It was a convincing weekend for Mickie, who won all of his four rides, taking him straight into the final where he was joined by Freddie Fox-Barron and Jake Mullford, with Jacob Clayton joining them by winning the B final.
Mickie, 12, was not to be beaten.
With three riders taking turns one and two side by side, Mickie eventually pulled away to a convincing win in his fastest time of the day.
He crossed the finish line three seconds faster than his previous rides.
That completed the summer season with Mickie winning 10 grasstrack titles, five amateur speedway events and claiming two seconds, three thirds, a fourth and a seventh-place finish at the British Young Lions Speedway series, before finishing sixth in the British Finals.
Mickie will now move into some winter riding with the six-round Scunthorpe Speedway Winter series between November and March.