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Marathon Co., Wisconsin, USA

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Marathon County displays some of the best outcrops of Precambrian rock in the state. Many of the rock occurrences are of interest to the mineral enthusiast.

The oldest rocks are gneisses and amphibolites, likely of Archean age, that have experienced amphibolite facies metamorphism. Overlying these, probably unconformably, are a complex sequence of Lower Proterozoic meta-volcanic and meta-sedimentary rocks that have undergone greenschist facies metamorphism. These appear to be the remnants of an island arc sequence caught between colliding continents during the 1.80 -1.85 billion year old Penokean Orogeny. These have been intruded by pre- and syn- and post-tectonic plutons, largely granitic in composition.

Notable post-tectonic and possibly anorogenic intrusions include the 1.4 billion year old Wolf River Batholith and the various plutons of the Wausau Complex. The Wausau Complex (including the Nine Mile Pluton and Stettin Pluton) is relatively well exposed, and consists of granites, syenites and nepheline syenites. These host complex pegmatites. Weathering has reduced many outcrops to “grus” which is produced in many quarries as crushed stone known as “rotten granite”. Unweathered granite is also produced for building stone and includes the red granite which is Wisconsin’s official state rock. A variety of minerals can be found in these plutonic rocks, including smoky quartz, zircon, anorthoclase (showing excellent moonstone schiller), phenakite and REE minerals. Xenoliths of quartzite occur in these plutons, the largest holding up Rib Mountain, where is can be readily examined in a state park, and represents the second highest elevation in the state..

Wide shear zones where the rocks have been cataclastically deformed cross-cut the Precambrian rocks. Examples are beautifully exposed in the Eau Claire Dells County Park along a scenic river gorge.

Several massive sulfide deposits and mineralized quartz veins are known, but so far (2013) no production has occurred. These potentially host gold, silver, zinc and lead.

Scattered outliers of Cambrian sandstone occur, and are worked for flagstone. Also several episodes of glacial drift coated the area. Interesting samples of glacially-transported rocks and minerals can be found by the dedicated collector.

Mineral List

Mineral list contains entries from the region specified including sub-localities
Actinolite
Aegirine
Agrellite
Albite
'Albite-Anorthite Series'
'Allanite'
Allanite-(Ce)
Almandine
Amphibole Supergroup
Anatase
Andradite
Anhydrite
Ankerite
Annite
'Anorthoclase'
'Apatite'
Arfvedsonite
Arsenopyrite
Augite
Baddeleyite
Baryte
'Bastnäsite'
'Bastnäsite Group'
Bavenite
Bertrandite
Beryl
var: Aquamarine
'Biotite'
Boulangerite
Brookite
Calaverite
Calcite
var: Manganoan Calcite
Cancrinite
Cassiterite
Catapleiite
Chalcopyrite
Cheralite
'Cheralite-(Ce)'
Chevkinite-(Ce)
'Chlorite Group'
'Columbite'
Columbite-(Fe)
Columbite-(Mn)
'Columbite-Tantalite'
Cookeite
Cordierite
Cryolite
Diopside
Elbaite
Epidote
Euclase
Eudialyte
Eudialyte Group
var: Eucolite

Euxenite-(Y)
Fayalite
Ferberite
'Fergusonite'
Ferro-hornblende
Florencite-(Ce)
Fluorapatite
Fluorite
Galena
'Garnet'
Goethite
Gold
Gorceixite
Grayite
Grossular
Gypsum
Hastingsite
Hedenbergite
Hematite
Hisingerite
'Hornblende'
Hübnerite
Ilmenite
Ixiolite
Jamesonite
Kaolinite
Kentbrooksite
'K Feldspar'
'var: Adularia'
Låvenite
Lepidocrocite
'Leucoxene'
Liandratite
'Limonite'
Magnetite
Malachite
'Manganese Oxides
var: Manganese Dendrites'

'Mica Group'
Microcline
var: Amazonite
Microlite Group
Miserite
Molybdenite
'Monazite'
Monazite-(Ce)
Monazite-(La)
Monazite-(Nd)
'Moonstone'
Muscovite
Natrolite
Nepheline
'Olivine'
Opal
var: Opal-AN
Orthoclase
'Parisite'
'Percivalite'
Perrierite-(Ce)
'Perthite'
Phenakite
Plumbogummite
Polycrase-(Y)
Prosopite
Pseudobrookite
'Psilomelane'
Pyrite
'Pyrochlore'
Pyrochlore Group
var: Bariopyrochlore (of Hogarth 1977)
var: Ceriopyrochlore (of Hogarth 1977) (FRL)
var: Plumbopyrochlore (of Skorobogatova et al.)
'Pyroxene Group'
Pyrrhotite
Quartz
var: Smoky Quartz
'Rhabdophane'
Rhabdophane-(Ce)
Rhabdophane-(La)
Rhabdophane-(Nd)
Riebeckite
Riebeckite Root Name
var: Crocidolite

Romanèchite
Rutile
var: Ilmenorutile
var: Strüverite
Samarskite-(Y)
Sanidine
Schorl
'Serpentine Group'
Siderite
Siderophyllite
Sodalite
Sphalerite
Staurolite
'Stibiconite'
Stilpnomelane
'Synchysite'
'Synchysite Group'
Talc
Tantalite-(Fe)
Tantalite-(Mn)
'Tapiolite'
Tapiolite-(Fe)
Thalénite-(Y)
Thorite
'Thorogummite'
Titanite
Topaz
'Tourmaline'
Uranophane
'Uranpyrochlore (of Hogarth 1977)'
'Uvite'
Wöhlerite
Wollastonite
Xenotime-(Y)
'Zinnwaldite'
Zircon


189 entries listed. 119 valid minerals. 1 (FRL) - first recorded locality of unapproved mineral/variety/etc.

Localities in this Region

USA
USA

The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

LaBerge, G. & P. Myers (1983) Precambrian geology of Marathon County, Wisconsin: Wisconsin Geological and Natural History Survey: Information Circular 46, 88 p. with 2 maps.

Falster, A. (1986), Minerals of the Stettin Pluton, Marathon County, Wisconsin: Rocks and Minerals: 61 (2): 74-78.

Falster, A. (1987), Minerals of the pegmatite bodies in the Wausau Pluton, Marathon County, Wisconsin: Rocks and Minerals: 62 (3): 188-193.

Simmons, W., Webber, K & Buchholz, T. (2000) Pegmatites and pegmatite minerals of the Wausau Complex, Marathon County, Wisconsin: Memorie della Societa di Scienze Naturali e del Museo Civico di Storia di Milano: XXX: 13-28.

Falster, A. U., Simmons, W. B., Webber, K. & Buchholz, T. (1999), The Wausau Syenite complex, Marathon County, Wisconsin: origin, geochemistry and mineralogy of a mid-Proterozoic anorogenic intrusive complex and its pegmatites: The Canadian Mineralogist : 37 (3): 835-836.

External Links

Wisconsin Mineral index - Wisconsin Geological and Natural History Survey http://wgnhs.uwex.edu/wisconsin-geology/minerals-wisconsin/

Mineral and/or Locality  
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