42
o
NAG effluent: Wyoming groundwater standards (Class 1 Domestic) exceeded for
manganese (one sample)
Breccia (six samples):
o
SPLP effluent: All water quality standards met
o
NAG effluent: Wyoming groundwater standards (Class 1 Domestic) exceeded for
manganese (two samples)
The short-term leach tests clearly suggest that there are three constituents of interest (COIs) for
effluent associated with the Bull Hill Resource Area: arsenic, iron, and manganese. SPLP tests
can be considered a ‘first flush’ of soluble surface material (oxidation products, salts, and
sorbates) similar to what waste material might encounter during a major storm event after a dry
spell. NAG tests can provide a ‘worst case’ water quality estimate for waste rock samples with
significant sulfides, given that the procedure oxidizes all sulfide minerals resulting in the release
of associated chalcophile metals. However, the waste rock samples have little sulfide, and it is
likely that the iron and manganese exceedances (also observed in the less conservative SPLP
tests) are simply rinsing of surface products that reflect non-sulfide weathering processes. It is
not known from what source or by what mechanism arsenic is released; however, results from
further planned static and kinetic tests will assist with identifying a source term, release rates,
and predicted concentrations. Such information is required in order to plan proper prevention
and mitigation strategies.
Additional static testing, including ABA, compositional, and short-term leach testing is currently
being conducted for the following reasons:
To better represent the expected lithology of the future waste pile based on new mine
plans and better sample availability. The improved sample selection includes 11
lithologies from three oxide zones, with both waste and low-grade ore represented.
To increase testing suite by including additional analyses such as X-Ray Diffraction
(XRD) and thin section petrography, which will lead to a better understanding of water-
rock interactions.
The behavior of low-grade ore separate from waste material is being evaluated.
Screen reject material is being sampled and characterized.
Initial results suggest the following:
NPR values (calculated using sulfide sulfur) range from 0.2 to 851 TCaCO
3
/kT. Six
samples (8%) are PAG, nine samples (13%) are Uncertain and 56 samples (79%) are
NPAG.
NNP values range from -17.2 to 272.7 TCaCO
3
/kT. Zero samples (0%) are PAG, 60
samples (84%) are Uncertain and 11 samples (15%) are NPAG.
Paste pH values range from 6.6 to 8.8.
The overall indication from the above results is that samples have low AGP and low to moderate
ANP. The paste pH values reinforce the initial observation that no samples are currently acid
generating. The samples with high ANP and NNP are primarily those taken from the deeper
Oxide-Calcite and Transitional oxide zones which have undergone less carbonate leaching.
Lithologies that have the highest likelihood to contain PAG material are oxide zone heterolithic
breccias, phonolites, and trachytes. This appears to simply be a function of the fact that these
are the three most common lithologies in the waste pile (comprising 24, 22 and 28% of the total
