What Makes the Walker Lane so Special?
What is so special about the Walker Lane and why do we care?
What is the Walker Lane?
Fundamentally, the Walker Lane is an area of faulting located adjacent to the San Andreas fault. As California slowly drifts away to become an island off the coast of British Columbia, the Walker Lane is hard at work separating California from the US continental landmass, creating a multitude of new avenues for younger mineralization to take along the entire trend.
The Walker Lane is an immense area of faulting directly related to San Andreas and the continent-sized forces at play. The Pacific tectonic plate and North American plate are pushing past each other causing immense tension in the earth’s crust. This tension often (in geologic terms) causes the San Andreas to slip with massive earthquakes. This tension is also released in the sub-faulting along the Walker Lane through a series of much smaller earthquakes.
Now that we’ve brushed up on Geology 101, we can jump back in to the importance of the Walker Lane as a mineralized trend.
Why do we care about the Walker Lane?
For the sake of time, we will focus on the Walker Lane from the Nevada perspective, although mineralization associated with the Walker Lane is prominent in southern California, and Western Arizona as well. From 1859 to today, Nevada has produced a little over 218 million ounces of gold. Of that 218 million ounces, the Walker Lane has produced a mere 40 million ounces or 19% of Nevada’s total gold production. Comparatively, the Carlin Trend has produced over 85 million ounces or 39% of Nevada’s total gold with operations starting in 1965! So, right off the bat, the Carlin trend has a 40 million ounce head start and has been in operation 110 fewer years. Not boding well for the Walker Lane, is it?
The Carlin Trend has seen modern mining methods, from 400-ton haul trucks to massive roasting, crushing, and processing facilities that greatly reduce the cost per ounce of gold production. When reviewing the largest producers of the Walker Lane, we come across names like Comstock, Tonopah, Goldfield, Aurora, and Bodie, deposits that were confined to operate when open pit and heap leaching were just dreams of the distant future.
Barrick’s Goldstrike roaster is a prime example of modern technology helping operations at a modern mine. Image by Marianne Kobak McKown
The size of Carlin Trend and other massive global operations like Kennecott’s Bingham Canyon mine allow for the generous use of economies of scale in lowering production costs. Image by Daniel Gleeson
I’m certain that, should the early Walker Lane have seen modern mining methods, production statistics would be much, much higher. As it stands, however, one deposit on the edge of the Walker Lane has seen modern mining methods and has proven the scale of mineralization that the Walker Lane can host. Kinross’s Round Mountain mine is a low-sulphidation epithermal deposit that has produced over 15 million ounces of gold. Comparatively, again, the Comstock produced around 9 million ounces using square set timbering and other expensive and primitive underground mining methods. A good open pit may have yielded several times that number. (+1 for the Walker Lane)
That said, the Walker Lane is host to some of the largest volcanic-hosted deposits in the west and has seen very little modern production. On top of this, the Walker Lane deposits frequently have associated silver and base metals. Although the Comstock produced around 9 million ounces of gold, it also produced over 200 million ounces of silver. The Carlin Trend and others produce little to no base metals or secondary precious metals like silver. This is in part due to the extensional nature of the Walker Lane.
A touch more geology… When the US as we know it was forming, it was most frequently being compressed with land being pushed up from the western and eastern edges of the continent. This pushing is what formed the Robert’s Mountain Thrust that the Carlin Trend is a product of. A few million years ago, the continental US became an extensional environment with the forces being reversed and the US being pulled apart by the same forces that once pushed them together (hence the basin and range topography that Nevada is so famous for). This extensional environment, coupled with the faulting on the Walker Lane, produced an exceptional combination of hosts for silver mineralization and part of what makes the Walker Lane a fantastic location for both silver and gold. (+2 for the Walker Lane)
The next perk to the Walker Lane is the relative ease by which gold is pulled from the ground and extracted when compared to other deposit types. Although the Carlin Trend boasts a higher grade per ton than most modern Walker Lane deposits, the ore is refractory and requires a significant investment in milling and processing. Autoclaves, to break down the refractory ores, and roasters, to remove the organic carbon from the ore, are a necessity that often costs many hundreds of millions of dollars to billions of dollars to build and operate. All of the costs to operate Carlin-type operations play into a higher all-in-sustaining cost or AISC. By comparison, Walker Lane deposits rarely encounter organic carbon (this is an almost Carlin-specific problem) and don’t have the impacted recoveries from refractory ores that Carlin-type deposits do.
Comparing a single ton of ore from the Carlin Trend and the Walker Lane shows an average savings of 40% in milling with the latter.
Looking at average recoveries between modern Carlin and modern Walker Lane operations shows an average 5% better average recovery from the latter.
The proof is in the pudding. When comparing the AISC the Walker Lane averages 180$ less per ounce.
Looking at both trends as a whole shows just how economically superior Walker Lane deposits are. Without considering economies of scale, the Walker Lane deposits are 43% more economical to operate than their Carlin alternative. In other terms, if you were to take a Carlin Trend deposit of, let’s say, 5 million ounces, the project economics based on the averages we just covered would mean you could mine an equivalent project on the Walker Lane of 2.85 million ounces and walk away with the same profit. (+3 for the Walker Lane)
The Walker Lane has so much more to give. With a massive land area, known significant deposits, and the emergence of new exploration models, the Walker Lane may very well take the top spot in gold production from the Carlin Trend sometime in the not-so-distant future.
After all, each mine is an individual business. Some are more profitable than others, some are larger, some have high-demand products (cobalt and lithium, for example), so it’s always in the investor and operator’s best interest to pick the best deposits to mine. Understanding that Walker Lane deposits have great potential for being economic producers is a great place to start. That is why we care about the Walker Lane and what makes it so special.
