Concentric Zones of Hydrothermal Alteration at Thor
Image Showing Some of the Concentric Alteration Zones Around the I-1 Intrusive at Thor. The most Distal Alteration is the South and North Tusks, where organic carbon-bearing sediments have been heated and now contain inorganic carbon (graphite). The Intermediate Alteration Zone is Characterized by a Lack of Graphite, and has Pervasive Quartz and Carbonate Alteration.
Concentric Alteration Zones at Thor
As Thor is cored by a central, deep underlying intrusive body, the the 'country' rocks show alteration effects (zonation) related to the large intrusive body. These are changes in mineralogy and textures of the host rocks that have been altered due to contact metasomatism.
Granites, or other intrusive bodies are very hot and profoundly transform the host rocks that they have intruded. Frequently this alteration can be measured or mapped, and the Expert Geophysics MT survey outlined a very large, conductive alteration shell that surrounds I-1.
The I-1 Intrusive Body cores the entire system, and it can be inferred that it is the heat source for the wide-ranging alteration effects outlined using the airborne geophysics. The Thor epithermal deposit is also centered in the middle of the alteration shells, but is located at least 500m and to the north of the I-1 Intrusive.