Geology of the Juazohn Quadrangle, 

Liberia 

By RUSSELL G. TYSDAL 

GEOLOGICAL SURVEY BULLETIN 1448 

Prepared in cooperation with the Liberian 

Geological Survey under the sponsorship 

of the Agency for International 

Development_, U.S. Department of State 

This report describes the geology shown 

on U.S. Geological Survey Miscellaneous 

Investigations Map 1-779-D 

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

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

W. A. Radlinski, Acting Director 

Library of Congress Catalo·ging in Publication Data 

Tysdal, Russell G 

Geology of the Juazohn quadrangle, Liberia. 

(Geological Survey bulletin ; 1448) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1448 

1. Geology-Liberia-Juazohn. I. Liberia. Geological Survey. II. Title. 

III. Series: United States. Geological Survey. Bulletin ; 1448. 

QE75.B9 no. 1448 [QE339.L5] 557.3'08s [556.66'2] 77-608150 

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

Washington, D.C. 20402 

Stock Number 024-001-03063-2 
CONTENTS 

Abstract -----------------------------------------------------------

Introduction -------------------------------------------------------

Location -------------------------------------------------------

Topography ----------------------------------------------------

Climate --------------------------------------------------------

Access ---------------------------------------------------------

~apping procedure ---------------------------------------------

Previous work --------------------------------------------------

Acknowledgments -----------------------------------------------

Geology ------------------------------------------------------------

~etamorphic rocks ---------------------------------------------

Granodiorite gneiss -----------------------------------------

Granitic gneiss ---------------------------------------------

Quartz diorite gneiss -------------------------------------- Calc-silicate gneiss ______ ..:. __________________ ------------ ___ _ 

Leucocratic gneiss ______________ ---------------------------

Composite gneiss -------------------------------------------

Composite gneiss unit 2 -------------------------------

Composite gneiss unit 4 --------------------------------

Schist ------------------------------------------------------ Amphibolite ______________________________________ ----------

Iron-formation ---------------------------------------------

~anganese-formation --------------------------------------

Igneous rocks --------------------------------------------------

GranUic rocks ---------------------------------------------

Diorite -----------------------------------------------------

Dioritic rocks ----------------------------------------------

Syenite and trachyte --------------------------------------

lJltramafic rocks -------------------------------------------- Diabase 

~etamorphism -----------------------------------------------------

Structure ---------------------------------------------------------- Foliation and bedding ------------------------------------------

Folds ----------------------------------------------------------

Faults --------------------------------------------------------- Northeast-trending faults ----------------------------------

Northwest-trending faults ----------------------------------

lJnconformities -------------------------------------------------

Age provinces ------------------------------------------------------

~ineral resources ----~----------------------------------------------

References cited _____ ---------- ____ --------------------------------

III 

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IV CONTENTS 

ILLUSTRATIONS 

Page 

FIGURE 1. Index map of Liberia showing the area of Juazohn quadrangle and location of principal towns and rivers -- 3 

2. Generalized geologic map of the Juazohn quadrangle ____ 6 

3. Generalized geologic map showing distribution of amphibolite, iron-formation, and manganese-formation in the 

Juazohn quadrangle -------------------------------- 21 
GEOLOGY OF THE JUAZOHN QUADRANGLE, 

LIBERIA 

By RussELL G. TvsoAL 

ABSTRACT 

The Juazohn quadrangle is underlain almost entirely by Precambrian 

crystalline rocks, both metamorphic and igneous. The predominant metamorphic rock is gneiss of quartz diorite composition, but granodiorite 

gneiss, amphibolite, quartzite, micaceous and pelitic schist, calc-silicate 

gneiss, and manganese-formation also are present. Iron-formation is present 

in narrow linear bands throughout the central part of the quadrangle. Most 

of the metamorphic rocks are probably of metasedimentary origin. The 

metamorphic grade is of the amphibolite facies. 

Igneous bodies include diorite batholiths in the western part of the quadrangle and a few small granite and granodiorite intrusive bodies elsewhere. 

An ultramafic intrusive body of unknown age is present near Juazohn and 

is composed largely of serpentinized dunite. Associated rocks include syenitic 

and dioritic rocks. Diabase dikes of probable Jurassic age trend northwestward across the quadrangle. 

Structural features include at least four major northeast-trending faults, 

three of which have wide zones of shearing along them. Northwest-trending 

faults in places offset the northeast faults, locally are associated with narrow shear zones, and many have been intruded by diabase. Isoclinal folds 

are common, but much of the itabirite-bearing central part of the province 

is characterized by broad open undulatory folds. Part of the north-central 

area of the quadrangle is marked by rocks having low dips that may be 

indicative of an unconformity. 

Iron-formation of the Putu Range constitutes the major deposit of potential economic importance in the quadrangle. Small quantities of gold have 

been won locally. 

INTRODUCTION 

A cooperative program for reconnaissance study of the geology 

of Liberia was carried out jointly by the Liberian Geological 

Survey (LGS) and the U.S. Geological Survey (USGS) from 

June 1965 through June 1972. The project was sponsored by the 

Ministry of Lands and Mines of the Republic of Liberia and the 

Agency for International Development, U.S. Department of State. 

1 
2 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

Systematic quadrangle mapping of Liberia began in late 1970 

when adequate base maps, prepared during the project, became 

available. The geologic map of the Juazohn quadrangle (Tysdal, 

1977b) was compiled from data acquired by field mapping, largely done from December 1971 to April 1972; from photointerpretation; from data supplied by colleagues in the cooperative program; from data supplied by private company geologists; and 

from interpretation of aeromagnetic, aeroradiometric, and gravity 

data obtained from geophysical surveys flown by Lockwood, Kessler, and Bartlett Co. under contract to the Government. of 

Liberia. This bulletin, in conjunction with the bulletin on the 

adjoining Buchanan quadrangle (Tysdal, 1978), describes the 

geology of the structurally and metamorphically critical area 

that spans the boundaries of the Liberian, Eburnean, and PanAfrican age provinces. 

LOCATION 

The Juazohn quadrangle is in the southeastern part of Liberia, 

West Africa (fig. 1), and its borders are at lat 5° and 6° N. and 

long 7°20' and 9°00' W. It encompasses about 18,540 km2 (about 

7,416 mi2 ) and makes up about 19 percent of Liberia. 

TOPOGRAPHY 

Much of the eastern and western thirds of the Juazohn quadrangle is gently undulatory topography ranging from about 75 to 

200 m (250 to 650 ft) above sea level. Local relief is as much as 

25 m (82 ft), but is commonly less. The central part of the 

quadrangle is higher and hilly, culminating in Jide Mountain at 

more than 800 m (2,600 ft) above sea level. Local relief in the 

central area commonly reaches 100 m (300 ft) or more. 

Details of topography and culture are shown on Miscellaneous 

Investigations Map I-779-A (U.S. Geological Survey-Liberian 

Geological Survey, 1973). 

CLIMATE 

The area receives more than 250 em (100 in) of rainfall per 

year, chiefly from April to'November, and the area is covered by 

dense rain forest. Streams and rivers are in flood stage during 

the rainy period, and the laterite-surfaced roads are at times 

nearly impassable. Fieldwork is limited mainly to the Novemberthrough-March dry period. Temperatures are commonly in the 

range of 80° to 85°F., though they may drop to the upper 70's 
go 

so 

70 I 

INTRODUCTION 

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FIGURE 1.-Index map of Liberia showing the area of Juazohn quadrangle 

and location of principal towns and rivers. 

during part of the rainy season and at night during the dry 

season. 

ACCESS 

Access by motor vehicle was generally limited to two main 

laterite-surfaced roads at the time the work was done. One, in the 

western part, extends southwesterly from Zwedru through Babu, 

Pyne Town, Juazohn, and on to Greenville at the coast in the 
4 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBE~IA 

adjacent Buchanan quadrangle (fig. 1). The other extends about 

south from Babu to Kahnwia, thence southeasterly to Watake, 

and into the Harper quadrangle, terminating at the coast in the 

city of Harper. Many short temporary logging roads locally 

branch from the main roads. 

Rock outcrops are sparse along the roads owing to tropical 

weathering that has produced thick laterite and saprolite. Observations of saprolite in road cuts provided many structural data 

and limited petrographic data. Certain rock types, such as quartzite, schist, amphibolite, diabase, iron-formation, and pegmatite, 

can be identified from saprolite quite readily (vVhite, 1971). 

Extensive areas of the quadrangle were traversed along footpaths, particularly by geologists of the Muller Co., where sporadic 

outcrops are found. Thus a major effort of USGS-LGS geologists 

was to traverse the larger rivers where rocks are exposed best and 

weathered least. Traverses were made by rubber boats down parts 

of the Cavalla, Dube, Grand Cess, Dugbe, Sehnkwehn, and Sino 

Rivers (fig. 2). 

Several airstrips in the western part of the quadrangle were 

used in gaining access to the interior. However, large parts of 

the Juazohn quadrangle are uninhabited and are thus not readily 

accessible. 

MAPPING PROCEDURE 

Complete aeromagnetic and aeroradiometric coverage of Liberia 

was flown by the Lock~ood, Kessler, and Bartlett Co. under 

contract to the Liberian Government. Extensive use was made of 

the magnetic map of the J uazohn quadrangle (W otorson and 

Behrendt, 1974) in compiling the geologic map of the quadrangle 

(Tysdal, 1977b). The radiometric map (Behrendt and Wotorson, 

1974a) was not nearly as useful. Interpretations based on these 

data are indicated on the map (Tysdal, 1977b). 

Aerial photographs (1 :40,000 scale) for about the western 

third and the southern fourth of the quadrangle were taken between 1967 and 1969. Most of the remaining area is covered by 

photographs taken in the early 1950's, but many of these are 

practically unusable for photointerpretation because of cloud 

cover and poor quality. The newer photographs were used extensively to delineate structures; such delineations were appropriately indicated on the geologic map. 

Field observations were plotted on "form lit::J.e" base maps or 

aerial photographs at a scale of 1: 40,000. These data were compiled on a base map at a scale of 1: 125,000, together with photo-
INTRODUCTION 5 

interpretation data, geophysical interpretation data, and field 

data from other sources. The final geologic map was compiled at 

1 :125,000 scale from these data for publication at 1:250,000 

scale ( Tysdal, 1977b) . 

PREVIOUS WORK 

Many workers have studied rocks in the Juazohn quadrangle 

and are noted in the text. The more comprehensive studies are 

mentioned here. Sherman1 (1947) made the first compilations and 

descriptions of mining properties in eastern Liberia. Jan Offerberg (written commun., 1955), working for the Liberian-American Swedish Minerals Co. (LAMCO), produced the first detailed 

description of itabirite and iron silicate rocks in Jide Mountain 

of the Putu Range. The German-Liberian Mining Co. 

(DELIMCO) 2 made a detailed study of Jide Mountain, and 

on the basis of extensive drilling, tunneling, and geologic mapping, 

produced geologic maps and cross se,ctions. 

The Diamond Mining Corp. of Liberia (DMCL) made reconnaissance studies of heavy minerals of the area west of the 

Babu-Pyne Town-Juazohn motor road, an area drained mainly by 

tributaries of the Sehnkwehn River. Results of the DMCL heavymineral studies are documented only in part.3 4 

The l\!Iiiller Co. undertook extensive geologic traverses throughout the J uazohn quadrangle as part of a large mineral exploration 

program encompassing the eastern part of Liberia. This work 

resulted in 14 unpublished reports and many maps and is summarized in part in a very condensed report of Griethuysen 

(1971). The MUller data were used extensively in compilation 

of the geologic map of the Juazohn quadrangle (Tysdal, 1977b) 

and in this report. Preliminary interpretations of the aeromagnetic and aeroradiometric maps of the Juazohn quadrangle were 

made by Behrendt and Wotorson (1974a, b) and Wotorson and 

Behrendt ( 197 4) . 

1 Sherman, Arthur, 1941, Mining possibilities in eastern Liberia : Liberia Bur. Mines 

and Geology, unpub. rept. on file with the Liberian Geolog-ical Survey, Monrovia, Liberia. 

2 German Liberian Mining Company (DELniCO), 1971, Report of the research works, 

Putu Range: Monrovia, Liberia, unpub. rept., 10 p., on file with the Liberian Geological 

Survey, Monrovia, Liberia. 

a Leuria, Basil, 1966, Quarterly report, December 1, 1965-February 28, 1966 : Diamond 

Mining Corp. of Liberia, unpub. rept .. 9 p., on file with the Liberian Geological Survey, 

:\Ionrovia, Liberia. 

4 Leuria, Basil, 1966, Quarterly report, March 1-:\Iay 31, 1966: Diamond Mining 

Corp. of Liberia, unpub. rept., 6 p., on file with the Liberian Geological Survey, 

Monrovia, Liberia. 
5000'1 Pl•oim"''' ""' boo"'"'"u"" I 

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EXPLANATION DESCRIPTION OF MAP UNITS 

CORRELATION OF MAP UNITS 

[3§ 

Stratigraphic succession not implied 

for the following units 

Plutonic 

igneous 

rocks 

I JURASSIC 

AGE 

UNKNOWN 

~~ I Jurassic dike 

0 Diabase dike 

0 Syenite 

0 Diorite 

0 Dioritic rocks 

0 Granitic rocks 

PRECAMBRIAN 8 Ultramafic rocks 

Metamorphic 

rocks 

PREPARED BY THE U.S. GEOLOGICAL SURVEY AND THE LIBERIAN 

GEOLOGICAL SURVEY UNDER THE JOINT SPONSORSHIP OF THE 

GOVERNMENT OF LIBERIA AND THE AGENCY FOR INTERNATIONAL 

DEVELOPMENT, US. DEPARTMENT OF STATE 

0 Iron-formation, silicate facies 

0 Iron-formation, oxide facies (itabirite) 

B Amphibolite 

8 Schist 

B Mica schist 

~ Composite gneiss unit 2 

FIGURE 2.-Generalized geologic map of the Juazohn quadrangle, 

B Composite gneiss unit 4 

0 Leucocratic gneiss 

~ Calc-silicate gneiss 

I gndq1 I Quartz diorite gneiss unit 1 

I gndq21 Quartz diorite gneiss unit 2 

~ Granitic gneiss 

I gngd I Granodiorite gneiss 

Contact 

Fault 

Thrust fault, sawteeth on upper plate 

--:::: Fault zone or shear zone -

---1- Antiform, showing trace of crestal 

plane 

-+- Synform, showing trace of trough 

plane and direction of plunge 

Liberia. 

-z 

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8 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

ACKNOWLEDGMENTS 

Many people have contributed to the compilation of the geologic 

map of the J uazohn quadrangle, and the areas each person traversed are shown on the responsibility diagram of the geologic 

map (Tysdal, 1977b). Fieldwork by personnel of the Liberian 

Geological Survey includes that of M. W. G. Baker, Geologist and 

Deputy Director of the Liberian Geological Survey; Jenkins Dunbar, Edward Philips, and Thomas Sherman, Geologists; and John 

Carr and Joseph Flomo, field assistants. Field traverses by U.S. 

Geological Survey personnel, in addition to those of 'the author, 

were made by George 0. Bachman, Robert L. Earhart, Philip T. 

Hayes, Thomas D. Hessin, Joseph M. Hoare, George C. Simmons, 

and Richard W. White; Roberts M. Wallace made a preliminary 

interpretation of the Juazohn aerial photographs. Brian Micke, 

U.S. Peace Corps, also made several geologic traverses. Many 

observations along the north-trending part of the Cavalla River 

were made previously by geologists working for the Ivory Coast; 

they are credited in the text. 

The hospitality of DELIMCO, National Christian Assemblies 

Missions, V ANPLY Logging Co., Maryland Logging Co., East 

Asiatic Logging Co., a CARE project, and assistance of Peace 

Corps volunteers made logistics and fieldwork less difficult. Local 

officials and townspeople· were ·very courteous and helpful in 

support of fieldwork in the rain forest of Liberia. 

GEOLOGY 

The Juazohn quadrangle forms part of the Guinean shield of 

West Africa and is made up largely of Precambrian igneous and 

metamorphic rocks. Exceptions are mainly diabase dikes of probable Jurassic age, laterite, canga, and young unconsolidated 

deposits. Most common are gneiss of quartz diorite composition 

with lesser granodiorite gneiss, schist, amphibolite, iron-formation, and dioritic to granitic rocks. Minor amounts of other rocks 

are also present. 

The classification of igneous and metamorphic rocks used here 

is, as far as possible, based on igneous composition as follows: 

Igneous rock 

Granitic, undivided 

Granite ----------------

Granodiorite ---------- Dioritic, undivided ______ _ 

Quartz diorite ---------

Diorite ----------------

~Ietamorphic rock 

Granitic gneiss -------

Granite gneiss ____ _ 

Granodiorite gneiss _ 

Diorite gneiss _______ _ 

Quartz diorite gneiss 

Diorite gneiss _____ _ 

Percent Percent 

potassium feldspar quartz 

of total feldspar in rock 

>10 

>50 

>10<50 

<10 

<10 

<10 

>10 

>10 

>10 

>10 

<10 
GEOLOGY 9 

An igneous origin is not necessarily implied for the metamorphic rocks classified according to this scheme. 

Rock samples were collected from more than 50 percent of the 

outcrops visited (about 1,300 stations) during field reconnaissance 

by members of the USGS-LGS group, and many of the samples 

were slabbed, etched with hydrofluoric acid, and stained with 

sodium cobaltinitrite for detection of potassium feldspar. Thus 

the percentage of potassium feldspar was determined fairly 

accurately. Thin sections from some samples were examined, but 

systematic detailed thin-section studies were not made. 

Rocks that do not fit the above scheme are noted by specific 

compositional names (such as manganese formation, ultramafic 

rocks) or, where little information is available, by a general name 

(such as leucocratic gneiss). Composite units are designated for 

areas containing combinations of specific rock types that cannot 

be separated appropriately at map scale. 

Systematic classification according to the above scheme has 

presented difficulties because data came from many sources and 

were collected by many geologists among whom geologic concepts 

and technical terminology varied widely. Because the classification was deemed essential, considerable effort was expended to 

reconcile the difficulties. 

METAMORPHIC ROCKS 

Metamorphic rocks make up by far the bulk of the rocks in the 

Juazohn quadrangle. The stratigraphic order of the units is unknown, and they are discussed in this section according to rock 

type. 

GRANODIORITE GNEISS 

Medium-grained hypidiomorphic granodiorite gneiss, varying 

locally to quartz diorite in composition, distinguishes a unit north 

of the Putu Range. Foliation in the gneiss is commonly faint. It 

is defined by oriented biotite (3 to 10 percent) and locally tabular 

quartz grains and by dips at moderate angles. Minor mica schist 

and hornblende amphibolite are also present, and small granitic 

intrusive bodies as much as 1.5 km ( 1 mi) across are present in 

the western part of the unit. Near some of the granite bodies, the 

gneissic country rock shows a gradual change in composition, 

over tens of meters, from quartz diorite gneiss (or granodiorite 

gneiss having low potassium feldspar content) to complexly 

folded granodiorite having moderate to high potassium feldspar 
10 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

content, and locally containing pegmatite. The granite itself forms 

abrupt hills, is poorly exposed, and is mostly covered by a thick 

lateritic cap. At other places, country rock of gneiss, schist, and 

amphibolite is truncated abruptly by granite. 

The southeastern and southwestern margins of the unit are 

marked by sharp magnetic contrasts (Wotorson and Behrendt, 

197 4), and both are believed to be fault controlled. At the southeastern margin, the generally diffuse, broad, flat magnetic pattern 

of the granodiorite gneiss is terminated abruptly along a northwest-trending linear magnetic break that is itself marked by 

magnetic and aerial photography patterns typical of diabase dikes. 

Hence, the linear element is probably a fault intruded by diabase. 

The position of the northwestern margin is in doubt, as diagnostic data are lacking.· 

The contact of the granodiorite gneiss with schist to the northeast is located only ·approximately. Possibly these are parts of 

one rock unit that has undergone different degrees of metamorphism. Specifically, the schist unit along strike in Ivory Coast 

(Papon, 1973, p. 67) is described as largely schistose, whereas 

the schist in Liberia seems to be transitional from schist to 

gneiss. 

The magnetic pattern (Wotorson and Behrendt, 1974) in the 

northern part of the gneiss unit is characterized by linear highs 

and lows and is similar to that of schistose rocks to the northeast. Southwestward, however, the magnetic pattern becomes 

more diffuse, broad, and flat. It thus appears to be taking on the 

characteristics of a pattern more typical of igneous rocks, like 

those in the western part of the quadrangle. Perhaps the faintly 

foliated gneiss was formed by recrystallization during potassium 

metasomatism associated with formation of the granitic bodies. 

GRANITIC GNEISS 

Granitic gneiss in the southeastern part of the quadrangle 

underlies a small area terminated on the east by the Dube shear 

zone. The unit is considered to correlate with granitic gneiss 

(described by Brock, Chidester, and Baker, 1977) cropping out 

in the Harper quadrangle to. the south. It is weakly foliated and 

is mainly of granodiorite composition but locally ranges from 

quartz diorite to granite in composition; intercalated amphibolite 

is present locally. 

In the Harper quadrangle, the unit has a distinct magnetic pattern which is less distinct in the Juazohn quadrangle. This, 

coupled with limited field data for the unit in the Juazohn quad-
GEOLOGY 11 

rangle, permits only approximate location of the boundaries. The 

unit does not have a distinctive radiometric pattern. 

QUARTZ DIORITE GNEISS 

Quartz diorite gneiss forms two mappable units in the Juazohn 

quadrangle; they are areally extensive, form few outcrops, and 

contain a variety of associated rocks, most of which are too small 

to map separately. 

Quartz diorite gneiss unit 1 crops out west of the Dube shear 

zone in a hilly area of few exposures. Most of the rocks observed 

are hypidiomorphic granular quartz diorite gneiss in which foliation is defined by oriented biotite (and locally hornblende) ; 

migmatitic rocks are also common. Biotite-quartz schist and interbedded quartzite were noted at two localities, and small granitic 

to dioritic bodies are present locally. 

The gneissic rocks in some areas have complex folds and 

segregations of quartz-rich pods and layers that weather differentially and give a ropy appearance to the outcrop. The mineral 

grains of these rocks are commonly fractured, and plagioclase 

porphyroblasts have distorted twin planes. 

The migmatitic rocks are agmatite (Mehnert, 1968), with fragments of quartz diorite gneiss and locally dark amphibolite-biotite 

rock caught up in a swirly matrix of dark-grey medium- to coarsegrained gneiss of granodiorite composition. At a quarry 3 km 

(2 mi) northwest of the Maryland Logging Co. camp, the quartz 

diorite gneiss has coarse-grained granitic texture and composition, 

apparently because of impregnation with potassium. The coarsegrained rock probably represents a zone of melting, as xenoliths of 

amphibolite and the quartz diorite gneiss are present in it. 

Quartz diorite gneiss unit 2 is present over much of the northwestern part of the quadrangle and along part of the Sino River. 

From the Sino River area to the Sehnkwehn River and northwest 

to the Cestos batholith, the unit is chiefly melanocratic and fine to 

medium grained. Biotite is present in some of the rocks, but hornblende is the common mafic mineral and typically makes up to 

15 to 25 percent of the rock. Northwest of the southeast-flowing 

length of the Sehnkwehn River, hornblende commonly constitutes 

20 to 35 percent of the rock. These rocks become coarse grained 

near the margins of large diorite plutons in the area. 

Much of the unit is conspicuously banded because of concentration of mafic minerals in some layers. Thin layers of amphibolite 

or hornblende quartz diorite alternate with layers of leucocratic 

biotite quartz diorite. Leucocratic biotite quartz diorite gneiss to 
12 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

granodiorite gneiss in layers that are tens to hundreds of meters 

across is interstratified locally with the hornblendic rocks. 

In the central part of the area underlain by quartz diorite 

gneiss unit 2, the abundance of hornblende decreases; in the 

northern part, biotite becomes the chief mafic mineral, commonly 

constituting 10 to 20 percent of the rock. The gneiss in the 

northern part is typically medium-grained, medium- to lightcolored rock of quartz diorite to granodiorite composition. Banding is less common than to the south, and foliation is defined by 

oriented biotite. Schist is interbedded locally with the gneiss, 

but most of it was observed in saprolite, and its composition is 

uncertain. Garnet is common in much of the gneiss. Metasedimentary manganese-formation (described separately) and finegrained quartzite are present in the central part of the unit, as 

are several small granitic intrusive bodies noted by the Muller 

Co. 5 Amphibolite units (described separately), many too thin 

to map separately, are common throughout the quartz diorite 

gneiss unit. 

CALC-SILICATE GNEISS 

Calc-silicate gneiss was noted in only one general area in the 

Juazohn quadrangle, along the main road about 20 km ( 12.5 

mi) southwest of Pyne Town. It forms low rounded hills and, 

locally, resistant outcrops, but the best exposures are in a roadmetal quarry about 1 km (0.6 mi) northwest of Shadi. The gneiss 

at the quarry is banded; layers a few meters thick have different 

concentrations of mafic minerals. The Muller Co.lj has described 

the gneiss components as mainly hornblende and prehnite, and 

lesser altered pyroxene, calcite, quartz, epidote, micas, apatite, 

serpentine, and leucoxene. Pegmatite dikes cut the gneiss, and 

pegmatite is also present adjacent to the necked areas of boudins. 

On the flank of a hill about 5 km (3 mi) north of Shadi, calc-silicate gneiss consists of alternating centimeter-thick bands of hornblende-poor and hornblende-rich calc-silicate rock. The hornblende 

content gradually increases up the ridge, and the rock is transitional into amphibolite. A granodiorite dike (dated as 2,140 m. y. 

old by Hurley and others, 1971) intrudes the gneiss unit. 

s ~fiiller Compan~·. 1969, Exploration Liberia. 7th progre>;l' report. ~Iarch-~Iay 1969: 

The Hague, Netherlands, ~Iiiller Co.. unpub. rept.. 11 p., on file with the Liberian 

Geological Survey, ~Ionrovia, Liberia. 

e Miiller Company, 1971, Exploration Liberia, final report, .Tul~· 1967-Julr 1971: Tbe 

Hague, Netherlands, ~Iiiller Co., unpub. rept., 8 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
GEOLOGY 13 

LEUCOCRATIC GNEISS 

The term leucocratic gneiss is used for light-colored rock for 

which only relatively few observations exist, or for rocks that 

were described previously in textural terms only (such as migmatite). In the Juazohn quadrangle, three areas of leucocratic 

gneiss were mapped: an area east of the Dube shear zone in the 

easternmost part of the quadrangle, an area along the Cestos 

River in the northwesternmost part of the quadrangle, and a large 

area in the central part of the quadrangle. 

East of the Dube shear zone leucocratic gneiss and minor associated schist crop out. The gneiss is chiefly banded mediumgrained rock of biotite quartz diorite composition. Less common 

leucocratic gneiss ranges from muscovite granodiorite to granite 

in composition and locally contains minor biotite. Quartz typically 

constitutes 20 to 30 percent of the gneiss but may reach 50 percent. Heavy minerals obtained from streams in the leucocratic 

gneiss area include mainly columbite-tantalite, rutile, and magnetite.7 

Along the Cestos River, leucocratic gneiss ranges from granodiorite to granite in composition and contains both biotite and lesser muscovite. Pegmatites contain abundant muscovite. Many of 

these rocks are sheared. 

The central part of the quadrangle contains the largest area of 

leucoc.ra.tic gneiss (fig. 2). The unit is composed of a variety of 

rocks, but itabirite, described separately, is distributed abundantly 

throughout most of it so as to form a distinct itabirite province. 

In the northeastern part of the itabirite province, rocks observed 

along the Cavalla and Dube Rivers are mostly leucocratic, fineand medium-grained biotite quartz diorite gneiss. and biotite 

granodiorite gneiss containing less than about 20 percent potassium feldspar. Good foliation results from the parallel orientation 

of biotite. A few of these rocks are banded, as more biotite is 

present in some layers than in others. Biotite constitutes about 

5 percent of most rocks and is more or less evenly distributed. 

Gneiss of granite composition is common near composite gneiss 

unit 4 in the northeasternmost part of the quadrangle, is medium 

grained, and contains biotite and locally muscovite. Some of it 

is weakly foliated, but much of it is massive and may represent 

small granite bodies. Pegmatite dikes were observed locally. 

Granitic gneiss, granite, and pegmatite also crop out along the 

7 Miiller Company, 1968, Exploration Liberia, ~rd progrel's report, April-June 15, 

1968: The Hague, Netherlands, l\Iiiller Co .. unpub. rept., 8 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
14 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

Dube River close to the northwestern border of the map unit. In 

one particular area northeast of the river, an irregularly shaped 

radiometric anomaly appears to interrupt the pattern of the surrounding rocks and is possibly caused by moderately potassic 

granitic intrusive rocks. The Dube River, which el,sewhere trends 

southeastward, flows northeastward along about an 8-km- (5-mi-) 

long quarter-circle section of arc skirting the southern margin of 

the anomaly before completing the semicircular diversion of its 

course. Strikes along the river commonly trend northeastward, 

but along the arcuate stretch of the, river, the strike direction is 

north to about N. 20° W. Dips in this area are at low angles to 

the northeast-toward the anomaly. Thus the structure and 

drainage also are influenced by the rocks causing the radiometric 

anomaly. 

Amphibolite forms tabular bodies at several places along the 

Dube River, and the MUller Co. 8 has noted them elsewhere in the 

northeastern half of the province. Some contain a few percent 

clinopyroxene, but most are hornblende-plagioclase-garnet rocks. 

Rocks associated with itabirite in the Juazohn area are hornblende quartz diorite gneiss and leucocratic biotite quartz diorite 

to granodiorite gneiss. Much of the gneis~ is banded, but in some, 

particularly the hornblende quartz diorite gneiss, foliation is faint. 

The hornblende content is commonly 20-30 percent, but reaches 

40 percent in some rocks. Amphibolite is fairly common in the 

area. 

In the south-central part of the itabirite province, the gneisses 

are largely banded and are of biotite quartz diorite composition. 

Granitic intrusive rocks form small hills about 30 to 100 m ( 100 

to 300 ft) high along the main road north from Kahnwia for at 

least 20 km (12.5 mi). Data of the MUller Co. 9 (see footnote 5 on 

p. 12) indicate that similar rocks ·crop out for 15 km (9.5 mi) on 

both sides of the road. These leucocratic rocks are medium- to 

coarse-grained biotite-bearing granite and granodiorite bodies 

that, in some places, clearly crosscut the gneissic country rock. 

Xenoliths of gneiss are present in the granitic rocks, and agmatite 

is common near the margins of intrusive rocks. Medium-grained 

banded biotite quartz diorite gneiss is present along the margin of 

the granitic rocks. Irregular pods of quartz, a few centimeters 

8 Miiller Compan~·. 1969, Exploration Uberia, 8th progresR report, June-August 

1969 : The Hague, Netherlands. l\1iiller Co., unpub. rept., 11 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 9 Miiller Company, 1970, Exploration Liberia, 9th progre~8 report, September-December 

1969: The Hague, Netherlands, l\1iiller Co., unpub. rept., 12 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
GEOLOGY 15 

(inches) across, were observed locally in the gneiss, and pyrite 

was observed frequently in association with the quartz. 

In the hilly southwestern part of the itabirite province near 

Wudekehn, the rocks are noticeably different because of their 

coarse grain size. Even the iron silicate rocks are coarse grained. 

The gneiss is banded rock of quartz diorite to granodiorite composition containing biotite, and locally, garnet. Foliation in some 

of the leucocratic rocks is indistinct. Small granite and quartz 

diorite intrusive bodies were noted by the MUller Co.,10 along 

with abundant migmatite. Also reported is a garnetiferous dioritic 

massif. 

Many of the folds in the area, as viewed on aerial photographs, 

have a swirly pattern, as if the rocks were deformed plastically. 

The area also is in part characterized by random crosscutting 

radiometric anomalies, and the narrow negative aeromagnetic 

anomalies accompanying itabirite are generally short and discontinuous. 

The central part of the itabirite province, south of the Putu 

Range, contains migmatite and anatectic granite striking N. 50° 

W. to N. 70° W., 11 a trend that is normal to the regional pattern. 

No outcrops of itabirite were noted in the area, perhaps because 

of the limited traverses; however, itabirite may simply not be 

present. The near-surface aeromagnetic map (Wotorson and Behrendt, 1974) indicates that rocks in the central part of the 

province, south of the Putu Range, differ from those elsewhere in 

the province, but the area is included in the itabirite province 

because of a lack of diagnostic data. 

COMPOSITE GNEISS 

Two composite gneiss units are mapped in the Juazohn quadrangle. Composite gneiss units consist of rock types grouped 

together because each type is individually too small to show on 

the map, the exact location of only a few of the rock bodies is 

known, and the areal extent of the associated rocks is best illustrated by a single grouping. 

COMPOSITE GNEISS UNIT 2 

Composite gneiss unit 2 is an isoclinally folded sequence of 

rocks trending east to northeast in the southern part of the 

10 Muller Company, 1970, Exploration Liberia. lOth progress report, January-March 

1970: The Hague, Netherlands. :\Hiller Co., unpub. rept., 10 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 11 l\Iiiller Company, 1969, Exploration Liberia. 6th progre!'s report. December 1968-

Februarr 1969: The Hague, Netherlands. :\Iiiller Co., unpub. rept., 12 p., on file with the 

Liberian Geological Survey, Monrovia, Liberia. 
16 GEOLOGY OF THE JUAZORN QUADRANGLE, LIBERIA 

quadrangle. The unit is composed of_ graphite-bearing quartz 

diorite gneiss, magnetite-bearing gneiss, amphibolite, quartzite, 

manganese-formation, abundant pegmatite, garnet, pyrite, and 

some gold. Graphitic rocks are characteristic of the unit; hence it 

is called the graphite belt for ease of reference. 

The most widely distributed rock in the graphite belt is fine- to 

coarse-grained biotite-quartz diorite gneiss. Locally the quartz 

content is as much as 60 percent. Banding is common; fine-grained 

biotite-rich layers alternate with coarse-grained quartz-feldspar 

layers. The fine- to medium-grained rocks contain plagioclase 

augen. Garnet and graphite are accessory minerals, and sillimanite is present in the southwesternmost part of the belt. 

Graphite flakes oriented parallel to the foliation commonly make 

up less than 5 percent of the rock, but in some layers constitute as 

much as 20 percent. Geologists of the MUller Co. (see footnote 5 

on p. 12) noted a graphitic gneiss horizon near Gbakehn that is 

many hundreds of meters long, is 8 to 25 m (25 to 80 ft) thick, 

and contains 5 to 15 percent graphite. In the western part of the 

belt, they noted graphitic rocks in 10 long parallel bands. Some 

of these bands probably represent one unit repeated by isoclinal 

folding. 

Magnetite-bearing biotite-quartz diorite gneiss in the graphite 

belt is not iron-formation of the itabirite-iron silicate-quartzite 

assemblage (described below). The rock causes some of the conspicuous linear magnetic anomalies on the aeromagnetic map 

(Wotorson and Behrendt, 1974), but others are caused by magnetite-bearing migmatite (Muller Co., see footnote 8 on page 14). 

Banded hornblende-quartz diorite gneiss crops out in the southern part of the unit. Its alternating layers consist of hornblendequartz diorite gneiss, mafic mineral-free quartz diorite gneiss, 

and hornblende amphibolite. Biotite, graphite, or garnet may be 

accessory minerals in any layer. Clinopyroxene-bearing hornblende-quartz diorite gneiss was observed locally along the Dugbe 

River. 

Lenses and bands of metagabbro are locally concordant with 

gneiss of the graphite belt. Geologists of the MUller CoY~ noted a 

gradation from metagabbroic gneiss into dioritic gneiss in one 

area. Sample assemblages of metagabbroic rocks include: diopside 

(30-35 percent), plagioclase (30 percent), hornblende (20 percent), and quartz (10-15 percent); augite (45 percent), plagiou Muller Company, 1970, Exploration Liberia, 11th progress report, April-July 1970: 

The Hague, Netherlands, l\Iiiller Co., unpub. rept., 10 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
GEOLOGY 17 

clase (30 percent), magnetite (15 percent), hornblende (5 percent), and biotite (5 percent); diopside-hedenbergite (45 percent), 

hornblende ( 40 percent), and plagioclase (15 percent). 

Quartzite beds were observed throughout the belt. Most of 

them have a fine- to medium-grained granoblastic texture and 

contain such accessory minerals as graphite, garnet, or hornblende. Manganese, in the form of spessartinite and gondite, is 

also present throughout the belt and is associated with beds of 

amphibolite and quartzite. 

Metamorphic rocks of probable volcanic origin were noted 

locally by the Muller Co. (see footnotes 6, 9, and 10 on p. 12, 14, 

and 15) in the westernmost part of the graphite belt. They include 

a metatuff, a fine-grained siliceous rock in which spherulities are 

visible. Grains of quartz and albite are also present. Another rock 

type, apparently meta-andesite, has microlitic porphyroblastic 

texture and contains remnant phenocrysts of clinopyroxene and 

amphibole in a matrix of andesine and chloritized hornblende. 

The significance of these low-grade metamorphic rocks in an 

area where many of the rocks are of highest grade amphibolite 

facies is uncertain. 

Near the eastern end of this gneiss unit of the belt, many 

poorly foliated to massive rocks crop out and have the same 

composition as the gneisses. Graphite is less common than farther 

to the west and is absent altogether in rocks east of the belt. 

High-amplitude aeroradiometric anomalies in the southwestern 

part of the belt appear to crosscut the regional stratigraphic and 

structural patterns. Limited data suggest they are caused by small 

granitic intrusive bodies. Pegmatite veinlets and lenses are widely 

distributed. Some pegmatite consists largely of plagioclase; other 

pegmatite colltains both plagioclase and potassium. feldspar. 

COMPOSITE GNEISS UNIT 4 

Composite gneiss unit 4, in the northeasternmost part of the 

quadrangle, underlies an area characterized by low topographic 

relief and a broad flat magnetic pattern. The unit includes both 

gneissic and granitic rocks, but because most of the outcrops observed are gneiss or migmatitic gneiss, the name composite 

gneiss unit is used. Rocks along the Cavalla River are chiefly 

dioritic to granitic gneiss and abundant pegmatite dikes and 

sills. Similar rocks crop out along the Dube River where small 

granite bodies are present also. Between the rivers, P. van Roojen 

(oral commun., 1972) noted that outcrops are few and are dominated by homogeneous granitic rocks ; both foliated and massive 
18 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

types being present. Large outcrops are generally migmatitic 

(agmatite). 

Bos (1964) described similar metamorphic rocks and noted 

many small outcrops of massive granitic bodies in rocks having 

the same magnetic_ pattern along strike in Ivory Coast. He also 

noted a large granite body about 9 km (5.6 mi) northeast of the 

northeasternmost part of Liberia. Bos speculated that the granite 

bodies and associated pegmatite and migmatite of the area may 

reflect a granite massif that does not crop out. The broad, uniform 

magnetic pattern, upon which the limits of the map unit in the 

J uazohn quadrangle were based, is similar to those of the batholiths in the western part of the quadrangle and thus lends support 

to Bos' interpretation. 

SCHIST 

Isoclinally folded micaceous schist in large areas east of the 

Dube shear zone consists of fine-grained muscovite-plagioclasequartz rock in which biotite is minor. Quartz commonly makes up 

20 to 35 percent of the rock and locally exceeds 50 percent, whereas plagioclase commonly makes up 40 to 60 percent. Accessory 

minerals include garnet and tourmaline. Correlative schist in 

Ivory Coast is reported to be mainly mesocratic fine-grained 

rock dominated by equigranular quartz, and containing lesser 

plagioclase and biotite and accessory muscovite (.Bos, 1964). 

Jeambrun (1965) noted a schist there in which muscovite and 

biotite make up more than 65 percent of the rock; the remainder 

being porphyroblasts of plagioclase and accessory tourmaline. 

Fine-grained equigranular quartzite is commonly interbedded 

with the micaceous schist and may contain garnet, pyrite, or 

hornblende as accessory minerals. Beds of metttsedimentary 

manganese-formation as much as 2m (6ft) thick are associated 

with quartzite; both spessartinite and gondite are present (Muller Co., see footnote 7 on p. 13) . A few thin amphibolite bodies 

are also present. The Muller Co. 18 (see footnote 7 on p. 13) reported peridotite and hornblende in rocks on ·strike with the 

schist unit to the south in the Harper quadrangle. 

Schist in the northernmost central part of the Juazohn quadrangle is characterized by few outcrops and low topographic relief. Outcrops along the Dube River are mainly leucocratic fine 

to very fine grained, gently dipping rocks of biotite-quartz 

u Miiller Company, 1968, Exploration Liberia, 2nd progress report, January-March 

1968 : The Hague, Netherlands, l\Iiiller Co., unpub. rept., 7 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
GEOLOGY 19 

diorite composition and are best termed schist-gneiss. Garnet 

is an accessory mineral locally, and muscovite is present in a 

few thin leucocratic granitic gneiss layers. A fine-grained finely 

laminated quartzite a few tens of meters thick crops out along 

the road north of Senitrudru, as do sillimanite schist and amphibolite. Heavy-mineral concentrates from streams in the area contain abundant kyanite. Similar schistose rocks crop out along 

strike to the northeast in Ivory Coast (Papon, 1973, p. 67). 

Isolated areas of schistose rocks southwest of the unit, and within 

the granodiorite gneiss and beyond, may be infolded remnants 

of this unit. 

Schist along the Cestos River, in the northwestern corner of the 

quadrangle, is partly pelitic, containing sillimanite and muscovite. Other schist is rich in biotite or hornblende and has accessory garnet. Intercalated gneiss units were also noted. These 

schistose rocks trend northeastward and are along strike of 

similar schist in the adjacent Buchanan quadrangle (Tysdal, 

1977a) and the adjacent Zwedru quadrangle (Force and Beikman, 

1977; Griethuysen, 1971; MUller Co. 14 ). 

AMPHIBOLITE 

The t-erm amphibolite is applied to rocks that are of the amphibolite facies of metamorphism and contain about equal amounts 

of plagioclase and hornblende, plus m\nor amounts of other 

minerals. Garnet is a common accessory mineral, but in one 

place, north of Galue, it makes up about 40 percent of the rock. 

Clinopyroxene is an accessory mineral in some amphibolite 

bodies, and where it constitutes a few percent of the minerals, 

the MUller Co. (see footnotes 6 and 8 on p. 12 and 14) has termed 

this rock amphibole-pyroxenite. 

Discontinuous tabular amphibolite bodies a few centimeters to 

a few meters thick are shown by a line on the map (Tysdal, 

1977b) ; some units tens of meters thick are also shown on the 

map. Most amphibolite units are parallel to foliation in the 

country rock, but others crosscut it. The thicker resistant amphibolite units form narrow ridges that commonly reflect the local 

structure. Many of the amphibolite bodies are associated with 

negative magnetic anomalies that not only give a measure of the 

extent of a body, but also may reflect folding and direction of 

dip. 

14 1\Iiiller Company, 1968, Exploration Liberia, 5th progress report, June 15-August 15, 

1968: The Hague, Netherlands, l\Iiiller Co., unpub. rept .. 10 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
20 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

Amphibolite is widely distributed in the Juazohn quadrangle 

(fig. 3). It appears to be most common in quartz diorite gneiss 

unit 2 and composite gneiss unit 2. No outcrops of it were noted in 

quartz diorite gneiss unit 1, although this may be in part d-Qe 

to fewer traverses across the unit. Amphibolite is present locally 

in the southwestern part of the leucocratic gneiss in the central 

part of the quadrangle (the itabirite-bearing rock unit), but a 

traverse across this unit along the main road from Babu to 

Kahnwia revealed no amphibolite bodies. Amphibolite is one of 

the more resistant rock types in Liberia and generally forms 

most of the outcrops along roads, even though it probably makes 

up only a small percentage of the total bedrock. 

An amphibolite body forms the eastern and central part of the 

large hill north of Tibowehn, but it appears to grade westward 

into a pyroxenite body composed almost entirely of clinopyroxene. 

Anomalous amounts of chromium were noted in geochemical 

samples from near the pyroxenite (Muller Co., see footnote 11 

on p. 15), but heavy-mineral samples collected by the writer 

from flanking streams did not contain chromite. 

IRON -FORMATION 

Iron-formation of probable metasedimentary origin is .present 

mainly in the central part of the quadrangle where it forms linear 

bands, some of which can be traced for more than 30 km (19 mi) 

(fig. 3). Two facies of iron-formation are present: oxide (itabirite) and silicate. Each is described below, mainly on the basis 

of outcrops in the Putu Range where these rocks form steepsided mountains and are best exposed. 

The itabirite is finely laminated rock, commonly very fine to 

fine-grained, as in Jide Mountain (Putu Range), but is locally 

coarse grained and granoblastic, as near J uazohn. It is composed 

of quartz, iron-oxide, and minor iron-silicate minerals. Magnetite 

is the main iron-oxide mineral, but some hematite is generally 

present; locally, as in Jide Mountain, hematite is the main ironoxide mineral (DELIMCO, see footnote 2 on p. 5). Chlorite is 

minor in the itabirite (DELIMCO, see footnote 2 on p. 5). Minor 

talc and manganese oxide (pyrolusite) were reported in drill 

cores examined by Jan Offerberg (written commun., 1955). The 

pyrolusite is a secondary weathering product, but some laminae 

of manganese silicate rock were noted. . 

Silicate facies iron-formation commonly flanks itabirite. Drill 

cores from Jide Mountain show that the iron silicate rock is a 

very fine to fine-grained quartz-chlorite schist (DELIMCO, see 
9°00' 8000' 6°00',-----;;r,--------------------r--------,---~---::r--.-----------------, 

aft!@ =r 

"""~ 

.... .,. 

.:P 

.... ,$'<:? 

gndq2 ~ 

.:P 

t7' 

~/ !i=.,-~ ~ ,;?. ·' t? ~ ~.: .1&9 .,rit-..e .. , ,.~ 

......... ... .. 

gn2 

,.. ,A' .j;, ' gnl 

........ ~ 

. ,. ........ . ...-:.,- .. ....... ..-.: .. ______ ___,. ...... . .. ,.. , ... ..... •;>;t . •••• ··-·· 

.,:~!::. •••• .. ••• .... gnl . ..... . ······ ~ 

--= 

j.q mn(* # 

~x><c::::> 

I ~ x><x X e ~m v> .::> ____.........- -:J / ,if ~ -.. ... ':::\. y 

5°00' "" 0 5 10 15 20 25 30 KILOMETERS 

0 5 10 15 20 MILES 

EXPLANATION 

m Diorite 

0 Dioritic rocks 

0 Ultramafic rocks 

~ Manganese-formation 

~ Iron-formation, silicate 

facies 

~ Iron-formation, oxide 

facies 

~ Amphibolite 

0 Schist 

§] Mica schist 

~ Composite gneiss 

unit 2 

~ Composite gneiss 

unit4 

~ Leucocratic gneiss 

~ Quartz diorite gneiss 

unit 1 

~ Quartz diorite gneiss 

unit2 

~ Granitic gneiss 

~ Granodiorite gneiss 

Contact 

Fault 

::::--.::::-£ Shear zone 

FIGURE a.-Generalized geologic map showing distribution of amphibolite, iron-formation, and manganese-formation in the 

J uazohn quadrangle. 

~ 

t'1 

0 

t"'4 

0 

~ 

t< 

~ 

1-' 
22 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

footnote 2 on p. 5). In Ghi Mountain (Putu Range), the ironsilicate is fine grained, finely laminated quartz-hornblende or 

actinolitic hornblende-plagioclase (oligoclase) -magnetite-biotite 

rock. Nearly pure quartzite beds are interstratified with the 

iron-silicate rocks. Magnetite forms laminae in some quartzite 

beds but constitutes a minor amount of the rock. 

Rock adjacent to the iron-formation of Jide and Ghi Mountains 

is leucocratic medium- to coarse-grained gneiss of dioritic to 

granodiorite composition. T. P. Thayer (unpub. data, 1952) reported black amphibolite and banded green actinolite-talc schist 

near the crest of Jide Mountain about 3 km (1.8 mi) south of 

the highest peak. 

A weathered zone as much as 50 m (165 ft) thick overlies 

unweathered itabirite in Jide Mountain and forms an enriched 

ore of hematite (see section on "Mineral Resources"). Blocks of 

this ore, in canga along the eastern slope of the mountain, form 

a dissected alluvial fan. An ironstone cap forms the crest of 

Ghi Mountain. 

The thickness of itabirite deposits ranges from a few centimeters 

to more than 80 m (260 ft); the latter thickness being at Jide 

Mountain. In areas of steep dips, the thickness of some of the 

mapped itabirite units is probably exaggerated. But in general, 

dips are low in the area east and northeast of the Putu Range 

and northeast of Juazohn, and the itabirite units, though thin, 

may be more extensive than shown on the map. 

Magnetic anomalies mark the location of most itabirite deposits. The largest anomaly, about 9,000 gammas (Wotorson and 

Behrendt, 1974), is at Jide Mountain and is caused by magnetite, 

which makes up about 40 percent of the itabirite. The other 

itabirite deposits in the quadrangle contain much less magnetite 

and have anomalies of only a few hundred gammas. Boundaries 

of many of the itabirite deposits shown on the geologic map 

(Tysdal, 1977b) are based on magnetic data; for some, however, 

the presence, as well as the mapped boundaries of the itabirite, 

are interpreted from magnetic data. However, some short, discontinuous itabirite units have no magnetic expression. The 

absence of a magnetic anomaly at Ghi Mountain indicates the 

paucity of magnetite in the iron-silicate sequence. 

MANGANESE-FORMATION 

Manganese-bearing rocks crop out in three main areas of the 

Juazohn quadrangle (fig. 3): in the schistose rocks east of the 

Dube shear zone, in the graphitic rocks of the southernmost part 
GEOLOGY 23 

of the map area, and in quartz diorite gneiss unit 2 northwest of 

the itabirite-bearing map unit. Manganese-formation appears to 

be most common in composite gneiss unit 2, but this may be more 

apparent than real, owing to the high density of observations 

there. 

Most of the manganese-formation is bedded metasedimentary 

manganese silicate, consisting of black fine-grained finely laminated rock containing much spessartite. Rock containing more 

than 80 percent spessartite is termed spessartinite; the term 

gondite is applied to rock containing about 60 to 80 percent 

spessartite and less than 20 percent mafic minerals, the remainder 

being largely quartz and minor goethite and hematite. The 

quartz is granoblastic and locally forms thin discontinuous laminations, veinlets, and irregular light-colored patches. 

Manganese silicate rock is resistant to erosion and forms 

prominent steep-sided ridges. The ridges are discontinuous, 

range from about 30 to 100 m (100 to 300 ft) in height, are as 

much as to 2 km ( 1.2 mi) long, and contain abundant colluvial 

manganiferous debris on their flanks. Near Gbakehn, in the 

southernmost part of the quadrangle, spessartinite and gondite 

are present in layers 5 to 25 em (2 to 10 in) thick and are 

interbedded with quartzite beds 0.5 to 1 m ( 1.6 to 3 ft) thick. 

Similar thicknesses of manganese formation were noted elsewhere 

(Muller Co., see footnotes 6 and 13 on p. 12 and 18), and the 

Muller Co. reported a layer 1 m (3 ft) thick near Watake in 

the southeasternmost part of the quadrangle. Amphibolite units 

are commonly associated with the manganese silicate rock. 

Richards15 noted manganese oxide (psilomelane and pyrolusite) 

at Mount Dorthrow 8 km (5 mi) east of Seiyu in the northernmost central part of the quadrangle. The Muller Co. concluded 

that the rocks observed were float blocks of (low-grade) manganese-formation enriched by weathering. 

Sherman (see footnote 10 on p. 15) reported manganese a few 

kilometers southwest of Juazohn and at three localities a few kilometers west of Kahnwia. None of these localities were found by 

later workers, and it is not known if they are bedded manganese 

or gimply weathering residuals; hence, they are not shown in 

figure 2 or 3. The three manganese deposits west of Kahnwia are 

the only ones reported from the itabirite province; they are close 

5 Richards, J. G., 1953, Report on tour in EaRtern ProYince from Nyaake to Mt. 

Dorthrow, Dwarbo Town, Gbaldrue Clan, Knobo Chiefdom: Liberia Bur. Mines and 

Geology, unpub. rept., 6 p., on file with the Liberian Geological Survey, Monrovia, 

Liberia. 
24 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

to the manganese-bearing composite gneiss unit 2, in which their 

presence would be more likely. 

IGNEOUS ROCKS 

Igneous bodies crop out throughout the J uazohn quadrangle 

but make up only a small percentage of the rocks. Massive 

diorite (batholiths) is prominent in the western part of the 

quadrangle. Ultramafic rocks, altered largely to serpentinite, crop 

out in an intrusive complex near Juazohn and are associated 

with intrusive syenite and dioritic rocks. Diabase is the most 

widespread rock type, occurring in dikes that trend northwest 

across the quadrangle, forming prominent narrow linear ridges. 

GRANITIC ROCKS 

Granitic rocks ranging from granodiorite to granite are present 

in both the schist and gneiss units east of the Dube shear zone. 

Muscovite is the dominant mica, but sparse biotite is present. 

Some of the granitic rocks are rich in apatite, others are tourmaline-rich (Miiller Co., see footnote 6 on p. 12). Some granitic rocks 

east of the Dube shear zone are too small to show at map scale. 

Pegmatites are abundant and cut all the rock units east of the 

Dube shear zone. Most of the pegmatites are of granite composition; they contain abundant muscovite and lesser tourmaline and 

apatite. Coarse-grained hydrothermal veins that have graphic 

textures and booklets of muscovite are present also and are related to the granitic rocks (Muller Co., see footnote 6 on page 12). 

DIORITE 

Hornblende diorite underlies areas characterized by few outcrops and low-lying topography in the western part of the quadrangle, where it forms the Cestos and Sehnkwehn batholiths 

(Tysdal, 1977a and b, 1978) and the Jubo batholith (Tysdal 

1977b). The rock is medium to coarse grained and consists of 

plagioclase ( 45-65 percent), hornblende (20-40 percent), quartz 

(2-12 percent), and potassium feldspar (0-10 percent). The texture is massive except where the rocks are foliated and grade 

into gneissic country rock. 

The diorite was observed mainly in the riverbeds where it 

forms many rounded boulderlike outcrops, some measuring as 

much as tens of meters across. Along the Cestos River, the outcrops are locally unusual in that they extend for more than 2 

km (1.2 mi) and are so abundant as to make river traversing a 

slow process. Elsewhere, outcrops are few and consist of isolated 

rounded boulders. 
GEOLOGY 25 

The known batholiths appear on the aeromagnetic map as broad 

uniform areas of low magnetic relief (Wotorson and Behrendt, 

1974). An area of similar magnetic expression northeast of the 

Cestos batholith is assumed to represent diorite pluton. 

DIORITIC ROCKS 

Intrusive dioritic rocks north and south of the ultramafic rocks 

at Taju Hill form massive rounded outcrops. The rocks are mainly diorite but also included are quartz diorite, trondhjemite, 

dioritic migmatites, gabbroic diorite, and locally, on the north 

,side of Taju Hill, gabbro. The intrusive dioritic rocks contain 

microscopic inclusions of the intrusive ultramafic rocks, and 

drill cores reveal small diorite veins in the ultramafic rocks. Thus 

the diorite is the younger of the two intrusives (Muller Co., see 

footnotes 6 and 12 on p. 12 and 16). 

SYENITE AND TRACHYTE 

Aegirine syenite forms a resistant knoll on the southern flank 

of Taju Hill, within dioritic rocks of the Juazohn ultramafic complex. The syenite grades locally into granodiorite, both within 

and marginal to the syenite body. The coarse-grained part of the 

aegirine syenite contains large booklets of biotite in addition to 

aegirine, orthoclase, and magnetite ( 5 percent) . Secondary apatite 

(as much as 15 percent) was noted, and sulfide and copper mineralization are also present. X-ray diffraction determinations show 

spinel in weathered "concretions" taken from the outcrop surface 

(Muller Co./ 6 see footnote 6 on page 12). 

Data from 80 to 100m (260 to 330ft) of drill cores of the Muller Co. show the aegirine syenite has been intruded by pegmatitic 

.syenite that contains less than 2 percent dark minerals. The 

medium-grained equivalent of this latter rock type is common in 

the basal few meters of three drill cores and apparently indicates 

that a syenite intrusive body underlies the area (Muller Co./6 

see footnote 6 on page 12). 

Sodic trachyte dikes have been observed along only the 

Sehnkwehn and Sino Rivers within a 12- to 15-km (7.5- to 9.4-

mi) radius of the Juazohn intrusive complex and are presumed to 

be related to the syenite of Taju Hill. The nearly vertical dikes 

are 1 to 5 m (3 to 16ft) thick. The trachyte contains phenocrysts 

of hornblende. 

16 Muller Company, 1971, Exploration Liberia, 13th progress report, November 1970-

March 1971: The Hague, Netherlands, Muller Co., unpub. rept., 11 p., on file with the 

Liberian Geological Survey, Monrovia, Liberia. 
26 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

ULTRAMAFIC ROCKS 

Ultramafic and associated rocks form a complex that intrudes 

the country rock about 10 km (6 mi) southwest of Juazohn and 

also about 15 km (9.5 mi) west of Juazohn. The ultramafic body 

10 km (6 mi) southwest forms the central part of Taju Hill, a 

ridge that measures about 5 km (3 mi) (east-west) by 1 km 

(0.6 mi) (north-south) and reaches a height of about 150 m 

(about 500 ft) above the surrounding terrane. Taju Hill is 

capped by a 10-m- (33-ft-) thick lateritic soil; thus outcrops are 

found only on steep slopes marginal to the body and in deeply 

incised valleys. The MUller Co. obtained eight drill cores ·from 

Taju Hill, and the following discussion is based on their data 

(see footnotes 6, 9, and 12 on p. 12, 14, and 16). 

The ultramafic rocks include serpentinite; serpentinized dunite, 

composed of a honeycomb of antigorite enclosing grains of olivine, 

with accessory chromite; and pyroxenite, composed of augite or 

diopside (70-95 percent), and minor hornblende (0-5 percent), 

actinolite (0-5 percent), magnetite (0-20 percent), olivine (0-10 

percent), or serpentine (0-5 percent). Contacts. with the surrounding dioritic rocks dip southward at the two places where 

observed (MUller Co., .see footnotes 6 and 12, p. 12 and 16). 

The Juazohn intrusive complex is characterized by a gravity 

anomaly of +40 mGal (Behrendt and Wotorson, 1974b) and an 

aeromagnetic anomaly of -1,800 gammas (Wotorson and Behrendt, 1974; Behrendt and Wotorson, 1974b). The MUller Co. 

made a detailed ground-magnetometer survey and concluded that 

six separate anomalies exist, oriented northwest, parallel to the 

foliation in the T·aju Hill area. Both of the ultramafic intrusives 

near Juazohn are about in line with the northwest trending deepseated Geni fault in the Buchanan quadrangle (Tysdal, 1977a). 

The residual magnetic map (Behrendt and Wotorson, 1974b) 

shows a corresponding lineation in the Juazohn quadrangle. The 

regional magnetic map (Wotorson and Behrendt, 1974) does not 

show such a lineation. 

DIABASE 

A swarm of diabase dikes trends northwest across the central 

part of the quadrangle, and a few widely spaced dikes crop out 

northeast and southwest of the main grouping. The diabase is 

fine grained and ophitic and is composed of labradorite, lesser 

augite, and as much as 10 percent magnetite and ilmenite. Some 

wide dikes show coarse-grained (gabbroic) interiors and chilled 

aphanitic borders. 

Diabase that has been weathered to saprolite is easy to recog-
GEOLOGY 27 

nize in road cuts because it generally retains its felted texture 

and is spotted with uniformly distributed tiny black grains of 

magnetite and ilmenite. At many places, the diabase weathers 

into rounded boulders. 

Much of the diabase apparently was intruded along a system of 

faults, dips steeply to the south or is vertical, and forms narrow 

linear ridges owing to its resistance to weathering. The dikes are 

commonly less than 30m (100ft) thick and form ridges as much 

as 60 m ( 200 ft) hig~. 

The diabase contains sufficient magnetite to produce a characteristic narrow linear negative magnetic anomaly (Wotorson and 

Behrendt, 1974; Behrendt and Wotorson, 1971, 1974b). A very 

few dikes, however, contain almost no magnetite. In areas where 

no outcrops are known, but where a characteristic long narrow 

magnetic anomaly exists and a coinciding characteristic long narrow ridge appears on the aerial photographs, a dike was mapped 

as an observed feature (Tysdal, 1977b). Many field checks of 

such features invariably corroborated the interpretation. 

Preliminary K-Ar dating of the northwest-trending diabase 

dikes of western Liberia yielded ages ranging from Jurassic to 

Devonian (White and Leo, 1969). Subsequent work by Gromme 

and Dalrymple (1972) has shown that whole-rock and mineral 

separates from dikes that intrude Precambrian crystalline rocks 

give K-Ar ages of 193 m.y. to 1,213 m.y. However, K-Ar ages 

of dikes intruding Mesozoic sedimentary rocks near the coast 

range from 173 m.y. to 192 m.y. Study of the K-Ar data shows 

that large and differing amounts of excess Ar40 are present in the 

dikes intruded into the crystalline rocks, and that all of the dikes 

are Early Jurassic in age. Gromme and Dalrymple stated that the 

mean paleomagnetic directions of six dikes intrusive into sedimentary rocks are very close to those of 19 dikes intrusive into 

Precambrian rocks, and that the poles of all 25 dikes are in agreement with other Mesozoic paleomagnetic poles from the African 

Continent. "' 

A single north-trending dike is present in the quadrangle near 

the Cavalla River north of Drube, close to the northern margin 

of the quadrangle. The dike, noted on a river traverse, had been 

mapped in Ivory Coast by Lemarchand (1965). Lemarchand 

described the diabase as a medium-grained rock composed of 

labradorite and pigeonite (locally bordered with hornblende) and 

minor magnetite. The dike is 10 to 15 m (33 to 50 ft) thick, 

strikes N. 15°-20° E., and dips 55° W. ( ?) . The age of this dike 

i& not known. 
28 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

METAMORPHISM 

Greenschist-facies metamorphic rocks are uncommon in the 

Juazohn quadrangle. The Muller Co. (see footnote 6 on p. 12) reported an isolated occurrence of albite-bearing metavolcanic rocks 

in the western part of composite gneiss unit 2, but its geologic relationship is unknown. The iron-formation of Jide Mountain may 

belong to the greenschist facies, but thin sections were not prepared 

for these rocks so plagioclase composition is not known. Chlorite, 

talc, and actinolite present in the rocks are indicative of the upper greenschist facies, or the lowermost amphibolite facies. The 

prehnite-bearing calc-silicate rocks southwest of Pyne Town are 

suggestive of contact metamorphism in the albite-epidote hornfels 

facies, the approximate equivalent of the greenschist f~cies. 

Most of the metamorphic rocks- in the Juazohn quadrangle are 

of the amphibolite facies. The upper part of this facies is reached 

in the southwesternmost part of the quadrangle where sillimanite 

gneiss and mafic gneiss having abundant clinopyroxene exist. A 

similar increase in metamorphic grade toward the same area was 

noted in the Harper quadrangle (Brock, Chidester, and Baker, 

1977). Sillimanite-bearing schist is present in many areas of the 

quadrangle. 

The presence of minor clinopyroxene in amphibolite is fairly 

common in the quadrangle, but the adjacent gneiss does not contain pyroxene minerals, even where the· composition is appropriate. Thus, such amphibolite is believed to represent rock that 

contained less water than neighboring rocks and, while undergoing the same temperature and pressure conditions of metamorphism as neighboring rocks, formed higher rank index 

minerals. 

The schist east of Babu is continuous with similar rocks in 

Ivory Coast which, according to Papon (1973), overlie a migmatite basement. Papon stated that the migmatite was metamorphosed retrogressively during metamorphism of the schist. Thus 

two (or more?) periods of metamorphism may have taken place in 

the Babu area. 

S1RUCTURE 

The Juazohn quadrangle can be divided into three broad northeast-trending structural provinces. Rocks southeast, and locally 

south, of the itabirite province are characterized by steeply dipping, narrow isoclinal folds, a distinct magnetic pattern, and a 

locally distinct pattern on aerial photographs. The itabirite 
STRUCTURE 29 

province itself more typically contains broad, open undulating 

folds, although isoclinal folds also are present. Aerial photographs 

show mainly broad open folds in the area northwest of the itabirite province, although isoclinal folds were reported by the 

Muller Co. (see footnote 6 on p. 12). 

A subtle northwest-trending structural province extends from 

the northwest corner of the quadrangle across quartz diorite 

unit 2 and across the central part of the itabirite-bearing unit 

(gnl on fig. 2). The province is marked by the greatest density of 

diabase dikes; by structural features in the gndg 2 map unit 

(fig. 2) that trend both northeast and northwest; and by a notable 

absence of iron-formation in the central part of the itabirite 

province (fig. 3). The width of this province is uncertain, but 

along the Babu-Juazohn road, it must extend at least from about 

Pyne Town to about 20 km ( 12.5 mi) southwestward. 

FOLIATION AND BEDDING 

Foliation in most of the Juazohn quandrangle reflects compositional layering or schistosity, but whether these planar elements 

are actually bedding is not known. Locally, however, foliation is 

coincident with bedding, mainly in areas of iron-formation and 

quartzite beds. Foliations interpreted from aerial photographs are 

presumed parallel to compositional layering. 

Foliations (and fold axes) trend northwest, swinging locally 

to more westerly trends in the western part of the quandrangle. 

Dips are steep in the isoclinally folded rocks, but moderate to low 

angles prevail elsewhere. 

FOLDS 

Large-scale isoclinal folds characterize the rock southeast and 

south of the itabirite province. East of the Dube shear zone isoclinal folds were seen only in hand specimens, whereas west of this 

zone· isoclinal folds several kilometers in wavelength can be seen 

on aerial photographs and were observed during river and road 

traverses. Most of the fold limbs dip to the south or southeast, 

parallel to the foliation, but some are vertical, and a very few dip 

to the north. 

In the itabirite province, river traverses along the Cavalla and 

Dube Rivers revealed broad undulating anticlines and synclines; 

the axes trend northeast, locally changing to east. Dips on the 

flanks of these folds are generally moderate, although steeply 

dipping synclinal limbs were also observed. Folds observed in 

outcrop were also gently undulating. 
30 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

The itabirite lenses in the northeastern part of the quadrangle 

are present within both tight, steeply dipping synclinal limbs and 

more open folds. The itabirite in Jide Mountain of the Putu Range 

forms a tight isoclinal syncline (DELIMCO, see footnote 2 on p. 

5), and isoclinal folds are visible in many outcrops. Farther to 

the northeast, itabirite crops out in a gently dipping syncline, 

giving way to gently dipping beds. 

The distribution and trends of the itabirite lenses in the northeastern half of the itabirite province show that the itabirite lenses, 

in aggregate, curve to form a broad nose south and southeast of 

the Putu Range. The few scattered dips and strikes of other 

rocks, in general, reflect the nose, too. Perhaps the entire itabiritebearing rock unit northeast of the nose area represents a very 

large fold. 

Folds in the southwestern part of the itabirite province are 

commonly broad and open, although some of them, on the basis 

of aerial photo interpretation, are not so open and reveal a swirly 

pattern, as if the rocks were plastic during deformation. The 

contrast of short discontinuous lenses of itabirite in areas of 

swirly folds with long lenses of itabirite elsewhere exemplifies 

the two patterns. In general, these areas of swirly folds show 

prominent topographic relief and patterns of crosscutting radiometric highs. Because these areas of high radiation are irregular 

and cut across the regional foliation, they, and consequently the 

associated folds, are thought to have formed after the broad open 

folds. 

Data on folding in the central part of the itabirite province are 

sparse. Distinctive fold patterns are absent from aerial photographs and the magnetic map. The few foliations measured in the 

area trend northwest, counter to the regional grain, and may 

indicate that folds also trend northwest. 

The most revealing traverse in terms of folds was made along 

the Sino River in the southwesternmost part of the quadrangle. 

The rocks are deformed moderately to intensely along much 

of the river traversed. The most common folds are open, have 

near-vertical axial planes that strike about normal to the trend 

of foliation, and plunge parallel to the dip of the foliation. At 

several localities, these folds are transected by pegmatite dikes 

that appear to have been emplaced after folding. Younger folds, 

which plunge westerly and locally northeasterly, deform both the 

gneiss and the pegmatite dikes. These latter folds are tight and 

some are isoclinal. 

Folds in the upper reaches of the Dugbe River, within the 
STRUCTURE 31 

itabirite province, are broad open folds that have axes normal to 

the strike of the foliation and that plunge parallel to the dip of 

the foliation. As are those along the Sino River, these folds are 

older than the pegmatite dikes that transect them. Folded pegmatite dikes were not observed. 

Major broad, open folds strike northwest to west in the subtle 

(northwest-trending) structural province northwest of the itabirite province. One of these folds immediately south of Pyne Town 

is unusual in that its northeastern limb contains an isoclinal 

recumbent fold, its axis striking about parallel to that of the 

major fold. 

FAULTS 

Two systems of faults are prominent in the Juazohn quadrangle. 

The older faults trend northeast and are commonly marked by a 

wide zone of strongly sheared rocks. The younger faults trend 

northwest; offset, at least locally, faults of the northeast trend; 

locally show a narrow zone of sheared rocks; and have diabase 

intrusion in many places. 

NORTHEAST-TRENDING FAULTS 

The Dube shear zone (Tysdal, 1977b) in the southeastern part 

of the quadrangle separates a unit dominated by schist on the 

southeast from gneiss, migmatite, and dioritic to granitic plutons 

on the northwest. It is named for the Dube River, the course of 

which it locally controls, where the intensely sheared rocks were 

first found. At the border with Ivory Coast, the shear zone connects with a major mylonite zone in the Tal 4a quadrangle of Ivory 

Coast, mapped by Bos (1964). Relationships of rocks on opposite 

sides of the shear zone imply a fault-contrasting rock type and 

different magnetic, radiometric, and gravity characteristics-but 

it was not possible to map an individual fault. The zone may 

actually consist of several closely spaced faults not discernible 

individually. 

South of the Dube River, the Dube shear zone is marked by 

strong linear trends on the magnetic and radiometric maps. On 

the total magnetic component map (Behrendt and Wotorson, 

197 4b), the shear is associated with a conspicuous linear magnetic 

feature along its entire length, indicating that the structure is 

deep seated. Furthermore, the Bouguer gravity map (Behrendt 

and Wotorson, 1974b), though based on very few gravity measurements, shows a negative gravity anomaly for the rocks southeast of the shear zone and a positive anomaly for rocks to the 
32 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

northwest. This suggests a relative downdropping of the schistose 

sequence to the southeast. Brock, Chidester, and Baker (1977) 

found evidence of left-lateral strike-slip movement along the shear 

zone in the Harper quadrangle. All these data strongly indicate 

that the sheared ro~ks delineate a major fault or series of faults. 

Most of the sheared rocks along the Dube fault are dark colored, 

fine to very fine grained, hard, dense, and resistant to erosion. 

Thin sections made from a few samples show the rock to be 

protomylonite and mylonite. Some of the protomylonite hand 

samples have a spotted appearance due to porphyroclasts of lightcolored feldspar set in a darker matrix. Mylonites are not spotted 

but have greater development of tabular ribbons of quartz that 

are prominent in thin section and on the weathered rock surface. 

Northwest of the Dube shear zone, a prominent magnetic lineation marks the southeastern boundary of the itabirite province, 

as previously noted by Wotorson and Behrendt (1974) and 

Behrendt and Wotorson (1971, 1974b). The lineation also marks 

a change in structure (fold style) and rock units and coincides 

with the southwestward continuation of a fault mapped by Bos 

( 1964) in the Ta'i 4a and 4c quadrangles of Ivory Coast. In 

Liberia, sheared rocks were noted along the lineation only near 

its southwestern terminus, but a host of other data suggest the 

lineation represents a fault. 

For more than half the distance from the Cavalla River to the 

Dube River, the lineation coincides with a markedly straight tributary of the Dube River. The drainage is similarly structurally 

controlled along the fault in Ivory Coast. From the Dube River 

to about 20 km (12.5 mi) to the southwest, the lineation closely 

parallels a prominent drainage divide. A topographic contrast 

exists across the lineation from the Dube River for about 40 km 

(25 mi) southwestward. Differential relief is considerably greater 

in the itabirite province than in the quartz diorite gneiss unit 1. 

Also, a slight difference in the direction of magnetic grain exists ; 

the magnetic grain of the itabirite province trends generally east, 

whereas that of the quartz diorite gneiss trends northeast. 

A search was made for sheared rocks along the road near 

Kahnwia, but no outcrops were found in the area where the magnetic lineation crosses the road. Outcrops to the north and south 

along the road are not sheared. 

A narrow zone of sheared rocks was found along the Dugbe 

River, northeast of Wamapu, yet no trace of shearing was noted 

a few kilometers to the northeast where the Dugbe River crosses 

the linear trend in several places. Outcrops seem to be sufficientlY 
STRUCTURE 33 

abundant to permit detection of a zone of shearing if it exists 

particularly because sheared rocks in riv~rs are commonly the 

most resistant to erosion. Thus, if the lineation represents a fault, 

perhaps it is not accompanied by a shear zone. 

Extension of the fault westward beyond the sheared rock near 

Wamapu is questionable. A magnetic contrast still exists but is 

less distinct, and a contrast in the style of folding exists; however, rocks on opposite sides of a westward extension of the fault 

are of the same type. Detailed study of the lineation should be 

undertaken along its full length. 

Two branching faults are mapped (Tysdal, 1977b) in the northcentral part of the quadrangle along the northwestern boundary 

of the itabirite province. The easternmost branch, immediately 

adjacent to the itabirite province, is mapped largely on the basis 

of magnetic evidence in the Juazohn quadrangle and is the continuation of a fault in the adjacent Ta'i 3d quadrangle of Ivory 

Coast (Lemarchand, 1965, map). Its inclination is not certain but 

may be at a moderate angle to the southeast. The rocks are not 

strongly sheared where the fault crosses the Cavalla River. 

The other branch is a continuation of the Mount Troll fault of 

Ivory Coast, which Papon (1973, p. 68) shows as a reverse fault 

dipping steeply to the southeast. Where the fault crosses the upper 

reaches of the Dube River, however, the rocks are strongly sheared 

protomylonite and mylonite and define a thrust fault dipping 

about 40 degrees to the southeast. The southwest terminus of the 

fault is uncertain. No definite trace of it was noted along the BabuJuazohn road, which, presumably, it should cross. Its projection 

southwestward would pass approximately through the Juazohn 

ultramafic complex. As mentioned earlier, this complex is also 

on line with the northwest-trending Geni fault of the Buchanan 

quadrangle (Tysdal, 1977b). 

The Cestos shear zone (Tysdal, 1977a, 1978) crosses the northwesternmost corner of the quadrangle. It is a near-vertical structure that is marked by a wide zone of protomylonite and mylonite 

and by a distinct magnetic pattern in the Buchanan quadrangle. 

However, the pattern is not conspicuous in the Juazohn quadrangle. 

NORTHWEST-TRENDING FAULTS 

A system of northwest-trending faults, some intruded by diabase, transects the Juazohn quadrangle. Some of the gneiss adjacent to the diabase dikes is sheared, and the strike of foliation 

changes locally from the regional northeast trend to northwest 
34 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

adjacent to the dikes. In the northwesternmost part of the quadrangle and in the adjacent Buchanan quadrangle (Tysdal, 1977a, 

1978) lateral offset is evident along some of the faults, on the basis 

of interpretation of aerial photographs and magnetic patterns. 

In the northwestern part of the Juazohn quadrangle, some of 

the magnetic patterns, which commonly have a northeast grain, 

are truncated abruptly along a northwest-trending diabase dike. 

A different magnetic pattern, which also has a northeast grain, 

is present on the opposite side of the dike. The different magnetic 

patterns probably represent different rock units on two sides of a 

fault that has been intruded by diabase. The rock units are probably not in their original positions because other, different magnetic patterns show similar relationships along the same dike. 

Thus, the lines separating areas having different magnetic patterns are interpreted to represent faults that have both left-lateral 

and right-lateral offsets. 

The pattern of contrasting magnetic properties on opposite 

sides of diabase dikes that have intruded faults is evident from 

the northwest corner of the quadrangle southeastward across 

quartz diorite gneiss unit 2 and across the leucocratic gneiss of 

the itabirite province. This pattern helps define the subtle northwest-trending structural province of the Juazohn quadrangle. 

The absence of iron-formation from the central part of the itabirite province, coupled with the change ~f the structural grain 

from northeast to northwest, further defines the northwesttrending structural province in the central part of the quadrangle. 

UNCONFORMITIES 

An unconformity may exist in the north-central part of the 

quadrangle. J. Stobernack (in White and Leo, 1969, p. 13) stated 

that itabirite of Jide Mountain unconformably overlies the gneisses beneath it. His map (DELIMCO, see footnote 2 on p. 5), on 

which the map pattern (fig. 2) of the Jide Mountain area is based, 

shows a tight isoclinal syncline along most of the backbone of the 

mountain and a shallow syncline at the northeastern end. Along 

this same trend, northeast of the mountain, itabirite dipping 15° 

S. crops out. This last outcrop area reflects the low-angle, and 

locally horizontal, dips of rocks over much of the area northeast 

of the Putu Range. All these shallow-dipping rocks, including the 

itabirite, probably are related; if the itabirite of Jide Mountain 

unconformably overlies older rocks, then it follows that the shallow-dipping rocks to the northeast may overlie older rocks 

unconformably. 
AGE PROVINCES 35 

If the itabirite and associated rocks overlie older rocks unconformably, then an explanation is needed for their preservation 

only in the itabirite province. Several possible explanations are 

discussed below: 

(a) The province could represent a downdropped block. The 

movement direction on the fault along the southeastern margin 

is unknown, but the fault along the northwestern margin of the 

block is a thrust, and its movement appears to be opposite that 

necessary for a downfaulted itabirite province. One solution to 

the enigma is for the gneiss units to the northwest to be upthrown 

along a low-angle fault. Another solution is for the itabirite 

province to have been a downfaulted block originally, in which 

the itabirite rocks were protected while neighboring blocks underwent erosion. Then at a later time, the movement direction on the 

faults was reversed. Such reversal of direction of movement is 

not uncommon on ancient faults. 

(b) Another possibility is that the itabirite sequence was originally a thicker deposit in the area of the province; thus the 

rocks would be last to be removed. 

(c) The high-amplitude magnetic anomalies in composite gneiss 

unit 2 may represent iron-formation; thus the itabirite would not 

be restricted to the itabirite province nor bordered by faults. The 

objections to this idea are numerous. ( 1) Anomalies investigated 

in composite gneiss unit 2 were caused by magnetite in migmatitic 

rocks associated with plutonic rocks or by magnetite in biotitequartz diorite gneiss; the itabirite-quartzite-iron silicate assemblage was not found. (2) The original depositional environments of the two units seem incompatible-a shelf origin is probable for itabirite rocks; a eugeosynclinal origin is probable for 

composite gneiss unit 2. Itabirite could have been incorporated 

into composite gneiss unit 2 during a thorough reworking, but 

it does not seem probable that the boundary between gneiss unit 

2 and the leucocratic gneiss then would be the abrupt feature it is. 

More important, reworked itabirite would be expected also in 

quartz diorite gneiss unit 1, which is adjacent to the itabirite 

province and which has the same fold style as gneiss unit 2. 

Itabirite has not been found in quartzdiorite gneiss unit 1. 

The problem of restriction of the iron-formation to the itabirite 

province is not resolved, but a study of the movement of faults, 

discussed in (a), might resolve the problem. 

AGE PROVINCES 

Hurley, White, and Fairbairn (1971) made whole-rock Rb-Sr 

age determinations on a few rocks from Liberia as part of a 
36 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

reconnaissance study to outline intracratonic age provinces in 

several of the more ancient regions of the continental crust. Their 

interpretation shows three age provinces for Liberia: The Liberian age province (about 2,700 m.y. old), the Eburnean age 

province (about 2,000 m.y. old), and the Pan-African age province 

(about 550 m.y. old). 

A 2,230-m.y. date was determined for gneiss on the western 

flank of Jide Mountain. A 2,070-m.y. date was obtained by Hurley 

and others ( 1971) from graphitic gneiss of composite unit 1 taken 

from a quarry near Greenville, about 1 km ( 0.6 mi) south of the 

quadrangle boundary. 

A 2,130-m.y. date was yielded by a gneiss of granodiorite to 

quartz diorite composition from Pola in the Zwedru quadrangle, 

about 7 km ( 4.5 mi) northeast of Babu (Juazohn quadrangle). 

The gneiss, which is slightly sheared, dips westward at a low angle. It is in the area of the gently dipping schist east of Babu and, 

as speculated in the section on granodiorite gneiss, it may be part 

of the same sequence of rocks as the schist, but it has undergone 

different conditions of metamorphism. Schist in Ivory Coast, continuous with the schist east of Babu, overlies "migmatite" that 

has been metamorphosed retrogressively (Papon, 1973, p. 70). 

Papon stated that the metamorphism of the schist unit was accompanied by refolding in "migmatite" of the basement, causing 

the two units to appear concordant. Thus, the writer is not certain whether the gneiss at Pola represents underlying basement 

gneiss or rock metamorphosed beyond the schist stage that is 

equivalent to the schist east of Babu. 

MINERAL RESOURCES 

The itabirite of Jide Mountain, Putu Range, is the only ironore deposit likely to be of economic significance in the Juazohn 

quadrangle. It has been noted briefly or described by many 

workers, including the Holland Syndicate (H. Terpstra, unpub. 

data, 1935) , Sherman ( 194 7 and footnote 1 on p. 5), T·. P. 

Thayer (unpub. data, 1952), Janelid, 17 Kun (1965, p. 230, 259), 

and the Miiller Co. (see footnote 6 on p. 12). Evaluation of the 

deposit was undertaken first by LAMCO in the mid-1950's (Jan 

Offerberg, written commun., 1955). DELIMCO currently holds 

the exploration concession to the area. Schulze (1964) described 

the early iron industry of the Jide Mountain area, noting the 

17 Janelid, Ingvar, 1953, The iron-ore deposit at Putu Range, Sweden, Royal Inst. 

Tech., Div. Min. and Survey, unpub. rept., 6 p., on file with the Liberian Geological 

Survey, Monrovia, Liberia. 
MINERAL RESOURCES 37 

manufacture of primitive implements, arrowheads, iron money, 

and other artifacts. 

Four main types of iron ore are recognized by DELIMCO (see 

footnote 6 on p. 12). (1) Soft ore forms the weathered zone on 

top of the itabirite, and the chief mineral is hematite, formed by 

the martitization of magnetite. The soft ore is enriched, and millfeed analysis shows that it contains an average of about 49.5 

percent iron. Preliminary data indicate that the soft ore makes 

up about 9 percent of the known reserves of iron in the Jide 

Mountain deposit. (2) Itabirite of the transition zone is partially 

weathered hard ore between soft ore and unweathered itabirite. 

It is only partially martitized, contains an average of about 42.5 

percent iron, and makes up about 4 percent of the known reserves. 

(3) Magnetite-itabirite containing more than 25 percent magnetite constitutes more than 75 percent of known reserves and 

contains an average of about 40 percent iron. ( 4) The remainder 

of the deposit is mainly hematite-itabirite that contains an average of about 44.5 percent iron and makes up about 11 percent of 

known reserves. This ore type is part of the unweathered material 

in which hematite is the chief mineral. The magnetite content is 

minor. Estimated reserves for the main ore body of Jide Mountain 

are about 450 million tons of ·crude ore (DELIMCO, see footnote 

6 on p. 12). 

Anomalous values for nickel and cobalt were detected in soils 

formed over ultramafic rocks at Taju Hill, but the underlying 

ultramafic rocks themselves did not yield high values for these 

elements. The high nickel (and cobalt) values decrease with depth 

in the soil, are greatest where the soil is thickest, and are considered residual elements of lateritic weathering processes in 

which mainly SiOz and MgO are removed from the soil. The 

anomalous values are apparently not related to sulfide mineralization, because nickel sulfides were not detected in the area, nor 

where high nickel values found in a distinct grouping. The nickelrich soil covers about 1 km 2 (0.4 mi 2 ) to an average thickness 

of about 5 m (about 16 ft) and is too small a volume to mine 

profitably (MUller Co./8 and see footnotes 6, 8, 9, 10, 12, 16 on 

p. 12, 14, 15, 16, and 25; Griethuysen, 1971). 

Chromium was detected in lateritic soil overlying a small area 

of ultramafic rocks containing chrome-diopside at Taju Hill. The 

concentration, apparently formed by lateritic-weathering proc18 Muller Company, 1970, Exploration Liberia, 12th progress report, August-October 

1970: The Hague, Netherlands, ~Iiiller Co .. unpub. rept., 7 p., on file with the Liberian 

Geological Survey, Monrovia, Liberia. 
38 GEOLOGY OF THE JUAZOHN QUADRANGLE, LIBERIA 

esses, is far too small for mining (MUller Co., see footnotes 6 and 

9 on p. 12 and 14). 

Small gold placers are present throughout the quadrangle but 

are notably abundant in the graphite belt, which has yielded more 

gold than any other part of Liberia (Sherman, 1947, and see footnote 10 on p. 15). The east-northeast-trending rocks in the belt 

commonly dip south, but locally they dip north. These local areas 

of northern dips include the old gold workings and have yielded 

most of the geochemical anomalies, especially near Boken Jide 

where the gold orjginated in small quartz veins (MUller Co., see 

footnote 9 on p. 14). Only minor placer mining is being done at 

present (1973). 

Molybdenum anomalies are related closely to the gold workings 

in the Boken Jide district (MUller Co., see footnotes 6 and 9 on 

p. 12 and 14; Griethuysen, 1971), which is located about 10 km 

(6 mi) southwest of Wamapu. Most of the high values are near 

contacts between north-dipping "metabasite" (probably metavolcanic rock) and typically south-dipping graphite gneiss. Assays showed that the molybdenum content is not economically 

exploitable. Most of the rocks give the impression of being enriched but are only weathered. 

The Diamond Mining Corporation of Liberia (Leuria, see footnotes 3 and 4 on p. 5) explored for diamonds in the western 

part of the Juazohn quadrangle, mainly in the area drained by the 

Sehnkwehn River. Diamonds were not discovered, but minute 

amounts of scheelite, corundum, and pyrite were found in the 

area of the Jubo batholith. The reports (Leuria, see footnotes 

3 and 4 on p. 5) list the heavy minerals from only a few sample 

sites. 

One of the prime targets of the MUller Co. exploration in 

eastern Liberia was bauxite. No deposits of bauxite were found 

in the Juazohn quadrangle, although scattered pisolitic material 

was noted on a few hill crests (MUller Co., see footnote 5 on p. 

12). 

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598-604. 

--1974a, Total-count gamma radiation map of the Juazohn quadrangle, 

Liberia: U.S. Geol. Survey Misc. Inv. Map I-779-C, scale 1:250,000. 

--1974b, Geophysical surveys of Liberia with tectonic and geologic interpretations: U.S. Geol. Survey Prof. Paper 810, 33 p. 

Bos, P., 1964, Rapport de fin de leve, coupures Ta'i 4a-4c, Cote d'Ivoire: 

Soc. Devel. Minier Cote d'Ivoire Rapport 127, 58 p. 
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Sherman, Arthur, 1947, Guidebook for Liberian prospectors: Liberia Bur. 

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White, R. W., [1971], Reconnaissance mapping of deeply weathered crystalline rocks in Liberia: Geol., Mining, and Metall. Soc. Liberia Bull., v. 4 

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