DRA-47a. IN SITU AND LABORATORY DIRECT SHEAR TEST SITES OF THE QUESTA MINE ROCK PILES AND ANALOG MATERIALS

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1 DRA-47a. IN SITU AND LABORATORY DIRECT SHEAR TEST SITES OF THE QUESTA MINE ROCK PILES AND ANALOG MATERIALS V.T. McLemore, December 21, 2008, revised February 16, 2009 (reviewed by Ali Fakhimi, D. van Zyl) 1. STATEMENT OF THE PROBLEM How were the in-situ test sites selected and why? What is the interpretation of the in-situ sample sites? This DRA explains the rational and purpose of the sites selected for in-situ testing. 2. PREVIOUS WORK Fakhimi et al. (2008) and Boakye (2008) described in-situ tests at Questa to measure cohesion and friction angle in place. McLemore and Dickens (2008) describe the mineralogy, texture, and chemistry of the samples collected from the in-situ test sites. 3. TECHNICAL APPROACH The in-situ test site locations were selected from three areas (Questa rock piles, Goathill debris flow, Questa Pit alteration scar) in the Questa mine site (Fig.1, Table 1, Appendix 1). Sites for the tests were selected by the QRPWASP Geotechnical committee based on Proximity to roads, safest, easiest to test (ability to get equipment to test site) Obtain a reative sample Near the top of the rock piles where finer grained material is most likely to occur Different weathering intensities based upon existing chemistry, paste ph, and maps from legacy data (Wagner and Harrington, 1995; URS Corporation, 2003; Norwest Corporation, 2004, 2005), remote sensing maps, and the simple field weathering index (1-5). Locations along other rock-pile slopes (besides SSW) and near the toe of some rock piles were attempted for testing, but a cohesive block could not be made in this cohesionless material. Areas of alteration scars and debris flows near the Questa mine have been identified as natural weathering analogs to the mineralogical changes in the rock piles expected during long-term weathering (Ludington et al., 2005; Campbell and Lueth, 2008; Graf, 2008). Note that the weathering processes operating in the natural analogs share many similarities to those in the rock piles, although certain aspects of the physical and chemical systems are different (DRA-19, 20, 22). Appendix 2 summarizes the natural analogs and the comparison between the rock piles and their natural analogs. In-situ direct shear tests were performed on these natural analogs to extrapolate the future shear strength of the rock piles. Questa Weathering Study p 1 of 11 February 16, 2009

2 FIGURE 1. Location of in-situ samples (red circles). Test site identification numbers are listed in Table 1. Location data are in Appendix 1. TABLE 1. The number of in-situ direct shear tests performed at each location. Location data are in Appendix 1. Location Number of in-situ direct shear tests performed Number in Figure 1 (Test site identification number) Middle Rock Pile 5 MID1 (MID-AAF-1-1, 2-1, 2-2, 3-1) MID2 (MID-VTM ) Spring Gulch Rock Pile 10 SPR1 (SPR-AAF , 1-2) SPR2 (SPR-VTM , 8-1) SPR3 (SPR-VTM , 12-2, 12-3, 19-1, 19-2) Sugar Shack South Rock Pile 7 SSS1 (SSS-AAF , 5-1, 5-2, 9-1, 9-2) SSS2 (SSS-VTM , 601-1) Sugar Shack West Rock Pile 17 SSW1 (SSW-AAF , 2-1, 2-2, 2-3, 4-1) SSW2 (SSW-AAF , 7-1) SSW3 (0016-1, 16-2, 23-1, , 600-2, 600-3) SSW4 (0026-1, 26-2, 30-1, 30-2) Questa Pit Alteration Scar 8 QPS (QPS-AAF , 1-2, 1-3, 8-1, 9-1, 20-1, 22-1, QPS-VTM ) Debris Flow 5 MIN (MIN-AAF , 4-1, 10-1, 12-1, 15-1) 4. CONCEPTUAL MODEL Cohesion for these unsaturated materials is composed of three components: 1) matric suction, 2) cementation, and 3) interlocking of grains. To obtain the cohesion parameters for the same values of matric suction, the modified Mohr-Coulomb failure criterion (Eqs. 1a to 1c) was used (Fredlund and Rahardjo, 1993) τ = c + (σ u a )tanφ c = c - (u a u w )tanφ b c = c + (u a u w )tanφ b (1a) (1b) (1c) where τ and σ are shear and normal stresses, u a and u w are air and pore water pressures, c and φ are cohesion and friction angle, and φ b is the angle that dictates the increase in cohesion due to the increase in matric suction, (u a u w ). With u a equal to zero, an Questa Weathering Study p 2 of 11 February 16, 2009

assumed φ b of 15º (Fredlund and Rahardjo, 1993), the cohesion c in Eq. (1b) can be used to find the cohesion c for zero suction. Eq. 1c then can be used to obtain the cohesion corresponding to a given matric suction.

STATUS OF COMPONENT INVESTIGATIONS The main purpose for performing in-situ shear tests was to measure the rock-pile cohesion to investigate the effect of cohesion on slope stability.

Lithology of the rock-pile material, debris flows, and alteration scars are similar and similar weathering processes are likely to occur in all three.

3 assumed φ b of 15º (Fredlund and Rahardjo, 1993), the cohesion c in Eq. (1b) can be used to find the cohesion c for zero suction. Eq. 1c then can be used to obtain the cohesion corresponding to a given matric suction.( c ) DRA-47 elaborates on the cohesion values that were measured through the in-situ shear testing using the above equations. 5. STATUS OF COMPONENT INVESTIGATIONS The main purpose for performing in-situ shear tests was to measure the rock-pile cohesion to investigate the effect of cohesion on slope stability. Two natural analogs to weathering processes that occur in the rock piles are the debris flow and alteration scars. Lithology of the rock-pile material, debris flows, and alteration scars are similar and similar weathering processes are likely to occur in all three. Therefore, debris flows and alteration scars would provide an analog to mineralogical changes expected in the rock piles due to weathering. Appendix 1 summarizes some similarities and differences between these environments. The matric suctions that were measured in the field using a tensiometer, ranged between 0 to 45 kpa for all 52 in situ test locations. In-situ test sites were chosen in the Goat Hill debris flow (Figs. 2, 3; also known as Goat Hill Gulch) and Questa Pit alteration scar (Fig. 4) in order to test this hypothesis. The two sites are somewhat different in physical characteristics and depositional processes, as explained in McLemore and Dickens (2008), Ayakwah et al. (2008) and summarized below. FIGURE 2. Photograph of sample location of sample MIN-SAN-0001 in the Goat Hill debris flow. This sample location is in the vicinity of the in situ shear test locations. FIGURE 3. Location of samples taken from the debris flow for the profile study (Ayakwah et al., 2008). In-situ tests were at the top of this profile. Questa Weathering Study p 3 of 11 February 16, 2009

FIGURE 4. Sampling site for QPS-SAN-0001. The pit is approximately 1 m deep. This sample location is in the vicinity of the in situ shear test locations.

Water was a mechanism of deposition. However, the debris flows re some of the best cemented material in the area and the in-situ tests were designed to examine that cementation.

4 FIGURE 4. Sampling site for QPS-SAN The pit is approximately 1 m deep. This sample location is in the vicinity of the in situ shear test locations. The debris flow consists of several different flows or landslides of material that washed out of the Goat Hill alteration scar upstream during heavy rainfall events (Fig. 3). Water was a mechanism of deposition. However, the debris flows re some of the best cemented material in the area and the in-situ tests were designed to examine that cementation. The in-situ tests were conducted in the forest at the top of a road cut into the debris slope. Ayakwah et al. (2008) describes the Goat Hill debris flow in more detail. The in-situ site within the Questa Pit alteration scar was selected in a talus or scree deposit of rock fall or landslide material that formed when the natural slope of the scar slid, possibly as a result of heavy rainfall (Fig. 4). This material was deposited in a similar fashion to the rock piles, in that the material most likely was largely rocks and soil that slid due to gravity and was deposited similar to end-dumping of rock-pile material. There was likely water involved in the failure, but mostly the material failed as a result of gravity. The in-situ tests were conducted on a bench cut into the scree slope. Several areas were selected in the Questa rock piles with variations in weathering (Table 4; McLemore and Dickens, 2008). TABLE 4. Lithology and texture of rock pile material at the in situ test locations (McLemore and Dickens, 2008). Test number Sample number SWI Lithology Original magmatic texture Indications of Weathering MID-VTM MIN-AAF MIN-AAF MID-VTM % MIN-AAF % intrusive, 2% MIN-AAF % textures visible, texture still visible but slightly overprinted by hydrothermal texture moderate-heavy feldspar Hydrothermal alteration and intensity QSP 40% QSP 50% QSP 55% skeletal feldspar crystals, rounded pyrite grains skeletal feldspar crystals Questa Weathering Study p 4 of 11 February 16, 2009

5 Test number Sample number SWI Lithology Original magmatic texture QPS-AAF QPS-VTM SPR-AAF SPR-AAF SPR-VTM SPR-VTM SPR-VTM SPR-VTM SPR-VTM SSS-VTM SSS-AAF SSS-AAF SSS-AAF SSW-AAF QPS-AAF % QPS-VTM % andesite SPR-AAF % andesite SPR-AAF % andesite SPR-VTM % 1% SPR-VTM % SPR-VTM % SPR-VTM % SPR-VTM % SSS-VTM % 20% SSS-AAF % SSS-AAF % SSS-AAF % andesite SSW-AAF % 5%, limited feldspar moderate-heavy feldspar Hydrothermal alteration and intensity QSP 25% Propyllitic 5% QSP 55% Propyllitic 1% Indications of Weathering, skeletal feldspar crystals textures visible Propyllitic 25% deterioration texture slightly visible, heavy texture slightly visible, heavy texture slightly visible, heavy moderate hydrothermal hydrothermal QSP 45% Propyllitic 3% QSP 45% QSP 60% QSP 50% QSP 50% QSP 55% QSP textures visible QSP 10% Propyllitic 20% texture slightly visible, heavy QSP 40% QSP 35% QSP 60% Propyllitic 2%, skeletal feldspar crystals skeletal feldspar crystals authigenic gypsum Questa Weathering Study p 5 of 11 February 16, 2009

6 Test number Sample number SWI Lithology Original magmatic texture SSW-AAF SSW-AAF SSW-AAF SSW-AAF SSW-AAF andesite hydrothermal SSW-AAF % 2% andesite hydrothermal 4 100% 4 99% 1% 3 100%, 3 100% andesite texture slightly visible, heavy texture not visible, heavy slight feldspar Hydrothermal alteration and intensity QSP QSP 40% QSP QSP 60% QSP 75% QSP 30% Propyllitic 2% Indications of Weathering iron oxides, skeletal feldspar crystals iron oxides, skeletal feldspar crystals, rounded pyrite grains texture visible Propyllitic 17%, presence of tarnished pyrite 6. RELIABILITY ANALYSIS There are other interpretations to the depositional environment of the QPS samples (i.e. a debris flow deposit). However, the purpose of the in-situ tests was to test alteration scar and debris flow material and the two chosen sites differ. Both sites are older than the rock piles. No other alteration scar site could be tested. Most of the rock-pile test sites were at the top of the rock pile where the material was cohesive and a block could be constructed. Some of the test sites on Sugar Shack West re the only tests midslope of that rock pile (Fig. 1, SSW1, SSW 2, SSW 4). Locations along other rock-pile slopes and near the toe of some rock piles were attempted for testing, but a cohesive block could not be made in this cohesionless material at these locations. 7. CONCLUSIONS OF THE COMPONENT RESULTS In-situ test sites were chosen in the Goat Hill debris flow (also known as Goat Hill Gulch) and Questa Pit alteration scar in order to determine if cohesion differed between the older analog sites and the rock piles. Several areas were selected in the Questa rock piles with variations in weathering. DRA-47 discusses these results. The debris flow consists of several different flows or landslides of material that washed out of the Goat Hill alteration scar upstream during heavy rainfall events. Water was a mechanism of deposition. However, the debris flows re some of the best cemented material in the area and the in-situ tests were designed to examine that cementation. The in-situ test site within the Questa Pit alteration scar was selected in a talus or scree deposit of rock fall or landslide material that formed when the natural slope of the scar slid, possibly as a Questa Weathering Study p 6 of 11 February 16, 2009

7 result of heavy rainfall. This material was deposited in a similar fashion to the rock piles. Both sites are older than the rock piles. 8. REFERENCES CITED Ayakwah, G., McLemore, V.T., and Dickens, A., 2008, Characterization of Questa debris flows: unpublished report to Chevron Mining Corporation, Task B1.4. Boakye, K., 2008, Large in situ direct shear tests on rock piles at the Questa Mine, Taos County, New Mexico: M.S. thesis, New Mexico Institute of Mining and Technology, Socorro, 156 p. Campbell, A.R, and Lueth, V.W., 2008, Isotopic and textureal discrimination between hypogene, ancient supergene, and modern sulfates at the Questa mine, New Mexico, Applied Geochemistry, v Fakhimi, A., Boakye K., Sperling D., and McLemore V., 2008, Development of a modified in situ direct shear test technique to determine shear strength of mine rock piles: Geotechnical Testing Journal, v. 31, no. 3, paper on line Fredlund, D.G., and Rahardjo, H., 1993, Soil Mechanics for Unsaturated Soils: Wiley. Graf, G.J., 2008, Mineralogical and geochemical changes associated with sulfide and silicate weathering, natural alteration scars, Taos County, New Mexico: M. S. thesis, New Mexico Institute of Mining and Technology, Socorro, 193 p., accessed April 28, Ludington, S., Plumlee, G., Caine, J., Bove, D., Holloway, J., and Livo, E., 2005, Questa baseline and pre-mining ground-water quality Investigation, 10. Geologic influences on ground and surface waters in the lower Red River watershed, New Mexico: U.S. Geological Survey, Scientific Investigations Report , 46 p. McLemore, V.T. and A. Dickens, 2008, Petrographic Analysis, Mineralogy, and Chemistry of Samples Analyzed by In-Situ Direct Shear Methods, Questa, New Mexico: report to Chevron, Task B1. McLemore, V.T., Donahue, K., Dunbar, N. and Heizler, L., 2008, Characterization of physical and chemical weathering in the rock piles and evaluation of weathering indices for the Questa rock piles: unpublished report to Chevron, Task 1.3, B1.1. Norwest Corporation, 2004, Goathill North Slide Investigation, Evaluation and Mitigation Report: unpublished report to Molycorp Inc., v. 3, 99 p. Norwest Corporation, 2005, Questa Roadside Rockpiles 2005 Operation Geotechnical Stability Evaluation: unpublished report to Molycorp Inc., 210 p., 3 vol. URS Corporation, 2003, Mine rock pile erosion and stability evaluations, Questa mine: Unpublished Report to Molycorp, Inc. 4 volumes. Wagner, A. M. and Harrington, J. T., 1995, Revegetation report for Molycorp, Inc. Questa mine site: unpublished report for Vail Engineering, 45 p. 9. TECHNICAL APPENDICES Boakye, B., 2008, Large In Situ Direct Shear Tests on Rock Piles At The Questa Mine, Taos County, New Mexico: M. S. thesis, New Mexico Institute of Mining and Technology, Socorro. Questa Weathering Study p 7 of 11 February 16, 2009

8 Fakhimi A., Boakye K., Sperling D., and McLemore V., 2008, Development of a modified in situ direct shear test technique to determine shear strength of mine rock piles, Geotechnical Testing Journal, v. 31, no. 3, paper on line McLemore, V.T. and A. Dickens, 2008, Petrographic Analysis, Mineralogy, and Chemistry of Samples Analyzed by In-Situ Direct Shear Methods, Questa, New Mexico: report to Chevron, Task B1. Questa Weathering Study p 8 of 11 February 16, 2009

9 APPENDIX 1. Location of in-situ test sites. Test number Date UTM easting (m) UTM northing (m) Elevation (ft) MID-AAF /12/ MID-AAF /1/ MID-AAF /1/ MID-AAF /2/ MID-VTM /7/ MIN-AAF /2/ MIN-AAF /4/ MIN-AAF /26/ MIN-AAF /27/ MIN-AAF /28/ QPS-AAF /11/ QPS-AAF /12/ QPS-AAF /13/ QPS-AAF /14/ QPS-AAF /15/ QPS-AAF /14/ QPS-AAF /15/ QPS-VTM /16/ SPR-AAF /5/ SPR-AAF /6/ SPR-VTM /17/ SPR-VTM /18/ SPR-VTM /18/ SPR-VTM /19/ SPR-VTM /20/ SPR-VTM /20/ SPR-VTM /21/ SPR-VTM /21/ SSS-AAF /28/ SSS-AAF /29/ SSS-AAF /3/ SSS-AAF /4/ SSS-AAF /4/ SSS-AAF /5/ SSS-VTM /9/ SSS-VTM /10/ SSW-AAF /3/ SSW-AAF /3/ Questa Weathering Study p 9 of 11 February 16, 2009

10 Test number Date UTM easting (m) UTM northing (m) Elevation (ft) SSW-AAF /4/ SSW-AAF /4/ SSW-AAF /6/ SSW-AAF /6/ SSW-AAF /7/ /13/ /14/ /15/ /20/ /21/ /21/ /22/ /7/ /8/ /8/ APPENDIX 2. THE IMPORTANCE OF NATURAL ANALOGS Comparison of the different weathering environments in the rock piles and analog sites in the Questa area. See McLemore et al. (2008b) for more details on the statistical analyses. QSP=quartz-sericite-pyrite. SP=poorly-graded sand, GP=poorly-graded gravel, SM=silty sand, SC=clayey sand, GW=well-graded gravel, GC=clayey gravel, GP-GC=poorlygraded gravel with clay, GP-GM=poorly-graded gravel with silt, GW-GC=well-graded gravel with clay, SW-SC=well-graded sand with clay, SP-SC=poorly-graded sand with clay. Feature Rock Pile Alteration Scar Debris Flow Colluvium and Rock types Unified soil classification (USCS) Andesite Rhyolite Aplite Porphyry Intrusion GP-GC, GC, GP-GM, GW, GW-GC, SP-SC, SC, SW- SC, SM % fines Mean 7.5 Std Dev. 6 No of Samples=89 Water content (%) 1-24 Mean 10 Std Dev. 4 No of Samples=390 Paste ph Mean 4.8 std dev 1.9 No of samples=1368 Pyrite content (%) Low to high 0-14% (mean 1.0%; std dev. 1.2%, No of samples=1098) Dry density kg/m Mean 1800 Std Dev. 140 No of Samples=153 Andesite Rhyolite Aplite Porphyry Intrusion Andesite Rhyolite Aplite Porphyry Intrusion weathered bedrock Andesite Rhyolite GP-GC, GP GP, SP, GP-GC GP-GC, GP Mean 5.2 Std Dev. 4 No of Samples= Mean 9 Std Dev. 4 No of Samples= Mean 4.3 std dev 1.6 No of samples=215 Low to high 0-11% (mean 0.7%, std dev 1.8%, No of samples=62) Mean 1900 Std Dev. 210 No of Samples= Mean 1.8 Std Dev. 2 No of Samples= Mean 5 Std Dev. 4 No of Samples= Mean 4.5 std dev 1.3 No of samples=58 Low to medium 0-0.2% (mean 0.03%, std dev 0.06%, No of samples=22) Mean 1900 Std Dev. 340 No of Samples= Mean 20 Std Dev. 11 No of Samples= Mean 14 Std Dev. 3 No of Samples= Mean 3.8 std dev 1.3 No of samples=45 Low to high 0-5.1% (mean 0.4%, std dev 1.1%, No of samples 26) 2200 No of Sample=1 Questa Weathering Study p 10 of 11 February 16, 2009

11 Feature Rock Pile Alteration Scar Debris Flow Colluvium and weathered bedrock Particle shape Angular to subangular to subrounded Subangular Subangular to subrounded Subangular to subrounded Plasticity Index (%) Mean 10 Std Dev Mean 12 Std Dev Mean 7 Std Dev Mean 13 Std Dev. 5 Degree of chemical cementation (visual observation) Slake durability index (%) Point Load index (MPa) Peak friction angle (degrees), 2-inch shear box (NMIMT data) Average cohesion (kpa), in-situ shear tests No of Samples=134 Low to moderate (sulfates, Iron oxides) Mean 96.6 Std Dev. 3.1 No of Samples= Mean 3.8 Std Dev. 1.7 No of Samples= Mean 42.2 Std Dev. 2.9 No of Samples= Mean 9.6 Std dev 7.3 No of samples=20 No of Samples=30 Moderate to high (sulfates, Iron oxides) Mean 89.2 Std Dev. 9.2 No of Sample= Mean 2.8 Std Dev. 0.8 No of Samples= Mean 40.7 Std Dev. 4.8 No of Samples= Mean 18.1 No of samples=2 No of Samples=18 Moderate to high (sulfates, Iron oxides) Mean 98.4 Std Dev. 0.9 No of Samples= Mean 4 Std Dev. 1 No of Samples= Mean 44.3 Std Dev. 3.9 No of Samples= Mean 38.8 No of samples=2 No of Samples=17 Moderate to high (sulfates, Iron oxides) Mean 95.7 Std Dev. 1.7 No. of Samples= 9 Not determined Mean 41.4 Std Dev. 2.5 No of Samples=22 Not determined Questa Weathering Study p 11 of 11 February 16, 2009

DRA-19. NATURAL ANALOGS AS PROXIES TO WEATHERING OF THE QUESTA ROCK PILES

DRA-19. NATURAL ANALOGS AS PROXIES TO WEATHERING OF THE QUESTA ROCK PILES V.W. Lueth, A.R. Campbell, V.T. McLemore, December 26, 2008, revised January 22, 2009 (reviewed by M. Logsdon) 1. STATEMENT OF