Trace elements in sulfide minerals from eastern Australian volcanic-hosted massive sulfide deposits; Part I, Proton microprobe analyses of pyrite, chalcopyrite, and sphalerite, and Part II, Selenium levels in pyrite; comparison with delta 34 S values and implications for the source of sulfur in volcanogenic hydrothermal systems

Abstract

Part I. Pyrite, chalcopyrite, and sphalerite from six volcanic-hosted massive sulfide (Mount Chalmers, Rosebery, Waterloo, Agincourt, Dry River South, and Balcooma) deposits in eastern Australia were analyzed using a proton microprobe to determine trace element abundances. In pyrite, trace elements can be divided into three groups according to the most likely occurrence of the element: (1) elements that occur mainly as inclusions (Cu, Zn, Pb, Ba, Bi, Ag, and Sb), (2) elements that occur as nonstoichiometric substitutions in the lattice (As, Tl, Au, and possibly Mo), and (3) elements that occur as stoichiometric substitutions for Fe (Co and Ni) or S (Se and Te). Hydrothermal and metamorphic recrystallization cleans pyrite of group 1 and group 2 elements, but does not appear to affect the concentrations of group 3 elements. Colloform pyrite grains have the highest levels of As and Au (up to 200 ppm), suggesting that rapid precipitation is important in incorporating Au into auriferous pyrite. Elements that occur as inclusions in chalcopyrite include Pb, Bi, Zn (P), and Ba. The occurrence of As and Sb is unresolved, although consistently high values of As in some samples suggest that As may substitute into the lattice of chalcopyrite. Elements that substitute into the lattice include Ag (for Cu), In, Sn and Zn (?) (for Fe), and Se (for S). Lead, Ba, Sb, possibly, and in some cases, Cu, occur commonly as inclusions in sphalerite. Lattice substitutions in sphalerite include Fe, Cd, Cu (to 4,500 ppm), Ni, In, Ag, Te, Ga and possibly Mo. In addition, consistently high (2,000-4,000 ppm) levels of As in the Rosebery barite zone may indicate As lattice substitution. Part II. The Se content of pyrite in volcanic-hosted massive sulfide deposits varies as follows: in Cu-poor, Zn-rich deposits, Se levels are low (mainly <5 ppm) throughout; in Cu-rich deposits, Se levels are highest (10-200 ppm) in stringer zones and the lower part of the massive sulfide lens, and decrease toward the top of the massive sulfide lens and into peripheral altered rocks. Metamorphic recrystallization does not affect these variations. Although delta 34 S values also vary systematically in individual deposits, no systematic differences were noted between Cu-rich and Zn-rich deposits...