Lucky?! Trick?!

Just a day before Mid-autumn Festival,i received three emails by Gmail from foreign country.First, i was surprised at it because i never show my Gmail address to any other people except my oi partners.I guessed that they were ads.But when i opened the first one, i was really astonished, for its contents. That email from Oxfam(GB)(an global organization) said that i was just lucky to be chosen by them, and i would be given some money from the fund(85 thousand pounds or so).
The second one is from a western African country called Burkina Faso(i wish i do not spell wrong).that guy expressed his hope that he wanted to cooperate with me to get some money from a dead rich man, since the dead didn't claim that who is the money belonged to.He said he is a clerk at the bank, and he needed a foreigner to help him move the money abroad.He promised to give me 40% at last.And the sum is 57 million dollars.
The last one is from UK Nation Board,who congratulated me on my winning 1000.00 pounds.Of course, they claimed that they chose me randomly.
i was really confused by them. How did they know my address? I've asked the man from Africa.But the reply is just searching on the net.
i realize that maybe some website leaked my private information, as i have registered some ids abroad by using this Gmail address.
i decided to talk to them, and find out their original purpose.