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SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH
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SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH

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SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH TEMPERATURES AND DIFFERENTIAL STRESSES: AN EXPERIMENTAL APPROACH

SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH TEMPERATURES AND DIFFERENTIAL STRESSES: AN EXPERIMENTAL APPROACH

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  • 1. SULFIDE REMOBILISATION FROM SULFIDE ORE AT HIGH TEMPERATURES AND DIFFERENTIAL STRESSES: AN EXPERIMENTAL APPROACH
  • 2. INTRODUCTION:  Remobilisation is the process of ore components being transported from pre-existing ore bodies (Mookherjee, 1976;Marshall et al., 2000a, b).  Radical modification of primary ore bodies due to mechanical and chemical remobilization (Mookherjee, 1976; Marshall & Gilligan, 1987). Marshall and Gilligan (1993) classified remobilisation into internal and external cases.  Previous experiments commonly separated mechanical from chemical remobilisation, and hence the simulations did not address the interactions between the two factors.
  • 3. STARTING MATERIAL:  Collected from -707 m level in the main ore zone of the Hongtoushan deposit, Liaoning Province, NE China.  It is a volcanic-hosted massive sulfide deposit metamorphosed at upper amphibolite facies at temperatures between 600 and 650°C during 3.0–2.8 Ga (Zhang et al., 1984; Liu et al., 1994).  The ore consists of pyrite (32 vol.%), chalcopyrite (9%),pyrrhotite (8%), and sphalerite (6%).  Gangue minerals are quartz (26%) and other silicates (19%, including hornblende, garnet, biotite, plagioclase, and muscovite  Average metal contents are 4.06 wt.% Cu, 2.48 wt.% Zn, 0.03 wt.% Pb, 0.36 ppm Au, and 94 ppm Ag which were observed by atomic absorption spectrometry (AAS)
  • 4. TEXTURE:  Pyrite occurs as euhedral to subhedral porphyroblastic crystals.  Pyrrhotite grains in the matrix are mostly hexagonal (Gu et al., 2001b).  Chalcopyrite and sphalerite also occur as subhedral to anhedral grains in the matrix  Most gangue minerals form globular textures, 2 to 5 mm in size.
  • 5. INSTRUMENTATION AND METHODOLOGY:  It was conducted in a horizontal compression chamber on a Changjiang 500 triaxial rock stress machine at the Guiyang Institute of Geochemistry, Chinese Academy of Sciences.  Argon gas provides the confining pressure, which is measured by means of a Heise gauge with a maximum capability of 600 Mpa with <1% uncertainty.  Auto-regulator transformer  The axial load was applied to the sample through a hardened and polished steel piston, 1.9 cm in diameter.
  • 6. CONTINUED….  The magnitude of the axial load is measured outside of the chamber by means of a load cell containing a resistance bridge of four foil strain gauges.  Ore sample for each run was cut into a cylinder 40 mm in length and 17 mm in diameter, and immersed in solution of 20 wt.% NaCl for 260 h.  The sample was enveloped in an aluminium foil and then mounted in a graphite tube.  At the termination of each experiment, power for the furnace was turned off, but pressures were held constant while the specimen cooled to room temperature.
  • 7. CONDITIONS FOR THE 4 RUNS:
  • 8. RESULTS
  • 9. DEFORMATION AND MECHENICAL REMOBILIZATION  Set of release fractures: Perpendicular to sample length  Become much better developed with increasing temperature  PYRITE:  Cataclastic deformation  Rotation shows plastic behavior of surrounding material
  • 10. CHALCOPYRITE-PYRRHOTITESPHALERITE  Plastic deformation with only local cataclastic textures  Deformation bands and twins
  • 11. CHEMICAL REMOBILIZATION: SULPHIDE VEINLETS  Cross-cut Pyrite-porphyroclasts  Show no displacement along strike  Abundance: Chalcopyrite > Pyrrhotite > Spherite  Chemical remobilization:  Discontinuity outside the grains  Change in composition of Sphalerite
  • 12. SULPHIDE VEINLETS: EFFECT OF TEMPERATURE  Remobilization becomes more intense with increasing temperature  At 362o C :   > 2vol% 55% Chalcopyrite, 45% Pyrrhotite, 1% Sphalerite At 682o C :  5%vol% 80% Chalcopyrite, 20% Pyrrhotite, 1% Sphalerite
  • 13. CHEMICAL REMOBILIZATION: SULPHIDE MICROCRYSTALLITES  Space fillings   Aggregates of worm-like bodies   Same minerals welded by same mineral e.g Chalcopyrite Pure pyrite growth along fissures of Chalcopyrite Lower in relief
  • 14. DISCUSSION
  • 15. MECHANISMS OF DEFORMATION  Minerals exhibit various degrees of cataclastic deformation in lowtemperature (362C)  The strength of minerals decreases markedly with increasing temperature.  brittle-ductile transition of pyrite  brittle-ductile transition of pyrrhotite, chalcopy- rite, and sphalerite  Annealing and recrystallisation  Annealing of pyrrhotite.
  • 16. MECHANISMS FOR CHEMICAL REMOBILISATION  All the present experiments were performed at temperatures below the melting points of all the sulfides in the samples (Vaughan & Craig, 1997; Stevens et al., 2005; Sack & Ebel, 2006)  Most of the veinlets cutting pyrite porphyroclasts were formed by chemical remobilisation
  • 17. THIS CONCLUSION IS SUPPORTED BY THE FOLLOWING EVIDENCE: 1. the amout of remobilised chalcopyrite in most veinlets markedly exceeds the remobilised pyrrhotite, particularly in the high temperature runs 2. sulfides in many veinlets are not connected to the same sulfides outside the pyrite cracks 3. pyrite grains are replaced by chal- copyrite in some of the runs 4. chemical composition of remobilised sphalerite in the veinlets deviates from that of the residual sphalerite.
  • 18. GEOLOGICAL APPLICATIONS   Syn-tectonic remobilisation of sulfides in the natural system is a complex process, and would be affected conspicuously by varying factors, such as: strain rate,  temperature,  fluid property,  composition of the original ore, and;  time length for the process
  • 19. CONT.  The present experiments show, however, that the extent of mechanical translocation is limited in comparison to chemical remobilisation.  The present experiments show that sulfides vary in ability of chemical remobilisation, particularly at higher temperatures.  The present experiments show that remobilisation could substantially modify the geometry and distribution pattern of syn- genetic orebodies, and produce a range of textures characteristic of epigenetic mineralisation
  • 20. CONT.  The present experiments demonstrate that remobilised sul- fides select preferentially pre-existing sulfide minerals, particularly pyrite, as substrate for overgrowth  Experiments and geology research suggest that pyrite is a favourable substrate for gold precipitation (Chen & Fu, 1992; Larocque & Hodgson, 1995; Zhang et al., 1996; Simon et al., 1999; Zhou et al., 2000; Gu et al., 2001a, 2007)
  • 21. ACKNOWLEDGMENTS This research was jointly supported by Natural Science Foundation of China (no. 40872064) and Foundation for Doctorial Research, Ministry of Education of China (no. 20060284013). We wish to thank Prof. Sun Yuan for his helpful discussion with the authors. The authors are also grateful to Yasushi Watanabe and one anonymous RGE reviewer for their constructive comments and language corrections on the early manuscript for this paper.
  • 22. REFERENCES  Barton, P. B. Jr. (1973) Solid solution in the system Cu-Fe-S Part I: the Cu-S and Cu-Fe-S joins. Econ. Geol., 68, 455–465.  Bellot, J. P. (2004) Shear zone-hosted polymetallic sulfides in the south Limousin area, massif central, France: remobilized sulfide deposits related to Variscan collisional tectonics and amphibolite facies metamorphism. Econ. Geol., 99, 819–827.  Berger, A. and Stu ̋nitz, H. (1996) Deformation mechanisms and reaction of hornblende: examples from the Bergell tonalite (Central Alps). Tectonophysics, 257, 149–174.  Bourcier, W. H. and Barnes, H. L. (1987) Ore solution chemistry: VII. Stabilities of chloride and bisulphide complexes of zinc to 350oC. Econ. Geol., 82, 1839–1863.  Bursnall, J. T. (1989) Mineralization and shear zones. Geology. Ass. Can., Short Course Notes, 6, 1–299.  SO0o0 0on..;)

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