Genetic Mechanism of the “Yucheng-Type” High-Grade Skarn Iron Deposits

doi:10.19657/j.geoscience.1000-8527.2024.003

Abstract

Abstract:

The discovery of high-grade skarn iron deposits in the Qihe-Yucheng area of northwestern Shandong Province is a significant breakthrough for iron prospecting in China.It is expected to become another potential important base of high-grade iron ore resource in Shandong Province after Laiwu, Jinling, and Jinan areas.Unlike traditional skarn iron deposits hosted in the contact zone between intrusions and carbonate rocks, the Litun iron orebodies in the Qihe-Yucheng area are hosted in the Carboniferous-Permian coal-bearing strata.The high-grade iron orebodies have a sharp contact with the surrounding rocks, which have been changed to horns in a large range.We attribute the occurrence of the iron orebodies in the Carboniferous-Permian coal-bearing strata far from the contact zone to the extremely low thermal conductivity of the overlying coal rocks, which allow the hydrothermal fluid to maintain a high-temperature state and long-distance migration.The formation of the Litun iron deposit may be ascribed to the rapid precipitation of magnetite due to decreasing temperature and salinity caused by the mixing of high-temperature magmatic fluid and low-temperature meteoric water.In addition, strong albitization commonly occurs near ore bodies, leading to the loss of iron in the dioritic rocks, which lays an important material foundation for the exsolution of iron-rich fluids and the formation of high-grade iron ores.Finally, we propose that the mantle-derived “highly differentiated” diorite and hypabyssal emplacement is favor for the exsolution of magmatic fluids, and is also prerequisites for the formation of the Hanxing-type iron deposit.

Key words: skarn, high-grade iron ores, fluid transportation, albitation, Yucheng-type

CLC Number:

P611

ZHANG Zhaochong, WANG Huaihong, XIE Qiuhong, SHEN Lijun, ZHU Yuzhen, LÜ Yunhe, JIN Bowen. Genetic Mechanism of the “Yucheng-Type” High-Grade Skarn Iron Deposits[J]. Geoscience, 2024, 38(01): 1-12.

Figures/Tables 11

Fig.1 Distribution of skarn iron ore concentration cluster in the western Shandong Province

Fig.2 Maps of aero-magnetic ΔT contour (a) and aero-bouguer gravity contour (b) of the Qihe-Yucheng area [11]

Fig.3 Correlation of the geological column of borehole cores in the Qihe-Yucheng area[6]

Fig.4 Sketch cross section of the drillhole-controlled iron orebodies at the Litun iron deposit

Fig.5 Sharp contact boundary between iron orebody and country rock (horn) and strong horn metamorphismat the Litun iron deposit (ZK5)

Fig.6 Early-stage angular skarn breccias (light color) cemented by magnetite (black) (ZK5)

Fig.7 Strong albite alteration of the diorite near iron orebody (a) and heterogeneous albite alteration of the diorite far from the iron orebody in a large scale

Fig.8 Sketch cross geological section of No.0 exploration line at the Dazhang iron deposit

Fig.9 Sketch cross geological section of the Pandian area[7]

Table 1 Thermal conductivity of different rock types[19]

岩性	热导率(W/(m·K))
岩性	最小值	最大值	平均值
煤	0.13	0.30	0.21
泥板岩、泥质页岩	0.25	3.01	1.22
粉砂岩	0.41	3.58	1.49
砂岩	0.38	5.17	1.66
砾岩、圆石砾岩	1.05	3.86	1.92
泥灰岩	0.50	3.91	1.92
片麻岩	0.94	4.86	2.02
正长花岗岩	1.30	2.97	2.05
花岗闪长岩	1.64	2.48	2.11
石英斑岩	1.76	2.60	2.11
灰岩	0.92	4.40	2.40
花岗岩	1.34	3.69	2.40
片岩	1.03	4.93	2.46
大理岩	1.59	4.00	2.56
石英-碳酸盐岩	1.61	5.01	2.71
石英闪长岩	1.98	3.80	3.00
白云岩	1.63	6.50	3.24
角岩	2.12	6.10	3.39
石英岩	2.68	7.60	5.26

Fig.10 Texture and structure of the diorites at the Litun iron deposit

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