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Long-Term Monitoring Of The Geochemistry Of Surface Water And Stream-Sediment Samples From The Upper Pecos River, From The Southern Pecos Wilderness To Brantley Dam, North Of Carlsbad, Eastern New Mexico

Virginia T. McLemore and Lynn A. Brandvold

February 9, 2001

INTRODUCTION

Water quality of the Pecos River has regional and international concerns as the population in eastern New Mexico increases. Four areas of concern were identified:

  • Pecos mine
  • Alamitos Canyon mill
  • Material from the mine waste pile had been used as fill in the campgrounds and roads north of Terrero
  • Lisboa Springs Fish Hatchery (New Mexico Game and Fish Dept)

Reclamation of the campgrounds, roads, and Alamitos Canyon mill site began in the early 1990s and is nearly completed. Reclamation of the Pecos mine began in 1999 and is on going. The Lisboa Springs Fish Hatchery closed, temporarily, in 2000 because the fish were diagnosed with Whirling disease, which is not related to the metals contamination from the Pecos mine.

Since reclamation of the Pecos mine, Alamitos Canyon mill, and campgrounds began in 1990-1991, there has been continued monitoring of base metals and trace element concentrations in stream sediments along the Pecos River, extending from the upper Pecos River to below Brantley Dam, north of Carlsbad.  In September 1992, the New Mexico Bureau of Mines and Mineral Resources (NMBMMR) personel sampled and analyzed water and stream sediments from the Pecos River at sites near the Pecos Wilderness boundary southward to below Brantley Lake, north of Carlsbad (McLemore et al., 1993). Subsequently, the U.S. Bureau of Reclamation, in cooperation with the New Mexico Institute of Mining and Technology (NMIMT) and NMBMMR, initiated a three-year multi-disciplinary study of the headwaters of the Pecos River (Pecos Wilderness boundary to Villanueva) in order to identify and prioritize point and non-point sources of contamination so that measures can be taken to protect water supplies for municipal, irrigation, and recreational use and to protect wildlife habitat (Brandvold et al., 1995; Brandvold and McLemore, 1999; McLemore et al., 1995a, b; Popp et al., 1996). In September 1992, 1996, and June 2000, the NMBMMR resampled water and stream sediments from the entire Pecos River from the Pecos Wilderness southward to below Brantley Lake. This report presents a summary of the first nine sampling trips in 1992-1995 (McLemore et al., 1993; Popp et al., 1996) and presents new data from the sampling trips in 1996 and 2000.

STUDY AREA

study area
Figure 1. Pecos River drainage basin, eastern New Mexico and western Texas. 

The study area covers the southern Pecos Wilderness to south of Brantley Lake and includes many tributaries and the main stem of the Pecos River (Fig. 1). The headwaters of the Pecos River are in the southern Sangre de Cristo Mountains, with additional drainages from the Pedernal uplift, Capitan Mountains, Sierra Blanca, and Guadalupe Mountains. Elevations range 1000 to over 3600 m. The river flows southward through the towns and cities of Pecos, Santa Rosa, Fort Sumner, Roswell, Artesia and Carlsbad into west Texas and finally enters the Rio Grande at the international border with Coahuila, Mexico. The Pecos River flows through the Santa Fe National Forest and the Pecos National Historical Park (U.S. National Park Service) and several state parks. Water from the Pecos River is stored in three main reservoirs: Santa Rosa, Sumner, and Brantley Lake. Eastern New Mexico is predominantly a rural agricultural area, but the larger cities have some light industry. Petroleum and potash production is important in southeastern New Mexico near Artesia and Carlsbad. There is currently no metals mining within the Pecos drainage basin.  

REGIONAL GEOLOGY

The geology of the Pecos River drainage basin is complex with rocks ranging in age from Proterozoic to recent. Lithologies are likewise diverse, ranging from metamorphic volcanic rocks to granites to syenites to shales, limestones, and sandstones (Fig. 2; Anderson et al., 1994). Proterozoic rocks crop out along the upper Pecos River and several tributaries north of Pecos. The oldest rocks are mafic metamorphic and volcaniclastic rocks that comprise the Pecos greenstone belt. The most abundant Proterozoic rocks are the plutonic rocks that consist of granite, tonalite-trondjemite, gabbro, diabase, and ultramafic rocks. Overlying sedimentary rocks consist of Mississippian limestone, sandstone, and shale of the Arroyo Penasco Group (Espiritu Santo and Terrero Formations) and unconformably overlie the Proterozoic rocks. Pennsylvanian siltstones, sandstones, shales, thin coals, and limestones overlie the Mississippian and, locally Proterozoic rocks in the Pecos River area. The Pennsylvanian-Permian rocks consist of the Magdalena Group and the Sangre de Cristo Formation. Permian siltstones, limestones, and sandstones overlie the Pennsylvanian-Permian rocks and consist of the Yeso, San Andres, and Bernal Formations. Triassic sandstones crop out in the area south of Pecos and consist of the Santa Rosa Sandstone. Permian evaporates that comprise the Permian Basin section crop out south of Roswell. Quaternary rocks are found throughout the area and consist of Pleistocene to recent alluvial, terrace, and floodplain deposits.

Figure 2. Simplified geologic map of the Pecos area
(Anderson, 1994; New Mexico Geological Society, 1982).

MINING HISTORY

  •  Mining began in the Sangre de Cristo Mountains in the late 1880s (Fig. 3, 4).
  •  The Pecos mine is a volcanogenic massive-sulfide deposit containing Pb, Zn, Cu, Ag and Au.
  •  The Pecos mine is largest of these deposits in New Mexico.
  •  The Pecos mine produced during 1902-1904, 1927-1939, and 1943-1944.
  •  The ore was shipped 18 km SW by aerial tram to the Alamitos Canyon mill where the mill tailings were deposited along Alamitos Canyon (Fig. 4).
  •  The Pecos mine was the largest lead and zinc producer in New Mexico from 1927 to 1939.
  •  Production from other deposits in the southern Sangre de Cristo Mountains is minor and insignificant (Fig. 3).
  •  The Pecos mine generated ~ 70,000 m3 of waste rock, which is a source of acidic drainage and a point source of Pb, Zn, Cu, Se, Cd, and Cr.
  •  The waste rock was used as fill in campgrounds and roads north of Terrero.
  •  Reclamation began in the early 1990s and continues today.
Figure 3. Location of sample sites and mining districts along the Pecos River, eastern New Mexico.
Figure 4. Location of sample sites, Pecos mine, Alamitos Canyon mill, and Lisboa Springs Fish Hatchery along the upper Pecos River, northeastern New Mexico.

DESCRIPTION OF THE PECOS MINE SITE

The waste rock generated during mining activities was piled at the Pecos mine site and consists of several dumps within an area of approximately 7.7 ha (Fig. 5). Estimates of the volume of waste rock vary from 66,151 to 72,630 m3 of material. The waste pile is underlain by a layer of colluvial materials, less than 5 m thick and consisting of clay and sedimentary rock fragments (limestone, shale, sandstones; Johnson and Deeds, 1995 a, b). Mineralogically and chemically the mine waste pile is very heterogeneous.

Figure 5. Pecos mine waste piles.

Mineralogy of the ore deposits at the Pecos mine, in order of perceived abundance:
(Stott, 1931; Krieger, 1932b; Northrop, 1959; Fulp, 1982; Fulp and Rensaw, 1985; Popp et al., 1996).
* Found on mine waste dump at Pecos mine (Popp et al., 1996).


Major Ore Minerals:

  • *sphalerite  ZnS
  • *galena  PbS
  • *chalcopyrite CuFeS2

Minor Ore Occurrences:

  • *bornite  Cu5FeS4
  •  tetrahedrite (Cu,Fe)12Sb4S13
  •  native gold  Au
  •  argentite  Ag2S
  •  proustite  Ag3AsS3

Oxidized Minerals:

  • *malachite  Cu2CO3(OH)2
  • *azurite  Cu3(CO3)2(OH)2
  • *angelsite  PbSO4
  • *smithsonite  ZnCO3
  • *chalcocite  Cu2S
  •   cerussite  PbCO3
  • *chalcanthite  CuSO4 × 5H2O

Selected Gangue Minerals:

  • *pyrite  FeS2
  • *pyrrhotite  Fe1-xS
  • *quartz  SiO2
  • *chlorite (complex silicate)
  • *actinolite  Ca2(Mg,Fe)5Si8O22(OH)2
  • *tourmaline (complex silicate)
  • *epidote  Ca2(Al,Fe)2(Al,Si3,O12)(OH)
  • *Fe and Mn oxides
  • *arsenopyrite  FeAsS
  • *biotite  K (Mg,Fe)3AlSi3O10(OH)2
  • *fluorite  CaF2
  • *kaolinite  Al2Si2O5(OH)4
  • *sericite  KAl2(AlSi3O10)(OH)2
  • *calcite  CaCO3

Chemical analyses of waste rock at the Pecos mine in ppm
(* from S. M. Stoller Corp., 1993).
Element *Average *Standard
deviation		 *Maximum *Minimum *Number of samples NMBMMR sample of Pecos mine piles (Pecos)
Cu 1,840 1,960 7,140 40 25 11,810
Pb 9,380 10,400 33,100 41.8 25 238
Zn 17,330 30,600 150,000 204 25 31,350
As 25 23 101 1 20 —
Cd 68 136 607 0.65 20 7.5
Hg 0.65 0.81 2.49 0.033 10 <0.10
Ag 10 11 32.6 0 20 —
Al 13,740 9,880 27,000 23 5 —
Fe 52,650 35,120 129,150 10,960 12 5.3
Co 18 14 59.5 3.2 13 —
Cr 18 13 52.4 2.4 20 —
Ni 12 6 23.3 1.7 13 29

Numerous discrete and diffuse seeps occur along the base of the mine waste pile (Fig. 6). The number of seeps and amount of water flow varies according to daily storm events and snowmelt as well as yearly fluctuations in precipitation. During August 1994 many seeps were dry and the total amount of flow was lower than on previous visits in 1992 and 1993. White and brown precipitates or froths are present along the course of the seeps that drain into Willow Creek. X-ray diffraction and chemical analyses (Popp et al., 1996) of the precipitates from the seeps indicate that they are a mixture of Fe, Cu, and Zn sulfates, and Fe and Al oxides and hydroxides including goslarite (ZnSO4·H2O). Chemical analyses of water samples from the seeps indicate a low pH and high total metals.

 Figure 6. Seeps below the Pecos mine waste piles.

DESCRIPTION OF THE ALAMITOS CANYON MILL SITE

The ore crushed at the mine and then transported by aerial tramway to the Alamitos Canyon mill (El Molino site) 18 km south of the mine (Fig. 4). The sulfide grains entering the mill were as large as 3 mm. A typical analysis of the mill feed was reported at 4.9% Pb, 15.4% Zn, 0.8% Cu, 113 ppm Ag, and 3.4 ppm Au (Bemis, 1932). Mill recoveries were good by the standard of the day although variable (Bemis, 1932). The rejected waste material was conveyed to the tailings pond in Alamitos Canyon and held in place by two earthen dams, 0.7 km and 1.5 km downstream of the mill site.

Today the tailings piles occupy approximately 14 ha in the bottom of Alamitos Canyon (Fig. 7; Sidle et al., 1991). The depth varies from 0 to 20 m and averages 9-12 m. The tailings consist of predominantly sand size material (Sidle et al., 1991). More silt is found in the southern, lower end of the pile than the north end. Higher concentrations of metals are found in the lower end as well. Discharge from the tailings pile enters Alamitos Creek, was acidic before reclamation and contained elevated levels of metals (Sidle et al., 1991; Brandvold et al., 1995). Wet meadows with pockets of water covered some of the tailings. Reclamation is currently underway with construction of a stream channel through the tailings pile and stabilization of the tailings by covering with clay, gravel, and soil (Johnson and Deeds, 1995 a, b).

Figure 7. Mill tailings in Alamitos Canyon before reclamation.

NMBMMR SAMPLING AND MONITORING PLAN

In September 1992, the New Mexico Bureau of Mines and Mineral Resources sampled and analyzed water and stream sediments from the Pecos River at sites near the Pecos Wilderness boundary southward to below Brantley Lake, north of Carlsbad (Fig. 4, 8, 9; McLemore et al., 1993). Subsequently, the U.S. Bureau of Reclamation, in cooperation with the New Mexico Institute of Mining and Technology (NMIMT) and NMBMMR, initiated a three-year multi-disciplinary study of the headwaters of the Pecos River in order to identify and prioritize point and non-point sources of contamination so that measures can be taken to protect water supplies for municipal, irrigation, and recreational use and to protect wildlife habitat (Brandvold et al., 1995; Brandvold and McLemore, 1999; McLemore et al., 1995a, b; Popp et al., 1996). In September 1996 and June 2000, the NMBMMR sampled water and stream sediments from the entire Pecos River from the Pecos Wilderness southward to below Brantley Lake. A report in preparation presents a summary of the first nine sampling trips in 1992-1995 (McLemore et al., 1993; Popp et al., 1996) and presents new data from the sampling trips in 1996 and 2000. The NMBMMR will continue to sample and monitor the metals concentration in water and stream sediment samples of the Pecos River in the future.

Figure 8. Pecos River, below Willow Creek (BW) and Pecos mine.
Figure 9. Pecos River at San Miguel dam (SM).

RESULTS

SUMMARY

  • Since reclamation of the Pecos mine, Alamitos Canyon mill, and campgrounds began in 1990-1991, Cu, Pb, and Zn concentrations have decreased overall while Cr concentrations have increased slightly.
  • The overall metal concentrations have dramatically decreased in stream sediments below Pecos village, mostly due to dilution of sediment downstream.
  • Although metal concentrations in the immediate vicinity of the mine have decreased, concentrations remain higher below the Pecos mine than above it, suggesting that metals continue to be eroded and leached from the Pecos mine waste piles.

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