A Preliminary Classification of Uranium Deposits

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GJ BX-63(78)

A PRELIMINARY CLASSIFICATION OF URANIUM DEPOSITS

Field Engineering Corporation Grand Junction Operations Grand Junction, Colorado 81501

May 1978

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PREPARED FOR. THE U.S. DEPARTMENT OF ENERGY GRAND JUNCTION OFFICE UNDER CONTRACT NO. EY-76-C-13-1664 GJ HX- 6 J: (7 8)

A PRELIMINARY CLASSIFICATION OF URANIUM DEPOSITS

Edited by

David G. Mickle

BENDIX FIELD ENGINEERING CORPORATION Grand Junction Operations Grand Junction, Colorado 81501

·' May 1976

PREPARED FOR THE U.S. DEPARTMENT OF ENERGY GRAND JUNCTION OFFICE UNDER CONTRACT NO. EY-76-C-13-1664

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CONTENTS

Preface . . vii

A CLASSIFICATION OF URANIUM DEPOSITS IN SEDIMENTARY ROCKS, by C. A. Jones •...•..•.••...... ••. 1

Abstract 1

Introduction 2

Classification • • • • i 2

Syngenetic deposits 2

Placer deposits 4

Quartz-pebble conglomerates 4

Marine black shale 5

Phosphorite 6

Water 7

Epigenetic deposits 7

Lignite, coal. and carbonaceous shale •. 8

.Evaporative precipitates 9

Limestone . 9

Sandstone 10 References ...... 13

I CLASSIFICATION OF URANIUM OCCURRENCES IN AND RELATED TO PLUTONIC IGNEOUS ROCKS. by _Geoffrey W. Mathews • • • . • • • • • • • • • • • • 17

Abstract 17

Introduction ...... 18

Classification ...... 18 Orthomagmatic' class ...... 19

Selected examples of the orthomagmetic class .. . . . 21 CONTENTS (cont~ued)

~ Bokan Mountain, Alaska 2,1

Bostonite dikes, Front Range, Colorado • 22 "'

Pegmatitic class • • • 23

Selected examples of the pegmatitic class 23

Bokan Mountain, Alaska 23

Bicroft mine, Bancroft area, Ontario • 24

Magmatic-hydrothermal class 24

Selected examples of the magmatic-hydrothermal class .. 25

Radium Hill, Australia •• 25

Boulder batholith, Montana • .25

Contact-metasomatic class 26

Selected examples of the contact-metasomatic class '27

Mary Kathleen, Australia • 27

Wheeler Basin, Colorado ,27 Autometasomatic class ...... 28 Selected examples of the autometasomatic class 28

Ross-Adams mine, Bokan Mountain, Alaska 28

Lireui complex, Nigeria 29

Authigenic class 29

Example of the authigenic class • 30

Daybreak mine, Washington 30

Allogenic class 30

Selected examples of the allogenic class 31

Midnite mine, Washington • 31 Nabarlek, Australia 31

iv S (continued)'

Anatectic class

Selected the anatectic class

th-West Africa 33

, Quebec • . . . . • • • . • •. 33

References 34

CLASSIFICATION OF VOLCANOGENI URANIUM DEPOSITS, by R. C. Pilcher ••.....• 41

Abstract . 41

Introduction 42

Theoretical basis for c sification 42

Classification • . • • • 43

Initial-magmatic c s 44

Pneumatogenic class 45

Hydroauthigenic cla 47

Hydroallogenic clas 48

References ...... 50 CLASSIFICATION OF URANIUM DE SITS OF UNCERTAIN GENESIS, by Geoffrey W. Mathews • • • ...... 53 Abstract .• ...... • ...... 53

Introduction 54

General discussion . 54

Source of leachable anium • . . . . . 54 ' Source of oxidizing solutions • ...... 56 Reducing agents ...... 56 'Ihi._,.. ' Hydraulic setting ...... 58 Sites of deposition • ...... 60

v CONT S (continued)'

Pa~e Classification ...... 6'o ' Unconformity-related 6:1

Selected of unconformity-related deposits llic subclass) • • • • . 62

.J ern Australia ~2 63

Selected of unconformity-related deposits ic subclass) • • • • • ~4

Key Lake, bern Saskatchewan, Canada . '64

Jabiluka Australia 65

Vein-type deposits tamorphic rocks • • • • • • • (>6

Example of a vei -type deposit in metamorphic rocks (monometal ic subclass) • • • • • • • • :68

Beaverlodge area, northern Saskatchewan, Canada •• :68

Example of a vei -type deposit in metamorphic·

rocks (polymetal subclass) • • • • . . • • . 1 69

ado mines, Northwest Canada . • 169

Vein-type deposits i rocks • 169

References ...... 72

vi PREFACE"'

The clastifications of ur ium deposits given in this report are designated to facilitate and systematize llection, analysis, and storage of uranium occurrence da a for the Nati 1 Uranium Resource Evaluation (NURE) prog#am being carried!out by Bendix F d Engineering Corporation under U.S. Dep4rtment of Energy contract no. EY-76- 3-1664. These classifications may have to be modified as more information b s available. When coupled with recog~ition criteria curr~ntly in preparat , the classifications will provide a ba,is for recognition o~ potentially fa rable environments, evaluation of the economic potential of ~ given area, and uranium occurrence modeling. I The foll~wing four catego deposits are classified anq discussed in sep~rate papers in t

1. Depofits in sedimenta y rocks

2. Occutrences in and re. ated to plutonic igneous rocks ! 3. Volc~nogenic uranium eposits

4. Urantum deposits of rtain genesis.

The clas~ification of ur ium occurrences in the first three categoties is based on gene+is and the natur of mineralization. Uranium deposits in sedi mentary rockslare classified b the type of mineralization (syngenetic o~ epigenetic). !Host-rock origin is a secondary basis of classification. Uranium occurrences i~ and related to lutonic igneous rocks are classified accotding to the behavi~r of uranium dur g magmatic evolution. Secondary criteri~ are the lithologyiof the host rock the nature of mineralization, and spatial relations with ~lutons. A model ef caldera evolution is the basis for cla~sifying volcanogenic *ranium deposits. The nature of mineralization within a vo~cano genic system is emphasized. U deposits of uncertain genesis are classified according to ~ssociated struct es and host-rock types.

Numbers ~ssigned to the c sses of uranium deposits will allow easy recall to informatiof regarding known uranium occurrences from the Grand Junction Offi¢e Information S stem (GJOIS) fil of the U.S. Department of Energy. Deposits in sedimentar rocks are assi ed numbers in the lOOs and 200s; those in and related to pl~tonic igneous ~o have numbers in the 300s; numbers in t~e 500s are resetved for volcano uranium deposits; and uranium deposit~ of uncertain gen$sis have numbers in the 700s.

The foll~wing is a list o all the classes of uranium deposits and ~heir _associated fi~e numbers. '

vii \.I Deposits in sedimentary rocks 110 Placer 120 Quartz-pebble conglomer 130 Marine black shale 140 Phosphorite ... 150 Water 210 Lignite, coal, carbonac 220 Evaporative precipitat 230 Limestone 240 Sandstone

sits in and related to eous rocks

310 Orthomagmatic 320 Pegmatitic 330 Magmatic hydrothermal 340 Contact metasomatic 350 Autometasomatic 360 Authigenic 370 Allogenic 380 Anatectic

Volcanogenic uranium deposits

510 Initial magmatic \.,I 520 Pneumatogenic 530 Hydroauthigenic 540 Hydroallogenic

Uranium osits of uncertain sis

710 Unconformity-related sits 711 Monometallic 712 Polymetallic i 720 Vein-type deposits in tamorphic rocks 72l·Monometallic 722 Polymetallic

730 Vein-type ~eposits in edimentary rocks

viii ···:-- I

A CLASSIFICATION OF URANIUM' DEPOSITS IN SEDIMENTARY ROCKS

C. A. Jones

ABSTRACT

For this classification, uvanium deposits in sedimentary rocks are divided into two groups, syngenetic and epigenetic. Syngenetic deposit~ are form~~ contemporaneously with deposition of the enclosing sediment; they include de trital uranium minerals and uranium absorbed or adsorbed at the sediment-water interface. Epigenetic deposits 1are formed by the precipitation of uraniu~i from solutions moving through pre-ex.tsting rock or previously deposited sedimeiJ!~. Uranium-bearing solutions include connate water, meteoric water, and hydroihermal solutions.

Five classes of syngenetic deposits and four classes of ep~genetic defosits are recognized. Each is classified according to its presumed genesis.

The five classes of syngeneitic deposits are as follows: placer, quar1tz pebble conglomerate, marine black shale, phosphorite, and water. Placer d~ posits include both fluvial and beach placers. Radioactivity is due primarily to thorium minerals, and uranium usually is present only as a minor constituent of resistant minerals such as monazite and zircon. Quartz pebble conglomefate deposits also are considered by many to be placers; however they are uniqu~ in three ways. They are pyritic, they are restricted to the lower Proterozoi(:, and they contain the primary uranium minerals uraninite and (or) brannerite. Marine-black-shale deposits contain uranium adsorbed from sea water by clay particles and organic material. Certain uraniferous, highly reduced muds ! forming today off the southwestern coast of Africa are included here, although as Holocene sediments they are not black. In phosphorite deposits, which •lso are marine in origin, the uranium substitutes for calcium in phosphate min~rals of the apatite group. Brines, sea water, and mine and mill waters constit~te sources of uranium. Conceivably, uranium could be extracted from sea watet if incentives were adequate, and uranium recovery from leach solutions at certain copper operations is now in operation. ,I Epigenetic deposits include lignite, coal, and carbonaceous shale; evap orative precipitates; sandstone; and limestone. Uranium in oxidized groun~ water may be reduced and precipi~ated by organic material in lignite, coaL~ or carbonaceous shale. Evaporative precipitates are characterized by seconda*y uranium minerals that precipitat~ on outcrop or in pore spaces, solution cav it~es, and fractures within the oxidized zone. The largest and most impor~ant class for U.S. exploration and production has been the sandstone de,posit. · Typical deposits of this class are in fluvial and marginal-marine aandston~s. Volcaniclastic sediments in whicp the uranium has been concentrated along redox boundaries also belong to this cll.ass. Uranium deposits formed along redox, boundaries in limestone are distinguished from the sandstone class on the ~asis of lithology. ·· INTRODUCT'tON

This cJnssification and the, supporting data are designed for use by B!fEC geologists and subcontractors conducting uranium resource evaluations for ~he NURE program. The purpose of the classification is to classify all recognized types of uranium occurrences in sedimentary rocks, and to provide a basis for uniformity in evaluating uranium favorability for the NURE program.

This classification (Fig. 1), adapted from Barnes and Ruzicka (1972), is genetic. It is based on the various processes whereby uranium, initially ~is persed in primary (igneous) sources, is thought to be transported, concentrated, and deposited in sedimentary rooks.

For this classification, uranium deposits in sedimentary rocks are dtfided into two groups: syngenetic an~ epigenetic. Syngenetic deposits are f_c>_EIJ!~d contemporaneously with. depositiqn of the enclosing sediment; they include ' detrital uranium minerals and uvanium absorbed or adsorbed at the sediment-water interface. Epigenetic deposits :are formed by the precipitation of uranium! from solutions moving through pre-existing rock or previously deposited s~diment. Uranium-bearing solutions include connate water, meteoric water, and hydro. thermal solutions.

Five classes of syngenetic deposits and four classes of epigenetic d~~osits are recognized. Each is classi~ied according to its presumed genesis. Hdwever, descriptive information and recognition criteria to be published later will permit the geologist to classify a deposit on the basis of observable feaq~res without recourse to interpretat~on of genesis.

CLASSIFICATION

SYNGENETIC DEPOSITS

The five classes of syngentltic deposits are as follows: placer, qua~tz pebble conglomerate, marine bla¢k shale, phosphorite, and water. Placer de posits include both fluvial and.beach placers. Radioactivity is due prim~rily to thorium minerals, and uraniurn usually is present only as a minor const~tuent of resistant minerals such as m~nazite and zircon. Quartz-pebble-conglom$rate deposits also are considered by many to be placers; however, they areuni~ue in three ways. They are pyritic, they are restricted to the lower Proterozo~c, and they contain the primary uqmium minerals uraninite and (or) branneri~e.

Marine-black-shale deposit~ contain uranium adsorbed from sea water ~y clay particles and organic material. Certain uraniferous, highly reduced! muds forming today off the southwestern coast of Africa are included here,! although as Holocene sediments they are not black. In phosphorit~ deposits, which also are marine in origin~ the uranium substitutes for calc~um in pqos phate minerals of the apatite group. Brines, sea water, and mine 'and mill! waters constitute sources of ur4!nium. Conceivably, uranium could ['be extra.. cted from sea water if incentives were adequate, and uranium recovery firom leach solutions at certain copper operations is now in operation. i

2 ( (~ \.

SOURCfS SEDIMENTARY MEANS OF CONCENTRAnON CLASSIFICATION PRODUCTS TRANSPORT ,...... AND DEPOSITION M..:henlcaUy dopooltH In ...... oalcllzod lluvlol and uraniuM t-----, r-- J no. PlACI:R OEPOSITI tHpoola I rnwv!nal-marine environ menta I I t Urenlum· s Itt- ot MKI\onleally depoelted In 1:ZO. QUARTZ PEBIL£ ~....,., mervinal·mariM y r..suc:ed fluvial J CONGLOMERA TEl mlnetala currt~nta - -to I u..- N I ....,.,. ..,_... U I rociLa G UraniuM- Surface. Adeorpdon 01 Ionic wb•urlae., E complexlng by or;onlc I>Mrins _,... J 130. MARINE ILACK IHAL£8 Uow T,PI ond merino motorlol. clay, pyrilo, 01 I wet en N pl>ooplloto ml,_olo I I - E s - Ionic oubodlutlon In I J 140. PHOSPHORITES s pl>ooplloto mlno

Conconttodon by J 1111. IRINES.IEA WATER -- WIIPOrotlon I l r-- J AdeorpdOfl or Ionic comploxlnu by or;onie J 210. LIGNITE. COAL materiel In """"'*''"' CAR80HACEOUS IHAL£ E l -onto I I p

I eonc .... tt.don and precipllodon primorlly by J ZID. EVAPORAnVE PRECIPITATES j G oveporotlon I E N

E ~xiEh-pHI J DO. LIMESTONE s changHIChomlcol c.Ual I I I s - ...... ------~--~ ~- rNIDSTONE - --~- L J ·- ~~ ~-~t ~ I

- Adapt8cf rrCifn ~-~Jt~'dc:k.;,- itml. 8nd others. Figure 1 ORIGIN OF SYNGENmC AND EPIGENETIC URANIUM DEPOSITS IN SEDIMENTARY ROCKS

~: -~ ~ Placer Deposits (110)

Placer deposits are concentrations of heavy minerals that fonjl in hig,p energy-fluvial and marginal-rnaripe environments. In these environments, · currents selectively concentrate, high-density mineral grains and w!nnow ou~ the' lighter grains and finer material. ·

In radioactive placers, most of the radioactivity will be fro$ thorit~~- · bearing minerals such as monazite, zircon, thorite, and euxenite btcause ~~orium minerals are generally more resistant to weathering and destructio~ durin~ trans port than are uranium minerals. Uraninite is one of the commonest and mos~ important uranium minerals, but a study by Davidson (1957) shows a worldwide absence of uraninite in placer deposits. Uranium normally will be present;,. in the radioactive placer, but only as a minor constituent of resistant minenals such as monazite, xenotime, and thorite. Exceptions are brannerite, and ura ninite in certain Precambrian quartz-pebble conglomerates (Class 1~0). Rq~io active minerals in these Precambrian conglomerates are probably also place'r in origin but were deposited in an anaerobic environment.

As a uranium resource, placers are low grade. However, uranium-bearing minerals may be associated with economic concentrations of thoritej, ilmen:l!.te, , . ,I rutile, cassiterite, or gold th;lt allow uranium to be economically recove~ed as a by-product or coproduct. Although placers are low-grade sourtes for r~ranium, volumes of individual deposits may be as large as 10 6 cubic yards.' · I

Radioactive placers are COI1!posed of minerals derived from dislintegra~ion of silicic igneous and metamorphic rocks. Such placers are locate!d both ¢m and peripheral to shields or regions of strongly deformed and int~uded ro~ks. On the basis of depositional environment, two subclasses of place~ deposi#s are recognized: fluvial and be;Jtch-barrier bar. Examples in the Upited St;ates include fluvial placers of central Idaho and Cretaceous beach plac~rs of t~e western interior (Houston and M~rphy, 1977).

~tz-Pebble Conglomerates (120)

The chief distinctions between quartz-pebble conglomerates a~d congl~mer atic placers. (Class 110) or conglomeratic sandstone deposits (Clas.s 240) .re the restriction of the quartz-pebble conglomerates to the lower PJtoterozo~c, their highly pyritiferous character, and the presence of detrital~?) uran~um minerals. On the rasis of these three distinctions, quartz-pebbl1 conglo~erates are considered a separate type of deposit. The term "quartz-pebble congl?mer ate" does not distinguish this type of; deposit from other conglom~ratic d~posits, but because the term is commonly used in the literature it is alsq used h~re.

Quartz-pebble conglomerates are restricted to Precambrian strata. ~e two classic localities are Wit\,';:ttersrand, South Africa, and Blind River-Elliot Lake district, Ontario. Similar but less important deposits are :f.n Brazi,l.. All of these deposits have been dated at 2.0 to 2.7 b.y. and all deposits unconformably overlie an Archean basement of granite and metamorp~ic rock~.

Origin of quartz-pebble conglomerates is controversial. It is. genep~lly. agreed that the ore-bearing rocks were deposited in fluvial, lacu~trine, and marginal-marine environments. Whether the uranium itself is sygenetic, ohat

4 I i is, placer, or introduced later by hydrothermal solutions is an untesolvedi; I question. Recent papers by Min~er (1976) and Robertson (1976) support a detrital or placer origin for the uranium. If so, these Precambtian deposits are unique among placers in that the uranium is containediin uraq~nite, brannerite (Blind River), and the hydrocarbon thucolite. Both min~rals aqtl thucolite are rare in Phanerozoic placers because they are unstabl~ during weathering and transport in an oxidizing environment. Survival of:· these easily weathered minerals and thucolite in a placer deposit is presumed d*e to an anaerobic atmosphere during the early Proterozoic.

Uranium minerals, together with pyrite and other heavy minerats, occur in the micaceous matrix of these conglomerates. Pyrite seems to bJ d+trital at both Witwatersrand and Blind River-Elliot Lake, although pyrite'~.e:f.nlets of later origin are also present at; Blind River-Elliot Lake. The conglomerat11'!S) ' are slightly metamorphosed. . ·

Precambrian quartz-pebble conglomerates are low-grade uranium1resourcl!s. At Witwatersrand, where uranium is a by-product of gold mining, gr-1tde may ~un as low as 0.01 percent U3 0 8 • However, individual deposits may ran~e in si~e from 5,000 to 150,000 st U3 0 8 • · '

Marine Black Shale (130)

Uraniferous black-shale deposits are marine in or1g1n and are:charac terized by dark color; high sap~opelic organic content; pyrite (or!marcasite) in thin lenses, nodules, or dis~eminated particles; and the lack ot sparsity of calcium and magnesium carbonates. Carbonates may be present as! thin beds, but are minor constituents of the shale itself. In addition to ur.nium, mpst uraniferous black shale also coqtains small quantities of other mefals sua~ as titanium, copper, chromium, molybdenum, manganese, vanadium, ph~sphorouF, and rare earths. These elements tend to be evenly disseminated thtough th~ shale. Phosphate minerals may he disseminated, concentrated in no~ules, a~ ! I concentrated in phosphate-rich layers.

Uraniferous black shale is usually associated with other shal~ and limestone, but may be interbedded with phosphorite, chert, or bentpnite. Some black shales are part of cyclic deposits with shale, sandstone, an~ limestone; other black shales are siliceous and may be lateral equivalents of. siliceous volcanic rocks. .I

Uranium content in black shale generally increases with incre~sing amounts of organic matter. Phosphate nodules are usually richer in uraniu~ than the surrounding shale, but there are exceptions.

Most uraniferous black shale is evenly laminated but dense, bteaking ~ith a conchoidal fracture when fresh. Different beds or units containjd~ffer~~t amounts of uranium but the grade of a particular bed is conunonly u~iform ~lnd predictable over large areas. Uranium content may be higher in be?s wher~l laminations are closely spaced or where grain size is finest. Urntljferous black shales are thin but' widespread stratigraphi~' units that accumulated very slowly on or adjacent to tectonically stable contijnental plat forms. The richest and thickest deposits seem to have been deposiqed near 'the platform margin. Preorogenic st

Deposits are typically several fppt thick and cover tens or h4ndreds ~f thousands of square miles. Uranium content ranges from O.OOX perc~nt to as much as 0.02 percent uranium. Otganic-rich beds may contain as muqh as O.J percent uranium.

Urnnium in black shale is b~lieved to have accumulated syngenhically 1 with the sediment. It may have been extracted from sea water by otganic i matter, phosphate minerals, pyrite, or colloidal clay'. Bottom con~itions 1were reducing. In some cases marine waters may have been enriched in s~luble uranium by nearby volcanism or intense weathering of granite terra~e in tq~ ' ,, source area.

No uranium minerals have been identified from black shales. !rhe uran!,ium

is apparently adsorbed in organic or phosphatic molecules, or absorbed by 1 clays.

All of the large and rich uraniferous black shales are Paleozpic in ~ge. Their distribution is worldwide. They are referred to in the varibus lit,r ature as carbonaceous shale, bituminous shale, phosphatic shale, aJl.um sha:J.fe, and other names., The two most studied uraniferous black shales ar'je the Gassaway Members of the Chattanooga Shale in the eastern U.S. and the alow shales of Sweden.

Phosphorite (140)

Phosphorite is a sedimentary rock composed of phosphatic min~rals. Some marine phosphorite, like marine black shale (Class 130), contains1enough ~ra nium to constitute large but low-grade deposits of uranium. Marile phosp~orite consists chiefly of microcrystalline carbonate fluorapatite in th¢ form of laminae, pellets, oolites, nodules, and skeletal or shell debris.: Uraniuf substitutes for calcium in the carbonate-fluorapatite lattice. A~sorptiqp of uranium is considered a syngene,tic process that occurs while apatite preq~p itates on the ocean floor .

The thickest •and richest phosphate deposits, and the most ur~niferoqs,. are those deposited on the outer eqge of the continental shelf or mio~eosync]linal platform. Thus, uraniferous marine phosphorite is found in thick! miogeo-TI synclinal sequences.

On the basis of their ass(}ciation with other marine sedimentjs, mari-de phosphorites can be divided into two groups: those associated w~th blacl shale and those associated with limestone. Phosphorite associatPd wit~ black $hale is usually uraniferous to some detree. An example is the phosphori~e of th~ Phos phoria Formation of Idaho, Wyoming, Montana, and Utah. Phosphor~te assoqiated with limestone is less likely to contain significant amounts of ~ranium. An exception is the Bone Valley Formation of Florida. ' i .( The grade of marine-phosphorite deposits is low. Uranium c~tent ranges from 0.005 to 0.02 percent with a general tendency for uranium to lincreas~ with increasing P 2 0 3 content. I There are four types of plwsphorite deposits in addition to lthe marfne phosphorites. These are residual phosphorites, phosphatized rock,! river pebble deposits, and guano. Re3idual deposits are concentrations bf phos~ phorite derived from the weathering of marine phosphatic limestone!. Phos~ phatized rock is formed by solution of phosphate from overlying rof.k and deposition by replacement or filling of interstices in underlying ~ocks. ! River-pebble deposits consist off fluvial concentrations of phospha~e matel!'ial released during weathering of marine phosphorite. All of these 1 del?osits ~re low in uranium and of little inuerest with the possible exception pf river pebble deposits, which depend upon the uranium content of the parept mateJtlial. Guano deposits are small and contain practically no uranium. : · I

Water (150)

Surface water, ground water, hot springs, and sea water are ,11 inc~uded in this class. None of these are deposits in the usual sense. Th~y are nbt concentrations of crystalline min. erals in rock. Nevertheless, somt of th~pl. do constitute a possible source pf uranium. Uranium-bearing water~ are 1 difficult to classify. They are classified here among the syngenefic depq~its for convenience. \ j·

Given present-day technolcgies and economic conditions, uran:f..· um in n:.atural waters is not a practical resource. Typical values for surface an~ ground] waters are in the parts-per-bill.ion range. Most samples of fresh tater range from 0. 05 to 1 ppb uranium. Therre are exceptions. Walker Lake, N vada, c.pntains 130 ppb uranium (Lawrence Liverrrore Lab., 1976), and water samples from kilibwn uranium districts may also contain several hundreds parts per bill on uraJJitum.

Such values are very high for fresh water. · ! 1

Sea water, which is estimated to contain as much as 5 billi01j1 tons O!F uranium, is potentially the largest resource (Woodmansee, 1975). tts grad1e is so low (3 ppb U3 0 8 ) that 5.5 !Ilillion cu ft of sea water is nece~sary to, recover 1 lb of uranium. Barnes' and Ruzicka (1972) mention the Ar41 Sea a1~ uranium bearing, but no details of the uranium content are given. !The Caspian Sea, which is similar to the Arail. Sea in geochemistry and geologic lhistorylr contains 3 to 10 ppb uranium (Rogers and Adams, 1970). :

Although not a natural source, uranium in uranium-mine water and in;.I leach solutions at copper operations may range from 1 to 15 ppm U3 0 8 dmansee·~ 1975). Recovery of uranium from mine and milling waters is not wi ely pra~ticed but it may become more important in the future.

EPIGENETIC DEPOSITS

Epigenetic deposits include the following classes: lignite, coal, attd carbonaceous shale; evaporative precipitates; sandstone; and 1 imes e. U~anium in oxidi;~ed ground water may be reduced and precipitated by organi materi~l in

7 lignite, coal, or cnrbonaceous shale. Evap~rative precipitates are· haractlj!!rized by secondary uranium minerals tha~ precipitate on outcrop or in por spaces~ solution cavities, and fractures within the oxidized zone. The lar stand' most important class for U.S. exploration and production has been t sands~one deposit. Typical deposits of thi~ class are in fluvial and margina rine'. sandstones. Volcaniclastic sediments in which the uranium has been centtated along redox boundaries also belong to the sandstone class. Uranium epositf formed along redox boundaries in limestone are distinguished from t sand-'· stone class on the basis of host-rock lithology.

Lignite, Coal, and Carbonaceous Shale (210) . ,. Lignite, coal, and carbonacuous shale are among the least uran ferous ,' sedimentary rocks, but locally they may contain enough uranium to a pot~ntial resource. Among the coaly rocks, high-ash lignite and subbitumino coal $eem to contain the largest amounts ot uranium. Some radioactive peat known.

Deposits of uraniferous lignite and coal in the U.S. usually frqm 0.005 to 0.01 percent uranium with certain deposits as high as 0.8 ercent'i uranium. Deposits range in size from less than 1 sq mi to about 1 sq mi:' and ;I contain from less than 100 to over 10,000 tons of uranium. Al many:' deposits are low grade, relatively small, and localized, ore grade materially upgraded by burning or retorting any of the combustible rocks. Most or all of the uran:ium remains in the ash.

Lignite, coal, and nonmarine carbonaceous shales have the features in common. Uraniferous lignite and coal are commonly Coaly rocks and carbonaceous shales are much less extensive than black shale. A bed may be mineralized in a zone a few inches to feelt thick near the top, or it may b(~ mineralized throughout. Other s are usually present (Ti, Ni, Co, Mo, Sn, V, and rare earths), but non are esple cially indicative of the presence of uranium. Identifiable uran minedils are either sparse or absent. Although secondary minerals, such meta-autunite

1 and metatyuyamunite, are found at some of the higher-grade deposi , most I of the uranium seems to be held in organic ionic compounds similar t humic .cids (uranyl humates).

I Fundamental differences are recognized between uraniferous rine ant;\ nonmarine carbonacebus rocks. Uranium in the marine rocks is rally ' syngenetic and coextensive with a particular bed. In the nonmar · rocks~ uranium is usually epigenetic a.nd locally distributed within a b Non- marine carbonaceous rocks are laterally much less extensive than carbonaceous rocks. Carbonaceous material in marine rocks tends sapropelic (algal) in origin, whereas in nonmarine rocks organic are mostly humic (derived from the vascular plants).

Most uraniferous nonmarin~ carbonaceous rocks were deposited in structural basins. At least in the western U.S., most are stratigraphical associ~ted with acid tuffs or tuffaceous $edimentary rocks or are within t drainaie basin of rocks known or likely to contain uranium (such as grani , urantferous sandstone, and mineralized zones in metal-mining areas). I '- Origin of uranium in lignite, coal, and carbonaceous shale ha been 1 t.1 attributed to precipitation from uraniferous ground water (epigene ic, posi~ coalification), concentration either by growing plants or decaying,plant material (syngenetic, precoalifi.f:ation), or precipitation from hyd'otherma,l solutions. In·the case of Upper Cretaceous and Tertiary lignite ald coal in

the Williston Basin, leaching of 1 overlying tuffs and tuffaceous sa dstone .. ~. nd transport by ground water is a favored explanation. Uranium also auld h~e been leached from veins or uraniferous marine· rocks. , :

Evaporative Precipitates (220)

In this paper uranium deposits that form in evaporites are f!llssed a~i evaporative-precipitate deposits. The only known economic evapora ive pre+ cipitates are the Australian calcrete deposits. Hypothetical poss bilities include sabkha and playa deposits. ,

The most important uraniferous calcrete deposit is at Yeelirrle, Wesqrrn Australia. Yeelirrie is in an area of internal drainage, deep val ey fil~f· abundant salt lakes, and well-developed claypans. Annual rainfall is less! than 10 in., and evaporation rate is 14 to 20 times the annual rai fall. Calcretes are typically elongate deposits parallel to subsurface v lley dr~inage courses; some calcretes are in deltalike deposits that fringe salt [lakes. •· Calcretes form where near-surface carbonate ground waters evaporat~. Ura~kum from weathered granites and vanadium from nearby greenstones are p esent i!P the ground water and valley-fill sediments. Uranium and vanadium comb ne in the oxidizing environment to form carnotite. Carnotite is present in he calcrete as cavity fillings and veinlets filling fractures and in the clay- uartz unit that underlies the calcrete. The richness of the Yeelirrie deposi is due1 in part to subsurface pending of ground water, a consequence of inter al dra~page in the area. Resources at Yeelirrie are estimated at 94 million 1 U30s. ·

Efflorescent deposits of secondary uranium mi~erals (such as yuyamunite, carnotite, uranophane, and schroeckingerite) are fairly common in emiarid re gions. These efflorescent minerals may coat cavities and open spa'es, or Jhey may appear on the face of the outcrop. Any transmissive rock type such ~~ sand stone and limestone, can serve as a host rock. The host rock itse f need ~ot be the source of the uranium because ground water can introduce urani~m from a dis tant source. The presence of efflorescent uranium minerals should~'encourage further investigation, but the efflorescent minerals themselves ar probab.. ly too superficial to be economic. Although efflorescent deposits are fo ed by 'rvapor ation and are mentioned ~ere, they are classified according to the.r host rock.

Limestone (230)

Limestone is seldom a favorable host rock for uranium deposit howe~~r, a few examples exist. Phosphatic marine limestones are discussed der Cli~ss 140, phosphorite deposits. Stra.tiform deposits comparable to epig etic s~nd stone deposits are not common. The Todilto Limestone of New Mexic is the 1 only well-known example. Subeconomic deposits include efflorescent de its in limestone and deposits in karst terrains.

The Todilto is a strongly fetid, chemically precipitated lime unit consists of thinly bedded limestone, some of which is silty. indication that the silty layers were once permeable. Mineralizat ~ . i small anticlinal structures adjacent to vertical fault zones. Uranium-b~aring solutions apparently entered along faults and fractures and were trapped{in the anticlinal folds.

The chances for discovery of another Todilto-type epigenetic deposit may not be likely; however, any limestone that has suitable porosity and per~eabil ity, that contains a reductant, and that has a possible source for urani~m should be examined.

Secondary uranium minerals may occur in karstic Jimestone, as at T~ya Muyun, Uzbeck S.S.R., and in the Madison Limestone of the Bighorn and Pr~or Mountains, Wyoming and Montana. Tyuyamunite in powdery forms, films, ar¢ crusts is the chief uranium mineral at both localities. It is associated with rubble, sinter, and sediment in caves, fissures, and solution channels. ; Whether the uranium mineralization is hydrothermal or supergene is not clear be9ause exploration has not proceeded deeper than the oxidized zone.

Sandstone (240)

There are two principal types of uranium deposits in sandstone, thdse that form by physical or mechdmical processes and those that form by ch~mical processes. The former are comsidered under syngenetic placer and quart~-pebble conglomerate deposits (Classes 210 and 220). The latter, epigenetic de~osits that form in reducing environments, are described here. 1 I Sandstone-type deposits are not limited strictly to sandstone but include rocks that are both silty and conglomeratic. Composition may be quartzbse, feldspathic to arkosic, tuffaceous to volcaniclastic. Medium- to coars~ grained, poorly sorted, quartzose and arkosic fluvial sandstones seem tb be the commonest host rocks.

Red or brown sandstones typically are reduced to gray, green, or t~n in the vicinity of uranium depo8its. Many ore-bearing sandstones also coll!tain pyrite. Pyrite and the non-:r:ed colors reflect the reducing environmen~ necessary for deposition and pr<1Servation of epigenetic uranium. :

Sandstones containing e).!dgenetic uranium generally were deposited 1 in fluvial, lacustrine, eolian, paludal, and marginal-marine environments~ Fluvial sandstones are the most common. Finch (1967) determined that, of 4,60~ sand stone deposits other than veln-type, 97 percent are in continental rocfs, 2 percent are in mixed continental and marine rocks, and 1 percent are i~ marine, ·I chiefly marginal-marine, rocks. In contrast, vein-type deposits (Clasf 730), for which structure is a major control, are distributed with much lessp1 regard' for depositional environment: 45 percent in continental rocks • 37 per:fent in mixed continental and marine rocks, and 18 percent in marine rocks.

Interbedded mudstone and disseminated plant debris are characteril1stic of uraniferous fluvial sandstones. Eolian sandstones are much less favor~ble I than fluvial sandstones because they lack mudstone and plant debris. ~rginal- marine host rocks consist of either wave-sorted or distributary sands 1i,deposited with organic-rich deltaic or lagoonal mud. The presence of m~dstone ~r shal~ interbeds and organic material is an important criterion of fqvorabiltty. Toe mudstone slows or acts as a barrier to ground-water movement; 'organic !'1material, [·I iii ill 1,' 10 ' l.,., either as debris in sandstone or finely divided material in mudstone, act~; as a reducing agent.

A reducing environment is essential for the formation of most epigen~tic deposits in sandstone. (An exc~ption is when vanadium is present; vanadium can cause uranium to precipitat~ as carnotite in an oxidizing environment~!) During weathering, uranium is oxidized to the soluble hexavalent form and •is carried in solution until it encounters a reducing environment. Reductio~ reverts hexavalent uranium to tme insoluble tetravalent form. The reduct$nt may be hydrogen sulfide or a more complex organic acid. Hydrogen sulfide fjis produced or introduced from thr~e sources: anaerobic destruction of orga~ic matter in the sediment, oil and gas, and oxidation of pyrite.

Most epigenetic deposits in continental sandstones are Devoni~n or younger because decayed land pl?nts provide the best reducing agent for u,a niu.m deposit formation. Deposits in older continental rocks are possible;j if a reducing agent such as hydrogen sulfide has been introduced. Deposits ~y have formed in marine sandstones as old as Precambrian without the aid of'l introduced reductants because of the presence of marine plant life. · '

I The most commonly cited sources of uranium in epigenetic sandstone d· posits are either granitic rocks or silicic tuffs and tuffaceous sediment$. Other possible sources include hydrothermal solutions and recycling or re~ distribution of uranium from older deposits.

Volcaniclastic rocks comprise a series from relatively pure air-fallj tuffs to stream- and wave-deposited sediments that contain a large proportion of nonvolcanic particles. Acid tuffs may be a source of uranium for sandt- stone and other types of uranium deposits in sedimentary rocks. In the · initially deposited tuff, uranium is dispersed and low grade (<20 ppm), a;tlthough secondary uranium minerals are occasionally found along fractures and beq~ing planes. Barring development of a mass solution mining technique applicab;le to low-grade tuffs, the initially deposited tuffs are probably not a favo!rable exploration target. Leaching and redeposition concentrates the uranium tip ,I, form an economic deposit. An economic deposit in volcaniclastic rocks is most likely in fluvially redeposited volcaniclastic sediments or in the cJHstal portion of a volcaniclastic st1:atum that lies some distance from the volq:anic source and either downdip from or stratigraphically below a deeply weath~·red tuff deposit. These deposits are covered in detail in the classificatio~ of uranium deposits in volcanogenic rocks.

Epigenetic sandstone-type deposits can be divided into three catego#ies on the basis of the relationshlp of the deposit to bedding or structure: I pene concordant, roll-type, or vein. Peneconcordant (stratiform) deposits in,'igeneral lie parallel to the bedding of the host sandstone. In cross section the:)r may be tabular, lenticular, or irregular; in plan, they may be equidimension!l to amoeba shaped (blanket deposits) or elongate in one direction (trend). ·e spite their generally concordant appearance, detailed study usually show~ that they are locally discordant (Finch, 1954, 1967). This local discordance is an indication of epigenetic rather than syngenetic origin of the deposits. ! :j Roll-tvpe (ore-roll, boundary-roll) 4eposits are C-or S-shaped in t .., vertical section and thus cut sh~rply across the bedding. Roll deposits form at the boundary between altered and unaltered sands tone. The .. J:>?_t_Il1_~_?rt is often called a "solution front" and is the result of oxidizinF; uranifer.9us ~round water moving progressively through a body of reduced (unaltered) sapd stone. The roll front may extend in sinuous fashion across a broad front 'Pr may be elongate in a particular direction. In some districts, rolls are dlosely associated or gradational with stratiform peneconcordant deposits.

The third type of deposit Js the vein deposit. Vein deposits are dia;-:_ tinguished from stratiform deposits by their discordant nature. Vein dep9sits usually cut across bedding at high angles. Vein deposits commonly involv« a wide variety of host rocks. Thurefore, they are considered separately in' this classification (see Class 730 deposits, Mathews, this volume).

Uraninite and coffinite are typical minerals of unoxidized sandstone deposits. Weathering produces $econdary minerals such as carnotite, tyuyl munite, and uranophane. Copper, vanadium, chromium, molybdenum, and sele.ium are also associated with sandstone-type uranium deposits. These elements!: may, of course, be present in rocks that contain no economic uranium.

Expected grade in sandstone deposits ranges from O.OX to O.X percent' UsOs. Many deposits are small and sea ttered but some contain as much as 1 .~0:~ tons of U3 0 8 • Most production in the U.S. has come from epigenetic sand~.tone deposits. '

Examples of sandstone-typo uranium deposits include deposits in the .1 fluvial Chinle and Morrison Formations of the Colorado Plateau, roll-frorit deposits in Tertiary basins of Wyoming, and deposits in fluvial and marg~nal marine sediments along the sou1;hern Texas Gulf Coast.

12 REFERENCES

INTRODUCTION

! Barnes, F. Q., and Ruzicka, V., 1972, A genetic classification of uraniu~ deposits: Internat. Geol. Cong., 14th, Montreal 1972, sec. 4, p. dl9-166. I

PLACER DEPOSITS

Davidson,· C. F., 1957, On the @ccurrence of uranium in ancient• conglomer

Dow, V. T., and Batty, J. V., 1961, Reconnaissance of titaniferous sandston~ deposits of Utah, Wyoming, New Mexico, and Colorado: U.S. Bur. Min~s Rept. Inv. 5860, 52 p.

Houston, R. S., and Murphy, J. F., 1977, Depositional environments of· Up~er Cretaceous black sandston~s of the western interior: U.S. Geol. Sufvey 'I Prof. Paper 994-A, p. Al-A29. 1

! Mackin, J. H., and Schmidt, D. L., 1955, Uranium- and thorium-bearing mi~era1s in placer deposits in Idamo, in Page, L. R., Stocking, H. E., and S~ith, H. B., comps., Contributi@ns to the geo1oRY of uranium and thorium ~y the U.S. Geological Survey and Atomic Energy Commission for the Un~ted Nations International Conference on Peaceful Uses of Atomic Energy, Geneva,

Switzerland, 1955: U.S. Geol. Survey Prof. Paper 300, p. 375-388 [1 1956].

QUARTZ-PEBBLE CONGLOMERATES

Minter, W.E.L., 1976, Detrital gold, uranium, and pyrite concentrations Jelated 'I to sedimentology in the Precambrian Vaal Reef placer, Witwatersrand~ South Africa: Econ. Geology, v. 71, p. 157-176.

Robertson, J. A., 1976, The Blind River uranium deposits: The ores and their setting: Ontario Div. Mines Misc. Paper 65, 45 .P·

·' MARINE BLACK SHALE

I' Mutschler, P. H., Hill, J. J., and Williams, B. B., 1976, Uranium from t'e Chattanooga Shale: U.S. Bur. Mines Inf. Cir. 8700, 85 p.

Svenke, Erik, 1955, The occurrence of uranium and thorium in Sweden, in Jage, L. R., Stocking, H. E., and Smith, H. B., comps., Contributions to the geology of uranium and thorium by the U.S. Geological Survey and Atqamic Energy Commission for the United Nations International Conf,rence on

Peaceful Uses of Atomic Energy, Geneva, Switzerland, 1955: 1 U.S. Ge.l. Survey Prof. Paper 300, p. 198-199 [1956]. REFERHNCES (cch\tinued)

PHOSPHORITE I Cathcart, J. B., 1955, Distripution and occurrence of uranium in the calci~m phosphate zone of the land-pebble phosphate district of Florida, in : Page, L. R., Stocking, H. E., and Smith, H. B,, camps., Contributions! to the geology of uranium and thorium by the U.S. Geological Survey ~d Atomic Energy Commission for the United Nations International Confer~pce on Peaceful Uses of Atomic Enerp;y, Geneva, Switzerland, 1955: U.S. Geol. Survey Prof. Paper 300, p. 477-481 [1956].

I McKelvey, V. E., and Carswell, 1.. D., 1955, Uranium in the Phosphoria For~- tion, in Page, L. R., Stocking, H. E., and Smith, H. B., comps., Con.ri butions to the geology of 11ranium and thorium by the U.S. Geological.! I Survey and Atomic Ene+gy Commission for the United Nations Internati~nal Conference on Peaceful Use$ of Atumic Energy, Geneva, Switzerland, 1~55: U.S. Geol. Survey Prof. Paper 300, p. 483-487 [1956]. 1

WATER

Barnes, F. Q., and Ruzicka, V., 1972, A genetic classification of uraniu~

deposits: Internat. Geol. Cong., 14th, Montreal 1972, sec. 4, p. +519-166.

I (_.~ Lawrence Livermore Laboratory, 1976, Preliminary report on the Walker Ri~er Basin study (California/Nqvada): U.S. Energy Research and Devel. Aclm. GJBX-40(76), Open-File Rept., 114 p. I

Rogers, J.J.W., and Adams, J.A.S., 1970, Uranium, in Wedepohl, K. H., ed,~, Handbook of geochemistry, v. II-2, chap. 92: Berlin, Springer-Verlfg, 50 p.

I Woodmansee, W. C., 1975, Uranium, in Mineral facts and problems: U.S. ~fr• Mines Bull. 667, p. 1177-1200.

LIGNITE, COAL, AND CARBONACEOUS SHALE I Vine, J. D., 1962• Geology of uranium in coaly carbonaceous rocks: U.s. Geol. Survey Prof. Paper 356-D, p. 113-170. I

I Carlisle, Donald, Merifield, P. M., Orme, A. R., Kohl, M. S., Kolker, Oded, 1978, The distribution of calcretes and gypcretes in southwestern 0nited States and their uranium favorability, based on a study of depositr· in Western Australia and So~th West Africa (Namibia): U.S. Dept. of ,nergy GJBX-29(78), Open-File Rept., 274 p. i li' I

EVAPORATIVE PRECIPITATES I I I 'I Renfro, A. R., 1974, Genesis of evaporite-associated stratiform:metall~tferous deposits--a sabkha process: Econ. Geolo~w. v. 69, p. 33-45. II; II! 14 'II I

REFERENCES (continued)

Carlisle, Donald, Merifield, P. M., Orme, A. R., Kohl, M. S., Kolker, Oded, · 1978, The distribution of calcretes and gypcretes in southwestelrn Unit,d States and their uranium favorability, based on a study of deposits in Western Australia and South West Africa (Namibia): U.S. Dept. of Ener,y GJBX-29(78), Open-File Rept., 274 p.

LIMESTONE

Bell, K. G., 1963, Uranium in carbonate rocks: U.S. Geol. Survey Prpf. Paper 474-A, 29 p.

Gabelman, J. W., 1970, The Flat T:Jp uranium mine, Grants, New Mexico1: U.S. Atomic Energy Comm. RME-4112, Open-File Rept., 81 p.

SANDSTONE

Finch, W. I., 1959, Peneconcordant uranium deposit--a proposed term: Econ. Geology, v. 54, p. 944-946.

_____1967, Geology of epigenetic uranium deposits in sandstone in the ll~ United States: U.S. Geol. Survey Prof. Paper 538, 121 p.

Fisher, W. L., Proctor, C. V., Jr., Galloway, W. E., and Nagle, J. S,., 1970 Depositional systems in the Jackson Group of Texas--their relationship to oil, gas, and uranium: Texas Univ. Austin Bur. Econ. Geology Geol. Circ. 70-4, p. 234-261.

Grutt, E. W., Jr., 1972, Prospectlng criteria for sandstone-type urapium deposits, i~ Bowie, S.H.U., Davis, Michael, and Ostle, Dennis, ~ds., Uranium prospecting handbook: London, Inst. Mining and Metallurgy, p. 47-75.

Melin, R. E., 1957, Selected annotated bibliography of the geology of sand stone-type uranium deposits in the United States: U.S. Geol. Survey Bull. 1059-C, p. 59-175.

Mickle, D. G., Jones, C. A., Gallagher, G. L., Young, P., and Dubyk, W. S., 1977, Uranium favorability of the San Rafael Swell area, east-central Utah: U.S. Dept. of Energy GJBX-72(77), Open-File Rept., 120 p!.

Quick, J. V., Thomas, N. G., Broglon, L. D., Jones, C. A., and Martin, T. S., 1977, Uranium favorability cf late Eocen.e through Pliocene rocks oft South Texas Coastal Plain: TJ. S. Energy Research and Devel. Adm. GJBX- (7 7), Open-File Rept., 48 p.

15/16 CLASSIFICATION OF URANIUM OCCURRENCES tN AND RELATED TO PLUTONIC IGNEOUS ROCK$

Geoffrey W. Mathews

ABSTRACT

Consideraq.. ons of the behavior of uranium in the ma~atic ~nvironment .1 provide the con~eptual basis for classifying uranium occ~rrences in and (o~) associated with plutonic igneous rocks. Eight distinct classes of uranium occurrences are. defined on the b~sis of the different st~ges of magmatic e1.o lution during which uranium may be deposited. Although this classificatio is based on thehretical considerations, the classes have identifiable char acteristics by w, hich field geologists can categorize deppsits without exte~sive laboratory analysis. · I • • ! Liquidus crystallization of uranium and uranium-bea~ing minerals in yeunger differentiates of the cogenetic sequence produces ortho~gmatic occurrence~. Uraniferous plu~ons of this class, which represent submarginal resources, ll!.re generally postorogenic and epizonal. They commonly have, porphyritic textutes, high differentirtion indices, and fluorite and sadie fe~romagnesian minera+. s.

Generally, orthpmagmatic-class plutons are alkalic to alkali-calcic and 1 subaluminous to peralkaline. Uranium occurrences formed during the pegmatttic stage of magmatic evolution (pegmatitic class) are chara1cterized by quartz~ alkali feldspar~mica assemblages which are commonly acco1mpanied by primary 1.. hematite, fluor!ite, and sadie amphiboles. These represent paramarginal to recoverable resources. Magmatic.-hydrothermal deposits occur as veins and vein networks wpich develop during very late stage magmaltic evolution. Thtse usually compris~ a quartz-sulfide-fluorite mineral assemblage. Brecciatio't and alteration halos are common.

Late-magmaltic or postsolidification metasomatic proc. eases operating it··· the country rock or in zones within the pluton itself may develop occurren es of either the contact-metasomatic or the autometasomatiq class. Both are characterized b~ replacement textures and alkali metasomatism, particularlf albitization. Postcrystallizatio? redistribution of ur<11nium within the pa ent plutonic body or the surrounding country rocks forms autlhigenic or allogen·c occurrences, relspec tively. Both classes possess concentirations of seconda:ty uranium minerals along shears, fractures, and microfractures.

Anatectic ·~occurrences form by partial melting and E~ubsequent crystallf zation of uraniferous metasediments. This class, which may represent paraf marginal to recoverable resources, characteristically has low-melting-frac ion mineralogy, ferromagnesian minerals similar to host roc~s, and concordant contacts; it o~curs in host rocks of the upper amphibol~te to granulite facies. 1

17 INTRODUCTt'oN

1 A comprehen~ive classification of uranium occurrences is an essential t • device for organizjng field and laboratory data. It is ohe basis for uranL·m occurrence modeling and leads to a sound set of recogni~ion crite~ia. Al~ ough classification critC!ria• differ for occurrences in igneouq,. sedimentary, and.I 1 metamorphic rocks, overlaps do exist. For example, in modeling uranium deppsits in volcanic and volcaniclastic rocks one must utilize comcepts from both i~neous and sedimentary geology. Similarly, aspects of igneous .Jlnd metamorphic ge~logy must be considered in classifying and modeling uranium occurrences in high~ rank, anatectic migmatites. I

This classification of uranium occurrences in and related to plutonic: igneous rocks is largely untested. It is designed to pr,ovide uniformity ip the National Uranium Resource Evaluation (NURE) program :being carried out fY Bendix Field Engineering Corpora~ion (BFEC) under the auspices of the U.S.1 Department of Energy. /

This report consists of a brief discussion of the '~bases for the propo1sed classification, followed by a discussion of the eight different classes oi uranium occurrences in and related to plutonic igneous tacks. Brief desc~·ip tions and characteristics of th~ classes are given, followed by synopses df selected examples of each class. References are organi~ed by class of ur~nium occurrence. / I

CLASSIFICATION

;j.r produce vein-type deposits in o1: near the pluton. Two classes of occurren es formed in this manner are based on the nature of the ho$t rock. An addit nal, problematic class includes uranium occurrences formed by anatexis. The a tectic class is incorporated because of similarities with clas$es produced strict y by magmatic processes and is a pos:lible link between occurtrences formed by i eo us processes and occurrences formed by metamorphic processes.

The eight classes of uranit~ occurrences in and re+.ated to plutonic if·gneous rocks follow. The number following each class name is included to allow €1. sy recall from the Grand Junction Office Information Syste1P (GJOIS) file of 'he U.S. Department of Energy. ,

ORTHOMAGMATIC CLASS (310) Formed dur:f.ng the orthomagmatlic stage of crystallization

PEGMATITIC CLASS (320) Formed during the pegmatitic I stage of ITJ.<1lgmatic differenti1!tion

MAGMATIC-HYDROTHERMAL CLASS (330) Formed during the hydrother 1 stage of ~gmatic evolution

CONTACT-METASOMATIC CLASS {340) Formed by contact

AUTOMETASOMATIC CLASS (350) Formed by ~utometasomatism

AUTHIGENIC CLASS (360) Formed aut~igenically by post magmatic ptocesses

ALLOGENIC CLASS (370) Formed all~genically by post1 magmatic processes

ANATECTIC CLASS (380) Formed by anatexis

These classes and their mu~ual relations are repre$ented in Figure 1.

Class descriptions contain~d in this section briefly introduce the e genetic classes of uranium occurrences in and related to plutonic igneous A more complete discussion of r¢cognition criteria is i~ preparation. Sy of selected examples of each cl~ss are given. Class as$ignation is based on an interpretation of descriptions siven in the literature.! As with uranium qccur rences in other geologic settin:,gs, igneous uranium asso~. iations may conta~... n more than a single genetic class. Therefore, some repetitions occur in the ex~mples.

ORTHOMAGMATIC CLASS (310)

Uranium occurrences of the orthomagmatic class con~ist of syngenetic !nations of uranium and uranium-bearing minerals formed during the ortho stage of magmatic crystallizati:m. They are products of late-stagj3 magma differentiation and they develo? through liquidus crystallization of uran I uranium-bearing minerals. Uranium exists in uranium minerals, as substit I 19 ( (~ r PROCESS

4--- .. ·ANATEXIS MAGMATIC DIFFERENTIATION CLASS STAGE CLASS

ORTHOMAGMATIC ORTH~MAGMATIC (310) '

PEGMATITIC ~- - __ PEGMATITIC N ·' } t320l "-.j t350l- ---- ANATECTIC 0 ,.. AUTOMETASOMATIC ,-(380} CONTACT -" "" ' HYDJOTHERMAL MAGMATIC METASOMATIC -' "" ...,..,HYDROTHERMAL t340l ..- .,. I - - .,• (330} ., , , ~ - -- AlJTHTGEMC/ALLOGENIG/ ___ _ POST-MAGMATIC (300) (370)

--~~~~~-~OCCURRENCES IN AND RELATED TO PLUTONIC IGNEOUS ROCKS- ' lw~ cations in either fixed or exchange cation positions in other minerals, and in intragranular fluids or fluid inclusions. Nonlabile uranium exists in small, finely disseminated primary uranium and uranium-bearin~ minerals.

Plutonic rocks containing orthomagmatic uranium occurrences are generally leucocratic with ferromagnesian mineralogies comprising sodic amphiboles (rie beckite) and (or) pyroxenes (aegerine). Most uraniferous plutonic rocks are quartz bearing, although some are feldspathoidal. Accessory fluorite, sphene, and primary hematite are common. The rocks are commonly porphyritic and have distinct alkaline affinities (subaluminous to peralkaline). Euhedral to sub hedral uranium and uranium-bearing minerals (such as uraninite, betafite, cof finite, brannerite, uranothorite, and xenotime) occur as finely divided minor accessory minerals poikilitically enclosed in major rock-forming minerals in the groundmass. Internal and peripheral albitization is common. These plu tonic rocks are characterized by anomalous uranium contents (>10 ppm), and high weight percentages of Si02, Na20, and K20. Thorium-to-uranium ratios are greater than 1.0 (generally 3.0 to 5.0).

Uranium-rich plutons of this class are generally located in mobile-belt areas, that is, areas of extensive crustal reworking. Strontium-isotope data from a few plutons suggest that the magmas were derived from crustal sources (Beck, 1969). The plutons are commonly postorogenic and epizonal in nature. They are often characterized by abundant roof pendants and xenoliths, discord ant relations with the country rock, chilled border facies, and thermally meta morphosed contact aureoles. They are usually near other classes of uranium ~ occurrences, some of which may represent recoverable resources. Orthomagmatic occurrences may be the source of uranium in associated deposits.

Because mechanisms of uranium concentration are not extensive up to the orthomagmatic stage of magmatic evolution and because of the finely divided nature of the uranium minerals, occurrences formed entirely by orthomagmatic crystallization represent submarginal to paramarginal resources. Postcrys tallization of enrichment processes may concentrate uranium into orebodies.

Orthomagmatic uranium occurrences are identical to occurrences of the initial-magmatic class of the volcanogenic classification (Pilcher, this volume). The distinction between the two should be made on the basis of observable geologic associations. Occurrences of the initial-magmatic class are restricted to subvolcanic intrusives and flows associated with collapsed calderas. Orthomagmatic. uranium occurrences are not restricted to volcano genic associations.

Selected-Examples of the Orthomagmatic Class

Bokan Mountain, Alaska. The Bokan Mountain area (extreme southern Alaskan panhandle) is situated in a terrane of eugeosynclinal sedimentary and volcanic rocks which display low- to medium-grade metamorphism. Two distinct Late Cretaceous(?) magma series are present. The oldest series, a synorogenic, calc alkaline kindred, contains no anomalous uranium. The second, which comprises the Bokan Mountain granite and minor related syenite-monzonite, contains the anomalous concentrations in the area. The Bokan Mountain pluton is a leucocratic, postorogenic, epizonal, albite-riebeckite, peralkaline (subaluminous?) granite. It may represent a late stage of magmatic evolution. It intrudes both the;

21 earlier plutonic series and the metase~ments. The granite is texturally variable but dominantly porphyritic. lt consists of potash feldspar, albite, quartz, riebeckite, and aegerine. Accessory minerals include zircon, xenotime, fluorite, uranothorite, and minor cordierite. Xenotime and uranothorite occur as sparsely disseminated euhedra whereas fluorite and cordierite are mainly interstitial and anhedral. Uranium and uranium bearing minerals occur as primary disseminations and segregations with the granite (although there may have been additional concentrations during autometamorphism; seep. 23 ). Cogenetic alaskitic aplites and pegmatities are abundant, particularly near the margins of the pluton. Some of these more silicic units extend into the country rock. Both the Bokan Mountain granite and the earlier plutonic rocks are heavily albi tized.

Diagnostic characteristics of the Bokan Mountain granite include its epizonal character, its peralkaline nature (as reflected by riebeckite and aegerine), the presence of fluorite, and its anomalous uranium content.

Bostonite Dikes, F-ront Range, Colorado. A series of bostonite dikes intrude Precambrian metasedimentary rocks in the Colorado Front Range and are well exposed near Central City, Colorado. These dikes show a wide range in texture and composition and include porphyritic bostonite, garnet-bearing bostonite, quartz-bearing bostonite, and quartz bostonite. They are associated with and appear to be late differentiates of the Late Cretaceous-early Tertiary alkaline magmatism of the Colorado mineral belt. The bostonites as a group contain the highest uranium concentra ...... , tions of all the Laramide intrusives. Quartz bostonite, the most highly differentiated of the series, contains the greatest uranium concentrations, as much as several hundred parts per million.

The quartz bostonites are characterized by a low color index, few phenocrysts, and the presence of anorthoclase rather than two feldspars. Ferromagnesian minerals are aegerine and biotite. Accessory minerals include zircon, apatite, and rare fluorite and carbonate minerals. The overall dark-reddish hue of the rock is caused by finely distributed hematite in the groundmass. Uranium in the bostonite occurs in dissem inated zircon, allanite, thorite, and an amorphous, brown, radioactive mineral found in microfractures.

The bostonite dikes were emplaced hypabyssally. Albitized aureoles

adjacent to the 1dikes are common but are not enriched in uranium. Alter ation of the dikes by albitization and argillization suggests that at least some of the contained uranium was introduced by late-stage hydro thermal activity.

The thorium-to-uranium ratio of the dikes ranges from 3.0 to 7.0. This ratio suggests magmatic origin and is consistent with other epizonal Laramide intrusives in the Front Range. The amount of uranium contributed by Pre cambrian rocks is thought to be small.

22 ' t,l PEGMATITIC CLASS (320)

Pegmatitic and aplitic uranium occurrences form from pegmatitic fluids during late-stage magmatic evolution. Processes of magmatic differentiation may make uranium much more concentrated in these deposits than in deposits formed during the orthomagmatic stage. Pegmatitic occurrences are charac terized by temporal, spatial, and probably genetic association with uranium rich plutonic bodies. They are found in or at the margins of uranium-rich parental plutons; they may be injected into the country rock. Albitization and (or) argillization of the country rock is commonly well developed.

Most uraniferous pegmatites and aplites are mineralogicalry simple, con sisting of quartz, feldspar, and mica, although some exotic pegmatitic minerals may be present. They may contain a few color-index minerals, most notable of which are alkali amphiboles. Fluorite, topaz, apatite, hematite, and garnet are common accessory minerals. Uranium and uranium-bearing minerals, such as uraninite, allanite, uranothorianite, and brannerite are disseminated throughout the dikes; higher concentrations may occur in quartz segregation pods. Although most uraniferous pegmatites are structurally simple, some may be zoned.

Uraniferous pegmatites may grade laterally into more typical hydro thermal deposits with decreasing amounts of pegmatitic minerals. The dis tinction between pegmatitic and hydrothermal deposits is made on the basis \: • ·• ~.. 1-- of mineralogy. Also, hydrothermal occurrences are commonly confined to veins and vein networks in brecciated zones, whereas occurrences of the pegmatitic class exist as distinct dikes.

Because magmatic differentiation normally concentrates uranium in peg

matitic fluids, occurrences of the pegmatitic class may represent para ( marginal to recoverable deposits.

Selected Examples of the Pegmatitic Class

Bokan Mountain, Alaska. Alaskitic aplites and pegmatites are abundant in and around and are cogenetic with the Bokan Mountain granite in southeastern Alaska (seep. 22). All textural gradations between aplite and pegmatite may be found. These leucocratic units consist of quartz and potash feldspar (perthite) with accessory biot~te, riebeckite, albite, and fluorite. Finely disseminated, uraniferous allanite constitutes the major uranium-bearing mineral. Primary uraninite, often accompanied by minor albite, potash feld spar, zircon, xenotime, sphene, and magnetite, exists in some quartz segre gations in the pegmatites.

The pegmatites and aplites are mainly confined to the Bokan Mountain granite, although a few extend beyond its limits into the older plutonic units. Albitization of the host rock is extensive. Internal albitization, extensive sericitization, and clay-mineral formation of some of the peg matites suggest secondary alteration by hydrothermal activity. Some of the uranium enrichment may have been introduced during this later hydrothermal stage.

23 Bicroft Mine, Bancroft Area, Onta~o. The Bancroft area in the Grenville province of Ontario contains more than 100 reported uranium occurrences, of which only the pegmatite deposits are economic. The Grenville province, an area of extensive crustal reworking, is characterized by a petrologically and structurally complex sequence of igneous and metasedimentary rocks.

The Bicroft mine lies within the Cardiff plutonic complex, which comprises two gneissic granites and a gneissic syenite, all of which were intruded into metasedimentary rocks of the upper amphibolite to granulite facies of meta morphism. The pegmatites of the Bicroft area are cogenetic with the Centre Lake Granite, a gneissic, leucocratic granite which contains a pegmatitic facies at the contact with the metasediments.

The pegrnatites of the Bicroft Mine are located in paragneisses and amphibolites adjacent to the Centre Lake Granite. Although four separate types of pegmatites are found in this area (pyroxene pegmatite, pyroxene granite pegmatite, granite pegmatite, and quartz-rich pegmatite), most of the uranium enrichment is in the quartz-rich pegmatites. These uraniferous pegmatites are the most highly differentiated rocks in the sequence. Ore comprises uraninite, uranothorianite, allanite, pyrochlore, and betafite set in gangue of smoky quartz and accessory zircon, molybdenite, fluorite, cal cite, amphibole, and anatase.

MAGMATIC-HYDROTHERMAL CLASS (330)

Hydrothermal solutions evolved during the final stages of magmatic differentiation are responsible for these occurrences. They occur in discordant veins and vein systems near uraniferous plutonic and pegmatitic units or with uranium-rich hypabyssal rocks. Zoned alteration of the country rocks adjacent to the veins is characteristic, often marked by an inner zone of silicification, and outer zones of chloritization and argil lization. Albitization of the country rock is generally not as pronounced in magmatic-hydrothermal occurrences as it is in pegmatitic occurrences. Brecciation of the vein material, often in multiple episodes, is common.

The uranium-bearing veins commonly pinch and swell, depending upon the nature of the rock units they cut. Smoky quartz with disseminated sulfides (pyrite, galena, and sphalerite), the common mineral assemblage, is often accompanied by accessory dark fluorite and (or) carbonate. Some veins consist almost entirely of microcrvstalline quartz. Associated ~ - gold and silver mineralization is common. Primary uranium minerals, generally uraninite and (or) pitchblende, are present in variable concen trations both as open fracture fillings and as replacement products.

Magmatic-hydrothermal uranium-vein occurrences are found within or near leucocratic, uraniferous, plutonic bodies of postorogenic epizonal character. Some exist in high-rank metamorphic terranes and appear to be very late stage differentiates of anatectically derived quartzo feldspathic melts. Magmatic-hydrothermal uranium occurrences may grade laterally into pegmatites.

24 -~------,...,....,,_-...,...,...,..,.,--,,----,-"'T-.... -· ..

" ' ~ w1 Ore-grade concentrations of primary uranium minerals are spotty and i occur in distinct areas along the veins. These minerals may be concentra ed along zones of dilatancy where uranium-rich fluids have migrated. Alt an individual vein might contain uneconomic tonnages of U30s, vein swarms may prove to be economically important. Therefore, magmatic-hydrothermal -occurrences represent paramarginal to recoverable deposits.

Selected Examples of the Magmatic-Hydrothermal Class

Radium Hill, Australia. Radium Hill uranium deposits are tocated in migmatized geosynclinal sediments in the Clary district of the western Australian shield in east-central South Australia. Hydrothermal veins in paragneisses are closely associated with sodic aplites and pegmatites of the country rock and are heavily albitized.

The orebodies are discordant and are generally confined to the axial 1 zone areas of anticlinal folds. The mineralized veins swell when crossi para-amphibolite layers.

Uranium minerals occur in fractures and shears in Archean and lower Proterozoic(?) metasediments. They probably formed as a result of replac t by hydrothermal solutions emanating from the sadie aplites and pegmatites Davidite, the primary urani~bearing mineral, is intimately associated intergrown with ilmenite and rutile. These minerals are set in ~.gangue quartz and biotite. ··

Boulder Batholith, Montana. The Boulder batholith, southwestern Montana, is a composite, epizonal, intrusive mass of Cretaceous age which appears to be the product of two separate but contemporaneous magmas (Tilling, 1973). It intrudes the Cretaceous Elkhorn Mountain Volcanics (andesitic) and is overlain by the Eocene Lowland Creek Volcanics (quartz latite). Post-Lowland Creek rhyolite plugs cut all older units.

Two similar types of uranium-bearing, hydrothermal, vein deposits, base-metal-sulfide-bearing veins (base-metal veins) and chalcedony veins (siliceous reefs), are found in the Butte Quartz Monzonite and alaskite in the northern part of the batholith. Although texturally distinct, these two vein types bear many· similarities and may be products of the same pervasive hydrothermal fluids. The only distinction between the two 1 is the macrocrystalline character of the quartz and the higher percentage of sulfides in the base-metal veins. Uraninite is the primary uranium mineral in each type. The quartz monzonite adjacent to both types of veins is characterized by a zonal alteration ranging from an internal selvage of silicification, through a discontinuous zone of sericitization to an outer zone of argillization. Brecciation, sometimes multiple, is common. Fractures and brecciated zones seem to have been the conduits for the mineralizing hydrothermal fluids.

Both types of veins, but especially the siliceous reefs, occur in multiple, anastomosing systems. Whereas any individual vein is probably economically insi.gnificant, vein swarms may prove to be of economic impor nee.

25 Th~ source of the uranium-bearing hydrothermal solutions is problema Ages of the pitchblende deposits and the age of the batholith preclude ge relations. The postbatholithic Lowland Creek Volcanics represent a possi source. However, confinement of the base-metal veins and sil:i.ceous reefs the north-ern part of the batholith and the wide distribution of the Lowla 1 Creek Volcanics suggest that they are not genetically related. Post Creek rhyolite plugs are restricted to the northern regions of the bathol Gross np,es of the uraniferous veins and the rhyolites are similar. Addit ally, nt least one of the rhyolites is anomalously radioactive (in a shea zone). The hydrothermal veins may be genetically related to the post-Low Creek rhyolites. ',. CONTACT-METASOMATIC CLASS (340)

Contact~etasomatic uranium occurrences form by reactions between uranif~rous magmatic emanations and the country rock during late-stage matitic or hydrothermal) magmatic activity. Alternatively, uranium or contained in the country rock may be remobilized and -concentrated by the adjacent intrusive. Zones of uranium enrichment in the contact-rnetasoma aureole are characterized by extensive alteration, including albitizati sericitization, silicification, and (or) argillization. The metasomatiz country rock may show enrichment in fluorine. Primary uranium and uran bearing minerals (generally uraninite and thorianite) are finely dissemi in basic host rocks (such as skarns and metapyroxenites) although concen may exist within individual basic-mineral constituents. Replacement tex !,..,,, are conunon.

Economic concentrations are governed both by the existence of condu through which metasomatizing fluids might pass and by the presence of d tiona! traps in the country rock. Porosity, permeability, and compositi the country rocks and the structure may contribute largely to the ultima concentration of the deposits. Secondary enrichment processes may make metasomatic occurrences economically important.

Contact-metasomatic occurrences are generally found in high-rank, d motherrually metamorphosed, basic sedimentary units adjacent to oversat uraniferous, plutonic and (or) pegmatitic rocks. They may represent par marginal to recoverable deposits.

· Because the same general petrogenetic processes are involved in the formation of metasomatic and magmatic-hydrothermal deposits, distinctio between the two may be difficult. Operationally and ideally, magmatic thermal deposits occur in veins whereas those formed by contact meta exist as fine disseminations in the host rock. As might be expected their common genesis, these two classes of occurrences, as well as uran pegrnatites, are often associated in time and space and may grade into another. ~·-·

'- ~ Selected Examples of the Contact-Metasomatic Class

Mary Kathleen, Australia. The Mary Kathleen uranium deposit, northwe Queensland, Australia, is a classic example of metasomatic uranium enr Uranium concentrations, uraninite and surficial alterations of uraninite, within the Corella Formation, which is a series of near-shore, arenaceous, silty, and calcareous sediments. These units have undergone extensive re metamorphism to the upper amphibolite facies. Two granites intrude these metasediments, one of which, the eastern or Mt. Burstall Granite, is beli to have caused extensive metasomatic alterations in the metasediments. Mt. Burstall Granite represents a differentiation sequence which becomes progressively more silicic toward the contact with the Corella Fdrmation. Dikes and apophyses of leucocratic granite porphyry and aplite extend into the metasediments.

Anhedral uraninite crystals are disseminated throughout heavily garne scapolite-diopside skarn and metaconglomerate-breccia of the Corella Forma Garnetization (almandite and andradite) preceded uranium emplacement. Ur anhedra are concentrated in areas of extreme garnetization, replacing an The main orebody skarn is characterized by allanite, garnet, feldspar, and scapolite. Accessory fluorapatite, diopside, and some sulfides are common

The Mary Kathleen uranium deposit occurs in a faulted, fractured sync in the Corella Formation. Pervasive garnetization along the fractures i that emanations from the Mt. Burstall Granite apparently followed the frac to suitable depositional sites. Controls of mineralization appear to be rock (breccia-conglomerate), garnetization, and structure (axial portion o 'syncline).

Wheeler Basin, Colorado. Wheeler Basin is located in the Colorado Range, Granby County, Colorado. Bedrock in the area consists of meta~~u~wq~• (upper amphibolite facies) and localized migmatites of the Precambrian Sorings Formation. The Silver Plume Granite displays intrusive relations and _presumably \lnderlies the metasediments near the uranium occurrence. activity of the Silver Plume Granite is three to four times background. niferous perthite-quartz-biotite-muscovite pegmatites are abundant in the

Uranium occurs in small, finely disseminated uraninite euhedra in c trations of titaniferous biotite in the metasediments. Unit-cell dimens of the uraninite suggest a. magmatic origin of the uranium.

The fine dissemination of the uranium minerals, the association with uraniferous pegmatites, the proximity to the Silver Plume Granite, the uni cell dimensions of the uraninite, and the corresponding radiometric ages o the uranium mineralization and the Silver Plume Granite combine to suggest that contact-metasomatic processes we.re responsible for at least some of the u mineralization. The amount of mineralization caused by either migmatizati or remobilization of syngenetic uranium in the metasediments in response t heat from the intruding Silver Plume Granite cannot be determined at this The fact that no reported anomalous uranium concentrations exist in the Id Springs Formation in Wheeler Basin suggests that migmatization and remobil zation did not play a significant role in this uranium occurrence.

27 AUTOMETASOMATIC CLASS (350) I Autometasomatic uranium occurrences are products of internal metas (autometasomatism) caused by replacement reactions between late-stage rna fluids and previously crystallized plutonic or pegmatitic rocks. Late-s magmatic fluids that permeate previously crystallized rock may introduce uranium as well as cause remobilization and enrichment of more. finely d uranium deposited during the orthomagmatic or the pegmatitic stage. Aut metasomatic activity is generally restricted to altered zones within the viously crystallized plutonic rock, particularly along shears, faults, joint systems which acted as conduits for the mineralizing fluids. Mo_st eralized fracture zones are brecciated and extensively altered, predomi by albitization.

Uraniferous zones normally grade outward into unmineralized areas o host rocks. They are enriched in fluorine and rare-earth elements and are deficient in potash. Uranium and uranium-bearing minerals (chiefly ninite, coffinite, pyrochlore, and thorianite) are disseminated throu altered zones and display replacement textures with the more common'min constituents. Accessory fluorite, hematite, and sulfides generally a the uranium minerals.

Autometasomatic uranium occurrences exist in epizonal, subalumi peralkaline, postorogenic intrusives which possess anomalous uranium centrations. Albitization and fluorine enrichment are characteristic. sits of this class may represent paramarginal to recoverable resources.

Although the distinction between autometasomatic enrichments and o magmatic or pegmatitic enrichments may be difficult, autometasomatic deposits are generally concentrated in distinct alteration zones within !the host rock. Autometasomatic deposits display extensive internal alterat ' in contrast to orthomagmatic or pegmatitic occurrences.

Autometasomatic uranium occurrences should not be confused with magmatic occurrences. Whereas uranium of the orthomagmatic class is distributed throughout plutons, autometasomatic uranium occurrences are re stricted to albitized and chemically altered zones within a pluton.

Selected Examples of the Autometasomatic Class

I Ross-Adams Mine, Bokan Mountain, Alaska. The Ross-Adams mine is in peralkaline (subaluminous?) granite along the southeastern margin o Mountain. The general geology of the Bokan Mountain area is briefly s ' rized on p. 21-22 (orthomagmatic occurrences). Uranium minerals are concen small ore zone which displays gradational contacts with the host grani Joint ing, fracturing, and faulting characterize the ore zone, although most f these features appear to be postmineralization. The granite in the orebody several textural aspects and is characteristically heavily stained by oxides associated with uranium mineralization. Albitization is extens Chemically, the ore-zone granite shows a depletion in potash and silic and an enrichment in Zr, Ti, Mg, Ca, Mn, and As.

28 i• ._; The ore minerals, primarily uranothorite and uranoan thorianite with minor uraninite and coffinite, are disseminated throughout the zone. sional concentrations of these minerals are in small veinlets. Minerals directly associated with uranium and uranium-bearing minerals are hematite fluorite, quartz, calcite, clays, and base-metal sulfides (pyrite and ga ). Minor amounts of secondary uranium minerals are found near the surface.

Characteristics which identify the Ross-Adams mine as an autometasoma c deposit are the anomalous concentrations of disseminated ore minerals in t granite, extensive albitization, the pervasive red staining by hematite, i ternally restricted development of clays and the ubiquitous fluorite, cal e, I and base~etal sulfides.

Lireui Complex, Nigeria. The Lireui complex is a multiple ring dike located near the southern end of a north-trending zone of Jurassic epizonal, anorogenic ring dikes. Five separate intrusive phases compose the Lireui complex. A uranium-enriched, albite-riebeckite peralkaline gr te (Kaffo Valley granite) is one of the youngest intrusive phases in the sequ ce. This unit exhibits a porphyritic texture and consists of large quartz and orthoclase perthite crystals set in a finer-grained groundmass of albite, riebeckite, and aegerine. Accessory minerals include, fluorite, topaz, cryolite, and pyrochlore. The unit has been extensively albitized; albite has replaced both quartz and orthoclase. Uranium enrichment is caused by the high percentages of disseminated pyrochlore, particularly in the highl albitized zones.

Chemically, the Kaffo Valley granite is characterized by high con centrations of rare-~arth elements, F, Nb, U, Rb, Li, Y, and Sr and by a very low K/Rb ratio. The high agpaitic coefficient (>1.3) is also charac teristic.

Extensive albitization, anomalous trace-element concentrations~ and the low K/Rb ratio all strongly suggest postsolidification modification of the Kaffo Valley granite (autometasomatism). Albitization and the format of pyrochlore occurred when fluids of albitic-acmitic composition "boiled off" the evolving magma and permeated the peralkaline granite during very late stages of magmatic differentiation. This metasomatizing fluid caused extensive recrystallization of alkali amphibole, generation of aegerine, a deposition of pyrochlore.

The Kaffo Valley granite is similar to the Bokan Mountain granite at the Ross-Adams mine in several ways: mineralogic and chemical composition, uranium enrichment in highly albitized zones (Na-rich, K-poor), anomalous! high concentrations of selected trace elements (Nb, Zr, rare-earth element and enrichment of fluorine in uranium-rich zones.

AUTHIGENIC CLASS (360)

Authigenic uranium occurrences are formed by postmagmatic redistribut and concentration of uranium within the parent pluton. Uranium minerals o in veins along shears, fractures, and microfractures adjacent to major she zones. Intersections of shears seem to be the most favorable structural s

29 for B1•condary uranium enrichments. Penec~ntemporaneous gangue minerals ar negligible. Massive, coherent volumes of the host rocks are usually devoi of se"ondary uranium minerals. Alteration of the host rocks is variable. ilt depends on the degree and extent of deuteric alteration and (or) weather!

Authigenic uranium occurrences exist in oversaturated uraniferous pl they xnay also be found in undersaturated, late-stage· differentiates. Pe may be associated with authigenic occurrences although pegmatitic emplace are not involved in the process of uranium concentration.

Authigenic vein occurrences commonly have a restricted vertical e.xt which seems to be related to the ground-water table. Climatic conditions! have affected the mobilization and distribution of uranium in authigenic Authigenic-class uranium occurrences are rare. They represent submargina I pararnarginal deposits.

Example of the Authigenic Class

Daybreak Mine, Washington. The Daybreak mine is located in an al pegmatite phase of a porphyritic quartz monzonite (Loon Lake batholith o older literature), on Mount Spokane, northeast of Spokane, Washington. epizonal, porphyritic quartz monzonite of Cretaceous age intrudes a se of highly metamorphosed Beltian sediments. Garnet-bearing felsic muscovit biotite pegmatites occur in a series of subhorizonal bands averaging les 1 m thick in the mine area. These pegmatites are separated by and alte with bands of hypidiomorphic-granular alaskite. The alternating bands o pegmatite and alaskite are roughly parallel to a series of subhorizontal arcuate joints (contraction fractures?). A few minor pegmatites are di dant to this dominant orientat{on. Pegmatites constitute nearly 50 pe of the rock.

The dominant structure of the mine area is a nearly horizontal sh whose hanging wall is marked by bleached fault gouge and breccia. The itself is largely mylonitic. A series of widely spaced, nearly vertica northwest-trending shears (tension gashes?) occur in the hanging wall. minerals, mostly secondary meta-autunite, are located in the shear zone particularly at the intersection of the northwest-trending shears with major horizontal shear.

Although felbspars in the alaskite are kaolinized, the biotite is Evidence of .extensive hydrothermal alteration is lacking. Meta-autunit occurs along fractures and microfractures in the alaskite and pegmatite fractures and open spaces in the fault breccia. Some autunite masses to 15 in. across. Mineralization is restricted to the near-surface en ment,

ALLOGENIC CLASS (370)

Allogenic occurrences are those in which uranium is hypothE;!sized have been remobilized, transported away from the source pluton, and deposit in suitable nearby environments. Redistribution of uranium, which may be

30 ~.Ia continuous process, takes place in a postmagmatic' environment. Uranium minerals, general~y pitchblende and associated secondary minerals, may be either disseminated in the country rock or concentrated in discordant, brec ciated shear zones. Higher concentrations occur at shear intersections. Associated disse~nated sulfides are common. Contemporaneous gangue mineral are negligible. Host rocks, usually carbonaceous and (or) sulfide-bearing metasediments, normally are highly metamorphosed and commonly show evidence of extensive retrogressive chloritization. Allogenic uranium concentrations are generally shallow.

The relation of allogenic uranium deposits with plutonic igneous rocks uncertain; Although allogenic deposits are located near plutonic ~r hypabys intrusives which have anomalous uranium contents, radiometric ages of crysta ' zation in the plutons and mineralization of the deposits are discordant. gardless, spatially associated plutons may be the sources of uranium in allogenic occurrences. Shear zones in carbonaceous and (or) sulfide-bearing metamorphic rocks adjacent to uraniferous plutons appear to be ideal deposi tional sites for uranium of this class.

Large occurrences of this class represent paramarginal to recoverable deposits.

Selected Example~ of the Allogenic Class

1~ Midnite Mine, Washington. The Midnite mine is located in the Beltain go Formation near the contact of a Cretaceous epizonal quartz monzonite porphyr , approximately 40 mi n?rthwest of Spokane, Washington. The ore, limited to ' pyritic schists and hornfels of the Togo Formation, occurs in a series of saddles between cupolas along a tongue of quartz monzonite. Ore is concentrated in a series of small step faults and shears in the metasediments. se postintrusive shears are barren where they extend into the quartz monzon~te. The orebodies are ellipsoidal in shape and have a nearly horizontal upper surface.

Pitchblende and uranophane are the most common uranium minerals in the mine. Secondary autunite i~ found near the surface. Evidence of extensive hydrothermal alteration is lacking from both the metasedimentary and pluton units.

Although no strong lithologic control over uranium mineral deposition is apparent, most uranit~ occurs in micaceous metasediments; less uranium found in calc-silicate hornfels. A high sulfide content and proximity to t uraniferous quartz-monzonite porphyry seem to be prime requisites for urani enrichment.

Conditions and times of uranium emplacement are uncertain. Uranium de position may have occurred continuously from the time of intrusion to the Holocene.

~ Nabarlek, A~stralia. The Nabarlek uranium deposit is situated in a heavily chloriti~ed shear zone in highly contorted, metasomatized Precambri schists in the Ptne Creek geosyncline, Northwest Territory, Australia. The schists have been intruded by a fluorite-bearing granite which is highly

31 sericit 1 zed a!long the contact. The lent4,cular orebody is truncated at by a thick diabase sill containing serpentinized olivine. The diabase retrogr~ssiv~ly metamorphosed the schists along the contact.

Thl' orebody at Nabarlek cuts across foliation. Pitchblende, the uranium minetal present, is associated with disseminated sulfides and Hematite is qbsent from nonmineralized areas. Ore grade is zonal in cha acter; higher grades are associated with higher percentages of hematite. No mi eralization is found in either the granite or the diabase.

This urqnium occurrence has many similarities with other hydrothe emplaced dep0sits, among which are its occurrence in a shear zone, a ha wall-rock alteration, and the unit-cell dimensions of th~ pitchblende. age of mineralization is 900 m.y., which is significantly younger than underlying granite. There is evidence that the uranium has been remobi several times. The source of the uranium-bearing hydrothermal solutio not known. !hey may have emanated from a deep source other than the magma. The uranium was deposited in a structurally and chemically f e environment.

ANATECTIC C~SS (380)

Uranium' occurrences of this class are found in pegmatites, aplites alaskites of anatectic origin and may be thought of as being partially and partial!~ metamorphic in origin. Uraniferous quartzo-feldspathic occur as tabular units and lens-shaped segregations in migmatitic compl They are normally conformable to foliation, although discordancies are in axial regions of folds.

Anatectic pegmatites are characterized by quartzo-feldspathic mine assemblages.; Ferromagnesian minerals are similar to minerals of the metasediments, although modal percentages differ. The enclosing metase are commonly impoverished in quartzo-feldspathic constituents adjacent felsic segregations. The anatectic segregations are in sharp contact the hosts and show little evidence of contact thermal effects. Euhedr subhedral, primary uranium minerals (uraninite, thorian uraninite, thorite) are disseminated throughout the felsic bodies. Secondary ura minerals may occur in the host metasediments. l\

With increased mobility of the anatectic fluid, pegmatites of I may resemble those of the pegmatitic class. The major distinctions be two are the nature of the ferromagnesian mineralogy and the geometric with the enclosing host. Whereas magmatic pegmatites are spatially a porally ass~ciated with uraniferous plutonic rocks, pegmatites of ana origin need not show such relations.

Anatectic-class uranium occurrences are found in structurally migmatized, uraniferous, metasedimentary terranes. Such environments in root zones of mobile belts. Because of the mobility of uranium in hi metamorphic environments (upper amphibolite to granulite facies~ and i resultant concentration in anatectically derived fluids, anatecijic ura occurrences' may represent paramarginal to recoverable deposits .I

32 !~Selected Examples of the Anatectic Class

Rossing, So~th-West Africa. The Rossing uranium deposit occurs along t e flank of a majoridomal structure in the central region of the late Precambr Damaran orogenic belt, South-West Africa (Namibia). Mineralization is asso ciated with anatectic alaskites whose textures range from pegmatitic to apli ic, These felsic bodies, which range from small secretionary lenses to large intrusive and replacement bodies, display concordant, discordant, and replac - ment relations with complexly folded metasedimentary and metavolcanic schist , gneisses, and marbles of the Khan and Rossing Formations. The alaskitic roc are emplaced along shears, fractures, bedding planes, and axial planes of folds. General rank of metamorphism is the upper amphibolite facies.

At least thtee pulses of regional metamorphism have been recognized the area. A later, superimposed thermal metamorphic event is evident in metasediments adjacent to some of the alaskites. It is particularly p ed in the marbles.

Uraninite, ~hich occurs as small euhedra disseminated throughout the alaskite, constitutes the bulk of the primary uranium minerals. It exists as inclusions in. quartz, feldspar, and biotite and interstitial to and along microfract~res in these minerals. The uraninite is most commonly associated with biotite, apatite, zircon, and sphene. Fluorite is a common accessory. Secondary uranium minerals, which make up as much as 45 percent of the ore, emphasize the importance of secondary-enrichment processes in ~~the deposit. The secondary minerals are not restricted to the alaskites.

The origin of the ore is speculative. Field, petrologic, and chemical data suggest an anatectic origin for the alaskite. Uranium appears to have been concentrated in the anatectic fluid, the location of which may be a function of the ~ranium content of the fused Precambrian metasedimentary units. Other factors, such as vertical zonation caused by chemical fixat of hexavalent uranium in areas of Eh and pH changes, may have played a significant role.

Mont Laurier, Quebec. The Mont Laurier area is located in province of Quebec. This is an Qrea of thick sedimentary accumulations wh have been subjected to high-rank metamorphism and migmitization. Anatectic fusion of uranif1erous biotite gneiss has yielded metamorphic pegmatites wh are enriched in uranium. These metamorphic pegmatites exist in migmatiteli fashion in biotite gneiss, calc-silicate rocks, marbles, metabasalts, and quartzites. They are characterized by sharp, conformable contacts, interna banding and fol~ation conformable with that of the enclosing metasediments, inclusions-of nonrotated xenoliths, and ferromagnesian mineralogies ident with those of the enclosing units. The pegmatites are of granitic composit n and contain thorian uraninite and uranothorite. Sphene, graphite, and mol denite are cormnoin accessory minerals.

Wall-rock alteration and contact-metamorphic effects are lacking. lacking is evidence of hydrothennal or metasomatic, vein-type uranium mine ~ izat ion in the area.

33 REFERE~CES

GENERAL

Bailey, R. V., and Childers, M. 0., 1977, Applied mineral exploration h special reference to uranium: Boulder, Colorado, Westview Press, 2 p.

Barnes, F. Q., and Ruzicka, V., 1972, A genetic classification of urani deposits: Internat. Geol. Cong., 14th, Montreal 1972, sec. 4, p.

Beck, L. S., 1969, Uranium deposits of the Athabasca region, Saskat Saskatchewan Dept. Mineral ReEources Rept ..129, 140 p.

Greenberg, J. K., Hauck, S. A., Ragland, P. C., and Rogers, J.J.W., 197 A tectonic atlas of uranium potential in crystalline rocks of the U.S.: U.S. Dept. of Energy GJBX-69(77), Open-File Rept., 94 p.

Larsen, E. S., Phair, George, Gottfried, David, and Smith, W. L., in magmatic differentiation, in Geology of uranium and thorium, United Nations Internat. Conf. on the Peaceful Uses of Atomic Ener Geneva 1955, Proc., p. 240-247 [i956].

McMillan, R. H., 1977, Metallogenesis of Canadian uranium deposits, in M. J., ed., Geology, mining, and extractive processing of uranium·. Internat. Symposium, Inst. Mining and Metallurgy and Co.mm. of Communities, London, p. 43-55.

Nisldmori, R. K., Ragland, P. C., Rogers, J.J.W., and Greenberg, J. K. Uranium deposits in granitic rocks: U.S. Energy Research and D Adm., GJBX-13(77), Open-File Rept., 298 p.

Rich, R. A., Holland, H. D., and Petersen, Ulrich, 1975, Vein-type ura deposits: U.S. Energy Research and Devel. Adm. GJ0-1640, Open-Fi 382 p.

Ruzicka, V., 1975, New sources of uranium? Types of uranium deposits unknown in Canada: Canada Geol. Survey Paper 75-26, p. 13-20.

Tilling, R. I., 1973, Boulder batholith, Montana: a product of two c aneous but ,chemically distinct magma series: Geol. Soc. America v. 84, p. 3879-3900.

ORTHOMAGMATIC CLASS

Beck, L. S., 1969, Uranium deposits of the Athabasca region, Saskatc n: Saskatchewan Dept. Mineral Resources Rept. 126, 140 p.

Lanphere, M.A., MacKevett, E. M., and Stern, T. W., 1964, Potassium- and lead-alpha ages of plutonic rocks, Bokan Mountain area, Alaska: . cience, v. 145, p. 705-707.

34 REFERENCES (continued)'

MacKevett, E. M., 1958, Geology of the Ross-Adams uranium-thorium deposit, Alaska: United Nations Internat. Conf. on the Peaceful Uses of Atomic Energy, Geqeva 1958, Proc., v. 2, p. 502-508.

1963, Geology and ore deposits of the Bokan Mountain uranium-thorium --- area, southeastern Alaska: U.S. Geol. Survey Bull. 1154, 125 p.

Phair, George, ~952, Radioactive Tertiary porphyries in the Central City district, Colorado, and their bearing upon pitchblende deposition: U. Geol. Surv~y TEI-247, 53 p., issued by U.S. Atomic Energy Comm. Tech. Inf. Serviae, Oak Ridge, Tenn.

---1957, Uranium and thorium in the Laramide intrusives of the Colorado Front·Rangtj!: U.S. Geol. Survey TEI-750, p. 103-108, issued by U.S. Atomic Ener!gy Comm. Tech. Inf. Service, Oak Ridge, Tenn.

Phair, George,.qnd Jenkins, L. B., 1975, Tabulation of uranium and thorium data on th¢ Mesozoic-Cenozoic intrusive rocks of known chemical compo sition in Colorado: U.S. Geol. Survey Open-File Rept. 75-501, 57 p.

Wells, J. D., 1960, Petrography of radioactive Tertiary igneous rocks, Fron Range mine~al belt, Colorado: U.S. Geol. Survey Bull 1032-E, p. 223-2

PEGMATITIC CLASS I Armstrong, F. C., 1974, Uranium resources of the future--"porphyry" uranium .I deposits, ~Formation of uranium ore deposits: Internat. Atomic Ene Agency, Atlitens 1974, Proc., p. 625-635.

Little, H. W., 1970, Distribution of types of uranium and favorable envi for uranium exploration, in Uranium exploration geology: Internat. Energy Agemcy, Vienna 1970: Proc., p. 35-48.

MacKevett, E. M., 1963, Geology and ore deposits of the Bokan Mountain thorium ar~a, southeastern Alaska: U.S. Geol. Survey Bull. 1154,

,I Robinson, S. C., 1960, Economic uranium mineralization in granitic dykes, Bancroft district, Ontario: Canadian Mineralogist, v. 6, pt. 4, p. 51 -521.

Satterly, J., 1956, Radioactive mineral occurrences in the Bancroft area: Ontario Dept. Mines, 65th Ann. Rept., v. 65, pt. 6, p. 1-181.

Wynn-Edwards, H. R., 1969, Tectonic overprinting in the Grenville province, southwestern Quebec: Geol. Assoc. Canada Spec. Paper 5, p. 163-182.

35 II

:II l1 ill REFERENCES (co~tinued) !! II MAGMATIC-HYDROTHERMAL CLASS ~I Becraft, G. E., 1953, Preliminary report of the Comet area, Jefferson Cou,ty, Montana: U.S. Geol. Survey Circ. 277, 8 p. 1 1956, Uranium deposits of the northern part of the Boulder batholith~ ---Montana: Econ. Geology, v. 51, p. 362-374. !Jj Becraft, G. E., Pinckney, D. M., and Rosenblum, Samuel, l963, Geology 'andtl 1 mineral deposits of the Jefferson City quadrang~e, Jefferson and Lew s and Clark Counties, Montana: U.S. Geol. Survey Prof. Paper 428, lOl,p. I Bieler, B. H., and Wright, H. D., 1960, Primary mineralization of uraniuml bearing "siliceous-reef" veins in the Boulder batholith, Montana, Paft II, The ve±ns: Econ. Geology, v. 55, p. 363-382. . !:1

1 Castor, S. B., and Robins, J. W., 1978, Preliminary study of uranium favo . ability of the Boulder batholith, Montana: U.S. Dept. of Energy GJB- 5(78), Open~File Rept., 28 p. ~

Johnson, W., 195~, Geological environments of some radioactive mineral deposits in South Australia: Australian Atomic Energy Symposium, Sydney 1958~~ sec. 1, Geology, p. 35-41. II ·I Parkin, L. W., and Glasson, K. R., 1954, The geology of the Radium Hill ~~ne, I South Australia: Econ. Geology, v. 49, p. 815-825. J,

Rich, R. A., Holland, H. D., and Petersen, Ulrich, 1975, Vein-type urani deposits: U.S. Energy Research and Devel. Admin. GJ0-1640, Rept., 382 p.

Roberts, W. A., 1953, Uranium-bearing deposits west of Clancy, Jefferson ty, Hontana: U.S. Geol. Survey Bull. 988-F, p. 69-87.

Ruppel, E. T., 1963, Geology of the Basin quadrangle, Jefferson, Lewis Clark, and Powell Counties, Montana: U.S. Geol. Survey Bull. 1151,

Sprigg, R. C., 195~, Geology of the Radium Hill mining field: South Aus ralia Geol. Survey Bull. 30, p. 7-50.

Thurlow, E. E., arid Reyner, M. L., 1950, Free Enterprise uranium prospec ,," Jefferson County, Montana: U.S. Atomic Energy Comm. RM0-678, .12 p. issued by U.S. Tech. Inf. Service Ext., Oak Ridge, Tenn.

_____1952, Preliminary report on uranium-bearing deposits of the nort Boulder batholith region, Jefferson County, Montana: U.S. Atomic gy Comm. RM0-800, 15 p., issued by U.S. Tech. In£. Service, Oak Ridge,'Tenn.

36 REFERENCES (continued)'

Tilling, R. I., 1973, Boulder batholith, Montana: a product of two contempo - aneous but chemically distinct magma series: Geol. Soc. America Bull., v. 84, p. 3879-3900.

Whittle, A.W.G., 1954, Mineralogy and petrology of the Radium Hill mining field: South Australia Geol. Survey Bull. 30, p. 51-69

Wright, H~ D., Bieler, B. H., Emerson, D'. 0., and Shulbert, W. P., 1957, Mineralogy of the uranium-bearing deposits in the Boulder batholith,. Montana: U.S. Atomic Energy Comm. NY0-2074, 229 p., issued by Natl. Tech. Inf. Serv., Springfield, Va.

CONTACT-METASOMATIC CLASS

Brooks, J. H., 1975, Uranium in the Mount Isa-Cloncurry district 1 in Knight, C. L., ed., Geology and mineral resources of Australia-and Papua, New Guinea: Australian Inst. Mining and Metallurgy Mon. Ser~ 5, p. 396-398.

Derrick, G. M., 1977, Metasomatic history and origin of uranium at Mary , Kathleen, northwest Queensland: Australian Bur. Mineral Resources, ~ Geology and Geophysics Jour., v. 2, p. 123~130.

Hughes, F. E., and Muqro, D. L., 1968, Uranium ore deposit at Mary Kathleen, in Berkman, D. A., Cuthbert, R. H., and Harris, J. A., eds., Symposium; uranium in Australia: Australian Inst. Mining and Metallurgy, Rum Jungle Branch, p. 45-56.

Ludwig, K. R., and Young, E. J., 1975, Absolute age of disseminated uraninite in Wheeler Basin, Grand County, Colorado; U.S. Geol. Survey Jour. Research, v. 3, p. 747-751.

Matheson, R. S., and Searl, R. A., 1956, Mary Kathleen uranium deposit, Mount Isa-Cloncurry district, Queensland, Australia: Econ. Geology, v. 51, no. 6, p. 528-540.

,I Young, E. J., and Hauff, P. L., 1975, An occurrence of disseminated uraninit iri Wheeler Basin, Grand County, Colorado: U.S. Ge.Jl. Survey Jour, Research, v. 3, p. 305-311.

AUTOMETASOMATIC CLASS

Bowden, P., and Turner, D. C., 1974. Peralkaline and associated ring compl s in the Nigeria-Niger proyince, West Africa, in Sorensen, H., ed., The alkaline rocks: New York, John Wiley & Sons,-p. 330-351~

~MacKevett, E. M., 1958, Geology of the Ross-Adams uranium-thorium deposit, Alaska: United Nations Internat. Conf. on the Peaceful Uses of Atomic Energy, Geneva 1958, Proc., v. 2, p. 502-508.

37 II I II I REFERENCES>. (continued) I! MacKevett; E. M., 1960, Geology of the Ross-Adams uranium-thorium depotit, Alaska: Am. Inst. Mining, Metall. and Petroleum Engineers Trans.~ v. 214, p. 915-919. 1li 1963, Geology and ore deposits of the Bokan.Mountain uranium-thor~~m ___a.rea, southeastern Alaska: U.S. Geol. Survey Bull. 1154, 125 p. 1!1--

1 AUTHIGENIC CLASS ljl 'Ill Norman, W. H., 1957, Uranium deposits of northeastern Washington: Mi1ing Eng., v. 9, no. 6, p. 662-666. ~/: Weissenborn, A. E., and Moen, W. S., 1974, Uranium iP Washington: Wa~hington Div. Mines and Geology Inf. Circ. 50, p. 83-97. II

II! ALLOGENIC CLASS !II II Anthony, P. J., 1975, Nabarlek uranium deposit, in Knight, C. L., ed.~l Geology; and mineral resources of Australia and Papua, New Guinea: Austrflian Inst. Mining and Metallurgy Mon. Ser. 5, p. 304-308. . II

Barrington, J., and Kerr, P. F., 1961, Uranium mineralization at the~--· idnite mine, Spokane, Washington: Econ. Geology, v. 56, p. 241-258. d Ill' Becraft, G. E., and Weis, P. L., 1957, Turtle Lake quadrangle, Washinj~ton: U.S. Geol. Survey TEI-700, p. 98-110, issued by U.S. Atomrl.c Energy Comm. Tech. Inf.. Serv., Oak Ridge, Tenn. 1: ,II Nash, J. T., 1975, Exploration for uranium deposits in metasedimenta~~ rocks in the light of geologic studies of the Midnite mine: U.S. Geo~r· Survey Open-File Rept. 75-638, 4 p. 'II ,,'II _____1977, Speculation on three possible modes of emplacement of ura~ium into deposits of the Midnite mine, Stevens County, Washington: .jiU.S.

Geol. Survey Circ. 753, p. 33-34. 1 ! II! Nash, J. T., aqd Lehrman, N. J., 1975, Geology of the Midnite uraniu. mine, Stevens County, Washington--a preliminary report: U.S. Geol. ' y Open-File Rept. 75~402, 36 p.

Norman, W. H., 1957, Uranium deposits of northeastern Washington: Eng., v. 9, no. 6, p. 662-666.

Sheldon, R. F., 1959, Midnite mine--geology and development: Mi v. 11, no. 5, p. 531-534.

Weissenborn, A. E., and Moen, W. S., 1974, Uranium in Washin~ton: shington Div. Mines and Geology Inf. Circ. 50, p. 83-97.

38 'I·.' .li !

REFERENCES (continued)

1/!

AJ.~ATECTIC CLASS II

Armstrong, F. C., 1974, Uraniwn resources of the future--"porphyry" uranium ,II deposits, in Formation of uranium ore deposits: Internat. Atomic Energl'.r· Agency, Athens 1974, Proc., p. 625-634. · i, il Berning, .J., Cook, R., Hiemstra, S. A., and Hoffman, U., 1976, The Rossing jl uranium deposit, southwest Africa: Econ. Geology, v. 71, no.,l, p. 351~ 368. !ij

Kish, L., 1975, Radioactive occurrences in the Grenville province of Quebec, I' I Mont Laurier-Cabonga district: Quebec Dept. Na~. Resources Mining Dept'

Service, DP-310, 30 p. 1 1

Rogers, J.J.W., 1977, Preliminary report on visit to southwest Africa, in rll

Nishimori and others, Uraniwn deposits in granitic rocks: U.S. Ener · ilr Research and Devel. Adm. GJBX-13(77), Open-File Rept., p. A3-l-A3-20 !I! von Backstrom, J. 1970, The Rossing uranium deposit near Swakopmund, II W., IIi southwest Africa, in Uranium exploration geology: Internat. Atomic Energy Agency, Vienna 1970, p. 143-150. !I:1'1 !I -'Wynn-Edwards, H. R., 1969, Tectonic overprinting in the Grenville province, ill I southwestern Quebec: Geol. Assoc. Canada Spec. Paper 5, p. 163-182. ~

II~r~

39/40 CLASSIFICATION OF VOLCANOGENIC URANIUM DEPOSITS

R. C. Pilcher

ABSTRACT

Considerations of volcanogenic facies and their associated tempera pressure environments are the bases for classification of volcanogenic uran deposits. · The volcanogenic system is a conceptual framework for ~tructural evolution and subsequent development of consanguineous lithologies favor for uranium deposition. Caldera formation, collapse, and resurgence are uranium-mobilizing and uranium-concentrating mechanisms.

Classification of volcanogenic uranium occurrences is based on charac istic ore-forming processes operating during different evolutionary stages volcanogenesis. Volcanogenic uranium deposits are divided into four clas

The initial-magmatic class comprises occurrences formed during crys tallization of the initial magma. Uraniferous subvolcanic intrusives and vitric and crystalline effusives are members of this class.

Pneumatogenic occurrences form during late-stage intrusive events of caldera formation and during the early posteruptive history of ash-flow tuf Pitchblende vein deposits in breccia pipes and subvolcanic intrusives are members of this class.

Hydroauthigenic occurrences form during degassing associated with pr devitrification of ash flows. Occurrences of uranosilicates in lithophysae flattened pumice fragments, and resorbed phenocrysts belong to this class.

The hydroallogenic class comprises occurrences formed by uranium-enric fluids released from intrusives and effusive flows, or by uranium-enriched ,! ground water migrating into porous and permeable intracaldera facies. Depo of uraniferous amorphous or microcrystalline silica or disseminated epigene minerals are members of this class.

·'

41 ·~ :1 ;

INTRODUCTION

Although information on volcanogenic processes is abundant and app ~cable to ore genesis, specific information regarding uranium deposits in volc~pic rocks is scarce. Volcanic processes responsible for structural ¢voluti r of a caldera and the development of its component lithologies are responsib~e for subse.quent uranium mineralization. A volcanogenic system is a framewor I which relates mineralization within a given facies to the dynamics of host-ro ~ genesis and subsequent alteration. Classification of volcanogenic uranit.Im depo11.'~ts is based on processes and responses resident in a volcanogenic system. ~ . II

!I' THEORETICAL BASIS FOR CLASSIFICATION

A study of volcanic centers throughout the world led Smith and Bai ley (1968) to develop a model of resurgent-caldera formation. They recogni.ed seven .distinct evolutionary stages in resurgent-caldera development: 'I

I ·I 1. Regional tumescense and generation of ring fractures

2. Caldera-forming eruptions

3. Caldera collapse

4. Preresurgence volcanism and sedimentation

5. Resurgent doming, intrusion, and effusion

6. Major ring-fracture volcanism

7. Terminal solfatara and hot-spring activity

This model relates the regional tectonic framework t of consanguineous lithologies. Tectonics and magmatism responsible for ca dera formation, collapse, and resurgence are uranium-concentrating m~chani They simultaneously generate structures and lithologies favorable for deposit ion •

. Concentration of uranium in economic quantities depends on the reg tectonic setting, magilla compositio~and evolutionary stages of ¢aldera ormation. The volcanogenic system, a series of interrelated processes, controls evolution of the structural and lithologic environments in which uran may migrate and become concentrated.

Magmatic differentiation concentrates alkalis and uranium tage derivative magmas. Late-stage alkalic effusives and intrusives have ical and physical properties necessary to generate, concentrate, and trap u ium- enriched fluids. Taphrogenic zones are favorable for the gener.tion o with these characteristics.

42 I 'I_,' Uranium escaping from the magmatic environment becomes oxidized and be concentrated and reduced in porous and permeable environments within a ii volcanogenic system. Mathews and Pilcher (in prep.) propose a model in whic~ hexavalent uranium may be reduced without a chemical reductant in th~ syste ~ The oxygen fugacity of a system may be lowered by dissipation of heat and (o,~) release of confining pressure. Upward migration of magma decreases the con ' fining pressure and slowly decreases the temperature. Regional tume~cence, fracturing, and effusive events are also important temperature-lower~ng pres urc-

release mechanisms. Thus, confining pressures on the magma chambers and 1

their subsequent release play a significant role in mobilization and 1 ment of uranium in a volcanogenic system. i

Both confining pressure and temperature decrease with upward migration of a magma. A temperature-pressure (TP) environment eventually is reached which uranium minerals are stable. Resultant mineralization may occ~r wit either the country rock or the chilled, brecciated margins of subvol~anic intrusives. Eruption may produce lava and ash flows which behave asj isolat thermal, differentially pressurized, chemically active cells. Thin,' fluid lava flows may rapidly degas and lose uranium-enriched volatiles. Cpnvers ash-flow and air-fall tuffs permit internal migration and accumulatipn of uranium-enriched fluids.

Physicochemical properties of the magma govern the location and nature mineralization. Physical alteration of an ash flow is an additional intern mechanism for uranium mineralization. The temperature above which an ash flow remains fluid enough to flow and undergo welding is determined by c sition. Viscosity and amenability to welding affect volatile retent~on and the time available for uranium concentration. Temperature equilibration differential confining pressures are affected by viscosity and thick~ess variations in the flow. These are related to both subflow topograph~ and r of accumulation of pyroclastic material.

Porosity and permeability, caused by opening of lithop.hysae and fract g of the cooling unit, create an environment in which temperature and pressur are released sufficiently to allow internal deposition of uranium minerals. , Erosion of the volcanic pile and deposition of volcaniclastic sediments ere ' a new receptacle for escaping fluids and an even lower TP environmen,t for uranium deposition.

CLASSIFICATION

A volcanogenic system is the basis for this classification. It reflec characteristic ore-forming processes during different stages of volcanogene Volcanogenic uranium deposits are divided into four classes.

The initial-ma~atic class comprises occurrences formed during frystal lization or-the 1n1t1al magma. No posteruptive concentrating mechanrsms ar active. Syngenetic dissem1nations of uranium and uranium-bearing mil erals \,..,..formed by liquidus crystallization within subvolcanic intrusives andi, vitric (or) crystalline effusives are members of this class. '

43 I The pneumatogenic class comprises' occurrences formed by uranium-belfiring gases. These gases emanate from the magma during late-stage intrusive i' vents of caldera formation or are released during the early posteruptive histI ry of ash-flow tuffs. Pitchblende vein deposits in breccia pipes within ash~ low tuffs and subvolcanic intrusives are members of this class.

The .hy_droauthigenic class comprises occurren'ces formed by degassi ' and condensation of fluids released during primary devitrification 9f ash-~ ow cooling units or other volcanic rock bodies. Uranosilicates within li~ ophysae, flattened pumice• fragments, lithic fragments, and other porous .jind per 1 able zones are members of this class. I

Hydroallogenic class occurrences form by migratio~ and entrapment fluids released from volcanic effusives and intrusives into adjacent p and permeable rocks. Uranosilicates in rocks surrounding late-stag~ intru ives and products of uraniferous silicification (opalization) of intracalde~~ or flanking sediments are members of this class. i

INITIAL-MAGMATIC CLASS (510)

Initial-magmatic occurrences are syngenetic disseminations! of ur and uranium-bearing minerals formed by liquidus crystallization within su intrusions and effusives. Uranium occurs as finely disseminateti uran in rock-forming and accessory minerals, and in vitric portions o~ effusi

Occurrences of this class are found in silicic and feldspathoidal of alkaline affinity. These late-stage magmatic derivatives occur within genic zones and are products of magmatic and tectonic processes associ with subduction. Magmas produced by subduction of oceanic plates bee gressively enriched in alkalis and lithophile elements with different! and distance from the subduction zone. Uranium enrichment may be furt as a result of contamination by crustal rocks.

Civetta and Gasparini (1972) noted a progressive enrichmen~ of u in volcanic rocks with distance from the west-northwestward subauction oceanic plate in the southeastern Tyrrhenian Sea. The volcanic, rocks progressively less silicic and more uraniferous northward from Pantell (sadie rhyolites; 15 ppm U) to the Sabatini Volcano (trachytes and al trachytes; 21 ppm U) to the Vico Volcano (trachytes and trachyphonolit ppm ·U).

Zentilli and Dostel (1977) noted a similar enrichment pattern in Central Andes. They stated: "K concentration systematically increase distance from the subduction zone while the highest U abundances are f in the rocks overlying the thickest segment of the continental crust"

Additional recycling and concentration of initial-magmatic! urani occur during caldera evolution. Subcaldera temperatures probab~y are enough to fuse the overlying rocks. Heat from subcaldera intru~ives re mobilize uranium in the overlying rocks, and drive it away from the in ives.

44 'I,,._, Initial-magmatic occurrences are analogous to those of the orthomagmati class (Mathews, this volume). They are products of identical magmatic proce s. Assignation of an occurrence to the initial-magmatic class should be based o" a demonstrable association with volcanic features and (or) processes.

One example of the initial-magmatic class of occurrences was described y Cupp and others (1977), who investigated the uranium favorability of the Har ford Hill Rhyolite. This unit lies within the Basin and Range province, a taphro genic region east of the Pacific plate subduction zone. Several small uranif.m occurrences and prospects were sampled and described. A collapse caldera wa, proposed to explain the stratigraphy and structural features in this area. he caldera, a semicircular feature approximately 25 mi wide, is locat'ed north o, Sparks, Nevada. .,

The Hartford Hill Rhyolite comprises a thick {>4,00Q ft) series of ash flow sheets. Their composition varies from andesitic to rhyolitic. They ra ge in age from Oligocene through early Miocene. Several rhyodacite and andesid subvolcanic intrusives intrude the ash-flow sheets in the ring-fracture of the caldera. Uranium content of the sequence ranges from 10 to 40 ppm. thorium-to-uranium ratios for various cooling units within the Hartford sequence range from about 2.0 to 4.0. II Although the probability of discovering a large deposit is low, numerojp small deposits have been found. Conversely, the probability of discovering .I large uranium deposits within the overlying Truckee Formation, where several! small occurrences have been found. is high. The Truckee Formation representlf sediments accumulated in the intracaldera moat during the resurgent phase ofli caldera formation. The resulting sedimentary units acted as intracaldera il conduits and receptacles for mineralizing fluids (see hydroallogenic class, I p. 48-49) . !

This example emphasizes the importance of recognizing occurrences of t ·~ initial-magmatic class and their relationship to other environments of a ,f volcanogenic system. Although initial-magmatic occurrences generally are economically submarginal, they may be sources for later remobilization and concentration of uranium.

PNEUMATOGENIC CLASS (520) ·' Pneumatogenic occurrences are formed by uranium-enriched gases evolved

during late-stage intrusive events of caldera formation or during the early 1 posteruptive history of ash-flow tuffs. Pitchblende, the dominant uranium J mineral, occurs in veins, breccia pipes, and stockworks in subvolcanic intri,·.~ sives or ash-flow tuffs. Pitchblende deposition is caused by entrapment of !I uranium-enriched gases in regions of lower temperature and pressure. I Zones of dilatancy created during caldera evolution are excellent sites jlor pitchblende deposition. Fracturing of the caldera floor and the margins of I subvolcanic intrusives creates a continuous conduit for migration of uraniu - ·V enriched gases emanating from a magma. This ring-fracture system is also t pathway for postintrusive eruptions. The porosity of ash flows may be incr 1 sed locally by tensional and cooling fractures formed during the early posterup ve

45 history. Uranium-rich gases are tr~ped in ash flows formed during s phase. The gases may subsequently migrate into more porous zones.

In a comparative study of the glassy and crystalline portions o a volcanic rock, Rosholt and others (1971) noted that loss of uranium and fluor ''ne are positively correlated during crystallization. Evidence suggests tha UF6 is one of the volatile gases released. I

Fluorite-pitchblende zonation in pneumatogenic vein deposits of the suggest that fluorite and pitchblende are deposited sequentially. concentrated in the lower part of the veins. Its abundance decrea Conversely, pitchblende is more abundant higher in the veins. This 1 onation suggests that UF 6 may diss~ciate by reaction witb the wall rock and ecipitate fluorite. The liberated U 6 may bypass the fluorite depositional ironment. and may be mechanically reduced and deposited in the lower-TP envi UIILUL<:::ut 0 f the upper part of dilatant zones. If UF 4 is the volatile gas being 1 the process is simplified because the uranium need not be reduced.

An example of pneurnatogenic uranium deposits within is taken from Vlasoz and others (1966). The location of is not known; it is described as a "volcanic depression" region of persistent caldera development.

The pitchblende deposits occur in subvolcanic andesite-prop which invaded previously deposited flows and volcaniclastics. Emp the intrusives accompanied large-scale ring fracturing and reactiva older block faults; extensive dikes formed in large ring fractures. cross-sectional diameter of the intrusive is 2 km.

Steeply dipping, en-echelon fractures of variable displacement :i ccurred within the early effusive rocks. Displacement is as much as an ord r of magnitude greater at the base than at the top of these units. Fra the subvolcanic intrusive are less steep and show smaller displac Fracturing around the margin of the intrusive is most pronounced the base and the upper subvolcanic neck. Open space created by these fract the orebody geometry.

The uranium deposits of this system occur along the margins ofi 1 the sub volcanic intrusive and extend from the base to the top of the intru ive body in envelope fashion. Ore zones at the base of the intrusive are rt, thin, individual veins. Zones in the middle of the intrusive are wider extend several meters into the country rock. The upper zones are charact by thinner, more laterally extensive veins.

Paragenesis is complex. It is difficult to decipher because to genic deposits are preceded by magmatic-hydrothermal carbonate-pitchbl blages and followed by pegmatitic quartz-barite-fluorite-chlorite Regardless, the apparent paragenetic sequence in these uranium-bea is from hematite to pitchblende to pyrite. This is consistent wit PI-release model of pitchblende deposition that the author and G. are proposing.

46 '- ~~ Pneumatogenic deposits may also occur in effusives. Two important exampl are the pitchblende deposit of Zletovska Reka in northeastern Macedonia, Yugoslavia, and the breccia-pipe deposit in the Nopal Formation of the Sierra Pena Blanca, Chihuahua, Mexico. Pneumatogenic deposits such as these are economic because of high concentration (as much as 20% U~0 8 ), and predictable geometry.

HYDROAUTHIGENIC CLASS (530) creat=~d~;·~~~!;:~~~n°~~u::~:~~=b~~m:~!~~c;~~=~e~~cl~:~~;~~~~~a~:~i~~e::i~~d in pores within pumic fragments. The uranosilicates are deposited from siliceous uranium-enriched fluids that were condensed from gases entrapped during erupti~n and from gases released during primary devitrification of ash flows or other if volcanic rocks.

Entrapped gases and gases released during devitrification migrate toward i! lower-TP environments (porous and permeable lithic fragments, pumic fragments,:lf resorbed phenocrysts, and brecciated zones). Gases released during devitrifi~jl

1 cation of spherulites often form gashes above the spherulites and may develop , well-formed lithophysae. The lithophysae are receptacles for migrating fluid~!

and sites for uranosilicate deposition. 11

The composition of the fluids is variable; they are silica and alkali II \q;nriched. Minerals infilling lithophysae suggest that the fluids are also li rich in iron, molybdenum, and uranium. As in the pneumatogenic class, these fluids probably have a .significant amount of dissolved metal halides. :li if I

Mineralization occurs when uranium-enriched fluids are concentrated in 1)) porous zones and undergo cooling and depressurization. Fluids are collected in thick, viscous cooling units and in those parts of cooling units which are locally thickened by filling subflow topographic lows. Rapid degassing, as indicated by tumuli (blister cones), minimizes the possibility of uranium mineralization. Anderson (1975) noted that unmineralized areas of the Buckshot Ignimbrite are marked by abundant silicified tumuli, which suggest 11 that uranium-bearing volatiles were not retained long enough for condensation1l

and precipitation of uranosilicates. rf

One example of the hydroauthigenic class of deposits is the Mammoth Prospect, Presidio County, Te.xas. The late Eocene or early Oligocene Buck shot Ignimbrite is a_comenditic ash-flow tuff in the Trans-Pecos volcanic field. It represents a simple cooling unit. Uranium mineralization occurs in densely and partially welded zones of the Buckshot Ignimbrite (Anderson, 1975). At the Mammoth Prospect, the Buckshot Ignimbrite is a densely welded basal vitrophyre approximately 1 m ,thick. This zone contains 2 to 3 percent crystals, 2 percent volcanic-rock fragments, and traces of clinopyroxenes se in a glassy groundmass. Overlying the basal vitrophyre is a 0.5-m zone of pink spherulites (averaging 2 to 3 rom in diameter) set in a brown, densely welded matrix. Vesicles up to 10 em in diameter are present in this £one. ~ verlying the spherulitic zone is a 2-m-thick, reddish-brown, densely' welded ~uff containing abundant lithophysae gashes near the top. Densely welded tu 1.5 m thick, forms the upper portion of the unit and is characterized by

47 numerous gashes and well-formed lithophtsae. The matrix in this zone consists of sanidine and quartz. ''Uranophane occurs in the Buckshot as acicular crystals filling lithophysal cavities, pore space filling in volcanic rock fragments, and in flattened vesicles in pumice lapilli within the zones of partial welding" (Anderson, 1975; p. 106). Ore grade in this deposit is 0-27 percent u,o •.

Economics of hydroauthigenic uranium occurrences are variable. If degas sing is rapid, mineralization is slight. Conversely, if uranium-enriched volatiles collect in relict and newly formed pore spaces, uranosilicate min eralization may create economic deposits. Tectonic setting, lithology, and type of mineralization of the Mammoth prospect are similar to some of the deposits in the Sierra Pena Blanca, Chihuahua, Mexico.

HYDROALLOGENIC CLASS (540)

Hydroallogenic occurrences are epigenetic concentrations of uranosilicates(' uraniferous microcrystalline silica, and uraniferous amorphous silica in porous.'· and permeable host-rock environments in the volcano system. They are formed by the entrapment of fluids released from volcanic effusives and intrusions and (or) from the redistribution of syngenetic uranium by ground water.

Volcanic rocks lacking properties necessary for concentration of siliceous, uranium-enriched fluids may transmit the fluids into adjacent intracaldera rocks or flanking volcaniclastic facies. Uranosilicate minerals derived from small shallow intrusives are restricted to narrow peripheral zones because the fluids, heat, and pressure differential are insufficient to drive the uranium far from the source. Moderate-temperature fluids escaping from rhyolite flows and ash-flow cooling units may migrate through subjacent vol caniclastic rocks. Hydroallogenic minera}jzation may occur anywhere within the caldera. Diatomites formed in the intracaldera moat are particularly susceptible to this type of mineralization.

Juvenile fluids migrating in an open system and waters of surficial origin carry uranium in its hexavalent state. Consequently, mineralization occurs in the form of uraniferous silica (opal or chert), uranosilicates, and (or) other epigenetic uranium minerals such as autunite, torbernite, soddyite, and carnotite. The type of uranium minerals deposited depends onfue TP environment of the host rock and the availability of complexing ions.

Economic pot~ntial of hydroallogenic deposits is highly variable because of compositional variations in the transporting fluids and the host rocks. Uranium concentration ranges from a few hundredths to 2 or 3 percent U3 0 8 • Mineralized areas vary from a few square meters to several square kilometers.

An example of hydroallogenic occurrences is the radioactive opal that occurs in tuffaceous beds of the late Miocene Virgin Valley Formation in the Virgin Valley area, Humboldt County, Nevada. The Virgin Valley Formation comprises a sequence of fluvial and lacustrine sediments interbedded with tuff. This sequence of volcanogenic facies is typical of tnoat-filling sediments within calderas. Locally, the Virgin Valley Formation has been extensively silicified.

48 ' ~ \.; Cupp and others (1977) report a gentle, northwest-trending syncline in tile Virgin Valley Formation. Prominent intraformational deformation and the upen fold may have been caused by the doming that preceded resurgent intra caldera volcanism. Such deformation could lead to damming and ponding of fluids and subsequent entrapment of uranium within the silicified beds. Gra of mineralization at the Virgin Valley prospects ranges from 0.002 to 0.2 percent U30e.

Although few data are available, Pantie and others (1965, p. 61) noted that the Spancevo deposit of the Kratovo-Zletovo volcanic area of northeaste Macedonia (Yugoslavia) contains a "rich concentration of secondary,minerals associated with the opalized agglomerated tuffs . • • running from a few . hundredths of one percent up to more than 1 percent. Autunite, torbernite, uranophane are the identified uranium minerals." This deposit is similar to occurrences in the Virgin Valley area.

49 REFERtNCES

GENERAL

Fenner, C. N., 1933, Pneurnatolytic processes in the formation of rninera s ., and ores, in Ore deposits of the western states (Lindgren volume): ' New York, Am. Inst. of Mining and Metall. Engineers, p. 58-106.

Locardi, E., 1977, Recent volcanoes and uranium mineralization~, in tion and evaluation of uraniferous areas: Internat. Atomic Energy Vienna 1977, Proc., p. 229-239.

Rosholt, J. N., Prijana, and Noble, D. C., 1971, Mobility of uranium thorium in glassy and crystallized silicic volcanic rocks: Geology, v. 66, p. 1061-1069.

Ross, C. S., and Smith, R. L., 1961, Ash-flow tuffs: their relations and identification: U.S. Geol. Survey Prof. 81 p.

Smith, R. L., 1960, Ash flows: Geol. Soc. America Bull., v. 71, no. 6 p. 795-842.

Smith, R. L., and Bailey, R. A., 1968, Resurgent cauldrons, in Coats, R. , Hay, Richard, and Anderson, Charles, eds., Studies in volcanology Geol. Soc. America Mem. 116, p. 613-662.

Torres, R. R., Dominguez, R. Y., Aguirre, R. C., and Constantino H. E. S. E., 1976, Rocas volcanicas acidas y su potencial como objetivos para 1 prospectar urania [Acidic volcanic rock and its potential as an o jective for uranium prospecting], in Exploration for uranium ore deposits Internat. Atomic Energy Agency, Vienna 1976, Proc., p. 601-623.

Zielinski, R. A., 1977, Uranium mobility during interaction of rhyolit c glass with alkaline solutions: dissolution of glass: U.S. Geol. Survey Open-File Rept. 77-744, 36 p.

INITIAL MAGMATIC CLASS

Civetta, L., and Gasparini, P., 1972, A review of U and Th distribut recent volcanics from southern Italy: magmatological and geoph implications, in Adams, J.A.S., Lowder, W. M., and Gesell, T. F. The natural radiation environment II: Second Internat. Symposium

1 , the Natural Radiation Environment, Houston 1972, Proc., p. 483-5 1 I' issued by Natl. Tech. Inf. Serv., Springfield, Va. ! I Cupp, G. M., Leedom, S. H., Mitchell, T. P., and Allen, D. R., 1977, uranium deposits, and uranium favorability of the Hartford Hill and Truckee Formation, southeastern Washoe County, Nevada, and e stern Lassen County, California: U.S. Energy Research and Devel. Adm. GJBX-16(77), Open-File Rept., 61 p.

50 REFERENCES (continued)

Zentilli, M., and Dostal, J., 1977, Uranium in volcanic rocks from the Central Andes: Jour. of Volcanology and Geothermal Research, v. 2, p. 251-258.

PNEUMATOGENIC CLASS

Rosholt, .J. N., Prijana, and Noble, D. C., 1971, Mobility of uranium and thorium in glassy and crystallized silicic volcanic rocks: tcon. Geology, v. 66, p. 1061-1069.

Vlasoz, V. P., Volovikova, I. M., Gladyshev, G. D., Kazhdan, A. B., Laverov M. P., Mel'nikov, I. V., and Tananayeva, G. A., 1966, The geology of

uranium-molybdenum ore formation beds [translation]: Moscow, The 1 Atomizdat Publishing House, translation issued by Oak Ridge Natl. Labs', ORNL-tr-4349, p. 47-61.

HYDROAUTHIGENIC CLASS

Anderson, W. B., 1975, Cooling history and uranium mineralization of the Buckshot Ignimbrite, Presidio and Jeff Davis Counties, Texas [M. A. 'l.l thesis]: Austin, Univ. Texas, 135 p.

HYDROALLOGENIC CLASS

Cupp, G. M., Leedom, S. H., Mitchell, T. P., Kiloh, K. D., and Horton, R. 1977, Preliminary study of the favorability for uranium in selected areas in the Basin and Range: U.S. Energy Research and Devel. Adm. GJBX-74(77), p. 4-13.

Pantie, R., Radusinovic, D., Sikosek, B., Obrenovic, M., 1964, Uranium de its in Tertiary volcanic rocks of northeastern Macedonia, in Nuclear Fuels - III Raw Materials: Peaceful Uses of Atomic Energy-,-v. 12, Geneva 1964, p. 55-63.

51/52 CLASSIFICATION OF URANIUM DEPOSIT~OF UNCERTAIN GENESIS

Geoffrey W. Mathews

ABSTRACT

Uranium-bearing veins not directly related to sedimentary, volcanon~ .. ~~~~ or plutonic igneous processes are classified according to their primary spat 1 associations and the host-rock type. Three classes are recognized:' unconfo ty related deposits, vein-type deposits in metamorphic rocks, and vein-type deposits in sedimentary rocks.

Uranium veins and vein systems are narrow, tabular bodies with parall or subparallel walls. They occur in faulted, fractured, and brecciated zone in sedimentary rocks and in retrogressively metamorphosed, chloritized meta sedimentary rocks. Uranium veins contain pitchblende and varying amounts of sulfides and sulfarsenides and are commonly associated with pervasive hema titization.

Uranium deposits of uncertain genesis consist of pitchblende dissemina and fracture fillings closely associated with major structural zones. Urau~~~ f, minerals occur in satellitic shears and seem to be at least partially contra ~~by lithology. Vein-type uranium deposits in metamorphic and sedimentary roc often extend to great depths, whereas unconformity-related deposits are re stricted to within a few hundred feet of the unconformity.

Unconformity-related deposits and vein-type deposits in metamorphic ro are subdivided into monometallic and polymetallic subclasses. is based on the presence or absence of economic concentrations of metals ot than uranium. Because of their limited occurrence, vein-type uranium deposi s in sedimentary rocks are not subdivided.

53 INTRODUCTION'

The classification of uranium vein deposits that are not directly to sedimentary, volcanogenic, or plutonic igneous processes (see other pers in this volume) is the subject of this report. Deposits included in classification are some of the "hydrothermal vein" deposits of Rich (1975), some chemical low- to moderate-temperature and moderate- to temperature deposits of Barnes and Ruzicka (1972), the structure- or ture- contro1led deposits of Bailey and Childers (1977), the "metamorphic othermal" deposits of Cornelius (1976) and Beck (1970), and the large "unconfo of McMillan.(1977).

GENERAL DISCUSSION

Uranium veins are narrow, tabular bodies with parallel or subpar walls. They occupy or are adjacent to closely spaced fracture syst brecciated or mylonitized zones. Pitchblende, the dominant ura.nium al, occurs as open fracture fillings, as coatings on breccia fragments, disseminations and replacements near the fractures.

Genesis of these deposits is a matter of continuing cont.roversy Langford, 1974, 1977; Morton, 1976; Knipping, 1974; McMillan, 1977). less of the origin of these deposits (which perhaps should be consid an individual basis rather than collectively), several aspects must in regarding their genesis. According to Rich and others (1975), d of an epigenetic uranium-bearing vein requires:

1. A source of leachable uranium.

2. A source of oxidizing solutions.

3. A reducing agent.

4. A hydraulic setting in which large volumes of uranium-bear solutions are channeled through a relatively small volume of rock.

To this list must be added a suitable site for pitchblende depos tion, that is, an appropriate• lithology in dilatant zones.

SOURCE OF LEACHABLE URANIUM

A prime requisite in the development of epigenetic uranium vein eposits is a source of leachable uranium. Granitic rocks constitute an a · te source of uranium because they contain an average of 5 ppm. Some may con over 100 ppm uranium. Granitic rocks generally have low percentages of reduc g minerals (ferromagnesian silicates), which may be important in allowing oxidi : uranium to be removed from the rock. Leachability of uranium from silicic i 1 has been demonstrated by Larsen and others (1956). They have shown 98 percent of the uranium in major rock-forming minerals of the Sout

54 ' l_.~ California batholith may have been leached by dilute acid solutions. Altho h the amount of uranium in silicic minerals is generally low (<5 ppm), their large volume in granitic rocks may release an appreciable quantity of urani to oxidizing solutions. In general, one might consider approximately half f the uranium in a granitic rock to be leachable (Barbier, 1974).

A potential source rock need not contain anomalous uranium. Minor leaching may release a significant amount of uranium from an exceptionally

small volume of rock. For example, 26,000 lb U5 0 8 could be released by leaching an average of 5 ppm uranium from a volume of rock measuring 300 X 300 X 8.5 m (7.7 X 10~ m~). However, the assumption of leaching uranium f the entire volume of rock in this example may be unrealistic. Leaching is governed largely by the distribution of channelways within the rock. There fore, in addition to considering the nature of possible source rocks, one must also be concerned with accessibility of the uranium.

Granitoid rocks are not the only sources of leachable uranium. Sed tary rocks contain variable amounts of uranium. Shales, for example, cont an average of 4 ppm uranium; some black shales may contain in excess of 1,

ppm uranium locally. However, because most major uranium vein deposits are 1 confined to igneous-metamorphic terranes, sedimentary source rocks are prob ably not volumetrically significant. Conversely, their metamorphic equival ts may be adequate source rocks.

Metamorphism may mobilize uranium. Hydrothermal solutions derived by metamorphic processes may concentrate syngenetic uranium into veins or into more enriched source regions. Zhukova (1973) noted that metasedimentary an metamorphosed igneous rocks of the Ukrainian Shield contain below average ium contents. She furtner noted that preorogenic rock units are characteristic low in uranium, whereas late-orogenic rocks contain three to four times the average uranium content of the shield. She attributed this distribution. to "geotectonic factors."

L. Tremblay, of the Geological Survey of Canada, Ottawa, at a seminar uranium ore genesis held at McGill University (1978), suggested that the source of the uranium in the veins of the Beaverlodge area was the highly granitized Fay complex of the Tazin Group. He proposed a model of a urani cycle in which syngenetic uranium was remobilized and concentrated in anat pegmatites by metamorphism and granitization. The uranium was later redist buted into veins by hydrothermal solutions. At the same seminar, R. Munday of the Saskatchewan Mining Development Corp., noted the presence of uranife anatectically derived pegmatites in the Wollaston, Mudjatik, and Virginia River domains on the south side of the Athabasca basin. This type of pegma concentration may be the source of the uranium in the Athabasca-rim deposit

Rocks associated with uranium veins throughout the world lend credence the hypothesis that granites and silicic metamorphics are the dominant sour for uranium in these deposits. Rich and others (1975, Table 2-1, p. 17) no the association of vein-type uranium deposits with "granite" throughout the world. Although this association is widespread, these authors (p. 97) caut that granites do not constitute the only source for uranium.

55 SOURCE OF OXIDIZING SOLUTIONS

Effective transport of uranium by aqueous solutions requires co within the hematite stability field (Rich and others, 1975). The so such aqueous solutions is problematic because achievement and mainte high f0 2 is a limiting constraint. A·uranium-leaching-and-transport may be surface-derived water, connate or juvenile water, or water rel during metamorphism. Any combination of these may prevail. A leac solution may migrate upward, downward, or laterally, and it may be hot or cold

Aqueous solutions must be oxidizing in order to take up and t uranium. Surface waters, those equilibrated with atmospheric be sufficiently oxidizing to cause significant dissolution of uranium. Solutions of deep-seated origin must be oxidized in and transport uranium.

Rich and others (1975) noted that typical hydrothermal solutions tain sufficient reduced sulfur to place them in the pyrite stability field they possess f0 2 values below the magnetite-hematite boundary. Such thermal solutions are incapable of oxidizing and leaching uranium. oxidizing, they must be either mixed with surface water or oxidized with rock units through which they percolate. Oxidized rocks capable the f0 2 of a common hydrothermal aqueous solution to values necessary development and transportation of hexavalent uranium are not common. bed sequences are the most likely to accomplish this. Solut~ons pass 1 through an oxidized aquifer might increase in f02 until they are in equilibr with the contained hematite. The degree of interaction between the solutions the red beds and the composition of the solutions prior to entering the r are controlling factors (Raymahashay and Holland, 1969).

No data are available to prove that the f0 2 of reduced subsurfac can be raised sufficiently to leach uranium by mixing with oxygenated waters. The oxidizing potential of the resultant solution depends on nature and relative amounts of the two types of water being mixed. and Ohmoto (1973) demonstrated that surface water can be involved in veins. McMillan (1977) noted that the lack of uranium vein deposits age is probably due to the lack of free oxygen in the Archean atmo Therefore, surface waters may be essential in the development of uran Alternatively, since oxidized sedimentary units could not form prior "oxyatmoversion," all Archean aqueous solutions must have been red regardless of their origin• or the rocks through which they percolated •

REDUCING AGENTS

Pitchblende is the dominant uranium mineral in veins. Brannerit occasionally present (for example, in the lower levels of the Fay mines in the Beaverlodge area). Most of the uranium in pitchblende brannerite is in the tetravalent oxidation state. Because uranium is st effectively transported in its hexavalent state in aqueous solutions, eduction is necessary for precipitation of pitchblende.

56 ' l.1 Several common reductants (such as ferrous-iron-bearing minerals, sulf s, and graphite) might decrease f0 2 in uranium-transporting solutions if they present in sufficient quantities. Pitchblende is variously associated with ch of these possible reductants. Oxidized, uranium-bearing solutions might be reduced by ferrous-iron-bearing minerals with which they are in contact. B tite, amphiboles, and (or) chlorite are commonly associated with pitchblende in uranium veins. Chlorite, although commonly rich in magnesium, is present in nearly all vein occurrences.

Pitchblende is commonly associated with sulfides in uranium veins. tions between sulfides and oxidized aqueous solutions might liberates-. Sulfur ions have the capability of removing oxygen from the solution, thereb reducing hexavalent uranium and allowing deposition of pitchblende. Sulfidi zation of detrital iron oxide and titanium oxide in the Catahoula Tuff of sou h Texas, for example, is believed to have been caused by H2 S which migrated up ward along a fault located downdip from roll-front uranium deposits (Reynolds and Goldhaber, 1977; Goldhaber and others, 1977). H2 S might also have caused reduction and deposition of uranium. The reducing action of bacterially ated H2S has been suggested as the cause of deposition of pitchblende in the Orphan mine, Arizona (Gornitz and Kerr, 1970). I Elemental carbon is an effective reductant in some vein deposits. Pitch' blende is often intimately associated with carbonaceous metasediments and graphite-bearing beds (for example, Key Lake and Koongara deposits; seep. 62 64).

\ Other possible reductants are hydrocarbons, but evidence of hydrocarbons •-'in uranium vein deposits is scarce. Minor hydrocarbons have been found in fluid inclusions in uraniferous fluorite from Oberfalz, Germany (Kranz, 1968) In addition, Poty and "others (1974) noted the existence of hydrocarbon-bear solutions in veins at the Bois-Noirs deposit.

The association of reduced minerals with pitchblende does not necessaril indicate that the "reductants" caused precipitation of pitchblende. Parage netic sequences are of prime importance in interpreting the role played by associated reductants. In a comparative study of the parageneses of 31 pitc blende plus base-metal-sulfide vein deposits, Rich and others (1975) found t pitchblende preceded the base-metal sulfides in 90 percent of the veins. Of the six deposits that contain Co-Ni arsenides along with the base-metal sul fides, five have parageneses which show that pitchblende preceded the base metal sulfides. Althoughfue number of veins used in the study constitutes a small statistical sample, it is apparent that deposition of pitchblende most often precedes that of associated sulfide "reductants." This observation makes it difficult to accept the hypothesis that associated base-metal sulf reduced the mineralizing solutions to promote precipitation of pitchblende. Instead, deposition of base-metal sulfides seems to be a result of progressi reduction of the transporting solution, not the cause.

Although many pitchblende-bearing veins are known to contain a preuran redu~tant, the occurrence of pitchblende in rocks devoid of identifiable red tants makes reliance upon predeposit reductants tenuous. For example, pitchb de is found in the orthoquartzitic Athabasca Formation at the Key Lake deposit. \ •.apparent reductants are associated. The lack of reductant in some uranium deposit leads to an intriguing question: Can oxidized, uranium-bearing soluti ns

57 become sufficiently reduced to promote p(tchblende deposition (commonly allowed by deposition of base-metal sulfides) without a predeposit chemical redu tant? This question is currently being addressed by Mathews and Pilcher (in p.).

The primary role of a reductant, be it a mineral constituent, H2S, a hydrocarbon-charged aqueous solution, is to reduce the f0 2 of the uran bearing solution. A sufficient decrease in f0 2 will cause precipitation 1 uo2 and, with further reduction, deposition of sulfides. This is the genetic sequence commonly observed in uranium vein deposits. Hostetler Garrels (1962) have demonstrated that the amount of uranium in an aqueo solution in equilibrium with uraninite increases with increasing f0 2 , re · less of the pH of the system. Garrels and Christ (1965) have shown that increases with total pressure on the system. Similarly, f0 2 increases increasing temperature. Therefore, a decrease in f0 2 and a concomitant sition of pitchblende might be caused by decreasing the temperature and sure on a uranium-bearing solution. If this mechanism is applicable, a predeposit reductant in the host rock may not be necessary. This hypoth mechanism for decreasing the f02 in uranium-bearing solutions explains troubling aspects of vein deposits, such as uranium occurrences in or quartzitic sedimentary rocks devoid of identifiable reductants. Pitchu~o,uuc occurrences in the Athabasca Formation and the Wingate Sandstone might explained by a pressure-temperature (PT) release model (Mathews and P in prep.). The paragenetic sequences commonly observed in pitchblend veins may be similarly explained. The nearly uniform restriction of uranium deposits to zones of dilatancy may be a function of PT Telease.

Dilatent zones act not only as channelways through which uran solutions might pass, but also as primary factors in decreasing the f0 2 the mineralizing solutions and in allowing precipitation of pitchblende. Chemical reductants may not be necessary for pitchblende deposition. ature and pressure reductants may decrease the f02 of the mineralizing

HYDRAULIC SETTING

Few generalizations may be made regarding the hydraulics of systems. Large quantities of solution may be required (Rich and others, but this has not been adequately tested.

The source of mineralizing solutions may be surface water, either d circulating or act~ng in a supergene environment; connate water; or phically derived hydrothermal solutions. Juvenile waters are considered es of magmatic-hydrothermal uranium occurrences (Mathews, this volume) and therefore, not discussed here. Factors causing deposition of uranium f magmatic-hydrothermal solutions and from solutions of nonmagmatic origin be the same.

The role played by surface waters in the development of vein deposi particularly unconformity-related veins, remains controversial. Propon of a supergene origin for these deposits rely heavily on the action of s and near-surface waters. Supporters of hypogene models minimize the imp of surficial and shallow-seated waters, except in near-surface regions o secondary uranium mineral enrichment. Sulfur-isotope data indicate that

58 ' ·~ surface waters were involved in some deposits (for example, Echo Bay/Eldor deposit, Northwest Territories, Canada, Robinson and Ohmoto, 1973; Orphan Arizona, Gornitz and Kerr, 1970). The study of these deposits implies that surface waters may circulate in deep(?) convective cells.

If preuranium chemical reductants are present in sufficient quantities, I pitchblende may be deposited in either the ascending, the descending, or t il lateral migration portions of such cells. According to the PT-release mode i proposed by Mathews and Pilcher (in prep.), vein deposits in rocks containi little or no preuranium chemical reductant are most likely confined to the ascending part of convective cells.

Rich and others (1975) discuss several criteria which may be used to distinguish deposits formed by ascending solutions from those formed by descending solutions. These criteria may not be applicable in practice.

The following are characteristic of deposits formed by ascending solut

1. Alteration sequences should show high-temperature products immediat adjacent to veins and successively lower-temperature minerals with increasin I" distance into the country rock (for example, zoned alteration halos around t magmatic-hydrothermal veins in the northern part of the Boulder batholith, Montana; Wright and others, 1957). This pattern will develop because the perature of an ascending solution is higher than that of the adjacent count t_, rock. l 2. Because the solubility of quartz decreases with decreasing temperat the presence of quartz in a vein may suggest deposition by an ascending solu · This criterion may be ambiguous because quartz may also be derived by altera reactions brought about by descending solutions.

3. Temperatures of deposition are outside the realm of near-surface tions as indicated by fluid-inclusion studies.

4. The direction of asymmetric crystal growth might indicate the direc I of movement of mineralizing solutions.

5. Distribution of ore grades may indicate movement direction of the t porting solution. Although this criterion may be valid in theory, it contai many assumptions and, therefore, it may not be applicable in practice. Unev distribution of reductants throughout the vertical extent of the vein, for example, may largely govern ore-grade distributions.

The following criteria might be used to indicate deposition of uranium descending solutions:

1. A limited vertical extent might imply near-surface conditions. criterion may not be applicable to veins exposed at the surface, because amount of erosion is generally unknown. The vertical extent of many of the newly discovered unconformity-related Australian deposits has not been adequ ~tely delineated by drilling.

59 2. Spatial association with an ~nconformity may imply descend! tions. The validity of this criterion is still in debate (see Langf 1977; Morton, 1976). Mineralization in these veins must have occurr the development of the associated unconformity. Age relations, not indicate the direction of movement of mineralizing solutions.

3. Isotopic, fluid-inclusions, and mineralogical data regarding emperatures of mineralization may suggest t-ither near-surface temperatures or the fluence of surface waters. Although near-surface conditions may be demonstra in certain deposits, the direction of movement of the mineralizing solut is not necessarily indicated by this criterion.

4. Uranium vein orebodies co~only pinch out at depth. criterion may suggest a supergene origin, not all veins that pinch out at depth are necessarily of supergene origin.

SITES OF DEPOSITION

Favorable depositional sites are essential for uranium vein depo Faulted, fractured, and brecciated zones of dilatancy are the best loc for vein deposits, particularly when the host rocks contain chemical uctants. In this sense, uranium veins are structurally controlled. These struc al zones provide convenient channelways for accumulation and migration of mineral izing aqueous solutions, regardless of whether the deposits are formed by ascending or descending solutions.

Uranium vein deposits are also lithologically ~ontrolled. Host containing adequate reductants might cause incipient precipitation of itch blende. In this sense, vein deposits within a given region may be ally controlled by stratigraphy.

CLASSIFICATION

Following and modifying the classifications given by Barnes and (1972), Beck (1970), and McMillan (1977), three general classes of vein deposits are recognized: unconformity-related deposits, vein-t deposits in metamorphic rocks, and vein-type deposits in sedimentary Unconformity-related and vein-type deposits in metamorphic rocks subdivided into•two subclasses: monometallic and polymetallic. refers to the presence of a single economic commodity (uranium), where polymetallic indicates two or more metals in economic concentrations. classification of vein-type deposits in sedimentary rocks is not cons necessary because of their minor economic importance.

An outline of this classification follows. The number following class or subclass is the reference number for the Grand Junction Offic Information System (GJOIS) file of the U.S. Department of Energy.

Unconformity-related deposits (710) Monometallic subclass (711) Polymetallic subclass (712)

60 Vein-type deposits in metamorphic rocks '(720) Monometallic subclass (721) Polymetallic subclass (722)

Vein-type deposits in sedimentary rocks (730)

UNCONFORMITY-RELATED DEPOSITS (710)

Unconformity-related uranium veins are associated with major unconform ities, commonly of Proterozoic age (basal Helikian unconformity in Canada; basal Carpentarian unconformity in Australia). Although spatial as~ciation does not necessarily imply genetic relations, the proximity of several large uranium deposits to major unconformities might suggest a cause-and-effect relationship. The nature of this relationship is still a matter of conjectur (compare Langford, 1974, 1977; Morton, 1976). Regardless, spatial relations j are undeniable and have become a significant part of uranium exploration t programs.

Unconformity-related veins are confined to the immediate vicinity of paleoerosion surfaces where terrestrial sediments overlie metamorphosed igneo Il and metasedimentary rocks of varying grades of metamorphism. They are commonl associated with faults and breccia zones which transect both the basement roc and the overlying sedimentary units. The faults and breccia zones often appea to be reactivated basement structures.

Pitchblende occurs in veinlets along faults, in brecciated zones, and in secondary parasitic structures associated with the major structural element. It also occurs as fine disseminations in the country rock. Mineralization is generally confined to either the underlying metamorphics or the overlying sediments. In some deposits, it straddles the unconformity.

Unconformity-related uranium veins have a limited vertical extent; they rarely extend more than a few hundred meters below the unconformity. They characteristically have a large horizontal projection.

The age of mineralization in unconformity-related veins is nearly always younger than the unconformity. This contradicts the concept that the upper reaches of the orebodies have been removed during the erosion cycle marked by the unconformity. The limited vertical extent of these vein systems cannot be explained by erosion. '

Unconformity-related veins are characterized by extensive chloritization. Higher-rank metasediments below the unconformity are usually retrogressively metamorphosed to the greenschist facies in the vicinity of these veins. The degree of chloritization sommonly decreases with increasing distance from the fault zone. In many deposits, the overlying terrestrial sediments also have been chloritized.

Hematitization is characteristic of unconformity-related veins. The dis ribution of hematite follows and sometimes extends beyond that of the \~hlorltization. In general, greater degrees of hematitization are associated with higher grades of uranium ore. Paragenetic relations suggest that 'I !

61 ~ld 1 hematitization follows chloritization,and precedes the deposition of blend e.

Base-metal sulfides and sulfarsenides commonly occur in the pitc veins and constitute a valuable resource in the polymetallic subclass position of sulfides follows that of pitchblende in most unconformit veins.

Carbonates and quartz commonly cement the breccia fragments in t zones. These minerals are normally paragenetically later than pitch

Pitchblende is mainly confined to the parts of the veins that cr either graphite-bearing or chlorite schists. Carbonates are also fa host rocks.

The distribution of uranium and the nature of the associated str indicate that unconformity-related veins may be largely controlled by The genetic influence of the associated unconformity is not known. (1974) suggested that the unconformity provided a channelway for-lat migration of uranium-bearing ground waters, and the structural fea were merely adequate receptacles for uranium deposition. The limited extent of these deposits lends credence to the Langford's

Fluid-inclusion studies suggest that temperatures of deposition higher than one might expect from ground-water percolation, unless either a very thick sedimentary section above the unconformity at the mineralization or an exceptionally steep geothermal gradient. The di ribution of alteration products around some vein systems suggests a hydrothe Higher temperature alteration products commonly occur immediately aaj the veins; lower temperature products occur farther into the country

The question of the origin of unconformity-related uranium vein remains unanswered.

Selected es of Unconformi

Koongara, Northern Australia. The Koongara uranium deposit is 1 the Pine Creek geosyncline, Alligator River area, Northern Territory, Intensely folded lower Proterozoic metasediments (amphibolite facies were later retrogressively chloritized) constitute the host rocks of posit. The met?sedimentary rocks are dominantly quartz-chlorite sch s, some of which contain muscovite and (or) garnet. One unit of graphite-qu z-chlorite schist is interlayered. These metasediments are unconformably overl by flat-lying, coarse sandstones of the middle Proterozoic (Carpentarian) Kombolgie Sandstone.

The dominant structure in the vicinity of the orebody is a stee reverse fault which places basal metasediments on top of the strati overlying Kombolgie Sandstone. Stratigraphic throw along the fault much as 600 m. Several smaller, parallel, and probably related shea in the hanging wall, particularly in the graphitic quartz-chlorite sc horizon. The fault plane itself is marked by a highly brecciated and zone as much as 7 m thick.

62 Chloritization along the fault zone is ubiquitous. It occurs in the foot wall Kombolgie Sandstone, in the metasediments of the hanging wall, and in the brecciated fault zone itself.

Crystalline uraninite and minor associated sulfides occur in veinlets both parallel and transverse to the foliation of the metasediments in the zone of primary uranium mineralization. Sooty pitchblende coats minor fracture surface The largest concentrations and highest grades of ore occur immediately below the graphite-quartz-chlorite schist horizon in the metasediments. Minor min eralization is found in the Kombolgie Sandstone adjacent to the fault.

The entire deposit is in the form of a steeply dipping wedge which pinches out at a depth of approximately 100 m. Most primary uranium mineralization occurs within 50 m of the fault zone. Extensive oxidation and secondary miner ization occurs in the upper reaches of the orebody and extends down to a depth of approximately 25 m. Secondary hydrous-uranium silicates and phosphates comprise the ore minerals in the overlying zone.

Uranium minerals at Koongara are thought to be of hydrothermal origin. Their association with retrogressive chloritization and the concentrations of higher ore grades immediately below the graphitic schist horizon suggest emplacement by ascending hydrothermal solutions. If the uranium mineralization was indeed caused by ascending solutions, then the spatial relation with the pre-Carpentarian unconformity may have little, if any, genetic significance.

\~~ Rabbit Lake, Northern Saskatchewan, Canada. The Rabbit Lake deposit is located in Aphebian metasedimentary rocks of the Wollaston fold belt along the eastern margin of.ths erosional edge of the Helikian Athabasca Formation. Ihe top of the Rabbit Lake deposit is within 50 ft of the eastwardly projected basal Athabascan unconformity.

Aphebian host rocks comprise a series of metamorphosed_ shelf-facies sed Lments. Meta-arkose makes up the bulk of the Aphebian rocks in the Rabbit Lake Jicinity. Lesser amounts of biotite paragneiss, plagioclase-rich, calc-silicate cocks (plagioclasites), and marble are present. These rocks were tightly folded 1nd metamorphosed to the cordierite-amphibolite facies (Abukuma facies series) luring the Hudsonian orogeny. Subsequently, they have been heavily chloritized. fhe projected Athabasca Formation rests on a well-developed regolith on the \phebian metasediments.

The Rabbit Lake uranium deposit occurs in a steeply dipping, highly chlor itized and brecciated zone in the metasediments. Dolomite, calcite, and quartz :ement the breccia fragments. Massive and sooty pitchblende occurs in veinlets 1nd as fracture fillings together with minor galena, sphalerite, pyrite, mar :asite, and chalcopyrite. The mineralized breccia zone is truncated at depth ;y a low-angle thrust fault (Rabbit Lake fault) which placed the Aphebian meta ;ediments on top of the Athabasca Formation. The brecciated ore zone is nterpreted as a pre-Athabasca fracture which was reactivated by the Rabbit Lake 'ault. The Rabbit Lake fault plane, marked by a thin zone of mylonite and r·~t gouge, is the footwall of the ore zone. Evidence of only minor mineral- :~.,.t ion is found below the Rabbit Lake fault.

63 Chluritic alteration is zonal. Th~ most intensely altered material the middle of the ore zone; alteration becomes progressively less inten ward. Both degree of alteration and extent of mineralization decrease w depth and become nonexistent below approximately 350 ft.

Two stages of mineralization have been recognized at Rabbit Lake. first stage comprises massive pitchblende which preceded the chloritic a ation. Subsequent oxidizing solutions leached some of the primary urani during a "red alteration" (hematitization) stage and redeposited it as pitchblende and coffinite during a reducing or "green alteration" stage, 1 I second generation of pitchblende deposition was synchronous with the ext chloritic alteration.

The radiometric age of initial pitchblende deposition is 1,100 m.y. pared to the 1,350 +50 m.y. age of the Athabasca Formation. Fluid-inc! studies on gangue minerals associated with the initial pitchblende gene suggest a minimum temperature of formation between 160° and 225°C.

Age, temperature of formation, and the fact that the chloritic alte postdates the Rabbit Lake fault, which is younger than the Athabasca Fo all suggest that the genesis of the ore is not directly related to the ering interval marked by the basal Athabascan unconformity. These facto s do not preclude the hypothesis of uranium deposition by ground waters perco,ating along the unconformity surface.

I I i,~ Selected les of Unconformit

Key Lake, Northern Saskatchewan, Canada. The Key deposit (consisting of two orebodies) is located along of the Athabasca basin in northern Saskatchewan. Basement rocks compris grade, deformed and metamorphosed (amphibolite to granulaite facies) metasediments which have been retrogressively metamorphosed to the gr facies. These rocks constitute graphite schist, chlorite-sericite schis , biotite gneiss, calc-silicate gneiss, and meta-arkose. A few small, co pegmatites have been noted in drill cores. The metasediments are overla a well-developed regolith beneath the flat-lying to gently dipping Atha Formation.

The two orebodies were probably part of a single depositional syst to being breached by Pleistocene erosion. Together they have a strike of more than 300 m, range in thickness from 10 to 100 m, and extend to of 150 m below the base of the Pleistocene overburden.

Uranium and nickel minerals are concentrated in a highly brecciat which transects both the underlying metasediments and the unconformably lying Helikian Athabasca Formation. The steeply dipping breccia zone the location of a high-angle reverse fault which has a stratigraphic t approximately 25 m.

Uranium (in pitchblende and coffinite) and nickel (in gersdorffite lerite, and niccolite) are present in roughly equal amounts. They are concentrated in and immediately below the graphite schist in the highly

64 ~breccia zone. Evidence of some mineralization is found in the chlorite Pyrite is a minor accessory mineral. Paragenetic relations indicate that i tial pitchblende deposition occurred prior to the sulfides and sulfarsenides (synchronous with gersdorffite).

Chloritization is ubiquitous in the Key Lake deposit. Key Lake be unique, however, because the chlorite is the Fe-bearing variety. implications of Fe-bearing chlorite are not known.

Too little data are available for the formulation of an acceptable hypo thesis regarding ore-forming processes. Although newly discovered,and known only through drill cores, several facts have been established about the Key Lake deposit. Deposition of uranium and nickel postdates the Athabasca Fo tion. Geothermometry of bravoite and uraninite indicate a temperature of fo mation of approximately 135°C. Mineralization is controlled by structure and lithology. Although genetic relations with the basal Athabascan unconformity have been postulated, the nature of the relationship is not yet known.

Jabiluka II, Northern Territory, Australia. The Jabiluka II deposit is located in the East Alligator River district, Northern Territory, Australia. This newly discovered deposit occurs in brecciated metased±ments beneath 20 70 m of gently dipping, unconformably overlying, orthoquartzitic Kombolgie

Sandstone. 1 i Host rocks for the deposit are brecciated, amphibolite-facies metasedi- t ' ~~.ruents which have been retrogressively metamorphosed to greenschist facies. These lower Proterozoic rocks (Cahill Formation) comprise pyritic quartz chlorite-graphite schist, chlorite-graphite schist, chlorite schist, and some calc-silicate rocks. They have been folded into a gently plunging, open, asymmetric syncline. Small, altered, unmineralized pegmatite and phonolite dikes cut the metasediments. The major structural element in the Jabiluka II vicinity is a low-angle reverse fault in which the Kombolgie Sandstone is in fault contact with the footwall metasediments. The fault truncates the basal Kombolgie unconformity and has thickened the sandstone section over the ore

Pitchblende, both massive and disseminated, is the dominant uranium mi 1 at Jabiluka II. It occurs as fracture coatings and in veinlets up to 2 mm wide. Native gold, which assays at 0.44 oz/st, occurs with the pitchblende one part of the deposit. Minor sulfides (pyrite and chalcopyrite) are asso ciated with the uranium minerals. , Associated hematite is less pronounced.

Uranium is concentrated in heavily chloritized and brecciated zones at Jabiluka II. It is most concentrated within and beneath graphite-schist and chlorite-graphite schist horizons in the Cahill Formation. Lesser amounts of uranium occur in the overlying Kombolgie Sandstone where it has been chloriti .d and silicified.

Mineralized-schist zones are characterized by increased MgO and depleted alkalis compared to unmineralized parts of the same units. This may suggest extensive magnesian metasomatism of the Cahill Formation and the Kombolgie ~ andstone in the vicinity of the ore deposit. Chloritization, silicification, "~nd mineralization appear to be directly related. Pre-existing uranium con centrations (in the Cahill Formation?) may have been mobilized and reconcentra d

! I 65 \ in favorable structural zones and rock units by hydrothermal soluti The genetic relations with the basal Carpentarian unconformity are not

VEIN-TYPE DEPOSITS IN METAMORPHIC ROCKS (720)

Vein-type deposits in metamorphic rocks ("classical veins" of 1977) are closely related to major fault systems. Although uranium may be absent from the major fault plane itself, deposits are found ciated secondary faults, fractures, and brecciated zones. Some bre may antedate the major fault system. Most large veins occur in Prot metasediments and metamorphosed igneous rocks.

Pitchblende, the major uranium mineral in these veins, occurs fracture fillings and as fine disseminations adjacent to uranium minerals (for example, coffinite and brannerite) are occasi encountered, but their overall volume is insignificant. Associated hematite, and pyrite are common.

Generally, vein-type deposits in metamorphic rocks are elongate dippin8. Bain (1977) emphasized that long, deep fracture systems wh active over long periods of geologic time were important for pitchbl position. Intermittently active deep structures provide access to radically open channelways for mineralizing solutions. They are eas accessible conduits which may collect large volumes of deeply eire uranium-bearing hydrothermal fluids. This factor may lend credence of the hypogene origin of many vein-type deposits. Deep structures necessary in supergene models.

Although structure appears to be the prime controlling factor vein systems of this class, the position of pitchblende concentrat the veins may be strongly influenced by the lithology of the host bonaceous slates, chloritized schists and gneisses, graphitic units, carbonates are favorable host rocks.

Vein-type deposits in metamorphic rocks have a very long strike relative to their thickness. They usually occur in anastomosing vei which extend to great depth. They may be associated with and contra cymoid structures related to a major fault system. These structures ~~~·wu•uL•~Y show evidence of reactivation •

Retrogressive• chloritization is common to most deposits of this lass. The genetic role of chloritization in uranium vein development is no known. It may prepare the host rocks for the deposition of pitchblende. rite may or may not be a product of the same fluid which transports and depos s uranium. It commonly develops prior to introduction of hydrothermal uranium-b ing solutions, as indicated by pitchblende-coated, chloritized rocks.

Hematitic alteration is very common in vein-type deposits in me rocks. Widths of the hematitized aureoles are variable. In general centration of uranium is directly proportional to the degree of red However, some strongly hematitized areas contain no pitchblende. whe areas, which contain larger quantities of pitchblende, show no hemat at ion.

66 Hematitization generally precedes deposition of pitchblende. during initial stages of hydrothermal activity and represents the more oxid nature of the transporting solution. As the solution becomes progressively reduced, development of hematite ceases and deposition of pitchblende begin This common paragenetic sequence is not restricted to vein-type deposits of this class. Many volcanogenic occurrences show similar parageneses (Pilche this volume).

Carbonatization and silicification of the host rocks are observed in several vein-type deposits in metamorphic rocks. Carbonates and quartz no mally follow pitchblende in the depositional sequence. Carbonat~ deposit may reflect the increase in pH brought about as the temperature and pressur decreases during upward migration of hydrothermal solutions. Quartz is dAnn,~ ited in a similar manner because the amount of silica held in solution deer with decreasing temperature.

Subdivision of vein-type deposits in metamorphic rocks into monometall and polymetallic subclasses is based on the mineralogy of the veins and fol the usage of Beck (1970) and McMillan (1977). Monometallic veins consist almost entirely of uranium minerals; other metallic minerals may be present minor amounts. Minor pyrite, chalcopyrite, and galena are associated with pitchblende in the monometallic veins of the Beaverlodge area, for example. Polymetallic deposits of this class contain economic concentrations of more than a single metal. The uranium deposit at Echo Bay/Eldorado, for example, contains significant concentrations of Co, Ni, Cu, and Ag (Robinson and Ohmoto, 1973).

It is not known.why some uranium deposits of this class are monometalli and others are polymetallic. The metal composition of the source rocks and (or) the ability of mineralizing solutions to leach and transport different : metals may be controlling factors. Conversely, the depositional site and (o') the nature of the transporting solution at the time of deposition may gove 1 the metal composition of the deposit. The metallic character of the differ t subclasses may be related to the location of the veins with respect to majo i tectonic elements, as proposed by Bedham (1976). He suggested that the na ' of mineralization is related to the steepness of an underlying subduction z Where the zone is steep, deposits of different metals will be closely assoc spatially, perhaps in the same deposit. A gently dipping Benioff zone may cause widely distributed and segregated metallogenic provinces (see Gablernan 1968).

Hydrothermal alteration is intimately associated with the pitchblende. In genera~, higher grades of ore are found in the more intensely altered 1 areas. Several types of alteration have been noted. Feldspathization, whic is probably related to the preuranium granitization of the Tazin rocks, is widespread. Chloritic and hematitic alterations are very common, particular y in areas of disseminated pitchblende. Two generations of chloritization are apparent. The first and most widespread generation seems to be a produc.t of! pervasive retrogressive metamorphism of the Tazin rocks. It preceded deposi ion of pitchblende. The second generation was synchronous with pitchblende de sition. Hematitic alteration, though very common, is not always associated ith ore. Some zones of highly hematitized rocks contain no pitchblende and,

67 conversely, some small pitchblende veiftlets are not associated with h tite. Argillic alteration is minimal.

Several episodes of mobilization and redeposition of uranium have een recognized. Initial pitchblende deposition occurred 1,780 m.y. ago; a ig nificant remobilizing thermal event occurred 1,140 m.y. ago. Temperat of formation ranged from 80° to 440° C.

There is some disagreement regarding whether the Fay-Ace-Verna at Beaverlodge belong to the class of veins in metamorphic rocks or to formity-related class. The large vertical extent ang high initial depo temperatures of the Fay-Ace-Verna veins suggest structural control of thermal solutions. A body of rock which has been identified as a horsejof Martin Formation in the St. Louis fault has been found deep in the mine . If this rock is indeed Martin Formation, then the criterion of close x1m- :i.ty to a major unconformity is met and the veins may be unconformity~re ! Some workers, however, befieve the block of ''Martin 1 0rma tion" is hi ciated, mylonitized, and altered Tazin rock, in which case the veins be unconformity related.

le of a Vei sit in Metamo ic Rocks tallic Subc

Beaverlodge Area, Northern Saskatchewan, Canada. The Beaverlodge located along the north shore of Lake Athabasca in northern Saskatchew one of the most extensively studied areas of pitchblende vein deposits North America. The regional geology has been well established. Miner paragenesis, and structures of the veins have been extensively studied. origin of the uranium ore, whether supergene or hypogene, remains a mat controversy.

The Beaverlodge area is underlain by the Tazin Group, a complex o metamorphosed and granitized orthogneiss and paragneiss of the amphib facies of metamorphism. These rocks were severely deformed and meta during the Hudsonian orogeny. They are unconformably overlain by tap continental, clastic sediments of the Martin Formation. Pitchblende primarily in the Tazin rocks; minor pitchblende occurs in the overly Formation.

The Fay-Ace-Verna deposits at Eldorado occur in veins associated major fault (St~,Louis fault) in the Tazin Group. Their overall str is in excess of 15,000 ft, and they extend to a depth of at least 5, Two general types of pitchblende occurrence are present in these depos distinct veins and disseminations. The occurrences are near the St. L fault but do not occur in the fault plane itself. Most of the ore ace related, closely spaced shears and fractures and in highly brecciated within a few hundred feet of the St. Louis fault.

Pitchblende, associated with calcite gangue, is the dominant uran mineral in these veins. It appears to be confined to a specific strat horizon within the Tazin Group. Minor amounts of brannerite are found lower levels of the mine.

68 Ex le of a Vei sit in Metamor hie Rocks tallic Subclass

Echo Bay/Eldorado Mines, Northwest Territories, Canada. The Echo Bay Eldorado uranium-silver mines are on adjacent properties in the same deposi in the Bear province of the Northwest Territories, Canada. Veins contain! U, Ag, Ni, and Cu occur in roof pendants of Aphebian supracrustal sediments and volcanics within Hudsonian granitoid intrusives. Although the margins of the roof pendants have been variously modified by contact metamorphism, the interior portions near the Echo Bay and Eldorado mines are only slight deformed and very slightly metamorphosed (lower zeolite facies).

The Echo Bay Group, in which the mineralized veins occur, cbnsists of thick series of tuffs, porphyritic andesite flows, and interlayered clastic sediments. Green-and-red-banded andesitic tuffs near the base of the Echo Bay Group contain most of the mineralized veins in the area.

The Echo Bay/Eldorado deposit comprises three steeply dipping veins ch have an average thickness of 0.5 m and a strike distance of 1.5 km. been mined to a depth of 400 m. The veins are encased in an alteration up to 3 m wide. Alteration types include feldspathization, hematitization chloritization, and carbonatization. The veins consist of pitchblende and native silver and bismuth, with lesser amounts of sulfides and Co-Ni ar Gangue comprises quartz, chlorite, and carbonates.

Several stages of mineralization are recognized. Hematite and quartz preceded deposition of pitchblende, which in turn was followed by depositio of Co-Ni arsenides, native silver, and native bismuth. Next came a sulfid carbonate stage, .foLlowed by a second generation of native silver. Temper atures of mineralization, as determined by geothermometry of mineral pairs, · oxygen isotopes, and fluid-inclusion studies, show an increase from 120°C the early stages to about 200°C in the middle stages. Final mineralizatio occurred at about 95°C. Oxygen and sulfur-isotope data, as well as the occurrence of hematite early in the paragenetic sequence, indicate an init ly high oxidation potential of the hydrothermal solutions. Their origin may have been saline surface waters, possibly sea water.

VEIN-TYPE DEPOSITS IN SEDIMENTARY ROCKS (730)

In contrast to other types of uranium deposits in sedimentary rocks (Jones, this volume), vein-type deposits in sedimentary rocks are dominant! controlled by structure. They are epigenetic and occur in fractures and breccia pipes which transect stratification. The cause of the mineralizati and the origin of the pipes is not known.

Uranium-bearing breccia pipes in sedimentary rocks show no definite re lationship to other structural elements. Whereas some pipes appear to be related to folds (Temple Mountain, for example), others, such as the Orphan mine, have no related structural association.

The roughly cylindrical breccia pipes, which host vein-type uranium deposits, may form by solution collapse and may represent multiple stages o structural development. The pipes comprise a core of brecciated, downdropp

69 strata surrounded by a nearly circula~ zone of vertical faults. The p pes commonly do not extend more than a few hundred feet deep.

Primary uranium minerals occur in tiny veinlets in the circular f acture zone and as fine disseminations in porous breccia fragments within t pipe cores. Uraninite and coffinite compose the bulk of the uranium minera Secondary uranium minerals (uranophane and tyuyamunite) may be present variable amounts. Sulfides are commonly associated with the uranium They are either synchronous with or follow the deposition of the urani Uraniferous asphaltite and native arsenic are found in at rrence of this class (Temple Mountain; Hawley and others, 1965).

Zonal alteration characterizes vein-type occurrences in sedimen Different types of alteration may be present. They are generally most within the pipes; adjacent units are less intensively altered. The c fracture zone surrounding the pipes marks an abrupt change in the deg alteration.

Bleaching of breccia fragments within the pipes is nearly unive The intensity of bleaching decreases with increasing distance outward the pipe margins. The width of the bleached aureole depends on the p bility of the rock; the bleached zone is widest in the most permeable units and narrowest in impermeable units.

Other types of alteration include silicification, hematitization. Argillic alteration has been noted in some occurr this class (at Temple Mountain, for example). ··~ The economic potential of vein-type deposits in sedimentary rock variable. Occurrences of this class represent submarginal resources. I

Example of Vein-type Deposits in Sedimentary Rocks

Orphan Mine, Arizona. The Orphan mine is located on the South Canyon National Park, Coconino County, Arizona. The orebody occurs cylindrical, vertical pipe consisting of brecciated fragments of d displaced, upper Paleozoic sediments. The pipe, which appears to t ate in the underlying Redwall Limestone, is believed to have developed by lution collapse. Alternative hypotheses of origin are explosive drilling by g matically derived gases, a deep-seated volcanic explosion which did vent at the surface (cryptovolcanic), and collapse caused by magma withdra

Uraninite, associated with copper sulfides and sulfarsenides (c chalcopyrite, and tennantite) and carbonate gangue, occurs principal! fracture zones along the margins of the pipe. Uraninite also occurs irregular masses in porous downdropped breccia fragments and in the within the ~ipe. The borders of the pipe, along which uraninite concentrated, are characterized by a set of circular fractures. probably tensional features developed during the collapse of the

70 ' \_, Uraninite deposition was dominantly controlled by structure. There are no preuraninite reductants in the host rocks. Porous blocks of sandstone contain more uranium than do those downdropped hlocks of siltstone and shale; therefore, deposition was also at least partially controlled by lithology.

A lateral and vertical zonal distribution of the ore minerals has been recognized. In general, concentrations of uraninite increase upward whereas copper mineralization is most intense low in the pipe.

Alteration within and adjacent to the pipe consists of bleaching of the 1 normally red Supai sandstone, development of hematitic halos around the ura- , ninite, and carbonatatization of the pipe matrix and porous-sandstone-breccia fragments. Argillic alteration has not been recognized. t 'it Fluid-inclusion studies on calcite gangue indicate temperatures of depo t sition between 60° and ll0°C. Because calcite developed late in the para ~;; genetic sequence, these temperatures were probably lower than the temperature ,-;• of the preceding uraninite deposition.

Uranium-bearing hydrothermal solutions are hypothesized to have migrated 1 upward along subpipe fractures and eventually to have entered the brecciated ' core and concentric fractures which surround the pipe. Oxidation-reduction :i: reactions, in which uranyl ions we~e reduced by bacterially generated H2 S, '~ caused precipitation of uraninite. The uraninite precipitation was accompani d ~~ by simultaneous deposition of sulfides and sulfarsenides. \.,;

71 REF{:RENCES

GENERAL

Bailey, R. V., and Childers, M. 0., 1977, Applied mineral exploration th special reference to uranium: Boulder, Colo., Westview Press,

Bain, J.H.C., 1977, Uranium mineralization associated with late Paleo acid magmatism-in northeast Queensland: Australian Bur. Mineral sources, Geology and Geophysics Jour., v. 2, p. 137-147.

Barbier, J., 1974, Continental weathering as a possible origin ur~nium deposits: Mineralium Deposita, v. 9, p. 271-288.

Barnes, F. Q., and Ruzicka, V., 1972, A genetic classification of ur deposits: Internat. Geol. Cong., 14th, Montreal 1972, sec. 4, 159-166.

Beck, L. S., 1970, Genesis of uranium in the Athabasca region and i ficance in exploration: Canadian Mining and Metall. Bull., v. 695, p. 367-377.

Bedham, J.P.N., 1976, Orogenesis and metallogenesis with r~ference silver-nickel, cobalt arsenide ore association: Geol. Assoc. Spec. Paper 14, p. 560-571.

Cornelius, K. D., 1976, Preliminary rock type and genetic classifica uranium deposits: Econ. Geology, v. 71, p. 941-942.

Gableman, J. W., 1963, Uranium in the Appalachian mobile belt: Energy Comm. RME-4107, issued by U.S. Govt. Printing Office, W D.C.,4lp.

Garrels, R. M., and Christ, C. L., 1965, Solutions, San Francisco, Freeman, Cooper and Co., 450 p.

Goldhaber, N. B., Reynolds, R. L., and Rye, R. 0., 1977, Origin of a Texas roll-type uranium deposit: II. Sulfide petrology and s isotope studies [abs.]: Geol. Soc. America Abstracts with Prog v. 9, no.• 7, p. 992-993.

Gornitz, V., and Kerr, P. F., 1970, Uranium mineralization and alter Orphan Mine, Grand Canyon, Arizona: Econ. Geology, v. 65, no. 7 751-768.

Hostetler, P. B., and Garrels, R. M., 1962, Transportation and prec of uranium and vanadium at low temperatures, with special ref sandstone-type uranium deposits: Econ. Geology, v. 57, p. 137~ 67.

72 REFERENCES (continued)

Knipping, H. D., 1974, The concepts of supergene versus hypogene emplac t of uranium at Rabbit Lake, Saskatchewan, Canada, in Formation of ur urn ore deposits: Internat. Atomic Energy Agency, Athens 1974, Proc., p 531-548.

Kranz, R. L., 1968, Participation of organic compounds in the transport o ore metals in hydrothermal solutions: Am. Inst. Mining and Hetall. Trans., sec. B, v. 77, p. B26-B36.

Langford, F. F., 1974, A supergene origin for vein-type uranium ores light of Western Australian calcrete-carnotite deposits: Econ. Geo v. 69, p. 516-526.

_____1977, Surficial origin of North American pitchblende and related ur deposits: Am. Assoc. Petroleum Geologists Bull., v. 61, p. 28-42.

Larsen, E. S., Phair, George, Gottfried, David, and Smith, W. L., 1956, nium in magmatic differentiation, in Geolo~y of uranium and thorium, . 6: Internat. Conf. on Peaceful Uses of Atomic Energy, Geneva 1955, Proc ,

P• 240-247. I

HdHllan, R. H., 1977, Metallogenesis of Canadian uranium deposits, in Jo '~wl M. J., ed., Geology, mining and extractive processing of uranium: Internat. Symposium, Inst. Mining and Metallurgy and Comm. of Europe Communities, London, p. 43-55.

Horton, R. D., 1976, The western and northern Australian U deposits-~expl ation guides or exploration deterrents for Saskatchewan? in Dunn, C. ed., Uranium in Saskatchewan: Saskatchewan Geol. Soc. Spec. Pu~ 3, p. 211-254.

Poty, B., Leroy, J., and Curey, M., 1974, Les inclusions fluides dans les minerals des gisements d'uranium intragranitiques du Limousin et du Forez (Massif Central, Fran~e) [Fluid inclusions in uranium ores f intragranitic deposits in Limousin and Forez]. in Formation of urani ore deposits: Internat. Atomic Energy Agency, Athens 1974, Proc., p. 569-582.

Raymahashay, B. C., and Holland~ H. D., 1969, Redox reactions accompany! wall rock alteration: Econ. Geology, v. 64, p. 291-305.

Reynolds, R. L., and Goldhaber, M. B., 1977, Origin of a south Texas roll type uranium deposit: I. Alteration of iron-titanium oxide mineral [abs.]: Geol. Soc. America Abstracts with Programs, v. 9, no. 7, p. 141.

Rich, R. A., Holland, H. D., and Petersen, Ulrich, 1975, Vein-type uran deposits: U.S. Energy Research and Devel. Adm. GJ0-1640, Open-File Rept., 382 p.

Robinson, B. W., and Ohmoto, H., 1973, Mineralogy, fluid inclusions, and able isotopes of the Echo Bay U-Ni-Ag-Cu deposits, Northwest Territories, anad;l; Econ. Geology, v. 68, p. 635-565. 73 REFERENCES (continued)'

Wright, H. D., Bieler, B. H., Emerson, D. 0., and Shulbert, W. P., 1957, Mineralogy of the uranium-bearing deposits in the Boulder batholith, Montana: U.S. Atomic Energy Comm. NY0-2074, Open-File Rept., 228 p , issued by Natl. Tech. Inf. Serv., Springfield, Va.

Zhukova, A. H., 1973, Average uranium contents of Precambrian formations. in the Ukrainian shield [trans.]: Geokhimiya, v. 8, p. 1245-1253.

UNCONFORMITY-RELATED DEPOSITS (SUBCLASS MONOHETALLJQ

Crohn, P. W., 1975, Mineralization in the Pine Creek geosyncline, in Kn c. L., ed., Economic geology of Australia and Papua, New Guinea: Inst. Mining and Metal!., v. 1, p. 269-271.

Dodson, R. G., Needham, R. S., Wilkes, P. G., Page, R. W., Smart, P. G. Watchman, A. L., 1974, Uranium mineralization in the Rum Jungle-Al Rivers province, Northern Territory, Australia, in Formation of ur ore deposits: Internat. Atomic Energy Agency, Athens 1974, Proc. 567.

Foy, M. F., and Pederson, C. P., 1975, Koongara uranium deposit, in C.~., ed., Economic geology of Australia and Papua-New Guinea: Inst. Mining and Hetall., v. 1, p. 317-321.

Hoeve, J., and Sibbald, T.I.I., 1976, The Rabbit Lake uranium C. E., ed., Uranium in Saskatchewan: Saskatchewan Geol. 3, p. 331-354.

Knipping, H. D., 1974, The concepts of supergene versus hypogene emplac uranium at Rabbit Lake, Saskatchewan, Canada, in Formation of uran deposits: Internat. Atomic Energy Agency, Athens 1974, Proc., p. 548.

Little, H. W., 1970, Distribution of types of uranium deposits and favo environments for uranium exploration, in Uranium exploration geolo Internat. Ato~ic Energy Agency, Vienna 1970, p. 35-46.

McMillan, R. H., 1977, Metallogenesis of Canadian uranium deposits, H. J., ed., Geology, mining and ~xtractive processing of uranium: t. Symposium, Inst. Mining and Metall. and Comm. of European Communit London, p. 43-55.

l1orton, R. D., 1976, The western and northern Australian U deposits- ation guides or exploration deterrents for Saskatchewan? in Dunn, . E., ed., Uranium in Saskatchewan: Saskatchewan Geol. Soc. Spec. Pub. p. 211-254.

74 REFERENCES (continued)

UNCONFORMITY-RELATED DEPOSITS (SUBCLASS POLYMETALLIC)

Dahlkamp, F. J., and Tan, B., 1977, Geology and mineralogy of the Key La~ U-Ni deposits, northern Saskatchewan, Canada: in Jones, M. J., ed., !: Geology, mining, and extractive processing of uranium: Internat. S~o sium, Inst. Mining and Metall. and Comm. of European Communities, London, p. 145-157.

Dodson, R. G., Needham, R. S., Wilkes, P. G., Page, R. W., Smart, P. G., : Watchman, A. L., 1974, Uranium mineralization in the Rum Jungle-Alli~tor Rivers province, Northern Territory, Australia, in Formation of uran:ijum ore deposits: Internat. Atomic Energy Agency, Athens 1974, Proc., P·! 551- 567.

HcMillan, R. H., 1977, Metallogenesis of Canadian uranium deposits, in Jo~es M. J., ed,~ Geology, mining, and extractive processing of uranium: ~nternat. Symposium, Inst. ~fining ana Metall. and Comm. of European Communitie~, London, p. 43-55.

Morton, R. D., 1976, The western and northern Australian U deposits--explqration guides or exploration deterrents for Sasakatchewan? in Dunn, C. E., ~d., Uranium in Saskatchewan: Saskatchewan Geol. Soc. Spec. Pub. 3,- p. 2~1- 254.

Rowntree, J. C., and Mosher, D. V., 1975, Jabiluka uranium deposits, in K~ight, C. L., ed., Economic geology of Australia and Papua, New Guinea:--Au+tralian Inst. Mining and Metall., v. 1, p. 321-326.

Smart, P. G., Wilkes, P. G., Needham, R. S., and Watchman, A. L., 1975, G'ology and geophysics of the Alligator Rivers region, in Knight, C. L., ed.~ Economic geology of Australia and Papua, New Guinea: Australian Ins$. Mining and Metall., v. 1, p. 285-301.

VEIN-TYPE DEPOSITS IN METAMORPHIC ROCKS

Bain, J.H.C., 1977, Uranium mineralization associated with late Paleozoicliacid magmatism in northeast Queensland: Australian Bur. Mineral Resourcef, Geology and Geophysics Jour, v. 2, p. 137-147. ·

Bedham, J.P.N., 1976, Orogenesis and metallogenesis with reference to the!silver nickel, cobalt arsenide ore association: Geol. Assoc. Canada Spec. taper 14. p. 560-571. II McMillan, R. H., 1977, Metallogenesis of Canadian uranium deposits, in Jo~es, M. J., ed., Geology, mining, and extractive processing of urani~: Internat. Symposium, Inst. Mining and Metall. and Comm. of European Communities, London, p. 43t55. I

75 REFERENCES'(continued)

Robinson, B. W., and Ohmoto, H., 1973, Mineralogy, fluid inclusions, aqd stable isotopes of the Echo Bay U-Ni-Ag-Cu deposits, Northwest Te~ritories, Canada: Econ. Geology, v. 68, p. 635-656.

VEIN-TYPE DEPOSITS IN METAMORPHIC ROCKS (SUBCLASS MONOMETALLIC)

Beck, L. S., 1970, Genesis of uranium in the Athabasca region and its .ignifi cance in exploration: Canadian Mining and Metal!. Bull., v. 63, ,o. 695, p. 367-377.

}~cDonald, B. C., and Kermeen, J. S., 1956, The geology of Beaverlodge; Cana dian Mining Jour., v. 77, no. 6, p. 80-83, 156.

Morton, R. D., and Sassano, G. P., 1972, Structural studies on the ura,ium deposit of the Fay mine, Eldorado, Northwest Saskatchewan: CanadJan Jour. Earth Sci., v. 9, p. 803-823.

Sassano, G. P., Fritz, P., and Morton, R. D.• 1972, Paragenesis and is~topic composition of some gangue minerals from the uranium deposits of tldorado, Saskatchewan: Canadian Jour. Earth Sci., v. 9, p. 141-157. '

Tremblay~ L. P., 1970, The significance of uranium in quartzite in thei!Beaver lodge area, Saskatchewan: Canadian Jour. Earth Sci., v. 7, p. 28~-305.

_____1972, Geology of the Beaverlodge mining ar~a, Saskatchewan: Canafa Geol. Survey Mem. 367, 258 p.

-----1978, Uranium subprovinces and types of uranium deposits-in the Pfecambrian rocks of Saskatchewan: Canada Geol. Survey, Current Research, Patt A, Paper 78-lA, p. 427-435.

VEIN-TYPE DEPOSITS IN METAMORPHIC ROCKS (SUBCLASS POLTIIETALLIC)

Robinson, B. W.,, 1972, The geology and geochronology of the Echo Bay atea, N.W.T., Canada: Canadian Jour. Earth Sci., v. 9, p. 158-171. I r Robinson, B. W., and Ohmoto, H., 1973, Mineralogy, fluid inclusions, apd stable isotopes of the Echo Bay U-Ni-Ag-Cu deposits, Northwest Territori~s, Canada: Econ. Geology, v. 68, p. 635-656. '

Ruzicka, V., 1971, Geological comparison between East European and ian uranium deposits: Canada Geol. Survey Paper 70-48, 196.

76 REFE~.NCES (continued)

'r: VEIN-TYPE DEPOSITS IN SED IMENTA :·' ROCKS 'II

'/r

Gornitz, Vivien, and Kerr, P. F., 1170, Uranium :~i Orphan Hine, Grand Canyon, Ar :ona: Econ. ~!:~:;~~z~~i~~ • a::. a~~e;~/J~~~: 768. :II (I Granger, H. C., and Santos, E. S., 1963, An ore-bearing cylind r.ical co u4.,Pse structure in the Ambrosia Lake uranium district, New Mexico: U.S. ~~ol.

Survey Prof. Paper 4 7 5-C, p. ClS)-8161. 11 1 ''I . ''I Hawley, C. C., Wyant, D. G., and Brook:>, D. D., 1965, Geology and uraniu11

deposits of the Temple Hountain district, Emery County, Utah: U.s.r , 1 Geol. Survey Bull. 1192, 154 p. '1, :li rll

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77 /7'ri