I am working on a RT endeavour where the npc's are exploring a newly discovered star system. What sort of resources are there in the Imperium that they might find? What kind of minerals would be worth starting a mining colony for and so forth?

In short.. almost anything.

But lets give a few examples.

Food: Could be a mass market type (deal in bulk sell to hive worlds and space stations) or some form a delicacy (sell to the rich).

Mineral: This is very varied as it could be anything from precious gems, to simple iron or high quality silicate sand to make optics. This may also be liquid or gaseous in nature.

Labour: There are alot of people there and or exploitable xenos. Indetured servants and slaves.

Ruins: Was a inhabited world at some point (imperial or xenos) and the remains of the civilization are there to be picked over. Everything from raw materials to rare archeo and xeno artifacts may be found as well.

Trade: The planet is inhabited and is a good prospect for trade. Could be basic commodities or do they have something special to trade?

Extra-Planetary: All of the above could also be in space such as asteroid belts, gas mining from jovians, etc. In addition are there derelict space craft or space stations that the players can salvage or refit? Does the system itself something of importance such as super stable warp routs to it, or for some reason the astronomicon can be seen with complete clarity from within the system (huge bonus to warp rolls).

Strategic: Is the system in an important location?

These are just a bare fraction of things that could make a system profitable hope it helps you get some ideas.

Population is a very important factor to consider. If the planet is inhabited, then the RT will need to pacify the locals, form alliances, start converting them to the Imperial Creed and so on. The plus side is that in some cases it can be easier to do this than to bring colonists through the Maw and set up a colony. If a primitive world can be made allies or subjects, then shipping Lasguns and Guard Flak in bulk to train them as soldiers will result in a larger force than shipping Imperial Guard equivelents.

Most of the worlds seen so far in the published material have been more primitive than the Imperium. Others aren't self-sustaining, and require shuipments of food and other consumables. This means a steady demend for Imperial goods from the Calixis Sector. When planning for what the RT can get from the expanse, don't forget that it's bad business practice for a ship to have it's holds empty on one half of the journey. Your ship is going out to wherever the trade goods are anyway, make sure it's carrying something when it does. Advanced Technology that's cheap in the Imperium (Luminators etc.) to the primitives, and supplies to maintain and/or expand the colony for Imperials.

Don't underestimate the value of basic necessities like food or promethium fuel. In the Koronus Expanse, large amounts of these have to be shipped from the Calixis Sector. It was stated in the official history (in a free .pdf download from FFG if I recall) that at one point Footfall nearly starved because the Maw became impassable for several years. A canny Rogyue Trader should immediately see the value of finding a world with a food surplus in the expanse to set up a cheaper and more reliable supply. I'm sure that many places in the Koronus Expanse are in a similar situation- every basic component that can be built in the Expanse is one less thing that needs to be brought in via a long and unreliable warp route.

Thanks guys that does help a lot. This is my first RT game to run so I appreciate all the ideas.

Just to toss out a few resources I've used:

Promethium, crystalline materials, adamantium deposits, high grade acids, exotic pets or beasts of burden, ornamental stone, pharmaceutical plants and herbs.

Nephium

Very rare, toxic and viscous material used to improve promethium. Found on Lucins' Breath. Could apply to other arctic deathplanets as well =)