Fugitive Mercury Emissions from Two Gold Mines in Nevada On November 20, 2009, Dr. Chris Eckley, a post doctoral researcher working with Dr. Mae Gustin presented a preview of hi s work and that by a graduate student, Matthieu Miller, on fugitive mercury emi ssions from two gold mines in Nevada (see the attached slides). The research focused on measuring mercury emissions from a variety of surfaces disturbed by mining activities at Newmont’s Twin Creeks Mine northeast of Winnemucca, Nev., and Cortez Pipeline, a Barrick property located south of Battle Mountain, Nev, and used this information to develop an estimate of emissions for the mine surf ace area. Fugitive emissions from waste rock, heap leaches, tailings impoundments, active pit surfaces, stockpiles and reclaimed sites were estimated and comp ared to mercury releases from sites undisturbed by mining. The results showed that mercury emi ssions from mining disturbances are approximately 20 percent of the total mercury emitted at these two gold mines. The study showed heap leaching and tailings impoundments produced the greatest emissions and that current reclamation practices can reduce the current emissions to near natural levels. Importantly, the work showed that the amount of mercury emitted from these types of disturbances can vary significantly among mines, depending primarily on the mercury concentration at the disturbed site, the moisture content of the tailings and whether or not the heaps are actively being leached with cyanide. Because there are a variety of factors (such as mercury concentration, age of the materials, climatic conditions, weather, ore type , ore processing techniques, etc.) that can affect the emission of fugitive mercury from different mining surfaces and the uncertainty associated with each of those factors, this data, developed for these two mines, cannot be extrapolated to come up withemissions estimates for other mines. Additionally since a mine is a dynamic entity with surfaces changing over time, and the emission estimates developed in the UNR study represent the surfaces present atthe two mines s in 2008, the amount of Hgreleased in future years may differ depending on the types and extent of mining related surfaces at each facility. The data contained in the attached power point presentation havenot been peer reviewed.

# Fugitive Mercury Emissions From Nevada, USA Gold Mines Eckley, CS a 

# , Gustin, Ma 

# , Miller, MB a 

# , Marsik, F b

a University of Nevada Reno, Department of Natural Resources and Environmental Science b University of Michigan, Department of Atmospheric, Oceanic and Space Sciences

# Acknowledgements

Note: Information presented has not be subjected to final scientific peer review Nevada’s mining companies Fugitive Mercury Emissions Project Oversight committee 

# Project Participation

# Numerous studies have identified Hg enriched

soils are a source Hg to the air

Transport and Transformation Hg emissions to air
Methyl - Hg 

### Mercury exposure through fish 

# Mercury (Hg) is a pollutant of global concern

# Project Context

~$1,000 oz 

# The modern gold rush

Graphs from Nevada Bureau of Mines and Geology 

### Mineral trends with high gold content are often enriched in Mercury (Hg)

NV Cinnabar (HgS)

### Hg Point Source Emissions 

# Nevada Gold mines contain point sources of Hg emissions:

# 2,000 kg/yr (NDEP 2006/2007)


# Nonpoint source Hg emissions from Nevada Gold mines: ???? kg/yr

# Project Objectives:

2) Quantify natural nonpoint source Hg emissions from 

# adjacent undisturbed areas 1) Quantify nonpoint source Hg emissions from active gold mines

# Introduction to Mine Processes Holes drilled and ore examined for grade and metallurgical properties
Based on gold content trucks deliver the ore to different processing locations 

### Blast rock

Schematic pictures from Nevada Mining Association BrochureSchematic pictures from Nevada Mining Association Brochure 

### Waste Rock/Overburden High grade ore

Gold Collected on Activated Carbon 

### Tailings pond Grinding Mill Carbonaceous Oxide Sulfide Low grade ore 

### Heap Leach Pad

# Two mines chosen for study

Twin Creeks Gold Mine Cortez Gold Mine 0 1,000 m 0 1,500 m

# Two mines chosen for study

Twin Creeks Gold Mine Cortez Gold Mine Old/Reclaimed Tailings Heap Leach

0 1,000 m 0 1,500 m 

### Different materials have different surface areas that change over the life of a mine 

### Waste rock

# Undisturbed Areas: Similar rock types excavated at mines Outcrops

Valley Alluvium 

## Twin Creeks Area Cortez Area
Hills Alluvium

0 3,000 m

# Method to measure emission :

Flux = (C inside

### - C outside 

### *(Q/A) Flux is emission or deposition per unit area per time Units 

## ng (10 - 9

## g) per m 2 

## per hour or ng per m 2 

### per day Tekran Total Gaseous Mercury Analyzer ng per m 3 

### of air Outside air sample line Inside chamber sample line 

# Dynamic Flux Chamber

## 1) Identify important factors controlling flux using laboratory 

# experiments

• 48 tubs — 3 from each surface type • Each tub: 24 hr fluxes twice per season • >400 diel flux measurements • Meteorological data collected on site • Develop algorithms 

### Active Gold Mine UNR Greenhouse 

# Methods: General Research Approach

## 1) Identify important factors controlling flux using laboratory 

# experiments 

# Methods: General Research Approach 2) Measure fluxes at the mines 

# compare with laboratory derived data develop data for surfaces not represented in lab study Winter
Summer Spring
Fall 

### ~ 1 week at each mine each season 24 hours sampled from each surface 

### Day Night

# Methods: General Research Approach

Winter
Summer Spring
Fall 

### ~ 1 week at each mine each season 24 hours sampled from each surface 

### Day Night 

## 2 flux chambers 2 Tekrans 1) Identify important factors controlling flux using laboratory 

# experiments 2) Measure fluxes at the mines 

# compare with laboratory derived data develop data for surfaces not represented in lab study

## 1) Identify important factors controlling flux using laboratory 

# experiments 

# Methods: General Research Approach 3) Estimate emissions for each mine based on current surface areas and environmental conditions over the year of study Cortez Pipeline Geographic Information System (GIS) 

### Twin Creeks 

## 2) Measure fluxes at the mines

## Results: Laboratory Fluxes vary : 

# Daily

## Results: Laboratory Fluxes vary : 

# Daily

Leach (pre - cyanide)Twin Creeks mine (2.7 μg g - 1 ) 

## Seasonally

## Fluxes influenced by: surface type, material Hg content Results: Laboratory

- 1000 9000 19000 29000

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 Hg Flux (ng m - 2 d - 1 )

Tub #

Winter Spring Summer Fall 

### Wet Dry

## Fluxes influenced by: surface type, material Hg content precipitation events—4 -fold emission increase Results: Laboratory

- 1000 9000 19000 29000

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 Hg Flux (ng m - 2 d - 1 )

Tub #

Winter Spring Summer Fall 

### Wet Dry Dry – November Wet— December Dry –January- 1000

9000 19000 29000

0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 Hg Flux (ng m - 2 d - 1 )

Tub #

Winter Spring Summer Fall 

### Daily Hg Flux (between materials) Hourly Hg Flux (individual materials) Parameter T -statistic p -value Median T -statistic Median

p -value Substrate Hg 15.2 <0.001 ----- ----- 

### Substrate moisture 3.4 0.001 ----- ----- Solar radiation 2.2 0.023 8.3 <0.001 Air temperature 3.3 0.001 2.8 <0.001 Relative Humidity 2.5 0.014 - 0.3 <0.001 Wind speed 3.3 0.001 - 0.2 <0.001 

## Use statistical analyses to determine most 

# important variables and develop model equations Results: Laboratory

### Twin Creeks dry tub data Cortez - Pipeline dry tub data 

## Develop equations that allows us to predict flux as a function of material Hg concentration and solar radiation

y = 71x + 568 r2 = 0.71 y = 99x + 1335 r2 = 0.50 y = 507x + 985 r2 = 0.77

0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000

0 20 40 60 80 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

low solar middle solar high solar y = 110x + 373 r2 = 0.25 y = 338x - 132 r2 = 0.66 y = 419x + 143 r2 = 0.60

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0 5 10 15 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

low solar middle solar high solar 

## Results: Laboratory

## Results: Laboratory simulation of surface disturbance Surface disturbance Increases flux 7 -fold Effect of disturbance decreases over time (~ 7 days)

## Field Measurements:

- Characterize Hg concentrations in substrate

- Collect data from field for comparison with laboratory data

- Measure flux from surfaces not represented in laboratory study

Tailings material Reclaimed tailings
Old leach pad 

### Active leach

## Characterization of Hg concentrations in substrate Twin Creeks Gold Mine Cortez - Pipeline Gold Mine Results: Field data

### Spatial Ave Substrate Hg: 5.9 μg/g Spatial Ave Substrate Hg: 1.3 μg/g

0 - 12 12 - 24 24 - 36 36 - 48 48 - 60 60 - 72 72 - 84 84 - 96 96 - 108 108 - 120 

### Solid Hg (μg/g) 

# Twin Creeks Gold Mine Cortez - Pipeline Gold Mine Characterization of Hg concentrations in substrate Results: Surface area/concentration

### Spatial Variability of Hg fluxes 

### Lowest Emissions: • Waste rock materials ( ~10’s to 100’s ng m - 2 

### d - 1 

### ) Highest Emissions: • Active leach pads & tailings 

### (~1,000’s to 100,000’s ng m - 2 

### d - 1 

### ) 

## Results: Surface area/flux Surface Area Cortez Twin Cks

### >80% of field measurements were within the 95% prediction intervals of the laboratory data

y = 507x + 985 r2 = 0.77

0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000

0 20 40 60 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

high solar-- lab high solar--field y = 419x + 143 r2 = 0.60

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0 5 10 15 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

high solar-- lab high solar--field 

## Twin Creeks Gold Mine Cortez - Pipeline Gold Mine

Old leach Tailings 

## Comparison of field data with laboratory derived modely = 507x + 985 r2 = 0.77

0 5000 10000 15000 20000 25000 30000 35000 40000 45000 50000

0 20 40 60 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

high solar-- lab high solar--field y = 419x + 143 r2 = 0.60

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0 5 10 15 Hg Flux (ng m - 2 d - 1 )

Substrate Hg (μg g - 1 )

high solar-- lab high solar--field 

## Twin Creeks Gold Mine Cortez - Pipeline Gold Mine

Old leach Tailings 

## Comparison of field data with laboratory derived model

## Hg fluxes from tailings Heterogeneous Hg content (19 to 177 μg g - 1 

### ), 

### Moisture (0.1% to liquid solution) Flux (889 to 684,000 ng m - 2 

### d - 1 

### ). 

### Magnitude of emissions best correlated with % moisture r 2 

### = 0.55 p=0.001 

# Twin Creeks

## Hg fluxes from substrate actively under leach only obtained at Twin Creeks Typical Cortez leach
Twin Creeks Leach 

## Results: Cyanide Heap Leaching

### Pre CN CN Addition Post CN 

### Pre leach: 2,280 ± 1,470 ng/m 2 

### /d Active leach: 101,300 ± 53,400 

### ng/m 2 

### /d Post leach: 1,750 ± 572 ng/m 2 

### /d Twin Creeks Spring Data 

## Results: Cyanide Heap Leaching

3 μg/g 4 μg/g 5 μg/g

### Daily Emissions increase ~4 -fold from the effect of wetting alone Daily Emissions ~35 -fold higher during leaching than from pre and post leaching A component of Hg emitted during active leaching is from the cyanide solution 

## Results: Cyanide Heap Leaching Mean Hg Content of leach solution: 17 μg/L (Cortez) 

## 470 μg/L (Twin Creeks) Nevada rainwater:0.002 - 0.4 μg/ L (Mercury Deposition Network Data Station: NV02, 2007 data)

## Emissions from capped tailings Twin Creeks (spring, 2008 data)



## Ave flux from tailings: 27,600 ng/m 2

## /d Ave flux from capped tailings: 1,160 ng/m 2

## /d Fluxes may be greatly reduced post - reclamation Results: Material age/reclamation



# Data from 5 year old/inactive leach suggest fluxes decline as materials age

### • 1) Calculate fluxes

– Use substrate Hg concentrations versus solar radiation relationship for dry and wet surfaces 

### Make adjustments based on field data

 Tailings



### – Leach pads during cyanide addition

– Account for surface disturbance

– Account for surface age


### • 3) Scale emissions: Flux (ng/m 2 

### /d) X surface area (m 2

### ) X days
• 4) Sum fluxes from each surface for all days of the year = total emissions
• 5) Sensitivity and Uncertainty analysis performed on the models 

## Annual Emission Estimates

### Total nonpoint source (NPS) emissions kg/yr: 

## Twin Creeks: 105 (range 60 to 121) Cortez- Pipeline: 19 (range 16 to 43) 

## Annual Emission Estimates

% of total mine emissions that are NPS: Twin Creeks: 19% (12 to 21%); Cortez - Pipeline: 17% (15 to 31%) % increase in total mine emissions from NPS: Twin Creeks: 23% (13 to 27%) Cortez - Pipeline: 20% (17 to 46%) Total emissions point and NPS kg/yr: Twin Creeks: 554 (509 to 570); Cortez - Pipeline: 113 (110 - 137) tailings and active heap leach < 15% area at both mines released >75% of Hg waste rock/reclaimed/inactive leach >85% area at both mines released <25% Hg 

### Total point source emissions kg/yr : Twin Creeks: 449 

## Cortez - Pipeline: 94 (Nevada Division of Environmental Protection data)

### Emissions prior to mining kg/yr:

Twin Creeks: 1.5 Cortez: 0.25 

## Annual Emission Estimates Total nonpoint source emissions kg/yr:

Twin Creeks: 105 Cortez- Pipeline: 19
Projected emissions post mine reclamation Twin Creeks: <8 kg/yr Cortez- Pipeline: <3 kg/yr

# Concluding remarks:

• Large differences in emissions between mines
• Emission estimate reflects one stage in the life of a mine

– Emissions will vary depending on activity, age, and reclamation


## • Factors important to consider: mercury concentration/host rock characteristics surface area of mining disturbed materials 

### characteristics of tailings impoundments climatic conditions 

### ore- processing techniques (i.e heap leaching) age of materials and reclamation

# Questions?