Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The Ropes deposit is in the Late Archean Marquette greenstone belt in Michigan's Upper Peninsula, near a northeast striking transition between basalt flows and dacite tuffs, along which serpentinitic peridotite is emplaced. A tabular trend of quartz-sericite-chlorite rock, which is altered dacite tuff, strikes east northeast from this transition and hosts ore. Carbonate-quartz-chlorite rock, which is sheared and altered peridotite, immediately bounds the quartz-sericite-chlorite rock. This is bound on north and south by carbonate-talc rock, then outward by serpentinitic peridotite.;The deposit is 2.8 million tonnes with 3.7 g/tonne Au; near vertical, 335 m in strike, 600 m down dip, and 12 m average thickness. 95% of the ore is characterized by dispersed sub 100 micron pyrite, with micron gold included and attached, in quartz-sericite-chlorite rock. Ore is zoned longitudinally into three subtypes with differing quartz, sericite, chlorite and pyrite proportions. Silver is with tetrahedrite, galena and electrum. Au/Ag is 0.65. 5% of ore is layered auriferous quartz veins with tetrahedrite, at the south side of the deposit.;The deposit is in a 080{dollar}\sp\circ{dollar} striking dilational bend in a nearly vertical, north side down, oblique dextral, brittle-ductile shear zone which strikes 070{dollar}\sp\circ{dollar} overall. Shear was along a line plunging 60{dollar}\sp\circ{dollar} east, indicated by oblique shear quartz veins and zones of gold concentration with dispersed pyrite which are oriented in right stepping en echelon low angle sigmoidal fashion, and by S-C kinematic indicators. Sericite, chlorite and locally auriferous pyrite along schistosity indicate hydrothermal alteration and gold deposition were contemporaneous with simple shear deformation. Contacts of quartz-sericite-chlorite rock with bounding rocks were weaknesses which facilitated shear. Quartz-sericite-chlorite rock which hosts ore dips less steeply near surface, and narrows up dip and eastward: this may have focussed ascending hydrothermal fluids. Carbonatization of serpentinitic peridotite, and sericite alteration of dacite tuff were sinks for CO{dollar}\sb2{dollar} and K. Simple mineral assemblages and limited compositional ranges of rock forming minerals suggest homogenization by pervasive fluid flow promoted by the dilational characteristics of the shear zone.



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.