This year’s virtual MassMin 2020 conference includes an in-depth paper from I Edgar, R Prasetyo and M Wilkinson from copper and gold mining major PT Freeport Indonesia that covers the extensive learnings from the Deep Ore Zone (DOZ) mine on dealing with wet ore, or so-called wet muck mining, including how it influenced the development of PTFI’s remote control mining fleet and ultimately how the company is now applying this experience in planning for a more comprehensive autonomous underground mining approach using the latest technology at its new Grasberg Block Cave (GBC) and Deep Mill Level Zone (DMLZ) mines.
Over the years, the Deep Ore Zone (DOZ) panel cave mine has experienced a steady increase in the prevalence of wet ore within the mine. “The mine has a unique data set on this challenge and has established sufficient empirical relationships to manage the hazards associated with it. This includes an understanding of not only the probability of wet ore rushes but also the potential severity of these rushes.” In parallel, the mine has progressed towards the goal of establishing a remote cave mining operation. To date, the mine has converted 100% of its LHD operations to remote; has updated 30% of the active chutes to remote operation; is largely complete converting its water cannons to remote operation and is in the process of finalising the work plan to convert the mobile rock breakers and other support equipment to remote operation. All remote operations will be housed in a single location on the surface. Although driven by the safety requirements of managing wet muck, this change points to the future of mining as a continuous and remote operation.
Wet muck is a term used at PTFI to describe ore that has a sufficient water and fines content to present an inrush hazard. This type of ore and resultant wet muck inrush, locally termed a “spill”, was first experienced in the underground operations in 1989 and is generally understood to be a consequence of comminution within the draw columns and the high rainfall experienced at the mine. The DOZ mine was established below the Intermediate Ore Zone (IOZ) mine, commencing production in 2001. The mine is a relatively large panel cave mine that achieved peak production of 80,000 t/d in 2008 and an average of 80,000 t/d by 2010. Approaching the end of its life, the DOZ is producing 30,000 t/d today with final ore expected to be extracted in 2022.
The bulk of PTFI’s wet muck experience has been acquired in this mine. During its operation, the wet muck hazard and the consequent management approach has evolved. Spills have become more frequent and very large spills, although rare, have begun to occur as the draw columns have matured. In addition, the location of inrushes has expanded from the production footprint to the haulage level, subsequently to oreflow circuit and ultimately to the mill stockpile. The mine has adapted to these changes by increasing the number of tasks completed remotely, developing spill hazard assessment criteria, increasing the pedestrian free areas and stand-off distances as well as pursuing an active blending strategy.
As a result of these changes, the mine has evolved as a prototype for an underground autonomous caving operation. This prototype has allowed PTFI to map a development plan that will see the Grasberg Block Cave (GBC) and Deep Mill Level Zone (DMLZ) mines operating autonomous, remote and manual operations seamlessly within the same Autonomous Mining Area (AMA) that is managed from a single Remote Operating Room (ROR) on the surface.
In DOZ mine, wet muck is identified by visual observation only with assessment by a small committee on a weekly basis using a simple classification scheme based on the fragmentation size and water content. The classification scheme was originally derived from a commissioned study and has evolved since then. Essentially the classification seeks to identify if the material is both fine and saturated. It is subjective although some basic tests can be done in the field, for example material that will form a ball when squeezed is type 2 and material from which excess water emerges when squeezed is type 3.
Drawpoints in green class do not pose a spill risk, yellow class drawpoints pose a low risk and can be mucked manually with constraints, red class drawpoints can only be mucked remotely. All persons working in a production area that contains wet muck must undergo training as a Wet Muck Assessor. This training enables each and every person in the wet muck area to determine the level of hazard of the drawpoints in their work area.
DOZ began experiencing wet muck in drawpoints while still constructing new drawpoints as part of the panel cave development. This provided the flexibility to produce from the new coarse and dry material in preference to the wet material. It also allowed the wet drawpoints to be closed and still maintain sufficient inventory of drawpoints to achieve the mining plan. In 2015, when the panel cave development completed, only 25% of the active drawpoints required remote mining. As time went on, with no new dry drawpoints to replace wet drawpoints, the percentage of wet drawpoints increased rapidly and by the end of 2018, all mining panels were being mined remotely.
Existing chute designs have proven incapable of successfully storing wet muck, loading a truck and then closing again. Although approximately 150 t of wet muck can be held by the existing chutes, if the door is opened to release a 50 t truckload it is often not possible to stop the flow and retain the remaining 100 t. The mine therefore operates a 50 t in, 50 t out process on the wettest material to ensure there is no risk of engulfing a truck. The Cat MineStar system, a commercially available mobile asset monitoring and management system, used for tracking production LHDs at PTFI has been extended to the truck haulage level providing improved management of orepass inventory. Further, trucks no longer drive through the chutes, but back into them so that any spill is away from the cab not toward it. Meanwhile, work continues on the development of a chute capable of both storing and controlling wet muck.
The extraction of ore from a caving mine requires ore be removed from a drawpoint, and that occasional blockages within the drawpoint be cleared to allow the continued extraction of ore. That ore is then delivered to an orehandling system, and transported to a crushing system before being conveyed to the mill stockpile. In an ideal situation, when wet muck is present, this process could be conducted remotely to ensure no one is within the active panels or wet muck oreflow areas.
Currently, in the DOZ all production LHDs are operated remotely using the MineStar Command for underground system from Caterpillar, and no manual loading occurs. The mine has also developed the ability to handle drawpoint blockages remotely using Getman water cannons equipped with a remote operating system from Remote Control Technologies (RCT) and mobile rock breakers. However, blasting continues to be required, and this is conducted manually after the 24 hour exclusion period.
Remote equipment is used to mitigate the risk to people from exposure to spills, but it does nothing to reduce the risk of spills and consequently remote equipment itself is frequently entrapped. Recovery of the entrapped equipment is done using remote loaders, as far as practicable, but still occasionally requires people in the panel for excavation and towing. This excavation is completed by a small excavator and in some cases in part by hand. Recovery is through towing with another loader or with a Beltor loader extraction device. Drawpoint securing is currently completed manually however, the team has worked with Australia’s Jacon on the development of a remote shotcreting unit and expects to begin a trial of this process in late 2020. If successful, this will allow drawpoints to be secured before anyone enters a panel.
Within downstream oreflow systems, spill recovery is largely completed manually by hand as excavations were not designed originally to accommodate remote excavating or loading equipment in proximity to the oreflow systems. The future goal is that the new underground caving mines at PTFI will deliver the right tonnes on a continuous basis at the lowest practicable cost. To achieve this, mines will be operated from a central location on a continuous basis using a combination of autonomous, semi-autonomous and manual equipment controlled through a semi-intelligent production management system. To this end, wet muck mining has led PTFI to develop the capability of operating LHDs remotely and it now operates the largest fleet of remote underground LHD’s in the world. Further, the resulting production interruptions from wet muck mining have guided PTFI on the requirements of a fully remote mining system.
The delivery of this goal will be achieved using a series of implementations, some of which are already complete. The first is to be able to track all tonnes from origin to destination to ensure the right tonnes are moved. This project is complete, however, in 2020 a replacement technology was implemented as the existing solution has been obsoleted. The replacement technology substantially lowers the price point to achieve this task. The second step is to operate remotely to achieve continuous operations and to remove operators from harm’s way. For LHDs, this has been achieved with current work focussed on updates to improve remote productivity. Ultimately, it is expected that higher productivity will be possible in remotely operated equipment than manually operated machines, as has been achieved in open pits.The third step is to operate without interruption. A large part of the standby and delay time is caused by implementation of remote capability on only one part of the production cycle (LHDs), necessitating 24-hour safety stand downs between mucking and any other activity. This is being addressed by expanding remote capability across the full production cycle.
Once this step is complete, the ability to move the right tonnes is substantially improved since the addition of location and cycle tracking for secondary breaking, recovery and road maintenance equipment and the monitoring of the cave health allows for the optimisation of resource assignment for the overall production process as a whole rather than local optimisations, which may be suboptimal for the overall production. It also will establish valuable data sets.
In the two-year horizon, it is expected that loaders will be able to operate the majority of cycles autonomously and in the five-year horizon trucks will be able to complete the majority of their cycles autonomously as well. This provides continuous operation with minimal harm to the equipment. Finally, as both data sets and equipment capability expand, the amount of decisions and consequent actions that can be optimised autonomously and continuously will become substantial.
The remote operating room (ROR) is the single location from which the DOZ, GBC and DMLZ will be operated as a predictable and reliable underground mining operation. The intent is that the full production cycle from cave to crusher is operated in a common area with clear visibility of the equipment and the people within the autonomous mining area. This visibility includes their location, activities and health. In addition, the health of the cave itself is also monitored to ensure the appropriate part of the cycle is being optimised to assure a consistent “manufacturing” of ore. The ROR will house operator stations, maintenance health stations, mine controller stations and system technicians. The majority of stations are designed to allow for the physical operation of the equipment, using controls that resemble those on the actual machine. Stations for maintenance health, mine controller and system technician are operations centre-type desks with multiple monitors displaying the relevant real-time information for each role and communications equipment. For autonomous machines, operator stations resemble those of the mine controllers and each operator oversees many machines simultaneously. In the medium-term this fully autonomous operation is expected to be achievable but is not part of the initial deployments.
The production management system will provide the mine controller a complete picture of the location, state (eg standby) and performance of all people and assets within the production areas as well as the general condition of the cave and panels. This information will be presented in general, graphical format enabling interpretation at a glance and better, faster decisions on work assignments. Further, much of the assignment will be handled automatically by the software reducing the burden on the controller to exceptions only. Equipment within the production areas will also have a clear view of their location as well as that of equipment or people within their area and the state of the zones in their vicinity (remote or manual).
The extraction level will include autonomous, remote and manual work within the same environment. This area will be described broadly as the Autonomous Mining Area (AMA). All entities within the AMA will be equipped with SafeDetect (a Minetec product) and will be managed by the Area Isolation Management System (AIMS). AIMS is being developed in partnership with Caterpillar for trial in late 2020 and allows both dynamic and remote changes in the allocation of sections of the mine to manual, remote or autonomous use. The boundaries of the AMA will be the only locations deploying physical barricades and those barricades demarcate the point beyond which entities must have the appropriate systems on-board and in which all persons entering or operating require competence in AIMS and AMA procedures.
The operation and maintenance of the systems associated with the highly mechanised, 100% network dependent production system will require a revision to organisation structure and skilled specialists who have attained a defined level of competence. The people who are engaged in developing, deploying, operating and maintaining the mine’s technology are what is broadly described as the Technology Group. This group includes Remote Plant, Remote Solutions, Remote Operations and Remote Projects. Remote Plant includes the configuration and maintenance of the physical componentry in the field. Remote Solutions includes the operation and maintenance of specialised networking, communication systems and their associated hardware as well as the management of the operating applications and massive volumes of data generated by their operation. Remote Projects is accountable to work in collaboration with OEMs establishing the development, project execution and operational readiness plans. The group also secures funding and project manages the initial deployment, as well as ensuring operations are sufficiently staffed, trained and provided with the appropriate systems for continuous operation of the completed projects. Remote Operations is accountable for the use of the remote equipment and systems to maximise safe production at the lowest possible cost. The team is a virtual team with members in multiple sub sections of the business.
The paper concludes that “the mining of wet muck is a challenging undertaking with substantial safety hazards that must be managed. PTFI has developed sufficient technical ability and empirical knowledge to safely operate a wet muck mine. The optimisation of this mine and further reduction of risk both point to the need to develop a continuous and largely remote mine with substantial autonomous capability. PTFI is well on track to achieving the first generation of this mine within the five year time horizon and is already operating the largest remote underground fleet in the world.”
