review. In D. Walker and I. S. McCallum (Eds.), Workshop on magmaticprocesses of early planetary crusts: Magma oceans and stratiform layeredintrusions. (LPI Technical Report 82-01) Houston: Lunar and Plane-tary Institute.

Schmidt, D. L., P. L. Williams, and W. H. Nelson. 1978. Geologic mapof the Schmidt Hills quadrangle and part of the Gambacorta Peak

quadrangle, Pensacola Mountains, Antarctica (scale 1:250,000). U.S.Geological Survey Map A-8. Washington, D.C.: U.S. GovernmentPrinting Office.

Willemse, J., and J. J. Bensch. 1964. Inclusions of original carbonaterocks in gabbro and norite of the eastern part of the Bushveld Com-plex. Transactions of the Geological Society of South Africa, 67, 1-87.

Minor-metal reconnaissance surveyrelated to possible resources in the

Dufek Intrusion

ARTHUR B. FORD

U.S. Geological SurveyMenlo Park, California 94025

approaches that of South Africa's resource-rich (vonGruenewaldt 1977) Bushveld Complex makes this speculationeven more attractive.

As part of a continuing petrologic study (with C. R. Him-melberg of the University of Missouri), a reconnaissance geo-chemical survey of minor metals of possible resource interest(table) has been made, including the platinum-group elements(PGE) platinum (Pt), palladium (Pd), and rhodium (Rh) that arenot shown averaged in the table because of the many resultsbelow limits of determination—Pt, 10 parts per billion (ppb);

The geology of the Dufek Intrusion (82°30'S 50°W), a differen-tiated layered mafic igneous complex of Jurassic age in thenorthern Pensacola Mountains (Ford 1976), was studied by U.S.Geological Survey field parties in the 1965-1966, 1976-1977, and1978-1979 summers. Of a total 8-9 kilometers estimated thick-ness, about 1.8 kilometer of a lower (but not the lowest) part isexposed in Dufek Massif (Ford, Schmidt, and Boyd 1978) andabout 1.7 kilometer of the highest part is exposed in the For-restal Range (Ford et al. 1978). Major unexposed stratigraphicparts are a 1.8-3.5-kilometer-thick basal part beneath the DufekMassif section and a 2-3-kilometer-thick interval beneath SalleeSnowfield between the two exposed sections. Preliminary pet-rologic studies [including electron microprobe analysis of thechief cumulus minerals, plagioclase (Abel, Himmelberg, andFord 1979), calcium-rich and calcium-poor pyroxenes (Him-melberg and Ford 1976), and iron-titanium oxides (Himmelbergand Ford 1977)] show compositions and variations approximat-ing those at inferred equivalent intervals in other complexes ofthis type. Characteristic chemical trends are enrichment of ironin pyroxenes and of albite in plagioclase with increasing strati-graphic height. In exposed parts, conspicuous mineralogicaldifferences from other differentiated complexes are the absenceof cumulus chromite and magnesian olivine. Aughenbaugh's(1961) reported occurrences of the minerals are probably inxenoliths (see Himmelberg and Ford this issue). Cumulus oc-currences of the minerals may exist at depth, however, as pe-trologic comparisons with other complexes, including use ofcumulus arrival of pigeonite as a correlation marker, suggestthat the Dufek Massif section lies above analogous sectionscontaining them in the other complexes (figure 1).

Mafic layered intrusions are well known for their variety ofeconomically significant metal deposits generally in lower strat-igraphic parts and associated with early crystallized mafic andultramafic cumulates (Wilson 1969). The Dufek Intrusion ac-cordingly has attracted considerable speculation on its possibleresources (Lovering and Prescott 1979; Runnells 1970; Zum-berge 1979; among many others). Behrendt's et al. (1980) deter-mination that its size (in excess of 50,000 square kilometers)

C00a)U)

Frost Pyroxenite-U)U)0

Neuburg Pyroxenite-PIGEONITE

__ .-

9IReef

Iv,I

-IKmII

III.I

oIC.)

I°0

rICAL ISCALEB_L

Bushveld Dufek

Figure 1. Possible stratigraphic comparison between lower parts ofthe Bushveld and Dufek Intrusions. Modified from Ford et al. (inpress). Bushveld from Wager and Brown (1967). A and B showBehrendt's et al. (1974) estimated limits (1.8-3.5 kilometers) forthickness of the concealed basal section of the Dufek Intrusion.

a)C0N

C

o U)

in

- U)oa0q,

LOWEST

ED X

—Merensky

EVE

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Averages of minor-element abundances, Dufek Intrusion, in parts per million

SectionRock types

Uppergranophyre(ForrestalRange)cumulatesa

Lower(DufekcumulatesaMassif)

NumberCuCo

2348

940063

132950

CrNiV Ti S

2<2116.8x103135

225182025.7x 103720

174761982.0x 10329

aincludes cumulates of gabbroic, anorthositic, and pyroxenitic composition.

Pd, 4 ppb; and Rh, 5 ppb. Twenty-four analyzed rocks fromstratigraphic levels representing a broad spectrum of differen-tiation stages include gabbro, anorthosite, pyroxenite, and gra-nophyre. A few atypical samples contain up to about 3 percentvisible sulfides. Details of procedures and sample materials aregiven in Ford et al. (in press).

Concentrations of the minor metals vary widely. Most showclose correlation with modal content of either pyroxenes oriron-titanium oxides (figure 2). Strong positive correlations withstratigraphic height imply that copper, vanadium, and titaniumwere enriched during differentiation by fractional crystalliza-tion. Variations with height for other elements are more irreg-ular, but differences in concentration ranges and averages be-tween the two exposed sections suggest enrichment also insulfur and cobalt and depletion in chromium and nickel relatedto differentiation. Similar variations are found in other layeredintrusions (Wager and Brown 1967). The PGE also seem to showdifferentiation-related enrichment. They have been found onlyin amounts near or below limits of determination in the lowersection but in greater amounts, up to 35 ppb platinum, 44 ppbpalladium, and 12 ppb rhodium, in the upper section.

0'0

T

Ti .. • •ss•H-LJ/Ni

C MWECo anCV •.S/ •>°Cu 30N + 69-55

S 0110 + ////• 54-50

PGE ERE• 49-44

+ -43-36

Basal parts of similar complexes are of greatest interest forresources such as PGE, chromium, nickel, and copper, but metalconcentrations also occur in higher parts (Wilson 1969; vonGruenewaldt 1977). The pyroxenitic Merensky Reef of the Bush-veld Complex is a leading producer of PGE and chromite oresand therefore pyroxenite layers of the Dufek Intrusion might beattractive exploration targets. However, we have not found themto contain anomalous metal values. Figure 1 suggests they lie ata position analogous to a level about 2 kilometers or more abovethe Merensky Reef. PGE abundances determined in this study(Ford et al. in press) are comparable to those in typical rocksabove the Bushveld's Merensky Reef reported by Page et al.(1982). As in the Bushveld above the Merensky, larger amountsof PGE are found in rocks containing abundant magnetite andassociated sulfides.

Although results to date have not yielded indications of metalconcentrations of possible present utility, the probability for achance discovery by this reconnaissance survey would beslight, even if the concentrations exist. Most deposit typesknown in similar complexes (Wilson 1969; von Gruenewaldt1977) must be considered as possibilities (speculative resources)in view of the immense area of concealed rock (particularlybasal units), the small number of analyzed samples, and ab-sence of studies directed toward a search for minerals. Antarcticoperating costs would probably limit primary utility to mate-rials having high unit value, such as PGE., but PGE utilizationmight benefit recovery of others. Lacking river activity in thisarea, traditional methods of prospecting for platinum-groupminerals by tracing alluvial placers or other surficial occurrencesby panning back to lode sources, as in the discovery of theMerensky Reef, would not be possible. If prospecting doessomeday take place, perhaps using geochemical methods, thecorrelations in figure 2 suggest that vanadium might be a usefulpathfinder element for the platinum-group minerals in exposedparts of the intrusion. Different correlations, perhaps withchromium, would be expected in the concealed basal part.

This research was supported in part by National ScienceFoundation grants DPP 77-22765 and DPP 80-20753.

References

Figure 2. Correlation of analyzed elements in 22 cumulates of theDufek Intrusion. Open symbols and (—) indicate negative correla-tion, others positive; r8 denotes Spearman rank correlation coeffi-cient [from Ford et al. (in press)].

Abel, K. D., C. R. Himmelberg, and A. B. Ford. 1979. Petrologic stud-ies of the Dufek intrusion: Plagioclase variation. Antarctic Journal of theU. S., 14(5), 6-8.

1983 REVIEW

Aughenbaugh, N. B. 1961. Preliminary report on the geology of DufekMassif. International Geophysical Year World Data Center A, GlaciologyReport, 4, 155-193.

Behrendt, J . C., D. J. Drewry, E. Jankowski, and M. S. Grim. 1980.Aero-magnetic and radio echo ice-sounding measurements showmuch greater area of the Dufek intrusion, Antarctica, Science,209(4460), 1014-1017.

Behrendt, J. C., J. R. Henderson, L. Meister, and W. L. Rambo. 1974.Geophysical investigations of the Pensacola Mountains and adjacentglacierized areas of Antarctica. (U.S. Geological Survey ProfessionalPaper 844.) Washington, D.C.: U.S. Government Printing Office.

Ford, A. B. 1976. Stratigraphy of the layered gabbroic Dufek intrusion, Ant-arctica. (U.S. Geological Survey Bulletin 1405D.) Washington, D.C.:U.S. Government Printing Office.

Ford, A. B., R. E. Mays, J. Haffty, and B. P. Fabbi. In press. Reconnais-sance of minor metal abundances and possible resources of the Dufek intru-sion, Pensacola Mountains. Proceedings of the Fourth InternationalSymposium on Antarctic Earth Sciences, Adelaide, Australia, 1982.

Ford, A. B., D. L. Schmidt, and W. W. Boyd, Jr. 1978. Geologic nap of theDavis Valley quadrangle and part of the Cordiner Peaks quadrangle, Pen-sacola Mountains, Antarctica (scale 1:250,000). (U.S. Geological SurveyMap A-101.) Washington, D.C.: U.S. Government Printing Office.

Ford, A. B., D. L. Schmidt, W. W. Boyd, Jr., and W. H. Nelson. 1978.Geologic map of the Saratoga Table quadrangle, Pensacola Mountains, Ant-arctica (scale 1:250,000). (U.S. Geological Survey Map A-9.) Wash-ington, D.C.: U.S. Government Printing Office.

Himmelberg, G. R., and A. B. Ford. 1983. Composite inclusion ofolivine gabbro and calc-silicate rock in the Dufek Intrusion, a possiblefragment of concealed contact zone. Antarctic Journal of the U. S., 18(5).

Himmelherg, G. R., and A. B. Ford. 1977. Iron-titanium oxides of theDufek intrusion, Antarctica. American Mineralogist, 62, 623-633.

Himmelberg, G. R., and A. B. Ford. 1976. Pyroxenes of the Dufekintrusion, Antarctica. Journal of Petrology, 17, 219-243.

Lovering, J . F., and J. R. V. Prescott. 1979. Last of lands . . . Antarctica.Melbourne: Melbourne University Press.

Page, N. J, G. von Gruenewaldt, J . Haffty, and P. J. Aruscavage. 1982.Comparison of platinum, palladium, and rhodium distributions insome layered intrusions with special reference to the late differenti-ates (upper zone) of the Bushveld Complex, South Africa. EconomicGeology, 77, 1405-1418.

Runnells, D. D. 1970. Continental drift and economic minerals in Ant-arctica. Earth and Planetary Science Letters, 8, 400-402.

von Gruenewaldt, G. 1977. The mineral resources of the BushveldComplex. Minerals, Science and Engineering, 9(2), 83-95.

Wager, L. R., and G. M. Brown. 1967. Layered igneous rocks. San Fran-cisco: W. H. Freeman.

Wilson, H. D. B. (Ed.). 1969. Magmatic ore deposits, a symposium.Economic Geology Monograph, 4. Symposium sponsored by the Societyof Economic Geologists at Stanford University, Stanford, Calif.1966.

Zumberge, J. H. 1979. Mineral resources and geopolitics in Antarctica.American Scientist, 67, 68-77.

Geochronologic studies in EastAntarctica: Reconnaissance uranium/thorium/lead data from rocks in the

Schirmacher Hills and Mount Stinear

EDWARD S. GREW

Institut far MineralogieRuhr-Universität Bochum

Bochum, Federal Republic of Germany

WILLIAM I. MANTON

Program and Institute forGeosciences

The University of Texas-DallasRichardson, Texas 75080

The Schirmacher Hills (70045S 11°50'E) are a coastal exposureof the Precambrian crystalline basement of Queen Maud Land(Ravich and Kamenev 1975; Ravich and Soloviev 1966). MountStinear (73'7'30"S 66°15'E) in the southern Prince CharlesMountains is composed primarily of a granitic and gneissicbasement complex and of an amphibolite-facies metasedimen-tary cover of Precambrian age (Tingey 1982; Grew 1982). Wereport here uranium/thorium/lead (U/Th/Pb) data on 3 samples

collected in the Schirmacher Hills and at Mount Stinear in 1973and 1974 when Grew participated in the 18th and 19th SovietAntarctic Expeditions (SAL) as U.S. exchange scientist. To theauthors' knowledge, the only other radiometric data reportedfrom these areas [aside from brief mention in Grew (1982; inpress) of the U/Th/Pb data to be presented here] are potassium/argon (K/Ar) dates from central Queen Maud Land (0-20°E)(Ravich and Soloviev 1966), and a rubidium/strontium (Rb/Sr)date of 2,580 million years from Mount Stinear (Tingey 1982).

The Schirmacher Hills in the vicinity of the Soviet StationNovolazarevskaya are underlain by metamorphic rocks consist-ing largely of sillimanite-garnet gneiss, garnet-biotite gneiss,mafic granulite, minor calc-silicate granulite and marble, andrare sapphirine-garnet-hiotite granulite (Grew in press). Theserocks were metamorphosed in the granulite facies and subse-quently in the amphibolite facies. Pegmatites containing al-lanite and tourmaline were emplaced during the amphibolite-facies event, and mafic dikes were emplaced both before andafter the amphibolite-facies event.

Samples analyzed for U/Pb/Th isotopes from the SchirmacherHills are 378X, a metamict allanite from pegmatite, and 39513,zircons from a quartzo-feldspathic gneiss containing unalteredgarnet, biotite, and hornblende; and accessory apatite, opaque,calcite, and optically active allanite. Biotite forms clots of flakesin random orientation. This texture and the absence of pyrox-ene suggests that the gneiss had completely recrystallized dur-ing the amphibolite-facies event. In thin section, zircon crystalsare commonly euhedral and some have cores. The analyzedzircons are clear and subhedral to euhedral. Cores were notapparent. Two size fractions were analyzed: 100-200 mesh andless than 200 mesh.

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