The Carolina kimberlite, Brazil — Insights into an unconventional diamond deposit

Hunt, Lucy; Stachel, Thomas; Morton, R. D.; Grütter, Herman; Creaser, Robert A.

doi:10.1016/j.lithos.2009.04.018

Cited by 31 publications

(21 citation statements)

References 36 publications

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“…When the concentrations and aggregation states for the diamonds are considered, the diamonds cover a wide range of model temperatures, as demonstrated in Fig. 8 (approximately 1050 -1250 °C when using a 1.5 Ga mantle residence time, following Hunt et al, 2009), indicating either diamond formation over a range of temperatures (and hence presumably depths) or multiple episodes of diamond formation. The overgrowths in diamonds P16 and P42 are clear textural and spectroscopic evidence for the latter hypothesis, but it is not possible to determine whether the entirely Type IaA stones relate to the younger growth events or are older diamonds that have remained unaggregated because of storage conditions that were up to 200 °C cooler than the Type IaB stones.…”

Section: Nitrogen Concentrations and Aggregation Statesmentioning

confidence: 90%

“…However, the Carolina kimberlite (Fig. 1b) is unlikely to have supplied a significant proportion of the Machado River diamonds because platelet degradation is seen in a large proportion of Carolina diamonds (Hunt et al, 2009), a feature uncommon at Machado. The Pimenta Bueno kimberlites have not yielded significant numbers of commercial-sized diamonds and hence are not a major supplier to Machado either.…”

Section: Possible Primary Sources Of the Machado River Alluvial Diamondsmentioning

confidence: 99%

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Diamonds from the Machado River alluvial deposit, Rondônia, Brazil, derived from both lithospheric and sublithospheric mantle

Burnham

Bulanova

Smith

et al. 2016

Lithos

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Diamonds from the Machado River alluvial deposit have been characterised on the basis of external morphology, internal textures, carbon isotopic composition, nitrogen concentration and aggregation state and mineral inclusion chemistry. Variations in morphology and features of abrasion suggest some diamonds have been derived directly from local kimberlites, whereas others have been through extensive sedimentary recycling. On the basis of mineral inclusion compositions, both lithospheric and sublithospheric diamonds are present at the deposit. The lithospheric diamonds have clear layer-by-layer octahedral and/or cuboid internal growth zonation, contain measurable nitrogen and indicate a heterogeneous lithospheric mantle beneath the region. The sublithospheric diamonds show a lack of regular sharp zonation, do not contain detectable nitrogen, are isotopically heavy (δ 13 CPDB predominantly-0.7-5.5) and contain inclusions of ferropericlase, former bridgmanite, majoritic garnet and former CaSiO3-perovskite. This suggests source lithologies that are Mg-and Ca-rich, probably including carbonates and serpentinites, subducted to lower mantle depths. The studied suite of sublithospheric diamonds has many similarities to the alluvial diamonds from Kankan, Guinea, but has more extreme variations in mineral inclusion chemistry. Of all superdeep diamond suites yet discovered, Machado River represents an end-member in terms of either the compositional range of materials being subducted to Transition Zone and lower mantle or the process by which materials are transferred from the subducted slab to the diamond-forming region. Keywords bridgmanite; majorite; subduction; carbon; superdeep; diamond 1. Introduction Although the vast majority of the world's diamonds are characterised by being inclusion-free (96-99 %), and ~ 28 % of inclusions are trace-element poor olivines and chrome spinels (Stachel and Harris, 2008), they have continued to draw keen interest from petrologists and geochemists. While diamonds undoubtedly offer a selective view of the deep Earth, in particular of the highly depleted Archaean cratonic mantle (Stachel and Harris, 2008), the fidelity with which the chemistry of inclusions is preserved makes them a valuable scientific resource. Around 5-10 % of diamonds are derived from beneath the base of the lithosphere (i.e. sublithospheric, or "superdeep") and are direct evidence of the mixing and recycling processes that lead to mantlederived lavas with diverse isotopic and elemental characteristics (e.g. Pietruszka et al., 2013). The minerals that are included in these superdeep diamonds may only represent a single fragment of a single geological event in a rock's life cycle, but this information is essential for reconstructing the geological history of subducted material. Variations in the characteristics of diamonds and their inclusions within and between localities testify about the spatial and/or temporal variability of the source region: they reveal, for example, the presence of multiple

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Section: Nitrogen Concentrations and Aggregation Statesmentioning

confidence: 90%

Section: Possible Primary Sources Of the Machado River Alluvial Diamondsmentioning

confidence: 99%

Diamonds from the Machado River alluvial deposit, Rondônia, Brazil, derived from both lithospheric and sublithospheric mantle

Burnham

Bulanova

Smith

et al. 2016

Lithos

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show abstract

“…Currently, a lower than expected concentration of platelets is often cited as evidence for short-lived high temperature events (e.g. Melton et al, 2013;Hunt et al, 2009). This interpretation is based on experimental results by Evans et al (1995).…”

Section: Introductionmentioning

confidence: 99%

The relationship between platelet size and the B′ infrared peak of natural diamonds revisited

Speich

Kohn

Wirth

et al. 2017

Lithos

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Platelets in diamond are extended planar defects that are thought to be generated during the nitrogen aggregation process in type Ia diamonds. They were subjected to intensive research during the 1980s and 1990s but the techniques used for observation of defects in diamond have improved since that time and new insights can be gained by further study. This study combines high resolution Fourier Transform Infrared (FTIR) analysis, with an emphasis on the main platelet peak, and transmission electron microscopic (TEM) imaging. By performing TEM and FTIR analyses on volumes of diamond that were closely spatially related it is shown that the average platelet diameter, D, follows the relationship D = a x−b where x is the position of the platelet peak in the infrared spectrum, a is a constant and b is the minimum position of the platelet peak. The best fit to the data is obtained if a value of b = 1360 cm-1 is used, giving a fitted value of a = 221. The observed variation in infrared (IR) peak width can also be explained in terms of this relationship. Additionally, platelet morphology was found to vary according to diameter with large platelets being more elongated. The tendency to become more elongated can be described by the empirical equation AR = 11.9 D+19.6 + 0.4 where AR is the aspect ratio. Using the relationships established here, it will be possible to study platelet abundance and size as a function of parameters such as nitrogen concentration, nitrogen aggregation and diamond residence time in the mantle. This work therefore will open up new methods for constraining the geological history of diamonds of different parageneses and from different localities.

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“…However, the temperatures for the majority of diamonds falls within the expected error limits (±50°C) and may indicate that the diamonds were sampled from a restricted depth range in the lithosphere that experienced a similar thermal history (e.g. Taylor and Milledge, 1995;Hunt et al, 2009).…”

Section: Nitrogen Aggregation and Temperature Calculationsmentioning

confidence: 60%

Re–Os isotopic composition of peridotitic sulphide inclusions in diamonds from Ellendale, Australia: Age constraints on Kimberley cratonic lithosphere

Smit

Shirey

Richardson

et al. 2010

Geochimica et Cosmochimica Acta

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The Carolina kimberlite, Brazil — Insights into an unconventional diamond deposit

Cited by 31 publications

References 36 publications

Diamonds from the Machado River alluvial deposit, Rondônia, Brazil, derived from both lithospheric and sublithospheric mantle

Diamonds from the Machado River alluvial deposit, Rondônia, Brazil, derived from both lithospheric and sublithospheric mantle

The relationship between platelet size and the B′ infrared peak of natural diamonds revisited

Re–Os isotopic composition of peridotitic sulphide inclusions in diamonds from Ellendale, Australia: Age constraints on Kimberley cratonic lithosphere

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