【摘要】 园珠顶铜钼矿床位于钦杭成矿带南段的大瑶山隆起北缘,为大型斑岩型铜钼矿床。通过LA-ICP-MS锆石U-Pb同位素测年,获得了花岗斑岩的高精度成岩年龄,为(154.3±1.7)Ma(n=12,MSWD=3.1),为晚侏罗世岩浆活动的产物,与辉钼矿的Re-Os同位素年龄155 Ma相吻合。岩石地球化学分析表明,园珠顶花岗斑岩高硅〔w(SiO2)为68.81%~70.21%〕、富碱〔w(Na2O)+w(K2O)为6.78%~8.01%〕、准铝质-弱过铝质(A/CNK为0.96~1.04);稀土元素总量中等(?REE为142.15×10-6~170.83×10-6),富集轻稀土元素(?LREE为135.05×10-6~162.34×10-6),轻重稀土元素分馏明显〔(La/Yb)N=30.97~32.10〕,弱的Eu负异常(δEu=0.86~0.89),稀土元素配分模式总体右倾;岩石相对富集Rb、K等大离子亲石元素(LILE)及高场强元素Th、U,亏损Nb、Ta、P、Ti等高场强元素(HFSE)及部分大离子亲石元素Ba、Sr。LA-MC-ICP-MS锆石Hf的原位分析表明,176Hf/177Hf值变化于0.282 500~0.282 801之间,εHf(t)值介于-6.27~4.19。综合分析表明,园珠顶花岗斑岩为准铝质-弱过铝质的I型花岗岩,具有壳幔混合源成因,锆石εHf(t)值反映了园珠顶花岗斑岩的成岩源区较为复杂,总体具亏损岩浆源区的特征,以幔源物质为主,但在岩浆侵位过程中遭受了古老地壳物质的混染。结合区域构造背景和前人研究成果,认为园珠顶斑岩体及铜钼矿,与钦杭成矿带北段的永平铜矿具有一致的成岩成矿构造背景,形成于板块俯冲环境。更多还原

【Abstract】 Located in Yuanzhuding area of Fengkai County in Guangdong Province,the Yuanzhuding Cu-Mo deposit lies on the northern margin of Dayaoshan uplift along the southern section of the Qinzhou-Hangzhou metallogenic belt.It is a large porphyry copper-molybdenum deposit.Based on the high-precise LA-ICP-MS zircon U-Pb isotope dating,the authors obtained an petrogenetic age of(154.3±1.7)Ma(n=12,MSWD=3.1)for the granite porphyry,suggesting that the intrusion was emplaced in Late Jurassic,corresponding to 155 Ma Cu-Mo mineralization age obtained by the Re-Os method.Rock geochemical analysis shows that Yuanzhuding porphyry granite has high silicon(SiO2=68.81%~70.21%),high alkali(Na2O+K2O=6.78%~8.01%),calc-alkaline(Litman indexσ=1.69~2.27),and metaluminous to weakly peraluminous(A/CNK=0.96~1.04)characteristics.Geochemical characteristics of rare earth elements are?REE=142.15×10-6~170.83×10-6,?LREE=135.05×10-6~162.34×10-6,?HREE=7.10×10-6~8.48×10-6,(La/Yb)N=30.97~32.10,δEu=0.86~0.89.The chondrite-normalized REE patterns demonstrate right-oblique linear REE patterns with weak negative Eu anomaly and significant fractionation between LREE and HREE.As for trace elements in the primitive mantle normalized spider diagram,the rocks are relatively enriched in Rb,K and other large ion lithophile elements(LILE)and high field strength elements(HFSE)Th,U,Nb,Ta,P,and they are relatively depleted in Ti and high field strength elements and large ion lithophile elementsBa,Sr.In situ zircon LA-MC-ICP-MS Hf analysis shows that176Hf/177Hf ratios vary from 0.282 500 to 0.282 801.εHf(t)values range from-6.27 to 4.19.Comprehensive analysis shows that Yuanzhuding granite porphyry is metaluminous to weakly peraluminous I-type granite,with crust-mantle mixed source.ZirconεHf(t)values suggest that the parental magmas of Yuanzhuding granite porphyry are rather complex.Zircon Hf isotopic composition suggests that the parental magmasof the rock bodieswere mainly derived from a young mantle partly mixed with old continental crust rock during the evolution.Mantle material in the Yuanzhuding deposit played an important role in the formation of the granite porphyry.Combined with regional tectonic background and previous research results,the authors hold that the Yuanzhuding porphyry Cu-Mo deposit might have been controlled by the subduction of the Pacific plate continental margin in Late Jurassic.It is the syn-collision-post-collision granite,which reflects the characteristicsof A type subduction and has the same tectonic background of the Yongping Cu deposit,formed in a plate subduction environment.更多还原