All,
I wouldn't rule out algal deposits on marine sediments however!
eric
On Jun 27, 2008, at 3:38 AM, Steve Jolley wrote:
> -----Original Message-----
> From: Michel CUNEY [mailto:[log in to unmask]]
> Sent: 26 June 2008 22:04
> To: Christian Hibsch; [log in to unmask]; Jolley, Steve J
> SUKEP-
> EPE-T-D
> Subject: Re: [toutG2R] Fwd: Re: 2.5 by old lichen from Witwatersrand
>
>
> Dear Steve,
>
> I totally agree that strong tectonic has affected the Wits basin.
> I totally agree that hydrocarbons have migrated from organic bearing
> marine
> sediment layers, but the fluviatil to deltaic deposition of the
> reefs was
> devoid of organic matter because there was no plants during Archean
> on the
> continents.
> Concerning the uranium oxides with organic matter I have two
> comments :
> (i) - If uranium was transported as uranyl ions and reduced by organic
> matter, these uranium minerals should no contain thorium which is not
> soluble at low temperature,
> (ii) - I wonder to what corresponds the "a radial mesophase structure
> around the uraninite grains showing preferred orientation of minimum
> reflectance".
> Typically uranium minerals induce alteration of the host minerals and
> especially organic matter with decrease of the reflectance. If it is
> radial
> relative to the uraninite it is probably related to a radiation
> effect.
> Have you pictures of these "radial mesophase structures" ?
>
> Your observations document clearly that at least some part of the
> gold and
> uranium have been remobilized, but do not contradict a possible
> initial
> detrital origin of these metals which in turn is clearly supported at
> least by :
> - for gold : by the Re-Os ages on gold particles at 3 Ba
> - for uranium : the presence of high and variable Th contents in
> coexisting
> uraninites.
>
> Best Regards
>
> Michel Cuney
>
>
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