Thorite inclusions in zircon of the monzogranite, Lower Nubia, SW Egypt

Kamaleldin M. Hassan; Irena Brunarska

doi:10.2478/mipo-2023-0007

Figures & Tables

Geological map of south-western Egypt (Revised from GSMA 1981).

Optical microscope images of the Lower Nubian monzogranite. (A) Image in cross-polarized light showing a gneissose texture—the segregation of felsic (feldspars and quartz) and mafic minerals (biotite and its alteration product clinochlore). (B) Image in plane-polarized light showing numerous grains of zircon widely distributed throughout the thin section. (C) Image in cross-polarized light for radioactive halos or pleochroic halos (burnt mark) around zircon enclosed in biotite and having a cloudy altered appearance. Mineral abbreviations in alphabetical order: Bt—biotite, Br-(Ce)—britholite-cerium, Ccl—clinochlore, Mc—microcline, Pl— plagioclase, Qtz—quartz, Ser—sercite, Ttn—titanite, Zrc—zircon.

BSE images of zircon grains in the studied samples: (A) Elbow-shaped zircon twin showing corrosion embayment on the right side of the grain. (B) Stubby zircon prism with one pyramidal termination and having vertical fractures and broken parts. (C) Corroded zircon prism, with weakly-rounded edges.

BSE images of zircon grains in the studied samples showing small micro-inclusions of thorite (white areas). (A) Pentagonal cone-shaped grain showing corrosion embayment on the upper left side of the grain. (B) Grain with slightly rounded edges. (C) Euhedral grain with unequally developed bipyramids, showing grooves and eroded surfaces.

BSE images of zircon grains in the studied samples containing larger micro-inclusions of thorite (white areas). (A) Heptagonal shape grain. (B) Another heptagonal grain slightly rounded edges, and corrosion embayment on the upper side of the grain.

Representative SEM-EDS analyses (wt %, above) and corresponding structural formulae [4 (O) apfu, below] for zircon and its thorite inclusions from the Nubian monzogranite_

	Primary magmatic zircon							Smaller thorite inclusions				Larger thorite inclusions
	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
SiO₂	29.06	29.47	29.53	29.81	30.42	29.85	31.59	29.77	28.52	31.17	30.24	24.71	26.08	19.12	25.32	22.81
ThO₂	BDL	BDL	BDL	BDL	BDL	BDL	BDL	3.12	6.61	3.71	11.56	47.97	65.98	53.18	67.02	48.69
UO₂	BDL	0.45	0.29	BDL	BDL	BDL	0.89	BDL	BDL	BDL	BDL	14.08	BDL	15.15	BDL	11.85
AI₂O₃	0.46	BDL	BDL	BDL	BDL	0.64	BDL	0.21	BDL	1.55	1.89	1.82	1.30	0.72	1.33	1.29
Ce₂O₃	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	1.70	BDL	BDL	BDL	1.91
Nd₂O₃	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	BDL	1.57	BDL	BDL	BDL	1.61
Fe₂O₃	0.75	BDL	0.27	BDL	0.28	0.33	0.64	BDL	0.63	0.89	1.07	BDL	BDL	BDL	BDL	BDL
ZrO₂	67.31	69.48	69.19	68.12	69.92	66.35	65.66	65.15	63.29	59.58	50.13	5.66	5.70	9.66	1.94	10.04
HfO₂	1.57	BDL	BDL	1.15	BDL	1.17	BDL	BDL	BDL	BDL	1.44	BDL	BDL	BDL	BDL	BDL
MgO	0.15	BDL	BDL	BDL	BDL	BDL	0.21	BDL	BDL	0.16	BDL	BDL	BDL	BDL	BDL	BDL
CaO	BDL	BDL	BDL	0.40	BDL	0.73	0.27	0.92	0.57	1.19	1.38	1.59	BDL	1.38	3.05	1.19
Na₂O	0.41	0.29	0.46	BDL	0.39	0.59	0.50	0.83	0.38	0.72	1.21	0.90	0.94	0.80	1.33	0.61
K₂0	0.26	0.30	0.25	0.52	BDL	0.34	0.24	BDL	BDL	1.02	1.08	BDL	BDL	BDL	BDL	BDL
Total	99.97	99.99	99.99	100.00	101.1	100.00	100.00	100.00	100.00	99.99	100.00	100.00	100.00	100.01	99.99	100.00
Si	0.93	0.92	0.90	0.94	0.94	0.93	0.97	0.94	0.92	0.97	0.99	1.10	1.15	0.94	1.13	1.07
Th	-	-	-	-	-	-	-	0.02	0.05	0.02	0.08	0.48	0.66	0.59	0.68	0.52
U	-	0.00	0.00	-	-	-	0.01	-	-	-	-	0.13	-	0.16	-	0.13
Al	0.04	-	-	-	-	0.05	-	0.02	-	0.13	0.16	0.09	0.15	0.09	0.07	0.16
Ce	-	-	-	-	-	-	-	-	-	-	-	0.03	-	-	-	0.07
Nd	-	-	-	-	-	-	-	-	-	-	-	0.02	-	-	-	0.06
Fe	0.01	-	0.01	-	0.01	0.02	0.03	-	0.06	0.07	0.06	-	-	-	-	-
Zr	1.04	1.06	1.06	1.04	1.05	1.01	0.99	1.01	1.00	0.90	0.79	0.12	0.12	0.23	0.04	0.22
Hf	0.01	-	-	0.01	-	0.01	-	-	-	-	0.01	-	-	-	-	-
Mg	0.01	-	-	-	-	-	0.01	-	-	0.00	-	-	-	-	-	-
Ca	-	-	-	0.01	-	0.02	0.01	0.03	0.02	0.02	0.04	0.08	-	0.07	0.13	0.06
Na	0.03	0.02	0.03	-	0.02	0.04	0.03	0.04	0.02	0.04	0.08	0.05	0.08	0.05	0.11	0.05
K	0.01	0.01	0.01	0.02	-	0.01	0.01	-	-	0.01	0.04	-	-	-	-	-
Sum	2.08	2.01	2.01	2.02	2.02	2.09	2.06	2.06	2.07	2.16	2.25	2.10	2.16	2.13	2.16	2.34

Thorite inclusions in zircon of the monzogranite, Lower Nubia, SW Egypt

Figures & Tables

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Representative SEM-EDS analyses (wt %, above) and corresponding structural formulae [4 (O) apfu, below] for zircon and its thorite inclusions from the Nubian monzogranite_

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