Though I would set it up more like this.
Detect artifact scales 35 shield/40 aura/47 barrier

Since shield is the weaker of the two and supposed to be the easiest to find. The level ranges are up to you imms, whatever you feel is balanced. But getting Aura or shield should be very newbie friendly.

Your suggestion about giving shield to mage classes is the best idea I've heard. ^_^ That makes it very newbie friendly. A mage without alteast aura or shield is just way too squishy. Obviously it would be too much to give them both aura and shield. But this is very good.

I give it a large thumbs up.