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News Archive
Field Study of Paraíba-type Tourmaline Mines in Mozambique
G&G Editor Brendan Laurs and Netherlands National Museum of Natural History researcher Hanco Zwaan traveled to Mozambique to explore the new Paraíba-type tourmaline deposits. Following is their report:
We visited Mozambique's copper-bearing tourmaline deposits to obtain information on their location, geology and mining in late August and early September 2007. We were hosted by Mozambique Gems in Nampula, which owns the first claim staked in the area for this tourmaline in 2003.
The Paraíba-type tourmaline deposit is located near the eastern border of the Alto Ligonha pegmatite district, adjacent to the village of Mavuco in northeastern Mozambique. An approximately 3 km2 area has been mined for the tourmaline, which is hosted exclusively by secondary deposits (paleoplacers) buried beneath as much as 5 meters of soil. The paleoplacers rest directly on top of weathered bedrock. The extent to which gem tourmaline is distributed in the paleoplacers has not yet been established.
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Figure 1: Most of the production of
copper-bearing tourmaline from
Mozambique has come from artisanal
miners using simple hand tools. Photo by Brendan M. Laurs.
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To date, most of the copper-bearing tourmaline mining in the Mavuco region has taken place in the area to the south and east of the Mozambique Gems claim by local diggers using simple hand methods (figure 1). The miners use picks and shovels to remove the overburden and dig through the material for gems with their picks when they encounter the tourmaline-bearing horizon. Although many stones are probably overlooked in the process, water for washing the soil is scarce or unavailable to the artisanal miners during most of the year; the paleoplacers are infiltrated by clay so dry screening is not feasible.
At the time of our visit, Mozambique Gems was preparing for a major mechanized operation on their 300-hectare mining concession. They had completed a comprehensive environmental impact report and performed systematic mapping and test pitting of their claim. They were also constructing a washing plant that will be capable of processing 150–200 tons of material per day. Mozambique Gems expects to complete the washing plant in early to mid-2008 and then will begin to simultaneously mine and reclaim the pits. The owners of the surrounding concessions have consolidated their claims and are making preparations for mechanized mining.
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Figure 2: A variety of colors is seen in this parcel of waterworn pebbles represented as unheated Cu-bearing tourmaline from Mozambique. Three of these samples proved to be imitations: an amethyst, a light yellowish-green fluorite and a light bluish-green glass. Photo by J. C. Zwaan.
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We purchased samples from a parcel of rough material that was reportedly mined from the Mavuco area while we were in the regional capital of Nampula (about 90 kilometers north of Mavuco). The parcel consisted of waterworn pebbles—all reportedly unheated—in a range of colors and sizes (figure 2). From the smaller pieces, they obtained samples that were representative of the color range in that parcel. Subsequent laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analyses were done to chemically characterize the tourmaline, but the data showed that three of the 20 pebbles were amethyst, light yellowish-green fluorite and light bluish-green manufactured glass. A light green pebble obtained directly from one of the miners at the pits was also identified as fluorite. Imitations, regardless of whether they are unknowingly or intentionally offered to buyers, are a concern in any gem mining area. Separating them out can be particularly challenging when dealing with multicolored parcels of waterworn rough.
The future production of copper-bearing tourmaline from Mozambique should be bolstered by the mechanized mining activities that are due to commence in the coming months. An article with more information on this tourmaline has been submitted to Gems & Gemology.
Laurs and Zwaan were guided by Salifou Konate and Chirindza Henrique from Mozambique Gems, which is owned by Moses Konate.
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