annexc - Newmont Mining Corporation

Annex C3 – Geology and Geochemistry Supplemental Information C3 - 14
Minor waste-rock types are represented by samples NCV 05 through NCV 12 in Table C3-
5. Based on the NCV results using ANPA analyses, one sample (quartz vein) is classified as
slightly acidic (-1 to -0.1 %CO 2) one sample (graphitic shear breccia) is inert (-0.1 to 0.1
%CO 2), 4 samples (saprolite, greywacke, mafic volcanic, quartz vein) are slightly basic (0.1 to 1
%CO 2), and 6 samples are basic (1-5 %CO 2). The slightly acidic, inert, and slightly basic NCV
classifications (6 samples) indicate an uncertain potential to generate acid, while the basic
classification (6 samples) indicates no potential for acid generation. The volume of minor
waste rock material present within the proposed mine pit is a small portion of the total rock
volume that would be mined so considered as a whole, the ANPA-based NCV data show that
ore and waste rock from the Akyem pit would have little potential to generate acid upon
exposure to atmospheric conditions.
Because the whole-rock chemical data from the 207 Phase 1 samples and the 16 composite
Phase 2 samples contain levels of some trace elements in excess of published estimates of
average crustal abundance for that element (Table C3-6), additional geochemical
characterization was performed on the 16 Phase 2 composite samples to evaluate the
possibility of release of trace metals exceeding water quality standards. While whole-rock
concentrations above those found in average crustal rocks does not guarantee that
constituents will be released to the environment, it raises the possibility that they could be
released in concentrations exceeding water quality standards. The specialized tests performed
included Synthetic Precipitation Leachability Procedure (SPLP), Biological Acid Production
Potential (BAPP), and Peroxide Acid Generation (PAG) analyses.
SPLP testing provides screening-level information about the potential to release metals and
anions when rinsed with rain water. Table C3-7 provides SPLP results, showing metals that
exceed the Ghanaian Drinking Water Company standards in boldface type. Exceedances are
found for the following metals: aluminum (Al), antimony (Sb), arsenic (As), beryllium (Be),
cadmium (Cd), lead (Pb), mercury (Hg), manganese (Mn), molybdenum (Mo), nickel (Ni),
selenium (Se), thallium (Tl). Those trace metals with exceedances in more than two samples
include Al, Sb, and As.
BAPP tests of seven selected samples were performed to determine if bacteria present can
generate enough sulfuric acid from oxidation of sulfides in the sample to maintain acidic
conditions. A final pH less than 3.5 combined with a final PAG pH (discussed below) less than
4.5 indicates a potential for bacteria to maintain acidic conditions, which can potentially
overwhelm the neutralizing capacity of the rock. In addition, BAPP solutions were analyzed
for trace metals to provide information on the potential to release metals under the BAPP
test conditions. Results of BAPP testing (Table C3-8) show that the slightly acid quartz vein
sample (sample NCV PII 14) has the potential for bacteria to sustain acid generation (BAPP
pH = 2.79 and PAG pH = 3.16). However, due to the small amount of waste rock
represented by this rock type, any acid generated would readily be neutralized by the basic
NCV characteristics of the waste rock types present in abundance in the mine pit. A limited
number of BAPP solutions (7) showed exceedances of the Ghanaian Drinking Water
Company standards for Al, Sb, As, Be, boron (B), Cd, chromium (Cr), copper (Cu), iron (Fe),
Pb, Mn, Hg, Ni, Se, and zinc (Zn).
Akyem Gold Mining Project August 2008 DRAFT EIS