AntiXray is a great tool to prevent cheaters on using xray. This will let you know when a player has mined too many diamonds in the time frame for them to find them.

Commands
/antixray status
/antixray toggle
/antixray check <player>
/antixray stats
/antixray reload

Permissions
antixray.admin:
description: Allows admin commands for anti-xray
default: op
antixray.check:
description: Allows checking players for xray
default: op
antixray.bypass:
description: Bypass anti-xray detection
default: false
antixray.alerts:
description: Receive anti-xray alerts
default: op