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Flambeau

Wisconson, USA

Main commodities: Cu Au Zn
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The Flambeau supergene enriched massive sulphide copper-gold deposit is located adjacent to the town of Ladysmith, in north-western Wisconsin, USA, 250 km north-east of Minneapolis-St. Paul.

The deposit is located within the Palaeoproterozoic (1.88 to 1.86 Ga) Rhinelander-Ladysmith greenstone belt (part of the Pembine-Wausau Subterrane) comprising mafic metavolcanics, gabbroic sills, lesser felsic metavolcanics and some cherty iron formations.   North of this belt is a thick platformal sequence of clastic and chemical metasediments and iron formations.   To the south are complexes of 1.86 Ga metavolcanics and granitoids intruding Archaean gneisses and 1.88 Ga amphibolite facies rocks unconformably overlain by 1.84 Ga felsic metavolcanics.   These latter rocks are intruded by large 1.51 Ga granitoid batholiths.

The Flambeau deposit lies within the Ladysmith felsic centre whose margin is defined to the west and north by granitoid intrusives.   To the east it grades into intermediate tuffs.   The host felsite sequence is up to 3000 m thick and has been isoclinally folded, sheared and structurally repeated.   The deposit is overturned and is in the thick part of the sequence, hosted by an inferred protolithic rhyolite lapilli tuff, now a fragmental quartz-sericite schist.

The immediate mine sequence comprises:
Stratigraphic Footwall
  * quartz-eye schist after rhyolitic-dacitic quartz crystal tuff,
  * actinolite & andalusite-biotite schist after dacitic-andesitic lapilli tuff,
  * actinolite and chlorite phyllite after andesitic tuff,
Ore Horizon
  * feldspar-clay schist after felsic tuff,
  * massive sulphides,
  * metachert,
  * quartz-sericite schist after rhyolitic tuffs & lapilli tuffs,
Stratigraphic Hangingwall
  * sericite-clay schist after felsic tuff,
  * chlorite, spessartite & andalusite-biotite schist after dacitic & andesitic tuffs & lapilli tuffs,
  * actinolite schist after dacitic flows and tuffs,
  * quartz eye schist after dacite quartz crystal tuff & rhyolitic quartz crystal lapilli tuffs,


The orebody is a steeply dipping, near tabular massive sulphide that averages around 15 m in thickness, with a maximum of over 20 m.   It has a strike length of 750 m.   The main massive sulphide contains > 50% sulphide.   At a depth of approximately 180 m it splits into thinner lenses and becomes a semi-massive sulphide with 30 to 50% sulphides.   The primary massive sulphides comprise 60% pyrite, 12% chalcopyrite and 2.5% sphalerite, with minor gold, silver, galena and pyrrhotite.

The deposit is unconformably overlain by 0 to 10 m of Cambrian sandstone and 3 to 12 m of Pleistocene till.   The upper 75 m of the deposit have been subjected to weathering and supergene enrichment, with an upper 5 to 10 m thick gossan zone which yielded 0.115 Mt @ 18 g/t Au.   This was underlain by a 0.3 to 1.5 m thick oxide zone of up to 20% Cu oxides, malachite, etc., and then the main supergene ore comprising 5 to 25 m of chalcocite, passing down to chalcocite-bornite.   This in turn gradesprogressively into a lower 10 to 40 m of bornite-chalcopyrite and then to 3 to 80 m of chalcopyrite-bornite-chalcocite, before passing into the primary, un-enriched massive sulphide.

The mine exploited approximately 1.71 Mt @ 10.3% Cu, 3.5 g/t Au, 56 g/t Ag of gossan and supergene mineralisation.

For more detail see the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1996.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
   Selected References:
DeMatties T A  1996 - A geologic framework for early Proterozoic volcanogenic massive sulfide deposits in Wisconsin: an exploration model: in LaBerge G L (Ed.) 1996 Volcanogenic massive sulfide deposits of northern Wisconsin: a commemorative volume Institute on Lake Superior Geology Proceedings, 42nd Annual Meeting, Cable, WI   v42, part 2 pp 31-65
DeMatties T A  1994 - Early Proterozoic volcanogenic massive Sulfide deposits in Wisconsin: an overview: in    Econ. Geol.   v 89 pp 1122-1151
May E R, Dinkowitz S R  1996 - An overview of the Flambeau supergene enriched massive sulfide deposit: Geology and mineralogy, Rusk County, Wisconsin: in LaBerge G L 1996 Volcanogenic Massive Sulfide Deposits of Northern Wisconsin: A Commemorative Volume Institute of Lake Superior Geology, Proceedings   v42 Part 2 pp 67-93


Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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