annexc - Newmont Mining Corporation

Annex C3 – Geology and Geochemistry Supplemental Information C3 - 5
analyzed for: 1) mineralogy and whole-rock chemistry, i.e. metals, using semi-quantitative xray
fluorescence, and 2) static acid-base accounting (ABA) parameters, including acid
neutralization potential (ANP), acid generation potential (AGP), and net carbonate value
(NCV).
ABA tests evaluate the potential for rock to release acid and trace metals. Rocks can
contain both sulfide minerals and carbonate minerals that affect release of acid and trace
metals. Sulfide minerals are unstable in the presence of oxygen (air) and weather (oxidize)
to sulfate, which produces acidity. Carbonate minerals can neutralize the acidity produced
by weathering of the sulfide minerals.
AGP represents the potential to produce acidity and is measured by analyzing total sulfur
and residual sulfur after pyrolysis in the laboratory. ANP estimates the rock’s potential to
neutralize acid and is measured by analyzing total carbon and hydrochloric acid insoluble
carbon, i.e. any carbon other than carbonate minerals.
NCV is the sum of ANP plus AGP. It provides an estimate of the net acid-base potential of
the rock. Positive NCV indicates a net neutralizing potential, while negative NCV indicates
a net acid-generating potential. The magnitude of the NCV provides an indication of the
strength of the neutralizing or generating potential. NCV is typically reported as percent
carbon dioxide. The U.S. Bureau of Land Management (US BLM 1996) and The Company
use the following criteria for classifying rock by NCV.
Criteria for NCV Classification
Highly Acidic (HA) NCV < -5 % CO 2
Acidic (A) -5 < NCV < -1 %
Slightly Acidic (SA) -1 < NCV 0.1 or AGP < -0.1)
Inert (I) -0.1< NCV < 0.1 and (ANP < 0.1 and AGP > -0.1)
Slightly Basic (SB) 0.1 < NCV < 1
Basic (B) 1< NCV < 5
Highly Basic (HB) 5 < NCV
(Source: Bucknam 2002)
The U.S. Bureau of Land Management (US BLM 1996) uses net neutralizing potential (NNP),
in units of tons of calcium carbonate per 1,000 tons of waste rock (CaCO 3/1,000 tons), and
ANP:AGP ratios to classify the acid generating potential of rock. If the US BLM NNP
criteria are converted to percent CO 2 (%CO 2) (NNP/22.7 = NCV), then rock with an NCV
less than -0.9 %CO 2 is considered to be acid generating and rock with an NCV greater than
0.9 %CO 2 is classified as non-acid generating. Rock with NCV in the range of -0.9 to 0.9
%CO 2 has an uncertain potential to generate acid. The US BLM criteria applied to the NCV
classification above is roughly as follows: acid generating (HA and A), uncertain (SA, N, I,
SB), and non acid generating (B and HB).
Akyem Gold Mining Project November 2008 FINAL EIS