Week 5 Sr. Design 2013

DIAMONDS

Constraints on Your Mining Plan• Building up years of diamond supplies in vaults is not good

for diamond valuation (and cash discounting will punish you severely – especially considering that you will not mine out your deposit for hundreds of years– Executive Edict

• Your estimated market size data is accepted• You may target 70-90% of each color fancy market but your production

rate should be based on the markets ability to adsorb stones (ie – no stashing 100 years of stones in a vault some place)

• You do not have to mine out your deposit in 40 years, however, your mine plan need only cover mining for the next 40 years (so long as you do not trash the future reserves)– What you mine in the next 40 years should maximize your NPV

Maximizing NPV• Your Pipe 1 will supply yellow diamonds

– How many years supply do you have in your yellow ground– Yellow ground has a low mining cost

• It is clay that can just be dug-up without blasting – scrapers and dozer could take it out – or dozers scraping up piles for front end loaders to put in trucks

• Blue ground will require light blasting before it can be dug and it will take some power to the teeth of a shovel to dig through it

• Country rock is hard gneiss and will require heavy blasting and hard digging– Soil thickness of the country rock is about 5 feet

– You maximize NPV by keeping mining costs down while filling your market allowance• Since country rock has the highest mining cost putting off stripping of country rock

will help your NPV• Blue ground will cost more to mine than yellow ground so getting what you can off

yellow ground before blue ground will help – but if you have to strip country rock to get more yellow ground suspect that mining blue ground is better

More for Pit 1

• How many years can you mine without being forced to mine country rock?– Develop stage pits for this mining showing where you will

be at the end of each year• Warning on your valuation– Remember that your yellow diamond sales cannot be

valued at the average price of yellow stones• Yours are smaller in size and the stones are included• Use appropriate prices• Also remember that 40% of your rough size will be lost in cutting

so the stones you sell will be smaller than your rough stones

You are Planning an Open Pit for Pipe 3

• In the yellow ground mined immediately you have– Champaign diamonds– Pink diamonds– Blue diamonds– Which type of diamond will you fill your market for first (needing to

mine the least total tonnage before the market saturates)?• If you max out on champaign diamonds first you can probably afford to

store some to make sure you max out on Pink stones – Since your blue stones are small it is probably true you can store blue stones to

maximize pink• If your pink maximizes first then storing pink to maximize your production

of lower value stones is probably not worth it (the NPV of your losses on pink diamonds in storage is probably greater than the NPV gain from selling more lesser stones now)

P3 Open Pit

• Your P3 has the same constraints on mining and mining costs as P1– Mining all you can without mining expensive

country rock will likely maximize your NPV• How many years can you mine your P3 pit

before you have to start stripping into country rock?

• How many years before you mine through the yellow ground into the blue ground?

Initial Pit Plans

• Initially you will be mining yellow ground with a 0:1 stripping ratio– How many tons per year of ground will you mine between

P1 and P3?– How many months per year is the weather good enough you

want to be mining?• (My guess – your production rate will not be huge – do you want to

do 5 truck loads per day all year round – including equipment for severe winter weather if you could do 10 trucks loads per day in good weather?)

– How many years can you mine before you will have to start stripping some country rock?

Revisiting Equipment

• If you can avoid rock that will require drilling and blasting or powerful loading shovels for 5 to 7 years you may want to revisit an initial equipment fleet– What would my cost per ton be if I just used scrapers with

dozer assist and just scooped up clay for a while. (just look at operating costs – not equipment capital cost)

– Now what would it cost if I used trucks and shovels (just look at operating cost)

– Did you save money with the scrapers?• If no – go directly to a truck fleet• If yes – go to step 2

Step 2 (if scrapers save you operating cost)

• You were looking at cable shovels– Cable shovels will last the life of the surface mine or at least till you hit 40 years

• Take the price of your cable shovels– Multiply by P/F for 15% interest for however many years you put off buying the

shovel– Example P/F for 5 years at 15% is about 0.5

• Suppose my shovel cost $12,000,000• If I put off buying it for 5 years I saved $6,000,000 on my NPV• But to do that I had to buy a fleet of scrapers

• How much did your scraper fleet cost to buy– Did you save enough by delaying the cable shovel purchase to pay for the

scrapers?• If yes start with scrapers• If no go to step 3

Step 3 (if you need to do it)

• How much do you save each year on operating costs when you use scrapers instead of truck and shovel?– Get the NPV of this annual savings at 15% interest

• Is the NPV of your operating cost savings plus your savings by delaying the shovel enough to pay for the scraper fleet?– Yes – buy the scraper fleet at first– No – go directly to truck and shovel

One Other Possibility?

• What is all this NPV business – I don’t remember how to do this?– Come see me for engineering econ help.

Plan Out the First 10 years of Open Pit Mining

• Show what P1 and P3 will look like at the end of each of the first 10 years

• Pick your haulage and loading fleet for your chosen production rate

• Pick you drills and powder loading equipment for the first 10 years

• Provide production rate information to your mineral process people.– You will mine kimberlite and Gniess separately and Gniess (which is a

very solid rock) will probably not dilute your ore much.– Base you processing capacity on the feed rate of ore – not the total

mined tonnage of ore and waste

Start Thinking Deep Levels

• You are getting easy cheap stuff with your open pits– You would mine underground to get stones now that

you cannot get with your surface operation• Goodies further down P3– The in-tact Kimberlite offers you larger pink stones– It offers you higher grade blue stones– It offers you purple stones– Way down it offers you red stones including maybe

some monster stones

Some Market Assumptions

• You estimated about a 350,000 caret pink diamond market each year– Assume that you can market 35,000 carets of purple– And 35,000 carets of red

• If I go after these added markets underground, what is my production rate?– Is this a logical production rate for Sublevel Caving?

• Sublevel caving is to a degree a mass mining method• If your production tonnage is small it may be a poor choice.

Thinking About the 500 to 1000 ft zone

• This zone will get you 35,000 carets a year of purple diamonds (assume priced like pink)– It will also offer better pink and blue stones than your open pit– Assume your mining rate is governed by purple stones

• How much added money will you make off of selling higher grade pink and blue stones now and putting lower grade stones from the surface mine in the vault?

• If this extra money justifies the higher cost of underground mining then– See whether you can justify running the P3 open pit for Champaign diamonds only

» If you can run the open pit for Champaign diamonds only and stash all the blue and pink from the open pit then run the underground to fill your blue and pink stones market and the open pit for Champaign

» If Champaign diamonds won’t pay to run the open pit then shut down the P3 open pit when your underground kicks in.

Building Off Your Underground

• You now know your underground production rate in the 500-1000 ft zone of P3– Size the shafts you will need for your P3

underground production rate – and chosen mining method• (I would not be surprised to find your production rate

too low for sublevel caving but we’ll see)– Extend these shafts down to the “red zone” from

1000 to 1250 ft.

Consider the “Red Zone”• Assume that the big stone were “freak events” and that the red zone

contains just the stones where you have a grade estimate• Assume your red stone market is 35,000 carets per year

– What tonnage would you mine each year to fill the red stone market?– What mining methods are suitable for this production rate and this high value

ground?• If you stayed with sublevel caving in the massive kimberlite above and still have sublevel

caving as a candidate method here– Can you sublevel cave on different levels to produce different color stones or will sublevel caving on

the 1,000 to 1,250 ft level potentially disturb the ground and make it harder to mine the levels above?– (My guess is the answer is yes and that you can’t sublevel cave the red zone without disturbing the

500 to 1,000 ft diamond zone above).

• Come up with a suitable mining method for the “red zone”– With this method in mind

• Tell the instructor as soon as possible what levels you want to go into the red zone with exploration drifts and what size you want the exploration drifts to be.

An Observation• You are in an unusual but not impossible mining situation

– Everyone wants to maximize the NPV of their project but for you this means mostly filling a market to a constrained maximum

– Your ore is extremely valuable so the contribution made to NPV by controlling mining costs is less than the contribution made by mining the exact right ground when the market is ready• You will note I have tried to guide you to target the right ground first and then

just pick a mining method that does what the market constraint economics say (market first – mining method second)

• I’ve given you more guidance than most because for most mining engineering experience controlling production costs is the big constraint and people focus first on “how do I mine”. In your case the big issue is “what do I mine when”

• If you don’t understand what I am guiding you to do or why – come consult with me.

You Will Have a Long Week

• You have a team member out on Monday/Tuesday – so you will present on Wednesday– You’ll have a bit more work this week as a result

Start Writing• Below is a suggested start of an outline• Objective• Description of Deposit• Land Access and Ownership Issues• Availability of Workforce• Availability of Water• Description of Diamond Market• Typical Values of Stones• Market Size for various types of stones• Valuation of Deposit Reserve areas• Life of orebody under a market constraint• Candidate Mining Methods• Accessibility and timing of access to ore reserves• Management of losses• Mining method costs and ore values• Picking Mining Zones to target to optimize net present value• Mining Methods Selected to allow the selected sequence• Production rates for selected mining methods• Open Pit Mine Design• Selection of trucks, loaders, drills, and other equipment suitable for the selected rate• Pit slopes to accommodate equipment and geologic constraints

Work on Writing Sections

• Green = first draft written• Blue means – assigned previously but not

done• Red means new this week• Get the writing indicated done this week

Coded Outline• Objective• Description of Deposit• Land Access and Ownership Issues• Availability and training of Workforce• Availability of Water• Description of Diamond Market• Typical Values of Stones• Market Size for various types of stones• Valuation of Deposit Reserve areas• Life of orebody under a market constraint• Candidate Mining Methods• Accessibility and timing of access to ore reserves• Management of losses• Mining method costs and ore values• Picking Mining Zones to target to optimize net present value• Mining Methods Selected to allow the selected sequence• Production rates for selected mining methods• Open Pit Mine Design• Selection of trucks, loaders, drills, and other equipment suitable for the selected rate• Pit slopes to accommodate equipment and geologic constraints

COAL

Try for Monday Instead of Tuesday• Your Current plan calls for Mine #6 first – then mine #2 by

longwall– Get your innerburden thicknesses between #6 and #5 and #5 and #3– Use the paper from NIOSH and estimate whether you are sterilizing

your thickest seam of low sulfur low chlorine coal.• If you mine 6 first and then 5 what effect will that have on minability of #5

(#6 has little sharp pillars)• If you have also undermined 5 with a longwall also what impact would that

have?– Next consider mining #5 first – It has very large pillars, low extraction

and highly distributed loads• If #6 mining followed slightly behind the advance of #5 what impact would

that have on #6 mining?• If #3 also followed behind #5 what impact would that have on longwalling

#3

More Coal Sterilization Issues

• If #6 coal is mined before #7 (low chlorine) will you sterilize the #7 coal reserve?– If #7 were mined first what impact would it have

on #6 given the 20 feet of massive stiff limestone in the roof?

Coal Economics Issues

• Estimate your coal mining cost– #7 coal has a thick shale roof and a solid sandstone floor

• How many feet of advance would be realistic to achieve in a shift

• What kind of roof bolt and consumable costs would you incur• Estimate your crew size and supervision costs• What is your direct mining cost per ton?• It is likely you will have to estimate pillar sizes, bolting needs

and extraction ratios to get this– Do the same direct mining cost estimates for #6, #5, and

#3

More Economics

• What costs would you have for a belt network and slope space for each seam?– Break your capital cost into a 20 year life schedule

at 15% interest (use a lesser life if you don’t have enough coal in a seam for a 20 year life)• What is the annual capital cost for the belt network

– What is the operating cost/ton?• What is the total direct mining and haulage

cost per ton for each seam?

More Economics

• For each of the 4 seams what would you have in outby support and ventilation cost?

• Would any of your coal seams require unique processing that would cause its cost/ton to be different?– The answer to this will probably come from what

you expect in differences from out of seam dilution

More Economics

• At this point you can probably estimate your cost per ton to mine and process each of your 4 coal seams

• Now take your expected sales price/ton and subtract the mining cost and processing cost/ton– What is your rough profit margin on each coal

seam

Seam Assessment

• Can any of your coal seams be eliminated based on economics of underground mining

• Are there any seams that will have interactions to where there is just no way to justify mining something no matter what the sequence– If the problem is localized to one area what are

those unminable areas for each coal seam

If All 4 coal seams might be economic

• Ie – that means they showed potential profit– But some seams are likely to be unminable if you don’t take

them now• If failure to mine a coal seam now puts its recovery later in

doubt consider this economic model– You plan to produce 3 million clean tons per year from #6 for a

38 year life– You plan to produce for the met coal market using a timing that

follows #6– You can use your cost and sale price to estimate an annual profit.

• Calculate the NPV of this profit

Next Step

• Consider what sequence would be necessary from a rock mechanics standpoint to add #7 and #5– Jack-up your clean coal production rate to about 3.7

million tons per year (since #7 and #5 could hit some special market)

– Estimate your annual profit this way (mine life will quite possibly go to more like 50 or 55 years)

– Take the NPV at 15% interest of a mine that mines all seams.

What to Look For

• If your #6 and #3 mining plan will likely sterilize your #7 and #5 for future mining you might justify that if the NPV from getting higher profit #6 and #3 coal offset the loss of the #7 and #5 reserve– If this is true your #6 and #3 plan will have a

higher NPV than an all seam plan– If not true then sacrificing future reserves for a

fast buck today is not justified.

Continue Building Up Your #6 Coal Seam Plan

• Get a timing map based on actual coal thicknesses and not just feet of advance– Try and time it throughout the life of mine

• Several coal seams are potentially sensitive to your #6 coal timing– Estimate your development sequence in those

seams• Does not need to be entirely timed out this week

Processing

• You have a model flow sheet for your coal prep plant and an estimate of out of seam dilution for each coal seam.– See what you need to run a prep plant simulation– How many of the needed washability curves can

you get estimates for?• If you can run the simulation do– (I’m betting you won’t be able to do it yet)

Processing Continued

• If you can’t run a full simulation yet– How much reject will you get from out of seam dilution– About how much waste will you have from in seam coal

• Estimate the total life of mine waste produced– Divide the estimate by waste type

• (Example – coarse coal refuse, belt press fines, fines settled in a pond)

– Estimate where and how you are going to store that much waste.

COPPER-GOLD

Biggies this Week

• You will determine final pit slopes and use them and your cost by bench to estimate the size of your ultimate pit– You’ll check your waste volume and see if you

have enough space planned out to handle that waste

• The largest task is nailing down your processing techniques – recoveries and costs

New Parameters for MSOPIT• At this point you seem to have determined that your mining

cost per ton increases 2 cents for every bench you go down– You probably also came up with a basic mining cost per ton.– Are there any differences in the cost of mining ore or mining

waste?• You would first look at things like transportation costs

– Are distances the same?– Are the fleets for ore and waste the same.– Is there any difference in unloading time?– Are there differences in the grade?

• Next look at differences in blasting– Will there be any difference in cost for blasting ore and waste?– Will there be differences in the care I take in loading material?

• While some of the answers will be yes is the cost difference significant?– Mining ore $4.05 – Mining Waste $4.01 probably not significant

Get Ready to Determine Pit Slope Angles

• You determined that an active face of your pit would have an over-all slope of 29 degrees– This pretty well makes equipment the controlling factor

over rock slope considerations• But!– Most of the time mines are not pushing back and expanding

in all directions at once.– If you had an ultimate pit slope that provided roads to get

out and catch benches and berms how steep could that be?• Now what impact would your pit rock and joint characteristics

have?

Determining a Pit Slope Angle for MSOPIT

• Suppose I had an ultimate pit slope– Suppose I wanted to push it back on one side of the pit?– Could I go to the top of the pit and start a top down cut?

• Often the answer will be yes• What is the steepest slope you could make a “push back

from”?– This will normally be the slope you use for sizing your ultimate pit –

unless» Check to see if your rock slopes will stand up to that» Your rock strength may constrain your slope

You Misunderstood the Fracture Pattern

Daylighted FracturePlane

Entire Side of Open Pit Slides In

All open pits have minor fracturePatterns that cause local slopeFailures commonly seen in openPits

Mega – Doomsday fracturePlanes can (and have) destroyedEntire open pits

You have a Doomsday fracturePattern dipping at 47 degreesToward the east

Fracture Impact By Direction

If you make this slope moreThan 47 degrees – you die

On this side the fracturesDip into the face and willNot cause slope failure

What About In-between

This side fractures dip into face andDo not constrain the slope

Here you have your slope maximum (47 degrees)

What happens toThe apparent dipAs you moveAround thecircle?

Apparent Dip• The apparent dip actually decreases as you move away from the

perpendicular to the strike– This can be checked using stereo nets

• In the strike direction the apparent dip actually has dropped to zero– This does not mean no slope allowed– Real fractures have angles of internal friction (ya I know I’m talking rock

mechanics)• If the friction angle is greater than the apparent dip there will be no sliding failure even

the fracture is daylighted– Use your slope stability training to estimate maximum sustainable slopes by

direction• (It is likely that the South east sides of the pit will have slopes controlled by rock

strength or pit geometry)• (It is likely that the North west portion of the pit will have slopes controlled by “the

doomsday fracture”)

Apply Your Pit Slope Work

• Set MSOPIT with your variable cost by bench• Use MSOPITs variable slope by azimuth and rock

type to set slope limits in different directions• Run your ultimate pit with your new mining costs

and slope constraints– What you want to see is what areas not to put things on

top of (cause they will be mined)– You also want an estimate of your waste tonnage

• You will use this tonnage to see if you really have space for your waste in the area you indicated in your presentation last week

Processing

• You have a basic sulfide process proposed– You will grind to the size that liberates the free milling gold

(250 micron)and copper minerals (150 micron) • It is not clear whether you grind initially to 250 micron or 150

micron– You next proposed to gravity process out your gold

• Look at your size• Look at the density of your gold• Look at the density of your copper minerals – if you only ground

to 250 micron the copper minerals are still not free from gangue minerals so they will have an intermediate density between gangue and copper sulfide

The Mystery of the Gravity Process• What type of gravity device can make a separation at this size (250 micron or

150 micron)– How good is the separation and recovery?– What software is available to simulate this process?

• Comment– If you grind to 250 micron you will be attempting to separate specific gravity 17

(impure gold) from specific gravity 2.2 to about 3.5 gangue and copper sulfides• If you choose a wet process you will need another stage of grinding ahead of flotation – will

that grinding work well after a dewatering step?– If you grind to 150 microns you will have 3 products – gold at sg 17 and 250 micron

size and copper sulfides at about sg 3.8 to 5.5 and gangue minerals at about 2.2 to 2.5• Can you get a separator that will make 3 products at 150 micron size with high recovery and

purity? – is the answer is yes you might be able to dump massive flotation operations– Be sure you also know where your silver sulfides went

• Some of your silver is an impurity in the gold – it will recover with the gold• Some of your silver is an impurity in the copper minerals – it will follow the copper minerals• Part is in free silver sulfide minerals – where do they go?

After the Gravity Process

• After you have figured out what your gravity process is to get the gold

• How are you getting the copper?– If you just got the gold by gravity how will you

dewater the waste so that you can grind it to 150 mesh and send it to flotation?

– If you decided to grind to 150 micron and make 3 products by gravity then your copper minerals might have been recovered by gravity

An Economic Pause• If someone delivered you a pyrite concentrate

– (assume pyrite outnumbers copper minerals 4 to 1)– How much gold would be in a pound of such a concentrate?– How could you break into the pyrite to get the gold?

• Assume the gold is microdispersed in the pyrite so that just trying to grind the pyrite down to 5 microns is only going to expose 50% of the gold at the surface and will not liberate any of it.

• What would it cost to go after the gold in the pyrite?• Will the gold in the pyrite bear the cost of what you are considering?

• Keep this answer in mind because later you will have to decide whether to make a pyrite concentrate– Obviously if you can’t economically get the gold out of a pyrite concentrate

then you won’t be thinking about a pyrite concentrate as we move through your process

Separation• Depending on what you did with gravity

– You might have a gangue, copper and silver sulfide mix to go to flotation• You probably have 3 things that will float – pyrite (a gold carrier), copper

sulfides, silver sulfides– Normally people float the most profitable item first (probably means floating copper

sulfides and depressing pyrite and silver sulfide– A two stage flotation process costs more than 1 stage but you would likely float the silver

sulfides next – are the silver sulfides enough to pay for another stage of flotation? – A third stage of flotation is still more expensive and would yield a pyrite concentrate that

would need another process to break in and get the gold – is the remaining gold enough to justify the cost?

– If you ground to 150 microns and gravity processed the copper sulfides then you have a middle concentrate made up of pyrite, copper sulfides, and silver sulfide• How will you separate that?• Or is it practical to try smelting the whole concentrate?

Get Your Sulfide Process Flow Sheet Figured Out

• Get a cost estimate for running the process– Is this price realistic for primary ore type 2,

primary-secondary transition type 3, and secondary enriched type 4?

Branch Out

• Zone #1 Primary is like Zone #2 Primary except the ore is loaded with carbon– If you leach the gold the carbon will re-adsorb

everything• You must destroy or separate the carbon before you

can leach the gold• Of course if you have a process for making a gold

concentrate that does not leach the gold you might not care

– Can you use your sulfide process on zone 1?

Now Its Oxide Time• Your gold is 100% free milling and liberates at 250 microns• 25% of your silver is mixed with your gold (gold in nature usually

contains silver), 25% is substituted into your copper minerals, 50% is metallic silver that liberates at 150 microns

• Your copper minerals are all oxides and carbonates. They are all acid soluble. None of them float even poorly

• Figure out a process flow sheet for such an ore– Get the details right so you don’t have to have a part 2 next week– What will the process cost to run?– What kinds of recoveries will you get from it– Be sure to consider the volume of oxide ore you have since costs are

influenced by the scale of the operation

Now the True Pain in the _ _ _ _• Zone 5 is 50% oxide – 50% secondary

– You cannot separate oxide and sulfide in mining – the ore all has both mineral assemblages in it

– How much tonnage do you have in your ultimate pit of zone 5?– For this week just consider how you could process the ore and run

some calculations as to what might and might not be practical to recover• Save the flow sheet cost estimate and recovery plan for next week

• Make sure this week that you can provide costs and recoveries for zones 1, 2, 3, 4, and 6 so that these processing costs and recoveries are ready to put into MSOPIT

Last Economic of Processing Consideration

• The Processes you are outlining here are not making the market forms of the metals– Your copper sulfide process yields a copper sulfide mineral concentrate with silver and

gold substitutions in the copper minerals• To make copper you must

– Smelt and refine the copper to make blister copper– You must electro-refine the blister copper to make pure copper cathode (the market ready form of copper)

» I think your gold and silver will go to anode slimes but you need to check that and how the gold and silver can be recovered

– Work back to the price of copper in concentrate• Example Copper price $3.50/lb

– Electrorefining blister copper – suppose we say 10 cents per lb– Blister copper price = $3.40/lb– Copper concentrate 30% copper

» Smelting and refining concentrate $90/ton» Shipping concentrate $6/ton» (gold and silver is often a credit at the refinery – suppose it is $6/ton)» Total copper in 1 ton 600 lbs» $90/ton / 600 lbs/ton = 15 cents per lb» Value of copper in concentrate - $3.25/lb

– This is an illustrative example not intended to tell you the value of copper in concentrate

Continue Working

• Your gravity process will yield a fine gold nugget concentrate (mixed gold and silver)– How will the gold nugget concentrate be refined?• Do you want to do that on site or do you want to ship it of?• If you ship it off – where will you ship it?

– What is the gold and silver worth in the nugget form?• You may have a silver sulfide concentrate– Do the same thing in figuring out its value

Your Oxides

• If you are leaching copper and then going through solvent extraction and electrowinning you will produce copper cathode– You will probably have silver bearing slimes– What are they worth?