Not a good assumption. I did a 8 week deca only cycle at 300mg/week and only gaind 12 lbs off of the whole thing. You gain 85% of your weight in the first 4-5 weeks. My advice to you is eat anything you can get your hands on.
Are you sure you have Deca for sure?? Sounds fishy to gain that much in 2 weeks. You usually don't even notice Deca until the 3rd or 4th week. Are you maybe taking dbol too????
Cheers,
Jay
Gaining weight is entirely up to diet. It takes rooughly 4500 cals to build a pound of body tissue, thus for every 4500 cals you "over consume" you will gain a lb. Wether it is muscle or fat is determined by your training and diet.