FMF - Friends of Minerals Forum, discussion and message board

[RayStraw]

I understand that these sulfides that are near the surface can be oxidized and then the products transported below the surface to form enriched deposits.
I am looking for chemical equations that describe possible processes. References would be helpful, but I am happy with just the equations.
Any help or suggestions would be appreciated.

Ray Straw

[Matt_Zukowski]

This is a huge topic and the answer depends upon what type of primary mineral deposit is being exposed. Look for books or sections of books titled supergene enrichment. I googled
the string: supergene Oxidation of Copper, Lead, and Zinc sulfides, and many things came up including a wikipedia page that gives you a good starting point to thinking about a general framework of supergene enrichment.
https (colon) //www.wikiwand.com/en/Supergene_(geology)

To find something about the depth of this topic just google the string: tsumeb supergene chemistry.

Here is a short report on supergene assemblages in various VMS deposits.
https://pubs.usgs.gov/sir/2010/5070/c/Chapter12SIR10-5070-C-3.pdf

[RayStraw]

Thank you for the quick reply.
I’ll start checking out the material and advise how it goes.
Ray

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[Roy Starkey]

I suggest that Peter Williams' book is the most accessible reference source on this subject.
P. A. Williams. Oxide Zone Geochemistry. London and New York (Ellis Horwood and Prentice-Hall), 1991. 286 pp. Highly recommended but long since out of print. Copies should be available via the library system but second hand copies are pretty scarce.

[Pete Modreski]

Ray, as I think you do understand, entire volumes have been written about the nature and details of this process of secondary enrichment in ore deposits. I don't think there is any simple answer(s) to your question. One can just start by writing the chemical formula of the original sulfide mineral and that of the end-product oxide, carbonate, (or, other sulfide) mineral, and just write a balanced chemical equation for the reaction, adding or subtracting water, CO2, O2, and SO2 or H2SO4 as needed, and this will give you the overall chemical reaction that must have taken place. The detailed mechanism--exactly what chemical reaction steps have taken place along the way--can be much more complex, may or may not be totally decipherable, and may differ from one locality and environment to another.