长江中下游成矿带鸡笼山矽卡岩型铜金钼矿床花岗闪长斑岩对成岩-成矿的指示: 来自地球化学和锆石U-Pb年龄的证据

    Geochemistry and zircon U-Pb age of granodiorite porphyry: Constraints on diagenetic and metallogenic processes of the Jilongshan Cu-Au-Mo deposit, Middle-Lower Yangtze River Valley Metallogenic Belt, China

    • 摘要: 长江中下游成矿带是燕山期古太平洋板块NW向俯冲背景下壳幔相互作用的外部响应,是长期成岩-成矿作用的直接结果,但丰山矿田的成岩-成矿事件并未得到深入的分析。以鄂东南丰山矿田鸡笼山矽卡岩型铜金钼矿床中与成矿有关的花岗闪长斑岩为研究对象,开展了详细的全岩地球化学和LA-ICP-MS锆石U-Pb测年分析,探讨丰山矿田的成岩-成矿过程。研究结果显示,来自鸡笼山矿床的花岗闪长斑岩为高钾钙碱性、准铝质花岗岩(A/CNK值多小于1),并且具有埃达克岩特征(高Sr/Y值);锆石U-Pb年龄为147.5±1.4 Ma,表明成矿岩体在晚侏罗世就位。综合已有研究,提出鸡笼山矿床成矿岩体为具有火山弧岩浆特征的埃达克质花岗岩,成矿岩体由富集岩石圈地幔的部分熔融形成,且岩浆上升过程中,遭受了地壳物质的混染。丰山矿田成岩-成矿事件统计分析结果表明,丰山矿田存在152~145 Ma和142~138 Ma两期成岩-成矿作用,第一期成岩-成矿事件对应形成斑岩-矽卡岩型铜-金-钼矿,第二期成岩-成矿事件对应形成斑岩型成矿系统。由于研究区西南侧和东北侧差异性隆升-剥蚀由大到小,东北侧丰山洞矿区现今保留完好的斑岩-矽卡岩型铜-金-钼矿和外围浅成低温热液金矿组成的斑岩型成矿系统,而其西南侧鸡笼山(斑岩-)矽卡岩型铜-金-钼矿外围无浅成低温热液金矿床,最西南侧的白果树岩体则剥蚀殆尽不见矿。

       

      Abstract: The Middle-Lower Yangtze River Valley Metallogenic Belt is an external response to the crust-mantle interaction in the background of NW subduction of the paleo-pacific plate during the Yanshannian, which is a direct result of long-term diagenetic and metallogenic activity.However, the diagenetic and metallogenic events in the Fengshan district have not been analyzed in detail.In this study, a comprehensive study for the ore-related granodiorite porphyry from the Jilongshan skarn Cu-Au deposit, Fengtian orefield, is conducted.The results reveal that the ore-related granodiorite porphyry from the Jilongshan deposit is high-K calc-alkaline and metaluminous granitoids (A/CNK generally below 1), which are also characterized by adakitic features(high Sr/Y).Zircon LA-ICP-MS dating yields an age of 147.5±1.4 Ma, indicating that the mineralized intrusion was formed in the Late Jurassic.Combined with previous studies, it is revealed that the ore-related granodiorite porphyry from the Jilongshan deposit is adakitic granitoids characterized by volcanic arc magmatic features.The ore-forming rock mass was derived from partial melting of enriched lithosphere mantle which had experienced contaminations from crustal materials during ascending.Based on the statistical analysis of the diagenetic and metallogenic events in the Fengshan field, this paper concludes that there were two diagenetic and metallogenic stages in the Fengshan field from 152 to 145 Ma and 142 to 138 Ma.The first stage of diagenetic and metallogenic events corresponds to the formation of porphyry-skarn Cu-Au-Mo deposits, while the second stage of diagenetic and metallogenic events corresponds to the formation of porphyry mineralization system.Due to the differential uplift-ablation on the southwest and northeast sides of the study area, it shows that the porphyry Cu-Au-Mo deposits and the shallow-formed low-temperature hydrothermal Au deposits on the northeast side of the study area were well preserved.On the other hand, there are no shallow-formed low-temperature hydrothermal Au deposits on the periphery of the Jilongshan(porphyry-) skarn-type Cu-Au-Mo deposits on the southwest side.The southwest Baiguoshu rock body was completely missed without any mineralization.This study is important for understanding the diagenetic and metallogenic process of the Fengshan deposit, as well as for mineral prospecting.

       

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