Contributions to Gemology No.7 - Winza rubies identified
Adolf Peretti; Detlef Günther; Francesca Peretti; Anong Kanpraphai; Kathrin Hametner; Willy Peter Bieri
Gemresearch Swisslab AG (2008)
In Collection
#96
10*
Science
Corundum, Gemology, Tanzania, Ruby, Pargasite
Hardcover 9783952335970
English
A new ruby occurrence was discovered in spring 2008 in the area of "Winza" in the province of Dodoman, Tanzania. The rubies are of excellent color and exceptional clarity. They are found mostly in primary mines or in the near-surface alteration zone. Other corundum varieties, such as blue sapphire, pink sapphire, orangy-pink sapphire ("Padparadscha"-color) and color-changing sapphire have also been discovered. However, only the rubies gained market importance.
The mine is situated SW of the capital (Dodoma) and can be reached by driving to the local town of Mpwapwa (pronounced "Papua") and by a further 3 hours of driving (in the dry season) to the mining site, locally known as "Winza Mine". Primitive methods were used to mine the sites rather than mechanized large-scale mining. A large number of companies, including gem dealers from Tanzania, Sri Lanka and Thailand established local buying offices in the town of Mpwapwa, about 100 km from the mining site. As a consequence, significant numbers of rubies appeared on the world market in the same year as the discovery. Later that year, production sharply declined as many miners rushed to a gold finding nearby and when it became clear that the simple methods used for mining wering not produce any further valuable ruby findings.
The purpose of this report is to identify these rubies at a critical time when synthetic or heated materials could have been mixed with parcels of “Winza” rubies. It is based on extensive fieldwork and sampling that was only possible after a special permission was granted to GRS by the Tanzanian government and with the support of the Thai and Sri Lankan gem community.
“Winza“-(Dodoma province) rubies can be identified and separated from all synthetic and natural unheated and heated counterparts. The identification can be largely based on inclusion analysis. In special cases, a combination of inclusion analysis with special analytical methods (LA-ICP-MS, UV-VIS-NIR, ED-XRF and FTIR) is needed. Heat-treatment can be identified by a combination of inclusion and FTIR-analyses.
The chemical compositions of the “Winza” Tanzanian rubies are characterized by equal amounts of chromium and iron. The iron concentrations are slightly lower than those of Thai rubies, but much higher than rubies from marble deposits (Burma, Vietnam, Afghanistan and Tajikistan). Vanadium and gallium concentrations are lower than in rubies from marble deposits (e.g. Burmese rubies).
Their chemical compositions can also be used to distinguish between most synthetic rubies, including flame-fusion type, and, with minor exceptions, from Flux and iron-rich synthetic hydrothermal rubies. FTIR spectroscopy may be necessary to separate Winza rubies from synthetic counterparts. FTIR spectra revealed a series of OH-absorption lines near 3158 wave numbers. These Infrared absorptions are in general not present in other unheated or heated rubies of other origin.
The new ruby material contains curved and circled long needle inclusions not found in any other ruby material. These inclusion features can easily be utilized to differentiate between all types of synthetic rubies known so far. The Winza rubies formed in garnet-pargasite-corundum rocks of upper amphibolite to granulite facies metamorphic grade. Consequently common ruby inclusions are pargasite and garnet, as well as apatite, whose normalized REE pattern show a prominent positive europium (Eu) anomaly.
Product Details
Edition 2nd
Series Contributions to Gemology
Issue No. 7
No. of Pages 97
Height x Width 305 x 217  mm
Personal Details
Read It Yes
Store Rubin & Son
Location A 3
Purchase Price 42.00 CHF
Purchase Date février 2013
Condition First hand
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