Geology & GeoMetallurgy

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Underground Continuous Mining Machine (18 replies)

(unknown)
7 years ago
(unknown) 7 years ago

Does anyone know of a technology that can successfully mine buried consolidated gold-bearing paleochannel? This would not include equipment suited for coal or tunnel boring machines.

Also, does anyone know how to estimate the cost per foot of movable conveyors? Say 1,000 feet total? 100 tph. Thanks!

(unknown)
7 years ago
(unknown) 7 years ago

It sounds like you are asking about a road header. https://en.wikipedia.org/wiki/Roadheader

Marshal Meru
7 years ago
Marshal Meru 7 years ago

The Road Header suggested cannot mine the consolidated Paleo Channel gravels economically. Because of the hardness of the siliceous materials .such as rounded Quartz boulders, Granite boulders and all the other consolidated material in the deposit, yes you can mine it but it would be heavy going and extremely costly per/tonne. What is the grade? How many tonnes? How deep? All the economically underground Paleo deposits I have seen mined you have to follow the old channel center. Where the money is. Some of these are very narrow. Where is the property? North America? Sounds like fun though.

(unknown)
7 years ago
(unknown) 7 years ago

You may want to check out http://www.autostemtechnology.com

(unknown)
7 years ago
(unknown) 7 years ago

Thanks for the suggestions. The pay streaks typically follow the inside of the curves of the river, not so much the center.

Yes, road headers do not work on consolidated (cemented) gravels. The technology is typically designed for mining material that is "the same," whether coal or granite. The machines usually abrade the material, often spinning at high speed, rather than excavating in the usual sense.

When sharp metal teeth spinning fast encounter a two foot diameter boulder, or even a 6" cobble, that is cemented in place, cutting teeth break. Not good.

Almost nobody knows anything anymore about mining buried paleo (tertiary usually) channels anymore. California has some of the best documented buried gold placers anywhere, but very hard to get permits to operate there. My current interest is in Montana, both open pit and underground gold placer.

I tried to re-open an old California buried placer gold mine in the 1980s. The partners lost $1.6MM over 3 years, about 4 million dollars now. Any other suggestions about something that would work? 100 tph X .10 oz./ton X $1,200/oz X 10 hours/day = a lot.

Jean Rasczak
7 years ago
Jean Rasczak 7 years ago

Where was the deposit you tried to mine in the eighties? I also was involved in a mine near Grass Valley C.A. I think 1981or 82 .Was near a hydraulic pit. We were using jacklegs and dynamite, Scoop-Tram into a trommel screen. That way, there was not much fine gold in those channels. All heavy and in center and in the fractures and faults. The price was terrible then Stay in touch I know where there is some real big deposits never been touched. West Africa. Hard rock not Alluvial. Straight down fifty feet then on consolidated Quartz. Constant over 100 grams p/t.

(unknown)
7 years ago
(unknown) 7 years ago

We were mining not far from Jackson. I know very little about mining and processing hard-rock. Are u suggesting that this quartz would be minable by the same technology that I'm describing for mining cemented buried gold placer? 100 gpt? 50 feet down? Why not into production?

(unknown)
7 years ago
(unknown) 7 years ago

This is a hydrothermal Quartz vein laying under 25 meters plus of soft Laterite. Need to timber down 3 meter by 3 meter until contact of vein then drills dynamite haul up by hand until the small Head Frame is operational. Then crush, ball mill, into a Falcon concentrator. This property is in West Africa. You need Balls and Money.

(unknown)
7 years ago
(unknown) 7 years ago

Depending on the setting there are a number of ways to mine it; do you have water through the deposit and how have you mapped it ? I would take Roberts advice and leave the outer "flood" gold and concentrate on the main channel. A lot has changed since even the 1980's, the old timers tended to go for the hit and miss approach bulk mining the whole river system (Dredge), today you can map the centre channel with ground radar quite cheaply hence obtain much better yields.

(unknown)
7 years ago
(unknown) 7 years ago

What are all these comments about the "center channel?" Buried placer gravels have gold pay streaks that generally follow the insides of the curves, where the water velocity drops and so does the gold. So do flowing rivers. The fast moving water on the outsides of the curves generally scours the bottom and sides of the river bank and leaves relatively small amounts of gold.

The old miners were trying to find and stay on those pay streaks. They did it by mining in an area that showed promise. If the values dropped off or never appeared, they went in a different direction.

The Montana property I'm looking at has 33 separate adits into the Paleo Channel, sitting 50 feet above the quaternary gulch bottom.

Near our property in California, there were several hand-dug circular 8-foot diameter shafts on claims that went through later gravel flows, missed the channel and just hit bedrock. There was no technology available that could predict the twists and turns of these buried rivers. No gold, no glory. The lucky ones, who also knew what they were doing, made a reported 1/2 to 1ounce to the ton, 10 - 35 tpd. Now imagine 100 tph. This is going to happen.

(unknown)
7 years ago
(unknown) 7 years ago

It depends on the amount of energy in the system. In most large deposits, gold tends to be found in the lowest spot in the channel along with the bigger rocks. In high energy systems, fine flood gold will indeed be found on the outer edges of bends but in the scheme of things this is usually not as significant as the coarse gold found in the channel centre. One major deposit I have done a lot of work on averages 0.3gm/m across a 200m wide flood plain but up to 60g/m in the main 20m wide channel. Also be on the lookout for perched channels, which can form above clay layers and can be considerably higher in the sequence than the bed-rock. A lot can be learnt from the shape and size of the gold particles and the composition of the matrix they are found in.

I would caution you on overestimating the size of your resource, most high grade channels are fairly narrow ~ 20m and almost always thin <1m, you will need quite a considerable stream length to support a 100tph mining rate for any length of time.

Zander Barcalow
7 years ago
Zander Barcalow 7 years ago

There are several mining companies here in Alaska that drift mine buried placer channels. They drill and blast the channel in permafrost. Sometimes they decide in which direction to drill with a metal detector.

(unknown)
7 years ago
(unknown) 7 years ago

And I recently heard that that mine had shut down. True? Anyone know why?

(unknown)
7 years ago
(unknown) 7 years ago

I think Silverado opened an open pit on the property. Maybe that is why the quit drifting.

There are other drift miners in Alaska, but few and far between.

(unknown)
7 years ago
(unknown) 7 years ago

How deep is this deposit? How much overburden if you open it up? The Nokami deposit in NZ moved over 100 ft of overburden for about 10 ft of wash dirt @ about 1 g/t and made good money. I personally mined consolidated paleo channels for nearly 10 yrs up to 75 ft overburden for average 8ft of wash dirt @ 0.3 g/t. We also mined a deep paleo with a roadheader. No problems technically but the low grade and very low gold price killed us.

(unknown)
7 years ago
(unknown) 7 years ago

I have a hard rock deposit that is actually fractured quartz. There is approximately 15 to 30 thousand tons of ore averaging three quarters an ounce per ton and higher. The overburden is a soft red clay saprolite and the ore body is 75 feet down. Dips at 30 degrees down to 125 feet before it anticlines. I have the Conditional Use Permit and I am working on State permitting. The property is located in central Virginia, USA. I need a two million dollar investment in exchange for one half of the profits. These estimates do not include the values of the anticline.

(unknown)
7 years ago
(unknown) 7 years ago

Forgot to state your micro fine gold is in your clay s and will not fire assay....leech at ambient temperature your isolated clays ...have to be removed from your sand and then leech clay s with aqua-regia, a large amount of acid wash gold will solubilize as chlorides in A/R as chlorides in the spent acid...next shoot for gold on a AA not ICP....may have remove niter to achieve the solubization of the chlorides complete.

(unknown)
7 years ago
(unknown) 7 years ago

1y

Please tell us about your roadheader success and the specific ground conditions. I would also look at open pit economics.

There is no 'economic' technology fix for modern drifting. I have visited UG permafrost placers in northern Alaska but they are not long-term profitable operations. As you mention, quartz boulders will destroy roadheaders, and other seam mining technology is too expensive to operate or not strong enough to handle the changing, difficult ground conditions. Similarly, calcrete/caliche will destroy bits.

Also, as you know, defining the pay limits is extremely challenging. This is perhaps more important than the technological mining solution you seek. Technology hasn't been developed because no deposits large and rich enough to warrant development risk. How rich is this deposit? What's the variability? Thickness? Extent? Country rock strength and dilution potential? Remember that the vast majority of those old timers were poor immigrants or semi-slaves, went broke and/or died scrambling around on their hands and knees. We've recovered their personal effects at one placer mine in AK when opening old drifts for a new open pit. You need to ensure this deposit is QUALITY. IMO, UG placer mining cannot compete with bulk, low-grade surface mining or hard-rock, high-grade UG mining but it's an interesting idea! Roadheaders have gotten stronger, but still not passing 150 MPa. A solution mine was proposed in AK, basically high-pressure injection wells and pumps to mine "pods" of an extensive horizontal pay layer on bedrock. Maybe a hydraulic fracturing system and conventional continuous miners?

B
bcaldrich
5 days ago
bcaldrich 5 days ago

Mining buried tertiary (Paleo?) river channels is (mostly) dead.  "Why" these mines stayed closed after WWII is a longer conversation, but primarily caused by a fixed $35. gold price.

Search in Google:  "Continuous mechanized mining buried tertiary paleo placer gravels" or something similar.  You will get few hits, only one that is truly relevant - this posting from seven years ago.

No ME schools teach this mining method that I am aware of.  "Why" is another related, longer conversation.  Does anybody know of such a curriculum?

Photo circa 1940 attached of a bucket line built on tracks that was designed specifically for mining buried tertiary gravels.  The inventor told me that the total horsepower of the electric motor that drove the unit was - 30!  Yes, 30.  And it worked. I met him when he was age 79.  The attached photo comes from a VHS video that I had copied about fifteen years agofrom a 16MM black and white film. The video shows the bucket line excavating at the face.

A modern version was built circa 1990 with 300 horsepower. Maximum capacity was 300 tph.   The developers had in mind uses beyond mining buried placer gravels, such as tunnel excavation.  I have a video of this machine also, excavating sandstone on the surface. This machine is gone as far as I know.

The development of this technology is heating up in 2022.  Why develop a robust continuous mining method for buried gold placer gravels?

Underground mines produced between 25 - 50 tons per day in the 1930's. What if:

(Modest) open pit quantities were paired with (modest) underground gold values?

Let's not look for rich pay streaks, not 1 oz or even 1/2 oz per ton. Let's use 1/10 oz per ton.  Let's excavate ore that is uneconomic with drill and blast LHD methods in quantities that are sufficient to turn a profit.  Because even 1/10 oz. of gold per processed ton can produce extraordinary yields if tonnage is sufficient, as follows:

(Assume) 25 tph @ 1/10 oz/ton = 2.5 ozs/hour x $1,700/oz = $4,250/hour x 10 operating hours per day =

$42,500/day x 250 working days = $10,625,000 gross revenue. 

All-in costs less than $10,000/day?  $20,000?  You get to decide.

Frankly, 25 tph is not really "open pit quantities."  I would suggest that 100 tph is a more accurate minimum.  However, the profit per day becomes enormous @ 100 tph @ 1/10 oz/ton.  And, based on the modern version already built and operated and referenced above, removing 100 tph from an underground mine will be much more difficult that excavating the ore.  Such volume will require substantial development costs.  Movable conveyors?  Or some sort of hydraulic method?

If hydraulic, how do you move the huge water volumes required to move 100 tph of ore moved to the surface, then control the flow introduced into your gravity gold recovery method to maintain recoveries of -20 mesh fine gold, especially -200 mesh?   Would a dewatering screw do the trick?  I don't think so.

The modern underground miner will excavate up to two feet below grade (to capture gold in the bedrock cracks and crevices) and high enough to create a seven-foot back.

The prototype doesn't have to last five or ten years.  We are planning to build a machine with which we can conduct exploration and eventually demonstrates profitability, then build a production model. 

Our current thinking is to acquire a heavy-duty excavator with a blown engine and/or other prohibitively expensive repairs.  Tracks, sprockets, slew ring, swing gear, swing bearing (turntable bearing) and swing drive in excellent condition, but priced close to scrap/salvage value. 

Then we will construct a modern bucket line with replaceable teeth (teeth developed for abrasive permafrost, for example) that mounts to the swing drive, once again modeled on the machine that was built in 1990. Then we will add electric over hydraulic controls and sufficient electric motor horsepower to excavate cemented buried placer gravels.

The machine can be built with off-the-shelf components, no speculative R&D required.  The video I have describes the engineering done, components used, where acquired and the construction methods used.

Of course, having access to a mine with known characteristics and substantial historical development, both surface and underground, is a necessary component to reduce risk.  We have that. Plus my direct knowledge gained my on-site participation and from our partners investing $1.6MM in a failed conventional mining attempt in the early 1980's.  (That's about $4MM in today's dollars.) 

We are in the process of acquiring a second tailing pile from the same mine.  This one is about 50,000 tons and lies across the fenced boundary, therefore considered "abandoned" under mining law and now the property of the surface title owner.  In 1984, I could not get my hands on this second pile that came from the same mine that operated consistently from 1932 - circa the beginning of WWII. 

One more thing - I missed probably half of the gold that was present in the 10,000 ton tailings pile I did process.  I estimate about .01 - .02 oz/ton remains to be captured @ $1,700/oz., mostly fine flaky gold that "surfboarded" its way through my (rather crappy) gravity gold recovery system, designed by someone who "knew more" than I did at the time. He did, but not enough more. School of hard knocks, baby.

Thus we will be processing about 60,000 tons of tailings during one six-month period. (Fortunately, we have a twelve-month operating season, interrupted only by occasional rain.)  We expect gold and gravel profit will range between $500,000 and $3MM.  Should the profits be sufficient, we intend to direct those profits towards building the prototype excavator described above.

One more advantage of mechanized mining - even the best drill and blast methods shake and weaken the ground many feet in all directions from the adit that is excavated.  The blast creates its own set of safety issues.  Mechanized mining in cemented gravels should require less support of the back to maintain safety.

P.S.  Process water for the 60,000 tons will come from a well I had dug in 1984 that hit the old works, just luck - only one well was drilled.  A 200 gpm pump ran for two weeks 24/7 to drain the 8MM gallons that were in the old works. Permitting should go pretty quickly, given the (relatively) little new surface disturbance required.

P.P.S.  No waste water discharge off the property. All process water will be directed from a small tailings pond back underground through the open decline shaft.   By the time the water dumped down the decline shaft makes its way the six hundred feet back to the well, all colloidal material will have settled out.

I've had thirty-eight years to re-think and plan our current venture.  We expect to be processing tailings in 2023.  Thanks for your consideration and comments. 

Multiple buckets on 1938 bucket line on tracks
https://www.911metallurgist.com/wp-content/uploads/2022/08/Multiple-buckets-on-1938-bucket-line-on-tracks.jpg

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