If it drains a specific quantum each turn, wouldn't you need to know what quantum types your opponent will be playing beforehand? So for instance if your opponent is using an Earth based deck, you would need to know that beforehand and put Earth Pits in your deck. The only solution I can think of is a card that converts any quantum type into a specific type, then using pits of that type. Perhaps it could be called quantum funnel, for the symbolicness (I sure did just make that up!) of a funnel leading into a pit.
I like the idea of determining the type drained based on your opponent's mark, though. To make it balanced I think it should drain a quantum of your mark type as well, instead of whatever it drained from them. So if they had a mark of Earth and you had a mark of Time, it would drain 1 Earth from them, and 1 Time from you each turn, instead of 1 Earth for both.
EDIT: Oh, as it turns out, I just saw the Void Pillar (
http://elementscommunity.org/forum/index.php/topic,21409.0.html) card, which basically does what I just described. Never mind the previous paragraph then.