Spawn in the forest close to you is a large river, to get the entrance of the cave system with lots of rare ores from the spawn you just need walk straight ahead and after a while you will reach to the little island, in the island have a small hole which you be shown on the images below.




At the entrance of the cave is some of lava, after falling down there you can see some diamond and gold ores, example in the images above but if you search careful you will found lots of diamond. More details in the video below.
Seeds : 1405463989 Work in PE ver0.9.0+ or ver0.9.5