I've found this...
In a description of the cotton industry-related history of Blackburn, Miller3 (p. 345-346) describes coal mining of the area around Darwen, including Eccleshill, and the Grimshaw connections to coal mining operations going back to the early 1600s (underline added by webpage author):
Without coal it would have been impossible for the engineering trade to establish itself so firmly in the borough. Hence it is not surprising to learn that the history of local coal mining goes back to Elizabethan times, and even to-day the precious mineral is being obtained from Coalpit Moor, near the southern border of the township….
Coalpit Moor is near the extremity of the rocky spur called Whinney Edge, which slopes rapidly down to the river Darwen at Ewood. All this area is dotted with the remains of old coal pits….
The cluster of coal pits on this moor, together with others in Livesey, Tockholes and Darwen, indicate the extent of this coal field. The Eccleshill coal pit was in full operation in the reign of Charles I., when it was owned by the Grimshaw family, of Okenhurst, Lower Darwen. The Eccleshill Brook was formerly called Grimshaw Brook, and Grimshaw Park still perpetuates the association. John Grimshaw was fined and had much of his property sequestrated for recusancy during the period of the Commonwealth. A petition of Nicholas Assheton, dated 21st January, 1650, shows (John's) estate included lands in Clayton, Eccleshill, Burnley, Yatebank and Preston.
"in which sayd sequestered lands there are certaine collieries of good value which for want of repayrs are almost utterly lost, the sayd premises consisting much of coalmines and the same will require at least L500 to put them in good repayre and made useful for the Commonwealth…"
During the following century there was a brisk trade in coal with the surrounding townships, and the improvement of road communications and the establishment of "gangs" of packhorse, outlying areas hitherto solely dependent upon turbaries and woodlands for their winter fuel were enabled to make fuller use of the precious mineral….
Clear evidence of coal mining that was underway during the mid-1800s is shown in the 1846 Ordnance Survey map of the Eccleshill area. In the area south of Grimshaw near Brocklehead, several coal pits and a "Brocklehead Colliery" can be seen.
Also the bull dozed entrance used to be accessible and always had a stream coming out, you could also see the tracks but as i remember as far as you could see in there were huge beams holding up a soil roof for as far as you could see.... very dodgy looking.