金伯利岩演化过程及金刚石含矿性评价的研究进展

doi:10.11867/j.issn.1001-8166.2016.07.0700.

金伯利岩是研究地幔动力学过程、探讨岩石圈演化等深部重大科学问题的有效载体,也是揭示金刚石这一稀缺矿产资源的形成环境、成因、来源及找矿实践等最为重要的研究对象之一。长期以来,由于受到研究手段、研究思路等的限制,对金伯利岩相关研究的核心与瓶颈性关键基础科学问题,即“金伯利岩的初始岩浆组成”、“金伯利岩的演化过程及其意义”、“金伯利岩的金刚石含矿性评价”等知之甚少,这极大地制约了人们对金伯利岩及其相关深部过程意义等方面的深入了解。例如,基于高压熔体模拟实验、基质矿物、细小同源包裹体及金伯利岩筒边部隐晶质物质的研究,可以有效分析金伯利质岩浆的初始组成特征,但却难于有效甄别金伯利质岩浆的源区特征,难于有效区分地幔同化/混染作用、流体分异以及就位期间的脱玻化作用等对岩浆的影响等;由于缺乏再结晶及(或)再生长矿物在微成分、微结构方面的系统研究报道,难于有效精准分析金伯利质岩浆组成的变化规律及脱气作用的影响,揭示金伯利质岩浆的演化过程;尽管根据共生矿物组合、橄榄石的含水性等可用于评估金伯利岩的金刚石含矿性,但存在指标体系过于简单、数据积累少等方面问题。理论上,从微区(微米级、纳米级)的角度,对金伯利岩各组成结构单元中矿物等的微成份、微结构进行系统研究,可以更为精准地提取金伯利质初始岩浆组成、演化过程等方面的信息,因此对含金刚石与不含金刚石的金伯利岩的微组构进行精细研究,可以为有效重建金伯利质岩浆的演化机制、深入揭示其对深部过程的响应等奠定科学基础。同时,也可以在对已知金刚石矿区研究的基础上,建立用于金刚石初始品位预测和保存潜力分析的模型,以实现有效评价未知金伯利岩区的含矿性的目的。

关键词: 金伯利岩, 岩浆演化, 金刚石含矿性, 微组构

Kimberlite is an effective vector for researches and discussions on mantle dynamics process, lithosphere evolution and other major scientific problems, which plays an important role in revealing the forming environment, origin, source and prospecting of diamond. Currently, the developing research process of Kimberlite is still hampered by several key scientific problems, such as the evolution and the significance of the Kimberlite, evaluation for diamond potential and so on. Based on high-pressure melt simulation experiments, researches about matrix mineral, fine syngenetic inclusion (cognate xenolith?) and cryptocrystalline in the margin area of Kimberlite pipe, it seems that the initial composition features of Kimberlitic magma can be effectively analyzed. However, these experiments and researches are not only difficult to identify source characteristics of Kimberlitic magma efficiently, but also difficult to distinguish those effects on magma from which is assimilation/contamination, fluid fractionation or devitrification. Lacking of systematic research reports about recrystallization and (or) regrowth mineral on micro-composition and micro-structure, it is hard to efficiently and accurately analyze the changes and degassing effects in Kimberlitic magma, so far as to reveal the process of Kimberlitic magma evolution. Although Kimberlite diamond potential can be evaluated based on mineral assemblage, water content of olivine, there still exist some kinds of problems, like the index system being too simple, and the data accumulation being too little. Carrying out the fine micro-fabric studies between diamond-bearing Kimberlite and non diamond-bearing one can establish the scientific foundation for rebuilding the Kimberlitic magma evolution mechanism effectively and reveal the response to deep geological process. Meanwhile, on the basis of known diamond mines, a model for initial grade prediction of diamond and analysis of preservation potential can be set up to realize final purpose to evaluate the diamond potential in unknown Kimberlite areas in effect validity.

Key words: Kimberlite, Magma evolution, Diamond potential, Micro-fabric.

中图分类号:

P581

表1 不同来源的金伯利质熔体的化学组成(单位:%) ^{[

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Table 1 Some estimates of kimberlite melt compositions(unit:%) ^{[

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]}

样品号	1	2	3	4	5	6	7
SiO₂	34.37	29.56	36.28	36.28	26	17.44	20.46
TiO	20.65	3.82	0.90	0.90	8.27	8.51	5.06
Cr₂O₃	1.65
Al₂O₃	0.26	2.74	0.92	0.92	4.19	3.73	5.84
Fe₂O₃	2.78	11.24	1.15	1.15	17.41	18.33	14.65
FeO	4.66	9.22	9.22	4.20
MnO	0.18	0.22	0.21	0.21	0.37
MgO	28.19	30.80	34.52	34.52	23.63	20.44	23.1
CaO	24.99	17.73	14.65	14.65	14.68	25.59	19.89
Na₂O	0.18	0.07	0.40	0.40	0.07	0.08	0.37
K₂O	0.52	1.35	0.34	0.34	1.32	1.28	0.08
P₂O₅	0.79	2.21	1.40	1.40	4.43	4.59	5.96
BaO	0.67
SrO	0.11
挥发份
CO₂	13.02	8.63	12.12	4.13	11.97	6.33	19.47
H₂O	6.68	4.92	10.35	5.67	7.09	8.04

表1 不同来源的金伯利质熔体的化学组成(单位:%) ^{[

4
]}

Table 1 Some estimates of kimberlite melt compositions(unit:%) ^{[

4
]}

样品号	1	2	3	4	5	6	7
SiO₂	34.37	29.56	36.28	36.28	26	17.44	20.46
TiO	20.65	3.82	0.90	0.90	8.27	8.51	5.06
Cr₂O₃	1.65
Al₂O₃	0.26	2.74	0.92	0.92	4.19	3.73	5.84
Fe₂O₃	2.78	11.24	1.15	1.15	17.41	18.33	14.65
FeO	4.66	9.22	9.22	4.20
MnO	0.18	0.22	0.21	0.21	0.37
MgO	28.19	30.80	34.52	34.52	23.63	20.44	23.1
CaO	24.99	17.73	14.65	14.65	14.68	25.59	19.89
Na₂O	0.18	0.07	0.40	0.40	0.07	0.08	0.37
K₂O	0.52	1.35	0.34	0.34	1.32	1.28	0.08
P₂O₅	0.79	2.21	1.40	1.40	4.43	4.59	5.96
BaO	0.67
SrO	0.11
挥发份
CO₂	13.02	8.63	12.12	4.13	11.97	6.33	19.47
H₂O	6.68	4.92	10.35	5.67	7.09	8.04

图1 2GPa下MgSiO ₃-H ₂O-CO ₂系统中的相位图 ^{[

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]}

Fig.1 Phase relations in the system MgSiO ₃-H ₂O-CO ₂ at 2GPa ^{[

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]}

图2 不同样品在不同缓冲剂下的温度—氧逸度图解 ^{[

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]}
MH:磁铁矿—赤铁矿;NNO:Ni-NiO;FMQ:铁橄榄石—石英—磁铁矿;WM:方铁矿—磁铁矿;IW:铁—方铁矿;QIF:石英—铁—橄榄石

Fig.2 Temperature vs oxygen buffers in Log fO ₂for different samples ^{[

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MH: Magnetite-Hematite; NNO: Nickel-Nickel Oxide;FMQ: Fayalite-Magnetite-Quartz; WM: Wustite-Magnetite;IW: Iron-Wustite; QIF: Quartz-Iron-Fayalite

表2 金伯利岩中各类橄榄石的含水量 ^{[

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]}

Table 2 Water content of olivine from different peridotite xenoliths ^{[

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样品编号	样品产地	橄榄石类型	含水量/×10^-6
865	南非芬什	含金刚石橄榄岩捕虏体	50±10
866	南非芬什	含金刚石橄榄岩捕虏体	20±5
XM46	南非芬什	含金刚石橄榄岩捕虏体	10±5
XM48	南非芬什	含金刚石橄榄岩捕虏体	15±5
BO01	南非博斯霍夫	不含金刚石橄榄岩捕虏体	120±20
BO02	南非博斯霍夫	不含金刚石橄榄岩捕虏体	115±15
BO18	南非博斯霍夫	不含金刚石橄榄岩捕虏体	100±10
BO20	南非博斯霍夫	不含金刚石橄榄岩捕虏体	150±25
LGS25-9	加拿大杰里科	不含金刚石橄榄岩捕虏体	230±30

表2 金伯利岩中各类橄榄石的含水量 ^{[

28
]}

Table 2 Water content of olivine from different peridotite xenoliths ^{[

28
]}

样品编号	样品产地	橄榄石类型	含水量/×10^-6
865	南非芬什	含金刚石橄榄岩捕虏体	50±10
866	南非芬什	含金刚石橄榄岩捕虏体	20±5
XM46	南非芬什	含金刚石橄榄岩捕虏体	10±5
XM48	南非芬什	含金刚石橄榄岩捕虏体	15±5
BO01	南非博斯霍夫	不含金刚石橄榄岩捕虏体	120±20
BO02	南非博斯霍夫	不含金刚石橄榄岩捕虏体	115±15
BO18	南非博斯霍夫	不含金刚石橄榄岩捕虏体	100±10
BO20	南非博斯霍夫	不含金刚石橄榄岩捕虏体	150±25
LGS25-9	加拿大杰里科	不含金刚石橄榄岩捕虏体	230±30

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摘要

Progresses and Perspectives of Research of the Evolution of Kimberlite and Evaluation for Diamond Potential