Page 48 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

GENERAL FEATURES
requirement of 2 ounces per shipment would be greatly reduced, thus permitting the prospector to make more frequent shipments and to deal directly with the Mint, where the maximum price is paid.
ORE DEPOSITS
GEOGRAPHIC DISTRIBUTION
The known ore deposits of Sierra County are confined en- tirely to the mountainous areas. Along the east slope of the Black Range an almost continuous belt of mineralization extends from the northern boundary of the county in a southerly direc- tion to beyond the Tierra Blanca and the Carpenter mining dis- tricts. A second group of mineralized areas starts near the northern boundary of the county north of Fairview and con- tinues with several breaks southward through the Sierra Cu- chillo, the Hillsboro area, and to the Lake valley end Macho dis- tricts. The third belt of mineralization is still less continuous and extends from north to south through the length of the Fra Cristobal Range and Sierra Caballos, probably the only area of any importance being that around Hot Springs and Palomas Gap, south of the Elephant Butte Dam.
GEOLOGIC DISTRIBUTION OF DEPOSITS
In his discussion of the ore deposits of New Mexico, Lind- gren21 classifies them under nine main headings, and his general remarks regarding the deposits of the State apply in large meas- ure to those of Sierra County. Lindgren's classification is as follows: (1) Pre-Cambrian deposits, (2) Contact-metamorphic deposits, (3) Veins connected with intrusive rocks of early Ter- tiary age, exclusive of replacement veins in limestone, (4) Cop- per deposits due to oxidizing surface waters, (5) Veins and re- placement deposits in limestone, exclusive of contact-metamor- phic deposits, (6) Veins connected with volcanic rocks of Ter- tiary age, (7) Lead and copper veins of doubtful affiliation, (8) Placers, and (9) Copper deposits in sandstone.
No ore deposits are known to exist in Sierra County that are of pre-Cambrian age, nor are there any known to be of later age but localized in the pre-Cambrian complex. The gold of the Pittsburg (Shandon) placers was probably derived from the pre-Cambrian basement of the Sierra Caballos, and is discussed in connection with those deposits.
The iron deposits in the north end of the Sierra Cuchillo are of the contact-metamorphic type, and so also are the lead- zinc deposits and the copper deposits somewhat farther south in the same range.
21Lindgren, Waldemar, op. cit. (U. S. G. S. Prof. Paper 6 I. pp. 47-49.