Tuesday, February 12, 2008

The solution: Zebra ore

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I think it is about time to solve my weekend fun picture. A few people made some guesses regarding carbonates and dolomite and indeed these do play a role here. However, no one got close enough to solve it. So what are you seeing? Everyone can notice the distinct light/dark colored layers that may remind some people of how a Zebra looks like. Indeed this is called a Zebra ore! It usually can be found in lead-zinc Mississippi Valley Type deposit that can usually be found in dolostone and less frequently in limestone. What you see here is rhytmic inter-layering of dark replacement and sparry dolomite typically called zebra structure. The brown to yellow layers are Sphalerite (with some minor Galena) occuring between dark and white sparry dolomite.

The fundamental mechanism in the formation of these structures is mainly selective replacement of primary rock by hydrothermal fluids but also of previous generations of hydrothermal dolomite along fractures, layers of higher permeability, stylolites and others.

The sample shown is from the MVT deposit of San Vicente in Peru.

References:
  • V. Badoux, R. Moritz & L. Fontboté, The Mississippi Valley-type Zn-Pb deposit of San Vicente, Central Peru: an Andean syntectonic deposit, In: A. Piestrzyñski et al. (eds. 2001), Mineral deposits at the beginning of the 21st century, Balkema, Amsterdam, p. 191-195.

2 comments :

Miguel Vera said...

Very nice man. I'm so glad to see someone lecturing on Peru's mineral deposits. I wish I can follow your steps someday, I'm just starting to learn about all this. Keep up blogging, and best of luck with your master.

The Lost Geologist said...

I do have some more samples from Peru. Perhaps I will make a small series. But only after I get back from my vacations in 2 or 3 weeks.
Too bad though that with two exceptions I never personally saw any of those sites my rocks are from.