Conadian Mineralogist Yol. 24, pp.247-258 (1986\
STRUCTURALAND COMPOSITIONALCHANGES IN COPPERSULFIDES DURINGLEACHING AND DISSOLUTION
LOWELL S. WHITESIDEAND RONALD J. GOBLE Department of Geologt, University of Nebraska-Lincoln, 214 BesseyHall, Lincoln, Nebraska 68588-0340,U.S.A.
ABSTRACT constants'€tablit, au coursduquel les grainsde digenite sonttout d'abordlixivi6s en anilite, mais reviennent ensuite Many recentstudies (ag., Potter 1977,Goble 1980,1985) rapidementi la structurede dig6nite.Avec chalcosine deal with the stability of blue-remziningcovelline. This synthdtique,on note au moinsdeux processus de lixivia- study shows that leaching and dissolution of synthetic tion: l) ensolution de concentration faible (= l0-2M), la digenite or anilite, in acidic ferric sulfate solution, produce chalcosinese transfonne en chalcosinet€tragonale, puis metastablepolymorphs of geerite, yarrowite, spionkopite, passed la dig6nite,dont elle continue ensuite le processus covelline and CuS2;the structurescontain the sulfur atoms delixiviation; 2) enconcentration plus forte, la chalcosine in cubic close-packing. Using X-ray-diffraction patterns, synthdtiquese transforme directement en djurldite. Si l'on eight stagesof transformation have been identified in the continuela lixiviation, lesphases r6sultantes montrent les leaching of digenite to forms containing less copper. The propridt€soptiques et les clich& de diffraction X dela spion- phasesproduced do not have the typical optical properties kopiteet la yarrowite,Dans des conditions sp6ciales, c'est of blue-remaining covelline, nor its hexagonal structure. la covellinequi seforme. La compositiondes grains lixi- Thesetransformations were produced at leachateconcen- vi6s,d6termin6e par analysei la microsondedlectronique, trations greater than l0-3 M. In weaker leachates,digenite indiqueque la lixiviationdu cuiwetend i s'acc€l4rerquand and anilite structures alternate in a constant time-cycle, in on accroitla concentrationde la lessive.Les relations entre which digenite grains first leach to anilite and then quickly compositionet structuredtablies par Goble (1985) sont con- return to the digenite structure. Using synthetic chalcocite, firmdespar I'additionde donndes qui ajoutentdes points at least two leach paths are observed: l) in weak solutions nouveau(i la courbeexpdrimentale. (= l0-t M, chalcociteleaches to tetragonal-phasechal- cocite and then to digenite, following the digenite leach- Mots-clds:sulfures de cuiwe, lixiviation, digdnite,anilite, ing paths from that time onward; 2) in stronger concen- geerite,chalcosine, djurldite, yarrowite, spionkopite. trations, synthetic chalcocite leachesdirectly to djurleite. With continued leaching,the rculting phaseshave the opti- cal properties and X-ray-diffraction patterns of spionkop- I}.ITRoDUC"IIoN ite and yarrowite. Under special conditions covelline is formed. Compositions of leached grains, determined by Blue-remaining(blaubleibmder) covellinehas been microprobe analysis, show a tendency for copper to be recognizedfor many years in the oxidation zone of leachedat an acceleratedrate as leachateconcentration is ore deposits,where it occursas an intemediate phase increased.Goble's (1985)composition-structure relation- in the alteration of copperand copper-iron $ulfides ships are confirmed by the addition of new data-points. to optically nonnal covelline. Researchby a num- on both natural (Sillitoe & Clark Keywords: copper sulfides, leaching, digenite, anilite, ber of investigators geerite, chalcocite, djurleite, yarrowite, spionkopite. 1969, Ottemann & Frenzel 1971, Goble & Smith 1973,Putnis et al.1977, Goble 1980)and synthetic materials (Frenzel 1959, 1961, Moh 1964', 1971, SOtvIUeInf Rickard 1972, Potter 1977, Putnis et al. 1977) has determinedthe presenceof two varieties of blue- De nombreux travaux recents(pax exemple,Potter 1977, remaining covelline, having compositionsof approx- Goble 1980, 1985)concernent la stabilitd de la covelline imately Cu1.sSand Cu1.aS. blaubleibende. Notre 6tude montre que, par lixiviation et Most investigator$(e.9., Frenzel 1959' Rickard dissolution de dig€nite synthetique ou d'anilite, dans une 1972) have interpreted X-ray patterns of blue- solution de sulfate ferrique, on obtient des formes poly- remaining covelline basedupon a covelline-like unit morphiquesmetastables de geerite,yarrowite, spionkopite, cell. Some (e.9., Frenzel 1959, Moh 1971, Potter covelline et CuS2; toutes leurs structures contiennent les 1977)havenoted a resemblancebetween the X-ray atomes de soufre en paquetagecubique csmpact. Par dif- pattern of one of the blue-remaining covellines fraction X, nous pu avons identifier huit stadesde trans- (Cu1.aS)and that of digenite(Cu1.6S). Using single- formation dansla lixiviation de dig6nite en formes teneur i (1980)has shown that two moindre en cuiwe. Les phasesproduites ne possddentni crystal X-ray data, Goble les propri6t6s optiques typiques de la covelline bloublei- of the natural blue-remaining covellines (yarrowite bende, rtt sa structure hexagonale.Ces transformations se CueS6or Cu1.12S,spionkopite Cu3eS4or Cu1.3eS) produisent lorsque la concentration de la lessive excdde have hexagonal symmetry and structures distinctly l0-r M. Lorsqu'elle n'atteint pas cette valeur, un cycle different from those of covelline and digenite. These 247 248 TIIE CANADIAN MINERALOGIST structuresare basedupon a combination of hexag- tem copper-sulfur can be directly related to uncer- onal close-packingof sulfur atoms and covalent tainties in differentiating natural and synthetic bonding of sulfur atomic layers (Goble 1985). phases.Many of the eight copper sulfide minerals Geerite(Cu6S, or Cu,.6S)is a recently described have similar optical properties. The geeritestructure coppersulfide (Goble& Robinson1980) that occurs can be maintained during synthetic leaching over a in epitacticreplacement of sphalerite.The structure compositionalrange extendingfrorn geeriteCu1.6S of geeriteis basedupon cubic close-packingof sul- to spionkopite Cur.oSto yarrowite Cu1.1S.If twin- fur atoms and is believedto be similar to the struc- ning is present,this material cannot be distinguished ture of digenite(Goble 1985);the dimensionsof the from the natural polymorphs using optical proper- close-packednetwork closelyapproximate those of ties and X-ray powder patterns. Becauseprevious the host sphalerite. workersrelied on theseto identify syntheticphases, The two niethods commonly used for synthesiz- uncertainties remain as to the validity of their con- ing blue-remainingcovelline consist of (l) leaching clusions. copper or copper-iron sulfides under oxidizing con- The principal objectiveof this study wasto deter- ditions in acidic aqueoussolutions or (2) sulfurizing mine the sequenceof structural and compositional digeniteor chalcociteunder reducing conditions in changesproduced in leachingchalcocite, digenite and organic solvents and in aqueous solutions (Moh anilite as a function of time and leachateconcentra- 1971);X-ray powderpatterns of the productsresem- tion. Oncethis information is quantified, it should ble those of natural yarrowite and spionkopite be possible1o test the validity of Potter's (1977)con- (Goble 1980).Electrochemical investigations of the clusions on the stability of blue-remaining covelline. productsof the secondtype of synthesiswere inter- An inherent pafl of the study is the relationship preted by Potter (1977)as proof that blue-remaining between the material produced and natural blue- covellinesof compositions Cut.rS and Cu1.aSare remainingcovelline and other coppersulfides. One metastablephases in the Cu-S system.Goble (1981) long-rangegoal is to identify the stableassemblages has shown that with anilite (Cut.rrS) as starting and to establisha hierarchy of metastabilitiesamong material, the first type of synthesis produces a the others. Another is to understandthe circum- material with a metastablestructure similar to that stancesunder which various paths of evolution and of geeritebut with a compositionof Cut.t,*6.6eS.X- transition of metastablephases can be predicted and ray powder patterns of this material strongly resem- by which the geneticprocesses operating can be inter- ble those of blue-remaining covelline synthesizedby preted from the characterof the final product. Frenzel(1959) and Moh (1971);these patterns are also similar to tJroseof yarrowite, although the struc- EXPERIMENTAL METHODS AND PROCEDURES ture, asrevealed by X-ray single-crystalpatterns, is distinctly different from that of yarrowite (Goble Synthesis 1985).Optical propertiesof the leachedphase can be used1o distinguishit from yarrowite provided that Synthetic digenite and chalcocite were prepared frvilning is absentand that extinction can be deter- using the standard techniquesof synthesisdescribed mined asoblique to cleavagetraces (Goble 1981).If by Morimoto et ql, (1969),Morimoto & Koto (1970) twinning is present,the leachedphase is optically and Moh (1971).Weiehed samples of research-grade indistinguishablefrom yarrowite. Therefore, whereas copperand sulfur powder were sealedin evacuated optical propertiescan be usedto drsprovethe exis- silica tubes, heated in tube furnaces and then tence of yarrowite (and spionkopite) in synthetic quenched.Evacuated conditions were maintained material, they cannotbe usedto prove its existence. until leaching was to commence. Synthesized Inasmuchas Potter's (1977)identification of blue- material had a sintered appearance,with numerous remaining covelline was based upon X-ray powder well-formed macroscopiccrystals. The sinteredpor- diffraction, optical properties and microprobe data, tion was gently crushedbetween the fingers to avoid the possibility exists that he was in fact looking at mechanical alteration of the structure from digenite varieties of the metastablegeerite (or leachedanilite- to anilite, and sorted by sieving so that investigated type) structuredetected by Goble (1981)rather than grains were between 150 and 250 micrometresin at yarrowite and spionkopite. Therefore, his conclu- diameter.Optical studiesof polishedsections show sion that blue-remainingcovellines of compositions that these grains are an aggregateof many smaller Cu1.'Sand Cu1.aSare metastablephases in the sys- grains, generally less than 50 micrometres in lem copper-sulfur needsto be testedfurther, for one diameter. may reasonablypostulate that yarrowite (Cu'.pS) and spionkopite (Cu,.*S) may be stablephases in Apparatus the system copper-sulfur, whereasthe geerite-type synthetic phases(Cu1.rS and Cu1.aS)are metastable. Leaching was done by immersing sulfide grains In summary,the unresolvedproblems in the sys- and a quartz standard into a solution containing a COPPER SULFIDES DURING LEACHING AND DISSOLUTION
TABLE I. COTTPOSITIONOF LEICIIED CRAINS OF DIGENI1E AS A FUIICTIOII OF CO}ICENTBATIONOF FERRIC SULFATE LEICHATE AIID DURATIONOF THE LEACHINC PNOCESS
$11-U-jerrlcjuLfels 1o-2 u rerrlrju.lfsle lo-l il Fefrtc sul.gre l-!-i9xr]eju!iaJe- -2-!,--Eer4.f!-+Jrtaie-- Leachr.n6 tsr t cr t rotat culs rb I rt I Torst cu:s .il-iii-iii"t d:s rtl si-i-iot;a curs rt t rt t totai cu:s rioa idiif_ju---f-----rf-I-ragi" cu---S---jr! i reiio Cu i {tj--rai.Lo-!r--l rgftatte----C!-5---ri-t--!e!tg 't't 't9,1 0 78.1 21.9 100.0 1.80 .1 21,6 99.'l 1.80 78,4 22.0 l00.rr 1.80 22.2 101.3 r .80 78.421.9 100.3 'I1.81 78.7 22.1 1OO.8 .80 1 79.1 22.1 101.2 r .80 7?.821.8 99.6 t.8o 76.821.9 98.7 1.77 77.5 22.1 99.6 77.\ 22.2 99.6 r .?6 't7 1.78 22.7 101.3 ?8.123.8 101.9 1.66 .3 22.1 'tO199.q 1 .77 78.1 22,1 100,2 78.6 79,o 22.6 .6 1.76 78.6 22.1 100.'l 1.79 78.9 22.7 101.6 77.3 23.3 100.6 't8.2 22.3 101.0 't.76 2 79,6 22.3 101.9 1.80 78.4 22.5 l00.g 78.2 22.6 100.8 76.7 22.0 98.7 76.6 22.3 98.9 1.'l\ 77.9 22.4 10O.3 78.522.8 101.3 L7q 77.8 22,5 100.3 77.6 22.7 1OO.3 'L50 77.0 .22.2 99.2 77.3 24.6 101.9 r.59 75.7 23.9 99.6 3 78.t1 22.',1100.5 1.?9 77.5 22.3 99,8 77.1 22.5 99.6 75.1 22.7 97.8 77.2 24.4 101'6 1.62 24.3 l0l.3 r.53 ?4.4 23.6 98.0 1.59 ?8.622.8 101.4 1.74 75.8 23.\ 99,2 'Ir.63 77.0 75.6 22.0 97.6 1 .73 77,3 24.2 101.5 .61 77.\ 24.1 141.5 1 ,62 76.7 25.6 102.3 '1 26.1 99'6 .42 3.5 77.0 2',1.'t 98,7 I .80 77,7 23.3 101,O 1.68 76.'t 2\.2 100.9 1.60 '14.775.3 23.7 99.0 1.60 73.5 75.tt 23,8 99.2 1,59 24.9 99,6 73.'t 26,2 99.3 1.tI1 2'1.0 102.2 1.41 73.0 28.2 101.2 1.3'l 76.1 25.rt101.5 '14.775.2 \ 78,2 22.O 100,2 1.80 77.5 23.3 100,8 1.58 75.8 24.0 99.8 1,60 24.9 99.6 73.0 27.9 100.9 1.32 '16.6 26.9 101.8 23.2 99,8 73.3 2/1.7 98.0 1.50 74,5 25.6 't01.7100.1 1.47 ?4.9't4.5 75,5 26.2 1 .45 28.O 102.5 1.34 't.c5 100.0 5 76,7 21.0 98.3 1.80 74,6 23.8 102.t| 75,1 26,2 10',1.3 72.0 28.0 100,0 1 ,32 't2.768.0 31.t1 ',t00.4 25.9 101.4 1 .47 25.1 9',1.8 1.46 77.0 23,q 1.66 75.2 27.-" 102.5 r.39 't2.175.5 72,7 21.4 100.1 1.34 25.',| 97.8 1,41 73.1 28.2 101.3 | .J I 6 't8.6 22.2 100,8 1.80 '17.7 22.3 100.0 75.0 23.6 98.6 1.60 72.5 26,4 9e.9 r.39 66.8 33.? r00.5 1.03 30.6 101.7 1.1'l 76,q 23.2 99.6 1.66 73.0 26.: 99.1 1.41 ?6.924,4 100.3 'r.301.59 ?1.r 73.',t27,2 100.3 1.36 ?0.8 27.5 98.3 69.4 29.2 98.6 'I 71.5 27,4 98,9 1.32 69,9 29.1 99.o 1.21 65.? 33.6 100.3 .00 73.2 27.2 100.4 1.36 26.2 101.3 1.45 58.9 40.7 99,6 7 77,2 21.8 99.0 1.80 78.9 22.8 1O1.',|1 .?4 75.6 2\.2 99.8 1.58 75.1'tA.2 77.123.3 100.4 ?4.1 26.8 100.9 1.40 27.6 1O1.8 r.35 66.4 33.2 99.6 1.01 1.33 .9 z',t.'t t .31 69.4 28.9 98.3 1.21 76.5 23.2 99.'l 1.66 't1.374,1 28.2 102.5 71 99.6 2't.7 99.0 1.30 '71.369.8 31.7 100.5 t.tl 23.6 1.60 29.2 100.5 1.23 r0 79.3 22.3 101.6 76.2't7 21,9 98.1 71.0 29,2 1OO.2 1.23 7r.o 98.6 .\ 21.8 101,2 1.64 72.5 27.O 99.5 1.36 7o,2 27,3 97.5 1.30 ?1.029.8 100,8 1 .20 ?2.0 30.0 102.0 ?0.q 28,9 99.3 1,23 61,2 4'1.2 102.4 67.3 30.3 9?.6 ?1,029.5 100.5 1.21 50.2 50.5 100.8 0,50 15 78.5 22.3 r00.8 1.?8 77.0 23.3 100.3 72.9 27.3 100.2 1.35 72.5 26,1 98.6 1.40 ?0.7 31.3 102.0 t.t4 '17 '11.o 101.4 1.01 65.3 33.3 99.6 0.99 .3 23,5 100,8 1 .66 27.3 '10194.3 1.31 57.7 33,7 't8.1 2\.2 102.3 1.63 ?1.2 30.0 .2 57.5 43.q 100.9 0.67 64.0 36.3 t00.3 0 ,89 q9.8 r rr3.8101 ,9 o.67 69.0 31.7 100.? 50.5 100.3 0.51'r.33 58. 50 '18,122.2 100.3 75.5 23.0 98.5 1.66 66.? 33.6 r00.3 1.30 72.3 27.4 99.5 68.3 34.t 102.4 76,6 21.9 98.5 ??.123.9 101,0 1.63 68.1 30.5 98.6 1.13 71.029.9 100.9 72.7 28.1 100.8 1.33 73.1 25.\ 99.5 1.q0 67.233.9 r0r.1 1.00 67.8 30.7 98.5 1,11 69.4 ?9.5 98.9 1.19 68.0 34,3 r02.3 1.00 ?0.1 31,.C101.5 't'1,3 't6.5 ,12,3 26.4 100.0 1.41 ?0.5 29.3 99.8 1.21 r00 22,3 99.6 23.',t 100.2 1 .62 27.tt 99.7 '|1.33 73.6 7\.3 /3.5 97,s 69.8 30.4 100.2 .16 69.831.5 101.3 71.628.8 r00.4 1 .21 7\.5 24.7 99.2 ,t.52 68.1 3{.q 102.5 1.00 65,6 32.7 98.3 6?.831.9 99.9 71..729.4 101.1 60.0 39.8 99.8 0.76 6r.? 38.q 100.2 0.8r 't2,368.8 32.2 r0!.0 1.08 300 76.5 21.9 98.4 76.q 24.1 100.5 1.60 72.8 27.8 100,6 71.tt 27,3 98.7 1,32 27.3 99.6 73,2 26.tl 99.6 1.40 70.2 29.1 99.3 66.4 32.9 99.3 1.02 67.733.8 101.5 1.01 66.9 1.06 66.3 101,l 0.96 69.130.9 100.0 't2,169.2 29.1 98.3 3r.8 98.? 3q.8 2',t.8 99,9 1.31 60.3 q0.5 100.8 0.75 59.6 40.0 99.6 o.15 67.C31.? 99.r 500 77.7 22.2 99.9. 73.4 27.r1100.8 66.5 33.5 100.0 1.00 71.6 29.9 101.5 1.21 68.9 33.q 102.2 1.04 74.1 25.6 99.',| 1.46 70.8 29.5 100.3 1.21 68.6 30.7 99.3 I.r3 68.830,8 99.6 72.2 27.\ 99.6 1.33 63.7 35.2 99.9 0.89 67.5 3q.1 101.6 1.00 58.331.0 99.3 1.11 71.7 2'.t..6 99.3 '|,3t 63.1 36.2 99.3 0.88 64.{ 36.C r00.3 0.89 66.8 31.? 98.5 1.06 26.1 1.40 66.4 33.9 100.3 0.99 'to1 72.1,t0.2 98,2 750 78.'l 22,'t .\ 29.5 99.7 1 .20 74.? 25.8 100..5 t.\6 73.2 27.9 101.1 1.32 68.9 28.9 97,8 1.20 69.8 30.6 100,4 1.15 ?1.6 30.1 101.? 1.20 6',t.931.9 99.8 '10.569.5 30.8 r00.3 1.',tq 'l 102.1 0.99 101.7 1.1q 72.8 28.2 10't.0 r.33 69.431.9 101.3 .10 67,7 3q.4 31,2 '| 1.08 66.5 101.7 0.98 62.9 36.1 98.0 0.88 6?.? 33.1 100.6 .03 6',t.3 31.\ 98,7 't2,0 34.2 't,32 1,000 77.2 22.1 99.3 1 .7'l 70.6 29.4 r00.0 27,6 99.6 71.7 29.5 101.2 1.2,'| 73.1 28.2 101.3 1.31 67.934.0 101.9 1.31 69.131.5 100.6 .11 65.036.8 ',100.8lol,8 0.89 57.4 43.9 10r..3 1.01 67.831.3 99.1 1.09 59.6 r{1.2 0.73 50.2 50.6 100.8 0.66 65.6 33.1 98.? 1.00 71.\ 27,5 98,9 0.50 66.9 33.4 100.3 1.01 't9.\ 3,ooo 22,9 1O2.3 1,75 70.3 29.5 99,8 1 .20 73.428.3 l0l.7 1.31 ?0.1 29,7 99.8 67.8 32,1 99.7 1,06 70.5 3r.8 102.3 1.'t2 67.0 32.2 99.2 1.05 6rr.436.9 101 .3 0.88 66.8 31.2 98.0 1.08 65.3 37,O 102.3 0.89 60.4 rr0.'t 100.5 o.76 65.9 34.3 r00.2 0.97 59.0 39.6 98.6 'lo,ooo 't7,8 22.5 100.3 1.75 71.6 27.4 99.0 1.32 69.5 31.'t 101.2 !.11 69.331.3 100.6 69.rt28.4 98.2 1.23 65.7 32.4 98.2 1.02 70.3 31.? 102.0 69.831,5 101.3 66.4 33.1 99.5 1.01 66.6 31.7 98.3 1.06 72.\ 30.1 102.5 1 .21 66.133.8 99.9 0 .99 67.0 33.8 100.8 1 .00 'loo,o0o 77.\ 22,4 99.8 1.75 73,1 28.3 10r,4 73.1 27.7 tOO.8 1.33 70,5 29.7 100.2 1.20 1.14 69.928,9 98.8 67.8 30.8 98,6 1.11 59.3 30.? 'tO1.7100.0 70.0 31.8 101,8 1.11 6?.4 31.8 99.7 1.07 68.5 33.2 1.04 66,',t 33.6 100.3 1.00 66,7 32.3 99.0 1.04 66.r 33.',1 99,2 1.01 56.9 32,4 t00.3 I .01
known concentration of ferric sulfate coatedwith a cyanoacrylateglue ("Krazy Glue"), Fe2(SO)3.H2Oin distilled water (Table l). Five which was allowed to partly set. Several hundred different concentrationsof leachatewere used (10-5, grains of samples were sprinkled onto the sticky l0-2, 10-1,I and2 M). A leachingcontainer and X- mylar, and the elue was allowedto dry. This lessened ray mount machinedfrom nylon (Fig. 1) held the preferredorientation in the grains and allowd in situ leachate,which was freshly preparedfor eachexperi- study of phase changes on our vertical-sample ment. The sulfide grains were placed in the solution General Electric X-ray diffractometer. The mylar using the following technique.A thin mylar filn was was then placed on the container with the sulfide 250 THE CANADIAN MINERALOGIST
mylor leoch ing In a secondprocedure, only peakheight and posi- f i lm copper tion were monitored. With this technique, the sulfide goniometerwas setat the top of a peak in the diffrac- tion pattern for the structure being investigated,and fer ri c elostic soluiion this peak were noted with time. bond changesin height of This procedurewas commonly utilized in conjunc- holde r tion with that previously describedto detectchanges in structure with time. Stretched mylar has a very strong peak at about 29oNi the position and height vary during the leach- compo' Frc. l. Leachingapparalus used while monitoring The other peaks from mylar and sition of leachinggrarns on X-ray diffractometer'The ing experiment. glue broad, and easily coppersulfide grains are held to the mylar with a thin those from the are weak and layer of cyanoacrylateglue. subtracted from the spectrum. However, becauseof the peak al 29o, a sectionbetween 25o and 34o 20 could not be investigated. grains in contact with the solution, avoiding trapped air bubbles,and sealedto the sampleholder with an Monitoring compositional changes elastic band. The ratio of solution to mineral was large (approximately 2.25 crfi to 0.001 cm3),so that After the structural change - time relationships all but the most dilute solutions remained essentially had beendetermined, grains were leached under simi- constantin compositiontlroughout the experiments. lar conditions, washedin distilled water and analyzed In strongerleachates, significant structural changes compositionally using a MAC-400 electron occur rapidly. Becauseof this, the aboveprocedure microprobe equipped with wavelength-dispersion neededto be very time-efficient, as monitoring with spectrometers.Operating conditions were: operat- the X-ray diffractometer had to begin within twenty ing voltage 12kV, samplecurrent l'2 nanoamperes. secondsof leach initiation. The holder was therefore The following standardswere used: natural covel- kept as simple as possible. line (for Cu, S), bornite and chalcopyrite(for Fe)' Leachingwas conductedusing both syntheticchal- Apparent concentrationswere correctedfor absorp- cocite and digenitegrains. All experimentswere con- tion, secondaryfluorescence and atomic number ducted over a narrow range of temperature (about effectsusing the generalZAF program MAGIC IV 23o :tt"C). Dutrizac et al. (1984)have shown that (seeTable I for analytical results). there is a considerableeffect on leachingspeed in bornite with temperature variation. A similar effect Rnsulrs AND DIScussIoN could be expectedwith chalcociteand digenite. Weak leachqte tests (1 l0-3 M ferric suwte) Monitoring structural chonges No compositional or structural changeswere Structural changeswere monitored during leach- observedwhen synthetic chalcocitewas immersedin ing by oscillatingthe X-ray diffractometer over 6o leachateswith concentrationsof less than l0-3 M 20(44"- 50o),an interval that containsmajor struc- ferric sulfate for periods of up to three years. tural peaksin eachof the mineralsbeing investigated. Weak leachates(< 10-3M) in contact with syn- Filtered copperradiation was used. When a major thethic digeniteunder the conditions of this study peak changein the 6o 20 intewal was noted, a con- producedcyclic variationsin which the structureof tinuous scan (35o - 65") was made while leaching the grains changed from the digenite to the anilte continued.Quenching of the leachin distilled water structure and back. In 10-5M ferric sulfate solq- was attemptedin someinstances, but in most cases tion, the digenitediffraction peak with d = 1.967A this failed to completely halt structural changes. (plane10.10.0) eradualy decreasedin intensityover After threedays of continuousmonitoring, samples the first l0 minutes of leaching(Fig. 2). At the same were removed from the diffractometer but kept in time, peaks gradually appeared representingtbe the sameleachate for up to three years, subject to aniliiebtanesMo (a: r.'s3rA), +oti(d = r.s17L) periodic re-investigation for additional structural and 224 (d : 1.962A). fne net result was a lessen- changes.When a structural changewas observed,a ing of intensity of the original peak, with a gradual grain was plucked from the mylar, mounted on a broadeningof the baseof the peak. A measureof glass fiber and further investigated using a the distortion from the digenite structure to the 114.6-mm-diameterGandolfi X-rhy camera. The anilite structurein thesegrains is obtainedby divid- resultingfilms were comparedto thoseof standard ing the intensity of the peak by the basewidth, while digenite, anilite, spionkopite, yarrowite and maintaining an equal areawithin the peak. Area was covelline. determinedby counting squareson the diffracto- COFPER €ULFIDES'DUNNG LEACHING AND DISSOLI'TION 25,r-
2e 4ro 41" , 4?2e T+S' + fc2e F-t--1 A J\, F E E 9 F lrl I r ' v ! ul lrJ I G
ELAPSED TIME (MtN.)
Frc. 2. Cyclic distortion of digenite plane (10. 10.0) to anilite planes (040), (4@) and (724) in ferric sulfate leachate of lQ-5M. Maximum distortion occursat a peak heieht to width ratio of approximately 2.14. Representativediffraction- traces at three points in the cycle (dominantly digenite, mixed digenite,/anilite and dominantly anilite) are shown above the main figure. meter chart. This ratio is plotted as a function of Intermediate leochqtetests (10-2to ItrI M ferric time in Figure 2. sulfate) After leaching had continued for about 100 minutes, the majority of grains with the anilite struc- When the concentrationof the leachateis held at ture changedrapidly back to the digenitestructure. between l0-2 and l0-r M, copper is leachedfrom The ratio of the peak height to basedoubled as the both synthetic chalcocite and digenite. As concen- intensity of the monitored peak increasedin lessthan tration of ferric sulfate is increased,leaching occurs one minute. All peaksrepresenting the anilite struc- at an acceleratedrate (Fig. 3).When approximately ture were lost at this time and in each succeeding 40t/o of the copper has been removed from the cycle. This changeoccurred simultaneouslywith the material, leachingseems to reachan equilibrium con- increasein height of the digenite peak, suggesting dition, as shown by the merging of the curvesin concurrent events and essentially eliminating solu- Figure 3. This equilibrium is independentofleachate tion reprecipitationas a possibility. Figure 2 shows strength,and must thereforereflect an approachto the diffractometer trace at three points in this cycle. a more stable structural state. As leaching continued, this pattern of change was In intermediateleachates (10-2 to 5 x l0-2 M), seento continue in a cyclical manner. The sudden chalcocite leachesslowly to tetragonal-phasechal- changealways occurred when a certain ratio ofpeak cocite (Roseboom196O and then to digeniteand ani- height to basewas reached(under the conditionsof lite. From thesestructures it follows the sameleach- theseexperiments, about 2.14). After 300 minutes ing pattern describedbelow for digenite. the variation in the periodicity of the cyclesstabilized As digenite leachesin ferric sulfate concentrations at 32 minutes 37 secondst 15 seconds(Fie. 2). greater than l0-3 M, a seriesof structural changes Although these experiments were halted after ten occur resulting in a group of interacting metastable hours, the material was left in the leachate for up structuresthat all seemto'be basedon the geerite to three yeaxs,and then re-examinedusing the above (sphalerite-like) cubic structure, with the possible lsehniquesia cyclical changewith a period of 32 exceptionof type VIII. Each of thesegeerite-type minutes was still observed. It should be noted that structures has a main diffraction-peak in the inves- the majority of the grains follow the same periodi- tigated 20 rcgion, which Goble (1985)has related to city in cyclic change,even though they are not in con- the approximate radius of atoms of sulfur within the tact on the mylar of the sampleholder. structure. 252 THE CANADIAN MINERALOGIST o 'rlrl ()
lrl o J F E E Lrj 30 ,''":",'^a?'*'* (L r.30 L q o t.40 = C) 20 l'ri.?f- .,-'^'^ (J F lrl z .60 (9 lrl to i,,:/ ,,*'^ () E E |r, ul (L o to to2 ro3 t04 ELAPSED TIME (MlN.)
FIc. 3. The leachingof copper from digenite grains leachedat 23oC in ferric sulfate media. Data are basedupon microprobeanalyses. A singledata-point may representmultiple analyses.Ferric sulfate concentrations:open cir- cles 10-5to l0-3 M, crossesl0-2 M, open squares l0-l M, open triangles I M, hexagons 2 M. "O" on the time axis indicates the origin of sample measurement, not zero time on this logarithmic scale.
The resultspresented are a compilation of thirteen Goble (1981).During the next hour, another series experimentsrun under similar conditions. Erratic ofthree discretestructural changesoccur, resulting patternsoccur in eachexperiment but, becausethe in a setof relatedX-ray patternsclosely resembling standarddeviation in counts is a function of total that of the blue-remaining covelline,^yarrowite counts, when the thirteen setsof resultsare added (Goble1980) (d 1.903,1.900 and 1.898A, type-Vl togetherthe random variationstend to canceleach structure).Again, thesegrains lack the typical opti- other out, leavingrelatively sharp peakswhose size cal properties of yarrowite, and appear to have a and position vary as leachingcontinues. cubic closest-packedstructure, as Goble (1981) A compilationof the structuralchanges produced showed in a leaching study of single crystals of on leachingdigenite as indicated in X-ray-diffraction anilite. data is shown in Figures 4a and 4b. Within two As leaching continues, a new structure, with weak minutes of leach initiation, the typical grain has reflections,appears. This seemsto be a cubic poly- alreadychange! from the digenite(d for monitored Forph of the hexagonalcovelline structure (d 1.895 peak : 1.967A) to qheanilite (dfor monitoredpeak A, type-VII structure). This structure is extremely averages - 1,962 A) structure. In the next ten unstable, and in severalhours degeneratesinto a minutes, anilite undergoesa seriesof three strucfural seriesof closelyrelated, very poorly developedstruc- g,hanges;d valuesfor the peak monitored are 1.957 tures whosediffraction patterns resemblethat of the { (elapsedtime - 5 minutes,type-I structure),1.945 high-plessureform CuS2(d 1.892,1.887,1.883 and A (elapsedtime - 7 minutes, type-Il structure), 1.933 1.877A, type-VIII structure).This form has been A (elapsedtime - l0 minutes, type-III structure). producedonly under pressuresin excessof l0 kbar After leachingfor about 20-30 minutes,a structure (Munson 1966, Taylor & Kullerud 1972),demon- whose X-ray-diffraction pattern matches that pf strating clearlythat this is a metastablestucture. With geerite(Goble & Robinson 1980)forms (d 1.918A, continued leaching, the last structure (type-VIID type-IV structure). After maintaining the geerite graduallydisappears over the next 15-20hours, and structurefor about 30 minutes,the grainschange to structuresof type VII and VI becomedominant with one of two closelyrelated structures whose diffrac- time. tion patternsresemble that identifiedin spionkopite As shown in Figure 4b, several structures are (Goble1980) (d 1.910,1.907 A, type-V structure). presentin the sampleat any one time. Thesestruc- However, in polishedsection these grains do not have tures are not stable,but changeback and forth into the parallel extinction observedin this mineral by one another. When the grains are plucked, washed COPPER SULFIDES DURING LEACHINC AND DISSOLUTION 253 and investigatedwith the Gandolfi camera, filrns do not show the discretelines identified by careful inves- tigation on the X-ray diffractometer chart, but show il instead a broad diffuse band covering the entire UJ region in which these lines can be found. The presenceof the broad bands on the Gandolfi films z. c suggeststlat cycling betweenthe structurescontinues E, after the samplesare removed from solution. This lrl is confirmed by direct observation on the diffracto- .L ur a! meter of structural changesafter removal of sam- E. (Spionkopite)o ples from contact with the leaching solution and by ? q our inability to quench samples. This is to be I z (Geerite) expectedifthese are metastablephases that change = lr= back and forth over a short interval of time. During : r the severalhours involved in exposing the film in a u) l r Gandolfi camerathe lines from severalstructures tend to mergeinto broad bands. tL Optical propertiesindicate that the structuresof minerals based on variations of hexagonalclose- UJ packing (i.e., covelline,yarrowite, spionkopite)are \nillte E not presentin this leachingsequence. Instead, all the ; major known structuresin this sequenceare based I (i.e., geerite on cubic close-packing is rhombo- -l'l'llllll hedral/pseudocubic,anilite is orthorhombic./pseu- tl t.97 1.94 l.9l t.ut, docubic, leached anilite forms are rhombo- d volue of peok (A) hedral,/pseudocubic,and high-pressure CuS2 is orthorhombic/pseudocubic). Therefore, it is Frc. 4A. Position of X-ray-diffractometer peaks reasonableto assumethat all the metastablestruc- (44-50"2q for various leaching-producedstructures as tures are also basedon cubic close-packing,and that a function of time of first appearance. Line $ridth no major changesoccur in the packingof the sulfur representsrelative intensity of peak. atomsthroughout the leachingof digenite.The struc- tural changesare the result of loss of copper from the structureand minor changesin the layersof sul- fur, resultingin compressionof the structure,as evi- VI dencedby the decreasein the d value of the X-ray U reflection monitored throughout the leaching(Fig. E :f 4a). This spacingis approximatelyequal to the radius IV of the sulfur atoms in this structure (Goble 1985). F Although it is difficult to obtain good complete diffraction-patterns for each of these structures E ll independentof othersunder the conditionsof these F experiments,it is clear from the sequenceof changes I o produced and from optical properties that the hexagonalblue-remaining covellines,yarrowite and ANILITE spionkopite are not forrned during the leachingof D IGENITE -VI digenite. The type-V and structures €ue me- 4 tastablepolymorphs of yarrowite and spionkopite, but have cubic close-packingof the sulfur atoms ELAPSED TIM E rather than the combination of hexagonal close- Frc.48. Relative proportion of eachof the observedstruc- packing and covalenl bonding observedin the yar- tural types present with time, base-don relative inten- rowite and spionkopitestructures by Goble (1985). sity of'X-ray-diffraction peaks (10-2M ferric sulfate). In this respect,our resultsagree with thoseof Goble "O" on the time axis indicates the origin of sam- (1981).However, we cannot as yet reach any con- ples measurements,not zero time on this logarith- clusions regarding the stability or metastability of mic scale. yarrowite and spionkopite. leaching of digenite produces no structural changes (> Strong leochote tests lft M ferric sulfate) other than those observed in weaker solutions (see With higher concentrationsof ferric sulfate, the above). The speed with which these structural 254 THE CANADIAN MINERALOGIST changesoccur is, however, greatly accelerated,as werebased on the samehexagonal subcell, and Evans shownin Figure 3. For example,at a concentration (1979)showed that the dominant co-ordination of of 2 M, the type-VIII structure is reachedin about sulfur about-cppperis triangular, basedon hexagonal ten minutes. close-packing,and similar in low chalcociteCurS Higher concentrationsof solution combinedwith and djurleite Cu1.eaS.Portions of the covellineCuS a chalcocitestarting material, however,gives drama- structure are similar. With this in mind the existence tically different results.When concentrationsof fer- of two pathways for the structural changesin the ric sulfate greaterthan l0-l M are used, insteadof leaching process, one built around cubic close- leaching from chalcociteto tetragonal chalcocite, packing and one around hexagonalclose-packing, chalcocitetransforms first to a form whosediffrac- is a natural consequence.The existenceof this second tion pattern is identicalwith that of djurleite, which pathway is further substantiatedby the optical obser- has hexagonalclose-packing of sulfur layers. As vation of Dutrizac et ql. (1984)of < l-micrometre leaching continues, instead of digenite a discrete, massesof blue-remainingcovelline in bornite leached poorly developedmgtastable state is observedwith in 0.2 M ferric sulfate. Their suggestionthat this a d value of - 1.92A for the reflection monitored. might have originated from leachingof chalcocite This transformation occurs within 20 minutes of impurities seemsto confirm our observations. leach initiation. As leaching continues, two ap- parently stablequenchable forms are produced;X- Sincethere are two pathwaysin the leaching,there ray-diffraction patternsstrongly resemblethose of is a further ambiguity in the observationsof Potter natural spionkopite and yarrowite (Goble 1980). (1977) and Goble (1980)relative to the $tability or Theseforms also showthe typical optical properties metastability of yarrowite and spionkopite in the sys- of these blue-remaining covellines, although as tem copper-sulfur. Whereasour results and those shown by Goble (1981),these properties are not by of Goble(1981, 1985) clearly demonstrate that phases themselvesproof that they havethe samestructures. produced by leaching digenite or anilite in ferric sul- When leachedfor three yearsin this sameleachate fate solutionsdo not havethe hexagonalstructures concentration, the structure doesnot changefurther. of yarrowite and spionkopite, it remainsto be shown However, in strongerconcentrations (i.e., - 2 M) that the phasesproduced by leachingchalcocite in a further changeto the covellinestructure appears the samesolutions, even though apparentlybased to occur after three days. This structurethen persists. upon hexagonalclose-packing of the sulfur atoms, Structurally, the existenceof this secondtype of havethese structrues. The starting products and con- leaching in copper sulfides is not surprising. Takeda ditions of leaching are clearly important factors that et al. (1961).showedthat low chalcociteand djurleite must be consideredin any studiesof stability.
G lrl = ts lrl G =' o lrl rrt JO !a ltt JT z E Ftr frl -v E G Jt! N 9 lrf o o o ul a (' z9 (, (t at CoMPosrrIoNALDETERMINATIoNS compositions for the leachedgpins tend to cluster about known valuesin the system'copper-sulfur(Fig. Once the structural variations with time and 5), but the grains are probably polymorphs of known leachateconcentration had been determined,com- minerals, as discussedabove. A number of other positional analysisof grains with each structure was compositional peaks also occur; the relationship performed using a MAC 400 electronmicroprobe. betweenthese compositions and the structurs deter- Synthesizedstarting material was leached under mined by X-ray-diffraction meansare indicatedon conditions approximating those previously deter- Figure 5. In addition to compositionsthat match mined for the production of eachof the eight struc- eachof the identified structures,several anomalous tural types.The only differencewas that the grains Cu:Svalues were found (i.e., 1.51,1.45,1.35,1.23 were not mounted on mylar, but leachedunmounted and 0.80). Theseilay representmixtures of two or in a sealedcontainer. At time intervals determined more phasesfound in the X-ray studies. by the previous experiments,several grains were In this study a number of grainswere analyzed that removed from the solution, mounted in cold-setting haveCu:S valuesof lessthan 1. Grains of this com- epoxy, polished and analyzedfor copper, sulfur and position are unknown in the natural system.Several iron. The data are summarizedin Table I and Figure additional leaching and analytical experimentswere 5. Iron was determined in all grains but never carried out to test the accuracyofthese findings, with exceededbackground values. As can be seen,com- similar results. Therefore; we believethat thesecom- positionsdetermined for individual grainsare occa- positions are real. sionallynot in keepingwith the grossconclusions of this study. This is probably dueto variationsin fac- tors suchas grain size,orientation and degreeof frac- NATU RA L turing. Such factors have been shown by Dutrizac et al. (1984) to influence the leaching speed of individual grains of bornite (and presumably digenite)to a considerableextent. It is also uncer- tain that conditions in the experimentsdone without the mylar film are completely equivalent to those previously determined(i.e., the questionsof how much influence the cyclic variation has on the struc- 1.6 tures and whether the cyclic variation is mylar- dependent are still not completely answered). However, as a group, grains leachedwithout the presenceof mylar or glue seemto behavein a simi- ol.4 lar fashion to those leachedon mylar in the nylon holder while being subjected10 X radiation. F E 1.2 TABLE 2. PERCEIITAOEOF SULFIDE GNAINS III EACN STRUC1UNALllPS AS A FUNCTIO'I OF TIME. TNE PERCENTACEOF TIIE ORIGIIIAL COPPEN LEACIIED FROUTIIE GBAINS I3 ILSO SHOUN Leaohlng Stfuotu.el Typa t Cu 6 r.o Tine (mrn) DIC AN I 1I III M VMMII Leaahed 01 1 l.J 3 3.6 3.5 ri l:::: 4.0 o'8 c 4.5 35 4,8 40 4,9 7 50 5.2 10 50 5.4 4510- 6.C 50 50 20 10 10 9.1 100 3030201010-'lo o.6 300 10 20 20 20 20 16.0 500 5 l0 20 lto 10 15 20.7 750 -525301523 22.O 1,000 --15302520 3,000 -403025 5 33.0 10,000 -204040 38.0 lo lo StartlnS nat€r1el ras dlgenlte; l€echsto cobcentratlon 1O-2 U NUMBER OF GRAINS ferric suLfato. !1I peraentage veluoa for slruotural typos arg approll@ately +/- 5 rt end ar€ based upo! s coEparlson of cooposttlon valuos fron Table 1 rlth pesk lntensitleB for esch Frc. 6. Comparisonof composition of gains leachedin staucture as observsd on iho X-ray diffractoaetea. DIo lndlcatea th€ dlgEtrlt€ and AN the atrtl.lte structure' ferric sulfate in this study and naturally occurring cop- respgcllvo1y, Tlte vafu€3 lor percent oopper leachgd are atooic (1973)' percenbages baaed upon ohdnges ln curs aailo. per sulfide grains analyzedby Goble & Smith 2s6 THE- C-ANADIAN MINERALOGIST -VII 1.98 ing and then changesback to a type-Vl or struc- Rr"=L86O+O.O58(Cu:$i ---\1-e-"-t ture with further leaching.This givesfurther evidence for the continued edstenceof the cubic close-packing t.96 p of sulfur atoms throughout the digenite leach, becauseGoble (1981)showed that material leached R (A) for sevento ten daysretains cubic close-packingof t94 *-h sulfur atoms. When the determinedcompositions are compared Rr=L86o+o.os;r,t1' with natural copper sulfide compositions,such as 192 those reported by Goble & Smith (1973), a close matchis found in the Cu:Srange 1.00 to 1.35,and in the anilite - digenite region (Cu,.rrS-Cu,.roS),but A agreementis poorer in the intermediate range and below CuS (Fig. O. In the rangeCur.oS - Cu,.,rSwe are apparently looking at polymorphs of the natural l'.2 t4 1.6 l.u 2o Cu:Srotio phases.The lack of natural analoguesin the ranges Cu1.35S-Cur.6eSand Cue.5S-Cu1.sSis not unex- pected,since the phasesin thesecompositional ranges have only short-term stability in the leachateand _or_r-i occur only under very specializedconditions. It #- l: r, ^: should be noted, however, that some anomalous r1 I valuesin the study of Goble & Smith (1973)appear t0 I. to match compositionsfound in this study and that tI l:l. we do find a significant compositional peak cor- dl_tt respondingto geerite(Cu1.6S). With the exception .:t.L of the starting material and anilite, this is probably -- 1.4 In a seriesof papers,Goble (1980, 1981, 1985) pro- Cu:Srotio posed a relationship between structure, as ftc.7A. The relationship betweenradius R of sulfur atoms representedby sulfur radius and spacingbetween sul- within sulfur layers and composition for copper sulfides fur layers,and compositionfor the coppersulfides. (after Goble 1985).Data points at Cu1.32Sand Cu1.5"S Becauseof lack of data and anomalousdata for indicate Goble's analyzedcomposilions for spionkopite djurleite, only a tentativerelationship between sul- and geerite;two data points at Cul.8Sindicate two pos- fur radius and compositionwas given for the inter- sible R valuesfor digenite;data points at Cu1.e3Sand val Cu1.75S-Cuz.oS(Fig. 7a). In addition, therewere Cu1.97Sindicate two possible compositions for no data points betweendigenite and geerite. djurleite. B. Changesin composition and d value When the new metastablestructures identified here produced grains during dissolution of of digenite and are added to Goble's (1985)plot of sulfur radius chalcocite. Circles indicate starting materials; squares indicate leached phaseshaving structures based upon velJa,tcomposition @g. 7b), it is seenthat the origi- cubic close-packing; triangles indicate leached phases nal relationship from digenite to covellite appears having structuresbased upon hexagonalclose-packing. to be approximately correct. Triangles representthe new data-points(Fig. 7b). The relationship shown can now be usedto indicatea pathwayof structural Cu:S values of less than I were not found in any transformationproduced upon leachingdigenite, as of the long-term leaching experiments (Table 2). This indicated by the arrows in Figure 7b. Chalcocite, suggests that had the grains been left to reach upon leachingin dilute ferric sulfate solutions, fol- equilibrium with the solution, they would have lows the Cu1.75S-Cu2.eSrelationship originally sug- returned to a Cu:S value of 1.06 in lessthan one day. gestedby Goble (1985).In addition, a new leaching This appears to be the composition that the grains pathway for hexagonalclosest-packed sulfur atoms approach with longer leach-times as well (Goble can now be added, in which chalcociteleached in l98l). This compositional change is in agreement more concentratedferric sulfate solutions is trans- with the X-ray observation that the structure of formed to djurleite to spionkopite to yarrowite to CuS2 (type-VIII structure, Fig. 4a) is produced as a covelline as shown in Figure 7b. It is particularly poorly developed metastable phase during the leach- interestingto note the path through djurleite and COPPER SULFIDES DURING LEACHING AND DISSOLUTION 257 near Cur.es, since this clears up the djurleite solutions used (10-5to 10-3M) will probably be anomaly in the earlier data of Goble (1985). depletedin ferric ion. However,even if equilibrium betweenthe solution and the sampleis reached,this SuurraenyAND CoNCLUSIONS fails to explain the cyclical changefrom digenite to anilite and back again. In this seriesof experiments,we have found that Sincethe changefrom the digeniteto the anilite chalcociteand digeniteleach differently as concen- occrlrswith great ease(simple physical grinding can trations of ferric sulfate leachateare varied. Chal- this transformation), the causeof this cyclic cocite can take at leasttwo paths as copper is leached neednot involve large exchangeof energy. from the structure. If leaching is done slowly, In t{risexperiment, the grainsare not in physicalcon- tetragonal-phase chalcocite forms and leaches so any simultaneous change in the individual through a seriesof structuresthat are all basedon gra must involve one of the two media that are cubic close-packingofthe sulfur atoms, but that have inr iical contactwith all the grains, i.e., the glue no apparentnatural analogues.With rapid leaching or tfie mylar. Any hypothesismust also explainwhy of chalcocite,cubic close-packingis never produced, occurs after a certain number of grains and all leachedforms seemto be basedupon hex- to the anilite structure,and why this occurs agonalclose-packing ofthe sulfur atoms, or avari- in al constant interval of time. ation of this, as in covelline. We suspectfrom the is possiblethat asthe digenitedistorts to the ani- optical propertiesofthese forms that they are true lire structure the energy lost from the digenite blue-remainingcovellines, possibly yarrowite and spi- on the mylar as an electric charge, and onkopite, which eventuallytransform to coveUine at the end of the cyclethe chargereaches a suffi- upon further leachingor dissolution. However, as high level to discharge back into the struc- noted by Goble (1981),we cannot be certain of this transforming the anilite back to digenite. In less sincewe did not do single-crystalstudies. experimentsother glues and petroleum Under were tried as replacements for the "Krazy the conditions of theseexperiments digenite ', doesnot appearto transform to structuresfound in with only minor variations on the original nature, with the exception of anilite and geerite. ts. There are many other variations on this Geerite,found in natureas an epitacticreplacement iment that could further elucidatethis process' of sphalerite(Goble & Robinson 1980),appears in using a variety of mounting media and this leaching system as only one of a series of the processwith other minerals whose metastablestructures, which all appearto be based do not transform as readily. At the very on cubic close-packingof sulfur atoms. , it can be said that the readily observabletrans- The appearanceof phaseswith Cu:S valuesof less tion from the digeniteto the anilite structure than 1.0 and the similarity of X-ray patterns of these ble and doesnot require a compositional structuresto that of CuS2,which is known to have covalent bonding ofsulfur atoms, suggestth4t given process,with different time-sequences,is also sufficient time in the leachate,covalent bonding of as structural transformationsoccur between 52 atoms will begin to form in the cubic close- the phasesidentified in this paper, and is a clear packed structures.However, the instability of the I that a transformation is actually occurring. phasesencountered and the observedcyclicify in their As check, a blank consistingof quartz on mylar stability suggestthat thesecovalently bonded sulfur glue was monitored. No cyclic variation was atoms are not oriented in layers as in the covelline, , eliminatingthe possibilitythat we wereactu- yarrowite and spionkopite structures.Instead they seeinga cyclic variation in our instrumentation are probably arranged in several differenl oriefta- imental setup. tions as in the structure of high-pressureCuS2. The cyclic variation of digenite to anilite and its many different type-VIII structures that we observe in weak solutionshas somevery interesting (Fig. 4a) and their transformation with time to a for investigationof other easilytransforma- phasewith the approximatecomposition of Cu1.5S ble res in other systems.Much work still may reflect an ordering of these covalent bonds rernains'to be done to establish the conditions toward the more stableconfigurations of covelline, governingthe transformation. yarrowite and spionkopite. Although the preponderanceofevidence from this An unusual aspectof the leaching behavior of study clearly suggeststhat both Goble (1981, 1985) digeniteis observedwhere very low concentrations and Potter (1977)were correct in their observations of ferric sulfateare used.In this case,a cyclictrans- regardingthe stability or metastabilityof the blue- formation from digenite to anilite and back again remaining covellines(i.e., under the conditions of is setup, with a setperiodicity establishedfor each Potter's work he would haveseen metastable forms cycle. Calculations indicate that with even the very resemblingthe natural stable(?) mineralsidentified minor changein compositioninvolved the very dilute by Goble (1980)as yarrowite and spionkopite),we 258 THE CANADIAN MINERALOGIST cannot as yet reach any conclusion with regard to & Svrrn, D.G.W. (1973):Electron microprobe the stability or metastability of yarrowite and spi- investigation of copper sulphides in the Precambrian onkopite. However, it is now obvious that further Lewis Series of S.W. Alberta, Canada. Can, work needsto be conductedon the leachingof chal- Mineral. 12, 95-103. cociteand its end products. This seemsto be the most (1964): Iikely way in which synthetic specimensof yarrowite Mon, G. Blaubleibender covellite. Carnegie Inst. Wash. Year Book 63,208-209. and spionkopitecan be produced.Such experiments must of course be conductedin conjunction with (1971): Blue-remaining covellite and its relatioru single-crystalstudies. to phasesin the sulfur rich portion of the copper- Further single-crystalX-ray work on all phases sulfur system at low temperatures. Mineral. Soc. producedwill be neededto fully demonstratetheir Japan Spec. Pap. 1,226-232. true nature. It is also necessaryto test the second techniqueused for synthesizingblue-remaining covel- Monnaoro, N. & Koro, K. (1970): Phase relations of line (sulfurization of anilite in organic solvents)using the Cu-S system at low temperatures: stability of zntlite. Amer. Mineral. 55. 106-117. the methodsof Moh (1971),to seeif similar struc- tural changesare produced. It would be useful to & Snuuazan, Y. (1969): Anilite, vary temperature at each concentration since Cu7Sa, a new mineral. Amer. Mineral. 54, Dutrizac et al. (1984) have shown that this is a fac- 12s6-t268. tor of some importance. Finally, electrochemical studies and differential thermal analysis (DTA) of MuNsor.r,R.A. (1966): Synthesis of copper disulfide. the materialsprepared using the two types of syn- Inorg. Chern. 5, 129G1297. thesisshould be employedto determinestabilities and (1971): similarities in behavior. OrrruaNr, J. & FneNzrI-, C. Neue mikrosonden-Untersuchungen an ldait, Covellin und blaubleibendem Covellin. Neues Jahrb. RSFERENCSS Mineral. Monqtsh., 80-89. Durntzac, J.E., CnnN, T.T. & Jalason,J.L. (1984): Porrrn, R.W., II (1977):An electrochemicalinvestiga- Mineralogical changes occurring during the ferric tion of the system copper-sulfur. Econ. Geol, 72, iron leaching of bornite. Minerals Research Pro- 1524-1542. gram, Mineral Sciences Laboratories, Division Report, MRP/MSL 84-94 (J). Prmqrs, A., Gnecr, J. & CatltenoN, W.E. (1977): Blaubleibender covellite and its relationship to nor- EvaNs, H.T., Jn. (1979): Djurleite (Cu1.eaS)and low mal covellite. Contr. Mineral. Petrologlt 60'2W217. chalcocite (Cu2S): new crystal structure studies. Science203, 356-358. Rrcranp, D.T . (1972): Covellite formation in low tem- perature aqueous solutions. Mineral. Deposita 7' FnENzsr,G. (1959): Idait und "blaubleibender Covel- 180-188. lin." Neues Jahrb. Mineral. Abh. 93.87-132. Rosesoolr4,E.H., Jn. (1966): An investigation of the (1961):Der Cu-Uberschuss des blaubleibenden system Cu-S and some natural copper sulfides Covellins. Neues Jahrb. Mineral. Monatsh., between 25o and 700oC. Econ. Geol. 61, Al-672. t99-204. Srruror, R.H. & Crenx, A.H. (1969): Copper and Gosrr, R.J. (1980):Copper sulfides from Alberta:yar- copper-iron sulphides as the initial products of rowite CueS6and spionkopiteCu,nS1. Caz. supergeneoxidation, Copiap6 mining district, north- Mineral.18, 5ll-518. ern Chile. Amer. Mineral. 54, 168+1710. - (1981):The leaching of copperfrom aniliteand TarEoa, H., Dor.rNev, J.D.H., Rossnool\4,E.H. & theproduction of a metastablecopper sulfide struc- Appr-pueN, D.E. (1967): The crystallography of lure. Can, Mineral. 19, 583-591. djurleite Cu1.e7S.Z. Krist. 725, 404413. (1985):The relationshipbetween cryStal struc- Teyron, L.A. & Kur-tsnup, G. (1972): Phaseequilibria ture, bonding and cell dimensionsin the coppersul- associated with the stability of copper disulfide. fides. Can. Mineral. 23. 6l-76. Neues Jahrb. Mineral. Monotsh., 458464. - & Roslr.rsoN,G. (1980): Geerite, Cu1.6nS,a new copper sulfide from DeKalb Township, New York. Received luly 20, 1985, revised manuscript ac- Can. Mineral. [E, 519-523. cepted November 20, 1985.