Determination of depleted rock volume in open cast mines using photogrammetric techniques for the purpose of royalty calculation

Abstract

In Sri Lanka, Geological Survey and Mines Bureau (GSMB) imposed royalty levy for aggregate production volume using an equation (indirect method) which utilises the quantity of explosives for the calculation. Since the equation resulted in higher deviations and the previous studies emphasise the advantages of photogrammetric 3-dimensional (3D) modelling (direct method) when determining production volume of bench blast, the present study focus on investigating its applicability to irregular faced dynamic quarry with uneven overburden. Pre and post 3D Digital Surface Models (DSMs) of the quarry were generated using the structure from motion (SFM) algorithm with Real-Time Kinematic (RTK) positioning system and Pix4D mapper software. Golden Software Surfer 16 was used to determine depleted rock volume as the difference between pre and post 3D DSMs. Results indicate a 5.50% deviation of the proposed method from true depleted rock volume determined by truck measurements due to uncleaned quarry face during the pre-Drone survey and unaccounted soil overburden removal. Presence of overburden while generating DSMs can be overcome by pile volume estimation of overburden and decreasing it from depleted rock volume when calculating production volume. GSMB equation calculated production deviate -32% from true production due to the unaccounted explosive amounts which contributed to the production and confirm the suitability of the proposed direct method (5.5% deviation) for determining the depleted rock volume in open-cast mines.