Hi Wez...I never let on how we detect xrayers, however after being aware of the issue ant was observed looking around at walls etc, then mining straight to diamond ores.

This is a list of his diamond finds since he joined the server, the first earliest two are not suspect.

AntiNeutrino
[Wed, 19-Aug-2015 07:09:35] (x: -2521, y: 10, z: -6902) in Castrovalva
[Wed, 19-Aug-2015 07:05:53] (x: -2467, y: 13, z: -6910) in Castrovalva
[Wed, 19-Aug-2015 07:04:07] (x: -2473, y: 12, z: -6918) in Castrovalva
[Wed, 19-Aug-2015 06:55:19] (x: -2480, y: 9, z: -6930) in Castrovalva
[Wed, 19-Aug-2015 03:07:09] (x: -2524, y: 13, z: -7031) in Castrovalva
[Mon, 17-Aug-2015 02:01:51] (x: -2559, y: 13, z: -6995) in Castrovalva

It's also possible to determine the path a player has taken using Coreprotect plugin.