Jack, per your Oro Grande question. The answer to your first suggestion is that all of the PGMs at the Oro Grande are not microclusters is true. Platinum wires are not microclusters. This is true now, but I do not believe the origional intrusion that brought the clusters from the earth's mantle had anything but microcluster PGMs as metals of value. In earlier posts I wrote that the Oro Grande had been hydrothermally altered when, first a quartz conglomerate formed and later the gold was introduced into the quartz rich area. That happened long after the PGMs and their host had been placed into the country side and metamorphosed. That event, I believe altered some of the PGMs to the larger ferro-metallic forms. At the Oro Grande some of the Ferro-Platinum wires, I understand are almost free of iron and thus are not truly Ferro-forms. The quartz breccia and thus the plumbing for the hydrothermal ascending fluids at the Oro Grande is at the edge of the PGM host and may not follow the PGM host down into the crust, therefore the bulk of the PGMs in the host may only have appreciable normal platinum where the two formations are in coincedence.
Another rule that I use with PGMs and gold is Microclusters will steal like elements or cause new microclusters to form or something like that. Sometimes you can add platinum to the fire assay of a microcluster PGM sample and neither the microcluster nor-the platinum you assay will report. Or at least some of the additional platinum will be lost. Remember from earlier posts, the ratio rules, they apply here.
As for the nuggets of gold and PGMs at the Oro Grande, I believe all of the gold at the Oro Grande is normal. There is no problems in assaying gold there. There are just too many inept assayers out there that don't know how to assay Oro Grande type ores. My goodness, the assayers in the first half of this century could assay the gold and they could produce it too.
Now the answer to your aqua regia question. Is a microcluster of gold or PGM normal if it is in Aqua Regia. Yes and no. After digestion of the sample, take the Aqua Regia solution and add amonia until the solution has a pH about 4.5 to 5.5. At this point the aqua regia will begin to smell of amonia.Filter out the precipitates of ferrous and other interferences. Remember, gold is soluble in amonia as a chloride. I believe platinum is also, but am not positive on that one. The true gold and platinum ions as chlorides salts will report to an AA analysis. I guarantee it. The ferrous interferences having been removed will not cause false readings to occur. In the beginning you started with a sample that contained gold and PGMs as clusters is my assumption for this presentation. The very stable microclusters will likely dissolve as gold and PGM microcluster colloid chlorides. The mega ions (clusters) in the acid will report as mega ions, but the AA will fail to recognize them because the microclusters will be in the acid as elemental clusters. There might be 39 gold atoms with only a +1 valence, or maybe a +3 and a -1 for the whole cluster. As individual atoms the gold has zero valence. The combinations are amazing. For the AA to identify the gold, it must be converted or dissassociated into single gold atoms with the appropriate ionic valences. Some microclusters are said to withstand temperatures above 10,000 degrees centigrade before dissassociation will occur. How could aqua Regia get the job done with chemical energy alone. It is physics that made the beasts and physics that dismantles the beasts. This is true for the more stable ones, however I am sure there are intermediate lesser stable forms as well. These are more easily recovered by the amateur.
Jack, you show an obvious knowledge of the Oro Grande and its suite of values. Than, if you think about it, with an understanding of the geology and mineralogy for that deposit, I think you will at least agree with how I see the deposit as a reasonable "hunch".
Good questions, shows that you have given this some thought. I hope I didn't go too far over the head of most readers looking at this post, but your question required a little more technical lingo.
mike |
