scholarly journals Chemical and textural characterisation of non-kimberlitic chromian spinel populations from diamond exploration programmes

2019 ◽  
Keyword(s):  
Chromian Spinel ◽  
Diamond Exploration

Use and misuse of Mg- and Mn-rich ilmenite in diamond exploration: A petrographic and trace element approach

Lithos ◽  
2017 ◽  
Vol 292-293 ◽  
pp. 348-363 ◽  
Author(s):  
Montgarri Castillo-Oliver ◽  
Joan Carles Melgarejo ◽  
Salvador Galí ◽  
Vladimir Pervov ◽  
Antonio Olimpio Gonçalves ◽  
...  
Keyword(s):  
Trace Element ◽  
Diamond Exploration ◽  
Element Approach

Sources of placer platinum in Yukon: provenance study from detrital minerals

2008 ◽  
Vol 45 (8) ◽  
pp. 879-896 ◽  
Author(s):  
Yana Fedortchouk ◽  
William LeBarge
Keyword(s):  
Unknown Origin ◽  
Heavy Mineral ◽  
Source Rocks ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Mafic Intrusions ◽  
Platinum Group Minerals ◽  
Mineral Sample ◽  
Back Arc ◽  
Ocean Ridge

Source rocks for the platinum group minerals (PGM), historically reported in a number of Yukon placers, remain either unknown or poorly understood. A study of heavy-mineral samples from five creeks draining bedrock in west and central Yukon was undertaken to confirm the presence of placer platinum, to determine which mafic–ultramafic rock is the source of PGM in Kluane area, southern Yukon, and to explain platinum occurrences in Canadian and Florence creeks, central Yukon, where no known mafic–ultramafic rocks are present. Diverse composition of chromian spinel and clinopyroxenes from three creeks in the Kluane area indicate several sources of ultramafic rocks, including fragments of Alpine-type peridotites formed in back-arc basin and mid-ocean-ridge settings, and a source rock for zoned zinc-rich chromites of unknown origin. The Kluane ultramafic sills are the most likely source of PGM in this area. The heavy-mineral sample from Canadian Creek returned one PGM grain, no chromite, and abundant ilmenite and titanomagnetite. A group of chromium-rich magnesian ilmenites (∼4 wt.% MgO) closely match the composition of ilmenites from continental mafic intrusions produced during continental rift magmatism. This supports the continental rifting event recently proposed for this part of Yukon and indicates the economic potential of the Canadian Creek platinum occurrence. Composition of spinel from Florence Creek sample indicates an Alaskan-type intrusion as the source of PGM.

scholarly journals Exsolution Lamellae in Orthopyroxene of Lherzolite from the Pauza Ultramafic Rocks, Ne Iraq: Evidence of Deep Mantle Signature in the Zagros Suture Zone

2013 ◽  
Vol 2 (9) ◽  
pp. 102-115
Author(s):  
Yousif Osman Mohammad ◽  
Nabaz Rashid Hama Aziz
Keyword(s):  
High Pressure ◽  
Upper Cretaceous ◽  
Suture Zone ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Spinel Peridotite ◽  
Incongruent Melting ◽  
Fine Grained ◽  
Ultra High Pressure ◽  
Deep Mantle

The Pauza ultramafic body is part of Upper Cretaceous Ophiolitic massifs of the Zagros Suture Zone, NE Iraq. The present study reveals evidence of Ultra-high pressure (UHP), and deep mantle signature of these peridotites in the Zagros Suture Zone throughout the observation of backscattered images and micro analyses which have been performed on orthopyroxen crystals in lherzolite of Pauza ultramafic rocks.Theorthopyroxen shows abundant exsolution lamellae of coarse unevenly distributed clinopyroxene coupled with the submicron uniformly distributed needles of Cr-spinel. The observed clusters of Opx–Cpx–Spl represent the decompression products of pyrope-rich garnet produced as a result of the transition from ultra-high pressure garnet peridotite to low-pressure spinel peridotite (LP). Neoblastic olivine (Fo92 – 93) with abundant multi-form Cr- spinel inclusions occurs as a fine-grained aggregate around orthopyroxene, whereas coarse olivine (Fo90-91) free from chromian-spinel is found in matrix. The similarity of the Cr-spinel lamellae orientations in both olivine and orthopyroxene, moreover, the enrichments of both Cr and Fe3+ in the Cr-spinel inclusions in neoblastic olivine relative to Cr-spinel lamellae in orthopyroxene, suggest that spinel inclusions in olivine have been derived from former Cr-spinel lamellae in orthopyroxene. Neoblastic olivine is formed by reaction of silica-poor ascending melt and orthopyroxene. It is inferred that the olivines with multi-form spinel inclusions has been formed by incongruent melting of pre-existing spinel lamellae-rich orthopyroxene.

Deep electrical structure of northern Alberta (Canada): implications for diamond exploration

2009 ◽  
Vol 46 (2) ◽  
pp. 139-154 ◽  
Author(s):  
Erşan Türkoğlu ◽  
Martyn Unsworth ◽  
Dinu Pana
Keyword(s):  
Subduction Zone ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Three Dimensional ◽  
Diamond Formation ◽  
Magnetotelluric Data ◽  
Diamond Exploration ◽  
Upper Mantle Structure ◽  
Resistivity Model ◽  
Northern Alberta

Geophysical studies of upper mantle structure can provide constraints on diamond formation. Teleseismic and magnetotelluric data can be used in diamond exploration by mapping the depth of the lithosphere–asthenosphere boundary. Studies in the central Slave Craton and at Fort-à-la-Corne have detected conductors in the lithospheric mantle close to, or beneath, diamondiferous kimberlites. Graphite can potentially explain the enhanced conductivity and may imply the presence of diamonds at greater depth. Petrologic arguments suggest that the shallow lithospheric mantle may be too oxidized to contain graphite. Other diamond-bearing regions show no upper mantle conductor suggesting that the correlation with diamondiferous kimberlites is not universal. The Buffalo Head Hills in Alberta host diamondiferous kimberlites in a Proterozoic terrane and may have formed in a subduction zone setting. Long period magnetotelluric data were used to investigate the upper mantle resistivity structure of this region. Magnetotelluric (MT) data were recorded at 23 locations on a north–south profile extending from Fort Vermilion to Utikuma Lake and an east–west profile at 57.2°N. The data were combined with Lithoprobe MT data and inverted to produce a three-dimensional (3-D) resistivity model with the asthenosphere at 180–220 km depth. This model did not contain an upper mantle conductor beneath the Buffalo Head Hills kimberlites. The 3-D inversion exhibited an eastward dipping conductor in the crust beneath the Kiskatinaw terrane that could represent the fossil subduction zone that supplied the carbon for diamond formation. The low resistivity at crustal depths in this structure is likely due to graphite derived from subducted organic material.

Geology and geochemistry of pillow basalt in the Huilvshan region (west Junggar, China): implications for magma source and tectonic setting

2018 ◽  
Vol 55 (12) ◽  
pp. 1339-1353
Author(s):  
Huichao Zhang ◽  
Yongfeng Zhu
Keyword(s):  
Tectonic Setting ◽  
Weighted Average ◽  
Early Carboniferous ◽  
Tectonic Activity ◽  
Chromian Spinel ◽  
Magma Source ◽  
Spinel Lherzolite ◽  
Pillow Basalt ◽  
Depleted Mantle ◽  
West Junggar

Geological characteristics and geochemical analyses are reported for the early Carboniferous pillow basalt in the Huilvshan region (west Junggar, Northwest China), with the aim to indicate its petrogenesis, magma source characteristics, and tectonic implication. This pillow basalt consists of clinopyroxene and plagioclase with trace amounts of magnetite, apatite, and chromian spinel. It is tholeiitic in composition with low concentrations of Na2O + K2O (1.52–4.74 wt.%). Similar to the N-MORB, the samples of this pillow basalt have nearly flat chondrite-normalized REE patterns ((La/Yb)N = 0.87–1.47) with insignificant Eu anomalies (Eu/Eu* = 0.84–1.18), and show no obvious enrichments of LILEs and insignificant depletions in HFSEs. Petrology and geochemical characteristics suggest that this pillow basalt is the product of MORB-like magma derived from a depleted mantle corresponding to ≤4% partial melting of spinel lherzolite. SIMS analysis of the zircons separated from tuff interlayered with basalt gives a weighted average U–Pb age of 328 ± 3 Ma (MSWD = 1.4), which represents the magma eruption time in the Huilvshan region. From these observations, in combination with the previous work, we conclude that an extensional tectonic regime dominated the tectonic activity of west Junggar during early Carboniferous.

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