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GEM SERVICES <br /> Dawson Project—Tailings Characterization Page 14 <br /> For this study,the typical crustal abundance of elements in granite was used as a basis of <br /> comparison(Price, 1997). The following elements were found to be significantly enriched: <br /> • Tailings: gold,bismuth, chromium and selenium <br /> • Development rock: chromium, selenium (one sample) <br /> Short term leach(shake flask extraction)tests were conducted on all development rock samples to <br /> assess whether soluble metal release is associated with these enrichments. Tailings filtrate was <br /> analyzed to assess the extent of soluble metal release associated with tailings. <br /> 3.1.4 Short Term Metal Release Potential <br /> Results of the shake flask extraction tests on development rock are presented in Table 8. While <br /> there are no regulatory criteria against which test results can be directly compared,the criteria for <br /> the Toxic Characteristic Leach Procedure(TCLP)(State of Colorado, 2020)and the effluent <br /> limitations for mine drainage and beneficiation mill discharges(EPA, 2021)are also included in <br /> Table 8 to provide context for the leach results. <br /> As discussed in Section 2.1 above,the Shake Flask Extraction(SFE)procedure is a more <br /> conservative approach compared to the Synthetic Precipitation Leaching Procedure(SPLP). The <br /> SFE is completed at a 1 to 3 solids to water ratio in a rotator operating for 24 hours, compared to <br /> the SPLP which is completed at a 1 to 20 solids to water ratio for 18 hours. The SFE tests were <br /> completed using de-ionized water at pH 5.51, similar to the pH of extraction water specified in <br /> the SPLP for materials west of the Mississippi River. In effect, metal concentrations will be <br /> higher in SFE results compared to SPLP test results due to lower dilution. <br /> Parameter concentrations in all samples were less than the TCLP criteria and effluent discharge <br /> limitations. All samples were neutral to slightly alkaline pH and within the pH range for effluent <br /> discharge. No chromium or bismuth was released, although these elements were identified as <br /> being enriched in the solid phase, as discussed above in Section 3.1.3. Selenium was present in <br /> the tailings samples only, at 0.005 and 0.0032 mg/L. In general,heavy metal concentrations are <br /> low(near the analytical detection limit)or were not detected. <br /> Short term metal release from tailings will be dominated by the quality of the filtrate remaining in <br /> the tailings filter cake. Filtrate from the metallurgical study that produced the tailings samples <br /> were analyzed by ICP-MS. The results are presented in Table 9. <br /> DDS/dds Zephyr Dawson Tallings_Characterizatlon_Final Report,Feb.3,22,1:18 PM Feb 2022 <br />