So I've just been doing a lot of caving in my survival world [1.12.2], while I suddenly stumbled across a vein of diamonds in a ravine. And to my surprise, while I was digging around:
Yep. Quite astonishing, right? 2 veins of 4 diamonds each, plus a vein of 9 diamonds (it only shows 6 diamond ores on the second screenshot). I got 42 diamonds from that, thanks to my (trusty) Fortune III pickaxe.
So, the title says it all. What's the chance of several diamond deposits being next to each other? Has anyone else been this lucky?
Note: I didn't set this up. This was all legit, considering the fact that I'm playing on Hardcore mode (look at the hearts texture in the hotbar) and that I didn't even open to LAN on this world. If I were trolling I wouldn’t even have made this thread.
Depending on the definition of "close", it can range from one in several hundred to one in thousands of chunks; for example, the chance of a single chunk having 4 veins of diamond (ignoring veins that tried to generate below bedrock or where a cave or another ore is) is one in 256 since there is a 25% chance of a vein being placed in the right quadrant (the game does not actually decorate whole chunks but chunk-sized areas offset by half a chunk, so whole chunks are actually partly decorated by 4 different areas, as detailed here, which is so that they can extend outside of the chunk-size area without loading new chunks). If you decrease the allowed area to a quarter chunk (8x8 blocks) the chance becomes one in 65536.
Two veins would be much more likely; here is a map somebody made of the distribution of diamond veins (ignoring altitude, which is another factor); you can see many areas with two veins close together, similar to what you found, and even a few areas with three (note that the grid shows "offset-chunks", not actual chunks, so this shows that it is quite common for a chunk to have multiple veins of diamond, but always only one in each "offset-chunk", unless you consider that they are often more than 1x1 block in size, so they can overlap by one block):
From this visualization a few things can be seen:
1. The range of 8 through 6 (i.e. blocks 8, 9, 10, 11, 12, 13, 14, 15, 0, 1, 2, 3, 4, 6) always contains at MOST one vein.
2. Veins can (and frequently do) overlap block 7, sometimes from block 8 and sometimes from 7.
3. A minority of chunks have no diamond veins at all.
I have seen some skepticism about the one-vein-per-chunk claim, and hopefully this will put it to rest. To reiterate, the squares shown in the diagram are not chunk boundaries. The blue lines correspond to block 7 (in X or Z) within the chunks and the squares correspond to the half-chunk offset zones within which the diamonds are generated.