The Mine is a type of Production Building that produces and stores metal. Metal produced over time is automatically stored in the Mine until it is harvested (by clicking on the mine) and transferred to metal storage. Metal is produced more slowly than wood. Upgrading the Mine increases its production rate and local storage capacity.
The amount of Metal produced per minute is increased by half a unit for each upgrade.
* assuming that Rally isn't used to speed up building or production
Advice on upgradingEdit
Because there is a gradual decrease in the rate at which storage increases per rank, one popular strategy for building and upgrading mines is to maximize the total number of mines and then upgrade them in parallel, without any mine being more than one level higher than the others.
Payback considerations & adviceEdit
"Payback Time" in the table above refers to the length of time for the production of the new upgraded mine (e.g. Rank 2) to match the production of the unupgraded mine (e.g. Rank 1). Since mines only produce metal, payback time is calculated taking only metals into account (e.g., pretending that the upgrade cost for rank 8 is only 14000 resources). However, since wood is not free a second column of payback times is provided that treats wood and metals as equal resources (e.g., pretending the upgrade cost for rank 8 is 42000 resources). Here is a simple example to illustrate payback time:
From Rank 7 to Rank 8, there is a cost of 14000 units of metal and a lost production time of 1 day. From the time the upgrade is started, it will be 27.44 days before the upgraded mine has caught up to the production of the mine if it had not been upgraded:
(Production for Rank 7) = (3.5 units/min) * (60 min/hr) * (24 hr/day) * 27.44 days = 138,298 units
(Production for Rank 8) = (4.0 units/min) * (60 min/hr) * (24 hr/day) * (27.44 - 1) days - 14000 units = 138,294 units
Comment from player with some maths background
It seems to me that upgrading your mines several times in a row might be more cost effective than doing it occasionally. Here's the math.
Above calculations basically solve simple linear equation that looks like this:
210 * (x + 24) = 240 * x - 14000,
where 210 and 240 are per hour productions of mines level 7 and 8 respectively, and "x" is time in hours that is needed for 8th level mine to surpass production of level 7. Solving this equation for x gives you 634.66 hours or 26.44 days as stated above. For upgrading from level 6 to level 7 this time is 16.11 days. But does this mean that upgrading from level 6 to level 8 will set you back for 40+ days? Not necessarily. Consider the following scenario: You upgrade mine from level 6 to level 7, wait for level 7 to mine just enough metal to upgrade it to level 8 and immediately upgrade it again.
Equation for this scenario will look like this:
180 * (x + 20 + 66 + 24) = 240 * x - 8000
where 20 and 24 - is time needed to build lv7 and lv8 mines and 66 is number of hours it takes for lv7 mine to accumulate 14000 metal.
Solving this equation gives us 463.33 hours or 19.3 days.
Adding more time and raising resulting production to 270 by upgrading to lv9 as soon as possible after lv8 we will have:
180 * (x + 20 + 66 + 24+117+36) = 270 * x - 8000
Once again 117 - number of hours to accumulate metal, 36 - to build lv9 mine. Result is ~25 days.
For upgrade 6 -> 10 result is 31 days. Similar calculation for lv5:
5 -> 6 : 8.47 days
5 -> 7 : 11.11 days
5 -> 8 : ~13 days
5 -> 9 : ~17 days
5 -> 10 : ~22 days
OK, now it's time for philosophy. Lv5 surpasses lv4 in 4 days, it's not a big deal, before lv5 you can upgrade whenever you want. However if you consider upgrading drom lv5 to lv6 you might think "will I still be playing this game in a week? And this question becomes harder with every level, two weeks for 6->7 upgrade, a month for 7->8. However if you commit to upgrading your mines from lv5 straight to lv10 you will have your investment back in 22 days and maxed out mines to greatly speed up your production. Whether it's worth your time is for you to decide.