Clay Minerals (1983) 18, 127-138

O R I G I N OF B A U X I T E AT E U F A U L A , A L A B A M A , USA

T. C. L U K A S , * : ~ F. C. L O U G H N A N ~ AND J. L. E A D E S *

*Dept. of Geology, University of Florida, G ainesville, Florida 32611, USA, and ~f School of Applied Geology, University of NS W, P.O. Box 1, Kensington, New South Wales 2033, Australia

(Received 3 August 1982; revised 29 October 1982)

ABSTRACT: An autochthonous origin for the bauxite deposits of the Eufaula district, south-eastern Alabama, appears to have received general acceptance but, compared with younger residual bauxites of the present day tropical regions of the world, the Eufaula deposits have a number of features that are difficult to reconcile with development in situ. In an attempt to resolve the enigma, a detailed study was undertaken of cores from three drill holes that intersected a complete succession through one of the Eufaula deposits. Although the results are not conclusive, it is believed that much of the observed phenomena can be explained on the basis of an essentially transported origin for the deposits.

From the time of their discovery in 1922, the bauxite and bauxitic clay deposits of the Eufaula district, south-eastern Alabama (Fig. 1), have incited interest not only because they represent an important source of alumina for the refractory and alum industries, but also because their origin is somewhat enigmatic. In his initial detailed description, Rettger (1925) assigned the occurrences to the Nanafalia Formation, which in this area is the lowermost unit of the Eocene Wilcox Group. They are, therefore, coeval or approximately coeval with similar deposits at Andersonville, Georgia (Shearer, 1917) and also with the residual and transported bauxites near Little Rock, Arkansas (Gordon et al., 1958).

In considering the origin of the deposits, Rettger (1925) believed the pertinent aspects to be: (i) their apparent restriction to a zone immediately above an erosion surface that separates the Nanafalia from the underlying Clayton Limestone (Table 1), (ii) the apparent lack of sedimentary structures in the bauxite and associated kaolin, and (iii) the evident downward gradation of the bauxite into kaolin. On the basis of these observations he concluded that sand and clay detritus derived from weathered crystalline rocks in the Piedmont to the north (Fig. 1) was transported and deposited 'in depressions such as lakes and lagoons, or in shallow waters off the coast'. In the on-shore area much of the clay was segregated to form large, elongate bodies, which during an ensuing regression were intensely leached of silica, leaving a residue correspondingly enriched in alumina.

Although Rettger's mode of origin for the bauxite has received general acceptance by subsequent workers, various modifications have been proposed. Thus, MacNeil (1945) believed that the lenticular form of the bauxite-kaolin bodies resulted from partial collapse of the Nanafalia into depressions created by karstifieation of the underlying Clayton Limestone, whereas Clarke (1966, 1972) and Jones (1972) argued that karstification of the Clayton mostly preceded deposition of the Nanafalia and that leaching of silica from clay

:~ Present address: Exxon Production Research Co., P.O. Box 2189, Houston, Texas 77001, U.S.A.

�9 1983 The Mineralogical Society

128 T. C. Lukas et al.

o o T e n n . i i , J E/j~L / krn

R 0 C K PAL EOZOIC \ \ /I ~ j BLUE RIDGE ~',~

r DMONT PROVINCE

I ~.-, ~ . I ~"

o. ,, ,,, , M i s s . i

. ,

/t i ~,k~ i / , ~,N DERSONVILLE i I , i A l a . G a . 1

t. . . . . . . / I I .~ J I I f\ 1 r ~ I A ) . . . . . . . . . . . \ I

, ,

FIG. 1. Sketch map of the south-eastern United States.

TABLE 1. Stratigraphic succession in the Eufaula area, Alabama.

Eocene WflcoxGroup

Disconformity Paleocene Midway Group

Unconformity Cretaceous Selma Group

Hatchetigbee Formation Tuscahoma Sand Nanafalia Formation

Clayton Limestone

Providence Sand Ripley Formation

infilling these sink holes and depressions was the principal factor contributing to development of the bauxite. Burst (1974), on the other hand, could find little evidence to support the sink-hole origin of Clarke and Jones. Rather, he envisaged the Nanafalia in the Eufaula area as representing deposition of elastics in an extensive, near-shore, freshwater swamp and the bauxite-kaolin bodies as 'meander fills in an ancient tidal fiat or barrier island'. Leaching of these meander-fills was believed to have resulted in discrete lens- shaped accumulations with a gibbsitic core surrounded by zones of bauxitic kaolin, kaolin and sandy kaolin (Fig. 2).

Inherent in all these proposals is the concept of selectivity by the bauxitization processes, whereby the somewhat impermeable clay lenses were stripped of a high proportion of their silica content while the enclosing, much more permeable, micaceous quartz sands remained virtually unaffected. However, selectivity to such a marked degree is not apparent in younger residual bauxites, e.g. those of western India and northern Australia, where, despite development from a wide array of rock types including basalt, granite, shale and

Origin of Eufaula bauxite 129

KAOLIN

SAND ~ ] BAUXITIC KAOLIN

SANDY KAOLIN ~ BAUXITE

FIG. 2. Zonal structure of a typical bauxite deposit in the Eufaula area�9 After Burst (1974).

V / I / / ) 1 . / i 1 , 1 i l / I I ,i/)~/~ij],/i/I/// I ~ �9 ( ~ ' 0 ~ "('3//, " P z / , , ~/

/0/~ / / 1 EufOula

4;//D?. :,

PROSPECT ";17~':( , -- - -

FIG. 3. Geological map of the Eufaula bauxite district. Modified from Clarke (1972). Dots represent worked areas.

kaolinitic quartz sands, they persist as thick, continuous, blanket-like crusts over extensive areas.

Therefore, to gain a better understanding of the origin of the bauxitic clays of Eufaula and, in particular, to examine the validity of Rettger's concept, a study was undertaken of the vertical variations in mineral and chemical composition through one of these bauxite-kaolin bodies. Complete cores were obtained, through the courtesy of A. P. Green Refractories, from three drill sites designated A, B and C at McLeod Prospect (Fig. 3) in Barbour County, situated about 5 km south of Baker Hill.

G E O L O G I C A L S E T T I N G

The oldest rocks in the Eufaula area are of late Cretaceous age and comprise sands, silts and clays of the Ripley Formation and Providence Sand (Table 1). An unconformity separates the Providence Sand from the Palaeocene Midway Group, which in this area is represented by the Clayton Limestone. The Clayton is variable in both thickness and composition in that it ranges up to 45 m (Warren & Clark, 1965) but in places is absent and, whereas fossiliferous limestone is the dominant rock type, locally the unit grades into chert, sandstone and conglomerate. The Wilcox Group, which disconformably overlies the Clayton Limestone, is of Eocene age and has been subdivided into the Nanafalia

130 T.C. Lukas et al.

Formation at the base, this being succeeded by the Tuscahoma Sand and the Hatchetigbee Formation.

South of Fort Gaines, the Nanafalia consists of marine strata, mostly quartz and glauconitic sands with some limestone, termed the Ostrea thirsae beds by Warren & Clark (1965). To the north, however, it is represented by the Gravel Creek Sand Member, a continental facies with a thickness between 18 and 36 m. The Gravel Creek Sand is characterized by cross-bedded, fine- to coarse-grained, micaceous quartz sand with lenticular to irregular shaped clay bodies that range from less than a metre to several km across. The smaller bodies are generally composed of kaolinite with or without quartz, whereas the larger ones commonly comprise a gibbsite-rich core that grades outward through envelopes of kaolinite and sandy kaolin into the surrounding, micaceous quartz sand. Nevertheless, gibbsite-rich lenses virtually devoid of kaolinitic envelopes have been encountered (Clarke, 1972). Sporadic, lenticular beds of lignite are evident in the Gravel Creek Sand and these may occur above, below or within the bauxite-kaolin bodies.

The succeeding Tuscahoma Sand marks a return to marine conditions throughout the entire area. According to Warren & Clark (1965), this unit consists of four distinct facies with either a white sandy clay or red sand at the base, succeeded by a glauconitic sand, a light grey to green shale and a fine-grained sandstone at the top. Clarke (1972) recorded the presence of clay balls in the basal sand and concluded that these were derived from erosion of the clay bodies in the Nanafalia Formation.

All units have a shallow dip to the south, the average being ~ 1.5 ~

A N A L Y T I C A L P R O C E D U R E S

From preliminary examination in the laboratory it was apparent that the cores from the three drill holes were similar and that each was readily divisible into a number of zones. The core from drill hole B was selected for detailed chemical and mineralogical analysis.

COMPOSITION CUMULATIVE %

I0 20 30 40 50 60 70 80 90 DNES

IO I D

12 IC

20

I - ~ KAOLINITE ~ GIBBSITE ~ QUARTZ

m M I C A ~ OTHERS

FIG. 4. Mineral composition in relation to depth in drill hole B, McLeod Prospect.

Origin of Eufaula bauxite 131

Determination of major elements was carried out by a combination of techniques, including X-ray fluorescence spectrometry, atomic adsorption spectrophotometry and gravimetric means. Moreover, since according to Adams & Weaver (1958) and Adams & Richardson (1960) the relative concentrations of thorium and uranium can be used as a measure of the extent of leaching to which a rock sequence has been subjected, analyses for these dements were made on kilogram core samples by means of a gamma ray spectrometer with counting times of 5400 s. The mineralogical analyses shown in Fig. 4 are based primarily on the X-ray diffraction results, although the chemical data were also used to supplement these. In addition, selected samples of the cores were examined with a scanning electron microscope in order to determine the textural relationships of the various mineral constituents.

M I N E R A L O G I C A L A N D T E X T U R A L V A R I A T I O N S

Zone I

Sediments at the base of the drill holes generally had a mottled appearance and consisted of argillaceous sand in which medium- to coarse-grained angular quartz was disseminated in an abundant matrix of disordered kaolinite. Small amounts of mica were also present. The rock generally broke with a conchoidal fracture and developed plasticity on wetting.

Zone H

The kaolinitic sand of zone I passed upwards into a dense, relatively pure clay composed almost entirely of b-axis disordered kaolinite. A few flakes of mica were observed in some samples from this zone and a reflection at 3.51 A, attributable to anatase, could be detected on most X-ray diffraction traces. The clay was frequently mottled and fine limonitic banding was evident in places. Gordon et al. (1958) described similar ferruginous banding in the transported bauxites of Arkansas and attributed the phenomenon to fluctuations in groundwater level.

Zone I I I

The boundary between zones II and III at the 18.3 m level was marked by a change in the crystal structure of the kaolinite from disordered below to predominantly well-ordered above. Throughout zone III gibbsite was almost invariably associated with the wdl-ordered kaolinite and frequently formed the dominant mineral constituent. In the core from drill hole B, gibbsite was generally fine-grained and disseminated but in drill hole A it was present also as nodules and oolites. Within zone III several distinct breaks in the mineralogical trend were apparent and, on the basis of these, division into subzones designated A, B, C and D, from the base upwards, was made.

Ferruginous banding was common towards the lower part of subzone IliA where well-ordered kaolinite predominated. Higher in the succession, however, gibbsite was also present and the clay showed a distinct mottled appearance. Toward the top of this subzone, mottling gave way to an overall maroon colour and gibbsite was almost as prevalent as kaolinite. Several of the samples contained scattered flakes of muscovite mica and in one from the 17.38 m level a granule of quartz was found. A scanning electron micrograph of a kaolinite 'book' from this subzone is shown in Fig. 5(a).

132 T.C. Lukas et al.

FIG. 5. Scanning electron micrographs: (a) kaolinite 'book' in zone IIID, drill hole B; (b) gibbsite 'book' from interior of pisolite, zone III, drill hole A; (c) gibbsite crystals in a pisolite

from zone III, drill hole A; (d) botryoidal kaolinite from zone IV, drill hole 13.

Subzone 11113 was characterized by the presence of mica in addition to kaolinite and gibbsite. The mica content rarely exceeded a few per cent of the total mineral constituents, but in the sample from the 16-3 m level up to 15% was present. At the equivalent interval in drill hole A, much of the gibbsite was present either as 'books ' (Fig. 5b), or euhedral crystals (Fig. 5c) contained within coarse-grained oolites.

The succeeding subzone I I IC was 4.73 m thick and comprised mostly fine-grained gibbsite with well-ordered kaolinite, together with small amounts of anatase and disseminated iron oxide. The iron oxide imparted a red colour to the material. At the 13.8 m level, pisolites of hematite and lepidocrocite were encountered.

In subzone I I ID gibbsite was subordinate to kaolinite. The clay had an earthy appearance and was, in places, heavily stained by iron oxides.

Despite the relative abundance of gibbsite in zone III, boehmite was not found in any of the samples and, indeed, has not been recorded from the Eufaula area generally.

Zone I V

In composition and texture this zone did not differ appreciably from zone II in that it was composed essentially of kaolinite. However, the kaolinite was well-ordered and mostly present as plates, although botryoidal masses (Fig. 5d) were also observed.

Origin of Eufaula bauxite 133

Zone V

The upper part of the succession exposed in drill hole B was composed of fine-grained to pebble-size, angular to rounded quartz with minor amounts of mica, ferruginous concre- tions, root remains and wood fragments, all embedded in a predominantly kaolinite matrix. The kaolinite gradually changed from predominantly well-ordered at the base to disordered at the top of the zone and, in places, was accompanied by minor amounts of mixed-layer clay minerals, gibbsite and gorceixite.

C H E M I C A L V A R I A T I O N S

S i O 2, A1203 and Fe203

In Fig. 6 the values for SiO2, A1203 and Fe203 have been plotted relative to depth of the sample for the interval between 7.1 and 21.3 m. The curves reflect the variations in mineral composition shown in Fig. 4. Alumina attains maximum development and silica is correspondingly depleted in zone III where gibbsite is abundant, whereas in zones II and IV free-alumina minerals are absent and the relative abundance of the two oxides is reversed.

Compared with younger, residual bauxite deposits developed on kaolinitic quartz sands, e.g. at Weipa, Queensland (Loughnan & Bayliss, 1961; Jepsen & Schellmann, 1974), the iron content in the Eufaula deposit is unusually low. This is probably due to post-depositional reduction and dissolution of the element and, as discussed later, there is evidence that the Eufaula bauxites accumulated, at least partly, in a reducing environment. However, much of the iron is now present in the form of hematite, although lepidocrocite is also abundant at the 13.84 m level.

TiO2/Al20 a relationships

Titanium and aluminium form hydrolyzate ions (Goldschmidt, 1954) and as such should be concentrated to much the same degree in weathered sequences developed on a relatively homogeneous parent rock. Consequently, if the Eufaula bauxite formed in situ through

8 ,

IO-

E ] ' ~ . "1-

B..~14-

t 6 .

18-

2 0 -

% C O M P O S I T I O N Z O N E S IO 2 0 3,0 4 0 5 0 6 0 i i I i I I

~.~--- . . . . Iii a IlIA

F e 2 0 3

_..s.Lo2 I 1 1 I i i I

FIo. 6. SiO 2, AI203 and Fc203 contents relative to depth in drill hole B.

134 T. C. Lukas et al.

TiOz x10 3 AI203

20 30 4o 50 60 7o ZONES l I I I

[ 8 IV

IO

12 IIIC I

E 14 I I

16 I I IB I

e-~ 18 I l i A I

i I I i i i i i i i

FIG. 7. TiO2/A1203 ratio against depth in drill hole B.

intense leaching of clay material, as Rettger (1925), MacNeil (1945), Clarke (1972), Burst (1974) and others have proposed, the TiO2/A1203 values plotted relative to depth of the sample should yield a straight line. Fig. 7 shows that this is not the case for the Eufaula samples; there is, however, a tendency for low values in the gibbsite-rich rocks. Possibly the composition of the parent material varied markedly or, alternatively, the gibbsite and associated minerals are of transported origin and represent the accumulation of detritus derived from contrasting source areas.

Th/U values

From examination of the thorium and uranium contents of a wide array of sedimentary rocks including bauxites, Adams & Weaver (1958) concluded that the relative abundance of the two elements is primarily a function of (i) the degree of oxidation and leaching to which the parent material has been subjected during the weathering stage and (ii) the redox potential prevailing in the depositional environment. Under oxidizing conditions uranium is readily lost to the leaching solutions during weathering, whereas immobile thorium tends to be concentrated in the residuum. Hence, products of intense weathering such as bauxite should have high Th/U values (>7 according to Adams & Weaver (1958)). On the other hand, relatively low values (< 2) are to be expected in sediments deposited in a reducing environment, due to the uptake of uranium from the associated waters through either fixation in organic complexes or adsorption by clay minerals. These authors also contended that sedimentary rocks with intermediate Th/U values (2-7) either comprise incompletely weathered products or represent mixtures of materials derived 'from low- and high-ratio environments'. If these proposals are correct, it follows that the Th/U values could furnish a suitable method for differentiating allochthonous bauxites from those formed in situ.

I0

12 o

E 14-

~ 16-

~ 18-

20

Origin of Eufaula bauxite 135

T h / U ZONES

I 2, 3, i 5 V

IIID

I

IIIC

I I i I I

I I IB

I l iA

II

I..2_,,-

FIG. 8. T h / U ratio against depth in drill hole B.

In Fig. 8, the Th/U values for sections of the core from drill hole B at McLeod Prospect are plotted relative to depth. However, the results are the reverse of those anticipated if the bauxite is essentially autochthonous. Thus, in the kaolinite-rich, gibbsite-deficient zones II and IV the values range from 2-3 to 4.9, corresponding to the intermediate geochemical facies of Adams & Weaver (1958), but in zone III, which is characterized by the presence of gibbsite (and therefore should represent the most intensely weathered material), the values are generally <2. An exception to this trend is in the sample from the 16.03-16.22 m interval where a value of 2.9 was recorded, but, as evident in Fig. 4, the gibbsite content of this core section is very low.

D I S C U S S I O N

Bauxitization is essentially a process of dissolution and leaching of mobile constituents, including silica, from a parent rock and the concomitant enrichment in alumina, which is mainly in the form of gibbsite. Critical to the process are the silica content and pH of the leaching solutions--for as Gardner (1970) has shown, gibbsite does not develop where the silica concentration exceeds 1.5 ppm, while at pH <4.2 the mineral tends to pass into solution. For bauxitization to proceed, therefore, silica must be flushed from the system as rapidly as it is released from the parent minerals and thus infiltration of copious quantities of fresh water is an essential prerequisite. It follows also that the process is inhibited by the presence of organic matter since the intense leaching necessary to maintain such an unusually low concentration of silica in the groundwater leads to the conversion of organic matter to humic and other acids, resulting in podsolization (depletion of alumina) rather than bauxitization (concentration of alumina). The specific requirements for bauxite development are a permeable parent rock containing aluminium, a well-drained site, a high rainfall and an environment facilitating rapid oxidation of organic matter.

Since bauxite and bauxitic kaolin occur within the Wilcox Group at locations as far afield as Arkansas (Gordon et al., 1958) and Georgia (Shearer, 1917), there seems little doubt that a climate conducive to bauxite accumulation prevailed over much of the south-eastern United States, including the Eufaula area, during the early Eocene. It does not necessarily follow, however, that the Eufaula deposits developed in situ. Indeed, when comparison is made with residual bauxite occurrences of the present day tropical regions of

136 T .C . L u k a s et al.

the world, such as those of western India (Balasubramaniam, 1978) and northern Australia (Loughnan & Bayliss, 1961; Grubb, 1970; Somm, 1975), it is evident that the Eufaula deposits have a number of features that are difficult to reconcile with autochthonous development.

Thus, unlike the younger residual bauxites, the Eufaula deposits occur as isolated masses within a sequence of micaceous, quartz sands. Consequently, if as Rettger (1925) and others have contended, the deposits formed in situ through intense leaching of segregated clay bodies, it would be anticipated that the much more permeable sands encompassing these bauxite-clay bodies would also have been affected by the percolating solutions, at least to the extent of breakdown of the mica. However, not only does the mica in the sands persist in a virtually unaltered state but, furthermore, flakes of the mineral can be found within the bauxite zone.

Again, if the zones enveloping the gibbsite-rich core represent intermediate stages in the transition of clay to bauxite, leaching must have attained maximum intensity at the core and declined in effectiveness outwards. A mechanism by which this was achieved is difficult to envisage.

Moreover, as Clarke (1972) observed, in places lignite beds up to several metres thick are intimately associated with the bauxite and, therefore, swampy conditions prevailed over at least part of the area, an environment that would seem least likely to promote intense leaching.

The alternative proposal, that the Eufaula bauxite deposits are essentially allochthonous, does not appear to have received serious consideration to date. Yet, the concept could furnish an explanation for much of the observed phenomena, including not only the lenticular and zoned structure of the individual deposits, and the intimate association of lignite and mica with gibbsite, but also the vertical variations in A1203, TiO2, Th and U contents, as well as the relatively low iron content and the absence of boehmite. A suitable but probably oversimplified model in this respect is that of a meandering stream (or streams) draining residual, blanket-like bauxite in the Piedmont to the north and dropping its load both on-shore and off-shore. That deposited off-shore in the area south of Fort Gaines probably intermingled with sediments of diverse source areas and lost its diagnostic characteristics, whereas on-shore, intermittent stream flooding could have carried much of the fine-grained material and occasionally coarser fragments into backswamps that approximately paralleled the stream course. The well-ordered kaolinite found within and above the gibbsite core at McLeod Prospect possibly resulted from reaction of gibbsite with silica-charged waters diffusing from the surrounding sands and, pertinent in this respect, De Kimpe et al. (1964) have shown that gibbsite, 'under suitable acid conditions favouring breakdown to boehmite' reacts with depolymerized silica solutions to yield kaolinite. This mechanism could also account for the absence of boehmite from the Eufaula deposits inasmuch that development of the mineral would be inhibited by the conversion of all available reactive alumina to kaolinite. Conceivably these processes are continuing at the present time.

The kaolinite in zone II below the gibbsite core at McLeod Prospect has a disordered structure and may represent original detrital material derived from a kaolinitic rather than bauxitic source area.

ACKNOWLEDGMENTS

We are indebted to Messrs J. F. Westcott and F. C. Heivilin of A. P. Green Refractories for permission to

Origin o f Eu fau la bauxi te 137

study the cores, to M. C. Walker of the University of New South Wales for the elemental analyses, and to Dr Paul Mueller of the University of Florida for advice on the thorium and uranium determinations.

R E F E R E N C E S

ADAMS J.A.S. & RICHARDSON K.A. (1960) Thorium, uranium and zirconium concentrations in bauxite. Econ. Geol. 55, 1653-1675.

ADAMS J.A.S. & WEAVER C.E. (1958) Thorium-to-uranium ratios as indicators of sedimentary processes: example of the concept of geochemical facies. Bull. Am. Ass. Petrol. Geol. 42, 387-430.

BALASUBRAMANIAM K.S. (1978) Mineralogy, geochemistry and genesis of bauxites of certain profiles of western India. Proc. 4th Congress. Bauxites, Athens !, 35-76.

BURST J.F. (1965) Genetic relationship of the Andersonville, Georgia, and Eufaula, Alabama, bauxite-kaolin areas. Am. Inst. Mining Eng. Trans. 256, 137-143.

CLARKE O.M. (1966) The formation of bauxite on karst topography in Eufaula district, Alabama, and Jamaica, West Indies. Econ. Geol. 61,903-916.

CLARKE O.M. (1972) Bauxite and kaolin in the Eufaula District. Geol. Surv. AIa. BuR. 100, 89 pp. DE KIMPE C., GASTUCHE M.C. & BRINDLEY G.W. (1964) Low temperature synthesis of kaolin minerals. Am.

Miner. 49, 1-16. GARDNER L.R. (1970) A chemical model for the origin of gibbsite from kaolinite. A m. Miner. 55, 1380-1399. GOLDSCHMIDT V.M. (1954) Geochemistry. Clarendon Press Oxford. GORDON M., TRACY J.I. & ELLIS M.W. (1958) Geology of the Arkansas bauxite region. U.S. Geol. Surv. Prof.

Paper 299, 117 pp. GRUBS P.L.C. (1970) Mineralogy, geochemistry and genesis of the bauxite deposits on the Gove and Mitchell

Plateaux, northern Australia. Mineral. Depostta 5, 248-272. JEPSEN K. & SCHELLMANN W. (1974) Uber don stoffestand und die bildungsbcdingungen der bauxitlager

statte, Weipa, Australien. Geol. Jb., Hanover 7, 19-106. JONES G.P. (1972) Origin, diagenesis and structure of bauxite deposits of southeastern Alabama. Proc. 7th.

Forum Geol. lndust. Minerals. Spec. Publ., Florida Bur. Geol. 7, 23-28. LOUGI-INAN F.C. & BAYLISS P. (1961) The mineralogy of the bauxite deposits near Weipa, Queensland. Am.

Miner. 45, 209-217. MACNEIL F.S. (1945) The Midway and Wilcox stratigraphy of Alabama and Mississippi. US Geol. Surv.

Strategic Minerals Inv., Prelim. Map 3-195. RETTGER R.E. (1925) The bauxite deposits of southeastern Alabama. Econ. Geol. 20, 671-686. SHEARER H.K. (1917) A report on the bauxite and fuller's earth deposits of the coastal plain of Georgia.

Georgia Geol. Suv. Bull. 31,340 pp. SOMM A.F. (1975) Gore bauxite deposits, Northern Territory. Aust. Inst. Min. & Metall., Mono. $, 964-968. WARREN W.C. & CLAng. L.D. (1965) Bauxite deposits of the Eufaula district, Alabama. US Geol. Surv. Bull.

1199-E, 310 pp.

K U R Z R E F E R A T : Allgemein wird angenommen, dab die Bauxit-Lagerst/itten des Eufaula- Distrikts, Siidost-Alabama, autochthonen Ursprungs sind. Verglichen mit jiingeren residualen Bauxiten der heutigen tropischen Regionen der Welt haben die Eufaula-Lagerst/itten jedoch eine Anzahl yon Merkmalen, die sich nur schwer mit einer Entwicklung in Situ vereinbaren lassen. Zur KI/irung dieses Sachverhalts wfirden drei Bohrkerne mit der kompletten Abfolge einer der Eufaula-Lagerst/itten untersucht. Obwohl entg/iltige Schlul3folgerungen noch nicht gezogen werden k6nnen, lassen sich die meisten der beobachteten Ph/inomene auf der Basis eines in wesentlichen transportierten Ausgangsmaterials der Lagerst/itte erkl/iren.

R E S U M E N : Se ha aceptado generalmente el origen aut6ctono de los dep6sitos de bauxita del distrito de Eufaula, al sureste de Alabama. Sin embargo, comparando con las bauxitas residuales m~is recientes de las actuales regiones tropicales del mundo, los depositos de Eufaula presentan una serie de caracteristicas que son diflciles de reeonciliar con su desarrollo in situ. En un intento de resolver este enigma, se ha realizado un detaUado estudio sobre muestras procedentes de tres perforaciones que atraviesan una serie completa en uno de los dep6sitos de Eufaula. Aunque los resultados no son concluyentes, creemos que muchos de los fendmenos

138 Origin of Eufaula bauxite

observados pueden explicarse suponiendo que los dep6sitos se forman esencialmente por arrastre del mineral.

R E S U M E: Une origine autochtone est g6n6ralement admise pour les gisements de bauxite du district d'Eufaula dans le Sud-Est de l'Alabama. Cependant, compar6s ~ des bauxites r6siduaires plus r6cents issues de r6gions actuellement tropicales, les gisements d'Eufaula pr6sentent un certain nombre d'aspects difficilement conciliables avec une formation in situ. Dans le but de r6soudre cette 6nigme, une &ude d6taill6es des carottes de trois forages effectu6s ~ travers un gisement entier d'Eufala a &6 entreprise. Bien que les r6sultats ne soient pas concluants, il est vraisemblable que la plupart des ph&mm6nes observ6s peuvent &re expliqu6s en admettant une origine essentiellement due au transport des s6diments.