干旱区生态环境知识资源中心(Arid): Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit, Eastern Desert, Egypt

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	Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit, Eastern Desert, Egypt
	Zoheir Basem; Goldfarb Richard; Holzheid Astrid; Helmy Hassan; El Sheikh Ahmed
来源期刊	Geoscience Frontiers
ISSN	1674-9871
出版年	2020
卷号	11 期号:1 页码:325-345
英文摘要	The Um Rus tonalite-granodiorite intrusion (~6 km~2) occurs at the eastern end of the Neoproterozoic, ENE-trending Wadi Mubarak shear belt in the Central Eastern Desert of Egypt. Gold-bearing quartz veins hosted by the Um Rus intrusion were mined intermittently, and initially by the ancient Egyptians and until the early 1900s. The relationship between the gold mineralization, host intrusion, and regional structures has always been unclear. We present new geochemical and geochronological data that help to define the tectonic environment and age of the Um Rus intrusion. In addition, field studies are integrated with EPMA and LA-ICP-MS data for gold-associated sulfides to better understand the formation and distribution of gold mineralization. The bulk-rock geochemical data of fresh host rocks indicate a calc-alkaline, metaluminous to mildly peraluminous, I-type granite signature. Their trace element composition reflects a tectonic setting intermediate between subduction-related and within-plate environments, presumably transitional between syn- and post-collisional stages. The crystallization age of the Um Rus intrusion was determined by in situ SHRIMP ~(206)Pb/~(238)U and ~(207)Pb/ ~(235)U measurements on accessory monazite grains. The resultant monazite U-Pb weighted mean age (643 9 Ma; MSWD = 1.8) roughly overlaps existing geochronological data for similar granitic intrusions that are confined to major shear systems and are locally associated with gold mineralization in the Central Eastern Desert (e.g., Fawakhir and Hangaliya). This age is also consistent with magmatism recognized as concomitant to transpressional tectonics (D2: ~650 Ma) during the evolution of the Wadi Mubark belt. Formation of the gold-bearing quartz veins in NNE-SSW and N-S striking fault segments was likely linked to the change from transpressional to transtensional tectonics and terrane exhumation (D3: 620-580 Ma). The development of N-S throughgoing fault arrays and dike swarms (~595 Ma) led to heterogeneous deformation and recrystallization of the mineralized quartz veins. Ore minerals in the auriferous quartz veins include ubiquitous pyrite and arsenopyrite, with less abundant pyrrhotite, chalcopyrite, sphalerite, and galena. Uncommon pentlandite, gersdorffite, and cobaltite inclusions hosted in quartz veins with meladiorite slivers are interpreted as pre-ore sulfide phases. The gold-sulfide paragenesis encompasses an early pyrite-arsenopyrite loellingite assemblage, a transitional pyrite-arsenopyrite assemblage, and a late pyrrhotite-chalcopyrite-sphalerite galena assemblage. Free-milling gold/electrum grains (10s m-long) are scattered in extensively deformed vein quartz and in and adjacent to sulfide grains. Marcasite, malachite, and nodular goethite are authigenic alteration phases after pyrrhotite, chalcopyrite, and pyrite and arsenopyrite, respectively. A combined ore petrography, EPMA, and LA-ICP-MS study distinguishes morphological and compositional differences in the early and transitional pyrites (Py I, Py II) and arsenopyrite (Apy I, Apy II). Py I forms uncommon small euhedral inclusions in later Py II and Apy II. Py II forms large subhedral crystals with porous inner zones and massive outer zones, separated by narrow As-rich irregular mantles.
英文关键词	Um Rus intrusion Whole-rock geochemistry SHRIMP U-Pb monazite dating Gold mineralization LA-ICP-MS data of pyrite and arsenopyrite
类型	Article
语种	英语
开放获取类型	DOAJ Gold
收录类别	CSCD
WOS研究方向	Mineralogy
CSCD记录号	CSCD:6654683
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/336243
作者单位	Zoheir Basem, Department of Geology, Faculty of Science, Benha University;;Institute of Geosciences, University of Kiel, ;;, Benha;;Kiel, Egypt;;Germany 13518;;24118.; Goldfarb Richard, China University of Geosciences (Beijing), State Key Laboratory of Geological Processes and Mineral Resources, Beijing 100083, China.; Holzheid Astrid, Institute of Geosciences, University of Kiel, Kiel, Schleswig-Holstein 24118, Germany.; Helmy Hassan, Department of Geology, Faculty of Science, Minia University, Minia, 61519, Egypt.; El Sheikh Ahmed, Department of Geology, Faculty of Science, Sohag University, Egypt.
推荐引用方式 GB/T 7714	Zoheir Basem,Goldfarb Richard,Holzheid Astrid,et al. Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit, Eastern Desert, Egypt[J],2020,11(1):325-345.
APA	Zoheir Basem,Goldfarb Richard,Holzheid Astrid,Helmy Hassan,&El Sheikh Ahmed.(2020).Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit, Eastern Desert, Egypt.Geoscience Frontiers,11(1),325-345.
MLA	Zoheir Basem,et al."Geochemical and geochronological characteristics of the Um Rus granite intrusion and associated gold deposit, Eastern Desert, Egypt".Geoscience Frontiers 11.1(2020):325-345.