Airborne Hyperspectral Mapping over the Dragon Mine, Tintic District, Utah
with the SFSI-2 / CASI system(s)1
José Lim and Gary Borstad (1999)
The Dragon Mine is a kaolinite-halloysite clay deposit located in the historic Main Tintic base metals District in north central Utah. It has the potential to be an acid mine drainage example. It is also a good metals exploration case study. Figures 1 - 3 illustrate the area, with an image-map and two 3D views of the area made from true colour CASI imagery we acquired in September 1999.
Figure 1. An image map of the Tintic-Eureka area of north central Utah, from true colour CASI imagery acquired in September 1999. The Dragon mine is the bright spot in the middle of the image.The large brown area around the mine burned in the weeks prior to our flight. The town of Eureka is at the upper left.
Figure 2. A 3D view of Figure 1, as seen from the south-west.
The Dragon Mine is in the center part of the image.
Figure 3. A 3D view of Figure 1 as seen from the west.
US Highway 6 can be seen running through
town of Eureka at the left side of the image. The grey spots on the north facing valley wall above
the town are the Centennial-Eureka and Snowflake-Eagle mine tailings. The Mammoth mine is
seen on the central slope, and the Dragon and the burned area is at the right.
The deposit was discovered in 1870; initially mined, unsuccessfully, for Au-Ag-Cu-Pb; then for smelter flux iron oxide ores (seen in Figure 4). From 1949-1976, halloysite was extracted for use as a petroleum cracking catalyst. The Dragon is a Halloysite Clay and iron oxide replacement body developed along the Sunbeam-Dragon Fissure Zone, a 150m wide, N-NE trending structure, which lies on the contact between the Silver City Monzonite and the Ajax Dolomite. Alteration minerals include halloysite, kaolinite, alunite, illite, montmorillonite, nontronite; calcite and dolomite, with minor jarosite, pyrite, gypsum, and gibbsite.
Figure 4. A photo of the pitwall of the Dragon showing staining from iron oxides.
The Dragon deposit was emplaced before Tintic District sulfide mineralization and has little sulfides. There are minimal sulfur and potassium sources available for acid generation. It was formed by Contact Metasomatism along the Dragon Fissure where the dolomite host was replaced with low temperature clays by hydrothermal fluids. Massive iron oxides and nontronite occur along the carbonate intrusive contact. The Dragon Fissure is the grey diagonal across the pit face in the photograph.
There is not an acid drainage problem at the dragon. The iron is limonite from oxides, not jarosite (sulfate), which is the acid indicator. Jarosite occurs only locally and is a product of minor disseminated pyrite from post Dragon emplacement. There are very little toxic metals present. The semi-arid climate does not provide sufficient ground water to move metals or toxic materials into the drainages.
Figure 5. A 20m pixel resolution AVIRIS image
(simulating Landsat bands 7, 4, 1) showing the entire Tintic District.
In the AVIRIS image in Figure 5, the pale blue areas highlight alteration at the mines and other clay bearing areas. Vegetation is green and red indicates grasslands, fields and slopes. The district extends from Eureka (E) south. The Dragon (D) is in the south central part and is on a N-NE trend into East Tintic. Note the blue speckles of dumps around the Dragon.
Figure 6. A small portion of the VNIR/SWIR mosaic made with SFSI-2 and
CASI using bands at 1320nm(r), 1755nm(g) and 2176nm(b).
In Figure 6, SFSI-2 and CASI data from two adjacent flight lines have been mapped and mosaiced together to form a seamless image map at 4 m resolution. The data file has 240 spectral bands with 5 nm band centers, producing spectra such as those in Figure 7.
Figure 7. Spectra extracted from the images representing mineral end members found in the SFSI-2 data.
Note that individual trees, small dumps and trails are clearly visible in the 4 m resolution imagery in figures 6 - 10. Figure 8 illustrates the spatial detail available in image data of the mine, while Figure 9 shows the classified distribution of kaolinite and halloysite at the Dragon. The colors represent degrees of "goodness of fit" of the reference spectra (from PIMA ground spectra) and range from blue-white to red to yellow/gold to green. The distribution of alunite in Figure 10 follows the structure and fills it where it is exposed on the face. SFSI-2 was able to discriminate the alunite along the structures in the Dragon Fissure zone.
Figure 8. A weakly enhanced image to show the spatial detail available in the SFSI-2 image of the mine.
Figure 9. Distribution of kaolinite and halloysite in the Dragon mine.
Figure 10. Distribution of alunite in the Dragon mine using ENVI's SAM.
Figure 11.Schematic cross section of the Dragon Mine.
The cross-section cartoon (from Morris) shows the relations between the host rock dolomite, the monzonite intrusive and the Dragon Fissure zone.Note there is more then one structure in the zone. To understand the detail detectable with the SFSI-2 imagery, compare the structures in the pit face in the cross-section cartoon to the alunite image (Figure 10)
[1] This case study was done in cooperation with Phoebe Hauff, Doug Peters, and Bill Peppin.
Phoebe Hauff - Spectral International Inc. P.O. Box 1027, Arvada, CO, 80001 USA
Phone 303 403 8383 Fax 303 403 8385
Douglas C. Peters - Peters Geosciences, Denver, CO
William Peppin - Advanced Software Applications, Reno NV
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