This list should help setting the limits:
imagick::RESOURCETYPE_AREA (integer) //equivalent of MAGICK_AREA_LIMIT
imagick::RESOURCETYPE_DISK (integer) //equivalent of MAGICK_DISK_LIMIT
imagick::RESOURCETYPE_FILE (integer) //equivalent of MAGICK_FILE_LIMIT
imagick::RESOURCETYPE_MAP (integer) //equivalent of MAGICK_MAP_LIMIT
imagick::RESOURCETYPE_MEMORY (integer) //equivalent of MAGICK_MEMORY_LIMIT