I wrote the following for a good friend who is desperate for Silver and only just unlocked the Lava Ruins so has not yet unlocked the Shortcut Stairway. Perhaps it will help other players who are looking for the most direct, quickest path to SILVER in Rune Factory Frontier:
If you have not unlocked the Shortcut Stairway, this is your route to your first piece of Silver in the Lava Ruins.
First of all, go north through the first chamber where there are both Killer Ants and Ants. Detonate the bomb and move back to allow it to clear a path for you. Proceed north throught the next chamber and continue north through the opening in the wall. Go round the lava crack in the floor and continue north through the opening in the wall in the northeast.
Now you must change direction briefly in the chamber with the Ghosts and Ants, and the cluster of Rocks that can be smashed for Ores/Gems. Go west through the sliding door into a small chamber filled with Ghosts. You will see another sliding door in the north. Go through it to find the isolated stairway to the 2nd Floor.
Descend to the 2nd Floor, then go west from the stairway to a little area containing Furpys. You will see a little stairway to the south. Descend and you will find yourself in the northwest corner of the largest area on the 2nd floor. This area is divided into four sections and has a large number of tillable fields. The section in which you find yourself contains two Ducks and their Generator. If you go east along the northern edge, you will find two smooth square boulders that you would need an upgraded Hammer to smash, making this route inaccessible at the start of your exploration of the Lava Ruins.
You ultimately need to make your way to the southeast corner of this large area and to do so, must go through a sort of maze.
First, find the stairs in the southwest corner of this section of the large area at the point where you cannot go further south because of a canal of water. Go up the little stairs through a sliding door, then take a short bridgeway south over the lava. In the next chamber, you will find a sliding door in the east that will take you to a short flight of stairs that descends east back into the original large area. Now, however, you will be on the southern side of the water canal in the southwest section of this area.
You need to find your way to the southeast corner now. Skirt the water that spills out of the canal and thread your way past the fallen pillars in the centre of the area, Go to the southeast corner of the large area and you will see a short flight of stairs ascending upward to the south.
Go up the stairs and you immediately will find yourself on the western end of a long causeway that goes east. Go east to the end of the causeway and through the sliding door there into a chamber containing two Mini-Golems, each with his own Generator.
You will see a sliding door in the north. Take it and you will see the isolated stairway to the 3rd Floor in front of you.
Descend the Isolated Stairway to the 3rd floor. You will find yourself in the middle of a long platform that extends along the eastern limits of the dungeon from north to south. Go north along this platform and you will see a cluster of Rocks that can be smashed for Ores/Gems, a bomb and two Scorpions. This is the Cluster of Rocks that usually contains at least one piece of Silver. You actually can detonate the bomb to crush at least one of the Rocks (and possibly a Scorpion) instead of using a Hammer. If you fail to find Silver in any of these Rocks, use Escape, leave the Dungeon, then re-enter and try again!