ZHAO Fu-de1, HUANG Fei1*, GAO Shang2, ZHANG Bao-yun3, MENG Lin1
(1. Northeastern University, Shenyang 110819, China;
2. Shijiazhuang Tiedao University，Shijiazhuang 050043, China;
3. Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geoscience, Langfang 065000, China)
Abstract: The Zhaishang gold deposit with various metal sulfides such as pyrite, arsenopyrite and chalcopyrite, is a critical Carlin-type deposit in Gansu Province, Northwestern China. Pyrite occurs during the whole geological processes, which is useful to understand the mineralization deeply. Pyrite is formed through the following three stages: 1) framboidal pyrite (Py1A) and porous pyrite (Py1B), 2) mid-coarser grained euhedral pyrite Py2 and 3) coarser grained euhedral pyrite Py3. Py1A is framboidal, with a diameter of 10～50 μm. It’s Co/Ni is lower than 1, and (S+As)/Fe is higher than 2. Part of the framboidal pyrite is transformed by hydrothermal fluid, so the Co/Ni is higher than 1, and S/Fe is lower than 2. Py1B is porous, and it’s (S+As)/Fe is smaller than 2. Py2 is a mid-coarser pentagonal dodecahedral crystal with Co/Ni between 1.41 and 3.78, (S+As)/Fe between 1.93 and 2.02 rising from the inside to the outside, and Au/As between 0.023 and 0.108. Py3 is a coarser euhedral grain with quartz pressure shadows around it, Co/Ni between 1.36 and 1.39, and (S+As)/Fe between 1.98 and 2.00. Combined with the geological background, the pyrite 1A (framboidal) is formed by the direct aggregation of pyrite micro-crystallites, indicating the sedimentary genesis. Pyrite 1B (porous) is cemented by loose pyrite microcrystals and subjected to hydrothermal superposition reformation. The pyrite 2 (mid-coarser pentagonal dodecahedral) is formed by direct crystallization of hydrothermal fluid around the porous nodules. The pyrite 3 (coarser euhedral grain) is formed by late hydrothermal crystallization and transformed by deformation. The pyrite from this deposit can be a set of standards for distinguishing geological processes.
Keywords: Carlin-type gold deposit; pyrite; polymorpholoy; genesis; typomorphic significance
ACTA MINERALOGICA SINICA Vol. 39, No.6, 2019, page 637-648
