Open Pit Planning and DesignOpen Pit Planning and Design

The Standard Approach for Open The Standard Approach for Open PitPit

©2007 Dr. B. C. Paul©2007 Dr. B. C. Paul

The Ajo Open Pit in ArizonaThe Ajo Open Pit in Arizona

They mined around the barren core

Lacks Clear Steps and Has A Lot of Lacks Clear Steps and Has A Lot of Interaction – Computers Almost a Interaction – Computers Almost a

NecessityNecessity In general need to know In general need to know

you have a large ore you have a large ore reserve close enough to reserve close enough to the surface to be open pit the surface to be open pit minedmined

Generally comes from Generally comes from geologic datageologic data– Open pit designs normally Open pit designs normally

represent ore reserves and represent ore reserves and geology as a block modelgeology as a block model Slice and dice the ore Slice and dice the ore

reserve up into small blocks reserve up into small blocks that sit end to end and on that sit end to end and on top of each othertop of each other

Building Block ModelsBuilding Block Models

Start by specifying block dimensionsStart by specifying block dimensions Look at drill and sampling data for how Look at drill and sampling data for how

continuous the mineralization iscontinuous the mineralization is– Use computer routines to estimate the ore Use computer routines to estimate the ore

grade of the blocks using samplesgrade of the blocks using samples– One of the most popular is Kriging (also One of the most popular is Kriging (also

polygonal and IDS)polygonal and IDS) Most going to study how interpolation is done in this Most going to study how interpolation is done in this

class. (You’ll be given a block model to work with)class. (You’ll be given a block model to work with)

Determine the Minable Ore ReserveDetermine the Minable Ore Reserve

Assume economics for material removalAssume economics for material removal Look at geology for how steep the pit slopes can Look at geology for how steep the pit slopes can

stand without sliding instand without sliding in Have the computer analyze the largest set of Have the computer analyze the largest set of

blocks that can be removed without taking stuff blocks that can be removed without taking stuff that looses moneythat looses money– This set measures the size of the pit that can ultimately This set measures the size of the pit that can ultimately

be mined (called the Ultimate Pit)be mined (called the Ultimate Pit) Too complex to visualizeToo complex to visualize

– Done with either a Floating Cone Miner or Learch-Done with either a Floating Cone Miner or Learch-Grossman computer routineGrossman computer routine

SequencingSequencing

Considering the need to work from top down Considering the need to work from top down and the grade of the oreand the grade of the ore– Calculate a series starting with richest ore and Calculate a series starting with richest ore and

working down in grade over timeworking down in grade over time

Usually accomplished with modified Usually accomplished with modified computer routinescomputer routines

Getting best ore early in life greatly Getting best ore early in life greatly improves the NPV of the projectimproves the NPV of the project

Developing a Practical LayoutDeveloping a Practical Layout

With a series of nested pit shells as a guide With a series of nested pit shells as a guide design a set of pits that follows the guides design a set of pits that follows the guides but has benches, and roads required for but has benches, and roads required for practical mining.practical mining.

Pick Equipment FleetsPick Equipment Fleets Work on intermediate and short term Work on intermediate and short term

equipment schedules to execute the over-all equipment schedules to execute the over-all planplan