IPGE-SULFARSENIDE CRYSTALLIZED FROM SULFIDE MELT: MICROSTRUCTURE EVIDENCE FROM THE JINCHUAN DEPOSIT

 LIANG Qing-Lin, SONG Xie-Yan, WIRTH Richard 

 Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, P. R. China 550081  

The Jinchuan Ni-Cu-(PGE) sulfide deposit in Gansu province, northwestern China, is hosted in a small ultramafic body with less than 1.5 km² surface expression. More than 500 million metric tons of sulfide ore is reserved in the Jinchuan deposit with average grades of 1.06 wt% Ni, 0.7 wt% Cu and PGE+ Au about 1ppm (Song et al., 2009).  

In this study, euhedral IPGE-sulfarsenides (IrRhAsS) have been identified in the No.24 ore body using SEM (Fig. 1A). Those IPGE-sulfarsenides are found not only enclosed by pyrrhotite, pentlandite but also by chalcopyrite, like the nanometer-size IPGE sulfarsenides in the Yangliuping deposit (Liang et al., 2019). And some of them are locally concentrated distributed. One IrRhAsS is found located at the pyrrhotite and chalcopyrite grains boundary at nanometer-scale using TEM (Fig. 1B).  

 Exsolved phases would form oriented plates or lamella within the matrix, or spherical lens at the boundaries of matrix, in order to minimum free energy (A Putnis, 1992). This is inconsistent with our observation. Thus, we prefer that the IPGE-sulfarsenides in the Jinchuan deposit crystallized from high temperature sulfide melt before the crystallization of MSS. 

References: 

     A. Putnis, Introduction to mineral sciences, 1992, Cambridge University Press, 457p. 

          Liang, Q.-L., Song, X.-Y., Wirth, R., Chen, L.-M. and Dai, Z.-H., 2019, Implications of nano-and micrometer-size platinum-group element minerals in base metal sulfides of the Yangliuping Ni-Cu-PGE sulfide deposit, SW China. Chem. Geol. 517, 7-21. 

         Song, X.Y., Keays, R.R., Zhou, M.F., Qi, L., IhIenfeld, C. and Xiao, J.F. (2009) Siderophile and chalcophile elemental constraints on the origin of the Jinchuan Ni-Cu-(PGE) sulfide deposit, NW China. Geochim. Cosmochim. Acta 73, 404-424. 

（矿床室 宋谢炎/供稿）