Iolite Lode

4 Minute Read

This article was originally posted on Userblogs on 2/18/2018.
By Gordon AustinMore from this author

The tiny state of Rio Grande do Norte, Brazil, has long stood in the shadow of the neighboring state of Paraiba, home to the famous Paraiba tourmaline mine. In fact, Rio Grande do Norte's most talked-about gem find to date is the CDM tourmaline mine - famous because it produces blue green tourmaline that's sometimes mistaken for Paraiba.

The state may finally have a chance to develop an identity of its own with the discovery of a vast iolite deposit near the city of Parelhas in Rio Grande do Norte. The mine produces iolite of exceptional color and quality that is only just beginning to hit the market.

Iolite Lode
Miners look for iolite nodules in a wall of rock

Around 1999, a miner named Horst Munch purchased the 320-acre property surrounding the iolite deposit and filed an exploration claim for it. But he did not immediately begin to work the deposit. In fact, he put the land to a much more profitable use — as a coconut and melon ranch. Local woodcutters also used the land to cut and gather wood for small tile factories.

Prior to Munch's purchase of the land containing the iolite deposit, there had been some surface mining by local miners. The local miners hand-dug four pits that were about three feet deep, five feet wide, and more than l0 feet in length. Reportedly, total production from these small surface pits was less than 100 kilograms of rough iolite.

The iolite forms in nodules, which must be broken apart to extract the high-quality rough

During this period, the author collected iolite from this deposit that was on or near to the surface of the ground. The material was generally small in size, but of excellent color. The samples cut individual pieces of one carat and smaller, which, regardless of quality, were simply too small to be of commercial interest.

A government report prepared in 1999 gave detailed information on gemstone deposits considered to be of commercial importance in the state of Rio Grande do Norte, including this iolite deposit. The report described the host rock containing the iolite (a quartz-biotite schist) as approximately two kilometers (1.2 miles) in length, and five meters (16.4 feet) to 50 meters (164 feet) in width. Later mining would prove the deposit to be at least 25 meters (82 feet) deep, a noteworthy find by anybody's standards.

It was not until late 2003 and early 2004 that Munch and partner David Sherman decided to commercially develop the deposit. Thus, the São Barbara Mine — named for Munch's 11-year-old daughter, Barbara — was born.

Currently, the São Barbara Mine has a workforce of seven miners and cobbers. They use a pneumatic drill with a portable compressor to drill blast holes. The blast holes are drilled about five feet apart and vary in depth from three to seven feet. For blasting, the holes are loaded with a primer and ANFO, a mixture of ammonium nitrate and fuel oil.

Sorting through the rock for pieces containing precious iolite.

The iolite is found in augens (lens-shaped recrystallized minerals) or nodules randomly located within the schist. The augens or nodules vary in size from about the size of a golf ball to as large or larger than a soccer ball. After blasting, the walls and bottom of the pit are scaled down with picks, and the blasted schist is broken up with sledgehammers to release the augens or nodules. Waste material is removed up a pit ramp by wheelbarrow, and the rough iolite is hand-carried to the mine office for cobbing. A small hand hoist has been installed to move material from the deeper parts of the mining operation to the surface.

Munch has designed and built a large hydraulic splitter to break down the augens and nodules to free the iolite without excess fracturing. Once the nodules are broken down with the hydraulic splitter, hand tools are used to nip and further clean the rough.

The mine is currently producing about 50 kilograms per month of rough. They call the rough cleaned like this "mine run rough." The price of the mine run rough varies according to the average size of the individual pieces of rough, which has increased as the mining operation has gotten deeper.

Past and current mining operations have resulted in the bulk sampling of the entire length and width of the schist formation. The sampling has indicated a fairly uniform distribution of the iolite over the length of the formation.

Production to date has included very fine facet-grade, cabochon-grade, and cat's-eye iolite rough. The clean material varies in size from approximately one gram to as large as 50 grams, but the bulk of the rough is in the small-to-medium size range. The rough is priced from 9400 to as much as $20,000 per kilogram for the much-prized large, clean pieces.

The iolite form this deposit is of exceptional color.

The cat's-eye cabochons that the author saw had sharp, very well-defined eyes with a wonderful, velvety blue or blue-purple body color. The body color of the stones was translucent to transparent. When the cabochons were moved or rotated, the cat's-eye moved nicely across the surface of the high-domed cabochons. To date, the mine has produced only a small percentage of cat's-eye material.

Sadly, iolite has never gained the market respect that some other blue or purple stones have — possibly because iolite tends to have low saturation and gray-brown undertones, so it doesn't dazzle the way a fine sapphire or even amethyst can. Low demand for iolite means that it's difficult to turn a profit even on a high-quality deposit like this one. At press time, the mine was for sale.

Whether you call it iolite, cordierite, or water sapphire, the material from the São Barbara Iolite Mine is beautifully colored, and the cat's-eye material is exceptional. São Barbara may yet put iolite on the world map.

by Gordon T. Austin

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Gordon Austin

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