"Assays - How Good Are They?"

Based on my experiences, it all depends on what you are looking for. This also probably explains why so many things are missed. You are looking for one mineral (usually Gold - the "Lust of Lucre" seems to blind people) and you miss, or ignore the others.

This takes me back to some letters I ran across in a genealogy project. There was this miner in California writing home to his wife in Ohio around the turn of the century (the last one, not this one - late 1890's). He was complaining that the State Geologist of California was refusing to take his Gold as it was too contaminated with Platinum and Black Spar (probably Tungsten). Both of these "contaminants" are pretty valuable and important today, even if they were just viewed as contaminants back then. The problem was, he was looking for Gold and nothing else.

We may laugh at this today and laugh at how primitive this miner's approach was; that he was ignoring the forest for the trees. Trouble is, it happens today all the time, even with "professional miners".

I was at the Prospectors and Developers Association of Canada annual exhibition two years ago and there was a booth touting a gold mine in South America. The sign said "9.0+ Grams of Gold to the Ton" in big block letters.

I stopped to look at the display and there were a number of samples lying on the counter. I picked one up and it was really heavy. I asked the Company's Vice President, who was manning the booth and seeking investors, what else was in the ore. He replied "over 9 Grams of Gold to the Ton". I asked if he had a full spectrum assay or a 30-plus-element assay and he advised that he did - somewhere.

It was a slow day so he started looking. After about 6 or 7 minutes he found them, in a box with some hand out literature, and handed them to me. The ore did have a lot of Gold in it, but what caught my attention was 2.2% Tungsten and 1.3% Bismuth. My guess was that the 9.0 grams per ton of Gold was probably a "Glory Hole"-type reading, but the likelihood of the high levels of Bismuth and Tungsten being representative were fairly good. Problem was, he was "going for the Gold" and nothing else mattered.

The same thing has happened on a historical basis in the West. When everyone was looking for Gold and Silver, many other things got missed. For example the Platinum Group Metals or PGMs (Platinum, Palladium, Rhodium, Ruthenium, Iridium and Osmium) often (probably usually) get missed in assays today. First off, they are difficult to assay for; secondly, the lead fire assay will not find some of them and thirdly, many of the assayers just aren't used to looking for them. The US Bureau of Land Management (BLM) did a study, on the ability of assayers to find PGMs, when they were known to be present, in 2000-2001. They supplied known samples to over 65 assay labs in the Western part of the US. The results are enlightening, or discouraging if you are a miner trying to capitalize on a find. PGMs were totally missed, identified as silver or ignored in the results. This study is something I would truly recommend reading. You can find it on the web at the following URL, http://www.admmr.state.az.us/BLMassaylabsreport.pdf#search='Bureau%20of%20Land%20Management%20assay%20results'

To put this in perspective, you have to remember that California contains the "Type Location" for Osmiridium (Osmium, Iridium and Platinum) for the world, and that PGMs have been found in over 100 locations in California, and many, possibly hundreds, more in the other Western States. I will cover PGMs and some potential locations in a couple of future columns. Let me know if you would be interested.

The types of assays done are just as daunting for the Weekend Miner. Different assay approaches include the standard Lead Fire Assay and its more expensive cousins Silver and Gold Fire Assays; Atomic Absorption; Inductively Coupled Plasma combined with various finishes such as Mass Spectroscopy, Atomic Absorption and others; Nickel Sulfide fusion and a myriad of others. In addition to assay types there are visual hints, especially where beads are produced, that can tell you a lot more about the sample you are using. It looks like I could do about a dozen columns here, on types and applications of assays, so I am sure I won't be running out of material soon.

Well, I don't want to drag on - some of us old timers may be prone to do that - so I will sign off for today. Read the BLM Study, it's worth it. We will get back to the specifics of assays and assaying in future columns.

"Old John"

Return to Home Page