宁夏香山—卫宁北山地区铁矿类型与成矿规律
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摘要
宁夏香山-卫宁北山地区大地构造位于北祁连褶皱系走廊过渡带(走廊南山岛弧)之东北端与阿拉善地(陆)块南缘、鄂尔多斯地块西缘的交汇部位,也是我国西部东西向构造带(北祁连)与东部的近南北向构造(贺兰山)带转换交接部位,整体为宁夏南部弧形推覆构造体系的重要组成部分。因其特殊的大地构造位置和复杂的地质背景,直成为宁夏金属矿产勘查的重点地区。近年来,随着矿产勘查工作的深入,相继在中卫香山、卫宁北山地区以及邻区阿拉善左旗境内发现了许多小型铁矿床(点),使其成为宁夏重要的铁矿床成矿区和找矿远景区。在该成矿区带内,照壁山铁矿、顾家岘铁矿和石盖沟铁矿的形成受不同的地质单元和成矿作用影响,且含矿层位多分布范围广,是本区最具有代表性的典型矿床。本文通过对宁夏中卫香山-卫宁北山地区成矿地质背景、地球化学、地球物理特征和典型矿床的综合研究,取得了如下进展：
(1)本区弧形构造体系主要由4期逆冲推覆作用形成,这几期构造相互叠加,形成复杂而庞大的逆冲推覆体系,为成矿作用的发生提供了条件。
(2)本区铁矿的形成受地层建造控制。中奥陶统香山群狼嘴子组黄河井段硅质岩建造、下石炭统(前黑山组、臭牛沟组)和上石炭统羊虎沟组碎屑岩建造、碳酸盐建造为本区主要的含铁建造,富含铁、硫、钙、硅等,具有一定的成矿物质基础,对铁矿形成有一定控制作用。
(3)由褶皱、断裂组成的弧形构造体系控制了含矿地层的展布和形态。次级褶皱、断裂、层间滑动破碎带、软硬岩层间因挤压所造成的裂隙组成的控容带为铁质的富集成矿提供了直接的运移通道和淀积空间。
(4)本区铁矿形成与岩相古地理环境关系密切。含铁建造或含铁层位,多产于海进序列的岩石中。下石炭统盐化泻湖相(前黑山组、臭牛沟组)各类岩石主要属于一个较封闭的古海湾或古海盆沉积,周围的古陆又有较充分的物质(包括铁质)供给,形成一个非常有利的古地理环境。
(5)依据成矿地质背景、矿石特征、矿石结构构造、矿物共生组合以及围岩蚀变等特征分析,认为顾家岘铁矿和石盖沟铁矿属于地表浅部环境下氧化和淋滤作用所成；照壁山铁矿床为中一低温热液和表生氧化作用复合成因。
Xiangshan-Weiningbeishan region of Ningxia is located in the connection place of northeast corridor transitional belt of north Qilian folds system, south edge of the Alashan block and west margin of the Ordos block, and it is situated in the intersectional part of the EW trending tectonic zone of the western China and SN trending tectonic zone of the eastern China. Also, Xiangshan-Weiningbeishan region, which has been an important part of arc-shaped thrust-nappe structure system of the southern Ningxia, is always the highlight to work for metallic mineral exploration, due to its especial tectonic and complicated geological background. With the progress of mineral exploration, a great number of small iron deposits have been found in the field of Xiangshan mountain and Weiningbeishan mountain and that of Alashanzuoqi, at the southern margin of Tengger Desert, helping the area to turn into the very significant iron deposit-froming and ore-searching perspective zone. In this zone, Zhaobishan deposit, Gujiaxian deposit and Shigaigou deposit are the most typical iron deposits, which have been affected by different geological unit and specific mineralization. By virtue of comprehensive research on mineralization, geological background, geochemistry, geophysics and the typical iron deposits of Xiangshan-Weiningbeishan region of Ningxia. In this paper progresses have been made. They are as follows.
(1) Resulted from 4 periods of thrusting nappe events, the complicated and giant arc-shaped structure system of the area have been openning the way to iron mineralization.
(2) Iron mineralization ruled by the sedimentary formation. The main iron formation included the chert and siliceous dolostone sequence of the medial Ordovician Xiangshan Group and the Carboniferous as well as the clastic rocks and carbonate formation of the Carboniferous, rich in Fe, S, Ca, Si, et al.
(3) The arc-shaped thrusting nappe system that consisted of a series of large-scale faults and folds, have taken control of the distributions and shapes of the ore bodies. And the ore-controlling and host structures is composed of the secondary folds and faults, the interlayered fracture belts, and the fissures caused by compression between the soft rocks and the hard ones. That does a find job of providing direct migration channels and deposition spaces for iron mineralization.
(4) The conformation of the iron deposits are on intimate terms with the sedimentary environment and paleogeography of this area. Iron formations or iron-bearing strata occurred in the rocks of transgression sequence. The salty lagoon facies rocks of the lower Carboniferous resulted from the deposition occurred in a comparatively closed or semi-closed inland paleo-basin or paleo-bay, around where ore-forming materials(including Fe) derived from paleo-continent were adequate for supply, to build up an advantageous sedimentary environment and paleogeographic condition.
(5) According to the analysis on the geological setting of ore-forming processes, the characteristics of ore, the structure and composition of iron minerals and the features of the the wall-rock alteration, it concluded that Gujiaxian iron deposit and Shigaigou iron deposit had their origin in the processes of oxidation and leaching in the shallow surface, and that Zhaobishan iron deposit resulted from the low-temperature hydrothermal activation and the oxidation of the shallow surface.
(1)本区弧形构造体系主要由4期逆冲推覆作用形成,这几期构造相互叠加,形成复杂而庞大的逆冲推覆体系,为成矿作用的发生提供了条件。
(2)本区铁矿的形成受地层建造控制。中奥陶统香山群狼嘴子组黄河井段硅质岩建造、下石炭统(前黑山组、臭牛沟组)和上石炭统羊虎沟组碎屑岩建造、碳酸盐建造为本区主要的含铁建造,富含铁、硫、钙、硅等,具有一定的成矿物质基础,对铁矿形成有一定控制作用。
(3)由褶皱、断裂组成的弧形构造体系控制了含矿地层的展布和形态。次级褶皱、断裂、层间滑动破碎带、软硬岩层间因挤压所造成的裂隙组成的控容带为铁质的富集成矿提供了直接的运移通道和淀积空间。
(4)本区铁矿形成与岩相古地理环境关系密切。含铁建造或含铁层位,多产于海进序列的岩石中。下石炭统盐化泻湖相(前黑山组、臭牛沟组)各类岩石主要属于一个较封闭的古海湾或古海盆沉积,周围的古陆又有较充分的物质(包括铁质)供给,形成一个非常有利的古地理环境。
(5)依据成矿地质背景、矿石特征、矿石结构构造、矿物共生组合以及围岩蚀变等特征分析,认为顾家岘铁矿和石盖沟铁矿属于地表浅部环境下氧化和淋滤作用所成；照壁山铁矿床为中一低温热液和表生氧化作用复合成因。
Xiangshan-Weiningbeishan region of Ningxia is located in the connection place of northeast corridor transitional belt of north Qilian folds system, south edge of the Alashan block and west margin of the Ordos block, and it is situated in the intersectional part of the EW trending tectonic zone of the western China and SN trending tectonic zone of the eastern China. Also, Xiangshan-Weiningbeishan region, which has been an important part of arc-shaped thrust-nappe structure system of the southern Ningxia, is always the highlight to work for metallic mineral exploration, due to its especial tectonic and complicated geological background. With the progress of mineral exploration, a great number of small iron deposits have been found in the field of Xiangshan mountain and Weiningbeishan mountain and that of Alashanzuoqi, at the southern margin of Tengger Desert, helping the area to turn into the very significant iron deposit-froming and ore-searching perspective zone. In this zone, Zhaobishan deposit, Gujiaxian deposit and Shigaigou deposit are the most typical iron deposits, which have been affected by different geological unit and specific mineralization. By virtue of comprehensive research on mineralization, geological background, geochemistry, geophysics and the typical iron deposits of Xiangshan-Weiningbeishan region of Ningxia. In this paper progresses have been made. They are as follows.
(1) Resulted from 4 periods of thrusting nappe events, the complicated and giant arc-shaped structure system of the area have been openning the way to iron mineralization.
(2) Iron mineralization ruled by the sedimentary formation. The main iron formation included the chert and siliceous dolostone sequence of the medial Ordovician Xiangshan Group and the Carboniferous as well as the clastic rocks and carbonate formation of the Carboniferous, rich in Fe, S, Ca, Si, et al.
(3) The arc-shaped thrusting nappe system that consisted of a series of large-scale faults and folds, have taken control of the distributions and shapes of the ore bodies. And the ore-controlling and host structures is composed of the secondary folds and faults, the interlayered fracture belts, and the fissures caused by compression between the soft rocks and the hard ones. That does a find job of providing direct migration channels and deposition spaces for iron mineralization.
(4) The conformation of the iron deposits are on intimate terms with the sedimentary environment and paleogeography of this area. Iron formations or iron-bearing strata occurred in the rocks of transgression sequence. The salty lagoon facies rocks of the lower Carboniferous resulted from the deposition occurred in a comparatively closed or semi-closed inland paleo-basin or paleo-bay, around where ore-forming materials(including Fe) derived from paleo-continent were adequate for supply, to build up an advantageous sedimentary environment and paleogeographic condition.
(5) According to the analysis on the geological setting of ore-forming processes, the characteristics of ore, the structure and composition of iron minerals and the features of the the wall-rock alteration, it concluded that Gujiaxian iron deposit and Shigaigou iron deposit had their origin in the processes of oxidation and leaching in the shallow surface, and that Zhaobishan iron deposit resulted from the low-temperature hydrothermal activation and the oxidation of the shallow surface.
引文
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[3]Kato Y, Nakao K, Isozaki. Y.Cheochemisty of Late Permian to Early Triassic pelagic cherts from southwest Japan.:implications for an oceanic redox change [J].Chem Geol,2002, 182:15～34
[4]Moore E.S.and Maynard J.E.. Solution, Transportation and Precipitation of Iron and Silica[J]. Econ.Geol.,1929,24(3、4、5):272～303、365～402、506～527
[5]Murray R W, Buchholtz Ten Brink M R,Gerlach D C, et al. Rare earth, major, and trace element in chert from Franciscan complex and Monterey Group:Assessing REE source to fine-grained marine sediments [J].Geochemical Cosmochim Acta,1991,55:1875-1895
[6]Murray R W.Chemical criteria to identify the depositional environment of chert:general principles and applications[J]. Sediment Geol,1994,90:213-232
[7]Murray R W, Brink M R, Jones D L, et al. Rare earth elements as indications of different marinade positional environments in chert and shale [J].Geology,1990,18(3):268-271
[8]Yamamoto K. Geochemical characteristics and depositional environments of cherts and associated rocks in the Franciscan and Shiman to Terranes [J]. Sedimentary Geology,1987, 52(1-2):65-108.
[9]陈毓川,朱裕生,等.中国矿床成矿模式[M].北京：地质出版社,1993
[10]邓昆,周立发,曹欣,等.香山群狼嘴子组硅质岩地球化学特征及形成环境[J].中国地质,2007,34(3)497～505
[11]邓起东,程绍平,闵伟,等.鄂尔多斯块体新生代构造活动和动力学的讨论[J].地质力学学报,1999,5(3)：13～21
[12]丁海军,孟祥化,葛铭.米钵山组复理石中的内潮汐沉积[J].安徽地质,2008,18(4)
[13]冯彩霞,刘家军.硅质岩的研究现状及其成矿意义[J].世界地质,2001,20(2)：120～123
[14]郭忠铭.陕甘宁盆地西缘带的掩冲推覆与构造演化,推覆构造专题论文集[C]中国地质科学院南京地质矿产研究所所刊,1986,总第25号
[15]黄汲清,黄汲清著作选读(第三卷)：地质学及大地构造学[M]北京：地质出版社,1992,1～329
[16]黄喜峰,钱壮志,逯东霞,等.贺兰山中南段奥陶系米钵山组的沉积环境与构造背景分析[J].地球学报,2009,30(1)：65～71
[17]霍福臣,潘行适,尤国林,等.宁夏地质概论[M].北京：科学出版社,1989.1～290
[18]]蒋镇亚.华中弧形构造体系及其控岩控矿作用[J].湖北地质,1995,9(2)：1～8
[19]李红中,杨志军,周永章等.造山带硅质岩的含矿特征及其变质作用[J].矿物岩石地球化学通报,2008,27(增刊)：372～373.
[20]李天斌.宁夏南部弧形推覆构造带特征及演化[J].地质力学学报,1999,22～27
[21]李天斌.鄂尔多斯西缘逆冲推覆构造特征及演化[D].北京：中国地质大学(北京),2006
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