Tertiary low sulfidation (LS) epithermal deposits in the western USA often show evidence of the former presence of nanoparticle-sized precious-metal and silica phases in the highest grade (bonanza) ores. Here, nanoparticles are defined to have a size less than ~10 ？ 7 m. The ore-mineral textures that formed from aggregation of nanoparticles (or colloids) observed to date in these ores include electrum and naumannite (Ag 2Se). Here it is proposed that chalcopyrite also forms nanoparticles in these ores, but sulfide nanoparticles apparently have significantly different physical (surface) properties than the precious-metal phases, and thus exhibit different mineral textures (e.g ., no textural evidence of previous chalcopyrite nanoparticles). Textures described here show that nanoparticles of precious-metal phases and silica were episodically and often repeatedly deposited to form the banded bonanza veins typical of many western USA epithermal deposits. Chalcopyrite is the most abundant metal-sulfide mineral in these bonanza ores, and it was also deposited episodically as well, and it appears to replace earlier formed naumannite dendrites. However, this apparent “replacement” texture may just be the result of naumannite dendrite limbs trapping chalcopyrite nanoparticles that later recrystallized to the apparent replacement texture. The episodic and repetitive nature of the metal-depositing events may record periodic “degassing” of magma chambers at depth, where metals are repeatedly delivered to the shallow epithermal environment by “vapor-phase” metal (loid) transport.
References
[1]
Saunders, J.A. Colloidal transport of gold and silica in epithermal precious metal systems: Evidence from the sleeper deposit, Humboldt County, Nevada. Geology 1990, 18, 757–760, doi:10.1130/0091-7613(1990)018<0757:CTOGAS>2.3.CO;2.
[2]
Saunders, J.A. Silica and gold textures at the sleeper deposit, Humboldt County, Nevada: Evidence for colloids and implications for ore-forming processes. Econ. Geol. 1994, 89, 628–638, doi:10.2113/gsecongeo.89.3.628.
[3]
Saunders, J.A.; Schoenly, P.A.; Cook, R.B. Electrum disequilibrium crystallization textures in volcanic-hosted bonanza epithermal gold deposits. In Geology and Ore Deposits of the America Cordillera; Proceedings of Nevada Symposium, Reno-Sparks, NV, USA, 10–13 April 1995; Coyner, A.R., Fahey, P.L., Eds.; Geological Society of Nevada: Reno-Sparks, NV, USA, 1996; pp. 173–179.
[4]
Saunders, J.A.; Vikre, P.; Unger, D.L.; Beasley, L. Colloidal and physical transport textures exhibited by electrum and naumannite in bonanza epithermal veins from western USA, and their significance. In Great Basin Evolution and Metallogeny; Proceedings of Geological Society of Nevada 2010 Symposium, Reno-Sparks, NV, USA, 14 May 2010; Steininger, R., Pennell, W., Eds.; Geological Society of Nevada: Reno-Sparks, NV, USA, 2011; pp. 825–832.
[5]
Shikazono, N. A comparison of temperatures estimated from the electrum-sphalerite-pyrite-argentite assemblage and filling temperatures of fluid inclusions from epithermal Au-Ag vein-type deposits in Japan. Econ. Geol. 1985, 80, 1415–1494, doi:10.2113/gsecongeo.80.5.1415.
[6]
Matsuhisa, Y.; Morishita, Y.; Sato, T. Oxygen and carbon isotope variations in gold-bearing hydrothermal veins in the Kushikino mining area, Southern Kyushu, Japan. Econ. Geol. 1985, 80, 283–293, doi:10.2113/gsecongeo.80.2.283.
[7]
Izawa, E.; Urashima, Y.; Ibaraki, K.; Suzuki, R.; Yokohama, T.; Kawasaki, K.; Koga, A.; Taguchi, S. The Hishikari gold deposit: High-grade epithermal veins in Quaternary volcanics of Southern Kyushu, Japan. J. Geochem. Explor. 1990, 36, 1–56, doi:10.1016/0375-6742(90)90050-K.
[8]
Shikazono, N.; Nagayama, T. Origin and deposition mechanisms of the Hishikari gold-quartz-adularia mineralization. Resource Geol. 1993, 14, 47–56.
[9]
Nagayama, T. Precipitation sequence of veins at the Hishikari deposits, Kyushu, Japan. Resource Geol. 1993, 14, 13–28.
[10]
Shimizu, T.; Matsueda, H.; Ishiyama, D.; Matsubaya, O. Genesis of epithermal Au-Ag mineralization of the Koryu Mine, Hokkaido, Japan. Econ. Geol. 1998, 93, 303–325, doi:10.2113/gsecongeo.93.3.303.
[11]
Lingdren, W. Mineral Deposits, 4th ed.; McGraw-Hill: New York, NY, USA, 1933; p. 486.
[12]
Lindgren, W. Geology and mineral deposits of the National District, Nevada. U.S. Geol. Surv. Bull. 1915, 601, 1–58.
[13]
Goldstrand, P.M.; Schmidt, K.W. Geology, mineralization, and ore controls at the Ken Snyder gold-silver mine, Elko County, Nevada. In Geology and Ore Deposits 2000: The Great Basin and Beyond; Proceedings of Nevada Symposium, Reno-Sparks, NV, USA, 15–18 May, 2000; John, D.A., Wallace, A.R., Eds.; Geological Society of Nevada: Reno-Sparks, NV, USA, 2000; pp. 265–287.
[14]
Saunders, J.A.; Unger, D.L.; Kamenov, G.D.; Fayek, M.; Hames, W.E.; Utterback, W.C. Genesis of Middle Miocene Yellowstone-hotspot-related bonanza epithermal Au-Ag deposits, Northern Great Basin Region, USA. Mineral. Dep. 2008, 43, 715–734, doi:10.1007/s00126-008-0201-7.
[15]
Simmons, S.F.; Christenson, B.W. Origins of calcite in a boiling geothermal system. Am. J. Sci. 1994, 294, 361–400, doi:10.2475/ajs.294.3.361.
[16]
Fournier, R.O. Silica minerals as indicators of conditions during gold deposition. U.S. Geol. Surv. Bull. 1985, 1646, 15–26.
[17]
Fournier, R.O. The behavior of silica in hydrothermal solutions. Rev. Econ. Geol. 1986, 2, 45–62.
[18]
Saunders, J.A.; Schoenly, P.A. Boiling, colloid nucleation and aggregation, and the genesis of bonanza gold mineralization at the Sleeper Deposit, Nevada. Mineral. Dep. 1995, 30, 199–211, doi:10.1007/BF00196356.
[19]
Saunders, J.A.; Schoenly, P.A. Fractal structure of electrum dendrites in bonanza epithermal Au-Ag deposits. In Fractal Geometry and Its Use in the Earth Sciences; Barton, C.C., La Pointe, P.R., Eds.; Plenum Publishing: New York, NY, USA, 1995; pp. 251–261.
[20]
Vikre, P.G. Precious metal vein system in the National district, Humboldt County, Nevada. Econ. Geol. 1985, 80, 360–393, doi:10.2113/gsecongeo.80.2.360.
[21]
Kamenov, G.D.; Saunders, J.A.; Hames, W.E.; Unger, D.L. Mafic magmas as sources for gold in middle Miocene epithermal deposits of the Northern Great Basin, United States: Evidence from Pb isotope compositions of native gold. Econ. Geol. 2007, 102, 1191–1195, doi:10.2113/gsecongeo.102.7.1191.
[22]
Heinrich, C.A.; Gunther, D.; Audetat, A.; Ulrich, T.; Frischknect, R. Metal fractionation between magmatic brine and vapor, determined by microanalysis of fluid inclusions. Geology 1999, 27, 755–758.
[23]
Heinrich, C.A.; Driesner, T.; Stefansson, A.; Seward, T.M. Magmatic vapor contraction and the transport of gold from the porphyry environment to epithermal ore deposits. Geology 2004, 32, 761–764, doi:10.1130/G20629.1.
[24]
Williams-Jones, A.E.; Heinrich, C.A. Vapor transport of metals and the formation of magmatic-hydrothermal ore deposits. Econ. Geol. 2005, 100, 1287–1312, doi:10.2113/gsecongeo.100.7.1287.
[25]
Freeze, A.R.; Cherry, J.A. Groundwater; Prentice Hall: New York, NY, USA, 1979.
[26]
Sherlock, R.L.; Lehrman, N.J. Occurrences of dendritic gold at the McLaughlin mine. Miner. Dep. 1995, 30, 323–327, doi:10.1007/BF00196368.
[27]
Hames, W.E.; Unger, D.L.; Saunders, J.A.; Kamenov, G.D. Metallogeny and magmatism in the early Yellowstone hotspot. J. Volcan. Geotherm. Res. 2009, 188, 214–224, doi:10.1016/j.jvolgeores.2009.07.020.
[28]
Fifarek, R.H.; Devlin, B.D.; Tschauder, R.J., Jr. Au-Ag mineralization at the Golden Promise deposit, Republic district, Washington: Relation to graben development and hot spring processes. In Geology and Ore Deposits of the America Cordillera; Proceedings of Nevada Symposium, Reno-Sparks, NV, USA, 10–13 April 1995; Coyner, A.R., Fahey, P.L., Eds.; Geological Society of Nevada: Reno-Sparks, NV, USA, 1996; pp. 1063–1088.
[29]
Saunders, J.A. Geologic Time and Epithermal ore Formation: SEG Newsletter; Society of Economic Geologists: Littleto, CO, USA, 2010; pp. 10–11. July; No. 82.
[30]
Simmons, S.F.; Brown, K.L. Gold in magmatic hydrothermal solutions and the rapid formation of a giant ore deposit. Science 2006, 314, 288–291, doi:10.1126/science.1132866.
[31]
Heinrich, C.A. How fast does gold trickle out of volcanoes? Science 2006, 314, 163–264.
[32]
Barton, P.B., Jr.; Bethke, P.M.; Toulmin, P., III. An attempt to determine the vertical component of flow rate of ore-forming solutions in the OH vein, Creede, Colorado. In Proceedings of IAGOD 1970 Meeting, Kyoto, Japan, 1971; pp. 132–136.
[33]
Roedder, E. Fluid Inclusions; Ribbe, P.H., Ed.; Mineralogical Society of America: San Francisco, CA, USA, 1984; Volume 12, p. 644.
[34]
Kouzmanov, K.; Pettke, T.; Heinrich, C.A. Direct analysis of ore-precipitating fluids: Combined IR microscopy and LA-ICP-MS study of fluid Inclusions in opaque ore minerals. Econ. Geol. 2010, 105, 351–373, doi:10.2113/gsecongeo.105.2.351.
[35]
Brown, K.L. Gold deposition from geothermal discharges in New Zealand. Econ. Geol. 1986, 81, 979–983, doi:10.2113/gsecongeo.81.4.979.
[36]
Wilkin, R.T.; Barnes, H.L. Formation processes of framboidal pyrite. Geochim. Cosmochim. A. 1997, 61, 323–339, doi:10.1016/S0016-7037(96)00320-1.
[37]
Yucel, M.; Gartman, A.; Chan, C.S.; Luther, G.W., III. Hydrothermal vents as a kinetically stable source of iron-sulphide-bearing nano particles to the ocean. Nature Geosci. 2011, 4, 367–371, doi:10.1038/ngeo1148.
[38]
Labrenz, M.; Druchel, G.; Thomsen-Ebert, T.; Gilbert, B.; Welch, S.A.; Kemner, K.M.; Logan, G.A.; Summons, R.E.; de Stasio, G.; Bond, P.L.; Lai, B.; Kelly, S.D.; Banfield, J.F. Formation of sphalerite (ZnS) deposits in natural biofilms of sulfate reducing bacteria. Science 2000, 290, 1744–1747.
[39]
Druschel, G.K.; Labrenz, M.; Thomsen-Ebert, T.; Fowle, D.A.; Banfield, J.F. Geochemical modeling of ZnS in biofilms: An example of ore depositional processes. Econ. Geol. 2002, 97, 1319–1329, doi:10.2113/gsecongeo.97.6.1319.
[40]
Southam, G.; Saunders, J.A. Geomicrobiology of ore deposits. Econ. Geol. 2005, 100, 1067–1084, doi:10.2113/gsecongeo.100.6.1067.
[41]
Saunders, J.A.; Lee, M-K.; Wolf, L.A.; Morton, C.M.; Feng, Y.; Thomson, I.; Park, S. Geochemical, microbiological and geophysical assessments of anaerobic immobilization of heavy metals. Bioremed. J. 2005, 9, 33–48.
[42]
Nairn, J.J.; Shapiro, P.J.; Twamley, B.; Pounds, T.; Wandruszka, R.V.; Fletcher, R.T.; Williams, M.; Wang, C.; Norton, M.G. Preparation of ultrafine chalcopyrite nanoparticles via the photochemical decomposition of molecular single-source precursors. Nano Lett. 2006, 6, 1218–1223.
[43]
Barton, P.B., Jr; Bethke, P.M. Chalcopyrite disease in sphalerite: Pathology and epidemiology. Am. Mineral. 1987, 72, 451–467.
[44]
Saunders, J.A.; Kamenov, G.D.; Hofstra, A.H.; Unger, D.L.; Creaser, R.A.; Barra, F. “Forensic” geochemical approaches to constrain the source of Au-Ag in low-sulfidation epithermal ores. In Great Basin Evolution and Metallogeny; Proceedings of Geological Society of Nevada 2010 Symposium, Reno-Sparks, NV, USA, 14 May 2010; Steininger, R., Pennell, W., Eds.; Geological Society of Nevada: Reno-Sparks, NV, USA, 2011; pp. 693–700.
[45]
Taran, Y.A.; Bernard, A.; Gavilanes, J.-C.; Africano, F. Native gold in mineral precipitates from high-temperature volcanic gases of Colima volcano, Mexico. Appl. Geochem. 2000, 15, 337–346, doi:10.1016/S0883-2927(99)00052-9.
[46]
Casadevall, T.; Ohmoto, H. unnyside Mine, Eureka mining district, San Juan County, Colorado; geochemistry of gold and base metal ore deposition in a volcanic environment. Econ. Geol. 1977, 72, 1285–1320, doi:10.2113/gsecongeo.72.7.1285.
