Geostatistical Determination of Smallest Mining Unit (Smu) For Damang Mine, Gold Fields Ghana Limited-A Case Study at the Saddle Pit

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2015-10

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University Of Ghana

Abstract

Historically, the operations of Goldfields Ghana, Damang Mine had generated grade control models using smallest mining unit (SMU) of 2 m x 5 m x 3 m. Management has introduced the use of larger excavators example the Bucyrus RH 90C and RH120E O&K with bucket size 3.5 m hence, there is therefore the need to review the SMU being used for various pits for the Grade Control Modeling Procedures which will relate to the ability of the equipment to select ore or waste with minimal dilution.The calculation of mineral resources and ore reserves from a block model requires the choice of a block of SMU size. Each block is assigned a grade or a distribution of grades. The resources/reserves are calculated from these block values. This dissertation proposes the optimal SMU size to be used at the Saddle Pit. The style of Au mineralization at the study area - Saddle Pit is being hosted within narrow, (<0.5m) shallow- dipping, and laterally discontinuous quartz veins and requires an excavator with smaller bucket size to effectively mine.The orebody is hosted within two main lithologies namely; Huni Sand Stone and Phyllite of the Tarkwaian System. A geostatistical reserve estimation procedure (Ordinary Kriging) was implemented for a range of SMU block sizes (2 m x 5 m x 3 m and 5 m x 5 m x 3 m) and the SMU size that gave an acceptable tonnes and grade of Au was recommended. The optimal SMU sizes will yield an estimate of tonnes and grade of ore that is close to the actual production. The krig efficiency of both SMU (2 m x 5 m x 3 m and 5 m x 5 m x 3 m) Block Models falls within 45% and 81% whilst the regression slopes is within 0.7 to 0.99. Although both cases are within acceptable limit of 40% and 0.4 for krig efficiency and regression slope respectively, the 2 m x 5 m x 3 m proved to be better for the Saddle Pit. When no cutoff grade was applied, the undiluted 2 m x 5 m x 3 m grade control block model reported 2,454,458t @ 0.43g/ t which gave a metal content of 1,050,465.56g whilst the 5 m x 5 m x 3 m grade control block model reported University of Ghana http://ugspace.ug.edu.gh v 3,033,501t @ 0.28g/ t. which gave a metal content 843,851.6g. This indicated an extra metal of 206,614g representing 19.6% increment for the 2 m x 5 m x 3 m. The mining equipment needed to effectively mine the SMU 2 m x5 m x 3 m due to the style of mineralisation with minimum dilution is the Liebherr 984 with bucket width of 2.0 m. It is recommended that for the Saddle Pit area, SMU of 2m x5m x 3m should be used. The same analysis should be carried out at the main Damang CutBack Pit and Juno Pit to establish which SMU should be used as the style of mineralisation are associated with the banket conglomerate and Tarkwa phyllite with extensive quartz vein density.

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Thesis(MSc)-University Of Ghana,2015

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Mining, Geostatistic, Ghana, Africa

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