Improvements in Blasting Technology at Cliffs Natural Resources

Blasting is one of the lowest cost yet most critical parts of the mining cycle. This paper discusses the findings of an audit conducted on the blasting operation at an iron ore mine. The purpose of the audit was to review current blasting practices in order to identify opportunities for production/cost improvements. The approach taken in the audit was to observe general blasting practices, their related downstream effects and to compare current procedures to established best practices. The findings of the audit indicated improvement could be achieved in productivity and lower costs for the shovels and loaders through improved diggability and reduced oversize material in the muck pile. The reduced occurrence of oversize would also improve the crusher operation and reduce the cost of rehandling material in the surge pile. Based on the findings of the blast audit, a Six Sigma ® Diggability Team was formed that utilized the audit report to develop productivity improvements, reduce oversize and lower overall mining costs. The paper discusses the principal blast optimization efforts undertaken and how they improved the mining operation in terms of production. In addition, an overview of the processes developed to quantify and maintain the achieved improvements is included. Description of additional continuous improvement projects currently being implemented and their anticipated benefits is provided. INTRODUCTION Cliffs Natural Resources (CNR) is an iron ore mining, concentrating and pelletizing operation located in Michigan, the second largest iron ore producing state in the United States. Near Palmer, Michigan on the Marquette Iron Range in northern Michigan, CNR will move 106 million long tons (104 million metric tons) in 2009 to support the production of iron ore pellets for sale in the United States and Canada. Michigan Operations was formed in 2003 by combining the Empire and Tilden mines. Recognizing that blasting is one of the lowest costs, yet most critical parts of the mining cycle, the mine began a thorough review of blasting technologies to improve mining operations. A key component of this process was a blast audit that occurred during the period of 23 April to 10 May, 2007. The principal objective of any production blast is to produce a muck pile with characteristics that optimize the downstream mining processes. Although many operators can describe the optimum blast results for a specific mining function, they typically lack a methodology whereby they can relate the key blast parameters to performance of the downstream mining processes and establish an overall optimum blast. The following describes how information obtained from an audit of the blasting operations was utilized to guide a project in optimizing downstream processes and the improvements achieved. KEY OPERATIONAL ISSUES AT TILDEN AND EMPIRE MINES The mine management had identified several areas of interest prior to the blast audit. It was requested that the audit consider these concerns which included the following: • The mine wanted to increase safe production. If the costs could also be lowered that would be an additional benefit. • The productivity of the LeTourneau loaders was a concern as they frequently experienced difficult digging conditions. The role of the LeTourneau loaders was to provide flexibility to the production while the shovels provide the base production. Due to the difficulty with the LeTourneau loaders, the mine lacked the desired production flexibility. • A variety of explosive formulations were used at Tilden and Empire mines. Many of these formulations contained aluminum which significantly increased the cost of the explosive. The mine wanted to determine if the aluminum was actually necessary. • Production was primarily limited by the truck fleet. However, production was also limited by the shovels. AUDIT FINDINGS Drilling and Blasting Practices: Design parameters traditionally were based on the last results obtained at the specific location of the blast and the type of rock being shot. The parameters adjusted for the production blasts were the burden, spacing, explosive, and delay timing. The traditional design methodology was to design the pattern to meet an average explosive energy level throughout the blast. The energy level targeted was based on past experience and personal judgment. Nominal blast information is provided in Table 1. Table 1. Description of nominal blast design at Empire/Tilden.