It doesn't work, Spell Economics only lets you activate spell cards without paying LP as cost, but you don't pay any LP to activate Mausoleum, you only pay to activate its effect. The first thing you must know: There is a HUGE difference between activate a CARD and activate its EFFECT in Yu-Gi-Oh!
But it's clear, you just need to read the rulebook properly. There's a golden rule in Yu-Gi-Oh! TCG, if 2 things have different names, so they're 2 different things. Actions like Discard, Send, Tribute, Destroy, in all of them the card ends in the GY, but they all 4 different actions that have different effects in the game. It's the same for activating a Spell Card and activating a Spell Effect.
I don't know what makes you think I don't read the rulebook properly because I know the difference between discard, send, tribute and tribute amongst others. Case in point I can see a lot of ppl making the same excuse as the op since it is isn't really obvious (unless you read the rulebook)that this doesn't work for "effects" of spell cards.