How is it determined that a mine has run out of gold?
In: 7119
Usually when the mine operates at a loss for some amount of time. If it costs them $20,000 per day to operate but they are only getting $5,000 in gold each day then that’s not good.
No mine really ever “runs out”. There’s always going to be some of whatever is being mined left. The point at which a mine is abandoned is when the concentration of what you’re mining in the rock you excavate is too low to justify operating the mine. It stops being economically viable.
If you have the desire, resources, and complete lack of self preservation (abandoned mines are lethally dangerous, DO NOT ENTER THEM) you could still dig up some trace amount of gold/coal/salt/whatever from a mine.
economic analysis.
typically mines go after the rich ore veins first.
when they run out of those they go lower and lower quality veins until it costs more to mine than the gold can be sold.
Mines have what is called a cut off grade. Ore is prospected by Geologist. The geologist than make up 3d maps with blocks of ore in them, the Gold grade in this ore is known (estimated). The grade being Gold content of the block often given in grams per tonne or whatever strange system the USA uses.
Depending on how deep down or how much earth needs to be moved to get at the block a cut off grade determines if it is to be mined or not. The cut of grade is the lowest amount of gold per tonne that is economic to mine. It is worth noting that this cut off grade also varies with the gold price too.
A mine will have a mining plan normally a long and a short term plan. A well run mine will know well in advance that it is running out of economically viable ore and will slowly start to shut down according to a well planned schedule.
It is true to say the gold never runs out it just becomes un economic. Sea water contains gold in minute amounts as there is so much sea water most of the worlds gold is in the sea just not economic to recover.
I am a mining Engineer with over 20 years experience in Gold mining. The above explination is far from exhustive but is aimed at a 5 year old before hundreds of correction appear below.
Happy to answer more detailed questions if you have them.
In large scale mining (not just for gold) core drilling is done to determine the size, concentration and extent of ore bodies underground. I used to work at what was the largest underground mine in North America, they had a very good idea of their target ore–the mine was on top of a large, roughly hemispherical ore body, the farther down they went the bigger it got.
It was a molybdenum mine high in the Rockies. They claimed that they were not in the gold business, though it was encountered from time to time–a well known historic gold mining area was just on the other side of the mountain ridge. Mine development was carefully planned by the engineers, where, when and how tunnels were drilled and shot, etc. Miners being miners, when they’d run across a gold vein, well, those carefully laid plans went out the window–the miners would start following the gold instead of the plans. Management teams would be brought in, concrete forms built to wall off the gold from access. For all that, though, rumors persisted that there was gold extraction going on behind locked doors up in the mill buildings.
See this hole, I can pull 10k a day out and it cost me 5k a day to do it.
1 month later:
See this hole, I can pull 4k a day out and it cost me 5k a day to do it.
Time to stop. Operation is at a loss.
If I really had to explain it to my 5 year old which I have:
You can reach into the cookie jar and get as many cookies as you can pull out if you give me 1 cookie before you do it.
The next day:
Cookie jar has half a cookie left in it. You can reach into the cookie jar and get as many cookies as you can pull out if you give me 1 cookie before you do it.
While most of these answers are somewhat correct the true answer is once a mine stops producing they will drill what are called condemnation holes to make sure they have exhausted the profitable resource.
An ancient process called fire assaying. Determines the ppm gold in a sample. I used to be a fire assayer. AMA.
As mines are operated, the activity of drilling to test for new resources and reserves becomes logistically easier and much less expensive. For example, in an underground mine where the ore body is very well defined and various tunnels and drifts are mined, operators can easily mobilize a drill at depth to punch several holes in a fan-shaped pattern in any vector within 3D space. This is much cheaper than mobilizing a rig at the surface which has to drill through a bunch of overburden and country rock to get to the potential mineral resource (ie, as in a typical early or advanced stage exploration project).
So as an orebody is mined out it’s constantly being drilled at depth to (hopefully) expand the resource and define mineable reserves. Typically operators are able to tell when either the continuity or the grade of the resource is tapering off, and the mine planning and wind down is taken from there.
There is some truth to what others are saying in that sometimes mines run at a loss for some period of time towards the end of its life, but I’d argue that this is generally an unexpected situation for the operator as they would have tested the resource and expected the mill output to generate a profit. As we know, capitalists don’t like to run an operation at a loss for very long, or at all really. In most cases, drilling during operations allows operators to plan for end of life ramp down.
just realised that when someone asks for info on reddit, 95% of people just google it and then speak on it as if they work in that field smh
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