Invisible gold in ore?

[fbeal]

Some questions:

I hiked up to a couple of old digs this weekend and did some detecting. Lots of blasting caps and nails in the tailings. One large piece of quartz sounded off with the detector. When I broke it open each piece would sound off as well.

Inside the rock was a greenish metallic looking mineral(?) I assumed it was a pyrite but that wouldn't be picked up by the Gold Bug II would it?

Also, can there be valuable ore in which gold would not be visible? Should I have the rock assayed?

There are areas of float on the slopes below. Some have a red color on parts.

At one of the digs they had built a sort of oven out of rock and firebrick. I have heard of "cooking" ore but don't know much about it. Were they cooking this quartz that contained the pyrite?

Thanks for the info on my other posts.

Lanny, got any more good stories to tell? You should publish them in a magazine!

 

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[GrantWA]

Sometime in the years past I read a story about how the old miners used to cook potatoes in some manner to recover the mercury they had used in recovering gold they had mined, wonder if this could have been the reason for the oven?

I can't remember the details, but I do remember them talking about miners accidently killing themselves by eating potatoes that had been used for this.

 

[stevewa]

When I find specimen pieces, I use one of those hand held microscopes from Radio Shack. It has a light which makes it easy to see any gold if it exists. I have found many specimen pieces that contain gold with my GB2. Hope this helps.

 

[bakergeol]

Pyrite is an Fe sulfide and will be detected by a metal detector. Odds are you have detected some pyrite in the quartz. However, as mentioned above a small hand lens should enable you to see the small cubic crystals characteristic of pyrite. Just learn the mineral characteristics of pyrite. No an assay is a lot of money for a one shot deal here. By the way sounds like a good area- The old timers used to say "the redder the better" with regards to the color of quartz. Red of course the sign of iron mineralization and possible gold occurrences.

Keep looking at this site for valuable visible gold
By the way I use a small magnetometer(detects iron only) with my metal detector when searching old dumps- if I get a hit on my detector and not on my mag the specimens is cracked open or taken home-saves some time dealing with iron specimens.
George

 

[Lanny in AB]

Fbeal,

If the color is green, it may be native copper. Your detector will definitely sound off if there's a concentration of native copper in the quartz. I'm not as familiar with VLF's and rock specimens. As I remember it, I'd sometimes get positive signals from rocks with my VLF that my PI would totally ignore. It's a fact that VLF's sound off on more rocks that are "hot", but just from your description of your rock, it's hard to tell what you're looking at. If in doubt, run it in to your local university and see if anyone there in the geology dept. is willing to ID it for you.

All the best,

Lanny
P.S. Some of my stories are already published in magazines, but I spend most of my time sharing them with other prospectors.

 

[wolfcreek]

The greenish color would more likely be a copper mineral than pyrite.

 

[ChuckNC]

Here in NC most of the gold ores are sulfide based. Simple heating up to a red heat will drive off most of the sulfer and leave the gold and other valuable minerals behind. You'd be supprised at how much gold can be in these pyrites.
I have a specimen that my dad and I found almost 30yrs ago. It has visible gold and pyrite next to each other, as well as greenish splotches scattered on the piece. Some of the pyrite was tested and was roughly 25% gold by weight. The remainder was pyrite and copper with a tiny amount of platinum. Wish I could get more, but it's now under a major interstate.
ChuckNC

 

[nebraskadad]

Beal,

Check out Chuck Ashworth's article on aqua regia,

pulverize ore to 100 mesh

follow instructions to a tee.. If acid scares ya, don't do it.

I've some good resources on AR for recovery, one uses electrolysis in AR solution to get the AU out.

scrap off the black gunk and into a borax pile in a crucible hit with a torch till the hole pile melts down.

 

[chucktx8]

Most hard rock mines built a forge to repair picks & shovels.

 

[Wild Boulder Bill]

If it was invisible gold what good would it do you. i find all kinds of silver ore that is no good to me. If it were a virgin vein, you might have something but it is not as you said it was an old dig. If you can't see the gold you're not going to open a mine and it is not a collectors piece so what good would it be to you anyway, unless you are like me and interested in collecting different ores.

 

[nebraskadad]

Beal,
Most Gold is found infused in some matrix and in minute quantities. can't be seen with the naked eye. I'd ain't invisible, but would take a lot of rock to produce an OZ o' AU. the Big Mines don't look for visible stuff, they test drill and look for veins containing gold in recoverable quantities. It means they run a bunch of dirt through crushers, and cyanide vats to leach out AU into it's elemental form from Sulphides, etc, etc. you here is said on "GOLLLLLLDDDDD FEV FEV FEV, R" that only about 5% of the US gold has been recovered.. Thats' because most of it is still in the ground!!