GMS Field Micromount Section Trip March 2023

GMS Micromount Section Field Trip
Micros, Slag, and Tour in Tennessee
Friday, March 24, 2023

A prior field trip to this location unveiled a world of micros to be explored, so we arranged a special Micromount Section trip. Rain delayed the first date scheduled and that rainwater took one of the locations we planned to visit off the list. Ultimately it didn’t matter, because there was plenty of material to peruse and collect. This unique geological area was once a large mining complex where copper bearing rocks were extracted and processed from about the mid-1850s through the late-1980s. Smelting released sulfur into the air causing acid rain. The entire area became a wasteland. Environmental remediation continues to this day, in particular by the company we visited.

We learned a bit about the history of the area during a tour of an old ore bin. Freshly mined ore was loaded into a large concrete structure where it would then be dropped into train cars below. The bin still contains ore, so as water leaches minerals from the ore and they combine with calcium carbonate leaching from the concrete, there are spectacular, colorful calthemites, i.e., “urban stalactites” forming. There is a lot of sulfur in the ground from the ore and from prior mining, so the soil is very acidic. This causes the rocks there to decompose. We saw several pyrite “ghosts” where once stood large chunks of pyrite. Members marveled at the mind-boggling pH of the water in a creek nearby – just 2! The unusual chemistry in the creek has formed terraces made of iron that are oddly beautiful while still a reminder of the horrendous pollution wrought upon the area by early mining practices.

The next stop was a pile of slag that had been processed only once through the ore extraction processes. It did not have enough copper to continue processing, so it was discarded, but that means there is still copper in it, just not at the levels desired years ago. We found a lot of green micros there along with some excellent flowy slag. Tiny clumps of white crystals were “blooming” on the slag. They are probably gypsum, but we need to test to confirm that. Artifacts of mining and processing were strewn throughout the piles. I saw an iron bolt with a weird growth of something on it that formed an almost honeycomb pattern. A pile of almost pure carbon sat nearby, so members collected a bit of that as well. I was even able to collect two samples of sand there.

Last stop of the day was at a massive pile of slag. Armed with loupes, we perused the pile by peeking into vugs and examining every spot of color. Members found a few specimens of what has tentatively been identified as gypsum crystals. The crystals I saw were clear and about a centimeter long. Other possible gypsum crystals look more like little flowers. Members found green, blue, yellow, and even a few red micros. One green specimen formed as tiny spires. I found some slag with yellow coated “fingers”. Broken ends reveal banding that is an indication of layers forming over time. Perhaps they are micro-calthemites? Some pale blue botryoidal specimens contracted a bit as they dried and they lost some of their blue hue as well. One member tested a sample with water and found that it dissolved quickly, so we know not to wash them. All of these things are considered anthropogenic, i.e., caused by human activity, so technically we can’t refer to them as minerals, but they are beautiful and they are fascinating and they are now in our collections. I am looking forward to the results of analyses on the specimens we found, and I am looking forward to many more discoveries there.

We cannot thank the owners of this property enough for welcoming us to this wonderful place. They have been so incredibly gracious, and accommodating, and fun! Every time we visit, there is something we haven’t seen before, and the possibilities of future discoveries make every trip special. Many thanks to all of the “loupey” members who shared this experience and their finds with us and each other. And, as always, thank you to Charles for arranging another fantastic trip!

Lori Carter
On behalf of Charles Carter, Field Trip Chair
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