how can i fix my alternator on a vauxhall corsa 1.7 di 2002?

i was diving along the road when there was a loud clunk i pulled over. red light came on. i look under the bonet, seen oil under the engine and the auxillaey belt was off and it looks like the lugs that holds the alternator has broken off from the engine block. what i like to kno is are they bolt on lugs if not has anyone came across this problem and solve it and how, i havent got manual any help is good help