in the Bio Grande Valley, New Mexico. 63 



stone." Just below this bed in the Graphic and Kelly mines 

 are located the most important ore bodies, in following which 

 the stratum furnishes a convenient guide. The beds dip from 

 30° to 40° south 65° west, and have been affected to a notable 

 degree by faulting. The area! extent of the Kelly limestone 

 is limited, being confined so far as demonstrated to the Magda- 

 lena region. 



Ore deposits in the Lake Valley Limestone. — The -discovery 

 of ore at Lake Valley was made by a cowboy in 1878 While 

 tightening the girth of his saddle his attention was attracted 

 by a peculiar piece of stone whose weight surprised him. On 

 having it assayed it proved rich in silver. The fame of the 

 discovery soon spread and the district quickly became noted as 

 a producer of silver. At present no ore is being mined, opera- 

 tions having practically ceased in 1894. 



The best description published of the nature and occurrence 

 of the silver ores of Lake Valley is that of Clark in the paper 

 above cited. He classes the ores as (1) siliceous, (2) neutral, and 

 (3) more or less basic. They occur chiefly along the bedding 

 plane between the blue limestones and the overlying shaly beds 

 at the base of the crinoidal limestone formation. 



The ores consist principally of gray, brown, chocolate, pearl, 

 and green flints, the last named usually \i elding a grade of ore 

 higher in silver than the other colors. The richest ore bodies 

 occur in cavities of varying size containing galena with massive 

 crystalline structure, and sometimes in the form of a pulver- 

 ulent mass known locally as " grey metal." The largest of 

 these ore cavities, called the Bridal Chamber, produced about 

 2,500,000 ounces of silver. Manganese and iron oxide have a 

 variable but usually prominent development as accessory min- 

 erals, while the silica content ranges from 5 to 60 per cent. 



The form and relations of the deposits and their occurrence 

 in pockets and as a siliceous replacement of the limestone along 

 the contact with overlying shales strongly suggests their origin 

 from ascending hot solutions. From the nature of the region 

 the presence at no great distance of an intrusive igneous body 

 from which the solutions come may be safely predicated. 



The region is one of extensive volcanic flows, to the erosion 

 of which is due the limited areas of sedimentary rocks exposed 

 in the vicinity of Lake Valley and northward along the slopes 

 of the range. The earliest of these eruptions consisted of 

 andesite, which occurs resting upon the eroded surface of the 

 sedimentary formations. 



Ores in the Kelly Limestone — At Kelly the ores occur 

 at several horizons along the bedding planes of the Carbonif- 

 erous formations, the principal deposits, however, being 

 found within the Kelly beds just below the " Silver 



