An uninhabited planet, blackened and scarred by a colossal impactor.
The meteor was not natural, it was a Space Hulk of colossal size, hundreds of miles wide and massing trillions of tons. When the Warp Storm abated, it was left behind like flotsam, too close to the gravity well of the planet.
It crashed with terrible force, but most meteors travel at colossal speeds as they orbit. This Hulk simply emerged near the atmosphere's edge, and though the impact shattered its surface, the Hulk remains largely intact.
A mountain beyond measure, jutting up far beyond the atmosphere into low orbit, the wealth it contains is incalculable, in the form of salvage if nothing else.
Genestealers lived within the wreck, consuming what native animals managed to survive the impact. There is no sentient life for them to infest, and no Tyranid Hive Fleet anywhere remotely nearby for them to contact, so they've simply lived as they pleased, roaming around aimlessly and eating the feral native tribesmen. Tyranids must evolve, though, and their social dynamics are becoming more and more complex as they finish consuming the last remaining humans on the planet. Over time, the line between Human and Tyranid has become blurred, and though they can no longer contact the Hive Mind, they are nevertheless much stronger, fiercer, and perhaps more intelligent than humans. Though operating at a very low level of technology, some of the human-xenos hybrid mutants have even begun fiddling with the remaining intact components of the Hulk, and the energy flares have been noticed sector-wide.
A treasure world it is, and many now covert its wealth. Who will claim it? None can say for sure. And its strange inhabitants are now developing their own culture.
They may not appreciate interlopers.