From Liquipedia Starcraft 2 Wiki
Minerals are the main resource in StarCraft Universe. It is the only resource needed for low tech units such as Marines, Hellions, Zealots, Zerglings, Queens or Harvesters, and also for many buildings such as Barracks, Gateways, or Hatcheries. Harvesters mine 5 minerals per trip, eventually depleting the mineral field.
Unlike StarCraft: Brood War, harvesters will automatically spread out among mineral patches. This makes harvesting minerals much easier.
Still, mineral patches can only support a limited amount of harvesters at a time. In addition, if a harvester attempts to mine from a patch that is already in use, the harvester will now select another patch to mine from. Consequently, some players will choose to 'harass' the opposing side by mining an enemy's mineral patch. This action prevents the enemy's worker from mining as the patch has reached its limit of worker(s). HuK is particularly notable for this sort of harassment.
Also, a harvester will sometimes go further than needed to mine a patch (e.g. to the other side). This can increase mining time and therefore many players choose instead to 'micro' (individually select) their harvester to a shorter distance or to a known less occupied patch. If the player allows the harvester to automatically switch, this can result in the harvester inefficiently switching to other occupied patches.
Finally, travel distances vary among mineral patches. Therefore, players may attempt to further maximize mining efficiency through timing when their harvesters movements. To do this, one must select a harvester to begin mining the other harvester (which has now finished mining and is returning the minerals). This action is made simple through being able to rally workers to a chosen patch.
 Rich Mineral Fields
StarCraft II introduced the Rich Mineral Field: yellow minerals fields that are mined at a faster rate of 7 per trip instead of 5.
The Terran MULE is a temporary unit that mines 30 minerals per trip on standard patches and 42 on High-Yield patches. Their time "on" the patch is longer than an SCV's. MULEs can mine over other SCV's already mining that patch, but not other MULEs unless all mineral fields are occupied in which case MULEs will start to mine over other MULEs. Their effective mining rate is approximately four times that of an SCV's.
as of Patch 1.4.3. the mule mining rate will be changed on gold patches: the Terran MULEs then harvest the same amount of minerals on both high yield minerals and normal minerals, namely 30 minerals per trip.
 Optimizing Mineral Harvesting
 Chart Realization/Methodology
This chart represents the number of minerals a group of workers can harvest on a "standard" base. Zergs Drones were used, on Lost temple. All Drones were gathered on a specific spot, then clicked on the middle mineral patch, and the mineral count was taken after 30 seconds. The Game Speed was set to Faster. Note that this chart is using real-time instead of game-time, so the mining numbers are roughly 20% inflated.
More measurements and math in this reference: (1) http://www.teamliquid.net/forum/viewmessage.php?topic_id=140055
Keeping more than 3 workers per patch is a complete waste. The 4th worker will not give you any additional income. Your income/worker ratio is reduced, strictly speaking, but your absolute income is not any less, of course.
The progression of minerals harvested per second is roughly linear (the only variation coming from patch distances, but this is minor) until you have 2 harvesters per patch.
MULEs do not factor in, as they are able to a mine a given mineral patch at the same time an SCV is.
 Marginal Efficiency
The 1st and 2nd worker on a close mineral patch will be more efficient than the first two on a far patch, But, the 3rd worker on a far patch will be more efficient than a 3rd worker on a close patch. (In other words, fill up the closest patches with 2 workers over far patches. But send any 3rd worker to the farthest patch before sending them to closer patches.)
However any patch with 3 workers will yield exactly the same rate regardless of distance. This is because the limiting factor becomes the time "on" the mineral patch, while the difference in travel distances is nullified by having a worker that is always waiting to be "on" the patch.
 Transferring Workers
Because the marginal income rate of third worker of a patch is less efficient than the first two, transferring all of the third workers to a newly completed expo is ideal. However, when there are two or one workers per patch, transferring has no short-term improvement in mining efficiency, since those workers would mine at exactly the same rate as they would have if they stayed. There is actually a loss of money due to the non-mining time (generally about 10 minerals per worker). But transferring without having any third worker is only done so with the long-term goal of saturating all bases in the shortest amount of time in mind, not just one.
In a real game situation you often don't have the spare time to devote your attention to micromanaging your workers with specific consideration to close mineral patches. Therefore, as a general rule, you should transfer all but two workers per each mineral patch to a new expansion. Also, because every expansion has at least some close mineral patches (usually 2 to 4), you should aim to saturate these patches first with your transferred workers. If your goal is to maximize long-term income, you should transfer, at minimum, workers equal to the number of close mineral patches there are at your new expansion and rally them individually en route.
Here is the worker transfer equation, which determines the time it takes for a worker to break even by transferring:
I(i) = Income (initial)
I(f) = Income (final)
t = time to break even
d = distance travel time (range is generally ~15-18 seconds)
The following is a table of the time to break even for transferring workers with an assumed 15 second travel time:
|Income (per minute)||Break Even Time|
|from 12 to 45||20.45 seconds|
|from 24 to 45||32.14 seconds|
|from 39 to 45||112.50 seconds|
|from 45 to 45||permanent loss of 11.25 minerals|
|from 12 to 39||21.67 seconds|
|from 24 to 39||39.00 seconds|
|from 39 to 39||permanent loss of 9.75 minerals|
|from 45 to 39||permanent loss of 11.25 minerals, then 6/min|
 Gold Expansions
Since a gold mineral patch will yield a 140% rate compared to blue minerals (7 minerals per trip compared to 5), transferring at least 12 harvesters (6 patches x 2 harvesters) ASAP is ideal, even if there are only 2 or 1 worker on all of your patches currently.
Likewise, a 3rd worker on a gold patch will not yield as much as a worker on an unsaturated regular patch. 40*140%/2 = 28 minerals/minute compared to 40 minerals/minute.
There is a loss in efficiency due to lost mineral income during the transfer period. The derivation and formula to calculate the time to break even after a worker transfer to a gold expansion is detailed below:
MPM1-2 = The mining rate per minute of the first and second worker on a mineral patch.
MW1-2 = The number of first and second workers on the regular mineral patch you are transferring.
MPM3 = The mining rate per minute of a the third worker on a mineral patch.
MW3 = The number of third workers on the regular mineral patch you are transferring.
GPM1-2 = The mining rate per minute of the first and second worker on a gold mineral patch.
GW1-2 = The number of workers transferred that will be first and second workers on the gold mineral patch.
GPM3 = The mining rate per minute of a the third worker on a gold mineral patch.
GW3 = The number of workers transferred that will be third workers on the gold mineral patch.
tm = The time in minutes it will take for the workers to travel to the gold expansion.
Tm = The amount of time that has to pass (including transfer time) to break even with the transfer.
The amount of minerals mined at the regular mineral patch if no transfer is done is equal to:
MPM1-2TmMW1-2 + MPM3TmMW3
The amount of minerals mined at the gold mineral patch if no transfer is done is equal to:
GPM1-2TmGW1-2 + GPM3TmGW3
But we also need to subtract the transfer time which makes the formula:
GPM1-2TmGW1-2 + GPM3TmGW3 - GPM1-2tmGW1-2 - GPM3tmGW3
To find the total time needed from initiating the transfer to breaking even we set the formulas equal to each other and solve for Tm:
MPM1-2TmMW1-2 + MPM3TmMW3 = GPM1-2TmGW1-2 + GPM3TmGW3 - GPM1-2tmGW1-2 - GPM3tmGW3
MPM1-2TmMW1-2 + MPM3TmMW3 - GPM1-2TmGW1-2 - GPM3TmGW3 + GPM1-2tmGW1-2 + GPM3tmGW3 = 0
Tm(MPM1-2MW1-2 + MPM3MW3 - GPM1-2GW1-2 - GPM3GW3) + GPM1-2tmGW1-2 + GPM3tmGW3 = 0
Tm + (GPM1-2tmGW1-2 + GPM3tmGW3)/(MPM1-2MW1-2 + MPM3MW3 - GPM1-2GW1-2 - GPM3GW3) = 0
Tm = -(GPM1-2tmGW1-2 + GPM3tmGW3)/(MPM1-2MW1-2 + MPM3MW3 - GPM1-2GW1-2 - GPM3GW3)
So, assuming the following is true:
MPM1-2 = 40
MW1-2 = 8
MPM3 = 20
MW3 = 4
GPM1-2 = 56
GW1-2 = 12
GPM3 = 28
GW3 = 0
tm = 0.5 (30 seconds)
Then we are modeling transferring twelve workers from a base with 24 workers and 4 patches remaining to a fresh 6 patch gold expansion where it takes 30 seconds for the workers to travel:
Tm = -((56*0.5*12)+(0*0.5*28))/((40*8)+(20*4)-(56*12)-(28*0))
Tm = ~1.235 minutes = 74 seconds
Note that this includes a 30 second transfer time which means your workers only need to mine uninterrupted for approximately 44 seconds after the transfer is complete in order to catch up.
 Approximate Absolute Rates
The first and second workers on a single mineral patch will each collect approximately 40 minerals per minute. The third worker will collect approximately 20 minerals per minute.
Each saturated mineral patch (3 workers) will yield approximately 102 minerals/minute.
Slight Rate Differences Due to Distance Variation
A mineral patch with 1 worker will yield between X (closest possible patch distance) and Y (farthest possible patch distance) minerals/minute. (the numbers for 2 workers on a patch would be exactly double that of 1 worker, since there is no waiting time incurred by the 2nd worker)
Each of the three workers on a single geyser will collect approximately 38 gas per minute, with saturation at approximately 114 gas/min.
A very close gas geyser may collect gas faster when having only 1 or 2 workers on it, but once they get a 3rd, the rates become exactly the same, due to the waiting of a worker at all times.
Very far gas geysers (common on some maps) may actually require 4 workers for full saturation, although having 3 workers on such a geyser results in only a ~10% decrease in your gas output. These geysers are generally the "far corner" placements. You can usually notice easily that the geyser is farther than normal.
An expansion will yield an average of 228 gas per minute (114/geyser x2).
Regular expos (which have 8 patches) 24 workers will yield approximately 816 minerals per minute (102/patch x8)
An island expo (7 patches), 21 workers, 714 minerals per minute
and a gold expo (6 patches), 18 workers, 856 minerals per minute. (102 x 7/5 x 6)
Return on Investment A worker will return a mineral advantage 92(±2) seconds after the initial investment is made (when it is put in the build queue), as long as there are less than 2 workers per mineral patch once it finishes. After partial saturation (in this case, 2 workers per patch), each worker will return on its initial investment 153(±4) seconds after the initial investment. In such cases, when an alternate base is available, it may be best to send workers there if that base is not saturated to two workers per patch yet. These numbers remain valid as long as the worker is built from the base location adjacent to the mineral patches, and as long as those minerals are standard yield minerals.
For Protoss, a fully chrono boosted probe will realize its investment 6 seconds earlier, due to the reduced build time.
 Comparison of Types of Expos
- A gold expo has 5% more mining rate than an 8 patch expo.
- A gold expo has 20% faster mining rate than a 7 patch expo
- A gold expo has 40% faster mining rate than an unsaturated (1 or 2 worker per patch) expo of the same number of workers.