Minecraft – Is it true that the best ores are found near lava in Minecraft

I've done some number crunching and I think I have your answer for you. These numbers assume that (a) you use the mining method in the accepted answer you link, (b) that the ores are uniformly distributed, and (c) that you're running a version of Minecraft between 1.6.0 and 1.7.3 (the chart you link hasn't been updated for 1.8 yet).

Mining for an hour with ~30 iron picks should yield you:

• 7,201 cobblestone
• 77 coal
• 308 redstone
• 46 iron
• 8 gold
• 8 diamond
• 37 lapis lazuli

Similarly, using ~6 diamond picks should get:

• 9,166 cobblestone
• 98 coal
• 392 redstone
• 59 iron
• 10 gold
• 10 diamond
• 47 lapis lazuli

As you can see, the iron and diamond yields are far below what goes into the picks. In other worlds, through solid stone, you operate at a loss. Caves make an enormous difference when it comes to mining efficiency.

(All this, of course, assumes my math is correct. Feel free to double-check my work in the spreadsheet.)

Since you have a skeleton spawner, that should make it easier. What I would do is build a wall/fence around it so that skeletons are contained, and leave some holes for you to shoot through. Next, if looking through the holes does not activate the monster spawner, I would have a doorway that leads inside the spawner room to activate it, then run out. The building will ensure that the skeletons do not wander off.

To kill the skeleton, first hit it with a sword through the hole until it's one hit away from death. Then, back off 50 blocks and snipe it!