Mining on Conservation Land at Te Ahumata

The Great Barrier Island Charitable Trust is opposed to the government’s proposal to facilitate mining on Conservation land at Te Ahumata on Great Barrier Island.

Schedule 4 lands – a social and ethical issue.

Land covered in native ecosystems, uninhabited and largely untouched by man, is an increasingly rare commodity worldwide. In the 1980’s the government of New Zealand, with much popular support, chose to place certain land areas, mainly in National Parks, into a special category – Schedule 4. The point of this Schedule was to protect the land from inappropriate developments, especially those having large environmental impacts, such as mining. This was in recognition of mankind’s dependence on a healthy planet in which at least some areas remained as examples of the natural order and beauty of the world. These places link us as a nation and as individuals to our past, both Maori and Pakeha, in ways that cannot be achieved in highly modified landscapes. There was also an understanding of the growing role of tourism in the New Zealand economy, and the role such places played in the furtherance of this, and in propagating a ‘clean-green’ international image.

Land was not put into Schedule 4 as some sort of land-bank, which could be exploited once the price was right. We do not believe that facilitating mining in Schedule 4 lands is appropriate or important for New Zealand’s economic well-being. On the contrary, we believe it could have serious negative repercussions on out tourist industry and on our agricultural exports.

Clearly there is an intention to mine in Schedule 4 lands. It is not logical to imply that the current exercise is merely a stock-take, solely to find out what is present in these areas, unless there is the possibility of mining. Such a cynical approach would be hugely wasteful of many people’s time and money.

The environmental case against mining on Te Ahumata.

Great Barrier Island is promoted to Aucklander’s and overseas tourists alike as “the jewel in the crown” of the Hauraki Gulf. The Gulf is a Marine Park, and mining is not permitted under the District Plan.

The island includes the largest area of Conservation Land within the Auckland Conservancy, and is regarded as significant for its high biodiversity values (endangered birds, reptiles and plants) and the absence of some significant mammalian pests (eg possums, deer).

It is inconceivable to us that the Minister of Conservation, Hon. Kate Wilkinson, should countenance the removal of any part of this island from Schedule 4. The Mayor of Auckland, John Banks, the National MP for Auckland Central, Nikki Kaye, and the chairperson of the local Community Board, Paul Downie, have all expressed strong opposition to any mining on Te Ahumata.

There will be strong opposition to this proposal from lobby groups such as the Enironmental Defence Society, The Royal Forest and Bird Society and Coromandel Watchdogs. The Great Barrier Island Charitable Trust can offer support to such groups in the form of information in its recently completed “Great Barrier Island State of the Environment Report”.

The area in question is crossed by the central portion of ‘The Great Walk’, which is being developed to encourage tourism on the island.

Te Ahumata is highly prominent feature of the central part of the island, visible from many points, including the administrative centre (Claris), and the airport. It is the most conspicuous feature seen by tourists as they approach the island from the air. In his 1980 report (Ministry of Development #372) Rabone noted that: “The scars of mining would tend to be obvious, both to the local population and to visitors by air”.

Rabone (1980) also notes: “In the event of open-pit mining, a suitable area for spoil/tailings is the adjacent Kaitoke swamp …. which would also provide soil material suitable for post-mining rehabilitation.”

He indicates that the vegetation of the Te Ahumata area is of no consequence, and suggests that hydrothermal power might be tapped at the hot springs.

While these views are now historic, and hopefully do not reflect current thinking, the points they raise, namely high visibility, the problems of an adequate power source, what to do with vast quantities of toxic tailings, and how to rehabilitate the site, remain pertinent.

The casual disregard of the local community by mining companies, as demonstrated in the above quotations, should not be furthered by the government, whose role is to serve the best interests of all New Zealanders; in our view, to create a large industrial site in this setting is totally inappropriate for the future long-term sustainable development of the island’s economy, and is likely to be resented and resisted by a significant proportion of the population.

The environmental case against mining on Great Barrier Island is very strong, and is backed by legal precedents, which demonstrate the high biodiversity, environmental and social values of the island.

The economic case against mining on Te Ahumata.

The economic case for mining on Great Barrier is very weak, and backed by a history of resource exploitation which has left no appreciable benefits for the local community.

Background Research

Three main quartz veins or reefs, the Iona, Sunbeam and Barrier reefs, have been worked in the past. The quartz in these veins carries on average about 3.6g/tonne of gold, and from 140 to 1100g/tonne of silver, but the grades vary greatly from sample to sample. When the mines closed (c. 1920) the Barrier reef was considered to be ‘worked out’.

Waihi's Martha Mine - open pit extraction of similar
epithermal gold deposits to GBI. Photo: Ugotravel blog

Since the old mines closed, very extensive exploratory investigations, drilling and sampling has been carried out on Te Ahumata (Quennell 1963, Quennell et al. 1973, d’Auvergne 1974, Rabone, 1980, 1981, Canyon Resources 1984).

In addition, according to Barker (2010) “over the last ten years, reviews and assessments of the mineral potential of the goldfields have been made”. However, no further reference is made to these additional, more recent, data.

Thus, the nature of the underlying geology, and the possibility of further gold and silver deposits, have both been very thoroughly investigated already.

Ten drill holes have been bored through the plateau, initially with the intention of intersecting the known reefs, and subsequently to investigate the potential for a larger stratified diffuse ore-body beneath the mountain. The latter was not found: “a large tonnage of ore-grade mineralisation within the rhyolitic tuffs is now virtually excluded” (Rabone 1981).

Referring to the Iona reef Rabone (1981) notes that some potential remains: “as a relatively small-scale quarrying proposition for a small mining company”. But he also notes that : “ At deeper levels, where intersected in drill holes, it (the Iona vein) was found to be much narrower and weaker than at the surface, and was not significantly mineralised”.

Canyon Resources (1984) reinterpreted the drill hole results, and assumed that the most significant drill hole (DDH2) did not in fact reach the main Iona vein, rather it sampled small veins penetrating the rock above the main vein.

Confusingly, Canyon Resources (1984) claim that (by analogy with similar veins on the Coromandel Peninsula): “ is likely that ….. mineralisation would reduce sharply with depth to the underlying andesites”, and also (without any drill-hole based evidence) that there is “good potential for significant grade improvement and increased gold/silver ratio in the deeper levels” (i.e. in quartz vein where it penetrates the underlying andesites).

The Tailings.

To realise the supposed value of the gold/silver in the Iona and Sunbeam reefs would involve the removal of 4.317 million tons of quartz rock. This then would be crushed and treated with cyanide before electrolytic separation and smelting. The resultant tailings are acidic and toxic for plant growth.

Depending on the thickness of the pile, this quantity of tailings could cover up to 400 ha. It would certainly require an area of tens of hectares.

A cover of new top-soil to at least 1m depth, and extensive planting of the area with native vegetation would be required.

Value of resource.

Inexplicably, the current value of the gold/silver resource on Te Ahumata has been stated as $NZ4.3 billion by the Ministry of Economic Development. This figure is not substantiated by Ministry’s own review (Barker 2010), which gives an estimate of $NZ1.28 billion (but concludes with the figure of “more than $NZ1 billion”). This much lower estimate supposes that average gold and silver concentrations (which vary widely in different samples) in the quartz are maintained throughout the reef, and that the reef thickness and lateral extent has been correctly estimated and is maintained in the underlying geological structure (andesite). Finally, it also assumes that all the quartz is removed, and all the metal extracted from it, from the surface to sea-level.

Moreover, Barker’s (2010) report also stresses the “substantial investment in exploration, feasibility investigations and development”, which would be needed to realise any potential economic benefits.

Rabone’s (1981) statement about the thinning of the reef with depth, calls into question even Barker’s (2010) lower estimated value, as he assumed that the Iona reef maintained both its thickness and mineralisation to sea level. Canyon Resources (1984) statements appear to be based on an optimistic assessment of drill hole 2 (DDH2) and analogy with supposedly similar situations on Coromandel.

Thus, while there is clearly some gold-silver mineralisation in the quartz veins and associated rock, we are left with no convincing evidence that an economic gold/silver ore body, or economic quartz reefs, lie under Te Ahumata.

We conclude that the value of the resource estimated by Barker (2010) is based on assumptions for which there is rather weak supporting evidence. The three-fold higher value given by the Ministry of Economic Development cannot be substantiated from any of the published reports referred to, and seems to be a wildly optimistic speculation.

The References used in the Trust’s submission can be viewed here.