Byrne, G 2019, 'Mine closure plans assumptions and optimism', in AB Fourie & M Tibbett (eds), Mine Closure 2019: Proceedings of the 13th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 1031-1038, https://doi.org/10.36487/ACG_rep/1915_82_Byrne
(https://papers.acg.uwa.edu.au/p/1915_82_Byrne/)
Abstract: Because planned closure is often many years into the future, most closure plans include the use of assumptions. Sometimes these are well documented, but more often they are inferred within the framework of the closure concept and do not always receive appropriate focus. Even when closure plans document where assumptions are used, the list is often incomplete.
It is entirely appropriate for closure plans to be based on assumptions. Indeed, assumptions will need to be made regarding the feasibility of the closure concept, regulatory regime, schedules, criteria achievement, mine life, etc. Often, however, assumptions are based on excessive optimism, in which case these assumptions really equate to risks if the assumptions do not come to fruition.
It is therefore imperative that all assumptions in a closure plan that can potentially have a material impact on outcomes and cost are identified and documented. However, the closure plan cannot simply just list and thereafter ignore them. The implications of the assumption not eventuating need to be assessed and incorporated into the closure risk register and possibly into a revision of the closure plan itself. They will also need to be assessed in terms of the potential impact to closure costs.
This paper discusses the approach to identifying assumptions forming the basis of a closure plan, their transition into closure risks, and how they should be addressed by the closure plan and associated closure cost estimates. The paper also discusses examples of typical closure plan assumptions and cases where optimism has not been realised.

Keywords: closure assumption, closure risks, optimism