Petrogenesis of the Ophiolitic Giant Chromite Deposits of Kempirsai, Kazakhstan: a Study of Solid and Fluid Inclusions in Chromite

Melcher, Frank

doi:10.1093/petrology/38.10.1419

Cited by 74 publications

(113 citation statements)

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“…Zhou et al (1996) used the phase relationships determined by Irvine (1977) to show the shift of the liquid line of descent towards the chromite field during the mixing of a primitive melt and a silicic liquid, which resulted from mantle/melt interactions. The primitive melts associated with high Cr-type podiform chromitites are either boninitic or arc tholeiitic in composition (Malpas and Robinson, 1987;Zhou et al, 1996;Melcher et al, 1997). Our evaluation of the composition of the liquid, which coexisted with the Danao chromitite led to 11.9-12.2 Al 2 O 3 (wt%) and FeO/MgO ratios of 0.86-1.4 using the expressions of Maurel and Maurel (1982) and Maurel (1984;in Augé, 1987).…”

Section: Implications To Vms and Chromitite Depositsmentioning

confidence: 97%

Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic Massive Sulfide and Podiform Chromitite Deposits

Tamayo

Yumul²,

Maury

et al. 2001

Resource Geology

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IntroductionVolcanogenic massive sulfides (VMS) and podiform chromitites commonly occur in ophiolite complexes. The VMS bodies are found in or near the contact of the pillow basalts and the overlying sedimentary rocks. A common feature of these deposits, particularly those relatively unaffected by tectonic deformation, is their mound-like morphology and subsurface stockwork-type mineralization, which are reminiscent of the structure of hydrothermal vents and their associated metal accumulations observed in modern mid-oceanic ridges (Hannington et al., 1995;Knott et al., 1998) and backarc basin rifts (Halbach et al., 1989;Binns and Scott, 1993). The podiform chromitites, on the other hand, occur in the transition zone dunites and residual upper mantle sequences of ophiolite complexes (Roberts, RESOURCE GEOLOGY, vol. 51, no. 2, 145-164, 2001 145 (IAB). The residual upper mantle sequence is harzburgitic and generally more depleted than the upper mantle underlying modern mid-oceanic ridges. Calculations using whole-rock and mineral compositions show that they can represent the residue of a fertile mantle source, which have undergone degrees of partial melting ranging from 9-22.5 %. Some of the mantle samples display chondrite-normalized REE and extended multi-element patterns suggesting enrichments in LREE, Rb, Sr and Zr, which are comparable to those found in fore-arc peridotites from the Izu-Bonin-Mariana (IBM) arc system. The Antique ultramafic rocks also record relatively oxidizing mantle conditions (∆log f O 2 (FMQ)=0.9-3.5). As a whole, the ophiolite probably represents an agglomeration of oceanic ridge and fore-arc crust fragments, which were juxtaposed during the Miocene collision of the PMB and the NPB. The intrusion of the serpentinites might be either coeval or subsequent to the accretion of the oceanic crust onto the fore-arc.Volcanogenic massive sulfide (VMS) deposits occur either in or near the contact between the pillow basalts and the overlying sediments or interbedded with the sediments. The morphology of the deposits, type of metals, ore texture and the nature of the host rocks suggest that the formation of the VMS bodies was similar to the accumulation of metals around and in the subsurface of hydrothermal vents observed in modern mid-oceanic ridge and back-arc basin rift settings. The podiform chromitites occur as pods and subordinate layers within totally serpentinized dunite in the residual upper mantle sequence. No large coherent chromitite deposit was found since the host dunitic rocks often occur as blocks within the serpentinites. It is difficult to evaluate the original geodynamic setting of the mineralized bodies since the chemistry of the host rocks were considerably modified by alteration during their tectonic emplacement. A preliminary conclusion for Antique is that the VMS is apparently associated with a primitive tholeiitic intermediate MORB-IAB volcanic suite, the chemistry of which is close to the calculated composition of the liquid that coexisted with the podiform chromitites.

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Section: Implications To Vms and Chromitite Depositsmentioning

confidence: 97%

Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic Massive Sulfide and Podiform Chromitite Deposits

Tamayo

Yumul²,

Maury

et al. 2001

Resource Geology

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“…The Al 2 O 3 and TiO 2 contents of chromian spinel in chromitites can be used to constrain the nature of their parental melts and their tectonic setting (Akmaz, Uysal, & Saka, 2014;Maurel & Maurel, 1982;Melcher et al, 1997;Pagé & Barnes, 2009). The calculated Al 2 O 3 and TiO 2 contents of the melt in equilibrium with chromian spinels (Kamenetsky et al, 2001;Maurel & Maurel, 1982) in chromitites from the Western Khoy ophiolite range from 11.7 wt% to 15.3 wt% and from 0.5 wt% to 1.0 wt%, respectively.…”

Section: Chromitite Genesismentioning

confidence: 99%

Mineral chemistry and petrogenesis of chromitites from the Khoy ophiolite complex, Northwestern Iran: Implications for aggregation of two ophiolites

et al. 2017

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The Khoy ophiolitic complex in Northwestern Iran is a part of the Tethyan ophiolite belt, and is divided into two sections: the Eastern ophiolite in Qeshlaq and Kalavanes (Jurassic–Cretaceous) and the Western ophiolite in Barajouk, Chuchak and Hessar (Late Cretaceous). Our chromitites can be clearly classified into two groups: high‐Al chromitites (Cr# = 0.38–0.44) from the Eastern ophiolite, and high‐Cr chromitites (Cr# = 0.54–0.72) from the Western ophiolite. The chromian spinels in high‐Al chromitite include primary mineral inclusions mainly as Na‐bearing diopside and pargasite with subordinate rutile and their formation was probably related to reaction between a MORB (mid‐ocean‐ridge basalt)‐like melt with depleted harzburgite, possibly in a back‐arc setting. Their host harzburgites contain clinopyroxene with higher contents of Al2O3, Na2O, Cr2O3, and TiO2 relative to Western harzburgites and are possibly residue after moderate partial melting (~15 %) whereas the Western harzburgite is residue after high partial melting (~25 %). The chromian spinel in the Western Khoy chromitites contains inclusions such as clinopyroxene, olivine and platinum group mineral‐bearing sulfides. These Western chromitites were possibly formed at two stages during arc growth and are divided into the moderately high‐Cr# chromitites (Barajouk and Hessar) and the high‐Cr# chromitites (Chuchak A and C). The former crystallized from island‐arc‐tholeiite (IAT) melts during reaction with the host depleted harzburgites, whereas the latter crystallized from boninitic melts (second stage melt) during reaction with highly depleted harzburgite in a supra‐subduction‐zone environment. Based on the mineral chemistry of chromian spinels, pyroxenes, and mineral inclusions, the chromitites and the host peridotites from the Eastern and Western Khoy ophiolites were formed in a back‐arc basin and arc‐related setting, respectively. The Khoy ophiolitic complex is a tectonic aggregate of the two different ophiolites formed in two different tectonic settings at different ages.

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“…Magnesiochromite is broadly acknowledged as one of the most significant petrogenetic indicators, thus the composition of unaltered magnesiochromite cores can be used to define the chemical signature of the melts from which chromitites formed (e.g. Melcher et al, 1997;Uysal et al, 2009;Akmaz et al, 2014;Zhou et al 2014). The Al 2 O 3 abundance of the melt from which magnesiochromite crystallized can be calculated using the following equation, which assumes that Al 2 O 3 in magnesiochromite is only a function of Al 2 O 3 in the melt: ].…”

Section: Genesis and Deformation History Of The Chromititesmentioning

confidence: 99%

Alteration of chromitites from the Voidolakkos and Xerolivado mines, Vourinos ophiolite complex, Greece: implications for deformation-induced metamorphism

Kapsiotis

2014

Geol. J.

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Chromitites, associated with upper mantle spinel peridotites from the Voidolakkos and Xerolivado districts, located in the Vourinos ophiolite complex, northwestern continental Greece, were re‐investigated with respect to their structural and textural mode of occurrence, as well as their compositional signatures. They include variably deformed banded and podiform chromitite bodies made up of massive, semi‐massive, nodular, anti‐nodular, schlieren and disseminated chromian spinel. Chromitites have suffered intense shearing that was more severe in all but disseminated textured ore. Deformation has partly produced elongation of chromian spinel nodules and widespread protocataclastic zones within chromitites. The examined deposits are composed of magnesiochromite that shows a quite restricted range of Cr# [Cr/(Cr + Al)] values varying between 0.76 and 0.83, whereas Mg# [Mg/(Mg + Fe2+)] ranges from 0.55 to 0.67 accompanied by relatively low content in TiO2 (<0.15 wt.% on average). Compositional data indicate that these high‐Cr chromitite bodies crystallized from melts of boninitic affinities that have been compositionally modified after reaction with depleted harzburgite, followed by interaction with relatively undifferentiated low SiO2 melts within an intertwined system of dunite channels in the mantle wedge below the fore‐arc region of a supra‐subduction zone (SSZ). Magnesiochromite displays limited textural modification, being scarcely transformed to an opaque spinel phase along grain boundaries and fracture walls. The opaque spinel phase is characterized by elevated Cr# (0.76–0.97), relatively low Mg# (0.33–0.63) and low Fe3+# (≤0.14) and corresponds to ferrian chromite. Microscopic studies revealed that ferrian chromite is paragenetically associated with clinochlore even in unaltered chromitite specimens and the degree of serpentinization does not correlate with the frequency and abundance of alteration effects on magnesiochromite. Therefore, it is supported that regional metamorphism prior to serpentinization was responsible for the formation of the ferrian chromite–clinochlore association. In addition, magnesiochromite alteration was systematically recorded only in variably sheared chromitites displaying protocataclastic brecciation, thus it can be claimed that metamorphism was mainly governed by deformation mechanisms, which took place during the transition from ductile to semi‐brittle conditions. Ferrian chromite can be locally erratically enriched in MnO and ZnO, which is attributed to a Mn‐ and Zn‐bearing, slightly acid post‐magmatic fluid that invaded the chromitites across weakness zones. Overall, the data suggest that after magnesiochromite equilibration with the intergranular olivine, both phases were partly replaced by ferrian chromite and clinochlore, respectively, during a brief, fluid assisted episode of retrogade metamorphism that took place within a temperature interval between 700 and 300 °C, before ocean‐floor alteration. Copyright © 2014 John Wiley & Sons, Ltd.

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Petrogenesis of the Ophiolitic Giant Chromite Deposits of Kempirsai, Kazakhstan: a Study of Solid and Fluid Inclusions in Chromite

Cited by 74 publications

References 0 publications

Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic Massive Sulfide and Podiform Chromitite Deposits

Petrochemical Investigation of the Antique Ophiolite (Philippines): Implications on Volcanogenic Massive Sulfide and Podiform Chromitite Deposits

Mineral chemistry and petrogenesis of chromitites from the Khoy ophiolite complex, Northwestern Iran: Implications for aggregation of two ophiolites

Alteration of chromitites from the Voidolakkos and Xerolivado mines, Vourinos ophiolite complex, Greece: implications for deformation-induced metamorphism

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