陕西省洛南县莲花沟钼(铜)矿岩体地质及岩石地球化学特征

Geology and Geochemical Characteristics of Rock Mass at Lianhuagou Molybdenite(Copper) Mine in Luonan County,Shaanxi Province

主要利用近年来在陕西洛南县莲花沟岩体中获取的一些实际资料,通过综合对比研究总结出一些与区域上其他成矿小侵入体完全不同的成岩成矿特征。主要包括:①莲花沟岩体是一个以闪长岩为主的二长花岗斑岩—闪长岩型岩体,其成分明显是以相对富钙、镁、铁,低硅、碱而别于同带其他类型小侵入体;②按岩石化学成分,岩体缺少w(SiO2)为55%～65%的中性岩石组合,呈一种较典型的"双峰式"岩套,且从稀土元素分配模式看,在两种类型岩石间不存在分离结晶作用成因关系,而似乎表现为一种分层熔融的双层岩浆房成岩模型;③所建的成矿模型,除岩体边缘接触带中的矽卡岩型铁铜矿和层控-构造蚀变岩型钼铅锌矿系列外,岩体内部主要以隐爆角砾岩筒-斑岩型钼铜矿化为特征,这种隐爆角砾岩既不同于北边祁雨沟含金片麻岩中的爆破角砾岩筒,也不同于南边河南镇平县秋树湾的碳酸盐岩型爆破角砾岩筒,且成矿元素组合主要是钼铜类型;④由岩石地球化学和锆石U-Pb同位素年龄数据揭示,形成二长花岗斑岩熔浆的源岩与中元古代熊耳群的一套富钾类型变火山沉积岩系有较好的源区关系,而闪长岩则与软流圈上涌,基性岩浆底侵及太华群源岩有较密切的关系。无疑,以上成果对丰富东秦岭地区钼多金属成矿作用认识将提供和补充一些新的资料和实例,特别是"双峰式"岩套的存在,对东秦岭地区主要成钼时代的地球动力学背景分析也是一个重要的证据,而且还提示在东秦岭地区有发现新类型岩体和矿床的潜在条件。

In this study,geochemical and isotopic geochronological data collected from Lianhuagou rock mass in recent years in Luonan County of Shaanxi Provence are used to compare with that of small intrusive rock within molybdenite（copper） mine in East Qinling,so that their genesis,metallogenic features and differences are discussed.Results show that： ①The Lianhuagou rock body is a monzogranite porphyry-type diorite rock dominated by diorite,and it relatively enriches in calcium,magnesium,iron,and low in silica,alkali,oposite from the small intrusions in the East Qinling area;②The Lianhuagou rock is lack of SiO2（55%-65%）,belonging to neutral rock composition and a typical ＂bimodal＂ rock set.REE distribution model indicates no fractional crystal genetic relationship existed between two types of rocks.Instead,it is a kind of double-layered magma chamber diagenetic model of melting within different layers;③Copper-molybdenum mineralization within the rock body is characterized by cryptoexplosion breccia pipe and porphyry Co-Cu mineralization within the diorite rock unit.This is different from the carbonate type explosion breccia pipe and widely distributed small scale skarn-type molybdenite deposits in Qiushuwan area,Zhenping County;④Indicated by the petrochemistry and two groups of zircon U-Pb isotopic age [（144.5±8.9）Ma and（1 516±12）-（1 596±17）Ma] from the monzogranites,the source rocks for formation of monzogranite porphyry might be related with a suite of K-rich meta-volcanic-sedimentary rocks of the Mid-Proterozoic Xiong＇er Group,however the diorite is more closely related to the asthenosphere upwelling and the mafic magma underplating and the source of Taihua Group rocks.Therefore,the above results will provide new knowledge and examples for understanding the molybdenum metal mineralization in Eastern Qinling.Especially the existence of ＂bimodal＂ volcanic rocks is also important evidence for analyzing the geodynamic background of molybdenum mineralization in Eastern Qinling,indicating a potential condition for discover some new types of rocks and mineral deposits in East Qinling.