COMSTOCK LODE

– Tonogold believes that a substantial mineable resource of gold and silver remains in the Comstock Mining District.

TONOGOLD CONTROLS 3 CONTIGUOUS KILOMETERS OF THE STRIKE

The Comstock Lode has a 5-kilometer strike length at Virginia City and Gold Hill, Nevada, about 40 km southeast of Reno.

Detailed geologic, economic, and historical analysis leads Tonogold to believe that significant gold and silver mineralization remains in the Comstock Lode.

Tonogold considers the Comstock Lode to be the portion of its holdings with the most exploration potential. Not because Tonogold expects to find high-grade bonanzas the old timers missed, but because of the tonnes of what to them was sub-economic material that they intentionally left behind as waste.

Thanks to immense changes in the economic circumstances of mining, rock that 19th century miners regarded as waste holds significant modern value.

Considering the nature of the Comstock’s epithermal mineralization and that the average breakeven head grade in the 19th century Comstock mines was around 50 g/t of gold equivalent (Au Eq) and never dipped below 30-35 g/t Au Eq, Tonogold believes that significant tonnages of gold and silver mineralization remain between 19th century breakeven head grades and the modern breakeven head grade for underground mining in Nevada of around 4-5 g/t Au Eq.

Prior drilling on the Comstock Lode.

So why does Tonogold think it knows this when no one has ever conducted a thorough drill exploration of the Comstock Lode? Which, considering the size and historical significance of the Comstock Lode, is by itself astonishing.

Most of the few holes that have been drilled were drilled in the late 1970s and early 1980s to define near-surface open pit targets. Tonogold’s 3D MineSight model suggests that the few deeper holes terminated too shallow and failed to intercept the mineralized structure. Tonogold began the first phase of its drill exploration of the Comstock Lode on September 20, 2020. Results to date have been encouraging, but the program is still in its early stages. See “News” for details.

To evaluate the opportunity in the absence of modern drill data, Tonogold uses a unique combination of historical, geologic, and economic analysis.

140-160 years ago, in the 1860s and 1870s, the Comstock Lode was the most valuable place on earth. In those days, Comstock happenings were every bit as important to San Francisco’s economy as tech industry developments are today. Consequently, San Francisco’s many 19th century newspapers covered the lode in detail. Due to the Comstock’s national significance, the United States government commissioned two mine surveys to accompany detailed studies of the lode’s geology and industry. Individual mining company records found their way into many historical archives. “Mining” that rich vein of previously neglected historical material has given Tonogold unique insights into the Comstock mines.

Much of Tonogold’s historical research and analysis is conducted by Comstock historian and author Gregory Crouch.

Working from the government-commissioned surveys and other maps of the Comstock mine workings—most of them more than a century old—Tonogold’s technical consultants at Mine Development Associates (MDA, a division of RESPEC) have developed an intricate 3D MineSight model of the Comstock Lode.

Constructed under the direction of MDA geologist Kiersten Briggs, the MineSight model of the Comstock Lode allows Tonogold to plot historical, geological, and modern drilling data with remarkable precision.

Tonogold’s 3D model of the Comstock Lode

3D MODEL OF THE COMSTOCK LODE

Plotting the historical data into the 3D MineSight model has given Tonogold the most detailed understanding of the Comstock Lode that it’s possible to obtain prior to the expenditure of tens of millions of dollars on a modern drill program. Tonogold’s knowledge of the Comstock structure isn’t speculative. We know the mineralized structure exists, and we know many of its physical attributes at a level of detail few other early-stage gold exploration projects can replicate.

Looking north 15 east with a portion of the geology turned on: Metavolcanics in footwall and VC andesites in the hanging wall.

Tonogold has been using its combination of historical and geological knowledge to de-risk the drill exploration program Tonogold began in September 2020.

The Segregated Belcher section of the Comstock Lode with historical data plotted on the mine workings

Due to the plethora of historical records available, Tonogold knows that the Comstock Lode dips east at around 45 degrees, is open at a depth of 1,000 meters (as measured vertically below a datum point at the lode’s highest surface croppings in the Gould & Curry mine), and that the lode’s mineralized horizon is up to 200 m wide. Tonogold estimates the Comstock’s average true width at 50 meters.

The separate claims of the Comstock Lode delineated by the vertical lines, running from the Caledonia and the Overman to the Union Con. and the Sierra Nevada on this 1875 map.

Through most of its history, the Comstock Lode has been divided up into about two dozen individual mines. Each mine operated as an independent company, issued shares to raise capital, and conducted its own underground development and mining operations. (The number of individual mines varied with different consolidations and divisions.)

Between 1859 and 1930, the Comstock companies mined approximately 9.4 million tonnes of rock at the impressive average head grade of 35 g/t Au and 726 g/t Ag.

Historic production data for Comstock Lode compiled by Tonogold as of 2020 04 17; assumes 65% metallurgical recovery; 15:1 Ag:Au ratio for Gold Hill mines; 25:1 Ag:Au ratio for Virginia City mines; Au price of $20.67 / oz; Ag price by year according to historic data.

Old-time miners would have left material below their breakeven grades in situ for the simple reason that they lost money when they extracted sub-economic material. (Just like miners do today).

AMONG MANY REASONS WE’RE CONFIDENT LARGE VOLUMES OF THAT MATERIAL EXISTS, THE OLD TIMERS TOLD US IT EXISTS

Here’s an excerpt from A History of the Comstock Silver Lode & Mines, published by famed Comstock journalist Dan de Quille (William Wright) in 1889, near the end of the Comstock’s 19th century heydays.

Click to read the original on archive.org (the quote is on page 98).

To follow a detailed analysis of what Wright would have considered “ore” and “waste” in 1889, click on the following.

DETAILED ANALYSIS

It makes absolutely no geologic sense to imagine that the process that mineralized the Comstock Lode magically “cut-off” the deposition of ore at 19th century breakeven grades, depositing nothing of lower grade.

THE GOLD IS STILL THERE

Reassuringly, William Wright wasn’t the only one of the old timers telling us of the existence of vast tonnages of what was then sub-economic mineralization. Here are a few other examples:

This, clipped from the July 22, 1893 issue of the Mining & Scientific Press. 10 of the 11 mines in that list fall inside Tonogold’s land package.

And in an article titled “The Comstock Mining Situation” clipped from the August 31, 1895 issue of the Mining & Scientific Press.

And two years later, in “Mining Share Market” in the September 25, 1897 issue of the Mining & Scientific Press. The hoped-for revival never happened.

THEY LEFT THE GOLD IN PLACE

Hampered as they were by the relatively low fixed price of gold, high per-ton costs, and low met recoveries, miners at the end of the 19th century simply couldn’t make that low-grade rock pay.

Happily, the economic circumstances of gold mining have improved drastically since those days.

With today’s much higher gold price in both absolute and relative terms following President Nixon’s abolishment of the gold standard in 1971, much lower per-unit mining and processing costs thanks to technological improvements and large-scale mining operations, and much improved met recoveries, Tonogold believes that significant quantities of economic gold and silver remain in the modern Comstock Lode.

Intending to validate that theory, Tonogold began the modern drill testing of the Comstock Lode in September 2020.

To see the results of that drill exploration, see Tonogold’s Press Releases in the News section.

NEWS