Placergold deposits in New Mexico byViginiaT. McLemore, New Mexico Bureau ot Minesand Mineral Resources, Socorro, New Mexico 87801 Abstract posits (Boyle, 1979,1987): eluvial, alluvial, and aeolian. Eluvial deposits occur in Thirty-six mining districts in New weathered detritus at or near the outcrop Mexico contain placer gold deposits. of gold-bearing lode deposits. Alluvial de- Production from thesedeposits began as posits occur in the sands and gravels of first gold early as 1828,resulting in the deltas. Al- produced from placer deposits through- westem States;how- streams, rivers, beaches,and rush in the United from 1828 to 1991 (up- ever, minor production by Pueblo In- luvial deposits are further subdivided into out New Meico dians and Spaniards probably occurred classesby Wells and Wootton (1932):hill- dated fromJohnson,1972). This production 200 or more years earlier. Most placer side (valley slopes not in discrete chan- is insignificant compared to larger placers deposits were discovered by 1900,and nels), gulch or creek, bench or terrace, found in Alaska, California, New Zea- almost all placer production occurred river-bar, gravel-plain, and buried plac- land, and South America that contain mil- before 1902.It is estimated that 662,000 ers. The aeolian deposits accumulate in lions of ouncesof gold. Only four districts oz of gold were produced from New windblown sand deposits and are rela- here have yielded more than 100,000oz Mexico placer deposits between 1828and tively minor and unimportant. Most of of placer gold production: Elizabethtown- 191. The deposits typically are found the gold deposits in New Mexico are al- Baldv, Hillsboro, Old Placers, and New in late Tertiary to Recentalluvial or elu- only one district is vial deposits; alluvial fan deposits, bench luvial deposits, but some eluvial deposits Placers. Currently or terrace deposits, river bars, strearn are found in many districts. There are no yielding some minor production (White concentrations,and residual placersthat known aeolian gold placer deposits in New Oaks) although small exploration activi- formed directly on top of lode deposits Mexico. ties and recreationalgold panning are oc- are known. New Meico placer gold de- This report presentsa summaryof con- curring in most areas of the state. G posits are derived from Oligocene-Mi- tinuing research on placer gold deposits Margin deposits, ocene Great Plains in New Mexico. Johnson (1972)published Laramide vein deposits,and Proterozoic one of the most comprehensive compi- in highly vein and replacementdeposits placer gold de- Alsoin thisissue weathered and eroded terrains. The fu- lations of information on the ture potential will depend on discovery posits in the state. This study updates (new), work by (1972) and North and Oso RidgeMember of large-volume, low-grade deposits. fohnson Abo Formation, Also, new technologiesminimizing wa- Mclemore (1986, 1988)and incorporates p.26 ter may stimulate activity becauselack additional field observationsand other data ZuniMountains of water has hampered production in from published and unpublished reports. JeffreyA. Grambling many districts. Thirty-six mining districts containing (1953-1993) p. 31 placer gold deposits in New Mexico are Introduction located in Fig. 1 and are listed in Table L NMGS1995 field conference papers p.34 A placer deposit is any natural accu- with year of discovery and production, if mulation or concentration of a material in known. Thesedistricts are arrangedin or- NMGS1994 Spring Meeting from unconsolidated sediments of a stream, der of estimated total production abstracts p. 35 bench, or residual deposit. Four condi- placerdeposits. tions are usually required to form placer NMGS1994 Field gold deposits (Boyle, 1979, D8n. A source History and production Conference p.37 terrain must crop out, usually containing The first known production of placer Upcomingmeetings p.37 gold-bearing lode deposits or dissemi- gold in New Mexico was in 1828 in the nated gold. The source terrain must be Ortiz Mountains in SantaFe County (Old Geographicnames p.37 exposed to mechanical and chemical This discovery resulted Placers district). Service/News p. 38 weathering for a fairly long time. The free in the first gold rush in the westem United gold is concentrated, typically by gravity States (|ones, L904),predating the Cali- MineralMuseum notes p. 38 and water. Finally, the deposit must be fomia gold rush by 20 years. Before 1828, preserved. Pueblo Indians and Spanish explorers en- Staffnotes p. 39 Placer gold deposits are a result of the gaged in some mining activities, espe- Topographicmaps p. 39 physical and chemical properties of gold. cially for turquoise. Undoubtedly, some Gold is relatively heavy (specific gravity placer gold was recoveredas well (Jones, Gomingsoon of 19.3) and is easily concentrated by grav- 1904;Johnson, 1972).Placers along the Rio ity with the aid of water. Gold is resistant Grande valley were reportedly worked in Pliocenemicrofossils from to corrosion and chemical ofdation and 1600,but total production is unknown and therefore can be transported long dis- presumed small (fohnson, 1972). MonticelloPoint maar tances after being freed from the source Placergold deposits were an important Largeexogyra from Dakota rock. The bright color, luster, and softness sourceof gold in New Mexico before 1902, enable easy identification by prospectors. but placer production after 1902has been Sandstone There are three types of placer gold de- rninor (Table1; Johnson, 1972). Most placer Lack of water has hampered produc- Geology pyroxenes, pyrite, zircon, garnet, rutile, tion of placer gold deposits in New Mex- All known placer deposits in New Mex- and other minerals. The gold-bearing ico. The Big Ditch was built in 1869near ico occur in late Tertiary to Recent rocks gravels at Pinos Altos have as much as Elizabethtown to divert water from the and occur as alluvial-fandeposits, bench 4frVoblack sand containing 83Vomagnet- Red River to the placers, a distance of 41 or terrace gravel deposits, river bars, ite, 37ogarnet, 2Vohematlte, and,0.45ozl mi (Wellsand Wootton, 1932;Bauer,1990). stream deposits (alluvial deposits), or as ton gold (Wells and Wootton, 1932).The Large-scaledredges have been operated residual placers formed directly on top of ore typically occursas narrow pay streaks, with limited successin only-(1901-1903), a few dis- lode deposits typically derived from Prot- zones, or layers of fine-grained, dissem- tricts: Elizabethtown-Baldy erozoic, Cretaceous,and Tertiary source inated gold, locally on top of basement Hillsboro (1935-L9A), and Pinos Altos rocks (eluvial deposits). During fluvial rock, clay, or caliche lenses in gravel de- events, large volumes of sediment con- posits. The best placer gold is found near taining free gold and other particles are the baseof gravel deposits where the gold transported and deposited in relatively is trapped by natural processessuch as poorly sorted alluvial and stream depos- riffles in the floor of the stream, fractures its. The gold is concentratedby gravity in either in the bedrock or along bedding or panning (Figs. 2, 3). In some areas, incised stream valleys and alluvial fans in foliation planes, and structures that are trenches, short adits, and shallow shafts deeply weathered highlands. Most placer transverseto the stream flow. Gold is also were dug along the pay streaks(Wells and gold deposits in New Mexico are found concentratedabove cemented gravels and in streamsor arroyos that drain gold-bear- clay layers in the gravel deposits, which ing lode deposits,typically as quartz veins. constrain downward migration of gold The lode deposits range in age from Prot- particles.Most depositsare thin and less erozoic to Laramide to mid-Tertiary (Ol- than 55 ft below the surface (Lindgren et igocene-Miocene)(Table 2). Thereare some al., L970;Johnson, 1972),bat thicker de- Various methods employing little or no alluvial deposits distal from any obvious posits occur in the Elizabethtown-Baldy water have been utilized periodically, but source terrains (Table2). Eluvial deposits district (as thick as 300ft; Wells and Woot- few if any of these operations were suc- are common in many districts; some of ton, 1932) and in the Rio Grande valley cessful. These and other techniques of the larger deposits are in the ficarilla dis- district (as thick as 1100ft; fones, 1904). mining placer deposits are described by trict. Native gold and electrum occur with Unfortunately, past development of most West (1971). quartz, magnetite, ilmenite, amphiboles, placers in New Mexico is undocumented, New A4exnco GEOLOGV o Scienceand Servicc tssN 0196-94AX Volume 16, No.2, May 1994 \i---J _l Editor:Carol A Hjellming Published quarterly by New Mexico Bureau of Mines and Mineral Resources a division of New Mexico lnstitute of Mining & Technology BOARD OF REGENTS Ex-Officio Bruce King, Gwrnor of Nru Mexico Alan Morgan, Supaintendentol Publiclnstruction Appointed CATRON Diane D Denish, Prcs,1992-1997, Albuquerque Michael Kelly, SeclTreas 1992-1997, Roswll Mls, J , '':o""urF" I LINCOLN Lt Gen Lo Marquez, 1989-195, Albuquqque ur" Steve Torres, 1991-197, Albuquerque CHAVES Charles Zimmerly, 1991-1997, SNoft o New Mexico lnstitute of Mining & Technology -1 a Roswcll Preident David H L6Dez SIERRA New Mexico Bureau of Mines & Mineral Resoures Directorand StateG@logist Charles E Chapin I 2 Sub*tiptim: Issued quarterly, February, May, August, November; subsription price $6 o0/calendaryear Editorial mttq: Articles submitted for Dublication EDDY should be in the editor's hands a minimum of five (5) months before date of publication (February, Carlsbod May, August, or November) and should be no longer a than 20 typewritten, double-spacedpages All oTERo O€laware scientific papers will be reviewed by at least two E9 Eaaln people in the apprcpriate field of study Address inquiriG to Carol A Hielmin& Fditor of Nru Meriq Ceology,New Mexico Bureau of Mines & Mineral Resources.Socono. NM 87801-4796 Publishedas public domain, thereforercWoducible uithout wrmission Soure crcdit requested Cilculation:l,6N 20 40 60 80km Printer: U^ivercity of New Mexico Printing Services FIGURE l-Placer gold deposits in New Mexico.