Geological Relationships Between the Intrusions,Country Rocks,and Ni-Cu-PGE Sulfides of the Kharaelakh Intrusion,Noril′sk Region:Implications for the Roles of Sulfide Differentiation and Metasomatism in Their Genesis

The Ni-Cu-platinum group element sulfide ore deposits of the Kharaelakh Intrusion,Noril′sk Region,Siberia,represent a large concentration of sulfides associated with a small differentiated intrusion formed at the edge of the Siberian Craton in the roots of the Siberian Trap flood basalt.The deposit is associated with an intrusion that occupies a flanking periclinal structure adjacent to the Noril′sk-Kharaelakh Fault.The intrusion is strongly differentiated and comprises taxitic gabbrodolerites,picritic gabbrodolerites,and gabbrodolerites within the main body which in turn forms a chonolith within a sheet-like intrusion that extends laterally to form extensive undifferentiated sills of gabbrodolerite.The intrusion substantially replaces the stratigraphy of the country rocks,and although it appears to have exploited the axis of structures developed in response to transtension,the intrusion has created space by both mechanical dilation of stratigraphy and magmatic replacement of pre-existing sedimentary rocks.The frontal lobes of the main intrusion have complex apophyses of gabrodolerite on a range of scales that demonstrate replacement of the sedimentary rocks and link to the development of an extensive metamorphic halo in the country rocks.This halo is much narrower over the main body of the intrusion,and these observations have implications for the thermal history of the intrusion.Mg-skarns and breccias are developed in the roof of the main body of the intrusion.Within the intrusion,the taxitic rocks contain vesicles and the blebby sulfides developed in the picritic and taxitic gabbrodolerites appear to have a linkage to volatile phases.Cuprous sulfide mineralization developed at the roof of the Kharaelakh Intrusion is associated with metamorphosed and skarn-bearing country rocks,and appears to have been generated by a combination of sulfide fractionation and associated metasomatism.The geological relationships appear consistent with a chonolith model for the development of the differentiated intrusion and mineralization,but the extent of metasmorphism of the country rocks appears to be related to the unusual thickness of gabbrodolerite apophyses at the flanks of the intrusion rather than metamorphism produced by the passage of mafic magma through the intrusion.Variations in disseminated sulfide compositions and metasomatic textures in the skarns are described,and a model is proposed which balances traditional views on the evolution of the magma conduits with the impact of magmatic fluids transported through the magma column(i.e.transmagmatic fluids).The importance of structures in controlling the nature of the conduit,and the resultant small intrusions with excess sulfide is a feature of many other Ni-Cu sulfide deposits including Voisey′s Bay,and it is suggested that the sulfides are more likely to have beentransported from depth into their final resting place rather than developed by in-situ equilibration of sulfide with fresh magma in the chonolith.

俄罗斯诺里尔斯克铜镍硫化物矿床研究进展

诺里尔斯克铜镍硫化物矿床赋存于西伯利亚大火成岩省,是全球最大的镍-铜-铂族元素硫化物矿集区。研究表明:1该矿床形成于二叠纪—三叠纪之交,与溢流玄武岩在时空上紧密相关,但由于未发现含矿岩体和矿体与溢流玄武岩之间直接接触,尚无法确定其成因联系;2幔源岩浆遭受过壳源物质的混染,但这种混染作用何时发生,混染程度如何,是否是成矿的必要条件?存在诸多争论;3成矿金属元素是从岩浆中沉淀出来的,但究竟是来自地幔还是地壳,有不同认识;4硫化物的熔离作用至关重要,在深部岩浆房曾发生过,但在浅部岩浆房中是否也曾发生过?还存在明显的分歧。尽管在矿床成因方面存在一定的分歧,但某些控矿因素对于诺里尔斯克铜-镍-铂族元素矿集区而言是有效的。