The idaite-nukundamite-bornite-chalcopyrite metastable solid solution : Crystal chemistry, superlattice architecture and bonding; thermochemistry and phase equilibria; natural occurrences, geochemistry and metallogenesis
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At temperatures below 300℃ restricted areas of metastable solid solution exist in the bornite(bn)-chalcopyrite(cp)-idaite(id)-nukundamite(nk) area of the Cu-Fe-S system; the solid solution is pronounced in the areas between id, bn and cp. The metastable phases of the solid solution are quenchable from above 500℃ to 220℃; examples observed in natural assemblages form as a result of kinetic and energetic effects and as an accornmo-dation of the Gibbs/Goldschmidt phase rule. The occurrence of phases is constrained by hydrothermal phase equilibria. The states of the systems involve small compositional adjustments which are dependent on solid state processes. Mineral phases exhibit slight variations in stoichiometry allowing ties to exist between them. An accornmodation noted in nature allowing covellite(cv)-nk-cp colinearity is observed in experiments at 150-250℃ where id compositions equilibrate so that the nk-cp tie connects. Transition metal (e.g., Zn) substitution occurs at low temperatures and chalcogenide ( e.g. , As) substitution occurs at high temperatures. Below 220℃ ( thermal maximum of non-stoichiometric chalcopyrite) and 260-270℃ ( where tie line switch reactions occur between id, cv and cp producing nk) the solid solution area becomes expansive widening toward cp; as a result of sympathetic energetic and kinetic effects a number of polytypes appear. The nk area remains restricted at high temperatures, variable stoichiometry and solid solution with id and an.bn polytypes is ob-served at, temperatures below 171-220℃. At high temperatures non integral superstructures decompose to integral types which are involved in tie-line switch reactions. Permissive metastability below 300℃ is associated with merged univariant equilibria and sustained by non relativistic atomic states in superlattices which influence spectacular solubility variations. Lattice distortion and electronic states indicated for these phases suggest the presence of strong bonding forces, imposed by vacancy superstructure nuclear interactions, not specified by current theory. Idaite exhibits 2 or 3 polytype and several polymorphous conditions; - 12 polytype phases are recognised in the an.cp solid solution between id and cp. Crystal symmetry varies from hexagonal ( 360℃ : cubic) in nk, pseudocubic/tetragonal ( 220℃ : cubic) in id to orthorhombic/tetragonal in an.cp; these symmetry transformations correlate with stoichiometry, metal vacancies and oxidation states ( dependent on environment of crystallization hence the variety of natural polytypes ) . Changing levels of site occupation and oxidation state result in distortion of the basic chalcogenide subcell with concomitant superstructure and optical effects. A new concept of bond development is introduced to explain ob-served physical and chemical variations-chalcogenide ligands are thought to be metallized; especially notable in nonstoichiometric phases. Analogous chalcogenide phases from other systems are discussed in terms of their multielement phase equilibria and periodic element topology. A restructured periodic table facilitates a better understanding of zonal/regional metallogenesis and multielement solid state phase equilibria applicable to broad fields of scientific research. The occurrence of Au and tectonically zoned chalcogenides-semimetals (e.g., Ge anomalies at tectonic inflections) with zones intermediate Cu-Fe-S solid solution-metastable solid solution (iss-mss) series will provide an inter-est for mineral exploration and natural hazard monitoring..
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