Volume 24, Number 1, January-March 2010

 Volume 24 No. 1 cover - our new look journal  
  • Foreword
  • The Argyle Diamond Mine in transition from open pit to underground extraction
  • Rubies and sapphires from Winza, Tanzania - summary of characteristic properties and short update of the mining situation.
  • Differing causes of colour in diamonds
  • The 31st Gemmological Conference
  • Tanzanite - naturally heat treated?

(Follow this link for abstracts of past issues)

Foreword from the President

Terry Coldham

I am very proud to introduce you to our Association's new format The Australian Gemmologist, produced by our new AG chairperson Francine Payette and her editorial panel. 

As you will have noticed by now we have chosen to go to a larger format allowing for better reproduction of pictures, diagrams and text. 

The AG has been continuously published since July 1958 and has seen several major format changes between then and the present. It seems that such changes have often ushered in a new stage in the development of, not only The AG, but also the operations of The Gemmological Association of Australia. I am sure the future of our organisation will prove to be as bright as this "new look" AG.

   The new look Australian Gemmologist
The new look Australian Gemmologist - A4 size with more colour

The Argyle Diamond Mine in transition from 
open pit to underground extraction

George Bosshart and John G. Chapman

ABSTRACT
 This article reports on the latest development of mining operations at the Argyle diamond mine site in the East Kimberley region, Western Australia, as well as on the outlook for the Argyle underground project which aims to extend the life of the mine to 2018. It is a challenging project using block caving techniques to mine the deeper portions of the volcanic pipe which hosts the diamondiferous lamproite ore. Distinguishing features of the mine include the high level of automation of equipment and measures to combat the monsoonal downpours.

Key Words: Argyle, diamonds, underground mining, block caving		 Argyle diamond colours
A non-representative selection of Argyle diamond colours, typically ranging from brown, grey, yellow, near-colourless, violet to pink and purple-pink hues. Photo by John Chapman.

Rubies and sapphires from Winza, Tanzania 
- summary of characteristic properties and 
short update of the mining situation

 Dr Karl Schmetzer, Werner Radl and Dr Dietmar Schwarz

ABSTRACT
 Since late 2007, large amounts of rubies as well as variously coloured sapphires have been mined from the Winza deposit, central Tanzania. While the alluvial overburden was exploited in the first two years of mining activities by up to several thousand diggers, smaller activities are performed now in the primary hard rocks. The rubies and sapphires occur within a garnet-bearing amphibolite and show a large variability in morphology. Two main groups of crystals are observed, with rhombohedral to prismatic and dipyramidal habits. The most common mineral inclusions are amphibole crystals. Colour zoning, consisting of bluish violet lamellae of sapphire within a ruby host, is common.

Key Words: corundum, morphology, habit, inclusions, colour zoning.

   Ruby on Amphibolite
Prismatic ruby on amphibolite matrix. Size of sample 25mm, size of crystal 9mm. Photo by W. Radl.

Differing causes of colour in diamonds

Chris Payne and Ronnie Bauer

ABSTRACT
A parcel of eight African diamonds of mixed colours was presented to the laboratory for certification. Included in the parcel were a 0.28 ct blue/grey/green Pear and a 0.19 ct green/grey Trillian. On investigation, the cause of the colouration in these two cases proved to be quite different.

Tanzanite - naturally heat treated?

Terry Coldham

ABSTRACT
 The September-October 2009 edition of The Mineralogical Record describes in its section on the history of Tanzanite rumours of grass fires causing zoisite to turn blue: "Legend has it that brown zoisite crystals exposed on the surface were caught in a fire set by lightning that swept across the grass-covered hills; the heat is said to have caused many of the crystals to turn blue. Some people doubt this story".		   Blue Tanzanite
Blue Tanzanite, after being separated from ash used in an experiment.

The 31st International Gemmological Conference

Terry Coldham and Francine Payette

ABSTRACT
 At the invitation of Dr John Saul and his son Mark the 31st International Gemmological Conference (IGC) took place in early October 2009 in northern Tanzania. The conference itself was held on 10 and 11 October in Arusha, a city well known to gem traders.

The conference was attended by 40 delegates and observers from 19 countries, two Australians were amongst the participants: Terry Coldham and Francine Payette, both as observers. Obviously some topics in the papers presented were related to gemstone deposits and gems from East Africa. Many other topics were covered including pearls, diamonds, coloured gems, and treatments and laboratory determinations. Terry spoke about ruby deposits in marble from Yunnan Province, Peoples Republic of China.

At the general meeting of the IGC that followed the presentation of papers, Francine was formally made an International Delegate and Member of the IGC, a great honour for her and for Australia. A proposition put forward by the Swiss Delegate Michael Krzemnivki to host the 32nd IGC in Switzerland in 2011 was unanimously approved.