Final supplemental environmental impact statement, Golden Sunlight Mine pit reclamation

2007·1.6 MB·English

by  United States.Bureau of Land Management.Butte District

Ghapter 3
Affected Environment

3A INTRODUCTION.

22 GEOLOGY AND GEOTECHNICAL
a1 Geology

$22. Geoshileal
38 WATER RESOURCES AND GEOCHEMISTRY

38.1 Hydiostsierspiy
322 Petantiomatne Sufaoe h he Tarte ato ay
28.2 Groundwater Quay -
354 Seeps and Sprinss

235 | Grourdwatr ibaa Saat Waste RaCk Cum CoWae
8 Groundwater nine Ft Aree...
337 Groudwalar Haw Palle

3.4 SOILS AND RECLAMATION
25 WILDLIFE

rer

3.6 CULTURAL RESOURCES

3.7 SOCIOECONOMIG CONDITIONS
244 Employment a

B72 larlownue

28 LAND USE AND AGCESS
39 AESTHETIC RESOURCES,
340 SAFETY,
Chapter 8 Affected Eovironmvant

Chapter 3

Affectad Environment

34 INTRODUCTION

The Affected Environment was described in the 1997 Draft EIS. Chaptar IIL This
chapter updates the existing resource conditions at or ngar GSM that would ke atfected
by the pit rectamalion atismatives, Resources that would rot be affected by the
alternatives cvaluated are not discussed ir detail These resourous are vege-acion,
aquatics, fisheries, noise, and air quality,

a2 GEOLOGY AND GEOTECHNICAL

Yhe 1997 Draft EIS, Section IIA2, ineluced a delalled discussion of the regioval and
local geology of the mine site, as Well as geotechnical aspacts of black movement vathin
the Tertiary and Quaternary sediments esat of the pit. ‘Tho SEIS includes a short
‘summary of regional geology, focusing oF the geology of the pit area snd portions of the
East Waste Rock Dump Gemplex overlying Ratllesimake Gulch, This provides a basis
for understanding the geological influence on potential flaw paths of eantaminated
groundwater from these fevilties. The geotechnical portion of the SEIS updates fo7g-
tem pit highwall stabilty analyses,

What has changed in Chapter 3 since the DSEIS?

(Chapter 3 describes the afecid area araxnd GSM, Based on adsionel ¢@'a 2nd pec

<atnmenis, ch felelng evanges have been mack:

Tho GSM 2004 Anca Report as used ta upeace al res, Tae GSM 2006 Annual
FRepartwse Load o updele sara auesyy nunae's

The net inflow rata was cbuned fom 16 gp ls bsliaen 28 ard 27 gpm based on tne
Updated water balance “othe No Acton ARematve {Na P Fond alerts

‘The lafenr Rivas luvin wae desuloud in rune dell

3 Infomation an the 2984 earthquske a its effete on the area

5 Adahions!tesks completed tu pei chia infatr abon ti

1” Rasotess and Geochamisty Were is

> Aadeitione Ffermation on springs waa provided,

> Tatie 0-1 rse pti’ lo nce Sunlight and Ariose Valley spsngs infometion,

4 Irfomaton on te erouaduace dae cn Ye eas! sce of ha pi wae ede

picvited
an Wa Wear

‘Aalonal wii species found ot thal ay be ound near area wece iste
‘Alex, ques end tables ere revised for dete rewided hy CSI ard va
‘ema as

> Text nar contented based ca references,
Chapter 3 Affected Environment

The geology of the open rit is the same as that discussed in the 1997 D-aft EIS, even
though CSM proposes to mine to the 4,525-foot elevation. The Water Resources and
Gecchemistry Section 3.3 vill discuss any changes in the geology of the pit highwall
and backiil [hat might affect water quality trom that analyzed in ite 1897 Draft EIS,
Section HL.B,

324 Gealagy
3244 Regional Geology and Geologic Structures

GSM is located on the southam flank of Bull Mountain, Figuio 3-4 shews a general
map ofthe suricial goology in the vcinty of he mine. Bul Mountain is composed of
ancient sedimentary rack that was daposized in a shallaw sea during late Precambrian
time appraximately 1.4 bilion years ago. Tre Precambrian rock types n the vicinity of
the mine include sandstone, sitetone, and shale, These rock units are part of the
Precambrian Belt Supergroup. and also have heer refertod tn as the | aHood, Groyson
‘and Nevland formations. and the Burl Mountain Shale

A period of mountain building or tectoni activity known as the Laramide Orageny
ccourred approximately 70 fo 85 milion years ayo during the Cretaceous, fn tre vieinily
cf lhe mine, regional compression of he earth's crust created folded hlocks of rock
followed by extension that resulted in nigh-angle (near vertical) fours. Precambsian
rocks were penatrated by igneaus intrusions and averlain by va'canic materials during
this period, Cretaceous intrusive racks in the vicinity of Bre mine include lalite posphyty
and numerous smaller kariprophyre dikes.

After the Laramida Orageny. the landscape was relatively stable. During this time,
residual (ir-placo} weathering of the roc surlace was the dominant geolepic process,
During the Tortiary Peried, tectonic activity continued in the forin of felaxalion of
‘compression, of extension of the exith’s crust, This foamed the shallow basin east o*
Bul] Mountain, which filed with Tertiary and Quaternary sediments. Part of this
sediment-flled vallgy is now the site of tha facility buildings, tal ings impoundments, and
the East Waste Rock Dump Complex. The geology of the sediments that underlie Liese
facilities, particularly as it inFuences groundwater flow pathe, is the focus of discuesion
inthe following ection. Local voleunic aetivly also is evident by lhe presence of
Eocene (44-nillon-year-clt) pasa, which is exposed near Tailings Impoundment No.

1

The Precambrian sodimentary rocks in the vicintly of the mire are aydrothema ly
aereel and contain sulfide minerais. When these a.ifide minerals are exposed ta water
and air, they can produce metal bearing, acidic ron sulfate solutions, These solutions
‘are ARD.
Foe Pinte zine GENERALIZED
Sewer EF Bah apc SURFACE GEOLOGY

pe

uses tccaniy ae FIGURE $4
Chapter Affected Eromment

Pyrite is by far the most abu dant sulfide mineral. The average abundanos of pyrite in
GSM ure fs between 3 and 5 percent. The average abundance of pyrite in ha waste
rock is hehween 0.5 ard 2 pereent, Concentrations of up “¢ 20 percent occur, but are
nat typical. The relatively fine texcure of this nyiite enhances ‘he surface area available
for ARD generafion. Otrer metallic minerals occur in rrinor amcurts and vary in
accordance with zoning in tha ore berly. Water treaiment constituents of concer in
ARD include alurrinum, arsenic, cadmium, copper, manganese, nickel, pH, su fate, and
Zine. With the exception of aluminurr, the other metals are pretiominanlly associated
‘with suifide complaxes and axides,

3242 Bull Mountain Geology and Geologic Structures

“The open pi is centered on a breccia pipe in the Precambrian host rocks, The pit cuts
through and ig bounded by s highly complex seiies of east and northeast trending high
angle faults (Foster and Chadwick, 1990; Foster, ct al, 1993; Foster and Smith, 1936,
‘The Range Front Faull is a major north-south high-angle sip faut that separates te
Piecambiian and Cretaceous rocks of the upland fram the late Tertiary valley fill
sediments. The Corrido Fault is a lens-shaped zone up to several hundred Sort thick ot
lew-angla faulting that dips approximately 18 degrees lo Ihe nostheast (Hydromatris,
1995). The major geologic struclures in the vicinity ofthe pit are shown in Figure 3-2

The breceta pipe contains diaserinated gold-bcaring suifide mineralization that extends
more than 100 feet into walrock in silefied fractures. ‘he pipe is an irreqular 700-foat
diameter aval, which plunges 35 degrees to the wes|-soulhwest. Individual fragments in
tho brocela range from legs [han 1 inch to greater than 30 feat in sizc and consist of all
Joual rack lypes except for the late intruding lampraphyre dikes. 4 low-grade porphyry
molybdenum system is located in and adjacent to the ming, as is a zone of massive
sulfides in Precambrian racks. Alteration consists of pyrtizalio, silicifeation, and
docarbonizatian with an alteration mineral assemblage containing sikca, pyrite, bart,
sericite, chalcopyrite, galena, sphalerite, and molybdentte, Gold occurs as
disseminated particles associated with pyrite andl minor tallride minerals iv the bievcia
matrix and surrounding rock. Suparimposed across the breccia p'pe and inte the
surrounding highwall tock are northeast trending gald quartz veins that may contain
pyiile, galona, sphalerits, and barite

a
POZ Principe Defomotn Zone

NOTE: Refers gus 5
prngand Menor Wal Leta
‘arconpstelosaton ral vele,

MAJOR BEDROCK GEOLOGIC
STRUCTURES IN THE
VICINITY OF THE PIT

=.3UREG2
Chapter Aected Environment

324.3 Tertiary/Quaternary Geology and Gaologle Structures,

‘The area east of Bull Mountain contains valey fil Trtiary Bozeman Group sediments
Up to 1.500 feet thick (Hanneman, 1989). Figures 3-3 and 2-4 show stratigraphic,
sections from two locations east of Bull ifounvain. These racks and secirrents have
diverse lithologies, inclueing low perreabilly clays, moderate permeability sandstone
and conglomerate, and carbonate-oearing shales anc limestones {1997 Draft EIS,
‘Chapter Il, Section A)

‘The Bozeman Group in the vicinity ef he mine has been recognized 2s having a lower
fluvial (stream deposits) facies (Tht) ad alluvin: facies (Tha) (Figure 3-4). The fluvial
facies gonorally consists of inferred medium to high plastic ¢ aye and silts, sands
and clayay sands. hs fluvial fasias contains unconsolidated channel sand interlayers,
but the bulk of the unit consists of clays, which are interpreted as overbank deposi.
exhibiting good lateral contirully (Golder, 19982). The alluval facies ecimmonly
contains less than 20 percenl clay and consists of light orown, ightly caleareaus, sity
sands and gravels,

Lato Tertiary mass-wasting depasits, consisting of landslide (Tls) and debs flow
deposits (Tat), overie the Bozeman Group sediments uncenformiably a ong the east
front of Bull Mountain, The mass-Wwasting Geposits ara generally canfinad to tha
Rattlesnake Block (Golder, 1996a) (Figure 3-3}. Tho dobris flow dopesits are described
as consiating of eandy and silty gravel that is tine to coarse and suzroundec: lo angular
with cobbles and boulders. The debris flow deposity are up Io 250 ‘est thick, massive to
bedded, and unconsolidated ta well cemented with iron oxide, Associated landside
deposits are composed of mate or less intact blocks of laite and other pre-Tertiary
‘bedrock blocks that may ke up to 1.509 fect Jong and 200 tect tai.
RAPHIC

svect THomess — SbLlini

Gr. ci,a5 ts 028

Te a0
Te oto"
%
sae sant ato
States tor
exciton

ro

a

GEOLOGY: TH. CHADWICK
BOURGE: GOLDER, 19852

DESCRIPTION

cues Salven fan torace gavel (2M,
Tats [0s colurin (Qe ant tal a) depos

Sen (Pg Ty ran gu gre
floc dotetan: gr ppt rs rose
Sed stcay ati

‘Tartar ©) Sane [alain bash and: has
odes barrister Me “ound
‘etecanre arenes quetelspa ile sere
“sie quar gio, news mpl rae cesn 2
‘ty nalr gal, Uso cea

axa dacs to an arate dapat (TevT
lyri supra seete beuldor ie ers”
‘blosaynel-oneria rn odds candace
Boos wos 1800 aon ety 2280 bk

Conran aus of shear (alpen rash a
operiag en eaten in Pe
Efforts to Reanare Block nova,

‘ertrySssenan Group Ful des 1b
Unoareaiesed subround chnoe sar
‘eee at monk enraring 760%
chy. Steet ante ora cocoa
rue tari etd cl pow,
“TPe upper 200-900" Is eane ance” basa of
Geedatocarmen sadrmay be "Oferta
er HO ketenes ool. Ten inisbocs

TYPICAL

STRATIGRAPHIC COLUMN
FOR RATTLESNAKE BLOCK

FIOQURESS
oRarnic
evo THickwess — EOLURN

ey Soe
ie

0

oh a. ce, a8 0
Te ot
Tt
%
Sr

Staion
Taraoectpton

ae

DESCRIPTION

‘Gusta Seinen fn ros rasa
Tae ee eclvara (eae snl) epee

Tera (erates Tak uncansoldsi segue gravels
alee aetvaon t supeord wh mote eae
ang toy me

Tern (7) Son iT: neuen heh en hoe ke
od ae wth coreg dtiton, We lrounded
(pad oerea graned daa Scope Dats soe
Fried ante ging nena an
‘Seana aly eter gel.

\

tir Borman Gieup- ls! Fen Dopsi(Ta)
ein

[rating Bansnan Gig All Fan Ospis Tts)

Semccnaotsses we oaty na erated by CaO,
Shy con, snc et, buns rods of ant at
inerueds ty ccmen concn cae tn
(elcanaar. Alita ga are ecaly anuraaee nest
Uo oma of mesma cone carmel deroat

GEOLOGY: T.H. CHADWACK
‘SOURCE: GOLDER, 1805

[cena ioce ost (atyoiir may ey
opanarg on keaton winnie

Unconvotdess cemented wth Ox 0,
use conaring 0S. Crane a) pores
Terr osctone angie foto mtbade
‘Focal pears, cepa nex fon eles.
‘haupger S000 cay: anintortecbn ot
fae rnraanene may t,> 10st Beh ath
ver 0 fot band sonra. Thirds
feos ath and pea

TYPICAL
STRATIGRAPHIC COLUMN
FOR SUNLIGHT BLOCK

FIGURES
Chapter 9 Atfected Environment

Alluvial Fan gravels (Tg) and intarealated lacustine sands (Ts) uncenformably ovadie:
the landsFide-dabris flaw complex, with = thickness of as much 38 360 feet,
Disconformably overlying the Tertiary gravels and sands is a vatiaty af thin Quatervary
over, including fan-terrace gravels, landslide, colluv‘al and alluvial dopasits (Golder,
19982) (Figure 3-3).

‘The Jefferson River alluvium is a sttoam éepesit consisting of unconsolidated,
permeable alluvium of tho river floodplain and the adjacent gravelly terrace deposits
(Spectrum Faginesting and Gallagher, 2004). This unt follows the flow direction of the
sleffersan Iver (Figure 3-1), Atleast one of the alluvial terracos is buried by 40 to 86
feet of more recent colluvium and alluvial deposits, It's likely the upper -erraces grade
into the recent alluvium of the Jefferson Rivar sysiem and are hydrologically connected
to some degree, The alluvial deposits consist of uncosclidated gravel, sand, and firer-
grained overbank dopasits. The well-rounded gravel fraction includes euartzites and
volcanics from up-river regions. Angular siiified silstones and latito appear ta be
derived from the mine area. Much of the gravel is ton stained. Fragments af ferricrete
are prasent from the Tertiary debris ow denosits. The six borings in the Jefferson
River alluviuin were dis(ibuted bath up gradient ard down gractent of the Tertiary
debris Now deposits. Rock types associated with the mine arew vere seen in gtoater
abundance in samples from dawngradient borings. Samples from the unsaturated
portion ef tha Jefferson River alluvium were caleareas and affermesced i hydrochlo-ic
acid, while samples from the saluraled parcion were nen-calcareous and did not
effervesce (Spectrum Engineering and Gallagher, 2004),

‘The Bozeman Group scaiiments to the exst of the vil were ihe subject af a detailed
geotechnical investigation related to block movements that wera obsaived ir the mide
1990s (Golder, 19983). A uelalled discussion of the block movoments was provided ir
the 1987 Drall EIS, Chapter Il, Secton A, Twe blocks were identified within Lhe
Tertiaty sediments that are gencrally detincaied as follows:

«The Ratllesnake Block lies hetween the Range Front Fault to the west and
the Rattlesnake Faull lo the east isee Figure 9-2 for stratigraphic section and
Figure 3-1 far lan view,

The Sunlight Block is situated between the Ralllesnake Fault to the west and
Midas Draw to the east (see Fiqure 3-4 for stratigraohie section and Figure &-
4 for plan view).

BRA East Waste Rock Dump Complex Geology and Geologic
Structures.

‘The East Waste Rock Durin Complex geology was described i1 derail in the 1997 Dralt
ELS, Chapier ill, Section A and is summatizad be‘ow. The Eas: Waste Rock Dump
Complex ties east of the pit and is Iecated pamarily an Tertiary ;raveis (Ta) end
Bozenian Group sedimerts (Tea} (Figure 2-1}. Tarleen percent of the dump ecmplex
lies over the Rattlesnake Guich drainage and sould contribu watar to grounderater
leaving the pit (Figure 3-7)

6