I had 150 Man-at-arms, 250 Swordsman, 71 archers, 23 marksman, and a hero. I set the aggression to 'range' and 'Ranged' attack range. My troops would just sit there and hammer them with arrows from afar. Every once in awhile too many groups came at once and that is when I lost a couple troops. I will probably beef up the archers/marksmen next time I go.
I didn't find anything when I explored the mine though and it took almost 2hrs to explore it.....lame!
Mainly, I would just sit in one place and let the groups come to me, and I stayed in areas with mountains around me - they move too fast in the open.
Good luck

P.S. - I was in the mine area for probably 20 hrs to get all those kills. (forgot them there overnight)

Just sending troops now. I take it the PRIZE that gets mentioned is just experience for your Hero, or is there something else.

Well that was a joke, as soon as i arrived i got attacked by 5x50 Barbarians. Lost 50 Rangers, 50 Swords, 10 Royal Guards, and 50 Pikemen. LOL and guess how many i killed...........0. Will not be trying that again. Had over 600 troops, did not think that was a good ratio for carrying on.

Quote Bane:

I take it the PRIZE that gets mentioned is just experience for your Hero, or is there something else.

you can get attack and defense bonus points for your hero