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Filling Mining Case Study | Mechanized Shallow-Hole Upward-Sectioned Filling Method at the Fankou Lead-Zinc Mine — Black Diamond Report
Filling Mining Case | Fankou Lead-Zinc Mine Mechanized Shallow-Hole Upward Layered Fill Method
As a mining engineer, one of the most frequent questions I hear from my peers is: “When mining complex, thick, and large ore bodies, how can we balance resource recovery, production safety, and environmental protection?” Today, taking the Fankou Lead–Zinc Mine—the benchmark for backfill mining in China—as our case study, we will dissect the practical details of its core mining method: mechanized shallow-hole upward slicing with backfilling. By integrating key considerations such as vein layout and sectional retreat mining, this discussion is packed with actionable insights—highly recommended for saving and referring to later.
Fankou Lead–Zinc Mine is affiliated with Zhongjin Lingnan, a subsidiary of GuangSheng Group, and is a leading mine in China’s lead–zinc industry as well as a benchmark for the application of the fill mining method. The ore body at the mine exhibits a complex geometry, occurring in lens-shaped and stratoid forms, with the main ore body having an average thickness of 20. 50 m, with a maximum thickness of over 100 m, and a dip angle of 60°. The dip angle is 70°, and the roof is overlain by water-bearing limestone; therefore, surface structures must be strictly protected, and no ground subsidence is permitted. Early methods such as gravel backfilling and tailings–water–sand backfilling suffered from high conveyance resistance, difficult dewatering, and low productivity. Ultimately, these were iteratively upgraded to a mechanized shallow-hole upward-layered backfilling method, which is perfectly suited to the mine’s complex mining conditions.
I. Why did Fankou Mine choose this filling method?
The selection of any mining method must be tailored to the mine’s specific geological conditions and production requirements. At Fankou Mine, the mechanized shallow-hole upward-layered filling method was chosen, with the core objective of addressing three major pain points:
• Pain point 1: The ore body is complex and Surrounding rock Uneven stability—while the ore body and surrounding rock are generally stable (f = 8–13), localized roof strata consist of sandstone or argillaceous marl (f ≈ 4), and fault fracture zones are well developed. Therefore, layered backfilling must be employed to control ground pressure and prevent stope collapse.
• Pain point 2: High demand for resource recovery—The mine holds substantial reserves of lead and zinc, with average grades of 5.65% lead and 9.30% zinc, necessitating maximum reduction of ore loss and improvement of recovery rates.
• Pain point 3: Stringent environmental and safety requirements—As an underground mining operation, it is necessary to address the management of mined-out areas and the disposal of tailings, while simultaneously implementing mechanized operations to reduce manual labor intensity and mitigate safety risks.
The mechanized shallow-hole upward-layered filling method, with “layered mining, real-time filling, and mechanized operations” as its core, not only controls the exposed area of the stope through layering to ensure operational safety, but also utilizes the fill mass as a working platform for the next layer of mining, thereby significantly improving resource recovery rates while simultaneously enabling the resource utilization of tailings. This approach perfectly aligns with the mining requirements of the Fankou Mine.
II. Detailed Process Description
Based on the ore veins and sectional markings at the Fankou Mine site—namely, the Chuan Vein I, Chuan Vein II, D3tb Vein, Sections 1 through 4, shafts, chutes, dewatering wells, and other features—we have decomposed the process flow into three core stages: stope layout, stratified mining, and backfilling operations.
(1) Stope Layout
The stope layout for the mechanized shallow-hole upward-layered filling method at Fankou Mine is strictly aligned with the strike of major ore veins such as Chuanmai I and Chuanmai II, with stopes delineated in accordance with the occurrence characteristics of the ore body. The key shaft and tunnel layouts and stope parameters are as follows:
• Sectional division: With a stage height of 40 m, the ore body is divided into multiple sections (e.g., Section 1, Section 2, Section 3, and Section 4 as you have labeled), each with a height of 8 m, serving two sublevels, each with a height of 3–4 m.
• Shaft and drift layout: Shafts are arranged along the vein trends, including ventilation and pedestrian shafts, ore-discharge shafts, and dewatering shafts (for dewatering the backfill). The dewatering shafts have dimensions of 1 m × 1 m and penetrate the bottom pillar to connect with the lower-lying vein, thereby resolving the challenge of dewatering the backfill. The stope boundaries are defined based on the vein trends, delineating clearly demarcated mining areas (as shown in Sections I–I and II–II).
• Bottom pillar design: The stope bottom pillars are 8 m high and constructed using cemented backfill, serving as the load-bearing foundation for the entire stope while also reserving Ventilation Channel , ensuring the ventilation function of the mining area.
This layout not only makes full use of the natural strike of the ore body, thereby reducing the volume of shaft and tunnel excavation, but also establishes a closed-loop system for ventilation, ore extraction, and dewatering through the coordinated arrangement of raise shafts, chutes, and dewatering wells, thus laying the foundation for mechanized operations.
(2) Stratified Mining
The mining operation adheres to the principle of “top-down, layer-by-layer advancement,” with a clearly defined extraction sequence for each layer and fully mechanized operations throughout, significantly boosting productivity:
1. Rock Drilling and Blasting: HS105 upward-feeding, automatic rod-connecting drilling rig is used to drill shallow blast holes arranged in a plum-blossom pattern, with a hole spacing of 0.8. 1.0 m, with a row spacing of 1.2 m; the hole pattern in the cut-hole zone is densified to 0.8 m × 0.8 m [6]. To protect the backfill on both sides, the side holes are spaced 0.4 m from the backfill, and every 3 5-meter side-bench control holes to reduce blast-wave damage;
2. Ore Extraction Operations: Following blasting, 2 m³ or 3 m³ imported scraper loaders are used to convey the ore via chutes to the intermediate-level haulage drifts, from where it is then hauled out by underground locomotives, thereby achieving mechanized ore extraction and reducing manual labor intensity.
3. Roof Management: Following ore extraction, promptly remove loose overburden from the stope roof and assess roof stability to ensure readiness for subsequent backfilling operations, thereby mitigating the risk of roof collapse.
It is worth noting that, during the mining process, the height of unsupported roof in the working face must be strictly controlled to prevent prolonged periods of roof exposure; at the same time, ventilation through the ventilation crosscuts should be utilized to ensure adequate ventilation in the working face and safeguard the safety of operating personnel.
(3) Grouting Operations: Layered grouting, strict strength control, and closed-loop management
Filling operations are the core of this method. At Fankou Mine, by optimizing the filling process, the dual objectives of achieving specified strength for the fill body and realizing the resource utilization of tailings have been attained. The specific procedure is as follows:
1. Preparation of filling material: A cemented backfill system comprising tailings and cement is employed. In conjunction with an integrated recovery process for mining waste rock [1], the waste rock is crushed and mixed with tailings, thereby achieving resource utilization of the waste rock while enhancing the strength of the backfill.
2. Layered Backfilling: Immediately after mining and site clearance for each layer, backfilling is carried out in two stages: bottom-layer backfilling and cemented interlayer backfilling. The bottom layer employs low-ash tailings cemented backfill with a sand-to-cement ratio of 1:8, with a backfill height of 2.5. 3.0 m, uniaxial compressive strength of the filling body: 1 1.5 MPa; the layer uses a high cement-to-sand ratio (1:4). Rod-milled sand-cemented filling , filling thickness 0.5 0.8 m, with a 28-day strength of 5 for the filling material. 7 MPa[2];
3. Dehydration Curing: Water is drained from the fill body through dewatering wells to ensure rapid setting and curing until the design strength is achieved, after which the next layer of mining is carried out, thereby establishing a closed-loop process of “mining–ore extraction–filling–curing.”
In addition, the patent “Method for Preserving Ventilation Shafts in Backfill Mining and Associated Embedded Components,” developed by Fankou Mine, maintains the ventilation function of the ventilation shafts during the backfilling process, thereby enhancing backfill quality, ensuring adequate ventilation for subsequent mining operations, and further optimizing the backfilling process.
III. Application Outcomes
Since the Fan’kou lead–zinc mine adopted mechanized shallow-hole upward-layered filling, it has achieved remarkable technical, economic, and environmental benefits, establishing itself as a benchmark case among similar mines in China.
• Technical benefits: underground Mining recovery rate The recovery rate reaches 95%, with dilution kept within an acceptable range; the two-stage stope has a production capacity of 300 t/d, with a loss rate of 3% and a dilution rate of 5%; ground pressure activity is effectively controlled to prevent surface subsidence, thereby ensuring safe mine operations and resolving the challenges associated with mining complex, thick, and large ore bodies.
• Economic benefits: Mechanized operations have reduced direct mining costs by approximately RMB 21 per ton and comprehensive backfilling costs by about RMB 20 per cubic meter; tailings utilization has exceeded 95%, cement consumption has been cut by 20%, resulting in a substantial reduction in production costs; meanwhile, valuable metals contained in mining waste rock are recovered, thereby enhancing the value-added of resources.
• Environmental benefits: Achieve the resource utilization of tailings and mining waste rock, reduce environmental pollution caused by waste rock stockpiling and tailings discharge, uphold the principle of green mining, and realize a win-win outcome for mining operations and environmental protection.
IV. Summary
As a mining engineer, drawing on practical experience from the Fankou Mine, I have summarized the core application scenarios for the mechanized shallow-hole upward-layered filling method, for reference by peers:
1. Orebody conditions: Applicable to ores with complex shapes and large thicknesses (thickness ≥ 20 100 m), with a steep dip angle (60° 70°), with moderate stability of the ore and surrounding rock, and requiring surface protection and ground-pressure control in metallic mines;
2. Core Advantages: High degree of mechanization, high resource recovery rate, safe and controllable operations, and environmental friendliness—effectively addressing key challenges in the mining of complex ore bodies, such as subsidence, resource wastage, and environmental concerns.
3. Key Lessons Learned: The success of the Fan’kou Mine hinges on “process optimization tailored to mine conditions”—specifically, aligning stope layouts with ore-body trends, optimizing the mix proportions of backfill materials, incorporating patented technologies to enhance backfill quality, and integrating mechanization with resource recovery. These principles represent the core takeaways for other mines in similar circumstances seeking to adopt this approach.
The mechanized shallow-hole upward-layered filling method employed at the Fan’kou Lead–Zinc Mine has not only resolved the challenging mining issues associated with its complex orebody but has also provided replicable and scalable practical experience for fill mining in domestic metal mines.
