REP35589

• Permit No: M1977215
• IBM Index Class Name: Report
• Doc Date: 4/14/1997
• Doc Name: EVALUATION OF UPPER & LOWER TAILINGS PONDS AT BULLDOG MINE
• Media Type: D
• Archive: No

Bul(doq Mine Tailings Pands Evakration
• 5.1.2.3 Thin Section Analysis
Polished thin sections of unconsolidated tailings impregnated with epoxy resin were examined
under microscope using transmitted and reflected light. The purposes of this investigation were
to determine the mineralogy and texture of sulfide grains and to determine if byproducts of active
sulfide oxidation were apparent. Thin sections from four of the boring intervals were
investigated: (1) UP-1 (36.5 to 41.0 ft), (2) UP-2 (11.5 to 16.5 ft), (3) LP-1 (4.5 to 9.5 ft), and (4)
LP-2 (17.0 to 22.0 ft). The corresponding NNP values as determined in ABA testing of these
intervals aze: (1) -30.3 T/kT, (2) + 215 T/kT, (3) + 4.8 T/kT, and (4) -22.3 T/kT. If oxidation of
the pyrite in the tailings were occurring, the secondary products of oxidation should be evident in
the form of iron oxyhydroxide grain coatings.
In general, the framework minerals in all of the thin sections contained greater than 90% quartz
with minor amounts of K-feldspar, bazite, and less than 2% sulfide minerals. Figures S.la -
Figure S.ld, and Figure 5.3 aze photomicrographs ofsulfide-bearing tailings using a combination
of transmitted and reflected light. The sulfides appear as bright grains under reflected light.
• Local pockets of material with as much as I S% to 20% pyrite were observed in boring interval
LP-1 (4.5 ft to 9.5 ft) (Figure S.lc). Reflected light microscopy reveals that the majority of
sulfides in the tailings are pyrite; however, trace amounts of chalcopyrite (CuFeS,) (Figure S.la)
and stibnite (Sb253) (Figure 5.2) were also observed.
The sulfide minerals in all of the thin sections show little to no signs of oxidation. Of all of the
materials investigated, only one pyrite grain showed any signs of oxidation (Figure 5.2).
Unoxidized pyrite grains, which aze adjacent to the oxidized grain in Figure 5.2, indicate that the
oxidation of that grain may have occurred prior to emplacement in the impoundment. The
abundance of fresh sulfide grains in near-surface tailings (such as those shown in Figures 5. ] a
through S.ld) indicate that the rate of sulfide oxidation has been negligible since the
impoundments were closed, and that future acid generation from sulfide oxidation is not likely.
•
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