They are peaceful, but very rare creatures that can spawn on nearly every solid natural block and even on crafted blocks though in every biome, during day and night. They most often spawn on the Corruption layer deep underground.
If a Keepa (of any kind) is near, you will be "alerted" by an Arcstone-symbol showing up on your compass-bar on top of your screen that radiates light blue semi-circles for a second or two.
If they spot player-characters or if player-characters approach them, Golden Keepas will react scared and will run away. They will usually run into the exact opposite direction, directly away from players, so players can use this habit to chase Keepas into traps of different sorts (by using "Shift" to run as the default key).
Keepas seem to lose stamina when running, so they have to take breaks, and sometimes (especially when taking a breath) they seem to get hypnotized by the Arcstone on their antenna which makes them pause a bit longer. Golden Keepas will not fight back when being attacked or while being tamed, but they will always attempt to run away if they are not trapped.
Golden Keepas can be cornered at "high" cliffs of at least 3 blocks height, they can be chased into pits (that have to be 3 blocks deep) or can be "trapped" by building walls around them. Even though Keepas can swim since R30 on April 6th 2016, it's possible for them to drown if staying in liquids for too long.
If killed, Golden Keepas might drop ca. 1-50 Arcstones in any case, Coal, Gunpowder, Moss Torches and/or Basic Extractors (can vary) in a significantly larger amount than ordinary blue Keepas. They might also often drop Stone Mining Cells, Wood Walls, Explosive Bombs, Obsidian Ore, TNT, Stun Bombs and/or Leather armor.
The pet-harvest of Golden Keepas consists of ca. 1-5 Arcstones every time, and they will also often give Coal Torches, Blue Pigments, other Pigments (more rarely), Brown Mushrooms, Extractors, Advanced Extractors, Stacked Stone Wall, Red Wood Walls, Melted Wax, Stun Bombs and other explosives, pieces of Obsidian armor, Obsidian Swords, Obsidian Mining Cells and occasionally even rare recipes like Dark Lumite Wall, Light Lumite Wall and Adobe building blocks (as of R26 in December 2015).