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硫化物熔融包裹体研究是认识硫化物矿床成矿元素来源和演化的重要手段,由于硫化物熔融包裹体的体积较小(粒径仅为10～20μm),其详细化学元素组分的难以获得一直是制约进一步研究的瓶颈。笔者在前人研究的基础上,借助于扫描电镜、电镜能谱和二次飞行时间离子探针(Tof-SIMS)对产于铜陵地区角闪石巨晶中的硫化物熔融包裹体进行了详细的研究,首次获得了一套精确的矿物化学资料和元素分布图。矿物学研究表明,角闪石巨晶在上地幔和下地壳均有结晶,温压区间分别为T:850～900℃(温度),P:0.70×109～0.82×109Pa(压力),对应深度D:23.10～27.06km;和T:900～950℃,P:1.09×109～1.17×109Pa,D:35.97～38.61km。元素分布图显示,硫化物熔融包裹体主要有两种元素组成体系:S-Fe-Mn-Ni-Rb-Sr-Ba和S-Fe-Cu-Sr,幔源硫化物体系中Mn、Ni、Rb、Ba等元素具有相似的性质特征可共溶,与Cu则表现出不混溶。在铜陵地区,上地幔的部分熔融形成了一套碱性玄武岩浆,后受岩浆底侵作用和壳幔相互作用影响,底侵进入下地壳深位岩浆房,发生结晶分异和同化混染作用,形成一套轻度演化的玄武岩浆,可能为辉长质。上地幔和下地壳的角闪石巨晶分别是由上地幔碱性玄武岩浆和下地壳轻度演化的玄武岩浆(辉长质)高压下结晶的产物。当上地幔碱性玄武岩浆上侵到下地壳深位岩浆房以后,发生结晶分异作用,又由于地壳硅镁层的混染作用,使得玄武岩浆中硫溶解度降低,促其熔离,从而释放大量的硫(S,以及Ni、Cu、Cr)。角闪石巨晶中的硫化物熔融包裹体正是在下地壳深位岩浆房中,由正在结晶的角闪石巨晶在结晶分异和轻度演化的玄武质岩浆中捕获的不混溶硫化物熔融液滴形成的。铜陵地区在中生代经历了一个长期的大规模的岩浆底侵作用和壳幔相互作用过程,由于下地壳硅镁层混染作用使得轻度演化的玄武岩浆释放大量硫,必然会在莫霍面附近形成大规模高浓度的硫富集区,这些组分在岩浆上侵作用、地壳减薄作用或者裂谷作用的影响下很容易再活化,进入区域岩浆-热液流体系统,最终参与形成区域大规模的硫化物矿床。
The study of sulfide melt inclusions is an important method to recognize the source and evolution of ore-forming elements in sulfide deposits. Due to the small volume of sulfide melt inclusions (particle size of only 10 ~ 20μm), the detailed chemical element composition is difficult to obtain It has always been the bottleneck restricting further research. Based on the previous studies, the author has studied in detail the sulfide melt inclusions in hornblende giant beryllium in Tongling area by means of SEM, TEM and Tof-SIMS For the first time, a precise set of mineralogical data and elemental profiles was obtained. Mineralogical studies show that the hornblende giant crystallites are crystallized in the upper mantle and the lower crust, the temperature and pressure intervals are T: 850 ~ 900 ℃ (temperature), P: 0.70 × 109 ~ 0.82 × 109Pa (pressure), the corresponding depth D: 23.10 to 27.06 km; and T: 900 to 950 ° C., P: 1.09 × 109 to 1.17 × 109 Pa, and D: 35.97 to 38.61 km. The elemental distribution maps show that there are mainly two kinds of elemental compositional systems in sulfide melt inclusions: Mn-Ni, Ni-Ni-Rb-Sr-Ba and S-Fe-Cu- Rb, Ba and other elements with similar properties can be co-dissolved, and Cu showed immiscibility. In Tongling area, a series of alkaline basalt magmas were formed by partial melting of the upper mantle. After that, due to the magmatic underplating and the crust-mantle interaction, the bottom intrusion entered the lower magmatic chamber in the lower crust, causing crystallization and assimilation , Forming a slightly evolved basaltic magma that may be gibelic. The amphiboles in the upper mantle and the lower crust, respectively, are the products of high-pressure crystallization from basaltic magma (gibbsite), which is slightly evolved in the upper mantle and basalts in the lower crust. When the upper mantle alkaline basaltic magma invaded the lower crust deep magma chamber, the crystallization of the differentiation occurs, but also because of crustal magnesia layer contamination, making the basaltic magma in the lower sulfur solubility, and promote its melting to release Lots of sulfur (S, and Ni, Cu, Cr). Sulfide melt inclusions in hornblende macroscopies are in the deep crust of the lower crust, where immiscible sulfide melt droplets are captured by the crystallizing amphibole giant mesogen trapped in crystalline differentiation and lightly evolving basaltic magma Forming. The Tongling area underwent a long-term large-scale process of magmatic underplating and crust-mantle interaction during the Mesozoic. Due to the contamination of the magmatic layer in the lower crust, a large amount of sulfur was released from the lightly evolved basaltic magma, which is bound to be near the Moho Large-scale and high-concentration sulfur enrichment zones are formed. These components are easily reactivated under the influence of magma intrusion, crustal thinning or rifting. They enter the regional magmatic-hydrothermal fluid system and eventually form a large area Scale sulfide deposits.