Selecting an underground mining method in a Kimberlite diamond deposit: (case study: Venetia Diamond Mine)
Date
2021
Authors
Mudau, Takalani
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Abstract
Due to the technological advancements, there have been a tremendous development in the mining sector in the cavings and mine design models that allow mining method applications to reach greater depths. The global mining challenges have been ushered into an era where many choices are available to exploit minerals in open pit underground systems. The most favourable mining method amongst the available options is the one that is safe nd has highest economic returns. The decision of using open pit, underground mining or both is determined by the geometric characteristics of the minerals being mined. Open pit is often considered easier to exploit than underground mining in terms of safety, flexibility, recovery rate, working environment and economics. However, as open pit continue to deepen, a transition decision will prevail either to mine push back or sink a shaft for going underground. Venetia mine is a diamond producing operation, currently mining a kimberlite orebody and in the process of transition from Open Pit (OP) to Underground (UG). Open pit activities are planned to cease in 2021. The study aims to investigate the mining method selection for Kimberlite Orebody 01 (K01). Previous studies conducted for the underground mining method selection proposed the block caving mining to exploit K01. The rigid assumption on the mining method presents a risk to the project. The challenge with block caving K01 is the narrow orebody width with highly discontinuous nature of contracts. The narrow width limits the caving radius to maximum of 30m with the narrowest area in the eastern part to be 20m. However, this put Venetia underground project in the transitional zone which it is not stable but not caving. Data analysis were done using Rock Mass Rating (RMR) and Modified Rock Mass Rating (MRMR) classification systems. The results of the geotechnical analysis were compiled into seven kimberlite facies. The calculated MRMR for Dark Volcaniclastic Kimberlite (DVK) facie is 45 and hydraulic radius is 35m. While the MRMR for Country Rock Brescia (CR) is 44 with hydraulic radius or 29m. The DVK facie constitute 92% of the kimberlite facies in K01 deposit which classified as strong and stable for caving. The lesser material from Coherent Kimberlite (CK) and CR are weak and constitute 8% of kimberlite facie om K01. Expected geotechnical conditions for DVK_HARD Intact Rock Strength (IRS) which is over 100MPa and DVK_MID IRS which is between 50MPa and 100MPa have significant impact on the mining method selection. Results of the analysis performed in the study indicate a competent ore body which require pre-drilling for caving to occur. Stress induced scaling and weathering are predicted in weaker lithological domains. The results for the study shows that sub level caving miming method should be implemented for the project and care must be taken to control dilution and mud rush
Description
A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Engineering, 2021