Turquoise in the Burro Mountains, New Mexico

TURQUOISE IN THE BURRO MOUNTAINS, NEW MEXICO.

EDWARD R. ZALINSKI.

[The following notes are from data collected during the year •9o5 while the writer was superintendent of the Azure Mining Company's property near Silver City. It was his intention to make a detailed study of the subject, but this professional duties have hitherto prevented and in the following pages are presented the tentative conclusionsof an unfinished investigation.]

HISTORY AND LOCALITIES. Turquoiseoriginally came fr4m' Persia by wayof Turkeyand was importedby the Venetians,who called it Turchesa,of which its presentname is the French variation. In America it has long been known to the southwesternIndians and was used by them for ornaments and mosaic work. Professor W. P. Blake, in •858 and '59, called attention to its occurrence at Cerrillos, New Mexico, where it had been mined by the aboriginesand early Spaniards. This locality has producedsome valuable gems, but the mines are not at present worked. Turquoise has been found also at Turquoise Moun- tain, CochiseCounty, and Mineral Park, Mohave County, Ari- zona; near Columbus and near Crescent, in southern Nevada; in Fresno County, California; and in Colorado. In New Mexico, besides Cerrillos mentioned above, it is known at Hachiti; in the Burro Mountains, Grant County; and in the Jarrilla Moun- tains, Otero County. The modern discovery of turquoise in the Burro Mountains dates from •875, but these depositswere known to the Indians and were worked by them. Remains of ancient operationsare still to be seen, while stone hammers, implements and fragments of pottery have been found near the old excavations. The finding of turquoiseornaments and of old excavationsin the Burro Mountains led to the rediscoveryof the district. As 464 TURQUOISE IN NEW MEXICO 465 to whom the actual discovery is due, there is some dispute, but the names of John E. Coleman, W. J. Foley and Nicholas C. Rascome are all mentioned in this connection. John E. Coleman, known as "Turquoise John," while on a hunting trip in •875, discoveredthe old excavations. The first claim located was the Calllate. It covered the largest dumps and was supposedto be the best. _Asit proved later, the richest claims,the SantaFe andGem, now owned by the AzureMining

FiG. 5o. Index map showing position of the Burro turquoise district.

Company, had no prehistoricdumps to mark them. The con-. solidatedholdings were sold to C. Armeny, of New York, whc organizedthe Azure Mining Companyin •89•; the controlling- interestsbeing held by New York jewelers,chiefly L. and M. Kahn& Co.,and M. Rothschild,not Tiffany& Co.,as commonly reported. The property acquired for a small amount has since produced stones to the value of several million dollars. 466 EDWARD R. ZALINSKI

GENERAL GEOLOGY OF THE REGION. Little has been publishedregarding the geology of the district. The turquoise deposits are situated fifteen miles southwest of Silver City. The country rock in the neighborhoodof the minesis granite. Intrusive andesiteporphyry and andesite and dacite dikes also occur. Across the Mangus Valley to the east are sedimentary rocks: limestone, shale, sandstone,and quartzite. To the west lies the great eruptive region in the neighborhoodof Bullard's Peak. The Burro Mountains consistlargely of granite. On account of the main topographicfeatures they are spokenof as the Big and Little Burros. The Little Burros rise in a gentle slopefrom the Mangus Valley, and reach an altitude of 6,500 feet. The rounded and smoothsurface is cut by abrupt carlons. St. Louis Cation in the central part and Dead Man's Cation on the west show severalabrupt drops, and afford good exposures. The Big Burros rise from behindthe Little Burros to an altitude of approximately8,000 feet. The Mangus Valley at the Azure Mining Company'swell has an elevation of 5,900 feet, and that of the turquoisedeposits is 6,200 feet. The Big Bur- ros consistof three peaks with rugged slopes. The sedimentarybeds on the east of the Mangus Valley dip away from the main granite core. Fossils found here in the limestone and sandstone were sent to Dr. Geo. H. Girty, of the U.S. Geol. Survey, and proved to be of Cretaceousage. A specimenfound severalmiles to. the northeastbelonged to the Carboniferous. Dr. Girty says:

"The single specimencan with reasonablecertainty be called Carbon- iferous. It differs lithologically from the shells preservedin the red sandstone,being a silicified coral, and belongingto the genus Chcetetes,which is rather abundant at certain horizons in the Carboniferous of New Mexico."

The remainder of the fossils from the limestone and iron- stainedsandstone beds on the MangusValley slope,two miles from the Azure miningcamp, were identifiedby Mr. T. W. Stantonas belongingto the Upper Cretaceous.Mr. Stanton says: TURQUOISE IN NEW MEXICO 467

"The fossilsare not very well preservedand for that reason it is impos-' sible to make definite specific determinations, but the presence of the genera Ostrea, Inoceramus, Cardium, Mactra, Lunatia and Turritella, is sufficient evidence that the rocks are of Upper Cretaceous age and the specific types representedsuggest a horizon in the lower part of the Upper Cretaceous." The gentle and uniform dip of the strata is observedfor some distance. To the north the dip is not so pronounced. The over- lying strata have been entirely eroded from the Burros. The uplift took place after the Cretaceous,previous to the great volcanicactivity of Tertiary times. Following the uplift and doubtlessafter a period of considerableerosion, andesitc porphyry was intruded into the granite, and last of all andesitc dikes which cut the porphyry and also the sedimentaryrocks of the section. The last intrusionswere undoubtedlyof Tertiary age. Fracturing and mineralization accompaniedthe intrusions. Copper occurs over an area three miles east and west by two miles north and south. The turquoise-bearingsection adjoins this ground to the northwest and copper staining is found throughout the turquoisearea. The principal copperminerals are malachiteand chrysocolla. In the minesof the Burro Moun- tain Copper Company some high grade cuprite and chalcocite are found.

GEOLOGY OF THE TURQUOISE DEPOSITS. The Azure mining camp is situatedin the Little Burros near the summit of the Mangus Valley slopeat an altitude of about 6,2oo feet. Figure 5 I, a map preparedfrom a plane table survey, showsthe locationof the Azure mine and the geologyin the immediateneighborhood of the turquoisedeposits. Granite is the country rock and for somedistance surrounding the turquoiseit is much altered. The feldsparis mostly kaolinized, giving the rock a light grayishcolor, and {erromagnesian minerals--chiefly biotite--have almost entirely disappeared. The rock when fresh showspink orthoclase,quartz and biotite. The latter is not plentiful. When altered the feldspar is white and partly kaolinized and the rock has a porous and leached 468 EDWARD R. ZALINSKI

LEGEND

Biotitegranite Alteredgranite Mica-andesfl:e Mmaoandes•te Prospects porphyry dikes

SCALE •) ' ' ' • 5•0 1000 1300 •0•0 feet 5t. Geologicmap of the Burro turquoisedistrict, New Mexico. TURQUOISE IN NEW MEXICO 469 appearance. Under the microscopethe orthoclaseis cloudedand all biotite has been removed or Changedto chlorite. Quartz veinlets containing fluidal inclusionscut the rock in various directions.Of the accessoryminerals, apatite and zirconare common. At ofie place titanite occursin wedge-shapedcrystals of yellowish to brown color up to one-half inch long. Ap.lite and pegrnatitewere noted in Dead Man's Cation. I/eins.--Turquoise is found in a strong vein or fissuredzone

Fro. 52. Intersecting fissuresin Azure mine. whichstrikes N. 47ø E., anddips S. at 45ø ) It hasa well- defined foot and hanging wall, both of which show polished faces and evidence. of movement. The material between the •valls, however, is not entirely vein filling, but rather a much altered zone in the granite, containing soft spotsand streaks of nearly pure kaolin, also secondaryvein quartz resulting from the decompositionof the feldspar. All ferromagnesian minerals • The magneticvariation is I2ø 20; easton the Azure Mining Company's claims. Directionsgiven here and' on the map are magneticreadings.

TURQUOISE IN NEW MEXICO 47• have disappeared. The turquoiseoccurs only betweenthe two well-definedwalls, and for conveniencethis zone will be spoken of as a veih,though strictly speaking it is a shearedand altered zone containingvein material in places. Two setsof fissures,Fig. 52, cut this zoneand showplainly in the lessaltered portions. These strike in the samedirection as the vein. One set dips S. at 45 ø, parallelto the walls, while the other crossesthe first set and dips N. at 6oø-7oø. This fissuring is not local, but occursover severalmiles of surrounding country. It can be seenin Dead Man's Cationover half a mile to the south. The vein is 4o to 6o feet betweenwalls and is developedby four levels. An opencut has been driven from the secondlevel workings for a distanceof over 6oo feet. Fig. 53 gives an idea of the large amountof rock removed. The secondlevel is 7ø to 8o feet below the surface. On account of the extreme kaolinization and relative softness of the altered zone, the vein forms a marked depressionalong the outcrop. The granite for somedistance surrounding the vein is more or less kaolinized. The altered area extends about half a mile on the õoutheastto St. Louis Cation. On the south it is prac- tically borderedby Azure Cation, though some altered portions occur beyond this. Northeast from the open cut it extends about I,ooo feet to the contactwith the porphyry,and the granite along the contact is much kaolinized. Fig. 5I shows the altered area. Porphyry.--The rock which has been spokenof as porphyry belongsto the mica-andesiteseries, and has a closeaffinity with dacite. It is not a surfaceflow and has cooledrelatively slowly, though rapidly enough to have some glass in the base. It is a fine-grained,co.mpact rock, of light color, carrying quartz, often in abundant dihexahedral crystals, from one-quarter inch to three-quarter inches in diameter, with a pyramid and prism developedon some crystals, while others are simply the double pyramid. Phenocrystsof feldsparare alsopresent. The micro- scope shows the feldspar to be largely plagioclase. Biotite 472. EDWARD R. ZALINSKI occurs,and has beenpartly altered to chlorite. A small amount of glassbase is present. The' accessoriesare apatite and zircon. The porphyrywas intrudedinto the granite, evidentlyin the form of a stock, but the exact extent was not determined. The contactis irregular, the general directionbeing northwestand southeast. It crossesa • gulch about 800 feet northeast of the Azure camp and can be followed south past the prehistoric workings on the Callfate claim tO Parker's large open cut. See Fig. 5 t. Thence it can be traced across St. Louis Cation and up the east slopeto the Burro Chief claim of the Burros Copper Mine. The mine lies within the porphyry. The contact with the granite is Severalhundred feet to the. southwest; thence it crossesthe ridge and continuessouth toward the settlementof Leopold and the Burro Mountain Copper Company. A tongue of porphyry apparently entirely surrounded by granite is exposedat the head of a small gulch about 9oo feet east of the Azure mine. Along the contacthere, in the granite, are some prehistoric turquoise workings. Turquoisestains and in somecases small quantities' of the mineral may be observedat many placesin the altered granite, and some staining occursin the porphyry, but the gem has not been found in paying quantitiesexcept in the well-definedAzure vein. Dike Rock.--Both the granite and porphyry are cut by andesite dikes. These strike northeast and in a general way are parallel to the Azure vein. Morrill's Cation also has the same trend and is in direct line of strike with the open cut. It was evidently erodedalong the lines of the strong fissuring. Up to date little turquoise has been obtained on the southwestside of Azure Cation, though the continuation of the vein has been soughtat this point. The dike rock is gray where fresh and weathers yellowish brown. It showslarge feldsparphenocrysts in a' compactfine- grainedgroundmass. The feldsparis orthoclasein finely devel- oped crystalswith Carlsbad twinning. Zonal structure is fre- quent. Quartz occurs in dihexahedral crystals as in the por- TURQUOISE IN NEW MEXICO 473 phyry and biotite can occasionallybe seen. A feldsparcrystal obtainedfrom the large dike near Dead Man's Cation meas- ured 3 inchesby 2I• inches. The combinationwas that of base, prism, brachypinacoidand an orthodome. Thin sectionsshow that aside from the phenocryststhe pre- dominatingfeldspar is plagioclase. The biotite is much chlori- tize(3. There is more glass in the base than in the porphyry, but the general mineral contentis the same. Apatite occursin some quantity. The dikes and porphyry are evidently succes- sive eruptionsof the same magma. It is difficult to determine whether the rock is a mica andesiteor dacite, as gradationsfrom one to the other occur. In placesthe rock carriesorthoclase in suchquantities as to approachthe rhyolites. Both the dikesand earlier andesiteare porphyritic. For distinctionthe latter has beenspoken of as porphyry,while the formeris termedsimply dike-rock. Three main dikes have been traced through the Azure property and can be followed northeastand southwesto.n adjoining ground, in all a distanceof over •i• miles. On the southwest they cross Dead Man's Cation. Exposureshere show the dip to be nearly vertical. Northeast.they can be followed into Parker'sproperty and are lost under the Mangus Valley wash. Similar dikes from 40 to 9ø feet in width cut acrossthe sedimentary beds previouslymentioned. The two dikes south of the mine are about 50 feet wide, while the dike north of the Azure vein near Morrill's camp is, in places,90 feet or more. The dike farthest to the southeastforks at two points and again joins enclosinggranite betweenthe branches. This dike and its neighborintersect about •,5oo feet southeastof the Azure camp. A small horizontal displacementwas observedin the north dike which was.not to be found on the first, indicating that the southern dike is probablythe younger. The line of faulting is ap- proximatelyparallel to Dead Man's Cation and-the west side of the fault moved about 3ø feet to the north. A fourth andesite dike crossesSt. Louis Cation and ridge near the Burro Chief Copper.Mine, having the same general trend as the others. 474 EDWARD R. ZALINSKI

Some copperstaining occurs at ' variousplaces along the dike•, but no traces of turquoisewere found.

OTHER TURQUOISE OCCURRENCES IN THE BURROS. Turquoise occurs at three other points in the Burros and in theCow Spring district several miles to thesoutheast. It is found at Parker'smine, a shortdistance southeast of the Azure camp. The workings are near the contact of granite and porphyry, the prehistoricworkings all being in the granite. Quan- tities of rude stone hammers were found here. These were made of harder portionsof the altered granite and in somecases this rock even containedturquoise. They are of rounded form, four to eight inches or more in diameter, and were evidently used without a handle. Charcoalfound in the excavationssuggests that fire and rapid cooling may have been used in the primitive mining, the rocl• afterwards being broken in small pieceswith the stone hammers. Turquoise of good color and quality is found at Parker's, disseminatedthrough the altered granite. About three-fourths of a mile southeast of Azure, near the Burro Chief Copper Mine, turquoise is found in two places, one on the summit of the ridge in the granite, and the other northeast across a small gulch in porphyry. The material is not of gem quality. Maroney's turquoiseprospect lies near the Silver City road northeast of Leopold. The granite here is kaolinized and some translucent dark blue turquoise has been found disseminatedin the altered rock. This is of good quality, but limited as to quantity and size. A few miles southeastof the Big Burros, in the Cow Spring district, is another turquoise occurrence. The conditionsare of the same general character, turquoise being associated with kaolinized country rock. Some turquoisewas noted here in thin seams,though of good color. In every casethe turquoiseis associatedwith kaolin. It occurs in small quantities as nuggets, concretionsand veinlets irregularly distributedin the altered country rock, but exceptingon the Azure property doesnot occur in definite well-definedveins. TURQUOISE IN NEW MEXICO 475

THE AZURE VEIN. The Azure vein strikes N. 47 ø E. and dips S. at 45 ø. Tur- quoiseof good quality was found here on the outcrop. After the organizationof the Azure Mining Companyin •89•, devel- opment proceededthrough four adit levels driven northeast on the vein, and resultedin the productionof turquoiseequal if not superiorin quality to the best Persian gems. In •893, Mr. ' Felix Vogel, then superintendent,opened up the famous Eliza- beth Pocket, which producedmore high-grade turquoise than any single depositon record. The color was mostly deepblue and the material being slightly translucentand above6 in hardness,made ideal gems. The turquoisewas found in two forms --as vein turquoisefilling cracks in the altered granite and as nuggetsor concretionsimbedded in kaolin. Overten kilograms of the finest material, mostly nuggets,were producedin one month. The Elizabeth Pocket extended from the second level to the surface,a distanceof 40 to 60 feet, and the same quality of turquoisewas found for x5o feet or more along the vein. The distancebetween walls is about 40 feet. Some good turquoisewas developedon the third level and sparinglyon the fourth, but here turquoiseof the best quality was not plentiful and is associatedwith malachiteand chrysocolla. It appearsthat an excessof copper gives the material a green color and also decreasesthe hardness. Whether depth is an important factor in the genesisor formation of ideal tur- quoisecannot be determined,but at the presenttime all the fine turquoiseis found at depthsof •oo feet or less. Possiblythe formation of turquoisetook place at a definite temperatureand pressure,which may accountfor its limited vertical range. Turquoise occursas vein turquoise and nuggets. The vein turquoise fills cracks and fractures in the rock and is from one sixteenthup to three fourths of an inch in thickness. Most of it, however, is probably from one eighth to three eighths inches,but it has been found up to one and a half inchesthick. Vein turquoiseoccurs with rounded edges and corners resem- 476 EDWARD R. Z.4LINSKI bli,,g nugget structure. The nuggetsor concretionsare usually in the softer portionsof the vein and along seams,entirely imbedded in kaolin. They have various shapesand sizes--reni- form, botryoidal, etc., and make the finest gems. Vein rock from near the Elizabeth Pocket showed a medium fine to coarse-grainedstructure, traversed by a more than usual amount of quartz in veinlets and bands up.to one half inch or more wide; these are sometimesopen and contain cavities lined with quartz ,crystals. Vein turquoisesometimes contains small quartz crystalspenetrating the turquoise from the sides of the vein. Borderingthese qua•z bandsis kaolinizedfeldspar. The quartz often gives way to bright blue turquoise,which partly or entirely fills the vein or occurs in isolated specks. Vein turquoise is often separatedfrom the granite on one or both sides by quartz and also occursin direct contactwith the rock without quartz filling. Turquoise when intimately mixed with quartz is usually light blue and of even grain. Some portionsof the vein rock are lessaltered and occasional pink orthoclasecrystals are found. In material of this character bright blue turquoise occurs. No pyrite has been observedin the vein, thougha few cubicalcavities partially filled with limon- ire occurand the rock is frequentlystained brown by limonite. The x•einmaterial in placesis almostentirely changedto kaolin. It is here that some of the best nuggets are found. The characterof the turquoisevaries from place to placealong the vein and different kinds are also found closely associated. An exampleof this was shown by veinlets of blue turquoiseof different shades crossing each other. A light blue veinlet of turquoise,slightly greenishcast, was crossedby a blue vein. Turquoise must have been depositedat successiveperiods and under somewhat different conditions. Movement and fracturing occurredbetween the periods of deposition. Northeast of the Elizabeth Pocket the color was a good blue for somedistance, then came a point where blue and green tur- quoiseoccurred together, farther northeastthe green shadepre- dominated. This again changed to the blue with varying amounts of green. TURQUOISE IN NEW MEXICO 477

'Near the mouthof the 6pen cut on the eastor hangingwall side of vein, fissureswere found in which'bdth turquoiseand copperminerals occurred. These fissuresbelong to the copper bearing set and dip to th'e northwest. The •'ein dips to the southeast. In the vein where the copper-bearingfissures cross it turquoiseof bright blue color was found. See Fig. 54, which

Fro.54. Sketchõhowing relation o• turquoiseto fissures. is a sketch showing the relations of the fissures,turquoise, and copper minerals at this point. Following the same turquoise- bearing fissuresfrom the vein into the hanging wall and five or six feet away from the turquoise,the fissurescontain .malachite, chrysocolla,and black oxide of copper,in thin seams. This has passedthrough the vein and must.have been in excessof the copper which combinedto form turquoiseat this point. The turquoiseexists only in the vein and not in the hangingwall, showingthat where the coppercrossed the phosphatesolutions the turquoise was formed. The largestmovement occurred on thosefissures which were parallel to the vein. They are frequently found slickensided. On the copper-bearingfissures no slickensideshave been observed. The geo!ogicalmap showsa seriesof coppershafts and prospectsin the graniteon the southwestside of Azure Cation. These are along a copper-bearingzone parallel to the turquoisevein and on the west, or footwall, side. The chief copperminerals in these prospectsare chrysocolla,malachite. 478 EDWARD R. ZALINSK!

and someblack oxide, chrysocoll a being the mostplentiful. No pyrite or other sulphideshave beenfound in the immediateneigh- borhoodof the turquoisevein. If such existedthey have been oxidized. The footwall of the vein is colored red by hematite. From all appearances,however, pyrite was not plentiful. The only place in the entire neighborhoodwhere it was observed fresh and unaltered was in a copper prospecton the ridge near the Burro Chief. In a shaft sunk here for copper, near an andesitedike, someearthy varietiesof greenand blue turquoise were found. Vein quartztaken from the shaftShowed pyrite disseminatedthrough it in fresh cubicalcrystals, also occasional grainsof chalcopyrite.In the Burro Chief, a short distanceto the east, chalcochite,malachite, azurite, and chrysocollaoccur. Followingthe abovedike northeasterlyacross the Burro Chiel[ gulchis anotheroccurrence of turquoise,which is the one de- scribedby C. H. Snow.• The turquoiseforms a networkof thin light blueveinlets in the dike,which at this pointis greatly altered and showsa structure similar to diorite. The turquoise is not of gemquality. The countryrock here is porphyry.

MINERALOGICALNoTEs. Turquoise.---Thespecific gravity of turquoiseis givenas from 2.60 to 2.89. There is undoubtedlya marked difference between the hard translucentblue and soft earthy varieties. Its hardness is rated at 6 but the averageturquoise is probablyslightly less. Somespecimens of vein turquoiseare over6 and are scratched with difficultyby a knife blade. Turquoisebreaks with conchoidalor unevenfracture. The texture varies from the fine-grainedsubtranslucent blue to the soft chalkyquality. Radiatingforms occurresembling wavel- lite in structure. Almost all shadesof blue and green are found: dark blue, sky blue, light blue, slate blue, bluish green, greenishblue, throughall shadesof greento dark green,reddish brown (pos- •Am. Jour. Sci., •89•, Vol. 4•, PP. TURQUOISE IN NEW MEXICO 479 sibly from the separationof cupric oxide, or admixture with ferric salts), chocolatecolor, violet and purple. Some pieces show different shadesand colors in the same specimen. Blue and green are the most common colors though the latter is not usedin jewelry. Turquoisemay be evenly blue or mottledby darker spotsin a mass of uniform color. The latter is spokenof as mottled matrix. The spotsmay be large or smalland occasionallyasso- ciated with these are irregular wavy lines of darker turquoise material. Occasionallythe spots predominate,leaving little of the plain blue or green turquoiseto be seen. This variety occursin various shadesof robins' egg blue. As a rule mottled veinturquoise of goodcolor i• foundin hardrock. Nuggets are usually coveredwith a characteristicwhite skin or coating,which probablyconsists of aluminumphosphate, per- haps mixed with some kaolin. Nuggets sometimes contain quartz grains and includedvein matter; occasionallythey are of good color on the outside,but containa yellowishor whitish portion in the center, or vice versa. Halloysite.--A mineral having many of the characteristicsof turquoise,though as a rule of inferior hardness,is found closely associatedwith turquoise in the vein, and Clark and Diller, in their article on "Turquoise from New Mexico,"• mention a similar occurrencein the caseof the Cerrillosturquoise, but con- sider it as epidote. They say in this connection:

"One of the most important constituentsof the rock, becauseof its very close associationwith turquoise, occurs in the form of bright yellow grains, in all probability epidote. It is evidently connected genetically with the turquoise for it is almost uniformly found on the border of the latter and most abundant in its neighborhood."

This describesalmost exactly the material here considered. The mineraloccurs in vein form and as white or grayishnug- gets. Some of this material is hard and coveredwith a white coating similar to the best kinds of turquoise. An open crack in one of thesenuggets was lined with small crystals. They are xU.S. Geol. Survey,Bull. No. 42, 1.887,pp. 39-44. 480 TURQUOISE IN NEW MEXICO entirelycolorless and pbssessconsiderable luster. With a mag- nifying glass they are seen to be short hexagonalprisms ter- minated by the base. The crystals are too small for actual determination,but from mode of occurrenceand crystal form suggesta phosphate,possibly apatite. , Several large nuggetswere found in a seam with kaolin, on the foot wall side of the vein. One of these measuring3• inches by 2 inches by 2?5 inches was solid and compact. It could barely be scratchedwith a knife, had a light olive tint and was slightly translucent. The central part of the nugget was borderedby radial fibers about one-half inch long of the same material, but softer than the center. This was the largest nugget found. Others are of olive green and grayish shadesand vary from opaqueto translucent,with waxy luster. The white coating is the same as on the turquoise nuggets. More commonly the mineral occurs in bright green grains, or yellowish green when fresh. It crackson exposureto the air. Some nuggetswith the white skin coating when broken show the center to be bluish or greenishshading off to white near the border, and the reverse is also true. These are really a poor qualityof turquoiseand appear to be dueto an excessof aluminum phosphate. Besidethe regular blue and green turquoise,local variations in color and quality occur. The following specialtypes were noted: pale blue vein-turquoisewith a network of yellowish-. brown, hydrousaluminum phosphate streaks; dark-greenmot- tled vein-turquoisepassing into almosta chocolatebrown; blue- greenvein-turquoise bordered by quartzand thicklycovered by a network of reddish-brownhematite veinlets; green mottled turquoisetranslucent on edges; peculiarblue-white vein turquoisecontaining open cracksand darker streaks,evidently cracksfilled with turquoisematerial; turquoise of dark slate-blue color,in placesalmost purple, of fine,even grain, but not good for gemmaterial; irregularly colored vein-turquoise; pale green turquoisepassing to a darkpurple-blue, then gradually into light blue,and this separatedfrom light greenby a dark purpleband; TURQUOISE IN NEW MEXICO 481

bright blue vein-turquoiseenclosing and intimatelymixed with olive greenaluminum phosphate distributed throughout the turquoisein patchesup to onehalf inchin diameter;light-blue vein- turquoisecontaining yellow spotsof phosphate,quartz grains and darker veinletsof purple and blue parallelto the walls.

EFFECT OF KAOLINIZATION. Where the kaolinization of the vein rock has been greatest and the rock is soft, turquoiseis found mostly in nugget form. In moderatelyhard spotswhich show kaolinizedfissures, both nugget and vein turquoiseare found. Where kaolinizationhas been less completevein turquoisealone exists. Acrossthe face of the opencut, some600 feet from its mouth. are three distinct zonesof kaolinization. Beginning on the east at the foot wall side of the horse is a zone 5-6 feet wide which is soft and contains little solid vein rock. It appearsto have been the main zone of kaolinizationand the path of the heated vaporsand solutions. The boundaryis sharpon the eastagainst the horse of almost unalteredgranite, and a distinct boundary with the neighboring zone (zone 2) exists on the west. Zone 2 is partly kaolinized and containssome solid vein material. Both nuggetsand vein turquoiseoccur and it is consideredgood rock. This shadesalmost imperceptiblyinto zone 3, againstthe footwall of the vein. Zone 3 is hard rock and shows plainly the two setsof fissuring--seeFig. 52. All turquoisefound here is vein turquoise. In the fissurescutting acrossthe vein near the footwall the turquoise is frequently green and appearsto contain a large percentageof copper. Higher in the vein it changesinto blue. Above the horse along the hanging wall to a light blue. From this it would seemas if the coppersolutions rising through the footwall gradually combinedwith the aluminum phosphateto form turquoise,the coppercontent in the higher part of the vein being lesson this account. In all parts along the vein it is noticeablethat light blue turquoiseoccurs near the hanging wall. 482 EDWARD R. ZALINSKI

COMPOSITION OF TURQUOISE. The microscopicstructure of turquoisewas first studied by ProfessorFischer of Freiberg, and later by H. Biicking,• F. W. Clark and J. S. Diller,2 and D. W. Johnsorea In thin sectionsturquoise is pale blue to almost colorless. Under crossed nicols it shows a fibrous structure of doubly refracting particles. These, in vein turquoise, are usually at right angles to the walls, but also show a tendencyto collectin small radial aggregates. In some casesthe radial structure is absent. The crystal system of the mineral has not yet been determined. Material has been collected for a detailed microscopicinves- tigation of turquoise,and over a hundredrock sectionshave been prepared. These include all the chief types of turquoise,aluminum phosphate,vein material, unalteredgranite, and the andesite and dike rocks of the neighborhood. Turquoiseis a hydrousphosphate of aluminumand copper. The chemicalstructure is complex,and has given rise to differ- encesof opinion as to the r61e played by the bases,more espe- c.ially the part taken by the copper. The followingtable shows analyses of varioustypes of turquoise,and comprisesmost of the data now obtainableon the subject. The analyseshave been discussed in part by Clark and Diller.x Also by ProfessorS. L. Penfield,2 and later reviewedby D. W. Johnson? The table indicatesa fairly constantcomposition. The water is not hydroscopic,but exists in combination. The alumina is •" MikroscopischeUntersuchung des Tfirkis," Zeitschr. [. Krystallog., Vol. II., •878, pp. •63. 2Amer. ]our. Sci., 3rd set., Vol. 32, 1886,p. 211 and U.S. Geol. Survey, Bulletin No. 42, x887, pp. 39-44. • Contributions from the Geological Dept. of Columbia University," Vol. X., No. 9o•School of Mines Quarterly, •9o3. 4 ,, Turquoise from New Mexico," Bull. 42 U.S. G. S., x887,pp. 38-4L • "The Chemical Compositionof Turquoise," Am. ]our. Sci., 4th set., Vol. X., x9oo,pp. 346-50. 6 Geologyof the Cerrillos Hills, New Mexico, School of Mines Quarterly, x9o3, pp. 2o•-2o3. TURQUOISE IN NEW MEXICO 483

ANALYSES OF TURQUOISE.

i 2 3 5 8 9 XO

H20 •8.85 I9.80 I9.60 x8.49 I9.34 x9.98 I8.6o x9.38 I8.24 •8.59 A120s 29.17 37.88 4 ø- x9 35.98 35-79 35.03 34.32 42.17 Fe20a 29.57 39.5336-882.4 ø 4.07 2.99 3.52 1.44 P20• 4.04 31.96 32.86 28.63 32.86 33.2x 34.42 34. x8 28.29 29.43 CuO I2.57 6.30 7.5x 6.56 5.27 7.8o 7.67 8.57 7.4x 5.•o SiO., 4.35 I.I 5 0. I6 4.20 FeO 1.6! 2.21 o. 9I 4.5 ø CaO o.x 3 0.38 undet. 7.93 MnO 0.36 Insol 0.93 __ __ 2.73 Total xoo.•6 9• 99•9799•.83- 99•- Sp. Gr. 2.8o5 f 2.426 2.75 J 2.798 2.89 2.79 ' • 2.65I- •2.8x5- 99.83xoo.oo I. Cerrillos turquoise, Dr. Oscar Leow, I875. 2. Cerrillos turquoise, bright blue faintly translucent in thin splinters, Professor Clarke, U.S. G. S. 3. Cerrillos turquoise, pale blue greenish cast, opaque and earthy, Clark and Diller, U.S. G. S. 4. Cerrillos turquoise, dark green, opaque, Blake. 5. Persian turquoise, bright blue, Professor A. H. Church. 6. Fresno County Cal., G. E. Moore,--Pseudomorph after apatite. 7. Karalinsk in Kirghiz Steppes, Nikolaieft. 8. Lincoln County, Nevada, Professor S. L. Penfield. 9. Burro Mountains,--M. Carnot (Mineral Industry •896-x897). xo. Persia, M. Carnot. replacedin some casesby small amountsof ferric oxide and is relatively constant, as is the phosphoricacid. Cupric oxide varies from 4 to 8 per cent., and in bright blue turquoiseis about 5 or 6 per cent. Ferrousoxide was determinedin severalof the analyses,and M. Carnot, from his analysisof the Burro Moun- tain turquoise(No. 9 in the table), emphasizesthe fact that all iron occursin the ferrous form. Analyses Nos. 2-5, both of bright blue turquoise,show a marked similarity. In No. t, Dr. Leow separatedthe turquoisefrom the matrix, and says the large percentageof silica occurredin the gem itself. Analyses Nos. 2-3- 4 are discussedby Clark and Diller, who considerthe silica in No. 4 to be part of the gem, but in No. 2 to be due to mechanicallymixed rock with the turquoise. The latter analysis is not completeowing to lack of material. Under the micro- x Sp. gr. for similar specimens. 484 EDWARD R. ZALINSKI scopesmall grains of quartz are often seen entirely surrounded by turquoise,and it seemsprobable all of the silica in the analysis came from this source. Clark and Diller, from the analysesNos. 2, 3, 5, 6, 7 (omit- ting the analysisof the dark green variety, No. 4), calculatethe atomic equivalentsfor the combinedbases, phosphoric acid, and water, and find for these analyses that the atomic ratios are nearly constant. The base stands to the acid in the ratio of a little over 2 to •, and the water is present in the proportion of a little under 5 moleculesto one of phosphoricacid. By calcu- lating the amount of phosphoricacid necessaryto satisfy the alumina, and figuring that this phosphaterequires 5 molecules of water, they obtain the formula 2A12Oa, P205, sHoO. The copper,acid, and water remaining is then representedby 2CuO, Pe05, 4HeO, and the turquoiseis regardedas a variable mixture of thesetwo salts. They considerthe hydrous copperphosphate as the coloring material, but say it exists merely as an impurity. From the analysisof the dark green turquoise(No. 4) Clark and Diller refer the green color to admixture of salts of iron. They say, "It is exceedinglyprobable that the purity of tint in gem turquoiseis due to the coppersalt alone and that degradationsof the color towards green are ascribableto a mixture of salts of iron. It is noteworthy that of three turquoisesanalyzed, the bluest contains the lowest percentage of copper. This could hardly be the casewere not the colorsof the other samplesmodi- fied by someimpurities, and compoundsof iron would naturally producean effect in the observeddirection." It doesnot seem necessarythat green colors shouldbe due to an excessof iron alone. Blue turquoiseof poor quality often turns green by a chemicalchange in the coppersalt. ProfessorPenfield concludesfrom his own and other analyses that copperand small quantitiesof iron are necessaryconstitu- TURQUOISE' IN NEW MEXICO 485 ents of turquoise,and not present merely as impurities. This view is substantiatedby the physicalcharacter of turquoiseof varioustypes, and by its closelyassociated mineral the hydrous aluminum phosphate. This appearsto be turquoisewithout the coloring matter. When copper is present and colors or partly colorsthis material, it very much increasesthe hardness. This can be seenin the same specimenwhere turquoiseis surrounded or coatedby the phosphate,and in vein phosphateand turquoise which show gradationsfrom one to the other. From the phys- ical propertiesof turquoiseit appearsthat the coloring material, the hydrouscopper phosphate, is not presentas an impurity, but is combinedwith the hydrousaluminum phosphate,probably in variable proportions,producing turquoise of different qualities and colors. For a definitekind of turquoise,however, as in the bestquality of bright blue color, the componentphosphates seem to be com- bined in definiteproportions. This is shown by analysesfrom widely different localitieswhich agree so closelyin the essential componentsas to leave little chancefor any part of the material being includedas a mechanicalmixture or existing as an impurity. The coppermust be presentin molecularcombination. Several forms of turquoiseand varieties of the doubtful mineral were obtained for analysis. Through the kindnessof ProfessorJ. F. Kemp, of Columbia University, it has been possibleto have an analysismade of the bright yellowishgreen mineralwhich nearly alwaysaccompanies turquoise. The writer is also indebtedto ProfessorKemp for his interest and kindly criticism. The green mineral was thoughtto be a phosphate,but differs from the other forms in being muchsofter. A nuggetof this materialwhen fresh from the mine is about the consistencyof a hard candle and contains no grit. The bright greenmineral is difficultto obtainclean and contains some adhering particles of vein rock--largely silica and kaolin. It was taken fresh from the mine and kept bottled and corked. An analysisof this materialwas madeby M. K. Adams, 486 EDWARD R. ZALINSKI of Columbia University, to whom the writer is much indebted. ' It gave the following results-

ANALYSIS OF GREEN MINERAL. SiO2 ...... 4e.59 AhO8 ...... I9.7o Fe:O...... 2.46 FeO ...... o6 MgO ...... 63 CaO ...... 2.7I Na20 ...... 53 IGO ...... 20

H•O...... 25.36{ belowabove IO8ø 17.86 7.50 P205 ...... 89 MnO ...... oo TiO: ...... xI Cu (metallic) ...... 3.89 99. I3 It is difficultt$ interpretthis analysis which is not that of a hydratedphosphate. It is rather too high in silica and too low in dluminafor copper-stainedkaolin, beside which it contains ar;unduly large percentage of water--nearlytwice that of kaolin. The percentagesof silica and water correspondclosely to some analysisof halloysite,a hydrousaluminum silicate,which occurs in veins as a secondaryproduct. It has a waxy luster, is often translucent, and is found in granite, being derived from the decompositionof feldspar. Consideringonly the silica alumina and water, the analysis,though lower in alumina than most an- alysesgiven for halloysite,resembles the following one by Zell- ner• from Striegau in Silesia:

ANALYSIS OF I-IALLOYSITE. Si0 ...... 42.00 AI:0• ...... 20. I2 Fe•O, ...... 8.53 MgO ...... 2.oi CaO ...... 2.8I IGO ...... 50 H:O ...... 24.oo 99.97

The iron is somewhatlower than in this analysis. From its nearly uniform appearancein differentparts of the vein it would • XJahrb. Min., I835, 467. 'TURQUOISE IN NEW MEXICO 487 seem that the material has a definite compositionand is closely related to halloysite. The copper,if not essential,may be due to admixed silicate. On the other hand the coloring is uniform with no sign of copperstaining, and we may have a mineral which is a hydrous silicate of alumina and copper, instead of turquoise, the hydrous phosphateof these two metals. The writer is inclinedto take the latter view, but at the presenttime it is still an openquestion. He hopesto be able to give analyses of other forms of turquoise,and phosphatesin the future.

GENESIS OF TURQUOISE. Concerningthe genesisof turquoisea number of hypotheses have been advanced. The occurrences in different localities each seem to be under somewhatdifferent conditions. Most agree in this, however, that the turquoiseis closelyassociated with decomposedfeldspathic rocks in which the feldspar is considers- ably kaolinized. Also where turquoiseexists more or less copper occursin the neighborhood. At Cerrillos the country rock is an augite andesite. Professor Silliman• believedthe alteration of this to be due to the escape of heatedwater vapor and perhapsother vaporsand gaseswhich destroyedthe original crystallinestructure of the rock, and produced new chemical compounds. Of these turquoise was the mostimportant. The feldsparwas kaolinized and furnished the alumina,while apatite which existedin the Countryrock contrib- uted the phosphoricacid. The copper diffused in the veins of this region gave the turquoiseits color. Clark and Diller, also speakingof the Cerrillos turquoise, regardedit as having replacedveins of apatite. They say that the small size of the veins and their limited distribution show the turquoiseto be of local origin, and probablyto have replaced someother mineral; also that the perpendiculararrangement of the fibersin rock sectionindicate that the mineralma• have been derived from the alteration of another substance with which the vein was formerly filled. This substancewas presumablya •" Notes on the Turquoise of New Mexico," Am. ]our. Sci., July, •88•, pp. 67-7•. 488 EDWARD R. ZALINSKI phosphateand turquoisehas been known to form pseudomorphs after apatite. The coloring was due to copperwhich exists as an impurity. Johnsonin his thesis on the Geology of the Cerrillos Hills, New Mexico, discussesthe origin of the turquoisein somedetail. He says: "There is every reasonto believethat the crushedand shearedzones in the andesiteformed passageways for the active agentswhich effecteddecomposition." Tourmaline also occurs in the decomposedcountry rock and suggeststhe actionof escap- ing vapors,gases or waters. The kaolin from the feldsparfur- nished the alumina, and the phosphoricacid undoubtedlycame from the apatite. The latter was found in thin sectionsin the unalteredportions of the rock, but had disappearedin the neighborhood of the turquoise. Sectionsunder the microscopesug- gestedthat the turquoiseformed in the crevicesdirectly as one of the. various alteration products of the minerals constituting the country rock. The copperwas suppliedby the solutions which gave rise to the copper-bearingores of the region. John- son finds that "the intimate association of fluorite with the turquoise is very suggestive. The relations and appearanceare such as we shouldexpect if the turquoiseformed first leaving the fluorine of the apatite to make fluorite which later formed about the turquoise. The proportionof fluorite to turquoiseis also suggestiveof the proportionof fluorineto phosphoricacid in apatite." Pyrite, limonite,and quartz are the other accom- panyingminerals. The pyrite is occasionallyfound imbedded in massesof bright blue turquoise. Regardingthe genesisof the Burro Mountain turquoisethe following pointsmay be emphasized. The country rock in the neighborhoodis granite. Into this was intrudedandesite porphyry, and later andesitedikes. The turquoiseoccurs through an altered•area in the granite. The intrusion of the dikes un- doubtedlyplayed an importantpart in the alterationof this area, though the fissuringmay have been due to other causes. It seemslikely that the alterationwas producedat least in part by pneumatolyticaction. The dikes themselvesare extensively TURQUOISE IN NEW MEXICO 489 altered. Near Morrill's camp large orthoclasecrystals while retaining their outward form are almost completelychanged to kaolin. That the kaolinizationbegan along cracksand fissures is clearly illustratedin a specimenof granite, from near Dead Man'sCation, containing a mass of. pink orthoclase. Through this ran a small quartz filled vein, borderingon which the orthoclase was white and kaolinized, while a short distance from the veinlet it was fresh and unaltered. The strike of the Azure vein and the lines of fracturing and greatest kaolinization are in a general way parallel to the dikes. Hot solutionsor water vapor which may have ascendedthrough the crushedgranite and along the fissuresparallel to the dikes were probablythe active agentsin producingthe extensivekaoN linization. The Azure vein dips toward the center of the altered area and was evidentlyone of the main avenuesof the escapingvapors. Nearly all biotite disappearedand the orthoclasechanged more or less completelyto kaolin. The iron in the vein was leached to the footwall which is heavily iron-stained. Silica was set free during the operationand may have also been brought in by the solutionsrising along the vein. It was redepositedin cracksand fractures with the turquoise. The phosphoricacid was probN ably derived from the apatite of the granite. Whether it com- bined with the alumina of the feldspar in depth or where the turquoise was depositedis an open question. It appears that the aluminum phosphaterose along the vein in fissuresparallel to the walls, for in these fissuresit is most commonly found. The copper solutionson the other hand rose along another set of fissuresparallel to the vein, but dipping northwest at about 60 ø and crossingthe aluminum phosphate-bearingfissures. The solutions must have been contemporaneousand after kaolinization was well advanced. Where they intermingled turquoise was found. The gem is found along both the copper-bearing and aluminum phosphatefissures. On the footwall side of the ' vein, along the copperfissures, the turquoisein placesis greenish, probablyfrom an excessof copper. In the other fissures 49o EDWARD R. ZALINSKI the aluminum phosphateis sometimesin excess. Good quality of turquoiseoccurs along botff sets of fissuresand between them throughout the vein. As a rule little valuableturquoise comes in the porphyry,but it occursmostly in the granite not far from the contact. The influenceof the porphyry, however,in the formation of the tur- quoisemust not be overlooked. It was intruded into the granite with crushing and fracturing of the latter near the contact. This formed a more ready passageway for the solutionsand vapors which accompaniedthe intrusion of the dikes and con- sequentlythe granite along this zone was most kaolinized and altered. Fluorite was mentionedin discussingthe genesisof the Cer- rillos turquoise. It is presentalso in the Burros.' About 9oo feet north of the Burro Chief on the west slope of the Burro Chief gulch is a fluorite vein which can be traced some 2oo feet on the surface. The strike is N. 2oø E., and the dip 760 S. E. The fluorite is on the contact of the granite and porphyry, and the vein is from one to two feet wide. Both walls are altered and contain cavities often several inchesin diameter. The pre- vailing color of the fluorite is light green, but other shadesalso occur. It occasionallycontains cavities lined with the somewhat rare form of pinkish octahedralcrystals. Calcite is found in massesseveral feet thick along the hanging wall. The depositwas developedby an inclined shaft sunk on the vein connectingwith a tunnel from the gulch. Some of the spar was shippedfor fluxing purposes. An examination of a number of rock sections failed to show any isotropicmineral presentin the turquoisevein. The fluorite appearsto have collectedin the one vein above mentioned and depositedon the granite-porphyrycontact, which evidently formed a ready passageway for the solutions. This depositis approximatelyat the same level as the turquoisein the Azure vein, and in depth the fluorite narrows and thins out, while copperminerals, malachite and chrysocolla,are more in evidence. An hypothesisis a tool, which may be used till a better one TURQUOISE IN NEW MEXICO 491 is found. The view that turquoisewas formed by solutionsrising along two sets of fissures,one of which brought the phosphoric acid and causedthe kaolinization, and the other coming from the footwall of the vein bringing the coppercomponent, led to the developmentof turquoisewhich had been passedby for years. Near the mouth of the open cut the footwall of the Azure vein slickensidedand iron-stained,and looksto all appearances the same as the remainder of the footwall. Close examination, however, showed it-to be more kaolinized. If the solutions, gases,etc., causingkaolinization brought the hydrousaluminum phosphateand the coppercame in through the footwall therewas every reason to expectturquoise .would be formedhere. This proved to be the case. The first round of shotswhich was put in this ground gave on the clean up three buckets full of bright blue Elizabeth quality turquoise. The true footwall of the vein was found somefifteen or twenty feet back of what had formerly appearedto be the footwall. This ground furnished desirable material. Movement occurredafter the turquoisewas formed and the gem was depositedat successiveperiods and possiblyunder different conditions. This is shown by faulted veinlets of turquoiseand by veinletsof different shadesof blue crossingeach other, also by cracksin the turquoisefilled by a later genera- tion of turquoiseof darker color.

TREATMENT OF MATERIAL. The turquoiseas it com•s from the mine passesthrough a sorting house and is shipped in x5o-poundcases. The best quality is sent in sealedcans. Turquoiseis usuallycut en cabochon,or ellipticalwith a low convex surface. It is also cut marquis, which is pointed at both ends. The most salablesize is from 5 to xo millimeters longestdiameter, and the standardshape is oval and of medium height. A stoneof this form 5 mm. long will weigh about 3• of a carat; one xo min. longestdiameter from 2 to 2½ carats. The material is cut from 2 min. up to 25 mm. in size, often 492 EDWARD R. ZALINSKI larger. Turquoise is sold by the carat, and ranges in price from $6 to $25 and higher, $15 a carat being perhapsan aver- age price for turquoiseof good color and quality. Mottled turquoise known to the trade as "mottled matrix" and also the regular matrix, i.e., turquoiseand enclosingrock, are popular and bring various prices. The Burro Mountains at the present time produce most of the turquoise mined in the United States. It is said to equal, if not excels,the gemsfrom the celebratedPersian minesat Abu Riah and Nishapur. The demandexceeds the supply.

The following referencesto the literature may be of use to any one interestedin the subject: "The Chalchihuitl of the Ancient Mexicans." W. P. Blake, `4rn. Jour. Sci., Vol. XXV., •858, pp. 227-232. "Observations on the Geol. of the Rocky Mountain Chain, in the Vicinity of Santa Fe, New Mexico." W.P. Blake, Pro- ceedings.4..4..4. Sci., I859, PP. 314-319ß "Observationson the Mineral Resourcesof the Rocky Mountain Chain near Santa Fe, New Mexico." ProceedingsBoston Soc. Nat. History, I859, pP. 64-7 o. "Notes on the Turquoise of New Mexico." Prof. Benj. Silliman, .4m. Jour. Sci., July, •88I, pp. 67-71. "Turquoise from New Mexico," Bull. 42, U.S. G. S., pp. 39-44- .4m. Jour. Sci., Vol. XXXII., I886, pp. 221, F. W. Clark and J. S. Diller. "The Chemical Compositionof Turquoise." Prof. S. L. Penfield,.4m. Jour. Sci., Vol. X., i9oo, pp. 346-35o. "Report of Chief of U.S. Engineers," I875, part ii., pp. •o27, Dr. Oscar Loew. "Mineral Resourcesof the United States," •891, pp. 544- "Turquoise in SouthwesternNew Mexico." C. H. Snow, .4•n. Jour. Sci., 189•, pp. 5•1, vol. 4•- "New Mexico Mines and Minerals," I9o4. F. A. Jones, pp. 267. "Geology of the Cerrillos Hills, N.M." D. W. Johnson. School of Mines Quarterly, •9o3 .