31 March, 2010

Calamine deposits and geobotanical exploration aids


Calamine deposits, which are known in Germany as Galmei deposits, are a type of non-sulfide zinc deposits that is fairly widespread throughout Europe. Contrary to today's main source of zinc in the form of zinc sulfides Calamine deposits are, in the extreme case, free of sulfides and have reduced concentrations of lead. Usually they contain zinc in the form of carbonates, oxides and silicates. Some of the most common non-sulfide minerals are Smithsonite, Hydrozincite and Hemimorphite in supergene and Willemite in hydrothermal deposits.

The most common formation mechanism for calamine deposits is the supergene weathering and oxidation of primary sulfides. In opposition deposits containing Willemite are seen by a number of researchers as an indication of the hydrothermal formation of calamine deposits. These are classed as hypogene deposits. The calamine deposits form either by direct replacement of the sulfides, wall-rock replacement of carbonates or residual and karst-fill deposits (Figure 1). They most commonly occur in carbonate host rocks.

Figure 1: Models of formation for supergene non-sulfide deposits (Hinzman et al.)

Known calamine deposits in Central Europe are, i.e. in Eastern Belgium, the Aachen district in Western Germany, the Brilon Galmei district, some supergene mineralization in the MVT deposit of Wiesloch and a number of deposits in Poland – just to name a few. The Belgian town of La Calamine (Moresnet) gave these kind of deposits the internationally known name.

Geobotanical exploration aids

Besides a number of exploration aids that I might discuss in another blog post I would like to concentrate here on a more unusual aspect – namely geobotanical exploration aids for non-sulfides. Although these may be rather minor aids in today's world I chose to discuss these. I simply like pretty flowers. The calamine deposits in Eastern Belgium and Western Germany have indicator plants growing on zinc rich mine dumps and soils. Viola calaminaria (Figure 2), Viola guestfalica and Thlaspi (Figure 4) calaminare are known to occur as useful indicator plants in Western Europe. Viola guestfalica (Figure 3) is endemic to the region of Blankerode in Germany. They can be used as exploration aids in the search of zinc rich soils and heavy metal contaminated mine dumps.

Figure 2:  Viola Calaminaria (from Vito Coppola et al.)

Figure 3: Viola guestfalica (from Burkhard Beinlich und Walter Köble)

Figure 4: Thlaspi calaminare (from Wikipedia)
  • Vito Coppola, Maria Boni, H. Albert Gilg, Giuseppina Balassone, Léon Dejonghe (2008): The “calamine” nonsulfide Zn–Pb deposits of Belgium: Petrographical, mineralogical and geochemical characterization, Ore Geology Reviews, 33
  • Maria Boni and Duncan Large (2003): Nonsulfide Zinc Mineralization in Europe: An Overview, Economic Geology, 98
  • R.R. Brooks (1979): Indicator Plants for Mineral Prospecting - A Critique, Journal of Geochemical Exploration, 12
  • Murray W. Hitzman,Neal A. Reynolds,D. F. Sangster, Cameron R. Allen and Cris E. Carman (2003): Classification, Genesis, and Exploration Guides for Nonsulfide Zinc Deposits, Economic Geology, 98
  • http://www.schmitzens-botanikseite.de/galmei2.htm
  • http://www.egge-weser-digital.de/htm-inhalte/19080082.html
  • http://de.wikipedia.org/wiki/Galmei-Hellerkraut

27 March, 2010

Accretionary Wedge #23: What I do - or want to do.

This is a contribution to the 23rd Accretionary Wedge blog carnival hosted by Geology Happens.

I work on the microfacies, diagenesis, geochemistry and raw material properties of Jurassic shallow-marine carbonate rocks. Unfortunately that is about as much as I can openly discuss about my work details because the project is sponsored by and part of a German constructon material supplier. But that does not matter. There are plenty of issues that I love. Let me tell you about a few of them.

Shallow-marine carbonates: Even though my thesis is related there are issues I would far more enjoy. These are the recent shallow-marine carbonate environments. I enjoy watching images and aerial fotos of reef systems. The Great Barrier Reef, the reefs of the Red Sea or the Bahamas. Just to name some of the better known ones. Nevertheless I am most curious about the non-skeletal carbonates like Ooids. Their deltas and formation is still a not completely solved puzzle and a variety of conclusions on their depositional environment can be drawn from their different internal structures. For example radial or tangential ooids. Yes and, maybe it is just a good excuse to some day actually go to see the Bahamas or the Red Sea.

Calamine Ore deposits: There used to be a number of Calamine (Galmei in German) mines in the Aachen region and around Brilon in central Germany. I would very much like to work on these kinds of deposits to find out about their mineralisation history, the palaeoclimatical controls on weathering  and supergene ore formation. There is a lot of recent interest into these because of the lack of sulfides in these which makes it more environmental friendly to mine and smelt the ores.

Phosphate deposits and terrestrial evaporites: Both of these I want to work on because I know little about them. I know their uses for fertilizers and the chemical industry but their formation is a mystery when considering the details, aside of the general parts I assume every geologists knows. Sedimentary phosphorites are the most common source and directly linked to the activity of life. They are peculiar. Rare. Geologically speaking. Island or Guano deposits are small, rather recent bird droppings. Last but not least some carbonatites and pegmatites rich in apatite. Nice, shiny minerals.

Tantalum and Niobium deposits: I don't even know why I like these so much but I would really love to work on some tantalite placers in Namibia or elsewhere. This would almost have been my Master thesis topic - if financial issues wouldn't have killed it. *sniff*

So I now told you what I want to do. Some of it. Because what I do now I cannot talk about. Now all that is missing is to find someone to support all of those interests or winning the lottery that I don't play.

I am a Carbonate and Economic Geologist - when I am not being lost or travelling. :-)

19 March, 2010

Accretionary Wedge #23

The Accretionary Wedge #23 is about to take place on Geology Happens. This time it is about sharing your current findings and discoveries. Take a look at the complete announcement! Entries are due march 26th on Geology Happens. I encourage you all to participate!

08 March, 2010

Geonauten blog

A German language blog which I should have added to my blog feed long ago is Geonauten. The visually very appealing blog focuses on volcanoes but also deals with other issues of geology. It is managed by a team of four geology enthusiasts who have a background in engineering and geology. Some of the highlights are their documentaries about travels and trips to geologically interesting places. Recommendable!

03 March, 2010

Geologists - Stargate Univers

Today I saw the 3rd episode of Stargate Univers on German TV. I was looking forward to it, especially because of the geologist's character. The problem was to find a substance to filter CO2 from the air. They travel to a desert planet to search for limestone (CaCO3) to act as an air filter. But one thing at a time.

Upon arrivel the geologist looks down and takes some grains of sand into her hand. She attests it to be Gypsum (CaSO4+2*H20). The next sentence she utters ruins my evening. She says that is good because Gypsum is 36% Calciumcarbonate (CaCO3). I am shocked. Numbers aside, there is no carbonate whatsoever in Gypsum!

She says Gypsum is Calcium-Sulfide...ehem...Sulfate is the word! 

Next she explains they need to find limestone. They use a funny red liquid that has to turn clear, they do not explain what it is, to show that the sand is limestone. Sounds complicated - bad geologist: Don't they have any weak acid? 5% or 10% HCl would be a much quicker and water (one drop instead of half a liter) saving method to determine limestone. Even without any acid a good geologists should be able to identify Calcite - especially in contrast to Gypsum.

Then we learn that they need to find a salt lake to discover limestone. I am confused. Although there are terrestrial and sabhka carbonate deposits, looking for those in the middle of a Gypsum desert seems not very promising. Salt lakes have a higher potential for finding evaporites or brines to use. The brines of a number of salts could theoretically be used to absorb CO2. Apparently the Stargate Univers geologists is completely unaware of that potential and fixed on limestone.

The geologist and some other guy rebell and go to some other planet through the gate. I assume they get stranded there for eternity. A good punishment!

Also, even with a couple of cubic meters of limestone they will first need to exert a lot of their precious energy to remove the CO2 from it to gain CaO which they need to dissolve in water (also rare on the spaceship). It would be much more practical to get a some of the natural brines from the salt lake. There seems to be an underground brine source even. They would no longer require massive amounts of energy or processing.

And then - if there is so much energy as to burn lime why not use the waste heat to drive the crystal water from the gypsum? Wouldn't it be an ingenious method to also replenish the small water supplies?!

Oh well - I shouldn't have paid attention to the geologist there. Sigh.