New Zealand

Waihi District - Marhta Project

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Overview

Mine TypeUnderground
 Archived Information
Commodities
  • Gold
  • Silver
Mining Method
  • Truck & Shovel / Loader
  • Pillar mining
  • Avoca
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Snapshot2021 Feasibility Study is related to the producing Martha mine at Waihi Operation

Owners

SourceSource
CompanyInterestOwnership
OceanaGold Corp. 100 % Indirect
The Waihi District Projects, 100% owned by wholly owned subsidiary OceanaGold (New Zealand) Limited

Contractors

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Deposit type

  • Epithermal
  • Vein / narrow vein

Summary:

The Waihi vein system is hosted within andesitic flows and pyroclastic units of the late Miocene (7.36-6.76Ma) Waipupu Formation. The Waipupu Formation in Waihi can be subdivided into an upper quartzphenocryst poor unit and a lower quartz-phenocryst rich unit which dip shallowly towards the SE. Some of the veining and gold mineralisation in Waihi appears to be better developed within the lower quartz-rich andesite flows, with the exception of the Favona, Moonlight and GOP deposits which are solely hosted within the upper andesite unit. Much of the mineralised andesites in Waihi are overlain by post-mineral rocks including dacite flows of the Uretara Formation (5.23Ma), Pleistocene ignimbrites and recent ash deposits.

Where veining is exposed close to the surface, the quartz-adularia altered andesites form resistant paleotopo ‘highs’ that project through the post-mineral cover sequences.

Martha Vein System
The Martha Vein System is the largest and most documented of the vein networks in Waihi. The veins are numerous and form a large network that extends for more than 1600m along strike and 600m 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 30m in thickness in places but averages 6 to 15m wide. Increased vein widths are closely associated with the steepening of vein dips from an average of 65-70 degrees to approximately 85 degrees to the SE. Steeper portions of the vein tend to contain higher concentrations of Au and Ag. The vein itself comprises mainly intact brecciated quartz vein material evidence for vein emplacement during the late stages of dip-slip faulting. The quartz is characterised by multiphase brecciation and banding (colloform and crustiform) and quartz textures are highly variable from a fine, microcrystalline and chalcedonic character to more coarsely crystalline particularly at depth. Apart from the main Martha vein, the hanging wall splay veins are also significant mineralised structures reaching 18m in width (e.g. the Empire Vein). The hangingwall splays closest to Martha link up with the Martha vein at depth often forming a higher-grade lode at the intersection. Hangingwall splays further away from Martha either thin out at depth or are not drilled deep enough to make out their relationship with Martha at depth (e.g. the Rex and Ulster Veins). Additional, smaller-scale splay veins are present linking the larger vein structures and form a valuable contribution to the mineralisation particularly in the Martha Open Pit. These splays typically comprise smaller veins between 5 and 50cm in width infilling extensional structures with no fault displacement, dipping moderately towards the NW. Two steeply dipping, NNE-trending and well mineralised vein structures known as the Edward and Albert veins also form an important part of the overall Martha vein network.

GOP
The GOP deposit is part of the greater Waihi epithermal vein system located approximately 2km to the east of the Martha Open Pit. It is situated along the southern strike extent of the Favona and Moonlight deposits. Veining at GOP occurs within the upper 250m below the surface, hosted within the upper andesite unit (devoid of quartz phenocrysts). The mineralisation is characterised by shallow-level, hydrothermal breccias and associated banded quartz veins interpreted to represent the top of the epithermal system. The uppermost mineralised quartz veins flare up into hydrothermal explosion breccias. The GOP veins are predominantly steeply dipping veins developed within the hanging wall of the Favona Fault that dips moderately towards the SE. GOP veining trends ENE to NNE between 010° and 070° and dips steeply towards the SE.

WKP
Low-sulphidation epithermal quartz veins at WKP are hosted in Whitianga Group rhyolites, typically rhyolite flow domes to sub-volcanic intrusions within polymict lapilli tuffs. Deep drilling to the west indicates the rhyolites are underlain by Coromandel group andesites. The mineralised sequences are partially overlain by strongly magnetic, fresh andesite flows, rhyolitic tuffs and recent ash deposits observed in drilling and regional mapping.

Gold mineralisation occurs in association with quartz veining developed along two types of structurally controlled vein arrays. The principal veins, namely the EG-, T-Stream and Western Veins occupy laterally continuous, NE trending (025-47°), moderately dipping (60-65°) fault structures reaching up to 10m in width. More subsidiary, extensional veins (1-100cm wide) are developed between or adjacent to the principle fault hosted veins. These veins often form significant arrays that are moderate to steeply dipping with a more northerly to NNE strike and appear to lack lateral and vertical continuity compared to the principle veins.

All the gold deposits outlined by OceanaGold to date in this report are considered to be typical of epithermal vein gold-silver deposits.

In the opinion of the QPs, features observed in Waihi and WKP deposits display the following features that are typical of epithermal gold deposits elsewhere in the world:
• Gold-silver mineralisation is predominantly confined to localised bands within multiphase quartz veins;
• Host lithologies for veins are volcanic units of andesitic and/or rhyolitic composition;
• Sphalerite, galena and chalcopyrite commonly occur with gold-silver mineralisation within the Martha Underground deposit. This base metal content increases at depth with galena reaching up to +3% Pb and sphalerite in some localised areas exceeding 2.5% Zn;
• Host rock volcanics have undergone pervasive hydrothermal alteration, often with complete replacement of primary mineralogy. Characteristic alteration minerals include quartz, adularia, albite, carbonate, pyrite, illite, chlorite, interlayered illite-smectite and chlorite-smectite claysextending over tens of metres laterally from major veins;
• The upper portion of veining at the GOP deposit contains intact hydrothermal eruption breccias. The northern strike continuation of the GOP veins at Favona also contain hydrothermal breccias and anintact siliceous sinter sheet; and
• Mineralisation is structurally controlled.

Reserves

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Mining Methods

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Comminution

Crushers and Mills

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Processing

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Production

CommodityUnitsLOM
Gold oz 589
Silver oz 1,223
All production numbers are expressed as metal in doré.

Operational metrics

Metrics
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Ore tonnes mined, LOM  ....  Subscribe
Total tonnes mined, LOM  ....  Subscribe
* According to 2021 study.

Production Costs

CommodityUnitsAverage
All-in sustaining costs (AISC) Gold USD  ....  Subscribe
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Assumed price Gold USD  ....  Subscribe
* According to 2021 study / presentation.

Operating Costs

Currency2021
UG mining costs ($/t milled) USD 62.1 *  
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G&A ($/t milled) USD  ....  Subscribe
Total operating costs ($/t milled) USD  ....  Subscribe
* According to 2021 study.

Project Costs

MetricsUnitsLOM Total
Initial CapEx $M USD  ......  Subscribe
Sustaining CapEx $M USD  ......  Subscribe
Total CapEx $M USD  ......  Subscribe
UG OpEx $M USD  ......  Subscribe
Processing OpEx $M USD 134.3
G&A costs $M USD 80.1
Total OpEx $M USD  ......  Subscribe
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Royalty payments $M USD  ......  Subscribe
Gross revenue (LOM) $M USD  ......  Subscribe
Pre-tax Cash Flow (LOM) $M USD  ......  Subscribe
After-tax Cash Flow (LOM) $M USD  ......  Subscribe
Pre-tax NPV @ 5% $M USD  ......  Subscribe
After-tax NPV @ 5% $M USD  ......  Subscribe
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Heavy Mobile Equipment

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Personnel

Mine Management

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Total WorkforceYear
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Aerial view:

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