GEOLOGIC MAP 63 NEW MEXICO BUREAU OF MI'\JES & MINERAL RESOURCES A DIVJSION OF NEW MEXICO [NSTrTUTE OF MINING & TECH'JOLOGY 103'·'.) (J' 107''5'.:'30 " 31 "' :,•,o ' CORRELATIO N OF UNITS ', ,
' ', " I Holocene I E / J Yo1mo1;r . / piedmont-slope '• c1lluvium Ope Opo end Opy undifferentiated
~, ·;- \ Late ··--~-+ Pleistocene E Older ! pied mont-slope alluvium Opu a rid Om i u n difforcn tifltP.d ! Late Pliocene cmd caly to middle Pleistocene Mimbres formation
rw C ~ 0 Basnlt plug :a,
Fan;;ilomera ce
~b~ [lasaltic-andesite flow.~
!'·, ~ LOW81 "'ang lomerate
Ttb <{' . .:;;"7,,/J , ,J'; T,jJi,'. '/ 'fl'/I l,1 I Ttb- Rhyol it 1c-tuff Tbd - Basaltic-a11desite _...--f / brer,cia dikP.s ~,,,. ------I C ' Tmb - Megabreccia Tfr - Flow-banded ',,_"~po ! 1"11yolile ~,._ ,\ I ' \ 1' t Andes1te porphyry Tf '
Tuff of Johnson Mountain
Tah n s ,....<,d10
' Tsi __..------. 28 S. 21: S _,,,,,s Tic : .ns • / C) s Tia 0 Tah - Ar1 c! es1te of Her m a1 ;as sidin~ Intermediate Tr. - Vnlc,1nic conglomcr::itc composition Tts - Tutfac1oous 8pidaslic rocks, bi-eccia, intrusive fresh-waler limestone, and intermcrlimc-composition flows Tic - Limastone conglonerate Ts i - \/:)lcaniclasti~ s1;1di111er1 lar·y ruGks Tia - lnermediate-com position flows Fl ~ Tuff of Carriza lillo Hi lls Tlcu - UppN member Ttr:I - Lower member
~ Lov1;er andesite
\'Ve il \•,.'Vi! 'if Lower rhyo lite tuff
-- ('. / ' ~ Rhyolitic tuttaceous breccia and epicl2s1ic rocks
/)
,11.5'. A I I~ ..c / '.:: 7 1'G 1i ~ /-Ji ~ I§, II :iX ,
Arproxim~te m~crn declimilion, 1980 A B Draftin\J d11d layout by K. Doherty and M. Brown Ba ss trom U.S. Geolo,11cal Su, ,ey Edill ,l\J b11 J C. Love G1:mlogy by W. R Seager, ', 983-1904 Thickness {ft) H~locene Low PIJiGtocene Alluvi1.:m Late Pl ,ocene-middle Ple,stoc:e ,e
Carrizal i llv Hi l ls Fanglomerate Johnson Min. Cedar Mts_ 8t!illi in C,1rfiz,1lillu Hills fault rnne fault C11rrizalillo Spring~ sec1 ion A' A fault zone 1 Johnccn 1Vltn. fault znnP. 5,UUU 5,000
Basaltic anrlesi1e 4,000 - 4,000
Lower fa nglomera te 3,000 Tsl!;I) 3,000
feet feet -3/' -
Carrizal1llo Hills l\1 eqabrncc1'.l and tuff hrP.cci/l B B' Carrizalillo Hills Johnson Mt11. G,500 fault zone Cedar Mts. 5,500 fault fault zone Tuff of Johnson Mountai11 ..,,.------...... 5,000 5,000 Tl" u 11(;,_...-....- Ttcl '~ ..___ Om Ttcl --/ :::-~ - - r ar·--- • ,;:J:;-,___ _ Qpy Tt~ITal Tal __..._"-...._ o Andesite nf Hcrmana5 5id111g i, ,: _> , T'.cl } ~-l_ajJ__) 11f~ 111 liJLl 111'_ -- ---. -~I __ _ \ ~1,-_~,l::>~c~s'-c:::~~ ±=CC''-:~--"-,W~ ]l!if'. F'7.[,:0,,~=~;Cc__ __ 1 1 ,I I , ' - ~- Ttd ~-c~\ Tl., I '1 / T\ ,)'11:,/ r iT:l ~/a \ 1,,Ta ]j I@: - - Q!Il!lJllit,\~""'Tallluj,tirtl _..-- ,,,-----T1cu \------~-r ------1 ---.....!., . 4,UU(J - T,l, \. r~u - - - · , ,Ttl ~,,:, I -· ---,.., II , ft 0 1 T•1'I) - 4,000 \ , •,, 1r.l1. . 1 ,, ------. .Jo..I.\-- --Teel , :c~/ ' · Tia fsb \• y Tcb . ~ 1 ------...,..}-':: 1~~- yA ' \y \ 1 \ ( 1/ Tub J \ ,Y ;Tsb -:--l]f0°ii ~~~' \:- r..1 · ;· Tcb ,\ _,. -1.1 I; ,n1 1111 ' h b \+--- 3,000 3,000 \ Ts:b~~...... - ...... - limeston e fe et foGt •0 C -ri~ estore conglomerate anrl "C • volca niclastic sedimentary rocks "0 u 0 -~ ------~ 0• 0 C •V 1,500 ] Tia lntermed1ate-comrosition flows u C •u C •u 0 Geology of Hermanas quadrangle, Luna County, New Mexico > Upper member
1,000 io-- '"'~ ---t+-- I I 0 0 ,J' ,J' ,, / ,,~ , ;<"' --w- -.,,, J_ by Vvilliarn R. Seager and Russell E, Clemons, 1988 I () -\'< ''- 1 Ttcl Lowr.r membEc1r C"""' . N ·;- c-''- ~ -I+- - ( ru u" ·/'-.. J-,. I ______j____ 5ca[e 1:24,000 Tai Lower andesite .5 u 1 mi 500 Ttl Lower rhyolite tuH ,5 0 1 km
Rhyolitic t'uttaceous breccia and epiclastic rocks
0 not exposed
.FIGURE ]-Composite stratigraphic colum!l
the lower member (12- 8% and 10-5%, respectively), only southern Nt•w Me ,><.irn. We presume that the basal series of distinguished by conspirnuuc, andesilic-lithic &agn1.en ts and to dramatically increasC' (14 -17% and 7 10o/c, respedively) INTRODUCTION volcanic and volcanidastic rocks is Oligocene 8S are simili'lf by bintite phenocrysts rendered bronze in color by oxida at the tup of the lower member and fall back to 3-7% in sequences of ash-flow luff, flow-banded _rhyolitc, ,md in tion. The lithic-vitric tuff contains xenocrysts of pl:'rthitP, Adjoining the State of Chihuahua, Mexico, the Hl·rmanas the upper member. These relationships suggest th21t the termediate-composition b vain southern New Mexico, such microcline, and oligoclase, which c1w intensely altered lo guaUrangle is located in Lunn O _nmty a pproximately 30 mi initial eruption tapped progressively more nphyric m,1gma as those in the Black Range (Elston, 1957; Seager et al., carbonates ;md day, 2nd 2ndesilic-lithic fragments. Xeno 5outh-southwest of Deming, Nt:!w Mexico (Fig. 1). NM-9 down to a cc rt.:iin IC'vcl, below which nvstals, especially traverses the c<'nhcr of tl1e quadrangle, providing principal 1':!82). The overlying fanglomerate is generally correlative crysls c1nd xenoliths total approximately 37% of the rock samdint:! and ,1uarl:c 1 were ~.rowing in abundance and were wilh the Santa Fe Group of the Rio Gr,md(• rq';iDn a11d tl1e The tuff also contains approximr, to llowi11g a gravel road from Henndnas lo Denting allow further access glomt:rate are probably late Oligocene-earliest Miocene and matrix is stained easily ,vith sodium cobaltinitrite, indicat ing its high potassium content. InterstitiDl pD tchl·~ .ind p ort" p<'rmd ot parti<1l or whole 1·eequilibrat1on of and, perhaps, to most parts uf the quadrangle. correlative with the Bear Springs Basalt and Uvc1 s Basaltic new thennal input into the magma chamber. Other schemes Andcsite of the Black Range-Sicrm de ];:if; Uv.is rt:giun. A fillings of carbonate are common. Mirnir spherulitic wnes ! C ,08' 0J' to account for the mineral and chemical•vnriations arc pos b8saltic plug neilr the top of th e fanglomerale section ap show som e rl1--vitrification of the matrix, A chemical analysis sible. pe.ws simil:::tr to Plioi,:ene dikes, plugs. and flow remnants of thi.~ nlter;.,d rock is included in Table L Some oxides, parti,·ularly sodium and polassmrn, have LJ orn ,oe in thP nead,y Palomas volcanic field (Seager et al. 1984) LO WER ANDESITE (Tal)-An andesitic flow, approxim.'.'ltely FIGURE 2- Tuff of Carrizalillu Hills forming cuest21 s in east-central no apparent trem.b. However, K/Na ralios for every sample Mod ern alluvial fans are mostly Quaternary, although th£ 60- 100 ft thick, overlies the lower rhvolitc tuff .1nd llnderlies of luff of Carnzalillo Hills are anomalously high, typically Carri :s <1l il!o Hills. oldest p arts of the oldest generation may mnge in to late in V,ctori c the tuft of Carriznlillo Hills thP CP~1tral and southern Car 8:<1 (Table 1). These anomalous ratios almost certainly re ,\ r-co, ntc,ns eventually resulted in a composite strc1tigraphic section. At Pliocene. riz,ilillo Hil ls. The dark-gray lo reddish-gray lava flows con flect extensive potflssium metDsom::iti sm, which also was the same time, several mining c,-:impani es became interested Descriptions of map ur1 its Lhal follow are grouped into t1in approximately 14''.'c: stout znd blocky feldspar (probably revea led in thin sections. in the area bec.rnst' u( the alteration, swarms of quartz cmd th!· thn ·t· main rock series, from oldest to youngest: vokc,nic sauidine) phenocrysts and 12% microcrystalline (0 .01-0.05 " rnrhun;__ite veins, 2nd indications of precious mC't,,l s. Al and vokaniclastic series, fanglomerate and basnltic-.1ndcs mm) anhedral-equant quartz patches and V('in s(?) in a ma lNTERMED1AT[- C0Ml'US1110N FT .CJY,S (Tlu}--Ovetlyin~ Lhe luff though the present study is not foc used on ct·o11om1c geol ite series, and Quatern.My Oeposits. Chemirnl datil for •;t• trix of small (0.05- 0.3 mm) plagioclase laths, iron oxides, of Carriwlillo Hills is a series of intennedi8te-cornpos1tion cith.-,rs to brown, tvpr !', plott['d as t\LK (o/c>la,0 + K,0 l w 1·s us Cf \,[ (%Ca0 + Bureau of Mines and Mineral Resources supported this study, boulder-strewn sl,JfW.~, r,-:iunded hills, or local cliffs. The uni! blende-nugite andesite, and dacite. SiO, content rilnges from pervasively rocks southward to thi"' M{•xican burder. To Lhe foO + MgO + MnO ), ·when thf' rock compo,: ition i~ rems! tu 57 to 59.5%. Many of th e flows have a distinctly basaltic nnd we e~pPc-ially Lhank Frank£!. Kottlowski, Director, fnr exknds so u thward several miles into Mexico. A LK + CFM - SIL (%5i0 ,.) = l0Cl%. The heavy broken line il north and north1.vf'sl of Nlv[- 9, in different fault blocks, app earance, so the field term basaltic andes1te may apply his conlinuing encouragement and support of our g;eulogic pffecb of altemtion appear to be essentially absent, or, at Two cooling units (members) of the h1ff of Cnrrizalillo lustr~ tcs the nearly liHecir rt' blion belwet'n the comp ositi:ms of ·,oo·o: · MEXICO studies in southern New Mexico Hills, which are separated by a few fed Df rnnglnmerate rocks in the norm:,.] {cak-a lklllinf' ) ~cqucncc, Th t= lighle1 do lled lines in gent>ral. J-'ldw llucknesse$ :range from 50 to 100 ft . 2nd leasl, far less severe. Potassium metasomati sm, such ns th,Jt 'Nhereas some flows seem to persist along strike for miles, FIGURE 1 lm.it=x map sh o·,nng location of Hermm1as quadranr,lc described here, has also been rf'ported in the Rio Gr;c:nde and sandstone, were w rng11 ized. The lmver men1.ber (Ttc/), are projecbor,s from th e Si01 corner to the .ihovr lin e lo ob :cra environments (Fenn er, 1936; Ra tte composition from andesine (An,_s) tu labradori-Le (An,,;) . av scattered juniper on some hills and mesquite ur de~erl wil ,mJ Sltcven 1967), to reddish-gray-weathering, crystal-rich tuff approximntcly member, except the upper member <1p pears Lo contain less rocks (> f sihrn: h-:i intermediate composition (including ,1sh 1 qunrtz (2- 4%) and sanictine (3-8%,). Consequently, some eraging An ,,. "Owy are typK2Jly euhedral. progres:;ively and low trees along sandy washes, vq;etation is scant and lim R.J-JYOLITl C TUFFS, TUFFACE OUS l3RECCIA, 4. ND EPICLASTIC fl(){ "I<' 60-100 ft thick. ited to grass, solol, yucm., cactus, and low bushes. mostly flow tuffs). Small subvokanic domes,. plugs, and dikes also D1.in -section studies show the lower tuft tu be a vilric ~amples of the uppe r tuff member are best described as oscillatorily zoned, and fresh. Euhedral o:.:yhornblende mi are present, as is a peculiflr seguence uf limeslone--granite (Tsb}---The oldest exposed rocks in the Herrn;mas cp1c1d rc1n creosote and mesyuite. crystill, rhyolitic ash-flow luff conlaining prominant xena \'itric ash-flow tuffs containing less th,m 10% crystal~. crophenocrysts (to 2.5 mm). present in some silrnplcs, havC' conglomerate, whirh is interbedded in the volcanic secti on. gle are a sequence of rhy(,Ji ti,·,. tuftaceous sands lone, rnud thin, dark, oxidized rims,. but thP interiors are pleuduui1. Thew are few published accounts of thf' geologv ut the stone, ;rn d fi nt'- to medium-grained brcccia, perhaps crysts- though less abundant than in the lower rhyolite In terms of SiO,, TiO" ,1nd CnO content, the lower and Hermanas quc,drangle. Darton (1916) briefly described rocks The volrnnic and vvlcanidastic rocks fo rm most of the up luff (Ttl,). Cr ystal content includes 5- 11. % qunrtz, 8- 17% upper members appedr to fo rm a chemically zoned unit light brown to rC'd brown and have exl mclion angles of land areas of the quadrangle. llnconformably ovt:rlymg the containing a few pumiceous air-fall beds. Pale purple or approxinwtdy 15°. Augite and orthopyroxene content ranges in the Cedar Mountc1.im ,mJ Carnzalillo H ills and noted maroon, gray to pin k, or cream i11 color, the stn1bJ ilrt> sil sanidine, and approximately 1.5% hiotitt". Lithic frai::;menls (Table 1). Silica content ranges from approximately 76% at that a sm.111 shipmt-'nl of rich copper ore with gold held hC'C'n vokamc series is a sequence of hPmudinctll_',- lilled fanglom comprise less 1forn 1 % ()I the rock and include nndesite the base to less than 70% at the top, d ccre,1sing rath<'r stead (ram 2 to 18%, with the equant crystals varyin g in size from erate manv h nndn°dc; ui !eel Lhick, at lec1st, which is derived iceous and bleached in piltch1's or uluag fraclmes. Locally, microlites to 1 mm. \'lagnetit"e contf'11t VJ.ries from 1 tu 4%. mad(• from a mine in the northwestern Cnrri7ali llu Hills. pl'rthik, ';andslone, and arkose. Abundant large axiolitic ily upward. Ti02 ,md C.10 also show a umsish:nt trend by from lorni' vok,mic rocks. The fanglomernte cont;:i in:, flow~ lirnonjtc is ;:i hmvy stain. At most, a iew hundred feet are Hypocrystalli1w groundmass tex,tmes include interserta!, (,riswold 0961) also brieflv dcscribl'd till-' rocks oi the Car expuseJ. The unil forms a narrov.1 horst wi thin the tuff of shards in a holocrystalline- microcrystallinc or microcrys their steady upwarJ im:rease from the basal lower member of b;is;i Iti c andesite near the base and D small plu ~ ol basall inh:'rgr,m u l;ir, hyalopililic, and pilotax.itic types. Carbonate rizali llo Ilihs, a~ well a.s we:1 k minernlization in several pros Curizalillo J lills at the Mexico-United States border, nnd lalline to cryptocrystalline matrix chnrildl'TiZl' the ground tuH to the upper member. These trends suggest progressive pects. Prior to the pr<'sl~nl study, the only published geologic near the top, The youngest stratigrnphic unils ifl the map rnass. Spherulitic ZllTH's are more common 1n the evacuation of a magma chamber from the silica-rich top and minor zeohtes(?) fill some vesicles area are several g('neratiom, uf alluvial-fan and arroyo sed the contacts with adjacent rocks nrc tnalts Intermediate-composition flows in thf' CnrrizaliUo Hills map of th1· neral litholoF;ic similarity ,ind strati dressed the geology of the Carrizalillu Hills. predominanlly ash-flo-w tu ff in the central and southern aod carbonate also occurs as small, irregular pntch c·s in tiw For t'xarn_ple, Lolal crystal content steadily decreases up This study of the Hl'nnanas quadrangle in 1982, 1983. t(·n~ nf feel thick in surface exposures, tlwsP de pos1Ls may cryptocrystalline groundmass Flattened shard~ in some ward in lhe lowe r member (22-14%) but increases more gnphic pos1lion above the tuff of Carrizalillo Hills. The be considerably thicker in thl:' ~ub~urface of major basins. Car:rizahllo Hills. The base of the tuff is not t'xposcd , but it main difference between the units in the t\VO are.is is the> and 1984 wa~ an outgrowth of $eager's mapping of the Las is overlain successively hy a thin .imll:'site fl ow and Lhe luff samples show comp.:iction and flowai;e around crystals. In than twofold at the top of the lm,:er m,,mh,•r (:Fi%), only Cruces and El Paso 1° X 2° sheets. During thC' course of None of the rocks lJr sediments in the Hermanas qt12d les3 v,,elded ~amples 5hards are loosely packed, curved , or to fall off to lowf'r w1h1C's (9- 20%) in the upper member. locally higher phenocryst conl·~·nt .:i n d widespread 21Lera rangle hnve bt'<'ll dc1led, so their age is inferred from phys-. of Cmi:mlillo Hilb, the latter unil being the major ash-flow that slud)', detailed mapping of thC' quadrangle revealed ov,1 1. SnnidinC' and quart~ like,vise decre<1se steadily upward in tion of the C,irrizalillo Hills rocks. Although alt~ration, of icnl mrrelatiort with better-dated sections in oHwr pads ol tutf shee! in the quadrangle. In hznd specimens the tuff is 1,.,r ,::or:!,mwd m, cia" /c complexly faulted and altered volcanic rocks1 and it also the flows is extensive, the most· intense alteration is re The Tt~ map unit includes the following lithologies: breccia. Locally, the matrix appears to be massive rhyolittc part of the landscape. Uplift of the modern ranges, such as rizalillo Hills. Stratigraphic separation on these faults is mer of 1985. stricted to areas of closely spaced fractures, such as those brownish-red to brick-red, tuffaceous rhvolitic sandstone, glass or devitrified rhyolite glass, which may be welded the Cedar Mountains, Tres Hermanas Mountains, and other 1,000 ft or less, the decrease in throw relative to the more Alteration is a dear aid for mineral explm:ation in the adjacent to Johnson Mountain, or to narrow envelopes mar breccia, and mudstone; gray to yellow, cUarse-graincd, tuf pumice masses or small intrusives, weathering yellowish fault blocks, segmented the earlier basins and piedmont westerly segment of the fault being a product oi the inter ginal to isolated fractures. Hcrmanas quadrangle. The area of most inten_sc alteration faceous rhyolitic sandstone; gray to purplish andesitic sand green to gray to cream. In places the matrix of tuff brcccia slopes, incorporating parts of them into the modern uplifts. section of the Cedar Mountains fault with the Carrizalillo and focus for precious-metal exploration is centered north In thin section the lavas of the Carrizalillo Hills arc mi stone and conglomeratic sandstone; beds of rhyolitic air is relatively free of large blocks and is mapped simply as Exactly when this segmentation took place is not clear from Hills fault zone. west of Johnson Mountain in the area where the four major croporphyritic, typically containing 18-25% pl.agioclasc fall(?) tuff and brecda; aphyric or slightly porphyritic an tuff brcccia (Ttb). Tn general, bedding is lacking or, at least, relationships in the Hermanas quadrangle but is thought fault zones converge. Rock units in this region are seg phenocry~ts (to 1.5 mm long), 7-11% hornblende pheno desite flows; rhyolitic ash-flow{?) tuff; and, near the base is not obvious in the limited exposures of matrix. Locally, to have taken place in the last 7-9 m.y. in the southern Rio Carrizalillo Springs fault zone mented by closely spaced faults, which apparently created crysts (to 1.5 mm long), and approximately 1.5% biotite(?) of the section, a fresh-water limestone bed 2-3 ft thick. The crude bedding dips away from the central rhyolitc dome. Grande rift (Chapin and Seager, 1975; Seager et al., 1984). The Carrizalillo Springs fault zone strikes northwesterly ground permeable enough to localize the core of a geo phenocrysts. These arc in a hyalopilitic-pilota.Xitic or inter andesitic flows are distinguishable from those of the Tiu The mcgabrcccia usually crops out as low hills or ridges sertal matrix. The plagiodase is progressively and oscilla through volcanic rocks along the northeastern flank of the thermal-hydrothermal system. Alteration and quartz-car map unit and are shown on the columnar section inter studded with boulders or blocks of every size and ori1c·n Quaternary deposits bonate veining is most intense, widespread, and pervasive torilv zoned, but it is so altered to davs, carbonate, sericite(?J , Cedar Mountains. Although the zone consists of faults with bl°'dded in Tts. One of the flows, andesite of I lermanas tation with finer-grained matrix material obscured by slope in this region, although somewhat weaker alteration of an and.epidote(?) that its original comPosition is obscure. The Several generations of alluvial fans have bee11 deposited opposing dips and direction of downthrow, the major fault siding (Tah), was locally differentiated on the map. wash. mafic minerals arc intensely oxidized, and typically thdr adjacent to the Carrizalillo Hills and Cedar Mountains dur in the zone seems to be downthrown to the northeast. Thus, de,;ite and ash-flow tuff persists southward to the Mexican Except for outcrops near Herrnanas, nearly alt of the rocks The origin of the megabreccia seems clearly related to the border. The dominant alteration is potash metasomatism as former presence is indicated only by hematite-magnetile in this sequence arc thoroughly altered, especially in the ing the Quaternary.These are distinguished from one an the main structural block (Tla) bctwee11 this fault zone and rise and emplacement of the central rhyolite dome. We vis other primarily by their geomorphic position and degree of the Cedar Mountains fault zone is a lnorsl. Stratigraphic revealed in whole-rock chemical analvsis and thin sections. ghosts outlining the cuhedral crystals. One thin section ;irea immediately northwest of Johnson Mountain. In some ualize disruption of the tuff of Johnson Mountain, as v"·ell contains small (0.2-0.8 mm) equant phenocrysts without soil development. separation is less than 1,000 ft. In addition to potassium feldspar, thC alteration assemblage instances, the type and composition of the original rock is as upper parts of the rhyolite intrusion itself, as the dome includes clays, sericite, chlorite, celadonite, quartz, calcite, apparent cleavage, which may be olivine. !"hey, too, have in doubt. Thin sections reveal that all mafic minerals are The oldest fans (Qm) are a5signed to the Mimbres for From Carrizalillo Springs southward, the fault zone wid rose explosively toward the surface. Although some of the mation of Clemons (1982a). On upper piedmont slopes these ens, consisting of a major down-to-the-northeast fault dip and various iron oxides (J. J. Kapler, written communica been altered to aggregates of magnetite, carbomite, and f'Xknsively oxidized to limonite, hematite, magnetite, and larger blocks may have slid to their present position in the fans are topographically highest and are deeply trenched ping northeast and numerous antithetic faults dipping tion 1985). The age of alteration is clearly younger than the microcrystalline quartz. Groundmass consists of tiny (0 .005- chlorite. feldspars are argillized and replaced by anhedral, megabreccia cone, much of the megabreccia was emplaced by arroyo systems; younger fans arc inset below them. Pc southwest. Most of the faults are filled with thick, promi tuff of Johnson Mountain and may be younger than flow 0.05 mm) plagioclase microlites and laths in a cloudy, cryp granular, microcrystalline potassium feldspar or sericite. as proximal air-fall material and, subsequently, was invaded trocalcic horizons up to 3 ft thick typically cement upper nent veins of quartz and carbonate, making the system banded rhyolite masses, as J. J. Kapler (v1:ritten communi tocrystalline to glassy material largely replaced by carbon Lithir frngments, some originally andesitic, others rhyolitic, irregularly from the side or from below by satellite mascws most Qm fan deposits. On middle and lower piedmont slopes, conspicuous as it crosses NM-9 and Baker Draw. As the cation 1985) reports quartz-carbonate veins cutting ba ate, iron oxides, clays, and some microcrysta!linc qu,1rt,-. are saturated with microcrystalline potassium feldspar and of rhvolite. however, Qm deposits are generally buried by younger fans. system approaches the Cedar Mountains fault zone west of saltic-andesite dikes (Tbd) within the rhvolite dome north A few nonporphyritic rncks are composed chiefly of piJo. yuartz in the ratio of 2:1. Groundmasses of original flmv Ar,tDESITE PORPHYRY (Tap)-Two outcrops of andesite pm Qm deposits are up to 50 ft thick on piedmont slopes and JOhnson Mountain, it appears to bend eastward into sem of NM-9. . taxitic-hyalopilitic plagiodase laths averaging 0.01-0.03 mm rocks are altered lo kaolin or patchy sericite. Delassitc, cc phyry are surrounded by megabreccia. Whether these out iparallelism with that zone. This region of convergence of wide. Hornblende ghosts are ubiquitous in trace amounts lc1donite, ,md calcite are also part of the alteration assem typically consist o f coarse gravelly alluvium grading down crops are blocks within the megabrecci.a, intrusives into it, slope to gravelly sand or loam. Except for petrocalcic ho Lhe two zones contains the most altered and fractured ground as are clay and carbonnte alteration products. blage (J. J. Kapler, written communication 1985). Thus, thin or remnants of the prc-megabreccia "basement" is not knmvn. rizons the deposits are either weakly cemented or in the quadrangle and has bee11 the site of extensive explo Comparison of chemical analyses of lavas from the Cedar sections indiectte that potassium mctasomatism of these flows The porphyry is unlike any of the volcanic section cropping ration for precious metals in 1983, 1984, and 1985. Mountains and Carrizalillo Hills reveals the extent to which and sedimentary rocks is as severe as that affecting the uncemented. Correlation with better~dated fans o_f the Camp REFERENCES out below the tuff of Johnson Mountain. It is composed of Rice Formation in the Rio Grande valley (Gile et al., 1981) the latter rocks have been altered (Table 1). L'naltered Cedar underlying intermediate-composition flo\vs (Tia). 2% andesine phenocrysts (to 5 mm), 2% hornblende phe Balk, R., 1962, Geologic map of Ires Hermanas Mountains: New Mountains andesites comistently exhibit K/Na ratios neilr suggests that the Mimbres fan deposits ;ire older than about Canizalillo Hills fault AJ\'DESITE OF HEl{t\1,\-".,\S SIDl:\'G (Ta/1)-Interbcdded near nocrvsts (to 2 mm), 2% biotite phenocrvsts (to 1 mm), c1nd Mexico Bureau of Mines and Mineral Resources, Geologic Map 1.5:4, typical of calc-alkaline andesites. Two samples of an the top of the volcaniclastic and lctva-flow section just dl'· 0.4 m.y., c1nd the oldest parts may range into latest Pliocene. Bordcri11g the Carrizalillo Hills on the south and west, 16 scale l ·48 000 l % dugite and orthopyroxene phenocr)'sts (to 4 mm) in il Qpo fans are similar in composition, thickness, cemen desites from the Carrizalillo Hills, however, show perturbed scriN'd (Tis) is a distinctive andesitic now that crops out in felted, holocrystalline matrix. The matrix contains andesiM the Carrizalillo Hills fault zone is one of the best exposed Bartiev, J. M.·, a~d Glazner, A. F., 1985, Hydrothennal systems and tation, and distribution to Mimbres fans, but the former are Ierliary low-angle normal faultin~ in the southwestern United ratios of 10:1 and 7:3. Clearly the alteration revealed in thin tlw h ills just north of Hermanas siding. TI,is flow was mapped laths, magnetite, enstatitc granules, and abundant uniden fault zones in the quadrangle and is a good example of tht' inset below the Mimbres fans on upper piedmont slope~ States: Geology, v. 13, nu. 8, pp. 062-564. sections has involved extensive c1ddition of K20 and re curving fault zones that border large lozenge-shaped struc separately and named andesite of Herman,1s siding. Near tified mafic microlites. Plagiodase is progressively zoned, Bornhorst, T. J., and Kent, G. R., 1985, Geochemistry of host-rock moval of Na20 in the Carrizahllo Hills rocks. Although these and exhibit weaker petrocakic horizons. They are, hm·vever, I lermanas siding (Herm,mas), the flow overlies rhyolitir and many appear "wormy." Biotite books are ragged and tural blocks. The faults in the zone dip moderately to steep!\· alteration at the Eberle mine, Mogollon mining district, south altered rocks plot as trachybasalt or alkali basalt in Irvine epiclastic ro(ks, mainly luffs and breccia, of the Tis map geomorphically above modern arroyo floors by several feel south or southwest, and the zone steps structural blocks oxidized, which produced much of the magnetite. to several tens of feet. On middle and distal piedmont slopes western New Mexico; in Eggleston, T. L. (t'd.), Epithennal de Baragar classification schemes, their original composition unit. Locally, a channel-form volcanic cobble conglomerate down to the south or southwest. Tuff of Carrizalillo Hills posits in New Mexico: New Mexico Bureau of Mines and Mineral fan df'posits underlie bro.id stable fan surfaces and was closer to dacite (Fig. 4). (fr), a few feet thick, underlies the andl•site. Quaternarv Q1,o (Ttcl), lm-ver rhyolite tuff (Tl/), or lower andesite flow (fol) Resources, Circular 199, pp. 7- 15. At the Calumet mine in the southeastern Carrizali\lo Hills illluvium overlies the andesite near Hermanas siding. Th~ Fanglomerate and basaltic-andesite series exhibit well developed, reddish, day-rich soil suitable for commonly form the footwall block at the surface, whereas Bromfield, C. S., and Wrucke, C. T., 1961, Reconnaissance geologic irrigated crops. Qpo fan deposits and surfaces are generally a pluglike mass of andesite, possibly correlative with in· z111desite of Hermanas siding is also present in outcrops of Unconformably overlying the andesite porphyry (Ta/1), higher pclrts of Ttcl or the overlying lava flows (Tia) form map of the Cedar Mountains, Grant and Luna Counties, New termediate-composition flows (Tia), transects the tuff of lilte Pleistocene (0.4-0.1 m.y.) based on correlation with Mexico: U.S. Geological Survey, Mineral Investigations Field Tl~ nortlnv 1..>st of Johnson Mountain but was included there mcgabrcccia (Tmb), and, in quadrangles to the north, var· the hanging wall. Stratigraphic separation is generally 400 Carrizalillo Hills. Labeled Tii on the geologic map, the in the Tfs map unit. Radiolarian-bearing lacustrine elastic ~1milar, better-dated fans in the Rio Grande valley (Gile et 800 ft. Approximately 1.2 mi southwest of the Carrizalillo Studies Map MF-159, scale 1:62,500. ious other rock units is a sequence of fanglomerate, inter al., 1981). Chapin, C. E., Chamberlin, R. M., Osburn, G. K, Sanford, A. R., greenish to purplish-gray andesite is intensely altered . Po rocks and air-fall tuff overlie the andesite at this locality (J. bedded basaltic-andesite flows, basaltic plugs, cinder cones, Hills fault, another fault, unnamed and projected into the tassium-feldspar(?) and plagiodase phenocrysts, which once Youngest deposits (Qpy) in the Hermanas quadrangle in and White, D. W., 1978, Exploration fram!:'work of the Socorro J. Kapler, \Vrittf'11 communication 1985). and dikes. The basaltic-andesite flmvs (Tba) occur near the quadrangle from exposures in Mexico, steps the volcanic geothermal_area, New Mexico, in Chapin, C. E., and Elston, \"\I. co.nslituted 10% of the rock, have been changed almost clude fans at the mouths of currently or recently active At least 100 ft thick, the dark-gray tu purplish-gray an base of the sequence. Fanglomerate below the flows is la section down again. Thus, the Carrizalillo Hills volcanic E. (eds.), .Field guide to selected cauldrons and_ mining districts cumpletely to kaolin and carbonate; amphibole(?) pheno df'site of Hermanas siding contains lf'SS them 5% euhedral drainage systems, as well as the deposi-ts on moderl1 arroyo rocks are stepped down by at least two major fault zones beled Tfl on the geologic map; fanglomerate above or within floors. These deposits are inset below all older fan remnants of the Datil-Mogollon volcanic field, New Mexico: New Mexico crysts arc now aggregates of magnetite, as is minor biotite. plagioclase phenocrysts (to 1.5 mm) dusten'd in a very into the basin that forms the southwestern corner of the Geological Society, Special Publication 7, pp. 115-130. the flo¼'s is identified by Tf. Basalt plugs transecting Tf are on upper piedmont slopes but have buried older deposits LOcally, spotty epidote alteration gives the rock a greenish Lif'nse hyalopilitic groundmass of tiny (to 0.1 mm) plagio noted by Tb. Hermanas quadrangle. Chapin, C. E., and Gla:mer, A. F., 1983, Widespread K~O meta· color. The nearly oval-shaped plug is approximately 0.4 mi clase laths and m;ignetite(?) microlites. Larger plagioclase and surfaces on middle to distal piedmont slopes. Pctro somatism of Cenozoic volcanic and sedimentary rocks in the The lower fanglomerate (Tfl) consists of a basal boulder rnkic horizons are weak or absent, but weak, clavey B ho long and exhibits chilled cont.acts with surrounding tuff, Gystals arc argill ized and partly replaced with cilrbonate. conglomerate several hundred feet thick derived from im Johnson Mountain fault zone southwestern United States (abs.): Gl'ological Sodety of America, c1lthough the \Vestern margin m;iy be a fault . TUFF OF JOHNSON MoUNTArN (Ti)-Named for Johnson rizons and A horizons mav be present. Deposits r~ni;-e from Abstracts with Programs, v. 15, no. 5, p. 282. mediately underlying volcanic rocks, as well as from older The curved Johnson Mountain fault zone, downthrown C 1985, Ll.\1FS TO.\JE CONCl.()Ml·.l~I\.TI A'.ll \'OLCA>-IICLAS1 il coarse gravel to loam or ~ven day depending on their pu Chapin, E., and Lindley, J. I. , PotaRsium metasomatism _\fountain in the northwestern part of the Carrizalillo Hills. volcanic rocks exposed elsewhere in the quadrangle. Boul to the north, northeast, and east, bounds the lozenge-shaped of volcanic and sedimentary rocks m rift basms, calderas, and Sl·DIM)'.N'J'A!{Y RO CKS (Tic and Ei)-Overlying the lavas just ~ition on the fan or in the arroyo system. In general, Qpy the tuff of Johnson Mountain was originally a widespread ders to 5 ft in diameter embedded in a sandy to gravelly Carrizalillo Hills block on the north and east. Poorly ex detachment terranes; in Papers presented to the conferem:e on described, (Tia), is a sequence of conglomerate, sandstone, unit, the second important ash-flow tuff sheet in the Her deposits are less than 15 ft thick. Based on charcoal dates matrix arc not uncommon. These rocks are the products of from correlative deposits in the Rio Grande region, Qpy posed on the south side of Johnson Mountain, the tllajor heat and detachment in crustal extension on continents and and mudstone several hundred feel thick. Exposed poorly manas quadrangle. Besides Johnson Mountain, the tuff crops mudflow or debris-flow deposition on ancient piedmont planets: Lunar and Planetary Im,titute, Contribution 575, pp. and discontinuously frnm Johnson Mountain northward st·diments are less than 15,000 yrs old. fault can be traced eastv,rard where it seemingly crosses the out in scattered low hills and valley sideslopes along the slopes. Upward, coarse conglomerate gives way to light Cedar Mountains fault zone in the NEi/4 sec. 34, T285, RllW 25-31. across NM-9, the sequence is notable for its content of northeastern flank of the Cedar Mountains in the north gray to lighHan, tuffaceous, vokanidastic sandstone, silt Chapin, C. E,, and Seager, W.R., 1975, Evolution of the Rio Grande limestone and granite dasb derived from Paleozoic, Lower STRUCTURE and, then, is exposed on the northern edge of the hills in rift in the Sornrrn and Las Cruces areas: New Mexico Geological western Hcrmanas quadrangle. Our mapping has revealed stone, and conglomeratic siltstone, also a few hundred ftc'et the center of sec. 35, T28S, RllW. From there, the fault zone Cretaceous('), and Precambrian rocks. Permian brachia only faults or intrusive contacts at the base of the unit, Society, Guidebook to 26th Field Conference, pp. 297-321 thick. This, in turn, is overlain by or interfingers with ba- General is buried but apparently bends south truncating the east pods and foraminifcra were identified from some dasts (J . ill though mapping by J. J. Kapler (personal communicalion Clemons, R. E., 1979, Geology of Good Sight Mountains and U\·as saltic-andesite flows (Tba). · trending cuestas of the central and southern Carrizalillo Valley, southwest New Mexico: New Mexico Bureau of .Mines J. K:ipler, vvrittcn communication 1985). The source of these 1984) revealed a small c1rca near Johnson Mountain where High-angle normal faulting dominates the structural fea Exposed only in one area in the Hermanas quadrangk, Hills. On.e possible piedmont scarp, 0.2 mi long, which cuts and Mineral Resources, Circular 169, 32 pp., 2 sheets, scale 1:48,000 clasts is unknown tures of the Hermanas quadrangle, and the tvvo principal the tuff depositionally overlies andcsitic volcaniclastic rocks the basaltic-andesite flows farther northwest in the Cedar a Mimbres fan (Qm), indicales that this zone has been active Clemons, R. E. , 1982a, Geology of Massacre Peak quadrangle, Luna Two lithologies, mapped separately, are present: lime of the Tts map unit. Approximately 230 ft thick, the tuff is upland regions, the Cedar Mountains and Carrizalillo Hills, Mountains are extensive and several hundred feet thick. in the Quatemarv. Other scarps along the zone are also C,mnty, New Mexico: New Mexico Bureau of Mines and Mmeral stone-granite cobble-boulder conglomerate (Tic) and an ilrc products of this faulting. The Cedar Mountains, a north- crystal rich, medium grained, and generally reddish gray There they consist of a series of black, gray, red, ur brmvn present in Mexic(). Resources, Geologic Map 51, ~cale 1:24,000. desitk mudstone, sandstone, and cobble conglomerate cr~i) in color. It is extensively altered in outcrops on or near vesicular to platy andesite to basaltic flows. One thin section 1vest-trending fault block, are bounded on the southwest CJ emons, R. E .. 1982b, Geology of Florida Gap quadrangle, Luna Age relationships bet\vcen these arc unclear. At least lornlly /ohnson "Mountain. and northeast by faults: the Cedar Mountains fault and County, New Mexico: New Mexico IJ.ureau of Mines and Mineral reveals microphenocrysts (0.05- 1.0 mm) of olivine, mostly Potassic alteration and normal faulting relationship they may intertongue, Both units represent deposits ot Crystal content and ratios vary considerably in this htff replaced with iddingsite, in an intersertal matrix of !abra C.uri7alillo Springs fault zone, respectively. Rocks in this Resources, Geologic Map 52, srnle 1:24,000. Clemons, R. E., and Seager, W.R., 1973, Geology of Souse Springs stream~channel svstems. owing, perhaps in part, to hydrothermal alteration or lack dorite-andesine laths, pyroxene{?), olivine, magnetite, and horst dip homoclinally northeastward approximately 10°. Recent papers have pointed out the widespread geo The limestone..:granite wnglomera te is best exposed in of it, to proximity to flmv-banded rhyolite masses (Tfr), and huther south, the Carrizalillo Hills consist of faulted rocks graphic correspondence between tilted rocks, low-angle (Juadrangle, New Mexico: New Mexico Bureau of Mines and glass. The fresh, slender, plagioclase laths are aligned in an Mineral Resources, Bulletin 100, 31 pp., 1 sheet, scale 1:24,0UO two patches north of NM-9. \Vhethtc'r thesP two outcrops perhaps to original compositional zoning. Total cryStal con excellent fluidal texture. Calcite fills most of the small (0.1- dipping generally northward c1pproximatcly 10°, although normal faults, and potassic alteration in the Rio Grande rift represent two beds or a single unit repeated by faulting is tent varies from approximately 40 to 55% of the ruff, av 0.8 mm) vesicles and forms a few interstitial patches. Chem there are also broad folds. The horstlike, lozenge-shaped and southern Basin and Range (Chapin and Glazner, 1983; DMton, N . fl., 1916, Geology and underground water of Lunc1 not clear, although a fault appears to separn!e the two out eraging approximately 45% (Table 2). Partly resorbed and Carrizalillo Hills uplift is bordered by two curved fault zones Lindley et al., 1983; Bartley and Glazner, 1985; Chapin and County, New Mexico: U.S. Geological Survey, Bulletin 618, 188 ical anillysis of this rock (Table 1) yields 32o/c Si02 and falls crops. At any rate, the conglomerate primarily consists of embayed euhedral to subhedral fragments (0.1-4.0 mm) of striking generally northwest: the Carrizalillo Hills fault zone I .indlcy, 1985). Bartley and Glazner (1985) show how hydro pp. in the tholeiite field of Ir-vine and Baragar (1971). Fenner, C. N., 1936, Bore-hole investigations in Y!:'lluwstone Park: cobble- to boulder- size dasts of Paleozoic and Lm·ver Cre qu.:irtz (0-6% ), sanidinc (l-9% ), plagioclase (22- 48<:'r ), and nn the southv.rest and the Johnson Mountain fault zone on thermal systems, the delivery system for potassic alteration, Above the basaltic andesite a sequence of volcanic fan Journal of Geology, v, 44, pp. 225-315. taceous(?) rocks, as well as coarse-grained, red Precambrian biotite (1.5 -- 3.5%) comprise the crystal population. An glomerate, conglomeratic sandstone, and sandstone (Tf), the northeast. The four m.ijor fault zones that outline the could modify regional stress trajectories in such a way that Elston, \N. E., 1957, Geology and mineral resources of Dwyer quad granite and substantial amounts of andesitic detrihts. Clas ts anomalous rock, thought to be tuff of Johnson Mountain probably 500-1,000 ft thick, dips gently northeastward ofi Cedar Mountams and Carrizalillo Hills converge and inter low-angle normal faults are initiated rather than high-angle rangle, Grant, Luna, and Sierra Counties, New Mexico: New range up to approximately 20 inches in diameter and arc but in intrusive contact with flow-banded rhvolitc (Tfr; the Cedar Mountains. These rocks are derived from the sect west oi Johnson Mountain, creating a zone of intensely ones. According to Bartley and Glazner (1985), high pore Mexico Bureau of Mines and Mineral Resources, Bull!:'tin 38, 86 well rounded and grain supported. In general, the con '.\JE 1/4NW 1 /4_\ 1\'V 1/~ sec. 21, T28S, R11W), contain's 27% sa·n basaltic andesite, as well as from all older local volcanic broken ground c1pproximately 1 mi'. Faults and fractures at pressure combined with a surface slope are required for the pp., 4 sheets, scale 1:48,000. glomerate and conglomeratic sandstone 1·ve<1ther to lo~v, idine and no plc1giodase, The rock is extremely altered, rocks. Unfortunately, they are poorly exposed except in n. this intersection are filled i,.vith quartz and carbonate, and formation of low-angle faults, the high pore pressure re Ferguson, H. G., 1927, Geology and ore deposits of the Mogollon boulder-strewn hills. Rare exposures reveal a reddish-brovv11 however. The groundmass in the tuff of Johnson Mountain few gully bottoms, but to the north ln the Hermanas N\V adjacent rocks are thoroughly altered and tilted at angles sulting from sealed geothermal systems. mining district, New Mexico; U.S. Geological Survey, Bulletin 787, 100 pp . color owing to abundant Precambrian detritus. In spite of is a cryptocrystalline to microcrystalline mosaic of minute quadrangle exposures are better and more frequent. of 15-90°. Locally, veins approach 50 ft in width; these have Although potassic alteration is well developed and wide the poor outcrops the conglomeraie and conglomeratic crystal fragments, magnetite-hematite, glass, and scarce, been the focus of precious-metal exploration in recent years. spread across the Carrizalillo Hills, the associated normal Gates, E. E., 1985, The geology of the Carrizalillo Hills, Luna County, A small plug(?) of basalt (Tb) apparently cuts the Tf fan New Mexico: M.S. thesis, University of Texas (.El Paso}, 133 pp., sandstone are moderately well cemented bv calcite. \·isible shards. Spherulitic wnes are common. Xenocrysts Although less intensely fractured compared to the four faulting is high angle without exception (>50°), and, except glomerate in the northeastern part of the map area. The 1 sheet, scale 1:12,000. Andesillc sandstone atld conglomerate l~raily underlies very locally, rocks are not strongly rotated (<15°). Thus, in the tuff have been altered to clavs and carbonate or ;ire plug contains sparse microphenocrysts {0.2-0.5 mm) of py fault intersection area, the Carrizalillo Hills block is thor Gile, L H., Hawley, J. W., and Grossman, R B., 1981, Soils and and is interbedded in the limestone- granite conglomerate empty cavities outlined by thin, blaCk, oxidized (magnetite roxene, plagiodase, and oxidized hornblende in an inter oughly dismembered by a pervasive fault system. The pat there is no one to one relationship between regions of po geomorphology m the Basin and Range drea uf southern New in exposures in Baker Draw, 1 mi west- southwest of Her hematite) rims. sertal, vesicular groundmass of plagiodase, pyroxene, tern of faulting is one of branching and anastomosing tassic alteration, strong strata! rotation, and low-angle nor Mexico-Guidebook to the Desert Project: New Mexico Bureau manas siding. Pink, pale-maroon, tan, pale-lavender, and FLOI.V· BA\JDED RH'r'OI.ITI (Tfr)-Three sizable flow-banded magnetite, and pale-brown glass. The blocky plagiodasc frachtres so that the whole system exhibits a braided pat mal faulting. Regions of extension characterized by high of Mines and Mineral Resources, Ml"moir 39, 222 pp gray mudstone, sandstone, and conglomeratic sandstone rhyolite domes or plug domes intrude rocks as young as laths are sodic labradorite. Pyroxene phenocrysts are pre tern. Faults typically enclose lozenge-shaped horst and gra angle faulting may also be the sites of potassic alteration Griswold, G. B., 1961, Mineral deposits of Luna County, New derived from andesitk volcanic rocks characterize the vol the tuff of Johnson Mountain in the Hermanas quadrangle dominantly hypersthene, whereas the ground mass pyrox ben blocks whose long axis may range from a fraction of a and their associated geothermal systems. In such areas, Mexico: New Mexico Bureau of Mines and Mineral Resources, canidastic rocks. Exploration trenches, open in summt>r uf Two plugs of rhyolite, one 0.4 mi in diameter and the other mile to several miles. "Whereas the overall trend of the braided however, the geothennal systems may not be sealed so that Bulletin 72, 157 pp., 10 sheets. ene appears to be mostly clinopyroxcnc. Hor11bkndc !n·ine, T. N., and Baragar, W.R. A., 1971, A Kuide to the chemical 1985 near the middle of sec. 21 , T28S, Rl 1\-V, revmled sim 0.2 mi in diameter, tramect the tuff of Carrizalillo Hills in phenocrysts may be xenocrysts, because they are partly fault system is N45°W, many segments of curved faults high fluid pore pressures are precluded, or surface slopes trend easterly or even northeasterly. may be negligible, or both. In any case, the Carrizalillo Hills classification of the common volcanic rocks: Canadian Journal ol ilar vokaniclastic rocks either overlying or faulted against the sou them and central Carrizalillo Hills, respectively. North resorbed and have thick oxidized borders of iron oxides. Earth Sciences, v. 8, pp. 523-548 rocks and structures argue against the notion that every the limestone-granite cobble conglomerate. of NM-9 a third intrusion has domed the tuff of Johnson Minor carbonate fills a few vesicles. In plan viev,, the geometry of the fault system is typical Lindley, J. I., D'Andrea-Dinkclman, J. F., Gla:>ner, A. F. and Os The section of limestone- granite conglomerate and as Mountain, which still remains as roof pendants and flank The basaltic-andesite flows (Tba) between Tfl and Tf are of strike-slip systems (Wilcox et al., 1973; Reading, 1980). region of potassic alteration is also the likely site of highly burn, G. R., 1983, Chemical ,md mineralogic variations assoc+ sociated vokaniclastic rocks is clearly underlain bv inter ing cuestas above the rhyolite. Also preserved on the flanks pctrographically and chemically similar to upper Oligo However, strike-slip faults are typically vertical or at least rotated rocks and low-angle faults. atcd with potassium mf'tasomatism of Tertiary volcanic rocks mediate-composition lava flows (rial ifl sec. 21, T28S~ Kll W. of this dome arc tuff breccia (Ttb) and megabreccia beds cene- lower Miocene lavas (29-26 m.y.) of the Uvas Basalttc steep, ,-vhereas fault surfaces in the Cedar Mountains and from the Rio Grande rift and Mojave Desert (..ibs.): Geological In sec. 22, T28S, RllW, the conglomerate is overl11in by (Tmb) interpreted to be the remains of a tuff cone. They are Andesite and Bear Springs Basalt (Elston, 1957; Clemons Carrizalillo Hills dip 50-80°. We found no evidence in the ECUNUM!C GEOLOGY Society uf America, Abstracts with Progrilms, v. 15, no. 5, p. 282. O'Neil, J. R., Silberman, M, L., Fabbi, 0. P,, and Chcslcrmc1n, C. rhvolitic and andesitic sedimentarv rocks. Near Johnson described in the next section. The rhvolite in these intru and Seager, 1973; Clemons, 1979; Seager et al., 1982). fur form of drag features, second-order folds or faults, slick Althou)a;h considerable prospecting in the Cedar Moun ensides, or offset rock bodies that might indicate more than iv., 1973, Stable isotope and chemical relations during miner M~untain, Tia lavas are succeeded ~pward by similar lime sions is delicately to coarsely flow baii'ded, locally stony or thermore, the basaltic andesitc of the Hermanas quadrangle tains, and especially Carrizalillo Hills, tvas done in the early stone-granite conglomerate and vokanidastic rocks con spherulitic, and ranges in color from gray to brown to yel a small component of strike slip. The faults in the map area alization in the Bodie mining district, Mono County, California is located near the base of a thick basin-fill sequence, as are pilrt of the century, very little ore was ever shipped. Darton Ernnomil Geoln?';y, v . 68, pp. 765-784. taining air-fall tuff and breccia, as ,veil as hvo intcrbedded low gray. The dome north of NM-9 is transected by a series all seem to be essentially dip-slip, high-angle normal faults. the l.lvas Basaltic Andesite (lower Santa Fe Group) and Bear (1916) notes that a small shipment of copper-rich ore with Ratte, f. C., and Steven, T. A., 1967, Ash flows and related vokanlc A Neogene age is based on the fact that the faults cut all ;mdesitic flows. Consequently, the limestone-granite con of basaltic-andesitf' dikes (Tbd). Springs Basalt (Gila Conglomerate). Consequently, we be c1ssociatPd gold was made from a Vt'in in the northwestern rocks ass:ociated with the Creede caldera, San Juan Mounh1ins, Oligocene(?) volcanic units, and some displace basal parts glomerate appears to mark a change from predominantl_v MECABRECCJA (Tmb) AND TUFF BRECCIA (Ttb)-Thc rhyolite lieve that the basaltic andesite of the southeastern Cedilr part of the Carrizalillo Hills. Griswold (1961) provides the Colorado: U.S. Geologlcal Sutvey, Professional Paper 524-H, 58 lava-flow emplacement (Tla) to deposition of volcanidastic dome north of NM-9 is surrounded on the east, north, and Mountains is roughly time correlative with the Uvas Basaltic (T.f/) of the overlying fanglomerate series. latest and best summary of mineral deposits in the Carri pp. rocks and relativelv minor air-fall tuffs and andesite flows northwest by a complex megabreccia (Tmb) and tuff breccia Andesite and Bear Springs Basalt. Furthermore, \•le corre zalillo Hills. He describes chrysocolla, millachite, and azur Reading, H. G., 1980, Characteristics and recogmtion of strike- slip Cl ts and Tah). , (Ttb) unit interpreted to be the remnants of a tuff cone late T~ and Tf with the bulk of the lower Santa Fe Group Cedar Mountains fault fault systems; in Ballance, P. F., and Reading, II. G. {eds.), Sedi ite associated vvith quartz, ca'rbonatc, and breccia veins in mentation in oblique-slip mobile zones: lnlemalional Association TUFJ·i\Cl·.OUS fl l'ICI.ASTIC HCJCKS, Hl{H Cl:\, FH FS H · V.·Arl ·. I{ created by the explosive emplacement of the rhyolite dome. and Gila Conglomerate, as did Balk (1962) in his mapping The Cedar Mountains fault zone borders the Cedar the broken region northwest of Johnson Mountain, gold of Sedimentologists, Special Publication, v. 4, pp. 7-26 LIMESTONE, AND l'\JTEr.:MEIJIATE.i-C:OMl'OSIT IOr-- f, J. O\'.'S (Tfs)-A The megabrecria overlies the tuff of Johnson Mountain and of the Tres Hcrmanas Mountains area. The basaltic pluh \fountains on the southwest where it has juxtaposed upper prospects located "just east of f fermanas and north of the varied suite of rhvolitic to andesitic volcaniclastic rocks with ;eager, W. R. , Clemons, R. E., Hawley, J. W., and Kelley, R. E., is unconfonnably overlain in the Hermanas quadrangle by that cuts Tf may be correlative with plugs, dikes, and cinder Tertiary fanglomerate (Tf) on the southwest against Oli highw.iy," which produced a few shipmf'nts of ore; and tlll' 1982, Gmlogy of northwest part of Las Cruces 1' x 2° sheet interbcddcd andC'site tlows and thin vitric ash-flmv tuff (Tl~! a basal fanglomerate (Tfl) of Gila(?) or Santa Fe type. Nu cones that crop out in the Tres Hermanas Mountains and gocene lavas (Tia) on the northeast. Exposures of the fault copper-beanng andesite at the Cillumet mine in the so11th (scale:1 :123,000). New Mexico: New Mexico Bureau of Mines and overlies the limestone-granile conglomerate (Tic) and in merous dikes and irregular musses of flow-ba11ded or de Palo mas basalt field a few miles east of the Hermanas quad <1re common in quadrangles west of the Hermanas quad crn Ci1rrizalillo Hills. Minenil Resources. Geologic Map SJ termediate-<:omposition lavas (I w). The unit crops out most vitrified stony rhyolite, presumably satellite bodies to the rangle. These latter rocks are 2.9-5 m.y. old (Seager et al., rangle. Stratigraphic separation may be approximately 2,500 ln rhc- C'Mlv to middle 1980's renewed interest in the di"' Seager, W. R., Shafiqullah, M., Hawley, J. W. , and 1\-larvin, R.. extensively in the highly faulted, veined, and altered region central rhyolite dome, invade the megabreccia. Agate-bear 1984), and they indicate that the bulk of Tf basin fill is prc tt in this area, with downthro•J to the southwest. Farther trict was trig"gered by favorable prices fur precious meL1l~ 1984, New K-Ar datt"s from basalt and the evolution of the south just northwest of Johnson Mountain, as \Veil as in the Im\ ing rhyolite masses, either intrusive or fragmented blocks, Plioeene. Tfl may range in age from late Oligocene to earJieq east, the Cedar Mountains fault enters the complex junction The intenselv veined and altered rocks ,)t the intersection ern Rio Grande rift: Geological Society of America, Bulletin, v. hills just northeast of Carrizalillo Springs and south of I kr also comprise part of the megabreccia, and some of these Miocene, whereas Tf is largely, if not entirely, Miocene of the four major fault zones and is not easily identified. of the four illajor fault zones vvere examined in detail b\· 95, no. 1, pp. 87-99. Smith, F. G., 1963, Physical geochemistry: Addison- Wesley, Read manas. Assembling a stratigraphic section from these out have been quarried extensively for their semiprecious stones We interpret the Tfl fanglomerates and Tba basaltic rocks V'r'e regard the major down-to-the-south faults on the north "'evernl companies. Trenches v,.,erc dug, samples analyLl'd crops proved difficult, so the section of Tis on the composite The megabreccia consists mainly of cobble- to room-size ing, Massachu!;Ctts, 624 pp. to record the onset of vigorous late Tertiary extension in i'rn side of Johnson Mountain and on the southern side oi detailed geologic maps prepared, and in 1984- 1985 tar,s;d \'Vikox, R. E., Harding, T. P., and Sedy, D.R., 1973, Basic wrench stratigraphic wlumn (.Fig. 3) is tentative and some,..;,hat dia blocks of tuft of Johnson Mountain and flow-banded rhv the Hermanas quadrangle and the Tfl and Tf fanglomerates the structurally high block cent~1ed on sec. 35, T28S, RllW areas Jnlk-d. Apparently the results of lhcsl' investigations kctoniGs: American Associ;ition of Petroleum GeoloJ.;:ists, l:lul grammatic. Total thickness may be 400-600 ft. olite embedded in a matrix of finer-grnined, pumiceous tl.lff to be the fill of a broad extensional basin that is no longe1 ;1s the probable continuation ot the fault zone into the Car- were encouraging a:, exploration continued into the sum- letin, v. 57, pp. 74-%.
TABLE !---Chemical analy,.es of selected vokank rolh lrom the Hermanas qual1rangk TABLE 2-Modal analyses nf ash-fl.o,... tuffs; av"eragc fmm 500 points counted on each of [WL) thin ~ctions.
Ttd Ttcl (middle) Ttcl (top) Ttl Tai (base) T"" Tl, Tia Tl, Tl, n, Tia Tj Total Rock Sample no. 84WSJ6 ~4WS1i 84WS7 34WS9 84\VS!O 84\VS l l 84WS22 84WS43 84WS44 84WS45 MWS46 84WS48 84WS14 84WS24 84WSl'.I Description Sample n11mber Q11artz Sanidine Pla11ioclasc Biotitc crystals Xenocrysts fragments Matrix Shards Ci>m7alillo Hills Cam2al1llo Hills Cam , al illo Hill.; Cam,ahlln Hills Camzahllo llilJ1 Cedar Mountains Cedar Mountains Cedar Mountain, Ce1 1 . , 1 Curri7alillo Hills Carri7alillo Hills NWl!,NE'-'• "IW !1NE1 ; , \/W •,.,NF Center Sl-' /, , Center NWL', NF•!,,.,~· ,;4 l\""Elt,NE•,4 SE •/,!il::1-'4 SE1 /4SE'i• NW 1!4SJ2 1.'4 SWL/4,.';EL,.,.. sw,:,NW•1., NE1;,~W'i• Mow1tain lTjl 84WS19 1.0 44.0 5 .0 50.0 2.7 47.3 scarce Center 1ec J5 , ,ec. 11. sec 1. ;;ec 11. sec. 2. ~~c 29, <;cc· . Center sec . 35 . ser 11. l sec. 3U. sec. 19, sec 19, 19. sec 35. sec 2, sec 34, 84WS34 6.5 26.7 1.8 3.'i {) 7.8 57.2 scarce Locali\!n T28S, RllW T28S, RJIW T29S. R I IW T29S. Rll'w T29S. R11W T2QS. RllW T29S, Rl!W T28S. Rl lW T28S, RllW T28S, RI IW T28S, RllW T28S, RllW T28S, RllW T28S, RllW l"28S . RIIW 84WS35 3 2 0.7 22.2 1.5 27 6 9.5 "tr 62.9 scarce Irvine 84WS37 5,7 5.9 28.J 4.1 44.0 0.8 55.2 none Baragar 84WS38 4.5 9.1 21.5 3 .7 38,8 6 1. 2 scarce tns1anne• trnch yha.,all • rhyde sit.: andes1cc andes1t~ alkali ha,alty trachybasal1 lr,,chyte* 84WS39 U.2 0.1 48.2 1.3 49.R :U 45.0 none SiO, 53 791 I 2.53) 57 .94{ -,. ~.9'1) 76.02( + 13 .31) 71 42( - ., _49) 71 4')1 - I 5'1) 70.5')( - 3 5]) 69.85( 8 90) 57.92 56.83 57.83 59.50 59.23 59.1(1(- 17 53] 53.08(- 12.40) 63 ,32(-3.91 ) 84WS50 2.0 2.4 0.4 2.0 6.8 5.0 0. 1 88.1 ~carre TiO, 0.56 0.89 0.20 0.23 0.23 0.28 O.Ji U.75 0.91 0.72 0.78 096 06(] 110 0.74 .",l:01 12.05 13.26 ll. 13 13.'fl 13 30 H .i2 15.06 18 .20 17.18 18 .28 16.47 l(i.41 nm l7 .28 15 68 Tuff of Carrizalillo 84WS1 I 2 9 5.7 14 1(),0 0.2 89.8 abundant re,O, j,l} 5.% 0.10 1.18 0.4 8 0.4D 1.44 4.35 4.26 3.49 1.40 3.13 _l .15 1.62 J 14 Hills (upper member; 84WS22 I.S 6.6 14 9.8 10.6 79.6 common FeO 06' 1.08 1.4~ OH, J 56 1 70 I.SI 1.20 l.52 2.33 4. 14 2.36 0.71 1.73 1.98 Tieu) 84WS22A 4.0 8.2 16 ns 8.2 78.0 abundant 0.29(+0.34) 0.1 7( +0.20) 0.02( - 0.02) 0.04(+004) 0.031 +0.o3) 0.03( " 0.031 0.03( I 0.0.ll M»O 0.09 om 0 09 O.UY O. lO 0 11(-0.09) 0.16(-0.14) 0.06( +0.061 84WS23 I 4 3.2 1.0 5.6 3.4 91.0 ahundam MgO o.~2( - o.551 D.33( 2.72) 0.29( -0.2\J 076(+0.43) 0.36( + 0.03) 0.41( , 0.02; 0.21(-0 )7 ) 3.96 ~.02 3.Q7 2.66 J.l l( 0.21) 0.57(-2.44) 2.JI U.61( - 1.411 84WS56 2.7 4.2 2.5 9.4 (,.4 84.2 cummoo c,o l0,20(+U4) 5.65( T J.13) 0.22( 1.52) 0.25( 1.30) 0.301 - 1. 27) 1.1 41,-0.55"1 0.16( - 1.651 6.45 6.45 6 72 5.l6 6.37 3.00( · 0.15) 7 91( + 2.07) o.s«~J.041 Na20 1.0J( -0.rn 0 .30(-2.57) 0.6& - 2 99) 0 47( 3.24) 1 281 - 2.44) (l.~4(-2 78"1 !.~8( - 2 59) 4.37 .H2 no 4.80 0.56( - 2.80) 2.96(-0 ..l.'J U.71(-2.661 Tuff of Carrizalillo K,O 649(+4.17) 11 .27{ -1- J0..)5) 7.89( - 4.81) 8.-12(+3.66) 9.231 I 4.97) 7.8ti( -,. .l..19) 10.21(+.'5 ZJJ 1.58 l.97 '°'1.55 2.74 2 62 l0.23( I 4 .78) 6.68( + 1.28) 12.67( +9.0S) Hills (lower member; P,O, 0 16 0.32 0.% 0.08 0.06 0.08 0.0'1 0.20 0 .27 0 .17 IJ.25 0.45 0. 19 0.22 0" Ttcn LOT 8.45 4.28 0.61 1.38 0 61 2.05 ().(,() 0.99 2.34 U.78 1.77 0.85 3.41 4.38 0.74 84WS7 9.6 l 1. 8 0.8 22 ~ H,O+ 0.43 0.10 0.4} 0 78 OAJ 0.26 0.32 1. 12 1.04 0 .23 0.10 0.39 l1.X9 U.22 0 25 77.8 abundant 84WS8 5.6 8.5 !.7 15.H " 0.3 83 .9 common total ., 04 !00.65 100.12 '19 .74 99 34 99.36 101.13 10! 18 W .80 IO(l.18 9~ 78 100 28 97.91 100 70 """ 84WS9 5.2 7.6 1.5 14.3 0.2 85.5 abundant 84\VSlU 6.5 16.5 SIL 81.7 7fi.45 86.83 87 ,'i I 87 4] 87.16 8/i.7.'i 84 .33 77.51 81.71 ,,, 1.6 24.6 8.6 66.8 abundam CP..I l0,1)4 l(d5 3. 76 :.94 JO<\ .D6 .U6 G.79 15.07 9 .97 upper part 84WS13 10.0 U.8 I.I 24.9 11.6 tr 63.5 abundant ALK 8.31 7.10 9.41 9 55 9 .53 9.48 9.39 8.88 7.42 8.32 base 84WS18 11 2 8. 9 0.7 20 8 3.1 0.3 75.8 abundant base 84WS55 9 6 14. 2 0.6 24.4 2.3 0.2 73.1 abundant fatima(ed precursor dacitc andc~i(C rhy\.llil~ rhyolitc rl,ynlile dac,tc-rh~olitc andcsne dKi(~ Lower rhyolitic 84WS16 4.5 0.9 2.3 7 .7 37.4 54.9 none ,ock ash-fluw tuff (Tti) "
~Rocks dc1cnnincd trom petrogrnpllic stmlie, to ht: ull~rclim1' or_altcrcd nx:ks _rdative to hypotheticJ! unaltered precursor rocks that have the ,ame Al,O,!Al,01 + wrnl tTABLE 3-Pelrugrnphic analyse~ of anPhenocrysts % Matrix composition Description Sample number Plagioclase Biotite Hornblende Pyroxene Olivine Total Plagioclase Biotite Hornblende Pyroxene Olivine Fe-oxides Carbonate Alteration Textures ----====------==------~----Basalt (Tb) 84\\.'S66 - - - --~-----~ none :l,6 near top of Tf ' ' '
Basaltic andesite (Toa) 84WS52 1.2 1.2 1race 2,3,6 between Tf and Tfl ' ' ' Andesile porphyry (Tap) 84WS40 23 .2 1.6 2.3 0.5 27.6 trace 84WS65 15.0 3.0 0.6 18.6 ' ' ' ' ' ' trace Basa!tic-anAndcsitc of Hcnna11as 84WS4l 0.5 0.5 mrn.lcratc 2.4 siding (Tah) 84WS54 3.Y ' ' 3.9 ' ' moderate 2.4 Intennediate-composition 84WS2~ 0.4 0.5 0.9 imense 5 flows (Tia) above Tic, 84WS29 4.0 4 .0 ' ' ' mlcnsc 5 Carrizalillo Hills 84WS31 74 7 .4 ' ' ' mtcnsc 2.6 84WS32 '> 54 ' ' ' ' mteme 1.3 84'WS33 8.8 ' ' ' ' ' ' ' ' mtcnsc 2.4 Intem1ediatc-composition. 84WS14 21.0 12 11.2 33.4 mtense 3 flows (Tla) below Tk, 84WSJ5 25.0 l.!1 7.4 33.4 ' ' ' intense ; Carrizalillo Hills 84WS21 18 .6 t.6 8.0 28.2 ' ' ' intense 3 84WS24 1.0 1.0 ' ' very mlcnsc 4.5 84WS2.'i 11.8 2.6 3.4 mtense 2,4,6 84WS26 1.0 I 0 2.0 ' ' ' intense 2.4 84WS30 0.2 10.8 11 .0 ' ' ' ' mtcnsc 2.4 84WS53 4.0 5.0 9.0 ' ' vay intense 2.4 84WS57 22.4 8.6 31.0 ' ' ' ' ' ' ' ' intense 1,3 Intermediate-composition oldest 84WS4J 14., 0.1 1.5 trace 1,3 Aows (Tla), southeastern 84WS44 4.6 ' ' ' ' trace [ ,J,6 Cedar Mountains 84WS45 26.0 J.5 27.5 ' ' ' Ir.Ke 1,3 84WS4(, 1.4 0.8 2.2 ' ' ' trace: 4.6 84WS47 ' ' ' trace 2,5,fi 84WS49 1.2 2.0 3.2 ' n,mL· 2.4,6 youngest 84WS48 4. 1 5.2 9.3 ' ' ' ' trace l 84WS17 ,, Lower andesite (Tai) U.8 13.8 ' ' mtcnsc 4
