2 | P a g e Class 1 Storage Location Assessment_Oceana Gold NZ Ltd Wharekirauponga Underground Mine 1. Executive Summary A location assessment for a proposed underground class 1 storage facility known as the ‘WUG Underground Magazine Facility’ is the subject of this technical report. The class 1 facility will be utilised for mining operations associated with the ‘Wharekirauponga Underground Mine’ (WUG). Initial development and mining operations associated with the WUG, will be supported by a proposed surface magazine facility known as ‘Willows Road – Surface Magazine Facility’. The initial surface magazine facility will be developed as part of the Waihi North Project (WNP). The underground storage facility is intended to be commissioned at a later stage in mine development (approximately four years after the underground portal is constructed). The proposed facility will be located in a low traffic area of the mine within a series of dedicated and purpose-built chambers. On establishment, the WUG class 1 underground magazine facility will be utilised concurrently with the WUG surface magazine facility and be treated as a stand-alone location with the same management requirements as other storage facilities. It would be commissioned and certified by an Independent Compliance Certifier as a separate compliant location to other class 1 facilities within the Waihi Gold operations. The ‘ Health and Safety at Work (Hazardous Substances) Regulations 2017 ’’ is the key legislation that must be considered when designing, constructing and licensing a class 1 storage facility. However, there is limited specific criteria and guidelines within these regulations relating to underground storage facilities. As such, alternate recognised standards have also been consulted with various relevant elements being adopted to complete the assessment. Use of a range of alternate recognised standards has allowed calculation of expected surface overpressures (kPa) at varying surface connections in relation to stored capacities and the internal tunnel and magazine chamber volumes within the underground operation. Appropriate interval distances between magazine chambers (known as Inter-Magazine Distance or IMD) are established in order to mitigate risk of propagation between each individual magazine chamber. The calculated controlled zones at surface are therefore based upon the stored quantity (Net Explosive Quantity or NEQ in kg) in each of the individual magazine chambers. The proposed facility will utilise up to seven individual magazine chambers. Six of the chambers will store up to 1,000 kg (Net Explosive Quantity (NEQ)) of High Explosives (H.E), one chamber will be used for storage of Initiating Explosives (I.E) with a capacity of up to 100,000 detonators (100 kg - NEQ). The underground facility would be suitable for a total storage capacity of up to 6,100 kg (NEQ). The stored substances at the facility would comprise of a variety of commercial explosives products that are commonly used in similar mining operations. The proposed location of the facility is shown in Figure 1. The assessment of this location considered a number of factors including operational efficiency, personnel safety and potential effects at surface connections. Controlled zone offset distances are measured from the outer perimeter of the underground portal and ventilation shafts. Surface connections identified as ‘Sites P0 and P1’ to the South are located on OGNZL owned property. Sites identified as ‘P2, P3 and P4’ to the North are located within Hauraki District Council (HDC) paper road. Controlled zone calculations have been based upon TNT equivalence (see definitions), whereby multiple grades and types of commercial explosives may be stored at the location within each underground storage chamber at any given time.
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