Page 79 - Geologic Investigations in the Lake Valley Area, Sierra County, New Mexico

of GSTE. Of the six dumps shown in the figure, dump 7 with its enrichment in Zn best fits these criteria. Other dumps with rela tively higher concentrations of total S are 4, 5, and 9. However, these three dumps also have significant carbonate contents to mitigate against the acid-generated leaching of their various enriched trace elements.
A better approach can be used to evaluate mine dumps by combining the highest GSTE scores, the presence of sulfide or carbonate, and solubility data generated from the leaching experiments. This approach has the advantage of using actual solubility information rather than inferred environmental release of GSTE based on bulk concentration in the mine dump solids.
Figure 4 shows these results for the four highest GSTE score samples that also have water leachate data. Of the three mine dumps with relatively similar GSTE scores, high CO2, and low total S (dumps 3, 4, and 8), the only GSTE that have solubility enhancement relative to most other samples are As, Pb, and Sb (dump 4), and Cd (dump 3). Dump 8 has no particular enrich ment of any soluble GSTE. All samples showed no particular enrichment of Ag or Zn, elements whose bulk concentrations in the solid fractions are always significantly enriched. Note that for GSTE with large enrichment in the solid fraction, specifi cally Pb, Sb, and Zn, the leachable amounts, expressed as a frac tion of solid concentration, are all low (fig. 2B). Nonetheless,
Scaled score 30
Scaled score 30
F
F
Dump 4
Scaled score 30
F
Zn ppm 9000 F
70 Sb ppm
Zn ppm 9000
F
F F
F
Scaled score 30
F
F F
Total S, % 0.25
Zn ppm 9000
70 Sb ppm
Zn ppm 9000
Total S, % 0.25
F 20 CO2, %
Total S, % 0.25
20000 Pb ppm
Dump 3
20 CO2, %
Total S, % 0.25
F 20000
Pb ppm
F
F
F
F
F
F
F
70 20 70 F 20
Sb ppm
Zn ppm 9000
F
20000 Pb ppm
Dump 7
Scaled score 30
F
CO2, %
Total S, % 0.25
F 20 CO2, %
Sb ppm
Zn ppm 9000
70 Sb ppm
20000 Pb ppm
Dump 8
Scaled score 30
F
F F F
20000 Pb ppm
Dump 9
CO2, %
Total S, % 0.25
F20 CO2, %
F
F F
F 70F
F
Sb ppm
F
F
20000 Pb ppm
Dump 5
Figure 3. Spider diagrams combining geoenvironmentally significant trace element (GSTE) highest scores, total S as a measure of acid generation potential, CO2 as a measure of carbonate to counteract acid generation, and concentrations of Pb, Sb, and Zn.
Geochemistry of Mine Dump Material from the Lake Valley Mining District 73