HomeMajor Colored StonesRubies and SapphiresRubies from Winza, Tanzania

In early 2008, a number of unique rubies has been discovered near Winza, a remote village in the southeastern Dodoma, Tanzania. Those Winza Rubies are of excellent colours, excellent brilliancy and excellent clarity that in some cases do not need enhancement. They display a very beautiful, vibrant colours of pure red, slightly orangy-red or orange-red colors.

 

The new deposit of Winza is not only producing such magnificent rubies, but it is also producing large rubies which are almost unheard of. Unusual large rubies of excellent clarity with the complete absence of any inclusions can be found as well. Faceted Winza Rubies of over 10ct are being trade with extremely high market prices.

Despite the uncertainty of supply, Winza ruby is making a big stir for several reasons besides the fortunate timing of its discovery. The best stones boast exceptional transparency—reminiscent of that seen in Vietnamese material back in the 1990s. But whereas Vietnamese ruby hovered near the borderline between red and pink, the robust red of Winza material keeps it securely in the red zone. Although early samples tend to be orangish, new material has slight purple and blue tints. The best of the material gives Burma a run for its money.

What’s more, Winza’s enviable reds are often completely the product of Mother Nature. This deposit produces the largest percentage in recent memory of material that doesn’t need any heating to develop its good looks. Even before the ban, dealers who specialize in fine ruby found unheated Winza ruby above five carats, often startlingly crystalline as well, impossible to resist.

The Mines

The mining area is located approximately 10 kilometers southwest of Winza, and can be reached by a four-wheel-drive vehicle in about 2½ hours (much longer during the wettest season, in March and April) from the nearest small town, Mpwapwa. Which is located near Mpwapwa, about 85 kilometers east-southeast of Dodoma. At least 5,000 miners have rushed to the deposit and are using hand tools to excavate shallow pits in eluvial soil. The excavated material is loaded into sacks, carts or trucks, and brought to the nearby stream for washing. There, the soil is wet-screened and the gems are removed by hand. Several shafts have also been dug by hand to depths reaching 30 meters to explore the underlying hard-rock deposits. The corundum occurs as well-formed isolated crystals, which are typically color zoned (e.g. with an irregular dark blue surface layer and a pink-to-red interior).

 

It appears that most of the ruby and sapphire from Winza has come from the eluvial workings. There was no evidence that any corundum has been produced from the alluvium within the stream where the material is washed. In one of the corundum parcels, however, we saw gem-quality pieces of a waterworn pinkish orange mineral represented as garnet, which were reportedly recovered from the same area.

 

Most of the ruby and sapphire production is being routed to dozens of Thai and Sri Lankan (and a few African) buying offices in Mpwapwa. The material we were shown in Mpwapwa consisted mostly of lower-quality fragments, in a range of colors (often zoned) from blue to violet, purple (rarely), pink and red. Due to the informal nature of the mining, it was impossible to determine how much material was being produced, but we estimate that during our visits the miners were gathering a few kilograms per day of mixed-quality material. By early June, however, the water in the stream had grown scarce, causing a corresponding decrease in production (D. Mantheakis, personal communication, 2008). So far, gem corundum from Winza has been recovered from an area measuring several square kilometers, but the overall size of the deposit is not yet known.

Description of material

These were new kind of rubies of high transparency that were presented by several dealers had all a rather saturated red and showed no indications of heating.

Characteristic inclusions

fissures and fine bent fibres. blue colour zoning. bent fibers that were actually hollow channels filled with a polycrystalline substance (probably secondary minerals; figure 2), and partially healed fissures consisting of idiomorphic cavities with a polycrystalline filling of white and black grains.

 

 

WinzaRuby   WinzaRuby

Figure 1. This 10.75 ct ruby from Winza has no fissures and shows no indications of heating. Photo by H. A. Hänni, © SSEF.

  Figure 2. Bent needles such as these appear to be characteristic of rubies from Winza. Photomicrograph by H. A. Hänni, © SSEF; magnified 30x.

Advanced Testing

Qualitative chemical analysis of all the samples with energy-dispersive X-ray fluorescence spectroscopy established that Cr and Fe were the main trace elements, while Ga was low and Ti and V were below detection limits.

Treatment

Heat treatment experiments to remove the blue colour zones in the Winza ruby had not success, as reported from people from Chantaburi.

The majority of the new Winza ruby does not need heat treatment, Prices are all over the board. It is reported some dealers are asking over $50,000 per carat for two carat gem red Tanzanian rubies and others are reporting large rubies selling for $10,000-$20,000 per carat.

Winza Ruby from Tanzania

New Type of Inclusion Seen by Gem Labs

Ruby photomicrograph image
Arcing needle-like inclusions are unique to ruby from Winza, Tanzania, according to gem labs. (Photo courtesy GAAJ)

New ruby material from Winza, Tanzania has been the topic of much discussion in the industry since it first surfaced last November. The stones made a debut at April’s Baselworld show. Identification characteristics set this material apart from that of other Tanzania localities, which have produced ruby since at least 1950 (Hughes, Ruby & Sapphire, p. 410). Winza lies about 300 km. east of Dar es Salaam, in the region of Dodoma. Here’s a roundup of the various reports and news items on this ruby.

  • GRS director Adolph Paretti issued a report after the lab’s Thailand team visited the Winza mine in April. The lab tested 200 rough, faceted, heat-treated, and unheated. The report states that the Winza material “offers a completely new type of inclusion”—arced and hairlike needles
  • At April’s Baselworld show, the SSEF Swiss Gemmological Institute received a number of Winza rubies. Its brief report covers the same ground as that of GRS, but added that heating of the material to remove blue color zones was not successful, according to sources in Chantaburi
  • International Colored Gemstone Association’s Spring 2008 issue of InColor includes an account by Jean Baptiste Senoble of a visit with Vincent Pardieu to Winza, triggered by Senoble’s own interest after seeing the new ruby material at Baselworld. Also included is an article by Drs. Michael Krzemnicki and Henry Hänni, of SSEF, giving a more detailed version of the SSEF findings
    • Pardieu and Dr. Dietmar Schwarz, both of Gübelin Gem Lab, recounted their experience in a July 1 Rapaport News field report
  • A lab report released last month by the Gemmological Association of All Japan (GAAJ) describes its own battery of tests on the Winza material
    • The GAAJ report mentions a June 2008 article in Jewellery News Asia about the research by Gübelin Lab and SSEF

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