The Decision Matrix Tool (DMT) assumes that you have completed adequate pre-closure assessments, including internal and external surveys at various seasons. Biological resources, especially bat' use of the mine, are key considerations in gate design and construction.
You should know the approximate size and geological stability of the opening where the gate or other closure would be placed.
Other factors may ultimately affect the final closure design, including difficulty of access, cultural resources present, availability of other nearby mines, etc.
This website also provides a great deal of general mine-closure information that can be valuable without accessing the DMT.