【作者】 郑建斌；

【导师】 曹志敏；

【作者基本信息】 中国海洋大学 ， 海洋地质， 2004， 博士

【摘要】 晚二叠世峨眉山玄武岩建造是世界上前第三纪五个最大的溢流玄武岩建造之一。伴随玄武岩的大量喷发有许多基性-超基性岩体、岩脉的侵入活动，在这些侵入体中已发现较多的V-Ti-Fe、PGE、Ni-Cu等矿床。本文以攀西地区PGE在暗色岩套（具有时空及成因联系的峨眉山玄武岩、基性-超基性岩、浅成脉岩的通称）中的富集机理为研究目标，以巨量玄武岩（喷出相）PGE相对贫化而局部侵入基性-超基性岩体（侵入体）PGE相对富集为切入点，系统研究了峨眉山玄武岩分布区的控矿构造、火成岩的分布及地球化学特征对矿床的控制作用，并重点解剖了丹巴杨柳坪岩浆Ni-Cu-PGE硫化物矿床的成矿机理。 区域地球物理特征研究表明，攀西地区上地壳存在的近地表高速地体与深部物质上涌有关。裂谷的地壳内部存在高密度强磁性地质体群，表明幔源超镁铁-镁铁质岩体大量贯入于地壳中。多个玄武岩分布区下存在基性-超基性岩体，暗示了玄武岩喷发时岩浆侵入活动的普遍性。 控矿构造的遥感信息解译表明攀西地区主要的控矿因素为断裂带和火成岩体。多种构造因素的复合是控矿的关键，大量的岩浆为矿床形成提供足量的成矿元素。 出露于丹巴地区的大石包组玄武岩是峨眉山玄武岩的组成部分，Zr／TiO₂-Nb／Y岩石类型划分图显示其为亚碱性-碱性之间的过渡系列。Th／Ta-Th、Ti／Zr-SiO₂和Gd／Yb-La／Sm图解表明该段玄武岩属岩浆结晶分异演化的产物，受地壳同化混染作用较小。Pd-Cu、Pt-Mg#、Ir-Mg#关系表明，形成该段玄武岩的岩浆是S不饱和的，该岩浆极具形成岩浆PGE矿床的可能性。玄武岩PGE陆海对比研究表明峨眉山玄武岩高的PGE含量、Pd／Ir值源于地幔柱活动下的幔源高度熔融。 杨柳坪含矿基性-超基性岩体为顺层一次性侵入形成的多岩相“杂岩体”，岩体自蚀变作用强烈，其岩浆期后热液主要为富CO₂、SiO₂流体。玄武岩、基性-超基性岩体岩石化学特征具Nb、Ta、Hf负异常，具有大陆溢流玄武岩的岩石化学特征。火成岩微量元素和PGE参数的一致性表明它们之间具有成生联系。中国海洋大学博士学位论文 杨柳坪岩浆Ni一Cu一PGE硫化物矿床按成矿作用的不同可分为岩浆熔离型、岩浆接触交代型和热液型三种，岩浆熔离型为其主要的矿体类型，其产出受岩相控制。从硫化物与岩体的比例来看，岩浆在最终就位之前经历过硫化物的预富集作用;东谷一鱼海子大断裂可能为岩浆通道，矿床S同位素组成也表明其成矿物质来源于地慢。综合矿石S同位素分析结果与岩体微量元素特征分析，岩浆的结晶分异或不同成分岩浆的混合作用是促使岩浆发生S过饱和及其硫化物熔离作用发生的主要机制。 研究认为，源于地慢柱作用下的具高PGE含量的慢源岩浆为矿床的形成提供了成矿元素，岩浆演化过程中可能发生的硫化物熔离作用所形成的硫化物熔体富集PGE并侵入于通道或构造薄弱地带就位成矿。因此PGE主要富集于基性一超基性岩体内的硫化物中，次为该类岩体的围岩裂隙中。溢流相（玄武岩）中PGE的亏损意味着熔岩经历了硫化物的熔离作用。更多还原

【Abstract】 Late Permian Emeishan basalt formation is one of the five biggest pre-Tertiary flood basalt formations. Accompanying the vast eruption of the basalts, there are a lot of mafic-ultramafic intrusions and dikes, in which magmatic V-Ti-Fe, PGE and Ni-Cu deposits have been detected. Aiming at the elucidation of the PGE enrichment mechanism in the Emeishan Traps (a general term for temporally, spatially and genetically associated Emeishan basalts, mafic-ultramafic intrusions and dikes) and based upon the fundamental phenomena that locally PGE enrichments in intrusions are connected with the depletion of PGE in the voluminous volcanics, we systematically studied ore-controlling structures in the Panxi rift, and the impact of the distribution and geochemistry of igneous rocks on the distribution of ore deposits with an emphases on the analysis of ore-forming processes of the Yangliuping magmatic Ni-Cu-PGE sulfide deposit.Studies of regional geophysical signatures reveal that near surface high-speed terrain in the Panxi area is related to the upwelling of deeplying matter. Highly distributed ferromagnetic geologic bodies under the rift hints the injection of many mantle-originated mafic-ultramafic intrusions, and the presence of these intrusive bodies under many basalts-distributed areas suggests the universalism of magma penetrating activity during the Emeishan flood volcanism.Interpretation of remote sensing information manifests that main ore-controlling factors in the Panxi area are fault belts and igneous bodies. The combination of multi-structures is the key to ore-forming processes, while voluminous magma provided metallogenetic elements necessary to the formation of deposits.Dashibao formation basalt outcropped in the Danba area is part of the EmeishanZr/TiCVNb/Y rock type discrimination diagram. Plots of Th/Ta-Th, Ti/Zr-SiOi and Gd/Yb-La/Sm demonstrate that sampled basalts are derivatives of magma experienced crystallization differentiation with little crustal contamination, if there is any. Scattergrams of Pd-Cu, Pt-Mg# and Ir-Mg# indicate that this section of basalts was formed from S-undersaturated magma, which had a great potential to form magmatic PGE sulfide deposit provided it reached S-oversaturation en route to the surface. Compared with basalts from Kolbeinsey ridge and other places, Emeishan basalts have high PGE concentrations and Pd/Ir values, and this indicates that they were mantle melts of high melting degree.Yangliuping ore-bearing mafic-ultramafic intrusions consist of multi-lithofacies intruded along strata in one period, and the intrusions had suffered a high degree of self-alteration, which reflected that post-magmatic fluids were mainly composed of SiC>2 and CO2- Intrusions and basalts have geochemical features of continental flood basalts with negative Nb, Ta and Hf anomalies. Consistencies of the trace elements and PGE parameters among basalts, intrusions and ore-bodies indicate a genetic link among them.Based on ore-forming processes, ore-bodies of Yangliuping magmatic Ni-Cu-PGE sulfide deposit can be divided into three subtypes: 1) ore-bodies formed through magma differentiation by liquation, which is the main ore type and their emplacement is strictly controlled by lithofacies, 2) ore-bodies formed by contact metasomatism between intrusions and their wall rocks, and 3) ore-bodies formed by hydrothermal fluids. The ratios of sulfides to intrusives indicate that magma had experienced sulfide pre-concentration process before its final emplacement, and Donggu-Yuhaizi fault could be the pathway of the magma. Sulfur isotope composition of the deposit also shows that ore-forming elements came from the mantle. Based on the S isotope composition and trace elements characteristics of the intrusion, magma crystallization fractionation or magma mixing is the main factor triggering the happening of S-oversaturation and unmixing of sulfide melts.Studies reveal that under mantle plume operation, magma originated from mantle with high PGE concentrations provided ore-forming elements for the d更多还原