The Potential for Porphyry 

Copper-Molybdenun1 Deposits 

in the Eastern United States 

G E 0 L 0 G I C A L S U R V E Y P R 0 FE S S I 0 N A L P A P E R 9 0 7 -E 
COVER PHOTOGRAPHS 

1 2 3 4 

5 6 

7 8 

9 10 

11 12 13 14 

1. Asbestos ore 

2. Lead ore, Balmat mine, N . Y. 

3. Chromite-chromium ore, Washington 

4. Zinc ore, Friedensville, Pa. 

5. Banded iron·formation, Palmer, 

Mich. 

6. A ibbon asbestos ore, Quebec, Canada 

7. Manganese ore, banded 

rhodochrosite 

8. Aluminum ore, baux ite, Georgia 

9. Native copper ore, Keweenawan 

Peninsula, Mich. 

10. Porphyry molybdenum ore, Colorado 

11. Zinc ore, Edwards, N . Y. 

12. Manganese nodules, ocean floor 

13. Botryoidal fluorite ore, 

Poncha Springs, Colo. 

14. Tungsten ore, North Carolina 
The Potential for Porphyry 

Copper-Molybdenun1 Deposits 

in the Eastern United States 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 907-E 
COVER PHOTOGRAPHS 

1 2 3 4 

5 6 

7 8 

9 10 

11 12 13 14 

1 . Asbestos ore 

2. Lead ore, Balmat mine, N . Y. 

3. Chromite-chromium ore, Washington 

4. Zinc ore, Friedensville, Pa. 

5. Banded iron-formation, Palmer, 

Mich. 

6. Ribbon asbestos ore, Quebec, Canada 

7. Manganese ore, banded 

rhodochrosite 

8 . Aluminum ore, bauxite, Georgia 

9. Native copper ore, Keweenawan 

Peninsula, Mich. 

10. Porphyry molybdenum ore, Colorado 

11. Zinc ore, Edwards, N.Y. 

12. Manganese nodules, ocean floor 

13. Botryoidal fluorite ore, 

Poncha Springs, Colo. 

14. Tungsten ore, North Carolina 
The Potential for Porphyry 

Copper-Molybdenum Deposits 

in the Eastern United States 

By ROBERT GORDON SCHMID'!' 

GEOLOGY AND RESOlJRCES OF c:OPPER DEPOSI'rS 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 907-E 

A descriptive resume of deposits of the 

porphyry type and an evaluation of 

potential areas for discovery of 

new deposits 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1978 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

Library of Congress Cataloging in Publication Data 

Schmidt, Robert Gordon, 1924-

The potential for porphyry copper-molybdenum deposits in the Eastern United States. 

(Geology and resources of copper deposits) (Geological Survey professional paper ; 907-E) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.16 :907-E 

1. Copper ores-United States. 2. Molybdenum ores-United States. I. Title. II. Series. II. Series: United 

States. Geological Survey. Professional paper ; 907-E. 

TN 443.A5S3 553 '.43 '097 4 78-606192 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 

Stock Number 024-001-03113-2 
APPRAISAL OF MINERAL RESOURCES 

Continuing appraisal of the mineral resources of the United States is 

conducted by the U.S. Geological Survey in accordance with the provisions 

of the Mining and l'iinerals Policy Act of 1970 (Public Law 91-631, Dec. 

31, 1970). Total resources for purposes of these appraisal estimates include currently minable resources (reserves) as well as those resources 

not yet discovered or not currently profitable to mine. 

The mining of mineral deposits, once discovered, depends on geologic, 

economic, and technologic factors; however, identification of many deposits 

yet to be discovered, owing to incomplete knowledge of their distribution 

in the Earth's crust, depends greatly on geologic availability and man's 

ingenuity. Consequently, appraisal of mineral resources results in approximations, subject to constant change as known deposits are depleted, new 

deposits are found, new extractive technology and uses are developed, and 

new geologic knowledge and theories indicate new areas favorable for 

exploration. 

This Professional Paper discusses aspects of the geology of copper as a 

framework for appraising resources of this commodity in the light of 

today's technology, economics, and geologic knowledge. 

Other Geological Survey publications relating to the appratsal of resources of specific mineral commodities include the following: 

Professional Paper 820-"United States Mineral Resources" 

Professional Paper 926-"Geology and Resources of Vanadium Deposits" 

Professional Paper 933-"Geology and Resources of Fluorine in the United States" 

Professional Paper 959-"Geology and Resources of Titanium in the United States" 
• 
CONTENTS 

Abstract 

Introduction ---------------------------------------- Porphyry copper deposits in Precambrian rocks _____ _ 

Mcintyre porphyry copper deposit --------------

Setting Net Lake porphyry molybdenum deposit __ 

Porphyry copper deposits in the Chibougamau area, Quebec ___________________________________ _ 

Breccia pipes and mineralized porphyry of the 

Batchawana area, Ontario ------------------

Porphyry copper and molybdenum deposits in Paleozoic 

rocks of New England, the Gaspe Peninsula, 

and New Brunswick ------------------------

Known deposits of porphyry type ----------------

Catheart Mountain exploration --------------

The Gaspe copper deposits ------------------

The Pekan deposit -------------------------- Woodstock, New Brunswick, prospect _______ _ 

Porphyrylike mineral prospects ------------------

Known deposits of porphyry copper affinity _____ _ 

Mount Pleasant deposits --------------------

Hydrothermal mineralization related to felsic 

stocks but not here included with porphyry-type deposits --------------------

Page 

E1 

2 

3 

3 

4 

4 

4 

5 

7 

7 

10 

10 

11 

11 

11 

11 

12 

Evandale stock, New Brunswick ------------

Nigadoo River mine, New Brunswick _______ _ 

Deboullie stock, Aroostook County, Maine ___ _ 

Eagle Lake, New Brunswick ----------------

Molybdenum prospects of the molybdenitic type __ 

Cooper mine -------------------------------- Catherine Mountain (Tunk Lake) prospects __ 

Machias occurrence, Washington County, Maine 

Granite Quarry Hill molybdenum prospect __ 

Other molybdenum occurrences --------------

Porphyry-type deposits in the Southeastern 

United States ------------------------------

Deposits that may be of the porphyry copper-type 

Conner-Neverson quarry area _____________ _ 

Deposits of porphyry copper affinity--------------

The Brewer mine area ----------------------

Prospects of copper and molybdenum not included 

in the porphyry type --------------------

Eastern Halifax County, North Carolina, 

prospects ------------------------------ Newell prospect, North Carolina--------------

Summary and conclusions --------------------------

References cited ------------------------------------

ILLUSTRATIONS 

FIGURE 1. Index map showing porphyry copper-molybdenum deposits and certain 

other mineralized localities in New England, New Brunswick, 

Page 

and Quebec -------------------------------------------------- E6 

2-4. Sketch maps showing: 

2. Hydrothermal alteration zones and sulfide content at Catheart 

Mountain, Somerset County, Maine -------------------- 8 

3. Cooper mine, Washington County, Maine, showing locations of 

samples analyzed ------------------------------~------- 14 

4. Field localities described at the Machias occurrence, Washington County, Maine ------------------------------------ 16 

5. Geologic map of the Cuttingsville pluton, Rutland County, Vt., showing location of the Granite Hill molybdenum prospect ---------- 18 

6. Index map of mines and mineralized prospects in North and South 

Carolina ---------------------------------------------------- 21 

7. Sketch map of the Brewer mine area, Chesterfield County, S.C ---- 22 

8. General geologic map of the Newell prospect, Cabarrus County, N.C., 

showing locations of Newell mine shaft and exploration drill holes 27 

v 

Page 

E12 

12 

12 

13 

13 

13 

14 

15 

17 

20 

20 

21 

21 

24 

24 

25 

25 

25 

26 

29 
VI CONTENTS 

TABLES 

Page 

TABLE 1. The ages or age limits of Paleozoic base metal deposits in New 

England and eastern Canada ---------------------------------- E7 

2. Analyses of composite samples from Cooper mine ------------------ 15 

3. Chemical analyses of two representative grab samples from the 

Machias occurrence, Washington County, Maine ---------------- 17 

4. Chemical analyses of four phases of the Cuttingsville pluton -------- 17 

5. Copper and molybdenum analyses of four samples from the Cuttingsville pluton, Rutland County, Vt -------------------------------- 19 

6. Chemical analyses of 11 samples of drill core from the Newell prospect, Cabarrus County, N.C ---------------------------------- 28 
GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

THE POTENTIAL FOR PORPHYRY C:OPPER-MOLYBDENl Tl\;I DEPOSrrs 

IN THE EASTERN lTNITED STATES 

By RoBERT GoRDON ScHMilJT 

ABSTRACT 

Several significant porphyry-type deposits of Paleozoic age 

are known in New England and eastern Canada. Disseminated copper-molybdenum deposits of Paleozoic age are in the 

Southeastern United States, and copper is produced from 

porphyry-type deposits of both Precambrian and Paleozoic 

age in eastern Canada. Although these old deposits are surely 

less abundant than those in Cenozoic and Tertiary porphyry 

belts, the known Precrambrian and Paleozoic deposits in 

Eastern North America appear to be valid exploration targets. The difficult of •prospecting in drift-covered and 

saprolite-mantled terrains suggests that all such deposits 

probably have not been discovered. Although such deposits 

are more costly to discover in this region than a massive sulfide deposit, the total amount of copper in even a medium-sized 

porphyry copper deposit is much greater than in most massive 

sulfide deposits. 

This report summarizes current knowledge of porphyry 

copper-molybdenum-type deposits in the Eastern United 

States and suggests more favorable areas for mineral exploration. Selected Canadian deposits are discussed because 

of their bearing on planning exploration in this country. 

Porphyry copper deposits are here defined as deposits of 

widely dispersed copper sulfide related to a felsic intrusive 

body and associated with a major system of hydrothermal 

alteration. 

Four deposits that are regarded as porphyry type have 

been identified in the Precambrian shield of Canada; copper 

is mined from two of these, Mcintyre mine (Timmins) and 

Batchawana area, Ontario. Five deposits of Paleozoic age 

are here regarded as certainly of the porphyry copper type, 

Copper Mountain, Needle Mountain, and Pekan in the Gaspe 

Peninsula, the Woodstock prospect in New Brunswick, and 

the Catheart Mountain deposit in Maine. In addition, one 

deposit in the Southeastern United States, the Conner-Neverson quarry prospect in North Carolina, is probably of the 

porphyry type. The Copper Mountain and Needle Mountain 

deposits, Quebec, are now mined. Several copper and (or) 

molybdenum prospects and deposits classed by others as 

porphyry-type occurrences are not included here. Inclusion 

or exclusion of these has a profound effect on metallogenic 

modeling of New England and Southeastern United States. 

Catheart Mountain, Maine, the most significant porphyrytype deposit known in the Eastern United States, covers an 

area of about 1.5 km~ of intensely hydrothermally altered 

rock. A substantial but subeconomic body of coppermolybdenum ore is found on the fringe of the alteration 

system. The southern and northwestern fringes of the system 

have been only partly explored and remain as favorable 

drilling targets. 

I believe that the known Paleozoic porphyry-type deposits 

in New England and eastern Canada are in Middle Devonian 

subvolcanic intrusive rocks in a narrow northeast-trending 

belt in northwestern Maine, New Brunswick, and southeastern Quebec, and perhaps also in New Hampshire. I propose 

that these porphyry copper-molybdenum deposits are related 

to a northwest-dipping Acadian subduction zone located near 

the Maine and New Brunswick coasts, and that a broad belt 

in western New Hampshire, northwestern Maine, and southeastern Quebec is the most favorable for further discoveries 

in this region. 

Only one deposit, in the Conner-Neverson quarry area, 

that is probably of the porphyry type, is now known in the 

Southeastern United States, but the upper Precambrian or 

lower Paleozoic thick volcanic successions included in the 

Carolina slate belt are considered to be favorable prospecting 

areas. Though only partly mapped on an adequate scale, the 

volcanic rocks are known to include several small plutonic 

intrusive bodies but surprisingly few subvolcanic intrusive 

bodies. Neither the existent mapping scale over much of the 

area nor the deep saprolitic weathering favor easy identification of small felsic porphyry bodies in felsic volcanic rocks1 

so I consider that the exploration conducted so far has not 

adequately tested the region. 

The area surrounding the Brewer mine in Chesterfield 

County, S.C., is not a typical prophyry copper system, but it 

has some of the same features. The old gold mines are in 

part of a much larger zone of hig·hly altered copper-bismuthtin-bearing volcanic rocks, part of which are now quartzandalusite and quartz-topaz rocks. The large alteration zone, 

evidence for a subvolcanic origin, and the metal suite provide 

only a sketchy picture of the whole hydrothermal system, 

but permit comparison with the large systems at Mount 

Pleasant, New Brunswick, and some of the deposits of Cornwall. The whole area of alteration and mineralization may 

be several kilometers in each dimension, and until the perimeters are defined and variations in both alteration and 

mineralization style are known, the Brewer area cannot be 

fully evaluated for its base-metal potential. 

The possibility of finding porphyry copper deposits of 

exploitable size in Eastern United States is good, although 

not as good as in the high-potential regions of parts of the 

Western States. Initial exploration should be concentrated 

El 
E2 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

in those parts of New England and the Southeastern States 

that seem to be the most favorable. Problems of detection of 

porphyry deposits in drift-covered regions and in areas having deep saprolitic soils offer a great challenge to exploration 

geologists. The combined use of geological, geophysical, and 

geochemical methods will almost surely be needed for successful exploration programs in these places. 

INTRODUCTION 

Although most economic geologists recognized no 

copper or molybdenum deposits of the porphyry type 

in eastern North America only a decade ago, several 

deposits are now known that fit the porphyry model 

well, and many more can be cited as probable or possible porphyry type. These deposits range in age 

from Archean to middle Paleozoic, possibly to Mississippian. The several deposits that are being mined 

at this time are all in Canada, but the ore body that 

is perhaps the best example of a porphyry deposit 

is at Catheart Mountain in Maine. Although the exploited ore bodies and the known prospects are small 

compared to many Cordilleran and Arizona porphyries, their ·discovery opens up new regions for potential discoveries. As our domestic copper is consumed, 

we must evaluate fully our remaining copper resources. The porphyry copper resources of the 

Eastern States probably never will exceed a few 

percent of our total minable copper, but a reasonable 

assumption is that one to five deposits, each containing 100-300 million tons of low-grade copper ore, 

exist in the Appalachian region. 

In this report, a porphyry copper- (or porphyry 

molybdenum-) type deposit is defined as a deposit 

of widely dispersed copper sulfide related to a felsic 

intrusive body and associated with a major system 

of hydrothermal alteration. A widely occurring 

porphyry type is typically subvolcanic and has many 

characteristics indicating formation close to the 

surface; however, some deposits clearly formed at 

depths as great as several kilometers. In many 

porphyry deposits, particularly those formed close 

to the surface, the hydrothermal rock alteration and 

the sulfides deposited tend to be arranged in symmetrical zones such as those described by Lowell and 

Guilbert (1970). Some near-surface porphyry deposits formed in association with volcanoes (Sillitoe, 

1975). Pipelike breccia bodies, many containing tourmaline, are associated with many porphyry copper 

deposits. Sulfides may occur mainly as veinlet fillings or as disseminated grains in different parts of 

the same deposit, generally in a systematic relationship to zonation. In the selection of deposits to be 

regarded as porphyries in this study, overall size was 

considered not as important as the presence of widely 

distributed sulfide accompanied by extensive hydrothermal rock alteration. Fluid inclusion studies in 

porphyry deposits (Nash and Theodore, 1971; Takenouchi and Imai, 1975, p. 769; Nash, 1976) have 

shown that halide-bearing inclusions are common in 

porphyritic bodies related genetically to mineralization, especially in the cores of porphyry copper deposits. In this study, abundant halide-bearing 

inclusions are considered a strongly favorable factor 

in classifying mineralized localities as porphyry 

copper-type deposits, but the apparent absence of 

such inclusions is weighted less heavily in a negative 

sense. 

Global tectonic principles may have been important controlling factors in the formation of Paleozoic porphyries, just as they seem to have been in 

Tertiary and Quarternary porphyries, and, therefore, 

appropriate plate tectonic models form a reasonable 

basis for selecting general regions for further prospecting. The relationship of porphyry copper deposits to the plate tectonic model has been described 

by Sillitoe (1970) and by others in more recent 

articles. Application of these principles to the search 

for additional Paleozoic porphyries in the complex 

Appalachian geological environment requires caution as well as good regional mapping and structural 

and stratigraphic analysis. The role of plate tectonics 

in Precambrian time, however, is still not clear. The 

tectonic history of the Appalachian region as reinterpreted according to "the new tectonics" is still 

hypothetical and subject to multiple interpretations, 

and the theoretical model of a relatively simple plate 

margin and its related mineralized porphyry intrusions is also interpreted in different ways. The attempt to use paleo-plate tectonics in the search for 

copper-molybdenum porphyry deposits in the complex Appalachian environment may now seem premature, but thought is being given to exactly this 

idea by exploration geologists, and exploration decisions have probably been based on these principles 

already. 

Porphyry copper-molybdenum deposits probably 

formed close to the surface ; furthermore, many or 

most of them probably formed in terrains that were 

undergoing simultaneous rapid erosion. Thus, many 

older porphyry deposits have been eroded away entirely, or only the deepest parts have been left; we 

do not expect porphyry deposits to be nearly as 

abundant in Paleozoic and Precambrian as in younger 

rocks. However, some deposits have been found, and 

the existence of these older minable ore bodies confirms that the older rocks are a legitimate exploration target. 
PORPHYRY qOPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E3 

The Mount Pleasant deposit in New Brunswick 

has been variously regarded as one of porphyry type 

(Hollister, Potter, and Barker, 1974) or as one 

having affinities to a porphyry-type deposit (Kirkham and Soregaroli, 1975). It resembles a porphyry 

copper deposit in its subvolcanic setting, large size, 

and structural control. The complex metal suite including tin, tungsten, and bismuth, the complex mineralogy, telescoped mineral zones, and areas of intense fluorine metasomatism are unlike typical porphyry copper systems, but some of these features 

are also found in the Climax and Henderson porphyry molybdenum deposits, Colorado, and I believe 

also in certain of the tin-copper deposits of Cornwall, 

England. Mount Pleasant is of the same general age 

as the Cornwall deposits. The Brewer Mine area, 

South Carolina, has a large zone of intense alteration, fluorine metasomatism, and a metal suite that 

includes copper, gold, tin, bismuth, arsenic, and 

molybdenum. The possibility that the Mount Pleasant and the Brewer Mine deposits have a similar 

origin and are also similar to the deposits of Cornwall may be important in determining how they 

should be evaluated and in searching for additional 

deposits of similar type. 

This report is a summary of current knowledge 

of porphyry copper- (and molybdenum-) type deposits in the Eastern United States and a preliminary attempt at placing the Paleozoic deposits in a 

metallogenic model ; more favorable areas for further 

mineral exploration are suggested. Selected deposits 

in Canada are also included in the summary because 

of their significance in developing metallogenic 

models and planning exploration in this country. 

In addition to the collection of information from 

published reports, this investigation included a detailed study of the Catheart Mountain deposit in 

Maine, examination of drill cores from the Newell 

and Ellis prospects in North Carolina and from the 

Brewer mine in South Carolina, and brief field visits 

to most of the other New England prospects described, as well as to the Woodstock prospect and the 

Mount Pleasant deposit in New Brunswick. 

The cooperation of many companies and individuals who gave permission to publish new data 

and who helped to provide the information in this 

report is gratefully acknowledged, especially the following: Scott Paper Co.; Noranda Exploration Co., 

Ltd.; A. W. Lockhart; Humble Oil and Refining Co.; 

Mrs. Harold Pelkey; Mr. and Mrs. John Sprague; 

Lindgren Exploration Co.; Bear Creek Mining Co.; 

and Perry, Knox, Kaufman, Inc. 

I am grateful to Paul Josefson of the U.S. Geological Survey for translation of part of the Russian 

article by Khrushchov ( 1959) . 

PORPHYRY COPPER DEPOSITS IN 

PRECAMBRIAN ROCKS 

At least four known mineral deposits in the Canadian shield are now considered to be of the porphyry 

copper-molybdenum type, and additional ones should 

be identified when this type of deposit becomes better known among prospectors and geologists working 

in Precambrian rocks. In evaluating the potential of 

the Canadian shield for discovery of porphyry deposits, Kirkham (1973) described similarities to 

younger porphyries: "close spacial associations with 

felsic and intermediate epizonal plutons, some of 

which may have been feeders for their host calcalkaline and alkaline volcanic piles." He said further 

that "many of the deposits and areas still show a 

zonal distribution of alteration minerals, sulfides and 

metals which could be useful in exploration." 

Kirkham stated that most known Precambrian 

porphyry deposits are of minor economic importance; 

however, some presently support o~rating mines 

or contribute to production of mines based mostly on 

ores of other types. 

The following deposits (three Precambrian Wand 

one Precambrian Y) have been selected from a much 

larger number of deposits and prospects in Canada 

because they are considered to be among the best 

examples of Precambrian porphyry copper systems. 

No examples are known in the United States, but 

large areas of Precambrian rocks in Minnesota, Wisconsin, and Michigan are generally similar to the 

areas where the Canadian deposits are known. 

MciNTYRE PORPHYRY COPPER DEPOSIT 

A copper deposit in the Mcintyre (now called 

Pamour) gold mine at Timmins in the Porcupine 

district, Ontario, contains 8 million tons of 0.7 percent copper ore ( Pyke and Middleton, 1971, p. 61) 

in rocks of Precambrian W age. Production of gold 

and silver at this mine started about 1912; mining 

of the copper ore body began in 1963. The operations are underground. 

The copper ore is associated with a sericitized 

and sheared leucocratic quartz feldspar porphyry, 

the Pearl Lake porphyry. Pyritization is extensive, 

and copper is in chalcopyrite and bornite. Some 

molybdenum and silver are also present; tungsten, 

zinc, and lead are associated with the gold ores. The 

geology as described by Pyke and Middleton (1971, 

p. 61) is as follows: 

The porphyry is about 5,000 feet long, 1,500 feet wide and 

plunges 50 degrees east, parallel to the pronounced lineation 
E4 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

so common in all the rocks in this part of the Timmins area. 

The porphyry is extensively sheared and sericitized and 

contains abundant gypsum, anhydrite and locally hematite 

around the ore zones. A 400-foot-wide zone characterized by 

extensive pyritization, contains disseminated chalcopyritebornite mineralization (minor tetrahedrite, tennantite, molybdenite and native silver are also present) and has been traced 

vertically for 5,000 feet (Griffis, 1962). Ore-grade material is 

confined to a zone about 1,200 feet long and 300 feet wide, 

and extends vertically from the 1,100-foot to the 3,600-foot 

elevation (Carter, 1967). The ore zone has the same plunge 

as the porphyry. Typically, the mineralization is concentrated 

along slip surfaces which plunge at the same angle as the 

porphyry. Less commonly, the sulphides are finely disseminated in non-sheared massive sections of the porphyry. The 

concentration of the sulphides along slip surfaces in the 

porphyry suggests a redistribution of the mineralization 

during shearing and hydrothermal alteration of the porphyry. 

That disseminated copper mineralization is present in massive porphyry suggests that the sulphides are indigenous to 

the porphyry. 

I wish to emphasize the statement by Pyke and 

Middleton (1971, p. 61) that the identification of 

the mineralized Pearl Lake porphyry in the McIntyre mine is very important becaus·e the deposit 

"demonstrates not only porphyry copper deposits 

formed during Early Precambrian times, but that 

the level of erosion has not been so great as to remove these deposits." 

SETTING NET LAKE PORPHYRY MOLYBDENUM DEPOSIT 

This low-grade molybdenum deposit in northwest 

Ontario, about 400 km northeast of Winnipeg, is 

associated with an epizonal lower Precambrian porphyritic granodiorite-quartz monzonite stock where 

four intrusive phases have been recognized (Ayres, 

Wolfe, and Averill, 1973; Wolfe, 1974). The mineralized zone, in altered quartz monzonite in the northern 

part of the pluton, consists of closely spaced 1- to 

2-mm-wide molybdenite-coated quartz veinlets and 

associated sericitic and chloritic alteration and 

pyritization. The highest grade material, occupying 

about half a square kilometer, contains about 0.06 

percent molybdenite and minor amounts of copper 

(Wolfe, 1974, p. 28, and fig. 4, p. 33). 

PORPHYRY COPPER DEPOSITS IN THE 

CHIBOUGAMAU AREA, QUEBEC 

A porphyry-type copper deposit has been reported 

from Precambrian rocks near Chibougamau in 

northern Quebec by Jules Cimon (oral commun., 

March 1973). Mineralized areas are associated with 

several magnetic anomalies in the southwestern part 

of the tonalite-diorite Chibougamau pluton, a felsic 

body 65 km long by 2-16 km wide. The pluton occupies the center of the Chibougamau anticline within the Lac Dore layered mafic complex (Duquette, 

1970, p. 10). 

The six magnetic anomalies are related to stockworks of magnetite-chalcopyrite formed along what 

Cimon (oral commun., March 1973) called strongly 

metasomatized zones. In the most important localities, d:::signated areas 3 and 4, the mineralization is 

confined to zones that are intensely intruded by a 

complex system of felsic porphyry dikes. The most 

common type of dike is a green aphanitic rock containing quartz phenocrysts, and other types are 

feldspar porphyry and quartz-feldspar porphyry. 

The intruded zones are locally highly brecciated, and 

some of the breccia has fine-grained tourmaline in 

the rna trix rna terial. 

Potassic alteration is reported to be ubiquitous 

close to sulfide-magnetite mineralization (Cimon, 

oral commun., March 1973). Primary plagioclase has 

been altered to potassium feldspar, either evenly 

or in patches, and secondary biotite is present in a 

few places. The increase in total K20 content is as 

much as 3 percent. Potassic alteration is of variable 

width along fractures. Outside the areas of potassic 

alteration, sericitization and chloritization are widespread, but the areas of these zones have not been 

defined. Regional greenschist facies metamorphism 

makes it impossible to delimit propylitic alteration 

related to the mineralization. 

Magnetite is the most important iron oxide, but 

exploration drilling has penetrated some hematite 

zones, suggesting that perhaps part of the deposits 

was formed at relatively shallow depths (Cimon, 

oral commun., March 1973). Pyrite is commonly disseminated, and locally it is abundant. 

Although still in a stage of preliminary investigation, this porphyry area is perhaps as important as 

the Pearl Lake porphyry at the Mcintyre mine, Ontario, in establishing the concept of deposits of the 

porphyry type in rocks of Precambrian X age. 

BRECCIA PIPES AND MINERALIZED PROPHYRY OF THE 

BA TCHA WAN A AREA, ONT ARlO 

Five known breccia pipes in the Batchawana area, 

64 km north of Sault Ste. Marie, Ontario, are presumed to have a common origin, and the Jogran porphyry stock, several kilometers to the southwest, 

may also be related. Two of the pipes are being 

mined by the Tribag Mining Co. for copper and silver; a third contains disseminated copper and 

molybdenum sulfide, as does the porphyry stock. 

One of the deposits now being mined, the Breton 

zone breccia, is underlain by a highly altered feldspar 

porphyry. 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E5 

The geology of the area has been described by 

Blecha (1965, 1973, 1974). The deposits are near 

the northern edge of a northeast-trending belt of 

Precambrian W greenstones, sedimentary rocks, and 

mafic intrusive rocks. Granitic rocks underlie the 

area both north and south of the belt. Five breccia 

pipes are at, or close to, the granite contact ; two of 

these are entirely within volcanic rocks and diabase 

of the greenstone sequence, and one is surrounded 

mostly by granite. The locations of the breccias are 

probably structurally controlled and related to 

lineaments (Blecha, 1965, p. 1079). Blecha (1965, 

p. 1079-1080) stated: "The breccia consists of angular fragments of granite, diabase and basic volcanics, 

and of basic and acidic dyke material. Each of these 

rock types occurs in the immediate vicinity of the 

breccia and no fragments truly foreign to the area 

have been found within it." However, Blecha (1973) 

further stated: "The pipes contain a high proportion 

of felsophyric fragments which suggest the presence 

of a deep-seated porphyry intrusive." 

Sulfides are most abundant in a vuggy quartzcarbonate matrix in open breccias, generally within 

distinct alteration halos as much as 46 m wide 

(Blecha, 1965, p. 1081) that have been used as guides 

in exploration. The alteration minerals are mainly 

sericite, chlorite, and clay minerals, depending on the 

composition of the original rock. Sulfide minerals 

are mainly pyrite and chalcopyrite and subordinate 

galena, molybdenite, chalcocite, and scheelite. Silver 

is an important product of ore concentration, but 

no silver mineral has been identified. The greatest 

alteration and the best ore are associated with domal 

fractures that are probably related to upward-propagating collapse. 

Sericite from the Breton breccia zone has been 

dated by K-Ar methods as 1.055 b.y. (Roscoe, 1965). 

Fluid inclusion studies by Norman (1974) indicate 

that there were five stages in the brecciation, void 

filling, and mineralization of the five breccias. 

These copper-molybdenum-bearing breccia pipes 

probably share many features with muc_h younger 

breccia ore bodies, such as those described by Sillitoe and Sawkins (1971), but the Batchawana deposits lack the tourmaline and specularite common in 

many of the younger ones. 

The Jogran quartz-feldspar porphyry stock, 6 km 

southwest of the breccia pipes, is partly altered and 

contains disseminated chalcopyrite, pyrite, and 

molybdenite (Blecha, 1974, p. 75). Giblin (1974) 

and Blecha (1973) suggested that the mineralized 

stock is of the porphyry copper type. 

PORPHYRY COPPER AND MOLYBDENUM 

DEPOSITS IN PALEOZOIC ROCKS OF 

NEW ENGLAND, THE GASPE PENINSULA, AND 

NEW BRUNSWICK 

The New England-Maritime Provinces-Gaspe area 

contains many deposits and prospects of disseminated copper and molybdenum sulfides. All, or only 

a few, of these deposits may be classed as the porphyry type depending on the definition or model 

used. The types of deposits tend to be grouped into 

types by region, and the inclusiveness of the definition that one uses for a porphyry system strongly 

biases the pattern of regional distribution. 

As explained in the introduction, the major criteria applied in this report for classifying deposits 

as porphyry-type were the presence of widely distributed copper (or molybdenum) sulfide and also the 

presence of extensive hydrothermal rock alteration. 

Some prospects regarded by other writers (such as 

Hollister, Potter, and Barker, 1974) as porphyries 

have been omitted here because they are only locally 

mineralized and (or) lack sufficient rock alteration. 

One deposit in Maine, one in New Brunswick, and 

three in the Gaspe Peninsula are, I believe, certainly 

members of the porphyry type (fig. 1). In addition, 

the Mount Pleasant deposit in New Brunswick has 

close affinity to the porphyry type and has been 

classed as a porphyry by Sillitoe, Halls, and Grant 

(1975, p. 925). Information sufficient for classification of a few other prospects is not available at this 

time. 

Of particular importance in metallogenic modeling 

is the classification of several p;ospects along the 

Maine and New Brunswick coast (fig. 1). Inclusion 

of the prospects in a model of porphyry-type copper 

deposits greatly extends the area of potential porphyry occurrence and is, I believe, very misleading. 

These coastal prospects fit well into the "molybdenite" class or type as defined by Khrushchov (1959), 

and he states that few of this type are known to be 

exploitable. The molybdenite type of molybdenum 

deposit (I hereafter refer to it as molybdenitic), as 

described by Khrushchov (1959), results from postconsolidation autometamorphism of plutonic rocks, 

essentially deuteric alteration. The molybdenum generally occurs as sparse disseminated molybdenite 

flakes in felsic rocks, characterized by lack of associated vein-type minerals and metallic sulfides, and 

lack of rock alteration of the enclosing rocks. The 

intrusive rocks include granite (perhaps interpreted 

broadly as quartz-monzonite to granite), aplite, and 

syenite. Some molybdenitic deposits cited by 
E6 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

7'!' 

0 

I 

0 

100 

I t I I I 

7f1' 

I 

100 

200 

I 

69" 

300 KILOMETERS 

I 

I 

200 MILES 

67" 66" 

EXPLANATION 

• Porphyry copper-molybdenum deposit 

t> Deposit of porphyry-copper affinity 

-<> Lean mineral occurrence of molybdenitic type 

o Uncategorized copper and(or)molybdenum deposit 

FIGURE 1.-Index map showing porphyry copper-molybdenum deposits and certain other mineralized 

localities in New England, New Brunswick, and Quebec. 

Khrushchov are near the contacts with country 

rocks, similar to the Cooper Mine and Quarry Hill 

prospect in New England; it is not clear to me if any 

of his molybdenittc examples are within the central 

parts of plutons. Small bodies up to a few meters 

across within one of the Soviet molybdenitic deposits 

contain as much as 10 percent molybdenum, and 

similarly, the Quarry Hill prospect may have yielded 

samples that analyzed as much as 30 percent molybdenum, but total molybdenum resources of deposits 

of this type are interpreted to be small. 

The geology of the northern Appalachian orogen 

has been interpreted by Bird and Dewey ( 1970) in 

terms of plate tectonics theory. Although the general 

concept, to say nothing of specific local details, remains controversial among geologists, new ideas on 

distribution of porphyry-type deposits are closely 

tied to the theory and may help to explain the distribution of the ore deposits in this area, as suggested by Halls and Simpson ( 1972, p. B180). Ore 

deposits at Catheart Mountain, Maine, and the 

Gaspe copper mines (Copper Mountain and Needle 

Mountain), Quebec (fig. 1), and other mines and 

prospects are associated with postorogenic shallow 

or subvolcanic plutons, probably of late Acadian age 

(table 1). Other intrusive bodies of this type seem 

to be the most promising loci for new porphyry copper prospects in the region. D. B. Stewart (oral 

commun., 1975) identified an "Ellsworth block" of 

European-African continental crust in the Maine 

coast area that collided with the North American 

continent during the Devonian Period. The approximate line or suture along which this collision took 

place is shown on figure 1. Although the exact location is still open to dispute, this approximate location is more than adequate for metallogenic modeling, and may have considerable implication in selecting areas for prospecting for porphyry copper deposits. Porphyry -type and other hydrothermal mineral occurrences, all of Devonian age, include Catheart Mountain, Maine, the Pekan, Copper Mountain, and Needle Mountain deposits, Quebec, and the 

Nigadoo River mine, New Brunswick, and form a 

broad northeast-trending belt (fig. 1). If the mineralized felsic intrusive bodies were related to subduction during the Devonian continental collision 

along the line suggested by Stewart, then the five 

mineralized localities listed above range from 100 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E7 

TABLE 1.-The ages or a.ge limits of Paleozoic base metal deposits in New England and eastern Canada 

Locality Age Reference 

Keene Dome, N.H -------------- 373± 15 m.y. (on related muscovite) ________ __ __ __ Foss, Scherffius, and Gaudette, oral commun., 1975. 

Catheart Mountain, Maine ______ Late Ordovician ---------------------------------- Boone, Boudette, and Moench, 1970, 

p. 19. 

Mount St. Sebastien, Quebec' ____ Devonian ---------------------------------------- Kirkham and Soregaroli, 1975, p. 

251. 

Deboullie stock, Maine' ---------- Later than stock which is post-Middle Devonian __ Boone, 1962, p. 1453. Pekan deposit, Quebec ___ ____ ___ Later than Silurian and Devonian sedimentary Perusse, 1969. 

rocks. 

Gaspe copper mines (Needle 

Mt. and Copper Mt.). 

Later than Middle Devonian sedimentary rocks __ __ McAllister and Lamarche, 1972. 

Mount Pleasant deposits ________ Mississippian ------------------------------------ McAllister and Lamarche, 1972, p. 

85. 

Woodstock, New Brunswick ___ ___ In rocks that that cut pre-Silurian strata _____ _____ Anderson, 1954, p. 2. 

Nigadoo River mine, Acadian or shortly after -------------------------- Suensilpong and Stumpfi, 1971, p. 

New Brunswick.' B105. 

Cooper mine, Maine ' __ ____ ____ Within rocks of Devonian age -------------------- Hussey and others, 1967. 

Catherine Mountain, Maine' ____ ---- ------ ------- do ------------------------ Do. 

1 I did not Include In porphyry-type deposits a~ defined In this paper. 

to 320 km in distance northwestward from it. (As 

the position of volcanism is believed related to the 

Benioff zone in the depth range of 100-200 km, the 

horizontal distance from the suture is a function of 

the dip of the Benioff zone. The average distance of 

volcanism and porphyry development from Benioff 

zones of intermediate dips is 200 km (Mitchell and 

Garson, 1972, p. B12) .) Thus, the distribution of the 

several porphyry copper and copper-molybdenum deposits in this region permits the construction of a 

hypothetical metallogenic model showing a broad 

belt that includes parts of western New Hampshire, 

northwestern Maine, and southeastern Quebec as 

much more favorable for further discoveries than 

areas to the northwest and southeast of the belt. 

Moench and Gates (1976) examined the chemical 

compositions of the volcanic rocks in the Maine and 

New Brunswick coastal belts and concluded that the 

volcanism had been bimodal, not andesitic ; therefore, 

it was probably not an island-arc suite. Acceptance 

of this conclusion does not preclude application of 

the continental-collision model to the origin of the 

porphyry-type deposits, however, as subduction and 

collision may have occurred without formation of 

an arc. 

KNOWN DEPOSITS OF PORPHYRY TYPE 

CATHEART MOUNTAIN EXPLORATION 

The porphyry copper-molybdenum deposit at Catheart Mountain, Maine (fig. 1), is in a large complex 

hydrothermal alteration system. To the extent that 

they have been identified, alteration and mineralization zones are moderately well developed on an overall scale as well as on smaller scales related to individual porphyry bodies and mineral veins. Mineralization is related to several subvolcanic porphyry 

intrusives, and copper and molybdenum occur within 

the porphyry as well as in a medium-fine-grained 

quartz monzonite country rock. 

The Catheart Mountain deposit is on land owned 

by the Scott Paper Co. It was discovered in 1963 and 

has been entensively explored by the Noranda Exploration Co., Ltd. A study of mineral and alteration 

zonation was started by the U.S. Geological Survey 

in 1970. Results of examination of drill cores from 

an ore body were described in an earlier report 

(Schmidt, 1974). 

Country rock in the vicinity of the Catheart 

Mountain deposit is gray uniform medium-finegrained quartz monzonite that occurs within the 

much larger pluton of Attean Quartz Monzonite 

(Lower Ordovician). No well-exposed contacts between the two rock types have been seen, and the 

relationships of the two are not clear. The quartz 

monzonite of Catheart Mountain is distinguished by 

the generally finer grain size and by the absence of 

the 1- to 2-cm feldspar megacrysts so characteristic 

of the Attean Quartz Monzonite. The Attean Quartz 

Monzonite was described by Albee and Boudette 

(1972), and chemical analyses of the two rocks were 

tabulated for comparative purposes by Schmidt 

(1974, p. 191). 

The hydrothermal alteration zones have been 

mapped from outcrop information and exploration 

drill cores (fig. 2). Despite gaps in some boundaries, 

the zonation pattern follows the well-known form of 

many other porphyry systems (Lowell and Guilbert, 

1970). 

Copper and molybdenum sulfides are present in 

most of the altered rock in the large hydrothermal 
ES GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

system, but they have been identified in potentially 

extractable amounts in only a limited area on the 

southwest flank of the mountain (hereafter called 

the ore body) and in small masses or pods at other 

localities. 

There are also two subsidiary nodes of potassic 

alteration on the southwestern flank, and one of 

these is the location of the known ore body; thus, 

the only sizable mass of potentially extractable ore 

is associated with its own small zonation pattern but 

is located well down on the flank of the main zone 

system. Folding later than formation of the deposit, 

as recorded in Devonian strata, 4 km to the east, 

may have rotated the zonal system from its original 

position. The most probable rotation seems to be 

downward to the southeast-perhaps as much as 

I . 

X 

0 

EXPLANATION 

Hydrothennal alteration ;rones 

Potassic 

Quartz-sericitic 

ProJ7:,1litic 

Rock-outcrop data point 

Drill-hole data point 

Total sulfide that generally 

exceeds 2 percent (110lume) 

Contact-Dashed where location 

is uncertain 

0 

0 500 HXXJ 1500 

500 

60°-around an axis that trends northeastward and 

may plunge northeastward at a low angle. If rotation 

has occurred in this fashion, it does not significantly 

change the conclusion about the position of the ore 

body on the flank of the system, but it may have 

made great changes in the apparent position of the 

features on the northwest and southeast sides of the 

system. Exploration of the southwest flank of the 

system has been thorough only close to the known 

ore body; parts of the northeast, northwest, and 

south flanks are covered by glacial drift and remain 

untested. 

A well-developed pyrite zone (mostly 2-5 percent 

sulfide) is present within the quartz-sericitic and 

potassic alteration zones of the main alteration system. Along the southeast side of the alteration 

2000 2500 

6000 N 

4000 N 

2000 N 

Mapped by R. G. Schmidt in 1976 

1000 METERS 

3000 FEET 

w 

z 

::::i 

w 

~ aJ 

FIGURE 2.-Sketch map showing hydrothermal alteration zones and sulfide content at Catheart Mountain, Somerset County, 

Maine. 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E9 

model, limits of the pyrite zone are close to the edge 

of the quartz-sericitic (phyllic) alteration zone, 

much like the "typical porphyry" as described by 

Lowell and Guilbert (1970, p. 379), but elsewhere 

the edge of the pyrite zone falls 500 m and more 

inside the limit of the quartz sericitic zone, and 

overlaps most of the central potassic zone, unlike the 

ideal Lowell-Guilbert model. Most of the rock associated with the ore body contains no more than 2.3 

percent sulfide (Schmidt, 1974, p. 193). 

Within the ore body, overall zonation is similar 

to the main system but on a smaller scale. The details of zonation are very complex and seem to be 

INDEX MAP SHOWING APPROXIMATE 

LOCATION OF FIGURE 2 

0 .5 2 3 KILOMETERS r---L-,_L----,--L-----~--, 

0 Y2 1 2 MILES 

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VERTICAL DATIJM OF 1929 

related to small dikes of porphyry and to veins and 

veinlets. In examination of drill-hole cores, most 

rock was assigned to one of seven alteration types, 

but the data did not generally permit interpretation 

of the alteration as simple successive zones. The 

average analyses of copper and molybdenum and the 

total contained sulfides in the rocks were found to 

be systematically different in the main alteration 

types (Schmidt, 1974, p. 193). When the alteration 

types were arranged on a chart in a sequence based 

on a combination of increasing copper plus molybdenum values and decreasing copper-molybdenum 

ratios, the resulting synthetic zonation was similar 

Base from U.S. Geological Survey, 

1:62,500, Long Pond, Maine, 1922 

FIGURE 2.-Continued. 
ElO GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

to that in the main Catheart Mountain system and 

in porphyry copper deposits elsewhere. 

Examination of fluid inclusions in hydrothermally 

altered rock from Catheart Mountain indicates that 

strong brines were present in at least part of the 

hydrothermal system. Relatively small bubbles in 

gas-liquid inclusions suggest that the part of the 

system we now see never closely approached a boiling 

condition. Local explosion breccias and a fine groundmass in the porphyry bodies indicate that the system was probably not more than a few kilometers 

deep at time of formation. Thus, these sparse depth 

indicators suggest an intermediate (perhaps 2-5 

km) depth of formation for the part of the deposit 

we now see. This contrasts with the relatively deeper 

burial during mineralization ascribed by Hollister, 

Potter, and Barker (1974, p. 627-628), and with my 

own earlier interpretations. 

A small exposure of sulfide-bearing pebbly siltite 

containing fragments of quartz and assorted volcanic porphyry is in the northeast part of Catheart 

Mountain. This exposure is probably bedrock outcrop, and the sulfide in it roughly corresponds to the 

sulfide content of rocks in other nearby outcrops, but 

it is also possible that this is a float boulder. This 

sedimentary rock, if it is local bedrock, suggests that 

some generally contemporaneous extrusive volcanic 

material was included in the zone of mineralization 

and supports the idea of formation of the deposit 

at a relatively shallow depth. 

The Catheart Mountain deposit is in the altered 

rock produced by a large hydrothermal system, and 

the altered area may extend outward beneath the 

glacial drift cover to the northeast, to the northwest, 

and perhaps also to the south into areas where there 

has been partial evaluation (northeast and south) 

or essentially no evaluation (northwest) by exploration drilling. It is my opinion that peripheral exploration will probably further extend the area of 

known alteration. The known ore body is peripheral 

to the central alteration system and therefore the 

remaining flanking areas seem at least as attractive 

for exploration as the center, if not more so. 

THE GASPE COPPER DEPOSITS 

The Copper Mountain and Needle Mountain deposits (fig. 1) at Gaspe Copper Mines, Ltd., Murdochville, Quebec, represent contrasting types of 

"typical" porphyry mineralization within a 6.5-km.2 

zone of intense hydrothermal alteration believed related to small quartz-feldspar porphyry bodies. The 

deposits have been described by Macisaac (1969), 

and McAllister and Lamarche (1972, p. 38-45). Mining at Needle Mountain began in 1955 and at Copper 

Mountain in 1968. Together they form the largest 

porphyry-type deposit in production in eastern 

North America and the largest of Paleozoic age 

known in the Americas. 

The Gaspe deposits are in an area of Lower and 

Middle Devonian sedimentary rocks, especially calcareous shale, siliceous limestone, siliceous shale, 

siltstone, and sandstone. Contact metamorphism and 

hydrothermal alteration have converted these strata 

to a variety of hornfels and skarns (Macisaac, 1969, 

p. 831 ; Allcock, 197 4) in the area surrounding small 

intrusive bodies of quartz-feldspar porphyry. Hollister, Potter, and Barker (1974, p. 624) cited a 

K! Ar age af 346 m.y. for intrusive rock here. 

The Copper Mountain deposit is a large low-grade 

stockwork ore body (230 million tons, 0.40 percent 

Cu (McAllister and LaMarche, 1972, p. 43)) in 

which chalcopyrite, the major copper mineral, occurs 

in fractures, veins, replacements, and as disseminated grains (Macisaac, 1969). The ore body is closely related in space to a large plug and many dikes 

and sills of quartz-feldspar porphyry, but especially 

to one east-trending dike. Ore occurs both around and 

in the intrusive bodies, and favors certain stratigraphic layers. The pyrite zone occupies much of the 

alteration zone; within the ore body the pyrite-chalcopyrite ratio is about 3: 1. Sparse molybdenite is 

distributed widely, mostly in veins, and is most 

abundant in the center of the ore body. Bismuth, 

silver, gold, selenium, and tellurium are other associated metals. 

The nature of rock alteration in sedimentary host 

rock is different from that in intrusive rocks. The 

sedimentary rocks have been intensely silicified and 

bleached, and diopside and garnet were formed. The 

porphyries are kaolinized, although it is not clear 

how much of this alteration may be supergene 

(Macisaac, 1969, p. 834). 

The Needle Mountain deposit is primarily a skarntype replacement ore body in sedimentary strata 

without known close spatial relationship to an intrusive body, but its occurrence within the same 

alteration zone as the Copper Mountain ore body 

suggests a common source of mineralizing solutions. 

Ores have been formed by selective replacement of 

four layers of calcareous sediments, separated by 

less calcareous units. Faults provided channels for 

solutions to reach the favorable layers, and faulting 

was an important ore control. . 

THE PEKAN DEPOSIT 

Located about 35 km southwest of Copper Moun-
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES Ell 

tain and Needle Mountain, this is also a disseminated 

copper-molybdenum deposit related to felsic subvolcanic intrusive bodies (Perusse, 1969). The intrusive bodies are a variety of small stocks, dikes, and 

sills of granodiorite and felsic porphyries that have 

different texture, color, and phenocryst composition. 

A breccia pipe about 300 m in diameter was described by Perusse (1969, p. 825), but he did not 

indicate that the pipe was mineralized. Copper occurs mainly as chalcopyrite and bornite in skarns 

that have formed in Silurian and Devonian limestone 

and siltstone. Molybdenum is present mostly as coatings on fractures in the porphyries and in quartz 

veinlets. 

WOODSTOCK, NEW BRUNSWICK, PROSPECT 

Extensive exploration for disseminated copper 

sulfide has been carried out on a complex of small 

felsic intrusive bodies and hornfelsic country rock 

near Woodstock in west-central New Brunswick. Appreciable copper mineralization is present in several 

localities within an area of 21 km2 , and trace 

amounts of molybdenite are also present in parts 

of the deposits. Reports on the copper grade, though 

not contradictory, give somewhat different impressions of the potential of the deposit. Lockhart (1976, 

p. 13) stated, "Significant areas containing 0.3 to 

1.0 per cent copper were discovered, but no orebody has been outlined to date." 

According to Kirkham and Soregaroli (1975, p. 

249), recent exploration "has indicated a large tonnage of very low grade copper mineralization." 

Fine-grained porphyritic rocks, probably hypabyssal, are present within at least part of the mineralized area, although I cannot determine if the mineralization is related to them. Rock alteration, sulfide 

mineralization, and possibly some post-mineralization metamorphism have acted on quartz diorite 

and dioritic plutonic rocks and on hornfelsic quartzite and argillite of Cambrian and Orodovician age. 

Potassium feldspar is generally absent, but muscovite is very common in some of the rocks and may 

indicate potassium enrichment. I have insufficient 

data to determine if any zoning patterns can be 

mapped. 

Fluid inclusions are relatively abundant in quartz 

grains, but halide crystal-bearing inclusions are 

sparse in the few specimens I examined, and there 

is no evidence for any particularly "potent" hydrothermal fluids in the system using the criteria described by Nash (1976). No gas-rich inclusions suggesting boiling fluids were seen. 

Most rocks from the area contain chlorite and 

epidote, the result of low-grade metamorphism or 

propylitic alteration, and perhaps both. It is not 

clear whether or not some secondary biotite formed 

during potassic alteration, later to be changed to 

chlorite during low grade metamorphism. We cannot assume that the widespread presence of chlorite 

and epidote indicate that no quartz-sericite zone or 

quartz-sericite-potassium feldspar zone was present. 

Although I have not seen evidence of zonation at 

the Woodstock deposit, I believe that the deposit 

represents an upper part of a major porphyry system. Old prospects for lead, zinc, and copper in the 

vicinity (Anderson, 1954) may represent peripheral 

veins related to the same hydrothermal system. 

PORPHYRYLIKE MINERAL PROSPECTS 

Kirkham and Soregaroli (1975) described two 

Canadian prospects that may be of the porphyrycopper type. The Benjamin River deposit, near New 

Mills, New Brunswick, consists of sparse pyrite, 

chalcopyrite, and trace amounts of molybdenite in 

fractures and disseminated in quartz monzonite 

dikes and hornfelsic volcanic rocks. The intrusive 

rocks are interpreted to be of Devonian age. The 

Mount St. Sebastien, Quebec, prospect is 70 km 

northwest of Catheart Mountain, Maine. Pyrrhotite, 

molybdenite, and minor chalcopyrite occur in small 

quartz veins in hornfels adjacent to a biotite quartz 

monzonite intrusive body. Kirkham and Soregaroli 

(19'75, p. 251) stated that "the intrusions in the area 

have been dated as Devonian by K/ Ar methods." 

KNOWN DEPOSITS OF PORPHYRY COPPER AFFINITY 

MOUNT PLEASANT DEPOSITS 

Although mainly of interest for their tin, tungsten, and molybdenum, the deposits of Mount Pleasant in southwest New Brunswick are also partly 

copper bearing. These deposits, in the volcanic rocks 

of a caldera of Mississippian age, have been described by McAllister and LaMarche ( 1972, p. 82-89) 

and Dagger (1972). The deposits probably most 

closely resemble the tin-copper deposits of Cornwall, 

and suggest that additional deposits of this type may 

be present along the eastern margin of North 

America. 

A mixed assemblage of volcanic rocks is present 

at Mount Pleasant. The mineralization is related 

to two pluglike bodies that are interpreted to be 

erosional remnants of volcanoes. The plugs are highly altered felsite, tuff, and breccia; the intruded 

rocks are primarily felsic ash-flow tuffs. Three overlapping but distinct zones of hydrothermal alteration 

concentric about the two plugs were mapped and de-
E 12 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

scribed by Ruitenberg (1963; 1972, p. 442). The 

mineralized "greisen" zone consists of quartz, fluorite, kaolinite, topaz, hematite, and chlorite. This is 

surrounded by a zone of intense silicification accompanied by kaolinization. The lowest grade alteration 

is weak pervasive silicification, sericitization, and 

chloritization (the report of chlorite in the most 

intensely altered central zone has a parallel in the 

chlorite of the deep central core of the porphyry 

copper model proposed by Lowell (1968, p. 652)). 

Two types of metallic deposits are present at 

Mount Pleasant. The most important consists of Mo, 

W, and Bi sulfides and lesser As, Zn, Cu, Sn, and Pb. 

The main deposit of this type is in the core of the 

southern volcano remnant. The Cu-Sn-Zn deposits 

(they also contain some Bi, In, Cd, W, and Ag) are 

small compared to the main Mo-W-Bi ore body. 

Three main Cu-Sn-Zn bodies are known, one near 

the northern volcano and two near the south vent 

(McAllister and LaMarche, 1972, p. 89) . 

HYDROTHERMAL MINERALIZATION RELATED TO 

FELSIC STOCKS BUT NOT HERE INCLUDED WITH 

PORPHYRY-TYPE DEPOSITS 

EVANDALE STOCK, NEW BRUNSWICK 

A quartz monzonite stock of Devonian age (Potter, 

Rutenberg, and Davies, 1969, p. 72) about 5 km 

in diameter is west of the Saint John River (approximately lat 45°35' N., long 66°05' W., 35 km 

north of Saint John). Chalcopyrite and molybdenite 

occurrences were discovered in the stock in 1968, and 

much exploration has been conducted since. 

The Evandale stock is medium to coarse grained, 

and gray to pink. Orthoclase and plagioclase are 

about equal in amount (Ruitenberg, 1970, p. 7). Red 

and buff aplite dikes up to 1.5 m wide trend northnorthwest. The stock has intruded dark-gray slate, 

argillite, and siltstone of Ordovician or Silurian age; 

an aureole of dark-brown hornfels 60 m thick has 

formed next to the contacts. 

Sulfide minerals, mostly chalcopyrite, have been 

discovered in fractures and quartz stringers in a 

zone 2,400 x 460 m in the northwestern part of the 

Evandale stock. Veinlets about 2 mm wide are spaced 

2-15 em apart and trend mostly north-northwest. 

Pink alteration of feldspars is up to 1 em thick 

along the mineralized fractures. Abundant molybdenite is reported from only one locality (Ruitenberg, 1970, p. 8). No genetic relationship of the sulfide minerals to the aplitic intrusive rocks has been 

suggested in published accounts. Too little is known 

of the copper and molybdenum mineralization for 

me to include this as a porphyry-type deposit at this 

time. 

NIGADOO RIVER MINE, NEW BRUNSWICK · 

The Nigadoo River mine is a vein deposit rather 

than a porphyry-type deposit, but the copper-leadzinc-silver veins occur within and adjacent to a 

small quartz porphyry plug intruded as a late phase 

of, or shortly after, the Acadian orogeny. A detailed 

description of the ore body was given by Suensilpong 

and Stumpff (1971). The mine is about 18 km 

northwest of Bathurst, New Brunswick, within the 

Tobique structural-metallogenic zone as defined by 

Potter, Ruitenberg, and Davies (1969). Sedimentary 

country rocks in the vicinity consist of "mainly 

gray-green, fossiliferous argillites and calcareous 

graywackes, with minor layers of conglomerate, 

slate and limestone" (McAllister and Lamarche, 

1972, p. 73). 

The quartz-feldspar porphyry is a rather narrow 

vertical pipe. Horizontal dimensions are roughly 

240 X 790 m at the surface, but several dikelike 

apophyses make the outline quite irregular in plan 

view. The intrusive body had been explored to about 

600 m in 1972 (McAllister and Lamarche, 1972, p. 

73-74). The same authors (p. 73) described the 

porphyry as "pale greenish yellow to light grey 

rock, containing quartz, orthoclase and plagioclase 

phenocrysts in an aphanitic matrix. Sericite and 

kaolinite are ubiquitous alteration minerals but are 

particularly abundant near veins. The porphyry pipe 

is enclosed by a zone of breccia two or three feet 

(30 to 90 em) wide, containing fragments of adjacent metasedimentary rocks and porphyry." 

Ore minerals occur in three successive vein-fault 

systems, each having different structural and mineralogic characteristics (Suensilpong and Stumpff, 

1971, p. B98-B99), but ore is mainly in the second 

vein group. A close spatial relationship of the mineralized veins to the porphyry intrusive body exists. 

Suensilpong and Stumpff (1971, p. B105) believed 

that the porphyry and ore are genetically related : 

either ore solutions came from the cooling, mostly 

solidified porphyry, or the mineralizing solutions 

were a late-stage consequence of the same Acadian 

orogeny that produced the felsic intrusive rock. The 

same authors believed that the ore mineral zonation 

in the ore veins relates to the higher vein temperature in the porphyry because the intrusive body was 

interpreted to be still cooling when the vein minerals 

formed. 

DEBOULLIE STOCK, AROOSTOOK COUNTY, MAINE 

A geologic description of this complex stock was 

published in 1962 (Boone, 1962), and a private exploration com·pany began an extensive drilling pro-
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E 13 

gram in 1971. I have not sought the results of the 

exploration program, and the following description 

is based on Boone's article plus a 1-day visit to the 

generally mineralized area of the prospect. 

The Deboullie stock was described by Boone as a 

postorogenic composite pluton. The compositions of 

the main types of intrusive rock range from 

pyroxene-biotite syenodiorite and monzonite to hornblende-biotite granodiorite. The stock is elliptical, 

the long axis is 5.5 km, trending northeast, and the 

greatest width is a little less than 3.0 km. Boone 

divided the stock into a relatively simple granodiorite south half and a complex north half which consists of calc-alkaline syenite and screens of monzonite, and which includes masses of country rock. 

The northwestern part has most of the sulfide 

mineralization. Sparse chalcopyrite and molybdenite 

occur in small fractures and are perhaps disseminated also. The extent of hydrothermal alteration is not known to me. Contact metamorphism 

has converted the wall rock Seboomook Formation 

(Lower Devonian) to andalusite-cordierite-biotite 

hornfels around the stock and in the inclusions. 

Boone mapped two hornfels areas of relatively large 

size that are perhaps roof pendants; these contain 

fairly abundant pyrite. Dikes of quartz-bearing 

latite, dacite porphyry, aplite, and fine-grained pegmatite were identified. Some of the porphyritic dikes 

appear to be hypabyssal. The alteration present in 

the dikes is like that associated with greenschist 

facies metamorphism and there is no evidence to 

link them to mineralization. 

EAGLE LAKE, NEW BRUNSWICK 

Prospecting near Eagle Lake, New Brunswick (approximately 45°16' N., 66°22' W.), indicated that 

copper, molybdenum, and silver are concentrated 

along fracture zones in a highly altered quartz 

monzonite stock (Ruitenberg, 1969, p. 13; Potter, 

Ruitenberg, and Davies, 1969, p. 72). Kirkham and 

Soregaroli ( 1975, p. 250) regarded the mineralization at this prospect as far too sparse to justify 

calling it a porphyry deposit. 

MOLYBDENUM PROSPECTS OF THE 

MOLYBDENITIC TYPE 

Several prospects containing rather sparse molybdenite on fracture surfaces and disseminated in felsic plutons have been found along the Maine and 

New Brunswick coasts, and also at Quarry Hill, near 

Rutland County, Vt. (fig. 1). These are best classed 

in the molybdenic type as described by Khrushchov 

( 1959). These prospects are generally lean, but local 

concentrations of material containing more than 1 

percent molybdenum were extracted from the 

Quarry Hill and Cooper mine prospects. Neither 

these nor the Catherine Mountain prospect and 

Machias occurrence have rock alteration of the kind 

or intensity that I associate with a porphyry-type 

deposit, even if I interpreted them to represent 

deeply eroded zones of porphyry systems such as 

Hollister, Potter, and Barker (1974) have done. 

COOPER MINE 

The now abandoned Cooper mine in Washington 

County, Maine, was first operated about 1902 and is 

said to be one of the oldest molybdenite mines in 

the country ; however, total production probably did 

not exceed a few tons of concentrate (Burbank, 1965, 

p. 61). Last mining seems to have been in 1919. 

The workings probably included an underground 

mine as well as the small flooded quarrylike open 

pit visible today. The mine has been described briefly 

by several authors; the most complete reports were 

by Hess (1908, p. 231-234), Young (1963, p. 67-68 

and 83-85), and Burbank (1965, p. 61-62). 

The country rock adjacent to the open pit is 

medium-fine-grained porphyritic quartz monzonite. 

In parts of the pit walls, some of the feldspar, presumably the potassium feldspar, is creamy yellow 

or pale brown, giving the rock a slightly buff color 

(not to be confused with patches of weak iron-oxide 

staining probably related to weathering). The feldspar phenocrysts are sparse and small, generally not 

exceeding 5 mm in length. Matrix plagioclase is more 

abundant than potassium feldspar and is mostly unaltered, but in thin section some grains are lightly 

dusted by "sericitic" alteration. Matrix potassium 

feldspar is mostly untwinned. Biotite is very darkly 

pleochroic. No rock alteration is present, and X-ray 

diffraction studies of the potassium feldspar by Mary 

Mrose and Patricia Loferski, U.S. Geological Survey, indicate that no clay mineral exceeds the 

detection limit of perhaps 5 weight percent. 

Burbank (1965, p. 61) described three modes of 

molybdenite occurrence in the mine: (1) associated 

with narrow pegmatite dikes and quartz veins, (2) 

as nests or pockets, and (3) disseminated in granitic 

rock. The nests and pockets as well as most of the 

pegmatite and vein concentrations seem to have 

been exposed in a trench in the quarry floor that was 

under water when Burbank visited in 1942 and also 

when I was there in 1971. I noted neither pegmatite 

nor aplite in the walls of the open pit, but Burbank 

found that "small seams of pegmatitic quartz are exposed in outcrops north of the quarry, but the 

amount of molybdenite in them is insignificant." 
E 14 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

Molybdenite in the pit walls is mostly in disseminated 1- to 2-mm grains, and in a few grains as 

large as 10 mm. Rock containing more molybdenite 

than can be seen in place today was removed during 

the active mining, as shown in old reports and by 

rock on the waste dump (Young, 1963, p. 68). I took 

representative chip samples from the pit walls in 

1971. The locations of these samples are shown in 

figure 3, and the analyses are given in table 2. My 

samples are substantially lower grade than the one 

collected by Burbank (see table 2). Presumed mill 

feed at the mine is reported to have contained 1,060 

ppm (0.106 percent) molybdenite (Young, 1963, 

p. 68). 

Hess (1908, p. 232-233) noted small amounts of 

fluorite and one specimen of native bismuth in the 

deposit. 

CATHERINE MOUNTAIN (TUNK LAKE) PROSPECTS 

The Catherine Mountain prospects (fig. 1) are in 

the central part of the Tunk Lake pluton, a circular 

granitic to quartz monzonitic zoned intrusive body 

in Hancock County, Maine. Sparse molybdenite is 

present over an extensive area on Catherine Moun-

--

N 

EXPLANATION 

~~~~~ Outline of dwnp 

o

1 

2

1

5 ~0 7

1

5 1 r METERS 

~~~~~--~------~----~----~----~~--~ 

~ ~ Pit 0 50 100 200 300 FEET 

0 Outcrop of quartz monzonite 

11 Mine shaft 

FIGURE 3.-Sketch map of Cooper mine, Washington County, Maine, showing locations of samples analyzed (see table 2). 

Map has been modified from Young (1963, p. 83). 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E 15 

TABLE 2.-A nalyses of composite samples from Cooper mine 

L l{e~mlt~ in parts per million. Analyse~ b,v K Y. Campbell, E. G. 

Lillie, and H. :\loore, U.S. Geological Survey. Bismuth was determine(l b,v a sub!-!toichiometric isotope dilution technique ; copper 

waR determined by atomic ab~wrptiou ~pectrometr:l'; mol;rbdenum 

nud tungsten were determined by newl,\' dP,·eloped hwtope dilution 

spectrophotometric techniques J 

Sample 

No. 

Cn l\lo Hi w 

PB30077 10 110 75 26.5 

78 11 36 . 120 92. 

79 10 43 66 15.4 

80 9.7 81 130 22.2 

81 12 70 100 44 

83 5.6 34 39 13.8 North wall 1 __________________ 720 _________________________ _ 

(0.12 percent MoS2) Ore pile 1 ______________________ 720 _________________________ _ 

( 0.12 percent MoS2) Crushed rock in mill bin 1 _____ lkO _________________________ _ 

(0.03 percent MoS2) ----- 1 From Burbank (1965, p. 62). 

tain, but it nowhere exceeds trace amounts, and no 

hydrothermal rock alteration is associated with it. 

The prospects have been described by Hess (1908, 

p. 234-235), Trefethen and Miller (1947), and Young 

(1963, p. 65, 67, and 79-82). Composition zonation 

in the Tunk Lake pluton was described by Karner 

(1968) and by Karner and Helgeson (1970). I visited 

the prospect areas for 1 day in 1971. 

The Tunk Lake pluton intrudes Ellsworth Schist 

(Upper Cambrian or Ordovician ( ?) ) , granite of Middle Devonian age, and various phases of rocks of the 

Bays-of-Maine complex (Karner, 1968, p. 195). 

Karner divided the pluton into six phases or types 

ranging from augite granite at the chilled margin 

to biotite monzonite in the interior. The best known 

molybdenum prospects are close to the northern 

edge of the innermost zone, where the quartz and 

oligoclase contents are relatively high and t'he total 

mafic mineral and potassium feldspar are low 

(Karner, 1968, p. 198, 203). Hess (1908, p. 236) was 

told of several other occurrences of molybdenite near 

Tunk Lake, but none of these are described in geologic literature. 

The quartz monzonite on Catherine Mountain is a 

medium-coarse-grained gray granitic rock containing 

modal percentages of about 35 percent quartz, 25 

percent plagioclase, 35 percent potassium feldspar, 

and a maximum of 5 percent biotite. In the vicinity 

of some of the prospects (probably those in area 5 

of Young, 1963, p. 80), the texture is very uneven, 

for it includes patches of fine-grained as well as pegmatitic material. None of the rocks examined in the 

prospects show any evidence of hydrothermal alteration. The feldspar minerals are generally fresh, and 

most of the biotite is only 5 percent altered to 

chlorite. A specimen from a sparsely mineralized 

prospect (probably area 4 of Young) has a little 

clinozoisite developed in plagioclase grains, and about 

half the original biotite has been replaced by chlorite. 

This degree of alteration is so common in old granitic rocks that to consider it a result of a major 

hydrothermal process seems unrealistic. 

Trefethen and Miller (1947, p. 55-56) described 

three modes for the molybdenum present: (1) as 

scattered crystals with pyrite on a few joint surfaces, mostly on the east-trending joint set; (2) with 

a few of the sparse small pegmatite bodies, also 

mostly with some associated pyrite; and (3) along 

the con tact or in the gradational marginal zone of 

aplitic bodies, particularly at the eastern end of the 

mountain. Disseminated molybdenite was seen only 

within a few centimeters adjacent to pegmatite and 

aplite bodies. Young (1963, p. 65) described two 

modes of molybdenite occurrence: (1) disseminated 

with or without pegmatite, and (2) on joint surfaces accompanied by pyrite. The paucity of sulfides makes it difficult to classify some of the prospects, and I did not get an impression of clearly 

separate modes of occurrence when I visited the 

mountain. 

The meager sulfide and the lack of evidence of 

hydrothermal alteration at Catherine Mountain 

make it highly improbable that the molybdenite 

there represents any part of a porphyry-type hydrothermal system. This deposit was placed in the 

molybdenite class by Khrushchov (1959). 

MACHIAS OCCURRENCE, WASHINGTON COUNTY, 

MAINE 

Molybdenite on the Sprague-MacKenzie property 

near Machias, Maine, was discovered by Cornelia 

Cameron, U.S. Geological Survey, in 1973. The 

molybdenum occurs in a quartz monzonite pluton 

close to the contact of the pluton with metamorphosed lower Paleozoic felsic volcanic conglomerate. 

The pluton is of Devonian age (Hussey and others, 

1967). 

The contact of the intrusive and the volcanic conglomerate is in generally low, partly swampy ground 

near the Sprague-MacKenzie property, and I did 

not see the actual contact when I visited there. The 

conglomerate forms large rock knobs protruding 

above the swampy surface (point A, fig. 4). Most 

clasts in the felsic volcanic rock are less than 5 em, 

but a few scattered boulders are as large as 40 em. 

Metamorphism is presumably related to contact 

effects of the quartz monzonite pluton. Faint iron-
E 16 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

Base from U.S. Geological Survey, 

1:24,000. Machias, Maine. 1949 

0 

0 

.5 

CONTOUR INTERVAL 20 FEET 

NATIONAL GEODETIC VmTICAL DATUM Of 1929 

EXPLANATION 

2 KILOMETERS 

1 MILE 

A Volcank: conglomerate D Medium-grained massive quartz 

8, C F'me-grained quartz monmnite monzonite 

containing molybdenite ---- Geologk: contact-Approximately located 

FIGURE 4.-Sketch map showing field localities described at the Machias occurrence, Washington County, Maine. 

oxide staining in some of the larger clasts suggests 

traces of sulfide, but no fresh sulfide was observed. 

The quartz monzonite crops out in a narrow easttrending band near the top of a short slope above 

the low and swampy land ; the margin of the pluton 

probably parallels this outcrop near the foot of the 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E 17 

slope. The rock at the top of the slope is a finegrained quartz monzonite (points B and C, fig. 4). 

It contains 40-45 percent quartz, and potassium 

feldspar exceeds plagioclase by l 1/2 to 2 times. 

Plagioclase grains are partly clear and fresh, and 

partly light to densely sericitized. Dark minerals, 

mostly chlorite derived from alteration of biotite, 

make up perhaps 2-3 percent of the rock. Abundant 

low outcrops 300 m to the north (point D, fig. 4) 

are medium-grained massive quartz monzonite, 

noticeably coarser that the marginal rock at points 

8 and C. 

Molybdenite is present at points 8 and C (fig. 4) 

as 1-cm rosettes, especially along certain joints in 

the fine quartz monzonite, and also disseminated in 

the quartz monzonite for as much as 3 em on each 

side of the joints. Limited rock alteration may also 

be in this 3-cm zone, but I have mode no petrographic study to substantiate this. The bulk of the rock 

has sericitization only in part of the plagioclase. 

Analyses for copper, bismuth, molybdenum, and 

tungsten in rock samples from points 8 and C are 

given in table 3. 

No molybdenite mineralization was seen in the 

volcanic conglomerate (point A, fig. 4) nor in the 

quartz monzonite more distant from the margin 

(point D, fig. 4). This type of molybdenum occurrence is considered not likely to form deposits of exploitable size and grade, but examination of the rest 

of the periphery of this pluton seems advisable 

because experience in evaluating molybdenite deposits in North America is limited and the periphery 

is a clearly defined target for geochemical reconnaissance. 

TABLE 3.-Chemical analyses of two -representative grab 

samples from the Machias occurrence, Washington· 

County, Maine 

r RPsults in part>~ }lf'l' million. Anal_rf;f'~ by P. Aru,:e:wagP and L. l\Iei, 

U.S. Geological Surve,\'] 

Lab. No. Field Cu Bi l\Io w 

lo<>ation 

\V~182107 ________ B ______ 2R 2.7 93 1.3 

W~l82108 ________ c ______ lH 0.67 60 1.9 

GRANITE (QUARRY) HILL MOLYBDENUM PROSPECT 

Molybdenite ore in small quantities and extensive 

weak sulfide mineralization are present in the syenitic Cuttingsville pluton on Granite Hill, at Cuttingsville, near Rutland, Vt. To my knowledge, no radiometric dates have been obtained for the pluton, but 

Chapman (1968, p. 389) included the pluton in the 

White Mountain Plutonic Series of Early Jurassic 

or Late Triassic age. 

The Cuttingsville pluton, a complex body mostly 

of potassic rocks about 2 X 2.5 km in size was described in detail by Eggleston (1918). Rock exposures were probably considerably better on much 

of Granite Hill when Eggleston mapped; the present 

dense woods and additional soil cover would make 

it difficult to reproduce his mapping today (fig. 5). 

The molybdenite prospect was merely mentioned 

by Eggleston (1918, p. 406), not surprising in a 

work that dealt mainly with the complex petrology 

of the pluton. 

Jacobs (1937, p. 24) described the molybdenite as 

occurring in "a mineralized zone over 3100 feet long 

and some 125 feet wide." Weak sulfide mineralization 

is extensive, and perhaps even pervasive through 

much of the pluton, so that I found it difficult to 

define a specific mineralized zone in the field. Molybdenite occurs only locally in the more widespread 

sulfide-bearing rocks. 

The pluton consists of five major rock types-in 

order of decreasing abundance, pulaskite, augitesyenite, essexite, hornblende-biotite syenite, and 

sodalite-nephelite syenite (Eggleston, 1918). Chemical analyses of four of these phases are shown in 

table 4. Hybrid rocks are found at many places 

where two phases adjoin. 

TABLE 4.-Chemical analyses of four phases of the Cuttingsville plutm~, from Eggleston (1918) 

[AnalrRe>~ of augite Rrenite b,\· C. D. TPRt; other anal,\'SeR of H. E. 

:'IIerwinl 

H•truhlPndeh:ot itP ",\'Pili tP 

Sodalitt>-

IIPllhelitf' Hyenite 

Si02 _________ _46.47 57.44 60.88 

Ti02 ---------- 2.86 .69 .35 Al20a _________ 16.86 21.60 ~0.75 

Fe202 -------- 3.21 .20 .63 

!<'eO ---------- 7.72 2.62 1.13 

.MnO ---------- .23 .14 .22 

l\IgO ---------- 5.16 1.09 .17 

CaO ---------- 9.45 2.90 1.08 

Na20 --------- 4.20 7.36 6.35 

K20 ---------- 1.35 4.12 5.57 

H20+ --------- .45 .58 .88 

fhO- ---------- .04 .03 .03 

P20s ---------- 1.15 .38 Trace 

C02 -----------Trace .39 .61 

Zr02 ----------None .02 Trace 

SOa ----------· None None None 

Cl ------------ .06 .07 .18 

F ------------ .10 .05 .05 

Cr203 --------- None None None 

BaO ----------'l'rflce .26 .02 

SrO ---------- .04 .04 Trace 

FeS2 ---------- .21 .15 .61 

Fe1Ss --------- .08 .14 .13 

.\ugite 

:o;yenite 

67.30 

.17 

17.44 

1.56 

1.76 

.16 

.14 

1.00 

7.08 

4.78 

.05 

.05 

.04 

-~osNone 

Li20 -----------=N:..:...:o:..::::n-"-e ___ N_on-=-e _____ N_on_e ____ _ 

Total _____ 99.64 100.27 99.64 101.61 

The pulaskite occupies most of the southern twothirds of the pluton (fig. 5). It is generally coarse 

grained and consists mostly of microperthitic feldspar and a little orthoclase ; biotite is generally present (Eggleston, 1918, p. 395). Minor constituents 

and accessories are biotite, cancrinite ( ?) , nephe-
E 18 

72"54' 

0 

I 

0 

GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

.5 

I 

I 

1 MILE 

CONTOUR INTERVAL 100 FEET 

NATIONAl GEODETIC VERTICAL DATUM OF 1929 

2 KILOMETERS 

I 

EXPLANATION 

[J] Essexite 

I fiJ]J1' 11-bmblende-biotite syenite 

1 ~ 1 Sodalite-nephelite syenite 

Country rock not distinguished 

except limestone, which is 

shown by pattern 

FIGURE 5.-Geologic map of the Cuttingsville pluton, Shrewsbury and Wallingford Townships, Rutland County, Vt., 

showing location of the Granite Hill molybdenum prospect. Modified from Eggleston (1918). 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E19 

lite ( ?) , titanite, magnetite, pyrrhotite, apatite, and 

zircon. The molybdenite prospect is along the western margin of the pulaskite phase and separated 

from the main pulaski te mass by a thin screen or 

lens of essexite (fig. 5). Northward-trending streaks 

of very coarse grained phases of pulaskite occur near 

the western edge of the pluton near the ridge crest 

of Granite Hill, including the vicinity of the molybdenite prospect. The pulaskite generally weathers to 

a rusty brown color that is locally related to the 

decomposition of sulfides; whether or not the brown 

color is everywhere related to disseminated sulfide 

is not certain. The analysis of copper and molybdenum in some of the coarse phase of the pulaskite 

is shown in table 5. 

TABLE 5.-Copper and molybdenum analyses of four samples 

from the Cuttingsville pluton, Rutland County, Vt. 

l Copper was determined by atomic absorption spectrometry. Molybdenum was determined photometrically. Analysts: P. Aruscavage and E. Campbell, U.S. Geological Survey] 

Lab. No. Field No. Cu Mo (ppm) (ppm) 

W-191!l06 ____ JX20210 ____ 5 3.9 

7---- 5 ____ 6 5.8 

8____ 6 ____ 60 6.0 

g____ 8 ____ 5 8.8 

Description 

Hornblende biotite-syenite, grab 

sample from waste, quarry on Granite Hill (fig. 5). 

Hornfels or border phase at edge 

of pluton, 30 m north of molybdenum prospect. 

Hornfels near contact, crest of 

Granite Hill, 110 m north of 

prospect. 

Coarse pulaskite, about 120 m north of quarry on Granite Hill. 

Augite-syenite (nordmarkite) makes up the northern end of the Cuttingsville pluton (Eggleston, 

1918, p. 398-401). Mostly medium grained, the grain 

ranges locally from fine to coarse. Seventy-five percent or more of the rock is feldspar, mostly microperthite, and also microcline, orthoclase, and albite. 

Green augite locally rimmed by green hornblende is 

the major dark mineral, and aegirite-augite, olivine, 

and primary quartz are minor constituents. Accessories are magnetite, zircon, apatite, and perhaps 

ilmenite. Although Eggleston detected no sulfide in 

the rock, he suspected it was there and reported 

that the rock gives a sulfurous odor on breaking, 

and weathers to a pale buff or very light brown. 

Essexite occurs in a large patch between the 

pulaskite and the augite-syenite, and also in several 

small scattered lenses and pods (fig. 5). It is a dark 

rock containing hornblende, pyroxene, and biotite in 

about equal quantities, and 60 percent feldspar, most 

of which is plagioclase (An=30-70 percent) (Eggleston, 1918, p. 388). Accessory minerals are olivine 

(partly serpentinized), magnetite, titanite, apatite, 

pyrite, and probably pyrrhotite. Eggleston (1918, p. 

388) considered this phase to have been the first to 

crystallize. It is not known to be sulfide bearing. 

The hornblende-biotite syenite is a gray mediumgrained rock consisting of light-gray feldspar 

speckled by hornblende and biotite (Eggleston, 

1918, p. 392-395). More than half the feldspar is 

plagioclase, and most of the orthoclase is present as 

antiperthitic intergrowths in the plagioclase. Biotite 

and hornblende are about equal in quantity, and together make up about 10 percent of the rock. Accessories are apatite, titanite, magnetite, zircon, and 

pyrite. No quartz was noted. The biotite is fresh 

and no claylike alteration of the potassium feldspars 

is present. Pyrite is locally more abundant, making 

up perhaps as much as 0.5 percent of a few blocks 

in the waste dump of the old quarry (see fig. 5). The 

copper and molybdenum analysis of a sample of the 

hornblende-biotite syenite is shown on table 5. 

The sodalite-nepheline syenite phase was described 

by Eggleston from only one relatively small lens 

near the east edge of the pluton. It is medium-coarsegrained gray rock consisting of 90 percent feldspar, 

and pyroxene, sodalite, and nepheline. More than 

half the feldspar is microperthite, orthoclase, and 

microcline, and the rest is plagioclase near albite in 

composition. Accessories are apatite, magnetite, titanite, and pyrite (Eggleston, 1918, p. 397). 

Molybdenite occurs at one prospect at the west 

edge of the pluton (fig. 5) ; I know of no other occurrence in the vicinity. Jacobs (1937, p. 24) cited 

"a mineralized zone over 3100 feet long and some 

125 feet wide," but I tbink that sparse pyrite rather 

than molybdenite probably determined the major 

boundaries of his zone. Sparse molybdenite can be 

seen in bedrock at the prospect. High-grade material 

in the dump probably came from the small shaft, 

which is too dangerous for thorough examination 

and is also flooded to perhaps 2 m from the surface. 

Relationships of the high-grade material to the enclosing rock must be deduced from the dump materials. 

Country rock at the prospect consists of fine to 

coarse pulaskite, made up mostly of perthitic orthoclase, and a fine-grained sugary hornfelsic rock, 

probably mostly metamorphosed wall rock but perhaps partly a chilled marginal phase of the intrusive rock. Some specimens seem to be fine hornfels 

injected along and across foliation by abundant 

pulaskite, and some mixing of the two rocks has 

taken place in the contact zone. The molybdenite 

mineralization seems to be very close to, if not in, 

the contact zone, because both rock types are present 

in the sides of the small prospect shaft. The hornfelsic rock at the shaft and dump and also in nearby 

outcrop contains from a trace to 3 percent pyrite, 
E20 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

and little molybdenite was observed in it. The copper 

and molybdenum content of two samples of the 

hornfels is shown in table 5. 

Molybdenite is disseminated in irregular patches 

in fine and medium-grained biotite pulaskite fragments found on the dump of the prospect pit. Some 

material is estimated to contain more than 10 percent molybdenite, a few percent pyrite, and perhaps 

some chalcopyrite. The amount of this high-grade 

material on the dump is small but it probably has 

been preferentially removed by mineral collectors. 

It is assumed that the "analyses showing as much as 

30 percent molybdenum" (Jacobs, 1937, p. 24) were 

made on selected pieces of rna terial. Traces of secondary molybdenum minerals are present in weathered dump fragments, but no secondary copper minerals were observed. Hand specimens of the richest 

molybdenum-bearing pulaskite are weakly radioactive, but the source of the radiation has not been 

determined. 

Although there is widespread weak sulfide mineralization and local high-grade molybdenum-bearing 

rocks, the Cuttingsville pluton completely lacks the 

pervasive hydrothermal alteration that one should 

expect in a porphyry-type deposit. It is proposed that 

the molybdenum is of the molybdenitic deposit type 

as defined by Khrushchov (1959). This type of deposit generally has a much lower potential for exploitation than a porphyry deposit, but a small highgrade deposit in the Cuttingsville pluton is still a 

possibility. Previous prospecting was probably controlled entirely by observations on natural outcrops, 

and I am not aware of any use of geochemical prospecting methods to explore the mineral potential of 

the pluton. Many unexposed areas are probably near 

the pluton margin that are large enough to obscure 

ore bodies of significant size. Drift cover is probably 

mostly thin, and geochemical soil sampling should 

be a rapid and efficient way to seek other molybdenum-bearing parts of the pluton. 

OTHER MOLYBDENUM OCCURRENCES 

Molybdenum has been reported from several other 

localities in southern and eastern Maine in addition 

to the Cooper mine and the Catherine Mountain deposit (King, 1970, p. 7). Although the brief descriptions given by King indicate that some of these 

are associated with pegmatites and small sulfide 

veins, some of them probably are deposits of the 

molybdenitic type. I know of no evidence that any 

of these localities are deposits of the porphyry type. 

Hollister, Potter, and Barker (1974, p. 625) discussed the sparse molybdenite mineralization that 

may be associated with a narrow breccia zone at 

Cadillac Mountain on Mount Desert Island, Hancock 

County, Maine. 

PORPHYRY-TYPE DEPOSITS IN THE 

SOUTHEASTERN UNITED STATES 

Several disseminated copper-molybdenum deposits 

associated with felsic stocks are known in eastern 

North and South Carolina, but information on them 

is somewhat limited. One prospect, the ConnerNeverson quarry area, is tentatively classified as the 

porphyry type, but none are proved to be of that 

type. These prospects are in, or close to, rocks of 

the Carolina slate belt, a sequence of metamorphic 

rocks derived from volcanic flows in tuffs intermixed 

and intercalated with rock waste. These slate-belt 

rocks and their presumed equivalents, extending 

from Alabama to Maryland, represent a very extensive belt of late Precambrian and early Paleozoic 

volcanism, perhaps related to an island arc or to the 

edge of a paleocontinent. One tectonic model for the 

southeastern Piedmont region would have had two 

continental masses collide about 450 m.y. ago 

(Glover, 1976), and the subduction zone dip southeastward. The distribution of small late-orogenic or 

postorogenic plutons in a thick sequence of volcanic 

sediments and volcanic tuffs and flows along the 

southeast edge of the Piedmont is compatible with 

this view. The subduction of oceanic crust prior to 

collision would have resulted in volcanism and perhaps the formation of porphyry copper-type deposits in a linear belt above the subduction zone. 

Small plutons within the slate belt may indicate the 

site of active volcanism and subvolcanic intrusion 

above the subduction zone, and I consider the small 

plutons to be the areas of highest potential for the 

occurrence of porphyry copper-type deposits. 

In an alternate interpretation, Spence and Carpenter (1976) considered the western part of the 

slate belt as the site of a major volcanic island arc 

during late Precambrian and early Paleozoic time 

associated with an arc-trench gap and trench to the 

east, now hidden under Coastal Plain sedimentary 

strata, and a westward-dipping subduction zone. 

Black and Fullagar (1976) cited Rb/Sr age dates to 

indicate that subduction and volcanism began before 

705 m.y. and ended 613 m.y. ago, then resumed in 

the early Paleozoic, and ended finally before the 

"Taconic" orogenic period. Presumably the interpretation by Black and Fullagar would permit more 

than one subduction zone, perhaps two of opposite 

dip. 

The extensive belt of volcanic rocks in the Pied-
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E21 

mont, though not well exposed in many areas, and 

as yet only partly mapped on an adequate scale, 

includes several small plutonic intrusive bodies, but 

has surprisingly few subvolcanic intrusive bodies 

known in it. The deep saprolitic weathering in the 

region does not favor the identification of felsic 

subvolcanic rocks in felsic volcanic country rock. 

There are many gold deposits and prospects, at least 

some of which are probably of volcanogenic origin 

(Worthington and Kiff, 1970), and some of these 

occurrences contained associated copper, lead, zinc, 

bismuth, and arsenic; a few such as the Haile and 

Blackmon mines, Lancaster County, S.C. (fig. 6), 

82" BO" 78° 

- - ___ _,_ VIRGINIA 

1 ----------------- TENNESSEE EUIS ~ 1 BOY SCOUT.JOIIES ......_~ 

,-J IIOSS-IIICHAIIDSON - ~ 

"' / NORTH CAROUNA Rocky Mount • SHARPSBURG QUARRY ~ 

Raleigh • ~ • / Wilson 

CONNER I'IIIJIIfCT, 

NEVERSON OUAIIRY • Concord 

<llarlotte ~ NEWBL .,...., "" - - • I'ROSI'fCT ---..,, 

SOUTH BLACK..~.::- - _iOl~erfield N 

CAROLINA lllllf ~'\ ', l cf$ 

\ HAI.E ,_E BREWER 118E""' (, 

GA.I CoiiDilbia • Camden '' /. 

0 100 

I I I I I I 

0 50 

I 

200 KILOMETffiS 

I 

100 MILES 

"" 

EXPLANATION 

• City or town 

X' Mine or prospect area 

FIGURE 6.-Index map of mines and mineralized prospects in 

North and South Carolina. See text for discussion. 

have associated potassic rocks that may indicate 

substantial hydrothermal potassic alteration (Pardee and Park, 1948, p. 112, 114). 

The disseminated molybdenum-copper mineralization at the Conner prospect and the Neverson quarry 

in North Carolina is sufficiently extensive to be of 

the porphyry copper type, but the intensity and 

extent of rock alteration are not known; hence the 

classification is tentative. 

The Brewer mine, Chesterfield County, S.C. (fig. 

6), is in a large zone of intense hydrothermal alteration that may be regarded as a deposit of porphyry 

copper affinity, possibly similar to the Mount Pleasant, New Brunswick, and the Cornwall, England, 

deposits. 

Three prospects in Halifax County, N.C. (the 

Moss-Richardson, Boy Scout-Jones, and Ellis), are 

not now classified as porphyry-type deposits because 

rock alteration and mineralization seem too limited, 

but more information about these prospects could 

easily change their category. 

Stratabound polymetallic mineralization of the type 

described by Maucher (1972) probably is present in 

the slate belt also (U.S. Geological Survey, 1973, p. 

2). Perhaps this is related in some way to the probably volcanogenic gold-base metal deposits. Neither 

deposit type can be considered directly associated 

with or indicative of porphyry copper-type mineralization, but both suggest that this long volcanic belt 

had metal-bearing hydrothermal emanations associated with it. 

Geologists working for private companies have 

searched for at least the last 10 years in the southeastern Piedmont for deposits of the porphyry type. 

Although none of the mineralized areas they found 

have yet proved to be minable, some may fit the 

porphyry model well enough to encourage further 

search. Six mineralized areas that I think deserve 

consideration as porphyry-type deposits are described here. 

DEPOSITS THAT MAY BE OF THE PORPHYRY 

COPPER-TYPE 

CONNER-NEVERSON QUARRY AREA 

The Conner stock is in Wilson and Nash Counties, 

N.C., about 53 km east of Raleigh. Exploration at 

the Conner stock was described by Cook (1972). 

Porphyritic biotite granite has intruded argillite and 

tuff of the Carolina slate belt. Part of the stock is 

overlapped by thin sediments of the Coastal Plain. 

Three areas of anomalous metal content were 

identified and two were explored. Two samples were 

taken and analyzed from the third area, the Neverson quarry near Sims, but no exploration was carried out. 

The areas explored were on the northwest and 

west edges of the intrusive body. Pyrite-chalcopyrite-molybdenite mineralization was intersected in 

altered granite and in rock described as greisen. 

Quartz veins bearing minor galena, sphalerite, chalcopyrite, and pyrite were found at the granite-slate 

belt contact. All analyses of drill samples were less 

than 175 ppm Mo and 650 ppm Cu, averaged over 

10-ft (3.05 m) intervals. Locally pyrite makes up 

as much as 15 percent of the "greisen" zone. 

The most intriguing part of the pluton is the 

N everson quarry where no drilling was done. Cook 

reported that argillic alteration is present here and 

alteration seems more intense than at the drilled 

locations. Some rock is abnormally red. According to 

Cook (1972), "Quarry blocks and greisen float contain up to 0.380 and 0.192 percent molybdenite re-
E22 

( 

I 

GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

... - .....,.-···-- ···.--··· 

/ 

/ .· 

( 

.··-- ;···--... -···-----

0 

0 

30 ~ / 

I ... / 

II 

II 

II 

II 

II 

I/ 

II 

II 

II 

,, 

,, 

II 

" II 

" II 

II 

II 

II 

II 

II 

II 

II 

II 

~="=,.._ " '~, 

.5 

65 

: --- \ · .. 

l KILOMETER 

FIGURE 7.-Sketch map of the Brewer mine area, Chesterfield County, S.C. 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES 

D 

-

25 

EXPLANATION 

MIDDENDORF(?) FORMATION (UPPER 

CRETACEOUS)-Ulconsolidated light-gray, 

yellow-brown, and reddish-brown day, silt, 

sand, and, especially at the base, gravel 

METAMORPHOSED \OLCANOSEDIMENT ARY ROCKS--Metamorphosed felsk: tuff, 

tuffaceous sand and argllite, felsic porphyry, 

and volcanic breccia; metamorphosed rocks of 

undetermined origin include diabase, hornblende gneiss, and amphibolite. Some areas 

covered by Middendorf Formation are not 

delineated 

ARGllllTE-Largely greenish-gray (brownishgray when weathered) ftne-grained laminated 

tuffaceous argllite 

Contact 

Strike and dip of bedding 

Inclined 

70 Strike and dip of foliation 

Inclined 

--+- Vertical 

Gossan (data from J. T. Pardee in Fries, 1942, 

pl.6) 

• Topaz rock (data from J. T. Pardee in Fries, 

1942, pl. 6) 

Silicified rock (data from J. T. Pardee in Fries, 

1942, pl. 6) 

8 o U.S. Bureau of Mines diamond drill hole. All holes 

contain significant fluorine believed to be present 

only as topaz (Peyton and Lynch, 1953). Hole 8 

contains the most topaz 

Q Outline of open pit 

---- Vehicle tran 

-+- Vertical 

82' 8,1' 

-, 

'" ' ' " ' 79' 

50 100 MILES 

0 50 100 KILOMETERS 

INDEX MAP OF SOUTH CAROLINA, SHOWING BREWER MINE AREA 

FIGURE 7.-Continued. 

E23 
E24 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

spectively ." J. B. Mertie, U.S. Geological Survey, 

prepared a panned concentrate from finely crushed 

rock collected at the Neverson quarry crusher in 

1947. Molybdenite is a major constituent of the 

heavy minerals in the concentrate. 

I examined thin sections of five specimens of potassic quartz monzonite and granite taken from the 

Neverson quarry in 1949 by J. B. Mertie. Plagioclase 

appeared mostly unaltered, and biotite had been 

partly altered to chlorite and a little epidote. These 

mineral changes indicate rather weak alteration 

compared with major porphyry-type deposits elsewhere. The most reasonable alternate classification 

of the sulfide mineralization here is probably the 

molybdenitic type mineralization of Khrushchov 

(1959). 

I also examined thin sections of two specimens 

collected by J. B. Mertie from a quarry about 4 

km south-southwest of Sharpsburg in Wilson 

County, N.C. (about 23 km northeast of the Neverson quarry). The rock is very potassic, containing 

perhaps 50 percent potassium feldspar. Feldspars 

do not appear altered but the high potassium feldspar content may itself indicate a form of highintensity potassic alteration. I know of no evaluation of the Sharpsburg quarry for contained sulfides. 

DEPOSITS OF PORPHYRY COPPER AFFINITY 

THE BREWER MINE AREA 

The Brewer mine, a producer of gold from about 

1828 until 1940, is in part of a much larger zone of 

highly altered copper-bismuth-tin-bearing volcanic 

rocks. The most outstanding alterations are quartzandalusite and quartz-topaz greissens. The large 

alteration zone (a minimum of 1.4 km in one dimension), the evidence for a subvolcanic origin, and the 

metal suite provide only a sketchy picture of the 

overall geology of the hydrothermal system, but 

they suggest and permit consideration of a large 

system such as Mount Pleasant, New Brunswick, and 

some of the deposits of Cornwall, England. Although 

not a typical porphyry copper system, it has some 

features in common with one. 

Gold-mining operations at the Brewer mine, near 

Jefferson in Chesterfield County, S.C. (fig. 7), at 

first by placer and later by openpit and underground, 

have been described by Leiber (1858, p. 63-68), 

Nitze and Wilkens (1896, p. 762-767), and McCauley 

and Butler ( 1966, p. 36-40). 

The Brewer mine area is in felsic volcanic rocks 

of the Carolina slate belt, close to and partly under 

the overlap of Coastal Plain strata. Arthur R. Kinkel, Jr. (written commun., 1968) described the 

country rocks in the mine as strongly silicified rhyolite, part of which is tectonic breccia, part pyroclastic breccia, and part tuff. According to Kinkel, the 

gold ore consists of silicified topazized pyritized 

rhyolite, in which local areas several centimeters 

across consist entirely of fine-grained granular pyrite. Small grains of pyrite are widely disseminated 

in the rock associated with the gold deposit and may 

constitute 2-5 percent of the rock (Pardee, Glass, 

and Stevens, 1937, p. 1058). 

Topaz was identified in the altered volcanic rocks 

of the Brewer mine by Pardee, Glass, and Stevens 

( 1937). In general appearance, the topaz-rich material here is difficult to distinguish from dense 

siliceous rocks unless the high specific gravity is 

noted, and the material was generally called flinty 

quartz or blue hornstone in the reports of earlier 

examinations. The topaz occurs as disseminated 

grains, as patches and streaks of aggregates, and as 

massive topaz. All these are made up of rounded individual grains only a few microns in diameter. 

Pardee, Glass, and Stevens (1937, p. 1062) reported 

that only a few grains had a euhedral form. I observed only rounded shapes. The identification of 

topaz in the mine led to a drilling program by the 

U.S. Bureau of Mines in 1951-52 to determine the 

extent of the topaz reserve and the possibility of the 

use of the topaz as mullite and for the production 

of calcium fluoride. The results of this exploration 

program were described by Peyton and Lynch 

(1953). The cores of the 10 holes drilled on this program, retained by the U.S. Bureau of Mines, are the 

best source of information on the nature and extent 

of the rock alteration northwest of the old mine 

workings. The locations of the holes are shown on 

figure 7. 

Compilation of the full suite of base metals identified in the mine depends mainly on old reports. 

Pardee, Glass, and Stevens (1937, p. 1058) observed 

that "small grains of enargite are sparingly scattered through parts of the rock." Other authors 

noted covellite, cassiterite, bismite, native bismuth, 

chalcanthite, and chalcopyrite, but these were not 

seen by Pardee, Glass, and Stevens (1937). Grab 

samples of pyritic rock from drill hole 1 close to the 

old open pit (Brewer pit, fig. 7) contained as much 

as 0.3 percent arsenic, 1.0 percent copper, 500 ppm 

bismuth, and 200 ppm tin (analyses performed in 

laboratories. of the U.S. Geological Survey). One 

sample in another hole near the mine contained 

0.07 percent molybdenum. 

Sulfides make up an estimated 1-5 volume percent 

of all the rock in the cores from 9 of the 10 U.S. 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E 25 

Bureau of Mines drill holes. In two cores taken near 

the old Brewer pit, average sulfide content was 

close to 5 volume percent, and in one hole (No. 1) 

the estimated sulfide content over an interval of 

33.2 m was 15 volume percent. 

No primary rock textures seem to have survived 

the rock alteration in the Brewer drill cores. Although volcanic textures have been described from 

the mine, primary textures were probably not everywhere recognizable. Kinkel (written commun., 1968) 

described a variety of breccias in the mine, and 

breccias were common in three drill holes. 

Much more neEds to be known about the detailed 

geology of the area around the Brewer mine. Little 

has been described in earlier studies except the mine 

exposures and the occurrence of gold, but we know 

that strong hydrothermal alteration has affected a 

much larger area, accompanied by introduction of 

much disseminated sulfide, trace amounts of bismuth 

and tin, and as much as 0.3 percent arsenic, 0.07 

percent molybdenum, and 1.0 percent copper. If the 

Brewer mine area is part of a large hydrothermal 

system of the Mount Pleasant type, the style of 

alteration and the associated metal suites may vary 

considerably in the different parts of a system that 

may be as large as several kilometers in each dimension. Until the perimeter of the alteration zone 

is defined, and variations in both alteration and 

mineralization style are known, the Brewer area 

cannot be said to be evaluated for its mineral 

potential. 

PROSPECTS OF COPPER AND MOLYBDENUM NOT 

INCLUDED IN THE PORPHYRY TYPE 

EASTERN HALIFAX COUNTY, NORTH CAROLINA, 

PROSPECTS 

At least three copper-molybdenum prospects in 

Halifax County, N.C., have been explored by diamond drilling (fig. 6) . 

The Moss-Richardson and Boy Scout-Jones prospects were explored by the U.S. Bureau of Mines 

in 1942-46 (Robertson, Mcintosh, and Ballard, 

1947). The Ellis prospect was explored by Perry, 

Knox, Kaufman, Inc., about 1970. Cores from the 

latter exploration have been examined by the U.S. 

Geological Survey. 

Mineralization at the Moss-Richardson and Boy 

Scout-Jones prospects is confined mostly to veins and 

is mostly near the contact between a small granitic 

body and siliceous chlorite slate, schist, and gneiss 

(Robertson, Mcintosh, and Ballard, 1947). Sparse 

disseminated sulfide also occurs in wall rocks within 

20-60 em of the veins. 

The ore minerals are molybdenite and chalcopyrite; some ferrimolybdite, chalcocite, and covellite 

are present as secondary minerals. Traces of lead, 

silver, and vanadium were detected spectrographically. The paucity of ore minerals, the seeming lack 

of extensive hydrothermal alteration, and the coarseness of the small intrusive body make it seem unlikely that these mineral occurrences have any relationship to a porphyry-type deposit, though molybdenum and copper are here associated with a felsic 

intrusive rock. 

Drilling at the Ellis prospect was mostly in metamorphosed felsic volcanic rocks and small bodies of 

alaskite. Much of the volcanic rock that was drilled 

is silicic and probably rich in potassium feldspar, 

probably as a result of hydrothermal alteration. 

Some phyllic alteration is present also. The effects 

that I attribute to hydrothermal alteration are mostly in the volcanic rocks, as is most of the visible sulfide. Some alaskite is altered and sparsely mineralized, but much is fresh and contains only traces of 

sulfide. 

Ore minerals are molybdenite, chalcopyrite, and 

scheelite; traces of lead, zinc, and bismuth are also 

present. The molybdenite and chalcopyrite are 

mainly disseminated and are probably most abundant where pyrite is locally as much as 2-5 percent. 

Some of the molybdenite and chalcopyrite are in 

films on fractures and in small veinlets. Both disseminated and fracture and vein sulfides seem to be 

more common where the quartz-potassic alteration 

is greatest. Rough visual estimates of chalcopyrite 

content indicate that of 1,003 m (3,291 ft) of core 

examined, 180 m (590 ft) probably contained more 

than 0.1 percent but less than 0.5 percent copper, 

and 18m (59 ft) contained at least 0.5 percent copper. Because of their crudeness, these estimates 

must be used with caution. No estimates were made 

for molybdenum. 

Scheelite was looked for only in relatively few 

pieces of core. The most abundant scheelite was in 

relatively unaltered laminated volcanoclastic rock, 

concentrated in a 2-mm-thick lamina and 2-cm-thick 

brecciated bed. The scheelite is probably volcanogenic, not hydrothermal, and resembles the widespread stratabound occurrences in mostly mafic 

metavolcanic rocks of Late Cambrian to Late Silurian age in Europe and Korea, as described by 

Maucher (1972). 

NEWELL PROSPECT, NORTH CAROLINA 

The Newell copper-molybdenum prospect is about 

15 km south of Concord, in Cabarrus County, N.C. 
E26 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

(fig. 6), in the vicinity of the old Dixie Queen goldcopper mine. Anomalous amounts of copper in 

stream sediments led in 1964 to exploration for copper ore. More than 760 m of drilling was performed 

in exploring an area of weakly mineralized rock near 

the old Dixie Queen mine by Bear Creek Mining 

Co., and the results of this work have been described by Worthington and Lutz (1975). Worthington and Lutz interpreted the deposit of sparsely 

mineralized rock to be a lean porphyry coppermolybdenum deposit, in part because of what they 

believe to be extensive supergene sericite in saprolite. The drill core from this exploration is now in 

the collection of the U.S. Geological Survey and I 

have examined and logged the drill core. 

The Newell prospect is in a region of gneiss and 

schist and felsic to mafic intrusive rocks generally 

known as the Charlotte belt. Country rocks at the 

prospect consist of diorite and several kinds of 

quartz monzonite (termed granite at Bogers Chapel 

by Bates and Bell, 1965) (fig. 8). Most of the mineralized rock is part of a pluton of quartz monzonite 

and alaskite .about 1.2X2.4 km (Worthington and 

Lutz, 1975, p. 4-6) in which the weak mineralization 

(0.03-0.04 percent Cu, 0.01-0.02 percent Mo) outlined by the drilling is perhaps 600 m in diameter. 

Details of the company chemical analyses of drilling samples were not sought for this study. 

Within the area of quartz monzonite and alaskite, 

metamorphosed potassium-rich granitic and rhyolitic rocks occur in several places, but I do not know 

their relationship to mineralization. Examination of 

thin sections shows that some of these rocks contain 

quartz, microcline, and biotite as major minerals, and 

plagioclase as only a minor constituent. In other 

specimens, part of the microcline seems to have been 

deposited as a late rim on the outside of plagioclase 

grains, suggesting potassium enrichment of the 

quartz monzonite toward the end of crystallization 

of the pluton. I observed no potassic feldspar that 

looks like the product of hydrothermal potassic alteration at typical porphyry copper deposits. The 

analyses for K20 in the rocks at the N ~well prospect 

range from 1.8 to 6.8 percent (table 6). I identified 

quartz-sericite and argillic alteration only in some 

very thin zones along fractures and veins. 

The origin of the sulfides is not clear. There is 

no evidence for hydrothermal mineralization since 

the time of metamorphism. If some hydrothermal 

alteration took place before metamorphism, the 

metamorphic grade is high enough that the fabric 

may have been considerably altered and perhaps the 

origin disguised. 

The association with a felsic pluton, the widely 

disseminated enrichment by potassium, copper, and 

molybdenum, and the quartz-sericite and argillic alterations are features characteristic of a porphyry 

alteration system, but the scantness of metal enrichment and quartz-sericite alteration makes the 

classification of the Newell prospect as a porphyry 

rather problematical. A zone of sericitic alteration 

based on clays that developed during formation of 

saprolite, as described by Worthington and Lutz 

(1975), does not, in my opinion, increase the likelihood of the prospect being of the porphyry type. 

Until more information about the geology of the 

Newell prospect is available, I prefer to not include 

the prospect with deposits of the porphyry type. 

The interpretation of the origin of mineralization 

at the Newell prospect is more important than just 

for understanding of that prospect alone. It lies 

outside the Carolina slate belt, the area I think to be 

of highest potential, and, if the prospect is classified 

as one of the porphyry copper type, then the potential area for the occurrence of lower Paleozoic porphyry copper deposits is larger than I have postulated. There seems to be no good reason to change 

the prospecting model on the basis of present knowledge of the Newell prospect. 

SUMMARYANDCONCLU~ONS 

Past discoveries of -porphyry copper deposits in 

eastern North America indicate that there is potential for finding new deposits of exploitable size, although the potential is considerably lower than in 

younger, less eroded, and less deformed porphyrybearing regions. 

I propose that porphyry-type mineralization in 

the New England-Maritime Provinces area is related to a northwest-dipping paleosubduction zone 

marking the line of collision of a European-African 

continent with North America during the Devonian 

Period. The collision line is near the Maine-New 

Brunswick coast; the most favorable structural 

zone for the occurrence of related porphyry copper 

deposits is parallel to the collision line and 130-320 

km northwest of it, especially in western New 

Hampshire, northwestern Maine, and southeastern 

Quebec. 

The upper Precambrian or lower Paleozoic volcanic 

piles included in the Carolina slate belt are proposed 

as favorable prospecting areas. Few subvolcanic 

intrusive rocks have been delineated in the metavolcanic rocks, but the geologic conditions are not favorable to easy recognition of such rocks. I believe 

that further detailed mapping and geochemical 
PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES 

0 

0 

.5 2 KILOMETERS 

Y2 1 MILE 

CONTOUR INTERVAL 20 FEET 

NATIONAl GEOOETIC VERTICAL DAlUM Of 1929 

EXPlANATION 

3 o Diamond drill hole-Numbers are keyed to table 6 

- Contact-Approximately located 

FIGURE 8.-General geologic map of the Newell prospect, Cabarrus County, N.C., showing the locations 

of the Newell mine shaft (old Dixie Queen mine shaft) and the exploration drill holes; modified from 

Worthington and Lutz (1975). The Newell mine is about 15 km south of Concord, N.C. 

E 27 
TABLE 6.-Chemical analyses of 11 samples of drill core from the Newell prospect, Cabarrus County, N.C. 

I HP~ult~ in pcrct•nt t•xccpt a~ indicated. UUJiid-rock anal.v~t>~ (oxidP~ a111l ~ulfurl hy 1'. L. D. J•:JuwrP. llt•l•Wkiah Hmith, .J. L. Glt•uu. and .TamP~ KPI~P.L Bi, l\lo, and W h.,. i~oto)H' dilution 

~peetrophotometrie methods; CU by wet chemh;try; analy~t~. 1•:. G. Lillie and Lt~tlll~ l\lt•i] 

W178523 W178524 W178525 W178526 W178527 W178528 W178529 W17llfi3U W17!lfi31 W17!lfi32 W17!lfi33 

Hole 3 Hole 4 Hole 5 Hole 6 Hole 7 Hole 10 Hole 10 Hole 10 Hole 11 Hole 15 Hole 16 

(45.1-46.0 m) (44.5-45.1 m) ( 26.5-27.4 m) (25.6-26.8 m) (17.0-19.2 m) (24.4-26.8 m) (43.6-46.3 m) (54_3-57.3 m) (32.6-34.4 m) (19.5-22.3 m) (37.2-39.9 m) 

felsic metadiorite alaskite metadiorite diorite quartz alaskite alaskite gneissic greenstone hornblendemetavolcanic monzonite quartz breccia plagioclaserock monzonite quartz schist 

SiO~----------- 68.2 60.7 70-3 65_0 57.4 70.3 70.3 68.9 71.1 52.4 52.2 AbOa __________ 14.7 14.4 13.9 14.5 14_0 15.4 14.5 14_8 14.2 15.7 16.0 Fe~Oa __________ 1.3 1.7 2.3 2.5 4.2 1.7 1.4 2.2 1.2 4.7 3.2 FeO ___________ 1.6 3.2 1.2 3.0 5.7 _52 1.0 1.2 1.4 5.0 5.9 MgO ___________ 1.3 3.8 .50 2.2 3.9 .42 .33 .25 .62 5.2 6.2 CaQ ___________ 2_5 5.0 .90 4.1 6.9 .73 .53 _54 2.3 7.9 8.7 Na~o __________ 3.3 3.0 3.2 3.6 2.7 3.7 3.1 3.6 3.9 2.7 2.8 

K20-----------· 4.9 4.9 5.8 2.4 1.8 5.8 6.8 6.3 3.1 2.7 1.8 H~o· ___________ 1.1 .93 .72 1.0 1.0 .60 .44 .50 .73 1.7 1.2 H~o- ___________ .26 .27 .21 .23 .11 .40 .32 .37 .11 .25 _15 

Tio. ___________ .30 .77 .22 .66 .95 .22 .18 .14 .36 .69 .48 

P~OL---------- .26 .69 .10 .24 .38 .07 .17 .08 .14 .17 -16 MnO ___________ .04 .10 .03 .10 .17 .00 .00 .05 .07 .14 .14 

C02------------ .11 .12 <.05 .35 .11 <.05 <.05 .21 .39 .22 .06 

TotaL ___ 100 100 99 100 99 100 99 99 100 99 99 

s ____ (percent)- .33 .21 .95 .53 .44 .13 .44 .56 .10 1.0 .89 

BL ___ (ppm) ___ .076 _096 .22 .089 .31 .070 .12 .093 .050 .15 .13 

Cu ____ (ppm) ___ 220 200 500. 360. 260. 480. 350. 320. 62. 510. 360. 

Mo ____ (ppm) ___ < .25 1.3 300. 18. 3.4 45. 110. 110. .45 12. 43. 

W ____ (ppm)---· <1. L6 1.5 2.6 2.2 <1.0 1.0 3.6 < 1.0 < 1.0 < 1.0 

tr.:l 

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PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E29 

sampling will locate more mineralized subvolcanic 

felsic intrusive bodies, and that some of them have a 

reasonable chance of being exploitable. 

The extensive Pleistocene glacial drift on Precambrian rocks in Minnesota, Wisconsin, and Michigan handicaps prosp2cting for porphyry-type deposits in the covered areas to the extent that it does 

not seem advisable at the present time. However, 

if exploration for other types of mineral deposits 

reveals evidence for deposits of the porphyry copper 

type, this evidence should not be overlooked. 

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E30 GEOLOGY AND RESOURCES OF COPPER DEPOSITS 

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PORPHYRY COPPER-MOLYBDENUM DEPOSITS, EASTERN UNITED STATES E31 

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*U.S. GOVERNMENT PRINTING OFFICE: 1978 0- 281-359/139 

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