 Jackling worked at the Cripple Creek & Victor Gold Mine from 1893 until 1895, first as a miner, then as a millman and metallurgist.Starting in 1896, Jackling worked for Joseph Raphael De Lamar in Mercur, Utah where he developed a cyanide process for extracting gold ore.

Jackling followed up at the Missouri School of Mines with a degree in metallurgical engineering in 1900, then worked a gold mine in Republic, Washington.In 1902, he managed Charles MacNeill's and Spencer Penrose's zinc-pigment plant in Canon City, Colorado and their gold mill at Colorado City, Colorado.