Any core drilling experts on here?

[mulletator]

Hey guys, I managed to get a small diamond drill for really cheap and I want to use it for placer gold testing. What I want to do is take core samples of alluvial material (gravel, glacial till, soil, overburden) and to sample the bedrock for a foot or two.

The drill that I have is called a Packsack, it's similar to a Winkie drill. Similar to the one in this picture: https://icedrill.org/sites/default/...rill_at_Hudson-Mnts_credit-BRENT-GOEHRING.jpg.

I know that sonic drilling is the best way to do this but I'm attempting to come up with a cheap way to get samples for early stage projects.

The drill is designed for traditional diamond drilling with a water feed and diamond-impregnated coring bits. It has a core tube, etc.

Here's what I need to do. Keep gravel and alluvial material in the core tube without losing it, cut through gravel, rocks, and the occasional boulder. I can't use water since it will cause the gold to move so I have to do this in the dry until I hit boulders or bedrock.

What kind of bits would work for this? I don't know a lot about different bits. I need one that can work without water. I'm thinking something like in this image: https://www.premat.com.sg/897-large_default/mazier-retractable-core-barrels-.jpg

Does anyone have experience with this?

I may need to modify the core barrel too. Are there any tricks to keeping loose material in the core barrel?

 

Amazon Forum Fav 👍

Cry Of The Eagle: History And Legends Of The Cherokee Indians And Their Buried Treasure - Grab it through Amazon!

[Oilfieldsafety]

It is an interesting concept but I don't know if there is anything bit wise that will work for you in that regard, the supply water is providing cooling, mild lubrication and to remove cuttings. With that being said it has been 35 years since I worked on a diamond drill and all of my drilling time was hard rock for a mine in the Yukon.

Best of luck
Shane

 

[mulletator]

Hi Shane, thanks for the input. You are correct about how diamond drilling usually works. I'm trying to do something different.

I have seen polymers that are advertised for drilling in overburden. I'd like to avoid that but it might be a solution. I've also seen systems using air as a drilling fluid. There are systems that don't use any fluid at all but they aren't designed for this type of drill.

It's pretty common to drill through overburden but I'm focussing on the alluvial material as the primary target. Casing the hole would work but I'm trying to avoid that as well, I might need to modify the drill to use a wireline core system. Just thinking out loud here.

Take a look at this system:
I'm trying to develop something in between that and a traditional diamond core drill. Same ideas but I want to go deeper and take continuous core as well as drilling through boulders and a small amount of bedrock.

 

[IMAUDIGGER]

A geotechnical engineer will be able to give you some advice. They do soils investigations all the time for construction projects.

 

[mulletator]

A geotechnical engineer will be able to give you some advice. They do soils investigations all the time for construction projects.

Do you know anyone in particular? What I'm describing is not something that is part of any standard geotechnical investigation.

 

[Mad Machinist]

Give me a little bit. They used to make a "core bit" specifically for alluvial stuff. It fell.out of favor to augers because it was kind of a pain to use.

 

[mulletator]

Hey Mad Machinist, I'd love to hear more about this "core bit" for alluvial stuff.

 

[Clay Diggins]

The "core bit" for alluvial deposits is the bucket drill. It's still in use worldwide.

Augers don't work for placer sampling because they mix the sample throughout leaving the sample useless as to determining gold location in the strata. The traditional drill used 100 years ago for placer was the churn drill. The churn drill has the same limitation but it does provide a way to pull samples for placer gold on bedrock which was useful in the Alaskan tundra and permafrost. Augers aren't capable of pulling material from 100 foot depth bedrock.

The bucket drill is the only method (besides bulk digging) that gives a decent sized sample that hasn't been mixed with other strata or fallback from the drilling process. Here's a PDF that shows a bucket drill and describes how they are used. The bucket drill contains the sample in the bucket pretty much as it was deposited but each bucket has to be emptied and sampled separately. As you can see this type of drill will not work with your equipment.

Although the bucket drill is a reasonable compromise to sample without hand digging it has the same drawback as all placer sample methods.
The nugget effect.
The nugget effect is the reason all drill methods of placer sampling are unreliable. Unless your sample is huge (tons) and processed as a whole by leaching you can't get an accurate assay from a placer deposit. Small drill samples will produce very different assays even when drilled close together.

All gold sample systems suffer from the nugget effect. Hard rock is no exception unless the gold is uniformly very small and evenly distributed throughout the deposit. Some of the Carlin type gold deposits meet this standard but no placer deposits can. The nugget effect is well known in all types of statistical modeling and it's named after the age old problem of trying to assay a placer deposit.

Heavy Pans

 

[mulletator]

Hey Clay, I haven't heart of the bucket drill before.* I don't think that's what Mad Machinist was talking about but it's interesting nonetheless.

You're correct about the nugget effect, I've been involved in several placer drilling programs.* In my opinion sonic drilling is the best method out there but you can't do it on the micro scale that I'm working on.* At least not without a massive investment in R and D.*

R/C is also good and auger drills have their place too.* There are pros and cons to every technique.

Augers actually work really well in frozen ground.* I've used them in the Yukon with excellent results.* Sonic is still better though.

What I'm working on is just another tool as part of early stage exploration.* It's not going to be perfect but will give me a way to do some testing that would otherwise be far too expensive.

I came across these cool core barrels (https://www.globalgeotech.co.uk/mazier-core-barrel.htm) that are used in geotechnical drilling.* I like the idea.* I'm leaning towards something like that but I'm interested in what other people are using for this kind of application.

 

[Clay Diggins]

Have you read "Placer Examination, Principles and Practice"?

If you haven't read it yet you can download the full text OCR version here:
Land Matters Library Item
It's all about sampling placers for a federal mineral examination. 195 pages of expert opinions.

Heavy Pans

 

[mulletator]

Hey Clay,

Thanks for the link. I've actually read part of that book before. I'll give it another look.

As far as I know I'm trying to develop something that hasn't really been done Before, at least not exactly the way that I'm attempting to do it.

There are lots of placer drills out there and they all ha e pros and cons. My main motivation is to do this with a very cheap and portable drill, which I already have. It won't be perfect and it won't be able to map out an entire placer deposit on its own but it will be another tool in the box.

I appreciate your input. All information is very helpful.

 

[Mgumby16]

I worked for about 6 years logging soils and core samples behind geotechnical drill rigs. A diamond tipped core barrel is made for removing cores from bedrock and will not work sampling soils or alluvial gravels.

For soils and alluvial gravels we used split spoon samples that were advance in front of the soil auger. This allowed for a quasi undisturbed sample to be collected. We generally used a 2 inch dia split spoon barrel, but i believe for placer sampling they have the ability to run a 3 inch dia split spoon. Once you advance through the soil and or alluvial material and hit auger refusal the soil augers would be switched out for NQ core, which is a 2 inch diameter diamond tipped rock core set up that can generally collect 5 foot runs of rock at a time.

Unfortunately i dont believe that your rig will have the ability to run any sort of split spoon sample in front of soil augers. The smallest style of these rigs can be set up on a small tripod set up but generally requires specialized equipment beyond a simple core tube.

I hope this helps. Feel free to ask me any questions.