GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 98 Table 5.2 Stratigraphy of the TSF3 area Unit Depths encountered (thickness where present) Description Topsoil Surficial (0.01 to 0.7 m) Occurs across the site, thickest near gully features. Fill is present at some locations. Volcanic Ash Surficial (typically) (< 2.2 m; averaging 1.1 m) Three ash units occur (Waihi, Hauparu, Rotoehu). The ashes are slightly variable, but typically comprise yellowbrown sandy silts. Ash occurs across the site, particularly in the hills, and is absent across the lower valley floor. Ash often overlies colluvium or alluvium, however in some locations more recent alluvium and colluvium may lie over the ash. Colluvium Surficial – hills (<3.3 m) Colluvium is typically sandy or gravelly silt with some cobbles. Alluvium Surficial – valley, gullies (0 to > 5 m) Alluvium is derived from the erosion of the surrounding rhyolite hills and is highly variable across the TSF3 site, from gravelly and sandy to clayey. There are also some buried organic or peaty layers A key zone identified is the highly plastic, low permeability, saturated clayey layers encountered near the drainage ditches in the lowest lying area of the TSF3 site (in the vicinity of AP1 and AP4). Rhyolite Redeposited Tuff 2.4 to 35 m bgl (1.7 to 30 m) Also referred to as “sensitive tuff”, this fine-grained rhyolite tuff material is likely to have been reworked by gravity or water, and infills a paleo-gully beneath the lower valley floor. This material is significantly weaker than welded crystal tuffs and tuff breccias at TSF3. Tuff 1.2 to > 42 m bgl (1 to > 32 m) Crystal tuff (weakly to moderately welded) is typically encountered in the upper valley floor and around the west paleo-ridge line. Tuff breccia refers to coarse tuff where particles are greater than 4 mm. CW–HW Flow MW-SW Flow 0.7 to > 27 m bgl (2 to 23 m) 0.5 to 125 m bgl Two types of flows were observed at TSF3: Flow rhyolite: Observed on site is described as flow banded phenocrystic, sometimes spherulitic, rhyolite lava, which shows various degrees of weathering typically from the surface (completely weathered near surface, to slightly weathered with depth). At depth, flow rhyolite has also been observed to be brecciated. Froth flow: A form of flow rhyolite which is partially vesiculated and likely derived from a gaseous lava flow or froth, which has been described as froth flow rhyolite (AP17a and AP20a). Ash and Tuff 125 – 156 m bgl Observed in the GT020 drill hole at depth. Rhyolitic ash and tuff deposits, possibly representing the initial phase of the rhyolitic eruption. Dacite – Tuff Breccia >156 m bgl Observed in the GT020 drill hole at depth. This is the dacite unit that outcrops to the west of the Ohinemuri River at Gladstone. The dacite dips to the south west, and does not outcrop at TSF3. Andesite – Tuff and Lava Flow >191 m bgl Observed in the GT020 drill hole at depth. This is the andesite unit that hosts the ore body at Favona, Gladstone and Martha. The andesite at TSF3 is separated from the mined andesite areas by faulting and does not outcrop at TSF3.
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