Ishpeming Greenstone Belt - Ropes

Michigan, USA

Main commodities: Au
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The Ishpeming Greenstone Belt is located just to the south of Lake Superior in northern Michigan, USA and contains the only significant Archaean greenstone hosted gold deposit in the US (in 1008), the Ropes MIne.

The greenstone belt comprises 13 000 m of mafic and felsic rocks dated at 2700 Ma.   Granitoids intruded the greenstones just prior to, duting and after intense late Archaean deformation.   The greenstone belt is just north of the Great Lakes tectonic zone which contains rocks as old as 3636 Ma and is on the southern limit of the Superior Province Archaean craton.

Both gold and silver-base metal bearing veins are known within the greenstone belt, controlled by faults or shear zones.   Silver-base metal veins are usually accompanied by quartz and carbonate.   At the Ropes mine gold is associated withquartz and pyrite within veins hosted by a shear zone, with accessory chalcopyrite, galena, sphalerite, tetrahedrite, pyrargyrite and freibergite.   These veins have been deformed.

The Ropes mine has produced a cumulative 10.5 tonnes of gold between 1882 and 1897 and from 1986 to 1989.

For detail, consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1997.    
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:
Bornhorst T J, Thorpe R I, Johnson R C  1998 - Lead isotope study of veins in the Archean Ishpeming Greenstone Belt, Michigan: in    Econ. Geol.   v93 pp 102-107

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at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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