Mineralium Deposita

, 44:415 | Cite as

A geochemical study of the Sweet Home Mine, Colorado Mineral Belt, USA: hydrothermal fluid evolution above a hypothesized granite cupola

  • Volker LüdersEmail author
  • Rolf L. Romer
  • H. Albert Gilg
  • Robert J. Bodnar
  • Thomas Pettke
  • Dean Misantoni


Deposition of quartz–molybdenite–pyrite–topaz–muscovite–fluorite and subsequent hübnerite and sulfide–fluorite–rhodochrosite mineralization at the Sweet Home Mine occurred coeval with the final stage of magmatic activity and ore formation at the nearby world-class Climax molybdenum deposit about 26 to 25 m.y. ago. The mineralization occurred at depths of about 3,000 m and is related to at least two major fluid systems: (1) one dominated by magmatic fluids, and (2) another dominated by meteoric water. The sulfur isotopic composition of pyrite, strontium isotopes and REY distribution in fluorite suggest that the early-stage quartz–molybdenite–pyrite–topaz–muscovite–fluorite mineral assemblage was deposited from magmatic fluids under a fluctuating pressure regime at temperatures of about 400°C as indicated by CO2-bearing, moderately saline (7.5–12.5 wt.% NaCl equiv.) fluid inclusions. LA-ICPMS analyses of fluid inclusions in quartz demonstrate that fluids from the Sweet Home Mine are enriched in incompatible elements but have considerably lower metal contents than those reported from porphyry–Cu–Au–Mo or Climax-type deposits. The ore-forming fluid exsolved from a highly differentiated magma possibly related to the deep-seated Alma Batholith or distal porphyry stock(s). Sulfide mineralization, marking the periphery of Climax-type porphyry systems, with fluorite and rhodochrosite as gangue minerals was deposited under a hydrostatic pressure regime from low-salinity ± CO2-bearing fluids with low metal content at temperatures below 400°C. The sulfide mineralization is characterized by mostly negative δ34S values for sphalerite, galena, chalcopyrite, and tetrahedrite, highly variable δ18O values for rhodochrosite, and low REE contents in fluorite. The Pb isotopic composition of galena as well as the highly variable 87Sr/86Sr ratios of fluorite, rhodochrosite, and apatite indicates that at least part of the Pb and Sr originated from a much more radiogenic source than Climax-type granites. It is suggested that the sulfide mineralization at the Sweet Home Mine formed from magmatic fluids that mixed with variable amounts of externally derived fluids. The migration of the latter fluids, that were major components during late-stage mineralization at the Sweet Home Mine, was probably driven by a buried magmatic intrusion.


Mo porphyry deposits Climax Sweet Home Colorado Mineral Belt Rhodochrosite Fluid inclusions Stable isotopes Lead isotopes Strontium isotopes 



We are most grateful to Bryan Lees (Collector’s Edge, Golden, CO) for providing numerous fascinating mineral specimens and detailed information. Special thanks go to T. James Reynolds (Denver) and Bernd Lehmann (Clausthal) for constructive comments. We are indebted to P. Dulski (GFZ Potsdam) for REY analysis and H. Strauß (University Münster) for sulfur isotope analysis. We thank G. Berger (GFZ) for preparing numerous doubly polished thick sections.


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Copyright information

© Springer-Verlag 2008

Authors and Affiliations

  • Volker Lüders
    • 1
    Email author
  • Rolf L. Romer
    • 1
  • H. Albert Gilg
    • 2
  • Robert J. Bodnar
    • 3
  • Thomas Pettke
    • 4
  • Dean Misantoni
    • 5
  1. 1.GeoForschungsZentrum PotsdamPotsdamGermany
  2. 2.Lehrstuhl für IngenieurgeologieTU MünchenMunichGermany
  3. 3.Department of GeosciencesVirginia TechBlacksburgUSA
  4. 4.Institute of Geological SciencesUniversity of BernBernSwitzerland
  5. 5.Colorado Calumet Company Inc.GoldenUSA

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