This is, at it's core, the [GURPS Magic] system, mixed someone with S. John Ross' [Unlimited Mana] modifications:  characters learn individual spells as M/H skills which cap in cost at 2 points/level.  So to learn a spell at +3 costs 8 points, to learn a spell at 0 costs 2 points, and to learn a spell at -1 costs 1 point.

To learn a spell requires first mastering its Prerequisites.

Every spell you cast has a cost listed.  Instead of causing Fatigue, this causes [Taint].  If you don't want to get taint, you need to use a [Spell Matrix].
Matrices filter the raw mana and deal with the Taint used.

Spells can be improved before casting by the process of tying [Spell Threads].

There's a [Black Magic and Taint] mechanic, but it is not public knowledge.  Please don't read it unless you know you should.

Many players of magicians are having trouble remembering it all, so here's [How to Cast a Spell]

High Circle magicians can use ImprovisedThreadWeavingMagic.

Check out [Known Threads for Spellcasting]