Naked Science Forum

Non Life Sciences => Geology, Palaeontology & Archaeology => Topic started by: ota on 10/09/2008 18:59:40

Title: when and how often are gold fire assays contaminated?
Post by: ota on 10/09/2008 18:59:40

I am an amateur. And that only because I have so many wonderful rocks on our 25 acres in the Adirondack Park area. They make great walls.
Anyway, after 5 years I wanted to find out what they are made of. I sent them off to a reputable lab in Calif.
The results of the assays showed 14.99g gold/ton and 5.23g silver/ton. Local geologist,including the state museum assures me there is no gold in NY. Also, the museum looked at a piece of the same rock under a microscope and told me there was absolutely no metal in it. Among the minerals in it ,the lab report showed 4.78 lbs titanium/ton. They told me I am looking at mica or pyrite. I sent the lab 3 more samples of the orginal rock and a few others that were nearby and giving off a flaked shiny gold color. I tried testing with a torch and scraping or bending it. Both inconclusive as I am a clutz.
My question then is, if the only logical explaination is (if the other reports are negative)contamination of my sample what are the chances of this happening with a showing of 14.99 g gold/ton? Also, is there any economic value in the titanium or do you think that is contamination. That was obtained with xray spectometry

Title: when and how often are gold fire assays contaminated?
Post by: Evie on 10/09/2008 21:33:07

This seems a little weird to me. The gold content seems very high; if you were to find 14.99 g/t gold in an exploratory drilling, your investors would be very happy.

I did find a site where someone found gold in NY state, though. It seems to be rare, but definitely not impossible. Here's the link: http://www.goldfeverprospecting.com/nogoinnywhos.html

Mica and pyrite are VERY different. Do you have a picture of this stuff?

Titanium is found in almost all igneous rocks, but is also always bonded with another element. You would have to determine the mineral the titanium is in, since only rutile and ilmenite have economic value.

Title: when and how often are gold fire assays contaminated?
Post by: JimBob on 11/09/2008 00:48:09

Bass has recently informed me that a few of the labs in California are not the most reputable of places. How much did the assay cost and how much will they do more assays for? They want a larger sample I'll bet.

But Bass is the mining geologist so I'll let him look at this 14 oz  per ton is way over the mark when you consider that 0.1 oz per ton is an economic bonanza almost.

Title: when and how often are gold fire assays contaminated?
Post by: Bass on 11/09/2008 17:35:54

There's gold in them thar hills!

Contrary to popular belief, that sentence was fist uttered in Dahlonega, Georgia- not California.

No gold in New York?  Don't believe it. 
I was once told by a very wise mining engineer that "there are two places to look for elephants [gold] in this world, in elephant country [places where gold has already been found], and in places that have never heard of elephants".  There are no known elephants in New York- but that may just mean people haven't looked for gold hard enough.  There is gold on the east side of the Adirondacks in Vermont.

JimBob is a bit over-exuberant by crediting your sample with 14 oz gold/ton (which would be very rich).  Not sure why a California lab would post results in grams/tonne, but 15 g/t works out to a bit under 0.5 oz/ton- still a rich assay.  As Evie said 14.9 g/t makes investors smile.

As to your question about contamination, it does happen- but labs go to extraordinary lengths to avoid it.  Your sample has to be crushed, dried, screened, split, chemicals added, then goes into fire assay with several other samples.  Contamination from prior samples can occur in any of those steps.

The most common minerals associated with gold are quartz and pyrite.  Do you see any iron staining on the rocks?  If so, a good indicator of pyrite.
Mica is shiny, but will flake off into flexible sheets if you probe it with a sharp knife or dental tool.  Pyrite may crumble, but not in flat sheets.

A picture would be helpful.

Title: when and how often are gold fire assays contaminated?
Post by: JimBob on 12/09/2008 02:36:34

OK, OK, this is why I leave the mining stuff to Bass. He is the expert on metals. My field of expertise is the black, oily stuff and the gas you can light with a match, i.e., petroleum.