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Two origins of illite at the Dexing porphyry Cu deposit, East China; implications for ore-forming fluid constraint on illite crystallinity

Jin Zhangdong, Zhu Jinchu, Ji Junfeng, Li Fuchun and Lu Xinwei
Two origins of illite at the Dexing porphyry Cu deposit, East China; implications for ore-forming fluid constraint on illite crystallinity
Clays and Clay Minerals (June 2002) 50 (3): 381-387

Abstract

Illite is a distinctive clay mineral formed by K alteration within hydrothermal alteration zones in porphyry Cu deposits. Based on differences in spatial distribution, Kubler index, number of swelling layers, and polytype, two kinds of illite are recognized within the Dexing porphyry Cu deposit, East China. One is a hydrothermal mineral within hydrothermally-altered granodiorite porphyry and altered tuffaceous phyllite near the contact zone with the granodiorite porphyry cupola. The hydrothermal illite is formed by illitization of plagioclase and/or micas during hydrothermal fluid-rock interaction. The considerable variation of their higher Kubler indices (0.17-1.41 degrees Delta 2theta ) with swelling layer is affected by fluid/rock ratio or fluid flux. The other type of illite is a product of low-grade metamorphism within tuffaceous phyllite away from the porphyry cupola (>2 km), and has a lower Kubler index (0.06-0.13 degrees Delta 2theta ), a 2M (sub 1) polytype, and no swelling layers. We suggest that, within the mineralized alteration zone, the lower the Kubler index, the stronger the degree of alteration, and the higher the copper grade. This is caused by a higher fluid/rock ratio in the middle-upper portions of the contact zone.


ISSN: 0009-8604
EISSN: 1552-8367
Coden: CLCMAB
Serial Title: Clays and Clay Minerals
Serial Volume: 50
Serial Issue: 3
Title: Two origins of illite at the Dexing porphyry Cu deposit, East China; implications for ore-forming fluid constraint on illite crystallinity
Affiliation: Chinese Academy of Sciences, Lake Sediment and Environment Laboratory, Nanjing, China
Pages: 381-387
Published: 200206
Text Language: English
Publisher: Clay Minerals Society, Clarkson, NY, United States
References: 33
Accession Number: 2002-064838
Categories: Sedimentary petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table, geol. sketch map
N28°09'02" - N28°09'02", E117°05'28" - E117°05'28"
Secondary Affiliation: Nanjing University, CHN, China
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 200220
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