GOLD DEPOSITS RELATED TO 

GREENSTONE BELTS 

IN BRAZILDEPOSIT MODELING 

WORKSHOP 

Part A Excursions

U.S. Geological Survey Bulletin 1980-A

A workshop sponsored by the International Union of Geological Sciences and the United 

Nations Educational, Scientific, and Cultural Organization Deposit Modeling Program. 

The workshop held December 1-10,1986, in Belo Horizonte, Brazil, was hosted by the 

Institute Brasileiro de Mineragao
WORKSHOP PARTICIPANTS

Group photograph at Quintas, Mineragao Morro Velho Club, Nova Lima, Brazil 

December 4,1986

1. Sergio C. Guedes

2. Antonio da Silva Wirz Leite

3. Alfaro Guillermo

4. Mauricio G. Ferreira

5. Jair Carlos Koppe

6. Noelvaldo Teixeira

7. Gregoiy Moseley

8. Euripedes Martins Siqueira

9. John A. Kerswill

10. Roberto Albuquerque e Silva

11. Joao Batista G. Teixeira

12. Antonio Madalosso

13. Gerd Peter Poppinga

14. Francisco A Medeiros Neto

15. Hannia Azuola

16. Stanton W. Caddey

17. Paschoal Luiz Caiafa Clemente

18. Luiz Henrique do Amaral Lisboa

19. Fernando L. Repetto

20. Rafael Lima de Oliveira

21. Eduardo Ladeira

22. Diogenes Scipioni Vial

23. Celso Frizzo

24. Sergio Maurus Ribas

25. Paulo Roberto Amorim dos Santos Lima

26. Marcel Fonseca

27. Ronald Fleischer

28. Bernardino Figueiredo

29. Milton Guimaraes Bueno do Prado

30. Joel Macambira

31. Eduardo Luis Barber

32. Frederico Wallace Reis Vieira

33. Stephanus Malan

34. Tarcisio Borin Junior

35. Charles H. Thorman

36. Vitor Hugo Silveira de Castro

37. Carl R. Anhaeusser

38. Hernando Lozano

39. Aurelian Antonio Lopez Sam
GOLD DEPOSITS RELATED TO 

GREENSTONE BELTS IN BRAZILDEPOSIT MODELING WORKSHOP 

Part A-Excursions

Edited by CHARLES H. THORMAN,

EDUARDO A. LADEIRA, and DIANE C. SCHNABEL

Field excursions of the 

surface geology and to 

several gold mines in the 

Quadrilatero Ferrffero, 

Minas Gerais, Brazil

Workshop:

Belo Horizonte, Brazil, December 1-10,1986 

Sponsors:

International Union of Geological Sciences (IUGS)

United Nations Educational, Scientific, and Cultural OrganizationDeposit Modeling Program (UNESCO) 

Host:

Institute Brasileiro de Mineragao (IBRAM)

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

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

purposes only and does not imply endorsement by the U.S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1991

For sale by the

Books and Open-File Reports Section

U.S. Geological Survey

Federal Center

Box 25425

Denver, CO 80225

Library of Congress Cataloging-in-Publicatlon Data

Gold deposits related to greenstone belts in Brazil Deposit modeling 

workshop; Part A Excursions / edited by 

Charles H. Thorman, Eduardo A. Ladeira, and 

Diane C. Schnabel.

(U.S. Geological Survey bulletin ; 1980-A)

91-3522 

CIP
U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

GOLD DEPOSITS RELATED TO GREENSTONE BELTS IN BRAZILDEPOSIT MODELING WORKSHOP

Part A-Excursions

CONTENTS

Introduction to a workshop on gold deposits related to greenstone belts in Brazil, Belo Horizonte, 

Brazil, 1986, by Charles H. Thorman and Eduardo A. Ladeira Al

Geological field excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil, by 

Eduardo A. Ladeira A23

Field excursion from Belo Horizonte to Ouro Preto Side excursion along the road to Moeda, 

Minas Gerais, Brazil, by Eduardo A. Ladeira and Ronald Fleischer A39

Surface and underground geological excursion around and in the Passagem de Mariana gold mine, 

Minas Gerais, Brazil, by Ronald Fleischer and Diogenes Scipioni Vial A49

Excursion to the Morro Velho gold mine, Minas Gerais, Brazil, by Frederico Wallace Reis Vieira, 

Luiz Henrique do Amaral Lisboa, Jose Lamas Chaves, Geraldo Antonio Ibrahim de Oliveira, 

Paschoal Luiz Caiafa Clemente, and Rafael Lima de Oliveira A63

Excursion to the Cuiaba gold mine, Minas Gerais, Brazil, by Frederico Wallace Reis Vieira, Mario 

Corbani Filho, Jose Teotonio de Faria Fonseca, Aguinaldo Pereira, Geraldo Antonio Ibrahim de 

Oliveira, and Paschoal Luiz Caiafa Clemente A75

Katherine Dorr Abreu 

IBRAM coordinator
EXCURSIONS

Above and below ground

Belo Horizonte to Ouro 

Preto - Stop 1 (lower left), 

Stop 14 (center right)

Morro Velho gold mine- 

(left, center left, lower right)
Introduction to a Workshop on 

Gold Deposits Related to 

Greenstone Belts in BrazilBelo Horizonte, Brazil, 1986

By CHARLES H. THORMAN and 

EDUARDO A. LADEIRA

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A1
Structural complexities, Passagem de Mariana gold mine

Mafic and ultramafic rocks at C6rrego dos Boiadeiros

A2
CONTENTS

Introduction AS

Regional geologic setting A8

Summary of the Precambrian history of the Quadrilatero Ferrifero A8

Structural modifications A10

Stratigraphic modifications A14

Summary of the concepts on the origin of the gold deposits in the Quadrilatero

Ferrifero A14 

References cited A19 

Appendix: Explanation of the deposit-model form used to organize data A21

FIGURES

1. Geologic map of the Quadrilatero Ferrifero (modified from Dorr, 1969) showing 

the field trip routes for the workshop A6

2. Geologic map of the Quadrilatero Ferrifero (modified from Dorr, 1969) showing 

the location of major gold mines and occurrences in the area A7

3. Generalized Stratigraphic column of Precambrian rocks of the Quadrilatero 

Ferrifero (modified from Dorr, 1969) A9

4. Chart showing correlation of Precambrian deformational events in rocks in the 

Quadrilatero Ferrifero by various workers All

5. Simplified geologic map of the Quadrilatero Ferrifero (modified from Dorr, 1969) 

showing interpretation of the Rio das Velhas and Minas Supergroups as 

allochthonous on the basement complex A13

6. Diagram showing gold deposits relative to syngenetic versus epigenetic 

origin A19

TABLES

1. Criteria for gold deposits examined or analyzed during the workshop and shown 

on figure 6 A16

2. Postulated criteria for overall setting of iron-formation-related gold deposits in 

greenstone belts examined or analyzed during the workshop and shown on 

figure 6 A17

3. Model for the origin of the deposits visited or discussed during the workshop A18

Contents A3
Cm.MINflSDflPPSSPGEM

FIELD-TRIP LEADERS

(from left to right):

Skip Cunningham, John Kerswill, Chuck Thorman, Eduardo Ladeira, Stan Caddey, and Carl Anhaeusser

A4
Introduction to a Workshop on Gold Deposits 

Related to Greenstone Belts in BrazilBelo Horizonte, Brazil, 1986

By Charles H. Thorman 1 and Eduardo A. Ladeira2

INTRODUCTION

This volume comprises two parts (Bulletins 1980-A 

and 1980-B) and presents the results and scientific 

contributions of a workshop and field trips on "Gold 

deposits related to greenstone belts in Brazil," held 

December 1-10,1986, in Belo Horizonte, Brazil (fig. 1). 

The workshop was sponsored by the International Union 

of Geological Sciences (IUGS) and United Nations 

Educational, Scientific and Cultural Organization 

(UNESCO) Deposit Modeling Program, a program 

designed to advance geoscientific knowledge and 

expertise in mineral-deposit modeling for use in 

exploration, assessment, and development of resources. 

The purpose of the Deposit Modeling Program 

workshops is to facilitate the transfer of knowledge and 

expertise in these subject areas and to assist in training 

and educating geoscientists so that they can more 

effectively explore and assess resources in their home 

countries. Belo Horizonte was chosen as the workshop 

site because of its location in the Quadrilatero Ferrifero 

("Iron Quadrangle"), famous for its world-class gold 

deposits (Morro Velho, Raposos, Cuiaba, Sao Bento) 

and iron deposits (Itabira, Aguas Claras, Itabirito, 

Alegria). The goals of the workshop were attained 

through a series of lectures, discussion groups, and 

several field trips and mine visits, beginning with the 

general geologic setting of the Quadrilatero Ferrifero 

and ending with the construction of deposit models for 

the gold mines visited. This mixture of formats 

introduced the participants to gold occurrences in a

Manuscript approved for publication February 22,1991.

1U.S. Geological Survey, Box 25046 MS 905, Denver, Colorado 

80225, USA.

Departamento de Geologia, Institute de Geociencias, 

Universidade Federal de Minas Gerais, Belo Horizonte, Brazil.

major gold province and resulted in the development of 

deposit models for greenstone belts that can be applied 

in South American and other Precambrian shield areas 

in the exploration for gold and related commodities 

(silver, lead, zinc, copper). Figure 1 shows the field trip 

routes for the workshop and figure 2 shows the locations 

of the major gold mines and occurrences in the 

Quadrilatero Ferrifero.

The Institute Brasileiro de Minerac.ao (IBRAM) in 

Belo Horizonte was the host agency for the workshop. 

The organizing committee for the workshop consisted of 

the following people:

Katherine Dorr Abreu, IBRAM. 

Aristides Eust£quio Machado, IBRAM. 

Paulo Bahia Guimaraes, Minerac.ao Marex Ltda. 

Charles G. Cunningham, U.S. Geological Survey. 

Charles H. Thorman, U.S. Geological Survey. 

Eduardo A. Ladeira, Departamento de Geologia, 

Institute de Geociencias, Universidade Federal de 

Minas Gerais. 

Ronald Fleischer, Andrade Gutierrez Minerac.ao

Ltda. 

Workshop leaders and coordinators were as follows:

Charles H. Thorman, workshop coordinator and

leader. 

Charles G. Cunningham, IUGS/UNESCO

coordinator and leader. 

Katherine Dorr Abreu, coordinator for all logistical

functions and support for the workshop. 

Eduardo A. Ladeira, field trip coordinator, editor of

field trip guidebook, and leader. 

Carl R. Anhaeusser, University of Witwatersrand,

leader. 

Stanton W. Caddey, Homestake Mining Company,

leader.

John A. Kerswill, Geological Survey of Canada, 

leader.

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts In Brazil AS
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A6 Gold Deposits Related to Greenstone Belts in Brazil-Deposit Modeling Workshop

Part A Excursions
.. 

IB.V:\ISANTA BARBARA! 15

Maquine Group 

Nova Lima Group 

undifferemiated granitic rocks

Thrust fault Sawteeth on upper plate

GOLD MINES AND

MAJOR GOLD OCCURRENCES

INACTIVE MINES OR BEING EVALUATED

1. Ouro Fino 26. Antfinio Pereira

de Cima 27. Maquing

2. Ouro Fino 28. Rocinha

de Baixo 29. Santana

3. Morro do Adao 30. Morro Redondo4. Carrancas 31. MataCavalo5. Juca Vieira 32. Taquaral6. Fazenda Velha 33. Bom Jesus

7. Carrapato das Flores

8. Fazenda Cutao 34. Palacio Velho9. Fazenda Ojeri/a 35. Veloso

10. Luis Soares 36. Bico de Pedra11. Congo Soco 37. Ouro Preto

12. Camara 38. Ajuda

13. Taquaril - 39. Passa Tempo

Cocaes 40. Ouro Fino

14. Brucutu 41. Paciencia

15. Pari 42. Marzagao

16. Santa Quiteria 43. Bahu

17. Sao Jorge 44. Cata Branca

18. Brumandinho 45. Casa de Pedra19. Quebra Ossos 46. Gordura

20. Picarra 47. Urubu

21. Pitangf 48. Limeiro

22. Paracatu - do Sul

Agua Quente 49. Limeiro

23. Fazendao do Norte

24. Cata Preta 50. Galo25. Bento Rodrigues

ACTIVE MINES

51.Faria 55. BelaFama52. Gabirobas 56. Espirito Santo53. Gaia 57. Raposos

54. Bicalho

MAJOR MINES VISITED

58. Morro Velho (active) 61. Passagem

59. Cuiaba (active) de Mariana

60. Sao Bento (active) (inactive-being 

evaluated)

SCALE

Figure 2. Geologic map of the Quadrilatero Femfero (modified from Dorr, 1969) showing the location of major gold mines and occurrences in the area.
The two parts of this bulletin are divided as follows: 

Part A-Excursions (1980-A) includes (1) a field trip 

from Belo Horizonte to Ouro Preto (fig. 1); (2) a 

supplementary side field trip; and (3) field-trip logs of 

visits to the Morro Velho, Passagem de Mariana, and 

Cuiab£ gold mines. Part B Geology of deposits 

(1980-B) includes (1) the geology of the Quadrilatero 

Ferrifero; (2) the geology of the Morro Velho, Passagem 

de Mariana, Sao Bento, and Cuiab£ gold mines; (3) the 

Homestake and Lupin gold mines in North America; 

and (4) deposit models for the Brazilian and North 

American deposits.

This introductory chapter covers the following 

topics that relate to the Quadrilatero Ferrifero: the 

regional geologic setting of the Quadrilatero Ferrifero; a 

summary of the Precambrian history of the Quadrilatero 

Ferrifero; structural and stratigraphic interpretations of 

the Quadrilatero Ferrifero; and a summary of the 

concepts on the origin of the gold deposits in the 

Quadrilatero Ferrifero. Some of the alternative regional 

stratigraphic and structural interpretations presented 

herein have been discussed for many years and are 

generally accepted by geologists working in the 

Quadrilatero Ferrifero, but these interpretations may 

not be widely recognized outside of Brazil. Other 

stratigraphic and structural interpretations are the 

subject of much debate and are far from settled. A 

byproduct of the workshop was the release of previously 

unpublished data by mining companies on the geology of 

several of the ore deposits visited in Brazil and on North 

American deposits.

This publication differs from most in presenting a 

mixture of new data in a variety of formats. The papers 

on the gold mines visited contain new data concerning 

both the basic geology of the mines as well as production 

and reserve information. Also, some of these papers 

describe trips through the mines, as made by the 

participants in the workshop. We have included these 

descriptions because they provide important insights into 

mine geology.

REGIONAL GEOLOGIC SETTING

The Quadrilatero Ferrifero has been an area of 

mineral exploration and geologic investigation for 

centuries, dating back to the search for gold and 

precious stones that began in the 16th century. The 

discovery in 1699-1701 of black gold-gold 

contaminated with iron and platinum-group metals in 

the southeastern corner of the Quadrilatero Ferrifero 

gave rise to the name Serra de Ouro Preto (Black Gold 

Range) and the name of the town Ouro Preto. The 

Quadrilatero Ferrifero contains world-class gold and

iron ore deposits, manganese ore, bauxite, and 

precious-stone locales. Much data has been generated 

about the mineral wealth and geology of the area. The 

best known and most easily available work, which forms 

the basic geologic framework of the Quadrilatero 

Ferrifero, resulted from a cooperative study between the 

Departamento National da Producao Mineral (DNPM) 

of the Ministe'rio das Minas e Energia (MME) and the 

United States Geological Survey (USGS) from 

1946-1962. This study was primarily a geologic 

mapping program designed to develop a solid geologic 

data base that would help in the future utilization of 

Brazil's natural resources. Many reports and maps on 

the general geology and economic geology of the 

Quadrilatero Ferrtfero have been published in Brazil 

and the United States. The summary report by Dorr 

(1969) includes a geologic map of the Quadrilatero 

Ferrifero at a scale of 1:150,000, based on the detailed 

and reconnaissance mapping of forty-seven 7}4-minute 

topographic quadrangles at 1:25,000 by DNPM and 

USGS geologists.

The following outline of the geologic history of the 

Quadrilatero Ferrifero was established by the 

DNPM/USGS program. The distribution of units, their 

relative positions in time, and the sequence of tectonic 

events is little changed. Dorr's 1969 summary paper of 

the geology of the Quadrilatero Ferrifero has truly stood 

the test of time. This is an impressive statement for the 

work of such a large group of geologists in a highly 

complex and, at the time, not easily accessible region. 

Work by many geologists in the past two and one-half 

decades has indicated the need for only a few revisions 

of Dorr's geologic outline. One revision, however, has 

major implications on the structural evolution of the 

Quadrilatero Ferrifero and is presented in the following 

section. Figure 3 shows a generalized stratigraphic 

section of the Precambrian rocks in the Quadrilatero 

Ferrifero modified from Dorr (1969).

SUMMARY OF PRECAMBRIAN HISTORY 

OF THE QUADRILATERO FERRIFERO

This summary is based on Dorr (1969); modifications 

to it are discussed in the section after this one.

1. The oldest rocks comprise the Rio das Velhas 

Supergroup, a metasedimentary and metavolcanic 

succession divided into the Nova Lima and Maquin6 

Groups (fig. 3). Dorr (1969) considered the Nova Lima 

Group to be a eugeosynclinal flysch unit and the 

overlying Maquine" Group to be eugeosynclinal molasse. 

The Rio das Velhas Supergroup is now recognized as a 

greenstone belt. The Nova Lima Group hosts most of 

the large gold deposits in the Quadrilatero Ferrifero.

A8 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
u

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PROFOUND OROGENY WITH REGIONAL METAMORPfflSM

Itacolomi Group 

PROFOUND ANGULAR UNCONFORMITY

Minas Supergroup

Piracicaba Group

Itabira Group

Caraca Group

Sabara Formation 

Barreiro Formation 

Tabooes Formation 

Fecho do Funil Formation 

Cercadinho Formation

Gandarela Formation

Caue Itabirite \

/

Batatal Formation 

Moeda Formation

Tamandua Group 

MAJOR OROGENY WITH REGIONAL METAMORPfflSM

W

DC 

U

Rio das Velhas 

Supergroup

Maquin6 Group

Nova lima Group

Casa Forte Formation

Palmital Formation \

/

Upper unit*

Middle unit* (includes Lapa Seca Formation) 

Lower unit*

CONTACT CONSIDERED INTRUSIVE BY DORR (1969) 

Granitic-gneissic basement rocks, including granitoids of various ages

Figure 3. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero Ferrffero (modified from Dorr, 1969). 

Asterisk (*) indicates units not included in Dorr's paper but discussed in the text of the present paper.

2. The Rio das Velhas Supergroup rocks were 

deformed and metamorphosed during a major erogenic 

event at about 2700 Ma (Herz, 1970), before deposition 

of the overlying Minas Supergroup. This orogenic event 

may have been accompanied by igneous activity.

3. The Minas Supergroup includes four groups. (1) 

The basal Tamandua Group contains a lower paralic 

prismatic clastic unit (Cambotas Formation) and an 

upper dolomitic phyllite, dolomitic oxide-facies 

iron-formation, and a quartzose phyllite unnamed unit. 

A local unconformity separates the overlying Caraga 

Group from the Tamandua Group. (2) The Caraca 

Group has a lower conglomerate, sandstone, and minor 

shale unit (Moeda Formation) and an upper phyllite, 

graphitic phyllite, metachert, and oxide-facies 

iron-formation unit (Batatal Formation). These rocks

are conformably overlain by (3) the Itabira Group, which 

comprises the lower Caue Itabirite and upper Gandarela 

Formation. The Caue Itabirite is made up of 

oxide-facies iron-formation (itabirite), dolomitic 

itabirite, amphibolitic itabirite, and minor phyllite and 

dolomite. The Gandarela Formation consists primarily 

of dolomitic marble, but includes dolomitic phyllite, 

dolomitic iron-formation, and phyllite. The world-class 

iron deposits in the Quadrilatero Ferrifero occur in the 

Caue Itabirite, and manganese is produced from both 

the Caue and the Gandarela formations.

(4) The Piracicaba Group unconformably overlies 

the Itabira Group. A local basal conglomerate (basal 

Cercadinho Formation) occurs at the base of the group 

along the unconformity with minor relief. A concordant, 

continuous sequence of deposition is interpreted from

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts in Brazil A9
the Cercadinho Formation through the Fecho do Funil 

Formation, Tabooes Quartzite, and Barreiro Formation. 

These units are primarily quartzites to quartzitic 

phyllites with minor dolomitic lenses. The Cercadinho 

includes ferruginous strata. The Barreiro, mainly 

fine-grained rocks, consists primarily of phyllite and 

graphitic phyllite. The uppermost unit, the Sabar£ 

Formation, rests on all the older units in the Piraticaba 

Group and locally has a basal conglomerate; beds above 

and below the contact are concordant structurally. The 

Sabar£ consists of schist and phyllite, probably derived 

from tuffaceous and graywacke protoliths, and local 

tilloid-like conglomerate. A stable shelf or blanket 

environment was interpreted by Dorr (1969) for the 

siliciclastic Cercadinho through Barreiro sedimentary 

cycle and a eugeosynclinal flysch environment for the 

Sabara.

4. An angular unconformity occurs at the top of the 

Minas Supergroup; it was interpreted to indicate broad 

uplift and erosion and to be epeirogenic.

5. The Itacolomi Supergroup, a quartzitic to 

conglomeratic unit with varied amounts of sericite, was 

considered by Dorr (1969) to be paralic (molasse?) in 

origin.

6. A post-Itacolomi orogeny probably formed the 

basic geologic framework of the Quadrilatero Ferrifero. 

The age of this event, according to Herz (1970), was 

about 1000-1350 Ma. This event caused all the complex 

large-scale folds and other major structures of the 

Quadrilatero Ferrifero, including the emplacement of 

the several domal granitic structures (Baclo Complex 

and others), considered intrusive igneous granitic rocks 

by Dorr (1969).

7. The area was probably covered by carbonate and 

pelitic rocks of the Late Proterozoic Bambui Group, and 

the entire region was folded and faulted by the Brasilian 

Cycle (about 600 Ma). Events post-dating these 

activities are not considered here.

Modifications to the basic geologic framework of the 

Quadrilatero Ferrifero just outlined that have been 

developed since the DNPM/USGS program and are 

generally accepted are presented next. These 

modifications include both stratigraphic and structural 

contributions.

STRUCTURAL MODIFICATIONS

The most fundamental and far-reaching modification 

to the geologic framework of the Quadrilatero Ferrifero 

outlined hi the summary of Dorr's work (1969) is the 

concept that the granitic-gneissic basement complex is as 

old or older than the Rio das Velhas Supergroup, which 

overlies it, and that the basement complex is cratonic.

This modification considers the Archean Rio das Velhas 

Supergroup as part of a greenstone belt deposited on 

oceanic crust somewhere east of the Quadrilatero 

Ferrifero and thrust westward onto the craton. In this 

model, the contact between the Rio das Velhas 

Supergroup and the basement was a major thrust. The 

Minas Supergroup is interpreted as a Proterozoic 

continental margin assemblage that was also thrust over 

the basement complex and the Rio das Velhas 

Supergroup. Some members of the DNPM/USGS team 

considered several major thrusts to be present (Guild, 

1957; Barbosa, 1969; Maxwell, 1972) although the 

concept of the Rio das Velhas and Minas Supergroups 

as allochthons thrust over the granitic basement was not 

included hi Dorr's geologic framework. These thrusts 

included one at the contact of the Rio das Velhas-Minas 

Supergroup with the basement and another between the 

Rio das Velhas Supergroup and the Minas Supergroup 

at many localities.

In addition to Dorr's (1969) summary of the region, 

Herz (1970), Drake and Morgan (1979), Ladeira and 

Viveiros (1986; this volume, Part B Geology of 

deposits ) and Morritt (1988) presented summaries that 

have many common aspects as well as some significant 

differences. Herz, who was part of the USGS team 

involved in the DNPM/USGS Quadrilatero Ferrifero 

mapping project, based his outline of the Quadrilatero 

Ferrifero geologic history largely on Dorr's work, but 

Herz's major contribution was to radiometrically date 

many of the rock units, thus giving substance to the time 

factor. Drake and Morgan (1979) added a new 

interpretation based on a plate tectonics model, hi which 

they considered ultramafic rocks at and near the base of 

the Archean Rio das Velhas Supergroup to represent 

ophiolite and the Rio das Velhas to be an allochthonous 

greenstone belt thrust westward onto a cratonic 

basement complex coeval with or older than the Rio das 

Velhas. Ladeira and Viveiros (1986; this volume, Part 

B Geology of deposits) identified six stages of 

deformation, but did not correlate them with any 

regional tectonic or thermal events. In contrast, Morritt 

(1988), in a more regional study, correlated the 

individual deformational events identified by the 

previous workers and placed them hi an order with 

regionally established events. Figures 4 and 5 show 

these summaries and the correlations of Morritt. 

Although ideas and interpretations differ among the 

workers, the basic concepts of Dorr (1969) remain 

unchanged except for the interpretation that the supracrustal Rio das Velhas greenstone suite is allochthonous.

It is difficult to know who to credit with the concept 

of the Rio das Velhas being allochthonous. The idea 

was considered by some of the DNPM/USGS geologists 

in the 1950's and 1960's (informal discussions by C.H.

A10 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
I

EVENT AGE DEFORMA- Dorr Herz

TION

South Atlantian

Brazilian

Espinhago 

Transamazonian

pre-Transamazonian 

pre-Transamazonian 

pre-Transamazonian

22-195 Ma

450-700 Ma

1000-1300 Ma 

2000-2100 Ma

2700 Ma 

+2700 Ma

8

7

6

5

4 

3 

2 

1

(1969) (1970)

"D6"-H

"D3"-D "D5"-H

"D4/3"-H 

"D2"-D "D2H-H

"D1"-D "D1H-H

Drake &

Morgan 

(1979)

_

-

"D3"-DM

"D2"-DM 

"D1"-DM

Ladeira &

Viveiros 

(1984, 1986)

"D6H -LV

"D5"-LV

"D4/3/2"-LV

"D1"-LV

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9

I

The following outline of Precambrian events includes the depositional history indicated by an ast

well as the numbered events (D).

* Accumulation of the Archean Nova Lima Group greenstone sequence in an oceanic setting. 

1,2. Nappe-forming events during which the Nova Lima Group was deformed and thrust nor

from an oceanic setting onto cratonic crust.

3. Subsidence of the deformed Nova Lima Group sequence to form depocenter for Minas 

4. Folding of entire Rio das Velhas Supergroup about broad east-west axes. Included emp

crystalline bodies, such as the Bagao and Moeda complex.

* Deposition of Minas Supergroup on folded Rio das Velhas Supergroup.

5. Broad warping and uplift of Minas Supergroup. Includes emplacement of granitic bodie

* Deposition of Itacolomi Group on Minas Supergroup with angular unconformity of as much as 

6. Post-Itacolomi .Group folding and thrusting with north-northwest vergence. Includes em

of granitic bodies as well as renewed activity in the Bagao and Moeda complexes.

7. West- to southwest-verging folding and thrust faulting of rocks as young as the Late Prot

Bambui Group.

8. Intrusion of diabase sills and small gabbroic stocks.

Figure 4. Precambrian defbrmational events in rocks in the Quadrilatero Ferrffero. The correlation of th

deformational events is from Morritt (1988), including the letter/numbered events by author(s).
Thorman with several members of the DNPM/USGS 

team); however, this interpretation is difficult to glean 

from their reports. Grossi Sad and Ladeira (1968), 

Ladeira (1976,1980), and Schobbenhaus and others 

(1981) all indicated a thrust relationship between the 

Archean basement complex and the Rio das Velhas and 

Minas Supergroups over much of the area. The 

following sequence of events indicates how one of us 

(Thorman) developed ideas regarding the allochthonous 

nature of the Rio das Velhas and Minas Supergroups in 

the Quadrilatero Ferrifero.

1. In February, 1973, Thorman was teaching a 

photogeology reconnaissance mapping course as part of 

an MME/USAID (United States Agency for 

International Development) program for MME 

geologists. One part of the course entailed constructing 

a geologic map of part of the Quadrilatero Ferrifero and 

then field-checking the work. The first area checked was 

in the Serra da Moeda, on the west side of the 

Quadrilatero Ferrifero, from the Minas Supergroup 

down into the granitic basement complex. The first 

traverse was on the dirt road from Highway BR-040 to 

Moeda (see Ladeira and Fleischer, this volume, Part 

A Excursions). Thorman and several geologists taking 

the course recognized that the contact of the Rio das 

Velhas-Minas Supergroups with the basement shown on 

the geologic map of Wallace (1965) was not intrusive but 

a major fault dipping gently to the east beneath the Rio 

das Velhas and Minas Supergroups. The fault is marked 

by many mylonitic zones within the basement (for more 

than 100 m (meters) below the contact) that increase 

upward to the contact and become more closely spaced 

and more intensely deformed toward the contact. 

Tectonic breccia occurs locally along the contact. 

Indications of the deformation disappear a short 

distance above the contact. A similar relation was noted 

farther north, where the contact is exposed in several 

locales. Thorman and the group looked at exposures of 

this contact in the southern and western parts of the 

Quadrilatero Ferrifero. At more than a dozen places, 

the contact was obviously a low-angle fault. In other 

places, however, the evidence was not as clear. For 

example, around the margin of the Bac.ao Complex, the 

deformed rocks have been annealed by subsequent 

metamorphism. However, both the map pattern, which 

suggests strongly thinned and pinched units against or 

near the contact, and the strongly sheared rocks at the 

contact indicate that the contact is a shear zone that 

resulted from thrust faulting and was later locally 

metamorphosed.

The overall map pattern of units at the base of the 

metasedimentary sequence throughout the Quadrilatero 

Ferrifero indicates either highly irregular stratigraphic 

relationships and (or) major structural complications

commonly observed at the base of allochthons. From 

March, 1973 until July, 1974, Thorman examined several 

other contacts of the basement with the overlying Rio 

das Velhas and Minas Supergroups in the Quadrilatero 

Ferrifero and became convinced that this contact is 

tectonic and locally modified by younger metamorphism 

or intrusion.

2. Later in the 1973 photogeology course, Oscar 

Braun (then with Companhia de Pesquisa de Recursos 

Minerals (CPRM)) took the group to visit several 

contacts of the Rio das Velhas Supergroup with the 

basement to show why he also thought the contact was 

tectonic. He also pointed out that other Brazilian 

geologists were of the same opinion.

3. Shortly before Thorman returned to the United 

States in 1974, he took Avery Drake of the USGS on a 

tour of the Quadrilatero Ferrifero during the planning 

stages for a field geology course for MME geologists to 

be run out of Belo Horizonte. During the tour, 

Thorman showed Drake the exposures on the west side 

of the Quadrilatero Ferrifero, as well as others, as 

potential sites for detailed geologic mapping for training 

in structure and stratigraphy. Thorman pointed out his 

interpretation of the allochthonous setting of the Rio das 

Velhas and Minas Supergroups. Subsequently, Drake 

and Morgan (1979) developed the concept that mafic 

and ultramafic rocks at and near the base of the Rio das 

Velhas Supergroup were part of an ophiolite sequence, 

out of place on cratonic basement, that had been thrust 

westward from an oceanic setting.

4. Charles Maxwell and Samuel Moore (part of the 

USGS team that mapped the Quadrilatero Ferrifero), 

pointed out to C.H. Thorman in the middle 1970's that 

the concept of the Rio das Velhas and Minas 

Supergroups being allochthonous was not new and that 

it had been discussed at great length earlier by many 

members of the team in the early 1960's. To present the 

idea in the context of the regional tectonics as 

understood in the 1960's, however, was difficult; if the 

concept of plate tectonics had existed at that time, the 

overall geologic framework established by the 

DNPM/USGS team would have been quite different. 

The idea that the Rio das Velhas-Minas/basement 

contact might not be intrusive was alluded to in indirect 

terms by several individual workers (including Johnson, 

1962; Pomerene, 1964; Wallace, 1965; Simmons, 

1968a,b; Moore, 1969), but it was not included in Dorr's 

(1969) summary of the geology of the Quadrilatero 

Ferrifero. Dorr believed all the basement rocks 

intruded, and thus were younger than, the metamorphic 

rocks.

5. It is now evident that many geologists who have 

worked or are working in the Quadrilatero Ferrifero 

believe that the allochthon concept is the only logical

A12 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
I

fit

I

I

CO

?

31

O

SCALE

Figure 5. Simplified geologic map of the Quadrilatero Ferrffero (modified from Dorr, 1969) showing the interpretation of the Ri

Supergroups as allochthonous on the basement complex.
way to explain the observed relationships. In the paper 

by Ladeira and Viveiros (this volume, Part B Geology 

of deposits), the allochthon concept is a major part of 

their geologic reconstruction of the Quadrilatero 

Ferrifero.

We show the concept of the supracrustal rocks as an 

allochthon juxtaposed on the basement complex in 

figure 5. The geology is that of Dorr (1969) with one 

major change. The contact of the basement with all 

overlying rocks is shown as a thrust fault; the basement 

complex is the footwall of the thrust fault. This 

interpretation does not exclude the possibility that some 

parts of the thrust fault have been modified by younger 

structures, by intrusion of igneous or granitoid bodies, or 

by the remobilization of basement in the form of partial 

melting or plastic flow as large domal masses or mantled 

gneiss domes. For example, (1) basement is faulted over 

the Rio das Velhas Supergroup on the east side of the 

area near Santa Rita Durao, (2) an igneous body 

appears to intrude the contact on the east side of the 

Quadrilatero Ferrifero south of Santa Barbara (C.W. 

Maxwell, oral commun., 1988), and (3) the Bacao 

Complex, a domal massif or mantled gneiss dome in the 

southern part of the area, intruded preexisting structures 

and has a contact aureole.

STRATIGRAPHIC MODIFICATIONS

Modifications of the stratigraphic column subsequent 

to Dorr's (1969) publication, have been few. Two 

changes in the Rio das Velhas Supergroup are included 

on the stratigraphic column of figure 3.

1. A succession of submarine ultramafic to mafic 

rocks (lower unit) forms the base of the Nova Lima 

Group; its relationship to the basement complex has 

been obliterated by shearing and (or) granitization. 

These submarine rocks were named the Quebra Osso 

Group by Schorscher (1978) and Inda and others (1984), 

but inasmuch as their work did not comply with the 

stratigraphic code of Brazil, we herein assign the rocks 

to the Nova Lima Group. The existence of these 

submarine rocks prompted Drake and Morgan (1979) to 

suggest that an ophiolite complex was at the base of the 

Rio das Velhas Supergroup greenstone belt and that 

these rocks had been thrust westward onto cratonic crust 

from an original oceanic setting.

2. The Nova Lima Group is divided into three 

informal units by Ladeira (1980) and company geologists 

working at the Cuiab£ mine (Vieira, Corbani, and 

others, this volume, Part A Excursions), Morro Velho 

and Raposos mines (Vieira, Lisboa, and others, this 

volume, Part A Excursions), and Sao Bento mine 

(Moseley, this volume, Part B Geology of deposits).

A major nomenclature and correlation problem 

exists in the use of the term "Espinhaco," a possible 

correlative either of the Itacolomi or Tamandu£ Groups, 

in the Quadrilatero Ferrffero region. Immediately north 

of the Quadrilatero Ferrifero is the Serra do Espinhac.o, 

the type area for the Middle Proterozoic Espinhaco 

Supergroup, a succession of quartzite, phyllite, and lean 

BIF (low-grade banded iron formation). About 20 km 

(kilometers) north of the Quadrilatero Ferrifero, similar 

rocks extend about 1200 km to the north into the state of 

Bahia from the Serra do Espinhaco, but the physical 

continuity with the former units of the Quadrilatero 

Ferrifero is not known at this time. The problem lies in 

the suggested correlations of the Espinhac.o Supergroup 

with the Tamandua Group, the basal unit of the Early 

Proterozoic Minas Supergroup, and with the Itacolomi 

Group, the Middle Proterozoic unit that overlies the 

Minas Supergroup. This correlation uncertainty is 

beyond the scope of this paper but it is mentioned to 

make the reader aware of what might be interpreted as 

discrepancies between authors. Ladeira and Viveiros 

(this volume, Part B Geology of deposits) discuss this 

problem and make structural interpretations based on 

their reinterpretation of Tamandua and Itacolomi 

correlations. Schobbenhaus and others (1981) and Inda 

and others (1984) revised Dorr's (1969) use of these 

units.

SUMMARY OF THE CONCEPTS ON THE 

ORIGIN OF THE GOLD DEPOSITS IN THE 

QUADRILATERO FERRIFERO

The topic most hotly and emotionally debated at the 

workshop was the origin of the gold deposits syngenetic 

versus epigenetic and combinations thereof. Individual 

geological experience strongly influenced a debater's 

position. After 10 days together in a wide range of 

working environments, from air-conditioned bars to the 

sweltering +120 °F heat in the Morro Velho mine 2.45 

km below the surface, the pendulum appeared to swing 

in every direction at one time or another, but no 

unanimous agreement as to the origin of the gold 

deposits could be reached. However, from the many 

hotly contested discussions, agreements were reached, 

not the least of which were the topics that needed 

further study.

Before launching into discussions of deposit models 

for the various gold deposits, we believed a definition of 

a greenstone belt was essential. This initial exercise in 

defining the belt was one of the most interesting we 

embarked upon in the workshop and clearly reflected 

the background and bias of individuals. The participants

A14 Gold Deposits Related to Greenstone Belts In Brazil Deposit Modeling Workshop Part A Excursions
readily formed into two camps those with a restricted 

definition and those with a looser definition. 

Fortunately, considerable common ground existed 

between the two camps and a concensus was not too 

difficult to arrive at. The following criteria made up the 

common ground.

 An elongate erogenic belt of supracrustal rocks 

20-200 km wide and 100-800 km long.

 Stratigraphic sequence commonly consists of the 

following rock types from base to top:

1. A lower suite of metavolcanic rocks with

ultramafic rocks at base and calc-alkaline mafic to 

felsic rocks at top that contains some chemical 

sedimentary rocks.

2. An upper suite of clastic argillaceous deep-water 

rocks that grade upward into shallow-water clastic 

rocks and chemical precipitates (carbonates, iron 

formation).

 Supracrustal belt rocks have been moderately to 

intensely deformed; typically more than one regional 

metamorphic event; complex structural setting.

 Metamorphic grade ranges from greenschist to

granulite facies; typically greenschist over large areas.

 Belt is bounded by and intruded by granitic plutons 

that form large massifs.

 The supracrustal rocks commonly occur in major 

synclinoria separated by granitic massifs.

 Marked increase in metamorphic grade adjacent to 

plutons is common.

 World-class metallic ore deposits related to plutons, 

volcanic rocks, and iron formation.

 Rocks contain earliest forms of life.

The camp favoring a restricted definition of a 

greenstone belt required the presence of considerably 

more ultramafic to mafic volcanic material than did the 

other camp. The amount of this volcanic material is 

extremely important, because the restricted view was 

applied to the Rio das Velhas greenstone belt our 

workshop area. Ultramafic to mafic volcanic rocks in 

the Rio das Velhas Supergroup in the Belo Horizonte 

area were considered to be minimal by several 

participants. And, therefore, they questioned referring 

to the Rio das Velhas sequence as a greenstone belt.

An upper suite of clastic and chemical rocks have 

long been recognized in the area, but not until recently 

has anyone emphasized the ultramafic to mafic volcanic 

rocks (Drake and Morgan, 1979). During our trip to the 

Sao Bento mine we saw pillow structures in mafic flow 

rocks in drill cores from the Rio das Velhas; these 

structures convinced participants that mafic volcanic 

rocks were more plentiful than previously realized. 

More recent work by Ladeira and other workers have 

documented the presence of komatiites with spinifex 

texture in the Quadrilatero Ferrifero (Ladeira and

others, 1985; Noca and others, 1990).

General consensus was reached that the presence of 

volcanic rocks is more important than the relative 

amount of such rocks. In addition, both camps agreed 

that the amount of ultramafic to mafic rock recognized 

commonly may be a function of the interpretation of 

previous workers and that further work will probably 

reveal more of these rocks. From this common ground, 

we mutually agreed that the Rio das Velhas sequence 

does indeed constitute a greenstone belt.

Some of the most productive time was spent 

developing deposit model forms for each of the mines 

visited and for most of the deposits discussed by the 

workshop leaders (the deposit-model form used for this 

task is explained in the appendix). In the discussion 

groups assigned to fill out the forms for the various 

models, a major part of the exercise was to separate fact 

from interpretation so that the deposits could be 

compared objectively. The deposit-model form for each 

of the deposits are presented in a separate chapter 

(Thorman, this volume, Part B Geology of deposits). 

The data for each deposit were compiled in tabular form 

in order to readily compare similarities and differences 

among the deposits (tables 1 and 2). A model for the 

origin of the deposits, based on these observed 

similarities and differences, is shown in table 3.

Two extremes or ends of the spectrum were taken 

with regard to the source and transportation of the gold. 

At one end, the gold was considered to be of strictly 

syngenetic origin in iron-formation, carbon-rich 

sedimentary rocks, or mafic-felsic volcanic units. During 

later remobilization (metamorphism) the gold was 

moved laterally within the system, for some unknown but 

probably small distance, to favorable sites determined by 

host-rock chemistry and structure.

At the other end of the spectrum, the gold was 

considered to be of strictly epigenetic origin and 

introduced to the system during deformation at the same 

time as or just after metamorphism. The final site of 

deposition was controlled by the rheology and chemistry 

of the host-rock environment and by favorable 

structures, such as dilational shear zones (see fig. 6).

Many of the workshop participants believed that 

some deposits visited could not be readily categorized as 

either syngenetic or epigenetic. However, other 

participants argued heatedly that most of the deposits 

were clearly epigenetic, whereas a few pressed just as 

strongly for a syngenetic origin. Perhaps a realistic view 

is that an environment characterized by volcanic activity 

(greenstone) and chemical sedimentation, including 

oxide, carbonate, sulfide, and silica-rich iron-formation 

facies and carbon-rich pelites, was later metamorphosed 

to produce the contained gold deposits. In such an 

environment, gold derived from exhalative activity

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts in Brazil A15
Table 1 . Criteria for gold deposits examined or analyzed during the workshop and shown on figure 6

[D, diagnostic criteria; P, permissive criteria; P/D, not certain if criteria is diagnostic or permissive; X, not 

present in deposit; ?, sufficient data are not available to determine the role of that particular factor or there is a 

question as to whether or not that particular item is present at the deposit; asterisk (*) indicates the option of 

two interpretations; first letter refers to a facies or syngenetic model and the second letter refers to a structural 

or epigenetic model]

Criteria

Greenstone belt ---------------------------

Chemical sediments (Algoma type) ------------

Oxide facies ---------------------------

Iron-rich carbonate ---------------------

Chert --------------------------------

Sulfur-rich chemical sediment ("sulfide facies")

Graphitic phyllite/rock ---------------------

Quartz-sericite schist ( + /- intermediate/volcanic rocks)

Itabirite (Superior type/Proterozoic/well developed)

Mafic volcanics ----------------------------

Orebody controlled by structure --------------

Stratabound -.............._-..-.........

Stratiform --------------------------------

Metamorphism in greenschist or lower amphibolite facies

Age of host rock --------------------------

Host-rock lithology:

BIF (includes iron-rich chemical sediment; not itabirite)

Graphitic phyllite -----------------------

Mafic volcanic -------------------------

Felsic volcanic -------------------------

Itabirite -------------------------------

Quartz veins in ore body --------------------

Quartz-carbonate veins in ore body -------------

Absence of base metals (except in trace amounts)

Iron sulfides ------------------------------

Pyrite --------------------------------

Pyrrhotite -----------------------------

Arsenopyrite ---------------------------

Tourmaline -------------------------------

Scheelite --------------------------------

Bismuth --------------------------------

Antimony --------------------------------

Silver (silvergold about 6:1) -------------------

Mercury ---------------------------------

Sphalerite -------------------------------

Galena ----------------------------------

Chalcopyrite -----------------------------

Alteration assemblages ----------------------

Sulfides -------------------------------

Carbonates ----------------------------

Sericite -------------------------------

Chlorite -------------------------------

Biotite -------------------------------

Hornblende ----------------------------

Complex structure -------------------------

Shear zones ------------------------------

Morro

Velho

D

D

X

D

P

D

P

P/D

X

P?

7

D

D

D?

Archean

D

X

X

X

X

P

7

D

D

P/D

D

P/D

P

P/D

X

P

D

X

P

P

P

77

X

77

P?

7

7

X

D

D

Cuiaba

D

D

X

D

P

D

P

P/D

X

P/D

P

D

D

D?

Archean

D

X

P

X

X

P

7

D

D

D

P/D

P

7

7

7

7

D

7

P?

P?

X

P?

P

P?

7

7

7

X

D

P/D

Sao

Bento

D

D

D

D

D

X

P

P/D

X

P/D

D

D

X

D?

Archean

D

P

X

X

X

D

D

D

D

P/D

D

D

X

D?

7

D

D(8:l)

D?

X

X

X

D

D

D

7

P

7

X

D

D

Passagem

P/D?*

P

X

P

P

X

P

P/D

P

X

P/D*

P/D*

X

D?

Early

Proterozoic?

X

P

X

P

P

D

D

D

D

P/D

P/D

D

P

D?

D?

7

D

7

X

7

X

D

D

D

7

7

7

X

D

D

Lupin

D

D

X

X

P

D

P

X

X

X

7

D

D

D

Archean

D

X

X

X

X

P

X

D

D

P

D

P

X

P

X

X

D

X

X

X

D

P

P

X

X

P

X

D

D

D

Homestake

D

D

X

D

D

P

P

P

X

P

D

P

X

D

Early

Proterozoic

D

P

X

X

X

D

D

D

D

P

D

D

P

P

X

X

D

X

P

P

P

D

D

D

P

D

D

P

D

D

A16 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
Table 2. Postulated criteria for overall setting of iron-formation-related gold deposits in greenstone belts examined or 

analyzed during the workshop and shown on figure 6

[Note that the general classification of the deposits to a syngenetic or epigenetic origin is highly controversial. 

An asterisk (*) indicates those deposits for which there is less agreement on their classification and are 

therefore listed under more than one heading; see figure 6 and discussion in text]

Morro Cuiaba Sao Passagem Lupin Homestake 

Criteria Velho Bento

Relative position to volcanic center

1, proximal; 2, intermediate; 3, distal ------- 2-3 1-2 2 3? 2-3 3

Tectonic setting of host rock when formed:

1, unstable; 2, intermediate; 3, stable -------- 3 3 3 1-2 3 3

Tectonic setting at time of mineralization:

1, strongdef.; 2, intermediate; 3, no def. ------- 2? 2 1 1 2? 1?

Igneous intrusive activity:

1, very active; 2, moderate; 3, no activity ------ 3 3 3 3 3 3

Igneous extrusive activity:

1, very active; 2, moderate; 3, no activity ------ 2 2 2 2 2 2

GENERAL GEOLOGIC SETTING: 

Greenstone belt. 

Periods of chemical sedimentation with BIF (including carbonate, oxide, sulfide, and minor silicate

facies) and carbonaceous rocks (graphitic association important). 

Bimodal volcanism may be important. 

Sulfur is needed hi the system. In a syngenetic model, the sulfur would have to be deposited with the

sediment, whereas in an epigenetic model the sulfur could be introduced later. 

Greenschist-facies metamorphism appears to be important in the Quadrilatero Ferrifero deposits and

elsewhere. This level of metamorphism may be the minimum required; the upper limit is probably

middle amphibolite facies. In a syngenetic model, regional metamorphism is not needed, whereas

in one variant of the epigenetic model the metamorphism would be the heat source for

hydrothermal activity. 

Moderately complex deformational history is common, typically with several episodic phases of structural

development. 

Ductile shear zones are important in some models.

MINERALOGICAL AND CHEMICAL SETTING: 

Sulfur occurs as abundant iron-sulfides.

Arsenic and tungsten more common in structurally controlled deposits. 

Silica is common to the overall system. 

Iron carbonate is common to the overall system. 

Iron important as catalyst to drop sulfur, both during chemical sedimentation and subsequent sulfide

mineralization associated with deformation and metamorphism. 

Carbon may be important to the overall system, but its exact relationship is not clear.

GENERAL CLASSIFICATION OF THESE DEPOSITS is considered to be as follows: 

Syngenetic-prdbably has some subsequent movement of gold;

Lupin, Morro Velho*, Homestake*. 

Syngenetic moderate amount of movement of gold due to later events;

Cuiab^, Morro Velho*, Sao Bento*. 

Epigenetic major control of mineralization due to deformation;

Homestake*, Passagem, Sao Bento*.

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts in Brazil A17
Table 3. Model for the origin of the deposits visited or discussed during the workshop

GENERAL GEOLOGIC SETTING:

 Greenstone belt.

 Periods of chemical sedimentation, with BIF (including carbonate, oxide, sulfide and minor 

silicate facies) and carbonaceous rocks (graphitic association important).

 Bimodal volcanism may be important.

 Sulfur is needed hi the system. In a syngenetic model, the sulfur would have to be deposited with 

the sediment, whereas hi an epigenetic model, the sulfur could be introduced later.

 Greenschist-facies metamorphism appears to be important. This metamorphism may be the 

minimal grade required; the upper limit is probably middle amphibolite facies. In a syngenetic 

model, regional metamorphism is not needed, whereas hi one variant of the epigenetic model, the 

metamorphism would be the heat source for hydrothermal activity.

 Moderately complex deformational history is common and typically includes several episodes or 

phases of structural development.

 Ductile shear zones are important hi some models.

MINERALOGICAL AND CHEMICAL SETTING: 

Sulfur occurs as abundant iron-sulfides.

Arsenic and tungsten are more common hi structurally controlled orebodies. 

Silica is common to the overall system. 

Iron carbonate is common to the overall system.

Iron is important as a catalyst to drop sulfur, both during chemical sedimentation and subsequent 

sulfide mineralization associated with deformation and metamorphism (see earlier comments 

regarding sulfur).

 Carbon may be important to the overall system, but its exact relationship is not clear.

during sedimentation was deposited as an extremely fine, 

disseminated stratiform component of the system and 

formed a gold occurrence, not an economic gold deposit. 

Whether the gold was originally tied up with the carbon, 

with sulfide minerals, or with other minerals, is 

unknown. The gold was probably confined to a 

particular stratigraphic horizon or interval, rather than 

disseminated throughout a large vertical section. The 

transformation of the gold from a disseminated element 

hi trace amounts to a major gold deposit appears to have 

depended on (1) regional metamorphism to at least the 

greenschist facies, and (2) on strong deformation that 

formed moderate- to large-scale folds and faults or shear 

zones. The metamorphism was the catalyst that 

provided the heat to drive the fluid system that 

remobilized gold, arsenic, sulfur, iron, boron, silica, 

calcium, and other elements. The folding and faulting 

provided the plumbing system for the fluids, forming 

porosity and permeability. Dilated shear zones, axial 

zones of folds (some of which cross shear zones), and 

fault zones became sites for ore deposition from 

mineralizing fluids. The fluids probably did not move 

great distances from original syngenetic source beds, for 

the gold in all the deposits is restricted to the same type 

of host rock oxide-, carbonate-, or sulfide-facies rocks,

silica-rich iron-formation, and (or) graphitic rock.

The favored explanation at the workshop for the 

Quadrilatero Ferrtfero gold deposits in the Rio das 

Velhas Supergroup was a combination of syngenetic and 

epigenetic processes. Figure 6 shows syngenetic and 

epigenetic origins as end members of a system and 

shows two alternatives to the interpretation of the 

genesis of these deposits. Figure 64 represents the 

general consensus of the participants at the end of the 

workshop and figure 65 that of Thorman hi view of 

recent data (this interpretation is discussed in Thorman, 

this volume, Part B Geology of deposits). The intent is 

to emphasize the generally strong inclination to favor an 

epigenetic origin for most of the deposits. The 

Homestake and Lupin deposits are included for 

comparison with the Brazilian deposits. Positioning a 

deposit on the scale is highly subjective. It appears to us 

that any origin must take into consideration a certain 

element of both ends of the system. Such a 

consideration becomes especially pertinent hi the 

development of a model for mineral exploration. For 

instance, continued detailed study of the Homestake 

deposit led company geologists to switch from a 

syngenetic to an epigenetic interpretation hi 1987, 

though during the workshop an syngenetic model was

A18 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
syngenetic syngenetic

Lupin

Morro Velho 

Homestake

Cuiabei 

Sao Bento

Lupin

Morro Velho 

Cuiab£

Homestake 

Sao Bento

Figure 6. Diagram showing gold deposits (as classified in 

table 2) relative to syngenetic versus epigenetic origin. The 

positioning of these deposits on this scale is highly 

subjective and is not intended to indicate that we are certain 

of any particular or exact relative position of one deposit 

versus another. Rather, the intent is to show that both 

syngenetic and epigenetic factors should be considered in 

the genesis of these deposits. A represents consensus of 

participants at workshop and B that of Thorman (this 

volume, Part B Geology of deposits).

presented. An epigenetic model is presented for 

Homestake in Part B of this bulletin by Caddey and 

others. S.W. Caddey (Homestake Mining Co., oral 

commun., 1990) believes that as more detailed studies 

are done elsewhere, there will be a strong shift to the 

epigenetic interpretation for many gold deposits 

throughout the world. Thorman (this volume, Part 

B Geology of deposits) describes the deposit models 

and discusses in more detail the conclusions forged 

during the workshop.

REFERENCES CITED

[* indicates references cited in this paper that are not available 

outside of Brazil or are unpublished dissertations. These references 

are used in the interest of crediting workers, even though their work 

is not published, and letting the reader know where to find these 

references]

Barbosa, A.L.M., 1969, Geologic maps of the Antonio Pereira, 

Sao Bartolomeu, Ouro Preto and Santa Rita do Ouro 

Preto, and Mariana and Rio das Bandeiras quadrangles, in 

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic, and

structural development of the Quadrilatero Ferrifero, 

Minas Gerais, Brazil: U.S. Geological Survey Professional 

Paper 641-A, 110 p.

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic and 

structural development of the QuadrMtero Ferrifero, 

Minas Gerais, Brazil: U.S. Geological Survey Professional 

Paper 641-A, 110 p.

Drake, A A., and Morgan, B A., 1979, Precambrian plate 

tectonics in the Brazilian shield; evidence from the 

pre-Minas rocks of the Quadrildtero Ferrifero, Minas 

Gerais: U.S. Geological Survey Professional Paper 

1119-B, 19 p.

*Grossi Sad, J.H., and Ladeira, E A., 1968, Esbogo tect6nico 

do estado de Minas Gerais: XXII Congresso Brasileiro de 

Geologia, Sociedade Brasileiro de Geologia, and Fundagao 

Goreix de Ouro Preto, scale 1:1,000,000.

Guild, P.W., 1957, Geology and mineral resources of the 

Congonhas district, Minas Gerais, Brazil: U.S. Geological 

Survey Professional Paper 290, 90 p.

Herz, Norman, 1970, Gneissic and igneous rocks of the 

Quadrilatero Ferrifero, Minas Gerais, Brazil: U.S. 

Geological Survey Professional Paper 641-B, 58 p.

Inda, HA.V., Schorscher, H.D., Dardenne, MA.,

Schobbenhaus, Carlos, Haralyi, N.L.E., Azevedo Branco, 

P.C., Ramalho, Ronaldo, 1984, O craton do Sao Francisco 

e a faixa de dobramentos Araguai, in Schobbenhaus, 

Carlos, Almeida Campos, Diogenes de, Derze, G.R., and 

Asmus, H.E., Geologia do Brasil: Brasil Departamento 

National da Produgao Mineral, Divisao de Geologia e 

Mineralogia, p. 193-248.

Johnson, R.F., 1962, Geology and ore deposits of the 

Cachoeira do Campo, Dom Bosco, and Ouro Branco 

quadrangles, Minas Gerais, Brazil: U.S. Geological Survey 

Professional Paper 341-B, 39 p.

Ladeira, E A., 1976, Principals feic,6es tectonicas do Escudo 

Brasileiro in Loczy, Louis de and Ladeira, E A., Geologia 

estructural e introducao a geotect6nica: Sao Paulo, Edgard 

Bliicher Ltda; Rio de Janeiro, Conselho National de 

Desenvolvimento Cientifico e Tecnologico, p. 433-462.

____ 1980, Metallogenesis of gold at the Morro Velho 

mine, and in the Nova Lima District, Quadrilatero 

Ferrifero, Minas Gerais, Brazil: London; Ontario, 

Canada, University of Western Ontario unpublished Ph.D. 

thesis, 272 p.

*Ladeira, E A., Cardoso, R.N., Castro, S.D.C., and Fonseca 

S.G., 1985, Relatorio dos trabalhos de pesquisas de 

serpintinitos e ouro nos locals denominados fazendas 

Gordura e Pau Branco, e de talco e serpentinito no locale 

denominado Ipe munitipio de Brumandinho: internal 

report to Rodiminas Mineradora Industria Ltda., Belo 

Horizonte, vol. 1, 72 p., vol. 2, sections and maps.

Ladeira, E A. and Fleiscner, Ronald, 1988, Field excursion 

from Belo Horizonte to Ouro PrSto Side excursion along 

the road to Moeda, Minas Gerais, Brazil: U.S. Geological 

Survey Open-File Report 88- 655, 4 p.

Ladeira, E A. and Viveiros, J.FM. de, 1984, Hipotese sobre a 

estruturagao do Quadrilatero Ferrifero, com base nos 

dado disponiveis: Sociedade Braseiro Geologia, Nucleo 

Minas Gerais, Boletim 4, 48 p.

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts in Brazil A19
1986, Brief introduction to the geology of

Quadrildtero Ferrifero-Hypothesis to its global structure 

with basis on available data: Deposit modeling program, 

Institute Brasileiro de Mineragao, p. 1 40.

Maxwell, C.H., 1972, Geology and ore deposits of the Alegria 

district, Minas Gerais, Brazil: U.S. Geological Survey 

Professional Paper 341-J, 72 p.

Moore, S.L., 1969, Geology and ore deposits of the Antonio 

dos Santos, Gongo S6co, and Conceigao do Rio Acima 

quadrangles, Minas Gerais, Brazil: U.S. Geological Survey 

Professional Paper 341-1, 50 p.

Morritt, R.F.C., 1988, The radar structure of Brazil south of 

the Amazon Basin, with special emphasis on the structural 

setting of the QuadrMtero Ferrifero, Minas Gerais State: 

Kingston, Ontario, Canada, Queen's University Ph.D. 

thesis, v. 1, 273 p.

Noca, C.M., Pinheiro, S.O., Ladeira, E A., and Grossi Sad, 

J.H., 1990, Ocorrencia de metakomatiitos com textura 

spinifex no Groupo Nova Lima oeste do Quadrilatero 

Ferrifero: XXXVI Congresso Brasileiro de Geologia, 

resumes das comunicagoes, Boletim 1, p. 215.

Pomerene, J.B., 1964, Geology and ore deposits of the Belo 

Horizonte, Ibirite, and Macacos quadrangles, Minas

Gerais, Brazil: U.S. Geological Survey Professional Paper

341-D, 84 p. 

Schobbenhaus, Carlos, Almeida Campos, Diogenes de, Derze,

G.R., and Asmus, H.E., 1981, Mapa geo!6gico do Brasil:

Brasil Departamento National da Produgao Mineral,

Divisao de Geologia e Mineralogia, scale 1:2,500,000. 

Schorscher, H.D., 1978, Komatiitos na estrutura "Greenstone

Belt" serie Rio das Velhas, Quadrilatero Ferrifero, Minas

Gerais, Brasil: XXX Congresso Brasileiro de Geologia,

resumes das comunicagoes, Boletim 1, p. 292-293. 

Simmons, G.C., 1968a, Geology and iron deposits of the

western Serra do Curral, Minas Gerais, Brazil: U.S.

Geological Survey Professional Paper 341 G, 57 p. 

____1968b, Geology and mineral resources of the Barao de

Cocais area, Minas Gerais, Brazil: U.S. Geological Survey

Professional Paper 341-H, 46 p. 

Wallace, R.M., 1965, Geology and mineral resources of the

Pico de Itabirito District, Minas Gerais, Brazil: U.S.

Geological Survey Professional Paper 341-F, 68 p.

A20 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
APPENDIX

Explanation of the Deposit-Model Form Used to

Organize Data

Introduction to a Workshop on Gold Deposits Related to Greenstone Belts in Brazil A21
EXPLANATION OF THE DEPOSIT-MODEL FORM USED TO ORGANIZE DATA

Deposit type: (fill in your preferred name for the deposit type and the author of model, if known, and the

reference)

Site name: (common name the area, mine, or district is best known by) 

Synonyms for site:

Site type: (mine, prospect, mining district) 

County, state, province, country: 

Latitude and longitude: 

Commodities: (include major and minor metals and (or) commodities produced; may include important

nonmetallic byproducts) 

Production: (include production history of the deposit, if any; include known dates of production,

commodities produced, and data on tonnage and (or) grade of ore produced) 

Deposit description: (general geologic description of the deposit) 

Rock types: (rocks typical of the geologic terrane) 

Textures: (special textures of rock units)

Host-rock lithology: (concise lithologic description of rock that forms the principal host for the deposit) 

Host-rock name: (formal and (or) informal name of the host-rock unit) 

Host-rock age: (give the most specific age possible; include any radiometric dates available) 

Mineralization age: (give the most specific age possible; include any radiometric dates available; if no

radiometric dates, then give line of reasoning that supports the inferred age) 

Lithotectonic setting and (or) depositional setting when host rock formed: 

Tectonic setting at time of mineralization: (regional tectonic features important in the genesis of the

deposit)

Associated iffieous rock: (briefly describe all igneous rocks genetically associated with the mineralization) 

Associated igneous rock age: (as above) 

Ore minerals: (give complete names of all ore minerals known at the site being described, in decreasing

order of importance; list important or guide minerals with + sign; list ore minerals hi assemblages;

show zonal or temporal relation between assemblages; group trace minerals separately; list byproduct

metals (such as Cu, Ag) that may not form minerals) 

Mineralogy: (describe completely but briefly alteration, gangue, and other mineral assemblages associated

with the mineralization) 

Alteration: (minerals produced by reaction of ore-forming fluids with rocks; list in assemblages; show

zonal or temporal relation between assemblages) 

Texture and (or) structure: (describe appearance of ore) 

Ore controls: (describe factors controlling mineralization, including structure, stratigraphy, chemistry, or

any other type of control) 

Geochemical signature and (or) metal concentrations: (regional geochemical anomalies that might

indicate the deposit or related associated deposits; elements expected to be anomalous, either

enriched or depleted, in and near the deposit; list element assemblages and show zonal arrangement

where possible) 

Weathering: (optional; list any special weathering characteristics or secondary minerals that might serve

as prospecting guides)

Associated deposits: (other deposit types associated with this deposit) 

Comments: (use this space for general comments on the deposit that don't seem to fit any other field; an

excellent place to include speculations concerning origin that should be kept separate from the facts

included in the other fields; a place to expound)

References: (include important references on the deposit and the general region of the deposit) 

Diagrams: (include a well-labeled map and (or) cross section of the deposit and (or) a sketch of an

idealized map or cross section showing ore controls, zoning, and approximate dimensions)

A22 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
Geological Field Excursion from 

Belo Horizonte to Ouro Preto, 

Minas Gerais, Brazil

By EDUARDO A. LADEIRA

Regional stratigraphy and tectonics of the 

Archean Rio das Velhas greenstone belt and the 

Proterozoic Minas Supergroup 

as background for gold metailogenesis

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A23
Town of Ouro Preto

A24
CONTENTS

Introduction A27

Scope Of excursion A27 BELO HORIZONTE

Road log A27

Stop 1 A30

Stop 2 A31

Stop 3 A31

Stop 4 A31

Stop 5 A31

Stop 6 A31

Stop 7 A32

Stop 8 A32

Stop 9 A33 

Stop 10 A33 

Stop 11 A34 

Stop 12 A34

Stop 13 A35

Stop 14 A35 ^V STOP15

Stop 15 A36 STOPS 13 &>

r OURO PRETO '

Stop 16 A37 SToTl6 

References cited A37

FIGURES

1. Geologic map of the Quadrilatero Ferrifero showing the stops for the field 

excursion A28

2. Geologic map of the Quadrilatero Ferrifero showing the location of major gold 

mines and occurrences in the area A29

3. Generalized stratigraphic column of the Precambrian rocks of the Quadrilatero 

Ferrifero A30

TABLE

1. Analyses of samples taken from bauxite prospect pit at Morro do Cruzeiro, Ouro 

Preto, Minas Gerais, Brazil A36

Contents A25
Folded specular hematite and quartz-muscovite schist of Caue Itabirite (stop 15)

A26
Geological Field Excursion from 

Belo Horizonte to Ouro Preto, 

Minas Gerais, Brazil

By Eduardo A. Ladeira1

INTRODUCTION

This geological field excursion should be used in 

connection with "Brief Introduction to the Geology of 

the Quadrilatero Ferrifero" by Ladeira and Viveiros (this 

volume, Part B Geology of deposits). A companion 

paper ("Field excursion from Belo Horizonte to Ouro 

Preto Side excursion along the road to Moeda"; this 

volume, Part A Excursions) by Ladeira and Fleischer 

begins at kilometer 27 of this trip. The side excursion is 

an integral part of understanding the tectonics and the 

basal Minas Supergroup.

SCOPE OF THE EXCURSION

The purpose of this field excursion is to provide 

insight into the regional stratigraphy and tectonics of the 

Archean Rio das Velhas greenstone belt and the 

Proterozoic Minas Supergroup, which will aid in 

understanding the geological setting and the 

metallogenesis of the Passagem, Morro Velho, Cuiaba, 

and Sao Bento gold deposits. Papers on the geology of 

the Passagem, Cuiaba, and Sao Bento gold deposits are 

included in Part B of this volume.

Figure 1 shows the field trip route on a geologic map 

of the Quadrilatero Ferrifero (Iron Quadrangle) that has 

been simplified from Dorr (1969). Figure 2 shows the 

location of major gold mines and occurrences in the 

same area. Figure 3 is a generalized stratigraphic 

column of the area.

ROAD LOG

For the convenience of the user, the highway 

(BR-040) kilometer marks (kmM), which are on the 

right margin of the southbound lane when one travels 

south, are listed as reference points. Distance in 

kilometers (km).

Marks Distance 

(kmM) (km)

0 0

1.8

Manuscript approved for publication February 22,1991.

Departamento de Geologia, Institute de Geociencias

Universidade Federal de Minas Gerais, Belo Horizonte, Brazil

Intersection of Contorno Avenue and 

Federal Highway BR-040, which links 

Belo Horizonte to Rio de Janeiro. Belo 

Horizonte was built on a granitic 

migmatitic terrane, but this part of the 

city lies along the contact of this terrane 

and rocks of the Sabara Group.

To the right and left, the road intersects 

schists and phyllites (some of volcanic 

origin) of the Sabara Group. The range 

to the left is the Serra do Curral, which 

was carved in an inverted homoclinal 

structure formed by metasedimentary 

rocks of the Minas Supergroup in such a 

way that the ridge is made up of Caue 

Itabirite overlying the dolomites, 

phyllites, and dolomitic itabirites of the 

Gandarela Formation. The dolomites 

have been mined at several quarries to 

be used as flux in metallurgy or for the 

production of refractory material. The 

lower hills are formed by strata of the 

Piracicaba Group.

Geological Field Excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil A27
o

o 

a

 §

(0st (»

3D (D5T

&>

o

DO

|

O1ft 

i

s. I

SCALE

Figure 1. Geologic map of the Quadrilatero Ferrifero (modified from Dorr, 1969) showing the stops for the field excursion. Details of the side excursion, stops 1 to 3, are described in the paper by Ladeira and Fleischer this volume Part A-Excursos
 \\V:SANTA BARBARA. J5 '^«* >" >'

GOLD MINES AND

MAJOR GOLD OCCURRENCES

INACTIVE MINES OR BEING EVALUATED

1. Ouro Fino 

de Cima

2. Ouro Fino 

de Babco

3. Morro do Adao4. Carrancas

5. Juea Vieira

6. Fazenda Velha 1. Carrapato

8. Fazenda Cutap

9. Fazenda Ojeriia

10. Luis Scares

11. Congo S6co12. Camari

13. Taquaril - 

Cocaes

14. Brucutu15. Pari16. Santa Ouiteria

17. Sao Jorge

18. Brumandinho

19. Quebra Ossos

20. Pigarra21. Pitangf

22. Paracatu - 

Agua Quente

23. Fazendao24. Cata Preta

25. Bento Rodrigues

ACTIVE MINES

51. Faria52. Gabirobas

53. Gaia

54. Bicalho

26. Antdnio Pereira27. Maquind

28. Rocinha

29. Santana30. Morro Redondo31. Mata Cavalo32. Taquaral33. Bom Jesus 

das Flores

34. Palacio Velho35. Veloso

36. Bico de Pedra

37. Ouro Preto38. Ajuda39. Passa Tempo

40. Ouro Fino

41. Paciencia

42. Marzagao43. Bahu44. Cata Branca45. Casa de Pedra46. Gordura

47. Urubu48. Limeiro 

doSul

49. Limeiro 

do Norte

50. Galo

55. Bela Fama56. Espirito Santo

57. Raposos

MAJOR MINES VISITED

58. Morro Velho (active) 61. Passagem59. Cuiaba (active) de Mariana60. Sao Bento (active) (inactive-being 

evaluated)

SCALE

Figure 2. Geologic map of the Quadrilatero Ferrffero (modified from Dorr, (1969) showing the location of major gold mines and occurrences in the area.
PROFOUND OROGENY WITH REGIONAL METAMORPfflSM

Itacolomi Group 

PROFOUND ANGULAR UNCONFORMITY

o

N 

O 

f*

w

H 

O

Minas Supergroup

Piracicaba Group

Itabira Group

Caraga Group

Sahara Formation 

Barreiro Formation 

Tabooes Formation 

Fecho do Funil Formation 

Cercadinho Formation

Gandarela Formation

CauS Itabirite \

/

Batatal Formation

Moeda Formation

v Tamandua Group 

MAJOR OROGENY WITH REGIONAL METAMORPfflSM

CU

U

Rio das Velhas 

Supergroup

Maquin6 Group

Nova Lima Group

\

Casa Forte Formation

Palmital Formation \

/

Upper unit*

Middle unit* (includes Lapa Seca Formation) 

Lower unit*

\

< CONTACT CONSIDERED INTRUSIVE BY DORR (1969)

Granitic-gneissic basement rocks, including granitoids of various ages

Figure 3. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero Ferrffero (modified from Dorr, 1969). 

Asterisk (*) indicates units not included in Dorr's paper but discussed by Thorman and Ladeira in the introductory chapter of 

this volume, Part A Excursions. The granitic-gneissic basement unit includes several informal units, including the Bacao 

Complex or Bacao Granitic Complex, which is the oval basement body in the south-central part of figures 1 and 2.

Marks Distance 

(kmM) (km)

2- 

2.5

STOP1

Contact of Sabara Group (the author 

prefers raising the Sabara Formation to 

Group status). In an inverted sequence 

along the road to the left, one finds the 

Sabara Group overlain by the graphitic 

phyllite of the Barreiro Formation. The

Marks Distance 

(kmM) (km)

Barreiro is overlain by very thin and 

brecciated Tabooes Quartzite, which is 

overlain by the weathered phyllites and 

dolomites of the Fecho do Funil 

Formation.

A30 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
Marks Distance 

(kmM) (km)

3- 

4

6.5

STOP 2

The cuts to the left are in the Cercadinho 

Formation, a sequence of interbedded 

silvery phyllites and ferruginous 

quartzites thrown into various 

asymmetric folds. The quartzites are 

medium to coarse grained and display 

cross-bedding and graded bedding that 

are used to determine the overturned 

nature of the beds. The roadcuts are 

now covered with concrete.

STOPS

Gravity fault transecting the Cercadinho 

Formation shows drag structures and 

"fault horses" along the fault zone. When 

the observer faces the structure, the drag 

structures indicate that the left block has 

moved up relative to the right block.

Belo Horizonte Shopping Center to the 

left, built on a filled-in karst lake that 

formed in dolomites of the Gandarela 

Formation. The hills to the right are on 

the Cercadinho Formation (ferruginous 

quartzites and phyllites).

Weathered dolomites of the Gandarela 

Formation with ochre as a weathered 

product, overlain by the Caue Itabirite, 

which is covered by a thick lateritic crust 

("canga"). At the open pits, iron and 

iron-manganese ore has been mined.

Railway bridge to Aguas Claras iron-ore 

deposits.

STOP 4

Outcrop of fresh dolomite of the 

Gandarela Formation, weathers to a 

peculiar soil known as "coffee powder." 

So //Si: N. 55° E., 60° SE. Gash quartz 

veins have attitude N. 10° E., 50° NW. 

S2:N.55°-60°W.,55°NE. 

Crenulations plunge E. 35° or S. 85° E. at 

35°.

Marks Distance 

(kmM) (km)

Highway to the right is the road to Sao 

Paulo; it passes through Cidade 

Industrial de Contagem, seen in the 

distance.

STOPS

9 The highway cuts asymmetrically folded 

Caue Itabirite. To the right, iron-ore 

mine of Mannesmann Company. The 

primary bedding-layering of the itabirite 

is strongly transposed by a foliation 

averaging N. 45° E., 55°-65° SE., which 

parallels the hinge surface of folds. 

Crenulations trend N. 75° E., 42° 

(intersection of So with Si). Slip striae 

trend S. 50° E., 60°. To the left, on the 

mountain top, are the Mutuca iron 

deposits in Caue Itabirite of the Minas 

Supergroup.

10 10 New Viaduto da Mutuca (Mutuca 

highway bridge). Drive over the old 

Mutuca bridge.

STOP 6

Both road cuts are on fragmental rocks 

and metaconglomerates of the Nova 

Lima Group, which contains stretched 

pebbles and is intersected by various 

quartz veins that probably formed during 

movement on the Mutuca thrust fault.

12 12 Quartz-chlorite schists with thin 

interlayered quartzites and minor 

graphitic phyllite of the Nova Lima 

Group are exposed in the road cut to the 

left.

13 13 Quartz-chlorite schists of the Nova Lima 

Group, interbedded with 

metaconglomerate (volcanic 

agglomerates?).

13.5 Highway Police station.

Geological Field Excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil A31
Marks Distance 

(kmM) (km)

14 14 Greenschists of the Nova Lima Group, 

interbedded with unweathered 

agglomerate, locally pyritiferous.

14.3 Turnpike to Rio Verde Mining 

Company.

STOP?

15.5 Drive about 0.5 km to the right on a

gravel road to a bauxite deposit. The ore 

probably is derived from aluminous 

sediments that accumulated on the 

argillaceous bottom of a Tertiary lake. 

Later upgrading was caused by 

supergene enrichment. Two mines can 

be visited. The first, and nearest one, 

belongs to Magnesita S A., a producer of 

refractory tiles from the local clay. The 

other is held by Alcan, which owns an 

aluminum plant near Ouro Preto and 

extracts bauxite at several sites in the 

Quadrilatero Ferrffero, including this 

one.

16.5 Gas station.

17.5 Jardim Canada, dry karst lake to the 

right.

20.2 Skol Brewery to the left.

22.1 Thick canga crust with pebbles, cobbles, 

and fragments of hematite and itabirite. 

This crust covers both the Gandarela 

Formation (which doesn't crop out) and 

part of the Caue Itabirite.

22.7 About 40° to the left, if the sky is not

cloudy, one can see the Pico do Itabirito 

(Itabirito Peak), carved in hard hematite 

ore, which will be seen again a couple of 

times during our trip; it is part of the 

range with the same name that 

constitutes the inverted limb of the 

Moeda synform, whose normal limb is to 

the right and is evidenced by the dip 

slopes to the right of the road and farther 

on. The inverted limb will be seen 

shortly.

Marks Distance 

(kmM) (km) 

27 27 Rodovia dos Inconfidentes 

(BR/MG-356, Inconfidente's Highway). 

Drive to the left to Ouro Preto, former 

capital of Minas Gerais State.

27.3 Highway Police station.

29 29 Exposure of ferruginous grayish

quartzites and silvery phyllites of the 

Cercadinho Formation overlain by 

weathered dolomites (which produce a 

brownish to black saprolite) and silvery 

phyllites of the Fecho do Funil 

Formation. Tight asymmetric folds have 

enveloping surfaces whose attitude is N. 

15° E., 58° NW. So //S i is N 10°E., 

45°-50°NW.

31 29.5- Cercadinho and Fecho do Funil, as 

31 above.

STOPS

34 34 Folded and faulted metaconglomerates 

mapped by Wallace (1965) as the 

Itacolomi Group, with distorted pebbles 

and cobbles of quartz and quartzite. 

So //Si: N. 15° W., 58° W., 65° NE. The 

current author, Ladeira, believes this 

may be a fragmental volcanic rock.

34.5 This area was a former Horto Florestal 

(forest station).

34.5 To the left, Codornas Lake. Three

hundred meters before the bridge to the 

right, varicolored phyllite interlayered 

with graphitic phyllite, both of Barreiro 

Formation, overlain by the younger, thin, 

saccharoidal Tabooes Quartzite. Dip of 

beds is vertical to near vertical. Strike is 

northeast.

35.8 Bridge over the Codornas Creek. 

Roadcuts are on the varicolored 

argillaceous phyllite and interlayered 

dolomites of the Fecho do Funil 

Formation.

36 36- Varicolored argillaceous phyllites of the 

36.5 Fecho do Funil Formation interlayered

A32 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
Marks Distance

(kmM) (km)

with "splash rock" (Guild, 1957), a name 

given to the saprolite of dolomite here 

the saprolite of Fecho do Funil 

Formation. Reduction or bleached spots 

with ellipsoidal shape and light color are 

oriented parallel to fold hinges. So: N. 

30° W., vertical; N. 16° W., 30° NE.

STOP 9

37 37 Alluvial deposit of a Tertiary lake, with 

quartz pebbles and cobbles in an 

arenaceous, argillaceous matrix, covers 

"splash rock" and phyllites of the Fecho 

do Funil Formation.

38 38 Cercadinho Formation (ferruginous

quartzites and phyllites) overlain by the 

Fecho do Funil Formation. So //S i: N. 

60°- 70° E., 60° SE. Contact with laterite 

and canga.

39 38.5- Roadcuts are cut successively deeper into 

39.5 the Cercadinho Formation due to folding 

with the underlying weathered dolomites 

of the Gandarela Formation. The 

weathered product of the Gandarela 

Formation is commonly referred to as 

"splash rock."

39.8 Highway Police station and truck 

balance.

40 40 As one approaches the police station, the 

hidden contact between the Gandarela 

Formation and the Caue Itabirite will be 

crossed. The section is the inverted limb 

of the Moeda synform in which the 

younger Gandarela Formation is overlain 

by the Caue Itabirite. To the right is 

Itabirite Peak.

40.1 Folded Caue Itabirite with kink folds. 

Canga crust derived from the itabirite 

caps the roadcut. To the left, 

ITAMINAS Mining Co. iron-ore deposit, 

hosted in Caue Itabirite.

40.8 The road cuts the inverted sequence

consisting of Caue Itabirite overlain by 

Batatal Formation, which in turn is

Marks Distance 

(kmM) (km)

41 41

41.5

42

overlain by the older Moeda Formation. 

Beds have a general trend of N. 15°-25° 

W. and are overturned 60°-70° NE. 

More incompetent Batatal Phyllite is 

crumpled between the Caue and Moeda 

Formations. Note thick canga crust on 

top of mountain to the right, carved in 

Caue Itabirite.

Bonga strike-slip fault with attitude N. 

70° E., 60°-70° NW. The northern block 

moved northeast relative to the southern 

block; total strike-slip is about 250 m 

(meter). This movement caused 

repetition of the inverted sequence: Caue 

Itabirite, Batatal, and Moeda 

Formations, having steeper dips 

of80°SE.

Quartzite quarry to the left, from which 

quartz sand is extracted, cleaned, and 

stockpiled (to the right).

42- From 42.0 to 43.5 km, the road swings 

43.5 through quartzites and minor

interlayered phyllites of the Moeda 

Formation, which crop out to the right, 

forming cuneiform controlled by a strong 

lineation ("pencil structure"). To the left 

is the Rio das Velhas Valley carved in 

the Nova Lima Group (Rio das Velhas 

Supergroup) of the Rio das Velhas 

Greenstone Belt (Ladeira, 1980).

STOP 10 "Santa" at the 

Serra do Itabirito.

43.5 Angular and erosional unconformity 

between the variegated schists of the 

Nova Lima Group and the Moeda 

Formation. The contact zone trends 

about N. 10° E. Immediately to the west 

of the rest area, the Nova Lima schists 

have two schistosities. The older, Si (N. 

40° W., 65° NE.), locally parallels 

bedding So of the schists; the younger, 

82 (N. 10°-35° E., 70° SE.), parallels the 

contact. Fracture cleavages are Ss (N. 

70° W., 30° NE.) and S4 (N. 70° E., 65° 

SE.). The Moeda Formation begins with 

a basal polymictic metaconglomerate

Geological Field Excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil A33
Marks Distance 

(kmM) (km)

44 44

44- 

49

49 49

with pebbles of quartz, quartzite and 

greenschist (the latter similar to Nova 

Lima Group greenschists). So in the 

Moeda quartzite trends N. 15° E., 80° SE, 

forming an angle of about 70° with So of 

Nova Lima Group schists. The 82 

schistosity in Nova Lima schists is also 

common to the Moeda Formation 

quartzites. Fracture cleavages parallel to 

Ss and 84 of the Nova Lima Group also 

intersect the Moeda quartzite. The 

angular pattern of So in both the Nova 

Lima Group and Moeda quartzite 

indicates the unconformable relation, 

which is proven by the presence of a 

basal conglomerate that contains clasts 

of schist from the Rio das Velhas 

Supergroup. However, the unconformity 

was disrupted during the deformation of 

the Minas Supergroup and is now a fault 

surface.

STOP 11

Cata Branca strike-slip fault. This 

structure follows the valley to the right. 

Nova Lima schists crop out along the 

highway. The fault trends 

northwest-southeast and dips 80° NE. 

and the hanging wall (northern block) 

has a total slip of 500 m towards the 

west. Gold associated with stibnite in the 

Moeda quartzite and related to this fault 

was mined nearby. The Cata Branca 

fault shifts the Bac.ao Complex-Nova 

Lima Group contact near the Esperanc,a 

Co. steel plant to the east of this plant. 

The Bacjio Complex is the oval body in 

the southern part of the Quadrilatero 

Ferrffero (figs. 1 and 2).

The highway swings through weathered 

Nova Lima variegated schists derived 

from interlayered metavolcanic and 

metasedimentary rocks.

STOP 12

Near the head of highway bridge over 

RFN (Rede Ferroviara National)

Marks Distance

(kmM) (km)

railway. To the right, Esperanga Co. 

blast furnace. Contact of the Nova Lima 

Group metavolcanic and 

metasedimentary rocks with the Ba^ao 

Granitic Complex, which thermally 

metamorphosed the rocks and resulted 

in a garnet-staurolite metamorphic 

aureole. These rocks are cut by 

numerous tourmaline-quartz veins, which 

elsewhere contain little gold. Metamafic 

rock and lean (low-grade) Archean type 

banded iron formation (BIF), not 

reported earlier by the DNPM-USGS 

(Departamento National da Produc.ao 

Mineral-United States Geological 

Survey) team and similar to BIF strata in 

the Nova Lima District, are interlayered 

in the local succession. See side-road 

roadcut (dirt road to the left to Rio 

Acima).

50 After the highway bridge, weathered 

metamafic dike cuts weathered Bacjio 

granite. To the right, a view of 

Esperanga Co. iron blast furnace.

51 51- Fresh exposure of Bac,ao Complex.

52.5 Itabirito Country Club to the left; city of 

Itabirito to the right. From here to 

Cachoeira do Campo (20 km ahead) and 

back to STOP 12, the highway runs 

through and exposes the 

granitic-migmatitic rocks of the Bacjio 

Complex.

52 52 Bagao Complex rocks.

54 54 Bac.ao Complex rocks.

54.5 Southeastern Itabirito turnoff.

57 CEMIG plant turnoff.

59 To the left, road to Acurui village (15 

km) and Camping Club do Brasil 

(22 km).

60 Alluvial flat.

62.5 Road to Minas Serra Geral (iron ore). 

Capanema mine.

A34 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
Marks Distance 

(kmM) (km)

72

74

78

78.5

78.5

Town of Cachoeira do Campo, built on 

Bac,ao Complex.

Alluvial flat.

Outcrop of migmatites of the Bacao 

Complex showing subvertical shear zones 

transecting earlier folded foliation.

STOP 13

Intersection of Inconfidente's Highway 

and CVRD (Companhia Vale do Rio 

Doce) Railway. Funil railway bridge. At 

the exposures to the right of the highway, 

the Moeda quartzite is tectonically 

concordant with the underlying Nova 

Lima schists (mostly staurolitechlorite-garnet schists) derived from 

volcanic and sedimentary rocks. These 

rocks are intruded by the Bacao 

Complex in an intricate contact zone in 

which Nova Lima schists are penetrated 

or invaded by numerous pegmatitic and 

aplitic bodies. The Bacao Complex is 

interpreted to be a mantled gneiss dome 

derived from a reworked basement 

(Ladeira, 1980). The Moeda quartzite is 

tectonically thinned, boudinaged, and cut 

by minor faults. Fresh Caue Itabirite 

crops out at the bottom of the valley, 

and, in addition to the normal itabirite, it 

also includes carbonate-amphibole 

(grunerite-cummingtonite) itabirite. The 

discordant relations can be observed only 

in the railway cuts above you, through 

which we will be driving.

STOP 14

Drive back 500 m, turn right on the dirt 

road, and drive up hill for 2 km to the 

CVRD railway station. Walk 500 m to 

the south along the railway tracks.

Faulted, originally discordant 

unconformable contact between the 

Moeda quartzites and fresh Nova Lima 

chlorite-garnet staurolite schist 

(greenschists). No conglomerate has

Marks Distance 

(kmM) (km)

been found at the base of Moeda 

quartzite at this site, but the 

unconformable relation (established at 

many localities in the region) can be 

deduced because the Nova Lima schists 

have two penetrative schistosities that are 

truncated at the contact, whereas the 

Moeda has just one schistosity; two sets 

of fracture cleavage intersect both units. 

In addition, the schists and Moeda 

quartzite have distinct structural styles 

that cannot be explained solely by the 

difference of competency. The schists 

are asymmetrically folded and refolded, 

and their axial surfaces trend differently 

from those in the quartzite. The present 

contact is clearly a tectonic one (thrust), 

which has been healed by 

metamorphism. The structural data 

indicate that the units were deformed 

under different conditions, lending 

support to the statement that the two are 

stratigraphically distinct units.

Attitude of S surfaces:

50 (schist, folded): N. 60° E., 35° SE.

51 (schist): N. 60° E.,35°-40°SE.

82 (schist): N. 15°-25° E., 45° SE.

Sa (common to schist and quartzite): 

N. 15°-25° E., 55° SE. refracts 

through the quartzite and changes 

toN.250 E.,60°-70°SE.

Thrust faults with related minor 

structures such as "mullions," slip striae, 

and sheath folds that have been 

dismembered and now appear as tectonic 

inclusions can be observed along the 

section. The Nova Lima schists locally 

have interlayers of Archean-type BIF 

(200 m north of this contact) that were 

not described at this locality by the 

DNPM-USGS team nor by other 

previous workers. Along this section, the 

author recently found intrafolial tight 

recumbent folds in the Moeda quartzite, 

which are also associated with shear zone 

and sigmoidal folds. Apparently these 

are the first reported recumbent folds in 

this formation at this site. Drive back to 

Inconfidente's Highway and head 

towards Ouro Preto.

Geological Field Excursion from Belo Horizonte to Ouro Preto, MInas Gerais, Brazil A35
Marks Distance 

(kmM) (km)

78.7

79

80 80

81 81

Folded dolomites of Gandarela 

Formation; 800 m ahead along the road 

the dolomites contain an 

intraformational metabreccia.

BEMIL crushing and milling plant for 

production of dolomite "dust," for soil 

correction, and broken stone. 

Conformable contact between the 

Gandarela and Cercadinho Formations.

Contact of Cercadinho and Fecho do 

Funil Formations.

81.3 Roadcut of Fecho do Funil dolomites 

and silvery phyllites; recumbent fold 

associated with thrust fault.

82 82 Fine-grained, banded ferruginous 

quartzites interbedded with silvery 

phyllites of the Cercadinho and Fecho do 

Funil Formations.

83 83 Farther to the right, at the mountain top, 

asymmetric synform hi Cercadinho and 

Fecho do Funil Formations.

83.6 Cercadinho Formation, normal and

ferruginous quartzite with cross-bedding 

and flaser structures; on right are 

asymmetric folds, that have thin laminae 

of silvery phyllite.

84 84 Fine-grained, fine-banded ferruginous 

quartzite of the Cercadinho Formation.

Marks Distance 

(kmM) (km)

86 86

87- 

88

STOP 15

"Black and White." This section has been 

mapped by Miranda Barbosa (in Dorr, 

1969) as Caue Itabirite. The "black" 

material is a tightly folded and laminated 

specular hematite rock. The "white" rock 

is a quartz-muscovite schist.

Si (schistosity): N. 70° E., 55° SE. 

Crenulations: S. 30° E., 50°; S. 20° W., 

50°.

The road intersects a thrust fault that 

juxtaposes the Sabar£ Formation on top 

of Caue Itabirite and then cuts down 

through the Caue Itabirite; farther 

ahead, another fault juxtaposes 

ferruginous quartzite of the Cercadinho 

Formation in thrust contact on the 

Sabar£ Formation, near the intersection 

of the roads to Ouro Preto and 

Saramenha.

Drive to Ouro Preto to the left.

View of Pico do Itacolomi (Itacolomi 

Peak) at 15° to the right.

89- This section of the road is mainly 

90 Cercadinho Formation ferruginous 

quartzite and silvery phyllites.

92.8 Cercadinho Formation underlying Fecho 

do Funil Formation.

Table 1 . Analyses of samples taken from bauxite prospect pit (altitude 1,223 m) at Morro do Cruzeiro, Ouro Preto, Minas 

Gerais, Brazil

[Table prepared by Professor Messias Gilmar Menzes from Guimaraes and Coelho (1945). All values shown in percent; 

L.O.I., loss on ignition; leaders (---) indicate interval not analyzed; n.d., not determined]

Depth, in 

meters

0.0-0.3 

0.3-0.9

0.9-2.1

2.1-3.6

3.6-5.1

5.1- 6 5

A12O3

36.79

38.70

40.61

42.30

FeO3

9.65

3.46

1.73

1.70

SiO2

32.80

40.14

40.30

43.78

TiO2

2.21

1.74

1.95

0.50

P2O5

0.116

0.075

0.043

 -

MgO

traces

traces

traces

0.87

CaO

0.45

0.67

0.50

0.70

Na2/ 

K2O

0.06

nil

0.09

n.d.

L.O.I.

17.80

14.%

14.76

9.77

TOTAL

I

99.88

99.74

99.98

99.62

Material

Lateritic crust 

Bauxite laterite

Ferruginous clay

Light-yellow clay

Yellow clay

White clay

A36 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
Marks Distance 

(kmM) (km)

93 93- Road follows the strike of Caue Itabirite, 

94 which overlies the Moeda quartzites (not 

seen).

95.0 Ouro Preto, Praca Tiradentes.

From here drive to Morro do Cruzeiro.

STOP 16

Bauxite deposit of Morro do Cruzeiro. 

This deposit is next to and partly 

underlies the campus of Universidade 

Federal de Ouro Preto. The Morro do 

Cruzeiro (Hill of the Cross) is a small 

plateau 1,230 m above sea level and is 

superficially covered by a lateritic crust 

("canga") and iateritic soil. The "canga" 

maintains the leveled surface and ranges 

in thickness from 1 to 1.5 m. The bauxite 

layer, which has been almost entirely 

mined out, overlies phyllite and 

dolomites of Fecho do Funil Formation. 

Before mining, the layer covered about 

130,000 square meters and had an 

average thickness of 1.5 m. The bauxite 

is light pink to intense red, which is a 

function of variable proportions of 

Fe2 Os . It is compact, has a specific 

gravity of 2.6, and occurs as disseminated 

concretions in laterite. Analyses of the 

bauxite ore in table 1 (facing page) 

indicate vertical migration of iron and 

alumina. Exploration and mining work 

demonstrated the presence of a large 

clay deposit underlying the bauxite layer.

REFERENCES CITED

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic and 

structural development of the Quadrilatero Ferrifero, 

Minas Gerais, Brazil: U.S. Geological Survey Professional 

Paper 641-A, 110 p.

Guild, P.W., 1957, Geology and mineral resources of the 

Congonhas district, Minas Gerais, Brazil: U.S. Geological 

Survey Professional Paper 290,90 p.

Guimaraes, G.D., and Coelho, I.S., 1945, Bauxita do Morro do 

Cruzeiro en Ouro Preto, Minas Gerais: Departamento 

National da Produc,ao Mineral, Divisao de Fomento da 

Producjio Mineral, Boletim 67,41 p.

Ladeira, E A., 1980, Metallogenesis of gold at the Morro 

Velho mine, and in the Nova Lima District, Quadrilatero 

Ferrifero, Minas Gerais, Brazil: London, Ontario, Canada, 

University of Western Ontario unpublished Ph.D. thesis, 

272 p.

Wallace, R.M., 1965, Geology and mineral resources of the 

Pico de Itabirito District, Minas Gerais, Brazil: U.S. 

Geological Survey Professional Paper 341-F, 68 p.

Geological Field Excursion from Belo Horizonte to Ouro Preto, Minas Gerais, Brazil A37
Bagao Complex along CVRD railroad (stop 14)

A38
Field Excursion from

Belo Horizonte to Ouro PretoSide Excursion Along the Road to Moeda,

Minas Gerais, Brazil

By EDUARDO A. LADEIRA and RONALD FLEISCHER

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A39
Sheared basement rock below Moeda Complex-Moeda Formation contact (stop 1)

A40
CONTENTS

Introduction A43

Scope of the excursion A43

Structural setting A43

Stratigraphic setting A43 

Road log A46

Stop 1 A46

Stop 2 A46

Stop 3 A47 

References cited A47

FIGURES

1. Geologic map of the Quadrilatero Ferrifero (modified from Dorr, 1969) showing 

the field trip routes for the workshop A44

2. Geologic map of the field excursion area showing the locations of stops 1-3 A45

Contents A41
Sheared basement rock of Moeda Complex (stop 1)

A42
Field Excursion from

Belo Horizonte to Ouro PretoSide Excursion Along the Road to Moeda,

Minas Gerais, Brazil

By Eduardo A. Ladeira 1 and Ronald Fleischer2

INTRODUCTION

This side excursion is an appendage to the 

"Geological field excursion from Belo Horizonte to Ouro 

Preto..." by Eduardo Ladeira (this volume, Part 

A Excursions) and is to be used in conjunction with it. 

The zero kilometer mark for this side excursion begins 

at the junction of Highway BR-040 and the Rodovia dos 

Inconfidentes (Inconfidente's Highway) (kilometer 27 in 

the Belo Horizonte excursion). Figure 1 shows the 

location of the side excursion in relation to the main 

excursion and figure 2 shows the location of the three 

stops and the geology of the area for the side excursion 

(Wallace, 1965).

SCOPE OF THE EXCURSION

The purpose of this side excursion is twofoldstructural and stratigraphic. The geology to be seen is 

extremely critical to the overall geologic setting of the 

Quadrilatero Ferrifero. This locale was chosen because 

relationships are more clearly displayed here than at 

almost any other place in the region and the access is 

excellent.

Manuscript approved for publication February 22,1991.

1 Departamento de Geologia, Institute de Geociencias, 

Universidade Federal de Minas Gerais, Belo Horizonte, Brazil

2 Construtora Andrade Gutierrez, Rua dos Pampas, 484, Belo 

Horizonte, Brazil

Structural Setting

The first purpose of the excursion is to examine and 

discuss the nature of the contact between the 

metasedimentary Moeda Formation of the Minas 

Supergroup and the Moeda Complex, a granitic-gneissic 

unit. For a discussion of the Moeda Complex and the 

interpretations applied to the contact between it and the 

overlying rocks, see Ladeira and Viveiros (this volume, 

Part B Geology of deposits) on the general geology of 

the region. Briefly, the problem is whether the contact 

between the Moeda Formation, at the base of the 

section observed in this immediate area, and the 

underlying granitic rocks of the Moeda Complex is 

depositional or tectonic. The presence of mylonitic 

rocks along the contact and for more than 100 m (meter) 

downsection into the complex, plus the presence of this 

same relationship all along the western side of the 

Quadrilatero Ferrifero, strongly suggest that the contact 

is faulted. Further discussion on this topic and its 

regional significance is presented in the introduction to 

Part A of this volume by Thorman and Ladeira.

Stratigraphic Setting

The second purpose of the excursion is to gain an 

insight into the stratigraphy of the Caraga and Itabira 

Groups and to examine the type section of the Moeda 

Formation, which is made up of three members 

(Wallace, 1965):

1. The lowermost member Moeda 1 starts at the 

base with local metaconglomerates and coarse quartzites 

that contain clasts of bluish quartz grains, and grades

Field Excursion from Belo Horizonte to Ouro Preto Side Excursion along the Road to Moeda A43
o

o E

o

!? "8

I

I

I tII

i

SCALE

Figure 1. Geologic map of the Quadrilatero Ferrffero (modified from Dorr, 1969) showing the stops for the side excursion. Details of the main excursion 

are described in the paper by Ladeira (this volume, Part A-Excursions).
20° 15'

43° 57' 30"

20° 17'30'

EXPLANATION

O

8O 

DC

£

r?

Q_

Q.

D

0

QC 

C3 

QC

LU 

Q.

W

CO

i

^

5Sg- 'aS

.t C3 D.

IP

|C5

05 ^

iiO 05

Fecho do Funil 

Formation

Cercadinho 

Formation

Gandarela 

Formation

Cau6 

Itabirite

^

Batata! 

Formation

Moeda 

Formation

^

1 mf It

::>>. ....... : : W:

jsftsssssg 

is »""" me 8>: "'

;: mg ;;:

;; mi : ;: :

% mb w,

|mra3 |

mm2

JH mm1 lij;

"5 3

> S

jl

Nova Lima 

Group

Undifferentiated granitic 

Crocks

PJ r n II

I! °r 1

Type section of 

Moeda Formation

Contact

Thrust fault- Sawteeth 

on upper plate

Road 

Paved , Unpaved

Figure 2. Geologic map (from Wallace, 1965) of the field excursion area showing the location of stops 1-3.

Field Excursion from Belo Horizonte to Ouro Preto Side Excursion along the Road to Moeda A45
upward to light-gray to light-reddish-brown, medium to 

fine cross-bedded and parallel-bedded quartzites.

2. The middle member Moeda 2 consists mainly of 

varicolored sandy phyllites that grade upward to thin 

intercalations of fine-grained quartzites.

3. The upper member Moeda 3 consists of 

light-gray to light-reddish-brown medium-grained to 

very coarse grained cross-bedded quartzites.

ROAD LOG

As noted in the "Introduction," the zero kilometer 

mark for this side excursion begins at the junction of 

Highway BR-040 and the Rodovia dos Inconfidentes 

(Inconfidente's Highway).

Kilometer

0 BR- 040 and Inconfidente's Highway junction. 

Continue south on BR-040, under the highway 

overpass.

I.8 To the right, gravel road to Piedade do 

Paraopeba. Continue along BR-040.

4.9 To the right, road to Retiro do Chale. From

here, if the sky is not cloudy, one can see Itabirito 

Peak at 40°-50° to the left on the overturned limb 

of the Moeda synform; to the right, one can see 

the normal limb, which will be crossed in a few 

minutes. At about zero degrees (straight ahead), 

one can observe the narrowing of the synform.

II.3 Highway Police and truck-weighing station.

12.5 Drive to right on the gravel road that leads to the 

town of Moeda. For practical reasons, drive 

directly to the base of the Minas Supergroup, 

down the foothills of the Moeda Plateau, because 

most of the route is winding and steep. Begin 

stop 1 at the base of the foothills.

Kilometer

metasedimentary sequence. Along the shear 

zones, some of the granitic rocks have been 

transformed, through cataclasis and 

accompanying recrystallization, into tremoliteactinolite-tourmaline schist. Up the hill towards 

the northeast (upwards structurally and 

stratigraphically, also), the sheared rock changes 

somewhat abruptly into a mylonitic augen gneiss; 

at least one of its foliations trends N. 60 ° E to N. 

80° E., discordant to the contact of the overlying 

quartzitic sequence. The cataclasites, mylonites, 

and phyllonites here have bluish quartz crystals, 

0.3-10 millimeters in size, which led Ferrari (in 

Loczy and Ladeira, 1976) to consider them as 

quartz of volcanic origin. Cataclastic foliation is 

N. 10° E., 80° SE. So/Si of overlying quartzite is 

N. 10° W. to N. 15° W., 55° NE. Fracture 

cleavage is N. 30° E., 70° SE.

The quartzite sequence begins with a fragmental 

rock whose fragments are made up of the same 

bluish quartz, but here grains are rounded and 

angular in a sericitic quartzose matrix; this rock 

was termed "metaconglomerate" by Wallace 

(1965). This "metaconglomerate" changes to 

medium- to fine-grained quartzites and, farther 

upsection, grades into cross-bedded quartzites. 

Both the foliation-bedding relation and the 

cross-bedding indicate a normal, rightside-up 

sequence.

Walk down the hill to a small waterfall on the 

granitic-gneissic complex. Note that the complex 

has several small shear zones in which the gneiss 

is transformed either to a mylonitic augen gneiss, 

cataclasite, or, in some places, a phyllonite. 

These zones are a few centimeters to a few 

meters thick. Older foliation in the augen gneiss 

is N. 60° E., 65° SE. Lineation crenulation is S. 

60° E., 55°. Return to vehicle and drive back 

upsection.

STOP1

16.1 Leave the vehicle, and walk about 100 m (meter) 

east to an exposure of the granitic rocks of the 

Moeda Complex. Many types of granitic rocks 

can be seen here in the foothills. At this stop, our 

objective is to examine a series of east-dipping 

shear zones in the granitic rocks and the 

relationship of the zones to the overlying

STOP 2

17.8 Outcrop of Moeda 2. This member is made up of 

fine-grained schists and phyllites; facies changes 

are normal to bedding. It is mostly a quartz-mica 

schist with subordinate intercalation of rhythmic 

phyllites that weather green. Here and there are 

thin intercalations (10-50 centimeters) of sericite 

quartzites, which locally have highly micaceous 

laminae. Continue up section.

A46 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
Kilometer

STOP 3

18.8 Contact between the Moeda 3 (medium-grained 

to very coarse grained quartzites) and the 

overlying, locally graphitic phyllites of the Batatal 

Formation (about 20 m thick). The Batatal is 

conformably overlain by itabirites of the Caue 

Formation. Return to the BR-040 Inconfidente's 

Highway junction where the excursion will 

continue on a traverse through the Moeda 

synform.

REFERENCES CITED

Loczy, L., and Ladeira, E.A., 1976, Geologia estrutural e 

introduce a geotectonica: Sao Paulo, Edgard Bliicher 

Ltda; Rio de Janeiro, Conselho National de 

Desenvolvimento Cientifico e Tecnol6gico, 528 p.

Wallace, R.M., 1965, Geology and mineral resources of the 

Pico de Itabirito District, Minas Gerais, Brazil: U.S. 

Geological Survey Professional Paper 341 F, 68 p.

Field Excursion from Belo Horizonte to Ouro Preto Side Excursion along the Road to Moeda A47
°tNERAL SECTION/OF WORKS.

SCALE: t to s 100.

 "V

July 1894 drawing of Passagem de Mariana stamp mill and 1986 photograph of 

stamp mill buildings

A48
Surface and Underground 

Geological Excursion Around and in the 

Passagem de Mariana Gold Mine, 

Minas Gerais, Brazil

By RONALD FLEISCHER and DIOGENES SCIPIONI VIAL

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A49
Quartz veins-Passagem de Mariana gold mine

A50
CONTENTS

Introduction A53 

Scope of excursion A56 

Road log A57

Stop 1 A57

Stop 2 (stops 2.1-2.22) A57 

References cited A62

FIGURES

1. Geologic map of the Quadrilatero Ferrffero showing location of the Passagem de 

Mariana gold mine, other major gold mines visited, and other gold mines and major 

gold occurrences A54

2. Generalized geologic map of the Ouro Preto-Mariana region in the southeastern 

part of the Quadrilatero Ferrifero A55

3. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero 

Ferrffero A56

4. Mine plan of the Passagem de Mariana gold mine showing the location of stops 

(2.1 to 2.22 in text) and major orebodies in the mine A58

Contents A51
Boudinaged and folded rocks with quartz fillings in Passagem de Mariana gold mine

A52
Surface and Underground Geological 

Excursion Around and in the 

Passagem de Mariana Gold Mine, 

Minas Gerais, Brazil

By Ronald Fleischer 1 and Diogenes Scipioni Vial ;

INTRODUCTION

The object of this field excursion is to see the 

stratigraphic and structural setting around and in the 

Passagem de Mariana gold mine in the southeastern part 

of the Quadrilalero Ferrifero (fig. 1). The deposit has 

been exploited discontinuously since the end of the 17th 

century and has produced at least 60 tons of gold. 

Figure 2 shows the location of the Passagem mine and 

other gold mines in the region. Figure 3 is a generalized 

stratigraphic column that includes nomenclature used in 

this paper.

The Passagem gold deposit has been described and 

interpreted by several geologists (Hussak, 1898; Derby, 

1911; Legraye, 1937; and Guimaraes, 1965). Classical 

metallogenetic textbooks have summarized these data 

and considered this deposit to be an example of 

epigenetic mineralization, foreign to its geological 

framework ( de Launay, 1913; Lindgren, 1933; Emmons, 

1937).

The emplacement of the ore was considered to be 

due to percolation of high temperature mineralizing 

solutions (pegmatitic-pneumatolytic or deuteric type) 

along inferred shear zones by the authors just listed. 

Geological maps on a 1:25,000 scale by Miranda Barbosa 

(in Dorr, 1969) show a thrust fault running exactly 

through the site of the Passagem mine (fig. 2), which had 

been assumed by the early authors to be the channelway 

for the mineralization. However, the mineralized 

interval along the thrust fault was not critically

Manuscript approved for publication February 22,1991.

1 Construtora Andrade Gutierrez, Rua dos Pampas, 484 

Belo Horizonte, Brazil

2 DOCEGEO Rio Doce Geologia e Minerac,ao, 

Rua Sao Paulo, 351, Belo Horizonte, Brazil

examined. The mineralized interval is composed mostly 

of vein quartz, carbonates, tourmaline, arsenopyrite, and 

gold and has a maximum thickness of 5 m (meter). It 

extends for more than 15 km (kilometer) in a definite 

stratigraphic position below the Caue Itabirite, 

concordant with the enclosing rocks.

Fleischer (1971,1973) concentrated his study along 

this mineralized interval, the thrust fault of Barbosa, and 

emphasized the relations of the ore horizon with the 

structural, metamorphic, and paleogeographic features 

of the surrounding rocks of the Passagem district. The 

thrust-fault hypothesis, which assumed the fault zone to 

be a conduit for mineralizing fluids, was discarded in 

favor of an syngenetic concept in which lateral 

fades-change explains why different lithologic units 

within the same narrow stratigraphic position are 

mineralized. This coexistence of different lithologic 

units, which are known elsewhere in the pre-Minas 

succession as well as in the Minas Supergroup, is the 

main reason for the debate concerning the genesis of the 

mineralization.

In view of these different interpretations, three 

hypotheses or models are presented for the genesis of 

the gold mineralization: the first two are epigenetic and 

depend on structural controls, and the third is 

syngenetic.

1. The deposit is Archean in age, because the 

thrusting juxtaposes the Caue Itabirite on top of 

different lithologic units interpreted to be part of the Rio 

das Velhas Supergroup, a volcanic-sedimentary 

sequence. The mine sequence would be of a more distal 

facies than that present at the Morro Velho mine. This 

hypothesis accepts the general structural picture of 

Barbosa (in Dorr, 1969), who showed a regional thrust 

at the base of the Minas Supergroup. This hypothesis 

differs from Barbosa's, however, in that Barbosa showed

Surface and Underground Geological Excursion, Passagem de Mariana Gold Mine, Minas Gerais, Brazil A53
A54 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A-Excursions
o

I

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Q.

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5

43° 30'

Itacolomi Group 

Piracicaba Group 

Itabira Group 

Caraca Group

Maquin6 Group

Nova Lima Group 

f - iron formation 

q - phyllite, chlorite schist, 

quartzite, dolomite, 

metavolcanic rock

Granite and gneiss

43° 22'30'

EXPLANATION

30

.65

CONTACT

FAULT 

High-angle

Thrust fault -sawteeth 

on upper plate

ANTICLINE - Arrows indicate 

dip and direction of 

plunge

STRIKE AND DIP 

Bedding

Foliation

GOLD MINES

1. Ant6nio Pereira

2. Veloso

3. PalacioVelho

4. Maquine

5. Rocinha

6. Santana

7. Morro Redondo

8. MataCavalo

9. Bom Jesus das Flores 

10. Taquaral

10 Kilometers

_A

Figure 2. Generalized geologic map of the Ouro Presto-Mariana region in the southeastern part of the Quadrilatero Ferrffero 

(modified from Barbosa in Dorr, 1969).

Surface and Underground Geological Excursion, Passagem de Mariana Gold Mine, Minas Gerais, Brazil ASS
u

> I

o

N 

O

* 

w

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PROFOUND OROGENY WITH REGIONAL METAMORPfflSM

Itacolomi Group 

PROFOUND ANGULAR UNCONFORMITY

Minas Supergroup

Piracicaba Group

Itabira Group

Caraca Group

Sahara Formation 

Barreiro Formation 

Tabooes Formation 

Fecho do Funil Formation 

Cercadinho Formation

Gandarela Formation

Caue Itabirite ^

/

Batatal Formation 

Moeda Formation

\Tamandua Group 

MAJOR OROGENY WITH REGIONAL METAMORPfflSM

w 

a 

u

Rio das Velhas 

Supergroup

Maquin6 Group

Nova Lima Group

\

Casa Forte Formation

Palmital Formation \

/

Upper unit*

Middle unit* (includes Lapa Seca Formation) 

Lower unit*

\

CONTACT CONSIDERED INTRUSIVE BY DORR (1969) 

Granitic-gneissic basement rocks, including granitoids of various ages

Figure 3. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero Ferrffero (modified from Dorr, 1969). 

Asterisk (*) indicates units not included in Dorr's paper but discussed by Thorman and Ladeira in the introductory chapter of 

the volume, Part A Excursions. The granitic-gneissic basement unit includes several informal units, including the Bacao 

Complex or Bagao Granitic Complex, which is the oval basement body in the south-central part of figures 1 and 2.

the rocks at the Passagem mine to belong to the lower 

part of the Minas Supergroup rather than as part of the 

Nova Lima Group.

2. The deposit is Middle to Late Proterozoic in age, 

of a typical epigenetic origin; the source of the 

mineralizing fluids is not specified. The low-angle to 

bedding-parallel thrusting would have provided the 

channelways for the mineralizing fluids. This hypothesis 

is the basic concept proposed by earlier workers 

(de Launay, 1913; Lindgren, 1933; Emmons, 1937) and 

reemphasized by Barbosa (in Dorr, 1969) in his regional 

work.

3. In the syngenetic lateral facies-change concept, 

the mineralization took place during Early Proterozoic

in a sedimentary (distal volcano-sedimentary?) 

environment. The rocks were deformed and the gold 

was remobilized and redeposited during at least three 

periods of folding related to an undetermined number of 

tectonic events.

SCOPE OF EXCURSION

On this excursion, we present features that support 

each of the three interpretations or models. Fleischer 

favors a syngenetic origin for the deposits, whereas Vial 

prefers an epigenetic origin.

The location of stop 1 at the abandoned Bom Jesus

A56 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
das Flores mine and the Passagem de Mariana mine are 

shown on figure 2, and stops 2.1-2.22 in the mine are 

shown on figure 4. For an overview of the geology of the 

Quadrilatero Ferrtfero and the geology of the Passagem 

mine, the reader is referred to the papers in Part B 

(Geology of deposits) of this volume by Ladeira and 

Viveiros and by Vial, respectively.

ROAD LOG

STOP1

3.4 Beginning at the Praca Tiradentes, in Ouro Preto, 

km just in front of the Ouro Preto School of Mines, 

take the road to Passagem de Mariana; at 3.4 km 

take a dirt road to the left toward the Bom Jesus 

das Flores do Taquaral chapel and drive 200 m to 

a small bridge over the Taquaral Creek. This 

stop is intended to show a profile through the 

basal part of the Minas Supergroup around the 

Sao Bartolomeu anticline (fig. 2). The Passagem 

gold mine and the Morro de Santana gold-mine 

workings (fig. 2) are on the nose of the anticline.

The profile from north to south begins with a 

chlorite-biotite-calc schist, which grades into a 

ridge-forming itabirite. In a drift of the 

abandoned Bom Jesus das Flores mine (mine 9, 

fig. 2), which follows this contact, one can 

observe, in the footwall, the sericite-quartz schist 

locally overlain by sericite quartzite, which is 

separated from the overlying itabirite by a gray 

graphitic phyllite a few centimeters thick.

Two interpretations or models are considered for 

this profile: the thrust-fault and the facies-change 

interpretations. The thrust-fault interpretation 

was first proposed by Miranda Barbosa and 

considers the chlorite-biotite calc schists as well 

as the sericite-quartz schist to belong to the 

Archean basement that has been overthrust by 

the Early Proterozoic Minas Supergroup, here 

represented by the itabirites and locally by slices 

of quartzite (Moeda Formation) and gray 

graphitic schist (Batatal Formation). In this 

interpretation, the gold mineralization occupies a 

thrust fault that cuts the Proterozoic sequence 

either at the basal quartzite level, at the gray 

graphitic horizon, or at the middle of the itabirite 

strata.

The facies-change interpretation (Fleischer, 1971, 

1973) considers the sericite-quartz schist to be the 

lateral equivalent to the Moeda fine-grained 

sericite quartzite at Ouro Preto. That this 

lithology is common to the Moeda Formation has 

been shown at the type locality at Serra da 

Moeda. The sericite quartzite is distinct from the 

underlying chlorite-calc schists, from which it can 

be distinguished by detailed mapping. It is 

important to note that in this southeastern part of 

the Quadrilatero Ferrifero, both the Moeda and 

Batatal Formations, as well as the overlying 

itabirites, are much thinner than in more 

northerly sectors. Some movement along the 

thin, gray, graphitic horizon surely took place 

during the two folding events during which rocks 

in the area were deformed, as will be seen in the 

Passagem Mine, but the movement was not 

strong enough to tectonically thin the Moeda and 

Batatal Formations over such a large area.

STOP 2

7.3 Return to the main road and continue to 

km Passagem de Mariana, and, after 3.9 km, turn left 

to the mine parking lot. In the mine, the tour will 

go down the PIA Nova inclined shaft. After 

visiting some exposures in this part of the mine, 

known as Fundao orebody, the tour will follow 

the 265 level to the east, passing by the PIA 1 

inclined shaft and back to the surface in the PIA 2 

shaft. Stops in the mine are shown in figure 4; 

stops are numbered in text from 2.1 to 2.22 and in 

figure 4 from 1 to 22.

STOP 2.1: PIA NOVA-175 level.

A typical sequence of a large section (Fundao 

orebody) of the mine: at the bottom, a fine-grained 

sericitic quartzite in a slightly calcareous matrix; above it, 

a dolomitic horizon that has common boudinage 

structures and that grades toward the top into gray 

graphitic phyllites interbedded with centimeter-thick 

light-colored laminated cherts containing pyrrhotite. At 

the roof, the phyllites grade over a short interval into 

itabirites.

Two important aspects of the dolomitic horizon are 

seen here. First, the presence of a centimeter- to 

decimeter-thick discontinuous intercalation of dark 

tourmalinite, which some workers have referred to as an 

important guide to the mineralization. All the steps of

Surface and Underground Geological Excursion, Passagem de Mariana Gold Mine, Minas Gerais, Brazil A57
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ASS Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
disruption of the tourmalinite bands can be seen, 

beginning with simple vertical fractures filled with white 

quartz, to total separation resulting in angular blocks 

drowned in a recrystallized quartz and dolomite vein-like 

mass. That this structure is due to tectonic thinning and 

plastic deformation resulting in boudinage structures 

and not to tectonic brecciation within a fault becomes 

obvious when one observes that the metamorphic 

banding of these blocks has a definite orientation, 

continuous with the banding of neighboring blocks and 

parallel to the enclosing rocks. Dolomitic 

recrystallization characterizes the upper part of the ore 

zone; milky quartz dominates the lower part. This 

distribution reflects the stratigraphy and shows an 

intimate relationship between the host rocks and the 

minerals of recrystallization. The recrystallized material 

was derived from nearby host rocks and was not 

transported more than a few meters.

Points to debate:

1. Sericitic quartzites in a slightly calcareous matrix 

grade into pure sericite quartzites. Is the pure sericite 

quartzite a product of silicification of the calcareous rock 

or is it a primary feature?

2. Why is the intense dolomite and quartz 

recrystallization restricted to the ore zone and why is it 

stratabound?

STOP 2.2: PIA NOVA between 

levels 175 and 265.

A crosscutting east-west oriented quartz vein.

STOP 2.3: PIA NOVA between levels 175 

and 265, about 20 m beyond Stop 2.2.

At this stop note the milky quartz mass. It is a 

concordant veinlike mass, which crosscuts both the 

tourmalinite-bearing dolomites at the top and the 

quartzites at the bottom. At one corner of the drift, the 

crosscutting relations become ambiguous. Although it 

clearly crosscuts the dolomites and tourmalinites, it 

seems to grade into the quartzite. Around the corner, at 

the beginning of the raise, both crosscutting and 

transition features occur simultaneously, which raises 

two questions:

1. Is the grading of the milky quartz into the quartzite

an argument for silicification of the quartzite or is it 

evidence that the quartzite is the source of the 

recrystallized quartz in the form of concordant veins?

2. The solution to this question is crucial to the 

further discussion about the significance of widespread 

quartz impregnation of the Passagem ore zone. Can this 

milky quartz impregnation be attributed to the 

percolation of fluids from an unknown source through a 

low-angle thrust fault, or is it the result of silica 

remobilization during the tectonic event during which 

boudinage and other disruptive structures were 

produced?

STOP 2.4: Level 315 to the west of PIA 

NOVA, where the drift becomes narrower, 

at the 12-14 channel sample.

The regularly bedded rock, on the hanging wall, is an 

actinolite-rich amphibolite. It contains interbeds of a 

quartz-biotite schist and 2-decimeter-thick beds of finely 

laminated chert. One of these chert beds is pinched out 

by boudinage, whereas the other one is in a tight 

synschistose fold. At the footwall, the same sericitic 

quartzite with a slightly calcareous matrix. The 

mineralized interval between is marked by the milky 

quartz concordant mass permeating dolomites with 

tourmalinite.

Recent gold assays on channel samples by 

DOCEGEO (Rio Doce Geologia e Minerac,ao) show 

that mineralized rock is more concentrated in the 20- to 

50-cm-thick concordant quartz veins; grades range 

anywhere between 0 and 18 g/t (gram per ton) and show 

no special affinity with the tourmalinite or where 

arsenopyrite is concentrated. These results tend to 

refute old mine descriptions by various authors, 

including those who were in charge of the workings. If 

confirmed in other sections of the mine, this observation 

can be explained by the higher mobility of gold relative 

to boron and arsenic during the boudinage-related 

deformation.

STOP 2.5: Level 315, west of PIA NOVA, 

at the 40-46 channel sample.

This channel sample illustrates the observation 

referred to at Stop 2.4. From footwall to hanging wall, 

the following lithologic units yielded the following gold 

contents (in grams per ton):

Surface and Underground Geological Excursion, Passagem de Mariana Gold Mine, Minas Gerais, Brazil A59
DOCEGEO 

channel 

sample No.

40 

41 

42 

43 

44 

45 

46

Dominant 

litholoev

Milky quartz without tourmalinite

Gold 

fe/rt

----- 0.27

_ - - _ . 0 43

..... 7* on

..... 4 7f]

- - - 35.00 

..... oon

..... 44n

STOP 2.6: Level 315, west of PIA NOVA.

Flooding level of the mine.

STOP 2.7: Level 315, west of PIA NOVA, 

at channel sample 102-105.

In this profile, no concordant milky quartz vein is 

present and only part of the ore zone has been cut. 

Channel sampling gave the following gold content (in 

grams per ton):

DOCEGEO 

channel 

sample No.

102

103

104

m<;

Dominant 

litholoev

Quartz-biotite-calc schist plus banded

Gold

re/o

 - 0.0

n 11

- - 0.14

nm

The hanging wall at this locality is amphibolitic 

dolomitic itabirite and the footwall is carbonate-biotite 

schist.

STOP 2.8: Level 315, west of PIA NOVA, 

near channel sample 102-103.

Biotite-calc schist of the hanging wall has late-stage 

isoclinal folds with axes oriented N. 35° W. and dipping 

to the SE. A "b" lineation parallel to the fold axis can 

also be seen and corresponds to the intersection between 

bedding planes and the mam schistosity. These 

intrafolial folds illustrate the intensity of the second 

folding phase and show that associated transposition 

must be taken into account when small-scale 

observations on detailed stratigraphy are made.

STOP 2.9: Level 315, east side of PIA 

NOVA.

From top to bottom, one can observe 

amphibole-bearing (mainly cummingtonite) itabirites 

that overlie biotite-garnet schists and contain 

centimeter-thick layers of carbonates and cherts. The 

cherts contain pyrrhotite. Note several vertical fractures 

that tend to be larger within the schists than within the 

carbonate and chert layers. The fractures are filled with 

quartz in the center and tourmaline plus arsenopyrite on 

the borders. They are a local feature and have no 

continuity with the itabirites at the top nor with the 

carbonates at the bottom.

These observations bring up the discussion of 

whether the filling material of the vertical veins 

originated from lateral secretion or by introduction of 

epigenetic fluids.

STOP 2.9a: 20 m to the east along the 

same drift.

Again the biotite-calc schists have late-stage isoclinal 

folds whose axes are oriented N. 5° E. and dip to the 

south. The fold asymmetry indicates an upright position 

for the sequence if tectonic movement from south to 

north is accepted.

STOP 2.10: Back to the 265 level and 

then to the east.

Dolomites have isoclinal folding, genetically 

associated with intersection lineation and crenulation, 

both oriented N. 10°-20° W. and plunging south. These 

folds are second-phase folds because they crenulate 

micaceous minerals. The folds show that the second 

phase was as strong as the first one in this area. On the 

roof, one can observe a boudinage axis oriented 

east-west.

Tight folding is observed in metachert bands within 

biotite-quartz schists. The geometry of the folds indicate 

they are upright, and thus movement was from southeast 

to northwest.

STOP 2.11: 265 level, near channel 

sample 284-285.

Note the discordant relationship between the 

overlying itabirites and the interbedded graphitic

A60 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
calc-schists and metachert. From this stop to the east, 

the ore zone becomes less and less dolomitic and more 

graphitic.

In the thrust-fault interpretation, the itabirites were 

thrust over two distinct lithologic units that dip gently to 

the east; the dolomites dip west, and the graphitic 

phyllites dip east.

In the lateral-fades change hypothesis, dolomites and 

graphitic phyllites interfinger and are lateral equivalents. 

Both are normally overlain by itabirites; local movement 

has occurred along the contact due to boudinage 

development.

A quartz shoot, within the quartzite, contains 

recrystallized tourmaline that differs from the 

tourmalinite above the quartzite, in the sense that the 

quartzite has a fractured and disrupted layer geometry.

STOP 2.15: Level 265 near channel 

sample 380-381.

From this point on, dolomite becomes scarce and the 

gray graphitic phyllite common.

STOP 2.12: Level 265 near sample 

channel 289-291.

Calc-schists have second-phase folding that caused 

intense transposition of earlier features.

STOP 2.13: Level 265 near channel 

sample 303-307.

The vertical succession from the hanging wall to the 

footwall of the gold ore zone shows the following 

sequence: tourmalinite + arsenopyrite in dolomites as 

well as recrystallization of carbonates; a 30-cm-thick 

horizon of metachert with thin pyrrhotite-rich layers; a 

60-cm-thick horizon of pyrrhotite-bearing graphitic 

calc-schists; a 20-cm-thick horizon of metachert with thin 

interbeds of pyrrhotite-rich layers and graphitic 

calc-schist. This succession illustrates the interfingering 

relationship between the dolomites at one extreme and 

the gray graphitic schists (or phyllites) at the other 

extreme. This section has no gold values.

STOP 2.14: Level 265 near channel 

sample 342-345.

Short drift toward the base of the sequence. The 

drift begins in graphitic calc-schists, just above the 

quartzites, which mark the base of the sequence, and 

cuts dolomites containing a zone of fractured 

tourmalinite associated with recrystallized quartz. 

Between the tourmalinite zone and the quartzites is a 

10-to 20-cm-thick graphitic phyllite.

STOP 2.16: Level 265 near channel 

sample 424-427.

A cross section near the base of the sequence is seen 

here. From the top to the base of the mine face, the 

succession is as follows: (1) itabirite; (2) garnet-bearing 

black graphitic schists with a 0.5-m-thick layer of pure 

quartzite near the contact with the itabirite; and (3) ore 

zone with tourmalinite and recrystallized quartz within 

the black graphitic schist and not far from the contact 

with the underlying sericitic quartzite.

STOP 2.17: Level 265 near channel 

sample 463-468.

Repetition of itabirite and black graphitic schist. Is 

this repetition due to a transitional contact or to slicing 

by overthrusting?

STOP 2.18: Level 265 near channel 

sample 1189-1190.

Quartzite at the base and mineralized rock in the 

overlying black graphitic schist.

STOP 2.19: Level 265 near channel 

sample 505-507.

Here, the black graphitic schist of the Batata! 

Formation has thinned to 1.5 m.

Surface and Underground Geological Excursion, Passagem de Mariana Gold Mine, Minas Gerais, Brazil A61
STOP 2.20: Level 265 near channel 

sample 508-512.

Short raise exposing a good example of the 

discordant relationship between the quartzite below and 

the black graphitic schists and tightly folded calc-schist 

with tourmalinite above. Near this feature is a quartz 

vein that trends N. 20° W., 70° E. Is the discordant 

relationship an evidence of thrust-faulting or is it a 

simple tectonic thinning and plastic deformation 

resulting in boudinage-appearing features?

STOP 2.21: Ore pass connecting 265 

level with PIA1 inclined shaft.

The ore pass crosses the footwall quartzite; below the 

quartzite a repetition of vein quartz + tourmalinite + 

arsenopyrite can be observed within the 

quartz-biotite-calc schist.

STOP 2.22: Level 265 at its junction with 

the PIA 2 inclined shaft.

From the last stop to this point, the 265 level drift 

was cut in the footwall quartzite, which has become 

thicker.

Take a maze-like path that cuts through the footwall 

quartzite and once again check a vein 

quartz-tourmalinite-arsenopyrite assemblage within the 

footwall biotite-calc schists.

RETURN TO SURFACE.

REFERENCES CITED

Barbosa, A.L.M., 1969, Geologic maps of the Ouro Preto and

Mariana quadrangles, in Dorr, J.V.N., 2d, 1969,

Physiographic, stratigraphic, and structural development of

the Quadrilatero Ferrifero, Minas Gerais, Brazil: U.S.

Geological Survey Professional Paper 641-A, 110 p. 

Derby, O A., 1911, On the mineralization of the gold-bearing

lode of Passagem, Minas Gerais, Brazil: American Journal

of Science, 4th series, v. 32, p. 185-190. 

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic and

structural development of the Quadrilatero Ferrifero,

Minas Gerais, Brazil: U.S. Geological Survey Professional

Paper 641-A, 110 p. 

Emmons, W.H., 1937, Gold deposits of the world: New York,

McGrawHill,562p. 

Fleischer, R., 1971, Le gisement aurifere a tourmaline de

Passagem de Mariana (Minas Gerais-Bresil) et son cadre;

Influence de 1'evolution structurale et du m£tamorphism

sur une mineralisation synggn&ique familiere: These de

Docteur d'Universite, Faculte de Sciences, Paris, 110 p. 

Fleischer, R., and Routhier, P., 1973, The "consanguineous"

origin of a tourmaline-bearing gold deposit; Passagem de

Mariana (Brazil): Economic Geology, v. 68, p. 11-22. 

Guimaraes, D., 1965, Principios de metalogSnese e geologia

economica do Brasil: Departamento National da Produgao

Mineral, Boletim 121,625 p. 

Hussak, E., 1898, Der goldfuhrende, kiesige quarzlagergang

von Passagem in Minas Geraes, Brasilien: Zeitschrift

praktische Geologic, v. 5, p. 345-357. 

Launay, de, L., 1913, TraitS de mgtalloggnie; Gites minSraux

et metalliferes: Paris, Ch. Beranger, v. 3, 934 p. 

Legraye, M., 1937, A propos de deux gisements auriferes,

Salsigne (France) et Passagem (Br6sil): Soti&g Geologic

Belgique Bulletin, v. 61, p. 83-87. 

Lindgren, W., 1933, Mineral deposits, 4th edition: New York,

McGrawHill,930p.

A62 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
Excursion to the Morro Velho Gold Mine, 

Minas Gerais, Brazil

By FREDERICO WALLACE REIS VIEIRA, 

LUIZ HENRIQUE DO AMARAL LISBOA, 

JOSE LAMAS CHAVES, 

GERALDO ANTONIO IBRAHIM DE OLIVEIRA, 

PASCHOAL LUIZ CAIAFA CLEMENTE, and 

RAFAEL LIMA DE OLIVEIRA

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A63
POCOWNIVEIS

Underground Morro Velho mine

A64
CONTENTS

Abstract A67

Introduction A67

Regional geology A67

Geology of the Morro Velho mine A72

Stratigraphy A72

Lithologic units A72

Structural geology A72

Economic geology A72 

Log of the excursion underground A73 

References cited A73

FIGURES

1. Geologic map of the Quadrilaiero Ferrifero showing the location of major gold 

mines and other important gold mines and occurrences in the area A68

2. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero 

Ferrffero A69

3. Geologic map of level 25 of the Morro Velho mine showing the location of stops 

1-8 for the mine excursion and the Main, X, South, and NW orebodies A70

Contents A65
Morro Velho gold mine is in town of Nova Lima (top); 

mining operations are shown at level 25 (bottom)

A66
Excursion to the Morro Velho Gold Mine, 

Minas Gerais, Brazil

By Frederico Wallace Reis Vieira, Luiz Henrique do Amaral Lisboa, 

Jose Lamas Chaves, Geraldo Antonio Ibrahim de Oliveira, 

Paschoal Luiz Caiafa Clemente, and Rafael Lima de Oliveira1

ABSTRACT

The Morro Velho gold mine, located in the northern 

part of the Quadrilatero Ferrifero, is a gold deposit 

related to banded iron formation (BIF) in the Archean 

Nova Lima Group. The orebodies are stratiform sulfide 

lenses in association with metarhyolitic and 

quartz-carbonate units in a complexly folded 

metavolcaniclastic-metavolcanic greenschist terrane. 

Gold occurs in sulfides or along sulfide-silicate grain 

boundaries.

INTRODUCTION

The Morro Velho mine is in the town of Nova Lima 

in the northern sector of the Quadrilatero Ferrifero (fig. 

1). Nova Lima is about 10 km (kilometer) southeast of 

Belo Horizonte and is accessed by highway MG-030.

Gold was first recovered at Morro Velho by Padre 

Freitas in 1810, although industrial mining did not begin 

until 1834, when the mineral rights were acquired by St. 

John del Rey Mining Co., Ltd.; the mine was active from 

1834 to 1960. The Moreira Sales Group bought the 

mining rights from St. John del Rey Mining Co., Ltd. in 

1960 and formed Companhia Mineragao Morro Velho 

SA. (MMV). In 1975, AngloAmerican Corporation 

joined MMV, and, in 1978, the Bozzano Simonsen 

Group acquired the Moreira Sales Group holdings in 

MMV.

The Morro Velho mine is exploited from two 

workings because of operational problems; both

Manuscript approved for publication February 22,1991. 

1 Affiliation and address for all authors: 

Minera^ao Morro Velho S.A., Prac,a do Mineiro, 83, 

Nova Lima, Brazil

workings are in the same orebody. The upper workings, 

Mina Velha, reach a depth of 156 m (meter) above sea 

level, and the lower workings, Mina Grande, go to 1,610 

m below sea level, a total depth of 2,453 m at level 27. 

The excursion was made to level 25 of Mina Grande, 

situated at 1,314 m below sea level, and there were eight 

stops in the mine (fig. 3).

REGIONAL GEOLOGY

The Quadrilatero Ferrifero is underlain by a 

sequence of Archean rocks of the Rio das Velhas 

Supergroup, which is in turn overlain by the Proterozoic 

Tamandua or Espinhac,o Group, Minas Supergroup, and 

Itacolomi Group. This entire sequence rests on and is 

bounded by a gneissic and migmatitic Archean complex 

that was widely remobilized during the Brazilian cycle 

(550-600 Ga). The Morro Velho mine is in the Nova 

Lima district, which was mapped and described by Gair 

(1962). The geology of the Quadrilatero Ferrifero was 

compiled and synthesized by Dorr (1969). Figure 2 

shows a generalized stratigraphic column for the 

Quadrilatero Ferrifero modified from Dorr (1969). For 

an overview of the geology of the Quadrilatero Ferrifero, 

the reader is referred to Ladeira and Viveiros (this 

volume, Part B Geology of deposits). The Rio das 

Velhas Supergroup comprises a typical greenstone belt 

sequence that Schorscher (in Schobbenhaus and others, 

1984) divided into three groups, from bottom to top:

1. Quebra Osso Group Ultramafic and mafic 

volcanic rocks of komatiitic character with intercalations 

of BIF. Thorman and Ladeira (this volume, Part-A, 

Excursions, p. A14) assign these rocks to the Nova Lima 

Group, as shown in figure 2.

2. Nova Lima Group Metapelites, metavolcanics, 

and BIF.

Excursion to the Morro Velho Gold Mine, Minas Gerais, Brazil A67
A68 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
u

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PROFOUND OROGENY WITH REGIONAL METAMORPfflSM

Itacolomi Group 

PROFOUND ANGULAR UNCONFORMITY

M Minas Supergroup

Piracicaba Group

Itabiia Group

Caraga Group

Sahara Formation 

Barreiro Formation 

Tabodes Formation 

Fecho do Funil Formation 

Cercadinho Formation

Gandarela Formation

Caue Itabirite \

/

Batatal Formation 

Moeda Formation

\Tamandua Group 

MAJOR OROGENY WITH REGIONAL METAMORPfflSM

E 

U

Pi

Rio das Velhas 

Supergroup

Maquin£ Group

Nova lima Group

\

Casa Forte Formation

Palmital Formation \

/

Upper unit*

Middle unit* (includes Lapa Seca Formation) 

Lower unit*

CONTACT CONSIDERED INTRUSIVE BY DORR (1969) 

Granitic-gneissic basement rocks, including granitoids of various ages

Figure 2. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero Ferrffero (modified from Dorr, 1969). 

Asterisk (*) indicates units not included in Dorr's paper but discussed by Thorman and Ladeira in the introductory chapter of 

this volume, Part A Excursions. In this paper on Morro Velho, the authors assign the Lapa Seca Formation to the Upper unit 

of the Nova Lima Group (see text below). The granitic-gneissic basement unit includes several informal units, including the 

Bacao Complex or Bacao Granitic Complex, which is the oval basement body in the south-central part of figure 1.

3. Maquine Group Quartzites, conglomerates, and 

phyllites (divided into two formations: Palmital and 

Casa Forte).

The Nova Lima Group was divided by Mineracao 

Morro Velho geologists into three units: the Morro 

Velho gold deposit is in the Upper Unit.

Upper Unit Metapelites interlayered with acidic 

metavolcanoclastics, a quartz-carbonate (dolomite and 

ankerite) rock (a lithologic unit called the Lapa Seca 

Formation), sandy metasiltites, and metaconglomerates.

Middle Unit Acid metavolcanoclastics interlayered 

with metapelites. The top is marked by meta-andesite 

and a layer ofBIF.

Lower Unit Meta-andesites, locally contain pillow 

lavas, and interlayered with ultramafic komatiites, 

metapelites, acid metavolcanoclastics, and BIF.

Rocks of the Nova Lima Group in this area have 

been deformed during four deformational events; the 

first two events were accompanied by greenschist fades 

dynamo-thermal metamorphism. The first event was 

related to the Rio das Velhas orogeny (2.8 Ga) and the 

other three to the Minas orogeny (2.0 Ga). Diabase 

dikes intruded during the close of the second 

deformational event, thermally metamorphosing the wall 

rocks. The dikes generally occupy shear zones that 

parallel the axial-planes of D2 folds.

Excursion to the Morro Velho Gold Mine, Minas Gerais, Brazil A69
A70 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A-Excursions
§ ?

I

o

mt

:HSM

EXPLANATION

Phyllitic meta-andesite

Metadacitic tuff

Chlorite-carbonate-quartz phyllite

Quartz-chlorite-carbonate-biotitesericite phylliteMetapelitic quartz-carbonate-sericite phyllite with graphite

Carbonate-sericite-quartz-chlorite phyllite 

(carbonatized metarhyodacitic tuff)

Chlorite phylliteQuartz-sericite-carbonate phyllite 

(metarhyolite tuff)

Lapa Seca Formation (carbonate-facies iron formation)

Sulfides

"^ Fault or zone of shearing'--- Mine workings -- dashed where inaccessible 5~-« Excursion stop

mapped by Diogenes S. Vial, 1982 modified by Frederico W. Vieira, 1986

J

Si

Figure 3. Geologic map of level 25 of the Morro Velho gold mine showing the location of stops 1-8 for the mine excursion and the Main, X, South, and 

NW orebodies.

09i
GEOLOGY OF THE MORRO VELHO MINE

Stratigraphy

The Morro Velho mine is in the basal part of the 

Upper Unit of the Nova Lima Group, which is a 

sequence of metapelites (xl ) and two units of Lapa Seca 

(LS). This sequence is complexly folded and intruded by 

a phyllitized diabase dike (a). Here and in the following 

sections, letters in parentheses refer to map-unit 

notations used on figure 3.

Sulfide orebodies are restricted to the lower unit of 

the Lapa Seca, which is usually intercalated with 

submarine rhyolite and rhyodacite tuffs. The upper unit 

of the Lapa Seca is barren and has no intercalated 

volcanic rocks. Above the Lapa Seca is a bed of 

metarhyolitic tuff (Xg), which is also intercalated in the 

metapelites (Xj ).

Lithologic Units

The rocks mapped on level 25 of Mina Grande (fig.

3) have been metamorphosed dynamothermally to the

greenschist facies (biotite subzone). The following is a

generalized description of the major lithologic units

observed on level 25:

(a) Dark-green phyllitic "meta-andesite" dike rocks 

composed of chlorite, plagioclase, quartz, and 

post-tectonic poikiloblastic carbonate. Originally 

called "meta-andesite" (Oliveira and others, 

1983), but is now recognized as metadiabase dikes 

with locally assimilated wall-rock material.

(mt) Brownish-grey massive metadacitic tuff composed 

of quartz, sericite, chlorite, and carbonate, as well 

as relict phenocrysts of andesine and minor 

quartz.

(clx) Dark-green phyllite composed of chlorite,

carbonate, and quartz with subordinate sericite, 

biotite, tourmaline, and andesine. Metavolcanic 

rock of basaltic composition.

(bix) Brown phyllite composed of quartz, chlorite, 

carbonate, biotite, and sericite with relict 

andesine phenocrysts. According to Vial (1982), 

the bix is a meta-andesitic tuff.

(xl ) Dark-grey phyllite composed of quartz,

carbonate, and sericite with minor chlorite, 

biotite, and graphite. A thinly laminated 

metapelite.

(x2 ) Greenish to greenish-beige phyllite composed of 

carbonate, sericite, quartz, and chlorite with relict 

andesine phenocrysts. A carbonate-altered 

metarhyodacitic to metadacitic tuff.

Grayish phyllite composed of quartz, sericite, and 

carbonate with minor chlorite and relict quartz 

phenocrysts. A metarhyolitic tuff.

(x3 ) Phyllite composed of chlorite, sericite, and 

carbonate; unit occurs locally (Vial, 1982).

(LS) Lapa Seca Formation. Gray, banded to massive 

quartz-carbonate rock with subordinate graphite, 

sericite, feldspar, and chlorite. Carbonate is 

primarily ankerite, but locally contains calcite and 

dolomite. Laminations vary in thickness from a 

few millimeters to more than a centimeter. Some 

aspects of the mineralogy (such as sericite, 

feldspar, chlorite) suggest that some of the Lapa 

Seca is altered volcanic or volcaniclastic material.

Structural Geology

The rocks in the region were deformed during four 

events; during the first two events, isoclinal folds were 

formed whose axes are parallel (fig. 3). The first event is 

readily identified by a schistosity parallel to the 

well-preserved bedding in the hinges of D2 folds. 

Deformation in the second event produced transposed 

isoclinal folds associated with the most prominent 

lineation and foliations, which, according to Vial (1982), 

have average attitudes of S. 85° E., 16°, and N. 35° E., 26° 

SE., respectively. Vial (1982) defined a lineation at N. 

60°-64° E.,16°-22° and a cleavage resulting from a 

fracture at N. 77° E., 77° SE, which are correlated here 

with the third event. Deformation during the fourth 

event produced open and monoclinal folds responsible 

for the reduction of the plunge (L2 ) at depth within the 

mine. The fourth event is characterized by fracture 

cleavage and crenulations, which, according to Vial 

(1982), have attitudes of N. 15° E., 74° SE. and S. 4° E., 

20°, S. 8° W., 10° and N. 12° E., 3°.

Economic Geology

At level 25, nearly all gold is in the sulfidic orebodies; 

free gold is rare in metachert, a minor constituent in the 

stratigraphic succession. According to Vial (1982), the 

sulfidic orebodies are of three types: massive, 75 percent 

of ore; banded, 20 percent of ore; and orebodies 

associated with phyllite (clx), 5 percent of ore. All 

sulfidic orebodies are stratiform. The massive and 

banded types are associated with the Lapa Seca. These 

types appear to be products of volcano-exhalative 

processes. The sulfidic orebodies associated with 

phyllite (clx) contain sulfides that occur as spheres 

disseminated throughout the micaceous material (Vial, 

1982).

A72 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
The principal sulfides are pyrrhotite (35 percent), 

arsenopyrite (8.5 percent), pyrite (3 percent), and 

chalcopyrite (0.5 percent). Cubanite, sphalerite, galena, 

tetrahedrite, and ullmannite are locally abundant. Gold 

varies in size from 1 to 110 microns and is included in 

sulfides or along sulfide-silicate grain boundaries. The 

principal host minerals are pyrite (40 percent), 

pyrrhotite (35 percent), arsenopyrite (10 percent), and 

cubanite and chalcopyrite (5 percent) (Ladeira, 1980, 

1985).

Pyrite and pyrrhotite were remobilized and 

concentrated in the hinge zones of folds during the 

second deformational event. Gold occurs with silver in a 

Au:Ag ratio of 5:1 (Ladeira, 1980,1985). The ore has a 

fairly constant grade throughout the plunge of the 

orebody.

LOG OF THE EXCURSION 

UNDERGROUND

The excursion consisted of a visit to level 25 of Mina 

Grande. Access to this level is by six separate shafts.

STOP1

Lapa Seca Formation with interbedded metapelite (x x ) 

and isoclinal folds of the second event.

STOP 2

Massive sulfide (NW orebody) in contact with bix.

STOP 3

Finely laminated Lapa Seca.

STOP 4

x2 -Carbonate-sericite-quartz-chlorite phyllite, 

brownish-grey, with some biotite.

STOPS

clx~Chlorite-carbonate-quartz phyllite with some 

sulfides.

STOPS

xx -Quartz-carbonate-sericite phyllite (metapelite);

massive sulfide (South orebody) is associated with clx.

STOP?

bix-Intercalations of brown 

quartz-chlorite-carbonate-biotite-sericite phyllite in 

beige-gray Lapa Seca.

STOPS

Area of mining of X orebody

Massive sulfide

Plunge S. 85° E.,18°

Mining Method: Cut and fill

Area of Mining: 1,151.1 square meters

Grade: 11.86 grams per ton (in situ).

REFERENCES CITED

[* indicates references cited in this paper that are not available 

outside of Brazil or are unpublished dissertations. These references 

are used in the interest of crediting workers, even though their work 

is not published, and letting the reader know where to find these 

references]

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic, and 

structural development of the Quadrilatero Ferrifero, 

Minas Gerais, Brazil: U.S. Geological Survey Professional 

Paper 641-A, 110 p.

Gair, J.E., 1962, Geology and ore deposits of the Nova Lima 

and Rio Acima quadrangles, Minas Gerais, Brazil: U.S. 

Geological Survey Professional Paper 341-A, 67 p.

*Ladeira, E A., 1980, Metallogenesis of gold at the Morro 

Velho mine and in the Nova Lima district, Quadrilatero 

Ferrifero, Minas Gerais, Brazil: London, Ontario, 

Canada, University of Western Ontario, unpublished Ph.D. 

thesis, 272 p.

*____ 1985, Metalogenese do ouro na mina de Morro 

Velho e no Distrito de Nova Lima, Quadrilatero Ferrifero, 

Minas Gerais, in Grossi Sad, J.H. and Barcellos da Silva, 

A., eds., Contribuic,6es a geologia e a petrologia Volume 

dedicado a mem6ria de D. Guimaraes, Patrocinio da 

CBMM,p.95-151.

Oliveira, G A.I., Clemente, P.C., and Vial, D.S., 1983, 

Excursao & mina de ouro de Morro VelhdT Anais, II 

Simp6sio Geologia Minas Geologia, Belo Horizonte, 

Sociedade Brasileira de Geologia, Nucleo Minas Gerais, 

Boletim3,p. 497-505.

Schobbenhaus, C., Campos, DA., Derze, G.R., and Asmus, 

H.E., 1984, Geologia do Brasil: Brasil Departamento 

National da Produgao Mineral, 501 p.

*Vial, D.S., 1982, internal company report for Morro Velho 

Mineragao, S A.

Excursion to the Morro Velho Gold Mine, Minas Gerais, Brazil A73

Excursion to the Cuiaba Gold Mine, 

Minas Gerais, Brazil

By FREDERICO WALLACE REIS VIEIRA, 

MARIO CORBANI FILHO, 

JOSE TEOTONIO DE FARIA FONSECA, 

AGUINALDO PEREIRA,

GERALDO ANT6NIO IBRAHIM DE OLIVEIRA, and 

PASCHOAL LUIZ CAIAFA CLEMENTE

U.S. GEOLOGICAL SURVEY BULLETIN 1980-A

A75
Entrance to Cuiaba gold mine property

A76
CONTENTS

Abstract A79 

Introduction A79 

Regional geology A79 

CuiabS mine geology A81 

Stratigraphy A81 

Lithologic units A81 

Structural geology A82 

Economic geology A82 

Log of the excursion A83 

References cited A86

FIGURES

1. Geologic map of the Quadrilatero Ferrifero showing location of the CuiabS gold 

mine, other major gold mines visited, and other gold mines and major gold 

occurrences in the area A80

2. Generalized stratigraphic column of Precambrian rocks of the QuadrilStero 

Ferrifero A81

3. Geologic map of level 3 in the Cuiab£ gold mine showing the excursion stops and main 

orebodies A84

Contents A77
|

Bedded, pyrite-rich ore from the Cuiaba gold mine (top) and the mine portal (bottom)

A78
Excursion to the Cuiaba Gold Mine, 

Minas Gerais, Brazil

By Frederico Wallace Reis Vieira, Mario Corbani Filho, Jose Teotonio de Faria Fonseca, 

Aguinaldo Pereira, Geraldo Antonio Ibrahim de Oliveira, and 

Paschoal Luiz Caiafa Clemente 1

ABSTRACT

The Cuiab£ gold mine, in the northeast part of the 

Quadrilatero Ferrifero, is a banded iron-formation 

deposit in the Archean Nova Lima Group. Most of the 

gold occurs in pyritic orebodies that are stratiform and 

stratabound in banded iron-formation sulfide-facies 

rocks. The main structure at the Cuiaba mine is an eastwest-trending anticline produced during the second of 

four deformational events recorded in the Archean 

rocks.

INTRODUCTION

The Cuiaba Mine is 5.5 km (kilometer) east of 

Sabara, beneath the town of Cuiaba, which is southeast 

of the Serra da Piedade in the northeast part of the 

Quadrilatero Ferrifero (fig. 1). Access is from Belo 

Horizonte on Highway MG-05, which connects Belo 

Horizonte to Caete; the mine is situated between Sabar£ 

and Caete and is finally reached by a private unpaved 

road.

The first work in the area was undertaken in 1740 by 

garimpeiros (prospectors). The mine was acquired by 

the St. John Del Rey Mining Co. Ltd. in 1877 and was 

operated intermittently for the next 100 years; 

Mineracao Morro Velho resumed development in 1977 

and began mining in 1985. As of 1986, Cuiaba had the 

largest reserves of all the gold mines owned by 

Mineracao Morro Velho.

Manuscript approved for publication February 22,1991.

Affiliation and address for all authors: 

Mineracjio Morro Velho S.A., Prac,a do Mineiro, 83, 

Nova Lima, Brazil

REGIONAL GEOLOGY

The Quadrilatero Ferrifero is underlain by a 

sequence of Archean metasedimentary and metavolcanic 

rocks of the Rio das Velhas Supergroup, which is in turn 

overlain by the Proterozoic Minas Supergroup and the 

Itacolomi Group of Dorr (1969). This upper Archean 

and Proterozoic sequence rests on and is bounded by a 

gneissic and migmatitic Archean complex, widely 

remobilized during the Brazilian cycle (550-600 Ga). 

The mine is within the Serra de Piedade quadrangle, the 

geology of which was mapped by Benedito P. Alves (in 

Dorr, 1969). The geology of the Quadrilatero Ferrifero 

was compiled and synthesized by Dorr (1969). Figure 2 

shows a generalized stratigraphic column for the 

Quadrilatero Ferrifero. For an overview of the geology 

of the Quadrilatero Ferrifero, the reader is referred to 

Ladeira and Viveiros (this volume, Part B Geology of 

deposits). The Rio das Velhas Supergroup comprises a 

typical greenstone belt sequence that Schorscher (in 

Schobbenhaus and others, 1984) has divided into three 

groups, from bottom to top:

1. Quebra Osso Group Ultramafic and mafic 

volcanic rocks of komatiitic character with intercalations 

of BIF (banded iron formation). Thorman and Ladeira 

(Part-A, Excursions, this volume, p. A14) assign these 

rocks to the Nova Lima Group, as shown in figure 2.

2. Nova Lima Group Metapelites, metavolcanics 

and BIF.

3. Maquine Group Quartzites, conglomerates and 

phyllites (divided into two formations: Palmital and 

Casa Forte).

The Nova Lima Group, which is the major host for 

the BIF-related gold deposits in the region, has been 

divided by Mineracao Morro Velho geologists into three 

units. Most of the CuiabS ore is near the top of the 

lower unit of the Nova Lima Group.

Excursion to the Cuiaba Gold Mine, Minas Gerais, Brazil A79
Jt I1

3o

SANTA BARBARA; 15

GOLD MINES AND

MAJOR GOLD OCCURRENCES

INACTIVE_MINES OR BEINGJJVALUATED

1. Ouro Fino 

de Cima

2. Ouro Fino 

de Baixo

3. Morro do Adao4. Carrancas5. Juca Vieira

6. Fazenda Velha

7. Carrapato8. Fazenda Cutao9. Fazenda Ojeriza

10. Luis Soares

11. GongoSoco12. Camara13. Taquaril - 

Cocaes

14. Brucutu15. Pari16. Santa Ouiteria17. Sao Jorge

18. Brumandinho

19. Quebra Ossos

20. Picarra21. Pitangf

22. Paracatii - 

Agua Quente

23. Fazendao24. Cata Preta

25. Bento Rodrigues

Itacolomi Group Piracicaba Group

Caraca Group 

Tamandui GroupMaquine Group 

Nova Lima Group 

undifferentiated granitic rocks

Rio das Velhas 

Supergroup ACTIVE MINES

51. Faria

52. Gabirobas53. Gaia

54. Bicalho

Thrust fault Sawteeth on upper plate

26. Am6nio Pereira27. MaquinS

28. Rocinha29. Santana

30. Morro Redondo31.MataCavalo32. Taquaral33. Bom Jesus 

das Flores

34. Palacio Velho

35. Veloso36. Bico de Pedra

37. Ouro Preto38. Ajuda39. Passa Tempo40. Ouro Fino

41. Paciencia42. Marzagao43. Bahu

44. Cata Branca

45. Casa de Pedra

46. Gordura47. Urubu48. Limeiro 

doSul

49. Limeiro 

do Norte

50. Galo

55. Bela Fama

56. Espirito Santo

57. Raposos

MAJOR MINES VISITED

58. Morro Velho (active) 61. Passagem

59. Cuiaba (active) de Mariana

60. Sao Bento (active) (inactive-being 

evaluated)

SCALE

Figure 1. Geologic map of the Quadrilatero Ferrffero (modified from Dorr, 1969) showing the location of the Cuiaba gold mine, other major gold mines 

visited, and other gold mines and occurrences in the area.
u

I I

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SI

o

rt 

w

H

o

PROFOUND OROGENY WITH REGIONAL METAMORPfflSM

Itacolomi Group 

PROFOUND ANGULAR UNCONFORMITY

Minas Supergroup

Piracicaba Group

Itabiia Group

Carac.a Group

Sahara Formation 

Barreiro Formation 

Tabooes Formation 

Fecho do Funil Formation

Cercadinho Formation \

Gandarela Formation 

Caue Itabirite

/

Batatal Formation 

Moeda Formation

Tamandua Group 

MAJOR OROGENY WITH REGIONAL METAMORPfflSM

PJ 

ffl 

u

Rio das Velhas 

Supergroup

Maquin£ Group

Nova lima Group

Casa Forte Formation

Palmital Formation \

/

Upper unit*

Middle unit* (includes Lapa Seca Formation) 

Lower unit*

< CONTACT CONSIDERED INTRUSIVE BY DORR (1969)

Granitic-gneissic basement rocks, including granitoids of various ages

Figure 2. Generalized stratigraphic column of Precambrian rocks of the Quadrilatero Ferrifero (modified from Dorr, 1969). 

Asterisk (*) indicates units not included in Dorr's paper but discussed by Thorman and Ladeira in the introductory chapter of 

the volume, Part A Excursions. The granitic-gneissic basement unit includes several informal units, including the Bacao 

Complex or 83930 Granitic Complex, which is the oval basement body in the south-central part of figure 1.

CUIABA MINE GEOLOGY 

Stratigraphy

The mine workings intersect the Lower, Middle, and 

Upper Units of the Nova Lima Group; the orebodies are 

near the top of the Lower Unit. The Lower Unit in the 

mine includes meta-andesites (man and manx) with 

intercalations of metapelites (xx and fg). (See following 

paragraphs for explanation of symbols.) Overlapping 

the andesite sequence are metapelites (x x ) with 

interlayers of metarhyodacitic tuffs (x2 ). A BIF bed, 

5-15 m (meter) thick, is at the top of this unit. The 

overlying Middle Unit includes metarhyodacitic tuff (x2 )

with intercalations of metapelite (fg); a metabasalt 

(mba) flow is close to the top. The Upper Unit is 

characterized by intercalated metapelites (xx ) and 

metarhyolitic tuffs (Xg).

Lithologic Units

The Nova Lima Group rocks in the Cuiaba mine 

area show evidence of having been metamorphosed 

during at least two episodes of chlorite-zone 

greenschist-facies metamorphism. Nine major 

lithologies are recognized in the mine and are described 

here. The letters in parentheses at the beginning of each

Excursion to the Cuiaba Gold Mine, Minas Gerais, Brazil A81
description correspond to units on the geologic map of

level 3 (fig. 3)

(mba) Moderately schistose, dark green metabasalt(?) 

with pillow structures, composed of actinolite, 

epidote, chlorite, carbonate, titanite, and laths 

of plagioclase with fine diabasic texture. 

Probably a metabasalt; possibly a 

meta-andesite.

(clx) Phyllitic bottle-green metabasalt(?) composed 

of chlorite, carbonate, and quartz with sericite 

and tourmaline; has lenticular shape; associated 

with BIF.

(man) Light green massive meta-andesite, locally with 

pillow structures and amygdules, composed of 

epidote, quartz, chlorite, tremolite, actinolite, 

and carbonate, with randomly oriented laths 

and phenocrysts of andesine.

(manx) Schistose to phyllitic dark green and gray

meta-andesite composed of chlorite, quartz, and 

carbonate with some epidote; contains 

randomly oriented laths and phenocrysts of 

andesine. The protolith was andesite that was 

erupted into, and subsequently interacted with, 

sea water and was later modified by 

hydrothermal solutions.

(x2 ) Beige phyllitic metarhyodacitic tuff composed of 

carbonate, sericite, and quartz with laths of 

andesine. The rock appears to have been 

carbonatized by hydrothermal solutions during 

or before metamorphism.

(Xg) Light grey phyllitic metarhyolite tuff composed 

of quartz, sericite, chlorite, and carbonate with 

relict volcanic quartz and plagioclase; contains 

minor amounts of graphite; typically has a 

rough and wrinkled parting plane and is locally 

distinctly layered.

(Xj) Dark grey phyllite composed of quartz, 

carbonate, and sericite with chlorite and 

graphite; thinly layered metapelite with acidic 

volcanic contribution.

(fg) Black graphitic phyllite with sericite, quartz and 

carbonate; thin layers of quartz, carbonate and 

sulfides; interpreted to be a metapelite.

(BIF) Carbonate and sulfide facies banded iron

formation in equal proportion; carbonate and 

sulfide facies rocks are distinctly laminated on a 

millimeter to centimeter scale; quartz (chert) 

and carbonate beds dominate in carbonate 

facies; rocks are generally light colored in 

carbonate facies, but become dark gray where 

graphite is present.

Structural Geology

Rocks at the Cuiab£ gold mine were deformed 

during four events. The first event is indicated by a relict 

schistosity (Si) parallel to the bedding; this schistosity 

may include transposed isoclinal folds, but such folds 

have not been identified in the mine area. The second 

event is represented by anisotropic isoclinal folds with a 

prominent foliation (82 ) and lineation (L2 ). Intense 

transposition along the schistosity caused segmentation 

and thrusting of fold structures. Shear zones along the 

foliation are characterized by swarms of quartz boudins. 

82 trends N. 55°-70° E. and dips 40° SE., and L2 trends 

S. 60°-70° E. and plunges 32°-34°. The third event is 

identified by lineation (Ls ) subparallel to Li and L2 

and is poorly represented in the area. The fourth event 

is represented by gentle folds whose axes trend S. 12° E. 

and plunge 17°. Fracture cleavage or transposition 

cleavage has an attitude of about N-S/650 E. The shear 

zones are parallel to cleavage and are characterized by 

sigmoidal structures.

The main structure at the Cuiab£ mine is an 

east-west-trending anticline (fig. 3) produced during the 

second deformational event. The inverted north flank of 

the anticline was strangled and broken during folding. 

The strangled area (Galinheiro Extensao) is 

characterized by tight folds associated with thrusts and 

shearing along 82.

All the structures can be projected at depth along 

L2, with minor deflections caused by interference effects 

from the subparallel fold axes of events 1, 2, and 3. The 

L2 plunge tends to flatten at depth due to refolding 

during the fourth deformational event.

Economic Geology

Most of the gold in the Cuiaba mine occurs in pyritic 

orebodies in the BIF sulfide facies. Thirteen orebodies 

are recognized and include Balanc.ao Leste, Centro, and 

Oeste; Galinheiro, Galinheiro Sul, and Galinheiro 

Extensao; Surucucu Leste and Oeste; Serrotinho; Fonte 

Grande and Fonte Grande Sul; Viana; and Canta Galo. 

The area of these orebodies totals 5,067 m2 (square 

meter) in level 3. The rocks in the sulfide orebodies are 

banded or homogeneous, are distinctly laminated and 

strongly deformed, and are locally separated by faults. 

The sulfide orebodies are stratiform and stratabound in 

BIF near the top of the Lower Unit. They are 

interpreted to have emanated from volcanoes, and they 

were reconcentrated and recrystallized in the D2 hinge

A82 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A Excursions
zones during regional metamorphism. Some gold is 

stratigraphically higher in basalt-hosted quartz veins and 

in the alteration zones associated with the veins, such as 

in the Viana orebody. Many fractures commonly 

crosscut the Serrotinho orebody.

Pyrite is the principal sulfide, followed by 

arsenopyrite and pyrrhotite. The pyrite is idioblastic to 

xenoblastic and ranges in size from 0.02 to 15 mm 

(millimeter). Arsenopyrite is idioblastic and ranges in 

size from 0.009 to 3.55 mm. White pyrrhotite ranges hi 

size from 0.02 to 2.8 mm. Accessory minerals include 

sphalerite, chalcopyrite, magnetite, marcasite, and rutile. 

The fine-grained sulfide minerals are finely banded and 

appear to be syngenetic, but the coarser ones are clearly 

later and most likely formed during subsequent events.

Gold is less than 60 microns in size and on average 

the Au:Ag ratio is 6:1. The gold is both within sulfide 

grains and along grain boundaries and is most commonly 

associated with pyrite, arsenopyrite, and pyrrhotite. 

Some free gold is associated with milky or smoky quartz 

orebodies (Viana orebody) along 82 and surrounded by 

a recrystallized, carbonatized, and chloritized zone.

LOG OF THE EXCURSION

The excursion was to level 3 of the mine, where the 

lithotypes and structural features were emphasized, as 

well as the different aspects of mineralization. See 

figure 3 for location of the stops hi the mine.

STOP 4.

(mba) Metabasalt with pillow structures that have 

dark-green coarse-grained nuclei and 

light-green fine-grained borders (chilled 

contact). The material between the pillows is 

chlorite-rich.

STOP 5.

Viana orebody sub-level. Milky or smoky quartz with 

free gold, enclosed by a zone of serialization, 

chloritization, and carbonatization.

Mining area: 90.2 m2 ; ore grade 4.70 g/t (gram per

ton) (in situ) 

PlungeS. 50° E./340

STOP 6.

Mining area: Serrotinho orebody 

Banded sulfide 

Plunges S. 58° E/30° 

Mining method: Cut and fill 

Mining area: 1,117 TET 

Grade: 5.18 g/t (in situ)

STOP1.

Quartz-sericite-chlorite-carbonate phyllite with 

phenocrysts of volcanic quartz (metarhyolitic 

tuff). (xx ) Well-bedded quartz-carbonated 

sericite phyllite with chlorite (metapelite).

STOP 7.

Folds of the fourth deformational event with 

transposition cleavage or fracture cleavage hi schistose 

meta-andesite.

STOP 2.

(man) Light-green massive meta-andesite. 

(manx) Dark-green schistose meta-andesite.

STOP 8.

Brecciated BIF in fault zone of the second deformational 

event.

STOP 3.

(mba) Moderately schistose dark-green metabasalt.

STOP 9.

Shear zone of the second event with quartz boudins in 

graphitic phyllite (fg).

Excursion to the Cuiaba Gold Mine, Minas Gerais, Brazil A83
A84 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
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Excursion to the Cuiaba Gold Mine, Minas Gerais, Brazil MS
STOP 10.

Mining area: Galinheiro Extensao orebody

Massive sulfide

Plunge S. 56° E./330

Mining method: Cut and fill

Mining area: 538.2m2

Grade: 13.50 g/t (in situ)

REFERENCES CITED

Dorr, J.V.N., 2d, 1969, Physiographic, stratigraphic and 

structural development of the QuadrMtero Ferrifero, 

Minas Gerais, Brazil: U.S. Geological Survey Professional 

Paper 641-A, 110 p.

Schobbenhaus, C., Campos, DA., Derze, G.R., and Asmus, 

H.E., 1984, Geologia do Brasil: Brazil Departamento 

Nacional da Produgao Mineral, 501 p.

STOP 11.

Shear zone of the fourth deformational event with 

sigmoidal structure in graphitic phyUite (fg). x2 

carbonate-sericite-quartz phyUite, beige; carbonatized 

metarhyodacitic tuff.

A86 Gold Deposits Related to Greenstone Belts in Brazil Deposit Modeling Workshop Part A- Excursions
Diane C. Schnabel edited and designed the book.

Charles H. Thorman prepared the text and many of the illustrations on his computer and 

programmed the computer for the Portuguese alphabet.

David P. Buscher digitized all the geologic maps.

William R. Stephens prepared final art for several geologic maps.

John Preisendorf and Gayle Dumonceaux prepared the photographs for the printer.

The text is printed in Helvetica and Times Roman.

A87

*U.S GOVERNMENT PRINTING OFFICE: 1991-573-049/26032