Geological Characteristics of the Shitoukengde Mafic-Ultramafic Rocks in East Kunlun and Related Metallogenic Conditions

The Shitoukengde mafic-ultramafic rocks, closed to Middle Kunlun fault, are located at the Wulonggou area in the eastern part of East Kunlun orogenic belt, which are mainly composed of rock mass I, Ⅱ and Ⅲ, with the main lithologies of pyroxenite, olivine pyroxenite, peridotite, gabbro, diorite.The Cu-Ni orebodies were mainly occurred in the pyroxenite, olivine pyroxenite and peridotite of rock mass I.After analyzing the geological and lithogeochemical characteristics of rock mass and the geological characteristics of these orebodies, the results show that the m/f values of these rocks range from 2.77 to 6.01, and the ore-bearing rocks belong to basic-ultrabasic rocks of iron series, which are favorable to copper-nickel mineralization.These rocks have low total rare earth element, the ∑REE values vary from 0.9×10^-6 to 35.61×10^-6, while their (La/Yb)_N, (La/Sm)_N and (Gd/Yb)_N ratios change from 0.63 to 5.5, from 0.4 to 3.65 and from 0.61 to 1.72, respectively, showing the obvious fractionation between LREE and HREE, with intense LREE fractionation but weak HREE fractionation.The primitive mantle-normalized spider diagram of trace elements shows the good consistent with the REE distribution patterns, and these rocks are enriched in LILE (Rb, Ba, Th and U) while they are depleted in HFSE (Nb, Ta, Zr and Y), generally show the sloping trend of lower right, with obvious positive Rb and U anomalies, as well as negative Nb and Ta anomalies.In the Shitoukengde deposit, the La/Sm ratios of ore-bearing rocks range from 0.62 to 5.65, with an average of 2.79, and most of them are more than 2 and less than 4.5, indicating that the diagenetic process was contaminated by a certain degree of crustal materials.Thus, the formation process of this deposit has been inferred.During the upwelling process of mantle-derived magma, the S was supersaturated in the magma due to the addition of crustal materials that accompanied with the occurrence of assimilation and contamination.And then, the immiscibility of the sulfides was occurred.The sulfide-enriched magma was migrated to the weak structural fracture zone of Middle Kunlun fault nearby the East Kunlun orogenic belt to form the related mineral deposit.The geological, geochemical and geophysical characteristics of the Shitoukengde rock mass all show a favorable metallogenic conditions for copper-nickel deposit, suggesting that the depth of this rock mass occurs a highly enriched Cu-Ni geological body and serves as a key direction of further ore prospecting.