Mineral. Deposita (Berl.) Ii, 83 - 92 (1976') MINERALIUM DEPOSITA ©by Springer-Verlag 1976

Lithospheric Plate Motions - One of the Factors Controlling Distribution of Ore Deposits in Some Mineral Belts

J. Kutina *

Bethlehem, Pennsylvania, U.S.A.

Determination of paleolatitudes of ore deposits, based on the reconstruction of lithospheric plate motions and the absolute ages of deposits, provides a basis for a new kind of space-time analysis of structural control of ore deposition. Such analysis shows that the formation of two ore deposits of different ages, each oc- curring at a different latitude along a north-south trend within a mineral belt, may be controlled by the same transversal fracture zone in the substratum underlying the lithospheric plate if rotation of the plate took place in the time-span between the formation of the two ore deposits (Fig. 3). This mechanism controlling ore de- position has been elucidated using a model which assumes horizontal movement of lithospheric plates on a mobile layer that originated within solid basement that is penetrated by a system of fracture zones. The distribution of porphyry copper de- posits of the Andes mineral belt is used to study this process.

INTRODUCTION

The discovery that the upper parts of the Earth are composed of a number of rigid plates that do not remain in fixed posi- tions but move through geologic time, in- volve processes that are of basic import- ance for structural and geochemical con- trol of ore deposition. One of the main observations of the last decade in metal- logeny was recognizing the relationship between distinct types and ages of miner- alization and certain types of plate

boundaries, as most comprehensively .discussed by Guild (1974). Of particu- lar importance is the role of subduc- tion or Benioff zones on metallogenic processes connected with partial melt-

>~ Present address: Laboratory of Global Tectonics and Metallogeny, Washington Technical Institute, Washington, D.C. 20008, U, S.A.

ing of the subducted oceanic crust and in generating a distinct type of magma (Sillitoe 1972 a, b).

Several authors have attempted to re- construct some metallogenic provinces by correlating the distribution of ore deposits in the pre-Cretaceous configu- ration of lithospheric plates. Petra- scheck (1968), for example, has de- monstrated that a good fit exists in some instances, especially between metallogeny of eastern South America and Western Africa, whereas consider-

able differences appear in other areas. Some of the disagreements may be due to paleoreconstructions of continents which did not have sufficient data on "missing" parts of some continental masses that have disintegrated or sub- sided. For instance, the disintegration of a landmass in the area of the western Indian Ocean, advocated by Kutina (1975), excludes derivation of India from the eastern coast of present Africa and Ma-

84 Jan Kutina

dagasear but does not exclude the possi- bility of its northern drift from the cen- tral part of the Indian Ocean as demon- strated by IVieKenzie and Sclater (1971, 1973). The recent collection of papers edited by Kahle (1974) shows that the question of continental drift is still far from being completely understood.

Systematic studies of deep-seated,

ore controlling fracture zones conducted in the last decade (Favorskaya, Tomson et al. 1974, Kutina 1973, 1974) have shown the existence of some ore control- ling structural lineaments that extend along the landward projection of some fracture zones of the ocean floor. If a continental lithospheric plate moves towards an oceanic plate, ~nvolving subduction of the oceanic plate, in a direction parallel to the oceanic frac- ture zones, then the existence of min- eral belts parallel to these fracture zones is plausible using the model of Kutina (1974). A problem may arise, however, if the continental plate is not moving parallel to the oceanic fracture zones. In this case, the lo- cation of endogenic ore deposits in the continent over projections of the ad- jacent oceanic fracture zones may be fortuitous.

The latter case concerns, for in- stance, correlation between the lati- tudes of some ore deposits of the Andes and the latitudinal positions of some east-west trending fracture zones of the East Pacific floor (observed name- ly by Favorskaya, 1971 and Favorskaya, Tomson et al. 1974).

The role of the respective fracture zones upon localization of some ore deposits of the Andes would be under- standable if the South American plate did not change its position by continental drift and the respective fracture zones extended into its basement. If, however, the concept of continental drift is cor- rect, the Andes deposits of different ages should correspond to different po- sitions of the South American plate. Then, a correlation between present latitudes of some ore deposits of the

Andes and the east-west fracture zones of the East Pacific floor could be acci- dental.

The history of the above process may actually be still more complicated. One of the possibilities may concern the following case: The ore deposits, for instance the porphyry coppers (Fig. 2), have originated at different positions of

the South American plate between its

pre-drift and present locations. The plate may have moved so that some of the porphyry copper deposits have reached a position which is now com- parable with latitudes of some of the major fracture zones of the East Pa- cific floor. If the plate movement pro- ceeded according to the model of Kuti- na (1974), the respective east-west trending fractur e zones of the East Pa- cific floor correspond to fracture zones of tectonic weakness that have the same trend and extend through a rigid mantle below both the oceanic plate and the ad- jacent lithospheric plate. In such a case an east-west fracture may propa- gate upwards from the asthenosphere through the lithospheric plate and mani- fest its'elf morphologically as a trans- versal tectonic feature in the Andes. As a consequence, a feature may result in the peripheral part of the liihospheric plate which resembles a "landward ex- tension" of the oceanic fracture zone. An endogenic ore deposit may thus be located along a "landward extension" of an oceanic fracture zone, though the given fracture zone need not have necessarily controlled its formation.. The ore deposit may, in fact, be older having originated at another latitude.

The above example indicates that the process leading to the present correla- tion between some structural features and location of ore deposits may be very complicated. This paper will not re- solve this problem but will contribute to a partial solution by analysing one aspect of the main query.

The assuptions of the present contri- bution are: (I) The South American plate has reached its present position

Lithospheric Plate Motions 85

cha (Ecuador)

, . , o u , , , °, , .. u , y// Pashpap (Peru)

i i 0 Antamina {Peru) ( / QCerro de Posco (Peru)

Morococha (Peru) I Cobriza (Peru)

0 Chocobambo- Ferrobamba (Peru) 0 Tintoya (Peru) _~_

Ouelloveco (Peru) Toquepala (Peru)

(Peru) / / ~ v Arequipa (Peru) Cuajone j "~ (Peru) / I Mocha {Chile)

A - / ' ~ , E I Abra (Chile) Cerro Colorado j ) dE.,]

(Chile) J V Chuquicamata (Chile) ' [ll~Ox-sierra Gorda (Chile) 1 -

. . c o . e / El Salvador (Chile)

La Alumbrero~, f~ q Potrerillos (Chile) ~ 1 (A[ge, ntln.a,) % ~ - M a n t o Verde (Chile) )

And,dco! lo~ ~ 0 Famatina (Argentina) tChile/ . t y I l e , . ~11 ~Cerro Rico(Argentlna) T 50° / / ~i~ej ~ ~ochon (Argenti no) / ' /

. - , ' . . . . . ~ ) " ~ O p . . . . il[os (Argentina) , / Los ,P.eJarnbresJ / ~ - S a n t a Clara(Argentina) /

tLnuej / ~ A N ~ - R i o Blanco (Chile) D'{sP~I~a El Teniente (Ch,le)

,..., Campana Mahuida 0 (Argentina)

0 < 1,000,000 tons Cu 0 1,000,000 to I0,000,000 tons Cu [~] > I0,000,000 tons Cu

O IN OPERATION OR EXHAUSTED RESERVES O ESTIMATED RESERVES

Fig. I. The main porphyry copper deposits of the Andes region, following Eimon's map (1974)

by rotation away from a rift zone that

is supposed to have separated South America from Africa and is essen- tially marked by the Mid-Atlantic Ridge. (2) The motion of the South American plate took place according to the scheme derived by Sclater and Mc Kenzie (1973). If the first concept is incorrect, the results of this paper are not applicable. If the motion of the plate

proceeded differently than that given by Sclater and McKenzie, the results need not loose their validity but the paleola- titudes of ore deposits would be different.

APPLICATION OF THE NEW MODEL

Some new observations bearing new light on the nature of the upper mantle come from marine geology and some from metallogeny.

86 Jan Kutina

75 ° +

0 0

d~-zo o

LOWER

00

TERT,

÷

60 ° - I - 0 o

O

0•29532 .2

TERZ ?

(}-8.0 0 + }o ~-~.9

C]I-4.~2

O~UPPER TERT.

~o-6o my ® 3o-4o my. • ~20 my ~ 4-,0 my

Fig. 2. Periods of porphyry copper formation in the Andes region with each cor- responding to a narrow range of orientations of the South American plate in the course of its movement from pre-drift into the present position. Note the zoning in the age of porphyry copper deposits, as already indicated by Sillitoe (1974). The absolute ages are taken from Hollister' s (1973) compilation

Bonatti and co-workers (Bonatti 1973 with quotations of earlier papers) have found that the submarine mountain ridges, extending parallel to fracture zones of the equatorial Atlantic (Vema, Romanche and others), are essentially made up of blocks of basic and ultra-

basic rocks, especially serpentinized peridotites, that seem to have been era- placed as upward protrusions of solid mantle material along old fracture zones existing before the openig of the Atlan- tic. Bonatti et al. (1974) have also pre- sented a schematic model showing the

Lithospheric Plate IVIotions 87

3 0 ° N

I 0 ° N

I0° !

3 0 o , c

50°~

3 0 ° N

IO°N

IOoS

3 0 o S

50oS

Fig. 3. Formation of a mineral belt during the motion of a crustal plate. The recent and pre-drift positions of South America and Africa are shown according to Sclater and McKenzie (1973). The illustration shows the difference between the paleolatitudes and present latitudes of ore deposits as eaused by rotation of the plate. Two deposits of a different age, originated along one and the same east-west trending zone of tectonic weakness of the asthenosphere, may appear north and south of eaeh other in the recent north-south trending mineral belt, if rotation of the plate proceeded in the time-span between formation of the two deposits

possibility of horizontal movements of crust over bodies of stagnant upper mantle during the initial stages of open- ing of an ocean basin.

Working independently, Kutina (1974) recently presented a model of lithosphe- tic plate motion over a solid mantle at the International Conference on the New Basement Tectonics. This model is based on a systematic study of struc- tural control of ore deposition in four continents and on similarities between the patterns of fractures of deeper parts of continental plates and the ocean floors (Kutina 1973, 1974). The model assumes horizontal movement of litho- spheric plates away from a rift zone, proceeding on a mobile layer that orig- inated within a solid basement pene- trated by a system of fracture zones

or tectonie zones of weakness. Zones of an east-west trend play a particular- ly important role.

If plate movement was in a direction other than east-west, the pattern of east-west zones of weakness of the lithosphere would be shifted with re- spect to the east-west zones of weak- ness of the asthenosphere. Consequent- ly, the pattern of fracture zones (or zones of weakness) of the plates loses its continuity with its "roots" below the mobile layer.

Since metallogenic processes also occurred in the time-span between the pre-drift and the recent positions of continents, it is important to analyse whether periods of metallogenesis were related to particular positions of the

88 Jan Kutina

South America

Present

P~sene ~ T ot o bef of | 30-#Om.y old |

E[ Abra

E[ Salvador\ Potrerillos

Pachon

El l"eniente

Caml~ Hanhuida

~ m . y . B . P

20 =

25 °

E[ Abra

30 °

PotreriL[os

Paleopos#ion of the same belt ~tepprox. 35m.y B.P.

35 °

~0 °

Fig. 4. Correlation of the present and former latitudes of some porphyry copper deposits of South America

moving plates in which coincidence coud be reached between the zones of weakness of the lithosphere and the asthenosphere.

This whole question is extremely complicated because the oceanic plates move. Thus, the pattern of fractures of the oceanic plates (which in the author' s model is supposed to be im- printed by upward propagation from zones of tectonic weakness that lie be- low) changes its orientation by rota- tion of the plates. Besides that, as Herron (1972) has shown in her analy- sis of the Pacific area, the pattern of oceanic plates has been reorganized at least here in the course of geological history and the newly formed plates show a pattern of fractures which differs from but shows similarities to the former. Besides that, it is not known, however, whether the mantle

below the moving lithospheric plates remains in a fixed position in the course of geological history. If it does, the paleolatitudes of major endogenic ore deposits may help in analysing the pre- sence and strike of the zones of weak- ness of the deep basement. If, however, the mantle below the mobile layer moves, the analysis will be much more diffi- cult, but perhaps not impossible.

The distribution of the porphyry cop- per deposits of the Andes region has been chosen asthe first subject of ana- lysis.

SPACE-TIME ANALYSIS OF STRUC- TURAL CONTROL OF PORPHYRY COPPER DEPOSITS OF THE ANDES MINERAL BELT

The distribution of the main porphyry copper deposits of the Andes region

Lithospheric Plate Motions 89

(Fig. i) is based on Eimon' s (1974) map. Fig. 2 gives the absolute ages of the same

deposits, as far as they are known, using values compiled by Hollister (1973). Some inaccuracy of the absolute ages may be expected. Further compli- cations may arise, as in the case of the Chauca deposit of Ecuador, where Goossens (1972) attributes its Miocene age to possible remelting of Laramide igneous intrusions.

Three definite periods of porphyry copper formation have been distinguished (Fig. 2): 50-60 m.y., 30-40 rn.y., and 4-10 m. y.B.P. The age of about 20 m. y. of the Peruvian deposit of Michiquil- lay is marked separately as it differs considerably from the values in the group of 30-40 m. y. old deposits. If the absolute age of 90 m.y. of the Anda- collo deposit of Chile (Llaurnett and

Ulloa, 1973, quoted by Lowell 1974) is correct, still another, older group of porphyry coppers should be distihguished in the Andes.

Accepting the concept of continental drift with the modifications as shown in the new model, each of the above

periods of porphyry copper formation should correspond to a narrow range of orientations of the South American plate as it drifted from its pre-drift location to its present position.

The intense magrnatic and metallo- genic activity along the Pacific margin of South America is understandable in the light of the enormous amount of the subducted material of the original Far- talon and Phoenix plates which are sup- posed to have been essentially consumed on the subduction zone (Fig. 7 in Larson & Pitman III, 1972, and the recent con- figuration of plates in Eastern Pacific in Fig. 2 of Herron 1972). Consequent- ly, the explanation of the origin of the porphyry copper and other endogenic deposits of the Andes in connection with subduction of oceanic crust on the Benioff zone as presented by Sillitoe (1972a, b) is accepted as the first struc- tural and geochemical control of their formation.

The second structural control of ore deposition along the Pacific margin of South America is ascribed to the frac- ture pattern of the continent, consist- ing of both major deep-seated fractures and fractures of relatively local import- ance. Some of the fractures are of Pre- cambrian age, with an orientation changed due to rotation of the South American Plate. Some of them have later been rejuvenated and some new fractures have originated during the later stages of development.

Sillitoe (1974) has shown a pattern of transverse fractures causing tec- tonic segmentation of the Andes oro- genic belt. Those appearing in a belt along the straight, north-south coast of South America mostly have an east- west trend. Carter's (1974) study of ERTS-I images shows that east-west trending fracture zones also play an important role in northern half of the Andes where the Pacific coastline is no longer north-south but trending NW- SE.

It is possible that still another very important structural control of ore de- posftion played a part in the Andes. This structural control may be condi- tioned by the presence of zones of tec- tonic weakness in the asthenosphere over which the lithospheric plate has moved. A possibility of such a control is demonstrated in Fig. 3 with hypo- thetical positions of ore deposits. Let us assume that there exists in the as- thenosphere a zone of tectonic weak- ness (essentially vertical) which in the present net of geographical coordi- nates, has an east-west trend. Let us further assume that this zone of weak- ness is in this coordinate system and that the lithosphere moves with re- spect to it. If an ore deposit has been controlled by such a lineament at po- sition B 1 o'r B 2 in marginal part of the pre-drift South America, and another deposit, C or D, when the plate was close to its recent position, we meet a case of structural control of two ore deposits of different age by the same tectonic zone of weakness with rotation

90 Jan Kutina

Table i. Preliminary classification of the relationships of ore deposits to tectonic zones of weakness in the substratum, over which the plates are supposed to rotate

Relationship Example in Fig. 3.

Isolinear isotemporal C and D isolinear - anisotemporal not shown pale0isolinear - anisotemporal B and C

B land D anisolinear isotemporal not shown anisolinear anisotemporal A l and C

A I and D

i Provided the origin of the deposit A is also controlled by a tectonic zone of weakness

of the plate in the time span between the two episodes of ore deposition. As a consequence of this, the two deposits, controlled by one and the same east- west trending structural lineament appear now north and south of each other in a north-south trending mineral belt.

The relationship of deposits C and D may be called isolinear-isotemporal, the relation of deposits C (or D) and B 1 (or B~ ) paleoisolinear-anisotemporal. Preliminary proposal for a classifi- cation of relationships of ore deposits to tectonic zones of weakness which are supposed to be present in the deep basement (substratum) over which the plates move, is presented in Tab. I. The possibility and the extent of appli- cation of this nomenclature to the re- lationship of ore deposits to structural lineaments of the moving plates re- quires further discussion.

Two porphyry copper deposits of the Andes have an absolute age close to 35 m.y.B.P., for which Sclater and IVicKenzie (1973) have reconstructed the position of South America. Their diagram may thus be used for reading paleolatitudes of the respective de- posits of E1 Abra and Potrerillos in Chile. Fig. 4 shows that the deposit of

E1 Abra with the age of 33.2 m. y., located at the latitude 21°56 'I has ori- ginated approximately at the latitude 26°S, close to the present location of the porphyry copper deposit of Potre- rillos. In turn, Potrerillos, 34. 1 m. y. old, occurring at the latitude of 26°29 ' S I , has originated approximately at the latitude of 31°S, corresponding to the present location of the Argentinian de- posit of Pachon. The lack of the abso- lute age of Pachon does not permit a calculation of its paleolatitude.

Before making any generalisation, it is now necessary to calculate paleola- titudes of all the porphyry coppers and other endogenic deposits of the Andes as far as their absolute ages are known. Nevertheless, the few calculations pre- sented in Fig. 4 already show that there may exist interesting relationships be- tween paleolatitudes of some ore depo- sits and present positions of others. It is possible that this phenomenon of coin- cidence of paleolatitudes and recent la- titudes of some deposits need not be accidental but may be caused by metallo- genic processes that have preferentially proceeded when a major deep-seated fracture zone of a lithospheric block

i Ruiz Fuller et al. (1965)

Lithosperic Plate Motions 91

reached a suitable coincidence with a zone of tectonic weakness in the sub- stratum over which the lithospheric block rotated (compare the model in Kutina 1974).

It does not imply, however, that the source of metals must occur in the as- thenosphere. The deep-seated zones of weakness may guide heat and the fluids may be mineralized on their way to the place of ore deposition. The source of metals need not always be at the same depth-level, sometimes in the astheno- sphere, sometimes not so deep.

Of special interest may be a eorrel- lation of the concept of zones of weak- ness in the asthenosphere, as present- ed in this paper, with the "hot lines" below the oceanic crust as assumed in the recent study byBonatti et ai.(1975).

Further attention to the deep-seated processes that may have joint influence on the magmatism and metallogeny in the continental and oceanic areas is re- commended.

CONCLUSIONS

i. If the concept of continental drift is correct, the ore deposits of the Andes, which are of different age, have origi- nated at different paleolatitudes. The location of the deposits is thus related to different locations of the South Amer- ican plate which it occupied between its pre-drift and present positions.

2. The model of Kutina (1974) suggests that zones of tectonic weakness may exist in the substratum over which the litho- spheric plates move. Such zones of tec- tonic weakness may represent one of the structural parameters controlling ore deposition in the lithospheric plates. If rotation of a plate proceeded in the time- span between formation of two ore depo- sits, they may occur north and south of each other even if controlled by the same zone of tectonic weakness over which the plate has moved (Fig. 3).

3. The reconstruction by Sclater and McKenzie (1973) has been used to cal-

culate paleolatitudes of some porphyry copper deposits of the Andes. The re- sults are encouraging, but further cal- culations are needed before any gene- ralization is made.

Acknowledgements. The author greatly appreciated the opportunity of prepar- ing this paper through a program on new methods of mineral exploration at the Bethlehem Steel Corporation, Be- thlehem, Pennsylvania. Sincere thanks are given Dr. Gilbert L. Hole and Mr. George K. Biemsderfer for facilitating the study. I thank Dr. Enrico Bonatti and Dr. Walter C. Pitman III of the Larnont-Doherty Geolo gical Observatory,Columbia University, who made constructive criticism of an earlier version of this paper. I thank Dr. Christopher Harrison of the Uni- versity of Miami for various comments on a later version of the manuscript. Best thanks are given Dr. Charles W. Finkl, Jnr., Resource Management & Mineral Exploration Consultants, Inc., Fort Lauderdale, Florida, for valuable suggestions and linguistic correction of the manuscript.

REFERENCES

Bonatti, E, : Origin of offsets of the Mid-Atlantic Ridge in fracture zones. J. Geology, 81,144-156 (1973) Emiliani, C., Ferrara, B., Honno- rez, J., Rydell, H.: Ultramafic- carbonate breccias from equatorial Mid-Atlantic Ridge. Marine Geology, 16, 83-102 (1974)

- Harrison, C.G.A., Honnorez, J., Fisher, D. : The Easter Island Frac- ture Zone and the "hot line" hypo- thesis. To be submitted to J. Geoph. Res. (1975)

Carter, W.D. : Tectolinear interpreta- tion of an ERTS-I mosaic, La Paz area, southwest Bolivia, southeast Peru and northern Chile. 17th Ple- nary meeting of the Committee of Space Research, S~oJose dos Cam- pos., Brazil, Preprint (1974)

Eimon, P. L : World Copper Resources, Scale 1-20. 000. 000 (approx.). A map publ. by the Mineral Research Company, United States (1974)

92 Jan Kutina: Lithosperic Plate Motions

Favorskaya, M.A. : On geochemical indicators of deep tectonics. Sovets- kaya Geologiya, vol. 1971, No. ii, 3-19 (1971). In Russian

- Tomson, I.N., Baskina, V.A., Vol- chanskaya, I.K., Polyakova, O.P. (Edited by Favorskaya, M.A. and Tomson, I.N. ): Global Regularities in the distribution of big ore deposits. Moscow (publ. byNEDRA), p. 192 (1974). In Russian

Goossens, P.J. : Metallogeny in Ecua- dorian Andes. Econ. Geol., 67, 458-468 (1972)

Guild, P.W. : Application of global tectonics theory to metallogenic studies. Symposium on Ore Depo- sits of the Tethys Region in Con- text of Global Tectonics. IAGOD meeting at Varna, Bulgaria, Sep- tember 1974. Preprint

Herron, E.M. : Sea-floor spreading and the Cenozoic history of the East- Central Pacific. Geol. Soc. America Bull, 83, 1671-1692 (1972)

Hollister, V.F. : Regional characte- ristics of porphyry copper deposits of South America: (a) Soe. Mining Eng. ofAIME, PrepringNo. 73-1-2, (1973). (b) Condensed in: Mining Eng., 25, No. 8, 51-56 (1973)

Kahle, Ch., F., Editor: Plate Tectonics-

Assessments and Reassessments. The Amer. Assoc. Petrol. Geol. Memoir 23, p. 514 (1974)

Kutina, J. : Structural control of vol- canic ore deposits in the context of global tectonics. Internat. Syrup. on Volcanism and Associated Metallo- genesis, Bucharest, Romania, Sep- tember 1973, Preprint (p. 14). Full text to be published in the Bull. Vol- canologic (in press) Relationship between the distribu- tion of big endogenic ore deposits and the basement fracture pattern - Examples from four continents. First In ternat. Conference on the New Ba sement Tectonics, Salt Lake City, June 1974, Abstracts, p. 23. Full text to be publ. in the volume of the conference by the Utah Geol. Assoc. (in press)

Tectonic development and metallo- geny of Madagascar with reference to the fracture pattern of the Indian Ocean. Geol. Soc. Amer. Bull., 86, 582-592 (1975)

L a r s o n , R . L . , P i t m a n III, W. C. : W o r l d - w i d e c o r r e l a t i o n of M e s o z o i c m a g n e t i c a n o m a l i e s , and i t s i m p l i c a - t i o n s . Geol . Soc. A m e r . B u l l . , 83, 3645-3661 (1972)

L l a u m e t t , C . , U l loa , G. : E s t a d o a c t u a l de l e s t u d i o g e o l o g i c o y e v a l u a c i o n de l y a c i e m i e n t o c u p r i f e r o A n d a c o l l o . E m p r e s s a N a c i o n a l de M i n e r a , Un- publ . R e p o r t 1973, quo ted b y J. D. L o w e l l (1974)

L o w e l l , J. D. : T h r e e new p o r p h y r y c o p - p e r mines for Chile? Mining Eng. , 26, No. Ii, 22-28 (1974)

McKenzie, D., Sclater, J.G. : The evo- lu±ion of the Indian Ocean since the Late Cretaceous, Royal Astron. Soc. Geophys. J. , 24, 437-528 (1971)

- The evolution of--the Indian Ocean. Scientific American, 228, No. 5, 63-72 (1973)

Petrascheck, W.E. : Koniinentalverschie- bung und Erzprovinzen. Min. Deposita, 3, 56-65 (1968)

Rui-z Fuller, C. : Geologia y yacimien- tos metaliferos de Chile. Santiago de Chile (Publ. by the Inst. de In- vestigaciones Geologicas), (1965)

Sclater, J.G., McKenzie, D.P.: Paleobathymetry of South Atlantic. Geol. Soc. Amer. Bull., 84, 3203 - 3216 (1973)

Sillitge, R.H. : A plate tectonic model for the origin of porphyry copper deposits. Econ. Geol., 67, 184-197 (1972a)

- Relation of metal provinces in Western America to subduction of oceanic lithosphere. Geol. Soc. Amer. Bull., 83, 813-817 (1972b)

- Tectonic segmentation of the Andes. Nature, 250, 542-546 (1974)

Received May 20, 1975

Dr. Jan Kutina Dept. of Geology Bethlehem Steel Corporation Bethlehem, Pennsylvania 18016 USA