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arkose and an upper unit composedof inter- Garbonatitesinthe Lemitar Mountains, beddedand foliated arkoses,subarkoses, and quartzites. The / is a litholog- ically heterogeneousunit ranging in composi- SocorroCounty, New Mexico tion from gabbro and diorite to quartz gabbro and quartz diorite. Cranitic rocks include a byVirginiaTMclemore,Geologist,NewMexicoBureauolMinesandl\4ineral Resources,socorro.NM gneissicgranite, a muscovite-biotitegranite, a biotite , and the Polvadera granite. dikes, pegmatites,and quartz veins in- Introduction mineralsare nlore likely to be presentin one or trude all of the Precambrianrocks exceptthe A carbonatite is a -richrock of the other type, and Armbrustmacher (1979) carbonatites. apparent magmatic derivation or descent. includesa table listing found in both Calcareous basic dikes that intrude the Carbonatites are generally characterized by primary magmatic and replacementcarbona- Precambrianrocks of the Lemitar Mountains ) 5090 carbonate minerals, , magne- tltes. wereoriginally reportedby Stroud and Collins tite, , and various other minerals The occurrenceof carbonatite dik€s in the (1954)and Anderson(1954, 1957).These dikes (Heinrich, 1966),and they may contain eco- Precambrianrocks of the Lemitar Mountains are distinct texturally, mineralogically, and nomic concentrationsof U, Th, Nb, rare_earth (7 mi northwestof Socorro, New Mexico) has geochemicallyfrom all other intrusive rocks elements,and phosphate.These rocks are gen- been confirmed. Since the 1950's a contro- of the area. Geologic, petrographic, miner- erally associatedwith alkalic rocks, although versy has existedas to the nature of thesecal- alogic, and geochemicalstudies indicate that there are rare occurrencesof carbonatites not careous dikes. Severalgeologists have called thesecalcareous basic dikes are carbonatites. associatedwith any alkalic complexes(Hein- these dikes carbonatites; others have called rich,1966). them altered or basaltic dikes. Description of carbonatite dikes Carbonatites generally Mineralogicand chemicalstudies indicate that form one or two The carbonatite dikes strike dominantly small plugs or stockssituated these dikes are carbonatit'es;they consist of more or lessin north-south and east-west,dip steeply, and the centerof a ring complex ) 5090 carbonate minerals and display the of cone sheetsor crosscut the entire exposed Precambrian se- ring dikes. The carbonatite plug chemistryand accessoryminerals characteris- may or may quence.The dikes range in thicknessfrom a not be exposed. Alkalic rocks generally tic of suchrocks. The Lemitar carbonatitesoc- are few centimetersto a few meters.Most ex- common around carbonatite cur as dike swarmsand are not associatedwith complexes. A posures are presently discontinuous due to halo of fenitesgenerally surrounds any alkalic rocks, providing another example the entire erosionand faulting; however,a few dikescan complex, as well as the cone of this rare occurrencewithout any associated sheetsand the be traced for several hundred meters along ring dikes.Fenites are the products alkalic rocks. The exact age of the Lemitar of fenitiza- strike. Flow structure or banding commonly tion, a distinctive alteration carbonatitesis unknown; however, Pennsyl- typically asso- parallelsthe contactsof the dikes. The dikes ciatedwith carbonatiteand vanian and Tertiary faults have offset the alkalic complexes. appear not to form any circular or elliptical This is the classic model for dikes,indicating a pre-Pennsylvanianage. the emplacement patternson a geologicmap (fig. l), suggesting of a carbonatite complex The economic potential of the carbonatites and includesexam- that the carbonatite fluids followed pre- plessuch as Fen, ; in the Lemitar Mountains encouragedthe New Alno, Sweden;and existing fracture zones in the Precambrian Magnet Cove, Arkansas (Heinrich, Mexico Bureau of Mines to undertake more 1966). rocks. The carbonatite fluids commonly fol- Carbonatitesmay also occur detailed studies of the Lemitar carbonatites. as dikes, stock- lowed earlier mafic dikes, partially or com- works, or sills, and This work was undertaken as part of a mas- be associatedwith alkalic pletelyreplacing them. complexes (McClure Mountain, ter's thesisthat includesmore detailed infor- Colorado; Petrologicvariability is characteristicof the Heinrich, 1966).Rare occurrences matlon on the geology and geochemistryof of carbon- Lemitar carbonatites. Their mineralogy is atite dikes and sills without the area (Mclemore, 1980). Highly radioac- any associated shown in table l. However, despite their alkalic rocks havs 315sbeen (Ravalli tive carbonatites(100 times background) oc- found variability, the Lemitar carbonatitescan be County, Montana, cur in secs.6 and 7, T.2 S., R.lW. (fig. and Verity, British Colum- l). subdividedas: bia; Heinrich, 1966). Two of thesehighly radioactivesamples were l) xenolith-bearing dikes ( and In , many analyzed and found to contain 0.08 and carbonatitescan be microbrecciadikes) and differentiated primary 0.0690 UrOa (Christopher Rautman, personal as to magmatic and 2) xenolith-freedikes. replacement carbonatites (Armbrustmacher, communication, August 1979). Eight car- The xenolith-bearing breccia and micro- 1979). Texture and mineralogy bonatite samplescollected by the author for are the pri- brecciacarbonatite dikes are light to medium mary criteria for this differentiation (Arni- this study were analyzedand found to range gray, weatheringto a medium- to dark-brown. brustmacher,1979). Primary magmaric from 0.001I to 0.004590U,O,. car- The dikes consist of 10-4090xenoliths and bonatites exhibit igneous textures. either ) 60Vo matrix consisting of carbonate hypidiomorphic-granular porphyritic. Geologicsetting or (50-7090), biotite,/phlogopite(5-15q0), mag- Replacementcarbonatites are characterizedby The Precambrian rocks of the Lemitar netite (5-10q0), apatite (5-1090), feldspar fine- to coarse-grained carbonate par- that Mountains consistof a sequenceof metamor- () ZVo), and trace amounts of , tially or completely replaced phenocrysts relict phosedand recrystallizedsediments: the Cork- quartz, and chlorite. The xenolithsvary in size of feldspar, pyroxenes,and amphiboles and screwCanyon sequence,intruded sequentially from a few millimeters to a meter across and thus preservedthe original textureof the . by mafic dikes; a diorite,/gabbrobody; gra- include fragments of the host rock: foliated Apatite is generallymore abundant primary in nitic rocks; and carbonatitedikes (fig. l). The granite, foliated arkoses,quartzites, gray and magmatic carbonatites, but magnetiteis more CorkscrewCanyon sequenceis divided into a green schists, phyllites, and red granitic abundant in replacementcarbonatites. Other lower unit composedof massivearkose to sub- fenites. Bastnaesitehas been identified by x- ray diffraction methods in a dike occurring in the northwest corner of sec. 7 (Mclemore, 1980). Xenolith-free carbonatite dikes can be fur- ther grouped according to mineralogical com- DOSltlOn: a) - carbonatite dikes and b) ankeritic carbonatite dikes. Calcite-dolomite carbonatite dikes are fine grained,light to medium gray, weatheringto a brownish gray. These carbonatite dikes consist of carbonate (50-9090), (5-1590), biotite/phlogopite (5-1590), and apatite (0-1090).The ankeritic carbonatite dikes are light brown with a mineralogiccomposition of /dolomite (50-9090) and varying amounts of calcite, barite, , and magnetite. These dikes generally crosscut the calcite-dolomite carbonatite dikes. An additional minor variety of thin, light- brown dikelets and veins of barite, calcite, dolomite, ankerite, and hematite fill the frac- tures in the Polvadera granite and form a

ALSOIN THISISSUE: Geothermalleasing inventory p.53 New Mexicotopographic index p.55 New Mexicoaeromagnetic map index p 56 RockHound StatePark p.59 Service/News p 62

340r0 COMINGSOON: Bariteon WhiteSands Missile Range \ 'l Carbonatitedikes ERTSohotomosaic mao of New Mexico StorrieLake State Park fTllll Potvadefa sranite

FI' Jntt...o Polvaderagranite

WZBiotit" gr^nite I IS New A4exnco gra f,2S lT'"'"*,T-lMu.. ouite-b iotite nite GEOLOGV lT*l Gn.i*ic snanite . Sciencoand Sorvice [-___l l..it"r diorite/gabbfo Volume2, Number4, November 198O publishcdquarterly by CORKSCREWCANYON SEQUENCE New Mexico Bureau of Mines & Resourccs Mining & Technology lfillll upp..unit a division of Nev M€xico lnstitule of I BOARD OF REGENTS L0Wer UnlT I l:-:-:l Ex Officio Corkscrew Conyon Bruce King, Goverror of Ne\| Mexico * Roads Leonard Delayo, Saperintendent of Public Irctruction i Appointed Wiffiam G Abbolt, Secty/Treas , l96l-1985, Hobbs I Judy Floyd, Pres , 1911-1981,Los Cruces m Owen Lopez, 197'l-1983,Sonta Fe Dave Rice, 1912- 1983, Carlsbod O lkm Steve Torres, 196'l-1985, Socorrc

New Mexico lnstitute of MininB & TechnoloSy Pr$ident Kenneth w Ford New Mexico Bureau of Mines & Mineral Resources Diectot Frank E Kottlowski DeputyDirector GeorgeS Ausrin BureouEditorceologisl RobenW Kelley Subscriptio6: Issued quarterly, February, May, AuSusr, November; subscription price S3 00/yr R 2w'a Editoriol motter: Contributions of possiblematerial for con- Geologyby V T McLemore,t9SO;T.M,Woodword, sideration in future issuesof NMC are welcome Materials cannot be returned unlessaccompanied by return postage FIGURE l-PnrceNrenrnNGEoLocyoFTsr Lrvrran MouNrerNs. Address inquiries to New Mexico Geology, New Mexico Bureau of Mines & Mineral Resources, Socorro, NM 87801 Ctrculstpn |,2N Prizter. University of New Mexico Printing Plant

50 November 1980 New Mexico Geolog! TABLE 1-MrNERALocy oF Lrvlren cARBoNATTTESBy wHoLE-RocK x,RAy DtFFRAcrloN oxidation and exsolution of molecules originally within the feldspar lattice (Von 305* 427a* 427b* 500* 5061 530t 531a. 531b" Eckermann, 1948, p. 29). Oxidation is be- lievedto be a result of the degassing Mineral of carbon biotite X dioxide from the carbonatite intrusive. chlorite x X The change in plagioclase composition and quartz x x other chemical differences between unaltered fluorite X x and altered diorite/gabbro reflect an increase calcite X X in with increase in fenitization dolomite x x (Mclemore, 1980). This sodium increase is ankerite consistent with chemical trends during apatlte x fenitization noted from other occurrences of magnetlte X carbonatites (Verwoerd, 1966; Currie and barite X bastnaesite Ferguson,1972; Robins and Tysseland,1979\.

x-present +-xenolith-bearing carbonatite dikes Discussion t-xenolith-f ree calcite-dolomite dikes '-xenolith-f ree ankerite dikes The carbonatite dikes were emplaced prob- ably at a great distance (laterally or vertically) from the source, as evidencedby: l) the lack of any radial or conical terns in the dike outcrop and 2) the lack of fenitizedhaloes aboutall of stockwork pattern. Carbonatite fluids ap- the higher iron contents, and the absence of the dikes. parently intruded the granite and followed apatite in the ankeritic carbonatites would ac- The lack of any radial or conical patterns in preexisting fractures or shatter zones. Original count for lower PrO, presence contents. The the dike outcrop in the Lemitar Mountains granitic textures and minerals are typically of barite would account for the higher Ba con- suggeststhat a carbonatite intruded preservedin thin section. The stockwork car- tents, and the abundance of magnetite would the crust at depth beneath the present erosion bonatites are rarely associatedwith xenolith- account for the higher Ni, Co, and Cr. surface. Carbonatite fluids apparently fol- free carbonatite dikes. lowed preexisting Precambrian fractures and The xenolith-bearing carbonatites generally zones of weakness in the crust (forming the are primary magmatic; primary hypidiomor- Alteration present outcrop pattern). The lack of any car- phic-granular or porphyritic textures are pre- A distinctive alkali metasomatic alteration. bonatitesin the southernarea (sec.18, T. 2 S., sent in thin section. The xenolith-free car- termed fenitization, has occurred adjacent to R. I W.) may suggestthat the carbonatite bonatites are generally replacement carbona- some carbonatite dikes that intrude the source is centered farther north in secs.6 and tites, although some xenolith-free primary diorite,/gabbro. This fenitization is primarily 7,T.2S.,R. lW. magmatic carbonatites are found. Relict por- characterized by the development of a thin The lack of fenitized haloes about most of phyritic or subophitic textures are preservedin zone that contains large, orange-pink albite the carbonatite dikes also suggests that the thin sections of replacement carbonatites phenocrysts. Phenocrysts in the unaltered carbonatites were emplaced at a distance from where carbonate minerals have replaced the diorite,/gabbro are white andesine and labra- the source. Fenitization is poorly developedin original phenocrysts. Apatite is more abun- dorite. The reddish color of the altered plagio- the Lemitar Mountains, partially because dant in the primary magmatic carbonatites, the clasesis common to other occurrencesof car- carbonatite dikes were emplaced at a tempera- but magnetite is more abundant in the replace- bonatites and is thought to be produced by the ture too low to initiate fenitization in the host ment carbonatites; however, both minerals rock. Lower temperatures and pressures may be presentin either type. would be expectedif the carbonatites were emplacedat a great distance from their source. Chemistry TABLE 2-CHEvrcel ANALysESor LeurrnR can- Only one other occurrenceof carbonatites is A representativesuite of samples from the BONATITES. reported from New Mexico and is located in various carbonatite dikes was analyzed for the Monte largo area, Bernalillo County major and minor elements (tables 2 and 3). (Lambert, 1961).This carbonatiteis a massive More detailed analysesthat will include rare- dolomitic carbonatite dike with apatite, mag- earth presently sio, 13.87 24.16 3.40 10.30 5.l9 elementsare being undertaken. netite, and and is associatedwith a mel- Tio, 0.48 r.78 0.28 0.06 The chemistry of the Lemitar carbonatites is 0.73 (alkalic Al,or 2.88 teigite rock containing ) 50Vo quite different from the chemistry of petti- 4.95 0.50 3.29 0.81 Fe'O, 3.39 7.68 3.04 0.54 ). Other occurrencesof Precambrian john's (1957)average (table 3.46 2). The FeO 4.80 6.8'7 il.75 3.60 alkalic rocks in New Mexico that have no Lemitar carbonatites are higher in TiO,, MgO 9.56 6.80 7.05 5.79 7.89 reported carbonatites include the Pajarito FerO,, and PrO, than the average limestone. CaO 29.9 t7.2 28.'7 36.1 42.57 Mountain syenite(l,120 m.y., Kelley, 1968);a The Lemitar carbonatites are higher in Ni, Cu, Na'O 0.37 0.'t5 0.01 0.42 0.05 syenite of the Priest pluton in the Man- Co, and Cr than 's average limestone K,O 0.63 l.5l 0.10 1.36 0.33 zano Mountains (1,470 m.y., Stark, 1956, (table MnO 3). This lack of similarity in chemical 0.64 0.35 0.48 0.68 Bolton, 1976); and the Florida Mountain sye- P,O, 3.44 1.32 0.06 2.09 0.M composition suggests that the Lemitar car- nite (420-700 m.y., Brookins, 1974). Seven co, 26.77 17.77 3s.80 28.52 4l.54 bonatites were probably not derived from small bodies of syenite intruded by Precam- TOTAL 96.]3 9t.14 95.56 91.17 99.O2 remobilization of . Experimental brian granite occur in the Burro Mountains data from carbonatites similar in composition I -average xenolith-bearing carbonatite, (Gillerman and Whitebread, 1956). Precam- to the Lemitar carbonatites also support this Lenitar Mountains brian radioactive syenite dikes, resembling (Heinrich, conclusion 1966). 2-average xenolith-f ree calcite-dolomite carbonatite, fenites in the Wet Mountains, Colorado, have Lemitar Mountains The Lemitar carbonatites have chemistries been reported from the southern Caballo similar to Heinrich's (1966) average 3-average xenolith-free ankeritic carbonatite, carbona- Lemitar Mountains Mountains (Staatz and others, 1965). Car- tite (tables2 and 3). Some differences exist but 4-average carbonatite (Heinrich, 1966) bonatites are associatedwith the alkalic com- can be attributed to variations in mineralogy. 5-average limestone (Pettijohn, 1957) plexes in southern Colorado (Heinrich, 1966) The presence of ankerite would account for Analyses are reported in weight q0.

New Mexico Geology November 1980 Precam- TABLE 3-Tnnce-rlEIr'IENT cHEMtsrRY oF LEMITAR cARBoNATITES' Lambert, P. W., 1961, Petrology of the brian rocks of part of the Monte Largo area, New 123456789 Mexico; M.S. thesis, University of New Mexico, 9l p. Ba t,294 2,490 2,155 450-1,120 830 1,000 5,300 15,000 Mclemore, V. T., 1980, Geology of the Precam- Sr 297 355 130 3,200 3,000 880 3,200 brian rocks of the Lemitar Mountains, Socorro Ni 44 286 598 85 20 200 5l County, New Mexico: M.S. thesis,New Mexico Technology; also New Cu IJ OJ 13 2.s 51 4 39 43 lnstitute of Mining and Co 36 64 54 11 nil 0.1 4'70 110 Mexico Bureau of Mines and Mineral Resources' Cr 16 231 15 48 nil-13 I I 470 I l0 Open-file Rept., 169 p. Li 36 40 7 8 Mitchell, R. H., and Krouse, H' R', 1975, Sulfur Zn 133 275 527 109 isotope geochemistryof carbonatites: Geochimica IT 8.7 8.4 4.7 40 zo et CosmochimicaActa, v. 39, p. 1505-1513 Olson, J. C., Marvin, R' F., Parker, R L', and Mountains l-average xenolith-bearing carbonatite, Lemitar Mehnert, H. H., 1977, Age and tectonic setting of 2-average xenolith-free calcite-dolomite carbonatite, Lemitar Mountains lower Paleozoic alkalic and mafic rocks, car- 3-average xenolith-freeankeritic carbonatite, Lemitar Mountains and veins in south-central 4 averagecarbonatite (Heinrich, 1966) bonatites, Survey, Journal of 5-average of 4 sovites,Sokli, Finland (Vartiainen and Woolley, 1976) Colorado: U.S. Geological 6-carbonatite, Magnet Cove, Arkansas (Erickson and Blade, 1963) Research,v. 5, p. 673-68'l 7-average limestone(Gold, 1963) Pettijohn, F. J., 1957, Sedimentary rocks: New (Armbrustmacher, 8-primary magmaticcarbonalites, Wet Mountains,Colorado 1979) York, Harper and Row,7l8 P. 9 replacementcarbonatites, Wet Mountains, Colorado (Armbrustmacher, 1979) Powell, J. L., Harley, P. M., and Fairbairn, H. W', Analyses are reported in parts per million (ppm). 1966, The strontium isotopic composition and origin of carbonatites, in Carbonatites, O. F. Tut- tle and J. Gittens, eds': London, Interscience Publishing,p. 365-378 M., 1979, Fenitization and are approximately 520 m.y. old (Olson greatly improved by critical reviews and com- Robins, B., and Tysseland, some mafic igneous rocks in the Seiland Prov- and others, 1977).This evidencesuggests that ments by J. M. Robertson, J. R. Renault, F. of ince, northern Norway: Norsk Geologisk Tids- the Lemitar carbonatites may have been E. Kottlowski, and R. H. Weber. skrift, v. 59,p. l-23 emplaced between 1,400 m.y. and 420 m.y. References Staatz,M. H., Adams, J. W., and Conklin, N'M.' ago, after the emplacement of the Polvadera Thorium-bearing microcline-rich rocks in Anderson,E. C., 1954,Occurrences of ores 1965, granite. Caballo Mountains, Sierra County, in New Mexico: New Mexico Bureauof Mines and the southern The Lemitar carbonatites are similar in New Mexico: U.S. Geological Survey, Prof. Mineral Resources,Circ.29,27 P. chemistry and mineralogy to the carbonatites Paper 525D, p.48-51 - ,1957, The metal resourcesof New Mexico of the south Manzano in Wet Mountains, Colorado (Armbrust- and their economic featuresthrough 1954: New Stark, J. T., 1956,Geology New Mexico Bureau of macher, 1979;Mclemore, 1980).Carbon and Mexico Bureau of Mines and Mineral Resources, Mountains, New Mexico: Bull. 34' 116p. oxygen isotopic studies in the Wet Mountains, Bull. 39, I 83 p. Mines and Mineral Resources, Colorado, carbonatite complex clearly indi- Armbrustmacher, T. J., 1979, Replacementand Stroud, R. B., and Collins, G. E., 1954,Preliminary Energy Research and cate that those carbonatites are from a deep- primary magmatic carbonatites from the Wet reconnaissance report: Counties. Development Administration, Open-file Rept.' seatedsource (Armbrustmacher, 1979).Other Mountainsarea, Fremonl and Custer EconomicGeology, v. 74' p. 888-901 DEC-RRA-1410, 4265,I P. carbon, oxygen,sulfur, and strontium isotope Colorado: Bolton, W. R., 1976, Precambriangeochronology Suwa,K., Oana, S., Wada, H., and Osaki, S., 1975' studiesfrom throughout the world also indi- of the Sevillita metarhyolite and the Los Pinos, Isotopic geochemistry and petrology of African cate a deep-seatedor upper-mantle source for Sepultura, and Priest plutons of the southern San- carbonatites, ln Physics and chemistry of the carbonatites (Hayatsu and others, 1965; dia Uplift, New Mexico: M.S. thesis,New Mexico Earth, v. 9, L. H. Ahrens, J. B. Dawson, A' R. Powell and others, 1966; Heinrich, 1966; Institute of Mining and Technology, 45 p. Duncan, and A. J. Erlank, eds.: Great Britain, Taylor and others, 1967; Suwa and others, Brookins, D. G., 1974,Radiometric age determina- Pergamon Press,p. 735-745 1975;Mitchell and Krouse, 1975).The Lemi- tions from the Florida Mountains, New Mexico: Taylor, H. P., Jr., Frechen,J., and Degens,E. G.' carbon isotope studiesfrom the tar carbonatites are probably also derived Geology,v.2, p. 555-557 1967, Oxygen and rocks of Canada: Laacher Sea district, West Germany and the Alno from a deep-seatedor upper-mantle source. Currie, K. L., 19'76,The alkaline GeologicalSurvey ofCanada, Bull. 239,228p. district. Sweden: Geochimica et Cosmochimica The Lemitar carbonatites may be derived from Currie, K. L., and Ferguson,J., 1972,A study of Acta, v. 31, p.4O'7-430 gave rise dikes a mafic source that to the mafic fenitization in mafic rocks with special reference Vartiainen, H., and Woolley, A. R', 1976, The and the diorite,/gabbro,although preliminary to the complex: Canadian Journal petrology, mineralogy, and chemistry of the fen- geochemical studies appear not to exhibit any of Earth Sciences,v . 9, p. 1254-1261 ites of the Sokli carbonatite intrusion, Finland: genetic relationships.An extensivegeochem- Erickson, R. L., and Blade, L. V., 1963,Geochem- Geological Survey of Finland, Bull. 280, 87 p. ical and isotopic study of these rocks would istry and petrology of the alkalic igneous complex Verwoerd,W. J., 1966,Fenitization of basicigneous have to be undertakenbefore constraintscan at Magnet Cove, Arkansas:U.S. GeologicalSur- rocks, ln Carbonatites, O. F. Tuttle and J. Git- p. be placedon the compositionof the source. vey, Prof. Paper425, 95 p. tins. eds.: London, IntersciencePublishing, 1957, The Experimentalevidence confirms that melts Gillerman, 8., and Whitebread, D. H., 295-308 --native von Eckermann, H., 1948,The alkaline district of with a variety of compositionscan producethe uranium-bearing deposits in the Black Hawk district, Crant Alno lsland: Sveriges Geologiska Undersokning wide variance in mineralogy and chemistry County, New Mexico: U.S. Geological Survey, Arsbok, no. 36, 176p. seenin carbonatitessimilar to those found in Bull. 10O9-K,p. 282-311 Watkinson, D. H., and Wyllie, P. J', 1971, Ex- the Lemitar Mountains (Heinrich, 1966; Gold, D. P., 1963,Averagechemical composition of perimental study of the composition join Wyllie, 1966; Watkinson and Wyllie, l97l). carbonatites: Economic Geology, v. 58, p. NaAlSiO,-CaCO,-H,O and the genesisof alkalic The evidencesuggests that carbonatitessimi- 988-99l rock-carbonatite complexes: Journal of Petrol- -378 lar in composition to those in the Lemitar Hayatsu, A., York, D., Farquhar, R. M., and Git- ogy, v. 12, p. 357 of the Lemitar Mountains may have been emplacedat tem- tins, J., 1965, Significanceof strontium isotope Woodward, T. M., 1973, Geology Mountains, Socorro County, New Mexico: M'S. peraturesof 450o-600"C and pressuresrang- ratios in theoriesof carbonatiteEenesis: Nature, v. p. 625-626 thesis, New Mexico lnstitute of Mining and ing from l-1000 bars (Heinrich, 1966). 207, Heinrich, E. W., 1966,The geologyof carbonatites: Technology,73 p. AcKNowLEDGMENTs-This study was fi- Chicago,Rand McNally and Co., 555P. Wyllie, P. J., 1966, Experimental studies of car- nanced in part by a grant from the New Mex- Kelley,V. C., 1968,Geology of thealkalinePrecam- bonatite problems: The origin and differentiation ico GeologicalSociety and by an assistantship brian rocks at Pajarito Mountain, Otero County, of carbonatite magma, in Carbonatites, O. F. from the New Mexico Bureau of Mines and New Mexico: Geological Society of America, Tuttle and J. Gittins, eds.: London, Interscience Mineral Resources. The manuscript was Bull., v. 79, p. 1565-1572 Publishing,p.311'352 n

November1980 New Mexico Geology