Tuesday, May 1, 2012

Morocco part 3: Bou Azzer

Bou Azzer is one of Morocco's best known mines, both for mineral specimens and for commercial production. It is the world's forth largest cobalt mine. Cobalt is a rare metal in the crust, and in our societies we need a lot of it. It is a metal very resistant to oxidation, so it is mixed with other metals to give anti-corrosion properties. This is critical for the aviation industry! In fact, cobalt prices rise and fall depending on the health of the industry. If airplanes rust and parts fail that is catastrophic. Cobalt is used to make the protective coating on galvanized steel. It is also used in lithium ion batteries in cell phones.  It is one of those substances that we do not realize we use.

Cobalt is also highly toxic!  Its name comes from the world "kobold" meaning "goblin" for its poisonous fumes that sickened miners.

The main ore mineral at Bou Azzer is skutterdite ((Co, Ni, Fe)As3)). The cobalt comes from the mantle and tends to have with it other mantle metals like nickel, iron, chromium, silver and gold. Millions of years of hydrothermal activity (again, during these period of continental collision which fracture the rocks and generate heat from melting at depth) as water leeches these elements and deposits them closer to the surface along fault planes. The Bou Azzer deposits are in the layer called Precambrian 1, the oldest rocks of Morocco.

The commercial mine, which is owned by the King of Morocco since 1953.  There is no smelting here.  They grind and sort the ore using only density separation in water.  The sorted minerals are then sent to Marrakesh for further refining (extracting the pure cobalt metal from the minerals).

We had a lecture on the geology of the deposit by geologist Mr Karfal.  Then a tour of the plant.  We got to see the shake tables, grinders and turbines up close!

First the ore minerals are crushed in grinders filled with steel ball bearings.  The now fine-grained material goes through many stages of sorting by density.  This is done using giant shake-tables with water flowing across them.  Denser particles don't travel as fast and fall off the side of the table while  the less dense grains fall off further away at the end of the table.  This allows them to separately collect cobalt-rich grains from silver-rich, iron-rich, etc. Very little is thrown out, "rejected material" merely moves on to a more sensitive means of sorting.  Here are the tables in action, notice the different color as the minerals separate from each other:

Mr Karfal lead a fabulous tour, with Eloïse and Georges translating for us!

An overview of the mining operation with a reservoir in background.  The mine relies heavily on water which they treat and reuse.

After the tour we head out to look for interesting cobalt-rich minerals in the vicinity of the mine.  Nearby in Khder quarry we found tiny red crystals of erythrite (Co3(AsO4)2·8H2O) and roselite (Ca2(Co,Mg)[AsO4]2·H2O).  This is the type locality for cobaltarthurite. Tony described this mineral and the specimen was collected by Georges. In fact all Moroccan minerals Tony has worked on were collected by Georges.

Next was Ait Ahmane mine which again was tiny crystals and only the very experienced mineral hunters (like Jean-Pierre) found anything. It did have a lovely view:

After that was Agoudal mine (a.k.a "Jackpot")!  

Here we found lovely pink cobaltocalcite, purple sphaerocobaltite, lollingite, erthyrite and roselite and even some cobaltlotharmeyerite.
We also had an additional stop at a the home of a nearby resident and collector. People were able to buy some very nice specimens from him.  On the table below are some large bright pink calcites.

What a busy day. We saw so much and got some nice minerals, back to Tamnougalt for couscous and tagine.

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