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Isotopic Studies 

Hosted Pb-Zn 
.... I! j 

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.
Geologic, Geochemical, and Isotopic Studies of a 

Carbonate- and Siliciclastic-IIosted Pb-Zn Deposit 

at Lion Hill, Vermont 

By Nora K. Foley, Sandra H.B. Clark, Laurel G. Woodruff, and Elwin L. Mosier 

U.S. GEOLOGICAL SURVEY BULLETIN 2145 

A study of Pb-Zn-Cu mineralization resulting from syngenetic 

sedimentary-exhalative and diagenetic replacement processes in 

structures in carbonate and siliciclastic platform rocks of 

Cambrian and Ordovician age that form the lowlands 

between the Green Mountain massif and the 

Adirondack massif in western Vermont 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

GORDON P. EATON, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center, Denver, CO 80225 

Any use of trade, product, or firm names in this publication is for descriptive purposes only and 

does not imply endorsement by the U.S. Government. 

Published in the Eastern Region, Reston, Va. 

Manuscript approved for publication July 10, 1995. 

Library of Congress Cataloging in Publication Data 

Geologic, geochemical, and isotopic studies of a carbonate- and siliciclastic-hosted Pb-Zn 

deposit at Lion Hill, Vermont I by Nora K. Foley ... [eta!.]. 

p. em.- (U.S. Geological Survey bulletin; 2145) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3:2145 

l. Lead ores-Vermont. 2. Zinc ores-Vermont. 3. Geology, Stratigraphic-Cambrian. 

4. Geology, Stratigraphic-Ordovician. 5. Geochemistry-Vermont. I. Foley, N.K. 

II. Series. 

QE75.B9 no. 2145 

[QE390.2.L43] 

557.3 s-dc20 

[553.4'4'097437] 95-37051 

CIP 
CONTENTS 

Abstract .......................................................................................................................... . 

Introduction..................................................................................................................... 1 

Acknowledgments................................................................................................... 3 

Geologic Setting.............................................................................................................. 3 

Regional Tectonic, Sedimentary, and Metamorphic Environment .......... ............ ... 3 

Local Tectonic, Sedimentary, and Deformational Environment............................. 4 

Lion Hill Zn-Pb-Cu Deposit........................................................................................... 6 

Shape and Extent of Mineralized Zones.................................................................. 6 

Host Rocks............................................................................................................... 6 

Mineralized Rocks................................................................................................... 8 

Geochemistry................................................................................................................... 9 

Geochemical Data.................................................................................................... 9 

Relation to Stratigraphy .. . .. .. .. .... .. .... .. .. .. .. .. .. .... .. .. . . . . . ...... . . . . . .. .. .. . .. .. .. . . . .... .. ... .. . .. .. .. . 14 

Fluid-Inclusion Study ...................................................................................................... 14 

Fluid-Inclusion Data ............................................................................................... 14 

Discussion of Data.................................................................................................. 17 

Model for a Diagenetic Origin .. .. .. .... .. .. .. .... .. .. .. .. .. .... .. .... .. .... .. .. .. .. .. .. .. .. .. .. .. .. .. 17 

Model for a Metamorphic Origin.................................................................... 18 

Isotope Studies . . .. .. .. .. . . . . . .. .. . . .. . . . .. . .. . .. . . . . .. .. .... .. .. .. .. .. .. .. . . . .. . .. .. .. . .. .. .. .. .. .. . .. .. .. . .... .. .. . . . . .. .. .. . 19 

Sulfur Isotopic Data................................................................................................ 19 

Lead Isotopic Data .... . .. . . . .. .. .. . .. .. . .. .. .. .. . . . . .... .. .. . . . . . .... .. . . . . .... .. .. . . . . . .. . . .... .... . . . . .. .. .... .. .. 21 

Comparison with other Sediment-Hosted Base-Metal Deposits .................................... 23 

Genetic Models . ... . . .. ... ..... . . . . ... . ... . . . . .... . .... . . . . . ..... . . . . .. ........ ... . . . ............ ............ .... ..... ... . . . . . 25 

Conclusions..................................................................................................................... 27 

Appendix A. Analytical Techniques .............................................................................. 27 

References Cited ............................................................................................................. 28 

FIGURES 

1. Location map showing regional geologic setting of base-metal sulfide deposits and occurrences in 

western Vermont .. .. . . .. .. .. .. .. .. . . .. .. .... .. .. . . . . . .. . . .. . . . . . .. . . .... . . . .. .. .... . . . .. .. .. .. .. .. .. . . . .. .. .. .. . . . . .... .... .. .. .. .. .................................... .... 2 

2. Photographs of host rocks of the Lion Hill area........................................................................................................... 5 

3. Geologic map of the Brandon area, Vermont............................................................................................................... 7 

4. Cross sections showing local geology.......................................................................................................................... 8 

5. Photographs of sulfide-bearing rocks from the Lion Hill area..................................................................................... 10 

6. Photomicrographs of sulfide-rich samples from the Lion Hill area .......................... ............ .... ............ .......... ............. 11 

7. Geochemical profiles of drillcore, Churchill prospect, Fay mine, and Nicklaw mine areas........................................ 12 

8. Reconstructed stratigraphic section for the Lion Hill area........................................................................................... 16 

9. Plot showing fluid inclusion data for sphalerite from Lion Hill................................................................................... 17 

10. Plot showing sulfur isotopic compositions of sulfides from the Lion Hill deposit .................. .... .. .. .. .. .... ...... .. ............ 21 

11. Plot showing lead isotopic data for galena from Lion Hill sulfide zones and magnetite iron formation near 

Brandon, Vt. .................................................................................................................................................................. 23 

12. Plot showing comparison of lead isotopic data, Lion Hill area and White Creek, N.Y., to data for similar 

deposits in Ireland......................................................................................................................................................... 24 

13. Plot showing comparison of sulfur isotopic data of MVT, Appalachian-type, and Irish-type deposits with 

data for the Lion Hill deposit........................................................................................................................................ 25 

III 
IV CONTENTS 

TABLES 

1. ICP-AES analyses of drillcore samples from the Lion Hill area................................................................................... 15 

2. Fluid inclusion homogenization temperature and salinity data for sphalerite from Lion Hill, Vt.................................. 18 

3. Sulfur isotopic data for the Lion Hill deposit, Vt., and the Fernville, Vt., and White Creek, N.Y., prospects............... 20 

4. Lead isotopic compositions of galenas from base-metal sulfide deposits hosted by carbonate-siliciclastic 

platform rocks of Vermont and the Taconic allochthon of New York ............................................................................ 22 
GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES OF A 

CARBONATE- AND SILICICLASTIC-HOSTED 

Pb-Zn DEPOSIT AT LION HILL, VERMONT 

By Nora K. Foley,' Sandra H.B. Clark, 1 Laurel G. Woodruff,2 and Elwin L. Mosier3 

ABSTRACT 

Zn-, Pb-, Cu-, and Fe-bearing rocks of the Lion Hill 

area in western Vermont formed during the Early Cambrian 

by syngenetic sedimentary-exhalative and diagenetic 

replacement processes. Sphalerite, galena, chalcopyrite, 

pyrite, and, locally, magnetite form stratabound and broadly 

stratiform lenticular zones, -300 meters long and 25-50 

meters thick, which are uneconomic at the present time. The 

lenses are structurally disrupted and metamorphosed to 

greenschist facies, probably due to the Taconic orogeny. 

Textural evidence suggests that mineralizing fluids permeated the sediments prior to lithification and that a dilatant 

fracture zone, possibly a feeder zone, contains some of the 

discordant veins at Lion Hill. The veins may have formed 

when the sediments were in a plastic, semiconsolidated 

state. The association of layered iron formation containing 

base-metal sulfide minerals provides possible lithologic evidence for syngenetic mineralization by submarine exhalative activity. Sand bars and tidal channels present in the 

sedimentary section could have acted as permeable pathways for movement of mineralizing fluids. The complex 

interlayering in the sedimentary sequence of carbonate and 

siliciclastic rock types having widely varying permeabilities 

created numerous fluid traps. 

Homogenization temperatures of primary and secondary inclusions in vein sphalerite range from 152°C to 

196°C; salinities range from 11.5 to 14.0 equivalent weight 

percent NaCl. o34S values of sulfides from Lion Hill vary 

from -25.9 to +10.0 per mil, and fall within the expected 

range for sulfide produced from bacteriogenic reduction of 

sulfate with o34S values of 25 to 30 per mil. In addition, 

some pyrite probably formed from sulfate in trapped pore 

fluid that resulted in heavier isotopic values characteristic of 

more closed-system behavior. Three sphalerite samples that 

1U.S. Geological Survey, National Center, MS 959, Reston, VA 

22092. 

2u.s. Geological Survey, 702 Post Office Building, St. Paul, MN 

55101. 

3u.s. Geological Survey, Denver Federal Center, Box 25046, MS 

955, Denver, CO 80225. 

have heavier sulfur isotopic values may reflect a change in 

the source of sulfur during a later episode of mineralization, 

perhaps a change to a deep-seated source. Lead isotopic 

compositions of galenas from mineralized zones at Lion 

Hill range from 18.351 to 18.632 for 206pbf204Pb, from 

15.546 to 15.618 for 207Pbf2°4Pb, and from 38.126 to 

38.496 for 208Pbf204Pb. The lead isotopic compositions of 

galena from Lion Hill and fluid inclusion and sulfur isotopic values for the Lion Hill sulfides are more like those of 

Pb-Zn-Ag deposits of Ireland than those of MVT or Appalachian-type Zn deposits. 

The prospect of an Irish-type sedimentary-exhalative 

origin for stratabound Pb-Zn deposits of the Paleozoic shelf 

of North America is of considerable importance to understanding the timing of mineralization relative to platform 

evolution and for evaluating the mineral resource potential 

of the region. Our study of the Lion Hill deposit indicates a 

potential for Irish-type Pb-Zn deposits in platform rocks 

of western Vermont; however, at Lion Hill they contain 

enrichments of Pb, Zn, and Cu rather than a Pb, Zn, and Ag 

association. 

INTRODUCTION 

Base-metal sulfide deposits and occurrences are 

exposed throughout an area approximately 300 km in length 

by 90 km in width of carbonate-siliciclastic platform rocks 

of Cambrian and Ordovician age that form the lowlands 

between the Green Mountain massif and the Adirondack 

massif in western Vermont (fig. 1 ). Lower Cambrian 

Monkton Quartzite (Cady, 1945) is the host for the largest 

stratabound Zn-Pb-Cu sulfide zones found at Lion Hill, 3-4 

km north of the town of Brandon, Vt., (fig. 1); lesser 

amounts of base-metal sulfide minerals occur in Winooski 

Dolomite. In other areas of the western Vermont lowlands 

(fig. 1), Zn-, Pb-, Fe-, and Cu-sulfide occurrences are found 

in carbonate-siliciclastic platform rocks of the Danby Formation (at Hinesburg, Vt.) and the Dunham Dolomite (at 

Fernville, Milton, and Zion Mountain, Vt., and at Dunham, 

Quebec) (figs. 1 and 3). Lower Cambrian clastics of the 
2 

D 

D 

--

GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

Explanation 

• Qunhai'T! "'., 

,. . " ,. " .. . " . ,. " .... ' 

,. . " ,. " ., 'I 

. " . ,. .... ·,. .. ' 

. " .. ,. 

20km 

I 

Rocks of parautochthonous shelf sequence (Ordovician and 

Cambrian)-Limestone, dolomite, and quartzite 

Rocks of eastem Green Mountain terrane (Ordovician and 

Cambrian)-Pelitic schist, metagraywacke, and minor 

amphibolite 

Rocks of taconic allochthon (Middle Proterozoic)-$1ate, 

graywacke, and minor carbonate 

Basement rocks (Middle Proterozoic )-Felsic gneiss, 

quartzite, minor amphibolite, and calc-silicate rock 

Thrust fault - sawteeth on upper plate 

Contact 

Figure 1. Regional geologic setting of base-metal sulfide 

deposits and occurrences in Cambrian and Ordovician 

siliciclastic platform rocks of western Vermont. The Lion 

Hill area is located just north of the town of Brandon, Vt., 

and includes the Churchill prospect and Fay and Nicklaw 

mines. Geologic map modified from Stanley and Ratcliffe 

(1983, 1985) and Thompson (1990). Other mineralized 

localities include Dunham, Quebec (Gauthier and others, 

1985, 1989; Boucher, 1986), and Orwell, Vt., and Saratoga 

Springs, N.Y. (Summarized in Clark and Slack, 1988; 

Clark, 1990; USGS Mineral Resource Data System; N .M. 

Ratcliffe and S.H.B. Clark, unpub. data, 1990). 

• Base-metal mine, occurrence, or prospect 
GEOLOGIC SETIING 3 

Nassau Formation host Zn-Pb-Cu sulfide mineralized rock 

at White Creek in southern Vermont (Slack and others, 

1987; Slack, 1990). Along the eastern side of the Green 

Mountains, small stratabound deposits of magnetite and 

hematite and siderite and pyrrhotite are found. These 

occurrences are contained in pelitic schist, metagraywacke, 

and minor amphibolite that make up the metamorphic cover 

sequence of the eastern Green Mountains (Slack and 

Schruben, 1990; Thompson, 1990). 

Most of the occurrences at Lion Hill are small and lack 

detailed production records. The earliest published reports 

of the area include mention of a shaft sunk in the 1870's 

from which ore was apparently mined and a core drilling 

program headed by St. Joseph Lead Company in 1941. The 

New Jersey Zinc Company carried out exploration work at 

Lion Hill from 1952 to 1954; during that time they mapped 

the Fay shaft, conducted soil sampling, and drilled 30 holes, 

some of which were-240m in depth. The Labradex Corporation conducted an exploratory drilling program of the 

area including the Fay mine, Churchill Prospect, and Nicklaw mine between 1981 and 1982; they drilled eight holes, 

one to a depth of 125 m. Studies of these materials provide 

information upon which some of this report is based. A 

dominantly synsedimentary origin was proposed for the ZnPb (±Cu) mineralized rock occurring in platform rocks at 

Lion Hill (fig. 1) as the result of a U.S. Geological Survey 

mineral resource study of the Glens Falls 1 o x 2° quadrangle (Clark, 1987; Clark and Slack, 1988; Clark, 1990; 

Slack, 1990; Foley, 1990). The present study characterizes 

in more detail the nature and origin of the Lion Hill deposit, 

including a consideration of the sedimentary environment, 

petrographic relations of sulfide minerals to sedimentary 

and deformational fabrics, geochemical signatures of mineralized and unmineralized samples, sulfur and lead isotopic geochemistry, and fluid inclusion thermometry studies. 

Interpretation of the mineralized rock in the Lion Hill area 

as a metamorphosed Irish-type sedimentary-exhalative PbZn deposit suggested a potential for commercially important sediment-hosted base-metal-Ag deposits in similar carbonate-siliciclastic shelf sequences that occur throughout 

western Vermont, eastern New York, northwestern Massachusetts, and southeastern Quebec (Clark, 1990). 

ACKNOWLEDGMENTS 

This study was made possible by the generous cooperation of the New Jersey Zinc Company and the Labradex 

Corporation, who provided drillcores, maps, and cross sections for study by the USGS. Special thanks is extended to 

John F. Slack (USGS), who accompanied Clark to the field, 

identified the magnetite iron formation and recognized its 

genetic significance; Slack initially encouraged Clark to 

pursue the study and reviewed earlier versions of the manuscript. The authors also are grateful to Jon Broderick and 

Christopher Scholz, formerly of Labradex, for supplying 

information and showing Clark the prospects at Lion Hill; 

to E--an Zen and Jane Hammarstrom (USGS) for sharing 

logs of the New Jersey Zinc Company cores; and to Nick 

Ratcliffe (USGS), Charles Ratte (Vermont Geological Survey), and Charlotte Mehrtens and Robert Butler (University 

of Vermont) for discussions that contributed to our study. 

Careful reviews by Douglas E. Crowe (Univ. of Georgia), 

Mary F. Horan (USGS), and John F. Slack substantially 

improved this manuscript. Maurice Ritzman (National Science Foundation) and an anonymous reviewer offered many 

constructive criticisms of the manuscript. 

GEOLOGIC SETTING 

REGIONAL TECTONIC, SEDIMENTARY, AND 

METAMORPHIC ENVIRONMENT 

Rocks of the Cambrian and Ordovician carbonatesiliciclastic platform were deposited on a shelf that formed 

the eastern margin of the North American continent following Late Proterozoic rifting (Thompson, 1990). The platform rocks rest unconformably over rocks of the 

Adirondack basement, which are part of the billion-year-old 

Grenville terrane that forms much of the southeast part of 

the North American craton. The carbonate siliciclastic shelf 

was downfaulted on its eastern margin, and deep-water 

environments that formed due to opening of the protoAtlantic Ocean (Iapetus) lay farther to the east. The stratigraphic succession that unconformably overlies Grenville 

basement begins with basal clastics of Late Proterozoic age 

to earliest Cambrian age (summarized in Thompson, 1990) 

that are succeeded in turn by the Cambrian sedimentary 

rocks. On the developing shelf margin, Cambrian sediments were deposited in a shallow sea; their compositions 

alternated between dominantly siliciclastic and dominantly 

carbonate facies (the stratigraphic section from base to top 

includes the Cheshire Quartzite, Dunham Dolomite, 

Monkton Quartzite, Winooski Dolomite, and Danby Formation) (Mehrtens, 1985). The terrigenous component was 

supplied to the sedimentary pile by a land mass located to 

the west of the platform in the vicinity of the present-day 

Adirondack Mountains. The lower units (Cheshire and 

Dunham) are not found to the west, probably due to westerly sedimentary onlap in Early Cambrian time (Zen, 1967). 

There is no evidence for volcanic rocks locally in the parautochthonous shelf sequence. 

Thrusting of deep-water sediments over the shallowwater platform sequence commenced in the Middle Ordovician as part of the Taconic orogeny when the continent collided with an island arc located to the east of the deep-water 

trench (Zen, 1972). The collision caused rocks of the shelf 

sequence to collapse and the development of mainly highangle longitudinal faults (Zen, 1972). The fault movement 

was accompanied by minor volcanic eruptions (Thompson, 

1990). The continental shelf was downfaulted into a deep-
4 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

water basinal environment of the proto-Atlantic to the east 

(Friedman, 1979). Sediments that originated on the continental slope were thrust over the platform to form the 

Taconic allochthon, and the underlying parautohthonous 

carbonate-siliciclastic platform was deformed into foreland 

folds (fig. 1). Mineralized rocks of the Lion Hill area are 

located in the overturned eastern limb of the south-plunging 

Middlebury synclinorium, a foreland fold that is strongly 

overturned to the west. 

The northern Appalachian region, including southeastern New York, Connecticut, Massachusetts, and Vermont, 

was subjected to medium-pressure regional metamorphism 

during the Taconic orogeny at about 450 Ma (Zen, 1967, 

1972). Metasedimentary rocks in the vicinity of Lion Hill 

contain chlorite, epidote, and, locally, rare, pale-green to 

green-brown biotite (Cady, 1945; Clark, 1990), indicating 

greenschist facies conditions. Pyrophyllite is not present in 

the pelitic rocks (Zen, 1960), and the limestones and dolomites do not contain talc, wollastonite, graphite, or other 

minerals that form by decarbonation reactions; the dolomites show only minor recrystallization. There is no evidence in the area for Acadian deformation (Sutter and 

others, 1985). 

LOCAL TECTONIC, SEDIMENTARY, AND 

DEFORMATIONAL ENVIRONMENT 

Lithofacies and environments of deposition of 

Monkton Quartzite have been studied in detail in the Burlington, Vt., area (fig. 1). Sedimentary features, such as ripple marks, mud cracks, rain-drop impressions, cross 

bedding, and trace fossils, are well preserved in the rocks, 

and Rahmanian (1981a,b) and Mehrtens (1985) have recognized seven lithofacies, each consisting of varying amounts 

of carbonate and siliciclastic rock. The textures and lithologic cycles led them to propose that the shallowing-upward 

siliciclastic and siliciclastic-carbonate cycles were characterized by repeated depositional sequences of ( 1) subtidal 

siliciclastic sand shoals and channels, (2) interbedded siliciclastic sand, silt, and carbonate intertidal zone sediments, 

and (3) carbonate mud of the high intertidal to supratidal 

zone. These supratidal, intertidal, and shallow subtidal sediments interfinger with, and grade into, subtidal oolitic 

dolostone and platform margin breccias (Mehrtens, 1985). 

The rocks at Lion Hill and at Burlington are lithologically 

similar and, hence, probably formed in similar environments, although the Monkton Quartzite at Lion Hill contains a greater proportion of carbonate rocks (metadolostone, arenaceous and phyllitic dolostone) and lesser 

amounts of siliciclastic rocks than Monkton Quartzite at 

Burlington. 

Deformation and metamorphism have obliterated most 

sedimentary features in rocks at Lion Hill; however, the 

lithologies and some rare preserved features support the 

suggestion that sedimentation was mostly in a shallowwater tidal-flat environment. Some of the rocks show fine 

color laminations, while others have a mottled appearance. 

The common occurrence of mottled reddish colors (pale to 

dark gray, pale orange, pink, orange-pink, and pale red in 

hue) and the presence of a terrigenous component suggest 

deposition in an intertidal zone. Admixing of carbonate and 

siliciclastic materials characterizes much of the Lion Hill 

section; in some samples, 1- to 2-mm-wide quartz grains 

appear to float in dolomite. The depositional environment 

for this rock may be analogous to that which formed intertidal mud-flat deposits in Monkton Quartzite in northwestern Vermont (Mehrtens, 1985). Possible algal fabrics, 

including laminar and small fingerlike structures and calcite-filled birds-eye (fenestrae) vugs, also are preserved 

locally in drillcore (fig. 2A). These fabrics suggest that 

intertidal to supratidal facies of deposition and evaporitic 

conditions could be a part of the depositional environment 

of Monkton Quartzite at Lion Hill (fig. 2A). Although there 

is no original textural evidence of evaporite conditions in 

the Monkton Quartzite, some features suggestive of an 

evaporite-bearing depositional sequence (basal quartzite 

overlain by metadolostone) indicate at least partial transition from shallow-water clastic to chemical sedimentation. 

Similar features, combined with fluid-inclusion data, have 

been used to postulate the occurrence of Silurian evaporites 

in southeastern Vermont, just south-east of Chester dome 

(Rich, 1979). 

Discontinuous layers of metasandstone are common in 

Monkton Quartzite at Lion Hill. In drillcore, the layers 

have medium-scale cross stratification and are characterized 

by sharp erosional bases and a transition upward into finely 

laminated material with clay drapes (fig. 2B). The textures 

suggest deposition in a tide-dominated environment, possibly a tidal channel or sand bar in the intertidal zone. A distinctive unit in Monkton Quartzite at Lion Hill is a 

discontinuous 10- to 20-m-thick metasandstone to quartzite 

that generally occurs about 50 m below the contact of 

Monkton Quartzite with Winooski Dolomite. The unit 

(informally referred to as Ethan Allen quartzite in New Jersey Zinc Company reports) is pale gray, medium- to 

coarse-grained, and well sorted, and is similar to a coarsegrained, well-sorted, cross-stratified siliciclastic unit in 

Monkton Quartzite in the Burlington area that Speyer 

(1983) proposed formed as a sand bar. 

Folds in rocks of the Lion Hill area formed predominantly by flexural slip (Burt, 1982). The folds have axes 

that trend about 1 oo west of north and plunge about 20° 

southeast; their axial surfaces dip about 50° to 60° to the 

east. The overturned Lion Hill anticline, a dominant structure, is representative of this style of folding (fig. 3). 

Numerous smaller scale folds that occur on its limbs 

include broad, open, and cylindrical similar folds found in 

competent strata and isoclinal folds that formed in calcareous rocks and near zones of shearing (Clark, 1990) (fig. 2C, 

D). Two stages of deformation of the rocks at Lion Hill are 
GEOLOGIC SETTING 5 

Figure 2. Rocks characteristic of 

the Lion Hill area. Scale in 

centimeters. A, Probable algal 

fabrics and calcite-filled fenestrae 

vugs (white) in dolostone from the 

Monkton Quartzite at Lion Hill 

(core L6 at a depth of 38 m). B, 

Medium-scale cross stratification 

in calcareous metasandstone from 

the Monkton Quartzite at Lion Hill 

(core L2 at a depth of 32 m). C, 

Sheared isoclinal folds in metadolostone and phyllite (core L3 at 

a depth of 7 m). D, Outcrop showing large-scale folding. 
6 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

indicated because the pervasive schistosity (S 1) that developed parallel to compositional layering is itself folded by a 

second schistosity (S2) that is parallel to the axial planes of 

F2 folds. Sulfide minerals commonly occur along both S 1 

and S2, and sphalerite layers that occur along S 1 are folded 

by S2; this folding indicates that some mineralization was 

syntectonic or pretectonic. The Richmond fault, a highangle reverse fault, displaces bedding and contacts at Lion 

Hill (fig. 3) (Clark, 1990). The primary evidence for this 

fault is stratigraphic offset and the presence of brecciated 

zones and deformed phyllites in drillcore. 

The thickness of the Monkton Quartzite increases 

abruptly at Lion Hill in the vicinity of the mineralized zones 

(fig. 3). At Brandon, the Monkton Quartzite is estimated to 

be about 60 m thick, but at Lion Hill the thickness is 

between 150 and 180m (New Jersey Zinc Company, unpub. 

reports, 1952-54). Lithologic sequences differ dramatically 

from core to core as a result of both discontinuous sedimentation in a tidal-flat environment (abrupt and irregular facies 

changes) and superimposed structural complexities (folds, 

shearing along axial surfaces, and faulting related to development of the foreland folds). The irregularity of patterns 

can be attributed to original features of tidal-flat deposition, 

tectonic instability at the time of mineralization, disruptions 

by Taconic folds and faults, or the effects of a combination 

of these factors. For example, dolostone breccias are found 

locally in drillcore, and while some may have formed as 

intraformational breccias (possible rip-up textures), other 

breccias clearly formed by dissolution. The apparent 

increase in stratigraphic thickness could be accounted for 

by facies control if the facies boundaries are not planar but 

are irregular and units are facies controlled (units are not 

necessarily of the same thickness). The apparent thickening 

also may be accounted for by folding during the Taconic 

orogeny. Synsedimentary faulting and subsidence could 

perhaps have resulted in the development of a local basin in 

which a thicker sequence of Monkton Quartzite was deposited; however, the tidal-flat environment would likely have 

been destroyed. Evidence for sedimentary breccias in 

Monkton Quartzite at Burlington and at Lion Hill may indicate some local synsedimentary faulting. 

LION HILL Zn-Pb-Cu DEPOSIT 

SHAPE AND EXTENT OF MINERALIZED ZONES 

The Churchill Prospect (northern ore body) is located 

in the northern portion of the Lion Hill area on the overturned limb of the Lion Hill anticline (figs. 3, 4A). Sulfides 

occur in a stratabound zone -10-25 m stratigraphically 

below the contact of the Monkton Quartzite with the overlying Winooski Dolomite (Clark, 1990). A small mineralized 

zone occurs near the Nicklaw mine on the upright limb of 

the Lion Hill anticline 300 m northeast of the Churchill 

prospect. Sulfides are found approximately 30 m below the 

contact and may be a continuation of the northern ore body 

(Churchill Prospect) (figs. 3, 4A). Sulfides also are found in 

the southern part of the Lion Hill area at the Fay (or Oram) 

mine (figs. 3, 4B). The southern mineralized zone is on the 

upright limb of the Lion Hill anticline. The southern zone 

occurs in the interval of -40-60 m below the contact 

between the Monkton Quartzite and Winooski Dolomite. 

The mineralized zones are stratiform and lenticular in 

overall form but irregular and discontinuous on a local scale 

(fig. 4A, B). Small clots and discontinuous stringers of Zn, 

Pb, and Cu sulfides also occur in rocks above and below the 

main sulfide bodies, in Monkton Quartzite and Winooski 

Dolomite. Gray metadolostone is the most common host 

rock for Zn-, Pb- and Cu-sulfide minerals, although they 

also occur in metasandstone and phyllite. Zones delineated 

by mining company personnel for both areas have fairly 

restricted thicknesses (15-60 m). Small- to large-scale tight 

folds seen in surface exposures and in samples of core 

appear to die out within short distances in alternating layers 

of metadolostone, phyllite, and quartzite. The structures 

shown in drillcore (fig. 2) mirror fold styles that are 

exposed in the shaft and drifts in the Fay mine. The sulfide 

minerals occur as metamorphic segregations along schistosity or shear surfaces parallel to bedding, stringers in 

matrix-supported dolostone breccia, intergranular sulfides 

in cross-stratified metasandstone, fillings in discordant fractures and veins, and layered sulfide-bearing magnetite iron 

formation. 

HOST ROCKS 

The predominant rock types in the Lion Hill area are 

arenaceous metadolostone, metasandstone, and phyllite. 

Distinctions between rock types generally are gradational, 

and individual units consist of varying proportions of these 

three rock types. 

In general, dolomite comprises 50 to 60 volume percent of the metadolostones; the rest of the rock is composed 

of quartz, K-feldspar, sericite, muscovite, and biotite intergrown with chlorite. Accessory minerals include pyrite, 

zircon, leucoxene, magnetite, ilmenite, and tourmaline. 

These commonly are rounded and occur with the micaceous 

minerals in phyllitic layers or are segregated into irregularly 

shaped dark layers. This segregation originally may have 

formed by bioturbation. Some parts of the metadolostones 

are composed almost entirely of a fine mosaic of dolomite 

grains with less than 5 percent accessory quartz, K-feldspar, 

and sericite. Isolated cubes of pyrite also occur in the metadolostones; deformed shapes and pressure shadows indicate 

pretectonic to syntectonic crystallization. Locally in the 

dolomite, breccia zones containing angular fragments occur 

that are probably tectonic in origin, although some could be 

dissolution features. Coarse-grained, pale-gray dolomite 
LION HILL Zn-Pb-Cu DEPOSIT 7 

prospect 

43° 50' 

-£w 

0 

0 0 0 NS N9 

L4 

Explanation 

I Os I Shelburne Marble (Ordovician) 

1-ccsl Clarendon Springs Dolomite (Cambrian) 

l-ed I Danby Formation (Cambrian) 

l-ew I Winooski Dolomite (Cambrian) 

lt:>ml Monkton Quartzite (Cambrian) 

lt.dbl Dunham Dolomite (Cambrian) 

Contact 

Fault 

~ Mine or prospect 

N22o Unmineralized drillhole 

N26e Mineralized drillhole 

-t-+ Anticline-Approximately located, 

showing plunge 

-{t + Overturned anticline-Approximately located, 

showing plunge 

-t-+ Syncline-Approximately located, showing 

plunge 

-A+ Overturned syncline-Approximately located, 

showing plunge 

Figure 3. Geology of the Brandon area, modified from 

Cady (1 945) and Burt (1982). Inset map shows local 

geologic setting. Locations of drillholes (closed circles 

identify holes that intersect an ore body; open circles 

represent holes that intersect weakly mineralized or unmineralized rock) and mine workings are given. 
8 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

and quartz fill the spaces between clasts in unmineralized 

breccias. In mineralized zones, sphalerite, galena, and chalcopyrite form the matrix of dolomite breccias. 

Phyllitic, dolomitic metasandstone is common in both 

Monkton Quartzite and Winooski Dolomite at Lion Hill. 

Grain sizes range from fine to coarse in some rocks, but a 

bimodal distribution is also common, with larger clasts of 

predominantly subangular to subrounded quartz and K-feldspar set in a finer grained matrix. The matrix material is 

composed of quartz, K-feldspar, mica, and carbonate. 

Potassium feldspar is a common constituent of the rocks, 

making up from 5 to 35 percent of the metasandstones. 

Micaceous minerals (sericite, muscovite, and fine-grained, 

pale-green and greenish-brown biotite) make up as much as 

35 percent of some of the metasandstones. Dolomite occurs 

both as fragments and as fine-grained material in the matrix. 

Accessory minerals include zircon, rutile, sphene, epidote, 

pyrite, tourmaline, and leucoxene (some with magnetite or 

ilmenite cores); these minerals are subrounded and probably are detrital in origin. Concentrations of leucoxene and 

rutile parallel to bedding, as defined by grain-size variations, suggest mechanical concentration during sedimentation. Tourmaline occurs in small amounts ( <1 percent), 

most commonly as rounded green grains that may have 

brown overgrowths. The alignment of brown euhedral 

grains of tourmaline in the plane of the schistosity suggests 

that tourmaline also grew during metamorphism. 

Arenaceous and dolomitic varieties of phyllite contain 

the same minerals as the metadolostones and metasandstones but have greater than 50 percent micaceous minerals 

and lesser amounts of quartz, feldspar, and dolomite. 

Effects of metamorphism, while evident in other rock types, 

are especially well developed in the phyllites. Schistosity 

and foliation are defined by orientation and segregation of 

micaceous minerals, elongation and recrystallization of 

quartz grains, and cataclastic flow features. Rotational 

snowball textures are seen in some grains, and micaceous 

layers curve around large clasts of quartz. Recrystallized 

pyrite forms euhedral crystals (0.5 em) in some phyllites 

and is spatially associated with possible algal structures 

(in dolomitic phyllite). The pyrite may be diagenetic (for 

example, recrystallized framboidal pyrite) and may reflect 

the former presence of organic matter that decomposed 

under reducing conditions in the sediments. 

MINERALIZED ROCKS 

Mineralized rocks at Lion Hill are primarily finegrained, massive pale-gray metadolostone and locally darkgray phyllite that contain stringers and small irregular 

masses of fine-grained sphalerite, galena, pyrite, and chalcopyrite (in decreasing order of abundance). Textures of 

the mineralized rocks can be grouped into four types: metamorphic segregations, intergranular fillings, layered sui-

~ Q) 

Q) 

E. 

c 

0 

~ 

> Q) 

w 

~ Q) 

Q) 

E. 

c 

0 

·~ 

> 

~ 

w 

200 

100 

0 

200 

100 

0 

Explanation 

Contact-Dashed where approximately located 

Fault-Arrows show relative movement 

Figure 4. Cross sections along lines A-A' and B- B' of figure 3 

showing mineralized zones (shaded) and sample locations: open 

squares locate samples used in sulfur isotopic study; open circles 

locate samples for lead isotopic study. Dashed line in 4A indicates 

possible fold geometry based on surface geology. Surface intersections of drillholes are labeled (for example, N 12); holes are 

located on figure 3. Prepared from Cady (1945), New Jersey Zinc 

Company (unpub. data, 1952-54), Labradex Corporation (unpub. 

data, 1982), and Clark (1990). See figure 3 for explanation of 

geologic map units. 

fides, and discordant veins with open-space fillings. The 

effects of metamorphism and deformation have obliterated 

most primary fabrics; however, premetamorphic features 

including sulfides filling intergranular spaces in dolomite 

and layered magnetite iron formation are preserved in some 

places. Pyrite occurs as inclusions and irregular grains 

intergrown with other sulfide minerals in mineralized horizons and also forms cubes that are widespread in unmineralized and mineralized sedimentary rocks. 

Metamorphic segregations are the most common sulfide occurrence. Sphalerite, galena, and chalcopyrite typically occur in discontinuous layers that are elongate within 
GEOCHEMISTRY 9 

schistosity and shear planes (figs. 5A and 6A). In the metamorphic segregations, sphalerite and galena are intergrown 

with quartz, carbonate, microcline, and schistose biotite and 

chlorite. Minerals in the segregations are coarser grained 

than those in the host rocks, reflecting mobilization and 

recrystallization during metamorphism. 

Pale-brown sphalerite fills spaces between dolomite 

grains and is concentrated along bedding planes, including 

cross stratification (fig. 5C). Sphalerite appears to completely permeate the rock and forms intergranular cementing material. In thin section, irregularly shaped, unzoned, 

yellow intergranular sphalerite fills spaces between dolomite and quartz grains of the host rocks and is concentrated 

along coarser grained basal portions of graded beds (fig. 

6B). The intergranular sulfide minerals are interpreted to 

have formed as the result of diagenetic introduction of 

metal-bearing fluids into the rocks. Pale-brown sphalerite, 

galena, and chalcopyrite that form the matrix of breccias 

(fig. 5B) also may have originated as diagenetic minerals, 

like the interstitial sphalerite. The sulfide minerals and carbonate fragments show evidence of recrystallization at contacts. 

Large pieces of layered magnetite iron formation consisting of finely laminated magnetite concentrated in layers 

about 2 to 3 em thick (fig. SF) are found in dumps near the 

Nicklaw mine. Disseminated accessory magnetite grains 

also occur in sulfide-rich stringers in drillcore, but samples 

having magnetite-rich layers have been observed only in the 

dump material. Iron formation has not been found in outcrop or drillcore from elsewhere in the area, but the size, 

abundance, and location of the pieces on a mine dump at the 

top of Lion Hill indicate that they probably were taken out 

of the mine. In addition to magnetite, iron formation contains brown sphalerite and chalcopyrite, minor pyrite and 

galena, and traces of specular hematite. Both galena and 

pyrite occur as inclusions in magnetite (fig. 6C) and as separate grains. Magnetite and sulfide minerals are interlayered with quartz, quartz-carbonate, or biotite-chloritebearing bands. A strong schistosity is developed in the 

micaceous minerals, and euhedral grain borders commonly 

are present in the magnetite grains. The presence of basemetal sulfides in the iron formation, especially inclusions of 

galena in magnetite that are isotopically like galena in other 

textures, further supports that the iron formation is related 

to mineralization in the Lion Hill area. 

Base-metal sulfide minerals also occur as discordant 

veins or irregular masses that cut bedding of the host rocks. 

The material filling the fracture cuts across bedding and, in 

turn, is cut by schistosity. For example, one small fracture 

preserved in drillcore is filled with carbonate and silicate 

grains like those of the surrounding rock and includes traces 

of sphalerite (fig. 5D). This texture suggests that matenal 

flowed into the fracture when the rock was in a semilithified 

state. More commonly, discordant veins cut obviously brittle host rocks, and quartz, dolomite, and microcline form 

thin borders between the host rock and the sulfide minerals. 

The textures of these veins may result from the reaction of 

hot, saline, water-rich fluids with carbonate wallrock in a 

feeder zone and by the movement of fluids through dilatant 

fracture zones in semilithified sediments. 

Other veins are composed entirely of sulfide minerals 

and cut both host rocks and early calcite-cemented solution 

breccia (fig. 5£). Euhedral quartz crystals line some veinlets, clearly indicating the presence of open space locally 

during at least one period of crystallization. These veins 

may represent either ( 1) local areas of late-stage mineralization that were not deformed during the Taconic orogeny, (2) 

veins formed by post-peak metamorphic crystallization, or 

(3) an entirely separate mineralizing event. Cross-cutting 

veins and blebs of gangue minerals (quartz, calcite, and 

microcline) occur sparsely in areas outside the mineralized 

zones, in addition to being associated with sulfide minerals 

in some veins. 

GEOCHEMISTRY 

GEOCHEMICAL DATA 

Lithologic logs and inductively coupled plasmaatomic emission spectroscopy (ICP-AES) analyses for 9 of 

the 38 drillholes (see appendix A) illustrate characteristic 

element distribution patterns for sections that contain established mineralized zones (N26, N28, Nil, N14; shaded 

zone on fig. 7A, B, E, and F) and for sections that are 

weakly mineralized or unmineralized (L2, L3, L6, NIO, 

Nl3; fig. 7C, D, G, H, !). For the purposes of this study, a 

weakly mineralized or unmineralized section is one that 

lacks a mineralized zone as delineated by mining company 

personnel, based on a combination of factors including proportion of sulfide minerals to wallrock, thickness of mineralized zone, and ore grades. Elements that show a 

systematic relationship to the mineralized zones based on 

ICP-AES analyses are Zn, Pb, Cu, Ag, Cd, and As. In the 

most intensely mineralized zones, Co, Ni, Mo, Sb, and W 

also are present in anomalous amounts relative to unmineralized and weakly mineralized zones (table 1). No conclusive geochemical patterns related to mineralization were 

detected for any other elements analyzed for the study. 

Lithologies and geochemical data for individual drillholes in the Lion Hill area are given in figure 7. Drillholes 

N26 and N28 (fig. 7A, B) intersect the Churchill prospect 

(northern mineralized zone) in an overturned section of 

Monkton Quartzite (figs. 3, 4A). Cores L2 and L6 (figs. 7C, 

D) are from holes drilled east of the Churchill prospect (fig. 

4A); L2 intersects a small weakly mineralized zone on the 

upper limb of the overturned syncline, and L6 penetrates 

weakly mineralized and unmineralized rock east of the 

mineralized zone. Cores Nil and N14 (fig. 7£, F) are 

from drillholes that intersect the Fay mine sulfide lens 

(southern mineralized zone) in an upright section of 
10 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

Figure 5. Sulfide-bearing rocks 

from the Lion Hill area. All scales 

in centimeters. A, Sphalerite and 

galena (s) in elongate metamorphic segregations along schistosity/shear surfaces parallel to 

bedding (core N24 at 158.8 m). B, 

lntergranular sphalerite, galena, 

and chalcopyrite (s) in matrixsupported dolostone breccia (core 

N14 at a depth of 166.7 m). 

C, Intergranular sphalerite (s, 

medium-gray material) in crossstratified metasandstone ( drillhole 

N28 at a depth of 158.5 m). D, 

Discordant fracture filled with 

material from surrounding rock 

including trace amounts of sphalerite (core L2 at a depth of 24 

m). E, Discordant, massive sphalerite (s) vein cutting gray 

dolostone and vein of calcitecemented solution breccia(?) 

(drillhole L2 at a depth of 82.3 m). 

F, Layered magnetite iron formation with later quartz veining. 

Darkest bands are sulfide and 

magnetite rich; lighter bands are 

silicate rich. 
GEOCHEMISTRY 11 

Figure 6. Photomicrographs of sulfide-rich samples from the 

Lion Hill area. Abbreviations: ccp, chalcopyrite; gn, galena; kspar, K-feldspar; mgt, magnetite; qtz, quartz; sph, sphalerite. A, 

Sulfides (black) in metamorphic segregation parallel to schistosity, 

plane transmitted light (from core B24 at a depth of 16.2 m). B, 

Monkton Quartzite and Winooski Dolomite (figs. 3, 4B). 

Cores NIO and N13, which were drilled south and southeast 

of the Fay mine (figs. 3, 4B), contain a much greater proportion of carbonate than cores that intersect the mineralized zones. Core L3 (fig. 7 I) intersects a weakly 

A 

calcareous 

metasandstone 

~ 

~ 

Interstitial sphalerite (black) concentrated in slightly less 

calcareous bed of calcareous metasandstone, plane transmitted 

light (sample from core B31 at a depth of 227.1 m). C, Inclusions 

of galena in magnetite from iron formation, reflected light (sample 

from dump near Nicklaw mine). 

mineralized zone in Monkton Quartzite at the Nicklaw 

mine, north of the two main mineralized areas (fig. 3). 

The patterns of metal distribution for the southern and 

northern ore lenses show that Zn, Pb, Cu, and Cd are the 

most strongly concentrated elements in the mineralized 
12 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

A, Churchill prospect 

01 ..I. ..I. 

o Zn 8o Pb 8o Cu ~o Ag co Cd ~o ~ ~ N28 

B, Churchill prospect 

N26 

Q) 

0 

() 

0 

z 

01 ..I. ..I. 

o Zn 8o Pb 8o Cu ~o Ag co Cd ~o As ~ 

1. Samples from this zone may contain up to 91 ppm 

Co, 69 ppm Ni, 7 ppm Mo, 20 ppm W, 15 ppm Sb, 

600 ppm Ti, and 23 ppm As. 

2. Samples may contain up to 22 ppm Co, 27 ppm Ni, 

and 36 ppm As. 

E, Fay Mine 

N11 

Zn 01 Pb o Cu ....~. Ag ....~. Cd N As N F, Fay mine 01 ....~. ....~. As 

0 8o oO ~o oo oO o N14 o Zn 8o Pb go Cu ~o Ag oo Cd ~o ~ 

4. Samples also contain 13-17 ppm Co, 22-58 ppm 

Ni, and 2-5 ppm Mo. 

I, Nicklaw mine 01 Zn 0 Pb 0 Cu ~ Ag ....~. Cd N As N L3 o 0 o 0 o 0 o oo oo o 

I I .J . ./ •• ··J.· ·f- • 1 ••. : 

L I 

·1 . . 

. I . . J" 

.·/ . 1• ··f..·.! . . J. · ./ • 

•• ··J.· ·I· . .I . :f.: · ·I. ·t 

8. Sample also contains 26 ppm Co and 32 ppm Ni. 

5. Samples also contain up to 9 ppm As and 9 

ppm Mo. 

6. Samples contain 29-100 ppm Co,45-61 ppm Ni, 

4-25 ppm Mo, 10-37 ppm W, 17-38 ppm Sb, and 

8 ppm Sn. 

~I 
GEOCHEMISTRY 

C, Churchill prospect 

L2 

• .fo • .f. 

:j:.,·!- 3 

•_1_:·1 

.·r·"I· 

•'fo •'], 

.J.· I . •• ··J: ·I· • J • :f.: . . J •f 

• ·I·. ·I· 

. : .·. : ... 

. · ·.·: ·.· .. 

·.: :.· .. ·.: .· .. "./ .. • •I ·t ··I·. of· ·. '1 •J. ·1 . , . 

• l"·.f 

01 ...1. ...1. 

0 Zn o0 Pb o0 Cu 01 0 Ag ...1. 0 Cd N0 As N 

0 0 0 0 0 0 

G, Fay mine 01 ...1. ...1. 

N1 o o Zn 8o Pb 8o Cu ~o Ag ~o Cd ~o As ~ 

I I A\ 

J I I I I 

I I I I I I I I I I I 

1 I I I 

I I 

I I 

I _j_ _j_ 

I I I I I I I 

_l_ I I I 

I I I 

I I 

I I I I 77 I 

77 

7_7_ 

I I I 

I I I 

I 77 

1 7 

I I I 7 

I 

I I 

3. Samples also contain up to 1 01 ppm Co, 45 ppm 

Ni, and 709 ppm Ti. 

D, Churchill prospect 

H, Fay mine 01 ...~. ...~. 

N13 o Zn 8o Pb 8o Cu ~o Ag ~o Cd ~o As ~ 

7. Samples from this zones contain 23-25 ppm Co 

and 27-44 ppm Ni. 

EXPLANATION 

[J . . . Predominantly siliciclastic rocks; includes quartzite, 

metasandstone, and minor phyllite; dolomitic . 

Winooski Dolomite, arrowheads indicate 

stratigraphic tops; contacts approximate . 

~ Mixed carbonate-siliciclastic rocks, alternating layers 

of metasandstone, metadolostone, and phyllite. 

Monkton Quartzite, arrowheads indicate 

stratigraphic tops; contacts approximate. 

~ Predominantly carbonate rocks; metadolostone with 

~ phyllitic layers or partings. 

Mineralized zone 

Figure 7. Generalized lithologies and contents of Zn, Pb, 

Cu, Ag, Cd, As, and other elements (in parts per million) 

present in anomalous amounts (indicated by footnotes) in 

samples selected to show characteristic geochemical patterns 

from west to east in the Churchill prospect area (A-D), from 

west to east in the Fay mine area (E-H), and in the Nicklaw 

mine area (!). Shaded areas highlight established mineralized zones. Locations of drillholes are shown in figures 3 

and 4. See text for analytical details. 

13 
14 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

zones (fig. 1A, B, E, F). Zinc has a high elemental abundance (up to >20,000 ppm) throughout the ore lenses, 

whereas Pb is generally most enriched (up to> 19,000 ppm) 

in the central, higher grade parts of mineralized zones. The 

pattern of Cu enrichment (up to 14,000 ppm) is similar to 

that of Pb in mineralized zones. The correlation of Cd (up 

to 560 ppm) and Zn suggests that Cd occurs in sphalerite 

because no other Cd-bearing phase such as greenockite is 

present at Lion Hill. Arsenic is also enriched greatly in the 

mineralized zones in three of the four drillholes (up to 40 

ppm). The distribution of Ag is erratic; Ag was found in 

anomalous amounts (up to 60 ppm) throughout some highly 

mineralized zones (for example, N26, N14), but was barely 

detected ( <5 ppm) in others (N28, N 11). 

Patterns of elemental abundance for the Nicklaw mine 

area match those described above for the southern and 

northern mineralized zones (fig. 7!). Samples of drillcore 

indicate that Zn, Pb, Cu, and Cd are concentrated in the 

weakly mineralized ore zone. Silver was not detected. 

Three samples of the magnetite iron formation collected at 

the mine dump were analyzed (table 2 of Clark, 1990). All 

three iron formation samples show concentrations of Fe 

(>24 ppm), V (>1,000 ppm), Zn (>10,000 ppm), Pb (>1,000 

ppm), and Cu (> 1,500 ppm) that are well above the upper 

limit of determination. In addition, these samples have high 

concentrations of Ag (19-84 ppm), Cd (620-840 ppm), Ni 

(160-210 ppm), Co (23-31 ppm), and Se (8.1-24 ppm); Au 

was not found (below detection level of 0.08 ppm). 

Zinc and Pb are generally the most widely distributed 

metals laterally in weakly mineralized halos surrounding 

the main mineralized zones; Cu and As show minor enrichment. For example, cores L2, L6, N10, and N13 all contain 

anomalous concentrations of either Zn, Pb, Cu, or As (fig. 

7C, D, G, H). Copper, and to some extent As, are present in 

slightly anomalous amounts in samples that lack anomalies 

in other metals (for example, L2, L6, table 1). 

RELATION TO STRATIGRAPHY 

Reconstructing the stratigraphic section for the area 

(fig. 8) was accomplished by unfolding the structures, making contacts generally horizontal, and positioning the sections relative to (1) the Monkton-Winooski contact, (2) 

possibly correlative siliciclastic layers, and (3) zones containing high contents of base-metal elements. The reconstruction of the stratigraphy and mineralized horizons is 

heavily dependent on data for drillhole Nil, near the Fay 

mine, because this section contains three metal-rich horizons, the Monkton-Winooski contact, and a variety of 

lithologies for rough correlation. The sections are positioned relative to the sedimentary contact and mineralized 

horizons. Individual lithologies are generally not perfectly 

correlatable, as described earlier. Figure 8 indicates that the 

complete vertical interval of mineralized rock may be on 

the order of 250 m, although mineralization was strongest in 

three broadly stratabound horizons within the interval that 

have thicknesses of about 30 to 100 m or less and are 

spaced approximately 50 and 100m apart. The bulk of the 

highly mineralized rock is contained in the middle horizon, 

located about 50 m below the Monkton-Winooski contact 

(fig. 8). Weaker horizons above and below the middle horizon may be a halo effect or may represent separate mineralizing events. 

The mineralized zones generally occur in mixed carbonate-siliciclastic rocks, at or above prominent well-sorted 

siliciclastic units (N26, N28, Nll, and N14, at -0 m, -50 m 

-30 m, and -0 m above, respectively) (fig. 1A, B, E, F). 

Weak mineralization occurs in some well-sorted siliciclastic 

units (Nll, N14) and in dominantly carbonate units (N10, 

Nl3). 

FLUID-INCLUSION STUDY 

Coarse crystals of sphalerite up to 5 mm in width were 

selected from four cores (total of 7 localities) intersecting 

the main mineralized lenses (N26, N14, N28, and L2). 

These crystals form discordant veins, some of which show 

evidence of open-space filling. Other occurrences of 

sphalerite (as intergranular aggregates and unambiguous 

metamorphic segregations) and most other minerals were 

too fine grained to contain inclusions suitable for analysis. 

The 20- to 50-j..Lm-wide liquid-vapor inclusions fall into two 

groups based on textural characteristics. They do not contain daughter minerals, trapped solids, or visible C02. The 

majority of the inclusions are secondary in nature and are 

aligned along healed microfractures; others, having the 

same general size range, are isolated or occur in small 

groups and may be primary in origin. 

FLUID-INCLUSION DATA 

Fluid-inclusion thermometry results for sphalerite 

from discordant veins of the Lion Hill deposit (Foley, 1990) 

are plotted on figure 9. Homogenization temperatures of 

possible primary inclusions in sphalerite (table 2) range 

from 152° to 196°C. Measurements of the bulk salinity of 

the same inclusions, based on temperatures of the melting 

point of ice, yielded values of 11.5 to 14 equivalent wt% 

NaCI. Eutectic temperatures of about -25° to -30°C suggest that sodium is the dominant cation in solution. The 

lack of daughter minerals in the inclusions at room temperature indicates that the solutions are undersaturated with 

respect to the common salt components. Both primary and 

secondary groups of inclusions yielded approximately the 

same ranges of temperature and salinity values, implying 

that the two groups of inclusions contain cogenetic fluids. 

The inclusions lack textural evidence for having formed in a 

boiling environment. 
Table 1. ICP-AES analyses of drillcore samples from mineralized, weakly mineralized, and unmineralized intervals from the northern mineralized area, the southern mineralized area, 

and the Nicklaw mine area and farther north (fig. 3). 

[Results are given in ppm and are rounded to two significant figures. *,near detection limit; 0, not detected] 

Core Depth1 Width2 Zn Pb Cu Ag Cd As Co Ni Mo Sb w Lithology3 

Southern mineralized area 

Nil 112.5 24.4 33-24,000 0-1,400 2.2-33 0 0-66 0-6.1 3.6-18 11-58 0-5.9 0 0 m- Dolostone. 

N11 162.2 21.9 16-48 0 1.3-8.6 0 0 0 2.6-8.1 10-23 0 0 0 u- Quartzite. 

N11 184.1 20.1 18-640 0-140 1.9-20 0 0 0-9.4 2.1-35 6.9-58 0-8.5 0 0 w- Dolostone and quartzite. "'''l 

N14 154.8 15.8 24->2,000 0-15,000 0-1,400 0-59 0-560 0-40 3.1-100 3.3-61 0-2.5 0-84 0-37 m- Dolostone. r 

e N10 112.2 14.6 13-2,100 0-92 *0.7-103 0 0-9.3 0-*9.1 <6.0-27 0-36 <1.2 0 0 w- Dolostone. 9 N10 197.2 5.2 19-2,200 *9.1-25 0-16 0 0-4.9 0-*9.5 <6.0 *4.3-8 <1.2-*1.3 0 0 w- Dolostone. z N13 210.3 6.1 500->2,400 0-190 3.8-9.5 0 0-5.0 0 23-25 27-44 0 0 0 w- Dolostone. n 

L4 68.0 6.4 16-85 0-140 1.3-30 0 0 0-31 4.1-11 4.0-11 0 0 0 w- Dolostone. r 

e 

L4 112.2 5.2 110-170 0 1.5-2.7 0 0 0 4.1-4.5 2.5-3.1 0 0 0 w- Siliceous dolostone. Cl:l 

0 

Northern mineralized area z 

Cl:l 

N26 64.3 14.6 8.2-21,000 0-7,800 2.3-250 0-8.7 0-190 0-23 3.0-91 5.2-69 0-7.4 0-15.1 0-21 m- Siliceous dolostone. >-3 

e 

N28 144.2 20.4 42->3,000 0-1,900 0-34 0-*1.2 0-82 0-36 <.6-22 0-27 0 0 9.6-19 m- Metasandstone. t? 

-< L2 20.1 10.3 58->2,400 15-100 4.6-63 0 0-13 0-6.6 5.8-26 4.6-32 0 0 0 w- Dolostone. 

L2 81.7 11.9 18-270 0-26 1.5-8.3 0 0-1.2 0-26.0 2.8-14 3.4-18 0 0 0 w- Dolostone and quartzite. 

L6 24.4 7.0 13-48 0-17 5.5-38 0-*1.4 0 0 3.0-8.3 7.6-110 0 0 0 w- Dolomitic metasandstone. 

Nicklaw mine area and to the north 

L3 23.8 5.2 >22,000 140-820 7.1-76 0 6.1-34 0 5.6-7.3 8.3-8.9 0 0 0 w- Dolostone. 

L5 0.7 90.8 12-50 0-8 0.3-34 0 0 0 2.8-7.5 2.8-18 0 0 0 u- Dolostone. 

1 Depth to the top of the analyzed interval in meters. 2Width of analyzed interval in meters. 

3m, mineralized zone; we, weak mineralization or anomalous Zn, Cu, or Pb; u, unmineralized. 

....... 

Ul 
Explanation 

III~~IIII Mineralized zone 

I·:·::;· :I Predominantly siliciclastic rocks 

~ Mixed carbonate-siliciclastic rocks 

~ Predominantly carbonate rocks 

WNNf Fault contact 

Winooski Dolomite L6 

--------------------- ----

L3 

Lv-J 

Nicklaw mine 

Monkton Quartize 

Northam mineralized area-unfolded 

(Churchill prospect) 

gi 

N10 

.,..---rv 

Southam mineralized area-unfolded 

(Fay mine) 

Figure 8. Reconstructed stratigraphic section for the Lion Hill area showing combined geochemical profiles. 

-0"1 

a 

§ 

a 

B 

a 

~ n 

::c: 

~ n 

> 

~r 

> z 

0 

(;) 

~ ::E 

n 

Vl 

...., 

c 

0 

-tTl 

5'1 

r 

a 

z 

::c: 

F 

r 

< tTl 

:;t) 

~ 

0 

z 

...., 
FLUID-INCLUSION STUDY 17 

Upper Mississippi Valley 

(3 -

m 

z 

55 20 ~ 

~ 

~Silvermines 

Silvermines 

Southern Illinois 

Timberville, Va. 

Austinville, Va. 

Navan 

0 ~--~~~~~~----L----L----L---~--~----~--~----~--_J 

80 100 120 140 160 180 200 

Homogenization temperature (°C) 

[/~~(·}/J Irish-type Zn-Pb-Ag b::t//ttd MVT Zn-Pb ~~I!~!~!!!!i!i!!~i!i!i~i] Appalachian Zn-Pb 

• Lion Hill Zn-Pb deposit 

Figure 9. Temperature-salinity relations for fluid 

inclusions in sphalerite from discordant veins at 

Lion Hill (filled circles). For comparison, fluidinclusion data are plotted for Mississippi Valley-type 

(MVT) deposits (Upper Mississippi Valley, Tri-State, 

and Southern Illinois districts, Roedder, 1976), 

DISCUSSION OF DATA 

Discordant veins at Lion Hill may have originated 

either as epigenetic veins that were conduits or feeder zones 

for near-surface exhalations or as open-space fillings of sulfides remobilized along small fractures and shears related to 

regional metamorphism during the Taconic orogeny. Larger 

pods of sulfide minerals that occur as apparent segregations 

along shears and fractures, and in small discordant veinlets, 

have small halos of recrystallized dolomite indicating that 

the minerals may have recrystallized. These textures can be 

accounted for by reactions of hot saline, water-rich fluids 

with the carbonate wallrock in a feeder zone or by recrystallization during metamorphism. Thus, fluids trapped in the 

inclusions may represent either diagenetic fluids related a 

feeder zone or fluids that were present during and after the 

peak metamorphic event. 

Appalachian-type Zn-Pb districts (Austinville, Va., 

Foley and Craig, 1989; Timberville, Va., Roedder, 

1976), and Irish carbonate-hosted deposits (Silvermines, Samson and Russell, 1984; Navan and 

Tatestown, Andrew and Ashton, 1985; Keel, Roedder, 

1976, Caulfield and others, 1986). 

MODEL FOR A DIAGENETIC ORIGIN 

Mineralizing fluids that precipitated synsedimentary 

and diagenetic sulfides near the seawater-sediment interface 

must have originated at depth and traveled through faults, 

fractures, and structurally weak zones in the sedimentary 

pile. Under the simple hydrostatic conditions expected to 

prevail in this environment (fluid column open to air-water 

interface), the thermometry data can be used to infer that 

the discordant veins formed at depths ranging from 30 to 

135 m (based on data of Haas, 1971) below the air-water 

interface. Elevated salinities are typical of many basinal 

brines and may indicate that the fluids interacted with an 

unknown evaporite sequence at depth; however, ultrafiltration and boiling to generate higher salinities also are possible explanations. Evaporitic conditions have been proposed 

to be an integral part of the supra-, inter-, and shallow subtidal environments indicated for the Lion Hill sedimentary 
18 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

Table 2. Fluid-inclusion homogenization 

temperature and salinity data for sphalerite 

from Lion Hill, Vt. 

Inclusion Th Tm Salinity 1 

No. (oC) ec) (wt% NaCl) 

1 168 

2 177 

3 150.9 

4 160.1 -7.8 11.47 

5 159.3 -7.8 11.47 

6 164.2 

7 165.1 -8.4 12.19 

8 170.1 -8.4 12.19 

9 159.3 

10 152.4 -8.3 12.07 

11 169.2 -8.9 12.76 

12 175 -8.9 12.76 

13 176 -9 12.88 

14 172.7 -8.9 12.76 

15 156 

16 165 -8.7 12.53 

17 167.6 -8.9 12.76 

18 159.1 -8.8 12.65 

19 156.2 -8.5 12.3 

20 176 -9.3 13.22 

21 170.4 -9.2 13.1 

22 166.5 

23 171.2 -9.2 13.1 

24 170.3 -9.2 13.1 

25 169.4 -9.1 12.99 

26 177.8 -9.8 13.77 

27 178.6 -10 13.99 

28 178.7 -9.8 13.77 

29 178.3 -9.8 13.77 

30 157.4 -8.5 12.3 

sequence (Clark, 1990; Mehrtens, 1985), although mineralogical evidence for evaporites is no longer present in the 

rocks, perhaps due to regional metamorphism related to the 

Taconic orogeny. The hot, saline solutions would provide a 

ready transport mechanism for the metals as chloride complexes. Possible precipitation mechanisms operating both in 

the epigenetic veins and at the seawater-sediment interface 

include mixing with a less saline, cooler fluid (for example, 

seawater), cooling by conduction, or a combination of 

these. 

This model for the inclusion data assumes that the 

inclusions in sphalerite withstood metamorphic overprint of 

the Taconic orogeny. Because such a scenario is unlikely 

without some degree of remobilization and reprecipitation, 

and due to the uniformity of data for secondary and primary 

inclusions, a metamorphic model is also presented. 

MODEL FOR A METAMORPHIC ORIGIN 

If the discordant veins formed as a result of a regional 

metamorphic overprint, as originally interpreted by Foley 

Table 2. Fluid-inclusion homogenization 

temperature and salinity data for sphalerite 

from Lion Hill, Vt.-Continued 

Inclusion Th Tm Salinity 1 

No. (OC) (OC) (wt %NaCl) 

31 164.8 -9 12.88 

32 162.5 -9.2 13.1 

33 160.4 -8.8 12.65 

34 161.8 

35 165.3 -9.4 13.33 

36 169 -9.5 13.44 

37 169.1 -9.4 13.33 

38 -9.4 

39 156.7 -9 12.88 

40 157.8 -9.2 13.1 

41 160.8 -9 12.88 

42 157.4 -9 12.88 

43 158.1 

44 159 -9.1 12.99 

45 169.1 -9.7 13.66 

46 166 -9.3 13.22 

49 165 -9.5 13.44 

50 168.9 -9.6 13.55 

51 158.9 -9.5 13.44 

52 175.8 -9.3 13.22 

53 198 -9.5 13.44 

54 174.7 -9.6 13.55 

55 161.2 -8.6 12.42 

56 165.3 -8.7 12.53 

57 171 -9.9 13.88 

58 171.2 -9.8 13.77 

59 181 -9.2 13.1 

60 178 -9.2 13.1 

1-rotal salinity expressed in equivalent weight percent 

NaCI using data of Hall and others ( 1988). 

(1990), they would probably contain minerals that formed 

by remobilization and recrystallization of preexisting sulfide enrichments. The original inclusion fluids may not 

have survived the deformation and recrystallization of the 

Taconic orogeny, and additional metamorphic fluids probably were generated by dewatering of the enclosing sedimentary rocks. The fluid preserved in inclusions in minerals 

that form in this manner may represent a combination of 

intercrystalline fluid, derived by the release of fluids 

trapped within inclusions in precursor sulfides and gangue 

minerals, and interstitial pore fluids. The fluid compositions obtained for Lion Hill are consistent with local metamorphosed rock and mineral assemblages. The lack of 

visible C02 in the fluid inclusions is consistent with the low 

regional metamorphic grade and suggests that little or no 

additional fluid was generated in situ by decarbonation 

reactions. Additional fluids possibly were added by migration of ground water to the site during metamorphism. 

Homogenization temperatures for the inclusions are 

somewhat cooler ( -1 00-200°C) than probable peak metamorphic temperatures in the study area (Foley, 1990). Dur-
ISOTOPE STUDIES 19 

ing Middle Ordovician time, prior to Taconic thrusting and 

deformation, at least 1,000 m of sedimentary rock overlay 

the Monkton Quartzite in the vicinity of Lion Hill (Cady, 

1945). Medium-pressure regional metamorphic environments generate lithostatic pressures of about 2-4 kbar at 

temperatures of around 400°C. Thus, the minerals could 

have formed at pressures as great as 4 kbar. Corrections to 

homogenization temperatures due to lithostatic pressure 

developed under peak metamorphic conditions are impossible to estimate accurately; however, they may be on the 

order of 200°C or less (Hall and others, 1988). A more 

likely scenario may be that the sphalerite formed during a 

retrograde stage of metamorphism when the fluids cooled 

along with a decrease in the regional temperature and pressure. 

ISOTOPE STUDIES 

SULFUR ISOTOPIC DATA 

Several small sulfide deposits hosted by the Dunham 

Dolomite and Monkton Quartzite were previously analyzed 

for sulfur isotopes by Boucher (1986). Three galena and 

four sphalerite samples from mineralized zones near Dunham, Quebec, and Franklin, Vt., have o34S values from -9.5 

to +0.8%o, and separates of sphalerite and galena from the 

Brandon prospect at Lion Hill had 334S values of -9.3%o 

a~ -11.3%o, respectively. These values are similar to 

res~lts of sulfur isotopic analyses from Lion Hill in this 

study (table 3, fig. 10). The entire range of values for 

galena, chalcopyrite, sphalerite, and pyrite is from -25.9%o 

to + 1 O.O%o, with marked distinctions among the different 

minerals. Galena, sphalerite, and chalcopyrite (-17 to 

+3%o) generally are isotopically lighter than pyrite that 

occurs as cubes disseminated in the sedimentary rocks (0 to 

+10%o). Pyrite from sample L6-162 which occurs as an 

intergrowth with other sulfides (lowermost mineralized 

zone, fig. 8) has a value of -25.9%o. Three sphalerite samples with o34S values near +2.5%o occur as irregular discordant veins (lowermost mineralized zone). The only 

apparent cogenetic pair of galena and sphalerite measured 

(N12-526), gave a temperature of about 500°C, which suggests disequilibrium sulfur isotopic fractionation between 

the two sulfides if they formed from syngenetic or diagenetic processes. 

Metamorphism and deformation of the Lion Hill 

deposit may have remobilized sulfides, but their effect on 

the sulfur isotopic composition of sulfides should be minimal, resulting in only a slight homogenization of values 

(Schwarz and Burnie, 1973). Thus, the wide variation in 

sulfur isotopic values of the sulfides from Lion Hill probably reflects sulfur isotopic variations present in the original 

depositional environment. 

A sulfide separate from magnetite iron formation at 

the Nicklaw mine has a o34S value of -14.3%o. Galena 

from the Fernville deposit in the Dunham Dolomite has a 

o34S value of -6.0%o, and galena from the White Creek 

deposit has a value of -14.9%o. 

Discussion.-The major source of sulfur for most sediment-hosted base metal deposits is interpreted to be contemporaneous seawater sulfate (Coomer and Robinson, 

197 6; Boast and others, 1981; Caulfield and others, 1986, 

Sangster, 1990). The relatively narrow range of sulfur isotopic values for barite in these deposits that is similar to values for contemporaneous seawater sulfate is evidence for a 

seawater sulfate source. Additional evidence is that sulfur 

isotopic values for sulfide minerals are about 25 to 50%o 

lighter than coexisting sulfate, which is the expected kinetic 

fractionation for bacterial reduction of sulfate under different environmental conditions (Schwarz and Burnie, 1973; 

Ohmoto and Rye, 1979). The lack of barite at the Lion Hill 

deposit makes it difficult to fully constrain the source of sulfur, but contemporaneous seawater sulfate is the most probable source of the bulk of the sulfur in the Lion Hill deposit. 

Early Cambrian seawater had probable 334S values ranging 

from 25 to 30%o (Claypool and others, 1980). The range of 

o34S values for sulfides from Lion Hill, from ...:.25.9 to 

+ 1 O.O%o, falls within the expected range for sulfide produced by bacteriogenic reduction of Early Cambrian seawater sulfate. 

Kinetic fractionation between sulfate and sulfide during bacterial reduction is dependent on the rate of reduction, 

which in turn is dependent on the type and supply of nutrients for sulfate-reducing bacteria (Ohmoto and Rye, 1979). 

An open system, such as a euxinic basin, has a constant supply of sulfate, and the kinetic fractionation factor between 

sulfate and sulfide will remain nearly constant, with values 

between 40 and 60%o (Schwarz and Burnie, 1973). Closed 

systems, such as shallow-marine or brackish tidal basins, 

have limited supplies of nutrients, and the rate of sulfide 

production outstrips the sulfate supply with the result that 

the kinetic fractionation factor is near 25%o (Schwarz and 

Burnie, 1973). Closed-system behavior also may be a factor when seawater is trapped as pore fluid in wet sediments 

and shut off from a supply of nutrients in overlying seawater (Schwarz and Burnie, 1973; Sweeney and Kaplan, 

1980). The majority of 334S values for galena and sphalerite from the middle mineralized zone of the Lion Hill 

deposit (fig. 8) fall between -6.6 and -16.8%o, approximately 35 to 47%o lower than Early Cambrian seawater sulfate, consistent with bacterial reduction of sulfate in an open 

system. The single pyrite value of -25.9%o, from pyrite 

associated with galena and sphalerite in the lowermost mineralized zone (fig. 8), also is typical of pyrite formed by the 

reduction of seawater sulfate in an open system. However, 

pyrite and sphalerite o34S values greater than O%o are more 

consistent with closed-system behavior or may indicate a 

source of sulfur other than contemporaneous seawater sui-
20 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

Table 3. Sulfur isotopic data for the Lion Hill deposit, Vt., and the Femville, Vt., and White Creek, N.Y., prospects. 

Sample No. ~34s (%o) Mineral I Host2 Lithology3 Texture4 

Lion Hill, Vermont-southern mineralized mine 

Ll-120 +.1 Py MQ Dol E: Fine-grained pyrite along fractures. 

L1-124 -6.6 Sph MQ Dol B 

L4-268 +7.7 Py MQ Dol E: Pretectonic cubes (early). 

N16-283 +6.2 Py WD Ph D: In late quartz vein that cuts earlier 

mineralization. 

N14-547 -11.4 Sph MQ Dol c 

N12-526 -16.8 Gn MQ Dol A: Matrix of dolomite. 

N12-526 -15.7 Sph MQ Dol ? :Breccia. 

Nl0-338 +5.8 Py WD Dol E: Fine cubes along small fractures. 

Nl0-387 +5.8 Py WD Dol E: Coarse to fine cubes, pretectonic. 

N15-65 -10.0 Py WD Ph E: Fine to coarse cubes, disseminated. 

N17-692 -14.2 Gn MQ Dol D: Calcite crystals along fractures in dolomite 

with galena. 

Lion Hill, Vermont-northern mineralized zone 

N24-53 -13.3 Gn MQ Ss A: Breccia matrix. 

N24-64 +2.5 Sph MQ Dol D: Late dolomite vein, green sphalerite, open 

space filling. 

N26-240 -15.3 Gn MQ Dol c 

N27-2835 -8.3 Sph MQ Dol D: Crystals in cross-cutting dolomite veins. 

N27-423 -13.9 Sph MQ Dol A: Breccia in matrix. 

N28-520 -14.8 Sph MQ Dol B 

N28-525.5 -15.7 Sph MQ Ss A: Intergranular in cross-bedded sandstone. 

N28-526 -11.7 Sph MQ Dol B 

N31-50 -13.7 Gn MQ Dol D: Crystals in coarse dolomite veins. 

L2-36 -3.0 Cpy MQ Ph B 

L2-84 -10.6 Sph MQ Dol B 

L2-270-1 +2.1 Sph MQ C: Late sphalerite, cuts dolomite vein. 

L2-270-2 +2.5 Sph MQ C: Late sphalerite, cuts dolomite vein. 

L2-364 +4.6 Py MQ Ph, Dol, Ss E: Fine-grained aggregated pressure features, 

pretectonic. 

L6-92 +4.9 Py MQ Ss B: In fine fractures that cut bedding. 

L6-162 -25.9 Py MQ Dol D: Crystals in quartz-dolomite vein. 

Lion Hill-Nick1aw mine area 

L3-845 -12.2 Gn MQ Dol B 

L3-885 -10.6 Sph MQ Dol B 

VCsl35A -14.3 Sph MQ iron formation A: Layered, with minor intergrown sulfides. 

VCS135B -11.5 Cpy MQ iron formation A: Layered, with minor intergrown sulfides. 

Fernville, Vermont 

VCs301 -6.0 Gn DD Dol Large galena crystal in quartz vein. 

White Creek, New York 

JS-86-5.1 -14.9 Gn MPQ? Crystal in galena-sphalerite matrix to quartzite. 

JS-86-5.2 -14.7 Gn MPQ? Crystal in galena-sphalerite matrix to quartzite. 

1Gn, galena; Sph, sphalerite; Cpy, chalcopyrite; Py, pyrite. 2DD, Dunham Dolomite; MQ, Monkton Quartzite; WD, Winooski Dolomite; MPQ, Mudd Pond Quartzite Member of the Nassau Formation. 3Dol, metadolostone; Ph, phyllite; Ss, metasandstone. 4A, intergranular; B, metamorphic segregation, along shears or small fractures; C, discordant veins; D, discordant veins with evidence of open-space filling; E, fine 

to coarse euhedral pyrite cubes, pretectonic. 

fate. For example, pyrite occurs in some mineralized zones, 

as noted above for sample L6-162, but more commonly 

occurs as single cubes that are widespread in unmineralized 

host rocks. This form of pyrite, found in the uppermost, 

middle, and lowermost zones (fig. 8), probably formed by 

reaction between metal-bearing fluid and sulfate in trapped 

pore fluid, and this reaction resulted in more closed-system 

behavior and subsequently heavier sulfur isotopic values. 

The three sphalerite samples with o34S values between 2.0 

and 2.5%o occur in cross-cutting veins that are obviously 
ISOTOPE STUDIES 21 

n=33 • Pyrite 

Ill Galena 

D Sphalerite 

~ Chalcopyrite 

D Sulfide.separate from iron 

formation 

' I 

-20 

~0011] I I 

-25 0 +5 +10 

Figure 10. Sulfur isotopic compositions of sulfides from the Lion Hill deposit, including the 

magnetite iron formation. 

later stage than the main stage of base-metal mineralization 

(see fig. 5C). The heavier sulfur isotopic values for these 

vein sphalerites may reflect a change in the source of sulfur, 

perhaps to deep-seated sulfur, during this later episode of 

mineralization. Several Irish sediment-hosted deposits with 

clusters of sulfur isotopic data ~ O%o (Keel, Tatestown, and 

vein sulfides from Silvermines) are interpreted to have an 

additional minor, deep-seated source of sulfur near O%o 

(Coomer and Robinson, 1976; Caulfield and others, 1986). 

LEAD ISOTOPIC DATA 

Lead isotopic compositions of 12 galenas from mineralized localities are listed in table 4, together with sample 

numbers and host lithology. The analyses include data for 

nine samples from mineralized zones delineated by 

drillcore at Lion Hill and for one sample of magnetite iron 

formation from the Nicklaw mine dump (Foley, 1990). 

New data are presented for galena from the Fernville, Vt., 

Pb-Zn deposit (fig. 3), and for galena from the White Creek, 

N.Y., Pb-Zn deposit (fig. 1). 

Lead isotopic compositions of the analyzed galenas are 

plotted on conventional lead isotopic diagrams in figure 11. 

Isotopic compositions of galenas from mineralized zones at 

Lion Hill range from 18.351 to 18.632 for 206pbJ2°4Pb, from 

15.546 to 15.618 for 207Pbf204pb, and from 38.126 to 

38.496 for 208pbf204Pb (table 4). Lion Hill galenas are 

moderately homogeneous, showing only a small spread in 

206JPbf204pb ( <5 times the measured standard deviation), in 

207pbf204Pb (<3 times), and in 2°8Pbf2°4Pb (<5 times). 

Galena from the magnetite iron formation, collected at the 

Nicklaw mine dump, is among the least radiogenic of galenas analyzed for the Lion Hill area (table 4). 

Galena from the small mine at Fernville, Vt., has lead 

isotopic values that overlap the composition of galena contained within the Winooski Dolomite at Lion Hill. Sulfide 

minerals at Fern ville are hosted by the Dunham Dolomite. 

Lead isotopic values for galena from the White Creek 

mine (18.424 for 206Pb/204Pb, 15.563 for 207Pb/204Pb, and 

38.264 for 208pbf2°4Pb) are virtually identical to those for 

Lion Hill galenas. The small stratabound Pb-Zn deposit at 

White Creek, N.Y. (Slack and others, 1987; Clark and 

Slack, 1988) is in Lower Cambrian clastic rocks of a 

Taconic slope-rise sequence that ranges in age from Late 

Proterozoic to Middle Ordovician (Zen, 1967; Potter, 1972). 

The lead isotopic values of galenas from the Lion Hill 

mineralized zones and iron formation, from the Fernville 

mine, and from the White Creek mine all yield model Pb-Pb 

ages based on the two-stage evolution curve of Stacey and 

Kramers (1975) of less than 212 Ma. The model ages are 

all significantly younger than the Early Cambrian age 

(approximately 550 Ma) of the host rocks and are much 

younger than mineralization or recrystallization of sulfides 

that may have taken place at 460-440 Ma, after the thermal 

peak of the Taconic orogeny (Zen, 1972, Sutter and others, 

1985). Calculated 207Pbf2°6Pb isochron ages for the galenas yield geologically unreasonable estimates for the age of 

the source of the lead. Known basement rocks in the region 

are Proterozoic in age, and the deposits lie immediately to 

the west of -1 Ga basement rocks that comprise the Green 

Mountain massif (fig. 1). 

Discussion.-Compared to the growth curves of the 

plumbotectonic model of Doe and Zartman (1979) and the 

reference curve of Stacey and Kramers ( 1975), lead isotopic 

data for the Lion Hill galenas overlap the oro gene curve and 

define a field that extends toward the mantle curve on a 

conventional 207Pbf2°4Pb-206Pbf2°4Pb diagram (fig. 12). 

The ranges in lead isotopic composition defined by these 

samples indicate that the lead was derived from a source or 

sources characterized by a somewhat variable lead isotopic 

composition. Because the data cannot be used to constrain 
22 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

Table 4. Lead isotopic compositions of galenas from base-metal sulfide deposits hosted by 

carbonate-siliciclastic platform rocks of Vermont and the Taconic allochthon of New York. 

Sample 206PbP04Pb 207Pb/204Pb 208pbp04pb Lithology of wallrock 1 

Lion Hill deposit, Brandon, Vt. 

B-31-50' 18.351 15.546 38.275 Monkton Quartzite. 

B-31-350' 18.463 15.552 38.368 Monkton Quartzite. 

B-26-240' 18.496 15.592 38.406 Monkton Quartzite. 

B-25-87' 18.483 15.587 38.404 Monkton Quartzite. 

B-17-692' 18.378 15.551 38.126 Monkton Quartzite. 

L3-84.5' 18.362 15.607 38.403 Winooski Dolomite. 

L3-84' 18.442 15.583 38.465 Monkton Quartzite. 

B-12-526' 18.374 15.566 38.318 Monkton Quartzite. 

B-28-531' 18.632 15.618 38.496 Monkton Quartzite. 

Magnetite iron formation, Nicklaw mine dump, Brandon, Vt. 

MIF-dump 18.253 15.536 38.496 Monkton Quartzite. 

Fernville mine, Fernville, Vt. 

86VCS301 18.400 15.596 38.387 Dunham Dolomite. 

White Creek mine, White Creek, N.Y. 

WC-1 18.424 15.563 38.264 Mudd Pond Quartzite Member 

of the Nassau Formation. 

1

See text for detailed geologic description of wallrock lithologies. 

either the age of the mineralization or the age of the source, 

it is unlikely that age was the most important control on the 

lead isotopic composition of these occurrences. 

A more likely factor controlling the isotopic composition of the galenas is the composition of different lead 

sources. Basement composition has been demonstrated to 

be the dominant control on the lead isotopic composition of 

galenas in carbonate-hosted base-metal deposits in western 

Newfoundland (Swinden and others, 1988). Carbonatehosted Pb-Zn occurrences at Franklin, Vt., (fig. 11) are 

thought to have developed their distinctive lead isotopic 

signature by leaching of lead from the underlying Cheshire 

Quartzite via a sandstone aquifer model similar to that proposed by Doe and Delevaux (1972) for Mississippi Valleytype (MVT) deposits of southeast Missouri (Balogh, 1991). 

Schrijver and others (1988) have shown that 206pbf204pb 

values of galena in epigenetic veins increase from southwest to northeast in the northern Appalachians of Quebec, 

Canada. They attribute the variations in lead isotopic composition of the galenas to a progressive change in the type 

of detritus derived from Grenville basement during Cambrian and Ordovician time, from a less radiogenic lead component in the southeast that was derived from K-feldspar to 

a more radiogenic composition in the northeast that was 

derived from phyllitic material. 

The lead isotopic composition of galena in the Lion 

Hill mineralization probably includes contributions from 

the sedimentary host rocks, their terrigenous sources, and 

lithologies traversed by the hydrothermal fluids that deposited the sulfide minerals. Although the isotopic composition of each of these sources may be distinct because of 

differences in the U/Pb and Th/U values of the rocks, the 

bulk lead isotopic composition measured in the galenas may 

reflect a regional lead fingerprint controlled by the integrated composition of basement source rocks in the area. 

Ayuso (1986) and Ayuso and Bevier (1991), in studies of 

basement terranes of Vermont, New Hampshire, and Maine 

in which they used plutonic rocks as geochemical probes of 

source regions, have identified important differences in the 

time-integrated lead isotopic compositions of Grenville and 

Avalonian basement terranes. A similar approach was tried 

for volcanogenic massive sulfide deposits in the Eastern 

United States and Canada (Slack and others, 1991). In figure 12, a field is shown outlining the data of Ayuso and 

Bevier (1991) for 400-Ma granitic plutons that have a 

source predominantly composed of Grenville basement as 

defined by rocks of the Adirondack, Green Mountain, and 

Chain Lakes massifs. The field for Lion Hill overlaps that 

of the Grenville source established by Ayuso and Bevier 

(1991) in 206pbf204Pb and 207Pbf204Pb, but has slightly 

higher values of 208pbf204Pb. 

Possible local lead sources for the Lion Hill and Fernville deposits are the Cambrian and Ordovician carbonatesiliciclastic platform rocks, including the Dunham and 

Winooski Dolomites and Cheshire and Monkton Quartzites. 

Late Proterozoic to Middle Ordovician slates and graywackes of the Taconic allochthon, especially the Late 

Proterozoic and Lower Cambrian Nassau Formation, are 

possible local sources of the White Creek ores. Much of the 

lead in the terrigenous component of the Monkton Quartzite 

was probably derived originally from relatively unradiogenic feldspathic and more radiogenic phyllitic rocks of the 
COMPARISON WITH OTHER SEDIMENT-HOSTED BASE-METAL DEPOSITS 23 

Proterozoic Grenville basement in the Adirondack Mountains (fig. 12; Zartman and Wasserburg, 1969). Selective 

weathering and erosion of coarser feldspathic versus finer 

grained phyllitic components would result in a mechanical 

separation of U/Pb reservoirs in the sedimentary sequence. 

Differential chemical leaching of lead and uranium by 

hydrothermal fluids could have further modified these reservoirs, resulting in dispersion in 206pbf204Pb, 207pbf204Pb, 

and 208Pbf204Pb values. 

COMPARISON WITH OTHER SEDIMENTHOSTED BASE-METAL DEPOSITS 

Fluid inclusions in sphalerite of the Lion Hill deposit 

have ranges of salinity and homogenization temperature 

that overlap those found for other occurrences of base-metal 

sulfides in rocks of the carbonate-siliciclastic platform in 

western Vermont. Fluid-inclusion measurements in sulfide 

samples from Dunham, Quebec, show a distribution of temperatures between 80° and 150°C and salinities of about 6 

to 12 wt% NaCl equivalent (Boucher, 1986). Mineralized 

and unmineralized samples from Franklin, Vt. ( -5 km south 

of Dunham, Quebec) yielded homogenization temperatures 

of fluid inclusions (Balogh, 1991) in sphalerite of60-170°C 

and salinities of 8-12 wt% NaCl equivalent. Inclusions in 

quartz homogenized at 210-330°C and had salinities of 2-

15 wt% NaCl. 

The temperature ranges for fluid inclusions in sulfide 

minerals of the western Vermont platform rocks overlap 

those of MVT and Appalachian-type deposits, although the 

salinity range is considerably lower than that typical of 

MVT deposits (fig. 9). Primary inclusions from MVT 

deposits generally homogenize at temperatures that range 

from about 100° to 150°C (Roedder, 1976) for the main 

ore-forming stages (fig. 9). Inclusion data for the Austinville, Va., Appalachian-type deposit show a 100° to 160°C 

temperature range (Foley and Craig, 1989). The salinities 

of ore fluids in MVT and Appalachian-type deposits typically are much greater than 15 equivalent wt% NaCl, and 

commonly exceed 20 wt% NaCl equivalent (Roedder, 

1976). Daughter crystals of halite are rarely found in these 

deposits; their scarcity suggests that there are appreciable 

quantities of ions other than sodium in the ore fluids. 

The base-metal sulfide occurrences at Lion Hill and in 

other parts of western Vermont and southeastern Quebec 

have homogenization temperatures and salinities that match 

those of many of the Irish carbonate-hosted deposits (fig. 

9), although the Lion Hill temperatures and salinities show 

more restricted ranges. Samson and Russell (1984) found 

that fluid inclusions in ore and gangue minerals from the 

Silvermines deposit homogenized at temperatures ranging 

from 50° to 260°C and had salinities primarily from about 0 

to 24 wt% NaCl equivalent (fig. 9). Andrew and Ashton 

(1985) cite values of 8 to 12 equivalent wt% NaCl and 140° 

39.0~------------------------------~ 

.0 

a. 

"'t 

0 

C\1 

:0 

a.. 

CX) 

38.5 

~ 38.0 

0 

0 

+ 

15.65 ..----------------. 

.0 

a.. 

~ 15.60 

C\1 

:0 

a.. 

,....... 

0 

C\1 

15.55 

• 

+ 

0 

0 

+ + 

18.0 18.5 

206 Pb/204pb 

19.0 

Base-metal-rich zones, ~:;. 

Monkton Formation • 

Magnetite iron formation 

Fernville mine 

White Creek 

deposit 

Base-metal-rich zone, 

Winooski Formation 

o Franklin, Vt. 

Figure 11. Lead isotopic data for galena from Lion Hill sulfide 

zones and magnetite iron formation near Brandon, Vt. Also 

shown are data points for a carbonate-hosted Pb-Zn deposit at 

Fernville, Vt., siliciclastic, sediment-hosted, stratiform Pb-Zn 

minerals at White Creek, N.Y., and an average galena composition 

for Zn-Pb minerals at Franklin, Vt. (Balogh, 1991). Orogene (0) 

and upper crust (UC) average lead evolution curves of Doe and 

Zartman ( 1979) are shown for comparison. 

to 200°C for the Navan and Tatestown deposits of Ireland 

that also have been proposed to have formed in a synsedimentary-diagenetic environment (Andrew, 1986). 

If the inclusions in sphalerite in the discordant veins at 

Lion Hill formed from trapped fluids in a feeder zone below 
24 GEOLOGIC,-GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

.c 

c.. 

~ C\1 

::c 

c.. 

~ 

1:::::::::::::::1 Lion Hill, Vermont, Fernville, Vermont, 

and White Creek, New York 

th\;::~1 Granitoid rocks of Vermont, 

40.0 New Hampshire, and northern 

Maine 

.·············~······ 

39.0 ( ............ . 

37.0 

36.0 

16.0 .-----------------------------------------~--~ 

Figure 12. Lead isotopic composition of 

carbonate-siliciclastic-hosted Pb-Zn minerals from the Lion Hill area, Vt., and 

White Creek, N.Y., compared to data for 

similar deposits in Ireland (Silvermines, 

Tynagh, Navan, Keel, and Gortdrum 

deposits; Caulfield and others, 1986). 

Fields are also shown for an Appalachiantype Zn-Pb deposit at Austinville, Va. 

(Foley and others, 1981 ), Rossie-type PbZn veins of northwestern New York State 

(Ayuso and others, 1987) and southwestern Ontario (Fletcher and Farquhar, 

1982a), Mississippi Valley-type (MVT) 

deposits including the southeast and central 

Missouri Pb-Zn district (Doe and 

Delevaux, 1972) and the Illinois-Kentucky 

and Tri-State areas (Heyl and others, 

1966), and the Balmat-Edwards district 

(Doe, 1962; Fletcher and Farquhar, 1982b); 

an average point is shown for carbonatehosted deposits of Newfoundland 

(Swinden and others, 1988). Uncorrected 

feldspar lead isotopic data for the -1 Ga 

Grenville province and the western 

Adirondack massif are from Zartman and 

Wasserburg (1969). Age-con:ected feldspar data for some granitoid rocks dated at 

400 Ma of the northern Appalachians of the 

United States and Canada are from Ayuso 

(1986) and Ayuso and Bevier (1991). 

Curves on both plots are the average lead 

environments of Doe and Zartman ( 1979). 

M, mantle; 0, orogene; UC, upper crust; 

LC, lower crust. 

Irish Pb-Zn-Ag deposits 

7- Silvermines, Tynagh, 

Navan, Keel, Gortdrum 

15.8 Other base-metal deposits 

8- Balmat-Edwards, New York 

15.4 Basement terranes 

9- Grenville province 

10- Western Adirondacks 

16.0 17.0 18.0 20.0 

the seawater-sediment interface, then the fluid-inclusion 

data for Lion Hill suggest that the mineralizing enviropment 

was more like that of Irish-type sedimentary-exhalative 

deposits than MVT deposits. If the discordant veins 

formed instead by remobilization of pre-existing sulfide 

minerals during the Taconic orogeny, then the data cannot 

be used to distinguish either an MVT or a sedimentaryexhalative (sedex)-type precursor. 

Sulfur isotopic values for Appalachian deposits, Irish 

sediment-hosted base-metal deposits, and for MVT deposits 

are shown for comparison in figure 13. In general, the 

21.0 

Irish-type deposits and Lion Hill have sulfur isotopic compositions with lower 834S values, indicating a larger kinetic 

fractionation factor between sulfate and sulfide relative to 

most MVT deposits. One of the factors controlling kinetic 

fractionation is the rate of bacterial reduction, which is 

partly dependent upon the amount of organic material. The 

difference in kinetic fractionation between the two deposit 

types may be related to amount of organic material and, 

thus, may be the result of different depositional processes 

and environments. 
GENETIC MODELS 25 

Mississippi Valley-type deposits __________ ._._ 

Appalachian-type deposits 

Irish-type deposits 

Lion Hill deposit 

I I I 

-40 -30 -20 -10 0 +10 +20 +30 +40 

o34 s (per mil) 

Figure 13. The range of o34S for Mississippi Valley-type (MVn, Appalachian-type, and Irish-type deposits compared 

with data for the Lion Hill deposit. Data compiled from Sangster (1990), Kesler and van der Pluijm (1990), and 

Caulfield and others (1986). 

Lion Hill galenas have lead isotopic compositions that 

are much less radiogenic than most carbonate-hosted MVT 

deposits, Appalachian-type deposits, or Rossie-type Pb-ZnF veins, which are structurally controlled, carbonate-hosted 

veins that are widespread in the Frontenac axis area of New 

York and Ontario (Ayuso and others, 1987) (fig. 12). Galenas from Lion Hill also show a much smaller spread in lead 

isotopic composition compared to these deposit types. The 

MVT, Appalachian, and Rossie-type veins are characterized 

by a strong imprint of upper crustal lead, whereas Lion Hill 

galenas have an average orogene signature. 

Stratabound and stratiform deposits of the Selwyn 

basin have been proposed as a possible analog of the marble 

and anhydrite-hosted Zn-Pb deposits at Balmat, New York 

(Whelan and others, 1990), that occur in rocks of the Grenville province of the Adirondack massif. Lead isotopic values of galenas from Balmat are only moderately heterogeneous (Doe, 1962). Lion Hill galenas differ from Balmat 

galenas in that Lion Hill galenas have relatively lower 

207Pbf2°4Pb values, again suggesting that any involvement 

of a component of upper crustal lead in the formation of the 

Lion Hill galenas was limited. 

Compared to galenas from carbonate-hosted Pb-Zn-Ag 

deposits of Ireland, galenas from the Lion Hill deposit show 

a similarly moderate spread in lead isotopic composition 

(fig. 12). Lead isotopic ratios of galenas from individual 

deposits in Ireland exhibit little heterogeneity, although 

there are larger differences among deposits (Caulfield and 

others, 1986). Lead isotopic data for both the Lion Hill 

galenas and those of the Irish deposits generally follow 

average-orogene evolution paths (fig. 12), and show only a 

slight deviation below the average-orogene evolution curve 

in 207pbf204Pb. The general similarity in lead isotopic values between Lion Hill and carbonate-hosted Pb-Zn-Ag 

deposits of Ireland may indicate that the source rocks for 

these deposits had overlapping lead isotopic signatures and, 

also, that the processes operating to extract lead from source 

rocks of Lion Hill were akin to those that formed the lrish 

deposits. 

GENETIC MODELS 

Genetic models considered for the Lion Hill deposit 

included sedex and diagenetic (Briskey, 1986; Ritzman and 

Large, 1986; Sangster, 1990), Mississippi Valley-type (Briskey, 1986; Kesler and van der Pluijm, 1990; Sangster, 

1990), and Appalachian zinc (Briskey, 1986; Foley and others, 1981). Although the Lion Hill deposit resembles many 

Zn-Pb deposits that are classified as MVT- and Appalachian-type deposits in general aspects (for example, carbonate host rock, vein structures, low temperature, and 

moderately saline fluid regime), a detailed analysis suggests 

that the Lion Hill depos~t is more closely analogous to the 

sediment-hosted base-metal deposits of Ireland (Navan, 

Tynagh, Silvermines). 

Many Pb-Zn-Ag deposits of Ireland, including Tynagh, 

Silvermines, and Keel, that were once thought to be sedex 

or early diagenetic in origin are now considered to have 

formed in a diagenetic to epigenetic setting (Taylor, 1984; 

Briskey, 1986; Samson and Russell, 1987; Ashton and others, 1992; Ritzman and others, 1992). Russell and others 

(1982) proposed a sedex origin for the Irish deposits, while 

others, such as Hutchinson (1983), suggested that the ores 

were actually epigenetic. Taylor and Andrew (1978) suggested a hybrid model for the origin of the Silvermines 

deposit in which stratigraphically lower epigenetic ores 

were deposited in a feeder zone and upper ores were deposited syngenetically from exhalations near the sediment-seawater interface. Caulfield and others (1986) applied this 

hybrid model to the epigenetic ores at the Keel deposit and 

stressed the dependence of syngenetic, diagenetic, and epi-
26 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

genetic processes of ore deposition on the rate of fluid 

expulsion and on local geologic controls. More recently, 

Ashton and others (1992) presented a model for the Navan 

deposit that incorporates diagenetic and epigenetic styles of 

mineralization. Some important characteristics that are 

shared by most Irish models include the following (M. Ritzman, National Science Foundation, written commun., 

1994): (1) the metals occur in stratigraphically low, nonargillaceous carbonate units, (2) the mineralized zones are 

near major structures available to serve as conduits for fluids, (3) in general the temperatures of deposition are> 175° 

to > 150°C, ( 4) wallrock alteration includes extensive dolomitization, (5) many of the sulfides formed by replacement 

and colloform banding is common, (6) the bulk sulfur 

source was probably Carboniferous seawater sulfate; minor 

amounts of deep-seated sulfur may occur in feeder zones, 

(7) mineralization occurred during a period of tectonic 

instability, so the carbonate shelf rocks are faulted and the 

local stratigraphic sequence indicates a complex facies 

mosaic of shallow- and deep-water environments. 

As noted above, the apparent overthickened stratigraphic sequence in the vicinity of Lion Hill suggests a 

remote possibility that growth faults were a factor in transporting fluids to depositional sites at Lion Hill. Current theories about the nature of mineralizing fluids in sedex 

deposits favor slightly acidic brines that are generated in 

clastic-dominated sedimentary basins (Lydon, 1983, 1986; 

Sangster, 1990). Metals leached in the transformation of 

clay minerals during burial and compaction (Lydon, 1983, 

1986) or by deeply circulating fluids (Russell, 1986) are 

thought to be transported, possibly along growth faults, to 

depositional sites near or on the sea floor. Growth faults 

have been identified in Cambrian shelf rocks of western and 

north-central Pennsylvania and east-central Kentucky 

(Wagner, 1976; Beardsley and Cable, 1983) and in carbonate shelf rocks north of Burlington, Vt. (R.W. Beardsley, 

University of Vermont, oral commun., 1992), and in westcentral Vermont (Rowley, 1982). 

The magnetite iron formation at Lion Hill may have 

formed from local exhalation of solutions that precipitated 

iron and associated minerals in a local basin. The presence 

of iron formation at Lion Hill indicates that iron-mineralizing fluids may have reached the sea floor, at least locally, 

and that some galena and other sulfide minerals were 

deposited syngenetically. Iron formation at Tynagh, Ireland 

(Boast and others, 1981; Clifford and others, 1986), was 

also thought to have formed by syngenetic exhalation; however, recent work suggests that the iron formation cuts 

across stratigraphy and is diagenetic. Studies are currently 

underway to address this question at Tynagh (M. Hitzman, 

National Science Foundation, written commun., 1994). 

Pb-Zn-Cu sulfides may have precipitated from warm, 

metal-bearing brines that migrated through poorly consolidated sediments near the seawater-sediment interface. The 

temperature-salinity relationships for fluid inclusions from 

Lion Hill (and for Silvermines and other Irish-type deposits) are consistent with such a model because they suggest 

that water (or water+ sediment) depths of 50-150m would 

have been required to prevent boiling of the hottest hydrothermal fluids in a sedex environment. The bulk of the sulfur isotopic data indicate that the system was relatively 

open to influx of seawater during the main interval of mineralization; however, closed-system behavior, typical of 

tidal basins and seawater trapped as pore fluid in wet sediments, was also an important control on the sulfur isotopic 

composition of some sulfides. 

Localization of metal-bearing brines may have been 

caused by variations in porosity and permeability, with 

reduction-oxidation (redox) differences providing a mechanism for early diagenetic precipitation of sulfide minerals. 

Other possible mechanisms for precipitation include fluid 

mixing, pH change, conduction, and so forth. Because the 

host rocks of the Lion Hill deposits may have formed as 

tidal-flat sediments (in contrast to Irish-type deposits), studies of variations in porosity and permeability in modern 

tidal flats provide evidence for possible routes for fluid 

migration and suggest favorable sites for sulfide precipitation. Studies of ancient and modern tidal flats have shown 

that porosity and permeability of different facies vary 

greatly; porosity and permeability are best developed in the 

subtidal to intertidal facies (typically composed of more 

permeable, coarser grained carbonate), especially in tidal 

channels, whereas supratidal sediments, composed of finegrained undisturbed muds, generally have low porosity and 

permeability (Shinn, 1983). Trap rocks are created by 

transgressions and regressions that cause intertidal and 

channel facies to pinch out beneath and within the relatively 

impermeable supratidal facies. Hydrothermal solutions 

moving through such permeable zones could be trapped at 

barriers formed by the supratidal facies. Sediments of the 

supratidal and upper intertidal zones characteristically are 

brown and oxidized relative to the gray and more reduced, 

lower intertidal to subtidal dolomites (Shinn, 1983), and 

this difference creates potential for sulfide precipitation at a 

redox interface. These sedimentation facies may account 

for the apparent displacement of the iron formation at Lion 

Hill away from the bulk of the base-metal sulfides, because 

they allow for development of parallel facies of iron formation, as conceptualized by James (1954). 

The occurrence of Zn, Ph, and Cu values for Lion Hill 

rocks in mixed carbonate-siliciclastic rocks, at or above 

prominent well-sorted siliciclastic units (fig. 8), suggests 

that the siliciclastic units may have acted as high-porosity 

and high-permeability pathways for transport of mineralizing fluids, which then were precipitated in the less permeable overlying mixed-carbonate and siliciclastic material. 

The occurrence of mineralized zones in siliciclastic and 

mixed-carbonate-siliciclastic sequences at approximately 

the same depth as weakly mineralized carbonate layers suggests lateral migration of fluids from high-porosity path-
APPENDIX A. ANALYTICAL TECHNIQUES 27 

ways to sites of deposition in adjacent, less permeable 

lithofacies. 

The possibility of an Irish-type origin for some Zn-Pb 

deposits of the Paleozoic shelf of eastern North America is 

of considerable significance for improving our understanding of basin evolution, of the timing of mineralization relative to platform evolution, and of the mineral resource 

potential of the region. The petrologic, geochemical, and 

isotopic data presented in this report support a sedex model 

incorporating diagenetic and epigenetic processes for the 

Lion Hill, Vt., Pb-Zn mineralization-a model akin to that 

proposed for economically important sediment-hosted PbZn-Ag deposits of Ireland. We believe that a high potential 

exists for discoveries of a number of additional stratiform 

Pb and Zn sulfide lenses hosted by the lower Paleozoic platform sequence rocks of western Vermont, as suggested by 

Clark (1990) and Slack (1990). The economic viability of 

such deposits at present will depend, however, on whether 

or not they contain enough Cu and Ag to offset mining and 

environmental costs of developing the ore bodies. At the 

present time, the apparent geochemical differences between 

stratiform sulfide deposits such as those at Lion Hill and at 

Silvermines or Navan (Zn+Pb±Cu versus Zn+Pb±Cu±Ag) 

and the size of the mineralized horizons result in grossly 

different economic potentials. This difference probably 

reflects the ultimate control of source rock on metallogeny. 

CONCLUSIONS 

The following elements summarize observations in 

support of our interpretation of the mineralized rock at Lion 

Hill as being of the class of deposits that include the carbonate-hosted deposits of Ireland. 

1. Sulfide bodies of the Lion Hill deposit include both stratabound and stratiform mineralization. Textural evidence suggests that mineralizing fluids permeated the 

sediments prior to lithification. Some of the discordant 

veins at Lion Hill may constitute a feeder zone, while 

others may have formed in a dilatant mineralized fracture zone soon after precipitation, when the sediments 

were in a semiconsolidated state. 

2. The association of layered magnetite iron formation containing base-metal sulfide minerals with the Zn-Pb-Cu 

deposit provides possible lithologic evidence for mineralization by submarine exhalative activity. We are 

unable constrain the timing of this activity; it was probably syngenetic or diagenetic but may have been epigenetic. 

3" Sand bars and tidal channels present in the sedimentary 

section could have acted as relatively permeable pathways for movement of mineralizing fluids. Pinching out 

of these pathways and the presence of less permeable 

mixed carbonate and siliciclastic layers in intertidal and 

supratidal sediments may have created trap rocks that 

localized sulfide deposition. 

4. Homogenization temperatures of primary and secondary 

inclusions in sphalerite range from 152°C to 196°C, and 

salinities range from 11.5 to 14.0 wt% NaCI equivalent. 

These values fall within the ranges expected for some 

Irish-type deposits; however, they also may reflect metamorphic remobilization of precursor sulfides. 

5. The range of 834S values for sulfide minerals from Lion 

Hill, from -25.9 to +10.0%o, falls within the range 

expected for sulfide produced from bacteriogenic reduction of sulfate with 834S values of 25 to 30%o. In addition, some pyrite probably formed from sulfate in 

trapped pore fluid, resulting in more closed-system 

behavior and subsequently heavier sulfur isotopic values. Three sphalerite samples with heavier sulfur isotopic values may reflect a change in the source of sulfur, 

perhaps to deep-seated sulfur, during a later episode of 

mineralization. 

6. The lead isotopic compositions of galena from Lion Hill 

indicate that Grenville basement rocks and (or) their sedimentary equivalents probably impose the strongest constraint on lead isotopic signature for the mineralization, 

although the host carbonate-siliciclastic rocks may constitute a secondary source of lead. 

7. Fluid-inclusion and sulfur and lead isotopic data for the 

Lion Hill deposit may support an origin like that of the 

Irish-type deposits, rather than MVT or Appalachian Zntype deposits. 

8. Our study of the Lion Hill deposit suggests a potential 

for Irish-type Pb-Zn deposits in platform rocks of western Vermont. 

APPENDIX A. 

ANALYTICAL TECHNIQUES 

Chemical analyses were made of samples selected 

from 9 of 38 drillcores based on detailed logs prepared by J. 

M. Hammarstrom and E-an Zen ( unpub. data, 1972) and by 

S.H.B. Clark ( unpub. data, 1985). Each sample is representative of a core interval of 3 m or less to coincide with 

lithologic changes. Cores were split and chip samples taken 

along the entire interval. Most samples were analyzed by 

inductively coupled plasma-atomic emission spectroscopy 

(ICP-AES); selected samples also were examined by semiquantitative optical emission spectroscopy (SOES) and (or) 

quantitative atomic absorption (AA). For the ICP-AES 

analyses, a partial digestion procedure was used to enhance 

the detection of ore-related metals and to depress the influence of metals that may reside in the lattices of silicates and 

sulfates (Mosier and Motooka, 1983). The dissolution procedure completely digests carbonate, sulfide, and iron oxide 

minerals, although the lattices of most sulfate and silicate 

minerals are not affected significantly. Samples were 
28 GEOLOGIC, GEOCHEMICAL, AND ISOTOPIC STUDIES, LION HILL, VERMONT 

digested in 6N nitric acid, and then gently dried with low 

heat and allowed to cool. They were redissolved in HCI 

(20%) on a warm hotplate and then filtered through paper 

and analyzed. The partial digestion ICP-AES method is an 

alternative to time-consuming preconcentration procedures 

for the detection of metal abundances that are too low to 

show meaningful patterns from whole-rock samples. In the 

present investigation, the ICP-AES method was utilized 

because of its precision. The results enable detection of element distribution patterns that can be related to distinct 

stratigraphic intervals. SOES and AA techniques followed 

standard analytical methods outlined in Baedecker ( 1987). 

Mineral separates of sphalerite, galena, chalcopyrite, 

and pyrite were hand picked for sulfur isotopic analysis 

from samples of drillcore from the northern and southern 

areas of the Lion Hill deposit, from the Fern ville mine, and 

from the White Creek deposit. A sulfide concentration 

(galena + sphalerite + chalcopyrite) was made from magnetite iron formation from the Nicklaw mine. Sulfide separates were converted to S02 by roasting with Cu20; galena 

and sphalerite were held at 1025 °C for 10 min, and pyrite 

and chalcopyrite at 1,125 oc for 15 min. so2 that was produced was purified in a glass vacuum-distillation line. 

Ratio measurements were made on a Nuclide 6" mass spectrometer at the U.S. Geological Survey in Reston, Va. Analytical precision based on duplicate analyses of samples is 

about ±0.1%o (1 standard deviation). 

Galena crystals 0.1 to 1.0 mm on edge were separated 

for lead isotopic analysis from samples of drillcore that had 

been cleaned in distilled water in an ultrasonic bath. The 

crystals were acid-washed in a 7N HN03 solution, dissolved in 14N HN03, and then precipitated as lead nitrate. 

After drying on a hot plate, the samples were loaded on rhenium filaments by using the silica gel-phosphoric acid technique (Cameron and others, 1969) and analyzed on a 12-inradius, NBS-type solid-source mass spectrometer. Instrumental fractionation was corrected by comparison of repeat 

analyses of NBS SRM-982. All errors are reported as standard error of the mean at the two-sigma level and are generally <0.15 % (2cr) of the measured ratios. 

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