Formation mechanism of Hanxing type iron deposit: Evidence from the iron-bearing melt-fluid assemblage in porphyritic monzonite from Wu’an, Hebei Province

doi:10.13745/j.esf.sf.2021.7.22

Abstract

Abstract:

The formation mechanism of the Hanxing type iron deposit has been controversial. In order to resolve this issue, we conducted a detailed mineralogical and petrological study of the iron-bearing melt-fluid veins and plaques found in the porphyritic monzonite from Zhaozhuang area, Wu’an, Hebei Province, located in the metallogenic belt of Hanxing. The iron-bearing melt-fluid mineral assemblage showed obvious zonal pattern, with the mineral assemblages Di + Amp + Mt + Ap + Pl at the core and Prh + Cal at the edge. The magnetite in the assemblage had a well-defined zonal structure. At the core the TiO₂ content was 2.23% and at the edge 0.36%-0.57%, while ∑REE was two orders of magnitude higher at the core than at the edge. The chondrite-normalized REE plot for the magnetite is a right dipping curve, suggesting its homology to the Wu’an intrusive rocks crystallized in a high temperature magmatic environment without fluid addition. The magnetite at the edge showed slight REE depletion and obvious negative Ce anomaly, indicating an addition of large amounts of volatile fluids in the crystallization environment. In the (Ti+V)-(Al+Mn) diagram, the magnetite from the assemblage fell under the same areas as porphyry-type and Fe-Ti- and V-type magnetites, and also between the areas of hydrothermal and magmatic magnetites. These results suggested that the iron-bearing melt-fluid is not distal skarn vein formed by metasomatic interaction between intrusive rock and wall rock, but rather a product of shallow crystallization of deep magma by the following proposed mechanism: First, high-Ti, REE-rich magnetite microcrystals are formed from deep magmatic fangtie pulp; then, as fluid overpressure is reached due to injection of fluid rich in volatile matter, the magnetite microcrystals are combined with bubbles and rise rapidly along the magmatic channel: eventually, low-Ti, REE-depleted magnetite is formed at depths of 1.55-2.19 km, then crystallized to form fluid crystal minerals such as amphibole.

Key words: melt-fluid bearing iron, magnetite, Hanxing type iron deposit, metallogenic mechanism

CLC Number:

YANG Yubo, SU Shangguo, HUO Yan’an, NING Yage, GU Dapeng. Formation mechanism of Hanxing type iron deposit: Evidence from the iron-bearing melt-fluid assemblage in porphyritic monzonite from Wu’an, Hebei Province[J]. Earth Science Frontiers, 2022, 29(3): 304-318.

Figures/Tables 18

References 62

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样品采集位置	相对位置	w_B/%
样品采集位置	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	MnO	MgO	CaO	Na₂O	K₂O	Total
辉石(脉)	边	53.17	0.26	1.79	8.04	0.01	0.52	13.56	21.62	0.46	0.00	99.45
	幔	53.91	0.25	1.24	7.87	0.00	0.56	13.95	21.78	0.44	0.00	99.99
	核	53.73	0.11	0.61	10.20	0.05	0.58	11.99	20.38	1.33	0.01	98.98
	幔	52.95	0.29	1.89	8.19	0.04	0.50	13.63	21.46	0.55	0.00	99.51
	边	53.45	0.26	1.60	9.12	0.03	0.64	13.06	21.14	0.52	0.01	99.82

样品采集位置	相对位置	w_B/%
样品采集位置	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	MnO	MgO	CaO	Na₂O	K₂O	Total
辉石(脉)	边	53.17	0.26	1.79	8.04	0.01	0.52	13.56	21.62	0.46	0.00	99.45
	幔	53.91	0.25	1.24	7.87	0.00	0.56	13.95	21.78	0.44	0.00	99.99
	核	53.73	0.11	0.61	10.20	0.05	0.58	11.99	20.38	1.33	0.01	98.98
	幔	52.95	0.29	1.89	8.19	0.04	0.50	13.63	21.46	0.55	0.00	99.51
	边	53.45	0.26	1.60	9.12	0.03	0.64	13.06	21.14	0.52	0.01	99.82

样号	相对位置	w_B/%														T/℃	p/ MPa	Depth/ km
样号	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	NiO	MnO	MgO	CaO	Na₂O	K₂O	F	Cl	Total	T/℃	p/ MPa	Depth/ km
团斑角闪石-1	边	52.63	0.37	3.11	11.55	0.04	0.02	0.21	16.44	11.92	0.83	0.21	0.17	0.05	97.47	745.92	40.93	1.55
	幔	49.80	0.91	4.19	12.02	0.09	0.01	0.27	15.47	11.54	1.07	0.28	0.17	0.04	95.77	773.93	54.56	2.06
	核	51.95	0.48	3.56	11.48	0.00	0.04	0.26	16.61	11.51	1.03	0.25	0.42	0.04	97.43	758.31	45.72	1.73
	幔	50.85	0.97	4.51	11.41	0.05	0.04	0.24	15.99	11.44	1.29	0.31	0.44	0.07	97.40	776.29	58.04	2.19
	边	51.75	0.50	3.37	10.82	0.00	0.00	0.24	16.34	11.78	0.85	0.24	0.17	0.05	96.02	754.78	44.17	1.67
团斑角闪石		51.85	0.53	3.51	11.33	0.02	0.00	0.28	16.61	11.58	0.91	0.25	0.57	0.02	97.22	760.61	45.20	1.71
		52.32	0.34	3.14	11.47	0.04	0.00	0.24	16.17	11.98	0.84	0.23	0.10	0.03	96.87	744.04	41.52	1.57
		51.41	0.73	3.57	11.06	0.00	0.04	0.33	16.35	11.44	1.03	0.23	0.03	0.05	96.23	761.42	46.25	1.75
脉角闪石		41.29	1.15	11.48	17.06	0.08	0.03	0.35	9.98	11.31	2.12	1.33	0.55	0.08	96.55	886.48	380.19	14.37
脉角闪石		41.83	1.38	11.43	14.82	0.07	0.00	0.35	11.67	11.76	2.29	1.41	0.36	0.06	97.25	894.95	356.88	13.49

样号	相对位置	w_B/%														T/℃	p/ MPa	Depth/ km
样号	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	NiO	MnO	MgO	CaO	Na₂O	K₂O	F	Cl	Total	T/℃	p/ MPa	Depth/ km
团斑角闪石-1	边	52.63	0.37	3.11	11.55	0.04	0.02	0.21	16.44	11.92	0.83	0.21	0.17	0.05	97.47	745.92	40.93	1.55
	幔	49.80	0.91	4.19	12.02	0.09	0.01	0.27	15.47	11.54	1.07	0.28	0.17	0.04	95.77	773.93	54.56	2.06
	核	51.95	0.48	3.56	11.48	0.00	0.04	0.26	16.61	11.51	1.03	0.25	0.42	0.04	97.43	758.31	45.72	1.73
	幔	50.85	0.97	4.51	11.41	0.05	0.04	0.24	15.99	11.44	1.29	0.31	0.44	0.07	97.40	776.29	58.04	2.19
	边	51.75	0.50	3.37	10.82	0.00	0.00	0.24	16.34	11.78	0.85	0.24	0.17	0.05	96.02	754.78	44.17	1.67
团斑角闪石		51.85	0.53	3.51	11.33	0.02	0.00	0.28	16.61	11.58	0.91	0.25	0.57	0.02	97.22	760.61	45.20	1.71
		52.32	0.34	3.14	11.47	0.04	0.00	0.24	16.17	11.98	0.84	0.23	0.10	0.03	96.87	744.04	41.52	1.57
		51.41	0.73	3.57	11.06	0.00	0.04	0.33	16.35	11.44	1.03	0.23	0.03	0.05	96.23	761.42	46.25	1.75
脉角闪石		41.29	1.15	11.48	17.06	0.08	0.03	0.35	9.98	11.31	2.12	1.33	0.55	0.08	96.55	886.48	380.19	14.37
脉角闪石		41.83	1.38	11.43	14.82	0.07	0.00	0.35	11.67	11.76	2.29	1.41	0.36	0.06	97.25	894.95	356.88	13.49

磁铁矿赋存位置	相对位置	w_B/%
磁铁矿赋存位置	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	NiO	MnO	MgO	CaO	Na₂O	K₂O	Total
团斑环带磁铁矿	边	0.04	0.57	0.17	90.21	0.34	0.00	0.03	0.05	0.01	0.01	0.00	91.42
	核	0.02	2.23	0.19	88.26	0.51	0.09	0.08	0.05	0.00	0.03	0.02	91.50
	边	0.07	0.36	0.25	90.26	0.41	0.00	0.06	0.00	0.11	0.00	0.00	91.52
磁铁矿赋存位置	相对位置	w_B/%
磁铁矿赋存位置	相对位置	SiO₂	TiO₂	Al₂O₃	FeO	Cr₂O₃	NiO	MnO	MgO	CaO	Na₂O	K₂O	Total
团斑中的磁铁矿		0.07	0.59	0.23	89.78	0.30	0.01	0.02	0.00	0.13	0.03	0.00	91.17
		0.07	0.31	0.34	91.23	0.31	0.04	0.03	0.00	0.00	0.00	0.01	92.35
		0.05	0.37	0.34	90.39	0.26	0.01	0.02	0.00	0.00	0.00	0.00	91.43
		0.05	0.48	0.28	89.68	0.28	0.05	0.01	0.00	0.03	0.00	0.00	90.85
		0.09	0.17	0.23	90.24	0.32	0.00	0.07	0.00	0.05	0.00	0.00	91.16
		0.03	0.27	0.12	89.38	0.25	0.05	0.08	0.03	0.20	0.00	0.00	90.41
		0.03	0.46	0.17	90.53	0.29	0.00	0.05	0.05	0.04	0.00	0.00	91.61
		0.09	0.39	0.14	90.04	0.28	0.02	0.06	0.00	0.08	0.03	0.00	91.13
		0.07	0.56	0.14	89.65	0.31	0.07	0.02	0.00	0.06	0.02	0.00	90.90
		0.04	0.87	0.15	89.40	0.32	0.06	0.05	0.03	0.06	0.00	0.00	90.96
		0.00	0.86	0.12	89.39	0.26	0.00	0.04	0.00	0.10	0.02	0.00	90.80
		0.07	0.52	0.16	90.00	0.25	0.03	0.06	0.02	0.04	0.00	0.00	91.14
		0.16	0.20	0.20	89.23	0.26	0.01	0.08	0.07	0.21	0.00	0.02	90.43
		0.12	0.28	0.11	90.01	0.21	0.00	0.05	0.03	0.09	0.00	0.02	90.92
		0.07	0.40	0.11	88.95	0.27	0.01	0.03	0.04	0.06	0.00	0.00	89.93
		0.91	1.19	0.43	84.54	0.10	0.03	0.03	0.31	0.01	0.00	0.01	87.56
		0.04	0.92	0.21	89.37	0.53	0.01	0.06	0.02	0.03	0.08	0.00	91.26
		0.02	0.58	0.27	88.82	0.54	0.05	0.05	0.01	0.04	0.08	0.00	90.46
		0.10	0.60	0.13	89.71	0.35	0.03	0.10	0.00	0.07	0.04	0.00	91.11
		0.02	1.18	0.28	89.98	0.82	0.05	0.12	0.00	0.00	0.01	0.00	92.46
		0.01	0.06	0.20	90.29	0.92	0.00	0.01	0.00	0.02	0.00	0.00	91.51
		0.00	0.40	0.20	90.14	0.09	0.05	0.11	0.00	0.00	0.04	0.00	91.03
		0.06	0.42	0.17	90.56	0.07	0.00	0.15	0.07	0.01	0.00	0.00	91.51
		0.27	0.26	0.17	89.02	0.10	0.05	0.18	0.02	0.02	0.04	0.00	90.12
		0.21	0.36	0.20	89.25	0.12	0.01	0.11	0.01	0.06	0.04	0.00	90.36
脉中的磁铁矿		0.00	0.40	0.20	90.14	0.09	0.05	0.11	0.00	0.00	0.04	0.00	91.03
		0.06	0.42	0.17	90.56	0.07	0.00	0.15	0.07	0.01	0.00	0.00	91.51
		0.27	0.26	0.17	89.02	0.10	0.05	0.18	0.02	0.02	0.04	0.00	90.12
		0.21	0.36	0.20	89.25	0.12	0.01	0.11	0.01	0.06	0.04	0.00	90.36
		0.28	0.54	0.25	88.19	0.06	0.00	0.09	0.00	0.06	0.04	0.00	89.51
		0.20	0.45	0.22	87.88	0.05	0.00	0.06	0.00	0.10	0.00	0.00	88.95
		0.16	0.13	0.15	90.59	0.13	0.00	0.00	0.00	0.07	0.06	0.00	91.30
		0.16	0.36	0.24	90.60	0.11	0.00	0.15	0.01	0.04	0.03	0.02	91.72
		0.12	0.26	0.17	89.71	0.14	0.01	0.08	0.00	0.06	0.03	0.00	90.58
		0.97	2.91	0.49	85.29	0.08	0.00	0.12	0.21	0.63	0.03	0.03	90.76
		0.16	0.22	0.30	88.96	0.04	0.05	0.08	0.00	0.38	0.02	0.00	90.22
		0.21	0.21	0.15	89.20	0.12	0.04	0.01	0.00	0.24	0.04	0.00	90.23
		0.14	0.11	0.15	89.80	0.09	0.01	0.05	0.07	0.17	0.03	0.00	90.61
		0.18	0.07	0.06	89.89	0.12	0.05	0.03	0.05	0.12	0.00	0.00	90.56
		0.22	0.10	0.09	87.97	0.12	0.04	0.02	0.01	0.21	0.01	0.00	88.81