The small trail to the Boston American mine spurs off to the right of the main trail to Monte Cristo, between the big rock with the signs and the rickety bridge before the buildings.
In the 1850s, prospectors began searching for gold along the banks of the Skagit River. After gold was discovered along Ruby Creek in the late 1870s, hundreds of miners swarmed over the upper Skagit valley. Mineral resources around Monte Cristo were first were located in 1889. With investment in the mines by a New York syndicate backed by John D. Rockefeller, a railroad was constructed to bring down ore for smelting at the new city of Everett. By 1894, the district could process up to 300 tons of mined ore per day. The Monte Cristo Mining District produced mainly gold, silver, copper, lead, and zinc. Peak production was in 1897. Hit by financial disasters during the panics of 1893 and 1907, active mining ended shortly before World War I.
Boston American gold and silver mine was founded in 1913 and was a consolidation of several mining firms in the area. The name derives from the American Mining Company and its treasurer, F. W. Boston. The O&B Mine already existed much higher on the side of Toad Mountain, and the newly formed company planned to run a crosscut tunnel to contact the ore at a great depth below the O&B tunnels. This was a standard mining strategy, to encounter the ore as low as possible and then work upward, using gravity to bring the ore down as the miners bored upward through the vein. Alas, the operators never found a rich vein, and eventually abandoned the tunnel. The final day for mining at the Boston American came just before Christmas in 1919.
Silver-Gold Ore
Gold is an inert element therefore it is not actually formed, but instead exists in its natural state contained within the earth’s crust. There are four primary types of gold deposits, including lode, intrusive, placer, and laterite deposits.
Lode gold deposits are caused by the collisions of the earth’s tectonic plates. When tectonic plates collide, magma is pushed upward and cools, creating metamorphic rocks. These rocks have natural fault lines through which hydrothermal water attempts to escape. This water carries molten gold into the cracks of the rock until the water cools down, causing the gold to solidify and become infused with the metamorphic stone.
Intrusive gold is formed in a way very similar to lode gold. Magma penetrates into solid rock walls carrying the gold within it. When the magma cools it leaves new layers of rock and minerals, including gold, inside of the existing rock.
Placer gold is formed from already existing lode and intrusive gold deposits, and develops as a result of the eroding effect of water upon rock. Rain and the flow of rivers against them will erode rock walls releasing the minerals contained within. These minerals, including gold, will flow downhill entering into rivers and streams. Gravity will then pull the gold downward in areas where the stream current is slower, forming these deposits. When the river beds dry up these deposits remain in place, and can be dug up. These deposits can either be flakes or nuggets.
Laterite gold deposits are also formed from existing deposits of gold. Laterite refers to rock types plentiful in iron that were created by the weathering of bedrock. They have a rusty red appearance and are usually found in both hot and tropical areas. Gold in the bedrock combines with iron oxide and forms the deposits.
Silver-Lead Ore
Silver is formed from sulfur compounds within the earth. The Earth’s crust is very hot, approximately 200 to 400 degrees Fahrenheit, depending on how close you are to the planet’s mantle. The salt water that exists within the crust concentrates into a brine solution where silver remains dissolved. As the brine solution moves out of the seabed and into the cold seawater, silver will fall out of the solution as a mineral on the seafloor.
Silver and gold are often found together since they exist in the same base ore material. Few silver ores are absolutely free from gold, and vice versa. The combination of the two can be obtained from a variety of ores, in some of which the gold predominates, in others silver is the primary value, while in still a third class these two metals may be mixed with base metals, such as lead, copper, zinc, and iron. For ores where the most valuable element is silver, the silver is normally contained in minerals colored gray to black in appearance. These minerals range from a metallic sheen to an earthy soot-like appearance. Some have gray spider-like veins running through the rocks, while others are a more solid gray or black color. Silver can also be found mixed with quartz and ruby crystal formations.
Silver-bearing ore typically contains very little silver. Only 27% of silver derives from mining activities where silver comprises the primary source of revenue. The remaining 73% comes from projects where silver is a by-product of mining other metals, such as copper, lead, zinc, and gold. The most common minerals that may constitute rich silver ores include native silver, acanthite (silver sulfide), pyrargyrite (dark ruby silver or silver antimony sulfide), proustite (light ruby silver or silver arsenic sulfide), stephanite (brittle silver, also a silver antimony sulfide), polybasite (also a silver antimony sulfide), cerargyrite (Silver Chloride), bromyrite (silver bromide), and Iodyrite (silver Iodide).
Because silver is often found in combination with other metals, its extraction requires elaborate technologies. Once removed from the mine, silver-containing ore is crushed into a fine powder to expose individual grains to chemical processing. As a byproduct of mining lead and copper, silver ores are often purified by froth flotation. After froth flotation, silver is extracted by a cyanide process, akin to technology used for gold extraction. In some cases, the ore is treated by smelting before cyanide treatment. Silver is also produced during the electrolytic refining of copper and by application of the Parkes process on lead ores. In this process the silver is removed from lead and some other types of metal through a liquid-to-liquid extraction procedure.
There are several possible gold and silver mining methods, including placer, open pit, and underground mining. The mining method used for an operation depends on the type of ore, its location to the surface, and the profitability of the endeavor.
Placer mining is the practice of separating heavily eroded minerals like gold from sand or gravel, often from creek or river beds. This method can be utilized at any scale, varying from large operations to hobbyists.
Open pit mining is the process of digging out rocks or minerals from the earth’s surface from an open pit or borrow. This method is used when deposits of ore are found near the surface
Underground mining is the mineral exploitation in which extraction is carried out beneath the surface of the earth. Choice of an underground mining method is closely related to the geology of the deposit and the degree of ground support necessary.
With underground mining there are three common methods to access ores from under deep cover. They are shafts, declines, and adits.
A shaft is a vertical or nearly vertical opening driven from the surface to the deposit. The shaft may be used to hoist ore to the surface, provide ventilation, or to transport people and supplies.
A decline can take the form of a slope or a ramp. Slopes are straight openings driven at an angle, while ramps are helical in shape. A slope may be outfitted with a belt conveyor or track to move ore out of the miner. Ramps are used primarily for access, to move people, supplies, and ore between levels or to the surface.
An adit is a horizontal or nearly horizontal passage that follows a seam or vein of ore. It can be used for access or drainage purposes.
To log this Earthcache:
Please include a picture of yourself or a personal item at the Boston American Mine, and send me the answers to the following questions:
1. Do you think the gold deposits that sparked the Monte Cristo gold rush were lode, intrusive, placer, or laterite deposits?
2. Why was there an attempt to mine both gold and silver at this location?
3. Examine the mine entrance to determine the specific method of mining used at this location. Considering the geological surroundings, why do you think this method was chosen?
References
Arduino, G. Mining. Britannica. https://www.britannica.com/technology/mining/Placer-mining
Geology of Silver. Provident Metals. https://www.google.com/amp/s/amp.providentmetals.com/knowledge-center/precious-metals-resources/geology-of-silver.html
Hall, S. B. Silver. How Products are Made. http://www.madehow.com/Volume-3/Silver.html
How Gold is Formed. AMRA. https://www.americanminingrights.com/how-gold-is-formed/#:~:text=Lode%20gold%20deposits%20are%20caused,hydrothermal%20water%20attempts%20to%20escape.
Kohler, J. Lesson 8.1: Orebody Access. Pennstate. https://www.e-education.psu.edu/geog000/node/699
Lumanao, M. The Four Main Mining Methods: Science and Education. Steemit. https://steemit.com/science/@mannylumanao/the-four-main-mining-methods-science-and-education
Mines. Monte Cristo Preservation Association. http://mcpa.us/?page_id=121#:~:text=Boston%20American%20Mine,and%20its%20treasurer%2C%20F.%20W.%20Boston
Mining Tour. University of Nevada, Reno. https://nbmg.unr.edu/scienceeducation/ScienceOfTheComstock/Tour-Mining.html
Monte Cristo Mining Area. Department of Ecology State of Washington. https://apps.ecology.wa.gov/cleanupsearch/site/4550#site-documents
Puplava, W. Silver Lining. Financial Sense. https://www.financialsense.com/blog/20618/silver-lining#:~:text=However%2C%20what%20sets%20silver%20mining,companies%20mining%20these%20other%20metals.