|
|
 |
|||||||||||||||||
|
|||||||||||||||||
 |
|||||||||||||||||
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Univ. Tasmania, Cent. Ore Deposit and Explor. Stud., Hobart, Tasmania, Australia
Underlying the 17 million metric ton, high-grade, polymetallic Hellyer volcanic-hosted massive sulfide deposit is a well-developed and preserved alteration zone and stringer vein system. Mineralogical zoning exists within a footwall alteration pipe, with a central siliceous core giving way to zones of chlorite, chlorite-carbonate, sericite, and finally sericite-quartz (stringer envelope zone) on the margins. Pervasive alteration started with development of sericite-quartz that was subsequently overprinted by sericite, then chlorite, and finally quartz as hydrothermal activity intensified in the center of the alteration zone.Compared to unaltered footwall andesite, the siliceous core is enriched in SiO 2 , K 2 O, MnO, Y, Fe 2 O 3 , and S but depleted in Na 2 O and CaO. Additions of MgO, MnO, Fe 2 O 3 , S, and Y and losses of Na 2 O and CaO occur in the chlorite zone. In the sericite zone SiO 2 , MgO, K 2 O, MnO, Fe 2 O 3 , and S are gained but Na 2 O and CaO are depleted. Only Na 2 O is depleted whereas MnO, K 2 O, P 2 O 5 , S, Y, and SiO 2 are gained in the stringer envelope zone. The alteration index (AI) value [(K 2 O + MgO)/(K 2 O + Na 2 O + CaO + MgO)] X 100 becomes progressively larger, with increasing intensity of alteration, from the unaltered andesite (AI = 36) to the siliceous core (AI = 91).The Hellyer stringer zone contains distinct thick synmineralization veins that represent the channelways for hydrothermal solutions passing up through the alteration zone to the sea floor. Eight stages of veining are distinguished in the stringer zone: one stage ofpremineralization (stage 1), three stages of synmineralization (stages 2A, 2B, 2C), and four stages of postmineralization veining (stages 3-6). Synmineralization veining closely follows the formation of the pervasive footwall alteration and is most intense in the siliceous core.Metal zoning indicates the presence, and alignment, of several feeder systems underlying the deposit. The main feeder is located under the middle of the deposit with secondary feeder systems underlying the southern and northern portions of the deposit. Iron and copper are concentrated in the cores of the feeders with zinc and lead, silver, gold and arsenic, and barium becoming increasingly dispersed away from the centers of hydrothermal activity.Distinct delta 34 S variations exist between vein stages within the stringer and stringer envelope zones. The main base metal-rich stage 2B veins display lower sulfur isotope values (3.8-8.9ppm, mean = 6.9ppm) than the earlier stage 2A veins (5.7-11.1ppm, mean = 9.9ppm). The delta 34 S values for stage 2A veins in the stringer envelope zone are significantly higher delta 34 S values (11.9-40.7ppm, mean = 25.0ppm) than those from the stringer zone. Variations in delta 34 S can be explained by a model where the hydrothermal fluid initially consists of totally to partially reduced seawater sulfate that evolves into a fluid dominated by igneous sulfur (ore-forming fluid) as the convection system intensified and penetrated deeper into the footwall. At the end of the hydrothermal system's life sulfate becomes more abundant in the fluid, and eventually dominant.
This record provided courtesy of AGI/GeoRef.
This article has been cited by other articles:
|
|
 |
|
  J. B. Gemmell Hydrothermal Alteration Associated with the Gosowong Epithermal Au-Ag Deposit, Halmahera, Indonesia: Mineralogy, Geochemistry, and Exploration Implications Economic Geology, August 1, 2007; 102(5): 893 - 922. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. Warren, S. F. Simmons, and J. L. Mauk Whole-Rock Geochemical Techniques for Evaluating Hydrothermal Alteration, Mass Changes, and Compositional Gradients Associated with Epithermal Au-Ag Mineralization Economic Geology, August 1, 2007; 102(5): 923 - 948. [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]
|
|
|
|
|
|
S. Jones, J. B. Gemmell, and G. J. Davidson Petrographic, Geochemical, and Fluid Inclusion Evidence for the Origin of Siliceous Cap Rocks Above Volcanic-Hosted Massive Sulfide Deposits at Myra Falls, Vancouver Island, British Columbia, Canada Economic Geology, May 1, 2006; 101(3): 555 - 584. [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]
|
|
|
|
 |
|
 M. Solomon, F. Tornos, and O.C. Gaspar Explanation for many of the unusual features of the massive sulfide deposits of the Iberian pyrite belt Geology, January 1, 2002; 30(1): 87 - 90. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. L. Allen and P. Weihed Global comparisons of volcanic-associated massive sulphide districts Geological Society, London, Special Publications, January 1, 2002; 204(1): 13 - 37. [Abstract] [PDF]
|
|
|
|
 |
|
 T. Monecke, S. Kohler, R. Kleeberg, P. M. Herzig, and J. B. Gemmell QUANTITATIVE PHASE-ANALYSIS BY THE RIETVELD METHOD USING X-RAY POWDER-DIFFRACTION DATA: APPLICATION TO THE STUDY OF ALTERATION HALOS ASSOCIATED WITH VOLCANIC-ROCK-HOSTED MASSIVE SULFIDE DEPOSITS Can Mineral, December 1, 2001; 39(6): 1617 - 1633. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. Solomon, M. Solomon, and O. C. Gaspar Textures of the Hellyer Volcanic-Hosted Massive Sulfide Deposit, Tasmania--the Aging of a Sulfide Sediment on the Sea Floor Economic Geology, November 1, 2001; 96(7): 1513 - 1534. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. B. Gemmell, J. B. Gemmell, and W. Herrmann A Special Issue on Alteration Associated with Volcanic-Hosted Massive Sulfide Deposits, and Its Exploration Significance Economic Geology, August 1, 2001; 96(5): 909 - 912. [Full Text] [PDF]
|
|
|
|
|
|
R. R. Large, R. R. Large, J. B. Gemmell, H. Paulick, and D. L. Huston The Alteration Box Plot: A Simple Approach to Understanding the Relationship between Alteration Mineralogy and Lithogeochemistry Associated with Volcanic-Hosted Massive Sulfide Deposits Economic Geology, August 1, 2001; 96(5): 957 - 971. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. C. Gifkins, C. C. Gifkins, and R. L. Allen Textural and Chemical Characteristics of Diagenetic and Hydrothermal Alteration in Glassy Volcanic Rocks: Examples from the Mount Read Volcanics, Tasmania Economic Geology, August 1, 2001; 96(5): 973 - 1002. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. B. Gemmell, J. B. Gemmell, and R. Fulton Geology, Genesis, and Exploration Implications of the Footwall and Hanging-Wall Alteration Associated with the Hellyer Volcanic-Hosted Massive Sulfide Deposit, Tasmania, Australia Economic Geology, August 1, 2001; 96(5): 1003 - 1035. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Schardt, C. Schardt, D. R. Cooke, J. B. Gemmell, and R. R. Large Geochemical Modeling of the Zoned Footwall Alteration Pipe, Hellyer Volcanic-Hosted Massive Sulfide Deposit, Western Tasmania, Australia Economic Geology, August 1, 2001; 96(5): 1037 - 1054. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
M. G. Doyle and M. G. Doyle Volcanic Influences on Hydrothermal and Diagenetic Alteration: Evidence from Highway-Reward, Mount Windsor Subprovince, Australia Economic Geology, August 1, 2001; 96(5): 1133 - 1148. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
W. Herrmann, W. Herrmann, and A. P. Hill The Origin of Chlorite-Tremolite-Carbonate Rocks Associated with the Thalanga Volcanic-Hosted Massive Sulfide Deposit, North Queensland, Australia Economic Geology, August 1, 2001; 96(5): 1149 - 1173. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
H. Paulick, H. Paulick, W. Herrmann, and J. B. Gemmell Alteration of Felsic Volcanics Hosting the Thalanga Massive Sulfide Deposit (Northern Queensland, Australia) and Geochemical Proximity Indicators to Ore Economic Geology, August 1, 2001; 96(5): 1175 - 1200. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Sharpe, R. Sharpe, and J. B. Gemmell Alteration Characteristics of the Archean Golden Grove Formation at the Gossan Hill Deposit, Western Australia: Induration as a Focusing Mechanism for Mineralizing Hydrothermal Fluids Economic Geology, August 1, 2001; 96(5): 1239 - 1262. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. W. Brauhart, C. W. Brauhart, D. L. Huston, D. I. Groves, E. J. Mikucki, and S. J. Gardoll Geochemical Mass-Transfer Patterns as Indicators of the Architecture of a Complete Volcanic-Hosted Massive Sulfide Hydrothermal Alteration System, Panorama District, Pilbara, Western Australia Economic Geology, August 1, 2001; 96(5): 1263 - 1278. [Abstract] [Full Text] [PDF]
|
|
| JOURNAL HOME | HELP | CONTACT PUBLISHER | SUBSCRIBE | ARCHIVE | SEARCH | TABLE OF CONTENTS |
