www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 2 2. BACKGROUND 2.1. GEOLOGICAL SETTING AND MINERALISATION The regional geological setting of the Coromandel Peninsula is built up of Miocene to early Pliocene andesite-dacite-rhyolite and subaerial volcanic rocks of the Coromandel Volcanic Zone (CVZ) overlying a Mesozoic basement. The CVZ hosts gold and silver deposits that make up the Hauraki Goldfield. The regional geology is flanked to the west by the Hauraki Rift, a large graben filled with Quaternary and Tertiary sediments, and to the south by volcanics deposited by the presently active Taupo Volcanic Zone (TVZ). The volcanism that produced the CVZ formed during three main phases. Coromandel Group (18 – 3 Ma) andesites and dacites constitute the first phase; with Whitianga Group (9.1-6.0 Ma) rhyolitic units, the second phase; and the Mercury Bay Basalts (6.0-4.2 Ma), dominated by Strombolian volcanoes and dykes, the third. The final phase volcanic phase is responsible for the epithermal Au-Ag and Cu porphyry deposits and mineralised quartz veins, with hydrothermal alteration observed throughout the Coromandel and Whitianga Groups. These veins are steeply dipping persisting for a 200 to 2,000m strike and up to 700m dip, with vein widths commonly 1 to 5m and up to 30m. The entire area is overlain by postmineralisation andesites and pyroclastics. Early mining at Wharekirauponga was short-lived in the late 1800s but revived in the 2000s with prospect drilling of underground mineable veins, namely the Western Vein, Teawamoamutu-Stream Vein (TStream) and the East Graben (EG) Vein, the latter being continuous for a kilometre. Both the T-Stream and EG veins are resource targets for the WUG and have associated hanging wall and footwall stringer vein sets. These veins are described as extensional in relation to their structural controls and are hosted by Whitianga Group rhyolites, rhyolitic flow domes and intrusions within polymict lapilli tuffs. Mineralised sequences are overlain by andesitic flows, rhyolitic tuffs and recent ash deposits. Hydrothermal alteration often completely replaces the primary mineralogy of the rhyolites with quartz and adularia accompanied by illite-smectite clay alteration. Where this alteration is associated with veins and displacement, mineralised clay gouge is often present. As the East Graben footwall is approached, these veins become brecciated indicating the degree of fault control as opposed to a more extensional derivation. 2.1.1. LOCAL LITHOLOGICAL AND STRUCTURAL CONTROL A block model is constructed in Vulcan1 that contains the resource drilling data held in an acQuire2 drill database that defines lithological domains and provides a geological model primarily for grade estimation. Lithological controls are associated with hydrothermal alteration predominantly in the rhyolites. The Waiwawa sub-group (7.9-5.6 Ma) of the Coromandel Group is the most extensive geological unit in the area comprising andesite and dacite lava flows and tuff breccias, and dacitic ignimbrite, tuff and siltstone. The younger Omahine subgroup (6.7-6.6 Ma) andesites, dacites tuffs and breccias (which will 1 Maptek Vulcan software 3D geological modelling, mine design and production planning. 2 acQuire geoscientific information database management system
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