How to tag a disused colliery tip?

As always in OSM, there is no definitive answer to those more exotic tagging questions. You can always use an English dictionary and the http://taginfo.openstreetmap.org site to determine likely candidates.

man_made=spoil_heap

is used 258 times and probably the most appropriate one, at least in my opinion.

Some information on how to map specific objects are on the wiki page at http://wiki.openstreetmap.org/wiki/Map_Features . If you have something that is disused, the osm preference for that is the disused prefix. So, if you have a disused colliery tip, you could tag it disused:landuse=colliery_tip.

Another good way to see how to tag a specific thing is to look at others in the are and see how they are tagged. And taginfo, as mentioned.

A prominent german colliery tip is tagged simply as landuse=landfill. I would think that is bad, though, because then there is no distinction between a waste dump landfill and a coal dump tip.

So, to sum it up:

disused:landuse=spoil_heap
landuse=forest/grass/heath/...

Hi here’s a link to the region of Belgium, a mining residue is called Terrill (France), http://www.openstreetmap.org/#map=15/50.3918/4.4309 since most Terrills or pits are reused there’s hardly a tag. Consider landuse - colliery, colliery:disused or abandoned -fi coal_mine. Or use historic instead of disused / abandoned, both are not appropriate since the mine is hardly or impossible to reopen.