Earth and Planetary Science

Magma Degassing and Gold Mineralization in the Alkaline Intrusion- Hosted Gilt Edge Gold Deposit,Northern Black Hills, South Dakota, USA

John A. Groff

South Dakota School of Mines and Technology 501 East St. Joseph Street Rapid City, SD 57701 USA Tuscaloosa Academy 420 Rice Valley Road Tuscaloosa, AL 35046 USA

DOI: https://doi.org/10.36956/eps.v3i2.1125

Received: 10 June 2024; Received in revised form: 13 August 2024; Accepted: 20 August 2024; Published: 14 October 2024

---

Abstract

Gold mineralization in the Gilt Edge  deposit was closely associated with magmatic differentiation and the formation of a Tertiary alkaline intrusive complex within the Lead–Deadwood dome.. Fluid inclusions and trace element geochemistry were used to study fluid evolution and determine sources. Quartz disseminated in unaltered trachyte porphyry  hosts two populations of primary inclusions: 1) hypersaline i S–L–V  a red hematite crystal and 2) mixtures of L–V and V– L  that record phase separation at ~700^oC. Whereas samples of hydrothermal quartz collected from in ore zones within and beyond structures (e.g., fault and breccia zones) contain dominant populations of V–L and L–V inclusions, respectively. Mineralization in structures formed from complex fluids of magmatic origin based on inclusions containing five transparent salt crystals and opaque crystals with cubic and round habits that have homogenization temperatures (T_h)  650^oC and salinities  63 wt.% NaCl equiv. In contrast, broader areas of disseminated mineralization in argillized and propylitized rocks contain hydrothermal quartz hosting large populations of L–V inclusions with T_h of 200^o360^oC and salinities of 10–30 wt.% NaCl equiv., which reflect fluid mixing.  Trace element concentrations are significantly higher in samples from structures and define zones of near surface Ag–As–Zn–Pb and deep Au–W–Mo–Cu. Whereas low trace element concentrations characterize propylitized quartz trachyte porphyry, except for high concentrations of Sb and Hg that occur at depth and likely track the retreat of isotherms as the hydrothermal system collapsed. These data show that during differentiation in a deep magma chamber, volatile-rich low-density fluids were periodically degassed into preexisting structures that were reactivated. Gold deposition during four stages of mineralization likely occurred due to boiling, changes in oxygen fugacity, and fluid mixing.

Keywords: Fluid in clusion microthermometry; Magma differentiation; Whole-rock geochemical data; Alkaline intrusive complex

---

References

[1] Jensen, E.P., Barton, M.D., 2000. Gold deposits related to alkaline magmatism. SEG Reviews 13, 279–314. DOI: https://doi.org/10.5382/Rev.13.08

[2] Kelley, K.D., Spry, P.G., McLemore, V.T., et al., 2020. Alkalic-Type Epithermal Gold Deposit Model. USGS Scientific Investigations Rept. 2010–5070–R, 74p. DOI: https://doi.org/10.3133/sir20105070R

[3] Begg, G., 1996. Genesis of the Vatukoula gold deposit, Fiji [PhD thesis]. Melbourne, Australia: Monash University. pp. 1–466.

[4] Zhang, X., Spry, P.G., 1994. Petrological, mineralogical, fluid inclusion, and stable isotope studies of the Gies gold-silver telluride deposit, Judith Mountains, Montana. Econ. Geol. 89, 602–627. DOI: https://doi.org/ 10.2113/gsecongeo.89.3.602

[5] Wang, F., Liu, F.Y., Bagas, L., et al., 2022. Genesis of the Zhongshangou Au-Te deposit linked to alkaline magmatism at the northern margin of the North China Block: Evidence from sulfides Re-Os geochronology. Ore Geology Reviews. 153, 105265, DOI: https://doi.org/10.1016/j.oregeorev.2022.105264

[6] Lang, J.R., Stanley, C.R., Thompson, J.F.H., 1995. Porphyry copper-gold deposits related to alkalic igneous rocks in the Triassic–Jurassic arc terranes of British Columbia. Arizona Geological Society Digest. 20, 291–236.

[7] Kelley, K.D., Romberger, S.B., Beaty, D.W., et al., 1998. Geochemical and geochronological constraints on the genesis of Au–Te deposits at Cripple Creek, Colorado. Econ. Geol. 93, 981–1012. DOI: https://doi.org/10.2113/gsecongeo.93.7.981

[8] Ahmad, M., Solomon, M., Walshe, J.L., 1987. Mineralogical and geochemical studies of the Emperor gold telluride deposit, Fiji. Econ. Geol. 82, 345–370. DOI: https://doi.org/10.2113/gsecongeo.82.2.345

[9] Cameron, G.H., Wall, V.J., Walshe, J.L., et al., 1995. Gold mineralization at the Porgera gold mine, Papua New Guinea, in response to fluid mixing. Australasian Institute of Mining and Metallurgy Publication Series. 9, 99–100.

[10] DeWitt, E., Foord, E.E., Zartman, R.E., et al., 1996. Chronology of Late Cretaceous igneous and hydrothermal events at the Golden Sunlight gold-silver breccia pipe, southwester Montana. U.S. Geological Survey Bulletin. 2155, 1–48.

[11] Mutschler, F.E., Griffen, M.E., Stevens, D.S., et al., 1985. Precious metal deposits related to alkaline rocks in the North American Cordillera–An interpretive review. South African J Geology. 88, 355–377.

[12] Pals, D.W., Spry, P.G., 2003. Telluride mineralogy of the low-sulfidation epithermal Emperor gold deposit, Vatukoula, Fiji. Mineralogy and Petrology. 79, 285–307. DOI: https://doi.org/10.1007/s00710-003-0013-5

[13] Wilson, M.R., Keyser, T.K., 1988. Geochemistry of porphyry-hosted Au-Ag deposits in the Little Rocky Mountains, Montana. Econ. Geol. 83, 1329–1346. DOI: https://doi.org/10.2113/gsecongeo.83.7.1329

[14] Kwak, T.A.P., 1990. Geochemical and temperature controls on ore mineralization at the Emperor gold mine, Vatuukoula, Fiji. J Geochemical Exploration. 36, 297–337. DOI: https://doi.org/10.1016/0375-6742(90)90059-J

[15] Richards, J.P., Kerrich, R., 1993. The Porgera gold mine, Papua New Guinea–Magmatic hydrothermal to epithermal evolution of an alkalic-type precious metal deposit. Econ Geol. 88, 1017–1052. DOI: https://doi.org/10.2113/gsecongeo.88.5.1017

[16] Müller, D., Franz, L., Herzig, P.M., et al., 2001. Potassic igneous rocks from the vicinity of epithermal gold mineralization, Lihir Island, Papua New Guinea. Lithos. 57, 163–186. DOI: https://doi.org/ 10.1016/S0024-4937(01)00035-4

[17] Richards, J.P., 1995. Alkalic-type epithermal gold deposits–A review. Magmas, fluids, and ore deposits. Canada Mineralogical Association Short Course Series. 23, 367–400.

[18] Sillitoe, R.H., 2010. Porphyry Copper Systems. Econ. Geol. 105, 3–41. DOI: https://doi.org/10.2113/gsecongeo.105.13

[19] Hurtig, N., Williams-Jones, A.E., 2015. Porphyry-epithermal Au–Ag–Mo ore formation by vapor-like fluids: New insights from geochemical modeling. Geology. 43, 587–590. DOI: https://doi:10.1130/G36685.1

[20] Groff, J., Paterson, C.J., 1990. Ore paragenesis and fluids in the Gilt Edge deposit, South Dakota. SEG Guidebook Series. 7, 67–72.

[21] MacLeod, R.J., Barron, J.N., 1990. The geology of the Gilt Edge gold deposit, Northern Black Hills, South Dakota. SEG Guidebook Series. 7, 60–66.

[22] Durkin, T.V., Holm, E.H., Burtts, D.K., 1999. SOUTH DAKOTA – 1998 Mineral Summary Production, Exploration and Environmental Issues. SD DENR Minerals & Mining Program. pp. 1–5. Available from: http://www.state.sd.us/denr/DES/mining/mineprg.htm

[23] Mukherjee, N., 1968. Geology and mineral deposits of the Galena Gilt–Edge area, northern Black Hills, South Dakota. Dissertation, Colorado School of Mines. pp. 1–207.

[24] Lisenbee, A.L., 1981. Studies of the Tertiary intrusions of the northern Black Hills uplift, South Dakota and Wyoming–A historical review. GSA Rocky Mtn Section Ann Mtg, Field trip guidebook. pp. 106–125.

[25] Meier, L.F., 1990. Structure and ore trend description of the Homestake mine. SEG Guidebook Series. 7, 95–102.

[26] Bachman R.L., Caddey S.W., 1990. The Homestake mine, Lead, South Dakota: An overview. SEG Guidebook Series. 7, 89–94.

[27] Armstrong, R.L., Ward, P., 1991. Evolving Geographic Patterns of Cenozoic Magmatism in the North American Cordillera: The Temporal and Spatial Association of Magmatism and Metamorphic Core Complexes. J Geophysical Res. 96, 13,201–13,224. DOI: https://doi.org/10.1029/91JB00412

[28] Duke, G.I., 2009. Black Hills–Alberta carbonatite–kimberlite linear trend: Slab edge at depth?

[29] Tectonophysics. 464, 186–194. DOI: https://doi.org/10.1016/j.tecto.2008.09.034

[30] MacLeod, R.J., 1986. The geology of the Gilt Edge area, northern Black Hills of South Dakota. Thesis, South Dakota School of Mines and Technology. pp. 1–146.

[31] Roedder, E., 1984. Fluid inclusions. Reviews in Mineralogy. 12, 1–646.

[32] Diamond, L.W., 1990. Fluid inclusions evidence for P-V-T-X evolution of hydrothermal solutions in late-alpine gold-quartz veins at Brusson, Val D’Ayas, northwest Italian Alps. American J Science. 290, 912–958.

[33] Goldstein, R.H., Reynolds, T.J., 1994. Systematics of fluid inclusions in diagenetic minerals: Society of Sedimentary Geologists (SEPM) Short Course. 31, pp. 1–199.

[34] Bodnar, R.J., 2003. Introduction to fluid inclusions: Mineralogical Association of Canada Short Course. 32, 81–99.

[35] Paterson, C.J., Uzunlar, N., Groff, J., 1989. A view through an epithermal–mesothermal precious metal system in the northern Black Hills, South Dakota: A magmatic origin for the ore-forming fluids: Econ. Geol. Monograph. 6, 564–570. DOI: https://doi.org/10.5382/Mono.06.43

[36] Potter, II, R.W., 1977. Pressure corrections for fluid-inclusion homogenization temperatures based on the volumetric properties of the system NaCl–H2O. U.S. Geol. Survey J. Res. 5, 603–607.

[37] Larocque, A.C.L., Stimac, J.A., Kieth, J.D., et al., 2000. Evidence for open-system behavior in immiscible Fe–S–O liquids in silicate magmas: Implications for contributions of metals and sulfur to ore-forming fluid. Canadian Mineralogist. 38, 1233–1249. DOI: https://doi.org/10.2113/gscanmin.38.5.1233

[38] Candela, P.A., 1997, A Review of Shallow, Ore-related Granites: Textures, Volatiles, and Ore Metals. J Petrology. 38, 1619–1633. DOI: https://doi.org/10.1093/petroj/38.12.1619

[39] Heinrich, C.A., Driesner, T., Stefansson, A., Seward, T.M., 2004. Magmatic vapor contraction and the transport of gold from the porphyry environment to epithermal ore deposits. Geology. 32, 761–764. DOI: https://doi.org/10.1130/G20629.1

[40] Davis, D.W., Lowenstein, T.K., Spencer, R.J., 1990. Melting behavior of fluid inclusions in laboratory-grown halite crystals in the systems NaCl–H2O, NaCl–KCl–H2O, NaCl–MgCl2–H2O, and NaCl–CaCl2–H2O. Geochimica et Cosmochimica Acta. 54, 591-601. DOI: https://doi.org/10.1016/0016-7037(90)90355-O

[41] Fornadel, A.P., Voudouris, P.C., Spry, P.G., 2012. Mineralogical, stable isotope, and fluid inclusion studies of spatially related porphyry Cu and epithermal Au-Te mineralization, Fakos Peninsula, Limnos Island, Greece. Minerology Petrology. 105, 85–111. DOI: https://doi.org/10.1007/s00710-012-0196-8

[42] Audetat, A., 2015. Compositional evolution and formation conditions of magmas and fluids relative to porphyry molybdenum mineralization at Climax Colorado. J Petrol. 56, 1519–1546. DOI https://doi.org/10.1093/petrology/egv044

[43] Fayol, N., Jebrak, M., 2017. Archean Sanukitoid gold porphyry deposits: A new understanding and genetic model from the Bachelor gold deposit, Abitibi Canada. Econ. Geol. 112, 1913–1936. DOI: https://doi.org/10.5382/econgeo.2017.4534

[44] Duex, T.A., Smith, T.J., McConnell, P.A., et al., 1987. Geology of the Richmond Hill gold deposit. 3rd AIME Western Regional Conference on Precious Metals, Coal, and Environment, Rapid City, Sept 23–26. pp. 67–71.

[45] Lisenbee, A.L., Roggenthen, W.R., 1990. Diatremes and breccia pipes of the northern Black Hills, South Dakota–Wyoming. SEG Guidebook Series. 7, 175–181.

[46] Emmanuel, K.M., Wagner, J.J., Uzunlar, N., 1990. The relationship of gold and silver mineralization to alkalic porphyry and breccia, Golden Reward mine, Lawrence County, South Dakota. SEG Guidebook Series. 7, 140–150.

[47] Uzunlar, N., Paterson, C.J., Lisenbee, A.L., 1990. Tertiary epithermal to mesothermal porphyry-related Au-Ag mineralization in the Homestake mine, Lead, South Datkota: mineral and metal zoning. SEG Guidebook Series. 7, 119–124.

[48] Hurtig, N., Williams-Jones, A.E., 2013. An experimental study of the transport of gold through hydration of AuCl in aqueous vapour and vapour-like fluids. Geochimica et Cosmochimica Acta. 127, 305–325. DOI: https://doi:10.1016/j.gca.2013.11.029

[49] Goldfarb, R.J., Pitcairn, I., 2023. Orogenic gold: is a genetic association with magmatism realistic? Mineralium Deposita. 58, 5–35. DOI: https://doi.org/10.1007/s00126-022-01146-8

[50] McPhail, D.C., 1995. Thermodynamic properties of aqueous tellurium species between 25o and 350°. Geochimica et Cosmochimica Acta. 59, 851–866. DOI: https://doi.org/10.1016/0016-7037(94)00353-X

[51] Grundler, V., Brugger, J., Etschmann, B.E., et al., 2013. Speciation of aqueous tellurium (IV) in hydrothermal solutions and vapors, and the role of oxidized tellurium species in Te transport and gold deposition. Geochimica et Cosmochimica Acta. 120, 298–325. DOI: https://doi.org/10.1016/j.gca.2013.06.009

[52] Cooke, D.R., McPhail, D.C., 2001. Epithermal Au-Ag-Te Mineralization, Acupan, Baguio District, Philippines: Numerical Simulations of Mineral Deposition. Econ. Geol. 96, 109–131. DOI: https://doi.org/10.2113/gsecongeo.96.1.109

[53] Audetat, A., Pettke, T., 2003. The magmatic-hydrothermal evolution of two barren granites: a melt and fluid inclusion study of the Rito del Medio and Cañada Pinabete plutons in northern New Mexico (USA). Geochimica et Cosmochimica Acta. 67, 97–121. DOI: https://doi.org/10.1016/S0016-7037(02)01049-9

[54] Hurtig, N., Migdisov, A., Williams-Jones, A.E., 2021. Are Vapor-Like Fluids Viable Ore Fluids for Cu-Au-Mo Porphyry Ore Formation? Econ. Geol. 116, 1599–1624. DOI: https://doi:10.5382/econgeo.4835

[55] Simon, A.C., Frank, M.R., Pettke,T., et al., 2005. Gold partitioning in melt-vapor-brine systems. Geochimica et Cosmochimica Acta. 69, 3321–3335. DOI: https://doi.org/10.1016/j.gca.2005.01.028

[56] Park, J.W., Campbell, I.H., Malaviarachchi, S.P.K., et al., 2018. Chalcophile element fertility and the formation of porphyry Cu ± Au deposits. Mineralium Deposita. 54, 657–670. DOI: https://doi.org/10.1007/s00126-018-0834-0

[57] Li, N., Zhang, B., Ulrich, T., et al., 2024. Magmatic degassing controlled the metal budget of the Axi epithermal gold deposit, China. American Mineralogist. 109, 51–60. DOI: https://doi.org/10.2138/am-2022-8610

[58] Leys, C., Schwarz, A., Cloos, M., et al., 2020. Chapter 29: Grasberg Copper-Gold-(Molybdenum) Deposit: Product of Two Overlapping Porphyry Systems. SEG Special Publication 23, Geology of the World’s Major Gold Deposits and Provinces, Richard H. Sillitoe, Richard J. Goldfarb, François Robert, Stuart F. Simmons. DOI: https://doi.org/10.5382/SP.23.29