Minecraft wiki entry for Development_versions, associated text: Changed ore generation of all ores making them have a spread value like lapis lazuli ore. Some still retain a linear generation alongside a spread generation.
Coal ore, emerald ore, and copper ore no longer generate below Y=0.
Copper ore generates between Y=0 and Y=96 and like all other ores, uses spread. It peaks at Y=48.
Emerald ore generates above Y=32 as a spread, peaking at Y=256 and decreasing in quantity as the altitude decreases.
Coal ore attempts to generate twice: once, evenly between an altitude of Y=136 and Y=256; and as a spread, peaking at an altitude of Y=96 and generating between an altitude of Y=0 and Y=192.
Other ores also generate differently.
Iron ore attempts to generate three times: once as a spread peaking at an altitude of Y=256, generating above Y=128; another as a spread peaking at Y=16 and generating with a minimum height of Y=-24 and a maximum height of Y=57, and a smaller one spreading evenly between the altitudes of Y=-64 and Y=-32.
Gold ore generates between the altitudes of Y=-64 and Y=32, peaking at Y=-16. The extra gold that generates in the badlands biome was left untouched.
Lapis lazuli ore attempts to generate twice: once, as a spread between the altitudes of Y=32 and Y=-32, peaking at an altitude of 0; and evenly between the altitudes of Y=64 and Y=-64, generating buried like ancient debris.
Redstone ore attempts to generate twice: once, evenly between an altitude of Y=15 and Y=-64; and as a spread, peaking at an altitude of -64 and generating below an altitude of Y=-32.
Diamond ore now generate as a spread, generating below Y=16 and peaking at altitudes near Y=-64.