The Holt brothers met
James Campbell Besley, a mine broker from nearby Hermosillo. In 1909 Besley had sold the Cerro de Plata mine, located in Sonora, Mexico, 25 miles southwest of Nogales to a group of Kentucky investors. After two years of disappointing results, the investors had asked Besley to find a purchaser for the mine. Besley brokered a deal with the Holt brothers who purchased the 150 acre mine. Holt said he started the mine with an "absurdly small cash capital of $ 200", adding "we have made the mine literally pay its own way". In July 1912, Holt made a deal with Roy & Titcomb, Inc. of Nogales, Arizona to build a mill and cyanide plant for treatment of silver ore from the Cerro de Plata mine. Acting as general manager of the mine, Holt claimed "five hundred thousand dollars of silver is in plain sight at the Cerro de Plata mine". The mill was started November 5, 1912. Mine development and ore shipments continued until thirty one lots of high grade ore had been shipped, mostly in railcar loads, aggregating more than 1400 tons and averaging 117 ounces of silver to the ton. 26,000 ounces of fine silver in the form of bars and precipitates were shipped to the Selby Reduction & Refining Works, near San Francisco, California during the first five weeks' production. In one section the silver content of the ore was assayed as high as 150 ounces to the ton. for a total of $ 15,250 ( - adjusted for current inflation) per month. The success of Holt's operation resulted in his expanding the mine's processing capabilities, erecting a larger 100-ton mill and cyanide plant. In 1913, Holt and his brother Walter reorganized the US Cerro de Plata Mining Company, combining it with the Mexican corporation Cerro de Plata Mining Company S.A.. James Campbell Besley, Roy & Titcomb, Inc. and Francis J. Hobson were named initial stockholders of the new corporation. Mexican revolutionaries stopped Holt on March 10, 1913, while he was transporting silver bullion from the mine to Nogales, Arizona. Traveling in an automobile under heavy guard, Holt was held up by 250 men. Holt and his party "were relieved of all arms and ammunition but otherwise unmolested, as the leader stated they did not want the bullion, only arms". A November 1913 newspaper article reported a 200% increase in net production receipts at the Cerro de Plata mine, growing from $7,000 realized in the month of October to an estimated monthly profit of $14,000 () from the production of "the little old dinky plant now in use". The article mentioned plans of doubling the production capacity at the mine. In 1914, the Cerro de Plata mine was reported to be a "silver bonanza" and "one of the coming big bonanzas of Mexico". Holt was president and manager of the mine and his brother Walter was secretary and treasurer. Holt displayed 16,000 ounces of silver bullion taken from the Cerro de Plata mine in December 1914. The bullion, estimated at the time being worth over $8,000 () was displayed in the window of the International drug store in Nogales, Arizona along with a silver "Savior on the cross" cast from the same refined silver ore. The display was taken to Phoenix, Arizona a week later, shown at the American Mining Congress. Holt was the delegate from Santa Cruz county, Arizona. By 1915, Holt was referred to as the "Silver King of Sonora". Holt claimed "during these (past) three years we have had a total production of nearly 700,000 ounces of silver" and "we already have 1,000,000 ounces of silver blocked out above the 300 foot level and will begin further sinking soon". Bandits, said to be
Yaqui insurgents burned the Cerro de Plata Mining Company store in October 1916. They destroyed the company assaying office and shot at the company caretaker, killing his mule. Holt estimated the loss at $1,000. The ore tailing mill and cyanide plant were not damaged. It was reported Holt still owned silver mines in the Sonora area in 1920. ==Later career==