A paste backfill plant is a purpose-built processing facility that converts mine tailings into a stable, cementitious fill material – used to support underground stopes, reduce surface tailings storage, and improve overall mine recovery rates.
Table of Contents
- What Is a Paste Backfill Plant?
- How Paste Backfill Plants Work
- Applications and Benefits of Paste Backfill
- Selecting the Right Paste Backfill System
- Frequently Asked Questions
- Comparison: Paste Backfill vs. Other Backfill Methods
- How AMIX Systems Supports Paste Backfill Operations
- Practical Tips for Paste Backfill Success
- The Bottom Line
- Sources & Citations
Article Snapshot
Paste backfill plant is a dedicated processing system that thickens mine tailings, blends them with cement binders, and distributes the resulting paste underground to fill excavated stopes. It improves ground stability, diverts tailings from surface storage, and enables higher ore recovery in underground hard-rock mining.
paste backfill plant in Context
- 88,500 tonnes per annum of tailings diverted from surface storage at Bluestone Mines Tasmania through paste backfill (Bluestone Mines Tasmania Joint Venture, 2024)[1]
- Paste slump consistency for backfill applications ranges from 8 inches minimum to 10 inches maximum (911 Metallurgist, 2024)[2]
- In advanced paste backfill operations, more than 30% of the weight of the ore is sold as product, and the entire tailings stream is disposed of underground (911 Metallurgist, 2024)[2]
- The Chambishi paste backfill system single supply line delivers up to 60 cubic metres per hour (University of Western Australia, 2022)[3]
What Is a Paste Backfill Plant?
A paste backfill plant is a purpose-engineered facility that processes mine tailings into a cementitious paste and delivers it underground to stabilize excavated voids. Unlike conventional hydraulic fill, paste backfill retains most of its process water before placement, producing a dense, low-bleed material that supports stope walls, reduces dilution, and eliminates the need for large surface tailings storage facilities. AMIX Systems designs and supplies the automated grout mixing plants and batch systems that form a critical part of the binder preparation and distribution circuit within these operations.
The term cemented paste backfill – also referred to as CPB – describes the finished product: a mixture of dewatered tailings, hydraulic binder such as Portland cement or slag, and water, combined in precise proportions. When placed underground, it cures to a specified unconfined compressive strength, allowing adjacent stopes to be mined safely while the fill mass provides structural support.
Paste backfill technology has become a standard practice in modern underground hard-rock mining across Canada, Australia, South America, and Africa. Operations in British Columbia, Quebec, Western Australia, and Peru rely on these systems to manage tailings responsibly while recovering ore from previously inaccessible areas. The scale of individual plants ranges from small modular units serving narrow-vein mines to high-capacity facilities producing hundreds of cubic metres per hour for bulk mining operations.
One documented example illustrates the environmental and operational value clearly. At Bluestone Mines Tasmania, the proposed paste backfill plant was assessed as a currently accepted mining best practice, with the Environmental Impact Statement noting that it would divert 88,500 tonnes per annum of tailings away from tailings storage by converting tailings to a productive resource (Bluestone Mines Tasmania Joint Venture, 2024)[1]. That single figure captures why operators across the industry are investing in paste backfill infrastructure.
How Paste Backfill Plants Work: Process Stages Explained
A paste backfill plant operates through a defined sequence of unit processes, each of which must be correctly engineered and controlled for the finished product to meet strength and pumpability specifications.
Tailings Thickening and Dewatering
Raw cyclone tailings or full plant tailings are first pumped to a high-rate or paste thickener, where flocculant is added to accelerate settling. The thickener underflow is drawn off at a target solids content – above 70-78% solids by weight depending on the ore type – and transferred to the paste mixing circuit. At the Bad Grund Mine, paste moisture content was documented at 12 percent (911 Metallurgist, 2024)[2], illustrating the degree of dewatering required before mixing begins.
Binder Addition and High-Shear Mixing
Thickened tailings are combined with a dry hydraulic binder – most commonly ordinary Portland cement, slag, or a blend – in a mixing unit that must achieve thorough, homogeneous distribution. This is where colloidal mixing technology provides a measurable advantage. High-shear colloidal mixers disperse cement particles more completely than paddle mixers, producing a more stable paste that resists bleed and delivers better pumpability through long underground pipelines.
Two-stage mixing configurations are common in high-capacity operations. As documented at Chambishi Copper Mine, two-stage mixing is important to produce paste with the desired strength and consistency, with the entire process interlocked by a distributed control system (DCS) responsible for monitoring, data collection, and regulation of most equipment involved in the backfill system (University of Western Australia, 2022)[3].
Paste Distribution and Underground Delivery
Mixed paste is pumped from the surface plant to the stope through a system of boreholes and steel pipelines. Positive displacement pumps – including high-pressure piston and peristaltic pump types – are selected based on paste rheology, pipeline distance, and static head. At Brucejack gold mine in British Columbia, Canada, three hydraulic-driven piston pumps rated for a continuous duty of 145 cubic metres per hour at 125 bar pressure handle paste distribution through the underground network (World of Mining, 2023)[4]. The Chambishi single supply line achieves 60 cubic metres per hour with a pipeline gradient reaching 7.73 at the deepest section (University of Western Australia, 2022)[3].
Stope filling proceeds in stages, with barricades installed at draw points to retain fresh paste while it cures. The fill mass is allowed to reach a minimum unconfined compressive strength before adjacent mining resumes, a quality control step that determines both safety and production scheduling.
Applications and Benefits of Paste Backfill in Underground Mining
Paste backfill delivers measurable benefits across a range of underground mining methods, and the reasons operations invest in a dedicated plant go well beyond simple void filling.
Ground support is the primary driver. When paste cures to the design strength, it acts as an artificial pillar, allowing miners to extract ore from adjacent stopes without leaving permanent crown or rib pillars. This directly improves overall resource recovery. In some advanced operations, more than 30% of the weight of the ore is sold as product, and the entire tailings stream is disposed of underground (911 Metallurgist, 2024)[2]. For narrow-vein and high-value gold, silver, or copper mines, this level of extraction efficiency justifies the capital cost of a full paste backfill facility.
Tailings management is an equally significant benefit. Surface tailings storage facilities require ongoing geotechnical monitoring, water management, and eventual closure obligations that represent a long-term liability. Diverting the tailings stream underground reduces the footprint of surface impoundments, lowers closure costs, and in many jurisdictions satisfies increasingly strict environmental permitting requirements. The Bluestone Mines Tasmania example – diverting 88,500 tonnes per annum of tailings – shows the scale of this diversion at even a mid-size operation (Bluestone Mines Tasmania Joint Venture, 2024)[1].
Water recovery is a third advantage. Paste backfill retains significantly less free water than hydraulic sandfill, but the water that does drain from the placed fill must be managed carefully. As Paterson & Cooke note, the backfill dewaters during placement, increasing demand on the mine dewatering system, and water cannot be allowed to accumulate in the stope because this poses a risk of failure or inundation (Paterson & Cooke, 2020)[5]. Properly designed drainage systems convert this recovered water into a usable process water resource, reducing fresh water consumption in the mill circuit.
For mines in Canadian provinces such as British Columbia and Quebec, as well as operations in Rocky Mountain states and Appalachian coal regions, paste backfill also supports regulatory compliance with tailings management requirements that are tightening under both federal and provincial frameworks.
Selecting the Right Paste Backfill System for Your Operation
Choosing a paste backfill system requires matching plant capacity, mixing technology, and pump selection to the specific tailings characteristics, binder demand, and underground distribution geometry of your operation.
Capacity and Throughput Requirements
Plant output must match the stope filling rate required to keep pace with mining production. Small underground operations using cut-and-fill or room-and-pillar methods require only 10-30 cubic metres per hour, while large sublevel open stoping mines demand 100 cubic metres per hour or more. Selecting a modular, scalable system allows capacity to grow with the mine without requiring a full plant rebuild.
For operations where capital expenditure for a full paste plant is not justified – particularly smaller hard-rock mines – a cemented rock fill approach using high-output colloidal grout mixing systems delivers comparable ground support outcomes at lower capital cost. AMIX Systems’ SG40 and SG60 platforms are designed for this application, producing automated, repeatable cement-aggregate mixes at outputs up to 100+ cubic metres per hour.
Mixer Selection: Colloidal vs. Paddle
The mixing unit is the quality-critical component of any paste backfill plant. Colloidal grout mixers use a high-speed rotor-stator configuration to produce a homogeneous, well-hydrated cement slurry before it contacts the tailings fraction. This delivers superior binder distribution, lower bleed rates, and improved long-term strength gain compared to conventional paddle mixing. The result is a more consistent fill product with better pumpability – reducing pressure surges in the underground pipeline and lowering wear on pump components.
Automated batching control is equally important. A distributed control system that monitors water addition, binder feed rate, and mixer output in real time allows operators to maintain paste quality within the slump and solids content specifications – a target range of 8 to 10 inch slump (911 Metallurgist, 2024)[2] – while logging production data for quality assurance and reporting purposes. You can explore Colloidal Grout Mixers – Superior performance results to understand how high-shear technology applies directly to paste and cemented fill production.
Pump Selection for Underground Distribution
Paste rheology – particularly yield stress and viscosity – governs pump selection. Positive displacement pumps, including peristaltic and piston designs, are preferred for paste because they handle high-density, high-viscosity slurries without the recirculation losses that affect centrifugal pumps. Pipeline design must account for static head, friction losses, and the potential for plug formation if the system is shut down under pressure. Peristaltic Pumps – Handles aggressive, high viscosity, and high density products are a reliable choice for binder slurry transfer and low-to-medium paste distribution applications because they tolerate abrasive materials and provide accurate metering without valve wear.
Your Most Common Questions
What is the difference between paste backfill and hydraulic sandfill?
Paste backfill and hydraulic sandfill both fill underground stopes, but they differ significantly in solids content, strength, and water management requirements. Hydraulic sandfill is pumped as a dilute slurry – at 65-70% solids – that drains freely through a barricade, leaving the solid fraction in place. Paste backfill is prepared at much higher solids content, often above 75-78%, so it retains its form on placement without requiring drainage barricades that handle large volumes of free water. Because of reduced porosity, paste backfill is more dense than hydraulic sandfill and has a higher confined strength (911 Metallurgist, 2024)[2]. This higher strength allows adjacent stopes to be mined with less pillar loss, improving overall resource recovery. Hydraulic sandfill is simpler and cheaper to produce but delivers lower structural performance and generates more process water underground that must be pumped back to surface. For operations in British Columbia, Quebec, or hard-rock mining regions in the Rocky Mountain States, paste backfill is increasingly preferred wherever ore value justifies the capital investment in a dedicated plant.
What binders are used in a paste backfill plant?
The most common binder used in cemented paste backfill is ordinary Portland cement (OPC), either alone or blended with supplementary cementitious materials. Ground granulated blast furnace slag (GGBFS) is widely used as a partial cement replacement because it reduces cost, lowers heat of hydration, and in tailings chemistries with sulphide content improves long-term durability. Fly ash and natural pozzolans are used in specific regional contexts where they are available and compatible with the tailings mineralogy. Binder selection is driven by the target unconfined compressive strength, curing time requirements, and the cost of binder delivery to remote sites. In underground hard-rock mines, binder represents the largest single operating cost in the paste backfill system, so optimising the blend through testwork is a critical step in plant design. Automated batching systems that precisely control binder addition rate – within tight tolerances – are needed for managing this cost while consistently achieving quality targets. Admixture systems are also incorporated to adjust set time, workability, or pumpability for specific underground conditions.
How is paste backfill quality controlled during production?
Quality control for paste backfill production focuses on three measurable parameters: solids content (or moisture content), slump consistency, and unconfined compressive strength of cured samples. During production, operators monitor slump using a standard cone test – a target range of 8 to 10 inches is standard for most underground applications (911 Metallurgist, 2024)[2]. This field test gives immediate feedback on whether paste is too stiff to pump reliably or too fluid to retain its position in the stope. Automated control systems log water additions, binder feed rates, and mixer power draw in real time, creating a production record for quality assurance reporting. Samples taken at the mixer discharge are cast into cylinders and cured underground at in-situ temperature before being tested for compressive strength at specified intervals – at 7, 14, and 28 days. At Chambishi Copper Mine, the DCS was responsible for monitoring, data collecting, and regulating most equipment and devices in the backfill system (University of Western Australia, 2022)[3]. Retrievable operational data supports quality assurance reporting to mine owners, an important safety transparency requirement in underground fill operations.
Can a paste backfill plant work for smaller mines that cannot justify a full paste plant?
Yes. Many smaller underground mines cannot justify the capital expenditure of a full paste thickening and distribution plant, but they achieve effective ground support and tailings management using cemented rock fill (CRF) or high-volume grouted fill systems. In a CRF approach, waste rock is used as the primary fill aggregate rather than thickened tailings, and a cement-water slurry is injected or mixed with the rock as it is placed in the stope. This eliminates the thickener and filtration circuits, significantly reducing both capital and operating costs. AMIX Systems designs high-output automated batch systems for this application – the SG series platforms deliver repeatable, accurately batched cement slurry at the volumes needed for continuous stope filling in small to medium hard-rock mines. Modular containerized designs make these systems practical for remote sites in Canada, Mexico, Peru, and West Africa where infrastructure is limited. Rental options through AMIX also allow mines to access high-performance mixing equipment on a project basis, avoiding capital commitment for operations with finite or uncertain production timelines. The result is a flexible, cost-effective path to underground ground support that delivers many of the same safety and resource recovery benefits as a conventional paste backfill plant.
Comparison: Paste Backfill vs. Other Backfill Methods
Underground mining operations choose from several backfill methods, each with different capital requirements, operational complexity, and ground support performance. The table below compares the four most common approaches across the criteria that matter most to mine planners and geotechnical engineers.
| Backfill Method | Solids Content | Binder Use | Strength Level | Water Management | Capital Cost |
|---|---|---|---|---|---|
| Paste Backfill | High (75-82%) | Yes – cement/slag | High (design-specific) | Low free water drainage | High |
| Hydraulic Sandfill | Moderate (65-70%) | Optional | Low to moderate | High drainage volume required | Moderate |
| Cemented Rock Fill (CRF) | N/A (rock aggregate) | Yes – cement slurry | Moderate to high | Minimal | Low to moderate |
| Dry Rock Fill | N/A | No | Low | None | Low |
Paste backfill delivers the highest confined strength and the best tailings diversion outcome, making it the preferred choice where ore value and regulatory requirements justify the capital investment. Cemented rock fill offers a practical, lower-cost alternative for mines where the paste plant capital expenditure is not feasible, and it is the approach for which AMIX Systems’ SG series automated batch plants are well suited.
How AMIX Systems Supports Paste Backfill Operations
AMIX Systems designs and manufactures the automated grout mixing and batching equipment that underpins effective paste backfill and cemented rock fill operations. Our equipment is used in underground hard-rock mining across Canada, Australia, South America, and Africa, where consistent binder preparation and distribution are needed for both ground support quality and operational efficiency.
For operations requiring high-volume cemented rock fill as an alternative to a full paste backfill plant, our SG20 through SG60 colloidal mixing platforms deliver automated, repeatable cement slurry batching at outputs up to 100+ cubic metres per hour. The self-cleaning mixer design reduces downtime during extended 24/7 operating periods, while the automated batching system logs production data for quality assurance reporting – a requirement for safety compliance in underground fill applications.
“We’ve used various grout mixing equipment over the years, but AMIX’s colloidal mixers consistently produce the best quality grout for our tunneling operations. The precision and reliability of their equipment have become essential to our success on infrastructure projects where quality standards are exceptionally strict.” – Operations Director, North American Tunneling Contractor
Our AGP-Paddle Mixer – The Perfect Storm range and Cyclone Series – The Perfect Storm grout plants are available in containerized configurations for straightforward transport to remote mine sites. Bulk bag unloading systems with integrated dust collection support high cement consumption rates while improving operator safety underground – an important consideration in confined working environments.
For binder slurry transfer and distribution within the plant circuit, our Complete Mill Pumps – Industrial grout pumps provide reliable, high-pressure performance in demanding applications. Rental options are available for operations requiring temporary backfill capacity or for mines evaluating cemented fill before committing to capital purchase.
Contact AMIX Systems at +1 (604) 746-0555 or sales@amixsystems.com to discuss your paste backfill or cemented rock fill mixing requirements.
Practical Tips for Paste Backfill Success
Getting the most from a paste backfill plant requires attention to process design, equipment selection, and day-to-day operational discipline. The following practices reflect what consistently works in underground mining operations across Canada and internationally.
Conduct thorough paste recipe testwork before plant design. The relationship between tailings mineralogy, binder type, binder content, and cured strength varies significantly between ore bodies. Testwork at a certified geotechnical laboratory is needed before finalising plant design parameters, particularly the target solids content range and binder dosage that achieves design strength at the lowest possible cost.
Size your thickener conservatively. Paste thickeners are the most common bottleneck in operating plants. Selecting a thickener with capacity headroom and appropriate flocculant dosing control allows the plant to handle variability in tailings feed without falling below the minimum solids content for paste quality.
Invest in automated batching and data logging. Automated control of water additions and binder feed rate is a quality assurance requirement. Production data logged by the DCS or PLC becomes the record of evidence for backfill quality reporting to mine owners, regulators, and certifying engineers. Manual batching introduces variability that undermines both quality and safety.
Design the underground pipeline system for restart after planned and unplanned stops. Paste sets in the pipeline if the system is shut down without flushing. Pipeline design should include flush water connections at strategic intervals, and operating procedures should specify maximum hold times before a flush cycle is required.
Monitor stope drainage and dewatering capacity. Even low-bleed paste releases some water during placement. Mine dewatering infrastructure must be sized to handle this additional load, and stope drainage design must prevent water accumulation that compromises barricade integrity.
Consider Typhoon AGP Rental – Advanced grout-mixing and pumping systems for pilot or temporary applications. A rental plant allows operations to show the performance of a cemented fill approach before committing to capital purchase, or to provide supplementary mixing capacity during peak production periods.
Follow LinkedIn industry updates to stay current on evolving paste backfill technology. Follow AMIX Systems on LinkedIn for technical updates on mixing plant developments relevant to underground fill applications.
The Bottom Line
Paste backfill plant technology is a well-established and economically justified approach to underground void management, ground support, and tailings diversion in modern hard-rock mining. The combination of high-density placement, cementitious binding, and automated quality control delivers both safety and resource recovery outcomes that conventional fill methods cannot match. For mines where the capital cost of a full paste plant is a barrier, automated cemented rock fill systems using colloidal mixing technology provide a practical and cost-effective path to the same core objectives.
Whether your operation requires a full paste backfill mixing circuit, a high-volume CRF batch system, or rental equipment for a finite project, AMIX Systems has the engineering expertise and equipment range to support your underground fill requirements. Contact our team at +1 (604) 746-0555, email sales@amixsystems.com, or visit our contact form to discuss your specific application.
Sources & Citations
- Paste Backfill Plant – Environmental Impact Statement. Bluestone Mines Tasmania Joint Venture.
https://epa.tas.gov.au/Documents/Bluestone%20Mines%20Tasmania%20Joint%20Venture%20Pty%20Ltd%20-%20Paste%20Backfill%20Plant%20-%20Environmental%20Impact%20Statement.pdf - Paste Backfill Fundamentals. 911 Metallurgist.
https://www.911metallurgist.com/blog/paste-backfill/ - Paste backfill system design and commissioning at Chambishi. University of Western Australia.
https://papers.acg.uwa.edu.au/d/1504_22_Xiuxiu/22_Xiuxiu.pdf - Paste Backfill. World of Mining.
http://www.womp-int.com/story/2023vol09/story027.htm - Backfill – Key Properties. Paterson & Cooke.
https://www.patersoncooke.com/2020/09/29/backfill-key-properties/