GEOLOGY OF THE PRECAMBRIAN ROCKS OF THE
LEMITAR MOUNTAINS,
SOCORRO COUNTY, NEW MEXICO
Virginia T. McLemore
Submittedin Partial Fulfillmept
of therequirements for the Degree of
Master of Science in Geology
V
New MexicoInstitute of Miningand Technology
Socorro, New Mexico
May, 1980 TABLE OF CONTENTS
ABSTRACT
ACKNOWLEDGMENTS . INTRODUCTION ...... 1 Purpose ...... 3 Methods of Investigation ...... 4 Previous Work ...... 6 SEDIMENTARY ROCKS ...... 7 Introduction ...... 7 Distribution and discussion of Lower Unit ...... 11 Distribution and discussion of Upper Unit ...... 12 Geochemistry ...... 20 Provenance and Sedimentation ...... 25 IGNEOUS ROCKS ...... 31 Introduction ...... 31 Lemitar dioritejgabbro...... 33 Introduction ...... 33 Description ...... 35 Migmitization...... 40 Geochemistry ...... 44 Gabbro of Garcia Canyon ...... 46 Origin ...... 4. Mafic Dikes ...... 48 Distribution...... 48 Description...... 49 I Geochemistry ...... 53 Origin of the Mafic Rocks ...... 54 Granitic Complex ...... 57 Introduction...... 57 Gneissic granite ...... 59 Muscovite-biotite granite ...... 61 Biotite granite...... 63 Leucogranite ...... 65 Polvadera Granite ...... 65 Pegmatites and quartz veins ...... 68 Geochemistry ...... 69 Origin...... ~4 Carbonatite Dikes ...... 76 Introduction...... 76 Distribution...... 77 Description...... 87 Geochemistry ...... 98 Fenitieation...... 104 Origin ...... 114 STRUCTURE AND METAMORPHISM ...... 117 MINERALIZATION ...... 127 GEOLOGIC HISTORY. TECTONIC SETTING. AND CONCLUSIONS .....130 REFERENCES CITED...... l36
APPENDICES A - Analytical Procedures...... 149 B - Brief Petrographic Description of the Analyzed Rocks...... 157 C - Chemical Analyses...... 162 TABLES
1 .Geochemistry of sandstones ...... 21 2 - Chemical classification of sandstones ...... 23 3 - Geochemistry of Lemitar sediments ...... 29 4 - Difference between gabbro and diorite ...... 36 5 - Chemistry of the mafic rocks ...... 45 6 - Chemistry of the Lemitar granitic complex ...... 70 7 - Chemistry of granites ...... 73 8 - Minerals of Carbonatite Complexes ...... 78 9 - Chemistry of.carbonatites ...... 79 10 - Trace element chemistry of carbonatites ...... 80 11 - Similaritiesand differences Lemitar carbonatites and other occurrences of carbonatites ...... 82 12 - X-Ray diffraction lines of bastnaesite ...... 83 13 - Mineralogy of the Lemitar carbonatites...... 89 14 - Distribution of elements in carbonatites ...... 102 15 - Minerals of the Lemitar carbonatite samples ...... 103 16 - Classification of fenites...... 105 17 - Summary of chemical changes due to fenitization ...109 18 - Chemical trends of fenitized mafic rocks ...... 110 19 - Summary of geologic history ...... 131 FIGURES
1 .Index map ...... 2 2 - Precambriangeologic map of the Lemitar Mountains
(inpocket) 3 - Diagrammatic stratigraphic section ...... 8 4 - Classification of sandstones ...... 9 5 - Na20 - K20 plot of sandstones ...... 22 6 - Geochemical classification of sandstones...... 22 7 - Tectonic provenance of Proterozoic sandstones ...... 26 8 - Classification of igneous rocks ...... 32 9 - AFM diagr.am...... 55 10 - Mafic - Felsic index diagram ...... 56 11 - CaO - Na20 - K20 diagramof Lemitar igneousrocks'.. 71 12 - Rb - Sr diagram of Lemitar granitic complex ...... 72 13 - Carbonate-apatite-magnetiteplot of the Lemitar carbonatites ...... 88 14 - Chemical plot of carbonatites ...... 100 15 - CaO-Na20-K20 plot of fenites ...... 108
PLATES
1 .Photograph. arkose and quartzite ...... 14 2 - Photograph. crossbedding in arkose...... 14 3 .Photomicrograph. arkose ...... 16 4 - Photograph. arkose ...... 16 5 - Photomicrograph. subarkose ...... 18 6 - Photomicrograph. dioritelgabbro ...... 38 7 - Photograph. dioritelgabbro ...... 38 8 - Photograph. dioritelgabbro ...... 39 9 - Photograph. foliated muscovite-biotite granite .....41 10 - Photograph. migmatitic layer in dioritelgabbro..... 41 11 - Photograph. agmatitic structure in dioritelgabbro.. 42 12 - Photograph. agmatitic structure in dioritelgabbro ..42 13 - Photograph.boudinage structure in diorite/gabbro.,43 14 - Photomicr.ograph, altered mafic dike ...... 51 15 - Photomicrograph. gneissic granite ...... 60 16 .Photograph. gneissic granite ...... 62 17 .Photomicrograph. muscovite-biotite granite ...... 64 18 .Photomicrograph. biotite granite ...... 64 19 .Photograph. breccia carbonatite dike ...... 84 20 - Photograph. breccia carbonatite dike .....:...... 84 21 .Photograph. banded carbonatite dike ...... 86 22 .Photomicrograph. primary carbonatite dike ...... 90 23 .Photomicrograph. replacement carbonatite dike ...... 91 24 - Photomicrograph. replacement carbonatite dike ...... 91 25 .Photograph. carbonatite dike ...... 93 26 - Photomicrograph. carbonatite dike ...... 94 27 - Photograph, carbonatite dike ...... 94 28 - Photograph,carbonatite dike...... 97 29 - Photograph,carbonatite dike...... 97
MAPS
1 - Geologic Map of thePrecambrian rocks (in pocket)
2 - Geologic Cross Sections (in pocket) ABSTRACT
ThePrecambrian rocks in the Lemitar Mountains consist of a sequenceof sediments, the Corkscrew CanyonSequence
(5%), intrudedsequentially by mafic dikes, a diorite/gabbro body(20%), granitic rocks (75%), andcarbonatite dikes.
Thesediments consist of a Lower Unit composed of a massive
arkoseandUpperan Unit composed of interbeddedand
foliatedarkoses, subarkoses, and quartzites. The sediments arehigh in Si02 (>62%) andhave low Si02/A1203ratios and
K20/Na20 ratiosequal to or greater than one. Theabundance
ofquartz and feldspar indicates a sourcearea consisting of
granite or gneiss,while bedding structures indicate a
fluvial or deltaicenvironment in either a continental-rift
or a rapidly rising continental-marginsetting.
The Lemitar diorite/gabbro is a lithologically
heterogeneous mafic unitranging in composition from gabbro
(>An50)and diorite ( diorite (5-10% quartz).This lithologic heterogeneity could be accountedbe for byeither late differentiationof a gabbroic magma orinjection and mixing of granitic magmas with a gabbroicbody. Three stages of maficdikes are recognized - Stage I, 11, and I11 (pre-diorite/gabbro, pre-granite, and post-granite). Themafic rocks plot in the tholeiite field of an AFM diagram. Thegranitic rocks are grouped into six variationsof one or moreplutons - gneissicgranite, muscovite-biotite granite,biotite granite, leucogranite, Polvadera granite, andpegmatites and quartz veins. Age relationshipsbetween thegranitic rocks are uncertain because the granites are notincontact with one another and probably are of a similar age.The granitic rocks fall intotwo groups - Group I (gneissicgranite and biotite granite) characterized by low Si02(66-702) andhigh CaO (1.5-32) and MgO (0.8-1.5%)andGroup. I1 (muscovite-biotitegranite. and Polvaderagranite) characterized by high Si02 (73-76%) and low CaO (<1.5%)and MgO (<0.8%). Carbonatitedikes intrude the earlier Proterozoic rocks and are composed>50%of carbonate (calcite, dolomite, and/orankerite) and are rich in apatite(up to lo$), magnetite (upto 15%), andbiotite/phlogopite (up to 15%). Thecarbonatites fall intotwo populations - lowiron and highiron, related thetopresence ankeriteof and magnetite.Carbonatites are rich in phosphorus (up to 4% P205),anduranium (upto 0.1% U308). Normalsodic fenitizationhas altered the Lemitar diorite/gabbro adjacent tothe carbonatite dikes as evidenced by theincrease in sodium inplagioclases and the increase in K-feldspar. Chemically,the igneous rocks fall intothree distinct populations - themafic rocks, the granitic rocks, and the carbonatites;no chemical trends are apparent between the groups.The bimodal nature of theserocks is consistent with a continental-riftsetting. ThePrecambrian rocks ofthe Lemitar Mountains have undergonesuccessive periods of metamorphismprior to retrogrademetamorphism and otheralteration andare structurallycomplex, consisting foliation,of faults, shearing,and brecciation (most of which are Laramide or Tertiarystructures 1. Mineralassemblages theof. Proterozoicrocks are representative of thetransition betweenthe greenschist and amphibolite facies. Foliation ofthe Corkscrew Canyon sequence approximately parallels relictbedding and is distinguished by texturaland color contrasts. A northeast-trendingshear zone cuts across the sedimentsand ends at theintrusive contact with .the -. muscovite-biotitegranite. Shearing ofthe dioritelgabbro may berelated to the emplacement of the&ranitic rocks. Detailedmapping, petrographic, and geochemical studies indicatethat the Proterozoic rocks are consistent with a continental-riftsetting. The lack of anychemical trend betweenthe mafic, granitic,and carbonatite groups suggests thatthere arethree separate magma sourcesforthe formation of igneousrocks in the Lemitar Mountains. However,contamination by crustal material and other magmas couldbe responsible in part for thislack of anychemical trend. An alkali province may haveexisted in New Mexico andsouthern Colorado, evidenced by thepresence of 0.4 to 1.2 bay.alkali rocks scattered throughout Colorado (Wet Mountains,Iron Mountains) and New Mexico(Monte Largo, FloridaMountains, Pajarito Mountain). The Lemitar Mountainswould be part of thisalkali province. ACKNOWLEDGMENTS Theaut hor is indet)t e d t'o Mr. and Mrs. J. B. Kelley foraccess to the field area.Special acknowledgment is made to Dr. K. C. Condiefor many helpfulsuggestions and commentspertaining to the field and laboratory work as well as duringthe preparation of themanuscript. Theauthor is gratefulto Dr. J. R. Renaultfor his helpwith someof theanalytical analysis. Robert North, JoanPendleton, Drs.' K. C. Condie, J. R. Renault,and 'J. M. Robertsonacknowledgedare for their critical reviewsof the manuscript. Other people have assisted with thisproject at varioustimes and are acknowledgedfor their assistance:Larry Holt (field' assistant), LynnBrandvold (assistedwith someof the chemical analyses), Gary Morris (exchangeof field and petrographic data and discussions of theoccurrence thecarbonatites),of and Dr. A. J. Budding(accompanied theauthor field inseveral on occasions). Dr. ClaySmith also lent the author maps and air photosof the area. Inaddition, appreciation is extendedto Dr. Frank Kottlowskifor his interest and support of this project. Finally,appreciation is extendedto my husband, James; field assistant,sample collector, andcameraman. This study was financed in part by a grant from the New Mexico Geological Society and by an assistantship from the New Mexico Bureau of Mines. Geologyof the Precambrian Rocks of the Lemitar Mountains, SocorroCounty, New Mexico INTRODUCTION The Lemitar Mountainsare l'ocated approximately eleven km. northwestSocorro,of New Mexico(fig. 1). Several unpavedroads west of Lemitar, New Mexico,provide excellent accesstothe area byeither two- four-wheel-driveor vehicles.Precambrian rocks crop outalong theeastern flanksof the mountains. The map area(fig. 2) extendsfrom the southern limit ofPrecambrian exposure (near the section line between sec. 18 and 19, T.2S., R.lE.), northwardto the microwave tower in sec. 32 (T.lS., R.1E.). Theeastern and'western boundaries of thefield areaare formedbythe end of Precambrianexposure. The area southof Corkscrew Canyon (located along the sectionline between sec. 7 and 18) hadbeen previously mappedbyChamberlin (1978 and1980, inpreparation) as Precambrianundifferentiated metamorphic rocks. This report dividesthe southern area into three mappable lithologic units (Map 1).Chamberlin (1978 and 1980, in preparation) alsorecognized deficiencies in the geologic mapping of the I I -. I I , LL 0 2 a a s 0 I fn I >- I- I z 3 0 I 0 0 I K K I 0 0 0 I v) LL I 0 I n Q I I -I I W r Page 3 Precambrianrocks by Woodward (1973) in thearea north of CorkscrewCanyon, but it was nothis intention to remapthe Precambrianrocks. As a part of thisreport, the area from CorkscrewCanyon northward tothe intrusive contact of the PolvaderaGranite has been remapped (Map 1). Whereverpossible, the names of particular lithologic unitshave been adopted or modifiedfrom the informal terminologyusedby Woodward (1973). In many cases, especiallywith the granitic rocks, new lithologicunits weremapped by the author and assigned informal, descriptive names - Several.periods of metamorphismhave affected the Precambrianrocks exposed in the Lemitar Mountainsand the lithologicnames should be prefixed with the term meta. However, the currenttrend among Precambriangeologists is touse the original lithologic nomenclature and leave off theprefix meta: thatstyle is adoptedfor this report. PURPOSE Thepurpose of this report is to describeand determine thegeologic history of the thick succession of Precambrian sedimentsand granitic, mafic, and carbonatite rocks exposed in theLemitar Mountains. This study includes detailed Page 4 mapping,petrographic studies, and major- and minor-element analysesof “a representativesuite of samples.Detailed chemicalstudies are included on eightcarbonatite samples. From the result’s thefollowing will bediscussed: (1) thesedimentary environment (2) thesediment provenance . (3) thenature of the mafic and granitic magmatism,and (4) thetectonic setting. METHOD OF INVESTIGATION Theauthor, assisted by Larry Bolt and James McLemore, spentapproximately five months mapping the area (fig. 2) indetail at a scaleof 1:6000. The U.S.G.S. Lemitar 7.5-minutequadrangle map was used as a base for geologic mapping.Areas ofmajor outcrop are shownon the map. A scintillationcounter was usedmeasureto thenatural radioactivityof the mafic andcarbonatite dikes and other rocksin the field. Rock colors were standardized,using therock color chart by Goddard, et al. (1975). One hundredthin sections were examined with a Zeiss polarizingmicroscope to determine lithologic and textural variations. Twentyof the thin sectionsofcarbonatites Page 5 were on loanfrom Garry Morris, also studying these rocks. Many. ofthe slides were stained to aid in the identification of K-feldspar.of Plagioclase compositions were determined usingthe Michel-Levy method (Kerr, 1959). Mineralidentifications in carbonatitesamples were determined from thinsection study and byX-ray diffraction. Mineralseparations were made with an aceticacid leach and a heavymineral separation technique using tetrabromo-ethane (specificgravity of 2.96)andidentified X-rayby diffraction.Analytical procedures discussedare in appendix A. Severalcomputer programs were used to calculate CIPW and MESO Norms (K. C. Condie,personal communication) and otherpetrologic parameters (Petcal byBingler, et al., 1976). Theediting mode ofthe DEC20 at New MexicoTech enabledrapid revision of a semi-formatedthesis text, while RUNOFF (a formaterprograi at New MexicoTech) was employed to obtain a completedversion of the thesis text. Page 6 PREVIOUS WORK ThePrecambrian rocks of theLemitar Mountains were first brieflydescribed by Darton (1928) and Lasky(1932). Lasky(1932) alsomentioned small fissure-fillingore depositsalong the western contacts of thePrecambrian exposures.The occurrence of 'uraniumthein calcareous basicdikes intruding the Precambrian rocks of theLemitar Mountains was first reported by Stroudand Collins (1954) andAnderson (1954, 1957). The first mining claims for uranium,fluorite, and sulphides in the area were filed in 1954 (SocorroCounty Courthouse Records). Bonnichsen(1962) made a generalstudythe of Precambrianrocks in the Lemitar Mountains and the area was mappedby Woodward (1973) as partof a mappingproject in the Lemitar Mountains.Condie and Budding (1979) describe thelithology and structural history of thePrecambrian rocksin the Lemitar Mountains as part of a'study of the Precambrianrocks in central New Mexico; Chamberlin (1978 and1980, in preparation)remapped the Lemitar Mountains, includingreconhaissance mapping of Precambrianthe exposures. Page 7. SEQIMENTARYROCKS INTRODUCTION A detailedcomposite Precambrian stratigraphic section ofthe Lemitar Mountains is difficultto determine because o f poor exposures,poor of faulting, shearing, otherand deformation.Thicknesses may onlybe broadly estimated due to poorlyexposed and faulted primary bedding structures. A diagrammaticsketch of the stratigraphic section is shown in f'ig. 3. Precambriansedimentary rocks compose approximately 5% ofthe Precambrian exposure (fig. 2) andhave aeen called theCorkscrew Canyon sequence (Woodward, 1973). 'Theycan be classified as quartzites (>90$ quartz),subarkoses (75 - 90% ' quartz),and arkoses ((75% quartz).The Corkscrew Canyon sequencecontains the oldest rocks exposed in the Lemitar Mountains. Two stratigraphicunits can be distinguished,an Upper andLower Unit; andboth units have been intruded by graniticrocks. The Lower Unit is a recrystallized, fine-grainedarkose, and,theUpper Unit consistsof recrystallized,interbedded arkoses, subarkoses, and quartzites(fig. 4). Smalllenses of green and gray schist MUSCOVITE- BIOTITE GRANITE *IINTRUSIVECONTACT UPPERUNIT INTERBEDDEDARKOSES, SUBARKOSES, AND QUARTZITES KEY c] ARKOSE SUBARKOSE 0QUARTZITE MAFICDIKES ,. GRADATIONALCONTACT . ._. . . LOWER UNIT MASSIVEARKOSE IlNTRuslvE CONTACT GNEISSICGRANITE FIGURE 3-DlAGRAMATlCSTRATIGRAPHIC SECTION OF THE PROTEROZO'ICCORKSCREW CANYON SEQUENCE, LEMITARMOUNTAINS QUARTZ &QUARTZITE SUBARKOSE 6 NUMBEREDSAMPLES WERE ALSOANALYZED FOR MAJOR ANDMINOR ELEMENTS (APPENDIX E), 523 524f ARKOSE LlTHlCARENlTE FELDSPAR FRAGMENTS FIGURE 4- CLASSIFICATION OF SANDSTONES FROM THE CORKSCREWCANYON SEQUENCE (MODIFIED AFTER PETTIJOHN, 1957) BASED ON ESTIMATEDMODAL ANALYSIS Page 10 are foundlocally throughout the sequence. The sequence is representativetheoffeldspathic quartzite and arkose associationexposed throughout southern and central New Mexico(Condie and Budding, 1979). Faintcrossbedding and graded bedding are preserved in arkosesand subarkoses in CorkscrewCanyon, indicating that theCorkscrew Canyon sequence exposed in Corkscrew Canyon is ? upright,younging toward the east. Althoughthin laminar crossbeds are common, they are notphotogenic because of poorexposure and lack ofcontrast. Foliation parallels relictbedding, making the distinction between the, two difficult.Faint crossbedding and graded bedding are often poorlypreserved in float and in poorly exposed outcrops south of CorkscrewCanyon. A conformable,gradational contact may exist between theUpper and Lower Units, althoughthe nature of the contact is doubtfulbecause of poor exposures and east-west faults. If foliationparallels relict bedding throughout theentire sedimentary sequence, as in CorkscrewCanyon and elsewhere,than the Lower Unit is olderthan the Upper Unit. Page 11 DISTRIBUTION AND DESCRIPTION OF THE LOWER UNIT TheLower Unit consistsof 250 to 300 meters of arkose to subarkoseand can be found in the southern half of sec. 18. TheLower Unit may begradational with the Upper Unit ofthe Corkscrew Canyon sequence and the southern contact is intrusivewith the gneissic granite (Map 1): Smallgneissic dikes(2-15 cm. thick)intrude the LowerUnit along the sharsintrusive southern contact where foliation inthe LowerUnit arkose is prominent. Also, small inclusions of the Lower Unit can befound within the gneissic granite, TheLower. Unit is locallyfoliated and consists of a darkgray, very fine-grained arkose tosubarkose. Outcrops are poorand good exposures occur only along the intrusive contactwith the granite. In thinsection, poorly sorted, roundedto subrounded sand grains are preserved and often aregraded. A fine-grained matrix (probablyquartz and sericite,35-40%) is present inthe arkose along with sand- 1, untwinned , muscovite Incontrast to the interbedded and foliated Upper Unit, the Lower Unit consistsof a massivearkose with only local foliation and relictbedding preserved. Quartzite and Page12 subarkoseinterbeds, although common in theUpper Unit, are notpresent in the Lower Unit. In handspecimen,the arkose ofthe Lower Unit is similar in generalappearance to the quartzitesfound in theoverlying sediments ofthe Upper Unit. Theunits differ in thinsection where the Lower Unit is not as wellsorted and is composedof a largerquantity offine-grained matrix than the arkoses in theUpper Unit. DISTRIBUTION AND DESCRIPTION OF THE UPPER UNIT Introduction Approximatelyonethousand metersinterbedded of arkosesand quartzites in theUpper Unit overliethe Lower Unit to the south. A muscovite-biotitegranite is in fault or intrusivecontact with the Upper Unit on thenorth forming a nearlyvertical contact in sec. 7. Becauseof poorexposures the nature ofthis contact is uncertain. Chamberlin (1978) mapped'thiscontact as theextension of a faultcutting the Kelley limestone; however, the lack of slickenslides and breccias is suggestive of an intrusive contactrather than a faultcontact. The occurrence of inclusionsgrayschistof and arkosewithin the muscovite-biotitegranite favorsalso an intrusive Page 13 relationship.Mafic dikes, pegmatites, quartz veins, and carbonatitedikes also intrude the sediments. A faultblock of sediments crops out in thesouthern portionsec.of 7. It is boundedmuscovite-biotiteby granite,Lemitarthe diorite/gabbro, Phanerozoicand sediments. At thislocality thesediments have been brecciatedand recemented. Thebestexposures of theUpper Unit arealong CorkscrewCanyon, where several hundred meters theof sequenceareexposed. Several Precambrian andTertiary faultscut the rocks, so theexact thickness of the sequence is difficultto determine. In addition,strong deformation andshearing in thewestern quarter of the section along CorkscrewCanyon obliterates original textures and structures.Lenses and dikeletsof granitic pegmatites and aplitesare common in thesheared rocks, and small lens-shapedboudinage structures are preserved. Bedding is distinguishablebycolor contrasts and texturalvariations (PI. 1 and 21, butmineralogical compositions can be determinedonly microscopically. A ten-meterbedhomogeneous, of massive quartzite can be distinguishedfrom the other sediments but is seenonly in CorkscrewCanyon (Map 1). Outcropsoutside Corkscrew Canyon arepoor and few in number. Relictcrossbedding and graded PL. 1: Thinlylaminated interbedded arkose and quartzite cutby an aplitevein. PL; 2: Relict crossbeddingin arkose. Page 15 bedding can bedetected in CorkscrewCanyon and elsewhere, indicatingthat the sequence is upright.Arkoses are the mostabundant sediment, followed by (in order of abundance) subarkoses,mafic dikes, quartzites, and green and gray schist. Arkose Thearkoses are common throughoutthe sequence and occur as fine-and medium-grained interbeds. Foliation of thefine-grained arkose is produceddark-grayby and grayish-pinklayers consisting of poorly sorted sand- and silt-sizegrains of quartz(25-30%), feldspar (15-25%), biotite (10-20%), muscovite (5-15%), and a traceamount of hornblendeand magnetite (fig. 4). Up to 15 - 20% matrix may bepresent in thefine-grained arkoses. Crossbedding and gradedbedding are often preserved along with .thin layers of coarsearkosic or subarkosic sand (pl. 3 and 4). Medium-grainedarkoses differ from the fine-grained arkosesby having little orno matrix and largerand more roundedsand grains. Foliation of the medium-grained arkose is similar thefine-grainedto arkose. Medium-grained arkosesconsist ofsand-size grains of quartz(50-70%), K-feldspar (5-15%), plagioclase, An10-40(15-30%), biotite (10-20%), muscovite(2-5%), and minor amounts of magnetite. PL. 3: Photomicrograph (25x, cross-polars) showing graded bedding in arkose. PL. 4: Fine-grained'arkose, showing crossbedding. Page 17 Theinterbedded and foliated arkoses ofthe Upper Unit differsfrom the massive arkoseof the Lower Unit byhaving quartziteand subarkose interbeds and thepresence of K-feldspar. Subarkose Thesubarkoses are distinguishable from the interbedded arkosesby their higher quartz content (75-90% quartz). The rocksare foliated with dark-gray and grayish-pink layers, similar toarkoses; they occur as thininterbeds (less than severalmeters thick) scattered throughout the sequence- In thinsection, rounded and well-sorted fine- to medium-sand grainsconsist ofquartz (70-80$), perthiticK-feldspar (probablymicrocline, 5-15$), biotite(10-15%), and minor amounts Of plagioclase,muscoirite, magnetite, and matrix r (fig. 4 and pl. 5). Quartzite Th e quartzitesThe are massive,pinkish grayto medium-gray,and very fined-grained. Thin laminar bedding is oftenpreserved along with well rounded,well-sorted, and fine-sandgrains, consisting ofquartz (>go%) withminor amounts .~ ofperthitic K-feldspar probably -microcl-ine), plagioclase,muscovite, magnetite, and matrix (see photomicrograph,fig. 8, p. 11, Woodward, 1973). The PL. 5: Photomicrograph (25x, cross-polars) of a subarkose. Page 19 quartzitesoccur as thinbeds (several . cm. thick) interbeddedwith arkoses and subarkoses. Schist Schistlenses occur scattered throughout the sediment sequenceand as inclusionswithin various granitic rocks. Theoriginal rocks may havebeen mafic dikes orshale lenses. Most ofthese lenses are too small tobe shownon thegeologic map withtheexception of some larger inclusionsfound within the granitic rocks (Map 1, sec. 7). .Theschists are stronglyfoliated, grayish olive green, fine-grained,.micaeous rocks and consist of chlorite and biotite (40-50%), plagioclase, An40-50 (30-35%), quartz (5-10%),and magnetite (5-105).The chlorite and biotite content may range as high as 905, withchlorite often more abundantthan biotite. Grayschist lenses occur as inclusionswithin the muscovite-biotitegranite andwithin several isolated outcropsof Precambrian rocks in sec. ~ 7 (Map 1); theyare composed of thin(several cm. thick)alternating layers of massivequartz, plagioclase, biotite, and muscovite. The grayschist often grades into a thinlybedded arkose and oftenoccurs as inclusionswithin the carbonatite dikes. Thesegreen chlorite and gray schist lenses are seldommore Page20 than a fewmeters long and are common alongsecondary arroyos in sec. 7 and12. GEOCHEMISTRY A representativesuite of samples from the Corkscrew Canyonsediments was analyzedfor eight major and four trace elements(Appendix B). Thesample lqcations are plotted on fig. 2. comparisonIn withaveragethe feldspathic quartzite-arkosefrom the Precambrian of south-central New Mexico(Condie Budding, and 1979), arkosesthe and subarkosesof the Upper Unit arelower in Si02, and higher in A1203,Fe203, MgO, Na20,Sr, Rb, and Ba (table 1). The arkosefrom the Lower Unit ofthe Corkscrew Canyon sequence (Lem 401) is higher in Si02,Fe203, MgO, CaO, Na20, Ba, Rb, and Sr andlower in K20, Ti02,and A1203 thanthe average Precambrianfeldspathic quartzite-arkose in New Mexico. Thesedifferences may representthe heterogeneity of source rocksfor the New MexicoPrecambrian feldspathic sediments. TheLemitar sediments can be compared toan average graywacke and arkose(table 2 andfig. 5). TheLemitar sedimentsare higher in Na20,and K20 thanthe average graywackeand arkose. Generally, the Lemitar sediments fall in thearkose field (fig. 5). Page 21 TABLE 1 GEOCHEMISTRY OF SANDSTONES 1 2 3 4 5 6 I Si02 77.5 77.1 66.1 66.7 77.8 65.6 75.2 Ti02 0.63 0.3 0.3 0.6 0.54 0.73 0.62 A1203 12.8 8.7 8.1 13.5 11.1 16.8 13.2 Fe203* 2.71 2.28 5.4 5.5 4.57 6.67 4.74 MgO 0.34 0.5 2.4 2.1 0.94 1.49 1.20 CaO 0.96 2.7 6.2 2.5 1.39 0.77 2.02 Na20 1.71 1.5 0.9 2.9 2.45 2.37 2.70 K20 3.14 2.8 1.3 , 2.6 2.9i 4.71 3.00 TOTAL 99.79 95.88 90.7 95.8 101.70 99.14.102.68 K20/Na20 1.8 1.9 1.4 0.7 1.2 2.0 1.1 Si02/A1203 6.0 0.9 8.2 4.9 7.0 3.9 5.7 Rb 113 139 223 202 Sr 52 78 156 162 Ba 530 1172 1189 1186 * - Total iron expressed as Fe203. 1 - average feldspathic quartzite-arkose fromthe Precambrian of New Mexico (Condie and Budding, 1979) 2 - average arkose (Pettijohn, 1963) 3 - average lithic arenite (Pettijohn, 1963) 4 - average graywacke (Pettijohn, 1963) 5 - arkose, Lower Unit, Lemitar Mountains (1 sample) 6 - average arkose, Upper Unit, LemitarMountains (average of 3 analyses) 7 - average subarkose, Upper Unit, LemitarMountains (average of 2 analyses) 2.8 e 523 2.6 e@ GRAYWACKE a 520 524 A - AVERAGE GRAYWACKE 2.4 AVERAGE ARKOSE FIELD 40 I 8 - Na20 2.2 ARKOSE FIELD 2.0 I .8 a 3 4 5 6 K20 FIGURE 5 - Na20 - K20 PLOT OF SANDSTONES FROM THE CORKSCREW CANYON SEQUENCE (DIAGRAM AFTERPETTIJOHN, 1963) 0.5 GRAYWACKE C Na20 K2° QUARTZITE'E ARENITE - 0.5 -I 7 0.52c.5 1 1.5 2.5 LOG 5102 A1203 FIGURE 6 -GEOCHEMICALCLASSIFICATION OF SANDSTONES FROM THE CORKSCREW CANYON SEQUENCE(AFTER PETTIJOHN, 1963) - Page 23 TABLE 2 CHEMICAL CLASSIFICATION OF SANDSTONES (modifiedfrom Pettijohn, Potter, and Siever, 1973) HIGH Si02/A1203 RATIO - Quartzarenites (quartzites) mature, little clay or detrital Al-silicate (1) alkalirich (carbonate cement) (2)alkali poor (silica cement) LOW Si02/A1203 RATIO ((12) immature, clay plus detrital Al-silicate (1) alkalirich (a) iVa20>K20 - feldspathicgraywackes (b) Na20 NOTE - graywacke is defined as a sandstonehaving >15% matrix. Page 24 \ A chemicalclassification, based on thecompositional maturityof the .sediment, has been proposed by Pettijohn (1963 andPettijohn, Potter, and Siever, 1973; seetable 2 andfig. 6). TheLemitar sediments fall thelowin Si02/A1203group and near the border between the high and lowalkali subgroups. This grouping is characteristicof youngerarkoses and lithicarenites. One mustuse caution when usingthese diagrams because theaffect ofregional metamorphism onsediments is not clearlyunderstood. Schwarcz (1966) studiedanarea of regionalmetamorphosed arkosic quartzites and found that no appreciablechange in modal or majorelement composition occurredwith increase in metamorphicgrade. Shaw (1954, 19561, Barth(1936), and Mason (1962)also found almost no significantcompositional changes in sediments metamorphosed upto the upper amphibolite facies. It is probablethat metamorphismhas not significantly changed the major element chemistryof the Lemitar sediments because their chemistries arenot significantly different from chemistries of younger arkosessubarkosesand (Pettijohn, 1963), although metamorphicaffects may account for someof the differences thatexist between theLemitar sediments andrecent sediments. Page25 PROVENANCE AND SEDIMENTATION Some constraintsoriginalthe sedimentary on environmentandtectonic setting can deducedbe from mineralogical,textural, geochemicaland variations. Sandstonecomposition is controlled by a number of factors (Potter, 1978): (1) composition and volumeof the source (2) relief (3) weathering (4) climate (5) methodand distance of transport. Theabundance of quartz and feldspar indicates a source areaconsisting graniteof gneiss. or By applying Dickinson'scriteria (1970, Dickinson and Suczek, 19791, a gneissicor granitic source is indicatedfor the Lemitar Mountainsbythe high quantities ofquartz and feldspar (>25%)and the low quantities of lithicfragments (O%, fig. 7). Rounded subroundedto textures suggest intermediate transportdistances, if thesetextures are not inherited fromthe reworking of a quartzsandstone in thesource area. Therelative abundance of feldspar in thesediments is indicativeof an environment in whichintense weathering did notexist. Such sediments may haveformed in a variable Q CONTINENTALBLOCK PROVENANCE CRATONINTERIOR CONTINENTALRIFT Q - TOTALQUARTZOSE GRAINS RECYCLED OROGEN PROVENANCE F - TOTALFELDSPAR GRAINS SUBDUCTIONCOMPLEX COLLISIONOROGEN L - TOTAL LITHIC GRAINS FORELANDUPLIFT MAGMATICARC PROVENANCE UNDISSECTED ARC DISSECTED ARC PROVENANCE MAGMATICARC PROVENANCE 25 F L FIGURE 7 - TECTONIC PROVENANCEOF PROTEROZOIC SANDSTONES FROMTHE LEMITAR MOUNTAINS (DIAGRAM PROPOSED BY DICK I NSON ANDSUCZEK, 1979) L climatein which erosion and burial were relatively rapid (Folk, 1974; Potter, 1978; Condie and Budding, 1979). The massivequartzite beds in the succession may reflect a local tectonicallystable source localized or reworking of quartzo-feldspathicsediments in a highenergy environment (such as anintertidal zone). The subrounded shapes and small sizethequartzof grains favor reworking of quartzo-feldspathicsediments. Themineralogical and textural evidence are consistent withdeposition in a fluvial or deltaicenvironment (Reineck andSingh, 1973). However,the evidence is notsufficient todifferentiate between a lacustrine or a marinesetting. The.Rinconada Formation (Precambrian) in northern New Mexicoconsists interbeddedof quartzites and pelitic schists similar tothe Corkscrew CanyonSequence (Barrett andKirschner, 1979). Thesedeposits have been interpreted to representdeltaic, fluvial, and shallow-marinedeposits basedon the presence ofcrossbedding, ripple marks, and gradedbedding and on the similarity between the Rinconada sedimentsand Holocene sediments from the Donjeck River, Yukon (fluvialdeposits), and Niger delta syst,ems (Barrett andKirschner, 1979). TheCorkscrew Canyon sediments may represent a similar depositionalenvironment because of the similarityin primary bedding structures and lithology. Page 28 Severalattempts have been made toapply mineralogical compositionplate-tectonicto settings (Dickinson, 1970; Dickinson and Suczek, 1979; Dickinson and Valloni,1980). Thedominance feldsparof andquartz (fig. 7) clearly indicatesthat the sediments found in theLemitar Mountains weredeposited in a continentalblock provenance, assuming Dickinson'stheory is applicabletothe Lemitar Mountain Precambriansediments. Two specifictectonic settings are recognized byDickinson and Suczek (1979) asoccurring in a continentalblock provenance - thecraton interior and the uplifted,basement (rift zone). Chemistryhasbeen used differentiate to between ancienttectonic settings (Schwab, 1975). Quartz-rich sandstones(characteristic of rift valleys and rising, stablecontinental- margins) have a highSi02 content and a K20/Na2O ratioequal to or greaterthan one. The Lemitar samples,with one exception, fit thesecriteria (table 3). Blockfaulting associated with rifting could uplift a graniticbasement; and rapid erosion along steep slopes couldproduce alluvial-fan deposits, resulting in thegraded and crossbedded,poorly tomoderately sorted feldspathic sedimentssuch as thoseexposed in theLemitar Mountains. Prolongedabrasion of any quartz-rich source could produce quartzites.Deltaic environments could develop further from Page 29 TABLE 3 GEOCHEMISTRY OF THE LEMITAR SEDIMENTS Si0265.2 76.5 69.6 62.0 77.8 73.8 Si02/A1203 3.8 6.2 4.8 3.3 7.0 5.3 K~O/N~~O1.6 0.8 1.6 3.2 1.2 1.5 Page 30 the uplifted terrain. A more tectonicallystable environment could be envisioned as well, suchas a risingcontinental-margin (Schwab, 1975) or a cratoninterior (Dickinson and Suczek, 1979). A graniticsource could exist at relativelystable conditionsfor a longtime; and, under dry or coldclimatic conditions,thefeldspars would notdecompose. Over a length of time,the abrasive action produced by water or wind couldproduce arkosic sands (Folk, 1974). Quartzites may derivedbe from locally reworked sediment in an intertidalzone. Fluvial or deltaic environments wou.ldbe consistentwith such a setting. Page 31 IGNEOUSROCKS INTRODUCTION ThePrecambrian igneous rocks in theLemitar Mountains consistof a maficintrusive body (Lemitar diorite/gabbro), a graniticcomplex, mafic dikes, and carbonatite dikes and aregrouped according to a classificationmodified by Hyndman (1972)after Streckeisen (1967, fig. 8). The igneousrocks have been metamorphosed and should be prefixed withthe term meta, but for the purposes of this report the originalnomenclature is used,leaving off the term meta. Precambriangranitic rocks inthe Lemitar Mountains compose 75% of thetotal exposed Precambrian terrain, while the Lemitar diorite/gabbrocompose 20% ofthe total exposed Precambrianterrain. In New Mexico,Precambrian granitic rockscompose approximately twothirds theofexposed Precambrianterrain (Condie and Budding, 1979) andthe majorityof the basement as well (Denison and Hetherington, 1969; Muehlberger,et al., 1966). Maficrocks, although not as common, arepresent throughout the Precambrian in New Mexico. A 1.5-b.y.(White, 1978) gabbrocrops out in the MagdalenaMountains (Loughlin Koschman, and 1942; Blakestad, 1976; Sumner,1980) that may berelated to the X GNEISSICGRANITE 0 POLVADERAGRANITE + MUSCOVITE-BIOTITEGRANITE QUARTZ A BIOTITEGRANITE CB MAFICDIKES 0 DlORITE/GABBRO OIA EA SE DIKE + OIAEASE TRONOHJEMITE GRANODIORITE QUARTZ-BEARING QUARTZ-MONZOGABBRO MONZONITE M ON ZO NITE DIORITE, NORITE,DIORITE, MONZONITE GABBRO ALKALI 10 , 35 65 90 'ELDSPAR PLAGIOCLASE FIGURE 8 - CLASSIFICATIONOF IGNEOUSROCKS (AFTER STRECKEISEN, I967 AND HYNDMAN, 1972) SHOWING SAMPLESFROM TH E LEMITAR MOUNTAINS BASED ON ESTIMATEDMODAL ANALYSIS P.age 33 Lemitardioritelgabbro. Recentgeochronologic studies (White, 1978; Brookins, et al., 1978; Condie and Budding, 1979) ofthe Precambrian rocksin central and southern New Mexicoimply that most graniticplutonism occurred between 1.5 and 1.1 b.y.These studiessuggest that perhaps the Precambrian granitic rocks in theLemitar Mountains were emplaced during this period. LEMITAR DIORITE/GABBRO Introduction The Lemitar dioritelgabbrocrops out norththeof CorkscrewCanyon sediments (fig. 2), forming many of the lowerhills and ridges along the eastern portion of the mapped area. Thedioritelgabbro continues as faultblocks andwindows farther north of the mapped area. Thesouthern boundary theofbody forms a nearly vertical,often migmitized, intrusive contact, where the dioritelgabbro is incontact with muscovite-biotite granite. Thewestern boundary is formedby unconformably overlying bedsPhanerozoicof sediments. Theeastern contact is formedby a series of faultsand unconformities with Phanerozoicsediments and volcanics. Page 34 Thenature of thenorthwestern contact is in doubt becausethelackof good of exposures. ThePolvadera Granite is in fault or intrusivecontact with the Lemitar diorite/gabbro on thenorth, forming a northeast-striking contact.Evidences ofbrecciation and slickenslidesoccur alongpart theof northeast- east-trendingto contact betweenthe diorite/gabbro and thePolvadera Granite and indicate a faultcontact (sec. 32, Map 1). Thisfault could form the remainder of thecontact between the two units as Chamberlin (1978) mapped it, butthe lack of brecciationand slickenslides are more suggestiveof an intrusivecontact. Near thecontact foliation thein diorite/gabbro and thePolvadera Granite parallels the contactsuggesting an intrusiverelationship. Themafic body is intruded by biotitegranite and leucogranitedikes and plugs, and portions of pegmatites and quartzveins arefound scattered throughout. Mafic and carbonatitedikes also intrude thediorite/gabbro. Some maficdikes may be a latestage ofthe diorite/gabbro; othersintrude this granite and are post-granite. Page 35 Description Thedioritejgabbro maintains a speckledappearance producedlargeby(several mm. in diameter)white phenocrysts of plagioclase. It is a lithologically heterogeneousunit ranging from gabbro and diorite to quartz gabbroand quartz diorite (table 4). Thedioritejgabbro varies in mineralogicalcomposition, but primarily consists of plagioclase, An40-60 (30-40%), darkblue-green and brown hornblende (30-40%), biotite(partially altered to chlorite, 10-20%), andtraceamounts garnet, of apatite, and magnetite.Augite, olivine, and/or pyroxene may havebeen originallypresent but have now beenaltered to hornblende. Theplagioclase composition contributes to the lithologic differencesbetween the diorite and gabbro. Quartz is often presentamountsin toup 10%. Ophiticsubophiticto textures,in which plagioclase is partially or completely enclosedby hornblende, are often preserved, suggesting the originalrock may havebeen a gabbro(table 4). However hypidiomorphic-granulartextures areoften present and suggestthat the rock may havebeen in part a diorite. Thediorite/gabbro undergonehas deformation and shearing near thecontact with the altered facies of the Polvadera,Granite,where larger amounts chloriteof and - .. Page 36 TABLE 4 DifferenceBetween Gabbro and Diorite (modified after Hyndman, 1972) CRITERIA GABBRO DIORITE plagioclase An>50 An<50 composition (laboradiorite, (andesine, bytownit e ) oligoclase) Other augite,olivine, hornblende, Minerals hornblende, pyroxenes, clinopyroxenes biotite Associated pyroxenites, granodiorites, RockTypes anorthosites quartzdiorites Colorof the grayto greenish white Plagioclase gray Texture subophitic, hypidiomorphic cumulus, or granular ophitic NOTE: Metamorphism may change someof thesevariables. Page 37 biotite are found,forming schistose zones. This contact appearsgradational and is poorlyexposed. Quartz and K-feldspar(probably microcline) oftenincreases in abundancenear the contact with the Polvadera Granite and othergranites. Inclusions are foundthroughout the dioritelgabbro and especiallyin the southern portion of the outcrop area. The inclusionsare generally fine grained, dark to lightgray, exhibitingsharp contacts with the enclosing mafic rock(pl. 6). Light-coloredleucosomes with mafic selvages occur in some parts ofthe dioritelgabbro suggestive of an 0rigi.n by. metamorphicdifferentiation (Pl. 7). Quartzite.and foliatedarkose occur as inclusionsup to 50 cm. across (P1. 8). Dark,fine-grained amphibolite inclusions occur andhave an appearanceand composition similar tothe mafic dikes.Hornblende and biotite, possibly derived from the diorite/gabbro,often-replaces original minerals within the inclusions. Large blocksof sediments are scatteredthroughout the Lemitar diorite/gabbro (a few meters to 10 meters across). Some theseof blocks aremappable (sec. 7, Map 1). Foliationand relict bedding are oftenpreserved. Most, if not all, of theseblocks are probably rotated xenoliths as opposed to roofpendants, because the attitude of foliation PL. 6: Photomicrograph (lox, cross-polars) of diorite/gabbrowith a fine-grainedsediment inclusion. PL. 7: Diorite/gabb.rowith a sedimentinclusion. c---"--l 0.35 mm PL. 8: Amphibolite inclusion in the diorite/gabbro. Page 40 varies fromthat of thegeneral attitude seen in Corkscrew Canyon. Migmitization MigmitizationtheofLemitar dioritetgabbro occurs a lon g the southernalongthe intrusive contact the with muscovite-biotitegranite. The granite is stronglyfoliated nearthe intrusive contact (Pl. 91, formingirregular, foldedbands of quartz and feldspar. Folded veins of quartz andfeldspar crosscut the melanocratic mafic rocks of the Lemitar diorite/gabbro (Pl. 10).Agmatitic structures (P1. 11 and 12) andleucocratic ptygmatic folds occur locally. Boudinagestructures (Pl. 13) are suggestive of theintense shearingand stretching. Fourpossible mechanisms of migmitizationhave been proposedbyYardley (1978): igneous injection, anatexis, external metasomatism,metamorphicand segregation. Agmatizationand rotation of individualxenoliths, as seen inthe Lemitar migmitites,are likely wherever extensive meltinghas occurred, whether produced byigneous injection o r anatecticor melts. It is unlikelythatexternal metasomatism or metamorphicsegregation could produce enough fluid to causerotations of large xenoliths(King, 1965). PL. 9: Strongly foliated muscovite-biotite granite. PL. 10: Migmititic layers in the dioritejgabbro of the Lemitar diorite/gabbro. PL. 11: Agmatitic structures in dioritefgabbro. PL. $2: Agmatitic structures in dioritefgabbro. PL. 13: Boudinage structures in diorite/gabbro. Page 44 Theappearance and composition of the leucosomes seen in the Lemitarmigmitites resembles adjacentthe of that muscovite-biotitegranite. Leucosomes can be locally traced intomuscovite-biotitethe granite (P1. 101, clearly indicating that igneousinjection of themuscovite-biotite graniteinto the Lemitar diorite/gabbro produced the Lemitar migmitites. Geochemistry A representativesample theofdiorite/gabbro was .analyzedfor eight major and fourtrace elements (Appendix C). Thesample locations areplotted onfig. 2. CIPW Norms werecalculated using a computerprogram (Appendix C). Thediorite/gabbro from the Lemitar Mountains is higherin Si02,Ti02, Fe203, and K20 andlower in A1203, MgO, and CaO thanother Precambrian mafic rocks from New Mexicoand an averageArchean basaltic andesite (table 5). In termsof Si02content, the diorite/gabbro is higherthan Nockolds' (1954) averagediorite. All samplesfivethe of diorite/gabbrocontain normative quartz (Appendix C). TABLE 5 Chemistry of theMafic' Rocks 1 2 3 '4 5 6 7 8 9 Si02 52.5 48.2 48.4 53.1 47.5 53.4 46.4 Ti02 1.41 1.53 1.32 0.96 1.89 2.16 1.63 A1203 14.2 13.0 16.8 . 14.2 11.4 11.0 13.4 Fe203* 12.1 14.5 10.4 11.2 16.8 18.3 15.5 MgO 5.49 8.20 8.06 7.77 7.36 2.15 8.43 CaO 9.00 9.50 11.1 9.35 8.58 6.89 9.16 Na20 2.052.57 2.26 2.47 1.94 2.39 3.14 K20 0.560.53 0.56 0.36 1.58 1.72 0.35 TOTALS 97.3198.03 98-90 99 * 41 97- 05 98.0198.01 Ba 25 356 366 108 Rb 205 55 47 11 Sr 108 109 150 . 191 1 - typicalamphibolite of Las Tablas Quadrangle, Barker, 1958 2 - average of 6 areasof Precambrian mafic rocks in south-central New Mexico,Condie and Budding, 1979 3 - average of 10 analysesof metatholeiite and metabasaltic ' andesite from theTusas Mts., Barkerand Friedman, 1974 4 - averagediorite, Nockolds, 1954 5 - averagegabbro, Nockolds, 1954 6 - averageArchean basaltic andesite, Pearce, et al, 1977 , 7 - averageLemitar mafic dike (average of 5 samples) 8 - averageLemitar dioritelgabbro (average of 5 samples) 9 - Magdalenagabbro, Condie and Budding, 1979 * - Totaliron expressed as Fe203. Page Gabbro of Garcia Canyon TheLemitar dioritelgabbro and the gabbro ofGarcia Canyon'(Magdalena gabbro) have very similar textures and mineralogies,although theyhavedifferent chemical compositions(Loughlin and Koschman, 1942; Sumner, 1980). Both mafic unitsintrude older sediments and are subsequentlyintruded youngerby Proterozoic granites, implyingthat the two mafic units may havebeen emplaced at the sametime. The gabbro of Garcia Canyon has been dated (1.5 b.y.,White, 1978) andfound to be of mantle derivation byRb-Sr isotopestudies, although the initial Sr86/Sr87 isotoperatio of 0.704 (White, 1978) is suggestiveof some crustalcontamination. differencesThe chemical in compositioncould be due to differences inherited from the sourcecontaminationto or of granitic magmas after emplacement.Differences in thedegree of contamination and metamorphismcould also account for the dissimilarity in chemicalcompositions between the two mafic units. Page 47 Origin T h e lithologicThe heterogeneity of Lemitarthe diorite/gabbrocould be accounted for by a magma of original dioritegabbroto composition. However, if theLemitar diorite/gabbrowere derived from a dioriteto gabbro magma fromthe upper mantle, other diorite/gabbros should be exposed in thePrecambrian terrain of New Mexico.Instead, dominantlygabbros or basaltsare seen. Contaminationby granitic magmas or crustalmaterial of a gabbroic magma couldaccount for lithologicthe heterogeneity of theLemitar diorite/gabbro. As a gabbroic magma ascendstowards the earth's surface, it couldbecome contaminated,altering parts ofthe gabbroic magma to a diorite.The quartz gabbro and quartzdiorite may result fromthe contamination of the diorite/gabbro by granitic magma or as a latestage differentiate fractionalof crystallizationof the diorite/gabbro or both. The presence ofquartz diorites near the intrusive contacts suggests that themafic body probably was contaminatedwith granitic magma. TheLemitar diorite/gabbro could also have been emplaced as a gabbro,and subsequent injection and mixing of granitic magmas wouldalter the gabbro to a dioriteor even Page 48 to a quartzdiorite. Such features as migmitization, presentin the Lemitar diorite/gabbro,would be consistent withsuch a model.Late differentiation ofthe gabbroic magma couldcrystallize as a diorite,and could also account forthe Lemitar maficbody. A combinationof both igneous injectionandmixing of a granitic magma andlate differentiationcouldalsoresult in Lemitarthe diorite/gabbro. Thepresence ofsediment and mafic dike inclusions Yndicatesthat the Lemitar diorite/gabbro is youngerthan thesediments and at, leastone early stage of mafic dikes. Becausefoliation is preserved in some of thearkose inclusions, a periodofmetamorphism occurred before the intrusionof the Lemitar diorite/gabbro. MAFIC DIKES Distribution Maficdikes intrude all ofthe exposed Precambrian rocks,except thecarbonatites. Careful mapping theof maficdikes indicates a complicatedhistory of two or more periodsof intrusion that can be recognized based on field relationships.The dikes strike dominantly in a northernly Page 49 directionwith almost vertical dips. A seriesof unmetamorphosed diabase dikes also intrude thePrecambrian section. Mostof these dikes are probably Tertiary in agebecause theirof lack metamorphic of characterand similar dikesarefound intruding the Phanerozoicsediments. One sample (Lem 56) is described (appendix B) andincluded with the analyses of the mafic dikes.Chemically, the diabase dike is similar tothe mafic dikes. Description Themafic dikes are greenish-black and fine-grainedand may includeinclusions of sedimentary rocks. Thin granitic veinsand carbonatite dikes often crosscut a fewof these maficdikes. In thinsection, mafic dikes are slightly foliatedand may exhibitsubophitic textures. They consist ofgreen hornblende (35-4021, altered plagioclase (30-35%), green and brown biotite (10-20$), magnetite(5-10$), and varyingamounts quartz,of chlorite, hematite, garnet, fluorite,and carbonate. Mortar textures often accompany secondarycarbonate, while carbonate fluids associated with theintrusion of thecarbonatite dikes often followed and partiallyreplaced these and earlierdikes. Page 50 A series offour thin sections along a mafic dike intrudedby a carbonatitedike were studied. Adjacent to thecarbonatite dike, the mafic dike exhibited extensive alterationwhere corroded magnetite, hornblende, and feldspar are replacedcarbonateby (pl. 14). Apatite (1-3b) was introducedinto themafic dike. Subophitic textures were presentin all fourthin sections. Further fromthe carbonatite dike, less alteration is observedalong withthe disappearance of apatite. In thesample located farthestfrom the carbonatite dike, only slight alteration was observed.Magnetite cores, hornblende, and feldspar wereonly slightly replaced bycarbonate. Thefield evidence suggests three periods of intrusion bymafic dikes - Stage I, 11, and 111. Thepresence of mafic dikeinclusions within the diorite/gabbro suggests that mafic dikes from Stage I wereemplaced prior to the intrusionof the Lemitar diorite/gabbro. Mafic dikes from Stage I1 intrudedLemitarthe diorite/gabbro and subsequently were crosscutby granitic and pegmatite dikes andveins, indicating intrusion after the emplacement of the diorite/gabbrobutbefore emplacement thegraniticof complex. Mafic dikesfrom the final stage,Stage 111, intruded all of theolder Precambrian rocks, including the graniticcomplex; but did not intrude the carbonatites. PL. 14: Photomicrograph(25x, cross-polars) showing extensife carbonatization of a maficdike,, where carbonate hasreplaced feldspar crystals. H 0.3 mm Page 53 Geochemistry A representativesuite of samples from the mafic dikes exposedinthe Lemitar Mountains was analyzedfor eight majorand four traceelements (appendix C). Thesamples are plottedon fig. 2. Themafic dike samples can becompared with other Precambrianmafic rocks from New Mexicoand anaverage Archeanbasaltic andesite (table 5) andfound to be higher in Fe203and K20 andlower in A1203, CaO, and Na20. In terms ofthe Si02 content the mafic dike samples ,have approximatelythe sameamount ofSi02 as Nockolds' (1954) averagegabbro (table 5). Two samplesofthe mafic dikes containednormative quartz (appendix C). ORIGIN OF THE MAFICROCKS Themafic rocks of the Lemitar Mountains plot in the tholeiitefield of an AFM diagram(fig. 91, withthe mafic dikesfalling close to the line between the tholeiitic and calc-alkalinefields, (using Irvine and Baragar definition, 1971). There is noobvious trend between the mafic and felsicrocks, although a bimodalpopulation exists. Two chemicalindices have been proposed as a measureof magmatic fractionation of minerals;the mafic and the felsic indices (Simpson, 1954). TheLemi.tar samples plot on a trend similar tothe Skaergaard trend (fig. 101, suggestingthat themafic rocks may bederived from a similar source. Metamorphism may beresponsible for the scatter of data pointsseen in fig. 10. Two maficbodies are exposed in theLemitar Mountains - three stages ofmafic dikes and the Lemitar diorite/gabbro. Mostmafic magmas originate in theupper mantle (Condie and Budding, 19791, and it is conceivablethat the mafic magmas producingthe mafic rocks seen inthe Lemitar Mountains couldhave emerged from the upper mantle as well. Althoughno definite chemical trends between the mafic dikesLemitartheand diorite/gabbro exist, it is conceivablethat both are derived from a similar source. F SKAERGAARD A-Na O+K20 2 F - FeO M - MqO FOR EXPLANATIONOF ". SYMBOLS SEEFIG.8 DASHED CURVESEPARATES CALCALKALINE FIELD (BOTTOM) FROMTHOLEIITIC FIELD (TOP) FROM IRVINE AND BARAGAR,1971 \ GROUP 2 GRANITES V V " v Y " v V v A N 100 - LEMITAR ,SKAERGAARD TREND DIORITE/GABBR~ 90 - 80 r 70 - 60 - MI 50 - OKONJEJE THOLEIITIC 40 - SERIES FOR EXPLANATION OF SYMBOLS SEEFIG. 8 20 301I 0 0 IO 20 30 40 50 60 70 80 90 100 FI (FeO+ Fe203) x 100 .M I = MAFICINDEX MgO + FeO+Fe203 (Na20 + K20) X 100 FI FELSICINDEX C aO+ Na20+%0 FIGURE 10: MAFIC-FELSICINDEX PLOT OF THE LEMITAR IGNEOUS ROCKS (FROM SIMPSON, 1954) Thedifferences between the two mafic units are exhibited by thedissimilarity in quartz(Si021 contents - themafic dikeshaving little or no quartzand the diorite/gabbro containingquartz in amountsup to 10%. If the diorite/gabbrowere contaminated by granitic magma at some point in its earlyhistory, it is withinthe bounds of possibilitythat the mafic dikes and the diorite/gabbro originated from the sameupper mantle source.Three stages of mafic dikeintrusion would be consistent with a unique source.Similar chemistries between the three stages of maficdikes and the diorite/gabbro support such a model. However,separate sources forthe mafic dikes and the diorite/gabbrocould exist. GRANITIC COMPLEX Introduction Graniticrocks makeupabout three fourths ofthe entireexposure Precambrianof rocks in theLemitar Mountains(fig. 2). Sixvariations of one or more plutons havebeen distinguished on Map 1, althoughthe relationship betweenthem is uncertainbecause of the lack of any field relationships.These map unitsare: (1) gneissicgranite (2) muscovite-biotitegranite (3) biotitegranite (4) leucogranite (5) PolvaderaGranite (6) pegmatitesand quartz veins Thegneissic granite intrudes the base of the sediments and is notin contact with the other granites nor with the Lemitardioritefgabbro. A fewpegmatites thecutdo gneissicgranite (Map 1). Thegneissic granite could be olderthan the other granites exposed in theLemitar Mountains;strong foliation is present in thegneissic graniteand absent from from the other granites. If the gneissicgranite is older,then the foliation theof gneissicgranite is possiblyrelated to the foliation of the sediments. It is difficultto foliate one granite (gneissic granite)without affecting the other granites in the Lemitar Mountains,unless the other granites were emplaced after the foliationoccurred. Pegmatites and quartz veins are common throughoutthe sediments, the Lemitar dioritefgabbro, and the Polvaderagranite. The granitic rocks may bederived from a similar sourcebecause thesimilarityof in compositionand texture. GneissicGranite Thegneissic granite crops out in theextreme southern portionof the mapped area (Map 1) and is bounded on the southby a brecciatedfault zone (forming an arroyo) and on the east and west byunconformities with the Phanerozoic sediments.The northern limit ofexposure is formedby. an intrusivecontact with the sediments, and thin dikes of gneissicgranite intrude the sediments along the intrusive contact. SeveralPrecambrian several andmaficdikes greenish-blackdiabase dikes of uncertain age intrude the gneissicgranite. Phanerozoic limestone caps the granite on a fewof the higher hills. Pegmatite dikes and veins are rare. The gneissic granite is a stronglyfoliated (see P1. 151, pinkish-grayto medium-gray, coarse- to medium-grained quartz-monzonite,weathering to a reddish-orangearkosic sand. ' Thegranite consists of quartz (30-35%), K-feldspar (25-30%),plagioclase (20-25%), biotite(10-15$), and trace amountshematiteof magnetiteand (fig. 8). Mortar texturesare often developed. This granite differs from otherPrecambrian granites inthe Lemitar Mountainsby strongfoli'ation produced stronglyby aligned biotite crystalsand by thelack ofmafic and abundant sediment PL. 15: Photomicrograph (25x, cross-polars) of gneissicgranite. U 0.3 mm Page 61 inclusions.Inclusions of the arkose are found along the intrusivecontact (Pl. 16), butmafic inclusions are absent. Muscovite-biotiteGranite Themuscovite-biotite granite crops out north ' of Corkscrew'Canyon, where it is in intrusive or faultcontact (as previouslydiscussed, see Sedimentary Rocks) with the sedimentson the south and the Lemitar diorite/gabbro on the north, it occupiesless than a fourthof a squarekilometer. Maficdikes and several Tertiary dikes intrude the muscovite-biotitegranite. Small lenses of darkgreen chloriteschist and sediments occur as xenoliths,suggesting an intrusiverelationship with the sediments. Migmitization occursalong the intrusive contact with the Lemitar diorite/gabbro as discussedearlierLemitar(see diorite/gabbro). Themuscovite-biotite granite is a slightlyfoliated, pinkish-grayto grayish-pink, fine-grained quartz monzonite or granite. It differsfrom the other granites in the LemitarMountains presencethe by large (oftenof megascopic)primaryflakes ofmuscovite (pl. 18). Porphyritic,white and black varieties are found along the crestof the westernmost ridge. The rock consists of quartz PL. 16: Arkose inclusionwithin the gneissic granite. Page 63 (30-40%),K-feldspar ,(10-30%), plagioclase, An40-50 (20-3521,biotite (5-10%), muscovite (3-10%), and trace amountsmagnetite,of hematite, and calcite(fig. 8). Mosaictextures dominate. BiotiteGranite The biotitegranite intrudes the central and northern portionstheLemitarof diorite/gabbro. It is often gradationalwith the leucogranite and forms the crests of theridges and appear as podsand small islandssurrounded bymafic rocks. The granite may representdikes and/or plugs. The biotitegranite is a grayish-pinkto gray, fine- to medium-grained,quartz monzonite and differs from the other LemitarMountain Precambrian granites by its fine-grained natureand granophyric texture (pl. 17). It is composedof quartz(30-40%), K-feldspar (30-4021, plagioclase, An40-50 (20-30%),biotite(5-10%), and trace amounts ofhematite, magnetite,hornblendeand (fig. 8). Distinctive granophyrictexture is welldeveloped in thinsections of thebiotite granite, distinguishing it fromtheother granitesin the Lemitar Mountains. Granophyric texture may indicatecrystallization at a eutectic (Hyndman,1972). Mosaicand porphyritic textures are also common. PL. 17: Photomicrograph (25x, cross-polars) of a muscovite-biotite granite. PL. 18: Photomicrograph (25x, cross-polars) of biotite granite showing granophyric texture. H 0.3 mm Page 65 Leucogranite Theleucogranite intrudes the central and northern portionsofthe Lemitar diorite/gabbro and differs from othergranites in the Lemitar Mountains by its coarsergrain sizeand whitish color. It is oftengradational with the biotitegranite and forms the crests of ridges and.occurs as small islandssurrounded by mafic rocks along the arroyos (Map 1). Theleucogranite probably represents dikes and/or plugs. Theleucogranite is a whiteand black, coarse-grained rock.The granite consists ofequal amounts ofquartz, perthiticK-feldspar, and plagioclase,with trace amounts of biotite (<5%) andmagnetite ( PolvaderaGranite ThePolvadera Granite (Woodward, 1971) cropsout in the northernthird of the mapped area andextends northward for aboutthree km. This granitecomprises about three fourths ofthe Precambrian rocks exposed in the Lemitar Mountains (seefig. 2). A medium- tocoarse-grained facies and an altered faciesare distinguished on Map 1, withthe medium- to coarse-grainedfacies being most theextensive. The southern limit ofexposure of the medium- tocoarse-grained Page 66 facies is formed by a northeast-trendingintrusive or fault contact (as previouslydiscussed) Lemitarwiththe dioritejgabbro.The western and eastern limits ofexposure are formedby faults and unconformitieswith Phanerozoic sedimentsand volcanics. Thealtered facies is locatedsouthwest of the medium- tocoarse-grained facies. It is bounded on thesouth, west, andnorth byfaults and unconformities with Phanerozoic sediments.The eastern limit ofexposure is formedby a gradationalintrusiveLemitar contactthe with dioritejgabbro. Bothfacies of the Polvadera Granite are intruded by maficand carbonatite dikes. The medium- tocoarse-grained faciesoften contains inclusions of mafic rocks and of gray andgreen chlorite schist. Themedium- tocoarse-grained facies of thePolvadera Granite is a palered, medium- tocoarse-grained, slightly foliatedrock that weathers to a moderateorange arkosic sand.This granite consists of equalamounts ofquartz, plagioclase,and K-feldspar, with varying trace amounts of biotite,hornblende, and magnetite(fig. 8). Mortar and porphyritictextures are often present in thinsection. Greenand gray schist, often several meters long, occur as inclusionswithin the granite. Page 67 Thealtered facies of the Polvadera Granite is poorly exposedand badly weathered. Pegmatites, mafic dikes, and Phanerozoicmineralization occur within granite.the Mineralizationconsists of quartz,feldspar, and barite. Some galena,calcite, and copper minerals are also present. Freshsamples of thealtered facies are similar in compositionand texture tothe medium- tocoarse-grained facies.The rocks areblack and dusky red, medium- to coarse-grainedgranites. The granite consists of quartz (25-30%),plagioclase, An40-45 (20-25%),perthitic K-feldspar(30-35%), biotite (15.-20%), and trace amounts of hornblende,magnetite, and hematite. Submortar texture is presentand granophyric texture is oftenpreserved. Inclusions of stronglyfoliated quartz and feldspar, sediments,gray and green schist, and mafic inclusions are scatteredthroughout. Dioritic to gabbroic inclusions are foundalong the intrusive contact. Inclusions are more common thanin the medium- tocoarse-grained facies. Thealteration of thisfacies of thePolvadera Granite resultsfrom somecombination of thefollowing: (1) partialassimilation of sediments and diorite/gabbrorocks (2) shearingand tensional stress (3) regionalmetamorphism Page 68 (4) fenitizationassociated with the intrusion of thecarbonatites (5) hydrothermalalteration produced byPhanerozoic mineralsolutions. Smallblocks sedimentof and diorite/gabbrooccur withinthe altered facies ofthe Polvadera granite and partialassimilation of these sediments and diorite/gabbro blocksalong the southern intrusive contact could result in thebrick-red, badly eroded altered facies seen inthe LemitarMountains. Shearing and tensional stress hasoften occurred as evidencednortheast-trendingby layers of foliatedquartz and feldspar in some outcrops (Map 1). Fenitizationassociated with the intrusion of a carbonatite body at depthcould also result in thealteration of the I granite,assuming that a carbonatitebody is at depth beneaththis altered facies theofPolvadera granite. Hydrothermalalteration is superimposedolder on metamorphismand alteration, complicating any interpretation whichmight have been possible. Pegmatitesand Quartz Veins Grayish-pinkand white pegmatite and whitequartz dikes andveins intrude thePolvadera Granite, thegneissic granite,theLemitar diorite/gabbro, and the sediments. Page 69 Some pegmatitetheof veins havebeen folded. The pegmatitesare of thesimple type, consisting of unzoned feldspar,quartz, mica, and a trace amountepidote.of Thesedikes and veins are discontinuous, with a northerly strikeand often form pod-like bodies surrounded by thehost rock.Inthe granite, numerous pegmatite dikes range in thicknessfrom a few cm. toseveral meters. It is possible thatthey represent a final stageof the Polvadera Granite. - Geochemistry Thegranitic rocks are either quartz monzonites or granites,however one sample (Lem 126) is a granodiorite (fig. 8). Generally,the granites fall into twogroups - Group I and Group I1 (table 6 and'fig. 9, 11, and 12); bothgroups fall withinthe calc alkaline field (fig. 9). Thesegroupings broadly correspond Condie'sto high Ca (Group I) andhigh Si or high K (Group 11) groups(table 6 and 7). More traceelement data arerequired to further differentiatebetween Condie's high Si and high K groups. Metamorphismand other alteration may haveaffected the Lemitargranites, shownby thescatter of points awayfrom thegeneral trend of New MexicoPrecambrian granites on a Rb-Srdiagram(fig. 12). Despitealteration and TABLE 6 Summary of theChemistry of the Lemitar Mountain Granites 1 2 3 4 si02 66-70% 73-76% 66-73% 70-77% CaO 1.5-3% (1.5% 1.7-4% 0.9-2% MgO 0.8-1.5% (0.8% 0.6-2.546 (1. 4% K20 (4% 3-6% 2.5-4% 4-5% Mn 550-900 ppm 200-450 ppm 1 - Group I granites,Lemitar Mountains Gneissic Graniteand Biotite Granite 2 - Group I1 granites, Lemitar Mountains PolvaderaGranite and Muscovite-biotite granite 3 - High Ca granite,Condie, 1978 4 - High K andHigh Si granite, Condie, 1978 FIGURE 11: CaO-No20-K20 PLOT OF THE IGNEOUS ROCKS FROM THE LEMITAR MOUNTAINS. NOTETHE LACK OF A TREND BETWEEN THE (SOLIDPOPULATIONS LINES ARE LEMITARSAMPLES. DASHED LINES ARE FROM CONDIE\AND BUDDING, 1978). ,"- . HIGH K I .. . \ .. . 300 .. \ I I \ \ \ IO0 HIGH co Rb 50 10 FIGURE 12: Rb-Sr PLOT OF THELEMITAR GRANITES. FIELDS SHOWING CRUSTAL THICKNESS AREFROM CONDIE, 1973. FIELDS OF HIGH Ca, .HIGH Si, AND HIGH K GRANITES (DASHEDLINES) ARE FROM CONDIE, 1978. SOLIDLINES REPRESENT FIELDS OF GROUP I AND 2 FROM THE LEMITAR MOUNTAINS. TABLE 7 CHEMISTRY OF THE GRANITES 1 2 3 4 5 '6 7 8 Si02 76.4 74.2 73.5 68.0 69.8 69.1 76.1 72.3 Ti02 0.460.07 0.45 0.78 0.79 0.63 0.19 0.40 A1203 12.5 13.6 13.2 14.3 12.2 14.4 12.6 14.~3 Fe203" 3.660.95 4.43 6.46 8.05 4.48 1.72 2.76 MgO 0.470.05 0.44 1.05 0.93 1.41 0.11 0.51 CaO 0.95 1.07 1.04 2.03 1.98 2.69 0.70 1.35 Na20 3.67 3.45 3.03 3.69 3.03 3.22 3.48 3.08 K20 4.81 4.40 5.20 3.94 3.85 3.53 4.63 4.79 TOTAL 99.4 101.31 101.29 100.25 100.63 99.46 99.53 99.49 Ba517 780 816 100820 1155 1279 779 Sr226 77 71 37110 274 255 Rb 168 218350 140 150 147 242 1 - Two mica granite,St. Francois, Missouri, Kisvarsanyi, 1980 (1 sample) 2 - Averagemuscovite-biotite granite, Lemitar Mountains (3 samples) 3 - AveragePolvadera granite, Lemitar Mountains (2 samples) 4 - Averagebiotite granite, Lemitar Mountains (3 samples) 5 - Averagegneissic granite, Lemitar Mountains (2 samples) 6 - AverageHigh-Ca granite, N.M., Condie, 1978(9 samples) 7 - AverageHigh-Si granite, N.M., Condie, 1978 (12 samples) 8 - Average High-K granite, N.M., Condie, 1978(15 samples) NOTE: 2 and 3 compriseGroup I1 granites and 4 and 5 compriseGroup I granites. Page 74 metamorphiceffects, it is apparentthat the granitic rocks were emplacedin a continentalcrust which was >25 km. thick(fig. 12; CondieBudding,and 1979). This is assumingthat the crustal thickness grid proposed by Condie (1973) canbe applied to such granites. Origin Experimental,chemical, and isotopic evidence indicate thatgranitic magmas, such as thosefound in the Lemitar Mountains, may formby fractional crystallization of mafic magmas or by partialmelting of lowerthe crust. Contaminationof a granitic magma of eitherorigin by crustalmaterial could produce heterogeneous granites as foundin the Lemitar Mountains. Geochemicalmodel studies on New MexicoPrecambrian granitesindicate that 30 - 50% partialmelting of siliceous granulites in thelower crust could produce granitic melts similar incomposition to granites of Condie'shigh Ca group (Condie, 19781, whichbroadly correspond tothe Group I granites in theLemitar Mountains. Granites from Condie's highSi and high K, whichbroadly correspond to Group II granites in theLemitar Mountains, could beproduced by fractionalcrystallization of granodiorite magmas. This may implythat the Lemitar granites may bederived from similar mechanismsthat may haveproduced other Precambrian granites in New Mexico. Differencesin depths of emplacement of the granitic rocksexposed in the Lemitar Mountains may account for the heterogeneityseen. The biotite granite is thoughtto be emplaced at a relativelyshallow depth dueto its fine-grainedand porphyritic nature and its similarityto thePuntigudo granite porphyry in theDixon-Pennasco area, also thoughtto be emplaced at 2 - 4 km. (Long, 1974). The Cine-grained,porphyritic muscovite-biotite granite is.also thoughttobe emplaced at shallowdepths because of its discordantrelationship- with the Corkscrew Canyonsequence (Buddington, 1959). However,the migmitization along the intrusivecontact withtheLemitar diorite/gabbro is suggestiveof deeper depths of emplacement than the biotite granite (2 -6 km.). The abundanceof pegrnatites throughout thePolvadera granite suggest deeper depths of emplacement (>6 km.).Pegmatites are rare in theepizone (depths of 2 - 6 km.) andthose few pegmatites known to haveformed at shallowdepths are characterized bybi-pyramidal quartz and sanidine,and are absent in theLemitar pegmatites. The gneissicgranite is thoughttobe emplaced at relatively deepdepths, 6 - 13 km.,due to its concordantrelationship withthe Corkscrew Canyon sequence, evidence offorceful injectionintrudingdikes(thin the sediments), coarse-grainedsize, and similarity with the Pennasco quartz monzonite(also emplaced at 8 - 13 km.,Long, 1974). Barker andothers (1975) proposed a modelfor the origin of the PikesPeak granite, which is similar in compositionto the Lemitar granites,suggesting that the Pikes Peak granite was emplaced at depthsof 3 - 7 km. Thisrange in depth.of emplacementcorrelates well withthe 2 - 8 km. range determinedfor the Precambrian granites exposed in northern New Mexico(Long, 1974) and in the Lemitar Mountains. CARBONATITE DIKES Introduction Carbonatites are igneousrocks consisting of >50% carbonate(Heinrich, 1966). Sovite (>80% calcite), rauhaugite (>80% dolomiteand/orankerite 1, and silicocarbonatite (50-80% carbonatespecies) dikes and veins occurthroughout the mapped area and in the Precambrian rocksto the north in the Lemitar Mountains. Distribution Thecarbonatite dikes strike dominantly north-south or east-westand dip steeply (Pl. 19 and 20) and crosscutthe entirePrecambrian sequence. The dikes range inthickness from a few cm. to a meters.few Mostdikes are discontinuousdue toerosion, however a few dikes can be TABLE a MINERALS OF CARBONATITE COMPLEXES LOCALITY MINERALS Mountain Pass, calcite,dolomite, ankerite, siderite, California bastnaesite,quartz, phlogopite, biotite, allanite,magnetite, hematite, galena, pyrite,fluorite, and otherminerals includingseveral sulphides Iron Hill, dolomite,calcite, apatite, limonite, Colorado aegirine,soda amphibole, phlogopite, microcline,quartz, fluorite, sulphides, pyrite,and other minerals MagnetCove, calcite,dolomite, ankerite, microcline, Arkan'sas apatite,magnetite, phlogopite, and others AlnoIsland, calcite,dolomite, ankerite, biotite, Sweden pyroxene,quartz, pyrite, albite, garnet,chlorite, barite, apatite, fluorite,and others Fen,Norway sovite - calcite,biotite, ap,atite, manganophyllite,microlite rauhaugite - carbonates,apatite, biotite, Wet Mountains, calcite,dolomite, barite, bastnaesite, Colorado biotite,phlogopite, apatite, garnet, galena,sphalerite, quartz, zircon, and otherminerals Lemitar calcite,dolomite, ankerite, barite, Mountains, bastnaesite,biotite, phlogopite, New Mexico fluorite,micas, apatite, garnet, zircon, quartz,magnetite, and microcline Page 79 TABLE 9 CHEMISTRY OF CARBONATITES 1 2 3 4 5 6 Si02 13.87 24.16 3.40 10.30 14.96 20.65 Ti02 0.48 1.78 0.28 0.73 1.10 0.47 A1203 2. 88 4.95 0.50 3.29 1.32 4.32 Fe203 3.39 7.68 3.04 3.46 6.53 1.91 FeO 4.80 6.87 11.75 3.60 3.13 8.92 MgO 9- 56 6.80 7-05 5.79 7.04 9.47 CaO 29.9 17.2 28.7 36.1 30.4 20.33 Na20 0.37 0.75 0.01 0.42 2.28 0.24 K20 0.63 1.51 0.10 1.36 1.44 2. 08 MnO 0.64 0.35 0.48 0.68 0.36 1.30 ~205 3.44 1.32 0.06 2.09 2.33 1.97 c02 26.77 17.77 35.80 28.52 26.81 26.25 TOTAL 96.73 91.14 95-56 91.17 97 - 70 97-91 1 - averageprimary magmatic carbonatite, Lemitar Mountains 2 - averagereplacement-type carbonatite, Lemitar Mountains 3 - averageankeritic carbonatite, Lemitar Mountains 4 - averagecarbonatite, Heinrich, 1966 5 - rauhaugite,Iron Hill, Colorado,Nash, 1971 6 - biotite,ankeritic-dolomitic carbonatite breccia, CastigonLake, Canada, Currie, 1976 7 - averagelimestone, Pettijohn, 1957 Page 80 TABLE 10 TRACEELEMENT CHEMISTRYOF CARBONATITES 1 2 3 4 5 6 7 8 Ba 1294 2490 2155450-1120 830 1000 530015000 Sr 297 355 130 3200 3000 880 3200 Ni 44 286 59 8 85 200 51 cu 13 63 13 2.5 5i 39 43 co 36 64 54 17 nil 470 110 Cr 16 23148 15 nil-13 470 110 Li 36 40 7 8 Zn 133 275 527 109 U 8.7 8.4 4.7 40 5 26 1 - average primarymagmatic carbonatite, Lemitar Mountains 2 - average replacement-typecarbonatite, Lemitar Mountains 3 - average ankeriticcarbonatite, Lemitar Mountains 4 - average carbonatite,Heinrich, 1966 5 - average of 4 sovites,Sokli, Finland, Vartiainen and Woolley, 1976 6 - carbonatite,Magnet Cove, Arkansas, Erickson and Blade, 1963 7 - primarymagmatic, Wet Mountains,Colorado, Armbrustmacher, 1979 8 - replacement, Wet Mountains,Colorado, Armbrustmacher, 1979 TABLE 11 SIMILARITIES AND DIFFERENCES BETWEEN THE LEMITAR CARBONATITE AND OTHER CARBONATITES SIMILARITIES A. Occurrence Nonalkalicigneous complex, examples: Ravalli County, Montana;Verity, British Columbia, Canada; Salmon Bay, Alaska;Turi Peninsula, U.S.S.R.; (Heinrich, 1966). Maficassociation, examples: MagnetHeights, Transvaal (gabbro,magnetite, albitite, Verwoerd, 1966), Stjernoy, Norway (gabbro,Verwoerd, 1966) ; Sokli, Finland, (amphibolite,Vartiainen and Woolley, 19761, Messum,South West Africa(basalt, dolerite, gabbro, Verwoerd, 1966). Structureand Texture Replacementcarbonatites common, example: Wet Mountains, Colorado(Armbrustmacher, 1979); Siilinjarvi,eastern Finland(Puustinen, 1969). Porphyritictextures common, example: Wet Mountains, Colorado(Armbrustmacher, 1979). Occurrence of xenolithswithin thecarbonatite dikes, examples : MountainPass,California; Matopon Hill, Nyasaland;Panda Hill, Tanganyika(Heinrich, 1966). Slightfoliation parallel tothe walls theofdikes, examples:Mountain Pass, California (Olson, et al. 1954); Wet Mountains,Colorado (Heinrich, 1966). Presence of zoningwithin thecarbonatite dike, example: MountainPass, California (Heinrich, 1966). C. Mineralogy Common mineralogy(table 8 Lackof feldspathoids and soda amphiboles, example: Mountain Pass,California (Olson, et al., 1954). Page82 TABLE 11 - continued D. Alteration (10) Fenitization, if present, is poorlydeveloped, examples: Magnet Heights, Transvaal (Verwoerd,1966); Sokli, Finland (Vartiainen andWoolley, 1976). DIFFERENCES A. Occurrence (1) Absenceofrelated alkalic rocks, examples: Fen, Norway (Heinrich, 1966); Alno,Sweden (von Eckermann, 1948). (2)Lack associatedof large mass orplug of carbonatite, examples:Mountain Pass, California(Olson, et.al., 1954); Alno,Sweden (vori Eckermann, 1948). (3) No associatedkimberlites which are often, but not always, associatedwithcarbonatite complexes, examples: Fen, Norway;southwest Tanganyika; Gibeon province, South-West Africa (Heinrich, 1966). B. Mineralogy (4) Apparentlack of sulphideminerals common toother complexes (table 2). (5) Lack of feldspathoids and sodaamphiboles, examples: Fen, Norway (Heinrich, 1966); Alno,Sweden (vonEckermann, 1948). C. Alteration (6) Absence of largehalo fenitization,of examples: Alno, Sweden (vonEckermann, 1948); Fen, Norway (Heinrich, 1966). Page 83 TABLE 12 X-RAY DIFFRACTION LINES OF BASTNAESITE FROM THE LEMITAR MOUNTAINS hkl Lem 500 PDF d I d I 002 4.84 40 4.88 40 110 3.54 60 3.56 70 112 2.89 100 2.88 100 114 2.02 60 2.02 40 202 2.62 40 2.61 20 300 2.09 60 402.06 302 1.90 60 1-90 40 Lem 500 - heavymineral separate from the Lemitar Mountains (see fig. 2 forsample location) PDF - PowderDiffraction File (19721, card 11-340 Chemicalformula of bastnaesite is CeC03F PL. 19: Brecciasilicocarbonatite dike crosscutting sediments in CorkscrewCanyon (looking north). PL. 20: Steeplydipping carbonatite dike intruding the Lemitardiorite/gabbro (looking north, in sec. 7). Page 85 tracedforseveral hundred meters along strike. Flow structures or bandingoften parallels the contacts of the dikes(P1. 21). Some dikesfollow pre-existing fracture zones.Feeder systems often fill fracturesadjacent to the main dike.The random orientation of thedikes (Map 1) suggeststhat the carbonatite fluids followed pre-existing fracturezones in thediorite/gabbro, the sediments, and the PolvaderaGranite. Often the carbonatite fluids followed earliermafic dikes, partially or completelyreplacing them, as discussed earlier (seeMafic Dikes). Apparently,fractures were rare in the granitic r.ocks, becausethick carbonatite dikes are not as abundantwithin thegranite as theywithinare diorite/gabbro. the Carbonatitedikes are not often found within the biotite, muscovite-biotite, or gneissicgranites, except occasionally alongtheintrusive contacts. Thecarbonatite fluids generallyshattered Polvaderathe Granite, forming a stockworkpattern. Carbonatitedikes are rare in thesouthern third of the area.This may suggestthat the source may becentered in thearea north of Corkscrew Canyon (northernportion of sec. 71, wherethe frequency of carbonatitedikes is greater. PL. 21: Bandedsilicocarbonatite dike. Page 87 Description One of thecharacteristics ofcarbonatites in the Lemitar Mountains is thepetrologic variations they exhibit. Thedikes vary in mineralogy(fig. 13, table 131, grain size,texture, and chemistry(Appendix C). Inthin section, the carbonatitesexposed in the Lemitar Mountains can be differentiated as primaryto magmatic andreplacement carbonatites(Armbrustmacher, 1979). Textureand mineralogy (table 131 are primarythe criteria thisfor differentiation.Primary carbonatites exhibit. igneous te xtu re s, either primary porphyriticor primary either textures, hypidiomorphic-granular(pl. 22). Primaryporphyritic carbonatites are characterized by largephenocrysts of apatite,magnetite, feldspar, and biotite/phlogopite. Replacementcarbonatites are characterized by fine- or coarse-grainedcarbonate partially or completelyreplacing relict phenocrystsof feldspar and/or hornblende, preserving theoriginal textures of therock (pl. 23 and 24). The originalrocks were dikes,maficgranites, or diorite/gabbro, as indicatedby relict textures.Apatite is moreabundant in the primarymagmatic carbonatites, while magnetite is moreabundant in thereplacement carbonatites, althoughboth apatite and magnetite may bepresent in CARBONATES 50 APATITE 50 MAGNETITE LEMITARMOUNTAINS 0 PRIMARYCARBONATITE DIKES X REPLACEMENTCARBONATITE DIKES ALNO, SWEDEN (von ECKERMANN,1948) 0 SOVITES SOKLI, FINLAND (VARTIAINENAND WOOLLEY, 1976) A AVERAGESOVITE A AVERAGERAUHAUGITE FI GURE 13: CARBONATE-APATITE-MAGNETITE PLOT OF THELEM ITAR CARBONATITES TABLE 13 MINERALOGY OF CARBONATITES OF THE LEMITAR MOUNTAINS MINERAL ABUNDANCE PRIMARY MAGMATIC REPLACEMENT Ankerite c ,E Apat i.te E Barite R Bastnaesite R Biotite/phlogopite C Calcite E Chlorite R Dolomite E Fluorite Garnet - Hematitelgoethite C Hornblende R Ilmenite R K-feldspar C Magnetite E Muscovite/sericite R C Plagioclase C C Pyrite - Pyrochlore - Sphene/leucoxene R Quartz C Zircon R E - essential to all samples, C - present in most samples, R - present in a few samples, - - not present PL. 22: Photomicrograph (25x, cross-polars)of a porphyriticcarbonatite. At thebottom of the photograph is partof a rockfragment. . H 0.3 mm PL. 23: Photomicrograph(25x, plane light) of a replacementcarbonatite, preserving the original porphyritictexture. PL. 24: Photomicrograph(25x, plane light) of a replacementcarbonatite preserving the original ophitic texture. Page92 either.This classification is inadequatein the field and furthergroupings according to mineralogy and texture are necessary. Thecarbonatite dikes in the Lemitar Mountainscan be broadlycharacterized as dikescontaining xenoliths (breccia andmicrobreccia silicocarbonatite dikes) and those without xenoliths.The breccia and microbreccia silicocarbonatite dikes are light to medium-gray,weathering to a dirtybrown, andgenerally primary magmatic. Thedikes consist of 10 - 40% xenoliths(rock fragments) and >60% carbonatite matrix (pl.25 and 26). Large phenocrysts, often megascopic (up toseveral mm. across),magnetiteof (5-10%), apatite (5-10$),biotite/phlogopite (5-15$), and feldspar (<2$) are foundscattered throughout, forming a porphyritictexture. Otherminerals occur throughout the fine-grained carbonate matrix (table 13). Oftenthese minerals are corroded or crackedreplacedandcarbonate. by Resorption of phenocrysts is common. On a weatheredsurface these phenocrystsoften stand out where the carbonate matrix has dissolved away. Soviteand rauhaugite veins often crosscut thedike (pl. 26).The carbonatite dikes often crosscut earlier -mafic dikes (pl. 27). PL. 25: Breccia silicocarbonatite dike (sample Lem 500). Pencil is approximately 20 cm. long. PL. 26: Photomicrograph (25x, cross-polars) of a sovite or rauhaugite vein crosscutting a replacement carbonatite. The vein is 0.7mm thick. PL. 27: Breccia silicocarbonatite dike (brown) crosscutting diorite/gabbro (lighter gray) and a mafic dike (darker gray, fine-grained). I”--) 0.3 mm Xenolithsvary in sizefrom a few mm. to a meter acrossXenoliths include fragments thehostof rock, foliatedgranites, foliated arkoses, quartzites, gray and greenschist, phyllites, and red granitic fenites. Some graniticxenoliths have similar appearance,composition, and texture as thePolvadera Gran.ite, while others have,been completely or partiallyaltered to a fenitecomposed of K-feldsparandbiotite with little quartznoor and plagioclase.The xenoliths are often rounded, possibly as a resultof chemical reactions with the carbonatite fluids and/or as a resultof collusi.ons with each other and the surrounding wall rock. Carbonatitedikes without xenoliths can befurther groupedaccording to mineralogical composition: (1)fine-grained dolomitic to calcitic silicocarbonatitedikes (2) ankeriticrauhaugite dikes (3) soviteand rauhaugite veins (<5 cm. thick) Bothprimary magmatic and replacement types are found within thinsections of the various groupings. Fine-graineddolomitic tocalcitic silicocarbonatite dikes are lightto medium-gray,weathering to a brownish gray.Both primary magmatic and replacementvarieties occur in bothtypes. Often fine-grained silicocarbonatite dikes Page 96 gradeinto mafic dikes. One occurrence of dolomiticto calciticsilicocarbonatite dikes (sec. '7) contained small veinsof megascopic purple fluorite and sulfide minerals. Ankeriticrauhaugite dikescrosscut fine-grained silicocarbonatitedikes (pl. 28 and 29). These dikes are lightbrown and consist of ankerite,calcite, barite, dolomite,hematite, andmagnetite. These dikes commonly occur in and northof sec. 6. Thinsovite andr.auhaugite veins crosscut other carbonatitedikes. Larger sovite veins (up to several mm. thick)often follow pre-existing fractures or earlier.mafic dikesand some are highlyradioactive (up to100 times background).Microscopically, rauhaugitesoviteand veinletscrosscut the carbonatite matrix, xenoliths,and phenocrysts.Clearly these veinlets represent a laterstage ofcarbonatite intrusion. Thin,light brown dikelets or veins fill the fracture systemstheinPolvadera Granite, forming a stockwork pattern (Map 1). Carbonatitefluids apparently intruded the graniteand followed pre-existing fracture or shatter zones. Theseveins consist of barite, calcite, dolomite, ankerite, and hematite.Original granitic textures and minerals are oftenpreserved. Feldspars havebeenpartially or completelyreplaced bycarbonate. These micas have been 8 PL. 28: Fine-graineddolomitic silicocarbonatite dike (sample Lem 530) cutby ankeritic rauhaugite dikes(sample Lem 531A and B). Pistol is approximately thirty cm. .long. PL. 29: Fine-graineddolomitic silicocarbonatite dike cutby ankeritic rauhaugite dikes. Pencil is .approximately 20 cm. long. left intact,suggesting low temperatures at thetime of replacement. Theage of the Lemitar carbonatites is difficultto determine.Tertiary faults truncate the carbonatite dikes insec. 6 (Map 1) indicatingthat the carbonatites were emplacedTertiary priortofaulting. Furthermore, carbonatiteshave not been found in anyrocks younger than th e Precambrianthe (personal reconnaissance and R.M. Chamberlin,personal communication). The carbonatites may havebeen faulted by a Pennsylvanianfault (sec. 7, Map l), suggesting a pre-Pennslyvanianage. Geochemistry A representativesuite ofsamples from the various carbonatitedikes was analyzedfor major and minor elements (Appendix C). A scintillationcounter was notavailable duringthe sampling period; therefore, the samples were collectedwithout anyknowledge theradioactivityof content. A few of thecarbonatites have major element oxide sums lessthan 100%. Thedifference can be accounted for by numerousother elements that were not determined. Thecarbonatite dikes fall intotwo populations based on ironcontent (table 9). Thehigher iron content is due tothe presence of ankerite and hematite. The high iron carbonatitedikes are not in contactwith the low iron carbonatitedikes, so theexact age relationship is unknown. However,evidence from other localities indicates that ankerite is oneof the last carbonatesto form (examples: EasternSayan Mountains, U.S.S.R.; Iron Hill, Colorado; MountainPass,California; Heinrich, 1966). highThe calciumcontent of thecarbonatites relative toother LemitarPrecambrian rocks is quiteobvious in fig. 13.. The carbonatiteshave a highvolatile content as well(table 9). Inany particular occurrence, the carbonatites are quiteheterogeneous mineralogically and chemically. Due to thisheterogeneity, normal variation diagrams commonly used inthe study ofigneous rocks are not very useful. A variationdiagram has been'used by Dawson (1967) to show the chemicalrelationship between carbonatites and kimberlites. A plot of numerouschemical analyses carbonatitesof throughoutthe world (misc. data compiledby the author), defines a carbonatitefield, which overlies the area between andwithin the kimberlite and mafic carbonatite fields. The Lemitar samplesfall nicely within this field (fig. 14). FIGURE 14: CHEMICAL PLOTSHOWlNO RELATIMISHIPBETWEEN CARBONATITES,KIMBERLITES, AND GRANITES SOLID LINESREPRESENT FIELDS DETERUINED BY DAWSON, 1967 DASHED LINE REPRESENTS FIELD DETERMINEDBY AUTHOR FROM MISC. ANALYSES 050) OF CARBONATITES FROU THRCUOHOUT\ THE 0 WRLD Page 101 T he LemitarThe carbonatites comparedbe can with Heinrich'saverage carbonatite (table 9 and 10). The Lemitarcarbonatites are grossly similar tothis average. Theaverage carbonatite represents an average of analyses withoutregardany as location,to mineralogy, or heterogeneityof the carbonatites. The average carbonatite doesnot reflect extremethe heterogeneity found in carbonatitesin general andeven within a particular locality. Thedistribution majorof and minor elements in carbonat it es have beenexamined by several authors (table 14, Olson,et. a1 1954; Russel,et al., 1954; Erickson andBlade, 1963; Heinrich, 1966; Barber, 1974). The differencesin CaO , MgO, and totaliron among the Lemitar Mountaincarbonat i tes probablyreflect differences in the amounts of calcite, dolomite,ankerite, and magnetite (table 15). K20 exceeds Na20 in all butone sample, reflecting the dominancemicaof and K-feldspar over plagioclase. The presenceof apatite is reflectedby the amount of P205 and H20 (includes F and C1). Ba and Srare found inearly carbonate minerals (Heinrich, 1966). Ba is also a major constituent of barite(table 15, samples Lem 427aand b, 506,530,and 531a). Differences in mineralogywould accountfor the differences in chemicalcomposition between Page102 TABLE 14 DISTRIBUTION OF ELEMENTS IN CARBONATITES OXIDEIELEMENT DISTRIBUTION Si02 quartz,feldspar Ti02 magnetite,sphene, garnet, pyrochlore, micas A1203 feldspar Fe203, FeO magnetite,ankerite, h.ematite MgO, CaO carbonates,magnetite (MgO) Na20, IC20 micas,feldspar MnO carbonates,apatite Sr carbonates,apatite Ba carbonates,apatite, barite U apatite,zircon, pyrochlore, sphene, fluorite P205 apatite H20, F, C1 mica,apatite, fluorite, bastnaesite Cr, Ni, Co pyrite,magnetite, apatite cu pyrite,calcite, niagnetite Zn magnetite,calcite Li phlogopite References:Olson, et al., 1954; Russell,et al., 1954; Ericksonand Blade, 1963; Reinrich, 1966 TABLE 15 MINERALOGY OF THE LEMITAR CARBONATITES BY X-ray DIFFRACTION M iner al 305Mineral 427a 427b500506530 531a 531b Biotite X X X X X X Chlorite X X X X X quartz X X X X X X X X fluorite X X X X .x X calcite X X X X X X X X dolomite X X X X X X ankerite X X X apatite X X X X X X magnetite X X X X X X barite X X' X X bastnaesite X x - present Page 104 theLemitar Mountain carbonatitesand other carbonatites throughoutthe world. Fenitization Fenitization is thealkali metasomatic' replacement' of countryrocks generally associated with the intrusion of carbonatitesalkalicor complexes. Rocks which have undergonecomplete metasomatic replacement areand associatedwith alkali intrusions have been termed fenites (Heinrich, 1966). Two processesfenitizationof are recognized(table 16). One involvesthe addition of sodium andpotassium (normal or sodicfenitization), and the other involvesadditionthe of potassiumonly(potassic fenitization). Normalsodicor fenitization is themost common alterationprocess associated carbonatitewiththe intrusivesin the Lemitar Mountains, as will bediscussed later. Some potassiumhas been added to the dioritelgabbro inthe form of K-feldspar, but this addition is minor. Some redgranitic fenites, consisting of microcline and biotite withlittle or no quartz, occur as xenolithswithin breccia a nd microbrecciaand silicocarbonatite dikesexhibit and potassicfenitization. Page 105 TABLE 16 CLASSIFICATION OF FENITES (after Vartiainand Woolley, 1976) FENITE TYPE FEATURES EXAMPLE NORMAL or SODIC Na and K added, FENITIZATION alkalipyroxenes and amphiboles Sodic .Type stronglysodic Sokli,Finland Alno,Sweden IntermediateType - major Na and K Potassictype major K, minor Na Amba Dongar,India POTASSIC K added,no alkali FENITIZATION pyroxenes or amphiboles,often phlogopite Potassictype UgandaBakusu,K only Late Stage K fenitization ChilwaIsland, Fenitizationsuperimposed on Nyasaland (Africa) normalfenitization Sokli,Finland Page106 A thinzone of sodic fenitization is developedalong some carbonatitedikes in the dioritelgabbro. This zone is notseen everywhere, but appears to be restricted to the westernsides of the thicker ((1 meter)carbonatite dikes. Thezone is two to ten cm. thickand is characterizedby large(up to 60 mm. diameter),in orange-pink albite crystals.The reddish color is common to otherfenite occurrences and is thoughttohave been produced by the oxidationand exsolution of ironmolecules originally within thefeldspar lattice (von Eckermann, 1948, p. 29).The oxidation is believedto be a resultof the degassing of carbondioxide from the carbonatite intrusive. Theplagioclase composition reflects an increase in sodiumby the change from An40 - An50 to An5 - An15.The fenitizeddiorite/gabbro appears also to increase slightly inquartz and perthitic K-feldspar content. A similar type offenitization is reportedfrom the Messum carbonatitevein inSouth WestAfrica. Four stages of fenitization can be distinguished at thislocality (in order ofincreasing fenitization,Verwoerd, 1966): (1) increase in albitecontent (2)introduction of perthitic K-feldspar (3) introductionof nepheline replacing plagioclase withaccessory sodalite and analcite Page107 (4) increaseof orthoclase, nepheline, and ferrohastingsite Fenitizationof the Lemitar dioritelgabbro appears to have progressed as far as stage 2 of thissequence. Two samples of thefenitized diorite/gabbro (samples Lem 532and 533, Appendix B) wereanalyzed for eightmajor elementsandtwominor elements (Appendix C). These preliminarystudies show a significantincrease in Na20 and a significantdecrease in CaO compared unfenitizedto samples(fig. 15). Otherchemical changes are summarized in table 17. Thesechemical changes are consistent with normalsodic fenitization as seen at Sokli,Finland (Vartiainand Woolley, 1976). Theincrease in Na20 is reflectedby the conversion of andesineand laboradiorite to albite and may bedirectly relatedto loss of sodiumby the adjacent carbonatite. The increase in Na20 is alsoreflected by an increasein normativealbite (Appendix C). The loss of CaO may bedue tothe formation of thincalcite veins crosscutting the diorite/gabbrointhe vicinity of the carbonatite dikes. Some CaO may migratetothe carbonatite dike. Ti02 and Fe203 may be loss tothe crosscutting hematite veins. Similar chemical trends are reportedfrom carbonatites throughoutthe world (table 16). FIGURE 15: C&-Na20-K20 PLOT OF THEEFFECT OF FENIT1ZATION ON THE LEYITARDIWITWGAQBRO, TRENDS REPORTED BY VERWOERD, IS66 FROM BASALT AND OAEBRO NEAR THE MESSUM CbRBONATITE,SOUTH WEST AFRICA TABLE 17 SUMMARY OF CHEMICAL CHANGES OF THE LEMITAR DIORITEIGABBRO DUE TO FENITIZATION Significant increase Na20 Significant decrease CaO Slight increase A1203, MgO Slight decrease Ti02, Fe203 No significant trend Si02, K20, Rb, Sr Page110 TABLE 18 , CHEMICAL TRENDSOF FENITIZED MAFICROCKS COMPLEX FENITIZED ROCKSREF. LOSSES GAINS Messum, basalt,dolerite, Na, Al, K Si, Ca, Fe 1 S.W. Africa gabbro Breivikbotn,metagabbroFe, Mu A1 2 Norway Khibina;-Koladiabase K, Na, Mg, Ca, Si 2 SovietUnion Fe, Al, Ti followedby K, Na, Al, Ca, Mg, Fe Si Ti Mbozi, S.W. gabbro K, Na, Al, Ca, Mg, Fe, 2 Tanzania Si Ti .. BlueMountain, amphibolite K, Na, A1 Ca, Mg, Fe 2 Ontario Callander Bay, garnetSi, Al, Na, Ti, Mg, Ca 3 O nta rio amphiboliteOntario K Lemitar,diorite/gabbro Na, Al, Mg Ca, Ti, Fe '4 New Mexico 1 - Verwoerd, 1966 2 - Robinsand Tysseland, 1979 3 - Currie andFerguson, 1972 4 - This report Page 111 , Fenitesarenotalways produced theLemitarin diorite/gabbro when adjacentcarbonatiteto dikes. At MagnetHeights, Transvaal, a sovitedike intrudes gabbro, magnetite,andalbitite with apparentno fenitization (Verwoerd, 1966). At Stjernoy,Norway, a gabbrohas been alteredto an hornblendite bygaseous H20 and C02 erupting fromthe carbonatite (Verwoerd, 1966). Fenitization is also absentwithin the amphibolite at Sokli,Finland (Vartiainen andWoolley, 1976). Fenitization is poorlydeveloped in countryrocks surrounding Siilinjarvithe carbonatite complex,Finland, and is characterizedlightby green alkali-amphibolesand bluish quartz (Puustinen, 1969). Theapparent lack of evidence for fenitization of the Lemitar diorite/gabbro is probably a resultof some combinationof these factors: stability of hornblende (resists fenitization) lackof conduits for fenitizing fluids insufficientvolatile content (H20, C02) ofthe carbonatiteto initiate fenitization insufficientpressures and temperatures of the carbonatitesto initiate fenitization compositionof the Lemitar diorite/gabbro is incompatiblewith fenitization quickcooling and crystallization of the Page 112 carbonatitedikes, allowing insufficient time forfenitization to occur (7) distance from thesource of the carbonatite dikes is great. Vartiainenand Woolley (1976) suggest that thelack of fenltes at Sokli,Finland may be a resultof the stability ofhornblende which resists alterationand the lack of fracturesand veinlets, which act as a pathforthe fenitizingfluids. This may partiallyexplain the lack of fenitestheinLemitar Mountains. Fenitization theof countryrock is dependenton volatile content, pressure, and temperatureof the carbonatite; if thesefactors are not, greatenough, fenitization may notoccur, as inthe Lemitar Mountains.Unfortunately, experimental evidence is lacking tosubstantiate this theory. Thecomposition of the country rock affects thefenitization process. The lack of alkalis wouldpartially explain the absence of fenitization effects (Verwoerd, 19661, and it hasalready been mentioned that the stability of hornblende is such as toresist fenitization. If thecarbonatite dikes cool and crystallize quickly, the temperatureand pressure would drop off, notallowing enough time forfenitization to take place. Furthermore, as the distancefrom thecarbonatite source becomes larger, fenitizationbecomes less pronounced. This was observed at Page 113 Alno,Sweden (von Eckermann, 19481, and may be a primary reasonfor the lack of fenites in the Lemitar Mountains. Theeffects offenitization have been minor in the PolvaderaGranite and thesediments. Some hematiteand carbonateveins are present and may berelated to the early stages of fenitization.Often an increaseinplagioclase andK-feldspar can be detected in the rocks adjacent to the carbonatitedikes. ThePolvadera Granite often becomes brecciatedand fractured, forming only veinlets ofthe *carbonatite and creates a stockworkpattern. A similar type offenitization occurs at Callander Bay., Canada,where fenitizationof granitic rocks progresses as follows(Currie andFerguson, 1971): (1) hematiteveins (first stage) (2) increase in theordering of K-feldspar (3) plagioclaseconverted to albite plus calcite (4) K-feldsparconverted to maximum microcline, pyroxenesbecome abundant (final stage). Thepresence of hematite-carbonate veins and the increase in plagioclaseand K-feldspar contents in theLemitar granites andsediments indicates that fenitization has occurred, but hasprogressed only to first stage. Page 114 Thin(several millimeters) hematiteveins occur within thePrecambrian rocks and as coatingsalong fracture and jointsurfaces. Theveins are oftendiscontinuous with a lateralextent of about a meter. In thinsection, hematite often occursaround corroded magnetite and biotite crystals. Themajority of this type of alteration is a result of the weatheringofiron-rich minerals, although some may be relatedoxidationto produced bythe degassing ofthe carbonatiteintrusive. Origin Thecarbonatite dikes were probably emplaced at a great distance(laterally orvertically) from the source, as evidencedby: (1)the lack of anyradial or conicalpatterns in thedike outcrop, (2) thelack of fenitized haloes about the dikes (3) the common occurrenceof replacement-type carbonatitedikes (4) thelack of carbonatitedikes in the southern portionof the area. .Page 115 Onlyone other occurrence of carbonatites is reported from New Mexico,located in the MonteLargo area (Lambert, 1961). Thiscarbonatite is a massivedolomitic carbonatite. dikewith apatite, magnetite, and mica. Other occurrences of carbonatitesof arefound associated with thealkalic complexes in southernColorado (Heinrich, 1966). Theage of thecarbonatites in Colorado is 520 m.y. (Olson, et al., 1977). Carbonatites are generallyassociated with alkalic intrusives(Heinrich, 1966). Alkalicintrusives of Precambrianage in New Mexico. includethe Pajarito Mountain syenite(1170 m.y., Kelley, 1968) andthe Florida Mountain syenite(420 - 700m.y., Brookins, 1974). Thisevidence may besuggestive of an alkalicigneous province occurring in Coloradoand New Mexicobetween 1100 and420 m.y. The Lemitar Mountaincarbonatites would partthis beof postulated province. Carbonand oxygen isotope studies in the Wet Mountain carbonatitecomplex, Colorado, clearly indicate that those carbonatitesare from a deep-seatedsource (Armbrustmacher, 1979). Othercarbon, oxygen, sulfur, and strontium isotope studiesalso indicate a deep-seatedor upper mantle source forcarbonatites (Hayatsu, et.al., 1965; Powell,et.al., 1966; Heinrich, 1966; Taylor, et.al, 1967; Suwa, et.al., Page 116 1975; .Mitchelland Krouse, 1975). Withthis abundance of isotopeevidence, it is probablethat the carbonatites in theLemitar Mountains also arederived from a deep-seatedor uppermantlesource. It is conceivablethethat carbonatites of theLemitar Mountains may bederived from a maficsource which gave rise tothe mafic dikes and the diorite/gabbro,although preliminary chemical studies appear no t to exhibitto notchemicalany trends. An extensive geochemicaland isotopic study ofthe Lemitar Mountains carbonatiteswould have to be conducted before constraints on thecomposition of the source could be achieved. Experimentalevidence confirms thatmelts with a varietyofcompositions can produce the wide variance in mineralogyand chemistry seen in carbonatites similar to thosefound the Lemitarin Mountains (Heinrich, 1966; Wyllie, 1.966; WatkinandWyllie, 1971). Theevidence suggeststhat carbonatites, similar in compositionto those in thein Lemitar Mountains, may havebeen emplaced at temperaturesof 450 - 600degrees C. andpressures ranging from 1 - 1000 bars(Heinrich, 1966). Page 117 STRUCTURE AND METAMORPHISM INTRODUCTION TheLemitar Mountains lie on the western edge of the RioGrande graben, where normal faults have uplifted' and ex po sed the Precambrianexposedthe metamorphosed rocks.The Precambrianrocks are structurallycomplex. Foliation, faults,shearing, andbrecciation, most of which are Laramideand Tertiary structures, affected the Precambrian rocks.Thedifficulty interpretingin thePrecambrian structure is in differentiatingyounger complex faulting and shearingfrom that of the Precambrian. ThePrecambrian rocks have undergone successive periods of metamorphism,of making theidentification of mineral associationsdifficult. The rocks are also affected by retrogrademetamorphism, such as thechloritization of biotiteand the sericitization of feldspars.The effects of metasomatism,such as carbonatizationand hematization, are superimposedover the metamorphic fabric indicating that metamorphismoccurred prior to alteration. The complicated structuraltrends in the Lemitar Mountains may suggest severalperiods of burial and uplift during the Laramide and Tertiaryorogenies. Contact metamorphic effects are rare. Page 118 METAMORPHISM Generally, the mineral assemblages of the Precambrian rocks in the Lemitar Mountains can be summarized as follows: quartz-muscovite quartz-muscovite-biotite-plagioclase-(garnet) quartz-biotite-potassium feldspar- plagioclase-(garnet) blue-green hornblende-biotite-plagioclase-(garnet) quartz-biotite-muscovite-potassium feldspar- plagioclase These mineral assemblages represent the transition between the greenschist facies (low grade metamorphism)and the amphibolite facies (medium grade metamorphism, Winkler, 1976; Condie and Budding, 1979). Regional metamorphism completely recrystallized the. sediments. The mineral assemblages and gneissic foliation areconsistent with theupper greenschist andlower amphibolite facies of metamorphism; undulatory extinction of crystals maypossibly be related to regional metamorphism. The presence of trace amounts of garnet in some of the thin sections is suggestive of metamorphism to the transitional zone between the greenschist and lower amphibolite facies. Well-preserved foliated arkose Page 119 inclusionsare found scattered throughout the dioritelgabbro suggestingthat this period of metamorphism occurred prior to thetoemplacement theofLemitar diorite/gabbro. The foliationwithin the arkose inclusions is randomlyoriented. At least oneother period of metamorphism that affected theCorkscrew Canyon sequence also affected the Lemitar dioritelgabbroand the mafic dikes. The presence of garnet andthe transformation of pyroxenes to hornblende, found in the Lemitar dioritelgabbro,are indicative of the transition betweengreenschistthe amphiboliteand grades of metamorphism,occurring after emplacementthe theof dioritelgabbro. It is difficultto determine whether the graniticrocks haveundergone metamorphism. Foliation within the granitic rocks is randomlyoriented andlocalized and may be partiallyrelated thetoemplacement theofgranites. Mortartextures are often present, but these too may be relatedtothe emplacement of the granites. Crosscutting maficdikes have been metamorphosed, as indicatedby the transformationpyroxenes ofhornblende, to clearly indicatingthat low grade metamorphism occurred after the emplacementof the mafic dikes and the granites. Page120 Thecarbonatites probably have been unaffected by metamorphismdue tothe lack of a metamorphicfabric. Mortartextures and undulatory extinctions feldsparof crystalsare, probably related tothe intrusion of the carbonatitedike. FOLIATION Foliation in Corkscrewthe Canyon sediments approximatelyparallels relict bedding. Relict bedding is distinguishedfromfoliation by colortexturaland contrasts.The trend offoliation along Corkscrew Canyon rangesfrom N40W to N40E, witheasterly dips of 40 - 70 degrees.Relict crossbedding and graded bedding indicates thatthe sequence is presentlyupright, younging towards the east. Veryfewoutcrops are foundbetween thesediments exposed in CorkscrewCanyon and the arkose from the lowest exposedunit in the southern portion of the map area (Map 1). Thefoliation ofthe arkose parallels the east-west trendfoliationof thegneissicin granite. If the sediments are still in an uprightposition in the southern portion of thestudy area, then the arkose is theoldest sedimentexposed. Thisage relationship is uncertain, Page121 becauseprimary textures are not well preserved in this arkoseand faulting may have offset thearkose from the sedimentsexposed in CorkscrewCanyon. The foliation of the arkose may alsobe due to the intrusion of the gneissic granite. A Tertiaryfault cuts the gneissic granite south of the intrusivecontact with the arkose (Map 1). North of this fault, foliationtrends east-west anddips to thenorth. Southof this fault, foliation is still inan east-west direction,but dips to the south, while further south the dipdirection changes to thenorth. This foliation may be partiallyinherited from the emplacement of thegranite. Foliation is absentto poorly developed in the northern graniticrocks, the Lemitar diorite.jgabbro, and the mafic dikes. Some foliation, parallel tothe edges of the dikes, occursin the carbonatite dikes and is probablyrelated to theemplacement ofthe dikes. Foliation in, the Lemitar diorite/gabbro is restrictedto shear zones and near the westernand northern contacts with the altered facies of the PolvaderaGranite. Foliation in the biotite and Polvadera Granite is poorlydeveloped to absent,and may represent primarystructures,flow whilefoliation the in muscovite-biotitegranite is relatedmigmitizationto occurringalong the intrusivecontact with the Lemitar Page 122 diorite/gabbro. FAULTS Faultinghas occurred on a largescale making the determination of thicknessand orientation of thesediments difficultto determine. The Laramide orogenyand Tertiary Basin-and-Range-typefaulting (rifting) overprinted the Precambrianfabric, reinforcing the northerly structural trends of thePrecambrian terrain. Laramide structures consist of broadfolds and reverse faults ~ woodw ward,^ 1973) androtational effects during the Laramide are minor (about 15 degreeswest, Woodward, 19731, whileTertiary faults, relatedto rifting, tilted the Precambrian rocks even more (approximately 40 degreeswest, Woodward, 1973). North-trendingfaults with silicified carbonated gouge zonescut the rocks along Corkscrew Canyon and also cut the PolvaderaGranite along the main arroyoin sec. 31 (Map 1). Not all of thesefaults can be mapped.Widths of thefault brecciazones range in thickness from a few cm. to a meter. Severaleast-west faults cut the sequence south of Corkscrew Canyon,forming arroyos such as CorkscrewCanyon. East-west faultsalso cut the Polvadera Granite and theLemitar dio;ite/gabbro.Tertiary Precambrianand faultsare Page123 difficult to distinguishoutside of Corkscrew Canyon due to thelack of goodexposures. A fewshear zones within the sedimentsand altered facies of the Polvadera Granite may be indicativeofpre-Laramide faults, for thesezones only affect thePrecambrian rocks. For the purposes of this report, breccia andshear zones have been described separately. A northwest-trendingTertiary fault (Chamberlin, 19.78) cutsthe Precambrian rocks in sec. 6 and 7 (Map 1). Local brecciationalong the northern part of thefault and the discontinuityof several mafic dikesin in the central part ofsec. 7 occursand is suggestiveof a fault.Generally, theexposures inthe Precambrian rocks are too poor to extendLaramide and Tertiary faults that cut the adjacent Phanerozoicrocks. SHEARZONES A northeast-trendingshear zone cuts across the western quarter of thesection along Corkscrew Canyon. Bedding has beenobliterated and in thinsection, cataclastic textures, undulatoryextinction of thegrains, and sutured grain boundaries are present.Boudinage structures (several cm. across) subparallel thetrend of the original bedding Page124 Boudinageindicates the stretching and shearing of layered competentand incompetent rocks. Foliation is formedby small-scale(wavelength of several cm.) highlyfolded quartz andfeldspar bands and by tight, ptygmatic folds which are oftensheared in places(see fig. 18-A and B, p. 54, Woodward, 1973). The120 - 150 meterwide shear zone is not seensouth of CorkscrewCanyon and ends at theintrusive contactwith the muscovite-biotite granite. This shearzone is Precambrianin age and probably occurred before or during theintrusion of themuscovite-biotite granite, as theshear zone affectsonly the sediments. It may evenbe related to theintrusion of the muscovite-biotite granite. Shearinghas also affected the altered facies of the PolvaderaGranite where zones of foliatedquartz and feldsparlayers occur, indicative of intense shearing. The trendof this foliation is northeastwith a western dip of about62degrees. This shearing may alsobe related to Precambrianfaulting, because faulting and shearingdoes not appearto have affected the Paleozoic sediments. Shearingoccurs within the Lemitar dioritejgabbro near thecontact with the Polvadera Granite. This shearing could bedue to a Pennsylvanianreverse fault (Chamberlin, 1978) ortothe intrusion ofthe Polvadera granite. Foliated chlorite-and biotite-rich zones, several meters across,are Page 125 I locallypresent along the intrusive contact. The foliation subparallelsthe intrusive contact and is absentwithin the PolvaderaGranite, suggesting a relationshiptheto emplacementof the Polvadera Granite. BRECCIATION Several small (severalmeters across) heterolithologic brecciazones occur within thesediments (Map 1) andare generallycemented by whitecarbonate. Angular rock fragmentsare composed of Precambrian gneissic and granitic rocksand are often surrounded with a light-coloredreac.tion rim. Brecciationoccurredhad aftermetamorphism as indicated by therandomly oriented foliated rock fragments. Incontrast, several monolithologic breccia zones occur withinthe muscovite-biotite granite (Map 1) wherethe rock fragmentsconsist entirely ofmuscovite-biotite granite. The matrix is blackand very fine-grained and carbonate is absentfrom the matrix. The rock fragments are angular and unsupported(surrounded by matrix) and randomlyarranged, similar torock fragments found in the brecciated sediments. Thisbreccia zone represents part of the low angle fault formingthe eastern contact between the Precambrian and Phanerozoicsediments and volcanics (Chamberlin, 1978). Page126 A brecciated and shearedzone occurs in thecentral portion of theLemitar diorite/gabbro (Map 1, sec. 6 and 71, wherefragments of diorite/gabbro have been cemented and forms an angularbreccia. Thediorite/gabbro hasbeen slightlyfoliated andaltered to a chlorite-and biotite-richgouge. Foliation within this shear zone dips totothe northwest about 44 degrees.Original textures havebeen obliterated and sheared. Some ofthese zones may representlenses ofsedimentary inclusions. This sheared brecciazone may haveresulted from faulting; Chamberlin (1978 showsthe area to be transected by two faults - an early Oligocenetransverse fault and a Pennsylvanianreverse fault Page 127 MINERALIZATION Five periods ofmineralization affected the Precambrian rocks in the Lemitar Mountains (in order of decreasing age): (1) Precambrian pegmatite and quartz veins (2) Carbonatite dikes (iate Precambrian) (3) Phanerozoic barite-galena-copper veins (4) Phanerozoic barite-galena-sphalerite veins (5) Barite veins Mining claims cover much of the eastern portions of the map area ( sec. 5, 6, and ~7,Socurro -County-eourthouse "Records Precambrianpegmatites are ofthe simple type, consistingof unzoned feldspar, quartz, and mica as previouslydiscussed (see Granitic Rocks). Quartzveins appear to be barren of any other mineralization. Both are discontinuous, forming poorly exposed outcrops. The carbonatite dikes arecomposed of rare-e?rth bearing minerals, radioactive minerals, and fluorite. High areas of radioactivity (100 times background) occur in sec. 6 and 7. Two samples of high radioactivity were analyzed and found to contain 0.08 (190 ppm U) and 0.06% (143 ppm U) U308(Christopher Rautman, personal communication). The eight-samples analyzed by the author ranged from 0.0011 to 0.0045% U308 (Appendix B). Megascopic fluorite is found Page128 alongthe walls of several prospectpits in sec. 7. The concentration of rare-earth elements may berelatively high becausebastnaesite is present. Phanerozoicbarite-galena-copper veins occur along the westerncontact with the Phanerozoic sediments. Prospect pitsand a shaft (sec. 18) exposethis mineralization. Copperminerals coat the fracture and joint surfaces of the Precambrianrocks in the vicinity of the mineralization. At onelocality within the altered facies of thePolvadera Granite, a vein of galena,sphalerite, chacolcite, quartz, fluorite,barite, and secondary copper minerals crosscuts a pegmatitedike. Some silver andzinc have been reported fromthese veins (Lasky,1932). Phanerozoicbarite-galena-sphalerite veins occur within Phanerozoiclimestone along the eastern contact (sec. 5). Thismineralization is localizedand restricted to some small outcropslimestone.of Thestudy of three thin sections of veinswithinthe limestone reveals coarse-grainedlimestone crosscut by thin veinlets ofbarite and calcite containinggalena and sphalerite. The lack of apatite,magnetite, and biotite clearly distinguishes these veinsfrom carbonatite dikes. Small quantities of barite were shippedfrom one theof larger zones within the limestone(sec. 5, Map 1). Page 129 Barite veins, also Phanerozoic,occur along the eastern contact,generally striking east-west. Bariteveins often intrudethe carbonatite dikes. This mineralization may be related to otherbarite mineralization in thearea. ThePhanerozoic mineralization is notassociated with thecarbonatite dikes. Themineralogies andtextures differ.The carbonatite dikes do not contain sphalerite or galena,and barite is rare in thecarbonatites. The barite mineralizationdoes not include apatite, magnetite, or biotite.Field relationships suggest that the carbonatites are older.than the limestone that hosts thebarite mineralization. Page130 GEOLOGIC HISTORY, TECTONIC SETTING, AND CONCLUSIONS A summaryof thePrecambrian geologic history of the Lemitar Mountains is presented in table 19. The first event recordedin the Lemitar Mountains is thedeposition of the CorkscrewCanyon sequence consisting of twounits - Un'it I characterizedby massive arkose and Unit I1 characterizedby interbedded,foliated arkoses, subarkoses, and quartzites. Thissequence ofsediments is similar tothe feldspathic quartzite-arkoseassociation exposed throughout central New .. Mexico(Condie and Budding, 19791, althoughcorrelation to a particularbasin is uncertain.The gneissTc granite may havebeen emplaced after thedeposition of thesediments, although it is possiblethat this foliated,granite may have beenemplaced at the same time as theyounger granites. The intrusionofStage I mafic dikesfollowed. Metamorphism, faulting,and shearing of of thesediments occurred ..before or duringor emplacement theofStage I maficdikes. The. emplacementof the Lemitar dioritelgabbro.followed by the intrusion of Stage I1 mafic dtkesoccurred next. The similarity inmineralogy and texture between the Lemitar diorite/gabbroand the 'gabbro of Garcia Canyon(Magdalena gabbro) suggests that the two mafic units may be relatedto a similar sourcethat crystallized about 1.5 b.y. according TABLE 19 SUMMARY OF THE GEOLOGIC HISTORY OF THE PRECAMBRIANROCKS (1) Depositionofthe Corkscrew Canyon sediments derived from a granitic or gneissicsource. (2) Possibleemplacement of the gneissic granite, although thisfoliated granite may havebeen emplaced along with theother granitic rocks later on. (3) IntrusionofStage I maficdikes and metamorphism, folding,faulting, and shearing of thesediments. (4) Emplacementof the Lemitar dioritelgabbro. (5) Intrusion of Stage I1 maficdikes. (6) Emplacementof the granitic rocks, often associated with migmitizationand/orLemitarshearing the of diorite/gabbro. (7) Intrusionof pegmatites and quartz veins and dikes and intrusionof Stage 111 maficdikes, followed by a final periodof metamorphism. (8) Intrusionof carbonatites and associated fenitization of theLemitar dioritejgabbro and granitic rocks. May includebrecciation, carbonatization, and hematization ofthe country rocks. Page 132. to Rb/Srisochron dating ofthe gabbro ofGarcia Canyon (White,1978). Thegranitic rocks intrude the Lemitar diorite/gabbroand often are associated with migmitization andshearing of the diorite/gabbro. Most granitic plutonism in central New Mexicooccurred between 1.2 - 1.4 bay. (Condieand Budding, 1979) andperhaps the Lemitar granites wereemplaced during this period due to the similarity in mineralogy,texture, and chemistry between these granites. Simple,unzoned pegmatites and quartz veins represent a finalstage of granitic magmatism in theLemitar Mountains. Stage I11 maficdikes intruded the granitic rocks, followed by a periodof metamorphism. The intrusion of carbonatite dikesand veins along pre-existing faults and fractures followedand was oftenassociated with normal sodic fenitizationof the Lemitar diorite/gabbroand the granitic rocks.Brecciation, carbonatization, and hematization of thecountry rocks may alsobe associated with the intrusion ofthe carbonatites. Laramide and Tertiarystructures are superimposedover the Precambrian fabric. Themafic rocks are probably mantle-derived from a similar source.The lithologically heterogeneous Lemitar diorite/gabbro may havebeen derived from either late differentiationof a gabbroic magma orinjection and mixing of granitic magmas with a gabbroicbody. The mafic dikes, Page 133 someof which intrude the granite, may represent a fraction of the samegabbroic source. Thegranites can be divided into two groups based on similar compositions - Group I (gneissicgranite, biotite granite)and Group I1 granites(muscovite-biotite granite, Polvaderagranite). Group I granitesare lower in Si02and K20 andhigher in CaO and MgO thanGroup I1 granites. Geochemicalmodel studies on granites similar in composition to Group I granites(Condie, 1978) suggestthat partial meltingof siliceous granulites in the lower crust could producemelts similar incomposition to Group I granites. Group I1 granites aresimilar in compositionmeltsto producedfractionalby crystallization of granodiorite magmas (Condie, 1978). Thegranitic rocks are thought to be emplaced at depths of 2 - 13 km. as evidencedby field and experimentalstudies. A carbonatite magma intrudedthe older Precambrian rocks as dikesand veins and was probablyderived from the uppermantle as evidenced by experimentaldata from other carbonatites similar in compositionLemitarthe to carbonatites.The random orientation of thecarbonatite dikessuggest that a carbonatite magma penetratedthe crust beneaththe present erosion surface and the carbonatite magma followedpre-existing fractures and zones of weakness Page 134 inthe Precambrian rocks. Preliminary geochemical studies do notexhibit any chemical trends between the carbonatites and the mafic dikes(fig. 11). Thetextures, mineralogy, andgeochemistry of the CorkscrewCanyon sediments are consistent with deposition in a fluvial or deltaicenvironment either in a continental-rift or a rapidlyrising continental-margin setting.Bimodal (fig. 9) and alkali magmatismfollowed thedeposition of thesediments and is consistentwith a continental-riftsetting. These conclusions suggest that thethe Proterozoic .terrain of the Lemitar Mountains is consistentwith a continental-riftsetting such as the multiple-riftsystem proposed by Condie and Budding (1979). Thecarbonatites in theLemitar Mountains may beof a lateProterozoic-Cambrian age and if so may berelated to otheralkali rocks found in Colorado(Wet Mountains, Iron Mountains)and New Mexico(Monte Largo, Florida Mountains, PajaritoMountain). The Wet Mountainsand Iron Mountain complexesColorado inconsist of syenites,mafic nepheline-bearingrocks, and carbonatites and are of a similar age - about 520 m.y. (Olson,et al., 1977). The MonteLargo carbonatite (New Mexico)has been identified on thebasis of carbonatitefloat in a narrowzone in the Monte Largoarea and is thoughtto be Precambrian in age on the Page 135 basis of fieldrelationships (Lambert, 1961). It is similar inappearance and mineralogy tothe carbonatites of the Lemitar Mountains.Radiometric determinations theof syenites of FloridaMountains range from 420 to 700 m.y. andare very uncertaindue to either a thermal (magmatic or metasomatic)event or mixingof younger syenitic material witholder granitic rocks (Brookins, 1974). The alkaline rocks at PajaritoMountain, New Mexico,consist of syenites andgneisses; radiometric dating shows the rocks to be near 1.17,b.y.(Kelley, 1968). Theoccurrence of these alkalic rocksand the carbonatites in the Lemitar Mountains may be suggestive .of.an alkali .prov.ince .in Colorado and N.ew Mexico rangingin age from 1.2 and 0.4 bey. 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Watkinson, D.H. andWyllie, P.J., 1971, Experimentalstudy of thecomposition join NaAlSiO4-CaC03-H20 andthe genesis of alkalicrock-carbonatite complexes: J. Petr., V. 12, p. 357 - 370. Page 148 White, D.L., 1978, A Rb-Sr Isotope Geochronologic study of Precambrianintrusives of south-central New Mexico: PhD dissertation, Miami Univ., 147 p. Winkler, H.G.F., 1976, Petrogenesis of Metamorphic Rocks: New York, Springer-Verlag, 334p. Woodward, T-M., 1973, Geology of the LemitarMountains, Socorro County, New Mexico: New Mexico Inst. Mining Tech., M.S. Thesis, 73 p. Wyllie, P.J., 1966, Experimentalstudies of carbonatite problems:The origin and differentiation of carbonatite magma, in Carbonatites, editors Tuttle and Gittins: London, Interscience Publ., p. 311 - 352. Yardley, B.W.D., 1978, Genesis of the Skagit gneiss migmitites, Washington and the distinction between possible mechanisms of migmitization: Geol.SOC. Am., Bull., v. 89, p. 941 - 951. Yoe, J.H., Fritz, 3rd, W., and Black, R.A., 1953, Colorimetric determination of uraniumwith dibenzoylmethane: Anal. Chem., v. 25, p. 1200 - 1204. Page 149. APPENDIX A ANALYTICAL PROCEDURES SamplePreparation Sampleswere first crushed in a rockcrus'her to silt-size fragments.Ten grams of eachsample were ground in an automatic mortarand pestle with acetone for thirty minutes. Duplicate briquetteswere made of eachsample and standard for subsequent X-rayfluorescence. Eightsamples of thecarbonatite dike were prepared as above,except that thirty grams ofeach sample were used. A singlebriquette was made of eachsample forfuture X-ray diffraction.The remainder ofeach sample was dried at 110 degrees C. forone hour and then used for wetchemical analyses. X-rayFluorescence X-ray fluorescencedatawere obtained on a Norelco 8-positionspectrograph (table 1). Ten thousandcounts were collectedfor each briquette. A standarddrift pellet was kept inposition four ofthe spectrograph and counted each time. Countrates for each sample and standard were divided by the count rates forthe drift pelletto correct for any instrumental Page 150 drift. A computerprogram was employedfor determining the ratio foreach briquette (J.R. Renault,personal communication). The countingstatistics are better than 2% for all elementsexcept Na20 and MgO, whichare better than 4%. Calibrationcurves were constructed,employing a secondcomputer program, using U.S.G.S. andintralab rock standards (table 2). The errors are summarized in table 3. ChemicalProcedure Majorminorand elements weredetermined eighton carbonatitesamples usingatomic absorption, titration, colorimetric,and gravimetric methods (table 4). A standard HF (hydrofluoric)dissolution process was usedtodecompose the samplesfor subsequent atomic absorption analysis (L. Brandvold, personalcommunication). Two dissolutionswere made;one containedone half to one gram of sample for thedetection of Al, Fe, Mg, Ca, Na, K, Mn, and Zn andthe other contained two grams forthe determination of Cr, Co,Cu, Xi, Sr, Ba, and Li. The sampleswere analyzed using a Perkin Elmer 303 or a Varian 1250 spectrometer(table 5). Standardswere prepared from analytical gradereagents. Calibration curves were determined foreach elementanalyzed. The relative error is within 5% formost of the elements. Some elementsanalyzed (such as Na, K, and ect.) are within 3%; whileother elements (such as Cu and Ba) are Page 151 within10% (L. Brandvold,personal communication). Modified titration procedures were employed todetermine FeO and C02 (table 41, usingone gram of eachsample to determine FeO andone half gram todetermine C02. Duplicatesamples were analyzed for eachsample and resulted in a reproducibilityof 0.3% for FeO and 1.5% for C02. The relativeerror 'for FeO is approximately 1%. Two standards(limestone and dolomite) were analyzed for C02 andwere within 3% theof knownC02 concentration.Fe203 was foundby subtracting Fe203 from total Fedetermined by atomic absorption. Variouscolorimetric procedures were employed to determine Ti02,P205, and U308 foreach sample (table 4). Silica was determined by theclassical gravimetric method (table 4) andthe filtrate fromthe silica determination was usedtodetermine Ti02.P205 was determinedusing 1 - 5 ml. of the 0.5 gram BF dissolutionsample. One to five gramseachof sample was decomposedusing nitric and perchloric acids for theanalysis of u308 (table 4). Absorbance was measuredusing a Bauschand Lomb Spec20. The relative error for Ti02 and P205 was within 1%, while the relative errorfor U308 is within 5% (L. Brandvold, personalcommunication). Page 152 TABLE 1 INSTRUMENTAL PARAMETERS FOR X-RAY FLUORESCENCE ELE TUBE CRYSTAL DETECTOR PATH PEAK PEAK 20 BKGRD 20 Si GYP Cr FPC VAC KA 1 26.00 Ti Cr QT Z FPC VA C KA 48.70 - A1 Cr GYP FPC VA C KA1 66.65 65.00 Fe , QTZCr FPC VAC KA 33.79 - Mg Cr GYP Cr Mg FPC VAC KA 81.32 80.00 Ca Cr QT Z FPC VA C KA 60.42 - K Cr QT z FPC VAC KA 68.24 - Na Cr GYP FPC VA C KA 1 103 * 35 102,105 Mn W LiF SCIN AIR KA 62.82 62.2,63.5 Ba w LiF SCIN AIR LB 78 - 92 78,79-5 Rb iFMoL SCIN AIR KA 26.34 25.5,26.8 Sr MoSr L iF SCIN AIR KA 24.85 24,25.5 FPC - Flow proportion counter SCIN - Scintillation counter VAC - Vacuum GYP - Gypsum QTZ - Quartz LiF - Lithium Fluoride Page 153 TABLE 2 ROCK STANDARDS USED FOR X-RAY FLUORESCENCE STD Si02 Ti02 A1203 Fe203* MgO CaO K20 Na20 BCR-1 54.5 2.20 13.6 i3.4 3.46 6.92 1.70 3.27 LOSP 75.9 0.20 12.3 1.81 0.07 0.93 4.83 3.49 BLCR 55.7 0.84 16.9 7-51 5.97 8.11 1.52 3.51 JB-1 52.1 1.34 14.5 9.04 7-70 9.21 1.42 2- 79 GSP-1 67.4 0.66 15.3 4.33 0.96 2.02 5.53 2.80 AGV-1 59.0 1.04 17.3 6.76 1.53 4.90 2.89 4.26 F-3 64.8 0.84 20.7 6.36 - 0.22 2.63 - G-2 69.1 0.50 15.4 2.65 0.76 1.94 4.51 4.07 JG-1 72.2 0.26 14.2 2.21 0.73 2.18 3.96 3.39 HI-31 58.8 0.88 16.7 6.47 4.21 6.50 2.88 3.11 w-1 52.6 1.07 15.0 11.1 6.62 11.0 0.64 2.15 BR .3a. 2 2.60 10.2 12.9 13.3 13.8 1.40 3.05 STD Mn Ba Rb Sr BCR-1 LOSP - BLCR 1080 JB-1 - ' GSP-1 331 AGV-1 763 F-3 - G-2 . 260 JG-1 - HI-31 - W-1 1280 BR - * - Total iron calculated as Fe203. Page 154 TABLE 3 ERRORS ELEMENT S C RMS$ ERROR Si02 0.590.4370 1.86 Ti02 0.0206 4.66 4.59 A1203 0.1162 0.80 0.70 Fe203 0.2336 5.17 1.77 MgO 9.920.0230 1.96 CaO 0.690.0096 3.25 Na20 2.240.1079 2.81 K20 0.0238'0.73 3.47 Ba 2.04 25.49 11.8 Rb 0.82 1.15 7.4 Sr ;0.58 0.85 7-25 Mn 17-19 7.39 4.45 S - standarddeviation C - coefficient ofvariation = S/meancomposition x 100 RMS$ ERROR - relativeerror = Page 155 TABLE 4 SUMMARYOF CHEMICAL PROCEDURESFOR ANALYSIS OF CARBONATITES ELEMENT METHOD REFERENCE Si02gravimetric Maxwell, 1968, 323p. - 332; Jeffery, 1975, p. 35 - 39, 470 - '471' Ti02colorimetric Maxwell, 1968, p. 379 - 381; Jeffery, 1975, p. 470 - 471 FeO titrationJeffery, 1975,281; Pratt,p. 1894 c02titration Jeffery,, 1975, p. 64 - 66; Shapiro, 1975; Grimaldi,Shapiro, and Schnepfe, 1966 ~205 colorimetricJeffery, 1975, p. 382 - 385 LO1 gravimetricJeffery, 1972, p.270 NOTE: LO1 = loss onignition - CO2 U308 colorimetricmodified from Yoe, Fritz, and Black, 1953 Al, total Fe, Mg, Ca, Mg, K, Mn, Cr, Co, Ni, Sr, Ba, Li, Zn, and Cu weredetermined by atomic absorption. TABLE 5 ATOMIC ABSORPTION INSTRUMENTALPARAMETERS ELEMENT WAVELEIiGTH STANDARDS, ppm FLAME INSTRUMENT A1 3100 10 - 200 a-N20 Varian 1250 Fe 2494 2 - 15 a-a Perkin Elmer303 Mg 2862 .1 - 2.0 a-a Perkin Elmer303 Ca 2122 0-5 - 5 a-a Perkin Elmer303 Na 2950 0.5 - 5 a-a Perkin Elmer 303 K 3838 0.5 - 5 a-a Perkin Elmer 303 Mn 2805 0.5 - 10 a-a Perkin Elmer303 Cr 3584 1 - 10 a-a Varian 1250 co ' 2412 0.5 - 15 a-a Perkin Elmer303 Ni 2369 1 - 15 a-a Perkin Elmer 303 Sr 2350 0.5 - 10 a-a Perkin Elmer 303 Ba 5542 10 - 50 a-N20 Varian 1250 Li 3394 0.5 - 10 a-a PerkinElmer 303 Zn 2152 0.5 - 2.0 a-a Perkin Elmer 303 cu 3254 0.5 - 5 a-a Varian 1250 * - a-N20:acetylene-nitrous oxide flame, a-a: air-acetylene flame APPENDIX B BRIEF PETROLOGIC DESCRIPTIONS OF THE ANALYZED ROCK SAMPLES SEDIMENTS Lem 401,Arkose, Lower Unit: a dark-gray,very fine-grained rock withminor foliation (relict bedding). Relict sand grains are verypoorly sorted, very fine sand-size'd with average roundness andspherecity. Possible graded bedding may existlocally. The rockconsists of a fine-grained matrix (probablysericite and quartz,35-40%), quartz (30-3521, untwinned feldspar (lO-l5%), greenbiotite (5-10%), magnetite (<5%), andmuscovite (5-10%). Lem 524,Medium-grained Arkose, Upper Unit: a pinkish-grayto dark-gray,medium-grained rock with strong foliation. Relict sandgrains are poorlysorted, fine- to medium-sand sizewith moderateroundness and variable sph.erecity. The rock consists of quartz(30-35$), altered plagioclase, An50 (20-25%), a fine-grained matrix (probablysericite, 10-15%), muscovite (10-20%),dark green tobrown biotite (partially altered to chlorites,5-10%), magnetite (5%) and a traceamount of garnet. Lem 525,Fine-grained Arkose, Upper Unit: a dark-gray , fine-grainedrock with strong foliation. Relict sand grains are poorlysorted, fine-sand sized with variable roundness and spherecity. Therock consists ofquartz (25-30%), untwinned feldspar(25-30%), fine-grained matrix (probablysericite, 20-25$),biotite (partially altered chlorite,to 15-20%), muscovite (5%), andmagnetite ((1%). Lem 523,Medium-grained Arkose, Upper Unit: a pinkish-grayto dark-gray,fine-grained slightly foliated rock. Relict sand grainsare poorly - sorted. fine- to medium-sand sized with fair roundne S s andspherecity. Graded bedding can be detected in thin section Therock consists of quartz(50-60$), plagioclase, An70 (20-25$ 1 , greenbiotite (10-15%), perthitic K-feldspar (5-10%), magnetit e (45%), andmuscovite (<5%). Lem 526 Subarkose,Upper Unit: a medium-gray,fine-grained, massive rock.Relict sand grains arewell-sorted, medium-sand size with goodroundness and spherecity. The rock Consists of quartz (70-80%), perthiticK-feldspar (5-10%), plagioclase, An20-40 (5-10%),biotite (5-10%), muscovite (5-10%), and magnetite (<5%). Lem 520,Subarkose, Upper Unit: a pinkish-graytomedium-gray, fine-grained,foliated rock. Relict sandgrains are fairly sorted, fine- to medium-sand sizedwith fair roundness and spherecity.Thin laminations of arkosicto subarkosic lenses can bedetected thinin sections. The rock consists of quartz (70-80%), greenbiotite (5-10$), perthitic K-feldspar (lo%), untwinnedplagioclase (<5%), muscovite (<5%), andfine-grained matrix (probablysericite, <%5). MAFIC DIKES Lem 56, Diabasedike: a porphyritic,greenish-gray, fine-grained unmetamorphosedrock consisting plagioclaseof (altered to calcite,(40-45%), hornblende (35-401, biotite (<5%), chlorite (<5%), magnetite(5-10%), and a trace amountof quartz. Ophitic texture is well preserved. Lem 15 and521, Mafic dike: a dark-grayblack,to very fine-grained,massive rockconsisting greenof hornblende (35-40%),feldspar, An50 (30-3521,green and brown biotite (partiallyaltered to chlorite, 10-20$), magnetite (5-10%), and a traceamount of quartz.Slight foliation can be detected in thin section. Lem 407and 502, Mafic dike: a black,aphanitic rock consisting of greenhornblende (40-45%), plagioclase, An50 (40-4521, magnetite(5-10%)), brown biotite (partially altered to chlorite, LEMITARDIORITE/GABBRO Lem 148, 439, 501,and 503, Diorite/gabbro: a whiteand black, speckled,coarse-grained rock consisting darkof blue-green hornblende(30-40%), altered plagioclase, An40-55 (30-40%),brown andgreen biotite (15-20%), magnetite (5%), quartz (<5%),and traceamounts ofapatite, sphene, and garnet.Subophitic to ophitictexture is preserved.Fine-coarse-grainedand inclusionscan be found within the central part of the pluton. Lern 449, Quartzdiorite: a blackwhite,and speckled, medium-grainedrock consisting greenof hornblende (25-30%), brownand green biotite (25-30%), altered plagioclase, An50 (2O-25%), crushed quartz (7-10%), perthitic K-feldspar (5-7%), corroded magnetite (5-7%), andtrace amounts of apatiteand garnet. Thequartz and garnet often form inclusions in the biotite.The K-feldspar is oftenzoned and altered to sericite. Subophitictexture is preserved. Lem 532,Fenitized dioritelgabbro: a pinkand black, speckled, coarse-grainedrock consisting of darkgreen and brownhornblende (35-4021,altered plagioclase, An5-15 (40-4521,magnetite (2-321, hematite(1-2%), and quartz (5-102). Lem 533, Fenitizeddioritelgabbro: a pinkand black, speckled, coarse-grainedrock consisting of greenand brown hornblende (40-4521,plagioclase, An15 (40-45$),perthitic K-feldspar (5-1021,quartz (5-1021, and a trace amount of magnetiteand zircon. GRANITIC ROCKS Lem 50, Gneissic granite: a pinkish-gray to medium-gray,medium- tocoarse-grained, foliated rock. Mortar texture is developed. Therock consists, quartzof (30-35%), K-feldspar (25-3021, plagioclase(20-2521, green biotite (10-15$), and hematite (<5%). Lern 55, Gneissicgranite: a pinkish-gray to medium-gray, medium-grained,foliated rock. The rock consists quartzof (30-35%),'K-feldspar(25-30%), plagioclase, ~n60-70 (25-3021, greenand brown biotite (partially altered to chlorite,l0-15%), and a trace amountof hematite, ' magnetite,and ~ disseminated fluorite. Lern 84, PolvaderaGranite: a pale-redand black, medium- to coarse-grainedrock ~ consistingof quartz (30-3521, perthitic K-feldspar(30-3521, plagioclase (25-3021, brown biotite (5-10%), and trace amounts of hornblende,garnet, and magnetite. A mortar texture is oftenpreserved. Lern 511, Polvadera Granite: a moderateorange andblack, coarse-grainedrock consisting ofquartz (30-35%), perthitic K-feldspar(30-3521, plagioclase (25-30$), biotite (partially alteredto chlorite, 5-1021, and trace amounts of magnetiteand garnet. A submortartexture is preserved. Lern 447A, Leucogranite: a whiteand black, coarse-grained rock cons-is-t-%nx- "of--equal-a-mou.nts--of- ~quar-t-z,- perthitic-K-f eldspar ,--and plagioclase, An40,and trace amountsbiotiteof (<5$) and magnetite( Lem 108,Muscovite-biotite granite: a grayish-pinkto medium-gray, ' fine-grained,slightly foliated rock, consisting of Page160 ,quartz(30-35%), perthitic K-feldspar (25-30%), plagioclase, An40 (20-25%),green biotite (lo%), muscovite (5%), andmagnetite (<3%). Lem 126,Muscovite-biotite granite: a grayish-pinktolight gray,fine-grained, porphyritic rock consisting of plagioclase (30-3521,quartz(25-30%), K-feldspar (20-25%), magnetite (alteredtoleucoxene, 3-5%), brown biotite(2-3%), muscovite (2-3%),and a trace amountofzircon. Granophyric texture is preserved. Lem 423,Porphyritic muscovite-biotite granite: a yellowish- to brownish-gray,porphyritic medium-grained rock, consisting of quartz(35-40%), perthitic K-feldspar (25-30%), plagioclase, An40-60(20-25%), biotite (5-10%), muscovite (5%), andtrace amounts of magnetite,hematite, greenhornblende.and Granophyrictexture is preserved. Lem 203,Biotite granite: a light-gray,medium-grained, slightly foliatedrock, consisting of quartz (25-30%), plagioclase, An50 (30-,35%),K-feldspar (25-30%), brown biotite (lo%), andmagnetite (<5%). Lem 302,Biotite granite: a grayish-red,medium-grained rock, consisting of perthiticK-feldspar (25-30%), quartz (25-30461, plagioclase, An40 (25-30%),brown biotite (5-10%), and magnetite (5%).Granophyric texture is preserved. Lem 438, Biotitegranite: a medium-gray,medium-grained, biotite-richrock. This rock consists ofplagioclase, An40-50 (45-50%),quartz (20-2551, brown biotite (10-15%), K-feldspar (10-15%),and magnetite and hematite (<2%). This rock was taken nearthe boundary between the Lemitar dioritejgabbroand the altered facies ofthe Polvadera Granite. CARBONATITES Lem 305,427a,427b, 500,and Primary silicocarbonates: medium-grained,gray tobrown, porphyritic rock consisting of carbonate matrix (dolomite,calcite 60-80%), apatite (5-10%), opaques(magnetite 5-10%), rock fragments (0-15%), disseminated fluorite(<5$), brown biotiteand phlogopite (5-15%), and trace amounts of quartz,feldspar, hematite, and hornblende. Often largerock fragments (1-2inches in diameter)are trapped in thesedikes. These rocks are very heterogeneous, often layered, showing relict crystalsreplaced by carbonate fluids. Individual crystals arecorroded and cracked with carbonate'replacement. Page 161 Igneoustextures, such as absorption, are prevelant.Sovite veinsoften crosscut phenocrysts and xenoliths. (Samples 427a and427b come fromthe same dike, about 5-6 feetapart along strike.) Lern 506,Replacement silicocarbonatite: layered, medium-grained, gray to brown,porphyritic rock consisting of carbonate matrix (70-75561, magnetite(10-15%), sericite (10-15%), and a trace amountof biotite. Subophitic texture is preserved.Sovite and hematiteveinlets crosscut the rock. Lem 530,Replacement silicocarbonatite: fine-grained, gray, porphyriticrock consisting of carbonate matrix (50-60%),green andbrown biotite and chlorite (20-25%), magnetite (10-15%), hematite (5%), quartz(1-2%), and a traceamount of feldspar. Relictsubophitic and porphyritic textures are preserved. Lem 531a and531b, Ankeritic rauhaugite: a fine-grained,brown rockconsisting of coarsecarbonate (80-90%), magnetite(2-10%), hematite(5-10%), and a trace amountof biotiteand chlorite. .(Bothsamples are fromthe same dike, about six feetapart along strike. DESCRIPTION OF ROCK SAMPLES NOT ANALYSED FOR CHEMISTRY Lem 3, Quartzite: a pinkish-graymedium-gray, to very fine-grainedrock. Relictsand grains are well-sorted, very fine-sandsized with goodroundness andspherecity. Therock consistsof quartz (>so%), K-feldspar (<5%),plagioclase (<5%), andtrace amounts of biotite,magnetite, muscovite, and a fine-grainedmatrix. Lem 522,Green chlorite schist: a foliated,grayish olive green, fine-grained,micaeous rock. The rock consists of chlorite and biotite(40-50%), plagioclase, An40-50 (25-30%),quartz (5-10%), andmagnetite (5-10%). Page 162 APPENDIX C CHEMICAL ANALYSES* SEDIMENTS Lem 401 Lem 524 Si02 77- 8 69.6 62.0 65.2 76.5 73.8 Ti02 0.54 0.72 0.72 0-75 0.59 0.65 A120311.1 14.6 18.6 17-3 12.4 13.9 Fe203* 4.57 6.09 7-52 6.66 4.42 5-05 MgO 0.94 1.54 1.54 1.38 1.03 1.37 CaO 1.39 CaO 1.05 0.20 1.06 2.65 1.39 Na20 2.45 2-53 1.76 2.83 2.86 2.54 K20 2.91 K20 4.03 5.63 4.48 2.22 3.79 MnO 0.07 MnO 0.08 0.06 0.07 0.08 0.07 TOTAL101.77 100.24 98.03 99.73 102.75 102.56 Mn 512 Mn 600 490 577 592 548 Ba 1172 Ba 1140 892 995 1534 1376 Rb .139 203 303 244 164 161 Sr 78 144 87 163 237 162 * - Total iron expressedas Fe203. Oxides expressed in weight$, elements expressed inppm. .. MAFIC DIKES Lem 56 Lem 15 Lem 407 Lem 502 Lem 521 Si02 49.8 47.8 46.9 45.0 48.0 Ti02 1.58 1-77 1.85 1.85 2.38 A1203 11.7 12.0 12.1 10.2 11.2 Fe203* 14.7 15-9 15.7 20.9 16.9 MgO 5.78 8.00 9.37 6.32 7.31 CaO 9.27 10.0 9.44 4.52 9-69 Na20 2.28 1.68 2.05 1.75 1.92 K20 1.58 0.71 0.60 4.37 0.67 MnO 0.26 0.25 0.19 0.35 0.22 TOTAL 96.95 98.11 98.20 95 * 26 98.29 Mn 2011 1936 1549 2677 1698 Ba 333 334 375 397 341 Rb 45 35 24 119 56 S r 120 Sr 99 122 98 108 CIPW Norms or 9.3 4.2 3.5 25.8 4.0 ab 19.3 14.2 17-3 14.8 16.2 an 17.1 22.023.1 7.1 19.8 di 24.0 20.421.9 12.8 23.3 hY 19.7 25-5 14.2 0.1 24.4 01 - 0.9 13.3 24.2 - mt 4.9 5.3 5.3 7.0 5.6 il 3.0 3.4 3.5 3.5 4.5 Q 0.3 - - - 0.6 or - orthoclase il - ilmenite ab - albite mt - magnetite an - anorthite 01 - olivine c - corundum Q - quartz di - diopside hy - hypersthene LEMITAR DIORITE/GABBRO Lem 148 Lern 439 Lem 449 Lem 501 Lem 503 Si0254.5 51.2 51.0 59.1 51.0 Ti02 2.88 1.46 2.29 1.17 2.99 A1203 11.1 12.1 9.26 11.8 10.6 Fe203" 18.2 17.7 21.1 15.9 18.6 MgO 3.08 1.01 2.58 0.98 3.12 CaO 7.63 6.10 7.97 5.34 7.43 2.43 2.83 1.73Na20 2.83 2.43 2.53 2.43 K20 1.50 1.90 . 1.50 2.03 1.65 Mn 0 0.19 0.33 0.31 0.32 0.27 TOTAL 98.2197 * 91 97 * 76 99 * 17 98.09 Mn 1502 2395 2538 2448 2063 Ba 386 346 404 329 366 Rb 35 55 44 52 49 Sr 176 214 86 185 89 CIPW Norms 6.4 9.7 9.1 Q 9.7 6.4 17.3 6.2 or 8.9 11.2 8.9 12.0 9.8 ab 20.6 14.6 23.9 21.4 20.6 an 14.7 15.0 13.1 14.7 13.2 di 19- 5 13.7 22.8 10.3 20.2 hy 17.4 17.0 18.5 16.7 17.0 mt 6.1 5.9 7.0 5.3 6.2 il 5.5 2.8 4.3 2.2 5.7 LEMITAR DIORITE/GABBRO - continued Lem 532 Lem 533 Si02 54.2 58.9 Ti02 1.17 1.30 A1203 11.8 13.1A120311.8 Fe203* 17.0 12.2 MgO 2.94 2.06 CaO 4.30 4.42 Ma20 3.75 3.16 K20 1.19 2.00 TOTAL 96.35 97-14 Rb 82 41 Sr 745 211 CIPW Norms . Q 8.8 16.6 or 7.0 11.8 ab 31.7 26.7 an 11.9 15.6 di 8.0 5.4 hy 19-77 13.4 mt 5.7 4.1 il 2.2 2.5 . Page 166 GRANITIC ROCKS f f Lem 50 Lem 55 Lem 84 Lem 511 Lem 447A Lern 108 Si02 70.1 69s.5 73.3 73.8 74.1 73.1 Ti02 0.73 0.85 0.43 0.48 0.50 0.56 A1203 12.2 12.1 13.0 13.3 13.8 14.6 Fe203" 7.06 9.04 5.00 3.86 3.86 3.57 MgO 0.94 0.91 0.40 0.49 0.60 0.79 CaO 1.90 2.06 1.14 0.93 1.51 0.99 Na20 3.06 3.01 3.01 3.05 3.89 2.74 K20 4 ..17 3.52 5.05 5.35 3.72 4.59 MnO 0.10 0.11 0. og 0.06 0.06 0.06 TOTAL 100.26 101.10 101.32 102.04 101.00 Mn 806 848 445 434 422 Ba 946 686 1378 1415 1248 Rb 173 120 242 208 191 Sr 105 115 78 154 85 CIPW Norms Q 29.4 30.6 31.9 32.1 35.5 C - - 0.8 0.7 3.3 or 24.6 20.8 31.6 22.0 27.1 ab 25-9 25.5 25.8 32.9 23.2 an 7.2 9-2 4.6 7.5 4.9 di 1.8 0.9 - - - hY 5.5 7.2 3.3 3.5 3.7 mt 3.8 4.9 2.1 2.1 1.9 il 1.4 1.6 0.9 3.0 1.1 GRANITIC ROCKS - continued Lem 126 Lem 423 Lem 203 Lem 302 Lem 438 si02 74.0 75.6 66.5 70.6 66.9 Ti02 0.44 0.39 0.77 0.94 0.64 A1203 13.1 13.2 13.9 13.1 16.0 Fe203* 4.52 2.89 6.46 7.39 5.54 MgO 0.22 0.40 1.20 0.66 1.30 CaO 1.38 0.83 1-55 1.62 2.91 Na20 4.83 2.78 3.86 3.39 3.81 K20 3.25 5.37 4.10 4.10 3.63 MnO 0.03 0.05 0.10 0.08 0.09 TOTAL 101.77 101.51 98.44 101.88 100.82 Mn 228 349 808 589 693 Ba 1248 1342 892 690 880 Rb. 70 244 139 108 174 Sr 68 59 190 107 382 CIPW Norms Q 29.5 35.8 21.6 28.9 21.3 C - 1.3 0.3 0.1 - or 19.2 31.7 24.2 24.2 21.5 ab 40.9 23.5 32.7 28.7 32.2 an 4.5 an 4.1 7.7 8.0 14.0 di 2.1 - - 0.3 hy 2.1 2.5 6.6 5:6 6.2 mt 2.5 1-5 3.5 4.0 3.0 Page 168 CARBONATITE DIKES Lem 305 Lem 427a Lem 427b Lem 500 Lem 506 Si02 21.45 11.20 11.57 10.89 19.11 Ti02 1.13 0.40 0.13 0.28 0.20 A1203 4.32 2.44 2.14 2.61 4.35 Fe203 2-75 3.50 3.57 3.73 5-78 FeO 5.44 4.22 4.28 5.27 7.38 MgO 8.92 10.10 9.67 9.53 9.90 CaO 24.5 32.5 30.9 31.6 17.8 .Na20 0 .:70 0.19 0.19 0.41 1.13 K20 1.45 0.22 0.47 0.37 2.20 MnO 0.53 0.72 0.67 0.65 0.30 c02 22.66 29.10 29.01 26.31 18.14 P20 5 3.26 3.72 3.47 3.33 1.05 LO1 4.19 1.46 1.05 3.95 1.47 TOTAL 101.30 99.77 97-12 98.93 88.81 CARBONATITE DIKES - continued Lem 530 Lem 531a Lem 531b Si02 27.93 3.20 3.59 Ti02 1-79 LO1 - Loss on ignition - C02; includes H20,F, C1, and other volatiles. NOTE: SeeAppendix A for analyticalprocedures. .. CARBONATITE DIKES - continued ...? r Lem 305 Lern 427a Lern 427b Lem 500 Lem 506 - Mn 410 560 520 500 230 Cr 20 10 24 10 64 co 3042 38 34 31 Ni 51 33 60 31 183 Sr 244 298 322 323 534 Ba 1262 1170 1516 1226 3200 Li 84 18 20 20 61 Zn 158 116 133 125 154 cu 20 10 9.8 13 100 U 7.2 10.3 5.9 11.2 13.4 ~30846 0.0023 . 0.0033 0.0019 0.0036 0.0045 CARBONATITE DIKES - continued Lem 530 Lem 531a Lem 531b Mn 400 470 490 Cr 398 25 5 co 97 56 52 Ni 390 48 70 Sr 177 136 123 Ba 1779 3658 652 Li 19 7.4 6-5 Zn 397 436 619 cu 26 24 2-5 U 3.4 5.0 4.4 U308% 0.0011 0.0016 0.0014 This thesis is acceptedon behalf of the facultyof the Institute by the following committee: ." 'IGURE 2- PRECAMBRIAN GEOLOGY OF THELEMITAR MOUNTAINS +4- + ++ 4-+r + ++ ++ A\c+ ii i i ++ +++ 4- +++++ i+ + + i+ + ++++ i + +++ + +++++++++++++++ ++++++++++++++ +++++++++++++++ c++++++++++++++- +++++++++++++++ +++++30++++++++++++29 ++++++++++++++++ ++++++++++-I-+++ ++++ +++++++++++ +++++++++++++++++ ++++++++ ++++++ f+ ++++ + +++++++++++++ +++if++++++++ ++++++++++++ tiif ++++++++ ++ +c+ ++ MI-CROWAVETOWER _...... I TTT ITT ++++++++++ +++++if ++++++++++ I+ c + i + +/+" .MAP AREA + + + + + + + + + + +,0449 + + + + + + + + +,/0447A ++++++++A i + ++++, + ++++++++/ t34 i + +++++I 07 ' +++++ i POLVADERAGRANITE ,c ++ + ++/ ALTEREDPOLVADERA GRANITE BIOTITEGRANITE MUSCOVITE - BIOTITE GRANITE TIS GNEISSICGRANITE T2 $ a LOWERUNIT 0 LOCATION OF SAMPLES 520-5 CORKSCREWCANYON - ROADS f 5 +."ii 8 401 N T + + RIW GEOLOGY BY T MCLEMORE. 1980. T WOODWARD. 1973