May 27, 2024
Azurite-mineralized fossil wood.

250 Million Year Old Copper-Mineralized Fossil Wood

Most people know what petrified wood is, and most people know that Copper makes really colorful mineral specimens, but did you know that there are some rare formations where the two actually come together?

The Nacimiento Mountains in Northern New Mexico, USA, is one such location.  The geological formation is basically unique, in that most other formations that produce material that might look similar are of a different age, or have mineralogical differences.  The Nacimiento material if of Triassic age, roughly 250 million years old, and the knowledge that it took that long to form before we unearth it and expose the seemingly still-fresh interiors is amazing.  Often, when we unearth a new piece, what looks like charcoal comes tumbling and crumbling off of the specimens, still wet and shiny like the very biological material that they once were.

Two Copper-petrified wood specimens from the Nacimiento area
Copper-petrified wood specimens, one with gemmy Chrysocolla and the other nearly pure Chalcocite

It takes years of experience and a keen eye to come back from the zone with high-quality specimens, and it takes a lot of work and artistic skill to improve the quality of the specimens beyond their raw form.  It takes even more paperwork and claim fees to keep it all going, but at least in this case, both the Forest Service and Bureau of Land Management have been very reasonably accommodating.  The fact that we just use manual labor and disturb very little ground helps ease things, too.  The manual labor involved in just carrying this stuff is brutal.  Here’s an example: what you see in the next picture is a 50 pound chunk.  That’s almost too heavy to haul on the steep slopes and through the jumbled boulder field between the claim site and the vehicles.

Fresh Nacimiento Copper Wood Chunk
50 Pound chunk of beautiful Copper-mineralized Nacimiento wood, fresh from the ground after 250 million years.

Note in the last image the end of the little rock hammer.  It has been put to lots of use…

The boulder field through which the material must be hauled is a steep, towering maze of crumbling sandstone monoliths, many with logs, parts, and pieces of wood embedded in them.  It is a frustrating sight, since most of the material is too deeply embedded to extract – all you would do is destroy the pieces, so they remain, waiting for Mother Nature to eventually erode them out intact, though the timeline to such events likely exceeds my lifespan.

The Nacimiento area is reported (USGS, 1905) to have produced up to 60 foot logs almost completely replaced by Copper minerals, especially Chalcocite.  What an amazing sight that must have been!  Nothing like that is known to have been extracted in the last several lifetimes, as the district has been mostly idle since the 1920’s, with the exception of some production in the 1960’s.  That such beauty was melted down into Copper wire to electrify turn of the century homes in Albuquerque stirs a number of emotions, from wonder, to irony, to loss.  I guess that “Everything you use originated from a Farm or a Mine…”, and in this case, wood washed downstream in a storm enabled someone to read by electric light 250 million years later – for it is the Carbon in the wood that created the chemical reduction conditions for the Copper-enriched hydrothermal fluids to drop their load in such a specific and concentrated way.

The degree to which the wood was enriched by Copper can be seen in this next picture, of a small specimen that has had one end ground down to expose the Chalcocite.  This small specimen feels great in your hand, as Copper is pretty dense stuff, and so even small pieces can be very heavy, limiting the maximum size that can be recovered.  So much for hauling out a chunk of 60 foot log in my backpack – that would be many, many tons in total.

Copper wood specimen with one end polished to show metal core
Small Nacimiento Copper-mineralized fossil wood specimen with one end polished to show pure, metallic core.

Another type of material that occurs in the area are Azurite spheres.  The really amazing spot for these is one someone else’s claim, but we occasionally find them on our claim, too, though not in the prolific swarms of the classical locality.  Here’s a sphere sitting on a bed of Malachite.  The picture does not do it justice in this case, but you’ll probably get the point.

Azurite ball on a bed of Malachite from the Nacimiento mine.
Azurite ball on a bed of Malachite from the Nacimiento mine.

Yes, there is a little Silver in the formation, too, though not enough to be of any major significance, overall.  I’ve heard of a nearby mine producing a native silver mass large enough to turn into a belt buckle, but I’ve not been to that mine, seen the buckle, or talked to the owner.  If it has tree rings or other woody structure, that would be amazing!

For sure the area has been mined back to the Colonial Spanish time, and probably before by the Natives.  The high-grade material is so close to being pure metal, that we are told modern processing actually discarded the super high-grade as it would otherwise gum up the processing plant.  There are some good treasure stories in the area (see our Lost DuPont Gold Mine article) and if you get out and about locally, you will see old stone dwellings, petroglyphs, and lithic scatter all over.  Then, there’s the story of the local, in modern times, who had been searching for a treasure, and up and left town overnight without notice…



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