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people online in the last 1 minutes - 0 members, 0 anon and 0 guests. (Most ever was 29 at 13:36:32 Sat Aug 3 2002)

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dredger
01:13:42 Sun
May 19 2013

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Interesting Placer read.


http://www.minelinks.com/alluvial/deposits8.html

smile:
[1 edits; Last edit by dredger at 01:14:58 Sun May 19 2013]

  
baub
15:07:47 Sun
May 19 2013

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Re: Interesting Placer read.

Interesting.

Thanks Dredger.

  
dredger
02:07:48 Mon
May 20 2013

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Re: Interesting Placer read.

My pleasure baub,

:smile:

Alot of good links too.

These placers may be buried under:
(1) volcanic deposits as in California and Australia ;xxxx
(2) glacial deposits as in Canada and Russia;
(3) talus and other slope deposits;
(4) aeolian deposits as in Australia; xxxx
(5) alluvial sands and gravels; xxxx
(6) marine and lacustrine deposits. xxxx

Mate, there are lots of interesting info here,
Anything there you like, ??. just off the hip, is good,
phil.


  
dredger
02:26:58 Mon
May 20 2013

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Re: Interesting Placer read.

Ouch,

GOLD

The chemical solubility of gold

This is a very complex issue that can't be resolved with a certainty in an overall approach. What follows is only a broad vision of some specific conditions that can play part in the oxidation of primary gold deposits.

Gold occurs in pyrite in three forms:

(1) Sub-microscopic, perhaps in the lattice of pyrite
(2) As native gold in small blebs, droplets and ramifying masses
(3) As irregular masses, plates and grains along fractures, slips and seams or coating of pyrite crystals

The aqueous chemistry of gold is essentially that of complex ions since the ions Au+1 and Au+3 are unstable in water because of their high oxidation potentials.

Complexing agents such as (S2O3)-2 or (CN)- or an excess of Cl- give soluble complexes of the type [Au(S2O3)]- [Au(CN)2]- and [AuCl2]- which render gold highly mobile in solution. Some humic complexes have the same facility.

Acidity (pH) of water plays important role in solubility of gold complexes.

Under acid conditions, such as where pyrite, pyrrhotite and other sulphides are undergoing oxidation, gold is more soluble and complexes with [AuCl2]-.

Under alkaline conditions gold complexes [Au(S2O3)]- and [Au(CN)2]- are mobile.

The pH seems to have little effect on the mobility of gold in the organic horizons.

The mobility of gold is decreased by the presence of H+ in alkaline environments and OH- in acid environments. The presence of Fe2+ and Mn2+, H2S or S2- may precipitate the sulphide or the free metal, thus greatly reducing the mobility of gold.
Where a high Fe3+ concentration is present gold is retained in the solution and hence mobile state. It should be noted that this applies to iron in solution; once hydrated oxides of hydroxides are precipitated these no longer play a part in the oxidation-reduction reactions.
Soluble manganous salts probably also play a role similar to those of ferrous salts in slightly acid, neutral and mildly alkaline solutions.

I like this,
"The aqueous chemistry of gold is essentially that of complex ions since the ions Au+1 and Au+3 are unstable in water because of their high oxidation potentials.".
:smile:
food for thought, ??.

  

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