UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

Bulletin 935-H

MANGANESE DEPOSITS IN COSTA RICA

BY

RALPH J. ROBERTS

'Geologic Investigations in the American Republics, 1941-43 

(Pages 387-414)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1944

For sale by the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.

Price 15 cents

CONTENTS

	Page

Abstract................................................. 387

Introduction............................................. 387

j Transportation and accessibility..................... 388

j History and production............................... 388

] Geology of the ore deposits.......................... . 389

Reserves............................................. 390

Costs................................................ 391

: Mines...o................................................ 391

 Santa Rosa district.................................. 391

Playa Real....................................... 392

Other properties near Playa Real................. 392

La Esperanza..................................... 392

La Bejia..-....................................... 393'

La Pedregosa........................;............ 393

El Encanto....................................... 394

La Seba.......................................... 394

A El Zapotalillo................................... 394

Other prospects near Playa Real and Puerto Vie jo. , 394

Playa Blanca..................................... 395

El Sesteo........................................ 395

El Mico.......................................... 396

Los Limones....................................... 396

El Licor......................................... 397

El Curiol........................................ 398

Loma Blanca...................................... 399

El Guas tomate.................................... 399

El Guacalito...................................... 399

La Catasolapa.................................... 399

Wolf............................................. 399

Carbon........................................... 400

El Jocote........................................ 400

Other properties near Santa Rosa................. ,400

Arenal district...................................... 400

' La Desdichada..................................... 401

Rio Seco-Lagarto district............................ 401

El Cuchofino..................................... 401

Filacho Mula...................................... 401

Judas............................................ 402

Pie Paloma....................................... .402

El Zapote........................................ 402

El Espavelar..................................... 402

Los Bolillos..................................... 403

El Cacao......................................... 403

La Victoria...................................... 404

t Rio Piedra Amarilla-Rio Guajiniquil district,........ 404

El' Pital......................................... 405

Los Saltos....................................... 405

Piedra Amarilla................................... 406

Los Munecos zone................................. 407

El Carrizal...................................... 408

Los Chanchos..................................... 408

Other properties in Rio Piedra Amarilla-Rio

Guajiniquil district........................... 408

III
IV CONTENTS

Page

Mines Continued.

Sardlnal district.................................... 408 ^

El France's....................................... 409

La Cuestacita.................................... 410

Other properties near El France's................. 410

El Panamd........................................ 410 I

Other'showings near Culebra Bay.................. 410 ,l

Justo Perez...................................... 410 ' 

La Libertad...................................... 411

Showings north of Sardinal....................... 411

Showings near Belen.............................. 411 ^~T

Nicoya-Pavones district.............................. 411

La Cuesta de Matambu............................. 411

Cerro Grande..................................... 412

Matina..........................................* 413

Pavones.........................................;. 413

La Colonia Carmona............................... 414

Tambor........................................... 414

ILLUSTRATIONS

Page

Plate 78. Map of the Nicoya Peninsxila, Costa Rica...... 390

79. Geologic map of El Curiol mine............... 398

80. Sketch map of Los Bolillos workings.......... 406

Figure 21. Sketch map of part of workings, Playa Real... 393

22. Sketch map of Playa Blanca workings.......... 395

23. Sketch map of El Sesteo workings............. 396

24. Sketch map of El Licor mine workings......... 397

25. Sketch map of El Cacao workings.............. 404

26. Sketch map of El Pital workings.............. 406

27. Sketch map of Los Saltos workings............ 407

28. Sketch map of El France's workings............ 409

29. Sketch map of Cerro Grande................... 412

30. Sketch maps of Los Pavones workings.......... 414
MANGANESE DEPOSITS IN COSTA RICA

By Ralph J. Roberts

ABSTRACT

The manganese deposits of Costa Rica are on the Nicoya 

Peninsula, in the Province of Guanacaate, on the Pacific coast. 

Between 1915 and 1920 nearly 32,000 long tons of high-grade ore 

was shipped from them to the United States, but since 1920 the 

mines have been inactive.

The sedimentary rocks of the Nicoya Peninsula are Tertiary 

sandstone, chert, shale, and limestone. They are interbedded 

with basalt, and are intruded by diabase and diorite.

The manganese deposits are of three types: hypogene, 

supergene, and residual. In the hypogene deposits the manganese minerals are the silicates braunite, bementite, and rhodonite; these minerals occur in Jasper, which replaces sedimentary and igneous rocks along bedding and fault zones. The 

deposits are tabular, lenticular, or irregular in shape. Some 

of them are as much as 120 feet long, 20 feet wide, and 100 

feet deep, but on the average, they are considerably smaller. 

The supergene and residual deposits are composed of pyrolusite, 

wad, and psilomelane, formed by weathering of the silicates. 

All of them are extremely irregular. The greater part of the 

ore mined and shipped was oxide ore, but braunite predominated 

in ore mined from the deeper workings at the Curiol mine. The 

depth of oxidation ranges from a few feet to more than 75 feet.

Since most of the old workings are inaccessible and many of 

the deposits have not been adequately explored, it is difficult 

to predict how much ore is available in the district. About 

1,000 tons of ore containing between 30 and 50 percent of manganese is estimated to be blocked out or on the dumps. Several 

thousand tons may remain to be developed in extensions of known 

ore bodies and in new ore bodies. Some of the ore can be 

sorted, or concentrated in simple washers, but part of it, possibly 50 percent or more, will have to be crushed and concentrated by more costly methods.

INTRODUCTION

The manganese deposits of Costa Rica are on the Nicoya 

Peninsula, in the Province of Guanacaste, on the Pacific coast 

(see pi. 78). Most of them are within 10 miles of the Pacific 

Ocean, in a belt about 45 miles long extending from San 

Juanillo to Culebra Bay. One deposit is near Puerto Thiel, on

387
388 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

the Gulf of Nicoya, and others are scattered through the central part of the peninsula.

The Nicoya Peninsula is separated from the central plateau 

of Costa Rica by the Gulf of Nicoya and the broad lowland of 

the Rio Tempisque. It is largely occupied by mountains. West 

of the Tempisque and as far south as Nicoya the mountains are 

but moderately rugged, the highest having altitudes of about 

2,000 feet, and here the vegetation consists largely of grasses 

and shrubs. South of Nicoya some peaks rise above 3,000 feet, 

and in the parts of this region that are at high altitudes or 

near the Pacific coast the vegetation Is dense and tropical.

Transportation and accessibility

The principal ports of Costa Rica are Port Limon on the 

Atlantic Ocean and Puntarenas, in the Gulf of Nicoya, on the 

Pacific Ocean. They are connected by the Northern Railway, 

which runs from Port Limon to San Jose, and by the Perrocarril 

al Pacifico, which runs from San Jose to Puntarenas. Many 

launches with regular schedules ply between Puntarenas and 

points on the Nicoya Peninsula, which are connected by bus or 

truck service with the principal towns.

The yearly rainfall on the Nicoya Peninsula is about 70 

inches, most of which falls between June and December. During 

the rainy months heavy hauling is difficult, and at times it is 

impossible on the dirt roads. Most of the hauling is still 

done with oxcarts, but the use of trucks is gradually increasing. At present few of the roads are surfaced, but the road 

from Puerto Jesus to Nicoya is now being macadamized, and it is 

expected that all-weather roads will be built between other 

towns in the next few years.

Most of the manganese ore produced in Costa Rica between 

1914 and 1920 was shipped from Playa Real, Puerto Viejo, and 

Lagarto. High tides and shallow water near shore required the 

use of lighters and long piers for loading the ocean-going 

steamers. The piers then used have been destroyed, and there 

are no loading facilities at the present time.

History and production

In the 1915-18 period the Costa Rica Manganese & Mining Co. 

operated the Playa Real and Curiol mines, and shipped some ore 

from nearby properties. Later this company was absorbed by the 

American Manufacturing Co. of Philadelphia, which continued to 

make shipments, largely from the Curiol mine, until 1920. In 

1930, control of most of the properties passed into the hands 

of Capt. W. R. Scott and Guadalupe Gatgens, but as these men 

failed to do the required work the denouncements lapsed and 

were taken up by others. The properties lay idle until 1936, 

when control of several of them was acquired by Otto Sauter, 

who did a little exploration work, and shipped 300 tons of ore 

from El Guacalito in 1938. In 1937, E. W. Creevy bought all of 

the properties except the Curiol and Guacalito. He carried on 

an active program of exploration until the end of 1940, but 

shipped no ore.

The manganese deposits of Costa Rica are now largely held 

by companies: the Guanacaste Manganese Co.'controls the 

Curiol, Playa Real, and Guacalito properties; La Compania
MANGANESE DEPOSITS IN COSTA RICA 389

Rotheberg controls properties near Santa Rosa, Rio Sequito, and 

Lagarto; and the Rothe Co. controls properties in the Rio 

Guajiniquil area and near Sardinal and Santa Rosa.

The first shipments of manganese ore from Costa Rica were 

made in 1915 from the Playa Real mine. This mine has been the 

largest single producer and, together with the Curiol mine, has 

yielded about 85 percent of the ore shipped. The recorded production is given in the following table:

Production of manganese ore in Costa Rica, 1915-58 I/ 

Year Long tons

1915. ............................. ?

1916. ............................. 1,244

1917.............................. 7,163

1918 .............................. 9 , 968

1919............ ................... 9,988

1920.............. ................ 3,202

1958.............. ................ _____ 500

Total.......... ............... 31,865

The manganese content of the ore shipped ranged from 40 to 

55 percent and averaged about 50 percent. Iron and phosphorus 

were low. The ore contained as much as 10 percent of silica, 

in part mechanically mixed with manganese oxides, but in part 

present in the mineral braunite.

Geology of the ore deposits

The rocks of the Nicoya Peninsula are partly sedimentary, 

partly igneous, and all of Tertiary age: the sedimentary rocks 

are predominantly shale, chert, and limestone; the igneous 

rocks include basalt flows, intercalated with the sediments, 

and intrusive dlorite and diabase. The bedded rocks have been 

folded into northwestward- trending anticlines and synclines, 

and in places they have been complexly faulted.

The manganese deposits in bedrock are associated with 

masses of red and yellow jasper, which replace both sedimentary 

and igneous rocks. In sedimentary rocks the jasper follows 

bedding planes, commonly along contacts with igneous rock. In 

igneous rocks it follows fracture zones. The manganese minerals replace jasper and the adjacent wall rocks .

The deposits are of three types: hypogene, supergene, and 

residual. These types are closely associated, and all three 

may be found at a single property. The hypogene deposits, 

which were formed by ascending hypo thermal solutions, contain 

manganese silicates replacing jasper; the supergene deposits 

consist of manganese oxides derived from the silicates by 

weathering in place; and the residual deposits consist of 

nodules and fragments of oxides in the soil that mantles the 

slopes below outcrops.

The hypogene manganese minerals are braunite (3

bementite (8 Mn0.5H20.7Si02) , and rhodonite (MnSi0 3 ). 

Of these, only braunite is rich enough in manganese to be 

shipped directly as metallurgical ore. Small veins of rhodochrosite have been found in two deposits. The manganese minerals found in the supergene and residual deposits, are pyroluslte,

I/ Webber, B. N., Manganese deposits of Costa Rica: Am. Inst. Min. Met. 

Eng. Tech. Paper 1445, February 1942.
390 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

psilomelane, and.wad, all of which grade at depth into silicates.

The hypogene ore bodies are tabular, lenticular, or irregular in shape. Some tabular ore bodies follow faults and extend 

to depths of 75 feet or more; others are.nearly flat or pockety, and shallow; still others are thin residual caps. The 

manganese silicates occur in layers, pockets, and veins within 

the jasper, which follows bedding planes and fault zones. Ore 

bodies along bedding planes may have any dip from nearly horizontal to vertical; those along fault zones commonly have steep 

dips.

As the oxides formed from the oxidation of silicates for 

the most part remained in place, the supergene ore bodies are 

mostly similar in form to the hypogene bodies; however, the 

oxides were in part transported downward by circulating waters 

and deposited along fractures and bedding planes in the wall 

rock adjacent to the jasper. The depth of oxidation in the 

Nicoya Peninsula is variable, extending from a few feet to 75 

feet or more below the surface; commonly, however, complete 

oxidation extends no deeper than 20 feet. At the Curiol mine 

(pi. 79), where the downward percolation of solutions was aided 

by fracturing and shearing in the ore zone, oxidation was 

nearly complete 75 feet or more below the surface; but at El 

Cacao (fig. 25) manganese silicates occur within 5 feet of the 

surface.

Individual ore bodies contain from a few tons to several 

thousand tons. One ore body at the Curiol mine was 120 feet 

long, 20 feet in average width, and in places at least 100 feet 

deep. Most of them, however, are smaller, and on the average 

they are less than 50 feet long, 5 feet wide, and 20 feet deep. 

There is commonly much waste material in the ore bodies, and in 

the 1915-20 period the ore was selectively mined and sorted 

before shipment.

Reserves

The principal factors that influence estimates 'of reserves 

are (1) mineral composition, (2) depth of oxidation, and (3) 

form of the ore bodies.

All of the oxide minerals may be high enough in grade to be 

shipped as metallurgical ore, but braunite is the only hypogene 

mineral that contains enough manganese to constitute shipping 

ore; oxidation thus increases the value of the ore, and it is 

consequently desirable to identify the principal minerals present and determine to what extent the ore is oxidized. As oxidation is influenced by local structures, the depth to which it 

extends in a given ore body must be determined before an accurate estimate of the reserves in that body can be made.

As not enough exploratory work has been done in most of the 

Guanacaste manganese deposits to determine these factors, and 

as many of the old workings are inaccessible, it is difficult 

to estimate reserves. About 1,000 tons of ore containing 30 to 

50 percent of manganese is already blocked out or on the dumps. 

About half of this could be sorted to give an ore of shipping 

grade (40 to 45 percent of manganese). Several thousand tons 

of ore containing about 40 percent of manganese can probably be 

found in extensions of known ore bodies and in newly discovered 

ore bodies. In addition, a considerable tonnage of ore containing 20 to 35 percent of manganese may be available on old 

dumps, in the workings, and in new deposits. This ore would
GEOLOGICAL SURVEY BULLETIN 935 PLATE 78

Bahio d» 

Polraro \i_

Bahi'a de o/! ^\ 'x 

Brasilito ) , \ x ^

,q:Tempote

MAP OF THE NICOYA PENINSULA, COSTA RICA 

MAPA DE LA PENINSULA DE NICOYA, COSTA RICA

GPO O - 44 - 588097 (Faces p. 390)
MANGANESE DEPOSITS IN COSTA RICA 391

have to be concentrated; part of it could be concentrated in 

simple washers, but most of it. would have to be crushed and 

concentrated by more costly methods.

Costs

Skilled labor is not plentiful in Costa Rica at the present 

time (1942), because of the demands for such labor in the Canal 

Zone and on the International Highway. Unskilled labor, however, is reasonably abundant in Guanacaste, and training for 

most mining operations would not require much time. The pay of 

unskilled laborers is now $0.50 to $1.00 a day.

Hauling is largely done with oxcarts at a cost of about 

$0.20 a ton per kilometer in the dry season. Truck hauling 

over dirt roads in the dry season is estimated to cost about 

$0.15 a ton per kilometer.

Mining costs will vary from mine to mine, and an average 

figure can hardly be given. Men who worked at Playa Real and 

Curiol between 1917 and 1920 estimated that costs for mining, 

sorting, transportation to ports, and loading ranged from $20 

to $30 a ton. . Costs will probably be about the same in 1942, 

and profitable operation may require a price of $1.00 a unit or 

more, depending upon the size of the operation, distance from 

the coast, and other factors. Loading facilities, housing, and 

administration costs would also have to be considered.

If the low-grade ores that would require concentration are 

to be used, other problems will arise. The deposits will have 

to be adequately explored and sampled, then tested to determine 

the best method of recovery. Portable equipment would be 

desirable, for it is unlikely that any single property will 

warrant an expensive installation.

The ore could be shipped by ocean to Pacific coast ports of 

the United States, or to Atlantic ports via the Panama Canal. 

In an emergency the ore could be sent overland to Puerto Limon 

by railroad, but the additional cost would be nearly $10 a ton 

and reloading would be required.

MINES

Most of the manganese ore deposits on the Nicoya Peninsula 

are within 10 miles of the Pacific coast, but some of them are 

farther inland and one is on the Gulf of Nicoya. For convenience they have been grouped in districts, named after the 

principal towns nearby.

Santa Rosa district

The Santa Rosa district Includes, among others, the Playa 

Real and Curiol mines, which together have produced about 

30,000 tons of high-grade manganese ore. Production from other 

properties has been small, and few of them have been explored.

The ore from the Playa Real mine was loaded from a pier at 

Playa Real. The first shipments of ore from the Curiol nine 

were transported by oxcart to Puerto Vie Jo, but later a railroad 2 miles long was built to Los Boquerones from Puerto VieJo.

588097 O - 44 - 2
392 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

If manganese ore is again shipped from Costa Rica, Puerto Vie jo 

will probably be the best shipping point. The roads from Playa 

Real and Curiol to Puerto Viejo (via Conchal) can be improved' 

at small cost so that they will be passable by truck even during 

the rainy season.

Playa Real

The Playa Real mine, 2 miles southwest of Puerto Viejo, on 

the Pacific coast, produced about 19,000 tons of manganese ore 

between 1915 and October 1918. The property is now owned by 

the Guanacaste Manganese Co. of San Jose. Sears 2/ examined 

the mine when it was in production and published a description 

of the workings, illustrated by a sketch map showing the general distribution of the ore bodies. Much of the following 

information is from his report.

The ore bodies are distributed throughout a northerly 

trending belt about 1,600 feet long and in places several hundred feet wide. The ore is found as a residual capping and in 

irregular pockets in red shale, chert, or jasper (see fig. 21). 

It consists for the most part of pyrolusite and wad. A little 

braunite was seen in the cores of boulders, and it appears 

probable that the oxides were largely formed from braunite. 

The ore bodies were shallow, and although some ore was taken 

from underground workings, most of it was mined from pits less 

than 15 feet deep. Several tunnels were driven during the 

1915-18 period, but only low-grade ore, shale, chert, or jasper 

were found. The ore mined at Playa Real was of high grade, 

averaging about 50 percent of manganese; it contained about 10 

percent of silica, and iron and phosphorus were low.

The' pits are now partly caved, but exposures in them indicate that the bulk of the shipping ore has been mined. Some 

material high in silica remains in the pits and on the dumps, 

and there are small ore bodies in the underground workings. 

The ore remaining will probably have to be concentrated before 

shipping, but further exploration to determine the available 

tonnage, ought to be made before operations are started. At 

present there are no shipping facilities at Playa Real.

Other properties near Playa Real 

Several other properties near Playa Real were visited, 

including La Esperanza, El Encanto, El Zapotalillo, La Pedregosa, and La Seba, all said to be owned by the Guanacaste Manganese Co. Ore was shipped from La Esperanza and El Encanto in 

1917 and 1918 by Robert Crespi for the Manganese Mining & Manufacturing Co.

La Esperanza

La Esperanza, a property half a mile south of Playa Real, 

was worked in 1918. The production is not known, but it is 

estimated to have been less than 200 tons. The workings, which 

are at an altitude of 350 feet, may be reached by oxcart road 

from Playa Real. They consist of shallow trenches in chert and

Z/ Sears, J. D., Manganese deposits of Coste Rice: U. S. Geol. Survey 

Bull. 710-C, p. 68, 1919.
MANGANESE DEPOSITS IN COSTA RICA 393

shale, which have been locally replaced by jasper and which 

extend for about 200 feet along a narrow ridge. One trench 

exposes a layer of low-grade siliceous ore 3§ feet wide, striking N. 40° W. The deposit appears to be'virtually worked out, 

though it still'might yield a few tons of low-grade ore.

La Bejia

The workings at La Bejia, three-quarters 

Playa Real, consist of a trench 50 feet long 

pit 40 feet long. They explore a pyrolusite 

dipping 75° SW., in chert, shale, and jasper 

now exposed in the workings is of low grade, 

good ore is piled on the dump. This ore was

of a mile south of 

and an adjoining 

-braunite ore body, 

Although the ore 

about 20 tons of 

probably mined

EXPLANATION 

EXPLICACION

Strike and dip of bod: 

Rumbo y buzamitmo da tos «rralc

CIS

Limit of pit 

Umite da/ hoyo

Dump 

Botaden

Contour interval 10 feet 

Datum assumed

Curvas de nival cada 10 pies 

Piano de referenda asumido

Figure 21. Sketch map of part of workings, Playe Reel

from the pit, but the bottom of the pit is now concealed, by 

debris. To the northwest the ore pinches, and, unless the ore 

extends to considerable depth or continues southeast of the 

present workings, the outlook does not appear to be promising. 

Ore from this property could be hauled to Playa Real by oxcart 

after road improvements had been made.

La Pedregosa

La Pedregosa is about a mile south of Playa Real. The 

workings consist of shallow cuts in a jasper zone, trending 

N. 50° E., which is 3 feet or more in width and can be traced 

for 100 feet. The ore fills fractures in the jasper and 

replaces jasper. Although part of it is of fair grade, much of 

it is siliceous. There is no road to the property at present.
394 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

El Encanto 

.El Encanto, a mile "south of Puerto Vie jo and a few hundred 

feet from the Playa Real-Puerto Vie jo road, is^at an altitude 

of 150 feet. About 1,000 tons of residual ore" is said to have 

been shipped from here in 1917-18. The ore came from shallow 

cuts, now overgrown with trees and shrubs, and from an adit 50 

feet long. The adit explores a manganese oxide- Jasper layer 2 

to 4 feet thick, which replaces shale and chert along the bedding and dips gently southeast. A sample of this ore was found 

to contain 34.23 percent of manganese, 7.06 percent of iron, 

and 30.91 percent of insoluble material, consisting largely of 

silica (SiOg) and alumina

La Seba

La Seba, about a quarter of a mile southwest of El Encanto, 

is at an altitude of 100 feet. This property is said to have 

shipped 70 tons of ore in 1918. The workings consist of several shallow cuts, which explore a jasper zone parallel to bedding in chert and shale. .The rocks strike N. 10° W. and are 

vertical. The material exposed in the trenches is of low 

grade, but about 10 tons of ore estimated to contain about 45 

percent of manganese is piled near the workings. This deposit 

appears to be worked out, but prospecting of nearby slopes for 

residual ore may be warranted.

El Zapotalillo

. El Zapotalillo is a quarter of a mile west of El Encanto, 

on a narrow ridge a few hundred feet from the Pacific Ocean. 

Manganese oxide showings follow the bedding in shaly chert, 

which is vertical and strikes N. 45° W., for a distance of 

about 400 feet along the ridge. The manganiferous material is 

in two lenses, one 75 feet and the other 100 feet long and each 

about 3 to 5 feet wide. The lenses consist of chert cut by 

discontinuous manganese-oxide veinlets that are commonly less 

than an inch wide. Thin crusts of manganese oxide cover the 

outcrops in a f'ew places. There may be some residual ore on 

the northeast-facing slope below the outcrop, but the available 

tonnage is probably small.

Other prospects near Playa Real and Puerto Viejo

Mlna de Barrante and Mina Cerro Zapote, Just southwest of 

Puerto Viejo, both show a little siliceous manganese ore, but 

neither showing appears to have promise.

If mining becomes active in this district again, other ore 

bodies may be discovered. It is unlikely, however, that any of 

them will prove to be even as large as that of the Playa Real 

mine, for bedrock exposures are fairly good on the slopes and 

the region has been thoroughly prospected.
MANGANESE DEPOSITS IN COSTA RICA 395

Playa Blanca

The Playa Blanca property is on the Pacific coast, 3 miles 

northeast of Puerto VieJo. The workings (fig. 22) are in chert 

and shale on a low ridge trending N. 60° W., parallel to the 

strike of the rocks. No ore has been shipped, but piled on the 

dumps is about 100 tons of sorted ore, a sample of which 

assayed 32.91 percent of manganese, 4.43 percent of iron, and 

30.33 percent of insoluble material. The ore body, mined in 

the course of exploration by E. W. Creevy in 1939, has been 

traced for 80 feet along the strike. It is as much as 30 

inches thick and consists of psilomelane and pyroluslte. For 

the most part it is siliceous and, as mined, probably does not 

contain more than 25 percent of manganese. About 100 or 200 

tons of this material may be available in the workings.

EXPLANATION 

EXPLICACION

c - Limit of pit 

Limits del hoyo

r

Adit

Strike and dip of beds 

Rumbo y bvzamiento de ha eatratoa

4

Depth of workings, in feet 

Pro/undidad de tos Irabajos. en pies

Chert and shale 

/'Horafeno y plzarra

I

Layer of manganese oxide ± 30 thick 

Cape de oxido de manganese, espesor i <5CT

Jasper 

Jaape

10 _ t t _ 0 

Contour interval 10 feet

_________20M«tro. 

Curvas de nivol cada 10 pies

Datum assumed Piano de referenda asumldo 

Figure 22. Sketch map of Playa Blance workings,

El Sesteo

The Sesteo workings are on the Puerto Viejo-Santa Rosa 

road, about a mile northwest of Matapalo. About 1,000 tons of 

ore was shipped from here in 1918 by the Manganese Mining & 

Manufacturing Co. Chert, shale, and jasper crop out east and 

west of the workings, but, though they contain small veinlets 

of manganese oxide, no ore bodies have been found in these 

rocks. Residual manganese ore, however, is revealed in shallow 

cuts and pits, distributed over an area of 200 by 100 feet, to 

a depth of 2 to 4 feet (see fig. 23). It is estimated that the 

soil in this area contains 5 to 10 percent by weight of manganese-oxide nodules. Possibly 500 tons of good ore could be 

obtained.here by washing and sorting, and further exploration 

might disclose residual ore in other areas nearby.
396 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

El Hico

The Mico workings, on a low hill half a mile southwest of 

El Sesteo, show a little siliceous manganese ore in chert and 

shale striking N. 40° E. Several shallow pits and a short adit 

explore the showings, which do not appear promising.

Los Limones

The Los Limones property, 1-|- miles south of Huacas-, was 

explored by E. W. Creevy in 1938. Except for a few tons of ore 

taken as a sample, no shipments have been made. The workings

EXPLANATION 

EXPLlCACrON

Pit (depth in feet) 

Hoyo fprofundidad en pies]

Trench 

Zanja

Soil containing nodules of manganese oxide 

Tierra con nodulos de oxido de manganeso

Soil 

Tierra \

Soil containing nodules of manganese oxide 

Tierra con nodulos de oxido de manganese

Figure 23. Sketch map of El Sesteo workings.

explore a manganiferous zone near the top of a narrow ridge in 

chert and shale striking N. 10° VJ. and dipping steeply east. 

The manganiferous zone is as much as 20 feet wide and can be 

traced by float for about 200 feet. In shallow cuts, manganese 

oxides are seen to be sparsely distributed in this zone. Pockets of fair-grade ore 1 to 3 feet wide are exposed in places, 

but they are only a few feet long. A 27-foot shaft which was 

put down near the top of the ridge connects with an adit driven 

from the slope below. The dump from the adit shows no ore. 

The portal, now partly caved, is in altered diorite.

A few tons of high-grade ore and possibly 100 tons or more 

of low-grade ore may be available at Los Limones. If exploration is undertaken the slopes should be prospected for residual 

ore.
MANGANESE DEPOSITS IN COSTA RICA 397

El Licor

El Licor, 500 feet north of the village of Santa Rosa, was 

explored by E. VJ. Creevy in 1938. It is now owned by the Rothe 

Co. of San Jose. No ore has been shipped, but 100 tons mined 

in the course of exploration is piled just west of the workings. Analysis of a sample of this'ore showed 34.23 percent of 

manganese, 1.13 percent of iron, and 32.32 percent of insoluble

EXPLANATION 

EXPLICACION

Strike and dip of beds 

Rumoo y buzamiento da loa estratos

Sparse manganese oxides in shale

Wodu/o.i escasos de oxidoa de

 jnanganeso en p/zarra

Contour interval 10 feet 

Datum assumed

Curvas de nival cada 70 pies 

Piano de referenda asumido

Figure 24. Sketch map of El Licor mine workings.

matter. Two ore bodies have been mined in the open pits shown 

in figure 24. One was 80 feet long, 20 feet wide, and 2 to 4 

feet thick; the other was 40 feet long, 15 feet wide, and in 

places as much as 6 feet thick. The ore consists of manganese 

oxides, probably derived from silicates, which replaced a chert 

lens along the bedding. The ore is in fault cpntact with diorite or basalt at the north end of the lower pit, and the two 

ore bodies may be parts of a single body repeated by faulting.
398 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

Workings near the divide to the south show small pods and veins 

of Jasper and manganese oxides in shale and igneous rock.

Most of the ore mined was obtained from the north workings; 

the material becomes siliceous and thinner toward the borders. 

Possibly a few more tons of fairly good ore could be selected 

from the pits.

El Curiol

El Curiol (pi. 79) is 2 miles southeast of Santa Rosa on 

the road to Santa Cruz. The mine was worked by the Manganese 

Mining & Manufacturing Co. from 1916 to 1920 and produced about 

9,000 tons of ore, said to have averaged 50 percent of manganese and 10 percent of silica. The property is now owned by 

the Guanacaste Manganese Co. of San Jose.

Two ore bodies have been mined. .The main ore body trends 

west and the other northwest; both dip steeply. Residual ore 

that covered the surface northwest and south of the main pit 3/ 

accounted for a considerable part of the total tonnage mined.

The ore bodies extend along fault contacts between diorite 

and cherty shale and converge at the caved shaft. The ore minerals replace the shale and to a less extent the diorite along 

the faults. The ore is a mixture of braunite and pyrolusite; 

pyrolusite predominated in the residual ore and in ore mined 

near the surface, but braunite was more abundant in ore mined 

from- the bottom of the pit. The ore was said to be solid and 

to have required little sorting.

The ore body in the main pit trends east, dips steeply 

south, and pitches 20° E. It is about 120 feet long and as 

much as 20 feet wide. The ore is cut off by a shear zone above 

the 175-foot level in the east face of the pit, but the short' 

drift 10 feet below the level follows ore for a short distance. 

The ore is reported to widen downward and to be 8 or 10 feet 

wide in the shaft at a depth of 50 feet below the bottom of the 

pit, but work ceased before the length of the ore body at this 

level was determined.

The shallow pits west of the main pit are said to have contained small, discontinuous lenses of ore, but in March 1942 

the pits were slumped and no ore was seen in them. An adit 

driven in beneath these pits at an altitude of 185 feet is 

entirely in diorite and jasper.

The other of the two principal ore bodies extends northwest 

from the caved shaft along a nearly vertical fault zone. Pockets of manganese oxides were mined in shallow pits for a distance of about 140 feet from the shaft, but the tonnage was 

small.

In view of the report that there is an ore body 8 or 10 

feet wide below the bottom of the main pit, further exploration 

appears warranted..

3/ Sears, J. D., op. cit., p. 71.
NOKTE MAONETICO
MANGANESE DEPOSITS IN COSTA RICA 399 

Loma Blanca

Lona Blanca, about 6 miles southeast of Santa Rosa, is 

owned by La Compania Rotheburg of San Jose'. The workings are 

two shallow cuts in silicified basalt and shale. Small veins 

and pockets of manganese oxide occur in these rocks, but they 

are of low grade and locally ferruginous. The few tons of 

selected ore piled on the dumps does not appear to be worth 

shipping.

El Guastomate

El Guastomate, owned by Octavio Jlmenez and others of San 

Jose, is about 2 miles northeast of Santa Rosa. Shallow cuts 

explore a manganese-oxide zone, which follows the bedding of 

shale and chert striking N. 50° W. and dipping steeply northeast. Two pods, each 30 feet long and as much as 7 feet wide, 

are exposed; the average manganese content of this material is 

estimated to be only about 20 percent, but there are small 

pockets of high-grade ore. Other showings of low-grade and 

siliceous ore nearby do not appear promising.

El Guacalito

El Guacalito, owned by the Guanacaste Manganese Co., is 4 

miles south of Santa Rosa. The ore body crops out on a low 

ridge trending N. 65° E. and is explored by shallow cuts. The 

ore consists of manganese-oxide pockets and veins in jasper and 

shale. The manganiferous zone extends for 200 feet and is as 

much as 20 feet wide. It is reported that 300 tons of ore was 

mined from this property in 1917 but was not shipped because of 

its low grade. About 300 tons of low-grade ore, said to have 

contained 30 percent of manganese, was shipped to Germany by 0.. 

Sauter in 1938. Possibly a few tons of siliceous ore is available in the present workings, but the outlook for future production is not promising.

La Catasblapa

La Catasolapa is 2 miles northwest of Santa Rosa, on the 

road to Matapalo. The workings, consisting of some cuts and a 

short adit, explore a manganiferous zone in chert and shale, 

which strike N. 5p° W. and dip 35° SW. The material exposed is 

of extremely low grade, though a little fair-grade float is 

found on the surface. This property appears unlikely to become 

a producer.

Wolf

The Wolf claim is half a mile east of Morro Hermoso, at an 

altitude of 50 feet, and appears to be the one that was listed 

by Sears 4/ as the Morro Hermoso. La Compania Rotheburg is the 

present owner. The workings extend along a low ridge for about 

100 feet; they consist of a trench 50 feet long with a 10-foot 

shaft near the south end, and several small pits. The ore consists of soft wad and hard manganese-oxide nodules in clay

4/ Sears, J. p., op. clt., p. 72.
400 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

derived from weathered shale, chert, and jasper. The ore zone 

parallels the bedding, which dips 30° SW. Some ore from this 

property is said to have been shipped in 1917 from Playa Real. 

Little ore is exposed in the present workings, but further 

exploration might reveal small ore bodies, and the slopes 

nearby-might yield a few tons of residual ore.

Carbon

The Carbon claim, on Iforro Hermoso, also owned by La Compania Rotheburg, has showings of low-grade ore a few hundred 

feet from the Pacific shore. This material is too siliceous to 

be of commercial importance.

El Jocote

El Jocote, owned by Adan Rodriguez of San Jose', is a mile 

east of Point Carbon. Shallow cuts were being dug in March 

1942 along a zone of siliceous manganese oxide, which follows 

the bedding of chert and shale. The zone can be traced by 

float for 75 feet and is as much as 3 feet wide where exposed 

in the cuts. It strikes N. 55° E. and is vertical. About 10 

tons of manganese-oxide boulders has been piled in. the stream 

below the outcrop, but the material is too low in grade to be 

shipped. The 'deposit does not appear to be promising.

Other claims nearby, also owned by Adan Rodriguez -El 

Congo, La Sopresa, La Conga, and La Quebrada have showings of 

low-grade manganese ore. All of it is siliceous, and the tonnage available appears to be too small to warrant further 

exploration.

Sears 5/ described.a number of manganese-oxide showings at 

the Matapalo, Guayaquil, San Francisco, Hatillo, 27 de Abril, 

Huacas, and Portegolpe properties. Some assays of the ore are 

said to have shown high percentages of manganese, but much of 

the ore is siliceous. About 100 tons of ore was shipped from 

the Iglesias mine near Huacas, but the other properties have 

been unproductive. Some of these properties might yield a few 

tons of high-grade ore from surficial material, and other showings may be discovered in this area.

Arenal district

Near Arenal, La Compania Rotheburg has denounced several 

properties. Of these the Cerro Diablo, half a mile southeast 

of Arenal, La Cuestacita, half a mile southwest of Cerro 

Diablo, and Canafitola, a prospect 2 miles west of Arenal, show 

manganese-stained shale. None, however, appear to have promise. At the Carbonal claim, 4 miles east of Arenal, a contact 

zone between shale and diorite is stained with oxides of copper 

and iron.

5/ Sears, J. D., op. clt., p. 73.
. MANGANESE DEPOSITS IN COSTA RICA 401 

La Desdichada

La Desdichada is 4 miles southwest of Arenal on the HuacasArenal road. There are showings of low-grade manganese oxide 

in red shale, and a little high-grade float has been found. 

The property does not appear promising.

Rio Seco-Lagarto district

Between the Rio Seco and Lagarto many properties have been 

denounced. Only two of them, the Espavelar and La Victoria, 

have been productive. Some of the others are new discoveries, 

and the rest were too small or of too low grade to warrant 

exploitation in the 1914-18 period.

It is unlikely that any of these properties will yield more 

than a few hundred tons of high-grade ore. For the most part 

they have not been sufficiently explored to determine their 

reserves, but it seems unlikely that any of them contain large 

ore bodies, of either high or low grade. Most of the deposits 

are difficult of access;" they are near .roads passable by oxcart, 

but these roads would have to be improved for heavy hauling. 

There are, moreover, no shipping facilities, and piers would 

have to be built or lighters used to load the ore. Lagarto was 

the shipping point for ore from the Victoria and Espavelar 

properties between 1914 and 1918, but the piers and loading 

facilities there have been destroyed.

 El Cuchofino

El Cuchofino, 7 miles south of Santa Rosa, near the farm of 

Gregorio Rodriguez, was explored by E. W. Creevy in 1940. No 

ore has been shipped, but several sackfuls were taken for laboratory tests, and a few tons is now piled on the dump. An 

assay of the ore'gave 39.11 percent of manganese, 11.07 percent 

of iron, 18.28 percent of insoluble matter. The workings, 

which are in jasper and shale, consist of an open cut 40 feet 

long and 20 feet wide, a pit 10 feet deep, and some shallow 

trenches. The ore that was mined came largely -from the open 

cut, but only small pockets are now visible in the walls of the 

cut. In the pit there is a little soft manganese oxide in. 

sheared jasper and shale. The ore zone appears to trend northwest and to dip steeply; it can be traced for 300 feet, but 

showings in trenches do not appear promising. Further exploration to the northwest might possibly disclose small ore bodies.

Filacho Mula

Filacho Mula, a mile southwest of Cuchofino, is also owned 

by La Compania Rotheburg. Shallow pits explore a silicified 

zone 150 feet long and as much as 25 feet wide in altered 

igneous rock. Veinlets and small pockets of manganese oxides, 

chiefly pyrolusite, occur throughout the zone. The zone trends 

N. 30° W., and the rock is locally sheared. The ore now.showing is of good grade, but the tonnage is small and the deposit 

does not appear to warrant further exploration.
402 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

Judas

The Judas property is a mile southwest of Filacho Mula. 

Three pits explore an outcrop of siliceous jasper in sheared 

and altered igneous rock. The jasper zone is 10 to 15 feet 

wide and about 50 feet long; it appears to trend N. 20° E. 

Small pockets and veins of manganese oxides occur in and adjacent to the Jasper, but the deposit does not show much promise,

Pie Paloma

Pie Paloma is at an altitude of 600 feet, half a mile 

southwest of the Judas and 2 miles from the Pacific Ocean. Two 

open cuts explore a jasper zone, with thin veInlets of manganese oxides on fracture planes. The zone is 20 to 30 feet wide 

.and about 300 feet long; it trends N. 20° E., following a fault 

zone in shale, in which the bedding strikes N. 20° W. and dips 

35° SW. The material is too low in grade to warrant further 

exploration.

El Zapote

El Zapote is a mile southwest of Pie Paloma, near the Villa 

Real-Rio Sequito road. A pit 5 feet deep was sunk alongside a 

jasper zone which crops out for a length of 40 feet and is in 

places as much as 15 feet wide. The pit shows only low-grade 

siliceous ore. Manganiferous jasper float is scattered over a 

wide area surrounding El Zapote, but the relief is low and the 

outcrops poor, and no ore was seen in place.

El Espavelar

The Espavelar mine, which is 7 miles east of Lagarto, at an 

altitude of '300 feet, is now owned by the Rothe Co. The workings are at the summits of rolling hills above the Rio Espavelar. According to Sears,6/ something less than 2,000 tons of 

ore waa shipped from here in 1917-18 via Lagarto; the grade of 

this ore is not known, but, to Judge from material "now on the 

dumps, some of it was of high grade and some was siliceous, in 

1917 and 1918, ore was hauled to Lagarto by oxcart o-ver a hilly 

road, but this road is now in such disrepair that much of it is 

impassable even for oxcarts.

The ore occurs in irregular, shallow pockets In jasper that 

was formed by replacement of shale along a shale-diorlte contact. The mass of jasper appears to be nearly horizontal, and 

its maximum thickness is only about 30 feet. The ore bodies, 

for the most part, follow fractures trending northwest and 

west. The individual ore bodies are said to have contained 

from a ton or less to 800 tons. The ore consisted largely of 

pyrolusite, but braunite was found in a few places.

Four areas in a northwest-trending belt 1,500 feet long 

have been explored. (1) Espavelar No. 1, at the southeast end 

of the belt, has yielded less than 100 tons of ore; the material showing in the pits is siliceous and of low grade. 

(2) Espavelar No. 2, about 500 feet northwest of No. 1, is said

6/ Sears, J. D., op. cit., p. 78.
.MANGANESE DEPOSITS IN COSTA RICA 403

to have yielded about 300 tons. Some of the ore was high-grade 

pyrolusite, but much of it was siliceous. (3) Espavelar No. 3, 

1,000 feet west of No. 2, is said to have produced about 500 

tons. (4) Espavelar No. 4, 300 feet south of No. 3, is said to 

have produced 800 tons of ore from an open cut 100 feet long. 

An adit 50 feet long was driven south into the nil] from the 

open cut4, but only jasper and diorite were encountered.

Except for a little ore remaining in the pits and on the 

dumps, the Espavelar mine appears to be worked out. Further 

prospecting in the jasper might disclose small ore bodies, but 

none as large as that on Espavelar No. 3.

Los Bolillos

The Bcilillos workings are. about 3.miles east of Espavelar 

by way of a hilly trail. This property may formerly have been 

called El Pavo or Las Masas. No ore has been shipped from it, 

but considerable exploration work has been done (see pi. 80). 

The trenches and shaft on the west side were made by the H. 

Mann Co. in 1918, and the open cuts on the east side by E. W. 

Creevy in 1940. These workings explore irregular jasper zones 

containing pockets and velnlets of manganese oxide. The jasper 

zones trend north and east and replace basalt. Exploration 

thus far has disclosed only small ore bodies. One of these, in 

the cut 200 feet east of Pozo Azul, was 45 feet long and as 

much as 8 feet wide in places, but it extended only a few feet 

below the surface. The ore bodies explored to the northeast of 

this cut were also shallow. The Pozo Azul, Pozo Norte, and 

other nearby workings are also in Jasper, but the pockets and 

veins of manganese oxide exposed in them are small. Although 

nearly all of the easily available manganese oxide has been 

mined from the present workings, a small tonnage might possibly 

be found by further exploration.

It is estimated that about 75 tons of ore is piled on the 

dumps. An analysis of a sample1 of this ore showed 28.03" percent of manganese, 12.45 percent of iron, and 27.10 percent of 

insoluble matter. A few tons of ore could be selected for 

shipment, but since there is no road it would have to be transported to Lagarto on pack animals. The present showings do not 

appear to warrant construction of an oxcart road.

El Cacao

El Cacao (fig. 25) is 4 miles east of Lagarto and 2 miles 

west of Espavelar. Although considerable trenching was done on 

the property in 1917, it is said that all the ore found was of 

such low grade that none 6f it was shipped. The workings are 

in jasper, which replaces red shale along bedding planes. In 

the largest pit, near the center of the area mapped, the bedding strikes N. 80° W. and dips 30° NE. Altered basalt-underlies the red shale in the pit. The jasper .contains partly 

oxidized braunite and bementite a few feet below the surface. 

The ore-bearing layer is as much as 4 feet thick in places but 

it appears to thin out northeast and southwest of the trench. 

In the other cuts there are veinlets and pockets of sparsely 

distributed manganese oxides. The reserves in the property 

appear to be only a few tons of siliceous ore.
404 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

La Victoria

The Victoria mine is 2 miles southeast of Lagarto. Sears 7/ 

reports that 200 tons of ore was shipped from it in 1918. The 

workings are shallow cuts in jasper and shale on a small knoll, 

and the ore consists of small veinleta and pods of manganese 

oxides in the jasper. A few tons of siliceous ore is piled on 

 the dumps, but further exploration, does not appear warranted.

EXPLANATION 

EXPLIGACION

Sparse manganese oxides in jasper 

\ Pockets'oTmarlganese oxide in jasper Oxidos de manganese espareWo en jasp

BoisiSos de oxido Of manganese en jaspe

Contour interval 10 feet 

Datum assumed

Curvas de nivel cada JO pies 

Piano de referenda asumido

Figure 25. Sketch map of El Cacao workings. 

Rio Piedra Amarilla-Rio Guajiniquil district

Deposits grouped near the headwaters of Rio Piedra Amarilla 

and Rio Guajiniquil have been known for many years, but because 

of their remoteness they have not been explored. They can now 

be reached by trail from San Juanillo or Los Bolillos. As the 

country is hilly and much of it is covered with dense tropical 

vegetation (the rainfall here is heavier than in other parts of 

the Nicoya Peninsula), road construction and maintenance would 

be difficult and expensive.

7/ Sears, J. D., op. cit., p. 72.
MANGANESE DEPOSITS IN COSTA RICA 405

There are no loading facilities near the mouth of Rio 

Guajiniquil, and, as along the coast to the north, the water is 

shallow, so that lighters or long piers would be required for 

loading ocean vessels.

The manganese oxides are in jasper, which appears to 

replace igneous rock along steeply dipping fault zones. 

Although few individual bodies of jasper are more than a few 

hundred feet long, the fault zones can be traced for several 

miles. Only a few of the deposits have been explored. The ore 

bodies thus far discovered are small and irregular or of low 

grade, but further exploration might possibly disclose ore 

bodies of minable size.

El Pital

The Pital zone (fig. 26) is 6 miles from the Pacific Ocean, 

on the Rio Pital, a tributary of the Rio Piedra Amarilla. The 

workings made by E. W. Creevy in 1938 consist of shallow 

trenches, which explore a north-trending zone of manganiferous 

jasper, about 100 feet wide and 350 feet long, in igneous rock. 

The contacts between jasper and igneous rock are commonly 

sheared, but the jasper appears to have been formed by replacement of basalt a,long steeply dipping or-vertical fault zones. 

No primary minerals were seen, but the manganese oxides were 

presumably derived from silicates.

The ore bodies exposed in the trenches are small and irregular; they commonly cannot be traced from one trench to the 

next. The manganese oxide mostly occurs in pockets and small 

veinlets, but it is also disseminated throughout the jasper. 

Some outcrops of the jasper are thinly coated with nearly pure 

pyrolusl.te, giving an exaggerated idea of the tonnage available. One body of ore is 40 feet long and 20 feet or more in 

width, but apparently too siliceous to be shipped. Locally the 

ore contains considerable iron oxide. An assay of a grab sample gave 11.15 percent manganese, 16.94 perc-ent iron, and 50.31 

percent insoluble matter.

At El Perro, 350 feet east of El Pital, manganese oxides 

form a thin crust on jasper. The showing is not promising. 

E. W. Creevy is' said to have core-drilled El Pital and El 

Perro, but with what result is not known. Careful mining and 

sorting might produce a few tons of shipping ore from El Pital 

and El Perro together, but there appears to be no hope of finding large high-grade ore bodies. Further exploration, however, 

might disclose small bodies of primary or oxidized ore of shipping grade.

Los Saltos

The Saltos workings (fig. 27), a mile north of Pital, 

explore a northwest-trending jasper zone 800 feet long. Several shallow pits have been dug along the zone, and they reveal 

small pockets and veing of manganese-oxide ore, part of it 

ferruginous. Not enough work has been done to determine 

whether the ore is continuous from one pit to another, but the 

outlook is not promising. Assay of a picked sample of the ore 

gave 34.23 percent manganese, 9.94 percent iron, and 28.02 percent insoluble matter.
406 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

Piedra Amarilla

The Piedra Amarilla zone is a mile southwest of the Pital 

zone. It has not been explored, but a layer of jasper trending 

northeast is exposed in a stream bed. The jasper locally

Yellow-jasper with incrustations 

of-manganese oxides . 

Jaspo amarillo con incrustaciones\ 

de oxides de manganeso

\

Basalt Yellow jasper with incrustations of 

Basalto 1< / ' ron anQl manganese oxides' 

\S "l if Jaspe amarillo con incruslaciones de 

/\jf«/os do hierro y mangeneso

\

\

Siliceous manganese-oxide ore 

Mineral siliceo del oxido de manganeso

ockets of manganese oxide in jaspe 

 -- ' ' V ' o'enjasp

El Perro workings 350' 

east of El Pital

Los trabajos El Perro, 

360 pies al este de El Pital

EXPLANATION 

EXPLICACION

Contour interval 10 feet 

Datum assumed

Curvas de nivel cada 10 pies 

Piano de referenda asumido

Figure 26. Sketch map of El Pital workings.

contains considerable hematite. A streak of low-grade manganese oxide extends for at least 20 feet along the stream channel, but exploratory work would be needed to determine its full 

extent.
GEOLOGICAL SURVEY BULLETIN 935 PLATE 80

EXPLANATION 

EXPLICACION

SKETCH MAP OF LOS BOLILLOS WORKINGS 

CROQUIS DE LOS TRABAJOS LOS BOLILLOS

GPO O - 44 - 588097 (Faces p. 406)
'sopfxo ^nq ev& -[Bf.i6q.Bta sf 003 opBaS oq. oq 

aedsBf Moqs Bins -[-[ s^Gspod PUB 

puB B7 GiqBeoBJ^ aoj x««i8A6s poapunti 

ore Manganese 

de Miadr&J m&ngAneso

>: ;;

EXPLANATION 

 EXPLICACION

GUOZ ST uioaj 02 o^ 08 j ^69 

J° Q06 '^.OGJ GJB Uf B IGdSBf 

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UB P ^^ ^ 

'BOOGUIXM

GUOZ

JO 13 

sooounu GUOZ 

siisodaa NI Visoo VOIH LOT?
408 GEOLOGIC INVESTIGATIONS IN THE AMERICAN .REPUBLICS, 1941-43

El Carrizal

El Carrizal is a quarter of a mile east of El Foco, at an 

altitude of 950 feet. A shallow cut shows manganese oxide 

sparsely distributed in jasper.

Los Chanchos

The Chanchos workings are 3 miles from the Pacific Ocean, 

on the ridge between Rio Los Chanchos and Rio Guajiniquil. It 

is reported that 50 tons of-ore was shipped from here in 1937 

but that the grade was low.

The ore was mined from two pits along a jasper zone trending northwest; one pit is 100 feet long, 10 to 20 feet wide, 

and 4 to 7 feet deep; the other, 175 feet to the southeast, is 

20 feet long, 15 feet wide, and 15 feet deep. The ore minerals 

are pyrolusite, braunite, and wad. At least a hundred tons of 

siliceous ore remains in the pits, and possibly other ore 

bodies may be found along the strike of the zone. A grab sample taken in the pits and from the dumps assayed 31.60 percent 

manganese, 13.10 percent iron, and 30.46 percent insoluble 

material.

Other properties in the Rio Piedra AmarillaRio Guajiniquil district

Just north of the mouth of the Rio Guajiniquil,. a red and 

yellow jasper zone about 20 feet wide crops out on the beach. 

The jasper strikes northwest and dips steeply southwest; along, 

the strike it grades into unaltered shale bounded on either 

side by basalt. Locally the jasper contains manganese oxides, 

but except for a lens of psilomelane 3 feet long and in places 

a foot wide the material is of low grade. The showing has no 

commercial importance.

Manganese deposits are also said to occur near San Juanillo 

and Nosara, but they were not visited, because no guides familiar with these deposits were available.

Sardinal district

Many denouncements have been made near Sardinal. Two of 

these, El Prances and La Libertad, were explored by E. W. 

Creevy in 1939; some .of the others were trenched in 1918, and 

the rest have no workings. These properties are owned by the 

Rothe Co. No large ore bodies of either high- or low-grade ore 

have been discovered in the area.

There are no ship-loading facilities on the Pacific beaches 

west of Sardinal. A road passable by car'runs from Sardinal to 

Coco Bay, and loading facilities could be constructed at the 

beach if it were desirable.
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410 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

long and 20 feet wide along a fault and bedding planes. The 

other pits reveal only sparse manganese oxides.

Along the ridge to the northeast and southwest there is 

shale stained with manganese oxide, but no promising showings 

have been found there. Although a little ore remains in the 

pits, it is unlikely that oxide ore will persist much below the 

present workings.

Samples of El Prances ore were concentrated by R. W. Hunt 

Co., but because of the intimate admixture of silica it was 

found necessary to crush to 150 mesh. The recovery ranged from 

40 to 60 percent, and a concentrate containing 50 to 55 percent 

of manganese was made from 30-percent ore.

La Cuestacita

La Cuastacita is about 1,500 feet northeast of El France's. 

Two shallow cuts explore manganese oxide-stained shaly chert 

striking N. 70° W. and standing vertical, and a few boulders 

nearby are thinly encrusted with manganese oxides. The property does not appear promising.

Other properties near El Frances

Cerro Grande and Nancite, a mile north of El France's on the 

other side of the valley, and Chapernal, 3 miles west of Nuevo 

Colon, were reported-to be manganese prospects. When examined, 

however, they proved to be in pyrite deposits along contacts of 

diorite and shale, with nothing more than stains of manganese 

oxide.

El Panam£

The Panama deposit, on the south side of Culebra Bay, is in 

altered diorite. Glassy material along fractures in this rock 

contains a little manganese, but the deposit is too low in 

grade and too small to be of commercial importance.

Other showings near Culebra Bay

Deposits of manganese ore are reported at Monte de Barco 

and Playa Hermosa, but only a slight staining of diorite along 

fractures was seen.

Justo Perez

The Justo Perez (also known as El Boquete del Ramo) is a 

mile soxith of Sardinal, near the San Bias road. The deposit 

consists of two lenticular ore bodies, which lie about 500 feet 

apart on a line trending N. 10° W. The ore is manganiferous 

iron oxide, of light to dark brown color; it replaces altered 

igneous rock and may have been formed by. oxidation of pyrite. 

One of the ore bodies, which is 25 feet long and as much as 10 

feet wide in places, is explored by shallow cuts. The other, 

35 feet long and as much as 15 feet wide, is explored by a pit 

10 feet deep and an open cut. Both ore bodies are considerably 

sheared along their walls. Analyses of the ore made by E. W.
MANGANESE DEPOSITS IN COSTA RICA . 411

Creevy are reported to average 1.5 to 4 percent of manganese 

and 30 percent each of iron and silica. The material has no 

commercial value.

La Libertad

La Libertad (also known as Cerro Colorado) is 1^- miles 

south of Sardlnal on the San Bias road. In 1939 E. W. Creevy 

cleaned out the old trenches and extended two of them. A siliceous manganese-oxide zone 3 feet wide striking N. 40° W. and 

dipping vertically is cut in one trench, and at several places 

there is rock stained with manganese. The 'property does not 

appear promising.

^ Showings north of Sardinal

At Tabor and at Piedras Pintades, 1 mile and 3 miles, 

respectively, north of Sardinal, there are showings of manganese-stained sandy shale locally cut by small veinlets of manganese oxide. The material is too low in grade to be of commercial importance.

Showings near Belen

About ! § miles north of Belen are poorly exposed croppings 

of iron oxide, locally stained with manganese oxide. The material has no value as an ore of manganese.

Manganese-oxide deposits are also reported about 4 miles 

north of Belen, near Ojochal, but this locality was not visited.

Nicoya-Pavones district

South and southeast of Nicoya are a number of ferruginous 

manganese-oxide deposits, from which no ore has been shipped. 

At Pavones there has been a small production of high-grade ore.

The Nicoya-Pavones area is favorably situated as regards 

transportation. An all-weather road runs from Nicoya to Puerto 

Jesus, and freight can be shipped on shallow-draft launches to 

deep-water anchorage in the Gulf of Nicoya. Ore from Pavones 

can be shipped from Puerto Thiel, another port on the Gulf.

La Cuesta de Matambu

The property called La Cuesta de Matambu is 2 miles southeast of Nicoya. Several showings of siliceous iron-manganese 

oxide may be seen near the road, halfway up the slope, at the 

farm of Vincente Fajardo, and there are others a short distance 

north of Matambu. The iron-manganese oxide occurs in small 

lenses replacing shale and chert, which are intercalated with 

basalt; in places the shale and chert have been converted to 

jasper. The ore bodies are poorly exposed, but one on the road 

is 6 inches to 3 feet wide and is exposed for a length of 10 

feet; another, also on the road, is a foot wide'and 5 feet 

long. Discontinuous outcrops of iron-manganese oxide may be 

found in the stream below the Fajardo house and on the slope to
412 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 1941-43

the east, and considerable float occurs on the slopes and In 

the 'stream beds.

As the ore bodies appear to be small and of low grade, they 

are probably not of commercial Importance.

Cerro Grande

The Cerro Grande property, a mile and a half south-southeast of Nicoya, is on the road to Dulce Nombre (see fig. 29).

EXPLANATION 

EXPLICACION

Contour interval 10 feet 

Datum assumed

Curvas de nivel oada 10 pies 

Piano de referenda asumido

Figure 29. Sketch map of Cerro Grande.

Four lenses of siliceous Iron-manganese oxide striking N. 50° W, 

are exposed near the road, and a fifth in the stream to the 

northwest.- The oxide, which contains approximately equal percentages of Iron and manganese, replaces shale intercalated 

with pillow basalt. The largest lens is 30 feet long and as 

much as 6 feet wide. Locally the ore contains veinlets and 

pockets of pyroluslte. Because of the small size and low grade 

of the ore bodies, the deposit does not appear to warrant 

exploration.
MANGANESE DEPOSITS IN COSTA RICA 413 

Matina

On the slope east of the village of Matina, on the road to 

Hoja Ancha, iron-manganese oxide crops out at several places. 

There is one lens 50 feet long and in places as much as 8 feet 

wide; the other showings are small and discontinuous and do not 

appear to be of commercial importance.

Manganese deposits are said to occur north of La Mansion, 

but that locality was not visited. Prospects near Quiriman 

were vi3ited, but since they are of the same unpromising character as those at Matina, La Cuesta de Matambu, and 'Cerro 

Grande'they need not be described. None of them appear to 

warrant exploration.

Pavones

The Pavones mine (also known _as Buena Vista) is 2 miles 

southwest of the village of San p'ablo. Sears 8/ reports that 

80 tons of ore containing 51 percent of manganese was shipped 

from this property in 1918. In 1939 E. W. Creevy did some 

exploratory work and piled aboxit 40 tons of high-grade ore on 

the dumps. The property is now owned by Dario Zuniga of San 

Jose".

The workings (fig. 30) explore a manganese-oxide zone 

trending northeast and are in two groups about 800 feet apart.

The northeast workings consist of three open cuts. The ore 

in the lowest cut is siliceous and ferruginous; the upper two 

cuts expose ore bodies that replace Jasperized shale along the 

bedding, which has a strike of N. 70° E. and a dip of 55° NW. 

The shale lies between altered igneous breccia on the footwall 

and massive igneous rock on the hanging wall. The ore mineral 

is pyrolusite, which in places has been brecciated by shearing 

parallel to the strike of the ore bodies and contains fragments 

of jasper and igneous rock. In both pits the ore zone is as 

much as 10 feet thick, but'only about a third of it is shipping 

ore; the remainder is low-grade ore and waste. The similarity 

of both the ore and the wall rock in the two upper pits suggests that they are part of the same zone, offset a few feet by 

a fault trending north or northwest, rather than separate ore 

bodies.

The southwest workings explore three jasper lenses, which 

are on strike with the northeast workings. The jasper is 

locally faulted but not strongly sheared. The ore occurs in 

the jasper, in veins and pockets that are so small as to 

require careful mining and sorting.

Although the easily available material at this property has 

been mined, neither the southwest nor northeast ore bodies are 

worked out; a few hundred tons of high-grade ore may still be 

obtainable by selective mining and sorting. It is also possible that additional ore bodies may be found along the strike 

of the ore zone.

8/ Sears, J. D., op. cit., p. 82.
414 GEOLOGIC INVESTIGATIONS IN THE AMERICAN REPUBLICS, 11941-4;,

i 

La CoIonia Carmona

Two deposits, reported to be of manganese ore, near the 

village of Colonia Carmona, were visited but they proved to be 

carbonaceous shale.

EXPLANATION 

EXPLICACION

If y':J Jasper^ith pockets of manganese oxide 

' ' "xidosde manganese en los estratos

Basalt and basalt breccia 

Baaalto y brecha basaltic*

Fault 

Falla

Strike and dip of beds 

Rum bo y buzamiento de los estratos

SOUTHWEST WORKINGS

Breccia of manganese oxides and^basaltBrecha de oxidos de manganese y di '

and manganese\oxides 

irro y^mangeneso de bajo ley

NORTHEAST WORKINGS

i i i i i

Contour interval 10 feet Curvas de nivel cada 10 pies 

Datum assumed Piano de referenda asumido

Figure 30. Sketch maps of Los Pavones workings. 

Tambor

Manganese deposits are also said, to occur at Tambor Bay. 

At the one locality that was visited, a little manganese stain 

was found. The other deposits were not examined, because no 

guides were available who knew where they were.

O