【作者】 傅飘儿；

【导师】 张铭杰； 胡沛青；

【作者基本信息】 兰州大学 ， 地球化学， 2009， 硕士

【摘要】 黄山铜镍硫化物矿床位于中亚造山带南部的黄山-镜儿泉成矿带,成矿镁铁-超镁铁质岩体(269Ma)侵位于下石炭统干洞群。该岩体长3.8km,最宽处约0.8km,出露面积1.71km~2。岩石分异较好,由橄榄岩、辉石岩、辉长岩和闪长岩组成,其中橄榄岩是矿体赋存的主要部位,辉石岩含有少量的矿体。本文对黄山铜镍硫化物矿床含矿镁铁-超镁铁质岩体的两个最新深钻(～800m)岩芯,通过岩石空间分布、造岩矿物组成、主量元素、微量元素、稀土元素和铂族元素地球化学分析,研究了成矿岩浆来源、母岩浆组成特征、岩浆演化过程、构造环境和硫化物熔离机制,获得如下认识。1)黄山铜镍硫化物矿床成矿镁铁-超镁铁质岩体根据岩石产状和岩性特征可分为三段岩石组合:顶部橄榄岩(Pdt-1)、中部基性-超基性杂岩和底部辉长岩(Gbr-3)。顶部橄榄岩与下伏辉长岩接触带具有热液蚀变特征,无矿体赋存。中部基性-超基性岩浆结晶序列,由下至上依次是橄榄岩(Pdt-2)、辉石岩(Pyt-2)、辉长岩(Gbr-2),不同岩相之间呈过渡接触;辉长岩与顶部橄榄岩突变接触且局部包含有少量顶部橄榄岩碎块。底部辉长岩(Gbr-3)厚约300米,与上覆中部橄榄岩(Pdt-2)突变接触,局部穿插橄榄岩中。2)顶部橄榄岩、中部基性-超基性岩序列和底部辉长岩分别由不同期次的岩浆侵位形成,具有不同的主量元素和微量元素等岩石地球化学特征。与中部橄榄岩(Pdt-2)相比,顶部橄榄岩(Pdt-1)偏基性,含有相对较高的镁、铝和钙;中部橄榄岩(Pdt-2)和辉石岩(Pdt-2)的大离子亲石元素和稀土元素丰度明显低于底部辉长岩(Gbr-3),且与成矿密切相关。底部辉长岩(Gbr-3)与中部辉长岩(Gbr-3)相比偏酸性,具有较高的FeO和较低的CaO。3)不同类型岩石的主要氧化物随MgO减少且呈连续变化趋势,微量元素和稀土元素具有相似的原始地幔配分模式,Ta/Yb与Nb/Y、Zr/Nb与Hf/Nb之间具有正相关性,揭示岩浆来自同一源区,且母岩浆可能是高镁的玄武岩浆。4)微量元素原始地幔配分模式中,明显亏损Nb和Ta,富集Sr,并且具有负的δEu异常,表明成矿岩浆在上升演化过程中经历了橄榄石、辉石和斜长石的结晶分异作用和地壳同化混染作用。5)黄山铜镍硫化物矿床成矿镁铁-超镁铁质岩部分橄榄石含有硫化物珠滴,微量元素Cu/Pd和Ti/Pd比值大于原生地幔岩浆,指示硫化物在深部曾发生过熔离。在岩浆演化过程中地壳富硅组分的加入是硫化物熔离的主要机制。更多还原

【Abstract】 The Huangshan Cu-Ni sulfide deposit is hosted in a mafic-ultramafic layered intrusion（269±2Ma）,which is one of the Ni-Cu-（PGE） sufide deposits in Huangshan-Jing’erquan Permian magmatic metallogenic belt,belong to southern part of the Central Asian orogenic belt.The Huangshan intrusion was intruded into sandstones,carbonaceous siltstones and interlayered limestones of the Gandun formation.It forms a lozenge-shaped multiphase intrusive body with a area of 3.8×0.8m².It is composed of peridotite,pyroxenite,gabbro and diorite.The peridotite hosts most of the Ni-Cu-（PGE） sulfide ores,and the pyroxenite hosts minor disseminated sulfide ores.In this study,peridotite,pyroxenite and gabbro samples were collected from two new drilling cores for the petrological,major elements,trace elements and platinum group elements（PGE） analysis to reveal the metallogenic processes.The following results have been obtained.（1） Huangshan intrusion is composed of three well-defined petrological units:The top unit is composed entirely of relatively homogeneous peridotite（20-40m thick） with commonly poikilitic texturex.The middle unit is composed of various types of rocks,which are gabbro,pyroxenite and peridotite from top to base.The basal unit is composed of a free-grained gabbronorite and gabbro.It is about 300m thick and occurs along the lower margins of the intrusion.There is a sharp boundary between the basal peridotite and the peridotite in middle unit,marked by a hydrothermal alteration zone, as well as the gabbro in middle unit and the top peridotite.The peridotite in midle unit hosts most of the Ni-Cu-（PGE） sulfide ores,but the top peridotite hosts few ore.（2） Three units are formed in different magam intrusive stages with different characteristics of major and trace elements.The top peridotite has higher MgO,Al₂O₃ and CaO contents than the peridotite in middle unit.The peridotite and pyroxenite in middle unit have similar trace element patterns and REE patterns with the basal gabbro.However the basal gabbro is more enriched than the middle units,and shows higher SiO₂ and FeO contents,and lower CaO content than the gabbro in middle unit.（3） The different types of rocks in the Huangshan Cu-Ni sulfide deposit display systematical variations of major element oxide,similar distribution patterns of trace element and REE,and correlationship between Ta/Yb and Nb/Y artios as well as between Zr/Nb and Hf/Nb ratios,suggested that they could be derived from the same source of the parent magmas,which were high-MgO（15wt.%） basaltic magmas.（4） Primitive mantle-normalized trace element distribution patterns diplay significantly Nb- and Ta- depleted,and Sr-riched.Above evidences combined with negativeδEu values sugested the basaltic magma related to the Huangshan Cu-Ni sulfide ores undergone several important processes including fractional crystallization of olivine pyroxene and plagioclase minerals in the deep magma chamber,crustal contamination and the addition of Si-rich volatiles.（5） Some sulfide droplets are found in olivine of peridotite,and the ratios of Cu/Pd and Ti/Pd are higher than primitive mantle value.The metallogenic magma is contaminated by crustal components.These evidences imply the contamination of Si-rich crustal components could be responsible for sulphur supersaturation as well as sulfide melt segregation in deep magma chamber.更多还原