Layered Intrusions: From Petrological Paradigms to Precious Metal Repositories

O’Driscoll, Brian; VanTongeren, J. A.

doi:10.2138/gselements.13.6.383

Cited by 31 publications

(9 citation statements)

References 22 publications

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“…The phase Fo 89.5 presumably crystallized close to the thermal maximum area in the center, and the opposite trends of cryptic variations involve progressively less forsteritic olivine (Figure 12a). voluminous Pados-Tundra complex [6] and other layered intrusions, which are located at a lower structural level [46,47]. The buildup of olivine in the core of concentrically zoned complexes of alkaline ultramafic rocks like Kondyor [48] seems unrelated in view of the important petrogenetic differences.…”

Section: Discussionmentioning

confidence: 99%

Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia

et al. 2019

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Dunite–harzburgite–olivine-bearing orthopyroxenite successions in the subvolcanic Chapesvara-I and Chapesvara-II intrusions in the Serpentinite Belt, western Kola Peninsula, are notably magnesian. The mean Mg# value (whole-rock) is 86.6, and the olivine is Fo84−89. The upper contact facies (UCF) displays a lower Mg# (81.6). It consists of grains of Fo92 and abundant chromian spinel, implying rapid crystallization of an almost unfractionated melt. On average, the whole-rock Al2O3/TiO2 value is 22.45, close to 22.9 (UCF) and to the primitive mantle, ~22. The rise of primitive ultramafic magma presumably occurred in a special tectonic setting at the boundary of the Paleoproterozoic Lapland Granulite Terrane and the Belomorian Composite Terrane of Archean age. The Chapesvara suite resembles examples of the Al-undepleted komatiites in the Barberton Belt, South Africa, with magmas of up to 30–35% MgO. The UCF rock yields an anomalously low molar MgO/SiO2 value, close to that of dunitic rocks located at the center of the Chapesvara-II body. This rock is the most primitive, as indicated by the maximum Fo content of olivine, the lowest value of (Gd/Yb)N, 0.52, and the lowest abundances of middle to heavy rare-earth elements (REE) in the chondrite-normalized spectrum. The crystallization of the Chapesvara-II sill-like intrusion likely proceeded in two stages, which are evident from the olivine compositions varying from the maximum Fo92 (UCF) to Fo≤89.5 (the central dunite zone). At Stage 1, the UCF rock (Fo92) crystallized first, close to the upper contact. The area of crystallization then shifted to a central portion of the Chapesvara-II body, in which the dunitic zone (Fo89.5) formed in situ (Stage 2). The compositional variations in chromian spinel are consistent with this suggestion. Two crystallization trends were recognized. The type-1 trend displays a relative maximum or minimum close to the center, and then diverges into two linear subtrends directed upward and downward. This pattern is manifested in the variations of Mg# in olivine and chromian spinel, the whole-rock contents of Al and Ca, and in levels of incompatible elements: Ti, V, Zr, Y, and Hf. The type-2 trend decreases or increases uniformly from top to bottom. Variations in amount of Ni in olivine, the Fe3+# index in chromian spinel, and in values of Mg# (rocks), follow a type-2 trend. Variations in total amounts of REE, Nb, and Th, which gradually increase downward, are also related to a type-2 trend. Thus, a contrasting development and possible interference of the two types of evolutionary trends were observed in the crystallization history of the Chapesvara-II sill-like body. A double-front crystallization, hitherto unreported, involved two fronts moving upward and downward, respectively. The upward subtrend appeared to be of subordinate importance, whereas the extent of fractional crystallization of the downward front was much greater. Crystallization proceeded from the top to the bottom, presumably because of the preferential loss of heat at the roof. Variations in the Fe3+# index indicate that the level of fO2 also increased downward with progressive crystallization. Convection cells were presumably the key mechanism of accumulation of the crystallizing olivine grains to form the central dunite zone close to the center of the sill-like intrusion. The observed characteristics of the Chapesvara complex indicate the existence of a primitive-mantle source and imply a highly magnesian composition of intruding magma not only for Chapesvara, but also for the Pados-Tundra layered complex and associated suites of the Serpentinite Belt in the Kola Peninsula.

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Section: Discussionmentioning

confidence: 99%

Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia

et al. 2019

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“…The formation of compositionally defined magmatic structures in mafic magmatic systems has been the focus of studies for decades (e.g., reviews by Namur et al, 2015;Holness et al, 2017;O'Driscoll and VanTongeren, 2017). For example, the Skaergaard intrusion preserves spectacular rhythmic layering as well as channel-shaped trough structures (e.g., Wager and Brown, 1968;Irvine et al, 1998;Vukmanovic et al, 2018).…”

Section: Background Compositionally Defined Magmatic Structure Modelsmentioning

confidence: 99%

Schlieren-Bound Magmatic Structures Record Crystal Flow-Sorting in Dynamic Upper-Crustal Magma-Mush Chambers

et al. 2020

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“…Layered mafic-ultramafic intrusions represent the solidified remnants of basaltic magmatic systems (Wager and Brown, 1968;Parsons, 1987;O'Driscoll and VanTongeren, 2017). These bodies are therefore important repositories of information for the geochemical and petrological processes that operate during the solidification of magma in the Earth's crust.…”

Section: Introductionmentioning

confidence: 99%

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A.

Parker¹,

Clay

Boudreau³

et al. 2022

American Mineralogist

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The activity of volatile-rich fluids may be important in the evolution of basaltic magmatic systems and associated precious metal ore formation. There is evidence for Cl-rich fluids within the Stillwater Complex (Montana, USA), which have been linked to platinum and palladium mineralisation in the economically important J-M Reef ore body. We present the first dataset for heavy halogens (Cl, Br and I) and natural noble gas isotopes in bulk rock and mineral separates from the Peridotite Zone and the Olivine-Bearing Zone I of the Stillwater Complex, including samples from the J-M Reef and G Chromitite bodies. Our data reveal concentrations of 4 to 13500 ppm for Cl, 26 ppb to 360 ppm for Br and <1 ppb to 9 ppm I over This is the peer-reviewed, final accepted version for American Mineralogist, published by the Mineralogical Society of America.The published version is subject to change. Cite as Authors (Year) Title. American Mineralogist, in press.

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Layered Intrusions: From Petrological Paradigms to Precious Metal Repositories

Cited by 31 publications

References 22 publications

Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia

Double-Front Crystallization in the Chapesvara Ultramafic Subvolcanic Complex, Serpentinite Belt, Kola Peninsula, Russia

Schlieren-Bound Magmatic Structures Record Crystal Flow-Sorting in Dynamic Upper-Crustal Magma-Mush Chambers

Magmatic volatiles and platinum-group element mineralization in the Stillwater layered intrusion, U.S.A.

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