?To explore the spatial strength distribution of backfill in the stope, a group of experiments in a large similar stope model was designed for simulating the consolidation of cemented tailings backfill (CTB) in a stope. The height of CTB in similar stope model was measured to analyse the flow and sedimentation characteristics. The unconfined compressive strength (UCS) test on specimens cored in the different position of CTB sample in similar stope model was conducted. Moreover, the particle size and cement content of CTB sample were tested to help to explain the mechanism. The results show that during the flow and sedimentation of filling slurry in the model, inconsistency of the particle size and cement content leads to the inconsistency of strength. In the flow direction (horizontal direction), the median particle size of CTB first increases and then decreases, the cement content of CTB decreases slowly and then increases sharply, and the strength of CTB first decreases and then rises. In the sedimentation direction (vertical direction), the cement content of CTB decreases with the increase of depth, while the strength of CTB increases with the increase of depth. The strength is affected by the interaction between particle size and cement content, and the higher cement content of CTB does not translate into higher strength. The results provide a theoretical basis for improving the quality of CTB and optimizing the design.
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.
In the early 1960s, a series of field instrumentations were initiated by the US Bureau of Mines on hydraulic fill. These studies were conducted in order to better understand the characteristics of hydraulic backfill. Cemented paste backfill (CPB) has gained wider acceptance in the mining industry and the number of operations utilising CPB has expanded significantly. One of the earliest attempts at field measurement in CPB occurred over 20 years ago. Since then, extensive scientific research has been conducted on CPB material in order to provide mines with a rational design process; however, there has been limited published instrumentation programs. The authors affiliated company has been involved with in-stope backfill instrumentation programs at numerous operations. Because of the data collection and field experience, the authors have a better understanding of how in situ backfill behaves, and how operations can use this information to safely improve the efficiency of their backfilling operation. In order to improve the safety and efficiencies of backfilling for other mines and other practitioners, a collection of published data along with additional case studies are provided. This paper summarises both hydraulic and CPB instrumentation results focusing on the important mechanical properties of backfill: time to onset of effective stresses and hydrostatic loading (i.e. fluid backfill to soil?like material), influences of flushes, thermal expansion and contraction, and influences of seismic and blast events.
?Inspired by the success of cemented paste backfill in the west orebody of Chambishi Copper Mine, integrated disposal of paste backfill and surface high-concentration tailings stacking was applied in the southeast orebody. This paper presents the integrated disposal system, including two deep cone thickeners, double-shaft horizontal mixer, two plunger pumps for underground backfill and three diaphragm pumps for surface stacking. The challenges of the integrated disposal system were deep backfilling (0.98 km) and long-distance discharging (15 km), so a combination of gravity flow and pumping was used in paste backfill and three diaphragm pumps with a preset pressure of 7 MPa were applied for surface stacking. The annual ore production in the southeast orebody is 3.3 Mt, which is 3.3 times larger than that of the west orebody. Therefore, the capacity of the integrated disposal system also needs to be expanded. The capacity of the paste backfill system and surface stacking system were 160 m3/h with paste concentration of 75 wt.% and 265 m3/h with slurry concentration of 55 wt.%, respectively. In the first phase, the cement to tailings ratios for primary and second stopes are 1/8 and 1/24 respectively. To meet the backfill strength and reduce the cost, waste rock will be added in paste backfill in the second phase, the waste rock to tailings ratio is 1/3, the cement to tailings and waste rock ratio for primary stopes are 1:12, and 1:30 for secondary stopes. As a result, the UCS after 28 days for primary and second stopes were 1.2 MPa and 0.5 MPa, respectively.
Cemented paste backfill (CPB) has been utilised globally in mines based on its benefits of non-segregation, non-bleeding and homogeneity. Due to a lack of research around the mechanism(s) driving anti-segregation properties, nowadays only some engineering empirical parameters including the slump or the fine particle content of backfill slurries can be used as the descriptive criterion for CPB. To better understand the antisegregation mechanism of CPB, so a quantitative criterion for its identification can be determined, the segregation-induced inhomogeneous properties of cemented tailings backfill have been experimentally investigated. Samples (diameter 75 mm and height 150 mm) with different solid contents were poured, cured and cut into sections of equal height. Thereafter, titration measures of EDTA-2Na and helium porosimeter have been used respectively to test the cement content and porosity of each section. Results show that the cement contents decreased from top to bottom along the curing height of samples, while the porosities increased along the settling direction. The inhomogeneity of cemented samples is affected obviously by the solids content of the paste, and it is notable that there is a turning point for the slurry concentration value over which the homogeneity will be improved dramatically. The turning point could be used as a new criterion for CPB definition from the perspective of inhomogeneity inhibition.
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.
Mavres Petres mine is an underground mine, located in Chalkidiki, northern Greece, that is owned and operated by Hellas Gold; a wholly owned subsidiary of Eldorado Gold Corporation. The mine extracts a highgrade lead and zinc orebody using drift and fill mining method. Backfill is an integral part of mining cycle at Mavres Petres mine. Filtered coarse tailings mixed with cement are used for making cemented hydraulic backfill in a surface batching plant. The paper will discuss and present an overview of the backfill optimisation efforts at Mavres Petres mine, which includes recent changes and upgrades in the backfill plant, improved mix design, backfill quality control, and backfill delivery and placement in order to improve the operational efficiency, product consistency, safety and economic viability of the mine.
Cemented aggregate fill (CAF) and cemented rockfill (CRF) have successfully been used as a low-cost, highstrength backfill material in underground mines. The placement of the material and flowability generally limits the technology to low throughput application and smaller stope sizes if tight filling is required. Optimisation of CAF/CRF flowability and strengths is most readily achieved by optimising the FullerThompson gradation curve. CAF/CRF relies on the materials available on the mine site and the additional costs of borrow pits or additional crushing adds significant cost to a material that is usually chosen due to low cost. This paper presents a case study of an optimisation of a CAF material by the addition of tailings in order to increase the paste fraction of the material. The main aim was to decrease the angle of repose to improve filling ability in addition to decreasing the required binder content.
This paper presents an optimisation loop that looked to improve how Newmonts Tanami Operations (NTO) determines its required stable stope strengths. In order to do this, a comparison exercise was completed, in which NTOs current stability assessment method was compared to other popular assessment methods ranging from analytical to numerical methods. From this comparison, it was decided to proceed with a different stability assessment method that uses shear stress reduction. The paper then presents how the use of this method was implemented and presents three case studies on how the new stability assessment method has benefited NTO.
Cemented paste backfill (CPB) has become known as a superior secondary ground support technique and mine tailings storage method for stoping. Extensive scientific research has been conducted by the authors on CPB to provide the Red Lake operation (RLO) of Evolution Mining with an optimised backfill placement process. Due to these complex factors and interactions, a rational CPB material design process was assessed to demonstrate the safety aspects related to a continuous pour. For this purpose, an extensive field monitoring program was required to quantify the CPB performance and characteristics. There are two different ways of optimising the CPB design to maximise placement rate: (i) optimising the type and amount of binder added to the system, and (ii) optimising the CPB placement process underground. Optimisation of binder type and dosage is relatively easy as the required backfill stand-up strength is based on block dimensions, stope stability, and extraction sequencing. Four stopes were instrumented with total earth pressure cells (TEPCs) and piezometers to capture the pressures acting on the fill fence structures and the strengthening response of the CPB plug within the stopes. This paper summarises the results of each of the tests performed. Based on the results obtained from this study, it was concluded that RLO can safely conduct continuous CPB pours with appropriate safeguards and protocols in place. It is important to note that this paper is a summary of the CPB performance and characteristics in RLO longhole stopes and does not reflect site-specific safety procedures, protocols, and critical controls required for a more aggressive pouring regime.