# Research Progress and Typical Case of Open-Pit to Underground Mining in China
## 3 Typical Case: Integrated Demonstration of Xinqiao Iron Mine
### Tailings Resource Utilization and Open-Pit Ecological Restoration Practices  
As mineral resource extraction continues to intensify, the mining industry generates vast amounts of waste rock and tailings each year. If improperly managed, these by-products can cause significant environmental and ecological damage [60]. For example, in Papua New Guinea, waste rock and low-grade ones are commonly stored in waste piles or tailings ponds, leading to severe land degradation and ecological decline [61]. In China, the total amount of solid waste from mining has exceeded 25 billion tons, with the number and size of tailings ponds continuously increasing. Traditional methods of tailings storage not only occupy large areas of land but also exacerbate environmental risks [62].  
In this context, the adoption of \"green mining\" practices, including the resource utilization and harmless treatment of tailings, has become a core issue for the sustainable development of the mining industry. Green mining initiatives focus on utilizing advanced mining technologies to achieve efficient resource recovery and environmentally friendly disposal of solid waste [63]. Among these approaches, tailings backfilling technology has emerged as a significant area of research in recent years.  
Tailings backfilling technology, an environmentally friendly method of tailings disposal, utilizes tailings as underground backfilling material, promoting the recycling of waste and significantly reducing the surface environmental burden [64]. [PERSON] [65] highlighted the notable advantages of cemented tailings sand backfilling technology in terms of environmental protection, technical implementation, and economic benefits. At the Laisvall lead-zinc mine in Sweden, coarse-grained tailings produced by flotation were used to create a cement-based slurry for underground mine backfilling, leading to effective ecological restoration [66]. Similarly, at the Pinto Valley Copper Mine in the United States, tailings were successfully used for open-pit backfilling, offering valuable technical insights for ecological restoration efforts in China.  
Xinqiao Mine is a representative polymetallic mine that employs a combined open-pit and underground mining method. The bottom of the pit reaches a depth of \(-\)156 m, forming steep and high slopes, with a reserve of 43.6 million cubic meters, resulting in significant slope stability and safety risks. In response to the national requirements for green mining, Xinqiao Mine has launched an open-pit ecological restoration project. Due to its low tailings sand output, which cannot fully meet the needs of underground backfilling, Xinqiao Mine has innovatively used tailings from Dongguashan Copper Mine to solidify and backfill the open pit. The schematic of the restoration project is shown in Figure 11a, and the tailings transportation pipeline layout is shown in Figure 11b. This solidification backfilling process not only solves the tailings disposal issue at Dongguashan Copper Mine but also eliminates safety hazards at Xinqiao Mine's open pit, facilitating regional mining resource synergy. The ecological restoration outcomes are illustrated in Figure 11c.  
In conclusion, the open-pit ecological restoration project not only effectively mitigates safety risks during the mine transition process but also plays a crucial role in supporting green mining construction and the sustainable development of the mine's environment. Future research should prioritize optimizing the performance of tailings backfill materials, innovating backfilling processes, and conducting long-term monitoring of ecological restoration outcomes. These efforts will contribute to the development of a standardized technical framework that can be adapted to various mining conditions, providing robust technical support for the green transformation of China's mining industry.