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18TH ANNUAL ARENA STUDENT SIMULATION COMPETITION

1 GENERAL BACKGROUND

This problem highlights the challenges of modeling material handling operations, common in mining and construction operations. These operations are characterized by cyclical processes with highly variable activity times resulting in uncertainty in estimates. Discrete event simulation, when used properly, can be a powerful tool to analyze such systems.

This problem is based on real data from an operating gold mine, which has been modified for the purposes of this competition. The modifications are to protect the mine owner and to ensure the scope of the problem is appropriate for this competition.

1.1 Problem Statement

The Spotted Dog Mine is an open pit gold mine located in the western United States. The mine produces gold from processing ore mined using a truck-shovel system. The mining process involves drilling and blasting to fragment difficult to dig rock; excavating and loading using large mining excavators (shovels); and hauling the material to predetermined destinations using dump trucks. The material destinations are determined based on the estimated gold concentrations in the mined rock. If gold can be recovered from the rock economically (i.e. at a profit) then the rock is classified as ore and is hauled to the leach dump or crusher. If gold cannot be recovered economically from the rock then it is classified as waste and hauled to the waste dump. The drilling, blasting, loading and hauling operations at the Spotted Dog Mine are contracted out to American Mining Services, Inc (AMS).

In a truck-shovel operation, trucks arrive at a shovel to be loaded and wait for their turn to be loaded (Fig. 1). Once a truck is loaded by a shovel, it hauls the load to the predetermined destination (crusher, leach dump or waste dump) and dumps the material. Sometimes, trucks need to wait their turn to dump into a crusher since only limited number of trucks can dump into the crusher, simultaneously. The trucks then return to a shovel for the cycle to repeat.

AMS is paid monthly by the schedule in Table 1, adjusted by the pay factor (PF), which is calculated monthly using Equation (1). p75, p100, and p130 are the ratio of production days in the month where production was <75%, between 75 and 100%, and between 100 and 130% of production targets, respectively. Spotted Dog Mine is designed to handle 75,000 t/day of ore and 150,000 t/day of waste. The mine works 30 days in a month.

75 100 130

75 100 130

0.8 1.2 where 1PF p p p

p p p= + +

+ + = (1)

Table 1 Payment schedule

Material type Rate ($/tonne/km)

Ore 0.90 Waste 0.65

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Fig. 1 Typical shovel loading a truck at an open pit mine (Courtesy: http://www.geomineinfo.com/mining_photos.htm)

Your team has been contracted by AMS to evaluate their existing production plan and determine:

i. What is the optimal number of trucks for the fleet for Phase 1 (i.e. is 30 trucks optimal)?

ii. As haul/travel distance increases with depth as mining progresses, what is the optimal number of trucks for the next three phases (Phases 2-4) of mining?

1.2 Project Requirements

Your team should specifically address the following:

i. Performance criteria and how they will be evaluated

ii. Arena model of AMS’ truck-shovel mining system to evaluate performance

iii. Experimental design to accomplish the task

iv. Justification for recommended actions

2 TRUCK-SHOVEL SYSTEM AT SPOTTED DOG MINE

AMS’ truck-shovel system at Spotted Dog Mine is made up of three P&H 2800XPC shovels and 30 Caterpillar793F trucks (see attachments for specifications). Spotted Dog Mine runs two 10-hour shifts, with 9 hours of effective operations, every day. Data is provided in the attached files on activity times

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and travel speeds for trucks and shovels. The crusher can allow only two trucks to dump simultaneously (Fig. 2).

Fig. 2 Trucks dumping at a gyratory crusher (Courtesy: http://www.geomineinfo.com/mining_photos.htm)

Shovel breakdowns cause significant production variability since each shovel constitutes a third of production capacity. At the beginning of a shift, the each shovel is assigned to mine ore or waste during that shift. The assignment is made such that the production goals are met for that day. The probability of a load from an ore shovel being leach material is 60%. All waste material goes to the waste dump. The current (Phase 1) and future average haul profiles are given in Table 2. The general layout of the operation is illustrated by Fig. 3.

Table 2 Haul road profiles

Haul Profile Phase 1 Distance (m)

Phase 2 Distance (m)

Phase 3 Distance (m)

Phase 4 Distance (m)

Gradient

Ore Shovel to pit ramp 327 327 327 327 Flat Ramp entrance to pit exit 1,565 1,715 1,865 2,015 1:10 Pit exit to crusher 1,292 1,292 1,292 1,292 Flat Pit exit to leach dump 1,026 1,026 1,026 1,026 Flat Waste Shovel to pit ramp 327 327 327 327 Flat

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Ramp entrance to pit exit 1,565 1,715 1,865 2,015 1:10 Pit exit to waste dump base 646 646 646 646 Flat Waste dump base to top 806 906 1,006 1,106 1:10 Waste dump ramp exit to dump site 410 410 410 410 Flat

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Fig. 3 Layout of open pit mine (Courtesy: http://www.geomineinfo.com/mining_photos.htm)

Shovel location

Ramps

Ramp exit

Leach dump

Ramp entrance

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3 TERMINOLOGY

Term Definition Ore A rock from which a metal(s) or mineral(s) can be economically extracted.

Waste Overlying rock or barren host rock. Also those parts of the ore deposit that are below the economic cut-off concentration.

Leaching An extraction method involving the slow passage of a solvent (including water, acids or chemicals such as cyanides or chlorides) through a layer of crushed or porous material to extract the valuable components into a solution. The metal is then recovered from the solution by further processing (electrowinning).

Leach dump A leach dump is a stockpile of rock built for the purposes of leaching the rock.

Waste dump Refers to waste material that has been moved by a truck and is formed into large, terraced dumps/stockpiles.

Crusher A machine for reducing the size of rock.

Ramp The name for a type of haul road found in surface mines that provides access from natural surface level, down into the pit.

Open pit Open pit mine. Meaning a surface mine, and generally used to describe metalliferous mines. Open pit mines, in contrast to open cast/strip mines, expand both laterally and in depth.

Truck Dump truck used to haul ore and waste from the shovel to the crusher, leach dump or waste dump. A loaded truck is full of waste or ore.

Shovel Excavator for extracting material from the ground and loading it into trucks.

4 ATTACHMENTS

1. P&H 2800XPC specifications 2. CAT 793F specifications 3. CSV files of activity times and truck speeds 4. Text files of shovel time between failures and time to repair

Data Units Empty truck speeds m/min Loaded truck speeds m/min Shovel loading times min Truck dumping times min Time to repair hours Time between failures hours