Significance of Tourmaline-Rich 

Rocks in the Grenville Complex of 

St. Lawrence County, New York

U.S. GEOLOGICAL SURVEY BULLETIN 1626-C

Chapter C

Significance of Tourmaline-Rich 

Rocks in the Grenville Complex of 

St. Lawrence County, New York

By C. ERVIN BROWN and ROBERT A. AYUSO

A study of tourmaline compositions 

and their possible use as indices 

of mineralization

U.S. GEOLOGICAL SURVEY BULLETIN 1626 

CONTRIBUTIONS TO THE GEOLOGY OF MINERAL DEPOSITS
DEPARTMENT OF THE INTERIOR 

DONALD PAUL MODEL, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

UNITED STATES GOVERNMENT PRINTING OFFICE: 1985

For sale by the Distribution Branch, U.S. Geological Survey, 

604 South Pickett Street, Alexandria, VA 22304

Library of Congress Catalog-card No. 84-600189
CONTENTS

Abstract Cl 

Introduction Cl

Purpose of study C2 

Stratigraphic and lithologic setting C2 

Petrography and summary of the bulk composition of

tourmaline-bearing rocks C3 

Sampling C7 

Analytical procedure C7 

Results of compositional studies Cll

Tourmaline end members in nature Cll

Compositional variation of tourmaline in North 

Gouverneur area Cll

Calcium content of tourmalines C20

Substitutions in hypothetical structural formula C20

Mineralized areas and tourmaline compositions C22 

Discussion C25

Comparison with the Balmat-Edwards district C29

Tourmaline genesis in the North Gouverneur area C29

Terranes showing most favorable implications for containing

stratabound sulflde deposits C31 

References cited C31

FIGURES

1. Index map of St. Lawrence County, N.Y. C2

2. Generalized geologic map showing sample localities for this study C4

3. Photographs of tourmalinite, brecciated tourmalinite, granular patches of 

black schorl, and schorl prisms C6

4. Photomicrographs of granoblastic tourmalinite and tourmaline-bearing 

rock C7

5. Distribution of selected elements in rocks from the North Gouverneur area, 

New York C8

6. TiO2-FeO/(FeO + MgO) plot for tourmalines in lithologic units from North 

Gouverneur, N.Y., compared with those from Sullivan Mine, British 

Columbia C19

7. Ternary plot of Na2O-MgO-FeO for tourmaline from North Gouverneur, 

N.Y., and the Sullivan Mine, British Columbia C20

8. CaO-Al2O3 plot for tourmalines from North Gouverneur, N.Y., compared 

with those from the Sullivan Mine, British Columbia C21

9. Al2O3 -FeO/(FeO + MgO) plot for tourmalines from North Gouverneur, 

N.Y. C22

10. (Na + Fe)-Al plot for tourmalines from North Gouverneur, N.Y., compared 

with those in rocks from Sullivan Mine, British Columbia C23

11. (Na + Ca)-Al plot for tourmalines from North Gouverneur, N.Y., compared 

with those in rocks from the Sullivan Mine, British Columbia C24

12. (Na + Mg + Al)-Ca + 2Fe plot for tourmalines from North Gouverneur area, 

New York, compared with those from Sullivan Mine, British Columbia C25

13. Ca-Na plot for tourmalines from North Gouverneur, N.Y., compared 

with those from Sullivan Mine, British Columbia C26

14. Al2O3 -Na2O/(Na2O + CaO + K2O) plot for tourmalines from North Gouverneur, 

N.Y., compared with those from the Sullivan Mine, British Columbia C27

Contents iii
TABLES

1. Summary of petrographic features of tourmaline-bearing rocks from the North 

Gouverneur area, New York CIO

2. Electron microprobe analyses and structural formulas of tourmalines in the 

North Gouverneur area, New York C12

3. Chemical analyses of selected tourmaline-bearing rock types in the North 

Gouverneur area, New York C17

4. Semiquantitative spectrographic analyses of tourmaline-bearing rocks in the 

North Gouverneur area, New York C17

5. Semiquantitative spectrographic analyses of tourmaline in Beaver Creek area, 

New York CIS

iv Contents
Significance of Tourmaline-Rich Rocks in the Grenville 

Complex of St. Lawrence County, New York

By C. Ervin Brown and Robert A. Ayuso

Abstract

Feldspathic quartzite and metapelite of Middle Proterozic age north of Gouverneur, N.Y., contain abundant 

dravite-uvite (magnesian tourmaline). These rocks, more 

than 1,000 feet thick, are regionally metamorphosed to the 

upper amphibolite facies, are pyritic, and locally contain 

porphyroblastic scapolite. The rocks are underlain by talctremolite schist and a thick sequence of calcitic and 

dolomitic marble, and are overlain by quartz, calc-silicate 

carbonate rock, and a pyroxene scapolite unit. All rocks are 

part of the metasedimentary Grenville Complex.

Individual tourmaline-rich layers in the quartzite are 

as thick as 3 cm and contain as much as 50 percent finegrained, brownish-green dravite. Subjacent talc schist contains fine-grained amber dravite, and silicated marble locally 

contains brown porphyroblasts of uvite. Gneissic granite, 

pegmatite, and migmatitic segregations cutting the 

tourmaline-bearing quartzite, gneisses, and schists are rich in 

black schorl.

Tourmalines from the tourmaline-rich quartzite and 

other metasedimentary and metaigneous rocks were analyzed by means of an electron microprobe. The compositions of tourmalines in the North Gouverneur area are 

clearly a function of the bulk composition of the rock. Tourmaline compositions in the quartzite have a wide range in 

FeO/(Fe+MgO) ratios, from 0.15 to 0.58, which are distinct 

from the ratios for tourmalines in granitic and pegmatitic 

rocks that range from 0.55 to 0.75. Tourmalines in the area 

have Na2O contents that range from 0.85 to 4.25 weight percent. Aluminum in all tourmalines ranges widely from about 

25 to 37 weight percent AI 2O3 . The most heterogeneous tourmaline compositions are in the quartzites, although most 

compositions cluster in the dravite-uvite solid solution 

series. Substitutions involving Na, Ca, Mg, Fe, and Al result in 

the following compositional schemes: Na+Fe = Al+vacancy, and Na = Ca. Such coupled substitutions probably 

represent valid constraints for tourmalines from North 

Gouverneur.

The abundance of magnesian tourmaline in the metasedimentary rocks of the North Gouverneur area is comparable 

to that of tourmaline-rich rocks associated with sedimenthosted massive sulfide deposits for example, Sullivan 

Mine, British Columbia. A recently described large lead-zinc 

deposit at Dugald River, Australia, is associated with 

tourmaline- and scapolite-bearing rocks similar in many respects to those north of Gouverneur. Compared with known 

tourmaline compositions in the Sullivan Mine area, tourmalines from North Gouverneur have comparable FeO and 

MgO values. We suggest that other tourmaline components

such as a low TiO2 content, variable Na/(Na + Ca + K) ratios, 

and the antipathetic correlation of Na and Ca might also be 

useful in discriminating tourmalines associated with ore 

deposits.

Ore bodies at the nearby Balmat-Edwards mining district 

are in marbles associated with rocks of evaporitic origin. The 

boron- and scapolite-rich rocks under consideration in this 

study possibly also are related to an evaporite-producing 

environment. Similar rocks that have an evaporite origin are 

associated with stratabound sulfide deposits at many places.

INTRODUCTION

Tourmaline is a common accessory mineral in 

rocks of the Grenville Complex in the Grenville Lowlands of St. Lawrence County, N.Y. It occurs disseminated in a variety of metasedimentary rocks ranging 

from marble to feldspathic gneiss, and also in 

pegmatitic segregations and granites that intrude the 

tourmaline-bearing metasediments. Although tourmaline is normally present only as an accessory mineral, 

it is very abundant in certain rock units in belts mainly 

in the Richville 7.5-minute quadrangle (fig. 1). Gushing 

and Newland (1925, p. 24-25) called attention to rocks, 

particularly along the Oswegatchie River west and north 

of Richville, N.Y., that contain 35 to 50 percent tourmaline. Such rock units are lithostratigraphic sequences 

consisting of feldspathic quartzite and quartz-feldsparmica granofels having layers that contain as much as 50 

percent fine-grained tourmaline, and are classified as 

"tourmalinite."

In 1966 Harold M. Bannerman (1972) mapped the 

belt of microcline-tourmaline-quartz gneiss along the 

Oswegatchie River (fig. 2), where at many outcrops the 

rocks are spectacularly brecciated in a zone of intense 

faulting. In an attempt to determine the significance of 

these tourmaline-rich rocks, and as an aid to future 

research, Bannerman had several chemical analyses 

made of rocks from this zone (Brown, 1980, analyses 45 

through 71) and indicated the locations of tourmalinerich rocks on his map of that area (Bannerman, 1972). 

The present study was in part instigated by his concern 

about the significance of these rocks, and by his encouragement that further research be done.

Subsequent geologic mapping by C. E. Brown in 

an area a few miles to the northwest of the Oswegatchie

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C1
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Figure 1. Index map of St. Lawrence County, N.Y., showing 

location of the Richville 7.5-minute quadrangle.

River revealed a second belt of tourmaline-rich rocks 

between Beaver Creek and its South Fork (fig. 2). This 

area is mainly in the low-dipping upper limb of a detached recumbent antiform or nappe. Stratigraphic relations in the upper limb of this fold are not disrupted by 

faulting,and, because of the low dip, the stratigraphy is 

more easily deciphered than in the faulted area along the 

Oswegatchie River. Although separated by folds and 

faults, the Stratigraphic column in the nappe is similar 

to that along the Oswegatchie River. The two principal 

differences are that (1) the sequence along the Oswegatchie at most places is in inverted order believed by 

Brown to be structurally overturned and (2) rocks in 

the nappe area were intruded by one large and many 

satellitic granite sheets, which transect the rock 

sequence at a low angle and which locally produced 

migmatite (Brown, 1969).

Purpose of Study

Studies of the Sullivan Mine area in British Columbia by Ethier and Campbell (1977), the Black Hawk 

Mine in Maine by Slack (1980), and the Elizabeth Mine 

in Vermont by Slack and Annis (1981) found that 

tourmaline-rich rocks are associated with and probably genetically related to the mineralized rock of 

stratabound sediment-hosted sulfide deposits. The tourmalines in these deposits are dravitic (and rarely uvitic)

in composition and are believed to be the result of boron 

and magnesium introduced syngenetically or diagenetically by hydrothermal solutions. Because of these relationships, Ethier and Campbell (1977) and Slack (1980, 

1982) suggested the use of tourmaline as a prospecting 

guide for stratabound sulfide deposits.

Brown (1983) speculated that the anomalously 

abundant tourmaline in the vicinity of North Gouverneur indicated depositional conditions possibly related 

to massive base-metal sulfides. The study reported here 

was undertaken to determine the composition of tourmalines in the metasedimentary and metaigneous 

lithologies in the Grenville lowlands, and to compare 

these tourmaline compositions with those from 

mineralized districts for which chemical data are 

available. Unfortunately, there is a general lack of published chemical analyses of tourmalines associated with 

ore deposits, especially stratabound sulfides in 

evaporitic terranes. Our study documents the range in 

the composition of tourmaline found in rocks of different bulk compositions in a possible evaporitic setting, 

but because of the absence of published analyses of 

tourmaline in stratabound deposits within evaporitic 

terranes, our comparisons rely for the most part on 

tourmaline compositions from the Sullivan Mine, a 

turbidite-hosted massive sulfide deposit in British Columbia. These comparisons and the geologic setting of 

the study area allow speculation on the genesis of the 

tourmaline-rich rocks and their possible economic implications (Brown and Ayuso, 1982).

STRATIGRAPHIC AND LITHOLOGIC SETTING

The metasedimentary rocks of the Grenville Complex under consideration have undergone multiple folding, were regionally metamorphosed to the upper 

amphibolite facies, and contain sillimanite. Layering 

and foliation in them are essentially parallel to the 

lithologic boundaries and thus are believed to be nearly 

parallel to bedding at most places, although no primary 

sedimentary features have been recognized.

Because the Stratigraphic section is more intact in the 

upper limb of the nappe north of North Gouverneur 

(fig. 2), the following description is of those rocks. The 

lowermost rock units constitute a thick sequence of 

marble labeled mm and qm (fig. 2) that is increasingly 

more siliceous and dolomitic upward, culminating in 

rocks that are now tremolitic quartzite and talctremolite schist containing minor amounts of anthophyllite (tt) (Brown, 1969). If essentially isochemical 

reactions during metamorphism are assumed (with loss 

of CO2), the tremolitic rocks can be inferred to represent a protolith of quartz-rich dolomite and magnesite, 

an assemblage suggesting an evaporitic environment 

during deposition. Overlying these carbonate and calC2 Contributions to the Geology of Mineral Deposits
cium-magnesium silicate lithologies are fine-grained 

clastic (noncarbonate) rocks that grade upward crudely 

from quartzite to biotite-muscovite-quartz schists 

(qmt). This upward fining gradation supports the 

assumption that the section here is not overturned. 

These rocks are oligoclase or microcline-rich quartzites 

interlayered with quartz-microcline-mica granofels, 

locally very micaceous. Porphyroblasts of muscovite, 

scapolite, and sillimanite are locally present in the 

micaceous rocks. Tourmaline occurs throughout, but is 

abundant only in the quartzite. The quartzite, present 

mainly in the lower part of the sequence, has layers as 

thick as several centimeters containing as much as 50 

percent fine-grained stubby, subhedral tourmaline crystals less than 0.1 mm across (fig. 3A and 44,5). Most 

rock types in this unit also contain pyrite, and many 

outcrops are intensely limonite-stained by the weathering of pyritic zones and local massive pyrite concentrations (Brown, 1983, loc. 57). Spectrographic analyses 

(C. E. Brown, 1969, unpub. data) of several rock specimens from this unit proved that some of the feldspathic 

rocks have anomalous amounts of barium probably occurring as a barium feldspar, although none has yet 

been identified (fig. 5).

Overlying unit qmt are quartz-rich, graphitic, dolomitic, and pyrrhotite-rich carbonate and calc-silicate 

rocks (csq). The contact with the underlying metapelites 

(qmt) is sharp and at places is marked by a 10-foot rusty 

feldspathic layer. At most places, this rock unit is very 

rusty from the breakdown of ubiquitous pyrrhotite. 

Also, it is altered extensively to light-green diopside and 

tremolite. The protolith probably was a quartzose 

ankeritic dolomite. The weathered rock surface and soil 

of csq are very distinctive because the outcrop surface is 

gritty, rusty, and hackly, and the soil is composed largely of limonite-stained granular quartz and diopside 

sand. Tourmaline is not a common accessory mineral in 

this unit, csq, and we have analyzed only one 

tourmaline-bearing sample from it (67-51, table 2).

The uppermost unit in the upper limb of the nappe is 

an extremely well layered paragneiss (pda) that occurs in 

a narrow isoclinal synform parallel and close to Beaver 

Creek (fig. 2). Thin layers of the paragneiss have a 

variety of mineral assemblages that contain mostly 

plagioclase or scapolite. Some of these assemblages consist of green diopside, scapolite, and quartz, and others 

contain microcline, tourmaline, quartz, and biotite (fig. 

4B), or biotite microcline and quartz. All rock types include many minute grains of sphene. A medium-grained 

vitreous diopside- and sphene-bearing quartzite (Brown, 

1980, analysis 41) forms prominent outcrop ridges on 

either limb of the synform and helps to outline the structure. Some layers also are rich in poikilitic tourmaline 

and biotite. Retrograde metamorphism has produced 

clotty areas of green hornblende and meionitic scapolite

in the diopside-rich granofels. The protoliths for this 

unit were probably interlayered shales, sandstones, and 

dolomitic muds.

A large outcrop area of granite (hg) is in the vicinity 

of Huckleberry Mountain (fig. 2). The granite has been 

folded with the metasediments and is foliated and locally lineated. Narrow strips of quartz, biotite, feldspar, 

and granofels of the tourmaline-bearing unit (qmt) are 

included in the granite area as fold keels or ridges. 

Along the eastern edge of the main granite body are similar infolded strips of the underlying quartz and silicaterich dolomitic marble. The main granitic body and 

numerous smaller satellitic masses are tongue-shaped 

slabs that were intruded at a low angle to the lithologic 

contacts of the metasediments and subsequently folded 

with them. In the western part of the area, the slabs are 

at the contact between the main tourmaline-bearing unit 

(qmt) and marble (qm). Farther to the east, the granite 

sheets are lower in the sequence where they intrude the 

marble unit. The granite sheets transect the stratigraphic 

section at such a low angle that at any one outcrop the 

granite is essentially concordant.

Numerous thin granitic sheets intrude the tourmalinebearing quartzite and metapelite (qmt) to the extent that 

the unit is locally migmatitic. Granite sheets around and 

to the north of Huckleberry Mountain contain abundant black tourmaline in grainy lineated patches (fig. 

3Q. The granites are rich in tourmaline only where they 

occur within or adjacent to the tourmaline-rich quartzites and metapelites (qmt). Small lenses of undeformed 

pegmatite also are common in the tourmaline-bearing 

quartzite and metapelite (qmt), all containing wellformed black tourmaline prisms mainly in their outer 

contact zone (fig. 3D).

PETROGRAPHY AND SUMMARY OF THE BULK 

COMPOSITION OF TOURMALINE-BEARING 

ROCKS

The most important petrographic characteristics 

of tourmalines in qmt, pda,and hg from the Gouverneur 

area are summarized in table 1. As seen in thin section, 

tourmalines from qmt are highly variable in color and in 

habit. Tourmaline grains forming distinct layers in this 

unit are typically green, subhedral, show patchy indistinct color zoning, and coexist with microcline or oligoclase and quartz. Additional petrographic variation is 

found in brecciated tourmaline-rich layers in unit qmt 

along the Oswegatchie River where brownish-yellow, 

subhedral tourmalines coexist with phlogopite, calcite, 

pyrite, and quartz. All tourmaline varieties in qmt 

generally show vague, indistinct color zoning from core 

to rim.

Lack of strong optical zoning and the dusty-green 

color in the tourmalines from pda are typical. In conTourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C3
44°22'30"

75°22'30" 

44°30'

75°30'

2 MILES

Figure 2. Generalized geologic map showing sample localities for this study. Geology along Oswegatchie River 

adapted from Bannerman (1972).

C4 Contributions to the Geology of Mineral Deposits
EXPLANATION

QUATERNARY

UPPER 

CAMBRIAN

MIDDLE 

PROTEROZOIC

Peat-filled valleys

Potsdam Sandstone 

Grenville Complex

Diopside scapolite paragneiss, tourmaline-bearing quartzite, 

and biotite-quartz-oligoclase granofels

Mixed tremolite-diopside-quartz-carbonate rock, 

all pyrrhotite-bearing

Tourmaline-rich feldspathic quartzite and interlay.ered metapelite 

Quartzite occurs mainly close to basal contact

Talc-tremolite schist. Includes laminated quartz-tremolite rock

Quartz-rich' graphitic marble. Increasingly dolomitic and silicated 

toward contact with talc-tremolite rock

Massive, blue-gray banded magnesian marble. Graphitic and 

phlogopitic

Undivided metasediments

Gneissic granite. Tourmaline-bearing (+) where intruding qmt

Thrust fault Sawteeth on upper plate, overturned where indicated

Recumbent antiformal axis

Fault Bar and ball on downthrown side, where known

Contact Showing dip

.81-1 Locality of sample analyzed by microprobe (see Table 2)

Figure 2. Continued.

,54 Locality of analyzed sample (see Table 3)

trast to tourmalines from qmt, the tourmalines from Tourmalines in granites (hg) have patchy zoning,

pda are embayed and show resorption features. Also, are dark green as seen in thin section, and occur typicaltourmaline is characteristically present only in trace ly in patchy poikilitic grains. The streaky clots of touramounts in pda, except for sample 68-70 that has about maline grains are commonly the principal dark mineral

5 percent. and are lineated weakly in the plane of foliation of the

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C5
c -i

Figure 3. A. Polished slab of tourmalinite from lower part of unit qmt from along Rock Island Road close to sample locality 

80-4. Dark layers are as much as 50 percent dravite. Light-colored layers are composed mainly of quartz, oligoclase, and 

biotite. B. Polished slab of brecciated tourmalinite from qmt from along Rock Island Road close to Oswegatchie River and 

sample locality 80-3. Matrix is composed of cataclasized qmt plus pyrite and minor calcite. C. Granular patches of black 

schorl (T) in granite sheet that intrudes qmt. Specimen collected from along Rock Island Road close to sample locality 67-27. 

D. Schorl prisms (T) around margin of small pegmatite lens in qmt at small road cut along Rock Island road close to sample 

locality 67-27. Note muscovite porphyroblasts in rock at bottom of view.

gneissic granite. Microcline, quartz, plagioclase, biotite, 

and muscovite coexist with the tourmalines, and the 

granite at places has accessory fluorite. Tourmaline in 

pegmatites occurs as well-formed black prisms arranged 

around wall-rock inclusions or along the border of the 

pegmatite mass (fig. 3D).

Composite tourmaline prisms (sample 68-5) in a 

quartzofeldspathic lens in qm have a dark-brown core, 

enveloped by indigo-blue rims. The surface between the

two tourmaline varieties is characterized by indentation, 

embayment, and resorption.

All textural features of the tourmalines from the 

North Gouverneur area, except sample 68-5, suggest 

that the tourmalines were generated during the metamorphic event that formed the rest of the mineral 

assemblage. Relic textures showing an earlier generation 

of tourmaline, subsequently transformed to other 

phases, are absent. Also lacking are features reminiscent

C6 Contributions to the Geology of Mineral Deposits
Figure 4. A Photomicrograph of granoblastic tourmalinite 

from unit qmt. All gray grains are dravite. White grains are 

quartz or oligoclase. B. Photomicrograph of tourmalinebearing rock from unit pda. Rock is microcline-tourmaline 

granofels having minor amounts of quartz and biotite. (T^ 

Schorl prisms.)

of tourmalinization, whereby other minerals show partial replacement by tourmaline. Although poikiloblastic 

tourmaline is evident in some rock types, the textures indicate that tourmaline formed at the closing stages of 

the same event in which the surrounding phases formed. 

Despite the relatively few bulk chemical analyses, 

it seems clear that the rock units in the North Gouverneur area have a wide range of compositions (tables 2, 

3, and 4; fig. 5). Individual rock units, as exemplified by 

qmt, range widely from 47.2 to 80.0 weight percent 

SiO2 , 6.9 to 17.2 weight percent A12O3 , 0.50 to 14.0

weight percent CaO, and 0.28 to 9.3 weight percent 

K2O. This suggests that significant compositional 

heterogeneity exists within individual rock units in a 

fairly restricted geographic area.

Figure 5 depicts some of the differences in the 

distribution of selected elements in the tourmalinebearing rock units. For example, boron is generally 

higher in unit qmt, whereas barium seems to be subequal in units qmt, pda, and hg. Iron and titanium are 

higher in pda and qmt than in hg and csq, and 

magnesium decreases from csq, pda, qmt, to hg. 

Despite the relatively higher iron and magnesium contents in units pda and qmt compared with hg, the most 

iron-rich tourmalines are in the granite gneisses (hg).

SAMPLING

Twenty-three tourmaline-bearing specimens from 

several lithologic units in the North Gouverneur area 

(fig. 2) were selected from a collection of representative 

lithologic specimens collected during routine geologic 

mapping of the area. The three most important 

tourmaline-bearing rock types are the tourmaline-rich 

feldspathic quartzite (qmt), the diopside-scapolite paragneiss (pda), and the tourmaline-bearing granite gneiss 

(hg). Pegmatite and migmatite segregations within qmt 

and pda were also sampled, as were other lithologies in 

the vicinity such as talc-tremolite schist (tt), calcsilicate 

rock (csq), and a quartzofeldspathic lens in marble 

(qm).

Most of the samples came from a small area, 

about 10 square miles (26 km2); therefore, we could 

determine tourmaline compositional variability resulting principally from differences in bulk composition of 

the host rocks. Rocks in qmt and pda have a wide range 

of lithologies; thus we expected that tourmaline within 

these units would be compositionally heterogeneous. In 

order to study the change in tourmaline composition 

across a lithologic unit, we selected closely spaced 

samples across pda. Tourmaline in pegmatites and 

migmatitic segregations were also studied for comparison with tourmalines in the nearby granitic bodies.

ANALYTICAL PROCEDURE

An automated, 3-channel, combined energy- and 

wave-length dispersive electron microprobe system at 

the U.S. Geological Survey, Reston, Va., was used for 

the partial chemical analyses of tourmalines from North 

Gouverneur (table 2). These analyses are necessarily incomplete because Fe2O3 , H2O, B2O3 , and LiO2 are not 

determined by means of the microprobe. Although B2O3 

and water determinations by means of wet-chemical 

methods are important in tourmaline studies, they require relatively large amounts of pure tourmaline separates. Because clean mineral separations are difficult to

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C7
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C8 Contributions to the Geology of Mineral Deposits
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EXPLANATION 

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Figure 5. Continued.

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CD O O CD O O C

B (ppm)
Table 1. Summary of petrographic features of tourmaline-bearing rocks from the North Gouverneur area, New York 

[Abbreviations are as follows: py, pyroxene; am, amphibole; pi, plagioclase; mi, microcline; bi, biotite; sp, sphene; q, quartz; mu, muscovite; 

ph, phlogopite; sea, scapolite; cc, calcite; ch, chlorite after biotite; X, present; , not present]

Sample no.

Opaque oxides 

Color Habit Zoning Inclusions and sulfides Assemblage

Tourmaline

abundance 

(in percent) Other

pda

68 75 

68-67

68-68 

68-70

Brown green Subhedral Fluid X py, am, pi

Brown green Subhedral Silicates ? py, am, pi, 

bi, sp, q

Brown green Subhedral X bi, pi

Brown green Anhedral Silicate X q, am, sp, py

< 1 

1 Embayed

1 Embayed

Poikilitic; same 

texture as diopside

hg

68-54

80-5

67-27

Brown green Anhedral Patchy Fluid, silicate X q, mi, bi, pi

Dark green Anhedral Patchy Fluid, silicate ? mu, mi, pi, q

Dark green Subhedral Patchy Silicate mi, q, mu

5 Poikilitic

5 Fluid inclusions near

core

5 Poikilitic

Pegmatite in qmt

71-124 

67-23

Dark green Anhedral Patchy Silicate mi, pi, q 

Brown green Subhedral X ? pi, q, mu

20 Poikilitic

5 Embayed, associated 

with quartz

qmt

67-26

67-21

71-126

80-4

80-3 

(clast)

80-3 

(matrix)

Green Euhedral X? Silicate, fluid bi, mi, q 

Patchy

Brownish yellow Subhedral X X ph, cc, q

Brown green Anhedral Silicate pi, sea, q, sp

Yellow Subhedral X? X mu, q, ch, pi?

Brown green Subhedral Silicate, fluid X q, mi, pi, ch

Yellow Euhedral X Silicate, fluid X ch, cc, q

10 In layers

25 Random distribution

5 Poikilitic 

intergrowth 

with scapolite

25 Random distribution 

and in layers

20 Random distribution

5 Embayed, larger 

than tourmaline in

clasts

obtain and equivalent data for tourmalines from 

massive sulfide deposits are unknown, such approach 

was deemed to be outside the scope of this study.

C10 Contributions to the Geology of Mineral Deposits

Tourmalines were carefully cleaned for semiquantitative spectrographic analyses (table 5), but most of the 

tourmaline included in the metasedimentary rocks was
too fine grained for hand cleaning, and thus the semiquantitative analyses were mainly from porphyroblastic 

tourmaline or from crystals in pegmatitic segregations.

Fe2 O3 is presumed to represent a major component in buergerite (Donnay and others, 1966), the ferric 

iron end member of the tourmaline group, and its abundance is assumed to be negligible in this region. Walenta 

and Dunn (1979) demonstrated that ferric iron is also an 

essential component in ferrodravite, the aluminum-poor 

iron analog of dravite. On the basis of new spectrographic analyses of tourmalines from Gouverneur (this 

study) together with previous investigations (Dunn and 

others, 1977), it seems reasonable to suggest that 

lithium-rich tourmalines (elbaites) are also volumetrically minor or nonexistent. Specialized geochemical environments exemplified by lithium-enriched pegmatites 

are known to be critical for the formation of elbaites 

(Deer and others, 1962). Such environments might exist 

in the pegmatites in the North Gouverneur area. However, because potentially favorable environments in this 

setting are very rare and because spectrographic analysis 

of tourmaline sample 71-124 from a pegmatite has more 

than 10 weight percent total iron and only 10 ppm lithium (table 5), we assumed that elbaites, if present in the 

Gouverneur area, are volumetrically negligible and 

therefore excluded discussion of them in this study.

Microprobe analyses were obtained on standard 

singly or doubly polished thin sections, carbon coated 

before analysis. Standards were chosen from a set of 

natural silicate minerals, with internal standardization 

checks made on compositionally well known silicates, 

including a San Luis Potosi tourmaline obtained from 

Brian Mason, Smithsonian Institution. Size of the electron beam ranged from 5 to 10 microns. Each grain was 

analyzed at a minimum of five spots, and each sample 

represents an average of at least five grains. The data 

were reduced on-line by means of the methods of Bence 

and Albee (1968). Compositional variations are shown 

on table 2. Structural formulas were calculated assuming a value of 3 boron atoms in the structural formula.

RESULTS OF COMPOSITIONAL STUDIES 

Tourmaline End Members in Nature

Tourmaline is compositionally variable in natural 

environments because it forms under many geologic 

conditions. The theoretical formula may be stated as 

XY3Z6 (BO3)3Si6O18 (OH)4 , in which X = (Na, Ca, K); 

Y = (Mg, Fe, Mn, Li, Al); and Z = A1 (Deer and others, 

1962). Two solid solutions are the most common in 

nature: (1) from Fe-rich (schorl) to Mg-rich (dravite); 

and (2) from schorl to the Li-rich (elbaite) tourmalines. 

Dunn and others (1977) documented another solid solution between dravite (Na>Ca) and uvite (Ca>Na), as

suggested earlier by Kunitz (1929). Fe3+ -rich tourmalines are known as buergerite and ferridravite 

(Walenta and Dunn, 1979).

The Gouverneur area in New York contains tourmalines that have compositions mainly within the 

dravite-uvite solid solution series (Dunn and others, 

1977). Our preliminary results, based on spectrographic 

analyses (table 5) also indicate that lithium-rich tourmalines probably do not occur here. Lithium content of 

tourmaline in the North Gouverneur area is restricted to 

values of less than 70 ppm, well below the composition 

of typical elbaites (>0.9 weight percent Li2O according 

to Nemec, 1969).

Compositional Variation of Tourmaline in North 

Gouverneur Area

Microprobe analyses of tourmaline present other 

problems in addition to their incomplete nature. For example, Ethier and Campbell (1977) indicated that for 

the Sullivan Mine tourmalines, grain size and volatilization of boron and sodium during microprobe analysis 

were significant problems. For the North Gouverneur 

tourmalines, neither the grain size nor the loss of 

alkalies and boron was a major obstacle. More disturbing results, however, were found in the compositional 

range of SiO2 (32.4 to 42.1 weight percent) and A12 O3 

(24.9 to 36.5 weight percent) for these tourmalines 

(table 2). A tendency toward higher contents in SiO2 and 

A12 O3 for the microprobe-analyzed tourmalines of the 

Sullivan Mine was also reported by Ethier and Campbell 

(1977), who cited previous determinations exemplifying 

similar analytical problems.

Several tourmaline samples from the North Gouverneur area showed anomalous microprobe compositions even after duplicate runs, use of different sets of 

microprobe standards, and a minimum of 25 spot 

analyses.

The average composition of tourmaline samples 

71-126 (qmt), and 80-3(a) (qmt) are lower in SiO2 

(<33.8 weight percent) than the range of welldetermined tourmaline compositions in Deer and others 

(1962) for schorls and dravites, and Dunn and others 

(1977) for uvites (<33.7 weight percent). Sample 80-4 

(qmt) is enriched in SiO2 (40.44 weight percent) and is 

similar to a uvite analysis given by Dunn and others 

(1977). The contents of A12 O3 in tourmaline samples 

71-126 (qmt) and 71-124 (pegmatite in unit qmt) are 

lower than the minimum value (28.5 weight percent) in 

Deer and others (1962), but are within the published 

range for uvites (23.1 to 34.4 weight percent) shown by 

Dunn and others (1977).

The average tourmaline compositions presented in 

table 2 generally show reasonable variations for most 

oxides except for SiO2 and A12O3 in samples 80-4 (qmt),

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C11
Table 2. Electron microprobe analyses and structural formulas of tourmalines in the North Gouverneur area, New York

[Analytical data represents the average composition of traverses with the reproducibility as 29 in parentheses. Cation proportions calculated assuming

near the Oswegatchie River, south of North Gouverneur. Columns 8, 9, and 11 are from the matrix; column 10 is from a clast]

Column 1 2

Lithologic unit qmt qmt

Sample number- 66-34 67-21

SiO2 34.87 (0.90) 33.08

TiO2 1.13 (.10) .60

A12O3 35.00 ( .26) 36.54

FeO 1 8.37 ( .29) 2.23

MnO .05 ( .06) .01

MgO 7.67 ( .17) 9.92

CaO 1.98 ( .11) 1.49

Na2O 1.53 ( .05) 1.65

K2O .17 ( .04) .11

Cl .02 ( .02) 0

Total 90.79 85.63

Si 5.493 5.345

B 3.000 3.000

Ti .134 .073

Al 6.498 6.959

Fe 1.103 .301

Mn .007 .001

Mg 1.801 2.400

Ca .334 .258

Na .467 .517

K .034 .023

Beaver Creek zone

qmt 

67-25

qmt 

67-26

qmf 

80-4

qmt 

71-126

Weight percent

(0.27)

.05) 

.62) 

.18) 

.02)

'.13) 

.06) 

.02)

37.38

.59

35.07

2.07

.02

9.53

.39

2.81

.07

.03

87.96

(0.39)

( .07)

.37)

.08)

.02)

.22) 

 19) 

.02) 

.01)

32.93

.92

34.22

5.03

.03

8.91

1.02

1.94

.20

.03

85.23

(0.08)

( -05)

.36)

 17) 

.06)

 11) 

.08) 

.06) 

.06)

40.44

1.70

30.90

5.22

.07

8.03

1.20

2.14

.02

89.78

(3.76) 

( -23) 

(1.98) 

( -09)

( '.62)

( -37)

( -13)

( -36)

( -01)

32.45

1.26

27.86

9.85

.10

9.58

3.04

4.25

.06

0

88.45

(0.25) 

( .06) 

.06) 

.10) 

.02) 

.11) 

.01) 

.07) 

.01)

Structural formula

5.857

3.000

.070

6.477

.271

.003

2.226

.065

.854

.014

5.436

3.000 

.114

o.o5o 

.694 

.004

2.193 

.180 

.621

6.211

3.000

.196

5.594

.670

.009

1.838

.198

.637

.012

5.533

3.000

.162

5.600

1.405

.014

2.435

.555

.413

.013

Ratios

FeO/(FeO + MgO) 0.522 

Na2O/

(Na2O + CaO + K2O) .416 

Fe/(Fe + Mg + Mn) .379

Na/(Na + Ca + K) .559

0.184

.508

.111

.648

0.178

.859

.108

.915

0.361

.614

.240

.737

0.394

.629

.266

.752

0.507

.578

.365

.421

80-3 (qmt), 68-68 (pda), and 68-54 (hg). Much of the 

variation, however, may result from the procedure of 

analyzing the same sample over a period of weeks. 

Typical variations for the other oxides are much lower, 

and no significant or consistent deviations from the 

mean were observed. It is likely, however, that samples 

showing substantial variation reflect different stages of 

tourmaline growth. In these samples, perhaps only the 

outermost zones may be in equilibrium with the coexisting minerals. Samples showing great compositional 

variability in the North Gouverneur area, however, 

generally have compositions that vary progressively 

from rim to core in individual grains.

Although only weight-percent oxide variations

could be used for comparison of the tourmalines in the 

North Gouverneur area, a more useful method of study 

depends on the calculation of cation abundances in the 

hypothetical tourmaline formulas. These calculations, 

however, because of the incomplete chemical analyses 

obtained with the electron probe (for example, B2O3 , 

H2O), and because of the observed large variation in the 

two major oxides of SiO2 and A12O3 , yield useful but 

probably only first-order approximations of the changes 

in the crystal chemistry of tourmalines in the North 

Gouverneur area. Despite these difficulties, the 

calculated cation proportions suggest general trends for 

the tourmalines of the area.

In addition to the changes in the ratios of

C12 Contributions to the Geology of Mineral Deposits
29 oxygen and 3 boron atoms in the structural formula. Columns 1-6 are from the area north of North Gouverneur; columns 7-11 are from

7 Q Q 10 11

South zone

81 1 80 3(a) 80 3(b)

qmt 

80-3(c)

qmt 

80-3 (d)

Weight percent Continued

SiO

TiO

Al D

FeO 1 

MnD

MgO

CaO

Na2O 

K r\

Total

 35.43

 1.63

 10.14

 9.11

 2.97

 1.48

 23***}

 .02

89.65

(0.68)

( -55)

( .63)

( .10)

( -37)

( .03)

( .oi)

33 73

X »V/^

4tJ .4*\.

6.07

.11

10.34

" V/^

.14

.03

85.56

(0.71)

( -20)

(1.20)

/ I/TV ( -26)

( -ID

( 44}

( -21)

( .07)

( -02)

35.48

2 40

Ji* * +-/

4t» X /

.15

12.50

2 27

1 Qfi

.11

0

89.49

(0.66)

( -25)

( -30)

( -15)

( .01)

( .14)

( .14)

( )

33 *j*j »**J 25

1 40

27.99

11.27

.09

8

17

3 04 J . VTT

1 23

-70

(\a

86.78

(0.65)

( .08)

(1.20)

( .09)

( -21)

( -19)

( -07)

( 04}

35 OT

1 64

30 52

.14

.01

12 1^.^3729

1.69

.03

02

84.22

(1.95)

( -10)

(1.50)

( -02)

( -02)

( -40) 

( -19)

( -16)

( -03)

( .02)

Structural formula Continued

Si

Ti

Al

Fe -

Mn

Mg 

Ca

Na

 5.757

3

AAA

1QQ

< 47Q

1 378

O/V1

2 207

 .517

. 466 tuu

(\AO

5.639

J.VAA/

.131

5.756

.849

.016

£** -/ / /

.724

.275

.030

5

C-7Q

J f\J\J\J

/7Q/7

j s t £t

TO'5

.020

9 OrtO

,JO\J 380

.593

.022

5 £-30

J \J\J\J

.179

5.594

T 5Q8

.013

2

A/C<

. jj£* 552

4O4

A£1

5 Q7/:

J 3 000 \J\J\J

.201

5

O/CI

.091

.Uvl 001

2QQC

295

.651

AH/;

Ratios Continued

FeO/(FeO + MgO)

Na2O/

(Na2O + CaO + K2O)

Fe/(Fe + Mg + Mn)

Na/(Na + Ca + K)

0.527

.316

.384

.452

0.370

.169

.247

.267

0.148

.452

.088

.596

0.580

.270

.435

.397

0.011

.545

.006

.684

Na2O/(Na2O + CaO + K2O) and FeO/(FeO + MgO), we 

discuss the change in the cation proportions for Na and 

Fe and suggest general compositional trends. The two 

oxide ratios generally, but only approximately, treat the 

occupancies of the X-sites (Na, Ca, K) and Y-sites (Mg, 

Fe, Mn, Li, Al). Besides ignoring the role of Al, these 

sample oxide ratios cannot be used, in contrast to cation 

proportions, for exploring the effect of coupled 

substitutions. Such substitutions have much broader 

value in explaining tourmaline compositions than the 

simple trends shown by oxide ratios.

A direct reflection of the variation in SiO2 and 

A12O3 contents of the tourmalines is given in the range 

of the calculated cation proportions. Although most

tourmaline samples have a value close to 6 for Si, some 

tourmalines have high Si values to a maximum of 6.514 

(sample 80-5 in unit hg), and others have low Si values 

of about 5.436 (sample 67-26 in qmt). For comparison, 

the highest Si value given by Deer and others (1962) for 

dravite is 6.172, whereas the lowest is 5.758 for a schorl. 

Low Al values, less than needed to fill the Z-site, were 

also obtained in some tourmalines. Such contents were 

masked by the inherent analytical problems of the 

microprobe technique, but also probably include geological uncertainty surrounding the effect of other cations substituting for Al (for example, Fe2+ , Fe3+ , Mg, 

Ti, and so forth) in the Z-site.

Occupancy in the X-site (Na, Ca, K) appears to be

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C13
Table 2. Electron microprobe analyses and structural formulas of tourmalines in the North Gouverneur area, New York Continued 

[Analytical data represents the average composition of traverses with the reproducibility as 29 in parentheses. Cation proportions calculated assuming 

near the Oswegatchie River, south of North Gouverneur. Columns 8, 9, and 11 are from the matrix; column 10 is from a clast]

Column 12 13 14 15 16

AT an

pC/3 

/: o /: *7

pu3

68-68 68-70

pda

/: o -re

Weight percent Continued

SiO2

TiO2 -

A12 03 -

FpfV

MnO

MgO

CaO

K r\

a .

Total

- 34

. i

. 24

IZi 19

7

9

1

84

.34

.13

88

.36

04

.22

.66

.12

.02

.6

(0.34)

( -11)

( -74)

( .19)

( .30)

( -10)

( -13)

( .03)

( -02)

34 20

1.51

17 CS)

8

/r-j

10.24

2

7/r

J. . ^T^T

.14

86.64

r 99}

( -51)

( -27)

( -05)

( -13)

( .10)

(

f\£.\ .06)

( -10)

( -05)

 5-5 s"7

78

32 64

7.71 

04

8.49

1 8Q

1.65

.20

.02

87.09

(1.23)

( -08)

(1.20)

I £.Q\ ( -60)

i r\c\ ( -06)

( -15)

( .11)

( -09)

( .03)

 a/r 7*3

1.^1

26.84

11.24

.07

2.75

.12

.03

89.32

(0.08)

( .08)

( -42)

( -02)

( -07)

( .21)

( -14)

( -02)

( -02)

33 38

o/c

27.72

9 64 .7« VJ*T

04

10.57

2.97

1.25

.15

02

86.60

(0.13)

( -13) 

( -19)

( -21) 

( .08)

( -15)

( -13)

( -05)

( -03)

( .03)

Structural formula Continued

Si

Ti

A1

Fe 

Mn

Mg -

Ta

Ma

- 6.057

i fifio,

isn

c 173

1 891

Oflfi

2 059

- .420

c/co

CY)(.

f 718

J.VAA/

ion

J 1 1^

1.207

.UU7 OOQ

2.552

.494

 ~VJ 467/

.030

5.531

j . \j\j\j

AH/C

6.319

1.059

.VA/U

2.079

.333

MA

.V/t^

6

/V11

J . V/V/V/

.149

5.170

1.536

.010

2

1 ^/;

 ^OM

 "VJ.7

.v/^J 025

5

/:Ts

J 3 .VAA/ 000

.109

5.503

1 3^8

AA/C

2.654

c^/c

 TAJO 408

032

Ratios Continued

FeO/(FeO + MgO)

Na20/

(Na2O + CaO + K2O)

Fe/(Fe + Mg + Mn)

Na/(Na + Ca + K)

0.612

.415

.469

.560

0.457

.332

.320

.471

0.476

.441

.337

.584

0.559

.340

.415

.481

0.477

.286

.338

.418

normal, and most tourmalines fall within the range of 

about 0.8 to 1.0. The lowest value for the total of 

Na + Ca + K is in sample 68-5 (in qm), specifically in the 

blue part of the composite tourmaline. The value for the 

total of Na + Ca + K is only 0.439 compared with 0.963 

obtained on the brown core of the same tourmaline 

crystal.

The analyses in table 2 show that tourmalines 

from each unit (fig. 6) have distinct iron and magnesium 

compositions. The most notable characteristic is that 

tourmalines from the granitic gneiss (hg) and from the 

pegmatitic segregations within qmt and pda have 

FeO/(FeO + MgO) ratios of 0.55-0.75 that are generally

higher than those of tourmalines from the metasediments. Compared to the field of granite and pegmatite 

tourmalines from Portugal (Neiva, 1974; 1976), those 

from Gouverneur are higher in MgO and thus have 

lower FeO/(FeO + MgO) ratios.

The lowest FeO/(FeO + MgO) ratios in tourmalines are in unit qmt. They also have the most 

heterogeneous ratio of FeO/(FeO + MgO), from 0.01 to 

0.58. Within qmt, tourmalines may be grouped according to whether they occur in the nappe structure north 

of North Gouverneur or along and southeast of the 

Oswegatchie River (fig. 2). The bulk of the data is from 

the northern area. Intrusions of granite and pegmatite

C14 Contributions to the Geology of Mineral Deposits
29 oxygen and 3 boron atoms in the structural formula. Columns 1-6 are from the area north of North Gouverneur; columns 7-11 are from

17

hg

/" "7 O"7

1 Q

Granites

hg 

68-54

19

hg

80 5

20

68 82

21

Pegmatites

71 124

22

r-t TD

Weight percent Continued

SiO2

TiT»

A12 03 -

FeO1 -

MnO

MgO

for*

Na2O

K c\

Cl

Total

is 87

. 71/ 1

IS AA

8

1£

.V/T"

6

Q£

88

9 15

- .12

- .04

90.19

(0.27)

( .05)

( -37)

(

t£.\ .26)

( .03)

V. -^J)

\ * * )

t c\e\ ( -06)

( .03)

( -01)

37.84

I

^f.

25.67

14.71

 £*£*

4.74

1 89

i on

.15

,\J£*

88.53

(1 QA\

( -14)

( .91)

( .35)

( .07)

( .37)

V. '* ->)

( -21)

/ A/C\ ( -06)

( .02)

42.10

.76

29 A*-/ * V^T 64

9.77

.15

4.91

1 . v/v/

2

c\a

 12L^

.01

90.52

(0.27)

( -07)

( .43)

( 781 I >^oj

( -02)

( -31)

( -15)

( .07)

( -02)

( -01)

i<; 04

2 or

"1C. 7£

i "5 sn

ns

8

£A

1 CO

2 29 _*..£r7

.14

.02

90.16

(0.23)

( -05) 

f 041 v. v*)

( -01)

( -01)

( -06)

( -03)

( -03)

( -03)

( .oi)

35.52

.93

IT Q£.

14.18

0

7.47

2.55

1.77

.15

04

90.47

(0 22)

( -14) 

( -51)

( -20)

( -25) 

( -10)

( -05)

( -10)

( -03)

35.80

.96

11 81

8 T\

.03

6 Of

QQ

2.12

12

0

87.45

(0.73)

( 041 V. ."T/ ( 401 V. ^J}

( -75)

( -07)

( .41)

/ A£\ ( .06) 

( .05)

( -01)

Structural formula Continued

Si

Xi _____________

Al

Fe

Mn

Mg -

/">,,

Na

5.659

3 Ann

084

- 6.520

1 AQA

AA<;

- 1.613

- .149

.705

 ^A/^

6 31 Q

J WV/V/

1 S8

5.051

2.054

.031

1.230

ii£

.615

.\jj^t

6.514

J . WV/V/

A88

J *T\JJ

1 264

.020

1 132

.166

£1 Q

.024

5.750

i ono

,jj£ 352

5.175

1.757

.011

2 ^1 104V^T

978

 / ^J7

.029

e Q-JQ

3 000

.115

5 188

1 946

0

1 807

448

 564 J\J^

.030

5.846

i 000

118

6.129

1.195

004

1

£-1 1

.172

.671

.025

Ratios Continued

FeO/(FeO + MgO)

Na2O/

(Na2O + CaO + K2O)

Fe/(Fe + Mg + Mn)

Na/(Na+Ca + K)

0.546

.701

.403

.803

0.756

.491

.620

.632

0.666

.648

.523

.765

0.598

.571

.454

.704

0.655

.396

.516

.541

0.561

.658

.416

.773

characterize this area, whereas postmetamorphic faultrelated brecciation and recrystallization typifies the belt 

of qmt found near the Oswegatchie River.

Tourmaline in two samples (80-3 and 81-1; table 

2) from a large roadcut in unit qmt along Rock Island 

Road, south of the Oswegatchie River, is consistently 

different in compositional trends from tourmalines to 

the north in this unit. The two samples may themselves 

be distinguished because sample 80-3 is from a greenishgray reduced breccia having a pyritic matrix and sample 

81-1 (fig. 3E) is an oxidized (hematite-stained) 

equivalent of sample 80-3. Field observations suggest 

that the pyrite formed after brecciation.

Sample 80-3 contains at least two generations of 

tourmaline enclosed in matrix and in clasts, and these 

are distinguished both optically and chemically. Tourmalines in the matrix of sample 80-3 are the most compositionally diverse found in this study. Their 

FeO/(FeO + MgO) ratios range from about 0.01 to 0.37, 

and contrast with tourmaline in the clasts that have 

ratios of about 0.58 (fig. 6). Matrix tourmalines in sample 80-3 contacting pyrite are depleted in iron 

(FeO/FeO +MgO = 0.11), whereas matrix tourmalines 

in the same immediate area but not in contact with 

pyrite have higher FeO/(FeO + MgO) ratios (0.15 to 

0.58). The composition of the tourmaline in sample

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C15
Table 2. Electron microprobe analyses and structural formulas of tourmalines in the North Gouverneur area, New York Continued 

[Analytical data represents the average composition of traverses with the reproducibility as 26 in parentheses. Cation proportions calculated assuming 

29 oxygen and 3 boron atoms in the structural formula. Columns 1-6 are from the area north of North Gouverneur; columns 7-11 are from near 

the Oswegatchie River, south of North Gouverneur. Columns 8, 9, and 11 are from the matrix; column 10 is from a clast]

Column 23 24 25 26

Quartzofeldspathic lens in qm

68 5 ro r

csq 

67 51

tt

67-37

Weight percent Continued

SiO2

TiO2 

A12 03 

FeO1

MnO

MgO 

faCl

Na2O 

K PI

Cl

Total

36 89

 .37

in QS

.92

 .03

12 64

"> "58

1 01

.05

02

85.99

(0.36)

( -13)

( -76)

( .20) 

( (Ml \ .tn-;

( .30)

( -15)

( -14)

( -02)

( -02)

34.91

.13

36.91

13.41

0

.01

.14

1.29

0

.07

86.87

(0.25)

( -05)

( -45)

( -35)

( -03)

( -15)

t f\£\ ( -06)

( -02)

37 24

 £**} 23

^8 on

1 34

.02

1 1 Q£

3.55

Q8

 04V^T

0

86.16

(0 \y.£y) 291

( .03)

( -13) 

( -34)

( -02) 

( 251 ^ .4j)

( -03) 

( 041 V. ***)

( -01)

37 73

1.77

30.05

.69

.01

12.52

1

"l£.

2.31

02

.03

86.39

(0.47

( -08) 

( -10)

( -19)

( -01)

( .13) 

( .13)

( -02)

( -03)

( -03)

Structural formula Continued

Si

B

Ti

Al

Fe

Mn

Mg 

Ca

Na

K

 5.907

 3.000

 .045

 5.847

 .123

.VAJH 004

 3.017

 .391

.562

 .010

5.775

3.000

.016

7.201

1.856

0

.002

.025

.414

0

6.016

3.000

.028

5.503

.316

 \J\JJ

3.097

.614

.251

.008

5.997

3.000

.212

5.630

.092

001

2.966

.215

.712

.004

Ratios Continued

FeO/(FeO + MgO)

Na2O/

(Na2O + CaO + K2O)

Fe/(Fe + Mg + Mn)

Na/(Na+Ca + K)

0.068

.437

.039

.584

0.999

.902

.999

.943

0.154

.214

.093

.288

0.052

.643

.030

.765

'Total iron as FeO.

81-1 (oxidized breccia) has a ratio of FeO/(FeO + MgO) 

of about 0.53 and falls well within the range defined by 

qmt to the north (fig. 6). Compositionally, tourmalines 

from 81-1 and from the clasts in sample 80-3 (c) have 

ratios that are more similar (0.53 compared with 0.58) 

than the ratio of the matrix tourmaline in sample 80-3 

(a,b,d).

In contrast to the tourmalines in unit qmt north of 

North Gouverneur, those from near the Oswegatchie 

River define a broad trend of decreasing TiO2 with increasing FeO/(FeO + MgO) ratio (fig. 6). This trend is 

opposite to that of unit qmt tourmalines from north of 

North Gouverneur, which show increasing TiO2 at 

higher FeO/(FeO + MgO) ratios. Despite the numerous

granites and pegmatites north of North Gouverneur 

(fig. 2), tourmalines in metasediments there do not show 

gradational compositional features arising from proximity to the igneous rocks. Also, because of the large 

range in TiO2 content (from 0.58 to 2.40 weight percent) 

and FeO/(FeO + MgO) ratios, these oxides cannot be 

used to distinguish samples in qmt. Possible exceptions 

are two samples of matrix tourmalines in sample 80-3 

(b, d; table 2) that appear to have both a low 

FeO/(FeO + MgO) ratio (0.011-0.148) and high TiO2 

content (> 1.6 weight percent).

Tourmalines in pda from samples that are closely 

spaced across a stratigraphic sequence show much less 

variation than those from qmt. The FeO/(FeO + MgO)

C16 Contributions to the Geology of Mineral Deposits
Table 3. Chemical analyses of selected tourmaine-bearing rock types in the North Gouverneur area, New York, in weight

percent

[n.d., not determined. See Brown (1980) for additional information about these analyses. Sample locality shown on figure 2 of this report]

Rock unit 

Chemical analysis no. 1 - 

SiO2

A12 03 

Fe2O, 

F«»n

MgO

PaO

N;i r»

K O

H f\ +

H fV

TiO2 

P

r\

MnD

ro

Aqua regia solution

ne CO

Granite (hg)

12 14

65.7 71.7 

16.8 14.7 

1.0 .10 

1.3 1.0 

.78 .50 

2.3 1.0 

3.8 3.7 

6.7 5.6 

.50 .90 

.05 .05 

.42 .26 

.19 .18 

.05 .08 

.11 <.05

.21 n.d.

15

71.6 

14.8 

.91 

.72 

.30 

1.3 

3.5 

5.8 

.05 

.63 

.24 

.14 

.02 

.05

n.d.

18

71.3 

15.0 

.49 

.92 

.30 

1.0 

3.7 

5.8 

.96 

.04 

.21 

.16 

.07 

<.05

n.d.

22

72.2 

14.7 

.73 

.24 

.40 

.90 

2.4 

6.2 

.56 

.17 

.21 

.21 

.00 

.03

n.d.

pda

40

Rapid

57.4 

10.9 

1.4 

2.7 

7.6 

11.9 

3.3 

2.6 

.38 

.17 

1.2 

.31 

.10 

<.05

n.d.

41 42

rock analysis

88.3 80.0 

3.0 6.9 

.64 1.5 

.60 3.3 

.90 2.7 

1.9 .50 

1.1 .20 

.11 2.6 

.57 .34 

.07 .11 

1.0 .71 

.10 .13 

.05 .05 

.78 <.05

.24 n.d.

43

77.2 

11.7 

.65 

.32 

1.3 

1.5 

4.4 

1.0 

.54 

.06 

.93 

.17 

.05 

.06

n.d.

qmt

53

63.4 

15.6 

3.2 

1.2 

3.6 

.78 

.63 

8.0 

1.6 

.08 

1.2 

.14 

.04 

<.05

n.d.

54

60.9 

17.2 

3.1 

.61 

2.2 

1.6 

.57 

9.1 

1.0 

.04 

1.2 

.12 

.06 

1.5

n.d.

68

47.2 

10.0 

4.6 

.51 

4.6 

14.0 

.50 

.28 

1.4 

.08 

1.1 

.16 

.24 

9.7

5.1

69

61.0 

17.0 

3.7 

.49 

2.5 

.58 

.70 

9.3 

.91 

.07 

1.2 

.10 

.06 

<.05

n.d.

Wet chemical analysis

B f)

Sum 

n.d. n.d. 

n.d. n.d. 

0.14 .068 

100.05 99.9

n.d. 

n.d. 

.039 

100.1

n.d. 

n.d. 

n.d. 

100.0

.58 

n.d. 

n.d. 

99.5

n.d. 

n.d. 

n.d. 

100.0

0.32 0.38 

n.d. n.d. 

n.d. n.d. 

99.7 99.5

0.38 

n.d. 

n.d. 

100.2

1.38 

n.d. 

n.d. 

100.9

1.78 

0.03 

0.83 

101.8

3.47 

n.d. 

n.d. 

102.9

2.31 

n.d. 

n.d. 

100.0

'These numbers identify sample locality on figure 2 and are from Brown (1980), where more information about analyses can be found.

Table 4. Semiquantitative spectrographic analyses of tourmaline-bearing rocks in the North Couverneur area, New York, 

in parts per million

[L, detected, but below limit of determination; N, not detected at limit of determination. See Brown (1980) for more information about samples. 

Sample locality shown on figure 2 of this report]

Lithologic unit 

Analysis number1 

^6Ao

Ba

Be 

Co

Pn

T -3

Mo

Nb 

Pb

"xr

<\n

Sr

V

Y

Ce

Ha

Yb 

Granite (hg) p

12

L

50 

1,000 

7 

N 

3 

200 

150 

N 

15 

N 

30 

7 

20 

1,000 

30 

50 

700 

500 

20 

5

14

L

50 

700 

7 

N 

N 

5 

100 

N 

10 

N 

20 

5 

N 

200 

15 

30 

200 

500 

20 

3

15

N 

N 

50 

N 

N 

N 

10 

N 

N 

N 

N 

N 

N 

N 

1,000 

7 

N 

N 

N 

N 

N

18

L

500 

500 

10 

N 

N 

3 

70 

N 

7 

N 

30 

5 

N 

150 

10 

30 

150 

200 

20 

3

22

N 

3,000 

300 

1.5 

N 

2 

3 

70 

N 

L5 

L10 

20 

N 

N 

70 

10 

30 

100 

100 

15 

1.5

40

L

700 

500 

3 

15 

50 

5 

100 

N 

10 

L 

N 

10 

N 

700 

70 

70 

200 

300 

10 

7

da

41

L

500 

30 

N 

N 

30 

15 

N 

N 

10 

N 

N 

3 

N 

10 

50 

20 

150 

N 

5 

2

42

L

1,000 

300 

1 

10 

20 

5 

N 

N 

10 

L 

N 

7 

N 

30 

70 

20 

150 

N 

10 

2

43

L

500 

200 

3 

N 

50 

5 

N 

N 

10 

L 

N 

7 

N 

30 

70 

15 

150 

N 

15 

1.

qmt

53

N 

20,000 

700 

N 

20 

150 

5 

50 

N 

10 

N 

10 

20 

N 

150 

150 

30 

200 

N 

20 

5 3

54

N 

20,000 

1,000 

N 

15 

150 

10 

N 

N 

L5 

5 

20 

20 

N 

200 

150 

15 

200 

N 

20 

1.5

68

L

30,000 

100 

N 

30 

100 

5 

N 

3 

N 

70 

7 

20 

N 

300 

100 

30 

150 

N 

20 

3

'These numbers identify sample locality on figure 2 and are from Brown (1980).

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C17
Table 5. Semiquantitative spectrographic analyses of tourmaline in Beaver Creek area, New York

[Results are reported as midpoints of interval data 1.0, 0.7, 0.5, 0.3, 0.2, 0.15, 0.1 (and multiples of 10). The precision of reported value is approximately plus or minus one bracket at 68 percent or two brackets at 96 percent confidence. Symbols used are G, greater than 10 percent or value 

shown; N, not detected at limit of determination or below value shown. Numbers in parenthesis indicate lower limit of detection. Looked for but 

not detected in all samples at lower limit of detection (in parenthesis): Ag (0.5), As (1,000), Au (20), Be (1.5), Bi (10), Cd (50), La (50), Mo (3), Nb 

(10), Pd (2), Pt (50), Sb (200), Sn (10), Te (2,000), U (500), W (100), Zn (300), K (7,000), P (2,000), Ce (200), Ge (10), Hf (100), In (10), Re (50), Ta 

(500), Th (200), Tl (50), Yb (1)). Analyst, Nancy M. Conklin ]

Sample number ^B-SO-I 2 EB-71-35 3 EB-80-2 "EB-71-124 5EB-77-7 6EB-69-99 7EB-69-

kjl \J \J \J

Al G G G

Na 0.7 0.7 0.7

Fe 1.5 .1 .7

Mg 7. 10. 10.

Ti .3 .15 .3

Mn(l) 50,000 70 150

B(20) G G G

Ba(3) 30 3 N3

Co(5) N N N

Cr(l) 30 700 70

Cu(l) 30 15 7

 533

 15 N N

 N N 15

V (7) N 1,500 150

Zr(10) N N N

Ga(5) 30 30 70

8Cs(10) N10 N10 N10

8Li(l) 20 20 50

8Rb(2) N2 N2 N2

Percent

G 

G

1.5 

G

5 

2. 

.7

G 

G

0.3 

.3

G

3. 

.3

G 

G

1.

3. 

7. 

2. 

.3

G 

G

1.5 

3. 

7. 

1. 

.150

Parts per million

3

15

7 

10

N

30

300

700

30

70

N10

10

N2

N3

N

30

2

3

N 

N

200

70

N

30

N10

10

N2

150 

G

3 

N 

70 

3 

3 

N 

70 

700 

1,000

N

100

N10

70

2

70

N 

N 

N 

N 

N 

N

700

N 

N

70

N10

70

3

'Wine-red tourmaline grains that occur with manganese-bearing tremolite (hexagonite) at Arnold Talc Mine, and Wight Mine near Fowler, 

N.Y. Described by Ayuso and Brown (1984).

2Pale-green tourmaline grains in coarse calcitic marble that includes much phlogopite and has crystals and irregular masses of scapolite as much 

as 3 inches across. Small quarry west of Rock Island Road 800 feet north of Beaver Creek Crossing.

3Light-brown tourmaline prisms in pegmatitic clots in coarse-grained marble. Locality 3, Brown (1983).

4Black tourmaline in pegmatite within tourmaline-rich rock. Locality shown on figure 2.

5Amber tourmaline in white phlogopitic marble. Locality 96, Brown (1983).

6Coarse black crystalline masses with quartz. Locality 29, Brown (1983).

7Pale-blue tourmaline that encrusts perthite crystals in small pegmatite. Locality 28, Brown (1983).

8Analyzed by means of a special method for alkalies that significantly lowers sensitivities for Na and Li and makes possible the determination of 

Cs and Rb.

ratios range from 0.476 to 0.612 (fig. 6), and samples 

collected near the csq contact showed no compositional 

change. In contrast to the trend in qmt tourmalines, 

those from pda occur in rocks having abundant sphene, 

and show no gradient in TiO2 abundance relative to the 

FeO/(FeO + MgO) ratio.

Analyses of tourmalines in a few samples from the 

other stratigraphic units, csq, tt, and a quartzofeldspathic lens in qm show that their compositions 

have a lower FeO/(FeO + MgO) ratio than the bulk of 

the data showed for qmt and pda (fig. 6). Samples 67-37

from unit tt also has a high TiO2 content (1.77 weight 

percent) and plots within the field defined by qmt tourmalines from near the Oswegatchie River.

Because of the overlap in tourmaline compositions for FeO/(FeO + MgO) ratios and in TiO2 content, 

the host rock for tourmalines cannot be clearly distinguished. It is, however, possible to distinguish the tourmalines in the granite and pegmatites because they have 

high FeO/(FeO + MgO) ratios and because they are 

similar to tourmalines in aplites and granites (Neiva, 

1977).

C18 Contributions to the Geology of Mineral Deposits
Tourmaline 

North Gouverneur

qmt(S)

Granitic gneiss

EXPLANATION

O pda

A qmt (S)

A qmt(N)

 Granite ~\ Granitic

A Pegmatite J gneiss

X csq

+ tt

D qm

Granites and pegmatites

FeO/(FeO+MgO)

Figure 6. TiO2 -FeO/(FeO + MgO) plot for tourmalines in lithologic units from North Couverneur, N.Y., compared with those 

from Sullivan Mine, British Columbia (Ethier and Campbell, 1977), and Portuguese granites and pegmatites (Neiva, 1974). Tie 

line connects the compositions of the composite tourmaline in the marble unit (qm).

Slack (1982) used a plot of the oxides FeOMgO-Na2O to show the compositions of tourmalines 

from selected stratabound sulfide deposits. The North 

Gouverneur tourmalines are also shown on the ternary 

plot of Na2O-MgO-FeO (fig. 7) and suggest the following: (1) All tourmalines, regardless of lithology, plot in 

a trend subparallel to the join MgO-FeO. Most of the 

MgO-rich tourmalines in each lithologic unit plot slightly above the MgO-FeO join; this probably suggests a 

trend toward higher Na2O contents with higher MgO. 

(2) Granites and pegmatites have tourmaline compositions plotting closest to the FeO-Na2O join, in accordance to the field defined by lithium-poor tourmaline 

from granites and pegmatites. Tourmalines from 

granites from North Gouverneur are, however, more 

magnesian than tourmaline normally found in such environments. (3) Tourmalines from pda as a group are 

more magnesian and less sodic than those from granites 

and pegmatites. (4) The qmt tourmalines are 

heterogeneous in FeO, MgO, and Na2O. Tourmalines 

from near the Oswegatchie River plot closer to the 

MgO-FeO sideline than tourmalines from north of 

North Gouverneur. (5) Tourmalines from tt, csq, and 

the brown tourmaline from qm are magnesian with a 

moderate range in Na2O content.

Tourmalines in this study show a strong trend subparallel to the MgO-FeO sideline, despite the wide

range of lithologic types and mineral assemblages that 

they represent. Because of the fairly constant Na2O content in these tourmalines, the FeO-MgO-Na2O plot emphasizes the range in FeO and MgO contents in the tourmaline. Control on the Na2O content of tourmaline 

might be a reflection of the equilibrium assemblage, 

particularly with respect to another phase that has varying ratios of Na2O/CaO (for example, plagioclase). 

Compared with the average compositions compiled by 

Slack (1982) of tourmalines that are intergrown with 

sulfide minerals, the North Gouverneur tourmalines 

overlap the field of tourmaline associated with stratabound sulfide deposits, despite their known coexistence 

with volumetrically minor sulfide concentrations. In 

fact, the area occupied by tourmalines intergrown with 

sulfides in the FeO-MgO-Na2O plot and that of tourmaline not immediately associated with sulfides but obtained from the same vicinity show similar ranges in 

FeO and MgO at roughly the same Na2O content. A 

reasonable conclusion from this comparison is that 

Na2O content of tourmalines plotted on the ternary 

FeO-MgO-Na2O does not distinguish between tourmalines abundantly intergrown with sulfides and those 

without sulfides.

The amount of aluminum in the North Gouverneur tourmalines cannot be used to distinguish the different host lithologies. Alumina (A12O3) ranges widely

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C19
Tourmaline 

North Gouverneur

Na20

MgO

qrrUblue)

FeO

Figure 7. Ternary plot of Na2O-MgO-FeO for tourmaline from North Couverneur, N.Y., the Sullivan Mine, British Columbia 

(Ethier and Campbell, 1977), and the field of granites and pegmatites (Neiva, 1974).

from 24.8 to 36.54 weight percent. Combined with the 

distribution of CaO, the fact that all tourmalines show 

slight decreases in CaO as A12O3 increases (fig. 8) suggests that higher alkali contents might be found in the 

more aluminous tourmalines. Tourmalines from granites and pegmatites from North Gouverneur tend to be 

the lowest in CaO content for a given range in A12O3 

especially for A12O3 <30 weight percent. Within 

individual rock units from North Gouverneur, the 

highest A12O3 content in tourmalines might be found in 

those with the lowest FeO/(FeO + MgO) ratio (fig. 9). 

However, the broad and general decrease in A12O3 as 

FeO/(FeO + MgO) ratio decreases, suggested in the 

metasedimentary units, is much less evident in tourmalines from the granites and pegmatites. Tourmalines 

from north of North Gouverneur are generally higher in 

A12O3 at a given FeO/(FeO + MgO) ratio than tourmalines from near the Oswegatchie River.

Calcium Content of Tourmalines

The CaO content in tourmalines from the North 

Gouverneur area ranges from 0.39 to 4.04 weight percent (table 2) and cannot be correlated with the 

FeO/(FeO + MgO) ratio. Samples from qmt are the 

most chemically heterogeneous tourmalines as they span 

compositions from near end-member dravite (12.29 

weight percent MgO) compared with dravite from 

Gouverneur which has 13.67 weight percent MgO (cited

in Deer and others, 1962) to uvite (4.04 weight percent 

CaO). Most tourmalines from qmt generally have, 

however, less than 3.0 weight percent CaO (except sample 80-3(a) with 4.04 weight percent). Tourmaline 

samples from the breccia near the Oswegatchie River are 

for the most part indistinguishable from the rest of the 

qmt samples on the basis of their CaO and MgO 

contents.

Inpda, most tourmalines range from 1.89 to 2.97 

percent CaO (table 2, fig. 8). The few analyses of magnesian tourmalines from tt, csq, and the brown tourmaline in qm suggest that, with the exception of csq, these 

tourmalines are low in CaO content (table 2, fig. 8).

Substitutions in Hypothetical Structural Formula

Although the microprobe analyses are incomplete, 

consideration of such hypothetical formulae is useful in 

indicating possible crystal chemical substitutions operating during crystallization of tourmaline. Such substitutions suggest that elemental chemical exchanges 

within individual lithologic units were generally 

adjusted in a regular manner to changing conditions 

during tourmaline growth.

The change in Na and Fe for Al in the Gouverneur 

tourmalines suggests that Na and Fe are generally but 

broadly inversely correlated with Al (fig. 10). The most 

sodic and iron-rich tourmalines are in the granites and 

pegmatites, whereas tourmalines most impoverished in

C20 Contributions to the Geology of Mineral Deposits
Tourmaline 

North Gouverneur

52

pda

EXPLANATION

O pda

A qmt (S)

A qmt(N)

 Granite "l Granitic

\A Pegmatite J gneiss

X csq

+ tt

D qm

qmt (N)

Granitic gneiss

Sullivan Mine

D qm (blue)

24 26 28 30 32 

AI203, IN WEIGHT PERCENT

34 36 38

Figure 8. CaO-Al2O3 plot for tourmalines from North Gouverneur, N.Y., compared with those from the Sullivan Mine, British 

Columbia.

these components are in qmt, tt, and csq. The overall 

pattern is in basic accordance with a change from 

schorl-like tourmalines in granite and pegmatites 

toward tourmaline compositions in the uvite-dravite 

series occurring in metasediments, especially in qmt. 

Tourmalines from the Sullivan deposit are distinct from 

this trend as they follow no consistent pattern. In contrast to the apparent Na + Fe = Al correlation (alkalidefect substitution), neither the Sullivan or the North 

Gouverneur tourmalines show a correlation in 

Na + Mg = Al as found by Schreyer and Abraham (1976) 

for dravites from an evaporite deposit.

The change between Na and Ca for total Al may 

occur on a regional basis, and it is shown by the slight decrease in Na+Ca as Al increases (fig. 11). However, no 

meaningful distinctions are evident between rock units. 

The most regular and gradual correlation is present in

pda, whereas the most scattered is in the granites and 

pegmatites. For comparison, tourmalines from Sullivan 

are aluminous and plot toward lower values of Na+Ca 

as defined by the North Gouverneur tourmalines.

The general variation between Na+Mg + Al and 

Ca + 2Fe might be one of the mechanisms controlling the progressive change in tourmaline composition 

in the North Gouverneur area. In this exchange, 

Na+Mg + Al are inversely correlated with Ca + 2Fe2+ 

(fig. 12). Tourmaline from north and south of the 

Oswegatchie River is not distinguishable on this 

plot. Sullivan Mine tourmalines seem to have compositions similar to tourmalines in the North Gouverneur 

area. Tourmalines from the granitic gneiss unit are 

generally higher in the sum of Ca + 2Fe compared with 

other tourmalines in the metasediments. The composite 

brown-blue tourmaline spans almost the entire range

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C21
Tourmaline 

North Gouverneur

38 r36

34

32

z 30

CD

23

26

24

Sullivan Mine

qmt (N)

EXPLANATION

O pda

A qmt (S)

A qmt(N)

 Granite ~l Granitic

U Pegmatite J gneiss

X csq

+ tt /

D qm

qmt (S)

tt

qm (blue)

D

\ n qm (brown)

Granitic gneiss

.4 .5 .6 

FeO/(FeO+MgO)

1.0

Figure 9. Al2O3-FeO/(FeO+MgO) plot for tourmalines from North Couverneur, N.Y.

shown by tourmalines from the metasedimentary rocks. 

Tourmalines from unit pda in the North Gouverneur 

area have a smooth variation in composition. On a 

regional basis, however, tourmaline from North 

Gouverneur shows substantial compositional overlap. 

As expected, tourmalines from North Gouverneur 

granite and pegmatite are somewhat higher in iron 

(more schorl rich) than those in the samples from unit 

qmt that belong to the dravite-uvite series.

The substitution of Na for Ca (fig. 13) in the Z site 

could serve as an indicator of similar crystallization conditions among different groups of tourmalines. However, the dispersal of values of tourmalines from North 

Gouverneur cannot allow appropriate comparison with 

Sullivan tourmalines. Contents of less than 2.5 weight 

percent CaO and higher than 1.2 weight percent Na2O 

encompass the compositional range of Sullivan, but 

most of the North Gouverneur samples also show this 

range. Clearly, the variation in sodium and calcium contents is not a definitive test of similarity between North 

Gouverneur and Sullivan tourmalines.

Mineralized Areas and Tourmaline Compositions

Although anomalous tourmaline concentrations, 

which have compositions near the dravite end member, 

exist in unit qmt, the range in FeO/(FeO + MgO) ratios 

of tourmaline in a geographically restricted area suggests that this ratio is insufficiently specific for selection 

of the most favorable area for potential mineralization. 

The use of other major and trace elements in conjunction with the FeO/(FeO + MgO) ratio may prove to be 

more useful indicators of tourmalines associated with 

mineral deposits. Tourmalines in the Sullivan deposit 

are characterized by large variations in the 

Na2O/(Na2O + CaO + K2O) ratio, in contrast to tourmalines from the enclosing Aldridge metasediments and 

nearby granites. Similar dispersals in compositional

C22 Contributions to the Geology of Mineral Deposits
Tourmaline 

North Gouverneur

3.0^

2.5

2.0

1.5

1.0

Granitic 

gneiss

qm (blue)D

qmt (S)

x csq

5.0 5.5 6.0 Al 6.5 7.0 7.5

Figure 10. (Na+Fe)-Al plot in number of ions per formula unit for tourmalines from North Gouverneur, N.Y., compared with 

those in rocks from the Sullivan Mine, British Columbia.

variations are found in qmt tourmalines relative to those 

from pda and hg (fig. 14). The variations in tourmalines 

from qmt are also in the same range as those in the 

Sullivan Mine. In addition, tourmalines from the 

Sullivan Mine are low in CaO (generally less than 2.00 

weight percent). An idealized profile of tourmalines

from mineralized areas should also note the prevailing 

low contents of TiO2 (<0.1 weight percent) for the 

Sullivan Mine (fig. 6). Chlorine and oxides such as K2O 

and MnO do not appear to have interpretable trends 

either in the North Gouverneur area or in the Sullivan 

ore body.

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C23
1.1 [ 

1.0

.9

.5 -

Tourmaline 

North Gouverneur

qmt (S)

qmt (N)

EXPLANATION

O pda

A qmt (S)

A qmt(N)

 Granite " > Granitic

B Pegmatite J gneiss

X csq

+ tt

D qm

D qm (blue)

5.0 5.5 6.0

Al

6.5 7.0 7.5

Figure 11. (Na+Ca)-AI plot in number of ions per formula unit for tourmalines from North Gouverneur, N.Y., compared with 

those in rocks from the Sullivan Mine, British Columbia.

C24 Contributions to the Geology of Mineral Deposits
Tourmaline 

North Gouverneur

10 EXPLANATION

O

A

A

a

X

+

D

pda

qmt (S)

qmt (N)

Granite 

Pegmatite

csq

tt

qm

1 Granitic 

/ gneiss

qmt (N) pda

Granitic gneiss

Ca+2 Fe

Figure 12. (Na + Mg + Al)-Ca + 2Fe plot in number of ions per formula unit for tourmalines from North Couverneur area, New 

York, compared with those from the Sullivan Mine, British Columbia.

In tourmalines from the Sullivan Mine, Na2O and 

CaO show a well-defined antipathetic correlation 

(Ethier and Campbell, 1977). A similar change in tourmalines from the North Gouverneur area is in agreement with regular substitution of Ca for Na in the Z site 

in tourmaline from all the rock units (fig. 14). Tourmalines from potentially mineralized areas, or from different units in the North Gouverneur area, cannot be 

distinguished on this basis.

In contrast to tourmalines from Sullivan, those 

from units hg and qmt show a broad increase in A12O3 

with higher Na2O/(Na2O-I-CaO-I-K2O) ratios (fig. 14). 

Sullivan tourmalines, on the other hand, generally show 

variable ratios of Na2O/(Na2O-I-CaO-I-K2O) at about 

the same content of A12O3 . Tourmalines from lithologic 

units within the North Gouverneur area, especially qmt, 

pda, and hg, show significant compositional overlap. 

Those from granites and pegmatites and qmt (North of 

the Oswegatchie River) show a broad positive correlation between A12O3 and Na2O/(Na2O-I-CaO-I-K2O) 

ratios.

The trend toward decreasing A12O3 as FeO/ 

(FeO + MgO) ratio increases (fig. 9), evident for individual units in the North Gouverneur tourmalines, is 

in contrast with the variable FeO/(FeO-I-MgO) values 

at constant values of A12O3 in the tourmalines from 

Sullivan. On this basis, tourmalines from North 

Gouverneur and those from the Sullivan deposit are 

significantly different.

DISCUSSION

The geological premise for using tourmaline as a 

prospecting tool is that the processes of tourmalinization and ore formation are temporally and spatially related. Although the absence of plutonic bodies is a 

strong indication of nonigneous origin, anomalous 

tourmaline concentrations may, however, arise from 

other processes. According to Slack (1982), other processes that might lead to tourmaline concentrations include authigenic, detrital, regional metasomatic,

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C25
.8 i 

Tourmaline 

North Gouverneur

csq x

EXPLANATION 

O pda 

A qmt (S) 

A qmt(N) 

 Granite "\ Granitic

Pegmatite

csq

tt

qm

gneiss

Granitic gneiss

Sullivan Mine

D qm (blue)

1.0

Na

Figure 13. Ca-Na plot in number of ions per formula unit for tourmalines from North Couverneur, N.Y., compared with those 

from the Sullivan Mine, British Columbia.

evaporitic-sabkha, and submarine hydrothermal. This 

follows because tourmaline has a wide stability field 

ranging from typical sedimentary environments 

(Krynine, 1946) to metamorphic conditions even at high 

pressure (Smith, 1971). Ethier and Campbell (1977) 

further suggested that pH ranges may be more important in determining tourmaline stability than pressuretemperature conditions. Because of this extensive stability field for tourmaline, to correlate ore deposition with 

tourmaline occurrence seems risky unless additional 

geologic information, especially modal abundance, is 

also taken into account. Thus, a close association between ore and tourmaline occurrence does not necessarily imply genetic equivalency. However, the anomalous occurrence of tourmaline in great abundance that 

is, more than 25 percent of a rock commonly in the

vicinity of sulfide deposits is compelling evidence of a 

genetic association. In addition to the anomalous concentration of tourmaline, a magnesian composition 

(dravite) was documented by Ethier and Campbell 

(1977) and Slack (1982) to characterize tourmalines intergrown with sulfides. However, Mg-rich dravites were 

also characteristic of tourmalines not directly associated 

with sulfides as depicted in Slack's compilation of 

selected stratabound deposits. Although Mg-rich 

dravites may occur without associated sulfides, the 

presence of anomalously large concentrations of tourmaline might still suggest proximity to stratabound 

sulfide deposits.

In the North Gouverneur area, tourmalinite layers 

in qmt and the ubiquitous presence of disseminated 

tourmaline in other rock units identify them as

C26 Contributions to the Geology of Mineral Deposits
38

36

34

32

S 30

m

CD

28

26

24

Tourmaline 

North Gouverneur

qmt (N)

n qm 

(blue)

qmt (S)

pda

Granitic gneiss

EXPLANATION

O pda

A qmt (S)

A qmt(N)

 Granite ""> Granitic

a Pegmatite J

X csq

+ tt

D qm

gneiss

Figure 14. AlzCV

the Sullivan Mine, British Columbia.

.4 .5 .6 .7 .8 .9 1.0 

Na20/(Na20+CaO+K20)

plot for tourmalines from North Couverneur, N.Y., compared with those from

anomalously abundant in tourmaline. The next step 

from an exploration standpoint is to compare the occurrence of tourmaline and tourmaline compositions near 

North Gouverneur with occurrences that are associated 

with major sulfide deposits. A good point of reference 

for such a comparison is the Sullivan ore body, a stratabound sediment-hosted deposit form jd within a turbidite sequence of Middle Proteroziic age (Freeze, 

1966; Hamilton and others, 1982). Tne abundance of 

carbonate rocks in the sequence under qmt also indicates that the rocks around North Gouverneur are 

similar to those near the deposits in northeastern 

Australia, especially at Dugald River. The deposit at 

Dugald River (Whitcher, 1975) is a large stratabound 

zinc-lead-silver lode in a local graphitic shale unit within 

a large area of scapolite-rich calc-silicate rocks. 

Scapolite-bearing calc-silicate rocks also are present in 

the North Gouverneur area in unit pda. They might 

represent impure lime-rich silts. In the Dugald River

deposit, parts of the carbonaceous shales commonly 

have 2,000 ppm boron and, locally, as much as 

5,000 ppm boron. Unfortunately, tourmaline compositions in the Australian deposits are unknown, and thus 

our comparison with them is incomplete.

Metamorphic conditions or ultrametamorphic 

processes that result in boron metasomatism are two 

mechanisms likely to result in the formation of tourmaline. But, transport of boron-rich fluids during 

regional metamorphism from qmt into the thin granitic 

sheets is not supported by the different compositional 

trend and by the compositional variations evident in 

qmt compared with those in granite tourmalines. However, the appearance of locally migmatitic areas in qmt 

suggests that the felsic sheets may represent partial melts 

of the tourmaline-rich metasedimentary rocks. As documented by Chorlton and Martin (1978) and Pichavant 

(1981), boron significantly lowers the liquidus and 

solidus of granitic melts. This suggests that partial

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C27
melting in qmt might have been localized by the presence of abundant tourmaline resulting in boron-rich 

felsic melts. From such felsic liquids, it is conceivable 

that tourmaline precipitated in equilibrium with silicate 

phases and silicate liquid. Tourmaline in these felsic 

sheets might thus reflect igneous crystallization in contrast to the tourmaline in the metasediments that reflects 

metamorphic reactions. Thus, it may be suggested that 

the two rock types (qmt and the granite sheets) reflect 

different processes leading to tourmaline formation. 

Although granitic plutons are common in the North 

Gouverneur area, compositions of tourmaline from the 

metasediments can be distinguished from those in the igneous bodies.

The occurrence of such diverse tourmaline compositions indicates that bulk composition and the presence of a felsic liquid leading to igneous crystallization 

are responsible for the tourmaline in the granite sheets. 

Where tourmaline compositions show regional trends, 

tourmalines from igneous bodies and from metasediments have different ranges in composition.

Although compositions of tourmalines in the 

pegmatites in qmt (samples 71-124, 67-23) and pda 

(sample 68-82) are similar to those of the hosts, the 

granite and pegmatite tourmaline suites clearly differ 

from the tourmaline fields of qmt and pda. We favor 

the conclusion that, in the North Gouverneur area, 

tourmalines from igneous and metasedimentary units 

reflect the bulk composition of the host rocks. The implication is that the tourmalines in metasedimentary 

rocks are not genetically related to the igneous plutons.

In the North Gouverneur area, tourmalines from 

single lithologic units show significant compositional 

variation. For example, tourmalines from both areas of 

qmt have FeO/(FeO -I- MgO) ratios that range widely 

from 0 to 0.58 (fig. 6), whereas a smaller but nevertheless substantial spread is also shown by tourmalines 

in pda (0.46-0.62). Tourmaline compositions in pegmatites and migmatitic segregations in qmt and pda tend to 

be higher in FeO/(FeO + MgO) ratios than those in the 

host metasediments and have values more characteristic of the granite gneiss tourmalines (0.56-0.75).

Tourmalines from qmt are as magnesian as tourmalines from the Sullivan Mine, but they also extend to 

more iron-rich compositions. Preliminary analyses of 

tourmalines from the calcsilicate-bearing rock (csq), 

talc-tremolite schist (tt), and the brown tourmaline from 

the quartzofeldspathic lens in marble (qm) show compositions similar to those from the Sullivan Mine. In 

contrast, tourmalines from pda, from the pegmatites in 

qmt and pda, the gneissic granite hg, and the blue tourmaline in the quartzofeldspathic lens in marble (qm) are 

all richer in iron than tourmalines in known mineralized 

areas elsewhere.

At first glance, the composition of tourmaline in 

qmt together with its anomalous abundance suggests that 

this unit and nearby units may be favorable for containing stratabound sulfide deposits. Because of the large 

compositional spread, tourmaline compositions from this 

unit apparently reflect primary lithological heterogeneity, 

local metasomatic or hydrothermal processes, or the integration of several tourmaline-forming events in the 

area. Detailed geologic mapping shows that lithologic 

diversity alone in this unit may control the spread in tourmaline compositions rather than any subsequent metamorphic or hydrothermal events. Because our samples 

came from a restricted geographic area, the chances of 

regional differences in pressure and temperature were 

minimized. Ethier and Campbell (1977) recognized such 

a variation of tourmaline compositions at the Sullivan 

Mine, although in their samples they determined a more 

narrow range in FeO/(FeO-I-MgO) ratio (0.23-0.32) 

than the range documented at North Gouverneur.

In the course of typical metamorphic reconstitution of mineral assemblages during and after tourmaline 

crystallization, the FeO/(FeO + MgO) ratios in tourmaline may show significant departures from initial 

compositions obtained from the premetamorphic fluids. 

Continuous readjustment in the FeO content of tourmaline depending on the coexisting assemblage (bulk 

composition) and changing intensity of metamorphism 

suggests that the measured FeO/(FeO + MgO) ratio may 

represent the integration of processes during metamorphism. If the FeO/(FeO-I-MgO) ratio is continuously 

readjusted, the compositions of earlier formed tourmalines (perhaps in equilibrium with sulfides) are irrevocably modified during subsequent events. This suggests that FeO/(FeO + MgO) ratios might be inadequate 

to completely characterize the composition of tourmalines deposited from primary fluids, especially 

because Bachinski (1976) demonstrated the enrichment 

of iron in sulfides coexisting with silicates as the grade 

of metamorphism increased. Ethier and Campbell 

(1977) suggested that tourmaline compositional variation in the Sullivan Mine was controlled by bulk composition and by solution pathways.

Bulk composition differences in the rock units of 

the North Gouverneur area are the predominant controls on the composition of tourmaline. Because of the 

apparent variability in the protolith of unit qmt, it 

seems reasonable to expect similar variations in the 

composition of tourmaline even without subsequent reequilibration. Despite the well-known large stability 

field for tourmaline, apparently the compositional 

heterogeneity reflects mainly the differences in bulk 

compositions within the units. The effect of local bulk 

composition was also recognized by Ethier and Campbell (1977, p. 2355) in the Sullivan ore body in the 

Aldridge Formation of British Columbia. By restricting

C28 Contributions to the Geology of Mineral Deposits
the area sampled in this study, we may assume that 

metamorphic conditions have been similar throughout. 

Thus, it seems unreasonable to suggest that the variability in tourmaline composition reflects reequilibration 

during a later tourmalinizing process. Furthermore, 

subsequent equilibration would strive toward compositional homogeneity rather than accentuate the differences. We conclude by suggesting that, for most 

samples, tourmaline compositions in the North Gouverneur area reflect the critical control of bulk composition 

of the rock.

Early crystallization of tourmaline is suggested by 

the lack of relics (as in partially recrystallized or reacted 

grains) and by the absence of tourmaline replacements 

in the North Gouverneur area. However, two exceptions 

are evident: (1) In sample 80-3, two tourmaline types, 

one in clasts and the other in the matrix, probably did 

not form simultaneously. The unit, where sampled, is 

brecciated in a fault zone, which may have served as a 

conduit for hydrothermal fluids. Some re-equilibration 

of the primary tourmaline could be expected, particularly in the matrix because of the presence of lateforming pyrite. As a result of recrystallization and coexistence with an iron sink (pyrite), the composition of 

tourmaline dramatically changed to the highly magnesian and variable character. (2) In sample 68-5, tourmaline from a quartzo-feldspathic lens in the marble 

unit shows that, during growth of the core of the grain, 

the composition was close to the dravite end member. 

As fluid conditions changed, the resulting blue tourmaline enveloping the brown interior became rich in 

iron and extremely poor in magnesium. The indented 

surface between the two compositional varieties suggests an interval of nondeposition or leaching of tourmaline before overgrowth of the blue tourmaline.

anhydrite, serpentine, talc, and diopside and is recognized as a metamorphosed evaporite (Lea and Dill, 

1968, p. 27). The other marker is talc-tremolite schist. 

The protolith of the schist, if isochemical reactions with 

loss of CO2 are considered, possibly was a siliceous 

dolomite containing magnesite this also suggests an 

evaporitic origin. Ore minerals are believed to have 

formed syngenetically (Solomon, 1963; Dill and deLorraine, 1978), and their association with evaporitic sediments suggests a related origin.

In the North Gouverneur area, dolomitic and silicated marbles in qm and also the talc-tremolite schist 

(tt) are similar to some rocks of the Balmat-Edwards 

district. In addition, occurrences of stratabound 

sphalerite are also known in the marble unit (Brown, 

1970; 1983). However, in contrast to the ubiquitous occurrence of tourmaline either as abundant accessory 

minerals or as tourmalinites in the sequence near North 

Gouverneur, the metasediments of the Balmat-Edwards 

district contain insignificant amounts of tourmaline 

(Brown and Engel, 1956). 12 Another important difference is that in the Gouverneur-North Gouverneur area 

the marbles are nearly all graphitic and phlogopitic, 

whereas those in the mining district (except for Brown 

and Engel's (1956) units 7 and 15) do not have notable 

phlogopite or graphite.

Probably the most significant difference between 

the two areas is the scarcity of tourmaline in BalmatEdwards rock units, and thus an absence of significant 

boron in the environment of deposition. Thus, the mineralization in carbonate rocks at Balmat and the implied 

mineralization in the tourmaline-rich clastic rocks of the 

North Gouverneur-Richville area are not closely 

related if at all because of the special conditions 

necessary to produce an excess of boron in the rocks.

Comparison with the Balmat-Edwards District

Speculation about stratabound massive sulfide 

mineralization associated with boron and magnesian 

minerals in the tourmaline-rich rocks of the North 

Gouverneur area should be compared with mineralization in the well-known nearby Balmat-Edwards zinc 

district, 15 miles (24 km) to the southeast. The rocks of 

the two areas have many similarities, but also striking 

differences.

The ore bodies at Balmat occur in a thick 

heterogeneous sequence of interlayered pure and 

quartz- or calc-silicate-bearing dolomitic marbles, 

described by Brown and Engel (1956). The ore consists 

of sphalerite, pyrite, and minor galena that occur in 

several of the marble units. Interlayered in the mineralized zones are two significant stratigraphic markers that 

bear important genetic implications. One contains much

Tourmaline Genesis in the North Gouverneur 

Area

Tourmaline is ubiquitously disseminated in rocks 

of the North Gouverneur area where it has concentrations as high as 50 modal percent in thin tourmalinite 

layers in feldspathic quartzites. Similar layers that have 

35 percent tourmaline in the Aldridge Formation of 

British Columbia were estimated by Ethier and Campbell (1977, p. 2359) to contain 12,000 ppm boron. Such 

concentrations, according to them, are anomalously

'Frondel and Baum (1974, p. 178) cited Brown and Engel (1956) and 

Lea and Dill (1968) for noting boron-rich rocks in their reports on the 

Balmat district. A thorough search of these reports and personal 

knowledge of the area proved this citation to be erroneous.

2The authors have reported on a rare occurrence of manganese-rich 

tourmaline in the talc-tremolite schist in the Fowler talc belt of the 

mining district. However, the quantity of tourmaline there is 

miniscule (Ayuso and Brown, 1984).

Tourmaline-Rich Rocks in Grenville Complex, St. Lawrence County, N.Y. C29
high. Their studies of the rocks close to the Sullivan ore 

body suggest that boron was "* * * introduced at or 

near the depositional surface * * *," thus discounting 

the effect of boron transport by residual magmatic 

fluids after sedimentary lithification. According to 

Ethier and Campbell (1977), metal- and boron-rich 

fluids used the same pathways (collapse breccias) upward to the sea floor; consequently, the direct precipitation of anomalous concentrations of tourmaline is 

closely associated with sulfide deposition. No evidence 

of evaporitic conditions was observed by them (1977, 

p. 2359). In contrast to the turbidite sequence prevailing 

at Sullivan, tourmalines from North Gouverneur are 

more clearly associated with rocks formed under 

evaporitic conditions (Brown, 1969, Moine and others, 

1981, p. 411).

The Dugald River lode in Australia occurs in 

graphitic shales and slates containing cordierite, andalusite, and accessory tourmaline (Whitcher, 1975). 

Evaporitic rocks are both higher and lower in the section, and these are represented by scapolite granulites 

and argillaceous limestone, respectively. As seen from 

figure 2, unit qmt in the North Gouverneur area also is 

enclosed by carbonate and calc-silicate rocks above and 

below. Mineralization at Dugald River consists of pyrrhotite, pyrite, and sphalerite in roughly subequal 

amounts, subordinate galena, and traces of chalcopyrite, pyrargyrite, tetrahedrite, and arsenopyrite 

(Whitcher, 1975). Although rocks of unit qmt are pyrite 

rich in places, no substantial concentrations of other 

sulfide minerals have been found, but an occurrence of 

chalcopyrite has been noted (Brown, 1983, loc. 53). 

Despite the lack of exposed significant sulfides here, the 

analogy to Dugald River appears especially applicable.

Whitcher (1975) proposed, as an ore-producing 

model, "chemical or biochemical precipitation of metal 

sulfides" in the Dugald River lode in a downwarped 

basin, dominated by carbonate rocks. Formation in a 

sabkha environment of stratiform metalliferous 

sediments was advanced by Renfro (1974) to account 

for deposits such as the Kupferschiefer (Germany and 

Poland) and the Roan (Zambia, Zimbabwe, and Zaire). 

Dugald River and this group of deposits may well have 

similar origins. Tourmaline occurs in anomalous concentrations closely associated to mineralized areas in the 

Zambian Copper belt (Mendelsohn, 1961; Garlick, 

1967), especially near the Chibiluma deposits. Abundant tourmaline occurs as stumpy crystals below the 

sulfide-rich horizons at Chibiluma and persists as finegrained tourmaline in the sulfide-rich beds (Fleischer 

and others, 1976). Unfortunately, the role of tourmalinization in these environments has not been properly addressed. Because of the lack of definitive data, we 

cannot assume that, as was true in the Sullivan deposit, 

tourmaline genesis and mineralization took place simultaneously. This is because, in evaporitic environments,

an additional boron source is available, namely from 

borate minerals (Rankama and Sahama, 1950), in contrast to the external source for boron formed in turbidite environments (Sullivan deposit), where boronand metal-rich brines were introduced concurrently.

At least two possibilities may be envisioned to explain tourmaline origin in the North Gouverneur area: 

(1) tourmalines were generated by diagenesis or regional 

metamorphism of borate minerals, and (2) tourmalinites and accessory tourmaline result from submarine 

fumarolic activity.

Because of the possible primary abundance of 

borate minerals within an evaporitic section, tourmalines in the Gouverneur area might have formed as a 

result of normal diagenetic or metamorphic reactions 

involving minerals already enriched in boron during a 

regional event, and need not be associated with metalrich brines. Presence of tourmalinite in nonevaporitic 

areas, on the other hand, is consistent with the idea that 

conformable and anomalous concentrations of quartz 

and tourmaline (tourmalinite) reflect precipitation from 

oozes at the sea floor (Ethier and Campbell, 1977, 

p. 2359). Or alternatively, in evaporitic terranes, 

because of the high solubility of alkali borates, boron 

may have existed in solution in basin pore fluids until 

crystallization as tourmaline during diagenesis or 

metamorphism.

The origin of the tourmalinites is unexplained by 

direct reconstitution of borate minerals (borate to tourmaline) as in alternative 1, unless the original lithology 

consisted of a mix of silica ooze and borates. 

Anomalous concentrations of tourmaline and quartz in 

tourmalinites from nonevaporitic terrances are more 

conventionally explained by deposition at the sea floor 

having an external boron source, although Abraham 

and others (1972) suggested that the tourmalinites may 

represent volcanic exhalations or highly saline environments. Field observations such as thickness and abundance of tourmalinite beds, as well as the evaporitic 

geological features in the North Gouverneur area, seem 

to exclude direct recrystallization of borate minerals and 

metasomatic quartz-tourmaline "sweat-outs," but 

allow the crystallization of tourmaline from boron-rich 

basinal brines. Remobilization by pore fluids and concentration of dispersed borates in the section to account 

for the origin of tourmalinite are generally in agreement 

with the conformable attitude of tourmalinites, their 

thickness, and their random distribution. Thus, because 

of the strong possibility of borate minerals intercalated 

within the section, tourmaline growth in the North 

Gouverneur area may be a result of remobilization of 

borates by basinal fluids during diagenesis and metamorphism. Because the tourmalinite layers are more 

abundant in some units (for example, qmt), bulk composition as in the typical boron-rich (borate-rich) layers 

of the protolith might have controlled the concentration

C30 Contributions to the Geology of Mineral Deposits
of tourmaline. Within these anomalous boron-rich 

units, tourmaline fixed the B2O3 in a manner similar to 

that proposed by Kulke (1976) for fixation of B2O3 by 

tourmaline in a metaevaporite environment. Kulke and 

Schreyer (1973) also documented the occurrence of 

tourmaline (dravite) in metaevaporites containing lapis 

lazuli in silicate marbles that enclose concordant beds of 

lime silicate and amphibolite units.

Because of the difference in geologic setting between the North Gouverneur area and the Sullivan 

Mine, we discount the obvious connection of tourmaline crystallization to fumarolic activity as in alternative 2. We emphasize that, as originally proposed by 

Ethier and Campbell (1977) and Slack (1982), the 

anomalous concentration of tourmaline remains the 

central issue to be explained for the potential use of 

tourmaline as an exploration guide. However, although 

magnesian tourmalines seem to be the norm in known 

mineralized areas, the composition of tourmaline may 

be significantly readjusted as a result of recrystallization. Thus, the composition of tourmalines closely associated with sulfides does not necessarily represent the 

equilibrium attained for the observed assemblage of 

tourmalines and sulfides.

Terranes Showing Most Favorable Implications for 

Containing Strata bound Sulfide Deposits

Occurrences of abundant magnesian tourmaline 

in metasedimentary rocks have been proposed as a prospecting guide. An objective of this study of tourmaline 

compositions was to determine whether anomalously 

abundant tourmaline in rocks in the North Gouverneur 

area was chemically similar to tourmalinites associated 

with stratabound sulfide deposits, such as at Sullivan, 

British Columbia.

Lithologies in rock unit qmt, particularly those 

for samples 67-21, 67-25, and 67-26 (fig. 2), show the 

strongest chemical similarities to the tourmalines at 

Sullivan in that they are dravitic, have low TiO2 and 

FeO, high A12O3 , low FeO/(FeO + MgO) and highly 

variable Na2O/(Na2O + CaO + K2O) ratios. Similar 

tourmaline-rich lithologies occur throughout the area of 

qmt north of North Gouverneur. Also, Bannerman 

(1972) showed many other localities of tourmaline-rich 

rocks in the zone along the Oswegatchie River that were 

not adequately appraised in this study (fig. 2). However, 

careful study of the stratigraphic section in the vicinity 

of North Gouverneur reveals that its depositional origin 

is distinctly different from that of the rocks at Sullivan, 

British Columbia, and the ore-producing model there 

does not apply here because these rocks have a strong 

mineralogic affinity to rocks of an evaporitic origin. At 

many places such as Dugald River, in northeastern

Australia, rocks formed in an evaporitic environment 

contain huge stratabound sulfide deposits. Many of 

these also are rich in tourmaline, but no chemical data 

are available for comparison. Nevertheless, these 

evaporite-associated deposits widen the range of lithologic varieties that could be mineralized namely, 

graphitic schists that are included within scapolite- and 

calc-silicate-rich rocks. Numerous occurrences of such 

rock have been observed in the belt of rock within 2 

miles northwest of Beaver Creek, shown by Buddington 

(1934, Hammond sheet) as crystalline limestone containing linear lenses of white quartzite. These rocks are 

tourmaline-bearing, graphitic, and are associated with 

diopside-scapolite-rich rocks. These are all similar to 

rock types that are associated with Dugald River-type 

deposits in Australia. Further appraisal of these for 

sulfide deposits requires geophysical or geochemical 

techniques.

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