GEOLOGY AND GOLD MINERALIZATION OF THE TURF DEPOSIT

8/8/2019 GEOLOGY AND GOLD MINERALIZATION OF THE TURF DEPOSIT

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Turf Deposit

GEOLOGY AND GOLD MINERALIZATION OF THE TURF DEPOSITJerry W. Mohling1

ABSTRACT

The Turf deposit is another significant discovery of deep, high-

grade, refractory gold ore on the Carlin trend. The deposit iscentered 2 miles (3 km) north of the Carlin Mine and about

a2

1 a

21

a2

1 a

21

a2

1

mile (0.8 km) north of the West Leeville deposit in Newmonts

North Area of Operations. Turf was discovered in 1994 by

Newmont Exploration Ltd. during the first drill test of the Four

Corners structural corridor. The deposit lies at a depth of 1,800 to

2,600 feet (540780 m) beneath the western flank of the main

Tuscarora Mountains at the eastern margin of Little Boulder Basin.

Turf is hosted by impure limestones and dolostones of the

Devonian Popovich limestone and the Devonian-Silurian Roberts

Mountains Formation in the lower plate of the Roberts Mountains

thrust. Gold mineralization in the Turf deposit is controlled

primarily by the north-striking, 5060W-dipping Turf fault and

by ancillary parallel structures in the footwall of the Turf fault.The ore-grade gold within the Turf fault ranges from 5 to 40 feet

(1.512 m) in true thickness (averaging approximately 30 feet

or 9 m). The ore zone extends 300 to 600 feet (90180 m) down

dip and rakes gradually to the north. Stratabound, high-grade

gold (>0.20 opt [troy ounces per short ton] or 6.86 g/t) extends

as much as 300 feet (90 m) laterally from the fault along favorable

carbonate beds, and ranges from 10 to 75 feet (323 m) in

thickness. In plan, the deposit is a north-trending body 3,800

feet (1,140 m) long by 300 to 800 feet (90240 m) wide.

The micron-sized, high-grade disseminated gold is

associated with decalcification, silicification, late-stage sooty

pyrite, and kaolinite. Calcite, barite, and dolomite occur as

fracture-filling veins that postdate the main episode of gold

deposition. Gangue minerals, such as montmorillonite, illite,

alunite, and K-feldspar, are minor and do not have a direct

correlation with gold ore. The bioturbated or wispy-

laminated units of the upper Roberts Mountains Formation and

the lower parts of the Popovich limestone were most susceptible

to decalcification and subsequent stratabound replacement

mineralization.

The geometry and litho-structural controls of the Turf

deposit have been interpreted from exploration diamond drill

holes and by limited infill definition drilling. No historical or

recent mine workings have been developed on the deposit.

Based on intercepts from 13 core holes that were analyzed

by fire assay, the main part of the Turf deposit was modeled by

computer and a gold resource was calculated to be 2.7 million

short tons (2.4 Mt [million metric tons]) with a 15% diluted

grade of 0.37 opt (12.7 g/t) gold (993,000 oz or 30.9 t gold).

Subsequent polygonal estimates applied to a 1,200-foot (360-

m) long continuation of the Turf deposit, north of the main

zone, suggest a further resource of 229,000 oz (7.1 t) gold with

an undiluted grade of 0.43 opt (14.7 g/t). Extensions remain

open to the north and northeast.

INTRODUCTION

Regional Geology

The Turf deposit lies within the North Lynn subdistrict of the

Carlin trend in Newmonts North Area of Operations and is

centered 2 miles (3 km) north of the Carlin minesite (fig. G-1).

The deposit is 100% controlled by Newmont Mining

Corporation. Turf straddles the eastern margin of Little Boulder

Basin adjoining the western range front of the main Tuscarora

Mountains. The name Turf is an acronym for Tuscarora Range

Front (Jackson and Bell, 1995).

The Paleozoic sedimentary sequence and the tectonic

evolution of the Carlin trend have been studied and documented

by numerous workers. The North Area of the Carlin trend was

mapped by the U.S. Geological Survey (Evans, 1980), and

recent overviews of the geology and structural framework of

the Carlin trend have been compiled by Christensen and others

(1988) and by Teal and Jackson (1997a). A brief overview of

the regional setting is given here as it pertains to the host rocks

and structural development.

During the Paleozoic, the area that is now northeastern

Nevada occupied part of the western margin of the North

American craton. Sedimentary rock units grade westward from

miogeoclinal shelf carbonates (eastern assemblage) to deeper

marine carbonates and siliciclastic slope facies of the western

assemblage (Christensen, 1993). The eastern assemblage strata

record a rapid bathymetric change in sedimentary environment

during Late Devonian time when eastern Nevada was evolvingfrom a passive to an active (compressive) continental margin.

This compressive event resulted in the Devonian-Mississippian

Antler orogeny wherein siliceous eugeoclinal rocks of the

western assemblage were thrust as much as 90 miles (145 km)

eastward, along the Roberts Mountains thrust system, over the

autochthonous eastern assemblage shelf facies carbonate rocks.

Subsequent regional compression during the Middle

Pennsylvanian Humboldt orogeny and the Triassic Sonoma

orogeny contributed to the development of the broad northwest

trending, north plunging Tuscarora antiform in the main

Tuscarora Mountains. Within the northern portion of the Carlin

trend, two dominant magmatic episodes of Late Jurassic and

late Eocene age are recognized. The Late Jurassic suite consists

mostly of equigranular diorite related to the Goldstrike stock

and Little Boulder Basin stock. Additionally there are

porphyritic lamprophyre dikes and porphyritic diorite sills and

dikes. The late Eocene intrusive rocks include the Betze dacite,

the Post rhyodacite, and the Beast dacite (Ressel, 1998).

Faults that underlie this region provided conduits for

circulation of hydrothermal fluids; however, the progenitor

thermomagmatic source(s) of the gold-bearing fluids remains

a topic of debate.1Geologic consultant, Tucson, Arizona


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Pete

We stBetze

WestLeeville

Turf

Winston

Ren

Tara

Bootst rap

Capstone

GoldenZia

NW Gene sis

WestRen

Banshee

South Meikle

Meikle

Barrel

WestGr iffi n

East Griffin

NorthBetze

WBazzaLongLac

N . Skarn Hil l

ShaloskyBetze

Pancana 5-0

West # 9

Gen esis

Bobcat

Payraise

BlueStar

Wi dge

BlueStarRidge

Beast

N W Extension

S. Lantern

N .Lantern

Hardie FW

Carlin East

?

D ee

FenceCar lin

Big Six

Antimon y Hill

Exodus

LEEVILLEFAUL

T

LYNN

FAU

LT

HARDIE

FAULT

Gold deposits

Granodiorite intrusions

Fault, solid where observed, dashed where inferred

DEE

FAULT

Rod eo

Screamer

Bazza Pt

Skarn Hill

Bazza

VIVIANGULCH

FAULT

Pancana

GOLDSTRIKESTOCK

LITTLEBOULDER

BASINSTOCK

(concealed)

FourCo rners

FOUR

CORNERS

FAULT

GEN

FAULT

CASTLEREEF

FAULT

Deep Star

Elko County

Eureka County

Perry

CASTLE

REEF

FAULT

0 5,000 10,000 feet

0 1,500 3,000 meters

TURF

FAULT

Island

N orth Star

Carlin West

Storm(Rossi)

Goldbug

D eep Post

Lower Post

POST

FAULT

Post

Winnemucca

Elko

Carlin

Ely

Reno

Lovelock

Las Vegas

80

80

H U M B O L D T E L K O

N Y EM I N E R A L

ESMERALDA

LYON

L I N C O L N

C L A R K

P E R S H I N G

C H U R C H I L L W H I T E

P I N EE

U

R

E

K

A

L

A

N

D

E

R

WA

SHOE

80

80

Figure G-1. Turf deposit location map, northern Carlin trend, Nevada. Modified from Teal and Jackson, 1997b.


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Turf Deposit

Late Tertiary tectonic extension of the North Lynn

subdistrict is manifested by the graben of Little Boulder Basin

(fig. G-1). Throw along the graben-bounding faults is estimated

to be on the order of 3,000 to 5,000 feet (9001,500 m) relative

to the adjacent rocks to the east and west of the graben. This

episode of tectonism crosscut and reactivated some of the earlier

structures. Along the Carlin trend, several structural and

erosional windows through the allochthonous rocks reveal the

lower plate, eastern assemblage carbonate rocks that host near-surface disseminated gold deposits. However, within the Turf

project area, the lower plate host rocks remain concealed by

1,500 to 4,000 feet (4501,200 m) of the upper plate, western

assemblage allochthonous rocks.

Previous Work

There has been no mine production in the immediate vicinity

of the Turf deposit; only a few scattered quartz-barite veins

and gossanous breccias have been prospected. Newmont has

episodically explored the North Lynn subdistrict since the 1970s.

Prior to 1992, exploration near the Turf deposit consisted of

geologic mapping, surface sampling, and intermittent drilling.Approximately fifty shallow rotary holes (mostly 10 feet [3 m] of0.20 opt [6.86 g/t] gold) that define

the gold deposit.

GEOLOGIC SETTINGOF THE TURF DEPOSIT

Overview

The Turf deposit spans at least 3,800 feet (1,140 m) in strike

length and lies at a depth of 1,700 to 2,400 feet (510720 m)

below the surface. It lies below the western flank of the main

Tuscarora Mountains rangefront to the east of Little Boulder

Basin (figs. G-1 and G-2). The surface lithology along this

western range front is dominated by rocks of the upper plate

of the Roberts Mountains thrust. These imbricately thrusted

rocks are flaser-textured, siliceous mudstones, chertymudstones, and interbedded limy siltstones of the Ordovician

Vinini Formation. Drill data from the project area indicate that,

here, the Vinini Formation ranges from 1,700 to 3,500 feet

(5101,050 m) thick.

In the north and northeast part of the project area, the Vinini

Formation contains semi-concordant granodiorite sills that

extend from the Jurassic Little Boulder Basin (LBB) stock that

underlies Little Boulder Basin. There are two principal outcrops

of the sub-horizontal sills; they are elongate northwest, and

occupy approximately b

13

b

13 b

13

b

13

b

13 square mile (~1 km2) in area (figs. G-

1 and G-2). The sills display weak propylitic and argillic

alteration assemblages. At the surface, an irregular

metamorphic aureole extends for about 2,000 feet (600 m) awayfrom the stock and sills and has converted the rocks of the

Vinini Formation to quartz hornfels and calc-silicate hornfels.

The Turf deposit is hosted entirely by carbonate rocks in

the lower plate of the Roberts Mountains thrust. Upper strata

of the Devonian-Silurian Roberts Mountains Formation and

upper parts of the Devonian Popovich limestone (directly below

the Devonian Rodeo Creek unit) are the principal host rocks

for replacement gold mineralization (fig. G-3).

Structural data derived from core logs and geologic models

indicate that the lower plate rocks at Turf strike northerly and

dip moderately to the east. This geometry is interpreted to result

from effects of pre- to post-mineral extension along north-

striking, west-dipping faults with attendant easterly rotation

of the segmented blocks (fig. G-2). In the northern part of the

project area, several northeast striking, steeply northwest-

dipping conjugate(?) normal faults have successively down-

dropped the strata to the north-northwest several hundred feet

in aggregate.

The metamorphic aureole from the LBB stock also extends

into lower plate rocks some 4,000 feet (1,200 m) laterally from

the intrusive margin. The approximate front of metasomatism

passes through the central portion of the Turf deposit and is

manifested by marbleization and lesser calc-silicate hornfels.


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Figure G-2. Block diagram of the Turf deposit, looking N30W, -30 degrees.

34

3

1

2

35

36

T36N,R50ET35N

TurfDeposit

W.Leeville

CG-110

CG-114

CG-113

CG-110

CG-114

CG-113

JULYFAULT

CG-109CG-90

CG-87

LBB-68

CG-111TURF

FAULT

JULYFAULT

CG-109

CG-90CG-87

CG-111TU

RF

FAULT

Carlin Formation

LBB stock, Vivian sill

Popovich Formation

Roberts Mountains Formation

wispy laminated units silty limestone 13

> 0.200 opt (6.86 g/t) Au, drill indicated

Fault, dashed where inferred

Roberts Mountains thrust fault

N

1000' 1000'

1000'

7000'

6000'

5000'

4000'

3000'

2000'

5000'

4000'


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Turf Deposit

The dominant structural feature in the project area is the

Four Corners structural corridor. This northeast trending, 500-

to 1,000-foot-wide zone of tectonic disturbance exhibits bothpre- and post-mineral faults and breccia. To the northeast the

Four Corners structural corridor flexes northward where it

coincides with the Vivian horst. The western edge of the Vivian

horst is demarcated by the Turf fault (fig. G-4, plate 1). At depth,

the Turf fault is the dominant ore-controlling structure in the

project area. The location and geometry of the fault have been

determined from mapping and drilling. The fault strikes nearly

due north, dips 5060 to the west and has accommodated 150

feet (45 m) or more of normal, pre-mineral displacement.

Tectonic breccias 5 to 40 feet (1.512 m) thick are everywhere

associated with the fault. Portions of the fault, most notably

within the southern part of the deposit, are intruded by a pre-

mineral monzonite porphyry dike (McComb, 1996a) that can

attain as much as 70 feet (21 m) of true thickness.

High-grade refractory gold (>0.20 opt [6.86 g/t]) was

deposited along the Turf fault and also as gently dipping

stratabound replacements where the fault cuts receptive units

within the Popovich limestone and Roberts Mountains

Formation. The ore zones, both stratabound and structural,

range up to 75 feet (23 m) in true thickness. Approximately

half the gold resource in the project is contained within the

Turf fault.

JKint

Viviansill

VininiFormation

Rodeo

Creek

Unit

PopovichFm.

RobertsMts.

Fm.

Popovich Formation


Dp1

Dp2

DSr1

DSr2

DSr3

DSr4

Debris flow marker bed; fine to coarse angular fragments oflimestone supported in limey sandstone matrix 5 to 30 feetthick

Upper Popovich limestone; micrite, commonly silty, variablycarbonaceous. Often displays contorted soft sediment de-formation. Average 120 feet thick

Lower Popovich limestone; thick to thin bedded siltymicrite, planar laminated. Distinct interbeds to 1/4 inch ofcalc-arenite and calcsiltite which may comprise 5-15% of therock. Variably carbonaceous. Average 90 to 140 feet thick

Silty limestone; planar laminated; upper 150 feet containrepetitive coarse, bioclastic interbeds to 2 feet thick. Fullthickness >700 feet thick

Silty limestone; wispy laminated; has distinctive fine-grainedbioclastic and calc-arenite interbeds up to 2 feet thickconstituting up to 25% of the rock. Average 85 feet thick

Silty limestone; with nearly uniform wispy bioturbatedlamination. Very minor detrital and bioclastic interbeds.Average 50 feet thick

Silty limestone; Gradational with Dp2 contains 10-20% siltinterbeds notable for wispy bioturbated lamination. Average40 to 50 feet thick

RelativeGoldMineralizationatTurf

Intercalated greenstone (up to 40 feet thick)

Roberts Mountains thrust

Popovich limestone


Ovi Vinini Formation (1,400 to 3,500 feetthick) Siliceous mudstone; distinctive flasershear fabric; may contain paraconcordant

dikes-sills of granodiorite (Goldstrike stockequivalent) up to 1,100 feet thickMetamorphic aureole surrounding sill hasconverted the siliciclastic rocks tocarbonaceous hornfels and quartz hornfels.

Vinini Lime Member (250 to 800 feetthick) Impure silty limestone and limysiltstone with intercalated mudstone.commonly metamorphosed to marble andcalcsilicate hornfels. Relict flaser texture

Rodeo Creek unit (10 to 300 feet thick)siliceous mudstone, cherty mudstone, thinbedded, planar laminated, rhythmicallybanded

Figure G-3. Generalized tectonostratigraphic column, Turf deposit, North Lynn subdistrict.


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FigureG-4.GeneralizedgeologicmapofpartoftheNorthLynnsub

districtshowingtheplanshapeoftheTurfgolddeposit.

T35N

T36N

R50E

36

35

2

1

Tur

f

W.Leeville

xxxx

xx

xxx

xxx

xxxxx

xxx

xxxxx

xxx xxxxx

xx

xx

xx

Trench

97-2

Trenc

h

97-3

Trench

97-1

Trench

97-4

Trench

98-1

Trench

98-2

Trench

98-3

Trench

98-4

Trench

98-5

Trench

98-6

ChevasPeak

AntimonyHill

Vivian

Sill

N.VivianHill

LBBStock

concealed

Jig

Jig

Jig

Jig

Jig

Jig

Ovi

Ovi

OvI

OvI

Vivian

Horst

Vivian

Sill

7

5

48

60

40

-50

45

Ovi

GULC

H

FAULT

VIVIAN

JULYFA

ULT

TURFFAULT

BASIN

FAUL

T

BO

UNDIN

G

LEEVIL

LE

FAULT

ZON

E

FOUR

COR

NERS

STRU

CTUR

ALCO

RRID

OR

SILB

AR

FAULT

LYNN

FAUL

T

48

CG

-87

A

A'

(Fig.

G-5)

DrillholestoLowerPlaterocks

Drillholesdescribedintext

Trench

Faultssh

owingdip,barandballwhere

inferred,arrow

whereobserved

Dikesofuncertainage,latiteto

lamproph

yrecomposition

Jig:grano

dioritedikesandsills

comagmaticwithLittleBoulderBasin

stock

Ovi:Vinin

iFormation,siliceousto

chertymudstone

Planshapeofgoldzone>10opt-foot

Lineofcr

osssectioninfigureG-5

0

1500feet

0

500meters

su

bcrop

outcrop

su

bcrop

outcrop

A

A'

CG-83

CG-87

CG-82 C

G-86


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Turf Deposit

Lithology

There are three principal lithologic regimes within the North

Lynn subdistrict: (1) allochthonous siliciclastic rocks in the

upper plate of the Roberts Mountains thrust; (2) impure

carbonate rocks in the lower plate of the Roberts Mountains

thrust and (3) the Little Boulder Basin (LBB) granodiorite stock

and sills. In addition, minor dikes of mafic to felsic composition

cut both the upper and lower plate. A generalized tectono-stratigraphic column for the project area (fig. G-3) depicts the

lithology and structural relationships. A brief summary of the

main lithologic units is given below.

UPPER PLATE ROCKS

At surface, the western range front of the main Tuscarora

Mountains is dominated by outcrops of the Vinini Formation.

These western assemblage siliciclastic rocks are part of the

Roberts Mountains allochthon. These rocks consist of

imbricately thrusted, flaser-textured siliceous mudstones and

cherty mudstones with interbeds of limy siltstones.

The depth to the Roberts Mountains thrust, and hence the

apparent thickness of the Vinini Formation, increases

progressively northward from the structural window at the

Carlin minesite. Drill data show that in the vicinity of Turf the

Vinini Formation ranges from 1,700 to 3,500 feet (5101,050

m) thick. Within the adjacent Little Boulder Basin graben,

drilled thickness of the Vinini Formation ranges from 3,600 to

6,100 feet (1,0801,830 m) (Clarke and others, 1998).

LOWER PLATE ROCKS

The stratigraphy and nomenclature of the lower plate host

rocks at Turf are the same as at the nearby deposits of Carlin

Underground, West Leeville, and Four Corners. The thickness

of some lower plate units, as measured in drill intercepts, is

highly variable due to extensional faults and to attenuation

by hydrothermal alteration and collapse. The autochthonous

rock assemblages are described below in descending

stratigraphic order.

Rodeo Creek unit (Drc) is highly variable in thickness because

the upper contact is determined by basal imbricate faults of

the Roberts Mountains thrust (fig. G-3). Drilled thickness at

Turf ranges from 5 to 280 feet (1.584 m), generally thinning

to the north. The unit consists of thin-bedded, planar-laminated

silty to siliceous or cherty mudstone. Repetitive thin interbeds

of siliceous muds and chert have prompted its categorization

as rhythmically banded argillite. It is not recognized as a host

rock at Turf.

Popovich limestone (Dp) has a drilled thickness that ranges

from 110 to 330 feet (33100 m) and averages approximately

230 feet (70 m) thick. It is typified by thin- to thick-bedded

micrite and silty micrite that are divided into two subunits:

Dp-1 and Dp-2 (fig. G-3).

Dp-1 has an average thickness of about 120 feet (36 m). The

upper 5 to 20 feet (1.56 m), directly below the Rodeo Creek

unit, are defined by fine to coarse clastic debris flows,

sandstone, and calcarenite. The remainder is distinctly micritic,

thin laminated, and commonly displays contorted soft-sediment

deformation.

Dp-2 averages 90 to 140 feet (2742 m) in thickness and is

gradational with the overlying Dp-1. This lower member is

typically a silty micrite that contains distinctive interbeds up

to c

41

c

41 c

41

c

41 c

41 inch (6 mm) thick of calc-siltite and calcarenite that may

locally comprise 5 to 15% of the rock. It is dark gray to black,variably carbonaceous, and typically has planar bedding.

Roberts Mountains Formation (DSrm) is the principal host

rock to replacement-style mineralization. The formation is

dominantly thin-bedded silty limestone that is divided into four

mappable units based on degree of bioturbation and quantity

of bioclastic and silt interbeds (Moore, 1995a). Total thickness

of the formation has not been drill tested because only the upper

three units are recognized as host rocks for high-grade

replacement ore. These individual units are shown on figure

G-3 but for visual clarity, units DSr-1, 2, 3 are combined in

figures G-2 and G-5.

DSr-1 averages 40 to 50 feet (1215 m) thick. The contact

with the overlying unit Dp-2 is gradational and marked by the

first consistent appearance of wispy lamination caused by

worm burrow bioturbation. The impure limestone is finely

laminated, dark gray to black, and carbonaceous. The wispy

texture occurs throughout and the unit may contain 10 to 20%

silt interbeds that range from 0.2 to 2 inches (550 mm) thick.

DSr-2 is a silty limestone that displays nearly uniform wispy

lamination with very minor bioclastic and detrital interbeds.

Where fresh, the limestone is medium to dark gray. Drill-

indicated thickness ranges from 25 to 105 feet (7.532 m), and

averages about 50 feet (15 m).

DSr-3. Most of this unit consists of wispy-laminated limestone;

however, fine to medium-grained bioclastic and calcarenite

interbeds up to 2 feet (0.6 m) thick that constitute up to 25% of

the section are diagnostic. It is dark gray, calcareous, and

variably carbonaceous. Drilled thickness ranges from 30 to

120 feet (936 m), averaging approximately 85 feet (26 m).

DSr-4 is more than 700 feet (210 m) thick but the total thickness

in the area of the Turf deposit is not known due to incomplete

drill testing of this unfavorable unit. It is dominantly silty

limestone that lacks bioturbation and has diagnostic thin-

bedded planar lamination. The upper 150 feet (46 m) contain

repetitive bioclastic interbeds 1 to 20 inches (2.550 cm) thickwith coarsely fragmented crinoids and rugose corals.

Throughout most of the Turf project area, this member is

variably metamorphosed to marble and calc-silicate hornfels.

The bioclastic interbeds contained within units DSr-3 and

DSr-4 are most prominent in the northern portion of the project

area and diminish to the south in the vicinity of the West Leeville

deposit. These interbeds are interpreted to be debris flows derived

from a Devonian bioherm whose northwest extension is exposed

at the Bootstrap Mine some 6 miles (10 km) to the northwest

(Teal and Jackson, 1997a).


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12'/0.23

62'/0.86

10'/0.27

71'/0.47

16'/0.23

15.5'/0.43

88'/0.48

84.5'/0.17

CG-82

CG-73

CG-83

CG-86

CG-73

CG-83 CG-82

CG-86

el 3500'

el 4000'

el 4500'

E1

7,0

00'

E1

6,0

00'

E1

5,0

00'

E1

5,0

00'

E1

6,0

00'

el 3500'

el 4000'

el 4500'

E1

7,0

00' ALTERATION

Gold mineralized zone,

>0.200 opt (6.86 g/t)

Silicification

Decalcification

Breccias, hydrothermal

and collapse

Faults

Roberts Mountains thrust

Drill holes with goldintercepts, thickness

(feet)/ opt gold

LITHOLOGY

Felsic dikes

Vinini Formation

Rodeo Creek unit

Popovich limestone


silty limestone units 1-3

silty limestone unit 4

0 500 feet

0 150 meters

0 500 feet

0 150 meters

A A'

A'A

RM THRUST

RM THRUST

TURF

FAU

LT

RM THRUST

RM THRUST

TURF

FAULT Alteration

Lithology

10'/0.27

Drc

Drc

Dp

Dp

DSr1-3

DSr1-3

DSr4

DSr4

Drc

Dp

Dp

DSr1-3

DSr4

Ovi

Ovi

Ovi

TintTint

intT

CG-73

Ovi

Figure G-5. Turf deposit section 33200N, looking north (section AA on fig. G-4).


9/15


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FigureG-6.Turfdeposit,schematicdiagram

showinggrade-thick

nessand11sectionswithgoldzones.

3500

ft

4000

ft

4500f

t

5000

ft

E 1

5 5 0 0

E 1

6 5 0 0

E 1 6 0 0 0

E 1

5 0 0 0

E 1

7 0 0 0

E 1

7 5 0 0

E 1

8 0 0 0

E 1

8 5 0 0

E 1

9 0 0 0

N32

000

N32

400

N32

800

N33

200

N33

600

N34

000

N34

400

N34

800

N35

200

N31

600

N35

600

N36

400

N36

000

VIVIAN

GULCH

FAULT

SILB

AR

FAULT

FOUR

CORNE

RSFAULT

CORRID

OR

JULY

FA

ULT

TUR

FFAULT

Faults

Goldzones,

>0.200opt(6.87g/t)

Planshapeofgrade-thickness:

shadow

ofgoldzonefrom

verticalillumination

N

400'

400'

500'

10

opt-footshape

20

opt-footshape


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Turf Deposit

TURF FAULT

At depth within the lower plate rocks the Turf fault is listric,

strikes northerly, and dips 50 to 60 to the west. The northerly

strike and extensional movement of the fault may be interpreted

as a dilational jog or step-over fault within the overall northeast

trend of the Four Corners structural corridor. As such, the Turf

fault became the principal conduit for the circulation of

hydrothermal fluids and for ore deposition along a mineralizedstrike of at least 3,800 feet (1,140 m). Details of the ore zones

within and adjacent to the Turf fault are discussed in following

sections.

VIVIAN GULCH FAULT

This fault marks the contact and northeastern limit of the main

body of the Vivian sill. This poorly exposed 5- to 10-foot (1.5

3 m) wide, sub-vertical structure extends 4,000 feet (1,200 m)

northwest from Antimony Hill to the Four Corners structural

corridor. The fault appears to predate the sill and limits its

emplacement. Drill hole CG-114, collared to the south of thefault, intersected 1,100 feet (330 m) of the exposed granodiorite

sill whereas CG-113, located 300 feet (90 m) north of the fault,

was drilled 3,439 feet (1,032 m) through upper and lower plate

rocks without intersecting intrusive granodiorite (fig. G-2).

Comparative depths to the lower plate rocks intercepted by

holes CG-113 and CG-114 suggest that vertical offset of the

Vivian Gulch fault is less than 200 feet (60 m). Strike-slip

motion along the fault is speculative, and the fault is not a

demonstrated conduit for mineralizing fluids.

SILBAR FAULT

This structure is parallel to and lies 3,000 feet (900 m) southwest

of the Vivian Gulch fault (fig. G-4). It is inferred from ground

magnetic data to extend northwest from the southern end of

Chevas Peak to the southern end of the July fault at the Four

Corners fault corridor. The sub-vertical Silbar fault marks the

northeast margin of a southern segment of the Vivian sill and

is named for silica-barite alteration in fault breccias seen in

prospects along its strike. The direction and magnitude of offset

along this fault are not known. No holes have been drilled to

test for mineral occurrences within or adjacent to the fault in

lower plate rocks.

LYNN FAULT

This is the easternmost structure within the area of the Turf

deposit (fig. G-4). This northeast-striking, northwest-dipping

fault is an important mineral control at the historic Big 6

workings and the jasperoid at Antimony Hill (fig. G-1). At

Antimony Hill, a small gold-bearing jasperoid developed in a

zone of dilation where the Lynn fault horsetails or deflects

into a dominant north-northwest striking, west-dipping fabric

with dip-slip and dextral strike-slip kinematic indicators (Teal,

1993).

HYDROTHERMAL BRECCIAS AND ORE

Solution collapse breccias are common in the Turf deposit.

Generally they are found in, and adjacent to, the strongest zones

of high-grade gold ore. The Turf fault was the principal conduit

along which breccias developed. Initially the rock was

brecciated tectonically; such tectonic breccia is clast-supported

and comprised of fine to coarse, rotated fragments up to 3 inches

(8 cm) in diameter. Tectonic brecciation was followed bydecalcification as the fault became a conduit for hydrothermal

fluids. Decalcification effected progressive volume loss in both

the tectonic breccias and adjacent carbonate host rocks; this

resulted in collapse with attendant brecciation. The textures of

collapse breccias range from jigsaw breccia having no

rotation or transport of the clasts, to strongly disaggregated

masses of decalcified silty limestone. These textures, absent

distinct fault planes, gouge, or kinematic indicators, are

interpreted to indicate collapse. The breccia clasts are usually

angular and corroded with stylolitic boundaries against an

interstitial filling of microcrystalline quartz.

Tectonic and collapse breccias are commonly crosscut by

ramifying hydrobreccia veins as much as several inches thick.

These siliceous veins, with matrix-supported, fine-fragmental

clasts of silicified wallrock, commonly contain several percent

cryptocrystalline sooty pyrite. Late-stage barite and calcite

locally fill open fractures and vugs (McComb 1996c,d).

Drilling shows that bodies of ore-grade gold (0.20 opt

[6.86 g/t]) in hydrothermal collapse breccias can exceed 40

feet (12 m) in true thickness contained within greater volumes

of breccia as much as 200 feet (60 m) thick. The mineralized

portions of the breccias are frequently enveloped by zones of

barren marble or by abundant calcite veinlets.

Paragenesis of AlterationThe intrusive events, alteration assemblages, and inferred

paragenesis at the Turf deposit bear many similarities to those

at the Carlin Mine (Bakken, 1990; Kuehn and Rose, 1992) and

those described at the Betze-Post Mine (Leonardson and Rahn,

1996). Based on crosscutting relationships at Turf, the

paragenetic sequence may be interpreted as (1) hornfelsing and

marbleization that resulted from intrusion of the Little Boulder

Basin granodiorite stock and the comagmatic Vivian sills (153

Ma); (2) intrusion of monzonite porphyry dikes (40 Ma?) along

structures such as the Turf fault; (3) decalcification of the

Popovich limestone and Roberts Mountains Formation to form

collapse breccia; (4) silicification of collapse breccia anddeposition of early barren pyrite; (5) main-stage gold deposition

with an alteration assemblage of kaolinite, illite, sooty pyrite

replacements and minor orpiment and realgar; (6) late-stage

calcite veins, drusy quartz, and barite that fill vugs and open

fractures; (7) basin-and-range extension along north and

northeast striking faults accompanied by minor hydrothermal

argillic alteration. Newmont Mining Corporation has not yet

dated the alteration minerals related to the mineralizing event;

however, Ressel (1998) has dated late Eocene mineralized dikes

at the Beast deposit one mile (1.6 km) to the west of Turf.


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102

Drilled interval Gold(feet) (opt) Qtz Ill Kao Mont Cal Dol Pyr Bar

20702088.5 49 0 49 0 0 0 2 02088.52111 68 0 23 0 0 0 9 1

21112126 47 10 28 0 0 0 9 321262134 0.47 52 10 16 8 0 2 11 021342144 0.47 66 15 5 5 0 0 8 0

21442154 0.47 80 7 8 0 0 1 3 021542164 0.47 70 12 15 0 0 0 3 0

21642172 0.47 79 7 10 0 0 0 3 121722182 0.47 75 5 8 5 0 2 4 0

21822192 0.47 55 13 3 5 0 18 4 021922202 57 9 7 0 6 17 4 022022219 49 0 6 0 40 3 1 0

22192237 55 0 11 0 28 5 1 0

Table G-1.MTurf drill hole # CG-82 X-ray diffraction analysis (data from McComb, 1996b)

Qtz = quartz Kao = kaolinite Mont = montmorillonite Ill = illiteCal = calcite Dol = dolomite Pyr = pyrite Bar = barite

Semiquantitative weight %

Ore Zones

The characteristics of gold depositional styles are interpreted

from select drill intercepts and are discussed below with respect

to ore deposit setting (i.e., hanging wall, footwall, and Turf

fault-hosted mineralization). Locations of these drill holes are

shown on the generalized geologic map (fig. G-4). A cross

section through the center of the deposit (fig. G-5) illustrates

the litho-structural controls, dominant alteration minerals, andgold grades as determined from drill intercepts.

Suites of alteration minerals were compiled from XRD-

XRF studies performed by Newmont Metallurgical Services

(McComb, 1996a,b,c,d; Baker, 1997c). These analyses were

from select core samples of prominent breccias, ore zones, and

intervals 40 feet (12 m) above and below the ore zones.

Semiquantitative X-ray diffraction analyses for portions of the

drill holes described below (CG-82, 83, 86, 87) are given in

tables G-1 to G-4.

TURF FAULT MINERALIZATION

Hole CG-82, centrally located in the Turf deposit, cut the most

intensely developed zone of breccia above and within the Turf

fault (figs. G-4 and G-5). The breccias include a variety of

textures that range from tectonic, to hydrothermal, to collapse.

Near the top of lower plate rocks at a drilled depth of 1,830

feet (558 m), hydrothermal collapse breccias are strongly

developed in the Popovich limestone and lower parts of the

Rodeo Creek unit. The breccias are both matrix and clast-

supported with intensely decalcified and moderately silicic- to

argillic-altered fragments up to 3 inches (7.6 cm) in diameter.

The main interval of high-grade gold (71 feet of 0.47 opt

[1.6 m of 14.6 g/t]) begins at a depth of 2,126 feet (648 m) in

the lower Popovich limestone. Here, the silty micrite is strongly

decalcified, moderately carbonaceous and sulfidic, with

variably silicified and argillized collapse breccias. This high-

grade interval directly overlies the Turf fault, below which gold

grades diminish to less than 0.05 opt (1.7 g/t) in marble and

calc-silicate hornfels of the Roberts Mountains Formation (unit

DSr-4). Table G-1 displays the suite of alteration minerals

within and adjacent to the ore zone.

Hole CG-87, located along the northern segment of the

Turf deposit (figs. G-2 and G-4), cut the Turf fault in unit DSr-

3 at a drilled depth of 2,500 feet (750 m). A significant ore-grade intercept (60 feet of 0.42 opt [18.8 m of 14.4 g/t]) occurs

in a zone of breccia. In this intercept, the breccia displays

tectonic and hydrothermal collapse textures with coarse angular

fragments that are both clast and matrix-supported. Clasts are

strongly decalcified, carbonaceous, and siliceous with weak

(12%) sooty disseminated pyrite. XRD-XRF analyses show

that the ore zone is strongly siliceous (4077% quartz) with

lesser kaolinite, illite, and montmorillonite (table G-2). The

calcite, barite, and dolomite represent late-stage veinlets and

druses within the breccia matrix.

TURF FOOTWALL MINERALIZATION

Hole CG-86 intersected the strongest gold mineralization found

thus far in the footwall of the Turf fault (figs. G-4 and G-5).

There are three significant gold intercepts in this hole. The

uppermost zone (16.5 feet of 0.23 opt [5.0 m of 7.9 g/t] gold)

is in the basal sandstone of the Rodeo Creek unit at the contact

with Popovich limestone. The gold mineralized zone is

siliceous and carbonaceous crackle breccia that is laced with

late barite veinlets. The second intercept is in the upper

Popovich limestone (unit Dp-1). This zone of stratabound

replacement in micritic limestone grades 15.5 feet of 0.43 opt

(4.72 m of 14.7 g/t) gold. The host rock is decalcified,

carbonaceous, moderately pyritic, and notably fractured by

incipient collapse. The third, and principal, gold intercept


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103

Turf Deposit


2467.52484 54 4 8 0 27 5 1 024822503 37 4 6 5 44 3 1 025032513 0.42 43 0 7 0 47 1 2 1

25132523 0.42 63 4 4 5 15 6 2 125232534 0.42 61 4 4 5 18 6 2 125342543 0.42 77 4 3 3 2 10 2 0

25432553 0.42 72 0 4 0 2 18 1 225532563 0.42 61 3 6 5 11 14 1 0

25632583 69 0 9 5 12 2 1 125832598.5 64 0 17 0 14 5 0 0

Table G-2.MTurf drill hole # CG-87 X-ray diffraction analysis (data from Baker 1997c)

Qtz = quartz Kao = kaolinite Mont = montmorillonite Ill = illiteCal = calcite Dol = dolomite Pyr = pyrite Bar = barite



1867.51885 89 5 4 0 0 0 2 0

18851906 91 4 2 0 0 0 1 119061923 0.23 80 7 3 6 0 0 3 1

19231937.5 68 9 10 9 0 0 4 01937.51951.5 86 5 6 0 0 0 2 0

1951.51967 0.43 61 4 23 8 0 0 4 019671984 74 5 12 7 0 0 2 0

19841999 82 0 11 5 0 0 2 019992017 78 5 16 0 0 0 2 020172027 0.47 76 0 13 8 0 0 2 0

20272042.5 0.47 81 0 17 0 0 0 2 02042.52053 0.47 79 0 10 6 0 0 5 0

20532064 0.47 78 4 14 0 0 0 3 020642077 0.47 76 2 12 6 0 0 4 0

20772087 0.47 82 4 11 0 0 0 3 020872095 0.47 74 0 16 6 0 0 4 0

20952107.5 0.47 59 4 9 0 17 7 3 1

2107.52124 63 0 5 0 29 3 1 021242141 72 0 3 4 14 6 1 0

Table G-3.MTurf drill hole # CG-86 X-ray diffraction analysis (data from Baker, 1997c)

Qtz = quartz Kao = kaolinite Mont = montmorillonite Ill = illite

Cal = calcite Dol = dolomite Pyr = pyrite Bar = barite



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104


20402060 58 9 4 5 3 18 3 020602079 70 9 5 5 0 8 3 0

20792091 78 10 5 0 1 1 6 0

20912100 78 9 4 4 1 0 3 021002110 0.866 79 5 5 5 2 0 5 021102122 71 10 7 5 0 0 6 2

21222132 69 8 9 4 0 3 7 021322143 68 10 5 3 4 2 8 021432152 12 10 6 5 61 3 4 0

21522162 54 13 8 3 14 2 7 021622172.5 40 21 5 4 26 2 3 0

2172.52190.5 66 13 10 5 0 1 5 02190.52210 63 12 10 5 0 4 6 0

Qtz = quartz Kao = kaolinite Mont = montmorillonite Ill = illite

Cal = calcite Dol = dolomite Pyr = pyrite Bar = barite


Table G-4.MTurf drill hole # CG-83 X-ray diffraction analysis (data from McComb 1996d)

occurs in the wispy laminated part of the Roberts Mountains

Formation (units DSr-1, 2). The mineralized zone (88 feet of

0.475 opt [26.8 m of 16.3 g/t] gold, including 37 feet of 0.80

opt [11 m of 27 g/t] gold) is controlled by both stratigraphy

and by a high-angle structure that is parallel to, and in the

footwall of, the Turf fault. This ore interval is moderately to

strongly siliceous, variably kaolinitic, and has up to 5% sooty

disseminated pyrite (table G-3). Below the ore intercept, gold

grades abruptly diminish to less than 0.02 opt (0.7 g/t) in

conjunction with a decrease of alteration.

HANGING WALL MINERALIZATION

Hole CG-83 has the most robust gold mineralization of the

holes drilled to date in the Turf deposit (figs. G-4 and G-5).

The several gold-mineralized intercepts include both

stratabound-disseminated and fault-hosted types. The main ore

zone begins at a depth of 2,100 feet (630 m) below surface in

hornfelsed and hydrothermally altered silty limestone (unit

DSr-1) of the Roberts Mountains Formation (fig. G-5). The

intercept from the sub-horizontal mineralized zone has a drilled

thickness of 62 feet (19 m) that grades 0.866 opt (29.7 g/t)

gold (including 27 feet of 1.46 opt [8.2 m of 50.1 g/t] gold).

The host rock in this intercept lacks evidence of tectonism or

hydrothermal brecciation. The original wispy laminated textureis preserved, thus indicating that the style of gold deposition is

this intercept was passive (volume for volume) replacement

similar to that at the West Leeville deposit (Teal and Jackson,

1997a). The Turf fault is interpreted to be the principal conduit

for gold-bearing hydrothermal fluids that migrated laterally

along this favorable stratigraphic unit.

Alteration in the highest-grade part of the intercept is

dominated by quartz, illite, kaolinite, and 38% sooty pyrite.

Montmorillonite and dolomite are minor in abundance (table

G-4). This gold intercept is underlain by sub-ore grade

disseminated mineralization (126 feet of 0.070 opt [38.4 m of

2.4 g/t] gold) in decalcified, argillaceous, and pyritic-altered

silty limestone (unit DSr-2). Deeper in the hole within unit

DSr-4, a broad interval of low-grade, disseminated and fracture-

controlled mineralization (84.5 feet of 0.170 opt [25.8 m of

5.8 g/t] gold) surrounds the Turf fault zone.

METALLURGY

Triple gold assays, preg-robbing carbon tests, and carbon-

sulfur assays were performed by Newmont on select intervals

of drilled-core that contain intercepts of >0.20 opt (6.86 g/t)gold. Generally these were the same intervals (approximately

from 40 feet [12 m] above to 40 feet [12 m] below the ore

zones) analyzed by semiquantitative XRD-XRF. These analyses

demonstrate that the gold zones at Turf are unoxidized and

sulfide refractory. The preg-robbing analyses determined that

the ore contains variable organic carbon with the deleterious

capability to adsorb gold from pregnant cyanide solution. These

metallurgical characteristics make the ore unfit for simple

crushing and heap leaching. Instead, the ore will need treatment

in a roaster or autoclave to liberate the micron-sized gold from

the sulfides and deactivate the organic carbon.

GEOLOGIC GOLD RESOURCE

The Turf deposit strikes and plunges northerly for a known

length of 3,800 feet (1,140 m). At the end of 1996, the Turf

deposit data were modeled using Newmonts Geomodel

software. The model was transferred to the Mines Engineering

Group for resource calculations. Based on 13 diamond-core

holes drilled at nominal 400-foot (120-m) centers in the main

part of the deposit, the Turf resource was calculated to be 2.7

million short tons (2.4 Mt) with a 15% diluted grade of 0.37

opt (12.7 g/t) gold (993,000 oz or 31 t of gold) (Perry, 1997).


15/15

Turf Deposit

During 1997, four infill holes were drilled in the central part

of the deposit to validate the geologic model and four more

diamond-core holes were drilled to test a northerly extension

of the Turf deposit. High-grade gold was intercepted in the

northern extension along a 1,200-foot (366 m) strike length of

the Turf fault. The drilled thickness of the intercepts ranges

from 15 to 60 feet (4.518 m) and is inferred to span a dip

length of 200 to 300 feet (6090 m). Manual polygonal

calculations of the resource in this northern extension suggestan addition of 532,000 short tons (483,000 t) with an average

undiluted grade of 0.43 opt (14.8 g/t) gold (229,000 oz or 7.1 t

of gold) (Mohling, 1998). This brings the total geologic

resource at the Turf deposit to 1.22 million ounces (38 t) of

gold. Geologic mapping and surficial geochemical sampling

indicate that extensions to the deposit are possible to the north

and northeast. Figure G-6 illustrates the plan and sectional

shapes of the deposit as inferred from the drilling programs.

DISCUSSION

The drilling programs substantiate that Turf is a significant

discovery of deep, high-grade gold qualified for inclusion inthe gold resource inventory of deposits along the Carlin trend.

Gold deposition at Turf is controlled by a combination of faults

and by strata receptive to disseminated replacement. At Turf,

the host rocks in the lower plate of the Roberts Mountains thrust

are variably marbleized and calc-silicated with the

metamorphism generally increasing toward the Little Boulder

Basin stock. Because of the range of pre-mineral metamorphism

of the host rocks, Turf is a hybrid of Carlin-type deposits such

as Deep Star (intense calc-silicate hornfels and structure-

controlled) and West Leeville (non-hornfelsed, stratabound

replacement) (Teal and Jackson, 1997a).

The Turf deposit is localized by steeply dipping faults

along the western side of the Vivian horst. The western horst

margin is part of a broader zone of extensional faults that adjoin

the eastern margin of the graben of Little Boulder Basin. The

gold mineralizing fluids were channeled along the north-

striking, west-dipping Turf fault: the fault may represent a

dilational jog internal to the 500- to 1,000-foot (150300 m)

wide, northeast-striking Four Corners structural corridor.

Recognition of the locations, orientations, and magnitude

of dominant fault zones that control low-level gold and trace

element anomalies at surface is key to targeting the related

deep orebodies. Southwest of Turf at the Four Corners deposit,

it was recognized that high-grade gold in lower plate rocks

was controlled in part by steep conduits in the Four Corners

fault corridor. This understanding guided the successful drilltesting and discovery of the Turf deposit beneath anomalous

gold and trace elements in soils along the northeast continuation

of this structural corridor (Jackson and Bell, 1995). Likewise,

successful drill testing of the northern extensions of Turf was

enabled by advanced understanding of the down-dip geometry

of mineralized and post-mineral faults (Lisle, 1996; Mohling,

1997).

The preliminary modeling by polygonal methods and by

Newmonts Geomodel system indicate that Turf, as presently

known, is a gold resource of approximately 1.22 million ounces

(38 t) with an average undiluted gold grade of 0.42 opt (14.4

g/t) and a sulfide content of 34%. This ore should be amenable

to processing in Newmonts refractory ore treatment plant.Some portions of the highly silicified gold zones may require

fine grinding. At the time of this writing, engineering studies

were underway by Newmont Mining Corporation to determine

the optimum mining plan.

ACKNOWLEDGMENTS

I would like to thank Mac Jackson and Richard Lisle for laying

the foundations of the Turf discovery and the general

framework for the interpretive model. Also, thanks to Brad

Leach and Helen Robinson for their contributions and insights

during the infill drilling stage of exploration. Much gratitude

is owed to Newmont Mining Corporation for permission to

publish this paper and to Lewis Teal, Don Hammer, Steve

Peters, Joe Tingley, Jon Price, and Steve Castor for their

constructive editorial comments from which this paper

benefited greatly.

Documents

GEOLOGY AND GOLD MINERALIZATION OF THE TURF DEPOSIT