Polaris is a late Devonian Mississippi Valley-type Zn-Pb deposit hosted by late Ordovician Thumb Mountain dolomitized carbonates rich in macro-and microfossils. Microfossils such as scolecodonts, chitinozoans, graptolites and hydrozoans exhibit anomalous reflectance values in oil (%Ro) which decrease with depth through the 150m mineralized stratigraphy, in contrast to the expected increasing reflectance with depth. This phenomenon is tentatively attributed to hydrogenation of microfossils by hydrogen evolved from organic material during the ore deposition process. Reflectances of 1.3%Ro in rocks above the zone of anomalous decreasing reflectance are consistent with observed oil generation and fluid inclusion temperatures of 105^oC, but exceed values expected from maximum estimated burial temperatures of 60^oC.

            Clay minerals exhibit a zonal pattern around and above the orebody.  Conversion of sedimentary illites to coarse kaolinite in and around ore was probably driven by acid generation during sulfide precipitation.  Illitization of pre-existing sedimentary diagenetic clays above the ore is likely related to the influx of potassium in the highly saline evaporative brines identified in fluid inclusions.

Clay mineral zones and organic matter alteration patterns are both potentially useful exploration tools when integrated with available geological data.