Causes and effects of backfill dilution in open stoping method

在加拿大和世界各地的地下坚硬岩矿中，采用空场采矿法充填开采急倾斜矿床是非常普遍的。在分段空场回采环境中，充填的使用允许采用纵向和横向采矿法对矿体进行安全、无柱和经济的开采。这在处理位于地表以下很深的矿床时尤其如此，那里的地应力场总是很高，而且经常遇到断层、岩脉和剪切带等复杂的地质特征。一旦一次采矿点被开采并回填，二次采矿点的开采可以按照计划的顺序进行，目的是在将高应力场推离被采矿区的同时，实现全面的无矿柱回收。虽然被广泛接受，但这一过程的固有弱点是，在矿石放矿过程中，面对采场的充填柱侧往往会部分坍塌或不进入二次采场，从而导致矿石贫化。这种充填稀释会因采场周期时间延长而延迟生产率，并因磨矿品位降低而导致矿山盈利能力下降。根据充填柱失效的严重程度，这也可能导致上部采场因底板修复和准备工作损失时间而延误采矿。因此，该项目的短期目标是：1)从采场类型、设计、顺序和周期、充填材料类型、强度和充填实践、采场爆破设计和爆破顺序等方面确定空场采矿法充填体稀释的原因；2)量化这种稀释对采场回收率、磨矿品位和生产率的影响。在目前的地下矿山设计实践中，充填贫化对矿山调度和经济效益的影响没有得到很好的考虑。这项拟议的研究是理解和记录回填稀释的原因和影响的第一次尝试。据信，拟议的研究将为与采矿业建立重要的研究伙伴关系奠定基础，共同制定加拿大首个防止矿石贫化的矿山设计最佳实践指南。

The use of mine backfill in open stoping method to mine steeply dipping ore deposits is very common in underground hard rock mines in Canada and around the world. In a sublevel open stoping environment, the use of backfill allows for safe, pillar-less, and economic extraction of an orebody with longitudinal and transverse stoping methods. This is particularly true when dealing with ore deposits that are situated at great depths below ground surface where the in situ stress fields are invariably high, and where complex geological features like faults, dykes and shear zones are frequently encountered. Once primary stopes are mined out and backfilled, mining of secondary stopes can be scheduled in accordance with a planned sequence that aims for full, pillar-less recovery while pushing high stress fields away from the area being mined. While widely accepted, the inherent weakness in this process is that, often enough, the backfill column side facing the stope will fail partially or not into the secondary stope during the ore mucking process, thus resulting in ore dilution. Such backfill dilution results in delayed productivity due to increased stope cycle time, and in lower mine profitability caused by the reduced mill grade. Depending on the significance of backfill column failure, this may also result in delays in the mining of upper stopes due to time lost in floor repair and preparation. The short term objectives of this project thus are: 1) to determine the causes of backfill dilution in open stoping method with respect to stope type, design, sequencing and cycle time, backfill material type, strength and fill practice, and stope blast design, and blasting sequence, and 2) quantify the effects of such dilution on stope recovery, mill grade and productivity. The impact of backfill dilution on mine scheduling and economics is not properly accounted for in the current practice of underground mine design. The proposed research is a first attempt to understand and document the causes and effects of backfill dilution. It is believed that the proposed research will set the stage for significant research partnership with the mining industry to develop together what would be the first Canadian best practices guidelines for mine design against ore dilution.