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Fluoritization in paleozoic biogerms, Tatarstan, Republic

 
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Dmitriy Volkov
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Joined: 03 May 2004
Posts: 4
Location: Moscow State University

PostPosted: 20 Nov 2007 14:24    Post subject: Fluoritization in paleozoic biogerms, Tatarstan, Republic Reply with quote

Hello, colleagues!
I'm a post-graduate from Moscow State University, Russia. Now I'm researching the structure and conditions of origin of Menzelinskoe (Мензелинское) oilfield in the northeast of Tatarstan Republic. This oilfield is associated with high carbonate "reef" of upper-devonian-tournais age. So, it is situated in the paraxial depression zone of Kama-kinel channel system and reaches the 381 m height. Having been studying the core material from it I discovered numerous occurence of green fluorite in white recrystallized calcite. Observations were taken through binocular of 0.6-7x zooming, because thin sections had not been prepared yet. :) So, distinct small crystals of fluorite in crystal calcite matrix or thin green films along the borders of organic debri are visible on the surface of core samples. Can you help me, what could cause such mineral association in biogerm carbonates? I consider this fluorite to be of low-temperature hydrothermal origin, but... I'm ebarrassed with the fact that these fluorite agregates are not intercommunicated, they are not located along fractures but their distribution is sporadic. Thank you. :)
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Jesper K. Nielsen
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Joined: 22 Mar 2004
Posts: 20
Location: SINTEF Petroleum Research, Norway

PostPosted: 27 Nov 2007 15:05    Post subject: Hydrocarbons and/or hydrothermal alteration Reply with quote

You are right! The fluorite and the blocky calcite could be result of low-temperature hydrothermal alteration of the carbonates. Is the carbonate "reef" located on a structural high? If yes, down-faulting of the tectonic block could have forced for instance metal-bearing fluids along the faults to the overlying carbonates. Have you looked for oil staining and oil inclusions? In the Norwegian Barents Sea region, minerals such as fluorite, blocky calcite and native sulfur occur in warm-water carbonates (Late Palaeozoic) which have experienced hydrocarbon migration. A combination of hydrocarbon migration and hydrothermal alteration is evident from late Permian carbonates in the East Greenland Basin. Well come to contact me for relevant literature.

Best regards,

Jesper Kresten Nielsen


SINTEF Petroleum Research, Norway
Email: jesper.nielsen@iku.sintef.no_nospam (remove: _nospam)
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Dmitriy Volkov
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Joined: 03 May 2004
Posts: 4
Location: Moscow State University

PostPosted: 28 Nov 2007 09:26    Post subject: Reply with quote

Oh, thank you! It seems to be exactly as you have described! The base of the reef is strongly faulted, it looks like broken plate, I suppose. :) Faults come from a depth of crystallic basement (we can trace them by seismic sections to depth at least 500 m under the basement top!) and penetrate the upper strata of sedimentary mantle. So, they break all the oil reservoires and we consider them to be fluid channels though the source oа oil is problematic: there aren't effective oil-generating formations within a radius of 120 km...
So, Jesper (may I say like this? :) ), I've found another evidence of low-temperature hydrothermal alteration: this recrystallized calcite with fluorite inclusions fills large caverns in weakly modified biogerm carbonate. And in the border of these two lithotypes we can see thin sulphide film (pyrite or, to be more likely, chalcopyrite).
I'd be glad to demostrate the photo of these caverns but I don't know the way to do it in this forum. :)
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PostPosted: 05 Dec 2007 14:56    Post subject: Photo Reply with quote

Hi, to post a photo in this forum:

Write the text below, but replace the http-text with the location of your photo:
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Or, send the photo to the Carbonet Network manager (brafaelsen@hotmail.com) and I will fix it.
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