Tuesday October 7th, Jim Walker entertained an enthusiastic group of DC GIA members with tales of his adventures in East Africa.
He also fascinated us with information on tsavorite and tanzanite from his mining operation with Campbell Bridges as well as prospecting and mining techniques.
He mentioned that the coloring agents for tsavorite are vanadium and chromium, and that a mixture of 85% vanadium and 15% chromium produces the ideal color.
He talked about how their mining operation is sensitive to safety issues and the environment, and has helped set the standard for safe mining in the area. He covered prospecting from the use of termite mounts for spotting potentially gem-rich pockets, to examining geological maps for concentrations of graphite gneiss and limestone to pinpoint areas.
Once the area has been identified, their mining operation lays out a prospecting grid, which is similar to the grid that archaeologists lay out on their site before excavation. The miners dig down to the limestone bedrock, and then break through it to the graphite gneiss below where the gem-bearing reef is located.
Jim talked about the two different types of reefs that tsavorite is located in, a recumbent curve and a plane. He said that they try not to do open mining, and use ventilation and supports in their tunnels; concepts that are not widely used in East Africa except by their mining operation. He also pointed out that their miners work the gemmy reefs by hand so that they don’t damage the tsavorite crystals. Once the tsavorite is recovered, it is sifted in water using a gravitation method, then graded and cut in house.
Mr. Walker topped off the evening by suggesting that AGTA organize a marketing campaign to educate the public and raise market awareness for colored gemstones, not unlike what DeBeers has done for the diamond market. He then shared some of his incredible tsavorite and tanzanite samples with our group. It was a “gem-packed” evening!
Meeting Summary by Etta Marie Dotson, PhD, GG, ISA AM
Photos by Melanie Marts, GG