of various colors
. Australian rubies
tend to be very small (usually less than a carat) and in most deposits are
alluvial in nature (Sutherland and Webb, 2000). Due to the rarity of ruby in
Australia, there is limited large-scale mining activity.
The only commercial ruby miner in Australia is Cluff Resources Pacific (an Australian public company) – Cluff has undertaken extensive exploration within the Gloucester area and is currently producing ruby and sapphire from their mine. Although only a relatively small operation, the company reports that a large resource has been mapped and production is consistent. Interest in this operation has been relatively high – perhaps enhanced by the association with the landowner who owns the mineral rights – the Packer family of PBL (Australia’s largest diversified media company). It is possible that investment in this project has been influenced by the association and original negotiations with the late Kerry Packer – a very successful entrepreneur well known for his business acumen. These rubies and pink sapphires are now marketed through Ellerston Gems - named for the property where they are mined.
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