Search
  • Caelen Burand

Rockhounding Colorado: The Pikes Peak Batholith Pt. 1

Years of struggle when rockhounding one of the greatest specimen localities in the world has yielded an extensive knowledge on rockhounding the magnificent Pikes Peak Batholith. In this guide we will provide background, tips, and tricks to effectively rockhound the Pikes Peak Batholith so you don't have to struggle for years as we did. Part 2 of this blog will reveal specific locales to rockhound.




Geologic Background:


Embedded 1.08 million years ago, by a massive igneous intrusion, the Pikes Peak Batholith long remained underground. As it slowly cooled, the Laramide Orogeny began uplifting and altering the surrounding landscape, creating the Rocky Mountains. As weathering occurred, the batholith rose to the surface as a massive patch of bright red to pink granite. Previously solid, the granite has slowly become a gravel in most areas today.

The batholith is characterized by its distinctive red granite speckled with biotite and smokey quartz. While this basic granite composes much of the area, Mindat.com reports 33 valid minerals being found in the area immediately surrounding Pikes Peak with several hundreds of species being reported throughout the batholith. To put it simply, the area is diverse in mineralogy. Everything from perfect topaz crystals to radioactive thorium and allanite can be found within the bounds of the batholith! Yet these deposits of mineral diversity are not common. This brings us to question, why/how did these deposits form?

Simmons, William & Webber, Karen & Falster, Alexander. (2016). Fieldtrip guide to the pegmatites of the South Platte pegmatite field. Second Eugene E. Foord Pegmatite Symposium July 15-19, 2016. 54-70. This image shwos us a brief summary of the very significant intrusive centers of the batholith. It additionally provides a good visual to the size of the batholith.



A road cut along South Rampart Range Road showing the bright red decaying granite.


Geologic Altering of the Batholith Giving Way to Diversified Mineralization:


The original igneous intrusion is distant from the batholith we see today. This is the result of geologic alteration through intrusive igneous plutons. These alterations are responsible for creating the minerals we seek to rockhound and have granted the batholith its fame.

Through the Laramide Orogony, several plutons rose towards the surface and altered the rock above. This process created what is commonly described as an intrusive center. This activity accounts for the diversification of mineralogy within the Pikes Peak batholith. Areas such as Lake George, Devils Head, Crystal Park, Crystal Peak, Pikes Peak, Tarryal, Rosalie (near Mt. Evens) have their fame from these plutons. When the plutons rose, they brought new metals and minerals dissolved in concentrated solutions of superheated water towards the surface. These fluids created various forms of alteration in the existing granite that allowed for intriguing mineral formation.

These intrusive centers created a pattern of concentric circles. The centers were the most altered while the edges were only exposed to cooler hydrothermal metamorphosism. The result is the centers of these intrusive centers being composed of a finer grained granite from the higher heat and pressure, with crystallization being minimal. The edges of the intrusive centers are a different story however. Only being exposed to the mineral rich waters of the plutons, created the perfect environment for diverse mineralization and crystalization. The hydrothermal fluids were able to rest in pre-existing gas pockets within the granite. This process of the hydrothermal fluids resting within the gas pockets creating miarolitic cavities that hold the sought after minerals.



 


Common Mineral Formation:


Within the edges of the intrusive centers there are miarolitic cavities that are the epicenters of our collecting pursuits. These cavities are lens-shaped pockets, in the granite, that were once filled with hydrothermal fluids that deposited a beautiful array of minerals. Cooling hydrothermal, mineral-rich, fluids create extravagant mineral deposits. Below we see a diagram of a typical miarolitic cavity in the Lake George region. We can see that the pocket is surrounded by more dense pegmatitic granite that gives way to a clay-filled pocket lined with the crystals we seek. This diagram is perfect for understanding how to rockhound and dig within the batholith.


Foord, Eugene E. et al. “Mineralogical and geochemical evolution of micas from miarolitic pegmatites of the anorogenic pikes peak batholith, Colorado.” Mineralogy and Petrology 55 (1995): 1-26.


Rockhounding:

To summarize, we know the most productive areas are the outer edges of the intrusive centers in the miarolitic cavities. In theory, this would limit the rockhounding search to a small area.

After reaching this conclusion several years ago, I began trekking the forest and realized the difficulty of finding a miarolitic cavity in the edge of an intrusive center. I was unaware of the sparse details that signaled a miarolitic cavity and with very few within the tens of square miles of possible land, I was not finding anything.

Through years of trial and error I began to understand how to pin down a miarolitic cavity within the intrusive centers. Following the tips below you will evade the trouble and be on the fast track to finding your own crystal filled cavity!


1.) Quartz

The first indication of a possible cavity is quartz. Large quantities of quartz is an indication of the hydrothermal events involved with the crystallization of miarolitic cavities. Seeking quartz is a general rule when rockhounding for any mineral. A unique feature of quartz is its solubility. Its deposition patterns parallel many metals and minerals. Because of this, quartz acts as a wide indicator for interesting mineral deposits. In this case the quartz is indicative of pockets that were exposed to hydrothermal fluids, the key prerequisite to finding all of the other minerals we seek.


2.) I found quartz, now what?

You may be realizing there are many areas with quartz and most will be very unproductive. The next indicator is quartz accompanied by crystallization of other minerals and using the quality of quartz to narrow down the best place to dig. Crystalline feldspar is a great indication for a location's exposure to hydrothermal fluids and slow cooling. This is indicative of a possible nearby cavity. Finding an area where the granite is pegmatitic in texture and feldspar begins forming crystals is critical. At this point begin searching for where the quartz displays the most clarity, or is the highest quality, among the crystalline feldspar as to find the area that is more likely to be productive.



In this road cut we see how there are disntinctive shifts in the grain size of the granite. The tougher, crystalized granite is a good indicator of rockhounding potential.


3.) Digging

At this point you have found a spot, probably in the middle of nowhere, among the pines, where there is some good quartz and crystalline feldspar near the edge of an intrusive center. Now what? Even with this spot in mind it is often difficult to know which way to dig. Do you follow the soft material, hard material? Down, Up, Sideways? It is hard to know the correct way to delegate your digging time.

This plagued my pursuits for years. I would begin digging in an area I predicted to be productive. Uneducated on how to dig, I would guide myself away from nearby miarolitic cavities and eventually give up, walking away with nothing.

There is no true way to be confident a digging direction will lead to a miarolitic cavity, but if one direction yields larger crystals and better mineralization, it is likely the correct direction. A general tip and guideline I follow when digging is to follow tree roots. Tree roots will take the path of least resistance. Thus they will grow in the gaps and spaces of a miarolitic cavity that also holds the rocks we seek.


General tips:

A.) Use Topography

We know that the sought after pockets are surrounded by a tougher, pegmatitic granite in comparison to the other, smaller grained phaneritic granite. This granite is far less susceptible to weathering and thus will often be towards the top of hills. So as a general rule, areas, like the tops of hills, that have resisted weathering, are more likely to hold good rocks.


B.) Be Curious

When Rich Fretterd found his legendary tribute topaz pocket, he dug adjacent to a small unusual outcropping he was curious about. His curiosity and hard work were the two key characteristics that allowed him to find world class topaz in the batholith. Rich searched for years for a topaz deposit and it was pure luck on that day that he found and followed that interesting outcropping to his world class pocket.


C.) Be prepared to dig

The batholith is tough, Digging is long and hard, be prepared to spend hours in a fox-hole searching for crystals. Yet there is simply no better feeling than pulling out a beautiful crystal after digging for hours!

Furthermore, the decaying granite is very sharp so always where gloves. Upon first glance it may seem appropriate to dig in the pockets with bare hands. This will only result in very sore fingers with hundreds of cuts. Instead where gloves and bring screw drivers to do the intricate digging.


D.) Telephone Poles

This tip works for general rockhounding but can be particularly effective when working with pegmatites. Although rare, telephone poles in the region give rockhounds a brief 10 foot deep view into the Earth. In areas that are weathered to gravel or are overgrown the dirt surrounding a telephone pole can show the ground below.


705 views0 comments