|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
U.S. Geological Survey, Box 25046, MS 973, Denver, Colorado 80225
U.S. Geological Survey, Box 25046, MS 963, Denver, Colorado 80225
Teck Cominco American Inc., 15918 East Euclid Avenue, Spokane, Washington 99216
Oak Ridge National Laboratories, P.O. Box 2008, Oak Ridge, Tennessee 37831
U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192
1175 C Bear Mountain Drive, Boulder, Colorado 80305
U.S. Geological Survey, National Center, MS 954, Reston, Virginia 20192
U.S. Geological Survey, Box 25046, MS 973, Denver, Colorado 80225
Corresponding author: e-mail, kdkelley{at}usgs.gov
The Red Dog Zn-Pb deposits are hosted in organic-rich mudstone and shale of
the Mississippian Kuna Formation. A complex mineralization history is defined by
four sphalerite types or stages: (1) early brown sphalerite, (2) yellow-brown
sphalerite, (3) red-brown sphalerite, and (4) late tan sphalerite. Stages 2 and
3 constitute the main ore-forming event and are volumetrically the most
important. Sulfides in stages 1 and 2 were deposited with barite, whereas stage
3 largely replaces barite. Distinct chemical differences exist among the
different stages of sphalerite. From early brown sphalerite to later
yellow-brown sphalerite and red-brown sphalerite, Fe and Co content generally
increase and Mn and Tl content generally decrease. Early brown sphalerite
contains no more than 1.9 wt percent Fe and 63 ppm Co, with high Mn (up to 37
ppm) and Tl (126 ppm), whereas yellow-brown sphalerite and red-brown sphalerite
contain high Fe (up to 7.3 wt %) and Co (up to 382 ppm), and low Mn (<27 ppm)
and Tl (<37 ppm). Late tan sphalerite has distinctly lower Fe (< 0.9 wt %)
and higher Tl (up to 355 ppm), Mn (up to 177 ppm), and Ge (426 ppm), relative to
earlier sphalerite. Wide ranges in concentrations of Ag, Cu, Pb, and Sb
characterize all sphalerite types, particularly yellow-brown sphalerite and
red-brown sphalerite, and most likely reflect submicroscopic inclusions of
galena, chalcopyrite and/or tetrahedrite in the sphalerite. In situ ion
microprobe sulfur isotope analyses show a progression from extremely low 
34S
values for stage 1 (as low as –37.2
) to much higher values for yellow-brown
sphalerite (mean of 3.3; n = 30) and red-brown sphalerite (mean of
3.4; n = 20). Late tan sphalerite is isotopically light (–16.4 to –27.2).
The textural, chemical, and isotopic data indicate the following paragenesis: (1) deposition of early brown sphalerite with abundant barite, minor pyrite, and trace galena immediately beneath the sea floor in unconsolidated mud; (2) deposition of yellow-brown sphalerite during subsea-floor hydrothermal recrystallization and coarsening of preexisting barite; (3) open-space deposition of barite, red-brown sphalerite and other sulfides in veins and coeval replacement of barite; and (4) postore sulfide deposition, including the formation of late tan sphalerite breccias. Stage 1 mineralization took place in a low-temperature environment where fluids rich in Ba mixed with pore water or water-column sulfate to form barite, and metals combined with H2S derived from bacterial sulfate reduction to form sulfides. Higher temperatures and salinities and relatively oxidized ore-stage fluids (stages 2 and 3) compared with stage 1 were probably important controls on the abundances and relative amounts of metals in the fluids and the resulting sulfide chemistry. Textural observations and isotopic data show that preexisting barite was reductively dissolved, providing a source of H2S for sulfide mineral formation. In stage 3, the continued flow of hydrothermal fluids caused thermal alteration of organic-rich mudstones and a build-up of methane that led to fluid overpressuring, hydrofracturing, and vein formation. Barite, red-brown sphalerite, and other sulfides were deposited in the veins, and preexisting barite was pervasively replaced by red-brown sphalerite. Hydrothermal activity ceased until Jurassic time when thrusting and large-scale fluid flow related to the Brookian orogeny remobilized and formed late tan sphalerite in tectonic breccias.
This article has been cited by other articles:
|
|
 |
|
  K. D. Kelley and T. Hudson Natural versus anthropogenic dispersion of metals to the environment in the Wulik River area, western Brooks Range, northern Alaska Geochemistry: Exploration, Environment, Analysis, February 1, 2007; 7(1): 87 - 96. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. L. Huston, B. Stevens, P. N. Southgate, P. Muhling, and L. Wyborn Australian Zn-Pb-Ag Ore-Forming Systems: A Review and Analysis Economic Geology, September 1, 2006; 101(6): 1117 - 1157. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. R. Seal II Sulfur Isotope Geochemistry of Sulfide Minerals Reviews in Mineralogy and Geochemistry, January 1, 2006; 61(1): 633 - 677. [Full Text] [PDF]
|
|
|
|
|
|
K. D. Kelley and S. Jennings A Special Issue Devoted to Barite and Zn-Pb-Ag Deposits in the Red Dog District, Western Brooks Range, Northern Alaska Economic Geology, November 1, 2004; 99(7): 1267 - 1280. [Full Text] [PDF]
|
|
|
|
|
|
C. S. Rombach and P. W. Layer Geochronology of the Western and Central Brooks Range, Alaska: Implications for the Geologic Evolution of the Anarraaq and Red Dog Zn-Pb-Ag Deposits Economic Geology, November 1, 2004; 99(7): 1307 - 1322. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. A. Dumoulin, A. G. Harris, C. D. Blome, and L. E. Young Depositional Settings, Correlation, and Age of Carboniferous Rocks in the Western Brooks Range, Alaska Economic Geology, November 1, 2004; 99(7): 1355 - 1384. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. F. Slack, J. A. Dumoulin, J. M. Schmidt, L. E. Young, and C. S. Rombach Paleozoic Sedimentary Rocks in the Red Dog Zn-Pb-Ag District and Vicinity, Western Brooks Range, Alaska: Provenance, Deposition, and Metallogenic Significance Economic Geology, November 1, 2004; 99(7): 1385 - 1414. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. A. Johnson, K. D. Kelley, and D. L. Leach Sulfur and Oxygen Isotopes in Barite Deposits of the Western Brooks Range, Alaska, and Implications for the Origin of the Red Dog Massive Sulfide Deposits Economic Geology, November 1, 2004; 99(7): 1435 - 1448. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. L. Leach, E. Marsh, P. Emsbo, C. S. Rombach, K. D. Kelley, and M. Anthony Nature of Hydrothermal Fluids at the Shale-Hosted Red Dog Zn-Pb-Ag Deposits, Brooks Range, Alaska Economic Geology, November 1, 2004; 99(7): 1449 - 1480. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. F. Slack, K. D. Kelley, V. M. Anderson, J. L. Clark, and R. A. Ayuso Multistage Hydrothermal Silicification and Fe-Tl-As-Sb-Ge-REE Enrichment in the Red Dog Zn-Pb-Ag District, Northern Alaska: Geochemistry, Origin, and Exploration Applications Economic Geology, November 1, 2004; 99(7): 1481 - 1508. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. A. Ayuso, K. D. Kelley, D. L. Leach, L. E. Young, J. F. Slack, J. F. Wandless, A. M. Lyon, and J. L. Dillingham Origin of the Red Dog Zn-Pb-Ag Deposits, Brooks Range, Alaska: Evidence from Regional Pb and Sr Isotope Sources Economic Geology, November 1, 2004; 99(7): 1533 - 1553. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Morelli, R. A. Creaser, D. Selby, K. D. Kelley, D. L. Leach, and A. R. King Re-Os Sulfide Geochronology of the Red Dog Sediment-Hosted Zn-Pb-Ag Deposit, Brooks Range, Alaska Economic Geology, November 1, 2004; 99(7): 1569 - 1576. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
