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 sub- ject, 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 south- west 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 spots and 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 fissur- ing 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 kaoliniza- tion 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.

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