brain food

In this case the deposit is rather high grade then low grade as usual when you use block caving. However...a lot of questions raising. PFS just the first step...might be a positive surprise or negative. See also advantages/disadvantages of block caving vs. stoping. Interesting anyway.

Block caving

https://queensminedesign.miningexcellence.ca/index.php/Block_caving

Underground mining methods compared

Block caving is an underground mining method that uses gravity to exploit massive, steeply dipping ore bodies located at depth. These ore bodies are generally low grade in nature and are too deep to be extracted through open pit mining. The technique is commonly used to extract low grade copper, copper-gold, iron and molybdenum ores although there are other applications. Due to the low cost and high productivity of this cave type mining interest is growing and new deposits that have the ability for block caving techniques are in high demand
Development
The time taken to establish caving operations varies, and it is not uncommon to take a period of at least 10 years from the time of study commencement to achieving project approval. For some large-scale planned caving operations, studies have been under way for more than 20 years with a final decision still yet to be made. The early stages of a block cave development involve a high level of construction activity, as the undercut and extraction infrastructure is created to last for the life of the ore body. During the construction period, the total number of personnel can easily reach 3,000 for a small block cave and up to 10,000 for a large block cave.[2] Once steady state production is achieved, the ongoing demand on logistics is drastically reduced, and is low compared with other underground mining methods. Once approved, establishing a cave mine can be very complex. Speed is of the essence, and it is not uncommon for development in the order of tens or even hundreds of kilometres to be required on some of the larger operations. This can be challenging, particularly if ground conditions are weak or wet in areas.
Geological/Geotechnical Requirements
Block caving mines require large horizontal extents that automatically cave when the orebody is undercut. Large vertical extents, ranging from 60-180m, justify the use of level developments. Grades should also be uniform. In order for the rock mass to break, there must be at least one horizontal and two vertical joint sets. Exhaustive mechanical characterization studies should be completed to confirm that the material will indeed cave by gravity.


Sub-level open stoping

https://queensminedesign.miningexcellence.ca/index.php/Sub-level_open_stoping
Orebody Requirements
Ore bodies that are ideal for sublevel stoping are very tall and have a medium to narrow width, but can have an extensive length. The ideal width of the orebody should be greater than 6 meters but less than 30 meters. Most of the time this type of orebody has a dip greater than the angle of repose of the ore, or steep enough so that the ore can fall efficiently into the open stope. Preferably the dip would be between 60 and 90 degrees, however anything above 45 degrees may be adequate.

Sublevel stoping requires a midrange ore grade in order to pay for its development. This mining method can be used at a wide range of depths. The ore bodies must be made of competent rock, and be surrounded by competent wall rock. Due to the nature of the drilling and blasting of the rock it is best if the orebody has a regular outline with well defined edges, as this lowers the amount of dilution. Since this mining method requires that the ore be blasted on multiple occasions, it is recommended that the ore have a high compressive strength and few planes of weakness such as joints, bedding planes or faults.[2]
Advantages
• Dilution may occur but 100% of the ore is usually recovered from the stope.
• Pillars that are left in place can be removed once adjacent stopes have been backfilled.
• Large scale blasting lowers costs.
• Stopes may be drilled before any blasting, to allow for larger and more efficient blasts.
• The early development can be done in ore rather than in waste.
• Easily to mechanize and can use large equipment.
• High productivity and efficiency, up to 110 tons/employee-shift, depending on the orebody.
• Repetitive techniques help facilitate training and safety.
• Mid-range mining cost (relative cost 20%).
• Little exposure to hazardous conditions ie: easily ventilated.
• Low Dilution (20%).
• Reasonable to high recovery (75%-90%).
Disadvantages
• Early production is low due to the lack of available drawpoints near the slot however production increases as new drawpoints are reached.
• Initial recovery is usually 35-50%.
• Not a highly selective method.
• Requires extensive early orebody developments with high capital expenditures.
• Inflexible mining plan.
• Drilling requires precision and should deviate less than 2% on any hole.
• Orebodies which are narrower, less than 6 meters in width, often have higher costs because there will be lower production for each blast.
• Support pillars may be left in place when a large ore body being mined.
• For orebodies with lower dips dilution increases.
• Fumes can leak back into stopes if secondary blasting is required.
Cost Minimization
In general sublevel stoping is a high production, yet low-cost method. It is a very popular method chosen when open pit mining activities are no longer economical and mines move to underground operations. The key to cost minimization when using this method is mechanization. Selection of the biggest equipment that the mine will permit allows for reduced total development in terms of drilling, and increased efficiency and production when loading and hauling.