Sequencing Mining Operations with MineSight® ©2007revised 2010 Dr. B. C. Paul {Note – The Name MineSight® and the Program described are property of Mintec Inc – Tucson, Arizona}

Maximizing Returns NPV is usually increased by bringing more early earnings and delaying expenses Sequencing pits for high grade ore with lower stripping ratios tends to do this We Need A Method of Finding the Best Grade Ore to Mine First

How to Make That Happen Method #1 - We try to Fake Out the Learch Grossman Routine Lerch Grossman will Find the Juiciest set of ore blocks that keeps producing more value Obviously this must mean that it either finds the maximum metal pit or the most lucrative ore Because not all ore is equally easy to process it is possible that a set other than maximum metal will be selected We Need to Get Learch Grossman to Pick the Best of the Best

To Do This We Perform What I Call A Price Fake We tell the computer we have a dismal market and then ask it to find the ultimate pit Under unfavorable economics only the better grade ore will get included in the “fake ultimate pit” Learch Grossman however has picked us the set of blocks that yields maximum value per ton which is just what we wanted.

We Will Gradually Raise Our Fake Price As We Do Multiple Runs Each Run will start with the previous pit in place Each Run will have the real final pit surface as a limiting surface The result will be a series of nested pits that go from the best ore to ore of progressively lower grade We have just tricked Learch Grossman into telling us how to optimize our NPV by sequencing our mining

The Pit Slope Problem Our Ultimate Pit Was Calculated at Our Final Pit Slope Our Stage Pits will have to maintain a working slope We accomplish this by telling Lerch Grossman to mine at our working slope, but then we tell it that it must never cut blocks beyond our ultimate pit.

MSOPIT Search Option #1 Start MSOPIT.

We Will Consider Only Screens for MSOPIT unique to our use My first cut will start with no Pit but will limit things to The area of the ultimate pit. (Note that Pit 1 is the Ultimate pit generated in An earlier step).

We Manipulate Our Product Price to Try to Guide the Program to Pick smaller pits with the maximum pay metal I varied copper and Moly in proportion to Each other setting copper At 50 cents in concentrate Instead of $1.05. (only the highest grade Material will be able to Pay off so it should dig Up the richest ore first)

Processing and Mining Costs are Held Constant well Metal price is artificially deflated Leach copper was Set at 60 cents We should understand That because our prices Are fake our block values Will be wrong. The function Of this procedure is just To pick off the richest pits This is the Leach Ore Screen

I Needn’t worry about Waste Since Recovery is zero.

I’m Going to Need a More Limiting Working Slope Note that while I allow 57 degrees for my Final slope I am only Allowing 42 degrees for Active working areas.

Again Select the Base Option

Specify the Pit to Store the Output In and Any Limiting Pit Surface I am going to put my first pit In Pit 2 I am going to limit the pit To be within Pit 1 (ie it cannot Go out of the ultimate pit)

Order the Program to Run the Procedure

Turning On and Looking We See A Small Initial Pit

We Can Also Milk Some Data Out of the Output Report on the Run It appears to have taken About 102,000 blocks 102,000*6000*1.308*1.9= About 1.5 billion tons It tells us about ore and waste Blocks but we don’t pay any Attention to that because the Price is messed up so the Processing decisions are Jibberish.

We Now Make A Second Run With a Little Higher Prices (Resulting in a bigger pit) This time we start our Run with Pit #2 (our initial pit) already Present.

As You Can See I Moved Up Another Increment In Pit Size Ok – I did a few things to get this display I turned off Pit 2, turned on Pit 3 and then On Pit 3’s cut-offs option I went to properties And picked blue as a global color In fact the report indicates we mined an Additional 1.4 billion tons of material

And Then Up Again The report assures me I have an additional 1.2 billion tons of material

And Again Note that Some areas are Now reaching to The final pit slope The report tells Me I took another 1.1 billion tons

And Again 815 Million Ton taken Out in this phase

And Again An Additional 685 million tons was taken

Problems with a Learch Grossman Price Fake No way to know how big a jump in pit size corresponds to a given price change Often want nice even guides that correspond to ore for 3 to 5 year increments Blind guessing of prices can be a long frustrating process Learch Grossman may inherently not be able to give evenly spaced pits – the Gap Learch Grossman transforms the problem mathematically and then solves a different problem The different problem does not have continuous solutions as a function of price – some pit size jumps are mathematically built into the routine.

Substitute Floating Cone for Learch Grossman Floating cone pits can have some rough surfaces. Floating cone projects cone up from profitable blocks one block at a time. It misses material that could be moved With the combined worth of several target blocks. – The rough surface is one way This limitation can be seen. (Learch Grossman produces smoother pits).

Problems Remain After the Floating Cone Substitution Of course with floating cones you are still blinding guessing prices and then Seeing what happens to the pit.

Real Life Pushbacks Pit nesting can’t just control ore tonnage We have treated working slopes as lower pit slopes around the whole pit. In fact we may have 3 slopes A final pit slope that may provide just enough space to catch rock and get a road out (fine for ultimate pit) An active slope – the benches may not be wide enough to work but we can get equipment in to start to widen them A working slope that provides space every so many benches for equipment to really work Our Pushbacks are usually directional and only involve full working slopes in the direction of the expansion Trying to guess the direction of expansion while guessing prices is so random that the guesses are not practical

Solving the Pushback Slope Problem Accept reality Your being told where the most profitable ore is at / not being guaranteed you can get to it in that order Part of the problem of asking for perfect stage pits is that your taking yourself too seriously MineSight has a Multi-Pit Option It takes vertical columns of ore blocks and then just picks the upper 90%, 80%, 70%, etc of each column without recalculating prices and values The approximation misses how prices change the difference between ore and waste – but they are fake prices anyway

Lets Try to Rapidly Generate A Series of Nested Pits In this case I am going to set a working slope less than my ultimate pit slope

I Will Use the MultiV Option The rest of the panels Are set for ultimate pit. I click the radio button For MultiV instead of Base. For stage pits I’m also Considering floating Cone as good enough For my approximation.

This Requires Me to Fill Out A Special Panel to Control the MultiV Remember my file 13 Has a number of Pit surfaces from 0 to 50 available. I have To say which ones I Want to fill.

I’m Trying for 21 Steps to Go in Pits 10 to 30 The bench and block Range allows us to limit How much of the block Model we run calculations On. (We’re not going to Do this. You would do it If your block model Covered a large area and The ore was only in one Area). The value factors need some explanation.

How MultiV Works It calculates the value of each block at full metal prices Then it multiplies the value of each positive block by the minimum factor It then will run a floating cone to pick the pit it will mine Next time around it increments the factor one even step up from the minimum value to the maximum It remultiplies the value of each positive block It runs a floating cone to pick the next pit surface And so on Of course a prices really change which blocks are even positive will change This is a different way of trying to pick the most valuable ore.

I Will Let My Values Go From Almost Nothing to Full Value Lastly I will order the computer to make sure all my pits are nested Inside my Lerch Grossman ultimate pit (which I have stored in pit Surface 2).

I’ll Give My Output Orders Note I am trying to speed Things up by not storing Values and destinations Back into the model. And I’m naming the run Appropriately for what I am Doing.

Give the Run Order

The Procedure Runs

Visual Examinations I Turn On My Limiting Ultimate Pit.

Nice 3D Views of Expanding Pits But A Little Hard to Get A Read On.

Lets Try to Look at Some 2D Cross Sections Go to the Root Directory in My Data Manager Warning – I am about to go On a detour to show you how To get a 2D Display I’ll get back to interpretation Later!

Drop Down The File Menu and Pick Creation of a New Folder I’m going to create a new Folder for something Called a “Gridset” which I can use to control where 2D cross section views Are taken.

Name My New Folder and Say OK Alright – maybe I don’t get a prize for The most creative file-names.

Now Click On the Gridsets Folder I Just Made

Drop Down the File Menu and Ask The Data Manager to Make Me A Gridset (Sounds like a logical Thing to put in a gridset Folder)

Naturally It Wants Me to Name My Gridset My Gridset will be a series of vertical Planes in the East West Direction Which explains the innovative name I selected.

It Then Brings Up the Gridset Panel I picked a radio button for vertical East-West Planes I excepted the default grid Structure which started the Grids in the corner of my Block model I then specified 10 planes at 250 meter intervals which should Allow me to take a series of Cross-sections through the pit (I knew the coordinates of my Block model)

Now My Pretty New Gridset Shows Up

Now I Am Going to “Attach My Gridset to the Viewer” I will click on the Funny looking Green lined block (Linking a Gridset to The viewer will allow The viewer to take 2D cross sectional Views on the vertical East-west planes)

When I Tell It to Link a Gridset it Goes to a Directory and Asks Me Which One In my case where I have only one this is Not rocket science. I highlight my gridset By clicking on it and then I click OK

Now I Go Up to the 2D and 3D Icons and Click on 2D to Put the Viewer in Cross-Section Mode

It Shows Me A Cross Section on the 4000 North – East/West Plane Of course black Is a crumby Background color For this.

I’m Going to Change My Background Color Click on the Viewer Properties Icon that Looks like a blue Topped list.

Up Comes the Viewer Properties Box On the viewer options tab There is a color pallet for the background Color. Click on the Color Pallet.

Up Comes a Color Tablet Select the color And adjust the darkness Arrow Then click ok

Now I Have My New Background Color

I’m Going to Turn On All My Stage Pit Surfaces I have to do control clicks for each one (because MineSight won’t let me do a shift and drag Across).

I Right Click and Pick Open on the Pop-Up Menu

To Page Through My Cross Sections I Go to My Plane Selection Area and use the arrows to page

I Can Start to See My Pits

Looking For A Sequence that Is Really Minable

Surface Mining Sequence Realities You'll start with an initial small pit This pit needs to be large enough for the equipment to work It will have to be mined top down Once a pit is open the mine will expand out in pushbacks Usually push back in only one direction at a time so that only some slopes will have to be shallow Push back has to be wide enough to allow working room

Figuring Out How Wide the Push Back Is Lets say a working bench has to be 150 feet wide to accommodate working room Suppose we will have 4 active working benches on a push back That’s an 600 feet of working space Suppose a regular bench is 40 feet wide 4 regular benches would be 160 feet The wider working benches need an extra 440 feet Thus our minimum push back width is 440 feet Most large mine pushback are about 150 to 250 meters

Pit 10 to 11 Remember our grid work is 250 meters by 250 meters This pushback has enough space This one does not

I’m Already Dis-Satisfied My initial Pit #10 is already pretty large for me to mine top down I’m going to try to get a smaller initial pit with the price fake method I’ll need working width benches all the way around to get this pit. The Multi-V option just reduces the relative profit on a block Lower prices in a price fake will in fact convert ore to waste I should be able to force a reasonable size initial pit with with a Price Fake on a Floating Cone

Trying for An Initial Mini-Pit I go to my economic Panel and set Very low fake Prices.

Finish Setting My Low Fake Prices

Switch to a Base Design Strategy with a Floating Cone

Store My Result in Pit 9

Run the Routine

Well I Wanted Small I’m not sure Digging the pit With Mighty Tonka Trucks Was what I had In mind. This is just to Small for me to Be running the Same equipment Around.

Try Another Run with Higher Prices You can see the Price Fake Problem – you Really can’t Predict in advance What you will get. My second try was Better but I still Feel it’s a little Small.

Try a 3rd Time This time I’m Satisfied. Now as I do push Backs the shallow Slope will only Be active during The push back. I’ll steepen at the End. (With the idea that I will look at push Backs at the end Of each phase when The slope has been Steepened. (I’ll now re-run Multi-V with a steeper slope)

Restore My Full Predicted Copper and Moly Prices

Set for the Steeper Slope

Set for Multi-V

Over-Write My Old Shallow Pits

Run and Check Out My First Push Backs Looks like I have Push-backs in two Directions. I’m not sure which Way will go first but I’ll make a guess. Push Back 2 Push Back 1

Turn On Pit 11 I can see I have A practical Width pushback To the west, But not the east Pushback 3

Turn on Pit 12 On the west side I’ll merge pit 11 and 12 into One pushback of practical width

Turning on 13 I can see the 12 to 13 jump has not Given me any Practical push backs. I’ll turn on and off pits And try to see jumps Large enough to be Practical pushbacks

Looks Like I Have Pushback #4 to the East Now I’ll push out to the Ultimate pit on the East side.

I Can See from my Pit 30 Surface that I Probably Need to Lower My Cost Per Bench to Get the Rest My ultimate pit was Run with a 5 cent Per bench penalty Instead of 12. I pit crushing and Conveying will Probably be what turns The economics for The final expansions.

Using Plan View Gridsets Start Push back 1 Push back 2 Push back 3 Push back 4 Push back 5 Then down to The bottom.