A lot of the ironstone remains in Northants have been lost over the years due to restoration, development, etc. however, if you know where to look.......
Some of the large opencast gullets still remain, but getting more overgrown as time passes, the Wembley Pit at Irchester & the Buccleuch Pit at Finedon come to mind. Thankfully, these last two have been incorporated into Country Parks.
Of the mines, some of the underground workings in the Islip area are mostly complete & accessible, probably very similar to the mines in the Scunthorpe area. Also in this area, the Twywell Quarry has been designated an SSSI, but is getting very overgrown.
At Irthlingborough, restoration & development has removed practically all traces, but at the Finedon end of the underground system, the bricked up adit to the tunnel leading to Irthlingborough can be found at the bottom of the quarry. A fascinating area, that Mr Pack will hopefully expand upon in his proposed book on the system - I'm really looking forward to that!!
Cheers
Alan