項目辦聯系方式
  • 秘書:趙亞楠
  • 電話:18811386654
  • 郵箱:[email protected]
  • 地址:北京市朝陽區北土城西路19號
成果展示
Minerals: In–Situ LA-ICP-MS Trace Elements Analysis of Pyrite and the Physicochemical...
發布日期:2019-05-09

Abstract: The Baiyun gold deposit is located in the northeastern North China Craton (NCC) where major ore types include Si-K altered rock and auriferous quartz veins. Sul?de minerals are dominated by pyrite, with minor amounts of chalcopyrite, sphalerite and galena. Combined petrological observations, backscattered electron image (BSE) and laser ablation analysis (LA-ICP-MS) have been conducted on pyrite to reveal its textural and compositional evolution. Three generations of pyrite can be identi?ed—Py1, Py2 and Py3 from early to late. The coarse-grained, porous and euhedral to subhedral Py1 (mostly 200–500 μm) from the K-feldspar altered zone is the earliest. Compositionally, they are enriched in As (up to 11541 ppm) but depleted in Au (generally less than 10 ppm). The signal intensity of Au is higher than background values by two orders of magnitude and shows smooth spectra, indicating that invisible gold exists as homogeneously or nanoscale-inclusions in Py1. Anhedral to subhedral Py2 grains (generally ranging 500–1500 μm) coexist with other sul?des such as chalcopyrite, sphalerite and galena in the early silici?cation stage (gray quartz). They have many visible gold grains and contain little amounts of invisible Au. Notably, visible gold has an af?nity with micro-fractures formed due to late deformation, implying that native gold may have resulted from mobilization of preexisting invisible gold in the structure of Py2 grains. Subsequently Py3 occurs as very ?ne-grained disseminations of euhedral crystals (0.05–1 mm) in late silici?cation stage (milky quartz) and coexists with tellurides (e.g. petzite, calaverite and hessite). They contain the highest level of invisible gold with positive correlations between Au-Ag-Te. In the depth pro?les of Py3, the smooth Au spectra mirror those of Te with high intensities, revealing that gold occurred as homogeneously/nanoscale-inclusions and submicroscopic Au-bearing telluride inclusions in pyrite grains. The high Te and low As in Py3, combined with high Au content, imply that invisible gold can be ef?ciently scavenged by Te. Abundant tellurides (petzite, calaverite and hessite) have been recognized in auriferous quartz veins. Lack of symbiosis sul?des with the tellurium assemblages indicates crystallization under low f S2 and/or high f Te2 conditions and coincides with the result of thermodynamic calculations. High and markedly variable Co (from 0.24 to 2763 ppm, average 151.9 ppm) and Ni (from 1.16 to 4102 ppm, average 333.1 ppm) values suggest that ore-forming ?uid may originate from a magmatically-derived hydrothermal system. Combined with previous geochronological data, the textural and compositional evolution of pyrite indicates that the Baiyun gold deposit has experienced a prolonged history of mineralization. In the late Triassic (220,230 Ma),   the magmatic hydrothermal ?uids, which had af?nity with the post-collisional extensional tectonics on the NCC northern margin, caused initial gold enrichment. Then, as a result of deformation or the addition of new hydrothermal ?uids, visible gold-rich Py2 was formed. The upwelling of mantle–derived magma brought in a lot of Te-rich ore-forming hydrothermal ?uids during the peak of the destruction of the NCC (~120 Ma). Amount of visible/invisible gold and Au-Ag-Te mineral assemblages precipitated from these mineralized ?uids when the physical and chemical conditions changed.  

新快3遗漏 山东群英会玩法技巧 北京11选5走势一牛 甘肃体彩十一选五走势一定牛 深圳股票开户 广西福彩快乐双彩走势分布图 时时乐开奖走势图 今日河南22选五开奖22 山东十一选五直选3 2020微信股票群二维码 河南22选5开奖