DETAILED ANALYSIS
– Tonogold believes that a substantial mineable resource of gold and silver remains in the Comstock Mining District.
— WILLIAM WRIGHT
excerpt from A History of the Comstock Silver Lode & Mines, 1889.
When William Wright wrote that sentence in 1889, during what historians consider to the Comstock’s “low-grade era” (perhaps it was, but only low-grade for that time), the producing Comstock mines for which Tonogold has managed to locate precise financial data reported bullion returns ranging between $13.53 and $24.43 per short ton.
Calculating from the average met recovery of 65 percent that the Washoe Pan Process obtained in those times, that means those 1889 miners were working rock with average head grades ranging between $20.81 and $37.58 per short ton. ($13.53/.65 = $20.81; $24.43/.65 = $37.58)
Considering the fixed price of gold in 19th century was $20.67 per ounce and that gold made up roughly half of the value of Comstock ore, the average Comstock head grades for gold alone ranged between .50 and .91 ounces per short ton in 1889. (($20.81/2)/$20.67 = .50; ($37.58/2)/$20.67 = .91)
Calculating from the average met recovery of 65 percent that the Washoe Pan Process obtained in those times, that means those 1889 miners were working rock with average head grades ranging between $20.81 and $37.58 per short ton. ($13.53/.65 = $20.81; $24.43/.65 = $37.58)
Considering the fixed price of gold in 19th century was $20.67 per ounce and that gold made up roughly half of the value of Comstock ore, the average Comstock head grades for gold alone ranged between .50 and .91 ounces per short ton in 1889. (($20.81/2)/$20.67 = .50; ($37.58/2)/$20.67 = .91)
With 31.1 grams in a Troy ounce and a metric tonne being 1.1023 of a short ton, they were probably mining rock that contained an average of 17 to 31 grams of gold (Au) per tonne.
Since Comstock ore generally held about 15 times more silver than gold, the silver quantities in that rock were likely running between 257 and 468 g/t silver (Ag) per metric tonne.
Combining the gold and silver values means that they were mining rock that ranged between (17 g/t Au + 257 g/t Ag) and (31 g/t Au + 468 g/t Ag) (per metric tonne).
In 1888 and 1889, the Comstock mines’ total costs for extraction, transportation, and processing ore ranged between $20 and $30 per tonne, not including surface and office costs.
The old timers would have left behind any rock holding significantly lower average values because they lost money when they mined subeconomic rock, just like miners do today.
Since Comstock ore generally held about 15 times more silver than gold, the silver quantities in that rock were likely running between 257 and 468 g/t silver (Ag) per metric tonne.
Combining the gold and silver values means that they were mining rock that ranged between (17 g/t Au + 257 g/t Ag) and (31 g/t Au + 468 g/t Ag) (per metric tonne).
In 1888 and 1889, the Comstock mines’ total costs for extraction, transportation, and processing ore ranged between $20 and $30 per tonne, not including surface and office costs.
The old timers would have left behind any rock holding significantly lower average values because they lost money when they mined subeconomic rock, just like miners do today.
Available data 1889.