Ann: Brumby Ridge Diamond Drilling Update, page-37

A north seeking gyro will work through the drill string regardless of the use of stainless lead rods.
We use a north seeking gyro for the basic surveys and is sent down the hole (during diamond drilling) with the tube retrieval tool attached to the bottom of the gyro. So all surveys are done in the drill string.

Another possibility is native copper could have been found and then smeared during the sample lab tests.
You would need to add in more standards and blanks or quartz flushes to help combat the native copper. If it’s actually present.

Also another issue could be that the mineralisation zone is super soft and the diamond drilling has actually washed the some mineralisation zone away.