All the gold deposits are considered to be typical of epithermal vein gold-silver deposits.

All known Au and Ag mineralisation in Waihi is confined to veining or vein fragment within hydrothermal eruption breccia. The major mineralised veins are typically coincident with dip-slip, normal faults believed to have formed in an extensional setting related to early, back-arc rifting of the TVZ dated at ca.6.1 Ma (Mauk et al 2011).

Some of the main mineralised veins within the Waihi area include the Martha vein system (which includes the Martha, Empire, Welcome, Royal, Edward, Rex and Albert veins among many others) in the Northwest (NW) and the Correnso, Daybreak, Union, Trio, Amaranth, Favona, Moonlight and Gladstone veins progressively SE.

Martha
The Martha vein system is the largest and most documented of the vein networks in Waihi. It has historically been mined from underground and more recently mined as an open pit and is currently being mined from underground once again. The veins are numerous and form a large network that extends for more than 1600 m along strike and 600 m below the surface. The vein network although complex in detail, simply comprises the dominant southeast-dipping Martha vein and several northwest-dipping hangingwall splays including the Empire, Welcome, Royal and Rex veins. The Martha vein is the largest vein structure reaching up to 30 m in thickness in places but averages 6 to 15 m wide. Increased vein widths are ........

The underground operations referred to as Waihi underground, comprises the two main mining areas of Correnso and Martha Underground. There is no more ore planned to be extracted from Correnso and backfilling of current drives in line with consent conditions is the only work being carried out. Development and production activities continue in Martha Underground.

In early 2021 the focus of underground mining activities transitioned to Martha following the completion of production from the lower levels of Correnso. Narrow vein mining continued in Correnso until mid 2022 before backfilling and other closure activities commenced.

No further ore is planned to be extracted from the Correnso Mine and backfilling activities as required by the consent conditions is expected to be complete by the end of 2023.

Martha underground
In February 2019, consents were granted for Project Martha comprising the Martha Underground mine and a small cutback of the north wall of the Martha open pit called Phase 4 (MOP4). Mining commenced in the Martha Underground mine in July 2019 with the development of access tunnels. There has been no mining undertaken in MOP4 at this stage. Production in the Martha mine commenced in June 2021.

The Martha underground is accessed via the existing Favona portal through the existing Trio and Correnso workings and shares the ventilation development and shafts as well as the Correnso workshop, Trio cribroom and dewateri ........

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