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News Archive
Ruby, Sapphire Mining at the New Deposit in Winza, Tanzania
As reported in the May 2 GIA Insider, some fine rubies recently produced from a new deposit near the village of Winza in central Tanzania. We undertook separate field research expeditions in April and May to the mining area to document its location, mining and geology, and to obtain research samples for characterization.
Since foreigners are prohibited from visiting the deposit, we had to obtain permission from several government officials, who also supplied police escorts. We are grateful to Dimitri Mantheakis (Lithos Africa, Dar es Salaam, Tanzania), the Saul family (Swala Gem Traders, Arusha, Tanzania) and Tanzanian broker Abdul Msellem for their assistance in arranging our trips to the Winza mining area.
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Figure 1. Miners use picks and shovels to excavate shallow pits in search of ruby and sapphire at Winza, Tanzania. Photo by
Vincent Pardieu.
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Figure 2. The eluvial soils are brought to the nearby river for washing and hand-picking of the ruby and sapphire. Photo by Brendan Laurs.
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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. At least 5,000 miners have rushed to the deposit and are using hand tools to excavate shallow pits in eluvial soil (figure 1). 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 (figure 2). 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.
Brendan Laurs
GIA, Carlsbad, California
Vincent Pardieu
Gübelin Gem Lab, Lucerne, Switzerland
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