Saturday, November 01, 2014

Talking with USGS geologist Floyd Gray about the Patagonia orange sludge

USGS geologist Floyd Gray [right, credit USGS] is my guest on the latest episode of "Arizona Mining Review," our online video magazine, that was broadcast on Wednesday, October 29.  Floyd described the "orange sludge" recently found in a drainage in the  Patagonia area in southern Arizona, and its relation to historical mining activities.

As usual, the show was recorded and posted to our YouTube channel.   The direct link to the show is at The interview with Floyd begins about half way into the 30-minute show.

One of our professional geologist viewers shared the following comments:

" the "environmental" half of my career I had the opportunity to study high-iron orange sludge associated with both closed mines and (active & inactive) landfills in many locations and many rock-chemistry environments.  In every case the causative mechanism is the same: low pH and Eh ground water puts ferrous iron into solution, and when that water comes into contact with more neutral, high oxygen (high Eh), the precipitation occurs virtually instantly as the iron goes to ferric.

I was impressed with Dr. Gray and his approach to the issue (which is same as mine; you must understand the causative mechanism or you will have not a prayer of undertaking a corrective action that will work).

One point I wish he had mentioned.  In the presence of ferric iron, the solubility of lead is a very low number, approaching the reciprocal of Avogrado's Number (i.e., one to one hundred atoms of lead per mole of water)."

The AZGS YouTube channel is at

All previous episodes of AMR are available at:

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