Mining For Diamonds

For diamonds, I have been doing branch mining on level 10. (Y = 12.62) Each branch 3 apart. I bring 2 diamond pickaxes and start digging one long corridor, and turn back when I use up the first pickaxe. Each run takes about 50 minutes. I usually dig out everything I see except redstones, since I have not been using much redstone lately.

Here are the numbers for the last mining trip I took. I'll update with more data when

Duration 50 minutes:
10 Diamond
27 Gold
73 Iron
122 Redstone
54 Coal
0 Lapis Lazuli
Rate = 12 diamonds / hour

10/17/2011
Duration: 58 minutes
18 Diamond
0 Gold
83 Iron
112 Redstone
136 Coal
0 Lapis Lazuli
Rate = 18 diamonds / hour