SEToolbox doesn't do as good a job on the range of ore created in an asteroid field in my opinion, because I've only allowed up to 7 ores. Space Engineers will fill out large asteroids will all 9 ores in an approximate amounts required for building most ships.
But SEToolbox does give you the flexibility of specifying how much (within the bounds of Space Engineers changing the outside of asteroids back to stone or any non-rare ore) ore, and size and number of asteroids.

Basic steps:
Fly to the centre of where you want a new asteroid field.
Select "Import", "Generate Asteroid Field"
Specify the minimum range that you want to limit the asteroids to. You can set it to zero (0), but I'd wouldn't go below 50m, just in case drops one right on top of your player.
Specify the maximum range. created means a larger field, but wider more spaced out dispersal. Which of course depends on how many asteroids you want!

Specifying asteroids has the following:
Select the asteroid by the it's name.
Select the main material. I would pick only Stone. Stone is practically required by Space Engineers for it's base material.
Select a second ore material if you want one. Iron, Gold.
Select the percentage of the asteroid you want to be the second ore material.
If you want a third, select the ore and the percent.
Remember that any percentages that you select must be less than 100, to leave at least 1 percent of the Stone.
Add a forth and fifth ore if you want.
Adding more asteroids. By default there is one asteroid.
You can press "Add", or Alt+A to add another asteroid.
Selecting an existing asteroid in the row and pressing "Add" to copy that same data.
This means you can press Alt+A 30 times, and quickly get 30 asteroids.
Or you can go crazy and hold down Alt+A. That's why there is a number on the left to tell you how many you have.
I've created a asteroid field of 300 of the "manymediumasteroids" in this manner, which looks good spread out.

You can tune or adjust the ore, or the base asteroid until you are happy, and then press "Create".
After a short moment, all asteroid will be created in your save 'world'.

Don't forget to press "Save", as the asteroids are not written to you save world until then.

An advanced hint.
If you have a custom generated asteroid (ie., one of mine, or from Miner Wars), you can place it in the VoxelMaps directory.
C:\Program Files (x86)\Steam\SteamApps\common\SpaceEngineers\Content\VoxelMaps
And the Asteroid Field Generator will present it as an option to choose from.

Currently the method that SEToolbox uses to distribute ore materials causes the asteroids to have a 'polka dot' or 'white noise' effect.
As asteroid materials can be changed at the byte level, random in reality means the bytes are randomly arranged.
Trying to clump them in a semi realistic fashion is a lot harder and something I wish to do in the future.
There is an open task to address this issue and create a more realistic method, or implement something similar to how it is done in game.

I have made a request of Keen to make the method for generating Ore more publicly accessible.

Last edited Sep 30, 2014 at 3:02 AM by midspace, version 2