# Research Progress and Typical Case of Open-Pit to Underground Mining in China
## 3 Typical Case: Integrated Demonstration of Xinqiao Iron Mine
### Selection of Mining Methods for the Transition from Open-Pit to Underground Mining at Xinqiao Mine  
In the mine transition process, the selection of mining methods directly influences resource recovery rates, safety, and environmental impact, making it a key factor in the transition from open-pit to underground mining at Xinqiao Mine. The choice of transition method varies significantly among mines, depending on factors such as ore body characteristics, geological conditions, and environmental policies. At Xinqiao Mine, the proportion of C-class medium-thick ore body resources reaches 79.4%. The ore body characteristics, including moderate thickness and stable strata, require the mine to prioritize the use of backfilling mining methods suitable for medium-thick ore bodies. This decision takes into account multiple factors, such as ground pressure control, resource recovery, and environmental protection. The selection of mining methods depends not only on the fundamental characteristics of the ore body but also on factors such as the coordination between open-pit and underground operations, the complexity of the ore body's structure, production capacity requirements, and the protection of surface infrastructure. Therefore, the choice of mining method in the transition process reflects the diverse strategies adopted by different mines in addressing similar challenges. For instance, globally, mines choose mining methods based on factors such as ore body dip, geological complexity, and economic conditions, highlighting the technical diversity in mining transitions.  
After evaluating several options, Xinqiao Mine identified two potential methods: mechanized upward horizontal layered backfill mining and segmented stope post-backfilling. The mechanized upward horizontal layered backfill method provides advantages such as simple processing, strong adaptability to the ore body, and effective ground pressure control. It uses horizontal deep-hole blasting combined with trackless equipment, significantly reducing loss and dilution rates. Although its drilling efficiency is relatively low, which may affect production capacity, its proven technology and higher safety levels make it a viable option. In contrast, the segmented stope post-backfilling method offers high recovery rates and good safety, making it suitable for multi-working face coordination. However, it demands complex construction techniques, causes substantial pillar resource loss, and results in higher secondary crushing costs due to uneven ore particle sizes, which negatively impacts its economic feasibility.  
After evaluating technical maturity, adaptability, and economic feasibility, Xinqiao Mine selects mechanized upward horizontal layered backfill mining as the preferred method. This method ensures safety and recovery efficiency while offering significant potential for broader application. It provides robust technical support for Xinqiao Mine's successful transition and serves as a valuable reference for the transformation of similar ore bodies.