Olympias Mine is operated by Hellas Gold S.A., a subsidiary of Eldorado Gold Corporation. The orebody shape and size are suitable for a drift and fill mining method. The mining sequence is overhand and the demand for backfill strengths are generally low except for the initial sill cuts. The design fill strengths are determined from the planned stope exposures to allow for safe extraction of the ore in adjacent drifts and immediately below the initial sill drifts with minimum dilution. Due to the permit constraints imposed on mining at Olympias Mine, after an environmental impact assessment, there is a requirement that the final backfill strength must reach a uniaxial compressive strength (UCS) of 4.0 MPa at 28-day cure age. By developing a suit of mix recipes incorporating superplasticiser admixtures, it was possible to achieve the strength demands and the workability of the backfill. This paper presents the results from comprehensive test work conducted on whole mill tailings and cyclone mill tailings to produce high strength backfill.
It took five years to bring mining with paste backfill to Maaden Barrick Copper Companys (MBCC) Jabal Sayid Mine in Saudi Arabia. The work involved various studies, multiple test programs, site visits for benchmarking and detailed engineering before the paste system was commissioned in October 2017. Barrick is a world leader in paste backfill and drew on international teams to conceptualise, design and construct this 225 m3/hr cemented paste backfill system. Value engineering, peer reviews and risk management workshops were held throughout the process to ensure MBCC received value for money and a reliable system. The paste plant was required to handle a tailings stream that was originally planned to produce hydraulic fill (the coarse fraction) but through the reintroduction of fine tailings was able to generate a good paste product that met mining needs. Challenges involved getting the most out of the tailings dewatering circuits (both fine and coarse streams), the local conditions (temperatures >50°C), large bulk stopes fed by a gravity system and the capital cost associated with building a high throughput system with significant cement storage. This paper presents the history of the project, test work, engineering design and construction, commissioning, and training required to fill the first stope. More recent backfill monitoring, data logging, improvements and ongoing optimisation of the system that have continued through the first year of paste production are also presented.
This paper looks at the design of a paste reticulation system, particularly a new method of diverting paste flows in critical situations, and the safeguards that were incorporated into the reticulation design to minimise the risk of line blockage during backfill operations. It also details the actions taken during a paste blockage event to flush and recover the entire line. The paper considers some of the restrictions that were imposed due to cost and time restraints on the schedule, and the impact these restrictions had on the profile and the flow characteristics of the reticulation network. Finally, a summary of key learnings and solutions that have been implemented to further safeguard the system has been provided.
As backfill systems become a more common method for managing tailings and enhancing ore recovery, safe and efficient methods for handling the backfill are adding value for mine owners. At Kirkland Lake Gold Fosterville mine (Victoria, Australia), automated diverter valves were installed at distribution switching points to direct paste to the intended stopes. The valves are operated remotely from a control room, removing the human element at the transition point during diversion. The other option for making changes in paste distribution is a manual operation where long sweep elbows are disconnected from the piping network and reconnected to a different downstream pipe. This process is tedious and time consuming, requiring many man hours and equipment that is not always readily available, resulting in much down time. This paper will discuss how using automated diverter valve operation in place of manual diversion of the paste at Kirkland Lake Golds reticulation system delivered dramatic uptime and minimised physical safety risks. Safety benefits not only eliminated the manual movement of piping components but include localised lockout access, safe evacuation of paste from upstream borehole (and piping) resulting from downstream blockage and diversion of flush water to a suitable collection area.
Since the introduction of paste backfill into underground mining operations in the 1990s, transport of paste underground has been primarily completed using steel pipes. Steel pipes have been required due to the relatively high friction loss of the thick paste material and therefore the moderately high operating pressures realised through the piping system. Steel pipes are both heavy and rigid which results in them being labour intensive to install in the underground environment. In most other underground mine applications high density polyethylene pipe (HDPE) is used, however its use in paste backfill is limited due to the low maximum allowable operating pressures (MAOP) of HDPE. To overcome the short comings of steel and HDPE pipe for paste fill transport, a new technology known as steel wire reinforced composite polyethylene pipe (SRCP) is now becoming widely used. SRCP pipe technology provides the high pressure benefits of steel piping, along with the low weight, corrosion resistance and flexibility properties of HDPE. This paper outlines the history of SRCP, the products details, how SRCP is used in a modern paste fill system and a number of case studies of its use in Australian and African underground mining operations.
An underground paste fill system will inevitably experience a system flow-loss event during its operational life. In a flow-loss event, the underground reticulation design, flow-control hardware, instrumentation specification and system recovery methods can greatly impact the time taken to safely and effectively achieve a full system clearance and recommence backfilling activities. In addition, the learnings and methods discussed in this paper minimise the opportunity cost of using valuable underground work crew resources to rectify the blocked pipe work and the associated paste plant downtime. This deficit of paste filling will further impact the mining production schedule by increasing mining activity interaction and disrupting the extraction sequence. Direct costs of a blockage may include piping replacement and work crew labour as well as an increased risk of injury and equipment damage during a time-critical activity. The management of a flow-loss event must consider each of the following three flow-loss conditions experienced: A case study (Scenario 1) is presented to demonstrate the management of a flow-loss event, which includes system blockage and stalling due to insufficient available head pressure being overcome by system segmentation. Segmentation highlights the advantages of the ability to carry out safe and effective system isolation from underground in a time-critical situation. Reticulation failure response is also discussed in this paper, with an explanation of the recovery method and the requirement of an adaptive approach as the flow-loss condition can transition from one type to another during the recovery effort.