Geological Characteristics of the Shitoukengde Mafic-Ultramafic Rocks in East Kunlun and Related Metallogenic Conditions
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摘要: 石头坑德镁铁-超镁铁质岩体位于东昆仑造山带东段五龙沟地区，邻近昆中大断裂，主要由Ⅰ号、Ⅱ号及Ⅲ号岩体组成。岩体主要岩性为闪长岩、辉长岩、辉石岩、橄辉岩、橄榄岩等，铜镍矿体主要赋存于Ⅰ号岩体的辉石岩、橄辉岩及橄榄岩中。岩体地质特征、岩石地球化学特征及矿体地质特征表明，岩石的m/f值变化范围为2.77~6.01，属铁质系列基性-超基性岩，有利于成铜镍矿。稀土总量总体较低，∑REE为0.9×10-6~35.61×10-6，全部样品的（La/Yb）N为0.63~5.51，（La/Sm）N为0.4~3.65，（Gd/Yb）N为0.61~1.72，显示了轻-重稀土元素之间、轻稀土元素之间分馏强，而重稀土元素之间分馏弱。原始地幔标准化微量元素蛛网图显示了与稀土配分型式较好的一致性，岩石总体富集LILE（Rb、Ba、Th、U），贫HFSE（Nb、Ta、Zr、Y），整体呈右倾趋势，同时表现为明显的Rb、U正异常及Nb、Ta负异常。石头坑德含矿岩体的La/Sm值为0.62~5.65，平均2.79，绝大部分样品的La/Sm大于2而小于4.5，说明在成岩过程中受到一定程度地壳物质混染。推测矿床形成过程为幔源岩浆上涌中，由于地壳物质的加入，伴随着同化混染作用的发生，岩浆中S达到过饱和，进而硫化物发生熔离，富含硫化物的岩浆运移至东昆仑造山带邻近昆中断裂构造薄弱的部位成岩成矿。石头坑德岩体地质特征、地球化学及地球物理特征，均表现了对铜镍矿有利的成矿条件，暗示岩体深部存在高度富集铜镍的地质体，具有进一步找矿的潜力。Abstract: 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.
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