St. Catharines 2004
Technical Program

SS19:  Molecules to Planets: Infrared spectroscopy in geochemistry, exploration geochemistry and remote sensing 
Organizers / Organisateurs:  Penny King, Mike Ramsay, Gregg Swayze
Room / Salle:  AS 201

Date:  05/12/2004
Time:  10:40 AM
Presenter:  Vicki L. Thomson

Integrating hyperspectral imagery and aeromagnetics to develop a 3D geologic model of the Cuprite Mining District, Nevada

Thomson, V., and Morris, W.A. Applied Geophysics and Earth Observation Group, McMaster University, 1280 Main St. W, Hamilton, ON, L8S 4K1,

The Cuprite Mining District, Nevada is a geologic province consisting of two acid-sulfate hydrothermal alteration centers.  Previous studies have attempted to understand the structural and hydrothermal history of the area using remote sensing techniques.  Remote sensing techniques however, provide only surface information.  Subsurface information is needed to determine the geologic structure.  This study focuses on two aspects; using aeromagnetic data to determine whether the structural model is consistent with that determined by previous research, and developing a 3D geologic model by integrating surface information derived from hyperspectral imagery with sub-surface information derived from the aeromagnetic data.

Two aeromagnetic surveys were acquired over Cuprite.  A high-resolution draped aeromagnetic survey over the eastern center and a low-resolution barometric survey over both centers.  Both data sets were processed and compared with mineralogy maps derived from hyperspectral imagery.  The results show that the eastern center is non-magnetic, while the western center is magnetic.  These centers are expected to be non-magnetic since magnetite, the primary magnetic mineral in volcanic rocks, is often destroyed during hydrothermal alteration.  Examination of the mineral maps derived from the hyperspectral imagery show that the western center contains abundant jarosite while the eastern center contains only minor amounts.  Jarosite is formed by the oxidation of pyrite.  Since pyrite is commonly associated with magnetite, magnetite may be producing the magnetic anomaly associated with the western center.  This observation supports previous research suggesting different levels of alteration for the two centers.  The western hydrothermal center was formed from a deep conduit situated directly below and the eastern center was formed from an offshoot of that same conduit.

3D inversion of the magnetic data was used to model the subsurface geology.  The inversion, constrained by the cross-sectional history results from previous research, also suggests that a source body is located beneath the western center.  Detailed interpretation of the western center is limited by the regional scale aeromagnetic survey.  The high-resolution aeromagnetic data help constrain the extent of the alteration zone in the eastern center but do not confirm the degree of alteration.  Individual geologic units are not well constrained due to a lack of magnetic susceptibility measurements, however zones of intense alteration are relatively well defined.  Overall, the aeromagnetic data show consistencies with the model proposed in literature.  A generalized 3D geologic model is possible by integrating hyperspectral and aeromagnetics but additional constraints are needed to improve the accuracy of the model.