Concrete Patio...what type of mix: 4 sack, 5 sack
Thr cement is NOT mined. They mine the limestone from a quarry any locate cement production plant right at the quarry to minimize the shipping of limestone, which represents raw vast portion of raw materials and the other materials (gypsum, iron, fly) are share shipped to the plant. In very rare cases the plant cannot be built at the plant site (usually because of zoning, ecology, etc. and some plants ship in limestone by water since it is often cheaper than rail.
The raw materials are ground along with the limestone and fired into a clinker in large rotary kilns that usually operate 24/7, except for scheduled downtime and maintenance.
If cement really existed in the ground, even grinding down (to get it fine) will not help and it would have no real strength.