I was wondering does anyone have any experience with methods for spreading soil forming materials (such as compost, spent grain etc) on top of a tailings dam. The only method I know is to drag a boom back and forth attached to a cable and two excavators at each site. Does anyone know of other methods. Obviously they cannot include methods where vehicles etc have to go onto the tailings for health and safety reasons.
All ideas, experience, is much appreciated.

An application technique for placing concrete on steep slope paving could be modified to place your soil.  A truck mounted extendable hydraulic conveyor with a forty to seventy foot reach might do the job.

I have done this.  Its way easier to place heavy equipment on the tails than you would think.  Get a couple of dewatering pumps... preferably submersibles running at the low spot to lower the phreatic surface.  Start dumping waste rock at he high end, and use dozers pushing the waste towards the pumps.  You will generate a large " wave" of displaced tals ahead of your rock face but all is stable.

Use geotextlie on the  tailings sand if you are nervous When adequately covered with rock, bring in your organics,  and spread with dozers.

The consultants ill tell you it cant be done, etc etc.  Just do it and you will be pleasantly surprised.