Sweet Home Mine (Home Sweet Home Mine), Mount Bross, Alma District, Park Co., Colorado, USA
|Latitude & Longitude (WGS84):||39° 18' 46'' North , 106° 7' 5'' West|
|Latitude & Longitude (decimal):||39.3127777778, -106.118055556|
A former Ag mine located SW of Mt Bross. Started 1895.
Famous for superb and large rhodochrosite crystals.
Originally a silver claim prospected in 1873, the underground mine was worked only sporadically and finally abandoned as a silver venture in 1966, after producing a total of $215,000 in then-current silver prices. However, with the discovery of the "Alma Queen" in 1966, development continued, albeit as a series of "poor boy" operations without applying geologic and mining principals to the efforts.
In 1991, the mine property was purchased and, using venture capital, the mine was modernized. Rail was removed, the main adit widened to accommodate LHD haulage, a ventilation system installed, a new portal reestablished, and the dump relocated. The mine was also mapped, sampled, and analyzed.
There is some question as to the details of how mining was approached. One story is that the basic approach, refined over time, was to use drill+blast, and after each round run ground penetrating radar (GPR). If a vug was detected, a hole was drilled, and a fiber-optic camera inserted to examine the contents. It was then a matter of using pre-splitting, expansive agents, or hydraulic chainsaws, whatever would minimize vibrations that would shatter the crystals. Another source omitted the use of GPR, and reported that the fiber-optic camera had too narrow a field of view to be useful and so exploration of vugs depended on the 'jump' felt when the drill bit entered the vug. Then, the drill hole was widened, and further exposure limited to hydraulic splitters for large vugs, and a diamond chainsaw for smaller ones.
Mineralization is generally in base metal-silver-rhodochrosite-fluorite veins predominately hosted by meta-igneous and metamorphic rocks, with minor mineralization in porphyritic dikes and pegmatites. There are five main veins in descending order of production: the Main, Tetrahedrite, Watercourse, Blaine and Blue Mud veins. The Blue Mud Vein is a barren post-mineralization fault-vein, and production from the Blaine Vein was minor. Overall, the planned extent of the mine is small (1000 feet x 400 feet) with about 5,000 feet of workings, and the overall hydrothermal alteration zone small, despite evidence of on-strike continuation of the veins in the collapsed Tanner Boy workings directly across Buckskin Gulch. And even within a vein, rhodochrosite finds were limited.
Three conditions were responsible for the formation of vugs: (1) changes in strike and dip of veins, (2) vein intersections, and (3) openings formed by fault bends controlled by host rock foliation. In general, the 2nd condition was responsible for major pockets, and the 3rd for most smaller pockets. Exploration focused on fault/vein intersections. Fluid inclusion studies suggest that the hottest fluid flow produced the gemmiest ruby-red rhodochrosites.
The veins strike predominantly SW at steep dips and unfortunately, several years of unprofitable, barren, upward raise development was undertaken before concluding that the upper limit to gemmy rhodochrosite deposition happened to occur at the adit level of the Main vein. This experience discouraged pursuing even more expensive development of the vein below the adit level. Similarly, lateral development such as advancing to the next known vein, inferred from outcrops, would have been expensive and risky, as would have reopening the old Tanner Boy workings--interpreted as location of cooler fluid flow.
In the 13 years of operation, an estimated 90% of vugs encountered were barren, and there were only 5 vugs that could be considered highly profitable finds; for many years the mine operated at a break-even or loss.
For more information narrated in diary format, excellent graphics, and specimen photos, see Murphy and Hurlbut (1998).
|Paleoproterozoic1600 - 2500 Ma||Paleoproterozoic metamorphic and undivided crystalline: sedimentary and volcanic gneiss|
Metamorphic and undivided crystalline: sedimentary and volcanic gneiss
|Paleoproterozoic1600 - 2500 Ma||Paleoproterozoic intrusive and metamorphic terranes|
Intrusive and metamorphic terranes
Mixtures of metamorphic and intrusive or plutonic rocks, tracts known as crystalline, migmatitic terranes, moderately to highly metamorphosed rocks of unknown origin with or without intrusions. This classification is inherently prone to variable interpretation, as other compilers might distinguish some packages by their metamorphic or gneissic protoliths, and the associated age ranges may be more variable.
|Paleoproterozoic1600 - 2500 Ma||Biotitic gneiss, schist, and migmatite|
References for regional geology:
Data provided by Macrostrat.org
Garrity, C.P., and Soller, D.R.,. Database of the Geologic Map of North America: adapted from the map by J.C. Reed, Jr. and others (2005). U.S. Geological Survey Data Series 424 .
USGS compilers. State geologic map data. State Maps.
Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d.
53 valid minerals.
Pearl (1958), Colorado Gem Trails & Mineral Guide.
Kosnar, R. A. (1979): Famous mineral localities: the Home Sweet Home Mine. Mineralogical Record: 10(6): 333-338.
Rocks & Minerals (1982): 57: 61.
Rocks & Minerals (1986): 61: 7 & 9.
Rocks & Minerals (1988): 63: 56.
Cobban, R., Collins, D., Foord, E., Kile, D., Modreski, P., and Murphy, J. (1997): Minerals of Colorado, updated & revised. 665p.
Murphy, J. A. and Hurlbut, J.F. (1998): Mineralogy: Sweet Home Mine. Mineralogical Record: 29(4): 115-122.
Jensen, M. (2004): A mystery mineral occurrence at the Sweet Home mine, Park County, Colorado: Mineral News: 20(5): 1-2.
Update on rare minerals at the Sweet Home mine, Park County, Colorado, Mineral News (2004): 20(9): 1, 3, 10, 11.
Mining Engineer, August 2007
Bartos, P.J., Nelson, E.P., and Misantoni, D. (2007), The Sweet Home rhodochrosite specimen mine, Alma District, Central Colorado: the porphyry molybdenum–fluorine connection. Mineralium Deposita: 42: 235-250.
Mineralium Deposita 44 (2009), 415-434.