www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 5 2.4. WHAREKIRAUPONGA UNDERGROUND PROJECT The WUG is intended to have an eight-year operating life at 800ktpa following five years of development which includes the construction of a 6.8km access tunnel and other mine infrastructure. The WUG orebody is hosted in the EG and T-Stream veins, dips between 65 and 70⁰ and is between 3m and over 20m in width with a median of 4.2m. The vein-hosted nature of the deposit makes the Modified Avoca mining method used by OGNZL in its existing Waihi underground mines appropriate. The Modified Avoca method is a productive, low-cost mining method involving semi-selective ore extraction within declines and stopes suited for moderately dipping deposits of varying thickness. Mining would progress from the mid-level sill both up and down, with wider sections in the southern East Graben Vein (EGV) area having multiple parallel stopes being mined using cemented rock fill (CRF). Waste rock will be delivered from underground to a surface stockpile and then transported back underground as part of the AVOCA mining method. Ore will be delivered directly to the processing ROM. 2.4.1. WUG GEOTECHNICS, HYDROGEOLOGY AND HYDROLOGY Standard geotechnical parameters are determined from the resource drilling core logs, including RQD, fractures per metre and hardness, with samples taken for standard laboratory test work. The drillhole database is held in acQuire. A preliminary hydrogeological assessment has been completed by GWS consultants according to the current level of understanding which is based on limited hydrogeological information. The deposit lies beneath the Wharekirauponga Stream which has a catchment area of 15km2 and receives 2,170mm rainfall annually on average, producing a total catchment volume of around 90 GLD. The intrinsic permeability of the host volcanic extrusive formations (rhyolites, dacites and basalts) is generally low and is not expected to produce significant inflows. The silicic epithermal veins introduced during late stage vulcanism may be expected to produce large inflows as a result of their more porous nature. The EGV may be associated with spring flow to the headwaters of the surface water catchment and is expected to dewater in response to underground drainage. The hydraulic connection of the EGV with the surface aquifer and potential headwater springs is uncertain and needs to be proven. Engineered controls introduced during ore extraction may be required where there is potential for changes in discharge and gains in surface water flows. The management of catchment water balance changes in response to mine development, groundwater/surface water interaction, and operational dewatering have become critical elements from a resource consent perspective, with the need to demonstrate no measurable change in the natural flows or water quality of surface water systems and no measurable dewatering of the soil Regolith which could have an adverse effect on vegetation a key outcome to be achieved. Superficial deposits, including weathering alterations, regoliths and soils, are highly clay altered and may form groundwater flow barriers that are unlikely to drain because of mine dewatering.
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