A 50k ore box is an item in Evony TKR (The King's Return). It can be found after killing certain monsters or bosses, with some of them listed below.
The description of 50K Ore Box in Evony TKR says:
Use it to gain 50,000 Ore.
50K Ore Box is known to drop from a number of bosses or monsters upon killing, including Zombie, Redcap, Centaur, Skeleton Dragon, Werewolf, Manticore, Yasha, Peryton, Minotaur, Griffin, Senior Nian, Medium Nian, Junior Nian, Ifrit, Kamaitachi, Fafnir, Lava Turtle, Warlord, Golem, Witch, Royal Thief, Behemoth, Phoenix, Junior Hydra, Medium Hydra, Senior Hydra, Viking Icebreaker, Viking Berserker, Viking Chief, Pumpkin Monster, Jormungandr, Typhon, Medium Cerberus, Senior Cerberus and Ymir.
Note: This list may be incomplete.
50K Ore Box is known to potentially be obtainable from opening Senior Resources Chest, Senior Alliance Boss Package, Lucky Box Ⅱ, Junior Lava Turtle Chest, Junior Golem Chest, Junior Witch Chest, Junior Warlord Chest and Common Ymir Chest. The links for each item are below:
Note: This list may be incomplete.