Phase Relations in the Cu-Fe-S, Cu-Ni-S, and Fe-Ni-S Systems*
The phase relations in the Cu-Fe-S, Fe-Ni-S, and Cu-Ni-S systems were investigated by silica-tube quenching, differential thermal analysis, and high-temperature X-ray powder diffraction experiments. In addition, portions of the Cu-Fe-S and Fe-Ni-S systems were studied by gold-tube quenching and differential thermal analysis experiments under high confining pressures.
At elevated temperatures extensive liquid immiscibility fields span the sulfur-rich region of each of the three systems, whereas homogeneous liquid fields dominate the phase relations in their central portions. The average composition of the Sudbury Cu-Fe-Ni sulfide ore, when projected onto the Cu-Fe-S plane, is accounted for above 860° C by a mixture of copper containing hexagonal pyrrhotite and copper-rich sulfide liquid. Thus at high temperatures a mechanism exists that may be responsible for certain copper-rich segregations observed in this type of ore. The minerals of the Cu-Ni-S system, with the rare exception of millerite, do not occur in Sudbury-type ores. Knowledge of the phase relations in this system is prerequisite, however, for systematic investigations of the complex Cu-Fe-Ni-S system. Applications of the phase relations in the Cu-Fe-S and Fe-Ni-S systems to typical ore assemblages show that extensive reequilibration took place among the sulfides after their initial deposition. The sulfides in Sudbury-type ores commonly have compositions and crystal structures that can be produced in the laboratory only at low temperatures.
Figures & Tables
This monograph on Magmatic Ore Deposits has resulted from a Symposium held at Stanford University on November 12 and 13, 1966. All except three of the papers that were presented are published in this volume as well as some of the discussion and the summation of the symposium. Unfortunately much of the discussion cannot be included because the volume is already so large. The best introduction to this volume is, perhaps, the introduction as it was presented at the symposium:
This symposium was conceived in 1962 when the Program Policy Committee recommended that the . Society of Economic Geologists should sponsor a symposium on magmatic ore deposits. The Committee under the chairmanship of John K. Gustafson believed this to be an effective method of advancing geologic thought. It is fitting that the symposium should finally be held during Gustafson’s presidential year. The proposal of the Program Policy Committee was approved by Council at its meeting in November, 1962. A special committee consisting of G. Kullerud, J. A. Noble, C. H. Smith, T. P. Thayer, with H. D. B. Wilson as chairman, was appointed by the President, Olaf N. Rove, in February 1963 to make arrangements for the symposium. E. N. Cameron, Secretary of the Society, was ex officio member of the special committee and remained as an active member when he resigned the secretaryship. C. H. Park, Jr. joined the committee shortly after its formation.
The Program Policy Committee was prompted to recommend the symposium by the realization that the underlying theory of the formation of magmatic ore deposits was formulated many decades ago., In the intervening years, much new data have been acquired from systematic research. It seemed to the Program Policy Committee that it was time for those with an abiding interest in the magmatic deposits to meet to assess this new data and to point out the unresolved problems.
The symposium was entitled “Symposium on Magmatic Ore Deposits.” The special committee accepted the terminology in the “Glossary of Geology and Related Sciences,” Edition 2, page 175.
Magmatic Deposits Certain kinds of mineral deposits form integral parts of igneous rock masses and permit the inference that they have originated, in their present form, by processes of differentiation and cooling in molten magmas. (Lindgren p. 863, 1929).
The symposium committee has added the term “ore” to attempt to keep the discussions centered on ore, or near ore material, or with