Causes and Consequences of Inefficient Drilling and Blasting in Mine Development Headings: A Case Study of Hard Rock Gold Mining Operations in Northern Tanzania

Despite the introduction of the perimeter blasting technique at the Tulawaka Gold Mine, the mine continued to suffer from an overbreak of mine development headings, with an average overbreak of 24% every 22 m, which is approximately twice the acceptable 10% overbreak. The causes of this problem include ineffective drilling practices and uneven and excessive charging of explosives, resulting in a slightly high powder factor of 3. 94 kg/m 3 instead of 3. 8 kg/m 3, as per the design. The problem of overbreak resulted in ore dilution, a longer mine development cycle time and additional costs of approximately US 45 per cut, especially in mucking and hauling processes. This study proposed and recommended new drill and blast designs to solve this problem. Compared to the existing design, the proposed new drill design has a total of 12 fewer drill holes; this is a significant number of holes, which significantly reduces drilling costs. The proposed new blast design consumes approximately 25 kg less ANFO than the existing practice. Moreover, the study showed that large drives in the Star and Comet in the Geita Gold Mine suffer the most from the problem of ineffective advance per cut. One of the causes of ineffective advances per cut is the low amount of explosives used per cut compared to the planned amount.