From the Skywards website
Tier Miles...
* Help you progress to Skywards Silver and Skywards Gold membership levels.
* Are earned only when you fly Emirates or SriLankan.
* Are earned at the equivalent rate of one tier mile for each Skywards Mile you earn on your flight, plus a bonus of 50% for Business Class and 100% for First Class.
* Are valid for one year.
So... yes, the 100% COS bonus for First Class will count towards Silver Status
Cheers