W. L. Cnmrrn Mineralogisk4eologisk Museum, Sa:S' Gate 1, Oslo 5, Norway

Canadian Mineralogist Vol. 18, pp. 59-70 (1980)

CONTACT-METAMORPHICLAPIS LAZULI: THE ITALIAN MOUNTATNDEPOS|T8, COTORADO

D. D. HOGARTH Department ol Geology, University of Ottawa, Ottawa, Ontario KIN 6Ns w. L. cnmrrN Mineralogisk4eologisk Museum, Sa:s' Gate 1, Oslo 5, Norway

ABsrRAcr Mots-cl6s:lapis lazuli, Italian Mountain, Colorado, formation Belden, m6tamorphisme de contact, la- In the Italian Mountain area (Colorado), lazurite zurite, m6tasomatisme. formed early, apparently in equilibrium with diopside, forsterite and perhaps barian phlogopite, whereas grossular formed later. Thomsonite re- INTRoDUcTToN presents a late-stage hydrothermal alteration of lazurite. Thomsonite, chlorite and hisingerite, just Lapis lazuli comprises a group of rare meta- beyond the lapis-lazuli zones, are also late minerals. morphic rocks having lazurite as an essential The deposits resulted from contact metamorphism constituent. The most common type, composed of subgreywacke and dolostone of the Pennsylvanian of coarse-grainedlazurite and diopside and in- Belden Formation by quartz monzonite and quartz diorite of the Tertiary Italian Mountain stocks. Na, terbedded with marble, is remote from any S, Ba, Sr, Cl and F were introduced in aqueous igneousrock that can be related to its formation. magmatic fluids. Early barite may have localized Recently, Kulke (1976a, b) and Hogarth & later barian phlogopite and lazurite. Late introduc- Griffin (1978) proposed that rosks of this type tion of Fe produced the Fe-rich silicates. unusual in Afghanistan and on Baffin Island constitute in lapis lazuli. Peak metamorpbis conditions were meta-evaporitesrecrystallized during high-grade P - 250 bars. T ry 600oC. regional metamorphism. The deposits in Gun- nison County, central Colorado, differ in many Keywords: lapis lazuli, Italian Mountain, Colorado, respects from these. They are comparatively Belden Formation, contact metamorphism, lazurite, metasomatism. fine grained, other minerals are significant, and the deposits lie within the contact-metamorphic Sovtvrlns aureole around an intrusive rock. Several occurrences are known, clustered in Dans la r6gion dite Italian Mountain (Colorado), two localities known as North Italian and Italian la lazurite s'est form6e t6t. vraisemblablement en Mountains. The lapis is restricted to impure Equilibre avec le diopside, la forst6rite et peut-etre marble layers of the Belden Formation @ennsyl- le phlogopite barifdre; le grossulaire a cristallis6 vanian) near their contact with quartz monzonite plus tard. La thomsonite repr6sente un stade tardif and quartz diorite of the Italian Mountain stocks d'alt6ration hydrothermale de la lazurite. Thom- (Tertiary). Locations are given in Figure 1. sonite, que chlorite et hising6rite, min6raux I'on Both localities are within the contact-meta- trouve au-deld des zones i lapis lazuli, sont aussi aureole of the Northern Intrusive Cen- de formation tardive. Ces gisements r6sultent morphic du comprising m6tamorphisme de subgrauwackes et de dolomies tre, the youngest of the three stocks du Belden (Pennsylvanien) au contact de monzo- the Italian Mountain Complex (Cunningham nite et diorite quartzifdres de plutons tertiaires. N4 1976). This northern stock is a composite in- S, Ba, Sr, Cl et F proviennent de fluides magma- trusive body with an outer zone of melanograno- tiques aqueux. Une premiEre g6n6ration de bary- diorite and quartz monzonite. The inner part, tine aurait amorc6 la cristallisation ult6rieure de made up of porphyritic quartz monzonite, is phlogopite barifdre et de lazurite. L'introduction tar- pierced by a plug of finer grained quartz mon- dive du fer a produit des silicates de Fe, rares dans interpreted as a vent facies by Cunning' le lapis lazuli. Les zonite, conditions m6tamorphiques ont (Fig. 1) atteint environ 250 bars et 600oC. ham. The Italian Mountain occurrences probably were also affected by contact metamor- (Traduit par la R6daction) phism during the intrusion of the quartz diorite 59 60 THE CANADIAN MINERALOGIST

Frc. 1. Geology and lapis lazuli occurrences in the Italian Mountain area. The oorth-trending faults are part of the bastle Cieek Fault system. Geology aftei Cunningham (1973, 1976), with minor altera- iions after Truebe (1977) and peisonal observaiions by D.D. Hogarth. Drawing by E.W. Hearn (Uni- versity of Ottawa).

from the Central Intrusive Centre, the oldest of fault zone (Frg. 1) predates the intrusive rocks' the three. and probably provided channels for movement The north-northwest-trending Castle Creek of fluiAs during and after the metamorphism. CONTACT.METAMORPHIC LAPIS LAZULI 61

The faults were reactivated in late Cenozoic time tain about llz km south of the Anderson oc- (Cunningham 1976). currence. Lapis lazuli is found in place at the upper occurrence(U in Fig. 1), prob- North ltalian Mountain and in float ably derived from nearby bedrock at the middle Locality A, the Anderson occurrence, has (M) and lower (L) @currences; adjacent blue produced a small amount of gem-quality lapis marble, in situ, contains scattered lazurite grains. lazuli over a number of years (Rosencrans1941, The upper occurrence is the largest and best Truebe 1977), The productive horizon has been exposed. Here lazurite occurs rn marble over stripped in an east-northeastdirection for 30 m. a width of 1.5 m but lapis lazuli of good color A pit, said to expose some lapis lazuli but now does not appear to exceed 2.5 bm in width. filled with debris, lies on strike 17 m to the west. The lazurite-bearinglayer can be followed about The rock dips 30 to 40o to the north and into 30 m down the slope of the mountain. It is cut the slope. Lapis lazuli of varying color is re- off by a fault to the east, but lazurite reappears stricted to a layer of dark tactite one m thick. in blue marble (specimen U20, Table 1) 15 m This layer is itself divided into centimetric to still further to the east. millimetric lazurite-rich sublayers alternating with lazurite-free horizons. MINERALoGY Lapis lazuli also occurs at two nearby localities. To the south, blocks of lapis are found The Italian Mountain peals have long been in a talus slope within an area of 0.4 hectares.At known as prolific mineral localities. Cross & one point (ocality B) an exposure of pale lapis Shannon (1927) described 28 minerals from several metres across appears to be in place. tastite developed in the Belden limestone. Al- The closest outcrop of the Italian Mountain though lazurite was not noted, the general as- stock is 40 m away. semblage is closely similar to that described The other locality, the Christopher occurrence, below. Grossular, diopside, scapolite,thomsonite, is on a spur of the steep northeast-facing slope sphene, calcite, pyrite and barite, described by of the mountain (ocality C). The rock here is Cross & Shannon,were also noted in our sfudies. intensely brecciated and composed of contorted The lapis lazuli occurrences comprise an in- fragments of limestone and mudstone cemented teresting mineral suite, but the size of grains and by coarse carbonate. It was mapped as part of their morphological developmentare no rival for the Castle Creek fault zone by Cunningham the minerals described by Cross & Shannon. (1976). Somewhat separated blocks of white, Rather, the grains are roundish to irregular and lazurite-bearing silicated limestone up to 25 cm microcrystalline, with individuals down to and long are found in the breccia over an area of beyond the resolution of the microscope. Speci- 8 m2. Some of the pieces contain sky-blue mens from the Christopher occurrence are ex- patches, but normally the color is very pale. tremely fine grained and quite unsuitable for Yellow and grey bloc*s are lazurite-free. point counting. The size of grains was a prime consideration in selecting specimensfor misro- Italian Mountain probe analysis. The Truebe occurrencesare on Italian Moun- From 54 thin-sectioned specimens of the lapis

TAALE 1. UODAI ANALYSES OF HAIBIA. LAPIS IAZULI AND TAqIITE FR.M IrAIIEN Uq'NIAIN AiEA

North ltali.u ltoutaLn Itali,e liloqtaLn A2 A4 AI0 A25 826 C2 C3 920 u2 3 '924

Diopaide Fo!sterlts 0.0 ]re. r Jzz.s]rz.o ]u.s )u.u )r.t jza.7 Iizrlte 0.0 Iho@onlts 12.3 ),., )rs.a \z.e ho.s ):.r ]zr.s Irr.2 Phlogoptt€ 11.3 0.0 0.0 0,4 0.0 0.0 9 Geaaularite 0.0 0.0 0.9 0.0 0.0 0.0 4.o 0.0 SaIDiLt9 0.0 h& 0.0 26-7 0.0 C:hlorit€ 0.0 gL6LDgerite 0.0 0.0 0.0 0.0 0.0 0.0 {.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Pyrlte 6 PyEhotlt€ LT.2 0.1 6.0 1.8 3.9 6

glEcl@a-pr€flxos A, B, C sdl U @lroslEnd to l@atlotra i.n Flgue l. l? Nodulo-ln 1l9ht yeII@ tactLte, 0.3 n abovE tapis lazult iayer. CoUect€d.. A4 Pale blue lapis lazull. WeaC €nil E6nch. Colleat€d. Al0 Brtgbt blu€ lapls lazulL. 10096 @t'orial oa slae of, t!e!ch. @ltscteal. 425 PaL6 blE-gteen 1ap16 lazuu.. at. Ada@, dlonor. 826 Pals blu6 lapLa Lazull. Contle of s@ll outcep. Collsctedt. q? g"iy tactLte. . t@dlately 6a6t of tapL6-tazutL- itetpsLe. Clttecled. C3 Palo ble lapLs lazull f,&D pqt o! outcrop rtcbsst t! lazrlts, Cou.gct€d. U20 Bl@ @!ble. I0 E €ast of lapls lazqll. !. frueb€, do@. u23 Palo blE lapls lazul.l. ptt 25. collsctgd. O24 Brtgbt bl@ lapl,s Lazutl. plt 24. q. trEbo, doror. 62 THE CANADIAN MINERALOGIST

All 10 specimens, as well as 2 specimens of relatively unaltered Belden Formation, were analyzed for 19 constituents by wet or instrumental methods under the direction of E.J. Brooker, X-ray Assay Laboratories, Toronto. Lazurite crystals are optically isotropic and normally anhedral or ovoid, although tiny dodecahedra were noted in thin section U24 (Italian Mountain) and in a thin section from locality B (North Italian Mountain). Grains greater than 0.1 mm in diameter are rare. Lazurite is distributed as inclusions in calcite (Fig. 2) and as many larger and paler crystals located on grain boundaries. It shows a slight tendency to be associated with other srlicates, Frc. 2. Anhedral grains of diopside and forsterite and some lazurite grains are rimmed by diop- lying mainly along the grain boundaries of cal- side. Pyroxene and olivine, where coarsegrained, cite, plus random grains of lazurite (dark grey are in contact with lazurite. to black). SpecimenA25. Plane-polarizedlight. Photograph by Georges Ben-Tchavtchavadze In Table 2,lanu.ite has been assignedthe for- (University of Ottawa). mula (Na,Ca,K,Fe,Mg)e-"(Si,Al)uOr4(SOa,Cl,F):. Sulfur valencies were not resolved, and the sur- lazuli occurrences, 10 were selected for modal plus of S+CI+F possibly is due to a replace- analyses(Iable 1). Of these, 8 were suitable for ment of O'- by S"- as proposed by Hogarth & microprobe work. Seven microprobe analyses Griffin (L976). Compared to lazurite from most were made at Carleton University (P. Morton, known occurrences,potassium in these samples analyst) with a Cambridge MK 5 probe using a (O.3VoKzO) is high. Similarly, chlorine is high defocused beam. Wherever possible several at Italian Mountain (O.4Vo Cl) but normal at (0.14.2/o grains (up to 8) per section were analyzed; ana- North Italian Mountain Cl). Light- lytical data are an average of these values. and dark-colored varieties @26, Table 2) show Standards were a combination of synthetic and little difference in chemical composition; the natural minerals. Data were reduced using a color variations must be ascribed to different the lazurite struc- modified EMPADR VII program @ucklidge & speciesof sulfur ions within Gasparrini L969). One sample (A25) was ana- ture, as previously proposed by Hogarth & lyzed in Oslo with an ARL-EMX microprobe Griffin (1976). using the methods outlined by Hogarth & Griffin Both diopside and forsterite are present as (L976, 1978). somewhat rounded grains and in thin sestion

IAAIIB 2. UICROPROBE ANALYSEB OI' IAZURITE

Italian UoeteLn North rtalle uo@tah u24 826(pa1g bluE) 826(brtgbt blue) sLo2 33.94 TlOr 0.01 0.0 0.0 A1Z6: 27.64 26.4 27.05 21.59 FeO. 0.05 0.03 o:o 0.04 0.02 unO 0.0 ugo 0.0 0.05 0.06 0.06 0.09 CaO 8.20 9.24 Na2O 16.36 13.45 13.08 Kzo 0.28 0.27 0.32 o.24 0.31 903rr 14.06 17.01 16.55 L7.40 0.42 0.38 0.L4 0. t9 0.19 F 0.0 0.07

61 6.034 g.l:ilrz.oo6.L24 rz.oo 5.966I rz.oo l.!l!)rz.oo| !.!!!|rz.oo 5.972] Fg 0.008 0.00s1 10.000.1 0.006) 0.003 Mi 0.000 -tt-t-l \ !{g 0.000l o.o24 ''','l.llt l?.56| i:!)l !z.zz !.!|! )o.sa1.798 e.r' NA 6.024 5.s351 l6.00r( 4.7971 1.579 i K 0.065I 0.063) | 0.078,,, 0.0s6 ,/ 0.0?1 ) s- L.929 2.L13\ | 2.437.l 2.284 cltorar 0.130 ,.0. 0.r1s 2.2e 0.04s 2.48 o.ose 0.058 | | l> I ,.n, F | o.0oo,/ | - t o-o29 tAll i.!on elErted aB FeO. rrAll gutfur !€Ibrt€d as SO3. CONTACT.METAMORPHIC LAPIS LAZULI 63

DlopsLds ForsbELte rtaltq Ilalie l.loetaib l{ostaXb u23 u24 u24

0.10 0.28 0.12 0.35 0.0 0.00 0.01 0.0 0. 88 1.20 0.42 0.48 0.0 0.13 0.0 0.23 0.94 o:o 0.09 0.48 0,12 0.03 0.54 0.06 0.08 0.6r 0. 15 0.04 18. tl 18.63 18.0 1?.93 5?.00 56.06 26.L 26.L7 0.23 0.09 0.06 0.06 0.0 0.0 0,0 0.0 0.0 0.0 0.03 0.03 0,0 0.0 0.0

99.72 99.96 100.30 100.34 100.16 100.48 99.55 L00.22 99.62 IonE baBeal on 4 catlons gana- 8i-, r.960)- ^^ r.995t- ^^ t.otsl" ^- i.il!]r.ssl.::;)1.,8 i.ililr.se o.oaol''uu o.oosl"'u ,':i!3)'.,, o.ooo;r'"" AI\TI 0.0001 0,000\ 0.000\ 0.011\ o,0r3l 0.0001 r.962l o.o03 I 0-008| o.oo3 i o.oos j 0.000/ 0,000I 0.0021 0,006)1.00 0.0011I.97 o.o or ir. or o.ozo fr. or 0.000lo.9s 0.00210.98 0.0r3)0.99 lal 0.017\ 0.oo2l 0.002t -l -t 0.0r9I 0.004I H9 0.977) 0.999' o-979) 0.9651 0.96L) o.962) 0.000| 0. 000/ ca 0.99?) 0,999) 1.009) r..009') r.00?) r.009) Na 0.015l|1.0r 0.00611.0r 0.00411.0r 0.004tl.0r o,orsfr.oz 0.0081r.02 K 0.000,t 0.000, 0.000) o. ool J 0.001 I 0.000, bl€cular !E! cent caTl-ta 0.21 0.74 0,32 0.94 0.00 0.00 Fo 99.32 Jd 0.94 0.4J. 0.56 Fa 0.11 k 0.65 0.00 0.00 0.00 0.00 0.00 !4ont 0. il3 Ca-[s 0.00 1.31 0.05 0.60 taph 0.15 Joh 1.63 0.18 o.24 1.84 caFa-ta 0.00 0. 15 o]oo o,64 qolL 4a,2a 48.19 49.L4 48.45 Fe 0.00 0.00 0.00 0.00 0.00 0.00 Br 18.23 1A.A7 4A.26 48.05 47.97 47.64 Fe,/Fo.ttDrut I . loo

rAlI lrd reported as Fe2O3

AABT,E 4. !{ICROP8OBE ANAJ,YSES OF PIIIJOGOPIIE' SAPONITE' SISINGEBITE AND CELORITE

Phlogopite salpnlte Ul-singsllte Chlorite North Igalie It€ 1lu &outaln North ltalie North ltalld lorth Itallu tdoutal-! Ilall.an !,loutain l.loutai! Mou!ain l'loutaln

v24 A2 826 v23 826 A2 A2 (core) A2 (rls)

L.86 0.44 3.95 0,0 0.0 0.02 0.0 17.21 L4.L2 18.57 L.79 0.09 17.00 24.06 23.08 0.L8 1.56 0.13 3.04 0.13 20.29 23.40 L7.24 MnO 0.0 0.0 .0.03 o-32 0. 06 0.48 0.26 tlqo 2s.93 26.60 24.LO 2A.32 28.6L 14.00 20.13 0.10 0.14 0.0 L.L2 0.45 2.48 0.05 0.05 BaO 3.89 0.0 13.54 0,0 Na2O L.32 0.08 0.42 0.05 0.0 0.04 0.0 0.0 K2o 7.18 10.1S 4.69 0.r7 o.L2 0.0 0.0 SOlr cf

96.19 96.60 96,88 9L.97 85.43 s6.07 87.98 88.43 n-n6 o-no qt -ql n5- n6-07 s7.98 88.43 Ions baaed on 44 lpsllivq charges 4 catLona ron6 baged or 20 €ttons st_,, 5.370'l- ^^ s.969)^ __ 4.674 7.926 sI-.. 1.9481- ^, ' \7 ,94 e.oo a.oo A1'" z.esofo'"u z.orrlo'"' l-se o.zeal "' 0.015J et" o.o5zJ"u' !'iii I l'i!!) Alvr 0.245\ 0.2s4\ 0. 000 0. 000\ alvr 0.864\ 3.409\ 3.020\ rl 0.1e81 0.04s1 0.450 0.000{ 0.000| mt-l 0.0031 0.0001 F6 0.021Is.78 0.L7915.92 0.016 0.343)6.07 0.015 ;; o-nsl 4.110I 2.9461 l'tn 0.0001 0.0001 0. 004 ,' litn 0.002 0.0371 I6.0s \, ^, us 5.4701 5.443) 5.441 5.6881 6.O34.) lrg 0.2021" " !' 33;ir,.oo2'.3211r.* 1, 0.0131 ca 0.14r I 0.0111 0.015] 0.021.1 0.000 0.162) 0. 068 0.000 l Na 0.004| 0.000| | 9'?llh.ag9'999|r.er 0.804 9'999 lo. zo ( 0.013/ o.ooo/ o.ooo/ u. roz I u. uzr I 0.L23 o.ooofo'oa L.296t I.743) 0.9061,.,,o. o29J 0.009J ont 4.24 16.84 15.50 F 0.2461 0.283 0.0641 0.000l cl - ia. oe - 0,0381""- 3'313f'.." "Total I I oF' r. sraj 7.2LA) ,. teoJ FalFe +lto +!{gli 10 0

0.4 5.6 0.25 79.2 47.9 32.3 rA11 tron as FeO. itALl eulf,ur a€ 60.. tOR calculatea f,roD def,lclt ln tatal. 64 THE CANADIAN MINERALOGIST are difficult 16 6islinguish one from the other. variation and indicate that the most Fe-rich In sontrast to lazurite, crystals commonly grow portions, which correspond to regions of lowest along the grain boundaries of calcite. birefringence, tend to be on the rims of the Pyroxene is close to end-member diopside crystals.In general, they are grossularwith some composition (Iable 3). At the Anderson occur- andradite and minor spessartine. Garnet was rence, some crystals are zoned with a sore of also observedin thin sectionsfrom the Anderson normal diopside (Zttc 42") and a rim of diop- and Christopher occurrencesas anhedral grains side with higher extinction angle (ZLc 48"). rimming diopside. These grains were not analyzed. However, the Soft, fibrus saponite (Mg,Fe)oSLOa(OH)a is analyzed thin section did show neighboring a major mineral in specimen U23 (seeTables 1 pyroxene grains of different chemical composi- and 4) and a minor mineral in several other tion. Cathodoluminescent diopside (specimen specimensfrom the area. It is nonpleochroic and 425-L, Table 3) is characterizedby appreciable pale brown (perhaps stained by decomposed Ti and Al but negligible Fe and Na; nonlumines- pyrite) to colorless. The mineral gave an X-ray- cent diopside (specimenA25-N) is characterized diffraction pattern of smectite, and saponite was by low Ti and Al but appreciable Fe and Na. establishedby microprobe analysis. Olivine is nearly pure forsterite (Iable 3). Chemically, saponite is of two types: iron-rich ALOg in A25 varies from grain to grain, perhaps (specimen U23) and iron-poor (specimen B26, owing to an impurity. Table 4). In order to avoid possible qontamina- Phlogopite tends to form the largest crystals tion with oxidized pyrite, only colorless grains of the silicate assemblage,.someas isolated meta- were analyzed in specimen U23. Small amounts crysts up to 0.5 mm diameter. They are sub- of Caz+,Na+ and K+ balancethe negative layer- hedral and relatively pure but contain some charge. Octahedral Al is very low, a feature round inclusions of calcite. apparently common to saponites from other The composition of this mineral (Iable 4) is regions (Deer er al. 1962, pp. 233-234, analyses remarkable. Barium concentrations are high; rz-rs). for example,in specimen826,'Na:Ba:K - O.l4z Thin section U23 is composed of carbonate O.89:1 (atomic). The other barium-rich phlogo- and silicate bands. The bulk of the carbonate pite analyzed (specimenU24) is also remarkable. band is made up of coarse calcite. Accessory Individual grains show little compositional zon- minerals are diopside, lazurite and sulfides in ing but the barium content varies greatly from minute, roundish grains. No saponite was ob- one grain to the next. One small crystal contains served in this part of the section. In contrast, about 8Vo BaO. The analysis is an average of the silicate portion contains major amounts of two parts of a single large phlogopite crystal. fine-grained saponite and, rarely, coarse vein- Garnet, occurring as subhedral dodecahedra up like aggregatesof saponitewith packets of fibres to I mm across,is associatedwith saponite and in random orientation. Grossular grains are lazurite in specimen U23. The dodecahedra are glomeroblastic and occur within or close to the anisotropic, zoned and complexly twinned. Anal- saponite, which is veined by late calcite. Tiny yses (fable 5) show considerable compositional diopside grains are scattered through calcite and lazurite. M 5. trICMPIOBE AIIALYSIs OF EAMTi Rather different is the saponite from North Italian Mountain (specimen 826) with only Glal.n 5 elain 5A (tain 6 &aLn I clain I (core) (@ie) (@!€) (!ts) (cor€) 0.137o FeO. This mineral occurs as isolated growths s10. 38.39 37.68 39.04 3?,91 38.86 cryptocrystalline aggregatesor as fibrous 0.0 r6.t4 13.92 19.09 t8.{2 forming a rim around olivine, apparently derived n#;l ?.3I 11.08 4.27 9.45 6.53 MoO 1.60 1.06 0.41 0.79 directly from it. 36,t9 36.37 parallel packets, is the uso 0.0 0.0 0.0 0.29 0.0 Thomsonite, in fibrous product in the t00.20 99.?2 r00.17 100.97 common alteration of lazurite area. An analysis of thomsonite from Italian Ions basaal on t6 catLona (specimen is presented in Table st 5.S9S 5.889 5.958 5.870 5.915 Mountain U24) d.* .l!$n.or North Italian Mountain Fe- ?.,litrF.nf 3.X;i]3.,,i.i3i],.,,i-fliia.os 6. Thomsonite frorn 0.208) 0.1,10) 0.239) 0.0541 0.1021 (specimen s.96816.18s.9s8f6.10 s.88016.r2 6.004)0.12 s.e3rl6.o3 826) has a similar composition. !r9 0.000/ 0.000J 0.000.1 0.0671 o.oooJ Fined-grained thomsonite in lapis lazuli seems (st Uol€alal ber to have formed by alteration of lazurite. In Anal 24.37 35.62 L2.02 27.25 18.61 Gloga 12.26 62.0A 84.08 71.86 79.70 thornsonite from lazu- SIESs 3.37 2.30 3.91 0.89 1.69 contrast, coarse-grained rite-free A2 shows no evidence whatsoever of .SIEcl,@n U23, I61t6 butal.n being an alteration product of lazurite or any CONTACT-METAMORPHIC LAPIS LAZULI 65

TASIiE 6. IIXCROPROBE ANA],YSES OT PYRRHOTITE, CAI,CIEE AND THOMSONIIE

Pyrrhotlte calclte Thoreon1te North Itallu !,loutain North Italian Itallan Ital-lm North Italiil !'1o&taLn !,loutatn Moutaln Moutain v23 v23 U24

Co 0.tq 0.0 0.0 o.20 llno 0.0 0.0 0'0 30. 3L 2t .55 N1 0.04 0.0 0.0 0.0 !4so 0.06 0.52 0.42 0.08 0.0 Mn 0.0 0. 04 0. 07 cao 54.90 55.1-7 54.90 !4nO 0.0 z\ 0. 0.0 0.0 0.0 SrO L,29 Mgo 0.0 38.83 38. caO l-3.56 L2.55 BaO 0.03 0.0 99.26 99.65 99.64 99.64 98.30 99.55 100.70 Na2o 3. 04 4.77 Kzo 00 0.0 Ions based on L aton s Ions based on 1 cation' 0. 889 0. 899 0. 894 0.884 Fe 0.002 0.000 0.000 Co 0.003 0.000 0.000 0,003 Mn 0.000 0.000 0.000 N1 0. 001 0. 000 0. 000 0. 000 rilg 0. 002 0. 0l-3 0. 0r0 Iona based on 40 z-IonE !&t 0.000 0.001 0.001 0. 001 Ca 0.99'1 0.987 0.977 ZV.LVz t^ ^^ 2L.323 ,^ ^^ zn 0. 000 0.000 0.000 0.000 sr 0.012 r^ --- {u.vu s 1.000 1.000 L.000 1.000 AI 19.Brg'"'"" t 0.107 0.101 0.105 O.LL2 !e 0.037 0.000 !4n 0.000 N tr'es 0. 9398 0. 9463 0.9435 0.9368 I'19 0. 174 0.000 8.06011.55 7.zLL !2.L7 ros rsj -6.9 -6. 0 BA 0. 007 0. 000 3.270 4,960 400 355 440 0. 000 0. 000 d2" 30. 32 23.9L

t tAll lron aaEred FeO. **Calculated aasumlng COj ae I aion. calculated from deficit in total. 8EoulllbratLon condltlonE fron Toulnin & Barton-(1964). other mineral. Rather. this thomsonite fills cav- notably low in magnesium (Table 6). Tiny ities in the rock. Both varieties are probably sphene anhedra were identified optically in products of late hydrothermal activity. specimen B.26 and in a thin section from the The opaque minerals pyrite, pyrrhotite and, Anderson occurrence. very minor sphalerite are present in all lazurite- bearing specimens. Pyrrhotite surrounds pyrite Hanging wall of the Anderson deposit and vice versa. Bolh have irregular outlines, but separategrains of each were also noted. Assum- The Anderson deposit it bounded by rock ing that pyrite and pyrrhotite representan equil- containing nodules of calcium and magnesium ibrium assemblage,pyrrhotite has'equilibrated silicates. The mineralogy of this horizon differs with pyrite at a moderatetemperature and sulfur markedly from that of lapis lazuli; although it fugacity (Table 6). contains no lazurite, the assemblageprovides An isotropic, grey, metallic mineral of low data pertinent to the origin of lapis lazuli. Its reflectivity with dark green internal reflections mineralogy was therefore studied in detail. was noted in pyrite in polished thin sectionsfrom The dark layer, containing lazurite, is overlain Italian Mountain (specimen U24) and North by a thin, barren, yellow, nodular layer. This, Italian Mountain (specimen B26). Analysis of in turn, is overlain by a cream-colored nodular specimenU24 gaveMn 54.64,Fe 6.87, Zn 0.O2, layer 1.2 m thick from which our sample (A2) S 34.78; tolal96.31/o. This reducesto alabandite was taken. A dark brown nodule, 7 x 3 cm, (Mno.eeFeo.uZno.ooos)S. is set in a mottled cream and grey microcrystal- Other minerals include the following: A very line groundmass.Individual diopside crystals in small grain of a mineral with the optical prop- the nodules are themselves centimetric. erties of scapolite was observed in grossular Prismatic diopside makes up the bulk of the at Italian Mountain (specimenU23). Microprobe nodule. Compared with diopside from lapis data suggest it is mizzonite, which is common lazuli, it is notably high in iron (Table 3). in other metamorphic rocks at Italian Mountain Phlogopite forms fine-grained patches. It is (Cross & Shannon 1927). A small amount of also high in iron but notably low in barium coarsely crystalline barite was collected from the compared with phlogopite from lapis lazuli of east end of the Anderson trench. and small the area Clable 4). The iron-rich minerals grains of barite were tentatively identified in a chlorite and hisingerite grow around pyrite. thin section of white limestone from the Christo- Colorless chlorite forms radiating groups of pher occurrence Qocality C, Fig. I), Calcite is crystals, richer in iron in the cores than on the 66 THE CANADIAN MINERALOGIST

IABIA 7. CSEMICAIJANATYSES OT' SPECU{ENSMENTIO}IED XN trEE IIIEXtr

Lapis Lazuli ad aEgoclated ffibLe

ItaUil !,butain North ItaLim ltloutatn Uret. Belden lb lertiey stock v23 B.26 z.4r J3,58 20.L5 47.7L L0.47 LO.24 15.51 L2.72 r.8.94 16.66 4.30 75.98 66,7 '0.1.6 ;i3; 0.0i. 0.49 0.08 0.22 0.07 0.06 0.05 0.07 0.06 0.03 0.93 0.46 Al2O3 0.s7 10.47 3.07 8.04 z.LX 1.73 0.93 3.70 2.O3 2.42 0.48 13.70 15.9 FeO* o.Lt 3.56 1..15 4.58 2.32 2.79 0.t5 3.08 o.92 0.65 0.90 r..t 0 3.5 lltrO 0.02 0.11 0.04 0.06 0.06 0.06 0.02 0.06 0.03 0.04 0.09 0.00 0.09 ugo L,28 8. 36 Ll. i-5 t 2. 37 4.66 7 .59 6.L2 7.L9 I0.30 L5.99 20.52 0.54 L.2 SrO 0.095 0.404 0.184 0.06 1.06 0.79 0.284 0.59 0.079 0,267 0.009 0.002 0.2L BaO 0.04 1.57 0.13 0.03 0.21 0.20 0.r.3 0.20 0.01 0.05 <0.006 <0.006 0.L2 CaO 53.94 15.90 33.60 17.75 41.43 39.15 44,90 38.30 38.93 32.50 29.44 0.14 3.3 Na20 0.03 3.45 0.25 0.58 0.47 0.15 0.40 0.45 0.07 0.25 0.045 0.08 3,6 K2o 0.03 0.22 0.52 0.52 0.08 0.07 0.07 0.L2 0.11 0.09 0.05 3.40 3. r c1 0.015 0.16 0.015 0.09 0.0L5 0.005 <0.005 <0.005 0.020 0.025 0.045 <0.005 BT <0.001 <0.00t <0.001 <0,001 <0.001 0.001 <0.001- <0.001 <0.001 <0.001 <0.00L <0.0 0L 0.04 0.09 0.20 0.25 0.05 0.18 0.08 0.04 0.13 0.L7 0.03r ,0.07 SO"r* 0.60 7.37 2.50 5.89 6.89 7.74 0.60 6.04 1.50 1.50 0.27 0.t0 38.7 6.6 22.3 0.'66 28.9 27,3 29.5 25.6 27.O 25.6 44.L 0.05 0.2L il;, 0.09 0.23 0.15 0.14 0.04 0.05 0.L7 0,06 0.15 0.t5 0.07 0.02 0.29 E2O+ 0.68 6.92 3.35 3.62 1.86 2.a6 t.t9 3.49 1.89 3.06 0.40 2.26 L.4 E2a- 0.16 L.27 0.48 0.48 0.35 0.40 0. 20 0. 35 0.14 0.29 0.19 0. 75 0.6

98.82 101..85 99.32 1.03.05L01.12 101.37 100.30 102.15 102.32 99.77 LOO.g7 99.12 100.1

Fe(atoDic) 4.9 1.81 1.95 1.r5 2.67 2.49 3.5 L,76 L,46 2.O7

rA11 Lron reportsd as tr'eo. trAl.l- sulfur re!rcrted as SO3. SlEclnen preftxes A, B, c. U eat su coneapond to Locations j.n !'igure 1, x-ray Assay Laboratorlaa, Tolonto, analysts. Uitl. lE an averaqe of 17 uaLysed. specl.rens fron Clmlnghm (1.973). rims (Table 4). Yellow hisingerite surrounds Baikal, Ba is contained in pblogopite (up to pyrite, sometimes as concentric growths (fable 0.9%) and to a lesser extent in lazurite and 4). Thomsonire, forming long crystals in re- calcite .(eachto O.l%). Ba-rich lazuritis horizons stricted areas,has normal composition (Iable O. are also notable at Italian Mountain (c1., Tables Calcite, occurring as isolated grains, is low in 1, 7). The lazurite-free specimens A2 and, C2 magnesium (0.25% MgO) but rather rich in iron contain a low amount of Ba, whereas the cor- (O.75Vo FeO), Pyrite is seen as local, coarsely responding lazuritic specimens(A4 and C3) are crystallized clusters but pyrrhotite is apparently enriched in Ba. The lowest values were en- absent.A small amount of chalcopyrile is found countered in specimensof the Belden Formation with the pyrite. The assemblage is therefore (sMl, SM2). comparatively rich in iron, with low-barium Consideringthe analyzedminerals, barium is a phlogopite, very different from the assemblage major constituent of phlogopite only, but Ba of lapis lazuli. abundances show poor correlation with the The fine-grained matrix was not examined by modal concentrationsof mica. U23, for example, microprobe, but X-raydiffraction studies by contains L.57Vo BaO but no phlogopite. Some N.M. Miles showed that it was composedmainly Ba is goncentrated in another phase, possibly of diopside, lesser amounts of epidote, small barite or celsian (not observed in thin section). amounts of calcic plagioclase and minor potas- Barite has been observed locally in lapis lazuli, sium feldspar. as noted above, and in lazurite-free tactites (Cross& Shannon 1921. Strontium is contained predominantly in cal- GEocHsrulsrny cite, as in lapis lazuli from the Lake Baikal Elemental abundances region (Ivanov L976). Calcite from occurrences rhererationship ormost erements tospeciric f,dili ?Sff'fitty"Ji'il'J',*;'l"ki3:r*1: minerals at Italian Mountain is obvious and Calcite from occurrences C and U is notably only a few elements will be considered here. lower in Sro- (0.4Vo or less). Bulk analyses are given in Table 7. As at Baffin Island (Hogarth & Griffin 1978), Barium is known to concentrate in lazuritic iron is contained largely in sulfides, with very horizons. Ivanov (1976) has shown that at Lake little entering the silicates. Thus about 9O Qta- CONTACT.METAMORPHIC LAPIS LAZULI 67 lian Mountain) or 95Vo (North Italian Mountain) parison with these, the analysesof Table 7 are of the iron in the system is in sulfides. Some notable for their low K and Na, low Na/K and 80 (North Italian Mountain) or 85Vo (Italian CllS ratios and relatively high Fe contents. Mountain) of the sullur is in sulfides. The re- These data alone suggest that the evaporite mainder is found in lazurite. model cannot be applied to the Italian Mbuntain The occurrence of lazurite is dependent on a deposits.This agreeswith the apParent absence high S:Fe ratio (Table 7). If this ratio exceeds of evaporite members elsewhere in the Belden a specific value, sulfur must enter silicate struc- Formation. tures. If S:Fe (atomic) is less than about 1.5:1 Two examples of "typical" unmetamorphosed (as in specimens A2 and C2), pyrite and pyr- carbonate and silicate membsrs of the Belden rhotite, but not lazurite, appear; if above 1.5:1 Formation were analyzedin an attempt to define (as in specimensU23, U24,826, A4, A10 and the probable compositional range of possible C3) pyrite and pyrrhotite coexist with lazurite. protoliths for the lapis lazuli. The samples, Pyrite and lazurite, but not pyrrhotite, were donated by C.G. Cunningham, came from ap- observed in specimens A25 and U20 (S:Fe = proximately the same horizon as the Anderson 3.6 and 4.9:l). This relationship is responsible lapis lazuli occurrence, but on the east side of for the absence of lazurite in the mineralogically the mountain (locality SM, Fig. 1)' similar but more iron-rich rocks of the hanging The carbonate specimenSMl consistsof fine- wall of the Anderson deposit. grained dolomite (subordinatecalcite). It is grey Chlorine is present in variable amounts. In in hand specimen, lacks noticeable bedding but general, shlorine is contained partly in lazurite, is brecciated and recemented with coarse, white but in certain specimensCl occurs in some other dolomite. Tiny anhedral rhombs, now composed manner not understood at present. Chlorine is of polygranular dolomite and quartz, are sprink- not necessarily enriched in lazuritic layers, as led sparingly throughout the fine-grained portion. shown by a comparison of A2 (900 ppm Cl, Very minor late calcite coats joint surfaces. lazurite-free) with the neighboring A4 (150 ppm Rari pyrite and hematite, a result of pyrite Cl, 8.3 modal Vo lazurite * zeolites) and Al0 oxidation, are the only other minerals noted, (50 ppm Cl, 19.4 modal Vo lazurite * zeolites). and the rock shows no evidence whatsoever The amount of phlogopite, the only fluorine- of metamorphism. Mineralogically and chemi- bearing mineral encountered in the study, is cally (Iable 7) the rock is dolostone. poorly correlated with fluorine content; some The silicate specimenSM2 is a finely bedded' other F-bearing mineral must be present in the blackish rock containing small grains of pyrite specimens. that have locally decompoeed to limonite and coated certain bedding planes with a yellow Source of elements ochre. In thin section it is seen to consist of about 6OVo round quartz grains (average dia- The major minerals of the lapis occurrences meter about 0.1 mm). The remainder is made of probably formed by contact metamorphism of finer grained illite, phlogopite, pyrite, limonite, the impure carbonates of the Belden Formation. varioui fine-grained unidentified minerals and However, several facts suggest that this meta- rare detrital zircon, tourmaline and plagioclase. morphism was not isochemical but involved This mineralogy illustrates very low-grade meta- considerablemetasomatic activity. Cross & Shan- morphism. The mineralogical and chemical com- non (1927) described the extensive development position (Iable 7) suggests subgreywacke as of massive garnet-diopside-vesuvianite in the defined by Pettijohn (1954). marbles, as well as fissure filling of these min- Also in Table 7 is an average of 17 analyses erals in the stocks. C"unningham (1976) noted [Ml) of the Italian Mountain stock represent- the zonal development of hydrothermal base- ing quartz diorite, granodiorite, quartz mon- metal deposits related to the Northern In- zonite and dacite porphyry. The data in Table trusive. It is thus of interest to determine to 7 show that mixtures of the silicate and car- what extent the occurrence of lapis lazuli was bonate components of the Belden Formation controlled by the metasomatic introduction of could explain the range in composition of the individual components. lapis lazuli samples for most of the analyzed Those lapis lazuli deposits that have been elements. Howevgr, the contents of Na, S, Fe, recognized as meta-evaporites(Kulke 1976a, b, Sr, Ba, Cl and F are all too high to be ex- Hogarth & Griffin 1978) are characterized by plained in this fasluon, and other possibilities high contents of Na and K, high Na/K and must be considered. CllS ratios and very low Fe contents. In com- The Italian Mountain stocks and lapis-lazuli 68 THB CANADIAN MINERALOGIST horizons are rich in Ba and Sr, whereas the of the stocks. He also identified hematite as a Belden dolostone and subgreywackecontain neg- daughter mineral in the fluid inclusions of quartz ligible amounts of these elements (Table 7). A veins. These observations,and the late formation similar trend was found in igneous rocks (sye- of vesuvianite, ferrian gtossular and epidote in nites, subalkalic granites), lapis lazuli and un- the tactites, imply that Fe and probably Al were metasomatized marble at Baikal by Ivanov mobile components during contact metaso- (1976). In both regions Ba and Sr may have matism. been introduced into the carbonate rocks by Textural and compositional relations between fluids that accompanied igneous intrusion. the iron-poor and iron-rich phasesin lapis lazuli In the Italian Mountain area, barite may have also point to the introduction of iron at a late been a primary (authigenic) phase in some stage. Some veinlets of ferroan saponite transect horizons of the Belden limestones, or it may grains of lazurite, diopside and calcite; others are have formed metasomatically during early interstitial, as in a specimen from occurrence stagesof the metamorphic cycle. In either case, U. Ferrian grossularis either in, or close to, its stability implies oxidizing, high-pl{ condi- the saponite. Zoned garnets suggestthat iron in tions. Cross & Shannon (1927) noted that red- the system increased with time. In specimens beds (the Pennsylvanian Maroon Conglomerate) from occurrencesA and C, overgrowths indicate change color from purple to green owing to that garnet postdates dioPside. reduction of Fea+ in the contact aureole. and that Some late iron may have contributed to the graphite was formed in the marbles. These obser- breakdown o'f lazurite. Deep blue lazurite be- vations suggestthat reducing conditions prevailed comes paler near pyrite and pyrrhotite, which during at least the latter part of the metamorphic implies that iron sulfides were generated at the cycle. Under such conditions, barite would have expense of lazurite, causing a bleaching effect. become unstable @jprlykke & Griffin 1973), Tde relevant reactions may be of the type: of and Ba for incor- leading to the liberation S -> poration into sulfides and silicates. This model CarNauAluSiuOrrSOnS* Fe'+ explains the presence of rare (relict) barite in blue lazurite * Ca'a+ + FeS the It the absenceof barium CaNaoAloSieOrnSOn tactite. also explains colorless hauvne in the phlogopite of A2 and the bulk rock of C2 (both lazurite-free) compared with the appreciable barium in phlogopite and bulk-rock anal- PETRoLoGY yses of lazurite-bearing specimens.A somewhat similar breakdown of barite, leading to the for- The textures described above suggest that mation of barium silicates and pyrite, was the major minerals formed early in the meta- postulared by Bjdrlykke & Griffin (1973). morphic history of the lapis lazuli, perhaps near The abundance of Na and S in lapis lazuli the peak of metamorphism. Lazurite, which is may also be related to magmatic fluids derived included in the other Jilicates, may have formed from the Tertiary stocks. Cunningham (1976) first. but the larger grain'size of forsterite and has demonstrated that the late-magmatic fluids diopside may reflect only kinetic factors. The were rich in Na, K, Ca, Cl and S. minor Fe-rich silicates seem to have formed The presenceof scapolite in zones and veins later, as a result of metasomatism, and are ob- near the contact (Cross & Shannon L927) sug' viously not in equilibrium with the earlier phases. gestsextensive metasomatic addition of.Cl (2.8Vo Hogarth & Griffin (1978, Fig. 18) presented Cl in scapolite) by late-magmatic fluids. On the a petrogenetic grid for lapis-lazuli assemblages other hand, Cl in lapis lazuli could well have in the condensedsystem CaO-MgO-SiOz-AlO', been supplied by a dolostoneprotolith (c1., Table as functions of p(NarO) and p(KrO) at unspeci- 7). The source of Cl must therefore remain fied P and T. in terms of this system, the ob- ambiguous. served assemblagelazurite 1 diopside * forster- Fluorine is a significant component of late- ite f phlogopite f calcite represents the re- formed'vesuvianite (O,67o)and epidote (0.4Vo) action (PA): phlogopite * diopside * NazO P in the contact rocks (Cross & Shannon 1927). forsterite + Kuo * CaO + H,O. This 5-phase It is thus reasonable tg assume that the F of assemblageis thus at least divariant; if the Ba the lapis horizons has, at least in part, been content of the phlogopite is considered, another introduced metasomatically, degree of freedom is added. All other observed Cunningham (1976) noted that late-magmatic assemblagescontain fewer phases.Thus, equil- hydrothermal activity has led to the breakdown ibrium among the major phases of the Italian of ferromagnesianminerals in the granitic rocks Mountain lapis laztrli is permissible on phase- CONTACT.METAMORPHIC LAPIS LAZULI 69

rule grounds. However, the grain-to-grain com- ningham's fluid-inclusion data, whereas zeolites positional variability of each phase implies that probably crystallized at even lower temperatures. chemical equilibrium was attained only on a very local scale at best. Survrrvreny In contrast, the metamorphic assemblagesof Baffin Island lapis lazuli are typically low in The data presented here show that the lapis variance (5- and 6-phase assemblages,including lazuli at Italian Mountain has formed bv con- calcite), and the minerals are very similar in tact metamorphism at very shallow levels. The composition within each specimen and from rapid heating, extensive metasomatic activity sample to sample. These features have been in- and presumably rapid cooling have resulted in terpreted as reflecting closed-systemequilibria relatively simple mineral-assemblages and a at high grades of regional metamorphism. We general failure to attain chemical or texfural therefore regard the relatively simple assem- equilibrium except perhaps on a very local scale. blages of the Italian Mountain deposits as re- The availability of hot, aqueousfluids with high flecting the mobility of one or several com- contents of Nq S, Cl, F and other components ponents during the metamorphism. probably was instrumental in producing lapis The occurrence of the assemblagesDi * Fo lazuli from protoliths that did not have high * Laz and Di * Phlog * Laz at Italian Moun- primary contents of these elements. The reduc- tain implies that g,(NaO), pK,O) and trl(Na,O)/ tion of primary barite may, on the other hand, p(KrO) were higher than the corri:sponding have been critical to the formation of sulfide values in the Baffin Island deposits (Hogarth and lazurite. & Griffin 1978, Fig. l8). The Italian Mountain deposits thus differ dramatically in their mode of formation from Conditions ol metamorphism the Baffin Island deposits. The latter are characterized by higher Na/K and CllS ratios, re- Cunningham (1976) has used fluid-inclusion fleciing their origin as meta-evaporites. They microthermometry to deduce a pressure of ca. have been subjected to high-grade (granulite- 250 bars and a temperature ca. 450'C during a facies) regional metamorphism, apparently iso- the late venting of the Northern Intrusion. This chemical at the peak of metamorphism, and they pressure corresponds to a depth of 2800 m show complex, but apparently equilibrium, min- (hydrostatic) or 95O m (lithostatic). Similar eral assemblages. pressures may also be assumed for the lapis- lazuli horizons during their contact metamor- AcrNowt-gDcEMENTS phism. The limited data available on unmetamor- Henry Truebe (Crested Butte, Colorado) and phosed - rocks of the Belden Formation show Garry Christopher @nglewood, Colorado) that a probable critical premetamorphic as- guided one of us (D.D.H.) to the lapis lazuli semblagein these rocks was dolomite * quartz. occurrences. A Natural Sciencesand Engineer- Subsequent metamorphism took the rocks ing ResearchCouncil of Canada operating grant through the reactions: (A2122) paid field expenses and the cost of bulk-rock and microprobe analyses (the latter -+ dolomite * quartz diopside + CO, done at Carleton University). J.L. Bouvier (Geol- -+ diopside * dolomite forsterite * ogical Survey of Canada) checked Na and Cl calcite * COz in specimen SMI by atomic absorption and colorimetric methods, respectively. Dr. A.G. pressures At of 250 bars, the sesond reaction Plant (Geological Survey of Canada) checked indicates a minimurn temperature of about Si, Mg, Fe and Al in saponite in specimen U23 600"C @ggler et al. 1976). The lower tempera- by microprobe analysis. The authors profited tures obtained from pyrrhotite-pyrite geother- from helpful comments by Drs. R. Kretz and (fable mometry 6; Toulmin & Barton 1964) C. Pride (both of the University of Ottawa). may represent re-equilibration during cooling from peak temperatures. We therefore suggest conditions of P - 250 bars, T - @OoC for the RErenENces formation of the lapisJazuli assemblagesin the Italian Mountain area. The secondary Fe-rich BJIRLyKKE,K.O. & Gnrrrnl, W.L. (1973): Barium phases may have formed closer to the 40f feldspars in Ordovician sediments, Oslo region, 450"C range of temperatures suggestedby Cun- Norway. l. Sed. Petrology 49, 461-465. 70 THE CANADIAN MINERALOGIST

Cnoss, W. & SneNNoN, E.V. (1927): The geology, Kur.rr, H.H.G. (1976a): Metamorphism of eva- petrography and mineralogy of the vicinity of poritic carbonate rocks (N.W. Africa and Af- Italian Mountain, Gunnison County, Colorado ghanistan) and the formation of lapis lazuli. U.S. Nar. Mus. Proc.7L, (18), 142. Int. Geol. Congr. 25th l, l3l-132 (Abstr.). CuNNrNcHeu, C.G., Jn. (1973): Multiple Intrusion (1976b): Die Lapislazuli - Lagerstiitte Sare and Venting of the ltalian Mountain Intrusive Sang (Badakhshan). Geologie, Entstehung, Kul- 'tirrgeschichte Complex, Gunnison County, Colorado. Yb.D. und Bergbau. Atghonistan l. I, thesis, Stanford Univ., Stanford, Ca. 43-56. (1976)z Petrogenesis and postmagmatic PatrtlonN, FJ. (1954): Classification of sand- geochemistry of the Italian Mountain intrusive stones. .1. Geol. 62, 360-365. complex, eastern Elk Mountains, Colorado. Geol. Soc. Anter. Bull. 87, 897-908. RosrNcnaNs, H.I. (1941): Colorado lapis lazuli. Gems Gemol. 8, 154-156. Dnrn, W.A., Howrc, R.A. & ZussrraN, J. (1962): Rock-Forming Minerals. 3. Sheet Silicates. Long- RucKmcr, J. & Gesrennlu, E.L. (1969): Electron mans, Green & Co., London. microprobe analytical data reduction, EMPADR YII. Dep. Geol, Univ. Toronto, Toronto, Ont. Eccr,rn,'D.H., Kusnno, l. & Horr,owev, J.R. (1976): Stability of carbonate minerals in a TouLMrN, P., nI & BanroN, P,8., Jn. (1964): A hydrous mantle. Carnegie Inst. Ilash. Yearb, 76, thermodynamic study of pyrite and pyrrhotite. 63t-636. Geochim. Cosmochim. Acta 28, 641-671, HocanrH, D.D. & GurFrN, W.L. (1976): New data TRUEBE, H. (1977): Lapis lazuli in the Italian on lazurite. Lithos 9,39-54. Mountain area of Colorado.' Lapidary J. 8t, 54-80. & - (1978): Lapis lazuli from Baffin Island - a Precambrian meta-evaporite, Lithos Ll, 37-60. IvANov, V.G. (1976): The geochemistry of formation of the rocks of the lazurite deposits of the southern Baykal rcgion, Geochem, Int. l8(l), Received April 1979, revised' manuscript accepted 26-31. July 1979.