My first exposure to stromatolites came from a field trip to the Finger Lakes Region of New York state, as an undergraduate student back in 2005. After learning of their old age, and the wonders of how they colonize, they became one of my favorite sedimentary structures. During a separate class trip (to Upper Michigan), I was enthralled by the formation of red and silver sedimentary jaspillite (a.k.a. banded iron formations or B.I.F.s). Therefore when I was invited for a trip to northern Minnesota’s Mary Ellen Mine for the first time, I was definitely in for a treat!
I was living in Ely, Minnesota and working for an exploration firm when I was first told about the Mesabi Range Geological Society (MRGS) by three of my co-worker geologists. After giving an invited talk at one of their meetings, they invited me along for their annual field trip as a guest. It was a brisk, early October morning when we first left Ely, and we started southwest along State Route 1 & 169. Just past the town of Tower, we turned south onto State Route 135 past Embarrass before turning west again to the “range” town of Biwabik. After a straight-shot through downtown, a right was made on County Road 715 with the Austin Powder gate turnoff to the left after approximately one thousand feet. A couple of the members stepped out to set up signs for the upcoming crowd. The rest of us continued straight past a set of abandoned mine infrastructure, and MRGS members flowed in convening at the 10-bay garage of then-owner Tom Gardner. As a relatively new member of MRGS, I spent some time exchanging pleasantries until 10 A.M. at which everyone gathered for the preliminary geology and safety talk.
Over 2 billion years ago in the Proterozoic Era, among the first organisms were blue-green cyanobacteria (Collenia undosa) that have evolved from the ancient seas. They harvested solar energy to process carbon dioxide via absorbing carbon for continual growth, and releasing oxygen as a byproduct. At this time in Earth’s history, the atmosphere was devoid of oxygen (less than one percent) and the slow buildup of an oxygenating environment, that all multicellular life can attribute its existence to, all started from these interesting critters. The bacteria would trap muddy sediment, washed in from rhythmic shallow tidal currents, by secreting biofilms. In order to access precious sunlight, the bacteria would mobilize upward resulting in building layers that would create stony colonial mats that we know of as stromatolites. It is also interesting to note that these layers are rarely planar; the curvature, or sinuosity, of these layers is a result of the bacteria wanting to face the sun at all times despite its changing position throughout the seasons. As a result of this phenomenon, scientists have used stromatolites to determine how the number of days per year has changed throughout earth’s history. At the time of primary iron ore creation, the planet’s rotation was significantly faster giving a whopping one thousand-plus day year! Once thought long-extinct, scientists discovered these “living fossils” in the southern end of Shark’s Bay, Western Australia in 1956. This alone is a testament of their adaptability through stark environmental changes and multiple mass extinctions.
As significant as their contribution to changing the atmosphere into a more livable state was, new oxygen was not immediately available for this role for at least another 100+ million years. At that time, Earth’s crust and oceans were loaded with iron and other readily oxidizable elements. This led to the creation of major iron ores that populate northern Minnesota, Wisconsin, Michigan and other locales. Some of the trapped sediment within some stromatolite mats oxidized into hematite (Fe2O3) and magnetite (Fe3O4), thus starting the creation of the jasper at around 1.85 billion years ago. The iron ore “factory” continued until there was nothing left to oxidize, roughly 1.1 billion years ago, and oxygen could start taking up residence in the atmosphere.
I was living in Ely, Minnesota and working for an exploration firm when I was first told about the Mesabi Range Geological Society (MRGS) by three of my co-worker geologists. After giving an invited talk at one of their meetings, they invited me along for their annual field trip as a guest. It was a brisk, early October morning when we first left Ely, and we started southwest along State Route 1 & 169. Just past the town of Tower, we turned south onto State Route 135 past Embarrass before turning west again to the “range” town of Biwabik. After a straight-shot through downtown, a right was made on County Road 715 with the Austin Powder gate turnoff to the left after approximately one thousand feet. A couple of the members stepped out to set up signs for the upcoming crowd. The rest of us continued straight past a set of abandoned mine infrastructure, and MRGS members flowed in convening at the 10-bay garage of then-owner Tom Gardner. As a relatively new member of MRGS, I spent some time exchanging pleasantries until 10 A.M. at which everyone gathered for the preliminary geology and safety talk.
Over 2 billion years ago in the Proterozoic Era, among the first organisms were blue-green cyanobacteria (Collenia undosa) that have evolved from the ancient seas. They harvested solar energy to process carbon dioxide via absorbing carbon for continual growth, and releasing oxygen as a byproduct. At this time in Earth’s history, the atmosphere was devoid of oxygen (less than one percent) and the slow buildup of an oxygenating environment, that all multicellular life can attribute its existence to, all started from these interesting critters. The bacteria would trap muddy sediment, washed in from rhythmic shallow tidal currents, by secreting biofilms. In order to access precious sunlight, the bacteria would mobilize upward resulting in building layers that would create stony colonial mats that we know of as stromatolites. It is also interesting to note that these layers are rarely planar; the curvature, or sinuosity, of these layers is a result of the bacteria wanting to face the sun at all times despite its changing position throughout the seasons. As a result of this phenomenon, scientists have used stromatolites to determine how the number of days per year has changed throughout earth’s history. At the time of primary iron ore creation, the planet’s rotation was significantly faster giving a whopping one thousand-plus day year! Once thought long-extinct, scientists discovered these “living fossils” in the southern end of Shark’s Bay, Western Australia in 1956. This alone is a testament of their adaptability through stark environmental changes and multiple mass extinctions.
As significant as their contribution to changing the atmosphere into a more livable state was, new oxygen was not immediately available for this role for at least another 100+ million years. At that time, Earth’s crust and oceans were loaded with iron and other readily oxidizable elements. This led to the creation of major iron ores that populate northern Minnesota, Wisconsin, Michigan and other locales. Some of the trapped sediment within some stromatolite mats oxidized into hematite (Fe2O3) and magnetite (Fe3O4), thus starting the creation of the jasper at around 1.85 billion years ago. The iron ore “factory” continued until there was nothing left to oxidize, roughly 1.1 billion years ago, and oxygen could start taking up residence in the atmosphere.
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The namesake of the Mary Ellen Mine is rumored to have originated from the first staker’s girlfriend (if that is not love, I do not know what is!). The jasper and associated iron ore comprise part of the extensive Biwabik Iron Formation which is composed of four distinct members or units (from bottom to top): Lower Cherty, Lower Slaty, Upper Cherty, and Upper Slaty. Historically, the upper cherty was mined by Erie Mining Company for its magnetite (Fe3O4) content; while the lower cherty was the principle iron ore mined throughout the Mesabi Range. The cherty members arose as a result of hydrothermal fluid circulation that has dissolved quartz in the area, and re-precipitated with iron minerals to form an intergrown texture. This same action also resulted in the pseudomorphism of the stromatolites, thus finishing the Mary Ellen’s transformation. The thermal source was none other than the emplacement of the Duluth Complex not too far to the east. This thermal, or contact, metamorphism also gave rise to other minerals found along the range which include: pyroxene, olivine, cummingtonite, and hornblende.
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In going over the general geology, Mr. Gardner was kind enough to bring some historical cross-sections of the mine used by Pittsburgh Pacific Company. After various club members chimed in with their own personal nuggets of historical Mary Ellen knowledge, we were given the treat of being shown some polished slabs of the prized stone from Mark Sutich at Laurentian Monument, Granite and Stone. It turned out he had a few slabs ripe for the picking to those that wanted a little bit of a head start with their collection. Knowing my particular luck at times (or lack thereof) I shamelessly helped myself to one! After an hour-long briefing, everybody proceeded to drive a few hundred meters down to the mine area and started to disperse to their initial digging spots of choice. The main pit area is approximately 2000 feet long by 700 feet wide, and consists of roughly two “levels” which piles of varying sizes and finds were present, as well as a filled pit lake, which some members elected to take boats out.
I started my hunt for Mary Ellen on the lower level at the biggest rock piles, which were just off of the main driving path. My plan was to start there and work my way, away from the lake, to where some senior society members set up shop. After a short while my first find was not of the pretty lady, but of some millimeter-scale botryoidal hematite crystals on a tabular massive limonite-cherty hematite matrix. In continuing northward, I began to spot some similarly-scaled intermixed smoky and clear quartz points on black and white banded iron formation matrix. After roughly a half hour of searching at this immediate area, the anomalously warm October sun forced me to take a short breather. After getting to know some of the other members and sharing experiences in teaching, I started to move west towards the upper level where prospects seem to be somewhat more promising (one could only help based on the steadily increasing number of people flocking to the area). Sure enough, it was there that I saw my first signs of m’lady. The first stromatolites I collected were whole columns in matrix no more than an inch wide, and were pinkish-cream in color. After collecting several pound-scale specimens, I continued on up to the top level and started to walk along the ridge where there were a few large boulders of jasper. In wishing I had brought a bigger sledgehammer I, however, was able to collect some medium boulders lodged in the dirt with my pick hammer and mini-sledge. After exploring away from the crowd, heading northwest, for a half hour with no additional luck, I started to backtrack when I heard vehicles starting to make their way towards the pit lake for lunch (probably to facilitate any fish cooking that might occur).
I started my hunt for Mary Ellen on the lower level at the biggest rock piles, which were just off of the main driving path. My plan was to start there and work my way, away from the lake, to where some senior society members set up shop. After a short while my first find was not of the pretty lady, but of some millimeter-scale botryoidal hematite crystals on a tabular massive limonite-cherty hematite matrix. In continuing northward, I began to spot some similarly-scaled intermixed smoky and clear quartz points on black and white banded iron formation matrix. After roughly a half hour of searching at this immediate area, the anomalously warm October sun forced me to take a short breather. After getting to know some of the other members and sharing experiences in teaching, I started to move west towards the upper level where prospects seem to be somewhat more promising (one could only help based on the steadily increasing number of people flocking to the area). Sure enough, it was there that I saw my first signs of m’lady. The first stromatolites I collected were whole columns in matrix no more than an inch wide, and were pinkish-cream in color. After collecting several pound-scale specimens, I continued on up to the top level and started to walk along the ridge where there were a few large boulders of jasper. In wishing I had brought a bigger sledgehammer I, however, was able to collect some medium boulders lodged in the dirt with my pick hammer and mini-sledge. After exploring away from the crowd, heading northwest, for a half hour with no additional luck, I started to backtrack when I heard vehicles starting to make their way towards the pit lake for lunch (probably to facilitate any fish cooking that might occur).
After showing off some current finds over burgers, brats, and beverages some younger guests were making their way a hundred feet south to the biggest rock pile on the edge of the pit lake. In being satisfied with my current finds, I decided I would take a stroll over for just a few minutes. It ended up being more than a few minutes, as it was there that I spotted the larger boulders of folded, deep-red stromatolitic jasper in magnetite matrix. It was a great thing I decided to move my collection pile down to the grill site beforehand, as I found myself making a couple trips retrieving some additional small boulders. It was at this point that I wished I owned a pickup truck since I looked up and saw the MRGS vice president lift a fifty pound boulder onto his tail bed!
Overall I ended up taking home about forty pounds of rough rock, and was quite content given that I only had a small sedan with me. I had gathered mostly light pink-cream colored fossils, with only a couple specimens that are the desirable deep red. A few had the added character of showing off some very thin, white quartz veins running parallel to some individual algal mats. It should also be duly noted that, probably unlike the Mary Ellen person herself, the vast majority of rough rock may not immediately make one fall in love at first sight. Most of the rough I collected was covered with some form of weathering, and some ends are regularly-pitted (like some rugose coral specimens). Only a couple pieces I found had some naturally smooth planes. The true beauty will come with cutting and/or tumble polishing. My conclusion is that Mary Ellen jasper is very much akin to geode hunting; oftentimes you never know of the true beauty within until you get cracking!
Overall I ended up taking home about forty pounds of rough rock, and was quite content given that I only had a small sedan with me. I had gathered mostly light pink-cream colored fossils, with only a couple specimens that are the desirable deep red. A few had the added character of showing off some very thin, white quartz veins running parallel to some individual algal mats. It should also be duly noted that, probably unlike the Mary Ellen person herself, the vast majority of rough rock may not immediately make one fall in love at first sight. Most of the rough I collected was covered with some form of weathering, and some ends are regularly-pitted (like some rugose coral specimens). Only a couple pieces I found had some naturally smooth planes. The true beauty will come with cutting and/or tumble polishing. My conclusion is that Mary Ellen jasper is very much akin to geode hunting; oftentimes you never know of the true beauty within until you get cracking!
Since the Mary Ellen Pit is considered an older mine site, hazards that present themselves are plentiful. Common sense should prevail but since it always does not, here are some points to consider. Do not climb on top of loose tailing piles and do not roll boulders downward. Extra care should be exercised when hammering on isolated boulders near cliff edges. Although visibility at the site is excellent, do not wander off alone. Lastly since specimens are quite hard and can be sharp, heavy-duty boots and safety glasses are a must.
Specimens of Mary Ellen take an exceptionally brilliant polish, due to the iron that is present, and depending on specimen quality can take a mirror-like finish with an amazing red-silver contrast. Most of the finished work I have seen are hand-sized cut slabs. The present owners - Mark and Kandi Surich of Laurentian Monument, Granite, and Stone - are in the process of hopefully extracting and cutting large specimens for use in countertops. In talking to some shop workers, the estimated cost of a Mary Ellen countertop will undoubtedly run at least $300 per square foot! Shortly before the time of writing, the company had been busy building new infrastructure and purchasing new equipment for their operations (they had moved from the nearby town of Hibbing). I personally called up Mr. Surich and he replied that requests for visits to the pit, at any time, will be entertained as long as at least one week of notice is given (although if one decides to visit during the winter in these parts, that’s a whole another level of a crazy rock hounder!). They are even gracious enough not to charge any entrance fees, nor for how much material are taken out. The company can be reached at 218-741-3641. I was also told that there are rarer green and golden varieties of Mary Ellen to be found. Mr. Surich said that it takes quite a bit of luck to find those, and more often than not, one will not know if they have found such a sample until sawing it open. If one can find either variety on their first tour (or two), you are much luckier than me! |
A trip to the Mary Ellen pit was definitely a highlight of a young rock hounder’s growing list of journeys. I cannot think of many other places that offers collecting metallic iron minerals, fossil pseudomorphs, fossils that have directly contributed to our hospitable natural conditions on earth, is extremely artistic to the lapidary artist, and is free all in one spot!