Minecraft plugin spice ore over the map?

I'm currently trying to write a plugin that will allow me to spawn ore at predefined locations. These are not supposed to spawn every time but appear every few minutes on a few random spawn points. Does anyone know a video or a forumpost on which this is explained?

For this you will need a Bukkit Schedular (Asynced Repeating Task and Synced Task). As well as a random value with threshold.

Pseudo code
int random = getRandom (0.100);
if (random <50) spawnBlock ();

A forum or in which this is explained, I do not know, but with a little brain lard and reserche in the Java Docs the Spigot API you get that already