【作者】 宋世明；

【导师】 胡凯；

【作者基本信息】 南京大学 ， 地球化学， 2011， 博士

【摘要】 广东地区在我国东南部古扬子与古华夏陆块接触部位发育有(超)大型的成矿带,本文选择其中的两个成矿典型实例,包括粤西大降坪黄铁矿矿床和粤北大宝山多金属硫化物矿床,针对目前矿床成因研究中存在的种种争议与不确定性,在全面掌握地质背景的基础上,通过开展系统的矿床地球化学研究,并尝试应用一些新的矿床地球化学方法,结合地质背景讨论了矿床成因,为区域找矿提供了参考信息,并且在理论与方法上对金属硫化物矿床的成矿地质地球化学研究具有参考意义。在粤西大降坪黄铁矿矿床的研究中,首先尝试探索开展了非传统稳定同位素Mo在中低温热液成矿中的地球化学研究,分析对象为与矿体同生热水沉积的硅质岩,结果发现,本区Ⅲ号矿体与Ⅳ号矿体具有明显不同的Mo同位素特征(Ⅲ号矿体的δ97/95Mo为-0.02‰～0.29‰,变化范围小；Ⅳ号矿体的δ97/95Mo为-0.70‰～0.62‰,变化范围较大,尤其是主矿层处的5个样品均以富集轻同位素为特征),前者的Mo同位素指示其成矿流体来自于海底热液,属热水沉积成因(或海底喷流)；后者则反映矿床形成过程中还受到后期热液改造作用；Ⅲ号矿体可能形成于一种开放的生物作用较强烈的缺氧环境；Ⅳ号矿体形成于一种封闭或半封闭的弱氧化—氧化的局限环境。Mo同位素在这种局限环境条件下可能存在一定的动力学分馏效应。Mo同位素可以作为一种示踪成矿流体以及成矿环境演化的有效手段。其他同位素(He-Ar-Pb-S)以及REE组成的地球化学特征也表明：大降坪的Ⅲ号矿体与Ⅳ矿体的成矿物质与成矿流体来源不同。Ⅲ号矿体的硫化物与围岩具有相似的Pb、S同位素特征(206Pb/204Pb、207Pb/204Pb、208Pb/204Pb分别为18.266、15.641、38.558 VS 18.244,15.712,38.647；δ34S为-19.4‰VS-18.5‰),3He/4He平均为1.48×10-6,R/Ra为1.04,反映Ⅲ号矿体的成矿物质主要来自碎屑围岩地层,成矿流体主要来自于当时的大气降水(海水)；相比而言,Ⅳ号矿体的铅同位素(206pb/204pb、207Pb/204Pb、208Pb/204Pb平均值分别为18.157,15.687和38.509)显示其成矿物质主要来自下伏基底地层,硫(δ34S≈17.9‰)主要来自于海水硫酸盐,R/Ra平均为为2.42,显示有部分深部地幔流体的参与,其硫化物中具有非常明显的Eu正异常,暗示矿体经历了中高温热液叠加成矿作用。在粤北大宝山多金属硫化物矿床的研究中,通过对不同产状、不同形态的硫化物进行He-Ar-Pb-S同位素示踪和稀土元素组成研究,发现块状和脉状矿体的的He-Ar同位素组成明显不同,前者的R/Ra平均为3.01,反映成矿流体为大气饱和水(海水)与地幔流体混合作用的结果,而脉状矿体的R/Ra仅为0.60,表明有地壳物质组分的加入；块状矿体与脉状矿体的铅硫同位素组成较为均一,大多数硫化物的δ34S为零值附近,铅同位素(206pb/204pb、207pb/204Pb、208pb/204pb平均值分别为18.946,15.735,38.990)主要落在上地壳与造山带之间,从而其成矿物质主要来自于地球深部。然而,二者硫化物的REE组成明显不同,块状硫化物具有典型的Eu正异常,轻稀土富集,具有海底热液喷流沉积特征,而脉状矿体的呈Eu负异常,具有跟矿区花岗闪长斑岩相似的稀土特征,暗示脉状矿体可能主要与花岗质岩浆流体有关,部分脉状矿体也可能来自对后期岩浆热液对块状矿体的活化转移。大宝山多金属矿床存在两期成矿作用,即泥盆纪与火山作用相关的热液成矿期和燕山期与岩浆热液相关的叠加成矿期。在以上两个典型矿床分别精细研究的基础上,综合对比分析认为,大降坪黄铁矿矿床与大宝山多金属硫化物矿床均为与热水沉积作用相关的块状硫化物矿床,都具有热水沉积+叠加改造成矿的特点。前者为与热水沉积相关的SEDEX型,后者为与火山作用相关的VMS型。构造背景、含矿地层以及同生断裂中的岩浆活动是区域找矿的重点。更多还原

【Abstract】 Super-large scale metallogenic belt was developed in Guangdong province between the ancient Yangtze and Cathaysia cratons, Southeast China. Two reprensentative deposits including the Dajiangping pyrite deposit and dabaoshan polymetallic sulfide deposit are selected in this study. As there are much controversy and uncertainties for mineral genesis till now. Based on the comprehensive geological setting, detailed studies on the systematic geochemistry including applied new mineral geochemical method for ore genesis have been carried in this study. Conbined with geological background, their ore deposit genisis are discussed. These explorations provide a important reference for regional metallogenic information as well as the theory studies on geochemical sulfide deposits.Molybdenum isotope was explored as a the new tracer for the low-medium temperature hydrothermal ore-forming systems. The results from twelve hydrothermal syndepositional sillcalite and chert samples from the Dajiangping pyrite deposit show that theδ97/95Mo values of the OrebodyⅢrange from -0.02‰to 0.29‰, with a narrow range, In contrast, the values of the OrebodyⅣdisplay a larger variation, especially, the five samples from the main ore bed all show strong negative values. The OrebodyⅢlikely deposited from submarine exhalative hydrothermal fluids under a relatively strong reducing environment and the OrebodyⅣmay have also been influenced by hydrothermal superimposition in a more oxidized disequilibrium condition. In addition, theδ97/95Mo values of the OrebodyⅣare clearly negative, together with the values increasing stratigraphically upward in the ore beds, suggesting that the metallogenic environment of the OrebodyⅣis different from the open oceanic systems. There might be dynamic fractionation in this restricted environment. The molybdenum isotope can be used as an effective tracer for the ore-forming fluid and metallogenic environment.Geochemistry characteristics from other isotopes such He、Ar、Pb and S also illustrated that the metallogenic materials and ore-forming fluids are different between the OrebodyⅢand OrebodyⅣ. There are similar pb and S isotope compositions between the sulfide and wall rock (206Pb/204Pb,207Pb/204Pb,208Pb/204Pb are 18.266、15.641、38.558 VS 18.244,15.712,38.647, respectively;δ34S was -19.4%o VS-18.5‰), as well as the average of 3He/4He is 1.48×10-6 and its R/Ra of 1.04, which indicates that the metallic ore-forming materials mainly derived from clastic formation and the ore-forming fluids might be atmospheric saturation water (seawater) in the OrebodyⅢ. However, the pb and S isotope compositions from Orebody IV show that the metallic ore-forming materials were from baseal statra and sulfur mainly derived from seawater sulfate. In addition, the average R/Ra of 2.42 indicates that the mantle ore-forming fluids might be involved. The sulfides with obvious positive Eu abonormal also infer that there has been experienced high-temperature hydrothermal superimposed during the orebody IV mineralization.Considering there are different bedding or formset in the sulfide ore, a comparative method between the massive orebody and vein orebody was introduced in the studies on the dabaoshan polymetallic deposit. The He-Ar isotope compositions between massive orebody and vein orebody was different. the average R/Ra of the massive orebody was 3.01 and its ore-forming fluids mixed with mantle fluids and atmospheric saturation water (seawater), in contrast, the ore-forming fluids of the vein orebody show the crust materials added characteristics with R/Ra of 0.6. The Pb and S isotope compositions in massive orebody and vein orebody was relative homogeneous that theδ34S values of most sulfide was zero balancing and the pb isotope compositions (the average values of 206Pb/204Pb、207Pb/204Pb、208Pb/204Pb was 18.946,15.735,38.990, respectively) mainly falled the field between the upper crust and fold belt, which suggested that both of their ore-forming materials were mainly from earth deep-seated. However, the REE distribution pattern of these two orebody was apparent different. The massive orebody has typical positive Eu abnormal and enriched LREE, showing the hydrothermal exhalative sedimentary characteristics. Meanwhile, The REE distribution pattern from vein orebody mainly displaying the similar specificities with Granodiorite porphyry that infer the ore-forming fluids of vein orebody might be related with the granitic magmatic fluids, besides some vein orebodies also may be from epimagma derived from the activated massive orebody transfer. There were indeed generated two mineralization in Dabaoshan Polymetallic deposit, One period was associated with volcanism hydrothermal mineralization in Devonian and the other was superposed magmatic mineralization during the stage of Yanshan.Based on fine systematical studies and comprehensive comparative analysis between the Dajiangping pyrite deposit and the Dabaoshan polymetallic sulfide deposit, both of them show hydrothermal sedimentary and superimposed mineralization characteristics. The former is SEDEX-type deposit associated with the hot water, the latter is VMS-type deposit associated with the volcanogenic mineralization. Structural setting, ore formation and contemporaneous fault with the magma emplacement should be as the main exploration point.更多还原