Gate closer for large wooden gate?
A well used traditional gate closer is very simply a weight on a length of rope (wire cable would be better for heavy gate) over a pulley. As the gate opens the weight is lifted. When the gate is released the weight pulls the gate shut. You can adjust the amount of weight to suit the gate. I've seen concrete blocks used or old brake discs. Anything heavy. Old sash window weights are good as they are slim.

Alternatively search for 'gate spring' on google. In the UK they are dirt cheap, you might need a few  but easy enough to fit.

hth