黑龙江佳木斯地块典型石墨矿床含矿岩石地球化学特征及成矿时代

佳木斯地块位于东北亚早前寒武纪陆块,区内变质岩系发育,是重要的晶质石墨富集地带。文章通过对佳木斯地块典型的萝北云山和鸡西柳毛石墨矿床含矿岩石进行SHRIMP锆石U-Pb年龄测定,结果表明:变质锆石和碎屑锆石207Pb/206Pb年龄分别为(1855±5)~(1979±13)Ma和(476±9)~(575±12)Ma。通过地球化学特征分析,萝北云山石墨矿和鸡西柳毛石墨矿含矿岩石富集Rb、Ba等大离子亲石元素和Zr、Hf、Th、U、Nb、Ta等高场强元素,含矿岩石Rb/Sr平均值均高于陆壳值0.24,表明循环沉积作用较弱;Sr/Ba比值较低,表明岩浆来源于陆壳重熔,显示以陆源物质为主;V/Cr平均值为4.58,V/(Ni+V)平均值为0.90,显示弱还原环境;两处典型矿床轻稀土元素含量均高于重稀土元素,萝北云山矿床负Eu异常明显,显示陆棚浅海沉积特征,鸡西柳毛矿床正Ce异常明显,显示海源物质为主的浅海沉积特征。研究区混合花岗岩脉的稀土元素配分曲线具有正Eu异常,显示出外来岩浆热液交代岩石特征。因此,佳木斯地块典型石墨矿床含矿岩石在古元古代晚期经受区域性高温高压变质作用,后经过早古生代强烈的泛亚构造作用,在构造岩浆侵入背景下进一步增生形成巨晶鳞片状石墨。

Ore geochemical characteristics and metallogenic epoch of typical graphite deposits in Jiamusi Massif, Heilongjiang Province

Jiamusi massif is located in the northeast Asia early Precambrian landmass, where metamorphic rocks well developed and constituted an important crystalline graphite enrichment zone. The SHRIMP U-Pb dating results of ore rocks from typical Luobei Yunshan and Jixi Liumao graphite deposits in Jiamusi massif show that ²⁰⁷Pb/²⁰⁶Pb age is (1855±5)-(1979±13)Ma and (476±9)-(575±12) Ma respectively for metamorphic recrystallization zircon and authigenic zircon. The geochemical characteristic analysis indicates that the ore rock is enriched in large ion lithophile elements such as Rb, Ba and high field strength elements such as Zr, Hf, Th, U, Nb and Ta, and Rb/Sr ratio of ore rock is higher than continental crust Value 0.24, suggesting weak cyclic sedimentation; Sr/Ba ratio is lower, implying that magma was derived from the continental crust remelting; terrigenous material is dominant; the average V/Cr ratio is 4.58, average V/(Ni+V)ratio is 0.90, suggesting a weak reduction environment; the light rare earth element values are higher than those of heavy rare earth elements in the two typical deposits; negative europium anomalies are obvious for Luobei Yunshan mineral deposit, implying shelf shallow sea sedimentary characteristics; cerium is abnormal in Jixi Liumao deposit, indicating that the source material was dominated by shallow sea sedimentary materials. Mixed granite dike of rare earth elements in the study area exhibits a positive europium anomaly distribution curve, suggesting the characteristics of foreign magmatic hydrothermal metasomatic rock. Ore rocks of typical graphite deposit in Jiamusi massif were subjected to regional metamorphism of high temperature and high pressure in Paleoproterozoic period, and later experienced the pan-Asian structural activity under the background of tectonic magmatic intrusion in early Paleozoic period, which caused further proliferation and formation of giant crystal flaky graphite.