Open Pit Planning and Design The Standard Approach for Open Pit ©2007 Dr. B. C. Paul

The Ajo Open Pit in Arizona They mined around the barren core

Lacks Clear Steps and Has A Lot of Interaction – Computers Almost a Necessity  In general need to know you have a large ore reserve close enough to the surface to be open pit mined  Generally comes from geologic data –Open pit designs normally represent ore reserves and geology as a block model  Slice and dice the ore reserve up into small blocks that sit end to end and on top of each other

Building Block Models  Start by specifying block dimensions  Look at drill and sampling data for how continuous the mineralization is –Use computer routines to estimate the ore grade of the blocks using samples –One of the most popular is Kriging (also polygonal and IDS)  Most going to study how interpolation is done in this class. (You’ll be given a block model to work with)

Determine the Minable Ore Reserve  Assume economics for material removal  Look at geology for how steep the pit slopes can stand without sliding in  Have the computer analyze the largest set of blocks that can be removed without taking stuff that looses money –This set measures the size of the pit that can ultimately be mined (called the Ultimate Pit)  Too complex to visualize –Done with either a Floating Cone Miner or Learch- Grossman computer routine

Sequencing  Considering the need to work from top down and the grade of the ore –Calculate a series starting with richest ore and working down in grade over time  Usually accomplished with modified computer routines  Getting best ore early in life greatly improves the NPV of the project

Developing a Practical Layout  With a series of nested pit shells as a guide design a set of pits that follows the guides but has benches, and roads required for practical mining.  Pick Equipment Fleets  Work on intermediate and short term equipment schedules to execute the over-all plan