Hi Ron, Good description on the hard rock stuff. A couple of terms that I recall from the Vercombe's report: Volcanic ash from erosion in the basin and hard-rock area came from epi-thermal fluids.
Many investors and indeed, the mining community don't understand the give and take that is going on in the assaying world about 'the weird mineralization assays.' The following comments are extracts from work by Dr. W D Groves, a Canadian who is a P. Eng, graduate chemist and graduate geologist. This dissertation was from a weekly news up-date by KJM capital. I have written authorization to use the material in whole or part from the author, Keith J. McKenzie. I believe this info. goes a long way in explaining the tug-of-war that is going on between the Cdn. labs and the U S labs. I think it also shows how complex these ores are and helps show us why the solution to these problems is taking so much time. Scientists such as this one, will solve the problems -- as science has solved so many others. When the supply of PGM's increases, the price will come down and industry will find new uses for them. All part of the learning curve. Dr. Groves:
"Assaying should be an example of the application of science, in this case the vast science of chemistry, and not the application of normative coercion by way of opprobrious use of buzz words like "scam, standard, more standard and some standards being more standard than others" (to misquote Orwell). The semi-veiled insinuation that US labs (who tend to use a little more chemistry than their Canadian cousins) are crooked, because of this also needs to be avoided if you want to stay out of the courtrooms. (Ethics vs. Methods mixup)"
"If you leaf through the table of Contents of Standard fire assay (of gold) text books you will notice:"
1) "All have about 20 chapters, most of the later ones devoted to necessary ADAPTIONS of the "standard" (gold quartz) assay recipe to take into account various groups of elements which severely interfere with or eliminate the gold determination, and have to be coped with by SPECIFIED departures from the "standard recipe" in order to get any appreciable gold recovery out of the rock being assayed. Among such groups are: Base metals like Copper, Nickel and Cobalt. Metalloids like Bismuth, Arsenic, Antimony, Selenium and MOST OF ALL Tellurium. The Platinum metals (horror of horrors) successively complicate the issues until fire assaying is usually abandoned in favour of flow sheet refining wet chemistry to isolate gold from the other metal groups."
2) "Non-standard" flux ADDITIONS, a few examples: An iron nail to remove Ir, Sb, As, S, etc.. CaF/2 to volatilize Ir, Os, Ru, as hexafluorides, NaCN to slag metalloids, borax to help slag the PGE, extra C to carburize Ir, Os, Ru, Pt, treatment of the lead button by boiling with rock salt to volatilize Te as Te Cl/3 ... and so on, need to be part of the assayers STANDARD bag of tricks to get reasonable gold recovery in the face of various specific interfering elements. To hem him in with hobbles of excessive STANDARDIZATION of procedure is to lose gold recovery from ores containing these elements, HENCE, future mines."
3) "Charging or mixing collector metal from lead to silver or copper and micro-wave pretreatment to break anionic compounds of gold (unknown until a few years ago) also can make an enormous increase in gold recovery in an assay of such deposits, and thus avoid missing these deposits."
"The mark of a good measuring stick is, does it measure? A zero assay can be EITHER a sign of no gold or (at least as often) the result of applying the wrong specific assaying procedure. One must not confuse ethics with methods, by castigating (as "non-standard") assays that get non-zero results. Very often if you measure "zip" by doing the assayer wrong, it's the measuring stick that's wrong, not the other assayer (who DOESN'T get 'zip') that's crooked. Mistaking chemical ability for ethical dishonesty can be expensive legally and a waste of potential new mines."
"I agree there IS no such thing as un-assayable gold, if you use the appropriate assay procedure. But there IS (frequently) UNDETECTED gold, for the above reasons, when the assay method is inadequate."
"If you look at data for, for example, a now-outmoded copper-nickel refining flow sheet for INCO (Sudbury Operations, Canada), you will note that the standard-lead-fire for gold is NEVER applied to gold recovery until AFTER it has been essentially isolated from the other elements by many steps of mostly wet chemistry. If the big producer-refiners rigorously applied the STANDARD FIRE method as a heads RECOVERY measure for gold on complex ores they handle, they'd go BROKE."
"This is a useful thing to factor into ones thinking when listening to their proposals for the use of STANDARD FIRE to judge the gold content of OTHER peoples ores, (Caveat vendor...?...) and an effective means of keeping new boys off the block. In current commercial lab practice, the secret lies in FAIR circulation of assay samples of a WIDE variety of ore types to calibrate BOTH assays and assayers."
"So much for gold"
"The Platinum group elements generally fare less well. Under current practice, samples are usually pre-scanned spectrograhically. The spectrographic STANDARDS (reference metal samples) and interpretative
software normally used actually screen for the PGE isotopes common in South African mines, again these being normally far less plentiful in PGE metal from other mines, which usually have very different characteristics "isotope mixes". (note: this isotope fingerprint effect is also present in other heavy metals, like lead, for example), making the source mine identifiable. This is BEFORE chemical assay. So PGE's are all too often thus all but screened out of the assay report. Whence, few new PGE mines in North America."
"So here, the enforcement of STANDARD assays involves a question of WHOSE standards, a DISTINCTLY Orwellian twist, no? STANDARD assaying has quite a subtext.....submerged beneath a cry for the enforcement of ethics, the question of METHODS becomes a submarine.....but usually STILL the main issue. Beware of the Mullahs of science.....they are administrators in sheep's clothing."
"There IS no single answer to assaying."
Dr. W D Groves 1996 |
