I'm echoing Willo's post, just don't do it.
Mines can cause you all kinds of issues with asphyxiation from the buildup of carbon dioxide and other chemicals (mistake a leeching pit for a mine and you are in for lots of pain from Mercury and/or arsenic) in the mines. Other issues also are that, in some places, these have been used as dumping grounds for all kinds of hard rubbish (Asbestos, 'nuff said) by those already ignorant enough to do such things with little thought about those dangers (let alone a potential mine collapse).
If you think mobile reception is patchy in some areas, try getting a signal out in the bottom of one if you fall down a shaft and break an arm/leg.
Mullock heaps, where not heritage listed (do your homework), are not so bad provided you exercise caution in the handling of the raw material as (you did do your homework first re heritage listing?) some heaps of refuse were made after being fed through (mercury laced, not sure there?) copper headed crushers and steam engines.
The dozer opened up ground looks like a good bet though and where I (a newbie myself doing the homework prior to actually grabbing a magic electric wand :lol: ) would want to start.
Hopefully you pick up something in my post, play it safe, and good luck out there.