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.