安徽铜陵晚中生代侵入岩磷灰石原位地球化学——成岩成矿制约

Geochemistry of apatite from Late Mesozioc intrusive rocks in Tongling area,Anhui Province: Constraints on rock-forming and ore-forming processes

安徽铜陵地区大规模铜、金矿床与晚中生代侵入岩密切相关.本文选取铜陵地区4个代表性成矿侵入岩体(金口岭花岗闪长岩、铜官山和冬瓜山石英二长闪长岩、朝山辉石二长闪长岩)进行了磷灰石原位地球化学研究,探讨其对成岩成矿的指示.铜陵侵入岩磷灰石有较高的Sr/Y值(平均值3. 19)和低Y含量,指示其为埃达克质岩. 4个岩体磷灰石F含量为2. 63%～4. 02%,属氟磷灰石.磷灰石样品有较高的REE含量(825×10-6～5 853×10-6)、中等的δEu值(0. 37～0. 88)、高log fO2值(-12. 3～-9. 86)、较高的Cl含量(多> 0. 2%)和Cl/F值,暗示铜陵侵入岩起源于高氧逸度的壳幔岩浆混合源区.研究结果表明,铜陵地区铜、金成矿作用可能与由板块而来的富Cl流体、氧化环境和壳幔混合作用密切相关.

Large-sized Cu-Au deposits are closely related to Late Mesozoic intrusive rocks in the Tongling area of Anhui Province. To discuss the potential of apatite as a petrogenetic-metallogenic indicator, the authors conducted a detailed in situ geochemical study of apatite from four representative intrusions(Jinkouling granodiorite, Tongguanshan and Dongguashan quartz monzodiorite, and Chaoshan pyroxene monzodiorite) in the Tongling area. The analyzed apatites of the Tongling intrusive rocks have high Sr/Y ratios(3. 19 on average) and lower Y values, indicating that they are adakitic rocks. The apatite samples have F values ranging from 2. 63% to 4. 02%, and are defined as fluorapatites. The studied apatite samples have high REE content(825 × 10^-6-5 853 × 10^-6), moderateδEu values(0. 37 ~ 0. 88), high log fO2values(-12. 3 ^-9. 86), relatively high Cl content(mostly > 0. 2%)and Cl/F ratios, showing that the Tongling intrusive rocks might have been formed from mixed source of mantle-derived and crust-derived magmas in a high oxygen fugacity environment. The results indicate that the Cu-Au mineralization in the Tongling area may be closely related to the slab-derived Cl-enriched fluids, an oxidizing environment and a mantle-crust mixed source.