http://www.gvrhc.org/Library/SlavinGulch.pdf has some great information on Slavin Gulch and the Abril Mine including a picture identifying this as the control building for the mine - beautiful spot.

Note the old ore chute from the Abril mine, here and from a distance on the hike it looks a bit like a water stain (which would have been welcome on this rather warm day!).

http://www.gvrhc.org/Library/SlavinGulch.pdf indicates that the Abril mine was worked from 1914 to 1952.