湖南现代河流砂矿金刚石的红外光谱测定及其源区指示

doi:10.3964/j.issn.1000-0593(2019)12-3833-06

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Abstract FTIR spectrometry provides a crucial means to explore the types of diamonds and their impurities, which would to some extent reflect the physical-chemical conditions of the diamonds and also their origin characteristics, revealing the source information and genesis of the diamonds. In this paper, a set of samples of diamonds from the modern river placer in Hunan are analysed by in-situ measurement of FTIR spectrometry. The results show that the diamonds are mainly IaAB type (93%), with minor IaA type (5%), IaB type (<1%) and IIa type (2%). Most diamonds have medium to low nitrogen contents (35.0~436 μg·g^-1) and medium to low nitrogen aggregation (3%~57%, ave. 37%), while the others are relatively high (517~2 848 μg·g^-1, even up to 6 829 μg·g^-1). The probable range of storage temperatures of the diamonds are between 1 100 and 1 230 ℃, similar to the formation temperature of mineral inclusion in diamonds reported by previous literature. In addition, their residence time in the mantle are generally short (most <0.2 Ga), indicating that the diamonds from the modern river placer in Hunan are probably mainly generated in the upper mantle, and their source rocks are related to both ultramafic and eclogitic parageneses. Few diamonds with high nitrogen contents and low nitrogen aggregation features may be more closely related to eclogitic parageneses. By further comparing with another place where we have found primary diamonds, Guizhou, Yangtze Craton, it shows that Guizhou diamonds have characteristics of high proportion of IIa type (75%), high degree of fragmentation, poor integrity, low quality and strong corrosion, indicating that the diamonds from Guizhou are derived from the deeper mantle than Hunan’s. The different types and features of the diamonds from Hunan and Guizhou may show the diversity of their sources. Furthermore, the placer diamonds from Hunan and primary diamonds from Guizhou may constitute a complete mineralization sequence in Yangtze Craton, which may correspond to different environment stages of diamond mineralization, respectively. The haul distance of the diamonds from Hunan placer is relatively short, indicating a near-field source. Therefore, FTIR spectrometry provides an approach to explore the origin features and formation condition of the diamonds in Yangtze Craton.

Key words：Diamonds; FTIR spectrometry; Nitrogen impurities; Source; Modern river placer

Received: 2018-10-29 Accepted: 2019-03-14

ZTFLH:

O657.3

Corresponding Authors: QIU Zhi-li E-mail: qiuzhili@mail.sysu.edu.cn

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https://www.gpxygpfx.com/EN/10.3964/j.issn.1000-0593(2019)12-3833-06 OR https://www.gpxygpfx.com/EN/Y2019/V39/I12/3833