Rockhounding the Rockies: Quartz and Fluorite in the San Juan Mountains

I got invited to Ft Lewis College in Durango, CO to give a talk on the Pikes Peak Batholith and prospecting to their geology club. I have given numerous talks to the Colorado Springs Mineralogical Society including the Crystal Club at a variety of venues. I usually give my talks in Senior Centers, VA Halls or church basements so it was a real treat to return to academia and give a talk in a classroom hooked up with real audiovisual support. The professor managed to bribe the students with pizza and extra credit for the classes he taught so we had a standing room only crowd of about 60 students. The talk went well and when several geology students came up to me afterwards I felt like a rock star The College was kind enough to put me up for the night at a local hotel so I was able to get some rock hounding in the following day near Silverton CO. One of the Geology students (Austin), instrumental in getting me to Ft Lewis as a guest lecturer, wanted to go rock hounding in the San Juan Mountains the following day. "Part of the Southern Rockies, the San Juan Mountains were created as two enormous continental plates slammed into one another, folding and faulting the earth’s crust. Volcanic activity associated with the tectonic mountain-building process produced rich mineral veins—the silver and gold deposits that drew miners to the region in the 1860s and 1870s." [https://coloradoencyclopedia.org/article/san-juan-mountains]
Austin had been to a few mining sites along CO 550 in the San Juan Mountains though first we went to a rock shop in Ouray and then we stopped at several mines to see what we could find in the tailings. The Million Dollar Highway (CO 550) is a very stimulating drive especially when snowing over the passes. Our best success was near the Mayflower Mill just east of Silverton. “The Mayflower Mill was the single longest running mill in the history of the San Juan Mountains. In its 61 year milling career from 1930 to 1991, it was shut down only a total of 12 years, resulting in 49 years of actual milling. The total amount of rock milled is estimated at 9,700,500 tons. The Mill produced 1,940,100 ounces of gold; 30,000,000 ounces of silver; and 1,000,000 tons of combined base metals -- a remarkable record for hard rock mining” http://www.sanjuancountyhistoricalsociety.org/mayflower-mill.html. Austin had garnered some intel from a local rock shop on where he could find some collectible quartz and fluorite and had some success there in the past so we checked out that site. The temperature was 40F and a few snow flurries suggested winter was almost upon us as we parked and checked out the site. We dug in an area that had country rock surrounding a seam of quartz and fluorite.

The seam is right in front of Austin, slope of the hill is close to 45 degrees

I was surprised at the amount of clay between rock surfaces. It almost seemed like a Lake George pegmatite with all the sticky mud. The difference here was the quartz was not growing out of the rock as in pegmatites, but lodged in an old hydrothermal seam. We dug for about an hour or so on that seam and both got several small plates of quartz with green fluorite. Both the fluorite and quartz crystals were fairly small but make for interesting combinations for display. We walked a little further down the road and looked through some of the tailing from a mine above us. There were some very interesting druzy quartz plates along with pale green fluorite. There was also some other worm-liked druzy quartz specimens which I gathered up. I really didn’t think I would find much in the way of collectible crystals from the tailings lying on a 45 degree slope flung out of a mine shaft but the damage to the specimens we found was minimal. The snow had now changed from flurries to heavy snow showers and visibilities were obscured to a half mile or less at times as the wind picked up and the temperature fell to 32F.

Snow and cold shuts us down

We were more than satisfied with our finds so we decided to call it a day and head back to Durango. Unfortunately the Silverton bakery was closed so we had no funnel cakes that day. During our prospecting trip we also visited an amethyst site (mostly massive) and found a little pyrite and sphalerite at a couple other spots