Estimated Emissions of HCN from 

Gold Mine Facilities in the U.S.

Metals and Minerals Group

Sector Policies and Programs Division

Office of Air Quality Planning and Standards

U.S. Environmental Protection Agency

Research Triangle Park, NC

 Final Draft

December 2010
Methods and Approach:

In year 2009 extensive emissions testing of hydrogen cyanide (HCN) was conducted at 

the three largest gold mine facilities in Nevada to gather data to be used to estimate emissions of 

hydrogen cyanide from these facilities. The main approach and method used was the application 

of the flux box chamber. The specific methods are described in the document titled “Quality 

Assurance Project Plan (QAPP), Comprehensive Air Emissions Testing for Hydrogen Cyanide at 

Three Nevada Gold Mine Sites Using the USEPA Surface Isolation Flux Chamber Technology”,

by Mr. Tom Card and Dr. C. E. Schmidt, October 7, 2009, which is available in the docket 

(Document number: EPA-HQ-OAR-2010-0239-0101.pdf). The comprehensive results of the 

testing completed for these 3 facilities are described in detail in the “Evaluation of Air Emissions 

of Hydrogen Cyanide from Fugitive Sources at Nevada Gold Mines Using the USEPA Surface 

Isolation Flux Chamber Technology: Cortez, Gold Quarry & Round Mountain Mines”, by Dr. 

C.E. Schmidt and Mr. Tom Card. This document is also available in the docket (Document 

number: EPA-HQ-OAR-2010-0239-0163.pdf).

Estimating HCN Emissions for the Three Largest Facilities: 

As described in the two documents cited above, fugitive emissions of HCN were 

estimated at the three largest facilities based on the test data gathered and application of various 

mathematical and scientific equations. Emissions estimates were also obtained for other 

facilities in the U.S., as discussed below. However, no testing of the fugitive emissions of HCN 

were conducted at those other facilities. The estimates of fugitive emissions for those other 

facilities were mainly based on application of emissions factors and various calculations. 

Therefore, the results for those other facilities are less reliable, and are presented separately 

below.

The specific calculations and emissions estimates for Cortez, Gold Quarry, and Round 

Mountain are presented on pages 16-18 (and on other pages) of the document mentioned above 

(EPA-HQ-OAR-2010-0239-0163.pdf). 

Correction Factors for Surface Area and Windspeed:

With regard to the mathematical and scientific equations (described in the two documents 

cited above), which were applied to estimate the emissions for the three largest facilities (Cortez, 

Gold Quarry, and Round Mountain), those equations and calculations include the use of 

correction factors for wind speed and large surface areas. The documents cited above explain the 

rationale for applying these factors and what they adjust for. 

However, there has been some debate among scientists as to whether and how the 

correction factors for surface area and wind should be applied, and for which surface areas they 

should be applied. If these correction factors are not used, then the estimated emissions for these 

types of sources are somewhat higher (e.g., about 40 – 60% higher) than the estimates derived 

when applying the correction factors. Since there has been some scientific debate about the 

appropriateness of using these correction factors, we decided to calculate a range for these 

emissions for the three largest sources, to ensure that we included high-end conservative 
estimates. Therefore, we recalculated the emissions estimates for those 3 facilities using the 

same equations, but without applying the correction factors. This resulted in conservative highend estimates of the emissions from the three facilities. The estimates of fugitive emissions for 

the 3 facilities are shown in table 1 below. The calculations to adjust for the correction factors 

are shown in Attachment #1. 

Stack emissions testing for HCN was also completed in 2009 for these 3 facilities. 

Estimates of the emissions based on those results are shown in Table 2. The data used to derive 

these estimates are available in the docket.

Table 1. Estimates of the Fugitive Emissions of HCN for the Three Large Gold 

Mines Facilities for year 2009 at which flux chamber testing was conducted

Facility Initial estimate of emissions, 

with use of Correction 

Factors (in pounds per year)

Conservative High-end estimate of 

emissions (in pounds per year), with 

no correction factors applied for 

surface area or wind applied) 

Cortez 8983 14996

Gold Quarry 8739 15109

Round Mountain 7380 12246

Table 2. Estimated Emissions of HCN from the Stacks (point sources)

Mine Facility total (lb/hr)

Facility total 

(pounds/yr)

Facility total 

(ton/yr)

Cortez 0.0009 7.9 0.0039

Round Mountain 0.008 69.4 0.035

Gold Quarry 0.10 885.6 0.44

Table 3. Estimates of the Total Potential Emissions for HCN from Three Large 

Gold Mines Facilities: stack emissions plus fugitive emissions for 2009 (in 

pounds per year)

Facility Initial estimate Conservative High-end estimate

Cortez 8991 15004

Gold Quarry 9625 15995

Round Mountain 7380 12246
Conclusions from the Results of Testing at the 3 Largest Facilities, and

Estimates of the Potential to Emit for these Sources:

As shown above, the Initial estimates for the three largest facilities, resulted in an 

estimate of 9,625 pounds per year (or about 5 tons per year) of HCN emissions for the largest 

source (i.e., Gold Quarry). Then, based the second set of calculations (i.e., without applying the 

correction factors), we derive a conservative high-end estimate of emissions for this same facility 

(Gold Quarry) of 15,995 pounds per year (about 8 tons). Based on these results, we estimate the 

largest emitting facility emits between 5 to 8 tons per year of cyanide. With regard to estimating 

potential emissions, based on our analyses and research of the industry, it is our understanding 

that these facilities operate continuous all year (24 hours per day, 365 days per year), or very 

close to continuous all year, and operate at full current capacity, or very close to full current 

capacity. Moreover, the calculations used to derive these estimates were derived based on such 

continuous operations at full current capacity. Therefore, the emissions estimates shown in 

Table 3 are estimates of potential emissions. Nevertheless, to ensure we include a conservative 

upper-end of the potential emissions from these facilities, we assume that they could possibly 

operate at about 10% higher production. Therefore, to calculate such a high-end estimate, we 

assume that potential emissions from the largest facility could possibly be about 10% higher, 

which results in an estimate of potential emissions of about 9 tons per year of HCN emissions. 

Thus, we estimate that the potential emissions of HCN from the largest facility is between 5 to 9 

tons. Moreover, we estimate that the other 2 large facilities mentioned above (Cortez and Round 

Mountain) have potential emissions less than 9 tons per year. 

 

Emissions of HCN from other gold mining operation facilities:

Emissions estimates were obtained for several other facilities in the U.S. However, no 

testing of the fugitive emissions was conducted at those other facilities. The estimates for those 

other facilities were based on application of emissions factors and various calculations. 

Therefore, the results for those other facilities are less reliable. Nevertheless, we present 

emissions estimates for two other large facilities (Newmont Twin Creeks and Barrick Goldstrike) 

in this document, which we believe are the 2 next largest sources after the 3 facilities described 

above. The emissions estimates for Twin Creeks and Goldstrike are available as separate 

documents in the docket. We also assessed information on estimated emissions for other 

facilities in the U.S., from various data sources including the Toxics Release Inventory (TRI). 

All those other emissions estimates are considerably less than 9 tons. We believe that the five 

facilities described in this document are the largest gold mine ore processing and production 

facilities in the U.S. Below we present the estimates of HCN emissions for Twin Creeks and 

Goldstrike. 
Table 4. Estimates of the Emissions (in pounds per year) of HCN from Twin 

Creeks and Goldstrike for 2009

Facility Estimate of Fugitive 

Emissions of HCN

(in pounds per year)

Estimate of 

Emissions of HCN 

from Stacks (point 

sources) 

Estimate of Total 

Emissions of HCN 

(in pounds per 

year)

Twin Creeks 10270 2899 13169

Goldstrike 5925 38 5963

Estimate of Potential Emissions for Twin Creeks and Goldstrike:

With regard to estimating the potential emissions, similar to the facilities described 

above, it is our understanding that these facilities operate continuous all year (24 hours per day, 

365 days per year), or very close to continuous all year, and operate at full current capacity, or 

very close to full current capacity. Moreover, the calculations used to derive these estimates 

were derived based on such continuous operations at full current capacity. Therefore, we believe 

the estimates shown in Table 4 are estimates of potential emissions. The data used to estimate 

the stack emissions for these facilities are also available in the docket. 

Overall Conclusion of all the Analyses Above:

We estimate that the potential emissions of HCN for the largest gold mine facility are 

between 5 to 9 tons per year, and we estimate that all other facilities emit less than this level.
 ATTACHMENT #1

Estimated Emissions (in pounds per year) for Three Large Gold Mine Facilities without using Correction Factors for Surface Area and Wind Speed (Draft - March 2010) 

Round Mountain HCN 

Emissions Estimate w/ 

Fa Fw 

Inverse of 

the Fa & 

Fw

Round Mountain HCN 

Emissions Estimate 

w/out Fa Fw 

Gold Quarry HCN 

Emissions Estimate w/ 

Fa Fw 

Inverse of 

the Fa & 

Fw

Gold Quarry HCN 

Emissions Estimate 

w/out Fa Fw 

Cortez HCN 

Emissions Estimate 

w/ Fa Fw 

Inverse of 

the Fa & 

Fw

Cortez HCN 

Emissions Estimate 

w/out Fa Fw 

11.90 1.92 22.88 898.10 2.13 1910.85 1427.90 2.13 3038.09

799.80 1.92 1538.08 170.80 2.13 363.40 71.50 2.13 152.13

1.10 1.92 2.11 307.20 1.00 307.20 281.40 1.00 281.40

0.10 1.00 0.10 220.80 1.00 220.80 2.90 2.13 6.17

569.50 1.00 569.50 138.50 2.13 294.68 2.70 2.13 5.74

0.00 1.00 0.00 19.80 2.13 42.13 1.50 2.13 3.19

1.00 0.00 146.10 2.13 310.85 1182.40 2.13 2518.51

1.00 0.00 1029.60 2.13 2190.64 313.80 2.13 668.39

127.70 2.04 260.61 197.80 2.13 420.85 966.50 1.00 966.50

1326.20 2.04 2706.53 349.80 1.00 349.80 2309.70 2.27 5249.32

0.30 2.04 0.61 257.10 1.00 257.10 444.90 2.27

0.10 1 0.10 174.00 2.13 370.21 634.50 1.00 634.50

0.10 2.04 0.20 169.20 2.13 360.00 1.90 2.27 4.31

0.10 1 0.10 0.30 1.49 0.45 0.70 2.27 1.59

2.00 1.00 2.00 3.90 1.49 5.82 0.10 2.27 0.23

130.60 2.04 266.53 393.30 1.64 644.75 5.20 1.39 7.22

1356.20 2.04 2767.76 31.60 1.43 45.14 2.10 1.32 2.76

118.10 1.85 218.70 19.90 1.39 27.64 5.90 0.76 4.48

460.90 1.85 853.52 1.80 1.61 2.90 29.00 1.45 42.03

36.00 1.00 36.00 0.80 1.54 1.23 21.80 1.43 31.14

36.70 1.85 67.96 0.60 1.52 0.91 21.80 1.43 31.14

12.00 1.10 13.19 428.50 1.64 702.46 21.80 1.43 31.14

1.00 0.00 13.30 1.33 17.73 21.80 1.43 31.14

124.60 1.18 146.59 1.10 1.59 1.75 26.90 1.43 38.47

124.60 1.18 146.59 0.50 1.52 0.76 26.90 1.43 38.47

124.60 1.18 146.59 0.40 1.49 0.60 26.90 1.43 38.47

124.60 1.18 146.59 7.90 1.79 14.11 26.90 1.43 38.47

124.60 1.18 146.59 12.20 1.79 21.79 22.90 1.45 33.19

124.60 1.18 146.59 328.50 2.44 801.22 22.90 1.45 33.21

124.60 1.18 146.59 1393.40 2.44 3398.54 6.20 1.23 7.65

124.60 1.18 146.59 907.00 1.00 907.00 6.20 1.23 7.63

124.60 1.18 146.59 548.00 1.00 548.00 6.20 1.23 7.63

0.20 1.27 0.25 374.70 1.00 374.70 6.20 1.23 7.63

1.80 1.27 2.29 191.40 1.00 191.40 6.20 1.23 7.63

7.50 1.27 9.53 1.50 1.00 1.50 820.90 1.00 820.90

32.50 1.86 60.58 0.00 179.40 1.00 179.40

142.70 1.86 265.42 0.00 26.20 1.00 26.20

207.20 1.86 385.39 0.00 0.00

0.00 0.00 0.00

0.00 0.00 0.00

789.00 1.00 789.00 0.00 0.00

87.90 1.00 87.90 0.00 0.00

TOTAL 7379.60 12246.14 8739.40 15108.91 8982.70 14996.06