Page 61 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

60 GEOLOGY AND ORE DEPOSITS OF SIERRA CO., N. M.
county. From the north border of the county nearly to Kingston, the Magdalena (Pennsylvanian) limestone is a prominent feature of the east face of the range. Here a continuous succession of faulted blocks of this formation, having gentle dips to the east, for the most part, form the foothills. In the Black Range mining district, which extends from the north border of the county to Bear Creek and the old town of Robinson, an isolated block of this limestone, with dip to the east, projects through the Tertiary flows of the region. It is in or near this exposure that the ore in this area has been found, and along the east border of which the old mining camps of Fluorine, Phillipsburg and Grafton were lo- cated. From Robinson south the faulted limestone blocks consti- tute the east foothills of the range. Through this same area, for 6 miles or more south of Chloride, faulted blocks of Permian strata lie to the east of the Pennsylvanian blocks. These consist principally of Abo sandstone of deep red color and subordinately of the Chupadera formation. At Hermosa the Magdalena lime- stone is much faulted, although displacements are small and dips are very slight. From 6 miles north of Kingston to a point 9 miles south, the entire sequence from the pre-Cambrian granite to the Tertiary flows can be seen, as the east face of the range has been broken by a series of north-striking faults, with a total dis- placement of 1,000-1,500 feet. Farther south the Paleozoic beds gradually disappear under a cover of Tertiary lavas. Alluvial fans form a prominent feature of the east slope of the Black Range.
INTRUSIVE ROCKS
Intrusive rocks are not observed farther north in the Black Range than Kingston, although their presence may be inferred at Chloride, where in two localities the sedimentary beds are slightly arched, and roughly radial groups of mineralized frac- tures are found. At the Midnight mine in the Apache (Chloride) district, the vein, which is in limestone, contains abundant contact-metamorphic minerals, indicating igneous rocks not far below. At Hermosa, Gordon 27believes that igneous rocks lie at no great depth below the ore bodies of that district, and that ore solutions have risen from them to precipitate their mineral load in the Magdalena limestone. A small dike of diabasic rock cuts the Magdalena limestone high up in the north wall at Palomas
Creek.At Kingston a dikelike mass of monzonite porphyry has cut through the Paleozoic sediments. This mass is at least 400 feet wide just west of the town of Kingston, and can be traced two miles to the north and to the south about the same distance. South of Kingston it is more irregular in shape and occupies a considerable area. Although Gordon28calls this mass a dike, the
2827ordon, C. H., op. cit. (U. S. G. S. Prof. Paper 68), p. 268. a.T4'In nif(TTgaCProfPsarlorAR1rt9g,1