A mining deck featuring Dáin Ironfoot and Gandalf isn't really anything new, but it is exceedingly strong, so this is my take on it.
Dáin Ironfoot can defend for 6 on the first turn, neutralizing threats like the famous hill troll and gaining benefits while doing so. Arwen Undómiel offers easy access to Elven-light, which ends up being incredible as an option to manipulate which card you discard. Say you're defending with Dain and the enemy has 6. You discard one card from your deck with his action, then see your next card is Emery. You Elven-light/Wizard Pipe/Gandalf's Staff to get Emery into your hand, use her action, and get her into play, possibly hitting more Ered Luin Miners or Hidden Caches as you go. You then continue discarding with Dáin's ability, vacuuming up any cards you want in hand right now and discarding all that aren't currently useful. Additionally, if Elrond's Counsel comes up, why not just play it for free? Gandalf allows you to do so once per phase, and the single wasted willpower is no great loss.
Glorfindel is just great with horses. No Asfaloth here, he's now tamed a Wild Stallion. Quest with him, discard Elven-light to ready him, play Elven-light at the right time to draw a card, and now you're free to defend with him against a weaker enemy if needed and still discard another card and make use of his 4 (as long as you initially readied him in a previous phase, such as the travel phase).
Zigil Miners and Hidden Caches generate plenty of resources, Gandalf's Staff is most often used for shadow control, Dwarven Tomb is there so you can get back whatever you need, and Will of the West so you can cycle through everything, especially your Elrond's Counsels in any threat-heavy scenario.
For RCO players, take out Emery and Elfhelm. Any of the cards in the sideboard will work to put in. My recommendation would be Armor of Erebor to ensure Dáin can defend the entire game. Thalion would be good too, especially if you're playing a scenario with lots of side quests or if you want to add in side quests.