The closest thing you'll get to an explanation on the LAN site:

http://www7.lan.com/lanpass/acumulando/lineas.html#1

Worth a read, if only for the amusing terminology.

Last time I passed through SCL I picked up the members' benefits guide and even this omits specific info on which flights qualify for earning, though I was able to glean:

Business Class earns a 25% bonus, First a 50% bonus
Min 800 kms earned on every OW / associated airline segment (except for IB, QF and BA)
Kilometres earned on LA flights expire after 36 months from the date of travel, all others for 3 calendar years (more or less the same thing?) - however if you fly at least once every 3 years your kms never expire

Three elite levels: Premium (OW Ruby), Premium Silver (OW Sapphire), Comodoro (OW Emerald). Qualification levels respectively: 40,000kms or 30 segments; 80K kms or 60 segs; 150K kms or 100 segs.