Genesis of the newly discovered Pb–Zn vein of the Sucha giant fluorite deposit in Inner Mongolia: Constraints from LA-ICP-MS trace element of pyrite and sphalerite

Abstract

The Sumochaganaobao (Sucha) deposit in Siziwang Banner, Inner Mongolia is considered to be the largest single fluorite deposit known in the world, and apart from a small amount of localized pyritization, no metal mineralization has been found for many years. In recent years larger scale Pb–Zn polymetallic veins have been uncovered which indicates the potential for large scale metal mineralization in this deposit in addition to fluorite ore. Laser-ablation inductively coupled mass spectroscopy (LA-ICPMS) technique is used to investigate the distribution and substitution of trace elements in sphalerite and pyrite. The confirming results show that sphalerite is mainly rich in Fe, Mn, Cd, Co, Ni, Cu, In and poor in Sb and Mo. Pyrite is mainly rich in Ni, As, Sb, Cr, Mn, Co, Cu, Sn, Pb, Tl, Se and poor in Cd, Au, Ga, In, Bi. Iron, Mn, Cd, In, Co, Ni, Cr, Bi and Cu in sphalerite and Ni, As, Sb, Mn, Co, Cu, Ni, As, Pb, Tl, and Se in pyrite are generally lattice-bounded, while Pb and Cd present both in solid solution and/or discrete micro/nano-inclusions. The elemental contents of Fe, Mn and In and elemental ratios of Ga/In, Zn/Cd and In/Ge illustrate the trace elemental characteristics of medium temperature sphalerite. The trace elements in pyrite are diverse along with both relatively high-temperature elements (e.g. Ni, Co, Sn, Cu, etc.) and relatively low-temperature elements (e.g. As, Sb, Pb, etc.). The Co/Ni ratios indicate that the pyrite formed under a low-temperature condition. The crystallisation from sphalerite to pyrite may have undergone a relatively rapid cooling process from medium to low temperature. The characteristics of sphalerite and trace elements indicate that the genesis of this deposit is closest to that of SEDEX type deposit. Considering the marine sedimentation or marine volcanic eruption, jasperite development, clastic rock hosting, layered ore-body, and the geochemical characteristics of trace elements of this deposit, the newly discovered Pb–Zn vein should belong to the SEDEX type.