2Luke,
Yep, using a higher gold price would result in a deeper pit shell, thus more mineral resources. This depends on the ratio between ore and waste at depth also. For example, if the orebody is thin at depth then your strip ratio (ratio of waste
re) will be so enormous it becomes uneconomical regardless.
Its normal for mineral resources to be reporting using a much higher gold price (say USD$1500), and mineral reserves to be reported using a more realistic gold price (USD$1200). Mineral Resources only have to show "reasonable expectation of economic extraction", and are therefore more optimistic in nature.
Factors that control the depth of a given pit optimisation ("pit shell"):
1) Thickness, dip and grade of mineralisation at depth. As mentioned, strip-ratios become much higher at depth, therefore the mineralisation must be either thicker, higher grade or dipping at a more favourable angle to deepen a pit shell.
2) Gold Price - Using a higher gold price will improve the economics, therefore making deeper tonnes economic to mine.
3) Recoveries - The old Oxide/Transition/Sulphide story. Oxide ore is easier to treat, therefore it can be mined at a lower cost and is close to surface with lower strip-ratios. Sulphide ore is usually at depth, therefore pit shells are sometimes limited at depth due to poorer gold recoveries.
4) Angles of the pit walls - This depends on rock mechanic studies. The weaker the rock and the more unfavorable the dip of the stratigraphy, the shallower the angle of the walls. Shallower angles = higher strip ratios = higher mining costs = shallower pit shells.
5) Economies of scale - Larger operations (+200,000kOz per annum) will have lower mining costs than smaller operations (per tonne) due to economies of scale. To be able to make these savings, they use larger machinery which is less selective, and mines mineralisation at faster rates. This can often make marginal tonnes at depth economical.
There are numerous other factors than control Mineral Resources that are not related to "pit shells", too many to mention...... Do you have a particular resource/company in question who have significantly reduced their mineral resources??
Hope this helps.
Desertpunter.
