SAPPHIRES FROM AUSTRALIA By Terrence Coldham
During the last 20 years, Australia has ew people realize that Australia is one of the major assumed a major role in the production of F producers of sapphire on the world market today. Yet a blue sapphire. Most of the gem material fine blue Australian sapphire (figure 1)competes favorably comes from alluvial deposits in the Anal
130 Sapphires from Australia GEMS & GEMOLOGY Fall 1985 Figure 1. Twofine blue sapphires, 1.11 ct and 1.61 ct, respectively, from the New England fields, New South Wales, Australia. Photo 0 Tino Hammid.
area were originally thought to be emeralds. Spo- Asia-was systematic mining resumed at Anakie. radic mining operations started in the Anakie By 1969, the Anakie fields were being fully ex- fields in the 1890s, and most of the early produc- ploited through a number of large-scale, fully tion went to tsarist Russia via German buyers. mechanized operations. Since the beginning of the The Anakie area was officially proclaimed a current decade, however, as the viable areas are mining field in 1902. Mining consisted of sinking exhausted and operating costs continue to mount, shafts or digging shallow alluvials and then wash- there has been a steady decline in production. ing the material with sieves. By 1913, two tons of Many small, semi-mechanized underground oper- sapphire and other corundum had been removed. ations now run alongside the large, heavily mech- Single pieces of gem-quality material as large as anized workings. 500 ct were reported (Anderson, 1971).Two small The second major mining field is centered villages, Rubyvale and Sapphire, appeared on the around the towns of Inverell and Glen Innes, in fields to service the miners. northern New South Wales, and is generally re- The advent of World War I, the collapse of ferred to as the New England fields. Although sap- imperial Russia, and the elimination of German phire was first found here in 1854, mining did not buyers brought mining to a virtual standstill. Not start until many years later, and even then was until the early 1960s-with the onset of a burgeon- only sporadic until 1959. As with the Anakie ing demand for rough sapphire throughout fields, the Asian buying power in the early 1960s
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 131 Figure 2. A miner's collection of the different-colored sapphires found at Inverell, in the New England fields, New South Wales. created favorable conditions for large-scale mech- town in Queensland and as far south as Tasmania anized mining that has continued to the present (again, see figure 3).In nearly every case, the sap- time. phires have been found in close proximity to Ce- Various attempts to mine at other localities in nozoic basalts. As mentioned above, however, in Queensland, New South Wales, and Tasmania only two areas have the deposits proved to be rich have been made, but thus far none has proved enough to allow commercial mining. viable. It is quite possible that future prospecting In most cases, the sapphire occurs in alluvial will produce new fields. gravels, termed "wash" by the miners. The gravels are associated with present-day rivers and creeks GEOLOGY in the New England region (Department of Min- All along the eastern seaboard of the Australian eral Resources, 1983), and occur as large sheets continent are scattered remnant dissected flows that cover extensive areas dissected by the present and pipes of Cenozoic volcanics (see figure 3).The drainage pattern in the Analzie fields. most common volcanic rock type is alkali basalt, The sapphire occurs as individual crystals and which in many localities contains xenocrysts of crystal fragments that in most cases have been such minerals as ilmenite, pleonaste, amphiboles, locally concentrated, presumably by normal allu- feldspar, zircon, corundum, and pyrope garnet. In vial processes. Other minerals associated with 1902, a geologist with the Queensland Mines De- sapphire are found in varying proportions and in- partment reported on the new Anakie sapphire clude (in order of abundance) pleonaste (spinel), fields, and stated that the sapphire found in the zircon, ilmenite, magnetite, olivine, pyroxenes, surrounding alluvials appeared to have been and amphiboles. Zircon is the only other mineral weathered out of the nearby basalts (Dunstan, that commonly occurs in gem quality. These zir- 1902). Since then, numerous occurrences of sap- cons are of "high type" and are either pale yellow phire have been discovered as far north as Cook- or reddish brown, ranging from sand-grain-sized
132 Sapphires from Australia GEMS & GEMOLOGY Fall 1985 particles to the occasional clear pieces of several hundred carats. Gemologically they appear to be similar to those found at the Pailin field in Cam- bodia, as described by Jobbins and Berrangd (1981). The pleonaste is usually much more abundant than the sapphire and zircon; since it has a specific gravity similar to that of sapphire, it is often used as an indicator mineral by the miner. All these minerals have been found at various localities in situ in solid basalt, pleonaste quite commonly and sapphire and zircon very rarely (McNevin, 1972). At certain localities, such as Lava Plains in northern Queensland (see figure 3), large amounts
1 of sapphire, along with pleonaste, have been found QUEENSLAND in soil directly overlying the basalts. The surfaces of material from this locality show no evidence of having traveled any distance from their source. However, while pleonaste xenocrysts are plentiful at Lava Plains, no xenocrysts of sapphire have been found in the basalt itself from which the soil ap- parently derives. Personal observations by the au- thor show that these deposits are very similar in rock type, mode of occurrence, type of stone, and associated minerals to those found at Prae in cen- tral Thailand. Recently, quite rich deposits of sapphire were found seven miles (11 kin) east of Inverell in what appears to be pyroclastic (volcanic ash) rocks in- terbedded with basalt flows. Accessory minerals t C I are zircon and ilmenite (Lishmund and Oakes, - NEW I 1983). SOurHl WALES - In all localities, the sapphire occurs as discrete crystals and crystal fragments, often elongated * hexagonal pyramids, and occasionally bipyramids. A Almost invariably, crystal faces and fracture sur- 4 faces alike show evidence of corrosion and etching. Some crystals are so corroded that they appear as "^P^ ¥ long cone shapes without any suggestion of their original hexagonal cross section. For quite a long 0 tat time it was thought that the material was "water worn," but it is now believed that these surfaces are a result of chemical corrosion (figure4). These
300 O- O- Figure 3. The distribution of basalts in eastern Kilometef s Australia. Major deposits of sapphire have been ----- Stale Boundaries found in the Anakie fields (Queensland)and the New England fields (NewSouth Wales).But some bsa~ sapphire has been recovered from as far north as Cooktown (Queensland) and as far south as Tasmania. Map adapted from an original by the I Mineralogy Section of the Australian Museum. Artwork by Lisa foko.
Sapphires from Australia cated commercial mining of the alluvial deposits through the use of heavy earth-moving equipment and large throughput processing plants (figure 5). Presently, mining techniques on both fields range from hand sieving, through small one-man opera- tions that use processing plants capable of han- dling only a few cubic meters of material per hour, to large syndicates and companies that employ up to 30 men on a site and process hundreds of cubic meters per day. Figure 4,Two corundum crystals (approximately On the New England fields, the mechanized 5 ct each) from InvereII, in the New England mines dot an area of some 4,000 km2. Each miner fields. Note that the left side of the piece on the usually works a section of creek or river that is right has been protected and shows the original often hundreds of acres in area. First, samples of crystal faces. wash are taken to delineate the richer runs, and then mining proceeds in a systematic manner. In contrast, on the Anakie fields, most of the features are the same as those reported at Pailin in mining activity is contained in an area of only a Cambodia (Jobbins and Berrangk, 1981) and ob- few square kilometers. Because the size of a claim served by the author in sapphire from Bo-Bloi, is restricted by the State Mining Law, the miners Chanthaburi, and Prae in Thailand. They also look tend to work almost on top of one another (figure very similar to the surface features reported on 61, and each miner must accumulate the rights to a corundum from Colombia (Keller et al., 1985). number of adjoining claims if he is to have suffi- Some minor water wearing is observed on the gem cient room to operate. However, Anakie miners material recovered from alluvials, particularly are to some extent compensated by the fact that from the Anakie fields. the wash here is usually thicker and richer in sap- Although it has been generally considered that phire than that in the New England area. the alkali basalt is the source rock for the alluvial In both areas, the gravel is normally covered by sapphire in the area, it is distinctly possible that 2-80 ft. (0.5-25 m) of barren overburden consist- the pyroclastic rocks associated with the basalts ing of fine grits and brown or black soils. This may, in fact, be the source. According to this sec- overburden is removed by either a backhoe or a ond hypothesis, the sapphires themselves crystal- bulldozer. The sapphire-bearing wash is then ex- lized originally in an unknown rock in the lower cavated and loaded into trucks for transport to the crustal/upper mantle regions and were eventually processing plant. Some areas of the Anakie fields released into a fluid phase that rose to the surface are reserved for hand miners who sink shafts up to during a period of volcanism. These fluids even- 100 ft. to reach the gem-bearing alluvials (in much tually consolidated to form the host basalt and the same manner as their predecessors operated at pyroclastic rocks. Evidence for either hypothesis is the turn of the century). somewhat conflicting and more detailed field work is necessary. Processing. On arrival at the processing plant, the Also of interest is the similarity in rock types gravel is tipped into dump boxes where it is between the Australian and Southeast Asian washed into a trommel with a high-pressure water (Jobbins and Berrangk, 1981) sapphire fields. For jet. Any large pieces of rock are, if necessary, bro- example, some of the basaltic rocks in Australia ken up and removed by hand from the dump box. near Inverell are very similar to those at Pailin and The trommel consists of a revolving screen that appear to be closely associated with sapphires. In usually has two different-sized meshes. The first contrast, the larger tholeiitic basalts of Australia section has a fine mesh through which sand-sized and Pailin are considered to be barren of sapphire. particles are sieved out. The mesh in the second section is usually about three-quarters to one inch MINING (2-2.5 cm) in size, and anything larger passes out The last 20 years (and, more specifically, the last of the trommel into rock bins to be returned to the 10 years) have seen the development of sophisti- excavation. The middle-sized fraction-i.e., of
134 Sapphires from Australia GEMS & GEMOLOGY Fall 1985 Figure y plant at Kings Plan, Inverell, in the New England fields.
Figure 6. Note how miners have Lorn up this area between Riibyvale and Sapphire in the Analzie fields.
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 135 Figure 7. Picking out the sapphire from the coarse concentrate at an Inverell (New England fields) mine site. plus one-sixteenth inch to minus one inch from collected in bins and then used to backfill the the second mesh-passes through the trommel original excavation. After all the processed gravel down to a pulsator or jig. The trommels may have has been returned, it is covered by the original revolving tynes and high-pressure water jets inside overburden and topsoils. All water used in the to break up the gravel. In areas with concentrates mining operations is stored in dams and recircu- of clay, the material is often passed through a sec- lated; only clean water can be returned to the ond trommel or over a vibrating screen to make rivers. sure all the sapphire is released. At the end of each day, the concentrate in the Because of the scarcity of water on the Anakie pulsator is removed. This gravel is composed fields, many mines there use dry sieving methods. mainly of highly iron-rich material in addition to After excavation, the material is laid out to dry and the sapphire, pleonaste, zircon, and the like. The then passed through large, semi-mobile vibrating sapphires from the coarser fractions are often screens to remove sand and oversized material picked out of the concentrate at the mine site near the excavation site. The middle-sized product (figure 71. The larger volumes of medium- and is trucked to the pulsator or jig which is located fine-sized concentrates are sent to an office to be adjacent to water, usually one of the series of ponds picked out and sorted. or setting dams through which this very scarce Sorting and Grading. The first step in recovering commodity is recirculated. The pulsator is the main recovery section; the Figure 8. Fine concentrate after removal from the various models range from 18 inches to several feet pulsator. Note the abundant black pleonaste. across. The pulsator is a simple heavy-media unit that pulsates water through a screen divided by a series of riffles. The gravel is fed over the screen, and the "heavier" sapphire and other minerals col- lect in front of the riffles. The lighter material washes out over the end of the pulsator and is returned to the excavation. Large mines may have banks of several pulsators to process the different sizes. The recovery rate is usually 90% -95%, but it may be less in alluvials with a high clay content. The mining operations in the New England district are much more rigidly controlled in terms of conservation and restoration than those in Analzie. The waste gravels, sands, and silts are
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 the sapphire from the medium- to fine-sized con- centrate (figure 8) is to dry it and pass it through a magnetic separator. This removes all the iron-rich material, black spinel, and anything else with a reasonably high magnetic attraction; it leaves a concentrate of corundum, zircon, quartz, and other minerals that usually represents 10% of the original concentrate. This material is then washed, dried, and given to the grading staff who select out all the corundum that shows any indi- cation of being cuttable. Usually women are em- ployed to handpick this material as it is passed over mirrors (figure 9). The mirrors reflect light through the rough material so that color and flaws can be observed without the sorter having to hold each stone up to a light. All blue material found is sorted at the mine's sorting office into what is termed "mine run" par- cels; blue sapphire represents approximately 95% by weight and value of the total salable production. A mine run is the total production of all salable blue material produced in a given (arbitrary)time from the one mine. Often' these parcels are quality graded by the Figure 9. Sortingsapphire on mirrors at an Inverell miner into firsts, seconds, and thirds and then mine office. sieved into various groups. A mine-run parcel var- ies considerably in quality from one miner to the about 10% -20% of the stone over 2 ct in weight, next, and a standard price per ounce cannot be 40%-60% of medium size (0.50 to 2 ct) and applied. Variations in a mine-run parcel depend on 30% -40% of small material (0.20 to 0.50 ct). Ma- the type of stone produced in the area mined as terial in mine runs from Anakie would be, overall, well as on the type of grading adopted by the miner. of a larger particle size (20% -40% are over 2 ct). The gradingprocess at this stage is very subjective. Other colors such as greens, yellows, and parti- DESCRIPTION colored sapphires are sold separately either in The gemological properties of Australian sapphire, small lots of a few ounces or as individual stones. as determined by the author, are given in table 1. A typical Inverell mine-run parcel may have As is the case with corundum from Thailand and
- p~ - - - TABLE 1. Gemological properties of Australian sapphire.'
Specific Color Refractive Birefringence gravityb Spectra Reaction to LW/SW index ultraviolet radiation
Light blue 1.761-1.769 0.008 4.02 Single band 455-458 nm Inert Strong band 455-460 nm Dark blue Narrow band 464-466.6 nm Green 4.00 Single line 478 nm Broad band 455-465 nrn Yellow 3.97 Inert Single line 478 nm Same as for yellow, Gold 4.01 but less distinct 'These properties were taken lrom a small range 01 Inverell and Glen Innes stones. ~~ecificgravity was determined by the hydrostatic method (+0.02). cWhilealmost all Australian sapphire is inert, thoseshowinganorange orpink to mauve color willshow some redlluorescence when exposed to long-wave ultraviolet radiation.
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 137 Figure 10. A variety of faceted Australian sapphire. Note that the proportion of yellow stones is much greater than is found in overall production. In fact, 90% ormore of all Australian sapphire occurs in various shades of blue. Photo by D. Barnes, courtesy of the Department of Mineral Resources, New South Wales.
Cambodia, Australian stones generally have a The vast majority of gem-quality Australian higher iron content than corundums associated sapphires, perhaps 90% by weight, occurs in vari- with metamorphic environments (Webster, 1983). ous shades of blue (again, see figure 10). These This results in a range of colors (figure 10) quite shades range from almost colorless through rich different from those found in Burma, Sri Lanka, royal blue to some that are so dark as to appear and Tanzania. Analyses of sapphire from Frazers black when cut. The greater proportion occurs as Creek, Inverell, show total Fe as over 1% medium to dark material. (MacNevin, 1972). The second most common color range covers The size of individual pieces ranges from less various tones of greenish blue, and most fre- than 0.05 ct to over 1,000 ct. Stones over one inch quently occurs in a light to medium, very slightly in diameter are rarely found these days, as they are greenish blue. removed with other coarse gravel by the trommel. The two other colors that often occur are yel- On average most of the cuttable material is under 2 low and green. The yellows range from light ct in the rough state; clean stones over 10 ct are through intense yellow to strong gold (figure 11). quite rare. Bright orange stones are also encountered, though
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 .- Figure 11. A range offine, natural-color yellow andgold sapphires from the Anakie fields. Thelarge stone in the center weighs 30 ct.
. I rarely. he greens occur in a great variety of the resultant gem can rank as one of the most shades, including yellow-green, yellowish green, beautiful of the corundum family (figure 12). and brownish green, with tones that range from Miners often collect them, and both Thai and Aus- very pale through almost black. Evenly colored tralian dealers give them to their wives or sell green, yellow, or gold gemstones of over one carat are quite rare, but the author has seen gem-quality rough that weighs over 300 ct. Figure 12, An approximately 6-ct parti-colored Occasionally pink, purple, and mauve stones ("wattle") sapphirefrom the New England fields. are found, but they are extremely rare. Also seen, Photo by D. Barnes, courtesy of the Department of Mineral Resources, New South Wales. but only rarely, are color-change sapphires, some of which show effects similar to those seen in alexandrite, while others change from greenish yellow to orangy pink. The coarser banding of colors such as green, blue, and yellow results in parti-colored stones, some of which are extremely attractive. This coarse banding seems to be much better developed in the Australian material than in that from other localities. One large (2,019.5 ct) piece of gold, green, and blue particolored rough was recently found. The term wattle sapphires has recently come into vogue to describe parti-colored stones that range from yellow with a touch of green to green with a touch of yellow. (Wattle, called mimosa in many countries, is Australia's national flower; it has a yellow to gold blossom with green to olive- green foliage.) When this material is cut correctly,
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 139 large pieces-one was recorded to weigh approxi- mately 11900ct. Overall differences in color can be noted in the sapphires from the Analzie and the New England fields. The AnaIzie fields produce darker blue sap- phires and more pure green and pure yellow stones than the New England fields! which may be related to the fact that the Analzie material crystallized in a more iron-rich environment. Glen Innes) and partic~~larlyReddistone Creel
Figure 13. This 1.5-cm thin section of un HEAT TREATMENT Austruliun supphire crystul, CUL ut right angles to The color of Australian sapphire is often greatly the c-axis, shows color bonding purullel to the affected by sillz. The blue shades are particularly crystul faces. prone to be silky to varying degrees. Evenly sillzed stones may be cut as star sapphire) but more com- monly the silk mars the beauty of the cut stone by them to friends) so the general retail customer making it appear dull and/or oily green (figure 14). rarely gets a chance to see fine wattle sapphires. The silk usually appears as very fine) needle-like Color banding is a very common feature of inclusions oriented parallel to the crystal structure Australian sapphire) and even very uniformly col- of the host corundum. Sometimes the individual ored stones will show fine banding under the needles cannot be resolved even under very high microscopej however) patches of color without magnification. The most common type of silk has clear planar boundaries are rare. The banding oc- a whitish appearance and only sometimes pro- curs in two directions (MacNevin) 1972))the first duces chatoyancyj it is most likely rutile [Nassau) being parallel to the c-axis)which often results in a 1984). hexagonally or trigonally banded cross section in The presence of sillz in the blue material re- which the colors generally are lighter toward the sults in a gridwork of reflective surfaces through- center of the crystal (figure 13).The second type out all or part of the stone that interferes with the occurs at right angles to the c-axis and generally body color and is probably one of the most com- grades from darker at the base of the crystal to mercially important features of Australian sap- lighter at the top. phires. When light enters sapphire! which is dou- In the blue material) darker and lighter shades bly refractive) it is split into two wavesj in ALE- of blue may alternate randomly with colorless or tralian blue sapphire) one ray is pure blue and the very pale yellow bands. As mentioned above) other is blue-green. The effect of the sillz is to coarse to very coarse banding gives rise to parti- reflect and scatter the two rays as they pass colored sapphire. When the bands are wide enough through the stone) such that the blue and blue- to give a clear separation between colors such as green dichroic colors merge into one unattractive green and gold or blue and yeI10w~the effect is oily greenish blue color. This effect can be so quite beautifulj however) alternating fine bands of coinplete in very evenly silked stones that the green and blue cause a rather unpleasant green- color is the same regardless of the orientation of blue parti that along with black or heavily in- the stone. cluded blue material makes up the lower quality Ba~icaIly~heat treatment the silk end of Australian commercial production. by forcing it back into solid solution within its Star sapphire is also found) the most common of which is black or bronze material very similar to that from Bang Kha Cha in Thailand. Asteriated *Us~iolIysopphire is cut with the toble ut r~ghtangles to the GOXIS to get t11e best blue When the stone is viewed thrvugl~ stones also occur in blue! blue-gray! and occasion- theside (e.g.,through theg~rdlerotherthon tl~rvughthe table), ally green and gold. Stars may occur in particularly u greener color IS norrnolly seen, t1111sthe tern] side color.
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 host; a subsequent quick cooling (1.e.) in a few hours) traps the silk there. Without heat treatment to clear the stone) the mining of Australian sap- phire would not be commercially viable. The treatment of silk in sapphire appears to have started about 25-30 years ago in Europe, where it was quietly practiced by a few people. At that stage) the demand for Australian sapphire was smalll and mechanized mining had just begun. Twenty years ago it was found that such pro- cesses worked very well on Australian sapphire, and Thai dealers-who had become very adept at heat treatment-started visiting Australia to buy. This increase in demand prompted increased pro- duction that resulted in the large-scale mecha- Figure 14. This single piece of Auslralian sapphire nized mining that continues to the present day. was cut in half and the pjece on the right heat Most of the Australian blue sapphire is treated treated. Note that while there is improvement in in Thailand. The method for treatment of blue clarity and color, the change caused by heat Australian sapphire is quite simple) although it treatment is not as dramatic as that commonly differs significantly from the treatment of the Sri seen in white or light-colored Srj Lankan Lankan material (which is done for the purpose of sapphires that are ~urnedblue by heat treatment. darkening color rather than removing silk). The Photo 0 Tino Hammid. rough Australian stones are first thoroughly washed afid any iron stains are removed by acid. The rough\stones are then packed in a white glazed chamber of the furnace and then a small amount of porcelain crucible and the lid is sealed with a coke is added until a glowing base is obtained (fig- high-temperature cement. ure 161. The whole chamber is then filled with Some years backl a great variety of chemicals coke and the crucible nestled into a hollow at the were placed in the crucible with the sapphire! in- top of the pile. A high-temperature brick cap is cluding cobalt salts) fluxes, chloride salts) and the added to narrow the gas exit to about one-third the like. While such treatment resulted in stones that diameter of the air inlet. An air blower is used to appeared to be a bright cobalt blue) it was soon force air up through the coke. realized that the effect was only superficial, a coat- Generally) a burn takes from 45 minutes to one ing that was removed in faceting. These days, if hour before the flame starts to die. As the coke any chemicals are used at all, they are fluxes such burns from below! the crucible moves down into as borax, and the rough stones are simply wet with the hottest part of the furnace. It is very difficult to a mild solution before treatment. The effect of the measure the actual temperature reached) as a flux after cooking is to slightly glaze the surface of pyrometric probe placed in the center of the cham- the stone, which results in brighter-looking rough. ber would be damaged by the movement of the It is hard to ascertain if the flux has any internal coke and the fluxing action of the slag that results effect. from the burning coke. The author's attempts at After the porcelain crucible has been prepared) such measurements indicate that the hottest tem- it is sealed (with clay) into a slightly larger black perature is in the area of 1600°-1700° assay crucible. Sometimes fine charcoal dust may As soon as the blower is turned off) the fumace be placed between the two crucibles, depending on is sealed at both inlet and outlet and is left to cool the type of stone (i.e.)its origin and general hue), to for from two to 12 hours or more. Tongs are then keep any oxygen from reaching the stone during used to remove the crucible (figure 17).The opera- the burning. While this practice used to be com- tion results in the stones being both heated and mon) most treaters no longer feel it is necessary. cooled in a reducing environment. Traditionallyl the fumace is a simple coke- Although the body color of the material may fired one (figure 151, around four and a half feet ( 1.5 be affected, such changes are usually slight and) in m) tall, First a wood fire is built inside the inner most cases) detrimental. The most common prob-
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 141 -F~re-br~ckcap
H~ghtempf~re-br~ck
,Area of maximum combuslion
AI~blower
Figure 16. This diagram of the furnace depicted in fig~~re15 ill~zstra~esthe process used to heat treal Australian blue sapphire. Artwork by R. Brightman.
Fig~~re15, A Thai furnace typical of those used to treat rough Australian sapphire. lem is that unsuitable timeltemperature parame- ters may result in a slight to fairly obvious darken- ing of the stone. Any leakage of air into the cruci- ble in the final stages of the burn or on cooling generally strengthens slightly any green hue that was originally in the stone. Up until about 10 years ago, a lot of innova- tions were tried with length of treatment and the Figure 17. The inner crucible has been broken lilzel but over the last decade) the procedure for open after treatment of these A~~straliunbl~ze removal of silk has become more or less standard. sapphires was completed. The only recent innovation is the use of gas-fired furnaces. Once the process has been mastered and minor adjustments are made for the particular type tered. Usually the green) yellow-gold) and parti- of stone [e.g.) colorl density of color) silkinessl and colored stones are heated in an electric furnace in locality of origin-Anakie or New England fields) crucibles open to the air (an oxidizing environ- being treatedl the results are quite predictable. Ex- ment) inside the chamber. perts at using this type of furnace have many sub- tle variations in their methods) which results in INCLUSIONS different people specializing in particular types of Very little detailed study has been done on inclu- stone. sions in Australian sapphire. As most of the rough Sapphire other than blue is only occasionally stone is processed in Thailand) it has been difficult treated) usually to remove silk. The effect on color for researchers outside of Australia to acquire ma- is usually not great) although occasional terial that can be clearly identified as Australian. strengthening of yellow and gold hues is encoun- Microscopic examination of Australian material
142 Sapphires from Australia GEMS & GEMOLOGY Fall 1985 for this study revealed inclusions similar to those rutile but rather to a needle-like precipitate of iron reported for Thai and Cambodian sapphire and titanium oxide (FeTi02)with or without lath-like may reflect their apparently similar geologic ori- particles of a brown material, possibly hematite gins. (Moon and Phillipsl 1984). For example! inclusion of feldspar crystals re- Different types of inclusions tend to predomi- ported by Gunawardene and Chawla (1984) for nate in sapphire from different localities. For ex- blue sapphire from Kanchanaburi, and by Gubelin ample! bright red crystallites (uranium pyro- (1974)for sapphire from Thailand! appear identical chlore?)commonly occur in stones from the New to inclusions commonly seen in Australian sap- England fields. The sapphires found at the Anakie phire (figure 18).Positive identification of feldspar fields commonly contain inclusions, as yet un- as an inclusion in Australian sapphire was re- identified! that are dark brown to opaque euhedral ported by Schubnel(l972).He described colorless platelets and stubby rods of what appear to be types transparent crystals between 20-400 microns! of mica and horneblende, respectively. sometimes euhedral and sometimes surrounded Other internal features commonly encoun- by circular fractures. These incl~lsionsalso sound tered are very well-developed polysynthetic similar to those shown in figure 18. twinning and fine "fingerprint1' inclusions. The Also very common in Australian sapphires are author is at present embarking on a detailed study euhedral to subeuhedral bright red to brownish red of Australian sapphires in which electron micro- crystals, sometimes associated with wing-shaped analysis will be used to identify individual inclu- liquid "feathers1!. They may sometimes have trails sions. of bubbles streaming from them like comet tails (figure 191, The red crystals look similar to those DISTRIBUTION TO identified as uranium pyrochlore in Pailin sap- THE MARKET phire by Gusbelin (1974).Such "comet tails1' have The greatest proportion of Australian production also beenobserved coming from other inclusionsl is purchased by visiting buyers from Thailand. The particularly from colorless crystals of high relief price is reached by bargaining between the buyer that may well be zircon. and the producer, and takes into account previous Unlike the silk in blue star sapphire! asterism selling prices! apparent quality of the stone! pro- in black star material does not appear to be due to portion of large stones! and the overall size of the parcel. The Thais buy anything from individual stones to mine-run parcels. Until two years agol it Figure 18, This colorless euhedral cryslal was not uncommon to hear of 10 separate buying surrounded by a tension halo and accompanied syndicates on the fields at one time. The galva- by a "comet tail" is a common inclusion in Australian blue sapphire. Photo by B. Scheos, Diamond Laboratory Services; magnified 40 X. Figure 19. A subeuhedral reddish brown crystal in blue Australian sapphire from Glen Innes. Such inclusions are very common in blue Australian sapphire, either done or accompanied by s~nall ljquid feathers and "comet tails.'' Photo by B. Scheos, Diamond Laboratory Services; magnified 40 X.
Sapphires from Australia GEMS & GEMOLOGY Fall I985 143 Figure 20. 'The office oj a Thai sapphire buyer on the Anakie fields. nized iron offices of the Asian buyers at Rubyvale to work only certain sizes or) because of their par- are an accepted part of the scenery (figure 20). ticular heat-treatment skillsl only one type of Apart from the inaterial purchased by the Thai stone) e.g.' all darker or lighter material. b~~yers'a small amount of rough stones are sold to Since the Thais first began buying Australian European and Australian cutters. sapphire in the late 1960~~the average combined Thailand) as a result of its own sapphire mines' annual production from the New England and the has long been a center for sapphire processing and Anakie fields has risen from $1 million [Aus- marketing. Now) with little production from Thai- tralian) per year in 1965 to more than $50 million land's own mines and the virtual cessation of min- in 1977. While the rise in production has not been ing in Cambodia' Australian production supplies steady in recent years (see figure 21)) it has not the raw material to keep a large number of lapidar- dropped below $25 million since 1971. ies and gem merchants going. Until the Thais began processing Sri Lankan sapphire as well a few DISCUSSION years ago' it is estimated that some 80% by weight In almost a11 cases) Australian miners sell their and value of Thailand-cut sapphire exports were of raw material without the knowledge that would Australian origin. Even with the present drop in enable them to assess the value of the finished productionl Australian sapphire could well ac- goods (likea farmer selling wheat and not knowing count for at least 50Y0 of the carat weight of Thai- the price of flour]. The miners cannot be blamed land's total exports of sapphire (pers. comm. with for this' as they were not' and still are not (to major Thai merchants). varying degrees)' familiar with the changes that Usuallyl when the rough parcels arrive in can be made in their raw materials by heat treat- Bangk01z~they are split up and sold in smaller lots ment. to the cutting factories. Oftenl the parcels are of This situation has allowed the Thais to virtu- selected rough stone to suit the particular talents ally monopolize the buying of Australian rough) of the individual lapidaries. Some lapidaries prefer purchasing approximately 95% of the total pro-
144 Sapphires from Australia GEMS & GEMOLOGY Fall 1985 duction. While various Thai buying groups com- At the lower end of the scale, all poor-quality pete against one another, it is interesting to note goods in Thailand are commonly referred to as that, historically, overall prices offered are always Australian, whether they are Thai or Australian in only slightly above average production costs. The origin. This has caused Australian sapphire to gain cut-stone business in Thailand is highly competi- an ill-deserved reputation as being of poorer qual- tive with an ever-continuing "price war" between ity than Thai sapphire. merchants. Business is generally conducted on a In addition to blue sapphire, Australia pro- 'high turnover, low profit" principle. This has duces some magnificent gold, yellow, and green kept prices very low. To reduce their overhead, sapphires. Because these goods are so rare in rela- lapidaries cut the rough stone for maximum tion to the blue production, and because their po- weight return and the least labor time required to tential is easily assessed in the rough form, they produce acceptable goods. Unfortunately, visiting are usually cut and marketed in Australia. How- cut-stone buyers are prepared to buy such goods, ever, all the yellow, green, and parti-colored sap- because they in turn need to be competitive in phire rough produced would not represent 1% by their own local markets with other mechants who weight or value of blue production. As beautiful as buy stock from Bangkok. Therefore, the full po- they are, they are only of very minor economic tential of a very large amount of excellent gem importance to the miners. material is not realized because of poor cutting. Almost any jewelry store in the world with a In addition, better-quality Australian sapphire reasonable range of jewelry set with sapphires is is often not sold as such in Thailand. Quite a con- bound to have within its doors an Australian sap- siderable amount of the best Australian material is phire, and perhaps as much as 80% of all the smal- sold mixed into parcels of Sri Lankan, Cambodian, ler, medium to dark blue stones come from "Down or Thai sapphire. While Thai merchants increas- Under." ingly refer't6 average and better-quality goods as Australian, many of their customers still insist on FUTURE PROSPECTS selling such goods on their home market as Thai or The aerial extent of the basalts of eastern Australia Cambodian-in origin when, in fact, they know and is huge (approximately 350,000 km2) compared ask for Australian goods when buying in Bangkok. with Southeast Asia (90,000 km2), so the potential
Figure 21. Production of Australian rough sapphire from the Anakie and New England fields, 1892 -1 984, as compiled by B. C. O'Leary (1985) from the Australian Bureau of Statistics. Note that the production returns on which these figures are based (given in Australian dollars) are only provided by the larger producers. The author suggests that actual production may be twice that indicated. Also, the values do not take into account increases in unit sellingprices; today's market value of pre- 1924 production would be considerably greater than the graph indicates. The current value Production of Rough Sapphire from Anakie and New England Fields, 1892-1984 of the Australian dollar is approximately US$0.75.
Sapphires from Australia GEMS & GEMOLOGY Fall 1985 145 for the discovery of new, economic sapphire fields Anakie approximately 60%, in the last five years is good. Considering the similarity of the deposits (pers. comm. with miners). and the types of gemstones produced in both Aus- It will be interesting to see what happens when tralia and Southeast Asia, it is surprising that only the effects of this reduced production filter down very few pieces of ruby have ever been found. Per- to the marketplace. In order for there to be an haps future prospecting will uncover deposits increase in mining activity, prices will have to rise similar to those of Cambodia and Thailand. considerably, to such an extent that current mar- During the last few years, however, there has ginally profitable deposits will become viable been a reduction in sapphire mining at both the propositions. Anakie and the New England fields. This is due to There is also the possibility that the virtual several factors and, at this stage, it is difficult to monopoly that the Thais have over Australian determine whether or not it will continue. Specifi- rough purchases may be eroded in the future. As cally, a number of presently known reserves ap- the number of miners is reduced, there is more pear to have been mined out. Also, the last few chance of regulation, either self-imposed or years have seen a rapid rise in fuel, labor, and government-enforced, of rough-sapphire market- equipment costs. As there has been no major in- ing techniques. This, combined with an increased crease in demand or in prices due to the recent worldwide knowledge of heat-treatment methods general world recession, many operators-both and a demand for better-quality cutting, could re- large and small-have stopped mining. Current sult in larger volume markets for rough stones production levels from New England are estimated within Australia and internationally at centers to have dropped approximately 40%, and at other than Thailand.
REFERENCES Anderson 0.(1971) A century of sapphire mining. Queensland Cretaceous/Tertiary diatremes in New South Wales. Geo- Government Mining Journal, February, pp. 41 -5 1. logical Survey of New South Wales, Quarterly Notes, No. Department of Mineral Resources, New South Wales (1983) 53, pp. 23 -27. Sapphires in New South Wales (brochure). MacNevin A.A. (1972)Sapphires in the New England District Dunstan B. (1902)The sapphire fields of Anakie. Report, Geo- of New South Wales. Records of the Geological Survey of logical Survey of Queensland. New South Wales, Vol. 14, Part 1, pp. 19-36. Gubelin E. (1974)Internal World of Gemstones. ABC Editions, Monteagle D.B. (1979) The Sapphire Fields 1879-1979. City Zurich, Switzerland. Printing Works, Rockhampton. Gunawardene M., Chawla S.S. (1984) Sapphires from Kan- Moon A.R., Phillips M.R. (1984)An electron microscopy study chanaburi Province, Thailand. Journal of Cemmology, Vol. of exsolved phases in natural black Australian sapphire. 19, No. 3, pp. 228-239. Micro and Microscopica Acta, Vol. 15, No. 3, pp. 143- 146. Jobbins E.A., Berrangi J.P. (1981)The Pailin ruby and sapphire Nassau K. (19841Gemstone Enhancement. Butterworths, Lon- gemfield, Cambodia. Journal of Gemmology, Vol. 17, No. 8, don, ~n~land. pp. 555-567. Schubnel H.I. (19721Pierres Precieuses. Dans le Monde. Paris. Keller P.C., Koivula J.I., Jara G. (1985) Sapphires from the Webster R. (1983)'~ems: Their Sources, ~escri~tionsand Mercaderes-Rio Mayo area, Cauca, Colombia. Gems ft) Identification, 4th ed. Revised by B. W. Anderson, Gemology, Vol. 21, No. 1, pp. 20-25. Butterworths, London, England. Lishmund S.R., Oakes G.M. (1983) Diamonds, sapphires, and
146 Sapphires from Australia GEMS & GEMOLOGY Fall 1985