Causes and effects of backfill dilution in open stoping method

在加拿大及世界各地的地下硬岩矿山中，采用空场充填法开采急倾斜矿床是非常普遍的。在分段空场回采环境中，充填体的使用允许矿体采用纵向和横向回采方法进行安全、无矿柱和经济的回采。在处理位于地表以下很深的地方的矿床时尤其如此，因为那里的原应力场总是很高，而且那里经常遇到断层、岩脉和剪切带等复杂的地质特征。一旦主采场被采出并进行回填，二次采场的开采就可以按照计划的顺序进行，目标是实现完全的、无矿柱的开采，同时将高应力场推离开采区域。虽然这种方法被广泛接受，但其固有的缺点是，在矿石排渣过程中，往往会有侧面向采场的充填柱部分破坏或不能进入二次采场，从而导致矿石贫化。充填体稀释导致采场周期时间延长，导致产能延迟；充填体稀释导致磨矿品位降低，导致矿山盈利能力降低。根据充填柱破坏的严重程度，这也可能由于底板修复和准备工作的时间损失而导致上部采场的开采延迟。因此，本项目的短期目标是：1)确定空场法充填体贫化的原因，包括采场类型、设计、顺序和周期时间、充填体材料类型、强度和充填实践、采场爆破设计和爆破顺序；2)量化这种贫化对采场回收率、磨粒品位和生产率的影响。在目前的地下矿山设计实践中，未充分考虑充填体贫化对矿山调度和经济效益的影响。提出的研究是了解和记录回填稀释的原因和影响的第一次尝试。人们相信，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，共同制定加拿大第一个防止矿石稀释的矿山设计最佳做法准则。

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.