Here it is.....
Difficulty: Medium
Quests needed:Rune Mysteries, Goblin Diplomacy
Items/skills needed:Lvl 17 mining, lvl 13 agility, lvl 13 thieving, any type pickaxe, light source(lamp suggested, one of the traps drops you into Lumbridge Swamp Caves), good food, weapon and armor if you wish to get the new items (bone spear, bone club, and mining helmet)
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1. Talk to Sigmund upstairs in Lumbridge Castle. He will tell you that while in the cellar he saw a hole in the wall and suspects that there is a monster invasion
2. Right after starting quest, pickpocket Sigmund and use the key you recieve to open the chest in the room next door. You will then recieve H.A.M. robes.
3. Go back to other room and inform the Duke of the horrible truth that Sigmund is a member of the H.A.M. cult.
4. Then you must go outside the castle and talk to Hans. He starts babbling on about seeing two bulging eyes poking out from the hole and is terribly relieved when you tell him you believe him.
5. Head down to the cellar and clear the tunnel by right-clicking "use" on pickaxe and use it with hole.
6. Climb through hole (be sure to have light on!) and proceed to pick up the brooch a couple feet foward on the ground.
7. Return to the Duke and show him the brooch. He will ask you to take it to Reldo, the Varrock Librarian.
8. Head to Varrock and show the brooch to Reldo. He will say he knows nothing of the brooch but he had recently gotten a book on goblin tribes.
9. Search the bookcases on the western side of the library and you should find a book that says something like "The History of Goblin Tribes".
10. Read through it and then you will see the same symbol as on the brooch.
11. Now head to the Goblin Village (the one you had to go to for the quest "Goblin Diplomacy") and talk to one of the generals.
12. They will show you how to greet the underground lost tribe by showing you how to do the Goblin Dance and Goblin Bow.
13. Go back to Lumbridge Castle into the tunnel (remember your light source!)
14. Now you must find the Lost Tribe. (a good idea is to follow someone else so that if they fall into a trap then you know thats not the way to go
) 
15. Eventually you should get to the mines.
16. Walk up to the head miner there and either do the Goblin Bow. Goblin Dance does NOT work! You must do Goblin Bow.
17. He will then greet you and tell you their story. You will tell him you will get a peace agreement between the humans and the lost tribe.
18. Go back to the Duke and tell him about the peace agreement. He will say that he will not have peace until they return the silverware they supposedly stole from the cellar.
19. Head to the H.A.M. HQ and search the first box you see inside of it. You should get the silverware.
20. Go back to the Duke and show him it. You will say you found it in the H.A.M. HQ. The Duke will get enraged and fire Sigmund. He should then give you the peace agreement.
21. Now once you go into the tunnel there should be a goblin guard there to guide you back to the mines (no more traps, hooray!). Give the peace agreement to the head miner and following it will be a short movie.
You will appear in the first floor of Lumbridge Castle and you will have finished the quest!
CONGRATS! YOU HAVE FINISHED THE LOST TRIBE QUEST!
Reward: 3k mining xp, free access to mines, and a ring of life.
NOTE: I am open to corrections/additions so go ahead and correct/add!
