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Carbonatite Dikes of the Chupadera Mountains, Socorro County, New

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Carbonatite Dikes of the Chupadera Mountains, Socorro County, New Garbonatitedikes of the Chupadera Mountains, SocorroGounty, New Mexico byBruce R. VanAllen and David L. Emmons,Tenneco Minerals Company, P.0. Box 27F, Lakewood, C0 80227 and TheodoreP. Paster, Consulting Geologist, 11425 E. Cimmanon Dr., Englewood, C080111 Introduction Bureauof Mines and Mineral Resourcesin- depths of t2-15 km, and metamorphosed at Calcitic carbonatites and thorium-bearing dependentlyidentified the carbonatites(Kent, temperaturesof 500-550"C.The exposed quartz deposits have been identified in the 1.982;Mclemore, 1983). stratigraphic thickness of metasedimentary southern Chupadera Mountains in Socorro rocks may exceed 3,000 ft. Schistosity ap- Counfy.The dikes and quartz veins arehosted profmates original bedding and is indica. by Precambrianmetamorphic rocks, whereas Geologic setting tive of two or more periods of folding before jasperoidoccurs in Paleozoiccarbonate rocks. The Chupadera Mountains are within a carbonatiteemplacement. There aPPearsto The depositsoccur in protractedsections 20, north-trending, west-tilted horst along the be at least one early west-northwest-trend- 21,28, and29,T5S, R1W on the northeastern western margin of the Rio Grande rift. Car- ing episode of isoclinal folding followed by portion of the Pedro Armendaris Spanish bonatitescrop out in a 2 mi'exposure of Pre- a'period of northeast-trendingopen folding Land Grant No. 34 and on the western edge cambrian rocks (Fig. 2), which has been (Bowring et al., 1983). of the Bosque del Apache National Wildlife mappedand describedby Kottlowski (1960), Narrow bodies of biotite schist and am- Refuge.The approimate location of these Condie and Budding (1979), Kent (1982), phibolite within the metasedimentary units depositsand the locationsand agesof other Bowring et al. (1983),and now by the au- are probably metabasalt flows and intru- carbonatitesin the region are shown in Fig. thors of this paper. The Precambrian host sives.Minor dikes of gneissicpegmatite and 1 and Table 1..The carbonatite dikes in the rocks are primarily interfingering quartzo- aplite are also present. Local porphyritic Chupaderaswere discoveredduring a con- feldspathicschist and gneiss,mica schist,and feldspathic schist may be metamorphosed tract uranium exploration program by United minor quartzite. These steeply dipping felsic plutons and perhaps volcanic flows. GeophysicalColporation in 1954(Reim, 1955). metamorphic rocks probably were inter- The youngest Precambrianmetamorphic rock At that time the intrusives were describedas bedded argillaceousand arenaceoussedi- is probably the foliated megacrystic granite "radioactive-calciteveins. " The "veins" were ments with locally abundant felsic, in the southern portion of the Precambrian recognized as carbonatite dikes in 7978 by volcaniclasticdetritus. Condie and Budding exposure.Based on zircon U-Pb isotopicdata, Tennecogeologists during a mineral recon- (1979)suggested that the rocks were depos- this metamorphosedgranite is 1,659 -+ 3 m.y. naissanceprogram. In 1980,the New Mexico ited during continental rifting, buried to old (Bowring et al., 1983).Carbonatite is the TABLE l-Ages of carbonatites and selected al- kalic rocks in New Medco and Colorado. See Fig. I for approximate geographic locations. Alsoin this issue Paleoenvironmentsof the Ate SouthHospah coal deposits p. 30 Locality (m.y.) Reference Gabaldonbadlands p. 34 1. Chupadera Mountains ? This paper gas p. carbonatite Oil and discoverywells 36, 2. Lemitar Mountains M9 Mclemore, 1982 Service/News p.41- carbonatite MineralSymposium abstracts p.42 3. Monte Largo Hills ? Loring and carbonatite Armstrong, 1980 Staffnotes p. 44 4. Lobo Hill <604 Loring and syenite and Armstrong, 1980; carbonatite Mclemore, 1984 Gomingsoon Albuqucrque '^4 5. PedernalHills <496 Loring and Reinlerpretationof a Precambrian syenite Armstrong, 1980 5. Caballo Mountains ? Staatz et al , 1965 angularunconformity, Manzano Mts. ChupoderoMls. syenite Cretaceousstratigraphy and bio- 7. Florida Mountains 418-750 Brookins, 1974 quartz syenite New Mexico stratigraphy,Clayton Lake State 8, Powderhorn dishict 543-731 Olson et a1.,7977 Park carbonatitesand Pennsylvanianpalynological analyses associatedalkalic rock of severalcoal beds, Santa Fe Co. 9. Wet Mountains 427-560 Olson et a1.,1977; RustlerFormation at the WIPPsite district Armbrustmacher FIGURE l-Location of carbonatites and selected carbonatitesand and Hedge, LateCenozoic Palomas Formation of alkalic rocks in New Mexico and Colorado and associatedalka.lic 7982 south-centralNew Mexico rock schematic location of the Rio Grande rift. See Table 1 for locality names and ages. youngest pre-Tertiary intrusive rock and is Carbonatites phyritic. Many of the intrusives are micro- not metamorphosed. The carbonatites occur as a northeasterly breccias, with rounded and irregular A thin wedge of Paleozoiclimestone and trending, arcuate swarm of steeply dippin! carbonatite fragments set in a carbonatite arkose unconformably overlies the southern dikes that cut the foliation of the Precam- matrix with similar composition. Pheno- margin of the Precambrianrocks. These sed- brian rocks. The dikes typically are exposed crysts, carbonatite fragments, and wall-rock imentary rocks contain no carbonatite dikes within a thin, laterally extensive colluvium inclusions generally align to form flow band- and are presumed to be younger. Poor ex- as rows of boulders. Wall-rock contacts are ing and localflowage segregation.Many dikes posures and major jasperoid zones make rarely observed (Fig. 3). The intrusives are are uniform in texfure, but some have vari- identification of the Paleozoicformations un- in long, narrow zones which, in some ex- able texture along strike. Wider portions of certain. However, Kottlowski (1950)and Eg- posures,contain up to three closelyspaced, others possibly are compositeintrusives with gleston (1982)have documented the CaloJo adjacentdikes. Individual dikes commonly sharp contactsbetween different phasesthat (Mississippian) and Sandia (Pennsylvanian) ar60.2-q.9 ft thick. Selectdikes have been are distinguished by textural contrast. Formations in the map area. traced continuously in outcrop for up to 200 The carbonatites are moderate brown on To the north and eastthe Precambrianrocks ft along strike. Four dike zonesexceed 1,000 fresh surfaces and yellowish brown to red- are covered by a thick Cenozoic section of ft in shike length and may exceed5,000 ft dish brown where weathered. Xenoliths and ash-flow tuff, felsicvolcanic flows, basalt,and with only minor lateral offset by faults. The phenocrystsof magnetite, apatite,and bio- sedimentary rocks, which compose most of extent of carbonatitesconcealed by Paleozoic the ChupaderaMountains (Eggleston,1982). and younger rocks is unknown. To the west the Precambrianrocks are down- Carbonatite textures range from fine to thrown by the Chupadera fault. coarsegrained and from equigranular to por- ExPlo I Alluvium I Gronile 5onlo Fe cenozoic .9 Porphyriticschist broup ,: terlroryvotcontc ; Amphiboliteond schist Ouorlzo{eldspothic Josperoid f schisl ond gneiss PoleozoicIimestone I lVico schist L Corbonolite dikes FIGURE 3-Outcrop of a 2.4-ft-thick carbonatite dike. Wall-rock coniacts are concealed by collu- vlum. New AAex[c@ GEOLOGY o . Soienceand Seruice Volume 8, No. 2, May 1946 Editor:Deborah A Shaw Published quarterly by New Mexico Bureau of Mines and Mineral Resources a division of New Mqio lnstitute of Mining & Tchrology BOARD OF REGENTS Ex Officio Toney Anaya, Gooernorof Nru Mexico Alan Morgan, Superintendentol Publiclnstruclion ADDointed SteveTorres, PieZ , t967-1997, Socorro \ "on,o., Judy Floyd, SeclTreas , 1977-7987,Ins Cruces Cilbert L Cano, 1985-1997,Albuquerque Lenton Malry, 1985-1989,Albuquerque Donald W Morris, 1983-1989,Ips Alamos : side; dotted New Mexico Institute of Mining & Technology if buried Ptridffit LaurenceH Lattman New Mexico Bureau of Mines & Mineral Resources strike ond dip Director Frank E Kottlowski Acting DeputyDirector JamesM Robertson Subscriptions:Issued quarterly, February, May, August, November; subsqiption price $6 O0/calendaryear foliotion Edttotiolmattq: Articles submitted for oublication should be in the editor'shands a minimum of five 15)months before date of publication (February, May, August, o! Novenber) and should be no longer than 20 typewrit- ten, double-spacedpages. All scientific pape$ will be reviewedby at least two people in the appropriate field Scole of study Address inquiries to Deborah A Shaw, Editor o 05 ot Nru MexicoGeology, New Mexico Bureau of Mines & Mineral Resources,Socorro, NM 87801 o I,OOO 2,OOOf t Published.as publicdomain, therelore reproducible without per fr5sion. Sourcecredit rcquested Circuletion:1 ,600 FlgUlE 2-Gene:alized geologicmap_ofcarbonatites in the Chupadera Mountains (precambrian rocks Prinler University of New Mexico Printing Plant atter Kent, 1982;Tertiary rocks after Eggleston, I98Z; and mapping by the authors of this paper). May 1986 Nm Mexico Geology tite characteristicallystand in positive relief feldspar commonly b from weathered carbonate matrix. Angular morphology and occa wall-rock xenoliths in the dikes are up to 0.7 polysynthetic plagiocle ft long and commonly have reddish rims be- apparentfrom oriented causeof hemat2ation. clear carbonateaggrei Minerarogy ;ffit,4'**".106'" The carbonatitesare composedof calcite eral^. Some samples contain partly nium oxides. with trace to moderate amounts of other recrystallized, fine-grained carbonate mo- Geochemistry minerals commonly found in carbonatites saicJ, making
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