Origin of the giant Allard Lake ilmenite ore deposit (Canada) by fractional crystallization, multiple magma pulses and mixing
Bernard CharlierOlivier NamurSimon MalpasCédric de MarneffeJean‐Clair DuchesneJacqueline Vander AuweraOlivier Bolle
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Ilmenite
Fractional crystallization (geology)
Anorthosite
Layered intrusion
Igneous differentiation
Magma chamber
Ilmenite ore bodies are deposited within the Precambrian anorthosite body distributed in the Hadonggun and Sancheonggun district, Gyeongsangnamdo. This study tries to identify the occurrence of ilmenite ore body in titanium mine area distributed in Wheolheongri, Okjongmyon, Hadonggun and six mining concession areas (Danseong claim no. 64, 65, 74, 75, 84, 85) in Danseongmyon, Sancheonggun. Wheolheongri ilmenite ore body occurs as vein with about 10~50 m width and 100 m length and shows NNE strike and NW dipping. High grade ore with 20 wt% in this area is distributed in intercumulated anorthosite and is sheared and brecciated. Ilmenite occurring in this type is commonly associated with hornbelnde. Ilmenite ore bodies distributed in Danseonggun, Sancheongmyon are deposited in layered anorthosite. They occur as stratiform with variable width from several and several tens meters. Ilmenite which is disseminated in the matrix is sheared and elongated. This type shows generally low grade ( 1.0~6.0 wt%). The ilmenite ore bodies occur as vein and stratiform, and the former shows higher grade than the latter.
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In a detailed study of the area of the Lake Sanford titaniferous magnetite deposits some interesting relations between anorthosite and gabbro came to light. Gabbro can be found grading into the anorthosite, showing the consanguinity of the two rocks, but in a few places the gabbro is intrusive into the already consolidated portions of the anorthosite.
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Peridotite
Chromitite
Layered intrusion
Chromite
Trough (economics)
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Size can be used as a criterion to select 18 large (> 1 cm) samples from among 148 melt‐rock fragments of all sizes. This selection provides a suite of large samples which represent the important chemical variants among highland melt rocks; each large sample has enough material for a number of sample‐destructive studies, as well as for future reference. Cluster analysis of the total data base of 148 highland melt rocks shows six distinct groups: anorthosite, gabbroic anorthosite, anorthositic gabbro (“highland basalt”), low‐K Fra Mauro, intermediate‐K Fra Mauro, and high‐K. Large samples are available for four of the melt‐rock groups (gabbroic anorthosite, anorthositic gabbro, low‐K Fra Mauro, and intermediate‐K Fra Mauro). This sample selection reveals two sub‐groups of anorthositic gabbro (one anorthite‐poor with negative Eu anomaly and one anorthite‐rich without Eu anomaly). There is a sharp distinction between those Apollo 16 melt rocks and glasses which have both been classified as “gabbroic anorthosite”.
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Ilmenite
Layered intrusion
Massif
Magma chamber
Igneous differentiation
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Abstract Abstract Granite, gabbro and anorthosite together constitute the Nordingrå massif. These igneous rocks have intruded a sequence of Svecokarelian metasediments and postdate the regional metamorphism and folding. Available field observations demonstrate that the granite intrudes the gabbro-anorthosite complex. Zircons separated from the granite and the anorthosite have an age of 1578 ± 19 Ma, which is considered to indicate the time of magmatic crystallization. The Rb-Sr whole rock age 1552 ± 18 Ma of the gabbro and anorthosite is slightly lower than the zircon age, whereas the Rb-Sr reference age of the granite, 1416 Ma, is considerably lower than the age of the zircons. Hypothetical models of genesis and history are discussed to explain this discordancy. It is suggested that post-crystallization hydrothermal fluids, circulating in the bedrock during the uplift and cooling of the orogenic belt and/or during subsequent epeirogenic movements, transported Rb and Sr isotopes in the whole rock system. This led to an apparent low Rb-Sr age and a high initial 87 Sr/86 ratio. The conclusions are supported by δ18O analyses, which indicate that the granite has been depleted in 18O, and by microscopical observation of mineral alterations. K-Ar ages of separated minerals from granite and gabbro may also have been influenced by these alterations. A thermal imprint on the bedrock at the intrusion of the Jotnian dolerite sheets may also have contributed to the observed considerable spread of the K-Ar ages from 1600 to 1100 Ma. Key Words: Rapakivigabbroanorthositeradiometric datingU-PbRb-SrK-Aroxygen isotopesNordingrånorth-central SwedenN6300N6300E1829E1829
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High-Al gabbro is reported here for the first time from three anorthosite complexes of Orissa sector of Eastern Ghats Granulite Belt (EGGB). It has distinctly different textural, mineralogical and chemical characters from the anorthosite within which it occurs, and also from the spatially associated Fe, Ti and REE enriched ferrodiorite suite. The high-Al gabbro of EGGB is comparable to similar rocks from other anorthosite complexes in major, trace element compositions and Mg# range (50-58). However, in contrast to the high-Al gabbro of the Laramie Anorthosite Complex (LAC), it does not form the most primitive rock of this association and exhibits negative Eu anomaly (Eu/EU * 0 2 0 6). The Mg enriched composition of the silicates of the high-Al gabbro and higher MgO contents of the associated anorthosite and ferrodiorite of the LAC are other critical differences. Variable composition of the parental melts for these rocks at EGGB and LAC is interpreted Derivation of these aluminous melts by partial melting of basalt under high pressure i s suggested.
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Baddeleyite
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Fractional crystallization (geology)
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Anorthosite
Norite
Layered intrusion
Magma chamber
Fractional crystallization (geology)
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