摘要
北山造山带是中亚造山带南缘镁铁-超镁铁质岩体的集中分布区之一,因其赋含二叠纪铜镍硫化物矿床而受到广泛关注。以往的研究多集中在北山造山带西部的新疆坡北地区,近年来随着对甘肃北山地区二叠纪镁铁-超镁铁岩体认识逐渐深入,新发现的矿化岩体有逐渐向东延伸的趋势。本文选择北山造山带中东部柳园地区骆驼山和西南山两个典型含铜镍硫化物岩体进行地质年代学、岩相学和岩石地球化学及同位素地球化学研究。岩体主要岩相包括橄榄岩相、辉石岩相、橄榄辉长岩相、橄长岩相和辉长岩相,其中硫化物主要出现在橄榄岩相和辉石岩相中。骆驼山岩体辉长岩锆石的U-Pb年龄为282.6Ma,与坡北地区矿化岩体的形成时代一致。骆驼山和西南山岩体母岩浆稀土元素配分模式为轻微右倾型,富集大离子亲石元素,强烈亏损高场强元素Nb-Ta,中等亏损Zr-Hf,与坡北和东天山地区同时代矿化岩体母岩浆特征相似。岩体具有较高的全岩εNd(t)值(+0.42~+6.10)和锆石εHf(t)值(+7.9~+14.1)的特征,与坡北地区矿化岩体类似,表明具有相似的亏损地幔源区。橄榄石Fo值与Ni含量的关系和母岩浆微量元素Cu/Zr比值特征表明岩浆在橄榄石结晶过程中发生了硫化物熔离。同位素模拟计算表明母岩浆在上升侵位过程中发生了约5%~15%的地壳物质混染,可能是岩浆硫饱和的主要原因。相同的成岩成矿时代、相似的岩石地球化学特征、母岩浆特征及硫化物饱和机制,表明甘肃北山地区二叠纪镁铁-超镁铁质岩体具有与坡北地区类似的成矿潜力,为在北山地区中东部进一步寻找铜镍硫化物矿床提供了重要信息。
The Beishan orogenic belt is one of the areas where mafic-ultramafic intrusions are concentrated in the southern margin of the Central Asian Orogenic Belt and has attracted widespread attention because of the reservoir of Permian Cu-Ni sulfide deposits.Previous studies have mostly focused on the Xinjiang Pobei in the western Beishan area.Recently,with gradual in-depth understanding of Permian mafic-ultramafic rocks in the Gansu Beishan area,the newly discovered mineralized rocks have a trend of extending eastward gradually.Here we selected two typical Cu-Ni sulfides mineralized Luotuoshan and Xinanshan intrusions in the Liuyuan area of the central-eastern part of Beishan for geochronological,petrographic and isotopic geochemical studies.The lithologies of the Luotuoshan and Xinanshan intrusions are composed mainly of peridotite,pyroxenite,olivine gabbro,troctolite and gabbro,among which sulfides predominantly appear in peridotite and pyroxenite.The zircons U-Pb concordant age of a gabbro from Luotuoshan intrusion is 282.6 Ma,which is consistent with the formation ages of mineralized maficultramafic intrusions in Pobei area.Chondrite-normalized REE and primitive mantle-normalized trace element patterns of parental magmas of Luotuoshan and Xinanshan intrusions show strong depletion of Nb-Ta and moderate depletion of Zr-Hf,which are similar to those of typical sulfides bearing intrusions in Pobei and Eastern Tianshan areas.The Luotuoshan rocks have both elevatedεNd(t)(+0.42~+6.10)andεHf(t)values(+7.9~+14.1),which are also similar to mineralized intrusions in the Pobei area,indicating their similar depleted mantle sources.The relationship between olivine Fo values and Ni contents and Cu/Zr ratios of their parental magmas indicate that the magmas underwent sulfide segregation during the process of olivine crystallization.Mixing calculations of isotopes indicate that about their parental magmas underwent 5%to 15%of crustal contamination during magma ascent and emplacement process,which may be the major reason for triggering sulfur saturation in magmas.The same diagenetic and metallogenic ages,similar geochemical characteristics of rocks and parental magmas,and similar sulfide saturation mechanism suggest that Permian mafic-ultramafic intrusions in the Gansu Beishan area probably have similar metallogenic potential to those in Pobei area,which provides important information for further prospecting of Cu-Ni sulfides deposits in the central-eastern part of the Beishan orogenic belt.
作者
马博骋
钱壮志
徐刚
段俊
顾笑龑
高文彬
MA Bocheng;QIAN Zhuangzhi;XU Gang;DUAN Jun;GU Xiaoyan;GAO Wenbin(School of Earth Sciences and Resources,Chang'an University,Xi'an,Shaanxi 710054,China;School of Earth Sciences,Zhejiang University,Hangzhou,Zhejiang310027,China;Shaanxi Branch of China National Geological Exploration Center of Building Materials Industry,Xi'an,Shaanxi 710003,China)
出处
《地质学报》
EI
CAS
CSCD
北大核心
2022年第12期4275-4293,共19页
Acta Geologica Sinica
基金
国家自然科学基金项目(编号41872076)
国家留学基金委联合培养博士研究生项目(编号202106560020)
陕西省自然科学基础研究计划(编号2021JM-157)联合资助的成果。
关键词
甘肃北山
二叠纪
镁铁-超镁铁质岩体
地质地球化学特征
铜镍成矿潜力
Gansu Beishan
Permian
mafic-ultramafic intrusions
geological and geochemical characteristics
Cu-Ni mineralization potential
