My mining claim is made up of quartz, slate, and hot rocks left over form the 1860's.  Most hot rocks contain high concentrations of iron bearing minerals predominately the iron oxides.  Has anyone ever experienced compass calibration issues with their drones in such localities?  I've never seen any posts pertaining to this on the forum.  

Thank you,
Chuck

I fly around a old iron mine and didn’t see any unusual. I did fly carefully in that area and afraid the rock may cause problems to compass but so far no problem. As iron level in rock won’t be same so the level of interference can be different in different location. Need to be careful when you fly in those locations. Perform compass check after takeoff by slowly turning aircraft and monitor the arrow on radio screen pointing to same direction or not. Return and land if see any unusual.

Take your drone to your mining claim, but don't fly it.  Instead check compass interference bars under Advance / Sensor State / Compass.

Both Compasses should have short green bars with low numbers.  If not, try setting drone about 1-meter off ground on non ferrous stable platform.  If ''hot rocks'' were causing interference with Earth's magnetic field, the bars should go green and shorten.

Personally, I would first check area using one of free (or nearly free) Magnetic Field Interference Apps that use your Android or iOS phone's builtin Compass (XYZ field strength detectors).  I also would not try to calibrate drone's compasses in that area, unless drone via GO-4 App absolutely says to.