Geochemistry of ultramafic and calc-llkaline lamprophyres from the Lac Shortt area, Quebec

Bourne, James H.; Bossé, J.

doi:10.1007/bf01164597

Cited by 10 publications

(10 citation statements)

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“…Ceux-ci appartiennent probablement à l'essaim de dykes d'Otish âgés d'environ 1 730 Ma (Chown et Archambault 1987;Chown et al 1996). On observe aussi quelques dykes de lamprophyres à caractères ultrabasiques (Bourne et Bossé 1991) d'âge incertain mais archéen tardif ou plus jeune.…”

Section: Roches Plutoniquesunclassified

Caractéristiques, chronologie et typologie des minéralisations aurifères de la région du Lac Shortt (Québec), sous-province archéenne de l'Abitibi /

Brisson¹

1998

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Section: Roches Plutoniquesunclassified

Caractéristiques, chronologie et typologie des minéralisations aurifères de la région du Lac Shortt (Québec), sous-province archéenne de l'Abitibi /

Brisson¹

1998

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“…Intrusions of the Lac Shortt alkaline complex were emplaced syn-to late-deformation within-and channelized by this shear zone. The alkaline complex contains the oldest carbonatite in Canada (2652 Ma;Morasse, 1988), undifferentiated mafic sills, massive and dike-like syenites and carbonatites, hornblendite dikes, diorite sills, calc-alkaline, alkaline and ultramafic lamprophyres (Bourne and Bosse, 1991) dikes and carbo-hydrothermal gold mineralization. The Lac Shortt fault zone contains blocs and clasts of carbonatites and syenites and the carbonatite contains syenite boudins.…”

Section: Geological Contextmentioning

confidence: 99%

“…The hornblendite, possibly a calc-alkaline lamprophyre (vogesite, with K feldsdpar N plagioclase, to spessartite, with plagioclase N K feldspar) consists of euhedral hornblende with apatite and olivine in a groundmass of secondary calcite, chlorite and epidote. Ultramafic and calc-alkaline lamprophyres trace element geochemistry collected mainly from drill cores in a radius of 10 km around Lac Shortt mine have ubiquitous phogopite, olivine replaced by serpentinechlorite-magnetite-carbonates, apatite, perovskite and ilmenite (Bourne and Bosse, 1991). Calcite is abundant in the matrix replacing olivine or as veinlets.…”

Section: Lamprophyresmentioning

confidence: 99%

“…The Lac Shortt Au-REE deposit hosted 2.7 Mt of ore at an average of 4.6 g/t Au (total 12.4 tons Au; Brisson, 1998). The mineralization was associated with a complex suite of intrusions consisting of alkali gabbros, syenite, carbonatite and silicocarbonatite plugs and dykes, undifferentiated mafic and dioritic sills, and ultramafic, calc-alkaline and alkaline lamprophyres (Morasse, 1988;Prud'homme, 1990;Bourne and Bosse, 1991;See, 1994). The Lac Shortt deposit is both locally (Prud'homme, 1990) and regionally (Dolodau carbonatite ;Bedard, 1988;Bedard and Chown, 1992) associated with coeval carbonatite magmatism.…”

Section: Introductionmentioning

confidence: 99%

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The Archean magmatic-hydrothermal system of Lac Shortt (Au-REE), Abitibi, Canada: Insights from carbonate fingerprinting

2014

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Trace element and isotopic data from the Lac Shortt (Abitibi, Canada) gold and rare earth element (REE) deposit sheds light on the cogenetic association between alkali magmatism (syenites and lamprophyres), carbonatation (magmatic and carbothermal) and gold -REE mineralization. Magmatic and carbothermal carbonates from comagmatic lithologies from the Lac Shortt gold-REE deposit were analyzed for major, minor and trace elements concentrations as well as for their 87 Sr/ 86 Sr 0 , δ 13 C and δ 18 O isotopic ratios. Carbonates from Lac Shortt have δ 13 C values ranging from −4.89 to 2.38 ‰ VPDB and δ 18 O values ranging from 8.28 to 15.02. The lightest values are found in carbonate from the carbonatites and the heaviest values are associated with the ore-carbonates.Carbonates from the various lithologies lie between these two extremes. Initial 87 Sr/ 86 Sr ratios from the carbonates cluster tightly around 0.7013-0.7016, i.e., depleted Archean mantle signatures, although some have slightly more radiogenic values, from 0.7026 to 0.7029. The small variation in the strontium isotope ratios compared to the C and O isotopic values suggests that carbonate anions (CO 3 2− ) were decoupled from the cations during hydrothermal alteration. Cations such as Sr 2+ and Ca 2+ in carbonates from the high grade ore and from magmatic and hydro-carbothermal carbonatite appear to originate from the Late-Archean, depleted mantle. Since gold is a cation and is strongly associated with carbonatite magmatism and associated carbo-hydrothermal carbonatation, we suggest gold too has a depleted mantle origin. The carbonates are enriched in mobile high field strength elements (HFS; Ba, Sr) elements, depleted in immobile HFS elements (Th, U, Ta, Nb, Zr, Ti) and have enriched-to slightly depleted REE patterns with flat to strong light-REE enrichments. These trace element concentrations support the fact that all the lithologies were comagmatic and that the ore itself was genetically related to these lithologies. Based on present day knowledge of Archean tectonics of Abitibi, post collision extension tectonics and mantle delamination, isotope geochronology, on the magmatic-hydrothermal system of Lac Shortt itself and on the present paper's carbonate fingerprinting, we propose that Lac Shortt calcalkaline dioritic magmatism-hydrothermalism was followed by alkaline syenitic, and eventually carbonatitic magmatism-hydro-carbothermalism, and that gold and REE originated from the carbonatite magmaticcarbo-hydrothermal system and its mantle roots, which agrees with mass balance calculations. The depletedmantle-rooted, carbonatite exsolved a hydro-carbothermal fluid enriched in REE and gold which fenitized and oxidized the syenite and out of which the gold and REE mineralization was deposited.

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“…for group-I kimberlites (red circle), group-II kimberlites and olivine lamproites (yellow diamond), aillikites (green triangle), meimechites (blue square), all with greater than 15 wt.% MgO, along with Archean komatiites and ferropicrites (gray square), Tertiary picrites (open circle) with greater than 12 wt.% MgO. Data sources : Arndt, et al, 1995, Baragar, et al, 2001, Bourne and Bossé, 1991, Digonnet, et al, 2000, Edwards, et al, 1992, Francis, 1995, Fraser and Hawkesworth, 1992, Jaques, et al, 1984, LeRoex, et al, 2003, Price, et al, 2000, Schmidberger and Francis, 2001, Scott, 1979, Scott Smith, et al, 1996, Taylor, et al, 1994 Until recently, sampling problems have limited our knowledge of the major element compositions of the magmas responsible for these rocks. A survey of recent chemical analyses of hypabyssal-facies alkaline ultramafic rocks, however, suggests they can be reliably distinguished on the basis of their Si and Fe contents in a standard whole rock chemical analysis.…”

Section: Introductionmentioning

confidence: 99%

Implications of major element composition for the mantle sources of kimberlite, aillikite, olivine lamproiite, and meimechite

International Kimberlite Conference Extended Abstracts: 2003

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Geochemistry of ultramafic and calc-llkaline lamprophyres from the Lac Shortt area, Quebec

Cited by 10 publications

References 18 publications

Caractéristiques, chronologie et typologie des minéralisations aurifères de la région du Lac Shortt (Québec), sous-province archéenne de l'Abitibi /

Caractéristiques, chronologie et typologie des minéralisations aurifères de la région du Lac Shortt (Québec), sous-province archéenne de l'Abitibi /

The Archean magmatic-hydrothermal system of Lac Shortt (Au-REE), Abitibi, Canada: Insights from carbonate fingerprinting

Implications of major element composition for the mantle sources of kimberlite, aillikite, olivine lamproiite, and meimechite

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