Authors: Duncan Bennett, Principal Metallurgist, PanAust Limited & Alan Tordoir Drill & Blast Superintendent, Phu Kham Operations, Phu Bia Mining Limited & Peter Walker, General Manager, Technical Services, PanAust Limited & Walter Valery, PhD, Senior Vice President, Global, Metso Process Technology & Innovation & David La Rosa, Manager, Mining Technology, Metso Process Technology & Innovation & Alex Jankovic, PhD, General Manager, Technology & Innovation, Metso Process Technology & Innovation
An open-pit mine with complex geology
Phu Kham is located approximately 100 km northeast of the Laos capital Vientiane. The geology of the deposit is highly variable due to weathering, alteration, faulting and folding. The rock mass strength and degree of weathering vary considerably across the deposit with extremely hard rock found in the deeper levels.
The operation comprises a large conventional open-pit mine feeding ore to a process plant consisting of crushing, grinding and flotation to recover copper and precious metals. The current capacity is 19.5
Mtpa. The concentrate contains 22 to 25 % copper, 7 grams per tonne (g/t) gold and 60 g/t silver.
The Phu Kham copper-gold deposit in Laos is an extremely heterogeneous orebody. The deposit has complex and variable mineralogical, geological and geotechnical properties, which affect plant throughput and metallurgical performance. To complicate things further, the operation is expecting harder ores as mining progresses deeper into the pit, which have the potential to limit throughput and poses a risk to long-term profitability.
To evaluate how to maintain the target throughputs – and profit – over the Life-of-Mine (LOM), the owner of the mine, Phu Bia Mining Limited, embarked on a throughput forecasting and optimisation project with the help of Metso’s Process Technology and Innovation team in 2012. The goal was to identify opportunities to increase throughput when treating hard ores, develop a throughput forecasting model, and determine if and when secondary crushing or other process changes would be required to maintain the target throughput over the LOM.
The project involved ore characterisation, detailed audits of blasting and comminution practices linked with ore characterisation data using Metso’s SmartTagTM ore tracking, and development of site-specific models for blasting and comminution processes. Integrating these models resulted in an optimisation tool for the overall operation, and for throughput forecasting.
A “Cookbook” for effective blasting
The optimisation process began with ore characterisation to define domains within the orebody that will behave similarly throughout the blasting and comminution processes. Ore within a domain will produce similar Run-Of-Mine (ROM) fragmentation for a given blast design. Improved plant throughput can be achieved by manipulating ROM fragmentation.
One of the main objectives was to develop strategies to maximize mill throughput to maintain LOM operational targets even when treating harder ores. As expected, the blast modelling and simulations that followed indicated that tightening the blast pattern to increase the powder factor resulted in a significant increase in the fines generated in the blast. Reduction of stemming length also generated more fines and reduced the top size of the rock due to the increased explosive energy at the stemming horizon. These simulations indicated the potential to increase throughput by increasing the fines and reducing the top size of the ROM fragmentation by optimising the blasting parameters.
Simulations were conducted for each of the ore domains defined at Phu Kham, and the blast design was optimized for each of the ore domains. This resulted in a “cookbook” which provides a “recipe” (i.e. an optimized blast design) for each ore domain. Blasting according to this cookbook provides a more consistent and optimized feed size distribution to the downstream processes, increasing throughput, process stability and efficiency. Following the cookbook also avoids excessive blasting in softer ore domains, thus reducing energy consumption and costs, and preventing the excessive production of ultrafines that can be detrimental to some downstream processes.