The rapid development of technology that had begun in the 1850s continued on into the 20th century. Mining companies working low-grade copper deposits were quick to adopt machinery that, although not intended for mine work, were of immeasurable benefit to the Lake Superior mines. Eli Whitney Blake, for example, had invented his mechanized rock crusher for use in road-building, but it was readily adapted to crushing copper rock being hoisted from the shaft, where it was then conveniently processed through Black crushers that had been installed in the upper levels of the rock houses built directly over the shafts.

The Calumet and Hecla company, by far the wealthiest of operations in Michigan, possessed the capital to invest in advanced concentrating methods. About 1907, it became apparent that the sands produced by the stamps were not fine enough to achieve the efficiency C&H’s metallurgists wanted to achieve. The Calumet & Hecla Mining Company: Semi-centennial edition, Keweenaw Miner, 1866-1916, reported that it was at this time that work was started on the No. 1 Regrinding Plant.

The Calumet and Hecla Historical Smelter Report, published in 2014, stated, in part:

“It was estimated when the plans were made for building the regrinding plants that about 37 1/2% of the copper contained in the sand could be recovered. No. 1 regrinding plant, however, started recovering 40% of the copper.”

Further experiments with regrinding and chemical leaching, led to the construction of the No. 2 plant, which included a leaching plant, increased copper recovery from stamp sands to approximately 75%.

While C&H continued to introduce and experiment with new concentrating methods, the Osceola Mining Company also kept pace with improvements to its milling practices. Between 1904 and the end of 1905, the Osceola mill was updated, upgraded and re-vamped. According the Annual Report for 1906, by Dec. 31, 1905, the mill was equipped with six compound steam-powered stamps five of which had replaced “simple” (steam-powered) stamps. Each of the compound stamps was equipped with a set of re-crushing rolls, and necessary jigs and other “concentrating apparatus.” One simple stamp was left in operation.

“By these changes,” reported Vice President and General Manager, Norman Haire, “at a very conservative estimate, we have increased the capacity of the mill over 25,000 tons per working month.

Publications such as the Engineering and Mining Journal, frequently wrote on comparisons between milling and concentrating practices in the Lake Superior copper district and those of the California gold mines. For example, the Nov. 13, 1909 edition of that publication stated, on page 967:

“With the exception of the Michigan copper district, where steam stamps are used for crushing of the ore after breakers, the usual concentrating plant begins with jaw or gyratory crushers, followed by rolls crushing either in stages or directly through limiting trommels of the maximum size at which jigging is to be done, the trommel oversize being returned to the rolls.”

Trommels were popular in mineral dressing of gold ore in the western states. A trommel is a rotating drum with a screen that allows fine material to fall through while retaining larger materials.

That the Lake Superior copper mines relied so heavily of steam stamps was partially due to the hardness of the rock and partially due to barrel copper. The Status of Research in Ore Dressing, published by the Bureau of Mines, in 1925, reported:

“The use of rolls is common in conjunction with the operation of steam stamps. The function here is usually to crush material to about 1/4-inch, which has passed the stamp through a mortar screen ranging from 1 1/2 to 5/8-inch. By subsequent sizing the coarser part of the pulp is returned for recrushing, and so may be reduced most expeditiously by rolls. The economy of this practice may be seen in the output and horsepower consumed, figures which are well known. This practice is perhaps best observed at the mills of the Lake Superior copper region, where the steam stamp is extensively employed. The difficulty with rolls, where there is mass copper, arises from the irregularities and strain upon the rolls … It is the mass copper that mostly justifies the employment of the heavy steam stamp in that region.”

The Report of the Directors to the Stockholders of the Mass Consolidated Mining Company for 1900 outlined the progress of the construction of its stamp mill on Keweenaw Bay, in Baraga County, 34 miles northeast of the mine, located in Ontonagon County. The plan called for the mill to be equipped with one compound steam stamp, built by the Nordberg Manufacturing Company, of Milwaukee, which would process 550 tons of rock per day. The foundations, stated the report, were constructed for two heads. At the same time, the company also placed an order with Nordberg for a water pump capable of providing the mill with 16 million gallons of water per day. By 1908, the mill was equipped with rolls, jigs, and slime tables which, by 1908, was considered the basic necessary machinery for a stamp mill in the Lake Superior district.

Through trials and comparisons with other similarly outfitted mills, the Mass Consolidated soon discovered that its rock was much harder than other Lake Superior lodes. ” …Perhaps the most refractory amygdaloid milled at present in the Lake district,” the Register stated. The Mass mill’s stamps were of the same capacity as the Osceola Mining Company mill, could only achieve an amount of 100 tons less than the Osceola mill.

In 1902, the Mines Register, Vol. 2 described the Isle Royale stamp mill, at the mouth of the Pilgrim River. The steel-frame structure was outfitted with three Nordberg stamps, Parnell-Krause, which were also used in the Osceola company’s mill and the Portage Lake Foundry and Machine Works. The Register reported that the mill had 72 rough jigs, 36 finishing jigs, along with circular (Evens-type) slime table, and additional vibrating “shaker,” or Wilfley tables.

By the turn of the 20th century, the advancements in milling practices and mineral dressing had reached a point of efficiency that “by judicious selection, the Calico (mine) can furnish large quantities of stamp rock that will return 1% and better, refined copper, and as the mill management becomes accustomed to the peculiarities of the rock, the percentage in tailings can be reduced, perhaps by one-third.”