Re-opening a 150 year old Gold Mine

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SamW

Member
Joined
Apr 1, 2022
Messages
9
Location
Queensland
Re-opening a 150 year old Gold Mine and solving the refining process

Hi All,

This thread will be to share my progress in an attempt to re-open an old gold mine and solve the refining process specific to my ore.

About myself, I am an industrial electrican and instrument technician by trade, and have spent a bit of time working as an operator / maintainer in the mining industry. I have worked both underground and above, and have had exposure to most types of machinery, including looking after all electrical/mechanical items in a large CIP plant.

By no means am I an expert in what I am attempting here, but I love a good challenge and look forward to any comments or suggestions you may have along the way!

This is a personal project and entirely self funded, so the budget is tight. Luckily I have some existing machinery to work with to get me started.

The Mine:
Originally discovered in 1869, it has historically produced around 4000oz of gold, mostly from running the quartz ore through a ten-head stamp and over a mercury amalgam plate.

The quartz orebody averaged 1metre wide and was mined to a depth of 30metres over a strike of 100m.

Back then, all the small underground mines in this area ran into difficulty as they got towards the water table and encountered sulphide ore. This mine was no different and was likely the reason it shut down. Luckily there is still enough unmined shallow ore to get me started before moving on to the more difficult sulphides. The surrounding mines in the area who went to cyanide recovery all reported good success, however this is currently not an option for me on this site right now.

The Crusher:
Already on site was a stamp mill consisting of 5 x 500kg stamps. I managed to get the whole thing running again and have fitted a 0.6mm screen on both discharge ports. With this screen I only get a total throughput of about 180kg/hr. This is not really enough to run a good profit, however it will do for now to get started and work out a reliable gold recovery method. It is fed by an ore bin with 50mm grizzly screen and a vibrating feeder into the mortar box of the stamp mill.

The Wilfley Table:
This table was apparently saved from a mine scrap heap and re-furbished by the previous site owner. This has been my biggest headache so far, mainly as I have no experience with these and finding support has been very challenging. Initially I could not get this table to perform at all, the ore would not travel over the first riffle, instead it would just go lengthways across the table! I later got ahold of some engineering drawings and found out all the riffle heights were wrong! many days were spent on a belt sander correcting this. I have now got it to a stage where it is producing a nice line of clean concentrate after many weeks of trial and error.

I found that a smooth and even water distribution was extremely critical and the original timber water feed trough was just too finicky to mess with. I replaced it with PVC pipe and holes drilled at 25mm spacings. This was a huge improvement but was having still having issues at the corner discharge end of the table. I added an experimental short spray bar at the corner which worked quite well in keeping the concentrate travelling properly, however I don't think this should be necessary if set up properly.

I still need to work on tuning the table correctly - spray bars need refining more, and I need to confirm the correct tilt and shaking frequency. I also believe my concentrate line may need to be discharging higher up the table (not at the corner?)

The Wave Table:
I purchased an Action Mining Wave Table to trial as a production table, it does do its job but I found it extremely sensitive to variations in feed or water and can actually loose gold quite easily if conditions are not perfect. I find it great for doing concentrate cleanups so that will be its purpose from now on.

Results so far?
At this stage I can produce a clean concentrate of sulphides and free milling gold. The next step is to further tune the table for correct operation and better recovery. I also need to perform proper lab testing to confirm how much I am losing to tails.

This morning I ran about 400kgs of ore through the plant, here are some photos and the end result:



 

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orvi

Well-known member
Joined
Apr 13, 2021
Messages
783
Location
EU
Jealous. In my country, this kind of ventures is practically prohibited for general public...
I wish that you keep it running smoothly and producing that yellow rock :)

How much do your average ore run ? Do you blast and continue with mining the tunnel, or just widen the hole, chasing the rich quartz seams ?
 

SamW

Member
Joined
Apr 1, 2022
Messages
9
Location
Queensland
Jealous. In my country, this kind of ventures is practically prohibited for general public...
I wish that you keep it running smoothly and producing that yellow rock :)

How much do your average ore run ? Do you blast and continue with mining the tunnel, or just widen the hole, chasing the rich quartz seams ?
Hi orvi,

The grades inside the mine are very patchy, but if averaged across the entire orebody and life of mine it works out to about 0.4oz/tonne. Current face in the mine is 1oz/t. I'm not doing any mining yet, but the quartz vein is very well defined and should be a matter of following it along underground. Previous operators sunk shafts on the quartz reef and developed cross cuts between the shafts. From here they stoped out the ore upwards.
 

orvi

Well-known member
Joined
Apr 13, 2021
Messages
783
Location
EU
Hi orvi,

The grades inside the mine are very patchy, but if averaged across the entire orebody and life of mine it works out to about 0.4oz/tonne. Current face in the mine is 1oz/t. I'm not doing any mining yet, but the quartz vein is very well defined and should be a matter of following it along underground. Previous operators sunk shafts on the quartz reef and developed cross cuts between the shafts. From here they stoped out the ore upwards.
That´s a fair ammount of gold. Should be nice to watch it on the table or sluice :)
 

Rick & Carrie

Prospectors Rick & Carrie of Geotech Analytical
Joined
Jan 30, 2022
Messages
101
Location
OR
Re-opening a 150 year old Gold Mine and solving the refining process

Hi All,

This thread will be to share my progress in an attempt to re-open an old gold mine and solve the refining process specific to my ore.

About myself, I am an industrial electrican and instrument technician by trade, and have spent a bit of time working as an operator / maintainer in the mining industry. I have worked both underground and above, and have had exposure to most types of machinery, including looking after all electrical/mechanical items in a large CIP plant.

By no means am I an expert in what I am attempting here, but I love a good challenge and look forward to any comments or suggestions you may have along the way!

This is a personal project and entirely self funded, so the budget is tight. Luckily I have some existing machinery to work with to get me started.

The Mine:
Originally discovered in 1869, it has historically produced around 4000oz of gold, mostly from running the quartz ore through a ten-head stamp and over a mercury amalgam plate.

The quartz orebody averaged 1metre wide and was mined to a depth of 30metres over a strike of 100m.

Back then, all the small underground mines in this area ran into difficulty as they got towards the water table and encountered sulphide ore. This mine was no different and was likely the reason it shut down. Luckily there is still enough unmined shallow ore to get me started before moving on to the more difficult sulphides. The surrounding mines in the area who went to cyanide recovery all reported good success, however this is currently not an option for me on this site right now.

The Crusher:
Already on site was a stamp mill consisting of 5 x 500kg stamps. I managed to get the whole thing running again and have fitted a 0.6mm screen on both discharge ports. With this screen I only get a total throughput of about 180kg/hr. This is not really enough to run a good profit, however it will do for now to get started and work out a reliable gold recovery method. It is fed by an ore bin with 50mm grizzly screen and a vibrating feeder into the mortar box of the stamp mill.

The Wilfley Table:
This table was apparently saved from a mine scrap heap and re-furbished by the previous site owner. This has been my biggest headache so far, mainly as I have no experience with these and finding support has been very challenging. Initially I could not get this table to perform at all, the ore would not travel over the first riffle, instead it would just go lengthways across the table! I later got ahold of some engineering drawings and found out all the riffle heights were wrong! many days were spent on a belt sander correcting this. I have now got it to a stage where it is producing a nice line of clean concentrate after many weeks of trial and error.

I found that a smooth and even water distribution was extremely critical and the original timber water feed trough was just too finicky to mess with. I replaced it with PVC pipe and holes drilled at 25mm spacings. This was a huge improvement but was having still having issues at the corner discharge end of the table. I added an experimental short spray bar at the corner which worked quite well in keeping the concentrate travelling properly, however I don't think this should be necessary if set up properly.

I still need to work on tuning the table correctly - spray bars need refining more, and I need to confirm the correct tilt and shaking frequency. I also believe my concentrate line may need to be discharging higher up the table (not at the corner?)

The Wave Table:
I purchased an Action Mining Wave Table to trial as a production table, it does do its job but I found it extremely sensitive to variations in feed or water and can actually loose gold quite easily if conditions are not perfect. I find it great for doing concentrate cleanups so that will be its purpose from now on.

Results so far?
At this stage I can produce a clean concentrate of sulphides and free milling gold. The next step is to further tune the table for correct operation and better recovery. I also need to perform proper lab testing to confirm how much I am losing to tails.

This morning I ran about 400kgs of ore through the plant, here are some photos and the end result:
Way cool. Keep us posted with your results.

As for the sulphides, I have read on the net that sodium hydroxide reacts with sulfur to create sodium thiosulfate, which will dissolve silver and gold.

The gold and silver can be recovered from this solution by electrowinning.
 
Joined
May 7, 2016
Messages
23
Hello Ohiogoldfever; Several things that might help in your mining adventures. First 0.6 mm is about 30 mesh which is still quite coarse and you could be loosing fine gold to your tailings. I would suggest that you try to get your table feed down to 60 to 80 mesh (0.30 - 0.21mm) preferably 100 mesh (0.150 mm). Two reasons for this : first you should be able to liberate more gold and sulfides. Second and most importanly you could start reprocessing the tailings from previous operators. Historically, mercury amalgamation only captured 50% to 65% of the contained gold and none of the sulfides. With your present setup this could be difficult to achieve. There is a company in California, Keene Engineering, that sells a small Jaw/ roller crusher that is rated at one an hour throughput. It is capable producing a minus 100 mesh product. Because the final crushing stage is the rollers it delivers a uniform particle size which will help in your recoveries.
The other idea is to further treat your middling fraction, this the material that falls off the table from the discharge corner of the table back about 25% - 30% of the length of the table. Generally the middling fraction contains an appreciable of mineral. If you acquired or fabricated a small batch style ball mill you could reduce that fraction down to 100 mesh and rerun it. For that matter you dry the middlings and run it through the roller crusher. I'm attaching a link to a web page detailing the operation and adjustments that you can make to optimize your table. I hope these suggestions will help increase your recoveries. I don't know if there is much mining your operating area but there are government mining geologists and engineers that would be delighted help you in you endeavours. I wish you great success in your mining adventure.

P.S I too am jealous.

Shrewdly

https:www.911metallurgist.co/blog/gold - shaking - tables
 
Joined
May 7, 2016
Messages
23
Hi Ohiogoldfever: There is one other thing I just thought of. That Keene crusher I mentioned would use a lot less power than those stamps and is highly portable as it comes on a small trailer. If you looked around some of the prospecting mining forums or attended a couple of the trade shows you could probably pickup a second hand one at a good price. Also you did an exceptional job at getting 100 year old equipment operational. Kiddos to you.
 

Deano

Well-known member
Joined
Feb 23, 2014
Messages
373
The problem with fine milling is that if you have gold reporting to the sulfide fraction of the ore and you want to recover this sulfide fraction for treatment by using gravity methods, most sulfides will slime when fine milled, this makes gravity recovery very difficult.
Most ores and tailings containing sulfides can get the bulk of the sulfides into either the cons or the middlings on a table without the need for fine milling.
This gives you the option of getting a high grade cons and mids fraction which you can cart to a cyanide plant elsewhere or sell to a similar plant.
Deano
 
Joined
May 7, 2016
Messages
23
You quite correct in the risk of producing slimes which would wash away instead being recovered on a shaker table. This is why I prefer a roller crush to reduce the coarser fraction as it would produce a product with a much narrower product size range as opposed to a ball mill that produces a much broader range of sizes.

I have extensive mineral processing experience and I would like to share with you one of my earlier experiences.

One of the operations I worked in was a 2800 TPD copper flotation plant. Our grinding circuit received -3/8" feed and supplied the flotation circuit with a 90% minus 200 mesh product. the slurry in the grinding circuit can be quite abrasive and to protect our pump boxes from excessive wear we mounted our pump suction pipes about 2 feet above the bottom of the pump box. This way the bottom of the pump box would fill with mud which protected the box from abrasion. The bottom of our pump boxes also collected a lot of tramp metals, and the heavier copper minerals. The accumulated tramp metals eventually reached a level where they would enter the pumps themselves and damaged the pump liners. To prevent this we periodically cleaned out the pump boxes. The material was then screened in a four deck screen and the minus 100 mesh product was saved. Once we had saved a sufficient amount of material we would process the material with an eight foot Wilfrey shaker table. This was first time I had seen a shaker table in action. I marveled at the result. Off the end of the table were fine fans of minerals and metals separated in order of their respective specific gravities. First was chalcopyrite (4.2), followed by covellite and bornite (4.7 & 5.0), then came magnetite and Chalcocite (5.2 & 5.6) then the metallics Iron and Copper (7.9 & 8.9) finally the fine gold (19.2). The fans were so cleanly separated that you could separate them with a razor blade.
 

SamW

Member
Joined
Apr 1, 2022
Messages
9
Location
Queensland
The problem with fine milling is that if you have gold reporting to the sulfide fraction of the ore and you want to recover this sulfide fraction for treatment by using gravity methods, most sulfides will slime when fine milled, this makes gravity recovery very difficult.
Most ores and tailings containing sulfides can get the bulk of the sulfides into either the cons or the middlings on a table without the need for fine milling.
This gives you the option of getting a high grade cons and mids fraction which you can cart to a cyanide plant elsewhere or sell to a similar plant.
Deano
Hi Deano,

I haven't completed the required lab work yet, only visual observations, but I think what you are saying is quite true to my particular ore - the bulk of sulphides are actually quite coarse and easily recovered by gravity from what I have seen so far. I cant really mill any finer at this stage with my particular setup - however I do have a full size berdan pan for fine grinding concentrates if needed.
 

SamW

Member
Joined
Apr 1, 2022
Messages
9
Location
Queensland
Time for an update! things have been on hold at the mine for some time while completing other projects.

However, last weekend some volunteers descended down into a shaft I have yet to explore and retrieved some samples for me. They found some good ore still left in the backs about a metre wide.

I dollied and panned a 1kg sample and got a surprisingly good result:
 

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goldshark

Well-known member
Joined
Aug 12, 2021
Messages
133
I hope you have enough experience to recognize a pillar. These are left in place to support the back ( roof ) from caving. Some of these pillars are high grade, but necessary for safe mining ops. No amount of Gold is worth dying over. And I have seen the greed kill several people in my time.
 

SamW

Member
Joined
Apr 1, 2022
Messages
9
Location
Queensland
I hope you have enough experience to recognize a pillar. These are left in place to support the back ( roof ) from caving. Some of these pillars are high grade, but necessary for safe mining ops. No amount of Gold is worth dying over. And I have seen the greed kill several people in my time.

Yes goldshark, thanks for your concern. I have previously been involved in larger scale room/pillar mining. Not planning on mining this section but was just an interesting excercise to see what was there! This was probably left behind as it wasn't high enough grade at the time. Elsewhere here they stoped all the way to the surface and backfilled as they went instead of leaving pillars.
 
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