Total coal supply in New Zealand

Coal supply: production of coal plus imported coal, minus exported coal and stock change.
Energy transformation: the conversion of primary energy to more useful forms of energy. It includes activities such as electricity generation, oil refining, and other transformation (including coal used for steel manufacturing) as well as losses.
Consumer energy demand: includes all energy used by final consumers. It does not include energy transformation.

FIELDS
Information about coalfields in New Zealand can be found here: http://www.nzpam.govt.nz/cms/investors/our-resource-potential/minerals/coal/operating-coal-mines

RANK
Bituminous coal (black coal): a relatively soft coal containing a tarlike substance called bitumen. It is of higher quality than lignite coal but of poorer quality than anthracite.
Sub-bituminous coal: a type of coal whose properties range from those of lignite to those of bituminous coal and are used primarily as fuel for steam-electric power generation.
Lignite (brown coal): a soft brown combustible sedimentary rock formed from naturally compressed peat. It is considered the lowest rank of coal due to its relatively low heat content.

MINING METHOD
Opencast: Open-pit mining is a surface mining technique of extracting rock or minerals from the earth by their removal from an open pit or borrow.
Underground: Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits.

https://www.nzpam.govt.nz/nz-industry/nz-minerals/minerals-statistics/coal/

At URL provided, click on 'Coal statistics'.