Some Chemical Experiments Bearing on the Origin of Certain Uranium-Vanadium Ores

SOME CHEMICAL EXPERIMENTS BEARING ON THE ORIGIN OF CERTAIN URANIUM- VANADIUM ORES.

FRANK B. 1N]'OTESTEIN.

Carnotite is found in many geologicalenvironments and is probablyformed in severalways. At Radium Hill, near Olary, Australia,• it is associatedwith minerals which were probably depositedby hot solutions. In thesedeposits it fills cavitiesand coats the walls of crevicesand may have been formed by secondary processesfrom the associatedprimary minerals. In the United States it is found far removed from igneousrocks, and its ores are supposedto have been depositedby cold ground water solutionsor to be alterationproducts, in place,of vanadium and uranium bearing sediments. The secondary character of carnotiteis practicallyundisputed, although the primary minerals from which the American depositsare derived are uncertain. The relative importanceof the two suggestedmodes of origin is still in doubt. This report deals with an investigationof certain natural solventsand precipitantsof vanadium and uranium, which are believedto throw somelight on possibleprocesses in- volved in at least one of the suggestedmodes of origin.2 • Crook, T., and Blake, G. S., "On Carnotites and an Associated Mineral Complex from South Australia." Min. Mag., Vol. I5, p. 27I, I9IO. 2 Some of the more important publications are: Hillebrand, W. F., and Ransome, F. L., "Carnotite and Associated Vana- diferous Minerals in Western Colorado," U.S. Geol. Survey Bull. '262, pp. 9-3I. Boutwell, Jl M., "Vanadium and Uranium in Southeastern Utah," U.S. Geol. Survey Bull. 260, pp. 2oo-2m. Gale, H. S., "Carnotite in Rio Blanco County, Colorado," U.S. Geol. Sur- vey Bull. 315, pp. IIO-Xt7. Gale, H. S., "Carnotite and Associated Minerals in Western Routt County, Colorado," U.S. Geol. Survey Bull. 340, pp. 257-262. Moore, Richard B., and Kithil, Karl L., "A Preliminary Report on Uranium, Radium, and Vanadium," U.S. Bureau of Mines Bull. 7o. 5 ø ORIGIN OF UR,•NIUM-V,•N,•DIUM ORES.

Carnotiteis essentiallya vanadateof uraniumand potassium. Other bases,especially calcium and barium, and severalof the metals,are thoughtto replacepart of thepotassium in somecases. I-Iessa givesthe formulafor carnotiteas K20'2UOa'V2Os-XH•O. It is usually'associated with and probablyforms isomorphous mixtures with tyuyamunite,4 CaO-2UOa.V•O'5.XH•O. The carnotitesare nearly always associatedwith amorphousores of vanadiumcontaining minor amountsof uranium. The compo.- sitionof theseores is uncertain,but theyare probably oxides and silicates. The principal carnotite depositsof the United States are located in the plateau country of southwesternColorado and southeasternUtah. Of thesethe most productiveoccur in or near the Paradox Valley, Colorado. Others are worked at several points in southernUtah. Minor depositshave been dis- coveredin northwesternColorado. A depositso far of no com- mei-cialimportance islocated near Mauch Chunk, Pa. Carnotite alsooccurs as an accessorymineral in the roscoelite5 deposits near Placerville, southwestern Colorado. Fleck, Herman,'and Haldane, William G., "A Study of the Uranium and VanadiumBelts of SouthernColorado," Report of the State'Bureauof Mines, Colorado, x9o5-•9o6. Wherry, Edgar T., "Carnotitenear MauchChunk, Pennsylvania," Bull. U. S. Geol. Survey No. 58o, pp. •47-•5x. Hess, F. L., "A Hypothesisfo.r the Origin of the Carnotitesof Colorado and Utah," EcoN. G•or..,Vol. 9, PP. 675-688. Hess,F. L., "Noteson the VanadiumDeposits near Placerville, Colorado," U.S. Geol. Survey Bull. 530, pt. •, pp. •42-I56. Hess,F. L., "Vanadiumin theSierra De LosCaballos, New Mexico,"U.S. Geol. Survey Bull. 530, pt. •, pp. •57-•6o. Hess,F. L., "Carnotitenear Green River, Utah," U.S. Geol.Survey Bull. 530, pt. •, pp. •6•-I64. Lindgren,Waldemar, "Copper, Silver, Lead, Vanadium, and UraniumOres in Sandstoneand Shale,"EcoN. GmL., Vol. 6, pp. 568-58•. Emmons,W. H., U.S. Geol.Survey Bull. 625,pp. 43o•-435. Crook, T., and Blake, G. S., "On Carnotite and an AssociatedMineral Complexfrom South Australia," Min. Ma#., Vol. •5, p. 27•, •9Io. a Hess,F. L., "A Hypothesisfor the Origin of the Carnotitesof Colorado and Utah," Ecoa. GF•oL.,Vol. 9, PP.675-688. • Idem. 5Hess, F. L., "Noteson theVanadium Deposits near Placerville, Colo.," Bull. U.S. Geol.Survey No. 530,Pt. I, pp. x4•-I56. 52 FRANK B. NOTESTEIN.

CHARACTER OF TtIE DEPOSITS. The Coloradoand Utah depositsare in white to buff, mod- erately coarse,cross-'bedded sandstones of Jurassicage. The bedsare usuallyflat or dip at low angles,but a few depositsare in bedswhich dip steeply. The productivebeds are hard and massiveenough to form the canyonrims and hogbacksso characteristicof western slope topography. Exposurestherefore are abundant. The carnotitein thesedeposits is an amorphous dusty coating on, or matrix between,grains of sand. It also coatsthe rock alongjoint planesand fractures,and fills openings causedby rock movements. The carnotitedeposits are small and lenticular, and conform to the beddingplanes of the rock. They are rarely over IOO feet in lateral extent and vary from a few inchesto severalfeet thick. Their distribution is very irregular. Many of the depositsare interbeddedwith thin beds containingdark colored amorphous ores of vanadiumwith only small amountsof uranium. Some, also, are found a'bove thin shales. Nearly all of the ore-bearingbeds are notably rich in fossil material made up largely of either petrifiedor carbonizedwood. Thin beds of carbonaceous material occur in which the fossils are indistinct but in which ferns and rusheshave been recog- nized. The carbonaceousmaterial is commonlyrich in vanadium, and petrified logs partly replacedby carnotitehave been found. The apparent abundanceof carbonaceousmaterial and plant fossilsin the ore-'bearingbeds is suggestivein view of the oc- currenceselsewhere of vanadium in coals,asphalts, and also in plant ashes.6 However the abundanceof carbonaceousmaterial in carnotitedeposits is not universal and may have no generic significance. The McElmo formatio.n, in which the Paradox Valley camoritedeposits occur, carries abundant petrified wood where exposednear Norwood, Colorado (between Placerville and Paradox Valley), but no carnotitehas yet beendiscovered in that locality. 6 Clarke, F. W., ",The Data of Geochemistry,"U.S. Geol. Survey Bull. 6•6, p. 705. ORIGIN OF URANIUM-VANADIUM ORES. 53

The ore-bearingsandstones are cementedby silica, calciteand gypsum,7 the cementprobably varying from place to place. It is, of course,probable that much original calcite has been re- placed by silica or convertedto gypsumby sulphateground waters. The carnotitedeposits typically occur in "rim rocks" along the sidesof canyons,and the ore almost universallydies out when followeda short distanceinto the hill. The depositsap- pear to be very superficial,a characteristicwhich was emphasized by Ransome,s who suggested,also, that the arid conditionof the dimate mighthave something to do with this surface.deposition. However, a few pocketshave beendiscovered which did not out- crop. There are also depositswhich occuron gently dipping mesa surfaces,the ore being so close to the surfac• as to be worked.by open cut. The shallow.overburden of manyof the depositssuggests that much might be learnedabout the extent and distributionof the depositsby systematicdrilling. Whether the apparentrelation to surfaceoutcrops along canyons is an es- sentialfeature or not canbe determined only by deeperand more systematicunderground exploration than has yet beendone. It has beenshown by severalwriters who have discussedthe subjectthat carnotiteis depositedalong fracture lines within the ore-bearingbeds even where the fracturesare very recen•and dueto slumpingon hillsides?This conditionpoints to solution by descendingground waters and to redepositionon exposure to air. The depositat MauchChunk, Pa., is in Pottsvilleconglom- erate just above its contactwith shales. The carnotiteis associatedwith lenses of blackvanadiferous shale. Wherry TM states that"the mineral presents the form of anamorphous tominutely crystallinebright yellow coating orimpregnation ina conglom- 7Hess, F. L., "A Hypothesisfor the'Origin oœ the Carnotitesoœ Colorado and Utah," Ecoa. G•t,., Vol. 9- 8 Hillebrand,W. F., and Ransome,F. L., op. cit. 9 Hillebrand,W. F., and Ransome,F. L., op. cit. x0Wherry, Edgar T., "A NewOccurrence of Carnotite," Am. Jour. Sci., 4th Ser., Vol. 33. 54 FRANK B. NOTESTEIN. erate, often penetrating cracks in quartz pebbles." He says further of this deposit"It is evidentlysimply a precipitatefrom the ground water and can be seenin the processof formation where water trickles out from the cracks in the rocks. "•x An analysisof this groundwater wouldbe of very great interest.

ORIGIN OF TI-IE DEPOSITS. Becausethe principal carnotite depositsare distant from igneousrocks the possibilityof origin throughhydrothermal action hasgenerally been rejected. Hess,•' however,considers this hypothesisin connectionwith the southwesterndeposits. Threehypotheses of originhave been advocated, as follows: I. First, that minerals carrying vanadium and uranium were widely disseminated,by mechanicalsedimentation or chemical precipitationthrough the bedsnow, or formerly, overlying the ore-bearingrocks and that these minerals have been dissolved by ground waters and the metalscarried down and reprecipi- ratedat the positionwhere now foundthrough some such agency as calciteor organicmatter or throughoxidation near outcrops. Ransome•a statesthat "the recencyof the depositsand the fact that they are sometimesdirectly connectedwith faults and dis- locations in the sandstones show that the vinadium and uranium compoundscould not havebeen the originalcementing material of the quartzgrains, but in all probabilitythey havelocally re- placedthe calcitethat actsas a matrix to the ordinarylight-colored sandstonesin which the ore bodiesoccur." While develop- mentshave shownthat the sandstoneis not universallycemented with calcite,yet this hypothesisseems very plausibleas applied to many of the reportedoccurrences. Moore x4 and Kithil adopt essentiallythis hypothesisand showthat the radioactivityof the bedsoverlying the carnotitedeposits is muchgreater than that of • Wherry, Edgar T., "Carnotite near Mauch Chunk, Pennsylvania,"U.S. Geol. Survey Bull. 580, pp. I47-I5I. x• Hess, F. L., "Vanadium Deposits near Placerville, Colorad(>,"U.S. Geol. Survey Bull. 530, Pt. •, p. •54. 18Itillebrand, W. F., and Ransome,F. L., op. cit. 14Moore, Richard B., and Kithil, Karl L., op. cit. ORIGIN OF URANIUM-VANADIUM ORES. 55 ordinarysandstones. They alsoobserve that the richnessof the depositseems to beara directrelation to the thicknessof the overburden. Gale•5 and Lindgren•ø supportthe hypothesisof concentration of theseores by circulatingground waters. Hillebrand•7 has shownthat vanadiumis widely disseminatedin small quantities in both igneousand sedimentaryrocks. 2. Second,that mineralscarrying vanadiumand uranium were concentratedby ordinary processesof sedimentationat or near the presentposition of the ore, and that the carnotiteis an oxidation productof suchminerals. Fleck and I-Ialdane,•s while not expressing a definite opinion, seem inclined to this view. Wherry•ø alsosupp6rts this hypothesisfor the Pennsylvaniade- posit. 3. A'third hypothesis suggested tentatively by Hess 2ø assumes that vanadiumand uranium were originally precipitatedfrom solution in sea water by .the reducingaction of decayingveg- eta'blematter and that the carnotiteis essentiallyan oxidation product,practically in place,of suchprecipitated uranium-vanadium salts. He lays specialstress on the abundanceof organic remainsas the only characteristiccommon to all the depositsand arguesthat the carnotitereplaces only thoseparts of petrified logs which were decayedbefore petrifaction.2• From this he deducesthat the replacementtook placealong with sedimentation. •5 Gale, H. S., "Carnotite in Rio Blanco County, Colorado,"U.S. Geol. Survey Bull. 315, p. I•6. a6Lindgren, Waldemar, op. cit. a7Hillebrand, W. F., "Distribution and Quantitative Occurrence 'of Vanadium and 3Iolybdenumin Rocks of the United States,"Am..four. Sci., 4th Series, Vol. 6, pp. 2o9-216. asFleck, Herman, and Haldane, Wm. G., op. cit. •9 Wherry, Edgar T., "Carnotite near 3Iauch Chunk, Pennsylvania,"U.S. Geol. Survey Bull. 580, pp. •47-•5L 2oHess, F. L., "A Hypothesisfor the Origin of the Carnotitesof Colorado and Utah," Ecoa. GEo•..,Vol. 9. 2aGale, in describingthe depositsin N. W. Colorado,in Rio Blanco County, takes a different view. See U.S. Geol. Survey Bull. 315, p. •6. 56 FRANK B. NOTESTEIN.

EXPERIMENTAL WORK.

An effort has been made to ascertain what natural solvents might be expectedto dissolveand transporturanium and vanadium, and what natural precipitantsmight be expectedto precipitate thesemetals from the most probablesolvents. It has been shown22 that ground waters may be classedas solutionsof chlorides,carbonates and sulphates. Accordingly tenth normal solutions of several chlorides, carbonates and sul- phateswere preparedand finely divided carnotitewas leached for variousperiods. The carnotiteore usedwas rich in calcite and iron and containedsome gypsum. The mineral was prepared by sifting partly crushedore througha 2oo-meshsieve in order to eliminateas much as possi'bleof the sandy ganguematerial. In each test 3ø c.c. of the solutionwas placedin a bottle with about one gram of the finely divided carnotite. The bottleswere shakenat frequentintervals during the leachingperiod. All the resultsof thesetests of solventsare basedon qualitative tests with equal amounts of material, and statementsof relative solubility are based on colorimetriccomparison which cannot be consideredquantitatively accurate. The tests used ar4, however, fairly delicate and negative results mean that neither metal was dissolved? It is plain that pure water and solutionsof alum, chlorides, the normalalkali sulphates,and calciumsulphate in water haveno solvent action on the mineral. The solutions o'f bicarbonates andbisulphates have a very slightsolvent effect. Tenthnormal sulphuricacid dissolvescarnotite fairly rapidly, and its solvent action is increasedby the addition of the alkali sulphates,alkali 22Emmons, W. H., and Harrington, G. L., "A Comparison of Waters of Mines and of Hot Springs," Ecoa. GEox..,Vol. VIII., No. 7, PP. 653-669. 2aFor methods of testing for vanadium and uranium see Roscoe and Schorlemmer,"Treatise on Chemistry,"pp. 942 and II2I. The test for uranium was modified in one respect: The ammonium carbonate tiltrate was very slightly acidified instead of "supersaturated" with hydrochloric acid. All of the sampleswere tested at the end of twenty-four hours and gave results essential13;the same as at the end of the period of leaching. Hence the length of the period of leaching is believed to be unimpo.rtant. ORIGIN OF URANIUM-VANADIUM ORES. 57

TABLE I.

Period Mineral. Solution. Leached, Result. IDays.

Camorite Distilled H•O 3 ø No vanadium or uranium dissolved. 200-mesh N/to NaC1 in H•O 30 N/to KC1 in H•O 60 N]xo NaHCOa in H•O 30 Trace of vanadium and uranium dissolved. N/xo KHCO• in H•O 60 Trace of vanadium and uranium dissolved. N[xo Na•CO• in H•O No vanadium or uranium dissolved. N/xo K•CO• in H•O N[xo K•SO4 in H•O N/xo Na•SO4. xoH•O in H•O Saturated Solution CaSO,. 2H•O in H•O N/xo KHSO• in H•O Strong trace of vanadium and uranium dissolved. N/xo NaHSO, in H•O Strong trace of vanadium and uranium dissolved. N/xo potassium alum in No uranium and vanadium dissolved. water N/xo H•SO• Some uranium and vanadium dissolved N/xo FeSO4in N/xo H•SO, N/io Fe•(SO4), in N/xo Considerable uramum and vanadium HIS04 dissolved. N/Io KIS04 in N/xo H•04 Considerable uramum and vanadium dissolved. N/xo Na•SO•.xoH•O in Considerable uramum and vanadium N/•o H•SO• dissolved. CaSO• in N/Io H•SO4 Considerable uramum and vanadium dissolved. N/Io KHSO• in N/io H•SO4 I5 Considerable uramum and vanadium dissolved. N/IO NailS04 in N/Io •5 Considerable uramum and vanadium H•SO• dissolved. H•S in Na•CO.• solution No vanadium or uranium dissolved. H•S in H•O H•S in N/Io H•SO4 Saturated solution NaCL in H•O CaCO, in H•O 5

bisulphates,calcium sulphate, and ferric sulphate. The effect of ferrous sulphateappears to be negative. Hydrogen sulphidein alkaline,acid, and water solutionhad no solvent effect, but it converted the mineral to a black colloidM substancesome of which remainedin suspensionfor hours after shaking. This substancewas probablya sulphide? •Bird, R. M., and Calcott, W. S., "The Association of Vanadium with Petroleum and Asphalt," Univ. of Va. Bull. Philos. Soc., Scientific Series, Vol. •, No. •8. 58 FRANK B. NOTESTEIN.

The very slight solubility of carnotitein alkali bicarbonates makesit improbablethat they have beenprimary agentsin the transportationof the metals. Sulphide solutionsare also elim- inated as solvents although colloidal uranium-vanadium com- poundsmight perhapsbe transportedmechanically where the cir- culationwas rapid and rocksporous. 25 The aboveresults show that sulphateground waters are quite capableof transportinguranium and vanadium, especiallywhere the solutions carry alkali sulphates, with which these metals readily form solubledouble sulphates? • With theseresults as a basisa mixture containingequal parts of approximatelytenth normal aqueoussolutions of vanadyl sulphate, V•O•(SO•)2, •7 and a soluble uranyl disulphate, UO•S207 •8 (?) and K2SO•, was prepared and an effort was made to synthesizecarnotite from this solution by the use of various precipitants. Thirty c.c. of the solutiondescribed above were placed in a dish and severalgrams of calcite were added. Carbon dioxide was evolved at once and a fine yellow cloudy precipitatecame down slowly. After 48 hoursthe solution.was neutral, and there was a heavy yellow precipitate. This precipitatewas filtered, washedand dried. It has not beenquantitatively analyzed, but qualitative test show it to contain a'bundantvanadium and uranium, and it also contains small amounts of carbonates and sulphates. The latter is supposedto be precipitatedgypsum. The compoundis very probablya mixture of carbonatesand vana- dates,but it is not carfiotitesince it is solublein dilute carbonate solutions. The solubility of the above describedprecipitate, hereinafter called "precipitateA" for convenience,was testedas shownin Table II.

25 Idem. 26Emmons, W. H., "The Enrichmentof Ore Deposits,"U.S. Geol.Survey Bull. 625, p. 435. s7Roscoe and Schorlemmer,"Treatise on Chemistry,"Vol. •, p. 938. 28Roscoe and Schorlemmer, "Treatise on Chemistry," Vol. I, p. I•8. ORIGIN OF URANIUM-VANADIUM ORES. 59

TABLE II.

TABLE SnOWiNG TESTS OF SOLUBILITY OF PRECIPITATE A.

Results. Solution. Period-- -- Leached. Distilled water ...... / 48 hours Insoluble. Distilledwater CO• was passed through for one hour../ 22 22 N/•oNa•COa in water...... Fairly soluble. N/•o NarCO8in waterCO2 was passed through one hour Very soluble. N/•o KHCOa in water ...... Fairly soluble. PureCaCO• in water. ' i " " Insoluble.

Chemicallypure calcium carbonate was placed in a bottlewith a small amountof precipitateA, distilledwater was added,and Carbondioxide was passed throt•gh for severalhours. This re- suited, of course, in a solution of calcium bicarbonate. The material was then filtered and the tiltrate dividedinto two parts. One part was boiledviolently for fifteen minutesto drive off the carbondioxide. The solutionswere then testedqualitatively for uranium and vanadium. A trace, only, of vanadiumwas found in both. In the part from which the carbondioxide had been driven off there was a faint trace of uranium while in the half still containingcalcium bicarbonatein solution there was abundant uranium in solution. Obviouslyprecipitate A is solu•blein alkali earth carbonatesbut sincecalcium carbonate is practically insolublein pure water it can act as a solventonly when in solution as a bicarbonate in the presenceof carbondioxide. As wouldbe expectedprecipitate A is readilysoluble in dilute sulphuricor hydrochloricacids. From the abovetests of the solubilityof precipitateA in calciumbicarbonate it is clearthat if it werenaturally precipitated in a calcareous bed the uranium at least could be redissolved and transported in solution with calcium bicarbonate,but it would be reprecipitatedwhenever the solution reachedthe surface or fissuresthrough which the carbondioxide could escape. Coaland rotten wood have not caused any visible precipitation after havingstood in a solutionof uranium-vanadium-potassiumsulphate for over 20 days. Evidentlythey reactvery slowly, if at all. In anotherexperiment •o c.c.of tenthnormal uranyl sulphate 60 FRANK B. NOTESTEIN. and IO c.c. of potassiumsulphate were mixed in a bottle and ap- proximately one tenth gram of vanadiumpentoxide was added. After standingtwenty-four hours there was a heavyyellow precipitate in the bottom of the bottle. This experimenthas not been followed up, but it indicatesthe possibility.that vanadium oxides may act as precipitantsof uranium compounds,presum- .ablybecause the higher oxidesof vanadiumare powerful oxidizing agents.

SUM MARY. I. Carnotite is readily soluble.in ground waters carrying free sulphuricacid and alkali sulphatesand bisulphates. It is very slightly soluble in weak solutionsof alkali bicarbonates,but is insoluble in most solutions of normal alkali bicarbonates, chlorides, normal alkali sulphates,and hydrogensulphide. 2. Calcitereadily precipitatesvanadium and uranium from vanadyland uranyl sulphatesolutions. The precipitatethus formed is readily dissolvedby solutionsof alkali carbonatesand bicarbonatesand by a solution of calcium bicarbonate. In the latter solutionthe lossof carbondioxide resultsin the precipitation of both lime and the metals. Rotten wood and coal have so far failed to precipitateeither metal. This point should be tested further. Vanadium pen- toxide, acting as an oxidizing agent, precipitatesuranium from a solution of uranyl sulphate.

GEOLOGICAL APPLICATION. Unfortunately no analysesof the ground waters from the region of the carnotite depositsare available. Emmons2ø men- tions the ocurrenceof springscarrying salineand alkaline waters and hydrogensulphide within the region where theseores occur but no analyseswere made. Lindgrenaø states: "The waters which traverse sedimentaryrocks are often rich in salts, par- 29Emmons, W. H., "The Cashin Mine, Montrose Co,unty,Colorado," U.S. Geol. Survey Bull. 285, p. 127. aoLindgren, Waldemar, "Mineral Deposits," p. 52. ORIGIN OF URANIUM-VANADIUM ORES. 6I ticularly in sulphates." He saysalso: "Sodium sulphatewaters are almost characteristic of certain formations in the western Cretaceous,for instance:these formationsconsist mainly of sandstonesand carbonaceousshales, the latter often pyritiferous, and the whole seriesmainly a product of near-shoredeposition. The oxidationof the pyrite furnishessolutions containing free sulphuric acid." This descriptionapplies excellently to the McElmo formationin and immediatelybelow which the carnotite depositsare located. The baseof the Cretaceousin southwestern Coloradois rarely more than •,ooo feet, stratigraphically,above the ore-bearinghorizon and in many placesit is lessthan that. The base mem'berof the Cretaceousin this region almost in- variablycarries a bed of pyritifer.ouslignite. It is true, of course,that the carnotitebeds now normallyhave a very shallow overburdenbut there is no reasonto doubt that they have beeh overlaidt)y the Cretaceousbeds within a period which is geo- logicallyshort.. The abundanceof crystallinegypsum a• in asso- ciationwith plant remainsin thesedeposits is important. The plant remainsseem to indicatethat the arid conditionsnecessary for precipitationof gypsumfrom sea water did not prevail at the time of sedimentation.It followsthat the crystallinegypsum is of secondaryorigin. and that sulphate-'bearingground watershave been active in thesebeds. The sulphuricacid probably was derivedby oxidationof pyrite in carbonaceousbeds. It is reasonableto supposethen that descendingsulphate waters woulddissolve any disseminateduranium and vanadiumpresent in the beds through which they passedand that thesemetals would be precipitatedfrom solutionby the first calcareousbed encountered.Assuming the groundwater to carry free sulphuric acid the reactionwould producecrystalline gypsum and carbon dioxideas well as the uranium-vanadiumprecipitates. In view of the frequentoccurrence of bothcalcit• and gypsum in carno- tire depositsit is probablethat manyof the depositshave formed in this manner. The solubilityof precipitate"A" in calciumbicarbonate solu- Moore,Richard B., and Kithil, K. L., op. cit., pp. 12, I7, 22, 24, 25, 27. 62 FRANK B. NOTESTEIN. tions suggestsan explanationof the apparentsuperficial character of the deposits. Assumingthat sulphateground waters carrying uranium and vanadium in solutionmeet calcareousbeds the first resultwould be the productionof crystallinegypsum, carbondioxide, and the uranium-vanadiumprecipitate. The second result would be the formation o.f calcium bicarbonate which would redissolvethe uranium and, to a certain extent, the vanadium. The further transportationwould, of course,be in the directionof ground water circulation. In a region of flat beds cut by deep canyonsthere must be a strong lateral circulation alongpermeable beds and aboveimpermeable shales. This lateral circulationis due not only to gravity but to capillary attraction inducedby rapid evaporationalong outcrops. Assuminga calcium bicarbonatesolution to 'be drawn laterally toward an out- crop it would transport any dissolveduranium and vanadium until the carbondioxide escapedeither at the surface or along fracture lines. On the escapeof carbondioxide both lime and the metalswould be thrown down and the metalswould probably oxidize, where closeto the surface,by contactwith air. In cross- bedded rocks the channels of ground water circulation would naturally be very irregular, hencethe pocketynature of the deposits. If this hypothesisis correctit would be expectedthat on following a carnotite deposit into the hill the vanadium values would be more persistentthan the uranium values sincethe latter, being more solublein bicarbonates,would be more readily con- centrated near the surface. Summarizing,it has beenshown that: •. Uranium and vanadiumare solublein ground water carrying sulphates. 2. There is good evidencefor believing that sulphateground waters have been active in the beds where the carnotite ores are found or at least in thoseimmediately overlying them. 3. Calcite precipitatesuranium and vanadium from sulphate solutions. 4. This precipitateis solublein calciumbicarbonate solutions but is reprecipitatedby the loss of carbon dioxide. ORIGIN OF URANIUM-VANADIUM ORES. 63

5. Calcite and gypsumare characteristicof many of the car- notire deposits. The abovefacts suggest the followingmode of origin for many of the carnotitedeposits. I. Descendingsulphate waters dissolvedisseminated uranium and vanadium minerals and the metals are carried down in the ground water circulation. 2. When this ground water solution meets a calcareousbed the metals are precipitated,gypsum is formed, and carbon dioxide is liberated. 3- Carbondioxide in solutionwould form calciumbicarbonate which would redissolve the 'uranium and to some extent vanadium salts. 4. These salts would 'be reprecipitatedand would tend to re- main undissolvedat or near outcropsor whereverthere was op- portunity for the escapeof carbondioxide. This is essentiallythe hypothesisof Ransome.a• It seemsto applywhere the ore-bearingbeds are characteristicallycalcareous but not so directly to thosedeposits whose matrix is siliceous. A corollary of this hypothesisis that camotire would be con- centratedalong joint placesand fracture or fault lines both becausethey are channelsof water circulation and becausethey offer meansof escapeof carbondioxide. It is suggestedthat a studyof the jointing systemmight aid prospecting. The abovehypothesis of origin may not apply to all of the westerndeposits and its validity as appliedto any of them can be determined.only ,by systematicstudy of the depositsand of the overlyingbeds. More completedata is desirableon the following points especially: I. The exactcharacter of the groundwaters in the ore-bearing beds. 2. The characterof the matrix of the ore-bearingrocks and of the overlyingbeds. a2Hillebrand, W. F., and Ransome, F. L., "CarnotiCe and Associated Vana- diferous Minerals in Western Colorado,"U.S. Geol. Survey Bull. 262, pp. 9-3I. 64 FRANK B. NOTESTEIN.

3. Local conditionsgoverning ground water circulation,as the abundanceof shalesunderlying the ore-bearingbeds, circulation due to capillarity,and localizationof ground water circulation by cross'bedding. 4. Abundanceof pyritiferousbeds in the rocksoverlying, or formerly overlying,the ore-bearinghorizons. 5. Relation,if any, of ore bodiesto the jointing system.