U.S. Department of the Interior

U.S. Geological Survey

Effects of Mining on t

Environment — A Natio

Overview

S.E. Church, T.S. Schmidt, 

C.A. San Juan, and G.S. Plumlee

NRDAR Conference, Phoenix, AZ

April 25, 2007
Two of the most important points of this 

are:

• Knowing the geology of the mine site is 

understanding the environmental impact mining at any given site

• Hydrothermal alteration associated with 

mineral deposit has a major effect on the premining geochemical background as won the postmining environmental impact watershed 
What is a mineral deposit?

An area within the Earth An area within the Earth’s crust wh

s crust wh

geologic processes have concentrate

geologic processes have concentrate

or more mineral commodities or more mineral commodities
What is an ore deposit? Bingham

Bingham

Utah

A mineral deposit in which A mineral deposit in which 

the commodities (i.e., the commodities (i.e., 

metals) are present in metals) are present in 

sufficient concentration sufficient concentration 

(grade) and amount (grade) and amount 

(tonnage) that they can (tonnage) that they can 

(ideally) be extracted (ideally) be extracted 

economically economically
Metallic mineral 

deposits

• Concentrations of metallic 

elements and minerals in the Earth’s crust

• Form by: 

– Crystallization of magmas– Cooling, boiling, mixing of 

hydrothermal fluids in the Earth’s crust 

– Chemical precipitation of 

minerals on the sea floor or in sediment

– Chemical reaction of two or more 

different fluids

– Chemical reaction of a 

hydrothermal fluid with a rock
Mineral deposit models

• Mineral deposits classified by geologic char

Mineral deposits classified by geologic cha

and geologic environment of formation and geologic environment of formation 

• Mineral deposit models developed for more 

Mineral deposit models developed for more 

deposit types deposit types

• Components: Components:

– Descriptive (general geologic characteristics) Descriptive (general geologic characteristics) – Genetic (how they form) Genetic (how they form)– Grade and tonnage Grade and tonnage – Hydrothermal alteration Hydrothermal alteration 
Hydrothermal alteration

• Acid-sulfate alteration• Potassic alteration (ore zone)• Quartz-sericite-pyrite (QSP)• Argillic (clay minerals)• Propylitic

Increasing pyrite content
Geoenvironmental Geoenvironmental mineral deposit mo

mineral deposit mo

• Use geologic characteristics of mineral dep

Use geologic characteristics of mineral dep

– Sulfide mineralogy Sulfide mineralogy– Hydrothermal alteration Hydrothermal alteration– Ore-deposit mineralogy deposit mineralogy

• Time frame of historical mining activity Time frame of historical mining activity

– Metal mobility from mine Metal mobility from mine-waste dumps waste dumps– Water chemistry Water chemistry– Smelter signatures in soils Smelter signatures in soils– Sediment geochemistry in surface streams Sediment geochemistry in surface streams
Take-home message

• A mineral deposit may not be an ore dep

The term “ore” is an economic descripto

• Physical processes of formation of the d

are the primary drivers controlling the imthe mined site on the environment

• Hydrothermal alteration controls the dist

of pyrite in many mineral deposits
Potential environmental and health impact

A complex but predictable function of:• Mineral deposit geology

– Environmental signatures, physical footprint

• The mining and mineral processing methods used 

– Typically mandated by the deposit geology

• Geochemical and biogeochemical processes 

– Bacterial activity can increase reaction rates by a million 

• The effect of climate on rates of weatheringEffective prediction, mitigation, and remediation strat

also dependent upon characteristics of the surrouwatersheds

– Geology, size, topography, ecology– Number and footprint of other environmental stressors
What data are available to ind

the extent of land disturbance throughout the Nation?

• USGS database of historical mines prov

representative look at disturbance by mi
Mines, prospects, and occurrences 

(USGS MAS/MILS data base)
What data are in the USGS MAS/MILS datab

• Four types of data that show the extent of 

disturbance

– Mines

• Active or• Inactive

– These data are current as of the time of data entry

– Prospects—minimal ground disturbance– Occurrences—no ground disturbance
Significant mineral deposits

• Cu, Pb, Zn, Au, Ag (Long et al., 2002) 

– Defined about 1,000 major ore deposits by d

type

– Upper 10 % of producers by commodity (Sin

1995)

• Uranium • Phosphate• Iron• Molybdenum• Mercury
#* Placer gold

b Mercury deposits

!( Carlin gold deposits

Significant gold deposits
Marcopp

Marcopp

Porphyry copper and molybdenum deposit

Porphyry copper and molybdenum deposit

Bingham, Utah Bingham, Utah

Grasberg Grasberg, Indonesia Indonesia
Schematic acid Schematic acid-drainage potential of a porphyry coppe

drainage potential of a porphyry coppe

Modified from Park and Modified from Park and Guilbert Guilbert, 1986

Near-neutral waters, some metals neutral waters, some metals
Development of pit lakes Development of pit lakes

3⁄4 Fracture flow hydrology, pit Fracture flow hydrology, pit wall geology, lake limnology, clima ll geology, lake limnology, climate are key 

te are key 
!( Porphyry deposits

Significant porphyry deposits
Porphyry deposits represent the biggest env

challenge that Federal Land Management Aface in terms of acid mine drainage (AMD)

• Many porphyry deposits are still being mi• Most porphyry deposits occur in arid regio

are on private land

• Most deposits that have been mined out 

continue to be held by mining companies are listed as inactive mines

• In the future these will be the major AMD 

FLMA will face 
Epithermal 

vein and Polymetallic vein deposits
") Epithermal veins

#* Polymetallic veins

Significant vein deposits
4,000

3,000

Elev. (m) Acid sulfate alteration

Quartz-sericitepyrite alteration

Weak propylitic

alteration

Argillic alteration

South Mountain

volcanic dome

3,500
Red Mountains, Silverton, Colo.
Footprint of 

hydrothermal alterationAnimas River watershedstudy areahttp://amli.usgs.gov
Formation of Al sulfate precipitat

Formation of Al sulfate precipitat

Paradise portal, Animas River watershe

Paradise portal, Animas River watershe

• Dilution by fresh ground water triggers A

Dilution by fresh ground water triggers A
VMS deposits

• Form on the 

sea floor

• Very pyritic• Little alteration• Buried by fresh 

volcanic rock or by sediment to be preserved

• Very large acid 

generators
E VMS deposits

Significant volcanogenic massive sulfide 
What controls water chemistry in AMD? 

• The amount of acid-generating minerals

– Pyrite isn’t the only one!

• The amount and type of hydrothermal a• The acid-neutralization potential in the 

watershed

• The amount of water available for dilutio

AMD

• Climate 
Acid-generating minerals generating minerals

PYRITE (FeS PYRITE (FeS2):

• By oxygen: By oxygen:

a) FeS2 + 3.5O2 + H2O Fe2+ + 2SO42- + 2H+

b) Fe2+ + 0.5O2 + H+ (+ bacteria) (+ bacteria) Fe3+ + 0.5H2O

• By ferric iron: By ferric iron:

FeS2 + 14Fe3+ + 8H2O 15Fe2+ + 2SO42- + 

• Bacteria speed up the key acid Bacteria speed up the key acid-d

formation reaction (b) by 1 millio

formation reaction (b) by 1 millio

• Dissolved ferric iron is a corrosiv

Dissolved ferric iron is a corrosiv
Acid-generating minerals generating minerals

Pyrite (FeS Pyrite (FeS2) Marcasite Marcasite (FeS2)

Pyrrhotite Pyrrhotite (Fe1-xS) Arsenopyrite Arsenopyrite (FeAsS)

Enargite Enargite (Cu3AsS4) Tennantite Tennantite (Cu12As4S13)

Realgar Realgar (As2S3) Orpiment ( Orpiment (AsS) 

OthersIf ferric iron is oxidant, above minerals plus: If ferric iron is oxidant, above minerals plus:Chalcopyrite (CuFeS Chalcopyrite (CuFeS2) Covellite Covellite (CuS) Sp

Sp

(ZnS)

Chalcocite Chalcocite (Cu2S) Acanthite Acanthite (Ag2S) Ga

Ga

If metal hydroxides (solid or aq If metal hydroxides (solid or aqueous) form, above mineral

ueous) form, above mineral

Siderite (FeCO Siderite (FeCO3) Rhodochrosite Rhodochrosite (MnCO3)
Comparison of water chemistry from “natural” a
Differences in rate of some types of reactions that influence 
Schwertmannite

Ferrihydr

Jarosite

Go

Precipitation of iron minerals

Pyrite weathering

pH = 2.3 - 2.8

pH = 3 - 5

pH = 4.5+

pH = 7+
Geological and geochemical controls on 

Geological and geochemical controls on 

natural natural

-drainage water compositio

drainage water compositio
Sampling water from the Reynolds adit Sampling water from the Reynolds adit

Seep, 8/95 Seep, 8/95• pH 3.1

• Conductivity 8,900 Conductivity 8,900 uS

• Cu 825 mg/L Cu 825 mg/L

• Fe 2,000 mg/L Fe 2,000 mg/L
...

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F

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0.01

0.1

1

10

100

1,000

10,000

100,000

-1 0 1 2 3 4 5 6 7 8 

Zn + Cu + Cd + Pb + Co + Ni (ppm)

Geologic controls on mine Geologic controls on mine-drainage comp

drainage comp

pH

Increasing pyrite conte

Increasing pyrite conte

decreasing acid bufferi

decreasing acid bufferi

capacity capacity

Increasing Increasing 

sulfide sulfide 

content; content; 

increasing increasing 

exposure exposure 

of sulfides of sulfides 

at ground at ground 

surface surface

Evaporation Evaporation
Colloidal Fe in the stream
Sorption onto Hydrous Iro

0

20406080

100

3 3.5

4 4.5

5 5.5

pH

Percent SorbedPb Cu ZnSO42- C

The effect of iron on trace-element concentrat

modified fr

Preferentially 

removing iron 

from a system 

may result in 

increased 

dissolved 

concentrations of other metals
Low-pH water 

(pH <5) Higher-p

water (pH 

Mixing zone

Iron coating

(pH > 3.5)

Mixing zone, Snake River drainage, Colo.

Example of changes in 

precipitation of colloids as a function of pH in a mixing zone downstream of the confluence of an acidic stream (undisturbed by historical mining) and a neutral stream
Acid-neutralizing minerals neutralizing minerals

• Carbonate minerals and some other minerals (some silicates, 

Carbonate minerals and some other minerals (some silicates

glasses) in mineral deposits, their host rocks, and watershed 

glasses) in mineral deposits, their host rocks, and watershed 

• Can react with and help consume acid generated by sulf

Can react with and help consume acid generated by sul

• Can also generate alkalinity in ground and surface wate

Can also generate alkalinity in ground and surface wate

increasing the waters increasing the waters’ ability to buffer acid ability to buffer acid

Calcite on Calcite on 

pyrite, pyrite, 

Silesia, Silesia, 

Poland

Limestone Limestonehttp://www.sirendesigns.co

m/elora_resources/gallery_1/pages/limestone_cliff_gif.htm
What geochemical data are available 

that would show where potentially toxmine sites might be?

• In the conterminous U.S.

– 330,000 analyzed NURE sediments– 150,000 analyzed USGS sediments

• In Alaska

– 65,000 analyzed NURE sediments– 25,000 analyzed USGS sediments
Abandoned Mines (MAS/MILS)
1 - 3

3 - 5

5 - 7

>10

Hazard quotient Copper – Obs. Conc. / PE

7 - 10
Hazard quotient – Cadmium (Obs. Conc. / PE

1 -

3

3 - 

5

5 - 

7

>10

7 - 10
Hazard quotient – Zinc (Obs. Conc. / PEC 

1 -

3

3 - 

5

5 - 

7

>10

7 - 10
http://mrdata.usgs.gov/website/MRData-US/viewer.htm
Central Colorado Assessment Pro
Central Colorado Assessment Project

• Provide an environmental assessment of th

1/3 of the State of Colorado

• Develop geochemical and biological baselin

– Sampled watersheds underlain by single geolog

provide a geologic signature

– Sampled watersheds underlain by hydrothermal

rock

– Sampled watersheds in which historical mining h

Trichoptera

www.tolweb,org

[Trace Metals]

www.tolweb.org

dmason@zebu.uorgeon.edu

Ephemeroptera

www.to

Plecoptera
0.1

1

10

100

1,000

Sites Ranked [Metals]

EPT richness 

Total metals 
0.1

1

10

100

1,000

Sites Ranked [Metals]

EPT richness 

Dissolved Metals- adjusted for hardness & DO

Total metals 
Chronic Criterion Accumulation Ratio 

Site-specific [gill-metal]

∑ US EPA standard water [gill-metal] 

•New model derived fro

Toxic Unit Model

– BLM derived

(Sprague, 1970; Playle, 2004)
Development of biological baselin

• Develop a model of bioavailability

– Determine that lithologic classes can different

bioavailability

– Validate that model can predict indigenous tax

responses

• Also develop bio-indicator species for assessment p• Infer adverse effect concentrations
Can lithologic classes differenti

bioavailability?

CCAR 

0.01

0.1

1

10

100

Sedimentary

Metamorphic

Igneous

Primary rocktype classifications Geologic 

Cenozoic

Meso/Pal
Can hydrothermal alteration 

differentiate bioavailability?

Presence/absenc

Absent

P

0.01

0.1

1

10

100

Unaffected

Propylitic

Argilic

QSP

Alteration classifications

CCAR 
0.01 0.1 1 1

Arctopsyche grandis

CCAR 

0.01 0.1 1 1

0.00.51.0

0.01 0.1 1 10 100 1,000

CCAR 

Rhithrogena sp.

0.01 0.1 1 10 100

0.00.51.0

Drunella sp.

CCAR 

0.01 0.1

1 1

1

0.00.51.0
0

5

101520253035

CCAR Cat

0.01 0.1 1 

05

101520253035

CCAR Cat

0.01 0.1 1 

Drunella sp.

0

1020304050

0.01 0.1 1 10 100

F = 5.295p = 0.001

*

Rhithrogena sp.

0

1020304050

F = 5.295p = 0.001

*

CCAR Category

02468

CCAR Ca

0.01 0.1 1 

02468

CCAR Ca

0.01 0.1 1 

Arctopsyche grandis
Intolerant taxa richness

(genus) 

02468

101214161820

Y = -3.74X + 9.76R2 = 0.54, p < 0.0001

0.01 0.1 1 10 100 1,000

CC

U

U

Y = R2 = 

0.01 0.1 1 

CCA

Y R

0.01 0.1 1 

CCAR

Taxa richness (genus)

05

1015202530

Y = -5.73X+16.52R2 = 0.54, p < 0.0001

0.01 0.1 1 10 100 1,000

CC

U
Are water-quality criteria protect

• Water Quality Criteria

– Protect 95% of all taxa– Genus-level mean 

responses

• 30% loss in richness• 70% loss in abundance Y = 

R 2 

0.01 0.1 1 10 

CCAR 

EPT abundance

0.1

1

10

100

1000

10000

Y = -4R2= 0.

0.01 0.1 1 10 

CCAR

Taxa richness (genus)

05

1015202530
Appropriate conservative benchmarks a

applicable for all lithologies

CCAR 

0.01

0.1

1

10

100

Sed.

Meta.

Igneous

Primary rock Geologic Age

Cenozoic

Meso/Pale.

Precambrian

P/A of pyrite

A

P

0.01

0.1

1

10

100

Unalt.

Propy.

Argilic

QSP

Alteration

CCAR 

Chron

Chro

Ecolo

Ecol
Summary

• Lithology and hydrothermal alteration co

bioavailability of metals

• Not all BMI endpoints are appropriate• CCAR is more descriptive than CCU• Are Water Quality Criteria protective end• Are remedial actions based on conserva

benchmark concentrations appropriate?
Colloidal Fe in the stream

Natural?