Key Points
- Research suggests the optimum block size for a small open pit mine with a porphyry deposit is around 10m x 10m x 10m, balancing accuracy and computational efficiency.
- It seems likely that block dimensions are influenced by bench height (typically 10m), shovel width (around 3m), and deposit uniformity, but exact sizes vary by mine specifics.
- The evidence leans toward smaller blocks (e.g., 10m x 10m x 5m) for small mines to capture detail, though larger blocks (up to 20m x 20m x 10m) may suffice for porphyry deposits due to uniform mineralization.
Direct Answer
The optimum block size for a block model in a small open pit mine with a porphyry deposit is likely around 10m x 10m x 10m, based on typical mining practices and deposit characteristics. This size balances the need for detail with computational efficiency, especially given porphyry deposits’ uniform, low-grade nature.
Factors Influencing Block Size
- Bench Height: For small open pit mines, bench heights are often around 10 meters, which typically sets the vertical (Z-axis) block dimension.
- Shovel Width and Mining Equipment: Shovel widths (around 3m for small mines) influence horizontal dimensions, but block sizes are usually larger (10-20m) to represent mining units effectively.
- Deposit Characteristics: Porphyry deposits are large and uniform, suggesting larger blocks may work, but small mine scale favors finer resolution for accuracy.
While you might expect block sizes to match equipment dimensions exactly, they are often scaled up (e.g., 10m x 10m x 10m) to manage data and computation, especially in small mines where precision is crucial for resource estimation.
For more detailed insights, you can explore mining software documentation, such as GEOVIA Surpac, which offers tools for block modeling.
Survey Note: Detailed Analysis of Optimum Block Sizes for Small Open Pit Porphyry Mines
This note provides a comprehensive analysis of determining optimum block sizes for block models in small open pit mines targeting porphyry deposits, integrating mining parameters, deposit characteristics, and practical considerations. The discussion aims to cover all relevant factors, offering a detailed foundation for practitioners and researchers in mining engineering.
Introduction to Block Modeling in Open Pit Mining
Block modeling is a critical process in mine planning, representing the orebody as a 3D grid of blocks, each assigned attributes like grade, density, and rock type. For small open pit mines with porphyry deposits—known for large, low-grade, disseminated mineralization—the block size must balance accuracy in resource estimation with computational efficiency. Porphyry deposits, often associated with intrusive igneous rocks, are typically mined in large open pits, but the “small” scale here suggests a smaller operation, possibly with production capacities under 1 million tons per year or pit diameters less than 1 km.
Key Factors Influencing Optimum Block Size
Several factors influence the choice of block size, particularly for a small open pit mine:
- Bench Height and Mining Method:
- Bench height, a fundamental parameter in open pit design, typically ranges from 6 to 15 meters for small mines, with research suggesting 10 meters as common (Selection of practical bench height in open pit mining using a multi-criteria decision making solution). This height often determines the Z-axis block dimension, as blocks align with mining levels for operational planning.
- In open pit mining, operations are conducted on benches, with working benches wider than safety benches to accommodate equipment like shovels and trucks. The bench height directly impacts the vertical resolution of the block model.
- Shovel and Truck Operations:
- Shovel width, typically 2.5 to 4 meters for small mines (e.g., hydraulic shovels with 5-20 cubic meter buckets, as seen in Hydraulic Mining Shovels | Mining Excavators | Cat | Caterpillar), influences horizontal block dimensions. Research suggests the X-axis block size may relate to shovel width, though practical models often scale this up (Research on the method of determining the block size for an open-pit mine integrating mining parameters and shovel-truck’s operation efficiency).
- The Y-axis size, determined by shovel-truck operation efficiency, considers the probability distribution of simultaneous operations, ensuring blocks align with mining panel widths (typically 10-20m for small mines).
- Selective Mining Unit (SMU):
- The SMU, the smallest volume selectively mined as ore or waste, is crucial for block size selection. For small open pit mines, the SMU might correspond to a shovel load (e.g., 5-10 cubic meters) or a blast hole pattern (spacing around 5m, with volumes calculated based on blast dimensions). However, block models often use larger blocks (10-20m) for mine planning to manage computational load, as detailed in Block size selection and its impact on open-pit design and mine planning.
- Deposit Characteristics:
- Porphyry deposits are characterized by large size, low grade (0.3-2.0% copper, as per Porphyry Copper Deposit Model), and uniform mineralization, suggesting larger block sizes (e.g., 20m x 20m x 10m) may suffice for resource estimation. However, for small mines, finer resolution (e.g., 10m x 10m x 5m) captures potential grade variations, especially near ore-waste contacts.
- The uniformity of porphyry deposits, often covering several square kilometers, contrasts with the small mine scale, necessitating a balance between detail and efficiency.
- Data Spacing and Geostatistical Considerations:
- Drill hole spacing, typically 50-200m for porphyry deposits in exploration, influences block size. For small mines, closer spacing (e.g., 20m) may be used, suggesting block sizes of 10m x 10m x 5m to ensure each block is informed by multiple data points, as discussed in geostatistical modeling (Direct block-support simulation of grades in multi-element deposits: Application to recoverable mineral resource estimation at Sungun porphyry copper-molybdenum deposit).
- In geostatistics, block size should be smaller than or equal to the variogram range to capture spatial variability, though exact ranges depend on deposit-specific studies.
Proposed Optimum Block Sizes
Based on the analysis, the optimum block size for a small open pit mine with a porphyry deposit likely falls within the range of 5m x 5m x 5m to 20m x 20m x 10m, with a recommended size of 10m x 10m x 10m for general purposes. This recommendation considers:
- Vertical Dimension (Z-axis): Set at 10m, aligning with typical bench heights for small mines, ensuring blocks correspond to mining levels.
- Horizontal Dimensions (X and Y axes): Set at 10m each, reflecting bench widths (10-20m) and balancing shovel operations with computational efficiency. While shovel widths (3m) suggest finer resolution, practical block models scale up for manageability.
Comparative Analysis of Block Sizes
To illustrate, consider the following table comparing potential block sizes and their implications:
| Block Size (m) | Suitability for Small Mine | Computational Load | Accuracy for Porphyry Deposit | Notes |
|---|---|---|---|---|
| 5m x 5m x 5m | High (detailed) | High | Very High | Suitable for fine-scale planning, high resource use |
| 10m x 10m x 5m | Moderate to High | Moderate | High | Balances detail and efficiency, good for vertical variability |
| 10m x 10m x 10m | Moderate | Low to Moderate | Moderate to High | Recommended for general use, aligns with bench height |
| 20m x 20m x 10m | Low (coarse) | Low | Moderate | Suitable for large, uniform deposits, less detail |
This table highlights the trade-off between accuracy and efficiency, with 10m x 10m x 10m offering a practical middle ground for small mines.
Practical Considerations in Surpac
In GEOVIA Surpac, blocking and sub-blocking enhance flexibility. Parent blocks (e.g., 20m x 20m x 10m) can be used for broad resource estimation, with sub-blocks (e.g., 5m x 5m x 2.5m) applied near ore-waste contacts for detail. For a small mine, starting with 10m x 10m x 10m parent blocks and using sub-blocking where needed ensures efficiency and accuracy, as detailed in GEOVIA Surpac.
Conclusion
The optimum block size for a small open pit mine with a porphyry deposit is likely 10m x 10m x 10m, balancing the need for detail with computational efficiency, given bench heights, shovel operations, and deposit uniformity. However, depending on specific mine characteristics, sizes from 5m x 5m x 5m to 20m x 20m x 10m may be considered, with finer resolutions preferred for small, potentially variable deposits.
Key Citations
- Selection of practical bench height in open pit mining using a multi-criteria decision making solution
- Hydraulic Mining Shovels | Mining Excavators | Cat | Caterpillar
- Research on the method of determining the block size for an open-pit mine integrating mining parameters and shovel-truck’s operation efficiency
- Block size selection and its impact on open-pit design and mine planning
- Porphyry Copper Deposit Model
- Direct block-support simulation of grades in multi-element deposits: Application to recoverable mineral resource estimation at Sungun porphyry copper-molybdenum deposit
- GEOVIA Surpac
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