New Ruby Source from Tanzania


Adolf Peretti (1,2,3), Francesca Peretti (2), Anong Kanpraphai (3), Willy Peter Bieri (2,3), Kathrin Hametner (4) and Detlef Günther (4) ,

(1) GRS Gemresearch Swisslab Ltd, Sempacherstr. 1, CH-6003 Lucerne, Switzerland
(2) GRS Gemresearch Swisslab Ltd, Rue du Marche 12, CH-1204 Geneva, Switzerland
(3) GRS (Thailand) CO LTD, Bangkok, Silom 919/257, 10500 Bangkok, Thailand
(4) Laboratory of Inorganic Chemistry, ETH Hönggerberg, HCI, G113, CH-8093 Zurich, Switzerland


A completely new type of ruby material has been discovered in Tanzania in the area of “Winza” in the province of Dodoma. 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”.

The rubies are found mostly in primary mines or in the near-surface alteration zone. Miners from many different parts of Tanzania rushed to the mining site when gem quality rubies of excellent colors and exceptional clarity were discovered in spring 2008. 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 positioned themselves in the local town of “Mpwapwa”, about 100km from the mining site, where they established local buying offices. As a consequence, significant numbers of rubies were excavated and appeared on the world market in the year 2008. (Fig. Tan01, 04)

Other corundum varieties, such as blue sapphire, pink sapphire, orangy-pink sapphire (“Padparadscha” -color) and color-changing sapphire have also been discovered from the Winza mine. However, only the rubies gained market importance.

We published a first report on the properties and identification of the new ruby material from this mine in Tanzania on our website (Lit. Tan07). The aim was to support the identification of these rubies at a critical time, when synthetic or heated materials could have been mixed with parcels of “Winza” rubies. In the same period of time other laboratories also noticed the importance of the materials (Lit Tan01-Tan11) particularly during the Basel Fair in April 2008. Our initial research was based on a first expedition by one of the directors of GRS (Thailand) to the mine in March 2008. Extensive fieldwork and sampling was only possible after a special permission was granted to GRS by the Tanzanian government on the initiative of a Tanzanian miner and the support of the Thai and Sri Lankan gem community in August 2008 (see acknowledgements). During the onsite investigation took place, the labor at the mine already sharply declined as many miners rushed to a gold finding nearby and when it became clear that the simple methods used for mining did not produce any further valuable ruby findings.

A new phase of mining is expected to begin in early 2009 when more advanced methods are eventually introduced at “Winza”.

Fig. Tan01 Top: A pair of gem-quality “Winza” rubies over 13 ct and a heart-shape “Winza” ruby over 7ct. Row 2 and 3: The two rough on the left were faceted to the rubies over 10cts that are shown on the right (tested by GRS in Bangkok in March 2008). These rubies were partly responsible for initiating the rush to Winza (Tanzania). These faceted rubies of over 10ct possess excellent color (“vibrant” red), are eye-clean and of high brilliancy, and are spared of thermal enhancement. Because of the magnificent quality of these rubies, the Winza ruby mine became a new landmark among the most important ruby sources (Fig. Tan02). For the total number of gem quality rubies tested by GRS see Fig. Tan04.
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