I am very passionate about the topic of afk mining as i have debated this for years with former cms in the past, i will respond with an open mind on what i really think needs to be done overall, miners fatigue to me looks like a Minecraft reference where it takes longer to mine an ore, this suggests you have suggested is not a slight nerf but overall a massive nerf to mining.
Why people afk mine
people use afk mining as a lazy method of making some money overnight as the risk of rulebreakers is lower at night and with the lower player base at night is the safest time, gems at the moment are somewhat easy to sell as there is a massive buyer at the moment but when there is no buyer the gems will just stay in the inventory until an update comes out, people like to hoard gems to reach a milestone and then maybe spend it on an update until they know the wheel/drop is good or not.
How many gems are made per hour
if we do the mathematics there are 3600 seconds in 1 hour, 3600 / 4 = 900 ores mined per hour, if we are talking about ruby mining and we convert those to gems we are getting 72,000 gems per hour, an iridium pickaxe is double the amount of a diamond so if we x2 the 72,000, that would be 144,000 for iridium, the golden pickaxe is the best on the server currently and it makes 3 ores per mine so that would be at the highest without bonus ores 216,000 gems per hour, taking into account the bonus ores thats maybe an additional 10% of ores over a long period of time.
Current gem prices are around $50 per
Diamond Pickaxe - $3,600,000 per hour
Iridium Pickaxe - $7,200,000 per hour
Golden Pickaxe - $10,800,000 per hour
To make these values you would have to invest more in pickaxes, prices of pickaxes go up drastically due to rarity or overall usefulness
Diamond Pickaxe - $500,000 - $1,000,000 (blueprints included)
Iridium Pickaxe - $15,000,000 - $25,000,000
Golden Pickaxe - $25,000,000 - $35,000,000
The ways to get these pickaxes are easier than others, doing daily objectives and opening some blueprint cases and you can get a change on a diamond pickaxe which are quite common and cost $500,000 to craft, for iridum pickaxes there wasnt a way to farm these until deep sea diver was out, deep sea diver takes along time to upgrade however you dont need to fully max it out, most people pay other people to max deep sea for them because it takes too long, iridum pickaxes from the deep sea crates are roughly a 10% chance to get and i believe 8 crates spawn so roughly after 1 round of running around you might get 1 iridum pickaxe, golden pickaxes are excusive and was available by the booster pack deal only meaning you cant get anymore, due to this their price is higher and since they are better than iridium they also get some value there, not many people mine with iridium because the price of iridium is high and the risk of getting killed and loosing money wouldnt be fun, thats why most people use iridum and diamond.
I do not fully disagree with this suggestion, however already there have overtime has been nerfs to afk mining and the counters of afk mining have only increased due to new items, the nerf that was added years ago was paying to convert gems, before there was no payment but they added payment of $250 per gem, then it was increased to $500 which is todays value, this removes money from the economy and your inventory so you are gaining less of a profit, i think the times to mine an ore listed are way to high on the higher end, maybe increase this but not by an insane amount which makes normal players suffer.
Current counters to afk mining that do not break rules are:
Nukes - Somewhat common as an item however only affects afk miners when the nuke is successfull
Hitman - hits for as cheap as 2500 (without the use of hit protection) the hitman can teleport to the mines instantly and kill the miners and rip the pickaxes
Lightning Strikes - when activated kills everyone on the map that is not in cover
Meteor Shower - when activated throws meteors that do significant damage and kills people around the map
Earthquakes - earthquakes being activated can move the miners and stop them from mining, which means they are practically afk with a pickaxe out leaving them a risk to the 4 counters above and below
Price Conversion - Explained Above
I do think there should be a counter to normal rock mining as afk gem mining has already been countered with many items and mechanics, i think this miners fatigue can be added however the times listed are not good and are too high, at the higher end you can only mine 6 ores per minuite, maybe if you have a better pickaxe this time should be cut down however at the base mining speed should not be countered, the server should punish players for using the worse pickaxes as they are so cheap.
During my discussions in discord we talked about some topics, its not the pickaxe themself that people complain about when getting killed during afk mining, its the potential profit they would have made if the didnt get rdmed and continued to afk mine, no one really cares about if you loose a diamond pickaxe they care about the potential money they lost, although iridiums are free if you do deep sea and get lucky it still wouldnt be nice to get rdmed.
i do have some counter suggestions which could nerf afk mining however buff other elements which are not afk, we talked about the methods that gems are removed from the eco, that is crafting and an update, other than these suggestions there should be something that players can spend their gems on that is a permanent feature.
Alternative Suggestions
Gem Convertion Price
Increasing the gem conversion again, some possible answers could be $750 per or $1000 per, this would be 25-50% more money removed from the eco and less profit if you sell the gems from afk mining.
Buffing Gem O Matic
Buffing gem o matic so people would instead use a gem o matic rather than afk mining, if a gem o matic would make more than a diamond pickaxe i think people would switch to use gem o matics which are always known for being a bad time, why not turn it to a good item.
Overal Mining Price
Why not add a price for mining every ore, after mining 1 ore remove some money from the players inventory, 250 per coal , 500 per stone , 750 per gold , 1000 per ruby.
More ways to remove gems from the economy
other than the ways i stated there isnt many methods that gems are removed from the eco, gems are practically useless unless an update is out.
A way of removing pickaxes from the economy
Pickaxes are practically permanent untill you die with it, why not make it so there is a chance that after breaking an ore the pickaxe will be removed from your inventory.
DarkRP 1 
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