Mining

Mineral carbonate sequestration relies on the availability of magnesium and calcium minerals, which must be mined.  Magnesium and calcium rarely occur in nature as pure oxides, MgO and CaO, which would be the best to react with the carbon dioxide.  Instead, they are often found as silicates, the reserves of which are known to well exceed even the highest estimates of what will be needed based on available fossil fuel reserves. [1]

Serpentine Mineral source: O'Connor p.7

The candidate minerals for carbonate formation are magnesium silicates, calcium silicates, and industrial residues. [2]   However, both Yegulalp et al. and O'Connor argue that magnesium silicate minerals are a much more attractive option due to the large number and size of deposits. [3]   Yegulalp et al. offers further arguments for the use of magnesium minerals as opposed to calcium minerals: magnesium minerals are more reactive than calcium minerals and often have a higher percentage by weight of the pure oxide than do calcium minerals (magnesium silicates can have 35-40% by weight MgO, while calcium silicates usually only have 12-15% by weight CaO). [4]

Serpentine (Mg₃Si₂O₅(OH)₄) and olivine (Mg₂SiO₄) (which primarily occurs in fosterite) are the two candidate magnesium minerals that have received the most consideration for use with mineral carbonation.  By weight, serpentine usually contains 38-45% MgO, 5-8% iron oxides, and 13% water. Olivine contains 45-50% MgO and 6-10% iron oxides by weight.  Olivine releases more heat when reacted with carbon dioxide, 95 kj/mole versus 64 kj/mole, than does serpentine and it requires less olivine to dispose of the same amount of carbon dioxide by a ratio of 2:3. [5]

Currently, both olivine and serpentine are mined for other reasons than mineral carbonation.  Olivine is mined for slag conditioning, foundry sand, refractories, abrasives, soil conditioning, and heat storage, but global resources are not well described. [6] Serpentine is used for road base and asphalt at a cost of approximately $3-5/ton. [7] O'Connor offers that the scale of serpentine mining right now is consistent with the requirements for carbonation. A 1 GW power plant requires 30-40 kt/day of serpentine with mining costs estimated to be $4-5/ton. [8]

For the reason that serpentine deposits are better characterized that olivine, it appears that serpentine will be the mineral of choice for mineral sequestration in the short term.  Because they are both currently mined for other uses, the technology is well developed and the cost of the mining is very reasonable.  Thus, the cost of sequestration of the carbon dioxide is not increased substantially by large mining costs. 

source: Lackner 10/7/2002 p.11