Wednesday, March 31, 2010

Calamine deposits and geobotanical exploration aids

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Introduction

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)
 References:
  • 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

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