In situ LA-ICP-MS trace elements in sphalerite from the Fankou Pb-Zn deposit, South China: Implications for ore genesis

Abstract

Sphalerite is one of the most ubiquitous and abundant sulfides in the Fankou Pb-Zn deposit, Guangdong province, South China, which is hosted predominately in Middle-Upper Devonian and Lower Carboniferous carbonate strata. Two main generations of sphalerites were identified during the filed investigation and microscopic observation: Sphalerite I (including Sp Ia and Sp Ib), “brownish-red” in color, coexists with pyrite, galena, pyrrhotite, chalcopyrite and minor arsenopyrite. By contrast, Sphalerite II (including sphalerite IIa and Sp IIb),“yellow” in color, is associated with galena, pyrite, calcite, and dolomite. The EMPA and LA-ICP-MS analyses show that: (1) Sphalerite I contains higher Fe, Ga, Ge, and Ag, but relatively lower Zn, Sn, Sb, and Pb, compared to sphalerite II; (2) Iron, Mn, Cd, Ga, Ge, In and Sn occur in solid substitution with rhythmically banded compositional changes, with Cu, Sb, and Pb likely also present in solid substitution or microscopic inclusions in the Fankou sphalerite; (3) Possible trace element substitution mechanisms are summarized as follows: (1) Zn2+ ↔ (Fe2+, Mn2+, Cd2+), (2) potential coupled substitutions of 2Zn2+ ↔ Cu+ + Ga3+, 3Zn2+ ↔ 2Cu+ + Ge4+ and 3Zn2+ ↔ 2Ag+ + Ge4+. Principal component analysis (PCA) of selected sphalerite from deposits of the Jinding Pb-Zn deposit, MVT, SEDEX, skarn, VMS, and the Fankou Pb-Zn deposit reveal significant differences. Our study suggests that crystallization temperatures and trace and minor element behaviors of sphalerite from the Fankou deposit were similar to those of sphalerite from typical Mississippi-valley-type (MVT) deposits.