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对氧化锰矿床的年代学研究不仅可以直接限定锰矿床次生富集成矿的时间及锰氧化物的生长速率,而且可为区域构造隆升、地貌形成过程和古气候演变等重大地质事件提供关键的年代学信息.本文报道云贵高原典型次生氧化锰矿-巴夜锰矿的高精度40Ar/39Ar定年数据,并根据40Ar/39Ar年龄计算了锰矿脉的生长速率.研究对象选自两条氧化锰矿脉(脉宽3～6cm),其中A脉与含锰岩系即中元古界锰铝榴石片岩的片理平行,产状平缓,而B脉则与锰铝榴石片岩的片理垂直,产状近于直立.矿相学观察、粉晶X-射线衍射、扫描电子显微镜-能谱分析和电子探针成分分析结果表明,上述两条矿脉均主要由隐钾锰矿组成,矿物结晶程度较高,具有针状和纤维状的良好晶形,K2O含量为0.96%～4.70%.激光阶段加热40Ar/39Ar同位素分析结果表明,A脉的形成时间为(1.35±0.05)～(1.16±0.04)Ma(坪年龄,2σ;n=14);根据样品的空间分布和坪年龄计算出其生长速率为115～153mm/Ma.B脉的年龄略微年轻,介于(1.23±0.05)～(1.01±0.09)Ma(坪年龄,2σ;n=7),计算的生长速率为34～67mm/Ma.A脉和B脉生长速率的差异反映氧化锰矿的生长与流体体系的压力大小有关.世界上其他地区氧化锰矿中锰结核的生长速率一般为0.3～9mm/Ma,比巴夜矿区氧化锰矿脉的生长速率低1～2个数量级,说明氧化锰矿的生长机制是控制其生长速率的重要因素:巴夜矿区的氧化锰矿脉由风化溶液中四价锰离子的直接沉淀而形成并充填在裂隙中,矿脉自脉壁向中心生长,而其他地区用于生长速率计算的样品均为环带状锰结核,受控于氧化锰的自催化氧化作用或锰-铁氧化物之间的催化氧化,锰氧化物自结核中心向外生长.隐钾锰矿的40Ar/39Ar定年结果还表明,更新世时期云贵高原以温暖潮湿的古气候为主,并经历了显著的构造抬升.
The chronology of the MnO deposits can not only directly define the secondary enrichment and mineralization time of manganese deposits and the growth rate of manganese oxides, but also provide the key for major geological events such as regional tectonic uplift, topography formation and paleoclimate evolution This paper reports the 40Ar / 39Ar dating data of typical secondary manganese oxide ore-barysite ore in Yunnan-Guizhou Plateau and calculates the growth rate of the manganese ore pulse according to the age of 40Ar / 39Ar.The object of study is from two manganese oxide veins (Pulse width 3 ~ 6cm). The A vein is parallel with the manganese-bearing rock series, that is, the Mesoproterozoic manganese-aluminum garnet schist. The formation of B vein is perpendicular to that of manganese-chalcopyrite schist, The results show that the two ore veins are mainly composed of cryptomelane and the degree of mineral crystallinity is higher than that of orthoporphyrin High, with acicular and fibrous crystals with a K2O content of 0.96% -4.70% .The 40Ar / 39Ar isotope analysis of laser heating showed that the formation time of A pulse was (1.35 ± 0.05) ~ (1.16 ± 0.04) Ma (Ping age, 2σ; n = 14); according to the sample The growth rate of 115 ~ 153mm / Ma.B pulse age was slightly younger, ranging from 1.23 ± 0.05 to 1.01 ± 0.09 Ma (Ping age, 2σ; n = 7) , The calculated growth rate of 34 ~ 67mm / Ma.A vein and B vein growth rate difference reflects the growth of manganese oxide and fluid system pressure on the size of the rest of the world manganese oxide manganese oxide in the growth rate of 0.3 ~ 9mm / Ma. The growth rate of manganese oxide veins in Biba night mine is 1 ~ 2 orders of magnitude lower, indicating that the growth mechanism of manganese oxide is an important factor controlling its growth rate. The ions are precipitated directly and fill in the fissures, and the veins grow from the veins to the center. The samples used for calculating the growth rate in other areas are all banded manganese nodules, controlled by the autocatalytic oxidation of manganese oxide or manganese - The catalytic oxidation between iron oxides, manganese oxide from the center of the outward growth of the tuberosity cryptocupnaite 40Ar / 39Ar dating results also show that during the Pleistocene Yunnan-Guizhou Plateau warm and humid paleoclimate-based, and experienced significant Tectonic uplift.