A variety of options are available for closing abandoned mines, and each can be further modified to address the specific needs of the feature.
No Action Needed
Small mines that present little risk to humans may require no further action, thus freeing available funds and personnel to address higher-priority sites.
Closure by Any Means
This is for sites of sufficient risk to require protection, but without the resources for complex action. Such features may be closed by the most expedient and inexpensive method, usually backfill. These are often referred to as "destructive closures", but well-designed backfills may be reversible.
Grates and Cable Netting
Complex, multi-entrance mines may have openings that are not used by bats, but which should be left open to maintain the airflow and temperature ranges required by bats and other wildlife. To secure these openings, it is possible to use gratings or cable nets to prevent human access while still allowing minimal bat movement.
Generally less secure than gates and gratings, fences are sometimes the best solution for large openings, including open pit mines, open stopes, and large, complex collapse areas.
Horizontal and near-horizontal openings, such as shallow declines, require a basic gate. These gates consist of few, widely-spaced vertical columns supporting horizontal bars spaced 5¾" from the top of one bar to the bottom of the bar above it. Many materials are used but 4" angle iron is the most common and biologically transparent.
For vertical openings such as shafts, and nearly vertical openings, such as steep declines, it is necessary to provide additional flight space for bats to help them avoid predators and strong winds. The solution is to build a cupola — essentially a series of basic gates enclosing the opening, with an angle-iron or expanded metal mesh grating covering the top.