Reopening a historic mine

November 7, 2019

by Graham Peterson, Geologist, Black Fox Mining LLC and GS Mining Company, LLC

Gold Rush in Colorado and a New Mining Era

In January of 1859, gold was discovered in Idaho Springs, Colorado. Several months later it was discovered in Central City, Colorado leading it to become known as the ‘Richest Square Mile on Earth.’ A few decades later, miners had extracted 113.40 tonnes (4 million ounces) of gold and 3345.24 tonnes (118 million ounces) of silver from the area. Here at the Bates Hunter Mine, one hundred and sixty years after the first discovery of gold in Colorado, we stand ready to pick up where the old timers left off. The last mine manager of the Bates Hunter Mine authored a fascinating historical report in 1934 right before the mine’s previous closure. The manager claimed there was still high-grade gold in the sill at a depth of 227.08 m (745 ft). Old assays claim more than 5 opt Au at the bottom of the Bates and other mines nearby mined to depths of up to 670.56 m (2200 ft) with equally impressive assays at those depths. All we have to do is de-water, rehab the entire mine, and bring everything up to code for twenty-firstcentury MSHA standards. No easy feat by any means but worth every challenge and a chance to bring a new mining operation into Colorado’s network. Our team is small and composed of fewer than 20 employees, being a mixture of miners, engineers, mechanics, water treatment techs, and a geologist – me. That’s not to say I am the only one who likes rocks! Together we are on a mission to reopen a historic mine with lots of potential and discovery around every corner.

Vug found underground with primarily quartz, pyrite, and chalcocite crystals growing and some yellow sulfidation

Geology and mineralogy

The Bates Hunter Mine sits in the foothills of the Rocky Mountains in the northeastern part of the Colorado Mineral Belt. It consists of Precambrian country rock metamorphosed and deformed to form thousands of feet of interlayered gneisses. During the Laramide Orogeny about 60 million years ago, intrusive dikes, pegmatites, fractures, and faults littered the district, providing a great host for hydrothermal fluids to flow through and emplace today’s ore deposits, which are chiefly mined for their valuable gold content. Alteration is always visible for multiple feet before passing through an identifiable vein structure. The alteration is often QSP (Quartz, Sericite, Pyrite) with a vein content consisting of a quartz gangue coupled with sulfide metallics, most commonly consisting of pyrite, chalcopyrite, chalcocite, sphalerite, occasionally, galena, and rarely, some visible gold. Less than 15 % of the gold is visible with the naked eye. Although dimensionally the neighboring stringers to the Bates vein are small, ranging in just a few inches, they still show robust Au assays not uncommonly higher than 1 opt Au. Fortunately for us and on behalf of the US Atomic Energy Commission, the USGS conducted an extensive study in 1963, creating USGS reports 359 and 474C, which focused on the central city mining district and left us with an abundant and trusted resource to learn from and build upon.

Boyles Packsack/Bazooka IEWX Core Drill, setting up to drill underground

Exploration with a Packsack Core Drill

Our primary goal is to dewater down and continue mining at the bottom. As we work down, we set up our own Boyles Bazooka Packsack drill in a Bazooka configuration in search of nearby gold-bearing vein structures. To date we have set up and drilled in two underground locations, one at a level of 34.14 m (112 ft) and another at a level of 49.68 m (163 ft) for a total of seven holes – two on the first level and five more on the second. All the holes are planned for a depth of no more than 36.58 m (120 ft). With a decent level of consistency, we have encountered QSP altered rock a few feet out from the ribs of the Bates vein and many stringers and small vein structures within the extent, which measured 36.58 m (120 ft).

We have conducted our underground exploration core drilling with a modified Boyles Bazooka Packsack drill with a core size of IEWX. It’s not very common to see a core with a diameter of 2.54 cm (1 in), but we are only in search of nearby ore depositsfrom within a small shaft, anything larger isunnecessary or infeasible. Our Packsack drill has seen many projects – and many owners. There isn’t much remaining on the drill that is original, except maybe the motor head and the leg. The drill is mounted on an adjustable metal frame with four legs that can slide, rotate, and tighten in the appropriate position. Almost all the clamps and hoses have been replaced at least once. Even the original leather cups inside the leg have been replaced with plastic cups and lubricated. In just the 228.60 m (750 ft) drilled underground at the Bates Hunter Mine, we broke the rotating pin at least half a dozen times only to weld it back together. Many hoses and clamps have burst off, the leg cups were replaced, and we continually have had to deal with icing within the motor. Since the pin broke the first time, it has lost its symmetry, causing a noticeable wobble once the drill rotation is in the thousandths-perminute and intense vibrations when drilling, which at one point, caused the drill rod to shear in half mid-run.

This is not to say the mechanical setbacks were the only challenges we faced, as this was my first time acting as the core driller’s hand and the first time this core driller led a drilling program. About halfway into the third hole, we hit clay when we were not pumping enough water, which allowed it to swell, making the bit jam, and nearly causing all of our rods to stick. We were stubborn and unwilling to lose 80 % of our drill rods in one go, so we spent the next two days attempting to retrieve what we could. Finally, with one last attempt, we unscrewed what aluminum rods we could and replaced them with steel rods. We then took two pipe wrenches and torqued them as much as possible before welding a loop attachment to the last rod. After attaching two 2000 lb chain hoists we miraculously pulled our rods free! We mushroomed a few of our aluminum drill rods, but we retrieved everything in that hole. We learned from our mistakes, and the following four holes went more smoothly.  We have continued exploration planned for deeper levels, as well as some surface drilling with a larger drill, still to be operated and conducted in-house.

Pyrite cubes in a vein in our IEWX core

My experience

I had just turned 23 when I started working at the Bates Hunter Mine. At the time, I was still living with my parents after graduating from Colorado State University with a Bachelor of Science in Geology. This was my first job within my field of study and I started at the mine primarily with site cleanup while studying and gathering historic mine research on the side. After months of organizing thousands of bolts, screws, nuts, etc., sealing leaks in the roof of the office, painting inside and out, cleaning up the boneyard, and dozens of other miscellaneous projects, I finally started to dive into geology-specific tasks. I was assigned with re-logging more than 3657.60 m (12 000 ft) of core drilled on the surface from more than ten years ago, as well as continuing my research, networking with local geologists, and regularly attending lectures at the Colorado School of Mines in Golden, Colorado. Soon after pumping began, the lead core driller and I started our drilling program. We started slowly as he showed me what my tasks would be, and it took a little while to get into the swing of everything without making mistakes or having to ask questions.

One entertaining memory I look back on taught me the great lesson to keep communication healthy. We were on our fourth hole drilling underground at a level of 49.68 m (163 ft) and were the only crew underground. We were determined to make progress after losing a few days to a jammed bit. As always, we had double hearing protection, were working hard and efficiently, and at the time, our bell squawker didn’t have a light. Late in the day, the surface crews were trying to get hold of us, but we couldn’t hear the bell or Femco Telephone because of how loud the drill was and our double hearing protection. After many attempts from the surface workers, they got fed up and decided to stench us, not that they needed our attention, but just because we weren’t responding to their calls. That was my first time getting stenched and I have never wanted to leave a mine so fast! Luckily, we have ladders to ascend on at our own pace.

IEWX core cut and ready to be assayed

Looking forward at the Bates Hunter Mine

The Central City Mining District and the Bates Hunter Mine have many studies and reports on the potential of mineral production dating back to the late 1800s. It isn’t a secret that gold was mined here and predicted to have potential to produce much more, but since the last closure of the mine in the late 1930s, no venture has successfully brought the mine back to life. Many such attempts have dewatered and explored the mine temporarily, even installing infrastructure to begin mining once more. These past efforts have led to our company taking on thе challenge of producing gold from the Bates Hunter Mine once again. We know from the assay samples I have taken that this is a viable project, but we still need to prove it to the rest of the world, so we will continue core drilling to help build a resource. The work is challenging, but almost every successful outcome begins with a great challenge.

One note that has stayed above the GM’s desk since day one is this: ‘People who say it can not be done should not interrupt those who are doing it’ (George Bernard Shaw).

Preparing to core drill into the hanging wall of an old stope

About the author

Graham Peterson is a Geologist at the Bates Hunter Mine, Central City, Colorado. He has a B.S. in Geology from Colorado State University, Fort Collins.


Black Fox Mining LLC:

GS Mining Company, LLC: