膏盐层氧化障在长江中下游玢岩铁矿成矿中的作用  

Effect of sulfate evaporate salt layer for formation of porphyrite iron ores in the Middle-Lower Yangtze River area

作　　者：李延河[1] 段超[1] 韩丹[1] 陈新旺 王丛林 杨秉阳 张成[1] 刘锋[1] 

机构地区：[1]国土资源部成矿作用和资源评价重点实验室、中国地质科学院矿产资源研究所,北京100037 [2]马钢集团矿业公司南山矿,马鞍山243033

出　　处：《岩石学报》2014年第5期1355-1368,共14页Acta Petrologica Sinica

基　　金：国家“973”项目(2012CB416801);公益行业科研专项项目(200911007、201011027、201211074);安徽省国土资源科技项目(2012-K-30)联合资助

摘　　要：长江中下游是我国著名的铁铜金等多金属成矿带，其中宁芜和庐枞盆地产出一系列与白垩纪中基性火山-次火山岩有关的玢岩铁矿床。前人根据玢岩铁矿的地质特征、空间分布规律及其与火山-次火山岩的关系建立了著名玢岩铁矿成矿模式，发展了成矿理论，有效指导了玢岩铁矿找矿工作。但三叠系膏盐层在成矿中的作用没有引起应有的重视，深部矿化基本没有涉及。最新研究和勘查结果揭示中下三叠统周冲村组顶部膏盐层与矿化关系密切，但膏盐层的控矿机理还不清楚，“膏盐层氧化障”在玢岩铁矿成矿中的作用鲜有报道，宁芜-庐枞盆地深部矿化类型和矿体赋存部位知之甚少。本文研究了长江中下游玢岩铁矿的硫同位素组成，探讨了膏盐层氧化障在玢岩铁矿成矿中的作用。宁芜和庐枞盆地玢岩铁矿、硫铁矿中普遍含有石膏，玢岩铁矿、硫铁矿和石膏矿三者密切共生。玢岩铁矿及伴生硫铁矿中黄铁矿的δ^34 Sv-CDT值异常高，平均值均在5‰以上，石膏的δ^34SV-CDT，值大部分位于20％。左右，与海相硫酸盐的值相似，指示矿床中硫主要来自三叠纪膏盐层。矿床中黄铁矿的硫同位素组成与矿床成因类型密切相关。宁芜盆地姑山矿田的δ^34 SV-CDT值最高，为10．8‰，梅山矿田次之，为7．85‰，凹山矿田最低，为5．01‰；矿床成因类型也发生相应变化，矿浆型→矿浆→热液型→热液型。矿床中黄铁矿的硫同位素变化主要由硫酸盐的还原温度和原始岩浆硫所占比例不同引起，还原温度越高，δ^34S值越高；原始岩浆硫所占比例越高，δ^34S值越低。计算结果表明矿床中约60％-80％的硫来自膏盐层硫酸盐的还原，还原温度多在450℃以上，但硫化物的沉淀温度相对较低，就位时间稍晚。提出膏盐层（富含碳酸盐、石膏和石盐等）不仅可以为成矿提供大量NThe Middle-Lower Yangtze Polymetallic Ore Belt is one of the most important metallogenic belts in East China, comprising more than 200 polymetallic （Cu-Fe-Au, Mo, Zn, Pb, Ag） deposits. Ningwu and Luzong ore distrcts are the most important component of this belt. In these districts, volcanic-subvolcanic rocks, intrusions and subvolcanic rocks-related iron deposits which are well known as porphyrite iron deposits in China are widespread, during the Late Mesozoic. Based on the geological characteristics, spatial distribution and relationship with volcanic-subvolcanic rocks, the famous iron porphyrite deposit model has been established which improved the development of metallogenic theory and the effective guidance of porphyrite deposit prospecting greatly. This mineralization model emphasizes mainly magmatic-hydrothermal role, but the sulfate evaporate salt layers, at the top of the Zhouchongcun group in Middle Triassic, did not cause the attention in the role of mineralization. And this model mainly reflects the mineralization in shallow. The latest researches and prospecting results reveal that the Middle Triassic sulfate evaporates salt layers and mineralization has closely relationship. However, the ore-controlling mechanism of evaporate salt layers has still been unrevealed, ＂sulfate evaporate salt layers as oxidation barrier＂ in porphyry ore mineralization role rarely reported. In this paper, sulfur isotope characteristics of porphyrite iron deposits have been studied in Middle-Lower Yangtze River Polymetallic Ore Belt, and evaporate salt layers oxidation barrier in porphyry ore mineralization role has been revealed. Porphyrite iron deposits and Fe-S deposits commonly contain gypsum, and iron deposits, Fe-S deposits and gypsum deposits are paragenesis closely. In these deposits, the values of sulfide δ^34 Sv-CDT are abnormally high, and the average values are higher than 5‰. Most of the values of gypsum δ^34 Sv-CDT are about 20‰, which are similar to the value of marine sulfate. Sulfur isotopic c

关 键 词：玢岩铁矿 膏盐层 氧化障 铁矿浆 硫同位素 长江中下游 

分 类 号：P611[天文地球—矿床学] P618.31[天文地球—地质学]