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氧化锰矿是我国仅次于沉积型碳酸锰矿的重要锰矿床类型,主要分布在广西、湖南、广东和福建等南方省区,但由于定年手段的限制,迄今对我国氧化锰矿形成时代的了解还极其有限。作者近几年利用激光阶段加热40Ar/39Ar同位素分析技术对华南地区典型氧化锰矿进行了系统和精确的年龄测定,获得了一大批可靠的成矿年龄,年龄值介于23.64±0.29 Ma和0.48±0.17 Ma(2σ),表明华南氧化锰矿的大规模成矿至少在渐新世末-中新世初就已开始并一直持续到更新世末期。基于多数氧化锰矿的上部矿石已被剥蚀或开采殆尽这一事实,可将华南氧化锰矿的成矿时间上溯到渐新世早期甚至始新世末期。研究发现,氧化锰矿的保存程度和年龄分布明显受新构造运动的影响;如果剔除后期剥蚀程度和采样系统性的影响,可以认为华南氧化锰矿的形成在区域上具有同时性。本次研究还说明,次生氧化锰矿的成矿是一个极其漫长的过程,形成一个具有工业意义的氧化锰矿可能需要上千万年的时间;这明显有别于多数内生热液矿床的成矿。本项研究为我国氧化锰矿以及其他类型的风化矿床(如红土型金矿和红土型镍矿)的年代学研究提供了新的思路和途径。
Manganese oxide ore is an important type of manganese deposit in China, which is second only to sedimentary carbonate manganese ore. It is mainly distributed in southern provinces such as Guangxi, Hunan, Guangdong and Fujian. Due to the limitation of dating methods, so far, the understanding of the age of formation of manganese oxide in our country is still extremely limited. In recent years, the author has systematically and accurately measured typical manganese oxide ores in South China by using 40Ar / 39Ar isotope analysis of laser stage heating, and obtained a large number of reliable metallogenic ages ranging from 23.64 ± 0.29 Ma to 0.48 ± 0.17 Ma (2σ), indicating that the massive mineralization of the Mn oxide ore in southern China started at the end of Oligocene-Miocene at least and continued into the late Pleistocene. Due to the fact that most of the upper ore of the manganese oxide ore has been eroded or mined, the mineralization time of the manganese oxide mine in southern China can be traced back to the early Oligocene or even the late Eocene. It is found that the preservation degree and age distribution of MnO are obviously affected by the neotectonic movement. If the post-ablation degree and sampling systematicness are excluded, it can be considered that the formation of MnO ore in southern China is synchronous in the region. This study also shows that the mineralization of secondary manganese oxide is an extremely long process that can take tens of millions of years to form an industrially oxidized manganese ore; this is clearly different from most endogenic hydrothermal deposits mine. This study provides new ideas and approaches for the chronology research of manganese oxide ore in our country and other types of weathering deposits such as lateritic gold and lateritic nickel ore.