| Xiangshan Cu-Ni sulfid deposit(central Cu-Ni deposit of Xiangshan), a medium-scale, is a part of Tudun-Huangshan-Tulaergen Cu-Ni minerals belt in Eastern Tianshan,which belongs to Huangshan Cu-Ni deposits field nearby Dacaotan fault in the northern margin of Jueluotage tectonic belt,and the deposit is a typical Cu-Ni deposit formed at279-300Ma,when is the post-orogenic stage in Eastern Tianshan.The deposit locates in the centre part of Xiangshan complex controlled by Xiangshan shear belt(F8) and Huangshan shear belt(F9), which adjacents to western part of the intrusions hosted Il(ilmenite)-Cu(Copper)-Ni(Pentlandite/Pyrrhotite) deposit.The central complex only hosted Cu-Ni-bearing minerals, at NE trend(58°), emplaced along the boundry of volcanic-sedimentary rocks in the lower Carboniferous Wutongwozi formation,which consists of pyroxene peridotite, harzburgite, hornblende pyroxenite, amphibolite gabbro and so on,whose shape looks like lenticular or rhombus with2.4km at length and200to450m at width or0.55m2at area.The orebodys form at the boundry of different facies(e.g. pyroxenite-gabbro or different gabbro facies),and also seen at the bottom of a simple facie or the top of it (e.g. peridotite, harzburgite or gabbro).The former usually comprise massive ore and dense disseminated ore,compared with the latter,which consists of sparse disseminated and less massive ore,and they respectively resulted from deeper immiscible sulfide melt and situ sulfide liquation with respect to mineralization.In addition to the metalogensis associated with magma,some sulfide-bearing quartz and calcite vein related to the magmatic-hydrothermal process can also been seen in the Xiangshan deposit.Through the actual geochemical analysis of rocks and ores(e.g.major element,trace element,REE and PGE),and EPMA of sulfide and olivine, some research based on the fluid inclusions of quartz and calcite in the hydrothermal vein,besides that, previous opinions also are used that Sr、Nd、Pb、O、S isotope of rocks and ores,and geochronology of zircon U-Pb and sulfide Re-Os,which accout for the following conclusions: 1.The metalogensis in the deposit includs magma and magmatic-hydrothermal ore-forming preocess,Cu-Ni orebody associated with magma mineralization is economic value,but it is barren resulted from magmatic-hydrothermal mineralization, which contains Cu-bearing minerals,2. The valuable element Cu and Ni in the deposit develop in the form of minerals such as copper, pentlandite and pyrrhotite, associated with some other elements,Co develops in isomorphous of pentlandite and pyrrhotite,and Pt also develops in isomorphous of copper,but in inclusions traped by pentlandite and pyrrhotite more than isomorphous.3.The ultramafic rocks with high m/f ratio(3.81-5.12,average3.57) is iron ultrabasic rock,meanwhile,the mafic rocks with lower m/f ratio(2.29-3.01,average2.75) is iron basic rock.Geochemistry of rocks indicate that parent magma is a kind of tholeiitic basalt magma,and gradually become to calc-alkaline magma with increasing evolvement of magma.Through the quantitative modeling based on equilibrium principle of olivine-melt,it is possible that MgO of the parent magma is10.81%at least.4.The evidences including trace element ratio, positiveeNd(285),and reducing-rich vapor in fluid inclusions of olivine and labradorite,indicate that magma source is mixing of depleted mantle and enriched mantle.Through the quantitative modeling based on initial value of Sr,Nd isotope, and the proportion of depleted mantle and enriched mantle metasomated by melt and fluid is80%and20%respectively,besides that,it is possible that the partial melting degree of the primary mantle is10-15%,based on the result of quantitative modeling on PGE.5.The parent magma, in the process of ascenting to the crust,underwent crystal fractionation of chromite,olivine, orthopyroxene, clinopyroxene and plagioclase.The Fo ratio of olivine in the perdotite arranges from79.7to83.7, which belongs to peridot. Beceause of new magma added to the champer,Fo ratio of olivine in a same rock just is a little change,Usually,the Ni content of the early olvine is more than the later olivine resulted from interacting with early olivines and residue sulfide melts,but Fo ratio is often less, which maybe due to interact with later olivines and residue silicate melts.6.The evidences including oxygen isotope(5.4-7.7‰) of rocks,sulfur isotope(-0.84-+2.4‰) of different sulfides,lead isotope of whole ore,and plots of trace elements of rocks,indicate that medium-lower crustal contamination of parent magma existed in the process of ascenting to the crust.7.The immiscible of sulfide melt and sulfur saturated exist in the parent magma,where the R (ratio of silicious magma and sulphide melts) is163.The factors of sulfur saturated in the parent magma are mafic minerals(e.g.olivine and chromite) segreation, crustal contamination and something else.8.Xiangshan complex is depleted on PGE,which maybe a reasonable factor for the exsiting form of Pt element in isomorphous and inclusions.The further reasearchs suggest that "ocean crust basement","low partial melting degree of mantle source" and "sulphide immiscible "are the influencing factors of depleted complex9.The hydrothermal metalogensis exsit in the late magma stage and post-magma stage.Some sulfide-bearing quartze and calcite vein can be seen along the joints of complex,within which homogeniztion temperature of fluid inclusions arranges from220to240℃,stands for a low-medium temperature hydrothermal evolved from ore-forming magma,which has a potential of Au mineralization.10.It is significative that develop a geology-geophysics-geochemistry-remote sensing prospecting model based on commercial origional and local prospecting symbol,and some useful prospecting methods for potential Au mineralization in the deposit. |
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