Abstract
New investigations are carried out on the mineralogy and mineral chemistry of sulfide assemblages obtained in samples from one core in the hydrothermally active, southwest basin of the Atlantis II deep, Red Sea. The most abundant sulfide phases are the exsolved intermediate solid solution (ISS) and chalcopyrite. Sphalerite, pyrrhotite, marcasite, mackinawite, and presumably wurtzite are also observed. Two distinct groups of paragenesis were encountered: (a) Intermediate solid solution with sphalerite incrustations and intergrowths, and (b) intermediate solid solution barren of sphalerite intergrowths. The first group is confined to the upper part of the Co zone and the SOAN zone (Bäcker and Richter 1973), and the second is present in the entire core 100-3-7. An optically isotropic chalcopyrite is found for the first time as a natural mineral in Atlantis II, Red Sea. Yet its existence as a novel phase needs x-ray confirmation. It exhibits a lower reflectivity than normal chalcopyrite and is isotropic. Chalcopyrite occurs either as a single phase or in association with tetragonal chalcopyrite. Our investigations indicate that the formation of Atlantis II deposits is a result of complex processes. These processes are characterized by compositional changes in the ore-bearing fluids and the change in sulfur fugacity (especially with depth). The presence of exsolved chalcopyrite lamellae in ISS indicates slow cooling below 450°C. However, it is difficult to understand why the cubic chalcopyrite is not converted to the tetragonal form even though the temperature of transformation lies above 450°C (470° – 500°C, Cabri 1973). The Cu/Fe ratio changes in the exsolved chalcopyrite lamellae from core to rim of the composite grains. The ratio is higher in the rims. This suggests that primary inhomogenous ISS grains formed from solutions with a continuous increase in the Cu/Fe ratio. Slow cooling is also required to account for the exsolution of chalcopyrite lamellae in ISS. The low sulfur content in isotropic chalcopyrite is also suggestive of low fs2. The low S content in the chalcopyrite may be the controlling factor for the sluggish conversion from cubic to tetragonal chalcopyrite. Mackinawite lamellae show the same orientation in ISS and exsolved isotropic chalcopyrite indicating that mackinawite exsolved before the breakdown of ISS. This strongly suggests that mackinawite is stable above 300°C (contrary to experimental results by Zoka et al. 1973). Pyrrhotite was probably formed by the sulfurization of ilvaite. The pyrrhotite grains with several complex successive zones show the sequence of the sulfurization episodes.
Metalliferous sediments related to hot brines were discovered in the Red Sea in 1964 (Miller et al. 1966). Since then, several papers have been published on this subject (Degens and Ross 1969, Bäcker and Schoell 1972, Bäcker and Richter 1973, Bignell et al. 1976, Shanks and Bishoff 1977, Weber-Diefenbach 1977, Nöltner 1979, Pottorf 1980, Pottorf and Barnes 1983, Oudin et al. 1984).
Complex sulfide phases including intermediate solid solution (ISS), chalcopyrite, and a chalcopyritelike mineral (which exhibits a lower reflectivity than normal chalcopyrite and appears to be isotropic occur in the metalliferous sediments. These phases were found in association with several minerals in different parageneses. In an attempt to understand the origin of the formation of the sulfide-bearing sediments in the Atlantis II deep of the Red Sea, a detailed study of the phase relations of the Cu-Fe sulfide ores of this locality was carried out.
Similar content being viewed by others
References
Amcoff, Ö.: Heating experiments of chalcopyrite-pyrrhotite ores: studies on the stability of the intermediate solid solution: N. Jb. Miner. Mh., 553–568 (1981)
Bäcker, H., Schoell, M.: New deeps with brines and metalliferous sediments in the Red Sea: Nature Phys. Sci., 24:153–158 (1972)
Bäcker, H., Richter, H.: Die recente hydrothermal-sedimentäre Lagerstätte Atlantis II — Tief im Roten Meer: Geol. Rundschau 62:697–740 (1973)
Bignell, R.O., Cronan, D.S., Tooms, J.S.: Red Sea metalliferous brine precipitates in Strong D. F., ed., Metallogeny and Plate Tectonics: Geol. Assoc. Canada spec. Paper 14:47–179 (1976)
Budko, I.A., Kulagov, E.A.: Natural cubic chalcopyrite: Doklady Akad. Nauk SSSR 152:408–410 (1963)
Cabri, L.J.: A new copper-iron sulfide: Econ. Geol., 62:910–925 (1967)
Cabri, L.J.: New data on phase relations in the Cu-Fe-S system: Econ. Geol. 68:443–454 (1973)
Clark, A.H.: Stability field of monoclinic pyrrhotite trans.: Inst. Min. Metall. 75:B232-B235 (1966)
Cronvold, F., Haraldsen, H.: On the phase relations of synthetic and natural pyrrhotites: Acta Chemica Scandinavica, 6:1452–1459 (1952)
Degens, E.T., Ross, D.A.: Hot Brines and Recent Heavy Metal Deposits in the Red Sea, a geochemical and Geophysical Account. Berlin-Heidelberg-New York: Springer 1969
Hiller, J.E., Probsthain, K.: Thermische und röntgenographische Untersuchungen an Kupferkies: Z. Krist. 108:108–129 (1956)
Kissin, S.A.: Phase relations in a portion of Fe-S system: Unpubl. ph. D. thesis, Univ. Toronto, 294 (1974) after (Kissin and Scott 1982)
Kissin, S.A., Scott, S.D.: Phase relations involving pyrrhotite below 350 C: Econ. Geol. 77:1739–1754 (1982)
Manheim, F.: Geochemical studies in the Red Sea. Ship-board analysis and sediment samples: U.S. geological survey, Woods Hole, Mass (1971)
Manheim, F.: Red Sea geochemistry: Washington, U.S. Govt. Printing Office, Deep Sea Drilling Proj. Initial Reports, 23:975–998 (1974)
Miller, H.E., Densmore, C.D., Degens, E.T., Hathaway, J.C., Manheim, F.T., McFarlin, P.F., Pocklington, R., Jokela, A.: Hot brines and recent iron deposits in deeps of the Red Sea. Geochim. Acta, 30:341–359 (1966)
Mukaiyama, H., Izawa, E.: Phase relations in the Cu-Fe-S system, the copper-deficient part, in Tatsumi, T., ed., Volcanism and Ore genesis: Tokyo, Univ. Tokyo Press: 339–555 (1970)
Nöltner, T.: Erzmikroskopische Untersuchungen an Erzschlämmen aus dem Atlantis II Tief, Rotes Meer: Diplomarbeit, Heidelberg Universität (FRG) (unpublished) (1979)
Oudin, E.: Hydrothermal Sulfide Deposits of the East Pacific Rise (21) Part 1: Descriptive mineralogy. Marine Minning, 4:39–72 (1983)
Oudin, E.: Isocubanite. Internal Report (1984)
Oudin, E., Thisse, Y., Romdoz, C.: Fluid Inclusion and Mineralogical Evidence for High-Temperature Saline Hydrothermal Circulation in the Red Sea Metalliferous Sediments: Preliminary Results. Marine Minning 5, no 1:3–31 (1984)
Pottorf, R.J.: Hydrothermal Sediments of the Red Sea, Atlantis II Deep — A model for massive sulfide-type ore deposits. Unpub. Ph. D. dissert., The Pennsylvania State Univ.: 193 (1980)
Pottorf, R.J., Barnes, H.L.: Mineralogy, geochemistry, and ore genesis of hydrothermal sediments from the Atlantis II deep, Red Sea. Econ. Geol. Mon. 5:198–223 (1983)
Shanks, W.C., Bischoff, J.L.: Ore Transport and deposition in the Red Sea geothermal system: a geochemical model: geochim. et cosmochim-Acta, 41:1507–1519 (1977)
Sugaki, A., Shima, H., Kitakaze, A., Harada, H.: Isothermal phase relations in the system Cu-Fe-S under hydrothermal conditions at 350 C and 350 C. Econ. Geol. 70:806–823 (1975)
Takenouchi, S., Fujiki, Y.: Synthetic study of the chalcopyritecubanite solid solution. Mem. Fac. Eng., Univ. Tokyo, A., 6:50–51 (in japanese) (1968)
Weber-Diefenbach, K.: Geochemistry and diagenesis of recent heavy metal ore deposits at the Atlantis II deep (Red Sea). In: Klemm, D.D. and Schneider, H.J., eds. Time and strata bound ore deposits: pp 419–436 Berlin-Heidelberg-New York: Springer 1977
Zierenberg, P.A., Schanks, W.C.: Mineralogy and geochemistry of epigenetic features in metalliferous sediments, Atlantis II deep, Red Sea: Econ. Geol. 78:57–72 (1983)
Zoka, H., Taylor, L.A., Takeno, S.: Compositional variations in the natural mackinawites and the results of heating experiments: J. Sci. Hiroshima Univ., ser. c. 7:37–53 (1973)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Missack, E., Stoffers, P. & El Goresy, A. Mineralogy, parageneses, and phase relations of copper-iron sulfides in the Atlantis II deep, red sea. Mineral. Deposita 24, 82–91 (1989). https://doi.org/10.1007/BF00206308
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00206308