We continue to find new ways to use energy more
efficiently in our operations, and are improving our
measurement and reporting of energy efficiency.
We aim over time to reduce our carbon footprint,
in terms of carbon dioxide emissions per tonne of
This year energy consumption remained one of our largest operational inputs.
In efforts to reduce our consumption, we have been working with
Mobil Oil New Zealand in assessing trials of Mobil Diesel Efficient
in the performance of two CAT 777 dump trucks at Maramarua.
It is expected that use of this new fuel will reduce consumption
by up to 3 percent, with lower emissions of nitrogen oxides
(up to 10 percent), particulate matter (22 percent), and carbon
dioxide (2.8 percent). In addition, we have been supporting a
project to assess the feasibility of a hydro scheme to generate
24 megawatts of power from the Stockton mine site water runoff,
where over six metres of rain falls each year.
Total energy consumption for FY20 is reported in terms of
energy consumed (fuel and electricity) by employees and
contractors and amounted to 992,267 gigajoules (“GJ”) at
our five operational sites, the Cascade mine rehabilitation
project and corporate offices. This is approximately a 3 percent
decrease on energy use reported in FY19. Overall total waste
rock stripping which is the key determinant of our energy
consumption decreased by 6 percent with 18.86 million banked
cubic metres (M bcm) of waste rock stripped at the five sites in
FY20, compared with 20.02 M bcm in FY19.
94 percent of the energy consumed at our sites includes
fuel used for operations, and power for the Canterbury mine.
The remaining 6 percent of energy consumed was purchased
When comparing energy consumption by operation, there are
significant differences reflecting the scale of each operation and
the mine life cycle stage. The Rotowaro mine was the largest
consumer at 366,760 GJ, reflecting the movement of more than
8 M bcm of waste rock in FY20, due to increased stripping ratios
at this mature site.
The Stockton mine was the second largest consumer of energy
at 354,344 GJ. This is consistent with producing and washing
the most coal of the five sites, and reflects the electricity used
in the coal handling and preparation plant, and the Ngakawau
coal loadout facility. To note, the Stockton mine did not operate
during the COVID-19 lockdown period or it would have been the
largest power consuming site.
Comparison of energy consumption by operation FY20
Greenhouse gas emissions
We measure greenhouse gas emissions and participate in the
New Zealand Emissions Trading Scheme (“ETS”) in which carbon
pricing is passed on to our customers.
We assist our customers in relation to ETS in terms of the quality
of energy supplied and efficiency in supply logistics. A key
advantage of our Canterbury mine is that it is located within 20
km from its major customer in Darfield, significantly reducing
transport emissions. This recognises that whilst we support a
transition from coal to renewable energies, this will take time –
so we will endeavour to provide coal in a responsible way as long
as our energy customers require it.
If Canterbury’s existing customers were to source coal from
elsewhere in New Zealand, this would require trucking the
resource from either the West Coast (250 km away) or from
Southland (610 km away), significantly increasing the transport
carbon footprint. Alternatively, and as is the case for the Huntly
power station, coal could be imported from overseas suppliers
such as Indonesia, which also has a much higher transport
Our mining operations use significant quantities of diesel fuel
to extract coal and transport coal within the sites. Electricity is
required for coal processing, water treatment plants and mine
management systems. Our coal also releases its own greenhouse
gases (“GHG”) to the atmosphere (fugitive emissions),
accounted for in the FY20 production tonnages under the
Scope 1 emissions category. We report our GHG emissions with
reference to their source as follows:
GHG emissions intensity
Our reporting of Scope 1 and 2 emissions is consistent with GRI
reporting guidelines. In accordance with GRI, we have reported
carbon dioxide in our GHG emissions calculations as carbon
dioxide equivalent (“CO2e”). This year we have also accounted
for sulphur hexafluoride gas emissions from transformers, and
emissions from the use of ammonium nitrate in blasting.
We work with blast consultants to ensure our blasting practices
optimise the recovery of clean coal. This reduces our GHG
emissions by reducing the tonnages of contaminated coal that
needs to be processed in energy-intensive coal washeries.
Total Scope 1 and 2 emissions for FY20 were 112,548 tonnes of CO2e, of which:
40 percent related to fugitive emissions from coal production;
1 percent related to electricity use; and
59 percent related to fuel consumption and blast emissions.
The data for FY20 is approximately 7 percent less emissions
than FY19. This is due to a 6 percent decrease in waste rock
stripping (partially due to the COVID-19 lockdown at the
Stockton mine), and reduced CO2e from fugitive emissions as
13.3 percent less saleable coal was produced in FY20 across the
five sites compared with FY19.
In FY20, the highest GHG emissions intensity per tonne of coal
produced was at the Canterbury and Rotowaro mines. Intensity
is high at Canterbury because electricity is supplied from diesel
generators in lieu of access to the national grid, and it has the
lowest production rate of the five mines.
Rotowaro had a higher emission intensity this year because
significant volumes of waste rock were stripped in the Waipuna
West pit which is in the development stage. Also, saleable coal
tonnages decreased due to a planned shift in supply to a key
customer over a longer period.
Overall total GHG emissions intensity across all our operations
were similar to FY19 at approximately 0.05 tonnes CO2e/tonne
coal in both years.
FY20 Scope 1 emissions (t/C0₂e)
FY19 Scope 1 emissions (t/C0₂e)
FY20 Scope 2 emissions (t/C0₂e)
FY19 Scope 2 emissions (t/C0₂e)
Scope 1 includes emissions from fuel and fugitive emissions from coal; Scope 2 are emissions related to electricity usage. The emissions are
calculated following the procedures in the New Zealand Ministry for the Environment May 2019 report ME1414 titled “Measuring emissions:
A guide for organisations – 2019 detailed guide”. Emissions for Escarpment and Sullivan were nil.
Managing overburden materials to create stable
landforms for rehabilitation is a key focus when
developing our mine plans. This includes focus
on implementing controls such as characterising
mineral wastes and managing site storage to limit
environmental effects and minimise closure costs.
The two mine sites that disturbed potentially acid forming (“PAF”) waste rock were Stockton and Canterbury.
PAF waste rock disturbed decreased by 2 percent compared
with FY19, as overall waste rock disturbance reduced by 1.16 M
bcm. The total amount of waste rock per tonne of saleable coal
across all sites increased from 8.6 bcm/t in FY19 to 9.3 bcm/t,
predominantly due to increased stripping ratios at Rotowaro
and Stockton mines and the effects of the COVID-19 pandemic
reducing coal output at Stockton.
Waste rock (bcm) disturbed in FY20
Following procedures in our Acid Mine Drainage management
plan, in the Cypress pit at the Stockton mine we have been
applying up to 16 kg of lime per tonne of PAF waste rock to
minimise AMD production. At Stockton we have also constructed
a second calcium oxide dosing plant to actively treat up to 3,000
tonnes of AMD per year in the St Patrick’s stream catchment.
This plant started treating AMD in July 2020.
The Canterbury site actively manages PAF rock by selectively
placing and compacting this material in areas of backfill where
it can be safely covered by a minimum five-metre thickness
of non-acid forming (“NAF”) rock. This minimises oxygen and
water entry into PAF waste rock, ensuring minimal acidic water
is produced from the backfill. Legacy AMD issues inherited from
the mine’s previous owner have been managed by excavating
an entire old overburden area that was the dominant origin of
legacy high acidic seeps. This historic PAF material was placed
into a new engineered landform and encapsulated, compacted
and covered with a five-metre thick NAF cover.
Small historic acidic seeps from former underground mines
in the Canterbury area are treated via two mussel shell bioreactors.
The waste mussel shells neutralise acidic water and
this is also a way of recycling the shells instead of disposal
Land use and biodiversity
We strive to avoid and minimise any significant
impacts our operations may have on sensitive species,
habitats and ecosystems. We integrate biodiversity
into our business decision-making and management
Our objective is to rehabilitate mine sites to ensure self
sustaining indigenous ecoystems are established or reestablished.
Where the post mining land use preference is
pasture by the landowner, we focus on enhancing the chemical,
physical and biological aspects of the soil before carefully
selecting climate adapted pasture species.
Currently we have several active biodiversity offset projects
underway that involve thousands of hectares of pest control
management (defined by consent conditions) on Department
of Conservation administered land. We are also working with
experts and stakeholders to deliver biodiversity outcomes in
the context of current or future mine closures. That includes
minimising our land disturbance footprint and progressively
restoring disturbed land.
Soil is salvaged and where appropriate vegetation direct transfer
(“VDT”) is undertaken to speed up and improve the quality of
indigenous ecological restoration. VDT is a method in which the
sods of intact plants and soils are moved intact from stripped
areas, usually in six cubic metre chunks. This method avoids
new plantings, boosts ecosystem recovery, maintains biological
activity within the soil and enhances erosion control.
Overall net total land disturbance over all sites in FY20
increased by 18 hectares (“ha”). The Stockton mine accounts for
53 percent of the total disturbed area. Mining of the Millerton
pit area at Stockton over the next few years will provide for a
more established strip mining operation, in which progressive
rehabilitation rates are projected to reach double the current
Stockton mine rehabilitation rate of approximately 20 ha per
year. Our budgeted rehabilitation area for FY21 is 72 ha across all
sites. It is noted that Maramarua is in a development stage, so no
areas will be available for rehabilitation during FY21.
Rehabilitation budget table
Rehabilitation budget FY21 (ha)
No rehabilitation was undertaken at the Escarpment or Sullivan
mines in FY20 as these mines are in care and maintenance, and
no rehabilitation was undertaken at Maramarua as it is in
Land disturbed and rehabilitated
We aim to manage our water inputs, use and outputs
to inform our management of water-related risks,
seeking to minimise the impact to other water users
and the environment.
All our mine site discharges have specific conditions related to
discharge consents to protect aquatic ecology. No downstream
water sources have been adversely impacted by water use at our
sites in FY20.
Overall water use this year was 927 million litres, a reduction
of 8.2 percent in water use compared with that of FY19. A
significant proportion of this reduction is due to approximately
200,000 less tonnes of coal being washed through the Stockton
mine coal washery as the mine was not authorised to operate
under the COVID-19 lockdown.
Success for freshwater ecology at the Takitimu mine has been
confirmed by a fish survey undertaken in May 2020 in the
diverted tributary stream of the Wairio stream, which reveals
a healthy population (juvenile and adult size ranges) of 111
nationally vulnerable Gollum galaxias fish (rare whitebait
Consumptive water use
FY20 Consumptive water use (MI/yr)
FY19 Consumptive water use (MI/yr)
Note that the Takitimu mine water usage was incorrectly reported in the
FY19 annual report as 121 Ml/yr.
Water use intensity
Based on estimates of consumption, water use intensity
(measured as litres of water used per tonne of coal produced) is
shown below. This year sites used between 169 to 621 litres of
water to produce a tonne of coal. Significant water use at sites
with a large disturbed area or close proximity to residences is
related to dust suppression using water carts and sprinklers.
The Canterbury mine had a particularly high water use intensity
due to an unusual, very dry summer period.
Stockton has the highest intensity of water use, which reflects
the intensive use of the coal handling and preparation plant,
accounting for 86 percent of the site water usage. It is noted
that the coal washery water is treated for acid and sediment load
and is returned to the Mangatini Stream.
The Takitimu mine had a 34 percent reduction in water use
due to significantly more rainfall during the summer months,
requiring less water use for dust suppression.