Week 6

1. Week 6 Sr. Design 2012

2. Special Issues • SME will begin Sunday and go through Wednesday. • Groups will not be presenting next week • Time from next week will feed into larger and more demanding accomplishments for the next week

3. Copper • Work out your pit slopes • The following geologic constraints exist • There is a massive regular fracture system that strikes 36 degrees at a dip of 42 degrees to the west • Daylighting the fracture system can be expected to cause massive sliding slope failures • As one moves around the pit away from the strike of the fracture planes the apparent dip decreases creating a greater constraint on the maximum slope of the pit up until the point that the rock mass angle of internal friction exceeds the apparent dip of the fracture. For porphyry copper deposits this internal friction angle is about 25 degrees

4. More Geologic Constraints • The rock types of themselves have maximum sustainable slopes • Unaltered rock (not types 1 to 6) can stand at 65 degrees • Altered rock can only stand at 47 degrees except • Alteration type 6 – oxide ore – will only stand at 37 degrees • These slope constraints apply to over-all pit slopes. Toe to crest slopes between benches will stand at 65 degrees in altered rock and 75 degrees in unaltered rock

5. Over-All Slopes for Pits • In addition to geologic constraints on pit slopes there are geometric constraints that depend on bench height, equipment selection, safety berms etc. • Determine which slopes are most constraining and put the results into MSOPT to allow complex slopes by azimuth

6. In This Week • You will develop a series of pit shells that represent your mining sequence. • These shells will have complex slopes by azimuth • The shells will be based on realistic minimum push back size • You will probably not want to be redoing roads on all sides of your pit at once so the push backs will likely be somewhat directional • You will need to make sure the pits do not add more benches going down than you could realistically develop in a given time. • You should aime for pit shells that represent about 2 to 3 years of production • The pit shells should consider that mining cost increases with depth • Your pit shells should progress out to an ultimate pit at the 90% percentile of your price data

7. Applying Processing Cost Constraints • Your Sulfide Ore Will Go to a Floatation Mill • Your mill was sized by comparison to a Chilean mill so assume it was designed for about 1% copper grade ore. • Your Mill has several constraints • Your grinding capacity fixes the amount of rock that can be fed to a mill of that size – if you feed more rock you won’t be able to grind it • Your floatation cells you can assume are sized based on how much froth they can carry. • If your copper feed grade is 1% or less the floatation cells will not choke • If your copper feed grade goes about 1% while grinding is at full capacity the froth will overload with copper – ie – there is a limit on the amount of concentrate the mill can produce • Your estimated copper and moly recoveries are reasonable.

8. Your Oxide Ore • Oxide ore can be ground to -48 mesh and put in agitated tanks at about 50% solids for about 5 hours. • The process will get around 94% copper recovery • Costs can be estimated from the U.S. Bureau of Mines Cost Estimating System • (The leaching copper section covers the leaching operation – not the grinding and SX-EW)

9. More on Oxide • One can also leach copper in giant vats. Grinding is more likely to average about 20 mesh and agitation costs are avoided. • You could estimate costs to be about 2/3rds of an agitated leach but recovery will only be about 82% • You could heap leach. You would generally grind to about -1/4th inch. Best results generally put down thin layers around 5 feet thick that can be stirred with dozers. • You have some cost estimates already • You are unlikely to beat 70% recovery (65% might be more realistic) – more like 50% if you are not doing thin layer leaching

10. Mixed Oxide and Sulfide • In your plan you used a pressure oxidation cycle • You probably had ground to fine size before pressure oxidizing • You would most likely go to an agitated tank or vat leach next • This approach would have the added cost of your pressure oxidation step.

11. Heap Leaching Mixed Ore • Some operations skip pressure oxidation and try to heap leach the mixed ore. Since the sulfides leach more slowly the leach time is longer and recovery will drop. • For your mixed ore you might guess 50% copper recovery

12. Heap Leaching Sulfide Ore • Heap leaching is more likely to be practiced on 2ndary enriched sulfide ore • Again thin layers are important • Leaching times are longer • For your purposes you might estimate 50% recovery

13. Dump Leaching • Dump Leaching takes run of mine sized waste without crushing and circulates leach solutions. • It costs are primarily pumping and handling of solutions • Recoveries will generally be low in the 10 to 20% range.

14. Consideration for Depth of Pit • MSOPIT allows you to adjust cost by depth • Right now most of your haulage costs are based on the average depth of the pit • You assumed 10% slope to get the haul distance out of the pit. • Now go bench by bench in adjusting cost for haul distance. • Your first bench is down about 15 meters so the haul distance to get out of the hole is 150 meters • It will increase 150 meters every time you go down a bench • What impact will that have on mining costs?

15. Consider this new process and depth information in developing your pit shells • When you have your pit shells set your metal prices back to the 50% point • (some of your last pit shells may be uneconomic when you do this) • Run VALP to get the estimated present value of the pit • Your pit shells will be moving from higher grade ore to lower grade resulting in a boost in present value from mining sequence.

16. More on Boosting Value • Another way to boost value • Right now your mining rate and mill size are designed to match when the mill is based on break-even cut-off grade • You can oversize your mining rate relative to the mill • When you do this the mill will only be able to take the higher grades • Lower grade ores will have to be wasted • Or stockpiled for later processing • You will mine a declining cut-off grade again tending to make the NPV go up. • You will have presentations on using VALP for optimizing facility size and Cut-off grade • You will do this this week but running VALP is not covered in the assignment slides.

17. Coal • Finish adding the last of your drill hole data to your coal reserve model • Remember to watch out for long narrow continuous features that can set up barriers that your mining would have to cross. • Faults almost surely will cause coal to be offset • Non-matching seams might line up or come close to lining up – this might be used to advantage • Faults are sometimes loaded with water and slurry gunk (fault gouge) – mining into it might create some wet surprises that could get exciting with a soft clay floor. • Channels and washouts – a stream that erodes out coal in one place most likely went someplace. It quite likely created a long washed out channel across a coal block • If the coal pinches and finally washes out you may be doing expensive rock cutting for a considerable distance. • If a sandstone wash out channel happens to be full of water you could have a stimulating water pumping adventure if you run into one unawares • Comment – the maps seen last week appear to have stream channels that appear only in patches – something that is unlikely to be repeated in real geology.

18. More Linear Feature • Dikes also tend to be long and linear • The rock is often unusually hard and expensive to cut through • The coal around them will usually be worthless and probably thins down due to some of the coal being burned off • You may need to impose your own boundaries for these features as Carlson’s block interpolation routines usually project things equally in all directions • This will misinterpret the shape of long linear features • A Carlson interpolation routine probably does not understand that two places where you hit stream channels are darn likely to be connected. (Scotty normally does not beam whole streams from one place to another – even when Captain Kirk tells him to). • If you need to drill to trace stream channels turn in your drilling program on Friday Feb. 24th

19. Fun With Rock Mechanics • For Our Conditions assume that when coal seams approach each other within 90 feet there will be interaction • If the seam beneath the one you are mining has been mined in the past (by a year or more) you should look for subsidence to have broken up your roof and coal • Cut your coal production rate 20% • Reduce your rock strength 20% • Increase your roof and ground control costs by 30% • If the seam above you has been mined the pillars above will punch down with high pressure bulbs of stress that will cause trouble • You will need to align working to try to control this • When seams get within about 30 feet of rock (does not count underclay) from each other the roof may cave all the way into the seam above • Mining both coal seams will not be possible unless you can create some special innovative plan

20. Roof Rock • Black Shale, Limestone, and Sandstone roof is pretty durable to moisture exposure • Energy and Dykersburgh shale don’t take moisture well. • If they get to be less than about 2.5 feet in thickness the shale will try to fall in while you are mining and before you can bolt • Figure you will take about a 30% lost time hit at the face for roof falls if you try to mine under thin Energy or Dykersburgh shale • If an Energy or Dykersburgh shale roof is exposed for more than about 18 months figure it will start slacking and probably need some sort of mesh support between bolts • If Energy or Dykersburgh shale roof is exposed for more than 5 years it will start to dump roof falls no matter how you bolt or mesh it (at a shaft or slope bottom where moist air enters expect this result within 2 years) • If you have active belt or travelways under old Energy or Dykersburgh shale figure you will loose 5 days per year per mile of such entries.

21. Floor Strata • You know procedures for designing both panel pillars and the rib pillars around your mains if you have a solid floor and coal strength is your limit. • If you have a clay floor pillars designed in this way will punch into the clay floor • Clay will heave up into the entry • For just a little clay you could just dig out the floor heave • When you start getting over about 16 inches the punching action will not only cause entry filling heave but will start shifting subsiding and breaking up roof • You need to design based on the clay floor • See special lecture on dealing with clay floor • Try to live with about a 1.2 factor of safety for short lived panels • Go for a 1.5 to 2 factor of safety around long term workings.

22. Water And Your Floor Strata • Wet Fireclay Floors = Trouble • Develop a contour map of the bottom of each of your coal seams so you will know where the lowest areas are that water might go • Consultation with Hydrogeologists indicate the following • The Shales and shaley rocks typical of most of the mine roof contain little water and will not support much water flow • The Fireclays do not support water flow and are not typically underlain by water bearing rocks. • The coal seams are not in most places acting as aquifers • In general you are expecting dry mining conditions • Estimate that seapage will be about 25 gallons per minute per square mile of opened workings • This does not count water from mining operations, water entering from the surface through mine openings or unpleasant water filled geologic structures.

23. More Hydrology • The Limestone roof above the #6 coal is fairly tight and should not produce more than usual water • Water in limestone is usually carried in fractures that are more open and common closer to the surface • Water producing fractures are possible but are not expected to be a common problem. • The potential for hitting a 200 GPM fracture somewhere is believed possible • The channel sandstones are believed to be aquifers capable of significant water production • Mining under a channel sandstone roof is expected to be a significant underground rainfall event (downpour?) • Punching a hole into a sandstone channel could be similar to putting a large diameter well into saturated porous rock • Fireclay in contact with channel sandstone will likely be wet. • Faults in the area have been known to be water bearing and even to be channels linked into aquifers • No one knows whether your fault has this characteristic since no one has ever seen anything more than a seismic signature

24. More Hydrology • The floor beneath your #2 coal is sandstone • It is believed to be somewhat tight but to contain a fossil brine with about 7% salt • Water flow rates from the floor of the #2 coal are expected to be about 300 GPM per square mile of opened floor • Sealing abandon panels is not expected to relieve you of water pumping.

25. Your Water Response • As you open up more area indicate how much pumping capacity you intend to have on-line and ready • Indicate how much contingent water pumping capacity you will have • What that capacity consists of • How you would deploy it if you needed extra • How long it would likely take to deploy it.

26. Get Ready to Apply Rock Mechanics • Find the needed rock mechanics properties for black shale, Dykersburgh or Energy Shale, Sandstone, and Limestone • 4” cubes of your Illinois #6 coal had a median Uniaxial Compressive Strength value of 3,900 psi. 4” cubes of your #5 coal had a median value of 2,800. 4” cubes of your #2 coal had median values of 2,000 psi. • Identify those areas of your mine that will not be controlled by underclay • Design and size your pillars using techniques from your Rock Mechanics course

27. More Rock Mechanics Applications • Identify areas where underclay floors control the design. Consult the slide set on soft clay floors. • Consider your shale roofs to be prone to bed separation and design a roof support system to meet Federal Regulations and the dictates of engineering design • Review the relationship of cutters to mining orientation • Figure about 5% of your at risk shale roof will actually develop cutters and plan for how you will deal with this

28. More Rock Mechanics • Your Limestone Roof is highly competent. • Assume you can get a variance for as needed bolting rather than a regular pattern • Assume about 1 bolt for every 10 ft of entry will do. • With your entries and pillars sized proceed to layout and time your mining sequence • How many years of truly minable reserves do you have?

29. Aggregate • Get a good 3D drawing of your mine after 5 years of operation. • Calculate the tonnage of rock products and wastes that have been produced • Examine the advance of your mine • If you advance to delay overburden stripping how will you advance • What costs will you trigger by mining in that way • If you advance in a systematic easy to plan sequence how much sooner will you face how much higher overburden costs • What costs will you delay or avoid if your sequence is based on planning convenience instead of overburden stripping delay

30. Add your waste to your drawing • Show where your mine waste will be. • This could be ponds of capacity you can demonstrate are sized to meet to 5 year needs • This could be solids dumped into a pile or backfilled into a pit • This might involve the pit expansion tool to demonstrate that you actually have laid out the required capacity.

31. Get An Agflow Model of Your Processing Plant • Make a first run with the model and see what it produces.

32. Do a Mining Fleet Spot Check • Using your mine layout at the end of 5 years and your production rate • Pick the production equipment you need for mining and demonstrate that it can meet production with that layout.